In recent years, inkjet printing is increasingly used as a flexible and digital patterning technique in order to deposit functional materials for the manufacturing of microelectronic devices[1] including organic light emitting diodes (OLED),[2] organic photovoltaics (OPV),[3] radio frequency identification tags (RFID)[4] and organic radical batteries (ORB).[5] Due to its minimal waste generation, its efficient handling of expensive materials and its mask-less processing, inkjet printing represents a widely accepted alternative to conventional patterning methods, such as spin-coating, vapor deposition and photolithography.
In the manufacturing process of flexible electronics, inkjet printing can be used for thin film deposition of active materials like conjugated polymers, metal ion containing small molecules as well as composites of redox active polymers and carbon nanoparticles.
Apart from the active layer materials, metal precursors, such as silver nanoparticle inks, are printed onto flexible substrates in order to provide electrical conductive antennas, electrodes, contacts and interconnects. However, silver nanoparticle inks are not conductive after printing, which is due to the presence of organic stabilizers that surround the single particles in order to prevent agglomeration in the ink and ensure processability.[6] Therefore, a post-printing procedure is required to remove the organic material from the particle surfaces, merge the particles to a continuous network, hence yielding electrical conductive structures. This procedure is called sintering. The conventional thermal sintering requires temperatures above 200 °C and is therefore not compatible with the thermo-sensitive foils used as substrate materials. Therefore, alternative approaches, like exposure to a non-thermal plasma, are used to successfully sinter inkjet-printed silver nanoparticle inks without affecting the substrate materials.[7] This approach allows the production of electrically conductive components on flexible substrates via inkjet-printing.
[1] J. Perelaer, P. J. Smith, D. Mager, D. Soltman, S. K. Volkman, V. Subramanian, J. G. Korvink, U. S. Schubert, J. Mater. Chem. 2010, 20, 8446-8453.
[2] A. Teichler, J. Perelaer, U. S. Schubert, J. Mater. Chem. C 2013, 1, 1910-1925.
[3] A. Teichler, R. Eckardt, S. Hoeppener, C. Friebe, J. Perelaer, A. Senes, M. Morana, C. J. Brabec, U. S. Schubert, Adv. Energy Mater. 2011, 1, 105-114.
[4] V. Subramanian, P. C. Chang, J. B. Lee, S. E. Molesa, S. K. Volkman, IEEE. T. Compon. Pack. T. 2005, 28, 742-747.
[5] T. Janoschka, M. D. Hager, U. S. Schubert, Adv. Mater. 2012, 24, 6397-6409.
[6] S. Magdassi, A. Bassa, Y. Vinetsky, A. Kamyshny, Chem. Mater. 2003, 15, 2208-2217.
[7] S. Wünscher, S. Stumpf, A. Teichler, O. Pabst, J. Perelaer, E. Beckert, U. S. Schubert, J. Mater. Chem. 2012, 22, 24569-24576.

Current and future flexible electronics applications require material deposition, patterning, and post-deposition processes that are rapid, low-cost, and compatible with heat-sensitive plastic substrates. We present a simple technique to deposit lines of high electrical conductivity without any thermal treatment during or post-deposition. We inkjet printed a water-based silver salt (AgNO3) solution followed by short exposure to the argon plasma generated by a reactive ion etcher. A skin-like layer of silver forms on the surface of a printed line with an average thickness and composition dictated by plasma treatment conditions. This layer exhibits optimum electrical resistivity twice that of bulk silver. The technique holds the potential for simple patterned metallization of electronic components on flexible substrates.

Invisible Ag-grid transparent electrodes (TEs) have been prepared by Electrohydrodynamic (EHD) jet printing using Ag nano-particle inks. Ag-grid width less than 10 mu;m was achieved by the EHD jet printing, which was invisible to the naked eye. Ag-grid line-to-line distance (pitch) was modulated in order to investigate the electrical and optical properties of the EHD jet-printed Ag-grid TEs. The decrease in the sheet resistance at the expense of the transmittance was observed as the Ag-grid pitch decreased. The figure of merit of Ag-grid TEs with various Ag-grid pitches was investigated in order to determine the optimum pitch condition for both electrical and optical properties. With 150 mu;m Ag-grid pitch, the EHD jet-printed Ag-grid TE has the sheet resistance of 4.87 #8486;/sq and the transmittance of 81.75 % after annealing at 200 oC under near-infrared (NIR). Ag filling factor (FF) was defined to predict the electrical and optical properties of Ag-grid TEs. It was found that the measured electrical and optical properties were well simulated by the theoretical equations incorporating FF. The EHD jet-printed invisible Ag-grid transparent electrode with good electrical and optical properties implies its promising application to the printed optoelectronic devices. The optimized Ag-grid transparent electrode is employed to the fabrication of optoelectronic devices and EMI (electromigration interference) sheilding layer.

Monolithic interconnects in photovoltaic modules connect adjacent cells in series, enabling their optimal power output by providing voltage addition, while also controlling current density to minimize ohmic loss. These interconnects are typically formed sequentially, involving multiple deposition & scribing steps, and widths of about 300 to 500 mu;m are common. The collective impact of shading & dead-zone area comprised by the interconnects in modules results in a reduction of power output by about 5 to 10 %. Thus, as one reduces the interconnect width, more power can be obtained. This work introduces an alternative interconnect formation method employing ink-jet printed metal and dielectric features, which we demonstrate on copper indium gallium diselenide solar cells. Ink-jet printed poly-vinyl-phenol (PVP) and silver (Ag) serve as the interconnect dielectric and metal in exemplary structures, respectively. A variety of other, more abundant, economical, selections can also be used. We demonstrate voltage addition with printed PVP/Ag interconnects, and aspects affecting fill factor and current density are discussed. We also show that printed interconnects can be made significantly narrower than those made by conventional practice. Furthermore, an apparatus that integrates scribing with interconnect material deposition allows the structures to be made in a single pass - after all large area solar cell material deposition steps; streamlining the process to make interconnects can reduce solar panel manufacturing costs substantially.

Inkjet printing has evolved from a graphic printing technology into a fabrication technology for creating complex structural and functional materials. Compared with photolithography, inkjet printing is an additive process, requiring no photomask preparation or etching steps and thus offers advantages in terms of flexibility, scalability, speed, and costs. To date, inkjet printing is capable of depositing a wide range of materials (e.g., metals, conducting polymers, and ceramics) onto substrates, such as paper and plastics, to produce flexible electronics and even 3-D objects. The challenge to achieve better resolution and consistency, however, remains in controlling the formation and precise deposition of the ink droplets carrying the functional materials (e.g., nanoparticles and pre-polymer). To overcome this challenge, we must first understand the fluid properties of the ink and corresponding drop breakup induced by surface tension, or Plateau-Rayleigh instability. In this presentation, we will present our research in (i) establishing relationships between the fluid properties of silver ink and the printing performance and (ii) exploring the minimum feature size attainable with inkjet printing.

Printing of metal based inks on plastic substrates is a promising approach towards the mass production of highly conductive structures for electronic devices using roll-to-roll manufacturing techniques. In order for the entire process to occur at high speed, however, also fast and efficient post-deposition treatment technologies for drying and sintering are required. Recently, the exposure of the wet ink deposits to short, but intense pulses of visible light (photonic flash sintering), has been presented as a highly interesting alternative to more conventional approaches like hot air treatment (thermal sintering). The advantages of photonic flash sintering are the localised heating of only the ink deposits, and the much higher processing speeds which can be attained. In addition, process parameters like light intensity and spectral distribution, pulse length and flashing frequency can be specifically adapted for the absorption and thermal properties of each individual ink-substrate combination. This approach allows to apply this technology on a R2R basis, enabling inexpensive and highly efficient high-throughput production.
During the sintering process, however, the ink properties can change drastically, as the solvents evaporate, the ink layer shrinks, and its reflectivity and thermal conductivity increase. As a consequence, optimal photonic sintering conditions are expected to vary as a function of the sintering degree. Using a single setting of flashing parameters during the entire process might therefore not be the most ideal strategy in terms of manufacturing speed, energy efficiency and final performance of the product. Instead, process optimisation should take into account these effects by adjusting the flashing parameters accordingly. Using a combination of experimental measurements (e. g. in situ temperature monitoring of an ink line exposed to light flashes) and theoretical calculations, we have been able to develop sintering protocols which vary the applied conditions in a well-considered manner. As a simple example, controlled solvent evaporation can be achieved by applying a number of rather gentle drying flashes, followed by very few high power pulses to achieve sintering of the dried ink. This approach has the advantage of limiting high peak temperatures to a minimum, circumventing foil damage, while at the same time avoiding sudden and uncontrolled boiling of the solvent, which would otherwise lead to ink splashing.
A similar approach is also possible using a R2R setup, where the flashing parameters of different lamps in a sequential arrangement can be individually optimised considering the sintering degree of the ink passing underneath them.

To fabricate cost-effective solar cells, it is imperative to develop a low cost transparent electrode with low resistivity and high transparency. Although crystalline indium tin oxide (ITO) has been widely adopted as a transparent electrode in solar cells, it is an undesirable material for use in low cost solar cells because of the scarcity of indium and its high deposition cost. Silver nanowires (AgNWs) network films have recently attracted substantial interest as a transparent conducting material. Transparent electrodes composed of random AgNW networks can be readily achieved by simple and scalable solution. However, the AgNWs film is easy to undergo local oxidation and melting on a heated substrate in the atmosphere, which adversely affects the conductivity of the AgNWs film. In addition, the low carrier collecting efficiency of AgNW films could pose another hurdle. The limited contact area of AgNWs with n-type or buffer layers is incapable of effectively collecting the charge carrier generated at the p-n junction. Here, we propose a sandwich composite electrode structure of Al doped ZnO (AZO)/AgNWs/AZO fabricated. The AZO/AgNW/AZO composite structure is suitable for cost-effective large area fabrication, because it involves relatively low-cost materials, and it is prepared by scalable solution processes. We also demonstrated the similar approach involving copper nanowire (CuNW) in form of AZO/CuNW/AZO. Copper nanowires (CuNWs)-network film is a promising alternative to the conventional indium tin oxide as a transparent conductor. However, thermal instability and easy oxidation tendency poses a hurdle for the practical applications of CuNWs films. We present highly oxidation-resistive copper nanowire based transparent composite electrodes with high transparency and conductivity as well as flexibility. Chemical treatment effectively removes both the organic capping molecule and the surface oxide/hydroxide from the CuNWs, allowing direct contact between the nanowires. This chemical approach enables us to fabricate the transparent electrodes with unprecedented properties (19.8 Omega;/sq and 88.7 % at 550 nm) at room temperature without any atmospheric control. Furthermore, the embedded structure of CuNWs with Al-doped ZnO (AZO) dramatically improves the thermal stability (up to ~140oC) and the oxidation resistance of CuNWs. Our AZO/CuNWs/AZO composite electrodes exhibit high transparency (83.9 % at 550 nm) and low sheet resistance (35.9 Omega;/sq), maintaining the properties even with the bending number of 1,300 under a bending radius of 2.5 mm. By being implemented in Cu(In1-x,Gax)(S,Se)2 thin film solar cell, this composite electrode demonstrate the substantial potential as a low-cost (Ag, In-free), high performance transparent electrode, showing the power conversion efficiency comparable to the conventional sputtered ITO based solar cell.

Advanced nanomaterials dispersed in solution offers opportunities to generate 2D and 3D mesoscale scaffolds with designed properties. Here I will present two areas of research to demonstrate the exciting applications. In one example, I will show novel metal nanowire networks as transparent conducting electrodes to replace the existing indium tin oxides. Metal nanowires with diameters smaller than and with separations larger than the wavelength of the light can allow the sunlight pass through without significant reflection or scattering back. I show that these metal nanowire networks provide high optical transmittance at very low sheet resistance and have extreme mechanical flexibility. In another example, I show how we integrate various nanomaterials into 3D scaffolds including paper, textile and sponge.

Silver nanowire (Ag NW) networks are promising candidates for replacement of indium tin oxide (ITO). However, transparent conductors based on single walled carbon nanotube and Ag nanowire networks often suffer from “haziness” resulting from surface roughness. Thus, in addition to achieving suitable transparency and conductivity, surface roughness must be minimized if realistic implementation of Ag NW networks as transparent conductors is to be realized. In this work, we have reduced the surface roughness of the Ag NW networks to below 5 nm as compared to 54 nm for as-deposited Ag NWs through optimization of low temperature annealing treatment and planarization by poly (3,4 ethylenedioxythiophene) - poly(styrenesulfanate) (PEDOT:PSS). Using this method, we have been able to produce Ag NW networks with transmittance and sheet resistance of 87% and 11 Omega;/sq, respectively. These are some of the best values reported for non-oxide based transparent conductors. Incorporation of these smooth Ag networks into polymer light emitting diodes fabricated in our laboratory yield device characteristics that are comparable to or better than those with commercially available ITO [1].
[1] S. Coskun, E.S. Ates, H.E. Unalan, Nanotechnology 24 (2013) 125202.

The application to zinc oxide (ZnO) thin-film transistor (TFT) has been recently attracting great attention due to its good electrical properties and excellent ambient stability in the fabrication of thin film at low temperature. In this work, zinc hydroxide (Zn(OH)₂ ) was synthesized from zinc nitrate and NaOH and Zn(OH)₂/NH₄OH solution can be prepared up to 5wt% for spin-coating. As the solution concentration increased, thermal treated ZnO film thickness increased linearly. In order to check the performance of solution-processed ZnO TFT, p-doped Si substrate was used as gate electrode with 100nm SiO₂ insulator layer. 2 and 4 wt % solutions gave 30 and 50 nm ZnO layer thickness, respectively after 150^oC thermal treatment on Si substrate. With 2 wt % solution, mobility of bottom gated ZnO TFT was 0.6 while 1.17 cm²/V.s with 4 wt % solution. Furthermore, a mobility of 2.91 cm²/V.s was recorded after a different post annealing treatment. The mobility of ZnO TFT device without any passivation layer has been tested over 1 month period and showed the stable behavior. Conversion process to ZnO from Zn(OH)₂ with low annealing temperature or/and a different post annealing treatment may open new future oxide TFT applications.

Among organic piezoelectric polymers, poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) promises a variety of applicability for flexible piezoelectric devices due to its piezoelectric activity, flexibility and also highly ordered piezoelectric crystalline structure. However, because of the much lower piezoelectric coefficient of P(VDF-TrFE) compared to piezoelectric ceramic materials, the practical application of this material has been restricted to sensors and actuators. An ultra-thin composite of piezoelectric nanocrystals and P(VDF-TrFE) can potentially enhance the piezoelectric properties for energy harvesting applications which has yet to be fully developed.
In this work we propose the development of a composite structure consisting of barium titanate (BTO) nanocrystals embedded into a P(VDF-TrFE) matrix which can be spin cast onto a flexible substrate. To obtain uniformly disperse nano crystals in the polymer matrix we have recently developed a new approach for the surface modification of aggregate-free, monodisperse hydrophobic BaTiO3 nanocubes which enables their stabilization in polar solutions of P(VDF-TrFE). The polymer solutions with and without BTO nanocubes were successfully spin-coated on Kapton flexible substrates to produce ultra-thin uniform films. These structures were interfaced with metal electrodes for piezoresponse characterization using photo-lithography. Piezoresponse force microscopy (PFM) was used to locally delineate polarization distribution, and piezoelectric coefficient. Moreover, piezoelectric properties and switching behavior of whole structure were investigated by integrating atomic force microcopy with ferroelectric tester. Results show higher value of piezoelectric coefficient and faster switching for composite sample.

In this talk, we will discuss silver nanoplates as potential candidates to replace nanowires as metallic inks for printed electronics. Ag nanoplates represent good examples of 2-D nanostructures with an extreme degree of anisotropy in their shape and unique features in their localized surface plasmon resonances properties. When compared with nanowires, plates have larger surface area with a strong tendency to form large, ultrathin sheets. We will introduce a new approach with the capability to produce Ag nanoplates with edge length of 40-500 nm in high yield using solvothermal and hydrothermal reactions. Most importantly, we will report a new strategy for the production of Ag-Au bimetallic nanoplates with oxide-free surfaces in high yield and large quantities. Specifically, we leverage the reduction of gold ions by a mild reducing agent to coat Ag nanoplates with an ultrathin layer of gold while preserving the plate shape and minimizing the etching of Ag by gold ions via galvanic replacement. Conceptually, the success of this reaction relies on the fact that reduction of Au precursors only occurs on the surface of Ag nanoplates and self-nucleation of Au nanoparticles can be effectively eliminated. Additionally, we demonstrated that reaction temperature can maneuver the deposition rate of atoms and the surface diffusion of atoms to promote the migration of Au atoms from corners to the top and bottom facets and the interatomic diffusion between Au, Ag to generate an alloy structure. Ultimately, we aim to minimize the amount of Au needed to decorate Ag nanoplates for an enhanced chemical stability and optimal conductivity.

Current progress in the formation of a CdTe/CdS photovoltaic by Electrochemical Atomic Layer Deposition (E-ALD) will be presented. E-ALD is a condensed phase equivalent of atomic layer deposition (ALD). In ALD the deposition of a compound is achieved by means of sequential surface limited reactions in which the components are deposited one atomic layer at a time. In E-ALD the individual atomic layers are formed using underpotential deposition (UPD), an electrochemical surface limited reaction. XRD results show that the CdTe layer has a strong preferred (111) orientation as deposited. EPMA results show stoichiometric CdTe, with a Cd/Te ratio of 1.02. Photoelectrochemical results indicated a band gap of 1.5 eV, with p-type conductivity achieved without annealing. Different CdS deposition methods were also investigated. CdS was deposited by chemical bath deposition (CBD), successive ionic layer absorption and reaction (SILAR) and E-ALD. Results showed that the average Cd/S ratio, determined using EPMA, was 1.07, 1.10, and 1.05 for CBD, SILAR and ALD respectively. Photoelectrochemical results show that the photoresponse for E-ALD grown CdS was the highest while CBD was the least photoactive. As exciton creation in the CdS layer is parasitic to the photovoltaic, CBD CdS was used in first attempts at PV construction. Solar cells were fabricated in the substrate configuration with Au on glass serving as the back contact, 200 nm (~600cycles) of E-ALD grown CdTe, 80 nm of CBD grown CdS, and 100 nm magnetron sputtered ITO to serve as to front contact. Cells achieve a maximum current density of 0.65 mA/cm2 when exposed to light; however appear to suffer from shunts. Work on these defects is underway.

Electroless and galvanic copper deposition are steps in manufacturing printed circuit boards. Excessive deposit stress may lead to contact failures and, for flexible circuit substrates, excessive warping. In industry, deposit stress is usually determined by observing bending of metal test strips that are varnished on one side for unilateral deposition. However, electroless processes are typically applied for insulating substrates. Differences are expected from the higher the thermal expansion of most non-conducting substrates, and the redox reaction in electroless plating may be affected by the presence of a metal substrate. Therefore results obtained with metal test strips cannot be generalized to non-conducting substrates. In the present study, time-resolved dual-leg cantilever tests were carried out with standard metal and acrylonitrile butadiene styrene (ABS) test strips for a range of electroless and galvanic plating baths. The results are compared with in-situ XRD-based strain measurements of copper films plated onto ABS.

Micro-ring resonators are designed, and a sol-gel solution process is used to fabricate them on rare-earth doped thin films. A high refractive-index titanium dioxide (nTiO2=2.45) is chosen as the waveguide matrix because it can efficiently confine the pump lightwave within the optical gain medium. Unlike a matrix with a low refractive-index that requires air-cladding underneath, our Er-TiO2 platform can be directly implemented on a silica-on-Si wafer without the need for an under-cutting process. In parallel, the concentrations of Er dopant are modified from 0.1% to 5 % to maximize the emission intensity. In addition, an Er-TiO2 micro-ring resonator with a high Q factor of 10^6 is utilized to enhance the photoluminescence efficiency by forming a whispering-gallery mode. We use finite difference time domain (FDTD) method to optimize the structures of our light emitting sol-gel resonator. Optical emission spectra and enhancement factors are characterized by confocal microscopy, and waveguide edge emission is measured between lambda; = 1.45 µm -1.65 µm. A successful sol-gel resonator can provide a light source for board level optical interconnect and three dimensional integrated photonic circuits.

3D polycarbonate (PC) nanocomposites reinforced with 1D multiwalled carbon nanotube and 2D graphene hybrid fillers covered with silver nanoparticles followed by wrapping uniform layer of PEDOT:PSS has been developed. In first stage, Graphene/MWCNT/Ag nanofiller has been assembled by acylation, amination and Ag decoration reactions before incorpoarating into PC matrix. The reaction confirmation and the effect of functionalization on the structural properties of hybrid nanofillers were studied by FTIR, TGA, Raman and UV visible spectroscopy. In order to observe the morphology of the nanofillers, SEM and TEM analysis have been carried out. In later stage Graphene/MWCNT/Ag nanofillers decorated with PEDOT:PSS and without PEDOT:PSS have been incorporated into PC matrix to study the influence of PEDOT:PSS on the electrical properties of the PC nanocomposites. It is noteworthy to mention that the PEDOT:PSS enhanced the conductivity of PC nanocomposites with increasing the concentration of Graphene/MWCNT/Ag nanofillers. The novelty of this work lies in the synergy arising from the combination of two conducting fillers with unique geometric shapes and aspect ratios as well as contribution of coating PEDOT:PSS, which have not been specifically considered previously.

The surface energy of UV-ozone treated Ba_0.7Sr_0.3TiO₃(BST) thin film derived by sol gel technology was modified by the storage environment. The variation of the surface energy and thus the contact angle allows the high-k dielectric materials to be used in both OFETs fabricated by solution processed 6,13-Bis(triisopropylsilylethynyl) pentacene (TIPs-pentacene) as well as thermal evaporated dinaphtho[2,3-b:2prime;,3prime;-f]thieno [3,2-b]thiophene (DNTT). The TIPs-pentacene ribbons are grown by drop casting on fresh BST with a small pinner and OFET shows mobility of 0.3cm² V^-1s^-1. By loading the samples into the evaporation chamber for 5 hours, the surface energy of the BST dielectric drops from 77.03 mJ/m² to 46.25 mJ/m². The work of adhesion between the BST and DNTT is around 86mJ/m² and results in island mode growth of the DNTT molecule. The tighter packing of the DNTT layer results in an averaged mobility of 1.73cm² V^-1s^-1. The in-plane and out of plane XRD results suggest the polycrystalline structure in the DNTT film and they are comparable with the recent findings in the single crystal devices. We also fabricated saturated load and depleted load inverters based on the DNTT OFETs with different W/L ratio. The saturated load one shows full-swing performance and shows a high gain as 25.

Lateral and vertical phase separation plays critical roles in the performance of the next-generation organic and hybrid electronic devices. A novel method is demonstrated here to switch between lateral and vertical phase separation in semiconducting 6,13-bis(triisopropylsilylethynyl) pentacene (TIPSE pentacene, or TP)/polymer blend films by simply varying the alkyl length of the polyacrylate polymer component. A series of polyacrylate polymers is used in this study: poly(ethyl acrylate) (PEA), poly(butylacrylate) (PBA), and poly(2-ethylhexyl acrylate) (P2EHA). The phase separation modes depend on intermolecular interactions between small molecule TIPSE pentancene and polymer additives. The blend film with a dominant vertical phase separation exhibits a significant enhancement in average mobility and performance consistency of organic thin-film transistors (OTFTs).

We have fabricated high-k dielectric films by the simple solution process incorporating TiO₂ nanoparticles into poly-4-vinyl phenol (PVP) for organic thin film transistors (OTFTs). The compatibility between polymer and nanoparticles was enhanced by introducing ligand to the surface of nanoparticles, which has a similar structure of repeating units in the polymer. No significant aggregation, even at a concentration of 31 wt %, was found in the nanocomposites, as observed by transmission electron microscopy (TEM). As a result, the nanocomposite exhibited a low leakage current density (~10^-8 A/cm²). With an increase in the concentration of TiO₂ nanoparticles added, the dielectric constant of the nanocomposites also increased proportionately as compared to that of pristine PVP. The performance of the OTFTs in terms of the charge carrier mobility, on/off ratio, threshold voltages, and hysteresis was evaluated. The relationship between the concentration of TiO₂ nanoparticles and the device performance will be discussed in detail.

Semiconductor nanostructures are ideal candidates for non-metallic plasmonic materials that operate in near-to mid-infrared (IR) range. In contrast to metal nanostructures, semiconductor nanomaterials have the advantage of possessing tunable carrier concentrations by engineering dopants, charge injection, or field effects. Here, we demonstrate that colloidal copper sulfide nanocrystals can serve as tunable plamonic building blocks. We characterize the surface plasmon response of anisotropic copper sulfide (Cu2-xS) nanodisks and triangles. We find that the surface plasmon modes of these semiconductor nanocrystals are strongly dependent on nanostructure shape and crystallographic orientation, particularly for highly anisotropic structures that possess direction-dependent carrier mobilities. We also demonstrate that these semiconductor nanocrystals can undergo strong plasmonic coupling upon assembly into superlattices. We use self-assembly to fabricate large-scale films and arrays of semiconductor nanocrystals that operate in the IR range andcan be extended to more sophisticated metamaterials and plasmonic devices.

Amorphous oxide-based semiconductor (AOS) thin-film transistors (TFTs) have attracted significant attention due to their excellent uniformity, high mobility and high transparency. Particularly, TFTs using indium gallium zinc oxide (IGZO) as an active channel have been studied intensively for their superior electrical properties and environment stability. However, Indium as the key element in the IGZO system is rare and expensive, which may be a limited factor for the AOS application. Therefore, it is required to search for a more abundant and economical candidate for the InZnO system. It was reported that Sn-Zn-O (ZTO) is promising to achieve high mobility but suffers from low on/off ratio [1]. It has been demonstrated that some proper dopants incorporated into ZTO are effective to suppress the carriers generation and to achieve high on/off ratio [2].
In this study, we investigated the effect of various metallic dopants such as Ce, Al and Y into ZTO system by using sol-gel process. The results show that Y doped ZTO present both high film quality and the improved TFT performances using Y-ZTO as the active channel layer of TFTs. Furthermore, the effect of different ratio of Y in Y-ZTO system (i.e., the mole ratios of Y-ZTO were Y:Sn:Zn=x:2:2, where x=0.1-0.8) was investigated. We prepared the Y-ZTO solution by mixing proportional yttrium nitrate hexahydrate, tin chloride dihydrate and zinc nitrate dihydrate in 2-methoxyethanol solvent. The results showed that the increasing Y ratio can cause the reduced saturation current of Y-ZTO based TFTs and the increased crystallization temperature of Y-ZTO films. The optimized Y-ZTO films without crystallization were fabricated at the mole ratio of 0.5:2:2 and at the 450 °C annealing temperature. The fabricated Y-ZTO based TFTs show the excellent devices performance such as the channel mobility of 0.23 cm^2/v.s,, subthreshold swing of 2.8V/decade, and on/off ratio of ~10^6.
Reference:
[1]Myung-Gil Kim, Mercouri G. Kanatzidis, Antonio Facchetti , Tobin J. Marks, “Low-temperature fabrication of high-performance metal oxide thin-film electronics via combustion processing”, Nature Material 10, 382-388 (2011)
[2] Seok-Jun.Seo, Hyuck Jeon.Jun , Hwan Hwang.Young, Byeong-Soo.Bae “Improved negative bias illumination instability of sol-gel gallium zinc tin oxide thin film transistors”,Applied Physics Letter,volume:99,Issue:15,pages: 152102 - 152102-3,Oct 2011

Ordered bulk heterojunction (OBHJ) hybrid photovoltaics promise high-efficiencies by ensuring alternating donor-acceptor domains at length scales commensurate with transfer-limiting dimensions. However, achieving such highly ordered nanostructures is challenging, especially in the context of large-area, low-cost fabrication. Solution-based roll-to-roll processing of polymer photovoltaics has been shown to address these issues but can not, as of yet, be applied for ordered systems in which inorganic nanocrystals serve as the superior electron-accepting material. Here, we demonstrate the achievement of solution-processed composite films of ZnO nanowires vertically arrayed in polythiophene, suitable for OBHJ photovoltaic active layers, using magnetic field-directed assembly. Cobalt-doped ZnO nanowires are synthesized in the bulk and surface modified with 1-dodecanethiol to allow dispersion in dichlorobenzene. The nanowire dispersions are added to solutions of poly(3-hexylthiophene-2,5-diyl) (P3HT) to form hybrid organic-inorganic composite blends. Room-temperature paramagnetic properties of the Co-doped nanowires provide a handle for alignment under a 6T magnetic field. In our case, a sample rotation process, deemed rotational annealing, is required during alignment to effectively break the degeneracy associated with the negative magnetic anisotropy of the nanowires. Finally, the desired vertically-oriented configuration is locked in place as the composite film dries under controlled evaporation in the presence of the magnetic field.

This talk is about an alternative strategy to prepare functional oxide thin films by solution processing at very low temperatures (< 350 degree C) compatible with integration with polymeric substrates for flexible electronics. The method is based on the combination of Seeded Diphasic Sol Gel (SDSG) precursors with Photo Chemical Solution Deposition (PCSD) methodology.
There is a current demand for cost-efficient, portable, high-tech electronic devices that is pushing the integration of active oxide thin layers with flexible substrates. However, the crystallization temperature is a key parameter in the preparation of these functional oxide thin layers. For example many of the perovskite thin films crystallize at temperatures well above 600 degree C, which degrade underlying electronics, semiconductor substrate or their metallization layers. This constitutes a major drawback for integration of functional oxide films with polymeric substrates. Low temperature synthesis of these functional oxide films, such as ferroelectrics is then of paramount importance.
In this work we report our solution base alternative method of fabrication of ferroelectric crystalline metal oxide thin films, namely lead zirconate titanate (PZT) with well-defined properties at crystallization temperatures lower than 350 degree C. The combination of the nucleation of the crystalline phase in the films at low temperatures, by the photo-activation of the precursors chemistry, in addition to the simultaneous promotion of the crystallization, by introducing nanocrystalline nucleus, allows the preparation of crystalline PZT films at temperatures <350 degree C with well-defined dielectric and ferroelectric response. In this talk we demonstrate the concept on the most important multifunctional oxide, PZT, but this methodoly is in fact a processing platform that can be used for many other functional oxide layers.

Silver nanoparticle inks are increasingly applied for the manufacture of inkjet-printed electrically conductive patterns. In order to obtain a high conductivity the printed, liquid patterns have to be functionalized by an appropriate post-deposition treatment step. This includes the evaporation of solvents, the removal of additives and the growing-together of the nanoparticles. Modern post-treatment methods using e.g. microwaves, intense pulsed light [1] or adopted infrared radiation, are nevertheless at the basis of the thermal process. The thermal treatment e.g. in furnaces or on heating plates, is applicable for a great variety of inks and ensures an efficient sintering without major technical efforts. It has been studied intensively whereby the reports mainly focused on the reducing of the resistivity by controlling the parameters of the thermal treatment. Our researches exceed this comparatively studies by investigate multi-layered systems, their manufacturing and post-treatment.
However, the functionality of a pattern is a result not only of the post-treatment, but of a comprehensive set of parameters of the overall workflow. Therefore we report on the influence of the parameters of the prepress step, the printing step and the post-treatment step on the functionality of the functional patterns.
In the experiments two silver nanoparticle inks were inkjet printed on a rigid and a flexible substrate. In the respective workflow steps the following parameters were varied:
(1) Prepress: The digital images were prepared to print patterns with a shape comparable to the shape of butterflies. Here the geometry of the patterns was varied.
(2) Printing: The geometry of the printed pattern was compared to the geometry of the digital images to consider effects of spreading. The different drying behaviors of both inks were investigated. In addition, the number of layers which were printed on top of each other was varied.
(3) Post-Treatment: The sintering temperatures and times were varied.
The patterns were studied by the application of versatile technologies: The morphology of the patterns is investigated by profilometry and optical microscopy; the microstructure is analyzed by scanning electron microscopy and X-ray diffraction; the electrical characteristics were determined by the measurement of the resistances.
The results show comprehensively the relation between the parameters of the workflow steps, occurring effects during the manufacture and the resulting microstructure and functionality of the patterns. The knowledge of these parameters enables us to control the industrial manufacturing of comparable conductive patterns.
[1] N. Marjanovic et al. ”Inkjet printing and low temperature sintering of CuO and CdS as functional electronic layers and Schottky diodes”, J. Mater. Chem. 21, 2011, 13634-13639.

Functional materials that can retain their conductivity over large ranges of mechanical strain are in demand for applications such as flexible electronic devices (displays, antennas, transistors, solar cells), smart textiles and polymer-based actuators. The current state of the art stretchable conductive materials include wavy metal structures placed on flexible substrates, composites made by backfilling networks of conductive nanomaterials with polymers, elastomeric fiber networks doped with conductive nanoparticles and patterned flexible substrates filled with liquid metal. Each approach has its own advantages and shortcomings. All reported approaches require fabrication on a planar substrate and subsequent patterning. Even though these materials can be fitted onto 3D substrates after fabrication by taking advantage of their flexibility, overall conductivity is sacrificed for conformal coverage. Here we report a method to fabricate and pattern highly conductive circuits conformally on 3D substrates. This method results in a stretchable conductor that consists of a rubber fiber mat-silver nanoparticle composite. The fiber mat is spun from a poly(styrene-block-isoprene-block-styrene) (SIS) toluene solution using solution blow spinning onto 3D substrates. The rubbery block of the block copolymer, isoprene, results in conformal coating of the substrate and elasticity. To establish conductivity, a silver precursor solution is applied to a pre-spun mat and nucleated to form conductive pathways around and inside the fiber, creating a percolating network of nanoparticles. The resulting composite has a uniform conductivity of 410 S/cm at zero applied strain, and retains its conductivity up to 100 S/cm at 100% strain. Conductive paths are formed on the fiber mat by spray coating the silver precursor solution through a patterned mask. The mat is released after the deposition of the precursor solution, then the silver particles are nucleated to form the conductive pathways. This allows for flexible conductive patterns to be directly transferred onto 3D substrates without loss of conductivity. We believe this method can be beneficial for fabrication of non-planar electronic devices such as 3D antenna geometries and spherical cameras in flexible form.

Directed assembly of nanoelements has been used to fabricate flexible devices for diverse applications. The challenge in using such techniques consists of developing highly scalable, high-rate (fast) assembly techniques for placing nanoelements precisely. Fluidic assembly, which employs the interfacial capillary forces, is a method used for assembling nanoelements onto many substrates (regardless of conductivity). However, fluidic assembly is a very slow process since it is diffusion limited. During fluidic assembly, nanoelement migration toward substrate is only driven by the concentration gradient between the assembly region and bulk solution. Here, we introduce a new, high-rate electro-fluidic assembly technique that enables nanoelement assembly directly onto polyimide surfaces up to 10mu;m thick. The significance of this technique is that the assembly process is 100 times faster than fluidic assembly. In the electro-fluidic assembly process, highly doped silicon is used beneath the insulating film as a conductive layer, and the electric field is applied through this layer. Under the influence of the applied field, nanoelements move towards the template and assemble onto desired regions. After assembly, the polyimide film can be easily peeled off from the silicon substrate. A dip coater is used to provide precise and constant pulling speed of the template from the solution. Polystyrene latex nanoparticles (50 nm-100 nm-200 nm), silica particles (30 nm), quantum dots (5 nm) and single walled carbon nanotubes have been successfully assembled. This approach could lead to many novel ways to advance various applications.

To improve the properties of high temperature polymers such as Polyimides which are processed at temperatures of about ge;350°C, organically modified layered silicates with enhanced thermal stabilities to withstand high processing temperatures and prevent premature decomposition were synthesized. The effect of pH and concentration (Cation exchange capacity and percentage composition) on the thermal stability of the organically modified layered silicates was investigated. Two main groups of OMLS were processed; those with only one surfactant (2-Dimethylaminoethyl triphenyl phosphonium bromide (DAETPB)) and those with 2 surfactants (DAETPB and 4, 4 oxydianiline (ODA)). The formation of the OMLS was confirmed by X-ray diffraction analysis (XRD), Fourier transform infrared (FTIR), scanning electron microscopy (SEM), Thermo gravimetric analysis and differential thermo gravimetric analysis (TG-DTA) as well as dispersibility analysis. In the case of single swelling agent OMLS nonacidified ones had higher thermal stability (385°C) than their acidified counterparts (330°C). For the double swelling agents increase in concentration resulted in increase in thermal stability with DAETPB: ODA (60:60) producing the highest onset degradation temperature at 500°C compared to the single swelling agents.

Doping rare-earth (RE) ions into semiconductor nanocrystals (NCs) host is attractive, as it allows efficient coupling between the f electrons of the RE ions and the host s electrons. This enables the possibility for both electrical and optical excitation of RE ions via semiconductor host. However, the doping of semiconductor nanocrystals is difficult due to self-purification effect, resulting in the segregation of dopant to the surface of nanocrystals.[1] Recently, we have developed different strategies for promoting native defects in ZnO QDs.[2,3] These native defects present in nanocrystals can trap dopants at the surface of nanocrystals by forming a chemical bond. [4] This turned our attention towards defect rich ZnO quantum dots (QDs) for RE ion doping.
In this work, we report microwave based synthesis of Eu3+ doped ZnO QDs. The rapid dielectric heating by microwave facilitates spontaneous crystallization of ZnO QDs at higher temperature in the presence of Eu3+ ions. This enables simultaneous incorporation of native defect along with Eu3+ doping in the host QDs. The size characterization by HR-TEM shows that the prepared QDs are in the quantum size range. The Eu3+ doping of QDs was confirmed by elemental imaging in DF-STEM mode. The doped QDs when photo excited at its band gap shows native defects emission along with emission from 5D1-->7FJ (J= 1,2,3,4) transition of Eu3+ ions.
REFERNCES:
[1] Erwin, S. C.; Zu, L.; Haftel, M. I.; Efros, A. L.; Kennedy, T. A.; Norris, D. J., Doping semiconductor nanocrystals. Nature 2005, 436 (7047), 91-94.
[2] Asok, A.; Gandhi, M. N.; Kulkarni, A. R., Enhanced visible photoluminescence in ZnO quantum dots by promotion of oxygen vacancy formation. Nanoscale 2012, 4 (16), 4943-4946.
[3] Asok, A.; Kulkarni, A. R.; Gandhi, M. N., Microwave accelerated one-minute synthesis of luminescent ZnO quantum dots. AIP Conference Proceedings 2013, 1512 (1), 404-405.
[4] Hu, L.; Huang, J.; He, H.; Zhu, L.; Liu, S.; Jin, Y.; Sun, L.; Ye, Z., Dual-donor (Zni and VO) mediated ferromagnetism in copper-doped ZnO micron-scale polycrystalline films: a thermally driven defect modulation process. Nanoscale 2013, 5 (9), 3918-3930.

Under suitable stimulation some materials can exhibit electronic spin crossover (SCO) phenomena, namely a transition from a low-spin to a high-spin state. The stimulation, often a temperature variation, also results in a (thermal) hysteresis where the bistability may be used as a memory device. While such potential applications were recognised almost 20 years ago, recent efforts have turned towards the synthesis of new compounds with the SCO phenomena occurring around room temperature for the realisation of SCO in nanoscale structures, notably thin films.
In the present work we have studied the SCO phenomena from a class of polynuclear iron(II)-triazole derivatives where the chemical properties can be tailored to achieve solubility in common solvents by adding appropriate sidechains to the main backbone. Two different compounds have been studied, with short and long sidechains, to examine how cooperativity between molecules is affected by the substituents. Characterisation of thermal hysteresis via dc magnetisation measurements performed on powders, gels and pellets serves to highlight the impact of the molecular environment, i.e. presence of water or uncoordinated solvent, crystallinity and packing, on the SCO behaviour.
Solution processing of the materials has further enabled the preparation and study of stable thick and thin films, with optical characterisation confirming the retention of SCO properties. Furthermore as a first step to deploy these SCO layers inside simple electronic devices, MIM structures (metal-insulator-metal) have been fabricated and tested. Our results show the presence of a thermal hysteresis loop that faithfully reflects the SCO phenomena through the values of the dielectric function around room temperature. Our studies clearly demonstrate that in addition to the previous studies on bulk powders, electrical bistability from thin films (30-50 nm) devices can also be achieved.

Stretchable electronics has emerged as a new class of soft electronics, which is considered potential and intriguing in applications such as biomedicine and sensing system. In general, microlithography process was employed to fabricate metal interconnects in stretchable electronics, but some alternative processes can also be used. In our earlier study, we tried using aerosol jet printing process with silver nanoparticles solution as ink to simplify the conventional microlithography process. However, subsequent dry etching process for removing excess polyimide (PI) substrate material unavoidably oxidized the Ag interconnects. To improve and reduce process steps, we herein present utilizing aerosol jet printing process to generate serpentine PI pattern which could be used as the underlying stretchable substrate for conductive interconnects in stretchable electronics. With 4~8% Polyamic acid (PAA) type PI, we could produce serpentine pattern on poly(methyl methacrylate) (PMMA)-coated glass by aerosol jet inking. By tuning the deposition head sheath gas, atomizer gas, and exhaust gas flow rate, PI patterns with different thickness and width were formed, which ranged from 1 to 3um in thickness and 100 to 160um in width. For potential applications in stretchable electronics, second layer of conductive material is necessary; therefore, we also printed silver ink on the preformed PI pattern. The PI-Ag pattern could then be peeled from the carrier glass or transfer-printed onto a PDMS stamp for further fabrication process. The aerosol jet printing process provides a simpler and direct method for patterning of PI substrate layer, which not only avoids the oxidation of oxygen-sensitive materials but also facilitates the fabrication process of stretchable electronics.

Plastic photovoltaics based on bulk-heterojunction concept consists of light-harvesting conjugated polymer and electron accepting fullerenes are perceived as a promising and effective potential alternative to silicon solar cells owing to their light-weight, large area, cost-effective and flexible organic photovoltaics. The classes of transition metal phthalocyanines (MPc&’s) are interesting and their opto-electronic properties are determined by the orbital occupation of the transition metal 3d orbitals incorporated in the molecular center. In the present study transition metal phthalocyanines (CoPC, NiPC, SnPC, TiOPC, FePC) are deposited by vapor phase deposition as the stacking layers in bulk heterojunction solar cells and efficiencies were analyzed. The film thickness of these phthalocyanines are applied as 5nm, 10nm and 20nm between the PEDOT:PSS and active (P3HT:PCBM) layer to elucidate and optimize the suitable condition to augment the efficiency. Comparisons of the devices made and found that stacking TiOPC and CoPC between the PEDOT:PSS and P3HT:PCBM layer demonstrate a significantly enhanced efficiency of 2.8% (JSC of 15mA/cm2, VOC of 0.59, FF of 44) and 2.6% with 10 nm of film thickness from the normal BHJ of 1.6% ((JSC of 7 mA/cm2, VOC of 0.60, FF of 37). However, NiPC and FePC shows degrading efficiency (1.3%) which can be attributed to potential loss of optoelectric properties. The thickness of 5nm and 20 nm also show reduce in efficiency, possible excition movement in bulk heterojunction solar cell is optimum at 10 nm. The enhanced efficiency of devices with TiOPC and CoPC can be conjectured due to better opto-electrical properties and undamaged tubes. The microstructures of the heterojunction active layer were examined by using AFM, SEM, UV-Vis spectra, IV curve and EQE techniques.

Although crystalline silicon (c-Si) wafers with thicknesses on the order of about 100 mu;m continue to provide a basis for the majority of the photovoltaics industry, c-Si thickness on the order of 10 mu;m suffices to absorb a majority of incident visible light. It follows that increasing attention focuses on thinner c-Si solar cell materials as a strategy to reduce costs. In addition, strongly absorbing films with grain size comparable to their thickness are well suited for solar cell applications due to efficient carrier generation and transport properties. Our work on Si nanocrystal (nc) suspension inks and those incorporating organometallic polysilane chemicals provides a pathway to realize such materials. First we investigate the dependence of annealing drop cast Si films, derived from nc suspension inks, on temperature, nc surface modification, ambient, as well as mono- vs. polydispersity and other variables. Correlations between annealing conditions and resultant optoelectronic properties are drawn. Then we examine the influence of adding polysilane chemicals to the inks, and subsequent changes in morphological evolution during annealing. Finally the topic of doping films derived from Si inks is discussed, with implications on device formation.

Cadmium sulfide (CdS) thin films play an important role in the development of cost-effective and reliable photovoltaic devices. The material is ideal as buffer layer in the copper indium gallium selenide (CIGS) solar cells due to its suitable band gap, high transmittance and low resistivity. Among the techniques used to deposit CdS thin films, chemical bath deposition (CBD) technique is well known to be simple, low cost and convenient to be applied in industrial scale. In this paper, CdS films were deposited onto glass substrates by CBD at 60°C for 40 and 60 min from a bath containing cadmium acetate, ammonium hydroxide and thiourea. The effect of ammonium acetate addition to the bath on the structure, morphology, thickness as well as the optical and electrical properties of the CdS films was investigated. Structure and surface morphology of the prepared films were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM), respectively. Elemental composition was obtained by energy dispersive spectrometer (EDS) and electron probe micro-analyzer (EPMA) with wavelength dispersive spectrometer (WDS).The optical and electrical properties of the CdS films were analyzed by UV-Vis spectrophotometer and Hall effect measurements, respectively. The thickness was measured by Dektak profilometer whereas atomic force microscopy (AFM) was used to measure the film roughness. Dense, crack-free and continuous films with average grain size of 78 nm and thickness of 100 nm were obtained from reacting baths without ammonium acetate. Average roughness obtained by AFM was found to be 48.45 nm. Elemental analysis by EDS revealed Cd/S ratio of 1.13, whereas WDS measurements showed Cd/S ratio of 1.04. The Cubic structure for the CdS film was confirmed at diffraction angle of 26.73°, corresponding to the (111) reflection. The average transmittance was found to be 72.64%. The Hall effect measurements confirmed the n-type conductivity with a resistivity of 1.04x10⁸ Ohm/sq. The average V-Hall was at -9.03x10^-6 V and the hall effect coefficient was at -9.34x10³ m²/C.

Among the various solar cells with high efficiency which can be developed by low cost than Si solar cell, CIGS type solar cell is intensively researched because of its attractive performances. At this time, this type solar cell is synthesized by gas phase method. However, since vaporizing temperature of four elements (Cu, In, Ga, Se) is extremely different, productivity under the gas phase is relatively low. Unfortunately, it is common that low productivity read the large amount of loss of resources and energy. Thus, to construct the environmental friendly CIGS type solar cell, synthesis method with high recovery rate should be developed.
It is also well known that liquid phase reduction methods can be easily produced the nano materials with high recovery rate. However, in many cases, crystallinity of the products was relatively low, consequently undesirable reaction was proceed at around of defects. On the other hand, we reported the synthesis method for well crystallized and uniform alloy nanoparticles by restrict controlling the homogenization of metallic complexes in the aqueous solution which reading the control of reduction rate, under the room temperature. However, ternary, or more, alloy nano materials with uniform structure can not be synthesized until now, because of difficulty of controlling these conditions. Therefore, at the first step to synthesis the CIGS nano-materials in aqueous solution, the relationship between copper and/or indium complex condition in the aqueous phase and its reduction potentials was evaluated.
Amine-based and/or carboxyl-based complexing reagent, were used for the complex reagents. Condition of metallic complexes in the aqueous solution can be restricted to homogenized species by utilizing the theoretical calculation method using the critical stability constants. Reduction potential of Cu (and/or In) complexes was measured, and synthesized materials were analyzed by XRD.
Results of calculation for the Cu-NO3-OH-malic acid system (dissolution of Cu(NO3)2 and malic acid) indicated that copper complex was successfully restricted to [(Cu2+)(mal)2] (pH 3-7), and to [(Cu2+)(OH)2(mal)2] (c.a. 92.8%) (pH 9-12). Thus, copper complex can be restricted to single species in the original solution by obeying to this calculation method. As the same manner, the condition of copper complex in the solution was restricted to single species by using various complexing reagents. Reduction potential was decided by using the results of cyclic voltammetry and XRD results of electrodeposited materials at corresponding potential. As the results, It become clear that correlation between reduction potential and stability constants showed the linearly interaction. To synthesize CuIn alloy which is base of CIGS materials, amine-based complexing reagent which have large stability constants will be needed. This work was supported by the Grant-in-Aid for Challenging Exploratory Research (No. 25550085).

The interest in research and development of inorganic light-emitting (LE) materials was recovered due the possibility to process these materials in solution using simple coating or printing techniques. In order to obtain a LE material with high efficiency, in the present research, we studied the electrical properties of a composite based on the LE inorganic material Zn2SiO4:Mn. This inorganic material was added in a polymeric blend solution composed by the high-conductive polymer PEDOT:PSS, poly (3,4-ethylenedioxythiophene) poly (styrenesulfonate), and the high-transparency polymer PVA, polyvinyl alcohol. Films with micrometric thickness were obtained by drop-casting technique and gold electrodes were deposited in both faces of the film in order to enable the electrical characterization. The electric measurements were performed using an impedanciometer Solartron 1260A (for AC characterization) and a source-meter unity Keithley 2410 (for DC characterization). The electrical characterization was performed into a Janis Cryostat with work pressure of 10-2 mbar and temperature controlled. Was verified that the DC conductivity of the PEDOT:PSS/PVA blends was invariant for weight concentrations of the conductive polymer between 40 % and 80 %. For concentrations lower than 40 % the DC conductivity of the blend decreased several orders of magnitude indicating a percolation process. For concentrations higher than 80 % the DC conductivity slightly increased only. The AC characterizations revealed a charge transport mechanism independent of the frequency of the excitation signal (between 1 Hz and 1 MHz) for blends with concentration of PEDOT:PSS above the percolation. Below the percolation two charge transport mechanisms were verified. The low frequency mechanism exhibited relatively high activation energy (25.0 ± 0.7 meV). The high frequency mechanism exhibited a low activation energy (3 ± 2 meV), which was quite similar to that obtained of pure PEDOT:PSS (1.4 ± 0.3 meV). The interpretation of these results, specifically for the high frequency charge transport mechanism, is a charge ransport mechanism which occurs in high-conductive phase (PEDOT:PSS). The low frequency mechanism was interpreted as a wide-range charge transport, which occurs in a non percolated blend. With the addition of the inorganic material (Zn2SiO4) in the polymeric blend, the DC conductivity of the hybrid material was linearly decreased with the increasing of the inorganic material concentration. However the dependence of the composite conductivity with the AC signal frequency and temperature were quite similar to that obtained for the blended material. These electrical characterizations are important to establish a background to relate the electrical properties of the studied composite with its light-emitting processes, which is the next step of the present research and we hope to show results about that in the conference too.

Recently, the superhydrophobicity and anti-reflection properties of the moth-eye nanostructure have attracted a great deal of attention in various applications such as solar cell, light emitting device. However, for the commercialization of moth-eye nanostructure, not only superhydrophobicity and anti-reflection properties but also the durability is very important. In this study, we present the highly durable moth-eye nanostructure for the application of the dye-sensitized solar cell (DSSC), a next generation photovoltaic device. Photocurable and highly durable sol-based materials were patterned upon moth-eye nano-pillar shape by direct nanoimprinting method. The substrate, in this experiment, was F/SnO2 glass (FTO-glass) in order to apply moth-eye nanostructure to the DSSC.
The optical transmittance of one-side patterned substrate was increased up to 3%. The hardness of the pattern and the increased conversion efficiency of the DSSC were also confirmed by nano indentation method and solar simulator, respectively. In addition, the optical transmittance of the cell, which is a critical factor for the building-integrated photovoltaics (BIPV) application, would be presented.

TiO2 multi-electrodes composed of nanoparticles and nanorods were prepared for use as electrodes in dye-sensitized solar cells (DSSC) in an effort to improve the light-to-electricity conversion efficiency. TiO2 nanorods have been successfully prepared via electrospinning methods using a solution containing titanium isopropoxide (TIP). Acetic acid is generally used as a catalyst in sol-gel processes involving TIP; however, acetic acid induces rapid solidification of the sol solution, resulting in clogging of the nozzle during electrospinning, thereby hindering the mass production of TiO2 nanorods. In this work, we introduced acetyl acetone as a new catalyst and optimized the electrospinning conditions of TiO2 nanofibers. The use of acetyl acetone catalysts dramatically extended the solidification time of the TIP sol solution. The DSSC efficiency was improved through the use of TiO2 multi-electrodes.

Novel Dye-sensitized solar cells (DSSCs), which emerged, have been studied, in order to obtain high photon-to-current efficiency. There are many factors limiting the cell performance, among which light trapping is important.
As reported by Arakawa et al., the light trapping layer consisting of larger TiO2 particles (hundreds size) was arranged between TiO2 nanoparticles semiconductor layer and platina coating glass in DSSCs, in order to provide high photon-to-current efficiency. For example, N719 has low absorption in the long wavelength light region. Therefore, the large TiO2 particles, with light-scattering effect, are incorporated into the DSSCs to enhance the photoresponse to long wavelength light. As their results, the up-conversion efficiency from 7.62% to 9.77 % to DSSCs was confirmed.
On the other hand, in our study, for the purpose of up-conversion of photon-to-current efficiency of dye-sensitized solar cell), we fabricated the DSSC photoelectrode with the light scattering layer constituted of core-shell particles. As the materials of shell moiety of core-shell microbead, high refractive index inorganic materials, i.e., CeO2, TiO2 and ZrO2 were adopted. Poly acrylic ester spherical microbead (5-10 mu;m) as core matrix was surface-modified with above-mentioned inorganic materials by an electrostatic interaction.
In DSSCs, the light scattering layer constituted of the core-shell particles were arranged onto the reverse side of semiconductor layer (single layer of TiO2 nanoparticles, size: 9 nm) to which the dye was adsorbed. As their results, the short circuit photocurrent density (Jsc) increase from 6.47 mA/cm2 to 10.95 mA/cm2, and the conversion efficiency eta; (%) increase from 2.58% to 4.82 %. The remarkable increase 1.69-fold in Jsc and 1.87-fold in eta; (%) in novel DSSCs with light scattering layer constituted of core-shell microbeads was confirmed, relative to that of DSSCs cell. This is considered that the multi Mie scattering effect of light that occurred on the shell of core-shell microbeads were significantly attributed to up-conversion.

In semiconductor and conductive nanocomposite research, three directions are of key importance: efficiency and viability, i.e. the maximization of desired properties through easy and cheap solutions; specificity, i.e. the ability to fine-tune specific properties to specific needs; and of course the understanding and implementation of new materials, among which conjugated polymers play a center stage role. Inorganic-polymer p-n nanocomposites are of special interest in this context, as they have been steadily gaining relevance while at the same time presenting challenges both in terms of optimization and basic understating.
In our research, we addressed the basic mechanics of n-type-induced conductivity enhancement in p-type systems, an effect upon which a general consensus is currently lacking. Additionally, the potential was tested for enhancement and tuning of electrical properties in complex materials through hierarchical control of a p-n junction&’s geometry. The geometry in particular was addressed as a function of interface area, shape, linear distance between structures within a length scale, and relationship between different structures at different length scales.
In the project, nanocomposites were created from PEDOT-PSS and novel metal oxide nanoparticles, in the form of both bulk systems and electrospun clothes. The systems were studied under four independent variables: nanostructure lateral size (addressing volume and interface area effects); nanostructure shape (addressing local symmetry, orientation, and electrostatic edge effects); nanostructure concentration (addressing the core mechanics of n-type-based enhancement in p-type systems); and finally bulk versus electrospun specimens (which allowed for the comparison between the length scale of the nanostructures and of the electrospun fibers containing them). The systems were tested via cyclic voltammetry and under both dark conditions and simulated solar illuminations.
The bulk systems had perfect ohmic behaviour and, through the manipulation of the nanostructures&’ geometry alone, presented up to +540% conductivity in the dark and up to +900% gained conductivity under solar illumination respective to PEDOT-PSS alone while keeping the nanostructures&’ weight fraction below 2%. The electrospun systems exhibited variable hysteresis around an ohmic baseline and inverse photoreactive behaviour, with total conductivity loss under solar illumination. Conductivity regeneration over time for the electrospun systems varied from 0 to 100% as a function of the nanostructures&’ parameters.
Based on our results, we additionally proposed and confirmed the coherence of a new and compact model for n-type-based conductivity enhancement in p-type systems which, combined with our findings, we are confident can push the boundaries forward for functional material research in semiconductor systems.

Recent focus on kesterite-based Cu₂ZnSn(S,Se)₄ (CZTSSe) solar cells has enabled pushing the record performance level above 11% power conversion efficiency, making CZTSSe one of the most promising thin-film solar cell materials based on metals that are “earth-abundant”—meaning that the technology is compatible with deployment at production levels of above 100s of GW per year. In this talk we will review various approaches that have been proposed for solution-depositing CZTSSe (e.g., nanoparticle-based, slurry, pure-solution) and highlight recent results using hydrazine-based chemical approaches that have led to the record performance devices. While most results of high-performance devices employ spin coating as a method for depositing the film (not very scalable to large area substrates), we will also show a recent result in which an automatic slit coater tool has been developed and used to make CZTSSe solar cells with efficiency of over 10%, using a homogeneous CZTSSe metal-chalcogenide ink. In contrast to the usual notion that solution-based processing can provide lower-cost, but generally also lower performance devices, these results demonstrate that solution-based processing can, in some cases, also provide benefits in terms of enabling high performance.

Chalcogenide solar cells based on Cu(In,Ga)Se2 (CIGS) absorbers exhibit the highest conversion efficiency among all thin film photovoltaic technologies, - currently 20.4% - on par with the best efficiency for the market leading polycrystalline Si technology. Solar cells based on the related materials kesterites, which comprise compounds Cu2ZnSnS4 (CZTS), Cu2ZnSnSe4 (CZTSe) and associated alloys, are less efficient than CIGS cells but can eventually offer lower manufacturing costs starting from abundant and non-toxic materials. In both cases the non-vacuum deposition of chalcogenide absorbers from true solutions or nanoparticle dispersions is expected to further lower the capital investment for the manufacturing equipment and enable a fast roll-2-roll processing on flexible substrates. This review will describe current challenges of the solution deposition of chalcogenide absorbers and present several innovative approaches on how to improve the sintering of precursor layers into high-quality CIGS or CZTSSe crystalline layers. Finally, a novel solution approach for depositing highly transparent and conducting ZnO:Al as front contacts will be presented in order to demonstrate a feasibility of a fully non-vacuum processed chalcogenide thin film solar cell.

A hydrazine-based approach has proven to be one of the more successful deposition methods for producing high-quality CuIn(S,Se)2thin films (CISSe). Although this approach is applicable in most solution-based processes, concerns aboutthe toxicity of hydrazine have limited it to the spin coating of the absorber layer of photovoltaic devices [1-3]. Here we report thin film fabrication through spray pyrolysis by ultrasonically spraying the hydrazine-based precursor solution onto a heated substrate. To prevent exposure to hydrazine, the entire spray system is housed within a nitrogen-filled plastic glove box with a recirculator and solvent condenser. Furthermore, the spraying technique allows for uniform deposition irrespective of solvent, so less toxic precursor solutions and the effects the solutions have on the CISSe film properties were investigated. The solutions used in these experiments consisted of a) metal saltsin aqueous solution, b) metal chalcogenide in anhydrous hydrazine solution, and c) metal chalcogenide in hydrazine hydrate solution.
The crystal size and orientation of the sprayed films were measured using X-ray diffraction (XRD) and compared, as were the morphology and composition of the films. Using Williamson-Hall analysis, the crystal sizes of as-sprayed films were calculated to be 14 nm, 28 nm and 57 nm for aqueous, anhydrous hydrazine, and hydrazine hydrate solutions, respectively. Additionally, the orientation factors of the (112), (220/204) and (116/312) planes change from 1.19: 1.08: 0.77 for the films fabricated using the aqueous solution to 1.74: 0.45: 0.41 and 1.93: 0.32: 0.19 using theanhydrous hydrazine and hydrazine hydrate solution, respectively. Morphology and compositional studies, performed using a scanning electron microscope with energy dispersive x-ray spectroscopy, reveal that the hydrazine-based films have better surface smoothness and compositional uniformity than water-based ones. These results indicate that that hydrazine is critical to crystal growth quality and film uniformity, but, at the same time, that the presence of water in the hydrazine does not hinder the crystal growth quality. If fact, these results indicate that the presence of water in the hydrazine improves crystal growth and orientation.
The synthesis of high-quality CISSe films by spray pyrolysis from a hydrazine hydrate solution demonstrates the potential for a low-cost, high-throughput fabrication method amenable with manufacturing processes. Furthermore, not only is the process made less toxic by replacing the anhydrous hydrazine with hydrazine hydrate, but the film quality improves with this change. The performance of CISSe solar cells prepared with the hydrazine-assisted spray process will be reported.
[1] D. B. Mitzi et. al., Adv. Mater., vol. 20, 2008
[2] B. Bob et. al., Adv. Energy mater., vol. 2, 2012
[3] T. K. Todorov et. al., Prog. Photovoltaics, vol.21, 2013

Inorganic cadmium telluride nanocrystals with diameters from 3 to 5 nm synthesized in solution are attractive elements for the fabrication of solution processed photovoltaic (PV) devices. The organic ligand shell encapsulating these materials enables them to be dissolved in organic solvents, and the resulting solutions can be sprayed onto substrates to produce photoactive thin-films of CdTe. The highest PV performance is achieved after removing the ligands with CdCl2 and sintering the devices at 380C. The spray deposition process has numerous advantages over spin coating, including the potential for producing large area coatings on flexible and irregular surfaces. This CdTe spray process was used to produce Schottky barrier solar cells following evaporation of Ca/Al contacts (glass/ITO/CdTe/Ca/Al) and testing under simulated AM1.5G illumination with an intensity of 100 mW/cm2. Improved performance was found to be directly tied to control over surface morphology obtained by adjustment of spray parameters such as concentration, pressure, distance, and surface temperature. SEM and optical profilometry were used to quantify the film morphology, which was found to be rough (200 nm) with low pressure and heated substrates, and smooth (20 nm) with high pressure and no substrate heating. Under optimized conditions, PV devices showing Jsc=10.5+1.0 mAcm-1, Voc=0.45+0.8V, FF= 40+5.0% and Eff.= 1.9+0.4 % under simulated 1 sun were produced.

Thin film solar cells with a combination of CdS/PbS were investigated with a high conversion efficiency of >5.0%. Modulation of band alignment between PbS and CdS was mainly studied by tuning band gap of PbS absorbers by means of growth temperature of chemical bath deposition process. Utilization of multi-layered absorbers obtained from PbS thin films with different band gaps induced an enhancement of photo conversion efficiency. The multi layer approach resulted in high performance, i.e., short circuit current density (J_sc) of of 27.7 mA/cm², open circuit voltage (V_oc) of 0.31 V and high conversion efficiency of 4.3 %. For further improvement, a ZnO nanostructure has been applied with the possibility of overcoming the thickness limitation of absorber layer. The photovoltaic cell with ZnO nanostructure demonstrated the best efficiency of ~5.5% with the value of 36.25 mA/cm² J_sc, and 0.3 V V_oc. Various experimental results will be discussed to support the observed high performance as a new potential structure of thin film solar cells.

Ordered nanostructures have long been considered a desirable component of developing hybrid-photovoltaic devices as they may i) overcome exciton diffusion limitations in organic materials, ii) maximise p-n interfacial area and iii) increase optical absorption. Numerous stand-alone efforts have been made to control the morphology of such nanostructures, influence surface properties, develop new processing regimes or simply preparing reproducible devices. However, such initiatives are often carried out in different research laboratories and results have been conflicting.
By developing protocols for the reproducible preparation of controlled aspect ratio ZnO nanorods by scalable solution based methods we have implemented these structures as i) heterojunctions for charge separation in exciton solar cells and as ii) electron extracting layers for charge collection in excitonic solar cells. As heterojunctions we have investigated a range of DPPT-T polymers (Mw 49-490) infilled via solvent free processing and the role of post deposition processing on device performance. As electron extracting layers we report on the influence on device performance as the composition of [60]bis-PCBM/P3HT active layers infilled into ZnO nanorod arrays over the active layer composition 1:4 to 4:1, again using solvent free methods. We correlate the structure of the active layers with the measured device performance and provide an insight into the issues influencing device performance in such hybrid devices.

Dye Sensitized Solar Cells (DSSCs) are entitled to be the 3rd generation solar cells in order to be an alternative of former generation photovoltaic cells. The common substrate for commercial DSSCs is glass, which is highly brittle and hinders it integration in mobile application. Considering in-situ recharging of mobile ware and mobile devices such as cell phones, laptop computers, mp3 players etc. via DSSCs, it is vital to produce “Flexible” DSSCs (FDSCs). The term “Flexible” stands for producing DSSCs using flexible substrate such as polymers (PEN, PET) and stable metals (Stainless Steel etc.) as foils. The matter with metallic substrate is that the only way to achieve light harvesting is via counter electrode, which must be definitely a polymeric substrate mentioned before. Therefore, in this study both the development of production method of FDSCs on polymeric substrates and increment in cell performances are in concern. Considering commercial DSSCs, the production of photo anode is conducted by deposition of Titania nanoparticles, which are immersed in a paste via binder, on the FTO coated glass substrates and sintering at around 550 °C in order to form Titania nanoporous thick film. However, in the aspect of production of FDSCs, the utilization of polymeric substrates precludes such a sintering process as for commercial DSSCs. Additionally, it is impossible to use highly viscous paste, binders for FDSCs, since such binders are easily eliminated during sintering process which is an another limitation for production of FDSCs. In order to overcome such limitations, methods for deposition of titania nanoparticles were replaced with “Electrophoretic Deposition (EPD)” while the nanoporous thick film formation method was replaced with “Cold Isostatic Pressing (CIP)”. Several types of alcohol-based colloidal solutions were investigated, most of which exhibited very high uniformity and controllability during the process. Obtained “as-deposited” film morphologies and thickness values were investigated via SEM. In order to obtain the most reliable EPD parameters such as solvent viscosity and dielectric constant, solution pH value, colloid concentration, applied electric field (voltage/current), electrode distance, deposition yield (thickness/time) and zeta potential of colloids were examined and still several results are being investigated, recently. The second step of this study includes determination of CIP parameters. In order to obtain highly interconnected particles to form nanoporous thickfilms which may be referred as “Pseudo-Sintering”, applied pressure vs time profiles were investigated. Furthermore, the characterization and the measurements were conducted via SEM, EIS, BET and Solar Simulator for overall cell efficiency under 1 SUN (AM 1.5 conditions).

Previously [1-3], our group has developed non-contact methods of spatially-selective etching dielectric layers for solar cell fabrication. Both inkjet and aerosol jet printers were utilized for implementing the developed concepts. In the 2013 MRS Fall Meeting and Exhibit, we would like to report our on-going progress in this research area.

Our current focus is on scaling up the process from lab-scale research to pilot-ready concept. We have successfully utilised aerosol jet printer to selectively etch 156 mm wafers. The front-side surfaces of the silicon-nitride-passivated silicon wafers were spin coated with polyacrylic acid (PAA) and then aerosol particles containing ammonium fluoride were deposited by the aerosol printing onto the PAA covered surface to selectively etch the passivation layer. Monocrystalline and multicrystalline wafers were patterned, and the effects of silicon surface morphology, apparent thickness of the coated PAA film, and operating parameters of the aerosol printing on the final etched features (i.e., line width, line width uniformity, and local surface etching percentage) were studied. It was found that, for textured multicrystalline wafers, different crystal grain orientations and grain-to-grain interfaces could result in non-uniform etching of the passivation layer. Future work will involve metallising the silicon exposed through the patterned opening using light-induced plating [4].

It is widely accepted that aerosol jet printing offers an alternative non-contact approach for flexible solar cell dielectric patterning that is amenable to the processing of thinner wafers which are expected in the future [5]. We believe that aerosol jet, compared to inkjet, offers a much higher throughput per nozzle, better material deposition directionality and liability, and, potentially, a wider range of dispensable materials. However, the current process that we have implemented suffers from low packing density (the number of nozzles per unit area) and the system liability was jeopardised by the undesirable condensation of aerosol particles in the fluid lines of the printer. These issues need to be addressed before any industrialization is possible.

References:
[1] Lennon, A., et al., Forming openings to semiconductor layers of silicon solar cells by inkjet printing, Sol. Energy Mater. Sol. Cells, (2008) 92, pp. 1410-1415.
[2] Lennon, A., et al., Direct patterned etching of silicon dioxide and silicon nitride dielectric layers by inkjet printing, Sol. Energy Mater. Sol. Cells, (2009) 93, pp. 1865-1874.
[3] J. Rodriguez, et al. Dielectric Patterning Using Aerosol Jet Printing, J. Imaging Sci. Tech. (2012), No.56(4), pp. 1-7.
[4] A. Lennon, et al., Evolution of Metal Plating for Silicon Solar Cell Metallisation, Prog. Photovolt: Res. Appl. (2012).
[5] International Technology Roadmap for Photovoltaic (ITRPV) 2013.

Inorganic nanowires can be formed using high aspect ratio M13 bacteriophages as templates for nucleation, alignment and growth of nanomaterials and their precursors. These bacteriophages can also be used to organized and spatially distribute nanoparticles along their length, in a substrate-specific manner. Organizing these phages into a three dimensional network creates a porous scaffold onto which metals, or metal oxides can be assembled, providing a means of manipulating electron and other carrier transport within electrochemical or photoactive devices.
Here, we report the covalent layer-by-layer assembly of nanoporous bacteriophage films of hundreds of nanometers in thickness, and the use of these films as a versatile porous nano-scaffold for the creation of three dimensional networks of nanowires and nanocomposites. Our assembly method allows for the tight control composition and thickness of different substrate-specific bacteriophage layers. The resulting bacteriophage nanotemplate is used to biomineralize titania or other photoactive materials, and its pores can be infiltrated with small molecules, polymeric materials or quantum dots, to form a nanostructured active layer for solar cells.

Despite tremendous efforts in research and development after the discovery of high-temperature perovskite-type layered superconductors, and high expectations expressed in market projection potential electrical commercial applications of these materials, the popularity of these superconductors is taking off very slowly. One of the biggest hurdles facing the widespread application of the (RE)Ba₂Cu₃O₇ is developing a manufacturing process of flexible multifilamentary coated conductors, comprised of a buffered metallic substrate and a superconducting layer [1] that will produce it in long lengths and at prices competitive with copper for applications such as motors, generators, transmission cables, and other power systems [2]. Deposition of a (RE)Ba₂Cu₃O₇ coating using physical deposition techniques is too expensive to provide low-cost highly textured coated conductor for AC applications. Therefore, the obvious choice is the chemical route and the sol gel deposited using ink-jet printing is currently recognised as potentially the best way to manufacture 3D multifilamentary high temperature superconductor. In this paper the results of deposition of the buffer layers and multifilamentary (RE)Ba₂Cu₃O₇ superconducting layer by sol gel ink-jet printing is discussed with respect to best conductor AC performance, and also addresses the future research that is required.
[1] B.A.Glowacki, in Frontiers in Superconducting Materials. Springer, New York, 2005
[2] Lectures on Superconductivity, University of Cambridge, Cambridge, 2008
http://www.msm.cam.ac.uk/ascg/lectures
[3] B. A. Glowacki and M. Mosiadz, Journal of Sol-Gel Science and Technology 51 (2009) 347

Substituting Indium Tin Oxide (ITO) for low cost and environmental friendly coatings to be used as transparent conducting electrodes (TCOs) or low emissivity and IR reflective windows is a topic of great interest among material scientists. Zinc Oxide doped with Aluminum (AZO) or Gallium (GZO) represents a valid and cheap alternative to ITO, but the current deposition techniques to obtain high quality coatings (sputtering, CVD, sol-gel) involve expensive setups and/or high temperature processing, and so they are not economically applicable for large scale depositions.
We present a new colloidal approach to synthesize GZO and AZO nanocrystals showing transparency in the visible range and absorption in the near infrared. Doped ZnO colloids are synthesized through hot injection of suitable precursors in a mixture of organic amines. Substitutional trivalent ions (Al3+ or Ga3+) inside the ZnO wurtzite crystals trigger a plasmonic resonance promoted by the increase in free electrons concentration. These nanocrystals can be dispersed in both polar and non polar solvents by using proper surface ligands, and deposited by spin coating, drop casting and spray coating resulting in homogeneous and high quality thin films. The effect of dopant type and concentration has been investigated analyzing the colloids morphology, the optical properties of the nanoparticles, and the optical and electrical properties of the deposited films.
The optical transmission of the nanoparticle assemblies in the visible is greater than 90%, and at the same time, the near-infrared absorption of the nanocrystals is maintained in the films as well.
Several strategies to improve the films performances are presented and discussed: UV light exposure on the thin films is found to remove the organic compounds responsible for the observed grain boundaries resistance, thus increasing the overall electrical conductivity; reducing atmosphere treatments on both colloidal solutions and thin films are found to increase oxygen vacancies concentration, improving both optical and electrical properties.
The electrical resistance of the nanoparticle assemblies is about 30 kOmega;/sq for the as-deposited, UV-exposed films, and it drops down to 300 Omega;/sq after annealing in forming gas at 450 °C, comparable with state of the art tin-doped indium oxide coatings deposited from nanocrystal inks.
These nanocrystal inks can be used to prepare active films for a variety of applications through cheap and simple techniques like ink-jet printing. Moreover, they can be easily dispersed inside polymers, obtaining flexible, conductive, UV-blocking, VIS-transparent and IR-absorbing coatings.

We have investigated the resistive switching (RS) characteristics of InGaZnO (IGZO) films fabricated by low temperature photochemical sol-gel method and compared their chemical components and RS properties with those of the referenced IGZO films prepared by conventional sol-gel method. The photochemical activated IGZO films sandwiched between Pt top and bottom electrodes exhibit high RS performance such as stable high resistance state (HRS) and low resistance state (LRS) as well as steady set and reset voltages. Hydrogen bonding in IGZO films formed by photochemical treatment enhances the RS performances. Based on the electrical conduction analysis, the charge transport in LRS is dominated by hopping conduction of electrons hopping through local filamentary path, while in HRS it is governed by a combination of Schottky emission and Poole-Frenkel emission.

There are so many electric devices in our daily lives. Function thin films prepared by the system operated under vacuum state are used for most of modern electric devices. At the same time, there is a report that over 13% energy in the semiconductor plant is used to just operate vacuum pump. Environmental load dramatically decreases if functional thin films fabrication system is converted from conventional vacuum process to non-vacuum process. Additionally, in non-vacuum system, there are a lot of advantages such as cheap utility cost, simple construction, and easy maintenance, compared with the vacuum process. However, reliabilities of thin films grown by non-vacuum system are poor especially on fabricating uniform and high quality thin film. High control technology on (a) behavior of fluid and (b) reaction is requested in order to improve these demerits.
Mist CVD is one of the techniques of thin film fabrication under atmospheric pressure. In mist CVD, the behavior of precursor is well controlled by using mist, which has the features of floating in air and evaporating with small energy. A precise control system of the precursor flow has been developed [1] and the fabrication of metal oxide thin films, such as, Li, Mg, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Ga, Al, Si, Cd, In, Sn, and their mixed alloy crystal has been achieved [2].
Recently, high quality metal oxide thin films have been grown by non-vacuum based mist CVD system with O₃ assistance. Noticeable influences were obtained in the properties of indium gallium zinc oxide (IGZO) thin films grown with O₃ assistance. From the electric properties of IGZO thin films, carrier concentrations were degradation to 10^-16 cm^-3 with O₃ assistance, while that were 10^-19 cm^-3 without O3 assistance. Mobility is not increasing along with decreasing of carrier concentration. This behavior is the same as high quality IGZO thin films reported in Ref.3. However, impurities in the films evaluated by SIMS were not changed so much. It is verified that O₃ assistance helps the fabrication of high quality IGZO thin films with a few defect. Also, these results suggest that the reaction is shifted from polar reaction to radical reaction. In a word, in polar reaction, there are a lot of dangling bonds in the film due to partial failure of precursor decomposition around such low temperatures. But, in radical reaction, there are few dangling bonds in the film due to higher reaction ability. From the results, binding defects in the IGZO thin films were repaired with O₃ assistance.
The properties and the reaction mechanism at the time of growth of IGZO thin films, in light of IGZO TFT characteristics, are reported in this conference.
[1] T. Kawaharamura: Ph.D. Thesis, Faculty of Engineering, Kyoto-Univ., Kyoto, 2008 [in Japanese]
[2] T. Kawaharamura, H. Nishinaka, and S. Fujita, Jpn. J. Appl. Phys. 47 (2008)
[3] Toshio Kamiya, Kenji Nomura, and Hideo Hosono, Sci. Technol. Adv. Mater., Vol.11 (2011) 044305.

Transparent conducting oxide (TCO) is the most widely used material for transparent electrodes due to its excellent performance and stability. In TCOs, high electrical conductivity and large transparency window are essential. Conductivity is product of carrier concentration (N) and mobility (µ), but higher electron concentration can deteriorate the transmittance in near-infrared (NIR) region. Therefore, for the development of high performance TCO, improvement of electron mobility is important. Molybdenum doped indium oxide (IMO) is the most representative high mobility TCO material. However, most of the reported IMO films were produced by vacuum deposition. We have developed high performance solution-processed IMO films by optimization of the post-annealing. Post annealing is essential for solution based deposition because of the decomposition of organic precursor and crystallization during annealing.
IMO films were deposited on glass substrate by spray pyrolysis. A solution for spray coating was made of indium chloride and molybdenum chloride in distilled water with the concentrations of 0.025 mol. Solution was directly sprayed using compressed air onto a glass substrate on a hot plate heated at 400 °C. Mo doping concentrations were 0 - 4 at %. After spray coating, oxygen partial pressure controlled annealing was conducted. The ranges of the temperature, time, and oxygen partial pressure were 400 - 700 °C, 1 - 3 h, and 10^-6 - 1.6 × 10² Torr, respectively. From X-ray diffraction analysis, the fabricated samples were identified as highly crystalline IMO films. Measured electrical conductivity of IMO films was changed significantly by Mo concentration and annealing atmosphere. In 2 at % of Mo after annealing under 1.1 × 10^-6 Torr of oxygen partial pressure, the highest conductivity (1618 Omega;^-1cm^-1) which was similar to solution-processed ITO films was obtained. Mobility was maximized in 1-1.5 at % and decreased as doping concentration increased. Mo substitution to In affected both electron concentration and mobility. Also, oxygen vacancy generation and microstructural change influenced the electrical conductivity of solution-processed IMO films. Microstructure evolution varied as the Mo contents and annealing ambient; as oxygen content increases, nanoparticle shape becomes circular to angular shape with the size increase. Transparency window increased by Mo doping. Solution-processed IMO films showed much higher transmittance in NIR region (>85 %) than conventional ITO films.

In the last decade metal oxide semiconductors have become serious candidates for use in thin-film electronic technologies with applications in display backplanes, smart windows, solar cells, and radio-frequency ID tags. There is therefore a motivation to study materials that offer mechanical flexibility, the ability to be processed on a roll-to-roll basis, and are low-cost. This potentially allows novel, large-area device arrays on plastic substrates. A combination of high electron mobility in the amorphous state, high optical transparency, and solution processability make metal oxides an excellent choice[1,2]. Many of the most commonly studied materials are based on indium oxide with the addition of elements such as gallium, yttrium, zinc or tin to induce amorphous structure and control lattice defect concentrations. For example, sputtered films of In-Ga-Zn oxide (IGZO) are the closest to commercialization of the current systems. However, moving to a solution-based deposition method would allow printed, dip-coated or spray-coated films, thus reducing the cost of large-area electronics.
In our group we have reported a very general method for the low-temperature solution processing of oxide films using combustion synthesis[3]. The precursor solution consists of the metal nitrates, with the nitrate ion acting as the oxidiser, a fuel molecule, such as acetylacetone, and a solvent. Compared to traditional sol-gel methods the required annealing temperature to form the oxide can be significantly reduced due to the strong exothermicity of the reaction providing local, rapid heating within the film. We have applied this method to several oxides including indium oxide, IZO, and IXZO with various secondary cations (X = Ga, Sc, Y, La), all annealed at 300 C or less. Solution processing allows us to systematically study the structural and electronic effects of different cations over a wide compositional phase space.
By studying the IXO system and varying the size of X from Sc to Y to La, we can better understand the role of each cation in solution-processed thin films, which will usually differ greatly from the bulk oxide. Increasing the concentration of X induces a change from crystalline to amorphous film, however, also tends to lower the electron mobility in field-effect transistors (FETs). Additionally, larger cation species such as La will tend to disrupt the indium oxide lattice more significantly meaning that the amorphous phase will be induced at a lower X concentration. We have used X-ray absorption fine structure (XAFS) analysis to probe the local coordination and bond lengths around indium and X cations in these amorphous films. Furthermore we have measured excellent FET mobilities in amorphous films by employing X = La with value of 9.7 cm²/Vs and 5.1 cm²/Vs when processed at 300 C and 250 C respectively.
[1] Nomura et al., Nature 432, 488 (2004)
[2] Fortunato et al., Adv. Mater. 24, 2945 (2012)
[3] Kim et al., Nat. Mater. 10, 382 (2011)

Inkjet printing technology has attracted attention for use in a variety of applications. The advantages of this technology include additive patterning, reduction of material waste, and compatibility with flexible and large area substrates. Recently, novel active materials such as conjugated polymers and semiconducting metal oxides have been explored for inkjet printing applications. Among them, metal oxide semiconductors have shown great electrical performance even in amorphous phase. However, for practical application of this material in logic circuits, a high performance p-type semiconductor is required. Complementary inverters, which are widely employed in digital logic applications, are composed of n- and p-FETs due to their low power dissipation. In this work, we present complementary circuits employing high performance zinc tin oxide (ZTO) and single-walled carbon nanotubes (SWCNT) for n- and p-FETs, respectively. Both semiconductor layers are formed by inkjet printing in ambient air. In addition, solution processed zirconium dioxide is employed as the gate dielectric for low voltage operation. Both FETs exhibit high field effect mobilities > 5 cm^2/Vs, much higher than inkjet printed organic semiconductors. The complementary inverter composed of the ZTO and SWCNT FETs shows sharp inverting operation and low static power consumption. In addition, five stage ring oscillators which operate at high frequency are demonstrated.

High dielectric constant thin films have widespread usage in embedded capacitors, multilayer capacitors, gate dielectrics for field effect transistors, memory and power storage devices. Self-assembled films built from high- dielectric-constant nanoparticles are attractive as a foundation for new dielectric media with increased efficiency and range of operation, due to the ability to exploit nanofabrication techniques and emergent electrical properties originating from the nanoscale. We present the use of chemically synthesized (Ba,Sr)TiO3 nanocrystals, and a novel deposition-polymerization technique, as a means to fabricate the dielectric layer. The effective dielectric constant of the film is tunable according to nanoparticle size, and effective film dielectric constants of up to 34 are enabled. Wide area and multilayer dielectrics of up to 8 cm2 and 190 nF are reported, for which the building block is an 8 nm nanocrystal. We describe models for assessing dielectric performance, and distinct methods for improving the dielectric constant of a nanocrystal thin film. The approach relies on evaporatively driven assembly of perovskite nanocrystals with uniform size distributions in a tunable 7-30 nm size range, coupled with the use of low molecular weight monomer/polymer precursor chemistry that can infiltrate the porous nanocrystal thin film network, post assembly.

Cyclic heating and cooling of components during service results in development of stresses which cause the materials to degrade and fail. Materials with high CTE are particularly prone to failure. By combining negative and positive CTE materials at the nanoscale, it is possible to design materials with low CTE.
Several compounds with AM2O8 general formula exhibit negative coefficient of thermal expansion (NCTE) over a wide range of temperature. ZrW2O8 exhibits isotropic NCTE from nearly absolute zero to over 777 °C, It is thermodynamically stable in a very narrow temperature range 1105-1257 °C but it is also metastable up to 777°C. Single crystals of ZrW2O8 are required to characterize its select intrinsic properties before proceeding with nanocomposite processing.
ZrW2O8 is in equilibrium with liquid phase between 1230 and 1257 °C and over a very narrow composition range of 67-74 mol %. This severely restricts the crystal growth conditions. Crystals with several mm in size were synthesized by self-fluxing technique. We also report the growth of ZrMo2O8 single crystals using Li2Mo2O4 flux for the first time. Synthesis of phase pure ZrW2O8 powders is also quite a challenge. Hydrothermal synthesis has been shown to be a viable approach for synthesis of ZrW2O8 with varying levels of Mo substitution for W. Synthesized nano powders showed anisotropic particle morphology with tens of nm in diameter and several hundred nm in length. In addition, ZrW2O8-ZrO2 composite nanopowders were also synthesized by hydrothermal processing route which were subsequently consolidated by uniaxial pressing and sintered at between 1150-1225 °C for 15 min. to 1 h. The structure and several mechanical and physical properties of sintered pellets were characterized.
Technical challenges as well as potential opportunities for design and development of CTE tailored nanocomposites for high temperature optical applications will also be discussed.
______________
This work was supported by the Office of Naval Research, Arlington, VA under award no. N00014-12-0316.

Ultraviolet (UV) photodetectors are important devices with applications in a wide range of applications. Among the most common applications are solar-blind detectors, sensors for biologically damaging or biologically stimulating UV irradiation, detectors of atmospheric UV-absorber ozone, and detection of UV light used for photolithography in semiconductor wafer manufacturing. Conventional UV photodetectors developed are based on wide-gap semiconductors such as SiC, GaN, and diamond which require vacuum processing that are expensive.
Here, we have successfully demonstrated an air-stable solution processed all-inorganic p-n heterojunction UV photodetector with a high gain (EQE - 25,300%). Solution processed NiO and ZnO films are used as p-type and n-type ultraviolet sensitizing materials, respectively. The high gain in the detector is due to the hole traps in the NiO film which result in interfacial trap-induced charge injection at an ITO/NiO interface. The detector gain can be controlled by post annealing of the solution processed NiO films. Furthermore, our all-inorganic UV detector consists of all oxide layers (ITO anode, p-type NiO layer, and n-type ZnO layer) except an Al top electrode, thus expected to good air stability. The EQE is enhanced in the device stored in atmosphere for the first 20 days, indicating that the oxide layers were further stabilized in the atmosphere. The EQE begins to decrease after 20 days but are still higher than the initial value even after 50 days. Therefore, the solution processed oxide p-n heterojunction UV photodetectors have great potential for replacing conventional vacuum deposited UV photodetectors and for opening up new applications.

In recent years, directed self-assembly have attracted growing interest for the formation of functional molecular or colloidal monolayers or even more complex, three-dimensionally (3D) ordered nano and micro structures. Examples for applications of these monolayers from various fields of science and technology are wettability tuning, which can be used e.g. in microfluidics, charge injection in field-effect transistors, recognition layers in biology, passivation for metals as corrosion prevention and many more. Next to monolayers, also complex 3D structures can be formed conveniently by directed self-assembly. Usually, the formation of 3D ordered nano and micro structures with conventional microfabrication methods such as photolithography is very challenging. Appropriate, reliable and well-elaborated experimental procedures are needed.
In this contribution, we combine directed self-assembly and inkjet printing as scalable additive production technique for the manufacturing of patterned and ordered structures on both nanoscopic scale and large area at the same time. Evaporating droplets ejected by inkjet printing technology can induce the self-assembly of alkylsilane molecules in molecular monolayers [1] or of colloidal particles in spherical aggregates [2]. We could successfully grow patterned alkylsiloxane monolayers molecules using inkjet printing on silicon oxide within a few hundred milliseconds. Even after several months, the molecules adsorbed to the silicon oxide surface. Next to the monolayers, 3D microstructures could be developed by inkjet printing of colloidal particles. In this case, the ejected droplet serves as a template for the colloidal particles. Under specific conditions, the colloidal particles arrange as ball-shaped 3D structured with a high degree of symmetry. In contrast to other approaches, the formation of aggregates is independent on surface properties of the substrate. Therefore, inkjet printing turned out as promising method for the deposition of 3D microstructures suitable for any solid surface in dry environment and in a fraction of a second. Our results show, that inkjet printing as digital manufacturing technology in combination with self-assembly is a powerful tool for the deposition of high functional molecular monolayers as well as 3D microstructures.
[1] E. Sowade, J. Hammerschmidt et al., Adv. Eng. Mater. 14, 2012, 98-100.
[2] C. Belgardt, E. Sowade et al., Phys. Chem. Chem. Phys. 15, 2013, 7494-7504.

To date, there have been a lot of interests about various metal nanostructures with fascinating surface plasmon properties which are determined by their shape, and the size of the metals. Among them, metal nanoshells, consisting of a dielectric core surrounded by metallic shells, are of great attention due to their unique plasmon resonance which can be tuned by varying relative thickness of core and metallic shell layer. Although several synthetic methods have been reported to prepare uniform and reproducible metal nanoshells, especially Au- or Ag- nanoshells (Au- or Ag-NSs), conventional strategies require metal seed to nucleate for further growth, which requires inefficient and time-consuming multi-step process. In this presentation, we describe a simple strategy that Ag ions are stabilized by ethylene glycol and subsequently reduced by ocytylamine followed by burst nucleation and growth of Ag shell on silica nanoparticles (NPs). As-prepared Ag-NSs are suitable as SERS active substrate to detect and identify molecules due to their rough surface structure, which can afford ‘hot spots&’ for localized near-field enhancement effects. Furthermore, Ag-NSs have great potential as on-site detector for direct surface detection of a pestiside as examplified in the detection of thiram residues.

Synthesis of highly-ordered nanostructures of valve metal oxides has recently attracted huge scientific and technological interest motivated by their possible use in many applications. The nanoporous Al2O3 - most established member of this group of materials - has been prepared by anodic oxidation of Al under suitable electrochemical conditions nearly two decades ago into perfectly ordered, honeycomb-like porous structures [1]. Owing to the flexibility of the pore diameter/length and the relative ease of the Al2O3 dissolution, its porous membranes have been since than widely used as templating material of the choice for a range of materials [2-4].
It is the TiO2 [5] that has received the highest attention after Al2O3 motivated by its range of applications, including photocatalysis [6], water splitting [7], solar cells [8] and biomedical uses [9]. Very significant research efforts have led to reproducible synthesis of self-organized TiO2 nanotube layers by means of anodic oxidation [10-14], during which the starting Ti substrate is converted into highly-ordered nanotubular layer by anodization in suitable electrolyte.
Although many applications of the nanotube TiO2 nanotube layers have been presented, their potential for the synthesis of advanced functional nanomaterials, in particular when considering all possible shapes and geometries, has not at all been exploited.
The presentation will focus in detail on various filling routes of anodic templates and supports and will show examples of various functional devices including some very recent results.
References
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Nano-sized particle (nanoparticle) has been studying for several decades due to it has unique physical/chemical properties, and it has been applied to various fields; electric, sensor and medicine. Recently, organic/inorganic nanoparticle has been focusing on various research fields due to it has electrical and fluorescence properties, and the preparation methods have been developed; hydrothermal, precipitation, and electro-chemical method etc. However, the general method is difficult to size-control of the nanoparticle and has very broad size distribution, which caused decreasing of the various properties.
Therefore, we present novel preparation method of organic/inorganic nanoparticle using nanocage. In this study, silica nanocage (hollow silica), having porous structure and empty space, is used for template, and the nanoparticle can be prepared in the nanocage. As results, we can more increase the uniformity and properties of the nanoparticle, and this method might be applied to preparation of various materials.

The integration of quartz on silicon in thin film form is appealing for its prospective applications in electronics. For instance, this could be used to make oscillators with higher resonance frequencies, in new electromechanical devices or as buffer layer for the growth of complex oxides on silicon. We have recently reported the epitaxial growth of quartz films on silicon following a soft-chemistry approach ¹.
The aim of this contribution is to discuss in detail the mechanisms of this synthesis. The films are obtained by the crystallization of amorphous silica films prepared by chemical solution deposition and . Two key components of the solution are Sr²⁺, acting as catalyst for the crystallization of silica, and amphipilic templates playing the role of structuring agents and assisting in the crucial phase separation of the catalyst. The good matching between the quartz and silicon cell parameters is also essential in the stabilization of quartz over other SiO₂ polymorphs and is at the origin of the epitaxial growth. The films are piezoelectric and can be tailored to be dense or to present an ordered porosity with pore diameters ranging from a few tenths of nanometer to the micron scale.
(1) A.Carretero-Genevrier et al. Science 340 (2013) 827

Highly uniform perovskite colloidal ABO3 (A=Ba, Pb; B=Ti, Zr) colloidal nanocrystals have been synthesized by a solvothermal method under alkaline conditions in the presence of oleic acid as a capping agent. The controlled synthesis of such nanostructured materials has been a tedious process as the transition metals undergo a nucleophilic attack by water molecules, thereby resulting into nanopowders which lack morphological and structural uniformity, which is detrimental to their macroscopic properties. In the proposed method transition metal ions are protected against water molecules upon the in-situ formation of metal fatty acid salts, which are subsequently decomposed under solvothermal conditions leading to the desired perovskite nanostructured material. The influence of various reaction parameters, such as temperature, time, and concentration of Ti and Ba precursors on the morphology of the nanocrystals was investigated in detail. Transmission electron microscopy (TEM), X-ray diffraction and Raman spectroscopy have been used to characterize the particle size, shape and internal structure of the BTO nanocrystals. It has been shown that by controlling the synthesis parameters the size of the nanocrystals can be varied from 5 to 35 nm. The size of particles strongly depends on the rate of the nucleation and the subsequent growth processes.
By using a controlled solvent evaporation process and varying the concentration of the nanoparticles dispersed in a non-polar solvent, these nanocrystals can be individually manipulated and assembled into highly ordered 2 or 3-D superlattice structures. TEM characterization of self-assembled particles shows the existence of a long range order in these superlattice structures. Self-assembled structures were also studied by piezoresponse force microscopy to obtain a glimpse onto their ferroelectric behavior. The experimental results unequivocally show that ferroelectricity is retained in these nanostructures and the 10 nm crystals present a primarily linear structure of the dielectric polarization.

HgTe colloidal quantum dots (QDs) is a promising material for photodetection applications due to their solution processibility and wide spectral tunability in the near-infrared to mid-infrared wavelength range. HgTe QD photoconductive photodetectors with sensitivity beyond 2 µm have been reported; however, these devices often suffer from slow temporal response and limited photoactive area due to the planar configuration. In this study, we demonstrate the first spray-deposited HgTe QD photodiode that exhibits photoresponse up to 3µm. Both the heterojunction-diode and Schottky-diode structures are fabricated and compared. The effects of the trap states and built-in electric field on the responsivity and bandwidth of the devices are studied using optical and electrical characterization techniques, including light intensity-dependent and temperature-dependent transient photocurrent measurements and time-resolved photoluminescence spectroscopy. Furthermore, making use of a wet-chemistry-based immobilization method, we implement a dispersed gold nanorod plasmonic structure into the HgTe QD photodetectors. The light absorption and scattering enhancement in the QD films are confirmed by optical measurements as well as finite-difference time-domain (FDTD) simulation. The performance of two device structures with the nanorods embedded in the active layer and the hole-transporting layer, respectively, is compared.

Oxide thin-film transistors (TFTs) have attracted significant attention in future displays owing to their high performance and optical transparency in the visible region. In oxide TFTs, however, high operating voltages are often required to achieve a high mobility and a high on/off current ratio. To deal with this problem, high-κ materials including inorganic binary oxides (Y2O3, HfO2, Ta2O5, and ZrO2) and ternary oxides (La-Hf-O, La-Zr-O, Sr-Ta-O and Bi-Nb-O) have been extensively studied as gate dielectrics for application of TFTs. Gate dielectrics must be smooth, dense, and pinhole-free to allow a high breakdown field. Further, dielectric-semiconductor interfacial quality, high dielectric constant, and low interface trap density are also key factors in determining the electrical characteristics of TFTs. Barium tantalum oxide (BTO) is an excellent candidate because of a combination of desirable electrical properties (wide band gap and relatively high dielectric constant) and chemical properties (solubility in common solvents and stable, complete stoichiometry). In addition, the stable amorphous phase of BTO could offer not only a high uniformity over a large area but also a low temperature process.
In addition, these high performance oxide TFTs are generally fabricated by using cost-effective vacuum deposition processes. In contrast, chemical solution deposition (CSD) methods could offer many advantages, such as low-cost, high throughput, flexibility and direct patternability. Therefore, formation of component TFT layers by a CSD process would be eventually required.
So far, study on BTO thin film dielectric and application of TFTs via CSD processing has not been reported yet. In this research, an indium oxide (In2O3) channel layer and a high-κ BTO gate insulator were both deposited using a CSD process for the fabrication of TFTs. A low turn-on voltage of -0.19 V, a low threshold voltage of 0.86 V, a high on/off current ratio of 5.0E7 at a low voltage of 5.0 V, and a high saturation mobility of 2.85 cm^2/(Vs)^(-1) were obtained. Furthermore, a very low sub-threshold swing value of 0.11 V/decade was achieved. This low value could be attributed to the atomically smooth surface (RMS ~ 0.29 nm) of amorphous phase and the high dielectric constant of 21 for the BTO thin film. In addition, we found that the concentration of carbon impurities in the In2O3 channel layer was reduced possibly by the diffusion of oxygen from the BTO insulator layer to the In2O3 layer through the interface, which in turn enhances channel mobility. These results show that high-κ BTO is a prominent dielectric material for the application of low-operating voltage oxide TFTs requiring a simple, high throughput, and low-cost process.

Surface plasmons are electromagnetic waves that can exist at metal interfaces, because of coupling between light and free electrons, which can be channeled, concentrated or otherwise manipulated by surface patterning. Therefore, a great effort has been devoted in designing and producing metal surfaces, which exhibit appropriate surface morphology that maximizes the occurrence of surface plasmons at specific spectral bands. Among the most promising applications of such metal surfaces is surface enhanced Raman scattering (SERS), which is widely used in biosensing.
In this work we present a simple and cost-effective route for the facile production of plasmonic templates for SERS, which is based on the selective electroless reduction of AgNO3 on Si surfaces from aquatic solutions of HF and AgNO3. The basic deposition parameters, such as the pH of the solution, the concentration of AgNO3 in the solution and the deposition time, are considered in terms of the structural and morphological features of the Ag deposits, which are studied by X-ray diffraction (XRD), reflectivity (XRR), X-ray Photoelectron Spectroscopy (XPS) and Scanning Electron Microscopy (SEM). The optical performance and the plasmonic behavior of the templates are evaluated by optical reflection spectroscopy. The morphology and plasmonic behavior of the deposited templates are further tuned by rapid thermal annealing and induction annealing. The irregularly shaped Ag clusters transform to hemispherical domes of varying sizes (of the order of few tens of nm) after annealing.
The SERS performance of the produced templates, before and after annealing, is evaluated by probing aquatic solutions of Rhodamine 6G (R6G). The produced templates do probe solutions with [R6G] concentrations below 1 nM; this performance is competitive to that of plasmonic templates produced by methods of higher degree of sophistication, cost and production time.
Acknowledgement: This work is financially supported by the European Union through the FP7 project ‘SMARTONICS&’, Grant Agreement No 310229.

Today, organic light emitting diodes (OLEDs) and displays have achieved commercial relevance due to their unique contrast and low power consumption. While most state-of-the-art OLEDs for OEM applications are deposited in vacuum, science and industry work hard on solution processable and hence potentially low-cost fabrication alternatives. The main objectives are to overcome solvent limitations during the deposition of multi-layer devices and to enhance the lifetime of the devices. One material class that was proven to be very beneficial for (vacuum deposited) OLEDs are transition metal oxides. In this work we use a variety of metal oxide precursors in order to fabricate charge carrier transport layers from MoO3 or WO3 for OLEDs from solution and to facilitate charge injection into solution processed small-molecule OLEDs. The respective layers are transparent to visible light and become insoluble to most solvents after deposition enabling the subsequent solution deposition of almost any emitters. In particular we have focused on processes that can be carried out at moderate temperatures to be suitable for roll-to-roll fabrication on flexible plastic substrates. While most precursors require oxygen to be converted into a metal oxide, we investigated processes that can be carried out under nitrogen atmosphere and hence can be beneficial for the device lifetime. By using metal oxides with very high work function, we were able to fabricate efficient phosphorescent blue emitting OLEDs from solution as holes could easily be injected into the low HOMO of the emitter matrix.

The purge separated pulsing of precursor and oxidation gases in atomic layer deposition enables self-limiting surface reactions that lead to dense conformal thin films with atomic scale control. From a sustainable manufacturing perspective however, ALD suffers from slow deposition rates, precursor waste, and the requirement of a vacuum system. Solution based methods are attractive in that they allow for deposition at atmospheric pressure and with shorter processing times. Traditional solution based approaches often involve organometallic sol-gels with bulky ligands which require high temperature post deposition anneals to be driven off. This results in deleterious changes in physical dimensions and films of poor electrical quality. More recently, a novel solution processing technique known as prompt inorganic condensation (PIC) has enabled the deposition of dense, smooth, high-quality films through the use of aqueous metal-inorganic precursors.
In this work we compare the electrical and physical properties of Al2O3 films produced by ALD and PIC. ALD of Al2O3 is performed using trimethyl-aluminum and H2O at 300°C. PIC of Al2O3 is performed using aqueous aluminum hydroxide clusters in nitrate ion solution at room temperature in atmosphere. Immediately following PIC, post deposition anneals convert the hydroxide to an oxide, remove nitrates, and densify the films. Using Al/Al2O3/Si MOS capacitors it is found that 300°C annealed 10 nm thick PIC Al2O3 films show higher leakage and lower breakdown strength than ALD Al2O3. When annealed at 500°C , PIC Al2O3 shows lower leakage current density than ALD Al2O3 at fields >2.5 MV/cm and equivalent breakdown strength. Conduction processes in each film are identified and compared. Capacitance vs. voltage data shows that PIC films have a lower dielectric constant than ALD films and an anneal temperature dependent flat band voltage shift. X-ray reflectivity indicates that as-deposited PIC films have a low density which increases with increasing anneal temperature to approach that of the ALD films. Finally, X-ray photoelectron spectroscopy and transmission electron microscope data are used to contrast the Al2O3/Si interfacial region in PIC and ALD films. Differences in interfacial layer formation may explain the reduced leakage current observed in the lower density PIC films. Our results show that PIC is a promising method for deposition of thin (~10 nm) Al2O3 films on silicon.

We observed the formation of self-assembled monolayers (SAMs) by coadsorption. Fluorinated phosphonic acid is utilized as the gate dielectric of organic thin film transistors (OTFTs). In combination with aluminum oxide, the strong electronegativity of the fluorine atom in the molecule shifts the threshold voltage of the OTFTs in the positive direction. The deterministic and continuous control of the threshold voltage by SAM coadsorption is reported [1] and applied to enhance the circuit properties by forming multiple SAMs on a substrate by soft lithography method [2], yet the detailed behavior of the two species of molecules on the surface is not known.
The isopropanol solutions of two species of phosphonic acids, octylphosphonic acid and perfluorooctylphosphonic acid, were prepared separately, then mixed. SAMs were coadsorbed on plasma-oxidized aluminium by dipping method and utilized as the gate dielectrics of OTFTs. The organic semiconductor of dinaphtho[2,3-b:2prime;,3prime;-f]thieno[3,2-b]thiophene [3] and Au source/drain electrodes were formed by thermal evaporation and transistor characteistics were measured. The threshold voltages of OTFTs were shifted from -1.0 V to 0.4 V and mobilities from 0.5 cm²/Vs to 2.5 cm²/Vs when the mixture proportion of the perfluoorooctylphsophonic acid was changed from 0% to 100%. The effect of the strong negativity of fluorine atom to shift the threshold voltage in the positive direction was observed, yet the relationship of the threshold voltage shift and the fluorine atom concentration in the solution was not linear. To investigate this further, the surfaces of the coadsorbed SAMs were observed by X-ray photoelectron spectroscopy (XPS) and the non-linear relationship of the fluorinated SAM mole fraction in the solution and that in the coadsorbed SAM was investigated. The mole fraction of fluorine on the surface was varied from 0% to 55% when the mixture proportion of perfluorooctylphosphonic acid was changed from 0% to 100%.
This work is partly supported by JST/ERATO, Special Coordination Funds for Promoting. A part of this work is conducted in Research Hub for Advanced Nano Characterization, The University of Tokyo, supported by the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan. One of the authors (I. H.) is grateful to the research fellowships for young scientists of JSPS.
[1] U. Zschieschang, F. Ante, M. Schlörholz, M. Schmidt, K. Kern, H. Klauk, Advanced Materials (Deerfield Beach, Fla.) 22 (2010) 4489.
[2] I. Hirata, U. Zschieschang, F. Ante, T. Yokota, K. Kuribara, T. Yamamoto, K. Takimiya, M. Ikeda, H. Kuwabara, H. Klauk, T. Sekitani, T. Someya, in:, 2012 MRS Spring Meeting, San Francisco, 2012, p. J6.21.
[3] T. Yamamoto, K. Takimiya, Journal of the American Chemical Society 129 (2007) 2224.

Three-dimensional (3D) YBO3:Tb3+ microspheres and microflowers constituted of nannoflakes successfully fabricated by a simple hydrothermal approach in the aqueous solution using inexpensive and environmental friendly agents. Morphology and dimensionality control of well-defined YBO3:Tb3+ hierarchical microstructures in hexagonal phase were achieved by simply adjusting the concentration of ethanol. The crystalline structure and morphology of as-prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and selected area electron diffraction (FFT). The growth mechanism of these YBO3:Tb3+ microstructures was explored based on time-dependent experiment and the result showed that the mechanism follows an in-situ growth process rather than self-assembly. Furthermore, a relationship between the morphology and the photoluminescence behavior was studied. Remarkable photoluminescence enhancement was observed YBO3:Tb3+ with microsphere morphology demonstrating the potential of these microstructures in future applications as a green phosphor.

Polyimides (PIs) have been used in many applications for their excellent thermal, mechanical, and electrical properties. For example, they can be used as insulation layers for semiconductor devices, or substrates for flexible printed circuits. Recently light and thin plastic substrates for displays are being actively developed, as portable device market expands. The substrate, where TFT is deposited, is one of the important components in display devices with determining the performance, reliability, and even the price of the devices.
However, most aromatic PIs usually show considerable coloration ranging from pale yellow to brown, which hinders their use in flexible substrate for display device. In general, aromatic PIs are thought to absorb UV/Visible light through formation of a charge-transfer complex (CTC) between the diamine and the dianhydride where the former acts as an electron donor and the latter as an electron acceptor. Interchain CTC formation is considered as a major factor for the coloration of PIs, but the oxidation of remaining solvent and polyimide backbone also contributes to the coloration of the film. Despite highly controlled purification of monomer and solvent, the coloration of the final film is not able to be avoided due to high temperature immidization condition.
Recently water or hydrophilic solvent-soluble HfO2 nanoparticles with several nm scales were synthesized. New organic-inorganic hybrid films (polyimide/HfO2) were prepared by simple solution mixing procedure. Highly compatible and well dispersed small size nanoparticles prevent PIs from interchain CTC formation, which results in transparency increase. Ligand exchange of acetic acid on the surface of HfO2 with carboxylic acid of polyamic acid enables pseudo-physical cross-linking between HfO2 and PIs, which results in enhanced physical properties like higher tensile strength, toughness and glass transition temperature (Tg) increase. Considering the percolation threshold, more than 1 wt% of nanoparticles should be incorporated to get enhanced property of nanocomposite resulting from synergetic effect between two components. In this study, less than 1 wt% of nanoparticle incorporation shows maximized optical and physical properties of nanocomposite due to the highly compatible and well dispersed nanoparticles with small size(< 2nm).

Tungsten oxides have been extensively investigated due to their outstanding physical and chemical properties, such as electrochromic, optochromic and gasochromic properties, resistance to photocorrosion in aqueous solutions.[1][2] Particularly, the hexagonal tungsten trioxide (WO3) has a unique tunnel structure, which can be used as an intercalation host for obtaining hexagonal tungsten bronzes MxWO3 (M = Li+, Na+, K+, etc), a promising electrode material for energy storage. Recently, nanostructured tungsten oxides are usually prepared under high temperature, long reaction time and/or on special substrates. In this work, we demonstrate a novel approach to grow hierarchically nanostructured porous tungsten oxide through a hydrothermal process at mild temperature (95 °C). Citric acid used in our experiments is the key to control the morphology of tungsten oxide nanostructures, especially the formation of porosities. The impact of pH value and concentration of solution has been investigated. As-prepared nanomaterials are further characterized by FETEM, SEM and X-ray diffraction spectrum. Such tungsten oxide nanostructures will be used in our latest developed photovoltaically self-charging cells for energy storage capacity. [3]
1. D. Chen and J. Ye, Adv. Funct. Mater. 2008, 18, 1922.
2. K.Huang, Q. Pan, F. Yang, S. Ni, X. Wei and D. He, J. Phys. D: Appl. Phys. 2008, 41, 155417.
3. X. Zhang, X. Huang, C. Li, and H. Jiang, Adv. Mater. DOI: 10.1002/adma.201301088.

Indium Tin Oxide (ITO), which is transparent and has a good electric conductivity, has been widely used for electric devices as ITO films. They have been produced by vacuum deposition methods. Meanwhile, there have been some researches to make ITO films by solution processes such as a metal-organic decomposition (MOD) method. The MOD method is attractive in terms of an eco-friendly process in fabricating metal-oxide. However, ITO films which are made by MOD method tend to have poorer electric properties than those by conventional vacuum deposition methods. One of major reasons could be attributed to a lack of knowledge about the structure change form solution to crystal via gel. As the first step of the understanding of conversion process, we investigated the structure of an ITO solution in this work.
In-acetylacetonate (In-acac) and Sn-acetylacetonate (Sn-acac) were dissolved propionic acid (PrA) to make the 5wt% ITO solution in which the ratio of In to Sn is 95 to 5. Then it was kept at 120 degree C for 1 hour in a closed bottle. To analyze the structure of the ITO solution, we carried out mass spectrum analysis by using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) and conducted pair distribution functions (PDF) analysis by measuring high energy X-ray diffraction.
In mass spectrum analysis, peaks corresponding to the molecular weight from 1000 to 2500 were observed, but peaks corresponding to In-Acac and Sn-Acac were not observed. Furthermore, it was found the peaks less than the molecular weight of 1850 came from molecules consisting of In, O, Acac, and PrA. And the peaks more than 1850 corresponded to molecules consisting of In, Sn, O, Acac and PrA. This result gives us a rough sketch of the structures of molecules in the ITO solution: In-O-In core surrounded by organic ligands of Acac and PrA.
To investigate the fine structure of molecules in the ITO solution, we performed PDF analysis to evaluate total correlated function T(r) of the ITO solution, together with an ITO gel and an ITO crystal made from the solution. The T(r) of ITO solution showed peaks at 1.3, 2.26 and 3.6 angstrom. The peak of T(r) at 1.3 angstrom may be resulted from carbon related substances such as C-O and C-H because the ITO-gel and crystal has no peak at this region. The peaks at 2.3 and 3.6 angstrom can be judged to correspond to In-O and In-In bonds respectively, because these peaks also appeared in T(r)s of the ITO gels and ITO crystal. Namely, it is demonstrated that the molecules in the ITO solution already have the same In-O-In structure as that of the ITO crystal.
As a conclusion, we clarified that same In-O-In structures as that of an ITO crystal were already formed in an ITO solution. That means the structure of a final ITO crystal can be affected by the structure of the ITO solution. If so, there is a great chance that the properties of an ITO crystal film could be improved by tuning the structure of ITO solution.

ZnO nanoparticles containing transition metal nickel were synthesized by sol-gel technique. The nanoparticles were given heat treatment at 7000C for 1h in electrical muffle furnace to remove the residue remains unreacted. The effect of Ni doping on structural properties of ZnO was investigated by using X-ray diffraction (XRD) and FTIR Spectroscopy. FTIR study indicates the formation of ZnO with stretching vibrational mode in Ni containing ZnO. XRD analysis of the material identifies hexagonal wurtzite structure of Ni doped nanoparticles. The average particle size was determined from the full width at half maxima (FWHM). The particle size increased with the increase in Ni concentration. Doping of ZnO with Ni2+was intended to enhance the surface defects of ZnO.

Usually quaternary oxide compounds were synthesized by solid state reaction, which was the most widely-used preparation process, and sometimes still the only way for preparing complicated multi-component oxide compounds. Recently, the study on hydrothermal process in supercritical water has attracted much attention due to the special chemical and physical properties of supercritical water system. Moreover, supercritical water hydrothermal method had been proved to be a potential technique for the preparation of functional oxide materials with single phase, uniform morphology and particular properties. Compared with the traditional synthesis methods, supercritical water hydrothermal process is green, quick and effective, particularly showing great advantages in preparing quaternary oxide compounds ultrafine particles.
BaTeM2O9 (M=Mo or W) is one of attractive noncentrosymmetric (NCS) oxide materials, containing both cation with nonbonded electron pairs (Te4+) and d0 transition metal cation (Mo6+ or W6+) susceptible to the second-order Jahn-Teller effect. Polycrystalline BaTeMo2O9 and BaTeW2O9 were first synthesized by solid state reaction. Such powders always showed undesired features such as serious particle aggregation and irregular particle morphology. Here we report a novel hydrothermal route via supercritical water system to prepare polycrystalline BaTeM2O9 (M=Mo or W) particles with uniform morphology and desired features by using barium carbonate, tellurium oxide and molybdenum oxide or tungsten oxide as starting reagents.
The XRD patterns of BaTeMo2O9 and BaTeW2O9 powders synthesized in supercritical water in this work match well with the standard pattern of BaTeMo2O9 and BaTeW2O9, indicating this novel hydrothermal process in supercritical water system is successful to prepare such complicated multi-component oxide compounds. We assume that high temperature and high pressure water in the reaction system plays a role like the flux used in traditional solid state method. In addition, mass transfer process has been accelerated in this system. Under SEM observation, the morphology and dispersity of the particles is improved effectively. Most of the BaTeMo2O9 particles exhibit polyhedron shape like cuboid with the size around 1-2 micrometer. The particles of BaTeW2O9 synthesized in this work show regular stick-shape with width 100nm and length 1-2 micrometer.
In summary, this work provides a novel, facile and green route to synthesize BaTeM2O9 (M=Mo or W) polycrystalline powders with uniform particles morphology, opening a new field for supercritical water process. This novel and unique supercritical water process might bring pivotal enlightenment and probability for more functional multicomponent compounds, and would be very significant in green chemistry and environmental protection.

Simple ways of controlling the deposition of nanoporous ZnO are of interest for the development of hybrid solar cells. In our work, ZnO seed layers were prepared by spray pyrolysis of zinc acetate in methanol solution. A deposition temperature of 440°C was found to be needed to fully decompose the precursor and form ZnO free from carbon contamination. By increasing the volume of solution sprayed, the crystal size in the resulting layer can be increased. When these seed layers are used for hydrothermal growth of nanorods, the spatial separation of the nanorods is controlled by the crystal size of the seeds, with larger seeds resulting in nanorods which are further apart. This control over the distance between the nanorods is important for applications where another material must be deposited in the pores around the ZnO, such as in ordered heterojunction solar cells. The spray pyrolysis seed layer deposition shown here, combined with the hydrothermal growth of ZnO nanorods, leads to a tailored nanorod array. Two solution processes are used to achieve this, both of which are scalable to large area production.

This research is aimed to develop electrically tunable ferromagnetic microwave resonance devices with reduced bias field, faster tuning speed, and minimized device size at low cost. Chemical solution deposition (CSD) process provides the opportunity for realization of cost-effective device manufacturing. Currently performance of solution-based devices is limited mostly by the deficiency in material quality control. At Boston Applied Technologies, Inc., a computerized chemical solution deposition (CCSD) technology is well developed for high quality, reproducible thin film processing. The major advantage of the CCSD technology is that the control of material structure is at the nanometric level, leading to function-specific materials with high reliability at low cost.
In this work, highly textured BaM thin films with a single hexagonal phase and an out-of-plane orientation (00l) were deposited on sapphire, silicon and silicon carbide substrates via a CCSD process. Effects of substrate, buffer layer and precursor solution on microstructures and magnetic properties of the BaM films were studied. Subsequently monolithic thin film multiferroic heterostructures consisted of BaM and BST layers were successfully fabricated. Highly textured BST thin films oriented in (111) direction were obtained on Pt(111)/BaM/sapphire multilayer structures. It was demonstrated that fine-tuning of microstructures and orientation controls could be achieved via engineering of interfaces and adjusting precursor solutions. XRD, SEM, magnetic hysteresis and ferromagnetic resonance (FMR) measurements were carried out and the results implicated the promise of the solution-processed monolithic multiferroic heterostructures for frequency agile RF electronics.

In this study, we report a high yield production method to produce ultra-large single crystalline Ag microplates with an edge length up to 30 mu;m. The Ag microplates were prepared by a modified polyol reduction method through the use of AgNO_3(aq), surfactant (polyvinylpyrrolidone, PVP) and reducing agent (nitric acid, HNO₃) in ethylene glycol (EG). Such single crystalline Ag microplates enlarging the (111) facets can reach the edge length from 3 mu;m to 30 mu;m at different reaction times, and can be readily employed as an outstanding plasmonic substrate to meet the stringent need of materials&’ physical properties for nanoantennas, plasmonic nanocircuits, plasmonic nanopixels and other applications. In the end, we also demonstrate periodic arrays of squares and split ring resonators (SRR) on our fabricated ultra-large single crystalline Ag microplates, by a single-step focus ion beam (FIB) direct patterning process, with a well-controlled geometry and gap sizes of 20-25 nm.

Printed electronic has received increasing attentions. Silver nanoparticles are usually used as a metal precursor in conductive ink system because silver has highest electrical conductivity. Moreover, its oxide has considerable conductivity. However, electrochemical migration and the high cost of silver are the main drawback of silver-based conductive ink. Copper has high electrical conductivity and low cost compared to other metals. However, copper inherits other drawbacks such as high melting temperature and high-reactive oxidation. Copper oxides presenting on surface of copper nanoparticles can increase the sintering temperature required, and reduce the electrical conductivity. An effective approach to protect the copper nanoparticles can be done by the formation of a protective shell made of a noble metal such as silver. Recently, the polyol-mediated synthesis of metal nanoparticles appears as an easy to carry out and versatile route. Polyols result to be an excellent reaction media to synthesize metal nanoparticles with controllable size and morphology due to their ability to act as solvent, reducing agent and protecting agent.
In this work, copper core-silver shell nanoparticles were synthesized through the polyol successive reduction process in the solution of glycerol and sodium hydroxide. Copper nitrate and silver nitrate were used as sources of the copper and silver ions. Glycerol was used as the solvent as well as reducing agent. The effects of copper ion concentration (0.01 M, 0.05 M, 0.1 M), wt% of silver loading (0.5, 2.5, 5, 7.5, 10) were investigated. The molar ratio of NaOH to metal ion was fixed at 3:1. Polyvinyl pyrrolidone (PVP) and octylamine was used as the surface stabilizer. The particle size, microstructure and morphology of nanoparticles obtained were characterized via transmission electron microscopy with Energy-dispersive X-ray Analysis (TEM/EDX), Scanning electron microscope (SEM) and X-ray diffraction (XRD), respectively. The influence of concentration of metal ion affects the morphology and particles size. The results of TEM/EDX, XRD and SEM confirmed the formation of spherical copper core- silver shell nanoparticles with size in range of 20-40 nm. The particles synthesized of 5-10 wt%, silver loading were stable under air, and copper oxide were not detected even after 1 month of exposure to air. This enhanced air-stability contributed to the enhanced electrical property. Further, the copper core-silver shell nanoparticles obtained were used to prepare a conductive ink. The conductive ink formulated was screen printed on polyethylene terephthalate (PET) substrate. The patterns printed were baked at 150 C in air for 15 min, and then further baked at 150 C in 2% hydrogen-nitrogen mixed gas for varying baking times (30-120 min).

Controlling the position and the inter-particle separation of colloidal nanoparticles on different substrates enables the fabrication of materials with interesting functionalities. To this end, block copolymer self-assembly provides a bottom-up approach to pattern nanoparticles in a controllable and convenient way. Here, we have developed a fabrication procedure for thin films composed of oil-soluble nanoparticles (e.g. quantum dots) and polystyrene-b-polydimethylsiloxane (PS-b-PDMS) block copolymer. We used oleic acid/oleylamine-capped nanoparticles and found that the nanoparticles tend to reside in the PDMS domains upon solvo-thermal annealing. This can be ascribed to the similarity in solubility parameters for alkanes and PDMS and is also in accordance with the experimental swelling measurements of PS-b-PDMS. As for block copolymers, PS-b-PDMS of two different volume fractions were used, i.e. spherical forming and cylinder forming PS-b-PDMS. In the spherical forming PS-b-PDMS, nanoparticles typically resided in the center of the PDMS domains; in the cylinder forming case, nanoparticles demonstrated a clear tendency to gather at defect points (e.g. X-shape, T-shape, L-shape of the PDMS cylinder domain) due to the fact that the incorporation of nanoparticles reduced the stretching of the polymers, leading to a gain in conformational entropy. This nanoparticle-block copolymer composite can be further treated by oxygen reactive ion etching to remove the PS domain and turn PDMS into oxidized PDMS (amorphous silica). In this way, the hydrophobic nanoparticle-block copolymer films can be transformed into hydrophilic silica protected nanoparticles patterns.

This nanoparticle-block copolymer co-assembled thin film can be easily fabricated on normal silica substrate through spin-coating and annealing processes. To further facilitate transmission electron microscopy (TEM) characterization, we have adopted a direct fabrication procedure on the copper/Formvar/amorphous carbon TEM grid. Moreover, another procedure was also developed in order to make free-standing thin films which can be transferred to different types of substrates. These fabrication methods not only enable us to make functional coating on different kinds of surfaces, but also have the potential of further controlling the position and inter-particle separation of functional nanoparticles by combining the solution-based bottom-up procedure with top-down lithographical methods.

As an example of modern technology, transparent conductors have been regarded as an extremely important component in optoelectronics applications such as solar cells, OLED displays, and touch panels. The most common material for transparent conductors is ITO, which has become a market leader due to its high transparency in thin film. However, its brittle ceramic properties and expensive vacuum deposition process are limitations to its further progress. Here, we developed a novel hybrid approach using AgNW - conducting polymer composite to demonstrate a high performance, very large area transparent conductor by a simple, room temperature, solution processible nano-soldering by a rod coating. Many studies have shown that AgNWs can serve as a good replacement for ITO because silver is the most conductive material on earth due to its high free-electron density. Silver can also be highly transparent at a very small dimension while maintaining good electrical conductivity. However, the need for a high temperature thermal annealing step to reduce the contact resistance and its poor adhesion to the substrate was one of the biggest problems for the AgNW transparent conductors. We demonstrated that using a AgNW/ PEDOT:PSS hybrid composite, contact resistance and substrate adhesion problem could be significantly enhanced even without a high temperature annealing step. Through the strong adhesion ehancement and the flexible nature of the AgNW and conducting polymer, a flexible transparent electrode on a flexible polymer substreate could be demonstrated. Furthermore, PEDOT:PSS assisted tight joining at the nanowire junction during the conducting polymer drying makes this process possible at room temperature. Typical AgNW network electrodes should be annealed at high temperature to create a strong inter-nanowire junction. A thermal annealing is a necessary step to creat a low resistance electrode in previous AgNW transparent conductor researches. Therfore, plastic substrate could not be used because the substrate also needs to be heated and may be thermally damaged. To reduce the production costs and create a flexible and mechanically strong transparent conductor electrode, a glass substrate should be replaced with a flexible plastic substrate which will experience thermal degradation problem. The proposed PEDOT:PSS assisted room temperature nano-soldering of AgNW mesh electrode can remove high temperature annealing steps while having similar high conductivity. Moreover, the developed simple fabrication process could be easily expanded to demonstrate a very simple, large-scale roll-to-roll process. In this experiment, glass and PEN substrates up to A4 size were used to create a large transparent electrode. Finally, a large area transparent conductor and a flexible touch panel on a non-flat surface were fabricated to demonstrate the possibility of cost-effective mass production as well as the applicability to the unconventional arbitrary soft surfaces.

By exploiting important colloidal phenomena, we propose to synthesize new magnetic and/or photonic nanomaterials (colloidal solution, powders, gels, thin films) based on ZnO or SiO2 matrix. This contribution highlights our efforts to elaborate and to characterize various nanostructures with low toxicity such as M@ZnO, (M = Ti, Eu, SiO2-[Mo6Br14]), M@SiO2 (M = g-Fe2O3, Au and/or [Mo6Br14] or [Re6X14]) colloids. In the first part, this contribution will show how by using high concentrations of different polymeric M@ZnO nanocolloids, we were able to prepare various functional luminescent colloids and thin films as well as versatile ZnTiON colored thin films (Figure 1) [1-4]. In the second part, this contribution will summarize our results on the synthesis and characterization of multifunctional SiO2 nanoparticles (Figure 2) [5]. Several types of materials with interesting catalytic, magnetic or optical properties have been coated with silica, in order to get functional nanoparticles and colloids such as: ZnFe2O4@SiO2 [6], CeO2@SiO2 [7], [Mo6X14]@SiO2 [8] and γ-Fe2O3-[Mo6Br14]@SiO2 [9], [Re6X14]@SiO2 [10]. Such nanoparticles with metal atom clusters are good candidate for photonic crystal [11] or bioimaging knowing that the red/infrared Mo6 cluster emission range could be selectively transmitted through tissues due to the low absorption at these wavelengths and could be coupled with magnetic nanoparticles for magnetic resonance imaging.
References
[1] F. Grasset et al., Adv. Mater., 17(3), 294, 2005 [2] D. Berthebaud et al., J. Phys. Chem. C, 111, 7883, 2007 [3] F. Grasset et al., Sci. Technol. Adv. Mater., 11, 044401, 2010 [4] T. Aubert et al, Part. Part. Syst. Charact., DOI: 10.1002/ppsc.201200047 [5] T. Aubert et al., J. Colloids Inter. Sci., 341(2), 201, 2010 [6] F. Grasset et al., Langmuir, 18 (21), 8209, 2002 [7] F. Grasset et al., J. Colloids Inter. Sci., 299, 726-732, 2006 [8] F. Grasset et al., Adv Mater., 20, 143, 2008 [9] F. Grasset et al., Chem. Comm., 4729, 2008 [10] T. Aubert et al., Langmuir, 26(23), 18512, 2010 [11] J.F. Dechezelles et al., Phys. Chem. Chem. Phys., 12, 11993, 2010.

Nanoparticle formation in the nano-size pores of mesoporous silica has an advantage of control of size and alignment. And also, the use of nanoparticles confined in the silica is attractive for electrical and optical device applications. For the purpose of device application, the processes of formation of mosoporous silica thin film and synthesis of nanoparticles in the pores of the film have been developed. Thin films of mesoporous silica SBA-15, the one-dimensional pores of which are spontaneously arranged in two-dimensional hexagonal-system, have been successfully formed on silicon substrates with chemical solution spin-coating and thermal process. X-ray diffraction revealed that the pores of SBA-15 are hexagonally ordered as a stacking of rows of pores and silica walls in the direction normal to the silicon substrate surface. The pore size was controlled between ~1.6 and ~5.5 nm. After penetrating the TiO2 precursor solution into the pores of the film the samples were sintered in a furnace and TiO2 nanoparticles were formed in the pores. The formation of particles was confirmed by X-ray reflectivity method and transmission electron microscope observation. The optical absorption edge of TiO2 nanoparticles shifted to higher energy side as the size decreased. In the capacitance-voltage characteristics of Au/TiO2-containing film/Si capacitor counter-clockwise hysteresis was observed, suggesting that electrons were trapped at the interface and/or in the film near the interface after positive gate bias. Furthermore, a characteristic shoulder was observed at gate bias 1V only on the C-V curve as the bias was swept from positive to negative. These results indicate that the electrons trapped in the nanoparticles under the higher positive bias were released simultaneously at a low bias by quantum tunneling through the silica wall.

Solution processed colloidal quantum dots (QDs) have unique properties that can lead to cost-effective and printable optoelectronic applications such as light emitting diodes, photodetectors, and photovoltaic cells. In particular, lead sulfide (PbS) QD has been extensively studied with much attention because it is highly desirable as light absorber for harvesting sunlight energy or for near-infrared (NIR) photo-detection. Recently, the commercial interest in NIR detection for the spectral region between 1 and 1.8 um is growing due to various imaging applications of optical tomography, process monitoring, and night vision. PbS QDs photoconductors or PbS QDs/organic semiconductor hybrid photodiodes for NIR detection have been already demonstrated. However, these two-terminal devices are not suitable for more practical photo-sense applications because they need to be additionally integrated on active matrix transistor backplane.
Here we introduce new approach of three-terminal PbS QD/InGaZnO (IGZO) hybrid phototransistor for NIR detection wherein colloidal PbS QDs play a role of NIR sensitized layer and can be easily formed on the top of IGZO thin film transistors (TFTs) array. This hybrid phototransistor responded to NIR light up to 1.4 um. The photo-generated electrons from the PbS sensitized layer can be transferred to the IGZO channel and consequently induced significant negative threshold voltage shift on the TFT. To further evaluate the real potential towards the development of more practical applications, a photo gating resistive-load inverter was implemented by connecting a unit phototransistor to an external load resistor. The photo-induced threshold voltage shifts of the hybrid phototransistor led to certain output voltage signals in static and dynamic characteristics of this photo-inverter. We expect that this hybrid phototransistor can be simply integrated on glass or plastic substrates that can be applied to pixels on flat panel photo imaging applications or building blocks on complex photo gating logic circuits.

Solution processed hybrid Ag nanowire (AgNW)-Graphene films were prepared using ultrasonic spraying and dipping method and the electrocatalytic activity for the cobalt redox electrolyte in dye-sensitized solar cells (DSCs) was examined. Cyclic voltammograms and Tafel polarization measurements confirmed the superior electrocatalytic activity of AgNW-Graphene electrode than that of standard Pt counter electrode (CE). Electrochemical impedance spectroscopic study also revealed the lower charge transfer resistance (R_ct) of AgNW-GNP compared to Pt based CE. However, the resistance of the electrolyte diffusion was higher for the AgNW-GNP based CE resulted from the porous structure of the hybrid CE. The photoconversion efficiencies of the DSSC prepared with AgNW-GNP based CE was compared with that of platinum based DSCs. This study proposed an alternative low-cost cathode material for the cobalt redox mediator based DSSCs.

Thin PZT films are a prominent material for ferroelectric random access memory (FRAM), MEMS and other integrated ferroelectric devices [1].
Despite the fact that formation of perovskite phase in PZT films prepared by sol-gel techniques has been the subject of investigation since 1990s, mechanisms of fine crystalline structure formation, nucleation and growth processes are as yet not fully understood. A comparison between results reported by different authors is complicated due to various precursor chemistry and preparation conditions. A comprehensive discussion of different approaches to sol-gel synthesis of PZT films and nucleation processes was made recently in refs. [2,3].
In this work we try to establish main regular trends in formation of fine crystalline structure (with the use of TEM techniques) of sol-gel PZT thin films annealed at different temperatures and its effect on electrical properties of the films.
For this purpose in addition to the range of annealing temperatures Ta = 600 - 750°C commonly used for preparation of sol-gel PZT films, we have studied both the film annealed at low temperature Ta = 550°C, where perovskite phase has not completely arisen, and one annealed at high temperature Ta = 900°C, that leads to degradation of multilevel heterostructure as a result of diffusion processes.
The structure of the films was studied by transmission electron microscopy (TEM), electron and X-ray diffraction; electrical properties were characterized by Sawyer-Tower, capacitance-voltage and current-voltage techniques.
Experimental data on film microstructure (grain size, texture, pyrochlore inclusions, interfaces), changes in structure and composition of the underlying layers are discussed in association with electrical properties of the films.
References
1. N. Setter, D. Damjanovic, L. Eng, et al. “Ferroelectric thin films: Review of materials, properties, and applications”, J. Appl. Phys., vol. 100, p. 051606, 2006.
2. T. Schneller, and R. Waser, “Chemical modifications of Pb(Zr0.3,Ti0.7)O3 precursor solutions and their influence on the morphological and electrical properties of the resulting thin films”, J. Sol-Gel Sci. Techn., vol. 42, p. 337-352, 2007.
3. A. C. Dippel, T. Schneller, R. Waser, D. Park, and J. Mayer, “Formation sequence of lead platinum interfacial phases in chemical solution deposition derived Pb(Zr1-x Ti x)O3 thin films”, Chem. Mater., vol. 22, p. 6209 - 6211, 2010.

PZT thin film is a promising material for nonvolatile memory and MEMS applications. Preparation of PZT thin films by sol-gel techniques suggests a high temperature annealing accompanied by lead oxide volatility. Sol-gel PZT films have a p-type conductivity mechanism as a result of lead vacancies formation. Doping by lanthanum is widely used to compensate hole conduction in PZT. In this report we have tried to establish main mechanisms of charge transport in sol-gel PZT films with different La concentrations in various regions of the electric field. Pb_1-xLa_x(Zr_0.48Ti_0.52)_1-x/4O₃ films with x = 0, 0.02, 0.05, 0.08, and 0.1 are deposited by spin-on sol-gel techniques on platinum plated silicon substrates with intermediate pyrolysis of each layer at 400 ^o C and final annealing at 650 °C for 20 min. The final thickness of the PLZT films is about 240 nm. As expected, doping by La effects on polarization behavior of PZT films, the values of remanent polarization Pr and coercive field Ec decrease with the increase of La content (23 µC/cm², 52 kV/cm respectively for undoped film; 7 µC/cm², 25 kV/cm for the film with x = 0.02, and so on). Current-voltage dependencies are studied at the voltage ramp speed of 0.005 and 0.0025 V/s. It was found that the I-V dependencies of all PLZT films have two characteristic regions: low- and high-voltage. In the low-voltage region (up to 80 - 90 kV/cm) the influence of La concentration is negligible and has no definite relationship. The leakage current in this region is determined mainly by the high resistance of depletion region of the reverse-bias Schottky barrier at the electrode-ferroelectric interface, as a result the current is practically independent of La content. In the high-voltage region the Schottky barrier breakdown occurs above some threshold voltage and the current is mainly determined by the film bulk resistance. As a result, the dependence of the leakage current on La concentration becomes particularly pronounced in this region. At the 2% La content, the leakage current in this region reduces by about two orders in contrast to an undoped PZT film. Further increase of La content leads to an increase of leakage current as a result of change in conductivity mechanism from p- to n-type. The conductivity mechanism in this case is a combination of a limited interface injection and bulk limited drift-diffusion.

Precursor chemistry has a pronounced effect on sequence of structural transformations during sol-gel processes and therefor on the crystal phase formation process.
The purpose of this research is an experimental definition of the chemical synthesis process influence of the initial solution formed with the use of various Ti and Zr compounds: isopropoxide zirconium monosolvate powder, solution of zirconium propoxide in 1-propanole, solution of zirconium buthoxide in 1-buthanole, titanium isopropoxide, titanium buthoxide. A water-free lead acetate is prepared by the solid state synthesis from lead oxide.
Ferroelectric lead zirconate titanate (PZT) thin films (Zr/Ti=48/52) are prepared by chemical solution deposition on 200 mm Si-SiO₂-TiO₂-Pt substrates. The samples were examined by XRD, SEM, TEM, HREM structural analysis, as well as by polarization-voltage, CV and IV measurements.
Basic structure of the films is (111) perovskite. Presence of (100) texture, pyrochlore nanocrystalline inclusions, and grain size (from 197 to 240 nm) depend from precursors. This leads to different electrical properties of the films. For example polarization lies in the range from 24.3 to 34.4 mu;C/cm², differential dielectric constant from 5788 to 8385, linear dielectric constant from 808 to 1125, etc.
It is shown that the most pronounced effect on the film properties has zirconium precursor. Alkoxide solutions in appropriate alcohol are proper precursor of zirconium component. This process allows to avoid long-time boiling procedure of the lead acetate solution in 2-methoxiethanole (as it takes place in the case of the isopropoxide zirconium monosolvate), resulting in etherification between ether alcohol and an acetic acid to occurrence of water uncontrollable amount and as a consequence in the film-forming solutions instability in the time.
The use of solutions of zirconium butoxide leads to a significant reduction of the polarization of the films crystallized at 650 ^oC, but provides a single-component (111) texture and high electrical properties of the films annealed at 600 ^oC.
The nature of introduced titanium alkoxide has no significant effect on the properties of PZT films. The film prepared from solution with titanium isopropoxide provides higher values of the residual polarization, in contrast to one prepared with titanium butoxide.
Acknowledgements. This work is partially supported by RFBR grant N 12-02-01363-a.

Silicon nanowires (Si NW) were commonly utilized in lithium-ion batteries and solar cells; however, their demonstration in supercapacitors is very limited. In this work, we report on supercapacitors with hybrid Si NW - single walled carbon nanotube (SWNT) network electrodes. SWNTs in this work provided high surface area, high conductivity and a template for the attachment of Si NWs. Si NWs, fabricated through metal assisted etching (MAE) route, were cut from Si wafer using sonication and vacuum filtered with SWNTs to form hybrid thin film electrodes. Electrode fabrication process of hybrid Si NW - SWNT thin films is simple, fast and allows large scale supercapacitor production over large areas. Si NW - SWNT thin films are also deposited onto flexible substrates such as PDMS and PET. Electrochemical properties of solid state hybrid SiNW-SWNT electrodes were then investigated using polymer gel electrolytes by cyclic voltammetry and chronopotentiometry to quantify specific capacity and cycling ability in full symmetric supercapacitor architecture. Hybrid SiNW-SWNT electrodes have four times higher specific capacitance than SWNT electrodes. We will present a detailed analysis of electrochemical properties of the fabricated supercapacitors to underline their capacitive behavior. Our results reveal the potential of the use of Si NWs in supercapacitor electrodes that can be fabricated through simple solution based methods and the method investigated herein can be simply adapted to industrial scale fabrication.

Magnetic nanoparticle dispersions are usually made from superparamagnetic materials since in the absence of an external magnetic field, the lack of magnetic particle/particle attraction allows the creation of stable dispersions [1]. Common attempts to prepare stable dispersions of ferromagnetic particles failed since the strong magnetic particle/particle interaction can overcome repulsive effects from surfactants or steric stabilizers (typically polymers).
In the present work, we demonstrate how the direct, covalent attachment of highly charged polymers can circumvent stabilizer detachment and permit the preparation of stable dispersions of ferromagnetic particles [2]. More specifically, carbon- coated metal nanoparticles were covalently functionalized with ionic polymer brushes via surface initiated atom transfer radical polymerization (SI-ATRP). Particle size distributions with an average diameter of 24 nm provided a ferromagnetic fluid with unprecedented stability in water over months. This novel material was tested for two different applications.
1. For inductive heating in medicinal chemistry or material science, the much higher magnetization of ferromagnetic metals over the currently used superparmagnetic oxides is attractive [3]. Measurements with inductive heating at different frequencies and various field strengths using this stable dispersion showed an average specific absorption rate of 360 W g-1.
2. Deinking of printed paper is within the most expensive steps in paper recycling. The application of the stable dispersion as ferromagnetic ink simplifies this step and might face current issues. As printed parts of paper are rendered distinguishable from non-printed parts, a reduction of the paper mass, which has to be deinked, by magnetic pre-separation can be achieved. Further, magnetically induced purification steps led to 84% of paper recovery from a model print without the use of expensive and harsh deinking chemicals.
[1] E. Kita, T. Oda, T. Kayano, S. Sato, M. Minagawa, H. Yanagihara, M. Kishimoto, C. Mitsumata, S. Hashimoto, K. Yamada and N. Ohkohchi, J. Phys. D. Appl. Phys., 2010, 43, 47401.
[2] M. Zeltner, R.N. Grass, A. Schaetz, S.B. Bubenhofer, N.A. Luechinger, W.J. Stark, J. Mater. Chem., 2012, 22, 12064.
[3] Q. A. Pankhurst, J. Connolly, S. K. Jones and J. Dobson, J. Phys. D. Appl. Phys., 2003, 36, R167.
[4] M. Zeltner, L. M. Toedtli, N. Hild, R. Fuhrer, M. Rossier, L. C. Gerber, R. A. Raso, R. N. Grass and W. J. Stark, Langmuir, 2013, 29, 5093.

A major drawback to solid state, dielectric capacitors for energy storage is their low energy densities. This can be remedied by increasing the total electric field that the energy storing dielectric material can withstand. An ideal capacitor's total energy storage increases with the square of the field being applied. The maximum applied field is reduced dramatically when extrinsic defects, such as pores, are present in the material. Although the material may have excellent performance, imperfections in the processing produce pathways for dielectric breakdown that reduce performance. Conventional synthesis methods involve thermal curing of polymers or ceramics that requires a great deal of energy, takes several hours, and produces significant waste heat. High-energy flash cure lamps process thin film materials (<50 um) within milliseconds and are able to deliver higher energy and power densities (20 J/cm2 and 20 W/cm2) allowing for a more complete curing, eliminating flaws that would exist in conventional treatment. Hexyl acrylate (HA) monomer was mixed with 1,6 hexanediol diacrylate (HDA) at various volume percents (10-50%) with 10 mg of 2,2 azobis(2-methylpropionitrile) to act as a photoinitiator. A thick film was formed by doctor blading onto copper electrodes using scotch tape as a guide for film thickness. The solutions were processed both thermally and with exposure to a xenon flash bulb. Thermal treatment consisted of heating the sample at 80°C on a hot plate over night. Flash curing employed a Novacentrix Pulseforge 1300 system. The energy and power densities were varied to determine their effects on porosity, degree of cross-linking, dielectric constant, breakdown field and energy storage. Porosity was measured through an Archimedes method using chloroform as a solvent. The degree of cross-linking was determined through comparative FTIR studies. Dielectric constant was measured using an Agilent 4294a impedance analyzer from 100 Hz-100 MHz with a two terminal set up. Breakdown strength and energy density measurements were taken using Radiant Technology's Precision Ferroelectric tester with a 10kV source. The printed thick films averaged 20 microns thick as observed by an optical cross section. The porosity was found to be less than 1%. Energy densities were measured both from PE loops and ideal capacitor calculation and were in excess of 2.0 J/cm3.

The electronic energy levels of colloidal quantum dots (CQD) are size-tunable, offering opportunities for solution-processed, flexible and compact electronic devices, not only for photovoltaic devices [1-2], but also for transistor and light-emitting devices. By changing the size of the QDs, the bandgap can be varied and the absorption edge as well as the emission peak can be tuned. Among the other unique properties of these NCs are the possibility to have multiple exciton generation (MEG), utilizing the discrete higher energy sub-bands formed by the quantum confinement of CQDs [3]. This properties has potential for achieving photovoltaic cell with higher efficiency, as well as another functionalities, i.e. multistate transistors and tunable emission electroluminescence device. Therefore, a complete understanding of the energy levels of CQDs is necessary, not only the size dependent bandgap but also the energy sub-bands beyond the valence and conduction band edge. Current methods to investigate the energy levels of nanocrystals are still having many limitation and technical complications. Moreover, there is a crucial question whether the quantum confinement is still persisting in the assemblies of CQDs, especially those which are crosslinked.
Here we demonstrate the probing of the quantized energy levels of colloidal nanocrystal field-effect transistors. Ambipolar FET of PbS CQDs by using ionic-liquid-based gating has been demonstrated to achieve high carrier mobility values (mu; > 1 cm2/V.s) despite driven with only 1.5 V gate, since this gating technique can fill virtually all carrier traps due to the very high accumulated carrier density [4]. Because of the effective trap filling achieved with this gating technique, the Fermi energy level shift can access into the valence and conduction band to observe the band fillings.
We successfully probed the band gap of the PbS CQDs of different diameters using the abovementioned method and clarify the results with TEM, optical absorption measurement, as well as ab-initio calculation of the energy level. Selecting specific ionic liquid gate materials, we can access the higher energy sub-bands beyond the conduction band edge. Finally, by correlating experimental and theoretical results we can provide a comprehensive understanding of the electronic energy structure of solution-processable colloidal quantum dots films.
Ref.: [1] K. Szendrei, M. A. Loi, et al. Appl. Phys. Lett. 97, 203501 (2010); [2] K. Szendrei, M. A. Loi, et al. Adv. Funct. Mater. 22, 1598 (2012); [3] A. J. Nozik, et al. Chem. Rev. 110, 6873 (2010) [4] S.Z. Bisri, M. A. Loi, et al., Adv. Mater. DOI: 10.1002/adma.201205041 (2013).

Because the brittleness and growing cost of indium tin oxide (ITO) limit its use as transparent electrodes in flexible electronics, developments of new conductive materials with high transparency are very important. Graphene and metal nanowire networks that exhibit high transparency and mechanical flexibility have been actively studied as promising alternatives to ITO. This talk presents a comprehensive study of the electrical, optical, and mechanical properties of hybrid nanostructures based on the graphene and silver nanowires, and their advantages as stretchable, transparent electrodes. These hybrid nanostructures show low sheet resistance (~ 33 Ohm/sq) with high transmittance (94%), and superb mechanical flexibility (folding capability) and stretchability (100% in tensile strain). Fabrications of single-pixel displays fitted on wearable, soft eye contact lenses and oxide semiconductor transistors using the hybrid transparent electrodes demonstrate a future promise for next generation electronics.

Numerous studies have been conducted to investigate possible substitute for current transparent conducting material, indium tin oxide (ITO). Many reports argue that metal nanowire networks are strong candidates to replace ITO. However, advancing metal nanowire networks to stretchable transparent conductor, which are essential for applications such as wearable electronics, has been challenging. Here, we propose hybrid material composed of 1-dimensional Ag nanowires and 2-dimensional graphene with polydimethylsiloxane (PDMS) as substrate to develop stretchable transparent conductor. Transmittance, sheet resistance, and changes in resistance under strain are measured. Conductivity is increased with little sacrifice in transparency as graphene layer is deposited on top of Ag nanowires. Relatively stable conductivity is achieved during and after stretching due to the structure of the hybrid material. Conductivity can be retained because contacts between 2-dimensional graphene layer and Ag nanowires help to conserve electron transport paths even after repetitive mechanical strains.

Colloidal semiconductor nanocrystals (NCs) have attracted considerable attention for cost-effective, solution-based deposition of quantum-confined thin films for optoelectronic devices. However, there are two significant challenges that must be addressed before practical NC-based devices can be realized. The first is coping with the ligands that terminate the NC surfaces. Though ligands provide the colloidal stability needed to cast thin films from solution, these ligands dramatically hinder charge carrier transport in the resulting film. Secondly, after a conductive film is achieved, doping has proven difficult for further control of the optoelectronic properties of the film.
Recent research efforts with silicon (Si) NCs have demonstrated the ability to confront both of these challenges using a single technique [1]. Polarization of the NC surface is achieved by terminating it with Chlorine. This renders surface Si atoms deficient in electron density (Lewis acidic), which tunes the NC surface to favorably interact with a donor molecule (Lewis base).
Though this phenomenon is well known to occur in molecular analogs, it is unexplored in the surface chemistry of nanostructures. We demonstrate hypervalent surface interactions to provide both colloidal stability as well as doping of silicon NCs. We discuss in detail the NC surface chemistry as well molecular donor characteristics that facilitate colloidal stability and surface doping effects.
[1] Wheeler, Lance M., Neale, Nathan R., Chen, Ting, Kortshagen, Uwe R. Hypervalent Surface Interactions for Colloidal Stability and Doping of Silicon Nanocrystals. Nature Communications (Accepted)

Doping silicon nanostructures presents some critical issues like conformality and control of the junction depth and dopant dose. Moreover the ideal method should not damage the surface neither the bulk. An effective method to dope nano-patterned Si specimens and create controlled and conformal junction profiles is proposed. It consists in forming onto the sample surface a monolayer of dopant containing molecules from a liquid solution, deposit a cap layer and process the samples with thermal annealing. By using the proper chemical precursor, both p- and n- type doping can be obtained [Ho et al. Nature 7 62 2008, Garozzo et al. MS&B 178 686 2013]. We applied the doping procedure on arrays of different 3D architectures such as holes or wires, presenting different characteristic sizes. The same processes on planar substrates are performed as references. Junctions properties such as depth, dose and conformality are investigated by using proper high resolution techniques such as SCM, TEM and spreading resistance profiling [Garozzo et al. PSSA in press]. These analyses demonstrate the formation of sharp junction profiles with depths in the nanometer range and peak concentraitions up to 1×10¹⁹ cm^-3. The doped layers are used as active materials for the fabrication of solar cells prototypes based on nanostructured silicon showing improved photoconversion performance respect to the reference samples, and thus demonstrating that the technique can be also exploited to create more efficient nano-electronic devices in the class of new 3D architectures.

We present highly efficient electroluminescent devices using size-separated silicon nanocrystals (ncSi) as light emitting material. The emission color can be tuned from the deep red down to the yellow-orange spectral region by using very monodisperse size-separated nanoparticles. High external quantum efficiencies up to 1.1% as well as low turn-on voltages are obtained for red emitters [1]. In addition, we demonstrate that size-separation of ncSi leads to drastically improved lifetimes of the devices and much less sensitivity of the emission wavelength to the applied drive voltage. We also study the morphological and compositional changes of silicon quantum dot (SiQD) light-emitting diodes (SiLEDs) upon device operation. By means of advanced transmission electron microscopy (TEM) analysis including energy filtered TEM (EFTEM) and energy dispersive X-ray (EDX) spectroscopy, we observe morphological changes and degradation for SiLEDs operated under high applied voltage ultimately leading to device failure. With this newfound knowledge it will be possible to devise ways to increase the lifetimes of SiLEDs in the future.
[1] F. Maier-Flaig, J. Rinck, M. Stephan, T. Bocksrocker, M. Bruns, C. Kübel, A. K. Powell, G. A. Ozin, U. Lemmer, Multicolour Silicon Light Emitting Diodes (SiLEDs) Nano Lett. 13, 475, (2013).

Nanoparticles (NPs) have been used in various applications including electronics, photonics, paint and cosmetics, to mention a few. Traditional chemical methods have been used to synthesize such particles. Recently, the use of inkjet to do chemistry on a given material to control some of its proerpties (1), or to synthesize nanoparticles (2) has been demonstrated. In this talk we will introduce the use of inkjet printing in the synthesis of Au NPs with a relatively narrow size distribution. In most known cases, Au nanoparticles are dispersed in a liquid phase before introducing them into the printer. Such an approach is lengthy and costly as it involves at least a two-step route: 1) synthesis of Au nanoparticles, and 2) printing them. In our case, only one step is needed whereby the Au nanoparticles are synthesized on the substrate surface after the printing process is carried. Spectroscopic, TEM, and SEM studies of the resulting nanoparticles will be presented . The effect of precursors, printing sequence and solvents on the formation of the nanoparticles will be discussed.

References:
1. Y. Yoshioka et al., Adv. Mat. 10, 1307 (2006).
2. P. Smith et al., J. Mater. Chem. 22, 10965 (2012).

Herein we show experimental examples of localized photon modes in solution processed periodic multilayer structures. [1,2] These experiments show the control of the spectral modification of the optical absorption of one-dimensional photonic crystal based resonators containing different types of gold nanoparticles. This control was achieved through the changes in the photonic environment of the gold nanoparticles by means of the interplay between planar optical cavity modes and localized surface plamons. [3]
Spin-casting of metal oxide nanoparticle suspensions was used to build multilayered photonic structures that host (silica-coated) gold nanorods and spheres. Strong reinforcement and depletion of the absorptance was observed at designed wavelength ranges, thus proving that our method provides a reliable means to modify the optical absorption originated at plasmonic resonances of particles of arbitrary shape and within a wide range of sizes. [4] Results are explained in terms of the calculated spatial distribution of the electric field intensity within the configurations under analysis.
References
[1] Calvo, M.E., Colodrero, S., Rojas, T.C., Anta, J.A., Ocaña, M. and Míguez, H. Adv. Func. Mater. 18 (2008) 2708-2715.
[2] Colodrero, S., Ocaña, M. and Míguez, H. Langmuir 24 (2008) 4430-4434.
[3] Sánchez-Sobrado, O., Lozano, G., Calvo, M.E., Sánchez-Iglesias, A., Liz-Marzán, L.M. and Míguez, H. Adv. Mater. 23 (2011) 2108-2112.
[4] Jiménez-Solano, A., Loacute;pez-Loacute;pez, C., Sánchez-Sobrado, O., Luque, J.M., Calvo, M.E., Fernández-Loacute;pez, C., Sánchez-Iglesias, A., Liz-Marzán, L.M. and Míguez, H. Langmuir 28 (2012) 9161-9167.

Noble metal particles feature intriguing optical properties, which can be utilized to manipulate them by means of light. Light absorbed by gold nanoparticles, for example, is very efficiently converted into heat and single particles can thus be used as a fine tool to apply heat to only a nanoscopic area. At the same time, gold nanoparticles are subject to optical forces when they are irradiated with a focused laser beam which renders it possible to print, manipulate, and optically trap them in two- and three dimensions.
Based on these properties, we demonstrate how gold nanoparticles can be used to control the polymerization reaction and thermal curing of polymers at the nanoscale and how these findings can be applied to synthesize polymer nanostructures such as particles and nanowires with sub-diffraction limited resolution.
This approach represents an all-optical analogue to conventional scanning probe lithography in a sense that only optical forces are used to move and heat the nanoparticle and no mechanical connection between the particle and the microscope is required. This approach therefore offers a new method for direct-writing of single polymer fibers or fiber networks with the potential application as optical waveguides.

Light emitting and organic light emitting diodes are a fascinating area of research and have attracted a large amount of interest because of their use in high efficiency lighting1-3. In the present work, we mainly focus on three main technical objectives relevant to the engineering of new materials for hybrid light organic-inorganic Quantum Dot LEDs. First, we emphasize on the synthesis of novel colloidal quantum dots (CdSe and ZnSe QDs) to use with functionalized conducting polymers in the creation of hybrid OLEDs. This objective will explore the critical role of the polymer/quantum dot interface and its ultimate role in device efficiency. Our second aim is focused onto the exploration of spin coating and inkjet deposition to lay down the quantum dot and polymer layers in discrete layers to produce light and finally we have explored the possible economical ways of integration and characterization of these novel materials into an active lighting device structure.
REFERENCES
[1] J. Kido, M. Kimura, K. Nagai, “Multilayer white light-emitting organic electroluminescent device,” Science, vol 267, pp. 1332-1334, 1995.
[2] W. Ki, J. Li, “A semiconductor bulk material that emits direct white light”, Journal of the American Chemical Society, vol 130, pp. 8114, 2008.
[3] H. J. Bolink, H. Brine, E. Coronado, M. Sessolo, “Ionically Assisted Charge Injection in Hybrid Organic-Inorganic Light-Emitting Diodes”, ACS Applied Materials & Interfaces, vol. 2, pp. 2694-2698, 2010.

Physical vapor deposition is currently used to deposit copper seed layers in through Si vias, but this approach is already close to its limit and may not be an option for future scaling of high performance integrated circuits. An alternative is electroless deposition (ELD) since it produces conformal, selective coatings at low temperature. ELD occurs by chemical reduction of metal ions without an externally applied potential. In the conventional approach, a metal catalyst such as Pt, Pd, or Ni is used that can be both expensive and increase the resistance of interconnect lines. Eliminating the catalyst reduces the cost and a possible source of contamination. Previous work was done using aqueous solutions and demonstrated low sheet resistance and good film continuity, but used a complexing agent or polymer to protect the particles (Armini and Caro, J. Electrochem. Soc. 2010, 157(1), D74-D80, doi: 10.1149/1.3258026 and Inoue et al. J. Electrochem. Soc. 2012, 159(7), D437-D441, doi: 10.1149/2.070207jes). In this paper, we report on a nonaqueous ELD process that uses a charge compensator, but not a ligand or complexing agent. The weak electrostatic attachment of the charge compensator to the ions and particles in solution and the high pH conditions improve the driving force for metal deposition. Si(100) coupons were hydroxylated using sulfuric acid-hydrogen peroxide mixture (SPM or piranha) followed by a sulfuric acid etch. The surface was terminated with an amine or mercapto group by immersing in a 4 mM solution of either (3-aminopropyl)-trimethoxysilane (APTMS) or (3-mercaptopropyl)-trimethoxysilane (MPTMS) in methanol followed by a 423 K anneal. Metal films were deposited by suspending samples in a bath made by dissolving Cu(II) chloride in ethylene glycol, which also served as the reducing agent, and adding 1-butyl-3-methylimidazolium tetrafluoroborate as a charge compensator. The surface plasmon resonance (SPR) of Cu nanoparticles in the bath was at 585 nm, and the SPR of the film was attenuated in comparison after deposition. Dynamic light scattering measurements of the bath yielded a bimodal particle size distribution with peaks at 3-7 and 7-30 nm. Annealing the coupons at 473 K in nitrogen promoted the formation of an electrically conductive thin film. The sintered films showed little mass loss in an adhesion test. Scanning electron microscopy images of the coated substrates showed a bilayer structure consisting of a porous film that was 200-800 nm thick containing large 200-600 nm agglomerates on top of a void-free continuous film that was less than 300 nm thick. Electrical characterization of these films yielded conductivities ranging from 105-106 S/m. The Cu particle core-ion shell complex is attracted to the positively charged amine or mercapto groups at high pH depositing a thin metal film that is both continuous and cohesive. The method is both one-pot and does not require a catalyst.

Solution-based techniques can introduce a lower cost alternative to traditional semiconductor technology and push the trade-offs between performance and cost for a number of important applications, including photovoltaics and electronics, just to name a few. At the same time, inorganic semiconductors apply stringent requirements to phase purity, structural perfection and impurity levels. It is still an open question whether high quality semiconductors can be synthesized by low cost, solution techniques. In this contribution we discuss and compare different synthetic strategies toward inorganic semiconductors, focusing primarily on the materials relevant to thin film photovoltaics. In one set of studies, we carried out a comprehensive study of various molecular and nanocrystalline precursors for solution processing of Cu₂ZnSnS₄ (CZTS) thin films. We monitored the transformation of precursors into the target CZTS phase (reaction stage) followed by the growth of small grains into a bulk material (sintering stage). Both stages revealed non-trivial kinetic trends related to composition and reactivity of the precursors. Our experimental results indicate that molecular precursors react to form CZTS at lower temperature, but subsequent sintering occurs at higher temperature compared to nanocrystalline precursors. We also found that sintering kinetics can be controlled through surface chemistry of individual grains. Observed trends were also applicable to a range of semiconductors from II-VI and III-V families. Using novel inorganic surface ligands for nanocrystaline materials, we demonstrated record electron mobility over 170 cm²(Vs)^-1 in a solution processed semiconductor. We also demonstrated solution processed CdTe solar cells with 12% efficiency. All these findings show great potential of solution-based techniques for semiconductor technologies and applications.

Thin film chalcogenide glasses have emerged as important materials for photonic applications due to their high refractive index, excellent transparency in the infrared, and large Kerr non-linearity. Chalcogenide glass films are traditionally deposited by thermal evaporation, sputtering, or pulsed laser deposition, and planar photonic components based on these glasses are usually fabricated by standard photolithographic methods. However, these processes require significant capital investment, and are not compatible with high-throughput roll-to-roll processing. Thus, developing low-cost methods for glassy film deposition and photonic devices fabrication while retaining high optical quality becomes highly desirable. In this paper, defect-free As2Se3 and As2Se8 amorphous thin films were prepared by spin-coating from their organic amine solutions with glass loading concentrations as high as 0.6 g/ml. The prepared films were stabilized at elevated temperatures. Physio-chemical properties of the spin-coated films were studied and compared with thermally evaporated As-Se thin films. We further demonstrated for the first time fabrication of chalcogenide glass micro-ring resonators using thermal nanoimprint lithography from the solution derived films. The imprinted resonators showed smooth surface finishing, and a high quality factor of 80,000 at 1550 nm wavelength was experimentally measured.

Cost reduction is the major impetus for the macroelectronic industry. Consequently, solution processing of active layer materials, which promises manufacturing at low cost, low energy, and low investment, is particularly attractive for the macroelectronic producers. Metal chalcogenide semiconductors are excellent active layer materials and are already present in commercial devices. However, the presently used vacuum deposition of the active layers involve high manufacturing cost as well as high capital investment in manufacturing equipment. Solution processed active layers could bring significant cost reduction [1].
Despite their covalently bonded nature metal chalcogenides can be rendered soluble through dimensional reduction, which effectively dismantles the insoluble (often 3D) metal chalcogenide into soluble molecular species. If the stabilizing cations are small and “volatile” species as e.g. N2H5+, metal chalcogenide thin films can be formed at minimal volume and mass loss by solution processing and mild thermal treatment. This allows deposition of high quality crystalline films at temperatures compatible with flexible organic substrates [2].
We have crystallized and characterized a number of dimensionally reduced metal chalcogenides, and will present details of the synthesis and structure. It will also be shown how active layers for thin film transistor devices can be processed from solutions based on these crystalline precursors.
[1] R. H. Reuss and B. R. Chalamala, in Solution Processing of Inorganic Materials, edited by D. B. Mitzi (John Wiley & Sons, Inc., 2008), pp. 1.
[2] D. B. Mitzi, Advanced Materials 21, 3141 (2009).

A low-cost synthesis method utilizing earth abundant and environmental benign elements has long been a goal for developers of macroelectronic devices such as photovoltaics and thin film transistor (TFT) devices. The focus has been on finding good active layer materials and promising candidate materials are tin chalcogenide based compounds.
We have characterized SnSe2-xSx thin films produced by an aqueous solution processed synthesis method. High quality films of the active layer can be deposited using hydrazinium metal chalcogenide complexes from solution in either hydrazine or other polar solvents. In the present synthesis method, the highly toxic hydrazine has been completely eliminated. Under mild heating the films become crystalline andcomplete control over thickness, crystallinity and stoichiometry is found in the system. Crystallographic and electron microscopic methods have established that all films are highly textured with the high mobility ab-plane parallel to the substrate surface. This is ideal for e.g. TFT devices where high mobility is required parallel to the substrate surface. Electronic devices based on the SnSe2-xSx films are presented and demonstrates the promise of the synthetic method for the fabrication of inorganic thin film electronic devices.

Diverse strategies are being explored for the future generation of solar cells and one such approach is to employ colloidally synthesized nanocrystals as the main absorber material for the device. Quantum confined nanocrystals have a size tunable band gap, can be synthesized with near unity chemical yield, can be formed into solid state films using inexpensive casting or printing techniques, and embody unique photophysics that can lead to suppression of thermalization losses found in conventional semiconductor absorbers. In this talk, we will discuss devices made from either PbS, PbSe or CdTe nanocrystals where post-synthetic ligand exchange procedures using either organic or inorganic molecules are used to promote electronic coupling of quantum dots. Such ligand stripping has also been found to lead to midgap trap state formation which can be passivated with further QD surface treatment or incorporation of passivation ions during QD synthesis. We will discuss carrier transport in films made from nanocrystals, including trap states as well as band tail state distributions which appear to be surprisingly sharp for PbS given the degree of disorder in the array. Impressive overall efficiencies have been achieved due to attention to these concepts as well as understanding appropriate charge selective contacting schemes. Additionally we will discuss extracting more than one electron per incident high-energy photon due to multiple exciton generation.

PbS quantum dots (QDs) are promising material for QD solar cells. At present, all the PbS QDs for solar cell are synthesized by the method developed by Hines, in which PbO was used as Pb precursor. However, all the PbS QDs-based devices suffer from poor surface passivation. Recent research shows that halide atoms are effective for passivation although all of them are accomplished after the synthesis of QDs. In this work, we developed an in-situ halogen (Cl, Br, I) -passivation method in a non-hot-injection manner for different-sized PbS QDs especially for small sizes. In our new synthesis, PbX2 (X=Cl, Br, I) and bis(trimethylsilyl) sulfide are used as Pb and S precursor, respectively. Due to halogen-containing precursor, the QDs are passivated by halogen during the growth of PbS QDs. All the reagents are mixed at room temperature, and are heated to a various temperatures subsequently to produce different-sized PbS QDs.
The growth kinetics was studied via monitoring the evolution of absorption spectrum. It is found that QDs smaller than critical size dissolve releasing monomer, and leading to oversaturation which results in size focusing. This temperature driven growth allowed us to obtain PbS QDs with a size distribution comparable with conventionally synthesized ones. Based on the analysis of the growth kinetics, this new method was successfully extended to the synthesis of PbSe QDs, in which two Se precursor with different reactivities were used. Bis(trimethylsilyl) selenide, which is highly reactive, was used to form small QDs, while a relatively lower reactive precursor, TBPSe (selenium dissolved in tributylphosphine), was applied to maintain an oversaturation condition.
The synthesized PbS and PbSe QDs have superior optical stability due to Cl- passivation. The absorption peak does not change when they were stored in air for 30 days. Both the PbS and PbSe QDs show much higher photoluminescence quantum yields compared to the conventionally synthesized ones.
To further demonstrate the well passivation, we fabricated solar cells using these PbS QDs (ITO/ZnO/PbS/MoO3/Al), which shows an efficiency of as high as 6.5%, while it is difficult to get >4.5% using conventionally synthesized PbS QDs without any other treatment.
As a new synthetic method for PbS QDs, it possesses several advantages: (1) It is very suitable for large scale synthesis due to the non-hot-injection strategy; (2) Effective passivation by halogen; (3) Oleylamine weakly binds to the as-synthesized QDs and can be easily and completely replaced by other ligands, which is desirable for different applications; (4) Very small PbS QDs with Eg below 800 nm can be easily synthesized; (5) Different-sized QDs can be obtained from one batch of synthesis.

Recently, bismuth (III) selenide (Bi2Se3) has attracted great attention for application in spintronics and quantum computing mostly due to its topological insulating property. Nanocrystalline films were deposited onto glass substrates using chemical bath deposition at room temperature. The deposition parameters, such as bath composition and time were optimized. The reacting baths contained bismuth nitrate, triethanolamine and sodium selenosulfate as selenium (Se) source. Ammonium hydroxide was used to adjust the pH of the bath. The films deposited in bathes containing Se source solution of 10 ml and 15 ml were characterized for structural, surface morphological and compositional properties. The average thickness was determined by Dektak profiler. Films deposited up to 24 h in bath with 10 ml Se source solution had thickness ranging from 37.6 nm to 232 nm. The deposition rate was found to increase up to 61 nm/h for 3h deposition. In the case of bath with 15 ml Se source solution, the film thickness ranged from 45 nm to 632 nm for 1 h to 24 h deposition, respectively. The deposition rate was found to increase up to 123 nm/h for 3h deposition. The optimum deposition time was about 3 hours. Film roughness of about 6.6 nm to 22.8 nm was measured by atomic force microscope for films deposited in bath containing 10 mL Se source and 15 ml of Se source, respectively. Morphology and elemental composition, were analyzed by Electron Probe Micro analyzer with Energy Dispersive Spectrometer . Crack-free layers were observed with randomly large plate-like particles on top of the layer. The films with typical composition of Bi21.8Se78.2 were found to be rich in Se. Additionally, structural analysis performed by x-ray diffraction (XRD) did not revealed well defined XRD patterns, which indicates that the films were constituted mostly of nanocrystalline grains.

Over the past few years, two-dimensional (2D) layered materials have attracted renewed interest for manufacturing of optoelectronic devices. High carrier mobilities, large surface area, and solution processability make these 2D nanomaterials interesting for application in photodetectors.¹ Although single-layers of MoS₂ exhibit a photoeffect,² their photoresponse could be augmented significantly and, most importantly, fine tuned when used in a hybrid form with semiconductor quantum dots (QDs). MoS₂ flakes act as a conducting support for QDs and facilitate the transformation of photoexcited states of the light-harvesting QDs into charge-separated states. This concept was applied with QD-graphene hybrids as active layers in photodetectors³ but no hybrid materials of QDs and MoS₂ nanosheets have been used until now.
We demonstrate a facile one-pot synthesis of hybrid materials consisting of near-infrared absorbing PbSe QDs and MoS₂ nanosheets.⁴ With this simple synthesis we are able to grow PbSe QDs directly and linker-free on MoS₂ flakes while maintaining surface passivation of the QDs with oleic acid ligands. Transmission electron microscopy (TEM) shows high density coverage of MoS₂ flakes with PbSe QDs. The dispersion of PbSe-MoS₂ hybrids was used for low-temperature fabrication of photodetectors both on glass and flexible substrates. The photodetectors exhibit clear and stable photo-switching when illuminated with near-IR light (wavelength > 1200 nm) without any laborious ligand-exchange steps. Due to the air-stability and solution-processability of the PbSe-MoS₂ hybrids, and the tunability of the PbSe QD size, this hybrid material is very promising for low-cost flexible near-IR photodetectors. Furthermore, PbSe-MoS₂ hybrid structures belong to the class of misfit layered compounds, which exhibit interesting structural and thermal properties.⁵ High-resolution TEM is applied to investigate the orientation of the PbSe lattice with respect to the MoS₂ lattice and thus elucidate possible epitaxial growth.
[1] Mak, K. F.; Lee, C.; Hone, J.; Shan, J.; Heinz, T. F. Phys. Rev. Lett.2010, 105, 136805.
[2] Yin, Z.; Li, H.; Li, H.; Jiang, L.; Shi, Y.; Sun, Y.; Lu, G.; Zhang, Q.; Chen, X.; Zhang, H., ACS Nano2012, 6, 74.
[3] Konstantatos, G.; Badioli, M.; Gaudreau, L.; Osmond, J.; Bernechea, M.; de Arquer, F. P. G.; Gatti, F.; Koppens, F. H. L., Nature Nanotech.2012, 7, 363.
[4] Schornbaum, J.; Schiessl, S. P.; Winter, B.; Katsukis, G.; Guldi, D. M.; Spiecker, E.; Zaumseil, J. Nano Lett.2013, submitted.
[5] Spiecker, E.; Garbrecht, M.; Jäger, W.; Tillmann, K. J. Microsc.2010, 237, 341

Metal complexes with ligands that incorporate xanthate moieties decompose at moderate temperatures to form metal sulphides. In this talk, we discuss how such solution-processable precursors can be effectively utilized for fabricating thin films that are appropriate for optical gain and photovoltaic applications. In the first example, we show how zinc xanthate species co-complexed by alkyl amines can be utilized to form a hybrid ZnS matrix with highly luminescent quantum dots. Amplified spontaneous emission measurements of such thin films exhibit low gain threshold behaviour and one of the highest temporal stability factors for such systems. As a second example, we show that cadmium xanthate co-complexed by pyridine is readily thermalized to grow high quality CdS thin films. Structural, optical and electrical characteristics of the CdS highlight its promise as a suitable alternative to the n-type windows conventionally deposited via chemical bath for thin films solar cells.

The ability to pattern functional materials in planar and three-dimensional forms is of critical importance for several emerging applications. Printing methods enable one to rapidly design and fabricate materials in arbitrary shapes without the need for expensive tooling, dies, or lithographic masks. In this talk, I will describe how we have created model, reactive solution-based, and viscoelastic inks and demonstrated their use in printed flexible electronics, stretchable sensors, rechargeable batteries, and optical waveguide networks.

Depending on energy level misalignment, significant barrier to charge injection may exist at interfaces between inorganic metals and metal oxides with organic semiconductors. The adsorption of self-assembled monolayers (SAM) onto inorganic metals and metal oxides represents a promising route to control their electronic characteristics and surface wettability with organic semiconductors. Many groups are thus developing experimental techniques that exploit SAM adsorption for interfacial engineering of such dissimilar materials, so that enhanced electronic properties become more accessible. To achieve optimal functionality and stability at the interface, a structurally well-defined, and covalently bonded monolayer is needed. Amongst metal oxides, ZnO is widely used in many technological applications, such as organic-light emitting diodes and solar cells because of its high electron mobility and efficient electron transporting properties. Yet, ZnO-polymer solar cells have shown disappointingly poor performance, likely because of surface defects. Surface functionalization of ZnO with SAM prior to the deposition of the polymer semiconductor thus represents an interesting approach that provides access to tunable chemical and physical properties of the inorganic-organic interface. Here, we provide the first examples of a stepwise functionalization method that allows binding of acidic small molecules to ZnO nanowire arrays with minimal surface degradation and etching. Given their high acidity, adsorption via dip-coating and spin-coating organophosphonic acid solutions on ZnO nanowire arrays uniformly degraded the structures. We found SAM adsorption via tethering-by-aggregation-and-growth (T-BAG) to yield the most robust surface-bound monolayers on ZnO nanowire arrays while retaining the nanostructures. These phosphonic acid-functionalized ZnO nanowires were incorporated in hybrid organic-inorganic solar cells with infiltrated poly(3-hexylthiophene), P3HT, as the polymer donor. Inverted solar cell devices fabricated with these treated interfaces exhibit power conversion efficiencies as high as 2.1 % due to improvements in both the short-circuit cuurent density (Jsc) and the open-circuit voltage (Voc) compared with analogous devices with untreated ZnO nanowire arrays that exhibit efficiencies of 1.6%. We attribute the enhancement in device characteristics to improved charge transfer between P3HT and ZnO and reduced recombination at the organic-inorganic interface due to enhanced wettability between the constituents with SAM treatment.

The nanoparticles (NPs) dispersed in solution are promising ink materials for solution-process because of following features. They can be readily deposited on substrates by solution-deposition techniques, and their tendency to make a self-assembly with the solvent drying facilitates building uniform thin films. As a well-studied transparent conductive oxide, indium tin oxide (ITO) is a good material choice to study solution-processed transparent electronics, and sputtered ITO thin films exhibit the transparency higher than 80% in visible spectral range and the resistivity of 10^-4 Omega;cm order. Here, we present the synthesis of indium tin oxide (ITO) NPs and the optoelectronic properties of their assemblies. The decomposition of In(acac)₃ and Sn(acac)₂Cl₂ in an organic solvent at 250 °C leads to the formation of ITO NPs, and by controlling reaction condition, two different shapes of ITO NPs form: 11 nm nanospheres and 14 nm nanocubes. As-synthesized ITO NPs are stably dispersed in organic solutions such as hexane, toluene, and chloroform. The uniform assemblies of both ITO nanospheres and nanocubes were made by spin-coating and dip-coating, respectively. The thickness of these assemblies is readily tuned from 30 to 200 nm by the concentration of ITO NP solution. After annealing at 300 °C, these assemblies exhibited the transparency over 85% in visible spectral range and the resistivity of 10^-3 Omega;cm order (sheet resistance down to 300 Omega;/sq)—the best performance among NP-based ITO reported to date, and it is applicable to resistive touch screen. This high optoelectronic performance is attributed to both monodispersity of and uniform, densely-packed assembly of ITO NPs.

In this work we present a series of porous one dimensional photonic crystals (1DPC) with superior optical quality and robustness that can be prepared in few minutes by spin or dip coating of colloidal suspensions of nanoparticles of different sort.[1] The nanostructure of these films allows us to integrate optically active nanoparticles with different shape and size. In particular, we integrate core-shell Au/SiO2 nanoparticles [2] or rare earth nanophosphors also by liquid processing. In addition, we demonstrate the interplay between the photonic features with the luminescence of rare earth nanoparticles or with the localized surface plasmon resonance of gold particles.[3] Finally, we show that these porous 1DPC structures are suitable candidates to be infiltrated with polymers, oligomers or monomers from the liquid phase to create hybrid organic-inorganic flexible photonic structures. These materials found applications in electromagnetic radiation protection.[4,5]
[1] M.E. Calvo, S. Colodrero, N. Hidalgo, G. Lozano, C. Loacute;pez-Loacute;pez, O. Sanchez-Sobrado, H. Miguez, Energ. & Envirom Sci. 4, (2011), 4800-4812
[2] O. Sánchez-Sobrado, G. Lozano, M.E. Calvo, A. Sánchez-Iglesias, L.M. Liz-Marzán, H. Míguez, Adv. Mater. 23 (2011) 2108-2112.
[3] A. Jiménez-Solano, C. Loacute;pez-Loacute;pez, O. Sánchez-Sobrado, J.M. Luque, M.E. Calvo, C. Fernández-Loacute;pez, A. Sánchez-Iglesias, L.M. Liz-Marzán,H. Míguez, H. Langmuir 28 (2012) 9161-9167.
[4] M.E. Calvo, J.R. Smirnov, H. Míguez J. Polymer Sci. Part B 50 (2012) 945-956
[5] J.R. Smirnov, M.E. Calvo, H. Míguez Adv Funct. Mater. (2013) DOI: 10.1002/adfm.201202587

Despite of the numerous efforts devoted to achieve uniformly ordered assembly of various low-dimensional nanomaterials, planar metal-oxide-semiconductor field-effect-transistor (MOSFET) is still the dominant configuration for implementing functional nanodevices. Novel architecture like 3D integrated circuits has also been adopted to facilitate integration of nanostructure-based planar building blocks, possibly with diverse functionalities, by sequentially assembling them into vertically stacked layers. Nevertheless, lack of cost-effective technology for aligning and integrating these nanodevices into circuitry with sufficiently high density hinders further practical applications.
For the emerging applications of bio-integrated electronics such as smart skin, prosthetics and human/machine interfacing, schemes for integrating functional nanomaterials with peripheral circuits on deformable/stretchable substrates at low temperature and low cost are highly desirable. To address these application needs, we demonstrate the first and by far the largest 3D array integration of vertical ZnO nanowire (NW) piezotronic transistors circuitry on 4-inch PET flexible substrates, by combining the patterned bottom-up hydrothermal synthesis of vertically aligned ZnO NWs at low-temperature (85 oC) with state-of-the-art top-down microfabrication techniques. The as-fabricated array circuit possesses device density of 8464/cm2, which is much larger than the number of mechanoreceptors embedded in the human fingertip skins and enables a 15-to-25-fold increase in number of taxels and 300-to-1000-fold increase in taxel area density compared to recent reports.
The position, dimension, crystal orientation, morphology and material properties of synthesized ZnO NWs can be well controlled by the hydrothermal solution synthesis and optimized via engineering measures. The solution-synthesized ZnO NWs array exhibits good uniformity in electrical characteristics and response to applied pressure among all of the devices. The reliability and stability of device operations have also been probed, which indicates a good stability of the array operation for future applications like in vivo physiological sensing in complex environments. Moreover, the feasibility of the fabricated array for self-powered active and adaptive artificial skin without external bias has been presented as well. The scalability of this demonstrated technology in integrating solution-derived single-crystalline with interfacing circuitry at low temperature and low cost enables future implementation of nanomaterials for bio-integrated applications in human-machine interfacing and biomedical diagnosis/therapy.
Ref: Wu W. Z.*, Wen X. N.*, Wang Z. L. Taxel-addressable matrix of vertical-nanowire piezotronic transistors for active and adaptive tactile imaging. Science 340, 952-957, 2013.
*Authors with equal contributions

The ability to directly pattern fine featured oxide materials offers a range of potential applications, in particular in microelectronics. In our study of new materials for EUV patterning, we have developed extremely radiation sensitive nanoparticle oxides (HfO, ZrO) capable of direct patterning. With a sensitivity of ~3 mJ/cm2, these are among the most sensitive EUV resists so far developed. These materials with diameters of 3 to 5 nm with carboxylic ligand shells when combined with photoactive compounds can be patterned as either positive tone or negative tone materials to a resolution as fine as 30 nm. In examining other cores, it appears that this method of patterning oxide nanoparticles can be applied to a range of materials. It has been our goal to better understand the nature of the patterning mechanism of these new lithographic materials and our current understanding will be discussed.

An ever increasing interest in the development and application of innovative optical and optoelectronic devices places greater emphasis for the advancement of new smart and functional materials that are readily processable. Significant progress has already been realised in the fields of organic light-emitting diodes (OLEDs) and photovoltaic cells (OPVs) through development of novel semiconducting materials. Further developments in these areas are turning to the deployment of photonic structures to aid and improve light management in these systems, e.g. input-/output-coupling, enhanced absorption and waveguiding. In this work, results from a novel class of hybrid material systems that offer an outstanding set of optical and material properties, including tunable refractive index, low optical losses and solution process ability, are presented. We show that the attributes of these novel hybrid material systems can be controlled and manipulated by a range of means that include ‘alloying&’ or suitable post-deposition treatments, such as thermal annealing and/or irradiation with UV-light. As a consequence, these hybrid materials can exhibit refractive indices of up to 2.1 while also being highly transparent over the entire visible, near- and mid- infrared (N-IR, M-IR) wavelength regime [1]. Furthermore, the processing properties allow the realisation of solution-based, optically low-loss photonic structures that are straightforward to implement in structures, such as OPVs. Given that the readily achievable nature of high quality optical properties and the exceptionally low loss from a single high-index up to several microns thick have already been demonstrated, the focus is here turned to the further development of this generic class of hybrid materials, which are based on metal oxide hydrates and bulk commodity polymers such as poly(vinyl alcohol). To this end, we highlight our recent efforts in introducing different metals, culminating in the successful development of mixed-metal oxide hydrate hybrid materials.

Quantum dots with 3-dimensional confinement structures are known to be very attractive because their electronic and optical properties depend on their size. Quantum dots are the unique class of semiconductor because at small sizes they behave differently with respect to bulk material and the band gap is controlled by the size of the dot. As one of the wide band gaps II-VI group semiconductor compounds, ZnSe nanodot has received much attention for its application in optoelectronic devices such as blue laser diode, light emitting diodes, solar cells, and IR optical Windows[1].
Different methods for the synthesis of nanoparticles are reported in literature. Among these, sol-gel technique is one of the most applied methods. This paper reports synthesis of SiO2 glasses doped with ZnSe quantum dots and Nd3+ ions for the first time. Three samples with compositions of (1% ZnSe - 99% SiO2), (2% ZnSe - 98% SiO2) and (2% ZnSe - 97% SiO2 - 1% Nd3+) were prepared by sol-gel method. Samples were annealed at 410 oC and 600 oC for one hour.
X-Ray diffraction (XRD) technique was used to identify the crystalline phases of ZnSe quantum dots. It was observed that 0 to 1 mol% of Nd2O3 addition produced single phase structure in XRD and SEM graphs.
Average sizes of ZnSe were determined using Scherrer&’s equation and both the size distribution and the average sizes of ZnSe quantum dots in SiO2 glasses have been computed through the method developed by Pielazsek [2].
The average particle sizes of ZnSe quantum dots were found to be in the range of 4-10 nm. Size distribution curves showed that the presence of Nd3+ ions in the glass matrix have led to smaller ZnSe quantum dot sizes and narrow size distribution.

Acknowledgements:
This study is a part of Thami Elboukhari&’s M.S. thesis and was supported by Scientific Research Projects Commission of Istanbul Technical University.
References:
[1] J.J. Andrade, A.G. Brasil Jr., P.M.A. Farias, A. Fontes, B.S. Santos, Synthesis and characterization of blue emitting ZnSe quantum dots, Microelectronics Journal 40 (2009) 641-643.
[2] R. Pielaszek, FW15/45M method for determination of the grain size distribution from powder diffraction line profile, Journal of Alloys and Compounds 382 (2004) 128-132.

Indium-gallium-zinc oxide (IGZO) nanopowders were successfully synthesized by homogeneous precipitation method. Heating of a mixture aqueous solution containing indium (In), gallium (Ga), and zinc (Zn) nitrates, urea, and ethylene glycol leads to white precipitation due to pH up by hydrolysis of urea. The collected white precipitation was repeatedly washed by centrifugation and decantation, resulting in formation of In-Ga-Zn hydroxide (IGZ-OH) nanopowder. IGZO nanopowder forms by annealing of the IGZ-OH nanopowder at higher than 250 degree C according to thermogravimetry-differential thermal analysis (TG-DTA). When the ratio of metal species is In: Ga: Zn = 35:20:45, the XRD patterns show amorphous structure by annealing at 300 and 400 degree C and polycrystal structure at 700 and 1000 degree C. The IGZO and IGZ-OH nanopowders are dispersed in an ethanol solution containing a polyethylene glycol derivative and acetic acid. Thin film transistor (TFT) structures were prepared using the resulting dispersion for electrical characterization of IGZO. Measurement of the transfer characteristic of the TFT structures indicates that sintering in an electric oven gives semiconductor property to the spin-coated dispersion layers. We also discuss other ways of dispersion of the IGZO nanopowders and sintering of the dispersion layers.

There has been significant recent interest in solution-processable organic-inorganic perovskite absorbers in solar cells following demonstrations of power conversion efficiencies exceeding the highest reported values for organic and dye-sensitized solar cells. This suggests they are very promising materials for reducing the cost of sunlight to electricity conversion. However, to date, the highest efficiencies have been achieved using an electron-transport layer which still requires sintering at 500 °C, which is unfavourable for low-cost manufacture on plastic substrates and multi-junction device architectures. Here we report low-cost, solution-based deposition procedure utilising a composite of graphene flakes and TiO2 nanoparticles as the electron-transport layer in solar cells based on the perovskite absorber materials. The graphene flakes provide electrical connectivity between the nanoparticles enabling the entire device to be fabricated at temperatures no higher than 150 °C. These solar cells show remarkable photovoltaic performances with a sunlight-to-electricity power conversion efficiency (PCE) up to 12.45 % under simulated AM 1.5 solar light illumination which is comparable to control devices using a standard “compact” TiO2 layer sintered at 500 °C. In this work, with the benefit of low-temperature and solution-based processing, the graphene/TiO2 composite has demonstrated the potential to contribute significantly towards the development of low-cost solar cells