Jose L. Endrino, Abengoa Research S. L.
Andre Anders, Lawrence Berkeley National Laboratory
Mohan Sankaran, Case Western Reserve University
Gintautas Abrasonis, Helmholtz Zentrum Dresden-Rossendorf
Symposium Support Abengoa
UU2: Plasma Applications and Ion Beam Methods: Thin Film Morphology, Patterning and Mechanical Properties II
Jose L. Endrino
Thursday PM, April 04, 2013
Moscone West, Level 2, Room 2007
2:30 AM - UU2.01
Effect of Excess Energy on Supersaturated Fe-IIIB Thin Films with Ion-plating Process
Mao Amano 1 Ryoichi Toyoda 2 Yoshihito Matsumura 1 Mitsuaki Takeuchi 3
1Tokai University Hiratsuka Japan2Tokai University Hiratsuka Japan3Kyoto University Kyoto JapanShow Abstract
Magnetostrictive materials have been investigated as potential materials for actuator of micro electro mechanical systems (MEMS). We recently have studied magnetostrictive thin films prepared by various preparation processes [1,2]. Clark et al. have reported that a Fe-17at%Ga alloy single crystal showed magnetostriction of about 300 ppm at 16kA/m . Matsuoka et al. also have reported that Fe-21at%Ga alloy thin film prepared by magnetron sputtering (MS) showed maximum value of magnetostriction of 180 ppm at 1200 kA/m . In this study, supersaturated Fe-IIIB thin films were prepared by dual vapor source of ion-plating (IP) process. Effect of excess energy on their nanostructure and magnetostrictive characteristics of thin films were discussed.
Ion plating is hybrid vacuum thin films process that combines the benefits of vacuum evaporation and plasma process. The requirement of ion plating is generally applied to high energy plasma deposition methods in which the surface to be coated is subjected to a small flux of high energy ions and a much larger number of energetic neutrals before and during the deposition of the thin films. The continuous bombardment of the substrate by these energetic ions and atoms of both the depositing material affect the characteristics of films in a wide variety. In this study the dual vapor sources have been using as resistance heated source and electron beam evaporation source. In this type of ion plating system, the flux of the source vapor is ionized by thermal electrons accelerated from molten pool to an electrode so called “anodic probe” . Composition of films was controlled by ratio of Fe and IIIB deposition rate and measured by crystal oscillator of “ULVAC CRTM-5000”. The value of excess energy was controlled by various substrate temperature, various substrate bias voltage and various anodic probe voltage.
Result and Discussion
Fe-In film samples were prepared by IP process as a function of probe voltage and composition of indium. It was found that the 0 to 17 at%In film had α-Fe bcc structure, although Fe-In system was immiscible in room temperature. These results had been attributed unrecognized non-equilibrium phase was formed by non-equilibrium condition as plasma-solid quenching peculiar of the IP. Increasing the value of negative substrate bias voltage and probe voltage can be increasing excess energy and promising can be controlling the solubility limit of alloy films.
M. Takeuchi, et al., Proc. 9th Int. Conf. on New Actuators Actuator 2004 (2004) 581-584.
K. Muramatsu and Y. Matsumura, J. Adv. Sci. 17 (2005)3-5.
A. E. Clark, IEEE Trans. Magn. 36 (2000) 3238-3240.
N. Matsuoka, et al., Proc. 9th Int. Conf. on New Actuators, Actuator 2004, (2004)371-373.
2:45 AM - UU2.02
Surface Modification of Magnetic Media by Low Energy C+ Ion Embedment for Improved Tribological and Corrosion Performance
Ehsan RismaniYazdi 1 Reuben Yeo 1 Hyunsoo Yang 1 Charanjit Singh Bhatia 1
1National University of Singapore Singapore SingaporeShow Abstract
Hard disk drives (HDDs) of the next generation are aimed at achieving magnetic recording areal densities beyond 1 Tbit/in2 which requires media carbon overcoats that are thinner than 1 nm. Decreasing the thickness of conventional carbon overcoats poses significant issues to their tribological and corrosion performance. This necessitates the development of alternative processes in terms of deposition techniques and materials that can help in decreasing the thickness of the overcoat while improving its desired tribological properties which are required for the next generation of magnetic recording.
In this work, filtered cathodic vacuum arc (FCVA) technique was used for surface modification of magnetic disk media in order to develop an overcoat-free magnetic media with improved corrosion resistance and tribological performance. Surface modification was done by bombarding the surface by low-energetic C+ ions and embedding the impinging ions into the outermost layer of the magnetic media without formation of an overcoat. Effects of plasma parameters such as ion density, substrate bias, ion source duty cycle, ion energy, and impingement angle on friction, wear, scratch and corrosion resistance of the samples was studied. It was observed that bombarding the surface with C+ ions at higher energy of 350 eV followed by embedment of C+ ions at lower energy of 90 eV with a normal impinging angle resulted in best tribological and corrosion performance which was better than that of a commercial magnetic media with 3 nm carbon overcoat and 2 nm lubricant.
In this work, bombarding of a thin interlayer (e.g. Si) by energetic C+ ions was also used to develop an atomically mixed layer thinner than 1 nm to protect the magnetic media against scratch and wear. In this work an ultra-thin interlayer with a total thickness of le; 1 nm is deposited on the magnetic film. This layer was bombarded with C+ ions of proper energy using FCVA technique form a Co/Si/C mixed layer. Angle resolved X-ray photoelectron spectroscopy (ARXPS) was used to study the chemical structure of the formed thin films in a non-destructive manner and confirmed formation of a Co/Si/C mixed layer.
The scratch resistance of the samples was qualitatively compared with that of the commercial HDD media using an atomic force microscope (AFM) based single asperity contact scratch test. Contrary to commercial magnetic disk, no visible scratches were observed on the media with the Si/C mixed layer. In addition this surface modification technique resulted in a remarkable improvement in the friction and wear life of the protection layer as compared with that of the commercial media.
Formation of a network of C-C and Si-C bonds at the outermost layer and the bulk of the Si/C film as well as formation of chemical bonds between the Co surface and the mixed layer was found as the main factors to improve the tribological properties.
3:00 AM - UU2.03
Atmospheric Plasma Modification of Polymer Surfaces for Adhesion Enhancement
Linying Cui 1 2 Geraud Dubois 1 3 Reinhold Dauskardt 1
1Stanford University Stanford USA2Stanford University Stanford USA3IBM Almaden Research Center San Jose USAShow Abstract
Atmospheric plasma is an emerging techinque for surface modification of large and curved substrate in ambient air. In this study, oxygen atmospheric plasma was explored for surface modification of polycarbonate (PC) and stretched poly(methyl methacrylate) (PMMA) for ahesion enhancement with plasma deposited silica coating. The evolution of chemical and morphological properties of the polymer surfaces with the amount of atmospheric plasma exposure was studied by x-ray photoelectron spectroscopy and atomic force microscopy (AFM). The changes of surface properties significantly affected the adhesion of the polymer to plasma deposited silica coatings, and different trends of adhesion versus atmospheric plasma treatment time were observed for PC and PMMA substrates. For PC, a short treatment increased the adhesion energy by more than four times, while a longer treatment decreased the adhesion gradually. In contrast, a monotonically decreasing trend of adhesion versus the plasma treatment time was observed for PMMA. The adhesion enhancement of PC by a short atmospheric plasma exposure was found to be the result of newly created surface functional groups and increased surface roughness. The decrease in adhesion for plasma treated PMMA and prolonged-treated PC resulted from over-oxidation of the substrate surface and the formation of a low-molecular-weight weak layer. Interestingly, this low-molecular-weight weak layer can be effectively removed by compressed air flushing or ethanol rinsing of the surface after atmospheric plasma treatment. Significant different surface morphology under AFM was observed after these treatments, together with dramatically improved adhesion. The combination of atmospheric plasma and compressed air/solvent treatments opened up a way to form well functionalized and at the same time highly crosslinked polymer surface for adhesion enhancemnt.
3:15 AM - UU2.04
Permeation Barrier Property of Al2O3/ZrO2 Multilayer Deposited by Remote Plasma Atomic Layer Deposition
Sanghun Lee 1 Hagyoung Choi 1 Seokyoon Shin 1 Joohyun Park 2 Giyul Ham 1 Hyunsoo Jung 1 Hyeongtag Jeon 1
1Hanyang University Seoul Republic of Korea2Hanyang University Seoul Republic of KoreaShow Abstract
Organic light emitting diodes (OLEDs) have been widely studied due to their potential applications in full-color displays, general illuminant light sources, and flexible devices. Especially, flexible devices with polymer substrates attract huge interest from researchers for use in displays however the flexible organic devices have a disadvantage of short lifetime property because of H2O and O2 permeation through their polymer substrate. Many research groups have tried to improve the lifetime and stability of flexible OLEDs by using various kinds of encapsulation techniques with single or multilayers of thin films. In organic devices, the organic materials are easily degraded by the presence of H2O and O2. Bare polymer films such as polyethersulfone (PES) in flexible devices exhibits high permeation rate. In a single inorganic protection layer, permeation is attributed to defects or pinholes in the film. To prevent such failures, a combination of protective coatings with multilayers of inorganic materials offers lower permeability than single film against gases.
Atomic layer deposition (ALD) is considered as one of the most appropriate methods to deposit dense, conformal and pin-hole free passivation film. Particularly, plasma-enhanced ALD (PEALD) is a very attractive technique for depositing oxide films because of its high chemical reactivity. However, the exposure of substrate to plasma during process could result in lattice damage by energetic ions. In this respect, remote plasma ALD (RPALD) was developed to minimize the plasma damage by generating the plasma remotely outside of chamber and the generated radicals and ions enter into the chamber by a downstream flow.
In this paper, total 100nm of Al2O3 single and Al2O3/ZrO2 multilayer films were prepared by RPALD and followed by the measurement of WVTR by Ca test at 50°C and 50% of relative humidity to investigate their permeation barrier properties. It was observed that when more number of alternative layers is deposited, it has lower WVTR value which means it has better properties for OLED encapsulation. In our results, single Al2O3 and ZrO2 films show 9.5x10-3g/m2day and 1.6x10-2g/m2day of WVTR but when they are deposited alternatively with 1 cycle of each layer, the value of WVTR decrease to 9.9x10-4g/m2day. To investigate the change of WVTR in detail, the properties of films were analyzed by X-ray reflectivity (XRR), Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM).
UU3: Plasmas and Surface Functionalization for Energy Applications
Thursday PM, April 04, 2013
Moscone West, Level 2, Room 2007
4:00 AM - UU3.01
Ion Energy Control during Plasma-enhanced Atomic Layer Deposition
Erwin Kessels 1 Harald Profijt 1 Richard Van de Sanden 1 2
1Eindhoven University of Technology Eindhoven Netherlands2Dutch Institute for Fundamental Energy Research (DIFFER) Nieuwegein NetherlandsShow Abstract
Atomic layer deposition (ALD) is the method of choice for the deposition of ultra-thin films with sub-monolayer growth control and excellent uniformity, and the method is unparalleled in terms of its ability to deposit conformal films on high-aspect-ratio structures. Recently, the extension of the technique with plasma steps has gained considerable interest. This so-called plasma-enhanced ALD process offers an increased level of freedom in material properties and processing conditions which can be attributed to the presence of reactive radicals and ions which interact with the material surface during deposition. For selected applications, this leads to several advantages over the strictly thermal ALD process such as enhanced growth rates, improved material properties and lower deposition temperatures (including several room temperature processes). A parameter that was not explored until recently is the substrate potential during plasma-enhanced ALD. This substrate potential directly affects the kinetic energy with which ions arrive at the film surface. In this contribution we report on the implementation of two substrate-biasing techniques, i.e., substrate-tuned biasing and rf biasing, which enable control of the ion energy during plasma-enhanced ALD. From ion energy distribution (IED) measurements it is shown that these techniques allow for an increase in the ion energy from a few eV&’s or few tens of eV&’s (under non-biased conditions, depending on the plasma pressure) up to a few hundreds of eV&’s. The effects of substrate biasing on the plasma properties during plasma-enhanced ALD have been investigated in terms of electron temperature and electron density, ion flux and ion energy distribution. Furthermore, the influence of the ion energies on the material properties of several metal oxides (Al2O3, Co3O4 and TiO2) has been explored . Thin films of these oxides have a multitude of applications in energy technologies such as photovoltaics, (photo)catalysis and energy storage. It is shown that the ion energy during the plasma step affects the growth per cycle and the mass density of the films while it can also be used to tailor the residual stress in substrates coated with Al2O3 films. Moreover, for two plasma-enhanced ALD processes of TiO2 (using Ti(CpMe)(NMe2)3 and Ti(CpMe5)(OMe)3 as precursors and O2 plasma as reactant) it is demonstrated that the ion energy can be used to control the crystalline phase of the films. It is shown that rutile TiO2 films can be deposited at 200 and 300 °C with ion energies of >200 eV while without biasing the films are typically amorphous and anatase, respectively. These results clearly demonstrate that ion energy control through substrate biasing is a promising method to tailor the material properties of ultrathin films synthesized by plasma-enhanced ALD.
 H. B. Profijt et al, Electrochem. Solid-State Lett. 15, G1 (2012); J. Vac. Sci. Technol. A 31, 01A106 (2013).
4:15 AM - UU3.02
Nanodiamond Formation at Ambient Conditions via Microplasma-assisted Dissociation of Ethanol Vapor
Ajay Kumar 1 Pin Ann Lin 1 Albert Xue 1 Boyi Hao 2 Yoke Khin Yap 2 R. Mohan Sankaran 1
1Case Western Reserve University Cleveland USA2Michigan Technological University Houghton USAShow Abstract
Nanoscale crystals of diamond, known as nanodiamonds, have been detected in outer space (meteorites, interstellar dust) and synthetically produced in powder form by detonation processes or as films by chemical vapor deposition. In addition to their potential technological use, the formation of nanodiamond is of great scientific interest. While bulk graphite is well known to be the more stable form of carbon at lower pressures and temperatures (e.g. ambient conditions), recent modeling has suggested that nanodiamond is thermodynamically favored as a result of surface energy considerations. Here, we show that nanodiamond can indeed be formed at ambient conditions by dissociating ethanol vapor in a continuous-flow, atmospheric-pressure microplasma. Previously, we have shown that this approach can be used to homogeneously nucleate metal nanoparticles with sizes less than 3 nm. Ethanol dissociation was monitored in situ by optical emission spectroscopy (OES) which indicates the generation of C2 and CH3 radicals, and aerosol size classification which shows the formation of nanoparticles. Materials analysis was carried out by collecting the nanoparticles on a filter and dispersing in methanol. High-resolution transmission electron microscopy (HRTEM) revealed a mixture of sp2 and sp3 material; however, crystalline particles with a highly uniform size (~2-4 nm) were clearly evident. Selected area electron diffraction (SAED) confirmed that these nanocrystals are diamond phase with structures corresponding to cubic, lonsdaleite, and n-diamond. To improve the purity of the as-grown product, we have explored the addition of H2 gas during particle nucleation. This has reduced the sp2 fraction, as indicated by X-ray diffraction and micro Raman spectroscopy. The formation of nanodiamond particles without extreme conditions confirms theoretical predictions and could enable new applications such as the coating of polymeric materials.
4:30 AM - UU3.03
Advanced Solar Absorber Coatings Based on Nanocomposites
Irene Heras 1 Ramamp;#243;n Escobar Galindo 2 Gintautas Abrasonis 3 Ainhoa Pardo 4 Mykola Vinnichenko 3 Jose Luis Endrino 1
1Abengoa Seville Spain2Instituto de Ciencia de Materiales de Madrid Madrid Spain3Helmholtz Zentrum Dresden Rossendorf Dresden Germany4Centre Tecnologic Manresa Manresa SpainShow Abstract
The design of an efficient and stable solar selective coating for photo-thermal conversion plants requires a complex study of the materials that composed the coating. The optimal optical properties for those absorber coatings are high solar absorptance in the wavelength range of 0.3 to 2.5 mu;m which corresponds to solar spectrum under atmospheric conditions and low thermal emittance in the infrared wavelength range.
Carbon-transition metal nanocomposites have been selected as absorber materials because they show appropriate optical properties as well as thermal and mechanical stability at high temperatures. The refractory metal carbide nanoparticles have been experimentally shown to stabilize the surrounding carbon matrix at least up to 700°C.
The computer simulation program CODE has been used to calculate solar absorptance and thermal emittance of various multilayers coatings material combinations of carbon - metal nanocomposites (NCTM). The optical properties of the inhomogeneous composite material were simulated with a physical model proposed by Bruggeman and Maxwell Garnett which average the dielectric function of the components of the composite. This allows treating the composite system as an effective medium.
This contribution compares simulated optical properties for different nanocomposite structural configurations (layer thickness, metal to carbon ratio). The calculated results are in the range of 0.91-0.97 for solar absorptance and 0.02 - 0.07 for thermal emittance at 300k.
4:45 AM - UU3.04
Atmospheric Pressure Plasma Functionalization of Dry-spun Multi-walled Carbon Nanotube (MWNT) Sheets and Their Incorporation in Polyvinyl Alcohol (PVA) and Epoxy Composites
Rachit Malik 1 Noe Alvarez 1 Bolaji Suberu 2 Yi Song 2 Vesselin Shanov 1 Mark Schulz 2
1University of Cincinnati Cincinnati USA2University of Cincinnati Cincinnati USAShow Abstract
Surface modification of aligned MWNT sheets made from dry spinning of carbon nanotube (CNT) arrays grown via chemical vapor deposition (CVD) is carried out using an atmospheric pressure plasma jet. Helium/Oxygen plasma was utilized to produce carboxylic acid (-COOH) functionality on the surface of the nanotubes. Due to the functionalization, carbon nanotube sheets can be made hydrophilic and thereby allowing better penetration of the polymer matrix occurs in case of the aqueous PVA solution, and it opens up a possibility for the CNTs to covalently bond to the 2-part Epoxy matrix. X-Ray Photoelectron Spectroscopy (XPS) confirms the presence of functional groups on the nanotube surface and the sheet is further characterized by Raman Spectroscopy, Fourier Transform - Infrared Spectroscopy (FT-IR), contact angle measurement and Scanning Electron Microscopy (SEM). Composite laminates made from functionalized CNT sheets show significantly higher strength than those made with pristine sheets as reinforcement material. The effects of plasma power and oxygen concentration have been studied in order to determine the best possible parameters for functionalization. Plasma presents itself a useful tool for fast, clean functionalization of CNTs and we demonstrate the easy of incorporating this tool in the manufacturing process of sheets leading to the production of strong CNT/Polymer composites.
5:00 AM - UU3.05
Effect of Off-angle RF Sputtering Deposited Nano-porous SnS Film on Anodic Aluminum Oxide
Ling-Hsuan Tsai 1 Chun-Jung Lin 1 Gong-Ru Lin 1
1National Taiwan University Taipei TaiwanShow Abstract
Tin sulfide (SnS) semiconductor has received considerable research interest due to its unique characteristics of tunable bandgap tuning from 1.3 to 2.18 eV, and special structure with orthorhombic and CdI2-type crystallinity. Recently, nano-scale SnS and SnS2 structures have emerged for applications in photodetection and solar cell. Up to now, the nano-scale SnS fabrications rely on the chemical solution process and most of the obtained structures are irregularly distributed nano-wires and nano-tubes. Either chemical vapor or sputtering deposition was never utilized to synthesize the SnS nanostructure successfully. This is mainly attributed to the lack of appropriate catalyst or template for these physical syntheses. Porous AAO membrane is a well-known template used to grow nano-wire(rod) of versatile semiconductors. The solution-type deposition of SnS2 nano-wire and the solvent-relief growth of SnS2 nanotube on nano-channels of AAO membrane have ever been demonstrated. Nevertheless, the physical synthesis of SnS and SnS2 nano-porous structures on AAO membrane has not yet been reported. This study employs an RF sputtering deposition to physically synthesize the SnS nanostructure at a relatively low plasma power. With the assistance of the AAO based solid-state nano-reactor, variable SnS nanostructures can be obtained by changing the oriental angle between the deposited ion-beam and the AAO surface normal from 0 and 90o. With a specific oriental angle at 0o, the two-dimensional (2D) nano-porous SnS film is successfully synthesized on AAO template with pore size of 250 nm. The room-temperature sputtering of nano-porous SnS film strictly relies on the plasma power in the RF sputter chamber and the oriental angle of the solid-state AAO nano-porous membrane. Larger RF plasma power fails to deposit the SnS nano-clusters on the AAO member orderly. This leads to random growth of the disordered SnS nanostructure on the crushed basement upon the AAO membrane. The off-angle sputtering deposition meets a similar problem on the side-wall strength of the deposited SnS, which results in numerous holes to weaken side-wall and to destroy the regularity of the deposited nano-porous SnS film. The SEM shows that the nano-porous SnS film on AAO template with at oriental angles of 45o and 90o reveal broken morphologies and behave more like nano-rods. In the meantime, the nano-rods of SnS are synthesized and followed the tilted direction of AAO membrane and lied down on the top of the AAO membrane. With the sputtered deposition at normal angle of 0o, the clusters of SnS sputtered have the largest deposition area to periodically grow on the porous AAO membrane. When reducing the oriental angle from 90o to 0o, a regular SnS nano-porous structure can be synthesized. however, the pore size and the density of porosity of the deposited SnS are significantly changed. The uniformly deposited nano-porous SnS film with an average pore diameter of 100 nm pore is synthesized.
UU4: Poster Session: Plasma and Low-energy Ion-beam-assisted Processing and Synthesis of Energy-related Materials
Thursday PM, April 04, 2013
Marriott Marquis, Yerba Buena Level, Salons 7-8-9
9:00 AM - UU4.01
Properties and Growth of Undoped and Metal-doped Zinc Oxide Thin Films
Adolfo Mosquera 2 Jose Luis Endrino 1 David Horwat 3 Patrice Miska 4 Jose Maria Albella 2
1Abengoa Seville Spain2Instituto de Ciencia de Materiales de Madrid Madrid Spain3Institut Jean Lamour Nancy France4Universite Henri Poincare Nancy FranceShow Abstract
Titanium and zinc oxide are the most investigated and used oxides in industry, due to their wide range of applications. For instance, ZnO can be utilized in different areas of industry such as varistors which are used to protect electronic devices against overvoltage, in rubber industry to extend the useful life time of rubber compounds, in paint to improve weatherability, in ceramic to protect against grazing, in pharmaceuticals industry such as in dental products and in photoelectronic devices such as LEDs. All these applications can be achieved because these oxides exhibit good physical and chemical properties. Zinc oxide has a hexagonal structure called wurtzite with a wide bang gap (3.37eV) and high excitonic binding energy (60 meV). These characteristics make that ZnO can be considered an alternative to GaN, that has low excitonic binding energy (28 meV), for device applications owing to its relatively low production cost and superior optical properties. In this study, titanium-doped zinc oxide deposited by reactive DC magnetron sputtering and pulsed cathodic arc are characterized by different techniques like X-Ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM), and optical spectroscopy (transmittance, reflectance, and absorption) in order to understand and improve the characteristics of the different devices mentioned above. In addition, morphological and optical properties of the doped and undoped zinc oxides with annealing have been investigated in order to improve the characteristics and properties of the coatings. The chemical composition and bonding of the samples were determined by XPS. In addition, transmittance and PL spectra were recorded in order to study the exciton response of the samples. X-ray absorption near edge structure measurements (XANES) at K-L3 and O-K edges evidenced a different bonding state for films. The weak exciton emission of the as-deposited ZnO films was correlated to the presence of contaminant H2O and -OH species absorbed by the surface of the samples likely due to the polar behavior of ZnO. After annealing all the samples showed improvement of the free exciton emission and revealed an exciton confinement effect in quantum dots observed for first time in thin films.
9:00 AM - UU4.02
The Structure and Properties of Inductively Coupled Plasma Assisted Nanocrystalline CrN Coatings for Wind Turbine Systems
Sung-Yong Chun 1
1Mokpo National University Jeonnam Republic of KoreaShow Abstract
Wind carrying large amounts of sand and water droplets can erode the leading edge of a turbine blade and increase surface roughness. Superior hard and corrosion-resistant coatings of chromium nitride (CrN) have been prepared in reactive sputtering system using inductively coupled plasma. CrN coatings have also been prepared using dc generator in the same sputtering system under identical deposition conditions. The properties of these coatings are compared with the ICP assisted coatings. FE-SEM, AFM, potentiostat and nanoindentation tester have been used to characterize the coatings. We present in detail coatings (e.g., growth rate, morphology, surface roughness, corrosion resistance and nanohardness). The columnar growth of the deposited films could be suppressed by using the ICP without increasing the deposition temperature. Our studies show that CrN coatings with superior properties can be prepared using ICP assisted deposition.
Keywords: Inductively Coupled plasma, Nanocrystalline CrN, Wind turbine
This research was supported (in part) by Research Funds of Mokpo National University in 2012.
9:00 AM - UU4.03
Optimization of Reactive-sputter-deposition of the ZnO Hole Blocking Layer to Improve Photoconduction Characteristics of High-gain Avalanche Photoconductor Devices
Tung-Yuan Yu 1 Fu-Ming Pan 1
1National Chiao Tung University Hsinchu TaiwanShow Abstract
A high-gain avalanche rushing amorphous photoconductors (HARP) flat panel imager using amorphous Se as the photoconductor requires a hole-blocking layer to reduce noise induced by hole injection from the anode so that a high contrast image can be obtained. In general, the hole-blocking layer is made of CeO2, which is sputtered deposited on the ITO glass substrate. The hole-blocking mechanism is suggested to be due to hole trapping in the hole-blocking oxide, which results in charge accumulation and subsequently the development of a potential barrier in the oxide, thereby suppressing further hole injection from the anode. In this study, we used reactive-sputter-deposition to prepare a ZnO layer as the hole-blocking layer for the HARP device, which has an a-Se photoconductor layer thermal-evaporation-deposited on the blocking layer at 36oC. An organic distributed resistive layer (DRL) was spin-coated on the a-Se layer to improve the breakdown field. Because the trap density must closely related to the stoichiometry of the blocking layer, we have prepared the ZnO layer under different fabrication conditions so that an optimized hole-blocking layer can be prepared. We varied the flow rate ratio of Ar and O2 during the plasma deposition of the ZnO layer and performed thermal treatment for the oxide. According to photoconduction measurement, the ZnO blocking layers prepared with an Ar/O2 flow rate (sccm) of 20:10 and thermally annealed at 300oC in vacuum has the best photoconduction performance, including the lowest dark current and the highest breakdown field. In this study, we used photoelectron spectroscopy for chemical analysis, and photoluminescence and deep level transient spectroscopy for the study of defects and traps present in the oxide layer.
9:00 AM - UU4.04
Nitrogen Doping and Nanofabrication by a Plasma Plus Thermal System for Energy Applications
Xiujuan Jane Dai 1 David Rubin de Celis 1 Gayathri Devi Rajmohan 1 Zhi Qiang Chen 1 Robert Lovett 1 Peter Ronald Lamb 1 Takuya Tsuzuki 1 Ying Chen 1 Xun Gai Wang 1
1Deakin University Geelong AustraliaShow Abstract
A plasma plus thermal (PPT) system, with various plasma sources, has been developed. This system combines a gas discharge and heating. It has the exciting advantages of allowing controllable element doping and effective nanofabrication of materials for energy generation, e.g. dye sensitized solar cells (DSSCs), and energy storage (e.g. batteries).
The key challenge in DSSCs is improved efficiency. An increase in Ti+3 charge states in TiO2 nanoparticles was found to increase the efficiency , as a strongly polarised Ti+3 species introduces electrons into the conduction band of TiO2 so helping transportation of electrons through the TiO2 network . N-doping of TiO2 reduces the amount of Ti+4 and increases Ti+3 enabling a better understanding of the mechanism. A nitrogen containing plasma in the PPT system can break Ti-O bonds and generate oxygen vacancies, allowing nitrogen replacement (N-Ti-O) which introduces inter-band gap states. The density of N-doping can be controlled by altering the total plasma energy input and temperature.
Nanofabrication and N-doping of SnO2, as an anode material for lithium batteries, addresses two main challenges (a very strong initial capacity loss and low cycling performance). The PPT system can be used to produce nanostructured SnO2 providing increased resistance to volume changes. It can also be used to nitrogen-dope SnO2 giving band gap control  which can maintain and possibly increase the initial energy storage capacity. It has been found that the amounts of SnO2 and Sn can be manipulated when SnO powders are treated using nitrogen-containing plasma and that the SnO powders can be fully converted to SnO2 and SnNO under optimum plasma conditions and temperature. Plasma etching to nanostructure materials can also be achieved in the system. A preliminary battery test using an N-doped SnO2 as the anode material has given promising results.
 G. D. Rajmohan, X. J. Dai, T. Tsuzuki, Approach to Improved Dye Sensitized Solar Cells by Using Plasma Technology, Conference Proceedings APMC 10 / ICONN 2012 / ACMM 22, 6-9 Feb., 2012, Perth, Western Australia
 K.H. Park, M. Dhayal, Electrochemistry Communications, 11 (2009) 75-79
 R. L. Xuequin, Journal of Physics and Chemistry C 112, 4 (2008)
9:00 AM - UU4.05
Confined-plume Chemical Deposition of Microcrystalline Coatings Using Pulsed Tabletop Laser Irradiation
Borislav L Ivanov 2 Jeremiah Beam 1 Andrew G Harris 1 Mohamed A Seif 3 Charles M Lukehart 1
1Vanderbilt University Nashville USA2Vanderbilt University Nashville USA3Alabama Aamp;M Normal USAShow Abstract
Developing plasma-mediated methods to achieve local control of materials deposition at moderate temperatures is a topic of current interest. We report a novel method of obtaining crystalline coatings on soft substrates, advancing fabrication of energy-related functional materials, such as photovoltaic and nanogenerator devices. Confined-plume chemical deposition (CPCD) occurs when pulsed laser irradiation initiates decomposition of chemical precursors with formation of a reaction plume (Tasymp; 3000 K) under spatial and temporal confinement, resulting in nucleated growth or deposition of microcrystalline thin-film coatings. Temporal confinement of laser pulses allows residual heat to dissipate throughout the substrate material, minimizing collateral thermal damage. This process has been demonstrated using both visible (Ti:Sapphire, 800 nm) and infrared (Er:YAG, 2.94 mu;m) tabletop lasers as the irradiation source. Formation of ceramic (ReB2), semiconductor (CdS), piezoelectric (ZnO), and metal (Au) microcrystalline coatings on polymer and biological substrates will be presented. Characterization methods include powder x-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectral (EDS), and Raman spectroscopy (where appropriate). Property measurements will also be included, as available.
9:00 AM - UU4.06
Characterization of Thermal Plasma Synthesized and Rapidly Annealed Zinc Oxide Films
Michael Julius Kinsler 1 Rabiah Harrison 1 Bret Cooke 1 Kwok-Siong Teh 1
1San Francisco State University San Francisco USAShow Abstract
Nanocrystalline zinc oxide thin films were synthesized using a rapid thermal plasma chemical vapor deposition process. The films are to be rapidly annealed in the same system with a modified setup. The goal is to reproducibly deposit transparent and conductive zinc oxide thin films. The synthesis process was performed on glass and silicon substrates in a vacuum environment at 1.35 PSIA and consisted of 99.8% argon and 0.2% oxygen. The total synthesis duration was approximately forty five minutes, which is significantly shorter than a sputtering deposition process. The environment pressure is well below atmospheric pressure, but much higher in comparison to conventional vacuum coating systems, it therefore does not necessitate an expensive vacuum pump. The films were characterized by scanning electron microscope, grazing angle x-ray diffraction, and four point probe resistivity measurements. The samples are to be annealed and then re-characterized. Annealing temperatures will range from 290C to 950C, corresponding to 25% and 55% of ZnO&’s melting temperature. The planned annealing run times will vary from 10 to 20 minutes. The only factor varying the total annealing time will be the amount of time it takes to reach the maximum holding temperature. The annealing portion of the experiment is in the final stages of development. Based on preliminary testing and surveyed literature, we are expecting decreases in the films resistivity on the order of one to two magnitudes. Annealing will occur in the same chamber as the synthesis process by modifying the synthesis chamber with a dedicated annealing platform which sandwiches the specimen between two nickel plates. During the annealing process, the energy from the induction coil is transferred to the annealing plates causing induction heating. Heat is also transferred to the annealing plates from the inductively coupled plasma. Due to conduction from the annealing plates to the specimen, heat is focused to the contact area between the specimen and the annealing plates. The small thermal mass of the annealing setup allows for thermal equilibrium to be reached rapidly. Synthesizing and annealing in the same system provides many benefits. Primarily, it proves the ability for a production based machine to synthesize and anneal optically clear and conductive ZnO thin-films. This would mean a zinc oxide semiconductor could be deposited and thermally treated in a single rapid operation which negates the need for additional handling.
UU1: Plasma Applications and Ion Beam Methods: Thin Film Morphology, Patterning and Mechanical Properties I
Jose L. Endrino
Thursday AM, April 04, 2013
Moscone West, Level 2, Room 2007
10:00 AM - *UU1.01
Texture Evolution in IBAD-MgO under Various Growth Conditions
Vladimir Matias 1
1iBeam Materials Santa Fe USAShow Abstract
We examine crystalline-texture evolution during ion-beam assisted deposition (IBAD) of MgO thin films. To perform these experiments we developed a unique experimental methodology based on linear combinatorics. This technique allows us to fabricate film-thickness wedges that maximize data collection and allow us to easily and systematically obtain texture evolution plots. MgO texture evolution can be separated into three different regions. During initial ion beam assisted deposition an amorphous layer is formed which is crucial for obtaining <100> out-of-plane grain alignment. Onset of texture appears in the first 1-2 nm of film deposit when MgO crystallizes. We separate out-of-plane <100> fiber texture that appears first, followed by in-plane grain alignment along the ion-beam assist direction. Texture improves with continued ion beam bombardment during deposition. Still further improvement is seen with growth of a homoepitaxial overlayer. We have studied texture evolution under different ion beam incidence angles and for combinations of different angles. We have developed an empirical quantification of the texture evolution in both IBAD and homoepitaxial layers. The best texture attained thus far in the MgO template layer on polished metal tape has an in-plane FWHM of 1.5°.
The artificially crystal-aligned films are used as templates for epitaxial growth of energy functional layers.
This work was supported by the Department of Energy Office of Electricity Delivery & Energy Reliability.
10:30 AM - *UU1.02
Thin Film Deposition and Surface Transformation Using Gasless Magnetron Sputtering, Self-sputtering and Temporally Rarefied Sputtergas
Joakim Andersson 1
1National University of Singapore Singapore SingaporeShow Abstract
High power impulse magnetron sputtering allows deposition and surface engineering using metal ions rather than metal atoms. The possibilities to affect texture, stress and density of the resulting thin films are vastly improved, compared to conventional DC sputtering, and this is therefore an interesting area of research. By biasing the substrate negatively, various degrees of sputtering and implantation can be achieved. This is used to improve adhesion but also to change the composition of the substrate/thin film interface with applications ranging from mechanical tools to microelectronics. One concern is the implantation of noble gas used for sputtering. For high sputter yield materials, such as copper, silver and nickel, it is possible to sustain the discharge without any appreciable pressure of noble gas, hence allowing deposition and surface engineering with drastically reduced incorporation of sputtergas. This has been used to create well-defined NiSi2 layers for semiconductor fabrication. A reduction in background pressure also affects the possibilities to coat 3D objects and an example of trench lining will be shown. In addition, the rate of deposition is improved in the gasless case, partly alleviating the infamous reduction in rate of deposition when using high power impulse magnetron sputtering.
11:00 AM - UU1.03
Ion Assistance Effects on the Morphology of Carbon-nickel Composite Films Grown by Physical Vapor Deposition at Various Metal Contents
Gintautas Abrasonis 1 Matthias Krause 1 2 Arndt Muecklich 1 Carsten Baehtz 1 3 Artem Shalimov 1 3 Matthias Zschornak 1 Sebastian Wintz 1 Jose Luis Endrino 4 Sibylle Gemming 1
1Helmholtz-Zentrum Dresden-Rossendorf e.V. P.O.Box 51 01 19 Dresden (Rossendorf) Germany2Technische Universitamp;#228;t Dresden Dresden Germany3European Synchrotron Radiation Facility Grenoble France4Abengoa Sevilla SpainShow Abstract
Phase separation occurring on the surface of growing films provides unique means to influence the microstructure of composite materials. Here, the influence of ion assistance on the morphology of carbon-nickel nanocomposite thin films for different metal contents is investigated. Carbon-transition metal nanocomposites are relevant in the context of solar-thermal energy conversion, fusion, fuel cells, tribology or sensing. The films were grown by dual ion beam sputtering in a temperature range of RT-300°C. The growing films were irradiated by an assisting Ar ion beam with energies ranging from 50 to 130 eV. It is found that the nickel content drastically influences the morphology of the films: while films with low Ni contents show regular self-organized structures consisting of ordered Ni nanoparticles embedded in the carbon matrix, higher Ni contents predominantly exhibit a columnar morphology. The results are discussed on the basis of the interplay of ion-induced effects and phase separation modes.
Acknowledgements: Funding by the European Union, ECEMP-Project D1, "Nanoskalige Funktionsschichten auf Kohlenstoffbasis", Projektnummer 13857 / 2379 is gratefully acknowledged.
11:45 AM - UU1.04
Low-energy Ion-beam-activated Growth of Ordered Nanocomposites -Modeling and Computer Simulations vs Experiments
Karl-Heinz Heinig 1 Gintautas Abrasonis 1 Liedke Bartosz 1
1Helmholtz-Center Dresden-Rossendorf Dresden GermanyShow Abstract
Co-sputtering of immiscible components like Al/Si, Metals/C, Metals/Si, Si/SiO2 etc. leads usually to artificially mixed solids which are metastable but nevertheless useful for applications up to a certain operation temperature. The components or their compounds are either mixed (on the atomic scale) into a state far from thermodynamic equilibrium, or they become phase separated (on the nanoscale) into a composite like a ceramic and a metal in a cermet. Phase separation can occur ion-beam-activated during growth, or thermally activated in a subsequent annealing step.
It will be shown how, during co-sputtering, a high atomic mobility in the growing top layer allows for an almost complete phase separation and, eventually, the fabrication of regular order of the precipitated components. Thus, growth of hexagonally ordered silicide nanowires embedded in silicon has been demonstrated by biased co-sputtering of metals and silicon at elevated substrate temperature [Yasui et al., Adv.Mater. 2007,19, 2797]. Here, well-ordered metal/carbon and Si/SiO2 nanocomposites will be shown, and their evolution will be demonstrated by 3D kinetic lattice Monte Carlo simulations. Predictive atomistic simulations on spatiotemporal scales of experiments will be presented which give a guideline for fabrication of nanocomposites having self-organized structures with a high degree of order.
12:00 PM - UU1.05
Angular Dependency of NbOx Thin Film Growth in HiPIMS Plasmas
Robert Franz 1 Andre Anders 1
1Lawrence Berkeley National Laboratory Berkeley USAShow Abstract
Recent studies of the plasma properties in high power impulse magnetron sputtering (HiPIMS) discharges have shown that self-organized plasma structures form in the vicinity of the target&’s erosion “racetrack.” These structures comprise ionisation zones which are thought to be responsible for the high degree of ionization of sputtered atoms and gas atoms as well as for the high current levels observed in HiPIMS. Ionisation zones are related to the ExB drift of electrons yet they disrupt the close drift and cause electron jets and plasma flares, which in turn are thought to be responsible for ionization far from the target. In this way, ionization zones are of critical importance to the flux of ions arriving at the target. The situation is made even more complicated in reactive deposition where we need to take into account target poisoning and several different types of ion species, including negative ions.
Traveling ionization zones and ejected electrons break the symmetry of magnetron discharges, with consequences for the properties of films deposited at different locations with respect to the magnetron. In particular, energetic (>10 eV) and multiply charged (often 2+, sometimes 3+, 4+) ions are ejected from the target. There is evidence that they move preferentially in the tangential-forward direction relative to an ionisation zone&’s motion. The motivation for the present work was therefore to study the influence of this spatially asymmetric ion distribution on the growth of thin films. As an interesting film material we picked Nb2O5, or more generally NbOx, although we believe that the study is also applicable to other film systems. Substrates were placed in different angular positions relative to the magnetron and the resulting NbOx thin films were analysed as to their morphology, microstructure, and other properties. A special factor in oxygen-containing magnetron plasmas are highly energetic (often > 100 eV) negatively charged oxygen ions. Since the electric field is distorted in the ionisation zones, special emphasis is given to the spatial distribution of negative oxygen ions and their influence on thin film growth. The results obtained contribute to the understanding of reactive HiPIMS plasmas and their applicability for synthesising thin oxide films.
This work was supported by the Erwin Schrödinger Program (Project J3168-N20) of the Austrian Science Fund (FWF) and by the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.
12:15 PM - UU1.06
Selection of Metal Ion Irradiation for Controlled Growth of Transition Metal Nitride Films via Hybrid HIPIMS/Magnetron Co-sputtering
Grzegorz Greczynski 1 Jun Lu 1 Jens Jensen 1 Ivan Petrov 1 2 Joseph E. Greene 1 2 Werner Koelker 3 Stephan Bolz 3 Christoph Schiffers 3 Oliver Lemmer 3 Lars Hultman 1
1Linkamp;#246;ping University Linkamp;#246;ping Sweden2Frederick Seitz Materials Research Laboratory Urbana USA3CemeCon AG Wurselen GermanyShow Abstract
Transition metal nitride alloy thin films are grown by high-power pulsed magnetron (HIPIMS) and dc magnetron (DCMS) co-sputtering from elemental targets. Two examples are discussed in this talk, Ti-Al-N and Ti-Si-N, where unique film properties are obtained through (i) selection of metal ion irradiation assisting film growth and (ii) advanced substrate-biasing schemes. This novel approach is based on the results of time-resolved in-situ mass spectrometry that is used to analyze composition and energy distributions of ion fluxes incident at the growing film surface. The distinctly different flux distributions obtained from targets driven in HIPIMS vs. DCMS modes allow the effects of Aln+, Sin+ and Tin+ (n = 1, 2, 3) ion irradiation on resulting film properties to be investigated separately. Markedly different film growth pathways are obtained depending upon which target is powered by HIPIMS. It is demonstrated that both phase content and nanostructure of metastable alloy films with similar stoichiometry is to a large extent determined by the type of target ion that assists growth (e.g., Tin+ vs. Aln+ for Ti-Al-N films). Further advantage is made of the fact that intensity of metal and gas ion fluxes at the substrate position varies with time. By using the pulsed substrate bias synchronized with the metal-ion-rich phase of the HIPIMS pulses, Ar+ ion irradiation is minimized in favor of metal ion irradiation, which is predominantly by target ions. This drastically decreases the concentration of trapped gas ions and the associated compressive stresses are greatly reduced. The evidence by x-ray diffraction, scanning electron microscopy, transmission electron microscopy, x-ray photoelectron spectroscopy, elastic recoil detection analysis, and nanoindentation is presented and discussed during the talk.
12:30 PM - *UU1.07
Combinatorial Thin Film Materials Science: From Materials Discovery and Optimization to Materials Design
Jochen M. Schneider 1
1Aachen University Aachen GermanyShow Abstract
The combinatorial approach, combining combinatorial materials synthesis of thin film composition-spreads with high-throughput property characterization has proven to be a powerful tool to delineate composition-structure-property relationships, and hence to efficiently identify composition windows with enhanced properties. Furthermore, and most importantly for alloy design, theoretical models and hypotheses can be critically appraised.
Exemplarily for alumina based coating systems and self healing MAX phases it is shown, that the combination of modern electronic structure calculations with the highly efficient combinatorial thin film composition-spread method constitutes an effective tool for knowledge based design of energy-related materials.
Jose L. Endrino, Abengoa Research S. L.
Andre Anders, Lawrence Berkeley National Laboratory
Mohan Sankaran, Case Western Reserve University
Gintautas Abrasonis, Helmholtz Zentrum Dresden-Rossendorf
Symposium Support Abengoa
UU5: Plasma Applications: Photovoltaics and TCOs
Friday AM, April 05, 2013
Moscone West, Level 2, Room 2007
9:00 AM - UU5.01
Low Cost Purification of Multicrystalline Silicon by Nanocavities Created by Plasma Immersion Ion Implantation (PIII)
El Amin Kouadri Boudjelthia 1
1CEMHTI-CNRS Orlamp;#233;ans FranceShow Abstract
To reduce the cost of silicon-based solar grade wafers, it is mandatory to set up a process able to both reduce the total amount of impurities which are detrimental to photovoltaic efficiency and to passivate the extended defects such as dislocations and grain boundaries always present in such materials. In this context the use of a low-cost technique is important for the purification of multicrystalline silicon.
The plasma Immersion Ion Implantation (PIII) is an important candidate for creating nanocavities and the gettering of impurities in industrial scale. But this multi-energy implantation provides a different implant distribution profile compared to the classical Gaussian profile characteristic of mono-energetic implantation and its impact on gettering should be assessed for the purification of multicrystalline silicon.
In this work we have studied the possibility of creating nanocavities and the gettering of impurities in these new conditions. We used 2cm ×2 cm multicrystalline silicon samples with a grain size of 2 to 5 mm, and implanted them with hydrogen by PIII at 20kV with a dose of 5×1016cm-2 We then studied the evolution of cavities according to the conditions by changing the annealing temperature from 800°C to 1000°C at different annealing time. The wafers were investigated by Transmission electron microscopy and positron annihilation in order to see the formation of cavities. The gettering of impurities is studied by time of flight secondary ion mass spectrometry in depth and photoluminescence. Results show that, cavities induced by PIII are able to getter various impurities including Fe, Cu, Cr,..
9:15 AM - UU5.02
Microplasma-based Synthesis of Vertically-aligned Metal Oxide Nanostructures
Travis Koh 1 Evan O'Hara 1 Michael Gordon 1
1UC Santa Barbara Santa Barbara USAShow Abstract
One-dimensional metal oxide and semiconductor nanostructures (i.e., nanowires, NWs) have the potential to play a pivotal role in many future technologies related to energy conversion, catalysis, chemical sensing, and microelectronics. In many of these applications, aligned nanowires on technologically relevant substrates (e.g., Si, transparent conducting oxides (TCO&’s), etc) are necessary. This talk will detail the use of high-pressure (> 10 torr), supersonic flow-stabilized, DC hollow cathode discharges (microplasmas, MPs) to directly grow dense films of aligned metal oxide nanowires, spirals, blades, and trees of CuO, NiO, PdO, Fe2O3, and SnO2 on a variety of substrates (Si, ITO) . We use the microplasma jet as a directed source of active metal species (e.g., atoms, metastables, etc.) produced by the dissociation of volatile organometallic metal precursors for the subsequent growth of nanostructured oxide films under oxidizing, high-pressure conditions. By adjusting the metal precursor flux, deposition time/temperature, substrate scanning speed, and jet-substrate distance, a range of anisotropic nanostructures were realized. Growth of CuO needles and nanotrees will be discussed to demonstrate how vertically-aligned structures could be formed; preliminary data suggest that spiral growth and twinning are responsible . Furthermore, film growth in different “shock” regions of the supersonic plasma will be discussed to understand how film morphology is affected by the complex fluid flow and shock patterns set up by the impinging jet. Overall, microplasma-based deposition is shown to be a viable route to realize a variety of nanostructured metal oxide coatings for applications in gas sensing and solar cell electrodes.
 Koh, O&’Hara, Gordon, Nanotechnology 23, 425603 (2012).
 Koh, O&’Hara, Gordon, J. Crystal Growth (2012) DOI: http://dx.doi.org/10.1016/j.jcrysgro.2012.10.005.
9:30 AM - *UU5.03
Plasma Synthesis of Photovoltaic Materials
Eray Aydil 1 Chris Leighton 1 Uwe Kortshagen 2 Steve Campbell 3 Andrew Baruth 4 Michael Manno 1 Xin Zhang 1 Banu Selin Tosun 1 Melissa Johnson 1
1University of Minnesota Minneapolis USA2University of Minnesota Minneapolis USA3University of Minnesota Minneapolis USA4Creighton University Omaha USAShow Abstract
Plasmas enable the synthesis of a wide range of thin films used in solar cells. These thin films range from the light-absorbing layers to transparent conducting oxide electrodes. Classical examples include (i) plasma enhanced chemical vapor deposition of amorphous and microcrystalline silicon absorbers for thin film silicon solar cells, (ii) plasma deposition of antireflection and passivation coatings, and (iii) reactive sputtering of transparent conducting oxides. Plasmas also enable the gas phase synthesis of group IV nanocrystals, which find applications in novel quantum dot solar cells and in films used for downconverting solar radiation. This talk will summarize some of the recent applications of plasmas in synthesizing materials used in solar cells. Specifically, the topics will include (i) sputter deposition of tin dioxide coatings for improving damp heat stability of copper indium gallium diselenide solar cells, (ii) reactive sputtering of iron disulfide, a potential solar absorber made of nontoxic, low cost, and abundant elements and (iii) plasma synthesis of nanocrystals.
10:00 AM - UU5.04
Self-assembled SiGe Core-shell Nanowires for Band Gap Engineering
Isabelle Berbezier 1 Adrien Gouye 1 Cyril Herrier 1 Abdelmalek Benkouider 1 Luc Favre 1 Elise Ruiz-Gomes 1 Antoine Ronda 1
1CNRS - AMU Marseille CEDEX 20 FranceShow Abstract
In this study, we develop two original ways for the self-organization of gold catalysts by Liquid Metal Alloy Ion Source Focused Ion Beam (LMAIS-FIB) induced clustering. The two ways produce well ordered arrays of Au clusters that serve during the subsequent deposition step, as seeds for the nucleation of SiGe NWs. We show that the temperature range for the growth of NWs is extremely restricted in MBE growth conditions. Moreover, the effect of epitaxial strain on the growth direction of NWs is also demonstrated. We highlight the strain-driven evolution of the energy requested to create new facets at the trijunction between solid, liquid, and vapor. As a consequence, on Si (100) substrates, after a first vertical growth step, the Ge NWs rapidly kink and crawl along (110) directions of the substrate. Such a directional change was not observed during the growth of Si NWs.
The combination of FIB patterning and MBE NWs growth, enable to gain fundamental understanding of the physical laws that govern NWs properties and how these laws can be harnessed to dramatically improve the future devices characteristics.
10:15 AM - UU5.05
Liquid-chemistry RF & DC Microplasma as a Tool for Stabilization of Opto-electronic Properties of Silicon Nanocrystals
Somak Mitra 1 Vladimir Svrcek 2 Davide Mariotti 1
1University of Ulster, NIBEC Jordanstown United Kingdom2National Institute of Advanced Industrial Science and Technology (AIST) Tsukuba JapanShow Abstract
Silicon nanocrystals (SiNCs), having size less than 10 nm exhibit quantum confinement effects that manifest a set of unique characteristics which are fascinating and very promising for a wide range of applications including bio-imaging(1) and photovoltaic (PV)(2). Furthermore surface characteristics may offer even greater opportunities for tailoring SiNC properties. However, control of surface states still remains technologically challenging. The development and understanding of SiNCs surface funtionalization process is therefore highly important.
Our recent studies show that atmospheric-pressure radio-frequency (RF) and direct-current (DC) microplasma give an opportunity to tune the surface of SiNCs directly in liquid media.(3,4,5) Specifically, we will demonstrate stabilization of PL properties of SiNCs mainly inside aqueous solution. Both DC and RF microplasma techniques will be discussed in details and compared. We find that RF microplasma in a jet configuration is more effective in providing SiNCs with stable surface characteristics as compared to DC microplasma which is directly coupled with the aqueous solution. The surface funtionalization of SiNCs due to microplasma processing involves 3-dimensional engineering, which will be discussed in details. The PL signal is enhanced 3-4 folds after RF plasma processing with stability for up to 20 days. We have studied the chemistry induced by the interaction of the plasma with the SiNCs/water colloid and verified that microplasma processing produces hydrogen peroxide (H2O2) with direct impact on the surface funtionalization of SiNCs.(6) We therefore propose a reaction model supported also by temperature-dependent PL results obtained before and after DC/RF microplasma processing.
We finally present initial results on microplasma-induced liquid chemistry utilizing water/polymer/SiNCs colloids (e.g. with PEDOT:PSS). The resulting polymer-SiNCs nanocomposite shows improvements in the opto-electronic and transport properties within PV device structures.
1) Bruchez, M., Jr.; Moronne, M.; Gin, P.; Weiss, S.; Alivisatos, A. P.Science 1998, (281), 2013.
2) Scaron;vr#269;ek, V.; Yamanari, T.; Mariotti, D.; Matsubara, K.; Kondo, M. Appl. Phys. Lett. 2012, 100 (22), 223904.
3) Mariotti, D.; Sankaran, R. M. J. Phys. D: Appl. Phys. 2011, 44, 174023.
4) Scaron;vr#269;ek, V.; Mariotti, D.; Kondo, M. Appl. Phys. Lett. 2010, 97 (16), 161502.
5) McKenna, J, Patel, J, Mitra, S, Soin, N, Svrcek, V, Maguire, PD and Mariotti, D. The European Physical Journal - Applied Physics, 2011, 56 (02). p. 24020.
6) Mariotti, D.; Patel, J.; Scaron;vr#269;ek, V.; Maguire, P. Plasma Processes Polym. (DOI: 10.1002/ppap.201200007)
11:00 AM - UU5.06
Strong Microstructural Evolutions in ZnO Thin Films Grown by Reactive Magnetron Sputtering at the Inset of the Compound Sputtering Regime
William Chamorro 1 2 David Horwat 1 2 Philippe Pigeat 1 2 Patrice Miska 1 2 Pascal Boulet 1 2 Sylvie Migot 1 2 Flavio Soldera 3 Frank Mucklich 3
1Universitamp;#233; de Lorraine Nancy France2CNRS Nancy France3Saarland University Saarbruecken GermanyShow Abstract
ZnO is a promising material for use in optoelectronics devices because of its excellent optical properties that depend on its crystal quality and microstructure. The characteristics of ZnO have been extensively reviewed1, 2 and it was stated the possibility to change its properties according to the crystal quality and the presence of defects (intrinsic or extrinsic). Several authors report the obtention of ZnO thin films with a well-textured growth by techniques such as Metalorganic Vapor Phase Epitaxy (MOVPE), Molecular Beam Epitaxy (MBE) or pulse laser deposition (PLD) but these techniques need the use of ultra-high vacuum, high temperatures, long deposition times.
In this work we describe the synthesis of ZnO thin films on fused silica and sapphire substrates by DC reactive magnetron sputtering at room temperature. We found that the poisoning of the Zn target leads to an oxygen ion O- bombardment (with high kinetic energy) into the substrate. This effect depends directly on the oxygen flow rate and it improves the crystal quality of the film. The ZnO films grow with a hexagonal structure and are exclusively C-axis oriented with a signal that peaks at 34.2° corresponding to the (0002) planes of the wurtzite structure of ZnO according to theta;/2theta; and phi; angle X-ray diffraction (XRD) measurements. The analysis of the film composition (EDX with enhancement of the low energy signal) evidences an increase in the oxygen content in the ZnO films as the oxygen flow rate increases, which can be interpreted by the placement of excess oxygen in interstitial sites. The increasing amount of interstitial oxygen with the oxygen partial pressure is further evidenced by increasing intensity of the yellow band with the oxygen partial pressure in photoluminescence measurements. This implantation leads to an elongation of the c-axis parameter caused by in-plane compressive stresses. TEM micrographs and diffraction patterns show a strong transition in the growth mode between low and high oxygen pressure.
1. Ü. Özgür, Y. I. Alivov, C. Liu, A. Teke, M. A. Reshchikov, S. Dogan, V. Avrutin, S.J. Cho, and H. Morkoccedil;, J. Appl. Phys. 98, 041301 (2005)
2. A. Janotti and C. G. Van de Walle, Rep. Prog. Phys. 72, 126501 (2009)
11:15 AM - UU5.07
Low-electrical Resistivity Polycrystalline TiO2-based Transparent Conductors by Millisecond Flash Lamp Annealing of Magnetron Sputtered Films
Marcel Neubert 1 Mykola Vinnichenko 1 Thoralf Gebel 2 Steffen Cornelius 1 Harald Liepack 2
1Helmholtz-Zentrum Dresden-Rossendorf Dresden Germany2DTF Technology Dresden GermanyShow Abstract
Transparent conductive oxides (TCO), mainly In2O3:Sn (ITO), ZnO:Al (AZO) and SnO2:F (FTO) are widely used as transparent electrodes in flat panel displays, thin film solar cells and solid state lighting. In contrast to these TCOs, TiO2 -based films offer unique combination of low cost, high refractive index, stability against humidity, the high chemical stability and the non-toxicity. The Nb or Ta doped TiO2 films epitaxially grown on crystalline substrates already show electrical and optical properties which are comparable to those of conventional TCOs. However, it is still a challenge to achieve low electrical resistivity polycrystalline TiO2 - based films as required for most of applications. Furthermore, it is not possible to get low resistivity in polycrystalline films by direct growth at elevated substrate temperatures. Only a two-step approach, i.e. the deposition of amorphous films followed by annealing for minutes up to hours in vacuum or hydrogen delivers films with resistivity values in the range of 1E-3 Omega;cm. Both, the direct growth on crystalline substrates and the post deposition annealing of the amorphous films require substrate temperatures of about 400°C to ensure desired resistivity, which drastically limits applications. Furthermore, the high demand for energy for an annealing time of several minutes or even hour is almost unacceptable for a cost-efficient and environmental friendly replacement of conventional by TiO2 - based TCOs, especially for large area applications. In order to address this problem, we studied the films formed on glass substrates without heating by direct current magnetron sputtering (DC MS) of reduced TiO2:Ta ceramic targets followed by flash lamp annealing (FLA) in the millisecond range to crystallize as-deposited amorphous films. The Ti/O ratio of the as-deposited films was varied using a DC MS process in conjunction with a plasma feedback system to achieve an oxygen fine-tuning. Using FLA, the heat treatment is confined to the film and the substrate is only partly heated (several µm at the surface) which drastically lowers the energy consumption and allows the use of temperature sensitive substrates. In addition, the short annealing enables the film processing at atmospheric pressure in argon or even in air. The emerging electrical, optical and structural properties are strongly affected by the Ti/O ratio in the as-deposited films adjusted by the plasma feeback system Our approach delivered films with an electrical resistivity in the range of 1E-3 Omega;cm, optical transmittance above 80% for 400nm thick films and electrical activation of Ta dopants up to 60%. The reference films obtained combining deposition onto unheated substrate and subsequent conventional annealing in vacuum at 425°C for 1 hour show almost the same electrical and optical properties.
11:30 AM - *UU5.08
Nanochemistry in Thin Films
David Horwat 1 2 Jean-Francois Pierson 1 2
1Institut Jean Lamour Nancy France2CNRS Nancy FranceShow Abstract
Microstructural and chemical analyses are routine characterizations in the field of materials science. Information at the molecular or atomic scales (coordination, oxidation states) is particularly relevant to understand the physical and chemical properties of materials. The far out of thermodynamic equilibrium conditions associated to the condensation process of physical vapour (PVD) deposition methods can lead to very specific local chemical and microstructural states in thin films. This is a direct way to modify the properties of the synthesized thin films. In this communication we treat the cases of oxide and oxide-based thin films relevant for the fields of transparent electronics, plasmonics and catalysis. We use X-ray absorption near edge structure (XANES) in combination to transmission electron microscopy (TEM), X-ray diffraction (XRD), optical and electrical characterizations to investigate the properties/microstructure of magnetron sputtered thin films in relation to the local chemical state of their constitutive elements.
We consider the problematic of dopant activation/inactivation in transparent conductive oxides (TCO). Following the approach described above, the activation/inactivation of dopants in wide bandgap semiconducting ZnO thin films can be revealed. The electrical properties are strongly affected by this effect of which the dependency on the synthesis conditions is discussed.
The local segregation of metal in metal/oxide nanocomposite films is also investigated with a special attention paid to the oxidation state of the metal atoms in relation to the size of the nanoparticles. The size is controlled by the synthesis parameters. The influence of the local state on the physical properties is demonstrated.
12:00 PM - UU5.09
Characterization of ZnO Quantum Dots Deposited on Ion Beam Textured Si Substrates
Liang-Chiun Chao 1 Syuan-Miao Lai 1
1National Taiwan University of Science and Technology Taipei TaiwanShow Abstract
ZnO is one of the materials that exhibit the richest variety of nanostructures. With a band gap of 3.37 eV and an exciton binding energy of 60 meV, ZnO is a promising candidate for the fabrication of low dimensional optoelectronic devices. ZnO quantum dots may be fabricated on profiled substrates, on cleavage facets, or by condensation in glassy matrices. In the present study, we demonstrate the successful deposition of ZnO QDs on ion beam textured Si substrates by reactive ion beam sputter deposition. Nano-scale ripples with quasi wavelength at 500 ~ 700 nm on Si (100) substrates were prepared by argon ion beam sputtering at 6, 8, and 10 keV, all with an ion fluence of 5×1017 ions/cm2. The spatial wavelength of the nano-scale ripple increases as the ion beam energy increases regardless of ion beam incident angles, indicating that ion beam induced diffusion is the dominant diffusion mechanism. AFM analysis shows that ZnO QDs exhibit an ellipsoidal shape that exciton experience strong confinement along the vertical direction while weak or no confinement along the horizontal direction. Photoluminescence study indicates a blue shift of 80 meV as the QD height drops from 4 to 2 nm which is due to the size dependent quantum confinement effect. Comparing with ZnO QDs deposited on pristine Si substrates, the ion-beam textured substrate provides a wider processing window, improved dot size, and increased QD density.
12:15 PM - *UU5.10
Comparative Study of HiPIMS and Filtered Arc Deposited Aluminum-doped Zinc Oxide Thin Films
Sunnie H.N Lim 1 3 Matthew R Field 2 Jeff Brown 4 Dougal G McCulloch 2 Andre Anders 3
1Seagate Technology Fremont USA2RMIT University Melbourne Australia3Lawrence Berkeley National Laboratory Berkeley USA4Acree Technologies Concord USAShow Abstract
Thin films of aluminum-doped zinc oxide (AZO) deposited by filtered cathodic arcs (FCA) exhibit highly ordered crystalline structure, low resistivity, and high optical transparency. However, in practice, it can be difficult to scale the FCA process for large area coating which is necessary for some industries such as photovoltaics and dynamic “smart” window coatings. Sputtering is still the preferred plasma-based deposition technique used in industry due to the scalability to large area and the relatively low cost involved in the process. Over the last years there has been increasing interest in high power impulse magnetron sputtering (HiPIMS). HiPIMS is a sputtering process which can deliver high power pulses to the target, thereby producing a population of relatively energetic ions assisting in the growth of the film. In this presentation, we compare the structure and properties of AZO films deposited by FCA and HiPIMS. We also describe an ion-filtering system designed to reduce the negative ion bombardment which is known to be detrimental to the properties and performance of AZO films. Filtered HiPIMS deposition resulted in films with enhanced crystallinity and improved electrical properties, compared to conventionally sputter-deposited films, whilst retaining the superior transmittance values.
12:45 PM - UU5.11
Atmospheric Plasma Deposition of Transparent Conducting ZnO Thin Films on Plastics in Ambient Air
Makoto Watanabe 1 2 Linying Cui 1 Reinhold H. Dauskardt 1
1Stanford University Stanford USA2National Institute for Materials Science Tsukuba JapanShow Abstract
Zinc oxide (ZnO) is an attractive alternative candidate for transparent conducting oxide films particularly if it can be deposited under atmospheric conditions at low temperature on polymer substrates. In the present study, we demonstrates a new strategy to deposit ZnO thin films on poly (methyl methacrylate) (PMMA), polycarbonate (PC), and polyethylene terephthalate (PET) substrates using atmospheric plasma deposition in ambient air at room temperature. Atmospheric plasma is a low cost, solvent-free, and highly versatile deposition process. The film structure, optical and electrical properties as well as adhesion energy to the substrates were investigated for various deposition conditions.
Films with thicknesses of up to 500 nm were successfully deposited on the three polymer substrates. XPS analysis of the films exhibited only peaks associated with Zn and O with an atomic concentration ratio of ~ 1:1. The film optical and electrical properties varied with deposition conditions. Remarkably high transmittance values above 95% were achieved with a wide range of semi-conducting and conducting electrical properties. The film surface exhibited a dome-shaped topography and the domes became larger for higher plasma power. There was no significant difference in the adhesion energy of the ZnO films on the three plastic substrates although the film adhesion was found to depend on the deposition conditions. Our research demonstrates that highly transparent ZnO films can be deposited on plastics in ambient air at room temperature. The research forms the basis for low temperature, large area, and low cost processing of transparent conducting films on plastics.
1:00 PM - UU5.12
The Effect of Reactive Ion Etching Parameters on the Electrical Properties and the Removal of Residual Organics in Spin-coated Colloidal ITO Thin Films
Salil M. Joshi 1 Rosario A. Gerhardt 1
1Georgia Institute of Technology Atlanta USAShow Abstract
Spheroidal colloidal indium tin oxide (ITO) nanoparticles, about 6 nm in diameter, were synthesized in-house and films were deposited onto glass substrates by spin coating. The as-deposited films had high electrical resistivity due to the presence of organic capping ligands around each nanoparticle. Although high temperature annealing has been shown to reduce film resistivity by over eight orders of magnitude, lower temperature processing is desirable for applications like flexible electronics. Preliminary studies showed that pre-treatment with alternating cycles of reactive ion etching (RIE) using oxygen and argon plasma could reduce the residual organic content in the films. Since this procedure could help to significantly reduce colloidal ITO film resistivity with no annealing or relatively low temperature annealing, a more comprehensive study was conducted. Colloidal ITO films were subjected to a series of alternating RIE treatments in oxygen (5 minutes duration per cycle) and in argon (1 minute duration per cycle), and parameters such as gas pressure, RIE power and number of cycles were varied. These RIE treatments were found to reduce the film resistivity significantly without the need to conduct high temperature annealing. Among the parameters studied, gas pressure during RIE was found to be the most important parameter in determining the effectiveness of the treatment. The residual carbon content was characterized by XPS depth profiles and Raman spectroscopy while the resistivity was monitored by impedance spectroscopy.
1:15 PM - UU5.13
Transparent Conducting Oxide Thin Films and Nanostructures for Energy-related Applications
Cesar Clavero 1 Jonathan Kolbeck 1 Jonathan Slack 1 Andre Anders 1
1Lawrence Berkeley National Laboratory Berkeley USAShow Abstract
Transparent conducting oxide (TCO) thin films combine efficient light transmission and electrical conduction, two extremely important properties for energy-related applications such as photovoltaic cells, catalytic devices and electrochromic windows. The fabrication cost of indium tin oxide (ITO), the most commonly used TCO material, has increased considerably in the last few years owing to the high demand of indium. This fact has brought a great deal of attention to other highly doped conducting oxides such as SnO2:F (FTO), ZnO:Ga (GZO) or ZnO:Al (AZO). Nevertheless, the fabrication of such TCO thin films using plasma based methods with high deposition rates while keeping high electron mobility values is challenging . Commonly used techniques such as magnetron sputtering have been shown to yield poor mobility values, far from those found in ITO. New developments in filtered cathodic arc deposition sources will be discussed as a possible alternative to create high quality AZO thin films.
In addition, while TCOs are mostly used as continuous thin film electrodes, the use of nanostructured TCO films to control the absorption of light for applications such as electrochromic windows or photovoltaic cells has been recently proposed. TCO nanoparticles have free electrons that upon illumination oscillate following the electromagnetic field of light. The confined electronic oscillations enter resonance for frequencies typically in the infrared range for these kinds of materials, giving rise to localized surface plasmon resonance (LSPR). This phenomenon is accompanied by a strong optical absorption highly dependent on size, concentration and carrier density of the TCO nanoparticles, that can be further controlled by applying an external bias voltage . Advanced plasma based cluster fabrication techniques such as terminated cluster growth are well suited for the fabrication of such nanostructured TCO films since they allow a very high control of cluster size and concentration. The use of terminated cluster growth for the fabrication of electrochromic TCO thin films and the obtained optical properties will be discussed.
1. R. J. Mendelsberg, S. H. N. Lim, Y. K. Zhu, J. Wallig, D. J. Milliron and A. Anders, Journal of Physics D: Applied Physics 44 (23), 232003 (2011).
2. G. Garcia, R. Buonsanti, E. L. Runnerstrom, R. J. Mendelsberg, A. Llordes, A. Anders, T. J. Richardson and D. J. Milliron, Nano Letters 11 (10), 4415-4420 (2011).