This talk will present our work on carbon nanotubes, graphene nanoribbons and graphene-metal oxide hybrid materials. Biological applications of carbon nanotubes will be discussed including a new fluorescence imaging method in the so called NIR-II region in the spectral window of 1000-1400nm. NIR fluorescence enhancement of carbon nanotubes and organic fluorophores will be presented on a novel plasmonic substrate. I will then talk about graphene nanoribbons, including several methods recently developed in our lab to form high quality graphene nanoribbons with narrow widths and smooth edges. Lastly, I will talk about our recent work on making nanoparticles and nanocrystals on graphene sheets for energy storage and photocatalytic applications.

For medical applications such as neuroprostheses and for fundamental research on neuronal communication, it is of utmost importance to develop a new generation of electronic devices which can effectively detect the electrical activity of nerve cells. Due to its maturity, most of the work with field effect transistors (FETs) has been done based on Si. However, the high electronic noise and relatively low stability associated to Si technology have motivated the search for more suitable materials. In this respect, the outstanding electronic and electrochemical performance of graphene holds great promise for bioelectronic applications. For instance, we have reported on arrays of CVD-grown graphene solution-gated FETs (SGFETs) for cell interfacing [1], demonstrating their ability to transduce with high resolution the electrical activity of individual electrogenic cells [2].
In this contribution, we will present a detailed discussion on the sensitivity of graphene SGFETs for in-electrolyte operation, together with a study of the electrolyte composition on the device performance. The sensitivity of SGFETs is dominated by two characteristic parameters: transconductance and electronic noise. The transconductance specifies how an initial gate voltage signal is converted to a current by the transistor. For graphene SGFETs, the transconductance is proportional to the interfacial capacitance at the graphene/electrolyte interface as well as the charge carrier mobility. We will present Hall-effect experiments performed in electrolyte demonstrating that both interfacial capacitance and carrier mobility in graphene are superior to other competing materials, including Si. A second relevant parameter to assess the performance of biosensors is the electronic noise of the device, as it defines the minimum signal that can be detected. We have investigated the electronic noise of graphene SGFETs and compared it to that of devices based on Si. It will be shown that, similarly to other semiconductors, 1/f noise is the dominant noise source in graphene devices. The origin of the 1/f noise will be discussed in this presentation, comparing the results of single-layer graphene and bilayer graphene devices. Finally, we will briefly report on the pH and ion sensitivity of graphene devices, and the influence of the chosen substrate for the device fabrication, as well as of surface contamination from the fabrication technology.
This work highlights the potential of graphene to outperform state-of-the-art Si-based devices for biosensor and bioelectronic applications [3].
[1] Dankerl et al., Adv. Funct. Mater., 20 (2010) 3117
[2] Hess et al., Adv. Mater., 23 (2011) 5045
[3] C. Schmidt, Nature 483 (2012) S37

Nanoelectronics-based detection schemes offer promising sensitive and label-free alternatives to bioanalysis. The large-scale synthesis, high carrier mobility and ambipolar transport make graphene potentially useful in the electrical detection of biomolecular targets. Here we report on the design, fabrication, and operation of novel oxide-on-graphene, bio-ready field effect sensors using graphene sheets synthesized by chemical vapor deposition. Our design uses thin layers of HfO2 and SiO2 films to isolate the graphene channel and electrodes from electrolyte and uses the top SiO2 surface for detection and further chemical functionalization. This design preserves the excellent transport characteristics of the graphene transducer while taking advantage of the well-established surface chemistry of SiO2 in facilitating specific biomolecular binding. The graphene transducer channel operates in solution with high stability and high carrier mobility of approximately 5000 cm2/Vs. By applying the solution gate voltage in pulse, we eliminate hysteresis in the transfer curve of the graphene channel, which is critical to achieving a high detection resolution of the sensor. We demonstrate the silanization of the SiO2 surface with aminopropyl-trimethoxysilane (APTMS), which can be further linked to biomolecular probes and targets. The pH sensitivity of the bare and APTMS-functionalized SiO2 is measured to be 46mV/pH and 43mV/pH respectively, in good agreement with literature results. With suitable linking chemistry, these graphene sensors can potentially be useful in the detection of biological events such as DNA hybridization, thus opening a new avenue for biosensing using nanoscale electronics.

Graphene, a one-atom thick sheet of sp2 carbon, offers many intriguing possibilities in the field of molecular sensing. Its unique combination of large areas with nanometer thickness and high electrical conductivity could enable small scale device sensitivity with large scale production methods. A major benefit of using graphene is the large toolbox of well-established chemistries for incorporating chemical functionalities or specific recognition elements at the device surface. Here, we will discuss our efforts to develop graphene-based biological field-effect transistors (BioFETs), which offer sensitivity comparable to sensors made with other nanoscale materials (carbon nanotubes, nanowires), but with greatly simplified production methods common in the semiconductor industry. Devices utilizing both graphene and graphene oxide will be covered, and surface spectroscopic studies of the material modification will be discussed. Successful results for the detection of specific DNA hybridization using graphene BioFETs will also be presented. We will further discuss our efforts to use graphene as a biofunctionalized interface for a number of materials, from polymers to dielectrics to semiconductors, of interest to the biosensing community. Graphene&’s ultrathin nature allows its inclusion in more traditional sensing platforms as a non-intrusive functionalization layer, discreetly lending its chemical flexibility to other, more inert materials without significantly impacting the sensing device.

Graphene has been identified as a promising material for different scientific disciplines due to its exceptional physiochemical, electronic and structural properties. The extremely high carrier mobility and capacity arouses enormous interest in the field of electronic sensor applications as well. However, it is a challenge to obtain constantly small size of graphene layers by mechanical exfoliation. In the present study, grapheme oxide (GO) was used as the transducer material for two different biosensor platforms:
In a first approach, interdigitated gold microelectrodes (IDEs) were fabricated with standard lithographical methods and used as a platform for label-free detection of specific DNA hybridization and denaturation events. GO flakes were dielectrophoretically immobilized onto the IDEs and reduced to conductive graphene oxide (r-GO) using a low-temperature, green fabrication route with L-ascorbic acid (Laa). These sensors were used for label-free, impedimetric detection of DNA hybridization and denaturation. This approach is very versatile and could be applied to different substrates such as polymeric materials, since this green fabrication route doesn&’t need harsh chemicals or elevated temperatures.
In a second approach, the ‘Micromolding in Capillaries&’ (MIMIC) technique was used to pattern GO lines with lengths up to 10 mm and width down to 10 µm on glass and Si/SiO2 substrates. The GO patterns were then reduced to r-GO using the same approach mentioned above. The lines were connected by evaporated gold contacts and encapsulated to be used with living cells for in vitro monitoring of cellular adhesion of tumor cells and for detection of extracellular field potential (exFP) of cardiac cells. We found that cells preferably aligned to the r-GO lines in contrast to the bare glass or SiO2 surfaces. The patterns can be used for the definition and stabilization of networks of neuronal cells on in vitro sensor platforms. Since in a typical application in this field, the transducer material of microelectrode arrays (MEAs) is made of metal and subsequently functionalized with cell growth supporting proteins such as laminin or fibronectin, our r-GO approach has the advantage that the transducer material and the cell adhesion promoting material is the same.
In conclusion it can be said that the r-GO material, even though it has distinctly reduced electrical performance compared the single sheets of graphene, has promising properties, which make it a favorable transducer material in biosensor applications.

Graphene&’s planar, conformal, and hydrophobic nature make it useful as an atomically thin coating which inhibits gaseous diffusion [1] and entraps liquids [2,3]. Most studies to date have only explored encapsulation of simple molecules with graphene, overlooking interactions between the hydrophobic sheet and other complex nanostructures like DNA and viruses.
We develop an atomically clean graphene transfer process using a poly(bisphenol A carbonate) (PC) scaffold for graphene grown by chemical vapor deposition (CVD). Large-area CVD graphene growth on Cu [4,5] allows the fabrication of large-area, conductive, encapsulating platforms between graphene and nanostructures of choice. Typically, graphene is transferred off the Cu growth surface in H2O [2] with a PMMA scaffold, and this scaffold is partially removed by a high-temperature anneal [6]. However, such high-temperature processing is incompatible with biomolecular nanostructures. PC transfers can be removed by dissolution at room-temperature, circumventing the annealing requirement. We confirm that the clean, PC-transferred graphene films have lowered residual doping by device transport and Raman spectroscopy. RMS roughness values, determined by atomic force microscopy (AFM), are 2-4 times lower (~0.6 nm) for PC- vs. PMMA-transferred films under the same growth and transfer conditions. Scanning tunneling microscopy (STM) of the PC-transferred graphene films reveals atomic resolution, despite degas temperatures lower than 100 °C.
Using the PC transfer process, we make graphene/biomolecule/graphene nanosandwiches on SiO2/Si and mica. We deposit a known rod-shaped biomolecule, the tobacco mosaic virus (TMV), on these substrates and examine the virions&’ heights before and after graphene-based encapsulation. With AFM, we find that the TMV heights, relative to the top-most graphene layer, decrease from 12.4 nm to 3.5 nm after encapsulation. These deformations occur despite the rigid TMV capsids. Here, the graphene conforms to the virions and exhibits a strong hydrostatic pressure on them, flattening and possibly dehydrating the capsid shell. Through AFM topographs, we determine that nanosandwiched TMV denatures at ~50 °C, much higher than the known value at ~42 °C [7]. The graphene/biomolecule/graphene system will elucidate fundamental fluid dynamics in this hydrophobic bilayer cell. Additionally, the conductive and electronically transparent character of graphene can allow biomolecular interrogation at the atomic-level by STM and by transmission electron microscopy.
[1] J. S. Bunch et al., Nano Lett. 8, 2458 (2008); [2] K. T. He et al., Nano Lett. 12, 2665 (2012); [3] J. M. Yuk et al., Science 336, 61 (2012); [4] X. Li et al., Science 324, 1312 (2009); [5] J. D. Wood et al., Nano Lett. 11, 4547 (2011); [6] Y.-C. Lin et al., ACS Nano 5, 2362 (2011); [7] M. Kelve et al., J. Biomol. Struct. Dyn. 5, 105 (1987).

Carbon nanotubes (CNT) are a promising biomimetic material, in part because smooth, narrow and hydrophobic inner pores of CNT are remarkably similar to the natural biological pores. Incorporation of nanotube channels into the biologically-relevant environments and measurements of ion transport in these assemblies would not only enhance out understanding of transport in these materials systems, but also open up ways to develop novel bioengineering applications. We will describe incorporation of carbon nanotube channels into a lipid membrane and measurement of osmotically-induced ion transport through these model nanopores using dynamic light scattering (DLS) experiments. We also discuss factors that govern ion rejection in these structures and compare the results with modeling results and measurements in macroscopic systems.

Nanometer-scale structures represent a novel and intriguing field, where scientists and engineers manipulate materials at the atomic and molecular levels to produce innovative materials for composites, electronic, sensing, and biomedical applications. Carbon nanomaterials, such as carbon nanotubes and graphene, constitute a relatively new class of materials exhibiting exceptional mechanical and electronic properties, and are also promising candidates for gas storage and drug delivery.
However, processing carbon nanotubes is severely limited by a number of inherent problems: purification from a variety of byproducts, difficult manipulation and low solubility in organic solvents and in water are only some of these problems. For these reasons, several strategies have been devised to make nanotubes “easier” materials. In particular, organic modification produces functionalized carbon nanotubes, which are much more processible and offer the possibility of introducing organic fragments useful for practical applications.
During this talk, we will discuss the use of functionalized carbon nanotubes and graphene as active surfaces for a number of practical applications. Glassy surfaces, covered with carbon nanotubes are ideal substrates for neuronal growth. Nanotubes are compatible with neurons, but especially they play a very interesting role in interneuron communication, opening possibilities towards applications in spinal cord repair therapy.
In addition, in combination with catalysts of different nature, carbon nanotube modified surfaces can serve for many scopes. Experiments aiming at the splitting of water to give oxygen, and therefore, molecular hydrogen, ideal for clean energy generation, will be described. Also, multiwalled carbon nanotubes, embedded inside mesoporous layers of oxides (TiO2, ZrO2, or CeO2), which in turn contain dispersed metal nanoparticles (Pd or Pt), result in nanocomposites with remarkable performance in catalytic reactions.
References
(1) Fabbro, A.; Bosi, S.; Ballerini, L.; Prato, M. ACS Chem. Neurosci. 2012, 3, 611-618.
(2) Toma, F. M.; Paolucci, F.; Prato, M.; Bonchio, M. et al. Nature Chemistry 2010, 2, 826-831.
(3) Cargnello, M.; Liz-Marzan, L. M.; Gorte, R. J.; Prato, M.; Fornasiero, P. et al. J. Am. Chem. Soc. 2012, 134, 11760-11766.

Functional electrical stimulation can be used to restore function in patients with a damaged nervous system. Electrical impulses delivered to the tissue can generate artificial action potentials (APs) that behave like APs naturally generated by a healthy nervous system. These APs will have the same effects and will propagate through neighboring neurons to induce motor function. Electrode morphology can impact the charge injection for neural stimulation as shown in literature reports on the electrochemical properties of vertically aligned multi-walled carbon nanotubes (CNTs), graphenated CNTs, and nanoribbons. For example, the roughness of carbon nanotubes increases the surface area of the electrode and in turn, decreases the impedance and power consumption.
In the present work, patterned CNTs were grown with the goal of improving the charge injection in two ways. The pores created by the roughness of the CNT structure may be too small for the ions in the electrolyte to penetrate. The patterns should increase the total surface area accessible by the ions. In addition, the activating function for neural cells is proportional to the spatial derivative of the current density in the tissue. When an electric potential is applied across a structure, the current density is higher at the edges. The patterns should also increase the total perimeter contributed by the array of pillars. By varying the dimensions of the pillared CNT structures, the total surface area accessible by the ions and the number of edges can be increased in order to achieve a maximum charge injection while simultaneously decreasing the impedance. A model of the pillared CNT structures was created in COMSOL. The optimal dimensions for the pillars were then chosen from the parameters that resulted in the most non-uniform current density. The electrochemical properties of the best structures were then characterized in vitro. Cyclic voltammetry was used to detect the presence of reactions with the electrolyte. Electrochemical impedance spectroscopy was used to measure the electrode-electrolyte interfacial impedance. Finally, potential transient measurements were used to measure the charge injection capacity of the electrode. It was observed that the charge injection of the CNT electrodes was not dependent on the total volume of the structure but was greatly affected by the surface area and the total edge contribution from the pillars. As both of these parameters were increased, the charge injection increased. The pillared structures with optimized aspect ratios had the highest charge injection compared to normal blanket CNT, graphenated CNT, and nanoribbon electrodes.

CVD Diamond thin-films are attractive as a material for construction of active bio-electronic devices. This is due to properties of Nano-crystalline diamond such as biocompatibility, wide potential window and substantially reduced bio-fouling or inflammatory reactions.
Here we present a novel approach for fabrication of all-carbon diamond Micro-electrode Arrays (MEAs) in which Nano-crystalline diamond (NCD) thin film represents the insulating layer and Boron-doped Nano-crystalline diamond (B-NCD) features conductive layer of the electrode as a replacement for conductive metals, such as Platinum or Titanium Nitride, with B-NCD showing better electrochemical performances[1][2]. The resulting MEAs are optimized and characterized in terms of their performances and impedance, and employed in vitro for recording/stimulation of neuronal electrical activity. The measurements are carried out using cultured dissociated neurons and compared with standard commercial MEAs to benchmark metallic MEA with full diamond MEA in the application of active neuron-device interface. The signal to noise ratio is evaluated and compared to results obtained by Dankerl et al. [2], showing higher signal to noise ratio in comparison to conventional metal MEAs.
[1] M. Bonnauron et al., phys. stat. sol. (a) 205, No. 9, 2126-2129 (2008).
[2] M. Dankerl, et al., Appl. Phys. Lett. 100, No. 2, 023510 (2012).

The huge potential of graphene in photonics and optoelectronics is shown by several recent results, ranging from solar cells and light emitting devices, to touch screens, photodetectors and ultrafast lasers [1]. Saturable absorption is observed as a consequence of Pauli blocking [2,3]. Graphene-polymer composites prepared using wet chemistry [2,3,4] can be integrated in a fiber laser cavity, to generate ultrafast pulses [2]. Graphene&’s suitability for high-speed photodetection was demonstrated in optical communication links operating at 10Gbits-1 [5].
I will first focus on solution processed graphene [6], the ideal starting point to produce printable graphene-based inks [7]. I will show how to achieve size selected graphene dispersions [8] via a sedimentation-based separation in centrifugal field and how Density Gradient Ultracentrifugation [9,10] can be exploited to produce graphene flakes with controlled number of layers [11].
Then, I will give a thorough overview of the state of the art of graphene photonic and optoelectronic devices, outlining the major stumbling blocks and development opportunities. In particular I will focus on solar cells where graphene can fulfill the following functions: as the transparent conductor window [12], antireflective material [13], photoactive material [14], channel for charge transport [15], and catalyst [16].
References
1. F. Bonaccorso, et al. Nat. Photon. 4, 611 (2010)
2. Z. Sun, et al. ACS Nano 4, 803 (2010)
3. T. Hasan, et al. Adv. Mat. 21,3874 (2009)
4. T. Hasan, et al. Physica Status Solidi B, 247, 2953 (2010)
5. T. Mueller, et al. Nature Photon., 4, (2010), 297
6. Y. Hernandez, et al, Nature Nanotech. 3, 563 (2008).
7. F. Torrisi, et al, ACS Nano 4, 2992 (2012).
8. O. M. Maragograve;, et al. ACS Nano 4, 7515, (2010)
9. M.C. Arnold et al. Nature Nanotech.1, 60, (2006)
10. F. Bonaccorso, et al. J. Phys. Chem. C, 114, 17267, (2010).
11. A. A. Green, M. C. Hersam, Nano Lett. 9, 4031, (2009).
12. X. Wang, L. Zhi, K. Mullen, Nano Lett. 8, 323 (2007).
13. X. Li et al. Adv. Mater. 22, 2743 (2010).
14. V.Yong, J. M. Tour, Small, 6, 313 (2009).
15. N. Yang, et al. ACS Nano 4, 887 2010.
16. W. Hong, et al. Electrochem. Commun. 10, 1555 (2008).

Nanoparticulate diamond (ND) surfaces possess faceted architectures that mediate enhanced cancer treatment efficacy and safety [1,2]. In particular, ND surfaces can prevent early anthracycline elution, resulting in markedly decreased side effects in vivo, while gradually sustained elution and increased retention results in increased therapeutic activity. Furthermore, their surface electrostatic properties have mediated among the highest per-gadolinium magnetic resonance imaging (MRI) contrast efficiencies ever reported. NDs can also be functionalized with a broad spectrum of therapeutics such as small molecules, proteins, antibodies, and DNA/siRNA for applications in cancer treatment, cardiovascular medicine, wound healing, and beyond. NDs also possess uniform dimensions and material stability that are coupled with observed biocompatibility in vitro and in vivo. Functional groups are also conducive towards facile, application-dependent molecular conjugation onto the diamond surface for integrative targeting, imaging, and therapy. Towards the continued translational development of both systemic and localized diamond-based nanomedicine platforms, recent work pertaining to the in vivo validation of ND-based treatment of drug-resistant tumors, synthesis of multi-modal targeted ND complexes, as well as emerging strategies to locally administer therapeutic compounds using micro/nanomaterial devices will be discussed.
1. E. K. Chow, X.-Q. Zhang, M. Chen, R. Lam, E. Robinson, H. Huang, D. Schaffer, E. Osawa, A. Goga, and D. Ho, Nanodiamond therapeutic delivery agents mediate enhanced chemoresistant tumor treatment. Science Translational Medicine 3, 73ra21, 2011.
2. V. Mochalin, O. Shenderova, D. Ho, Y. Gogotsi, The Properties and Applications of
Nanodiamonds, Nature Nanotechnology, 7, 11-23, 2011.

The dye sensitized solar cell (DSC) is an attractive alternative to solid state photovoltaics [1,2]. The generic device is a photoelectrochemical DSC with sensitized nanocrystalline titanium dioxide photoanode, electrolyte solution with a redox mediator and the counterelectrode. The latter is typically a film of Pt nanoparticles on F-doped tin oxide (FTO) and the former is the triiodide/iodide couple in aprotic electrolyte medium. Graphene nanoplatelets (GNP) in the form of optically transparent films on FTO are useful counterelectrode material to replace Pt [3]. They exhibit good electrocatalytic activity towards I-based mediators particularly in ionic liquid medium. Recently, the triiodide/iodide couple was exchanged with Co(III/II)-based redox mediators [4,5]. The obvious motivation consisted in enhancing the voltage of DSC. GNP exhibit high electrocatalytic activity for Co(III/II) based mediators [6,7], sometimes even outperforming the activity of Pt [7]. The exchange current densities scaled linearly with the electrode optical absorbance, and they were by 1-2 orders of magnitude larger than those for the I-based systems. Dye-sensitized solar cells achieved energy conversion efficiencies between 8 to 10 % for both GNP and Pt-based cathodes. However, the cell with GNP cathode is superior to that with Pt cathode particularly in fill factors and in the efficiency at higher illumination intensities. Graphene oxide (GO) showed almost no activity as DSC cathode, resembling the properties of basal plane pyrolytic graphite. However, the activity of GO improved dramatically upon reduction with hydrazine and/or heat treatment. The reduced GO/GNP composite films are favored by excellent adhesion to FTO and by higher stability against aging.
References
[1] B. E. Hardin, H. J. Snaith, M. D. McGehee, Nature Photonics 6, 161 (2012).
[2] K.Kalyanasundaram, Dye Sensitized Solar Cells, EPFL Press & CRC Press, Lausanne, 2010.
[3] L. Kavan, J-H. Yum, M. Grätzel, ACS Nano 5, 165 (2011).
[4] A. Yella, H. W. Lee, H. N. Tsao et al., Science 334, 629 (2011).
[5] J-H. Yum, E. Baranoff, F. Kessler et al., Nature Comm. 3, 631 (2012).
[6] L. Kavan, J-H. Yum, M. K. Nazeeruddin et al., ACS Nano 5, 9171 (2011).
[7] L. Kavan, J-H. Yum, M. Grätzel, Nano Lett. 11, 5501 (2011).

Carbon nanotubes (CNTs) possess various unique properties such as a needle-like shape with nanometer-size diameter, high mechanical strength, chemical stability and high electrical conductivity, which are advantages as field electron emitters. Graphene is also a promising field emitter due to its low dimensionality (2-dimensional sheet), outstandingly high carrier mobility, mechanical strength and chemical inertness. We have studied field emission (FE) of electrons and dynamic behavior of CNT and graphene field emitters by field emission microscopy (FEM) and in-situ transmission electron microscopy (TEM).
1. FEM of CNT Emitters
FEM images from Multiwall carbon nanotubes (MWCNTs), which are highly graphitized like those produced by arc discharge, exhibit pentagons present on their caps when the surfaces of MWCNT caps are clean. Adsorption of residual gas molecules on the MWCNT surfaces enhances electron emission through the molecules, and the adsorbed molecules are observed as bright spots or sometime exhibit its molecular shape in FEM images. Effects of deposition of metals (Al, Au, Ti) on the CNT emitter were also studied. Improvement of emission stability and enhanced emission current were found for some conditions. For Al, FEM images of Al clusters with atomic resolution were observed.
2. In-situ TEM of CNT Emitters
A MWCNT was manipulated inside a TEM, and a single MWCNT emitter freestanding on a platinum (Pt) surface was fabricated by welding the MWCNT with a Pt nanoparticle. FE properties of the single MWCNT were in situ measured, and found to provide higher emission current by over an order of magnitude than a MWCNT emitter without the welding (i.e., simple van der Waals contact).
3. FEM and in-situ TEM of multilayered graphene emitters
Exfoliated multilayered graphene, which was attached on the tip of tungsten needle, was used as electron emitters. TEM revealed that edges of multilayered graphene that were open before FE measurement changed to closed edges after FE under high emission current, say over a few tens miro-ampere. Corresponding to this change of edge structure, FEM images evolved from a striped pattern for an open edge to a dim one for a closed edge. The structural change under the high current condition is presumably induced by Joule heating of the graphene tip.

Carbon nanotubes (CNTs) have been considered as a good field emission material due to their unique morphology and excellent properties. It is possible to classify CNT field emitters according to an emitter shape, one is a planar typed field emitter and the other is a point typed field emitter. There have been many studies on the planar typed field emitters made by CNTs. However, it was very difficult to find some reports on the point typed field emitters. For x-ray source or e-beam source applications, it is necessary to get a focused electron beam from the CNT emitters. Thus, the point typed CNT emitters are very useful candidates to get a focused electron beam. Especially, the point typed field emitters are required to exhibit large emission current and high emission stability with a small electron beam size. A few reports announced point emitters made by CNTs. Among them, some results still have suffered from reproducibility and low emission current and poor emission stability. Here, we demonstrate the CNT point emitters which introduce very high emission performance.

Flower-like clusters of ultra nanocrystalline diamond (UNCD) decorated carbon nanotubes (CNTs) were synthesized in a single step process via hot filament chemical vapor deposition. The UNCD decorated CNTs were characterized by Raman spectroscopy, scanning electron microcopy (SEM), transmission electron microscope (TEM).The fabricated material shows a hierarchical growth of flower-like clusters of vertically aligned carbon nanotubes with diameters in the range of 30-50 nm coated with UNCD having a grain size in the range of 3-5 nm. A mixture of diamond nanopowder and saturated hydrocarbon polymers forms a matrix which acts as a nucleation site for Ni catalyzed growth of flower-like clusters of CNTs. The UNCD decorated tubes show good field emission properties with a low turn-on field, large field enhancement factor, and an excellent current stability over a period of 400 hrs.

Direct energy conversion transforms heat into electricity by employing thermionic electron emission and transfer of this charge across a gap to the collector. A self generated thermionic voltage appears between emitter and collector that will establish a current in the circuit. The power output of the device is related to the thermionic electron emission current and its transport across the inter-electrode gap. Surface ionization effects at the emitter present a means to enhance the thermionic electron emission current and can increase the total power output. We have prepared a nitrogen doped diamond electron emitter and a phosphorus doped diamond collector as electrode pair for a thermionic energy converter. At an emitter temperature of 750 °C the device generated an open circuit voltage of 0.2 V. Power output of the converter was characterized in vacuum and in an atomic hydrogen ambient to utilize surface ionization effects of the gaseous species. In vacuum the reduced power output can be attributed to space charge and diamond resistivity effects. These were alleviated by applying a small bias to the converter which resulted in a significant increase in output power. Under the same bias and with the introduction of atomic hydrogen into the gap a seven fold increase in output power was measured. This was indicative of surface ionization of atomic hydrogen at the emitter surface and de-ionization at the phosphorus doped diamond collector. This is the first demonstration of energy conversion from a nitrogen doped diamond emitter and phosphorus doped diamond collector pair. Enhancement of output power by surface ionization of atomic hydrogen will be discussed in terms of electron affinity level of the atom and band structure of the doped diamond films.
This research was supported by the Office of Naval Research and the EU FP7 through the Marie Curie ITN "MATCON" (PITN-GA-2009-238201).

Diamondoids (nanometer-sized molecular diamonds) are a novel class of carbon nanomaterials that exhibit negative electron affinity (NEA) and strong electron-phonon scattering. Surface-bound diamondoid monolayers exhibit monochromatic photo-emission, a unique property that makes them ideal electron sources for electron-beam lithography and high-resolution electron microscopy. In addition, diamondoid monolayers can reduce turn-on voltages for electron field emission and can be used to seed chemical-vapor deposited (CVD) diamond thin films, enabling the growth of synthetic diamond with tailorable properties. However, these applications are limited by the stability of the chemical bonding of diamondoids on surfaces. Here we demonstrate the stable covalent attachment of phosphonic dichloride-functionalized diamondoids on oxide surfaces. Monolayers of medial-diamantane phosphonic dichlorides were self-assembled on tungsten substrates with surface oxide. This generic approach can be applied to diamondoid molecules of varying sizes and shapes, and potentially to all oxidized and nonplanar oxidized substrates. Temperature-dependent Fourier-transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) revealed that the diamondoid phosphonic dichloride monolayers on tungsten oxide were stable up to 300-350 °C, substantially higher than the conventional diamondoid thiolate monolayers on gold, which dissociate at 100-200 °C. Extreme-ultraviolet (EUV) stimulated photoemission of these diamondoid phosphonic dichloride monolayers showed characteristic monochromatic NEA peak with <1 eV full width at half maximum (FWHM). Our results demonstrate that phosphonic dichloride bonding is a promising approach to form stable diamondoid monolayers and opens up a large variety of opportunities for this new carbon nanomaterial in electron emission, diamond growth, as well as micro/nano electromechanical systems (MEMS/NEMS).

Protein-immobilization on solid electrodes is up-to-now very hard to realize without generation of unintended structural variations. The characterization of protein properties suffers severely from this fact as little variations of the folded protein structure causes dramatic variations of the electronic properties. In this presentation we introduce diamond with adjusted surface properties to interact with the redox protein cytochrome c without causing structural modifications of cyt c. The adjustment of the surface of boron-doped diamond for optimized protein interaction can be achieved by realizing electrochemically a mixed surface of hydrogen (H) and OH termination. We demonstrate that the mixed H/OH termination of the diamond surface mimics perfectly a protein-like surface.
We have applied variously characterization methods to investigate the detailed properties of the diamond/protein interaction. We applied a combination of electrochemical techniques and atomic force microscopy (AFM) with single molecule resolution, XPS and phenyl-grafting to identify H-bonding on the surface of diamond. These experiments reveal that moderately OH-terminated diamond shows stable immobilization of Cytochrome c with high electron transfer activity, driven by a combination of electrostatic and hydrophobic interaction. This surface mimics natural binding partners, where coarse orientation is governed by electrostatic interaction of the proteins dipole and hydrophobic interactions are involved in formation of the electron transfer complex. The results will be introduced an discussed in detail in this presentation.

The chemical fuctonalization of diamond surfaces with organic molecules is a crucial aspect to be considered for any bio-application of this material. In order to introduce different functional groups and to tailor the surface properties, there is a great interest in broadening the range of short linker molecules which can be covalently bound to the diamond surface. An effective surface modification can promote cell adhesion or enable the controlled grafting of functional biomolecules such as proteins or DNA, often used in biosensors. When it comes to protein immobilization, the hydropathicity of the surface has a major influence on the protein conformation and on the possibility to preserve protein functionality on the electrode surface. The ability to tailor the surface properties is required for the design of a suitable environment for proteins, allowing them to maintain their functionality even after surface attachment. For bio-electrochemical applications, particular attention is needed to avoid that the charge transfer between the electrode and the redox center embedded in the protein is prevented by unnecessarily long insulating linker molecules.
Recent effort in grafting short carboxylic acids on OH-terminated diamond surfaces have opened the way to a successful covalent immobilization of cytochrome C on diamond without lost of functionality. In this contribution, we present our work on the grafting of organophosphonic acids on OH-terminated diamond surfaces, serving as linkers to tether electro-active of photo-reactive protein on diamond. This novel functionalization process has been optimized in order to get a stable monolayer on the surface. Thus, we have assessed the functionalization using atomic force microscopy and spectroscopic techniques like X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). The study of coverage and charge transfer as a function of the distance between proteins and substrate is provided by electrochemical characterization, using linker molecules with different lengths. Finally, we demonstrate the suitability of OH-terminated diamond functionalized with carboxylic acid for photo-electrochemical applications, by reporting on photocurrent experiments from reaction centers immobilized on such surfaces.

Biosensors have been widely developed in recent years. Various mechanisms have been applied in biosensors such as electronics, electrochemistry, optics and piezoelectrics. Although these biosensors exhibit high sensitivity, the incorporated expensive sensing systems still limit the application in livelihood.
With high absorption coefficient, light-scattering ability and biocompatibility, carbon nanotubes (CNTs) reveal great potential for the application of colorimetric biosensors.
In this study, the low cost biosensor providing colorimetric and real time detection was composed of antigen-detecting specimen and functional CNTs immobilized with antibody to detect antigen. To improve biocompatibility, both antigen-detecting specimen and CNTs were modified with amino functional groups. Human serum albumin (HSA) was chosen as the model of the mechanism for the importance as a biomarker of kidney function. The correlation among the color change observed at different HSA concentrations was investigated by ultraviolet-visible spectroscopy (UV-Vis). With the successful demonstration of its application, this biosensor shows the feasibility of different antigen detection.

We implemented a nanoelectronic interface between graphene field effect transistors (FETs) and soluble proteins. This enables production of bioelectronic devices that combine functionalities of the biomolecular and inorganic components. The method serves to link polyhistidine-tagged proteins to graphene FETs using the tag itself. Atomic force microscopy and Raman spectroscopy provide structural understanding of the bio/nano hybrid; current-gate voltage measurements are used to elucidate the electronic properties. As an example application, we functionalize graphene FETs with fluorescent proteins to yield hybrids that respond to light at wavelengths defined by the optical absorption spectrum of the protein. (This work was supported by the Nano/Bio Interface Center (NBIC) through National Science Foundation NSEC DMR08-32802; Z.J.Q. acknowledges supportfrom NSF IGERT # DGE-0221664)

Given its exceptional chemical and mechanical stability as well as unique electrical properties, graphene is an extremely promising platform for biosensors. [1] To use graphene in biological environment and to improve sensing specificity and device sensitivity, a well-defined functionalization method for graphene is required. As the characteristic properties of graphene are due to the sp2 hybridization of carbon in a 2D geometry, non-covalent modifications based on π-π stacking or ionic interactions have been demonstrated in order to realize good dispersion and accessibility to the graphene sheet. However, for long term and reliable use of graphene-based devices in demanding biological environments, a stable, irreversible modification is needed. As such a functionalization may result in a sp2 to sp3 conversion, direct attachment of chemical moieties to the 2D-graphene has to be balanced with the desired modulation of the electronic properties of graphene. Moreover, the large reactivity differences for covalent addition onto the basal plane versus the edges of graphene make a defined modification difficult. Recently, we could show that graphene can be directly modified at its basal plane by covalent grafting of polymer brushes using self-initiated photografting and photopolymerization (SIPGP).[2] It was found that this facile grafting from polymerization using only UV-light, bulk monomer and copper-supported graphene results in homogeneous polymer brushes on the basal plane of single, few and multiple layer graphene. Micro-Raman spectroscopy showed that grafting occurs only from residual defect sites, presumably related to hydrogenated sp3-carbon. We also found that the photografting process is selective for aromatic monomers (styrene) while acrylates do not result in detectable polymer layer formation. For a further development of the method, a better control of the brush layer morphology as well as introduction of other vinyl monomers is needed. In this account, we first show that the degree of hydrogenation of the graphene can be finely tuned using a remote hydrogen plasma system, which is confirmed by Raman spectroscopy. Furthermore, we observe a strong correlation between the degree of hydrogenation and polymer brush layer thickness i.e. polymer brush grafting density. Moreover, two alternative routes to polymer brushes comprising of styrene and acrylate monomer units are presented. Both aspects are crucial steps towards the development of functional graphene-based materials for biosensing. Furthermore, graphene field effect devices have been modified with polymer brushes using SIPGP in order to assess the effect of functionalization on the electronic properties as well as the functionality in aqueous environments.
[1] - L. H. Hess et al., Adv. Mater. 2011, 23, 4968.
[2] - M. Steenackers et al., J. Am. Chem. Soc. 2011, 133, 10490.

Carbon nanotube (CNT) has been intensively studied as a prominent field emitter cathode because of its high aspect ratio with a nanometer-scale diameter and high chemical inertness. Especially, the cold-cathode x-ray sources using the CNT emitters have attracted a lot of attention since they have great advantages compared with conventional hot-cathode ones. The CNT emitter-based x-ray source can be digitally addressed with a rapid speed and low power consumption in a relatively small volume, which can open a new digital x-ray source era over 100-year-older hot-cathode analog x-ray.
We developed a highly reproducible CNT paste by optimizing a ball-milling procedure of thin multi-walled CNT, selected nano-sized fillers, ethyl cellulose binder and terpineol solvent. The constituent materials were sequentially mixed in a closed bucket for an effective dispersion of the paste components and a strong adhesion of CNT emitters to a cathode electrode. The filler materials in the paste were also optimized to make the CNT emitters reliable under high-temperature conditions. As a result, a negligible change was observed both in the surface morphology and the field emission behavior even after annealing at around of 950 °C in a vacuum. We have obtained a high emission current density of over 100 mA/cm² at a field of 2.5 V/mu;m for planar CNT emitters and around of 5 A/cm² at 8 V/mu;m for tip type emitters.
The two kinds of x-ray tubes were fabricated by using the developed high-temperature endurable CNT emitters. One is for a stationary digital breast tomosynthesis system and the other is a miniaturized x-ray source for a brachytherapy of cancer disease or a special radiography like the intra-oral dental imaging. The fabricated x-ray tubes showed a good operation with a high stability and long lifetime, confirming our design and fabrication technology for x-ray sources using the CNT emitters.

Nanocrystalline n-type diamond (NCD) has become an interesting material for electron emitter applications due to its low work function and its negative electron affinity when hydrogen-terminated. Thermionic emission at temperatures below 600°C has been recently reported from nitrogen and phosphorous doped diamond, opening up interesting prospects for their use as thermal energy converters [1,2]. Compared to its p-type counterpart, i.e. B-doped NCD, the main characteristics of P-doped NCD remain largely unstudied. Here, NCD films have been grown by chemical vapor deposition (CVD) on different substrate materials (silicon, fused silica, Mo or Re) using phosphine as an in-situ dopant gas. Standard characterization tools such as scanning electron microscopy and Raman spectroscopy reveal homogeneous, high quality thin films with pronounced crystalline grains. The sp2/sp3 ratio within the films, which evidently plays a role in the engineering of the electron emission barrier, can be controlled by the growth conditions, but is also influenced by the amount of phosphine that is used. Although higher concentrations seem to have a detrimental effect on the grain size, the presence of a higher sp2 fraction might play a beneficial role in the increase of grain boundary governed conduction paths. Aiming at a high phosphorus incorporation, experimental parameters are optimized towards CVD at elevated temperatures and up to 10,000 ppm P/C in the gas phase. Photocurrent measurements are used to evaluate electronically active defects sensitive to visible and UV light excitation. After hydrogen-termination P-doped NCD films feature surfaces with a work function of 1-2 eV which is an extremely promising characteristic for detailed thermionic emission studies.
[1] F. A. M. Koeck et al. Diamond Relat. Mater. 20 (2011), 1229-1233
[2] T. Sun et al. Appl. Phys. Lett. 99 (2011), 202101
This research was supported by the EU FP7 through the Marie Curie ITN "MATCON" (PITN-GA-2009-238201), and the Office of Naval Research.

Growth of NCD layers on plastic substrates has been demonstrated in [1]. In this reported work we aim to expand this work by the use of pulsed microwave linear antenna system [2] leading to larger area growth (20cm x 20cm) and doping of these layers via the addition of boron to the growth chemistry.
We report on the systematic optimisation of growth conditions for preparation of intrinsic and boron (B) doped nano-crystalline diamond (NCD) layers on organic based substrates, such as polyimides, polyphenylene sulphide (PPS), PTFE, PEEK and PDMS, using microwave plasma enhanced linear chemical vapour deposition (MW PELCVD) apparatus [1] using H2/CH4/CO2 gas mixtures and trimethylboron as a dopant.
Prepared layers have been studied with Raman spectroscopy to ascertain the sp3/sp2 ratio, AFM and SEM to indicate coverage and crystalline quality of the layers. Using reference quartz substrates, ellipsometry has been employed to investigate the optical quality of the prepared layers and electrical and magneto transport measurements have been carried out to establish charge transport parameters
1. K Tsugawa et al: PHYSICAL REVIEW B 82, 125460 2010
2. A Taylor et al: Diamond & Related Materials 20 (2011) 613-615

A Piezoelectric Aluminum Nitride (AlN) film was integrated on electrically conductive nitrogen-grain boundary incorporated ultrananocrystalline diamond (N-UNCD) and Boron-doped UNCD (B-UNCD) contact layers for fabrication of nano-switches for a new generation of nanoelectromechanical system (NEMS) logic based on nano-switches with negligible leakage current when open. The research described in this paper enabled the growth of extremely smooth UNCD contact layers, via chemical mechanical polishing (CMP), and overcoming delamination from thermal expansion and crystallization quality. The piezoelectric AlN layer grown on the atomically smooth B-UNCD surface exhibit a (002) orientation perpendicular to the surface, which induce a high piezoelectric coefficient, as measured using Piezoresponse Force Microscopy (PFM). Electrically conductive N-UNCD contact film, developed and patented by researchers at Argonne National Laboratory, and B-UNCD films, developed and patented by Advanced Diamond Technologies provide excellent contact layers for nano-switches due to their robust mechanical and excellent surface chemical and tribologiocal (negligible stiction and wear) properties, which provide long lived nano-switches. The tailoring of electrical conductivity of UNCD films via B substitutional doping in the UNCD grains or N incorporastion into grain boundaries during film makes feasible to fabricate robust nano-switches for NEMS logic. In this paper, we present the successful integration of piezoelectric AlN films on CMP polished conductive N-UNCD and B-UNCD contact layers The AlN films are actuated via application of electric fields between Platinum (Pt) bottom and top electrodes sandwiching the AlN layer. The surface roughness of N-UNCD and B-UNCD layers is critical to induce crystallization of the AlN film with (002) orientation perpendicular to the surface to yield high piezoelectric coefficeint. Three N-UNCD contact layers were grown with different surface roughness in the range 0.6-2.4 nm. The smoothest N-UNCD surface induced the growth of AlN films with the narrower X-ray Diffraction (XRD) peaks from the XRD rocking curve analysis. The piezoelectric coefficient (d33) of the AlN films depended on the film thickness up to 240 nm. A thin AlN film 980 nm thick) shows 1.51 pm/V piezocoefficient, while 160 nm and 240 nm thick AlN films exhibited 2.05 pm/V and 5.3 pm/V piezoelectric coefficients respectively.
Piezo-driven UNCD nano-switches were fabricated, using Focused Ion Beam (FIB) nano-patterning and Xenon-diflouride (XeF2) etcher. Studies, involving in-situ actuation of nano-switches, are currently underway The early prototype AlN/N-UNCD nanoswitches enabled the integration of piezoelectric film on nanoscale N-UNCD structures and piezo-actuated UNCD membranes for biomedical applications.

In recent years, electromagnetic wakefields produced by high energy electrons transiting through dielectric structures have pushed electric fields to over GV/m at the GHz frequency range. Dielectric materials such as metal oxide ceramics and fused silica are encountering their physical limits. Diamond is an attractive material for dielectric loaded accelerating (DLA) structures due to very low microwave loss tangent at Ka-W frequency bands, excellent thermal conductivity and high RF breakdown field. The current status of diamond DLA structures for wakefield electron accelerators will be presented.
Typical wakefield experiments are performed using the 250 GHz frequency structure at the accelerator test facility of Brookhaven National Laboratory and the 25 GHz structure at the Argonne wakefield accelerator facility of Argonne National Laboratory. We anticipate that the diamond surface will sustain a 0.5-1.0 GV/m short pulse (~10 ns) RF field without breaking down.
We report on the deposition and characterization of high quality cylindrical diamond tubes for advanced DLA structures, grown by microwave plasma-enhanced chemical vapor deposition (CVD). We have modified a 5 kW AsTex diamond CVD research reactor by adding an actively cooled cylindrical mandrel for diamond tube deposition and have modified/tuned the reactor cavity for deposition on the rotating mandrel. Typical conditions for tube deposition ranges from 90 to 120 Torr with 1 to 3% of methane (99.999 % purity) in hydrogen at a mandrel temperature of 800 to 1000 °C. No additional additive gas is used. After the growth, the diamond tube is released from the mandrel by acid etching. Cylindrical diamond tubes produced by this method are 3 mm inner diameter or larger, with a tube length up to 40 mm, and wall thickness up to 2.5 mm. Trimming and final finishing is accomplished by laser machining.
In this investigation, Raman spectroscopy is used to characterize the phase purity of the diamond (e.g. sp² vs. sp³ carbon). The FWHM of the diamond peak from the Raman spectrum can be used as one measure of the diamond quality. As DLA structures are often exposed to high energy electron beams, low temperature photo luminescence analysis for neutral vacancies, i.e. the GR1 center, is a valuable tool to characterize e-beam damage to the DLA assembly during accelerator tests. We report photo luminescence to characterize defects and impurity content after growth, and to characterize beam damage during accelerator tests.

Fluorescent probes and sensors constructed from nanodiamonds have several optical advantages including extreme photostability of luminescent NV centers, favourable emmision wavelength, possible external influencing of luminescent spectra and good transparency. For preparation of fluorescent particles the irradiation by high-energy particles is used. The lattice vacancies are formed and after thermal recombination with nitrogen impurities, luminescent NV centers are formed. This process is widely used, however, the optimized procedure for NV centers formation is still badly needed. Using systematic optimization procedure we revealed set of annealing conditions showing up to three times increase of luminescence intensity of nanodiamond particles. We analyze and discuss the influence of temperature, annealing time, and residual traces of oxygen. We also introduced a new oxidative approach further improving the particle brightness. Overall increase of particle luminescence of approximately one order of magnitude was reached.

Nanoparticle adsorption properties are connected with charge presence on their surface in expense of the functional groups ionization at a surface, and also as result of reaction complex formation due to surface active centers interaction with ions or molecules from the solution. Adsorption ability of a surface of ultra-disperse diamond (UDD) of detonation synthesis depends on a way of its chemical processing after synthesis. The research objective contained in revealing different type UDD&’s behavior in relation to water, simple and complex salts water solutions, organic molecules and some metal nanoparticles. Suspensions of several types UDD in NaCl water solution have pH (5-3) well below (~ 6) measured in initial solutions caused by own acidity of the UDD surface and due to equilibrium exchange of metal ions with the surface protons. Techniques of quantitative determination of the protonogenic surface groups&’ by pH-potentiometry are used. According to alkali titration of UDD suspensions in 0.9 M NaCl solution and desorption kinetics of protons from UDD the desorption constants (pK₁) of acid groups are estimated. Adsorption from chloride solutions of H[AuCl₄], RhCl₃, and also a methylene blue are ruled by Freundlich's equation. It was shown, that with reduction of the protonogene groups content both Rh(III) sorption and UV-absorption of the clarified UDD suspensions reduced. The adsorption at UDD of gold nanoparticles with various numeric concentration and the particles size was defined. Their final size distribution by SEM and appropriate calculation program was performed. The relatively low particle sorption value can be explained by identical charge sign both gold hydrosol surface and the UDD one.

We report a laser photolysis reaction of nanodiamonds in H₂O that produces hydrogen and carbon monoxide via C(s)+H₂O→CO+H₂. This reaction leads to the transformation into the graphitic nanocages. The Au-, Pt-, Pd-, Ag-, and Cu-ND nanocomposites were synthesized using the ND as photocatalytic reducing agents. All metal nanoparticles increase the reaction rate and specifically, Au was found to be most efficient amongst other nanoparticles with an order of Au > Pt asymp; Pd > Ag > Cu. The observed result had a good correlation with standard reduction potential. The Au-ND hybrid on the reduced graphene oxide sheets produced a greater photocurrent than the ND upon irradiation with 514 nm argon ion laser. Both the results proposed an efficient photoelectron transfer from the Au NP to the ND, which was supported by X-ray photoelectron spectroscopy. This simple yet efficient photo reaction system is expected to contribute toward the development of improved solar energy conversion systems.

The purpose of this study is to investigate a high gravity effect in diamond synthesis with hot-filament chemical vapor deposition (CVD) on a centrifuge. We already reported diamond synthesis with graphite rod heating under high gravity, and we suggested that nucleation density of diamond particles were increased with increasing gravity.
In this study, we tried to perform high gravity experiments with a centrifuge for diamond synthesis by hot-filament CVD under 300 and 600 Torr as total pressure, and surface of Si substrate was scratched by diamond powder (phi; 0-2 mu;m) or with no scratch treatment. The reaction chamber was mounted on the centrifuge in Japan Aerospace Exploration Agency. Each experimental condition was as follows: tungsten filament was placed 1.0 mm above the silicon substrate, substrate temperature was around 710°C, reaction time was 20 minutes, and the initial total pressures were 300 Torr (1 Torr for carbon source, and 299 Torr for hydrogen) or 600 Torr (5 Torr for carbon source, and 595 Torr for hydrogen). Types of experimental conditions were 4 pattern: total pressure was 300 Torr or 600 Torr, and surface of Si substrate was scratched or with no scratched.
Diamond particles were successfully synthesized with the present study. Nucleation density was increased in one level gravity condition (magic number) on surface of Si substrate with no scratch treatment under 300 Torr and 600 Torr. In addition, nucleation density in high gravity experiments was increased compared with that in 1.0 g0 experiment under 300 Torr and 600 Torr on scratched surface for Si substrate. We found significant difference between 1.0 g0 and high gravity conditions for synthesis trend of diamond particles. We will report the details of the present experiments in the meeting.

There is a considerable interest in diamond as a future material for electronic applications (high power-high temperature electronics, radiation-hard electronics, radiation detectors, and vacuum electronics). Diamond is generally recognized as an insulating material. Once successfully doped it is a wide-bandgap semiconductor material with excellent potential due to the unique combination of its physical and electronic properties. The small boron (B) atom seems to be the only efficient dopant atom in diamond, which can be incorporated with high reproducibility and high enough concentration to be useful for electronic devices.
A combination of theoretical (Density Functional Theory) and experimental techniques (Raman Spectroscopy, 2-point resisitivity, Neutron Depth Profiling, Atomic Force Microscopy) was used to describe the specific boron defects in diamond and their impact on the electrical properties [1]. Boron-doped diamond films resistance changes with boron content in a complicated manner. Smaller boron concentrations have a big influence on the resistance showing a strong decrease in resistivity but for higher amount of boron in diamond film the resistance decrease is reduced. Two types of boron defects in boron-doped diamond were determined as most probable: boron monomer and boron dimer. The electronic structure calculations for B monomer in the diamond lattice demonstrate the formation of the B occupied levels located in the valence band and B unoccupied band is a continuation of the valence band. Conductivity in such a system resembles that of a metallic material. Calculations for boron dimer complex indicates the existence of non-conductive states located above the diamond valence band. Simulated Raman spectra showed specific features of single boron substitution and two boron atoms: the experimentally observed 500 cm-1 band in the heavily boron-doped diamond with high probability originate from boron dimer defects.
In the wider perspective we can conclude that when the concentration of boron in diamond lattice is low , single substitution defects are predominant and with an increase in boron concentration the probability of creating more complex defects (mainly boron dimers) is much higher.
[1] H. Okazaki, T. Arakane, K. Sugawara, T. Sato, T. Takahashi, T. Wakita, M. Hirai, Y. Muraoka, Y. Takano, S. Ishii, S. Iriyama, H. Kawarada, T. Yokoya, Journal of Physics and Chemistry of Solids 72, 582 (2011).

In previous works it has been demonstrated that a disruption of artificially formatted lipid bilayers, deposited on the nanodiamond thin films can be detected by Electrochemical Impedance Spectroscopy (1,2). In this work we construct membrane-mimicking environment on boron doped nanocrystalline diamond (B-NCD). B-NCD simultaneously serves as a solid support for the membrane and an electrode for in-situ study of antimicrobial peptides (AMPs) induced membrane disruption. The emergence of bacterial pathogens resistant to conventional antibiotics has stimulated the search for new antimicrobial agents. AMPs possess unique action mechanisms that offer new possibilities for developing drugs against resistant bacteria.
B-NCD films were grown by a plasma enhanced chemical vapor deposition (PECVD) reactor and subsequently polished to achieve low surface roughness. Negatively charged dioleoyl-phosphatidylserine/dioleoyl-phosphatidyl-choline (20% DOPS/80% DOPC) supported lipid membrane was constructed while the formation of a SLB was monitored by confocal fluorescence microscopy. Functionality of membrane was investigated by fluorescence correlation spectroscopy. EIS measurements were used to study changes related to lipid membrane formation and disruption. Biosensing properties of constructed bioelectronics element were be demonstrated by detection of natural and artificially synthesized antimicrobial peptides.
[1] P. K. Ang et al, Adv. Funct. Mater. 19, 109 (2009)
[2] V. Petrak et al. Phys. Status Solidi A 9, 208 (2011)

This study demonstrated that the surface crystallinity of carbon nanostructures is an additional independent factor that should be considered for the inhibition of cancer proliferation without activating reactive oxygen species (ROS). In addition, cytotoxic evaluation of both proliferating cancer cells and fully differentiated nerve cells (i.e. non-proliferative) showed selective cytotoxicity: single walled and highly crystalline carbon nanostructures aggressively inhibited the proliferation of glioma cancer cells, but exhibited no notable cytotoxicity effects on differentiated nerve cells. Although single wall carbon nanotubes have been shown to elicit potent pro-inflammatory responses by means of trigger ROS, our results demonstrated that highly crystalline carbon structures can be utilized as a selective anti-proliferative agent against brain tumor cells without increasing ROS level and without significant cytotoxic effects to adjacent nerve cells.

In-cell recording is a novel technique for the analysis of neural network, which brings the insight to neuroscience and neural diseases. Demonstrated by a harmless extracellular electrode with improved neuroelectronic interface, this technique could provide attenuated intracellular recordings.
In this study, functionalized biocompatible carbon nanotubes (CNTs) were developed on three-dimensional gold electrodes at low temperature (lE;400°C) for long-term and in-cell neural sensing. The three-dimensional structures of electrodes were fabricated by semiconductor processing and electroplating on SiO₂/Si substrates, leading to larger surface area and better neural adhesion. With electroplated Ni as a catalyst layer covering the entire surface of the structure, CNTs were directly grown on gold electrodes to improve coupling coefficient and signal-to-noise ratio. In addition, the surface of CNTs was modified with carboxyl and amino groups to enhance the attachment of cells. The surface functionalization of CNTs contributes to better electrical properties and biocompatibility.
The morphology and structure of gold electrodes with CNTs were observed by scanning electron microscope. The electrical properties of the electrodes were characterized by electrochemical impedance spectroscopy. The capability of neural sensing of the electrodes was demonstrated by cultural rat hippocampus.

The translation of excellent mechanical properties of the MWCNTs into the MWCNT enabled nanocomposites depends on good dispersion of MWCNTs in epoxy matrix. The primary objective of this study is to develop an effective methodology to disperse MWCNTs in epoxy matrix and to characterize the dispersion of MWCNT in epoxy resin. For this study, functionalized (epoxy, hydroxyl and amine) and pristine MWCNTs were dispersed in Bisphenol F based epoxy resin (trade name Epon Resin 862) using several solvent-free processing methods (MicroFluidizer (MF), Planetary Shear Mixer (PSM), Ultrasonication (US) and combinations thereof). The formulated nanocomposites were characterized for the MWCNTs dispersion by two non-destructive techniques (optical microscopy and Raman imaging). Quantification of the optical microscopic images of MWCNT nanocomposite was performed using NIH&’s Image J software. Using Raman images and intensity ratio of D band (1314 cm-1) to epoxy band (1049 cm-1), the dispersion of MWCNTs was measured. The optical and Raman imaging results have shown that the combination of microfluidics and planetary shear mixing yield good dispersion of pristine MWCNTs in epoxy resin. Preliminary optical microscopy results of epoxy functionalized MWCNTs showed phase separation, while, amine and hydroxyl functionalized MWCNTs showed network formation in the epoxy resin matrix. Efforts are underway to quantify the degree of dispersion of functionalized MWCNTs in epoxy matrix using Raman imaging method.
Source of Support : US Army Subcontract 5710002978

Despite carbon nanotubes (CNTs) owing superior electrical and thermal properties, the contact resistance between CNTs and substrate has always remain as one of the major challenges that restrict its potential in electrical interconnect and thermal transport applications. One of the key factors that is accountable for the high interfacial resistance is the limited contact length/area between CNTs and the substrate. Here, we present an innovative method to infuse catalytically-active metal nanoclusters into an amorphous carbon (a-C) matrix thin film, before synthesizing CNTs with the conventional chemical vapour deposition (CVD) method. As a result, the root of these CNTs would be embedded within the a-C matrix and significantly increases the contact surface and hence, reduces the overall resistance.
The infusion of metal nanoclusters is achieved through the intermixing of two plasma sources with Filtered Cathodic Vacuum Arc (FCVA) deposition technique. Unlike other premix composite deposition method, the density, size of the nanoclusters and therefore, the properties of the synthesized CNTs can be simply controlled by the coupling of an external magnetic field. The fundamental principle of this newly developed infusion technique will be discussed and the improvement of the contact resistance will be presented.

In the last decades many new carbon-based materials have been discovered. Examples of these materials are fullerenes, carbon nanotubes, and, more recently, graphene.
Graphene is a two-dimensional (2D) hexagonal array of carbon atoms in sp²-hybridized states. Graphene presents unique and exceptional electronic, thermal and mechanical properties. However, in its pristine state graphene is a gapless semiconductor, which poses some limitations to its use in some transistor electronics. In part due to this, there is a renewed interest in other possible two-dimensional carbon-based structures similar to graphene. Examples of this are graphynes [1] and graphdiyne, which are two-dimensional structures composed of carbon atoms in sp² and sp hybridized states. Graphdiynes (benzenoid rings connecting two acetylenic groups) were recently synthesized and intrinsically nonzero gap systems. These systems can be easily hydrogenated and the relative level of hydrogenation can be used to tune the band gap value [2].
In this work we have investigated using fully reactive molecular dynamics (ReaxFF), the structural and dynamics aspects of the hydrogenation mechanisms of graphdiyne membranes. The simulations were carried out exposing graphdiynes membranes to hydrogen atmospheres and investigating the chemical reactions in time. This approach has been successfully applied to the study of hydrogenated graphenes [3].
Our results showed that the hydrogen attacks have different rates of atom incorporation and that these rates change in time in a very complex patterns. Initially the most probable site of hydrogenations are the carbon atoms forming the triple bonds, as expected. But it changes in time and then the carbon atoms forming single bonds become the preferential attack sites. The formation of correlated hydrogenated domains observed in hydrogenated graphene is no longer observed into case of graphdiynes. We have also carried out ab initio DFT calculations for model structures in order to test the reliability of ReaxFF calculations.
[1] Baughman, RH, H Eckhardt, and M Kertesz. "Structure-property predictions for new planar forms of carbon: Layered phases containing sp² and sp atoms." The Journal of chemical physics 87.11 (1987): 6687.
[2] Psofogiannakis, George M, and George E Froudakis. "Computational Prediction of New Hydrocarbon Materials: The Hydrogenated Forms of Graphdiyne." The Journal of Physical Chemistry A (2012).
[3] Flores, Marcelo ZS, Pedro AS Autreto, Sergio B Legoas, and Douglas S Galvao. 2009. Graphene to graphane: a theoretical study. Nanotechnology 20, no. 46: 465704.

Supercapacitors are promising candidates for energy storage due to high power performance, long cycle life and low maintenance cost. Here, we have successfully fabricated three-dimensional (3D) nanohybrid supercapacitor electrodes consisting of MnO2 nanowires, carbon nanofibers (CNFs) and 3D graphene. Uniform, CNFs and 3D graphene films with large area have been produced in a simple fashion using a single-step chemical vapor deposition (CVD) on nickel foams, and MnO2 nanowires have been deposited on the as-obtained CNFs/3D graphene films by a simple chemical bath deposition process. The structure of the MnO2/CNFs/3D graphene films can be simply controlled by deposition time and nanowire solution concentration. The scanning electron microscopy (SEM) and the scanning transmission electron microscopy (STEM) have been used to investigate the surface morphology, and the energy-dispersive X-ray spectroscopy (EDS) has been performed to characterize the MnO2 nanowires on the surface of the film. The measurements of cyclic voltammetry and electrochemical impedance spectroscopy (EIS) are conducted to determine its performance for the electrodes of supercapacitors.

In recent years, supercapacitors are widely studied for memory backup systems, hybrid electric vehicles and fuel cell vehicles. Supercapacitor electrodes are usually made to coat the activated carbon sludge on the current collect electrodes. And the activated carbon sludge is composed of the activated carbon particle, polymer binder and high conductivity materials. Polyvinylidene fluoride (PVDF) is usually used as the polymer binder in the activated carbon based supercapacitors. The PVDF is an insulator material, but the activated carbon is a conducting material. The reduced conductivity as adding the PVDF is enhanced by adding other high conductivity materials such as conductive carbon black.
In this presentation, we propose a composite system based on the activated carbon and the crosslinkable polymer binder for high performance supercapacitor electrodes. We used the crosslinkable polymer binder instead of the PVDF binder and conductive carbon black to form the activated carbon clusters. The crosslinkable polymer binder has a merit such as minimizing the binder contents. We minimized the crosslinkable polymer binder contents to overcome the reduced conductivity of activated carbon clusters. And we demonstrate the effects of the minimized crosslinkable polymer binder on the electrical properties of supercapacitor electrodes.
**This study was supported by a grant (B551179-10-01-00/ KM3000/ NK167D/ SC0860) from the cooperative R&D Program funded by the Korea Research Council Industrial Science and Technology, Republic of Korea.

We present nanoscale friction force microscopy (FFM) measurements and simulations of the model layered material, graphite. Friction as a function of applied normal load is recorded using an atomic force microscope (AFM). While frictional forces always oppose motion, they increase linearly with decreasing load on aged graphite surfaces. This friction-load relationship results in an effectively negative nanoscale coefficient of friction during unloading, where the magnitude of the friction coefficient increases with adhesion between the AFM tip and graphite surface [1]. We control tip-sample adhesion by varying surface oxygen content, as characterized by X-ray photoemission spectroscopy. We find that the negative coefficient begins to emerge on exfoliated graphene (supported by a silicon dioxide substrate) when the graphene consists of more than one layer. Atomic-level stick-slip measurements further show that the observed effect is not a result of an anomalous variation in lateral potential corrugation with load.
Nanoscale contact mechanics (area-load) models do not exist for anisotropic materials. Thus, we apply continuum mechanics models developed for isotropic materials to estimate a lower limit for the tip-sample work of adhesion based on the measured adhesive forces. These calculations suggest that the magnitude of the friction coefficient increases faster in a regime where the tip-surface adhesion is comparable in magnitude to the binding energy of graphene to bulk graphite (the exfoliation energy). Furthermore, through molecular dynamics (MD) and finite element method (FEM) simulations, we show that the negative coefficient behavior is reproduced when the tip-sample adhesion energy exceeds the exfoliation energy. The MD and FEM simulations span both time and spatial scales, and both show that the negative coefficient occurs as a consequence of the AFM tip lifting the topmost graphene layer.
As the negative friction coefficient is related to the exfoliation energy, we believe that FFM may potentially be used for straightforward determination of the exfoliation energies of layered materials, in general.
[1] Z. Deng et al., Nature Materials, DOI:10.1038/nmat3452 (2012).

The nanoscale properties of two bodies in contact cannot be fully analyzed on an atomistic level using experimental methods or understood solely using continuum mechanics. Molecular dynamics (MD) simulations allow nanoscale behavior to be modeled by resolving the positions, velocities, and forces of discrete atoms in the system. Diamond has been of interest as both as an object of scientific study and as an ideal material for applications such as, cutting tool coatings, waste water purifiers, chemical sensors, electronic devices, and micro- and nanoelectromechanical systems (M/NEMS) because of its unique electrical, mechanical, and tribological properties. Due to its high fracture strength and chemical robustness, it can withstand exposure to harsh environments and resist mechanical wear. It can be grown in nanocrystalline form with nearly equivalent mechanical performance to the crystalline form. In this work, MD was used to simulate the nanoscale adhesion and tribological behavior between diamond, diamond-like carbon (DLC), and ultrananocrystalline diamond (UNCD) materials. Work of adhesion values from the MD simulations with axisymmetric tips are compared to, and discussed within the context of, complementary AFM experiments, finite element simulations, and continuum mechanics-based analytical models. MD simulations show that the work of adhesion is sensitive to the identity of the contacting materials because they have inherent roughness differences. In addition, work of adhesion values obtained from continuum mechanics-based analytical models are consistently higher than values obtained using the atomic-force microscope, which are higher than the simulated values. The tribological response of these carbon-based materials is also very sensitive to environmental conditions. The presence of water has been shown to have a beneficial effect on the friction performance of UNCD, but a negative effect on the friction performance of DLC. A recently developed bond-order potential for C-, H-, and O-containing systems [1] has been integrated into a new model for extending charge-transfer to bond-order potentials. The novel aspects of this model will be discussed and its potential application to the tribology of hydrocarbon systems in the presence of water will be outlined.

**Supported by The National Science Foundation and The Air Force Office of Scientific Research.

Carbon xerogel is a porous material which posses a wide varieties of excellent properties such as high surface area, light weight, high porosity, etc. due to their unique physical structure and controllable porous structure. Carbon xerogel is normally synthesized by the condensation reaction between resorcinol and formaldehyde under basic catalyst.
However, a new type of additional-cure phenolic resin, called polybenzoxazine has been chosen as an alternative starting material for carbon xerogel due to its excellent properties such as high thermal and chemical stability, high char yield, low water adsorption, high crosslink density, and great molecular design flexibility.
In this work, we aim to study the effects of non- and cat-ionic surfactants on textural properties of polybenzoxazine-based carbon xerogel. By using cationic surfactant, polybenzoxazine-based carbon xerogel shows the specific surface area of 369 m²/g and pore volume of 0.70 cc/g, whereas the surfactant-free synthesized polybenzoxazine-based carbon xerogel shows the specific surface area of 275 m²/g and pore volume of 0.33 cc/g. Moreover, the pore diameter is increased from 3.50 nm up to 56 nm. The 3D-interconnected structure is observed from polybenzoxazine-based carbon xerogel by SEM technique.
In case of non-ionic surfactant, the spherical particles of 500 nm are observed. The specific surface area and pore volume are 154 m²/g and 0.12 cc/g with pore diameter of 1.90 nm, respectively. Furthermore, according to IUPAC classification, polybenzoxazine-based carbon xerogel shows the standard isotherm of type I which represents the microporous material.

Graphene, the two-dimensional (2D) unit of three-dimensional (3D) bulk material graphite, has captured the imagination of engineers for a variety of electronics, optical, sensing, microfluidics, manufacturing, and heat transfer applications. Meanwhile, it has also provided the scientific community an opportunity to experimentally investigate the unique characteristics of 2D materials. One of the most intriguing questions which otherwise is mostly irrelevant in the case of 3D materials is how the background substrate affects the properties of an atomically thin graphene coating? Studies focused on understanding the wettability of graphene have been sparse and the existing results have been contradictory and highlight the lack of a clear understanding of the underlying physics that dictates wetting behavior.
In this work, we use experimental measurements, molecular dynamics simulations, and theoretical calculations to demonstrate that the wettability of graphene coated on a substrate closely matches the wettability of its 3D bulk structure graphite. Dynamic contact angle experiments with water droplets on mono-, bi-, and tri-layer graphene sheets on copper, thermally grown silica, and glass substrates were performed. High contact angle hysteresis (16°-37°) was observed where the advancing contact angle was independent of the number of layers of graphene sheets and in good agreement with corresponding molecular dynamics simulations and theoretical calculations. Meanwhile, the resulting receding contact angles were influenced by defects in graphene. These results suggest that the advancing contact angle for a graphene surface is representative of the actual surface material and the wetting opacity of graphene is attributed to the large interlayer spacing resulting from the loose interlamellar coupling between the individual graphene sheets. The fundamental insights on graphene-water interactions in this study is an important first step towards developing graphene assisted surface-coatings, heat transfer and microfluidics devices.

Moiré patterns are generated by the superposition of two periodic structures with a lattice mismatch or a rotation between them. They have been observed by means of Scanning Tunneling Microscopy (STM) on different systems and their interpretation, in some cases, is not straightforward. The influence, at the atomic scale, of these patterns in the local density of states of the overlayer is not clear.
The growth of graphene on metallic substrates allow us not only control the periodicity of the moiré pattern, but also tailor the interaction strength between the carbon atoms and the metallic substrates. This modulation in the interaction gives rise to regions with larger (H-areas) and shorter (L-areas) height of the graphene layer over the Ru(0001) surface. Field Emission Resonances (FERs), which are detected by STM when applying voltages larger than the work function, can be used to explore with nanometer resolution, the inhomogeneities in the local surface potential landscape. Operating the STM in constant current mode implies a constant electric field between tip and sample and the expected energy position for the FERs gives information about the surface potential.
The dZ/dV curves measured on gr/Ru(0001) present three unexpected features: (i) the first graphene image state is localized on the H-areas, while it is more extended on the L-areas, (ii) it does not shift in energy following the 0.25 eV increase of local work function from L- to H-areas, and (iii) a new interfacial state at +3 eV appears in the L-areas. To further investigate and understand the origin of these features we performed first principle calculations based on density functional theory, which explain the experimental behaviour of the first FER in gr/Ru(0001) as consequence of the splitting and spatial localization of quasi-two dimensional bands due to the modulation of the strength of the interaction between the graphene layer and the metal surface [1]. The interfacial state, resulting from the hybridization of an unoccupied Ru(0001) surface resonance with the first image state component localized in the low areas of the moiré, was suggested to be responsible for the inversion of contrast observed in gr/Ru(0001) STM experiments at a bias voltage Vssim; +2.6 V [2].
[1] B. Borca et al., Potential Energy Landscape for Hot Electrons in Periodically Nanostructured Graphene, Phys. Rev. Lett. 105, 036804 (2010)
[2] D. Stradi et al., Electron localization in epitaxial graphene on Ru(0001) determined by moiré corrugation, Phys. Rev. B 85, 121404(R) (2012)

Graphene exhibits exceptional electronic and optical properties [1]. So far, the main research focus using graphene has been on fundamental physics and electronics devices [2], being the potential applications in photonics not yet fully exploited [3]. Within the several areas of possible application of graphene-based photonics devices, we give emphasis to the recent development of the optical communications, boosted by the data traffic increase and the need for larger scale coverage, for instance, in the access network layer [4]. In this context, the use of low cost devices with an enhanced performance can be viewed as a viable solution to reduce the optical technology deployment cost.
In this work we propose the usage of spectroscopic ellipsometry (SE) as a standard optical technique for the identification and characterization of the graphene sheets. In particular, we present a simplified model to handle SE data in order to obtain the grapheme thickness. The hereafter designated phase shift simplified model considers that the graphene is deposited over an oxidized Silicon substrate (OSS), which exhibits a periodic behavior for the phi parameter spectrum. The presence of a graphene layer on this substrate will shift the spectrum by an amount proportional to the phase shift induced by the graphene on the optical signal. For example, for deposition on OSS a typical spectral shift of 0.42 nm (at 650 nm), per graphene layer is expected.
In this work, high quality large area graphene layers produced by filament thermal CVD on metal substrates were transferred to OSS (1.0 um) by dissolving the metal substrates in an aqueous iron (III) chloride (FeCl3) solution (1 M) as an oxidizing etchant [5]. Atomic force microscopy (AFM) was used to characterize the film in order to independently validate the results achieved from SE. For example, SE was applied to the characterization of a graphene sample with a thickness value of 5-8 nm and an average surface roughness of 1-2nm, estimated by AFM. The SE data show a shift of 4.89 nm for the graphene layer phi parameter spectra when compared with that of the substrate. Two distinct methods were applied to model the SE data. In particular, using the simplified phase shift approach model a thickness of 3.69 nm was estimated for the graphene layer. The traditional SE data analyze for the multi-layer sample (Si-SiO2-Graphene) reveals a thickness of 3.14 nm and a refractive index of 2.0 - 0.4i, in good agreement with previously reported data [6].
[1] Geim, A.K. and K.S. Novoselov, Nature Materials 6, 183, 2007.
[2] Palacios, T., A. Hsu, and W. H., IEEE Communications Magazine. 0163-6804, 122, 2010.
[3] Bonaccorso, F., et al., Nature Photonics, 4, 611, 2010.
[4] André, P.S., et al., Next-Generation FTTH Passive Optical Networks, 2008: Springer. 65-110.
[5] Hawaldar, R., et al., Nature Scientific Reports, 2, 682, 2012.
[6] Ni, Z.H., et al., Nano Letters, 7, 2758, 2007.

Carbon nanodots (C-dots) are attracting intense interest due to their many unique and novel properties. The strong and tunable luminescence of C-dots, due primarily to the quantum size effect, is extremely interesting both fundamentally and technologically. We report simple synthetic methods of C-dots with sizes of 1.2-3.8 nm, which possess size-dependent photoluminescence (PL) and excellent up-conversion PL properties. To enable the use of the full spectrum of sun light, the remarkable optical properties are exploited in the photo-catalyst systems of TiO2/C-dots and SiO2/C-dots and in the dye-semiconductors photoelectric conversion system. We show that C-dots can enhance the UV-Vis absorbance of Rhodamine-B (RhB) and improve the photocurrent density by 10 times when compared to the RhB/TiO2 system. Study of the mechanism of energy transfer in C-dots-containing nanosystem reveals that the high conversion efficiency is attributed to the up-converted PL as well as the photo-induced electron donors and acceptors properties of C-dots. C-dots provide an inexpensive and environmental-friendly route to improve the efficiency of solar cells and photo-catalysis via efficient utilization of the full solar spectrum.
References
(1) S.T. Lee, et al. “Carbon nanodots: synthesis, properties and applications”, J. Mat. Chem. 2012, in press
(2) S.T. Lee, et al. Angew. Chem. 2010, 49, 4430.
(3) S.T. Lee, et al. Chem. Comm. 2011, 47, 8025
(4) S.T. Lee, et al. Carbon, 2011, 49, 605.

Dye-sensitized solar cells are regarded as the next-generation solar cells due to their low fabrication cost and decent power conversion efficiency. The regeneration of the redox species on the counter electrode of dye-sensitized solar cells is one of the key steps during the light-to-electricity conversion. Platinum has been considered as the best materials for the counter electrode of dye-sensitized solar cells due to its high electrocatalytic activity. But Pt is expensive. Various materials have been investigated to replace Pt as the counter electrode of dye-sensitized solar cells, but they give rise to lower photovoltaic efficiency and low open-circuit voltage. In this paper, we will report highly efficient dye-sensitized solar cells with composites of graphene and carbon nanotubes as the counter electrode of dye-sensitized solar cells. They exhibit higher photovoltaic efficiency and higher open-circuit voltage than the control dye-sensitized solar cells with Pt as the counter electrode. The open-circuit voltage reaches 0.90 V for iodide/triiodide dye-sensitized solar cells, the highest for efficient iodide/triiodide dye-sensitized solar cells. The mechanism for the high performance of the graphene/carbon nanotube composites will be presented.

Direct conversion of heat into electrical energy based on thermionic energy conversion may provide a highly efficient approach for waste energy and also for solar energy conversion. New approaches are presented for energy conversion through the use of doped diamond films in a novel vacuum gap configuration that combines effects related to thermionic electron emission, molecular charge transport and direct photo excitation. Thermionic electron emitters based on diamond require control of the surface electron affinity, doping levels and concentration, and band bending. Significant thermionic electron emission has been measured at temperatures less than 500°C from engineered multilayered structures of nitrogen and phosphorus doped, nanocrystalline diamond films. Results are presented that show the electron emission can be amplified by utilizing surface ionization processes where charge is transferred from the conduction band of the emitter surface to the negative ionization level of the scattered molecule. The electron emission can be further enhanced with the application of visible light, and results are presented that indicate the potential for combined photo and thermionic emission in an energy conversion configuration. The results suggest potential application of the diamond films in a new type of concentrated solar cell.
This research was supported by the Office of Naval Research and the EU FP7 through the Marie Curie ITN "MATCON" (PITN-GA-2009-238201)

Diamond is a wide-bandgap semiconductor with a bandgap of 5.5 eV. When the surface is terminated with hydrogen atoms, the conduction-band energy lies ~0.8-1.3 eV above the vacuum level; this property is termed ‘negative electron affinity (NEA). NEA materials have a unique property that when illuminated with above-bandgap photons, the resulting conduction-band electrons can be directly emitted into vacuum. Due to diamond&’s very high chemical stability, it can be used as a photoelectron emitter even in non-vacuum environments. We are investigating the photo-initiated emission of electrons into water. When illuminated with ultraviolet light, electrons are photoemitted into water where they are able to initiate very difficult electrochemical reduction reactions, including reduction of N2 to NH3 (nitrogen fixation). This reaction typically requires high pressure and temperatures, but can be initiated by illuminated diamond at atmospheric pressure and temperature. A comparison of different diamond types, including single-crystal, thin-film, polycrystalline, and diamond powder shows that all diamond samples exhibit photocatalytic activity for N2 reduction, albeit with different efficiencies. A comparison of H-terminated and O-terminated surfaces shows that the electron emission and nitrogen reduction processes are both a direct result of diamond&’s NEA property. In this talk we will discuss the factors that influence the ability of diamond to act as a solid-state electron source in aqueous environments and the implications of this for inducing new types of chemistry.

The growth rate of carbon nanotubes (CNT) is traditionally held to be limited by the carbon solubility in the catalyst and the carbon diffusion rate through the catalyst particle. We recently showed that a related view is that efficient CNT growth catalysts must balance the need to dissociate the incoming hydrocarbon precursor with the need to release the CNT product, so that surface catalyst sites are not blocked with absorbed carbon [1]. We should here that the two models are equivalent, because the solubility depends on the carbon dissolution energy in the bulk metal, and the latter depends on the carbon atom adsorption energy of the metal surface. Both values are found to be linearly correlated when calculated by density functional theory. The nucleation and growth rate of graphene during CVD on copper has been related to the energy barrier of adding carbon atoms to existing graphene islands [2]. Our density functional calculations of the adsorption energy of CHx species on various transition metal surfaces shows that the energy barrier for growth on copper is in fact related to the cost of progressive dehydrogenation of the CHx species. For earlier transition metals, the barrier is lower. For copper, the surface diffusing species is CHx groups not atomic carbon [3], but for the earlier transition metals [4] the diffusing species can be carbon atoms.
[1] J Robertson, J Mater Chem 22 19858 (2012)
[2] H Kim et al, ACS Nano 6 3614 (2012)
[3] W Zhang, P Wu, J L Yang, J Phys Chem C 115 17782 (2011)
[4] S Wang.. J Norskov, T Bligaard, Phys Chem Chem Phys 13 20760 (2011)

Ordered graphene films have been fabricated on diamond surfaces in the presence of a transition metal catalyst. The temperature at which diamond converts into sp2-bonded carbon can be significantly reduced in the presence of such a catalyst. Photoelectron spectroscopy applied in real-time (REES) allows the reaction kinetics to be followed during the conversion of sp3 to sp2 bonded carbon of the graphene films, as well as providing a control mechanism for the amount of catalyst deposited and the number of graphene layers formed. The epitaxial growth of the catalyst plays a crucial role in the quality of the grown graphene layers. Synchrotron techniques such as photoelectron microscopy (PEEM) and angle resolved photoelectron spectroscopy (ARPES) have been used to investigate the quality, order and electronic structure of the graphene films. As the graphene is only formed on the treated regions of the diamond surface the possibility of growing patterned graphene structures in the solid state at industrially viable temperatures is attainable.

Among many renewable energy sources, ethanol stands out as one of the most promising candidate since it allows the generation of electricity via a direct ethanol fuel cell (DEFC) with high energy efficiency, non-toxicity, natural availability, and greenhouse gas free. However, to realize the future of DEFC, current challenges such as slow reaction kinetics of ethanol oxidation, fuel cell fabrication costs, and low durability of catalysts need to be overcome.
To date, researchers have successfully attempted to explore the use of metal alloys and metal oxides as catalysts for the ethanol oxidation process. Differing from the conventional inorganic-based approach, we are utilizing organic materials as functional supporting matrices to enhance the performance of low-loaded noble metal-based catalysts. We discovered that the functionalized multiwalled carbon nanotubes (f-MWCNTs) layer acts as an “-OH carpet” by creating H-bonds with water, similar to the role of Sn/SnO2 in conventional so-called “bi-functional catalysts”. Concerning the role of the -OH species, Markovíc et al. recently studied non-covalent interactions on Pt active sites and suggested that adsorbed -OH species could stabilize the hydrated cations in the double layer and therefore significantly enhance the reactivity trends of alcohol in alkaline solutions. However, the merit of neutral/low pH fuel cell urges us to search for a functional supporting matrix that could promote the dehydrogenation process to ultimately and adequately enhance ethanol oxidation reaction (EOR) at neutral/low pH. We expected that by creating functional groups nearby the metal active surface, the dissociative adsorption of ethanol in the double layer would be stimulated by the adsorbed -OH on f-MWCNTs via H-bonding and/or by the functional groups themselves, and these non-covalent interactions might play an important role in enhancing dehydrogenation rate. Thus, different types of functional groups are studied to reveal the tunability of functional matrices in creating different degrees and types of non-covalent interactions, while a number of reaction parameters are studied to understand how non-covalent interactions work in EOR. Furthermore, by varying the assembly directions of the f-MWCNTs, the interactions between f-MWCNTs and Pt/MWCNTs can be significantly changed to enhance ethanol oxidation reaction kinetics. These results provide important strategies for exploring ways to tune catalytic activities of organic material-based catalysts, paving the way for future development of organo-metallic fuel cells.
References: [1] Hoa, L. Q.; Vestergaard, M. C.; Yoshikawa, H.; Saito, M.; Tamiya, E. J. Mater. Chem. 2012, 22, 14705-14714. [2] Hoa, L. Q.; Yoshikawa, H.; Saito, M.; Tamiya, E. J. Mater. Chem. 2011, 21, 4068-4070.

High-surface-area nitrogen-doped graphitic carbon materials have elicited interest as versatile electrode materials for electrochemical device applications, due to their high thermal and chemical stabilities and high electrical conductivities. In addition, they have recently been reported to exhibit high electrochemical reaction activities, which open the possibility to use them to replace expensive precious metal catalysts. In particular, the oxygen reduction reaction (ORR) that occurs at the cathodes of fuel cells usually relies on dispersed Pt catalysts supported on carbon. By comparison, N-doped graphitic porous carbon materials show similar, and in some cases, superior oxygen reduction activities that make them potentially cost-effective alternatives to expensive Pt catalysts. We have developed a facile pyrolysis method based on an inexpensive N-containing precursor with transition metal salts to synthesize N-doped graphitic mesoporous carbon materials that have high porosities (~800 m2/g), are highly graphitic, and exhibit enhanced ORR catalytic activities.
Specifically and of high technological interest, N-doped graphitic mesoporous carbon materials show excellent electrochemical catalytic properties under alkaline conditions. ORR activities evaluated by linear sweep voltammetry show favorable onset potentials that are significantly higher than recently reported for Co3O4 on N-doped graphene oxide (0.88 V vs. RHE) and are comparable to costly carbon nanotube-graphene complexes (1.05 V vs. RHE) and carbon-supported Pt (20 wt%, Pt/C) catalysts. Furthermore, N-doped mesoporous carbon catalysts show high half-wave potentials (0.88 V vs. RHE) and manifest low Tafel slopes (53 mV/decade), both of which are favorable compared to Pt/C catalysts (0.85 V vs. RHE and 67 mV/decade). In addition to the superior ORR activities, N-doped graphitic mesoporous carbon materials also exhibit better stabilities and selectivities than Pt/C catalysts under alkaline conditions, notably superior methanol tolerance that eliminates detrimental fuel crossover effects. In addition, N-doped mesoporous carbon catalysts exhibit high oxygen-evolution activities, as manifested by low onset potentials and Tafel slopes, which show promise for their use as cathodes in rechargeable metal-air batteries (e.g., lithium-air battery) or water-splitting electrocatalysts. The results demonstrate the synthesis and characterization of potentially cost-effective surface-functionalized carbon materials with excellent electrocatalytic properties compared to more expensive alternatives.

Boron-doped conductive diamond is a promising platform for electron-transfer and electrocatalysis because of its exceptionally large window of electrochemical stability, good electron transfer properties, strong covalent bonds to surface modifiers and low cost. Tethering electrocatalytically active molecules to diamond surface takes advantage of above properties along with efficient conversion of electrical energy into chemical energy of electrochemical systems and the convenience and low catalyst loading of heterogeneous catalyst systems.
Catalyzed CO2 reduction has been studied extensively and metalloporphyrins represent an important class of catalysts for this process. However, the poor solubility of metalloporpyrins in reductively stable solvent hinders their application. Here we report first covalent attachment of a cobalt porphyrin CO2 reduction catalyst onto conductive boron-doped diamond. Cobalt porphyrin complexes bearing four alkyne groups were prepared and attached onto azide-functionalized boron-doped diamond via CuI-catalyzed azide-alkyne cycloaddition (CuAAC OR “click”) reaction. The functionalized surface was then characterized by X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy (FTIR). The catalytic behavior was observed by cyclic voltammetry in acetonitrile and CO was detected by FTIR as a product of the reduction process, which further demonstrates the exceptional stability of our heterogenous catalyst system.
Our results show that the use of diamond substrates provides a convenient route to ultra-stable electrocatalytically active surfaces. The approach demonstrated here can be extended to iron porphyrins and other tetrapyrrole macrocycles, metallocorrins, metallophthalocyannines and metallocorroles with well demonstrated CO2 reduction ability.

The formation of bonds between carbon atoms with the participation of three sp3, sp2 and sp1 hybridization types and combinations thereof determines the existence of a long-known forms of pure carbon - graphite and diamond, and recently opened its states as fullerenes, carbon nanotubes, astralenes, tubulenes, graphene, particulate nanodiamond, and others. A vital problem of the alternative energy development and exploration have many prospects of solution with help of abovementioned different kinds of carbon both in nanosized and nanostructured states[1]. The intention our short review is to consider direct and indirect ways to use nanosized and nanostructured carbon (NNC) for production, conversion, storage, savings and recovery of the alternative energy.
We can start from not well explored prospects of reversible storage of simplest - mechanical energy on base of CNT both in their static and kinetic form.
Several samples of the NNC benefits in the solar cell (SC), fuel cells(FC), electrochemical batteries(ECB), supercapacitors (SC), etc. will be considered.
E.g. nanodiamond crystals, coated by nanothin heavy boron doped diamond film able seriously improve resistance of Pt catalyst carrier in FC and highly enlarge it life-cicle. In many cases the use of the NNC provide topmost efficiency comparatively with noncarbon materials. Special emphasis will be done for use of active carbons and the NNC contained nanocomposites for effective and reversible molecular hydrogen (as outstanding energy relay) in tradition and alternative energy storage and environmentally friendly applications.
REFERENCES
1. B.V.Spitsyn et al. 8-th Int.Conf. on Carbon. September 25-28, 2012. Troitsk, Russia.
2. G.M.Swain et al. J. Electrochem. Soc. 2008. 155(10) B1013.

Graphene oxide (GO) is a chemically versatile atomically thin material that is interesting for a variety of applications ranging from large area electronics to catalysis. The ability to tune the chemical, electronic and atomic structures of GO via controlled reduction to obtain reduced GO (rGO) provides pathways for accessing its novel properties. Interesting chemistry can be performed on as synthesized GO using its numerous functional sites arising from the presence of epoxy, hydroxyl, carboxyl and other oxygen groups. Recently there has been interest in decorating rGO with metal nanoparticles for catalysis applications. In this study, we present the properties of metal nanoparticles decorated graphene oxide. We find that when placed on graphene oxide, the nanoparticles retain their catalytic activity and their electrochemical stability is also enhanced. We present the results of our structural and theoretical studies to explain the enhanced stability.

We report on the use of simple and scalable solution processing techniques to control and manipulate the non-covalent binding of multiple conjugated polymers to carbon nanotubes to utilise the favorable properties of each polymer.
We create nanostructured materials consisting of carbon nanotubes wrapped in sequential coatings of two different semiconducting polymers of the type typically used in photovoltaic (PV) devices, namely poly(3-hexylthiophene) (P3HT) and poly(9,9&’-dioctylfluorene-co-benzothiadiazole) (F8BT). We show that we can control the ordering and proportions of wrapping polymers in the solid state by varying the solution processing steps. Using steady-state and ultrafast photoluminescence measurements, we demonstrate the role of the different layer structures in controlling energy levels and charge transfer in both solution and film samples.
We also demonstrate that the purity of the nanotube distribution obtained from the selective binding of the polymer poly(9,9-dioctylfluorenyl-2,7-diyl) (PFO) to specific semiconducting nanotubes can be transferred to other more technologically important polymer-nanotube combinations, such as P3HT and F8BT, using a solution-based polymer exchange technique. This process provides a means to eliminate unwanted metallic nanotubes and also leads to an additional purification of the system by removing almost all of the excess polymer while the wrapping polymer remains as a high quality monolayer coating.
Finally, we demonstrate how these methods to bind multiple polymers to carbon nanotubes can be combined to produce nanostructures comprised of dual-polymer coated monochiral semiconducting carbon nanotubes. We show how the polymers, nanotubes and solvents can be recycled and we provide details of how the processes can be carried out on a large scale. The products can be dissolved in any organic solvent to any desired concentration, making the processes suitable for preparing the highly purified samples required for a range of electronic and optoelectronic applications. In particular, the highly purified and optimised dual-polymer nanostructures have the required electronic alignments and properties to allow construction of potentially highly efficient PV devices.

The study of carbon nanotube (CNT) thin-film transistors generates significant research interest particularly towards their applications for low-cost, scalable fabrication, large-area and high performance electronic devices. Solution-processed CNT networks are much easier to be fabricated than the manipulation of single strand CNT, giving more opportunities for device applications. However, the true potentials of CNT, i.e. high carrier mobility, ambipolarity, and high on/off ratio are still difficult to be achieved in thin films made of CNT networks. One of the challenges is the quality of the CNT dispersion used to make the device, due to the random nature of nanotube growth where both semiconducting and metallic tubes are mixed. Although the many efforts to separate the semiconducting carbon nanotube from the metallic species, most of the fabricated devices still could not demonstrate high carrier mobility together with high on/off ratio. Generally devices demonstrating high carrier mobility suffer of low on/off ratio value, and vice versa, due to the residual metallic nanotubes.
Here we present the fabrication of ambipolar transistors of CNT networks that demonstrated a combination of high carrier mobility both for hole and electron, together with high on/off ratio. We exploited polymer-assisted CNT separation that shows an effective separation of semiconducting nanotube from the metallic species. A combination of high-speed ultracentrifugation and post-processing of the devices was used to remove the excess polymer left after the preparation. In order to evaluate the quality of the nanotube dispersion, we investigate the dependency of the device performance on the coverage density of the nanotube film. The charge carrier mobility values increased in denser film together with improvement of on/off ratio values. The off-current remained similar for all devices with different nanotube coverage. These trends indicate that the purity of the semiconducting nanotube dispersion is very high, with almost no signature of metallic species as well as significant residual polymer. A similar interpretation is found for the fact that channel-length variations from 20 mu;m down to 2.5 mu;m show almost constant values of charge mobilities and on/off ratio. The fabricated devices demonstrated carrier mobilities as high as 3 cm^2/Vs for both hole and electrons, with on/off ratio value of >10^6. To our knowledge, these values are among the highest ever obtained for ambipolar transistor made from solution-processed CNT networks. These results indicates that the fine tuning of the polymer-assisted CNT separation together with optimization of device fabrication process are important in achieving high performance device of CNT network. Efforts to exploit the ambipolar characteristics of the fabricated device in order to investigate the electron transport behavior in the device will be also discussed.

Semiconducting single-walled carbon nanotubes (SWNTs), with high charge carrier mobility and solution processibility, hold a great promise for high-performance low-cost thin film transistor applications. However, separating semiconducting SWNTs from metallic ones in large quantities still remains a challenge. It has been reported that conjugated polymers such as polyfluorene or polythiophene can sort small diameter semiconducting SWNTs. Large-diameter SWNTs are longer, less prone to defects and easier to align than small diameter SWNTs and hence are potentially better for electronic applications. In this work, we have developed a method to disperse and sort large-diameter arc-discharged SWNTs using dithiafulvalene/thiophene copolymers. We found that by altering the number of thiophene repeating units in the polymer backbone, the polymer rigidity and wrapping conformation can be tuned, resulting in a selective dispersion of semiconducting SWNTs. From Small Angle X-ray Scattering (SAXS) measurements and Molecular Dynamics (MD) simulations, we found that the amounts of SWNTs dispersed are proportional to the available contacts sites from the polymers and the increased polymers flexibility leads to improved selectivity. Thin film transistors from polymer sorted SWNTs showed on/off ratios greater than 10^4, confirming preferential sorting of semiconducting SWNTs. The sorted, concentrated and stable large-diameter semiconducting SWNT solutions have great potential for applications in TFTs, sensors and semiconductor active layer in solar cells.

Carbon nanostructures with a defined number of extended dimensions such as carbon nanotubes (1D) or graphene (2D) constitute promising components for high performance composites, lithium storage materials, or nanoelectronics. Mitigating the poor dispersibility of such materials in organic matrices by chemical functionalization should allow for the preparation of novel types of electronically active nanocomposites. The typically employed methods to prepare carbon materials, however, rely on high-energy processes that impede the tailored preparation of carbon nanostructures with controlled morphology and chemical functionalization. In this context, we developed a novel strategy for the low-temperature wet-chemical preparation of carbon nanostructures with a predefined nanoscopic morphology and surface chemistry based on the synthesis, self-assembly, and subsequent mild carbonization of oligo(ethynylene) (also called oligoyne) amphiphiles as reactive molecular precursors. Here, we demonstrate that these amphiphiles are unique molecular carbon precursors suitable for the preparation of carbon sheets at the air-water interface. To this end, a concise synthetic route was developed for the gram-scale synthesis of the desired carbon-rich amphiphiles that resemble fatty acids but comprise a reactive, “carbon-only” hexayne segment. Our investigations at the air-water interface by means of IRRA spectroscopy, BAM, GIXD, and X-ray reflectivity showed that these novel amphiphiles reliably self-assembled into films with a thickness on the molecular length scale containing a densely packed domain of the reactive, carbon-only rod segments. In the self-assembled state, UV irradiation served as a mild external stimulus for the carbonization of the reactive molecular precursors, leading to novel carbon sheets with extended lateral dimensions and a thickness on the order of a few nanometers. The obtained carbon sheets were transferred to solid substrates for characterization by Raman spectroscopy, TEM, as well as AFM, and investigations of their electrical properties are in progress.

It is well-established in molecular electronics that the alignment of molecular and contact energy levels determines many important features of charge transport in a molecular junction. However, measurement of these energy levels in a completed junction has been a challene. This presentation discusses recent measurements of the energy levels within a completed molecular junction using optical excitation. Molecular tunnel junctions are fabricated by covalently bonding molecules to flat, graphitic carbon substrates. The circuit is completed by deposition of Cu metal films in a cross-bar format. Measurement of the photocurrent intensity as a function of incident photon energy, molecular layer thickness, and molecule type reveal a two-regime mechanism for photocurrent generation in these devices. At low photon energy, an internal photoemission process is observed, where hot carriers generated in the contact traverse the tunnel barrier as long as the photon energy is sufficient. In this regime, the cut-off energy for the photocurrent can be used to determine the height of the tunnel barrier. For higher photon energy, and for aromatic molecules that show optical absorption, interfacial electronic transitions lead to a strong photocurrent effect. In this regime, external quantum efficiencies exceeding 1%, corresponding to internal quantum efficiencies exceeding 70%, are demonstrated in the ultraviolet spectral region. Possible mechanisms for charge separation in this regime are discussed, including the potential role of hybrid carbon-molecule orbitals resulting from coupling of the molecules to the carbon substrate.

Charge transport in molecular electronic junctions with molecular layer thicknesses below ~20 nm differs fundamentally from that in thicker layers common in organic electronics, since quantum mechanical tunnelling and ballistic electron transport are possible. However, the variety of conceivable molecular electronic devices will be severely constrained if the dimensions of the molecular component are restricted to typical tunnelling distances of a few nm. Carbon/BTB/carbon/Au molecular junctions were fabricated by covalent bonding of bis-thienyl benzene (BTB) oligomers to a flat, sp2 hybridized surface followed by vapour deposition of carbon and gold 1-3. Carbon electrodes act not only as covalent conductors with excellent temperature tolerance but also a flat surface to which molecular components can be covalently bonded. Investigation of charge transport in such devices as a function of temperature (5-300K), voltage (± 6 V) and molecular layer thickness (d= 4.5 to 22 nm) revealed three distinct transport mechanisms, with attenuation coefficients (β) of lnJ vs d plots of 3.0, 1.0, and <0.1 nm-1. The current density of 10-22 nm layers converged at high electric field, and depended exponentially on the square root of the field for all temperatures. We propose that field induced ionization of molecular HOMOs or interface states with possible polaron formation and activationless intrachain charge transfer are responsible for the intermediate region between coherent tunneling and activated hopping. The three mechanisms observed in carbon/BTB/carbon devices bridge the gap between tunnelling in molecular junctions and activated transport common in most organic semiconductors, and reveal a new transport mechanism enabled by the high electric fields present in nm-scale all carbon molecular junctions having dimensions comparable to that of a single polaron.
(1) Sayed, S. Y.; Fereiro, J. A.; Yan, H.; McCreery, R. L.; Bergren, A. J.; Charge transport in molecular electronic junctions: Compression of the molecular tunnel barrier in the strong coupling regime; Proceedings of the National Academy of Sciences 2012, 109, 11498.
(2) Yan, H.; Bergren, A. J.; McCreery, R. L.; All-Carbon Molecular Tunnel Junctions; Journal of the American Chemical Society 2011, 133, 19168.
(3) Bergren, A. J.; McCreery, R. L.; Stoyanov, S. R.; Gusarov, S.; Kovalenko, A.; Electronic Characteristics and Charge Transport Mechanisms for Large Area Aromatic Molecular Junctions; Journal of Physical Chemistry C 2010, 114, 15806.

Monolithic graphene and carbon nanotube (CNT) based carbon foams with hierarchical 3D architectures and high mass-specific surface areas have many promising applications ranging from hydrogen and electrical energy storage to desalination, catalysis and actuation. Here, we will discuss fundamental phenomena related to interfacial charging of the carbon/electrolyte interface and how these cause macroscopic effects such as reversible electrical conductivity changes and mechanical strain. To explore these phenomena, we apply a combination of atomistic simulations (DFT and MD) and various in-situ characterization techniques, including synchrotron-based in-situ electron spectroscopy to study interfacial charge induced changes of the electronic structure. Our results will guide the development of next generation carbon-based storage materials, and open the door to new applications of monolithic nanocarbon foams including all-carbon bulk actuator and transistor technologies.
Work at LLNL was performed under the auspices of the U.S. DOE by LLNL under Contract DE-AC52-07NA27344.

Large-scale high quality graphene transfer has been a formidable obstacle for graphene devices batch manufacturing. In this study, SiO2 substrates engineered with different organosilane self-assembled monolayers (SAM) have been proven to apparently assist graphene transfer process. Three different types of organosilanes, including 3-Aminpropyltriethoxysilane, 3-Chloropropyltriethoxysilane and Phenyltrimethoxysilane, have been tested. To apply those organosilanes, substrates with 300 nm thermally grown SiO2 are dipped into 2 wt % organosilane ethonal solution. Graphene in this study is synthesized by APCVD method and transferred by electrochemical bubbling technique. This transfer technique is nondestructive to Pt substrates and avoids metal contamination to graphene. Large-scale flawless single layer graphene (SLG) on organosilane treated SiO2 is observed through optical microscope. Atomic force microscope (AFM) images show ultra-smooth graphene surface on organosilane SAMs. Raman peak positions and G/2D peak intensity ratio vary from case to case which indicate different chemical doping in transferred graphene. The absence of D peaks proves high quality of graphene film. To further study the proximity effects of different organosilane SAMs on graphene, back-gate field effect transistors (FET) are fabricated and tested. Interestingly, hysteresis and carrier mobility vary significantly in each case. Graphene on phenyl-terminated organosilane SAM shows the best extrinsic field effect mobility of 2500cm2v-1s-1, nearly twice as much as its counterpart on bare SiO2. In NH2-silane case, a stable over 100 volts Dirac point hysteresis shift is observed, which shows great potential in nonvolatile memories for low thermal budget flexible electronics. In general, carrier mobility decreases with the increase of graphene channel hysteresis. Charge is injected from graphene to gate dielectric interface during gate voltage sweeps and acts as Coulomb scattering centers.

To obtain stable luminescence from NV centres in diamond one has to control precisely NV charge states by the position of the Fermi level [1, 2]. The aim of our work was to determine experimentally the dynamic behaviour of the Fermi level position of the NV-/0 ground states in the diamond as a function of the laser power and the excitation wavelength. To carry out this experiment we used single photon (CW, pulsed) and two photon (pulsed) excitation as well as monochromatic light. Additionally, we have performed optical absorption measurements to detect the energy position of the NV ground state energy in the gap. Data were fitted using Inkson formula for the optical cross section and gave the position of the NV0 and NV- states, which data was compared is predicted from theoretical calculations [3]. Experiments were compared with PL excitation/quenching spectra. The results give information about the energy position and occupation of NV centre in diamond upon the photon excitation, needed for chemical luminescence driving.
[1] V. Petrakova et al, Adv. Funct. Mater. 2012, 22, 812-819 2012
[2] K. Iakoubovskij et all, J. Phys. C, 12, 189-199, 2000
[3] Goss et al, Phys Rev. B, 2000

There is growing interest in thin, lightweight, and flexible energy storage devices to meet the special needs for next-generation, high-performance, flexible electronics. We synthesized a novel graphene foam, a three-dimensional, flexible, and conductive interconnected network, by chemical vapor deposition on a Ni foam. Using it as a current collector and loaded with Li4Ti5O12 and LiFePO4 as anode and cathode, respectively, we assembled a thin, lightweight, and flexible lithium ion battery. No metal current collectors, conducting additives, or binders are used. The excellent electrical conductivity and pore structure of the hybrid electrodes enable rapid electron and ion transport. For example, the Li4Ti5O12/graphene foam electrode shows a high rate up to 200C, equivalent to a full discharge in 18 s. Using them, we demonstrate a thin, lightweight, and flexible full lithium ion battery with a high-rate performance and energy density that can be repeatedly bent to a radius of 5 mm without structural failure and electrochemical performance loss.
Reference:
Z.P. Chen, et al, Nature Materials 10 2011, p. 424-428.
N. Li, et al, PNAS, 2012, doi:10.1073/pnas.1206839109.

Electric double-layer capacitors (‘EDLCs&’) are electrical energy storage devices with high power density, but relatively low energy density compared to batteries. One might expect a simple increase (such as linear) of the specific gravimetric capacitance (C_g, the capacitance per gram of electrode material) as a function of the specific surface area of carbon materials used as the electrode in an EDLC supercapacitor. However, significant deviations from a linear dependence have been observed and ascribed to the space charge capacitance [1] or to the quantum capacitance (QC) [2], especially for carbon materials with high surface area and thin walls composed of sp²-bonded carbon and only one or a few layers thick, including chemically-modified graphene. The QC of a 2-D material is usually smaller than that of the EDL capacitance owing to the low density of states (DOS), thus QC might be a critical factor that limits the interfacial capacitance and thus the overall capacitance of a supercapacitor. Understanding the relationship between the QC and the type of carbon materials having a high specific surface area is an important goal for both fundamental science and to obtain higher energy density in such supercapacitors.
Monolayer graphene grown by chemical vapor deposition (CVD) on copper foils has a calculated specific surface area of 2,630 m²/g. Monolayer graphene was sequentially transferred onto a dielectric substrate to obtain stacked (i.e., multilayer) graphene that was configured as electrodes with a controllable specific surface area. The QC of multilayer graphene was expected to increase with the number of stacked layers. However, electrochemical measurements showed that the QC was essentially constant and also close to that measured for the basal plane of the top surface of highly oriented pyrolytic graphite (HOPG) samples. A self-consistent electrostatic calculation showed that this is due to strong screening by the inner graphene layers in the stacked graphene samples and in HOPG, i.e, the charge carrier densities in these multilayer graphene samples did not increase with the number of stacked layers: It is the charge carrier density of mono- and multi-layer graphene and of bulk graphite, and not the specific surface area, that determines the QC. A series of N-doped monolayer graphenes with differing concentration of N atoms substituted in the graphene lattice were grown by CVD and a linear relationship between the charge carrier density and the QC was observed. We propose that increasing the charge carrier density and thus the DOS (e.g., via doping) is an important factor in the design of better performing high surface area carbon electrodes for EDLC systems. We appreciate funding support from the U.S. Department of Energy (DOE) under award DE-SC0001951 (LLZ, HJ, XZ, and RSR) and award DE-FG03-02ER45958 (JJ, ZQ, AHM). [1] O. Barbieri, et al., Carbon, 43 (2005) 1303-1310. [2] J.L. Xia, et al., Nature Nanotech., 4 (2009) 505-509.

Defects in carbon nanotubes can be exploited for the synthesis of interesting coiled structures or in electrodes exhibiting fast electron transfer kinetics. For example, while the introduction of disclinations into graphene sheets can motivate helical structure, the exact mechanism for coiling is unknown. I will propose a thermodynamic model, based on exclusion volume principles, common in chemical and biological systems, to explain helix formation. Experiments that verify some of the underlying assumptions of the model and applications to novel components, such as electrical inductors, optical frequency metamaterials, etc. will be outlined. In the next part of the talk, I will review the influence of defects in determining the electrochemical properties of carbon nanostructures. We have seen that exposure of carbon nanotubes to argon and hydrogen irradiation can be used to either increase/reduce the defect density.Raman spectroscopy revealed an increase in the disorder in MWCNTs with the introduction of argon and hydrogen, as evidenced by an increase in the ID/IG peak intensity ratio. However, argon is intercalated into the CNTs, and charges the nanotubes (in the form of dangling bonds), while hydrogen treatment terminates residual dangling bonds in the CNTs. We have also seen a corresponding modification of the in-plane nanotube correlation length, from 2- 4 nm, by measuring the area ratios of the Raman peaks. In cyclic voltammetry (CV) measurements, we have seen that only the Ar treated samples exhibit perfect reversible Nernstian behavior characteristic of ideal electrodes. The application of such studies to novel devices, sensors, capacitors, etc. will be discussed.

Graphene derivatives are attractive as supercapacitor electrodes because they are lightweight, chemically inert, have high surface area and conductivity, and are stable in electrolyte. Nevertheless, devising reliable strategies for improving energy density relies on an understanding of the specific factors that control electrode performance. We have performed density-functional theory calculations in order to identify specific factors that limit quantum capacitance, and to suggest structural changes that could contribute to their mitigation. We have tested a variety of structural point defects, lattice strain, curvature, and surface rippling. Certain structures and morphologies are found to have a significant impact on the density of states near the Fermi level, and by extension, the quantum capacitance. Together, our calculations suggest strategies to engineer carbon electrodes for improved device performance. The results are combined with predicted and measured in situ X-ray absorption spectra in order to give insight into the structural and chemical features present in synthesized graphene derivatives. Performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52- 07NA27344.

Electrochemical capacitors, known also as supercapacitors, are very interesting devices for energy storage. Process of energy storage is based on charging and discharging of electrical double layer (EDL) formed on electrode/electrolyte interface. High energy/power demands can be satisfied only with materials characterized with great conductivity and suitable porosity preserving excellent charge propagation. Activated carbons with high specific surface area should be used as electrode materials to reach satisfactory capacitance values and power characteristic, however, the capacitance values reported for these electrodes do not exceed usually 150-180 F/g. Higher capacitance values can be provided by using pseudocapacitive materials like transition metal oxides. This additional capacitance origins from faradaic reactions. Besides pseudocapacitance originating from electrode material, a novel and very interesting way to increase capacitance is to apply electrolytes with species able to undergo faradaic reactions and which could additionally make an electrode grafting process. In this case electrolyte could generate particular functional groups on the surface of carbon electrode which would be able to undergo reversible redox reactions and provide additional charge.
This study is focused on electrochemical behaviour of the activated carbon electrodes electrochemically grafted by three different dihydroxybenzenes: hydroquinone, catechol and resorcinol. Electrochemical grafting with these agents diluted separately in sulphuric acid, potassium hydroxide and lithium sulphate strongly changes the carbon surface functionality and affects the capacitance values of carbon electrodes.
Three different electrochemical techniques: cyclic voltammetry, galvanostatic charging/discharging and electrochemical impedance spectroscopy were used for electrochemical investigations of grafted activated carbons operating in acidic (1 mol/L H2SO4), alkaline (6 mol/L KOH) and neutral (1 mol/L Li2SO4) medium. Briefly, addition of 1,4-dihydroxybenzene in acidic electrolyte caused increase of capacitance value, reaching 350 F/g. For unmodified electrode (without 1,4-dihydroxybenzene as electrolyte additive) it was only 130 F/g. Energy released by capacitor built from such electrodes was improved to the level of 12 Wh/kg. Galvanostatic charge/discharge investigation proved a good electrochemical behaviour of this capacitor. Cyclic voltammetry carried out in the range of 1-20 mV/s scan rates, revealed significant faradaic contribution to charge storage mechanism. Electrochemical impedance spectroscopy (100 kHz - 1 mHz) confirmed good charge propagation and small charge transfer resistance. Apart from electrochemical measurements, physicochemical investigations of the electrodes such as thermogravimetry coupled with mass spectroscopy, potentiometric titration with functional pKa distribution, Raman spectroscopy and elemental analysis were also performed and will be discussed.

This paper will focus on a discussion of the science and technology to develop an ultrananocrystalline diamond (UNCD)-coated membrane as a bioinert/biocompatible efficient (no fouling) aqueous humor drain device for treatment of glaucoma. The device will consists of a metallic multi-hole circular grid, made of Ti, similar to those used for holding thin films for transmission electron microscopy (TEM) studies, implanted in the trabecular region where the natural draining conduits have been clogged. The grid can provide efficient drainage of the eye humor liquid though the many holes existing in the structure. The grid is coated with an encapsulating bioinert/biocompatible UNCD film, grown by microwave plasma or hot filament chemical vapor deposition (grain size of 2-5 nm). The biocompatibility of the UNCD-coated grid was tested via implantation of UNCD-coated and uncoated copper grids in the sclera of several NZ rabbit eyes. Since Cu is known to be a toxic material for the eye, it was used as one of the grid materials to demonstrate the strong bioinertness/biocompatibility of the UNCD film.
The UNCD coating protected the eye against toxicity of the metallic Cu grid, exhibiting no fouling whatsoever after months of implantation, while uncoated Cu grid implants were extruded from the eye in about 24 hours.
This work demonstrated a novel biocompatible UNCD-coated grid for efficient drainage of the eye aqueous humor for treatment of glaucoma. In the projected commercial device, Ti grids will be used because Ti provide an excellent platform material for growing UNCD films, due to the formation of a template layer of Ti-carbide during the initial nucleation for growing UNCD films. The UNCD-coated grid provides a smaller, less intrusive and more efficient device for treatment of glaucoma than the current commercial much larger valves based on polymers, which exhibit extensive biofouling.

The DNA sequencing approach based on the combination of nanopores and electron tunnelling has seen considerable advances in recent years, and particularly carbon nanomaterials such as carbon nanotubes (CNTs) and graphene nanoribbons (GNRs) have emerged as promising candidates to replace metal electrodes. Applying a first-principles computational approach combining density-functional theory and matrix Green's function calculations, we here explore the potential of modified CNTs and GNRs as advanced sensor electrodes for DNA sequencing. First, we discuss the dual mechanisms of DNA sequencing realized with nitrogen-doped capped CNTs, which have significantly enhanced transmission as well as chemical sensitivity over their pristine counterparts. Interestingly, we find that two complementary DNA sequencing mechanisms can be achieved simply by setting up two different gap sizes and probing small-gap face-on nucleobase and large-gap edge-on nucleobase configurations. Particularly, analyzing the origin of conductance orderings in the two sequencing modes, we find that, while the face-on mode mostly probes the highest-occupied molecular orbital ordering, the edge-on mode maximally exploits the chemical nature of electron-accepting or electron-donating natures of functional groups within nucleobases. Through intensive statistical analysis, we conclude that the combination of these two sequencing modes allows the reliable and efficient whole genome sequencing. In the second part, we similarly observe the possibilities of GNR as nanosensor electrodes through edge-functionaliations. First, we show that the conductance of zigzag GNR (ZGNR) electrodes can be significantly enhanced by functionalizing the edges of ZGNRs with ketone groups. We further show that functionalizing the gap-side armchair edges can provide different DNA sequencing modes. Our work thus demonstrates that modified CNT and GNR electrodes provide an efficient tool to achieve tunneling-based DNA sequencing as well as molecular sensing in general.

Over the past few years, fluorescent nanodiamonds (FNDs) have been recognized as an potential fluorophores for use in bioimaging, owing to their unique and attractive chemical and particularly spectral properties. FNDs are capable of fluorescing with almost quantitative quantum yields from point defects of crystall lattice - nitrogen-vacancy (NV) centers. In particular, the long-wavelength emission, no photobleaching, no photoblinking, and an exceptional resistance to chemical degradation make them almost ideal core for development of fluorescent probes. On the other hand, the improper colloidal properties of FND surface still represent an important issue in construction of bioimaging probes for intracellular applications.
We developed a method enabling dense decoration of FND by biocompatible hydrophillic polymers. The polymers are grown directly from the nanoparticle surface and they contain alkyne or azide groups enabling the covalent attachment of targeting and/or reporting moieties. The versatility of the concept for preparation of different molecular constructs will be demonstrated.

In the last decade, it has become clear that certain heterogenous tumors contain subpopulations of cells that have enhanced tumor-initiating properties. These cells, termed CSCs, are thought to be responsible for tumorigenesis, metastasis and recurrence following initial treatment. As such, these cells appear to have the ability to self-renew, differentiate into other cancer cells and also appear to have intrinsic chemoresistant properties in some models. Because of their chemoresistant properties, conventional chemotherapy does not appear to be useful in fully eradicating these CSCs and alternative methods of therapy are needed to target and eliminate these tumor-initiating cells. We have previously demonstrated that CSCs express specific cell surface markers and mechanisms of chemoresistance based on the initiating oncogenes. Additionally, we have previously demonstrated that nanodiamonds (NDs) can be complexed with standard chemotherapeutics to overcome one of these methods of chemoresistance in chemoresistant breast and liver cancer mouse models resulting in enhanced drug efficacy while lowering the toxic effects of conjugated chemotherapeutics.
NDs are a versatile drug delivery platform that can be functionalized with a broad array of molecules, including small molecules, proteins and genetic material. The uniformity, stability and size (~4nm) of NDs lend themselves to clinical use as biocompatible drug delivery and imaging reagents. As such, we evaluated the use of NDs in targeted drug-delivery and imaging in multiple cancer models. This includes the specific targeting of CSCs in oncogene-specific mouse models of cancer. In vitro and in vivo experiments with NDs conjugated to fluorescent dye esters demonstrated enhanced homing of cancer cell targeted ND-drug complexes to tumors compared to non-targeted controls. Furthermore, addition of a targeting component greatly enhanced tumor treatment efficacy by ND-drug complexes with regression seen in some cases. Enhanced efficacy was seen while ND-drug association maintained lower systemic toxicity. As such, this work demonstrates the powerful potential of nanodiamonds as the basis for targeted cancer therapy, particularly in the treatment of oncogene-specific cancer stem cells. As cancer therapy moves towards a more personalized medical approach where diagnosis is combined with targeted patient-specific treatment, nanodiamonds-based targeted therapy should be useful in providing better therapeutic option to cancer patients over current conventional therapy.