The focus of this work was to examine the direct plating of Cu on Ru diffusion barriers for use in interconnect technology and the substrate mediated growth of graphene on boron nitride for use in advanced electronic applications. The electrodeposition of Cu on Ru(0001) and polycrystalline substrates (with and without pretreatment in an iodine containing solution) has been studied by cyclic voltammetry (CV), current-time transient measurements (CTT), in situ electrochemical atomic force microscopy (EC-AFM), and X-ray photoelectron spectroscopy (XPS). The EC-AFM data show that at potentials near the OPD/UPD threshold, Cu crystallites exhibit pronounced growth anisotropy, with lateral dimensions greatly exceeding vertical dimensions. XPS measurements confirmed the presence and stability of adsorbed I on the Ru surface following pre-treatment in a KI/H2SO4 solution and following polarization to at least −200 mV vs. Ag/AgCl. CV data of samples pre-reduced in I-containing electrolyte exhibited a narrow Cu deposition peak in the overpotential region and a UPD peak. The kinetics of the electrodeposited Cu films was investigated by CTT measurements and applied to theoretical models of nucleation. The data indicated that a protective I adlayer may be deposited on an air-exposed Ru electrode as the oxide surface is electrochemically reduced, and that this layer will inhibit reformation of an oxide during the Cu electroplating process. A novel method for epitaxial graphene growth directly on a dielectric substrate of systematically variable thickness was studied. Mono/multilayers of BN(111) were grown on Ru(0001) by atomic layer deposition (ALD), exhibiting a flat (non-nanomesh) R30(3x3) structure. BN(111) was used as a template for growth of graphene by chemical vapor deposition (CVD) of C2H4 at 1000 K. Characterization by LEED, Auger, STM/STS and Raman indicate the graphene is in registry with the BN substrate, and exhibits a HOPG-like 0 eV bandgap density-of-states (DOS).

To study the effect of the substrate support on the nanoscale contact, three different regimes, i.e., graphene on rigid (ultra-crystalline diamond) and on elastic (Polydimethylsiloxane) supports and free-standing graphene, were considered. The contribution of the graphene support to the mechanical and electrical characteristics of the graphene/metal contact was studied using the conductive atomic force microscopy (AFM) technique.The results revealed that the electrical conductivity of the graphene/metal contact highly depends on the nature of the graphene support. The conductivity increased when transitioning from suspended to elastic and then to rigid substrates, which is attributed to the changes in the contact area being higher for the suspended graphene and lower for the rigid substrate. The experimental observations showed good agreement with theoretical results obtained from modeling of the studied material systems. Further, the results indicated that in addition to the substrate support, the nature of the contact, static or dynamic, results in large variations of the electrical conductivity of the graphene/metal contacts. In case of the static mode, the contact made with supported graphene was very stable for a wide range of applied normal loads. Transitioning to the dynamic mode led to instability of the graphene/metal contact as demonstrated by lowering in the electrical conductivity values. This transition was even more pronounced for free-standing graphene which is attributed to graphene sagging during rapid scanning of the tip over the graphene surface. This study creates a new knowledge on understanding of the nanoscale contacts forming with 2D materials thus enabling further advances in the applications of 2D materials in highly stable and reliable electronic devices.

In this project, the synthesis of carbon encapsulated copper nanoparticles using sustainable bioproducts as raw material was systematically studied. The synthesis mechanism, process parameters, and functionalization of carbon encapsulated copper nanoparticles were well established. In a preliminary study, carbon encapsulated copper nanoparticles were successfully synthesized at 1000 ºC, 1h, 20 ºC/min, and 1800 sccm argon gas flow rate using BCL-DI lignin as the carbon source. Carbon encapsulated copper nanoparticles were mainly located at defect sites. Copper was found not tightly encapsulated by graphene shells. The carbon encapsulated copper nanoparticles were uniformly distributed. The conversion of copper ions into copper atoms occurred at above 300 ºC, with the company of decomposition of BCL-DI lignin into CO, CO2, and hydrocarbon gases. The growth of graphene layers was proposed to start above 300 ºC. TEM images illustrated the onset of growth of graphene at the edge of the surface at 400 ºC, and the formation of graphene bands at 500 ºC. Copper catalyst continued to facilitate the decomposition of lignin functional groups at 600 ºC. Further increasing the temperature retarded the degradation of lignin, while assisted the reconstruction of the defective sites of the graphene layers, producing higher quality products. Plastic film phase of lignin dominated on the synthesis of carbon encapsulated copper nanoparticles, while gaseous phase had little impact. The orthogonal experiment revealed that temperature played the most important role in the growth of graphene: high temperature was preferred in order to obtain less defective sites. The optimum synthesis parameters were suggested as 1000 °C, 30 min duration time, 20 °C/min temperature rising ramp, and 1200 sccm argon gas flow rate. Post heat treatment was proved to be a feasible way to improve the crystallinity of graphite. Amorphous carbon was removed or converted into crystalline graphite under heat and oxygen. FTIR spectra confirmed the covalent linkages between carbon encapsulated copper nanoparticles and N-methyl-2-pyrrolidone and polyvinylpyrrolidone, indicating a successful functionalization. This study has presented a homogeneous carbon encapsulated copper nanoparticles solution in water and ethanol, and paved ways for further functionalization of CECNs.

Lignin is the most abundant natural aromatic polymer on the earth. In this work, lignin properties were studied in order to explore its use as a low cost carbon precursor for graphene production. Initial studies focused on kinetics of lignin pyrolysis using ‘Kissinger method’ and ‘ASTM E 1641’ using thermogravimetry. The values obtained for kinetic parameters varied for the two methods and activation energy increased with increase in lignin purity. Lignin was solvent fractionated, using three organic solvents to extract the high molecular weight fraction suitable for the production of highly ordered graphene nano platelets. Acetone and Methanol were successful in sequential fractionation. Finally, polycrystalline graphene was produced using Protobind 1000 and lignosulfonate lignins by carbonization. The acid purified graphene had relatively less catalytic material remaining, and nitric acid purification was successful compared to HCl purification. However, HNO3 purification introduced minor structural damages to the sample.

No description available.

Yes / The peptide sequence GrBP5, IMVTESSDYSSY, is found experimentally to bind to graphene, and ex situ atomic force microscopy indicates the formation of an ordered over-layer on graphite. However, under aqueous conditions neither the molecular conformations of the adsorbed peptide chains, nor the molecular-level spatial ordering of the over-layer, has been directly resolved. Here, we use advanced molecular dynamics simulations of GrBP5, and related mutant sequences, to elucidate the adsorbed structures of both the peptide and the adsorbed peptide over-layer at the aqueous graphene interface. In agreement with a previous hypothesis, we find GrBP5 binds at the aqueous graphene interface chiefly via the tyrosine-rich C-terminal region. Our simulations of the adsorbed peptide over-layers reveal that the peptide chains form an aggregate that does not evolve further into ordered patterns. Instead, we find that the inter-chain interactions are driven by hydrogen bonding and charge–charge interactions that are not sufficiently specific to support pattern formation. Overall, we suggest that the experimentally-observed over-layer pattern may be due to the drying of the sample, and may not be prevalent at the solvated interface. However, our simulations indicate sequence modifications of GrBP5 to promote over-layer ordering under aqueous conditions.

Yes / Research in graphene-based energy materials is a rapidly growing area. Many graphene-based energy applications involve interfacial processes. To enable advances in the design of these energy materials, such that their operation, economy, efficiency and durability is at least comparable with fossil-fuel based alternatives, connections between the molecular-scale structure and function of these interfaces are needed. While it is experimentally challenging to resolve this interfacial structure, molecular simulation and computational chemistry can help bridge these gaps. In this Review, we summarise recent progress in the application of computational chemistry to graphene-based materials for fuel cells, batteries, photovoltaics and supercapacitors. We also outline both the bright prospects and emerging challenges these techniques face for application to graphene-based energy materials in future. / veski

GaSb Thermophotovoltaics are a key technology in the search for the ability to power small scale autonomous systems. In this work, MBE grown GaSb photovoltaic devices are fabricated and tested under AM 1.5 conditions. These devices displayed short circuit current values as high as 40 mA/cm2 but were found to have poor series resistance. The parasitic resistive characteristics were factored out of the measured cell data and it was found that the photocurrent for the fabricated devices could be as much as 6 mA/cm2 higher then the measured short circuit current. An additional layer of metal was added to the reduce the deleterious resistance characteristics, and it was found to lower the series resistance down to a 4 Ω average across almost all of the devices. The average JSC for all of these devices increased to over 30 mA/cm2, with highs well over 40 mA/cm2, a more consistent result than the original single metal deposition devices. Graphene was applied to the originally fabricated devices in an attempt to remove the series resistances issues as well as act as a surface passivation layer. The graphene was able to reduce series resistance by as much as 50% on some of the devices, with a corresponding 6 mA/cm2 increase in short circuit current exhibited. The photocurrent and diode current values were not changed by more than a measurement error, an indication that surface passivaiton may not have taken place. Graphene was a suitable approach for solving the series resistance issue and its use as both a transparent conductive layer and surface passivation material deserve further investigation. / Master of Science

Although young in its existence, graphene has already shown many potential uses in nuclear engineering. Graphene has unique electrical, mechanical and optical properties that give it unmatched potential for applications raging from sensors to composites. Before these applications can be fully developed, the response to neutron and gamma irradiation must be understood. In this study, graphene grown from chemical vapor deposition was irradiated by the High Flux Isotope Reactor at Oak Ridge National Laboratory and characterized using Raman spectroscopy. It was found that the amount of structural damage was minimal, but that the graphene was doped reversibly with H₂0₂ and irreversibly. The irreversible doping is a type of soft etching process related to the exposure to O₂ as well as ionizations and heating caused by irradiation. The reversible doping is related to the products generated through the radiolysis of the water trapped between the sample and the substrate. By removing the water through evaporation the dopants related to the radiolysis products were found to be removed as well. These results are promising as they show that graphene is resilient and sensitive to the effects of irradiation simultaneously. / Master of Science

Graphene – a two-dimensional honeycomb lattice of sp2-bonded carbon atoms – has been attracting a great deal of research interest since its first experimental realization in 2004, due to its various novel properties and its potential for applications in futuristic nanodevices. Being the fundamental building block for carbon allotropes of other dimensionality, it can be stacked to form 3d graphite or rolled into 1d nanotube. Graphene is the thinnest known material in the universe, and one of the strongest materials ever measured in terms of its in-plane Young modulus and elastic stiffness. The charge carriers in graphene exhibit giant mobility as high as 20 m2/Vs, have almost zero effective mass, and can travel for micrometers without scattering even at ambient conditions. Graphene can sustain current densities six orders of magnitude higher than that of copper, shows record thermal conductivity and stiffness, is impermeable to gases, and renders easy accessibility to optical probes. Electron transport in graphene is described by a Dirac-type equation, which allows the investigation of “relativistic” quantum phenomena in a benchtop experiment. This results in the observation of a number of very peculiar electronic properties from an anomalous quantum Hall effect to Kien paradox and the absence of localization. All these enticing features make this material an excellent candidate for application in various electronic, photonic and optoelectronic devices. For instance, its ballistic ambipolar transport and high carrier mobility are the most useful traits for making ultrafast and low-power electronic devices. Its high surface area shouldmake it handy in manufacturing tough composite materials. The extreme thinness of graphene could also lead to more efficient field emitters that release electrons in the presence of strong electric fields. Its robustness and light weight are useful for micromechnical resonators. The tunability of its properties could make it possible to build so-called spin-valve transistors, as well as ultra-sensitive chemical detectors. Many of such applications of graphene require tuning of its properties, which can be achieved by varying the number of layers or/and by doping. There are several ways to dope graphene: (i)electrochemically gated doping, (ii)molecular charge-transfer doping, and (iii) substitutional doping by atoms like Boron or Nitrogen.Moreover, for graphene, a zero band gap semiconductor in its pristine form, to become a versatile electronic device material it is mandatory to find means to open up a band gap and tune the size of the band gap. Several strategies have been adopted to engineer such a band gap in graphene in a controlled way. Some of these are based on the ability to control the geometry of graphene layers, some use graphene-substrate interactions, while others are based on chemical reactions of atoms or molecules with the graphene layer. Motivated by these considerations, in this thesis we present a systematic and thorough study of the structural, electronic and vibrational properties of graphene and their dependence on the number of layers, and on doping achieved electrochemically, molecularly and substitutionally, using first principles density functional theory (DFT). In Chapter 1, we give an introduction to the hitherto beguiling world of graphene. Here, we briefly discuss the structure, novel properties and potential applications of graphene, and the motivation for this thesis. In Chapter 2, an overview of the DFT formalism adopted here is given. We clearly state the theorems of the formalism and the approximations used when performing calculations. We succinctly explain how the various quantities like total energies, forces, stresses etcetera are calculated within this formalism. We also discuss how phonon frequencies, eigenvectors, electron-phonon couplings are obtained by using density functional perturbation theory (DFPT), which calculates the full dynamical matrices through the linear response of electrons to static perturbations induced by ionic displacements. Calculations are done first using a fully ab-initio approach within the standard Born-Oppenheimer approximation, and then time-dependent perturbation theory is used to explore the effects of dynamic response. In Chapter 3, using such first-principles density-functional theory calculations, we determine the vibrational properties of ultra-thin n(1,2,...,7)-layer graphene films and present a detailed analysis of their zone-center phonons. We present the results (including structural relaxations, phonons, mode symmetries, optical activities) for bulk Graphite, single-layer graphene and ultrathin n-layer graphene films. and discuss the underlying physics of our main results together with a pictorial representation of the phonon modes. We demonstrate that a low-frequency (∼ 112 cm−1 ) optical phonon with out-of-plane displacements exhibits a particularly large sensitivity to the number of layers, although no discernible change in the interlayer spacing is found as n varies. Frequency shifts of the optical phonons in bilayer graphene are also calculated as a function of its interlayer separation and interpreted in terms of the inter-planar interaction. The surface vibrational properties of n-layer graphene films are presented in Chapter 4, which renders a detailed and thorough analysis of all the surface phonon modes by determining, classifying and identifying them accurately. The response of surface modes to the presence of adsorbed hydrogen molecules is determined. As an illustrative adsorbate, hydrogen is chosen here mainly because of its huge importance in fuel cell technology and as a molecular sensor. We demonstrate that a doubly degenerate surface phonon mode with low-frequency (~ 35cm−1)exhibits a particularly large sensitivity to the adsorption of hydrogen molecules, as compared to other surface modes. Futhermore, we show that a low-frequency (108.8 cm−1)bulk-like phonon with out-of-plane displacements is also very sensitive and gets upshifted by as much as 21 cm−1 due to this adsorption. In Chapter 5, we determine the adiabatic frequency shift of the and phonons in a monolayer graphene as a function of both electron and hole doping. The doping is simulated here to correspond to electrochemically gated graphene. Compared to the results for the E2g -Γ phonon (Raman G band), the results for the phonon are dramatically different, while those for the phonon are not so different. Furthermore, we calculate the frequency shifts, as a function of the charge doping, of the (K + ΔK) phonons responsible for the Raman 2D band –a key finger print of graphene, where [ΔK] is determined by the double resonance Raman process. Doping graphene with electron donating or accepting molecules is an interesting approach to introduce carriers into it, analogous to electrochemical doping accomplished in graphene when used in a field-effect transistor. In Chapter 6, we use first-principles density-functional theory to determine changes in the electronic structure and vibrational properties of graphene that arise from the adsorption of aromatic molecules such as aniline and nitrobenzene. Identifying the roles of various mechanisms of chemical interaction between graphene and the adsorbed molecules, we bring out the contrast between electrochemical and molecular doping of graphene. Our estimates of various contributions to shifts in the Raman active modes of graphene with molecular doping are fundamental to the possible use of Raman spectroscopy in (a)characterization of the nature and concentration of carriers in graphene arising from molecular doping, and (b) graphene-based chemical sensors. Graphene doped electrochemically or through charge-transfer with electron-donor and acceptor molecules, shows marked changes in electronic structure, with characteristic signatures in the Raman spectra. Substitutional doping, universally used in tuning properties of semiconductors, could also be a powerful tool to control the electronic properties of graphene. In Chapter 7, we present the structure and properties of boron and nitrogen doped graphenes, again using first-principles density functional theory. We demonstrate systematic changes in the carrier-concentration and electronic structure of graphenes with B/N-doping, accompanied by a stiffening of the G-band and change of the defect related D-band in the Raman spectra. Such n/p -type graphenes obtained without external fields or chemical agents should find device applications.