Basic physics teaches us that the frictional force (lateral force) needed to move objects on surfaces are proportional to load (normal force) – Amonton’s Laws. In tribology, this force is proportional to contact area, whereas Amonton is just a special case for contact area scaling with load. Such established laws do not seem to apply to small drops on flat, smooth surfaces in which frictional forces have an inverse relation to contact area and have time component prior to movement. Such phenomena can be explained by Shanahan-deGennes were intermolecular forces are considered for a deformed surface. Graphene is a special case where no time component is observed and frictional forces are attributed to its chemical homogeneity and stability. In the second part of this thesis, graphene is considered as nanofiller to build up polymer nanocomposites via Layer by Layer (LbL). Graphene Nanoribbons derived from multi-walled carbon nanotubes (MWCNT) offers a special case for thermoplastic polyurethane nanocomposites in that of thermally activated twisting morphology influences nanocomposite properties. Finally an electric field driven transdermal hydrogel drug delivery device has been demonstrated by just using CNTs, polyvinyl-borax gel and a CNT membrane

Graphene-based materials have generated tremendous interest in the past decade. Manipulating their characteristics using wet-chemistry methods holds distinctive value, as it provides a means towards scaling up, while not being limited by yield. The majority of this thesis focuses on the surface functionalization of graphene oxide (GO), which has drawn tremendous attention as a tunable precursor due to its readily chemically manipulable surface and richly functionalized basal plane. Firstly, a room-temperature based method is presented to reduce GO stepwise, with each organic moiety being removed sequentially. Characterization confirms the carbonyl group to be reduced first, while the tertiary alcohol is reduced last, as the optical gap decrease from 3.5 eV down to 1 eV. This provides greater control over GO, which is an inhomogeneous system, and is the first study to elucidate the order of removal of each functional group. In addition to organically manipulating GO, this thesis also reports a chemical methodology to inorganically functionalize GO and tune its wetting characteristics. A chemical method to covalently attach fluorine atoms in the form of tertiary alkyl fluorides is reported, and confirmed by MAS 13C NMR, as two forms of fluorinated graphene oxide (FGO) with varying C/F and C/O ratios are synthesized. Introducing C-F bonds decreases the overall surface free energy, which drastically reduces GO’s wetting behavior, especially in its highly fluorinated form. Ease of solution processing leads to development of sprayable inks that are deposited on a range of porous and non-porous surfaces to impart amphiphobicity. This is the first report that tunes the wetting characteristics of GO. Lastly as a part of a collaboration with ConocoPhillips, another class of carbon nanomaterials - carbon nanotubes (CNTs), have been inorganically functionalized to repel 30 wt% MEA, a critical solvent in CO2 recovery. In addition to improving the solution processability of CNTs, composite, homogeneous solutions are created with polysulfones and polyimides to fabricate CNT-polymer nanocomposites that display contact angles greater than 150o with 30 wt% MEA. This yields materials that are inherently supersolvophobic, instead of simply surface treating polymeric films, while the low density of fluorinated CNTs makes them a better alternative to superhydrophobic polymer materials.

Thermal annealing 4H-SiC(0001) substrates to produce epitaxial graphene on Si-terminated SiC was performed using five different procedures, i.e. direct and indirect current heating at different based pressures and a temperature of about 1300 . The aim is to study the effects of graphene growth under different conditions and also to produce large homogeneous graphene. To investigate the prepared samples, two surface analytical techniques, i.e. low energy electron microscopy (LEEM) and photoelectron spectroscopy (PES) have been used. LEEM was first used to observe the surface morphologies of the prepared samples. In combination with LEEM instrument, low energy electron diffraction (LEED) was used to verify the existence of graphene on SiC substrate. The number of graphene layer was determined by collecting electron reflectivity at different electron energies. The number of dips observed in the electron reflectivity curve corresponds to the number of graphene layer. The experimental results obtained from LEEM and LEED have demonstrated that a film consisting of fairly large domains of 1 and 2 monolayer (ML) graphene was obtained by direct current heating of SiC under high vacuum (HV) condition with the based pressure of 10-6 Torr. A domain size in the range of up to about 5 to 10 μm have been observed. Meanwhile another graphene film prepared by the same method and the same temperature but under ultra high vacuum (UHV) condition with the based pressure of 10-10 Torr has much smaller domain size of 1 ML graphene compared to that grown under HV condition. We therefore suggested that the based pressure during the graphene growth has a strong influence on the morphology of graphene. This is because the Si evaporation rate is suppressed when heated in a high pressure environment, which normally leads to the improvement of the surface quality. The suppression of the Si evaporation rate has also been verified by a result obtained from the other sample directly heated under much higher based pressure, i.e. in an argon (Ar) environment of 1 atm. In addition to LEEM and LEED, the existence of graphene on SiC substrate has also been verified by the PES measurement. The C1s spectrum of graphene sample grown on SiC(0001) substrate showed three components, i.e. bulk SiC, graphene (G) and the buffer layer (B) located at 283.7 eV, 284.5 eV and 285.1 eV, respectively. The intensity ratios of the three components in the C1s spectrum were also used to estimate the number of graphene layer. The estimated number of graphene layer corresponds to the result obtained from LEEM.

The atomic and electronic structures of Au-intercalated graphene buffer layer on SiC(0001) surface were investigated using first-principles calculations. The unique Dirac cone of the graphene near K point reappeared as the buffer layer was intercalated by Au atoms. Coherence interfaces were used to study the mismatch and strain at the interfaces. Our calculations showed that the strain at graphene/Au and Au/SiC(0001) interfaces also played a key role in the electronic structures. Futhermore, we found that at Au coverage of 3/8 ML, Au intercalation leads to strong n-type doping of graphene. At 9/8 ML, it exhibited weak p-type doping, meaning that graphene is not fully decoupled from substrate. The shift of Dirac point resulting from electronic doping is not only due to different electronegativities but also strains at the interfaces. Our calculated positions of Dirac points are consistent with those observed in the ARPES experiment [Isabella Gierz et al., Phys. Rev. B 81, 235408 (2010).].

The graphene-polymer SA thin film using solution blending method and atomic layer graphene as saturable absorber (SA) used to generate femtosecond laser pulse were measured. Stable soliton-like pulses with the pulsewidth of 403 fs and 432 fs, the spectral linewidth of 6.32 nm and 6.16 nm, and the time-bandwidth product of 0.315 and 0.329 using graphene-PVA film and atomic layer graphene as SA were achieved, respectively, in mode-locked Er-doped fiber ring laser. The graphene-PVA SA suffered from larger loss caused by graphene flake aggregating, while the atomic layer graphene had smaller nonsaturable loss which exhibited lower mode locking threshold power. Atomic layer graphene also had stable fabricated process and controllable modulation depth depended on its layer numbers. To compare the mode locking performance of single wall carbon nanotubes (SWCNTs) and graphene SA, the same solution blending fabricated sample was used. Under similar nonsaturable loss and modulation depth, the SWCNTs SA with optimized concentration of 0.5wt% and thickness of 188£gm had shortest pulsewidth of 440 fs and 3-dB spectral linewidth of 6 nm. The shortest pulsewidth of 403 fs and broad spectral linewidth of 6.32 nm was obtained using graphene SA with concentration of 6.25wt% and thickness of 18£gm. Graphene has broad band absorbance and larger modulation depth, the experimental result indicates that graphene SA can generate shorter pulse and has chance to become the potential candidate of SA.

Thesis (M.S.)--Rutgers University, 2009. / "Graduate Program in Physics and Astronomy." Includes bibliographical references (p. 65-68).

Thesis (Ph. D.)--University of California, Riverside, 2009. / Includes abstract. Available via ProQuest Digital Dissertations. Title from first page of PDF file (viewed March 19, 2010). Includes bibliographical references. Also issued in print.

The main goal of this project was to write a review about different quantum Hall effects. This review focuses on the integer and relativistic quantum Hall effect in graphene. The quantum Hall effect is a newly discovered phenomena that was experimentally observed in 1980 and relativistic quantum Hall effect in graphene was observed in 2005. This project takes a theoretical approach to describe the quantum Hall effects and graphene itself. Experiments has shown that for very strong magnetic fields applied to 2D systems, the Hall resistance becomes quantized, RH=h/ne2 and only depends on the charge of the electron and Planck's constant, two fundamental constants of nature. This sets a new standard on how to define resistance, and gives a good tool for precise measurements of the fine structure constant.

In this thesis we investigate the electronic band structures and the correlations in chirally (ABC) stacked N-layer graphene with N ≥ 2. We use ab initio density-functional theory and k · p theory to fit the parameters of a p-band tightbinding model. External potential differences between top and bottom layers are strongly screened by charge transfer but still open an energy gap at overall neutrality. Perpendicular magnetic field drives the system into the quantum Hall region with 4N-fold zero energy Landau levels. We predict that Coulomb interactions spontaneously break the SU(4N) symmetry and drive quantum Hall effects at all integer fillings n from −2N to 2N with exotic spin and pseudospin polarizations. Based on mean-field theory and perturbative renormalization group analysis, we predict that the ground state of bilayer graphene spontaneously breaks inversion symmetry for arbitrarily weak electron-electron interactions and conclude that this instability is not suppressed by quantum fluctuations but that, because of trigonal warping, it may occur only in high quality suspended bilayers. Remarkably flat conduction and valence bands that touch at charge neutrality point and Bloch states with large pseudospin chirality combine to make the bilayer graphene gapless band state strongly susceptible to a family of broken symmetry states in which each spinvalley flavor spontaneously transfers charge between layers. We explain how these states are distinguished by their charge, spin, and valley Hall conductivities, by their orbital magnetizations, and by their edge state properties. We further analyze how these competing states are influenced by Zeeman fields that couple to spin and by interlayer electric fields that couple to layer pseudospin, and comment on the possibility of using response and edge state signatures to identify the character of the bilayer ground state experimentally. We demonstrate that similar insulating broken symmetry states and spontaneous topological orders also occur in bilayer’s thicker cousins, chirally stacked multilayer graphene systems. / text

In a strong magnetic field, the psuedospin chirality of bilayer graphene’s low energy bands results in degenerate, zero energy n=0 and n=1 Landau or- bital states. In this thesis, we find that in addition to endowing states with energetic broadness disorder strongly mixes the zero energy orbitals of the lowest Landau level. We study the dependence of mixing and conductivity on inter-layer bias. Quantum Hall ferromagnetic states emerge when electronic interactions are included at the mean-field level. We study the character of ground states and quasiparticle excitations in the context of orbital degen- eracy and in the presence of interactions with the filled Dirac sea of states. Lastly, we study the effect of interactions in ABA-stacked trilayer graphene, and discover a metal-insulator transition and a separate propensity to break mirror symmetry in certain areas of parameter space. / text