Fabrication of graphene nanostructures it is important for both investigating their intrinsic physical properties and applying them into various functional devices. In this work we present a study on atomic layer deposition (ALD) of Al2O3 to produce patterned graphene through area-selective chemical vapor deposition (CVD) growth. A systematic parametric study was conducted to determine how the number of cycles and the purging time affect the morphology and the electrical properties of both graphene and Al2O3 layers.

The discovery of graphene based materials has led to significant advancement in several different areas. The large surface area, nanoporous structure and availability of delocalized electron network provide a unique opportunity for purification of solvents via adsorption, absorption or simple trapping. This makes graphene based materials as potential candidates for purification and desalination of water. Here we report synthesis of 3D porous network of oxidized graphene for purification of sea water. The membranes fabricated using these frameworks are hierarchically linked intrinsically defected oxidised graphene sheets by long micro-channels and capable of filtering small ions such as Na+ and Cl-. These are easy to fabricate, reusable and economically viable especially for point of use application. We finally show a fabricated device using membrane made from these 3D networks of oxidized graphene.

Defect formation in the samples of graphene, graphene oxide and silicon irradiated with Ar cluster and highly-charged ion irradiations were studied. Ar cluster ions, with acceleration energy E = 30 kV (Exogenesis nAccel00, Boston, USA) and total Ar cluster ion fluences ranged from 1x109 cm-2 to 1x1013 cm-2 were directed toward various surfaces. Highly-charged ions (HCI) bombardment on surfaces with highly charged Xeq+ (q = 22) was employed at Eurasian National University, Kazakhstan, using a DC-60 cyclotron accelerator. Multi-layer graphene oxide, single-layer graphene- (SLG), few-layer of graphene (FLG) and polished Si are used for irradiation experiments. The study of irradiated samples was conducted by Raman spectroscopy, atomic force microscopy (AFM). Uniformly distributed defects and craters were observed on the surfaces of graphene, graphene oxide and silicon irradiated with cluster and HCI beams in our experiments. Ab-initio density-functional theory (DFT) was used to study point defects and molecular-dynamics (MD) simulations were used for studying formation of craters due to gas cluster ion impacts in graphene. The results of simulations were compared with experimental craters and surface shape.

The behavior of nanostructures under high strain-rate conditions has been object of interest in recent years. For instance, recent experimental investigations showed that at high velocity impacts carbon nanotubes can unzip resulting into graphene nanoribbons. Carbon nanoscrolls (CNS) are among the structures whose high impact behavior has not yet been investigated. CNS are graphene membranes rolled up into papyrus-like structures. Their unique open-ended topology leads to properties not found in close-ended structures, such as nanotubes. Here we report a fully atomistic reactive molecular dynamics study on the behavior of CNS colliding at high velocities against solid targets. Our results show that the velocity and scroll axis orientation are key parameters to determine the resulting formed nanostructures after impact. The relative orientation of the scroll open ends and the substrate is also very important. We observed that for appropriate velocities and orientations, the nanoscrolls can experience large structural deformations and large-scale fractures. We have also observed unscrolling (scrolls going back to planar or quasi-planar graphene membranes), unzip resulting into nanoribbons, and significant reconstructions from breaking and/or formation of new chemical bonds. Another interesting result was that if the CNS impact the substrate with their open ends, for certain velocities, fused scroll walls were observed.

Recent studies on graphene hydrogenation processes showed that hydrogenation occurs via island growing domains, however how the substrate can affect the hydrogenation dynamics and/or pattern formation has not been yet properly investigated. In this work we have addressed these issues through fully atomistic reactive molecular dynamics simulations. We investigated the structural and dynamical aspects of the hydrogenation of graphene membranes (one-side hydrogenation, the so called graphone structure) on different substrates (graphene, few-layers graphene, graphite and platinum). Our results also show that the observed hydrogenation rates are very sensitive to the substrate type. For all investigated cases, the largest fraction of hydrogenated carbon atoms was for platinum substrates. Our results also show that a significant number of randomly distributed H clusters are formed during the early stages of the hydrogenation process, regardless of the type of substrate. These results suggest that, similarly to graphane formation, large perfect graphone-like domains are unlikely to be formed. These findings are especially important since experiments have showed that cluster formation influences the electronic transport properties in hydrogenated graphene.

To measure the Raman scattering spectrum of a monolayer graphene sample, we describe the design and development of a high-efficiency optical measurement device for operation within the small bore of a high-power magnet at low temperature. For the high-efficiency measurement of light emitted from this small region, we designed a compact confocal optics with lens focusing and tilting systems, and used a piezodriven translation stage that allows micron-scale focus control of the sample position. In addition, we show a detailed technique of adjustment of optical axes, and explain the importance of the focusing and tilting systems. The operation of the device was confirmed by Raman scattering measurements of monolayer graphene on quartz glass with a high signal-to-noise ratio. Though the light collection efficiency of the device is about 240-fold smaller than that of a conventional optical microscope, the device has a sufficient collection efficiency for detecting the Raman scattering light of monolayer graphene.

Graphenic carbon (GC) x-ray transmission windows for EDX and XRF applications with a high transparency for x-rays below 2.5 keV have been fabricated on 6 inch wafers with a CMOS-compatible CVD process. GC windows with an open diameter of 7.4 mm and a thickness of 770 nm withstand up to 6.5 bars of differential pressure. A high transmissivity of 40 % for fluorine Kα (0.677 keV) radiation is demonstrated for a GC thickness of 650 nm. The GC membranes outperform beryllium (Be) windows, in terms of higher x-ray transmission and better mechanical stability while avoiding the toxicity of Be. Optical profilometry has been employed to visualize a large deformation of the GC layer during the window fabrication. This seems to limit the thickness of the GC windows that can currently be fabricated. A two-step growth process can overcome these limitations and windows with a thickness of up to 6 µm have been realized.

Carbon nanotubes (CNTs), with exceptional thermal and mechanical properties as well as inherently high surface area, are an attractive candidate for integrating into thermal structures of advanced power electronics. Growth of vertically aligned carbon nanotubes (VACNTs) directly onto copper (Cu) substrates is a promising approach to apply CNTs as novel thermal interface materials (TIMs) in electronics packaging. However, compared to growing CNTs on conventional inert substrates such as SiO2, direct growth of controllable CNT arrays onto Cu substrates is significantly more challenging due to the diffusion of metallic catalyst into the substrate during growth. By depositing an appropriate buffer layer on the Cu substrate surface, VACNTs of good alignment and high quality were reproducibly synthesized on the Cu substrate via the chemical vapor deposition (CVD) method in this study. The effect of different buffer layers on the CNT growth, nanotube structure and quality was investigated (SEM, Raman), particularly in terms of the interfacial properties between the CNT array and Cu substrate (Tensile compression force tester, Laser Flash Analysis). Our experimental results indicated that the buffer layer material, deposition method, and thickness play a key role in regulating the CNT layer growth/structure, leading to variable mechanical and thermal properties. The fundamental understanding thus obtained allows the successful synthesis of VACNT on copper substrates with desired structure and properties.

Novel flexible composites were received by modification of polyurethane-carbon fiber interface. The modification was done by carbon nanotube grafting onto a surface of the fiber. The almost inevitable grafting-induced deterioration of the fiber properties was avoided due to sophisticated grafting technique, which includes introduction of a protective aluminium oxide layer. Re-enforced composites were fabricated with polyurethane as a matrix. The measurement of interfacial shear strength (IFSS) was used for estimation of polymer-fiber interface properties. It was shown that IFSS increased more than twice due to nanotube grafting. Thermal conductivity and mechanical properties enhancement was registered for composites with modified interface. Significant improvement of delamination resistance was proven for composites with modified polymer-fiber interface.

Graphene quantum dots (GQDs), a nano version of graphene whose interesting properties that distinguish them from bulk graphene, have recently received significant scientific attention. The quantum confinement effect referring to the size-dependence of physical and chemical properties opens great possibility in the practical applications of this material. However, tuning the size of graphene quantum dots is still difficult to achieve. Here, an edge-etching mechanism which is able to tune the size of GQDs in a quasi-continuous manner is discovered. Different from the ‘unzipping’ mechanism which has been adopted to cut bulk graphitic materials into small fragments and normally cut through the basal plane along the ‘zig-zag’ direction where epoxy groups reside, the mechanism discovered in this research could gradually remove the peripheral carbon atoms of nano-scaled graphene (i.e. GQDs) due to the higher chemical reactivity of the edge carbon atoms than that of inner carbon atoms thereby tuning the size of GQDs in a quasi-continuous fashion. It enables the facile manipulate of the size and properties of GQDs through controlling merely the reaction duration. It is also believed the as discovered mechanism could be generalized for synthesizing various sizes of GQDs from other graphitic precursors (e.g. carbon fibres, carbon nanotubes, etc).

Efficient water desalination constitutes a major challenge for the next years and reverse osmosis membranes will play a key role to achieve this target. In this work, a high-performance reverse osmosis nanocomposite membrane was prepared by interfacial polymerization in presence of multiwalled carbon nanotubes. The effect of carbon nanotubes on the chlorine resistance, antifouling and desalination performance of the nanocomposite membranes was studied. We found that the addition of carbon nanotubes not only improved the membrane performance in terms of flow and antifouling, but also inhibited the chlorine degradation of these membranes. Several reports have acknowledged the benefits of adding carbon nanotubes to aromatic PA nanocomposite membranes, but little attention has been paid to the mechanisms related to the improvement of flow rate, selectivity and chlorine tolerance. We carried out a comprehensive study of the chemical and physical effects of carbon nanotubes on the fully crosslinked polyamide network. The chemical structure, chlorine resistance and membrane degradation was studied by several analytical techniques, permeation and fouling studies, whereas the microstructure of the nanocomposite was studied by small and wide angle X-ray scattering, high resolution transmission electron microscopy, and molecular dynamics. We found that the addition of the nanotube affects the interfacial polymerization, resulting in a polymer network with smaller pore size and higher sodium and chlorine rejection. We simulated the hydration of the membrane in seawater and found that the radial distribution function of water confined in the pores of the nanocomposite membrane exhibited smaller clusters of water molecules, thus suggesting a dense membrane structure. We analysed the network mobility and found that the nanotube provides mechanical stability to the polymer matrix. This study presents solid evidence towards more efficient and robust reverse osmosis membranes using carbon nanotubes as mechanical reinforcing and chlorine protection additive.

The Polymer Electrolyte Membrane Fuel Cells (PEMFCs) platinum catalyst’s susceptibility to poisoning by carbon monoxide (CO) reduces its output power. In an effort to diminish poisoning, gold and platinum nanoparticles were incorporated onto partially reduced graphene oxide (Au/Pt-prGO) sheets to reduce both nanoparticle aggregation and the amount of precious metal needed. Applying this material onto the electrodes and Nafion membrane of a PEMFC was hypothesized to increase CO tolerance as well as power output.

Aliquots of graphene oxide (GO) were functionalized with platinum and/or gold nanoparticles using a simple desktop synthesis at room temperature. Partial reduction with NaBH4 maintained hydrophilic solubility. Test solutions applied to electrodes and to electrodes + Nafion membrane were first tested in a PEM fuel cell with a pure H2 gas feed and then repeated with a H2 gas feed containing 1000 ppm of CO. Test arrangements averaged doubling the output power of the poisoned control, with the most effective yielding an output power ∼250% that of the poisoned control. Additionally, each system’s poisoned output power (PP) was compared to its highest possible output power (PM), with the most effective setup showing no reduction in output power, even with a H2 gas feed containing 1000 ppm of CO. Thus, this offers promise of a simple, cost-effective method of both improving PEMFC power output while reducing or even eliminating CO poisoning at room temperature.

There is pressing need in computation of a universal phase change memory consolidating the speed of RAM with the permanency of hard disk storage. A potentiated scanning tunneling microscope tip traversing the soliton separating a metallic, ABA-stacked phase and a semiconducting ABC-stacked phase in trilayer graphene has been shown to permanently transform ABA-stacked regions to ABC-stacked regions. In this study, we used density functional theory (DFT) calculations to assess the energetics of this phase-change and explore the possibility of organic functionalization using s-triazine to facilitate a reverse phase-change from rhombohedral back to Bernal in graphene trilayers. A significant deviation in the energy per simulated atom arises when s-triazine is adsorbed, favoring the transformation of the ABC phase to the ABA phase once more. A phase change memory device utilizing rapid, energy-efficient, reversible, field-induced phase-change in graphene trilayers could potentially revolutionize digital memory industry.

Measurements of the induced acoustoelectric (IAEC) current in graphene subjected to a surface acoustic wave (SAW) discovered a quantisized character of acoustoelectric current at low bias voltage (Vbias) . The quantisized nature of IAEC has been obtained in all measurements as a result of interaction of SAW and an applied an external electric field. The acoustoelectric currents were studied near the point of electrical neutrality at room temperature. Raman spectra of graphene under the in-situ SAW influence and at an external electric field bias are presented.