Graphene film has been produced on untreated Cu substrate by a chemical vapor deposition technique in ambient pressure with liquid ethanol serving as the carbon precursor. The obtained material has been subjected to morphological study, directly on Cu substrate, by means of optical microscopy, scanning electron microscopy, atomic force microscopy, and a detailed Raman analysis. As a benchmark material, graphene obtained on Cu by a conventional CVD from gaseous methane was used. This simple experimental setup has proved to enable obtaining large area graphene samples with nearly 100% substrate coverage and large domains of one carbon layer. As compared to graphene from gaseous precursor, the presented approach resulted in visibly more defects and impurities. These imperfections are due to more complex precursor molecular structure and lack of Cu pretreatment with hydrogen, the later cause being easy to eliminate in course of further optimization of the method. The described approach can be regarded as a viable, low-cost, and experimentally simple alternative for the existing techniques of producing large area graphene. By providing direct comparison with the conventional method, the paper's intention is to provide deeper insight and to fill gap in the understanding of mechanisms involved in graphene formation on copper.
In this paper energy bands and Berry curvature of graphene was studied. Desired Hamiltonian regarding the next-nearest neighbors was obtained by tight-binding model. By using the second quantization approach, the transformation matrix is calculated and the Hamiltonian of system is diagonalized. With this Hamiltonian, the band structure and wave function can be calculated. By using calculated wave function the Berry connection and Berry curvature of our system are calculated. Our results are exactly consistent with previous methods and also the Berry curvature throughout the Brillouin zone get zero.
The paper presents influence of diverse shapes and dimensions of carbon nanostructures on physical properties of polymer composites. Graphene nanoplatelets, carbon nanotubes, graphite nanofibers, and graphite microflakes have been investigated as fillers in polymethacrylate resin. Layers were deposited with printing techniques used in printed electronics technology such as screen printing and spray coating, both elaborated in our earlier works. Different sets of measurements have been performed for obtained layers with particular carbon nanofillers. Thickness and topography have been examined using optical profilometer. Morphology of nanostructures has been observed with scanning electron microscope. Moreover, sheet resistivity and optical transmission in visible wavelength have been measured. Also mechanical properties have been characterized for each polymer composite by conducting fatigue test which consisted of multiple bending cycles.
The paper presents results of the studies concerning aluminum-graphene composites produced with use of step technique; first mechanical alloying of Al and graphene powders and later intensive deformation by the high pressure torsion. As a result small, thin and round samples of composites, about 10 mm in diameter were achieved. For comparison similar samples not containing graphene were investigated. The X-ray diffraction, transmission electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy were applied to study composites structures and analyze graphene content and atomic bonds. The Raman spectroscopy method suggested multilayer graphene, which could also be identified as the defected nano-graphite as a component of the composite structure as well as some small content of the aluminum carbides. The highly dispersed microstructures of aluminum matrices were identified with the transmission electron microscopy, showing difference between the samples produced with the increased number of rotations, leading to the increased deformation realized. This method revealed carbon and aluminum oxides in large amounts which is interpreted as a surface effect. This method suggested also formation of the carbon-metal and carbon-metal- oxygen atomic bonds, which might partially result from formation of the carbides.
This contribution reports on theoretical studies of electronic transport through graphene nanoribbons in the two-terminal geometry. The method combines the Landauer-type formalism with Green's function technique within the framework of the standard tight-binding model. The aim of this study is to gain some insight on how fundamental electric current characteristics (conductance and shot noise) depend on interface conditions imposed by graphene nanoribbon/metal-electrode contact details. Calculations have been carried out for both end- and side-contact geometries, and metallic (zigzag-edge) as well as semiconducting (armchair-edge) graphene nanoribbons. It turns out that results for side-contacted systems depend on the ratio between the free-standing graphene nanoribbon length to that covered by the electrode. For sufficiently long nanoribbons the results start converging when this ratio exceeds 0.5. In the case of ferromagnetic contacts, the giant magnetoresistance coefficient is also discussed.
We investigate theoretically the electronic properties of graphene functionalized with nitrogen and boron atoms substituted into the graphene monolayer. Our study is based on the ab initio calculations in the framework of the density functional theory. We predict the dependence of the energy band gap, binding energy per atom, and the shift of the Fermi level on the concentration of dopants. Moreover, we examine the influence of the distribution of B/N atoms on the specified properties.
The ultimate physical limit approach is applied to the case of electrode nanostructures of double electric layer (DEL) supercapacitors (SCs) on the basis of advanced superionic conductors (AdSIC) required for the development of many high-tech directions. New nanoionic fundamentals (notion, criteria and estimations) are introduced and the ways for the creation of advanced carbon-based nanostructures suited for different types of SCs are proposed.
The aim of this study is to gain a deeper insight into the impact of geometrical dimensions (aspect ratio) and current direction (zigzag vs. armchair) on transport characteristics. It is found that there is a pronounced dependence of the giant magnetoresistance (in setups with 2 ferromagnetic electrodes), as well as the spin polarization of current (in the case of one paramagnetic and one ferromagnetic electrode) on the bias and gate voltages, meaning a possible electrical control of magnetic properties of these quantities.
In this paper using scanning electron microscope, contactless microwave electronic transport and the Raman spectroscopy we studied the properties of graphene deposited on GaN nanowires and compared it with the graphene deposited on GaN epilayer. The Raman micro-mapping showed that nanowires locally change the strain and the concentration of carriers in graphene. Additionally we observed that nanowires increase the intensity of the Raman spectra by more than one order of magnitude.
Elastic anisotropy and acoustic attenuation in bulk material consisting of consolidated graphene nanoplatelets are studied. The material was prepared by spark plasma sintering, and exhibits highly anisotropic microstructure with the graphene nanoplatelets oriented perpendicular to the spark plasma sintering compression axis. The complete tensor of elastic constants is obtained using a combination of two ultrasonic methods: the through-transmission method and the resonant ultrasound spectroscopy. It is shown that the examined material exhibits very strong anisotropy both in the elasticity (the Young moduli in directions parallel to the graphene nanoplatelets and perpendicular to them differ by more than 20 times) and in the attenuation, where the dissipative effect of the internal friction in the graphene nanoplatelets combines with strong scattering losses due to the porosity. The results are compared with those obtained for ceramic-matrix/graphene nanoplatelet composites by the same ultrasonic methods.
It is common to describe graphene as ideally flat plane, however there exists both theoretical and experimental evidence that it is most usual to find it in a rippled state. The ripples can be either induced by the substrate or formed spontaneously in suspended graphene. The lateral size of such features ranges between several and tens of nanometers with the height of up to 1 nm. It has been suggested that the presence of ripples could be one of the factors ultimately limiting mobility of carriers and that it may be also responsible, by introducing an effective gauge field, for the lack of weak localization observed in certain graphene samples. In the present contribution the transport properties of the rippled graphene are studied theoretically starting with the simple case of one-dimensional modulation. Using either single-band or the full sp^3 tight-binding Hamiltonians we compare and discuss the importance of two ripple-related mechanisms of scattering: the variation of interatomic distances and hybridization between π and σ bands of graphene.
Discussion of the origin of paramagnetic centres observed by electron paramagnetic resonance in graphene oxide (GO) and reduced graphene oxide (rGO) is done on the assumption that GO can be considered as a functionalized graphene. This leads to the conclusion that the narrow signal with g close to 2, observed for GO and thermally reduced GO, is due to paramagnetic centres localized on defects and exchange coupled to conduction electrons. Randomness of graphene modification results in variety of parameters of EPR signals. The broad signals observed in GO and rGO and ascribed to magnetic clusters on the zig-zag edge states indicate that the edge magnetism can be preserved by functionalization.
Due to its peculiar properties graphene is a good candidate for sensor materials. Therefore, it is important to study influence of different fluids on graphene layer. The presented studies showed pinning of NaCl microcrystals to graphene surface after immersing graphene in NaCl solution and subsequent careful rinsing with distilled water. The atomic force microscopy images revealed presence of many NaCl-related structures over 100 nm high on graphene surface. The electron spin resonance spectrum for magnetic field perpendicular to the graphene layer consisted of several lines originating from NaCl. The pinning of NaCl microcrystals resulted in increase of electron scattering, as confirmed by the Raman spectroscopy (the increase of intensity of D and D' bands) and weak localization measurement (the decrease of coherence length).
We studied one-dimensional electron transport in a system composed of two monolayer graphene sheets with an optional arrangement of different constant rectangular electrostatic potential barriers between them. We derived a generalized transfer matrix for the electron which passes through this system. Finally, we examined our model by applying it on a well known rectangular shape constant potential barrier and we obtained the same result from our method similar to the others.
Theoretical analysis of the electron excitations in graphene on substrate by twisted, linear and circular polarization light is presented. We use a model of graphene with constant Rashba spin-orbit interaction. In this case, the band structure of electrons includes four energy bands. The main objective of this work is to compare light absorptions in graphene for different kinds of light, namely, twisted (with nonzero orbital angular momentum) and linear polarized light. The orbital angular momentum light is characterized by some parameters q and l, which can modify the response, while for the linear polarization, the absorption is modified only in the region determined by the Rashba spin-orbit coupling α.
The effect of three types of topological defects, single vacancy, double vacancy and the Stone-Thrower-Wales defect on the atomic arrangement in a single graphitic layer is studied using computer simulations. The topological defects were positioned on the perfect hexagonal graphitic layer 20 Å in diameter with different distance from the layer edge and then the geometry of the system was independently optimized using the reactive bond order potential, the semi-empirical quantum-chemical PM7 and the density functional theory method. Curvature and the distortion of the graphitic layer caused by the defects are analyzed and their influence on the pair correlation function is discussed.
The crucial measurements aspects of X-ray photoelectron spectroscopy, such as chemical state analysis, depth profiling, mapping, and thickness calculation have been presented. The metal alloys, Ti_2O_5, graphene and type-II InAs/GaSb superlattice structures have been examined by using the new Thermo Scientific K-Alpha X-ray Photoelectron Spectrometer.
The classical, electrodynamic definition of the ampere is incoherent with quantum electrodynamics. The problem, although insignificant at the macroscopic scale, manifests clearly at the nanostructure level, where the consistently quantum approach is necessary. In this paper, we consider the Casimir effect to quantify inconsistencies that could have resulted if electric metrology of microstructures and nanostructures (including graphene) had been based on classical electrodynamics and the current SI definition of the ampere. The issue is discussed in the context of the New SI program, where the base electric unit is to be redefined by fixing the numerical value of the elementary charge. The conclusion supports the case for a prompt redefinition of the base electric unit, which will make the electric metrology in general, and the electric metrology of nanostructures in particular, coherent with the international system of units.
The paper describes the design, development, and investigation of a new type of Hall-effect sensors of a magnetic field made of graphene. The epitaxial growth of high-quality graphene structures was performed using a standard hot-wall CVD reactor, which allows for easy integration with an existing semiconductors production technologies. The functional properties of developed Hall-effect sensors based on graphene were investigated on special experimental setup utilizing Helmholtz coils as a source of reference magnetic field. Monolayer and quasi-free-standing bilayer graphene structures were tested. Results presented in the paper indicate that graphene is very promising material for development of Hall-effect sensors. Developed graphene Hall-effect sensor exhibit highly linear characteristics and high magnetic field sensitivity.
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