Electronic Properties Of Carbon Research Articles

First-principles calculations to investigate structural, mechanical and electronic properties of carbon (tP8) allotrope under high-pressure

The structural stability, electronic and mechanical attributes of the tetragonal carbon (tP8) allotrope at high-pressure are examined in the proposed research. The crystal structure of tP8 carbon is different and possesses unusual properties owing to electron localisation. Moreover, tP8 carbon allotrope exhibits remarkable mechanical stability and resilience, making it a strong contender for various applications owing to its plastic deformation and resistance to fracture. Furthermore, the results of the current work show that the band gap of tP8 carbon increases under high pressures, making it a useful material for nanoelectronic device applications. The present report on high-pressure studies of tP8 carbon will pave the way for novel applications in semiconductor technology and high-pressure material applications.

Rational Design of Carbon Nitride Materials by Supramolecular Preorganization of Monomers

AbstractThe control over the chemical and electronic properties of carbon nitride‐based materials is highly challenging due to limitations of the traditionally used solid‐state reaction. Tailoring parameters, such as morphology, surface area, or energy band positions, in this kind of materials is essential for the improvement of the overall performance in a given application, namely photo‐ or electrocatalysis, sensing, or water treatment, amongst others. The supramolecular preorganization of carbon‐nitrogen based monomers via non‐covalent interactions prior to the thermal condensation has made it possible to design graphitic carbon nitride‐like (CN) materials and target specific properties. In this review, we discuss the latest developments in the synthesis of CN and other carbon‐based materials from the supramolecular preorganization of monomers and the consequences on the photocatalytic performance. The monomer sequence, solvent, and reaction conditions which determine the final structure of the supramolecular assembly, and therefore the final CN properties after calcination, are thoroughly discussed.

BNC nanoshells: a novel structure for atomic storage

Quantum molecular dynamics (QMD) and density functional theory are employed in this work in order to study the structural and electronic properties of carbon, boron nitride or hybrid BNC nanoshells. The studied nanoshells can be formed by stacking two zigzag graphene nanoribbons, two zigzag boron nitride nanoribbons or one zigzag graphene nanoribbon on a boron nitride nanoribbon. In all cases only one of the edges of the ribbon is passivated, while the other one is left unpassivated. Our QMD results show that these nanoribbons collapse just a few femtoseconds after the beginning of the simulation, forming a coalesced structure in the shape of a shell. Our band structure calculations revealed that this structures may be metallic or semiconductor, depending on its stoichiometry. Furthermore, a spin splitting for energies near the Fermi level is predicted for both the pure carbon and the hybrid BNC-nanoshell systems. We further show that when a transverse electric field is applied to these systems, the nanoshell structure tends to open up. This effect can lead to the application of these nanoshells for molecular storage. As a proof of concept, We investigate this storage effect for the H2 molecule.

Physical Properties of C-Si Alloys in C2/m Structure**Supported by the Natural Science Foundation of China under Grant No. 61474089, Open Fund of Key Laboratory of Complex Electromagnetic Environment Science and Technology, China Academy of Engineering Physics under Grant No. 2015-0214. YY.K

Using the first principles calculations based on density functional theory, the crystal structure, elastic anisotropy, and electronic properties of carbon, silicon and their alloys (C12Si4, C8Si8, and C4Si12) in a monoclinic structure (C2/m) are investigated. The calculated results such as lattice parameters, elastic constants, bulk modulus, and shear modulus of C16 and Si16 in C2/m structure are in good accord with previous work. The elastic constants show that C16, Si16, and their alloys in C2/m structure are mechanically stable. The calculated results of universal anisotropy index, compression and shear anisotropy percent factors indicate that C-Si alloys present elastic anisotropy, and C8Si8 shows a greater anisotropy. The Poisson’s ratio and the B/G value show that C8Si8 is ductile material and other four C-Si alloys are brittle materials. In addition, Debye temperature and average sound velocity are predicted utilizing elastic modulus and density of C-Si alloys. The band structure and the partial density of states imply that C16 and Si16 are indirect band gap semiconductors, while C12Si4, C8Si8, and C4Si12 are semi-metallic alloys.

First-principles study of nanotubes within the tetragonal, hexagonal and dodecagonal cycle structures

A systematic study has been done on the structural and electronic properties of carbon, boron nitride and aluminum nitride nanotubes with structure consisting of periodically distributed tetragonal (T ≡A2X2), hexagonal (H ≡A3X3) and dodecagonal (D ≡A6X6) (AX=C2, BN, AlN) cycles. The method has been performed using first-principles calculations based on density functional theory (DFT). The optimized lattice parameters, density of state (DOS) curves and band structure of THD-NTs are obtained for (3, 0) and (0, 2) types. Our calculation results indicate that carbon nanotubes of these types (THD-CNTs) behave as a metallic, but the boron nitride nanotubes (THD-BNNTs) (with a band gap of around 4eV) as well as aluminum nitride nanotubes (THD-AlNNTs) (with a band gap of around 2.6eV) behave as an semiconductor. The inequality in number of atoms in different directions is affected on structures and diameters of nanotubes and their walls curvature.

First-principles investigation of carbon substitution for lead in ferroelectric lead titanate

ABSTRACTLead titanate, a room-temperature ferroelectric, dielectric material, is of great interest for technological applications. Defects play an important role upon its properties, such as remnant polarization, motion of domain walls, dielectric constant and leakage current, and organic species present during growth make carbon a key impurity. This paper presents a first principles study of the structural and electronic properties of carbon substituting for lead in tetragonal lead titanate. Highly characteristic vibrational modes are predicted to provide a route to experimental identification.

Nitrogen-Doped Activated Carbon-Based Ammonia Sensors: Effect of Specific Surface Functional Groups on Carbon Electronic Properties

Wood-based commercial activated carbon (BAX) and its oxidized counterpart (BAX-O) were treated with melamine and then heated at 450 °C in nitrogen. Further oxidation with nitric acid was also applied. The carbons were tested for ammonia sensing (45–500 ppm of NH3). Even though all samples exhibit p-type conduction, their exposure to NH3 led to different electrical outcomes. It was found that the electronic and transport properties of the carbons strongly depend on the type of nitrogen groups/surface defects, their concentration, and distribution in the carbon matrix. Pyridines and nitropyridines are the most important. A competition between the structural and chemical features of the carbons as those governing the sensing signals was observed. Exposure to ammonia altered the surface chemistry of the samples, and therefore their electrical properties. When sensitivity to H2S was tested to evaluate the selectivity of our sensors, the results showed that the chips are selective to NH3 in terms of the respons...

Influence of oxygen impurity on electronic properties of carbon and boron nitride nanotubes: A comparative study

Influence of oxygen impurity on electronic properties of carbon and boron nitride nanotubes (CNTs and BNNTs) is systematically studied using first principle calculations based on density functional theory. Energy band structures and density of states of optimized zigzag (5, 0), armchair (3, 3), and chiral (4, 2) structures of CNT and BNNT are calculated. Oxygen doping in zigzag CNT exhibits a reduction in metallicity with opening of band gap in near-infrared region while metallicity is enhanced in armchair and chiral CNTs. Unlike oxygen-doped CNTs, energy bands are drastically modulated in oxygen-doped zigzag and armchair BNNTs, showing the nanotubes to have metallic behaviour. Furthermore, oxygen impurity in chiral BNNT induces narrowing of band gap, indicating a gradual modification of electronic band structure. This study underscores the understanding of different electronic properties induced in CNTs and BNNTs under oxygen doping, and has potential in fabrication of various nanoelectronic devices.

Structural, Elastic, and Electronic Properties of a New Phase of Carbon* *Supported by the National Natural Science Foundation of China under Grant Nos. 61006028 and 61204044

Based on density function theory with the ultrasoft pseudopotential scheme in the frame of the local density approximation and the generalized gradient approximation, the structural, elastic, and electronic properties of carbon with P2221 phase have been systematically studied in this paper. The calculated results show that the P2221 phase of carbon is mechanically stable and dynamically stable at ambient pressure. The anisotropy studies of Young's modulus, Poisson's ratio, shear anisotropic factor, the percentage of elastic anisotropy for bulk modulus, the percentage of elastic anisotropy for shear modulus and the universal anisotropic index show that P2221 phase of carbon exhibits anisotropy. In addition, P2221 phase is an indirect semiconductor with bandgap of 3.423 eV. But, the band gap of P2221 phase for carbon increase with increasing pressure.

Tuning Electronic Structures of BN and C Double‐Wall Hetero‐Nanotubes

First principle calculations based on density functional theory with the generalized gradient approximation were carried out to investigate the energetic and electronic properties of carbon and boron nitride double‐wall hetero‐nanotubes (C/BN‐DWHNTs) with different chirality and size, including an armchair (n, n) carbon nanotube (CNT) enclosed in (m, m) boron nitride nanotube (BNNT) and a zigzag (n, 0) CNT enclosed in (m, 0) BNNT. The electronic structure of these DWHNTs under a transverse electric field was also investigated. The ability to tune the band gap with changing the intertube distance (di) and imposing an external electric field (F) of zigzag DWHNTs provides the possibility for future electronic and electrooptic nanodevice applications.

Pd nanoparticles supported on phenanthroline modified carbon as high active electrocatalyst for ethylene glycol oxidation

Modified carbon is fabricated by applying phenanthroline as nitrogen source and used as support (PMC) to immobilize Pd nanoparticles. Because the nitrogen-doping not only changes physicochemical and electronic properties of carbon but also serves as basic or coordination sites to stabilize and produce additional electronic activation for Pd, the Pd/PMC exhibits excellent electrochemcial performance for ethylene glycol oxidation. Compared to conventional Pd/C catalyst, the Pd/PMC catalyst has a larger electrochemically active surface area, 50mV more negative onset potential, 1.77 times oxidation current and superior stability.

Stability and electronic properties of carbon in α-Al2O3

The stability and electronic properties of carbon in α-Al2O3 are investigated using density functional theory. In the host lattice, the substitutional C prefers the Al site under the O-rich conditions, whereas the O site is preferred by carbon under the Al-rich conditions. The calculated results predict a direct relationship between the thermodynamic and optical transition levels with the degree of the local distortion induced by C in the alumina lattice. We also find C at the O site acts as a charge compensator to stabilize the F+ center, thereby enhancing the TL signal at 465K. Also, C at Al site can serve as electron traps for TL emission process in α-Al2O3.

Vacancy Complexes in Carbon and Boron Nitride Nanotubes

The effect of divacancies on the stability, structural and electronic properties of carbon and boron nitride nanotubes is studied using the ab initio density functional method. V(B)B(N) is more stable in the boron-rich and less stable in the nitrogen-rich growth conditions, and V(N)N(B) is more stable in the nitrogen-rich than in the boron-rich conditions. We find that stoichiometric defects V(B)V(N), V(B)C(N) and V(N)C(B) are stable in both the boron and nitrogen rich environments. The relaxation energy in the V(C)V(C) is lower in the armchair than in the zig-zag and the opposite trend is seen for V(C)B(C) and V(C)N(C). The divacancy is found to be particularly effective in changing the band gap of the semiconducting nanotubes due to the appearance of additional energy levels within the band gap region. For the zig-zag systems, we observe a drastic reduction of the band gap in V(B)B(N), V(N)N(B) and V(N)C(B) and a complete removal of the band gap in V(B)V(N) and V(B)C(N), negating the semiconducting behaviour of the nanotube.

Structural and electronic properties of carbon adsorbed on Fe(100)

Density functional theory within general gradient approximation (GGA) has been used to investigate sub-monolayer carbon atom adsorbed on Fe(100) as a function of coverage. The carbon atoms prefer to adsorb in the fourfold hollow site and bind strongly with the Fe surfaces. There is a substantial and strong coverage dependence of the carbon-induced expansion of the first interlayer spacing, reflecting a weakening of Fe–Fe bonds between the two outermost substrate layers. Some charge is found to transfer from substrate Fe to the adsorbate C atoms, which is responsible for the increase of work function. The density of states (DOS) analysis indicates the bonding of carbon with the first surface layer Fe atoms is primarily due to the interaction between Fe 3dx2-y2, xy and C 2px, y orbitals, and the bonding of carbon with the second surface layer Fe atom that sits directly below the carbon atom is mainly from interaction between the minority spin Fe 3dz2 and C 2pz orbitals.

Continuum Theory of Amorphous Carbon Nanostructures

Carbon is often considered to be silicon of the future because of the unique properties resulting from the variety of possible structural forms. A wide range of electronic properties of carbon yields many possible applications. Classical thermodynamics successfully describes bulk equilibrium of the diamond-graphite system in a wide range of temperatures and pressures. Equilibrium in the carbon system at nanoscale, however, has not been clarified despite the significance of this information for numerous existing and possible applications of carbon in nanoelectronics. In the present paper, we analyze the transition between diamond and graphite phases using the continuum Landau theory. The theory sheds light on the details of such transitions, and more importantly, predicts a new stable phase at nanoscale that can be used in carbon-based nanodevices. We find that the transition state of a system capable of undergoing a graphite/diamond phase transition gains thermodynamic stability against the bulk phases under the conditions of a limited volume if the barrier height of the transition is below the critical value. In a large-size closed system, a heterogeneous mixture of the graphite and diamond phases is the most stable state. In a small system (below the critical size), the heterogeneous mixture is not possible and the transition state becomes the globally stable state-a phase. Based on the present analysis, we hypothesize that the transition state is associated with the amorphous phase of carbon observed experimentally. The theoretical results allow us to interpret the experiments on focused ion beam scanning irradiation of single crystal CVD diamond films, which produce highly conductive regions on the diamond surface.

Structural and electronic properties of carbon in hybrid diamond-graphite structures

In this paper we report on ab initio pseudopotential density-functional calculations of some possible high-pressure phases of carbon. The total energies of several hybrid diamond-graphite structures were calculated as a function of volume using density-functional theory and the local density approximation. The lowest calculated transition pressures between hexagonal-graphite and hybrid structures were 17 and $20\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$, which compare well with the experimental value of $14\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ for the transition at low temperatures between graphite and a still unidentified hard transparent phase. The electronic densities of states for the different structures are presented. Also, the x-ray powder diffraction patterns for a few structures were simulated and qualitatively compared to published experimental diffraction patterns.

Oxidation behavior of furan-resin-derived carbon alloyed with Ta or Ti

The effect of Ti, Nb and Ta on the anti-oxidation of furan-resin-derived carbons was investigated by thermogravimetric analysis combined with gas/mass spectroscopy, Hall coefficient and magnetoresistance measurements, transmission electron microscopy, and X-ray diffraction analysis. Hall coefficient and magnetoresistance measurements revealed that the electronic properties of carbons with the above metal elements, and thus their crystallinity, are similar to that of neat carbon. The oxidation rates of the carbons with a small amount of Ti or Ta are decreased up to 1000 °C compared to that of neat carbon. The number of working active sites in carbons with Ta or Ti is smaller than that in carbons with Nb or neat carbon. Ta or Ti terminates some active sites in the carbons, or somehow modifies the structures of the active sites and retards the formation of oxygen–carbon intermediate products (surface complexes) on the materials. Thus, the oxidation rate of the carbons is decreased.

Mechanical and electronic properties of carbon and boron–nitride nanotubes

In this contribution we provide an overview of our recent work on the mechanical and electronic properties of carbon and boron–nitride (BN) nanotubes, which are of key relevance to practical applications and to our present understanding of low-dimensional structures. On the mechanical properties we look at the nanotube axial stiffness, bending and torsion dynamics. We found that chiral tubes exhibit an interesting asymmetric torsional behaviour with respect to left and right twist that is absent in armchair or zig-zag tubes. Topological defects are seen to modify slightly the mechanical response of the carbon network under applied strain. On the electronic properties we present an analysis of the role of the environment in nanotube density of states relevant for scanning tunneling spectroscopy (STS). Finally we present results on the electronic density of states for BN nanotubes that can be used as a complementary fingerprint of those structures in STS experiments and for their applications in composite (C–BN) electronic devices.

Electronic properties of model compounds simulating carbons prepared at low temperatures

The effect of the separation distance between the aromatic ring systems on the electronic properties of carbons were simulated by model compounds. The model compounds included perylene nuclei separated by aliphatic chains with varying numbers of methylene groups. They were prepared by polycondensation of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) and ω-diamines with various lengths of methylene chains. The optical absorption spectra consisted of two components. The first was a peak characteristic to PCTDA and the other was a broad absorption decreasing towards the near infra-red. The latter developed at the expense of the former with the decrease in the number of methylene units (n). Electrical conductivity and photocurrent were found to increase exponentially with decreasing n. Analyses of these trends in terms of a parameter proportional to the separation distance revealed that both the electrical conductivity and the photocurrent obeyed the relation expected for hopping conduction. The analyses were also applied to polycondensates doped with iodine or ammonia. The dopants were found to facilitate the hopping by lowering the potential barrier for tunneling or by extending the overlap of the wave functions of the π-electrons. The importance of the control of the separation distance in designing electronically functional carbons is emphasized.

High-pressure structural and electronic properties of carbon.

The high-pressure properties of carbon in eight different structures are calculated using an ab initio pseudopotential local-orbital method. In particular, the structural properties of hexagonal diamond and variation of its fundamental band gap with pressure are calculated for the first time. The variation of the fundamental gap in hexagonal diamond is found to have the opposite sign to that in cubic diamond, although the cubic and hexagonal forms have almost identical structural properties. Among the structures examined, diamond is found to transform under hydrostatic pressure first to the fourfold coordinated bc-8 (or Si-III) structure. The bc-8 form is favored at pressures greater than 11.1 Mbar. This is a slightly lower transformation pressure than that recently calculated using the pseudopotential plane-wave method. The sixfold coordinated structures, simple cubic and \ensuremath{\beta}-tin, are found at low pressure to be kinetically unstable, transforming spontaneously, without an energy barrier, into the cubic diamond structure. This result suggests that sixfold coordination of liquid carbon will be unlikely to occur at moderate pressure and temperature. Similarly, sixfold coordination is not expected in carbon clusters. A method of fully utilizing crystal symmetry to reduce the amount of computation in evaluating two- and three-center integrals needed in the local-orbital method is developed for the present calculations.