SiC Sheet Research Articles

Atomistic Study on the Tensile Properties of Hexagonal AlN, BN, GaN, InN and SiC Sheets

Atomistic Study on the Tensile Properties of Hexagonal AlN, BN, GaN, InN and SiC Sheets

Extraction and scattering analyses of 2D and bulk carriers in epitaxial graphene-on-SiC structure

Hall effect measurements of a graphene-on-SiC system were carried out as a function of temperature (1.8–200K) at a static magnetic field (0.5T). With the analysis of temperature dependent single-field Hall data with the Simple Parallel Conduction Extraction Method (SPCEM), bulk and two-dimensional (2D) carrier densities and mobilities were extracted successfully. Bulk carrier is attributed to SiC substrate and 2D carrier is attributed to the graphene layer. For each SPCEM extracted carrier data, relevant three-dimensional or 2D scattering analyses were performed. Each SPCEM extracted carrier data were explained with the related scattering analyses. A temperature independent mobility component, which may related to an interaction between graphene and SiC, was observed for both scattering analyses with the same mobility limiting value. With the SPCEM, effective ionized impurity concentration of SiC substrate, extracted 2D-mobility, and sheet carrier density of the graphene layer are calculated with using temperature dependent static magnetic field Hall data.

A density functional study on the acidity properties of pristine and modified SiC nano-sheets

Surface acidity is an important property that is frequently used to characterize the reactivity of surfaces. NH3 is well known as a probe molecule in determining the acidity of surfaces experimentally. Here, the adsorption of an NH3 molecule at different sites of a SiC nanosheet was investigated based on density functional theory framework. It was found that NH3 can be weakly adsorbed on the surface of the pristine with the adsorption energy (Ead) of about 3.5kcal/mol with no sensible effect on the electronic properties of the sheet. Replacing a Si or C atom with both Al and B atoms increases the Ead, indicating that the acidity of SiC sheet can be controlled by doping of B and Al atoms. Relative magnetic order of the acidity for different surfaces was found to be: AlC, a C atom was replaced with a Al, (Ead=86.4kcal/mol)⪢AlSi (Ead=39.2kcal/mol)>BC (Ead=30.9kcal/mol)>BSi (Ead=12.3kcal/mol)⪢pristine h-SiC (Ead=3.5kcal/mol). Moreover, it was found that when a C atom of the sheet was doped by an Al atom, HOMO–LUMO gap of the sheet becomes highly sensitive to NH3 adsorption so that it is decreased by about 31.3% after the adsorption process. It shows that the AlC-doped sheet may be used in the detection of NH3 gas molecules.

Layered SiC Sheets: A Potential Catalyst for Oxygen Reduction Reaction

The large-scale practical application of fuel cells cannot come true if the high-priced Pt-based electrocatalysts for oxygen reduction reaction (ORR) cannot be replaced by other efficient, low-cost, and stable electrodes. Here, based on density functional theory (DFT), we exploited the potentials of layered SiC sheets as a novel catalyst for ORR. From our DFT results, it can be predicted that layered SiC sheets exhibit excellent ORR catalytic activity without CO poisoning, while the CO poisoning is the major drawback in conventional Pt-based catalysts. Furthermore, the layered SiC sheets in alkaline media has better catalytic activity than Pt(111) surface and have potential as a metal-free catalyst for ORR in fuel cells.

Curvature effect of SiC nanotubes and sheets for CO2capture and reduction

CO2adsorption and reduction on SiC nanomaterials display a curvature effect.

STRUCTURAL AND ELECTRONIC EVOLUTION FROM SiC SHEET TO SILICENE

The evolution of the structural and electronic properties from SiC sheet to silicene is studied by using first-principles density functional theory. It is found that the planar configurations of the Si – C monolayer systems are basically kept except for the increase of the buckling of the planar structure when the substitution ratio of Si increases. Band gaps of the Si – C monolayer system decrease gradually when the substitution ratio of Si atoms ranges from 0% to 100%. The energy and type of the band gaps are closely related with the substitution ratio of Si atoms and the Si – C order. Further analysis of density of states reveals the orbital contribution of Si and C atoms near the Fermi level. The discussion of the electronic evolution from SiC sheet to silicene would widen the application of the Si – C monolayer systems in the optoelectronic field in the future nanotechnology.

Density Functional Theory Study of the Silicene-like SiX and XSi3 (X = B, C, N, Al, P) Honeycomb Lattices: The Various Buckled Structures and Versatile Electronic Properties

Using the density functional theory calculations, we systematically investigate the structures and properties of silicene-like SiX and XSi3 (X = B, C, N, Al, P) hexagonal heterosheets. For the SiX systems, the SiP sheet favors a chairlike buckled structure akin to silicene, the SiB, SiN, and SiAl ones prefer the washboard-like buckling type, and the SiC sheet adopts the flat plane as graphene. The planarity is also favored in the XSi3 sheets with X = B, C, Al, while the rests with X = N and P prefer the chairlike buckled structures. The energetic stabilities and mechanical properties are also investigated for these SiX and XSi3 systems, and all the heterosheets are found to be stable. Unlike the semimetallic silicene, most of the SiX sheets are transformed to metals except for the SiC one with a wide band gap. For the XSi3 systems, they can be metals, semimetals, or narrow-band gap semiconductors depending on the X elements. The BSi3 and NSi3 sheets exhibit metallic behaviors, which behave like the p-type...

Conformers of hydrogenated SiC honeycomb structure: A first principles study

The structural and electronic properties of fully hydrogenated SiC graphane-like nano-structures have been investigated. The objective of this study is to underscore the relative stability of different conformers of hydrogenated SiC sheet. All calculations are carried out using plane wave based pseudo-potential approach under the density functional theory. The results reveal that the fully hydrogenated SiC sheet forms five stable isomers, and the chair conformer is most stable. Further study through molecular dynamic simulation strategy demonstrates that even at room temperature the chair conformer remains stable.

Study of physical properties of single walled SiC nanotube (8,8) in crystalline bundles by DFT

The physical properties of single walled armchair SiC nanotubes crystalline bundles (8,8) in tetragonal crystalline bundles with a common tubule axial direction have been studied by the density function theory using the Quantum SPRESSO Software. Being bundled changes the physical properties of tubule such as structural parameters, charge density, band gap and density of state, bulk modulus and also stability due to inter-tube interactions. Calculations show that these changes are positive and in the direction of increasing stability of the tubule. For comparison, the physical properties of the isolated SW-SiC-NT and the single SiC sheets have been tested in the same way.

Adsorption of formaldehyde (HCOH) molecule on the SiC sheet: A first-principles study

We investigated the adsorption of HCOH molecule on the SiC sheet using density functional theory (DFT) calculations. It is found that the C atom of the SiC sheet is the active adsorption site and the HCOH molecule prefers to the C atom rather than the O and H atoms close to the SiC sheet. The calculated charge-transfer, electronic density difference image and the densities of states (DOS) show that the HCOH molecule could be firmly adsorbed by the SiC sheet and the electronic properties of the SiC sheet are affected by the adsorption of HCOH molecule. The SiC sheet would be promising candidate to detect the HCOH gas.

Excitonic effects in the optical properties of a SiC sheet and nanotubes

The quasiparticle band structure and optical properties of single-walled zigzag and armchair SiC nanotubes (SiC-NTs) as well as single SiC sheet are investigated by ab initio many-body calculations using the GW and the GW plus Bethe-Salpeter equation (GW+BSE) approaches, respectively. Significant GW quasiparticle corrections of more than 1.0 eV to the Kohn-Sham band gaps from the local density approximation (LDA) calculations are found. The GW self-energy corrections transform the SiC sheet from a indirect LDA band gap to a direct band gap material. Furthermore, the quasiparticle band gaps of SiC-NTs with different chiralities behave very differently as a function of tube diameter, and this can be attributed to the difference in the curvature-induced orbital rehybridization between the different chiral nanotubes. The calculated optical absorption spectra are dominated by discrete exciton peaks due to exciton states with large binding energy up to 2.0 eV in the SiC sheet and SiC-NTs. The formation of strongly bound excitons is attributed to the enhanced electron-hole interaction in these low dimensional systems. Remarkably, the excited electron amplitude of the exciton wavefunction is found to peak on the Si atoms near the hole position (which is on the C site) in the zigzag SiC-NTs, indicating a charge transfer from an anion (hole) to its neighboring cations by photoexcitation. In contrast, this pronounced peak structure disappear in the exciton wavefunction in the armchair SiC-NTs. Furthermore, in the armchair SiC-NTs, the bound exciton wavefunctions are more localized and also strongly cylindrically asymmetric.

Hydrogen storage on Ti decorated SiC nanostructures: A first principles study

In the present study we report the hydrogen adsorption behavior of two SiC nanostructures; a planar sheet and a nanotube (10, 0) of 1 nm diameter decorated by Ti atoms on it. All calculations have been performed using a plane-wave based pseudopotential method. The lowest energy structure of the Ti adsorbed SiC sheet shows that Ti atom distorts the sheet in such a way that one of the Si atoms goes down the plane and the Ti atom bind with nearest three C atoms. The interaction of this Ti decorated sheet with hydrogen suggests that each Ti atom can bind up to four hydrogen molecules (all hydrogens are adsorbed in the molecular form) with an average binding energy of 0.37 eV. For SiC nanotube, the adsorption of Ti favors the hexagonal hollow site. Moreover, on interaction of this Ti decorated tube with hydrogen leads to dissociation of the first hydrogen molecule in the atomic form and thereafter adsorbs hydrogen in the molecular form. The average binding energy of hydrogen molecules on this Ti decorated tube is estimated to be 0.65 eV. Based on these results we infer that the Ti decorated SiC nanostructures moderately bind with hydrogen molecules (within the energy window for hydrogen storage materials) and therefore, can be considered as one of the potential hydrogen storage material.

Structural stabilities and electronic properties of fully hydrogenated SiC sheet

The intriguing structural and electronic properties of fully hydrogenated SiC honeycomb sheet are studied by means of ab initio calculations. Based on structure optimization and phonon dispersion analysis, we find that both chair-like and boat-like configurations are dynamically stable, and the chair-like conformer is energetically more favored with an energy gain of 0.03 eV per C atom relative to the boat-like one. The chair-like and boat-like conformers are revealed to be nonmagnetic semiconductors with direct band gaps of 3.84 and 4.29 eV, respectively, both larger than 2.55 eV of pristine SiC sheet. The charge density distributions show that the bondings are characterized with covalency for both chair-like and boat-like conformers.

Ferromagnetic and antiferromagnetic properties of the fluorinated bilayer SiC sheets

The intriguing electronic and magnetic properties of the fluorinated bilayer SiC sheets are studied using density functional theory. The fluorinated bilayer SiC sheets exhibit diverse electronic and magnetic behaviors: a ferromagnetic half metal for structure I which means that all corresponding carbon and silicon atoms from bilayer sheets have same coordinates of a- and b-axes, while an antiferromagnetic metal with intralayer ferromagnetism for structure II with same coordinates only for silicon atoms, and each carbon atom in one layer facing the center of corresponding hexagon in the other one. The fluorinated bilayer SiC sheets for structure II is more stable than that for structure I. So, controlling different structure types can effectively modulate the electronic and magnetic properties of the fluorinated bilayer SiC sheets, which endows the fluorinated bilayer SiC sheets with great potential applications for future functional nanodevices.

Ferromagnetic and antiferromagnetic properties of the semihydrogenated SiC sheet

The intriguing electronic and magnetic properties of the semihydrogenated SiC sheet are investigated by means of the first-principles calculations. The semihydrogenated SiC sheet exhibits diverse electronic and magnetic properties: a ferromagnetic semiconductor when Si atoms are hydrogenated, while an antiferromagnetic semiconductor with C atoms hydrogenated. The semihydrogenated SiC sheet with the C atoms hydrogenated is found to be more stable than the sheet with the Si atoms hydrogenated. Thus, controlling the hydrogenation on the different atom sites can precisely modulate the electronic and magnetic properties of the semihydrogenated SiC sheet, which endues the semihydrogenated SiC sheet great potential applications in the future functional nanodevices.

Fabrication of Porous SiC Sheets with Controlled Porosity from Waste Clutch Boards

AbstractWhen clutch boards are fabricated as friction sheets in automatic transmission of motorcars, their useless fragments are disposed of. In this study, an effective reuse of their waste clutch boards will be proposed. Clutch boards are composed of diatomaceous earth, carbon powder/fiber and phenol resin. Excess carbon in carbonized clutch boards was reacted with SiO formed from Si and SiO2 at 1500 °C in Ar to produce porous SiC sheets (79% porosity). High temperature treatment at 1700-1900 °C in vacuum made it possible to control the pore size of SiC sheets, having a main pore diameter range of 10 to 20 μm.SiC sheets with porosity (79% to <60%) were also fabricated by heating carbonized/impregnated sheets with phenol resin in SiO gas at 1500 °C. SiC sheets obtained by the repeated cycle of impregnation/decomposition of resin heating at 1700 °C gave a tensile strength of 19 MPa.When Aluminum-tri-sec-butoxide (ASB) solution was impregnated into SiC sheets oxidized at 1000-1200 °C in air and heated at 1400-1500 °C in Ar, SiC-mullite composite sheets with porosity (77%) were produced.

Aqueous tape casting process for SiC

The condition for the preparation of stable SiC slurries by aqueous tape casting was identified. To acquire stable uniform slurries, the influences of dispersant, solid loading, sintering additives, binder and plasticizer on the rheological properties and viscosity were investigated. The conditions for preparing stable SiC slurries were studied and optimized. After tape casting and drying, the green SiC sheets showed smooth surface and homogeneous microstructure. The SiC ceramic can be densified to 98.89% after hot-pressing at 1850 °C (at 25 MPa in Ar for 30 min). The flexural strength, hardness, and toughness are 779.5 ± 39.2 MPa, 21.51 ± 0.70 GPa and 5.54 ± 0.26 MPa m 1/2, respectively. SEM shows a fine microstructure with few pores in the sintered samples. The fracture surface exhibited predominantly intergranular fracture type.

Band-gap unification of partially Si-substituted single-wall carbon nanotubes

The atomic and electronic structure of a set of pristine single wall SiC nanotubes as well as Si-substituted carbon nanotubes and a SiC sheet was studied by the local-density approximation (LDA) plane wave band structure calculations. Consecutive substitution of carbon atoms by Si leads to a gap opening in the energetic spectrum of the metallic (8,8) SWCNT with approximately quadratic dependence of the band gap upon the Si concentration. The same substitution for the semiconductor (10,0) single wall carbon nanotubes (SWCNT) results in a band gap minimum $(0.27\phantom{\rule{0.3em}{0ex}}\mathrm{eV})$ at $\ensuremath{\sim}25%$ of Si concentration. In the Si concentration region of $12--18\phantom{\rule{0.2em}{0ex}}%$, both types of nanotubes have less than $0.5\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ direct band gaps at the $\ensuremath{\Gamma}\text{\ensuremath{-}}\ensuremath{\Gamma}$ point. The calculation of the chiral (8,2) $\mathrm{SW}{\mathrm{Si}}_{0.15}{\mathrm{C}}_{0.85}\mathrm{NT}$ system gives a similar $(0.6\phantom{\rule{0.3em}{0ex}}\mathrm{eV})$ direct band gap. The regular distribution of Si atoms in the atomic lattice is by $\ensuremath{\sim}0.1\phantom{\rule{0.3em}{0ex}}\mathrm{eV}∕\text{atom}$ energetically preferable in comparison with a random distribution. Time dependent density functional theory (DFT) calculations showed that the silicon substitution sufficiently increases (roughly by one order of magnitude) the total probability of optical transitions in the near infrared region, which is caused by the opening of the direct band gap in metallic SWCNTs, the unification of the nature and energy of the band gaps of all SWCNT species, the large values of $⟨\mathrm{Si}3p\ensuremath{\mid}r\ensuremath{\mid}\mathrm{Si}3s⟩$ radial integrals and participation of $\mathrm{Si}3d$ states in chemical bonding in both valence and conductance bands.

High-fluence Si-implanted diamond: Formation of SiC nanocrystals and sheet resistance

The sheet resistance and structural properties of high-fluence Si-implanted diamond were investigated. In order to minimize the radiation damage and to facilitate SiC formation the implantation was performed at 900 °C. All samples were subsequently annealed in a rf-heated furnace at 1500 °C for 10 min in order to remove defects and thermally unstable phases. X-ray diffraction, infrared absorption spectrometry, and high-resolution cross-sectional transmission electron microscopy revealed the formation of a buried layer inside the implanted diamond, which contains SiC nanocrystallites. These SiC nanocrystals have a cubic structure and are nearly perfectly aligned with the diamond lattice. Raman spectroscopy was applied to analyze radiation-damage-induced graphitization in dependence on the implantation conditions. The sheet resistance of the samples was measured as function of temperature by four point probe technique in van-der-Pauw geometry. The decrease of the sheet resistance with increasing ion fluence unambiguously shows the influence of implantation-induced damage. The behavior of the sheet resistance can strongly be modified by additional nitrogen implantation. The resulting higher conductivity is interpreted as partial incorporation of the nitrogen donor into the SiC nanocrystals. However, when the Si fluence exceeds a critical value of 5.3×1017 Si+ cm−2 at 900 °C the diamond is irreversibly damaged and defect related conductivity dominates.

Fabrication of silicon carbide fiber-reinforced silicon carbide composite by hot-pressing

Continuous SiC fiber-reinforced SiC composites (SiC/SiC f) are one of the most attractive structural materials for future fusion reactors. To date, the only successful manufacturing process of SiC/SiC f composites is the chemical vapor infiltration technique, which is a very delicate and expensive process. In this study, therefore, a new method to fabricate the composite with higher density is developed using a conventional hot-press procedure. Matrix SiC sheets and Nicalon or Hi-Nicalon two-dimensional cloths without any coatings were stacked alternately and then this stacked green body was hot-pressed at 1750°C under 40 MPa applied stress in Ar. The matrix SiC sheet consists of fine, β-SiC powders and Al, B and C sintering aids. A sheet of SiC was formed using the doctor blade technique. The relative density of sintered bodies was 66–99%. The load–displacement behavior of the composites with Nicalon cloth showed a slightly ductile load–displacement behavior with low maximum strength, whereas the composite with Hi-Nicalon cloth showed brittle fracture with high maximum strength at room temperature.