Properties Of Silicon Carbide Nanowires Research Articles

Formation mechanism and luminescence properties of silicon carbide nanowires with core-shell structure

For the preparation of SiC nanowires (SiC NWs) by carbothermal reduction, it is of great significance to study the formation mechanism of sic nanowires for process optimization and the controllable preparation. Although first-principles molecular dynamics (FPMD) can simulate systems of hundreds of atoms on a picosecond time scale, the results of FPMD are still insufficient to elucidate the formation mechanism of core-shell SiC nanowires. To make up this deficiency, this article has conducted Deep Potential Molecular Dynamics (DPMD) simulation on nanoseconds timescales with near FPMD accuracy for systems containing thousands of atoms, the results more concretively show the formation process of core-shell SiC nanowires. DPMD simulation results show when CO molecules react with SiO molecules, CO molecules are wrapped by SiO molecules to form agglomerates, SiO molecules in the agglomerates that can come into contact with the wrapped CO molecules will react with wrapped CO molecules to form the SiC core, and SiO molecules that in the outer layer of the agglomerates will disproportionate into the amorphous SiO2 shell. Furthermore, the formation mechanism of SiC nanowires was validated in combination with thermodynamics and experimental methods. Thermodynamic results show that vacuum conditions are favorable for the formation of SiO and CO and lower the temperature of SiC preparation. Finally, the core-shell structure of SiC NWs with good luminescence properties were successfully prepared by carbothermal reduction method using carbon black and silicon dioxide as raw materials under the pressure of less than 5 kPa.

Effects of different atomic passivation on conductive and dielectric properties of silicon carbide nanowires

Based on the transport and polarization relaxation theories, the effects of hydrogen, fluorine, and chlorine atom passivation on the conductivity and dielectric properties of silicon carbide nanowires (SiCNWs) were numerically simulated. The results show that passivation can decrease the dark conductivity of SiCNWs and increase its ultraviolet photoconductivity. Among them, the photoconductivity of univalent (H) passivated SiCNWs is better than that of seven-valent (Cl, F) passivated SiCNWs. In terms of dielectric properties, the passivated SiCNWs exhibit a strong dielectric response in both deep ultraviolet and microwave regions. Hydrogen passivation SiCNWs produce the strongest dielectric response in deep ultraviolet, while fluorine passivation SiCNWs produce the strongest dielectric relaxation in the microwave band, which indicates that atomic passivation SiCNWs have a wide range of applications in ultraviolet optoelectronic devices and microwave absorption and shielding.

Recent progress in synthesis, growth mechanisms, and electromagnetic wave absorption properties of silicon carbide nanowires

With the research and development of nanomaterials, one-dimensional (1D) nanowire structures have received a lot of attention due to their unique physical and chemical properties. Among them, silicon carbide nanowires (SiC NWs) have low density, excellent oxidation resistance, dielectric properties, and electromagnetic (EM) wave absorption properties, which can well meet the development needs of civilian equipment and military weaponry. SiC NWs have outstanding research and application potential in the field of EM wave absorption. However, comprehensive summaries of SiC NWs have not been available so far. Based on this, this paper reviews the research progress of SiC NWs microwave absorbing materials, various micro-morphologies of SiC NWs are introduced in detail, as well as diverse preparation strategies and multiple growth mechanisms are also stated. Ultimately, recent advances in research progress of SiC NWs and their composites in EM wave absorption are elaborated, along with the future research directions of SiC NWs in the field of EM wave absorption.

Effects of different valence atoms on surface passivation of silicon carbide nanowires

In this paper, based on the first principles, we study the properties of silicon carbide nanowires (SiCNWs) passivated by monovalent hydrogen (H), heptavalent fluorine (F) and chlorine (Cl) atoms at the electronic level to reveal the mechanism of interaction between different valence electrons in the passivation process. The results show that the passivation can improve the inhomogeneity of the surface and internal Si–C bonds, and improve the stability of the SiCNWs structure. The structure of F-SiCNWs is the most stable. Meanwhile, passivation increases the bandgap of the SiCNWs, and the bandgap of H, F and Cl passivation SiCNWs decreases successively, this is because the potential energy of H-1s, F-2p and Cl-3p interacting with Si-3p decreases in turn. Besides, heptavalent F and Cl passivation can regulate some optical properties of the SiCNWs to the deep-ultraviolet light regions such as absorption, conductivity, refractive index and loss function. Monovalent H passivation can regulate some optical properties of the SiCNWs to the vacuum ultraviolet light region (UVD). These studies have potential application value for the development of deep-ultraviolet micro–nano devices.

Conductance and dielectric properties of hydrogen and hydroxyl passivated SiCNWs* *Project supported by the National Natural Science Foundation of China (Grant No. 11574261) and the Natural Science Foundation of Hebei Province, China (Grant No. A2021203030).

Based on the transport theory and the polarization relaxation model, the effects of hydrogen and hydroxyl passivation on the conductivity and dielectric properties of silicon carbide nanowires (SiCNWs) with different sizes are numerically simulated. The results show that the variation trend of conductivity and band gap of passivated SiCNWs are opposite to the scenario of the size effect of bare SiCNWs. Among the influencing factors of conductivity, the carrier concentration plays a leading role. In the dielectric properties, the bare SiCNWs have a strong dielectric response in the blue light region, while passivated SiCNWs show a more obvious dielectric response in the far ultraviolet-light region. In particular, hydroxyl passivation produces a strong dielectric relaxation in the microwave band, indicating that hydroxyl passivated SiCNWs have a wide range of applications in electromagnetic absorption and shielding.

Strong structural occupation ratio effect on mechanical properties of silicon carbide nanowires

Materials’ mechanical properties highly depend on their internal structures. Designing novel structure is an effective route to improve materials’ performance. One-dimensional disordered (ODD) structure is a kind of particular structure in silicon carbide (SiC), which highly affects its mechanical properties. Herein, we show that SiC nanowires (NWs) containing ODD structure (with an occupation ratio of 32.6%) exhibit ultrahigh tensile strength and elastic strain, which are up to 13.7 GPa and 12% respectively, approaching the ideal theoretical limit. The ODD structural occupation ratio effect on mechanical properties of SiC NWs has been systematically studied and a saddle shaped tendency for the strength versus occupation ratio is firstly revealed. The strength increases with the increase of the ODD occupation ratio but decreases when the occupation ratio exceeds a critical value of ~ 32.6%, micro twins appear in the ODD region when the ODD segment increases and soften the ODD segment, finally results in a decrease of the strength.

Effects of hydroxyl groups and hydrogen passivation on the structure, electrical and optical properties of silicon carbide nanowires

The effects of hydrogen and hydroxyl passivation on the structure, electrical and optical properties of SiCNWs were investigated. The passivation performance of different atoms (groups) were discussed by analyzing the distribution of electronic states and the polarity of chemical bonds. The results show that passivation can improve the stability of SiCNWs structure, and the effect of hydroxyl is better than hydrogen passivation. And hydrogen and hydroxyl passivation both increase the band gap of SiCNWs, and the changing trend of band gap is relevant to the polarity of the covalent bond formed by the passivation of surface atoms. Moreover, passivation enhances the stability of the optical properties of SiCNWs, resulting in narrowing of light absorption, photoconductivity and other spectra, and the response peak shifts to the deep ultraviolet region, which means that hydrogen or hydroxyl passivation of SiCNWs is likely to be a candidate material for deep ultraviolet micro-nano optoelectronic devices.

Inhibition of quantum size effects from surface dangling bonds: The first principles study on different morphology SiC nanowires

In recent years, we investigated the structure and photoelectric properties of Silicon carbide nanowires (SiCNWs) with different morphologies and sizes by using the first-principle in density functional theory, and found a phenomenon that is opposite to quantum size effect, namely, the band gap of nanowires increases with the increase of the diameter. To reveal the nature of this phenomenon, we further carry out the passivation of SiCNWs. The results show that the hydrogenated SiCNWs are direct band gap semiconductors, and the band gap decreases with the diameter increasing, which indicates the dangling bonds of the SiCNWs suppress its quantum size effect. The optical properties of SiCNWs with different diameters before and after hydrogenated are compared, we found that these surface dangling bonds lead to spectral shift which is different with quantum size effect of SiCNWs. These results have potential scientific value to deepen the understanding of the photoelectric properties of SiCNWs and to promote the development of optoelectronic devices.

Structural and optical properties of silicon-carbide nanowires produced by the high-temperature carbonization of silicon nanostructures

Silicon-carbide (SiC) nanowire structures 40–50 nm in diameter are produced by the high-temperature carbonization of porous silicon and silicon nanowires. The SiC nanowires are studied by scanning electron microscopy, X-ray diffraction analysis, Raman spectroscopy, and infrared reflectance spectroscopy. The X-ray structural and Raman data suggest that the cubic 3C-SiC polytype is dominant in the samples under study. The shape of the infrared reflectance spectrum in the region of the reststrahlen band 800–900 cm–1 is indicative of the presence of free charge carriers. The possibility of using SiC nanowires in microelectronic, photonic, and gas-sensing devices is discussed.

Electronic properties of fluorinated silicon carbide nanowires

The control and modulation of the electronic properties of silicon carbide nanowires (SiCNWs) are crucial for the obtention of materials with specific electronic features for the design of stable and robust electronic devices. Tuning the band gap by chemical surface passivation constitutes a way for the modification of the stability and the electronic band gap of these nanowires. In this work, the structural and electronic properties of fluorinated 3C-SiCNWs, grown along the [111] crystallographic direction, are investigated by using the density functional theory within the generalized gradient approximation. We consider nanowires with five diameters, varying from 0.71nm to 2.13nm, and six surface covering schemes including fully hydrogen- and fluorine-terminated ones. Relative stabilities and electronic band gaps were calculated for the different surface functionalization schemes and diameters considered. The effects of chemical passivation on the size and nature of the band gap of the various studied nanowires are discussed.

Theoretical Study of Elastic Properties of SiC Nanowires of Different Shapes

The atomic structure and elastic properties of silicon carbide nanowires of different shapes and effective sizes were studied using density functional theory and classical molecular mechanics. Upon surface relaxation, surface reconstruction led to the splitting of the wire geometry, forming both hexagonal (surface) and cubic phases (bulk). The behavior of the pristine SiC wires under compression and stretching was studied and Young's moduli were obtained. For Y-shaped SiC nanowires the effective Young's moduli and behavior in inelastic regime were elucidated.

XPS Analysis by Exclusion of a-Carbon Layer on Silicon Carbide Nanowires by a Gold Catalyst-Supported Metal-Organic Chemical Vapor Deposition Method

Silicon carbide (SiC) nano-structures would be favorable for application in high temperature, high power, and high frequency nanoelectronic devices. In this study, we have deposited cubic-SiC nanowires on Au-deposited Si(001) substrates using 1,3-disilabutane as a single molecular precursor through a metal-organic chemical vapor deposition (MOCVD) method. The general deposition pressure and temperature were 3.0 x 10(-6) Torr and 1000 degrees C respectively, with the deposition carried out for 1 h. Au played an important role as a catalyst in growing the SiC nanowires. SiC nanowires were grown using a gold catalyst, with amorphous carbon surrounding the final SiC nanowire. Thus, the first step involved removal of the remaining SiO2, followed by slicing of the amorphous carbon into thin layers using a heating method. Finally, the thinly sliced amorphous carbon is perfectly removed using an Ar sputtering method. As a result, this method may provide more field emission properties for the SiC nanowires that are normally inhibited by the amorphous carbon layer. Therefore, exclusion of the amorphous carbon layer is expected to improve the overall emission properties of SiC nanowires.

Atomistic simulations of the mechanical properties of silicon carbide nanowires

Molecular-dynamics methods using the Tersoff bond-order potential are performed to study the nanomechanical behavior of [111]-oriented $\ensuremath{\beta}\text{-SiC}$ nanowires under tension, compression, torsion, combined tension-torsion, and combined compression-torsion. Under axial tensile strain, the bonds of the nanowires are just stretched before the failure of nanowires by bond breakage. The failure behavior is found to depend on size and temperatures. Under axial compressive strain, the collapse of the SiC nanowires by yielding or column buckling mode depends on the length and diameters of the nanowires, and the latter is consistent with the analysis of equivalent continuum structures using Euler buckling theory. The nanowires collapse through a phase transformation---from crystal to amorphous structure---in several atomic layers under torsion strain. Under combined loading the failure and buckling modes are not affected by the torsion with a small torsion rate, but the critical stress decreases by increasing the torsion rate. Torsion buckling occurs before the failure and buckling with a big torsion rate. Plastic deformation appears in the buckling zone by further increasing the combined loading.

Uniaxial-stress effects on electronic properties of silicon carbide nanowires

First-principles calculations are performed to study the mechanical properties, electronic structure, and uniaxial-stress effects of β-SiC nanowires (NWs). It is found that the band gap of SiC NWs becomes larger as their diameter decreases because of the quantum confinement effect, but increases (decreases) slightly with increasing tensile (compressive) stress up to about 12GPa. The calculated Young’s modulus and tensile strength of SiC NWs are about 620 and 52GPa, respectively, in accordance with the experimental data. The characteristics of their mechanical and electronic properties suggest that β-SiC NWs may be used in electronic composites as reinforcement nanomaterials or in nanoscale electronic/photoelectric devices under harsh environments.