Nanostructured Carbide Research Articles

A Solvothermal Approach for the Preparation of Nanostructured Carbide and Boride Ultra‐High‐Temperature Ceramics

The use of a solvothermal process for the synthesis of tantalum carbide (TaC) and lanthanum hexaboride (LaB6) powders in fused‐quartz test tubes is reported in order to demonstrate the synthesis of these powders using thermal and chemical ignition techniques and to prove that the process is of a self‐propagating high‐temperature synthesis type, obviating the need for an autoclave. X‐ray powder diffraction showed phase pure powders with crystallite sizes of 25 and ∼80 nm, while dynamic light scattering showed average particle sizes of 97 and ∼130 nm, for TaC and LaB6, respectively. The data demonstrates that the powders have a very low level of agglomeration. Scanning electron microscopy shows that the TaC powders have a spherical morphology, while the LaB6 powders have a mixture of cubic and spherical morphologies.

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.

Combustion Formation of Novel Nanomaterials: Synthesis and Cathodoluminescence of Silicon Carbide Nanowires

This paper presents the combustion synthesis and characterization of one-dimensional silicon carbide nanostructures (nanowires of 3C-SiC polytype with zincblend structure) by means of cathodoluminescence technique. Cathodoluminescence spectra of nano-SiC samples and, as a reference, of a commercially available SiC micropowder are compared. It is shown that the emission band at 1.97 eV which is slightly evidenced in the spectrum of the commercial SiC under 10 keV electron beam irradiation becomes the prevailing band in CL of the purified silicon carbide nanowires.

Syntheses and Growth Mechanisms of 3<I>C</I>-SiC Nanostructures from Carbon and Silicon Powders

Cubic silicon carbide (3C-SiC) nanostructures such as needle- and Y-shaped nanowhiskers, smooth and pagoda-shaped nanorods are synthesized on a large scale from activated carbon and silicon powders at 1250 degrees C under atmospheric pressure. The use of ball-milled silicon powders results in the formation of nanowires and nanowhiskers, whereas non-milled silicon powders lead to nanorods together with unreacted silicon powders. Residual oxygen in the growth chamber initiates the carburization reactions which can proceed without further oxygen consumption. The size and morphology of the as-synthesized 3C-SiC nanostructures are observed to be related to the size and morphology of the starting silicon particles. An oxygen-assisted gas-solid model is proposed to explain the observed nanostructures.

Synthesis of β-SiC nanostructures via the carbothermal reduction of resorcinol–formaldehyde/SiO2 hybrid aerogels

The novel resorcinol–formaldehyde/SiO2 (RF/SiO2) hybrid aerogels were chosen to synthesize the cubic silicon carbide (β-SiC) nanostructures via a carbothermal reduction route. In this process, the in situ polymerized RF/SiO2 aerogels were used as both the silicon and carbon sources. The morphologies and structures of SiC nanostructures were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and high-resolution transmission electron microscope (HRTEM) equipped with EDS. The effects of C/Si atomic ratios in RF/SiO2 aerogels and heat treatment temperatures on the formation of SiC nanomaterials were investigated in detail. It was shown that β-SiC nanowhiskers with diameters of 50–150 nm and high crystallinity were obtained at the temperatures from 1400 to 1500 °C. The role of the interpenetrating network of RF/SiO2 hybrid aerogels in the carbothermal reduction was discussed and a possible mechanism was proposed.

A New Route of Forming Silicon Carbide Nanostructures with Controlled Morphologies

Mesoporous silica-carbon nanocomposites (C-SiO2) were synthesized and used as a host carrier in carbothermal reduction to fabricate highly crystalline silicon carbide nanoparticles and nanofibers. SiC nuclei were introduced into the mesopores as seeds by infiltration of preceramic precursor polycarbosilane (PCS) prior to the heat-treatment of carbothermal reduction. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and nitrogen adsorption-desorption analysis were used to characterize C-SiO2 nanocomposites and SiC products. Crystalline SiC was not formed in the mesoporous C-SiO2 nanocomposites with a low carbon content (e.g. C/SiO2 ratio = 1.01) at 1450 °C. However, when a given amount of PCS was infiltrated into the mesoporous C-SiO2, SiC nanofibers and nanoparticles were produced at 1450 °C even in the low carbon content sample. The major morphology formed from the mesoporous C-SiO2 nanocomposites without PCS infiltration was nanoparticles, while nanofibers dominated in the products of the PCS infiltrated compositions. The results indicate that the conversion of PCS into SiC nuclei in mesopores prior to carbothermal reduction has facilitated the formation of SiC nanofibers. Therefore infiltration of seeds into mesopores of C-SiO2 precursors appears to be an effective means in accelerating the reaction and controlling of nanostructures of silicon carbide.

Silicon Carbide Nanostructures from Reactions between Vapors of Organochlorosilanes and Liquid of Sodium‐Factors Affecting Morphology and Composition

AbstractCubic shells and spherical nanoparticles of β‐SiC were produced at 1273 K by processing the ceramic precursors formed from the reactions between vapors of organochlorosilanes, Me2SiCl2, MeSiCl3, MeSiHCl2, and PhSiCl3, and liquid Na at 523‐723 K. From Me2SiCl2, a flexible linear polycarbosilane precursor was synthesized and covered the NaCl byproduct surface to form a cubic shape. Hollow cubic β‐SiC shells were produced after the NaCl templates were removed. From MeSiCl3, a rigid cross‐linked polycarbosilane was produced and phase segregated from the NaCl byproduct. The precursor was transformed into nanoparticles without special morphology. MeSiHCl2 produced a cross‐linked polysilane precursor at low temperatures, which can be converted into a mixture of β‐SiC and Si nanoparticles. At high temperatures, the polysilane converted to polycarbosilane and produced hollow cubic β‐SiC shells. The carbon‐rich PhSiCl3 generated cube‐like particles as the final product, which contained β‐SiC and carbon.

Kinetic Monte Carlo simulation of vapor-liquid-solid nanostructure growth

The vapor-liquid-solid growth of nanostructures is simulated using a two-dimensional kinetic Monte Carlo model. The model considers the deposition of reactants from the vapor, solute diffusion in the solution droplet, and the nucleation and growth of the precipitated solid phase. The extrusion of the solid from the solution into the vapor is also modeled. A morphological transition from one-dimensional to two-dimensional growth is observed in response to changes in reactant vapor pressure and to changes in the solute diffusivity at the liquid-vapor interface. The morphology is determined by the dominant growth direction of the solid and is dependent on the speed at which deposited solute species can be diffused from the surface. Such a fundamental change in morphology has been observed experimentally in the growth of silicon carbide nanostructures and insight into the cause of this transition is achieved.

Role of Pores in the Carbothermal Reduction of Carbon−Silica Nanocomposites into Silicon Carbide Nanostructures

Silicon carbide nanostructures were synthesized by carbothermal reduction of carbon−silica (C−SiO2) nanocomposites. C−SiO2 nanocomposites with C/SiO2 molar ratios of 1.90−4.21 were used in this study. Thermogravimetric analysis, nitrogen sorption, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and infrared spectroscopy were used to characterize C−SiO2 nanocomposites and SiC products. Highly crystalline SiC nanoparticles and nanofibers (CS-3.28 and CS-4.21) were obtained from mesoporous C−SiO2 nanocomposites with the carbon content greater than a C/SiO2 stoichiometric ratio of 3 (e.g., C/SiO2 = 3.28 and 4.21 by mole), and they had a BET surface area of 83.0−76.7 m2/g after unreacted silica and carbon were removed. In contrast, SiC was not formed in the mesoporous C−SiO2 nanocomposites with a lower carbon content (e.g., C/SiO2 = 1.91 and 2.51 by mole). However, when such mesoporous nanocomposites were infiltrated with a small amount of carbon, SiC nanoparticles and nanofi...

Multi-Scale Simulation of MBE-Grown SiC/Si Nanostructures

The main obstacle for the implementation of numerical simulation for the prediction of the epitaxial growth is the variety of physical processes with considerable differences in time and spatial scales taking place during epitaxy: deposition of atoms, surface and bulk diffusion, nucleation of two-dimensional and three-dimensional clusters, etc. Thus, it is not possible to describe all of them in the framework of a single physical model. In this work there was developed a multi-scale simulation method for molecular beam epitaxy (MBE) of silicon carbide nanostructures on silicon. Three numerical methods were used in a complex: Molecular Dynamics (MD), kinetic Monte Carlo (KMC), and the Rate Equations (RE). MD was used for the estimation of kinetic parameters of atoms at the surface, which are input parameters for other simulation methods. The KMC allowed the atomic-scale simulation of the cluster formation, which is the initial stage of the SiC growth, while the RE method gave the ability to study the growth process on a longer time scale. As a result, a full-scale description of the surface evolution during SiC formation on Si substrates was developed.

A novel technique for the fabrication of nanostructures on silicon carbide usingamorphization and oxidation

A novel technique for fabricating silicon dioxide(SiO2) and silicon carbide (SiC) nanostructures on SiC substrates is reported in this paper.The technique involves amorphization of crystalline SiC at the nanoscale using afocused ion beam followed by selective thermal oxidation that results in oxidenanostructures due to the enhanced oxidation rate of amorphous SiC. Selectiveetching of the oxide results in crystalline SiC nanostructures. Nanostructures(SiO2 and SiC) withminimum feature sizes of ∼55 nm have been fabricated. Oxide nano-channels with channel widths of less than 20 nm aredemonstrated. The physical mechanisms that control the evolution of the structures andlimit the resolution have been addressed.

Beaded silicon carbide nanochains via carbothermal reduction of carbonaceous silicaxerogel

Novel silicon carbide nanostructures, beaded nanochains, are prepared from thecarbothermal reduction of a carbonaceous silica xerogel with cetyltrimethylammoniumbromide and lanthanum nitrate as additives. The nanochains consist of a stemwith a diameter of about 50 nm and uniform beads with diameters of 100–200 nm.It is demonstrated that the tensile strength of an epoxy composite filled withthe SiC nanochains improves significantly due to the unusual morphology of thenanochains.

Microgrinding of Nanostructured Carbide Coatings: Ground Surface and Subsurface Damage Observations

Surface microgrinding of the nanostructured WC/12Co coatings have been undertaken with diamond wheels under various conditions. Nondestructive and destructive approaches were utilized to assess damage in ground nanostructured coatings. Different surface and subsurface configurations were observed by scanning electron microscopy. This paper investigates the effects of microgrinding conditions on damage formation in the surface and subsurface layers of the ground nanostructured WC/12Co coatings. And the material-removal mechanism has been discussed.

A new one-dimensional tungsten carbide nanostructured material

A new medium specific surface area one-dimensional tungsten carbide nanostructure was obtained by the Shape Memory Synthesis method, in which the macrostructural features of a carbonaceous 1D-preformed template were maintained during the carburization of tungsten oxide and determined the resulting carbide morphology.

Formation of novel nanostructures using carbon nanotubes as a frame

Molecular nanostructures, such as nanotubes and nanorods, represent ideal building blocks for nanoelectronic devices due to their unique electronic properties. We present recent progress in the formation of novel nanostructures which have been produced by substitution reaction from carbon nanotube templates. We report on the synthesis of boron doped single wall carbon nanotubes with different substitution levels, multiwall boron nitride nanotubes, boron nitride nanocapsules, silicon carbide nanostructures and gallium nitride nanostructures. The morphology, crystal structure and atomic ratio of the samples have been characterized by various techniques.

Fabrication of Alpha-Iron and Iron Carbide Nanostructures by Electron-Beam Induced Chemical Vapor Deposition and Postdeposition Heat Treatment

We succeeded in fabricating crystalline alpha-iron nanostructures with desired shapes. Electron-beam-induced chemical vapor deposition with iron carbonyl gas, Fe(CO)5, was carried out at room temperature in a field-emission-gun scanning electron microscope to fabricate nanodots, nanorods and square frames. The as-deposited structures exhibited an amorphous phase containing iron, carbon and oxygen in their entire volumes and iron oxide nanocrystals existed near their surfaces. Postdeposition heat treatment at about 600°C resulted in the formation of crystalline alpha-iron and iron carbide phases in their structures, while maintaining their shapes. Quantitative elemental analyses using electron energy loss spectroscopy suggested that the original as-deposited iron-to-carbon compositional ratio is crucial in determining the stoichiometry of the produced structures after the heat treatment.

Synthesis of Silicon Carbide Nanostructures via a Simplified Yajima Process—Reaction at the Vapor–Liquid Interface

Synthesis of Silicon Carbide Nanostructures via a Simplified Yajima Process—Reaction at the Vapor–Liquid Interface

GROWTH OF SiC NANOSTRUCTURES ON Si (100) USING LOW ENERGY CARBON ION IMPLANTATION AND ELECTRON BEAM RAPID THERMAL ANNEALING

A combination of 10 keV 13 C low energy ion implantation and electron beam rapid thermal annealing (EB-RTA) is used to fabricate silicon carbide nanostructures on (100) silicon surfaces. These large ellipsoidal features appear after EB-RTA at 1000°C for 15 s. Prior to annealing, the silicon surfaces are virgin-like flat. Atomic force microscopy was used to study the morphology of these structures and it was found that the diameter and number of nanoboulders are linearly dependent on the implantation fluence. Further, a linear relationship between nanoboulder diameter and spacing suggests crystal coarsening is a fundamental element in the growth mechanism.

Atomic scale control and understanding of cubic silicon carbide surface reconstructions,nanostructures and nanochemistry

The atomic scale ordering and properties of cubic silicon carbide(β-SiC) surfaces and nanostructures are investigated by atom-resolved room andhigh-temperature scanning tunnelling microscopy (STM) and spectroscopy (STS),synchrotron radiation-based valence band and core level photoelectron spectroscopy(VB-PES, CL-PES) and grazing incidence x-ray diffraction (GIXRD). In this paper, wereview the latest results on the atomic scale understanding of (i) the structure ofβ-SiC(100) surface reconstructions, (ii) temperature-induced metallic surface phasetransition, (iii) one dimensional Si(C) self-organized nanostructures havingunprecedented characteristics, and on (iv) nanochemistry at SiC surfaces withhydrogen. The organization of these surface reconstructions as well as the 1Dnanostructures’ self-organization are primarily driven by surface stress. In thispaper, we address such important issues as (i) the structure of the Si-rich3 × 2, the Si-terminatedc (4 × 2), the C-terminatedc (2 × 2) reconstructionsof the β-SiC(100) surface, (ii) the temperature-induced reversible metallic phase transition, (iii) the formation of highly stable (up to900 °C) Si atomic and vacancy lines, (iv) the temperature-induced sp tosp3 diamondlike surface transformation, and (v) the first example of H-induced semiconductor surface metallizationon the β-SiC (100) 3 × 2 surface. The results are discussed and compared to other experimental and theoreticalinvestigations.

Assembly of carbide nanostructures at low temperature

We have developed a simple and efficient technique for the assembly of carbide nanostructures at low temperature, such as SiC, TiC, ZrC, B4C, Mo2C nanowires, hollow nanospheres, nanocables, or nanoparticles. The morphology can be efficiently assembled by verifying the experimental parameters, such as reaction temperature, source materials, or using catalyst. The growth of carbide hollow nanospheres (SiC, TiC, ZrC) may be explained by the template-confined effect of the intermediate carbon hollow spheres, while the growth of SiC nanowires and nanocables are controlled by the VLS mechanism and TiC, ZrC nanowires by the template-confined effect of the intermediate carbon nanotubes.