Carbide Films Research Articles

Influence of Substrate Temperature on Electrical and Optical Properties of Hydrogenated Boron Carbide Thin Films Deposited by RF Sputtering

Amorphous hydrogenated boron carbide films were deposited on silicon and glass substrates using radio frequency sputtering. The substrate temperature was varied from room temperature to 300 °C. The substrate temperature during deposition was found to have significant effects on the electrical and optical properties of the deposited films. X-ray photoelectron spectroscopy (XPS) revealed an increase in sp2-bonded carbon in the films with increasing substrate temperature. Reflection electron energy loss spectroscopy (REELS) was performed in order to detect the presence of hydrogen in the films. Metal-insulator-metal (MIM) structure was developed using Al and hydrogenated boron carbide to measure dielectric value and resistivity. Deposited films exhibited lower dielectric values than pure boron carbide films. With higher substrate deposition temperature, a decreasing trend in dielectric value and resistivity of the films was observed. For different substrate temperatures, the dielectric value of films ranged from 6.5–3.5, and optical bandgap values were between 2.25–2.6 eV.

Thein situremoval of surface molybdenum oxide for making binder-free porous Mo1.98C1.02film a more efficient electrocatalyst for alkaline rather than acidic hydrogen production

A binder-free porous film of molybdenum carbide is synthesized by a facile approach, and exhibits superb performance in the alkaline hydrogen evolution reaction, producing a current density of 10 mA cm−2at an overpotential of 47 mV.

Механические свойства композитного покрытия SiC на графите, полученного методом замещения атомов

The mechanical properties of composite coatings made of silicon carbide on graphite are studied for the first time. For the deposition of coatings, a new method of annealing the initial graphite was used, which was in contact with a silicon melt in an atmosphere of carbon monoxide.The samples were studied by nanoindentation and scanning electron microscopy. It is shown that the formed coating consists of a continuous film of monocrystalline silicon carbide lying on the surface, dendrites and crystalline druses, with roots going deep into the sample through a system of pores. It is shown that the coating significantly increases the mechanical characteristics of the graphite surface, including the microhardness.

A new approach to increasing the sensitivity of a gas sensor based on nanocrystalline silicon carbide films

It was shown the possibility of increasing the sensitivity of a gas sensor based on nanocrystalline SiC films by using a scheme of a two-component sensing element, one of which is an n-nc-SiC film with electronic conductivity, and the second is an p-nc-SiC film with hole conductivity. It is shown that due to the opposite polarity of changes in resistance in the films under the simultaneous action of gases, the difference in relative resistance changes ∆ in the n-nc-SiC and p-nc-SiC films will always be greater than in each film separately. The expediency of using a two-component sensing element of a gas sensor based on nc-SiC films with electron and hole conduction is shown.

Anomalous Properties of the Dislocation-Free Interface between Si(111) Substrate and 3C-SiC(111) Epitaxial Layer.

Thin films of single-crystal silicon carbide of cubic polytype with a thickness of 40–100 nm, which were grown from the silicon substrate material by the method of coordinated substitution of atoms by a chemical reaction of silicon with carbon monoxide CO gas, have been studied by spectral ellipsometry in the photon energy range of 0.5–9.3 eV. It has been found that a thin intermediate layer with the dielectric constant corresponding to a semimetal is formed at the 3C-SiC(111)/Si(111) interface. The properties of this interface corresponding to the minimum energy have been calculated using quantum chemistry methods. It has turned out that silicon atoms from the substrate are attracted to the interface located on the side of the silicon carbide (SiC) film. The symmetry group of the entire system corresponds to P3m1. The calculations have shown that Si atoms in silicon carbide at the interface, which are the most distant from the Si atoms of the substrate and do not form a chemical bond with them (there are only 12% of them), provide a sharp peak in the density of electronic states near the Fermi energy. As a result, the interface acquires semimetal properties that fully correspond to the ellipsometry data.

Epitaxial growth of cubic WCy(001) on MgO(001)

Tungsten carbide films are sputter-deposited onto MgO(001) substrates at 400 °C in 5 mTorr Ar - CH4 gas mixtures with CH4 fractions fCH4 = 0.4–6%, yielding total C-to-W ratios x = 0.57–1.25 as determined by ion beam analyses and energy-dispersive X-ray spectroscopy. The C-to-W ratio y in the cubic WCy phase is smaller than x, ranging from y = 0.47–0.68, as determined from lattice constant ao measurements in combination with first-principle calculations that predict an increasing ao = (0.4053 + 0.0295 y) nm for y = 0.3–1.0. This suggests that the cubic phase is stabilized by carbon vacancies and that the layers contain amorphous C with a volume fraction increasing from 4% to 26% for fCH4 = 0.4–6%. X-ray diffraction (XRD) θ-2θ scans, ω-rocking curves, and reciprocal space maps in combination with high-resolution transmission electron microscopy (TEM) indicate the growth of epitaxial rock-salt structure WCy(001) layers with a cube-on-cube epitaxial relationship with the substrate: (001)WC || (001)MgO and [100]WC || [100]MgO. The measured XRD out-of-plane coherence length of 8 – 14 nm is nearly independent of the film thickness d = 10 or 600 nm, suggesting that growth beyond d = 10 nm leads to an epitaxial breakdown and the nucleation of misoriented hexagonal or orthorhombic W2C grains for fCH4 ≤ 1% and cubic nanocrystalline WCy grains for fCH4> 1%.

Production of low-energy SiCH3+ and SiC2H7+ ion beams for 3C-SiC film formation by selecting fragment ions from dimethylsilane

Fragment ions produced from dimethylsilane (DMS) in a Bernas-type ion source were investigated. Dominant fragment ions were identified to be CH3+, Si+, SiH3+, SiCH3+, and SiC2H7+. We mass-selected SiCH3+ and SiC2H7+ ions and then produced low-energy SiCH3+ and SiC2H7+ ion beams. Subsequently, these ion beams were used to irradiate Si(111) substrates at 800 °C. The energies of SiCH3+ and SiC2H7+ ions were set at 100 eV. We found that the irradiation of these ions led to the deposition of silicon carbide (3C-SiC) films on the Si substrates. For comparison, SiC film formations on Si(111) substrates were also attempted by the chemical vapor deposition (CVD) method using DMS. The X-ray photoelectron spectroscopy measurements showed that atomic ratios of C to Si (C/Si ratio) of the films obtained by the irradiation of SiCH3+ and SiC2H7+ ion beams were 1.2 and 1.2, respectively. Conversely, the C/Si ratio of the film obtained by CVD was 1.9. Raman spectroscopy showed that the film obtained by CVD included diamond-like carbon. These results suggest that the low-energy mass-selected ion beam deposition technique using DMS-derived fragment ions is practicable for the 3C-SiC deposition on Si substrates.

Synthesis of optically active chiral mesoporous molybdenum carbide film

A chiral nematic mesoporous molybdenum carbide film (CN-Mo2C) was fabricated through the self-assembly of cellulose nanocrystal with peroxomolybdate. CN-Mo2C exhibits a tunable chiral nematic structure by varying the ratio of constituents, enabling a surface area of 210m2g−1. Importantly, it shows a typical chiroptical feature through polarized optical microscopy and circular dichroism spectral analysis. As it has an excellent conductivity of 2.4×10−2 S cm−1, we try to use CN-Mo2C in the electrocatalytic HER production, presenting an efficient H2 production capacity. It is a versatile synthetic strategy that can conveniently enable other large-area macroscopic chiral metal-based materials.

Drastic change in surface electronic properties and creation of a new carbon-based nanostructure on the vicinal SiC(111)-4° surface

Novel carbon based nanostructure on the vicinal SiC(111)-4° surface has been found as effect of Cs adsorption. The SiC(111)-4°sample was grown by method of epitaxy of low-defect unstressed nanoscaled silicon carbide films on vicinal Si(111)-4° substrate. Electronic structure of the SiC(111)-4° surface and the Cs/SiC(111)-4°interface has been detailed studied in situ in an ultrahigh vacuum using synchrotron-based photoelectron spectroscopy. The C 1s and Si 2p core level spectra have been investigated as a function of Cs submonolayer coverage. A unique fine structure of the C 1s core level spectrum was revealed to appear under Cs atomic layer deposition. The effect was ascertained and shown to be originated from the interaction of the silicon vacancy with adsorbed Cs atoms that leads to both the redistribution of electron density and surface reconstruction with formation of a new type of the C-enriched aromatic-like nanostructure.

Investigation of boron carbide and iridium thin films, an enabling technology for future x-ray telescopes.

We present an experimental examination of iridium and boron carbide thin-film coatings for the purpose of fabricating x-ray optics. We use a combination of x-ray reflectometry and x-ray photoelectron spectroscopy to model the structure, composition, density, thickness, and micro-roughness of the thin films. We demonstrate in our analyses how the two characterization techniques are complementary, and from this we derive that an overlayer originating from atmospheric contamination with a thickness between 1.0-1.6 nm is present on the surface. The magnetron sputtered iridium films are measured to have a density of 22.4g/cm3. The boron carbide film exhibits a change in chemical composition in the top ∼2nm of the film surface when exposed to the ambient atmosphere. The chemical reaction occurring on the surface is due to an incorporation of oxygen and hydrogen present in the ambient atmosphere. Lastly, we present a correlation between the absorption edges and the emission lines exhibited by the thin films in an energy range from 50-800 eV and the impact on the reflectivity performance due to contamination in thin films.

Nonlinear Optical Response of Reflective MXene Molybdenum Carbide Films as Saturable Absorbers.

Molybdenum carbide (Mo2C) is a two-dimensional (2D) MXene material which makes it a promising photoelectric material. In this study, reflective type MXene Mo2C thin films were coated on a silver mirror by a magnetron sputtering method and were subsequently used in a passively Q-switched solid-state pulsed laser generator at the central wavelengths of 1.06 and 1.34 μm, respectively. The fabricated thin films of reflective type MXene Mo2C exhibited large modulation depth of 6.86% and 5.38% at the central wavelengths of 1064 and 1342 nm, respectively. By inserting the Mo2C saturable absorbers (SAs) into V-shaped Nd:YAG laser, short pulses were generated having a pulse duration, pulse energy, and average output power of 254 ns, 2.96 μJ, and 275 mW, respectively, at a wavelength of 1.06 μm. Similarly, shorter laser pulses were obtained in Nd:YVO4 laser at 1.34 μm. Our results illustrated potential of the 2D MXene Mo2C films for laser applications.

Towards reliable X-ray photoelectron spectroscopy: Sputter-damage effects in transition metal borides, carbides, nitrides, and oxides

Ar+ sputter etching is often used prior to X-ray photoelectron spectroscopy (XPS) analyses with the intention to remove surface oxides and contaminants. Since the XPS probing depth is comparable to the thickness of the ion-beam modified layer the signal from the latter dominates the spectra. We check here the conditions for reliable XPS analysis by studying ion irradiation effects for single-phase Group IVB transition metal (IVB-TM) boride, carbide, nitride, and oxide thin film specimens. The extent of sputter damage, manifested by changes in the surface composition, binding energy shift, peak broadening, and the appearance of new spectral features, varies greatly between material systems: from subtle effects in the case of IVB-TM carbides to a complete change of spectral components for IVB-TM oxides. The determining factors are: (i) the nature of compounds that may form as a result of ion-induced mixing in the affected layer together with (ii) the final elemental composition after sputtering, and (iii) the thickness of the Ar+-affected layer with respect to the XPS probing depth. Our results reveal that the effects of Ar+ ion irradiation on XPS spectra cannot be a priori neglected and a great deal of scrutiny, if not restraint, is necessary during spectra interpretation.

Sputter-deposited low-stress boron carbide films

Significant challenges have been faced in the manufacturing of low-stress B4C films. Here, we demonstrate a set of process parameters for direct-current magnetron sputter deposition of smooth, high-purity, amorphous B4C films with near-zero total residual stress and with thicknesses up to 10 μm. Films are characterized by a combination of high-energy ion scattering, x-ray diffraction, electron microscopy, and stress measurements based on substrate curvature. In order to facilitate the process transfer to other sputtering geometries, the favorable deposition conditions are correlated with distributions of landing energies and incident angles of depositing species estimated by Monte Carlo simulations of ballistic collisions and gas phase atomic transport. Based on such simulations, a decrease in compressive stress with increasing Ar working gas pressure is attributed to the corresponding broadening of the angular distribution of depositing species and associated atomic shadowing effects.

Ultrasensitive and reversible room-temperature resistive humidity sensor based on layered two-dimensional titanium carbide

The nanostructured two-dimensional (2D) materials for humidity sensing applications have become increasingly attractive. However, 2D materials have negative aspects of easily stacking and agglomerating multilayers. Here, a novel resistive-type humidity sensor utilizing multi-layer titanium carbide (Ti3C2Tx) films as sensitive material is demonstrated. The humidity sensor exhibits an ultrasensitive and reversible sensing performance in a wide relative humidity range. Furthermore, the ultrafast response and recovery properties are achieved at room temperature. The Fourier transform infrared spectroscopy is used to investigate the adsorption of water vapor on Ti3C2Tx surfaces. A rapid capillary condensation of water vapor on the unique accordion-like microstructures and the hierarchical nanostructures of hydroxyl-riched Ti3C2Tx surface are supposed to be responsible for the super adsorption capability for water vapor. The electrostatic field induced by adsorbed water molecules is proposed to explain the resistance change of the titanium carbide humidity sensor. This work highlights the unique advantages of humidity sensor with layered 2D materials of Ti3C2Tx MXenes, including ultrasensitive, good reversibility and fast recovery at room temperature.

Kinetics of vanadium reduction from slags by solid carbon

The laboratory investigation results of the vanadium reduction are presented. Experiments were performed with CaO–SiO2–Al2O3–MgO–V2O3 slags in an air atmosphere. The solid carbon was used as a reducing agent. The reduction kinetics was studied by sampling. It has been shown that reduction proceeds to VC carbide. The process rate is inversely proportional to the slag viscosity. The formation of a carbide film on the carbon surface leads to a sudden, by an order of magnitude, reduction in the rate. The process of vanadium reduction from oxide melts by solid carbon is electrochemical in nature and is limited by the stage of carbon anodic oxidation. The influence of slag viscosity on the process kinetics is explained by the fact that it is controlled by the growth rate and removal of gas bubbles. The appearance of the carbide film, apparently, transfers the reduction process into the intra diffusion mode, when the transfer of carbon and vanadium through the carbide film is limiting.

One step co-sintering of silicon carbide ceramic membrane with the aid of boron carbide

To reduce the sintering cycles and shorten the preparation periods of silicon carbide membrane, we report a fabrication route for silicon carbide membrane by co-sintering process with the aid of boron carbide. In this process, the SiC selective layer was coated on the SiC- B4C green substrate with spray method followed by sintering at 1900 ℃. With the increase of B4C content from 7 to 13 wt.%, the grain size and pore size of the substrate decreased, ascribing to the interface reaction between boron carbide and silica film on the silicon carbide surface. A straight and homogeneous selective layer formed on the substrate, presenting average thickness of 30 μm and average pore size of 0.28 μm. Thus, this technique is considered as a cost-effective and short-period method for the preparation of silicon carbide membrane.

Mechanical properties of helical milling deep hole on QFRP using cryogenic cooling process

The structure and physical properties of quartz fiber reinforced polyimide composite (QFRP) lead to the milling hole defects of crimp, ablation and delamination, as well as serious tool wear and limited hole making depth. Based on three kinds of defects of helical milling holes of composite materials, the cutting force model was constructed considering the cutting micro-zone temperature. This article presents the first comprehensive investigation on cryogenic (83K) milling deep hole process of QFRP through liquid nitrogen injection by carbide film blades with 10 mm cutting diameter. In this project, the surface morphology, cutting force, cutting temperature and tool wear performance were analyzed compared with dry milling ones. The results show that the three kinds of defects are all affected by cutting force and mechanical properties of composites. In dry milling shallow hole with low speed, the type I crimp defect of hole entry, the type II lamination defect of hole middle and exit are all serious, as well as the type III ablative defect of hole exit with 1.06 mm machining error at high speed. The milling hole cutting forces are mainly related to axial feed, tangential feed and composite properties considering temperature. At the same time, the axial and tangential forces are more affected by the change of tool axial feed than tangential feed. After cryogenic cooling intervention, milling hole defects and tool wear are well inhibited. And the accuracy of shallow hole was up to 0.03 mm at hole exit, as well as 0.05 mm for deep hole without delamination tear and ablation defects. Conclusion, the properties change of matrix and composite at low temperature are the main reason for preventing type I and II milling hole defects, and the eliminated passivation and adhesion of tool side blade and flank surface are the reasons for restraining type III defects.

Mid-IR photothermal measurement of substantial heat transport by surface waves of polar amorphous films supported on silicon

We present measurements of significant thermal diffusivity by surface electromagnetic waves of an ultra-thin polar and amorphous dielectric film deposited on silicon (Si). We used a photothermal-beam-deflection technique with a modulated mid-infrared heating source to excite and launch surface electromagnetic waves onto the surface of an amorphous silicon carbide (a-SiC) film deposited on Si and generate periodic temperature and refractive index gradients above the sample surface. These gradients are capable of periodically deflecting a probe beam, passing very close to the surface, at the modulation frequency of the heating beam. We have fitted the measured probe beam deflection to an analytical model for the mirage effect that takes into account the thermal anisotropy of the measured sample to infer the contribution of the surface electromagnetic waves of the a-SiC film to thermal diffusivity in the plane of the sample under study. We found that reducing the thickness of the a-SiC film promotes the interaction between the surface electromagnetic waves propagating on either side of the a-SiC film, which significantly enhances thermal diffusivity in the plane of the measured sample. We also found that in-plane thermal diffusivity by surface electromagnetic waves on an amorphous silicon carbide film a few nanometers thick is several orders of magnitude greater than thermal diffusivity by phonons in silicon. We believe that the results obtained provide a better understanding of the physics of electromagnetic waves confined to solid surfaces.

Progresses in Synthesis and Application of SiC Films: From CVD to ALD and from MEMS to NEMS.

A search of the recent literature reveals that there is a continuous growth of scientific publications on the development of chemical vapor deposition (CVD) processes for silicon carbide (SiC) films and their promising applications in micro- and nanoelectromechanical systems (MEMS/NEMS) devices. In recent years, considerable effort has been devoted to deposit high-quality SiC films on large areas enabling the low-cost fabrication methods of MEMS/NEMS sensors. The relatively high temperatures involved in CVD SiC growth are a drawback and studies have been made to develop low-temperature CVD processes. In this respect, atomic layer deposition (ALD), a modified CVD process promising for nanotechnology fabrication techniques, has attracted attention due to the deposition of thin films at low temperatures and additional benefits, such as excellent uniformity, conformability, good reproducibility, large area, and batch capability. This review article focuses on the recent advances in the strategies for the CVD of SiC films, with a special emphasis on low-temperature processes, as well as ALD. In addition, we summarize the applications of CVD SiC films in MEMS/NEMS devices and prospects for advancement of the CVD SiC technology.

Graphene Trails on PECVD Hydrogenated Amorphous Silicon Carbide Films SiC-a: H by Laser Writing at Room Temperature

The production of high quality graphene without the need for catalyst metals as in the case of chemical vapor deposition (CVD) techniques remain a challenge. Silicon carbide is one of the materials with potential to form graphene films on its surface through thermal decomposition when subjected to high temperatures and ultrahigh vacuum. This technique is highly desirable since it enables the elimination of corrosion and transfer steps, which can leave residues in the graphene structure and alter its quality, as well as its electrical proprieties, however it is a costly and time consuming method. In this work, we present the production of graphene trails by direct laser radiation writing at room temperature and atmospheric pressure on hydrogenated amorphous silicon carbide films (SiC-a:H) produced by Plasma Enhanced Chemical Vapor Deposition (PECVD). Graphene trails of approximately 1cm x 4μm were obtained with patterns designed by computer Aided Design (CAD) software. Variations were made in both scanning speed and laser focal length, identifying a great dependence on the graphene quality with these two parameters. The best results of the Raman Spectroscopy Mappings showed high quality graphene with distance between point defects (LD) of 20nm, crystallite size (La) of 25nm and few layers (2-3). In addition, the electrical measurements from Au/Ti (20nm/100nm) electrodes deposited by electron beam evaporation showed high conductivity, with sheet resistances (Rs) from 0.7kΩ to 1.3 kΩ per square. This technique opens a great possibility of manufacturing devices for applications in electronics, being a fast, efficient and low cost method.