Boron-doped Silicon Carbide Research Articles

Removal of caffeine from aqueous and vacuum environments using Si12C12, Si11GeC12, Si11BC12 fullerenes: A DFT and TDDFT studies

Caffeine (CFI) adsorption upon the perfect, boron-doped (Si11BC12 and Si12BC11), and germanium-doped (Si11GeC12 and Si12GeC11) silicon carbide (SiC) fullerenes have been studied to assess the feasibility of caffeine removal from aqueous and vacuum environments by using density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations. The adsorption energy and charge transfer of caffeine through its nitrogen atom of the imidazole ring upon the surface of Si12C12 nano-cage is stronger than that of the oxygen atoms of the pyrimidinedione ring with moderate adsorption energy. The theoretical infrared (IR) spectrum shows that the vibrational frequency of CFI changes after interacting with the pure Si12C12 fullerene, and this change is comparable to the experimental data. According to the TDDFT method, Ultraviolet–Visible (UV–Vis) techniques reveal that the optical features of the pure, Si11BC12, Si11GeC12 fullerenes changed after interacting with CFI. The density of state (DOS) analysis confirmed that the caffeine adsorption via imidazole ring with a robust electron hybridization can be remarkably altered the electronic features of Si12C12 fullerene, being too sensitized to the binding of caffeine. The results demonstrate that CFI adsorption on Si12C12 is stronger than on Si11BC12 and Si11GeC12 fullerenes. The presence of a boron (B) atom in the Si11BC12 fullerene improves the dipole moment and optical properties as compared to the Si11GeC12 fullerene. Upon caffeine adsorption, the Si12C12 and Si12BC11 fullerenes could be promising adsorbents for caffeine removal and detection because of the strong interaction, increasing dipole moment, and short recovery time.

Investigation of structural and electronics properties of boron co-doped silicon carbide nanoribbons

In this analysis, we investigated the structural and electronic properties of boron-doped armchair silicon carbide nanoribbons (B-doped ASiCNRs). By making use ofdensity functional theory (DFT) approachthe binding energy (BE), density of state (DOS), energy band structure, and bond length are computed. Calculation shows that B-doped ASiCNRs have strong structural stability as compared to ASiCNR. Before doping, the energy band-gap of armchair silicon carbide nanoribbons is relatively higher than that of the boron-doped armchair silicon carbide nanoribbons. It is found that when boron (B) atoms are doped in the center, the Fermi level shifts towards the valence band. This indicates that the doping of B atoms results in emerging of new energy bands which transform semiconductor to the P-type nature of B-doped ASiCNRs. Our findings give a theoretical framework for adjusting the electronic characteristics of B-doped ASiCNRs. It can be used in future nanoelectronic devices, etc.

Enhanced Photocatalytic Activity of Boron Doped Silicon Carbide Nanofibers and Its Composite with Polyvinyl Borate

ABSTRACT Boron doped silicon carbide (B-SiC) and its composite with polyvinyl borate (PVB) were studied due to the role of boron acting as an electron-acceptor, which can reduce the recombination rate of the photoinduced electron–hole pair on SiC upon UV light irradiation. The structure and morphology of SiC and B-SiC, and their PVB composites were characterized by FTIR, X-ray diffraction spectroscopy and field emission scanning electron microscopy. The optical property and the band gap energy of the as prepared samples were evaluated from UV-Vis absorption spectroscopy. When compared to SiC and PVB/SiC, boron doped SiC and its PVB composite exhibited enhanced photocatalytic activity toward the model dye (methylene blue) degradation owing to the effective separation of the photoinduced electron-hole pair on the photocatalyst nanofibers.

Fabrication and electrochemical properties of boron-doped SiC

Silicon carbide (SiC) has excellent properties such as chemical and physical stability, biocompatibility, and high thermal conductivity. However, electrical conductivity of SiC is not high enough for electrochemical applications, which has been a major challenge. Here, in order to improve the conductivity, we prepared boron-doped SiC (SiC:B) and evaluated the electrochemical properties. SiC and SiC:B were fabricated by a microwave plasma chemical vapor deposition method. Structural characterization revealed that the main phase of SiC:B is 3C–SiC where the concentration of doped boron could be controlled by tuning the growth conditions. Electrochemical properties were evaluated by cyclic voltammetry measurements, indicating that the reactivity and sensitivity of the SiC:B electrode was comparable of that of the glassy carbon electrode.

Influence of the Carbon Concentration on (p) Poly-SiC x Layer Properties With Focus on Parasitic Absorption in Front Side Poly-SiC x /SiO x Passivating Contacts of Solar Cells

Passivating contacts based on polycrystalline silicon (poly-Si) on an interfacial oxide are limited by parasitic absorption, which may be reduced by incorporation of foreign elements in the poly-Si layer. In this study, the influence of carbon incorporation in the concentration range of 6.9–21.5 at% on boron-doped polycrystalline silicon carbide (poly-SiC x ) layer properties is investigated and interpreted in the context of an application as full-area passivating contact on the front side of a solar cell. For constant annealing parameters, higher carbon concentrations reduce the crystallinity of the layers. A high crystallinity in turn is confirmed to be a key parameter for the application in a solar cell as it ensures both low resistivity as well as low parasitic absorption. Low recombination current densities in the range of 7.2–12.2 fA/cm2 are determined for all layers on interfacial oxides on planar surfaces, whereas the differences are rather related to variations in the boron concentration than to the carbon concentration or the deposition parameters. A reduction of the ( p ) poly-SiC x layer thickness down to 10 nm would yield a parasitic absorption current density of 1.13 ± 0.13 mA/cm2. Using this value and the lowest measured recombination current density, a simple model predicts a theoretical solar cell efficiency limit of 26.7 ± 0.2%.

Boron-doped silicon carbide (SiC) thin film on silicon (Si): a novel electrode material for supercapacitor application

In this work, we report the synthesis of silicon carbide (SiC) thin film on silicon by modified chemical vapour deposition technique using boron-doped liquid polycarbosilane as a precursor. Subsequent microscopic and physical characterizations of this film show the presence of SiC nanocrystal along with boron in the SiC thin film. The electrochemical characterizations of the film shows a highest capacitance of 232F/g at 2.2A/g current density from Galvanostatic charging–discharging method with good cyclic stability upto 2000 cycles. The high capacitance value is attributed to the surface defect states and amorphous carbon which acts as the charge active sites. The result further infers that the (B)SiC/Si is a promising electrode material for high-performance energy storage application.

Deposition of boron-doped nanocrystalline silicon carbide thin films using H2-Ar mixed dilution for the application on thin film solar cells

Hydrogen-argon mixed dilution has been applied for the deposition of boron-doped nanocrystalline silicon carbide (nc-SiCx) thin films. The variations of structural, compositional, electrical and optical properties with the varying H2/Ar ratio are systemically investigated through various characterizations. It is shown that by using H2-Ar mixed dilution for deposition, B-doped nc-SiCx thin film possessing both wide optical band gap (∼2.22 eV) and high conductivity (∼1.9 S cm−1) can be obtained at the H2/Ar flow ratio of 360/140. In addition, the B-doped nc-SiCx thin films are fabricated as the window layers of a-Si thin film solar cells, and the highest conversion efficiency (8.13%) is obtained when applying the window layer with the largest optical band gap energy.

Silicon-Rich Silicon Carbide Hole-Selective Rear Contacts for Crystalline-Silicon-Based Solar Cells.

The use of passivating contacts compatible with typical homojunction thermal processes is one of the most promising approaches to realizing high-efficiency silicon solar cells. In this work, we investigate an alternative rear-passivating contact targeting facile implementation to industrial p-type solar cells. The contact structure consists of a chemically grown thin silicon oxide layer, which is capped with a boron-doped silicon-rich silicon carbide [SiCx(p)] layer and then annealed at 800-900 °C. Transmission electron microscopy reveals that the thin chemical oxide layer disappears upon thermal annealing up to 900 °C, leading to degraded surface passivation. We interpret this in terms of a chemical reaction between carbon atoms in the SiCx(p) layer and the adjacent chemical oxide layer. To prevent this reaction, an intrinsic silicon interlayer was introduced between the chemical oxide and the SiCx(p) layer. We show that this intrinsic silicon interlayer is beneficial for surface passivation. Optimized passivation is obtained with a 10-nm-thick intrinsic silicon interlayer, yielding an emitter saturation current density of 17 fA cm-2 on p-type wafers, which translates into an implied open-circuit voltage of 708 mV. The potential of the developed contact at the rear side is further investigated by realizing a proof-of-concept hybrid solar cell, featuring a heterojunction front-side contact made of intrinsic amorphous silicon and phosphorus-doped amorphous silicon. Even though the presented cells are limited by front-side reflection and front-side parasitic absorption, the obtained cell with a Voc of 694.7 mV, a FF of 79.1%, and an efficiency of 20.44% demonstrates the potential of the p+/p-wafer full-side-passivated rear-side scheme shown here.

Conductive Si-B-C Ceramics As Durable Catalyst Supports

Long recognised as key to the reduction of precious metal loading in PEMFC is the use of small catalyst nanoparticles (c.a. 3nm) stabilised by supporting them on high surface area carbon. However, PEMFCs using this technology achieve only 50% of the lifetime required by the US DOE’s target [1] with the oxidation of carbon supports a major lifetime limitation [2]. We have previously reported that catalysts on composite boron carbide, graphite supports show an increased durability to potential cycling below 1V and remarkably high ORR specific activities, 85% higher than commercial Pt/C [3]. Despite their excellent performance at low potentials, the presence of carbon in these catalysts still limits their durability during cycling to high potentials. We will present our latest work on catalyst supports in the Si-B-C system with the focus on eliminating carbon. Hybrid DFT/HF calculations were used to highlight boron doped boron carbide and boron doped silicon carbide as ceramics with intrinsic conductivity [Figure 1a]. To synthesise these doped ceramics with high purity, low temperature synthetic routes based on the carbo-thermal reduction of polymers were developed. These routes gave carbides with low levels of carbon impurities and provided control over the morphology of the support. This allowed the creation of high surface area supports on which platinum nanoparticles have been deposited [Figure 1b]. Electrochemical characterisation (ORR activity, accelerated degradation, etc) of the produced catalysts will also be presented. [1] Fuel Cell Technical Team Roadmap, 2013, US DOE [2] E. Antolini, and E. R. Gonzalez. Solid State Ionics, 2009, 180.9, 746 [3] C. Jackson et al. 18th Topical ISE Meeting 2016. [Manuscript in preparation] Figure 1

Bare and boron-doped cubic silicon carbide nanowires for electrochemical detection of nitrite sensitively.

Fabrication of eletrochemical sensors based on wide bandgap compound semiconductors has attracted increasing interest in recent years. Here we report for the first time electrochemical nitrite sensors based on cubic silicon carbide (SiC) nanowires (NWs) with smooth surface and boron-doped cubic SiC NWs with fin-like structure. Multiple techniques including scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and electron energy loss spectroscopy (EELS) were used to characterize SiC and boron-doped SiC NWs. As for the electrochemical behavior of both SiC NWs electrode, the cyclic voltammetric results show that both SiC electrodes exhibit wide potential window and excellent electrocatalytic activity toward nitrite oxidation. Differential pulse voltammetry (DPV) determination reveals that there exists a good linear relationship between the oxidation peak current and the concentration in the range of 50–15000 μmoL L−1 (cubic SiC NWs) and 5–8000 μmoL L−1 (B-doped cubic SiC NWs) with the detection limitation of 5 and 0.5 μmoL L−1 respectively. Compared with previously reported results, both as-prepared nitrite sensors exhibit wider linear response range with comparable high sensitivity, high stability and reproducibility.

Boron-doped silicon carbide supported Pt catalyst for methanol electrooxidation

Boron-doped silicon carbide (B0.1SiC) synthesized by the carbothermal reduction method was used as support to prepare Pt/B0.1SiC catalyst by cyclic voltammtric deposition of Pt nanoparticles. The crystal structure, surface property and morphology of the catalysts were studied with X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy and transmission electron microscopy techniques and N2 adsorption-desorption experiment. It is shown that B atoms have been incorporated into the SiC lattice sites by substituting Si, which increases the electrical conductivity of SiC. Pt nanoparticles uniformly dispersed on the B0.1SiC support with an average size of 2.7 nm. The prepared Pt/B0.1SiC had a larger electrochemically active area and exhibited higher electrocatalytic activity and stability for methanol oxidation than the Pt/SiC synthesized by the same method. This shows that B-doped SiC is a promising support for preparing high-performance methanol oxidation electrocatalysts.

Improvement of Single-Junction a-Si:H Thin-Film Solar Cells Toward 10% Efficiency

ABSTRACTThe hydrogenated amorphous silicon (a-Si:H) single-junction thin-film solar cells were fabricated on SnO2:F-coated glasses by plasma-enhanced chemical vapor deposition (PECVD) system. The boron-doped amorphous silicon carbide (a-SiC:H) was served as the window layer (p-layer) and the undoped a-SiC:H was used as a buffer layer (b-layer). The optimization of the p/b/i/n thin-films in a-Si:H solar cells have been carried out and discussed. Considering the effects of light absorption, electron-hole extraction and light-induced degradation, the thicknesses of p, b, n and i layers have been optimized. The optimal a-Si:H thin-film solar cell having an efficiency of 9.46% was achieved, with VOC=906 mV, JSC=14.42 mA/cm2 and FF=72.36%.

Structural and electronic properties of boron-doped double-walled silicon carbide nanotubes

The effects of boron doping on the structural and electronic properties of ( 6 , 0 ) @ ( 14 , 0 ) double-walled silicon carbide nanotube (DWSiCNT) are investigated by using spin-polarized density functional theory. It is found that boron atom could be more easily doped in the inner tube. Our calculations indicate that a Si site is favorable for B under C-rich condition and a C site is favorable under Si-rich condition. Additionally, B-substitution at either single carbon or silicon atom site in DWSiCNT could induce spontaneous magnetization.

Transport properties of boron-doped single-walled silicon carbide nanotubes

The doped boron (B) atom in silicon carbide nanotube (SiCNT) can substitute carbon or silicon atom, forming two different structures. The transport properties of both B-doped SiCNT structures are investigated by the method combined non-equilibrium Green’s function with density functional theory (DFT). As the bias ranging from 0.8 to 1.0 V, the negative differential resistance (NDR) effect occurs, which is derived from the great difficulty for electrons tunneling from one electrode to another with the increasing of localization of molecular orbital. The high similar transport properties of both B-doped SiCNT indicate that boron is a suitable impurity for fabricating nano-scale SiCNT electronic devices.

Specific heat of aluminium-doped superconducting silicon carbide

The discoveries of superconductivity in heavily boron-doped diamond, silicon and silicon carbide renewed the interest in the ground states of charge-carrier doped wide-gap semiconductors. Recently, aluminium doping in silicon carbide successfully yielded a metallic phase from which at high aluminium concentrations superconductivity emerges. Here, we present a specific-heat study on superconducting aluminium-doped silicon carbide. We observe a clear jump anomaly at the superconducting transition temperature 1.5 K indicating that aluminium-doped silicon carbide is a bulk superconductor. An analysis of the jump anomaly suggests BCS-like phonon-mediated superconductivity in this system.

AC susceptibility study of superconducting aluminum-doped silicon carbide

In 2007, type-I superconductivity in heavily boron-doped silicon carbide was discovered. The question arose, if it is possible to achieve a superconducting phase by introducing dopants different from boron. Recently, aluminum-doped silicon carbide was successfully found to superconduct by means of resistivity and DC magnetization measurements [1]. In contrast to boron-doped silicon carbide, the aluminum doped system is treated as a type-II superconductor because of the absence of an hysteresis in data measured upon decreasing and increasing temperature in finite magnetic fields. In this paper, results of a recent AC susceptibility study on aluminum-doped silicon carbide are presented. In higher applied DC magnetic fields and at low temperatures, a weak indication of supercooling with a width of a few mK is found. This supports the conclusion that aluminum-doped silicon carbide is located near to the border between type-I and type-II superconductivity, as pointed out in a recent theoretical work, too.

Origin of superconductivity in boron-doped silicon carbide from first principles

We investigate the origin of superconductivity in boron-doped silicon carbide using a first-principles approach. The strength of the electron-phonon coupling calculated for cubic SiC at the experimental doping level suggests that the superconductivity observed in this material is phonon mediated. Analysis of the $2H\text{-SiC}$, $4H\text{-SiC}$, $6H\text{-SiC}$, and $3C\text{-SiC}$ polytypes indicates that superconductivity depends on the stacking of the Si and C layers and that the cubic polytype will exhibit the highest transition temperature. In contrast to the cases of silicon and diamond, acoustic phonons are found to play a major role in the superconductivity of silicon carbide.

Superconductivity of hexagonal heavily-boron doped silicon carbide

In 2004 the discovery of superconductivity in heavily boron-doped diamond (C:B) led to an increasing interest in the superconducting phases of wide-gap semiconductors. Subsequently superconductivity was found in heavily boron-doped cubic silicon (Si:B) and recently in the stochiometric "mixture" of heavily boron-doped silicon carbide (SiC:B). The latter system surprisingly exhibits type-I superconductivity in contrast to the type-II superconductors C:B and Si:B. Here we will focus on the specific heat of two different superconducting samples of boron-doped SiC. One of them contains cubic and hexagonal SiC whereas the other consists mainly of hexagonal SiC without any detectable cubic phase fraction. The electronic specific heat in the superconducting state of both samples SiC:B can be described by either assuming a BCS-type exponentional temperature dependence or a power-law behavior.

Modeling and Simulation of Boron-Doped Nanocrystalline Silicon Carbide Thin Film by a Field Theory

This paper presents the application of a multiscale field theory in modeling and simulation of boron-doped nanocrystalline silicon carbide (B-SiC). The multiscale field theory was briefly introduced. Based on the field theory, numerical simulations show that intergranular glassy amorphous films (IGFs) and nano-sized pores exist in triple junctions of the grains for nanocrystalline B-SiC. Residual tensile stress in the SiC grains and compressive stress on the grain boundaries (GBs) were observed. Under tensile loading, it has been found that mechanical response of 5 wt% boron-SiC exhibits five characteristic regimes. Deformation mechanism at atomic scale has been revealed. Tensile strength and Young's modulus of nanocrystalline SiC were accurately reproduced.

Superconductivity in heavily boron-doped silicon carbide

The discoveries of superconductivity in heavily boron-doped diamond in 2004 and silicon in 2006 have renewed the interest in the superconducting state of semiconductors. Charge-carrier doping of wide-gap semiconductors leads to a metallic phase from which upon further doping superconductivity can emerge. Recently, we discovered superconductivity in a closely related system: heavily boron-doped silicon carbide. The sample used for that study consisted of cubic and hexagonal SiC phase fractions and hence this led to the question which of them participated in the superconductivity. Here we studied a hexagonal SiC sample, free from cubic SiC phase by means of x-ray diffraction, resistivity, and ac susceptibility.