Hexagonal Silicon Research Articles

New 5-6-6-5 (fourfold) and 5-9-6 defect Configurations in g-SiC (graphene-like hexagonal monolayer silicon carbide)

Abstract Computational studies using the density functional theory (DFT) were employed to analyze defect configurations in g-SiC. The SiC supercells containing 72 atoms were used for simulation. We simulate C-vacancy (VC) and Si-vacancy (VSi). We relaxed all atoms so that the atomic force tolerance is 1.0 × 10−4 Ha/Bohr. The unrelaxed defective configurations have the same symmetry as the perfect configuration, which is a D3h symmetry. During relaxation, atoms neighboring the vacancy were displaced to reach a ground state condition. In the case of VC, a Si atom at the center of the defect has four bonds, resulting in a new 5-6-6-5 fourfold configuration with a C2v symmetry. In the case of VSi, a C atom forms bonds with two other C atoms, resulting in a new configuration, namely a 5-9-6 configuration. We identified that this configuration also has a C2v symmetry. Thus, symmetry breaking (lowering) occurs from D3h to C2v. We calculated the formation energy, which is 3.28 eV for the 5-6-6-5 fourfold and 3.92 eV for the 5-9-6 configuration. We also calculated the Density of States (DOS), and the results show that both configurations have semiconductor material properties suitable for promising optoelectronic devices with an infrared spectrum for future applications.

First Principle Investigations of Structural, Electronic and Thermal Properties of Pristine, Metal and Non-Metal Doped Silicene for Thermoelectric Applications

Silicene, a two-dimensional hexagonal silicon layer, exhibits exceptional electronic and thermoelectric properties. However, its application in semiconductors is hindered by its zeroband gap, which could be overcome by modifying its electronic properties through doping. In this paper, Density Functional Theory (DFT) calculations were performed to investigate the band gap opening in silicene by studying the effect of magnesium and sulphur doping on its electronic, structural and thermal properties. Pristine silicene has a lattice constant of 3.86 Å and a zero-band gap. Upon doping with 12.5% S and Mg atoms, the lattice constant modifies to 3.45 Å and 3.93 Å, respectively, resulting in a direct band gap opening. For 25% Mg and S doping, the result shows that Mg and S effectively alter the band structure and the band gap of silicene monolayer at various configurations. The maximum band gap was 0.98 eV and 1.22 eV for Mg and S doping into the meta position to the reference point R, respectively. The power factor significantly increases with doping, reaching 1.20 x 1011 WK-2m-1 and 1.40 x 1011 WK- 2 m-1 for 12.5% Mg and S doping compared to 7.4 x 1010 WK-2m-1 for pristine silicene. This substantial enhancement indicates improved thermoelectric performance, making silicene a promising candidate for thermoelectric applications. Results demonstrate that tuning the band gap through doping can simultaneously enhance the power factor, highlighting the potential of Mg/S-doped silicene for efficient energy harvesting and conversion.

Cavitation-assisted synthesis and chracterization of a novel catalyst from waste coconut trunk biomass for biodiesel production

In the current study, a novel heterogeneous catalyst has been prepared from waste coconut trunk biomass using an ultrasound-assisted batch reactor. It is observed from the characterization studies that the raw coconut trunk biomass consists of the maximum amount of silicon dioxide (SiO2) present in it which is further converted to mullite (composition of 3Al2O3.2SiO2) with a composition of 94.18 % (analyzed through Energy Dispersive Spectroscopy (EDAX) studies) is formed through the reaction in an ultrasound reactor processed at a very mild reaction temperature and reaction time 80℃ and 90mins. Synthesis of catalyst at mild process conditions will help to enhance the formation of energy-intensive products at a low cost. It is also observed from the XRD studies of raw feedstock and synthesized catalyst a change in the crystalline structure from hexagonal silicon dioxide to orthorhombic mullite shape. In comparison with the surface area of the raw biomass and mullite, a large amount of surface area ∼ 32 m2/g is observed which is due to the process of reaction in a highly intense ultrasound reactor. A change in the morphological structure of raw feedstock and synthesized catalyst is also observed through scanning electron microscope (SEM) analysis. The activity of the synthesized catalyst has been analyzed through its application in the production of biodiesel from waste cooking oil is also studied., and a yield of 75 % with a conversion of 74 % is observed at process conditions of 1:3 (oil: ethanol) (volumetric ratio), 3 (wt%) of catalyst concentration and 3hrs of reaction time. A prospective aspect of the implication of the entire work to analyze the life cycle analysis (LCA) is also reported in terms of environmental friendliness and sustainability.

[formula omitted] magnetism engineering in the low-buckled hexagonal SiS monolayer: A first-principles study

In this work, vacancy- and doped-induced magnetism engineering is investigated to functionalize the non-magnetic low-buckled hexagonal silicon sulfide (SiS) monolayer. This monolayer is an indirect gap semiconductor two-dimensional (2D) material with an energy gap of 2.20(3.02) eV obtained from the PBE(HSE06)-based calculations. Creating a single Si vacancy leads to a significant magnetization of SiS monolayer with the feature-rich half-metallic nature. Herein, a total magnetic moment of 1.89 μB is obtained and magnetic properties are produced mainly by S and Si atoms closest to the defect site. In contrast, single S vacancy preserves the non-magnetic nature inducing a band gap reduction of the order of 26.36%. n-type doping with P atom metalizes the monolayer, meanwhile As impurity leads to the emergence of the half-metallicity with a total magnetic moment of 1.00 μB. Similarly, this value is also obtained by p-doping using P and As atoms as dopants, where the diluted magnetic semiconductor nature is obtained. Moreover, doping with IA- (Na and K) and IIIA-group (Al and Ga) atoms is also proposed to engineer the magnetism in SiS monolayer. It is found that these impurities induce either half-metallic or diluted magnetic semiconductor behaviors with total magnetic moment between 0.99 and 1.00 μB. The electronic and magnetic properties are regulated mainly by the interactions between impurities and their neighbor S atoms, which modify the charge distribution in their outermost orbitals. In addition, the Bader charge analysis asserts that dopant atoms gain charge from the host monolayer when substituting S atom, meanwhile they act as charge loser — transferring charge to the host monolayer when doping at Si sublattice. The presented results may suggest efficient approaches to properly engineer SiS monolayer electronic and magnetic properties, making new 2D candidates for spintronic applications.

Self-power, multiwavelength photodetector based on a Sn-doped Ge quantum dots/hexagonal silicon nanowire heterostructure.

Tin-doped germanium quantum dots (Sn-doped Ge QDs)-decorated hexagonal silicon nanowires (h-Si NWs) were adopted to overcome the low infrared response of silicon and the excess dark current of germanium. High-quality Sn-doped Ge QDs with a narrow bandgap can be achieved through Ge-Sn co-sputtering on silicon nanowires by reducing the contact area between heterojunction materials and Sn-induced germanium crystallization. The absorption limit of the heterostructure is extended to 2.2 µm, and it is sensitive to 375-1550 nm light at 0 V, which has optimality at 1342 nm, with a photo-to-dark current ratio of over 815, a responsivity of 0.154 A/W, and a response time of 0.93 ms. The superior performance of the Sn-doped Ge QDs/h-Si NW photodetector in multiwavelength is attractive for multi-scenario applications.

Direct bandgap quantum wells in hexagonal Silicon Germanium

Silicon is indisputably the most advanced material for scalable electronics, but it is a poor choice as a light source for photonic applications, due to its indirect band gap. The recently developed hexagonal Si1−xGex semiconductor features a direct bandgap at least for x > 0.65, and the realization of quantum heterostructures would unlock new opportunities for advanced optoelectronic devices based on the SiGe system. Here, we demonstrate the synthesis and characterization of direct bandgap quantum wells realized in the hexagonal Si1−xGex system. Photoluminescence experiments on hex-Ge/Si0.2Ge0.8 quantum wells demonstrate quantum confinement in the hex-Ge segment with type-I band alignment, showing light emission up to room temperature. Moreover, the tuning range of the quantum well emission energy can be extended using hexagonal Si1−xGex/Si1−yGey quantum wells with additional Si in the well. These experimental findings are supported with ab initio bandstructure calculations. A direct bandgap with type-I band alignment is pivotal for the development of novel low-dimensional light emitting devices based on hexagonal Si1−xGex alloys, which have been out of reach for this material system until now.

Hydrogen generation via water splitting with hexagonal silicon monolayers as (photo)catalysts

Here, we explore the possibility of using pristine hexagonal silicon (hex‑Si) monolayers as (photo)catalysts for water splitting. We found that pristine hex‑Si monolayers show promise as H2O activation site, promoting oxygen evolution reaction (OER), and energetically favorable O2 production in both acidic and alkaline media. However, hydrogen evolution reaction (HER) and OER on this surface do require a substantial overpotential due to the weak bond between H2O and the pristine hex‑Si monolayer, strong H and OH adsorption on the hex‑Si surface, and the energy needed for OOH binding in both acidic and alkaline conditions. Understanding these findings aids in developing hex‑Si-based (photo)catalysts for future water splitting reactions.

Study on thermal conductivity of micron BN-nano SiO2 combined modified epoxy resin composites

Epoxy resin has attracted widespread attention in the field of power electronic packaging due to its favorable processing technology, high adhesion, and excellent dielectric properties. The enhancement of thermal conductivity in epoxy resin through the incorporation of diverse particles is a prominent area of interest in the realm of modified insulation materials. In this study, hexagonal boron nitride (h-BN) and silicon dioxide (SiO2) with good thermal conductivity were used as doped fillers to modify epoxy resin (EP). The analysis of experimental results indicated that the thermal conductivity of materials with a total doping amount of 20 wt% and a mass ratio of BN to SiO2 of 70:30 to 60:40 could increase the thermal conductivity by 118.1~126.0%. In contrast to pure EP, the thermal conductivity of composite epoxy resin materials has been significantly enhanced.

Theoretical prediction of a novel hexagonal narrow-gap silicon allotrope under high pressures

Silicon material plays a vital role in contemporary technology-related fields, including electronics and the photovoltaics. There is a growing demand for exploring new silicon structures with potential applications, and numerous metastable structures have been reported. In this study, we present the prediction of a novel stable sp 3 hybridized silicon allotrope using particle swarm optimization global structure search. The predicted Si allotrope is a semiconductor with an indirect band gap of approximately 0.21 eV. It possesses three Si basis atoms in the unit cell, and we named it Si3. Interestingly, when subjected to strain, it undergoes a transition from a semiconductive state to a metallic state. Furthermore, moderate tensile strain enhances the interactions between silicon and lithium atoms, suggesting its potential for Li-ion batteries. Additionally, Si3 exhibits exceptional sunlight absorption across a wide range of wavelengths, with a significantly higher light absorption intensity than cubic diamond silicon. These findings have important implications for photovoltaic applications.

Molecular dynamics simulating the effects of Shockley-type stacking faults on the radiation displacement cascades in 4H-SiC.

Four-layer hexagonal silicon carbide (4H-SiC) is a promising material for high-temperature and radiation-rich environments due to its excellent thermal conductivity and radiation resistance. However, real 4H-SiC crystals often contain Shockley-type stacking faults (SSF), which can affect their radiation resistance. This study employed molecular dynamics (MD) simulation method to explore the effects of SSF on radiation displacement cascades in 4H-SiC. We conducted a comprehensive study of various SSF within the crystalline framework of 4H-SiC, and analyzed their stacking fault energy (SFE). We simulated the radiation displacement cascade in 4H-SiC with SSF and analyzed the effects of SSF on the distribution of radiation displacement defects. We simulated the radiation displacement cascade in 4H-SiC with SSF under different energies of primary knock-on atom (E PKA) and temperatures (T) conditions, and analyzed the variation pattern of the number of radiation displacement defects and clusters. The results indicated that SSF limits defect distribution position. SSF has an effect on the defects and clusters of 4H-SiC in the displacement cascade, and SSF can affect the maximum working temperature of 4H-SiC.

Preparation and tribological properties of hybrid nanofluid of BNNs and SiC modified by plasma

Aviation superalloy is widely used in aviation parts because of its high temperature strength and good fatigue resistance. Due to its high yield strength and low thermal conductivity, it is easy to produce lots of heat during processing, and its hardening tendency is serious, in the case of insufficient cooling lubrication easy to cause burns and poor processing quality. However, the traditional coolant has insufficient cooling performance, which is difficult to solve the thermal problem of aviation superalloy processing. In order to solve these problems, this paper uses plasma hydroxyl modified hexagonal boron nitride nanosheets (BNNs) and silicon carbide (SiC), and then adds sodium dodecyl benzene sulfonate (SDBS) in deionized water to prepare water-based BNNs/SiC hybrid nanofluid. The method of improving dispersion stability was studied by experimental means, and a single factor experiment was designed to study the influence law of mass ratio, mass concentration and temperature on heat transfer performance. Then the tribological properties of the formula were verified by friction and wear test. The results show that the Zeta potential of the nanofluid prepared by plasma hydroxyl modification is greatly improved, and the nanoparticles are effectively dispersed in the water-based liquid under the action of electrostatic stability mechanism. The viscosity reaches a minimum of 0.36249mPa·s, and the thermal conductivity reaches a maximum of 0.99496 W/(m·K). BNNs and SiC particles produce a synergistic structure like the rolling bearing due to the interface effect, which greatly enhances the anti-wear and anti-friction effect of the base fluid. The average friction coefficient is reduced to 0.068, and the volume wear rate is 37.03%, 30.8% and 69.35% lower than the traditional coolant, BNNs nanofluid and SiC nanofluid, respectively.

Tailoring thermoelectric properties through carbon doping and magnetic field variation: A comparative study in 2D h-BN and h-SiC

The purpose of this work is to study the effects of carbon doping on the thermoelectric properties of monolayer hexagonal boron nitride (h-BN) and hexagonal silicon carbide (h-SiC) in the presence of a magnetic field. We use a tight-binding model and Kubo formalism to calculate the effects of doping concentration, dopant type and applied magnetic field on the heat capacity, electrical conductivity, magnetic susceptibility, and thermoelectric figure of merit. Heat capacity displays a Schottky anomaly that is more prominent at lower dopant concentrations. In the presence of the magnetic field, the Schottky anomaly shifts to lower temperature and its intensity is reduced. The magnetic susceptibility of the doped structures is enhanced by both doping and a magnetic field. The p-type doped structures exhibit higher magnetic susceptibility intensity compared to the n-type doped structures, especially for h-SiC structure. The electrical and thermal conductivities rise from zero at low temperatures, with higher intensity for p-doped structures. Doped h-SiC has higher conductivity at low temperatures, but doped h-BN exceeds it at higher temperatures. A comparison of p- and n-doped h-SiC and h-BN reveals enhanced thermoelectric performance for p-doped structures, further improved by lower dopant concentrations and applied magnetic fields. Overall, the work provides new insights into optimizing the thermoelectric properties of doped h-BN and h-SiC nanostructures through doping and external fields.

Optimized Design of a Hexagonal Equal Gap Silicon Drift Detector with Arbitrary Surface Electric Field Spiral.

In our previous studies, the silicon drift detector (SDD) structure with a constant spiral ring cathode gap (g) and a given surface electric field has been partially investigated based on the physical model that gives an analytical solution to the integrals in the calculations. Those results show that the detector has excellent electrical characteristics with a very homogeneous carrier drift electric field. In order to cope with the implementation of the theoretical approach with a complete set of technical parameters, this paper performs different theoretical algorithms for the technical implementation of the detector performance using the Taylor expansion method to construct a model for cases where the parameter "j" is a non-integer, approximating the solution with finite terms. To verify the accuracy of this situation, we performed a simulation of the relevant electrical properties using the Sentaurus TCAD tool 2018. The electrical properties of the single and double-sided detectors are first compared, and then the effects of different equal gaps g (g = 10 μm, 20 μm, and 25 μm, respectively) on the electrical properties of the double-sided detectors are analyzed and demonstrated. By analyzing and comparing the electrical characteristics data from the simulation results, we can show that the double-sided structure has a larger transverse drift electric field, which improves the spatial position resolution as well as the response speed. The effect of the gap size on the electrical characteristics of the detector is also analyzed by analyzing three different gap bifacial detectors, and the results show that a 10 μm equal gap is the optimal design. Such results can be used in applications requiring large-area SDD, such as the pulsar X-ray autonomous navigation. in the future to provide navigation and positioning space services for spacecraft deep-space exploration.

Engineering hexagonal-silicon monolayer for high-performance water splitting electrocatalysts

We report on the performance of hexagonal silicon (hSi)-based electrocatalysts with lattice substitution using a single Ge (Ge/hSi) and a single Ti (Ti/hSi) in promoting the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) via the water splitting process. All data provided in this work is generated using density functional theory (DFT)- based total energy calculations. Based on the results, we conclude that both Ge/hSi and Ti/hSi surfaces have the potential to be developed as HER and OER electrocatalysts. The Ti/hSi electrocatalyst outperforms Ge/hSi in terms of performance in decomposing H2O molecules and promoting OER due to its twice lower overpotential than the OER overpotential on the Ge/hSi surface. However, in comparison to H bonding to the Ti/hSi surface, Ge/hSi is somewhat weaker at binding H∗, making Ge/hSi slightly easier to induce HER compared to Ti/hSi. These findings will have a considerable impact on the development of new non-Pt group metal (non-PGM) catalysts.

Full-Stokes polarization photodetector based on the hexagonal lattice chiral metasurface.

A hexagonal lattice silicon (Si) metasurface formed by the displacement of two mirrored isosceles trapezoid blocks in opposite directions is integrated into an InGaAs/InP photodetector to sense the circularly polarized light, whose optical properties mainly are controlled by the Fabry-Pérot (FP) cavity mode supported in the air slit called the Tunnel A. The Si metasurface can also be equivalent to the combination of the electric quadrupole (EQ) and the magnetic quadrupole (MQ) for the right circularly polarized (RCP) mode and the magnetic quadrupole for the left circularly polarized (LCP) mode. The external quantum efficiency of the circular polarization photodetectors is 0.018 and 0.785 for the RCP and LCP incidence, respectively. In addition, the full Stokes pixel based on the six-image-element technique can almost accurately measure arbitrary polarized light at 1550 nm operation wavelength, whose errors of the degree of linear polarizations (Dolp) and the degree of circular polarizations (Docp) are less than 0.01 and 0.15, respectively.

Formation of hexagonal phase 9R-Si in SiO2/Si system upon Kr+ ion implantation

Hexagonal silicon polytypes are attracting significant attention from the scientific community due to their potential applications in next-generation electronics and photonics. However, obtaining stable heterostructures based on both cubic and hexagonal polytypes is a complicated task. In the present work, the possibility of formation of hexagonal silicon of the 9R-Si phase using the traditional method of microelectronics, i.e. ion implantation, is shown. Implantation of Kr+ ions was carried out through a SiO2 layer, the thickness of which was approximately twice the projected range of Kr+ followed by high temperature annealing. High resolution transmission electron microscopy reveals that a thin amorphous layer forms in a Si substrate at the interface with the SiO2 film under implantation, upon recrystallization of which the formation of the 9R-Si polytype occurs during annealing. It is assumed that mechanical stresses are created during implantation through the oxide layer, that contributes to hexagonalization during high-temperature annealing. The dependence of the efficiency of hexagonalization on the substrate orientation is established. In addition to the formation of the 9R-Si phase, at the implantation and annealing parameters used, light-emitting defects are formed in silicon, the photoluminescence of which at a wavelength of ∼1240 nm is observed up to a temperature of ∼120 K. The obtained results can stimulate and expand the range of applications of ion-irradiated silicon in micro-, nano-, and optoelectronics

Enhancing Thermal Conductivity of hBN/SiC/PTFE Composites with Low Dielectric Properties via Pulse Vibration Molding.

In order to enhance the thermal conductivity of polytetrafluoroethylene (PTFE)-based composites, while maintaining relatively low dielectric constant and dielectric loss for high-frequency and high-speed applications, hexagonal boron nitride (hBN) and silicon carbide (SiC) compounded fillers are filled into the PTFE matrix. The hBN/SiC/PTFE composites are prepared by pulse vibration molding (PVM), and their subsequent thermal conductivities are comparatively investigated. The PVM process with controlled fluctuation in pressure (1Hz square wave force, 0-20MPa, at 150°C) can reduce the sample porosity and surface defects, improve the orientation of hBN, and increase the thermal conductivity by 44.6% compared with that obtained by compression molding. When hBN:SiC (vol) is 3:1, the in-plane thermal conductivity of the composite with 40vol% filler content is ≈4.83Wm-1 K-1 , which is 40.3% higher than that of hBN/PTFE. Regarding the dielectric properties, hBN/SiC/PTFE maintains a low dielectric constant of 3.27 and a low dielectric loss of 0.0058. The dielectric constants of hBN/SiC/PTFE ternary composites are predicted by using different prediction models, among which the effective medium theory (EMT), is in good agreement with the experimental results. PVM shows great potential in the large-scale preparation of thermal conductive composites for high-frequency and high-speed applications.

Electrical properties of a high-precision hexagonal spiral silicon drift detector

With the deepening and expansion of semiconductor technology and research, in order to continuously optimize the structure and performance of semiconductor detectors, a high-precision hexagonal spiral silicon drift detector (SDD) is proposed in this paper. In order to obtain a more accurate spiral ring structure, this paper goes beyond the first-order formula in the Taylor expansion for calculating the radius of the spiral ring. Based on the first-order formula, the second-order formula for calculating the radius of the spiral ring is further developed and derived. The point coordinates are obtained by combining the radius, angle, and ring spacing change formula to obtain a more accurate spiral ring structure. The actual number of turns is more accurate than that obtained from first-order approximation, which better solves the problem of accurate calculation of the number of spiral rings and the structure of the spiral SDD in the existing technology, that is, the accurate calculation of the radius of the spiral ring. In order to verify the abovementioned theory, we model this new structure and use Technology Computer-Aided Design to system simulate and study its electrical properties, including potential distribution, electric field distribution, and electron concentration distribution. According to the simulation results, compared with the first-order formula, the second-order formula has better electrical properties; more uniform distribution of potential, electric field, and electron concentration; and a clearer electron drift channel.

The phase selection law in the growth of hexagonal diamond silicon nanowires by controlling chemical potential

Large-scale and whole hexagonal diamond silicon nanowires (h-SiNWs) were synthesized with aluminum-gold (Al–Au) alloy-catalytic assistance to reduce the nucleation barrier by regulating the chemical potential. Here, we demonstrate the effect of the catalyst on the structure in silicon nanowires by correlating the experimental observations with a theoretical interpretation based on thermodynamics. It was found that high chemical potential is necessary to enhance the nucleation of the hexagonal diamond phase, and the addition of Al into the Au catalyst can increase the supersaturation of silicon atoms in the catalyst and reduce the contact angle of solid-liquid to tune the chemical potential. When the supersaturation is high enough and the alloy catalyst is almost perpendicular to the top of the nanowire, the hexagonal diamond phase is more likely to appear than the cubic phase, whereas others are not. Additionally, a 1319 nm photodetector was fabricated using the h-SiNWs network with a smaller band gap and a lower conductivity compared with cubic silicon nanowires (c-SiNWs), whose dark current is as low as 5.03 × 10 −12 A with a high responsivity of 0.5 A⋅ W −1 at an applied bias of 1 V.

Influence of hybrid nanofluid on tool wear and surface roughness in MQL-assisted face milling of AISI 52100

ABSTRACT With escalating demand for machinability, economical production, health, and environment-related aspects are pushing the present industrial units to drop the usage of harmful-cutting fluid in machining. However, the adaption of this approach for machining difficult-to-cut materials does not ensure favourable outcomes of the tool performance, surface qualities, etc., as friction and heat seriously disturb machining efficiency. This study is focused on near-dry machining employing recently developed hybrid nanofluids-based lubrication in the machining of AISI 52,100 steel. Hexagonal boron nitride (hBN) and silicon carbide (SiC) nanoparticles are added to the lubrication oil to enhance the performance of the Minimum Quantity Lubrication (MQL) system. Taguchi’s method-based Grey relational analysis (GRA) is used for the concurrent optimisation of the tool flank wear and surface roughness. The best parametric setting for the multi-response is achieved as: a lubricant flow rate of 150 ml/h, depth of cut of 0.2 mm, and nanofluid with 0.8 wt % of hBN and 0.2 wt % of SiC nanoparticles. The confirmation experimentation concluded that the multi-response factor is enhanced by 2.48% at the optimum setting with the mean values of TFW and SR as 84 and 0.36 µm, respectively.