Effect Of Si Doping Research Articles

Combined effect of silicon doping and thermal treatment on microstructures and mechanical properties of Ti50Nb20V20Al10 refractory high-entropy alloy

This study investigates the effects of Si doping and thermal treatment on the microstructures and mechanical properties of Ti50Nb20V20Al10 refractory high-entropy alloy (RHEA) with a BCC/B2 dual-phase structure. The as-cast RHEAs exhibit typical dendrite and inter-dendrite structure. Upon Si doping, eutectic M5Si3 phase gradually precipitates along the grain boundaries (GBs), resulting in the increase of yield strength (YS) by over 200 MPa. After recrystallization, all the RHEAs exhibit fully recrystallized microstructures. The eutectic M5Si3 phase disappears while forming nanoscale M5Si3 phase distribute along GBs, thereby enhancing the mechanical properties of the RHEAs. Notably, the recrystallized RHEA with 1 at% Si exhibits favorable specific YS (SYS, 172.9 ± 2.9 MPa·cm3·g−1) and fracture elongation (22.8 ± 6.8 %), respectively. The hindrance effect of nanoscale M5Si3 phase on dislocations motion and the transition from planar slip to cross-slip significantly enhance strain hardening capability and plasticity of the RHEAs. Our research findings are of constructive significance to the study of lightweight energetic structural materials.

Investigation of mechanical behavior of porous carbon-based matrix by molecular dynamics simulation: Effects of Si doping

Understanding the mechanical properties of porous carbon-based materials can lead to advancements in various applications, including energy storage, filtration, and lightweight structural components. Also, investigating how silicon doping affects these materials can help optimize their mechanical properties, potentially improving strength, durability, and other performance metrics. This research investigated the effects of atomic doping (Si particle up to 10 %) on the mechanical properties of the porous carbon matrix using molecular dynamics methods. Young's modulus, ultimate strength, radial distribution function, interaction energy, mean square displacement and potential energy of designed samples were reported. MD outputs predict the Si doping process improved the mechanical performance of porous structures. Numerically, Young's modulus of the C-based porous matrix increased from 234.33 GPa to 363.82 GPa by 5 % Si inserted into a pristine porous sample. Also, the ultimate strength increases from 48.54 to 115.93 GPa with increasing Si doping from 1 % to 5 %. Silicon doping enhances the bonding strength and reduces defects in the carbon matrix, leading to improved stiffness and load-bearing capacity. This results in significant increases in mechanical performance. However, excess Si may disrupt the optimal bonding network, leading to weaker connections within the matrix. Also, considering the negative value of potential energy in different doping percentages, it can be concluded that the amount of doping added up to 10 % does not disturb the initial structure and stability of the system, and the structure still has structural stability. So, we expected our introduced atomic samples to be used in actual applications.

Effect of Si doping on elastic-plastic fracture toughness (JIC) of T91 ferritic/martensitic steel in liquid lead-bismuth eutectic

This work was devoted to understanding the effect of Si doping (1.27 wt%) on elastic-plastic fracture toughness (JIC) of T91 ferritic/martensitic (F/M) steel in liquid lead-bismuth eutectic (LBE, Pb44.5Bi55.5, wt%) under various parameters. The results showed that Si doping significantly promoted occurrence of liquid metal embrittlement (LME) and led to more severe degradation of fracture toughness at 350 °C, especially in oxygen-poor LBE. The LME susceptibility of T91-Si steel was found to be nearly independent on the loading speeds, while T91 F/M steel exhibited a stronger LME effect when the loading speed was decreased from 0.02 mm/min to 0.002 mm/min. Oxygen concentration had a mild effect. Detailed microstructural analyses showed that the fracture behavior of the T91-Si steel in LBE environment at 350 °C was analogous to cleavage fracture and the crack propagation was mainly transgranular. The crack wall was quite rough and locally faceted to low-index crystallographic planes of {110}. Numerous dislocations were also present in the vicinity of the crack tip. No solid evidence of diffusion of Pb and Bi into the steel bulk was discovered even at the atomic scale, which strongly suggests a crack tip surface adsorption-based LME mechanism.

Electrical transport in epitaxially grown undoped and Si-doped degenerate GaN films

This study investigates the electrical transport properties of undoped and Si-doped, degenerate GaN heteroepitaxial films grown on sapphire by reactive rf sputtering of GaAs (and Si) in Ar-N2 mixture. The room temperature electrical measurements showed that the resistivity of undoped GaN film grown at 100% N2 was ∼2 × 105 Ω cm, which reduced to ∼1 Ω cm in Si-doped film, revealing the effect of Si doping. With decrease of N2 from 100% to 75%, the carrier concentration of Si-doped films increased from ∼7 × 1018 cm−3 to ∼2 × 1019 cm−3, but remained practically unchanged as N2 was decreased to 20%, which is explained by effects due to saturation of Si doping and increase of Ga interstitials as well as compensation by N interstitials and Ga vacancies. Undoped and Si-doped films grown below 20% N2 displayed similar carrier concentrations (∼1020 cm−3), due to dominance of Ga interstitials. Both undoped and Si-doped films were degenerate and displayed increase of mobility with carrier concentration and temperature, which was analyzed by the combined effect of ionized impurity and dislocation scattering, using compensation ratio as fitting parameter. At carrier concentrations ≲1019 cm−3, the mobility was governed by both ionized impurity and dislocation scattering, while at higher carrier concentrations, ionized impurity scattering was found to dominate, limited by compensation due to acceptors. In spite of the degenerate character, the films displayed a small decrease of carrier concentration with temperature, along with a nearly linear decrease of mobility, which are explained by a marginal increase of compensation ratio with decrease of temperature, taking into account the band edge fluctuation effects. These features of electrical transport have not been much explored for heteroepitaxial, n-type degenerate GaN films, possessing high density of dislocations and point defects.

Effect of Si Doping and Active Carbon Surface Modifications on the Structure and Electrical Performance of Li4Ti5O12 Anode Material for Lithium-Ion Batteries

Effect of Si Doping and Active Carbon Surface Modifications on the Structure and Electrical Performance of Li4Ti5O12 Anode Material for Lithium-Ion Batteries

Superior Effect of Si Doping on Interfacial Reaction of LiPON Solid Electrolyte for the Silicon-Rich Oxide (SiO1/2) Anode in All-Solid-State Batteries: A First-Principles Prediction

Silicon oxide is considered an alternative silicon anode for lithium-ion batteries, possessing high lithium capacity and excellent cycling performance. However, the application of silicon oxide in a solid-state lithium battery is still not reported; exploring the atomic-scale mechanism at its interface with the solid-state electrolyte is critical for further study. In this work, atomic-scale electrochemistry of Si-, B-, and C-doped LiPON solid electrolytes for the silicon-rich oxide (SiO1/2) electrode is explored by first-principles simulations. Our calculations reveal that the interfacial stability and conductivity are significantly enhanced upon doping of Si in LiPON. The SiO1/2/LiSiPON interface presents the highest adhesion energy and the lowest interface formation energy, suggesting a superior stability of the interface. An obvious shift of the DOS curve and large charge overlap area can be observed for LiSiPON with incorporation of the SiO1/2 layer, which shows a much smaller band gap compared with primitive LiSiPON. Moreover, lithium tends to diffuse along the LiSiPON/SiO1/2 interface, and the doped elements provide a channel for lithium transport due to mutual electrostatic interaction. Our work provides theoretical guidance for designing electrode/SSE interfaces for silicon oxide-based ASSBs.

Effect of Si content on microstructure, mechanical properties, and cutting performance of TiSiN/AlTiN dual-layer coating

Ti1-xSixN/AlTiN dual-layer coatings with different Si content were prepared by cathode arc evaporation to study the effect of Si-doping on the coatings. The composition, morphology, and microstructure of the coatings were characterized using SEM, XRD, and XPS. The hardness, elastic modulus, and adhesion strength were measured by nano-indentation and micro-scratch. Results show that coatings all consist of TiN grains and Si3N4 amorphous phases. Ti1-xSixN/AlTiN dual-layer coating has the highest hardness of 43.07 GPa at a Si content of 0.19 and the lowest elastic modulus of 314.46 GPa at a Si content of 0.25. High-speed milling of Ti-6Al-4V alloy was performed to evaluate the cutting performance of the coated tools. The value and amplitude of the cutting force were collected to analyze the wear condition of tools. When cutting speed at 120 m/min, the coating with a Si content of 0.19 shows the best cutting performance, having the lowest cutting force and flank wear. The higher silicon content increases the bonding of titanium alloy, influencing the stability during cutting. The lower silicon content reduces the wear resistance of the coating and shorten tool life. Suitable Si content of the coating has been proved effective in improving the cutting performance on Ti-6Al-4V alloy.

First-principles study of influence of Si on <i>γ</i> phase in Inconel 718 alloy

Inconel 718 (IN 718) is the most widely used nickel-based high-temperature alloy today. It is widely adopted in important fields such as aerospace, energy and chemicals, and is also one of the few high-temperature alloys, of which some can be fabricated by using additive manufacturing. There is a lack of research on the effect of Si on the structure and properties of IN 718 alloy on a microscopic scale. In this paper, the effect of Si doping on the γ phase in IN 718 alloy is investigated by first-principles calculations through using the CASTEP package. The lattice constants, total energy, defect formation energy, formation enthalpy, cohesive energy, density of states, and electron density difference of the γ phase are calculated before and after Si doping, and population analysis is performed. The calculation of the lattice constant reveals that the doping of Si atoms expands the cell volume of the γ phase supercell, which contributes to a certain solution strengthening effect, and is conducive to the improvement of the hardness of the alloy. The energy and electronic structure calculations show that the Si atoms prefer to occupy the Ni atomic positions in the γ phase. The number of valence electrons between the atoms, the distribution of the charge density, and the strength of the bonds between the atoms also change with Si doping, thus modifying the interaction of the atoms within the γ phase, reducing the stability of the γ phase, and favouring the precipitation of the second phase. Besides, uniform and dense IN 718 coatings with low-coat Si doping are successfully fabricated by using plasma cladding. The experimental results demonstrate that Si doping has no significant effect on the type of matrix structure of IN 718 coatings, but causes a slight expansion of the lattice of the alloy, which is consistent with the calculation result. The addition of Si can result in a transformation of the alloy coating from columnar crystal to equiaxed crystal, refining the grain size of the alloy, while reducing the volume fraction of the γ phase and increasing the volume fraction of the second phase. Moreover, the addition of Si exacerbates the segregation of Nb and Cr elements in the IN 718 coatings.

Structural and electronic properties with respect to Si doping in oxygen rich ZnSnO amorphous oxide semiconductor

The effect of Si doping in the presence of excess oxygen on the zinc-tin-oxide (ZTO) thin-film transistor is investigated. The threshold voltage increases from 3.86 to 10.8 V, and the ON current reduces from 4 × 10 -4 to 1.1 × 10 -4 A for the undoped and 1 wt% Si-doped ZTO transistor, respectively. The changes in the threshold voltage and the ON current are attributed to the suppression of free charge carriers due to excess oxygen in the film. The annihilation of oxygen vacancy-related defects states is substantiated by the density of states extracted from the photonic capacitance-voltage characteristic of the undoped and Si-doped ZTO thin-film transistors. Moreover, due to the high binding energy of Si and oxygen, excess oxygen is introduced into the film. The excessive oxygen forms the O-O ex dimer that acts as the electron trap and degrades the device's stability. From the bias stress measurement and the density of states extraction, it is concluded that 0.5 wt% doping of Si in ZTO is optimal for moderate device performance, less defects density, and high stability.

Role of twin defects on growth dynamics and size distribution of undoped and Si-doped GaAs nanowires by selective area epitaxy

We report the effects of Si doping on the growth dynamics and size distribution of entirely catalyst-free GaAs nanowire (NW) arrays grown by selective area molecular beam epitaxy on SiO2-masked Si (111) substrates. Surprising improvements in the NW-array uniformity are found with increasing Si doping, while the growth of undoped NWs appears in a metastable regime, evidenced by large size and shape distributions, and the simultaneous presence of crystallites with tetrahedral termination. Correlating scanning electron microscopy and transmission electron microscopy investigations, we propose that the size and shape distributions are strongly linked to the underlying twin defect formation probabilities that govern the growth. Under the present growth conditions, Si-doping of GaAs NWs leads to a very high twin defect formation probability (∼0.4), while undoped NWs exhibit a nearly threefold decreased probability (∼0.15). By adopting a model for facet-mediated growth, we describe how the altered twin formation probabilities impact the competing growth of the relevant low-index NW facets, and hence, NW size and shape. Our model is further supported by a generic Monte Carlo simulation approach to highlight the role of twin defects in reproducing the experimentally observed size distributions.

High-order mode bulk acoustic wave resonators based on polarity-inverted SiAlN/AlN multilayered films for high-frequency operation

AlN film bulk acoustic wave (BAW) resonators operating at above 5 GHz for next generation mobile communications present some problems, such as the very thin thickness of the piezoelectric film and electrode films. These cause degradations of the power handling capability, electromechanical coupling factor, and Q value in film BAW resonators. Polarity-inverted multilayered AlN film BAW resonators can operate in high-order mode resonance. Therefore, an n-layer polarity-inverted film BAW resonator has n-times thicker piezoelectric film thickness than a standard BAW resonator with a monolayer piezoelectric film operating at same frequency. However, fabrication methods for polarity-inverted multilayered AlN films have not been established. This paper examines the effect of Si doping on AlN films on the crystal orientation, polarity direction, and electromechanical coupling factor (kt2). Furthermore, we fabricated and evaluated two- to eight-layer polarity-inverted SiAlN/AlN film high-overtone bulk acoustic wave resonators (HBARs). The polarity of the SixAl1−xN films inverted around x = 0.024–0.13. The crystal orientation and kt2 of the SixAl1-xN films were degraded with increasing Si concentration x. The eight-layer polarity-inverted SiAlN/AlN film HBAR resonated in the eighth mode. Moreover, the experimental longitudinal wave insertion loss exhibited a similar trend to the theoretical curve calculated by a Mason's equivalent circuit model considering the polarity inverted structure. The eight-layer polarity-inverted HBARs had approximately eight-times thicker piezoelectric film thickness than the monolayer AlN film HBAR. The insertion loss improved with increasing the number of polarity-inverted layers.

Synergistic effect of Si-doping and Fe2O3-encapsulation on drug delivery and sensor applications of γ-graphyne nanotube toward favipiravir as an antiviral for COVID-19: A DFT study

In this work, the behavior of favipiravir (FAV) adsorption on the pristine (2,2) graphyne-based γ-nanotube (GYNT) was theoretically studied. Also, the Si-doped form (Si-GYNT) and its composite with encapsulated Fe2O3 (Fe2O3@Si-GYNT) were investigated within density functional theory (DFT) calculations, using M05 functionals and B3LYP. It was found that FAV is weakly to moderately adsorb on the bare GYNT and Si-GYNT tube, releasing the energy of 2.2 to 19.8 kcal/mol. After FAV adsorption, the bare tube's electronic properties are changed. Localized impurity is induced at the valence and conduction levels by encapsulating a tiny Fe2O3 cluster. As such, the target composite becomes a magnetic material. The binding energy between the Fe2O3@Si-GYNT and the FAV molecule becomes substantially stronger (Ead = -25.2 kcal/mol). We developed a drug release system in target parts of body, during protonation in the low pH of injured cells, detaching the FAV from the tube surface. The drug's reaction mechanism with Fe2O3@Si-GYNT shifts from covalence in the normal environment to hydrogen bonding in an acidic matrix. The optimized structure's natural bond orbital, quantum molecular descriptors, LUMO, HOMO and energy gap were also investigated. The recovery time can be reduced to less than 10 s by increasing the working temperature properly during the experimental test.

Theoretical prediction on structure evolution and optimal properties of silicon modified hexagonal boron nitride as interphase in SiCf/SiC composite

To predict the effects of Si doping on hexagonal boron nitride (h-BN) and to achieve a balance between mechanical and oxidation properties for the interphase modification in SiCf/SiC composites, we herein calculate and analyze the crystal structures and mechanical properties of (BN)64Six (x = 4, 8, 16, 32) models by means of density functional theory (DFT) calculations and ab initio molecular dynamics (aiMD) simulations. The possible trends of crack deflection and self-healing ability are discussed. The modeling shows an obvious transition of (BN)64Six from the layered crystal structure and anisotropic mechanical property to amorphous structure and isotropic mechanical property as the Si doping content up to 36.1 wt%. Regarding to the application of interphase in SiCf/SiC composites, (BN)64Si16 model structure possess the highest debonding potential according to Cook and Gordon’s criteria and illustrates the higher self-healing capacity at elevated temperature.

Efficient Si Doping Promoting Thermoelectric Performance of Yb-Filled CoSb3-Based Skutterudites.

Nanocomposites have become a widely popular way to assist in the enhancement of thermoelectric performance for filled skutterudites. Herein, we unveil the distinctive effect of Si doping on the classic Yb0.3Co4Sb12. On the one hand, the reduced Yb filling fraction is accompanied by the in-situ precipitated CoSi nanoparticles, which not only enhances the power factor in the intermediate-low temperature range but also reduces electronic thermal conductivity for decreasing the carrier concentration. On the other hand, CoSi nanoparticles intensively disrupt the phonon transport, hiding the increased lattice thermal conductivity due to reduced Yb filling fraction. Although the residual YbSb2 second phases have an adverse effect on the thermoelectric properties, the integration effects achieve a peak ZT value of 1.37 at 823 K and increase ZTave by 21% for the Yb0.3Co4Sb12/0.1Si sample.

Crystallization and magnetic properties of ThMn12-type Sm-Fe-Co-Ti-Si based magnetic materials

Si-doped Fe-rich compounds, i.e., Sm(Fe0.8Co0.2)11Ti + Six (x = 0, 0.5, and 1.0), with ThMn12-type structure in forms of ribbons and bulks were fabricated using melt-spinning process and high pressure pressing and heat treatment processes. Physical and magnetic properties of the ribbons and bulks were analyzed to investigate Si doping effects on the Sm(Fe0.8Co0.2)11Ti. The Si-free ribbons were found to be amorphous, while the small amount of Si doping resulted in dramatic crystallization of the ThMn12 phase. Coercivity of the ribbons increased with the increasing Si content from 43 to 3140 Oe, while the magnetization decreased from 146 to 78 emu/g. It was observed that the Si-free ribbons consisted of nano-sized grains in the matrix of an amorphous phase. On the other hand, the Si-doped ribbons exhibited submicron-sized grains with high crystallinity. The crystallized phases of the heat-treated bulks varied with the Si concentrations; the main phase was the ThMn12 phase in all samples, but concentrations of soft magnetic α-Fe phase decreased with the increasing Si concentration, and corresponding saturation magnetizations of the bulks also decreased.

The Effects of Si Doping on the Endurance and Stability Improvement of AlN-Based Resistive Random Access Memory

The Effects of Si Doping on the Endurance and Stability Improvement of AlN-Based Resistive Random Access Memory

Effects of Si doping well beyond the Mott transition limit in GaN epilayers grown by plasma-assisted molecular beam epitaxy

The effects of Si doping well beyond the Mott transition limit on the structural, electrical, and optical properties of plasma assisted molecular beam epitaxy grown GaN layers were studied. Si doping up to a doping density of <1.0 × 1020 cm−3 resulted in smooth surface morphologies and almost strain free 500 nm thick GaN layers on 50 mm Si (111) substrate. In this doping range, the crystal quality improved with increased Si doping. However, GaN layers with doping density of >1.0 × 1020 cm−3 resulted in rough surface morphology and degraded crystal quality. It also showed higher tensile strain, but did not result in cracking. Irrespective of the surface morphology and structural quality, the sheet resistance systematically decreased with increased carrier concentration up to and beyond the doping density of 1.0 × 1020 cm−3. PL study revealed three distinctive characteristics with Si doping: first, yellow luminescence is absent in Si doped samples— an indication of occupied VGa-ON and CN states in the bandgap; second, a distinctive luminescence peak is observed next to the band edge luminescence (BEL) for the samples doped beyond 2.1 × 1019 cm−3—probably an indication of localization of some of the electrons either at donors or at excitons bound to defects; third, blue shift of the BEL is not matching with the calculated Moss–Burstein shift for doping densities beyond 2.1 × 1019 cm−3—an indication of some of the electrons not occupying higher levels of conduction band, which is consistent with the second observation of localization of electrons near the donors or excitons bound to surface defects.

Growth of Si-Doped Polycrystalline Diamond Films on AlN Substrates by Microwave Plasma Chemical Vapor Deposition

Microcrystalline diamond films doped with silicon have been grown on aluminum nitride substrates by a microwave plasma CVD. The doping has been performed via adding silane in various concentrations to CH4-H2 reaction gas mixture in course of the deposition process. The films produced at the substrate temperatures of 750 to 950°C have been characterized by SEM, AFM, Raman and photoluminescence (PL) spectroscopy to assess the effect of Si doping on the diamond structure. The doped films showed bright photoluminescence of silicon-vacancy (SiV) color centers at 738 nm wavelength as well as noticeable side band at 723 nm. The optimum doping condition (SiH4/CH4 = 0.6%), that maximize the SiV PL emission, was determined for the range of silane concentrations SiH4/CH4 (0.0 - 0.9%) explored. A further PL enhancement can be achieved by increase in the substrate temperature. The applied in situ doping from gas phase is shown to be an easy and effective method to incorporate Si in diamond in a controllable way.

Electronic structure, magnetic properties and martensitic transformation of Ni50Mn36.5Sb13.5-xSix alloys

A series of Ni50Mn36.5Sb13.5-xSix (x = 0 - 2.5) Heusler alloys was prepared. Effect of Si-doping on the formation, martensitic transformation and magnetic properties of Ni-Mn-Sb alloys was investigated experimentally and theoretically. The increasing Si content leads to the increase of the Curie temperature TC and decrease of the saturation magnetization Ms at 5K. The martensitic transformation temperature Tm also shows a decreasing tendency with the substitution of Si for Sb. First-principles calculations indicate that the martensite has a lower total energy comparing with the austenite, which supports the phase transition observed experimentally. The energy difference between the martensite and austenite ΔEM suggests that the martensitic transformation temperature TM will decrease with a small amount of Si-doping, but increase when Si content is high. This explains the decrease of TM observed in the experimental samples, for in these samples, the Si content is in the ΔEM-decreasing region. The calculated total spin moment of the martensite shows a decreasing tendency with increasing Si content, which agrees with the variation of saturation magnetization Ms at 5K.

Influence of Si doping on the microstructure and hardness of an AlTiSiN coating deposited by low pressure chemical vapor deposition

The effect of Si doping on the microstructure and hardness of an AlTiSiN coating deposited by the low pressure chemical vapor deposition (LPCVD) method was studied in detail using grazing incidence X-ray diffraction (GIXRD), field-emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), and a nanoindenter instrument. The results show that Al0.82Ti0.18N coating exhibits a typical columnar crystal structure, while Al0.88Ti0.09Si0.03N and Al0.82Ti0.08Si0.10N coatings show a fine equiaxed crystal structure. The number of internal substructures (dislocation, stacking fault, etc.) decreased, while the volume fraction of the amorphous structure increased with the increase of Si content. The results of GIXRD and HRTEM show that all AlTiSiN samples mainly consist of fcc AlN phase with a small amount of hcp AlN phase. Furthermore, a small amount of fcc TiN phase can only be observed in Al0.82Ti0.08Si0.10N coating. The hardness of Al0.82Ti0.18N, Al0.88Ti0.09Si0.03N, and Al0.82Ti0.08Si0.10N coatings is 33.0 ± 0.6 GPa, 38.3 ± 1.2 GPa and 27.0 ± 0.8 GPa, respectively. Al0.88Ti0.09Si0.03N coating has obvious potential value for industrial applications.