Tetragonal Silicon Research Articles

Unlocking and optimizing the thermodynamic potential of tetragonal Si and Ge: Strategies and insights from a tight-binding simulation framework for material engineering

This study theoretically explores the effects of external fields and doping on the electronic and thermoelectric properties of tetragonal silicon (T-Si) and tetragonal germanium (T-Ge) structures using a tight-binding model, Green’s function formalism, and the Kubo formula. External parameters modify the positions and intensities of the density of states (DOS) peaks, influencing charge carrier excitation and conductivity trends. Applying bias voltage introduces zero-intensity regions in thermal conductivity due to band gap opening, reducing thermal properties. In contrast, chemical potential and magnetic field significantly enhance thermal properties by increasing intensity and shifting the peak position. T-Ge exhibits higher thermal properties than T-Si across the selected parameter ranges. The findings highlight the potential for optimizing and enhancing the thermoelectric properties of tetragonal structures through external controllable parameters.

Thermoelectric performance of tetragonal silicon allotrope tP36-Si from first-principles study

Thermoelectric performance of tetragonal silicon allotrope tP36-Si from first-principles study

Hydrogen storage in lithium, sodium and magnesium-decorated on tetragonal silicon carbide

Motivated by the widespread application and fascinating properties of various silicon-carbon nanomaterials, we have extensively investigated the properties of tetragonal silicon carbides (t-SiC) monolayer as a novel 2D material for hydrogen storage.Using calculations of the density functional theory comprising van der Waals interactions of type vdW-DF2-C09x, the structural stability, electronic properties and hydrogen molecules adsorption energies on the surface of pure t-SiC were investigated.The results show that adsorption energies of H2 molecules in this system are stronger than that of graphene. We also found that the decoration with alkali (Li, Na) and alkaline-earth (Mg) metals atoms increases the stability of hydrogen compared to the pure system. The studied system decorated with 8 elements of Li/Na/Mg is able to adsorb up 24 molecules of hydrogen and reaches a gravimetric capacity of 6.50, 5.54 and 5.48 wt%, respectively. The desorption temperatures found are significantly high compared to other 2D systems.

New Al3Si7 phase with tetragonal silicon structure in quasicrystal-forming near-eutectic Al-Cu-Fe-Si alloys

• FCI quasicrystal forms as primary phase for 7 at% Si:Cu/Fe substitution. • The Al 3 Si 7 (Al 4 Si 19 ) phase was synthesized for the first time. • Al 3 Si 7 coexists with ω -CuAl 2 forming an eutectic. • The melting point of Al 3 Si 7 was found to be 514 °C. • Eutectic-containing alloys were 43% less hard than undoped base alloy. A range of aluminum-based quaternary alloys was prepared by arc melting, followed by suction casting. Silicon doping was proven to exhibit the high potential of stabilization of face-centered icosahedral (FCI) quasicrystal. The FCI phase stability region in pseudoternary Al-Cu-Fe-(Si) diagram agrees with compositional limitations imposed by Hume-Rothery electron-counting rules. It was found that FCI forms as primary phase for 7 at% Si:Cu/Fe substitution. The finding might allow crystallization of the FCI phase monocrystals directly from the melt. The study revealed the presence of eutectic in Al-Cu-Fe-Si system. It is composed of tetragonal Al 3 Si 7 that form between CuAl 2 orthorhombic dendrites and isolated needles of hexagonal Al-Fe-Si intermetallic. The stability of Al 3 Si 7 phase was proven experimentally for the first time, but was previously predicted by a number of ab-initio studies. The overall Vickers hardness of the studied alloys was not significantly affected by Si content if doping did not exceed 7 at%. For 10 at% Si:Fe or Si:Cu doping, the hardness dropped by as much as 330 HV1 or 43% with respect to the undoped base alloy. This could be explained by the formation of soft eutectic.

The Dirac cone in two-dimensional tetragonal silicon carbides: a ring coupling mechanism.

The exploration of novel two-dimensional semimetallic materials is always an attractive topic. We propose a series of two-dimensional silicon carbides with a tetragonal lattice. The band structure of silicon carbides with tetragonal carbon rings and silicon rings exhibits Dirac cones. Interestingly, the Dirac cone of tetragonal SiC originates from a "ring coupling" mechanism. This mechanism refers to the mutual coupling between the four carbon atoms in the tetragonal C ring, and the same coupling in the tetragonal Si ring. Additionally, the "ring coupling" mechanism is applicable to other group IV binary compounds such as monolayer GeC and SnC. This work provides reliable evidence for the argument that two-dimensional tetragonal materials can produce Dirac cones.

First-principles study on the structural, electronic, elastic and thermal properties of P42/mnm-BSi

Using first-principles density functional theory, a tetragonal silicon–boron binary structure with space group P42/mnm is predicted in present work. This structure is confirmed to be dynamically and mechanically stable below 19.3 GPa, and possesses lower energy than other candidates. Based on the plane wave pseudopotential method, the electronic structure, elastic constant, bulk modulus, shear modulus, Young’s modulus, lattice thermal conductivity and phonon lifetime of P42/mnm-BSi are systematically studied. Interestingly, a four-center and six-electron delocalized π bond is found in P42/mnm-BSi, which is the most important factor for its structural stability. The optical spectra calculations reveal that P42/mnm-BSi is a wide band-gap semiconductor with an indirect band-gap of 2.5 eV and has a promising application in the photoelectric devices. The calculated lattice thermal conductivity along the [001] crystal direction is 145 Wm−1 K−1 that is about three times higher than that along both the [100] and [010] directions, which is originated from the different group velocity along the crystal axis. Moreover, the acoustic–optical coupling has some positive influences on lattice thermal conductivity. This study gives a fundamental understanding of the structural, electronic, elastic and heat transport properties in P42/mnm-BSi.

Electronic and electrical properties of two single-layer tetragonal silicon carbides

We studied the electronic, optical, and electrical conductivity properties of the two types of the single-layer tetragonal silicon carbides (SiC), termed as T1 and T2, by using DFT and Boltzmann theory. The latter two theories are implemented in the wien2k code and Boltztrap package, respectively. We detected that the behaviors of these 2-D nanomaterials are both affected by and dependent on the sites of the C and Si atoms in the SiC structures. Our results demonstrated that T1 is a semiconductor nanomaterial with direct electronic band gap; but the second type of the SiC (T2) is a conductor nanomaterial. Furthermore, we found out that the optical properties of these 2-D nanomaterials are also influenced by the positions of the C and Si atoms in the T1 and T2. Another significant result is the electrical conductivity. The T1 has a better electrical conductivity comparing it to T2. In brief, we predict that T1 will be very useful in various applications such as being used to create solar cells, nano-devices, transistors and phototransistors.

Studying the properties of a predicted tetragonal silicon by first principles

Silicon is a very important material in many technological fields. It also has a complicated phase diagram of scientific interest. Here we reported a new allotrope of silicon obtained from crystal structure prediction. We studied its electronic, vibrational, dielectric, elastic and hardness properties by first-principles calculations. The results indicate that it is an indirect narrow-band-gap semiconductor. It is dynamically stable with a doubly degenerate infrared-active mode at its Brillouin zone center. Born effective charges of the constituent element are very small, resulting in a negligible ionic dielectric contribution. Calculated elasticity-related quantities imply that it is mechanically stable but anisotropic. There exist slowly increasing stages in the stress-strain curves of this crystal, which make it difficult to estimate the hardness of the crystal by calculating its ideal strengths. Taking advantage of the hardness model proposed by Šimůnek, we obtained a value of 12.0 GPa as its hardness. This value is lower than that of the cubic diamond-structural Si by about 5.5%.

Versatile electronic properties and exotic edge states of single-layer tetragonal silicon carbides.

Three single-layer tetragonal silicon carbides (SiCs), termed as T1, T2 and T3, are proposed by density functional theory (DFT) computations. Although the three structures have the same topological geometry, they show versatile electronic properties from a semiconductor (T1), a semimetal (T2) to a metal (T3). The versatile properties originate from the rich bonds between Si and C atoms. The nanoribbons of the three SiCs also show interesting electronic properties. Especially, T1 nanoribbons possess exotic edge states, where electrons only distribute on one edge's silicon or carbon atoms. The band gaps of the T1 nanoribbons are constant because of no interaction between the edge states.

Elastic anisotropy and shear-induced atomistic deformation of tetragonal silicon carbon nitride

First-principles calculations are employed to provide a fundamental understanding of the structural features, elastic anisotropy, shear-induced atomistic deformation behaviors, and its electronic origin of the recently proposed superhard t-SiCN. According to the dependences of the elastic modulus on different crystal directions, the t-SiCN exhibits a well-pronounced elastic anisotropy which may impose certain limitations and restrictions on its applications. The further mechanical calculations demonstrated that t-SiCN shows lower elastic moduli and ideal shear strength than those of typical hard substances of TiN and TiC, suggesting that it cannot be intrinsically superhard as claimed in the recent works. We find that the failure modes of t-SiCN at the atomic level during shear deformation can be attributed to the breaking of C-C bonds through the bonding evolution and electronic localization analyses.

Electronic, elastic properties and hardness of the novel tetragonal silicon

Silicon is an important material for technical applications. Recently, a long-puzzling metastable phase of silicon (T12-Si) has been theoretically identified. In this work, we used first-principles calculations to study the electronic and elastic properties and the hardness of this new silicon allotrope to enrich the relevant information. These properties of cubic Si (c-Si) were also calculated for comparison. The results show that the T12-Si is mechanically anisotropic and has a lower bulk modulus and shear modulus than c-Si. Its theoretical hardness is 10.3 GPa, smaller than the value of 13.5 GPa for c-Si. Analyses of the electronic properties reveal that T12-Si is an indirect band gap crystal with a gap value of 0.69 eV, making it a promising semiconductor for future technical applications and that covalent sp 3-hybridization is the main interaction in this crystal. The reason the calculated hardnesses of c-Si and T12-Si are rather small compared to that of diamond is also discussed.

Structural properties of amorphous silicon prepared from hydrogen-diluted silane

A systematic structural analysis was carried out on amorphous silicon films prepared from hydrogen-diluted silane using plasma-enhanced chemical vapor deposition. Hydrogen dilution of silane during the growth of a-Si:H absorber layers is used to suppress light-induced degradation of a-Si:H solar cells. Transmission electron microscopy (TEM) shows that for higher hydrogen dilution ratios the growth of films becomes strongly inhomogeneous and the transition from amorphous to microcrystalline phase occurs at a smaller thickness. A detailed X-ray diffraction (XRD) analysis of the amorphous films reveals that the strongest peak in the XRD patterns is located around 27.5° and corresponds to the signal from the ordered domains of tetragonal silicon hydride and not from cubic silicon crystallites. The full width at half maximum of this peak narrows from 5.1° to 4.8° as the ratio of hydrogen to silane flow (R) increases to 20 and does not change significantly for higher hydrogen dilutions. The presence of silicon hydride ordered domains in amorphous films is confirmed by the lattice imaging method applied to the high resolution TEM recordings. The amorphous silicon films fabricated at different hydrogen dilution were applied as absorber layers in single-junction solar cells. The degradation experiment confirms that the cells with absorber layers deposited using hydrogen dilution are more stable to light exposure. A clear reduction of the degradation is observed when the dilution ratio is increased from R = 0 to R = 20. The degradation of solar cells with absorber layers prepared at R > 20 is not reduced by further increasing R.

Structural Properties of a-Si:H Films with Improved Stability against Light Induced Degradation

AbstractX-ray diffraction (XRD) analysis of thin silicon films was carried out using both the symmetric Bragg-Brentano and asymmetric thin-film attachment geometries. The asymmetric configuration allows quantitative phase analysis of the films and reveals that amorphous silicon films deposited from silane diluted with hydrogen have the strongest peak in the XRD patterns located around 27.5 degrees. This peak corresponds to the signal from ordered domains of tetragonal silicon hydride and not from cubic silicon crystallites. The full width at half maximum (FWHM) of this peak narrows from 5.1 to 4.8 degrees as the ratio of hydrogen to silane flow (R) increases to 20 and does not change significantly for higher hydrogen dilutions. The amorphous silicon films fabricated at different hydrogen dilution were applied as absorber layers in single-junction solar cells. Degradation experiments confirm a substantial reduction of the degradation when the dilution ratio is increased from R=0 to R=20. The light induced degradation of solar cells with absorber layers prepared at R > 20 is not further reduced by increasing R.

Structural changes of silicon upon high-energy milling investigated by Ramanspectroscopy

This study showed pronounced changes in the Raman scattering of silicon powder duringhigh-energy ball milling. The powders were milled for 1–18 h in a steel ball mill in argon.The approximate pressure imposed on particles was 2 GPa. The spectra of the as-milledpowders were compared with the initial silicon. It was found from the Raman peak positionshifts that milling generated strains in the silicon lattice, bringing about a transformationof cubic silicon to tetragonal silicon and amorphization. The relative amount ofnew phases was determined from the area under the measured Raman peaks.

Molecular Dynamics Simulation on the Mechanism of Nanometric Machining of Single-Crystal Silicon

Molecular dynamics (MD) simulation can play a significant role in addressing a number of machining problems at the atomic scale. This simulation, unlike other simulation techniques, can provide new data and insights on nanometric machining; which cannot be obtained readily in any other theory or experiment. In this paper, some fundamental problems of mechanism are investigated in the nanometric cutting with the aid of molecular dynamics simulation, and the single-crystal silicon is chosen as the material. The study showed that the purely elastic deformation took place in a very narrow range in the initial stage of process of nanometric cutting. Shortly after that, dislocation appeared. And then, amorphous silicon came into being under high hydrostatic pressure. Significant change of volume of silicon specimen is observed, and it is considered that the change occur attribute to phase transition from a diamond silicon to a body-centered tetragonal silicon. The study also indicated that the temperature distributing of silicon in nanometric machining exhibited similarity to conventional machining.

Structure changes in mono-crystalline silicon subjected to indentation — yexperimental findings

This paper investigates the subsurface deformation in silicon induced by indentation. With the precise cross-sectioning technique and high-resolution electron microscopy, a number of new phenomena were discovered. These include the phase transformation to amorphous, bcc and tetragonal silicon, the emergence of planar defects and the onset of microcracking. The study drew a relatively complete picture of silicon deformation under a range of indentation conditions.