Phase Transformation Of Silicon Research Articles

Atomic scale defect formation and phase transformation in Si implanted β-Ga2O3

Atomic scale details of the formation of point defects and their evolution to phase transformation in silicon (Si) implanted β-Ga2O3 were studied using high resolution scanning transmission electron microscopy (STEM). The effect of Si implantation and the formation of defects was studied as a function of the dose of implanted atoms, and the detailed mechanism of lattice recovery was observed using both in situ and ex situ annealing of the implanted β-Ga2O3. The implantation created nanoscale dark spots in STEM images, which we identified as local γ-Ga2O3 inclusions generated by the relaxation of lattice due to ⟨010⟩ screw dislocations created by the implantation. The number and size of γ-Ga2O3 regions increased as the Si dose increased, and eventually the γ-Ga2O3 crystal phase (with stacking defects) took over the entire implanted volume when the peak Si concentration was over ∼1020 cm−3. Annealing above 1100 °C disintegrates the local γ-Ga2O3 phase and returns the structure to defect-free, single crystal β phase, likely indicating that point defects (such as Si interstitials and cation vacancies) are spatially redistributed by the annealing. However, when the structure is completely transformed to γ-Ga2O3 by the implantation, post-annealing leaves a high concentration of dislocations within the β phase, which relates to the inhomogeneous distribution of Si atoms detected by secondary ion mass spectrometry.

The Phase Transformation of Silicon Assessed by an Unloading Contact Pressure Approach

Silicon is of great economic importance for the semiconductor industry as well as of academic interest because of its high-pressure phase transformations. These transformations also occur during the indentation of silicon. To further investigate these transformations, a modified method using the continuous stiffness measurement (CSM) during unloading is presented in this work. The use of the CSM signal allows directly calculating the mean contact pressure while unloading. The measurements will be compared to conventional indentation tests and data from high-pressure cell experiments reported in the literature. Furthermore, the influence of constant load holding segments on the phase transformation during unloading is investigated.

Surface integrity of monocrystalline silicon nanostructured with engineered multi-tip diamond tools

The ability to fabricate micro/nanostructures on large surface areas would enhance product performance in optics and solar energy systems, where maintaining high productivity is also critical. Recently, diamond tools structured with nanoscale features have been used to machine ductile materials such as copper and electroless nickel. This study uses engineered diamond tools featuring multi-tip cutting edges to investigate nanoscale grooving of silicon. Multi-tip cutting edges create a certain level of pressure and temperature at the cutting zone, which leads to phase transformations in silicon. Experiments were performed using an ultra-precision machining setup to identify conditions leading to nanoscale ductile-mode machining of silicon. As nanogrooves reach 300 nm depth, hexagonal-Si (Si-IV) phase formation was observed based on laser Raman spectroscopy measurements. Hexagonal allotropes of silicon are known to improve light absorption of silicon. Additional experiments with non-structured diamond tools did not yield any Si-IV phase transformation, indicating the importance of obtaining necessary pressure and temperature conditions at the cutting zone.

Fast Reversible Phase Change Silicon for Visible Active Photonics

AbstractBoth amorphous and crystalline silicon are ubiquitous materials for electronics, photonics, and microelectromechanical systems. On‐demand control of Si crystallinity is crucial for device manufacturing and to overcome the limitations of current phase‐change materials (PCM) in active photonics. Fast reversible phase transformation in silicon, however, has never been accomplished due to the notorious challenge of amorphization. It is demonstrated that nanostructured Si can function as a PCM, since it can be reversibly crystallized and amorphized under nanosecond laser irradiation with different pulse energies. Reflection probing on a single nanodisk's phase transformations confirms the distinct mechanisms for crystallization and amorphization. The experimental results show that the relaxation time of undercooled silicon at 950 K is 10 ns. The phase change provides a 20% nonvolatile reflectivity modulation within 100 ns and can be repeated over 400 times. It is shown that such transformations are free of deformation upon solidification. Based on the switchable photonic properties in the visible spectrum, proof‐of‐concept experiments of dielectric color displays and dynamic wavefront control are shown. Therefore, nanostructured silicon is proposed as a chemically stable, deformation free, and complementary metal–oxide‐semiconductor compatible (CMOS) PCM for active photonics at visible wavelengths.

Numerical Investigation of Effect of Operating Parameters on the Phase Transformation During Vibration-Assisted Nano-Impact Machining of Silicon by Loose Abrasives

Abstract Vibration-assisted nano-impact machining by loose abrasives (VANILA) is a newly developed process based on the atomic force microscope (AFM) platform, where the nanoabrasive (diamond particles) slurry is injected between the workpiece and the vibrating AFM probe. This study aims to use the commercial finite element method (FEM) software package abaqus to simulate the phase transformation experienced by the silicon workpiece and to study the effects of VANILA process parameters, such as impact speed, impact angle, and coefficient of friction between the nanoabrasive and silicon workpiece, on the volume of phase transformation of silicon. Among these three parameters, impact speed is found to have the most dominating effect on the phase transformation process, followed by impact angle and friction coefficient. It is found that the volumes for Si-VII, Si-VIII, and Si-X phases increase with the increase of impact speed from 100 m/s to 200 m/s. The phase volumes of Si-VII and Si-VIII are found to decrease slightly with the increase of friction coefficient from 0.05 to 0.5. The phase volumes for Si-VII, Si-VIII, and Si-X are found to increase with the increase of impact angles from 20 deg to 90 deg. Finally, the multiple linear regression modeling using a design of experiments is carried out to study the relationship among the three parameters and the volume of different phases of silicon.

Effect of scratching speed on phase transformations in high-speed scratching of monocrystalline silicon

This paper investigates the phase transformation of (100) monocrystalline silicon in high-speed scratching tests. Various phase transformations of silicon are detected using micro-Raman spectroscopy over a wide range of speeds from 1 mm/min to 25 m/s. Wurtzite silicon (Si-IV) phase with strong Raman intensity is observed in all scratches. The Raman intensity ratio of amorphous silicon to Si-IV in the scratched groove center increases exponentially beyond a scratching speed of 105 mm/min, resulting in a decreased residual scratched depth. The tests provide a basic understanding of the effect of scratching speed on the phase transformation of silicon.

Quantitative Description of External Force Induced Phase Transformation in Silicon-Manganese (Si-Mn) Transformation Induced Plasticity (TRIP) Steels.

Transformation Induced Plasticity (TRIP) steels with silicon–manganese (Si–Mn) as the main element have attracted a lot of attention and great interest from steel companies due to their low price, high strength, and high plasticity. Retained austenite is of primary importance as the source of high strength and high plasticity in Si–Mn TRIP steels. In this work, the cold rolled sheets of Si–Mn low carbon steel were treated with TRIP and Dual Phase (DP) treatment respectively. Then, the microstructure and composition of the Si–Mn low carbon steel were observed and tested. The static tensile test of TRIP steel and DP steel was carried out by a CMT5305 electronic universal testing machine. The self-built true stress–strain curve model of TRIP steel was verified. The simulation results were in good agreement with the experimental results. In addition, the phase transformation energy of retained austenite and the work borne by austenite in the sample during static stretching were calculated. The work done by austenite was 14.5 J, which was negligible compared with the total work of 217.8 J. The phase transformation energy absorption of retained austenite in the sample was 9.12 J. The role of retained austenite in TRIP steel is the absorption of excess energy at the key place where the fracture will occur, thereby increasing the elongation, so that the ferrite and bainite in the TRIP steel can absorb energy for a longer time and withstand more energy.

Scratching of silicon surfaces

Nanoscale scratching of silicon surfaces is the elementary abrasive event for various machining techniques including fixed abrasive wire saw slicing, grinding, elliptical ultrasonic cutting and single-point diamond turning. The understanding of this process is essential for improving the surface quality and reducing sub-surface damage. Nanoscratching experiments are performed using a well characterized diamond tip geometry. The finite element method is employed in order to simulate the scratching process with a continuum constitutive model developed for phase transformation in silicon (Budnitzki, M., Kuna, M., 2016. Stress induced phase transitions in silicon. JMPS 95, 64–91). The required material parameters were determined from indentation experiments in a (111) single crystal Si wafer. The simulation results agree very well with data from scratch experiments without requiring additional calibration.

Investigation on the phase transformation of monocrystalline silicon during nanoindentation at cryogenic temperature by molecular dynamics simulation

High-pressure phase transformation of silicon is an important phenomenon as it is of scientific and technological importance for semiconductor industry and micro/nano electromechanical system. However, there are limited studies on the phase transformation at cryogenic temperature. In this study, molecular dynamics simulation was conducted to investigate the nanoindentation of monocrystalline silicon at 1 K. The force-displacement curve and the corresponding phase transformation were studied in details. During the loading process, the contact zone was affected by the applied stress and the original diamond cubic structure of silicon was distorted. With the increase of the depth, the distorted diamond cubic structure (DDS) was transformed into body-centered-tetragonal structure (bct-5) and Si-II. With the release of the force, the reverse transformations of Si-II to Si-III and Si-XII in junction with the pop-out events in the unloading curves can be clearly seen. It was also found that the phase distribution during the reverse transformation was strongly influenced by the indenter radius and indentation depth due to the different stress fields. At the higher depth, the unloading curves showed the unusual absence of pop-out and the appearance of surface extrusion. This can be ascribed by that the retained DDS outside the indentation after unloading not only restricts the transformation of Si-II but also brings the material extrusion on the surface due to the residual internal stress.

In situ detection of the phase transformations in silicon during nanoindentation

A method for the in situ detection of the phase transformations of silicon Si-I → Si-II → Si-XII/Si-III during indentation is developed. The method is based on the simultaneous detection of a P–h diagram and the electrical resistance during indentation into a narrow (≈2 μm) gap between metallic films deposited on the silicon surface. The sensitivity of the method makes it possible to resolve an increase in the Si-II silicon volume during indentation.

Laser Recovery of Subsurface Damages in Chemomechanically Polished Silicon Wafers

Silicon wafers are the most widely used semiconductor substrates. It has been considered that silicon wafers after chemomechanical polishing (CMP) have no subsurface defects. However, in fact, defects such as dislocation and latent microcracks will remain in the wafers if CMP is performed under unsuitable conditions. In this study, we confirmed the existence of subsurface damages at a depth of submicron level in a silicon wafer after CMP, then used a nanosecond pulsed Nd:YAG laser to repair the subsurface damages. It was found that subsurface defects were recovered to a single crystalline structure by laser irradiation without changing the surface topography. The phase transformation of silicon before and after laser irradiation was confirmed by laser Raman spectroscopy and chemical etching using saturated aqueous solution of Ca(OH)2. The findings from this study contributes to improve the quality of silicon wafers for high-performance semiconductors.

Influence of Environmental Humidity on the Wear and Friction of a Silica/Silicon Tribopair Lubricated with a Hydrophilic Ionic Liquid.

In this study, the tribological behavior of silica/silicon surfaces lubricated with the ionic liquid 1-ethyl-3-methylimidazolium ethylsulfate ([EMIM] EtSO4) was investigated. Tests were carried out in the presence of either humid air (45-55% relative humidity) or in a nitrogen atmosphere, and the results were compared with those obtained using pure water as a lubricant. The cross-sectional analysis of the contact area performed by focused-ion-beam scanning electron microscopy indicated the presence of cracks in the subsurface region, showing that brittle fracture contributed to wear. Sliding promoted the formation of a third body, the presence of which was indicated by optical and secondary electron microscopy. X-ray photoelectron spectroscopy showed that the third body was mostly composed of silicon oxides. The accumulation of the debris was controlled by the presence of water: in the presence of a nitrogen atmosphere, particles were trapped between the sliding surfaces, whereas in the case of humid air, the debris was progressively removed from the contact. Notably, the presence of trapped particles was associated with higher values of wear coefficients of both disks and pins. In addition, a lower roughness was observed along the direction of sliding in the case of water-containing ionic liquid. The observed trends in wear and the combined results of the various techniques, as well as the comparison with tests carried out in the presence of pure water, all point to the characteristic tribochemical reactions of water with silicon-based materials, namely, the formation of a sacrificial layer of hydrated oxide and the dissociative adsorption of water at crack tips of SiO2. In the absence of water, the lack of a tribochemical mechanism forming a sacrificial layer leads to a microfracture-dominated wear mechanism over the entire duration of the test, thus leading to more severe wear. The possible occurrence of stress-induced phase transformation of silicon during sliding is also discussed.

Influence of Silica on the Lime-Free Roasting of Chromium-Containing Slag

The evolution of silica during the lime-free roasting and their roles were investigated using chromium-containing slag with high content of ferric oxide and silica. The siliceous salt phases were analyzed by means of X-ray diffraction, scanning electron microscope, and energy-dispersive X-ray spectroscopy. The reaction rule involved with silicon-containing compounds in the roasting process was also discussed. The results showed that both oxidation of Cr2O3 and leaching of Na2CrO4 were influenced by the siliceous salts. It suggested that roasting temperature and the amount of alkali act as important factors for the phase transformation of silicon. NaFe(SiO3)2 was formed in the temperature which is best for the production of Na2CrO4, while excess amount of alkali could decompose acmite into NaFeO2 and Na2SiO3. It was observed that a large amount of insoluble NaFe(SiO3)2 took shape during the lime-free roasting when the temperature was above 1273 K (1000 °C). The extracting rate of chromium from chromium-containing slag roasted at 1373 K (1100 °C) was only 29.99 pct and almost no silicon was leached out.

In situ observation of the spatial distribution of crystalline phases during pressure-induced transformations of indented silicon thin films

Abstract

The effect of beta radiation on Si-I → Si-II phase transformations in silicon under an indenter

The phase transition from a diamond-like crystalline lattice of the Si-I phase to the β-tin type structure of the Si-II phase has been studied by measuring electric resistance under an indenter incorporated into a narrow (d ≈ 2 μm) crevice between metal contacts. It was established that the relative volume fraction of the metalized Si-II phase formed during indentation decreases under the action of a low dose (fluence F = 3.24 × 1010 cm−2) of low-intensity (I = 1.8 × 105 cm−2 s−1) beta radiation.

Study of phase transformations in silicon by scanning tunneling spectroscopy and nanoindentation

The results have been reported of the experiments on nanoscratching and nanoindentation of the surface of silicon using scanning tunneling microscope equipped with diamond semiconducting probe. Physical phenomena in silicon occurring at various contact pressures have been discussed.

Quantitative prediction of phase transformations in silicon during nanoindentation

This paper establishes the first quantitative relationship between the phases transformed in silicon and the shape characteristics of nanoindentation curves. Based on an integrated analysis using TEM and unit cell properties of phases, the volumes of the phases emerged in a nanoindentation are formulated as a function of pop-out size and depth of nanoindentation impression. This simple formula enables a fast, accurate and quantitative prediction of the phases in a nanoindentation cycle, which has been impossible before.

Effect of residual stresses on the stability of bct-5 silicon

This paper investigates the effect of residual stresses on the stability of the bct-5 silicon phase induced by nano-scratching using a diamond cutting tip. The molecular dynamics method was used to simulate the scratching process and stress analysis. The Tersoff potential was employed to describe the interaction of silicon atoms and the Morse potential was used for the interaction of silicon and carbon atoms of the cutting tip. It was found that scratching the {100} surface of silicon along the 〈110〉 direction can initiate the phase transformation of silicon from its diamond structure to bct-5 in the subsurface. The study concluded that the hydrostatic stress component under the cutting tip plays an important role in the initiation and development of the bct-5 phase during nano-scratching, but a residual octahedral shear stress of 6–8GPa is required to make the bct-5 silicon stable after the nano-scratching.

Influence of loading holding time under quasistatic indentation on electrical properties and phase transformations of silicon

The quasistatic Vickers indentation of Si (100) were applied to investigate the influence of loading holding time on the changes of electrical resistance and phase transformation in the indentation zone. For all used loading regimes with different holding times (2 s, 10 s, 1 h and 10 h) in combination with constant loading-unloading rate (250 mN/s) the electrical resistance in the region of residual indentations was found to be lower than before indentation. It was shown that this is connected with the formation of semimetallic Si-III phase and amorphous Si of higher pressure induced by creep process developed under long lasting pressure. The longer the holding time, the greater lowering of electrical resistance in the indentation region was observed, with the exception of the holding time above 1 h, this being explained by a decelerating creep rate of Si for this interval of time leading to a halt of further extending of amorphous and Si-III regions of lower electrical resistance.

A thermomechanical constitutive model for phase transformations in silicon under pressure and contact loading conditions

Most of the technologically relevant abrasive machining techniques for silicon (Si) such as lapping, sawing and grinding are based on the interaction of the silicon surface with a hard particle or asperity. It has been long established that the governing deformation mechanism for Si under such contact loading conditions is stress induced phase transformation. The present work introduces a novel phenomenological constitutive model for phase transformations of silicon set up in a thermomechanical framework of broad applicability. Taking into account experimental observations as well as first principle and molecular dynamics calculations, it captures both the cd-Si→β-Si transition upon compression and the β-Si→a-Si transition upon rapid decompression, which are most relevant for indenter loading. The model was numerically implemented in analogy to incremental plasticity and successfully applied for finite-element (FE) simulations of nanoindentation.