Silicon Deposition Research Articles

Morphology and optical properties of Ge nanocrystalline films grown by nonequilibrium epitaxy on Si (001) surface

Optical properties and morphology of thin films with Ge and SiGe nanocrystallites are studied by using the methods of Raman scattering, multi-angle ellipsometry, and X-ray measurements. Our observations showed that low-temperature Ge epitaxy on Si(001) surface at 350 °C and at high growth rate leads to the formation of thin films consisting of Ge nanocrystallites with the porosity of about 50%. Deposition of Si adatoms on the film surface stimulates the reconstruction of the surface with nanocrystallites and results in the increase of the degree of Ge crystallinity, coalescence of adjacent nanocrystallites, and in a slight Si-Ge mixing. The change in the values of the optical constants due to silicon deposition is described by means of Bruggeman approximation. The main reasons for these changes are the film crystallization and the appearance of Si crystalline phase in the structures with Si capping layer. The prepared Ge nanocrystalline solids, as well as the films covered with Si, may be used in quantum dot solar cells due to the high absorption capacity of the films and devices working in the hopping regime.

Deposition and melting behaviors for formation of micro/nano structures from nanostructures with femtosecond pulses

This study reported the fabrication of a large area of micro/nano structures with different morphologies and sizes by the deposition of ablated material and melting of material on silicon through a line-shaped femtosecond laser beam irradiation. The evolution of micro/nano structures on the silicon surface was demonstrated with the laser fluence of 0.64 J/cm2. It was found that the melting of material was responsible for the formation of the micro-protrusions from laser-induced periodic surface structures (LIPSSs). Additionally, the deposition fell on the surface of the micro-protrusions in oblique incidence way, causing LIPSSs obscure and even invisible. As a consequence, those micro-protrusions gradually evolved into the micro-spikes with the ladder-like surface. Then, various laser fluences were applied to regulate the deposition and melting behaviors of silicon, to obtain the micro/nano structures with different morphologies and sizes. The formation mechanism of these micro/nano structures was analyzed. On this basis, the optical properties test showed that best anti-reflectivity was referred to the sample full of micro-spikes with the ladder-like surface, and the average reflectance has decreased from ∼38.17% of the planar silicon to∼4.75% in the waveband between 300 and 1000 nm.

Rice gene, BBH/Lsi1, regulates the color of rice hull by reducing the absorption and deposition of silicon and accumulating excess flavonoid

The color of grain hull is one of the remarkable traits which can be easily identified after heading, especially at the mature stage. In present study, a discoloration hull mutant named black–brown hull (bbh), was obtained from an indica cultivar Zhenong 34 by mutagenesis with ethyl methane sulfonate (EMS). The hull color of bbh mutant initially appeared black–brown on the 15th day and became completely black–brown on the 30th day after heading. The root of bbh was shorter than that of WT during the whole growth period. Furthermore, the total flavonoids content in the hulls and the silicon deposition in the leaves of bbh were both remarkably higher than WT. The results of map-based cloning indicated that the mutant trait of bbh was controlled by a single recessive nuclear gene, which was located on the long arm of chromosome 2 with a physical distance of 64.9 kb. The comparison of gDNA sequence between bbh and WT showed that there was a substitution from T to C (+ 2360) in the third exon of LOC_Os02g51110. BBH was an allelic gene of Lsi1, which encoded a water channel protein (aquaporin) involving in silicon uptake. The expression levels of the genes related to silicon absorption, transportation and distribution were detected to be up- or down-regulated at different stages in bbh root. Moreover, the transcripts of structural enzymatic genes involved in flavonoid biosynthesis in hulls also had apparent differences between WT and bbh mutant. Above all, the results revealed that BBH/Lsi1 was responsible to the black–brown hull by reducing the absorption and deposition of silicon and accumulating overmuch flavonoid.

Electrochemically controllable coating of a functional silicon film on carbon materials

A silicon deposit of various forms was successfully coated on graphite by electrodeposition in molten CaCl2 containing nano-SiO2 as a silicon precursor. The morphologies of the deposited silicon can be tuned from Si nanowires to a dense film by controlling constant electrolysis cell voltage. In addition to controlling electrochemical polarizations, the substrate plays a key role in forming a dense silicon film. By analyzing the interface between the Si film and graphite substrate, a thin transition layer comprising of Si, SiC and C enables the good adhesion of the Si film with the carbon substrate and thereby helps the growth of a dense Si film. Besides the application for photovoltaics, the electrolytic p-type Si film was employed as a binder-free anode for lithium-ion batteries delivering a capacity of over 2500 mAh g−1 in the first 10 cycles and retaining 800 mAh g−1 after 40 cycles. Moreover, this method was applied for coating Si on carbon fibers, which could be a general way to prepare Si with controllable forms and silicon/carbon core-shell structures for functional materials.

Synthesis of 28SiC from 28SiF4 and Methane in Radiofrequency (13.56 MHz) Arc Hydrogen Plasma

Some features of atmospheric-pressure radiofrequency (13.56 MHz) arc discharge and its use for obtaining bulk samples of isotope-enriched silicon carbide via the reaction between SiF4 and methane in a hydrogen medium have been considered. It has been shown that power in this type of discharge is released mainly in the near-electrode regions. The deposition of silicon and graphite occurs in a layer-by-layer mode, so that the product carbide contains up to 40% free carbon; therefore, the process requires optimization. At the same time, the proposed type of RF arc discharge with the product deposition zone localized at the ends of the electrodes makes it possible to avoid not only additional heating of the reactor space and walls, but also the loss of expensive isotope-enriched silicon fluoride.

Phytolith‐associated potassium in fern: characterization, dissolution properties and implications for slash‐and‐burn agriculture

AbstractIn recent time, phytoliths (silicon deposition between plant cells) have been recognized as an important nutrient source for crops. The work presented here aims at highlighting the potential of phytolith‐occluded K pool in ferns. Dicranopteris linearis (D. linearis) is a common fern in the humid subtropical and tropical regions. Burning of the fern D. linearis is, in slash‐and‐burn regions, a common practice to prepare the soil before planting. We characterised the phytolith‐rich ash derived from the fern D. linearis and phytolith‐associated potassium (K) (phytK), using X‐ray tomographic microscopy in combination with kinetic batch experiments. D. linearis contains up to 3.9 g K/kg d.wt, including K subcompartmented in phytoliths. X‐ray tomographic microscopy visualized an interembedding structure between organic matter and silica, particularly in leaves. Corelease of K and Si observed in the batch experiments confirmed that the dissolution of ash phytoliths is one of major factors controlling K release. Under heat treatment, a part of the K is made available, while the remainder entrapped into phytoliths (ca. 2.0–3.3%) is unavailable until the phytoliths are dissolved. By enhanced removal of organic phases, or forming more stable silica phases, heat treatment changes dissolution properties of the phytoliths, affecting K release for crops and soils. The maximum releases of soluble K and Si were observed for the phytoliths treated at 500–800 °C. For quantitative approaches for the K provision of plants from the soil phytK pool in soils, factors regulating phytolith dissolution rate have to be considered.

Morphology of Thin Films Formed by Oblique Physical Vapor Deposition

Physical vapor deposition is a fundamental tool to create thin films for countless applications. Deposition at oblique vapor incidence angles can lead to the growth of thin films with dramatically changed morphological features. Techniques such as oblique angle deposition (OAD) and glancing angle deposition (GLAD) utilize this fact to create self-organized nanostructures on surfaces. The changed columnar microstructure of such thin films significantly influences the film properties. The film density, for instance, influences the refractive index and therefore has impact for optical applications, like filters or antireflection coatings. Understanding the influence of the incidence angle in physical vapor deposition is an important step that allows tailoring the nanostructured surfaces for specific applications not only in optics, but also for catalysis or biosensing usage. To investigate thin film growth at oblique deposition conditions, silicon, germanium, and molybdenum nanostructured thin films were dep...

Optimization of operating parameters in polysilicon chemical vapor deposition reactor with response surface methodology

In the polysilicon chemical vapor deposition reactor, the operating parameters are complex to affect the polysilicon’s output. Therefore, it is very important to address the coupling problem of multiple parameters and solve the optimization in a computationally efficient manner. Here, we adopted Response Surface Methodology (RSM) to analyze the complex coupling effects of different operating parameters on silicon deposition rate (R) and further achieve effective optimization of the silicon CVD system. Based on finite numerical experiments, an accurate RSM regression model is obtained and applied to predict the R with different operating parameters, including temperature (T), pressure (P), inlet velocity (V), and inlet mole fraction of H2 (M). The analysis of variance is conducted to describe the rationality of regression model and examine the statistical significance of each factor. Consequently, the optimum combination of operating parameters for the silicon CVD reactor is: T = 1400 K, P = 3.82 atm, V = 3.41 m/s, M = 0.91. The validation tests and optimum solution show that the results are in good agreement with those from CFD model and the deviations of the predicted values are less than 4.19%. This work provides a theoretical guidance to operate the polysilicon CVD process.

Finite element analysis of hollow out-of-plane HfO2 microneedles for transdermal drug delivery applications.

Transdermal drug delivery (TDD) based on microneedles is an excellent approach due to its advantages of both traditional transdermal patch and hypodermic syringes. In this paper, the fabrication method of hollow out-of-layer hafnium oxide (HfO2) microneedles mainly based on deep reactive ion etching of silicon and atomic layer deposition of HfO2is described, and the finite element analysis of the microneedles based on ANSYS software is alsopresented. The fabrication process is simplified by using a single mask. The finite element analysis of a single microneedle shows that the flexibility of the microneedles can be easily adjusted for various applications. The finite element analysis of a 3×3 HfO2 microneedle array applied on the skin well explains the "bed of nail" effect, i.e., the skin is not liable to be pierced when the density of microneedles in array increases. The presented research work here provides useful information for design optimization of HfO2 microneedles used for TDD applications.

Novel pathways for elimination of chlorine atoms from growing Si(100) surfaces in CVD reactors

Reactions leading to elimination of chlorine atoms from growing Si(100) surfaces were simulated using clusters of silicon atoms of different sizes and shapes, and at the UB3LYP/6–31 g(d,p) level of theory. The reactions of type SiCl2(s) + 2 H2(g), where (s) indicates an adsorbed species at the surface and (g) a gas-phase species, were found to proceed in two steps: SiCl2(s) + H2(g) → SiHCl(s) + HCl(g) and SiHCl(s) + H2(g) → SiH2(s) + HCl(g), each having activation energies around 55 kcal/mol, a value which is comparable to experimental values published in the literature. In addition, the results suggested that H-passivation of Si(100) surfaces support reactions leading to canonical epitaxial growth, providing a plausible explanation for the convenience of passivating the surfaces prior to silicon deposition. The reactions analyzed here can therefore be seen as important steps in the mechanism of epitaxial growth of Si(100) surfaces.

Towards sub-micrometer high aspect ratio X-ray gratings by atomic layer deposition of iridium

X-ray grating interferometry is an excellent technique for X-ray phase contrast imaging and X-ray wavefront sensing with applications in materials science, biology and medical diagnosis. Among other requirements, the method depends on the availability of highly X-ray absorbing metallic gratings. Here, we report on the fabrication and characterization of high aspect ratio iridium gratings with a period of 1 μm and a depth of 30 μm combining deep reactive ion etching of silicon and atomic layer deposition of iridium. The implementation of such structures can greatly enhance the sensitivity of grating-based X-ray phase contrast imaging and thus, expand further its broad range of applications.

Morpho-anatomical and physiological alterations of passion fruit fertilized with silicone

Abstract: The objective of this work was to evaluate the effect of silicon fertilization on gas exchange, leaf anatomy, and ultrastructural characteristics of passion fruit (Passiflora edulis). The treatments comprised four concentrations of silicon (0, 0.28, 0.55, and 0.83 g per pot) at 1% silicic acid solution (SiO2.XH2O). This solution was applied around the stems of the plants. The first application was made 15 days after seedlings were transplanted. In total, three applications were made at 15-day intervals. The pots that constituted the control treatment received water in the same amount. After the final application, the plants were subjected to analyses of gas exchange, anatomical changes, and ultrastructural characteristics. The use of silicon promotes anatomical changes in passion fruit seedlings, such as increased adaxial epidermis thickness, reduced palisade parenchyma, and increased polar diameter/equatorial diameter ratio, which is related to stomata functionality. The concentrations of 0.55 and 0.83 g silicon per pot provide higher rates of photosynthesis, of transpiration, and stomatal conductance. The concentration of 0.83 g silicon per pot results in the greatest deposition of silicon in the abaxial epidermis of leaf surface.

Single-material Bragg reflectors and their applications in VCSELs

We present single-material distributed Bragg reflectors (DBRs) fabricated by oblique-angle deposition of amorphous silicon (a-Si). The high and low refractive indices of a-Si films were obtained at two incident vapour flux angles (θα) of 0° and 80° by determining the quarter-wavelength thicknesses of 67 nm at 0° and 128 nm at 80°. The fabricated single-material Bragg reflectors with only five pairs provide high reflectivity values of over 95%. The proposed DBRs were applied to intra-cavity contacted vertical-cavity surface-emitting lasers (VCSELs) to reduce fabrication costs and step. For the fabricated five pair a-Si/a-Si DBRs on VCSELs, the normalized stop bandwidth of 31.63% was measured while high reflectivity values over 95% were maintained over a wide wavelength range of 710 - 1020 nm. The fabricated VCSELs with Da = 7 μm obtained output power and threshold current, which are reasonable measured results.

Modeling and Control of SiNX Thin Film Surface Morphology Using Kinetic Monte Carlo Method

This work focuses on the study of the formation of amorphous silicon clusters embedded in SiNx thin films prepared by low-pressure chemical vapor deposition technique at a temperature of 1023 K by using a mixture of silane (SiH4) and ammonia (NH3). The deposition process is modeled via kinetic Monte Carlo simulation on a triangular lattice. The distribution of ammonia molecules in the simulation matrix is described using our previous pattern. This pattern includes adsorption and migration microscopic processes. The influences of the NH3/SiH4 gas flow ratio and the deposition time on the deposition kinetics are analyzed. The obtained results describe well the different stages of the nitrogen doped silicon deposition process. Indeed, an increase in the gas flow ratio leads to the formation of a high density of smaller amorphous silicon clusters. Moreover, larger clusters can be formed by increasing the deposition time. Simulation results are also compared to our previous results to better understand, on the one hand, the interest of using disilane instead of silane in order to make such deposits, and on the other hand to evaluate the role of ammonia in the SiNx film deposition process.

Silicon deposition in roots minimizes the cadmium accumulation and oxidative stress in leaves of cowpea plants.

Silicon (Si) frequently accumulates in plants tissues, mainly in roots of dicotyledons, such as cowpea. By contrast, Cadmium (Cd) is a metal that is extremely toxic to plant metabolism. This research aims to investigate if the deposition of Si in root can reduce Cd contents and minimize its negative effects on leaves, measuring gas exchange, chlorophyll fluorescence, antioxidant metabolism, photosynthetic pigments and growth, which may explain the possible role of Si in the attenuation of Cd toxicity incowpea. This study had a factorial design, with all factors completely randomized and two Cd concentrations (0 and 500µM Cd, termed as -Cd and +Cd, respectively) and three Si concentrations (0, 1.25 and 2.50mM Si). Si reduced Cd contents in the roots and in other plant organs, such as stems and leaves. The Si contents were highest in roots, followed by stems and leaves, which was explained by the passive absorption of Si. The application of Si promoted increase in both the macro- and micronutrient contents in all tissues, suggesting that Si mitigates the effect of Cd on nutrient uptake. Si attenuated Cd-mediated effects on light absorption of photosystem II (PSII), increasing the effective quantum yield of PSII photochemistry and the electron transport rate. Additionally, toxic effects induced by Cd on gas exchange were mitigated by the action of Si. Plants treated with Cd+Si showed increase in the activities of antioxidant enzymes and reductions in oxidant compounds; these modifications were promoted by Si via detoxification mechanisms. Increases in the photosynthetic pigments and growth of plants treated with Si and exposed to Cd stress were detected and were due to the reduced deterioration of cell membranes and maintenance of chloroplasts, which had positive repercussions on growth and development. This study validated the hypothesis that the accumulation of Si in roots induces benefits on metabolism and alleviates the toxic effects caused by Cd in leaves of cowpea.

Characterization of SixOyNz coating on CF/PPS composites for space applications

This work deals with the processing and surface treatment of thermoplastic composites carbon fibers/Polyphenylene sulfide (CF/PPS) for aerospace applications. After the production of the thermoplastic composites through hot compression molding, a silicon deposition was carried out on its surface using Plasma Enhanced Chemical Vapor Deposition (PECVD). Then, the Plasma Immersion Ion Implantation (PIII) process was executed on the silicon coated samples to create an amorphous silicon nitride layer. Subsequently, the coated and uncoated samples were characterized by means of the following techniques: optical microscopy, atomic force microscopy (AFM), X-ray diffraction (XRD) and X-ray excited photoelectron spectroscopy (XPS). By analyzing all the results obtained from the characterizations, it was concluded that a layer of amorphous silicon oxynitride was generated on the CF/PPS composite without damaging it. This result is an innovative step concerning the application of this material in a space environment (low earth orbit).

Lifetime Extension of the Gas Discharge Detectors with Plasma Etching of Silicon Deposits in 80%CF4 + 20%CO2

A method of elimination of silicon compounds from the anode wire of an aged proportional counter is presented. The aging of a counter with a 70%Ar + 30%CO2 and a 60%Ar + 30%CO2 + 10%СF4 working mixture was stimulated by a 90Sr β source. To accelerate the process of aging, the gas mixture flow to the counter was supplied through a pipe with RTV coated wall. As a result, the amplitude of the signal decreased 70% already at accumulated charge of Q = 0.03 C/cm. The etching of the silicon compounds on the wire surface with an 80%CF4 + 20%CO2 gas mixture discharge led to full recovery of the operating characteristics of detector and an increase in the lifetime. A scanning electron microscopy and X-ray spectroscopy analysis of the recovered wire surface were performed. In accordance with the results, a good quality of wire cleaning from SiO2 compounds was obtained.

Electrochemical Formation of a p-n Junction on Thin Film Silicon Deposited in Molten Salt.

Herein we report the demonstration of electrochemical deposition of silicon p-n junctions all in molten salt. The results show that a dense robust silicon thin film with embedded junction formation can be produced directly from inexpensive silicates/silicon oxide precursors by a two-step electrodeposition process. The fabricated silicon p-n junction exhibits clear diode rectification behavior and photovoltaic effects, indicating promise for application in low-cost silicon thin film solar cells.

RF bias to suppress post-oxidation of μc-Si:H films deposited by inductively-coupled plasma using a planar RF resonant antenna

One challenge for microcrystalline silicon (μc-Si:H) deposition is to achieve high deposition rates while maintaining high quality films. In this work, an inductively-coupled plasma (ICP) is used to deposit μc-Si:H on glass substrates by means of a novel planar resonant antenna at 13.56 MHz. No particle formation occurs in the low pressure (5 Pa) plasma, but the films suffer post-oxidation. By embedding a 5 MHz RF-biased substrate, films deposited simultaneously with and without RF bias are compared. It is shown that large area, low pressure (5 Pa), particle-free ICP deposition at 1 nm/s of μc-Si:H films can be obtained without post-oxidation by means of a planar resonant antenna, provided that RF substrate bias is included for independent control of the ion energy.

A comparative study on the direct deposition of μc-Si:H and plasma-induced recrystallization of a-Si:H: Insight into Si crystallization in a high-density plasma

Abstract Deep insight into the crystallization mechanism of amorphous silicon is of theoretical and technological significance for the preparation of high-quality microcrystalline/polycrystalline silicon. In this work, we intensively compare the present two plasma-involved routes, i.e., the direct deposition and recrystallization of precursor amorphous silicon (a-Si) films, to fabricate microcrystalline silicon. Both the directly deposited and recrystallized samples show multi-layered structures as revealed by electronic microscopy. High-density hydrogen plasma involved recrystallization process, which is mediated by the hydrogen diffusion into the deep region of the precursor a-Si film, displays significantly different nucleation configuration, interface properties, and crystallite shape. The underlying mechanisms are analyzed in combination with the interplay of high-density plasma and growing or treated surface.