Papers by Keyword: Silicon

Abstract: Boron diffusion in Si and strained SiGe with and without C was studied. Using gassource molecular beam epitaxy (MBE), B containing epitaxial layers of: (i) Si, (ii) Si containing 0.1% C, (iii) SiGe with 11% Ge and (iv) SiGe with 11% Ge and with a 0.1% C, were grown on substrates. These samples were then rapid thermal annealed (RTA) at 940, 1000 and 1050°C in an O2 ambient. Self-interstitial-, vacancy- and non-injection conditions were achieved by annealing bare, Si3N4- and Si3N4+SiO2-coated surfaces, respectively. Concentration profiles of B, Ge and C were obtained using Secondary-Ion Mass Spectrometry (SIMS). Diffusion coefficients of B in each type of matrix were extracted by computer simulation. We find that B diffusivity is reduced by both Ge and C. The suppression due to C is much larger. In all materials, a substantial enhancement of B diffusion was observed due to self-interstitial injection compared to non-injection conditions. These results indicate that B diffusion in all four types of layers is mediated primarily by interstitialcy type defects.

Abstract: We present a unified simulation of diffusion in silicon (Si) and silicon dioxide (SiO2) that is based on the diffusing dopant species and point defects that primarily contribute to the diffusion. We first present the simulation of phosphorus (P) diffusion in Si based on the integrated diffusion model that we have developed and elucidate the mechanism of the appearance of the anomalous P in-diffusion profile. The vacancy mechanism governs P diffusion in the plateau region, while the kick-out mechanism governs it in the deeper region, where Si self-interstitials dominate in the kink region and P interstitials dominate in the tail region. Next, we present the simulation of boron (B) diffusion and Si self-diffusion in SiO2. We examined the co-diffusion of implanted B and 30Si in thermally grown 28SiO2, which shows increasing diffusivities with decreasing distance between the diffusers and Si/SiO2 interface and with higher B concentration in SiO2. We propose a model in which SiO molecules generated at the interface and diffusing into SiO2 enhance both B diffusion and Si self-diffusion. The simulation showed that the SiO diffusion is so slow that the SiO concentration at the B and 30Si region critically depends on the distance from the interface. In addition, the simulation predicts the possibility of time-dependent diffusivities for B and Si because more SiO molecules should be arriving from the interface with time, and this time dependence was experimentally observed. Moreover, based on the B concentration dependence, the simulation result indicates that B and Si atoms in SiO2 diffuse correlatively via SiO; namely, the enhanced SiO diffusion by the existence of B enhances B diffusion and Si self-diffusion.

Abstract: In elastic plastic solids, approaching the sub micron scale, critical experiments indicated significant differences in the mechanical response. Thus, mainly in small volume behavior a length scale issue is introduced with implications on the basic understanding of deformation and fracture processes. The current study is centered on the mechanical response of silicon particles in the range of 20-50 nm on sapphire substrate. Monotonic and cyclic mechanical tests have been performed by contact mechanics methodology at ambient temperature. Mechanical information and visualization assisted by scanning probe microscope-based nano indentation alluded to a model founded on dislocation dynamic effects. This facilitated developments regarding the length scale subject in the light of fatigue concepts and structural integrity aspects.

Abstract: Tricalcium phosphate modified by silicon and zinc was synthesized as a candidate for resorbable temporal bone implant having a controlled solubility and improved biocompatibility. Since Si and Zn are essential trace elements with stimulatory effects on bone formation, Si,Znmodified tricalcium phosphate can also promote bone formation. From XRD and ICP analyses, it was shown that up to 10 mol% Si and Zn can be incorporated in the tricalcium phosphate lattice without formation of a second phase. Changes in lattice parameters and unit volume of TCP as calculated by Rietveld refinement analysis indicate that Si and Zn substitute for P and Ca respectively.

Abstract: 0.8 wt.% silicon-containing hydroxyapatite (Si-HA) thin films of thickness 600 nm have been successfully developed using a magnetron co-sputtering technique, through careful selection and control of the processing conditions. These films were immersed in simulated body fluid (SBF) to investigate the nucleation and growth of an apatite layer on their surfaces. A newly-formed apatite layer with similar characteristics to that of the biological bone apatite, was observed after 4 days of immersion in SBF. X-ray diffraction and infrared analyses confirmed this layer to be calciumdeficient micro-crystalline carbonate HA. These results demonstrated that the novel Si-HA films were highly bioactive and the time frame required for apatite formation was reduced by approximately 76 % (from 17 days to 4 days).

Abstract: Indentation-induced structural phase transitions in single crystal Si(100) and amorphous silicon a-Si have been investigated for indentations made at room temperature and at 77 K. The experimental techniques employed were (1) Raman microscopy and (2) in situ electrical resistance measurement of the indentation region of the plastically deformed silicon. The Raman spectra from residual indentations revealed that although phase transitions did occur when indentations were made at room temperature, there were no phase transitions when indentations were made at 77 K. This difference in behaviour has been explained on the rise of temperature during the room temperature indentations, which may assist the phase transition process. The in situ electrical measurements have revealed that the deformed Si(100) yielded Ohmic behaviour, consistent with the view that during the indentation the cubic silicon transforms to the beta-Sn metallic phase (i.e. body-centre tetragonal).

Abstract: GaN films are grown on Si(111) with low-temperature GaN (LT-GaN) layers as buffer layers by hydride vapor phase epitaxy (HVPE). The LT-GaN layers are deposited at different temperatures ranging from 400 to 900 °C. The surface property, the structure and optical properties of the GaN films with different LT-GaN layers are studied. When deposition temperature of LT-GaN layer is 600 °C, the GaN film shows the best properties.

Abstract: There are several commercial processes for producing metallic parts by selective laser sintering (SLS) followed by infiltration of a molten metal at 700-900C. These parts are used in rapid manufacturing and rapid tooling applications. The present work centers around research to produce non-metallic parts infiltrated with materials at temperatures exceeding 1300C. Specific systems include siliconized silicon carbide. Of primary concern are: process control during the high-temperature infiltration; the binder system which must bind powder together during SLS, provide structural strength continuously from room temperature to the infiltration temperature, and react favorably with the infiltrant. This research was funded by State of Texas Technology Development and Transfer Grant Number 003658.

Abstract: The images of the growing crystal in the growth process of the undercooled droplets of silicon were lively recorded by using a high-speed camera. The number of crystal that nucleated spontaneously from the undercooled liquid was found to decrease to 1 when the undercooling was higher than 5K. The morphology of the growing single crystal of silicon was a thin plate. A model for predicting the critical undercooling of growing single crystal of silicon from undercooled liquid has been developed. The theoretically predicted value of the undercooling from present model for silicon is in agreement with the experimentally measured result.

Abstract: The relationship between the toughness and silicon content of high strength Mn-Si-Cr series bainitic steels has been investigated. The results show that with increasing in silicon content, the onset temperature of the steel’s tempered martensite embrittlement (TME) rises; moreover, the minimum value of tested toughness decreases and the tempering temperature corresponding to the minimum value of toughness increases. This phenomenon results from the effect of silicon on the stability of filmy carbon-enriched retained austenite in carbide-free bainite/martensite (CFB/M) microstructure.