Excess Si Content Research Articles

Excess silicon concentration dependence of the structural and optical properties of silicon nanocrystals embedded in silicon oxide matrix

Silicon (Si) nanocrystals embedded in Si oxide matrix have been formed by rapid thermal annealing of sub-stoichiometric Si oxide films (SiOx with x < 2). The SiOx films were deposited by co-sputtering of Si oxide and Si target using magnetron RF sputtering technique. The Si-to-SiO2 ratio was controlled by varying the number of Si chips being placed on the pure SiO2 target during sputtering. Rapid thermal anneal in nitrogen gas at 1100°C lead to the decomposition of SiOx into Si nanocrystals and SiO2. The structural (size of nanocrystals) and optical properties (absorption and luminescence) of Si nanocrystals embedded in oxide matrix, were found, strongly depend on the initial excess Si concentration in SiOx films.

Si-rich-[formula omitted] layers with high excess silicon content: Light emission and structural properties

Si-rich- SiO2 layers with high excess Si content grown by radio-frequency magnetron sputtering were studied by Raman scattering, X-Ray diffraction, electron paramagnetic resonance, and photoluminescence methods. It was found that high temperature annealing stimulates the formation of Si crystallites with preferred orientation in 〈111〉 direction. It was shown that the effect of crystallites orientation depends on excess Si content. Besides, comparable contribution of amorphous and crystalline silicon phases in the structure was observed for the annealed layers with Si excess more than 55%. It was observed that both crystalline and amorphous Si inclusions give the essential contribution to the photoluminescence spectra.

The structure of Si–SiO 2 layers with high excess Si content prepared by magnetron sputtering

Si–SiO 2 layers with high excess Si content prepared by magnetron co-sputtering of Si and SiO 2 and subsequently annealed were studied by electron paramagnetic resonance and photoluminescence methods. It was shown that adding oxygen during the deposition run or aging in air of as-deposited films influences the characteristics of the oxide layer surrounding the silicon crystallites. It was found that for layers with more than 55 vol.% of excess silicon the silicon crystallites are oriented. After high-temperature annealing not all the excess silicon was in crystalline form but part of it was in the amorphous phase. The depth distribution of the crystallites was found to be homogeneous while the distribution of amorphous silicon has a maximum around the middle of the layer.

Effects of alloy compositions on hydrogen embrittlement of Al–Mg–Si based alloys

Effects of alloy compositions on hydrogen embrittlement was studied by means of slow strain rate testing, using Al–Mg–Si based alloys containing different amounts of excess Si, Mg2Si and Cu. An Al–1.12 mass%Mg2Si–0.35 mass%Si alloy hardly showed degradation in ductility when tested at the strain rate of 10−7/s in a high humidity atmosphere of 90% R.H, compared to the ductility obtained by testing at the strain rate of 10−4/s. In contrast, the ductility of an Al–1.11%Mg2Si–0.81%Si alloy obtained by testing at 10−7/s was lower than that at 10−4/s in the humid air. By means of SEM/EDS analysis, Si-rich precipitates were observed on intergranular fracture surfaces of the embrittled alloy. These results suggested that hydrogen embrittlement was clearly observed with an increase in excess Si content. The ductility of an Al–1.81%Mg2Si–0.80%Si alloy obtained by testing at 10−7/s, however, was larger than that at 10−4/s in the humid air. The same tendency was observed in commercially available 6070, 6013 and 6066 aluminum alloys. These results meant that the Al–Mg–Si based alloys with excess silicon contents did not always show hydrogen embrittlement. Discussion was made on the above phenomena.

Effects of up-quenching on age-hardening behaviors in Al–Mg–Si alloys

Inspired by a success in applying a fluidized bed furnace to high-temperature solution treatments, the present authors have attempted to modify the age-hardening characteristics of Al–Mg–Si alloys by utilizing its superior heating rate. Two-step ageing treatments have been applied to five kinds of alloys with different Mg2Si and excess Si contents. Heating rates for the first and the second ageing treatments have been varied as well as ageing temperature for the first ageing treatment. It has been clarified that the rapid heating to the first ageing temperature enhances strength compared to the standard T6-temper for all the alloys tested, especially for a balanced alloy with a low Mg2Si content. It has been confirmed that small precipitates are formed in high density in such cases. In most cases, the improvements in hardness have been observed by adding the ageing treatment at 353 or 373 K for only 0.8 ks before the ordinary ageing at 450 K. We attribute this to the suppression of unfavorable clusters which ordinarily form below those temperatures during heating.

THE DEPOSITION AND CONTROL OF SELF ASSEMBLED SILICON NANO ISLANDS ON CRYSTALLINE SILICON

The formation of nano sized Si structures during the annealing of silicon rich oxide (SRO) films was investigated. These films were synthesized by low pressure chemical vapor deposition (LPCVD) and used as precursors, a post-deposition thermal annealing leads to the formation of Si nano crystals in the SiO 2 matrix and Si nano islands ( Si nI ) at c-Si /SRO interface. The influences of the excess Si concentration, the incorporation of N in the SRO precursors, and the presence of a Si concentration gradient on the Si nI formation were studied. Additionally the influence of pre-deposition substrate surface treatments on the island formation was investigated. Therefore, the substrate surface was mechanical scratched, producing high density of net-like scratches on the surface. Scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM) were used to characterize the synthesized nano islands. Results show that above mentioned parameters have significant influences on the Si nIs . High density nanosized Si islands can epitaxially grow from the c-Si substrate. The reported method is very simple and completely compatible with Si integrated circuit technology.

Characterization of amorphous and crystalline silicon nanoclusters in ultra thin silica layers

The nucleation and structure of silicon nanocrystals formed by different preparation conditions and silicon concentrations (28–70 area %) have been studied using transmission electron microscopy (TEM), energy filtered TEM, and secondary ion mass spectroscopy. The nanocrystals were formed after heat treatment at high temperature of a sputtered 10 nm thick silicon rich oxide on 3 nm SiO2 layer made by rapid thermal oxidation (RTO) of silicon. Nanocrystals precipitate when the excess silicon concentration exceeds 50 area %. Below this percentage amorphous silicon nanoclusters were found. In situ heat treatment of the samples in the TEM showed that the crystallization requires a temperature above 800 °C. The nanocrystals precipitate in a 4 nm band, 5 nm from the Si substrate, and 4 nm from the SiO2 sample surface. The silicon nucleates where the excess Si concentration is the highest. The top surface has less excess Si due to reaction with oxygen from the ambient during annealing. The SiO2-RTO layer is more Si rich due to Si diffusion from the SiO2–Si layer into RTO. Twinning and stacking faults were found in nanocrystals with 4–10 nm in diameter. These types of defects may have large effects on the usability of the material in electronic devices. Both single and double twin boundaries have been found in the nanocrystals by high resolution TEM. Image simulations were carried out in order to obtain more information about the defects and nanocrystals. The stacking faults are extrinsic and located in the twin boundaries.

A combined approach to fabricating Si nanocrystals with high photoluminescence intensity

This work demonstrates that by combining three methods with different mechanisms to enhance the photoluminescence (PL) intensity of Si nanocrystals embedded in SiO2 (or Si-nc:SiO2), a promising material for developing Si light sources, a very high PL intensity can be achieved. A 30-layered sample of Si-nc:SiO2/SiO2 was prepared by alternatively evaporating SiO and SiO2 onto a Si(100) substrate followed by thermal annealing at 1100°C. This multilayered sample possessed a fairly high PL efficiency of 14% as measured by Greenham's method, which was 44 times that of a single-layered one for the same amount of excess Si content. Based on this multilayered sample, treatments of CeF3 doping and hydrogen passivation were subsequently applied, and a high PL intensity which was 167 times that of a single-layered one for the same amount of excess Si content was achieved.

Investigating the use of sedimentary geochemical proxies for paleoenvironment interpretation of thermally mature organic-rich strata: Examples from the Devonian–Mississippian shales, Western Canadian Sedimentary Basin

Shales and mudrocks are enriched with diverse suites of major elements and trace metals that reflect their depositional environment, provenance and diagenesis. Here we present geochemical data for Devonian–Mississippian shaly strata (Western Canadian Sedimentary Basin) to assess the use of geochemical proxies for thermally mature deposits (> 1.5% vitrinite reflectance; VRo), and the ability to apply such proxies to elucidate the paleoceanographic conditions responsible for element distributions. Specifically, excess silica contents, C–S–Fe relationships, Ni/Co, V/Cr, Mo/Al and Re/Mo are utilized. Although regional in scope, the data presented here has broader implications for utilizing trace element geochemistry from geologic periods (Devonian–Mississippian) in which significant organic-rich sediment accumulation occurred, and subsequently underwent high levels of thermal diagenesis. Comparison of thermally mature lower Besa River, Golata, Muskwa and Fort Simpson shales (> 2% VRo for lower Besa River, and between 1.5% and 2% VRo for Golata, Muskwa and Fort Simpson), show that: 1) thermal maturation has had no effect upon the distribution of redox-sensitive elements (e.g., Ni, V, Mo, Tl, Cd and U); and 2) these elements are delivered to the sediment in association with the organic matter under anoxic (possibly euxinic) water-column conditions. Major element geochemistry (and optical microscopy) indicates organic-rich lower Besa River and Muskwa sediments are enriched in biogenic silica (proxied by excess SiO 2 concentrations), hence the use of Si as a proxy of detrital quartz input must be used with caution. Excess Si concentrations could be used as paleoproductivity proxies in reducing sediments where elements such as P and Ba are mobilized and not retained in the sediments. Golata sediments also have high excess Si contents, but the enrichment of Ti, Nb, Th, Ce, Hf and La (detrital-proxying elements) relative to average shale implies a detrital source of the quartz. Organic-rich, sulfur-rich upper Besa River shales were deposited in anoxic conditions (based upon C–S–Fe and Re/Mo relationships), akin to lower Besa River and Muskwa shales. However, upper Besa River shales show no enrichment of redox-proxying elements Mo, U and V, indicating benthic anoxia was not a ubiquitous requirement for element sequestration. Thermal maturation levels are similar to that of lower Besa River shales; hence element loss through diagenesis is not implied. A possible explanation is differing sedimentation rates which can affect the diffusion and concentration of elements into the sediment, and subsequent authigenic enrichment. This behavior makes Mo, U and V of limited use as paleoredox proxies under these sedimentary conditions.

Electrical and light-emitting properties of silicon dioxide co-implanted by carbon and silicon ions

In this paper, we explore the electrophysical and electroluminescence (EL) properties of thermally grown 350 nm thick SiO2 layers co-implanted with Si + and C + ions. The implanting fluencies were chosen in such a way that the peak concentration of excess Si and C of 5-10 at.% were achieved. Effect of hydrogen plasma treatment on electroluminescence and durability of SiO2 (Si,C) - Si-system is studied. Combined measurements of charge trapping and EL intensity as a function of the injected charge and current have been carried out with the aim of clarifying the mechanisms of electroluminescence. EL was demonstrated to have defect-related nature. Cross-sections of both electron traps and hole traps were determined. EL quenching at great levels of injected charge is associated with strong negative charge capture, following capture of positive charge leading to electrical breakdown of SiO2 structures.

Structural and light emission properties of silicon-based nanostructures with high excess silicon content

Structural and light emission properties of Si-rich SiO 2 layers with high excess Si content grown by radio-frequency magnetron sputtering were studied by Raman scattering, X-ray diffraction, electron paramagnetic resonance and photoluminescence methods. After high temperature annealing of the layers with Si excess more than 55% comparable contribution of amorphous and crystalline silicon phases in the structure was observed. Besides, the preferable orientation of Si crystallites in 〈 1 1 1 〉 direction was found for the layers grown on both silicon and quartz substrates. It was shown that the effect of crystallites orientation depends on excess Si content. It was observed that both crystalline and amorphous Si inclusions give the essential contribution to the photoluminescence spectra.

Garnet-pyroxene barometry for the assemblages with Na-bearing majoritic garnet

The majority of diamonds from kimberlite and lamproite pipes were formed within a quite narrow range of 140‐220 km, as evident from calculations of pressures and temperatures for the formation of their silicate inclusions [1]. The upper boundary of this range corresponds to the graphite‐diamond transition in the Earth’s mantle. The lower boundary is limited by the maximal lithosphere thickness that is typical only for the old parts of continents (cratons). Mineral inclusions in ultradeep diamonds comprising majoritic garnet, magnesiowustite, and phases of CaSiO 3 and MgSiO 3 compositions (presumably, with a perovskite structure), as well as tetragonal phase of pyrope-almandine composition (TAPP) [2] are direct samples from mantle depths, which allow us to test models of the Earth’s deep structure based on geophysical and experimental investigations. Of special interest among all the ultrahigh-pressure phases is majoritic garnet, because its composition and parageneses are most indicative for estimation of physicochemical conditions of the formation of deep mineral assemblages. According to the experimental data, pyroxene component starts to dissolve in garnet at a depth of ~250 km, resulting in the increase of Si and Na and the decrease of Al concentrations in this mineral according to the scheme Na + + Si 4+ = Mg 2+ + Al 3+ [3]. Experiments performed for mantle eclogite systems in a wide PT range using a high-pressure multianvil apparatus [4‐8] confirmed the influence of pressure on the composition of garnets (mainly Na admixture and excess Si contents) obtained in experiments (Fig. 1). In our study, we have analyzed the experimental data in the multicomponent Na 2 O–CaO–MgO–FeO–Al 2 O 3 – SiO 2 system and suggested a model of the garnet‐clinopyroxene barometer based on the change of Na concentration in garnet. In the opinion of Haggerty and Sauter [9], jadeiterich pyroxene lamellae in garnet are related to the decomposition of high-pressure Na-bearing garnets. The increase of pressure may lead to the opposite process of pyroxene microlite dissolution in garnet. This fact provides an explanation for the increase in the Si content up to 3.3 f.u. and a decrease in the Al content down to 1.3 f.u., as observed in garnets from the Monastery kimberlite pipe. According to the experimental data, such garnets were formed at a pressure of >10 GPa. Therefore, Na incorporation in garnet may be considered as a result of jadeite dissolution accompanied by Na and Si ingress according to the reaction [1]

Structure and Optical Properties of Magnetron Sputtered SiO&lt;sub&gt;x&lt;/sub&gt; Layers with Silicon Nanoparticles

The properties of SiOx layer prepared by magnetron sputtering is studied by photoluminescence Auger and SIMS methods. The depth distribution of emission characteristics and chemical composition is obtained. It is shown that as-sputtered SiOx layers are non-emitted and characterized by homogeneous enough chemical composition. High-temperature annealing in nitrogen atmosphere stimulates not only the Si nanocrystal formation but also the redistribution of silicon and the appearance of Si depleted region near layer-substrate interface. The last process is found to be dependent on excess Si content. It is found that decrease of silicon content in the depth of annealed layers is followed by the decrease of particle sizes that is proved by the blue shift of photoluminescence maximum. The possible reasons of the appearance of Si depleted region are discussed.

Dissolution and re-crystallization processes in multiphase silicon stabilized tricalcium phosphate

Ultrasonically accelerated dissolution of multiphase silicon stabilized tricalcium phosphate powders in water or Earle's balanced salt solution transforms the powders into needle-like calcium deficient apatite crystals with the c-axis (001) oriented along the needle. Ion exchange with the solution occurs primarily in the first hours of immersion. The transformation is driven by an interaction between the crystal surface and adsorbed water leading to the growth of crystallites which have the most stable surface configuration. First principles calculations of the surface energies of various hydroxyapatite surfaces with and without adsorbed water shows that depending on the ion concentrations in the fluid that determine the chemical potential of tricalcium phosphate, either Ca-rich (010) or stoichiometric (001) layers are the dominant surfaces. The higher the chemical potential, the more elongated in the (001) direction the crystallites become to minimize the total surface energy. The loss of a calcium Ca(2+) compensated by the addition of two H(+) is strongly favoured energetically on the (001) and Ca-rich (010) surfaces. A high concentration of excess Si at grain boundaries may be partly responsible for the rapid transformation of multiphase Si-TCP.

Growth peculiarities of silicon nanoparticles in an oxide matrix prepared by magnetron sputtering

AbstractThe process of thermal decomposition of SiOx layers prepared by magnetron sputtering is studied by photoluminescence, AFM, Auger and SIMS methods. The dependence of the depth distribution of the chemical composition on excess silicon content is obtained. It is shown that as‐sputtered SiOx layers are characterized by homogeneous enough chemical composition and do not exhibit photoluminescence. High‐temperature annealing in nitrogen atmosphere stimulates not only Si nanoparticle formation but also the appearance of a Si depleted region near layer‐substrate interface. This last process is found to be dependent on excess Si content. The decrease of silicon content in the depth of the annealed layers is accompanied by the decrease of Si particle sizes as proved by the blue shift of the photoluminescence maximum. The mechanisms of SiOx decomposition and possible reasons for the appearance of the Si depleted region are discussed. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Aerosol advection and sea salt events in Genoa, Italy, during the second half of 2005

Atmospheric aerosols in the PM(10) fraction have been simultaneously sampled at three sites in the Genoa urban and suburban area during the second half of 2005, and information on the elemental composition has been gathered through energy dispersive X-ray fluorescence. Thanks to the simultaneous measurements and wind information, a few aerosol transport and transformation processes originated from the nearby sea and in the neighbouring Po Valley have been described. Sea salt concentrations at the three sites were well correlated and often related to Southern sector winds; moreover, by examining the Cl/Na ratio at two sites the time scale for Cl depletion in particulate matter has been estimated as 1-1.5 h for the Genoa atmosphere. During a Northerly gale, excess elemental Si concentrations (peaking more than 4 mug m(-3)) were found at two sites, and were ascribed to an unknown local source. Finally, during an 11-day long 'heat wave' large concentrations for total PM(10), dust and secondary compounds have been found; these large concentrations lead to a number of exceedances of air quality standards, and have been ascribed to advection from the Po Valley.

Photoluminescence from Si Nanocrystals Embedded in In2O3/SiO2 Glass Thin Films

The photoluminescence (PL) properties of Si nanocrystals embedded in In2O3/SiO2 thin films are studied. The PL properties strongly depend on In and excess Si concentrations. For the samples with an excess Si concentration larger than 3.4 at. %, the PL intensity increases as In concentration increases up to 0.46 at. %, while the PL decay rate is nearly constant. This suggests that the number of Si nanocrystals contributing to the PL increases. On the other hand, when the excess Si concentration is low (1.4 at. %), the PL intensity monotonically decreases with increasing In concentration. The decrease in the PL intensity is accompanied by the increase in a decay rate, indicating that the nonradiative recombination process is introduced by In doping.

Photoluminescence of Si-rich silicon nitride: Defect-related states and silicon nanoclusters

The photoluminescence (PL) from defect-related states and Si nanoclusters was observed in the Si-rich silicon nitride films simultaneously. The weaker red-light emission of Si nanoclusters was obtained in the 1100°C annealed films with the 514.5nm excitation. Due to the quantum confinement effect, the PL peaks redshift with the increase of the excess Si concentration. Excited by the 325nm line, strong PL from N and Si dangling bond centers was observed in either the as-deposited films or the 1100°C annealed ones. The results demonstrate that the luminescence from defect-related states or Si nanoclusters is selected by the excitation energy.

Depth redistribution of components of SiO x layers prepared by magnetron sputtering in the process of their decomposition

The process of thermal decomposition of SiO x layers prepared by magnetron co-sputtering of Si and SiO 2 on Si and quartz substrates is studied by Auger and secondary ion mass spectroscopies. It is found that high temperature annealing of the layers causes a Si-depleted region near the layer/substrate interface. It is shown that the formation of this region does not depend on the type of substrate but depends on the content of excess Si and is observed at high content of excess Si. When the excess Si content decreases, the Si-depleted region at first smears and then disappears. The mechanism of SiO x decomposition and possible reasons for the appearance of the Si-depleted region are discussed.

Cavity $Q$ Measurements of Silica Microspheres with Nanocluster Silicon Active Layer

In this paper, the effect of the nanocluster-silicon (nc-Si) active layer on the cavity Q of silica microspheres is investigated. The silicon-rich silicon oxide (SRSO) (140plusmn10 nm thick) films with excess Si content ranging from 5 to 14 at.% were deposited on the silica microspheres formed by the CO2 laser melting of an optical fiber, and subsequently annealed at temperatures ranging from 650degC to 1100 degC. The cavity Q of the spheres with the active layer was measured at 1.56 mum using a tunable external cavity coupled laser diode and a tapered fiber coupling. We find that the presence of the nc-Si active layer reduces the Q value of the microsphere from ges 2times107 to (2-5) times105. However, we found no correlation between the formation, size, and density of the nc-Si and the cavity Q-factor, indicating that the scattering by the nc-Si does not present the dominant optical loss mechanism in the SRSO film