Significant Amounts Of Silicon Research Articles

Interactions of copper with oxidized TaSiN

Tantalum rich TaSiN exposed to the ambient results in a homogenous surface composition of a silicon rich Ta x Si y O z mixture. The interaction of sputter deposited copper with oxidized TaSiN (O/TaSiN) is investigated using X-ray photoelectron spectroscopy (XPS). Copper is found to wet (grow conformally on) O/TaSiN at 300 K. For copper coverages of less 0.4 ML (based on the Cu to O atomic ratio), copper is present as Cu(I). At higher coverages, Cu(0) is observed. A change in slope of the copper coverage curve is coincident with the change in copper oxidation state. The data indicate that copper is initially deposited in a conformal ionic layer followed by Cu(0) formation in subsequent depositions. The data also show that although the O/TaSiN surface contains significant amounts of silicon and oxygen, the ability of copper to wet O/TaSiN is superior to that of SiO 2. Post-deposition annealing experiments performed indicate that although diffusion does not occur for temperatures less than 900 K, copper “de-wetting” occurs for temperatures above 500 K.

Silicon contamination of substrates in fluorocarbon plasmas produced in glass reactors

AbstractExtensive research has been carried out in recent years using fluorocarbon plasmas for modification and depositions on polymer substrates. In some cases anomalous results have been obtained that are not explainable based on conventional fluorine chemistry. In this investigation pure polypropylene films were exposed to carbon tetrafluoride plasmas in a Pyrex glass reactor. At short reaction times (less than 1 min) significant amount of silicon was detected by ESCA on the surface of the films. Analysis of liquid nitrogen trapped fluorocarbon plasma gases and molecular fragments indicated high concentrations of silicon and carbon containing species, the former indicative of ablation and etching reactions of the glass reactor walls. The production of a relatively high quantity of fluorosilicon derivatives was explained by the greater affinity of silicon for fluorine than for carbon, with the tendency to readily form SiF4. These fluorosilicon radical and ionic species generated under cold plasma conditions can easily react with polymeric substrates causing unexpected surface modifications. In addition Si–F bonds could be readily hydrolyzed to SiOH islands on the surface of the substrate to impart anomalous characteristics. © 1994 John Wiley & Sons, Inc.

Surface analysis of carbon fibres modified with PVAL coating and the composite interfaces

High-resolution X-ray photoelectron spectroscopy (XPS) has been used to analyse the fibre surface and composite interfaces with and without polyvinyl alcohol (PVAL) coating (both fibres being commercially surface-treated and sized). Major functional groups on the fibre surface are also identified by Gaussian curve-fitting of carbon peaks to study the correlations of surface chemistry with the observed failure mechanisms of the uncoated and coated fibre composites. The main difference in the fracture surface of the fibre composites with and without the coating is that the latter has a significant amount of silicon (about 6 at% concentration) associated with the epoxy matrix, but silicon is almost absent in the PVAL-coated fibre composites. This suggests that the debonding mechanism in the uncoated fibre composite, which has a strong interfacial bonding, is controlled by the combination of cohesive failure of the matrix material and adhesive failure at the interface. In contrast, the PVAL coating promotes adhesive failure due to the weak bonding at the fibre-matrix interface. This observation is consistent with SEM observations in that the uncoated fibre composite consists of significant deformation of matrix material which covers the majority of the fracture surface and tiny epoxy resin particles adhering to the debonded fibre surface, whereas the coated fibre composite shows a lesser amount of matrix deformation with relatively clean fibre surface.

Electromigration and microstructural properties of AI-Si/Ti/AI-Si VLSI metallization

Texas Instruments, Inc., Houston, Texas 77001 Al-Si(l%)/Ti/Al-Si(l%) interconnect lines produced by dc Magnetron sputtering were subjected to standard electromigration tests. Their time to failure proved to be superior to that of simple Al-Si(l%) films. The titanium tended to form TiAl3 in which significant amounts of silicon were dissolved. Investigation by SEM revealed that most of the electromigration damage occurred in the portion between the protective oxide and the titanium layer.

Parabolic dissolution kinetics of silicate minerals: An artifact of nonequilibrium precipitation processes?

The rate-limiting step for the dissolution of many primary silicate minerals is thought to be a surface-controlled reaction. This should result in dissolution rates that are linear functions of time. However, the observed dissolution rates for aluminosilicate minerals have commonly been characterized as “parabolic”—that is, the apparent rates of release of silicon and of the alkali ions are linear functions of the square root of time ( t ½). Here, data are presented which suggest that this discrepancy may result in part from the precipitation of secondary aluminosilicates during the dissolution experiments. In simulated dissolution studies, the kinetics of formation and the stoichiometries of precipitates can be studied unambiguously as functions of time, component concentrations, and pH. Results of these studies indicate that significant amounts of silicon are incorporated into amorphous aluminum-rich precipitates at dissolved silicon concentrations greater than 170 μm. At higher concentrations, silicon precipitation rates increase. These precipitation reactions result in apparent rates of addition of dissolved silicon to solution which are linear functions of t ½. As a result of the type of precipitation reactions observed here, estimates for the rates of dissolution obtained for aluminum-rich silicate minerals may be low by as much as a factor of two.

Marine alga Platymonas sp. accumulates silicon without apparent requirement

THE role of silicon in living systems has only recently begun to be understood. Apart from being an important structural component of diatoms and silicoflagellates1, some freshwater flagellates2, higher plants, sponges and other organisms3, it is necessary for DNA polymerase activity in diatoms4 and for bone and tooth development in certain vertebrates5. Silicified algal species are known (or assumed) to have an obligate, concentration-dependent silicon requirement for growth6,2, and transport systems for the accumulation of silicic acid (Si(OH)4) have been described7; however, the uptake of Si(OH)4 by nonsilicified algae has never been reported. Here we report the accumulation of significant amounts of silicon by the planktonic marine alga Platymonas sp. (isolated during the summer of 1954 from Great Pond, Falmouth, Massachusetts). This alga is very close to, or may be an isolate of P. suecica (personal communication from R. Norris) and has no known silicon requirement, growing equally well in Si-rich and Si-poor environments. Because Si(OH)4 is a potentially limiting nutrient for diatoms8, the removal of available Si(OH)4 from the environment by organisms that do not require it could play an important role in phytoplankton competition and succession. This phenomenon could also be important in the cycling of silicon in the ocean.

Electron Microprobe Analysis of the Distribution of Silicon and Other Elements in Rice Leaf Epidermis

Using electron microprobe analysis, significant amounts of silicon were detected in a few long epidermal cells, mostly along their cell walls, in the silica cells, and in the trichomes of both surfaces of the leaf blade and leaf sheath of the rice (Oryza) plant. This analysis did not reveal detectable amounts of silicon in the stomatal apparatuses of these organs. In the ligule, silicon is present in significant quantities in some of the epidermal cells, while in other long epidermal cells no significant amounts of silicon were detected. The effect of accumulation of large quantities of silicon in the long epidermal cells of the ligule on the accumulation pattern of K, Ca, Mg, P, Mn, Fe, and Na is described. This effect of silicon, particularly on the accumulation of potassium, is discussed.

Electron-probe microanalysis of silicon in the epidermis of rice (Oryza sativa L.) internodes

Electron-probe X-ray microanalysis showed that significant amounts of silicon are accumulated in the entire epidermal system of the rice internode except in the stomatal apparatuses. Thus, there is a lack of specific sites for Si deposition from levels just above the base to the tip of the rice internode. In the intercalary meristem region, 1 cm above the base of the internode, point-count data indicate more Si accumulation in the dumb-bell shaped silica cells than in the long epidermal cells. Above this region, Si is accumulated essentially in a uniform pattern in all epidermal cells. Such a pattern for Si accumulation in rice internodes markedly contrasts with that for Avena internodes and may explain, in part, why rice plants have a higher percentage Si (dry weight basis) in their shoots. The adaptive significance of this silicification pattern in rice is discussed.

Evidence that Polywater is a Colloidal Silicate Sol

Abstract : A study was made of the 'anomalous' condensation of water and its conversion to 'polywater' in glass and silica capillaries. The condensate was expelled as a sol-like material that on evaporation frequently gave a particulate appearance. The residue was analyzed using the electron probe and found to contain significant amounts of silicon and sodium. These results suggest that the unusual properties of 'polywater' may be due to the presence of silica or silicate. It is further shown that, since alkaline silicate solutions can absorb CO2, the infrared spectra of 'polywater' may actually be due, in part, to bicarbonate ion. (Author)