Silicon dioxide

Summary

Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz. In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and most abundant families of materials, existing as a compound of several minerals and as a synthetic product. Notable examples include fused quartz, fumed silica, silica gel, opal and aerogels. It is used in structural materials, microelectronics (as an electrical insulator), and as components in the food and pharmaceutical industries. Structure In the majority of silicon dioxides, the silicon atom shows tetrahedral coordination, with four oxygen atoms surrounding a central Si atom (see 3-D Unit Cell). Thus, SiO2 forms 3-dimensional network solids in which each silicon atom is covalently bonded in a tetrahedral manner to 4 oxygen atoms. In contrast, CO2 is a linear molecule. The starkly diff

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https://en.wikipedia.org/wiki/Silicon_dioxide

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A method and apparatus to produce a net list of gates and Flip-Flops for one algorithm in order to find the best compromise between power consumption, speed and silicon surface by using a two step process. First the algorithm is written for a processor that has no restrictions in terms of number and size of register, core, operations set, memory handler and instructions. The program assembly of this processor fits into a two-dimensional table. To increase speed, the tables are configured to place the program operation in as many columns as possible, and to reduce silicon the tables are configured to place operations in a single column with many rows. The second stage consists of converting this virtual processor with its program tables into an HDL file ready for synthesis.

2010

Effect of femtosecond laser-induced high pressure on fused silica polymorphism

Arunkrishnan Radhakrishnan

High-pressure studies in silica are of great interest to earth and planetary sciences. Highpressure phases are rarely found in nature as a result of shock events like meteorite impacts orvolcanic events in nature. Recreating these phases remains a challenging task in lab conditions and can synthesize only very limited volume using static loading techniques like diamondanvil cell. In this thesis, we aim at recreating high pressure phases in silica using shock waves generated from a femtosecond laser. We put forth three different approaches for the high pressure generation in the bulk of the silica matrix. The frst method being a double beam exposure method; it potentially offers a means to create arbitrary patterns of laser-induced high-pressure impacted zones by scanning the two beams across the specimen volume. Tightly focused femtosecond laser-beam in the non-ablative regime can induce a shockwave suffciently intense to reach local pressures in the giga-Pascal range or more. In a single beam confguration, the locationof the highest-pressure zone is nested within the laser-focus area, making it diffcult to differentiate the effect of the shockwave pressure from photo-induced and plasma relaxation effects.To circumvent this diffculty, we consider two spatially separated focused beams individually acting as quasi-simultaneous pressure-wave emitters. The zone in between the two laserbeams where both shockwaves superpose forms a region of extreme pressure range, physically separated from the regions where the plasma formed. Here, we present a detailed materialinvestigation of pressured-induced densifcation in fused silica between the foci of two laser beams.Further, we investigated the effect of ultrashort-pulsed laser (50 fs) on material transformation by the shockwave emitted by the pulses and the repeated hammering effect of cumulativepulse exposure. This was done by characterizing the ablated particles after oblique writing on a fused silica substrate. Finally, we used a simultaneous spatial temporal focusing technique(SSTF) to achieve higher energy confnement inside a limited volume within the substrate, thereby inducing high pressure in the material. All materials were characterized using a Ramanspectroscope to evaluate the phase transformation introduced by the dynamic laser shock loading. Although this study focused on fused silica due to its relevance for both geophysicaland engineering investigations, the methodology used is generic and can be implemented in a variety of other transparent substrates for high-pressure physics studies.

EPFL2022

One of revolutionary technologies to sequence single molecules, such as DNA, is using nanopore devices. A single-channel with nanometer-scale aperture allows an extremely rapid electric analysis of such single molecules. The objective of this work is to fabricate nanopores into robust, solid-state membranes to achieve better performances. The technological challenge is in the small required dimension of the nanopore, around 50-100 nm in diameter and depth. To reach this objective, we used two different techniques: the ion track technique and a microfabrication method associated with Focused Ion Beam (FIB). A literature review has been done on the ion track technique. Threshold values of the ion track formation have been found for different insulator materials (polymers, SiO2, SiN). We did experiments with the linear accelerator UNILAC (Universal Linear Accelerator) at the GSI (Darmstadt, Germany) where we irradiated our samples with heavy gold ions (11.4 MeV/nucleon). On very thin membranes, we expect that a direct perforation would occur, and we chose SiN membranes and SU-8 thin films as samples. However, the experiment of ion bombardment was not possible to be done early enough, thus TEM analysis have not been done yet. If the direct perforation by ion bombardment is not possible, a chemical etching step would be necessary. About the microfabrication method associated with Focused Ion Beam (FIB) perforation, we did experiments at the Center of Micro Nano Technology (CMI) in EPFL. First trial with FIB was done on SiN membranes. In order to obtain required aperture size, reduction of membrane thickness before perforation by FIB was attempted, but this process was difficult to be achieved because of charging. To overcome this dimension limitation we chose a silicon membrane. With silicon membranes, oxidation would be performed after perforation by FIB, since channel opening will be reduced by SiO2 growth. Moreover, this oxide layer allows a functionalisation of the inner surface of the nanopore by silane chemistry. That should improve the resolution of DNA analysis. Though the aperture size reduction by oxidation has not been done yet, refining and perforation by FIB will be done according to this idea. We should reach ca. 100 nm-aperture size. Even if validation measurements are not easy, our specifications should be reached with the oxidation. More experiments and analysis have to be performed for further improvement.

2004

Effect of femtosecond laser-induced high pressure on fused silica polymorphism

Arunkrishnan Radhakrishnan

EPFL2022

2004