Halo-like structures studied by atomic force microscopy

Nanometer-sized clusters of copper have been produced in a hollow cathode sputtering source and deposited on SiO_x. Halo-like structures consisting of micrometer sized protrusions in the silicon oxide surface surrounded by thin rings of smaller particles are observed. The area in between seems to be depleted of particles. We propose that the halo-like structures are a result of electrostatic forces acting between the incoming charged clusters and charged regions on the surface. A simple computer simulation supports this suggestion.     

Correction of the influence of baseline artefacts and electrode polarisation on dielectric spectra

The deconvolution of biological dielectric spectra can be difficult enough with artefact-free spectra but is more problematic when machine baseline artefacts and electrode polarisation are present as well. In addition, these two sources of anomalies can be responsible for significant interference with dielectric biomass measurements made using one- or two-spot frequencies. The aim of this paper is to develop mathematical models of baseline artefacts and electrode polarisation which can be used to remove these anomalies from dielectric spectra in a way that can be easily implemented on-line and in real-time on the Biomass Monitor (BM). We show that both artefacts can be successfully removed in solutions of organic and inorganic ions; in animal cell and microbial culture media; and in yeast suspensions of varying biomass. The high quality of the compensations achieved were independent of whether gold and platinum electrodes were used; the electrode geometry; electrode fouling; current density; the type of BM; and of whether electrolytic cleaning pulses had been applied. In addition, the calibration experiments required could be done off-line using a simple aqueous KCl dilution series with the calibration constants being automatically calculated by a computer without the need for user intervention. The calibration values remained valid for a minimum of 3 months for the baseline model and indefinitely for the electrode polarisation one. Importantly, application of baseline correction prior to polarisation correction allowed the latter's application to the whole conductance range of the BM. These techniques are therefore exceptionally convenient to use under practical conditions.     

Magnetic iron oxide nanoparticle enrichment of phosphopeptides on a radiate microstructure MALDI chip

Several methods can be used to improve the enrichment of phosphorylated proteins. In this paper, phosphopeptides were enriched using magnetic iron(II,III) oxide (magnetite, Fe(3)O(4)) nanoparticles (NPs) on a radiate microstructure silicon chip and then analyzed using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) without further purification processes. We have developed a radiate microstructure chip on which samples can be concentrated for analysis by MALDI-TOFMS. The phosphoprotein digests and magnetic iron oxide NPs aqueous solution were deposited onto the central zone of the radiate microstructure silicon chip and enabled the on-chip enrichment of phosphopeptides. Microscopic analysis confirmed that the applied samples were confined to the central zone. Sample spots focused on the chip were much smaller than those on an unmodified plate with the same total volume. Different additives were used and optimized processes were performed to minimize non-phosphopeptides interference. These data collectively demonstrate that our on-chip phosphopeptide enrichment protocol is a rapid and easy-to-use method for phosphoproteome analysis.     

Room-temperature ferromagnetism in silicon oxide/silicon nitride composite films

Room-temperature ferromagnetism has been observed in silicon oxide/silicon nitride composite films formed on Si substrates at different substrate temperatures, and the ferromagnetic properties of the samples have been found to depend on the silicon nitride content of the films. It is proposed that the ferromagnetism is related to the interface states between the silicon oxide particles and silicon nitride particles. The saturation magnetization (M_S) reached its maximum value in the film produced at a substrate temperature of 400 °C. A further study on the magnetic properties of the film has been carried out using first-principles calculations based on the density functional theory. The calculations suggest that the magnetic moments of the film originate from N 2p and Si 2p states in the vicinity of the hetoro-interface.     

Determination of Diclofenac Sodium in Synovial Fluid by High Performance Liquid Chromatography

Abstract

Due to the limited supply of blank synovial fluid, the usual practice of preparing a calibration curve for the biological sample of measurement is not practical for synovial fluid drug level determination. The linearity and correlation of peak height ratio between plasma and synovial fluid samples were investigated in this study. Excellent linear relationship is obtained from the calibration curves for both biological samples. In addition, excellent correlation of peak height ratios between plasma and synovial fluid indicates that the plasma calibration curve can be used in lieu of a synovial fluid calibration curve (slope 0.9154; intercept not statistically different than zero; and r-0.999 with N=13). According to this linear relationship, synovial fluid levels can be calculated based on the concentration as determined from the plasma calibration curve and divided by 0.9154. The extraction efficiences were comparable when diclofenac was spiked into human plasma or synovial fluid samples but the extraction of internal standard is better from synovial fluid than from plasma. The results are in good agreement with those observed in correlation between plasma and synovial fluid. Linearity and sensitivity of diclofenac in synovial fluid were determined in this study, but precision, accuracy and specificity were not determined due to the difficulty to obtain blank synovial fluid. Nevertheless, the same assay has been applied to plasma where all parameters have been well established and it is reasonable to assume the same results would have been obtained from synovial fluid samples.     

Direct determination of silicon in powdered aluminium oxide by use of slurry sampling with in situ fusion graphite-furnace atomic-absorption spectrometry

A direct method for determination of silicon in powdered high-purity aluminium oxide samples, by slurry sampling with in situ fusion graphite-furnace atomic-absorption spectrometry (GF-AAS), has been established. A slurry sample was prepared by 10-min ultrasonication of a powdered sample in an aqueous solution containing both sodium carbonate and boric acid as a mixed flux. An appropriate portion of the slurry was introduced into a pyrolytic graphite furnace equipped with a platform. Silicon compounds to be determined and aluminium oxide were fused by the in situ fusion process with the flux in the furnace under optimized heating conditions, and the silicon absorbance was then measured directly. The calibration curve was prepared by use of a silicon standard solution containing the same concentration of the flux as the slurry sample. The accuracy of the proposed method was confirmed by analysis of certified reference materials. The proposed method gave statistically accurate values at the 95% confidence level. The detection limit was 3.3 μg g^–1 in solid samples, when 300 mg/20 mL slurry was prepared and a 10 μL portion of the slurry was measured. The precision of the determination (RSD for more than four separate determinations) was 14% and 2%, respectively, for levels of 10 and 100 μg g^–1 silicon in aluminium oxide.     

Direct determination of silicon in powdered aluminium oxide by use of slurry sampling with in situ fusion graphite-furnace atomic-absorption spectrometry

A direct method for determination of silicon in powdered high-purity aluminium oxide samples, by slurry sampling with in situ fusion graphite-furnace atomic-absorption spectrometry (GF-AAS), has been established. A slurry sample was prepared by 10-min ultrasonication of a powdered sample in an aqueous solution containing both sodium carbonate and boric acid as a mixed flux. An appropriate portion of the slurry was introduced into a pyrolytic graphite furnace equipped with a platform. Silicon compounds to be determined and aluminium oxide were fused by the in situ fusion process with the flux in the furnace under optimized heating conditions, and the silicon absorbance was then measured directly. The calibration curve was prepared by use of a silicon standard solution containing the same concentration of the flux as the slurry sample. The accuracy of the proposed method was confirmed by analysis of certified reference materials. The proposed method gave statistically accurate values at the 95% confidence level. The detection limit was 3.3 microg g(-1) in solid samples, when 300 mg/20 mL slurry was prepared and a 10 microL portion of the slurry was measured. The precision of the determination (RSD for more than four separate determinations) was 14% and 2%, respectively, for levels of 10 and 100 microg g(-1) silicon in aluminium oxide.     

Time‐of‐flight secondary ion mass spectroscopic characterization of the nitrogen profile of shallow gate oxynitride thermally grown on a silicon substrate

Silicon oxynitride has been used as a shallow gate oxide material for microelectronics and its thickness has been reduced over the years to only a few tens of angstroms due to device size scaling. The nitride distribution and density characteristic in the gate oxide thus becomes imperative for the devices. The shallow depth profiling capability using time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS) has huge potential for the nitrogen characterization of the shallow gate oxide film. In this article, both positive and negative spectra of TOF‐SIMS on silicon oxynitride have been extensively studied and it was found that the silicon nitride clusters Si_xN^? (x = 1–4) are able to represent the nitrogen profiles because their ion yields are high enough, especially for the low‐level nitride doping in the oxide, which is formed by the annealing of nitric oxide on SiO₂/Si. The gate oxide thickness measured by the TOF‐SIMS profiling method using ¹⁸O or CsO profile calibration was found to correlate very well with transmission electron microscope measurement. The nitrogen concentration in the gate oxide measured using the TOF‐SIMS method was consistent with the results obtained using the dynamic SIMS method, which is currently applied to relatively thicker oxynitride films. Copyright © 2012 John Wiley & Sons, Ltd.     

Fluorescent Determination of Glucose Using Silicon Nanodots

ABSTRACT

Here is reported a fluorescent biosensor for glucose detection based on water-soluble and pH-responsive silicon nanodots. The silicon nanodots were prepared using a facile hydrothermal method. The advantages of using the silicon nanodots as glucose sensor are twofold. Firstly, the fluorescence of silicon nanodots was quenched by hydrogen peroxide that was produced from glucose oxidation. Secondly, the fluorescence of silicon nanodots was highly sensitive to gluconic acid that was also produced by glucose oxidation. Our results show that this method detected glucose as low as 0.54?µM with a good selectivity and allowed the determination of glucose in serum samples. This method is also simple, rapid, low-toxic and low-cost, thereby hold high application potential for biological assays.     

Recent developments in ESR techniques and results for semiconductor surface regions

In recent years new electron spin resonance (ESR)-based techniques have been developed, mostly with application to silicon-oxide interface regions. In this article we give the first full theoretical analysis for these techniques, namely photoconductive resonance (PCR) and spin dependence resonance (SDR), and a summary of results obtained to date. We also refer to some other recent ESR work on semiconductor surfaces including crystalline and amorphous hydrogenated silicon.Both PCR and SDR have sensitivities up to 2 orders of magnitude greater than ESR but are confined to samples where paramgnetic centers induced by incident light, affect the photoconductivity. This occurs through trapping and recombination processes. A number of different PCR and SDR centers have been found at silicon oxide interface regions, which were undetectable by normal ESR measurements. The PCR centers appear to be related to effects of water vapor, and occur in concentrations of order 10¹⁰ cm^-2 of oxide interface. In the case of SDR centers, they appear to be formed in the oxide and diffuse through it to the silicon interface, being also of low concentration and associated with impurity groups, whereas the centers directly detectable by ESR appear to be unfilled Si bonds.     

Calibration of reference materials for total-reflection X-ray fluorescence analysis by heavy ion backscattering spectrometry

Total-reflection X-ray fluorescence (TXRF) is widely used for the control of metallic contamination caused by surface preparation processes and silicon materials. At least three companies supply a variety of TXRF systems to the silicon integrated circuit (IC) community, and local calibration of these systems is required for their day to day operation. Differences in local calibration methods have become an issue in the exchange of information between IC manufacturers' different FABs (Fabrication Facility) and also between silicon suppliers and IC FABs. The question arises whether a universal set of fluorescence yield curves can be used by these different systems to scale system sensitivity from a single element calibration for calculation of elemental concentrations. This is emphasized by the variety of experimental conditions that are reported for TXRF data (e.g. different angles of incidence for the same X-ray source, different X-ray sources, etc.). It appears that an instrumental factor is required. We believe that heavy ion backscattering spectrometry (HIBS) provides a fundamental method of calibrating TXRF reference materials, and can be used in calculating this instrumental factor. In this paper we briefly describe the HIBS system at the Sandia National Laboratories HIBS User Facility and its application to the calibration of TXRF reference materials. We will compare HIBS and TXRF mapping capabilities and discuss the issues associated with the restrictions of some older TXRF sample stages. We will also discuss Motorola's cross-calibration of several TXRF systems using different elements as references.     

Directed electrodeposition of polymer films using spatially controllable electric field gradients

We report a method for the directed electrodeposition of polymer films in various patterns using spatially controllable electric field gradients. One- and two- dimensional surface electric field gradients were produced by applying different potential values at spatially distinct locations on an electrode surface. Variations in the resulting local electrochemical potentials were used to spatially manipulate the rate of electrodeposition of several polymers. By controlling the electric field gradient in the presence of sequentially varying deposition solutions, complex polymer patterns could be produced. One-dimensional structures consisting of alternating bands of polyaniline and either poly(phenylene) oxide or poly(aminophenylene) oxide were produced, as well as more complex two-dimensional structures. Film characterization was achieved through optical imaging, UV-vis spectroscopy, and ellipsometry. Results indicate that this directed deposition technique is a simple strategy to create complex, millimeter-sized surface patterns of electrodeposited materials.     

Chemical etching of silicon: Smooth, rough, and glowing surfaces

Scanning Force Microscope images of silicon surface morphology are presented for samples exposed to various oxidizing environments followed by oxide removal. These are contrasted with samples exposed to HNO₃/HF solutions. The former samples consistently produced surface roughness on the order of a few nanometers, while the latter solution exhibited surface roughness of several hundred to over a thousand nanometers. This rough surface is photoluminescent and is known as porous silicon. Careful observation of the onset of the reaction (which is proceeded by a concentration dependent induction period) suggests that the reaction mechanism is autocatalytic; some etchant product species catalyzes the further attack of the surface. Surface features of co-existing fluorescing and non-fluorescing regions emphasize the heavy etching present in the porous silicon region. Local control of the porous silicon formation by a photoinduced etching process is reported for the first time suggesting the possibility of a non-resist lithographic procedure.     

Influence of Synthesis Conditions on the Electrokinetic Characteristics of Titanium–Oxygen Nanostructures

Influence of synthesis conditions of titanium–oxygen nanostructures on their electrochemical behavior is studied. The nanostructures were prepared by molecular layer-by-layer deposition from the gaseous phase onto the substrates (silicon oxides titanium oxide, and silicon covered with oxide film). It is found that the deposition of a titanium–oxygen nanolayer onto the titanium oxide does not change the position of isoelectric point and the value of electrokinetic potential. Deposition of the titanium–oxygen nanostructure on the initial, as well as on the thermally and chemically modified silicon and silicon oxide substrates at various temperatures yields samples whose isoelectric points lie between the values for the substrate and deposited titanium oxide.     

液固相水热法制备氧化硅纳米线

利用液固相水热反应方法, 以硅溶胶为硅源, 在三价铁辅助下与乙二胺的水溶液在180 ℃反应4 d后生成具有P21212空间群结构的单晶氧化硅纳米线. 用扫描电子显微镜、透射电子显微镜和多晶X射线衍射对制备的样品进行了表征, 系统研究了有机胺、金属盐、反应时间及反应温度等条件对氧化硅纳米线生长的影响. 结果表明, 随着有机胺碳链的增长, 产物形貌逐渐由纳米线转变为纳米片; 金属阳离子的存在对纳米线形貌有较大的影响, 而阴离子的存在并不影响纳米线的生成; 过低的铁含量导致反应进行不完全, 而过多的铁盐加入则会导致反应中剩余铁氧化物吸附到氧化硅纳米线表面, 进而影响到产物纯度; 反应时间延长及反应温度的提高都有利于氧化硅纳米线的生长. 最佳反应条件为: 有机胺为乙二胺, 硝酸铁为铁源, 硅溶胶为硅源, 硅/铁摩尔比为1∶0.4, 乙二胺与水的体积比为8∶5, 温度为180 ℃.     

Enhancement of the ionic response of field effect transducers using porous silicon

Oxidised porous silicon samples prepared from highly and weakly doped p-type silicon substrates, have been functionalised with calix[4]arene (CA) molecules. They have been used for sodium detection as electrolyte/insulator/silicon (EIS) structures. An over Nernstian behaviour was observed and correlated with physical parameters of porous silicon samples (porosity, resistivity). A generalised Nernstian equation was proposed in order to describe this property. CA functionalised EIS structures based on porous silicon present higher lifetime compared to flat structures.     

Chemical assembly of chromium oxide structures on the surface of disperse silicon carbide

The possibility was studied for synthesizing chromium oxide structures on the surface of K3–6 granular silicon carbide [GOST(State Standard 26327-84)] by its multiple successive treatment with chromium(VI) oxochloride, ethyl alcohol, and water vapors. The change in the chromium concentration in the modified samples was studied as a function of the number of successive treatment cycles. The samples were characterized by the X-ray phase analysis, X-ray photoelectron, IR, and electronic diffuse reflectance spectroscopies before and after the modification.     

Structure of dislocation cores in the silicon crystal

We have recently produced a Lifson–Warshel force field for the silicon crystal. This field, that goes further than the harmonic approximation, is particularly adapted for the calculation of defect structures. It requires five free parameters, but one of them in the field already produced, the linear bending term, is significant for the perfect lattice structure only and should be eliminated in dealing with defect structures. Also, one of the fixed parameters can be adjusted to fit precisely the experimental value of the stacking fault energy. We show that an excellent fitting of the phonon dispersion curves, in the least squares sense, is obtained with the parameters thus changed. We illustrate the use of this field in discussing the problem of reconstruction of the 90° partial dislocation in silicon.     

Reversibility of pH-induced dewetting of poly(vinyl pyridine) thin films on silicon oxide substrate

Thin PVP films deposited on a silicon oxide surface have been found to form a dewetting pattern when treated with basic solutions (pH > or = 10). We studied the dependence of pattern morphology on the polymer's molecular weight and thickness of the polymer layer, and observed the formation of three distinctive structures. The structure formed by large drops of polymer is characteristic of a polymer with low molecular weight and the thinnest polymer layer, whereas other samples form holes or a weblike pattern upon dewetting. These experiments have demonstrated for the first time the reversibility of the dewetting process in a liquid environment. The polymer layer has revealed reversible behavior toward flat film when exposed to a pH 4 buffer solution. More complex structures can be obtained by consecutive treatments with acidic (pH 4) and basic (pH 10) solutions. We used atomic force microscopy (AFM) to study both the morphology and elastic properties of polymers in media with different acidity, in order to determine the mechanism behind the dewetting process.