Comparing the chemical properties of evaporated and sputtered niobium films on oxidized Si(1 0 0) wafers - preparation of oxynitride films

Five hundred nanometers of niobium films have been deposited on silicon(1 0 0) wafers with 100 or 300 nm thermally grown oxide by electron beam evaporation and DC magnetron sputtering. SEM and AFM investigations revealed smaller crystallites and rougher surfaces for the evaporated films. The differences in film morphology resulted in lower reflection intensities in XRD for the as-deposited evaporated films. In order to investigate the influence of the structural properties on their chemical reactivities, in a first set of experiments the films were nitrided with molecular nitrogen by rapid thermal processing (RTP) at varying temperatures. In another set of experiments after nitridation in nitrogen at 1000 °C an oxidation step in molecular oxygen at varying temperatures followed. The films showed different reactivities, leading to different rates of nitridation and oxidation. Sputtered films were less reactive than the evaporated films, deduced from the sequence of reaction products dependent on reaction temperature. XRD data indicated that oxynitrides have formed. Elemental depth profiles were measured by secondary ion mass spectrometry (SIMS).     

高温高压条件下富硼固体B7O的合成与表征

 在高温高压条件下采用过量氧化锌氧化单质用的方法合成了富硼固体以B₇O，并利用X射线衍射、X射线光电子能谱、红外光谱、二次离子质谱等测试手段，对合成产物进行了表征。测试结果表明，组成富硼固体B₇O的基本结构单元是十二个硼原子组成的正二十面体，氧原子存在于这些结构单元的间隙之间，并与结构单元中的硼原子互相成键。本文所采用的合成方法较其它方法可以更方便地得到结晶情况很好的单相富硼固体B₇O。     

Comparative study of the oxidation of thin porous silicon layers studied by reflectometry, spectroscopic ellipsometry and secondary ion mass spectroscopy

We present a systematic study on ultrathin porous silicon (PS) layers (40–120 nm) of different porosities, formed by electrochemical etching and followed by thermal oxidation treatment (300°C and 600°C) and by electrochemical oxidation. The oxidised and non-oxidised PS layers have been analysed by spectroscopic reflectometry (SR), spectroscopic ellipsometry (SE) and secondary ion mass spectroscopy (SIMS). The SR and SE spectra were fitted by a multiparameter fit program and the composition and the thickness of the PS layers were evaluated by different optical models. PS layers, formed electrochemically in the outermost layer of a p/n⁺ monocrystalline silicon junction were successfully evaluated using a gradient porosity optical model. The non-oxidised PS, formed in p-type silicon, can be well described by a simple optical model (one-layer of two-components, silicon and voids). The spectra of the oxidised PS layers can be fitted better using an optical model with three interdependent components (crystalline-silicon, silicon-dioxide, voids). The SIMS results give a strong support for the optical model used for SR and SE.     

Coadsorption of Ba and O on polycrystalline W

The thin film properties of the barium-oxygen-tungsten system were studied using a combination of AES, Δφ, and low-damage SIMS techniques. Due to the extreme reactivity of barium toward residual gases, all experiments not requiring oxidation (including simultaneous SIMS and barium deposition) were completed at operating pressures never exceeding the 10^-11 Torr range. The barium-oxygen-tungsten system was found to have work function-coverage properties similar to those of the cesium-oxygen-tungsten system. The order of adsorption was found to give different structures; and in the case of Ba → O/W, a patchy surface was discovered. The low-damage SIMS yields showed correlation with work function.     

Impact of ultrasound on galactooligosaccharides and gluconic acid production throughout a multienzymatic system

Galactooligosaccharides (GOS), recognised prebiotic, can be industrially produced from lactose and commercial β-galactosidase (β-gal) from Kluyveromyces lactis. Residual lactose and glucose limit GOS applications. To handle this problem, a multienzymatic system, with β-gal and glucose oxidase (Gox), was proposed to reduce glucose content in reaction media through its oxidation to gluconic acid (GA). Besides, ultrasound (US) probe effect over the multienzymatic system to produce GOS and GA has been evaluated. A production around 40% of GOS was found in all treatments after the first hour of reaction. However, glucose consumption and GA production was significantly higher (P < 0.05) for sequential reaction assisted by US, obtaining the best production of GOS (49%) and GA (28%) after 2 h of reaction. The conformational and residual activity changes of enzymes under US conditions were also evaluated, Gox being positively affected whereas in β-gal hardly any change was found.     

Influence of ionic dopants on the conductivity of electrochemically synthesized polypyrrole

Comparison of elemental analytical, XPS and SIMS data allows a semi-quantitative assessment of the dopant and oxidation states of polypyrrole synthesized using a variety of potentials and electrolyte concentrations. Studies of polypyrrole grown in aqueous solution indicate, contrary to previous reports, that a maximum in the conductivity is observed for films grown close to the oxidation-reduction potential and in agreement with our previous observations on organically grown polypyrrole.Treatment of electrochemically synthesized polypyrrole with sodium hydroxide leads to a reduction in the electrical conductivity by three orders of magnitude and similarly the addition of hydrochloric acid causes an increase in the electrical conductivity by several orders of magnitude. It was found, by comparison of films of different thicknesses that the initial time lag in the decrease in the conductivity on exposure to sodium hydroxide is a result of diffusion controlled deprotonation, whereas the protonation reaction causes an almost instantaneous increase in the electrical conductivity.     

First experimental evidence by SIMS of different surface binding energies for uranium according to its oxidation state

The existence of two peaks in the energy spectrum of uranium was evidenced for the first time with SIMS during the sputtering of a UO₂ sample as a function of the oxidation state of the surface. The surface oxidation state was quantitatively determined using the O18 method. These two peaks were attributed to two different surface binding energies of uranium. Since their relative intensities change as a function the surface oxidation state, the two surface binding energies must be associated with two different oxidation states of uranium.     

Functionality of novel black silicon based nanostructured surfaces studied by TOF SIMS

A functionality of the novel black silicon based nanostructured surfaces (BS 2) with different metal surface modifications was tested by time-of-flight secondary ion mass spectrometry (TOF SIMS). Mainly two surface functions were studied: analytical signal enhancement and analyte pre-ionization effect in SIMS due to nanostructure type and the assistance of the noble metal surface coating (Ag or Au) for secondary ion formation. As a testing analyte a Rhodamine 6G was applied. Bi⁺ has been used as SIMS primary ions. It was found out that SIMS signal enhancement of the analyte significantly depends on Ag layer thickness and measured ion mode (negative, positive). The best SIMS signal enhancement was obtained at BS2 surface coated with 400 nm of Ag layer. SIMS fragmentation schemes were developed for a model analyte deposited onto a silver and gold surface. Significant differences in pre-ionization effects can play an important role in the SIMS analysis due to identification and spectra interpretation.     

Effect of ultrasonic treatment on the defect structure of the Si–SiO2 system

The effect of ultrasonic treatment (UST) on the defect structure of the Si–SiO₂ system by means of electron spin resonance (ESR), metallography, MOS capacitance technique and secondary ions mass-spectroscopy (SIMS) is presented. The non-monotonous dependence of the defect densities on the US wave intensity has been observed. The influence of the UST frequency on the ESR signal intensity of the defect centres has been studied. It is shown that observed changes in the ESR intensity are caused by vibrational dissipative mechanisms which are a function of defect centre type and crystallographic orientation. The influence of the UST on the Si–SiO₂ interface properties depends on the time of oxidation. The density of point defects at the Si–SiO₂ interface can be reduced and its electrical parameters improved by an appropriate choice of the UST and oxidation conditions.     

碱性介质中葡萄糖在铂电极上的阳极氧化

为了进一步探明葡萄糖在铂电极上的氧化机理 ,用循环伏安法 (CV)在 - 0 .9～ 0 .4V(相对于饱和甘汞参比电极 )内研究了葡萄糖在铂电极上催化氧化行为 ,首次详细报道了葡萄糖在电化学氧化过程中的电位振荡现象 ,并用电流扫描法表征了葡萄糖的电位振荡情况 .电流扫描结果表明 ,在较慢的电流扫描速度下 ,电极过程出现了明显的电位振荡 .说明电极上产生了毒化中间物 ,电位振荡是由于毒化中间物在电极上的吸附和在高电位下氧化除去引起的 .     

An isotopic labeling study of the diffusion mechanism during oxidation of Si(100) in water vapor by successive oxidation

The diffusion mechanism during the wet oxidation of Si(100) at 1373 K was investigated by successive oxidations finally containing isotopic water. SiO₂ was first thermally grown on Si in non-labeled oxidizing ambient (dry O₂ or H₂O) followed by isotopic water (H₂¹⁸O) to trace ¹⁸O species in SiO₂. The distributions of ¹⁶O and ¹⁸O in the oxide film were analyzed by means of secondary ion mass spectroscopy (SIMS). SIMS depth profiles show that there was a wide overlap of both isotopes (¹⁸O and ¹⁶O) throughout the SiO₂ layer, no matter whether the first oxidation step was carried out in dry O₂ or H₂O, and the concentration gradient of ¹⁸O decreased with increasing oxidation time at the second oxidation step by H₂¹⁸O. The results suggest that the diffusion mechanism in SiO₂ during water vapor oxidation is exchange diffusion; H₂O related oxidizing species diffuse through the network with significant exchange with the pre-existing oxygen in it.     

Ultrasound in carbohydrate chemistry: sonophysical glucose oligomerisation and sonocatalysed sucrose oxidation

Both aspects of the interest in using ultrasound are illustrated by our results in the field of carbohydrate chemistry. The course of the heterogeneous reaction of glucose with hydrophobic alcohols in acidic medium is directed towards the oligomerisation of glucose because of the wetting of the glucose suspension due to the efficiency of the sonophysical mixing. On the other hand, a sonocatalysis is observed during the course of the oxidation of primary hydroxyl groups in homogeneous aqueous medium by the NaOCl/TEMPO system.     

Analyses of HF/NH4F buffer-treated Si(111) surfaces using XPS,REM and SIMS

The effect of different cleaning procedures on Si(111) wafers has been studied. A three-step cleaning process was used. The first two steps (thermal oxidation followed by RCA cleaning) were common to all samples. The final step involved rinsing in one of a set of HF/NH4F buffer solutions with a wide range ofpH values. Three different surface techniques were used for characterizing the chemical condition and morphology of the treated surfaces: XPS (X-ray Photoemission Spectroscopy), REM (Reflection Electron Microscopy) and SIMS (Secondary-Ion Mass Spectroscopy). It has been found that thepH value of an HF solution does significantly affect the etching rate and morphology of the Si(111) surface: For the same type of solution, the smaller thepH value, the higher the etching rate. Basic solutions withpH values larger than eight have a much weaker etching effect on the surface, which is contradictory to some previous reports. The most effective solutions for the etching of the Si(111) surface are the solutions of HF buffered by NH₄F, with thepH in the range of 2–6. REM images indicate that the surface morphology after etching in the HF solution is strongly affected by the length of the etching time: Overetching will roughen the surface. The SIMS data show that water rinsing in air during the cleaning process does speed up oxidation, but it is necessary to use water to clean off the residuals from the HF solutions.     

葡萄糖催化氧化反应用Pd-Co/C催化剂的XPS研究

活性炭为载体，制备了Pd/C、Pd-Co/C催化剂，并进行了活性评价和XPS表征。在Pd-Co／C催化剂上反应3h后，葡萄糖的转化率达92％，选择性为94％，较Pd/C催化剂有显著提高。Co的添加及焙烧过程改变了Pd/C催化剂的表面组成及结构，提高了贵金属Pd在催化剂表面的分散程度，有利于Pd的还原，使Pd-Co/C催化剂表现出良好的催化活性和选择性。     

Dynamic SIMS analysis of cryo-prepared biological and geological specimens

The modification of a dynamic magnetic sector secondary ion mass spectrometry (SIMS) instrument to permit the analysis of frozen biological and geological samples is described. The SIMS instrument used for this study combines SIMS analysis with the generation of ion-induced secondary electron images, allowing direct superposition of the SIMS image onto the image of cellular structures. Secondary ion maps have been acquired with sub-micron resolution, permitting the characterisation of sub-cellular elemental distributions in plant cells and human fibroblast cells, as well as the distribution of chemical impurities at grain boundaries in polar ice samples. This cryo-preparation technique clearly extends the applicability of SIMS analysis to a wide range of samples.     

SSIMS analysis of organics, polymer blends and interfaces

This paper gives a critical review on the applications of ToF SIMS in the areas of polymer additive characterization and in the study of polymer blends and interfaces. Polymer additives can readily be identified by ToF SIMS using their parent molecular ions or characteristic fragments. This analytical capability has been successfully applied to monitor the migration or segregation of additives during polymer processing. ToF SIMS is an ideal analytical tool for the study of polymer blends and interfaces because it is able to provide information on both surface composition and morphology. In combination with other analytical techniques such as AFM and XPS, ToF SIMS chemical imaging capability has opened up new horizons in the investigation of complex polymer blend systems. Finally the main advantages and limitations of ToF SIMS in these application areas are also discussed.     

Improved determination of phosphorus contamination during ion implantation by SRP and simulations

Experimental determination of phosphorous cross-contamination during antimony implantation is presented. As a suitable structure for this experiment, a buried layer was employed which is created by implanting antimony followed by a long diffusion process. The implanted samples were analysed by SIMS and spreading resistance (SRP) methods. SRP method has been improved by applying a correction for the carrier spilling effect. A conversion chart for p-n junction depth dependence on phosphorus doping has been calculated by program SUPREM-IV. Comparison of SRP and SIMS methods has shown that SRP method can be used for monitoring the phosphorus cross-contamination and can be easily implemented as an in-line monitor and present an alternative to expensive and time consuming SIMS analysis.     

New approach to the preparation of GaAs oxide films utilizing an ultrathin Sm overlayer

The effect of an ultrathin (≤1.5 nm) Sm overlayer on the kinetics of the plasma anodic oxidation process of GaAs is investigated. Oxidation of Sm/GaAs structures proceeded ≈10 times faster compared to a free GaAs surface. SIMS analysis showed that the oxide layer is contamined by Sm up to the oxide/semiconductor interface. A fitting procedure applied to the growth kinetics revealed two aspects of using the Sm overlayer: an increase in both the oxygen migration coefficient in the oxide and the concentration of O^? ions on the dielectric surface during the oxidation procedure.     

Thermal oxidation induced during laser cleaning of an aluminium-magnesium alloy

During laser cleaning of metallic materials by pulsed lasers surface, modifications can be induced mainly by the transient thermal effect. In ambient conditions an oxidation of the cleaned surface can be detected. The aim of this work was to characterize this transient oxidation that can occur below the laser energy domain leading to any phase change (melting, ablation) of the cleaned substrate.A Q-switched Nd:YAG laser with pulse duration of 10 ns and wavelength of 1064 nm was used for the purposes of this study. For the surface analysis of the treated samples X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS) were used.It was found that thermal oxidation took place on the aluminium-magnesium alloy during the irradiation in air with a laser energy ranged from 0.6 to 1.4 J cm^-2. It has been demonstrated that this thermal oxidation had the same mechanism as in the case of the steady state thermal oxidation of the aluminium-magnesium alloys even though the laser irradiation was applied only for the very short time of 10 ns. When the laser energy reached the value of 1 J cm^-2, the oxide formed by the thermal oxidation became in a large extent crystalline and its outer part was entirely covered by a continuous layer of magnesium oxide. PACS 61.82.Bg; 81.65.Mq; 61.80.Ba     

Characterization of oxidized CdS by SIMS/XPS

Although adsorption of simple gases is not detected on CdS by analytical means, oxidation is induced, for example, by exposure to a negative corona discharge [1] as well as by electron stimulation [2–4]. In the former case it was found that O attaches only to S, but in the latter case Cd is also oxidized. In this paper we investigate these processes by SIMS and XPS in an attempt to characterize and understand further these differences in behavior.