The angle-resolved self-ratio technique for surface depth profile investigations by XFS,EMA, XPS and AES

The angle-resolved self-ratio (AR/SR) technique is a non-destructive, low-damage measuring technique in which the intensity I of an excited, analyte-characteristic radiation is measured as a function of the take-off angle from the surface plane for the purpose of obtaining quantitative depth information about the chosen analyte from the gradient dI/d. The depth information may be any of the following: the type of depth profile, the centroid depth of this profile, the thickness of a uniform overlayer, the stoichiometry of a uniform overlayer, the thickness of a uniform buried layer, and others. The AR/SR technique is one of a number of variants of the angle-resolved technique which is particularly suited for practical application because this mode combines an acceptable measuring effort with a simplicity and transparency of evaluation (by use of analytical formulae) not available with other procedures. The capabilities and limitations of the AR/SR technique in particular are reviewed, with special reference to four methods with which the technique has found application, viz. X-ray fluorescence spectrometry (XFS), electron microbeam analysis (EMA), X-ray photoelectron spectrometry (XPS) and Auger electron spectrometry (AES). Emphasis is placed on the role assigned to AR/SR/XFS and AR/SR/EMA in certification of ion-implanted reference materials.Invited lecture at 15th Colloquium on Materials Analysis, Wien, May 27–29, 1991     

XPS study of silicon spheres as a density standard

As density is one of the basic physical properties of materials, an accurate density standard is absolutely essential. To determine density with high accuracy and precision, two 1-kg single-crystal silicon spheres (NMIJ-S4 and NMIJ-S5) are used as the primary standard at the National Metrology Institute of Japan. For the accurate measurement of the mass and volume of the silicon spheres, the effects of the surface layer must be carefully considered. In this work, a surface layer model of NMIJ-S4 and NMIJ-S5 was proposed and the thicknesses of each surface layer were determined using X-ray photoelectron spectroscopy. A detailed uncertainty budget is presented to aid use of the density standard.     

Combined IR and XPS analysis of the native (1 0 0) surface of single‐crystalline silicon after HFaq etching

A combined analysis, based on angle‐resolved X‐ray photoelectron spectroscopy and multiple‐internal‐reflection infrared spectroscopy, of the (1 0 0) silicon surface after etching in dilute aqueous solution of HF is presented. The analysis shows that the surface is mainly formed by a heterogeneous distribution of SiH, SiH₂ and SiH₃ terminations, but contains (in addition to sub‐stoichiometric oxidized silicon) a form of reduced silicon, not consistent with the currently accepted picture of the native HF_aq‐etched surface. Copyright © 2007 John Wiley & Sons, Ltd.     

Contamination inspection on wafer with oxide or nitride film by using a vibrating contact potential difference probe

Contamination inspection on the oxide and nitride films deposited on silicon wafer surface by using vibrating contact potential difference (CPD) probe is presented in this paper. Contaminants induce the variation of the CPD between a dielectric layer and the probe material. However, the screening effect of the charges on the surface, interface and in the dielectric layer overwhelms the contamination signals when using the vibrating CPD monitor. This obstacle can be overcome using the signal characteristic diagnosis by which most of the charge signals can be filtered out. The validity of this approach was verified by means of the vapor phase decomposition coupling with inductively coupled plasma mass spectrometry (VPD‐ICP‐MS), and we found that the filtrated contamination signals were correlated closely with the metallic concentration. Moreover, the proper annealing process could enhance the response signals of contaminants, especially for Ni and Cu, in the nitride film monitoring. This inspection method was effectively applied in the trace metallic contamination routine monitor and the contamination source tracing of the furnace tools. Copyright © 2010 John Wiley & Sons, Ltd.     

Considerations of the intermediate oxides via XPS elemental quantitative analysis for the thickness measurements of ultrathin SiO2 on Si

The thicknesses of intermediate oxides at the interface between ultrathin SiO₂ and Si substrates have been measured via XPS elemental quantitative analysis for some SiO₂/Si(100) and SiO₂/Si(111) samples with the silicon oxide thickness less than 2 nm. The measurements involve XPS determination of the Si relative atomic ratio, calculation of Si atomic densities for the intermediate oxide, etc. and then the intermediate oxide thicknesses and the number of monolayers are obtained by referencing the thickness data from two international comparisons for these samples. The results show that the thickness of the intermediate oxides is in the range 0.14–0.16 nm with an average value of 0.15 nm. The number of monolayers for the intermediate oxides at the interface is less than one monolayer with an average value of 0.60. In the present work, there are a series of approximations. By making these approximations many parameters, including L and R₀, used in the conventional calculation method are removed to give a simpler equation, which is valid when the thicknesses of SiO₂ overlayer and the intermediate oxides are very small. This, therefore, appears to be a simple and quick method to obtain approximate oxide thicknesses of modest accuracy. The present work does not in any way replace or improve on Eqns ( 2 –6) cited in the text. Copyright © 2010 John Wiley & Sons, Ltd.     

XPS法测量铝箔表面氧化铝的厚度

介绍了一种无需溅射、无需变角，只需一次简单的ＸＰＳ（Ｘ射线光电子能谱）窄扫描，即可根据谱图中氧化态和金属态的相对强度算出铝金属表面氧化铝的厚度。用该法测量了一系列不同方法处理的铝表面氧比铝厚度，并与椭偏法及ＮＲＡ法（核反应分析法）测定结果进行了对比，结果表明，该法是一种简便准确的膜厚测量法。     

XPS investigation of the composition of the external surface of concrete after demoulding,cleaning and carbonation

X‐ray photoelectron spectroscopy (XPS) coupled with ion beam etching allows the measurements of concentrations gradients at the external surface of concrete. The chemical modifications, caused by the moulding and cleaning operations and due to carbonation, are efficiently investigated. Based on the detection of specific elements (such as chlorine, carbon and silicon), the presence of formworks residues is established on the concrete surface. Similarly, aliphatic (C –(C,H) and carbonaceous (C –O) residues of the demoulding agent can be detected. The concentration gradients show the presence of moulding residues is mainly superficial and decreases rapidly according to the depth. However, certain of these contaminants (and especially polydimethylsiloxane residues) could alter the wetting of aqueous‐based coatings. The sandblasting process can partially remove the moulding residues, but the decontamination remains incomplete in spite of the high increase of the roughness of the samples. On the contrary, the concentrations in aliphatic and carbonaceous residues increase after cleaning with solvents, which can be trapped in the pores of concrete to contaminate the surface. The carbonation process is also investigated by XPS. The concentration gradient of the carbonate component of the C 1 s peak shows a front of carbonation progressing as a function of the time after demoulding. Copyright © 2012 John Wiley & Sons, Ltd.     

Ultrathin SiO2 on Si IV. Intensity measurement in XPS and deduced thickness linearity

The procedures for measuring the intensities and for subsequent calculation of the thickness of thermal SiO₂ layers on Si in the range 0.3–8 nm have been evaluated to determine the best measurement protocols. This work is based on earlier work where the measurements for (100) and (111) Si surfaces indicate the need to work at a reference geometry. In the spectra, the Si 2p peaks may be separated clearly into the substrate Si and the overlayer SiO₂ but it is recommended here that, for accuracies better than 1%, the interface oxides are also analysed. The analysis here is for thermal oxides. Oxides grown by other routes may require a modification of this analysis. It is shown that, in evaluating the data to determine the layer thickness, the failure to remove x‐ray satellites or the use of a straight‐line background will both lead to unacceptable errors that may exceed 5%. On the other hand, if a Shirley background is used consistently for both the peak area analysis and for evaluation of the ratio of intensities for bulk SiO₂ and Si, R_o, the results should be linear over the above range to within ±0.025 nm. This excellent result includes the non‐linearities arising from elastic scattering effects and the data reduction method. Equations are provided, together with a value of R_o for Mg and Al x‐rays, to calculate the oxide thicknesses with the above linearity. In order to determine the oxide thickness accurately, the relevant inelastic mean free paths also must be known. Theoretical evaluations are only accurate to 17.4% and so better values need to be obtained by calibration. This paper provides the infrastructure to do this. Crown Copyright © 2003 Published by John Wiley & Sons, Ltd.     

XPS and AFM characterization of aminosilanes with different numbers of bonding sites on a silicon wafer

The aim of this work was the preparation and characterization of a silicon surface modified by different self‐assembled aminopropylsilanes with the purpose of using them in sensor applications. Single‐crystal silicon wafers (111) were modified with aminosilanes that have different numbers of bonding sites: 3‐aminopropyltrimethoxysilane (APTMS), 3‐aminopropyldiethoxymethylsilane (APRDMS) and 3‐aminopropylethoxydimethylsilane (APREMS). We deposited the self‐assembled layers from a solution of aminosilanes in toluene under various reaction conditions. The surface composition and the chemical bonding were determined using X‐ray photoelectron spectroscopy. Furthermore, the surface morphology was investigated using atomic force microscopy. Our results show that the reactivity with the Si‐oxide layer and the polymerization of aminosilanes depend on the number of possible bonding sites. The APTMS reacted the most intensively with the Si‐oxide layer; a less intensive reaction was observed for the APRDMS; and the least intensive reaction was observed for the APREMS. Copyright © 2013 John Wiley & Sons, Ltd.     

Observation of surface contamination layer by X‐ray reflectometry (XRR) analyses

Ultra‐thin HfO₂ films of 3.5, 5.0, and 8.0 nm nominal thicknesses were prepared, respectively, on silicon substrates by using atomic layer deposition method. Through the analyses of X‐ray reflectometry (XRR), X‐ray photoelectron spectroscopy, and transmission electron microscopy for HfO₂ films with and without sample cleaning, the effects of surface contamination on XRR curve and film thickness were investigated, and contamination layer was observed and the thickness of the layer was determined. X‐ray photoelectron spectroscopy results indicated that the amount of surface contamination varied considerably because of the surface cleaning. XRR curve shapes and the positions of thickness fringes changed and the thickness from Fourier analyses of the curves were different for the same sample due to the different surface contamination. Contamination layer of about 1 nm thickness was observed by Fourier analysis of XRR curve. Simulation for XRR curve showed the best fit to data when contamination layer of about 1 nm thickness was considered, and the result was consistent with that of the Fourier analysis. Copyright © 2016 John Wiley & Sons, Ltd.     

Glow discharge deposition of silicon dioxide and aluminum oxide films: A kinetic model of the surface processes

Silicon oxide films have been deposited in a RF discharge plasma using hexamethyl-disiloxane (HMDSO) and Ar/O₂ or N₂O. Also, aluminum oxide layers have been deposited using trimethylaluminum (TMA) and N₂O or CO₂. The influence of the nature and the proportion q( the oxidizing gases and file suhstrate temperature effect have been studied. As far as the films obtained with HMDSO and TMA tire concerned, the most important experimental finding is the decrease of the deposition rate with increasing substrate temperature. FTIR, ESCA, and refractive index measurements show that the decrease of the deposition rate correlates with a nearly stoichiometric film. Low negative apparent activation energies are deduced from Arrhenius plots and are representative of deposition rates controlled hr fire adsorption of radical and surface di fusivities. A kinetic rnodel shows that the rate-limiting step is the adsorption of HMDSO or TMA radicals at low temperatures while for temperatures above 250°C the oxidation reactions control the deposition rate.     

Si 2p XPS spectrum of the hydrogen‐terminated (100) surface of device‐quality silicon

An experimental study of the Si 2p XPS spectrum at different take‐off angles of atomically flat, hydrogen‐terminated 1 × 1 Si(100) is reported. The observed spectrum can be described accurately by considering three additional contributions to the spectrum of elemental silicon. Each contribution is attributed to a chemical state of silicon on the basis of its chemical shift with respect to elemental silicon and the depth of the region where it was originated. Copyright © 2003 John Wiley & Sons, Ltd.     

Isoelectric points of plasma‐modified and aged silicon oxynitride surfaces measured using contact angle titrations

Acid‐base properties of metal oxides and polymers can control adhesion properties between materials, electrical properties, the physical structure of the material and gas adsorption behavior. To determine the relationships between surface isoelectric point, chemical composition and aging effects, plasma‐surface treatment of amorphous silicon oxynitride (SiO_xN_y) substrates was explored using Ar, H₂O vapor, and NH₃ inductively coupled rf plasmas. Overall, the Ar plasma treatment resulted in nonpermanent changes to the surface properties, whereas the H₂O and NH₃ plasmas introduced permanent chemical changes to the SiO_xN_y surfaces. In particular, the H₂O plasma treatments resulted in formation of a more ordered SiO₂ surface, whereas the NH₃ plasma created a nitrogen‐rich surface. The trends in isoelectric point and chemical changes upon aging for one month suggest that contact angle and composition are closely related, whereas the relationship between IEP and composition is not as directly correlated. Copyright © 2010 John Wiley & Sons, Ltd.     

Thermodynamic investigation of the state of water adsorbed by carbonaceous adsorbents

The state of water adsorbed on active carbons and canal soot was studied using the “chemical potential—entropy—temperature” diagram. In the range of the relative pressures from 0.174 to 1, the state of adsorbed water is similar to the state of a stretched liquid. The molar volume, heat of evaporation, and surface tension of stretched water were calculated at different relative pressures. Near the spinodal, the molar volume of stretched water is 25% higher, and the surface tension is considerably lower compared to water. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 3, pp. 464–468, March, 1997.     

Ultra‐thin SiO2 on Si VIII. Accuracy of method,linearity and attenuation lengths for XPS

In the study of ultra‐thin films (<10‐nm thick), there is a range of methods that can provide accurate measurements of differences in thickness. However, in a pilot study under the auspices of the Consultative Committee for Amount of Substance (CCQM), results for the archetypal system of SiO₂ on Si show that the methods have different offsets such that, at all thicknesses, positive or negative amounts in the range up to 1 nm may be observed between methods. All the methods studied give thicknesses that are greater than those measured by X‐ray photoelectron spectroscopy (XPS) by amounts between 0.2 nm and approximately 1 nm. Significant parts of these offsets, of other methods with respect to XPS, may be attributed to contaminations which increase the apparent thickness but that do not affect XPS. However, not all of these offsets can yet be explained at the 0.2 nm level. The remaining part of the offsets could be thought to have arisen either from the XPS or from the other methods. In this study, by measuring SiO₂ deposited in situ on amorphous Si by XPS it is shown that the XPS linearity is consistent with the previous estimate of ± 0.025 nm, down to fractions of a monolayer, with no significant offset and that, therefore, it is the offsets seen using other methods that need further study. Recent calculations of the film thickness dependence of the attenuation lengths (ALs) for this system, using NIST SESSA software, are not consistent with these data although earlier calculations are. This work shows that XPS, with the AL calibrated by one or more other methods that are valid for differences in thickness, can provide a traceable measurement of thickness in all laboratories. © Crown Copyright 2007. Reproduced with the permission of Her Majesty's Stationery Office. Published by John Wiley & Sons, Ltd.     

第一性原理模拟氢气分子在氧化硅团簇上的吸附

基于密度泛函理论,采用广义梯度近似(GGA)分析了H2分子吸附在氧化硅团簇上的几何结构、电子性质以及吸附能.结果发现:H2分子与Si3O4团簇相互作用时,H2分子被分解,游离的H原子优先吸附在末端Si原子上,表明Si3O4团簇体系对氢气的存储主要依赖于末端存在悬挂键的Si原子,接着H2分子才以分子的形式以较小吸附能吸附在Si3O4H4团簇上.氢气分子主要引起与其邻近的原子电荷的重新分布.该团簇体系的红外、拉曼光谱图有效地鉴定了H2分子的吸附状态,为理论上确定团簇的稳定结构和实验上对观测结果的分析提供有力的途径.     

XPS study of the effect of aluminium on the atmospheric corrosion of the AZ31 magnesium alloy

The surface characteristics and corrosion behaviour of the AZ31 magnesium alloy exposed to a high relative humidity (RH) atmosphere were investigated. During the first 15 days of humidity test at 98% RH and 50 °C, a significant increase of magnesium carbonate and a decrease of magnesium oxide were detected on the surface film by XPS; after this stage, increased exposure times did not produce substantial changes on the relative amounts of these compounds. The surface film of commercially pure magnesium, also examined for comparison purposes, revealed more magnesium carbonate and less magnesium oxide compared with the AZ31 alloy. Unlike the AZ31 alloy, the surface of pure Mg disclosed almost complete substitution of MgO by magnesium carbonate after 30 days of exposure time. Mass gain values of tested specimens and scanning electron microscope characterisation of corroded surfaces indicated lower corrosion susceptibility of the AZ31 alloy compared with the commercially pure Mg, suggesting superior chemical stability of the oxide/hydroxide film formed over the magnesium–aluminium alloy surface. XPS and energy dispersive X‐ray (EDX) analyses did not revealed any substantial enrichment of aluminium in the corrosion products film on the AZ31 alloy after 30 days of testing. Copyright © 2008 John Wiley & Sons, Ltd.     

碳质表面异相还原NO2的反应机理

基于量子化学密度泛函理论（DFT），研究了碳质表面异相还原NO₂的反应机理，针对Zigzag与Armchair两种碳质表面，采用M06-2X方法与6-311G （d）基组联用，优化得到了不同反应路径下所有驻点的几何构型与能量，并对各路径进行了热力学与动力学分析，重点探究了CO在NO₂异相还原反应中的作用规律，同时考察了碳质表面与反应温度对异相反应的影响。计算结果表明，NO₂在碳质表面的异相还原过程主要分为两个阶段，即NO₂还原阶段与碳氧化物释放阶段。通过对比无CO分子参与的反应可知，参与反应的CO分子可以降低各阶段的反应能垒并且加快各阶段的反应速率；CO分子存在时，NO₂还原阶段的反应能垒被降低，促进了NO₂还原成NO的异相反应过程，同时参与反应的CO分子与碳质表面剩余氧原子结合，形成CO₂分子并释放，使碳氧化物释放阶段的反应能垒降低，从而促进了整体还原反应的进行。此外，与Armchair型相比，基于Zigzag型碳质表面的NO₂异相还原反应能垒更低且反应速率更快，说明NO₂异相还原反应更容易在Zigzag型碳质表面进行。最后，由反应动力学分析可知，随着温度上升，各阶段的反应速率均增大，说明提高温度对碳质表面的NO₂异相还原能够起到促进作用。     

Surface oxide development on aluminum alloy 6063 during heat treatment

We report on the influence of oxygen partial pressure for the development of surface oxides covering the industrial aluminum alloy standard 6063 at temperatures ranging from room temperature to 500° C. Using an array of synchrotron-based techniques, we followed the change in oxide thickness, chemical composition, and the lateral distribution of alloying elements. The impact of the oxygen chemical potential is most visible at high temperatures where the oxide composition changes from mostly Al based to mostly Mg based. This is in stark contrast to the ultra-high vacuum (UHV) conditions where only a partial compositional transition is observed. The microscopy data demonstrate that in the UHV case, Mg segregation onto the surface occurs firstly at grain boundaries at 300° C and secondly at sites over the entire surface at 400° C. Further, the initial oxide thickness is 45 Å, as determined by XPS and XRR, decreases in all observed cases after heating to 300° C. At higher temperatures, however, the oxygen partial pressure highly influences the resulting oxide thickness as evident from our X-ray reflectivity data.     

玻璃表面特性的XPS研究

本文用XPS表征了玻璃表面铜、铅和锡离子的价态,并测定在浮法玻璃底表面锡离子价态的深度分布。对沾锡现象与锡离子价态之间的关系进行了讨论。