Study of GaAs and GaN based heterostructure surfaces and interfaces using ion beams and other complementary techniques

GaAs and GaN semiconductors and their heterostructures have been of interest for a few years now, because of their promising applications. Ion beams and other complimentary techniques are used for characterization of the surface and interfaces, to understand the novel properties of these materials. In this work we have reported the use of complimentary techniques like high-resolution X-ray diffraction (HRXRD), Rutherford backscattering/channelling (RBS/C), atomic force microscopy (AFM), and transmission electron microscopy (TEM) for characterization of these materials. We have studied InGaAs/GaAs heterostructures of various thicknesses by RBS/C, HRXRD, AFM, and TEM before and after irradiation. Bulk epitaxial layers of GaN grown on sapphire with and without AlN cap layer were characterized by HRXRD and AFM while the AlGaN/GaN heterostructures were characterized by RBS/C. The results are analyzed by taking account of the information extracted from these complementary techniques.     

Study of “liquid gold” coatings: Thermal decomposition and formation of metallic thin films

Organo-metallic solutions called liquid gold are largely used to obtain thin gilded films which are employed for decorative, technological and functional uses. However, these films often prove to be fragile with respect to use, resulting in loss of brilliance or even eventual film removal. An understanding of the behaviour of the layers requires good knowledge of the materials themselves. The present work was undertaken to better understand the evolution of the structural properties of liquid gold as it undergoes heat-processing. Accordingly, we followed the thermal decomposition processes of liquid gold coatings and the formation of the gilded metal layer using a combination of experimental techniques. First, thermal analyses coupled with mass spectrometry and infrared spectroscopy gave information concerning the decomposition of the organic medium. It has been found that the process of film formation can be decomposed into three steps, the second of which is an abrupt transition between 300 and 350 °C. Details on this transition have been obtained using real-time X-ray Diffraction and Rutherford Backscattering Spectrometry. Above 350 °C, the microstructure of the coating is reorganized to obtain a final layer which contains particles, of the size of a few hundreds nanometers, as shown by Transmission Electron Microscopy.     

Raman and X-ray absorption near-edge structure characterization of GaN implanted with O, Ar, Xe, Te and Au

GaN samples implanted with O, Ar, Te, Xe and Au ions, at fluences high enough to cause the formation of an amorphous surface or buried layer, are studied using Raman, X-ray absorption near-edge structure (XANES) and Rutherford backscattering (RBS) spectroscopies. The amorphous character of the as-implanted layers is verified by RBS and confirmed also by the XANES spectra. The Raman spectra of the amorphous surface layers are characterized by broad bands that simulate the phonon density of states, while the contribution of the underlying material is also detected. On the contrary, the spectra of the samples containing a buried amorphous layer are more structured due to the contribution of light scattered from the partially damaged layer which exists in between the surface and the buried amorphous layer.     

Surface and electrical studies of CuO:V2O5 thin films

Results from the studies of multicomponent CuO:V₂O₅ bulk material and thermally evaporated thin films of highly conducting bulk composition prepared at different substrate temperatures are thus compared and discussed. The electronic conductivity is enhanced on increase in the substrate temperature T_s and reaches a maximum value of 12.3 × 10⁻⁶Ω⁻¹ cm⁻¹ for T_s = 423 K. X-ray photoelectron spectroscopy studies indicate an increase in the reduced states of vanadium and copper ions in going from the bulk glass to the thin film. Dynamic secondary-ion mass spectroscopy studies on thin films over a depth of 3000 Å show a strong dependence of T_s on the Cu-to-V intensity ratio. Even though stoichiometric values for thin films are achievable by varying the T_s, the oxidation states of Cu in these films are predominantly monovalent. The electrical behaviors of these materials and their thin film counterparts are finally being discussed in relation to the surface analysis data.     

Elaboration and characterization of yttrium implanted low manganese steel.

Low manganese steel samples were yttrium implanted using ion implantation technique. Sample compositions and structures were investigated before and after yttrium implantations to determine the yttrium distribution in low manganese steel. Yttrium implantation depth profiles were characterized using conventional techniques such as X-ray photoelectron spectroscopy (XPS), reflection high energy electron diffraction (RHEED), X-ray diffraction (XRD), glancing angle X-ray diffraction (GAXRD) and a nuclear analytical method: Rutherford backscattering spectroscopy (RBS). The aim of this study is to show that correlation between composition and structural analyses allows to understand the effect of implanting yttrium in low manganese steel.     

Role of metal ions of Langmuir–Blodgett film in hydrophobic to hydrophilic transition of HF-treated Si surface

Hydrophobic to hydrophilic transition of HF-treated Si surface strongly depends upon the metal ions, which are present in the headgroups of the deposited Langmuir–Blodgett (LB) film. Structure of LB films studied by X-ray reflectivity technique and chemical analysis of LB film–substrate interfaces studied by X-ray photoelectron spectroscopy combinedly suggest that the partial transition or partial oxidation of the HF-treated Si surface takes place under the subphase water but further transition or oxidation is possible only in the presence of metal ions. Electrovalent and covalent natures of the metal ions tune this transition or oxidation. Ni ions, for which bonding with headgroups are electrovalent in nature, are favorable for such transition/oxidation and as a result, complete transition/oxidation takes place when nickel arachidate LB film is deposited. On the other hand, Cd ions, for which bonding with headgroups show covalent nature, is not favorable for such transition and can not oxidize the underlying H-passivated Si substrate totally when cadmium arachidate LB film is deposited on such HF-treated Si surface. This ion-specific hydrophobic to hydrophilic transition is visualized by X-ray reflectivity, contact angle and X-ray photoelectron spectroscopy measurements.     

Implications of stimulated resonant X-ray scattering for spectroscopy,imaging, and diffraction in the regime from soft to hard X-rays

The ultrahigh peak brilliance available at X-ray free-electron lasers opens the possibility to transfer nonlinear spectroscopic techniques from the optical and infrared into the X-ray regime. Here, we present a conceptual treatment of nonlinear X-ray processes with an emphasis on stimulated resonant X-ray scattering as well as a quantitative estimate for the scaling of stimulated X-ray scattering cross sections. These considerations provide the order of magnitude for the required X-ray intensities to experimentally observe stimulated resonant X-ray scattering for photon energies ranging from the extreme ultraviolet to the soft and hard X-ray regimes. At the same time, the regime where stimulated processes can safely be ignored is identified. With this basis, we discuss prospects and implications for spectroscopy, scattering, and imaging experiments at X-ray free-electron lasers.     

Investigation of the interfacial structure of ultra-thin platinum film deposited by cathodic–arc

Ultra-thin films are of interest in the production of X-ray mirrors that use a multilayer structure. The most commonly used deposition techniques are dc magnetron sputtering and electron beam evaporation; this paper presents results of cathodic–arc deposition. Ultra thin films of platinum with nominal thicknesses in the range 15–65 Å were deposited on silicon substrates and the film structure investigated using X-ray reflectivity and X-ray photoelectron spectroscopy. It has been found that the structure of the deposited films consists of three layers—the platinum film, a silicon oxide layer and a platinum silicide layer. In contrast to dc magnetron and electron beam deposited films, the silicide layer of cathodic–arc deposited films have a higher density and greater thickness, which is attributed to the higher energy process of this deposition technique. These attributes of the cathodic–arc deposited films suggest that the deposition technique is not suitable for production of mirrors of materials that react with each other, but for materials that do not the deposition technique is potentially more favourable than that of e-beam and magnetron sputtering.     

同步辐射技术在核材料研究中的应用

先进同步辐射光源具有高通量、高相干性、高脉冲重复率等优点,将基于其的X射线衍射、小角散射、成像、谱学等表征方法与原位环境(如温度场、应力场、气氛、溶液介质等)实验装置配合,可为系统表征与评价核能系统用材料与部件的服役行为和损伤机制提供重要技术手段.核材料在高温/应力/介质/中子辐照等复杂多场环境下的服役损伤行为长期以来...     

分析薄膜厚度与成分的卢瑟福背散射技术

对卢瑟福背散射分析技术的基本原理、试验设备、样品要求及数据处理方法进行了介绍,并举例分析了硅衬底上钛膜厚度的测定,以及钼衬底上钛钼合金膜的实际组分以及氦离子注入杂质的分布范围和实际剂量测定。讨论了卢瑟福背散射技术的发展和应用,介绍了弹性反冲、高能非卢瑟福散射和沟道技术三种分析方法。     

Acidity characterization of a titanium and sulfate modified vermiculite

A natural vermiculite has been modified with titanium and sulfated by the intercalation and impregnation method in order to optimize the acidity of the clay mineral, and characterization of samples were analyzed by X-ray fluorescence (XRF), X-ray diffraction (XRD), nitrogen adsorption isotherms, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and temperature programmed desorption with ammonia (TPD-NH₃). All the modified solids have a significantly higher number of acidic sites with respect to the parent material and in all of these, Brönsted as well as Lewis acidity are identified. The presence of sulfate appears not to increase the number of acidic centers in the modified clay. For the materials sulfated with the intercalation method, it is observed that the strength of the acidic sites found in the material increases with the nominal sulfate/metal ratio. Nevertheless, when elevated quantities of sulfur are deposited, diffusion problems in the heptane reaction appear.     

Exploring nanoscale magnetism in advanced materials with polarized X-rays

Nanoscale magnetism is of paramount scientific interest and high technological relevance. To control magnetization on a nanoscale, both external magnetic fields and spin polarized currents, which generate a spin torque onto the local spin configuration, are being used. Novel ideas of manipulating the spins by electric fields or photons are emerging and benefit from advances in nano-preparation techniques of complex magnetic materials, such as multiferroics, ferromagnetic semiconductors, nanostructures, etc.Advanced analytical tools are needed for their characterization. Polarized soft X-rays using X-ray dichroism effects are used in a variety of spectroscopic and microscopic techniques capable of quantifying in an element, valence and site-sensitive way basic properties of ferro(i)- and antiferromagnetic systems, such as spin and orbital moments, nanoscale spin configurations and spin dynamics with sub-ns time resolution. Future X-ray sources, such as free electron lasers will provide an enormous increase in peak brilliance and open the fs time window to studies of magnetic materials. Thus fundamental magnetic time scales with nanometer spatial resolution can be addressed.This review provides an overview and future opportunities of analytical tools using polarized X-rays by selected examples of current research with advanced magnetic materials.     

Surface analysis techniques and their application to materials characterisation

Surfaces of materials, the top few atomic layers, are of critical importance because it is here that a material interacts with its environment. The surface properties of materials dominate their corrosion behaviour, wettability, electrical contact resistance, frictional behaviour, adhesion properties and chemical reactivity. Over the last 25 years the vital role that surfaces play and the need to characterise them have been increasingly recognised and this has been paralleled by the development of many new surface analysis techniques. Of these, just a few have become pre-eminent for materials and devices characterisation: X-ray photoelectron spectroscopy, Auger electron spectroscopy and secondary ion mass spectrometry. The principles and capabilities of each of these techniques are briefly described. Application include the study of semiconductors, metallic and ceramic materials.     

Mechanochemical synthesis of zinc-apatitic calcium phosphate and the controlled zinc release for bone tissue engineering

Abstract

In this study, in order to control zinc (Zn)-release from calcium phosphate (CaP), the crystalline forms of CaP-containing Zn were modified by wet ball milling and/or heat treatment. The CaP (CaO:CaHPO₄:ZnO?=?7:20:3, molar ratio) was ground in a ball mill with the addition of purified water, and the ground products were heated to 400?°C and 800?°C. The physicochemical properties of these ground products were measured by powder X-ray diffraction (XRD), infrared spectroscopy (IR), scanning electron microscopy and energy-dispersive X-ray spectroscopy. Zn release characteristics from the samples were evaluated using a dissolution tester. The results of XRD and IR suggested that the structures of the starting materials were destroyed after 2.5?h of grinding, and new apatite-like amorphous solid containing Zn was generated. The Zn-release from the ground products was markedly suppressed after 2.5?h of grinding.     

X-ray photoelectron spectroscopy study of Langmuir–Blodgett films of N-octadecyl-8-hydroxy-2-quinoline carboxamide deposited from subphases containing metal ions

The Langmuir–Blodgett films of N-octadecyl-8-hydroxy-2-quinoline carboxamide (HOQ) deposited from subphase containing metal ions were investigated by X-ray photoelectron spectroscopy (XPS). The amphiphilic HOQ with its complexing head group in contact with the aqueous phase can form metal complexes with the metal ions present in the aqueous phase. The formation of HOQ–metal complexes leads to the appearance of new XPS peaks assigned to the metal ions. The information on stoichiometry provided by XPS indicates that a metal ion is coordinated by one HOQ molecule for transition metal ions of the fourth period, but by two HOQ molecules for the metal ions after the fourth period.     

X射线吸收光谱及发展

X射线吸收精细结构光谱是一种比较复杂的光谱,因其发生机理在不同能量段是不同的,故不同段有不同的用处,经历了一个数十年的发展过程,本文按其发展逐步深入地介绍了其各能量段的产生机理及由此可得的结构参数,择要介绍了它在一些领域的应用及在技术和应用等各方面的发展近况,还简要总结了它在我国的发展历程。     

Characterization of sol-gel derived scintillating LuBO3 films doped with rare earth ions

Rare earth doped LuBO₃ thin films have been prepared by combining sol-gel process and coating techniques such as spin coating and spray pyrolysis. Annealing treatment results in the crystallization of the film as vaterite phase and incorporation of the doping ions in solid solution. XPS and RBS spectroscopies showed that the composition of the films is close to the nominal one. Adventitious carbon has been observed and attributed to incomplete pyrolysis of metal-organic precursors. XPS concentration profiles show a good homogeneity for the films. RBS demonstrated some inter-diffusion between amorphous carbon substrate and borate films resulting in a gradient of carbon at the interface between the substrate and the film itself. Finally scintillation spectra have been recorded and demonstrate the potentiality of these films to be used as X-ray intensifying screens.     

X-ray photoelectron spectroscopy on implanted argon as a tool to follow local structural changes in thin films

Argon ions were implanted in metallic, semiconducting or insulating substrates, and investigated with X-ray photoelectron spectroscopy. Analysis of the Ar2p core level of argon showed clear differences in binding energy position and width as function of the matrix material, implantation energy, and post-annealing treatment. Although argon is not expected to form chemical bonds with the host matrix, the electronic shells within the gas atom can react to their environment according to different effects. It is shown that the precise determination and correct interpretation of the binding energy levels of the embedded gas atoms provides information about the local environment of the matrix such as amorphization of the crystalline structure, defect healing or gas bubble formation.     

氮化钛薄膜的高分辨AES谱和XPS谱研究

着重讨论了TiNx薄膜俄歇电子谱的定量分析方法和X射线光电子谱中线形的变化。利用已知组元强度定量分析技术和Ti的LMV俄歇电子峰，探讨TiNx薄膜中N含量的定量方法。由该方法给出的定量结果与X射线光电子谱定量结果相一致。同时，利用X射线光电子谱测定了TiN和Ti2N2p轨道的结合能。并针对Ti2p峰形随N含量的变化，给出新的解释。     

Temperature effects on the chemical composition of nickel-phosphorus alloy thin films

Electroless Ni-P (EN) alloys are widely used as coating materials. Their properties depend on the level of phosphorus present and the extent of thermal treatment. We report the results of two complimentary electronic structure techniques, X-ray absorption near edge structure (XANES) and X-ray photoelectron spectroscopy (XPS), and the site-specific surface chemistry in EN alloys of different phosphorus compositions and thermal treatments. In XANES experiment, absorption at the Ni L_3,2 edge and the P K edge were measured and the P 2p, Ni 2p, and Ni 3p bands were measured by XPS. Heating EN alloys to high temperatures result in a competitive reaction between phosphorus and nickel on the surface for oxygen. There is an increase in the level of phosphates and other forms of phosphorus oxides and a decrease in the oxidized nickel on the surface of the EN alloy thin film. Changes in the electronic structure and chemical composition in the bulk of the EN alloy are not obvious.