Combined SIMS,AES, and XPS investigations of tantalum oxide layers

Thick layers of tantalum oxide prepared by thermal and anodic oxidation have been studied by combined SIMS, AES, and XPS during depth profiling by 3keV Ar⁺ ion sputtering. The chemical composition of these films is revealed by the OKLL and O 1s signals and by the “lattice valence” parameter determined from the TaO _n ^± intensities. Thus the anodic film consists of a contamination layer, an oxygen-rich reactive interface and a thick homogeneous oxide layer followed by an interface to the Ta metal. The thermal oxide shows an oxygen concentration decreasing with depth and a broad oxide-metal interface. In both cases, carbon contamination (carbide) prevents the application of the valence model to the clean Ta substrate. The sputtering yield of the oxides was found to be 0.6 Ta₂O₅/ion.     

Characterisation of molybdenum intermediate layers in Cu-C system with SIMS method

In the design of new high-speed chip generations a huge problem is bleeding off process heat during their operation. The installation of heat sinks onto such chips is necessary. Possible materials are copper-coated carbon composites. They combine high thermal conductivity with low density and a tailorable coefficient of thermal expansion (CTE). The low wettability of copper onto carbon necessitates a surface pretreatment.Flat slices of nitrogen-plasma etched vitreous carbon (Sigradur G) made up as a model system for carbon fiber material. The later serial fabrication of these fibers includes a hot pressing step after the deposition joining them to solid composites. It is simulated by a heat treatment step of the compound. The first sample series consisted of samples with 100 nm molybdenum and 500 nm copper layers (sputter deposited), as deposited and heat treated. The second run concludes samples without molybdenum layer but an additional 50 nm cap layer deposited after heat treatment.All samples were investigated with secondary ion mass spectrometry (SIMS), showing a diffusion of carbon into the molybdenum layer. Measuring MCs⁺ secondary ions, both matrix elements and trace elements were detectable sufficiently.     

SIMS diagnostics of the structure of nanometer-sized semiconducting layers doped with impurities

The possibility of analyzing the structure of nanometer-sized silicon layers doped with boron and antimony (at a concentration level of 10⁻²–10⁻³ at %) via secondary-ion mass spectrometry (SIMS) is investigated. A recoil-atom implantation process has been evaluated from the standpoint of its contribution into the total recorded signal of secondary ions of impurities. It is demonstrated that SIMS can be used for qualitative determination of the structure formed in doped δ-layers.     

Nano- and microstructured polymer LB layers: A combined AFM/SIMS study

Ultra thin structured polymer films have been prepared by horizontal precipitation Langmuir-Blodgett (HP-LB) method of polymer blends. In particular we used mixtures of two incompatible polymers, poly-2-vinylpyridine and polystyrene, the former giving the necessary surface activity for LB film formation. Upon spreading at the air-water interface, the blend forms different surface structures depending on the relative amount of the two components. By adjusting the experimental parameters it is possible to obtain relatively regular structures in the submicron size range, which can be transferred on a solid substrate. These systems have been investigated by means of SIMS and atomic force microscopy.     

Investigation of Diffusion of Magnesium in Lithium Fluoride Crystals by the SIMS Method

Using secondary ion mass spectroscopy, diffusion of magnesium impurity in lithium fluoride is investigated. A temperature dependence of the magnesium diffusion coefficients within the temperature interval 870–1073 K is established, which is described by an expression of the following type: D = 2.8·10^–3·exp(–1.5/kT). Combining the data on self-diffusion of cations with the results of the ion conductivity measurements, estimation is made of the thermodynamic parameters characterizing the jump of a diffusant. The calculated frequencies of the impurity ion jump to the cation vacancy are reported.     

Thermal stability of nanocrystalline layers fabricated by surface nanocrystallization

A nanocrystalline layer with ultrafine grains (about 30-40 nm) on the surface of 7050 aluminum alloy was fabricated by a new technique called High Pressure Shot Peening (HPSP) which is the combination of common Shot Peening equipment with a pressurizing vessel. Relationship between hot flow and temperature was observed by Differential Scanning Calorimetry (DSC) and the activation energy, calculated by Kisssinger equation, of the as-treated sample increased 26.6 kJ/mol when it is compared with the as-reserved sample. The Bragg peaks of the as-prepared samples, respectively treated with various annealing treatments were characterized by XRD and the microhardness distribution along the depth from the treated surface were measured at the same time, which indicated that the broadening of Bragg peaks decreased with the increasing of anneal temperature; the grain size, calculated by Scherrer-Wilson equation, increased obviously during 180-220 °C, accordingly, the microhardness obviously decreased. According to the results of DSC, XRD and microhardness, it is reasonable to deduce that the temperature range of thermal stability for aluminum alloy nanocrystalline layer is lower than 200 °C.     

Analysis of coatings and surface layers of materials by proton-backscattering spectrometry

Experience in the use and the potential of proton-backscattering spectrometry as applied to problems of modern materials science are discussed.     

Structure and surface layers of Mg-C nanocomposites produced by ball milling

X-ray diffractometry (XRD), X-ray photoelectron spectrometry (XPS), Auger electron spectrometry (AES) and transmission electron microscopy (TEM) were used to investigate the structure and surface layers properties of nanocomposites produced by the mechanical activation (ball milling) of elemental magnesium with carbon materials (amorphous carbon and graphite). Amorphous carbon was synthesized by electric discharge treatment in kerosene. It was shown that ball milling, the allotropic form of carbon materials, and features of hydrogenation have a considerable effect on the structure, surface layer properties, and hydrogen adsorption of a formed composition. XPS and Auger spectroscopy revealed the surface layer of the composite particles to be enriched with carbon. In addition, there were oxide layers on their surfaces due to the particles’ interaction with the environment.     

Investigation of 4H-SiC epitaxial layers implanted by Al ions

4H-SiC epitaxial layers 26 μm thick with N _d ?N _a = 1 × 10¹⁵ cm^?3 grown by the CVD method on 4H-SiC commercial wafers were implanted by Al ions with energy of 100 keV and a dose of 5 × 10¹⁶ cm^?2. To produce the p ⁺?n junction, a rapid thermal annealing for 15 s at 1700°C was used. The obtained samples were studied by the local cathodoluminescence, X-ray diffractometry, and transmission electron microscopy. It was established that under specified conditions of implantation, the width of a region with a high content of radiation defects exceeded by two orders of magnitude, the depth of the projective range of Al ions and was equal to 40 μm. This result is explained by the combined contribution of the radiation enhanced defect diffusion and long-range action effect. A short-term high-temperature annealing resulted in the recrystallization of the specimen surface layer and enhancement of CVD layer structure.     

Adsorption compression in surface layers

A recently elucidated aspect of adsorption, compression in confined phases, is discussed. Grand Canonical Monte Carlo simulations were performed for the adsorption of Lennard–Jones molecules and new details of intermolecular interactions in adsorbed layers are analysed. It is shown that a strong attraction to a surface can cause adsorption compression not only in the first layer, but also in higher layers. Compression of the first layer creates a pattern of active sites; the second layer tends to be commensurate with this pattern and has density higher than that of a ‘free’ layer. This pattern propagates to higher layers. However, there is a wide range of chemical potentials where the first layer is compressed and the second layer is not yet formed. It was found that transition to adsorption compression results in oscillations of the isosteric heat of adsorption. These oscillations are determined by a combination of (a) changes in adsorbed layers’ structure and (b) exchange of molecules between layers. In particular, at high affinity to adsorbent, the adsorption isotherm for the first layer has a slight maximum because an increase of the chemical potential causes molecules to leave the compressed first layer and move to the second layer. For this reason, the isosteric heat of adsorption decreases and can become negative. Analysis of adsorption compression mechanisms in the context of theory and emerging experimental results indicates that the significance of this phenomenon is not limited to fundamental aspects of adsorption and capillarity. These mechanisms play a crucial role in various applications, such as heterogeneous catalysis, membrane separations, and self-assembly on surfaces. Results are discussed in a broader context of theory, experiments and previous simulations.     

SIMS investigations of hydrogen interaction with a zirconium getter alloy surface

The results from secondary ion mass spectrometry (SIMS) investigations of the surface of Zr₅₀V₅₀ intermetallic getter alloy under residual and elevated partial pressures of hydrogen at different temperatures are reported.     

Positron states on surface and in defective surface layers of semiconductors

The paper discusses the possible spectrum and properties of positron states on the surface of real semiconductors.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 71–75, July, 1979.     

Nonlinear dynamics of incommensurate surface layers

We describe analytically the nonlinear dynamics of the incommensurate surface layer ("self-modulated" system) with a spatially periodical structure. In the framework of the Frenkel-Kontorova model the nonlinear excitations of the periodic soliton lattice, such as moving additional kinks and gap solitons, are investigated.     

Spectroscopy of surface space charge layers

Spectroscopic studies of the semiconductor surface space charge layer system complement and enlarge on the information derived from dc transport experiments. The paper fkst gives an account of far-infrared cyclotron resonance and dynamical conductivity studies in the surface layer. Such work explores the carrier motion in the plane of the space charge layer. A later section discusses intersubband spectroscopy, experiments in which the quantized motion in bound levels normal to the surface is probed.     

Measuring the parameters of dielectric layers by periodically charging the surface

It is shown that the parameters and characteristics of a dielectric layer can be determined by the periodic dosed deposition of a charge on the layer surface combined with the synchronous measurement of the accumulated charge and surface potential, as well as by measuring the surface potential when the layer is both freely discharged and discharged when exposed to light. The measurements data are used to plot the surface potential of the layer versus the charge density, as well as to find the dependences of the effective capacitance, differential capacitance, and leakage resistance on the surface potential. It is demonstrated that the characteristics thus obtained may provide an insight into the physics of processes occurring in the layer; determine time parameters, such as the half-value periods of the potential in the dark and under exposure to light; and find the capacitance, limiting value of the surface potential, permittivity, leakage resistance, and photosensitivity of the layer.     

Study of carbon material surface layers modified by nitrogen and argon ion irradiation

We present the results of the study of the elemental composition and defects of the electronic structure of the surface layer modified by high-dose irradiation (10¹⁸–10¹⁹ ion/cm²) of highly oriented pyrolytic graphite (UPV-1T) by 30-keV N ₂ ⁺ and Ar⁺ ions in the temperature range from 180 to 400°C. The EPR spectra observed during irradiation with argon ions at high temperatures and with nitrogen ions at temperatures near the liquid-nitrogen temperature T = 77 K exhibit anomalously narrow lines which probably result from the exchange interaction inside paramagnetic clusters of displaced carbon atoms. During nitrogen ion irradiation at room and higher temperatures, paramagnetic defects typical of many carbon materials (single EPR lines with g = 2.0027–2.0029) and belonging to carbon atoms bound to one or three nitrogen atoms were detected.