Unique ion beam scattering technique on depth profile determination

Abstract

By combination of energy and time of flight detection in ERDA or NRA measurement, the particles' masses can be determined, additionally to the depth information. This leads to unique depth profile determination even for complex targets. Combination with th concept of Jacobi transformations results in extremely fast measurements. In this paper, a way is shown how this concept can be realized even for accelerators ofenergies as low as about 1 MeV.     

Effect of Ar+ irradiation on the electrical conductivity of BaCe0.9Y0.1O3−δ

The effects of 10 keV Ar⁺ ion irradiation on the electrical characteristics of BaCe_0.9Y_0.1O_2.95 subject to fluences of 0, 1.0 × 10¹⁷, 5.0 × 10¹⁷ and 1.0 × 10¹⁸ ions/cm² at room temperature, has been investigated using elastic recoil detection analysis (ERDA), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS) and alternating current (AC) impedance measurements. It was confirmed from the ERDA results that the hydrogen concentration near the surface increased with increase of Ar⁺ ion fluence. This increase may be associated with the increasing quantities of hydrogen generated by interaction between oxygen vacancies, formed by irradiation, and H₂O from exposure to air. SEM images showed clearly that the number of surface defects due to modification increased with increasing fluence. In addition, the size of the defects showed a tendency to increase with increasing fluence. From the results of XPS analyses, providing information on the electronic states on the surface, it was evident that with increase in the Ar⁺ ion fluence, the quantity of excess oxygen, such as hydroxide, increased in the oxygen 1s XPS spectrum. In addition, it was indirectly found, from decomposition of the Ce 3d, spectrum that the concentration of oxygen vacancies increased with fluence, since the percentage of Ce³⁺ also increased. Accordingly, the surface modification led to the formation of more oxygen vacancies and a greater hydrogen concentration on the surface, since the H₂O interacted with some of them. From the results of the DC conductivity and AC impedance measurements, the proton conductivity was shown to predominate over the temperature range from 473 K to 823 K. It was concluded that the increase in these protons and vacancies generated from surface modification contributed to the increase of proton conductivity.     

Investigation of semi-insulating oxygen-doped GaAs

We found Oxygen-doped GaAs crystals to be suitable materials for CO₂ laser optical component preparation, with application at 10.6 μm. An optical transmission of 55% in the IR spectrum range, between 2 and 15 μm has been reached for such a GaAs type material. The GaAs crystals that we have analysed were grown by two procedures: Horizontal Bridgman (HB) and Liquid Encapsulated Czochralski (LEC). The HB method has been used for obtaining pure (undoped) crystals, while the oxygen-doped GaAs ingots were grown by LEC technique. The two types of samples processed in the same manner as regards mechanical polishing and chemical etching, which were investigated by Hall measurements, optical transmission spectrometry and elastic recoil detection analysis (ERDA) technique. The GaAs:O (LEC) has near semi-insulating properties as can be observed from the results of the electrical resistivity and Hall effect measurements. The ERDA spectrum shows an intense signal of oxygen in the bulk of GaAs:O (LEC) crystals, while the oxygen signal is not present in the ERDA spectrum of the undoped GaAs (HB). We consider that these results could recommend the ERDA technique as a possible qualitative and quantitative analysis in an ion-beam accelerator for oxygen content in oxygen-doped GaAs crystals. The analysis is not sensitive to the native oxide, as could be seen by measuring GaAs (HB) undoped crystals.     

Elastic recoil detection analysis (ERDA) in hydrogenated samples for TNSA laser irradiation

This paper provides an overview of theory, method, and examples concerning the elastic recoil detection analysis employed in forward recoil spectrometry to monitor the hydrogen content of hydrogenated targets prepared to be irradiated by high‐intensity lasers in target normal sheath acceleration regime. Polymers, semiconductors, and ‘advanced foils’ were analyzed to evaluate their hydrogen content as potential source for plasma proton acceleration. Helium ions at 2.0 MeV were employed as a target probe in a glancing angle to induce recoil hydrogen atoms and to measure the hydrogen concentration in the first superficial layers of the target. Results demonstrated that the hydrogen degassing occurs under ion beam irradiation, that its content depends on the polymer specie and porosity, that it is possible to control thin hydrogenated film thickness, and that the technique has sufficient isotope resolution to separate hydrogen from deuterium content. Copyright © 2015 John Wiley & Sons, Ltd.     

Elemental depth profiling of a-Si1−xGex:H films by elastic recoil detection analysis and secondary ion mass spectrometry

The hydrogen content in a-Si_1−xGe_x:H thin films is an important factor deciding the density and the optical band gap. We measured the elemental depth profiles of hydrogen together with Si and Ge by elastic recoil detection analysis (ERDA) combined with Rutherford backscattering (RBS) using MeV He²⁺ ions. In order to determine the hydrogen depth profiles precisely, the energy- and angle-dependent recoil cross-sections were measured in advance for the standard sample of a CH₃⁺-implanted Si substrate. The cross-sections obtained here are reproduced well by a simple expression based on the partial wave analysis assuming a square well potential (width: r₀ = 2.67 × 10⁻¹³ cm, depth: V₀ = −36.9 MeV) within 1%. For the a-Si_1−xGe_x:H films whose elemental compositions were determined by ERDA/RBS, we measured the secondary ions yields of HCs₂⁺, SiCs₂⁺, H⁻, Si⁻ and Ge⁻ as a function of Ge concentration x. As a result, it is found that the useful yield ratios of HCs₂⁺/SiCs₂⁺, H⁻/Si⁻ and Ge⁻/Si⁻ are almost constant and thus the elemental depth profiles of the a-Si_1−xGe_x:H films can be also determined by secondary ion mass spectrometry (SIMS) within 10% free from a matrix effect.     

Structure of MgO/V/MgO(0 0 1) thin films studied by the combination of X-ray photoemission and ion beam analysis techniques

The structure of epitaxial 40 Å thick V(0 0 1) films grown at room and high temperature (723 K) in MgO/V/MgO(0 0 1) model heterostructures is studied in detail by means of X-ray photoemission spectroscopy, Rutherford backscattering spectrometry and elastic recoil detection analysis. The resulting structures of samples grown at both temperatures is very similar, including the eventual contamination by hydrogen in the V layer, and only subtle modifications at the V/MgO(0 0 1) interface have been observed. These differences at the very first V layers grown on MgO(0 0 1) surface could infer in the growth of the subsequent V layers. The influence of the nature of the V oxides at the V/MgO(0 0 1) interface on the properties of the 40 Å thick V(0 0 1) films is discussed.     

Investigations on PECVD boron carbonitride layers by means of ERDA, XPS and nano-indentation measurements

The deposition of boron carbonitride layers on silicon substrates by a microwave plasma enhanced chemical vapour deposition (MW-PECVD) process using N-trimethylborazine (TMB) and benzene as precursors is presented. As plasma gases argon and nitrogen were used. In this investigation we focus on the influence of the gas composition, substrate temperature and -bias on the layer composition, layer structure as well as the thermal stability. The films were analyzed with respect to their composition and bonding structure using elastic recoil detection analysis (ERDA) and X-ray photoelectron spectroscopy (XPS). Furthermore, nano-indentation measurements before and after annealing tests at 500 and 700 °C were performed. The measurements show a strong dependence of the structure and mechanical properties on the substrate temperature. The hydrogen content strongly decreases to 8 at.% with higher substrate temperatures. Simultaneously, the layer hardness and Young’s modulus increase up to 21 and 173 GPa, respectively. The hardness does not decrease after annealing for 1 hour at 700 °C.     

Heavy‐ion elastic recoil detection analysis as a useful tool for tracking experimental modifications in bulk calcium silicates

Chemical modifications carried out on unique amorphous nano‐structured calcium silicate have been traced by time‐of‐flight heavy‐ion elastic recoil detection analysis (HERDA). It could be shown that this ion‐beam analysis method allows not only surface but also depth analysis of the silicate samples and the modifications effected upon it. While providing a challenge for standard analysis methods, the highly porous, low‐density nature of the calcium silicate proved to be an asset for the ion‐beam analysis technique chosen. Presented are depth profiles giving elemental compositions and providing the bases for representative chemical formula for the silicates studied. It was proven that a study of the surface composition of this nano‐structured silicate is sufficient for indicating the bulk composition of a sample of this material. Copyright © 2005 John Wiley & Sons, Ltd.     

Structure and morphology of nickel-alumina/silica solar thermal selective absorbers

Nickel-alumina/silica thin film materials for the use in solar thermal absorbers have been investigated using Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Elastic Recoil Detection Analysis (ERDA). The TEM images revealed that all layers have a very small thickness variation and that the layers are completely homogenous. High resolution images showed 5-10 nm (poly) crystalline nickel nano-particles. ERDA showed that both the silica and alumina compositions contain more oxygen than 2:1 and 3:2 respectively. SEM showed the surface morphology and characteristics of the top silica anti-reflection layer. Hybrid-silica has showed to generate a smoother surface with less cracking compared to pure silica. The final curing temperature revealed to be of importance for the formation of cracks and the surface morphology.     

Depth profiling of light elements in PAMBE‐grown GaN and helium‐implanted titanium with heavy ion time‐of‐flight elastic recoil detection

The heavy ion time‐of‐flight elastic recoil detection analysis (HI‐ERDA) technique was used to investigate the possibility of measuring near‐surface elemental depth profiles of light and mid‐Z elements in thin films of plasma‐assisted molecular beam epitaxy (PAMBE)‐grown GaN and helium‐implanted titanium. The great advantage of HI‐ERDA is the ability to measure mass‐separated elemental depth profiles simultaneously. However for some materials it is not certain whether HI‐ERDA can be used successfully because significant sputtering or other beam‐induced damage may occur. The damage to the surfaces by a 77 MeV iodine beam was assessed using RBS, AFM and profilometry. The results show that for thin PAMBE‐grown polycrystalline GaN films and for titanium that has been heavily implanted with helium a significant modification of the near‐surface region is caused by the probing heavy ion beam. For the PAMBE‐grown GaN films the most significant loss trend is observed for nitrogen. Surprisingly this was not accompanied by a change in surface topology. In contrast, an almost complete removal of the heavily helium‐implanted surface layer was measured for the titanium specimens. The investigation shows that reference measurements with additional techniques such as RBS, AFM and profilometry have to be performed to ascertain sample integrity before HI‐ERDA data can be used. Copyright © 2004 John Wiley & Sons, Ltd.