F. Rauch

Density of thin TiO2 films

Abstract Thin oxide films have a broad range of applications in optical devices. Titania (TiO2) is a frequently used oxide material for optical coatings because of its high refractive index (≈ 2.4) and low absorption. The development of devices and optimization of production parameters require proper knowledge of the film properties, such as refractive index, composition, contaminations and density. In thin-film analysis, RBS is usually employed for the determination of the film stoichiometry and contaminations. We have used a combination of RBS analysis and optical measurements to deduce absolute values for the density of thin films. Results for thin TiO2 films are presented demonstrating the usefulness of this approach. A strong correlation of density and refractive index is found. The density values are compared with data gained by X-ray reflection spectrometry. The differences of the density values obtained by both techniques are discussed, focusing on the uncertainties of the 4He stopping power values.

Nuclear reaction analysis of hydrogen in optically active coatings on glass

Abstract Films of WO3, Ta2O5, SiO2 and indium tin oxide as well as combinations of such films were analyzed for hydrogen with the 15N technique. Such coatings are used in optical devices for controlling reflectance and transmittance. H content and its changes during storage and in coloration experiments are reported. Effects of ion irradiation are described.

Nuclear reaction analysis of hydrogen at levels below 10 at.ppm

Abstract A setup for sensitive hydrogen analysis with the H ( 15 N , αγ) 12 C reaction has been developed. The detector for the reaction γ-rays is a bore-hole BGO scintillation counter with an efficiency of 27%. The natural-radiation background count rate is reduced by lead and anticoincidence shielding to 25 counts/h. This detector system is used in combination with a specially designed UHV chamber which enables measurements under vacuum in the 10−10 mbar region. Various kinds of background arising from interaction of the ion beam with parts of the beam line and with contaminations on the sample surface (H, D, C) as well as possibilities for background quantification and reduction have been investigated for 15N ion energies up to 12 MeV. Profiling examples demonstrating a detection sensitivity of better than 10 at.ppm are presented.

Hydrogen dynamics in electrochromic multilayer systems investigated by the 15N technique

Abstract The resonant reaction 1H(15N, αγ)12C was used to determine the depth distribution of hydrogen in two electrochromic multilayer systems. The systems can be bleached and colored by applying an external voltage. To test models explaining this effect by a change of H content (cH) in electrochromic layers, H profiles of the systems were measured as a function of the applied voltage. For NiOx, cH was found to vary as predicted, whereas for WO3, cH changes were smaller than expected. Additionally, H uptake into the ITO electrode was observed.

Compaction of tungsten oxide films by ion-beam irradiation

Abstract Evaporated amorphous tungsten oxide films with low densities, deposited on different substrates, have been irradiated with various types of ions of different energies up to 30 MeV, and with fluences up to 10 18 cm −2 . Compaction of the films up to nearly the bulk density was observed. No changes of the stoichiometry as determined by various ion-beam analysis techniques were detectable. Raman measurements showed that ion-beam-modified films are also amorphous, but have a different microstructure from as-deposited films. The irradiated films have a higher refractive index than the as-deposited films. A low threshold for the compaction effect of a few times 10 12 ions cm −2 was found, leading to the conclusion that one ion displaces more than 10 5 tungsten oxide molecules.

A low-background detection system using a BGO detector for sensitive hydrogen analysis with the 1H(15N, αγ)12C reaction

Abstract A geometrically compact detection system with a low cosmic-radiation background rate, 0.55 cts./min in the energy range 3.8–4.8 MeV, and good detection efficiency (14%) for the 4.4 MeV reaction γ-rays, is described. It consists of a 3 in. × 3 in. BGO detector, a plastic-detector anticoincidence shield and a Pb shield. The detection sensitivity of this system is ≲ 20 at.ppm. The performance of BGO detectors in comparision to NaI detectors for measuring 4.4 MeV γ-rays is discussed.

Concentration profiles of hydrogen in technical oxidic thin films and multilayer systems

SummaryThe hydrogen concentration, C(H), of oxidic thin films (SiO2, WO3, Ta2O5, TiO2, ITO) produced by reactive evaporation has been determined by means of nuclear reaction analysis. For comparison Ta2O5 layers deposited by reactive ion plating were investigated. The results show differences in the time-dependent behaviour of the H uptake for various single film materials and layer combinations. For single layers the kinetics for the hydrogen absorption is as follows: WO3 > Ta2O5 > SiO2 > ITO. An appreciable amount of hydrogen-containing species is found only in the layers created by evaporation.

Application of the 15N nuclear reaction technique for hydrogen analysis in polymer thin films

The 15N nuclear reaction technique for hydrogen analysis is applied for the first time to study hydrogen depth profiles in polymer thin films. Relevant details of this technique are given and in particular the important question of depth resolution is discussed. By using an optimized geometry a depth resolution of the order of 10 nm is achieved. Energy straggling data for 15N ions in polystyrene have been deduced from measured H-profiles. The ion dose necessary for the analysis is found to be low enough that radiation damage in the sample is of minor influence. Since the 15N technique discriminates between the isotopes H and D a suitable contrast between different components of a film system is obtained by deuterating one of them. This is illustrated by several examples, including interdiffusion of polystyrene layer systems and surface enrichment of one component of a diblock copolymer.

Analysis of tungsten oxide films using MeV ion beams

Abstract Tungsten oxide films produced by reactive evaporation were analyzed using the 15N technique for H profiling, RBS with 4He ions and ERD with 40Ar ions. The film stoichiometry was determined as WO3.0H0.3+aH2O, where the second term describes the uptake of water molecules during storage after film production. It was found that the stoichiometry of the films is not influenced by ion irradiation over a large range of ion doses and that the coloration of the films induced by ion irradiation is not connected with changes of the H content.

Gettering of hydrogen in iron and nickel caused by the implantation of titanium ions

Abstract Large amounts of hydrogen were found to be gettered in the near-surface region of iron and nickel after titanium implantation. This effect was studied as a function of various implantation parameters. Hydrogen and titanium depth profiles were measured using the nuclear reactions 1H(15N, αγ)12C and 48Ti(p, γ)49V. The gettering starts at a titanium fluence of about 1 × 1017 ions cm−2 for iron and about 2 × 1017 ions cm−2 for nickel (Eion = 30 keV). The amount of gettered hydrogen increases with increasing titanium fluence, and concentrations of up to 30 at.% are reached. A rough correlation exists between the shape of the hydrogen profile and that of the titanium profile. Release temperatures for the gettered hydrogen were found to be in the range 420–610 K in annealing experiments. The structure of the hydrogen traps and the gettering mechanism are discussed.