T. Laursen

Decomposition of Langmuir-Blodgett films to form metal oxide layers

Abstract Ultraviolet/ozone (UVO) treatment is investigated as a processing step in the fabrication of metal oxide thin films from Langmuir-Blodgett (LB) precursor films. UVO processing was found to reduce LB films to metal carbonates at a rate of approximately 1 min per layer. Subsequent thermal treatment resulted in dense, uniform metal oxide thin films. The structure and composition of these films are studied ellipsometry, X-ray diffraction, and Rutherford backscattering spectrometry.

RBS analysis of Langmuir-Blodgett films

Abstract Rutherford backscattering spectrometry (RBS) has been used to characterize thin films of yttrium and erbium arachidate deposited on a silicon substrate by a Langmuir-Blodgett technique. RBS can measure film thickness as well as the stoichiometry. Beam effects do not influence these results at moderate beam currents and fluences, although the films visual appearance was very sensitive to beam exposure. Beam-induced hydrogen desorption is also expected, and evidence for this is presented at high doses. RBS has also been used to characterize LB films during thermal decomposition and to analyze the metal-oxide end products (Y 2 O 3 and Er 2 O 3 films). An example is also given where a mixed YBaCu-oxide film is deposited by this method.

Yttrium oxide film deposition by a Langmuir-Blodgett processing technique and its incorpiration into oxide scales by substrate oxidation

Abstract Thin films (about 10 nm) of Y 2 O 3 have been deposited by a Langmuir-Blodgett processing technique onto a variety of substrates: type 304 stainless steel, low carbon steel, titanium, zirconium and silicon. The substrates were afterwards oxidized in air at 800, 1000 (304 steel), 400 (low C steel), 500 (Ti), 450 (Zr) and 1000 (Si) °C. The effects of the film on the oxide scale thickness and the interaction between Y 2 O 3 and the oxide of the substrate have been studied by ion backscattering. In stainless steel, the Y 2 O 3 film reduces the oxidation rate by orders of magnitude and Y is distributed throughout the oxide scalw (1–10 at.% level). In other substrates, the effect on oxidation rate was less pronounced, but changes in the visual appearance often took place. The Y 2 O 3 incorporation varied for the different substrates, and Y 2 O 3 remained as a surface film in the cases of Ti and Si. Such films exhibited good adherence and could not be removed by wiping. The potential use of metal oxide thin films for surface analysis standards and diffusion marker studies is discussed.

The effect of ion-implanted yttrium on the oxidation of austenitic stainless steel

Abstract The effect of ion-implanted yttrium on the oxidation of austenitic stainless steel is studied by combining ion backscattering (RBS) and SIMS characterizations of implanted and unimplanted specimens. Elemental depth distributions are measured after oxidation in 〈114〉 single crystals (17Crue5f813Ni) and type-304 polycrystalline samples (18Crue5f810Ni). Implantation of 5 × 10 15 and 2 × 10 16 Y/cm 2 (200 keV) reduces the extent of oxidation (10 min at 800°C) by ~ 20%. In addition, the 2 × 10 15 Y/cm 2 implantation changes the oxidation mechanism from being iron out-diffusion to be predominantly oxygen in-diffusion. This effect is believed to be beneficial for preventing spallation. While the single crystal oxidizes more than a micron for 10 min at 800°C, type 304 oxidizes less than 100 nm. At 1000°C the oxidation of 304 steel amounts to less than 200 nm. Yttrium implantation reduces the oxidation rate, but both in the implanted and unimplanted case, the oxidation mechanism appears to be chromium out-diffusion.

Corrosion of Zr-2.5 wt% Nb pressure tube material in D2O steam: deuterium depth distributions measured by nuclear reaction analysis

Abstract The corrosion of Zr-2.5 wt% Nb pressure tube material in D 2 O steam at 763 K has been studied by nuclear reaction and backscattering spectrometry. The oxide thicknesses — ranging from 3–7 μm — were determined by backscattering of 2.5 MeV protons. The deuterium depth distributions from the surface to beneath the oxide have been determined using the d( 3 He, p) 4 He nuclear reaction. The oxide contains high deuterium concentrations (0.003–0.005 D/Zr). Samples which have been “pickled” prior to corrosion have slightly thinner oxides, increased deuterium levels in the metal, and the deuterium depth profiles show a micrometer-wide depletion in deuterium, which may reflect an interfacial region with stress and plastic deformation.

The effect of anodic oxidation on near-surface deuterium in Zr-2.5 wt.% Nb

Abstract The effect of anodic oxidation on near-surface deuterium in thin ( ∼ 3.5 μm) foils of Zr-2.5 wt.% Nb has been studied with the 2 D( 3 He, p) 4 He nuclear reaction. To introduce deuterium into the foil, the native oxide was etched with a solution of 0.1% NH 4 HF 2 in D 2 O. The foils were anodized, in a compact cell in a vacuum chamber, to oxide thicknesses of 160, 200 and 280 nm and the remaining D concentration measured. The D content was also measured, in separate experiments, with the anodized surface towards the beam. Detailed analysis shows that the effect of oxidation is to return most of the D in the anodized region to the solution.

A comparative study of deuterium ingress from solution into Zr, Zircaloy-2 and Zr-2.5wt.% Nb by nuclear reaction analysis at the liquid-solid interface

We have compared deuterium ingress into thin (1.5–4.5 μm) foils of Zr, Zircaloy-2 and Zr-2.5wt.% Nb using the D( 3He, p) 4He nuclear reaction. The foils were mounted in a compact cell in a vacuum chamber and the foil and liquid in the cell were analyzed with a 3He beam. We introduced deuterium into the foils by etching their native oxide layers with a solution of 0.1% NH 4HF2 in D2O. The amount of deuterium taken up by the foils was measured in situ as well as in separate experiments ex situ in which the etched surfaces were turned toward the beam. The results show that deuterium uptake occurs in the order Zr-2.5wt.% Nb < Zr < Zircaloy-2.

Hydrogen ingress into oxidized Zr-2.5Nb

Abstract Deuterium (D) distributions in D2O-corroded Zr-2.5 wt% Nb samples have been measured for three different corrosion temperatures: 763, 673 and 573 K. The oxide thickness and details in the D profile for 763 K show considerable variation due to changes in surface preparation. Nevertheless, the D concentration in the central part of the oxide is within 0.002−0.005 D Zr atomic ratio. At lower temperatures − 673 K and below — the D concentration is somewhat higher: ∼ 0.01 D Zr . These concentrations are less than the 2–5% level observed with Zircaloy-2 after corrosion at 763 K. D distributions in O2-oxidized Zr-2.5 wt% Nb have been measured following a subsequent exposure to either D2 or D2O exposure at 573 K. D ingress into the metal is enhanced with D2 compared to D2O, supporting the expectation that reducing conditions (D2) may lead to a degradation of the protective oxide. Evidence is presented that two different diffusing species are responsible for the different D distributions measured in the oxide for the two types of exposure.

Hafnium diffusion in Zircaloy-2 and Zr-2.5 wt.% Nb: A Rutherford backscattering study

Rutherford backscattering has been applied to the determination of the temperature dependence of Hf diffusion in the commercial alloys Zr−2.5 wt.% Nb and Zircaloy-2. The diffusion anneals were made, under vacuum, in the temperature interval 830–1101 K; the specimens were well annealed with large (7–20 μm) grains. The diffusion coefficients, D, are of the same order of magnitude as self-diffusion values (10−17 to 10−21 m2/s) over the comparable temperature range; also they display broadly similar temperature dependences. These results indicate that diffusion in the alloys, like that in pure Zr, is controlled by the presence of trace Fe in solid solution. The D values for Zircaloy-2 are generally higher than those for Zr-2.5 wt.% Nb, but the difference is relatively small. The small differences in substitutional diffusion among Zircaloy-2, Zr-2.5 wt.% Nb and Zr may be attributable to “compositional and microstructural effects”.

In situ channelling analysis during thermal annealing of 4He+ implanted LiNbO3

Abstract LiNbO 3 has been implanted with 1.0 MeV 4 He + in order to create a buried layer of crystal lattice damage which acts as the lower boundary of an optical waveguide with the air surface forming the upper boundary. The annealing behaviour of this damage, in the temperature range 20 ° C to 350 ° C, has been studied in vacuo by performing in situ channelling analysis of the disorder during the thermal processing. It is concluded that the minimum annealing temperature required to reduce waveguide attenuation is 150 ± 10 ° C and the optimum is 180 ± 15°C. The results are seen to be in overall agreement with recent optical waveguide measurements.