Diffusion Annealings Research Articles

Towards Measuring the Pu Self-Diffusion Coefficient in Polycrystalline U<sub>0.55</sub>Pu<sub>0.45</sub>O<sub>2±x</sub>

This paper describes an original method to measure the plutonium self-diffusion coefficient in the mixed oxide U0.55Pu0.45O2±x. This method is based on using 242Pu as a tracer atom. A thin film of the tracer was deposited on the well-polished surface of the samples and then diffusion annealings were performed from 1500°C to 1700°C, in an Ar-H2 5% atmosphere. The oxygen potential was fixed at-395 kJ.mol-1. After annealing, the 242Pu self-diffusion profiles were established by means of secondary ion mass spectrometry (SIMS). The 242Pu concentration profiles were determined by assessing the relative U, Am and Pu ionisation yields according to the experimental parameters. The choice of favourable experimental conditions and the relevance of the resulting concentration profiles are discussed at length.

Self-diffusion of lithium, hydrogen, and oxygen ions in crystalline lithium hydroxide

The self-diffusion coefficients of ions of the three chemical elements forming lithium hydroxide have been determined by the crystal-crystal and crystal-gas isotope exchange method in the temperature range 500–720 K. Crystal samples with different isotope compositions have been grown by the Bridgman method from melts. The melting temperature is 743 ± 2 K. Original methods have been developed for high-precision measurements of the isotope ratios of all three elements, i.e., lithium (6Li/7Li), hydrogen (H/D), and oxygen (16O/18O), and their changes after diffusion annealings with the use of the same sample. The self-diffusion coefficients of lithium and hydrogen ions differ but by a factor of no more than 3–5; however, their values exceed those for oxygen by several orders of magnitude. In particular, at 670 K, they are equal to 6.0 × 10−9, 3.2 × 10−9, and 2.0 × 10−12 cm2 s−1 for hydrogen, lithium, and oxygen, respectively. In the range 680–720 K, the self-diffusion coefficients of hydrogen and lithium increase sharply with increasing temperature to approximately 10−6 cm2 s−1. A probable mechanism of migration of protons and lithium ions in LiOH and the role played in this process by the oxygen ions with a lower mobility have been discussed.

Study of Oxygen Diffusion in Polycrystalline ZnO by SIMS

Oxygen diffusion coefficients were measured in polycrystalline ZnO by means of the gas-solid exchange method using the isotope 18O as the oxygen tracer. The diffusion annealings were performed at 892oC and 992oC, in an Ar+18O2 atmosphere under oxygen partial pressures from 0.1 to 1atm. After the diffusion annealings, the 18O diffusion profiles were established by secondary ion mass spectrometry (SIMS). Increasing the oxygen pressure leads to an increase of the oxygen diffusion in ZnO. The bulk diffusion coefficients depends on oxygen pressure according to , at 882oC, or , at 992oC, which indicates that the oxygen bulk diffusion mechanism should preferentially take place by means of interstitial oxygen having a null effective charge. The grain boundary diffusion coefficients show little dependence on oxygen pressure at 882oC, given by , which should correspond to a diffusion mechanism by means of interstitial oxygen, with a double negative charge, but at 992oC this dependence is corresponding to a diffusion mechanism by interstitial oxygen having a null effective charge. The results also show that the grain boundary is a fast path for the oxygen diffusion in polycrystalline ZnO.

First Study of Oxygen Diffusion in a ZnO - Based Commercial Varistor

Oxygen diffusion coefficients were determined in a commercial ZnO-based varistor by means of the gas-solid exchange method using the isotope 18O as the oxygen tracer. The diffusion annealings were performed at 892, 942, 992 and 1092oC, in an Ar + 18O2 atmosphere under an oxygen partial pressure of 0.2 atm. After the diffusion annealings, the 18O diffusion profiles were established by secondary ion mass spectrometry (SIMS). The results show an increase of the oxygen diffusion in the varistor, both in bulk and in grain boundaries, when compared to the oxygen diffusion in undoped ZnO. The increase of the oxygen bulk diffusion in the varistor agrees with an interstitial mechanism for the oxygen diffusion. The results also show that the grain boundary is a fast path for the oxygen diffusion in the varistor. However, the oxygen diffusion in the grain boundaries of the varistor seems to depend on several chemical and microstructural parameters and does not allow a simple explanation.

Grain boundary diffusion and recrystallization in ultrafine grain copper produced by equal channel angular pressing

The diffusion of 63Ni radiotracer in ultrafine grain (UFG) Cu produced by equal channel angular pressing (ECAP) was studied using the serial-sectioning method. The diffusion annealings were performed in the temperature range of 424–553 K for annealing times at which volume diffusion is negligible and only short-circuit diffusion occurs. Complete or partial recrystallization occurred during all heat treatments, and the explicit expression describing the kinetics of recrystallization was obtained from observations of the microstructure after annealing treatments. The measured radiotracer penetration profiles exhibited two distinct slopes, indicating the co-existence of “slow” and “fast” short-circuit diffusion paths in the system. Based on the results of previous studies, the former were associated with the general high-angle grain boundaries in the non-recrystallized, UFG matrix. A model that considers diffusion in UFG polycrystal undergoing recrystallization was developed. Application of this model enabled us deriving the diffusion coefficients along the grain boundaries in UFG matrix from the experimentally measured radiotracer penetration profiles.

Oxygen diffusion in Bi2O3-doped ZnO

In order to clarify the influence of Bi-doping on oxygen diffusion in ZnO, the bulk and grain boundary oxygen diffusion coefficients were measured in Bi2O3-doped ZnO polycrystals by means of the gas-solid exchange method using the isotope 18O as the oxygen tracer. The experiments were performed on ZnO sintered samples containing 0.1, 0.3 and 0.5 mol% Bi2O3. The diffusion annealings were performed at 942, 1000 and 1092 °C, in an Ar+18O2 atmosphere under an oxygen partial pressure of 0.2 atm. After the diffusion annealings, the 18O diffusion profiles were established by secondary ion mass spectrometry (SIMS). The results show an increase in the oxygen diffusion in the Bi2O3-doped ZnO, when compared to the oxygen diffusion in the undoped ZnO polycrystal under the same experimental conditions, both in bulk and in grain-boundaries. Moreover, it was observed that the higher the Bi2O3 concentration, the higher the oxygen diffusion. These results suggest that the incorporation of Bi2O3 increases the interstitial oxygen concentration which agrees with an interstitial diffusion mechanism both in bulk and in grain-boundaries.

Zinc Self-Diffusion in ZnO

This work deals with the study of zinc self-diffusion in ZnO polycrystal of high density and of high purity. The diffusion experiments were performed using the 65Zn radioactive isotope as zinc tracer. A thin film of the tracer was deposited on the polished surface of the samples, and then the diffusion annealings were performed from 1006 to 1377oC, in oxygen atmosphere. After the diffusion treatment, the 65Zn diffusion profiles were established by means of the Residual Activity Method. From the zinc diffusion profiles were deduced the volume diffusion coefficient and the product dDgb for the grain-boundary diffusion, where d is the grain-boundary width and Dgb is the grain-boundary diffusion coefficient. The results obtained for the volume diffusion coefficient show good agreement with the most recent results obtained in ZnO single crystals using stable tracer and depth profiling by secondary ion mass spectrometry, while for the grain-boundary diffusion there is no data published by other authors for comparison with our results. The zinc grain-boundary diffusion coefficients are ca. 4 orders of magnitude greater than the volume diffusion coefficients, in the same experimental conditions, which means that grain-boundary is a fast path for zinc diffusion in polycrystalline ZnO.

Oxygen diffusion in pure and doped ZnO

Oxygen diffusion coefficients in pure and doped ZnO polycrystals were determined by means of the gas-solid isotope exchange method using the isotope 18O as oxygen tracer. The diffusion experiments were performed from 900 to 1000 °C, under an oxygen pressure of 10(5) Pa. After the diffusion annealings, the 18O diffusion profiles were determined by secondary ion mass spectrometry. The results of the experiments show that oxygen diffusion in Li-doped ZnO is similar to the oxygen diffusion in pure ZnO, while in Al-doped ZnO the oxygen diffusion is enhanced in relation to that observed in pure ZnO, in the same experimental conditions. Based on these results is proposed an interstitial mechanism for oxygen diffusion in ZnO. Moreover, it was found that oxygen grain-boundary diffusion is ca. 3 to 4 orders of magnitude greater than oxygen volume diffusion in pure and doped ZnO, which means that the grain-boundary is a fast path for oxygen diffusion in ZnO.

Implantation and diffusion of 73 As in GaAs and GaP

Self-diffusion on the As sublattice in intrinsic GaAs and foreign-atom diffusion on the P sublattice in intrinsic GaP were investigated in a direct way by As tracer diffusion measurements using the radioisotope 73As. For this purpose 73As was implanted in both materials at the ISOLDE facility of CERN. Then diffusion annealings were performed followed by serial sectioning and counting of the radioactivity in each section. The resulting profiles were simulated within a computer model which accounts for the observed loss of tracer to the diffusion ambient. The so-obtained diffusion coefficients for As in GaAs and GaP are compared with existing diffusivities in these compounds.

Impurity states in grain boundaries and adjacent crystalline regions. I. Temperature dependence of the population of states in the grain-boundary diffusion zone.

We present the results of an investigation by emission nuclear \ensuremath{\gamma}-resonance spectroscopy of the population of states in the grain-boundary diffusion (GBD) zone. It is shown that atomic probes in polycrystals of some fcc and bcc metals only populate two discrete states in the GBD zone: one in the core of the grain boundary and one in the lattice sites adjacent to the grain boundary. For the typical fcc metals Pd, Pt, and Au, we investigated the dependence of the impurity-state populations on the temperature of the atomic-probe diffusion. It was shown that the ``intrinsic'' temperature dependence of state populations can be distorted owing to the formation of interstitial impurity segregation. In gold, where the volume solubility of such impurities is low, there is a temperature range of diffusion annealings, where the population-state regularities are determined by the ``intrinsic'' parameters of the atomic-probe diffusion. We made a suggestion concerning the atomic-probe diffusion mechanism in the interstitial impurity segregation zone, which causes the atomic-probe ``pumping'' parameters to change at low temperatures.

A Deep Level Transient Spectroscopy Study of the Internal Gettering of Cr in Czochralski‐Grown Silicon: Efficiency and Reversibility upon Lamp Pulse Annealings

The interaction of lamp pulses with the internal gettering of chromium (Cr) in Czochralski‐grown silicon (Si) has been studied by deep level transient spectroscopy profiling of the electrically active Cr concentration on beveled samples. B‐doped Si wafers were submitted to various sequences of thermal treatments consisting in different combinations of Cr diffusion, gettering treatments (high‐low‐high or high‐low), and lamp pulse annealings. An inhibition of the internal gettering mechanism was observed whenever Cr was diffused in a lamp furnace before gettering, or when a lamp pulse was applied before Cr diffusion in a quartz tube furnace. In addition, the stability of the Cr precipitates, formed inside the wafer after internal gettering, was found to depend significantly on the gettering temperature. These results were consistently explained in the framework of the “oxygen precipitation” gettering model, taking into account the two basic requirements of efficient denuded zone formation by oxygen nucleation, and further oxygen precipitate growth rate enhancement of the metal precipitation.

Diffusion of dopants in tungsten disilicide: effects of diffusion paths

Dopants, mostly boron, but also arsenic and antimony, implanted in unannealed WSi 2 films prepared by chemical vapor deposition diffuse quite readily at temperatures as low as 600°C. Complete homogenization in layers 200 nm thick is obtained at that temperature in periods of time less than 24 h. These results can be attributed to the large density of grain boundaries in layers that are initially amorphous and crystalline during the course of the diffusion annealings. They are in sharp contrast to what is observed when the layers are annealed at high temperature to cause grain growth and stabilization of the silicide structure prior to implantation. The dopants then are largely immobile not only at 600°C, but even during prolonged oxidation procedures at 800°C. Similar low temperature diffusion of boron in WSi 2 had been observed earlier in bilayers of polysilicon and WSi 2, but it is only presently that one is aware of the huge difference in diffusion behaviors between annealed and unannealed silicide layers.

Diffusion behaviour of Au/Ni bilayers deposited by electron beam evaporation and sputtering onto massive copper substrates

We have studied the diffusion behaviour of Au/Ni bilayers deposited onto massive copper substrates by electron beam evaporation and sputtering. The structure of the gold films is characterized by transmission electron microscopy. The diffusion of Ni through Au and of Cu through the Au/Ni bilayer is controlled by Auger spectroscopy using the method of the “first arrival”. Diffusion annealings were performed between 300 and 400 °C. The results are discussed in relation with the structure of the films. It appears that a small deposition rate favours single crystal areas in the deposited film and consequently makes a more effective diffusion barrier.