Lattice and grain boundary diffusion of copper in thin aluminum films

The lattice D₁ and grain boundary δD_b diffusivities of Cu in Al thin films at 130–185°C are calculated from measurements employing Auger electron spectroscopy and Ar ion beam etching. The calculated values are D₁ = 0.065 cm² s^-1 × exp(-122 kJ/RT) and δD_b = 4.5 × 10^-9 cm³s^-1 exp(-97.4 kJ/RT). The D₁ value is 3–5 times larger at 130–185°C than that predicted by an extrapolation of radioactive tracer measurements of large grain bulk specimens at 433–652°C. The higher value measured here is attributed to the higher density of subgrain defect structures in the thin film.     

Grain boundary self-diffusion in evaporated Au films at low temperatures

Direct self-diffusion measurements in vapor-deposited polycrystalline Au films have been made using ¹⁹⁵Au radioactive tracer and an r.f. back-sputtering technique for serial sectioning. A temperature range of 117°–177°C was investigated. It has been demonstrated that self-diffusion in thin Au films at these low temperatures takes place by rapid transport of the tracer atoms along the grain boundaries. The grain boundary self-diffusion parameters are Q_b=1.0±0.1 eV and δD_b⁰ = 9 × 10^?10 cm³/sec, which compare well with those in bulk polycrystalline Au.     

Role of diffusion-annealing temperature on the microstructural and superconducting properties of Cu-doped MgB2 superconductors

This study deals with not only investigate the effect of the copper diffusion on the microstructural and superconducting properties of MgB₂ superconducting samples employing dc resistivity as a function of temperature, scanning electron microscopy (SEM) and X-ray diffraction (XRD) measurements but also calculate the diffusion coefficient and the activation energy of copper for the first time. Electrical-resistivity measurements indicate that both the room-temperature resistivity value and zero resistivity transition temperatures (T _c ) increase with increasing the diffusion-annealing temperature from 650 to 850?°C. SEM measurements show that not only the surface morphology and grain connectivity improve but also the grain size of the samples increases with the increase in the diffusion-annealing temperature up to 850?°C. As for the XRD results, all the samples contain the MgB₂ phase only and exhibit the polycrystalline superconducting phase with more intensity of diffraction lines, leading to the increasement in the lattice parameter a and c. Additionally, the diffusion coefficient is observed to increase from 6.81?×?10^?8 to 4.69?×?10^?7?cm²?s^?1 as the diffusion-annealing temperature increases, confirming that the Cu diffusion at lower temperatures is much less significant. Temperature dependence of the Cu diffusion coefficient is described with the aid of the Arrhenius relation D?=?3.75?×?10^?3 exp (?1.15?±?0.10?eV/k _B T) and the corresponding activation energy of copper in MgB₂ system is found to be about 1.15?eV. The possible reasons for the observed improvement in microstructural and superconducting properties of the samples due to Cu diffusion are also discussed.     

Chromium diffusion in GaAs in an open system

We have studied chromium diffusion from a surface layer produced by thermal evaporation into n-type GaAs in a flowing inert-reducing atmosphere. The temperature dependences of the Cr diffusivity and solubility in GaAs are well represented by Arrhenius equations with D ₀ = 1.7 × 10^?2 cm²/s and Q _D = 1.43 eV for the diffusivity and C _Cr ⁰ = 8.9 × 10²¹ cm^?3 and Q _Cr = 1.22 eV for the solubility.     

The effect of interdiffusion on moiré patterns of thin bimetallic films

Observations are described of a diffusion-induced change in the spacing of moiré fringes from thin bimetallic films at low temperatures where the diffusion coefficients are small (<10^-15 cm² s^-1). Experiments were carried out with specimens consisting of a layer of approximately 400 Å Cu vapour deposited onto an electropolished Ni substrate approximately 1000 Å thick. After annealing in the electron microscope at different temperatures an increase in the average spacing M of the moiré fringes was observed. It was found that $\text{1?}\text{M}{}_0\text{M}$ varies linearly with t^{$\text{1}\text{2}$}, where M₀ is the original moiré spacing and t is the annealing time at a given temperature. According to a highly simplified model of electron diffraction the diffusion coefficient can be obtained from the slope of the $\text{1?}\text{M}{}_0\text{M}$versus t^{$\text{1}\text{2}$} plot. From experiments at 450°C, 500°C and 550°C the frequency factor D₀ and the activation energy Q for diffusion were established: D₀ = 0.2 cm² s^-1, Q = 54.6 kcal mol^-1. These values are in good agreement with published data for volume diffusion in the Cu-Ni system at higher temperatures.     

Applications of grain boundary diffusion studies to soldering and thermocompression bonding

This paper describes the application of grain boundary diffusion and oxidation to the technologically important topics of solderability and thermocompression bondability. Copper leads plated with 0.73 μm of gold were studied. Arrhenius plots were constructed and extrapolated to expected storage conditions. A storage life of greater than 2 a at 50°C is predicted for both properties. The time to loss of solderability is given by t_s = 1.6 x 10^-7 exp(0.8 eV/kT) h and the time to loss of bondability by t_B = 4 x 10^-10 exp(1.0 eV/kT) h. The effective activation energies 0.8 and 1.0 eV compare with 0.91 eV for the grain boundary diffusion of copper through gold. Loss of solderability and loss of bondability were modeled as a two-step series event. First the copper diffuses to the gold surface via its grain boundaries. The copper then oxidizes. Auger analysis indicates that the surface oxide is Cu₂O.     

Preface

The diffusion of platinum and gold in nickel at relatively low temperatures (250–725 °C) was measured by Rutherford backscattering spectrometry (RBS). The diffusion profile of the noble metal in nickel was calculated from RBS spectra. This method takes fully into account the dependence of the energy losses of the backscattered particle along the inward and outward paths on the changing energy of the particle and the changing composition of the target. Diffusion coefficients are calculated from the measured diffusion profile. The dependence of the diffusion coefficient on temperature obeys the Arrhenius law. The activation enthalpies are 78.2 kJ mol^-1 and 119.6 kJ mol^-1 for the diffusion of platinum and gold respectively into nickel. The frequency factors are respectively 2.6 × 10^?9cm²s^?1 and 1.4 × 10^?7cm²s^?1. Experimental data suggest that diffusion along the grain boundaries is 2–3 times as fast as bulk diffusion.     

Low temperature interdiffusion in the Au-Pd and Au-Rh thin film couples

Interdiffusion profiles in thin polycrystalline multilayer films of Pd-Au and Ti-Rh-Au at temperatures up to 490°C have been measured by Rutherford backscattering. Room temperature grain boundary diffusion of Au into Rh was observed and analyzed to give D_B = 3.5 × 10^-17 cm² sec^-1. The Whipple analysis is applied to our data for the diffusion of Au in Pd; using the lattice diffusivity of Neukam, an activation energy for grain boundary diffusion of 0.9 eV is found. The diffusion of Pd in Au has also been analyzed using the Whipple model, which gives a grain boundary activation energy of 0.6 eV.     

Diffusion of copper in thin TiN films

The diffusivity of copper in thin TiN layers was determined in specimens prepared by r.f. sputtering a copper (80 nm) layer onto a TiN (200 nm) layer on sapphire and silicon substrates. Specimens were isothermally heat treated at 608, 635 and 700 °C at pressures lower than 2 × 10^?6 Pa; they were compositionally analyzed by Rutherford backscattering spectroscopy and Auger sputter profiling; and they were microstructurally characterized by transmission electron microscopy and electron diffraction. The diffusivity D = 9 × 10⁷cm²s^?1exp(?427 kJmol^?1/RT) from 608 to 700 °C. The mechanisms of copper diffusion were not bulk processes, but they were probably processes involving primarily grain boundaries in the TiN. This very low diffusivity at these temperatures makes TiN/Cu an excellent candidate for a high temperature metallization for silicon solar concentrator cells.     

Diffusive motion of hydrogen in mordenite studied by quasi-elastic neutron scattering

Neutron time-of-flight experiments have been done with hydrogen adsorbed in Na-mordenite at temperatures between 35 and 130 K and densities betweenn = 43 andn = 13 H₂ molecules in the unit cell of the zeolite lattice. The quasi-elastically scattered neutrons give rise to a peak that is not broadened at half-height with respect to the experimental energy resolution of 90 μeV (46 ns). A Lorentzian broadening at the bottom of the quasi-elastic peak has been interpreted in terms of a diffusion model yielding a rotational diffusion constantD_r = 2 · 10^{11rad s−1} and a translational diffusion constantD_t = 2 · 10⁻³cm² s⁻¹ atT = 130K andn = 35 H₂ molecules/unit cell.     

Charge carrier transport in gate-voltage-controlled heteroepitaxial indium arsenide layers

The charge carrier transport coefficients of InAs epilayers, grown on semi-insulating GaAs by chemical vapor phase heteroepitaxy, were investigated by means of gate-voltage-controlled electrical and galvanomagnetic measurements made on metal-oxide-semiconductor structures. The capacitance versus gate voltage dependence of such structures indicates that in the extrinsic temperature region the epilayer surfaces are accumulated for V_g = 0 and flat-band conditions apply for V_g ≈?31 V. It is shown that if the epilayer thickness is corrected for depletion then the epilayer Hall coefficients and conductivities are independent of V_g and have bulk-like values and that the electron mobility has its bulk-like value and is independent of V_g in depletion. In accumulation, the epilayer properties are considered in terms of a composite two-layer model: a bulk-like region of thickness d_b with an average flat-band electron density n_b = 2.5 × 10¹⁵ cm^?3 and mobility μ_b = 7.5 × 10⁴ cm² V^?1 s^?1 and a surface-like region of thickness d_s with a gate-voltage-dependent surface charge density n_sd_s and mobility μ_s where n_sd_s (+30 V) = 2.06 × 10¹² cm^?2 and μ_s(+30 V) = 1.47 × 10⁴ cm² V^?1 s^?1. The monotonic decrease in μ_s with V_g is attributed to scattering of the conduction electrons by localized surface charges which decrease the specularity of the epilayer surfaces.     

Grain growth in copper and alpha-brasses

The wires of 99.999% copper and alpha-brasses containing 12, 20, 30 and 35 at % Zn have been annealed in vacuum for 30 to 240 min at 873, 923, 973 and 1023 K. The grain-growth data obtained are well encompassed by the relationD ², —D ₀ ² , =Kt exp(-H/kT), whereD is the instantaneous mean grain diameter at the time,t, of isothermal anneal andD ₀ refers to the initial mean grain diameter. In alpha-brasses the activation energy for grain-boundary self-diffusion,H, and the pre-exponential factor,K, depends on the zinc concentration,c, asH = (H ₀ — 1.1c) eV andK =K ₀ exp(-10.7c) cm² sec^–1. The values ofH ₀ andK ₀, referred to the base metal are respectively 0.87 eV and 3.0 × 10^–4 cm² sec^–1, which are in good agreement with those (0.85 eV and 3.6 × 10^–4 cm² sec^–1) found for copper.     

Nickel diffusion in samarium sulfide

The diffusion of nickel atoms in samarium monosulfide (SmS) has been studied for the first time. Using the sequential layer removal technique, it was found that the coefficient of diffusion of the ⁶³Ni radioactive isotope at a temperature of T = 1050°C amounts to D ～ 1.8 × 10^?10 cm²/s in SmS single crystals and to 5.3 × 10^?9 and 1.2 × 10^?10 cm²/s for the fast and slow diffusion components, respectively, in polycrystalline SmS. The process of nickel diffusion in thin polycrystalline SmS films was studied using an X-ray diffraction technique. The coefficient of diffusion at T = 400°C in thin-film samples according to these data is ～10^?13 cm²/s.     

Acoustic-wave-stimulated transformations of radiation defects in γ-irradiated n-type silicon crystals

The effect of an ultrasonic treatment (UST) in various regimes (f _UST = 4?30 MHz; W _UST = 0.1?2 W/cm²) on the electrical activity of radiation defects in γ-irradiated (D = 10⁸ and 10⁹ rad) n-type silicon crystals doped with oxygen (～10¹⁸ and <5 × 10¹⁵ cm^?3) has been studied. The energies and concentrations of the electrically active centers have been determined from an analysis of the temperature dependence (100?300 K) of the Hall effect characteristics, assuming a multilevel structure of these centers. The main types of the acoustically active defects, which change the properties of the semiconductor material upon UST, are the A-type centers (E _c ? 0.20 eV) and divacancies (E _c ? 0.26 eV) in Czochralski-grown single crystals and the divacancies and/or P _s?C _i complexes (E _c ? 0.23 eV) in floating-zone-melted samples.     

Growth kinetics of the θ phase in AlCu thin film bilayers

The growth kinetics of the θ (Al₂Cu) phase in AlCu thin film bilayers were studied by MeV He⁺ backscattering and X-ray diffraction. In the temperature range 160–200°C the growth is diffusion limited with an activation energy of 1.02 eV and a pre-exponential factor of 7 × 10^?3cm²s^?1. Nucleation of the γ₂ phase occurs at 200°C with long annealing times. There is no evidence of the presence of other phases in the investigated temperature range.     

X-ray photoelectron spectroscopic study of non-stoichiometric nickel and nickel–copper spinel manganites

The surface of non-stoichiometric nickel and nickel–copper spinel manganites has been investigated by X-ray Photoelectron Spectroscopy (XPS). The oxidation states of the nickel, copper and manganese cations present on the surface of the samples were determined from the analysis of the M 2p_3/2 core levels (M=Ni, Cu, Mn). In particular, both Cu²⁺ and Cu⁺ were evidenced in the structure whereas only bivalent nickel was observed. The partial substitution of manganese by copper led to a chemical shift towards lower binding energy in the Ni 2p_3/2 region, which was explained by the displacement of some Ni²⁺ cations from tetrahedral to octahedral sites of the spinel structure. Finally, the surface atomic ratios Ni/Mn for nickel manganites, Ni/(Mn+Cu) and Cu/(Mn+Ni) for nickel–copper manganites, determined from XPS data, were compared to the ratios corresponding to the bulk composition. This study shows in all cases a nickel enrichment at the surface which is not affected by the copper content of the oxide. On the contrary, the ratio Cu/(Mn+Ni) was found to be lower than the corresponding bulk value.     

An ultrasonic study of the diffusion of Ag in CdSe in the temperature range 20°–400 °C

The diffusion of Ag in CdSe has been studied using an ultrasonic technique. The diffusion coefficient was found to be D = 3 × 10^?4 exp (?0.53 eV/kT) cm² s^?1 Diffusion was found to be Fickian in the region up to a depth of 10^?2 cm and one diffusion mechanism was found to dominate. No significant anisotropy was found in diffusion coefficients measured parallel or perpendicular to the c-axis.     

The ohmic stability and low temperature coefficient of resistance of Cu-Ni/Au-Ni multilayers obtained in ultrahigh vacuum by controlled co-evaporation

For compositions around 43 at.% Ni, thin films of CuNi alloys more than 1200 Å thick deposited in ultrahigh vacuum (UHV) onto a fused silica substrate by controlled co-evaporation from two separate copper and nickel sources show low negative temperature coefficients of resistance (TCRs) (-10^-4 to -10^-6 °C^-1) and a satisfactorily high stability in the temperature range 20–300 °C in UHV. In the atmosphere, however, the ohmic behaviour of the films shows hysteresis and appreciable instability due to oxidation.Thin Au-Ni films (38 at.% Ni) have a higher positive TCR (+2 × 10^-4 °C^-1) but they have the advantage of being less oxidized in atmospheric air up to 150 °C.In order to obtain unoxidizable multilayers with a low TCR we prepared CuNi films 1300 Å thick and stabilized them by annealing. AuNi films 200 Å thick were then deposited onto the CuNi films by controlled co-evaporation.After the annealing process the TCR was about -3 × 10^-6 °C^-1 from 20 to 150 °C. The ohmic stability tested from 20 to 150 °C in nitrogen and then in the atmosphere showed no appreciable zero balance drift or ohmic instability.     

The growth and structure of copper films on (0001) ruthenium surfaces

The structural and electronic properties of clean evaporated copper films on (0001) Ru surfaces were studied by low energy electron diffraction, Auger electron spectroscopy and thermal desorption and work function measurements. Two-dimensional epitaxial growth and three-dimensional epitaxial growth are clearly discernible from “extra” spots in the low energy electron diffraction patterns and from Auger spectroscopy as well as from thermal desorption measurements which show the formation of two states β₁ and β₂. The β₂ state is identified as arising from two-dimensional copper growth and is almost saturated after the deposition of about 5 × 10¹⁴ Cu atoms cm^-2; the β₁ state is caused by the three-dimensional growth of copper. The binding energies of the two states were evaluated from the maximum desorption temperatures; we found that the binding energy of β₂ exceeds that of β₁ (which is identical with the sublimation energy of copper) by about 3–4 kcal mol^-1. The work function increases up to 800 meV; an intermediate maximum indicates a small charge transfer from ruthenium to copper.     

Thermomechanical properties of iron: viscoplasticity of ferrite and of austenite—ferrite mixtures

The available data on secondary creep in creep tests and on maximum stress in hot deformation tests obtained for δ and α ferrite have been reviewed and expressed in the form of the equation ? = K(σ/E)^P_c sinh(Vσ/RT) exp(—Q_c/RT) with p_c = 2·5, V = 0·0013 m³ mol^?1, and K = 2·6 × 10¹⁷ s^?1, E and Q_c being temperature dependent functions. The approximate range of validity is Z = ? exp (Q_c/RT) ≈ 10¹—10¹¹ s^?1. Together with the corresponding equation for austenite the data can be used to predict the viscoplastic behaviour of austenite—ferrite mixtures.

MST/1538