Effect of Reaction Products on the Kinetics of Copper Dipivaloylmethanate Reduction to Copper

The effects of 2,2-dimethyl-1-propanol, acetone, carbon monoxide, and water vapors on the kinetics and mechanism of copper deposition from Cu(dpm)₂ vapor are studied in the range 200–350°C. The results demonstrate that 2,2-dimethyl-1-propanol has no effect of the deposition process, while acetone inhibits Cu deposition and impairs the quality of the resulting film. Carbon monoxide reduces the deposition rate and raises the activation energy of the process to 46 ± 8 kJ/mol. The introduction of water vapor accelerates film growth and reduces the activation energy to 10 ± 7 kJ/mol.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 7, 2005, pp. 792–798.Original Russian Text Copyright © 2005 by Bakovets, Levashova, Dolgovesova, Danilovich.     

Studies on the presence of copper in the galvanized coating on weathering steel and the adherence characteristic of the protective copper complex formed on galvanized weathering steel

Following the hot-dip process for zinc coating on weathering steel, the galvanizing bath was found to have picked up copper. The galvanizing bath was observed to pick up Cu from the weathering steel at an average rate of 1.83×10^–3% s^–1m^–2 at 452±2C. EDAX/SEM studies exhibited a concentration gradient of copper to exist across the thickness of the galvanized coating on weathering steel. XRD studies revealed the formation of a protective copper complex, {Cu[(OH)₂Cu]₃}SO₄, on galvanized coating containing 0.739% Cu, when exposed in marine and industrial atmospheres. The adherence characteristic of the copper complex to the galvanized coating was found to be very satisfactory.     

Mechanism of copper chemical vapor deposition from copper dipivaloylmethanate in hydrogen

The kinetics and mechanism of catalyzed copper deposition via hydrogen reduction of copper(II) dipivaloylmethanate are studied between 200 and 350°C. A multistep mechanism is proposed which involves the formation of a polychelate on the surface of the growing Cu film. Film growth is accompanied by the transfer of the organic ligand of the polychelate to the adsorbed products of Cu(dpm)₂ dissociation. The low activation energy of the process is interpreted in terms of formal kinetics. The introduction of H(dpm) further reduces the activation energy of the process, to 10 ± 5 kJ/mol, owing to the dissociative adsorption of the diketone.Translated from Neorganicheskie Materialy, Vol. 41, No. 1, 2005, pp. 23–27. Original Russian Text Copyright © 2005 by Bakovets, Levashova, Dolgovesova, Maksimovskii.     

Thermodynamic Approach to Optimization of SrTiO3 Chemical Vapor Deposition from Volatile Metalorganic Precursors

Thermodynamic analysis is used to examine the possibility of producing SrTiO₃ films in two precursor systems containing different volatile Ti compounds: TiO(dpm)₂–Sr(dpm)₂–N₂O–Ar (I) and Ti(OPr ⁱ )₂(dpm)₂–Sr(dpm)₂–N₂O–Ar (II). The results demonstrate that, at an initial Ti : Sr atomic ratio of 1 : 1 and a ratio of flow rates /f _Ar = 1, system I contains no region of single-phase SrTiO₃ deposition. Raising the N₂O concentration in the vapor phase makes it possible to deposit SrTiO₃. System II contains a broad temperature range of SrTiO₃ deposition (400–1300 K) over the entire pressure range examined, p _total = 1–100 Pa. These conclusions are verified by depositing films in systems I and II (in particular, in system I in the presence of N₂O activated in an rf discharge). The films grown in system I are found to consist of crystalline SrTiO₃ and an amorphous phase containing residual organics, in particular in the form of CH _x groups with x = 1–3. The films produced in system II consist of nanocrystalline SrTiO₃. In this system, the equilibrium phase SrTiO₃ is formed on the substrate surface via solid-state reaction between TiO₂ and SrO intermediates. The rf activation of N₂O makes it possible to grow crystalline SrTiO₃ at much lower temperatures.     

The growth of thin films of copper chalcogenide films by MOCVD and AACVD using novel single-molecule precursors

Highly oriented crystalline films of copper sulfide and copper selenide have been grown on glass by low-pressure metal-organic chemical vapor deposition (LP-MOCVD) and by aerosol-assisted chemical vapor deposition (AACVD), using the novel air-stable compounds Cu(E₂CNMeⁿHex)₂]* (where E=S,Se). Thin films of non-stoichiometric cubic CuS and CuSe have been deposited in the temperature range 450–500 °C.     

Blue a.c. electroluminescence of Zn1−xMgxS:Cu,Br powder phosphors

Blue a.c. electroluminescent (EL) powder phosphors with brightness of 300 Cd/m² and half life of over 10³h can be prepared from Zn_1–x Mg _x SCu,Br. Replacement of zinc by the more electropositive magnesium increases the percentage ionicity of metal-sulphur bonds leading to the stabilization of the 2H structure. Incorporation of 15 mol% Mg shifts the EL emission peak from 525 to 436 nm. The green side band is completely absent when the copper concentration is 0.3mol%. When copper is 10^–4 mol%, both the green and blue bands are observed in the photoluminescence (PL) emission spectrum. It is proposed that hexagonal Zn_1–x Mg _x S with 0.3 mol% copper contains predominantly (Cu _Zn ^– Cu _i ⁺ ) pairs due to increased electrostatic energy. The recombination involving this isoelectronic hole centre and an isolated donor produces the blue emission. Since a large fraction of the acceptor is present as independent Cu _Zn ^– at low copper concentrations, the green band persists, which originates from distant donor (Br _S ⁺ )-acceptor (Cu _Zn ^– ) pairs.     

Density Determination of Liquid Copper, Nickel, and Their Alloys

A method for the determination of the density of electromagnetically levitated metallic liquids has been developed. This method employs an enlarged beam of parallel laser light to produce a shadow image of the sample. The shadow is recorded by a digital CCD-camera, and the images are analyzed using an edge detection algorithm. The circumference is fitted by Legendre polynomials that can be used for calculations of the volume of the sample. The method has been tested successfully on various alloys of copper-nickel (Ni _x Cu _y ), as well as on the pure elements, Cu and Ni. Densities were measured for each sample at different temperatures below and above the melting point, and a linear behavior was observed. At the melting point the densities for copper and nickel were 7.9 and 7.93gcm^–3, respectively. For T=1270°C liquid copper has a density of 7.75gcm^–3 which strongly increases up to roughly 8.1gcm^–3 if a small amount (10–40 at.%) of nickel is added to the system. For nickel concentrations larger than 50at.% the density remains nearly constant.     

Zinc Doping Profile in AlGaAs/GaAs Heteroepitaxial Structures Grown by Metalorganic Chemical Vapor Deposition

The Zn profile in Al _x Ga_{1 – x} As/GaAs (x = 0.2–0.4) quantum-well heteroepitaxial structures doped during growth by metalorganic chemical vapor deposition is modeled with allowance made for the diffusional broadening of the nominal doping profile. Experimentally determined carrier distributions in the heterostructures are used to refine the diffusion coefficient of Zn at a growth temperature of 770°C. The average value of D _Zn is determined to be 6.0 × 10^–14 cm²/s. The position of the p–n junction in Al _x Ga_{1 – x} As/GaAs heterostructures is assessed as a function of the nominal Zn profile and growth rate. The ways of optimizing the doping profile are outlined.     

Intermetallic compound layer formation between Sn–3.5 mass %Ag BGA solder ball and (Cu, immersion Au/electroless Ni–P/Cu) substrate

The growth kinetics of intermetallic compound layers formed between eutectic Sn–3.5Ag BGA (ball grid array) solder and (Cu, immersion Au/electroless Ni–P/Cu) substrate by solid-state isothermal aging were examined at temperatures between 343 and 443 K for 0–100 days. In the solder joints between the Sn–Ag eutectic solder ball and Cu pads, the intermetallic compound layer was composed of two phases: Cu₆Sn₅ (-phase) adjacent to the solder and Cu₃Sn (-phase) adjacent to the copper. The layer of intermetallic on the immersion Au/electroless Ni–P/Cu substrate was composed of Ni₃Sn₄. As a whole, because the values of the time exponent (n) are approximately 0.5, the layer growth of the intermetallic compound was mainly controlled by a diffusion-controlled mechanism over the temperature range studied. The growth rate of Ni₃Sn₄ intermetallic compound was slower than that of the total Cu–Sn(Cu₆Sn₅+Cn₃Sn). The apparent activation energy for growth of total Cu–Sn(Cu₆Sn₅+Cu₃Sn) and Ni₃Sn₄ intermetallic compound were 64.82 and 72.54 kJ mol^–1, respectively.     

MOCVD of p-Cd x Hg1 – x Te/GaAs Heteroepitaxial Structures

Metalorganic chemical vapor deposition from Cd and Te alkyl compounds and Hg vapor is used to grow p-type Cd _x Hg_{1 – x} Te epitaxial layers on semi-insulating GaAs(111)Bsubstrates by the interdiffused multilayer process (alternating CdTe and HgTe layers) at a substrate temperature of 350°C, followed by postgrowth annealing. Layers are obtained with x = 0.2–0.4, 77-K carrier concentrations in the range (1–5) × 10¹⁶ cm^–3, and 77-K carrier mobilities from 200 to 400 cm²/(V s). The rocking curves of the epilayers have a full width at half maximum in the range 2–4 min of arc.     

Hydriding kinetics of the La1.5Ni0.5Mg17–H system prepared by mechanical alloying

In the study of reaction kinetics between hydrogen and hydriding alloys, what is the most important is to obtain intrinsic kinetic data. The hydriding kinetics of 0.5 g La_1.5Ni_0.5Mg₁₇ sample in the two-phase (-) region was investigated as a function of temperature and pressure in the ranges 553–573 K and 0.256–0.992 MPa H₂ respectively. Mathematical analyses of the time-dependent hydrogen absorption curves indicate agreement with Jander diffusion model, [1 – (1 – )^1/3]² = k(T, P)t, which suggests that the rate-controlling step for hydrogen absorption is three-dimensional diffusion. An apparent activation energy for such diffusion process of 83 ± 1 kJ/mol H₂ has been obtained from the absorption data.     

Effects of High-Temperature Carbonizing and Plasma Processing on the Optical Properties of Porous Silicon

The morphology of porous Si was found to vary over a long period (>100 days) after the electrochemical fabrication. This process was accompanied by adsorption of oxygen, carbon, and, possibly, OH groups. Experimental data were used to evaluate the 273-K diffusion coefficient of the oxidant (4.25 × 10^–24cm²/s) and the total (X= 1.94 × 10^–8 >t m) and actual (x _i= 1.21 × 10^–11 t m) thicknesses of the SiO₂films grown in 92 days on quantum wires of PSi. High-temperature carbonizing of PSi in acetone vapor and plasma processing in oxygen-containing atmosphere produce dramatic changes in the adsorbed layer and luminescent properties owing to the formation of a thin silicon carbide layer. The assumption is made that the marked shift of the high-frequency wing of the absorption band is due to substitution of carbon for one oxygen in each O–Si–O linkage.     

Copper chemical vapour deposition using copper(I) hexafluoroacetylacetonate trimethylvinylsilane

The effects of the deposition temperature on the microstructure and the electrical resistivity of copper films prepared by chemical vapour deposition (CVD) were studied at the deposition temperatures between 160 C and 330 C. Copper films were prepared on titanium nitride (TiN) substrates in a low-pressure warm-wall reactor using copper(I) hexafluoroacetylacetonate trimethylvinylsilane, Cu (hfac)(TMVS), as the precursor. The activation energy for the deposition was found to be 45.4 kJ mol^–1 at the total pressure of 66.7 Pa. The films deposited at below 200 C, where the deposition is limited by surface reaction, were dense and had low resistivity of approximately 2 cm. Moreover, they exhibited excellent step coverage. However, the films deposited at above 200 C, where the mass transport processes become important, were composed of poorly connected globular grains, resulting in considerably high resistivities and rough surfaces. Effects of the deposition temperature on the grain size and the preferred orientation of the films were also investigated.     

Thermodynamic functions of Americium metal

A critical analysis of the data for the specific heat from 15 K to 300 K of two samples of ²⁴¹Am and one sample of ²⁴³Am leads to a set of best values. From these the thermodynamic functions are calculated, giving (C _p)₂₉₈ = 25.5 ± 1 J mol^–1 K^–1 and S ₂₉₈ = 55.4 ± 2 J mol^–1 K^–1. The derived Debye characteristic temperature _D is estimated as 120 ± 20 K and the electronic specific heat coefficient as 1 ± 1 mJ mol^–1 K^–2.     

The Density of UO2–ZrO2 Alloys

The density of a UO₂–ZrO₂ melt (atomic ratio U/Zr = 1.528) is experimentally measured by a pycnometric method in the temperature range of 2973–3373 K. The found temperature dependence of density has the form (T) = (7.0 ± 0.01) – (4.5 ± 0.4) × 10^–4 × (T – 2973 K), g/cm³. The temperature dependence measured enables one to calculate the values of the density of UO₂–ZrO₂ melts depending on the temperature and composition for any atomic ratio U/Zr.     

Optimization of the Parameters of a Porous Coating under Conditions of Pool Boiling of Propane

Results of an investigation of the influence of the parameters of a sintered porous copper coating on heat transfer under conditions of propane boiling are reported. The experiments were carried out within the ranges of specific heat fluxes of q = 10²–6.4·10⁴ W/m² and of saturation vapor pressures of p _s = 0.48–1.08 MPa (T _s = 0–30°C). Optimum parameters of the porous coating were determined within the investigated saturation pressure range. A dimensionless equation is suggested for determination of the heattransfer rate in propane boiling on sintered porous copper coatings.     

Vibronic Superconductivity in the Copper Oxides

Two equilibrium bond lengths coexist in the (001) CuO₂ planes of the copper-oxide superconductors; (Cu–O)_loc > (Cu–O)_itin correspond, respectively, to the antiferromagnetic parent and overdoped phases. In the range 0 < p 0.1 holes/Cu atom of these planes, each hole occupies an itinerant-electron cluster of 5 to 6 Cu atoms in a (CuO)_loc matrix at temperatures T > T*; below T*, a spinodal phase segregation between parent and vibronic phases occurs. Evidence is cited for a condensation in the vibronic phase on lowering the temperature to one hole per 3 Cu atoms in alternate Cu–O–Cu rows. Ordering of the holes at a leads to the formation of itinerant vibronic states, and BCS coupling of the heavy fermions below T _c gives a superconductive condensate of symmetry .     

Dissolution kinetics and diffusivity of silver in glassy layers for hybrid microelectronics

Silver and palladium/silver compositions are widely used in hybrid microelectronics, as electrodes for dielectric layers and multilayers, terminations of thick film resistors and interconnections. Interactions between Ag and the adjacent films are known to affect the microcircuit performances. The present study is aimed at collecting data on the behavior of Ag-based films in contact with glassy layers. Most experiments were performed with a glass with composition 68.2 PbO : 30.5 SiO₂ : 1.3 Al₂O₃ wt %. Two different systems were analyzed. The first system consists of thick films prepared from a paste containing glass and either 3 or 15 wt % silver particles; both fine (spherical grains, 0.5–1 m diameter) and coarse (flakes, 2–5 m, <1 m thick) Ag powders were used for these pastes. The distribution of Ag in the film was studied with X-ray diffraction, scanning electron microscopy and fluorescence analysis. The results show that Ag floats on the glassy layer. Diffraction of X-rays generated by a synchrotron radiation source allowed us to study the kinetics of silver dissolution in the glass; this phenomenon is consistent with the Avrami theory, with an apparent activation energy E _dis=0.69±0.04 eV. The second system analyzed, Ag-based terminations of glass layers fired at various peak temperatures, enabled us to obtain quantitative values for both Ag solid solubility (about 2.5 wt %) and Ag diffusion coefficients D _Ag(T ). Typical values of D _Ag(850 °C) are 30.3±11.9 10^–8 cm²/s; an apparent activation energy of the diffusion process is E _a=0.6±0.1 eV.     

CO/pH2: A Molecular Thermometer

We utilize reversible temperature dependent changes in the IR absorption spectrum of CO molecules isolated in solid parahydrogen (pH₂) to probe bulk temperature changes during rapid vapor deposition. The intensity of a well resolved feature near 2135 cm^–1 increases monotonically with temperature over the 2 to 5 K range. The thermally populated initial state of this transition lies 12 K above the CO/pH₂ ground state. During the deposition of 100 ppm CO/pH₂ samples, we detect temperature gradients 10 K/cm in 0.1 cm-thick samples subjected to heat loads 10 mW/cm². The resulting estimated thermal conductivity (TC) is 3(±2) mW/cm-K, averaged over the 2 to 5 K region. This value is 1000 times lower than the TC of single crystal solid pH₂, and 10 times lower than previously measured for pH₂ solids doped with 100 ppm concentrations of heavy impurities [Manzhelii, Gorodilov, and Krivchikov, Low Temp. Phys. 22, 131 (1996)]. We attribute this abnormally low TC to the known mixed fcc/hcp structure of the rapid vapor deposited solids.     

Microstructural analysis of Au/Pt/Ti contacts to p-type InGaAs

A detailed study on the microstructural changes that occur on annealing of Au/Pt/Ti ohmic contacts to n-type InGaAs has been carried out. The metal layers were deposited sequentially by electron beam evaporation onto InGaAs, doped with Zn to a level of 7 × 10¹⁸ cm^–3, that was epitaxially grown on < 100 > InP substrates. The deposition sequence and metal layer thicknesses were: Ti (25 or 30 nm), Pt (25 or 30 nm) and Au (250 or 300 nm). Samples were annealed at temperatures ranging from 250–425 C in a nitrogen atmosphere. As-deposited contacts were Schottky barriers, while a minimum contact resistance of 2 × 10^–5 cm² was obtained by annealing in the 375–425 C range. Annealing resulted in the inward diffusion of Ti and outward diffusion of In and As, leading to the formation of TiAs, metallic In and Ga-rich InGaAs at the Ti/InGaAs interface. The Pt diffusion barrier was effective in preventing In diffusion into the outer Au layer and minimizing Au diffusion to the semiconductor.