Heterogeneous nucleation of solidification of cadmium particles embedded in an aluminium matrix

A hypomonotectic alloy of Al-4.5wt%Cd has been manufactured by melt spinning and the resulting microstructure examined by transmission electron microscopy. As-melt spun hypomonotectic Al-4.5wt%Cd consists of a homogeneous distribution of faceted 5 to 120 nm diameter cadmium particles embedded in a matrix of aluminium, formed during the monotectic solidification reaction. The cadmium particles exhibit an orientation relationship with the aluminium matrix of {111}_Al//{0001}_Cd and 110_AlAl//11¯20> _Cd, with four cadmium particle variants depending upon which of the four {111}_Al planes is parallel to {0001}_Cd. The cadmium particles exibit a distorted cuboctahedral shape, bounded by six curved {100}_Al//{20¯23}_Cd facets, six curved {111}_Al/{40¯43}_Cd facets and two flat {111}_Al//{0001}_Cd facets. The as-melt spun cadmium particle shape is metastable and the cadmium particles equilibrate during heat treatment below the cadmium melting point, becoming elongated to increase the surface area and decrease the separation of the {111}_Al//{0001}_Cd facets.The equilibrium cadmium particle shape and, therefore, the anisotropy of solid aluminium-solid cadmium and solid aluminium -liquid cadmium surface energies have been monitored by in situ heating in the transmission electron microscope over the temperature range between room temperature and 420 °C. The anisotropy of solid aluminium-solid cadmium surface energy is constant between room temperature and the cadmium melting point, with the {100}_Al//{20¯23}_Cd surface energy on average 40% greater than the {111}_Al//{0001}_Cd surface energy, and 10% greater than the {111}_Al//{40¯43_Cd surface energy. When the cadmium particles melt at temperatures above 321 °C, the {100}_Al//{20¯23}_Cd facets disappear and the {111}_Al//{40¯43}_Cd and {111}_A1//{0001}_Cd surface energies become equal. The {111}_Al facets do not disappear when the cadmium particles melt, and the anisotropy of solid aluminium-liquid cadmium surface energy decreases gradually with increasing temperature above the cadmium melting point.The kinetics of cadmium solidification have been examined by heating and cooling experiments in a differential scanning calorimeter over a range of heating and cooling rates. Cadmium particle solidification is nucleated catalytically by the surrounding aluminium matrix on the {111}_Al faceted surfaces, with an undercooling of 56 K and a contact angle of 42 °. The nucleation kinetics of cadmium particle solidification are in good agreement with the hemispherical cap model of heterogeneous nucleation.     

Preferred orientation of NiAl2O4 spinel grown on sapphire

The orientation relationships between the spinel nickel aluminate (NiAl₂O₄) and the aluminum oxide single crystal from which it is grown have been investigated. A variety of sapphire surface orientations were used. The nickel source was primarily nickel vapor, but nickel metal was also used. The large grained spinel layer growing in contact with the sapphire is highly textured, and a thinner fine grained layer on its outer surface is only lightly textured. Two principal textures were observed: for sapphire surfaces oriented near the basal plane, the {111} spinel is parallel to the (0001) sapphire; for surfaces oriented away from the basal plane the {111} spinel is parallel to the {1120} sapphire. In both cases the directions 〈110〉 spinel and 〈1010〉 sapphire are aligned. Considerable twinning and several secondary textures have also been seen.     

Copper crystals on the (11\bf{\bar{2}}0) sapphire plane: orientation relationships, triple line ridges and interface shape equilibrium

The orientation relationships (ORs) of copper crystals on a $ (11\bar{2}0) $ sapphire substrate equilibrated at 1253 K are presented. They barely depend on the procedures used in sample preparation, i.e. dewetting of a copper film in the liquid state or in the solid state. The most frequent OR found is Cu(111) || Al₂O₃ $ (11\bar{2}0) $ and Cu $ [1\bar{1}0] $ within few degrees from Al₂O₃[0001]. A secondary, lower frequency OR is also observed: Cu(001) || Al₂O₃ $ (11\bar{2}0) $ with Cu $ [1\bar{1}0] $ within a few degrees from either Al₂O₃ $ [1\bar{1}00] $ or Al₂O₃[0001]. These ORs do not follow the Fecht and Gleiter model which proposes that dense directions of the metal should align with dense directions of the oxide. On annealing, even at a temperature about half of the melting point of sapphire, fast diffusion of sapphire at the copper/sapphire interface is observed: the copper particles tend to achieve their interfacial equilibrium shapes by sinking into the substrate, and sapphire ridges form at the triple line. Finally, it is shown that the Cu(111) || Al₂O₃ $ (11\bar{2}0) $ interface remains flat at the atomic scale, and is therefore part of the copper/sapphire equilibrium interfacial shape.     

Orientation dependence of fracture toughness measured by indentation methods and its relation to surface energy in single crystal silicon

Fracture toughness of silicon crystals has been investigated using indentation methods, and their surface energies have been calculated by molecular dynamics (MD). In order to determine the most preferential fracture plane at room temperature among the crystallographic planes containing the 〈001〉, 〈110〉 and 〈111〉 directions, a conical indenter was forced into (001), (110) and (111) silicon wafers at room temperature. Dominant {110}, {111} and {110} cracks were introduced from the indents on (001), (011) and (111) wafers, respectively. Fracture occurs most easily along {110}, {111} and {110} planes among the crystallographic planes containing the 〈001〉, 〈011〉 and 〈111〉 directions, respectively. A series of surface energies of those planes were calculated by MD to confirm the orientation dependence of fracture toughness. The surface energy of the {110} plane is the minimum of 1.50 Jm⁻² among planes containing the 〈001〉 and 〈111〉 directions, respectively, and that of the {111} plane is the minimum of 1.19 Jm⁻² among the planes containing the 〈011〉 direction. Fracture toughness of those planes was also derived from the calculated surface energies. It was shown that the K _IC value of the {110} crack plane was the minimum among those for the planes containing the 〈001〉 and 〈111〉 directions, respectively, and that K _IC value of the {111} crack plane was the minimum among those for the planes containing the 〈011〉 direction. These results are in good agreement with that obtained conical indentation.     

Defect structure of acceptor-doped calcium titanate at elevated temperatures

The defect structure of acceptor (Al or Cr)-doped polycrystalline calcium titanate was investigated by measuring the oxygen partial pressure dependence (at 10° to 10–18 atm) of the electrical conductivity at 1000 and 1050° C. The observed electrical conductivity data were proportional to for the oxygen pressure range < 10^–10 atm and proportional to for the oxygen pressure range ( 10^–7 atm. The conductivity values were observed to increase with the acceptor concentration in the p-type region with the shift in the conductivity minima towards lower oxygen partial pressure. The absolute value of the electrical conductivity in the acceptor-doped samples were lower in the n-type region compared to the values in the undoped CaTiO₃. Aluminium and chromium were found to be equally effective in acting as acceptor impurities in CaTiO₃. The defect chemistry of CaTiO₃ is dominated by the added acceptor impurities for the entire oxygen partial pressure range used in this investigation.     

Galvanostatic electrodeposition and microstructure of copper (I) oxide film

 Polycrystalline copper (I) oxide films were deposited on stainless steel substrate by galvanostatic electrodeposition method and were characterized by X-ray diffraction and scanning electron microscopy. The effect of bath temperature, bath pH and current density on the compositon, grain size, surface texture and surface morphology of the electrodeposited films were investigated. The films deposited at low bath pH (≤7) consisted of copper (I) oxide and metallic copper; while the films deposited at bath pH between 8 and 12 and bath temperature of 60°C were pure copper (I) oxide. The preferred orientation of the copper (I) oxide films depended on the relative growth rate of {111} and {200} faces and could be controlled by adjusting the bath pH and/or the cathodic current density. (100)-oriented copper (I) oxide films could be deposited at pH=9 and current densities in the range of 0.25–1 mA/cm², while (111)-oriented films could be prepared at pH=12 or at pH=9 using the current densities between 1.5–2.5 mA/cm². Computer simulated crystallite shapes showed that the crystal shape changed from octahedral for (100)-oriented film to trucated pyramids and cubs for (111)-oriented film. And they were approved by scanning electron microscopy. Received: 1 December 1997 / Accepted: 13 December 1997     

Etch pits in flux-grown corundum

Procedures have been developed for chemically polishing and etching {0001}, {10¯11}, {10¯12}, {11¯20}, and {1¯100} planes in crystals of ruby and sapphire grown from a PbF₂ flux. The shape and the orientation of the etch pits were found to be characteristic for each plane and the density of the pits was 10² to 10⁴/cm². Similar pits were produced in flame-fusion material, but the density was 10⁶ to 10⁸/cm². Ruby and sapphire crystals grown by the same process behaved similarly. There is evidence that etch pits reveal dislocations which emerge normally to the basal or to the prismatic planes, since similar patterns of pits were produced after the removal of successive layers of material parallel to these planes, and a correlation was found between the pit patterns on opposite {0001} faces. Inconclusive evidence on this point was obtained for the rhombohedral planes.     

Ni–YSZ(111) solid–solid interfacial energy

Solid-state dewetting of continuous Ni films deposited on the (111) surface of yttrium stabilized zirconia (YSZ) was used to produce equilibrated Ni particles, and the solid–solid interface energy was determined using Winterbottom analysis. The ~150 nm thick Ni films were dewetted (annealed) at 1350 °C in Ar + H₂ (99.9999 %) at an oxygen partial pressure of 10^?20 atm for 6 h. Transmission electron microscopy of equilibrated particles was conducted, and two low-energy low-index orientation relationships were found: $ {\text{Ni[1}}\overline{ 1} 0 ] ( 1 1 1 )\left\| {{\text{YSZ[1}}\overline{ 1} 0 ]} \right. ( 1 1 1 ) $ and $ {\text{Ni[}}\overline{ 1} 1 0 ] ( 1 1 1 )\left\| {{\text{YSZ[1}}\overline{ 1} 0 ]} \right. ( 1 1 1 ) $ , and the interface energies were measured to be 1.8 ± 0.1 and 2.1 ± 0.1 J/m², respectively. A model including grain growth concurrent with dewetting is used to explain the formation of the higher energy orientation relationship.     

Microstructure of electroplated Cu(Ag) alloy thin films

Electroplated Cu(Ag) alloy thin films are potential candidates for future electronic devices in terms of lifetime and reliability compared to copper as the state of the art interconnect material. In the present paper we focus on the microstructure of Cu(Ag) alloy films considering the grain evolution as well as silver incorporation and segregation. We show that Ag alloying addition prevents room temperature recrystallization. Thermally induced grain growth occurs mainly between 180 °C and 330 °C. Silver can be incorporated as solid solution into the Cu matrix by up to 0.8 at.% after annealing and even in higher concentrations in the as-deposited state, which is significantly above the equilibrium solubility limit. Precipitations are formed by the continuous mode and can be mainly found at the film surface but also inside the Cu(Ag) grains as ball-shaped particles. Based on our results a reliability improvement is expected by mechanical strengthening due to alloying effects while maintaining a low electrical resistivity and a {111} fiber texture.     

Creep of (Mg,Fe)O single crystals

The creep behaviour of (Mg, Fe)O single crystals compressed along 1 0 0 has been investigated over the temperature range 1300 to 1500° C, at stresses between 20 and 70 MPa, for oxygen partial pressures between 10^–4 and 10² Pa, and with iron concentrations between 70 and 11 900 p.p.m. Under these conditions, the dependence of the steady-state strain rate on stress, temperature, oxygen partial pressure, and iron concentration can be summarized by the flow law, exp (–445 kJ mol^–1/RT. These results suggest that the steadystate strain rate is controlled by dislocation climb with a jog velocity which is limited by lattice diffusion of oxygen by a vacancy pair mechanism. The activation energy for creep, 445 kJ mol^–1 is larger than that reported for self-diffusion of oxygen, 330 kJ mol^–1, because the formation energy for jogs is relatively large, 115 kJ mol^–1.     

Electrical conductivity in non-stoichiometric titanium dioxide at elevated temperatures

The electrical conductivity of polycrystalline titanium dioxide prepared by a liquid mix technique was measured for the oxygen partial pressure range of 10° to 10^–19 atm and temperature range of 850 to 1050° C. The data were found to be proportional to the –1/6 power of oxygen partial pressure for the oxygen pressure range 10^–19 to 10^–15 atm, and proportional to for the oxygen pressure range >10^–15 atm. The region of linearity where the electrical conductivity varied as the –1/4 power of increased as the temperature was decreased. There was evidence of p-type behaviour for 10^{ - 2}$$ " align="middle" border="0"> atm in the temperature range 950 to 850° C, although the measured data were insufficient to assign a pressure dependence. Electrical conductivity minima in the log against log plot moved to lower as the temperature was decreased in the range 950 to 850° C. The measured oxygen pressure dependence of electrical conductivity in the lowest region supports the oxygen vacancy defect model. The observed data are consistent with the presence of very small amounts of acceptor impurities. A binding energy of 0.67 eV between the acceptor impurity and its compensating oxygen vacancy was also determined.     

Heteroepitaxy of Ir films on silicon with a ceria/yttria stabilized zirconia buffer layer

Heteroepitaxial Ir films on Si(001) with a double ceria/yttria stabilized zirconia heteroepitaxial buffer layer were grown by magnetron sputtering. As-deposited CeO₂ films covered with {111} faceted pyramids resulted in iridium films with the [001] axis normal to the substrate plane. The buffered substrates annealed at 1115 °C have a smooth surface; Ir films on such substrates have the (111) orientation and consist of grains turned at 90° toward each other.     

Au–Sapphire (0001) solid–solid interfacial energy

This work presents an experimental methodology for the measurement of interfacial energy (γ_SP) and work of adhesion (W _ad) of a metal–ceramic interface. A thin Au film was dewetted on the basal surface of sapphire substrates to form submicron-sized particles, which were analyzed using the Winterbottom method to determine the equilibrated particle–substrate solid–solid interfacial energy. Electron microscopy showed that a large portion of the particles contained grain boundaries, while all of the single crystalline particles had three distinct morphologies and orientations with the substrate. Two orientation relationships were determined from transmission electron microscopy, for which the interfacial energy in air at 1000 °C was determined: Au (111)–sapphire (0001): γ_SP = 2.15 ± 0.04 J/m², W _ad = 0.49 ± 0.04 J/m²; Au (100)–sapphire (0001): 2.18 ± 0.06 J/m², W _ad = 0.55 ± 0.07 J/m².     

Microstructure and ionic conductivity of alternating-multilayer structured Gd-doped ceria and zirconia thin films

Multilayer thin film of Gd-doped ceria and zirconia have been grown by sputter-deposition on α-Al₂O₃ (0001) substrates. The films were characterized using X-ray diffraction (XRD), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The Gd-doped ceria and zirconia layers had the fluorite structure and are highly textured such that the (111) plane of the films parallel to the (0001) plane of the α-Al₂O₃. The epitaxial relationship can be written as and , respectively. The absence of Ce³⁺ features in the XPS spectra indicates that the Gd-doped ceria films are completely oxidized. The ionic conductivity of this structure shows great improvement as compared with that of the bulk crystalline material. This research provides insight on designing of material for low temperature electrolyte applications.     

氮气压对自蔓延高温合成AlN后烧的影响

研究了氮气压力对自蔓延高温合成AlN的影响和后烧机理.结果表明,自蔓延高温合成AlN的生长机制为气相-晶体(Vapor-Crystal,VC)机制.气相沉积的台阶平面为AlN的基面({0001)面).为了降低表面能,生长台阶必须以六棱柱形态形核.在后烧阶段,AlN颗粒中心的小台阶被重新"蒸发",并沉积到远离中心的大台阶上,使AlN颗粒棱角分明,形状规则.随着氮气压力的增加,燃烧温度逐渐提高,后烧的时间缩短.     

Site preferences for Nd in YAG films grown by LPE

We have made spin-resonance measurements of the concentration on different, though crystallographically equivalent, sites, of Nd³⁺ dilutely incorporated into thin films of yttrium aluminum garnet (YAG). The films were grown on {001}, {110}, and {111} substrates of pure YAG by liquid phase epitaxy (LPE). Sites which differ only in the orientation of their local axes relative to the growth direction are found to be unequally populated. The site preferences found for {110} films are close to, though larger than, those found previously for {110} facets of bulk crystals grown from the flux. This result supports the view that the growth-induced magnetic anisotropy of LPE films of mixed rare earth iron garnets arises from the same site preference mechanism as the anisotropy found under natural facets of bulk crystals. Very large site preferences, up to 4.5:1, are found in {001} films; but for {111} films they are only slight. Site preferences are not greatly affected by changes in growth temperature (850°C to 1044°C) or in overall concentration (0.1% to 5% atomic). The effective distribution coefficient varies with concentration and substrate orientation.     

On the growth of cuprous oxide films

{lcub;001}rcub; cuprous oxide (Cu₂O) films were epitaxially grown. From the two methods which were used (the oxidation of copper films and the direct evaporation of bulk Cu₂O) only the oxidation of copper yielded good single-crystal films. It was found that the optimum conditions were an oxidation temperature of 450°C with a partial pressure of oxygen of 2×10^-5 Torr and, after oxidation, a further annealing at a pressure of 10^-8 Torr.     

Effects of nitrogen partial pressure on microstructure,morphology and N/Ti ratio of TiN films deposited by reactive magnetron sputtering

Abstract

TiN films were deposited on Si(111) substrates at different nitrogen partial pressures with reactive magnetron sputtering. The crystal structure and preferred growth orientation of the films were determined using X-ray diffraction (XRD) analysis. Their morphology and composition were analysed using field emission scanning electron microscopy (FESEM) and energy dispersive spectroscopy (EDS). It is found that with the increase in nitrogen partial pressure, the growth of TiN films varies from the {111} preferred orientation to the {100} preferred orientation and the deposition rate of TiN films decreases. When the {111} preferred orientation is presented, TiN films reveal a kind of surface morphology of triangular pyramid with right angles; while the {100} orientation is dominant, TiN films characterise another kind of domelike surface morphology. Furthermore, the N/Ti ratio of the TiN films first increases, then decreases and increases again as nitrogen partial pressure enlarges.     

Crystal orientation changes of Ag thin films on the Si(111) substrate due to tribo-assisted recrystallization

Crystal orientation changes of Ag thin films due to the tribo-assisted recrystallization have been studied using grazing incidence X-ray diffraction with synchrotron radiation. After preparation of an Si(111) √3 × √3-Ag surface, a 5-nm-thick Ag film was deposited on the surface at the substrate temperature of 303 K in an ultra-high vacuum chamber. The friction experiments were carried out using a diamond pin-on-plate type tribometer just after the Ag deposition in the same UHV chamber. We found that the coefficient of friction of the Ag films on the Si(111) √3 × √3-Ag surface decreases from 0.07 to 0.03, with increasing reciprocal sliding cycles. In synchronization with the coefficient change, Ag{100} grains are gradually disappearing. As a result, the Ag{111} grains cover the entire surface after 50 sliding cycles. Moreover, we found that the domain size of the Ag{111} grains increases with increasing reciprocal sliding cycles by measuring the rocking curve width. These results directly show that the Ag(111) plane is the sliding plane of friction and the coefficient of friction of Ag films is determined by the fraction of the Ag(111) grains in the Ag films. Moreover, to clarify the reaction between the Ag film and the Si substrate due to the tribo-assisted recrystallization, the substrate strain has been studied by an extremely asymmetric X-ray diffraction technique using synchrotron radiation.     

Influence of sintering atmosphere on the microstructure and water durability of SnO–MgO–P<Subscript>2</Subscript>O<Subscript>5</Subscript> glass

Effects of sintering atmosphere (Ar, air, and O₂) on the sinterability and crystallization at 380–470 °C of 60SnO, 10MgO, 30P₂O₅ (mol%) glass powder, and the water durability of the sintered glass were investigated. Increasing the oxygen partial pressure (P_\textO2 ) (P_{{{\text{O}}_{2} }} ) in the sintering atmosphere enhanced the oxidation tendency of Sn²⁺ to Sn⁴⁺ near the surface region of the glass particles. Therefore, the glass viscosity was increased, resulting in the increase in both the temperature of densification and the temperature at which crystalline phases developed. Phase assemblage and the amounts of crystalline phases were also affected by P_\textO2 . P_{{{\text{O}}_{2} }} . The water durability of the sintered glasses is discussed in terms of the above microstructural parameters.