Strain Mismatch Induced Tilted Heteroepitaxial (000l) Hexagonal ZnO Films on (001) Cubic Substrates

A novel strain mismatch induced tilted epitaxy method has been demonstrated for producing high quality (000l) hexagonal films on (001) cubic substrates. Highly oriented hexagonal (000l) ZnO films are grown on cubic (001) MgO substrates using Sm_0.28Zr_0.72O_{2? δ} (SZO) as a template. The large lattice mismatch of >13% between the obvious crystallographic matching directions of the template and substrate means that cube‐on‐cube epitaxy is energetically unfavorable, leading to growth instead of two high index, low energy compact planes, close to the {111} orientation. These planes give three different in‐plane orientations resulting from coincidence site lattice matching (12 in‐plane orientations in total) and provide a pseudo‐hexagonal symmetry surface for the ZnO to grow on. The texture of the ensuing (000l) ZnO layer is markedly improved over the template. The work opens up both a new avenue for growing technologically important hexagonal structures on a range of readily available, (001) cubic substrates, as well as showing that there are wide possibilities for heteroepitaxial growth of a range of dissimilar materials.     

Microstructure of SiC Whiskers with Different Cross-sections Perpendicular to the Whiskers Axis

Microstructure of β-SiC whiskers with differ-ent cross-sections perpendicular to their growingdirection was studied in detail by transmission elec-tron microscopy (TEM).It was indicated that therewere three types of cross-sections:round,hexagonal and trigonal.The whiskers with roundand hexagonal cross-sections had a high density ofplanar faults lying on the (111) close packed planesperpendicular to the whisker axis.There existed afew stacking faults on the other {111} planes insome hexagonal whiskers.The whiskers withbicrystals were also found in hexagonal whiskers.The microstructure of trigonal SiC whiskers wasbasically perfect but there were a few intrinsic stack-ing faults on the (11) planes (mostly) and (111)planes.The characters of electron diffraction pat-terns of β-SiC whiskers with different cross-sec-tions were reasonably analyzed using a reciprocalspace model with continuous diffraction streaksalong the [111] reciprocal direction.     

高能微波辐照条件下SiC晶粒的生长过程分析

利用高能真空微波辐照, 仅以SiO₂和人造石墨粉为原料, 便捷快速地合成得到结晶良好的β-SiC晶粒。在利用各种表征手段综合分析SiC晶粒微观结构的基础上, 确认高能微波辐照条件下, β-SiC晶粒的生长过程符合“光滑界面的二维形核生长”机制。借助于电子背散射衍射技术(EBSD)进行的原位解析发现, 生长最快的{211}面在晶粒长大过程中逐渐被超覆, 通过形成{421}过渡晶面而最终演变为{220}晶面, 并成为晶粒的侧面; 而生长最慢的{111}面则成为最后保留下来的六角形规则晶面。EBSD的解析结果为SiC晶粒生长过程中晶面演变提供了直接的实验证据。     

甲烷浓度对CVD金刚石薄膜晶体学生长过程的影响

采用X射线衍射技术、电子背散射衍射技术和扫描电镜分别观察了不同甲烷浓度条件下沉积的CVD自支撑金刚石薄膜的宏观织构、微区晶界分布和表面形貌.研究了金刚石晶体{100}面和{111}面生长的晶体学过程.研究表明,{100}面通过吸附活性基团CH^2- 2,而{111}面通过交替吸附活性基团CH^-3和CH^-3后脱氢堆积碳原子.低甲烷浓度时,{111}面表面能低于{100}面,使{111}面生长略快于{100}面.甲烷浓度升高,动力学作用增强使{100}面生长明显快于{111}面,使金刚石薄膜产生{100}纤维织构;同时显露的{100}面平行于薄膜表面,竞争生长使位于晶体侧面的{111}面由于相互覆盖而减小,形成了不同于单晶体自由生长的薄膜表面形貌组织.     

CRYSTALLOGRAPHIC FATIGUE CRACK GROWTH IN NIMONIC AP1

Recently a controversy has developed over whether crystallographic crack growth near threshold in Ni-base superalloys occurs along {111} slip planes or {100} planes at room temperature. In this work on Nimonic API crack propagation is shown to occur on both {100} and {111} planes. The most common facet plane is {111} and this is the only orientation observed at the lowest stress intensities, but at higher stress intensities occasional {100} facets are also produced. This behaviour is compared with similar results in aluminium alloys.     

Computer simulation study of the atomistic mechanism of deformation and fracture initiation in thin fcc metal films

A molecular dynamics computer simulation was performed using a potential of embedded atom method (EAM) of copper so as to study the atomistic mechanism of plastic deformation in thin metal films. When a thin film of Cu crystal is elongated by more than 8%, small islands of surplus atoms start to nucleate between (111) planes. The formation of new (111) islands occurs by the movement of atoms along the 111 direction from two successive (111) planes. Multiplication of these (111) planes serves as the mechanism of elongation, releasing the accumulated elastic stress. Vacancies and small clusters, thereof, are left behind at the positions from which atoms have migrated and also at the part of newly nucleated (111) planes in which atoms were not filled completely. Stacking fault tetrahedra (sft) are nucleated directly in the deformed region as a result of movement of atoms along 111 on the tetrahedral (111) cap.     

Initial epitaxial growth of (111) Au/(111) Cu and (111) Cu/(111) Au

The room temperature modes of growth of Au/(111) Cu and Cu/(111) Au are described. For the former growth mode initial deposits (2.4 Å) of gold on copper form smooth flat islands delineated by coincidence lattice misfit dislocations. For 6.0 Å of gold deposit, both thick and thin gold areas were observed with almost complete substrate coverage. For a 10 Å deposit, surface coverage was complete. Strain measurements and dislocation densities obtained on the (111) Au/(111) Cu films suggest the presence of two separate misfit dislocation networks at the interface. The coincidence lattice networks were large enough for transmission electron microscopy observation but contributed little to total overlayer strain. The (van der Merwe) natural lattice misfit dislocations were too closely spaced for direct observation but their presence was inferred because of the strain measurements. The initial epitaxy of Cu/(111) Au was similar to the Stranski-Krastanov model: the initial monolayer of copper (also delineated by coincidence misfit dislocations) grew smoothly on the gold; additional copper formed essentially stress-free “nuclei” on top of the initial copper layer.     

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.     

Interdiffusion phenomena in Au/Cu and Cu/Au bilayers

The microstructures of epitaxial deposits of (111) Cu/(111) Au and (111) Au/(111) Cu at various stages of interdiffusion are described. The most prominent microstructural features of Au/Cu films (where gold deposition occurred at temperatures less than 400 °C) were (Matthews) coincidence lattice misfit dislocations lying along < 1$\text{1}$0 > directions in the film plane with $\text{|b| =}\text{a}\text{2}\text{< 110 >}$ directed out of the film plane. Their spacings, transmission electron microscopy (TEM) hot stage behavior and generation mechanisms are discussed. For more severe diffusion anneals, the coincidence dislocation density decreased and hexagonal networks identified as ( van der Merwe) natural lattice misfit dislocations became resolvable. They are edge type (lying along <11$\text{2}$> directions in the film plane) with $\text{|b| =}\text{a}\text{2}\text{< 1}\text{1}\text{0 >}$. For the case of Cu/(111) Au bilayers, copper deposited at and below 315 °C with a 20 min anneal again showed coincidence misfit networks. Higher temperature deposition of copper (or hot stage annealing) resulted in natural lattice misfit dislocations in the microstructure. The densities of both types of dislocations were determined and their TEM hot stage behavior was investigated. The method by which the two networks contribute to the relief of misfit strain in both bilayers is discussed.     

AFM Study on Interface of HTHP As-grown Diamond Single Crystal and Metallic Film

The study for the interface of as-grown diamond and metallic film surrounding diamond is an attractive way for understanding diamond growth mechanism at high temperature and high pressure (HTHP), because it is that through the interface carbon atom groups from the molten film are transported to growing diamond surface. It is of great interest to perform atomic force microscopy (AFM) experiment; which provides a unique technique different from that of normal optical and electron microscopy studies, to observe the interface morphology. In the present paper,we report first that the morphologies obtained by AFM on the film are similar to those of corresponding diamondsurface, and they are the remaining traces after the carbon groups moving from the film to growing diamond. The fine particles and a terrace structure with homogeneous average step height are respectively found on the diamond(100) and (111) surface. Diamond growth conditions show that its growth rates and the temperature gradients inthe boundary layer of the molten film at HTHP result in the differences of surface morphologies on diamond planes,being rough on (100) plane and even on the (111) plane. The diamond growth on the (100) surface at HPHT could be considered as a process of unification of these diamond fine particles or of carbon atom groups recombination on the growing diamond crystal surface. Successive growth layer steps directly suggest the layer growth mechanism of the diamond (111) plane. The sources of the layer steps might be two-dimensional nuclei and dislocations.     

Epitaxial growth of antimony electrodeposits on oriented single-crystal surfaces of copper

The epitaxial growth of antimony electrodeposits obtained at 25 and 50° C from chloride and citrate baths on copper single-crystal cathodes orientated along (1 0 0), (1 1 0) and (1 1 1) crystallographic planes has been studied by electron diffraction. Current densities ranging from 10 to 1000 A m^–2 and thicknesses between 0.2 and 10m have been investigated. Amorphous electrodeposits were usually obtained from the chloride bath at a temperature of 25° C. The monocrystalline deposits obtained from both baths on (1 0 0) and (1 1 1) copper planes were oriented with their (1 1 0) and ( ) planes and with their (1 0 0) plane, respectively, parallel to the substrate. On the (1 1 0) copper substrate, monocrystalline deposits were only obtained from the citrate bath, their ( ) plane being parallel to the substrate face. For the sake of completeness, some bismuth electrodeposits on the same copper substrate faces were also studied. The results are discussed in terms of work of nucleation, symmetry of the deposit-substrate interface region and mismatch along close packed directions. They are also discussed in connection with the results related to bismuth electrodeposits.     

The role of grain orientation in microstructure evolution of pure aluminum processed by equal channel angular pressing

A new approach describing the role of crystallographic orientation in the microstructural refinement of commercially pure aluminum during the successive passes of equal channel angular pressing (ECAP) is introduced. The study is based on analysis of X-ray diffraction texture data that is used to calculate the geometrical position of crystallographic slip planes with respect to the shearing plane of the ECAP die. The angular deviations of {111} slip planes from the macroscopic deformation plane for different processing routes were calculated and compared. The microstructure evolution was investigated using electron back-scattered diffraction (EBSD). The grain size and grain boundary character distribution obtained for each processing route are related to the angles between {111} planes and the shearing plane. It was shown that the more effective routes in grain refinement have higher angles between {111} slip planes and the shearing plane.     

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     

A microscopic study of preferred orientation and adhesion of solid copper particles on (0001) sapphire substrates

The microscopic phenomena of solid copper particles equilibrating on (0001) sapphire surfaces have been investigated by scanning electron microscopy. Very sharp and clear silhouettes of the particles are developed. At temperatures between 900 and 1080° C, with the oxygen partial pressure lower than 10^–17 atm, the copper particles tend toward their equilibrium shape as the {111} and {110} preferred faces develop eventually into truncated octahedra or tetrakaidecahedra. Recrystallization of the particles originating at the particle-substrate interface by a heteroepitaxial mechanism is discussed. The {111} plane of the copper particles does not grow parallel to the (0001) sapphire surface as previously reported, but rather with about 20° of tilt, suggesting epitaxial growth of the Cu {112} plane on the (0001) sapphire surface. The surface energy of solid copper decreases with the increase of temperature and/or oxygen partial pressure while the work of adhesion between solid copper and (0001) sapphire can be enhanced by increasing the temperature and/or decreasing the oxygen partial pressure.     

X-ray determination of strain and texture in sputtered molybdenum and titanium films on silicon

Molybdenum and titanium films prepared with a rotating r.f. diode system were examined by X-ray diffraction for strain and texture. Both films were deposited onto (111)-oriented silicon crystal substrates. Molybdenum films 1.13 μm thick sputtered with a target voltage of -2.7 kV, a zero substrate bias and an average temperature of 180°C were in compression on cooling to room temperature. Pole density plots for the (200), (211), (220), (222), (301) and (321) planes gave relatively sharp peaks. The (220) plane showed a strong peak parallel to the (111) plane on silicon. In contrast, a 1.25 μm titanium film was found to be in tension after sputtering at -2.7 kV, a substrate bias of -50 V and an average temperature of 180°C. Relatively broad pole density plots were found for the (002) and (110) planes. The (100) and (110) planes gave peaks parallel to (111) Si. Intrinsic strains from embedded argon were determined from χ scan X-ray data.     

Structural phase control in self-catalyzed growth of GaAs nanowires on silicon (111)

Au free GaAs nanowires with zinc blende structure, free of twin planes and with remarkable aspect ratios, have been grown on (111) Si substrates by molecular beam epitaxy. Nanowires with diameters down to 20 nm are obtained using a thin native oxide layer on the Si substrates. We discuss how the structural phase distribution along the wire length is controlled by the effective V/III ratio and temperature at the growth interface and explain how to obtain a pure twin plane free zinc blende structure.     

Unit cell structure of crystal polytypes in InAs and InSb nanowires

The atomic distances in hexagonal polytypes of III-V compound semiconductors differ from the values expected from simply a change of the stacking sequence of (111) lattice planes. While these changes were difficult to quantify so far, we accurately determine the lattice parameters of zinc blende, wurtzite, and 4H polytypes for InAs and InSb nanowires, using X-ray diffraction and transmission electron microscopy. The results are compared to density functional theory calculations. Experiment and theory show that the occurrence of hexagonal bilayers tends to stretch the distances of atomic layers parallel to the c axis and to reduce the in-plane distances compared to those in zinc blende. The change of the lattice parameters scales linearly with the hexagonality of the polytype, defined as the fraction of bilayers with hexagonal character within one unit cell.     

Preparation of copper coated carbon nanotubes by decomposition of Cu(II)acetylacetonate in hydrogen atmosphere

In this paper, copper coated carbon nanotubes (CNTs) was synthesized by decomposition of Cu(II) acetylacetonate (Cu(acac)₂) in hydrogen atmosphere at 300 °C. The thickness of the copper coating was in nanoscale according to scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images, and Raman spectra indicated that certain intermediate bonds were formed between copper and the template CNTs. The crystalline structure of copper and its growth orientation were determined by X-ray diffraction (XRD) and selected area electron diffraction (SAED). The copper coating on CNTs had a face-centered cubic structure and its growth orientation was parallel to planes. The method developed in this paper had the advantages of simplicity in both process control and experiment equipments, so that it might provide a possibility of large-scale production.     

Computer simulation of atomic properties and dynamic behavior of interstitial clusters in Ni*

The atomic structure and dynamic behavior of interstitial clusters, i.e., a bundle of <110> crowdions, have been investigated in a model Ni lattice. An extended dislocation loop was obtained after full relaxation of a loop of hexagonal shape, consisting of four dislocation segments lying on {111} slip planes and two dislocation segments on {100} slip planes. The dislocation segments on {111} slip planes are extended, but the segments on {100} slip planes are not extended. By observing the motion of a dislocation loop under axially symmetrical shear stress, the Peierls stress for the dislocation loop was obtained. Also, a diamond-shaped dislocation loop was constructed in the model lattice, consisting of four dislocation segments on {111} slip planes and no segments on {100} slip planes. The Peierls stress for this diamond-shaped dislocation loop was found to be less than that for the hexagonal-shaped dislocation loop. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effects of Chloride Ion on the Texture of Copper and Cu-ZrB2 Coatings Electrodeposited from Copper Nitrate Solution in Different Plating Modes

For the first time, the texture of copper and Cu-ZrB2 coatings produced from copper nitrate solution was studied. Chloride ion shows different effects on the deposit texture under direct current （DC） and pulse current （PC） conditions. Copper deposits are strongly 〈220〉 textured in DC plating with and without chloride ion. While in PC condition, the predominant texture shifts from 〈220〉 to 〈200〉 as the chloride ion concentration exceeds 20 mg/l. The addition of ZrB2 particles enhances the cathodic polarization of copper deposition, which improves the growth of （111） plane. However, this improvement can be eliminated by further addition of chloride ion.