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.     

Dislocation wall formation during interdiffusion in thin bimetallic films

Transmission electron microscopy observations are described of the diffusion-induced behaviour of misfit dislocations originally present in the interface of thin bimetallic films. Experiments were carried out with specimens consisting of a layer of approximately 500 Å Cu vapour deposited onto an electropolished Ni substrate approximately 1000 Å thick. Diffusion anneals were performed in situ in the electron microscope at annealing temperatures in the range 450–600°C. The dislocation behaviour in Cu/Ni bicrystals with originally a (100) interface was photographed and video-recorded. A cross-grid of misfit dislocations parallel to 〈110〉 directions was present in the original interface. The Burgers vectors were of type $\text{1}\text{2}$a〈110〉 lying in the interface. During diffusion the misfit dislocations became distributed in the diffusion zone. When $\text{2Dt}$ (where D is the diffusion coefficient and t is the annealing time at a given temperature) exceeded a value of 40–50 Å, the dislocations started to align vertically forming dislocation walls along 〈110〉 directions parallel to the original interface. This resulted in a dislocation cell structure. Lengthwise the dislocation walls grew with shocks. The elastic strain energy of a finite edge dislocation array was estimated. Using this result an energy criterion for the formation of dislocation walls was derived. From this criterion it followed that dislocation wall formation may start to occur when $\text{2Dt}$≈ 45 Å, in good correspondence with the experimental results. Some additional observations of recrystallization phenomena during interdiffusion are reported.     

Generation of grown-in dislocations at NiCu misfit boundaries during three-dimensional nucleation and growth

The origin of a high density of grown-in dislocations in electrolytic nickel films grown epitaxially on bulk single-crystal Cu{001} and their relationship to misfit dislocations were investigated using transmission electron microscopy. Consistent with previous observations, two types of misfit dislocation were found to be present at the NiCu interface; the first type had the mixed Burgers vector of $\text{1}\text{2}\text{〈011〉}$ inclined at 45° to the interface and it probably originated from the deposit top surface and slipped into the interface. The second type, being most effective in accomodating an interfacial lattice misfit (about 2.5%), had the Burgers vector of $\text{1}\text{2}\text{〈110〉}$ which is parallel to the interface. Weak-beam imaging revealed that these two types of dislocation were segmented, actually forming a half-loop, suggesting that they must have been generated locally during three-dimensional nucleation and growth stages. Furthermore, these half-loop segments are replicated into the deposit side approximately perpendicular to the interface and eventually become a part of grown-in dislocations. The second type, the origin of which was not well understood previously, is shown to be generated during coalescence of three-dimensional epitaxial islands. The segmentation of misfit dislocations is found to be responsible for the production of the high density of grown-in dislocations observed in epitaxially grown nickel deposits on copper.     

Heteroepitaxy of chalcogenide compounds II. Monolayer overgrowth process accompanied by lattice transformation

The growth processes of orthorhombic SnSe and rhombohedral GeTe on NaCl-type PbSe, PbTe and SnTe have been studied by still and in situ electron microscopy, with the following results. (i) Growth proceeds in the monolayer overgrowth mode, as for the substrate-deposit combinations of chalcogenides of the same NaCl-type structure reported in Part I. (ii) Lattice recovery of the overgrown films from the initial pseudomorphic structure to the natural structure proceeds by the development of sets of differently spaced misfit dislocations in appropriate directions, with the formation of doubly positioned regions. (iii) The growth of GeTe on PbTe shows a different aspect from that observed for all other cases in Parts I and II, which exhibit straightforward monolayer overgrowth. Initially, bundles of closely spaced short-segmented misfit dislocations are formed into many island-like patches, suggesting that overgrowth proceeds in the nucleation and growth mode. At a later stage, however, generation and extension of the patches takes place, piloted by a singly extending misfit dislocation; this suggests the monolayer overgrowth mode, which is confirmed by Auger electron spectroscopy. (iv) Climb plays a primary role in the formation of misfit dislocations. For SnSe growth on (001) PbSe, PbTe and SnTe, however, misfit dislocations are glissile along the interface and their rearrangement by slip during growth leads to a well-defined configuration of doubly positioned regions in the later stages, with the overgrown lattices in the two regions in coherent twin contact with each other at the boundaries.     

Some observations on the fracture of electrodeposited single-crystal nickel films

Single-crystal films of nickel with (110), (111) and (211) as the film plane were fractured with the applied stress in different directions; the resulting fracture edges were examined using electron microscopy. The type of fracture depended upon the plane and orientation, varying from twin-free cleavage on (110) with the applied stress along the [001] to lattice distortion with no twins and disintegration of the sample on (110) with the applied stress along [1$\text{1}$0]. In the intermediate cases where twins were associated with the fracture, evidence of extrinsic faults was observed but no unambiguous evidence of intrinsic twins.     

Dislocations interfaciales et cohérence dans le système épitaxique fer-or

Iron was deposited in ultrahigh vacuum onto thin single-crystal films of gold oriented with (111) parallel to the surface plane. Study by electron diffraction and electron microscopy has shown that the initial growth of iron occurs by successive monolayers. Three stages in the deposit growth have been found: first the deposited film of iron is strained to match the gold substrate exactly; then interfacial dislocations appear at the gold-iron interface; and finally iron nuclei of b.c.c. structure are formed. The interfacial dislocations are in mixed orientation with their Burgers vectors $\text{1}\text{2}$a 〈110〉 inclined to the gold-iron interface; it is found that they have a poor efficiency for accommodating the misfit between the substrate and the deposit, so that for deposits of average thickness greater than 8 Å the interface is mostly incoherent.     

Reflection high energy electron diffraction and X-ray studies of AlN films grown on Si(111) and Si(001) by organometallic chemical vapour deposition

The crystallinity of AlN films on silicon substrates grown by organometallic chemical vapour deposition was investigated using X-ray diffraction and reflection high energy electron diffraction (RHEED). Single-crystal films of good quality with atomically smooth surfaces can be epitaxially grown on Si(111) substrates. Epitaxial films can also be grown on Si(001) substrates. These films have previously been reported to have a fibre structure. Different RHEED patterns were observed from the films on Si(111) and Si(001). It is established that the films grown on Si(001) consist of two types of crystallite with the following orientations: [11$\text{2}$0]_AlN//[110]_Si and [11$\text{2}$0]_AlN//[1$\text{1}$0]_Si The thickness dependence of the crystallinity was also investigated. The standard deviation σ of the X-ray rocking curve for the films grown on Si(111) is less than that for the films on Si(001) and is independent of the film thickness. The σ values for the films on Si(001) decrease markedly with increasing film thickness. On the basis of these observations, the growth mechanism of AlN epitaxial films on Si(111) and Si(001) is discussed.     

Structural characterization of a Cu/MgO(001) interface using CS-corrected HRTEM

Epitaxial Cu(001) layers were deposited on MgO(001) substrates by magnetron sputtering and the atomic structure of the Cu-MgO interface was characterized by spherical aberration (C_S)-corrected high-resolution transmission electron microscopy (HRTEM). The interface structure and the misfit dislocation network were determined by imaging in both the <100> and <110> directions. The dislocation network was found to lie along the <100> directions with a Burgers vector of ½ a_Cu <100> deduced from HRTEM images and geometrical phase analysis. The dislocations do not fully accommodate the lattice mismatch, yielding residual stress at the interface and an elongation of the Cu lattice along the [001] direction.     

Etude optique,par microscopie electronique des dislocations dans l'oxysulfure de lanthane II. Dislocations dans un plan pyramidal

Observation of the deformation of thin lanthanum oxysulphide specimens inside the transmission electron microscope has revealed the intimate connection between defects and structure. A pyramidal glide system was identified, from slip propagation and slip steps next the 〈101&#x0304;0〉 directions, screw dislocations with a Burgers vector $\text{1}\text{3}$ [1&#x0304;1&#x0304;23] and pyramidal dislocation loops. With this type of crystal, the glide plane {101&#x0304;1}, is parallel to the faces of the OLa₄ tetraedron.     

Microstructure of Epitaxial La_(0.7)Ca_(0.3)MnO_3 Thin Films Deposited by Direct Current Magnetron Sputtering on LaAlO_3 Substrate

Transmission electron microscopy (TEM) and high resolution electron microscopy (HREM) have been used to study the microstructural properties of La0.7Ca0.3MnO3 films on (001) LaAlO3 substrates prepared by direct current magnetron sputtering technique.The as-grown thin films with different thickness are perfectly coherent with the substrates.The film suffers a tetragonal deformation in the area near the interface between the film and the substrate.With increasing thickness, the film is partially relaxed.It was found that La0.7Ca0.3MnO3 films consist of two types of oriented domains described as: (1) (110)f[001]f||(001)s[100]sand (110)f[001]f||(001)s[100]s and (2) (110)f[001]f||(001)s[010]s and (110)f[001]f//(001)s[010]s.Upon annealing, the film is relaxed by the formation of misfit dislocations.Other than misfit dislocations, two types of threading dislocations with Burgers vector of <100> and <110> were also identified.     

Roles of lattice fitting in epitaxy

The epitaxial orientations of three series of materials-alkali halides, chalcogenide compounds and face-centered cubic metals-and of indium (face-centred tetragonal structure) and iron (body-centred cubic structure) on a (001) MgO substrate were examined by in situ electron microscopy and diffraction. The lattice parameter ratio ? = a_d/a_s (d, deposit;s, substrate) ranges from 0.95 for LiF to 1.68 for KI, from 1.41 for PbS to 1.53 for PbTe and from 0.84 for nickel to 1.18 for lead. A systematic dependence of the epitaxial orientation on ? is found: alkali halides and chalcogenide compounds with ? around 1 or 1.5 prefer the (001) parallel orientation with (001)_d(001)_s, [100]_d[100]_s, but those with a value of ? around √2 prefer the (001) orientation with (001)_d(001)_s, [110]_d[100]_s. Metals with ? near 1 also prefer the (001) parallel orientation, but copper and nickel with ? around 0.85 prefer the (1$\text{1}$0) orientation with (1$\text{1}$0)_d(001)_s, [11$\text{2}$]_d[100]_s, and gold, indium and lead with values of ? of 0.97, 1.17 (1.09) and 1.18, respectively, favour the (111) orientation with (111)_d(001)_s, [1$\text{1}$0]_d[1$\text{1}$0]_s. The epitaxial relation is discussed in terms of the fit of the lattice spacings of the deposit and substrate crystals.     

Dislocations in GaAs p-i-n diodes grown by hydride vapour phase epitaxy

Hydride vapour phase epitaxy grown all-epitaxial p-i-n structures were studied by synchrotron X-ray topography. Three types of process induced dislocations were found: short threading dislocations, long straight interfacial dislocations and circular arc dislocations. The majority of the dislocations observed are short straight threading dislocations, the density of which is typically about 5000 cm⁻². The dislocations at the p-i interface are long straight lines parallel to [110]. They are screw dislocations having their Burgers vector parallel to [110], calculated from the contrast analysis of the well resolved dislocation images. One sample also showed a dense misfit dislocation network at the n-side. However, no misfit dislocations were seen in the back-reflection topographs of the n-side of the other samples, which shows that it is possible to grow a misfit-dislocation free n-type GaAs layer onto the substrate side of a hydride vapour phase epitaxy grown GaAs surface after proper substrate removal.     

Orientation dependence of cyclic deformation behavior and dislocation structure in Ti–5at.% Al single crystals

Cyclic deformation behavior and substructure in single crystal Ti–5at.% Al alloy with different orientations fatigued at Δε_t/2=0.4% were examined. The selected loading orientation includes: single prism slip, A; double prism slips [$\text{2}\text{1}\text{̄}\text{1}\text{̄}\text{0}$], B; pyramidal slip, C; and twinning [0001], D. The testing results show that the crystallographic orientation has a strong effect on the cyclic stress response and the plastic deformation mode of Ti–5at.% Al single crystals. The crystals displayed an initial cyclic hardening followed by a striking softening period, and then a saturation stage was reached in specimens A and B. In contrast, an obvious cyclic saturation stage was obtained after first cyclic hardening until to fracture in specimens C and D. Trace analysis on the surface of specimens with an optical microscope shows that the ($\text{1}\text{1}\text{̄}\text{00}$) single prism slip was operated in specimen A during cycling. The ($\text{10}\text{1}\text{̄}\text{0}$) and ($\text{1}\text{1}\text{̄}\text{00}$) double prism slips can be distinguished from the traces on the (0001) surface in specimen B. The ($\text{1}\text{1}\text{̄}\text{01}$) pyramidal slip and the ($\text{1}\text{1}\text{̄}\text{00}$) prism slip were activated simultaneously in specimen C. Twinning is the primary plastic deformation mode in specimen D. The twinning type includes: {$\text{11}\text{2}\text{̄}\text{1}$}, {$\text{10}\text{1}\text{̄}\text{1}$}, {$\text{11}\text{2}\text{̄}\text{2}$} and {$\text{10}\text{1}\text{̄}\text{2}$}. The substructure in the fatigued specimens was examined using TEM. Typical dislocation configuration is well developed saturation bundle structure (SBS) in specimen A, while it is the planar edge dislocations which are tangled on the primary ($\text{10}\text{1}\text{̄}\text{0}$) plane and arranged parallel to the [0001] direction in specimen B. Fully developed loop patches were formed in specimen C. Typical deformed structure was the twin bundles and dislocations among twins in specimen D. The effects of plastic deformation mode on the cyclic stress response and the corresponding dislocation configuration of Ti–5at.% Al single crystals are then discussed.     

The structure of nickel and cobalt films on the (111) surface of n-type silicon

Films of Ni and Co have been grown on the (111) surface of phosphorus doped n-type silicon by evaporation in high vacuum. For both systems polycrystalline films resulted for all substrate temperatures except in the range 250° to approximately 400°C when f.c.c. Ni or Co grew with the orientation Ni/Co (110)6Si (111); Ni/Co [$\text{1}$10]6Si [$\text{2}$11].     

Growth of monocrystalline CdS films on mica surfaces through amorphous interfacial layers of silicon monoxide and carbon by chemical transport reactions

The oriented crystallization of CdS through amorphous interfacial layers of silicon monoxide and carbon by the method of chemical transport reactions has been studied. Cleaved mica (muscovite) single crystals were used as substrates. The interfacial layer thicknesses ranged from 70 to 150 Å. The informative ability of the interfacial layers was checked using the method of decoration with anthraquinone. Epitaxial CdS films 3–15 μm thick were obtained on top of the amorphous interfacial layers, with the (0001) CdS plane parallel to the (001) cleavage plane of mica and the direction [10$\text{1}$0]_CdS coinciding with [110]_mica, which corresponds to the orientation of CdS films prepared directly on the mica surface. The structural perfection of CdS films obtained through interfacial silicon monoxide and carbon layers was practically the same as that of films grown on the mica surface with no interfacial layers. For interfacial layer thicknesses exceeding 120 Å for SiO and 100 Å for carbon, the informative properties of the layers vanished and the CdS films were polycrystalline. The suggestion is made that chemical transport reactions leading to oriented crystallization can proceed without direct contact of the reacting components with the surface of the single-crystal substrates.     

Structure de TlFeBr3: Distorsion du type perovskite hexagonale 2L

TlFeBr₃ crystallizes in the hexagonal system with $\text{a}\text{= 12.444(7)}\text{A}\text{?}$, $\text{c}\text{= 6.23(2)}\text{A}\text{?}$, Z = 6. The crystal structure has been determined from 229 independent reflexions in the space group P6₃cm. The final R index and the weighted R_w are respectively 0.050 and 0.063. This structure is tightly related to the 2L (CsNiCl₃) hexagonal perovskite type. Its $\text{a}$ axis coincides the [110] direction of the 2L phase and its length is accordingly multiplied by √3. Furthermore the face-sharing chains of octahedra are shifted along the $\text{a}$ axis.     

Epitaxial growth and reaction between Ag and SnTe substrates

The vacuum deposition of silver on thin film SnTe substrates at temperatures between 110 K and 620 K was studied by transmission electron microscopy and diffraction. It was found that at temperatures up to 370 K silver deposits grow in nearly perfect (001)[100]Ag//(001)[110]SnTe orientation. At higher substrate temperatures a topotactic exchange of Sn and Ag atoms between the substrate and deposit takes place leading to two perfectly oriented reaction products: Ag₂Te and Ag₃Sn. Their orientation relations were determined, and possible formation mechanisms are briefly discussed.     

Epitaxy of copper on muscovite mica

The vapour deposition of copper onto air-cleaved mica (001) has been studied by reflection high energy electron diffraction in ultrahigh vacuum. At room temperature, crystallites with random orientation and crystallites with Cu(111)mica (001) and Cu[1$\text{1}$0]mica [100] (orientation I) or Cu[1$\text{1}$0]mica [010] (orientation II) are observed. On annealing, either orientation I or orientation II dominates. Also at room temperature, good epitaxy of copper on Cu(111) occurs. Deposition at 570 K always leads to a single-crystal film in orientation I. During early growth, however, crystallites in both orientations appears to have comparable importance, but those with orientation I grow at the expense of those with orientation II during coalescence.