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The formation process of intermetallic compound under Ni+ion implantation into pure Al was studied at lower temperature below room temperature. Ion implantation was carried out using 250KeV ion accelerator. Cascade damage was introduced Ni+ions implantation at 223K without new phase nucleation. However, when Ni+ions were implanted at room temperature, the grown larger plate-like phases were observed during implantation up to 1x1017 Ni+/cm2. Ni concentration in Al matrix and newly formed phase were 0.3-0.5 and 8.5-13.3at%,respectively. It was identified that the formed phases were close to the ordered orthorhombic structure of Al3Ni type. It was also confirmed from observation with high resolution HVEM that these phases grew with continuous ion implantation. Thus it was clarified that cascades act as preferential nucleation site for intermetallic compound, and the phases nucleated at cascades coalesce in the growth process of each phase during continuous implantation through ion irradiation enhanced diffusion.

Single crystals of SrFeO3−δ iron(IV) oxides (δ⩽0.05) have been investigated by selected area electron diffraction (SAED) and high-resolution transmission electron microscopy (HRTEM). The crystals are characterized by a coherent intergrowth of multiple twinned tetragonal and cubic domains. According to Mossbauer spectroscopy and XRD, the cubic domains are the main component, particularly for SrFeO3.00(2). The domain structure transforms significantly when performing HRTEM at room temperature. In a first and very rapid step of transformation the amount of the tetragonal domains increases dramatically. In a subsequent step the sizes of the tetragonal domains are changed via cubic intermediates. All in-situ transformations can be suppressed at low temperature where the typical SAED patterns of the cubic SrFeO3 are observed. It is concluded that low temperature experiments are useful for an unambiguous characterization of the crystal structure and microstructure of high-valent transition metal oxides.

GaN films were grown on sapphire substrates by laser-induced reactive epitaxy. The domains in the films were determined to be the Ga-polarity by the convergent beam electron diffraction (CBED) technique, while the adjacent matrices had the N-polarity. The domain boundaries were characterized as inversion domain boundaries (IDBs). An atomic structure of the IDB is proposed based on high-resolution transmission electron microscopy (HRTEM) investigations. Control of the polarity of GaN/sapphire films was achieved by suppressing the formation of IDBs with an interlayer of AlGaN and a low-temperature GaN buffer layer.

The atomic structures of dislocations in BaF2/CaF2 (111) multilayers grown on Al2O3 were studied by high-resolution transmission electron microscopy on ( ) and ( ) cross-sections. It was found that dislocations generated in these multilayers have structures significantly different from those observed in bulk materials, and that the dislocation structure depends on the morphology of the multilayer. Most dislocations are misfit dislocations along and have Burgers vectors of a/2 on the (111) interfaces. Interface dislocations with a Burgers vector of a/2⟨ 110 ⟩ on (11 ) planes are also observed in multilayers of medium layer thickness l with wavy interfaces. Occasionally, edge dislocations with Burgers vectors a/2⟨ 110 ⟩ and a/2⟨ 001 ⟩ are observed along [1 0]. Edge dislocations with Burgers vectors a/2[ 10] are found dissociated into two partials with an in-plane Burgers vector component of a/4[ 10], and form low-angle boundaries. The influence of these crystal defects on the chemistry of point defects in t...

The orientation and texture of Cr(110) films on the basal plane of α-Al2O3 was investigated by transmission electron microscopy. The Cr was deposited via molecular beam epitaxy at a substrate temperature of 110 °C resulting in the formation of crystallites with columnar mophology. Two orientation relationships (OR) were observed between Cr(110) and α-Al2O3(0001): Cr[001] // α-Al2O3[ 1 10] and Cr[ 1 11] // α-Al2O3[ 1 10]. Each of these orientation relationships exhibited two variants which were rotated ±5.26° around the substrate normal. The orientation relationships can be rationalized on the basis of geometry, rotational symmetry and lattice mismatches of the Cr/(110)/α-Al2O3(0001) interface. The occurrence of all OR can be related to Nishiyama-Wassermann (NW) and Kurdjumov-Sachs (KS) orientations and are discussed with respect to previous experimental results and geometrical parameters of other bcc metals which were grown on α-Al2O3(0001).

Elucidation of a complex defect configuration arising from the interaction between eight first-order twin boundaries in a diamond thin film prepared by chemical vapour deposition on a silicon substrate is reported. The defect has been identified by ultrahigh-resolution electron microscopy at 0.12nm resolution. It is shown to consist of a nearly perfect fivefold twin centre closely connected to two smali portions of original ∑= 9, {122} and ∑= 27, {255} grain boundaries (GBs). Extensive image simulation has been used to deduce the detailed core structure and to propose a plausible three-dimensional atomic-scale model, which contains no dangling bonds. The observed a bond stretching and bond bending are found to be remarkably consistent with recent ab initio calculations of minimum-energy configurations for related defect structures in diamond and in silicon carbide. Moreover, the core structure of the two particular GBs, which consists of alternating columns of five- and seven-membered rings of ca...

The paper summarizes recent studies of the structure and atomic diffusion properties of gas-phase synthesized nanocrystalline solids. The atomic structure of interfaces in nanocrystalline solids with vacancy-like free volumes and nanovoids of triple junctions is specifically studied by positron lifetime spectroscopy. The recently studied temperature variation of the positron lifetime indicates a strong temperature dependence of the positron trapping rate of these free volumes. From the investigation of the orientation correlationship of pairs of two adjacent crystallites in n-Pd by atomic resolution microscopy it can be concluded that predominantly high-energy interfaces are present in nanocrystalline metals after gasphase synthesis. Tracer substitutional-diffusion and self-diffusion studied in highly dense nanocrystalline metals demonstrate that the atomic diffusion is similar to that in conventional grain boundaries. The 18O diffusion in the interfaces of n-ZrO2 is by 3 to 4 orders of magnitude faster than volume diffusion which gives prospects for an increase of oxygen conductivity in nanocrystalline ion conductors. Nanocrystalline ordered intermetallics as, e.g. n-FeAl and n-NiAl can be prepared by gasphase condensation in a partially disordered state. The ordering in n-FeAl occurs at lower temperatures than in n-NiAl which is correlated to the different vacancy migration enthalpies in the two intermetallic alloys.

An elucidation of the core structure of fivefold twin centres arising from the interaction between less than five first-order twin boundaries in plasma-assisted chemical vapour deposition (CVD) of diamond films is reported. These particular twinning centres have been identified by ultra-high resolution electron microscopy at 0.12 nm resolution, with the help of image calculations. Plausible three-dimensional atomic-scale models are proposed for two specific structural variants, which have been found closely connected to high-order twin boundaries via original heptagonal or octagonal structural units. To our knowledge, this is the first time that such types of fivefold twin centres and associated structural units, which are quite representative of the growth defects observed in CVD diamond, have been reported.

An investigation of complex defect configurations arising from the interaction between stacking faults in diamond thin films prepared by thermal-enhanced chemical vapour deposition (CVD) on silicon substrates is reported. The defects have been determined by ultra-high resolution electron microscopy (UHREM) at 0.12 nm resolution. Extensive image simulation has been used to deduce their detailed core structures and to propose plausible 3D atomic-scale models. Two particularly interesting examples are shown: the first consists of intrinsic and extrinsic stacking faults intersecting to form two opposite stair-rod dislocations, while the second results from the interaction between adjacent extrinsic stacking faults and a parallel twin interface. To our knowledge, this is the first time that such types of extended defect configurations, which are quite representative of the dominant defect structures in CVD diamond, have been reported.

An elucidation of defect core structures in diamond thin films prepared by microwave plasma-assisted chemical vapour deposition (CVD) on silicon substrates is reported. The defects have been identified by ultra-high resolution electron microscopy (UHREM) at 0.15 nm resolution and associated image calculations. Three-dimensional atomic-scale models are proposed for three illustrative examples. The first two result from the interaction between a ∑ = 3 twin and (i) a perfect 60° dislocation and also (ii) a dissociated 0° dislocation. The last one (iii) consists of an original intrinsic stacking fault step. To our knowledge, it is the first time that such a type of defect has been reported. The experimental applicability of UHREM to the study of such complex defect configurations is also confirmed.

Diamond coatings prepared by microwave plasma-assisted chemical vapour deposition (CVD) on silicon substrates have been studied by two complementary transmission electron microscopy techniques, high resolution electron microscopy (HREM) and extended energy loss fine structure spectroscopy (EXELFS). HREM observations allowed a wide range of growth defects, mainly based on coherent twinning on {111} planes, to be identified. But 5-fold twin centres were very rarely found, whereas the images often revealed extended areas exhibiting the perfect diamond structure, both observations indicating a film quality higher than usual for synthetic diamonds. Moreover, the radial distribution functions (RDFs) derived from EXELFS spectra confirmed that the material was quite well-ordered. Typical examples are given, of a 〈110〉 image exhibiting different twin and grain boundaries of types Σ = 3, 9, 19, 27, 33 and 81, as well as one 5-fold twin centre, and of an extended perfect structure area viewed along the 〈111〉 direction. A particularly interesting defect configuration, consisting of three neighbouring dissociated dislocations, is also analysed: one of these, a pure extended-screw dislocation, allowed us to determine the intrinsic stacking-fault energy in diamond, yielding a value of 276±3 mJ m −2 . This value, although lower than the theoretical predictions, agrees very well with mean values previously determined from weak-beam experiments.

A high-voltage electron microscope (HVEM) was used to investigate the nature of intrinsic point defects in α-Zr by direct observation of dislocation climb and cavity growth or shrinkage. The material used was Marz grade Zr that had been pre-irradiated with neutrons at about 740 K in the Doureay Fast Reactor. Dislocation loops of vacancy character that had been produced during the neutron irradiation were studied by further irradiation with electrons in the HVEM. Growth of the loops was observed at temperatures as low as 230 K indicating that, under the conditions of the experiment, some vacancy-type defects were mobile in the temperature regime 230–300 K. The nature of these defects is unknown. One possibility is that these defects are not intrinsic in nature, but may be vacancy-Fe complexes. In addition to the climb of dislocation loops, c-component network dislocations and cavities were also studied. Basal-plane climb of the network dislocations was observed at 573 K, but was not readily apparent at 320 K. This suggests that preferred climb planes (and possibly loop habit planes) are sensitive to temperature. Cavities that were already in the foil after neutron irradiation, or were induced by electron irradiation, grew along the c-axis and shrank along a-directions during electron irradiation. This radiation-induced shape change of the cavities strongly suggests the existence of a diffusional anisotropy difference between interstitials and vacancies in α-Zr.

We describe methods of improving the metalorganic vapour phase epitaxy (MOVPE) growth of heteroepitaxial GaAs on Si. The low temperature growth step at the start is optimized by using the new alternative group III precursor dimethylethyl-amine-gallane (GaH 3 ·N(CH 3 ) 2 C 2 H 5 (DMEAGa)) as a substitute for the conventional group III compound TMGa. Further improvements in surface morphology and X-ray diffraction linewidth are obtained by applying the modulated atomic layer epitaxy (ALE) for this growth step. Thermal cycle annealing which is much more effective in dislocation reduction than constant temperature annealing has been optimized with respect to the high as well as the low temperature steps. We present a model of low temperature behaviour of dislocations to explain the role of cooling the samples during thermal cycle annealing. An additional improvement of layer quality is achieved by introducing a thin (AlGa)As-layer after the low-temperature-GaAs-layer leading to a confinement of dislocations after performing thermal cycle annealing as established by TEM-investigations.

Gallium nitride (GaN) thin films were grown by laser induced molecular beam epitaxy (LIMBE). Their microstructures were studied by transmission electron microscopy (TEM). Threading dislocations with Burgers vectors of 1/3 , 1/3 and [0001] were observed as common linear defects with predominantly the first type. Additionally, nano-structured planar defects as called domain boundaries were found. Convergent beam electron diffraction (CBED) technique coupled with chemical and cathodoluminescence measurements was employed to characterize the nano-structured domains, indicating that a domain is of Ga-polarity with respect to the adjacent matrix which is of N-polarity. It was found that experimental parameters such as N/Ga ratio were closely associated with the development of domains as well as the surface morphology. High-resolution transmission electron microscopy (HRTEM) results indicate that IDBs have Ga-N bonds between domains and the adjacent matrix without displacements along the c-axis in the basal planes. Upon the determination of the polar property of a thin GaN film and the optimization of experimental conditions, the nano-structured GaN films can be modified and controlled by changing substrate and pre-growing an AlGaN layer and a GaN buffer layer.

The solid solution series is reported to exist from x = 0 up to x = 0.69 (e.g. [1] and references therein) at ordinary pressures. A phase boundary between structures adopting space group Pnma and I2mb was found close to x = 0.28 [2]. Crystals with higher Al-contents can be synthesised using high pressure [3, 4]. HT phase transitions are known for the iron end-member and the structures crystallising in Pnma [2]. The HT phases were considered to conform to I2mb or Imma space group symmetry. Recent single crystal diffraction studies have found that Ca2Fe2O5 transforms to a modulated structure in the range of 960–980K. This incommensurate phase can be described in superspace group Imma(00γ)s00 [5]. The modulated structure exhibits an aperiodic sequence of tetrahedral (FeO4) chains. The temperature range of the transition is characterised by phase-coexistence, which can be observed by in situ HT single crystal X-ray diffraction experiments Diffraction data collected in this region can be used to perform a two-phase refinement using Jana2006 [6]. Furthermore, domains of the two phases were observed by HT high-resolution transmission electron microscopy (TEM) and dark field TEM. The aluminium end-member Ca2Al2O5 shows an isotypic incommensurate structure above 1075(10)K.

The interface structures of YBa 2 Cu 3 O 7-δ (YBCO) thin films, as prepared by pulsed laser deposition, on substrates of different materials have been investigated by transmission electron microscopy (TEM). It is found that the interfaces on SrTiO 3 substrate are in general sharper than those on LaAlO 3 , where extended defects such as misoriented grains and continuous layers of misoriented material occur. When the substrate temperature is lower during the deposition process, the film can have different orientation. Films with c-axis oriented in the interfacial plane can also grow epitaxially with a sharp interface.

We present a study of changes in the layer morphology of symmetrically strained (GaIn)As/Ga(PAs) superlattices as a function of strain and off-orientation of substrates. The samples were deposited by metal-organic vapour-phase epitaxy (MOVPE). For samples grown on exactly oriented (100) GaAs substrates sharp 2-dimensional interfaces are observed up to a lattice mismatch (Δd/d)⊥ = 2.4 · 10-2. The use of off-oriented (100) substrates leads to a strain induced surface roughening (3-dimensional growth mode) and the formation of laterally ordered thickness modulations during further growth. The surface steps due to the substrate off-orientation are regarded as a cause for this effect. We discuss the structural properties of the samples investigated by transmission electron microscopy (TEM) and high-resolution X-ray diffraction (XRD) as a function of the strain in the individual layers for samples grown on (100) GaAs substrates exactly oriented, 2° off towards [110] and 1.7° off towards [011], respectively.