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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...

Thin Cr films were deposited on single crystal α-Al2O3, SrTiO3 and TiO2 (rutile) substrates under ultrahigh vacuum conditions using molecular beam epitaxy (MBE). The growth behavior and thermal stability of the films were investigated with scanning tunneling microscopy (STM), X-ray phototelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and transmission electron microscopy (TEM). Cr grew as 3D clusters on all substrates. For all three Cr/oxide systems a strong temperature dependent interfacial reaction was observed. The results suggested that these reactions depended greatly on thermodynamics and on transport properties in the oxide substrates.

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).

The nucleation of nano-crystallites in as-pyrolysed Si–B–C–N ceramics derived from polymers has been investigated by transmission electron microscopy and electron energy loss spectroscopy. While the material rests in a purely amorphous state until 1300 °C, the formation of α-Si 3 N 4 and β-SiC/α-Si 3 N 4 crystals with sizes ranging from 2 to 5 nm has been detected at 1350 and 1400 °C respectively.

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...

We report here recent electron microscopy observations of defect core structures in diamond thin films prepared by microwave plasma-assisted chemical vapour deposition (CVD) on silicon substrates. The defects have been identified by ultra-high resolution electron microscopy (UHREM) at 0.15 nm resolution. These results clearly reveal the core structure of two particular fault systems arising from the zig-zag shaped interaction between three nanotwin lamellae, with the occurrence of one as yet unreported structural unit of octagonal type. We analyse the UHREM images of these complex defect configurations and we propose plausible 3D models for each of them, on the basis of image-matching with computer simulations. The identification of these defect structures with growth defects provides valuable insights into the mechanisms involved in the CVD production of diamond films.

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.

The microstructure of nanocrystalline BaTiO 3 prepared by microemulsion or sol-gel techniques is compared by means of transmission electron microscopy. After microemulsion a completely crystalline structure with a narrow size distribution is found. A log-normal distribution (statistical variance s = 1.66) observed for sol-gel-prepared crystallites after crystallization (T a = 873K) is compared with other synthesis routes. The microemulsion or sol-gel techniques were found to differ significantly with respect to crystallite growth which is related to the different degrees of agglomeration.

We report on the growth of InP/GalnP islands on GaAs substrates by solidsource molecular beam epitaxy. It is shown by reflection high energy electron diffraction and atomic force microscopy that a rapid change from a twodimensional to a three-dimensional growth mode occurs at about nominally 1.5 monolayers (MLs) InP. Transmission electron microscopy measurements demonstrate the coherent incorporation of InP islands in an GalnP matrix for nominally 2.5 MLs InP. The energy of the InP photoluminescence (PL) shifts to lower energies (100 meV) when the growth interruption time between the island and cap layer growth is increased from 1 to 300 s in case of nominally 3 MLs InP. Simultaneously, an increase of the PL linewidth is observed from 30 to 60 meV. Room temperature photoreflectance measurements on samples with various InP thickness have been performed. Compared to PL measurements, an additional feature in the photoreflectance spectra is observed for samples with more than 7 MLs InP, which is attributed to a transition between excited electron and hole states of the islands.

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.

Uniform and step-shaped Bi nanowire (NW) arrays have been synthesized by electrochemical deposition inside the uniform and step-shaped nanochannels of an anodic aluminium oxide template. These Bi NWs are highly oriented and single crystalline. The current-voltage characteristics of the parallel uniform Bi nanowires show that the contacts between Bi NWs and gold film do not make significant contributions to the I-V characteristics of the step-shaped Bi NWs. The diameters of the thick segment and the thin segment of the step-shaped Bi NWs are about 70 and 40 nm, respectively. Their current-voltage characteristics show conventional metal-semiconductor junction behaviour. The approach can be exploited to produce one-dimensional metal-semiconductor junctions using step-shaped NWs consisting of other semi-metals without any external doping, which may find various applications in nanotechnology.

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.

A major aim in the development of new instruments and novel techniques in rransmission electron microscopy is the improvement of the spatial resolution for structural studies on an atomic scale. Reducing the wavelength of the electrons by increasing the accelerating voltage is the route towards higher resolution followe since a long time. Compared to other techniques available at present, it offers the advantage of a more direct interpretation of the micrographs. By employing accelerating voltages of 1.25 MV or 1.3 MV, the new generation of high-voltage atomic resolution microscopes approaches now a point resolution of 0.1 nm, provided the electrical and mechanical stability of the instruments is high enough, to realise the theoretical performance. The JEM-ARM1250 high-voltage atomic resolution microscope in Stuttgart is the only instrument of this generation installed outside of Japan. In extended resolution tests it has been shown to reach its theoretical point resolution of 0.105 nm at an accelerating voltage of 1.25 MV. Owing to the proper installation conditions and a specially developed high-voltage stabilising system, an information transfer limit of 0.085 nm has been realised. Examples for the application of this instrument to structural studies in various materials demonstrate the performance of the instrument and the benefits of its atomic resolving power.

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.

High-dose irradiation of metals employing dpa values (= displacements per atom) substantially larger than unity may lead to ordered arrangements of defects at temperatures well below the temperature of void formation. We report on a systematic study of defect-ordering phenomena in three fcc metals with markedly different stacking-fault energies, viz. Cu, Ag, and Ni.5N-pure foils of Cu, Ag and Ni were prepared for in-situ electron microscopy in the conventional way. They were irradiated in an AEI-EM7 high-voltage electron microscope (HVEM) with lMeV electrons (e-) at various temperatures (Tirr) between 20 and 500K (Ag and Cu) or between 300 and 600K (Ni). The electron flux density and the total dose, Φ, were typically 7×l023e-m-2s-1 and 1x1027e-m-2, respectively. The development of the defect patter was investigated in the HVEM during the irradiation.In all three metals a temperature regime has been found in which visible defects are regularly arranged along directions after a minimum dose of ∼1026 e-m-2 (Fig.l).

Defect-free silicon layers grown on insulators (SOI) are an essential component for future three-dimensional integration of semiconductor devices. Liquid phase epitaxy (LPE) has proved to be a powerful technique to grow high quality SOI structures for devices and for basic physical research. Electron microscopy is indispensable for the development of the growth technique and reveals many interesting structural properties of these materials. Transmission and scanning electron microscopy can be applied to study growth mechanisms, structural defects, and the morphology of Si and SOI layers grown from metallic solutions of various compositions.The treatment of the Si substrates prior to the epitaxial growth described here is wet chemical etching and plasma etching with NF3 ions. At a sample temperature of 20°C the ion etched surface appeared rough (Fig. 1). Plasma etching at a sample temperature of −125°C, however, yields smooth and clean Si surfaces, and, in addition, high anisotropy (small side etching) and selectivity (low etch rate of SiO2) as shown in Fig. 2.

During in-situ radiation damage experiments aiming on the investigation of vacancy-migration properties interstitial-type dislocation loops are used as probes monitoring the development of the point defect concentrations. The temperature dependence of the loop-growth rate v is analyzed in terms of reaction-rate theory yielding information on the vacancy migration enthalpy. The relation between v and the point-defect production rate P provides a critical test of such a treatment since it is sensitive to the defect reactions which are dominant. If mutual recombination of vacancies and interstitials is the dominant reaction, vαP0.5 holds. If, however, annihilation of the defects at unsaturable sinks determines the concentrations, a linear relationship vαP is expected.Detailed studies in pure bcc-metals yielded vαPx with 0.7≾×≾1.0 showing that besides recombination of vacancies and interstitials annihilation at sinks plays an important role in the concentration development which has properly to be incorporated into the rate equations.

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.

The dependence of the atom displacement rate in Nb, Mo, and Ta on electron energy and irradiation direction has been determined at elevated temperatures by high-voltage electron microscopy. The minimum displacement threshold energy of 24 eV (Nb), 27 eV (Mo), and 14 eV-22 eV (Ta) occurs along the 〈100〉 directions.

Reactive ion etching (RIE) of silicon in a nitrogen trifluoride (NF 3 ) plasma is studied at temperatures between +20 and −140°C. The etch rates decrease with decreasing temperature and follow an Arrhenius-type dependence below −70°C. Cross-sectional transmission electron microscopy gives evidence that the low temperature RIE in NF 3 does not create crystallographic damage in the silicon. Low sample temperatures during RIE promote smoothness of the etched silicon surfaces and anisotropy of the etched profiles.