Search

Since the initial observation of melting-point reduction with size for gold nanoparticles, the relative stability of crystalline phases has also been demonstrated to be size-dependent in a number of technologically important materials, including CdSe and CdS, Al2O3, [4] and various other metal oxides and chalcogenides. As the surface free energy contribution to the total free energy becomes increasingly important as the size of a system is decreased, a crystalline phase with lower surface free energy may be favored with respect to the thermodynamically stable bulk phase when the crystallite size is smaller than a critical value in one or more dimensions. The role of size as an effective thermodynamic parameter is of fundamental importance, but also provides a mechanism for controlling the crystal structure of a material, and therefore its properties. Although precise control of surface chemistry and nanocrystal size in well-defined material systems is prerequisite to understanding and controlling size-induced phenomena, it nevertheless remains challenging to achieve. Although impressive progress has been made in the preparation of ensembles of inorganic nanocrystals with relatively narrow size distributions, the preparation of nanocrystal ensembles of completely uniform size that can be tuned with atomic precision would constitute a significant synthetic advance, in particular for the application of size-dependent structural and physical properties. Using a combination of experimental and computational techniques, we demonstrate herein that chemically designed nanolaminates, consisting of an intergrowth of chemically and structurally distinct components, comprise a class of materials in which this level of control can be achieved for one crystallographic direction. As a consequence of the ability to precisely control size, the crystal structure of the components can be tuned via a size-induced transformation. In contrast to epitaxial superlattices, which experience structural distortions due to strain induced by epitaxial interfaces, the intergrowths reported on in the present work lack an epitaxial relationship between the components. This structural independence of the constituents allows the effect of size on crystal structure to be delineated from strain effects. It was recently discovered that [(MSe)1+d]m[TSe2]n intergrowths can be prepared by the modulated elemental reactants (MER) synthetic route. Here M= {Pb, Sn, Bi, Ce}, T is an early transition metal, and the integers m and n denote the number of consecutive layers of the respective components in the repeating unit of the intergrowth (Figure 1). The value of d reflects the difference in the inplane atomic packing density for the independent component structures in the intergrowth (hereafter we use the designation [MSe]m[TSe2]n for convenience). We chose to explore the SnSe-MoSe2 system for several reasons. Along with the prospect of developing novel nanocrystalline SnSe materials for optoelectronic and photovoltaic applications, bulk crystalline SnSe undergoes a secondorder (continuous) structural phase transition from a-SnSe (GeS structure type) to b-SnSe (ThI structure type) as the temperature is increased. As the parent compounds SnSe and MoSe2 (Figure 1a and b) are both layered semiconductors, significant charge transfer between the components in the intergrowth is not expected. A stable interface exists

Synthesis and structural characterization of a turbostratically disordered polymorph of (PbSe)1.18(TiSe2)2 is reported. The structure of this compound consists of an intergrowth between one distorted rock salt structured PbSe bilayer and two transition metal dichalcogenide structured Se–Ti–Se trilayers. In addition to the lattice mismatch, there is extensive rotational disorder between these constituents. The electrical resistivity of (PbSe)1.18(TiSe2)2 is a factor of 9 lower at room temperature, and the Seebeck coefficient is almost double that reported for the crystalline misfit layered compound analogue.

The turbostratically disordered misfit layer compound (SnSe) 1.15 VSe 2 was synthesized and structurally characterized. Electrical transport measurements suggest this compound undergoes a charge or spin density wave (CDW or SDW) transition, which has not been observed in previous misfit layer compounds. The (SnSe) 1.15 VSe 2 compound, created through the modulated elemental reactants technique, contains highly oriented intergrowths of SnSe bilayers and VSe 2 structured Se–V–Se trilayers with abrupt interfaces between them perpendicular to the c -axis. X-ray diffraction data and transmission electron microscope images show that each constituent has in-plane crystallinity but that there is a random rotational disorder between the constituent layers. Temperature-dependent electrical resistivity data and Hall measurements are consistent with (SnSe) 1.15 VSe 2 being a metal, however an abrupt increase in the resistivity occurs between 30 and 100 K. The carrier concentration decreases by approximately 1 carrier per vanadium atom during this temperature interval.

A modification of the modulated elemental reactants synthetic technique was developed and used to synthesize eleven members of the [(SnSe)1.15]m(TaSe2)n family of compounds, with m and n equal to integer values between 1 and 6. Each of the intergrowth compounds contained highly oriented intergrowths of SnSe bilayers and TaSe2 monolayers with abrupt interfaces perpendicular to the c-axis. The c-lattice parameter increased 0.579(1) nm per SnSe bilayer and 0.649(1) nm per Se–Ta–Se trilayer (TaSe2) as m and n were varied. ab-plane X-ray diffraction patterns and transmission electron microscope images revealed a square in-plane structure of the SnSe constituent, a hexagonal in-plane structure for the TaSe2 constituent, and rotational disorder between the constituent layers. Temperature dependent electrical resistivity, measured on several specimens, revealed metallic behavior, and a simple model is presented to explain the differences in resistivity as a function of m and n.

New methods of electron crystallography, particularly modern methods of electron diffraction have opened new strategies for the structure analysis of nanostructured materials and materials systems. The possibilities and limitations of the combined use of electron crystallography methods will be demonstrated for a semi-automatic orientation determination of MnAs clusters in a GaAs matrix and structural investigations of ferecrystals.

Several new metastable layered intergrowths based on tin monoselenide and molybdenum diselenide, [(SnSe)1+δ]m[MoSe2]n, have been prepared by self-assembly from elemental nanolaminate precursors deposited by physical vapor deposition. The thin-film specimens were characterized by laboratory x-ray reflectivity and diffraction, synchrotron x-ray diffraction, electron probe microanalysis, and scanning transmission electron microscopy techniques, all of which indicate the formation of intergrowths with precise layering and well-defined composition. Analysis of in-plane diffraction originating from the individual components yields a structural misfit of δ = 0.06 and suggests turbostratic misorientation of the individual layers. In contrast to most known [(MX)1+δ]m[TX2]n-type chalcogenide compounds, electrical transport data for the [(SnSe)1+δ]1[MoSe2]1 composition are consistent with semiconducting behavior.

Catalyst-free self-assembled InP nanoneedles are grown on (0 0 1) InP-substrates using gas-source molecular beam epitaxy. The nanoneedles are investigated using SEM and TEM imaging, as well as micro-Raman measurements. Two nanoneedle orientations were observed: vertical (0 0 1)-oriented with the zincblende crystal structure and tilted needles with mixed zincblende and wurtzite structure.

We have studied the MOVPE regrowth of AlGaAs over a grating for GaAs-based laser diodes with an internal wavelength stabilisation. Growth temperature and aluminium concentration in the regrown layers considerably affect the oxygen incorporation. Structural characterisation by transmission electron microscopy of the grating after regrowth shows the formation of quaternary InGaAsP regions due to the diffusion of indium atoms from the top InGaP layer and As–P exchange processes during the heating-up procedure. Additionally, the growth over such gratings with different facets leads to self-organisation of the aluminium content in the regrown AlGaAs layer, resulting in an additional AlGaAs grating, which has to be taken into account for the estimation of the coupling coefficient. With optimized growth conditions complete distributed feedback laser structures have been grown for different emission wavelengths. At 1062 nm a very high single-frequency output power of nearly 400 mW with a slope efficiency of 0.95 W/A for a 4 μm ridge-waveguide was obtained.

Effects of electron irradiation damage in γ -LiAlO2 were analysed using energy loss near edge fine structure (ELNES) of the O K-edge. Simulations of the O K-fine structure by means of a density functional theory (DFT) code show that under the electron beam γ -LiAlO2 undergoes the following transformation: LiAlO2→ LiAl5O8→ Al2O3. O K-edge spectra, which were recorded during this decomposition process, contain an additional peak at 531 eV. This peak can be attributed to a π ∗ -transition, which is observed for molecular oxygen O2. This result suggests that the electron beam-induced LiAlO2 decomposition occurs through the loss of O2.

The mopholological, structural and chemical properties of InxGa1–xN nanopillars directly grown on Si (111) substrates, by molecular beam epitaxy, were investigated employing transmission electron microscopy related techniques. Single crystalline, single phase nanopillars were observed exhibiting a low density of crystal defects, which contribute to good crystal quality. Initial nanostructures merge through subgrain boundaries to form final nanopillars. Energy dispersive X-ray analysis revealed a very low InN mole fraction near the interface with the substrate, owing to high desorption rates from the elevated growth temperature, and gradually higher In incorporation rates near the tips of the nanopillars. This compositional fluctuation is maintained due to poor segregation of indium adatoms along the c-axis of the nanopillars towards the Si interface. A second species of long and narrow nanopillars was found In-free. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

(Zn,Mn)Te nanowires were grown via vapor-liquid-solid mode as test structures for spintronic applications. The structural and chemical properties of the nanowires were inspected by transmission electron microscopy. The nanowires contain much less stacking faults compared to ZnTe nanowires. This high structural perfection can be attributed to a rough liquid-solid interface as found by high-resolution transmission electron microscopy. The composition of the nanowires and, in particular, the Mn distribution is homogeneous. A ZnO cover layer forms after the growth of the nanowires.

Thin Ni/Al and Ni/Ga layers of different atomic ratios were codeposited onto Si(001) at room temperature followed by subsequent annealing. Influence of annealing temperature on morphology and composition of ternary disilicide NiSi2-xAlx and NiSi2-xGax layers was investigated by transmission electron microscopy. Addition of Al or Ga leads to a decrease of the disilicide formation temperature from 700°C down to at least 500°C. Depending on the composition closed, uniformly oriented NiSi2-xAlx and NiSi2-xGax layers were observed after annealing at 900°C, whereas reaction of a pure Ni film with Si leads to the island formation with a mixture of A- and B-type orientations.

Specimens of single crystal superalloy SC16 were creep-strained at 1223 K along the [0 0 1] direction up to rupture using a creep stress of 150 MPa. After creep strain, structural changes were monitored by X-ray diffraction measuring fundamental and superlattice reflections. Measurements were performed in the temperature range between room temperature and 1173 K as a function of temperature and time. The data indicate two relaxation processes which are ascribed to thermally activated rearrangement of damage structures created during creep deformation.

We review our results on the growth of ZnTe- and CdTe-based nanowires (NWs) and on their basic structural and optical properties. The nanowires were produced by using molecular beam epitaxy (MBE) with the use of a mechanism of catalytically-enhanced growth. The growth of ZnTe, CdTe, ZnMgTe and ZnMnTe nanowires was performed from elemental Zn, Cd, Mn, Mg and Te sources on the surfaces of (001)-, (110)- and (111)B-oriented GaAs substrates with Au nanocatalysts. The morphological and structural properties of the nanowires were assessed by using X-ray diractometry, field-emission scanning electron microscopy, and high resolution transmission electron microscopy. Additional studies of the compositions of both the nanowires and the Au-rich nanocatalysts were performed with the use of energy dispersive X-ray spectroscopy. The optical properties of the NWs were assessed by using photoluminescence and Raman-scattering studies performed in both macro and micro modes. The studies revealed that binary and quaternary nanowires with average diameters from 30 to 70 nm and lengths from 1 to 2.6 µm were monocrystalline in their upper parts, their growth axis was h111i, and they grow along the [111] direction of the substrate, independent of the substrate orientation used. A Au-rich (with 20 % Ga) spherical nanocatalyst was always visible at the tip of a nanowire, thus indicating that a vapor-liquid-solid mechanism was responsible for the growth of the ZnTe- and the CdTe-based nanowires. The formation of homogeneous mixed crystal ZnMnTe and ZnMgTe nanowires was demonstrated by measurements of the variation of the lattice constant and by Raman experiments that revealed the expected shift and appearance of new phonon lines and a strong enhancement of the LO-phonon structures for an excitation close to the exciton energy of the NW materials. The photoluminescence from the internal Mn 2+ transition between crystal-field-split energy levels ( 4 T1 ! 6 A1) was observed in the ZnMnTe nanowires.

Freestanding c-plane GaN layers were grown by hydride vapor phase epitaxy on γ-LiAlO2(100) substrates. The layers appear transparent and colorless. However, they contain a large number of dodecagonal pinholes (V-pits), which are surrounded by brownish GaN pyramids. It is shown that the V-pit formation occurs at the top of N-polar inversion domains, which appear in the Ga-polar GaN matrix. The GaN layers contain threading dislocations, which are partly attracted to the V-pit surface in order to minimize the dislocation energy. The appearance of brown GaN pyramids around the V-shaped pinholes seems to be a direct consequence of impurity incorporation, which might stem from the LiAlO2 substrate. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

ZnTe nanowires were grown via a vapour-liquid-solid pro- cess. Nano-sized droplets of a gold-based eutectic act as catalysts. The comprehensive transmission electron microscopy studies reveal that the nanowires are single crystals with numerous stacking faults and twins. The dimension of the wires is several micrometers in length and a few tens of nanometers in diameter. At the sidewall of the nanowires additional nanocrystals of ZnO embedded in an amorphous layer are identified. The formation process of the nanowires can be understood as a two-step process. The first step is the one-dimensional growth along the wire axis by consuming all the material deposited near the droplet. In a second step, facets are formed due to lateral growth of the nanowire. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

III-nitride semiconductor nanostructures are subject of intense studies with respect to their optoelectronic, structural and chemical properties. Important parameters for the wavelength of the emitted light are the chemical composition and the dimensionality of the nanostructures. Transmission electron microscopy is used to determine these characteristics at a nanometer scale. In this work, the information provided by diffraction contrast images of (In,Ga)N/GaN quantum wells (QWs) is studied. Experimental dark-field images alternatively using the 0001 and the 0002 reflection show a different contrast regime. In order to understand the contrast, one has to calculate the intensity Ig of the individual diffracted beam g. The intensity of the 0002 beam is a function of the sum of the atomic scattering amplitudes of the group III and the group V element. Consequently, the 0002 reflection is strain sensitive. According to the kinematical theory the 0001 reflection is forbidden. However, it is excited in the experiment. Therefore, dynamical effects have to be taken into account. The corresponding intensity is calculated by the Howie-Whelan equations. It turns out that the intensity of the 0001 beam strongly depends on the In content of (In,Ga)N. A good agreement of intensity profiles of 0001 dark-field images compared to the theory is found. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The study reports on the structure of thin ternary NiGaxSi2–x silicide layers grown on Si(001) by Ni/Ga codeposition at room temperature followed by subsequent annealing. The influence of both the Ga content and the annealing temperature on the phase formation and orientation of the layers was investigated for the first time. Addition of Ga leads to a decrease of the disilicide formation temperature down to less than 500 °C. Island formation is observed for the Ga content of 0.17 after annealing above 900 °C. The NiSi2-xGax islands grow with a NiSi2–xGax(110) ‖ Si(001) texture. In contrast, closed epitaxial NiSi2–xGax layers of A-type are obtained for the Ga content of 0.28 after annealing at 900 °C. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The strain distribution and defects in a graded AlN/GaN heterostructure comprising AlN layers from 3 nm up to 100 nm grown by plasma-assisted MBE were studied using transmission electron microscopy techniques. Gradual strain relaxation was observed as well as strain partitioning between the GaN spacers and the thicker AlN layers. Elastic strain is retained even in the thicker layers of the heterostructure. Extensive introduction of threading and misfit dislocations is observed at and above the 7 nm AlN layer. The threading dislocations adopt inclined zig-zag line directions thus contributing to the relief of alternating compressive-tensile elastic strain across the the layers of the heterostructure. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The paper reports on the influence of the growth temperature on the structural and chemical properties of (In,Ga)N quantum wells (QWs) on GaN. Two different samples A and B were fabricated. The QWs of the sample A were grown at a constant temperature of 600 °C. For the QWs of the sample B the temperature was 530 °C, while for the GaN barrier it was raised to 600 °C. The chemical and structural properties were studied by electron diffraction contrast imaging using the 0001 and 0002 reflection, respectively. Sample A exhibits homogeneous (In,Ga)N QWs. For sample B some undulated strain contrast of the QWs is visible hinting to the formation of quantum dots (QDs). The self-organisation of (In,Ga)N QDs in sample B is also evidenced by composition sensitive STEM-HAADF imaging, where the individual (In,Ga)N layers exhibit inhomogeneous intensity as well as varied thick- 0 ness. Moreover, energy dispersive X-ray spectroscopy yielded enrichment of indium at QD sites.

High surface area (HS) metal fluoride supported palladium catalysts (Pd0/MFx) (MFx = AlF3, MgF2, CaF2 and KMgF3) together with the respective Pd-free HS-MFx catalysts have been prepared via a novel sol–gel synthesis. In a first step, the reaction of anhydrous hydrogen fluoride (aHF) with the respective solutions of the metal alkoxides containing up to 10% Pd(acac)2 yielded the catalyst precursors as HS-gels. In a second step, gas phase fluorination followed by H2-treatment was employed to obtain the final Pd0/MFx catalysts. X-ray diffraction (XRD) indicated the formation of mainly amorphous AlF3 and Pd0/AlF3, whereas bulk MgF2, CaF2 and KMgF3 and the respective Pd-loaded phases were partially crystalline. The XRD patterns of Pd0/MFx revealed besides the occurrence of broad MFx-reflections only very weak reflections for Pd0 supporting a uniform dispersion of Pd nanoparticles inside the highly distorted MFx structures as it was independently reconfirmed by TEM-investigations. FTIR photo-acoustic spectroscopy with pyridine chemisorption (FTIR-PAS) and dismutation activities showed that AlF3 and MgF2 bulk as well as the supported Pd samples possess strong to moderate Lewis acidities. CaF2 and KMgF3 bulk as well as the respective Pd samples were found to be neutral. BET specific surface areas of MFx and Pd0/MFx are very high, up to ten times higher than known from literature. TEM showed homogeneously dispersed Pd nanoparticles on MFx matrices with a mean particle size of ∼5 to 8 nm. Catalytic activities of the samples were tested for the conversion of CHClF2 into valuable compounds by gas phase dismutation, hydrodehalogenation and pyrolysis, in presence as well as absence of hydrogen. Based on the obtained results and D/H-isotope exchange measurements, a carbene mechanism involving competitive dismutation coupled with consecutive reactions is proposed for the hydrodehalogenation process.

Two-inch-diameter γ-LiAlO 2 single crystals were grown from the melt by Czochralski method. The crystals were examined by optical methods, high-resolution X-ray diffraction and transmission electron microscopy (TEM). Inductively coupled plasma optical emission spectrometry (ICP-OES) was used to determine the Li/Al ratio in the residual melts. The Li-evaporation from both melt and grown crystal is the main problem in the γ-LiAlO 2 growth and has to be controlled by acting on the vertical temperature gradient. Shallow gradients increase the Li-evaporation from the crystal surface resulting in boules with a milky rim. On the other hand, steep gradients may induce cracks in the boule and enhance the Li 2 O escape from melt with consequent variation of the composition. ICP-OES investigations reveal that melt compositions can vary in the range from 46.5 to 50 mol% Li 2 O to obtain transparent LiAlO 2 crystals. Beyond this value, the formation of inclusions inside the crystals is probable. We have established an optimized growth assembly, which allows remaining the melt composition stoichiometric. The as-grown crystals exhibit defects like subgrains, twins and a core of voids and fine-grained inclusions. The latter could be characterized by TEM as submicron LiAl 5 O 8 crystallites.

Pulsed UV laser drilling can be applied to fabricate vertical electrical interconnects (vias) for AlGaN/GaN high electron mobility transistor devices on single-crystalline silicon carbide (SiC) substrate. Through-wafer micro holes with a diameter of 50–100 μm were formed in 400 μm thick bulk 4H–SiC by a frequency-tripled solid-state laser (355 nm) with a pulse width of ≤30 ns and a focal spot size of ∼15 μm. The impact of laser machining on the material system in the vicinity of micro holes was investigated by means of micro-Raman spectroscopy and transmission electron microscopy. After removing the loosely deposited debris by etching in buffered hydrofluoric acid, a layer of

In this study, various CuGaS 2 layers were grown on GaAs (001) substrates using metalorganic vapour phase epitaxy, for the purpose of studying the effect of sulphur-termination of the substrate on layer quality. The resultant films were investigated using X-ray diffractometry, and transmission electron microscopy, with high-resolution transmission electron microscopy providing additional insights into crystallite growth on the control substrates. This paper will demonstrate that sulphur-termination limits substrate degradation. In the absence of sulphur-termination, atypical three-dimensional MOVPE growth is observed, with epitaxial crystallites varying in size from 10 nm to 200 nm. Substrate degradation inhibits lateral growth at the interface resulting in amorphous regions, cavities, and epitaxial crystallites demonstrating overgrowth into mushroom-like structures.

The profiles of 001 and 002 reflections have been measured at 1173 K as a function of time by means of X-ray diffraction (XRD) on tensile-creep deformed specimens of single crystal superalloy SC16. Decrease in line width (full width at half maximum: FWHM) by about 7 % and increase in peak position by about 3x10-4 degrees was detected after 8.5x104 s. Broadening of the 002 peak profile indicated a more negative value of the lattice misfit after the same time period. The results are discussed in the context of the anisotropic arrangement of dislocations at the γ/γ’ interfaces during creep and their rearrangement during the thermal treatment at 1173 K.

The growth properties of InN quantum dots on GaN (0001) surfaces by molecular beam epitaxy are being investigated. The dependence of the dimensions and density of the dots on the nucleation temperature and their evolution during growth at a constant substrate temperature are described. It is shown that both dimensions and density can be accurately controlled through nucleation temperature and deposition time. In the range from 400 °C to 450 °C, the formation of InN quantum dot structures of small dimensions and high density is feasible. InN dots with less than 3nm height, less than 22 nm diameter and with density higher than 1.7×1011 cm–2 have been obtained. Finally, vertical alignment of dots was observed for a multi-period InN quantum dot structure in GaN matrix, grown at 430 °C. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Specimens of single crystal superalloy SC16 were creep deformed at 1223 K along [0 0 1] up to ±0.5% creep strain using stresses of −150 MPa and +150 MPa, respectively. Line widths and peak positions of superlattice reflections were measured by means of X-ray diffraction parallel and perpendicular to the load axis in the temperature range between 293 K and 1173 K. The line widths were found to decrease with the increase of temperature for both directions on the two specimens after tensile and compressive creep deformation. After both kinds of creep deformation the crystal lattice showed tetragonal distortion which decreased with increasing temperature. The tetragonality after tensile creep deformation was larger than unity while it was smaller than unity after compressive creep deformation. The peak positions and widths restored after cooling back to room temperature. The experimental results can qualitatively be explained by the creation of dislocations during deformation and their anisotropic arrangement at the γ/γ′ interfaces.

The relationship between microstructure and magnetic properties of a (Fe,Co)NbB-based nanocrystalline soft magnetic alloy was investigated by analytical transmission electron microscopy (TEM). The microstructures of (Fe0.5Co0.5)80Nb4B13Ge2Cu1 nanocrystalline alloys annealed at different temperatures were characterized by TEM and electron diffraction. The magnetic structures were analyzed by Lorentz microscopy and off-axis electron holography, including quantitative measurement of domain wall width, induction, and in situ magnetic domain imaging. The results indicate that the magnetic domain structure and particularly the dynamical magnetization behavior of the alloys strongly depend on the microstructure of the nanocrystalline alloys. Smaller grain size and random orientation of the fine particles decrease the magneto-crystalline anisotropy and suggests better soft magnetic properties which may be explained by the anisotropy model of Herzer.

High-resolution diffraction using synchrotron x-ray radiation was applied to study γ' precipitates with an L12 superlattice crystal structure in the single crystal superalloy SC16 after creep deformation at 1223 K with a creep strain of ±0.5% for tensile and compressive loads, respectively. The measurements of full width at half maximum (FWHM) of 001 and 100 γ' superlattice reflections were performed at various temperatures from ambient temperature to 1173 K in vacuum. The experimental results revealed that the FWHM of both reflections decrease with increasing temperature. It is well-known that changes in particle size and lattice distortion in materials could lead to a variation of FWHM. The observed behaviour is discussed in the light of both the above-mentioned aspects. The decrease in the peak width is mainly attributed to the temperature dependence of the internal strain state.

The plastic relaxation of SiGe/Si is closely related to the nucleation of misfit dislocations at early stages. We have investigated the very early stages at annealing temperatures ranging from 520°C to 670°C by means of x-ray topography (XRT), atomic force microscopy (AFM) and transmission electron microscopy. At misfit dislocation densities within the range accessible by XRT, i.e. up to about 1000 cm−1, dislocations bundles predominate. This is verified by AFM and is explained by heterogeneous nucleation. The fewer the dislocations that are contained within dislocation bundles the rarer the blocking and cross slip that are observed. It is demonstrated that laser heating increases the number of nucleation centres drastically and is well suited to induce nucleation at selected sites. Furthermore, these nucleation centres provide dislocation bundles containing only a few dislocations. In contrast to this, implantation can produce defects that stop dislocation propagation quite effectively at the comparatively low temperatures used in our experiments.

The potential of combined use of conventional transmission electron microscopy (CTEM), high-resolution TEM imaging (HRTEM) and digital analysis is applied to study (Si,Ge) islands grown by liquid phase epitaxy (LPE) on Si substrates and Ga(Sb,As) quantum dot (QDs) structures grown by metal-organic chemical vapour deposition (MOCVD) on GaAs substrates. The classical diffraction contrast method is applied to visualize the strain field in the surrounding of the QDs. Dark-field imaging allows a qualitative imaging of chemical composition using chemically sensitive reflections. Furthermore, it will be presented how the techniques of quantitative HRTEM (qHRTEM) can be used to determine the local strain and structural peculiarities on atomic scale.

Results obtained in a study of the structural and optical properties of GaAs-based heterostructures with InAs quantum dot layers overgrown with InGaAsN quantum wells are presented. Transmission electron microscopy has been applied to analyze how the thickness of the InGaAsN layer and the content and distribution of nitrogen in this layer affect the size of nanoinclusions and the nature and density of structural defects. It is shown that the size of InAs nanodomains and the magnitude of the lattice mismatch in structures containing nitrogen exceed those in nitrogen-free structures. A correlation between the luminescence wavelength and the size and composition of nanodomains is demonstrated. Furthermore, a correlation between the emission intensity and defect density in the structure is revealed.