V. Klemm

Interference phenomena observed by x-ray diffraction in nanocrystalline thin films

An increase of the X-ray diffraction line broadening with increasing diffraction angle was observed experimentally in nanocrystalline thin films. Such a change of the line width is usually related to the microstrain in the sample, which, however, contradicts the assumptions that the microstrain is relatively low in nanocrystalline materials and that the line broadening is caused mainly by small crystallite size. For nanocrystalline thin films, the observed changes in the diffraction line broadening are explained by a partial coherence of adjacent crystallites, which is stronger at low diffraction angles than at high diffraction angles. Furthermore, it is found that the degree of coherence of the adjacent crystallites depends on their size and preferred orientation. Smaller crystallites show better coherence, because the corresponding reciprocal-lattice points are broadened compared with those related to large crystallites. A strong preferred orientation improves further the coherence of the adjacent crystallites. Theoretical results are confirmed by experimental data obtained on nanocrystalline (Ti,Al)N thin films using a combination of glancing-angle X-ray diffraction, high-resolution transmission electron microscopy and X-ray texture analysis.

Disclinations in Plastically Deformed Metallic Materials

Cold-working of metallic materials up to large strains is usually characterised by simultaneous substructure evolution on different length scales and accompanied by the formation of significant lattice rotations. A promising tool for the description of such microstructure development is the concept of partial disclinations. Transmission electron microscopy (TEM) studies illustrate clearly, that defects of this kind are frequently existent in cold-worked metals and have to be accepted as an important defect entity in the substructure evolution at larger strains. Moreover, it is shown that substructure modelling on the base of a coupled dislocation-disclination dynamics leads to satisfying correspondence of calculated substructure characteristics with experimental results obtained by TEM, X-ray diffractometry, and EBSD (electron backscattering diffraction), and to a satisfying prediction of the macroscopic deformation behaviour, i.e., especially the transition from stage III to stage IV of crystal plasticity.

Transmission electron microscopy analysis of disclination structures in plastically deformed metals

The disclination concept can be used to describe rotational substructures developing under large-strain deformation of crystalline metals. The paper presents transmission electron microscopical investigations which allow disclination configurations to be characterized. Copper crystals rolled down to more than 50% thickness reduction at room temperature were investigated and partial disclination dipoles and multipoles were found in nodes of the cell block boundaries.

A microdiffraction method for the characterization of partial disclinations in plastically deformed metals by TEM

The disclination concept can be used to describe rotational substructures developing under large-strain deformation of crystalline metals. The paper presents a TEM microdiffraction method using local misorientation measurements which allows the identification of disclinations. Copper single as well as polycrystals rolled down to 50% and 70% thickness reduction at room temperature were investigated and partial disclinations were found in triple junctions of cell-block boundaries. The power of the partial disclinations lies in the range of 1.5° to 2°, in agreement with theoretical expectations.

Charge trapping of Ge-nanocrystals embedded in TaZrOx dielectric films

Ge-nanocrystals (NCs) were synthesized in amorphous TaZrOx by thermal annealing of co-sputtered Ge-TaZrOx layers. Formation of spherical shaped Ge-NCs with small variation of size, areal density, and depth distribution was confirmed by high-resolution transmission electron microscopy. The charge storage characteristics of the Ge-NCs were investigated by capacitance-voltage and constant-capacity measurements using metal-insulator-semiconductor structures. Samples with Ge-NCs exhibit a maximum memory window of 5 V by sweeping the bias voltage from −7 V to 7 V and back. Below this maximum, the width of the memory window can be controlled by the bias voltage. The fitted slope of the memory window versus bias voltage characteristics is very close to 1 for samples with one layer Ge-NCs. A second layer Ge-NCs does not result in a second flat stair in the memory window characteristics. Constant-capacity measurements indicate charge storage in trapping centers at the interfaces between the Ge-NCs and the surroundi...

Characterization of microstructural defects in melt grown ZnO single crystals

Various nominally undoped, hydrothermally or melt grown (MG) ZnO single crystals have been investigated by standard positron lifetime measurements. Furthermore, optical transmission measurements and structural characterizations have been performed; the content of hydrogen in the bound state was determined by nuclear reaction analysis. A positron lifetime of 165-167 ps, measured for a brownish MG ZnO sample containing (0.30 ± 0.03) at.-% of bound hydrogen, matches perfectly the value found for colorless MG ZnO crystals. The edge shift, observed in the “blue light domain” of the optical absorption for the former sample with respect to the latter samples, is estimated to be 0.70 eV, and found equal to a value reported previously. The possible role of zinc interstitials is considered and discussed. Microstructure analysis by X-ray diffraction and transmission electron microscopy revealed the presence of stacking faults in MG crystals in a high concentration, which suggests these defects to be responsible for ...

Magnetic response of (Cr,Al,Si)N nanocrystallites on the microstructure of Cr—Al—Si—N nanocomposites

Abstract A combination of microstructure analysis and ab initio calculations helped us to describe the interplay between the microstructure of Cr—Al—Si—N thin film nanocomposites and the ordering of the magnetic moments in the chromium-rich phase of (Cr,Al)N. The microstructure of the Cr—Al—Si—N nanocomposites was modified through the degree of ionisation of the deposited species in three physical vapour deposition processes – cathodic arc evaporation, unbalanced magnetron sputtering and high power impulse magnetron sputtering. According to the results of the ab initio calculations, the magnetic ordering was concluded from the expansion of the elementary cell and from the change of the crystal anisotropy of the elastic constants of (Cr,Al)N; these microstructure features were obtained from X-ray diffraction experiments. The microstructure of the Cr—Al—Si—N nanocomposites was furthermore characterised using the combination of X-ray diffraction and transmission electron microscopy with high resolution in order to obtain information about the phase composition of the thin films, distribution of individual elements and the crystallite size.

Nano- and microstructure of diamond-like carbon films modified by Ca-O incorporation

Abstract In the present study, the nano- and microstructure of diamond-like carbon (DLC) coatings on Ti6Al4V substrates were changed by Ca–O incorporation. For the deposition of Ca–O-DLCs, a gaseous hydrocarbon precursor (e.g. methane) and CaO–H2O vapour were decomposed together in plasma using a direct current discharge. The hardness, Youngs modulus and relative elastic recovery of Ca–O-modified DLCs are reduced in comparison to unmodified DLC. However, the adherence of the Ca–O-DLCs is improved. With increasing relative partial pressure of the CaO–H2O vapour during DLC coating deposition, the size of the sp2-hybridised carbon islands, which were observed via high-resolution transmission electron microscopy, increased and the shape changed from oval islands to strips of several 10 nm. This finding is in good accordance with the results from Raman spectroscopy, which also pointed to an increase in the size and/or number of sp2-hybridised crystalline carbon clusters in the amorphous carbon matrix. The DLCs have increased oxygen content due to the decomposition of CaO–H2O vapour, in addition to hydrocarbon. As detected by IR and X-ray photoelectron spectroscopy, Ca is incorporated as carbonate into the DLC.

Microstructure of austenitic stainless steels of various phase stabilities after cyclic and tensile deformation

Abstract The microstructures of two metastable high-alloyed CrMnNi cast TRIP steels and a stable AISI 316L austenitic stainless steel were studied in detail after tensile and cyclic deformation. Electron backscattered diffraction was employed to localize the martensitic phase transformation and electron channelling contrast imaging to describe the typical dislocation arrangements. These were complemented by transmission electron microscopy and by scanning transmission electron microscopy performed in a scanning electron microscope. The TRIP steel with the lowest austenite stability shows a more pronounced martensitic phase transformation realized from the austenite via the intermediate formation of ∊-martensite. Martensitic phase transformation also occurred in the stable 316L austenitic stainless steel with a small volume fraction of α′-martensite, but only with cyclic deformation at low temperatures and/or at very high plastic strain amplitudes.

Transmission Electron Microscopy Image Contrast of Disclination Defects in Crystals (Computer Simulation)

(a) Institute for Problems of Mechanical Engineering, Russian Academy of Sciences,Bolshoj 61, Vas. Ostrov, 199178 St. Petersburg, Russia(b) Institute of Physical Metallurgy, Freiberg University of Mining and Technology,Gustav-Zuener-Str. 5, 09596 Freiberg, Germany(c) Ioffe Physico-Technical Institute, Russian Academy of Sciences, Polytechnicheskaya 26,194021 St. Petersburg, Russia(Received August 27, 2001; in revised form March 1, 2002; accepted March 4, 2002)Subject classification: 61.72.Lk; 68.37.LpTransmission electron microscopy (TEM) images of disclination defects are modeled in the fra-mework of Howie–Whelan two-beam approach and by taking into account elastic distortionsassociated with the defects. Disclinations are generated in crystalline materials in the course ofplastic deformation and can be observed in the junctions of several grain or cell boundaries. Thelines of disclinations are assumed to be parallel or perpendicular to the free surfaces of a thinfoil. For such a geometry disclination elastic fields (e.g. displacements and stresses) in the foilinterior are constructed by applying the technique of “virtual” surface defects. The obtainedresults demonstrate the possibility to extract the disclination parameters from the data of TEMobservations.