Mn-doped ZnO nanowires prepared by chemical vapor deposition (CVD) were obtained in the temperature range of 450–500°C. X-ray diffraction patterns, SEM and TEM images indicate that crystals with a hexagonal structure grow along the c axis. At low Mn-doped concentrations, photoluminescence (PL) and Raman scattering (RS) spectra are almost independent of the Mn doping. However, the increase in concentration of Mn above 1.6 at% weakens significantly the PL signal and the RS-lines intensity in the low wavenumber range of 300–480 cm-1, and concurrently increases the RS-lines intensity in the higher wavenumber range of 480-700 cm-1.. Magnetic measurements determined the Curie temperature of Mn-doped ZnO nanowire to be about 37 K.

We first review the application of transmission electron microscopy to incchnmensurate crystals drawing attention to the different techniques available. There follows a discussion of proposed differences between AlFe inccm~lensurate and quasi-crystals introducing some new results on an AlFeCe quasi-crystal. Finally, a brief reprt is given of incmsurate phases recently identified in crystallized mrphous films of Alrn.

The large angle method of convergent beam electron diffraction (LAMED) has been used to examine multi-quantum well (M1W) and single quantum well (SQW) samples of AlGaAs/GaAs and InP/InGaAs viewed approximately along the growth direction. The method combines an image of the specimen with the rocking curve, typically over about 6° for a selected reflection. LACBED patterns fran MQW samples show many orders of superlattice satellite reflections and can be used to profile compositions in both periodic and less regular structures. For SQW samples, we can measure the local quantum well thickness to near-monolayer precision.

We present the growth of ZnO nanocombs by using chemical vapor deposition (CVD) under atmospheric pressure. Two types of single- and double-side teethed nanocombs have been obtained. Structural analyses based on electron microscopy reveal the diameter and the period of teeth to be about 50 nm and 75 - 100 nm, respectively, while the length of the comb ribbons is 7 - 10 Am. For the single-teethed type, the entire nanocomb is a single crystal with the teeth grown along the [0001] direction, and the comb ribbon grown along the [10-10] direction. For double-side teethed nanocombs, they are twin crystals with twin boundaries of {10-13}. The comb ribbons grow along the directions of (10-11) while the teeth grow along the [0001] direction. With the results obtained, we believe that the growth of nanocombs follows the vapour-solid process. Studies of the optical properties basing on photoluminescence and Raman spectroscopy have indicated that the ZnO nanocombs have good crystal quality.

We have studied systematically room-temperature photoluminescence (PL) properties of many nanostructured ZnO samples grown by chemical vapour deposition (CVD). Their PL spectra consist of two emissions peaked in the ultraviolet (UV) and green regions. The relative intensity of these emissions depends on the excitation energy density, size and morphology of ZnO nanostructures. Based on the excitation-density dependence of the integrated intensity ratio of UV-to-green emission, we could classify PL spectra of ZnO nanostructures into three groups characteristic of size and morphology. Our study also reveals that with increasing excitation density, the UV-peak position shifts slightly towards longer wavelengths while the green emission around 514–520nm is almost unchanged. This green-luminescence emission is dominant when the nanostructure sizes range from 20 to 200nm, which is related to a large surface-to-volume ratio.

We prepared Zn1−xMnxO nanorods by thermal diffusion. These samples were then studied the structural, optical, and magnetic properties. The structural analyses basing on x-ray diffraction and transmission electron microscope revealed the absence of Mn-related secondary phases. The study of photoluminescence spectra revealed the blueshift in the UV emission when the Mn doping concentration was increased, as a consequence of the extension of the band gap energy. Besides this situation, the increase in emission intensity associated with extrinsic defects at about 680 nm also took place. Concerning the Raman scattering spectra, apart from conventional phonon modes related to the ZnO wurtize-type structure, there were some additional modes introduced by the doping. Their origin was assessed carefully. Particularly, the shift in peak position of E2(high) toward low frequencies due to the increase in the Mn doping concentration could be explained well by means of the spatial correlation model. Magnetic measurements proved the samples with Mn concentrations above 1.15 at. % exhibiting the weak-ferromagnetic order at low temperatures. The nature of the ferromagnetism was discussed by means of the results of the structural and optical investigations.

The crystal polarity of wurtzite zinc oxide nanorods grown hydrothermally parallel to the c = [0001] direction has been determined by convergent-beam electron diffraction using a defocused probe. The method enables a simple comparison of the diffracted intensities in +/- 0002 reflections across side-on nanorods, demonstrating growth in this case is in the c = [0001] direction. The method is shown to be viable for nanorods down to about 11 nm in diameter.

Influence of annealing on the electron spin resonance (ESR) spectra of Zn1-xMnxO:l mol% Zn3P2) (X = 0.01 and 0.02) ceramics was systematically investigated. The samples were annealed at temperatures (Tall) between 200 and 1100 degrees C for 12 h. The ESR spectra revealed the three characteristic regions. In the first region (200 <= Tar, < 700 degrees C, the ESR spectra exhibited a broad Lorentzian-type single line, and the ESR intensity decreased with increasing Tan . In the second region (700 <= Tan < 1000 degrees C), the ESR spectra appeared Mn2+ hyperfine lines within a broad Lorentzian sinale line. indicating that Mn2+ ions Zn(2+)2 lattice sites. The sigmal intensity and number of Mn2+ hyperfine lines increased with increasing T-an. In the third region (T-an >= 1000 degrees C, the Mn2+ hyperfine lines became broadened and finally blurred into the background line, resulting in a strong increase in the ESR signal. The origins of the ESR spectra, in relation to their X-ray diffraction patterns, are elucidated. (C) 2007 Elsevier Ltd. All rights reserved.

A temperature dependent electron diffraction study has been carried out on UAsSe to search for evidence of As–As dimerization at low temperature. A highly structured characteristic diffuse intensity distribution, closely related to that recently reported for ThAsSe, has been observed at low temperature and interpreted in terms of a gradual charge density wave type phase transition upon lowering of temperature involving disordered As–As dimerization within (001) planes. Plausible models of the proposed As–As dimerization have been obtained using a group theoretical approach. Electronic band structure calculations of ThAsSe and UAsSe have been used to search for potential Fermi surface nesting wave-vectors. The results are in good agreement with the experimentally observed diffuse intensity distributions in both cases.

The Vincent-Midgley precession technique has been used to collect three-dimensional electron diffraction intensity data from a dispersion of coherent precipitates in a matrix. In order to suppress severe effects from multiple diffraction via matrix reflections, a fairly large precession (tilt) angle had to be used. This implied a high background from the surrounding matrix, and limited the number of reflections that could be measured from patterns on image plates. The heavily faulted hexagonal η′-precipitates (a=0.496nm, c=1.405nm) with thickness 3–5nm occur in four equivalent orientations relative to the aluminium matrix; with frequent overlap of reflections. A model of the average structure in the space group P63/mmc with assumed composition Mg2Zn5−xAl2+x, have been derived by Patterson analysis and intensity comparisons.

Resolution Microscopy and Atom Probe Analysis of Nano-Size Precipitates in Al-Zn-Mg Industrial Alloys. V. Hansen, A. Kverneland, R. Vincent, X.Z. Li, K. Stiller and J. Gjonnes, Faculty of Science and Technology, Stavanger University College, N-4068 Stavanger, Norway, H.H.Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL UK, Center for Materials Science, University of Oslo, N-0439 Oslo, Norway, Center for Materials Research and Analysis, University of Nebraska, Lincoln, NE 68588-0113, Department of Physics, Chalmers University of Technology, S-4196 Goteborg, Sweden. E-mail: vidar.hansen@tn.his.no

A low-temperature electron diffraction study has been carried out on ThAsSe to search for evidence of structural disorder associated with the low-temperature non-magnetic Kondo effect. A highly structured and extremely complex characteristic diffuse intensity distribution has been observed at low temperature and interpreted in terms of a gradual charge density wave type phase transition upon lowering of temperature involving disordered As–As dimerization within (001) planes. Plausible models of the proposed As–As dimerization have been obtained using a group theoretical approach.

Journal of MicroscopyVolume 211, Issue 2 p. 188-190 Large-Angle Convergent Beam Electron Diffraction – Applications to Crystal Defects R. Vincent, R. Vincent University of BristolSearch for more papers by this author R. Vincent, R. Vincent University of BristolSearch for more papers by this author First published: 29 July 2003 https://doi.org/10.1046/j.1365-2818.2003.01202.xRead the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Volume211, Issue2August 2003Pages 188-190 RelatedInformation

As an alternative to sideband holography in an electron microscope, methods for phase recovery by in-line holography utilising Fresnel images of aperiodic objects were tested with computed simulations and experimental data. Phases were recovered by minimising an error functional defined as a measure of the differences between experimental and calculated image intensities. The probability of convergence to local minima of the error function was reduced by increasing the ratio of known to unknown parameters, partly by use of several Fresnel images at different defoci, and also by an incremental relaxation of the phase bandwidth. Iterative methods did not converge reliably to a global minimum, but a conjugate gradient algorithm usually recovered the phases exactly, even for object arrays which included large phase variations. In practice, it was essential to use analytic expressions for the error gradients with respect to the phases, defoci and beam direction. Phase shifts of several radians were measured near the edge of a contaminated aperture. The factors that limit the accuracy and reliability of phase recovery from Fresnel images are discussed.

It has been found that the β-(Al-Fe-Si) precipitate with approximate composition Al5FeSi and lamellar microstructure is not a single-phase compound but a multiphase composite. An orthorhombic phase has been identified from the precipitate and its crystal structure determined by means of convergent-beam electron diffraction. This phase has an orthorhombic A-centred lattice with parameters a = 6.18 Å, b = 6.20 Å and c = 20.8 Å, point group mmm and space group Amam, equivalent to Cmcm (No. 63) in standard notation.

In the two-beam limit, the intensity distribution in the dark field disc of a convergent beam electron diffraction (CBED) pattern represents a rocking curve mapped across the Bragg condition. For kinematic scattering from crystal planes which are bent or displaced within the illuminated column, the diffracted amplitude and phase is the Fourier transform of a phase function with an exponent proportional to the displacement normal to the planes. Recovery of the phase profile is formally equivalent to the one-dimensional phase retrieval problem for an object function with constant modulus within a compact support, given only the diffracted intensity distribution. In simulations using the error reduction algorithm, the computed solution always converged to the original phase profile. As a practical test, the asymmetric rocking curves diffracted from planes inclined to the surfaces in ion-thinned Si specimens were used as the diffraction constraint, with support width equal to the crystal thickness. The calculated displacement curve was S-shaped, interpreted as a dilation of 1% induced by Ar atoms implanted in the surface layers. The factors which limit the accuracy and spatial resolution for phase recovery along the beam direction are discussed.

The crystal structure of Al-Fe-Si-Be intermetallic precipitates has been investigated by transmission electron microscopy and convergent-beam electron diffraction. The precipitates showed Chinese script morphology with the composition Al8Fe2SiBe. The crystal structure was bce with a = 1.234 nm, point group and Im(3) over bar (No. 204) space group. This phase is an approximant to the related icosahedral quasicrystalline phase. X-ray diffraction peaks published previously by Murali et al. (1994, Scripta metall. mater., 29, 1421) are reindexed and the role of Be atoms in crystal growth is briefly discussed.