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X-ray analysis of ZnO nanoparticles by Williamson–Hall and size–strain plot methods

ZnO nanoparticles were prepared by coprecipitation method at 450C. X-ray diffraction result indicates that the sample is having a crystalline wurtzite phase. Transmission electron microscopy (TEM) result reveals that the ZnO sample is spherical in shape with an average grain size of about 50nm. X-ray peak broadening analysis was used to evaluate the crystalline sizes and lattice strain by the Williamson-Hall (W-H) analysis. All other relevant physical parameters such as strain, stress, and energy density values were also calculated using W-H analysis with different models, viz, uniform deformation model, uniform deformation stress model and uniform deformation energy density model. The root mean square strain was determined from the interplanar spacing and strain estimated from the three models. The three models yield different strain values; it may be due to the anisotropic nature of the material. The mean particle size of ZnO nanoparticles estimated from TEM analysis, Scherrers formula and W-H analysis is highly intercorrelated.

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Williamson-Hall analysis in estimation of lattice strain in nanometer-sized ZnO particles

The stability of two-dimensional (2D) layers and membranes is subject of a long standing theoretical debate. According to the so called Mermin-Wagner theorem, long wavelength fluctuations destroy the long-range order for 2D crystals. Similarly, 2D membranes embedded in a 3D space have a tendency to be crumpled. These dangerous fluctuations can, however, be suppressed by anharmonic coupling between bending and stretching modes making that a two-dimensional membrane can exist but should present strong height fluctuations. The discovery of graphene, the first truly 2D crystal and the recent experimental observation of ripples in freely hanging graphene makes these issues especially important. Beside the academic interest, understanding the mechanisms of stability of graphene is crucial for understanding electronic transport in this material that is attracting so much interest for its unusual Dirac spectrum and electronic properties. Here we address the nature of these height fluctuations by means of straightforward atomistic Monte Carlo simulations based on a very accurate many-body interatomic potential for carbon. We find that ripples spontaneously appear due to thermal fluctuations with a size distribution peaked around 70 \AA which is compatible with experimental findings (50-100 \AA) but not with the current understanding of stability of flexible membranes. This unexpected result seems to be due to the multiplicity of chemical bonding in carbon.

Intrinsic ripples in graphene

Welding Metallurgy of

Zirconia (ZrO2) films were deposited by metal-organic chemical vapour deposition (MOCVD) on (1 0 0) Si single crystals using Zr(thd)4 precursor. The crystalline structure determined by X-ray diffraction (XRD) spectrum showed that the films exhibit the metastable tetragonal phase at room temperature. A method based on the pseudo-grazing incident X-ray diffraction (GIXRD) geometry was applied to study the residual stress gradient on the zirconia (ZrO2) films. By varying the X-ray beam penetration depth and the associated geometry angles, the residual stress profile can be described in detail. The residual stress profile revealed that tensile residual stress was present in the near-surface region and then it decreased rapidly as a function of depth; whereas, in the deeper regions, the films were under compressive stress. The origin of the residual stresses, which are assumed to consist of the film growth stress during the MOCVD process and film thermal stress during film cooling after deposition, is discussed.

Vincent Ji

Papers

Residual stress gradient analysis with GIXRD on ZrO2 thin films deposited by MOCVD

Anisotropic elasticity in hexagonal crystals

Influence of humidity on high temperature oxidation of Inconel 600 alloy: Oxide layers and residual stress study

A comparison study of the structural and mechanical properties of cubic, tetragonal, monoclinic, and three orthorhombic phases of ZrO2

Atomistic simulation of point defects at low-index surfaces of noble metals