Papers by Keyword: TEM

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Authors: Holm Kirmse, Wolfgang Neumann, Slawomir Kret, Elzbieta Janik, Wojciech Zaleszczyk, Grzegorz Karczewski, Tomasz Wojtowicz
Abstract: (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.
Authors: Li Ping Chen
Abstract: The hydrophobic gold nanoparticles with monodispersity are synthesized by using n-butanol reduction in situ under the condition of alkali promotion in cetyltrimethylammonium bromide (CTAB)/n-butanol/n-heptane/HAuCl4/NaOH(aq) W/O microemulsion at 30°C. The CTAB-stabilized gold nanoparticles are characterized by UV-vis, TEM , XRD and so on. The replacement of simple surfactant (CTAB ) with mixed surfactant CTAB/ octadecylamine can weaken the direction of CTAB to the growth of gold nanopartices and increase the monodispersity of gold nanoparticles. The effects of components of the microemulsion system on the shape, size and monodispersity of gold nanoparticles are also explored. The results show that the size of gold particles is changed by the amount of CTAB and C18NH2.
Authors: Li Mei Cha, Helmut Clemens, Gerhard Dehm, Zao Li Zhang
Abstract: In-situ heating transmission electron microscopy (TEM) was employed to investigate the initial stage of lamellae formation in a high Nb containing γ-TiAl based alloy. A Ti-45Al-7.5Nb alloy (at %), which was heat treated and quenched in a non-equilibrium state such that the matrix consists of ordered a2 grains, was annealed inside a TEM up to 750 °C. The in-situ TEM study reveals that g laths precipitate in the a2 matrix at ~ 750 °C possessing the classical Blackburn orientation relationship, i.e. (0001)a2 // (111)g and [11-20]a2 // <110]g. The microstructure of the in-situ TEM experiment is compared to results from ex-situ heating and subsequent TEM studies.
Authors: Qian Liu, Jun Qing Hu
Abstract: Cd2Ge2O6 nanowires have been synthesized via a simple and facile hydrothermal route using GeO2 and CdO as the source materials with the surfactant. The structure and morphology of the Cd2Ge2O6 nanowires were fully analyzed by field emission scanning electron microscope (FESEM) and HRTEM. With a focused electron beam irradiation, the Cd2Ge2O6 nanowire became unstable and tended to heavily destroyed under a long time irradiation. Using the TEM-STM holder, electrical properties of an individual Cd2Ge2O6 nanowire has been measured and the obtained I-V curve demonstrated the semiconductor property.
Authors: Eri Morita, Akifumi Ono, Shigehito Isobe, Yong Ming Wang, Naoyuki Hashimoto, Somei Ohnuki
Abstract: We carried out in-situ observation on the catalytic effect of Nb2O5 in MgH2 by using a high voltage transmission electron microscope (HVEM). We synthesized two kinds of samples, which were prepared by ball milling and by hand mixing. In milled sample, Nb2O5 was not confirmed from high resolution images, however, NbO was identified. As the temperature increased, the decomposition of MgH2 proceeded, while Mg formed and grew. It suggested that NbO had the catalytic effect to promote the dehydrogenation of MgH2. In mixed sample, which was prepared to clearly observe the boundary between the catalyst and Mg phase, it was revealed that the dehydrogenation started from the boundary of MgH2 and Nb2O5. This result suggested that the dehydrogenation could proceed with hydrogen diffusion from MgH2 through Mg phase to the boundary.
Authors: Władysław Osuch, Adam Kruk, Grzegorz Michta, Aleksandra Czyrska-Filemonowicz
Abstract: The electron tomography and transmission electron microscopy studies of the carbides in the 0.5Cr-0.5Mo-0.25V (13HMF) low-alloy steel after service during 160 000 h at 540 °C were carried out. Identification of the carbides was performed by means of electron diffraction analysis. Meso-scale tomography technique, mainly FIB/SEM tomography, was used for detailed characterization of spatial distribution and metrology of the carbides in 13HMF steel. The results achieved confirm the ability of FIB tomography to get 3D reconstruction of internal microstructure of steel as well as to obtain information about the shape and spatial distribution of carbides.
Authors: Robert S. Okojie, Ming Xhang, P. Pirouz, Sergey P. Tumakha, Gregg Jessen, Leonard J. Brillson
Authors: Teddy Robert, Sandrine Juillaguet, Maya Marinova, Thierry Chassagne, Ioannis Tsiaousis, N. Frangis, Efstathios K. Polychroniadis, Jean Camassel
Abstract: The electronic structure of in-grown 8H stacking faults in 4H-SiC matrix has been investigated in detail. After assessment of the structural properties by high resolution transmission electron microscopy, we focus on the electronic structure. We show that one unit cell of 8H does not behave like a single type-II quantum well but, rather, like two type-II quantum wells of 3C coupled by a thin hexagonal barrier. Using a transfer matrix method, we compute the corresponding transition energies, taking into account the effect of the valence band offset and built-in electric field. A good agreement is found with the experimental data collected from low temperature photoluminescence spectroscopy.
Authors: Le Zhou, Anit Giri, Kyu Cho, Yong Ho Sohn
Abstract: The ferromagnetic shape memory and magnetocaloric properties of NiMnGa alloys are closely related to the martensitic transformation from high temperature austenitic phase to low temperature martensitic phase. The transformation temperature and the resulting microstructure and crystallography of the martensites can be very complex, but are crucial to the optimization of the material performance. A combinatorial study with a series of solid-to-solid diffusion couples and various characterization techniques, including scanning electron microscopy, focused ion beam, transmission electron microscopy, electron probe microanalysis, and nanoindentation, was carried out to investigate the microstructural and crystallographic development, and mechanical properties in NiMnGa alloys. Both austenitic and martensitic phases were found at room temperature in each diffusion couple with a clear interphase boundary. Crystallographic variations in martensitic phase, including non-modulated (NM) martensite and modulated (5M or 7M) martensite, were found in the diffusion couples. All martensitic microstructure consists of variants with different orientations and the twinning relationship. A decrease of reduced elastic modulus (Er) was observed with Ni substituting for Ga in the austenitic phase. However, an opposite trend of an increase in Er was found in the martensitic phase. The softening of the elastic constants near the vicinity of martensitic transformation contributed to a sharp decrease in Er near the interphase boundary. The measured Er had a larger scatter for the martensitic phase than that for the austenitic phase.
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