Browsing by Author "Wang, Jinguo"
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Item Creating a Single Twin Boundary between Two CdTe (111) Wafers with Controlled Rotation Angle by Wafer BondingSun, Ce; Lu, Ning; Wang, Jinguo; Lee, Jihyung; Peng, Xin; Klie, R. F.; Kim, Moon J.The single twin boundary with crystallographic orientation relationship (1‾ 1‾ 1 ‾)//(111) [0 1‾1]// [011‾] was created by wafer bonding. Electron diffraction patterns and high-resolution transmission electron microscopy images demonstrated the well control of the rotation angle between the bonded pair. At the twin boundary, one unit of wurtzite structure was found between two zinc-blende matrices. High-angle annular dark-field scanning transmission electron microscopy images showed Cd- and Te-terminated for the two bonded portions, respectively. The I-V curve across the twin boundary showed increasingly nonlinear behavior, indicating a potential barrier at the bonded twin boundary.Item Enhanced Shape Stability of Pd-Rh Core-Frame Nanocubes at Elevated Temperature: In Situ Heating Transmission Electron MicroscopyLu, Ning; Wang, Jinguo; Xie, S.; Xia, Y.; Kim, Moon J.Shape stability of Pd-Rh core-frame nanocubes was studied by in situ heating transmission electron microscopy. Pd-Rh nanocubes could maintain cubic shape at elevated temperature compared with pure Pd. The surface diffusion process of Rh onto {100} side surfaces is believed to postpone the degradation to higher temperature.Item Enhanced Thermal Conductivity in Cu/Diamond Composites by Tailoring the Thickness of Interfacial TiC Layer(Elsevier Ltd) Wang, Luhua; Li, J.; Catalano, Massimo; Bai, G.; Li, N.; Dai, J.; Wang, X.; Zhang, H.; Wang, Jinguo; Kim, Moon J.; Wang, Luhua; Catalano, Massimo; Wang, Jinguo; Kim, Moon J.Diamond particles reinforced Cu matrix (Cu/diamond) composites were fabricated by gas pressure infiltration using Ti-coated diamond particles with Ti coating from 65 nm to 850 nm. The scanning transmission electron microscopy (STEM) characterizes that the Ti coating transforms from elemental Ti to TiC after infiltration, and the crystallographic orientation relationship between diamond and TiC is [1 1 0]_{diamond}//[1 1 0]_{TiC} and (1 1 1)_{diamond}//(1 1 1)_{TiC}. The thermal conductivity of the Cu/Ti-diamond composites firstly increases and then decreases with increasing Ti coating thickness, giving a maximal value of 811 W m⁻¹ K⁻¹ at 220 nm Ti-coating layer. The results clearly manifest the effect of interfacial layer thickness on the thermal conductivity of Cu/diamond composites.Item Luminescent LaF₃:Ce-Doped Organically Modified Nanoporous Silica XerogelsYao, Mingzhen; Hall, Ryan; Chen, Wei; Mohite, Dhairyashil P.; Leventis, Nicholas; Lu, Ning; Wang, Jinguo; Kim, Moon J.; Luo, Huiyang; Lu, HongbingOrganically modified silica compounds (ORMOSILs) were synthesized by a sol-gel method from amine-functionalized 3-aminopropyl triethoxylsilane and tetramethylorthosilicate and were doped in situ with LaF3:Ce nanoparticles, which in turn were prepared either in water or in ethanol. Doped ORMOSILs display strong photoluminescence either by UV or X-ray excitation and maintain good transparency up to a loading level of 15.66% w/w. The TEM observations demonstrate that ORMOSILs remain nanoporous with pore diameters in the 5-10 nm range. LaF3:Ce nanoparticles doped into the ORMOSILs are rod-like, 5 nm in diameter and 10-15 nm in length. Compression testing indicates that the nanocomposites have very good strength, without significant lateral dilatation and buckling under quasi-static compression. LaF3:Ce nanoparticle-doped ORMOSILs have potential for applications in radiation detection and solid state lighting.Item New Intrinsic Mechanism on Gum-Like Superelasticity of Multifunctional AlloysLiu, J. -P; Wang, Y. -D; Hao, Y. -L; Wang, Y.; Nie, Z. -H; Wang, D.; Ren, Y.; Lu, Z. -P; Wang, Jinguo; Wang, H.; Hui, X.; Lu, Ning; Kim, Moon J.; Yang, R.Ti-Nb-based Gum Metals exhibit extraordinary superelasticity with ultralow elastic modulus, superior strength and ductility, and a peculiar dislocation-free deformation behavior, most of which challenge existing theories of crystal strength. Additionally, this kind of alloys actually displays even more anomalous mechanical properties, such as the non-linear superelastic behavior, accompanied by a pronounced tension-to-compression asymmetry, and large ductility with a low Poisson's ratio. Two main contradictory arguments exist concerning the deformation mechanisms of those alloys, i.e., formation of reversible nanodisturbance and reversible martensitic transformation. Herein we used the in-situ synchrotron high-energy X-ray scattering technique to reveal the novel intrinsic physical origin of all anomalous mechanical properties of the Ti-24Nb-4Zr-8Sn-0.10O alloy, a typical gum-like metal. Our experiments provide direct evidence on two different kinds of interesting, stress-induced, reversible nanoscale martensitic transitions, i.e., the austenitic regions with B2 structure transform to α" martensite and those with BCC structure transform to ō martensite.Item Tailoring Interface Structure and Enhancing Thermal Conductivity of Cu/Diamond Composites by Alloying Boron to the Cu Matrix(Elsevier Inc.) Bai, G.; Wang, Luhua; Zhang, Y.; Wang, X.; Wang, Jinguo; Kim, Moon J.; Zhang, H.; Wang, Luhua; Wang, Jinguo; Kim, Moon J.Diamond particles reinforced Cu matrix (Cu/diamond) composites were prepared by alloying 0.1–1.0 wt% B to the Cu matrix in order to tailor the interface structure. The interface structure evolves from discrete triangular carbides into continuous jig-saw carbides depending on the availability of boron source in the Cu-B matrix. We report the highest thermal conductivity of 868 W/mK so far in boron-modified Cu/diamond composites, which originates from the discontinuous carbide interface in the Cu-B/diamond composites. The parallel connection of interfacial thermal resistances of the discontinuous carbide interface reduces the total interfacial thermal resistance and therefore promotes phonon transfer across the Cu/diamond interface. We clarify the formation mechanism of discontinuous carbide interface in the Cu-B/diamond composites and demonstrate the decisive role of discrete triangular carbides in enhancing thermal conductivity of Cu/diamond composites. The results help to establish the method of metal matrix alloying to prepare Cu/diamond composites with high thermal conductivity for thermal management applications. © 2019 Elsevier Inc.Item Tunable Coefficient of Thermal Expansion of Cu-B/Diamond Composites Prepared by Gas Pressure Infiltration(Elsevier Ltd) Bai, G.; Zhang, Y.; Dai, J.; Wang, L.; Wang, X.; Wang, Jinguo; Kim, Moon J.; Chen, X.; Zhang, H.; Wang, Jinguo; Kim, Moon J.Cu-B matrix composites reinforced with diamond particles (Cu-B/diamond) were prepared by gas pressure infiltration (GPI). The effect of boron addition in the range of 0–1.0 wt% on the thermal expansion behavior of the Cu-B/diamond composites was evaluated. The coefficient of thermal expansion (CTE) of the Cu-B/diamond composites initially decreases and then increases with increasing boron content. The minimum CTE value of 4.88 × 10 -6 /K is obtained at 0.5 wt% B addition, which satisfies the requirement of CTE of semiconductors (range of 4–8 × 10⁻⁶ /K) for electronic packaging applications. The variation of CTE of the Cu-B/diamond composites is attributed to the formation of interfacial carbides and their morphological evolution. The interface structure evolves from discrete triangular carbides into continuous carbide layer with increasing boron content. The increase in the quantity of discrete carbides enhances the interface, but the formation of continuous carbides impairs the interfacial bonding of the Cu-B/diamond composites. The results suggest that alloying B to Cu matrix is an effective route to tune the coefficient of thermal expansion of Cu/diamond composites. © 2019 Elsevier B.V.