Browsing by Author "Wu, KH"

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    Magnetic ordering anisotropy in epitaxial orthorhombic multiferroic YMnO3 films
    (American Institute of Physics, 2008-11-15) Hsieh, CC; Lin, TH; Shih, HC; Hsu, CH; Luo, CW; Lin, JY; Wu, KH; Uen, TM; Juang, JY
    Orthorhombic YMnO3 thin films with (200), (020), and (001) orientations were, respectively, obtained by pulsed laser deposition on SrTiO3(110), LaAlO3(110), and SrTiO3(001) substrates. The results demonstrate that the strain between film and substrate can serve as an alternative in transforming the thermodynamically stable hexagonal YMnO3 into the orthorhombic phase, which previously could be obtained with high-pressure high temperature syntheses and epitaxy-stabilized thin film processes. More importantly, these films allow us, for the first time, to unambiguously disclose the intrinsic magnetic property along different crystallographic orientations. Our results show that, although the antiferromagnetic (AFM) ordering remains the same, there is an additional spin reordering transition which is very much dependent on the crystallographic orientation along which the measuring field was applied and on the in-plane crystallographic alignment of the films. Detailed analyses indicate that the origin of the observed second reordering may be due to some strain-induced canted AFM state instead of the incommensurate lock-in transitions conceived previously. © 2008, American Institute of Physics
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    Reconstructing Cu nanoparticle supported on vertical graphene surfaces via electrochemical treatment to tune the selectivity of CO2 reduction toward valuable products
    (ACS Publications, 2022-04-07) Ma, ZP; Tsounis, C; Toe, CY; Kumar, PV; Subhash, B; Xi, SB; Yang, HY; Zhou, SJ; Lin, ZH; Wu, KH; Wong, RJ; Thomsen, L; Bedford, NM; Ng, YH; Han, ZJ; Amal, R
    Reconstructing a catalyst with tunable properties is essential for achieving selective electrochemical CO2 reduction reaction (CO2RR). Here, a reduction–oxidation–reduction (ROR) electrochemical treatment is devised to advisedly reconstruct copper nanoparticles on vertical graphene. Undercoordinated sites and oxygen vacancies constructed on the Cu active sites during the ROR treatment enhance the CO2RR activity. Moreover, by varying the oxidation potential while maintaining the reduction potential during the ROR treatment, CO2RR selectivity can be tuned between *COOH- and *OCHO-derived products. Specifically, rich grain boundaries are formed on the ROR catalyst with a high oxidation potential (+1.2 VRHE), favoring the *COOH/*OCCO adsorption and leading C–C coupling to *COOH-derived products, while the catalyst undergoing ROR at a low oxidation potential (+0.8 VRHE) lacks grain boundaries, resulting in highly selective formate (*OCHO-derived) production. Our findings are evidenced by combined in situ and ex situ characterizations and theoretical calculations. © 2022 American Chemical Society