Khuong Phuong Ong

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Gold, silver, platinum and palladium typically crystallize with the face-centred cubic structure. Here we report the high-yield solution synthesis of gold nanoribbons in the 4H hexagonal polytype, a previously unreported metastable phase of gold. These gold nanoribbons undergo a phase transition from the original 4H hexagonal to face-centred cubic structure(More)
We show, using Boltzmann transport calculations and analysis of experimental data, that hexagonal PdCoO2 and PtCoO2 have a highly unusual metallic transport. The in-plane transport is typical of a very good metal, with high conductivity and low positive thermopower. The c-axis transport is completely different, with 2 orders of magnitude lower, but still(More)
We explore BiFeO3 under tensile strain using first-principles calculations. We find that the actual structures are more complex than what had been previously thought, and that there is a strong shear deformation type structural instability which modifies the properties. Specifically, we find that normal tensile strain leads to structural instabilities with(More)
Ferroelectricity has been believed to be an important but controversial origin of the excellent photovoltaic performance of organometal trihalide perovskites (OTPs). Here we investigate the ferroelectricity of a prototype OTP, CH3NH3PbI3 (MAPbI3), both theoretically and experimentally. Our first-principles calculations based on 3-D periodic boundary(More)
We employ first-principles methods to study the mechanism controlling the electrical conduction in BiFeO3 (BFO). We find that under oxygen-rich conditions, Bi vacancies (V(Bi)) have lower defect formation energy than O vacancies (V(O)) (-0.43 eV vs. 3.35 eV), suggesting that V(Bi) are the acceptor defects and control the conductivity of BFO, making it a(More)
The organic-inorganic hybrid perovskite, in particular, methylammonium lead iodide (MAPbI3), is currently a subject of intense study due to its desirability in making efficient photovoltaic devices economically. It is known that MAPbI3 undergoes structural phase transitions from orthorhombic Pnma to tetragonal I4/mcm at ∼170 K and then to cubic Pm3̅m at(More)
The methylammonium lead iodide perovskite (MAPbI3) is presently a desirable material for photovoltaic application. Its structure is orthorhombic at low temperature and tetragonal at room temperature. Most theoretical works have focused on either tetragonal or orthorhombic phase alone leaving a gap in the understanding of the structural phase transition in(More)
Ferroelectric perovskites with strongly elongated unit cells (c/a > 1.2) are of particular interest for realizing giant polarization induced by significant ionic off-center displacements. Here we show that epitaxial BiFe0.6Ga0.4O3 (BFGO) thin films exhibit a stable super-tetragonal-like structure with twinning domains regardless of film thickness and(More)
A retrospective study was conducted to assess the surgical outcomes of degenerative lumbar spinal stenosis. Twenty-five patients treated with decompressive surgery in Hospital Kuala Lumpur between January 1992 and August 1996 were reviewed. There were seven males and eighteen females. The average age was 51 years old (range 33 to 64 years old). The(More)
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