Browsing by Author "Lee, Shih-Kuang"

Now showing 1 - 3 of 3

Electron Beam Irradiation-Induced Deoxidation and Atomic Flattening on the Copper Surface
(2019-10-30)
Lin, Ting-Yi
;
Lee, Shih-Kuang
;
Huang, Guan-Min
;
Huang, Chun-Wei
;
Tai, Kuo-Lun
Electron beam (e-beam) has been developed for nanomaterial observation and moreover to induce structural evolutions in atomic scale. In this work, we demonstrate the deoxidation of cuprous oxide (Cu2O) and the formation of an atomically flat surface on a Cu nanowire by e-beam irradiation. To develop e-beam irradiation applications, the relation between e-beam radiation and the atomic surface is significant. Through the density functional theory simulation of atomic sputtering, an obvious disparity in the sputtering threshold has been found under different structural conditions, which leads to different structural evolutions. Both surface deoxidation and atomic surface flattening reactions have been identified as self-limiting and irreversible processes via in situ transmission electron microscope observation. Under e-beam irradiation, the dynamic mechanism of atomic surface flattening is driven by the convergence of total surface energy and confirmed by climbing-image nudged elastic band (ci-NEB) calculations. With precise control, e-beam irradiation reveals enormous potentials in atomic surface engineering.
Facet-Dependent Photocatalytic Behaviors of ZnS-Decorated Cu2O Polyhedra Arising from Tunable Interfacial Band Alignment
(2019-01-23)
Naresh, Gollapally
;
Hsieh, Pei-Lun
;
Meena, Vandana
;
Lee, Shih-Kuang
;
Chiu, Yi-Hsuan
ZnS particles were grown over Cu2O cubes, octahedra, and rhombic dodecahedra for examination of their facet-dependent photocatalytic behaviors. After ZnS growth, Cu2O cubes stay photocatalytically inactive. ZnS-decorated Cu2O octahedra show enhanced photocatalytic activity, resulting from better charge carrier separation upon photo excitation. Surprisingly, Cu2O rhombic dodecahedra give greatly suppressed photocatalytic activity after ZnS deposition. Electron paramagnetic resonance spectra agree with these experimental observations. Time-resolved photoluminescence profiles provide charge-transfer insights. The decrease in the photocatalytic activity is attributed to an unfavorable band alignment caused by significant band bending within the Cu2O(110)/ZnS(200) plane interface. A modified Cu2O-ZnS band diagram is presented. Density functional theory calculations generating plane -specific band energy diagrams of Cu2O and ZnS match well with the experimental results, showing that charge transfer across the Cu2O(110)/ZnS(200) plane interface would not happen. This example further illustrates that the actual photocatalysis outcome for semiconductor heterojunctions cannot be assumed because interfacial charge transfer is strongly facet-dependent.
Observing phase transformation in CVD-grown MoS2 via atomic resolution TEM
(2018-09-14)
Tai, Kuo-Lun
;
Huang, Guan-Min
;
Huang, Chun-Wei
;
Tsai, Tsung-Chun
;
Lee, Shih-Kuang
We utilized in situ transmission electron microscopy to observe phase transformation in CVD-grown MoS2. Significantly, the reaction was performed under electron irradiation through appropriate control of the electron dose and exposure time. Moreover, we proposed a new route between the 2H and 1T phases that involved the higher energy states TS1/TS2.