Browsing by Author "Liu, WL"

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Growth and field emission of carbon nanofibers on electroless Ni-P alloy catalyst
(2003-09-01)
Tsai, TK
;
Chuang, CC
;
Chao, CG
;
Liu, WL
;
材料科學與工程學系
Carbon nanofibers (CNFs) were grown on a Ni-P alloy catalyst deposited on a silicon substrate in a microwave heating chemical vapor deposition system with methane gas at 650 degreesC. The Ni-P alloy catalyst films with various thicknesses were produced using an electroless plating nickel technique. The nanosized clusters on the clustered surface of the Ni-P alloy catalyst film directly provided the nucleation sites for CNFs without any pretreatment before the growth of the CNFs. The CNFs grown on the Ni-P alloy catalyst showed random orientation and it composed of parallel graphite planes with defects tilted from their axis. Field emission measurement indicated that the Ni-P catalyzed-CNFs exhibited excellent field emission properties. The diameter, growth rate and field emission properties show a strong correlation with the thickness of the Ni-P alloy catalyst film. (C) 2003 Elsevier Science B.V. All rights reserved.
Sensitivity of complete bandgaps to the shift of movable dielectric rod in two-dimensional photonic crystals with complex lattices
(2004-06-30)
Liu, WL
;
Yang, TJ
;
Gu, BY
;
電子物理學系
;
Department of Electrophysics
Two-dimensional tunable photonic crystals (TPCs) with movable components are proposed, which consist of a circular dielectric rod inserted into a square lattice of square dielectric cylinders in air. The band gap structures of TPCs can be tuned by adjusting the shift of the position of the circular rod in each unit cell. Band gap structures are calculated with the use of the plane-wave expansion method for various structural parameters, such as different filling fractions, ratio of the radius of the circular rod to the side-length of the square cylinder, different shifts or shifting orientations of the circular rod, etc. We find that there is a region of parameters in which the ratio of the gap width to the midgap is insensitive to the shift of the position of the circular dielectric rod. It is anticipated that the proposed TPC may become a favourable candidate of PCs owing to the benefit of facilitating fabrication, allowing a large tolerance.
Variation of group velocity and complete bandgaps in two-dimensional photonic crystals with drilling holes into the dielectric rods
(2005-11-01)
Liu, WL
;
Yang, TJ
;
電子物理學系
;
Department of Electrophysics
Two-dimensional square lattices of square cross-section dielectric rods in air, designed with an air hole drilled into each square rod, are studied theoretically. By adjusting the shift of the hole position in the square rod in each unit cell, the dielectric distribution of the square rod will be modified. A sizable complete band gap occurs for certain structural parameters and exhibits very flat photonic bands near such gap edge. which resulting in a sharp peak of density of states. In addition, the zero or small group velocities are observed in a broad region of k-space. This structure can be fabricated with materials widely used today and opens a fascinating area for applications in optoelectric devices. (c) 2005 Elsevier B.V. All rights reserved.