Mode splitting in an optical slab waveguide filled with nematic liquid crystals

Mode splitting was observed when a He-Ne laser beam was reflected through a prism-coupled liquid-crystal slab waveguide under an applied electric field. The splitting manifests itself as the imposed voltage reaches a critical level, and diminishes when the voltage increases above a critical high value. If the applied voltage increases even further, mode splitting vanishes, attributing to the result that almost all the directors of the liquid crystal turn upright to the surface. The multi-layer matrix simulation can satisfactorily account for this phenomenon by exploiting the property of the anisotropic optical birefringence of a liquid crystal under applied voltages. Received: 2 December 2002 / Revised version: 24 January 2003 / Published online: 23 May 2003 RID="*" ID="*"Corresponding author. Fax: +886/3572-3052, E-mail: jtlue@phys.nthu.edu.tw     

拉曼散射研究微尺寸圆锥形状的GeSi合金薄膜的应力(英文)

pacc:7830,7850C Wepresentthemicro-Ramanstudyof curvedGexSi1-x/GeySi1-yheterostructure,and foundthestrainofthecurvedthinlayerispropor tionaltothecurvature,i.e.inverselyproportional tothediameter.TheopticalandelectricpropertiesofSi1-x GexalloygrownonSisubst…     

光学尘埃粒子计数器自动校正的实现

光学尘埃粒子计数器是利用尘埃粒子在强光照射下产生散射光,通过检测散射光强度设计而成,仪器接收灵敏度的稳定性是保证测量准确度的关键。提出了一种尘埃粒子计数器实现自动校正的方法,使仪器始终处于定标时的接收灵敏度。     

Design of square-shaped heat flux cloaks and concentrators using method of coordinate transformation

A square-shaped heat flux cloak and a square-shaped heat flux concentrator have been designed theoretically according to the invariance symmetry of steady state thermal conductive equation. The direction of heat flux in these devices can be modulated as desired. Using the method of coordinate transformation, the inhomogeneous and anisotropic thermal conductivity in the transformation region have been acquired. Two-dimensional finite element simulations were performed to confirm the theoretical results.     

Improvement of <Emphasis Type="Italic">n</Emphasis>-ZnO/<Emphasis Type="Italic">p</Emphasis>-Si photodiodes by embedding of silver nanoparticles

The photo-current of n-ZnO/p-Si heterojunction photodiodes was improved by embedding Ag nanoparticles in the interface (ZnO/nano-P_Ag/p-Si), and the ratio between photo- and dark-current increased by about three orders more than that of a n-ZnO/p-Si specimen. The improvement in the photo-current resulted from the light scattering of embedded Ag nanoparticles. The I–V curve of n-ZnO/p-Si degraded after thermal treatment (A-ZnO/p-Si) because the silicon robbed the oxygen from ZnO to form amorphous silicon dioxide and left an oxygen vacancy. Notably, the properties of ZnO/nano-P_Ag/p-Si were better in the time-dependent photoresponse under 10 V bias. Ag nanoparticles (15–20 nm) scattered the UV light randomly and increased the probability for the absorption of ZnO to enhance the properties of the photodiode.     

Improvement of water and oil repellency on wood substrates by using fluorinated silica nanocoating

We have investigated a one-step fabrication of fluoro-containing silica coating on wooden substrates, showing multi-functions including super repellency toward water and sunflower oil, low sliding angles, good durability, and low adsorption capacity of moisture. The repellent slurry, consisting of well-mixing silica nanospheres and perfluoroalkyl methacrylic copolymer, is simply prepared and subsequently sprayed over wooden substrates with good adhesion. It has shown that the decoration of silica nanospheres on microscaled wooden texture acts as a crucial role in improving the repellency toward water and sunflower oil droplets. The maximal contact angles can reach as high as 168.3° and 153.6° for water and sunflower oil drops, respectively. These analyses of wetted fraction and work of adhesion also demonstrate the improved repellency due to the addition of silica. This improvement of the repellencies is ascribed to the fact that the drops partially sit on F-coated silica spheres, leaving a layer of air underneath the droplet (i.e., Cassie state). On the basis of the results, the multi-functional coating on wooden substrates delivers a promising commercial feasibility on a variety of woodworks.     

Effects of post-annealing on the structural and nanomechanical properties of Ga-doped ZnO thin films deposited on glass substrate by rf-magnetron sputtering

In this study, the effects of post-annealing on the structure, surface morphology and nanomechanical properties of ZnO thin films doped with a nominal concentration of 3 at.% Ga (ZnO:Ga) are investigated using X-ray diffraction (XRD), atomic force microscopy (AFM) and scanning electron microscopy (SEM) and nanoindentation techniques. The ZnO:Ga thin films were deposited on the glass substrates at room temperature by radio frequency magnetron sputtering. Results revealed that the as-deposited ZnO:Ga thin films were polycrystalline albeit the low deposition temperature. Post-annealing carried out at 300, 400 and 500 °C, respectively, has resulted in progressive increase in both the average grain size and the surface roughness of the ZnO:Ga thin film, in addition to the improved thin films crystallinity. Moreover, the hardness and Young's modulus of ZnO:Ga thin films are measured by a Berkovich nanoindenter operated with the continuous contact stiffness measurements (CSM) option. The hardness and Young's modulus of ZnO:Ga thin films increased as the annealing temperature increased from 300 to 500 °C, with the best results being obtained at 500 °C.     

Influence of anisotropic dipole matrix element on optical response of AB-stacked graphene superlattice

When the polarization direction of the laser beam ê lies on the graphene plane, the absorption spectrum A(ω)is isotropic and includes one sharp peak and some shoulders. As for ê along the stacking direction, A(ω) is much weaker, and shows only one broadened peak. Because of the dipole matrix element M(cv), the optical excitations do not fully reflect the features of electronic structures [or the joint density of states (JDOS)]. M(cv) plays an important role in the relationship between A(ω) and JDOS. It is strongly dependent on ê, showing an anisotropic property.     

Resolving band-structure evolution and defect-induced states of single conjugated oligomers by scanning tunneling microscopy and tight-binding calculations

We study single conjugated polyphenylene oligomers consisting of 3n (2 ≤ n ≤ 12) phenyl units by means of cryogenic scanning tunneling microscopy and spectroscopy. The spatially resolved local densities of states reveal a progressive development of a continuous conduction band out of discrete molecular orbitals as the length of the oligomers increases. The experimental results are satisfactorily described by tight-binding calculations which gave a conduction band bandwidth of 4.5 ± 0.2 eV and a band gap of 3.1 ± 0.2 eV for an infinitely long polymer. We observed two types of defects, known as conformational torsional angle misfit and metasite kink. Tight-binding as well as density-functional theory model calculations confirm that both types of defects effectively destroy the delocalization.     

An improved planar-gate triode with CNTs field emitters by electrophoretic deposition

An improved planar-gate triode with carbon nanotubes (CNTs) field emitters has been successfully fabricated by conventional photolithography, screen printing and electrophoretic deposition (EPD). In this structure, cathode electrodes and ITO arrays linked with gate electrodes were interdigitated and paralleled on the same plane although the gate electrodes and cathode electrodes were isolated by dielectric layer, a so-called improved planar-gate triode structure. An electrophoretic process was developed to selectively deposit CNTs field emitters onto cathode electrodes in the CNTs suspension by an applied voltage between the gate electrodes and cathode electrodes. The optical microscopy and FESEM image showed that the CNTs emitters with the uniform packing density were selectively defined onto the cathode electrodes. In addition, field emission characteristics of an improved planar-gate triode with CNTs field emitters were investigated. The experiment results indicated that the turn-on voltage of this triode structure at current density of 1 μA/cm² was approximately 55 V. The anode current and gate current came to 396 μA and 325 μA, at gate voltage and anode voltage of 100 V and 4000 V, respectively and at the anode-cathode spacing of 2000 μm. The emission image became brighter and the luminous image with dot matrix on the anode plate obviously increased with the increase of the gate voltage. Moreover, the emission current fluctuation was smaller than 5% for 11 h, which indicated that the improved planar-gate triode has a good field emission performance and long lifetime.