Synthesis optimization and characterization of multiwalled carbon nanotubes

The unique properties of carbon nanotubes (CNTs) have suggested applications in a variety of fields. Multiwalled nanotubes were synthesized using chemical vapor deposition (CVD) procedures and subsequently characterized. Reaction parameters such as catalyst type and carrier gas flow rate were optimized to produce well-aligned multiwalled nanotubes with lengths between a few microns to several millimeters. Characterization was performed with scanning electron microscopy (SEM), transmission electron microscopy (TEM), x-ray diffraction (XRD), energy dispersive x-ray spectroscopy (EDS), thermo-gravimetric analysis, and Raman spectroscopy, focusing on composition and purity. Results show the synthesis of high-purity nanotubes of several millimeters in length from iron, nickel, cobalt, and titanium carbide catalysts with thermal stability to above 550°C.     

Planar optical waveguides prepared in GIL49 and BK7 glass substrates by K+-Na+ ion exchange with the electric field assistance

This report focuses on research into waveguides prepared by K⁺-Na⁺ ion exchange with the help of an electric field, and the subsequent comparison with waveguides prepared by pure thermal ion exchange. The goals of this work were to determine the characteristics of and to address the technological problems associated with waveguides prepared in two types of highly pure optical glass: special soda-lime silica GIL49 glass produced from pure raw materials and commercially prepared borosilicate BK7 glass. An appropriate chemical mixture, KNO₃:Ca(NO₃)₂ in the molar ratio of 41:59, was used as the source of potassium ions. Experiments were conducted at temperatures between 250 and 410°C, and electric field values between 0 and 150 V/mm. The number of modes, depth, profile, and the change in refractive index (Δn) were measured for samples from each type of glass under various technological conditions. All of these parameters can be controlled accurately and repeatedly by the electric field. These experiments have also shown that a particular advantage of these types of pure glass is the low waveguide optical losses (0.1 to 0.2 dB/cm) attainable.     

Combined use of three-dimensional X-ray diffraction imaging and micro-Raman spectroscopy for the non-destructive evaluation of plasma arc induced damage on silicon wafers

The practicality of plasma etching, combined with low temperature and directional process capabilities make it an integral part of the IC manufacturing process. A significant cause of damage to wafers during plasma processing is arcing damage. Plasma arcing damage results in large pits and non-uniformities on the wafer surface which can lead to wafer breakage and high yield losses.Thus a non-destructive wafer damage metrology is crucial to the understanding of wafer failure mechanisms. We report on the successful use of a combined suite of non-destructive metrology techniques to locate the arc damage sites and examine the physical processes which have occurred as a result of the damage. These consist of 3D X-ray diffraction imaging (3D-XRDI), micro-Raman spectroscopy (μRS), and scanning electron microscopy (SEM).In the case of the two examples examined in this study the plasma induced damage on the wafer surface appears as regions of damage ranging from 100 μm to 1000 μm in diameter. 3D-XRDI shows that the strain fields propagate out from the damage site in all directions, with the damage penetrating up to ? of the way through the substrate. K-means clustering and false colouring algorithms are used to highlight the regions of interest in 3D-XRDI, and to enhance the analysis process. Sectioning of the 3D images has enabled non-destructive imaging of the internal damage in the samples at any location. Micro-Raman spectroscopy results indicate the presence of both crystalline and amorphous silicon. Strain measurements at the damage site show tensile strains as high as 500 MPa in certain situations, with strain levels increasing from the surface towards the bottom of the dislocation cell structures, which can be distinguished in the synchrotron X-ray topographs. 3D-XRDI and μRS results are in close correlation, proving the potential for 3D-XRDI as non-contact, non-destructive metrology particularly suited to these problems.     

In vivo electrochemical impedance measurement on single cell membrane

The electrochemical characteristics of the plasma membranes of single cells and organelles were investigated. Silicon fabrication technology was used to produce a metal ultra-microelectrode (UME). Furthermore, the UME was characterized in a cell medium using electrochemical impedance spectroscopy (EIS). A single rat fibroblast cell, or chloroplast purified from Peperomia metallica leaves, was immobilized by a micropipette after which the UME was inserted into its cytosolic space through cell membrane using a piezo actuator. An in vivo EIS measurement between the UME and the counter electrode outside of a single cell was taken. The measurements were analyzed using equivalent circuits in order to estimate the membrane impedance of a single cell.     

Electrical property dependence on thickness and morphology of nanocrystalline diamond thin films

In this study, we investigate the influence of nanocrystalline diamond (NCD) thin film morphology and thickness on their electrical properties. NCD films are grown on p-type Si substrates with varied thicknesses from 250 to 788 nm. Electrical contacts are formed from combination of Ti/Au metal layers (100 nm thick each). The I-V and breakdown field measurements are used to analyze the electrical properties of metal/NCD/Si sandwich structure. In addition, NCD films are analyzed by scanning electron microscopy and Raman spectroscopy for better interpretation of the I-V measurements.     

Negative giant surface potential of vacuum-evaporated tris(7-propyl-8-hydroxyquinolinolato) aluminum(III) [Al(7-Prq)3] film

Negative giant surface potential was realized in a vacuum-evaporated film of tris(7-propyl-8-hydroxyquinolinolato) aluminum(III) [Al(7-Prq)₃]. Electroabsorption response of the film presented an inverted polarity to that of tris(8-hydroxyquinolinolato) aluminum (Alq₃), suggesting opposite noncentrosymmetry of molecular orientation. Asymmetric dice model with molecular geometric effect has been proposed, and propyl substitution at 7 position of the ligands was indicated to affects the molecular posture on the surface to invert the polarity of noncentrosymmetry. Our results opened a new possibility of controlling molecular orientation in a film for device applications.     

基于空芯带隙型光子晶体光纤的单端置入式同源甲烷检测仪

为了提高复杂环境中甲烷气体探测的适用性,选择空芯带隙型光子晶体光纤(单端镀全反膜)作为光学气室,实现了置入式同源甲烷浓度的探测。采用可调谐半导体激光吸收光谱(TDLAS)技术,结合长度为0.5 m的空芯带隙型光子晶体光纤,实现了甲烷气体的在线测量,系统的检测下限可达到1.92×10^-5,稳定性波动小于±2.18%。单端全反射设计配合同源探测方式使复杂环境中的甲烷浓度的置入式探测成为可能,为单光源分布式探测提供了研究基础。     

Accurate Whole-Chip Diagnostic Strategy for Scan Designs with Multiple Faults

Fault diagnosis of full-scan designs has been progressed significantly. However, most existing techniques are aimed at a logic block with a single fault. Strategies on top of these block-level techniques are needed in order to successfully diagnose a large chip with multiple faults. In this paper, we present such a strategy. Our strategy is effective in identifying more than one fault accurately. It proceeds in two phases. In the first phase we concentrate on the identification of the so-called structurally independent faults based on a concept referred to as word-level prime candidate, while in the second phase we further trace the locations of the more elusive structural dependent faults. Experimental results show that this strategy is able to find 3 to 4 faults within 10 signal inspections for three real-life designs randomly injected with 5 node-type or stuck-at faults. Part of this work has ever appeared in the proceedings of Asian Test Symposium in 2003. Yu-Chiun Lin received his BS degrees in Electrical Engineering from National Central University in 2000, and MS degree from Electrical Engineering of National Tsing Hua University in 2002. Since then, he has been with Ali Corporation as a design engineer. His current interests include the design of USB controllers and imaging periperals. Shi-Yu Huang received his BS, MS degrees in Electrical Engineering from National Taiwan University in 1988, 1992 and Ph.D. degree in Electrical and Computer Engineering from the University of California, Santa Barbara in 1997, respectively. From 1997 to 1998 he was a software engineer at National Semiconductor Corp., Santa Clara, investigating the System-On-Chip design methodology. From 1998 to 1999, he was with Worldwide Semiconductor Manufacturing Corp., designing the high-speed Built-In Self-Test circuits for memories. He joined the faculty of National Tsing-Hua University, Taiwan, in 1999, where he is currently an Associate Professor. Dr. Huang’s research interests include CMOS image sensor design, low-power memory design, power estimation, and fault diagnosis methodologies.     

Study of defect levels in CdTe using thermoelectric effect spectroscopy

We have studied the defect levels in as grown and post growth processed cadmium telluride (CdTe) using thermoelectric effect spectroscopy (TEES) and thermally stimulated current (TSC) techniques. We have extracted the thermal energy (E_th) and trapping cross section (σ_th) for the defect levels using the initial rise and variable heating rate methods. We have identified 10 different defect levels in the crystals. Thermal ionization energy values obtained experimentally were compared to theoretical values of the transition-energy levels of intrinsic and extrinsic defects and defect complexes in CdTe determined by first-principles band-structure calculations. On the basis of this comparison, we have associated the observed ionization levels with various native defects and impurity complexes.     

Photocatalytic reduction of chromate oxyanions on MMnFe2O4 (M=Zn,Cd) nanoparticles

Spinel M_xMn_1−xFe₂O₄ ferrites (M=Zn or Cd) synthesized via the co-precipitation method were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), diffuse reflectance UV–vis and Mössbauer spectroscopy. MnFe₂O₄ exhibited mainly cubic structure when Cd was incorporated, whereas the Zn incorporation stimulated a mixed phase consisting of MnFe₂O₄ and ZnMnFe₂O₄. The IR spectra of both Cd- and Zn modified MnFe₂O₄ samples revealed vibration of the chemical bond Fe²⁺O²⁻ in A location of the tetrahedron which infers that dopants were uniformly distributed over the system. The optical band gap energy showed large variations; a smaller value was determined for Cd_0.2Mn_0.8Fe₂O₄ (1.46 eV) when compared with those of MnFe₂O₄ (2.16 eV) and Zn_0.2Mn_0.8Fe₂O₄ (2.8 eV). The analysis of Mössbauer spectra gave inversion values of Fe³⁺ distribution in tetrahedral coordinated sites of 24%, 57% and 65% in MnFe₂O₄, Zn_0.2Mn_0.8Fe₂O₄ and Cd_0.2Mn_0.8Fe₂O₄, respectively. It was found that Cd_0.2Mn_0.8Fe₂O₄ exhibited the best performance in the photocatalytic reduction of Cr(VI) to Cr(III) having a maximum value of 96% within 30 min, and the experimental data obeyed pseudo-second-order rate kinetic model. Also, the linear model of Langmuir attained a maximum adsorption capacity of 37 mg g⁻¹ for Cd_0.2Mn_0.8Fe₂O₄.