Key Engineering Materials Vols. 562-565

Abstract: SOI Ridge nanowire waveguide (RNW) has advantages of strong confinement of optical mode, low propagation loss, small bend radius and fully compatible with CMOS technique, etc. An ultra-compact Y-branch coupler based on SOI RNW was designed and fabricated. Based on the finite-difference beam propagation method (FD-BPM), key parameters of the coupler were analyzed. Then the device was fabricated by electron beam lithography (EBL) and inductively coupled plasma (ICP) reactive ion etching. Results showed that the propagation loss of RNW was 1.89 dB/mm, and the radiation loss of the coupler with branch angle of 30° was only 0.66 dB. Compared with traditional Y-branch coupler, the proposed structure were more promising for high density optical integrated circuits.

Abstract: In this paper, influence of nitrogen content on growth mode, surface morphology and the optical properties of copper nitride (Cu_xN) films was investigated. Cu_xN films were prepared on glass substrates by direct current (DC) magnetron sputtering at various nitrogen contents. X-ray diffraction (XRD), profilometer, atomic force microscope (AFM) and spectrophotometer were used to analyze the characteristics. The XRD measurements showed the films were composed of Cu and Cu₄N crystallites at working pressure with a low nitrogen content, while the structure of the films were conformed to anti-ReO₃ structure at a high nitrogen content and the preferred growth orientations of the Cu₃N films changed from (111) to (100). The transmittances of Cu_xN films increased with the increase of nitrogen content (r) in working gas flow from 0 to 0.6, while decreased when r increased from 0.6 to 0.9. Additionally, the lowest reflectivity and the maximum band gap of 1.35 eV for Cu_xN film were obtained at r = 0.6. The Cu_xN films deposited at various nitrogen contents have large differences on optical properties which provide a potential application in optical storage devices.

Abstract: Based on DFBLD (Distributed Feedback Laser Diode) and harmonic detection technique, a novel fiber-optic methane detection system is constructed. The system can be applied to broad-range concentration detection of methane. Based on the approximation express of the law of Beer-Lambert, detection of methane with various concentration from 0% to 20% is completed using subtraction of background and ratio processing method, as the atmosphere surroundings are treated as background noise. The direct absorption spectra for various concentration is measured using GRIN gas cell, combined with DFBLD. The R5 line of the 2v3 band of methane is selected as the absorption peak. The system is tested online during gas mixing process and the linear relationship between system indication and concentration variation is validated. Also the stability and dynamic response characteristics are confirmed by the experiments. The sensitivity of the system can be adjusted according to the concentration level of various field environments by changing the prism distance using step motor. In the range of 0% to 20% the sensitivity of methane detection can arrive at 0.001%. So the system can be applied to various application fields and adopted as monitoring instruments for coalmine tunnel and natural pipeline.

Abstract: This paper presents method and performance of the photoacoustic resonant cell remodified from Helmholtz cavity that can be used to detect photoacoustic signal of multi-gas. This technique has its physical basis in a phenomenon called the photoacoustic effect. The experiment system is composed of a resonant Helmholtz cavity, a sensitive microphone and two infrared lasers with high adsorption capability and specificity to the analyte. In our experiments, the average optical power at the laser operating point is 200mW for the 972nm laser (H₂O detection) and 800mW for the10.653um laser (CO₂ detection), which are modulated at two different frequencies f1=175Hz and f2=125Hz. The remodified Helmholtz resonant on-line and real time measurement of the water vapour (300ppm) and carbodioxide (300ppm) conducted at their respective resonant frequency shown large signals about 4.41mV and 19.77mV respectively. The result demonstrated this cell used to test multi-gas is also feasible.

Abstract: In the laser interferometer system based on the four quadrants photoelectric, phase difference between two quadrants photoelectric is the way of identifying the fringe width and rotating angle, in order to achieving the measurement of two-dimensional small angle. Due to the temperature instability of the laser itself, the system installation error, the electronic device noise, and wave-front error etc, interference fringes prone to bending, and the received optical signal contains unequal amplitude and DC offset error, which will have a serious impact on measurement. Therefore, this paper analysis these impact of the wave-front error on the interferometer system and propose improvement measures. New hardware circuit is designed to eliminate the DC offset and the new algorithm based on multiple linear regression models is proposed to achieve the high-precision extraction of phase difference. The experiment results show that the methods reach the angle accuracy 0.1 arc second.

Abstract: Small grain X zeolite molecular sieve was synthesized using calcined kaolin and sodium hydroxide directly and crystallization for 3.5h without template agents，directing agents and seed. The products were characterized using the transmission electron microscopy (TEM) and x-ray diffraction (XRD) analysis. TEM observed that the small grains in 70-80 nm size were well distributed. The hydrothermal crystallization products was X zeolite with complete crystal analysised by XRD. Fourier transform infrared spectroscopy (FTIR) characterization showed that the basic structural unit of component in the solid phase of calcined kaolin and X zeolite had no significant change. After an induction phase of calcined kaolin in the hydrothermal system, large numbers of Nanocrystalline of X zeolite molecular sieve were formed and became the growth unit. And then it has turned into the main structure growth mechanism of the X zeolite. Therefore, rearrangement of crystal phase rotating is believed to be the mechanism of calcined kaolin synthetizing X zeolite.

Abstract: Three-dimensional analysis of the effects of atom beam divergence angle on the process of fabricating nanograting is discussed based on the three-dimensional motion model of Cr atoms in Gaussian standing wave laser field. From the simulative results it can be seen that Atomic beam spreading plays an important role in determining the deposition nanometer quality, so the preparation of a high-collimated and transversely cooled atomic beam, typically under 0.6mrad, is essential to minimize the severely disadvantageous effects for deposition of atoms in laser standing wave

Abstract: A novel method to prepare TiO₂-coated Ag nanowire arrays for use as surface enhanced Raman scattering (SERS) active substrate is studied. First, Ag nanowires with an average diameter of 60 nm and length of several μm were synthesized in an anodic aluminum oxide (AAO) template by direct electrodeposition into the template. Then TiO₂ thin layers with a 20 nm thickness were coated on Ag nanoarrays in large scale by a hydrolysis approach of tetrabutyl titanate. The SERS substrates prepared by this strategy have been proved as excellent candidates for the detection of organic pollutants by enhancing the SERS signals of these target species. The detection limit of methyl-parathion (MP) can be reduced to 10^-6 M.

Abstract: Currently, most wireless sensor networks (WSNs) are powered by batteries. When energy stored in batteries is exhausted, the life of the WSNs goes to the end. The concept of energy harvesting provides a practical solution to the problem of the energy limitation. In this article, the feasibility and performance of a simple and low-cost analog solar energy harvesting circuit with the function of maximum power point tracking (MPPT) are investigated. The technique provided is based on the approximately linear relationship between the maximum power point (MPP) voltage and the open-circuit voltage of a solar panel under different irradiation levels. Several experiments have been carried out regarding the accuracy and efficiency of MPPT as well as the working process of the circuit. Results show that the maximum power point with different loads can be effectively tracked by the self-powered MPPT circuit, and in the meantime, a stable output voltage can be generated. The efficiency of energy conversion is guaranteed by a commercial off-the-shelf DC-DC chip. The detailed description of the circuit design and the comprehensive analysis of the circuit performance will provide a useful guide for the future applications.

Abstract: A micro piezoelectric cantilever beam array is designed for vibration energy harvesting. A single degree of freedom analytical model is developed to predict the properties of the device and is verified by finite element method. The piezoelectric material Aluminum Nitride was chosen for the compatibility with the CMOS process. The devices consisting of 5 piezoelectric cantilever beams and one proof mass were fabricated using micromachining technology. The resonance frequency, voltage and power were tested at excitation acceleration of 5.0 g. The maximum output power of the device is 9.13 μW at the resonance frequency of 1315 Hz when piezoelectric beams are connected in parallel.