Editor in chief：Jun-Hao CHU
International standard number：ISSN 1001-9014
Unified domestic issue：CN 31-1577
Domestic postal code：4-335
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Abstract:Colloidal Cu2CdSnS4 nanocrystals were synthesized by a facile solution chemistry method. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and UV-vis-NIR absorbance spectroscopy measurements indicated that the Cu2CdSnS4 colloidal nanocrystals have uniform size-distribution and good crystalline quality with a tetrahedral coordinated structure. The stoichiometric ratio Cu/Cd/Sn/S is about 2.07:0.75:1.26:3.92 in Cu2CdSnS4 nanocrystals, and the chemical states of Cu, Cd, Sn and S elements are of +1, +2, +4 and -2, which correspond with the states in the molecular formula of Cu2CdSnS4. The band gap of Cu2CdSnS4 nanocrystals is estimated to be ~1.3 eV by extrapolating method.
Abstract:The effect of CH4 flow rate on the structural and optical properties of boron-doped amorphous silicon carbon films as window p-layer in the industrial hydrogenated amorphous silicon solar module was investigated. The p-layer amorphous hydrogenated silicon carbon films were deposited from SiH4-CH4 gas mixtures in the Applied Materials SUNFAB radio frequency-plasma enhanced chemical vapor deposition Gen8.5 system with dimensions of 2.2 m 2.6 m. Infrared and transmittance/reflectance spectra were employed to analyze the bond configurations and optical properties of the films associating with structures of the p-layer films which are sensitive to the deposition condition. The optical band gap of the p-layer films increased as the CH4 flow rate ranged from 3000 sccm to 8850 sccm with other deposition conditions unchanged. With increasing CH4 flow rate, the deposition rate of p-layer amorphous silicon carbon films decreased slowly, because of the reduction of SiH3 radical in the SiH4-CH4 plasmas. The uniformity of the hydrogenated amorphous silicon carbon films was also investigated, by sampling and analyzing the deposition rate on four different locations of the large area films.
Abstract:Back-illuminated 640×1 linear InGaAs detector arrays were fabricated on the In0.78Al0.22As/In0.78Ga0.22As material of N-on-P configuration by the inductively coupled plasma (ICP) etching. The photoelectric characteristics of the detector were investigated. The results indicated that the cutoff-wavelength and peak-wavelength are 2.36 μm and 1.92 μm, respectively, at room temperature. The average value of R0A is 16.0 Ω·cm2 and the quantum efficiency of the peak wavelength reaches to 37.5%. Otherwise, the average peak detectivity of linear detector array reaches to 2.01×1011 cmHz1/2/W, the response nonuniformity is about 8.77% and the defective pixel ratio is 0.6% for 1 ms of integrate time.
Abstract:The properties of As-doped HgCdTe epilayers grown by Te-rich LPE were investigated. The Hall measurements showed that the electrical parameters varied greatly with the samples even though they were grown under the same conditions. If the epilayers are assumed homogeneous, Hall parameters cannot be interpreted well theoretically. By using the secondary ion mass spectrometry (SIMS) and temperature dependent Hall measurements, the accumulation of arsenic atoms was observed on the surface of the HgCdTe epilayers after the Hg-rich activation annealing at high temperature. The arsenic atom concentration of the accumulation layer is 1~2 orders of magnitude higher than that inside, which introduced a nonuniform distribution of acceptor AsTe in HgCdTe epilayer. Based on the characteristic of arsenic atom distribution, a simplified double layer model was applied to describe the distribution of the acceptor in HgCdTe epilayer. Hall parameters of the epilayers can be explained well by using the above method. The concentration and activation energy of acceptor are obtained.
Abstract:The Nd doped BiFeO3 thin films are prepared on LaNiO3/Si (100) substrate by chemical solution deposition method. The results of x-ray diffraction show that the lattice constant of thin films decreases with the increase of Nd content. The impurity phases are found in the thin film with 20% Nd content. The results of dielectric measurement indicate that the dielectric constant and loss of thin films decrease with the increase of Nd content. A very strong dielectric frequency dispersion and relaxation of dielectric loss peak occurs in the thin film with 2% Nd content and it follows Debye-like law. The leakage current of thin films decreases with the increase of Nd content. The current transport follows SCLC model in low electric field region and follows Poole-Frenkel model in high electric field region. These results suggest that Nd doping has a strong influence on microstructure and electric properties of BiFeO3 thin films.
Abstract:The results of high-density hydrogen plasma modification for HgCdTe long-wavelength n+-on-p photodiode arrays were presented in this paper. n+-on-p HgCdTe long-wavelength photodiode arrays with photodiode modified by hydrogen plasma immediately after B+-implantation were fabricated from a Hg1-xCdxTe/CdTe film grown by MBE. The maximum values of the dynamic resistance of the photodiodes in the arrays treated by hydrogen plasma were increased by one to two times compared with those of diodes without modification. The dynamic resistances of the diodes at larger reverse biases away from the maximum point of dynamic resistances were increased more significantly. Thus, it is obvious that hydrogen plasma modification was beneficial to the uniformity of operation dynamic range and detection performance of HgCdTe long-wavelength photodiode arrays because it can suppress the band-to-band tunneling currents and the trap-assisted tunneling currents in the diode.
Abstract:The effects of the incident wave polarization on the boresight error induced by the radome of a Ka-band monopulse antenna-radome system were analyzed. The boresight errors in the scanning space are determined by the ray tracing method. The results indicate that the in-plane boresight errors of the radome are independent on the incident wave polarization, the cross-plane boresight errors are less dependent on it, and the boresight errors in the scanning angles away from the azimuth and elevation planes are very sensitive to the incident wave polarization. The counter maps of the boresight errors with different incident wave polarization angles were also plotted and it shows that the boresight errors are rotating slowly with the change of the incident wave polarization.
Abstract:The relationship between the filling factor and the circumcircle radius of the regular polygon scatter is deduced in a two-dimensional triangular lattice photonic crystal. The photonic band gaps (PBGs) are calculated with the plane wave expansion method in Ge-based two-dimensional triangular lattice photonic crystals. When Ge cylinder is placed in air background, the TM band gaps and TE band gaps appear with the TM band gaps dominating. As Ge filling factor increases, the width of the photonic band gaps increase initially but then decrease and the center frequency decrease. The width of the first band gap of the TM band gaps reaches the maximum at the radius of 0.14a. On the contrary, when air cylinder is placed in Ge background, the TM band gaps and TE band gaps as well as the complete band gaps appear with the TE band gaps dominating. With the air filling factor increasing, the width of the photonic band gaps also increase initially then decrease, whereas the center frequency increase. The width of the first band gap of TE band gaps and the largest complete band gap reaches the maximum at the radius of 0.46a and 0.49a, respectively.
Abstract:A shaped scheme based on geometric optics for offset fed dual reflector antenna is presented. A ray tube emerging from a symmetric feed horn is transformed, after reflections, into a circular beam with a uniform phased and a prescribed radial power distribution on the aperture. Snell’s law was imposed on the subreflector. Based on this design solution, theoretical analysis, numerical simulation and experimental test were carried out for a 110 cm dish baseline system with a angle of 20 degrees between X axis and the beam. The experiment shows that at 95 GHz, the antenna has a 78% aperture efficiency and the minor lobe meets a -19 dB criterion and the gain is 59.7dB.
Abstract:To suppress clutter in infrared image, a novel clutter suppression method based on adaptive subspace construction is proposed. An over-complete dictionary for modeling target is learned based on the sparse coding theory at first. Then the image patch is extracted from the test image in order . Representation coefficients are computed according to the dictionary. According to the difference in the representation coefficients of the target patch and the background patch in sparse domain, adaptive subspace is generated to reconstruct the image patch. Thus a residual image between original image patch and reconstructed patch is obtained. The experiment results show that the residual image obtained by the proposed method can effectively suppress background clutter and significantly improve signal-to-noise ratio of the infrared image.
Abstract:Normal tissues may be damaged due to the high temperature if heated by continuous microwave. We proposed that the temperature distribution of heated area inside the bio-tissues could be effectively controlled if the bio-tissues is radiated by pulse modulated microwave coded with computer. Infrared thermography was applied to image temperature distribution of sliced homogeneous simulating biomaterial. Effects of temperature distribution in heated area of bio-tissues were analyzed and discussed while duty cycle, power and frequency of pulse modulated microwave were changed. The results showed that raising the duty ratio and power, or changing frequency in certain range can make distinct heating effects in bio-tissues. It provides a new effective heating method for tumor hyperthermia.
Abstract:A novel low contrast IR image enhancement method based on multi-scale mirror-extended curvelet transform was proposed to solve the problems of the palm vein IR images, such as low SNR (Signal/Noise) and low grayscale contrast as the results of incorrect feature extraction of palm vein. Based on the analysis of the strong relationship between multi-scale curvelet coefficients and different scales of detailed vein features, coefficients of high frequency subbands, where most of the noises and few features located, were set zero. The coefficients of middle frequency subbands, where most of the features concentrated, were nonlinearly enhanced during the denoising process. The coefficients of low frequency subbands who determined the global grayscale contrast were stretched. Experimental results show that the proposed method can efficiently enhance the features of low contrast palm vein IR images with increased evaluation indexes such as SNR and Entropy. By this method the features of vein edges are better preserved and more smoothly emphasized than enhancement methods of biorthogonal wavelet and histogram equalization.
Abstract:This paper proposed an unsupervised technique for detecting changed areas between multitemporal SAR images. Different with the original ones, the clustering method was used here to find the change map by minimizing mean square error with evolution algorithm. After introducing the image character, a new search strategy in Memetic algorithm was given here, which adjusted the local search algorithm according to the current detection result. The approach was distribution free and did not need priori knowledge. The experimental results obtained on the real SAR images showed that the proposed method had a higher convergence speed than GA,ICSA and original MA, the detection results demonstrated the effectiveness of the proposed algorithm.
Abstract:The vectorial total variation model and algorithm are studied for multi-channel SAR image denoising. After introducing the vectorial total variation model, an accelerative fix-point iterative algorithm was proposed and its convergence was proved. By improving the filter coefficient of the fix-point iterative process, an adaptive vectorial total variation model was developed for multi-channel SAR image denoising, whose iterative algorithm and convergence theorem were present. The performance of denoising and resolution preservation of our models was tested by multi-polarimetric, multi-temporal RADARSAT-2 images, in addition to the validation of the convergence and the convergent speed of the proposed algorithms.
Abstract:The quality and error distribution of atmospheric motion vectors (AMVs) derived from the water vapor band of FY-2C meteorological satelite of China in 2009 were analysed. The results indicate that the errors of AMVs varies inhomogeneously in different climate zones, seasons, and vertical positions in space. Based on the thermal wind theory, we noticed that over estimation in the value of height may be the dominant origin of the AMVs errors. We verified the conjecture by reassigning the AMVs to new heights, with the NCEP/FNL reanalysis wind field as a reference. The quality of AMVs before and after reassignment was compared with the NCEP/FNL data and radiosonde observations of international exchange stations. It’s found that the negative biases of the U-winds of AMVs decrease explicitly from -9.73 ms-1 to -1.1 ms-1, the standard deviations of errors from 10.24 ms-1 to 4.5 ms-1, the quality of which is improved over 50%. The V-winds are also improved obviously. The seasonal errors of AMVs are removed well. All of the improvements justify the aforementioned viewpoints. This paper suggests a preliminary method which assigns the AMVs to reasonable heights with the reanalysed wind field of a NWP model as a reference, and also supplies an idea of detecting algorithm for AMVs producers.
Abstract:Spatial and temporal fusion of remote sensing data is a technology that can generate dense time series and high spatial resolution data whose spatial resolution is similar with high spatial resolution date, and temporal resolution is the same as the one with high temporal resolution data. This paper presented a new spatial and temporal data fusion model (STDFM) for blending Landsat and MODIS surface reflectance. Temporal change information was detected from sequence coarser resolution surface images, and new high resolution reflectance was predicted from former high resolution reflectance. This algorithm was tested in red and near-infrared MODIS and Landsat ETM+ images, and over a study area in Jiangning country, Nanjing, Jiangsu, China. Results showed that STDFM was able to produce images very similar with actual observed images. The correlation coefficient r between synthetic imageries and actual observations was 0.939. The correlation coefficient r between NDVI calculated by synthetic imageries and actual observations was 0.938.
Abstract:Developing automatic shallow water bottom topography detection algorithm is a key technique for coastal ocean monitoring. A new method was proposed to retrieve the orientation of shallow water bottom topography from SAR imagery, and the result was in accordance with SAR image characteristic. The feasibility and adaptability of using invariant moments to descript region of shallow water bottom topography were studied. We proved that this method can be used to detect a region with or without shallow water bottom topography. Finally, we proposed a shallow water bottom topography detection algorithm for SAR images based on average invariant moments and redefined distance of invariant moments with reasonable accuracy.
Abstract:After analyzing quantitatively the sensitivity of sea surface emissivity, sea surface wind, sea water salinity, atmospheric transmittance, and atmospheric upwellward/downward radiation on the sea surface temperature (SST) retrieval from a single channel physical-based SST algorithm, it was concluded that that sea surface emissivity and atmospheric transmittance have greater impact on the accuracy of SST retrieval than the others. Deriving SST with different single infrared channel (3.7 μm), we found that the mid-infrared single channel physical-based SST algorithm is less sensitive to the accuracy requirements of these input parameters than that based in thermal band (11 μm and 12 μm). The night-time MODIS data taken in the Gulf of Mexico around the year of 2009 was used to validate the feasibility and accuracy of this algorithm and the sensitivity analysis. The result shows that the single physical channel method based on mid-infrared band is the optimal choice in case only one infrared channel is available on the space instrument. Furthermore, the algorithm at mid-infrared band can help to derive the operational coefficients for traditional split-window algorithm.
Editor in chief：Jun-Hao CHU
International standard number：ISSN 1001-9014
Unified domestic issue：CN 31-1577
Domestic postal code：4-335