Nov 2015, Volume 8 Issue 4

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    Wei XIONG,Yunshen ZHOU,Wenjia HOU,Lijia JIANG,Masoud MAHJOURI-SAMANI,Jongbok PARK,Xiangnan HE,Yang GAO,Lisha FAN,Tommaso BALDACCHINI,Jean-Francois SILVAIN,Yongfeng LU

    Advanced micro/nanofabrication of functional materials and structures with various dimensions represents a key research topic in modern nanoscience and technology and becomes critically important for numerous emerging technologies such as nanoelectronics, nanophotonics and micro/nanoelectromechanical systems. This review systematically explores the non-conventional material processing approaches in fabricating nanomaterials and micro/nanostructures of various dimensions which are challenging to be fabricated via conventional approaches. Research efforts are focused on laser-based techniques for the growth and fabrication of one-dimensional (1D), two-dimensional (2D) and three-dimensional (3D) nanomaterials and micro/nanostructures. The following research topics are covered, including: 1) laser-assisted chemical vapor deposition (CVD) for highly efficient growth and integration of 1D nanomaterial of carbon nanotubes (CNTs), 2) laser direct writing (LDW) of graphene ribbons under ambient conditions, and 3) LDW of 3D micro/nanostructures via additive and subtractive processes. Comparing with the conventional fabrication methods, the laser-based methods exhibit several unique advantages in the micro/nanofabrication of advanced functional materials and structures. For the 1D CNT growth, the laser-assisted CVD process can realize both rapid material synthesis and tight control of growth location and orientation of CNTs due to the highly intense energy delivery and laser-induced optical near-field effects. For the 2D graphene synthesis and patterning, room-temperature and open-air fabrication of large-scale graphene patterns on dielectric surface has been successfully realized by a LDW process. For the 3D micro/nanofabrication, the combination of additive two-photon polymerization (TPP) and subtractive multi-photon ablation (MPA) processes enables the fabrication of arbitrary complex 3D micro/nanostructures which are challenging for conventional fabrication methods. Considering the numerous unique advantages of laser-based techniques, the laser-based micro/nanofabrication is expected to play a more and more important role in the fabrication of advanced functional micro/nano-devices.

    Kun LI,Weiwei QIN,Yan XU,Tianhuan PENG,Di LI

    Studying the activity of individual nanocatalysts, especially with high spatiotemporal resolution of single-molecule and single-turnover scale, is essential for the understanding of catalytic mechanism and the designing of effective catalysts. Several approaches have been developed to monitor the catalytic reaction on single catalysts. In this review, we summarized the updated progresses of several new spectroscopic and microscopic approaches, including single-molecule fluorescence microscopy, surface-enhanced Raman spectroscopy, surface plasmon resonance microscopy and X-ray microscopy, for the study of single-molecule and single-particle catalysis.

    Ming LUO,Qi MO,Xiang LI,Rong HU,Ying QIU,Cai LI,Zhijian LIU,Wu LIU,Huang YU,Wei DU,Jing XU,Zhixue HE,Qi YANG,Shaohua YU

    A few-mode fiber (FMF) is designed to support three spatial modes (LP01, LP11a, and LP11b) and fabricated through plasma chemical vapor deposition (PCVD)and rod-in-tube (RIT) method. Using PDM-DFTS-OFDM-32QAM modulation, wavelength division multiplexing, mode multiplexing, and coherent detection, we successfully demonstrated 200 Tb/s (375 × 3 × 178.125 Gb/s) signal over 1 km FMF using C and L bands with 25 GHz channel spacing. After 1 km FMF transmission, all the tested bit error rates (BERs) are below 20% forward error correction (FEC) threshold (2.0 × 10−2). Within each sub-channel, we achieved a spectral efficiency of 21.375 bits/Hz in the C and L bands.

    Xu YE,Haobo CHENG,Zhichao DONG,Hon-Yuen TAM

    Three-dimensional (3D) profile measurement is an indispensable process for assisting the manufacture of various optic, especially aspheric surfaces. This work presents the measurement error calibration of a 3D profile measurement system, namely PMI700. Measurement errors induced by measuring tool radius, alignment error and the temperature variation were analyzed through geometry analysis and simulation. A quantitative method for the compensation of tool radius and an alignment error compensation model based on the least square method were proposed to reduce the measurement error. To verify the feasibility of PMI700, a plane and a non-uniform hyperboloidal mirror were measured by PMI700 and interferometer, respectively. The data provided by two systems were high coincident. The direct subtractions of results from two systems indicate RMS deviations for both segments were less than 0.2λ.

    Jianguo YUAN,Yantao YUAN,Feilong LIU,Yu PANG,Jinzhao LIN

    To solve the large noise problem for the low-precision gyroscopes in micro-electro mechanical systems (MEMS) of inertial navigation system, an improved noise reduction method, based on the analyses of the fast Fourier transformation (FFT) noise reduction principle and the simple wavelet noise reduction principle, was proposed. Furthermore, the FFT noise reduction method, the simple wavelet noise reduction method and the improved noise reduction method were comparatively analyzed and experimentally verified in the case of the constant rate and dynamic rate. The experimental analysis results showed that the improved noise reduction method had a very good result in the noise reduction of the gyroscope data at different frequencies, and its performance was superior to those of the FFT noise reduction method and the simple wavelet noise reduction method.

    Binbing LIU,Haiqing CHEN

    No-reference quality assessment aims at designing objective assessment criteria consistent to subjective perceived quality without any knowledge about reference image. This paper proposes a no-reference quality assessment algorithm specific to JPEG images. Blocking artifact in JPEG images is caused by the block based quantization of frequency coefficients, which is equivalent to applying low pass filtering in each block. In view of this idea, the algorithm in this paper was used to realize the quality assessment of JPEG images by quantizing the difference of power spectrum distribution between inner-block and inter-block. The assessment method proposed in this paper owns low algorithm complexity, clear physical meanings, free from learning and training and other advantages. Compared with most presented algorithms, the assessment results of proposed algorithm demonstrate a higher correlation to the subjective perceived quality.

    M. Venkata SUDHAKAR,Y. Mallikarjuna REDDY,B. Prabhakara RAO

    This paper presents the design and analysis of optical filters that are placed at the output of directly modulated vertical cavity surface emitting laser (VCSEL) in the process of inexpensive transmitter’s implementation for upcoming generation optical access network. Generation of non return to zero (NRZ) optical signal from the transmitter for 110 km error-free single mode fiber (SMF) transmission at 10 Gb/s with bit error rate (BER) of 10−30 in the absence of the external modulator and encoder was proposed. Effects of super-Gaussian and Butterworth optical filters at VCSEL output were demonstrated to maximize performance of SMF optical systems without need of any dispersion compensation technique.

    Lili MAO,Qizhen SUN,Ping LU,Zefeng LAO,Deming LIU

    A new in-line Mach-Zehnder interferometer (MZI) sensor consisting of a stub of multi-mode fiber and an up-taper was proposed and demonstrated. Temperature measurement can be carried out by detecting wavelength shift. Dependency of sensitivity on interferometer length and dip wavelength was discussed. Experimental results showed a maximum temperature sensitivity of 113.6 pm/°C can be achieved, which is superior to most fiber temperature sensors based on in-line MZIs within the range from 20°C to 80°C, also a good mechanical strength can be obtained. The proposed sensor is a good candidate for temperature measurement, due to the advantages of simple structure, easy fabrication, cost-effective and high sensitivity.

    Liping ZHU,Kai XU,Yanping WANG,Jiangshan CHEN,Dongge MA

    High efficient yellow organic light emitting diodes (OLEDs) based on exciplex were reported. The exciplex was formed by 4, 4′, 4′′-tris [3-methylphenyl (phenyl) amino]-triphenylamine (m-MTDATA) and 4, 7-diphenyl-1, 10-phenanthroline (BPhen). The resulting yellow OLEDs exhibited an external quantum efficiency of over 7%, which is attributed to the effective energy back transfer from exciplex triplet state to exciplex singlet state. The maximum power efficiency of 25 lm/W was achieved. Doping a yellow phosphor Ir(bt)2(acac) into m-MTDATA:BPhen blend, a high efficiency device was achieved with a turn-on voltage of 2.1 V, maximum power efficiency and external quantum efficiency of 86.1 lm/W and 20.7%, respectively.

    Xiaoyue LI,Sheng YIN,Dong XU

    In this paper, ATLAS 2D device simulator of SILVACO was used for device simulation of inverted-staggered thin film transistor using amorphous indium gallium zinc oxide as active layer (a-IGZO-TFT) with double active layers, based on the density of states (DOS) model of amorphous material. The change of device performance induced by the thickness variation of each active layer was studied, and the interface between double active layers was analyzed. The best performance was found when the interface was near the edge of the channel, by optimizing the thickness of each active layers, the high performance device of threshold voltage (Vth) = −0.89 V, sub-threshold swing (SS)= 0.27, on/off current ratio (ION/IOFF) = 6.98 × 1014 was obtained.

    Yuxiang WU,Tao SONG,Guodong XU

    The sport performance of swimming athletes in three different levels including 5 national high-level swimming athletes, 5 ordinary swimming athletes and 5 college students was investigated by near-infrared spectroscopy (NIRS). Four parameters of muscle oxygenation and blood lactate (BLa) concentration were simultaneously monitored during incremental exercise on the ergometer. It was found that inflection points of muscle oxygenation and BLa concentration were consistent with the human sport capacity. Moreover, inflection points of muscle oxygenation occurred earlier than those of BLa concentration in ordinary athletes and college students. It implies monitoring changes of muscle oxygenation is superior to BLa measurement under this condition, since BLa test has an unavoidable time lag. Significant correlation (r2 = 0.948; P<0.05) was observed between inflection points of muscle oxygenation difference and inflection points of BLa concentration on workload. This relationship suggests changes of muscle oxygenation detected by NIRS is beneficial to the evaluation of athletes’ physiologic function and training load. Considering that muscle oxygenation could be in-vivo and non-invasively measured by NIRS, it may be a better indicator of exercise intensity than BLa measurement in the near future.

    Bo SHEN