The abundant intrinsic point defects of ZnO are an important factor affecting its photoelectric performance. Identification and quantification of point defects is important both for the luminescent and optoelectronic applications, as well as for understanding the microscopic of spontaneous resistive switching behavior. As a shallow acceptor defect, zinc vacancy (VZn) plays an important role in ZnO photoluminescence, resistive switching, and electroluminescence. However, it is difficult to regulate the behavior of VZn defects, which leads to unclear effects on the photoelectric properties of ZnO. In this work, the effects of different VZn defect behaviors on the photoelectric properties of acceptor-rich ZnO (A-ZnO) microrod/tubes devices were studied by adjusting the concentration of VZn defects.
Three ortho-, meta-, and para-linked polymers derived from 9,9-dioctylfluorene (FO) and dimethoxyl-biphenyl (DMBP) were designed and synthesized via catalyst-transfer Suzuki coupling polymerization with palladium(0) catalyst as initiator. Compared to PFO, the conjugated polymers of PFO-o-DMBP, PFO-m-DMBP, and PFO-p-DMBP displayed a significantly blued-shifted absorption and emission spectra with the change of the connecting site from ortho-, meta- to para-position, and the varying degrees were ascribed to the different types of steric hindrance of ortho-, meta-, and para-linkage, which partly hinder the intermonomer rotation of the polymer backbone, giving rise to molecular configuration from linear, zigzag to intertwined structure, and resulting in shortened conjugation length. The optical bandgap calculated from the onset of absorption spectra of the three polymers in solid film are all wider than that of the PFO, indicating that the incorporating of dimethoxyl-biphenyl increased the chain-twisting hindrance and influenced the molecular conformation of the copolymer. Systematical investigation of electrochemical and photophysical properties of the conjugated polymers suggests that the incorporation of dimethoxyl-biphenyl via ortho-, meta-, and para-linkage is an efficient and economic way to modify the properties of polyfluorenes.
Five kinds of heterofluorenes (silafluorene, oxygafluorene, sulfafluorene, phosphafluorene, carbazole) and 2,5- dihexylbenzene alternative conjugated copolymers have been developed via Suzuki coupling reaction. The successful preparation of the conjugated copolymers opens a door for a new kind of host materials with high triplet state energy as excellent host materials and special optical properties with tremendous potential in the field of organic electronics without the typical defects of polyfluorene.
A new and facile procedure for the preparation of 6,6′-diiodo-5,5′-dibromo-3,3′-dimethoxylbiphenyl has been found. From this compound, a general synthetic strategy for the preparation of 1,8-dibromo-9-heterofluorenes will be developed. The Synthesis of 1,8-dibromo-9-heterofluorenes will open the door to new classes of inorganic and organometallic conjugated polymeric materials of polyheterofluorenes.
Digital medical 3D printing technology is a new hi-tech which combines traditional medical and digital design, computer science, bio technology and 3D print technology. At the present time there are four levels application: The printed 3D model is the first and simple application. The surgery makes use of the model to plan the processing before operation. The second is customized operation tools such as implant guide. It helps doctor to operate with special tools rather than the normal medical tools. The third level application of 3D printing in medical area is to print artificial bones or teeth to implant into human body. The big challenge is the fourth level which is to print organs with 3D printing technology. In this paper we introduced an application of 3D printing technology in tumor operation. We use 3D printing to print guide for invasion operation. Puncture needles were guided by printed guide in face tumors operation. It is concluded that this new type guide is dominantly advantageous.
We provide an overview of the development and current structure for cultivating the success of graduate student in Optical Engineering at Beijing University of Technology. Using the educational environment for graduate students in Advanced Laser Manufacturing as an example, we present the environment, the curriculum and some specific programs which demonstrate a multifaceted strategy combining production, study and research, including international cooperation, applications engineering and technology-based research. The programs are tightly linked to the national economic goals and specifically to development of the manufacturing industry which has a critical need for highly skilled and motivated graduates.
Light-trapping structures are fabricated on crystalline (100) silicon (c-Si) surfaces by picosecond (ps) laser irradiation followed by chemical etching. First, 1064-nm ps laser scanning is used to form micropore arrays on c-Si. The ps laser processing causes little reconsolidation of the silicon surface, which is beneficial to achieve precise etching. Control of the laser scanning interval, number of scans, and etching time gives a micro-nano hierarchical structure. In this hierarchical structure, the average diameter of the micropores is 25 to 30 μm, while the size of the finer nanostructures on the micropore inner walls ranges from dozens to hundreds of nanometers. Unlike traditional laser texturing techniques, the whole laser process is carried out without mask and photolithography. The reflectance of the c-Si surface with a micro-nano hierarchical structure is as low as 6% in the wavelength range from 400 to 1000 nm without coating. Moreover, the samples also show good hydrophobicity. This is a potential method to fabricate economical antireflective structures that are ideal for applications in c-Si solar cells and self-cleaning c-Si microelectronic devices.
A groove-shaped array with average 25 μm interval, 25 μm wall thickness, 75 μm depth and a columnar array with average 30 μm side length, 25 μm interval, 43 μm depth are processed by 1064 nm picosecond laser on polytetrafluoroethylene (PTFE) surface at room temperature. The water contact angle of modified PTFE surface can reach 167°, which show super hydrophobic surface of PTFE is prepared. It is observed super hydrophobic surface reflects metal luster underwater through the glassware when super hydrophobic PTFE entirely immerses in pure water. The experiment conducts super hydrophobic surface will enhance intensity of reflection of visible light underwater, which is due to total internal reflection of super hydrophobic surface und erwater.
We propose the fabrication of two types high performance texturized antireflective structures on crystalline (100) silicon (c-Si) surface by hybrid picosecond laser scanning irradiation followed by chemical corrosion. The design and the fabrication with high controllable performance were studied. The hybrid method includes 1064 nm picosecond (ps) laser scanning to form micro-hole array and subsequently short-time alkaline corrosion. After ps laser processing, there is little reconsolidation and heat affect zone on the silicon surface, which is beneficial to achieve the precise chemical corrosion effect. Depending on the laser scanning intervals, scanning times and chemical corrosion time, a variety of surface texture morphologies, even a special micro-nano hierarchical structure in which finer nano-structures formed in the micro units of the texture, were achieved. Observing with SEM, the average diameter of the micro-holes in the micro-nano hierarchica is 25~30 μm, while the average size of the nano-level ladder-like structures on the micro-hole wall is from dozens to hundreds of nanometers. Comparing to the traditional laser texturing techniques for c-Si solar cell, the whole laser processing was carried out in an open air ambient without using etch mask and SF6/O2 plasma. The results show the reflectance value of the fabricated c-Si surfaces can reach as low as 6% (400 nm~1000 nm). This is a potential method for economical antireflective structures fabrication which is ideal for using in the high-efficiency silicon-based photoelectronic devices.
We report high power all fiber mid-infrared (mid-IR) supercontinuum (SC) generation in a single-mode ZBLAN (ZrF4- BaF2-LaF3-AlF3-NaF) fiber with up to 21.8 W average output power from 1.9 to beyond 3.8 μm pumped by amplified picosecond pulses from a master oscillator power amplifier (MOPA) based on small-core single-mode thulium-doped fiber (TDF) with injected seed pulse width of 24 ps and repetition of 93.6 MHz at 1963 nm. The optical-optical conversion efficiency from the 793 nm pump laser of the last stage thulium-doped fiber amplifier (TDFA) to mid-IR SC output is 17%. It is, to the best of our knowledge, the highest average power mid-IR SC generation in a ZBLAN fiber to date. In addition, a noise-like fiber oscillator based on a nonlinear loop mirror (NOLM) with wavepacket width of ~1.4 ns and repetition rate of 3.36 MHz at 1966 nm is also used as a seed of the MOPA for mid-IR SC generation in the ZBLAN fiber. At last, a mid-IR SC from 1.9 to beyond 3.6 μm with average output power of 14.3W, which is limited by injected noise-like pulses power, is generated. The optical-optical conversion efficiency from the 793 nm pump laser of the last stage TDFA to mid-IR SC output is 14.9%. This proves the amplified noise-like pulses are also appropriate for high power mid-IR SC generation in the ZBLAN fiber.
We have demonstrated a high-power all-polarization-maintaining thulium-doped all fiber picosecond pulsed master oscillator power amplifier. The thulium-doped all fiber oscillator was mode locked by a semiconductor saturable absorber mirror to generate average output power of 100 mW at a repetition rate of 611.5 MHz in a short linear cavity. The first PM thulium-doped fiber preamplifier produced 4.5 W average output power for 17 W incident pump power, and the pulse width was measured to be 18 ps. In the second PM thulium-doped fiber preamplifier and the final PM thulium-doped fiber power amplifier, a segment of 4.5 m LMA PM thulium-doped double-clad fiber were used as the gain medium. Both the thulium-doped active fiber has a core diameter of 25 μm, a core NA of 0.09, inner cladding diameter of 400 μm and a NA of 0.46. The second PM fiber preamplifier produced 73 W average output power for 135 W incident pump power. In the final PM fiber power amplifier, the maximum average output power was up to 203 W at the available pump power of 300 W, the slope efficiency for the final PM fiber power amplifier was 50.7%. The PER at the highest average output power was measured to be <15 dB. The pulse width was 15 ps and the central wavelength was 1985 nm, which corresponds to peak power 22 kW. To the best of our knowledge, this is the highest average output power ever reported for an all fiber ultra-short-pulsed laser at 2 μm wavelength region.
(formula available in paper)thin films have been deposited on Si substrate by 248 nm pulsed laser deposition in O2 gas environment. The structure and properties of (formula available in paper)polycrystalline thin film were investigated as a function of the deposition temperature, oxygen pressure and the substrate-target distance. The film with the thickness of 190 nm showed a dielectric constant (epsilon) r equals 56.
In accordance with the practical demand for excimer laser micro- machining technology, an imaging projection lens with a resolution of 2micrometers is designed and produced. Through the practical micro-machining test, the lens achieves the designed specifications and could be put into practical use.
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