仿植物叶子表面微纳结构的光学性能

采用双液相转写法制备具有植物叶子表面微纳结构的有机玻璃.采用透光率雾度仪检测仿叶子有机玻璃薄膜(LM-PMMA)的光学性能.研究仿叶子薄膜的透射、反射率、散光、及其对光伏效益的影响,并采用蒙特卡洛法计算光学性能及模拟光路传播.结果表明:与光滑有机玻璃相比,仿生有机玻璃具有高达85;的雾度率,并有效提高硅太阳电池的效益;仿生微纳表面结构均有效减少反射、增透及增加硅的光吸收率;另外,光在“乳突”结构中的转播过程模拟结果说明:折射、聚焦、散射是仿叶子有机玻璃散光主要原因.     

掺杂Ni/Al对热障涂层抗高温氧化性和结合强度的影响

YSZ(Ni,Al)粉末颗粒通过电泳沉积技术在高温镍基合金600上沉积一层厚度均匀的YSZ(Ni,Al)复合热障涂层,并在室温下干燥24 h后,进行真空烧结致密化处理.真空致密化处理后的YSZ(Ni,Al)复合热障涂层在1100℃下氧化不同小时并测量涂层的结合强度.由于掺杂了镍铝氧化初期在涂层表面形成一层致密的氧化薄膜,有效地阻止了空气中的氧气进一步进入涂层内部从而提高了涂层的抗高温氧化性能,另外在陶瓷涂层YSZ中掺杂了金属元素,降低了陶瓷涂层与高温镍基合金的热膨胀系数的不匹配,使涂层表面更加平整致密,同时也提高了涂层与基体的结合强度.     

高压对Ti2AlX(X=C,N)结构、弹性和电子性质的影响

采用第一性原理方法,对比研究了Ti2AlC和Ti2AlN在高压下的结构、弹性和电子性质.结果表明,Ti2 AlC和Ti2AlN的品格常数a、c和体积V均随着外压的增大减小,但二者变化规律略有不同,都体现了材料的各向异性.通过对弹性常数、体模量、剪切模量、杨氏模量等弹性性质的分析,发现它们均随外压的增加而增大,并验证了Ti2AlC和Ti2AlN在0～50 GPa范围内的力学稳定性.此外,还从电子态密度的角度考察了Ti2AlC和Ti2AlN的电子性质,认为它们均具有共价键和金属键的双重特性,并发现在0 ～ 50 GPa范围内压力对态密度影响较小.本文计算结果与已有实验值和理论值吻合较好.     

内蒙古草原植被最大光能利用率取值优化研究

针对目前CASA (carnegie-ames-stanford approach)模型等植被生产力模型植被最大光能利用率的取值未对草原进行区分的问题,以内蒙古草甸草原、典型草原和荒漠草原为研究对象,结合野外实测NPP(net primary productivity)数据和CASA模型的建模思路优化了三大草原类型植被最大光能利用率,并以此为基础模拟分析了其植被光能利用率和NPP时空格局。结果表明,基于99个地面采样点所建立的一元二次方程模拟的草甸草原、典型草原和荒漠草原最大光能利用率分别为0.654,0.553和0.511 gC·MJ-1,平均为0.573 gC·MJ-1。与未对草原类型进行区分而统一取值为0.541 gC·MJ-1的结果相比,实测NPP与模拟NPP之间的决定系数和和均方根误差分别提高了0.024和2.62 gC·(m2·month-1)-1。受水热组合和草原类型的空间格局的影响,内蒙古草原植被光能利用率和NPP总体上由东北向西南逐渐下降趋势,呈明显的单峰季节变化特征。但光能利用率和NPP的最大值出现的月份有所不同,分别出现在8月份和7月份,这可能与植被吸收的光合有效辐射和光能利用率的最高值出现的月份不同有关。光能利用率和NPP平均值按草甸草原>典型草原>荒漠草原的顺序依次降低。     

Design of LD in-band direct-pumping side surface polished micro-rod Nd:YVO_4 laser

To diminish the thermal load, two ways, that is, in-band direct pumping and micro-rod crystal, could be adopted at the same time. The efficiency of LD in-band direct-pumping side surface polished micro-rod Nd:YVO_4 laser is numerically analyzed. By optimizing parameters such as crystal length, laser mode radius, pump beam radius, doping concentration and crystal cross-section size, the overall efficiency can reach over 50%. It is found that with micro-rod crystal implemented in the laser oscillator, high overall efficiency LD in-band direct-pumping Nd:YVO_4 laser could be realized. High efficiency combined with low thermal load makes this laser an outstanding scheme for building high-power Nd:YVO_4 lasers.     

Ultra-low specific on-resistance high-voltage vertical double diffusion metal–oxide–semiconductor field-effect transistor with continuous electron accumulation layer

A new ultra-low specific on-resistance(Ron,sp) vertical double diffusion metal–oxide–semiconductor field-effect transistor(VDMOS) with continuous electron accumulation(CEA) layer, denoted as CEA-VDMOS, is proposed and its new current transport mechanism is investigated. It features a trench gate directly extended to the drain, which includes two PN junctions. In on-state, the electron accumulation layers are formed along the sides of the extended gate and introduce two continuous low-resistance current paths from the source to the drain in a cell pitch. This mechanism not only dramatically reduces the Ron,sp but also makes the Ron,sp almost independent of the n-pillar doping concentration(Nn). In off-state, the depletion between the n-pillar and p-pillar within the extended trench gate increases the Nn, and further reduces the Ron,sp.Especially, the two PN junctions within the trench gate support a high gate–drain voltage in the off-state and on-state, respectively. However, the extended gate increases the gate capacitance and thus weakens the dynamic performance to some extent. Therefore, the CEA-VDMOS is more suitable for low and medium frequencies application. Simulation indicates that the CEA-VDMOS reduces the Ron,sp by 80% compared with the conventional super-junction VDMOS(CSJ-VDMOS)at the same high breakdown voltage(BV).     

Structural transitions of SWNT filled with C_(60) under high pressure

Raman spectra of C_(60) filled single-walled carbon nanotubes(C_(60)@SWNTs) with diameters of 1.3–1.5 nm have been studied under high pressure. A plateau in the pressure dependence of the G-band frequency at around 10 GPa was observed in both experiments with 514 nm and 830 nm excitation lasers, which is similar to the high pressure behaviors of pristine SWNTs. This structural transition has been assigned to the transformation into a peanut-like structure of the nanotubes. At pressure below 2 GPa, no obvious Raman signature related to the structural transition of nanotubes was observed, unlike what has been reported for C_(70) filled nanotubes. We discussed this point in terms of the arrangement differences of C_(60) and C_(70)molecules inside the nanotubes. At higher pressure up to 15 GPa, a graphite-like pressure evolution was observed in our C_(60)@SWNTs.     

A 12.1-W SESAM mode-locked Yb:YAG thin disk laser

Pumped by a 940 nm fiber-coupled diode laser, a passively mode-locked Yb:YAG thin disk oscillator was demonstrated with a semiconductor saturable absorber mirror(SESAM). 12.1 W mode-locked pulses were obtained with pulse duration of 698 fs at the repetition rate of 57.43 MHz. Measurement showed that the beam quality was close to the diffraction limit.     

High temperature characteristics of bilayer epitaxial graphene field-effect transistors on SiC Substrate

In this paper,high temperature direct current(DC) performance of bilayer epitaxial graphene device on SiC substrate is studied in a temperature range from 25℃ to 200℃.At a gate voltage of-8 V(far from Dirac point),the drainsource current decreases obviously with increasing temperature,but it has little change at a gate bias of +8 V(near Dirac point).The competing interactions between scattering and thermal activation are responsible for the different reduction tendencies.Four different kinds of scatterings are taken into account to qualitatively analyze the carrier mobility under different temperatures.The devices exhibit almost unchanged DC performances after high temperature measurements at 200℃ for 5 hours in air ambience,demonstrating the high thermal stabilities of the bilayer epitaxial graphene devices.     

Theoretical design of diamondlike superhard structures at high pressure

Diamond, as the hardest known material, has been widely used in industrial applications as abrasives, coatings, and cutting and polishing tools, but it is restricted by several shortcomings, e.g., its low thermal and chemical stability. Considerable efforts have been devoted to designing or synthesizing the diamond-like B–C–N–O compounds, which exhibit excellent mechanical property. In this paper, we review the recent theoretical design of diamond-like superhard structures at high pressure. In particular, the recently designed high symmetric phase of low-energy cubic BC3 meets the experimental observation, and clarifies the actual existence of cubic symmetric phase for the compounds formed by B–C–N–O system,besides the classical example of cubic boron nitride.