Spectroscopic ellipsometry study of In2O3 thin films

In2O3 films grown by helicon magnetron sputtering with different thicknesses were characterized by spectroscopic ellipsometry in the energy range from 1.5 to 5.0 eV. Aside from one amorphous sample prepared at room substrate temperature, polycrystalline In2O3 films with cubic crystal structure were confirmed for other four samples prepared at the substrate temperature of 450 A degrees C. Excellent SE fittings were realized by applying 1 and/or 2 terms F&B amorphous formulations, building double layered film configuration models, and further taking account of void into the surface layer based on Bruggeman effective medium approximation for thinner films. Spectral dependent refractive indices and extinction coefficients were obtained for five samples. The curve shapes were well interpreted according to the applied dispersion formulas. Almost similar optical band gap values from 3.76 to 3.84 eV were obtained for five samples by Tauc plot calculation using extinction coefficients under the assumption of direct allowed optical transition mode.

Thermal performance of a micro-combustor for micro-gas turbine system

Premixed combustion of hydrogen gas and air was performed in a stainless steel based micro-annular combustor for a micro-gas turbine system. Micro-scale combustion has proved to be stable in the micro-combustor with a gap of 2 mm. The operating range of the micro-combustor was measured, and the maximum excess air ratio is up to 4.5. The distribution of the outer wall temperature and the temperature of exhaust gas of the micro-conbustor with excess air ratio were obtained, and the wall temperature of the micro-combustor reaches its maximum value at the excess air ratio of 0.9 instead of 1 (stoichiometric ratio). The heat loss of the micro-combustor to the environment was calculated and even exceeds 70% of the total thermal power computed from the consumed hydrogen mass flow rate. Moreover, radiant hunt transfer covers a large fraction of the total heat loss. Measures used to reduce the heat loss were proposed to improve the thermal performance of the micro-combustor. The optimal operating status of the micro-combustor and micro-gas turbine is analyzed and proposed by analyzing the relationship of the temperature of the exhaust gas of the micro-combustor with thermal power and excess air ratio. The investigation of the thermal performance of the micro-combustor is helpful to design an improved microcombustor.

Phonon-limited mobility in two-dimensional semiconductors with spin-orbit coupling

The authors demonstrate that the Rashba spin-orbit interaction in low-dimensional semiconductors can enhance or reduce the electron-phonon scattering rate by as much as 25%. The underlying mechanism is that the electron-phonon scattering phase space for the upper (lower) Rashba band is significantly enhanced (suppressed) by the spin-orbit interaction. While the scattering time decreases for the upper level, the mobility of the level increases due to an additional term in the electron velocity. (C) 2007 American Institute of Physics.

Optical response in a quantum dot superlattice nanoring under a lateral electric field

The optical absorption of a GaAs/AlGaAs quantum dot superlattice nanoring (QDSLNR) under a lateral dc electric field and with magnetic flux threading the ring is investigated. This structure and configuration provides a unique opportunity to study the optical response of a superlattice under an inhomogeneous electric field, which is not easily realized for general quantum well superlattices (QWSLs) but naturally realized for QDSLNRs under a homogeneous lateral electric field. It has been shown that a lateral dc electric field gives rise to a substantial change of the optical absorption spectra. Under a low field, the excitonic optical absorption is dominated by a 1s exciton. And with the electric field increasing, the optical absorption undergoes a transition from 1s excitonic absorption to 0 excitronic WSL absorption. (The number of 0, and -1 and +1 below are WSLs index.) The -1 and the +1 WSLs corresponding to the maximum effective field can also be identified. Due to the inhomogeneity of the electric field, the peaks of the -1 and the +1 WSLs are diminished and between them there exist rich and complicated structures. This is in contrast to the general QWSLs under a homogenous electric field. The complicated structures can be understood by considering the inhomogeneity of the electric field along the ring, which results in the nearest-neighbor transition, the next-nearest-neighbor transition, etc., have a different value repectively, at different sites along the ring. This may give rise to multiple WSLs. We have also shown that the line shape of the optical absorption is not sensitive to the threading magnetic flux. The threading magnetic flux only gives rise to a slight diamagnetic shift. Thus the enhancement of the sensitivity to the flux allowing for observation of the excitonic Aharanov-Bohm effect in the plain nanoring is not expected in QDSLNRs.

Eye-safe, high-energy, single-mode all-fiber laser with widely tunable repetition rate

We present a novel high-energy, single-mode, all-fiber-based master-oscillator-power-amplifier (MOPA) laser system operating in the C-band with 3.3-ns pulses and a very widely tunable repetition rate, ranging from 30 kHz to 50 MHz. The laser with a maximum pulse energy of 25 mu J and a repetition rate of 30 kHz is obtained at, a wavelength of 1548 nm by using a double-clad, single-mode, Er:Yb co-doped fiber power amplifier.

骨修复用纳米生物玻璃/聚乳酸复合材料的研究

本文首次制备了纳米生物玻璃左旋聚乳酸复合材料，并针对两者之间界面不相容的现象，对生物玻璃表面进行了有针对性的改性；对其纳米颗粒的分散能力进行了表征，并对复合材料的力学性能和生物相容性进行了研究，以期能得到一种具有良好力学性能和生物活性的可降解骨组织修复材料。 （1） 以正硅酸乙酯为硅源，以磷酸氢二铵为磷源，硝酸钙为钙源制备了纳米生物玻璃的凝胶颗粒(BAG, SiO2: CaO: P2O5 =37/54/9, mol/mol) ；以其表面的硅羟基为引发点，采用丙交酯开环聚合原位改性的方法对其进行了表面改性得到了改性纳米生物玻璃的凝胶颗粒（m-BAG）；通过改性，使其表面性质由亲水性变为亲油性，提高了其在聚乳酸基体内的分散能力；m-BAG/PLLA复合材料改变了改性以前BAG/PLLA力学性能随生物玻璃含量增加而不断下降的趋势，保持了聚乳酸的力学性能，在m-BAG含量为2%的时候其拉伸强度相对于纯聚乳酸提高16%左右，模量达到纯聚乳酸的1.4倍；而当m-BAG含量为10wt%，复合材料保持与纯聚乳酸相似的拉伸强度，而此时10wt%BAG/PLLA复合材料的力学性能只有纯聚乳酸的80%; 生物玻璃凝胶/聚乳酸复合材料在模拟体液中表现了较高的钙沉积能力，最后在其表面都形成了羟基磷灰石的晶体，但是表面改性使其钙沉积的速度降低，在一定程度上减小了其活性；细胞试验表明，不论生物玻璃凝胶/聚乳酸复合材料还是改性后的复合材料都表现出了很高的细胞黏附性能和增殖性能。 （2） 通过煅烧将生物玻璃的凝胶颗粒制备了生物玻璃纳米颗粒，通过XRD和TGA确定该组成类型的生物玻璃的结晶温度在826ºC，我们选择其经过600ºC煅烧的非晶态的材料作为我们进一步研究的对象。通过六次甲基异氰酸酯作为偶联剂，我们将低分子量的Mn=9,700Da的聚乳酸偶连到生物玻璃纳米颗粒的表面；通过改性提高了生物玻璃/聚乳酸的拉伸强度和拉伸模量，并提高了其分散能力；模拟体液试验表明，其复合材料具有很强的钙沉积能力，细胞培养证明了优异的生物相容性；而且通过试验可以看出，生物玻璃相对于其原始的纳米凝胶颗粒具有更优异的钙沉积能力和细胞相容性。 （3） 通过将三臂聚乳酸添加到线性聚乳酸的内部，大幅度的提高了其冲击强度，当三臂聚乳酸含量达到2wt%-8wt%时，冲击强度达到线性聚乳酸的2倍左右；通过偏光显微镜观察，可以看到三臂聚乳酸提高了线性聚乳酸的结晶成核速度，使其最后晶体数量增多，形态变小；而通过等温结晶试验表明其结晶速度提高，结晶是以异相成核的三维生长方式进行的；流变学试验表明加入三臂聚乳酸有力的降低了体系的复数粘度，当三臂聚乳酸含量达到8%时候，在频率为1-10rad/s其数值仅为线性聚乳酸的60%左右，这种变化将提高其加工成型能力。 （4） 通过十六烷基三甲基溴化铵作为模板剂，制备了具有多孔结构的生物玻璃纳米颗粒，其孔径在2nm左右，比表面积为264m2/g； 通过模拟体液试验表明，其具有很强的生物活性，规整结构在浸泡的前8小时被破坏，体系中P和Ca的含量大幅度上升，在24小时以后形成了羟基磷灰石的晶体。该类型的材料有望应用于制备药物缓释材料，用于骨修复初期的感染和炎症治疗。

长余辉发光材料的合成，缺陷及发光性质

近十年间，长余辉发光材料备受人们关注，其研究和开发得到了迅猛的发展。究其原因，长余辉材料是一种新型能量存储与电子俘获材料，它不仅可以应用到紧急照明与显示等传统领域，而且在高能射线探测、光纤温度计、工程陶瓷的无损探测以及超高密度光学存储与显示等高新科技领域具有潜在的应用价值。这一时期，研究兴趣主要集中在稀土离子特别是Eu2+激活的蓝色和绿色长余辉材料如铝酸盐、嫁酸盐、硅酸盐、硅铝酸盐、锗酸盐及氧化物等体系，而严重医乏红色长余辉材料。长余辉发光主要由三个过程，也就是能量吸收、能量存储与能量释放即余辉发光组成。而整个过程主要涉及两个中心，即发光中心和陷阱中心，它们之间的能量传递是产生余辉发光的主要原因。因此，本论文围绕这两个中心，选择以下两个角度为切入点：（a）选择具有较高发光性能的现有荧光体，通过各种辅助激活离子的共掺杂，主动引入陷阱中心；（b）选择具有丰富陷阱中心的现有荧光体，主动引入具有余辉发光性能的主激活离子，致力于新型长余辉特别是红色长余辉发光材料的开发，最终获得了红、绿、蓝三色共十种长余辉体系。其中，新型红色长余辉体系有：β-Zn3(PO4)2:Mn2+、γ-Zn3（PO4）2:Mn2+、Zn3B2O6:Mn2+和Y2O3：Eu3+；新型绿色长余辉体系有：Ca8Mg（SiO4）4Cl2:Eu2+、Zn4B6O13:Mn2+、α-Zn3(PO4)2：Mn2+和Zn2SiO4:Mn2+。我们还对已有红色长余辉体系Y2O2S:Eu3+和caO：Eu3＋进行了余辉性能的改善。在合成上述长余辉材料的基础之上，详细地分析并研究了组成、结构、缺陷和余辉性能之间的关系，得到了影响长余辉发光的一般规律。此外，首次在多晶粉末中报道了β-Zn3(PO4)2:Mn2+，Ga3+和Zn2SiO4:Mn2+，Al3+的红色和绿色光激励长余辉发光现象。