Epitaxial growth of Ge_(1-x)Sn_x films with x up to 0.14 grown on Ge(00l) at low temperature

We characterize the structures of Ge1-xSnx films with x up to 0.14 grown on Ge(00l) by molecular-beam epitaxy at low temperature. The results show that Ge1-xSnx films are fully strained even at high Sn composition. The in-plane lattice parameters remain exactly the same as that of the substrate. Depth sensitivity analysis of the lattice parameters indicates that the strains of the epitaxial films are all in homogeneity. The films are fully strained. Poisson ratios, the force constants for the bonds between Ge and Sn are estimated and discussed in the present paper. Raman results show Ge–Ge, Ge–Sn,Sn–Sn vibrational modes. The Sn–Sn bond aggregation may respond to the high quality of our films. The fully strained epitaxy films with high content of Sn may be useful in designing the high quality GeSn films.     

First-principles calculations on Si(220) located 6H–SiC(10■0)surface with different stacking sites

6H–SiC(10ˉ10) surface and Si(220)/6H–SiC(10ˉ10) interface with different stacking sites are investigated using first-principles calculations. Surface energies of 6H–SiC(10ˉ10)(case I, case II, and case III) are firstly studied and the surface calculation results show that case II and case III are more stable than case I. Then, the adhesion energies, fracture toughness values, interfacial energies, densities of states, and electronic structures of Si(220)/6H–SiC(10ˉ10) interfaces for three stacking models(AM, BM, and CM) are calculated. The CM model has the highest adhesion energy and the lowest interfacial energy, suggesting that the CM is stronger and more thermodynamically stable than AM and BM. Densities of states and the total charge densities give evidence that interfacial bonding is formed at the interface and that Si–Si and Si–C are induced due to the hybridization of C-2p and Si-3p. Moreover, the Si–C is much stronger than Si–Si at the interface,implying that the contribution of the interfacial bonding mainly comes from Si–C rather than Si–Si.     

组织凝固性坏死对基于纵向弛豫时间的磁共振测温的影响

高强度聚焦超声（High Intensity Focused Ultrasound,HIFU）治疗肿瘤时,为了保证治疗的安全性和有效性,需要对组织温度分布进行实时监测.磁共振成像（Magnetic Resonance Imaging,MRI）具有对温度敏感的成像参数,可以无创检测组织温度.本文结合组织相变对测温的影响,探讨了磁共振测温（Magnetic Resonance Thermometry,MRT）技术能否用于实时监控HIFU治疗.利用两态快速交换模型,提出在组织凝固性坏死的相变前后,MRI的纵向弛豫时间（T₁）参数与组织温度之间具有不同关系.并通过实验验证了上述假设.相对于传统的磁共振测温方法模型,本文考虑了HIFU治疗过程中组织相变对检测温度的影响,对利用磁共振测温引导HIFU治疗具有重要的参考价值.     

纳米ZnS中的自激活发光

在水和乙醇体系中分别制备了尺寸在５ｎｍ左右的掺杂和未掺杂的ＺｎＳ纳米粒子,观察到了所谓自激活发光,在乙醇溶胸体系中这种发光比水溶胶体系不强两个数量级。对这种纂扩活发光的机理及其与纳米粒子形成过程的关系,表面活性剂的作用等进行了分析。     

R452B应用于空调(热泵)机组的性能研究

对比分析了R452B、R32和R410A应用于空调(热泵)机组理论循环特性,并对R452B在空调(热泵)机组中直接替代R410A的性能进行了试验研究,测试了空调(热泵)机组在不同工况条件下的制冷/热量、功率、性能系数以及压缩机的排气温度等参数。结果表明:相较于使用R410A而言,机组使用R452B的制冷/热能力、功率略有下降,制冷能效提高在5%以内,压缩机的排气温度提高约1℃,压比有所降低。当R452B的充注量达到R410A的85%时,机组性能达到最佳。总体来讲,R452B与R410A的运行性能相近。R452B比R410A具有更低的GWP值,符合行业的制冷剂替代趋势,可以在空调(热泵)机组中作为R410A的直接替代制冷剂。     

光学坐标变换实现光束轨道角动量模式分束的技术研究

实现不同OAM光束的空间分离在许多领域都起到重要作用。通过光学坐标变换原理可以实现不同轨道角动量模式的空间分离,而且可以降低相邻模式之间的串扰,从而提高OAM模式分辨率。研究为OAM模式分束提供了一种更具可行性的新方案。     

1.57 times diffraction-limit high-energy laser based on a Nd:YAG slab amplifier and an adaptive optics system

In this Letter, a 116-actuator deformable mirror(DM) was used to correct the wavefront distortion in a 10.7 J,10 Hz neodymium-doped yttrium aluminum garnet(Nd:YAG) slab amplifier. By applying a pump-light homogenizer to transform the 3 × 1 near-field beam array into an integrated beam, the beam quality was greatly improved from 5.54 times diffraction limit(TDL) to 1.57 TDL after being corrected by the DM. To the best of our knowledge, this is the first investigation on beam quality control of an arrayed near-field beam in high-energy diode-pumped solid-state lasers.     

高密度光盘循轨伺服中盘片径向倾斜的影响分析

基于标量衍射理论,根据实际光盘的参数,对数字多用途光盘(DVD光盘)的循轨行为进行了分析。在此基础上,针对盘片产生径向倾斜的情况引入了倾斜参数,对盘片模型进行了补充。对光盘的径向倾斜误差和系统循轨伺服的交叉影响进行了分析和讨论。     

CeO2@Au核壳结构纳米粒子的合成与性质研究

采用沉淀法制备了球形CeO2纳米粒子,将其作为核粒子溶液,然后向其中滴加四氯合金酸溶液,在CeO2胶体表面利用柠檬酸钠还原[AuCl4]-离子,得到了CeO2@Au核壳结构纳米粒子。TEM分析表明,CeO2纳米粒子分散效果好,粒径为5 nm;CeO2@Au核壳粒子为球形,无团聚,平均粒径为15 nm。XRD分析表明,CeO2@Au核壳粒子为晶型结构,属于立方晶系,CeO2空间群为O5H-FM3M,Au的空间群为Fm-3m。UV-vis分析发现,CeO2@Au核壳粒子在300和520 nm处呈现出两个比较强的吸收峰,分别对应于CeO2胶体溶液的吸收峰和金粒子的表面等离子共振吸收峰。EDS分析了核壳结构CeO2@Au纳米粒子中存在Ce,O和Au 3种元素。XPS分析表明,Ce3d3/2和Au4f电子结合能与标准结合能相比发生了变化,说明CeO2与Au之间存在着相互作用。