冲击载荷下石英的一维极化电流研究

从石英在冲击波作用下的状态方程出发，根据高斯定理、动量守恒以及欧姆定律，采用拉普拉斯变换对压电电流进行了计算，其结果与Z．P．Tang^[1]进行了比较，并简单分析了其它一些因素对在冲击波作用下石英压电电流的影响。     

分布反馈太赫兹量子级联激光器实现高功率单模输出

太赫兹量子级联激光器(THz QCL)是一种基于超晶格或耦合多量子阱中电子共振隧穿和子带间跃迁的单极光源,其辐射频率可通过能带和波函数设计进行调控,具有响应速度高、体积小、便于集成等优点。近年来,国际上多个科研团队展开了对THz QCL的密集研究,器件性能取得了显著的进展。针对THz QCL的实际应用,目前急切需要解决两个方面的问题:第一方面,受限于严重的大气衰减、光束合成等困难,急需解决THz QCL功率输出提升的问题。第二方面,研制窄线宽、高功率单模输出的太赫兹本振源。     

Investigation of Zn_(1-x)Cd_xO films bandgap and Zn_(1-x)Cd_xO/ZnO heterojunctions band offset by x-ray photoelectron spectroscopy

A series of Zn_(1-x)Cd_xO thin films have been fabricated on sapphire by pulsed-laser deposition(PLD), successfully. To investigate the effect of Cd concentration on structural and optical properties of Zn_(1-x)Cd_xO films, x-ray diffraction(XRD),ultraviolet-visible spectroscopy(UV-vis), and x-ray photoelectron spectroscopy(XPS) are employed to characterize the films in detail. The XRD pattern indicates that the Zn_(1-x)Cd_xO thin films have high single-orientation of the c axis. The energy bandgap values of ZnCdO thin films decrease from 3.26 eV to 2.98 eV with the increasing Cd concentration(x)according to the(αhν)~2–hν curve. Furthermore, the band offsets of Zn_(1-x)Cd_xO/ZnO heterojunctions are determinated by XPS, indicating that a type-I alignment takes place at the interface and the value of band offset could be tuned by adjusting the Cd concentration.     

Temperature dependence of surface and structure properties of ZnCdO film

Zn1-xCdx O films are grown on c-sapphire substrates by laser molecular beam epitaxy(LMBE) at different temperatures. Their crystallographic structures, compositions, surface electronic structures are investigated. The a-axis lattice constant of Zn0.95Cd0.05 O is 3.20. Moreover, the epitaxial relationship shows a 30°-in-plane rotation of the film with respect to the c-sapphire substrate. When the substrate temperatures arrives at 500℃, the in situ reflection high-energy electron diffraction(RHEED) pattern of Zn Cd O film shows sharp streaky pattern. The maximum Cd content of Zn Cd O film grown at low substrate temperatures increases up to about 29.6 at.%, which is close to that of the ceramic target. In situ ultraviolet photoelectron spectroscopy(UPS) measurements demonstrate that Zn Cd O film exhibits intense peaks at 4.7 e V and 10.7 e V below the Fermi level, which are assigned to the O 2p and Zn 3p states. Energetic distance between Zn 3d and Cd 4d is 0.60 e V. Above 470 nm, the thin film shows excellent optical transmission.     

2.5 THz量子级联激光器的研制

基于束缚态到连续态跃迁有源区能带结构,实现了2.5 THz量子级联激光器的连续波工作。激光器的输出频率随电流可在2.45~2.47 THz之间可调,在连续波工作模式下的最高输出功率大于6.0 mW,最高连续波工作温度为60 K,阈值电流密度为120 A/cm2,经Si透镜整形后的输出光斑为高斯分布。     

新型金阴极及其紫外光电发射特性

采用直流磁控溅射法制备了不同厚度的金纳米薄膜,在高纯氮气气氛、800 ℃条件下快速退火,在石英基底上制备了具有表面微纳颗粒的新型金阴极。应用扫描电子显微镜对阴极的表面形貌进行表征,结果表明：阴极表面形成了均匀分布的金纳米颗粒,平均粒径随金纳米薄膜厚度的增加（5 nm至20 nm）从300 nm增大到800 nm。在190~360 nm紫外光下,对阴极的光电子发射特性进行了研究,结果表明：相对于平面阴极,新型金阴极的光电子发射效率提高了10倍以上,最高可达到平面阴极的16倍,且随颗粒粒径的减小而增大。采用三步光电发射模型对上述结果进行理论分析,表明阴极光电效率的提高主要由于阴极光电发射面积的增加和局域强电场导致的表面势垒降低。     

脉冲激光气相沉积法制备的非晶CH薄膜特性分析

采用脉冲激光气相沉积(PLD)法,研究了氢气压强对非晶CH薄膜性能的影响。原子力显微镜图和白光干涉图显示,薄膜表面平整致密,随着氢气压强增大,粗糙度变大。拉曼光谱分析表明,氢气压强增加,G峰和D峰位置都在向高波数方向移动。傅里叶变换红外光谱分析显示,薄膜中存在sp3—CH2和sp2—CH等基团。最后,采用PLD漂浮法在最优参数氢气压强为0.3 Pa下,成功制备了不同厚度（100~300 nm）、满足一定力学强度、无明显宏观缺陷的自支撑CH薄膜。     

First-principles study of the electronic structure and optical properties of cubic Perovskite NaMgF_3

The structural, electronic, and optical properties of cubic perovskite NaMgF3 are calculated by plane-wave pseudopo- tential density functional theory. The calculated lattice constant a0, bulk modulus B0, and the derivative of bulk modulus B~ are 3.872/~, 78.2 GPa, and 3.97, respectively. The results are in good agreement with the available experimental and theo- retical values. The electronic structure shows that cubic NaMgF3 is an indirect insulator with a wide forbidden band gap of Eg = 5.90 eV. The contribution of the different bands is analyzed by total and partial density of states curves. Population analysis of NaMgF3 indicates that there is strong ionic bonding in the MgF2 unit, and a mixture of ionic and weak covalent bonding in the NaF unit. Calculations of dielectric function, absorption coefficient, refractive index, electronic energy loss spectroscopy, optical reflectivity, and conductivity are also performed in the energy range 0 to 70 eV.     

分布反馈量子级联激光器光栅反馈特性北大核心CSCD

为探究Bragg光栅结构对TM模反馈特性的影响,利用有限时域差分法对具有TM模的分布反馈(DFB)量子级联激光器Bragg光栅结构进行仿真研究。重点分析了侧向耦合光栅的光学特性以及光栅侧壁倾角对光栅反射谱、损耗的影响及原因,并探究了光栅刻蚀深度及占空比与TM模的耦合系数、损耗的关系。结果表明有效折射率是影响Bragg波长的主要因素,而光限制因子是不同周期的侧向耦合光栅结构耦合系数产生巨大差别的原因,当光栅侧壁倾角90°时镜面损耗最小。光栅周期、占空比、刻蚀深度与耦合系数的关系表明:这些参数不仅影响光栅的相对介电常数,也会对光限制因子产生作用,从而影响耦合系数的大小;耦合系数与刻蚀深度具有正比关系,大周期光栅耦合系数随占空比的变化率较小。对光栅光反馈特性的理论研究有利于提升对DFB量子级联激光器的认识,促进激光器性能的提升和发展。