Ni2+掺杂近化学计量比铌酸锂晶体的生长及光谱特性

以K2O为助熔剂,在较大的固液界面温度梯度条件下,应用坩埚下降法技术生长了初始Ni2 掺杂摩尔分数为0.5%的近化学计量比铌酸锂晶体。测定了晶体的吸收光谱,观测到由Ni2 离子在八面体中3A2g(F)→3T1g(P)、3A2g(F)→3T1g(F)、3A2g(F)→3T2g(F)能级的正常自旋允许跃迁所产生的381 nm,733 nm,1280 nm吸收峰和3A2g(F)→1T2g(D)和3A2g(F)→1E(D)能级的自旋禁戒跃迁产生的430 nm与840 nm吸收峰。从晶体紫外吸收边的位置初步估算其摩尔分数比x(Li )/x(Nb5 )为0.981。根据晶体分裂场理论和吸收光谱,计算了Ni2 在该铌酸锂晶体中的晶格场分裂参量Dq=781 cm-1、Racah参量B=1096 cm-1与C=4353 cm-1。研究了在不同激发波长下晶体在可见光波段的荧光特征,观察到500~630 nm的绿色与800~850 nm的红色荧光发射带,它们归结为1T2g(D)→3A2g(F)与1T2g(D)→3T2g(F)的能级跃迁所致。     

Three-dimensional electric-field vector measurement with an electro-optic sensing technique

A new technique for three-dimensional (3D) electric-field (e-field) vector measurement is presented. Three laser beams with different propagation paths in an electro-optic (EO) crystal were used to resolve 3D components of e-field vectors. We adopted a special geometric shape of bismuth silicon oxide EO crystal so that the three beams would propagate within it. A sensitivity of 0.6 V/cm radicalHz was achieved. A commercial Ansoft Maxwell 3D field simulator was also used to verify our measurements.     

Epitaxial crystal growth of charged colloids

A pattern of repulsive, charged lines is shown to direct three-dimensional (3D) crystallization in a system of long-range repulsive, density-matched colloids. At volume fractions where the bulk phase behavior leads to bcc crystallization, the 1D template was found to induce formation of a metastable fcc crystal. The bcc crystals were oriented with the (100) or the (110) plane, with twofold twinning, parallel to the template. The template further induced prefreezing of the (100) plane. At a large mismatch between template and interparticle spacing, 1D strings form in the surface layer of a 3D crystal.     

Diffractionless flow of light in all-optical microchips

We introduce the concept of a hybrid 2D-3D photonic band gap (PBG) heterostructure which enables both complete control of spontaneous emission of light from atoms and planar light-wave propagation in engineered wavelength-scale microcircuits. Using three-dimensional (3D) light localization, this heterostructure enables flow of light without diffraction through micron-scale air waveguide networks. Achieved by intercalating two-dimensional photonic crystal layers containing engineered defects into a 3D PBG material, this provides a general and versatile solution to the problem of "leaky modes" and diffractive losses in integrated optics.     

2D and 3D electrically switchable hexagonal photonic crystal in the ultraviolet range

Two holographic lithography systems are demonstrated for easy and large-area fabrication of 2D and 3D photonic crystal (PhC) microstructures in a polymer dispersed liquid crystal (PDLC) by applying a single top-cut hexagon prism. A six-beam system has been used to produce 2D hexagonal PhCs. By adding an additional mirror, a twelve-beam system is demonstrated to fabricate 3D PhCs with ultraviolet (UV) band-gap along the z direction. A good agreement is obtained for measured PhCs structure and theoretical results. Far-field diffraction patterns and electrical switching characteristics of the 2D and 3D PhC HPDLC films have been investigated. PACS 42.15.Eq; 42.40.Eq     

Ni2+:RbMgF3的电子顺磁共振谱的研究

含有过渡金属离子的晶体的光学吸收谱、零场分裂D值和g因子与晶体结构有密切关系,应用Ni^2 的参量化d轨道和三角晶场中d^8电子组态的强场能量矩阵,通过建立完全对角化方法,精确地计算了具有C3ν和D3d两种对称的Ni^2 ：RbMgF3的电子顺磁共振谱,分析了Ni^2 ：RbMgF3的零场分裂D值和g因子与晶体结构参量R和θ的依赖关系。理论值与实验值符合得很好。     

Three-dimensional photonic crystal with a stop band from 1.35 to 1.95 microm

A combination of advanced silicon-processing techniques was used to create three-dimensional (3D) photonic crystals with a 180-nm minimum feature size. The resulting 3D crystal displayed a strong stop band at optical wavelengths from lambda=1.35 mum to lambda=1.95 mum . This is believed to be the smallest 3D crystal with a complete 3D photonic bandgap ever created.     

“In vivo” STM studies of the growth of Germanium and Silicon on Silicon

A scanning tunneling microscope (STM) capable of imaging during crystal growth from the vapour is described. This method (MBSTM) opens the possibility to follow the growth process of semiconductor molecular beam epitaxy (MBE) in vivo. The ability of the microscope to access the evolution of specific features during growth is demonstrated by images of the Si homoepitaxy. The transition from initial multilayer to layer-by-layer growth was imaged in Si(1 1 1) homoepitaxy. In Si/Si(1 0 0) homoepitaxy the fractional coverage of non-equivalent terraces was studied as function of coverage and a theoretically predicted transient growth mode was observed. In Ge on Si(1 1 1) heteroepitaxy the nucleation of 3D Ge islands was observed. When 3D islands occurred on the surface an etching of the 2D Stranski-Krastanov layer was observed.     

Experimental demonstration of self-collimation inside a three-dimensional photonic crystal

We present our experimental demonstration of self-collimation inside a three-dimensional (3D) simple cubic photonic crystal at microwave frequencies. The photonic crystal was designed with unique dispersion property and fabricated by a high precision computer-controlled machine. The self-collimation modes were excited by a grounded waveguide feeding and detected by a scanning monopole. Self-collimation of electromagnetic waves in the 3D photonic crystal was demonstrated by measuring the 3D field distribution, which was shown as a narrow collimated beam inside the 3D photonic crystal but a diverged beam in the absence of the photonic crystal.     

Classical motion in two-dimensional crystals

The classical motion of an electron of high enough energy in a two-dimensional crystal is diffusive for many potentials with Coulomb singularities. A simple model of the dynamics is developed which predicts the dependence of the diffusion constantD on the particle energyE in the high-energy limit:D(E)const·E ^3/2. This diffusion law is checked for a concrete crystal by numerically integrating the Hamilton equations for an ensemble of initial conditions. Finally this method is compared with other models of the classical dynamics in a crystal, especially the Sinai billiard.     

Evaporation of the pancake-vortex lattice in weakly coupled layered superconductors

We calculate the melting line of the pancake-vortex system in a layered superconductor, interpolating between two-dimensional (2D) melting at high fields and the zero-field limit of single-stack evaporation. Long-range interactions between pancake vortices in different layers permit a mean-field approach, the "substrate model, " where each 2D crystal fluctuates in a substrate potential due to the vortices in other layers. We find the thermal stability limit of the 3D solid, and compare the free energy to a 2D liquid to determine the first-order melting transition and its jump in entropy.     

Dual photonic band gap and reversible tuning of 3D photonic crystal fabricated by multiphoton polymerization with photoresponsive polymer

A 3D woodpile photonic crystal (PhC) composed of two parts with different periodic parameters was fabricated with a novel photoresist containing photoresponsive azobenzene moieties by multiphoton polymerization. Dual photonic band gaps (PBGs) were experimentally measured, which were attributed to two independent parts of the 3D PhC with different periodicities. Under light irradiation, PBG tuning of 36 nm was obtained, and this tuning behavior showed good reversibility.     

Electronic properties of 2D and 3D hybrid organic/inorganic perovskites for optoelectronic and photovoltaic applications

We herein investigate theoretically both 2D and 3D Hybrid Organic/inorganic perovskite crystal structures based on density functional theory (DFT) calculations and symmetry analyses. Our findings reveal the universal features of the electronic band structure for the class of lead-halide hybrids (R-NH \(_{3})_{n}\hbox {PbX}_{m}\) , where \((\mathrm{{n}}, \mathrm{{m}})=(2,4)\) and (1,3) respectively for 2D and 3D structures. Among those, the large spin-orbit coupling acting on the conduction band is shown to play a major role on the band gap of these materials. Moreover, this approach can easily be generalized to related layered and 3D hybrids, thus providing a clear-sighted inside in their electronic and optical properties.     

Ionic liquid-assisted hydrothermal synthesis of three-dimensional hierarchical CuO peachstone-like architectures

Uniform peachstone-like CuO 3D architectures consisting of single-crystal nanosheets have been successfully synthesized by using ionic liquid 1-octyl-3-methylimidazolium trifluoroacetate ([Omim]TA) as capping reagents under the ionic liquid-assisted hydrothermal condition. Detailed proofs indicated that the process of crystal growth was dominated by an oriented aggregation and self-assemble growth mechanism. The morphology of CuO evolved from nanoparticles to two-dimensional (2D) nanosheets and three-dimensional (3D) peachstone-like nanostructures. A formation process is proposed to illustrate the growth of peachstone-like CuO crystal. The influence of the ionic liquid cations on the morphology of CuO materials was studied in detail. The cations of the ionic liquids control the morphology of crystals. Additionally, it was also found that the concentration of ionic liquids and the reaction time have direct influences on the morphology of the products. Their optical absorption spectra were also studied. The synthetic strategy could be extended to assemble 3D architectures of other materials.     

Magnetic anisotropy and electronic structure of iron films on W(1 1 0) by spin-polarized two-electron spectroscopy

Low-energy spin-polarized two-electron spectroscopy was applied to study the spin-dependent electronic structure of 3 ML and 50 ML epitaxial iron films grown on single crystal W(1 1 0). Such films are known to show an in-plane rotation of the easy magnetization axis between thicknesses [M. Donath, Journal of Physics: Condensed Matter 11 (48) (1999) 9421; D. Sander, Journal of Physics: Condensed Matter (20) (2004) R603, O. Fruchart, J.P. Nozieres, D. Givord, Journal of Magnetism and Magnetic Materials 207 (1999) 158, H.J. Elmers, U. Gradmann, Applied Physics A: Materials Science & Processing 51 (3) (1990) 255]. Momentum distributions of correlated electron pairs I(k₁, k₂) excited from the films by 25 eV primary electrons were measured for two opposite polarizations of the incident beam. Energy and momentum conservation laws in the electron scattering events allow the extraction of information on the spin-dependent Bloch spectral density function of the valence electrons in iron films. The observed difference in the electronic structure of these two films is most likely due to the different crystal structures of the films.     

Effect of nonuniform mechanical stresses on the domain structure of iron borate

A magnetooptic method is used to study the effect of nonuniform radial mechanical stresses on the domain structure, magnetic susceptibility, and magnetic hysteresis loops of a FeBO₃ single crystal. When a magnetic field is applied in the basal plane of FeBO₃ along the stress vector, a system of tapered domains appears in the crystal during magnetization. These domains exist in a certain temperature-dependent field range H₀ ≤ H ≤ H _c . The appearance of a system of tapered domains is found to substantially affect the technical magnetization of a stressed crystal. The results obtained are discussed within the thermodynamic theory of a domain structure. A theoretical model used is shown to adequately describe the experimental temperature and field dependences of the ratio \({D \mathord{\left/ {\vphantom {D {\sqrt L }}} \right. \kern-\nulldelimiterspace} {\sqrt L }}\) (where D and L are the average width and length of a tapered domain, respectively). The calculated value of D is approximately 1.3 times smaller than the experimentally observed domain width.     

Optical properties of CH3NH3PbI3 crystal grown using inverse temperature crystallization

Perovskite CH₃NH₃PbI₃ (MAPbI₃) single crystal was grown using inverse temperature crystallization method. Crystallinity of the perovskite was confirmed by X-ray diffraction. Photoluminescence (PL) spectra revealed abnormal behavior due to a temperature-induced orthorhombic to the tetragonal phase transition. Four PL emission peaks, A, B, C, and D, were observed in the low temperature regime. Peaks A and B were observed at 756 and 776?nm?at 12?K, and were blue-shifted and disappeared at 130 and 70?K, respectively. Peaks C and D were observed at 789 and 807?nm?at 40?K and were also blue-shifted to 780 and 794?nm?at 100?K. On the other hand, the peak C red-shifted to 799?nm from 100 to 140?K because of an orthorhombic to the tetragonal phase change and was also blue-shifted above 140?K. From the excitation intensity- and temperature-dependent PL results, peaks A and B were assigned to the free-exciton and bound-exciton of the orthorhombic phase crystal, respectively. In addition, peaks C and D were associated with the free-exciton and bound-exciton of the tetragonal phase crystal, respectively. The activation energy of peak C was calculated to be 98?meV from temperature dependence of the PL intensity.     

Thermal emission properties of 2D and 3D silicon photonic crystals

We present measurements of the thermal emission properties of 2D and 3D silicon photonic crystals with and without substrate heated resistively as well as passively with an aluminium hotplate. The out-of-plane and in-plane emission properties were recorded and compared to numerical simulation. It turned out that for the in-plane 2D photonic crystal and out-of-plane 3D photonic crystal emission a photonic stop gap effect is visible. For the out-of-plane 2D photonic crystal emission, no photonic bandgap effect is observable but instead strong silicon oxide emission from native oxide inside the pores of silicon are observable. A model for the modified thermal emission is presented.     

A full resolution autostereoscopic 3D display based on polarizer parallax barrier

A full resolution autostereoscopic three-dimensional （3D） display prototype is developed. It is composed of a time division thin film transistor liquid crystal display panel with an optical controlled birefringence liquid crystal polarization switch and a polarizer parallax barrier. Fast driving circuits operating at 120-Hz frame rate are fabricated. The 3D images on the display have the same resolution as the corresponding two-dimensional images, which is significantly different from conventional parallax barrier autostereoscopic 3D displays having degraded 3D image resolution.     

A new fabrication technique for photonic crystals: Nanolithography combined with alternating-layer deposition

We propose two photonic crystal structures that can be created by combining nanolithography with alternating-layer deposition. Photonic band calculations suggest that a drilled alternating-layer photonic crystal combining two-dimensional (2D) alternating multilayers and an array of vertically drilled holes may achieve a full photonic bandgap. In addition, a 3D/2D/3D cross-dimensional photonic crystal, which sandwiches a 2D photonic crystal slab between three-dimensional (3D) alternating-layer photonic crystals, should provide better vertical confinement of light than a conventional index guiding slab. Fabrication techniques based on existing technologies (electron beam lithography, bias sputtering, and low-pressure ECR etching) require very few process steps. Our preliminary fabrication suggests that, by refining these technologies, we will be able to realize photonic crystals.