Theoretical investigations on the spin Hamiltonian parameters for Er3+ ion in LiYF4

The spin Hamiltonian parameters g_∥, g_⊥, A_∥ and A_⊥ for Er³⁺ ion in LiYF₄ are investigated by using the perturbation formulas of these parameters for a 4f¹¹ ion in tetragonal symmetry. In these formulas, the contributions to the spin Hamiltonian parameters from the second-order perturbation terms and the admixtures of different states are considered. The relevant crystal field parameters are calculated from the superposition model and the local structural parameters of the Y³⁺ site occupied by impurity Er³⁺. The theoretical optical spectra within ⁴I_15/2 and ⁴I_13/2 states and the spin Hamiltonian parameters obtained in this work are consistent with the observed values.     

Structural models and electronic properties of cage-like C3N4 molecules

We have proposed the atomic models and, using the Hückel approach, studied the electronic properties of various kinds of nonspherical C₃N₄ cage molecules (octahedral-, cubic- and dodecahedral-like structures) assembled from triazine rings and nitrogen bridges. Results of E_tot estimations reveal that octahedral-like cages (OLC) are the most stable ones. The carbon nitride cages have the HOMO–LUMO gaps in the interval 1.4–2.1 eV. This is the first reported comparison of the possible forms of nonspherical cage-like C₃N₄ molecules, which could be of interest to the current efforts in the synthesis of nanoscale-sized faceted forms of carbon nitride species.     

Effect of LiAl5O8 additions on the sintering and optical transparency of LiAlON

LiAl₅O₈ (zeta alumina) was reaction sintered with α-Al₂O₃ and AlN to produce γ-LiAlON. Zeta alumina transforms from a primitive to a face-centered cubic structure above 1290 °C with a lattice parameter similar to γ-AlON. Weight loss measurements combined with XRD suggest solubility of Li in the spinel structure at elevated temperatures. The Vickers hardness, at a 1-kg load, of the pressureless sintered LiAlON was 16.5 ± 0.5 GPa, independent of the grain size or amount of zeta alumina added, for LiAl₅O₈ additions ranging between 0 and 16 wt.%. In-line transmission in the visible and near-IR regions increased with increasing grain size, most likely due to pore coalescence.     

Structural and Electric Properties of Sol–Gel-Derived Ba0.9Sr0.1TiO3 Multilayers

Crack-free Ba_0.9Sr_0.1TiO₃ (BST) and Mn-doped Ba_0.9Sr_0.1TiO₃ (BSTM) multilayers with thickness over 2 μm have been prepared by chemical solution deposition based on one single precursor. Both multilayers exhibit good performance as Bragg reflectors. Mn doping tends to suppress the leakage current in BST multilayers effectively by smoothing the layers and the reduction of the charge carries. The Mn-doped BST multilayer displays an excellent ferroelectric property, with an average remnant polarization ( P _r⁺– P _r⁻)/2 of 12.69 μC/cm² and an average coercive field ( E ⁺ – E ⁻ )/2 of about 72.95 kV/cm under an applied field of 440 kV/cm.     

Organic–inorganic hybrids containing polyimide,organically modified clay and in situ formed polydimethylsiloxane

A series of organic–inorganic hybrid consisting of polyimide (PI) prepared from pyromellitic dianhydride (PMDA) and 4,4′-oxydianiline (ODA), organically modified montmorillonite (OMMT) and polydimethylsiloxane (PDMS) were successfully prepared by in situ sol–gel process. OMMT was prepared by surface treatment of montmorillonite (MMT) with hexadecyltrimethylammonium bromide. X-ray diffraction (XRD) analysis showed that the OMMT layers were exfoliated into the polymer matrix at 2% of OMMT content. The PI–OMMT–PDMS hybrids at 2% of OMMT content were transparent when PDMS content was less than 5%. The PI–OMMT–PDMS hybrid showed better tensile modulus, strength and elongation at break than that of pristine PI due to the reinforcement effect of OMMT and toughening effect of PDMS. The thermal stability of hybrids such as the decomposition temperature and weight residue at 800 °C also increased with the increase of PDMS content as evidenced by thermogravimetric analysis (TGA).     

Effects of ZrO2 on the structure and magnetic properties of CoPt thin films

[CoPt 1.5 ml/ZrO2 xnm]10 multilayer films were deposited on glass substrates by magnetron sputtering and then annealed in vacuum at 600℃ for 30 min. Their structures and magnetic properties were investigated as a function of ZrO2 content. The results show that the grain size and coercivity first increase and then decrease with the increase in ZrO2 content. The maximum coercivity and grain size are obtained at 37 vol.% of ZrO2. The content of ZrO2 in the film plays an important role in the separation of CoPt grains and in the reduction of intergrain exchange interaction. On the basis of the studies of angular dependent coercivity, it is found that the magnetization reversal of CoPt films with （111 ） texture is different from either the domain wall motion or the S-W type of rotation mode.     

Relaxations and bonding mechanism of arsenic in-situ impurities in MCT： first-principles study

1 Introduction Mercury cadmium telluride (Hg1?xCdxTe, MCT) is currently one of the most widely used semiconductor materials for infrared detector arrays. It is well known that the applications of the semiconductor materials, especially for Ⅱ-Ⅵ compound…     

基于载波表的GPS载波跟踪环路研究

实时GPS软件接收机可以使用查找表的方法得到本地复现载波以减少运算量。载波表是由一组具有一定频率间隔和固定初始相位的正弦和余弦信号组成。传统的载波跟踪环路无法使用具有离散频率和不连续相位的复现载波完成GPS载波跟踪。针对这一问题,使用相位补偿算法对载波进行相位补偿,设计了基于载波表的载波跟踪环路。仿真结果表明该载波跟踪环路能有效实现GPS信号的载波跟踪,且与传统的载波跟踪环路相比仅有微小的信噪比损失和频率跟踪精度衰减,可用于实时GPS软件接收机设计。     

基于时间域读出的大动态范围CMOS图像传感器

设计了一款基于时间域读出的大动态范围CMOS图像传感器。传感器基于一种新型的结构,其可在时间域下探测高输入光强,在模拟域下探测低输入光强。该设计在传统电容反馈式跨阻放大器(CTIA)的基础上,新增了时间域测量电路,在不改变原有积分过程的同时可实现连续的大动态范围。基于0.35μm,5V-CMOS工艺进行了256×1线列CMOS图像传感器流片,光电二极管面积为22.5μm×22.5μm,并对器件的光电特性进行了后仿真验证。仿真测试结果表明,基于时间域读出的图像传感器可实现96dB的大动态范围,且时间域和模拟域的两路输出信号可同步输出,功耗为7.98mW。     

小像元量子阱FPA抗光学串音的FDTD仿真

采用光栅耦合结构的焦平面阵列(Focal Plane Array,FPA)在工艺上难以制备,反射耦合结构较为容易。为探究反射耦合结构是否可以在小尺寸范围内替代光栅耦合结构,文章使用FDTD电磁场仿真软件MEEP构建了光栅耦合结构和反射结构GaAs/AlGaAs量子阱红外焦平面阵列三像元模。通过对器件内部光学串音进行仿真,验证了在逼近衍射极限时,采用全内反射结构的FPA在5~7μm和8.5~10μm之间的抗串音效果强于光栅耦合结构,而在6.5~8.5μm和10~12μm之间,光栅耦合结构的抗串音效果更好,在12~15μm范围内,两种结构的抗串音能力相当。针对15μm中心距全内反射结构量子阱FPA,探究了反射角度、刻蚀深度和量子阱周期对其串音的影响。