Al(N3)3和P(N3)3结构与性质的理论研究

在B3LYP/6-311++G(3df)理论水平,对二元叠氮化合物Al(N3)3和P(N3)3进行密度泛函理论计算研究,获得其稳定分子的几何构型、电子结构、红外光谱以及稳定性.研究结果表明,P(N3)3分子中的磷原子拥有一对孤对电子,给予临近氮原子(Nα)上的孤对电子较大斥力,从而使其表现出三角锥形结构特征,而Al(N3)3表现为平面三角形结构特征.自然键轨道分析表明,Al-Nα和P-Nα键本质上均属于共价键.与叠氮自由基相比较而言,Al(N3)3和P(N3)3的每个叠氮基内部的总成键度显著增大,从而导致N3基的振动频率发生明显蓝移.前线分子轨道能级差和叠氮自由基键离解能的计算结果均表明Al(N3)3比P(N3)3更稳定.     

Al(N3)3和P(N3)3结构与性质的理论研究

在B3LYP/6-311++G(3df)理论水平,对二元叠氮化合物Al(N3)3和P(N3)3进行密度泛函理论计算研究,获得其稳定分子的几何构型、电子结构、红外光谱以及稳定性。研究结果表明,P(N3)3分子中的磷原子拥有一对孤对电子,给予临近氮原子(Nα)上的孤对电子较大斥力,从而使其表现出三角锥形结构特征,而Al(N3)3表现为平面三角形结构特征。自然键轨道分析表明,Al–Nα和P–Nα键本质上均属于共价键。与叠氮自由基相比较而言,Al(N3)3和P(N3)3的每个叠氮基内部的总成键度显著增大,从而导致N3基的振动频率发生明显蓝移。前线分子轨道能级差和叠氮自由基键离解能的计算结果均表明Al(N3)3比P(N3)3更稳定。     

脉冲高能量密度等离子体沉积(Ti,Al)N薄膜组织及其性能研究

利用脉冲高能量密度等离子体技术在室温条件下在45＃钢基材表面沉积了高硬度耐腐蚀(Ti, Al)N薄膜. 利用扫描电子显微镜、X射线衍射、X射线光电子能谱、俄歇电子能谱分析了薄膜的显微组织.利用纳米压痕仪测试了薄膜的纳米硬度.测试了薄膜在05mol/L H2SO4水溶液中的耐蚀性. 测试结果表明：薄膜主要组成相为(Ti, Al)N，同时含有少量的AlN,薄膜的纳米硬度高达26 GPa,薄膜具有良好的耐蚀性，与1Cr18Ni9Ti奥氏体不锈钢相比，耐蚀性提高了一个数量级. 关键词： 脉冲高能量密度等离子体 薄膜 纳米硬度 耐蚀性     

Al-O,C元素添加对FeCo合金薄膜磁性和频率特性的影响

用磁控射频溅射法制备了FeCoAlOC薄膜,研究了Al-O和C元素的添加对FeCo合金薄膜的软磁性和高频特性的影响.随着Al,O,C元素添加量的增加,薄膜微结构发生了由多晶到纳米晶再到非晶状态的转化,软磁性得到提高;薄膜电阻率则由最初的87 μΩ·cm增至900 μΩ·cm,高频特性得到改善: 截止频率最高可达2.9 GHz,低频实部磁导率最高可到达400. 关键词： 纳米晶 非晶 软磁薄膜     

Influence of thickness,width and temperature on critical current density of Nb thin film structures

The density of critical currents j_C in Nb thin films with thickness smaller than 15 nm and width between 100 nm and 10 μm has been measured in a wide temperature range. We have found that the temperature dependencies of j_C in sub-micrometer wide bridges at 0.7T_C < T < T_C are well described by the Ginzburg–Landau de-pairing critical current. In wider bridges already at T < 0.9T_C the j_C value is significantly reduced due to the penetration and de-pinning of magnetic vortices.     

Influence of thickness of electrochemically deposited hole-transport film on electroluminescent properties

Polybithiophene (PBTh) film was used as a hole-transport layer in an electroluminescent (EL) device. The PBTh was electropolymerized on indium tin oxide (ITO)-coated glass acting as a working electrode. From the change of full width at half maximum (FWHM) of the EL spectrum with the thickness of the PBTh film, it could be deduced that the PBTh film efficiently blocks the injection of electrons into the ITO electrode. The thickness of the hole-transport layer used in the EL device has a significant influence on the EL intensity and efficiency. Experimental data showed that there is an optimal thickness of the electrodeposited PBTh-hole-transport layer for high-efficiency EL devices.     

Influence of localized states in a semiconducting film of critical thickness on the electrical properties of thinfilm ms' is structures

The current-voltage and high-frequency capacitance-voltage (C-V) characteristics have been used to investigate the electrical properties of thin Ga₂Ses films in Me-Ga₂Se₃-Si structures (n and p type). The features of the high-frequency C-V dependences of the structures based on p-type Si are explained in the framework of a model of the MS' IS structure with donor type centers in the semiconducting S'film (the thickness of the S' film is comparable with the generalized screening length). It is shown that in the investigated structures the charge transport mechanism is due to ionization of volume centers (the activation energy of a deep donor center is 0.72 eV) in the Ga₂Se₃ film, the mechanism being enhanced by an electric field. Analysis of the high-frequency C-V characteristics showed that the majority carriers in the Ga₂Se₃ films are electrons with concentration 10¹² cm^–3; the concentration of the deep donor centers is 5·10¹⁶ cm^–3.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 83–88, January, 1981.     

厚度对非极性聚合物薄膜驻极体电荷储存及电荷动态特性的影响

以Du Pont公司的商用Teflon FEP A型薄膜为例，通过热脉冲技术、等温表面电位衰减测量和开路热刺激放电电流谱分析等实验结果，讨论了经常温和高温电晕充电后样品厚度对薄膜驻极体的沉积电荷密度、薄膜驻极体的内电场、体电导率以及电荷储存稳定性的影响.通过热脉冲技术组合电导率温度曲线的测量，研究了在不同温度条件下样品厚度对沉积电荷层的平均电荷重心移动的影响.结果表明：在充电参数一定的条件下，随着膜厚的降低，储存电荷密度上升，但电荷稳定性有所下降.因此，合理地调控薄膜厚度，可以有效地优化驻极体的电荷储存能 关键词： 厚度 驻极体 电荷储存能力 电荷稳定性     

Comparison of one and two-neutron transfer near the coulomb barrier for the27Al(18O,16O)29Al,27Al(180,17O)28Al and27Al(13C,12C)28Al reactions

Total reaction cross sections for the transfer reactions²⁷Al(¹⁸O,¹⁶O)²⁹Al,²⁷Al(¹⁸O,¹⁷O)²⁸Al and²⁷Al(¹³C,¹²C)²⁸Al are reported for center-of-mass energies between 13 and 20 MeV for¹⁸O projectiles and between 11 and 17.5 MeV for¹³C projectiles. The reaction products,²⁹Al and²⁸Al, beta decay to²⁹Si and²⁸Si, respectively, and the subsequentγ decays of²⁹Si and²⁸Si were measured. Due to the relatively long beta decay half lives, data were taken in a beam-off mode, resulting in very clean spectra. Total cross sections were calculated and compared with a theoretical model for barrier penetration proposed by C.Y. Wong. Differences between¹⁸O induced one and two-neutron total transfer reaction cross sections are discussed.     

3d过渡金属元素掺杂Al12N12纳米线几何结构和电子性能的第一性原理研究

基于密度泛函理论的第一性原理计算方法,系统地研究了不同3d过渡金属元素(Sc、Ti、V、Cr、Mn、Fe、Co和Ni)掺杂Al₁₂N₁₂纳米线的几何结构、稳定性和电子结构.结果表明：所有掺杂体系均是热力学稳定的;掺杂Ni时体系保留了原有的非磁性间接带隙半导体特性;当掺杂其它原子(Sc、Ti、V、Cr、Mn、Fe、Co)时体系仍然保持为半导体,但带隙明显减小.掺杂过渡金属原子对于Al₁₂N₁₂纳米线的电子结构具有明显的调控作用,在能带调控和光电方面有潜在的应用前景.     

Dependence of electron and positron backscattering coefficients on Al film thickness

The backscattering coefficient of 1-4 keV electron and positron beams normally incident impinging on Al thin film targets is stochastically modeled within a Monte Carlo frame work. The aim of the present paper is to study the behavior of the backscattering coefficient as a function of the Al film thickness. To the authors’ knowledge, no theoretical or experimental work on the dependence of the positron backscattering coefficient on film thickness targets has been reported so far. It is found that the backscattering coefficient for both electron and positron beams presents different behaviors when the Al film thickness belongs to the nano-scale. Beyond this scale, the behavior becomes qualitatively similar.     

X-ray topographic imaging of (Al, Ga)N/GaN based electronic device structures on SiC

Structural defects and their impact on the performance, lifetime and reliability of electronic devices are of permanent interest for crystal growers and device manufacturers. This is especially true for epitaxial (Al, Ga)N/GaN based high electron mobility transistor (HEMT) structures on 4H-SiC (0 0 0 1) substrates. This work points out how micropipes, dislocations and grain boundaries present in a 4H-SiC (0 0 0 1) wafer and subsequently overgrown with an (Al, Ga)N-GaN-HEMT layer sequence show up in X-ray topographic images and two-dimensional XRD maps. Using X-ray topography in transmission geometry, micropipes and other structural defects are localized non-destructively below structured metallization layers with a spatial resolution of a few tens of micrometers.     

Exploring the electronic structure and optical properties of new inorganic luminescent materials Ba(Si,Al)5(O,N)8 compounds for light-emitting diodes devices

Due to growing demand on discovering new materials for light-emitting diodes devices, many efforts were made to discover and characterize new inorganic materials such as phosphors. Using the full potential method within density functional theory the electronic and optical properties of BaAl₂Si₃O₄N₄ and BaAlSi₄O₃N₅ semiconductors have been investigated. The electronic structure and the optical properties of these phosphors were calculated through a reliable approach of modified Beck-Johnson (mBJ) approach. We found that BaAl₂Si₃O₄N₄ and BaAlSi₄O₃N₅ have wide direct band gaps positioned at Γ about 5.846 and 4.96 eV respectively. The optical properties, namely the dielectric function, optical reflectivity, refractive index and electron energy loss, are reported for radiation up to 15 eV. Our study suggests that BaAl₂Si₃O₄N₄ and BaAlSi₄O₃N₅ could be promising materials for applications in the LEDs devices and optoelectronics areas of research.     

Structural properties of size-selected FeCo nanoparticles deposited on W(110)

Size-selected iron and iron–cobalt alloy clusters have been studied with high resolution transmission electron microscopy (HRTEM) and scanning tunneling microscopy (STM). The clusters were produced by a continuously working arc cluster ion source and subsequently size-selected by an electrostatic quadrupole deflector. The crystalline structure of pure clusters has been investigated with HRTEM to ensure a reliable determination of the lattice parameter for the alloy clusters. The composition of the alloy clusters was checked with energy dispersive X-ray spectroscopy (EDX). The height of the deposited FeCo clusters on the (110) surface of tungsten was determined via STM. These results were compared with the lateral size distribution being investigated by TEM and allow a conclusion on the shape of the deposited alloy clusters. Furthermore, the behavior of the alloy clusters on the W(110) surface at elevated temperatures has been examined, at which the clusters show anisotropic spreading.     

Influence of the thickness on structural,magnetic and electrical properties of La0.7Ca0.3MnO3 thin film

We have studied the effect of thickness on the structural, magnetic and electrical properties of La_0.7Ca_0.3MnO₃ thin films prepared by pulsed laser deposition method using X-ray diffraction, electrical transport, magneto-transport and dc magnetization. X-ray diffraction pattern reflects that all films have c-axis epitaxial growth on LaAlO₃ substrate. The decrease in out-of-plane cell parameter specifies a progressive relaxation of in the plane compressive strain as the film thickness is increases. From the dc magnetization measurements, it is observed that ferromagnetic to paramagnetic transition temperature increases with increase in the film thickness. Magneto-resistance and temperature coefficient of resistance increases with film thickness and have maximum value near its metal to insulator transition temperature.     

Influence of carbon black content and film thickness on vapor detection properties of polyvinylpyrrolidone composite sensors

Chemoresistive carbon black–polyvinylpyrrolidone (CB-PVP) composite sensors were prepared with different physical properties in CB dispersion, CB content and film thickness by using the fabrication method of a drop casting or a spin coating. To verify the influences of the physical properties, their vapor detection characteristics were measured and evaluated in terms of the magnitude in sensor responses. From these evaluations, the highest response was observed around at the optimized CB contents of 12.5 wt.% for the drop casting and 17.5 wt.% for the spin coating. Furthermore, homogeneous CB dispersion and careful thickness regulation were found to be necessary to achieve a sensor with good performance.     

Optical characterization of periodically polarity-inverted ZnO structures on (0001) Al2O3 substrates

We investigated the optical properties of periodically polarity-inverted (PPI) ZnO structures formed on (0001) Al₂O₃ substrates by evaluating the cathodoluminescence (CL) as a function of the acceleration voltage (V_acc). At surface regions with a low V_acc, the emission from the interface region was dominant but the dominant emission source changed to the Zn-polar regions as V_acc was increased, which can be explained by the different exciton diffusion lengths. The dependence of the emission properties on V_acc showed a slight red shift as V_acc increased and a larger red shift was observed in the Zn-polar regions. Moreover, the interface regions showed the highest intensity compared to other regions, which can be explained by the results of the geometrical analysis conducted using a finite-differential time domain simulation.     

Influence of ferromagnetic thickness on dynamic anisotropy in exchange-biased MnIr/FeCo multilayered thin films

A comprehensive study of the influence of ferromagnetic thickness on the static and dynamic magnetic properties in exchange-biased FeCo/MnIr multilayers for both strong and weak exchange-bias coupling cases is presented. The results demonstrate that static and dynamic magnetic anisotropy fields decrease with ferromagnetic thickness in both cases. The rising of rotational anisotropy is discussed in conjunction with the enhanced coercivity and exchange bias by taking into account the roles of the rotatable and frozen antiferromagnetic spins in each of the two cases. Due to the contributions of the exchange bias and rotational anisotropy, the resonance frequency can be tailored up to 10 GHz. In addition, the behaviors of the frequency linewidth and the effective damping factor are discussed and ascribed to the dispersion of magnetic anisotropy.     

Comparisons of ZnO codoped by group IIIA elements (Al, Ga, In) and N: a first-principle study

The electronic structures and effective masses of the N mono-doped and Al-N,Ga-N,In-N codoped ZnO system have been calculated by a first-principle method,and comparisons among different doping cases are made.According to the results,the impurity states in the codoping cases are more delocalised compared to the N mono-doping case,which means a better conductive behaviour can be obtained by codoping.Besides,compared to the Al-N and Ga-N codoping cases,the hole effective mass of In-N codoped system is much smaller,indicating the p-type conductivity can be more enhanced by In-N codoping.