沉积参数对铯铅溴钙钛矿薄膜中CsPb2Br5相结构演变和发光特性的影响

基于化学气相沉积(CVD)法制备的铯铅溴钙钛矿薄膜具有优异的光电特性，然而薄膜通常存在CsPbBr₃和CsPb₂Br₅两个不同的相结构区域。本文通过CVD法制备了铯铅溴钙钛矿薄膜，并利用X射线衍射(XRD)、扫描电镜(SEM)、电子能谱仪(EDS)及荧光光谱仪研究了反应气压与N₂流量对其中的CsPb₂Br₅相结构的影响。实验结果表明，反应气压的变化对CsPb₂Br₅相结构无影响；与此不同，随着N₂流量的减少，薄膜中部分CsPb₂Br₅相结构逐渐转变为CsPbBr₃相结构，其发光也由以～630 nm为主的宽带发射转变为以～530 nm为主的窄带发射。实验表明，N₂流量是调控CsPb₂Br₅相结构和发光特性的有效手段。     

超声冷却SO2( 1A2— 1A1)激光诱导荧光激发谱的转动分析

通过改变SO₂/Ar配比，研究了超声膨胀冷却SO₂( ¹A₂— ¹A₁)系统315—330nm波段振动分辨的激光诱导荧光(LIF)激发谱.获得了属于两个完整带系(1,m,1),(0,n,1)—(0,0,0)的高分辨转动结构谱.其中(ν′₁,ν′₂,ν′₃)=(0,9,1),(0,10,1),(1,7,1),(1 关键词：     

基于N2 LBH带的中高层大气氧分子柱密度反演

给出了一种利用气辉探测反演中高层大气氧分子柱密度的新方法。氧分子对N₂ Lyman-Birge-Hopfield (LBH)短波带(LBH_S)的吸收作用较强,而对N₂ LBH长波带(LBH_L)的吸收作用较弱,根据这一特性,利用N₂ LBH_S与N₂ LBH_L的比值来反演中高层大气氧分子柱密度。通过气辉模型计算得到一个用于估计氧气含量的插值表,计算得到在不同氧分子柱密度、不同太阳天顶角、卫星观测角和太阳活动条件下的N₂ LBH长短波带比值的自然对数ln(LBH_S/LBH_L),根据探测的ln(LBH_S/LBH_L)及相应的太阳天顶角、卫星观测角和太阳活动指数,拟合得到氧分子柱密度。最后,采用模式模拟的方法对反演结果进行验证,所得反演结果与模拟真值的误差在百分之十以内,证明了这种探测中高层大气氧分子柱密度新途径的可行性。     

AlH分子10个Λ-S态和26个Ω态光谱性质的理论研究

在修正了各种误差(自旋-轨道耦合效应、标量相对论效应、核价相关效应及基组截断)的基础上,本文利用内收缩的多参考组态相互作用(icMRCI)+Q方法计算了AlH分子10个Λ-S态和26个Ω态的势能曲线.利用包含自旋-轨道耦合效应的icMRCI/AV6Z~*理论计算了X¹∑_((0⁺)⁺),a³Π_0⁺,a³Π₁,a³Π₂和A¹Π₁态之间的跃迁偶极矩.计算得到的光谱常数和跃迁数据与现有的实验值符合很好.研究发现:1)A¹Π₁-X¹∑_((0⁺)⁺)(0,0),(0,1),(0,2),(1,0),(1,1),(1,2),(1,3),(1,4)和(1,5)带Q(J")支的跃迁比较强,随着J"的增大,Δv=0带的爱因斯坦A系数和振...     

高压高温处理对A15Nb3(Al,Ge)结构成分及其超导性能的影响

在0—67kbar压力范围,对名义成分为Nb₃(Al_1-xGe_x)的合金(x=0.20,O.23,0.25;含有Al5+σ相)进行了热处理。X射线分析表明:1)随着压力的升高,Al5相的晶胞参数a₀出现极大值;2)与Al5相结构成分密切相关的衍射峰(211),(210)的相对累积强度I²¹¹/I²¹⁰随压力的变化与a₀的变化类似;3)Al5相结构成分随压力向着富Nb的方向移动。低温测试结果表明:随着压力的升高,试样的超导转变温度降低,转变宽度出现极大值。 关键词：     

Cu掺杂β-Si3N4的力学性能和电子结构的第一性原理研究

采用基于密度泛函的第一性原理方法研究了(Si_3-xCu_x)N₄(x=0,0.25,0.5,0.75,1)晶体的稳定性、力学性能和电子结构,分析了Cu掺杂对β-Si₃N₄力学性能的影响机制.结果表明,(Si_3-xCu_x)N₄为热力学稳定结构,Cu掺杂降低了β-Si₃N₄的稳定性.由弹性常数和Voigt-Reuss-Hill近似看出,(Si_3-xCu_x)N₄满足波恩力学稳定性判据,Cu掺杂使得β-Si₃N₄的体模量、剪切模量和杨氏模量降低,当x=0时,(Si_3-xCu_x)N₄的体模量、剪切模量和杨氏模量最大,分别为234.3 GPa、126.7 GPa和322.1 GPa.根据泊松比和G/B值判断出(...     

不同驱动力下瓦斯水合物生长过程Raman光谱特征

基于煤矿瓦斯(CH₄∶C₂H₆∶N₂=67.5∶22.5∶10)水合物相平衡曲线开展四种驱动力ΔP水合动力学实验,利用可见显微Raman光谱仪获取水合物生长过程光谱图,根据水合物相中C₂H₆ C-C键伸缩振动特征峰Raman位移确定了4组实验中水合物为sⅡ结构。基于van der Waals与Platteeuw模型获取瓦斯水合物生成过程中水合物相气体组分及水合指数变化规律。研究表明： 驱动力的大小影响水合物的稳定性,随着驱动力的增加,CH₄相比C₂H₆逐渐占据更多的孔穴结构,CH₄在水合物相内比例增加,水合物稳定性越强;瓦斯中N₂,CH₄和C₂H₆进入水合物孔穴优先级可以通过分子与水合物孔穴的直径比进行确定,分析认为在sⅡ水合物结构中小孔穴CH₄优先级最高,大孔穴C₂H₆最高;基于瓦斯水合物稳定性,对水合物生长过程客体分子的物质传递规律进行描述,为瓦斯水合物的微观生长提供理论基础。     

采用N2-RF等离子体氮化GaAs(001)

研究了在MBE系统中,GaAs(001)表面的氮化过程。GaAs(001)表面直接和间接地暴露在等离子体激发的N₂气流下。两种氮化过程显示了完全不同的表面氮化结果。在打开N₂发生器挡板的情况下,氮化导致GaAs(001)表面损伤,并且形成多晶结构。当增加N₂气压时,损伤变得更严重。但是,在关闭N₂发生器挡板的情况下,在500℃下,经过氮化将观察到(3×3)再构的RHEED花样,表面仍保持原子级的平整度。上述结果表明,不开N₂发生器挡板,低温(500℃下)氮化将在GaN外延生长之前形成平整的薄层c-GaN。     

介质阻挡均匀大气压氮气放电特性研究

基于一维流体力学模型，对介质阻挡均匀大气压氮气放电特性进行了数值计算研究.模型中考虑了氮气中主要的电离、激发过程，所包含的粒子种类为e，N₂，N⁺₂，N⁺₄，N₂(a¹∑^-_u)，N₂(A³∑⁺_u).模拟结果显示，氮中的放电具有低气压下汤生放电的特性.放电电流幅度较小，放电过程中气体电压变化缓慢，电子密度远低于离子密度，而且最大值出现在阳极，电子不能在放电间隙中被俘获，不存在中性等离子体区，气体中的电场趋于线性变化.亚稳态N₂(A³∑⁺_u)和N₂(a¹∑⁺_u)在整个放电空间都具有非常高的密度，比电子密度高三个量级以上，亚稳态密度的最大值出现在阳极，这样的分布决定了放电的空间结构.放电所需的种子电子主要由亚稳态之间潘宁电离提供，这种机理使放电的电离水平较低，导致氮气中的放电只能是汤生放电.随着放电参数的变化，多电流峰放电也可在氮气中获得. 关键词： 大气压均匀放电 介质阻挡放电 数值模拟 氮气     

大气压空气纳秒脉冲阵列式线-线SDBD等离子体的电学及发射光谱特性研究

提出了一种阵列式线-线沿面介质阻挡放电结构,利用双极性高压纳秒脉冲电源,在大气压空气中激励产生了相对大面积的放电等离子体。其中,高压电极、地电极均为圆柱形金属,放电反应器由20组相间排列的阵列式线型高压电极和套有介质管的阵列式线型地电极组成。利用电压探头、电流探头、示波器等测量了放电电压和放电总电流,并计算得出了放电的实际电流。利用光纤、光栅光谱仪、CCD等测量了波长范围在300～440 nm和766～778 nm的发射光谱,即氮分子第二正带N₂ (C3Π_u→B3Π_g)包括Δν= +1, 0, -1, -2, -3、氮分子离子第一负带N+₂(B2Σ+_u→X2Σ+_g),N₂ (B3Π_g→A3Σ+_u)和O (3p5P→3s5S₂)的发射光谱。比较了氮分子第二正带N₂ (C3Π_u→B3Π_g)的各个振动峰和各个活性物种的发射光谱强度,以及这些发射光谱强度随着脉冲峰值电压的变化。测量了N₂(C3Π_u→B3Π_g, 0-0)的二次、三次衍射光谱,与原始光谱在转动带、背景光谱等方面进行了比较,并计算了二次衍射和原始光谱之间的峰值比。利用氮分子第二正带N₂ (C3Π_u→B3Π_g, Δν=+1, 0, -1, -2)和氮分子离子第一负带N+₂ (B2Σ+_u→X2Σ+_g, 0-0)模拟了等离子体的转动温度和振动温度,对模拟结果进行了比较,并研究了脉冲峰值电压对等离子体振动温度和转动温度的影响。通过测量放电的电压和计算得到的放电电流发现,当脉冲峰值电压为22 kV,脉冲重复频率为150 Hz时,阵列式线-线沿面介质阻挡放电的放电电流在正脉冲、负脉冲两个方向上均可达75 A左右。通过诊断放电等离子体的发射光谱发现,在测量的波长范围内,放电产生的活性物种主要有氮分子第二正带N₂ (C3Π_u→B3Π_g)、氮分子离子第一负带N+₂(B2Σ+_u→X2Σ+_g),N₂ (B3Π_g→A3Σ+_u)和O (3p5P→3s5S₂)。在脉冲峰值电压22～36 kV的变化范围内,氮分子第二正带N₂(C3Π_u→B3Π_g, 0-0)的发射光谱强度始终保持最强,N₂ (B3Π_g→A3Σ+_u)次之,而氮分子离子第一负带N+₂(B2Σ+_u→X2Σ+_g)和O (3p5P→3s5S₂)的发射光谱强度较弱。同时,当脉冲峰值电压升高时,氮分子第二正带N₂ (C3Π_u→B3Π_g)的所有振动峰,以及氮分子离子第一负带N+₂(B2Σ+_u→X2Σ+_g),N₂ (B3Π_g→A3Σ+_u)和O (3p5P→3s5S₂)的发射光谱强度均随之升高。通过比较氮分子第二正带N₂(C3Π_u→B3Π_g, 0-0)的原始、二次衍射、三次衍射光谱发现,二次、三次衍射光谱的转动带更清晰,但三次衍射光谱的背景更强,因此氮分子第二正带N₂(C3Π_u→B3Π_g)的二次衍射光谱更有利于模拟等离子体的转动温度。通过比较模拟得到的振动温度和转动温度发现,氮分子第二正带N₂ (C3Π_u→B3Π_g, Δν=-2)在N₂ (C3Π_u→B3Π_g)四个谱带Δν=+1, 0, -1, -2中最适于模拟等离子体振动温度,而利用氮分子离子第一负带N+₂ (B2Σ+_u→X2Σ+_g,0-0)模拟得到的等离子体转动温度要比N₂ (C3Π_u→B3Π_g, Δν=-2)的模拟结果高约10～15 K。同时,当脉冲峰值电压升高时,由N₂ (C3Π_u→B3Π_g, Δν=-2)和N+₂ (B2Σ+_u→X2Σ+_g, 0-0)模拟得到等离子体的转动温度均出现了略微上升的趋势,而利用N₂ (C3Π_u→B3Π_g, Δν=-2)模拟得出的振动温度则略微下降。     

Phase separation in strained cation- and anion-deficient Nd0.52Sr0.48MnO3 films

The magnetic and transport properties of anion- and cation-deficient Nd_0.52Sr_0.48MnO₃ films with different thicknesses, as well as of two films from this system grown on different SrTiO₃ and LaAlO₃ substrates, are studied. Below Curie temperature T _C, the films with different thicknesses exhibit phase separation: they represent magnetic clusters (drops) embedded in a nonconducting paramagnetic (at T > T _N, where T _N is the Néel temperature) or antiferromagnetic (T < T _N) matrix. The temperature dependences of the resistivity of the films are well described in terms of the polaron mechanism of conduction. In external magnetic field H = 0.01 T, the drops may reach 15 nm in size. They consist of magnetic polarons with a small radius (1–2 nm). The drops are shown to interact with each other in the films. Because of competition between drop-drop dipole interaction and the magnetic energy, the drops disintegrate into droplets with a size comparable to that of a magnetic polaron in a field of 1 T. An explanation is given for the discrepancy between our results and the frequently observed growth of the drops with a rise in the external magnetic field. As the film gets thicker, the fraction of the ferromagnetic phase grows with thickness nonlinearly. In the film grown on SrTiO₃ (compressed by 0.9%), the characteristic Néel and Curie temperatures are lower than in the film grown on LaAlO₃. The diameters of ferromagnetic drops (both maximal at H = 0.01 T and minimal at H = 1 T) turn out to be roughly the same as in the films with different thicknesses.     

First-principles investigation of structural,electronic and optical properties of IVA group spinel nitrides

The Si₃N₄ and Ge₃N₄ are important structural ceramics with many applications because of their attractive high temperature and oxidation resistant properties. The high-pressure and high-temperature spinel phases of these two materials were noticed to have wide, direct electronic band gaps. Other single and double spinel nitrides formed from IVA and IVB group elements have also attracted much attention. Present research focuses on selecting a special substance with promising optical properties and stability besides the attractive electronic properties. The formation energies of spinel nitrides are calculated and stabilities of a group of spinel nitrides are discussed, the structural and electronic properties of them are investigated in detail. By random phase approximation (RPA), the optical properties of spinel nitrides are researched. We obtain that γ-SiGe₂N₄ has some promising properties with potential technological applications from various aspects. The band transitions which contribute most to the peak of ε₂ have been identified. An assumption is proposed to raise the peak of ε₂.     

Mass spectrum in SQCD and problems with the Seiberg duality. Another scenario

The N = 1 SQCD with SU(N _c ) colors and N _F flavors of light quarks is considered within the dynamical scenario that assumes that quarks can be in the two different phases only: the heavy-quark phase, where they are confined, and the phase of higgsed quarks, at the appropriate values of the Lagrangian parameters. The mass spectra of this (direct) theory and its Seiberg dual are obtained and compared for quarks of small equal or unequal masses. It is shown that in those regions of the parameter space where an additional small parameter exists (it is < [`(b)]₀ /N_F = (3N_c - N_F )/N_F << 1< \bar b_0 /N_F = (3N_c - N_F )/N_F \ll 1 at the right end of the conformal window, where the direct theory is weakly coupled in the vicinity of its IR fixed point, or its analog 0 < b ₀/N _F = (2N _F − 3N _c )/N _F ≪ 1 for the dual theory at the left end of the conformal window), the mass spectra of the direct and dual theories are parametrically different. A number of other regimes are also considered.     

Investigation of the running-in process and friction coefficient under the lubrication of ionic liquid/water mixture

The tribological properties of three different films commonly used in microelectromechanical systems (MEMS) under the lubrication of ionic liquid (IL)/water mixtures with various concentrations in the running-in process have been investigated. Results show that coefficients of friction (COFs) and wear rates for low temperature silicon oxide (LTO)/Si₃N₄ vary in a similar way to the ones for poly-Si/Si₃N₄ under the lubrications of different IL/water mixtures. In contrast, the differences in COFs and wear rates are more significant in that the COFs and wear rates increase dramatically with the decrease in IL/water concentration in the case of self-mated Si₃N₄, while the differences in COFs and wear rates for the two other tribopairs are relatively small when the concentration is changed. The period of the running-in process reduces with the increase in IL/water concentration for all the tribopairs. Effective hydrodynamic lubrication can be found in the case of Si₃N₄/Si₃N₄ tribopair at higher IL/water concentrations without an evident running-in process, however, such a phenomenon cannot be observed for the other two tribopairs. Different wear mechanisms will also be analyzed in this paper.     

Magnetic and structural properties of nanocomposite Co-Ni-Cr-Al-Y-N thin films

The relation between structural and magnetic properties of Co-Ni-Cr-Al-Y-N thin films deposited by reactive r.f. magnetron sputtering was investigated. A marked change in the magnetic behaviour of the films with the different nitrogen partial pressure in the Ar/N₂ deposition atmosphere was observed and qualitatively explained in correlation with the phase composition. The nanocrystalline metal solid-solution obtained at low N₂ content and the nanocrystalline nitride/amorphous composite obtained at high N₂ content are not magnetic, whereas the amorphous phase produced for intermediate N₂ pressures behaves like a ferromagnetic semi-permanent material. The results demonstrate the possibility of modulating the magnetic properties of r.f. magnetron sputtered Co-Ni-Cr-Al-Y-N thin films, thus opening a new route for magnetic multilayer deposition. PACS 68.55.-a; 75.70.Ak; 75.75.+a; 85.70.-w     

SiOxNy thin films with variable refraction index: Microstructural, chemical and mechanical properties

In this work amorphous silicon oxynitride films with similar composition (ca. Si_0.40N_0.45O_0.10) were deposited by reactive magnetron sputtering from a pure Si target under different N₂-Ar mixtures. Rutherford backscattering (RBS) studies revealed that the coatings presented similar composition but different density. The mechanical properties evaluated by nanoindentation show also a dependence on the deposition conditions that does not correlate with a change in composition. An increase in nitrogen content in the gas phase results in a decrease of hardness and Young's modulus.The microstructural study by high resolution scanning electron microscopy (SEM-FEG) on non-metalized samples allowed the detection of a close porosity in the form of nano-voids (3-15 nm in size), particularly in the coatings prepared under pure N₂ gas. It has been shown how the presence of the close porosity allows tuning the refraction index of the films in a wide range of values without modifying significantly the chemical, thermal and mechanical stability of the film.     

Effect of annealing temperature on microstructure, hardness and adhesion properties of TiSixNy superhard coatings

A series of TiSi_xN_y superhard coatings with different Si contents were prepared on M42 steel substrates using two Ti and two Si targets by reactive magnetron sputtering at 500 °C. These samples were subsequently vacuum-annealed at 500, 600, 700, 800 and 900 °C, respectively. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), microindenter, Rockwell hardness tester and scratch tester were applied to investigate the microstructure, phase configuration, hardness and adhesion properties of as-deposited and annealed samples. The results indicated that there were two bonds, TiN and Si₃N₄, in all presently deposited TiSi_xN_y thin films, that structure was nanocomposite of nanocrystalline (nc-) TiN embedded into amorphous Si₃N₄ matrices. Annealing treatment below 900 °C played a little role in microstructure and hardness of the coatings although it greatly affected those of steel substrates. The film-substrate adhesion strength was slightly increased, followed by an abrupt decrease with increasing annealing temperature. Its value got to the maximum at 600 °C. Annealing had little effect on the friction coefficient with its value varying in the range of 0.39-0.40.     

双模腔场中具有不同耦合常数的两原子多光子辐射谱

研究了与双模腔场具有不同耦合常数的两个二能级原子的多光子辐射谱,给出了双模多光子辐射谱的一般表达式.结果表明,当双模腔场分别处于不同数态时,虽然两原子与双模腔场之间具有不同的耦合常数,但对于任意的N₁和N₂(N_i(i＝1,2,)为模i腔场被每个原子吸收或发射的光子数),辐射谱总是关于共振频率ω₀对称分布;并且,当N₁＝N₂时,对于任意的数态光子数n₁和n₂交换,辐射谱不变.上述特点用解析方法给予了解释.计算了非简并双光子情况下的辐射谱,并得到了一些新结果.双模腔场中单原子及具有相同耦合常数的两原子辐射谱可从本文结果分别做为特例而得到.     

Molecular orientation of lyotropic nematic phase in a mixture of two non-mesogenic compounds

We report the results of our studies on the optical and thermal properties of the mixture of two non-mesogenic compounds, namely, sodium dodecyl sulfate (SDS) and glacial acetic acid (GAA). The mixture exhibits very interesting schlieren texture of lyotropic micellar nematic (N_D) phase, SmA and SmB phases, respectively, at different concentrations of SDS in GAA sequentially when the specimen is cooled from its isotropic phase. The order parameter (S) of the lyotropic micellar nematic (N_D) phase is estimated with the help of temperature dependence of optical anisotropy from the measured values of refractive index and density data. The experimental curve showing the temperature variation of order parameter is very well fitted with the Mayer–Saupe theoretical curve. X-ray studies have also been discussed. The formation of the above phases has been confirmed by optical and differential scanning calorimetry studies.     

Thermodynamic properties of noble metal clusters:molecular dynamics simulation

The thermodynamics properties of noble metal clusters Au_N, Ag_N, Cu_N, and Pt_N (N = 80, 106, 140, 180, 216, 256, 312, 360, 408, 500, 628, 736, and 864) are simulated by micro-canonical molecular dynamics simulation technique. The potential energy and heat capacities change with temperature are obtained. The results reveal that the phase transition temperature of big noble metal clusters (N ⩾ 312 for Au, 180 for Ag and Cu, and 360 for Pt) increases linearly with the atom number slowly and approaches gently to bulk crystals. This phenomenon indicates that clusters are intermediate between single atoms and molecules and bulk crystals. But for the small noble clusters, the phase transition temperature changes irregularly with the atom number due to surface effect. All noble metal clusters have negative heat capacity around the solid-liquid phase transition temperature, and hysteresis in the melting/freezing circle is derived in noble metal clusters.