FeBN(N≤6)团簇的结构与磁性

利用密度泛函理论中的广义梯度近似(GGA)，在考虑自旋多重度后，预测了FeB_N(N≤6)团簇的基态结构.结果表明基态团簇的自旋多重度分别为4，3，2，1，2和1，其中FeB₄团簇比较稳定.同时对FeB_N(N≤6)基态团簇的磁性做了系统地研究，发现除了FeB₅团簇外，FeB_N(N≤6)团簇的总磁矩和Fe原子磁矩随团簇尺寸的增大而减小. 关键词： N团簇')" href="#">FeB_N团簇 自旋多重度 磁矩     

密度泛函理论研究Zrn(n=2—16)团簇的基态结构及其稳定性

从第一性原理出发，利用密度泛函理论中的广义梯度近似(GGA)对Zr_n(n=2—16)团簇进行了结构优化、能量和频率计算.在充分考虑自旋多重度的前提下，对每一具体尺寸的团簇，得到了多个平衡构型，并根据能量高低确定了团簇的基态结构.综合团簇的结合能、离解能、二阶能量差分以及团簇的最高占据轨道(HOMO)和最低未占据轨道(LUMO)间的能隙可知Zr₂，Zr₅，Zr₇，Zr₁₃ 关键词： n团簇')" href="#">Zr_n团簇 密度泛函理论(DFT) 基态结构 自旋多重度     

金属颗粒-半导体膜Cu:CdS的制备及结构研究

利用磁控溅射产生金属Cu团簇，同时蒸发半导体介质CdS，将Cu团簇包埋在CdS介质中，制备出金属颗粒 半导体膜．团簇大小可通过改变溅射气压控制．用TEM研究了嵌埋团簇的结构．分析表明：CdS很好地包埋了Cu团簇，都呈多晶结构；团簇尺寸在5—20nm，Cu晶格发生了膨胀，膨胀量在7%左右 关键词：     

密度泛函理论研究Scn，Yn和Lan(n=2—10)团簇的稳定性、电子性质和磁性

通过采用密度泛函理论对Sc₂,Y₂和La₂基本性质的计算,选择在较优理论水平下系统地研究了Sc_n, Y_n和La_n(n=2—10)团簇的几何结构、稳定性、电子性质和磁性及其随团簇尺寸的变化趋势.此同族三种团簇的稳定性由原子密堆集几何结构效应决定,幻数均表现出一致的结果.La_n团簇的能隙比 关键词： n')" href="#">Sc_n n和La_n团簇')" href="#">Y_n和La_n团簇 密度泛函理论 电子性质 磁矩     

密度泛函理论计算GenFe(n=1—8)团簇的基态结构及其磁性

基于第一性原理，利用密度泛函理论中的广义梯度近似 (GGA)对Ge_nFe(n=1—8)团簇进行了结构优化、能量及频率的计算，得到了 Ge_nFe(n=1—8)团簇在不同自旋多重度下的平衡构型及其基态结构.结果表明：Ge_nFe混合团簇的平均结合能明显比相应纯锗团簇的平均结合能有所增大，即掺杂Fe原子可以提高锗团簇的稳定性；纯锗团簇的基态除了Ge₂为自旋三重态外其他均为单重态，而混合团簇Ge_nFe(n=1—8)的基态均为自旋三重态；对Ge_nFe(n=1—8)团簇的磁性做了较系统的研究，发现团簇总磁矩随团簇尺寸增大基本稳定在2μ_B (只有Ge₈Fe的总磁矩2.391μ_B较明显地偏离了2μ_B)，另外团簇中Fe原子的磁矩在2.5μ_B左右振荡. 关键词： nFe团簇')" href="#">Ge_nFe团簇 密度泛函理论(DFT) 自旋多重度 磁矩     

第一性原理对GanPm小团簇的结构及稳定性的研究

利用密度泛函理论（DFT）对Ga_nP和Ga_nP₂ (n=1—7)团 簇的几何结构、电子态及稳定 性进行了研究. 在B3LYP/6-31G^*水平上进行了结构优化和频率分析，得到了Ga _nP和Ga_nP₂(n=1—7) 团簇的基态结构. 结果表明，n≤ 5团簇的几何结构基本上为平面结构，n ＞ 5的团簇均为立体结构；在Ga_nP₂ (n=1—6)团簇中，P-P比Ga-P容易 成键；在Ga_nP和G a_nP₂ (n=1—7) 团簇中，Ga₃P, Ga₄P, Ga P₂, Ga₂P₂ 和 Ga₄P₂的基态结构最稳定，在所研究的团簇中，稳定性随团簇总原 子数的增大而减小. 关键词： nP_m团簇')" href="#">Ga_nP_m团簇 密度泛函理论（DFT） 几何结构 电子态     

Aln(n=13–32)团簇熔化行为的分子动力学模拟研究

基于半经验的Gupta原子间多体相互作用势, 采用分子动力学方法并结合模拟退火及淬火技术, 系统研究了小尺寸铝团簇Al_n (n=13–32)的熔化行为. 模拟结果表明: 除个别尺寸(Al₁₃ 和Al₁₉) 外, 团簇熔化过程比热曲线普遍呈现杂乱无规(无明显单峰)现象, 这与实验观测小Al团簇比热普遍无规的结果完全一致. 通过分析不同温度点上团簇淬火构型的势能分布图给出了小Al团簇比热呈现无规或有规现象的成因. 对于比热无规团簇, 可以利用原子等价指数判断给出团簇熔点, 所得团簇熔点随团簇尺寸的变化趋势与实验观测结果完全一致. 关键词： Gupta势 团簇 分子动力学 熔化     

第一性原理对NaBen(n=1—12)团簇最低能量结构及其电子性质的研究

从第一性原理出发对NaBe_n(n=1—12)团簇的最低能量结构和电子性质进行了研究.结果表明，掺杂原子(Na)导致主团簇Be_n的几何结构发生显著变化；出现了共价键和金属键的成键特性；Na-Be最近邻间距和能隙随着团簇尺寸的增加出现了振荡;n=4是团簇的幻数. 关键词： n团簇')" href="#">NaBe_n团簇 最低能量结构 电子性质     

H+5团簇离子及其中性团簇产物H3和H4

报道了H⁺₅的实验结果.分析讨论了H⁺₅的 形成和分解途径.根据理论分析，以稳定的H⁺₃为核心与一个或多个氢分子结合可能形成稳定的H^{+_n氢团簇离子.另一方面，在高频离子源中, 有发生H+₃与H₂反应的条件.实 验中，从高频离子源引出的离子束被静电加速器加速，然后用9 关键词： +}₅团簇离子')" href="#">H⁺₅团簇离子 3中性团簇')" href="#">H₃中性团簇 4中性团簇')" href="#">H_{4中性团簇}     

低温高背压氘团簇源特性研究

为了产生大尺度氘团簇用于与强激光相互作用研究，研制了低温高背压团簇源.利用瑞利散射法对团簇尺度与气体背压相关性和团簇的形成演变过程进行了研究.得到团簇尺度N_c随背压的指数变化关系为N_c∝P^2.89₀，当气体温度为80K，背压P₀为48×10⁵Pa时，氘团簇尺度N_c≈2630，并得到了团 关键词： 氘团簇 团簇源 瑞利散射 激光与团簇相互作用     

Size dependence of non-linear optical properties of SiO2 thin films containing InP nanocrystals

SiO₂ composite thin films containing InP nanocrystals were fabricated by radio-frequency magnetron co-sputtering technique. The microstructure of the composite thin films was characterized by X-ray diffraction and Raman spectrum. The optical absorption band edges exhibit marked blueshift with respect to bulk InP due to strong quantum confinement effect. Non-linear optical absorption and non-linear optical refraction were studied by a Z-scan technique using a single Gaussian beam of a He-Ne laser (632.8 nm). We observed the saturation absorption and two-photon absorption in the composite films. An enhanced third-order non-linear optical absorption coefficient and non-linear optical refractive index were achieved in the composite films. The nonlinear optical properties of the films display the dependence on InP nanocrystals size. Received: 27 June 2000 / Accepted: 27 June 2000 / Published online: 13 September 2000     

InP/SiO2纳米复合膜的微观结构和光学性质

应用射频磁控共溅射方法在石英玻璃和抛光硅片上制备了InP/SiO₂复合薄膜,并在几种条件下对这些薄膜进行退火.X射线光电子能谱和卢瑟福背散射实验结果表明,复合薄膜中InP和SiO₂的化学组分都大体上符合化学计量配比.X射线衍射和激光喇曼谱实验结果都证实了复合薄膜中形成了InP纳米晶粒.磷气氛保护下的高温(520℃)退火可以消除复合薄膜中残存的In和In₂O₃并得到了纯InP/SiO₂纳米复合薄膜.实验观察到了室温下纳米复合薄膜的明显的光学吸收边蓝移现象和光学非线性的极大增强 关键词： InP 纳米晶粒 微观结构 光学性质     

Homogeneous Si films on CaF2/Si(1 1 1) due to boron enhanced solid phase epitaxy

The structure and morphology of Si/CaF₂/Si(1 1 1) structures have been investigated by X-ray diffraction (XRD, GIXRD) and X-ray photoelectron spectroscopy (XPS). While CaF₂ films were grown via molecular beam epitaxy (MBE), Si films on CaF₂/Si(1 1 1) are fabricated by surfactant enhanced solid phase epitaxy (SE-SPE). Here Boron was used as a surfactant to obtain semiconductor films of homogeneous thickness. The Si films are entirely relaxed while the CaF₂ films have both pseudomorphic and relaxed crystallites. After exposure to ambient conditions, the Si films have a very thin native oxide film. The homogeneous Si film partially prevents the incorporation of impurities at the interface between the Si substrate and CaF₂ via migration along residual defects of the CaF₂ film.     

Study of the effect of initial conditions on the scaling properties of CaF2 thin films

The growth of thermally deposited CaF₂ films was studied using three different substrates for deposition: glass, gold and silicon. Each substrate was chosen because of its different topography and used to determine the effect of substrate roughness on the growth of CaF₂ films. After thermally depositing a range of CaF₂ film thicknesses on the substrates, the CaF₂ surfaces were imaged using atomic force microscopy. The images were then used to determine the characteristic exponents which described the surface. In each case the Hurst exponent, H was found to rapidly increase from the initial substrate condition to a constant value (H ≈ 0.85) with increasing CaF₂ film thickness. This rapid crossover is quite remarkable and occurs in films with nominal thicknesses less than ≈20 nm. These data indicate that the roughness of the substrate, or in other words the initial conditions, have little effect on the growth properties of CaF₂ films beyond the crossover at very small values of the film thickness. The scaling of the dynamic exponent, β, is also presented as are measurements of the CaF₂ film porosity.     

Struktur und ultrarote Gitterschwingung von CaF2 und LiF

Thin films of CaF₂, LiF and LiF +20% KF are condensed on to substrates at 20 °K. Immediately after condensation and after annealing to 373 °K the infrared absorption is measured between 15 and 43 microns. Also Debye-Scherrer-diagrams are taken for investigating the structure of the layers. After condensation at 20 °K LiF has a high degree of disorder, CaF₂ and LiF+20% KF show amorphous phases. The infrared lattice vibration of such films is shifted to shorter wavelenghts.     

Nonlinear processes in UV optical materials at 248 nm

Nonlinear processes in UV optical materials were investigated by using 280-fs, 248-nm pulses. Nonlinear absorption in CaF₂ was confirmed to be a two-photon process by using the luminescence of self-trapped excitons, which was also used for the single shot pulse width measurement. The absorption bands due to F centers were identified in CaF₂, MgF₂, and LiF after several hundred shots at 100 GW/cm². Absorption at 248 nm was considerable especially in MgF₂ and LiF. Self-focusing and self-phase modulation were observed in CaF₂.     

Solid phase epitaxy of Ge films on CaF2/Si(1 1 1)

At room temperature deposited Ge films (thickness < 3 nm) homogeneously wet CaF₂/Si(1 1 1). The films are crystalline but exhibit granular structure. The grain size decreases with increasing film thickness. The quality of the homogeneous films is improved by annealing up to 200 °C. Ge films break up into islands if higher annealing temperatures are used as demonstrated combining spot profile analysis low energy electron diffraction (SPA-LEED) with auger electron spectroscopy (AES). Annealing up to 600 °C reduces the lateral size of the Ge islands while the surface fraction covered by Ge islands is constant. The CaF₂ film is decomposed if higher annealing temperatures are used. This effect is probably due to the formation of GeF_x complexes which desorb at these temperatures.     

Effect of gamma irradiation on undoped and uranium doped calcium fluoride crystals

Color centers in undoped and U³⁺-doped CaF₂ crystals induced by γ-irradiation with different doses were studied by differential absorption and Raman spectra. Multiple color centers and conversion among them were caused in undoped CaF₂ with the creation of radiation defects. In U³⁺:CaF₂ crystal, trivalent uranium was demonstrated to act as hole trap in the process of γ-irradiation, which was ionized to tetravalent. This process was accompanied by the formation of F₂⁺ centers, but without additional background absorption due to radiation defects.     

Time-resolved spectroscopy of self-trapped excitons in fluorides of alkaline-earth metals under pulsed electron irradiation

Nanosecond-resolution absorption spectroscopy at room temperature was used to study the laws governing the creation and evolution of the primary defect structure in CaF₂, SrF₂, and BaF₂ crystals exposed to an accelerated electron pulse. It is shown that the spectral-kinetic characteristics of self-trapped excitons created in undamaged parts of the crystal lattice are qualitatively similar. Partial polarization of the absorption of self-trapped excitons is observed in CaF₂. The structure of the transient absorption spectra becomes more complex in the sequence CaF₂, SrF₂, BaF₂ because of the formation of excitons trapped in phase inclusions of homologous cationic impurities. The spectral characteristics of excitons trapped in undamaged parts of the CaF₂ and SrF₂ lattice and in their phase inclusions in BaF₂ are the same although the latter have a considerably shorter relaxation time. Short-lived (τ⩽100 ns) absorption of unknown defects was observed in the spectral range ⩾5 eV. Fiz. Tverd. Tela (St. Petersburg) 40, 1228–1234 (July 1998)     

Atomic structure of CaF2/MnF2-Si(1 1 1) superlattices from X-ray diffraction

X-ray reflectivity and non-specular crystal truncation rod scans have been used to determine the three-dimensional atomic structure of the buried CaF₂-Si(1 1 1) interface and ultrathin films of MnF₂ and CaF₂ within a superlattice. We show that ultrathin films of MnF₂, below a critical thickness of approximately four monolayers, are crystalline, pseudomorphic, and adopt the fluorite structure of CaF₂. High temperature deposition of the CaF₂ buffer layer produces a fully reacted, CaF₂-Si(1 1 1) type-B interface. The mature, “long” interface is shown to consist of a partially occupied layer of CaF bonded to the Si substrate, followed by a distorted CaF layer. Our atomistic, semi-kinematical scattering method extends the slab reflectivity method by providing in-plane structural information.