飞秒强激光脉冲与H原子团簇相互作用的库仑爆炸过程模拟

运用经典粒子动力学模拟方法，研究了飞秒强激光脉冲(10^15～10^16W／cm^2)与正二十面体构型氢原子团簇H13,H55，H147和H309的相互作用。通过模拟分析团簇的膨胀过程，发现团簇的膨胀是各向同性的，团簇的膨胀尺度R(t)／R(0)随团簇尺寸的增大而减小，即团簇尺寸愈大，与激光相互作用后膨胀碎解过程愈慢。研究结果表明，随着团簇中原子数目的增多，团簇库仑爆炸后所产生的离子的动能相应增大。由于正二十面体的对称壳层结构，离子动能分布具有尖峰结构。团簇库仑爆炸后离子的最大动能Emax与团簇库仑爆炸前的尺寸的平方成正比。且Emax随激光光强I增加而增大。但是当I增大到一定值Is时，Emax将出现饱和，这是因为I的增强已经不再改变团簇内原子的电离状态。随着团簇尺寸的增大，激光光强饱和值和离子能量将会继续提高。     

深冷中性铝团簇的产生和光电离

报道了用激光蒸发／分子束方法产生深度冷却的中性金属团簇。产生的铝团簇Ａｌ．（ｎ＝２，……，６，７）用１９３ｎｍ的准分子激光电离，由飞行时间质谱（ＴＯＦＭＳ）探测。对激光蒸发／分子束技术产生的团簇束的特点作了简单评述并与其它团簇源作了比较。     

甲醇/乙醇/水混合团簇多光子电离质谱

利用355nm激光电离由氩气载代的甲醇/乙醇/水脉冲分子束,飞行时间质谱观测到多个序列的质子化团簇离子:(CH3CH2OH)nH ,(CH3OH)(H2O)(CH3CH2OH)nH ,(CH3OH)(CH3CH2OH)nH ,(CH3CH2OH)n(H2O)2H 和(CH3CH2OH)n(H2O)H (n=0至4)。通过改变激光与分子束之间的延时,观测到团簇离子强度分布的变化特征。     

飞秒激光脉冲加热氘团簇引发原子核聚变

作为一种介于分子和块状固体之间的物质形式,原子团簇已得到广泛的研究[1]。团簇中的光感应过程[2,3]能导致光子分裂和库仑裂变[4],产生带几个电子伏(ｅＶ)能量的原子和离子碎片。然而,最近对于高强度(>1016Ｗｃｍ-2)飞秒激光脉冲导致原子团簇光致光致电离的研究表明,这种相互作用可以非常强烈[5～13]。大原子团簇的激发能够产生超高温等离子体,喷射出的离子动能高达1ＭｅＶ。这个现象表明,通过照射氘团簇,有可能产生具有足够平均离子能量的等离子体,导致重大的原子核聚变。本文报告,在用高重复率紧凑台式激光器加热氘团簇使其爆炸的实验中,…     

醇/水混合团簇的多光子电离质谱及从头算研究

利用多光子电离技术和飞行时间质谱仪实验研究了醇/水混合团簇的光电离质谱。在脉冲激光波长为355nm条件下,观测到以质子化(ROH)n(H2O)H+ 混合团簇离子和(ROH)nH+团簇离子为主的电离产物。醇水混合团簇电离后团簇离子发生内部质子化转移反应是形成质子化团簇离子的主要原因。应用量化计算,构造了质量数较小的几个团簇离子的可能的空间几何构型,发现二元团簇离子(CH3OH)n(H2O)H+是以(CH3OH)H+作为内核离子,再通过氢键与其它分子组合而构成团簇离子。     

瑞利散射法诊断大尺寸团簇

瑞利散射法的优点是实验易行,对于团簇是非破坏性的。利用这种方法Ａ．Ｊ．Ｂｅｌｌ等人测出了尺寸在１５０－４０００的氩团簇。Ｒ．Ｋｌｉｎｇｅｌｈｏｅｆｅｒ测量瑞用射信号强度同散射角的依赖关系,推断以团族尺寸分布。Ｔ．Ｄｉｔｍｉｒｅ等在散射角固定不变的情况下,测量散射信号同气体滞止压强Ｐ０或温度Ｔ０的关系,从而推断团簇的尺寸。     

乙醇/水混合团簇的多光子电离质谱研究

利用激光器(输出波长355nm)激发乙醇和水二元混合团簇中的离子-分子反应,运用飞行时间质谱技术检测反应后生成的团簇离子.实验观测到多个序列的质子化团簇离子:(C2H5OH)nH 和(C2H5OH)n(H2O)mH (n=1-12,m=1-4),其产生是通过团簇内的质子转移反应.通过对团簇离子的峰强度同乙醇数目n和水分子数目m的关系的研究发现,团簇离子(C2H5OH)8(H2O)H 是幻数结构.     

掺Eu3+聚合物光纤的团簇现象

用热聚合法制备了掺Eu(DBM)3Phen螯合物的聚合物光纤,建立了团簇化铕离子相互作用模型,以此为基础研究该掺杂聚合物光纤的团簇现象。利用速率方程理论,结合光纤的抽运光透射率实验,得到所研究光纤中团簇化铕离子浓度。掺铕质量分数为0.1%,0.2%,0.3%,0.4%,0.5%,1%的聚合物光纤中团簇化铕离子的浓度分别为0.045,0.07,0.07,0.07,0.07,0.08。因此,该掺杂聚合物光纤的团簇化铕离子浓度较低且基本不随掺杂浓度的增加而增加,铕离子之间的团簇化现象不明显。     

Si_xN~±_y团簇离子的形成和稳定性研究

结合ＤＶ－Ｘα方法的理论计算结果，对激光蒸发方法产生的ＳｉｘＮ团簇离子的形成和稳定性进行了细致的研究。发现上述四簇离子可能以ＳｉＮ３或ＳｉＮ４作为初始单元，较大的团簇离子可由某种单元与另一质谱上较稳定的复合分子组成。质谱强度变化的规律表明：若团簇离子质量是Ｓｉ原子量的倍数时，呈现极大值，此时，团簇离子包含偶数个Ｎ原子。其奇偶性是由初始单元强度差异引起的。     

紫外激光多光子电离下甲醇团簇中的反应

应用Nd：YAG脉冲激光器输出的355nm紫外激光实现了对甲醇的多光子电离，通过质谱技术观测到了两个质子化圃簇离子系列：（CH3OH）nH^＋（n=1—15）和（CH3OH）n（H2O）H^＋（n=7—15），结合在HF／STO-3G和B3LYP／6—31G＋＋水平上的从头计算对其反应通道做了分析，发现其产生经过了团簇内部的质子转移反应。且质子主要来自于羟基上的氢离子。并分析了（CH3OH）nH^＋系列的结构，给出了幻数团簇（CH3OH）3H^＋的构型。同时对（CH3OH）n（H2O）H^＋系列只在n≥7时出现做了相应的解释。     

Reactive epitaxy of Co nanoparticles on (111)Si

The formation of epitaxial CoSi2 islands of nanoscopic dimensions is reported using the technique of reactive cluster deposition. Co clusters in the size range 5-50 nm were synthesized by sputtering of a high purity Co target inside a ultra high vacuum (UHV) sputtering chamber, using the technique of inert gas condensation. The clusters were then deposited on the reconstructed Si (111) surface. Upon annealing, the particles reacted with the Si substrate to form epitaxial CoSi2. Our observations were made using a JEOL 200CX transmission electron microscope modified for in situ sputtering and UHV conditions.     

Electron traps in thin layers of low-temperature-grown gallium arsenide with As-Sb nanoclusters

Electron traps in low-temperature-grown ～40-nm-thick GaAs layers containing nanometer As-Sb clusters have been studied using deep-level transient spectroscopy. Measurements at various bias voltages and small-amplitude filling pulses have allowed the identification of two groups (T1 and T2) of traps with substantially different thermal electron emission rates. It is shown that the density of traps T2 (with an activation energy of 0.56 ± 0.04 eV and electron capture cross section of 2 × 10^?13?10^?12cm²) is ～2 × 10¹²cm_?2, while the density of traps T1 (0.44 ± 0.02 eV and 2 × 10^?14?10^?13 cm², respectively) is ten times lower. It is assumed that, according to the existence of the two cluster groups observed in the layers under study, traps T2 are associated with clusters 4–7 nm in diameter and traps T1, with clusters up to ～20 nm in diameter.     

High-Intensity Femtosecond Laser Interaction with Rare Gas Clusters

With a 45 fs multiterawatt 790 nm laser system and jets of argon and krypton atomic clusters, a study of the interaction of fs intense laser pulses with large size rare gas dusters was conducted. The maximum laser intensity of about 7 × 1016 W/cm2 and dusters composed of thousands of atoms which were determined through Rayleigh scattering measurements were involved inthe experiments. On the one hand, the results indicate that the interaction is strongly cluster size dependent. The stronger the interaction, the larger the clusters are. On the other hand, a saturation followed by a drop of the energy of ions ejected from the interaction will occur when the laser intensity exceeds a definite value for clusters of a certain size.     

Kinetic Monte Carlo simulation of low-pressure chemical vapor deposition of silicon nitride: Impact of gas flow rate and temperature on silicon cluster size and density

In the present study, the deposition process of SiN_x thin films obtained by a low-pressure chemical vapor deposition technique with a mixture of disilane (Si₂H₆) and ammonia (NH₃) was simulated by using the kinetic Monte Carlo method. A new pattern describing the distribution of ammonia molecules in the simulation matrix was proposed. The influences of the NH₃/Si₂H₆ gas flow ratio and the deposition temperature on the obtained films structure in terms of silicon cluster size and density were analyzed. The simulation results indicate that an increase in the gas flow ratio leads to the deposition of amorphous silicon clusters characterized by small sizes. Nevertheless, an increase in the temperature values of the process provokes an enhancement in the silicon cluster size along with a decrease in their density.     

泡生法生长KYb(WO4)2晶体及其结构与光谱性能

对顶部籽晶提拉法(TSSG)进行了改进,采用泡生法生长KYb(WO4)2晶体(简称KYbW),以0.05℃/h的速率降温生长,转速5~10 r/min,生长周期10~15 d,降温速率15~20℃/h。研究了KYbW晶体的结构,给出了两种晶胞的选取方法。通过晶体的X射线衍射(XRD)谱,计算出晶体的两种晶格常数分别为a=1.061 nm,b=1.029 nm,c=0.749 nm,β=130.65°;a′=0.807 nm,b′=1.029 nm,c′=0.749 nm,β′=94.34°。测得晶体的吸收光谱,结果表明其吸收带在920~1000 nm,计算出主吸收峰981 nm处的吸收截面为11.12×10-20cm2。测得晶体的荧光光谱,结果表明KYbW晶体在1007 nm和1037 nm附近都有较强的发射峰,主峰1037 nm处的发射线宽(FWHM)达13 nm,因此KYbW晶体可作为可调谐激光增益介质,计算出1037 nm处的受激发射截面积eσm=3.4×10-20cm2。     

激光蒸凝法制备氧化锰纳米粒子

以 15 0WCWCO2 激光器为光源 ,Mn(Ac) 2 ·4H2 O为靶材 ,采用激光蒸凝法制备出了氧化锰纳米粒子。初步研究了反应参数对纳米粒子性能的影响 ,并用X射线衍射、电子衍射、透射电镜等技术对纳米粒子的性能进行了表证 ,同时对纳米粒子的形成机理进行了初步探讨。实验结果表明 ,激光功率密度、反应压力、载气种类及流量等工艺参数对产品的粒度、晶型等性能均有影响。在惰性气氛下 ,产物主要是Mn3 O4 5 6F ,粒径分布范围较宽 (5～ 10nm和 30～ 10 0nm)且不均一 ;在氧气气氛下 ,产物主要是立方晶系的Mn3 O4 和少量的立方晶系的MnO ,粒径分布范围变窄了 (5～ 10nm和 15～ 6 0nm) ,也不均一。     

低气压下制备金刚石薄膜的研究

利用我们自己研制的磁约束直流等离子体设备，在低气压（＜１Ｔｏｒｒ）下。用Ａｒ＋Ｈ２＋ＣＨ４的混合气体在基片上进行了沉积金刚石薄膜的工艺研究。利用扫描电镜和拉曼光谱对不同的进气方式所制备出的金刚石薄膜的形貌和质量进行了比较。结果表明。当在基片表面附近引入碳源气体和大约５０％氢气时，可以大大提高薄膜质量。     

Algorithms for finding best locations of cluster heads for minimizing energy consumption in wireless sensor networks

Clustering is a widely adopted energy-saving technique in wireless sensor networks (WSNs). In this paper, we study algorithms for finding the best locations of cluster heads in WSNs to minimize the overall energy consumption. Specifically, based on the assumption that the global information of all the sensors’ locations or location distribution is available, algorithms are proposed for finding (1) the best location of the cluster head in a single given cluster; (2) the best formation of a given number of clusters where each cluster head has to communicate with base station directly; and (3) the best formation of a given number of clusters where there can be ad-hoc transmission between cluster heads, respectively. For each case, algorithms are designed for free-space and multipath energy consumption models respectively. Theoretical analysis and extensive simulation results show that the proposed algorithms can steadily and quickly achieve satisfactory results. The calculation results of the proposed algorithms provide a useful benchmark for evaluating various local information-based distributed clustering schemes or schemes based on partial or inaccurate global information.     

氨化Ga_2O_3/Mg薄膜制备簇状GaN纳米线

通过在1050°C时氨化Ga2O3/Mg薄膜制备出簇状GaN纳米线。用X射线衍射(XRD),傅里叶红外吸收光谱(FTIR)扫描电子显微镜(SEM)和高分辨电子显微镜(HRTEM)对样品进行测试分析。结果表明,GaN纳米线为六万纤锌矿结构单晶相并且成族生长,直径在200～500nm米左右,其长度可达5～10μm。几乎所有纳米线的直径均有逐渐缩小的趋势。对Mg膜的作用进行了初步的分析。