银团簇纳米颗粒的制备及其光吸收谱性质

 采用自悬浮定向流技术制备银团簇纳米颗粒，理论分析了银团簇的成核机理与影响因素，实验研究了制备条件和工艺。结果表明：惰性气体的冷却效率、气体流速和压强、金属熔球的温度和大小是控制颗粒尺寸大小及分布的关键条件，制备粒径小于10 nm的团簇颗粒须采用氦气为载流气体；团簇颗粒流速越大，颗粒粒径越小，尺寸分布越窄，但颗粒生成数量越少。性能表征说明：制备的颗粒呈较规则的球形，为面心立方结构，分散均匀，表面纯净无氧化，粒径分布窄。理论与实验研究了银团簇纳米颗粒的光学吸收谱性质，证明表面等离子共振吸收峰与颗粒的尺寸有很强的相关性，随着颗粒尺寸的减小，由于量子尺寸效应，吸收峰将发生宽化和蓝移。     

氩气中铝丝电爆炸沉积能量对制备铝纳米粉体特性的影响

研制了基于脉冲电容器放电回路的亚微秒金属丝电爆炸纳米粉体制备实验平台,包括电爆炸过程电流和电压测量系统。利用透射电子显微镜(TEM)观察纳米粉体的形态与结构,并通过电镜统计观察法分析TEM图像得到纳米粉体的粒度大小及其分布。在氩气中电爆炸铝丝制备铝纳米粉体,通过改变电容器充电电压,即初始储能,实验研究沉积能量对铝纳米粉体特性的影响规律。结果表明:铝纳米粉体颗粒形态与结构主要由氩气气压的高低决定,与沉积能量基本无关。增大丝爆过程的沉积能量可显著缩小铝纳米粉体粒度分布范围,减小颗粒平均粒径,并有效地抑制纳米粉体中亚微米颗粒的形成。随着沉积能量E与氩气气压p比值(Ep-1)增大,铝纳米粉体颗粒平均粒径、最大粒径和粒径大于100 nm颗粒所占比例均呈指数函数单调减小。     

自悬浮定向流技术中铜纳米微粒的粒度控制研究

 采用自悬浮定向流技术制备了金属铜纳米微粒，根据TEM的行貌像对样品平均粒度进行标定，并结合样品制备的条件对制备工艺进行了研究。结果表明，自悬浮定向流技术可以方便地制备出不同粒度的金属铜纳米微粒，微粒平均粒径随熔球温度的降低而减小，随冷却气体流速的增大而减小；在1 200℃下微粒平均粒径随惰性气体压强的增大而减小，而在1 300℃时惰性气体压强对微粒平均粒径的影响不再具有规律性。     

磁控溅射气体团簇源中团簇形成的DSMC研究

利用直接模拟蒙特卡洛方法(DSMC) ,模拟了磁控溅射气体团簇源中Cu+ (Cu-)的含量比例不同的条件下,Cu团簇的尺寸分布。模拟结果表明：随着含量比例的增加,团簇的尺寸分布变窄了,不带电的团簇的比例增加,不带电的铜团簇分布的最大值减小,相应的带正电荷和带负电荷团簇的比例减小;相同的含量比例下,带正电的团簇的尺寸分布与带负电荷的团簇的尺寸分布基本相同;初始Cu- 比Cu+ 的含量比例大时,输出的主要是带负电荷的团簇,带正电荷和不带电的团簇占很小的比例;Cu-含量比例的增加,负Cu团簇的尺寸分布减小。     

磁控溅射气体团簇源中团簇形成的DSMC研究

利用直接模拟蒙特卡洛方法(DSMC) ,模拟了磁控溅射气体团簇源中Cu+ (Cu-)的含量比例不同的条件下,Cu团簇的尺寸分布。模拟结果表明：随着含量比例的增加,团簇的尺寸分布变窄了,不带电的团簇的比例增加,不带电的铜团簇分布的最大值减小,相应的带正电荷和带负电荷团簇的比例减小;相同的含量比例下,带正电的团簇的尺寸分布与带负电荷的团簇的尺寸分布基本相同;初始Cu- 比Cu+ 的含量比例大时,输出的主要是带负电荷的团簇,带正电荷和不带电的团簇占很小的比例;Cu-含量比例的增加,负Cu团簇的尺寸分布减小。     

第十五届全国原子与分子物理学术会议:大尺寸贵金属纳米团簇热力学性质的分子动力学模拟研究

采用分子动力学方法和原子嵌入模型势模拟了大尺寸金（n=1136--1556）、银（n=1088--1724）、铜（n=1000--1600）、铂（n=1004--1800）原子纳米团簇的熔化过程,得出了相应纳米团簇的势能随温度的变化曲线以及热容量随温度的变化曲线,研究了各种原子纳米团簇熔点与其团簇尺寸的关系。模拟结果表明团簇的熔点随团簇尺寸增大而升高,并逐渐向大块晶体靠拢。所有纳米团簇在熔化过程中在熔点附近都出现负热容现象,通过对团簇熔化前后结构的比较研,分析了导致这种现象的原因。     

氧化硅层中的锗纳米晶体团簇量子点

采用氧化和析出的方法在氧化硅中凝聚生成锗纳米晶体量子点结构. 其形成的锗晶体团簇没有突出的棱角和支晶结构，锗晶体团簇的轮廓较圆混，故可以用球形量子点模型来模拟实际的锗晶体团簇. 对比了在长时间退火氧化条件下和在短时间退火用激光照射氧化条件下所生成的锗纳米晶体结构的PL光谱和对应的锗纳米晶体团簇的尺寸分布. 短时间退火氧化条件下生成的锗纳米晶体较小(3.28—3.96nm)，长时间退火用激光照射氧化条件下所生成的锗纳米晶体较大(3.72—4.98nm)；其分布结构显示某些尺寸的锗纳米晶体团簇较稳定，适当的氧化条件可以得到尺寸分布范围较窄的锗纳米晶体团簇. 用量子点受限模型计算了锗纳米晶体团簇的能隙结构，用Monte Carlo方法模拟了PL光谱和对应的锗纳米晶体团簇的尺寸分布，分别与实验结果符合较好. 关键词： 锗晶体团簇 纳米晶体 量子点 激光照射     

纳米团簇熔化过程的分子动力学模拟

本文采用分子动力学结合嵌入原子多体势,模拟了不同半径的Ni纳米团簇的升温熔化过程,研究团簇尺寸对熔点和表面能的影响.模拟结果表明:团簇的熔点显著低于体材料的熔点.团簇熔化的过程首先是在团簇的表面出现预熔,然后向团簇内部扩展,直到整个团簇完全熔为液态.在模拟的纳米尺度范围内,团簇的熔点与团簇尺寸基本成线性关系.团簇的表面能随着团簇尺寸的增大而减小,而且表面能均高于体材料的表面能.     

大尺寸贵金属纳米团簇热力学性质的分子动力学模拟研究

采用分子动力学方法和原子嵌入势模拟了大尺寸金(n=1136～1556)、银(n=1088～1724)、铜(n=1000～1600)、铂(n=1004～1800)原子纳米团簇的熔化过程,得出了相应纳米团簇的势能随温度的变化曲线以及热容量随温度的变化曲线,研究了各种原子纳米团簇熔点与其团簇尺寸的关系.模拟结果表明团簇的熔点随团簇尺寸增大而升高,并逐渐向大块晶体靠拢.所有纳米团簇在熔化过程中在熔点附近都出现负热容现象,通过对团簇熔化前后结构的比较,分析了导致这种现象的原因.     

Ptn(n=1-9)团簇结构及磁性的第一性原理计算

采用密度泛函理论中的广义梯度近似泛函BPW91和三参数杂化密度泛函B3LYP研究Ptn团簇的结构,稳定性和磁性.两种方法得到了相同的稳定结构,基态结构也相同,只是次稳定结构的稳定顺序稍有不同.两种方法得到的平均配位数和平均键长有相似的变化规律,总体上随团簇尺寸的增大而增大,n=2-3时增幅较大,n=4-9时增幅较小,且有一定的振荡.两种方法得到团簇能量的二阶差分、分裂能、HOMO-LUMO能隙随团簇尺寸的演化都没有表现出明显的奇偶振荡行为,但在n=2、5、8时均有较大的值,说明相对应的团簇具有较高的稳定性.两种方法得到团簇的平均每原子磁矩随团簇尺寸的增大有逐渐减小的趋势,个别团簇有振荡.结果表明两种泛函都可以描述团簇结构、稳定性和磁性.     

Gas-phase preparation and size control of Fe nanoparticles

The magnetic, electrical and optical properties of nanoparticle systems often depend on the size and size distribution of nanoparticles. In order to optimize those properties of nanoparticle-assembled materials, only varying the mean size of nanoparticles was not enough, and narrowing the size distribution was also of immense importance. In this study, uniform-sized Fe nanoparticles with different diameters were prepared using a magnetron sputtering combined with inert gas condensation technique. The size and morphology of nanoparticles were observed by transmission electron microscopy (TEM). The statistic results revealed that the size of Fe nanoparticles increased with increasing the flow rate of Ar gas, but a reverse trend was observed when increasing the flow rate of He gas. By adjusting the flow rate of Ar and He gases, uniform-sized Fe nanoparticles with diameter ranging from 6 to 13?nm were obtained. Moreover, the size effects on the electrical and magnetic properties of Fe nanoparticle-assembled films with thickness of about 500?nm were also investigated. The magnetic properties showed that the coercivity increased with increasing the nanoparticle size. The in-situ resistance measurement results of Fe nanoparticle assembled-films also showed a size-dependent behavior.     

Size-controlled Pd nanocluster grown by plasma gas-condensation method

Syntheses of palladium (Pd) nanoclusters by sputtering gas-condensation technique are reported in this work. The Pd nanocluster size distribution and number of nanoclusters are found to depend on several factors which include the inert gas flow rate (f), sputtering discharge power, and growth region length. The discharge power and the length of the growth region are optimized to produce high nanocluster yield. It is found that low f produces small number of large nanoclusters which can be attributed to the formation of nanoclusters via the two-body collision mechanism. For high f, nanocluster size decreases and the number of nanocluster increases with f. This phenomenon can be assigned to nanocluster formation through three-body collision mechanism.     

溅射法制备Ag/Ag2O超微粒子的分析

用Ｘ射线衍射、Ｘ射线光电子能谱、透射电子显微镜和差示扫描量热法对溅射法制备的Ａｇ超微粒子的晶体学结构、表面组成、微粒形态和热力学性质进行了分析。结果表明，所制备的微粒为内部为Ａｇ、表面为Ａｇ₂Ｏ的两相微粒，以及单一的Ａｇ₂Ｏ微粒，粒径在１０ｎｍ以上的微粒没有确定的外形，粒径在１０ｎｍ以下的微粒为球形。微粒有不同于块体金属Ａｇ的异常热效应。到４０天时，沉积在碳膜上的Ａｇ，Ａｇ₂Ｏ两相微粒有一部份还原形成了单一的金属Ａｇ超微粒子。 关键词：     

Photoluminescence properties of size-selected Si nanocluster films prepared by laser ablation

Size-dispersed Si nanocluster films have been synthesized by a method of crossing an Ar gas beam perpendicularly to a silicon cluster beam that is produced by a laser ablation technique. Flight directions of the nanoclusters are changed due to Ar gas collisions, and smaller nanoclusters are deflected further from the axis of the primary cluster beam. The size-dispersed nanocluster films exhibit strong red photoluminescence (PL) after exposure to the air. The PL peak energy changes between 1.42 and 1.72 eV depending on the sample position. The average diameter of the oxidized nanoclusters characterized by transmission electron microscopy is 10 nm at the position of the primary cluster beam axis and becomes smaller as deviated from the axis. The relation between the PL peak energy and the size of the oxidized Si nanoclusters is discussed. Received: 4 May 2000 / Accepted: 9 May 2000 / Published online: 13 July 2000     

高阻隔铝塑膜辉光放电发射光谱深度谱测量参数的优化

脉冲-射频辉光放电发射光谱（GDOES）深度剖析是一种基于辉光放电原理的原子光谱技术，广泛应用于薄膜材料与功能多层膜结构中成分随深度分布的表征。该技术具有真空度要求低，灵敏度高，溅射速率快等优点。同时脉冲-射频电源所采用的瞬间高功率模式可使得氩离子周期性轰击样品表面，避免了由于热量积累所导致的熔融或碳化，因此脉冲-射频辉光放电发射光谱可以用于热敏材料、柔软或脆性等材料的测试，使得GDOES的应用范围由导体扩展至半导体，绝缘体甚至是有机物材料，是深度谱测量的理想选择。铝塑膜作为一种多层复合膜材料是重要的包装材料，具有耐温、耐候性、耐水以及耐酸碱等性能，广泛应用于食品，电子类，国防尖端产品的包装。利用脉冲-射频辉光放电发射光谱深度剖析技术对市场上同一款的高阻隔铝塑膜进行了Pulsed-RF-GDOES深度剖析测量，分析了在不同气压、不同功率、不同气体氛围下，测量深度谱的深度分辨率，溅射速率和信噪比的变化，获得了对铝塑膜进行深度谱测量优化的工作参数。并以相对强度较大的铝信号作为标定，定量计算了测量铝塑膜深度谱的深度分辨率，溅射速率和信噪比。实验结果表明，利用脉冲信号以及氩-氧（4 Vol%）混合气体能有效降低铝塑膜进行深度剖析的热效应，从而扩大参数的调节范围；溅射速率随着功率和工作气压的增加而增加；深度分辨率与功率并非是一个单调函数，存在多个拐点。当溅射功率为40 W时，深度分辨率为最佳；在溅射压强大于950 Pa时，深度分辨率基本不变；信噪比随功率的增加而增加，随气压的增加而减少；使用氩-氧（4 Vol%）混合气体作为溅射气体时，测量信号的分辨率与信噪比均大幅优于纯氩气。实验获得的最佳深度谱测量参数为：氩-氧混合工作气压950 Pa，功率40 W, 脉冲频率3 000 Hz，占空比为0.187 5。     

Influence of inert gas pressure on deposition rate during pulsed laser deposition

The deposition rates of permalloy and Ag are monitored during pulsed laser deposition in different inert gas atmospheres. Under ultrahigh vacuum conditions, resputtering from the film surface occurs due to the presence of energetic particles in the plasma plume. With increasing gas pressure, a reduction of the particle energy is accompanied with a decrease of resputtering and a rise in the deposition rate for materials with high sputtering yield. In contrast, at higher gas pressures, scattering of ablated material out of the deposition path between target and substrate is observed, leading to a decrease in the deposition rate. While in the case of Xe and Ar these processes strongly overlap, they are best separated in He. A He pressure of about 0.4 mbar should be used to reduce the kinetic energy of the deposited particles, to reach the maximum deposition rate and to avoid implantation of the particles. This is helpful for the preparation of stoichiometric metallic alloy films and multilayers with sharp interfaces. Received: 27 March 2002 / Accepted: 3 April 2002 / Published online: 5 July 2002     

Formation of silver nanoclusters in transparent polyimides by Ag-K ion-exchange process

Silver nanoclusters embedded in two transparent fluorinated polyimides, 4,4'-hexafluoroisopropylidene diphthalic anhydride – 2,3,5,6-tetramethyl paraphenylene diamine (6FDA-DAD) and 3,3',4,4' – biphenyltetracarboxylic acid dianhydride – 1,1-bis(4-aminophenyl)-1-phenyl-2,2,2-trifluoroethane (BPDA-3F), have been produced by surface modification with KOH aqueous solution followed by K-assisted Ag doping and thermal reduction in hydrogen atmosphere. The reaction rate of the nucleophilic hydrolysis in KOH, studied by Fourier transform infrared spectroscopy (FT-IR) and Rutherford backscattering spectrometry (RBS), depends on the polyimide chemical structure. After ion-exchange in AgNO₃ solution and subsequent annealing, the polyimide structure recovery was monitored by FT-IR whereas the characteristic surface plasmon absorption band of silver nanoparticles was evidenced by optical absorption measurements. The structure of silver nanoclusters as related to size and size distribution in the different polyimide matrices was thoroughly investigated by Transmission electron microscopy (TEM) and X-ray diffraction (XRD). The collected data evidenced a uniform distribution of Ag clusters of nanometric size after thermal treatment at 300 ^○C in both polyimides. For the same ion-exchange treatment parameters and annealing temperature, XRD analyses evidenced the presence of crystallites with similar sizes.     

Deposition of MgO films by pulsed mid-frequency magnetron sputtering

MgO films were deposited by pulsed mid-frequency magnetron sputtering from metallic targets in the mixture of Ar and O₂ gas. The surface morphology, crystalline structure, and optical properties were characterized by using atomic force microscopy (AFM), X-ray diffraction (XRD), and spectroscopic ellipsometry, respectively. The secondary electron emission coefficients of MgO films were measured by using a self-made apparatus in He gas. A pronounced hysteresis phenomenon of target voltage, current, and deposition rate with increasing and decreasing O₂ flow rate was observed. The structure of films deposited at a metallic mode changes from Mg phase to the mixed Mg and MgO phase, and the films have a very rough surface. All the films deposited at oxide mode have high transparency and smooth surface, and show (2 2 0) preferred orientation growth. The refractive index and extinction coefficient at a wavelength of 670 nm for MgO films deposited at oxide mode with a O₂ flow rate of 3 sccm are 1.698 and 1.16×10⁻⁴, respectively. The secondary emission coefficient at a E/p of 57.8 V/(cm Torr) for MgO films deposited at a O₂ flow rate of 3 sccm is 0.16, which is higher than that of MgO films deposited by e-beam evaporation.