H3+团簇离子与固体相互作用

报道了H3+团簇通过碳膜对产生的各种产物的测量结果.分析讨论了三原子离子团簇与固体相互作用中的电荷交换过程.证明在产物的形成中,电荷交换过程起关键作用.分析研究了H3+团簇与固体作用中的团簇效应和尾流效应. 关键词： H3+团簇 电荷交换 团簇效应 尾流效应     

多壁碳纳米管薄膜的压阻效应研究

对多壁碳纳米管薄膜的压阻效应进行了研究. 实验所用的多壁碳纳米管用热灯丝化学气相沉积法合成, 压阻效应用三点弯曲法测量. 研究发现: 在室温下与500微应变内, 原始的多壁碳纳米管薄膜无明显压阻效应, 而经化学修饰处理的碳纳米管膜的压阻因子最高可达120左右, 大大超过多晶硅(Si)在35°C时的压阻因子30, 并且压阻因子与制备方法密切相关. 重点讨论了多壁碳纳米管薄膜产生压阻效应的机制.     

平面环状碳团簇Cn(n=6,10,13,24)振转能谱特性研究

采用密度泛函DFT中的B3P86方法,选用6-311g**基组,对平面环状碳团簇Cn(n=6,10,13,24)的振转能级特性进行了研究.结果表明,碳团簇环状结构的转动能谱恰好处于微波区域,且随碳环面积增大而向低频方向移动.同时对环状碳团簇Cn的能级分布,最高占据轨道HOMO,最低空轨道LUMO及能隙HLGs进行了研究.最后指出,利用环状碳团簇转动能谱位于微波区域的特性,设计出具有低频吸收功能的新型吸波和电磁屏蔽材料.     

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Scn,Yn和Lan(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.Lan团簇的能隙比Scn和Yn团簇的能隙大,计算获得了团簇的电离势和电子亲和势数据,Yn团簇的电离势与实验值相符,最小极化率规律可很好地表征团簇的稳定性.三种团簇均具有较大的磁矩,磁矩与团簇的自旋多重度、几何和电子结构密切相关,理论值与实验值符合较好,随着团簇尺寸的增加三种团簇的平均磁矩总体上都呈递减的趋势并有局部振荡的特征.     

氢离子与碳膜相互作用的实验研究

此文报道了H+、H+2和H+3离子通过碳膜后,在其中产生的各种微量产物的测量结果.讨论了离子与碳膜作用中的电荷交换过程.分析了这些微量产物的形成机理.实验证明在产物的形成中电荷交换过程起关键作用.研究了离子与碳膜作用中的团簇效应和尾流效应.     

Si_n团簇/石墨烯(n≤6)结构稳定性和储锂性能的第一性原理计算

目前,硅/碳复合材料是锂离子电池最有潜在应用前景的高容量负极材料之一,硅与碳材料的界面状态是影响其电化学性能的重要因素.本文在作为碳材料结构单元的石墨烯表面构建了 Si_n(n≤6)团簇,采用基于密度泛函理论(DFT)的第一性原理方法研究了 Si_n团簇/石墨烯(Si_n/Gr)的几何构型、结构稳定性和电子性质.结果表明,当Si原子数n≤4时,Si_n团簇优先以平行于石墨烯的二维构型沉积在石墨烯表面,当n ≥ 5时,Si_n团簇优先以三维立体构型沉积在石墨烯表面.随着n的增大,Si_n团簇在石墨烯表面的热力学稳定性显著降低,两者之间的界面结合减弱,并且伴随着Si_n团簇与石墨烯之间的电荷转移也越来越少.同时还研究了Si_n/Gr复合构型的储锂能力,Li原子主要存储在Si_n团簇临近的石墨烯表面和Si_n团簇周围,Si_n团簇与石墨烯复合形成的协同作用增强了 Li原子吸附的热力学稳定性.当n≤4时,存储2个Li原子有利于提高xLiSi_n/Gr体系的热力学稳定性,继续增加Li原子数x会导致稳定性降低;当n≥5时,稳定性随着Li原子数x的增多而逐渐降低.     

碳团簇型雷达隐身涂料环境稳定性研究

平面环状碳团簇是一种特殊的大分子,利用其转动能级跃迁的谱线富集于1～20 GHz的微波区的特性,研究了碳团簇型隐身涂料的吸收性能稳定性及其机械特性,结果表明,该隐身涂料基本满足吸波材料的技术要求,是一种实用型的隐身材料.     

铁铬合金团簇点阵中与成分相关的磁性耦合

本文采用气相团簇束流沉积法制备了不同铁铬比的铁铬合金密集团簇点阵,研究了团簇点阵中复杂的多相结构和各种耦合效应.当合金中铬含量较大时,在团簇中能够观测到一种晶格失配的类四方结构,这种结构的出现导致了不同铁铬比的合金团簇中交换偏置效应的不同.随着铬的含量增加,合金团簇的交换偏置场减小,而团簇间的偶极相互作用增强.在合金团簇的铁磁-超顺磁转变温度以上,能明显观察到在类四方结构团簇中有更大的残存矫顽力与剩磁.在场冷条件下,对矫顽力和偏置场随温度变化的研究表明含有更多类四方结构的合金团簇有更好的热稳定性和更大的各向异性.     

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     

纳米材料的一支新军—碳纳米管

纳米材料是指介于小团簇(microcluster)与大块物质之间的一种过渡状态.由于其本身尺寸在纳米(nm)量级而具有许多特性,例如量子尺寸效应、表面界面效应等.这些特性使它在科学研究和国民经济中起着或即将起着重要的作用.正当各种各样的纳米材料通过物理、化学方法制备成功并进行广泛研究和应用之时,纳米材料的一支新军——碳纳米管诞生了. 碳纳米管或布基管是近两年在研究碳团簇及富勒烯过程中发现的一种新型的纳米材料.它由纯碳元素组成,是由类似石墨六边形网格翻卷而成的管状物,管子两端一般也是由含五边形的半球面网格封口.碳纳米管尺寸一…     

紫外光引发合成阴离子聚丙烯酰胺及其表征

选择了三种单体：丙烯酰胺(AM)、2-丙烯酰胺基-2-甲基丙磺酸(AMPS)和丙烯酸(AA),在复合引发剂的作用下,紫外光照射共聚得到阴离子聚丙烯酰胺(APAM)。研究了单体配比、单体总质量分数以及引发剂浓度等因素对聚合反应的影响,以产物特性粘度为目标进行了制备条件的优化,并对聚合产物的紫外、红外、电镜等结构和热性能进行表征。结果表明,在单体配比为70∶10∶10、单体质量分数为40%、引发剂浓度0.20%、反应体系pH值为9.0以及光照60 min条件下,能够制得特性粘度为1.6×103 mL·g-1的阴离子聚丙烯酰胺。     

Thermal conductivity of a composite medium with a disperse graphene filler

The possibility of decreasing the effective heat-transfer coefficient of insulating materials due to the introduction of small amounts of graphene-like clusters is considered. It is shown that the effect of screening thermal radiation by introduced clusters at their low concentration significantly exceeds the effect of increasing the thermal conductivity     

Experimental and theoretical studies of interactions between Si<Subscript>7</Subscript> clusters

The possibility of using magic Si₇ clusters to form a cluster material was studied experimentally and theoretically. In experiments Si₇ clusters were deposited on carbon surfaces, and the electronic structure and chemical properties of the deposited clusters were measured using X-ray photoelectron spectroscopy (XPS). A non bulk-like electronic structure of Si₇ was found in the Si 2p core level spectra. Si₇ is suggested to form a more stable structure than the non-magic Si₈ cluster and Si atoms upon deposition on carbon surfaces. Theoretically it was possible to study the interaction between the clusters without the effect of a surface. Density functional theory (DFT) calculations of potential curves of two free Si₇ clusters approaching each other in various orientations hint at the formation of cluster materials rather than the fusion of clusters forming bulk-like structures.     

Thermal stability of Pt nanoclusters interacting to carbon sublattice

The catalytic activity of Pt clusters is dependent not only on the nanoparticle size and its composition, but also on its internal structure. To determine the real structure of the nanoparticles used in catalysis, the boundaries of the thermal structure stability of Pt clusters to 8.0 nm in diameter interacting with carbon substrates of two types: a fixed α-graphite plane and a mobile substrate with the diamond structure. The effect of a substrate on the processes melting of Pt nanoclusters is estimated. The role of the cooling rate in the formation of the internal structure of Pt clusters during crystallization is studied. The regularities obtained in the case of “free” Pt clusters and Pt clusters on a substrate are compared. It is concluded that platinum nanoparticles with diameter D ≤ 4.0 nm disposed on a carbon substrate conserve the initial fcc structure during cooling.

     

Giant room-temperature piezoresistance in a metal-silicon hybrid structure

Metal-semiconductor hybrids are artificially created structures presenting novel properties not exhibited by either of the component materials alone. Here we present a giant piezoresistance effect in a hybrid formed from silicon and aluminum. The maximum piezoresistive gage factor of 843, measured at room temperature, compares with a gage factor of -93 measured in the bulk homogeneous silicon. This piezoresistance boost is not due to the silicon-aluminum interface, but results from a stress induced anisotropy in the silicon conductivity that acts to switch current away from the highly conductive aluminum for uniaxial tensile strains. Its magnitude is shown, via the calculation of hybrid resistivity weighting functions, to depend only on the geometrical arrangement of the component parts of the hybrid.     

A study on the DC-electrical and thermal conductivities of epoxy/ZnO composites doped with carbon black

Thermo-electrical characterizations of hybrid polymer composites, made of epoxy matrix filled with various zinc oxide (ZnO) concentrations (0, 4.9, 9.9, 14.9, and 19.9 wt%), and reinforced with conductive carbon black (CB) nanoparticles (0.1 wt%), have been investigated as a function of ZnO concentration and temperature. Both the measured DC-electrical and thermal conductivities showed ZnO concentration and temperature dependencies. Increasing the temperature and filler concentrations were reflected in a negative temperature coefficient of resistivity and enhancement of the electrical conductivity as well. The observed increase in the DC conductivity and decrease in the determined activation energy were explained based on the concept of existing paths and connections between the ZnO particles and the conductive CB nanoparticles. Alteration of ZnO concentration with a fixed content of CB nanoparticles and/or temperature was found to be crucial in the thermal conductivity behavior. The addition of CB nanoparticles to the epoxy/ZnO matrix was found to enhance the electrical conduction resulting from the electronic and impurity contributions. Also, the thermal conductivity enhancement was mostly attributed to the heat transferred by phonons and electrons hopping to higher energy levels throughout the thermal processes. Scanning electron microscopy and energy-dispersive spectroscopy were used to observe the morphology and elements’ distribution in the composites. The observed thermal conductivity behavior was found to correlate well with that of the DC-electrical conductivity as a function of the ZnO content. The overall enhancements in both the measured DC- and thermal conductivities of the prepared hybrid composites are mainly produced through mutual interactions between the filling conductive particles and also from electrons tunneling in the composite's bulk as well.     

Actuation behavior of waterborne polyurethane/conductive filler nanocomposite electrode

This study dealt with the Maxwell stress effect of waterborne polyurethane (WPU)/conductive filler nanocomposite, which was a promising candidate for a material to be used in a dielectric elastomer actuator electrode. Conductive nanocomposites were produced by using three types of conductive filler: carbon black (CB), vapor grown carbon fiber (VGCF), and silver powder (Ag). Among them, conductive nanocomposite containing VGCF exhibited the lowest threshold concentration; and the mixture of CB and VGCF (CB/VGCF) filler had a synergistic effect to electrical conductivity. Actuation test revealed that CB/VGCF nanocomposite electrode had the largest displacement. Then it could be stated that the improvement of the displacement in CB/VGCF nanocomposite electrode originated from the increase in relative dielectric constant. In addition, a unique feature for the hysteresis of bending deformation was observed. This feature is that the prior application of an electric field significantly improves the bending speed in the successive application. Also, the effect of electrode thickness on the displacement and breakdown strength was examined.     

U形阵列式微机械悬臂梁的研究

为提高悬臂梁的分辨率，实现悬臂梁的多功能性，设计了一种U形阵列式压阻悬臂梁.从理论上对悬臂梁的应力、噪声和灵敏度进行分析，优化了悬臂梁及力敏电阻的几何尺寸.选用多晶硅为力敏材料，基于硅微机械加工技术，制备U形阵列式悬臂梁.测量悬臂梁的噪声及灵敏度，得到多晶硅力敏材料的Hooge因子和应变灵敏度系数，分别为3×10^-3和27.在6V偏压和1000Hz测量带宽条件下，计算悬臂梁的最小可探测位移为0.5nm.同时对多晶硅力敏电阻噪声的产生机理进行了探讨. 关键词： 悬臂梁 噪声 灵敏度 最小可探测位移     

Mechanism of inhibition of nanoparticle growth and phase transformation by surface impurities

Experiments have shown that thermal stability of nanoscale titania is significantly enhanced by the presence of low concentration yttrium dopants, but the mechanism of this effect is unclear. We present extended x-ray fine structure and wide-angle x-ray scattering measurements showing that yttrium is not incorporated in the nanoparticle interior but forms yttrium-oxygen clusters at the nanoparticle surfaces. The surface clusters modify the interfacial free energy, affecting the unit cell parameters, strongly inhibiting nanoparticle growth, and stabilizing the anatase phase up to 700 degrees C. Molecular dynamics calculations reproduced the experimentally observed Y-O bond lengths in surface yttrium clusters and predict a substantial lowering in anatase surface energy, in agreement with the inferred mechanism for suppression of growth and phase transformation.