Surface potential images of polycrystalline organic semiconductors obtained by Kelvin probe force microscopy

P-type copper phthalocyanine (CuPc) and n-type hexadecafluorophthalocyanina-tocopper (F16CuPc) polycrystalline films were investigated by Kelvin probe force microscopy (KPFM). Topographic and corresponding surface potential images are obtained simultaneously. Surface potential images are related with the local work function of crystalline facets and potential barriers at the grain boundaries (GBs) in organic semiconductors. Based on the spatial distribution of surface potential at GBs, donor- and acceptor-like trapping states in the grain boundaries (GBs) of p-CuPc and n-F16CuPc films are confirmed respectively.

平面酞菁弱取向外延薄膜的KPFM研究

载流子传输一直是有机半导体研究中最核心的问题，通过弱外延生长方法可制备高取向、大面积连续的平面酞菁化合物薄膜，其迁移率可达到单晶水平。本论文中应用建立起来的有机半导体开尔文探针力显微镜(KPFM)表征方法，从微观水平研究了这种弱取向外延薄膜和常规的多晶有机半导体薄膜中结构和电特性的关系。 1. 建立了有机半导体的KPFM表征方法。KPFM用微探针方法同时获得样品的表面形貌和电势，本文第二章中论述了KPFM的工作原理、操作方法和成像机制，解释了相关的有机半导体表面态的问题。并且定量验证我们所建立的这种方法的可靠性。 2. 运用KPFM研究了多晶态的有机半导体CuPc和F16CuPc，直接观察到晶界势垒的存在，说明CuPc晶界处存在类施主的缺陷能级，F16CuPc晶界处存在类受主的缺陷能级，这两两种缺陷态分别俘获空穴和电子，使晶界周围的载流子耗尽而形成空间电荷区，限制了载流子的传输，我们从实验的角度证明了有机半导体中晶界限制载流子传输的理论。另外得到多晶CuPc高能量分辨的局域功函图像，越是π电子暴露的表面其功函越高。 3. 在导电的H-Si(111)衬底上制备出6P诱导弱取向生长的CuPc和F16CuPc薄膜，比较了和SiO2衬底上的弱外延生长薄膜的特征。KPFM观察到在CuPc界面处的能带弯曲和空穴累积，这大大降低了载流子传输沟道内CuPc晶界的势垒，从而其迁移率得到很大提高，这说明6P除了具有在结构上诱导使酞菁取向的作用外，还具有电子结构上的效应。另外研究了6P弱外延生长的亚单层F16CuPc薄膜，直接观察到在6P-F16CuPc界面存在强烈的电荷累积，这从微观上说明了有机异质结的电特性。

Isotype heterojunction between organic crystalline semiconductors

We report the effect of n-n isotype organic heterojunction consisting of copper hexadecafluorophthalocyanine (F16CuPc) and phthalocyanatotin (IV) dichloride (SnCl2Pc). Their interfacial electronic structure was observed by Kelvin probe force microscopy (KPFM), and there is band bending in two materials, resulting in an electron accumulation region in F16CuPc layer and an electron depletion region in SnCl2Pc layer. The forming of organic heterojunction was explained by carriers flowing through the interface due to thermal emission of electrons. Furthermore, the carrier transport behavior parallel and vertical to heterojunction interface was also revealed by their heterojunction field-effect transistor with normally on operation mode and heterojunction diodes with rectifying property.

Electrochemical investigations of micro-droplets formed on metals during the deliquescence of salt particles in atmosphere

CORROSION; WATER; SPECTROSCOPY; CHLORIDE; ZINC; NUCLEATION; INTERFACE; ELECTRODE; SURFACES; GROWTH

Effects of spark discharge on the anodic coatings on magnesium alloy

Spark discharge was the representative phenomenon of Micro-arc oxidation (MAO) method distinguished from other electrochemical oxidation methods. Under the spark discharge treatment, characteristics of the anodic layer were significantly changed. To investigate the influences of the spark discharge, a piece of magnesium alloy AZ91D specimen was partly treated by MAO method in alkaline silicate solution. And the microstructure, element distributions as well as the surface potential distributions of the specimen were studied by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and scanning Kelvin probe (SKP) technique. As a result of intensive spark discharge treatment, porous external layer with dense internal layer were formed on Mg alloy surface. At the same time, the depositions of OH- and SiO32- ions were accelerated, which resulted in the enrichment of element oxygen and silicon at the spark discharge region. Moreover, due to the compact internal layer, the intensive spark discharge region exhibited more positive potentials with respect to other regions, which meant this region could restrain the ejection of electron and provide effective protection to the substrate. In addition, it was found that oxygen played a vital role in determining the intensity and size of sparks, and abundant oxygen resulted in intensive and larger sparks. (c) 2005 Elsevier B.V. All rights reserved.

Combined effect of surface tension, gravity and van der Waals force induced by a non-contact probe tip on the shape of liquid surface

Aiming at understanding how a liquid film on a substrate affects the atomic force microscopic image in experiments, we present an analytical representation of the shape of liquid surface under van der Waals interaction induced by a non-contact probe tip. The analytical expression shows good consistence with the corresponding numerical results. According to the expression, we find that the vertical scale of the liquid dome is mainly governed by a combination of van der Waals force, surface tension and probe tip radius, and is weekly related to gravity. However, its horizontal extension is determined by the capillary length.

Probe for Measurements of Density/Conductivity in Flows of Conducting Fluids

A probe utilizing the bipolar pulse method to measure the density of a conducting fluid has been developed. The probe is specially designed such that the concentration of a stream tube can be sampled continuously. The density was determined indirectly from the measurement of solution conductivity. The probe was calibrated using standard NaCl solutions of varying molarity and was able to rapidly determine the density of a fluid with continuously varying conductance. Measurements of the conductivity profiles, corresponding density profiles, and their fluctuation levels are demonstrated in a channel flow with an electrolyte injected from a slot in one wall.

非线性Kelvin-Helmholtz不稳定性

本文用导数展开法对液体薄层与亚音速气流接壤时的界面稳定性作非线性分析.文中考虑了液体的表面张力与体积力,故非线性的Rayleigh-Taylor不稳定性可作为特例而导出;液体与气体均不计粘性.虽然Nayfeh曾算过这一情况,但其三阶方程有遗漏(如213页的式(2.29)).同时解也不自洽(如其一阶解(2.31)并不满足他的初始条件(2.20)),此外,在截止波数附近,对行波他并未考虑.本文弥补了这些,并得出了新的结论.

Tokamak中的Kelvin-Helmholtz不稳定性

<正> Tokamak中的一个重要问题是加热。中性束注入加热是加热的一个有效手段,它使美国PLT上的离子温度达到7.1KeV.但PLT上的中性束注入的不对称性引起等离子体的快速环向旋转,转速可达1×10~7厘米/秒。1979年5月Suckewer等在PLT上测量了速度分布。 在具有速度剪切进行旋转的等离子体中,会不会形成新的磁流体力学不稳定性?1980年

Measurement of Electron Density Profile Behind Strong Shock Waves with a Langmuir Probe

At the shock velocity range of 7~9km/s, the variations of electron density behind strong normal shock waves are measured in a low-density shock tube by using the Langmuir electrostatic probe technique. The electron temperature, calculated based on Park’s three-temperature model, is used in interpreting the probe current data. The peak electron densities determined in the present experiment are shown to be in a good agreement with those predicted by Lin’s calculation. The experimentally obtained ratios of the characteristic ionization distance to the mean free path of freestream ahead of the shock wave are found to be in a good agreement with the existing experiments and Park’s calculation.

Kelvin方程的一种理论推导

从液滴平衡条件推导出严格意义的Kelvin方程,验证了其在宏观尺度可以转化为经典形式.利用Tolman方程,在考虑表面张力与曲率半径关系的条件下,给出在液体压缩性可忽略时,饱和蒸气压、蒸气密度、蒸气摩尔体积和曲率半径等关系;液体压缩性不可忽略时,得出以等温压缩系数和Tolman长度表示的饱和蒸气压与液滴半径的关系.

Group velocity of probe light pulse in an open lambda system

The group velocity of the probe light pulse (GVPLP) propagating through an open Lambda-type atomic system with a spontaneously generated coherence is investigated when the weak probe and strong driving light fields have different frequencies. It is found that adjusting the detuning or Rabi frequency of the probe light field can realize switching of the GVPLP from subluminal to superluminal. Changing the relative phase between the probe and driving light. elds or atomic exit and injection rates can lead to GVPLP varying in a wider range, but cannot induce transformation of the property of the GVPLP. The absolute value of the GVPLP always increases with Rabi frequency of the driving light field increasing. For subluminal and superluminal propagation, the system always exhibits the probe absorption, and GVPLP is mainly determined by the slope of the steep dispersion.

Controllable group velocity of the probe light in a Lambda-type system with two fold levels

The group velocities of the probe laser field are studied in a A-type system where one lower state has two fold levels coupled by a control field. It is found that the interaction of double dark states leads to controllable group velocity of the probe field in this system. It can be easily realized, due to the interacting double dark resonances, that one of the group velocities at transparency positions is much slower than the other by tuning the control field to be off resonance. In particular, when the control field is on resonance. we can obtain two equal slow group velocities with a broader EIT width, which provides potential applications in quantum storage and retrieval of light. (c) 2005 Elsevier B.V. All rights reserved.