用STM的纳米导电图形加工技术的研究

用STM针尖对有机络合物电双稳薄膜材料施加强电场作用，可在材料表面产生纳米线度的导电几何图形。实验证明：对针尖本身的几何构形、施加在针尖上的脉冲幅度、周期和占空比都必须进行细致的选择。用Ag-TCNQ络合物进行实验，在适合的针尖-样品距离下，发现所加脉冲偏压的极性为负时，容易进行加工。     

用扫描隧道显微镜对材料进行表面修饰的研究

扫描隧道显微镜(STM)是对材料表面进行表面修饰(surface modification)和表面原子操纵(atomcraft)的重要工具。为了了解其机理,选择了场蒸发阈值从大到小有代表性的钨、铂、金、铜做针尖,扫描过程中在针尖与石墨表面之间施加针尖为正的脉冲电压,获得了一些新现象,并对实验结果作了比较,从而在一定程度上确定了脉冲制STM表面修饰实验中针尖与样品之间电场的重要作用。     

原子力显微镜探针针尖修饰的研究进展

介绍了当前几种AFM探针针尖修饰技术,以及它们在高分子材料、生物材料、微观摩擦学、粘附力、纳米级电化学、碳纳米管及纳米加工方面的研究进展。AFM探针针尖修饰的目的主要是:提高扫描图像分辨率,其分辨率可达纳米或亚纳米级别;用力曲线探究特定基团间的相互作用,定量分析端基与端基之间、分子链与分子链之间及端基与分子链之间的相互作用力,避免针尖对生物样品表面的损坏;对分子材料结构进行修饰,特别是在生物细胞、DNA分子链上及分子识别;避免Si或Si3N4针尖与表面硬度较大的样品直接接触,延长探针针尖的使用寿命。在研究天然橡胶硫化的作用机理时,可以用针尖修饰技术来模拟这个过程,探究天然橡胶分子链与单个硫原子的相互作用方式与作用力。通过电化学接枝聚合把高分子接枝在AFM针尖上,为研究单链的弹性力、引起构象转变的力、相互作用的双分子的分离力及特定的官能团的相互作用提供了许多可能性。分析了影响AFM探针针尖修饰的因素,结合材料领域方面的发展,对针尖修饰技术的发展及应用前景做了分析和预测。     

适用于针尖增强拉曼的银针尖物理制备方法研究

提出两种可适用于针尖增强拉曼光谱(TERS)系统的拉曼针尖及其物理制备方法,制备针尖分别为银与镀银针尖。基于时域有限差分法(FDTD)仿真,对4种不同中间层材料、无中间层材料的不同膜厚镀银针尖及不同针尖曲率的银针尖进行仿真研究,并对入射光与针尖夹角,针尖与样品间距对电磁场增强的影响进行了探究。结果显示:以钛、铜为中间层膜厚为45nm的镀银针尖以及针尖曲率为55nm的银针尖具有最佳的电磁场增强效果。入射光与针尖夹角为39.27°,针尖与样品间距小于1nm时具有最佳的电磁场增强效果。基于仿真,采用磁控溅射成功制备以钛为中间层的镀银针尖,聚焦离子束(FIB)切割成功制备出银针尖。     

专利信息

用扫描隧道显微技术聚合制备高分子微晶薄膜的方法 公告号:1116214 申请人:复旦大学 文摘:本发明属高分子材料技术领域,是一种用扫描隧道显微技术聚合制备高分子微晶薄膜的方法,本法利用扫描隧道显微镜（STM）内针尖与样品之间所固有的高电场进行单体聚合。先用液状的单体均匀地涂布在某种固体单晶表面,然后放入STM,用STM针尖进行扫描。针尖产生的强电场使单体开始聚合,慢慢形成有序的单晶薄膜,其尺寸可达到亚微米级至纳米级。这种材料可用于制备纳     

SPM抑振系数的理论与实验研究

为分析外界振动对扫描探针显微镜（SPM）针尖一样品副的影响,提出“抑振系数”的概念．围绕SPM针尖一样品副的动态力学模型,对抑振系数的物理含义、影响因素等进行了理论分析．搭建了SPM激振、测振的实验系统,对不同的SPM扫描器、探针、样品、针尖预应力以及针尖一样品副开／闭环对SPM抑振系数的影响进行了实验研究．在理论分析上和实验研究中,都证实SPM抑振系数与悬臂梁的有效质量、弹性系数、空气阻尼系数、针尖与样品的接触弹性系数和接触阻尼系数等相关,反映在实际SPM部件参数上,则较短的扫描器、较长的悬臂探针、较软的样品表面、较大的探针预应力、闭环控制的针尖一样品副等都是提高SPM抑振性的途经．     

于FDTD仿真的高增益拉曼镀金针尖的可重复准确制备

提出一种可适用于针尖增强拉曼系统(TERS)的基于时域有限差分法(FDTD)的高增益拉曼针尖及其制备方法。在汇聚光条件下,仿真分析镀Au厚度为5～100nm,中间过渡层材料分别为5nm的SiO₂,Ta₂O₅,Ti,Cu的内凹型W针尖,在Au基底金半球样品处的近场电场分布情况。仿真结果表明:50nm镀金厚度,Ti,Cu为中间层的针尖具有更强的增强效果。在此基础上通过磁控溅射,设定镀Ti时间7s,镀Au时间120s,成功制备出所设计的高增益针尖,通过聚焦离子束(FIB)沿轴向切割针尖并借助扫描电镜(SEM)观察针尖剖面结构,验证该镀膜针尖的尺寸形状等结构参数达到设计要求。经4批次,每批次20根针尖进行重复镀膜实验,从而证明所设计的针尖稳定可重复准确制备。     

基于AFM的纳米级表面加工中切屑形成的影响因素

以原子力显微镜（AFM）为加工工具进行了纳米级加工实验,对不同加工条件下的材料去除过程和切屑形态进行了研究．切屑形态通过扫描电子显微镜（SEM）进行观察,分析了不同垂直载荷、循环次数和针尖加工方向下铝铜被加工表面的切屑形成过程．实验结果表明：低栽下切屑呈细小断屑,散布在加工区域周围;随着垂直载荷的增加,切屑逐渐变成连续的带状切屑．不同循环次数、针尖加工面时切屑形成都有很大影响．在此基础上,对比分析了相同实验条件下,不同力学性能材料的切屑形成过程．最后,通过检测被加工表面得出被加工表面质量与切屑的数量和形态之间的关系,提出了改善被加工表面质量的方法,以帮助人们更好地理解基于AFM的纳米级加工技术．     

有机纳米整流器的STM研究

金属有机络合物Ag TCNQ的薄膜在STM针尖电场的作用下 ,当电压达到某一阈值后可以从高阻态跃迁至低阻态。在一定的条件下 ,在低阻态的保持时间很短 ,且高低阻态间的转换可以重复。由于它们都是有机材料 ,根据这种特性 ,提出了一种新型有机纳米整流器的设想 ,并成功地制作了输出可控的有机纳米整流器的原型。     

极浅压入下纳米压痕仪针尖面积函数校准方法的研究

采用原子力显微镜直接扫描纳米压痕仪针尖法、球面拟合法和熔融石英标准样块的间接测量法对极浅压入下纳米压痕仪的针尖面积函数进行比较分析。实验表明,在极浅压入下,原子力显微镜直接法由于真实地反映了针尖尖端的几何形貌因而获得的面积函数更为准确可靠。建立了相应的数学模型,对于直接法测量中主要的误差,即由于原子力显微镜针尖曲率半径带来的误差进行了分析,结果表明在极小压入深度下压入深度越小,原子力显微镜针尖曲率半径带来的压痕仪针尖面积函数相对误差越大。     

Scanning tunneling microscopy with chemically modified gold tips: in situ reestablishment of chemical contrast

A method was developed for the reestablishment of chemical contrast in STM images obtained with chemically modified gold tips. Such tips display selective chemical contrast, which allows the selective imaging of specific species on the sample surface. Chemically modified STM tips can be fabricated by forming a self-assembled monolayer (SAM) on an electrochemically etched gold tip. One difficulty with this method thus far has been the relatively short lifetime of SAM-treated tips. The method described here utilizes the brief application of a high bias voltage between the sample and the tip to cause SAM molecules to reoccupy the tip apex, thereby allowing the tips to display selective chemical contrast in imaging. These treatments consist of applying a +1.9-V sample bias for 0.5-10 min under tunneling conditions. The usable lifetime of SAM-modified tips could be increased by more than 2 orders of magnitude, from hours to at least a month, dramatically increasing the efficiency of using SAM-modified gold tips. SAM molecules can also be removed from the tip apex by application of a negative sample bias (-2.0 V for 0.5-10 min) making it possible to alternate between conventional STM images and STM images with chemically enhanced contrasts.     

A rack-and-pinion device at the molecular scale

Molecular machines, and in particular molecular motors with synthetic molecular structures and fuelled by external light, voltage or chemical conversions, have recently been reported. Most of these experiments are carried out in solution with a large ensemble of molecules and without access to one molecule at a time, a key point for future use of single molecular machines with an atomic scale precision. Therefore, to experiment on a single molecule-machine, this molecule has to be adsorbed on a surface, imaged and manipulated with the tip of a scanning tunnelling microscope (STM). A few experiments of this type have described molecular mechanisms in which a rotational movement of a single molecule is involved. However, until now, only uncontrolled rotations or indirect signatures of a rotation have been reported. In this work, we present a molecular rack-and-pinion device for which an STM tip drives a single pinion molecule at low temperature. The pinion is a 1.8-nm-diameter molecule functioning as a six-toothed wheel interlocked at the edge of a self-assembled molecular island acting as a rack. We monitor the rotation of the pinion molecule tooth by tooth along the rack by a chemical tag attached to one of its cogs.     

Localized deposition of coronene molecules on Si(001)-2x1 using a scanning tunneling microscope tip source

The deposition of coronene molecules from scanning tunneling microscope (STM) tips onto a clean Si(001)-2x1 surface at 25 degrees C was investigated. The STM tips, contaminated with coronene, were found to deposit coronene molecules on the clean Si(001) surface, allowing patterns to be generated. Covalent Si-C chemical bonds, formed between the coronene molecules and the Si substrate, froze the flip-flop motion of the adjacent Si-Si dimers on the substrate. In most cases, the mode of coronene bonding to Si(001) is independent of whether deposition occurs from the gas phase or from the STM tip. Despite the covalent chemical bonds formed between the coronene molecule and the Si substrate, the STM tip can drag the coronene laterally on the Si substrate without inducing a chemical change in the molecule. Sharp spikes observed in the tunneling current during the coronene deposition reflect the abrupt decrease of the tip-substrate distance at the instant of transport of the molecule from tip to surface.     

Exploring the interatomic forces between tip and single molecules during STM manipulation

The interaction between a single molecule and the STM tip during intramolecular manipulation is investigated in detail. We show that the conformational change of complex organic molecules can be induced reversibly and very reliably by using exclusively attractive forces. By studying the dependence of this process on the bias voltage and the tip position, the driving forces are characterized. Different regimes of tip-molecule interactions are observed as a function of the distance.     

Active nanocharacterization of nanofunctional materials by scanning tunneling microscopy

Recent developments in the application of scanning tunneling microscopy (STM) to nanofabrication and nanocharacterization are reviewed. The main focus of this paper is to outline techniques for depositing and manipulating nanometer-scale structures using STM tips. Firstly, the transfer of STM tip material through the application of voltage pulses is introduced. The highly reproducible fabrication of metallic silver nanodots and nanowires is discussed. The mechanism is thought to be spontaneous point-contact formation caused by field-enhanced diffusion to the apex of the tip. Transfer through the application of z-direction pulses is also introduced. Sub-nanometer displacement pulses along the z-direction form point contacts that can be used for reproducible nanodot deposition. Next, the discovery of the STM structural manipulation of surface phases is discussed. It has been demonstrated that superstructures on Si(001) surfaces can be reverse-manipulated by controlling the injected carriers. Finally, the fabrication of an atomic-scale one-dimensional quantum confinement system by single-atom deposition using a controlled point contact is presented. Because of its combined nanofabrication and nanocharacterization capabilities, STM is a powerful tool for exploring the nanotechnology and nanoscience fields.     

Patterning of sub-1 nm dangling-bond lines with atomic precision alignment on H:Si(100) surface at room temperature

We have patterned sub-1 nm dangling-bond (DB) lines on a H-terminated Si(100)-2 × 1 surface aligned with atomic precision at room temperature using a scanning tunneling microscope (STM) to controllably desorb hydrogen atoms from a H:Si(100) surface. In order to achieve continuous and aligned DB lines, we have performed a detailed investigation of the effects of patterning parameters such as the writing voltage, writing current and electron dosage, as well as STM tip apex geometry on the fabrication and alignment of Si DB lines. We show that there exists an optimum set of patterning parameters which enables us to obtain near-perfect Si DB lines and align them with near atomic precision in a highly controllable manner. In addition, our results indicate that the pattern quality is weakly dependent on the STM tip apex quality when the patterning parameters are within the optimum parameter space.     

Active nanocharacterization of nanofunctional materials by scanning tunneling microscopy

Abstract

Recent developments in the application of scanning tunneling microscopy (STM) to nanofabrication and nanocharacterization are reviewed. The main focus of this paper is to outline techniques for depositing and manipulating nanometer-scale structures using STM tips. Firstly, the transfer of STM tip material through the application of voltage pulses is introduced. The highly reproducible fabrication of metallic silver nanodots and nanowires is discussed. The mechanism is thought to be spontaneous point-contact formation caused by field-enhanced diffusion to the apex of the tip. Transfer through the application of z-direction pulses is also introduced. Sub-nanometer displacement pulses along the z-direction form point contacts that can be used for reproducible nanodot deposition. Next, the discovery of the STM structural manipulation of surface phases is discussed. It has been demonstrated that superstructures on Si(001) surfaces can be reverse-manipulated by controlling the injected carriers. Finally, the fabrication of an atomic-scale one-dimensional quantum confinement system by single-atom deposition using a controlled point contact is presented. Because of its combined nanofabrication and nanocharacterization capabilities, STM is a powerful tool for exploring the nanotechnology and nanoscience fields.     

Switching kinetics of a Cu2S-based gap-type atomic switch

The switching time of a Cu(2)S-based gap-type atomic switch is investigated as a function of temperature, bias voltage, and initial off-resistance. The gap-type atomic switch is realized using a scanning tunneling microscope (STM), in which the formation and annihilation of a Cu-atom bridge in the vacuum gap between the Cu(2)S electrode and the Pt tip of the STM are controlled by a solid-electrochemical reaction. Increasing the temperature decreases the switching time exponentially with an activation energy of about 1.38 eV. Increasing the bias voltage also shortens the switching time exponentially, exhibiting a greater exponent for the lower bias than for the higher bias. Furthermore, faster switching has been achieved by decreasing the initial off-resistance between the Cu(2)S electrode and STM tip. On the basis of these results, we suggest that, in addition to the chemical reaction, the electric field in the vacuum gap plays a significant role in the operation of a gap-type atomic switch. This investigation advances our understanding of the operating mechanism of an atomic switch, which is a new concept for future electronic devices.     

有机电荷转移体系用于超高密度信息存储研究

采用有机电荷转移复合材料和共轭Ｃｃｈｉｆｆ碱作为存储介质。通过ＳＴＭ脉冲电压存储实验实现了存储密度大于１０＾１２ｂｉｔｓ／ｃｍ＾２的超高密度信息存储。用ＵＶ－Ｖｉｓ、Ｘ射线四圆衍射分析等方法对材料结构进行了表征,并用量子化学计算讨论了可能的存储机制。     

Local modification of NaCl thin films on Cu(111) under different bias voltages

The local modification of NaCl thin films on Cu(111) under different bias voltages is investigated using a scanning tunneling microscope (STM) at room temperature. We find that the type of modification of NaCl thin films is dependent on sample bias voltage (V_s). Defects in a triple-layer-thick NaCl film are destabilized and repelled away from the region beneath an STM tip by applying V_s in the range of 0.3 V ≤ |V_s| ≤ 0.5 V. When V_s is larger than + 1.2 V or smaller than − 4.0 V, the removal of NaCl films takes place and a bare Cu surface appears. In this case, the removed NaCl is transferred to the STM tip and can be supplied back to the surface from the STM tip. The redeposition of NaCl enables not only the reformation of single-crystalline NaCl films on a bare Cu surface but also the formation of additional NaCl films on a clean NaCl film surface.