DNA结构的扫描探针显微学研究

1．利用原子力显微镜，我们研究了DNA与邻菲咯琳钻之间的反应。乙醇溶液中DNA复合物的形貌改变很好地说明了静电力在引起DNA凝集中的重要地位。随着醇浓度增加，对应更低的介电常数，静电反应增强。当介电常数降低，平衡离子就会在DNA的磷酸骨架上聚集，并中和负电荷到能引起凝集的程度。2，为了深入认识DNA-表面活性剂复合物的形貌特征，我们对阳离子表面活性剂CTAB引起的DNA凝集体进行了研究。由环状凝集体的体积分析，我们认为DNA发生单分子凝集。除环状体之外，许多不规则的环状体有助于说明DNA环状体的形成过程。部分绕转体和核小体状环状体对应于绕转模型而棒状中间体显示DNA分子也可能采取棒状体到环状体的转化模型。3．DNA分子在形成稳定的凝集体之前会经过一系列的中间体。因为温度是DNA结构的一个重要的决定因素，在其他凝集条件一定时，我们观察了DNA凝集中间体在温度升高时的结构转变。AFM分析得出质粒DNA pBR322的凝集结构受温度的影响很大。低温时，单个分子花束体是DNA分子采取的主要凝集结构。较高温度时，分子变得舒展，但链上有许多可能利于多分子凝集的小环。继续升高温度，DNA分子大范围地发生分子间的单中心、交联。4．在Mg2+，Ca2＋，Sr2和Ba2+分别作为DNA在云母表面的平衡离子时，我们观察了DNA分子在云母表面扩散平衡或被动力俘获的形貌特征。末端距和伸展长度可由原子力显微镜的数据分析结果得到。实验结果表明当Mg2＋，Ca2+和Sr2+为平衡离子时，DNA分子能够在云母表面扩散平衡。然而Ba2+作用时，严重交接的DNA结构说明DNA分子不易在云母表面反应平衡，俘获的程度也随实验条件而改变。在醇溶液中，我们还观察了B-A构象转变对平衡离子种类的依赖关系。四种碱土金属引起B-A构象转变的能力不同，其中Sr2-导致B-A构象转变的程度最大。

DNA、纳米微粒及其相互作用的扫描探针显微学研究

1．采用改进的蒸发液滴中流体毛细流动法，用于展开和固定适于AFM研究的大环状DNA。对长达148.9 kbp的人类基因组3号染色体上一个完整的酵母染色体DNA分子和pB孙22质粒DNA进行了展开固定研究，长度测定显示偏差小于3.5％，结果优于其它展开线性DNA的方法。对其相应的展开机理进行了初步探讨：利用AFM考察了不同长度的DNA分子在云母基底上的分子级分形图案。实验证明DNA分子级的分形图案与DNA的浓度、长度和其它辅助因素相关。我们认为DLA理论或许更适合描述DNA分子在云母基底上形成不同分形图案的体系。2．我们利用阳离子的桥合作用，将质粒DNA固定并展开在云母基底上制得了DNA网络结构。结合实验数据，对质粒DNA形成的机理和可控的参数：离子种类、离子浓度、网孔大小和网孔高度进行了讨论，提出了相应的模型进行解释。我们在半透明的云母基底以及玻璃和蓝宝石等透明基底上构建了不同结构的DNA网络。结合实验数据，讨论了在各种固体基底上形成DNA网络的影响因素，我们认为，固体基底表面的亲水性对于构建DNA网络起重要作用。我们通过控制乙醇的浓度与温度结合原子力显微镜样品定位技术发现，云母基底上形成DNA膜的DNA分子是否移动与处理DNA样品的乙醇浓度有直接关系。对于纯乙醇溶液无论是高温（6O℃）或常温，均未引起DNA分子的移动（无论是吸附在云母基底上的，还是吸附在DNA分子链上的）；如果用混合有水的乙醇溶液（无论其中水的含量多少），不管是高温（60℃）或常温，都会引起DNA膜结构发生变化，即DNA分子发生了移动。热乙醇水溶液对DNA分子的作用比常温情况下更明显1可能是热力学上的因素导致的。3．通过控制银纳米微粒在云母基底上的聚集行为，而非直接通过化学合成的方法，构建了一种新的银结构一纳米银盘。详细阐述了如何得到这种结构的过程，通过原子力显微镜、紫外可见光光谱和X一射线电子能谱技术等工具对其性质也作了相应的表征。这种由纳米粒子组成的银盘与文献报道的单晶纳米银盘相比具有更大的比表面积，在纳米催化等方面有更广阔的应用前景。通过自聚集方式构建纳米银盘结构的方法，对于人们通常认为在溶液中合成的纳米结构与在各种固体基底上表征的纳米结构是一致的观点提出了新的理解。利用戊二醛试剂与发光的纳米微粒萘酰亚胺通过醛胺加成反应形成酰胺键，组装形成二维发光粒子网络。结合原子力显微镜高度形貌图和光谱数据，发现粒子间形成了两种典型的网络结构即，实心六方堆积和空心六方堆积结构。对此我们提出了相应的模型给予解释。4，利用展开的质粒DNA为模板诱导形成了环状的氯化镁纳米结构。原子力显微镜考察表明，这些纳米结构的高度是6.2±1.3-8.2±1.80nm，长度为1.35±0.18到2.93±0.25um。我们以CTAB包裹18nm纳米金和3.5nm纳米银使之形成带正电荷的外壳，利用。NA磷酸骨架带负电荷特性，通过静电自组装方式形成了金属化的纳米网络结构。通过AFM、UV-vis光谱和XPS谱的表征说明，带正电荷外壳的纳米金和纳米银被DNA模板高度地组装形成有序的二维网络结构。5．利用自制的样品定位系统，重复性地对整个基底范围内的样品实行定位，定位的精确度达400nm。这种方法对于样品旋转角度或取出后进行进一步处理都适用。该定位方法依赖于一台个人电脑，一个样品定位仪，一个CCD相机和一套可视光学系统，用于监测透明或半透明基底如，云母、玻璃、蓝宝石、石英和钦酸银等原子力显微镜广泛使用的基底表面或背面特征。作为对这种定位方法的应用，我们用不同的灯M操作模式，不同的针尖对单个的DNA分子、单个的DNA-蛋白质复合物和DNA网络在样品移动或拿出样品台后进行了定位实验。这种方法的精度和分辨率，对于一般的商用或自制SPM（AFM,STM，sNOM）系统都可以适用。

DNA-聚苯胺体系的电化学及扫描探针显微学研究

DNA-聚苯胺复合物在低维纳米材料制作、生物传感器、DNA杂交反应检测以及生物芯片开发等方面具有潜在的应用价值。鉴于此，我们在本论文中着重研究了以下两方面内容：1．利用循环伏安法研究了DNA的存在对聚苯胺电化学行为的影响。研究发现，虽然，苯胺的循环伏安聚合过程不受DNA的影响，但是DNA的存在会显著降低聚苯胺修饰电极在HCl空白溶液中循环伏安扫描时的峰电流值。初步推测可能是由于DNA分子在聚苯胺膜上的吸附阻碍了电极上电子的传递而造成的。2．通过自组装方法从水溶液中构造出了分散性良好的苯胺-DNA复合物纳米线，并以此为前驱体构造出了以DNA为模板的聚苯胺纳米线。另外，利用改进后的气流展开法可以将所得到的纳米线有序排列到基底上。用原子力显微镜对所得到的纳米线进行了表征，结果显示纳米线形貌规整、排列有序、背景清晰。

Effects of Thickness on Properties of ZnO Films Grown on Si by MOCVD

High quality ZnO films are successfully grown on Si（100） substrates by metal-organic chemical vapor deposition at 300℃. The effects of the thickness of the ZnO films on crystal structure, surface morphology,and optical properties are investigated using X-ray diffraction, scanning probe microscopy,and photoluminescence spectra, respectively. It is shown that the ZnO films grown on Si substrates have a highly-preferential C-axis orientation,but it is difficult to obtain the better structural and optical properties of the ZnO films with the increasing of thickness. It is maybe due to that the grain size and the growth model are changed in the growth process.

Immobilization of the nanoparticle monolayer onto self-assembled monolayers by combined sterically enhanced hydrophobic and electrophoretic forces

The immobilization of surface-derivatized gold nanoparticles onto methyl-terminated self-assembled monolayers (SAMs) on gold surface was achieved by the cooperation of hydrophobic and electrophoretic forces. Electrochemical and scanning probe microscopy techniques were utilized to explore the influence of the SAM's structure and properties of the nanoparticle/SAM/gold system. SAMs prepared from 1-decanethiol (DT) and 2-mercapto-3-n-octylthiophene (MOT) were used as hydrophobic substrates. The DT SAM is a closely packed and organized monolayer, which can effectively block the underlying gold and inhibit a variety of solution species including organic and inorganic molecules from penetrating, whereas the MOT monolayer is poorly packed or disorganized (because of a large difference in dimension between the thiophene head and the alkylchain tail) and permeable to many organic probes in aqueous solution but not to inorganic probes. Thus, the MOT monolayer provides a more energetically favorable hydrophobic surface for the penetration and adsorption of organic species than the DT monolayer.

Incorporation of surface-derivatized gold nanoparticles into electrochemically generated polymer films

Stable colloidal solutions of gold nanoparticles surface-derivatized with a thiol monolayer have been prepared using two-phase (water-nitrobenzene) reduction of AuCl4- by sodium borohydride in the presence of 2-mercapto-3-n-octylthiophene (MOT). This kind of surface-functionalized gold nanoparticles can be easily incorporated into the poly(3-octylthiophene) (POT) films on electrode in the process of electrochemical polymerization leading to POT-gold nanoparticle (POT-Au) composite films. Scanning probe microscopy (SPM) and X-ray photoelectric spectroscopy (XPS) have been employed to characterize the surface-derivatized particles and the resulting films. The method of incorporation of nanoparticles into polymer by surface-derivatization and in situ polymerization can also be employed to prepare many other polymer-nanoparticle compostie materials.

Nanoscale electronic properties of conjugated polymers and nanocrystals

The objective of this thesis is the exploration and characterisation of the nanoscale electronic properties of conjugated polymers and nanocrystals. In Chapter 2, the first application of conducting-probe atomic force microscopy (CP-AFM)-based displacement-voltage (z-V) spectroscopy to local measurement of electronic properties of conjugated polymer thin films is reported. Charge injection thresholds along with corresponding single particle gap and exciton binding energies are determined for a poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] thin film. By performing measurements across a grid of locations on the film, a series of exciton binding energy distributions are identified. The variation in measured exciton binding energies is in contrast to the smoothness of the film suggesting that the variation may be attributable to differences in the nano-environment of the polymer molecules within the film at each measurement location. In Chapter 3, the CP-AFM-based z-V spectroscopy method is extended for the first time to local, room temperature measurements of the Coulomb blockade voltage thresholds arising from sequential single electron charging of 28 kDa Au nanocrystal arrays. The fluid-like properties of the nanocrystal arrays enable reproducible formation of nanoscale probe-array-substrate junctions, allowing the influence of background charge on the electronic properties of the array to be identified. CP-AFM also allows complementary topography and phase data to be acquired before and after spectroscopy measurements, enabling comparison of local array morphology with local measurements of the Coulomb blockade thresholds. In Chapter 4, melt-assisted template wetting is applied for the first time to massively parallel fabrication of poly-(3-hexylthiophene) nanowires. The structural characteristics of the wires are first presented. Two-terminal electrical measurements of individual nanowires, utilising a CP-AFM tip as the source electrode, are then used to obtain the intrinsic nanowire resistivity and the total nanowire-electrode contact resistance subsequently allowing single nanowire hole mobility and mean nanowire-electrode barrier height values to be estimated. In Chapter 5, solution-assisted template wetting is used for fabrication of fluorene-dithiophene co-polymer nanowires. The structural characteristics of these wires are also presented. Two-terminal electrical measurements of individual nanowires indicate barrier formation at the nanowire-electrode interfaces and measured resistivity values suggest doping of the nanowires, possibly due to air exposure. The first report of single conjugated polymer nanowires as ultra-miniature photodetectors is presented, with single wire devices yielding external quantum efficiencies ~ 0.1 % and responsivities ~ 0.4 mA/W under monochromatic illumination.

Chemical etching of optical fibre tips - experiment and model

The formation of chemically etched fibre tips for use in optical scanning probe microscopy is addressed. For tips formed at a cleaved fibre end in the bulk of a buffered HF acid solution the morphological features (tip height, cone angle) are found to depend strongly on the temperature and etchant composition. The tip formation process is analysed and explained in terms of a simple model in which the only pertinent physical parameters are the fibre core diameter and etch rates of the fibre core and cladding. The etch rates are determined in separate experiments as a function of temperature (in the range 24-50 degreesC) for etchant solutions of de ionised water: 50% HF acid: 40% NH4F in the volume ratio 1 : 1 : X for X=2, 4 and 6, and used in the model to yield a correct description of the experimental tip cone angles. The model is successfully extended to the intriguing case of negative tip formation which initiates in a normal, positive tip structure. By contrast, tip formation in the meniscus region of a bare fibre/etchant/organic solvent system is found to be independent of etchant composition and temperature. (C) 2000 Elsevier Science B.V. All rights reserved.

Measuring oxygen reduction/evolution reactions on the nanoscale

The efficiency of fuel cells and metal-air batteries is significantly limited by the activation of oxygen reduction and evolution reactions. Despite the well-recognized role of oxygen reaction kinetics on the viability of energy technologies, the governing mechanisms remain elusive and until now have been addressable only by macroscopic studies. This lack of nanoscale understanding precludes optimization of material architecture. Here, we report direct measurements of oxygen reduction/evolution reactions and oxygen vacancy diffusion on oxygen-ion conductive solid surfaces with sub-10 nm resolution. In electrochemical strain microscopy, the biased scanning probe microscopy tip acts as a moving, electrocatalytically active probe exploring local electrochemical activity. The probe concentrates an electric field in a nanometre-scale volume of material, and bias-induced, picometre-level surface displacements provide information on local electrochemical processes. Systematic mapping of oxygen activity on bare and platinum-functionalized yttria-stabilized zirconia surfaces is demonstrated. This approach allows direct visualization of the oxygen reduction/evolution reaction activation process at the triple-phase boundary, and can be extended to a broad spectrum of oxygen-conductive and electrocatalytic materials.

Ionically-Mediated Electromechanical Hysteresis in Transition Metal Oxides

Nanoscale electromechanical activity, remanent polarization states, and hysteresis loops in paraelectric TiO2 and SrTiO3 thin films are observed using scanning probe microscopy. The coupling between the ionic dynamics and incipient ferroelectricity in these materials is analyzed using extended Landau-Ginzburg-Devonshire (LGD) theory. The possible origins of electromechanical coupling including ionic dynamics, surface-charge induced electrostriction, and ionically induced ferroelectricity are identified. For the latter, the ionic contribution can change the sign of first order LGD expansion coefficient, rendering material effectively ferroelectric. The lifetime of these ionically induced ferroelectric states is then controlled by the transport time of the mobile ionic species and well above that of polarization switching. These studies provide possible explanation for ferroelectric-like behavior in centrosymmetric transition metal oxides.

Mapping Irreversible Electrochemical Processes on the Nanoscale: Ionic Phenomena in Li Ion Conductive Glass Ceramics

A scanning probe microscopy approach for mapping local irreversible electrochemical processes based on detection of bias-induced frequency shifts of cantilevers in contact with the electrochemically active surface is demonstrated. Using Li ion conductive glass ceramic as a model, we demonstrate near unity transference numbers for ionic transport and establish detection limits for current-based and strain-based detection. The tip-induced electrochemical process is shown to be a first-order transformation and nucleation potential is close to the Li metal reduction potential. Spatial variability of the nucleation bias is explored and linked to the local phase composition. These studies both provide insight into nanoscale ionic phenomena in practical Li-ion electrolyte and also open pathways for probing irreversible electrochemical, bias-induced, and thermal transformations in nanoscale systems.

Controlling magnetoelectric coupling by nanoscale phase transformation in strain engineered bismuth ferrite

The magnetoelectric coupling in multiferroic materials is promising for a wide range of applications, yet manipulating magnetic ordering by electric field proves elusive to obtain and difficult to control. In this paper, we explore the prospect of controlling magnetic ordering in misfit strained bismuth ferrite (BiFeO3, BFO) films, combining theoretical analysis, numerical simulations, and experimental characterizations. Electric field induced transformation from a tetragonal phase to a distorted rhombohedral one in strain engineered BFO films has been identified by thermodynamic analysis, and realized by scanning probe microscopy (SPM) experiment. By breaking the rotational symmetry of a tip-induced electric field as suggested by phase field simulation, the morphology of distorted rhombohedral variants has been delicately controlled and regulated. Such capabilities enable nanoscale control of magnetoelectric coupling in strain engineered BFO films that is difficult to achieve otherwise, as demonstrated by phase field simulations.

In Situ Formation of Micron-Scale Li-Metal Anodes with High Cyclability

Scanning probe microscopy methods have been used to electrodeposit and cycle micron-scale Li anodes deposited electrochemically under nanofabricated Au current collectors. An average Li volume of 5 x 10(8) nm(3) was deposited and cycled with 100% coulombic efficiency for similar to 160 cycles. Integrated charge/discharge values agree with before/after topography, as well as in situ dilatometry, suggesting this is a reliable method to study solid-state electrochemical processes. In this work we illustrate the possibility to deposit highly cyclable nanometer thick Li electrodes by mature SPM and nanofab techniques which can pave the way for inexpensive nanoscale battery arrays. 

Nanoscale mapping of oxygen vacancy kinetics in nanocrystalline Samarium doped ceria thin films

The position-dependent oxygen vacancy dynamics induced by a biased scanning probe microscopy tip in Samarium doped ceria thin films grown on MgO (100) substrates is investigated. The granularity of the samples gives rise to spatially dependent local electrochemical activity, as explored by electrochemical strain microscopy. The kinetics of the oxygen vacancy relaxation process is investigated separately for grain boundaries and grains. Higher oxygen vacancy concentration variation and slower diffusion are observed in the grain boundary regions as compared to the grains.