碳纳米管原子力显微镜针尖的研究

本文研究了制作碳纳米管原子力显微镜针尖的方法和过程。在光学显微镜下，通过两个微工作台操纵将纯化后的多壁碳纳米管粘结在传统的原子力显微镜的Si针尖上。运用电蚀的方法优化碳管针尖的长度使其达到高分辨率的要求。我们运用制作的碳纳米管针尖在敲击模式下时G型免疫球蛋白进行扫描成像，结果显示了其典型的Y形结构，这是传统AFM的Si针尖无法获得的。     

Atomic force microscopy with carbon nanotube probe resolves the subunit organization of protein complexes

Among many scanning probe microscopies, atomic force microscopy (AFM) is a useful technique to analyse the structure of biological materials because of its applicability to non-conductors in physiological conditions with high resolution. However, the resolution has been limited to an inherent property of the technique; tip effect associated with a large radius of the scanning probe. To overcome this problem, we developed a carbon nanotube probe by attaching a carbon nanotube to a conventional scanning probe under a well-controlled process. Because of the constant and small radius of the tip (2.5-10 nm) and the high aspect ratio (1:100) of the carbon nanotube, the lateral resolution has been much improved judging from the apparent widths of DNA and nucleosomes. The carbon nanotube probes also possessed a higher durability than the conventional probes. We further evaluated the quality of carbon nanotube probes by three parameters to find out the best condition for AFM imaging: the angle to the tip axis; the length; and the tight fixation to the conventional tip. These carbon nanotube probes, with high vertical resolution, enabled us to clearly visualize the subunit organization of multi-subunit proteins and to propose structural models for proliferating cell nuclear antigen and replication factor C. This success in the application of carbon nanotube probes provides the current AFM technology with an additional power for the analyses of the detailed structure of biological materials and the relationship between the structure and function of proteins.     

Acquisition of high-precision images for non-contact atomic force microscopy

The atomic force microscope (AFM) system has evolved into a useful tool for direct measurements of intermolecular forces with atomic-resolution characterization that can be employed in a broad spectrum of applications. The distance between cantilever tip and sample surface in non-contact AFM is a time-varying parameter even for a fixed sample height, and typically difficult to identify. A remedy to this problem is to directly identify the sample height in order to generate high-precision atomic-resolution images. For this, the microcantilever (which forms the basis for the operation of AFM) is modeled as a single mode approximation and the interaction between the sample and cantilever is derived from a van der Waals potential. Since in most practical applications only the microcantilever deflection is accessible, we will use merely this measurement to identify the sample height. In most non-contact AFMs, cantilevers with high-quality factors are employed essentially for acquiring high-resolution images. However, due to high-quality factor, the settling time is relatively large and the required time to achieve a periodic motion is long. As a result, identification methods based on amplitude and phase measurements cannot be efficiently utilized. The proposed method overcomes this shortfall by using a small fraction of the transient motion for parameter identification, so the scanning speed can be increased significantly. Furthermore, for acquiring atomic-scale images of atomically flat samples, the need for feedback loop to achieve setpoint amplitude is basically eliminated. On the other hand, for acquiring atomic-scale images of highly uneven samples, a simple PI controller is designed to track the desired constant sample height. Simulation results are provided to demonstrate the feasibility of the approach for both sample height identification and tracking the desired sample height.     

AFM的DNA样品制备技术研究

AFM应用中最为关键的一步无疑是样品的制备。本文介绍DNA样品制备的几种主要方法,通过实验发展了两种适合对DNA及其碎片进行长度测量和做统计分析的制样方法,它们分别采用APS-云母和纯云母为衬底。这两种方法不仅丰富了DNA样品制备方法,对推广AFM在生物研究中的应用也具有重要意义。     

The application of the atomic force microscope to studies of medically important protozoan parasites

Both living and fixed specimens of the medically-important parasitic protozoa, Trypanosoma cruzi, Toxoplasma gondii, Giardia lamblia, Entamoeba histolytica, and Acanthamoeba spp. were studied by atomic force microscopy (AFM). The preparation of fixed specimens was similar to methods used for either scanning or transmission electron microscopy. AFM scanning was performed using both contact and tapping modes. A classical fixation procedure utilizing glutaraldehyde followed by ethanol dehydration was not suitable for all parasite species. AFM images could not be obtained from fixed samples of T. cruzi, T. gondii or E. histolytica. However, excellent topographic images could be obtained from specimens of G. lamblia and Acanthamoeba under identical conditions. Critical point drying permitted AFM imaging of both trypomastigote and epimastigote stages of T. cruzi. Phase imaging of T. cruzi elucidated unique surface details at a level of resolution not visible using any other imaging modalities. AFM elasticity map imaging of T. cruzi-infected and T. gondii-infected cells demonstrated that both parasites were markedly firmer than the surrounding host cell cytoplasm. The parasitophorous vacuole surrounding replicating T. gondii tachyzoites was also visualized by elasticity map imaging. These data suggest that although much remains to be learned about preparing parasitic protozoa for AFM imaging, the technique has the potential of providing unique and important insights into these disease causing organisms.     

Deconvolution of atomic force microscopy data for cellular and molecular imaging

The restoration of image features in cellular and molecular images is a crucial problem in nanobiological investigations. Scanning probe microscopy (SPM) offers the potential for direct investigative capability at nanometer resolution necessary for imaging biological units and macromolecular protein control blocks. The distortion of the measured image due to tip-sample interaction is a major challenge for nanoscale metrology, and signal processing solutions are needed for increasing the accuracy and reliability of the data. Two candidate approaches have been described in detail in this article for modeling the tip-sample interaction from a topographical perspective, which is then used for reconstructing the sample surface from known tip geometry. When the aspect ratio of a feature is comparable with that of the tip, the two methods produce similar results, but when the aspect ratio is larger than that of the tip, the MM method produces a sharper estimate than the LT method. When the tip geometry is not known, blind-tip estimations methods are needed for iterative estimations of tip and sample surfaces.     

单个人体黑素瘤细胞的原子力显微图像及拉曼光谱的研究

利用原子力显微镜对人体单个黑素瘤细胞进行扫描,观察其表面形貌,得到了人体黑素瘤细胞在原子力显微镜扫描下的清晰成像,介绍了原子力显微镜在观察单个人体黑素瘤细胞表面超微结构方面的优势.通过其原子力图像,发现黑素瘤细胞形态各异,表面粗糙,有大小不一的突起.同时给出了单个黑素瘤细胞的拉曼光谱,并对谱峰进行指认,从分子水平对黑素瘤细胞的结构进行分析.将原子力图像及拉曼散射光谱技术应用于人体黑素瘤的研究,为人类黑素瘤的早期和快速诊断提供实验依据.     

原子力显微镜在聚合物溶液结构研究中的应用

驱油用水溶性聚合物溶液的应用性能由其聚合物溶液的微观结构所决定,因此在驱油用聚合物合成及配方研究中迫切需要研究其溶液的微观结构。本文使用原子力显微镜（AFM）、环境扫描电镜（ESEM）和透射电镜（TEM）观察了水溶液中聚合物（HAWSP,AP-P4）的微观结构。研究发现常温常压下原子力显微镜观察到的聚合物网络结构图案清晰,边界分辨率高。透射电镜观察到的聚合物网络结构较模糊且网络结构有断裂现象。环境扫描电镜观测到的网络结构尺寸大小是AFM观测到的几倍甚至是十几倍。动态光散射（dynamic light scattering,DLS）结果证明AFM和TEM所观测到的聚合物结构最接近于真实结构。结果表明使用原子力显微镜在观察水溶性聚合物类样品时,能够较真实反映其微观结构。     

Atom world based on nano-forces: 25 years of atomic force microscopy

Scanning tunneling microscopy (STM) has opened up the new nanoworlds of scanning probe microscopy. STM is the first-generation atomic tool that can image, evaluate and manipulate individual atoms and consequently can create nanostructures by true bottom-up methods based on atom-by-atom manipulation. Atomic force microscopy is a second-generation atomic tool that has followed the footsteps of STM, and which is now opening doors to a new atom world based on using nanoscale forces.     

X-ray reflectivity and atomic force microscopy studies of MOCVD grown AlxGa1-xN/GaN superlattice structures

The grazing incidence X-ray reflectivity (GIXR) technique and atomic force microscopy (AFM) were exploited to obtain an accurate evaluation of the surfaces and interfaces for metalorganic chemical vapor deposition grown Al<,x>Ga<,1-x>N/GaN superlattice structures. The X-ray diffraction results have been combined with reflectivity data to evaluate the layer thickness and Al mole fraction in the AIGaN layer. The presence of a smooth interface is responsible for the observation of intensity oscillation in GIXR, which is well correlated to step flow observation in AFM images of the surface. The structure with a low Al mole fraction (x = 0.25) and thin well width has a rather smooth surface for the R<,rms> of AFM data value is 0.45 nm.     

Clean boxes with artificial climate for atomic force microscopy: New possibilities for diagnostics of nanodimensional objects

A clean box with an artificial climate is developed and designed to increase the accuracy of measurements by atomic force microscopy in the air and to improve the reproducibility of the results of diagnostics of the surface. The main functions of the box are the provision and maintenance of the temperature and humidity in the working zone with a high degree of accuracy and in various combinations. The main technical characteristics of the box are presented. The main advantages of operation under the conditions of an artificial climate are analyzed. It is shown that the special procedures give the possibility to eliminate the distorting effect of the static electricity on the surface under investigation and, specifically, to remove the already accumulated charge and prevent its appearance in the course of the experiment. The use of the suggested procedures allows one to correctly describe the specific features of the surface topography of dielectrics at the microscopic and nanoscopic levels.     

原子力显微镜在生殖支原体研究中的应用

为了确定生殖支原体在活性条件下的结构形貌,并在较高的分辨水平上观察其三维形貌结构,本研究采用原子力显微在常温常压下对生殖支原体标准株及分离株进行形态学的初步观察,将标本固定于云母上,在ｔａｐｐｉｎｇ模式下扫描成像,结果显示：生殖支原体多呈烧瓶状或鸭梨状,有突出的颈产及膨大的头端,与电镜观察结果类似,其大小亦与银镜测量结果类似。     

X-ray reflectivity and atomic force microscopy studies of MOCVD grown AI_xGa_(1-x)N/GaN superlattice structures

The grazing incidence X-ray reflectivity（GIXR） technique and atomic force microscopy（AFM） were exploited to obtain an accurate evaluation of the surfaces and interfaces for metalorganic chemical vapor deposition grown Al_xGa_1-xN/GaN superlattice structures.The X-ray diffraction results have been combined with reflectivity data to evaluate the layer thickness and Al mole fraction in the AlGaN layer.The presence of a smooth interface is responsible for the observation of intensity oscillation in GIXR,which is well correlated to step flow observation in AFM images of the surface.The structure with a low Al mole fraction（x = 0.25） and thin well width has a rather smooth surface for the R_rms,of AFM data value is 0.45 nm.     

Chemical-Mechanical polishing of parylene- n films: evaluation by X-Ray photoelectron spectroscopy and atomic force microscopy

The surface quality of parylene-N(PA-N) films, as determined by x-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM), after chemical-mechanical polishing (CMP), is influenced mostly by two factors: quality of the as-deposited film and the slurry composition. The higher the quality of the as-deposited film (more specifically, less oxygen content), the higher the quality of the polished film. The XPS and AFM results show that PA-N film polished in 1% A1₂O₃ abrasive (0.3 Μm particles), NH₄OH (2% by volume), and water, has better quality compared to the other slurries investigated. With high quality PA-N films, the film surface quality affected by CMP is relatively independent of polishing time, indicating that changes in surface chemistry occur in the initial seconds of polishing.     

制样溶剂及基底对原子力显微镜观测单壁碳纳米管的影响

本文选用不同基底和溶剂进行单壁碳纳米管(SWNTs)样品制备,采用原子力显微镜(atomic force microscope,AFM)观察进行表征和观测。结果表明,溶剂和基底对样品制备十分重要,会直接影响AFM观测效果。以去离子水为溶剂进行样品分散时,SWNTs在石英、硅片和云母三种基底上都出现了不同程度的聚积和重叠,影响观测效果。而采用乙醇为溶剂,在石英或云母为基底进行成像时,均可获得质量良好的图像。选择云母作为基底,可以大大减少基底处理时间,制样方便快速,并且能够获得理想的观测效果。     

The application of fluorescence decay measurements in studies of biological systems

Synchronously pumped, cavity dumped dye lasers provide moderately intense stable pulses of circa 10 ps duration, at a high repetition rate. Such a laser system is an ideal excitation source for the measurement of energy-resolved fluorescence decay profiles. When used in conjunction with photon counting electronics and well tested deconvolution procedures the system is capable of measuring complex (multi-component) fluorescence decays in the time range of < 100 ps- >100 ns. Different fluorophores, when incorporated into membranes or proteins (i.e., extrinsic probing), exhibit different types of interactions with each system. Many simple aromatics are relatively insensitive to the medium, thus the fluorescence decay contains little information of interest. However, in these cases the decay of the anisotropy, which may be extracted from the fluorescence decays, will yield information about the environment. Many heteroaromatic systems are more polar in the first excited singlet state than in the ground state. Consequently there is a strong interaction between the excited state and the surrounding field, this results in a relaxation of the environment about the excited state, resulting in a shift in the fluorescence spectrum to lower energy. When the relaxation is slow, the spectral shift can be time resolved, which can give further information about the structure of the probed system, usually a biological membrane. These types of measurements are discussed, as are some of the problems involved in extrinsic probing, such as multiple siting of the probe.     

MOCVD AlxGa1-xN/GaN超晶格结构的X射线反射谱与原子力显微研究

采用掠入射X射线反射谱技术与原子力显微技术对属有机化合物化学气相淀积生长的AlxGa1-xN/GaN超晶格结构的表面和界面进行了精确表征。结合高分辨率X射线衍射谱与反射谱数据分析获得外延层各层厚度与AlGaN层的Al摩尔组分。掠入射x射线反射谱的显著强度振荡与原子力显微镜所观察到的台阶流动形貌表明了平整的界面和表面的存在。研究发现,低Al组分（x=0.25）且阱宽小的样品界面与表面粗糙度最小,通过原子力显微技术得到的表面粗糙度均方根偏差为0.45nm。