Application Of Atomic Force Microscopy Research Articles

Fabrication and characterization of cantilevers with integrated sharp tips and piezoelectric elements for actuation and detection for parallel AFM applications

We have developed a new process to fabricate arrays of cantilevers with integrated tips for atomic force microscope (AFM) imaging and a piezoelectric layer for vertical actuation and detection. A good homogeneity of the tip shape is obtained thanks to a self-sharpening effect. The cantilevers have been characterized mechanically and electrically.

Multimodal atomic force microscopy: Biological imaging using atomic force microscopy combined with light fluorescence and confocal microscopies and electrophysiologic recording

Because the atomic force microscope (AFM) allows molecular resolution imaging of hydrated specimens, it provides a unique window to the microscopic biological world. A high signal-to-noise ratio in AFM images sets them apart from the images obtained from other techniques: One does not need extensive image analyses often required by other techniques to obtain high-resolution information. AFM can provide molecular details on crystalline as well as amorphous materials. However, it is often limited in providing identity of the imaged structures, especially in a complex system such as a cellular membrane. AFM's application for biological imaging will rely on an unambiguous identification of imaged structures. For mixed macromolecules, it may be essential to make critical comparisons of the same structural features imaged with AFM and other techniques such as light fluorescence and confocal microscopies, electron microscopy and X-ray diffraction, and biochemical, immunologic, and pharmacologic techniques and electrophysiologic recordings. Significantly, the simple design of AFM allows it to be integrated with other techniques for simultaneous multimodal imaging. Recent combined multimodal imaging include light fluorescence, confocal, and near-field optical imaging as well as electrophysiologic recordings. Preliminary studies from such multimodal imaging include 1) an independent identification of macromolecules in a complex specimen using appropriately labeled markers such as fluorescent-dye labeled antibodies or dark-field microscopy; 2) imaging real-time reorganization of surface features using laser confocal and AFM; 3) a direct correlation of structural features and ion transfer via pores in a membrane; and 4) macromolecular complexes such as receptor-ligand and antigen-antibody. These features of a multimodal imaging system will provide new and significant avenues for a direct real-time structure-function correlation studies of biological macromolecules. © 1997 John Wiley & Sons, Inc. Int J Imaging Syst Technol, 8, 293–300, 1997

Quantitative Analysis of the Transcription Factor AP2 Binding to DNA by Atomic Force Microscopy

Atomic force microscopy (AFM) allows to study the molecular structure of biological macromolecules with nm to Å resolutions without crystallization. We show here the applicability of AFM in the quantitative analysis of the molecular mechanisms of DNA/protein interaction: (i) Protein-binding sites can be mapped over a few kilobases of target DNA. (ii) Multimerization state of DNA-binding proteins can be determined simply by measuring the sizes of proteins bound to the DNA. These features are significant advantages over the capabilities provided by conventional techniques in biochemistry and molecular and structural biology.

Chemical vapor deposition diamond for tips in nanoprobe experiments

Diamond is the most suitable material for many experimental methods in nanoprobe microscopy and materials testing. The extreme hardness, the high Young’s modulus, the inert nature of the surface, and the electrical conductivity obtained through doping make this material particularly attractive. We have coated silicon atomic force microscope (AFM) levers with thin (100 nm) doped diamond layers by chemical vapor deposition (CVD). A continuous diamond coating was obtained, resulting in tips with 100–200 nm radii. Owing to their electrical conductivity, these tips were found to be adequate for conducting AFM and scanning tunneling microscope applications, some of which are briefly discussed and reviewed in this article. We have also demonstrated CVD diamond tips, microfabricated in a controlled fashion, that have a 20 nm apex radius. These tips are particularly promising for nanomechanics and general AFM use.

Biological atomic force microscopy: what is achieved and what is needed

Biological atomic force microscopy (AFM) has become a rapidly developing interdisciplinary field of research in recent years. Not only has the technique, including instrumentation and specimen preparation methods, become increasingly sophisticated, but also its applications have encompassed a broad range of interesting subjects in biology. In this review, we present an extensive overview of the current status of biological AFM, including both the instrumentation and the application of AFM. In addition, we discuss the major problems that have yet to be fully resolved and present our analysis of the various factors involved. The published results so far clearly demonstrate the great potential of AFM in structural research and the ability of AFM to make unique contributions to our comprehension of various biological processes.

Applications of atomic-force microscopy in environmental colloid and surface chemistry

Abstract Atomic-force microscopy (AFM) is a powerful technique for imaging mineral surfaces in air or immersed in solution and at sub-nanometer-scale resolution. As the technique continues to develop, AFM is emerging as an important means not only for imaging the surface structure and microtopography of environmental particles, but also for determining changes in microtopography over the course of dissolution, growth, sorption, heterogeneous nucleation, and redox reactions. Additionally, AFM can provide a direct means of probing the structure of the double layer. As AFM use continues to proliferate, there is an increasing need for critical evaluation of image acquisition and processing techniques. This manuscript reviews the “state of the art” in force microscopy with regard to theoretical considerations, technological advances, and current and potential applications. Some common artifacts are discussed, with the purpose both of preventing new users from re-making old mistakes and of enabling non-users to evaluate AFM results. Finally, examples of applications in colloid and surface chemistry are used to illustrate the potential of AFM for providing new insight into a wide range of environmental processes.

Atomic force microscopy in histology and cytology.

This review briefly introduces the principles of the atomic force microscope (AFM) and shows our own results of AFM application to biological samples. The AFM, invented in 1986, is an instrument that traces the surface topography of the sample with a sharp probe while monitoring the interaction forces working between the probe and sample surface. Thus, the AFM provides three-dimensional surface images of the sample with high resolution. The advantage of the AFM for biologists is that AFM can visualize non-conductive materials in a non-vacuous (i.e., air or liquid) environment. AFM images of the plasmid DNA are comparable to those by transmission electron microscopy using a rotary shadowing technique, and have the advantage of examining directly the molecule without staining nor coating. The surface structure of human metaphase chromosomes and mouse collagen fibrils demonstrated in air by the non-contact mode AFM is comparable to that obtained by scanning electron microscopy. Quantitative information on the heights of structures is further obtainable from the AFM images. Embedment-free thin tissue-sections are useful for observing intracellular structures by AFM. The present review also shows AFM images of living cultured cells which have been collected in a contact mode in liquid. This technique afforded us three-dimensional observation of the cellular movement with high resolution. Although there are some innate limitations for AFM imaging, the AFM has great potential for providing valuable new information in histology and cytology.

Application of atomic-force microscopy to metallography

Atomic-force microscopy (AFM) was applied to study the surface undulations (reliefs) resulting from the martensitic transitions in Fe-Ni-C and Cu-Zn-Al alloys. Both the morphology of the surface undulations determined by a profile line across the surface and the height of the undulation could be measured directly and easily with AFM. The results show that AFM can be a powerful tool in metallography.

AFM for the imaging of large and steep submicroscopic features, artifacts and scraping with asymmetric cantilever tips

Very high and steep features of a microporous membrane from regenerated cellulose and of chemically generated solids, which are produced by photodimerization of crystalline 9-chloroanthracene (1) or by surface hydration of crystalline hydroxylamine hydrochloride with moist air, are probed with contact atomic force microscopy (AFM) using pyramidal Si 3N 4 tips. Wide scans under high and rapid feedback control produce stable images if the cantilever tips do not scrape and if all scan parameters are properly set. Both tip/sample convolutes of closely packed cones (about 1 μm high and steeper than 55 °) and virtually undisturbed floes (with slope angles of 42 ° at both sides) are reliably imaged. Validity tests are provided by establishing image stability during more than ten consecutive scans, by imaging with high magnification in the Z direction, and by comparing perspective views at 0 ° and 90 °. The stability proves an absence of surface alterations and an absence of nanoliquids, and the images show an absence of scan tracks and of scan-generated asymmetries in all 3D features. The artifact of a tip not hitting the ground while the cantilever slides over remote obstacles is investigated on a microporous membrane. Odd planes and very steep wedge-like indentations amongst the regular features are artificially imaged. Materials of low hardness are probed and scraping of the surfaces must be strictly avoided. Thus, the reasons for erratic surface alterations in contact AFM are elucidated. Asymmetric cantilever tips scrape at low forces already, while symmetric ones do not at low or higher forces. Conversely, asymmetric cantilever tips are used for writing nanostructures of considerable deepness into organic surfaces. No piling up of material occurs at the edges when deep square holes are scraped out of crystalline trans-3-benzylidenebutyrolactone (3). Depths of 50 nm or 120 nm are achieved within five or ten AFM scans with an asymmetric cantilever tip at a 10 −8 N force. The application of AFM for elucidation of further types of organic solid-state reactions is discussed.

Atomic force microscope lithography using amorphous silicon as a resist and advances in parallel operation

Lithography on (100) single-crystal silicon and amorphous silicon is performed by electric-field-enhanced local oxidation of silicon using an atomic force microscope (AFM). Amorphous silicon is used as a negative resist to pattern silicon oxide, silicon nitride, and selected metals. Amorphous silicon is used in conjunction with chromium to create a robust etch mask, and with titanium to create a positive AFM resist. All lithographies presented here were patterned in parallel by arrays of two piezoresistive silicon or two silicon-nitride cantilevers. Parallel arrays of five piezoresistive cantilevers were fabricated and used in imaging and lithographic applications. A 400 μm×100 μm parallel image is obtained in the time it would normally take to obtain a 100 μm×100 μm image. In our method of parallel operation, it is only possible to image and lithograph in modes that do not require feedback. In imaging, this limits the possible applications of the parallel AFM. During parallel lithography, discrepancies are seen between the tip in the feedback loop and those that are not. To overcome these differences it will be necessary to devise a system where each of the tips in the array are controlled by individual feedback loops.

Development and Application of Atomic Force Microscope with Integrated Fluoresence Microscope.

Development and Application of Atomic Force Microscope with Integrated Fluoresence Microscope.

Atomic Force Microscopy in Ultrahigh Vacuum

Since its invention in 1986, atomic force microscopy (AFM) has been used mainly in ambient conditions. Recent advances in instrumentation have fostered the application of AFM in ultrahigh vacuum (UHV). AFM experiments performed in UHV have led to a better understanding of the tip-sample interaction. This article reviews the theory related to achieving true atomic resolution of AFM in UHV in both contact- and noncontact-modes. Preliminary experimental results with unprecedented resolution on KCl and Si (111)7×7 achieved by noncontact AFM in UHV are presented.

Probing toward atomic resolution in molecular topography.

Probing toward atomic resolution in molecular topography.

Tunnel current controlled atomic force microscope designs

The atomic force microscope (AFM) designs described here are based on the high sensitivity of scanning tunneling microscopy (STM) technology. It utilizes short range repulsive contact forces between a small stylus and a sample surface to produce high resolution images of defects and structural features of the surface. An adjacent tunnel gap controls contact forces and provides a very sensitive feedback signal for a Z-direction piezoelectric drive to maintain a constant force value during raster scanning. A STM may serve as an AFM by attaching an AFM adapter. The same piezoelectric drive mechanism, electronics, and recording system can be automatically employed to produce AFM images. This report contains a progression of AFM designs, based on the tunnel current control principle, construction and calibration of AFM levers, AFM applications, and high resolution AFM images.

Detection of displacements in the nanometre range by optical tunnelling

Abstract Our concern is the exploitation of the so-called optical tunnelling effect to detect the cantilever deflection in atomic force microscopy (AFM) caused by the interatomic forces established between a sample surface and the force sensor. Towards this end, we have developed a displacement sensor based on the phenomenon of evanescent wave coupling or the optical tunnelling effect. Furthermore, we have implemented a computer programme simulating a planar model of a three media system (optical tip, gap and waveguide where total internal reflection occurs). The proposed method is particularly suitable for biophysical applications of AFM.

TEM/AFM correlative studies of thin-film metallization

Since the invention of AFM (atomic force microscopy) applications of the technique have grown from year to year. It is expected that with time, there will be an increased use of AFM in the semiconductor industry for analysis of surface-topography and microstructure of thin films and heterostructures. However, before the technique can be used on its own for analyzing the behavior of thin films, it is necessary to establish legitimate areas of application of the technique. The present study uses AFM and TEM (transmission electron-microscopy) to study a few examples of thin-film metallizations and then looks at the extent of correlation between the two. It turns out that TEM and AFM work very well as complementary techniques. Caution is required in interpreting AFM micrographs.As examples of metallization Al(Cu), polysilicon and TiW thin films were investigated using AFM and TEM. Al(1.5%Cu) films were sputtered onto SiO2/Si substrates for ∼1 second (unbiased) at a substrate temperature of 450°C.

A computational study of the imaging of a molecular crystal with the atomic force microscope

Atomic force microscopy (AFM) has the capacity to probe the surface topography of a variety of materials with atomic scale resolution.Unlike scanning tunneling microscopy AFM does not depend on the sample being an electrical conductor and therefore provides an ideal way to image the surfaces of nonconducting molecular crystals. Many studies have focused on characterizing the surfaces of metals or semiconductor crystals. An alternative and potentially important application of AFM is to the characterization of the surfaces of biochemical crystals, with a view to mapping out active sites in proteins. While AFM has been able to resolve the surface structure of crystals with atomic scale resolution, an important issue is the unique identification of individual surface atoms; for example, to use AFM to determine which cleavage plane of a molecular crystal is exposed. This letter reports a numerical simulation of a recent AFM study of the {100} surface of a DL-leucine crystal performed by Hansma and co-workers using a shattered diamond tip.

Nanometer-sized tungsten tips for STM and AFM

An essential requirement in the pursuit of atomic resolution by scanning tunneling microscopy (STM) or atomic force microscopy (AFM) is the use of a tip with an apex of dimensions comparable to or preferably smaller than those of the specimen to be identified. Although atomic resolution of mostly planar specimens has been obtained even with atomically blunt tips, the above requirement appears indispensable for determining 3D surface structures extending equally in all three dimensions.Tips most commonly used so far in STM or AFM applications are made by grinding or by etching a thin and rigid Pt/Ir or W wire. Mechanical grinding occasionally leaves protruding spikes typically several tens of nm in radius that can play the role of scanning stilus even though neither adequately oriented nor particularly sharp and symmetric.

Atomic resolution on the surface of LiF(100) by atomic force microscopy

Atomic force microscopy (AFM) has already demonstrated its usefulness on a nanometer scale surpassing the resolution of conventional profilometers and probing different interactions such as repulsive contact, electrostatic, and magnetic forces. On an atomic scale the fundamental contrast mechanisms are still under investigation. The atomic resolution on layered materials such as graphite, boron nitride, transition metal dichalcogenides, and MnPS3 shows the great potential of this technique. Several experimental and theoretical investigations on these layered materials have shown that the presence of the AFM tip can lead to a significant distortion of the electronic and atomic structure. For small loadings (≤10−8 N) the tip causes long-range elastic deformations while for higher loadings a sharp tip can puncture the sample. To explain the atomic scale features being measured with higher loadings, different mechanisms such as the dragging of flakes or shearing of layers have been suggested. The application of AFM to nonlayered structures gives the opportunity to exclude several of these influences. Here we present atomically resolved images of LiF(100). The measurements are compared to results from different surface sensitive techniques such as helium scattering and low energy electron diffraction (LEED). The contrast mechanisms of AFM are discussed in relation to these experiments.