Reviews

1. Bhushan, B.;Koinkar, V. N.;Ruan, J. A., "Microtribology of magnetic media" Proc. Inst. Mech. Eng. J, J. Eng. Tribol. (UK) 208,, 17-29 (1994).
   • Scanning tunnelling microscopy (STM), atomic force microscopy (AFM) and the modifications of AFM (such as friction force microscopy (FFM)) are becoming increasingly important in the understanding of fundamental mechanisms of friction, wear and lubrication and in studying the interfacial phenomena in micro- and nanostructures used in magnetic storage devices and microelectromechanical systems (MEMS). The authors describe modified AFM and FFM techniques and present data on microtribological studies of magnetic media-magnetic tapes and disks. Local variation in microscale friction is found to correspond to the local slope, suggesting that a ratchet mechanism is responsible for this variation. Wear rates for magnetic tapes are approximately constant for various loads and test duration. However, for magnetic disks, the wear of the diamond-like carbon overcoat is catastrophic. Evolution of the wear has also been studied using AFM. AFM has been modified for nanoindentation hardness measurements. It has been shown that hardness of ultra-thin films can be measured using AFM. AFM has also been shown to be useful for nanofabrication.
2. Josefowicz, J. Y.;Yamagishi, F. G.;van Ast, C. I., "Atomic force microscopy structural characterization of polyaniline thin film sensors", 605-11 (1994).
   • The surface structure of polymer sensors which incorporated polyaniline (PAn) films that were deposited electrochemically across narrow insulating gaps between interdigitated gold electrodes was determined using tapping mode atomic force microscopy (TMAFM). The sensitivity and response time for such sensors, which can be used for the detection of low levels of gases and low concentrations of impurities in liquid media, critically depend on the quality and structure of the polymer film in the gap region between the gold electrodes. TMAFM images of the PAn films ranging in thickness between approximately=1.5 mu m and approximately=5 mu m reveal that films approaching 5 mu m (typically used in such sensors) develop deep cracks at the edges and along the length of the Au electrodes. The cracks, which appear to be a consequence of stress build-up in thicker films, can lead to reliability problems and inferior sensor performance. Simple modeling analysis of cracked films indicates that they can lower sensitivity and increase response time. TMAFM images of sensors with thinner approximately=2.5 mu m PAn films show no cracks as well as continuous PAn bridges across the gap between Au electrodes. Analyses of TMAFM images are presented and compared for thin and thick film PAn sensors.
3. Quate, C. F., "The AFM as a tool for surface imaging" Surf. Sci. (Netherlands) 299-300,, 980-95 (1994).
   • The atomic force microscope was introduced in 1986 as a new instrument for examining the surface of insulating crystals. There was a clear implication in the first paper that it was capable of resolving single atoms. Unambiguous evidence for atomic resolution with the AFM did not appear until 1993. In the intervening years the AFM evolved into a mature instrument that provides us with new insights in the fields of surface science, electrochemistry biology and the technology. In this paper the author discusses the evolution of this new high resolution microscope and describes some of the events that led up to the present state-of-the-art instrument.
4. Ruan, J. A.;Bhushan, B., "Atomic-scale friction measurements using friction force microscopy. I. General principles and new measurement techniques" Trans. ASME, J. Tribol. (USA) 116,, 378-88 (1994).
   • Friction force measurements using modified atomic force microscopy, called here friction force microscopy (FFM), are becoming increasingly important in the understanding of fundamental mechanisms of friction, wear, and lubrication, and to study interfacial phenomena in micro- and nanostructures used in magnetic storage systems and microelectromechanical systems (MEMS). FFMs can be used to study engineering surfaces in dry or wet conditions. A review of existing designs of FFMs and methods of friction force measurements is presented. In terms of friction force measurements, there are important issues related to the basic operation and calibration of these instruments which have not been fully studied. A new method of measuring friction fore using a commercial FFM and a calibration procedure for conversion of measured data to normal and friction forces are presented. Microscale friction data of selected materials are presented and discussed in light of macro-friction measurements.
5. Schmidt, W. U.;Alkire, R. C., "Use of atomic force microscopy to image surfaces during fluid flow" J. Electrochem. Soc. (USA) 141,, L85-7 (1994).
   • Use of atomic force microscopy (AFM) to image surfaces held under electrochemical control in the presence of fluid flow has been demonstrated. The performance of AFM during fluid flow was evaluated on (i) the atomic level (10 to 200 nm) using cleaved mica as the substrate, (ii) on the micron scale (1 to 12 mu m) using a gold calibration ruling as the substrate, and (iii) on the micron scale during in situ electrodeposition of Cu onto Pt(100). The Reynolds numbers associated with the fluid flow were evaluated by using the diameter and height of the cell as cross-sectional area, and the hydraulic diameter based on the same area as characteristic length. Maximum Reynolds numbers of 8 for atomic imaging (1 to 25 nm) and 130 for larger scales (1 to 12 mu m) may be maintained without loss of imaging quality. The engagement force was the significant parameter which influenced whether images could be obtained during flow. The critical engagement force required for imaging varied linearly with flow rate.
6. Zasadzinski, J. A.;Viswanathan, R.;Madsen, L.;Garnaes, J.;Schwartz, D. K., "Langmuir-Blodgett films" Science (USA) 263,, 1726-33 (1994).
   • The controlled transfer of organized monolayers of amphiphilic molecules from the air-water interface to a solid substrate was the first molecular-scale technology for the creation of new materials. However, the potential benefits of the technology envisioned by Langmuir and Blodgett in the 1930s have yet to be fully realized. Problems of reproducibility and defects and the lack of basic understanding of the packing of complex molecules in thin films have continued to thwart practical applications of Langmuir-Blodgett films and devices made from such films. However, modern high-resolution X-ray diffraction and scanning probe microscopy have proven to be ideal tools to resolve many of the basic questions involving thin organic films. Here, studies are presented of molecular order and organization in thin films of fatty acid salts, the prototypical system of Katharine Blodgett. Even these relatively simple systems present liquid, hexatic, and crystalline order; van der Waals and strained layer epitaxy on various substrates; wide variations in crystal symmetry and interfacial area with counterions; modulated superstructures; and coexisting lattice structures. The wide variety of possible structures presents both a challenge and an opportunity for future molecular design of organic thin-film devices.
7. Hues, S. M.;Colton, R. J.;Meyer, E.;Guntherodt, H. J., "Scanning probe microscopy of thin films" MRS Bull. (USA) 18,, 41-9 (1993).
   • This review focuses on the use of scanned probe microscopy namely, atomic force microscopy, to study the properties of thin films. The principles of the technique are described in some detail, and examples of the types of images-topography, frictional force, elasticity mapping, etc.-are given. In addition to imaging, the force microscope is capable of measuring a wide variety of surface forces in many different environments and obtaining a quantitative measure of the mechanical properties of materials through analysis of force curves.
8. Binnig, G., "Force microscopy", , Ultramicroscopy (Netherlands), 42-44, pt.A, 7-15 (1992).
   • Although tunneling microscopy at the age of ten years is a fairly young technique, it has already produced several offspring. One of them is force microscopy, which at present is in fact the most important one in terms of the number of people dealing with it directly or indirectly. This paper discusses its strengths and limitations as well as its potential future applications.
9. Jahanmir, J.;Haggar, B. G.;Hayes, J. B., "The scanning probe microscope" Scanning Microsc. (USA) 6,, 625-60 (1992).
   • Scanning probe microscopy has evolved into a powerful tool since its inception in 1982. The scanning probe microscope has found applications in metrology, spectroscopy, and lithography. The authors review the background of the technology, discuss the different types of scanning probe microscopes including the scanning tunneling microscope and the scanning force microscope, and present many of the applications for the instrument.
10. Meyer, E., "Atomic force microscopy" Prog. Surf. Sci. (UK) 41,, 3-49 (1992).
    • The basic principles of atomic force microscopy are discussed. Various deflection sensors are described and compared with each other. A simple theoretical basis of the fundamental forces, such as van der Waals, electrostatic, magnetic, capillary, ionic repulsion and frictional forces, is given and the relevant experimental work is summarized.
11. Morita, S., "Principles and status of AFM" Solid State Phys. (Japan) 27,, 531-9 (1992).
    • Principles and status of atomic force microscopy (AFM) were reviewed. The presented summary includes atomic scale imaging, atomic manipulation, atom craft, atomic devices, atomic science tools and AFM/STM. Associated microscopes such as a scanning probe microscope (SPM) were also reviewed briefly.
12. Haberle, W.;Horber, J. K. H.;Binnig, G., "Force microscopy on living cells", , J. Vac. Sci. Technol. B, Microelectron. Process. Phenom. (USA), 9,, 1210-13 (1991).
    • The authors have developed an underwater atomic force microscope (AFM) based on detection by tunneling for investigations of single living cells. The AFM setup allows compensation of the electrochemical potentials involved and is integrated into a high magnification optical microscope. Small living cells are sucked onto a microcapillary and are brought into contact with a cantilever for imaging. The cells are kept alive under appropriate physiological conditions while maintaining high resolution to image their molecular structures. For the first time, images of red blood cells made under these conditions with resolution down to about 10 nm are shown. In addition, changes induced by higher salt concentration and by the sticking of antibodies to the cell surface were observed. This indicates the wide range of possibilities of this method for studying dynamical processes of living organisms in situ with high spatial resolution.
13. Kumar Wickramasinghe, H., "Scanned probes old and new", , AIP Conf. Proc. (USA), 9-22 (1991).
    • The scanning tunneling microscope (STM) has stimulated a range of new microscopies which essentially use the same scanning and feedback principles to obtain nanometer resolution images. The author reviews the history of scanned probe techniques and discusses some of the new directions that have evolved with particular reference to work done in this research group.
14. Sarid, D.;Elings, V., "Review of scanning force microscopy", , J. Vac. Sci. Technol. B, Microelectron. Process. Phenom. (USA), 9,, 431-7 (1991).
    • The authors present an overview of scanning force microscopy with applications to electrostatic, magnetostatic, and atomic forces operating in the contact and noncontact mode, and highlight the main achievements in this field.
15. Schonenberger, C.;Alvarado, S. F., "Understanding magnetic force microscopy" Z. Phys. B, Condens. Matter (West Germany) 80,, 373-83 (1990).
    • Magnetic force microscopy is a new method for imaging ferromagnetic domains with a high lateral resolution (10 nm). The authors give the basic tip parameters that have to be taken into account to achieve a quantitative image interpretation. For the electrochemically etched polycrystalline iron, nickel and cobalt wires, the tip-apex domain is found to be oriented along the tip axis, because of shape anisotropy. The stray field emerging from the tip apex is comparable to the size of the tip saturation field. The effective domain length L determines the image formation: the force due to magnetization patterns of scales which are large compared to L follow the point-dipole approximation. In the opposite case, a single-pole model is more appropriate. While a cobalt tip can be treated as an isolated domain, for nickel and iron a net polarization in the tip wire induced by the front apex-domain has to be considered. A new analytical theory provides an overall understanding of the image formation and allows the determination of the magnetic field vector and the estimation of its magnitude from measurements.
16. Edel'man, V. S., "Scanning tunneling microscopy (review of techniques and applications)" Prib. Tekh. Eksp. (USSR) 32,, 25-49 (1989).
    • The principles and techniques of scanning tunneling microscopy (STM) and scanning atomic-force microscopy (AFM) are described. The results of STM and AFM studies of solid surfaces with atomic resolution are presented, and the use of such instruments in the study of large molecules and biological structures, in nanometry, and in submicron lithography is described.