A quantitative formulation of the resolution of optical imaging systems is discussed in regard to both conventional far-field optics and near-field scanning optical microscopy. A simple near-field model is introduced, followed by a discussion on the refmements of this model. Experimental results are compared to a more rigorous theory with excellent agreement

Several issues concerning lateral spatial resolution in scanning optical microscopes, SOM's, are addressed. After identifying what is meant by resolution in an SOM, the role of probe tip morphology is discussed. Consideration of the physical mechanism of signal transduction is made, and fundamental differences between near field SOM's and evanescent field SOM's are underscored. Therole of dithering of the probe tip in improving resolution is demonstrated and discussed.

Work is described on the development of a £canned Near-field Qptical Microscope (SNOM) to observe magnetization distributions with sub-wavelength resolution. Contrast is provided by the magneto-optic Kerr effect. A single Ag particle of -30 nm diameter was chosen as a SNOM probe for reasons unique to magnetic imaging. Sub-wavelength Ag particles interact strongly with incident light due to an effect called the localized surface plasmon resonance. An apparatus is described for the characterization of the plasmon resonance in isolated Ag particles. Data obtained from the apparatus is presented and present work in the measurement of the magneto-optic Kerr effect in a near-field geometry is described.

We present a theory of the frustration of the field by the fiber optic probe of the Photon Scanning Tunneling Microscope (1) and compare theoretical and experimental images obtained on lamellar or crossed gratings fabricated on insulating substrates. The calculation take into account the polarization of the light incident on the prism and the direction of the plane of incidence with respect to the grating lines. We show that the overall behavior of the experimental curves is consistent with the calculations but that great care must be taken to interpret the images.

This paper deals with the effect of C, Co, and Cr additions on the surface profile of Fe78 B13Si9 metallic glass at a nanoscopic scale. The seperate addition of the elements was successful in a way that three new metallic films with better properties were produced. The composition of the new films are namely Feg1B13Si35C2, Fe66C018B15Si1, and FeCr2 B16Si5. Furthermore the new films have shown balanced physical and magnetic properties as compared to the Fe78B13Si9 film. Consequently, this study was focused on revealing the three dimensional surface profile of the films in as-received and annealed conditions. The surface profile was determined by a scanning tunneling microscope (STM).

We report the use of the techniques of scanning tunneling microscopy and impact-collision ion scattering spectrometry to study the in-plane geometry of both the (root)3X(root)3 and 2(root)3X2(root)3 reconstructions of Sn on Si(111). For the (root)3X(root)3 reconstruction, the Sn adatoms were found to prefer fourfold atop (T₄) sites. For the 2(root)3X2(root)3 reconstruction, a two-layer epitaxial Sn model with a four-atom unit cell on the top layer is found to provide the best agreement with experimental data.

Visible light is emitted from roughened metal-oxide-metal tunnel junctions subjected to a small (2 - 4 V) dc bias. The color of the emitted light is voltage tunable but device quantum efficiency is generally very low (10^-5 - 10^-7). The optical emission is due to the roughness induced scattering of electronically excited surface plasmon polaritons. The characteristics of the surface roughness are clearly important in determining the overall device efficiency and spectral output. With a view to better understanding and improving the efficiency we have examined the surface topography of variously roughened devices and relate this to the optical output. For example, we have roughened devices by means of holographic crossed diffraction grating substrates which possess surface topography of greater rms roughness height and larger transverse correlation length than that of devices roughened by a pre-deposited CaF₂ layer. Devices roughened by means of a particulate aluminum substrate are also discussed.

We describe a procedure for imaging DNA molecules using atomic force microscopy (AFM). Double-stranded DNA binds to a mica surface modified by treatment with 3- aminopropyltriethoxysilane to yield AFM images that are stable under repeated scanning. We used this procedure to obtain high quality images of unstained linear DNA molecules and circular DNA molecules. The resolution was limited to tens of nanometers by the profile of the AFM tips.

Bilayers of cadmium stearate (Cd-stearate) and monolayers of dipalmitoyl phosphatidylcholine (DPPC) have been assembled on highly oriented pyrolytic graphite (HOPG) substrates and investigated in air using the scanning tunneling microscope (STM). STM images of Cd- stearate bilayers reveal a regular two-dimensional lattice of high tunneling current vertices which are separated by 4 - 6 angstroms. Few defects are observed in these lattices. 'High (tau) ' bilayers, which were deposited with a transfer ratio, (tau) approximately equals 2.0, have monoclinic lattices whereas the lattices of 'low (tau) ' bilayers, with (tau) equals 1.4 - 1.6, are orthorhombic. Molecular resolution STM data is also presented for DPPC monolayers prepared by the conventional Langmuir-Blodgett vertical deposition method. In monolayers of these structurally more complex amphiphiles, greater disorder is evident. Prolonged STM scanning of either Cd-stearate bilayers or DPPC monolayers induces modification of the 'native' crystalline structure presumably due to tip-film interactions.

The interpretation of scanning tunneling microscopy (STM) images of adsorbed molecules requires a redefinition of the current, that goes beyond the limitations imposed by the Transfer Hamiltonian formalism. Here we discuss two expressions for the tunneling current we derived, both suitable for situations in which an adsorbate is placed between tip and substrate. The former is still based on a perturbative approach, but emphasizes the contributions to the STM current due to the adsorbate. The latter is an exact expression obtained by treating the STM current like an electron transport process. This allows the inclusion of both the quantum aspects of the transport and thermal effects, and it can be used in widely different situations.

We present a procedure for imaging metal-coated biomolecules with the scanning tunneling microscope. This procedure is simple, easy to implement and gives reproducible results. The biomolecules are adsorbed on glow discharged mica, then coated with a thin film of platinum- carbon. We have applied this method for visualizing two different kind of biomolecules: planar membranes and DNA molecules. The contrast and lateral resolution of the images are comparable to electron micrographs of the same molecules. The lateral resolution is limited by the grain size of the coating film while the vertical resolution seems to be unaffected for very small coating thickness (less than 3 nm).

A high resolution, high sensitivity magnetic force microscope (MFM) with the ability to image in an in situ magnetic field will be described. This MFM has been used to investigate the micromagnetics of nanolithographically produced magnetic particles. It will be shown that the particles' switching field can be determined without being perturbed by the stray fields from the sensing tip. This allows the study of the evolution of the particles' magnetic states as a function of applied field and the direct observation of cooperative switching. The MFM has also been used, in conjunction with an external biasing field, as a localized source of flux for testing the stability of magnetic states and setting model magnetic configurations. MFM images of the particles are compared with numerical simulations. These comparisons have also provided insight into the magnetic behavior of the MFM sensing tips.

Atomic force microscopy (AFM) was used to investigate the (010) surface of Amelia albite, the basal and (001) planes of CaCO₃ (calcite), and the basal planes of rectorite and bentonite. Atomic scale images of the albite surface show six sided, interconnected en-echelon rings. Fourier transforms of the surface scans reveal two primary nearest neighbor distances of 4.7 and 4.9 +/- 0.5 angstroms. Analysis of the images using a 6 angstroms thick projection of the bulk structure was performed. Close agreement between the projection and the images suggests the surface is very close to an ideal termination of the bulk structure. Images of the calcite basal plane show a hexagonal array of Ca atoms measured to within +/- 0.3 angstroms of the 4.99 angstroms predicted by x-ray diffraction data. Putative images of the (001) plane of carbonate ions, with hexagonal 5 angstroms spacing, are also presented and discussed. Basal plane images of rectorite show hexagonal symmetry with 9.1 +/- 2.5 angstroms spacing, while bentonite results reveal a 4.9 +/- 0.5 angstroms nearest neighbor spacing.

In situ growth of CaCO₃ on a cleaved (1014) calcite surface from aqueous solution is observed with an atomic force microscope. Growth layers form by the nucleation of steps at spiral sources centered on screw dislocations. The kinetics of simple (isolated) and composite (clustered) spiral sources and the development of spiral plateaus, growth-induced domain walls, and interdomain budding sites are described. Single and double-armed spirals, counterclockwise and clockwise spirals, and hollow-cored and uncored spirals are exhibited. Spiral arms rotate faster along the long rhomb diagonal, thereby pairing the steps emitted from double-armed spirals. Clustered spirals interact in ways which can increase their step nucleation rates above those of isolated spirals.

We describe a lithographic technique using atomic force microscopy (AFM) to expose commercially available photoresists in a controllable manner. In contrast to scanning tunneling microscopy lithography on photoresists, the AFM has the advantage of having better control of the contact force between the probe tip and sample and thus reduces the possibility of physical damage to the resist material during exposure. Using a metal coated cantilever, we have been able to create resist patterns at the nanometer-scale.

Recent advances in AFM technology allow direct observation of solution growth and dissolution (etching) processes important in industry and nature, and direct tests of crystal growth models. We present results of studies of calcite and quartz, including real-time, in situ observations. While both crystals experience layer growth/dissolution, calcite grows by direct addition of material to growth steps without an important contribution from surface diffusion; quartz surfaces are consistent with more traditional, BCF-type growth models. Dynamic AFM observations of growth processes may allow optimization of industrial systems.

Atomic force microscopy was used to image surfaces and cross sections of different types of microporous membranes used for ultrafiltration and dialysis. Characteristic surface structures with funnel-shaped pores could be detected with resolution better than 10 nm. Ultrafiltration membranes with molecular weight cutoff values between 5,000 and 100,000 show wide variations in homogeneity, roughness, size and density of pores, but with a basic network-like fine structure. Cross sections allow one to compare inner structure and surface. An evident change of the surface of one membrane was observed after using the membrane over a long time for clearfiltration of juice. Cellulosic dialysis membranes with different biocompatibility were compared in air and under water. Structural differences could be observed between modified and unmodified type. Under water the structures are considerably changed due to swelling processes.

The gap junction is a specialized region of the plasma membrane that consists of an array of cell-to-cell ion channels. These channels form where the membranes from two cells come together, and the gap junction is therefore composed of two lipid bilayers. The atomic force microscope (AFM) can be used to dissect the gap junction, removing one membrane and exposing the extracellular domains of the second. The force required to dissect the membrane, near 10^-8 N vertical force for gap junctions adsorbed to mica, provides a measure of the strength of the interaction between the two membranes. Since a single membrane is left in contact with the mica, this interaction must be stronger than the membrane-membrane interaction. Non-junctional membrane attached to the gap junctions is easily removed with the AFM tip while the gap junction membrane remains attached to the mica, providing evidence that the interaction with the mica is mainly mediated by protein-mica interactions. Consistent with this hypothesis is the observation that material trapped under the membrane sometimes results in pieces of membrane above the material being pulled out during dissection. These results lay the foundation for examining the molecular details of the basis for membrane- membrane and membrane-substrate adhesion.

We have developed an atomic force microscope (AFM) with an integrated optical microscope. The optical microscope consists of an inverted epi-illumination system that yields images in reflection or fluorescence of the sample. With this system it is possible to quickly locate an object of interest. A high-resolution image of the object thus selected can then be obtained with the AFM that is built on top of the optical microscope. In addition, the combined microscopes enable a direct comparison between the optical image and the topography of the same object. The microscope is used to study the structure of metaphase chromosomes of eukaryotic cells. The topography of metaphase chromosomes reveal grooved structures that might indicate spiral structure of the chromatin. High resolution images reveal structures that can be ascribed to the end loops of the chromatin. The resolution of the AFM images was improved by using sharper tips obtained by carbon deposition on the Si₃N₄ cantilevers using a scanning electron microscope. Chromosomes which are treated to reveal the G- banding pattern in the optical microscope display a similar pattern when viewed with the AFM, as is shown by a direct comparison.

High resolution electron micrographs of microtips show nanometer surface irregularities. We propose that the lower contact forces, and consequent greater sensitivity, from imaging in propanol enables small biomolecules to be imaged at higher resolution by these 'nanotips'. However, larger molecules, such as the nucleosomes of chromatin, are still imaged by the bulk of the tip and no improvement of resolution is obtained.

Images obtained with a scanning near field optical microscope (SNOM) operating in reflection are presented. We have obtained the first results with a SiN tip as optical probe. The instrument is simultaneously operated as a scanning force microscope (SFM). Moreover, the instrument incorporates an inverted light microscope (LM) for preselection of a scan area. The SiN probe is operated in the contact regime causing a highly improved lateral resolution in the optical image compared to an alternative set-up using a fiber probe, which is also presented. The combined microscope is operated either in open loop or as a force regulated SNOM. Near field optical images can be directly compared with the topography displayed in the simultaneously recorded SFM image.

A new imaging mode, the error signal mode, is introduced to atomic force microscopy. In this mode, the error signal is displayed while imaging in the height mode. The feedback loop serves as a high-pass filter that filters out the low spatial frequency components of the surface, leaving only the high spatial frequency components of the surface to contribute to the error signal and to be displayed. At a scan rate of typically 10 lines per second, images taken in this mode show very fine detail. Since the applied force stays nearly constant, the error signal mode is especially suitable for imaging soft biological samples with a high level of detail without damaging the surface.

The design and theory of operation of a new form of near field scanning optical microscope are presented. In this system, the tip/sample distance regulation is achieved in a feedback system utilizing the topography information derived from the attractive force sensed between the tip and the sample. The technique affords the possibility of correlative microscopy. Results are presented on imaging blood smears and thin film integrated circuits.

We have immobilized chemically-fixed cellular microtubules and microtubule protein polymers on glow-discharged glass discs for scanning by atomic force microscopy (AFM). The images obtained by AFM resembled those obtained by conventional transmission electron microscopy of the same material. The AFM images can resolve some of the surface features of microtubules to 10 nm. Improvements in the techniques promise resolution approaching molecular dimensions.

Recent results on scanning force microscopy of cells and membrane proteins are presented. Whole immune system cells (rat basophil leukemia cells) can be imaged either alive and moving in aqueous medium, frozen, and exposed by freeze fracture (and imaged at -25 degree(s)C), fixed with glutaraldehyde in buffer, or fixed and dried (as if for scanning electron microscopy). Living cells can be stimulated with antigens or drugs and then observed as they move and change shape as a function of time after exposure. In either living or fixed cells it is possible to visualize and map cytoskeletal networks under the cell membrane, and, in living cells, to observe changes in the network with time. Membrane proteins (e.g., the F1 fragment of ATP synthase) can be imaged by simple passive adsorption to freshly cleaved mica. The resolution is about 50 angstroms, which is high enough to identify individual protein molecules, but still too low to distinguish internal structure. Factors which limit resolution and methods that may overcome these limitations are also discussed.