While electron holography has been around for many years (1948, see [1]), the process of obtaining a view into the phase world stayed a tedious one for a long time. When CCD cameras became available and started to replace film, many attempts were made to obtain a “live” view into the phase world. By far the most successful setup for a live phase display is described in [2]. There, Chen et al. use a mixture of digital and analog techniques to obtain phase images at TV-rate. This setup allows to move the sample and/or watch time dependent specimen changes in a unique way, i.e., live in the phase world. The reason why Chen uses a mixture between analog and digital methods is the capability of an optical lens system for fast Fourier processing.

Computers have become significantly faster since Chen's introduction of the mixed setup in 1992 and allow to process holograms rapidly and obtain about one phase image per second on present standard computer systems and acquisition cameras.

Pure phase objects having low spatial frequency such as electromagnetic fields in a vacuum can be visualized by electron holography or three-wave interference.1,2) Wavefront-division interference using a biprism requires a field-emission electron gun having high spatial coherency. On the other hand, amplitude-division interference using a thin crystal does not need high spatial coherency of electron source, i.e. an ordinary electron microscope with a LaB6 filament is good enough to form lattice fringes of high contrast. This is an advantage of amplitude-division interference.3,4)

We previously reported three-wave interference achieved by using two electron biprisms. Recently, we have realized amplitude-division three-wave interference by using a Si crystal as a splitter of an electron wave. Figure 1 shows the experimental set-up used to form an amplitude-division threewave interference pattern. A thin crystal prepared by ion-milling is installed at the standard specimen position, and a thin carbon film on which latex particles are sticking is placed at the selected area aperture position.

The problem of observing reverse-biased p-n junctions by means of transmission electron microscopy techniques is very challenging both from the experimental and theoretical points of view. In particular, in addition to standard Lorentz microscopy techniques, whose image contrast is able to give some information on the region of high field, also holographic methods have been successfully applied and an interference map of the twodimensional phase on the specimen plane obtained.

In this work we consider, in particular, the theoretical and interpretative aspects, as we have improved a model for the electric field associated to a periodic array of alternating p and n stripes lying in a half plane (physically corresponding to an array of zero-width step junctions) by taking into account that the junctions are tilted with respect to the specimen edge.

Scanning Probe Microscopy (SPM), in particular Atomic Force Microscopy (AFM), has become well establish member of the IC metrology tool arsenal which few IC manufacturers are without. Although Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) remain the “workhorse” metrology techniques, SPM (standard AFM, as well as Scanning Capacitance Microscopy (SCM), Scanning Spreading Resistance Microscopy (SSRM), Scanning Kelvin probe, Nanoindentaion and others) are being increasingly called upon to help solve IC production problems and to aid in research and development for next generation devices.

Topographical metrology with standard AFM is by far the most common application of SPM in the semiconductor industry. It is typically used to gain surface roughness and grain size information about thin films that can be used as feedback to modify deposition conditions until the desired film properties are obtained.

Atomic force microscopes (AFMs), which generate three dimensional images with nanometer level resolution, are increasingly being used as tools for sub-micrometer dimensional metrology in a wide range of applications. Measurements commonly performed with AFMs are feature spacing (pitch), feature height (or depth), feature width (critical dimension), and surface roughness. To perform accurate measurements, the scales of an AFM must be calibrated regularly. Presently available standards for this purpose are calibrated using stylus instruments and optical techniques. The effectiveness of this approach, however, is limited by the differences in the working ranges of the various techniques and by questions of methods divergence. Such divergence may occur between measurements made by instruments using different techniques to measure the same feature. A reflected light microscope and an AFM, for example, may have differing sensitivity to the cross-sectional profile of measured lines. For sufficiently steep lines, an AFM tip will only contact the features near the tops.

With the continuing push for reduction in the device dimensions into the deep sub-u,m dimensions, the critical need for physical and electrical characterization on this sub-μ,m scale is evident. The National Technology Roadmap has identified need for two-dimensional (2D) dopant/carrier profiling with a spatial resolution of 10 nm. Though current techniques used for dopant profiling such as secondary ion mass spectroscopy (SIMS) and spreading resistance profiling (SRP) have a high sensitivity, these offer good resolution only in the depth direction. The spatial resolution in the lateral direction in these techniques is limited to several tens or hundreds of microns. To acheieve the required lateral spatial resolution different scanning probe based techniques have been explored. One of the most promising of these class of techniques is scanning capacitance microscopy (SCM). In SCM a conductive atomic force microscope (AFM) probe tip is scanned across the surface and simultaneously an a.c. bias is applied between the tip and the sample.

Recent advances have been made on two fronts regarding the capability of the atomic force microscope (AFM) to characterize the mechanical response of polymers. Phase imaging with the AFM has emerged as a powerful technique, providing contrast enhancement of topographic features in some cases and, in other cases, revealing heterogeneities in the polymer microstructure that are not apparent from the topographic image. The enhanced contrast provided by phase images often allows for identification of different material constituents. However, while the phase changes of the oscillating probe are associated with energy dissipation between the probe tip and the sample surface, the relationship between this energy dissipation and the sample properties is not well understood.

As the popularity of phase imaging has grown, the capability of the AFM to measure nanoscale indentation response of polymers has also been explored. Both techniques are ideal for the evaluation of multi-phase and multi-component polymer systems.

Self-assembled monolayers (SAM) and multilayers of organic materials have been intensely studied in the past years, due to their numerous potential applications as, for example, lubricants, corrosioninhibitors and/or adhesion-promoters [1,2]. In this talk, we will present results of several studies carried out using Atomic Force Microscopy to investigate octadecylphosphonic acid (OPA) SAM deposited on mica. We have assessed various mechanisms of assembling, disassembling and reassembling the SAM on mica. The SAM deposition method employed in this work was drip coating using an OPA solution. We have used two different solvents, which exhibit very different OPA solubility, in this work: ethanol and trihydrofuran (THF). Regarding the assembling studies, we will show the formation of groups of OPA double-layers as the initial deposition stage (deposition time < 2 seconds) when using ethanol-based solutions. We will also show that annealing such samples at 60°C produces, favorably, OPA quadruple-layers, as shown in figures la and lb, respectively.

Numerous scanning tunneling microscopy (STM) studies of organic adsorbates at the gas/solid and liquid/solid interfaces have been reported. Although early STM experiments of these systems were concerned primarily with visualizing molecules at the atomic level, the focus has shifted to extracting chemical information from STM images, including the identity of atoms or functional groups within an adsorbed molecule. However, STM image interpretation continues to be an immense challenge and one currently debated issue of critical importance is the mechanism(s) by which image contrast reveals atomic and molecular structure. Recently, a combination of electronic and geometric factors was proposed. The electronic factor addresses the coupling between the energy levels of the adsorbate and the Fermi level of the surface whereas the geometric factor is related to the spatial overlap between the STM tip and the functional group.

A study in our laboratory of a homologous series of para-halogenated phenyloctadecyl ethers (XPOEs, where X = H, Cl, Br, I) adsorbed on highly oriented pyrolytic graphite (HOPG) has contributed significantly to the understanding of the image contrast mechanism for molecular adsorbates and of the chemical specificity of STM.

Quantum dots and nanocrystalline films are interesting materials due to their novel properties, not achievable from the bulk materials [1]. New materials fabricated by assembling of quantum dots and nanostructured materials exhibit, for example, high optical nonlinearities. Fractal structures [2] can be formed from quantum-dot aggregates or films. Scanning probe microscopy is the essential technique to characterize these nanometer-scaled materials?

Gold nanocluster colloids are synthesized in the interior of surfactant aggregates known as inverse micelles, without the use of water to solubilize the metal salt [3]. The size of the Au quantum dots is well controlled in the colloid synthesis and selected using chromatography. The Au clusters are then sprayed onto a glass slides to form thin films made of Au quantum dots. We have also used the laser ablation technique [4] to grow Ag nanoparticles, fractal aggregates and thin films. These samples have been studied using atomic force microscopy (AFM) and nearfield scanning optical microscopy.

Scanning Probe Microscopy (SPM) is a superb tool for topographical analysis of samples. However, traditional varieties of SPM such as Atomic Force, Scanning Tunneling and Near-field Scanning Optical Microscopy have limited chemical contrast capability. Recently, several advanced techniques have been reported which provide chemical information in addition to topographical data. All these methods derive advantage from combinations of scanning probe methodologies and some other, chemically sensitive technique. Examples of such approaches are: Near-field Scanning Raman Imaging, Near-field Scanning Infrared Microscopy and mass spectrometric analysis with laser ablation through fiber probes.

In this contribution we report the development of a new method in this family of chemically sensitive scanning probe techniques: Laser Induced Breakdown Spectroscopy with Shear Force Microscopy, LIBS-SFM. Traditional LIBS experiments involve focusing a pulsed laser beam onto the sample and observing optical emission from the plasma formed in the ablation area. The emissions are mostly in the UV/visible range, and the signal is due to electronic transitions in excited atoms and ions in the plasma plume. The spectra are analyzed to identify chemical elements. The spatial resolution of LIBS is limited by the wavelength and beam quality of the laser used for ablation. The experiments may be conducted in vacuum, controlled atmosphere, or ambient air.

The atomic force microscope (AFM) is a powerful tool for probing surface topography, in addition to chemical and mechanical properties of surfaces. To investigate the chemical properties of a sample, force measurements are made between the AFM's “molecular finger,” or probe, and the sample. Force measurements can be made in many environmental conditions, which makes the AFM a versatile technique. However, in ambient conditions most samples are covered by a thin layer of water. When the AFM probe comes into contact with the thin water layer, a capillary bridge forms between the AFM probe and sample. Because of this water layer, it is believed that in ambient conditions a non-surface specific capillary force dominates the adhesive force between the AFM probe and sample. The non-surface specific capillary force should obscure any information about the surface. Currently, we are studying to what extent the capillary forces are non-surface specific and what influence this has on pull-off-force measurements.

In a number of situations and applications, the tribological wear of ceramic and minerallike surfaces is often greatly enhanced in the presence of a corrosive fluid. Examples are the wear of surfaces associated with joints (biomaterials) subject to and the extremely active application to high density circuit production which requires chemical mechanical polishing (CMP). The physics and chemistry of these enhanced wear rates are needed to reduce wear and to improve and extend CMP to new applications. In both situations, surfaces experience simultaneous tribological loading and corrosive chemical exposure, which together produce high wear rates and altered topography. In CMP, the goal is to efficiently achieve very flat surfaces. As feature sizes diminish further, it is conceivable that atomically flat surfaces will be necessary. In almost all tribological situations, it is the interaction of asperities, often micron and sub-micron in dimensions, that control the wear processes due to the high stresses associated with these small structures.

It is important to be able to image biological samples in a manner that is non-invasive and allows the sample to retain its functionality during imaging.

A member of the SPM (scanning probe microscopy) family, SNOM (scanning near-field optical microscopy), has emerged as a technique that allows optical and topographic imaging of biological samples whilst satisfying the above stated criteria. The basic operating principle of SNOM is as follows. Light is coupled down a fibre-optic probe with an output aperture of sub-wavelength dimensions. The probe is then scanned over the sample surface from a distance that is approximately equal to the size of its aperture. By this apparently simple arrangement, the diffraction limit posed by conventional optical microscopy is overcome and simultaneous generation of optical and topographic images of sub-wavelength resolution is made possible. Spatial resolution values of lOOnm in air and 60nm in liquid[1,2] are achievable with SNOM.

Scanning capacitance microscopy (SCM) is currently one of the most promising tools for twodimensional carrier profiling. This technique, based upon atomic force microscope (AFM) operated in the contact mode, uses a conductive probe which is scanned over the semiconductor surface. The conductive probe, oxide on the surface of the semiconductor, and the semiconductor substrate form a metal-oxide-semiconductor (MOS) structure. An a.c. bias is applied to the tip and the capacitance of the MOS structure is monitored. The a.c. bias changes the depletion of carriers in the semiconductor and thus the total capacitance of the structure. The maximum capacitance of the MOS structure is obtained when the semiconductor is in accumulation and the total capacitance of the structure is the capacitance of the semiconductor surface oxide. The minimum capacitance is obtained when the semiconductor region under the tip is in inversion. Since SCM the output signal is proportional to the differential capacitance, to get a high signal we need to maximize the difference between the maximum and minimum in the total MOS capacitance.

In “ac” scanning thermal microscopy, an “active” thermal probe is used also as a heater, so as to inject evanescent temperature waves into a sample and to allow sub-surface imaging of polymers and other materials [1]. The sub-surface detail detected corresponds to variations in heat capacity or thermal conductivity. By suitably choosing the temperature modulation frequency, and hence the penetration depth of the wave, we control the depth of material below the sample surface that is contributing to the image.

Micro-Thermal Analysis [2, 3] builds upon this technique, in order to add spatial resolution to two well-established methods of chemical fingerprinting, DTA and DMA. In both cases, a temperature ramp is used to subject the sample to “events” such as a glass transition or melting. The chief advantages of using the active thermal probe to provide the temperature ramp as well as the modulation, without the use of a heating stage, are: (a) the data are obtained from localised regions chosen from a previously-obtained thermal image, (b) apart from these regions, the rest of the sample is preserved in its original unheated state.

The performance of many industrial polymers is determined by the microscopic morphology of the polymers. For example, surface morphology can influence properties such as adhesion, friction, sealing, blocking, printability, wettability, and haze. Furthermore, bulk morphology often controls mechanical properties such as toughness. strength, wear, and tear resistance. In order to optimize polymer performance, quick reliable methods of determining surface and bulk morphology are essential.

In the past, electron microscopy (in particular TEM) has been the primary method for determining polymer morphology. However, the usefulness of electron microscopy has been limited by the destructive nature of the electron beam, the naturally poor contrast between polymer types, and the difficulty in preparing (staining, etching, cryogenic ultramicrotoming, etc.) high quality specimens.

Recently, the tapping phase-shift mode of atomic force microscopy (TPSAFM) has provided the polymer scientist with a simple, quick, flexible and quantitative method for determining polymer surface and bulk morphology.

Mechanical properties were determined from the organic matrix of a mollusc hard tissue using a nanomechanical testing instrument attached to an atomic force microscope (AFM). Shells of molluscs are two-tier functionally-gradient ceramic/polymer biocomposites used by organisms as impact resistant materials. The inner section of the red abalone (Haliotis refuscens)shell, nacre (mother-ofpearl), has a brick and mortar microarchitecture with pseudo-hexagonal-shaped bricks made of aragonitic (orthorhombic) CaCO3 platelets (0.25 μn thick, and 5 μm edge length) surrounded by a thin (10-25 nm thick) proteinaceous organic matrix (Fig. 1). This higly ordered biocomposite has submicron-layered structure that result in excellent bulk mechanical properties, not achieved by manmade composites with similar phase compositions and, therefore, offers biomimetic lessons for novel materials design. In this model biomimetic composite, mechanical properties of its constituents need to be evaluated in addition to the details of the microstructure. We previously determined nanomechanical properties (hardness and modulus) of individual (twinned, single crystalline) aragonitic platelets.

In industrial applications, such as paints or adhesives, composite latex particles are very common. Most of the properties which are obtained from composite latexes and their films cannot be achieved by physical blending of different polymer components. Therefore it becomes crucial to examine the morphology of composite latexes formed by a multiple-stage polymerization process. The latexes for this study have been examined by transmission electron microscopy (TEM) and atomic force microscopy (AFM). Various staining methods were used such as ruthenium tetroxide (RuO4), cesium hydroxide (CsOH), and uranyl acetate (UAc) as a negative stain.

The poly(n-butyl acrylate/ poly(methylmethacrylate) (PBA/PMMA) composite latex particles consist of a soft core phase and a hard second phase with varying amounts of acrylic acid in the core, the shell and in both core and shell. The latexes were examined before and after cleaning by a centrifugation technique with 100,000 molecular weight filters.

Confocal microscopy was developed in 1957 by Minski, who was awarded a patent for this work in 1961. Since that time many advances have been in new designs and implementations. There are two basic classes of confocal microscope: the Nipkow-disk-based confocal microscope which allow real-time direct viewing of the sample, and the confocal scanning laser microscopes (CSLM). The CSLM will be focussed on in this presentation.

The CSLM scans a focussed beam over, across or through the sample, collecting the reflected, scattered or emitted light. This light is directed towards an optical spatial filter, which passes light returning from the on-axis focus position, and rejects light that is returning from anywhere else. By detecting the light passing through the spatial filter synchronously with the moving beam and/or sample, an image that has only in-focus information is acquired. Typically a set of images is acquired as the sample is moved through focus: from this “image stack” both an extended-focus image and topographic information can be obtained.