EXELFS, extended energy loss fine structure, is one of the spectroscopic techniques provided by electron energy loss spectrometer in the transmission electron microscope. Here, EXELFS is described for its potential use for determining nanoscale physical properties of complex materials. It is demonstrated that EXELFS analysis, like EXAFS, extended X-ray absorption fine structure in bulk materials, provides short-range structural information such as atomic nearest-neighbors and their distances in amorphous an crystalline samples. Some of the problems that hindered the development and wide use of EXELFS were discussed and their solutions are presented. Further solutions and future prospects are discussed.

The method of cross-sectional scanning tunneling microscopy (STM) is described. Illustrative examples are given of studies of III-V semiconductor systems, including low-temperature-grown (LT) GaAs, and InAs/GaSb superlattices. In each case, the STM permits the observation of structural features on an atomic scale. The associated electronic spectroscopy for states a few eV on either side of the Fermi-level can be determined. Such information is relevant for the operation of devices constructed from these layered semiconductor systems.

Recently the first experiments in magnetic resonance force microscopy (MRFM) have been conducted. In these experiments a force microscope cantilever is used to detect the magnetic force exerted by electrons and nuclei in a sample. The magnetization of the sample is modulated at the resonant frequency of the cantilever, using standard magnetic resonance techniques. The resulting excitation of the cantilever is detected optically. This article reviews the present status of MRFM technology, emphasizing the physical principles involved and the opportunities for further research and development. Particular emphasis is placed on single spin detection by MRFM and potential applications in biomolecular imaging.

Structural information on the atomic scale is readily accessible from thin samples using the technique of high-resolution electron microscopy. Electron micrographs recorded under well-defined operating conditions can be directly interpreted in terms of atomic arrangements around defects of interest such as dislocations and interfaces. Digital image recording with slow-scan CCD cameras and quantitative comparisons with image simulations based on structural models are starting to lead to improved accuracy and reliability in structure determinations. Techniques based upon holographic methods are utilizing the superior illumination coherence of the field emission electron source to enhance resolution beyond the conventional extended Scherzer limit. Innovative methods for combining image and diffraction pattern information are also leading to improved levels of resolution for periodic objects. Care is needed to ensure that electron irradiation damage and surface cleanliness do not impose unnecessary restrictions on the details that can be extracted from recorded micrographs. It is proposed that the complex wavefunction emerging from the exit-surface of the sample should be considered as a basis for comparing the differences between experimental micrographs and image simulations.

Flux lines in superconducting thin films are observed statically in a holographic electron interference micrograph, and dynamically in a Lorentz micrograph with a “coherent” and 300kV electron beam. In interference microscopy, projected magnetic lines of force in a tilted Nb thin film are observed quantitatively as contour fringes drawn on an in-focus electron micrograph. Whereas in Lorentz microscopy, flux lines are observed as spots with bright and dark contrast pairs due to defocusing of the image. Although the image is blurred due to a large amount of defocusing, this method is suitable for real-time observation. By making the best use of this feature, flux line movement can be observed when the applied magnetic field or the film temperature changes.

In situ hot-stage high-resolution transmission electron microscopy (HRTEM) provides unique capabilities for quantifying the dynamics of interfaces at the atomic level. Such information is critical for understanding the theory of interfaces and solid-state phase transformations. This paper provides a brief description of particular requirements for performing in situ hot-stage HRTEM, summarizes different types of in situ HRTEM investigations and illustrates the use of this technique to obtain quantitative data on the atomic mechanisms and kinetics of interface motion in precipitation, crystallization and martensitic reactions. Some limitations of in situ hot-stage HRTEM and future prospects of this technique are also discussed.

Methods for epitaxial growth of two dimensional materials are described. The lack of interlayer bonding in these materials allows for epitaxial growth with large lattice mismatches. Growth of MoSe2 on MoS2 (a 5% mismatch) or on SnS2 (10% mismatch) can be demonstrated. Scanning tunneling microscopy (STM) revealed remarkable structures in the epilayer as a result of the large mismatches. A technique using the STM or atomic force microscope (AFM) to selectively remove single molecular layers from the surface of layered materials is also described. The combination of these two technologies may result in the ability to produce nanoscale devices exhibiting quantum size effects.

We have utilized scanning soft X-ray photoelectron spectromicroscopy-MAXIMUM to investigate the microstructural evolution induced by localized corrosion in the Al-Cu-Si alloy thin films. We present energy-specific photoelectron micrographs showing the distribution of Cu-rich precipitates and corrosion products for the thin films after corrosion. Microspectroscopy performed across a corrosion site reveals that the O 2p valence band shifts in energy with location and the amount of shift can be related to the degree of corrosion. The photoelectron micrographs also show that the Cu-rich phase precipitates near the surface region and grows with annealing temperature.

We have used atomic force microscopy (AFM) and friction force microscopy (FFM) techniques for microtribological studies including microscale friction, nanowear, nanoscratching and nanoindentation hardness measurements. The microscale friction studies on a gold ruler sample demonstrated that the local variation in friction correspond to a change of local surface slope, and this correlation is explained by a friction mechanism. Directionality effect is also observed as the sample was scanned in either direction. Nanoscratching, nanowear and nanoindentation hardness studies were performed on single-crystal silicon. Wear rates of single crystal silicon are approximately constant for various loads and test duration. Nanoindentation hardness studies show that AFM technique allows the hardness measurements of surface monolayers and ultra thin films in multilayered structures at very shallow depths and low loads. The AFM technique has also been shown to be useful for nanofabrication.

Indentation using the AFM is a powerful method for determining elastic properties of small supported clusters. However, a theoretical framework has yet to be developed to interpret such measurements. The elastic deformation of nanometer sized gold clusters are modeled using the Embedded Atom Method (EAM) potential of Foiles et al. [1]. Force versus deformation curves are obtained for a series of truncated octahedral clusters having FCC symmetry (N=38, 201, 586, 1289, 2406). It is found that the MD results both for static compression and for harmonic vibration can be analytically estimated by using an elastic constant for the clusters analogous to the elastic modulus of a bulk material. However MD predictions for static compression are not in agreement with the deformation results of Schaefer et al. [2].

We have constructed an inexpensive sample mounting stage for studies of temperature dependent processes in a surface force microscope (SFM). The stage is constructed from a Peltier thermoelectric heater secured to a standard SFM mounting stage with silver paint. The sample temperature can be varied from room temperature to about 100°C thus making it possible to use the SFM to observe thermally activated processes at lateral spatial resolutions of 10-20 nm. Approximately 10 minutes is required to reach thermal equilibrium following a 5°C temperature change. The lateral magnification must be calibrated at each temperature. We illustrate the capabilities of the stage with images of polystyrene spheres just below their glass transition temperature of 100°C.

In this paper we present electron microscopy results near and below the melting temperature, both in dark field and high resolution mode, of lead nanoparticles embedded in a dielectric matrix of amorphous SiOx. Three different size dependent regimes are distinguished. Indications of solid particles rotations as well as of a new phenomenon amenable to spontaneous solid-liquid phase fluctuations will be briefly discussed.

Deintercalation processes for the model neutral intercalation system HgxTiS2 (1.25≥x>0.00) have been investigated using dynamic high-resolution transmission electron microscopy. X-ray powder diffraction and thermogravimetric analysis demonstrated the intercalation process is thermally reversible, both structurally and compositionally. In situ deintercalation of stage- 1 compounds was induced by thermal/electron-beam heating during DHRTEM observation. The resulting deintercalation processes were followed with 0.03 second time resolution. The deintercalation processes observed possess a strong similarity to nucleation and growth processes. Deintercalation was observed to “nucleate” by the initial deintercalation of an external-most or internal guest layer, with further deintercalation of the guest “growing” away from the onset layers. This results in generally randogmuelsyt lsatyaegresd greengeiroanllsy, occasionally containing regions of short-range order, that expand away from the deintercalation onset layers.

It is extremely important to characterize the various bare copper surfaces in situ before any subsequent corrosion or deposition chemistry can be understood. In this paper, in situ Atomic Force Microscopy (AFM) was used to image the low-index faces of Cu single crystals in H2SO4 and HClO4 acidic solutions. Cu(100) surfaces exhibited potential-dependent c(2x2) adlayers in pH=1 solutions which were attributed to oxide (or hydroxide) overlayers. Images of Cu(1 10) obtained in pH 2.5-2.7 solutions revealed the growth of primarily [001] oriented (nxl) adlayer chain structures, where n is an integer. Preliminary measurements on Cu(111) did not reveal any adlayer structures between pH's of 1-3. The oxide monolayers on Cu(100) and Cu(110) crystals were observed in the thermodynamically forbidden region of the pH-potential phase diagram, which indicates that stable oxide adlayers develop prior to bulk oxide formation.

The addition of a Gatan imaging parallel electron-energy loss spectrometer (IPEELS) to a Hitachi HF 2000 cold field emission TEM has allowed us to produce high quality energy-filtered coherent electron diffraction patterns and electron holograms from a wide variety of materials. In this paper we review the recent achievements and make an assessment of the use of coherent electron diffraction in solving problems at high spatial resolution in materials science.

One of the most challenging areas of materials research is the imaging of technologically relevant materials with microscopic and atomic-scale resolution. As part of the development of these methods, near-surface atoms in single crystals were imaged using core-level photoelectron holograms. The angle-dependent electron diffraction patterns that constitute an electron hologram were two-dimensionally transformed to create a three dimensional, realspace image of the neighboring scattering atoms. We have made use of a multiplewavenumber, phased-summing method to improve the atom imaging capabilities of experimental photoelectron holography using the Cu(001) and Pt(111) prototype systems. These studies are performed to evaluate the potential of holographic atom imaging methods as structural probes of unknown materials.

A convergent beam electron diffraction method was used in a transmission electron microscope to determine residual thermal stresses from nanometer-scale areas in a ceramic-metal (cermet) composite material. It is demonstrated that the method is simple, but requires a standard sample for each of the phases in the composite. The principle of the technique is that the stresses are determined by comparing higher order Laue zone line shifts, due to lattice strain, in high-symmetry zone-axis electron diffraction patterns recorded under the same experimental conditions from the unknown phases and the standards. The application of the method to composite systems containing dissimilar phases, such as ceramic-metal composite systems, demonstrates the universality of the technique in obtaining local structural information of anisotropic strain unambiguously with a high accuracy. The procedure involved is described in detail with application to B4C-AI, a three-dimensional intertwined ceramic-metal composite.

The interfacial structure of CVD diamond grown on silicon was studied using spatially resolved electron energy loss spectroscopy (EELS) in a UHV STEM with a subnanometer probe size. Both the plasmon and core excitations in the bulk appear to be localized on this scale. Spatial maps of the different bonding configurations of carbon were obtained by forming images from transmitted electrons that had undergone energy losses characteristic of threefold and fourfold coordinated carbon. Films grown on both prescratched silicon and intermediate amorphous carbon layers were examined. In the latter case, diamond nucleation on a narrow sp2 a-C occurred. For diamond grown directly on silicon, at some regions of the interface, threefold coordinated defect states smaller than 1 nm are observed on the diamond side of the interface while at other regions along the interface the presence of an intermediate 2nm thick SiC layer preserves the fourfold coordination of the carbon.

Valence electron energy-loss (EEL) spectroscopy in a dedicated scanning transmission electron microscope (STEM) has been used to study the Σ11 grain boundary in α-A12O3 in comparison with bulk α-A12O3. The interband transition strength was derived by Kramers-Kronig analysis and the electronic structure followed from quantitative critical point (CP) modelling. Thereby differences in the acquired spectra were related quantitatively to differences in the electronic structure at the grain boundary. The band gap at the boundary was slightly reduced and the ionicity increased. This work demonstrates for the first time that quantitative analysis of spatially resolved (SR) valence EEL spectra is possible. This represents a new avenue to electronic structure information from localized structures.

In this work, digital image processing techniques are used to study the structure of small metallic particles imaged under high resolution conditions. An algorithm is devised to extract directly from the micrographs the coordinates of columns of atoms in such a way that the crystal structure of the particles and their boundaries can be determined. For distorted regions (such as grain boundaries) the actual positions can be compared to the ones in the ideal lattice so that a general trend of the distortion field can be elucidated.