The geometric structure of GaAs (100) surfaces, treated in a (NH4)2Sx solution and annealed in N2 environment, has been studied in an atomic scale using high-resolution Rutherford backscattering (RBS), X-ray photoemission spectroscopy (XPS) and scanning tunneling microscopy (STM). RBS analysis using medium energy ion scattering (MEIS) could provide the thickness of the sulfur layer on the GaAs surface of about 1.5 monolayers. RBS channeling spectra indicated that the disorder of atoms in the surface region of S-terminated samples was smaller than that of untreated one. XPS spectra showed that S atoms on the surface bonded only As atoms. STM observation revealed that S atoms had a periodicity of 4 Å corresponding to that of Ga or As atoms in the (100) plane.

It was found that porous silicon (PS) layers formed on 0.01 Ωcm (111) and 0.02 Ωcm (100) Si substrates show high photoluminescence (PL) peak energies on both lower and higher porosity sides and a minimum of PL peak energy at the moderate porosity, while those formed on 0.8 and 10Ωcm (111) p-type Si substrates show an increase of PL peak energy with porosity on the lower side and a saturation of PL peak energy with porosity on the higher side. These experimental facts are not consistent with the quantum confinement model for light emission of PS, which predicts a monotonous increase of PL peak energy with PS porosity.

Atomic-scale resolution scanning tunneling microscope (STM) images of cleaved (0001) surfaces of the hexagonal tungsten bronze, Rbl/3WO3, show two distinct contrast patterns. We have interpreted these images using simulated constant current STM topographs. These simulations are constructed based on calculations of the tunnel current as a function of the lateral and vertical position above the surface. By calculating simulated images for the limiting cases of different termination layers, different tip sizes, and different electronic structures, it is possible to systematically explore the important parameters and choose a model that most closely matches the experimental observations. In this case, we conclude that two distinct termination layers have been imaged, a W-O terminated surface and a Rb-O terminated surface. Also, we have found that the O atoms on the W-O surface relax to new positions nearer the 6-fold axis of rotational symmetry. Some of the advantages and disadvantages of this model are discussed.

Single crystals of Na0.003V2O5 and Mo18O52 were grown by chemical vapor transport and cleaved surfaces were imaged in ultrahigh vacuum using scanning tunneling microscopy (STM). Because the Mo18O52 (100) and Na0.003V2O5 (010) surfaces of these layered materials have a bulk terminated structure, the atomic-scale contrast in constant current images can be directly compared to components of the bulk structure. Among the structural features identified in the STM images are the surface/crystallographic shear plane intersections, the different MoOx coordination polyhedra on the Mo18O52 (100) surface, and the VO5 square pyramids that make up the Na0.003V2O5 (010) surface. In each of these cases, it was found that the atoms closest to the tip dominate the image contrast.

We present a technique for the fabrication of InP nano-columns and GaInAs/InP quantum-dots based on the use of sintered aerosol Ag particles as a mask in an electron cyclotron resonance etching process. The sintered particles have much more regular shapes than the unsintered ones used in previous studies and are more resistant to the etching environment, which results in the formation of more regular and reproducible structures. For example, we have been able to produce columns 100 nm in height which have an average diameter of 24 nm and a density of 109 cm−2.We have investigated the shape of the etched columns as a function of the Ag particles’ size, and characterized their electrical and optical properties using a combination of scanning electron microscopy, scanning tunneling microscopy, atomic force microscopy, and photoluminescence.

Scanning tunneling microscopy (STM) and spectroscopy (STS) were used to characterize highly oriented pyrolytic graphite (HOPG) which was oxidized by two different methods, furnace heating in atmosphere and immersion in oxygen plasma. The character of the surfaces was found to be dissimilar on a micron scale but comparable on a nanometer scale, at which both appear to be comprised of sharp step edges. Variations in local electronic structure near a step edge were compared.

Grazing incidence X-ray reflectivity may be used to measure surface topography including roughness and correlation lengths to sub-nanometre precision. A study is made of a technically important surface, a carefully-polished specimen of Zerodur glass-ceramic, which has been measured by diffuse scatter of CuKα X-radiation and atomic-force profilometry methods. The data have been analysed in terms of a fractal representation of the surface correlation function. Results from the two methods agreed within their estimated errors, with the X-ray data showing roughnesses of 1.3 nm, correlation length of 1 μm and fractal parameter (bandwidth) of 0.35. The X-ray methods have a lower cut-off length, are much more rapid for averaged information and are both non-contacting and non-destructive. They also show potential for the study of interface roughness in thin films.

Using a CO2 laser to drive the pyrolysis of W(CO)6 and O2, we have synthesized nanocrystalline WO3-x particles. These nanopowders are found to exhibit a narrow size distribution with an average particle size produced in the range 5 to 10 nm, depending on the experimental conditions. Typical production rates are ∼ 2 g/h. Results from a Raman scattering study on WO3 nanopowder samples annealed in O2 indicate that a smaller particle size appears to stabilize the low-T ferroelectric phase ( < -40 °C) at room temperature.

Glass strength is controlled by microscopic surface flaws. Attempts to quantify the strengthflaw relationship for corroded silica fibers have been unfruitful, principally because of the difficulty in identifying the nanometer-sized, strength-controlling flaws on a uniformly corroded surface. In this paper, studies on corrosion of pristine silica optical fibers by HF vapor are presented. The HF-treated fibers exhibit strength degradation and contain well-defined, spatially-resolved surface flaws, which are characterized with an atomic force microscope. Excellent strength agreement is obtained for all chemically corroded fibers when the flaws are modeled as partially embedded hemispheres (i.e., blunt flaws). The implication of these results to the corrosion and fatigue process of silica glasses is discussed, since all previous analyses have assumed the strength-controlling flaws to be sharp.

Photon scanning tunneling microscopy (PSTM) has been used to obtain effective refractive indices of optical channel waveguide structures. The local evanescent field intensity associated with the propagation modes of optical channel waveguides are measured at two different wavelengths. Both a tapered optical fiber tip and a semiconductor heterostructure tip are employed for detection. Local values of effective refractive index are measured for both TE and TM polarizations and compared to model calculations.

The electrochemical modification of H-passivated Si(100) surface is produced and characterized by Scanning Tunneling Microscopy and Spectroscopy (STM/STS) operating in air. In order to better understand this nanometer scale modification, we have characterized spectroscopically the modified region. From the current-voltage (I/V) curves, dI/dV versus V curves and tip to sample spacing versus voltage (s/V) curves (at constant current) we have concluded that the modification induces a local electrochemical change on the surface, which in turn produces both, a decrease of the local density of surface states and a variation of the band bending in the silicon surface.

The morphology of Ge(001) has been investigated with a UHV - Scanning Tunneling Microscope. The Ge(001) surface was misoriented towards the [011] direction with a miscut angle varying from 0.4° to 5°. The surface stress was found to have considerable influence on the step edge configuration as well as the position of the steps with respect to each other.

Electron crystallography has now been used to investigate the structures of inorganic materials in three dimensions. As a test of the method, amplitudes and phases of structure factors were obtained experimentally from high resolution images of staurolite taken in a number of different projections. From images in five orientations, a three-dimensional Coulomb potential map was constructed with a resolution of better than 1.4Å. The map clearly resolves all the cations (Al,Si,Fe) in the structure, and all of the oxygen atoms. This method promises great potential for structure determinations of small domains in heterogeneous crystals which are inaccessible to x-ray analysis. Three-dimensional structure determinations should be possible on small domains only approximately 10 unit cells wide, and may resolve site occupancies in addition to atom positions. Given a microscope stage with a suitable range of tilt and enough mechanical stability, the method could also be applied to small crystalline particles larger than about 50Å to 100Å. In addition, it may be possible to apply the method to derive the two-dimensional structure of periodic defects.

Transition metal impurities such as Fe, Ni, and Co can be intercalated into the van der Waals gap of layer structure dichalcogenides and these modify the charge-density wave (CDW) structure and CDW energy gaps. Ordered superlattices associated with antiferromagnetic phases can be detected by both scanning tunneling microscopy (STM) and atomic force microscopy (AFM). STM spectroscopy indicates the formation of a mixed spin-density-wave (SDW) and CDW (SDWCDW) in the doped materials. The quasi-one dimensional trichalcogenide NbSe3 exhibits two CDW transitions and the presence of dilute transition metal impurities produces ordered superlattices due to long range screening of the impurities.

Much of the current activity and excitement in materials science involves processing and understanding materials at the atomic scale. Accordingly, it is necessary for materials scientists to control and characterize materials at the atomic level. There are only a few microscopies that are capable of providing information about the structure of materials at the atomic level: the atom probe field ion microscope, the high resolution transmission electron microscope, and the scanning tunneling microscope. The three-dimensional atom probe (3DAP) determines the 3D location and elemental identity of each atom in a sample. It is the only technique that provides 3D information at the atomic scale.

The origin and underlying concepts behind the 3DAP are described. Several examples of actual images from existing 3DAPs are shown with emphasis on nanometer-scale analysis. Current limitations of the technique and expected future developments in this form of microscopy are described. It is our opinion that 3D atomic-scale imaging will be an indispensable tool in materials science in the coming decades.

In this paper, we report on the use of cross-sectional scanning tunneling microscopy (XSTM) to analyze several aspects of MBE-grown III-V quantum structures on an atomic scale. In particular, we discuss our recent work to identify various atomic species within the same chemical group (e.g. Al and Ga within the group Ill sublattice of AlGaAs) thereby allowing the determination of atomic roughness at GaAs/A1GaAs interfaces and alloy clustering in AlGaAs. We demonstrate and discuss the sensitivity of the STM to individual dopants in the near surface layers, as well as to the local carrier concentration. Lastly, we use XSTM to obtain images of cross-sectioned GaAs/AIGaAs quantum well wires with atomic detail.

By averaging phase correlations between scattered electrons a high angle detector in the scanning transmission electron microscope (STEM) can provide an incoherent, Z-contrast image at atomic resolution. Phase coherence is effectively destroyed through a combination of detector geometry (transverse incoherence) and phonon scattering (longitudinal incoherence). Besides having a higher intrinsic resolution, incoherent imaging offers the possibility of robust reconstruction to higher resolutions, provided that some lower frequency information is present in the image. This should have value for complex materials and regions of complex atomic arrangements such as grain boundaries. Direct resolution of the GaAs sublattice with a 300kV is demonstrated.