In proportion to the extent of down-scaling of silicon devices, surface microroughness causes more serious problems in device performance. Scanning probe microscopes were used as a powerful tool to evaluate the surface microroughness. In order to investigate the influence of heavily doping on surface morphology, heavily phosphorus doped samples of both Si(100) and polycrystalline silicon together with non-doped ones were examined using atomic force microscopy (AFM). Comparing to a smooth surface moderately doped Si(100) and heavily P-doped Si(100) surfaces exhibited unique geometrical AFM image patterns. The characteristic features of the patterns remained almost unchanged by annealing. The unique pattern still exists on the surface of 50 nm thick thermal oxide films of P-doped Si(100). Moreover, after removal the oxide film, the SiO2/Si interface also showed a similar pattern, though it was somewhat diffused. In the case of polycrystalline silicon, the grain size increased with heavily doping, but the unique pattern was not observed.
An attempt is made to provide a physical basis for DIET (desorption induced by electronic transitions) at metal surfaces. For this purpose, a theoretical description for DIET is given from a microscopic point of view. From the calculation for the dependence of the DIET probability on the penetration depth of the laser light and on the band-width of the electron system of the metal substrate, it is suggested that the spatial locality of electronic excitations affects the probability significantly. It is shown, furthermore, that the DIET probability increases, as the shape of PES (potential energy surface) is changed such that the number of adsorbate bound-states in the PES is decreased. As an order of magnitude, the result of calculation for the DIET probability of NO from Cu(111) agrees with the probability estimated experimentally.
Patterning of metal surfaces by using chemical reactions is a promissing method for the atomic-scale surface fabrica-tion. In this paper we present patterning reactions involving self-assembly processes with two examples: (1) (-Cu-O-) on Ag(110), which is prepared using such a chemical reaction as (-Ag-O-)+Cu→(-Cu-O-)+Ag on Ag(110) and the de-composition of (-Cu-O-) strings on Ag(110) forming a uniform size Cu6 cluster; (2) Depositing Ni on c(2×2)-N Cu (100), where Ni thin films with an average size of 50Å are grown at the crossing of the boundaries of c(2×2)-N patches. In addition, we also show HREELS and ARUPS data in the (-Cu-O-) Ag(110) surface.
Ferroelectric thin film materials, which are expected to find their applications in future nonvolatile memory devices, are reviewed. In those applications high speed, large capacity nonvolatile memory is required because electronic devices become portable and use battery drives. Memories that use ferroelectric thin films are proposed to fulfill those requirements. Ferroelectric materials for ferroelectric memories are then reviewed as the main theme of this paper, centering on two types. One type has perovskite structures containing lead (Pb) and the other group is made up of bismuth layerstructured materials. The former group, represented by lead zirconium titanate (PZT), has been frequently studied in ceramics research. This group, however, has two problems: fatigue, deterioration due to polarization switching and environmental problems resulting from its lead content. The latter group also has two problems: high crystallization temperature and low process-resistance especially in annealing under a reducing atmosphere. By partially overcoming the above problems, ferroelectric memories have begun to be applied to low-capacity memories. Higher capacity devices are now awaiting finding a compete solution to the above problems.
Dynamic behavior of surface atoms on Si(001) and Ge(001) was investigated by a Variable-Temperature (VT) STM. In a range of sample temperature from 30 K to 1200 K, a variety of dynamical atomic-processes were observed on the surfaces. (1) The flip-flop motion of buckled dimers was detected on Ge(001) surface at room temperature (RT). (2) The structural phase-transition from 2×1 to c(4×2) was observed both on Si(001) and Ge(001) surfaces upon cooling from RT. (3) The detachment and attachment of dimers at step edges were observed at high temperatures on Si(001) and Ge(001) surfaces. It is emphasized that time dependent VT-STM will provide fruitful information concerning the dynamic processes of surface atoms with atomic resolution.
Zeolite membranes were classified into four types, that is, self-supporting membrane, supported membrane, oriented self-supporting membrane, and disk membrane. Preparation, properties and applications of these membranes are described. Self-supporting membranes are obtained by using Teflon and cellulose as the substrates, but they are fragile. Supporting membranes can be prepared by both traditional hydrothermal synthesis and solid dry-conversion via vaporphase transport, and they have enough mechanical strength to be used for separation by pervaporation. An oriented self-supporting membrane can be obtained by using mercury surface as the substrate, which is transparent and shows molecular sieving effect for permeation of hexane isomers. A disk membrane can be prepared by heating a shaped mixture of silica or aluminosilicate containing an organic amine in a sealed system and used for a catalytic membrane.
Computer-aided simulation is one of ideal vehicles for the study of dynamic growth process in thin film formation. The initial growth process of GaAs thin films is theoretically investigated from a viewpoint of quantum mechanics using Monte Carlo simulation. An ab initio-based Monte Carlo simulation study implies that Ga adatom migration behavior on the GaAs(001)-(2×4)β1 surface strongly depends on the adatom coverage. This can be successfully interpreted by the electron counting model. Based on this finding, newly developed electron counting Monte Carlo method is applied to the surface structural change during adatom impingements. The GaAs(001)-(2×4) surface changes its structure from initial (2×4)β2 to another electronically stable (2×4)β1 via (2×4)α. The Ga adsorption of 0.5 monolayer on the GaAs(001)-c(4×4) surface induces As desorption to form (2×4)-like structure with As coverage θAS=0.75. These results qualitatively consistent with experimental results suggest that quantum mechanical contribution is essential to thin film growth process of compound semiconductors.
It is important for atomic layer control to carry out in-situ analysis of the topmost atomic species and structure. Although RHEED (Reflection High Energy Electron Diffraction), AFM (Atomic Force Microscopy) and XPS (X-ray Photoelectron Spectroscopy) are considered to appropriate methods for this purpose, each method is not sufficient enough to obtain necessary information. Recently several papers describe that CAICISS (Coaxial Impact Collision Ion Scattering Spectroscopy) is appropriate to in-situ analysis for an atomic layer control. This analyzer was applied to observations of topmost atomic planes of several crystals such as SrTiO3, GaAs, InP and SiC. As a result, the topmost planes of these crystals were analyzed successfully for atomic layer control. Therefore, we introduce these applications and discuss the possibility of atomic layer control by in-situ CAICISS analysis in this paper.
Field emission of electrons from carbon nanotubes was first demonstrated in 1995 by the two research groups; one is led by R.E. Smalley and the other by W.A. de Heer. The former group showed high emission from a single open multiwalled nanotube (MWNT) under low applied voltages, and the latter demonstrated electron emission from an aligned MWNT film. Recently, field emission microscopy was performed for both MWNTs and single-walled nanotubes (SWNTs). In this article, the background of these studies is briefly described, and then the characteristics of electron emission from carbon nanotubes are reviewed. Finally, electronic display elements (lighting-elements with the structure of a triode-type vacuum tube) are shown as a practical application of nanotube field emitters.