Tsuneo Urisu

Influence of Substrate Roughness on the Formation of Aliphatic Self-Assembled Monolayers (SAMs) on Silicon(100)

The peak shifts of the CH2-vibrations are an indicator of the amount of gauche-conformational disorder present in aliphatic self-assembled monolayers (SAMs). We have investigated the relationship between the surface roughness and the peak position as a function of temperature. With increasing substrate roughness, the CH2 vibration peaks shift to higher wave-numbers. The magnitude of the shift is up to 6 cm-1 which corresponds to a change from a condensed, almost all-trans conformational phase to a liquid-like, gauche-disordered phase. On polished substrates although increased temperatures lead to a slightly more ordered SAM, the layers are in almost an all-trans conformational phase independent on the coverage. From these results an island growth and annealing effects-model is proposed.

Hydrophobic/hydrophilic interactions of cytochrome c with functionalized self-assembled monolayers on silicon

Abstract Cytochrome c (C c , horse heart) has been adsorbed onto self-assembled monolayers (SAM) on silicon single crystal substrates. Layer thickness was determined using ellipsometry and atomic force microscopy in the DFM tapping mode. Both hydrophilic (COOH containing SAM) and hydrophobic self-assembled monolayers were used. The protein layers were found to consist of adsorbed 2-dimensional islands. Concentration, exposure time and the defect-density of the self-assembled monolayer substrates determined the wetting properties of the resulting layer, indicating that the surface orientation of the protein is driven by the interaction with the substrate. On well ordered self-assembled monolayers, the protein layer thicknesses were 1.76 nm for charged surfaces and 2.3 nm for hydrophobic surfaces. Self-assembled monolayers of a lower density resulted in a prevalence of C c islands of 3.2 nm thickness for both cases.

SR-stimulated etching and OMVPE growth for semiconductor nanostructure fabrication

Abstract Synchrotron radiation- (SR-)stimulated etching and selective area growth by organometallic vapor phase epitaxy were performed to form an ordered array of InP crystals on SiO 2 -patterned InP (001) substrate. The SR-stimulated etching was used to pattern the SiO 2 film, because photochemical reaction using SR was expected to provide smooth surfaces, vertical side walls and fine patterning. In the first place, we investigated the basic properties of the SR-stimulated etching by using a mm-size pattern of SiO 2 mask. The etched depth was observed to increase linearly with the irradiation dose. It was found that the etching depth was controlled very accurately. Next, we used μm-size patterns of SiO 2 masks for fabricating the ordered array of InP crystals. In a atomic force microscope image of the sample after etching, a steep side wall was observed. However, the etched surface was not smooth, contrary to our expectation. Moreover, some dust were observed on the surface. From this dust it was found that the SR-stimulated etching had a resolution of ≤100 nm at most.

Shrinking of Spin-On-Glass Films Induced by Synchrotron Radiation and Its Application to Three-Dimensional Microfabrications

Photoinduced etching of siloxane-type spin-on-glass (SOG) by synchrotron radiation (SR) using a SF6/O2 etching gas and a Co contact mask has been investigated. The SOG film was etched by direct SR irradiation similarly to the case of thermally oxidized SiO2. We found that the indirect exposure to SR caused shrinkage of SOG under the Co mask. The shrinkage depth of SOG was attenuated by the thickness of the Co mask, but not eliminated even by a Co mask 350 nm thick, due to the high-energy photons (≥230 eV) being transmitted through the mask. The shrinkage phenomenon was successfully applied in the fabrication of a three-dimensional structure of the SOG thin film on Si(100). Atomic force microscopy observations showed that the surfaces were very smooth both on the completely etched Si area and on the shrunken SOG area. We investigated the mechanism of the shrinkage of SOG by Fourier-transform infrared spectroscopy.

Hydrogen Diffusion and Chemical Reactivity with Water on Nearly Ideally H-terminated Si(100) Surface

A nearly ideally H-terminated condition for a Si(100) 2×1 surface is determined from the dependence of the peak intensity and the linewidth of the coupled monohydride symmetric stretching vibration on the hydrogen exposure and exposure temperature, which has been investigated with infrared reflection absorption spectroscopy (IRRAS) using CoSi2 buried metal layer substrate. Even for nearly ideally H-terminated surfaces, the linewidth significantly changes depending on the hydrogen exposure and the exposure temperature. The concentration of deuterium atoms incorporated in the Si bulk is measured by temperature programmed desorption, and it is concluded that hydrogen diffusion into the subsurface of Si has a significant influence on the linewidth broadening. The chemical reactivity with water on the H-terminated Si surface is also investigated.

Shrinking of spin-on-glass films induced by synchrotron radiation and its application to the 3-D microfabrications

Spin-on-glass (SOG) is an important material in semiconductor integrated circuit fabrication and widely used for flattering of the inter level dielectrics. Typical thickness of SOG films are hundreds of nanometers. It is usually cured with reducing the thickness by heating to high temperatures in the last stage of the processes. In this paper, we have found that the thickness is also reduced by the irradiation of the synchroton radiation (SR) beam with covering the surface by Co mask. We are considering that this phenomenon is applied to three dimensional microfabrications, the degree of the shrinking depends on the thickness of the mask.

Characterization of dipalmitoylphosphatidylcholine (DPPC)/cholesterol Langmuir-Blodgett monolayers by AFM and FT-IR

In this paper we study the interaction of cholesterols with L/sub /spl alpha// phase of DPPC monolayer prepared by the langmuir-Blodgett method and characterization of dipalmitoylphosphatidylcholine (DPPC)/cholesterol Langmuir-Blodgett monolayers by AFM and FT-IR spectra.

Influence of substrate roughness on the formation of self-assembled monolayers (SAM) on Silicon [100]

We have investigated the relationship between surface roughness and morphology and the formation of self-assembled monolayers (SAM). Rough surfaces were prepared by abrading polished Si[100] wafers with SiC paper. Dodecan (-C/sub 12/H/sub 25/) SAM were prepared by refluxing the samples in a 30% dodecene solution in mesithylene. The FTIR spectra of these samples were analyzed with respect to the CH/sub 2/- and CH/sub 3/- peak positions, peak intensities and peak widths.

Design and construction of UVSOR-BL4A2 beam line for nano-structure processing

Abstract We have designed and constructed a new beam line BL4A2 at UVSOR mainly for nano-structure fabrication based on synchrotron radiation stimulated surface photochemical reactions. In order to obtain high-photon flux, we use white ray beam focused with only one mirror. The beam line is connected with ultra-high vacuum scanning tunneling microscope for in-situ atomic scale observations, low energy electron diffraction and Auger electron spectroscope for surface crystal structure characterization, and photo-stimulated surface reaction chamber. In order to monitor the optical properties with atomic scale, a near field optical microscope is planned to be installed.

Nanostructure formation on Si (111) surface assisted by synchrotron radiation illumination: Characterization by scanning tunneling microscopy

Abstract The surface structures after the synchrotron radiation (SR) stimulated removal of native oxide on Si (111) exactly oriented and 4° misoriented surfaces were investigated by scanning tunneling microscopy. The exactly oriented surface showed large regions of atomically flat Si (111)-7×7 structure, and was characterized by the formation of single bilayer steps nicely registered to the underlying crystal structure, clearly different from the disordered step edge obtained by the usual high temperature thermal cleaning. The 4° misoriented sample showed nearly uniformly spaced step bunches and terraces terminated by 7×7 unit cells in both SR assisted and thermal cleanings.