Yuichi Utsumi

Synchrotron radiation excited Si epitaxial growth using disilane gas source molecular beam system

Silicon photoepitaxy excited by synchrotron radiation (SR) has been observed for the first time. The epitaxial growth is observed even at lower than a 400 °C substrate temperature. The surface of the as‐grown film exhibits a 2×1 reconstruction reflection high‐energy electron diffraction pattern, indicating two‐dimensional growth. At lower than 600 °C, the SR‐irradiation growth rate is larger than that of thermal growth. This result suggests that SR irradiation enhances the dynamic surface reactions, such as desorption of hydrogen and surface migration of adsorbed species.

Photostimulated evaporation of SiO2 films by synchrotron radiation

Irradiation by synchrotron radiation on SiO2 films induces continuous removal of this material at elevated temperatures. The photostimulated evaporation rate for a thermally grown SiO2 film increases steeply with temperature giving an activation energy of 0.7 eV. The experimental results indicate that photon‐induced bond breaking assists decomposition and thermal desorption of the film. Applications to microfabrication of a line‐and‐space pattern and low‐temperature cleaning of Si(100) surface are demonstrated.

Large area and wide dimension range x-ray lithography for lithographite, galvanoformung, and abformung process using energy variable synchrotron radiation

We developed an x-ray lithography system for the “lithographite, galvanoformung, and abformung” process using synchrotron radiation at the NewSUBARU facility of the University of Hyogo, Hyogo, Japan. The x-ray lithography system can utilize two different energy regions: one is a high-energy region: from 2 to 12 keV, and the other is a low-energy region from 1 to 2 keV. Each energy region can be selected in accordance with the size and shape of the desired microstructures. Large-area patterning across an A4-size area was successfully performed with a highly uniform pattern thickness. Furthermore, high-aspect-ratio patterning using a high-x-ray-energy region was also achieved using this x-ray lithography system.

Large-Area X-ray Lithography System for LIGA Process Operating in Wide Energy Range of Synchrotron Radiation

We developed a new X-ray lithography system for the lithographite, galvanoformung and abformung process (LIGA process) using synchrotron radiation at the NewSUBARU facility of the University of Hyogo. The X-ray lithography system can utilize two different energy regions: one is a high-energy region: from 2 keV to 12 keV, and the other is a low-energy region from 1 to 2 keV. Each energy region can be selected in accordance with the size and shape of the desired microstructures. Large-area patterning across an A4-size area was successfully performed with a highly uniform pattern thickness. Furthermore, high-aspect-ratio patterning using a high-X-ray-energy region was also achieved using this X-ray lithography system.

Synchrotron radiation stimulated semiconductor processes: Chemical vapor deposition and etching

A synchrotron radiation beamline and reaction chamber were constructed for the study of synchrotron radiation excited photochemical reactions, especially for their application to semiconductor processes. Characteristics of this experiment and experimental results with chemical vapor deposition and etching in this beamline are described. The potential of this new application is discussed.

Abiotic synthesis of amino acids by x-ray irradiation of simple inorganic gases

1–2 keV x-ray irradiation was carried out using a synchrotron radiation source on simulated primitive earth environment: a gas mixture of carbon monoxide, nitrogen, and water at atmospheric pressure. High-speed liquid chromatography of the hydrolyzed product solution detected amino acids. The amount of amino acids increased with the total energy absorbed by the gas molecules, and the antipodal optical isomers were generated in almost equal quantities. These imply that the precursors for amino acids were produced through x-ray-induced photolysis of inorganic molecules followed by recombination and polymerization into bio-organic compounds. These results suggest that prebiotic formation of amino acids is possible in primitive earth atmosphere by x ray as well as cosmic ray.

Reaction kinetics in synchrotron‐radiation‐excited Si epitaxy with disilane. I. Atomic layer epitaxy

We investigated the mechanism of silicon crystal growth mediated by a surface photochemical reaction. The growth process consists of reactive sticking of disilane (Si2H6) onto a partially hydrogen covered surface followed by the photon‐stimulated desorption of hydrogen atoms and consequent regeneration of dangling bonds. The saturation coverage of Si admolecules resulting from self‐limiting chemisorption of disilane was found to be 0.42 monolayer (ML), and the ejection of H+ and H+2 ions was observed by time‐of‐flight mass spectroscopy. Hydrogen removal by the purely electronic process differs from thermal desorption, however, in that not all of the hydrogen is removed. Analysis of film growth by repetition of the cycle of disilane exposure, evacuation, and synchrotron radiation irradiation showed that the onset temperature of thermal growth (350 °C) is the same as that of H2 desorption from the dihydride species. Below 350 °C a digital growth of 0.18 ML/cycle occurs over a wide range of gas exposure time...

Proposal of a new microreactor for vertical chemical operation

The authors proposed and fabricated a new microreactor stack which would be able to achieve a vertical fluid flow operation for the environment analysis, postgenome analysis, gene diagnosis, and screening of useful materials for medicine manufacture. This reactor is characterized as a simple structure with new aspects of the vertical fluid transportation using a proposed fluid filter with array of micro-through-bores. The deep x-ray lithography process using synchrotron radiation was used for the fabrication of the fluid filter. The feasibility of vertical liquid transportation was investigated using computational fluid dynamics analysis. It is indicated that the vertical liquid transportation is possible using the proposed fluid filter, and high efficiency mixing of liquid was also expected during transportation through the fluid filter. It was confirmed that the fluid flow velocity through the filter can be controlled by varying the load pressure around several kilopascals. A rapid enzyme reaction was s...

Crystallinity Improvement by Synchrotron Radiation Irradiation in Low-Temperature Si Epitaxial Growth Using Disilane

Si films were grown on Ge substrates by Synchrotron Radiation (SR)-excited crystal growth around the low substrate temperature limit for epitaxial growth. From the observation of Reflective High Energy Electron Diffraction and Raman scattering spectra, it was found that the crystallinity of the Si film was clearly improved by SR irradiation. From the temperature dependence of the growth rate, it was confirmed that SR irradiation greatly enhances the growth rate in the lower temperature region below 500°C.

Surface-enhanced Raman spectroscopy using a coffee-ring-type three-dimensional silver nanostructure

We demonstrated surface-enhanced Raman spectroscopy using a coffee-ring-type three-dimensional silver nanostructure (Ag3D). Ag3D has high activity for surface-enhanced Raman scattering (SERS). We fabricated Ag3D using convective self-assembly to form a ‘coffee-ring’ structure that consisted of a mixed solution of silver particles and polystyrene latex beads. The mechanism of the formation of Ag3D is described by the competition among a radial flow, a Marangoni recirculating flow, DVLO interactions and sedimentation. Using Ag3D, measurements of a trace amount of 4,4′-bipyridine (4bpy) in aqueous solution were performed, and typical spectra of 4bpy were observed within 1 min of dropping 4bpy. By optimizing the Ag3D preparation conditions, we could observe the characteristic enhanced Raman spectrum of 1 nM 4bpy solution. In addition, we succeeded in observing chloride activation, which increased the intensity of the Raman spectra by a factor of two to three on addition of sodium chloride to Ag3D. SERS measurements using Ag3D were stable even with passing time, whereas the peak intensity drastically dropped within a few minutes in the case with silver nanoparticles only.