Faculty Profiles - SAITO, Nagahiro

Papers - SAITO, Nagahiro

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Reversible nanochemical conversion

Sugimura H., Lee S., Saito N., Takai O.

Journal of Vacuum Science and Technology B: Microelectronics and Nanometer Structures Vol. 22 ( 6 ) 2004.11

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Vacuum Science and Technology B: Microelectronics and Nanometer Structures

Local chemical conversion of an organic surface that consists of a surface-confined monolayer is demonstrated in a reversible manner based on electrochemical reactions induced beneath a conductive probe tip of an atomic force microscope. The monolayer was prepared by a self-assembling technique from the precursor, p-aminophenyltrimethoxysilane. The chemical state of this self-assembled monolayer was regulated by probe-tip scanning with a bias voltage applied between the tip and substrate. With a positive substrate bias scanning, the monolayer surface was oxidized to be nitroso-terminated. With a negative bias scanning, this monolayer could be amino-terminated. These oxidation and reduction processes could be reversibly repeated. © 2004 American Vacuum Society.

DOI： 10.1116/1.1825020

Contribution of primary chemical bonding states of amorphous carbon nitride to hardness

Saito N., Ohta R., Lee K.H., Kobayashi Y., Okazaki S., Inoue Y., Sugimura H., Takai O.

Electrochemical and Solid-State Letters Vol. 7 ( 8 ) 2004.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Electrochemical and Solid-State Letters

The hardness of amorphous carbon nitride (CN) was investigated by solid-state nuclear magnetic resonance (NMR) spectroscopy and Fourier transform infrared spectroscopy (FTIR). The results of NMR measurements showed that sp2 and/or sp hybrid orbitals controlled the hardness of amorphous-CN films, which had been determined by nanoindentation tests. The intensity of the C-H and CN stretching modes observed in the FTIR spectra was the weakest in the hardest sample. The decreases of -CH3 and -CH2 groups indicated that the amorphous network had increased. The sp2 hybrid orbital forms a cross-linker which plays an important role in improving of the hardness of the film. © 2004 The Electrochemical Society. All rights reserved.

DOI： 10.1149/1.1763791

Organosilane self-assembled monolayers directly linked to the diamond surfaces

Ohta R., Saito N., Inoue Y., Sugimura H., Takai O.

Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films Vol. 22 ( 5 ) page： 2005 - 2009 2004.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films

The organosilane self-assembled monolayers (SAM) which were linked to diamond surfaces were investigated. It was observed that the SAM were prepared from p-aminophenyltrimethoxysilane (H2N(CH)6Si(OCH 3)3, APhS) on diamond substrates and were irradiated by vacuum ultraviolet (VUV) light. It was also observed that the thickness of the SiOx layer was increased by the APhS-SAM formations and VUV irradiations. It was found that the APhS-SAM/ nano-scale SiOx/ diamond could be used for diamond-bio hybridized devices.

DOI： 10.1116/1.1776184

Fabrication of piezoelectric self-assembled fluorinated polyether monolayer on hydrogen-terminated Si(111) surface.

Okano, T; Inari, H; Saito, N; Takai, O

ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY Vol. 228 page： U471 - U471 2004.8

Photochemical reaction of organosilane self-assembled monolayer as studied by scanning probe microscopy

Sugimura H., Saito N., Ishida Y., Ikeda I., Hayashi K., Takai O.

Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films Vol. 22 ( 4 ) page： 1428 - 1432 2004.7

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films

The study of a patterning process of an alkylsilane self-assembled monolayer (SAM) using vacuum ultraviolet (VUV) light at 172 nm, by charaterizing the VUV-irradiated SAM surfaces through lateral force microscopy (LFM) and Kelvin force microscopy (KFM), was presented. The relative frictional forces and surface potentials of the VUV-irradiated regions at various irradiation dose rates were measured by LFM and KFM. VUV-irrated SAMs showed particularly lower surface potentials than the other SAM surface potentials than the other SAM surfaces with different dose rates, at a certain dose rate of 10-15 J/cm 2. It was observed that LFM and KFM measurements were promising in order to probe chemistries on organic thin films proceeding.

DOI： 10.1116/1.1764818

Exploration of the chemical bonding forms of alkoxy-type organic monolayers directly attached to silicon Open Access

Saito N., Lee S., Maeda N., Ohta R., Sugimura H., Takai O.

Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films Vol. 22 ( 4 ) page： 1425 - 1427 2004.7

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films

The preparation of alkoxy-type organic monolayers on hydrogen-terminated silicon from 1-undecanol (UN), 1-nonanol (NO), 1-heptanol (HP) and 4-phenylphenenol (PP) was discussed. The characterization of these monolayers was based on X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR). A SiOx peak was clearly observed for the HP, NO and PP monolayers. It was shown that the generation of SiO x in the PP monolayer was due to steric hindrance of the aromatic rings. It was found that the the -CH2-region in the FT-IR spectra showed that the shorter alkyl chains promoted the formation of gauche conformers in the monolayers.

DOI： 10.1116/1.1759353

Generation of amino-terminated surfaces by chemical lithography using atomic force microscopy

Saito, N; Maeda, N; Sugimura, H; Takai, O

LANGMUIR Vol. 20 ( 13 ) page： 5182 - 5184 2004.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Langmuir

Self-assembled monolayers (SAMs) covered with nitroso end groups were reduced using an atomic force microscope. As the bias voltage become more negative (beyond -4 V), the surface potential of the scanned area become closer to that of the amino-terminated SAM. Following this chemical change, however, no change in topographic features was detected, implying retained stability of the underlying SAM layer. We then released carboxylate-modified polystyrene (PS) spheres into a pH 4 solution containing the sample. Subsequent imaging with atomic force microscopy (AFM) revealed that these PS spheres were only selectively immobilized on the regions that were originally scanned at -6 V to form amino termination. In summary, using AFM set to a specific voltage, we were able to selectively generate micropatterned regions of the SAM with amino termination.

DOI： 10.1021/la0353428

UV Raman spectroscopic probing into nitrogen-doped hydrogenated amorphous carbon

Ohta R., Saito N., Okazaki S., Inoue Y., Sugimura H., Takai O.

Thin Solid Films Vol. 457 ( 1 ) page： 128 - 132 2004.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Thin Solid Films

From the viewpoint of hardness, chemical bonding states of nitrogen-doped hydrogenated amorphous carbon film were characterized by Ultra violet (UV) Raman spectroscopy and Fourier transform infrared (FT-IR) spectroscopy. UV Raman spectra revealed that disorder of the structure in nitrogen-doped hydrogenated amorphous carbon was promoted by applying higher bias voltages in the preparation. FT-IR spectra showed that N-H bonds decreased and sp 3C-sp3N bonds increased with the increase of the bias voltages. The content of sp3C-sp3N bonds was maximized at the bias voltage of -800 V. We found out a guarantee that the content of sp 3C-sp3N bonds against bias voltages correlated with the hardness obtained by nanoindentation test. The structural disorder and the increase of sp3C-sp3N bonds are possible source of the hardness in the case of nitrogen-doped hydrogenated amorphous carbon. © 2003 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tsf.2003.12.049

Electrodeposition of CuInTe<inf>2</inf> film from an acidic solution

Ishizaki T., Saito N., Fuwa A.

Surface and Coatings Technology Vol. 182 ( 2-3 ) page： 156 - 160 2004.4

Language：English Publishing type：Research paper (scientific journal) Publisher：Surface and Coatings Technology

Copper-indium-telluride films were electrochemically deposited from solutions containing CuCl2, InCl3, TeO2 and HCl. Although a flat and smooth film with closely stoichiometric composition was deposited at -660 mV vs. Ag/AgCl at 303 K from a solution of 2.5×10-4 mol dm-3 CuCl2, 1.0×10-2 mol dm-3 InCl3, 5.0×10-4 mol dm-3 TeO2 and 0.1 mol dm-3 HCl, a polycrystalline CuInTe2 film was not obtained. Increasing the temperature from 303 to 363 K allowed the deposition at lower overpotential of a polycrystalline CuInTe2 film with closely stoichiometric composition and increased indium content. The band gap of the polycrystalline CuInTe2 film electrodeposited at 363 K at -660 mV was 0.98 eV. © 2003 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.surfcoat.2003.07.004

Surface potential microscopy for chemistry of organic self-assembled monolayers in small domains

Sugimura H., Saito N., Maeda N., Ikeda I., Ishida Y., Hayashi K., Hong L., Takai O.

Nanotechnology Vol. 15 ( 2 ) 2004.2

Language：English Publishing type：Research paper (scientific journal) Publisher：Nanotechnology

Micropatterning techniques using vacuum ultra-violet light at 172 nm in wavelength and an ultra-violet laser at 244 nm were applied to organosilane self-assembled monolayers (SAMs) formed on Si substrates covered with a 2 nm thick oxide layer. These SAMs were prepared from precursors, that is, octadecyltrimethoxysilane (ODS) or p-chloromethylphenyltrimethoxysilane (CMPhS). Polar functional groups such as COOH were generated through photochemical oxidation of the SAMs. Furthermore, the SAMs were Simultaneously etched and finally removed from the photoirradiated area. Surface potentials of the photoirradiated areas at various irradiation dose rates were measured by Kelvin-probe force microscopy (KFM) using the unirradiated area on each of the photopatterned samples as a reference. Changes in the surface chemical composition of the SAMs could be clearly and sensitively measured by KFM through the difference in surface potential between the irradiated and unirradiated SAMs.

DOI： 10.1088/0957-4484/15/2/015

Oxygen gas assisted electron beam lithography in organosilane self-assembled monolayers

Yamaguchi M., Saito N., Takai O.

Digest of Papers - Microprocesses and Nanotechnology 2004 page： 198 - 199 2004

Microstructured π-conjugated organic monolayer covalently attached to silicon

Saito N., Hayashi K., Sugimura H., Takai O.

Langmuir Vol. 19 ( 26 ) page： 10632 - 10634 2003.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Langmuir

A phenylacetylene (PA) monolayer was prepared on hydrogen-terminated silicon. Through vacuum ultraviolet (VUV) lithography, micropatterned PA-monolayer/SiO2 samples were subsequently fabricated. The surface potential and electrical conductivity of the microstructured PA monolayers were examined by Kelvin probe force microscopy (KPFM) and conductive atomic force microscopy (C-AFM), respectively. KPFM measurements showed that the PA-monolayer surface regions were negatively charged. C-AFM measurements demonstrated that, in the microdomains, the PA-monolayer regions had a higher conductivity than the SiO2 regions fabricated by VUV lithography. This is the first report of electronic property images of a monolayer directly attached to silicon being demonstrated in microregions.

DOI： 10.1021/la034187u

Origin of N 1s spectrum in amorphous carbon nitride obtained by X-ray photoelectron spectroscopy

Ohta R., Lee K.H., Saito N., Inoue Y., Sugimura H., Takai O.

Thin Solid Films Vol. 434 ( 1-2 ) page： 296 - 302 2003.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Thin Solid Films

This paper focuses on determining a reasonable peak assignment for the N 1s spectrum of amorphous carbon nitride (a-CN) measured by X-ray photoelectron spectroscopy (XPS). Unfortunately, several peaks of a-CN have not been identified, that is, there has yet to be any shared understanding of their chemical bonding states. We investigated this by monitoring changes in spectra before and after vacuum ultraviolet (VUV) irradiation, thus obtaining information about the changes of chemical bonds. The observed changes were discussed based on the chemical shifts of components of a-CN determined from ab-initio molecular orbital (MO) calculations. We have proposed the following peak assignment for N 1s. The peaks located at approximately (1) 397.6, (2) 398.2, (3) 399.0, (4) 400.0, (5) 400.9 and (6) 401.9 eV were assigned to the chemical bonding states of (1) β-C 3 N 4 , (2) pyridine, (3) formonitril, (4) methylmethyleneamine, (5) pyrido[2,1,6-de]quinolizine, and (6) a nitroso group. This assignment did not agree with oft-quoted ones. However, only this peak assignment provides a reasonable interpretation for the changes we observed in a-CN introduced by VUV irradiation, and allows us to understand the chemical bonding states of a-CN film. © 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0040-6090(03)00457-7

Selective immobilization of functional organic molecules onto a microtemplate fabricated using an amino-terminated self-assembled monolayer

Hayashi K., Hozumi A., Saito N., Sugimura H., Takai O.

Surface Science Vol. 532-535 page： 1072 - 1078 2003.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Surface Science

Micropatterned amino-terminated self-assembled monolayers (SAMs) were applied as templates to promote selective chemical reactions in minute spatial scale. The surface charge properties of the SAMs were investigated through zeta-potential measurements conducted in solutions of various pH values. These SAMs were then utilized in order to selectively immobilize carboxylate-modified fluorescence spheres (CM-FluoSpheres) on the sample surface. Each SAM was uniformly formed onto a clean Si(1 0 0) substrate covered with a thin oxide layer (SiO2) by chemical vapor deposition using n-(6-aminohexyl)aminopropyltrimethoxysilane [AHAPS:H2N(CH2)6NH(CH2)3S i(OCH3)3] as a precursor. Through a photolithographic technique employing vacuum ultraviolet light at 172 nm, microstructures consisting of AHAPS-SAM and SiO2 were fabricated. The micropatterned AHAPS-SAM/SiO2 samples were then immersed in a solution dispersed with CM-FluoSpheres. The solution was adjusted to pH = 2, 6 or 8. At pH = 8, the CM-FluoSpheres did not adsorb on the micropatterned AHAPS-SAM/SiO2. At pH = 2 and 6, the CM-FluoSpheres adsorbed specifically on the regions covered with AHAPS-SAM. In particular, the adsorption behavior at pH = 6 was highly selective. These results were predictable considering the isoelectric points of AHAPS-SAM and SiO2, that is, pH = 7.5 and 2.0, respectively. At pH = 6, the SiO2 surface was negatively charged while the AHAPS-SAM surface was positive. Since the CM-FluoSpheres, which are terminated with carboxyl groups, were negatively charged at this pH value, the SiO2 and AHAPS-SAM surfaces had repulsive and attractive interactions, respectively, with the CM-FluoSpheres. These opposite electrostatic interactions were the origin of the complete selectivity achieved in the adsorption. © 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0039-6028(03)00211-5

Chemical resistivity of self-assembled monolayer covalently attached to silicon substrate to hydrofluoric acid and ammonium fluoride

Saito N., Youda S., Hayashi K., Sugimura H., Takai O.

Surface Science Vol. 532-535 page： 970 - 975 2003.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Surface Science

Self-assembled monolayers (SAMs) were prepared on hydrogen-terminated silicon substrates through chemical vapor deposition using 1-hexadecene (HD) as a precursor. The HD-SAMs prepared in an atmosphere under a reduced pressure (≈50 Pa) showed better chemical resistivities to hydrofluoric acid and ammonium fluoride (NH4F) solutions than that of an organosilane SAM formed on oxide-covered silicon substrates. The surface covered with the HD-SAM was micro-patterned by vacuum ultraviolet photolithography and consequently divided into two areas terminated with HD-SAM or silicon dioxide. This micro-patterned sample was immersed in a 40 vol.% NH4F aqueous solution. Surface images obtained by an optical microscopy clearly show that the micro-patterns of HD-SAM/silicon dioxide were successfully transferred into the silicon substrate. © 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0039-6028(03)00158-4

Micropatterned 1-alkene self-assembled monolayer on hydrogen-terminated silicon by vacuum ultraviolet lithography

Saito N., Kadoya Y., Hayashi K., Sugimura H., Takai O.

Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers Vol. 42 ( 4 B ) page： 2534 - 2537 2003.4

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers

We fabricated micropatterned 1-alkene self-assembled monolayers (SAMs) on p-type Si(111). 1-Alkene SAMs were prepared from 1-hexadecene (HD) and 1-octadecene (OD) through reduced pressure chemical vapor deposition. Those SAMs were micropatterned by vacuum ultraviolet (VUV) light lithography. The 1-alkene SAMs irradiated for 30 min were measured by X-ray photoelectron spectroscopy (XPS). The sample surface irradiated for 30 min was covered with shorter alkyl chains with carboxyl end groups on SiOx since the O and OH radicals produced by VUV irradiation react with alkyl chains. We measured surface potential images of those micro-patterned SAMs with Kelvin probe force microscopy (KPFM). The surface potentials of HD- and OD-SAMs were +60 and +90mV against irradiated regions. The regions of 1-alkene SAMs show higher surface potential than those of irradiated regions due to the presence of carboxyl end groups. The regions of HD- and OD-SAMs showed positive surface potentials against those of irradiated regions. This irradiated region was confirmed to be a carboxyl-terminated surface with short alkyl chains based on XPS analysis. The carboxyl groups are negatively charged, so the surface potential of the irradiated regions is negative against the HD- and OD-SAM regions.

DOI： 10.1143/jjap.42.2534

Principle in imaging contrast in scanning electron microscopy for binary microstructures composed of organosilane self-assembled monolayers

Saito N., Wu Y., Hayashi K., Sugimura H., Takai O.

Journal of Physical Chemistry B Vol. 107 ( 3 ) page： 664 - 667 2003.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Physical Chemistry B

Field-emission electron microscopy (FE-SEM) was applied to observe coplanar microstructures composed of two different types of organosilane self-assembled monolayers (SAMs). These binary microstructures were prepared on silicon substrates covered with native oxide by a lithographic technique. Four types of organosilane precursors, they are n-octadecyltrimethoxysilane (ODS), heptadecafluoro-1,1,2,2-tetrahydro-decyl-1-trimethoxysilane (a type of fluoroalkylsilane, FAS), n-(6-aminohexyl)aminopropyltrimethoxysilane (AHAPS), and 4-(chloromethyl)phenyltrimethoxysilane (CMPhS), were used in this study. Micropatterns composed of the SAMs were clearly imaged by FE-SEM at low acceleration voltages, around 0.6 kV. The brightness order of the SAMs in FE-SEM was ODS > AHAPS > CMPhS > FAS. Through ab initio molecular orbital calculations, the origin of this FE-SEM contrast was ascribed to the electron affinity between the SAMs, which governed the FE-SEM image contrast. It has been successfully demonstrated that FE-SEM could provide us chemical information on organic films with a monomolecular thickness on a solid support.

DOI： 10.1021/jp021362r

Imaging micropatterned organosilane self-assembled monolayers on silicon by means of scanning electron microscopy and Kelvin probe force microscopy

Wu Y., Hayashi K., Saito N., Sugimura H., Takai O.

Surface and Interface Analysis Vol. 35 ( 1 ) page： 94 - 98 2003.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Surface and Interface Analysis

Field-emission scanning electron microscopy (FE-SEM) and surface potentiometry based on scanning probe microscopy, i.e. Kelvin probe force microscopy (KFM), have been applied to study microstructures consisting of organosilane self-assembled monolayers (SAMs) terminated with -CH3 or -CF3 groups. Onto cleaned Si substrates covered with a thin oxide layer of 2 nm thick, SAMs were formed by chemical vapour deposition using n-octadecyltrimethoxysilane (CH3(CH2)17Si(OCH3)3, ODS) or fluoroalkylsilane (CF3(CF2)7(CH2)2Si (OCH3)3, FAS) as a precursor. Through a photolithographic technique employing vacuum ultraviolet light at 172 nm, microstructures composed of ODS, FAS or both were fabricated. Micropatterns of the SAMs on SiO2/Si substrates were clearly imaged by FE-SEM at an acceleration voltage of the electron beam below 1 kV, but image contrasts became faint with an increase in the acceleration voltage. At a voltage of 5 kV there was almost no detectable contrast. An FE-SEM image of the ODS-FAS microstructure acquired at an acceleration voltage of 0.8 kV clearly demonstrated that the region covered with ODS was brighter and thus, emitted secondary electrons more efficiently than the region covered with FAS. Furthermore, as indicated in a KFM image, the region covered with FAS had a surface potential ∼180 mV lower than that of the region covered with ODS. The origin of these image contrasts between ODS- and FAS-SAMs was the large difference in electronic states between ODS and FAS owing to the electron negativity of fluorine atoms.

DOI： 10.1002/sia.1501

Scanning probe surface modification: Chemical conversion of terminal functional groups on organosilane self-assembled monolayers

Sugimura, H; Saito, N; Hayashi, K; Maeda, N; Takai, O

SCANNING TUNNELING MICROSCOPY/SPECTROSCOPY AND RELATED TECHNIQUES Vol. 696 page： 150 - 157 2003

Alkyl self-assembled monolayer prepared on hydrogen-terminated Si(111) through reduced pressure chemical vapor deposition: Chemical resistivities in HF and NH<inf>4</inf>F solutions

Saito N., Youda S., Hayashi K., Sugimura H., Takai O.

Chemistry Letters ( 12 ) page： 1194 - 1195 2002.12

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