Influence of Surface Morphology and Substrate on Thermal Stability and Desorption Behavior of Octanethiol Self-Assembled Monolayers

Eisuke Ito,강훈구,Hiromi Ito,Masahiko Hara,노재근 한국진공학회 2012 한국진공학회 학술발표회초록집 Vol.2012 No.8

Comparative Study of Tetrahydrothiophene and Thiophene Self-Assembled Monolayers on Au(111): Structure and Molecular Orientation

Eisuke Ito,Masahiko Hara,Kaname Kanai,Yukio Ouchi,Kazuhiko Seki,노재근 대한화학회 2009 Bulletin of the Korean Chemical Society Vol.30 No.8

Surface structure and molecular orientation of self-assembled monolayers (SAMs) formed by the spontaneous adsorption of tetrahydrothiophene (THT) and thiophene (TP) on Au(111) were investigated by means of scanning tunneling microscopy (STM) and carbon K-edge near edge X-ray absorption fine structure (NEXAFS) spectroscopy. STM imaging revealed that THT SAMs have a commensurate (3 × 2√3) structure containing structural defects in ordered domains, whereas TP SAMs are composed of randomly adsorbed domains and paired molecular row domains that can be described as an incommensurate packing structure. The NEXAFS spectroscopy study showed that the average tilt angle of the aliphatic THT ring and π-conjugated TP ring in the SAMs were calculated to be about 30o and 40o, respectively, from the surface normal. It was also observed that the π* transition peak in the NEXAFS spectrum of the TP SAMs is very weak, suggesting that a strong interaction between π-electrons and the Au surface arises during the self-assembly of TP molecules. In this study, we have clearly demonstrated that the surface structure and adsorption orientation of organic SAMs on Au(111) are strongly influenced by whether the cyclic ring is saturated or unsaturated.

Influence of Surface Morphology and Substrate on Thermal Stability and Desorption Behavior of Octanethiol Self-Assembled Monolayers: Cu, Ag, and Au

Ito, Eisuke,Ito, Hiromi,Kang, Hungu,Hayashi, Tomohiro,Hara, Masahiko,Noh, Jaegeun American Chemical Society 2012 JOURNAL OF PHYSICAL CHEMISTRY C - Vol.116 No.33

<P>The formation and thermal desorption behaviors of octanethiol (OT) SAMs on single crystalline Au(111) and polycrystalline Au, Ag, and Cu substrates were examined by X-ray photoelectron microscopy (XPS), thermal desorption spectroscopy (TDS), and contact angle (CA) measurements. XPS and CA measurements revealed that the adsorption of OT molecules on these metals led to the formation of chemisorbed self-assembled monolayers (SAMs). Three main desorption fragments for dioctyl disulfide (C8SSC8<SUP>+</SUP>, dimer), octanethiolate (C8S<SUP>+</SUP>), and octanethiol (C8SH<SUP>+</SUP>) were monitored using TDS to understand the effects of surface morphology and the nature of metal substrates on the thermal desorption behavior of alkanethiols. TDS measurements showed that a sharp dimer peak with a very strong intensity on single crystalline Au(111) surface was dominantly observed at 370 K, whereas a broad peak on the polycrystalline Au surface was observed at 405 K. On the other hand, desorption behaviors of octanethiolates and octanethiols were quite similar. We concluded that substrate morphology strongly affects the dimerization process of alkanethiolates on Au surfaces. We also found that desorption intensity of the dimer is in the order of Au ≫ Ag > Cu, suggesting that the dimerization process occurs efficiently when the sulfur–metal bond has a more covalent character (Au) rather than an ionic character (Ag and Cu). The relative desorption intensity of the octanethiolates to the octanethiols follows the order of bond strength, Cu > Au > Ag. Alkanethiolates may be a dominant desorption product as metal–sulfur bonds become stronger. In this study, we clearly demonstrate that the thermal stability and desorption behaviors of alkanethiol SAMs are strongly influenced by the surface morphologies of metal substrates, bonding character of the sulfurs, the bond strength of metal–sulfur, and van der Waals interactions. Our results provide new insights into understanding the thermal stability and desorption behaviors of alkanethiols on Au, Ag, and Cu surfaces.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2012/jpccck.2012.116.issue-33/jp3041204/production/images/medium/jp-2012-041204_0008.gif'></P>

Comparative Study of Tetrahydrothiophene and Thiophene Self Assembled Monolayers on Au(111): Structure and Molecular Orientation

Ito, Eisuke,Hara, Masahiko,Kanai, Kaname,Ouchi, Yukio,Seki, Kazuhiko,Noh, Jaegeun Korean Chemical Society 2009 Bulletin of the Korean Chemical Society Vol.30 No.8

Surface structure and molecular orientation of self-assembled monolayers (SAMs) formed by the spontaneous adsorption of tetrahydrothiophene (THT) and thiophene (TP) on Au(111) were investigated by means of scanning tunneling microscopy (STM) and carbon K-edge near edge X-ray absorption fine structure (NEXAFS) spectroscopy. STM imaging revealed that THT SAMs have a commensurate (3 ${\times}\;2\sqrt[]{3}$) structure containing structural defects in ordered domains, whereas TP SAMs are composed of randomly adsorbed domains and paired molecular row domains that can be described as an incommensurate packing structure. The NEXAFS spectroscopy study showed that the average tilt angle of the aliphatic THT ring and $\pi$-conjugated TP ring in the SAMs were calculated to be about $30^o\;and\;40^o$, respectively, from the surface normal. It was also observed that the $\pi$* transition peak in the NEXAFS spectrum of the TP SAMs is very weak, suggesting that a strong interaction between $\pi$-electrons and the Au surface arises during the self-assembly of TP molecules. In this study, we have clearly demonstrated that the surface structure and adsorption orientation of organic SAMs on Au(111) are strongly influenced by whether the cyclic ring is saturated or unsaturated.

Surface Potential Change Depending on Molecular Orientation of Hexadecanethiol Self-Assembled Monolayers on Au(111)

Ito, Eisuke,Arai, Takayuki,Hara, Masahiko,Noh, Jaegeun Korean Chemical Society 2009 Bulletin of the Korean Chemical Society Vol.30 No.6

Surface potential and growth processes of hexadecanethiol (HDT) self-assembled monolayers (SAMs) on Au(111) surfaces were examined by Kelvin probe method and scanning tunneling microscopy. It was found that surface potential strongly depends on surface structure of HDT SAMs. The surface potential shift for the striped phase of HDT SAMs chemisorbed on Au(111) surface was +0.45 eV, which was nearly the same as that of the flat-lying hexadecane layer physisorbed on Au(111) surface. This result indicates that the interfacial dipole layer induced by adsorption of alkyl chains is a main contributor to the surface potential change. In the densely-packed HDT monolayer, further change of the surface potential was observed, suggesting that the dipole moment of the alkanethiol molecules is an origin of the surface potential change. These results indicate that the work function of a metal electrode can be modified by controlling the molecular orientation of an adsorbed molecule.

Surface Potential Change Depending on Molecular Orientation of Hexadecanethiol Self-Assembled Monolayers on Au(111)

Eisuke Ito,Takayuki Arai,Masahiko Hara,노재근 대한화학회 2009 Bulletin of the Korean Chemical Society Vol.30 No.6

Surface potential and growth processes of hexadecanethiol (HDT) self-assembled monolayers (SAMs) on Au(111) surfaces were examined by Kelvin probe method and scanning tunneling microscopy. It was found that surface potential strongly depends on surface structure of HDT SAMs. The surface potential shift for the striped phase of HDT SAMs chemisorbed on Au(111) surface was +0.45 eV, which was nearly the same as that of the flat-lying hexadecane layer physisorbed on Au(111) surface. This result indicates that the interfacial dipole layer induced by adsorption of alkyl chains is a main contributor to the surface potential change. In the densely-packed HDT monolayer, further change of the surface potential was observed, suggesting that the dipole moment of the alkanethiol molecules is an origin of the surface potential change. These results indicate that the work function of a metal electrode can be modified by controlling the molecular orientation of an adsorbed molecule.

Nutritional status of calcium and other bone-related nutrients in Japanese type 2 diabetes patients

Eisuke Tomastu,Eri Ninomiya,Mizuho Ando,Izumi Hiratsuka,Yasumasa Yoshino,Sahoko Sekiguchi-Ueda,Megumi Shibata,Akemi Ito 대한골다공증학회 2016 Osteoporosis and Sarcopenia Vol.2 No.2

Objective: Traditional Japanese food appears to be healthy but contains a small amount of milk products. Type 2 diabetes (T2DM) patients commonly reduce their energy intake to control their blood glucose levels. However, nutritional guidance for diabetes does not emphasize calcium (Ca) consumption. The aim of this study is to estimate the nutritional status of Ca and other nutrients, which affect bone and Ca metabolism, in T2DM patients. Methods: This observational study was conducted with Japanese T2DM patients (n ¼ 96; M/F ¼ 50/46; age: 61.6 ± 10.1 years). We estimated nutrient intake using a simple food frequency questionnaire. Results: Median total energy intake was 1750 kcal/day (1440e1970). Their median daily intake of Ca, vitamin D, and vitamin K was 451 mg (336e560), 10.2 mg (8.5e12), and 206 mg (84e261), respectively. Only 17.7% of the study subjects were found to take more than 600 mg/day of Ca. Protein and salt intake was 78 (64e90) and 10.6 (9.3e12.2) g/day, respectively. Male subjects had more salt, less Ca and vitamin K than female. Daily Ca intake was positively associated with total energy, protein, and lipid intake but not with carbohydrates. Vitamin D intake correlated only with protein intake. Conclusion: The daily Ca intake of Japanese T2DM patients appears to be insufficient and could depend on protein and lipid intake. Additionally, these patients should have specific recommendations to ensure sufficient intake of Ca with protein and lipid during energy restriction. © 2016 The Korean Society of Osteoporosis. Publishing services by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Control the Au(111) Work Function by Substituted Aromatic Thiol Self-Assembled Monolayers

강훈구,Eisuke Ito,Youichi Okabayashi,Masahiko Hara,노재근 한국진공학회 2012 한국진공학회 학술발표회초록집 Vol.2012 No.2

Effect of Solution Concentration on the Formation of Ordered Domains in Pentachlorobenzenethiol Self-Assembled Monolayers on Au(111)

Kang, Hungu,Ito, Eisuke,Hayashi, Tomohiro,Hara, Masahiko,Noh, Jaegeun American Scientific Publishers 2016 Journal of nanoscience and nanotechnology Vol.16 No.6

<P>The surface structures of self-assembled monolayers (SAMs) formed by the adsorption of pentachlorobenzenethiol (PCBT) molecules on Au(111) as a function of solution concentration were examined by means of scanning tunneling microscopy (STM) to understand the effect of concentration on the formation of ordered domains. STM imaging revealed that PCBT SAMs formed in a 0.01 or 1 mM ethanol solution at room temperature for 20 min contained small ordered domains in the range of several to 20 nm(2) and disordered phases, while PCBT SAMs formed in a 0.1 mM ethanol solution were composed of long-range ordered domains in the range of 20 to 50 nm(2), which can be assigned as a (4 x root 3) R45 degrees packing structure. Interestingly, the bright aggregated domains stacked by pi-pi interactions between PCBT rings were usually observed around boundary regions of ordered domains. In addition, X-ray photoelectron spectroscopy measurements revealed that ordered PCBT SAMs on Au(111) were formed via the chemical interactions between the sulfur atom of PCBT and gold surface. Our results obtained here will be very useful in understanding the formation and structure of PCBT SAMs on gold surfaces.</P>

Formation of Ordered 4-Fluorobenzenethiol Self-Assembled Monolayers on Au(111) from Vapor Phase Deposition

Kang, Hungu,Ito, Eisuke,Hara, Masahiko,Noh, Jaegeun American Scientific Publishers 2016 Journal of nanoscience and nanotechnology Vol.16 No.3

<P>Self-assembled monolayers (SAMs) were formed by the spontaneous adsorption of 4fluorobenzenethiol (4-FBT) on Au(111) using both solution and ambient-pressure vapor deposition methods at room temperature. The surface structure and thermal desorption properties of 4-FBT SAMs were examined by scanning tunneling microscopy (STM) and thermal desorption spectroscopy (TDS). STM imaging showed that 4-FBT SAMs formed in solution at room temperature mainly contained disordered phase with gold adatom islands, while those formed by ambientpressure vapor deposition had well-ordered phase, which can be described as a (2x2 root 13)R45 degrees structure. In addition, thermal desorption spectroscopy (TDS) measurements showed that strong desorption peak for parent mass fragment (m/z = 128, FC6H5SH+) for 4-FBT SAMs on Au(111) was observed at 460 K, as a result of hydrogen abstract reaction of chemisorbed thiolates during desorption.</P>