Riichiro Ohta

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

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-C3N4, (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.

Organosilane self-assembled monolayers directly linked to the diamond surfaces

An amino-terminated self-assembled monolayer (SAM) was prepared from p-aminophenyltrimethoxysilane (H2N(CH)6Si(OCH3)3,APhS) on diamond substrates irradiated by vacuum ultraviolet (VUV) light (wavelength: 172nm) through chemical vapor deposition. Furthermore, the APhS-SAM was irradiated by VUV light in air. After the VUV irradiation, only one layer of siloxane (SiOx) was left as a result of the selective decomposition of organic compounds. APhS-SAM was reprepared on the SiOx surface. The evidence as to the respective processes was clearly obtained by x-ray photoelectron spectroscopy (XPS) and water contact angle measurements. Based on the chemical bonding states analysis, APhS-SAMs were confirmed to be directly linked to the diamond substrates and SiOx layers with bonding types of Si–O–C and Si–O–Si, respectively. The compositions obtained by XPS measurement indicate that the thickness of the SiOx layer was increased gradually by repeating the APhS-SAM formations and VUV irradiations in this order. Finally, we are successful in controlling the nano-scale thickness of the SiOx layer, which is the interface between APhS-SAMs and diamond substrates.An amino-terminated self-assembled monolayer (SAM) was prepared from p-aminophenyltrimethoxysilane (H2N(CH)6Si(OCH3)3,APhS) on diamond substrates irradiated by vacuum ultraviolet (VUV) light (wavelength: 172nm) through chemical vapor deposition. Furthermore, the APhS-SAM was irradiated by VUV light in air. After the VUV irradiation, only one layer of siloxane (SiOx) was left as a result of the selective decomposition of organic compounds. APhS-SAM was reprepared on the SiOx surface. The evidence as to the respective processes was clearly obtained by x-ray photoelectron spectroscopy (XPS) and water contact angle measurements. Based on the chemical bonding states analysis, APhS-SAMs were confirmed to be directly linked to the diamond substrates and SiOx layers with bonding types of Si–O–C and Si–O–Si, respectively. The compositions obtained by XPS measurement indicate that the thickness of the SiOx layer was increased gradually by repeating the APhS-SAM formations and VUV irradiations in this order. Finally...

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

Alkoxy-type organic monolayers on hydrogen-terminated silicon were prepared from 1-undecanol (UN), 1-nonanol (NO), 1-heptanol (HP), and 4-phenylphenenol (PP). These monolayers were characterized based on x-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR). XPS spectra showed that the lowest amount of SiOx oxide on the sample of the UN monolayer. On the other hand, a SiOx peak was clearly observed for the HP, NO, and PP monolayers. The generation of SiOx in the PP monolayer may have been due to steric hindrance of the aromatic rings. The–CH2–region in the FT-IR spectra showed that shorter alkyl chains promoted the formation of gauche conformers in the monolayer. This increase of gauche conformers was determined to have caused the generation of SiOx in the alkyl monolayers.

Contribution of Primary Chemical Bonding States of Amorphous Carbon Nitride to Hardness

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 sp 2 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 -CH 3 and -CH 2 groups indicated that the amorphous network had increased. The sp 2 hybrid orbital forms a cross-linker which plays an important role in improving of the hardness of the film.