Low energy Si+, SiCH5+, or C+ beam injections to silicon substrates during chemical vapor deposition with dimethylsilane.

We found that the atomic-concentration-ratio of carbon to silicon (C/Si ratio) in silicon carbide (SiC) films formed by thermal chemical vapor deposition (CVD) was much greater than 1 when the source gas for CVD was dimethylsilane (DMS). Thus, we tried to change carbon-inclusion levels in the film by injecting some ion beams into a depositing SiC film during the CVD process with DMS. Three ion beams, i.e., Si+, SiCH5+, or C+ ions were injected to depositing SiC films. The energy of Si+, SiCH5+, and C+ ions was 110 eV. The temperature of the substrate was 800 °C. X-ray diffraction of the deposited films showed that 3C-SiC was included in all three samples. X-ray photoelectron spectroscopy (XPS) showed that the C/Si ratio of the obtained SiC film increased significantly following the Si+ or C+ ion beam irradiations. The XPS measurements also showed that the C/Si ratio of the SiC film obtained by injecting SiCH5+ beam during thermal CVD with DMS was lower than that of the SiC film formed by thermal CVD with DMS alone.

Low-energy Ar+ ion-beam-induced chemical vapor deposition of silicon dioxide films using tetraethyl orthosilicate.

This study was conducted to determine whether the simultaneous injections of Ar+ ions and tetraethyl orthosilicate (TEOS) to a substrate are able to fabricate a film on the substrate. The Ar+ ion energy was 100 eV. After the injections, we found a film deposited on the substrate. Following the analyses of the film with X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy, it was found that the deposited film was silicon dioxide (SiO2). We conclude that the low-energy Ar+ ion-beam-induced deposition method using TEOS is useful for the growth of SiO2 films.

Low-energy Ar+ and N+ ion beam induced chemical vapor deposition using hexamethyldisilazane for the formation of nitrogen containing SiC and carbon containing SiN films.

We proposed an experimental methodology for producing films on substrates with an ion beam induced chemical vapor deposition (IBICVD) method using hexamethyldisilazane (HMDS) as a source material. In this study, both HMDS and ion beam were simultaneously injected onto a Si substrate. We selected Ar+ and N+ as the ion beam. The energy of the ion beam was 101 eV. Temperature of the Si substrate was set at 540 °C. After the experiments, films were found to be deposited on the substrates. The films were then analyzed by Fourier transform infrared (FTIR) spectroscopy, stylus profilometer, X-ray diffraction, atomic force microscopy, and X-ray photoelectron spectroscopy (XPS). The FTIR and XPS results showed that silicon carbide films containing small amount of nitrogen were formed when Ar+ ions were injected in conjunction with HMDS. On the other hand, in the cases of N+ ion beam irradiation, silicon nitride films involving small amount of carbon were formed. It was noted that no film deposition was observed when HMDS alone was supplied to the substrates without any ion beam injections.

Identification of fragment ions produced by the decomposition of tetramethyltin and the production of low-energy Sn+ ion beam.

Tetramethyltin was decomposed in an ion source and the fragment ions produced were identified using a low-energy mass-selected ion beam machine. Dominant fragment ions were found to be H+, CH2+, and Sn+. Subsequently, fragment ions were mass-selected. The mass spectrum of the selected ions indicated that only a single peak appeared at the mass number of 120 u, being suggestive of the presence of 120Sn+ ions. The ion energy was set at the range of 20-100 eV. The Sn+ ion beam was irradiated to a Si substrate, and a film was then found deposited on the substrate after the ion beam irradiation. An X-ray diffraction measurement showed that the film obtained was metallic Sn. Then, the Sn+ ion beam was irradiated to a quartz crystal microbalance substrate. We found that most of the irradiated Sn+ ions were adhered to the substrate, at the ion energy levels of 25 and 58 eV, producing the Sn film, whereas a 107 eV Sn+ beam caused a significant proportion of Sn atoms in the film to detach from the substrate, probably due to sputtering.

Mechanism for odd-electron anion generation of dihydroxybenzoic acid isomers in matrix-assisted laser desorption/ionization mass spectrometry with density functional theory calculations.

RATIONALE: Proton and radical are transferred between matrices and matrix and analyte in matrix-assisted laser desorption/ionization (MALDI) and these transfers drive ionization of analytes. The odd-electron anion [M-2H]•- was generated in dihydroxybenzoic acids (DHBs) and the ion abundance of the 2,5-DHB was the highest among six DHB isomers. We were interested in the mechanism of the ion generation of the odd-electron anion. METHODS: The observed [M-2H]•- and [M-3H]- ions, which were generated with the hydrogen radical removed from the phenolic hydroxyl groups (OH) in DHB isomers, were analyzed using negative-ion MALDI-MS. The enthalpy for ion generation and their stable structures were calculated using the density functional theory (DFT) calculation program Gaussian 09 with the B3LYP functional and the 6-31+G(d) basis set. RESULTS: The number of observed [M-2H]•- and [M-3H]- ions of the DHB isomers was dependent on the positions of the phenolic OH groups in the DHB isomers because the carboxy group interacts with the ortho OH group due to neighboring group participation, as confirmed from the stable structures of the [M-2H]•- anions calculated with the Gaussian 09 program. The DHB isomers were placed into three categories according to the number of the ions. CONCLUSIONS: Odd-electron anions ([M-2H]•- ) and [M-2H• -H]- ([M-3H]- ) ions were generated from DHB isomers due to removal of the hydrogen radical from the phenolic groups. The enthalpy for ion generation revealed that ion formation proceeds via a two-step pathway through the [M-M]- ion as an intermediate. © 2016 The Authors. Rapid Communications in Mass Spectrometry Published by John Wiley & Sons Ltd.

N-Cα Bond Cleavage of Zinc-Polyhistidine Complexes in Electron Transfer Dissociation Mediated by Zwitterion Formation: Experimental Evidence and Theoretical Analysis of the Utah-Washington Model.

Electron capture dissociation (ECD) and electron transfer dissociation (ETD) of gas-phase ions are widely used for peptide/protein sequencing by mass spectrometry. To understand the general mechanism of ECD/ETD of peptides, we focused on the ETD fragmentation of metal-peptide complexes in the absence of remote protons. Since Zn(2+) strongly binds to neutral histidine residues in peptides, Zn(2+)-polyhistidine complexation does not generate any remote protons. However, in the absence of remote protons, electron transfer to the Zn(2+)-polyhistidine complex induced the N-Cα bond cleavage. The formation pathway for the ETD products was investigated by density functional theory calculations. The calculations showed that the charge-reduced zinc-peptide radical, [M + Zn](•+), can exist in the low-energy zwitterionic amide π* states, which underwent homolytic N-Cα bond dissociation. The homolytic cleavage resulted in the donation of an electron from the N-Cα bond to the nitrogen atom, producing an iminoenol c' anion. The counterpart z(•) radical contained a radical site on the α-carbon atom. The iminoenol c' anion then abstracted a proton to presumably form the more stable amide c' fragment. The current experimental and computational joint study strongly suggested that the N-Cα bond cleavage occurred through the aminoketyl radical-anion formation for Zn(2+)-polyhistidine complexes in ETD.

Influence of metal-peptide complexation on fragmentation and inter-fragment hydrogen migration in electron transfer dissociation.

The use of metal salts in electrospray ionization (ESI) of peptides increases the charge state of peptide ions, facilitating electron transfer dissociation (ETD) in tandem mass spectrometry. In the present study, K(+) and Ca(2+) were used as charge carriers to form multiply-charged metal-peptide complexes. ETD of the potassium- or calcium-peptide complex was initiated by transfer of an electron to a proton remote from the metal cation, and a c'-z• fragment complex, in which the c' and z• fragments were linked together via a metal cation coordinating with several amino acid residues, was formed. The presence of a metal cation in the precursor for ETD increased the lifetime of the c'-z• fragment complex, eventually generating c• and z' fragments through inter-fragment hydrogen migration. The degree of hydrogen migration was dependent on the location of the metal cation in the metal-peptide complex, but was not reconciled with conformation of the precursor ion obtained by molecular mechanics simulation. In contrast, the location of the metal cation in the intermediate suggested by the ETD spectrum was in agreement with the conformation of "proton-removed" precursors, indicating that the charge reduction of precursor ions by ETD induces conformational rearrangement during the fragmentation process.

Effects of the silicon core structures on the hole mobility of star-shaped oligothiophenes.

Star-shaped compounds with three or four oligothiophene units linked by an organosilicon core were prepared and their hole-transport capabilities were studied. A top-contact type thin film transistor (TFT) with a vapour-deposited film of tris[(ethylterthiophenyl)dimethylsilyl]methylsilane (3T(3)Si(4)) showed field-effect mobility (µ(FET)) of 4.4 × 10(-5) cm(2) V(-1) s(-1), while the device with the carbon centred analogue tris[(ethylterthiophenyl)dimethylsilyl]methane (3T(3)Si(3)C) showed no TFT activity. Intrinsic intramolecular hole mobility of 3T(3)Si(4) and 3T(3)Si(3)C was determined by time-resolved microwave conductivity measurements to be 8 × 10(-2) and 2 × 10(-2) cm(2) V(-1) s(-1), respectively, arising from higher degree of σ-π interaction in 3T(3)Si(4). To know more about the effects of the organosilicon core structures on the intermolecular hole mobility, we calculated internal reorganization energies for hole transfer at the (U)B3LYP/6-311+G(d,p)//(U)B3LYP/6-31G(d) level, which suggested smoother intermolecular charge transfer in the silicon derivative than the carbon and germanium analogues. Star-shaped compounds with quarterthiophene units behave in a different manner from the terthiophene derivatives and tris[(ethylquarterthiophenyl)dimethylsilyl]methane (4T(3)Si(3)C) showed higher TFT mobility of µ(FET) = 1.2 × 10(-3) cm(2) V(-1) s(-1) than its silicon analogue (4T(3)Si(4): µ(FET) = 5.4 × 10(-4) cm(2) V(-1) s(-1)). This is probably due to the more condensed packing of 4T(3)Si(3)C in the film, arising from the shorter Si-C bonding. Compounds with four terthiophene units were also prepared and tetrakis[(ethylterthiophenyl)-dimethylsilyl]silane (3T(4)Si(5)) showed the mobility of µ(FET) = 2.0 × 10(-4) cm(2) V(-1) s(-1), higher than that of 3T(3)Si(4), indicating the potential of tetrakis(oligothiophenyl) compounds as the TFT materials. Tetrakis[(ethylterthiophenyl)dimethylsilyl]germane (3T(4)Si(4)Ge) was less thermally stable and could not be processed to a film by vapour-deposition, but was found to be TFT active in the spin-coated film, although the mobility was rather low (µ(FET) = 7.7 × 10(-7) cm(2) V(-1) s(-1)).

Distinct features of matrix-assisted 6 microm infrared laser desorption/ionization mass spectrometry in biomolecular analysis.

Midinfrared-matrix-assisted laser desorption/ionization mass spectrometry (mid-IR-MALDI MS) with a laser emission in the 6 microm wavelength range, which utilizes energy absorption at the C=O double-bond stretch region, was applied to biomolecular analysis. The softness of IR-MALDI MS was evident in the negative ion mode yielding clean mass spectra of [M - H](-) ions for acidic biomolecules with sulfate, phosphate, or carboxylate groups, resulting in better sensitivity than ultraviolet (UV)-MALDI MS. There was no substantial loss of sialic acid due to the prompt fragmentation occurring in IR-MALDI of sialylated glycoconjugates such as gangliosides. Furthermore, the advantage of the low photon energy of IR is that, for the first time, intact protonated molecules of S-nitrosylated peptides can be detected by MALDI MS. In the analysis of redox-sensitive molecules including methylene blue and riboflavin, reductive hydrogenation was minimal, suggesting few hydrogen radicals to have formed in the plume, in contrast to UV-MALDI. In conjunction with a potent new matrix, oxamide, requiring smaller laser fluence, distinct features of the 6 microm IR wavelength range are anticipated to remove one of the limitations of MALDI MS for biomolecular analysis.

Preparation and conformational analysis of C-glycosyl beta(2)- and beta/beta(2)-peptides.

Ten C-glycosyl beta(2)- and beta/beta(2)-peptides with three to eight amino acid residues have been prepared. Solution and solid-phase peptide syntheses were employed to assemble beta(2)-amino acids in which C-glycosylic substituents are attached to the C-2 position of beta-amino acids. Conformational analysis of the C-glycosyl beta(2)-peptides using NMR and CD spectra indicates that the tripeptide can form a helical secondary structure. Besides, helix directions of the C-glycosyl beta/beta(2)-peptides are governed by the configuration at the alpha-carbon of the peptide backbone that originates from the stereocenter of the C-glycosyl beta(2)-amino acids.

Experimental and theoretical study on gas-phase ion/molecule reactions of silver trimer cation, Ag3+, with 12-crown-4.

The reaction mechanisms of silver trimer cation, Ag3+, with 12-crown-4 (12C4) were studied experimentally and theoretically. Using a cylindrical ion trap time-of-flight mass spectrometer, gas-phase ion/molecule reactions of Ag3+ with 12C4 were observed. Metal-ligand complexes of [Ag(12C4)]+, [Ag3(12C4)]+ and [Ag3(12C4)2]+, and of [Ag(12C4)2]+ and [Ag3(12C4)3]+, were observed as the reaction intermediates and terminal products, respectively. The formations of the [Ag12C4]+ and [Ag(12C4)2]+ complexes indicated that the neutral dimer (Ag2) had been eliminated from the trimer cation. From the results of ab initio calculations at the HF/LanL2DZ level of theory and the experiments, it is suggested that three 12C4 molecules can attach to Ag3+ through consecutive reactions and that neutral Ag2 can be easily eliminated from [Ag3(12C4)]+.

Solvents inducing oxidation of hydroxylamines.

Hydroxylamines gradually undergo oxidation to their oximes on being dissolved in organic solvent (e.g. methanol). This phenomenon was followed by (1)H-NMR and liquid chromatography-mass spectrometry (LC-MS). The oxidation rate was estimated from the peak area observed on the mass chromatogram at the protonated molecule or fragment ion on LC-atmospheric pressure chemical ionization (APCI)-MS. The results showed that the oxidation rate of hydroxylamines depended on the solvent type.