Band bending at the Si(1 1 1)–SiO2 interface induced by low-energy ion bombardment

Experiments employing photoreflectance spectroscopy have uncovered band bending due to electrically active defects at the Si(1 1 1)–SiO₂ interface after sub-keV Ar⁺ ion bombardment. The band bending of about 0.5 eV resembles that for Si(1 0 0)–SiO₂, and both interfaces exhibit two kinetic regimes for the evolution of band bending upon annealing due to defects healing. The healing takes place about an order of magnitude more quickly at the (1 1 1) interface, however, probably because of less fully saturated bonding and higher compressive stress.     

A new cytotoxic limonoid from Odontadenia macrantha from the Suriname rainforest

Bioassay‐guided fractionation of the methanol extract of Odontadenia macrantha afforded a new limonoid, odontadenin A (1) and two known triterpenoids, lupeol (2) and α‐amyrin (3). The structure of 1 was established on the basis of 1D and 2D NMR and high‐resolution fast atom bombardment mass spectrometric data. The new compound was found to possess moderate cytotoxicity against A2780, the ovarian cancer cell line. Copyright © 2003 John Wiley & Sons, Ltd.     

On the effect of low-energy ion bombardment on polystyrene and polymethylmethacrylate etch rates in rf plasmas

The effect of low-energy ion bombardment on CD₄/O₂ and CF₃X (X=F, Cl, Br) plasma etching has been assessed by applying controlled rf bias voltages on polystyrene (PS) and polymethylmethacrylate (PMMA) samples. In both cases ion bombardment has been found to have a chemical effect. In the case of CF₄/O₂ discharges, ion bombardment has been found to change the relative etching efficiency of different mixtures. In the case of CF₃X plasmas, ion bombardment has been found to alter PMMA and PS etch rates in a different way. In particular, the ratios between CF₄ and CF₃X (X=Cl, Br) etch rates of PS have been found to decrease with increasing bias voltage. This effect has been tentatively attributed to an ion bombardment-induced enhancement of the reaction between the aromatic ring and halogen molecules formed in CF₃Cl and CF₃Br discharges.     

有机锗氨基酸酯类系列化合物的快原子轰击质谱规律

为增强有机锗化合物的生物活性，合成了一系列有机锗氨基酸酯类倍半氧化物，并重点研究了它们的快原子轰击质谱（ＦＡＢＭＳ）。研究结果表明：该系列化合物的各碎片离子峰与其组成及结构均有很好的对应关系及很强的规律性     

Comparison of EI and metastable atom bombardment ionization for the identification of polyurethane thermal degradation products

Polyurethanes are widely used in the manufacture of commercial products such as foams and paints. During combustion, these polymers can generate isocyanates, which induce adverse health effects. Polymer pyrolysis (Py) hyphenated with mass spectrometry (MS) allows the investigation of polymer thermal degradation over time/temperature. A diphenylmethanediisocyanate (MDI) polyurethane foam was analyzed with electron ionization (EI) and metastable atom bombardment (MAB) ionization at a pyrolysis temperature of 400 °C. The recently introduced MAB ionization source uses discrete energy stored in metastable atoms of gases to ionize the analytes. This characteristic allows modulation of the ionization energy by simply changing the ionization gas. The extensive fragmentation of molecular ions observed using EI 70 eV is not totally eliminated with EI 10 eV. However, only molecular ions are observed with MAB using N₂ as the ionization gas. Temperature gradients were used to separate the products generated during the thermal degradation of a 1,6-hexamethylenediisocyanate (HDI) polyurethane paint. The analysis of mass spectra was facilitated owing to a selective desorption of pyrolysis products. Furthermore, changing the MAB ionization gas allows elucidation of the structure of the pyrolysis products by controlling the extent of their fragmentation. During these experiments, isocyanic acid, methyleneisocyanate, ethyleneisocyanate, propylisocyanate and butylisocyanate were detected.     

MeV Si ions bombardments effects on thermoelectric properties of SiO2/SiO2+Ge nanolayers

The performance of the thermoelectric materials and devices is shown by a dimensionless figure of merit, ZT=S²σT/K, where S is the Seebeck coefficient, σ is the electrical conductivity, T is the absolute temperature and K is the thermal conductivity. ZT can be increased by increasing S, increasing σ, or decreasing K. We have prepared the thermoelectric generator device of SiO₂/SiO₂+Ge multilayer superlattice films using the ion beam assisted deposition (IBAD). The 5 MeV Si ion bombardments have been performed using the AAMU Pelletron ion beam accelerator at five different fluences to make quantum structures (nanodots and/or nanoclusters) in the multilayer superlattice thin films to decrease the cross plane thermal conductivity, increase the cross plane Seebeck coefficient and cross plane electrical conductivity. To characterize the thermoelectric generator devices before and after MeV Si ions bombardments at the different fluences we have measured the cross-plane Seebeck coefficient, the cross-plane electrical conductivity, and the cross-plane thermal conductivity, Raman spectra to get some information about the sample structure and bond structures among the used elements in the superlattice thin film systems.     

Observation of thermoluminescence induced by fission fragments

Abstract

Thermoluminescence induced in CaF₂ powder by fission fragments emanating from a uranium foil bombarded by fast neutrons has been measured as a function of neutron fluence. A linear relationship between the glow produced and the fast neutron fluence between 5 × 10¹⁰ and 6.5 × 10¹¹ n/cm² has been obtained, thus establishing the feasibility of the use of this method for fast-neutron dosimetry. A limitation of the method is that, if the fissile foil is not separated from the phosphor after irradiation, the TL produced by the α-disintegration of ²³⁸U may eventually mask the fission-induced TL.     

快原子轰击离子化质谱研究酚类化合物抗氧化作用

为了建立简便、快速筛选高效、低毒的新型抗氧化药物的方法,本研究采用快原子轰击离子化质谱( FAB-MS)对酚类化合物抗氧化作用强弱进行了研究。考察了基质、轰击时间和样本浓度对FAB-MS 谱中分子离子(M+·)相对强度的影响,研究了黄酮类化合物在FAB-MS谱中的I(M+·)/I([M+H]+)比值与其抗氧化活性的相关性。对12种酚类化合物的抗氧化活性进行了预测与评价,并与硫代巴比妥酸法( TBA)检测的脂质过氧化抑制率进行比较,验证 FAB-MS 方法的可靠性。结果表明,由 FAB-MS 获得的 I ( M+·)/I([ M+H]+)比值能较好地反映酚类化合物抗氧化作用的强弱,可以作为抗氧化剂的体外筛选或预测方法,有助于加速新型抗氧化药物的发现。     

Characterization of gem-difluoropropargyl synthons through HF loss from protonated molecules in methane chemical ionization mass spectra

Electron impact and methane chemical ionization mass spectra were obtained following gas chromatography/mass spectrometry for several gem-difluoropropargyl compounds, which had been synthesized as potential intermediates for synthesis of gem-difluoromethylene-containing C-3 acetylenes. EI spectra were variable with respect to the presentation of molecular ions, depending on substituent functional groups present. Methane-CI spectra were characterized by loss of 19 mass units from molecular weight with all compounds examined. These [M − 19]⁺ ions often presented as base peaks of the CI spectra, and were more reliably present and abundant than [M + 1]⁺ ions for these compounds. These ions could have been formed by elimination of HF from the protonated molecules under conditions of methane chemical ionization.     

Formulation for XPS spectral change of oxides by ion bombardment as a function of sputtering time

XPS measurement revealed that the original state of TiO₂ was changed to Ti₂O₃ and TiO by ion bombardment. TiO₂ decreased and Ti₂O₃ increased at the initial stage. TiO increased at a later stage than Ti₂O₃. Each of them saturated after enough sputtering time.A formulation was proposed in order to explain the change of XPS spectra for oxides as a function of ion sputtering time. This formulation was based on reaction equations that contain two reduction processes (from TiO₂ to Ti₂O₃ and from Ti₂O₃ to TiO), and sputtering effects. Using four fitting parameters (two reduction coefficients, sputtering yield and information depth), the present formula was fitted to the experimental results. The fitting results agree satisfactorily with the experimental results. The calculation shows that the reduction coefficient from TiO₂ to Ti₂O₃ is about ten times larger than that from Ti₂O₃ to TiO. This calculation predicts that surface composition of an oxide that is changed by ion bombardment will reach a different value depending on its bulk composition. Moreover, the present formulation can determine the chemical states of compounds changed by ion bombardment.