Mass Spectrometry Study of C60 and C60-NiF2 Fluorination with Molecular Fluorine

Abstract

Fluorination of [60]fullerene and [60]fullerene-NiF₂(s) has been studied in situ by Knudsen cell mass spectrometry with admission of molecular fluorine. The fluorination processes were controlled in the temperature range 500 ? 800 K at molecular fluorine pressure 10^?4 ? 10^?5 atm. Temperature, time of fluorination and fluorine pressure were varied during the investigation. It was found that variation of these parameters did not lead to the selective fluorination. It was shown that NiF₂(s) significantly influences the composition of the product mixture: a large amount of nickel difluoride in the system suppresses the fluorination reaction while the presence of a small amount promotes the selective fluorination. C₆₀Fi₁₈ (50% in the gas phase) was produced in our experiments under the following conditions: 20 h, 720 K, P(F₂) = 2 10^?4 atm in the prefluorinated (inner surface covered with NiF₂(s) layer) Ni-reactor. An important point of the study was verification of the thermodynamic equilibrium in the system. It was concluded that the equilibrium is not established in the system under study, and the fluorination is governed by kinetic factors.     

Mass Spectrometry Study of C60 and C60-NiF2 Fluorination with Molecular Fluorine

Fluorination of [60]fullerene and [60]fullerene-NiF₂(s) has been studied in situ by Knudsen cell mass spectrometry with admission of molecular fluorine. The fluorination processes were controlled in the temperature range 500 - 800 K at molecular fluorine pressure 10^-4 - 10^-5 atm. Temperature, time of fluorination and fluorine pressure were varied during the investigation. It was found that variation of these parameters did not lead to the selective fluorination. It was shown that NiF₂(s) significantly influences the composition of the product mixture: a large amount of nickel difluoride in the system suppresses the fluorination reaction while the presence of a small amount promotes the selective fluorination. C₆₀Fi₁₈ (50% in the gas phase) was produced in our experiments under the following conditions: 20 h, 720 K, P(F₂) = 2 10^-4 atm in the prefluorinated (inner surface covered with NiF₂(s) layer) Ni-reactor. An important point of the study was verification of the thermodynamic equilibrium in the system. It was concluded that the equilibrium is not established in the system under study, and the fluorination is governed by kinetic factors.     

离子轰击碳膜形成碳尖端的研究

用CH4、NH3和H2为反应气体,利用等离子体增强热丝化学气相沉积系统在沉积有碳膜的Si衬底上制备了碳尖端.利用原子力显微镜和显微Raman光谱仪对沉积的碳膜表征的结果表明碳膜是非晶碳膜,并且粗糙不平.用扫描电子显微镜对碳尖端表征的结果表明碳尖端的形貌与偏压电流有关,即随着偏压电流的增大,碳尖端的顶角减小,高度增大.由于在碳尖端形成的过程中,既有离子的沉积又有离子的溅射,结合有关等离子沉积和溅射的理论,建立了碳尖端的形成模型,并根据模型分析了实验结果.     

二次离子质谱的深度分辨本领

深度剖析是二次离子质谱在半导体以及各种其它薄膜材料分析中最重要的应用,深度分辨本领是表征其分析能力的重要参数,国际标准化组织（ＩＳＯ）最近 在研究和制定这方面的国际标准。本文在概述了ＳＬＭＳ深度分辨本领影响因素的基础上,推导了δ掺杂层深度分辨函数的解析表达式,讨论了其物理意义,特别是分辨参数的定义。在ＣＡＭＥＣＡ ＩＭＳ ４ｆ仪器上用５．５ｋｅＶ的氧束对Ｓｉ中ＧａＡｓδ掺杂多层膜样品进行了深度剖析,讨论了所得分辨参数及影响因素。结合国外实验室ＩＳＯ巡回测试的结果,对深度分辨参数的定义和评估方法进行了简要评述。     

矩形离子阱质谱仪软件系统的设计

摘要:针对矩形离子阱质谱仪时序控制复杂,控制软件的设计与开发困难的问题.提出一种控制离子阱质谱仪的时序可配置模型和模块化的软件系统结构,并开发出软件系统.在GC-EI-Trap联用仪和LC-ESI-Trap联用仪上应用测试表明软件系统具有实用性和可扩展性.     

用当代飞行时间二次离子质谱分析航天器污染

随着对航天器长寿命和高可靠性的要求日益提高，其污染问题已引起国内外高度重视。在监测污染物总量的基础上，需要有效的分析手段确定污染物的化学成分才能判断污染源。用当代飞行时间二次离子质谱仪器（TOF-SIMS）对我国地面空间环境模拟污染的典型样品进行了探索性实验，结果表明：与国内外现有的检测手段相比，当代TOF-SIMS最适于样品量有限的航天污染物的成份分析；具有高质量分辨的TOF—SIMS，对航天污染物包含的所有元素、同位素和化合物具有指纹鉴别能力；成像分析可解析出污染物形成历史的一些相关信息。TOF-SIMS有望在航天污染系统工程中发展成为一种独具特色的航天污染检测新技术。     

He Ion Bombardment of C70 Fullerene: An FT-IR and Raman Study

C₇₀ fullerene films deposited on a silicon substrate have been bombarded with He⁺ ions at 30 keV at room temperature in vacuum. The structural changes undergone by C₇₀ have been followed by both FT-IR and Raman spectroscopy. The results have been compared to the behavior of C₆₀ fullerene and discussed in an astrochemical context. The main conclusion is that C₇₀, contrary to C₆₀, does not form oligomers at low radiation dose but it is directly and gradually degraded to amorphous carbon (carbon black).     

半导体材料二次离子质谱定量分析中的基体效应

通过对Wilson等人由实验得出的Si，Ge，GaAs，GaP，InP，CdHgTe半导体和SiO2，Si3N4等绝缘基体中70多种注入元素相对灵敏度因子（RSF）值的综合分析，定义logFRS－Ii直线斜率为基体效应因子。发现基体效应因子值随基体平均原子序数的增加而增大，随基体平均电负性值的增大而减小，随基体氧化物生成热的增加而减小。应用本文提出的二次正离子发射理论分析式较好地解释了这些实验现象，并对影响基体效应的其他因素进行了进一步的讨论。     

Efficient Ion Remeasurement Using Broadband Quadrupolar Excitation FTICR Mass Spectrometry

Quadrupolar excitation is achieved over a wide mass range by using repetitive chirp excitation, filtered noise excitation, and high-amplitude, single-frequency excitation for matrix-assisted laser desorption FTICR mass spectrometry. These methods efficiently axialize ions over a wide range of masses in a 4.7 T FTICR spectrometer. Remeasurement efficiencies are >99.5% for broadband repetitive chirp excitation, 99% with filtered white noise, and 99.4% with high-amplitude, single-frequency broad-band quadrupolar excitation. Results indicate that z-axis ejection of ions during detection is the primary mechanism for ion loss during remeasurement experiments. Capacitive coupling of the excitation signal to the trapping plates of the open-ended cylindrical analyzer cell is required for high remeasurement efficiency.     

Applications of Secondary Ion Mass Spectrometry (SIMS) in Materials Science

Secondary Ion Mass Spectrometry (SIMS) is a mature surface analysis technique with a vast range of applications in Materials Science. In this review article the SIMS process is described, the fundamental SIMS equations are derived and the main terminology is explained. The issue of quantification is addressed. The various modes of SIMS analysis including static SIMS, imaging SIMS, depth profiling SIMS and three-dimensional (3D) SIMS are discussed as are specialized analysis strategies such as the imaging of shallow bevels and cross-sections and reverse side analysis. SIMS is shown to be a useful sample preparation tool based on ion beam milling (with SIMS and Scanning Electron Microscopy (SEM) analysis providing end-point detection). The case studies shown illustrate the application of SIMS to several important materials including semiconductors, superconductors, glass, stainless steel, micrometeoroids, solid oxide fuel cell components, museum artifacts, aerospace alloys and biomaterials. Strategies for introducing SIMS into undergraduate education and thus increasing awareness are described. Finally some informed guesses are made as to the future directions of SIMS.     

Electrospray Ion Chromatography-Tandem Mass Spectrometry of Bromate at Sub-ppb Levels in Water

An electrospray ion chromatography-tandem mass spectrometry (IC-MS/MS) method has been developed for the analysis of bromate ions in water. This IC-MS/MS method improves the limit of detection of bromate ions by a factor of 10. The method consists of solid phase extraction with an ion exchange column and elution of the analyte with water/methanol ammonium sulfate eluent on-line with a negative ion electrospray mass spectrometry detection. SPE requires sample pretreatment to remove any major ions that displace bromate, consisting of eliminating SO(4)(2)(-), Cl(-), and HCO(3)(-) ions respectively with barium-form, silver-form, and acid (H(+)-form) exchange resins. The methanolic sulfate eluent permits IC-MS coupling via an electrospray interface. BrO(3)(-) was selected in the first quadrupole (Q1) at two m/z values, 127 and 129, according to the isotope contributions of (79)Br and (81)Br. After fragmentation in the collision cell (second quadrupole, Q2), the third quadrupole (Q3) analyzes the product ions as (M - O)(-), (M - 2O)(-), and (M - 3O)(-). Among the six recordable transitions, four were selected, the other two yielding high background. A lowered resolution raised sensitivity by a factor of up to 3. The limit of quantitation of this method was 0.1 μg/L.     

Computer Simulation of C60 Fullerene Fragmentation by Electron Beam

Abstract

Computer simulation of electron‐induced ionization and fragmentation of free C₆₀ fullerenes, as well as of fullerenes in fullerite films, was carried out. It was found that stable complexes of heavy fullerene's fragments are formed under electron irradiation in fullerite films. These complexes are characterized by different spatial configurations and electron structures and can cause long‐term mechanical stresses.     

Electrical and Optical Properties of Ion Implanted C60

Abstract

Electrical studies (based on conductivity and thermopower) and optical studies have been performed on implanted C₆₀ thin films. In order to obtain the doping effect by charge transfer from alkali atoms to C₆₀ molecules or to large fragments (stemming from degradation effects), the optimization of implantation parameters leads to the values: E = 30keV, D  10¹⁵ions/cm², T=77K. The conductivity [sgrave] and the thennopower S reach the values: σ ? 10²ωcm^?1 and S ? -50μV/K.     

Combined Ion Mobility/Time-of-Flight Mass Spectrometry Study of Electrospray-Generated Ions

A commercially available ion mobility spectrometer was interfaced to a custom-built linear time-of-flight (TOF) mass spectrometer for the purpose of examining electrospray-generated plumes. Ionic species that were separated in the ion mobility spectrometer could be selectively determined with the TOF mass spectrometer. Tetraalkylammonium salts, a peptide, and proteins were examined. Their ion mobility spectra typically comprised a few peaks; some of these mobility-resolved species produced characteristic electrospray ions, while others of lower relative mobility did not. The TOF mass spectra of cytochrome c, injected from the ion mobility spectrometer at an indicated temperature of 90 °C or lower, showed signs that were characteristic of protein-solvent clustering.     

离子束轰击对电子束蒸发制备二氧化钛薄膜应力的影响

在硅基底上用电子束蒸发方法制备了二氧化钛薄膜.通过XRD、AFM和薄膜应力测试仪研究了离子束轰击对薄膜应力的影响规律.结果表明沉积温度为323K、沉积速率为0.2nm·s-1时,二氧化钛薄膜具有较小的应力值,平均应力为48.2MPa.用能量为113eV的离子束轰击300s时,平均应力由72.9MPa的张应力变为16.7MPa的压应力.二氧化钛薄膜的微观结构变化是影响薄膜应力的主要因素.     

Improvements in LC/Electrospray Ion Trap Mass Spectrometry Performance Using an Off-Axis Nebulizer

Charged residues from the electrospray process have been hypothesized to limit the sensitivity and dynamic range of an ion trap mass spectrometry operation. Incorporation of an off-axis nebulizer (positioned 90-95° from the sampling orifice) was found to drastically reduce the detrimental effects caused by the charged particles or droplets compared to typical on-axis nebulization configurations (spraying 10-20° from sampling orifices). The off-axis nebulizer reduced total ion currents that enter the ion trap (through the reduction of charged residues) by a factor of 5-7 while resulting in an increase of analyte [M + H](+) signal by a factor of 6 compared to an on-axis sprayer at flow rates of 20 μL/min. At higher flow rates (e.g., 800 μL/min) these enhancements are more evident. At flows greater than 200 μL/min, off-axis nebulization reduced total ion current that enters the ion trap by a factor of 30 and resulted in a factor of more than 20 increase in [M + H](+) signal relative to on-axis nebulization. Incorporation of the off-axis nebulizer improved the detection limit and precision for determination of dihydroxyvitamin D(3) in plasma compared to on-axis nebulization. The LC/MS/MS detection limits obtained for the off-axis nebulizer on the ion trap was within a factor of 2 from the detection limit determined by the triple quadrupole. The relative standard deviation of the dihydroxyvitamin D(3) determination was less than 8% for both off-axis ion trap and triple-quadrupole determinations.     

Large Molecule Characterization Based upon Individual Ion Detection with Electrospray Ionization-FTICR Mass Spectrometry

We report a new method for mass spectrometric measurements of high-molecular-weight species based on the summation of sequential Fourier transform ion cyclotron resonance (FTICR) spectra of individual multiply charged ions. This approach produces statistically useful mass spectra for large multiply charged molecular species formed by electrospray ionization and circumvents conventional limitations upon achievable resolving power and precision for high-molecular-weight species which arise due to Coulombic constraints. For very large molecules with tens to thousands of charges each, the total number of charges required to define the charge-state distribution, and thus provide accurate mass information, greatly exceeds the useful charge capacity of the FTICR cell. As trapped ion populations approach or exceed this capacity, FTICR performance degrades due to large frequency shifts, peak coalescence phenomena, and rapid loss of ion packet coherence, which effectively precludes high-resolution and precision measurements for molecules above ～80-kDa size for a 7-T magnetic field strength. The present approach is based on the summation of many spectra having moderate populations of individual ions and relies on sensitivity sufficient for individual ion detection. While the number of trapped ions contributing to each mass spectrum may generally be insufficient to define the isotopic or charge-state distributions (and thus produce accurate information on the molecular weight distribution in a conventional fashion), the present data processing and summation approach suppresses the noise component (as well as smaller signals) that would otherwise be problematic. Importantly, this approach circumvents natural limitations for very high molecular weight species due to Coulombic interactions and thus provides a basis for much greater resolution and mass measurement accuracy than otherwise possible. This paper presents the details of this approach and its demonstration for the 66-kDa protein bovine serum albumin (where the conventional approach is also feasible) and discusses important aspects of the data manipulation.     

显像管残余气体分析及离子轰击研究

显像管中的残余气体是影响显像管质量和寿命的重要因素,通过四极质谱残余气体分析系统,可以对显像管中的残余气体进行有效的分析,对带消气剂的真空器件,本底要考虑扣除消气剂作用的影响.在此基础上可以进行残余气体离子轰击的计算机模拟研究,并对显像管电子枪进行优化设计.