飞行时间二次离子质谱在生物材料和生命科学中的应用(上)

飞行时间二次离子质谱（TOF-SIMS）成为材料表面化学分析越来越重要的手段,随着分析仪器性能的不断提高,尤其是团簇离子源的发明和使用,使得TOF-SIMS在生物材料和生命科学研究中能够更接近常规性地被使用。它可以用来鉴定表面的生物分子,并且描述生物分子在单细胞表面和内部及组织切片上的二维分布。TOF-SIMS的主要测试功能包括表面质谱,化学成像及深度剖析3种。本综述（分上、下两篇）围绕这3项仪器功能,简单综述近20年内TOF-SIMS在生物材料和生命科学中的应用。本篇主要讨论应用质谱功能表征生物医学有机高分子材料表面化学特性及在表面的生物分子,包括氨基酸、多酞、蛋白质、核苷酸、DNA、磷脂膜及多糖。重点举例介绍的科学问题包括蛋白质吸附、生物材料表面化学改性以及生物降解高分子药物释放机理。     

PM2.5-铵的单颗粒表征

在北京空气重污染期间,以石英膜采集的PM2.5为样本,采用飞行时间二次离子质谱(TOF-SIMS)结合质量高分辨模式与正负离子成像模式表征了PM2.5-铵。实验观察到了硫酸氢铵(NH₄HSO₄)单颗粒物,未见硝酸铵或氯化铵。实验验证了正、负离子成像之间微米级偏差的人工校正方法,同时阐明了TOF-SIMS表征PM2.5水溶性无机盐等成分的特点、优势和应用潜力。     

铜合金表面元素的飞行时间二次离子质谱微区原位分析

铜合金中含有Pb、Sn、Zn、Ni等元素,其分布和相对含量对铜合金的性能具有重要影响。本工作采用飞行时间二次离子质谱（TOF-SIMS）法对铜合金标准样品GBW02137和GBW02140的表面进行了微区原位分析;采用束斑直径约5 μm的一次离子束轰击500 μm×500 μm区域内的混合固体合金样品,实现了Cu、Pb、Ni、Sn和Zn元素的表面成像,并测量了各元素在铜合金样品表面的分布情况;利用标样校准法对GBW02137、GBW02140中的⁶⁴Zn/¹²⁰Sn、²⁰⁸Pb/¹²⁰Sn值进行相对含量分析。实验结果表明：TOF-SIMS法可用于铜合金中Cu、Pb、Ni、Sn和Zn等元素的表面成像和相对含量测定;采用标样校准法进行相对含量分析时,测得的⁶⁴Zn/¹²⁰Sn相对误差小于5.1%,RSD优于2.5%,²⁰⁸Pb/¹²⁰Sn的测量相对误差较大,接近27%,但其RSD仍低于5%。     

基于LabVIEW面向对象的TOF-SIMS仪器控制软件

飞行时间二次离子质谱仪（TOF-SIMS）作为一种重要的表面分析工具被广泛应用,本研究为其开发了一套仪器控制软件。基于LabVIEW面向对象方法建立了仪器部件控制类库,结合消息驱动机制完成了软件结构设计。所开发的软件能够实现对离子光学系统、真空系统和三维样品台等仪器子系统的部件控制。应用该软件控制仪器进行了锆石样品的TOF-SIMS实验,完成了锆石样品谱图的获取,结果表明,该软件能够满足仪器对控制软件的要求。此外,软件结构具有良好的可重用性和可扩展性,以及硬件更改对软件影响小等优点,该软件设计方法可用于类似仪器控制软件的开发。     

磺隆类除草剂的飞行时间二次离子质谱研究

采用飞行时间二次离子质谱(TOF-SIMS)分析6种磺隆类除草剂,获得了它们的正离子和负离子谱图.数据显示,这类除草剂在TOF-SIMS谱图中均出现准分子离子峰和特征碎片离子峰.裂分机理讨论进一步表明,这类除草剂的典型碎片化发生在化合物结构中酰胺基团的C-N键之间,可获得较大质量片段的碎片化离子以及准分子离子的主要原因...     

二次离子质谱的一次离子光学系统

二次离子质谱仪作为一种强大的表面分析工具,在表面分析领域有着非常广泛的应用。本文报道了一种用于二次离子质谱仪的一次离子光学系统,它可以对电子轰击电离源产生的一次离子进行有效的加速与聚焦,形成稳定的、能量在0～5kV范围内连续可调的离子束流。同时,该光学系统可以在两种聚焦模式下工作,产生两种不同性能的离子束流。实验结果表明,采用电子轰击电离源作为一次离子源的条件,该离子光学系统能够将离子束聚焦至直径为20μm的束斑,其一次离子束流密度最高可达到503.2mA/cm2,可以实现对一般样品(如材料或生物样品)的表面成分分析。     

TOF-SIMS样品光学成像系统设计

本研究为飞行时间二次离子质谱仪（TOF-SIMS）设计了一种具有高空间分辨率的样品光学成像系统。该系统由一种改进的Schwarzschild双反射系统、45°反射镜、变焦镜头及CCD图像传感器构成。采用ZEMAX软件对传统Schwarzschild模型进行计算和改进,得出系统优化参数并进行仿真验证。仿真结果表明：系统最佳的成像分辨率达1 μm,极限分辨率为0.4 μm,RMS半径小于艾里斑直径,波像差满足瑞利判据,成像质量良好。     

宋代黑釉茶盏油滴的飞行时间二次离子质谱表征

本研究利用飞行时间二次离子质谱(TOF-SIMS)表征典型黑釉茶盏釉面上银色反光斑纹,即华北油滴。高分辨质谱测定油滴的主要成分是氧化铁,由显微拉曼光谱确定其矿物形式是赤铁矿(α-Fe₂O₃)。二次离子质谱(SIMS)离子成像进一步揭示：该赤铁矿呈六方柱晶体(约2～10μm);近百余枚这样的晶体自组织分散排列构成类似雨滴状的斑纹(约120μm);与其形貌互补的是含硅、铝、钙、钠等元素的碱性石灰质釉质。SIMS深度剖析发现,α-Fe₂O₃晶体的连续深度不小于5μm。基于SIMS表征结果,还探讨了赤铁矿沉积薄膜状镜铁矿(α-Fe₂O₃)引起华北油滴呈银色与镜面反射现象的原理,以及TOF-SIMS在表征和研究古瓷方面的潜力和局限。     

133型铯离子源

在二次离子质谱分析过程中,如果在一次离子所轰击的样品表面附近存在金属铯(Cs)的原子,则将引起二次负离子产额的提高。尤其是Ⅵ族元素以及位于元素周期表右端的那些元素,铯原子的存在,可以使它们的负离子产额高于存在氧时的正离子产额。因此,利用铯作为一次离子源,可以提高这些元素的二次离子质谱分析极限。本文对IMS-3f型离子探针使用的133型铯离子源的结构和原理作一简介。     

现代表面分析技术在半导体材料中的应用

本文简要介绍TOF-SIMS(飞行时间二次离子质谱仪)、XRD(X射线双晶衍射仪)、SIMS(二次离子质谱仪)和XPS(X射线光电子能谱仪)等现代分析仪器的特点,着重报道这些分析技术在分析砷化镓抛光片的表面痕量沾污、表面晶体完整性、表面镓砷比、表面化学组成、表面氧含量以及氧化层厚度等方面的应用。     

Investigation of Initial and Steady-State Sliding Behavior of a Nearly Frictionless Carbon Film by Imaging 2- and 3-D TOF-SIMS

Using imaging time-of-flight secondary ion mass spectrometry (TOF-SIMS), we investigated the initial and steady-state sliding behavior of a nearly frictionless carbon (NFC) film. Specifically, TOF-SIMS images (both 2-D and 3-D) of these surfaces were constructed to highlight the spatial distributions of ionized and molecular species that were present on as-received and friction-tested NFC surfaces and as a function of depth. As a complementary technique, we used X-ray photoelectron spectroscopy (XPS) to gain further insight into the chemical nature of the sliding surfaces. The NFC films were produced on Si wafers and steel substrates in a gas discharge plasma that consisted of 25 vol.% methane and 75 vol.% hydrogen using a plasma-enhanced chemical vapor deposition (PECVD) system. They were then subjected to sliding friction and wear experiments in a pin-on-disk machine under 5- and 10-N loads and at sliding velocities of 0.2–0.5 m/s in dry nitrogen. The initial friction coefficients of the NFC films were in the range of 0.05–0.1, but decreased rapidly to values less than 0.01 at steady state. Positive and negative TOF-SIMS spectra and 2- and 3-D images reconstructed from selected masses revealed that the elemental distribution of certain chemical species differs substantially between undisturbed and tribo-tested areas of the NFC films. Specifically, the tribo-tested areas are essentially made up of carbon and hydrogen, while undisturbed or as-received areas are covered by a layer that is rich in oxygen and other species. These findings correlate well with the initial and steady-state friction coefficients of these films and help further explain their superlubricity in inert test environments.     

TOF-SIMS analysis of boundary films derived from calcium sulfonates

Tribological properties of over-based and neutral calcium sulfonate were examined under boundary lubrication conditions by using a ball-on-flat type tribo-tester. It was found that over-based calcium sulfonate reduced friction and wear of steel–steel contacts, whereas the neutral calcium sulfonate did not. It was found that boundary film composed of calcium oxide plays significant role on improving the tribological properties. Surface analyses by XPS and Time-of-flight secondary mass spectroscopy (TOF-SIMS) revealed that the major component of the film on upper surfaces is calcium carbonate and that at subsurfaces are composed of calcium oxide. A depth profile of the film obtained by TOF-SIMS using an etching technique revealed that thickness of the film is up to 240 nm. A static pyrolysis of the over-based calcium sulfonate on steel surface affords a thin film composed of calcium oxide, indicating that rubbing process is essential for the formation of the boundary film.     

Depth profiling by secondary ion mass spectrometry

The principles and applications of depth profiling by secondary ion mass spectrometry (SIMS) are reviewed. Discussed are the basic physical processes and instrumental factors which influence the shape of depth profiles and which have to be understood or controlled for successful experimental measurements. Microroughness caused by sputtering, atomic mixing by primary beam knock-on, and sample consumption limit the depth resolution which can be achieved while the chemical effect of ion yield enhancement by reactive species, matrix effects, and preferential sputtering can strongly affect the secondary ion signal. Instrumental effects to be controlled include beam uniformity, sample charging, and beam, and residual gas contamination. High depth resolution and sensitivity are the reasons for a wide variety of applications for SIMS depth profiling. Reviewed are measurements of the range distribution of ions implanted into semiconductors and their redistribution by subsequent annealing, studies of thin films and of oxide layers, diffusion measurements in metals, semiconductors, and minerals, measurements of elemental surface enhancements in airborne particles, and lunar glass spherules, and the search for solar wind implanted ions in lunar crystals.     

SIMS instrumentation and imaging techniques

Secondary ion mass spectrometry (SIMS) has evolved as a technique for characterizing solids and surfaces which is distinguished by high sensitivity and its applicability to all elements. It can be used for surface research, in-depth concentration profiling, isotopic work, and the identification of compounds. Combined with imaging techniques, these applications can be made with high spatial resolution. In this respect, ion probe microanalysis complements electron probe microanalysis (XRMA and scanning AES).     

Preparation of cells cultured on silicon wafers for mass spectrometry analysis

The distribution of specific atoms and molecules within living cells is of high interest in bio-medical research. Laser secondary neutral mass spectrometry (laser-SNMS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS) detect atoms with high sensitivity and spatial resolution. The application of these methods to cultured cells requires special preparation techniques preserving morphological and chemical integrity of the living cells. The cells should, therefore, be grown on a conducting material preventing charging of the sample during ion bombardment. Silicon is currently used as the preferred support material for non-biological samples in mass spectrometry. This study investigates (1) the influence of silicon surfaces on cell growth and (2) the suitability of a sandwiched, rapid freezing method to analyse transmembrane ion gradients. Human melanoma cells were grown on silicon with polished or etched surfaces. Growth kinetics were studied using the Sulforhodamine-B assay. Number, shape, and morphology of the cells were assessed by epifluorescence microscopy of calcein AM- and DAPI-stained cells. Cells were subjected to rapid freezing, freeze-fracturing, and freeze-drying prior to analysis by TOF-SIMS and laser-SNMS. While cell numbers and morphology on the rough silicon wafers were impaired, morphology and growth kinetics of cells on polished silicon were identical to control cells on cell culture tested polystyrene. TOF-SIMS and laser-SNMS resulted in high-resolution elemental images and mass spectra. Measurement of the intracellular Na+ and K+ concentrations revealed a ratio as observed in living cells. In conclusion, culturing cells on polished silicon wafers followed by sandwiched, rapid freezing is an adequate preparation method to study intracellular ion distribution with mass spectrometry.