低能离子散射谱分析中的荷电效应及中和作用

用低能离子散射谱（ISS）对比分析了与样品托有良好电接触的和与样品托绝比的金属银片，观察到荷电效应对ISS分析有严重影响。实验还表明在ISS分析时使用低能电子中和枪可以有效地消除荷电效应，还发现电子中和枪的使用对于惰性气体离子的中和作用无明显影响。     

Topography and field effects in secondary ion mass spectrometry Part II: insulating samples

A study is conducted on the effects of sample topography on the secondary ion mass spectrometry (SIMS) analysis of insulating samples, using poly(ethylene terephthalate) fibres (100 µm diameter) as a model system and simulations of the ion extraction field using finite element analysis. We focus on two significant issues: topographic field effects caused by the penetration of the extraction field into the sample, and the effect of charge compensation on the secondary ion images. Guidance is provided for setting the reflector voltage correctly for insulating fibres in reflectron SIMS instruments. The presence of the topographic sample distorts the extraction field, causing the secondary ions to be deflected laterally. This results in the severe loss of ion signals from the sides of the fibres because of the limited angular acceptance of the analyser. Strategies to reduce topographic field effects, including alternative sample mounting methods, are discussed. We also find that, in general, insulating samples are charged by the flood gun electrons resulting in a negative surface potential. This causes large variations in the SIMS images depending on the electron current, electron energy, raster mode and secondary ion polarity. Recommendations are given for analysts to obtain more reproducible images and reduce the effect of differential electron charging, for example by using a lower electron flood beam energy. © 2011 Crown copyright.     

XPS分析中使用样品磁透镜引起的谱峰位移和峰形畸变

发现当使用Mg/Al双阳极和样品磁透镜进行非导电样品（或与样品托绝缘的导电样品）的X射线光电子能谱分析时，谱峰出现异常大的位移和谱形出现畸变；在同时使用电子中和枪时谱峰位移变小，当导电样品与样品托有良好的电接触时谱峰位移消失；作者提出这种异常大的位移来自样品荷电效应，后者是由于样品磁透镜的磁场与来自X射线枪A1窗的低能杂散电子发生了相互作用并使这些杂散电子不能到达样品表面起中和作用所致。     

ESCA applied to polymers. XXII. An investigation of sample charging phenomena for polymeric films on gold

Sample charging phenomena arising in the ESCA experiment have been investigated for gold and polymer films of known thickness ranging from 5 Å to 20 μ deposited on gold either insulated from or in electrical contact with the spectrometer. Charging induced by a monochromatic x-ray source is typically an order of magnitude greater than that induced by a nonmonochromatized source and exhibits a marked time dependence. A novel source of secondary electrons which employs a low-power, low-pressure mercury lamp external to the spectrometer source chamber as an alternative to an electron flood gun is described, and the charging and biasing characteristics of polymer films as a function of film thickness are discussed and demonstrated to provide an extra informational dimension for the study of polymeric materials.     

Summary of ISO/TC 201 Standard: XXIII,ISO 24236:2005—surface chemical analysis—Auger electron spectroscopy—repeatability and constancy of intensity scale

This International Standard specifies a method for evaluating the constancy and repeatability of the intensity scale of Auger electron spectrometers, for general analytical purposes, using an electron gun with a beam energy of 2 keV or greater. It is only applicable to instruments that incorporate an ion gun for sputter cleaning. It is not intended to be a calibration of the intensity/energy response function. 1 , 2 That calibration may be made by the instrument manufacturer or other organization. The present procedure provides data to evaluate and confirm the accuracy with which the intensity/energy response function remains constant with instrument usage. Guidance is given to some of the instrumental settings that may affect this constancy. © Crown Copyright 2006. Reproduced with the permission of the Controller of HMSO.     

Optimizing the performance of an electron gun design followed by lenses and apertures

The electron gun plays an important role in atomic, molecular, and surface physics. Different types of electron guns have been designed for producing different electron beam energies. In this study, we present the modeling and construction of a seven-element electron gun with deflector system for electron impact studies. The electron optics of the electron gun was simulated and optimized using electron-beam ray-tracing simulation program SIMION 3D 7.0. Different operation mode of the gun, afocal, broad, and zoom beam mode, can be accommodated by adjusting various potentials. This modeling proposed here may help to design new types of electron guns and applications using cylinder and aperture lenses in collision experiments.     

Investigation of the influence of voltage parameters on decay times in an ion mobility spectrometer with a pulsed non-radioactive electron source

Ion mobility spectrometry (IMS) is a well-known method for detecting hazardous compounds in air. Most ion mobility spectrometers use a radioactive source to provide electrons with high energy (5–50 keV) to ionize analytes in a series of chemical reactions. Instead of a radioactive source, we use a non-radioactive electron gun which can be operated in pulsed mode. Thus a delay time between ionization and ion extraction can be introduced which offers the possibility to use the signal decay characteristic of substances as a further discrimination parameter. The influence of voltages supplied to the reaction region and to the electron gun on signal intensities and decay times will be investigated in order to obtain further insight into the dependence of this signal decay on different experimental parameters and correspondingly into the underlying mechanisms.     

Summary of ISO/TC 201 Standard XII. ISO 17973:2002—Surface chemical analysis—Medium‐resolution Auger electron spectrometers—Calibration of energy scales for elemental analysis

This International Standard specifies a method for calibrating the kinetic energy scale of Auger electron spectrometers with an uncertainty of 3 eV for general analytical use for identifying elements at surfaces. It is suitable for instruments used in either the direct mode or the differential mode where the resolution is equal to or less than 0.5% and the modulation amplitude for the differential mode, if used, is 2 eV peak to peak. The spectrometer shall be equipped with an inert gas ion gun or other method for sample cleaning and with an electron gun capable of operating at 4 keV or higher beam energy. This International Standard further specifies a calibration schedule. Crown Copyright © 2003. Published by John Wiley & Sons, Ltd.     

AES investigation of inhomogenous metal-insulator samples.

In this article, the secondary electron-emission properties of both vertically and laterally inhomogeneous samples are discussed. To study the effect of surface coverage, the total electron-emission yield of tungsten and niobium samples was measured as a function of primary electron energy and oxide thickness. A method is suggested to avoid charging difficulties during AES measurements of samples that consist of both metal and various insulator parts.     

Electron capture dissociation of substance P using a commercially available Fourier transform ion cyclotron resonance mass spectrometer

Electron capture dissociation of the peptide Substance P is reported for the first time, with an unmodified, commercially available Fourier transform ion cyclotron resonance (FTICR) mass spectrometer. The fragmentation pattern is compared with that obtained with collisionally induced dissociation of the ions in the electrospray ion source, and note that electron capture dissociation gives a more easily interpreted spectrum, showing mainly C-fragments. With the exception of the proline residues, which require cleavage of two chemical bonds, we observe all C-fragmental we find the bias voltage of the electron gun not to be very critical.     

Ion permeability of SAMs on nanoparticle surfaces

This article reports on the ion permeability of self-assembled monolayers (SAMs) formed on the surface of charged alkanethiol-protected gold nanoparticles, so-called monolayer-protected clusters (MPCs). The capacitance and thus the charging energy required to add/remove an electron from the metal core are extremely sensitive to ions entering the monolayer, and the extent of ion penetration can be tuned by the charge and size of the ions and the permittivity of the solvent. Experimentally, this effect is comparable to ion association with conventional redox molecules, indicating that MPCs despite their large size and the fundamentally differing nature of the electron transfer process can be treated analogously to redox molecules.     

Electron beam coater for reduction of charging in ice-embedded biological specimens using Ti(88)Si(12) alloy.

Biological macromolecules embedded in vitreous ice are known to suffer from charging while being imaged in an electron transmission cryomicroscope. We developed an electron beam coater that deposits conductive films onto the surface of frozen-hydrated specimens. The conductive films help to dissipate charge during electron irradiation of poorly conductive ice-embedded biological samples. We observed significant reduction in charging of ice-embedded catalase crystals suspended over holes in a holey carbon film after coating them with a 30-A-thick layer of an amorphous alloy, Ti(88)Si(12). Images of the crystals after coating showed diffraction spots of up to 3 A resolution.     

Sample preparation for precise and quantitative electron holographic analysis of semiconductor devices.

Wedge polishing was used to prepare one-dimensional Si n-p junction and Si p-channel metal-oxide-silicon field effect transistor (pMOSFET) samples for precise and quantitative electrostatic potential analysis using off-axis electron holography. To avoid artifacts associated with ion milling, cloth polishing with 0.02-microm colloidal silica suspension was used for final thinning. Uniform thickness and no significant charging were observed by electron holography analysis for samples prepared entirely by this method. The effect of sample thickness was investigated and the minimum thickness for reliable results was found to be approximately 160 nm. Below this thickness, measured phase changes were smaller than expected. For the pMOSFET sample, quantitative analysis of two-dimensional electrostatic potential distribution showed that the metallurgical gate length (separation between two extension junctions) was approximately 54 nm, whereas the actual gate length was measured to be approximately 70 nm by conventional transmission electron microscopy. Thus, source and drain junction encroachment under the gate was 16 nm.     

Status monitoring of ion sputter relevant parameters of an XPS depth profiling instrument

An X-ray photoelectron spectroscopy (XPS) instrument is utilized for sputter depth profiling of thin films. Relevant instrumental parameters are the ion gun sputter rate, the contamination level of the sputter ion gun, and the purity of the sputter ion gun gas supply as well as the vacuum quality of the instrument at the sample position. A long-term recording of these instrumental parameters ensures the reliability of the measured depth profile data. The ion gun sputter rate was estimated using the standard ISO conform depth profiling of a SiO₂ reference layer of known thickness. Two new procedures are developed to determine the other relevant parameters. Gases that are emitted by the ion sputter gun get implanted into a Si target. An analysis of the implanted gases allows judging on the contamination level of the sputter gun and the purity of the sputter gun gas supply. The vacuum condition of an XPS microprobe at the sample position is monitored by the recontamination of a sputtered Ti surface by adsorbed residual gas particles.     

Charging megadalton poly(ethylene oxide)s by electrospray ionization. A charge detection mass spectrometry study

Ions from compounds of megadalton (MDa) molecular weight were produced in an electrospray ionization source from solutions of poly(ethylene oxide) (PEO) samples with average molecular weights ranging from 1,000,000 to 7,000,000 Da. Charge detection mass spectrometry (CDMS) has been used to determine the mass of the MDa PEOs. Simultaneous measurement of the charge and velocity of individual ions allows the mass determination of the ion, after calibration of the instrument with independent samples. In addition to the mass spectra, CDMS generates charge-versus-mass plots, which allow investigation of the charging of electrosprayed ions over a broad range of masses. The experimental charging capacity of MDa PEOs is compared with a simple model based on the affinity of alkali cations for oxygen sites and on the electrostatic potential energy of the charged polymer. The charging capacity of PEOs was also investigated as a function of the concentration of and the type of alkali ions.     

Surface Study of Polymers by Static Secondary Ion Mass Spectrometry Using a Magnetic-Sector Mass Spectrometer

Results from static SIMS analysis of six thermoplastic polymers — polytetrafluoroethylene (PTFE), polyethylene (PE), polymethyl methacrylate (PMMA), polyethylene terephthalate (PET), polystyrene (PS) and polycarbonate (PC) — using a magnetic-sector SIMS instrument and O₂⁺ primary beam are presented. For PTFE as a representative sample, the charging effect is reduced only with a metal grid when analyzing positive secondary ions. When negative secondary ions are analyzed, excessive charges are self-compensated with a normal-incidence electron gun. Positive-ion spectra collected agree with spectra obtained using either a quadrupole or time-of-flight SIMS instrument and noble-gas ion beams. The agreement is objectively demonstrated by means of the capability to compare spectra in the NIST/EPA/MSDC mass spectral database. The merits of the use of high-mass resolution, of which magnetic-sector SIMS is inherently capable, to provide analytical information about the molecular species native to the sample are demonstrated in distinguishing three ambiguous peaks with nominal mass ratios m/z = 27, 39 and 59 from PMMA.     

Dissociation of peptide ions by fast atom bombardment in a quadrupole ion trap

A new technique for fragmentation of cations and anions of peptides stored in ion traps including radiofrequency devices is described. The technique involves irradiation of peptide ions by a beam of particles generated by a fast atom bombardment (FAB) gun. This irradiation leads to fragmentation of N--C(alpha) backbone bonds (c- and z-fragments) and S--S bonds for cations and C(alpha)-C backbone bonds (a- and x-fragments) for anions of peptides. The fragmentation patterns observed are hypothesized to be due to the interaction of peptide ions with metastable, electronically excited species generated by the FAB gun. Interaction of a metastable atom A* with a peptide n-cation M(n+) leads to the electron transfer from the metastable atom to the polycation through the formation of an ion-pair collision complex A(+.) . . . M((n-1)+.) and subsequent fragmentation of the peptide cation. Thus, for polycations, this metastable-induced dissociation of ions (MIDI) is similar to the phenomenon of electron capture dissociation (ECD). Interaction of A* with an anion leads to the deexcitation of the metastable species and detachment of an electron from the anion. This in turn leads to backbone fragmentation similar to that in electron detachment dissociation (EDD). The MIDI technique is robust and efficient, and it is applicable to peptides in as low charge states as 2+ or 2-.     

导电环氧树脂消除扫描电子显微镜图像荷电问题的原理与实践

荷电问题常造成扫描电子显微镜(SEM)图像上产生亮度不均、条纹等伪影.提出一种利用导电环氧树脂镶嵌样品以消除SEM图像荷电的方法,并与传统导电胶粘贴制样方法对1 000℃高温混凝土、瓷土与河南双槐树考古土三种样品的适应性进行了对比研究.结果表明,利用铜粉与环氧树脂混合制备导电环氧树脂并将样品镶嵌其中所制备样品的SEM图像基本无荷电问题,而传统导电胶粘贴方法所制备样品的SEM图像存在较严重的荷电问题,通过增加导电层厚度并不能对此进行改善,且易造成微纳结构被掩盖.最后对传统制样方法导致荷电问题的原因与导电环氧树脂对荷电问题的改善原理进行了分析.     

团簇离子枪对CH3NH3PbI3钙钛矿薄膜的影响研究

以氩离子团簇为溅射源,对采用一步旋涂法制备的CH₃NH₃PbI₃钙钛矿薄膜进行溅射实验,通过XPS分析检测样品表面Pb元素的价态变化。结果表明,新制备的钙钛矿薄膜材料表面没有检测出Pb⁰,而经过团簇离子枪溅射的样品中部分Pb²⁺还原成Pb⁰,证明了氩离子团簇刻蚀对钙钛矿材料具有破坏作用。一方面,溅射时间的增加以及团簇离子枪能量的增大均会加大钙钛矿材料的损伤程度;另一方面,离子枪团簇规模大小与溅射损伤程度呈近抛物线关系。因此,在进行此类样品表面清洁时,应尽量减小离子枪能量和溅射时间,选择较小或较大的团簇规模以减少对样品的损伤。该研究对于钙钛矿样品在进行XPS检测和数据分析时具有参考价值。