A method of dynamic chromatic aberration correction in low-voltage scanning electron microscopes

A time-of-flight concept that dynamically corrects for chromatic aberration effects in scanning electron microscopes (SEMs) is presented. The method is predicted to reduce the microscope's chromatic aberration by an order of magnitude. The scheme should significantly improve the spatial resolution of low-voltage scanning electron microscopes (LVSEMs). The dynamic means of correcting for chromatic aberration also allows for the possibility of obtaining high image resolution from electron guns that have relatively large energy spreads.     

Detection and registration of ion clots in laser time-of-flight mass spectrometers

A number of factors influencing the measurement errors of analytic signals detected with secondary electron multipliers (SEMs) and registered with fast ADCs are analyzed. Such signals are generated in laser time-of-flight mass spectrometry at the stage of ion detection and recording of mass spectra. In particular, the effect of statistical factors and sources of systematic errors during both measurements of isotope ratios and elemental analysis is considered. Such errors as the statistics of formation of ion clots, the limited range of ADC records, discrimination during detection of ions of different masses, and others are considered. It is shown that, without taking into account the features of operation of SEMs and ADCs, both the statistical and systematic errors of measuring isotope ratios may reach several percent. The proposed operating modes of the detector, with allowance for its features, the design of the recording system, and use of formulas for calculating and correcting errors, allow their reduction to ～0.10–0.01%     

Reflection-time-of-flight spectrometer for two-electron (e,2e) coincidence spectroscopy on surfaces

In this article, a novel time-of-flight spectrometer for two-electron-emission (e,2egamma,2e) correlation spectroscopy from surfaces at low electron energies is presented. The spectrometer consists of electron optics that collect emitted electrons over a solid angle of approximately 1 sr and focus them onto a multichannel plate using a reflection technique. The flight time of an electron with kinetic energy of Ekin approximately 25 eV is around 100 ns. The corresponding time- and energy resolution are typically approximately 1 ns and approximately 0.65 eV, respectively. The first (e,2e) data obtained with the present setup from a LiF film are presented.     

电子轰击源垂直加速式飞行时间质谱仪的研制

介绍了自制的电子轰击离子源（electron ionization, EI）垂直加速式飞行时间质谱仪（orthogonal acceleration time-of-flight mass spectrometer, Oa-TOF MS）的原理,结构以及初步的实验结果。搭建了电子轰击源垂直加速式飞行时间质谱仪,并得到室内空气成分谱图。结果表明,仪器分辨率优于2 000（full width at half maximum,FWHM）,质量精度优于4×10^-5,可以用于气体成分的快速定性分析。     

Time-of-flight electron velocity spectrometer using transverse electric field deflectors

A time-of-flight electron velocity spectrometer using two transverse electric field deflectors as fast electronic shutters has been constructed. Square-wave voltage pulses applied to the two shutters limit the transmitted current to electrons in selected narrow velocity ranges. Analysis of the magnitude of this transmitted electron current as a function of the time delay between the two shutter openings leads to the electron velocity or energy spectrum in the incident charged particle beam. Time resolutions of 5 ns (FWHM) can be obtained with the present apparatus for electrons in the 5-100 eV range.     

Angle-resolving time-of-flight electron spectrometer for near-threshold precision measurements of differential cross sections of electron-impact excitation of atoms and molecules

This article presents a new type of low-energy crossed-beam electron spectrometer for measuring angular differential cross sections of electron-impact excitation of atomic and molecular targets. Designed for investigations at energies close to excitation thresholds, the spectrometer combines a pulsed electron beam with the time-of-flight technique to distinguish between scattering channels. A large-area, position-sensitive detector is used to offset the low average scattering rate resulting from the pulsing duty cycle, without sacrificing angular resolution. A total energy resolution better than 150 meV (full width at half maximum) at scattered energies of 0.5-3 eV is achieved by monochromating the electron beam prior to pulsing it. The results of a precision measurement of the differential cross section for electron-impact excitation of helium, at an energy of 22 eV, are used to assess the sensitivity and resolution of the spectrometer.     

The CORSET time-of-flight spectrometer for measuring binary products of nuclear reactions

The CORSET time-of-flight spectrometer has been developed at the Flerov Laboratory of Nuclear Reactions of the Joint Institute for Nuclear Research (Dubna, Russia) for investigating binary products of nuclear reactions. The spectrometer has been used to study the dynamics of fusion-fission and quasi-fission of superheavy elements. The design and the main characteristics of the spectrometer, as well as the algorithms for deducing the mass-energy distributions of fragments and the cross sections of nuclear reactions, are presented. The spectrometer contains two time-of-flight arms based on microchannel-plate detectors and three telescopes, each of which is composed of two microchannel-plate detectors and one semiconductor detector. A system of four semiconductor detectors is used to obtain the absolute value of a cross section. The time resolution of the time-of-flight arms is 150 ps, which allows the time-of-flight distances to be set at 10–20 cm, thus providing a mass resolution of 3 amu and an angular resolution of 0.3°. Owing to these characteristics, the spectrometer can be used as a trigger in multidetector setups for measuring light charged particles, neutrons, and γ rays in coincidence with reaction fragments.     

In situ laser heating in an environmental scanning electron microscope

The environmental scanning electron microscope (ESEM) offers improved capabilities for coupling a scanning electron microscope (SEM) with an in situ laser device compared with conventional SEMs. Such coupling generally enables, for example, the observation of laser glazing effects or high-temperature behaviour as well as thermal shock behaviour of materials and devices. In an ESEM, decomposition caused by high-temperature gas reactions can additionally be studied while monitoring the gaseous environment online with a mass spectrometer attached to the specimen chamber. In this work, we demonstrate the capabilities of an in situ laser system suitable for heating specimen in an in situ deformation stage, thus enabling the further study of the mechanical properties of materials far beyond temperatures accomplished by thermal heating stages.     

A high-resolution add-on in-lens attachment for scanning electron microscopes

A compact add-on objective lens for the scanning electron microscope (SEM) has been designed and tested. The lens is < 35 mm high and can be fitted on to the specimen stage as an easy-to-use attachment. Initial results show that it typically improves the spatial resolution of the SEM by a factor of three. The add-on unit is based upon a permanent magnet immersion lens design. Apart from the extra attachment to the specimen stage, the SEM with the add-on lens functions in the normal way. The in-lens unit can comfortably accommodate specimen heights up to 10 mm. The new add-on lens unit opens up the possibility of operating existing SEMs in the high-resolution in-lens mode. By using a deflector at the top of the add-on lens unit, it can also operate as a quantitative multichannel voltage contrast spectrometer, capable of recording the energy spectrum of the emitted secondary electrons. Initial experiments confirm that a significant amount of voltage contrast can be obtained.     

新型电子电离源线型离子阱-飞行时间杂化串联质谱研究进展

本研究介绍了一种新型电子电离源线型离子阱-飞行时间杂化串联质谱仪,该仪器结合了线型离子阱质谱和飞行时间质谱的优点,具有较强的定性分析能力。选用全氟三丁胺(PFTBA)、四氯化碳和丙酮为测试样品对开发的仪器样机进行性能测试,包括对PFTBA碎片离子的离子分离（ISO）和碰撞诱导解离（CID）实验,以及样品同位素离子间的分离实验。测试结果表明,该仪器基本实现了离子碎裂、离子储存和串联质谱分析等功能,能够进行高精度母离子选择。本研究所开发的EI LIT-TOF质谱,在易挥发类有机化合物的结构和化学性质等研究中具有特殊的应用前景。     

A time-of-flight detector of low-energy ions for an accelerating mass-spectrometer

The results of experiments with a time-of-flight detector for detecting rare ions at the output of the accelerating mass spectrometer of the Institute of Nuclear Physics (Siberian Branch, Russian Academy of Sciences) are described. The operation of this detector is based on detection of electron emission from thin films by means of microchannel plates. Owing to the small thickness of films, ions can sequentially pass through several films—this is the basis of the time-of-flight system for identifying isotopes. The high time resolution of detectors allows a significant decrease in the external-radiation background compared to one semiconductor complete-absorption detector that measures the ion energy.     

Time-lapse scanning electron microscopy for measurement of contamination rate and stage drift

Measurements done with scanning electron microscopes (SEMs) may lose their validity due to contamination and charging caused by the primary electron beam. The sample stage and the electron beam also slightly drift during the course of the measurements. Consequently, it is essential to find out the time limit of valid measurements, that is, the maximum time before the sample or its position changes too much. This paper describes digital time-lapse SEM, a useful tool for investigating the extent and effects of contamination and stage drift. It works with hardware and software that create a stack of sequential images. Later these images can be viewed as a short movie; it is also possible to apply all the image processing and analysis procedures that are otherwise applied to separate, individual images. This method gives a reliable way of measuring the rate of contaminant deposition and of stage and electron beam drift of SEMs, and it could be helpful in controlling these problems.     

Time-of-flight photoelectron spectroscopy of gases using synchrotron radiation

A gas-phase time-of-flight (TOF) photoelectron spectrometer has been developed for use with synchrotron radiation. The excellent time structure of the synchrotron radiation at the Stanford Positron Electron Accelerator Ring (SPEAR) has been used as the time base for the TOF measurements. The TOF analyzer employs two multichannel plates (MCPs) in tandem as a fast electron multiplier with a matched 50-Omega anode to form an electron detector with a timing resolution of 相似文献   

A simple method for the acquisition of high-quality digital images from analog scanning electron microscopes

A method is described for converting video signals of analog scanning electron microscopes (SEMs) into digital images of high quality. A plug-in card commercially available for personal computers is used for the on-line analog/digital conversion. A Windows application program written by the authors, together with low-level software drivers supplied with the plug-in card, allow digital images to be recorded, to be displayed simultaneously on the computer monitor and to be saved as a file in a standardized format. Compared to conventional photographic images obtained from the SEM camera system, the digital images possess superior sharpness of outline, excellent image definition, diminished noise and well-defined grey-scale tones. This method provides SEM images of high quality for less than $1000 from most older analog SEMs. In addition, the advantages of digital image processing can be applied to analog SEMs, including contrast enhancement, digital filtering and multichannel recording.     

Measuring the performance of scanning electron microscope detectors

A simple digital method of measuring the performance of detectors in the scanning electron microscope (SEM) is described. The value derived is absolute and can therefore be used to compare both different detectors on the same instrument as well as different detectors on different instruments. The technique can be applied to secondary electron, backscattered electron, and energy-dispersive x-ray detectors. Examples are given of measurements made on a variety of commercial detectors installed on a number of current SEMs.     

Correlation time-of-flight spectrometry of ultracold neutrons

The features of the correlation method used in time-of-flight spectrometry of ultracold neutrons are analyzed. The time-of-flight spectrometer for the energy range of ultracold neutrons is described, and results of its testing by measuring spectra of neutrons passing through interference filters are presented.     

Secondary Ion Time-Of-Flight Mass Spectrometers and Data Systems

ABSTRACT

Some recent improvements to the Manitoba linear time-of-flight mass spectrometer are reviewed. A new data system gives greatly improved performance. A detector assembly with a small 45° ion mirror and separate detectors for neutral and charged particles has been added. In conjunction with the new data system, it enables measurement of correlations between neutral and charged fragments resulting from unimolecular decay in the flight tube.

A new time-of-flight spectrometer has been constructed. It is a reflecting instrument with a relatively long ion mirror. Resolution and signal/background ratio are much better than in the linear instrument, and correlation measurements can be made with considerably higher accuracy in mass determination than with the small mirror.     

Time-of-flight spectroscopy of the energy distribution of laser-ablated atoms and ions

The growth of ultrathin films, deposited by laser ablation, crucially depends on the energy of the ablated species. Therefore, a time-of-flight (TOF) spectrometer has been constructed and measurements have been carried out in order to determine the energy distribution of laser-ablated Fe and Pt atoms and ions in the plasma created by nanosecond pulses of a frequency-doubled neodymium doped yttrium aluminum garnet laser. The experiments have been performed in ultrahigh vacuum at relatively low laser power. For measuring the spectra of the neutrals, a cross-beam electron source for postionization and electric as well as magnetic fields for repelling the ions are employed. Nevertheless, measurements of neutral particles are restricted to low plasma densities due to electrostatic shielding within the plasma, leading to an inefficient deflection of charged particles by electrostatic and magnetic fields. Test measurements have been performed by utilizing the TOF spectrometer as a pressure gauge and also by chopping the electron beam, running the TOF spectrometer as a residual gas mass spectrometer. The spectra of the laser-ablated plasmas have shown plasma conditions with a Debye length of approximately 10(-4) m, densities of 10(15)-10(16) m(-3) and ion energies up to 150 eV. Neutral spectra have shown an unexpectedly low fraction of neutrals (10(-3)-10(-4)) and hyperthermal energies up to several 10 eV, possibly contributed by recombination of ions and electrons in the plasma. Even though gas spectra had demonstrated the expected sensitivity of the TOF spectrometer for low-energy neutrals, no thermally evaporated neutral atoms could be found.     

Combining high mass resolution and velocity imaging in a time-of-flight ion spectrometer using pulsed fields and an electrostatic lens

We describe a momentum resolving time-of-flight ion mass spectrometer that combines a high mass resolution, a velocity focusing condition for improved momentum resolution, and field-free conditions in the source region for high resolution electron detection. It is used in electron-ion coincidence experiments to record multiple ionic fragments produced in breakup reactions of small to medium sized molecules, such as F(3)SiCH(2)CH(2)Si(CH(3))(3). These breakup reactions are caused by soft x rays or intense laser fields. The ion spectrometer uses pulsed extraction fields, an electrostatic lens, and a delay line detector to resolve the position. Additionally, we describe a simple analytical method for calculating the momentum from the measured hit position and the time of flight of the ions.     

瞬短脉冲辉光放电飞行时间质谱仪

本文介绍了本实验室研制的瞬短脉冲辉光放电飞行时间质谱仪。其中，辉光放电离子源具有离子产额高、工作稳定可靠等特点，可用于对金属（合金）样品的直接分析。该仪器为国内首台自制的常压（低真空）等离子体飞行时间质谱仪，亦为国际上首台瞬短脉冲辉光放电质谱仪，为研究瞬短脉冲辉光放电及其应用这一新兴领域打下了基础，仪器的分辨本领优于５００。