100-femtosecond MeV electron source for ultrafast electron diffraction

A near-relativistic 100-fs MeV electron beam is developed by using a photocathode rf gun for revealing the hidden ultrafast dynamics of intricate molecular and atomic processes in materials through experimentation of ultrafast time-resolved electron diffraction (UED). The transverse and longitudinal dynamics of femtosecond electron beam in the rf gun were studied theoretically by particle simulation. The growths of the emittance, bunch length and energy spread due to the rf and space charge effects were investigated by changing the laser parameters, field gradient and electron charge. The theoretical studies indicate that a 100-fs MeV electron beam with the transverse emittance of 0.1 mm mrad and the relative energy spread of 10⁻³–10⁻⁴ at bunch charge of 0.1–2 pC (10⁶–10⁷ electrons per pulse) is achievable for UED, in which the intensity is three orders of magnitude higher than that produced by the conventional dc or pulsed guns.     

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.     

Determination of flux from a saddle field fast-atom bombardment gun

The flux or beam density (equivalent current/area) of xenon atoms striking the sample target from a saddle field fast-atom bombardment (FAB) gun has been compared with that from a cesium ion gun mounted on the same instrument. A shielded Faraday cup mounted on the end of a solids probe was used to measure directly the flux of the Cs⁺ beam. Samples of methylene blue in glycerol solution were then exposed to the ion beam at different fluxes and the extents of reduction were measured. The extent of reduction varied linearly with flux up to a value of about 1.16 × 10¹³ particles s^?1 cm^?2 (1.85 μ cm^?2); above this level, the reduction effect appeared to saturate. FAB spectra were obtained from the same dye solution by using varying settings of the FAB gun. By comparing the extents of reduction of the dye from the two guns, the flux from the atom gun could be estimated. Observation of luminescence from a CsI-coated target allowed estimation of the area of the atom beam. The atom beam “equivalent current” could then be calculated by multiplying the flux times the area. It was noted that for given settings, the flux from the atom gun depended on the physical condition of the gun electrodes. With new electrodes, a flux ≥ 1.16 × 10¹³ particles s^?1 cm^?2 was obtained with nominal gun emission currents of 0.60–1.0 mA. Electrodes used extensively, but freshly cleaned, provided a flux of ～ 8 × 10¹² particles s^?1 cm^?2 at nominal emission currents of 0.40–1.0 mA. With dirty electrodes this flux could only be achieved at the highest (1.0 mA) emission current. This decline in performance occurs over a matter of months as a result of contamination and erosion of the electrodes during use. Such behavior can adversely affect spectral reproducibility even when nominal FAB gun voltage and emission current are carefully reproduced.     

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。     

Development of compact coherent EUV source based on laser Compton scattering

High-power extreme ultra-violet (EUV) sources are required for next generation semiconductor lithography. We start to develop a compact EUV source in the spectral range 13–14 nm, which is based on a laser Compton scattering between a 7 MeV micro-bucnhed electron beam and a high-intensity CO₂ laser pulse. The electron beam extracted from a DC photocathode gun is micro-bunched using a laser modulation techinque with the Compton wavelength at a harmonic of the seeding laser before the main laser Compton scattering for EUV generation. A considerating scheme for the compact EUV source based on the laser Compton scattering with micro-bunched electron beam and the analytical study of micro-bunch generation are described in this paper.     

Performance of compact pulse radiolysis system using a photocathode RF gun

A compact pulse radiolysis system using a photocathode RF gun was installed at Sumitomo Heavy Industries. Some performance tests were conducted concerning the electron beam and the laser pulse. The energy and the per-pulse charge of the electron beam were measured to be 1.75 MeV max. and 1 nC. The fluctuation of the charge was restricted within 2%. The pulse widths of the electron pulse and the analyzing laser pulse were 20 ps and 15 ps, respectively. The timing jitter between electron pulse and the laser pulse was ±5.7 ps. Based on these measurements, the all-over time resolution can deduced to be about 25 ps.     

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.     

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.     

脉冲光电子枪中光电子束性能研究

利用新设计的脉冲光电子枪,研究了光电子束的能量分布,光电子数密度与激光强度的关系和光电子在电离区内的滞留时间。大部分电子的能量为光发射电子的剩余能量,但是由于电子的空间电荷效应,电子能量分布具有加宽现象·每个激光脉冲发射到电离区内的光电子数密度在109/cm3以上。     

Combined infrared multiphoton dissociation and electron-capture dissociation using co-linear and overlapping beams in Fourier transform ion cyclotron resonance mass spectrometry

A novel set-up for Fourier transform ion cyclotron resonance mass spectrometry (FTICR) is reported for simultaneous infrared multiphoton dissociation (IRMPD) and electron-capture dissociation (ECD). An unmodified electron gun ensures complete, on-axis overlap between the electron and the photon beams. The instrumentation, design and implementation of this novel approach are described. In this configuration the IR beam is directed into the ICR cell using a pneumatically actuated mirror inserted into the ion-optical path. Concept validation was made using different combinations of IRMPD and ECD irradiation events on two standard peptides. The ability to perform efficient IRMPD, ECD and especially simultaneous IRMPD and ECD using lower irradiation times is demonstrated. The increase in primary sequence coverage, with the combined IRMPD and ECD set-up, also increases the confidence in peptide and protein assignments.     

Electron Flood Gun Damage Effects in 3D Secondary Ion Mass Spectrometry Imaging of Organics

Electron flood guns used for charge compensation in secondary ion mass spectrometry (SIMS) cause chemical degradation. In this study, the effect of electron flood gun damage on argon cluster depth profiling is evaluated for poly(vinylcarbazole), 1,4-bis((1-naphthylphenyl)amino)biphenyl and Irganox 3114. Thin films of these three materials are irradiated with a range of doses from a focused beam of 20 eV electrons used for charge neutralization. SIMS chemical images of the irradiated surfaces show an ellipsoidal damaged area, approximately 3 mm in length, created by the electron beam. In depth profiles obtained with 5 keV Ar₂₀₀₀ ⁺ sputtering from the vicinity of the damaged area, the characteristic ion signal intensity rises from a low level to a steady state. For the damaged thin films, the ion dose required to sputter through the thin film to the substrate is higher than for undamaged areas. It is shown that a damaged layer is formed and this has a sputtering yield that is reduced by up to an order of magnitude and that the thickness of the damaged layer, which increases with the electron dose, can be as much as 20 nm for Irganox 3114. The study emphasizes the importance of minimizing the neutralizing electron dose prior to the analysis. Figure

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Characterization of THz radiation generated by ultra-short bunch from energy chirping cell attached RF electron gun

The coherent radiation spectrum extends into the far-infrared/THz region when the electron bunch is shorter than 1 ps (0.3 mm). Such ultra-short electron bunches can be produced using a variety of bunching schemes in electron accelerators. We have designed a photocathode RF electron gun, named ECC RF gun, specifically for ultra-short bunch generation. ECC stands for energy chirping cell. This paper describes the brief principle of the ECC RF gun, CTR (coherent transition radiation) observation using Schottky barrier diodes (SBD) and spectrum measurement using interferometry with SBDs. We have successfully confirmed the generation of 0.05–0.3 THz high peak power pulsed CTR.     

弹着点射击残留物转印介质的比较研究

为了考察应用于弹着点射击残留物(Gunshot Residues,GSR)收集的转印介质其显色效果、影响因素、提取次数、后续高光谱分析的质量、易用性和成本等,通过实验比较BenchKote、相纸(230 g)、彩激纸(160 g)、白卡纸(260 g)、超滑纸(300 g),采用湿法提取纺织品上的GSR,然后利用红氨酸...     

Time-resolved spectroscopy at the picosecond laser-triggered electron accelerator ELYSE

ELYSE is a fast kinetics center created for pulse radiolysis with picosecond time-resolution. The facility is a 4–9 MeV electron accelerator using a subpicosecond laser pulse to produce an electron pulse from a Cs₂Te semiconductor photocathode and RF gun technology for the electron acceleration. The pulse duration is around 5 ps at low charge (<2 nC) and high energy (9 MeV), and is under routine conditions 10 ps at higher charge (5 nC) and >8 MeV. The dark current at the target is less than 1% of the pulse photocurrent.Time-resolved absorbance measurements in cells placed in front of the electron beam are achieved using pulsed laser diodes, or a xenon flash lamp as light sources, and photodiodes connected to a 3 GHz transient digitizer or a streak camera (250–800 nm range and 3.7 ps time resolution) as detection instruments. In addition, the synchronization between the laser beam and the electron beam is exploited to measure the absorbance by a pump-probe set-up, the pump being the electron pulse produced by the laser pulse, and the probe being part of the laser beam (120 fs–3 ps) delayed by a variable optical line.     

涤纶薄膜拉伸过程中的电镜研究

<正> 聚对苯二甲酸乙二酯(PET)是用于纤维和薄膜的最重要的高分子材料之一。在拉伸过程中拉伸温度、拉伸比、应变速率等不同因素对PET的结晶、取向以及所形成的织态等的影响已有过广泛的研究。但用电镜直接观察PET薄膜在不同拉伸条件下的高分子聚集态结构的变化则报道很少。我们选择丙烯胺作刻蚀剂处理拉伸方式、拉伸温度、应变速率和拉伸比不同的PET试样,用扫描电镜直接观察其形态的变化。     

HRTEM-EELS cross-sectional structural analyses of glassy carbon substrate irradiated by platinum ions using a coaxial arc plasma gun

A glassy carbon (GC) substrate was irradiated by Pt ions using a coaxial arc plasma gun in vacuum. The structure of the substrate was studied in the atomic scale using high-resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy (EELS) with a thin foil specimen prepared by cross-sectioning using focused ion beam milling. HRTEM combined with the EELS measurements of the cross-sectioned sample indicated a disordering of the GC substrate surface and the detection of phenol-type species, carbon atoms in aliphatic chain molecules, and carboxyl groups, which are considered to have been formed by chemical reaction between the carbon atoms of the GC substrate surface and hydrogen or oxygen atoms. Penetrated Pt atoms were observed inside the GC substrate, and the surface position of the GC substrate was located from the depth profiles of the EELS spectra. STEM-EELS analyses of a pristine GC substrate without Pt ion irradiation were also conducted for reference.     

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.     

High resolution FESEM and TEM reveal bacterial spore attachment.

Transmission electron microscopy (TEM) studies in the 1960s and early 1970s using conventional thin section and freeze fracture methodologies revealed ultrastructural bacterial spore appendages. However, the limited technology at that time necessitated the time-consuming process of imaging serial sections and reconstructing each structure. Consequently, the distribution and function of these appendages and their possible role in colonization or pathogenesis remained unknown. By combining high resolution field emission electron microscopy with TEM images of identical bacterial spore preparations, we have been able to obtain images of intact and sectioned Bacillus and Clostridial spores to clearly visualize the appearance, distribution, resistance (to trypsin, chloramphenicol, and heat), and participation of these structures to facilitate attachment of the spores to glass, agar, and human cell substrates. Current user-friendly commercial field emission scanning electron microscopes (FESEMs), permit high resolution imaging, with high brightness guns at lower accelerating voltages for beam sensitive intact biological samples, providing surface images at TEM magnifications for making direct comparisons. For the first time, attachment structures used by pathogenic, environmental, and thermophile bacterial spores could be readily visualized on intact spores to reveal how specific appendages and outer spore coats participated in spore attachment, colonization, and invasion.     

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-.     

A parallel acquisition charged particle energy analyser using a magnetic field

A new form of charged particle energy analyser is proposed. It is broadly based on the 180° magnetic spectrograph, but is intended to detect charged particles moving out of the dispersion plane with a helical motion. The analyser has the capability to acquire charged particle energy spectra over a large energy range, similar to those acquired in Auger electron spectroscopy, ca. 2500 eV and large angular range, up to 90°, in parallel. These conditions are more favourable for surface analysis by electron spectroscopy at high vacuum, where for example an electron energy resolution of 0.2% to 0.5% is typical. Expressions showing how the landing positions of the charged particles on the detector vary as a function of energy and polar take off angle are determined as well as the conditions for optimum energy resolution at a range of polar take off angles. The equations reveal that in general, the device obtains the highest resolution at angles of revolution greater than 180°. The design is simple and could be easily put into practice using available material and technologies and be used to analyse the energies of electrons emitted from a sample placed in a scanning electron microscope. It can be made to function with a primary electron beam of any desired energy and could fit in to the small space between the sample and the end of an electron column. However, the device is difficult to retrofit into existing SEMs and ideally an SEM column needs to be designed to work in association with the analyser. The direction of the magnetic field of the analyser is coincident with the axis of the electron gun so that the primary beam is little influenced by the magnetic field and symmetry can be maintained in the primary beam electron column. Because the device is intended to acquire electron spectra in parallel, any movement of the primary beam on the sample because of a ramping field in the analyser is avoided. The field of view and the effect of the analyser upon the operation of the SEM are discussed. Spectra including elastic and Auger peaks reveal an energy resolution of ~4 eV at 900‐eV electron energy. Copyright © 2016 John Wiley & Sons, Ltd.