Generation of surface plasmon excitation of supported metal particles by an external electron beam

The relative probabilities for excitation of the various surface plasmons have been derived by use of the coherent state approach for two cases of small aluminum particles, coated with a thin oxide layer and half embedded in a supporting film. Previously [Wang and Cowley, Ultramicroscopy 21 (1987) 77] it was shown that if the supporting film is a dielectric, AlF₃, two surface plasmons (ω₁=8 eV and ω_Lo=4 eV) are predicted. If the supporting film is metal Al, there are four surface plasmons (ω₁=11.5 eV, ω₂=10 eV, ω₃=8 eV and ω₄=4 eV). Each frequency was shown to be associated mainly with the excitation of a particular interface. In this paper, the calculations show relative probabilities of excitation which confirm these associations with particular interfaces. Results obtained as a function of impact parameter along different radial directions from the center of the particle and for various directions of the incident beam provide a basis for predicting the form of the STEM images expected to be formed with electrons which have lost the corresponding amounts of energy. Observations of energy loss spectra and images obtained with the particular energy losses made with an HB5 STEM instrument are in general agreement with the predictions except that the relative probabilities for excitation are more nearly equal for the various surface plasmons than predicted. It is suggested that these discrepancies arise from differences between the models used for the theoretical calculations and the actual geometry in the experimental situations.     

A facility for metal surface treatment with an electron beam

A design for a facility for the surface treatment of metal samples is described, and the results from investigating the source of a high-current low-energy electron beam are presented. The electron beam, which has a current as high as 300 A, a pulse duration of 30 µs, and a pulse repetition rate of up to 10 Hz, is formed in a plasma-cathode gas-filled diode at an accelerating voltage of 20 kV. The space-charge compensated electron beam is transported a distance of 20 cm in a longitudinal magnetic field to the region of its interaction with a solid body. At a current density as high as 100 A/cm², the power density produced by the beam is sufficient for the metal surface to be melted in the duration of one or several pulses. Samples can be replaced in the facility without breaking the vacuum.Translated from Pribory i Tekhnika Eksperimenta, No. 1, 2005, pp. 135–140.Original Russian Text Copyright © 2004 by Koval, Shchanin, Devyatkov, Tolkachev, Vintizenko.     

Surface plasmon excitation for supported metal particles

Classical dielectric theory has been used to study the effects of a support on the surface plasmon excitation frequencies for small metal particles. Two experimentally accessible cases have been considered and the theoretical results have been compared with observations. For small spherical Al particles, coated with a thin oxide layer and half-buried in an infinite support of Al, four surface plasmon frequencies (ω₁ to ω₄) are predicted. Comparison with results for isolated particles and planar interfaces suggests the identification of ω₃ as the normal small particle surface plasmon; ω₁ and ω₂ are generated by the presence of the support and ω₄ is related to the oxide shell. The ω₂ and ω₃ frequencies are observed in accord with the predictions. For the second case considered, the Al support is replaced by a dielectric, AlF₃. The support then contributes a new peak at about 5 eV which has been observed. The observations were made with the EELS attachment to a conventional analytical electron microscope.     

Excitation of high-intensity laser radiation of semiconductor targets by a subnanosecond electron beam

The results of the excitation of СdS semiconductor targets by a subnanosecond electron beam (EB) with an electron energy of 60–230 keV are presented. The maximum intensity of laser radiation from targets for a 1-mm EB diameter exceeded 10⁷ W/cm² at an efficiency of ~10%. Lasing was initiated at the leading edge of the EB current; laser radiation then reproduced the shape of the excitation pulse. At low excitation levels, a single-mode lasing regime with the wavelength λ = 522 nm was observed. The maximum power of laser radiation (10 MW) was achieved on a multielement CdS semiconductor target. The duration of laser pulses changed in the range of 100–500 ps.     

电子束选区熔化技术的粉末预热系统设计

通过对电子束选区熔化技术中金属粉末的预热方式进行分析和比较,得出了成形底板采用加热板和成形活塞缸上部采用环形加热器进行粉末预热的两种热传导方案;采用短波段的红外辐射灯,并通过旋转装置保证粉末预热和辐射灯不被金属蒸气蒸镀.金属粉末预热后的成形效果明显提高.     

High-efficiency finishing process for metal mold by large-area electron beam irradiation

A new finishing process for metal molds by large-area electron beam (EB) irradiation is proposed in this study. In the large-area EB irradiation equipment used here, an EB with high-energy density is irradiated without focusing the beam, and so the EB with a maximum diameter of 60 mm can be used for melting or evaporating metal surface instantly. Experimental results show that the surface roughness decreases from 6 μmRz to less than 1 μmRz in just a few minutes under proper machining conditions. The corrosion resistance of metal mold surface also could be greatly improved by large-area EB irradiation. Furthermore, the surface roughness of tilting surface close to 90° could be well improved. Therefore, large-area EB irradiation method has a possibility to become a high-efficiency finishing process for metal molds.     

金属表面经脉冲电子束作用后的改性研究

利用扫描电子显微镜,对高功率毫微秒脉冲电子束作用后金属表面的显微组织作了观察,对其显微硬度进行了测试,并对其组织和性能的变化进行了分析和探讨.将高功率脉冲电子束用于金属材料表面的改性是非常有价值的.     

Studies of supported metal catalysts using high resolution secondary electron imaging in a STEM

An additional technique for use in the characterization of catalysts by electron microscopy is presented. High resolution secondary electron images obtained in a VG HB501 scanning transmission electron microscope have been used to study the surface topography of catalysts consisting of small metal particles on high surface area carbon supports. Surface features down to nanometre dimensions can be seen, allowing the examination of micropores in the support as well as larger pore structures. The results are compared with pore size distributions determined by gas adsorption methods, and are shown to yield valuable additional information. In addition, the method in principle allows examination of the locations of small metal catalyst particles on the support.     

Liquid metal alloy ion source based metal ion injection into a room-temperature electron beam ion source

We have carried out a series of measurements demonstrating the feasibility of using the Dresden electron beam ion source (EBIS)-A, a table-top sized, permanent magnet technology based electron beam ion source, as a charge breeder. Low charged gold ions from an AuGe liquid metal alloy ion source were injected into the EBIS and re-extracted as highly charged ions, thereby producing charge states as high as Au(60 +). The setup, the charge breeding technique, breeding efficiencies as well as acceptance and emittance studies are presented.     

Vacuum pumping with an electron beam

The results of preliminary vacuum tests of an electron cooler with an electron beam that was designed for the LEIR lead-ion storage device (currently being built at CERN) are presented. The tests were performed at the Budker Institute of Nuclear Physics, Siberian Division, Russian Academy of Sciences (Novosibirsk, Russia). It has been shown that, after degassing the collector, injection of an electron beam improves the vacuum level in the setup.     

Production of low-Z ions in the Dresden superconducting electron ion beam source for medical particle therapy

We report on experiments with a new superconducting electron beam ion source (EBIS-SC), the Dresden EBIS-SC, with the objective to meet the main requirements for their application in particle-therapy facilities. Synchrotrons as well as innovative accelerator concepts, such as high-gradient linacs which are driven by a large-current cyclotron (CYCLINACS) and direct drive RF linear accelerators may benefit from the advantages of EBISs in regard to their functional principle. First experimental studies of the production of low-Z ions such as H(+), H(2)(+), H(3)(+), C(4+), and C(6+) are presented. Particular attention is paid to the ion output, i.e., the number of ions per pulse and per second, respectively. Important beam parameters in this context are, among others, ion pulse shaping, pulse repetition rates, beam emittance, and ion energy spread.     

Scanning electron microscopic examination of the scolex and external tegumental surface of Proteocephalus ambloplitis

This examination represents the first scanning electron microscopic study of a proteocephalid tapeworm, Proteocephalus ambloplitis, and it also serves as the first comparative study between the adult and larval stages of a tapeworm. Proteocephalus ambloplitis has numerous microtrichs whose densities and diameters differ greatly from those of cyclophyllidean and pseudophyllidean tapeworms previously examined. Proteocephalus ambloplitis also has an external apical organ and a subcuticular organ.     

Probing large area surface plasmon interference in thin metal films using photon scanning tunneling microscopy

The interference of surface plasmons can provide important information regarding the surface features of the hosting thin metal film. We present an investigation of the interference of optically excited surface plasmons in the Kretschmann configuration in the visible spectrum. Large area surface plasmon interference regions are generated at several wavelengths and imaged with the photon scanning tunneling microscope. Furthermore, we discuss the non-retarded dispersion relations for the surface plasmons in the probe–metal system modeled as confocal hyperboloids of revolution in the spheroidal coordinate systems.     

Calculation of the variable-profile electron beam for electron coolers

Interaction of an electron beam with a cooled ion beam makes it possible to reduce its phase volume, perform accumulation of particles, and suppress various “heating” effects. The electron beam can also be used as a target for an electron-ion recombination reaction, which offers a chance to carry out atomic physics experiments and ensure slow uniform extraction of the ion beam from the storage ring. A high-perveance electron beam with a variable profile is required for effective cooling, while a high current density and a low energy of transverse motion of electrons in the beam is needed for extraction by means of recombination. It is shown that a convex cathode placed in a magnetic field can be used to form such a beam. A high current density can be attained with this shape of the cathode, but additional efforts must be focused on optimizing the gun’s optics in order to obtain a low energy of transverse motion of particles. Since ions repeatedly pass through the cooling section during their lifetime at different values of the betatron oscillation phase, the rates of recombination and cooling are dependent on the rms electron velocity averaged over the volume in which the beam interaction occurs. The proposed design of the gun with a convex cathode 10.2 mm in diameter ensures formation of a variable-profile electron beam with a nominal current of 1 A and a current density of 1.2 A/cm². The rms energy of Larmor gyration of electrons at the exit from the gun, averaged over the beam cross section (the “transverse” temperature) is 1 eV. A focusing electrode that forms the Pierce optics near the edge of the cathode, an electrode controlling the beam profile, and an anode are included in the optics of the electron gun.     

Electron-acoustic and surface electron beam induced voltage signal formation in scanning electron microscopy analysis of semiconducting samples

The conditions for the detection of electron-acoustic (EA) and surface electron beam induced voltage (SEBIV) signals using a common sample mount and bottomside detection scheme are hereby discussed. It is shown that while the intrinsic properties of the sample under electron-beam irradiation would chiefly determine the presence of these contrast mechanisms, the manner in which the sample is mechanically and electrically configured in relation to the signal detection is crucial in determining the actual signal coupling mechanisms at work and hence the assumptions by which a robust and consistent interpretation of experimental results can be made. EA signals are detectable only if electrical coupling between the sample and the detector is defeated, a necessary pre-requisite as the signal magnitude of carrier-generated SEBIV coupling is 2-3 orders larger in most cases. With regards to SEBIV detection, bottomside SEBIV detection may be preferable to topside detection owing to minimization of topographic signal contribution, higher signal coupling efficiency and a less complex sample-detector mounting procedure.     

Specimen preparation technique for high resolution transmission electron microscopy studies on model supported metal catalysts

A new technique is described which can be used for preparing transmission electron microscopy (TEM) specimens suitable for high resolution studies on supported metal catalysts. By conventional silicon processing techniques 200 × 200 μm² Si₃N₄ membranes on Si wafers are produced. These membranes are extremely flat and have a uniform thickness of 13 nm. They can be used as a support in various kinds of thin film deposition. A TiO₂ film, optimally structured with respect to the requirements for high resolution TEM work in TiO₂–metal cluster systems, is deposited on the Si₃N₄ layer. It consists of one monolayer of 10–25 nm TiO₂ crystallites. TiO₂ lattice images show that a line resolution down to 0.19 nm is possible. Examples of TiO₂–Pd and TiO₂–Rh are given using respectively photodeposition and impregnation reduction to produce l.5–4 nm metal clusters.