Low Energy Scanning Electron Microscopy Research Articles

Detection of the Angular Distribution of the Signal Electrons in VLESEM

The topic of this work is the study of direct detection of electrons by Charge-Coupled-Devices (CCD). The aim is to design a detector for the angle and energy-selective detection of signal electrons in very low energy scanning electron microscopy (VLESEM), using an electron-bombarded CCD sensor (EBCCD). We concentrate upon two problems—the design of appropriate electronics and determination of an appropriate energy of the signal electrons for the CCD sensor.

Real image resolution of SEM and low-energy SEM and its optimization: distribution width of the total surface emission

The real point resolution of an SEM image is treated in a two-dimensional model where the decisive quantity is the root-mean-square distance of the emitted electron from the pixel centre. This quantity is computed taking into account the direct illumination of the specimen surface by the primary spot the dimensions of which are given by the electron optical column and the indirect illumination from a virtual source of the backscattered electrons in the specimen depth the properties of which depend on the specimen. Because the second order movement of the full distribution is considered here instead of some measure of the central narrow peak of secondaries, the backscattered electron influence significantly deteriorates the resulting resolution. Reasonable approximations regarding both contributions, particularly the Monte-Carlo modelling of the backscattering process by algorithms providing acceptable results down to 1 keV and the approximate relations describing the secondary and backscattered electron emission again down to 1 keV, enabled us to bring the considerations up to numerical results for some typical instruments, namely a “cheap” SEM, a “top” SEM and a low-energy SEM (LESEM) adapted from the cheap SEM by using the cathode lens. The optimum landing energy providing the best point resolution, computed for the individual chemical elements, falls into the range 1 to 5 keV for the cheap SEM and it remains around 1 keV (with some uncertainty caused by the approximations mentioned) for both the top SEM and LESEM. Similarly, the real resolution for the elements ranges between 16 and 45 nm when the cheap SEM with a 3.4 nm nominal spotsize at 30 keV is used, between 3.5 and 9 nm for the 0.7 nm top SEM and between 5.5 and 7 nm for the cheap SEM adapted to LESEM.

Separator of primary and signal electrons for very low energy SEM

High resolution can be obtained in the scanning electron microscope (SEM) for a very low landing energy of electrons, even for that below 50 eV, when a cathode lens is used with the specimen as a cathode held at a high negative potential but the detection of signal electrons is totally different compared with classical SEM. Primary electrons with an energy of the order of tens of keV are decelerated in the field of the cathode lens to a very low landing energy and signal electrons originating in the specimen are accelerated and collimated by the same field to a narrow beam with an electron energy nearly the same as that of the primary beam. To detect these signal electrons we must deflect them from the optical axis without deteriorating the properties of the primary beam. The design of a novel type of separator of the primary and signal electrons consisting of two stages, each of them formed by the electric and magnetic crossed fields, is presented, together with calculated trajectories for both primary and signal electrons.

表面構造評価法 低エネルギー走査型電子顕微鏡

表面構造評価法 低エネルギー走査型電子顕微鏡

Low energy scanning electron microscopy combined with low energy electron diffraction

Low energy scanning electron microscopy combined with low energy electron diffraction

Low energy scanning electron microscopy combined with low energy electron diffraction

An ultra-high-vacuum (UHV) scanning-electron microscope (SEM) with a field-emission gun (FEG) is operated in a low energy region from 100 eV to 3 keV. The functions of scanning low energy electron diffraction microscopy and scanning Auger microscopy have been implemented and their performance is demonstrated. Observations in the SEM mode, the low energy electron diffraction (LEED) mode and the Auger mode have been made on the following examples: the step structure of the clean Si(111) surface, the structure of islands and their movement on the Au evaporated surface of Si(111), different orientations of grains on the polycrystalline Si surface and the coexistence of different super-structures on the Au-evaporated surface of Si(111).

Elastic peak electron spectroscopy

AbstractElastic peak electron spectroscopy (EPES) determines the elastic peak intensity N (Ep) in absolute units (percentage). The experimental curve N (Ep) is affected by the type of electron spectrometer used (CMA, RFA, etc.) and represents the probability Pe (E, Z) of elastic electron reflection detected by the angular window of the spectrometer.Pe (E, Z) = NAσeff (E, Z) Δ is the product of the inelastic mean free path Δ, the density NA of atoms and the effective elastic scattering cross‐section σeff (E, Z). Elementary processes of elastic scattering are treated with a simplified model based on a single scattering process. A more refined analysis will be to use the Monte‐Carlo approach. σeff is given by the differential elastic scattering cross‐section determined by the atomic number Z, the energy Ep, and the input and scattering angles. Results of σeff (E, Z) are presented based on tabulated differential cross‐section data published in the literature. Angular effects are discussed. A number of EPES applications are described for AES, plasmon‐, ionization‐, and low energy loss spectroscopies and SEM. EPES has been successful in the experimental determination of the inelastic mean free path Δ for a number of elements and compounds.

Surface structure analyses by low-energy scanning electron microscope in ultra-high vacuum

Surface structure analyses by low-energy scanning electron microscope in ultra-high vacuum

Surface analyses by low energy SEM in ultra high vacuum

The design and performance of an ultra high vacuum SEM with a field emission gun for solid surface are described. In situ observations of an Si surface are demonstrated for processes of surface cleaning by flashing, step formation of Si(111) surface by annealing, epitaxial growth of metal-deposited layers on Si surfaces by heat treatment, surface segregation of Ni-contaminated layer on the Si(110) by heat treatments and phase transitions of reconstructed structures by electron energy loss spectroscopy.

Microscopic analysis of surface state of SUS-304L stainless steel by low energy scanning electron microscopy in ultra high vacuum

The variation of surface state of SUS-304L stainless steel with heat treatment in a vacuum of 10 −9 Torr was observed by the ultra high vacuum low energy scanning electron microscope (UHVLESEM) by detecting the absorption electron current. The absorption electron current was very sensitive to the surface state and a large effect of the electron beam irradiation was observed. The variation of the absorption electron current with the surface segregation was measured within a microscopical dimension of 0.3 microm on a selected area of the scanning electron microscopic image. At the same time, the surface state was characterized by Auger electron spectroscopy and relations between surface states and the absorption electron current were discussed in relation to the secondary electron and backscattered electron yields.

Microscopic analysis of surface state of SUS-304L stainless steel by low energy scanning electron microscopy in ultra high vacuum

Microscopic analysis of surface state of SUS-304L stainless steel by low energy scanning electron microscopy in ultra high vacuum

A scanning electron microscope (SEM) sturon me the magnetic domain structure of ion meteorites and their synthetic analogues.

Magnetic domain observations were carried out on iron meteorites and on sputter-deposited thin films of meteoritic composition (10, 20% Ni-Fe), by two SEM techniques: 1) high voltage (30kV) backscattered electron mode and 2) low-voltage (2kV) secondary electron image. To confirm and complement these, 3) Bitter-powder patterns were also observed in reflected-light microscopy. High energy SEM magnetic contrast revealed parallel-oriented arrays of stripe domains in kamacite (k) regions, at 60° (for ‹111› face) or 90° (for ‹100› face) to their taenite (t) boundaries, depending on the crystal orientation. Magnetic domain widths ranged from 15-25μm in the Gibeon meteorite (finest octahedrite, 8% Ni-Fe, average k-bandwidth 0.2mm) to 40-80μm in the Odessa meteorite (coarsest octahedrite, 7.29% Ni-Fe, 3.3mm k-bands). Finer domain substructure (-10μm) was resolved by Bitter-pattern microscopy in Odessa, as magnetic grids in each k grain, whose orientation was discontinuous across boundaries. Based on low-energy SEM observations of Gibeon, it appears that each micro-kamacite grain in plessite regions is a single domain. By the same technique, 1-5μm stripe domains separated by ≤0.5μm Bloch walls were resolved in a 20% Ni-Fe film and 0.2-2μum domains with 90° “elbow”-walls, typical of Fe3O4, were observed in a laboratory-produced Fe3O4 film. The much finer scale of magnetic domain structure in meteorites, by comparison with their metallographic-compositional features, may explain the presence of stable paleoremanence in the coarsely crystalline iron meteorites.The application of even higher-voltage (50kV) SEM to similar studies of terrestrial, lunar, and meteoritic materials promises to reveal the bulk domain-structure of their magnetic carriers and may thus afford a better understanding of their paleomagnetic record.

Analysis of accelerating lens system in field-emission scanning electron microscope

This paper is composed of five sections. Section III analyzes the Butler-type and flat-plate lenses of the accelerating lens system in the scanning electron microscope (SEM) using a field-emission gun. Section IV presents the result of an analysis of some new accelerating lens systems when three anodes are present. The lens systems described in sec. IV are designed particularly for the low-energy SEM. Their major advantage is that the accelerating voltages can freely be changed in a wide range (from 300 V to about 100 kV) by merely adjusting the control voltages between the tip and the second anode without changing the focal point, etc. The resolution of the system and the beam current on the specimen seem to have the possibility of reaching 1000 Å and 10−8 A respectively, at accelerating voltages higher than 3 kV. Therefore, these lens systems also seem appropriate for the scanning Auger electron microscope.