Ellipsoidal Mesh Research Articles

Variable-deceleration-ratio wide-acceptance-angle electrostatic lens for two-dimensional angular and energy analysis.

Variable-deceleration-ratio wide-acceptance-angle electrostatic lens (VD-WAAEL) is proposed as a potential technique for two-dimensional angular and energy analysis. The basic features of the lens are studied using the charge simulation method and ray tracing calculation. The lens uses an ellipsoidal mesh electrode and allows a wide acceptance angle of ±50°. Two possible applications of the VD-WAAEL are discussed. One is a simple combination of the VD-WAAEL-projection-lens, in which an aperture is used for energy analysis. The other is a combination of the VD-WAAEL with a conventional electron spectrometer, which is responsible for obtaining higher energy resolution. The former is discussed in detail and the latter is described briefly. While the ray tracing calculation is only for the case of an ideal mesh, a note on the disturbing effect of mesh holes is presented. The best possible energy resolution of the simple VD-WAAEL-projection-lens analyzer seems to be around 1/1000, given a fine mesh electrode to suppress the disturbing effect of mesh holes.

Three-dimensional atomic arrangement around active/inactive dopant sites in boron-doped diamond

Boron-doped diamond has received significant attention as an advanced material for power devices owing to its high breakdown characteristics. To control the characteristics of diamond related to band conduction, it is essential to determine the atomic structure around dopants and to develop a method of controlling the atomic arrangement around dopants. We measured the photoelectron diffraction of a boron-doped diamond using a display-type ellipsoidal mesh analyzer to examine the dopant sites in heavily boron-doped diamond. The B 1s photoelectron spectrum shows two peaks for different chemical bonding sites. These two dopant sites were identified as the substitutional and interstitial sites in diamond.

Development of display-type ellipsoidal mesh analyzer: Computational evaluation and experimental validation

An advanced measurement system for two-dimensional photoelectron spectroscopy has been developed to overcome the difficulties faced in the display-type spherical-mirror analyzer (DIANA) having been used so far. One difficulty is to realize selected small area analysis and another is to obtain higher energy resolution. The developed system, which we call “display-type ellipsoidal mesh analyzer (DELMA)”, has an ellipsoidal mesh electrode as its key element, which allows a wide acceptance angle (>∼±45°) comparable to that of DIANA. In this paper we provide details of DELMA on its design and performance. For the imaging performance, we evaluated, using ray-tracing, some important factors that can affect the spatial resolution: off-axis aberration, the effect of shape and position errors, the disturbing effect of mesh holes, and chromatic aberration. In test experiments, a spatial resolution of around 20–30μm was obtained. The ray-tracing results suggest that this resolution can be improved to be less than 10μm by decreasing the size of mesh holes and the error of the mesh shape. We also provide computational results for the energy resolution obtained in various conditions. It depends not only on the size of the energy-selecting aperture but also on the size and shape of an irradiation spot. Experimental results for the energy resolution were in good agreement with computational results. An available resolution seems to be as good as in DIANA (∼0.5%). A much better resolution is possible in our system by the combination of DELMA and a high resolution concentric hemispherical analyzer. In test experiments using an angle-measurement device, a wide acceptance angle of around ±45° has been successfully confirmed. As a practical example of the angular analysis by DELMA, a photoelectron diffraction pattern measured for single crystalline graphite is shown.

Development of Display-Type Ellipsoidal Mesh Analyzer

We have been developing a new display-type ellipsoidal mesh analyzer (DELMA), which is composed of a wide acceptance angle electrostatic lens (WAAEL) unit and a transfer lens system. By using this analyzer, both photoelectron angular distribution patterns and magnified images of the sample can be obtained on a screen. When the screen is taken away from the electron path, the electrons are introduced to an energy analyzer (VG SCIENTA R4000) and high energy resolution spectra are obtained. A performance test of DELMA using synchrotron radiation was carried out at BL07LSU in SPring-8. We succeeded in measuring for the first time the magnified image of the sample, the angular distribution patterns, and x-ray photoelectron spectra. The magnified image from a mesh sample (SUS316, #100) was measured by using DELMA. The measured acceptance angle of angular distribution patterns using DELMA combined with the energy analyzer was about $±45°. We measured x-ray photoelectron spectra from a Ta plate to evaluate the energy resolution of DELMA. The measured total energy resolution of DELMA combined with the energy analyzer was 0.2% at kinetic energy around 700 eV. [DOI: 10.1380/ejssnt.2011.311]

New 1π sr acceptance angle display-type ellipsoidal mesh analyzer for electron energy and two-dimensional angular distribution as well as imaging analysis

We propose a Display-type Ellipsoidal Mesh Analyzer (DELMA) using a newly developed 1p sr wide acceptance angle electrostatic lens (WAAEL), energy aperture and some other electrostatic lenses [1–5] .I t can display two-dimensional angular distributions of charged particles within the acceptance angle of 7 601, which is much larger than the largest acceptance angle range so far and comparable to the displaytype spherical mirror analyzer (DIANA) developed by Daimon et al. [6,8–11]. It also has a focusing capability with 5 times magnification and � 30 mm lateral resolution. The relative energy resolution is typically from 2 to 5 � 10 � 3 depending on the emission area of the sample, as well as on the diameter of

Approach for simultaneous measurement of two-dimensional angular distribution of charged particles. III. Fine focusing of wide-angle beams in multiple lens systems

This paper provides a way of focusing wide-angle charged-particle beams in multiple lens systems. In previous papers [H. Matsuda, Phys. Rev. E 71, 066503 (2005); 74, 036501 (2006)], it was shown that an ellipsoidal mesh, combined with electrostatic lenses, enables correction of spherical aberration over wide acceptance angles up to +/-60 degrees . In this paper, practical situations where ordinary electron lenses are arranged behind the wide-angle electrostatic lenses are taken into account using ray tracing calculation. For practical realization of the wide-angle lens systems, the acceptance angle is set to +/-50 degrees . We note that the output beams of the wide-angle electrostatic lenses have somewhat large divergence angles which cause unacceptable or non-negligible spherical aberration in additional lenses. A solution to this problem is presented showing that lens combinations to cancel spherical aberration are available, whereby wide-angle charged-particle beams can be finely focused with considerably reduced divergence angles less than +/-5 degrees .

Approach for simultaneous measurement of two-dimensional angular distribution of charged particles. II. Deceleration and focusing of wide-angle beams using a curved mesh lens

Recently, it was shown that using an ellipsoidal mesh in an einzel-type lens, spherical aberration can be corrected over a wide acceptance angle of up to 120 degrees. The present paper creates the possibility for beam analysis by achieving dramatic improvements in deceleration lens capabilities. This provides a scheme for simultaneous angular distribution measurement suitable for application to high-energy charged-particle beams up to around 10 keV. We consider the behavior of wide-angle charged-particle beams in electrostatic fields given by simple solutions of the Laplace equation, starting with a discussion on a spherically symmetric deceleration field. A beam focusing over a wide acceptance angle of 100 degrees is found in a special spherically symmetric field. However, in many cases of the spherically symmetric field, focusing of wide-angle beams is obstructed by the presence of spherical aberration. We show that the spherical aberration can be corrected by two kinds of deformation of the spherically symmetric field, a deformation of the field under a spherical boundary condition and an ellipsoidal deformation of the field. We study practical realization of such fields under the use of a few electrodes and a curved mesh (spherical or ellipsoidal mesh). Some variations of the arrangement of electrodes are considered, and simple designs of deceleration lenses with wide acceptance angles of up to 120 degrees are obtained. Here fine focusing of wide-angle beams can be achieved in a three-electrode deceleration lens with an ellipsoidal mesh.

Approach for simultaneous measurement of two-dimensional angular distribution of charged particles: Spherical aberration correction using an ellipsoidal mesh

An approach for simultaneous measurement of two-dimensional angular distribution of charged particles is proposed. This concerns spherical aberration correction in electrostatic lenses with potential use of a mesh. In an earlier work, an effective use of a spherical mesh has succeeded to obtain a large acceptance angle limited to around 60 degrees (+/- 30 degrees). The present work is aimed at dramatically increasing acceptance angles limited in conventional lenses. For this purpose, spherical aberration behavior of mesh lenses is studied in detail using an analytical approximation and ray tracing, with particular attention paid to the effect of the mesh shape. It is shown here that the lens ability to correct spherical aberration over wide aperture angles can be effectively enhanced by the ellipsoidal deformation of a spherical mesh. We demonstrate that an effective use of an ellipsoidal mesh provides remarkable performance characteristics for electrostatic lenses, which opens new possibilities in surface and materials analysis techniques. Simple examples of ellipsoidal mesh lenses are presented that allow very wide acceptance angles of up to 120 degrees.

Video-based face motion measurement

In this paper, we describe and evaluate a noninvasive method of measuring face motion during speech production. Reliable measures are extracted from standard video sequences using an image analysis process that takes advantage of important constraints on face structure and motion. Measures are made by deforming the surface of an ellipsoidal mesh fit to the face image at successive degrees of spatial resolution using a two-dimensional wavelet transform of the image frames. Reliability of the measures is evaluated through comparison with 3D marker data recorded for the same utterances and speaker, and perceptual evaluation of the talking head animations created from the measures are underway.