Display-type Spherical Mirror Analyzer Research Articles

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.

Lattice distortion of porous Si by Li absorption using two-dimensional photoelectron diffraction

Lithiation and delithiation of porous silicon were studied using reflection high energy electron diffraction (RHEED), two-dimensional photoelectron diffraction, and a stereo atom-scope, which is realized by the combination of a display-type spherical mirror analyzer and circularly polarized soft X-ray. A nanosized porous silicon layer was prepared by electrochemical etching of p-type silicon (001) wafer in ethanolic solutions containing hydrofluoric acid. The morphology of the as-grown porous silicon as observed using SEM was filled with about 9 nm holes. This porous silicon also retains the crystallographic orientation of the wafer from which it was etched and is optically active with visible photoluminescence. The measured RHEED pattern and 2π steradian Si 2p photoelectron diffraction pattern from Si (001) surface showed an increase in lattice constant by lithiation, and that change in lattice constant was restored to its original values by delithiation.

Details of 1π sr wide acceptance angle electrostatic lens for electron energy and two-dimensional angular distribution analysis combined with real space imaging

Abstract We propose a new 1π sr Wide Acceptance Angle Electrostatic Lens (WAAEL), which works as a photoemission electron microscope (PEEM), a highly sensitive display-type electron energy and two-dimensional angular distribution analyzer. It can display two-dimensional angular distributions of charged particles within the acceptance angle of ±60° that is much larger than the largest acceptance angle range so far and comparable to the display-type spherical mirror analyzer developed by Daimon et al. [1] . It has good focusing capabilities with 5-times magnification and 27(4) μm lateral-resolution. The relative energy resolution is typically from 2 to 5×10–3 depending on the diameter of energy aperture and the emission area on the sample. Although, the lateral resolution of the presented lens is far from those are available nowadays, but this is the first working model that can form images using charged particles collected from 1π sr wide acceptance angle. The realization of such lens system is one of the first possible steps towards reaching the field of imaging type atomic resolution electron microscopy Feynman et al. [2] . Here some preliminary results are shown.

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

Direct imaging of three-dimensional atomic arrangement by stereophotography using two-dimensional photoelectron spectroscopy

Abstract We have developed a new method, “stereo-atomscope”, to obtain a stereophotograph of the three-dimensional atomic arrangement around a specific atom at the surface, with which one can view the three-dimensional atomic arrangement directly by naked eyes. The azimuthal shifts of forward focusing peaks in the photoelectron angular distribution pattern obtained with left and right helicity lights are the same as the parallax in a stereo-view. Taking advantage of this phenomenon of circular dichroism in the photoelectron angular distribution, one can realize a stereoscope of atomic arrangement. A display-type spherical-mirror analyzer has been used to obtain stereoscopic photographs directly on the screen without any computer-aided conversion process.

Improvement of display-type spherical mirror analyzer for real space mapping of electronic and atomic structures

We have improved a display-type spherical mirror analyzer (DIANA) at Ritsumeikan University SR Center BL-7 for in situ real space mapping of electronic and atomic structures that uses a focused electron beam and a linearly polarized synchrotron radiation (SR). The outer sphere was fully optimized. Compared to the previous analyzer, the energy resolution ( Δ E / E ) has been improved from 1% to 0.09 ± 0.02 %. A newly designed electron gun for measurement of atomic structures was installed inside the analyzer. Thus the measurement of electronic and atomic structures at the same sample position became possible. Here we report on the improvements of the new DIANA and the results of the first in situ measurement of real space mapping of the valence band and scanning Auger electron microscopy (SAM) of a multiple domain Kish graphite. The crystal orientations of each domain were determined from the electronic structures.

Atomic orbitals and photoelectron intensity angular distribution patterns of MoS 2 valence band

The ratio of atomic orbitals contributing to the valence band can be determined from the photoelectron intensity angular distribution (PIAD) by using linearly polarized light and display-type spherical mirror analyzer. The experiment was done for MoS 2 using a linearly polarized light at the photon energy of 45 eV perpendicularly incident to the sample surface. Atomic orbitals contributing to the bands near the Fermi level were investigated. The PIAD patterns around the Γ point showed splitting of intensity. The intensity at the top and bottom K points was strong, while the intensity was weak at the left and right side K points. The PIAD patterns from various kinds of atomic orbitals were calculated. By comparing the experimental PIAD patterns to the simulated ones, we concluded that at the Γ point Mo 4d z2 and S 3p z atomic orbitals are the main components and at the K points the Mo 4d xy atomic orbital is dominant. The atomic orbital Mo 4d x2− y2 also gives contribution to the PIAD pattern. These results were in good agreement with the coefficients of the atomic orbitals derived using ab initio band calculation.

Total analysis of surface structure and properties by UHV transfer system

We have developed an ultrahigh-vacuum (UHV) complex sample preparation and analysis system, which realizes a reliable surface science analyzing various characters on an identical surface. The system contains three sample-preparation-and-characterization chambers and five analysis chambers. They are (1) an electronic-properties-characterization chamber, (2) a magnetic-properties-characterization chamber, (3) an organic-molecule chamber, (4) UHV SEM, (5) a high-energy-resolution angle-resolved photoelectron spectrometer, (6) a high-energy-resolution display-type spherical mirror analyzer, (7) a room-temperature (RT) STM, and (8) an optical-properties characterization chamber. A special sample holder is used with six electrodes on it, which enables accurate temperature measurement of a sample by connecting a thermocouple directly to the sample even if it is transferred. Four other electrodes can be used for construction of various circuits including evaporators. Some examples are shown.

Circularly polarized X-ray photoelectron diffraction: Stereo photograph of atomic arrangement

We have developed a new method, “stereo atomscope”, to obtain a stereophotograph of the three-dimensional atomic arrangement around specific atom at the surface, with which one can view the three-dimensional atomic arrangement directly by the naked eyes. The azimuthal shifts of forward-focusing peaks in the photoelectron angular distribution pattern obtained with left and right helicity light are the same as the parallax in a stereo view. Taking advantage of this phenomenon of circular dichroism in the photoelectron angular distribution, one can realize a stereoscope of atomic arrangement. A display-type spherical-mirror analyzer can obtain stereoscopic photographs directly on the screen without any computer-aided conversion process. As the acquisition time of the stereophotograph became shorter, the real-time stereo observation will be possible in the near future.

Photoelectron angular distribution of 2H‐NbSe2 studied by a display‐type spherical mirror analyzer and circularly polarized light

AbstractPhotoelectron angular distributions (PEAD) of 2H‐NbSe2 were studied by using a display‐type spherical mirror analyzer (DIANA) and circularly polarized light. Forward focusing peaks in a wide acceptance angle of ± 60° are clearly observed. The forward focusing peaks in the two PEAD patterns taken with clockwise (cw) and counterclockwise (ccw) circularly polarized light show the three‐dimensional atomic arrangements around specific atoms. Three‐dimensional atomic arrangements up to at least the third nearest‐neighbor layer atoms upon the Nb layer were observed. The characteristic of this experimental method is the full application of the forward focusing peak rotation due to the exciting circularly polarized light. Copyright © 2006 John Wiley & Sons, Ltd.

ATOMIC STRUCTURE ANALYSIS OF ULTRA THIN IRON SILICIDE FILMS BY STEREO ATOMSCOPE

Three-dimensional atomic arrangements of ultra thin Fe silicide films were directly revealed. By using circularly polarized light with opposite helicities, forward focusing peaks with their positions shifted in photoelectron angular distribution (PEAD) patterns can be obtained. We successfully observed the PEAD patterns of ultra thin Fe silicide films from different core levels of Fe and Si atoms by display-type spherical mirror analyzer (DIANA). The element selective stereo photographs indicate similar hexagonal atomic arrangement with three-fold symmetry for Si and Fe atoms, which is consistent with a model based on a CsCl -type structure with B-type stacking. This is the first observation of stereoscopic atomic arrangements for ultra thin compound films, which implies that the stereo atomscope is very powerful structure analysis tool also for complex structures on surface.

Magnetism-induced symmetry breaking in photoelectron diffraction patterns

The magnetism-induced symmetry breaking in photoelectron diffraction patterns of $2{p}_{3∕2}$ photoelectrons from a ferromagnetic Fe(001) single crystal surface is studied experimentally and theoretically. Two-dimensional photoelectron intensity angular distribution patterns were recorded at 1193 eV photon energy for both helicities of the circularly polarized light and for opposite magnetization directions of the sample by a display-type spherical mirror analyzer, which allows simultaneous energy and momentum analysis of emitted photoelectrons. The macroscopic magnetization of the sample induces an additional symmetry breaking in the circular dichroism of the $\mathrm{Fe}\phantom{\rule{0.3em}{0ex}}2{p}_{3∕2}$ photoelectron angular distribution patterns which is related to the presence of magnetic moments on the Fe atoms. Multiple-scattering cluster photoelectron diffraction calculations agree well with experiment, and reproduce even fine details of the observed photoelectron diffraction features. The details of that breaking of mirror symmetry of photoelectron scattering in the plane spanned by light incidence and electron emission due to the presence of a magnetization within that plane depends both on the structure and the magnetism of the sample. In connection with multiple scattering calculations, measurements of the magnetism-induced symmetry breaking by two-dimensional photoelectron diffraction patterns may thus be used as a powerful tool for simultaneous structural and magnetic investigations of single crystalline magnetic samples and ultrathin films.

Atomic structure of Fe thin-films on Cu(0 0 1) studied with stereoscopic photography

The complex magnetic properties of Fe films epitaxially grown on Cu(001) have been discussed in relation to their atomic structure. We have studied the Fe films on Cu(001) by a new direct method for three-dimensional (3D) atomic structure analysis, so-called “stereoscopic photography”. The forward-focusing peaks in the photoelectron angular distribution pattern excited by the circularly polarized light rotate around the light axis in either clockwise or counterclockwise direction depending on the light helicity. By using a display-type spherical mirror analyzer for this phenomenon, we can obtain stereoscopic photographs of atomic structure. The photographs revealed that the iron structure changes from bcc to fcc and almost bcc structure with increasing iron film thickness.

Stereoscopic photographs of atomic arrangements in MoS2 single-crystal

Taking advantage of the circular dichroism in photoelectron angular distribution (PEAD), stereoscopic photographs of atomic arrangements can be obtained directly by using two-dimensional display-type spherical mirror analyzer (DIANA) and circularly polarized lights. By measuring the PEAD patterns from different core levels, the stereoscopic photographs of atomic arrangements surrounding two kinds of atoms Mo and S in MoS2 single-crystal were taken separately. The stereoscopic photographs show us the same hexagonal arrangements resulting from the unique sandwich and the long interlayer structure. The element selective stereo-photography has been confirmed to be efficient not only for single element crystals, but also for compound crystals.

Three-dimensional band mapping of graphite

We developed a method to visualize the curved surfaces of valence band dispersion by a display-type spherical mirror analyzer. The π and σ band “surfaces” of graphite measured and displayed three dimensionally contain fruitful information compared to the conventional band dispersion “curves” along a certain direction in k space. The slope and the curvature of local band structure correspond to the velocity and the mass of the valence electrons. By integrating band energy over the entire Brillouin zone, the electronic part of the condensation energy is obtained. Furthermore, the atomic orbitals composing each band are determined from two-dimensional photoelectron intensity distribution by using linearly polarized synchrotron radiation.

Photoelectron diffraction stereograph by display-type spherical mirror analyzer

Display-type spherical-mirror analyzer was newly modified for higher energy resolution and wider acceptance angles. A stereograph of atomic arrangement was displayed directly on its screen without any computer-aided conversion process for the first time. This stereoscopic photograph, which enables viewing three-dimensional atomic arrangement, was realized taking advantage of the phenomenon of circular dichroism in photoelectron diffraction. The azimuthal shifts of forward focusing peaks in a diffraction pattern taken with left and right helicity light in a special arrangement are the same as the parallaxes in a stereo view of atoms. Hence a stereoscopic recognition of three-dimensional atomic arrangement is possible, when the left eye and the right eye respectively view the two images obtained by left and right helicity light simultaneously.

Construction of two-dimensional photoelectron spectrometer at SPring-8

A new type of display-type spherical mirror analyzer has been constructed at BL25SU of SPring-8 to study atomic arrangement on surface and spin arrangement on magnetic surface, and to analyze the atomic orbital of the electrons constituting the valence band and the other interesting electron spectroscopy. The advantage of this analyzer is that the emitted photoelectrons are converged to a focal point with keeping both kinetic energy and momentum. Hence we can realize energy and momentum analyses at once. To perform these studies accurately, the display-type spherical mirror analyzer should satisfy the following specifications such that the energy resolution should be higher than 1% of the pass-energy and the angular resolution should be higher than 1° at least. The improvement was estimated by LEED and photoelectron diffraction of Si(0 0 1). Finally, we could confirm that the energy resolution is 0.2% of the pass energy and the angular resolution is 0.6°. We conclude that the new analyzer satisfy the above requirement.

Stereoscopic microscopy of atomic arrangement by circularly polarized-light photoelectron diffraction.

A principle for stereoscopic photographs that enables viewing three-dimensional atomic arrangements is proposed. The azimuthal shifts of forward-focusing peaks in the photoelectron diffraction pattern obtained by left and right helicity lights enables a stereoscopic image when the two images are, respectively, viewed by the left eye and the right eye simultaneously. By taking advantage of this phenomenon, a display-type spherical-mirror analyzer can obtain stereoscopic photographs directly on the screen without any computer-aided conversion process.

立体原子顕微鏡

An atomic stereo-microscope that enables viewing three-dimensional atomic arrangements was developed. The azimuthal shifts of forward-focusing peaks in photoelectron diffraction pattern obtained by left and right helicity light enable a stereoscopic image when the two images are respectively viewed by the left eye and the right eye simultaneously. Taking advantage of this phenomenon, a display-type spherical-mirror analyzer can obtain stereoscopic photographs directly on the screen without any computer-aided conversion process.

Recent Progress of Photoelectron Spectroscopy and Holography. Electronic Structure Analysis by Linearly Polarized Light Two-dimensional Photoelectron Spectroscopy.

The photoelectron angular distribution (PEAD) from single-crystalline graphite is measured by using a two-dimensional display-type spherical mirror analyzer and a linearly polarized synchrotron radiation by varying the photon and photoelectron kinetic energies. From the study of the photon energy (hν) dependence of umklapp processes, it is found that their intensities are reduced considerably at hν = 50–60 eV. The mechanism of the umklapp process is discussed. The atomic orbitals composing the valence band is shown to be specified from the PEAD pattern by considering a transition matrix as well as umklapp processes. Furthermore, the band structure of graphite over the entire Brillouin zone is measured. The three-dimensional [EB-kx-ky] dispersion of the π and σ bands are extracted and presented for the first time.