Angle-resolved Photoelectron Spectrometer Research Articles

Development of a photoelectron spectrometer for hard x-ray photon diagnostics.

The development and characterization of an angle-resolved photoelectron spectrometer, based on the electron time-of-flight concept, for hard x-ray photon diagnostics at the European Free-Electron Laser, are described. The instrument is meant to provide users and operators with pulse-resolved, non-invasive spectral distribution diagnostics, which in the hard x-ray regime is a challenge due to the poor cross-section and high kinetic energy of photoelectrons for the available target gases. We report on the performances of this instrument as obtained using hard x-rays at the PETRA III synchrotron at DESY in multibunch mode. Results are compared with electron trajectory simulations. We demonstrate a resolving power of 10eV at incident photon energies up to at least 20keV.

Commissioning of a photoelectron spectrometer for soft X-ray photon diagnostics at the European XFEL.

Commissioning and first operation of an angle-resolved photoelectron spectrometer for non-invasive shot-to-shot diagnostics at the European XFEL soft X-ray beamline are described. The objective with the instrument is to provide the users and operators with reliable pulse-resolved information regarding photon energy and polarization that opens up a variety of applications for novel experiments but also hardware optimization.

A collinear angle-resolved photoelectron spectrometer

In the present paper we describe a newly designed collinear photoelectron spectrometer for angular distribution measurements. We will henceforth refer to this instrument by the acronym PEARLS (PhotoElectron Angle-Resolved Linear Spectrometer). The design was motivated by the desire to collect electrons emitted from an extended linear source consisting of collinear photon and ion beams at a synchrotron radiation site. The electrons could be produced in either photoionization or photodetachment events. The primary advantage of a collinear beams geometry is that the effective interaction volume can be made much larger than that obtainable with a crossed beams geometry, which has been used in many earlier photoelectron spectroscopic studies. The present apparatus is capable of collecting electrons over a beam source length of 22 cm. The electrons are detected using Channel Electron Multipliers (CEMs). There are 4 detector planes placed perpendicular to the direction of the beam source, where each plane contains 4 CEMs. The use of all 4 detector planes with a total of 16 CEMs enhances the photoelectron signal, which is important at a synchrotron radiation site where the photon flux is typically low. If photoelectrons of different energies are emitted, the design allows for electrostatic energy analyzers to be placed in front of the CEMs. We have performed a photodetachment experiment to demonstrate the functionality of the PEARLS apparatus using a pulsed laser as the photon source. In particular, we have measured the angular distribution of photoelectrons ejected from Ag- at two different photon energies.

Characterization of Stoichiometric ZrO<sub>2</sub> Thin Film on Si by Angle-Resolved X-Ray Photoelectron Spectroscopy

Simultaneous thermal oxidation and nitridation technique was utilized to transform sputtered Zr to stoichiometric ZrO2 thin films on Si substrate. The stoichiometry of this type of oxide has high dielectric constant value of ~25 may be applied as dielectric in metal-oxide-semiconductor-based power devices. Through nitrous oxide gas environment, the oxidation/nitridation process was performed at 700°C for a set of time of 5–20 min. Chemical properties of the fabricated films have been characterized by angle-resolved x-ray photoelectron spectrometer. From the characterization, it was found that stoichiometric Zr-O (ZrO2) was formed. Nitrogen content in the samples was investigated. It was identified that sample oxidized/nitrided for 15 min gives the highest atomic percentage of nitrogen of 2.64 at% in the interfacial layer. This nitrogen content in the near interface region may help to passivate the Si dangling bonds, which may thus enhance the interface quality of oxide-semiconductor.

High-resolution three-dimensional spin- and angle-resolved photoelectron spectrometer using vacuum ultraviolet laser light.

We describe a spin- and angle-resolved photoelectron spectroscopy (SARPES) apparatus with a vacuum-ultraviolet (VUV) laser (hν = 6.994 eV) developed at the Laser and Synchrotron Research Center at the Institute for Solid State Physics, The University of Tokyo. The spectrometer consists of a hemispherical photoelectron analyzer equipped with an electron deflector function and twin very-low-energy-electron-diffraction-type spin detectors, which allows us to analyze the spin vector of a photoelectron three-dimensionally with both high energy and angular resolutions. The combination of the high-performance spectrometer and the high-photon-flux VUV laser can achieve an energy resolution of 1.7 meV for SARPES. We demonstrate that the present laser-SARPES machine realizes a quick SARPES on the spin-split band structure of a Bi(111) film even with 7 meV energy and 0.7(∘) angular resolutions along the entrance-slit direction. This laser-SARPES machine is applicable to the investigation of spin-dependent electronic states on an energy scale of a few meV.

レーザー光励起スピン・角度分解光電子分光装置の開発

Spin- and angle-resolved photoelectron spectrometer using a laser light of 6.994 eV as a photon source has been developed at Laser and Synchrotron Research Center in Institute for Solid State Physics. The spectrometer consists of a high-energy resolution photoelectron analyzer and two high-efficient spin detectors associating very low energy electron diffraction, which allows us to analyze the three-dimensional spin polarization of electrons with high-energy and -angular resolutions. Fermi surface mapping and spin- and angle-resolved photoelectron spectroscopy of a surface state of Bi(111) have been performed to demonstrate the performance of the new spectrometer.

Efficient spin resolved spectroscopy observation machine at Hiroshima Synchrotron Radiation Center

Highly efficient spin- and angle-resolved photoelectron spectrometer named ESPRESSO (Efficient SPin REsolved SpectroScopy Observation) machine has been developed at the beamline BL-9B in Hiroshima Synchrotron Radiation Center. Combination of high-resolution hemispherical electron analyzer and the high-efficient spin detector based on very low energy electron diffraction by the ferromagnetic target makes the high-energy resolution and angular resolution compatible with spin- and angle-resolved photoemission (SARPES) measurement. 7.5 meV in energy and ±0.18° in angular resolution have been achieved with spin resolution. The ESPRESSO machine, combination of quick energy-band dispersion measurement and Fermi surface mapping by two-dimensional electron detector for the spin integrated ARPES and the high-efficient spin analysis by the efficient spin detector realizes the comprehensive investigation of spin electronic structure of materials.

A spin- and angle-resolving photoelectron spectrometer

A new type of hemispherical electron energy analyzer that permits angle and spin resolved photoelectron spectroscopy has been developed. The analyzer permits standard angle resolved spectra to be recorded with a two-dimensional detector in parallel with spin detection using a mini-Mott polarimeter. General design considerations as well as technical solutions are discussed and test results from the Au(111) surface state are presented.

Measuring spin polarization vectors in angle-resolved photoemission spectroscopy

The quantitative analysis of spin-polarized photoemission data is discussed. An angle-resolving photoelectron spectrometer equipped with a three-dimensional (3D) spin polarimeter produces complete data sets consisting of photoemission intensities as well as spin asymmetry curves for three orthogonal vector components. In a two-step fitting routine, the photoemission spectrum is first dissected into individual peaks and background. Assigning trial spin polarization vectors to each of them, the asymmetry curves can be modeled until the best fit is reached. This procedure is crucial when analyzing strongly overlapping peaks or weak signals sitting on a large unpolarized background, especially in the presence of non-collinear spins. It is robust against strong intensity variations due to matrix element effects because it references the spin polarization contribution of each band to the measured peak intensity. The method is applied to 2D systems where spin–orbit effects lead to spin splittings and complex momentum-dependent spin structures. Presented case studies include surface alloys of Bi and Pb on Ag(111) that show a giant Rashba effect.

A spin- and angle-resolved photoelectron spectrometer

A spin- and angle-resolved X-ray photoelectron spectrometer for the study of magnetic materials will be discussed. It consists of a turntable with electron lenses connected to a large hemispherical analyzer. A Mini-Mott spin detector is fitted to the output of the hemispherical analyzer. This system, when coupled to a synchrotron radiation source will allow determination of a complete set of quantum numbers of a photoelectron. This instrument will be used to study ferromagnetic, antiferromagnetic and nonmagnetic materials.

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.

Beamline for angle-resolved photoemission spectroscopy at low-temperature constructed at NTT Atsugi R&D Center

A vacuum ultra-violet beamline for in situ angle-resolved photoemission spectroscopy of MBE-grown high- T c superconductors at low temperature has been constructed at beamline ABL-6B of the normal-conducting ring in the synchrotron radiation facility of the NTT Atsugi R&D Center. The constant-deviation-angle varied-line-spacing plane grating monochromator covers the energy range of 20–200 eV by using two gratings. A photon flux of the order of 10 11s −1 with a resolving power of 2000 or more was achieved in the whole energy range. The endstation is equipped with an angle-resolved photoelectron spectrometer, an rf-stimulated He discharge lamp, a custom-designed sample manipulator for low-temperature measurements and a loadlock system for in situ measurements. Total energy resolution of about 13 meV has been obtained for the photoemission spectrum of the Au Fermi edge, in spite of the bending-magnet light source of a second-generation synchrotron radiation ring.

Time- and angle-resolved photoelectron spectrometer based on a picosecond Nd:glass laser system

A time- and angle-resolved photoelectron spectrometer based on an amplified picosecond Nd:glass laser system is described. The kinetic energy of photoemitted electrons, excited by 0.4 ps laser pulses at 264 nm, is measured with a time-of-flight electron energy analyzer. A theoretical model that takes into account the electron drift inside the μ-metal shielded tube as far as the electron analyzer has been introduced to calculate the energy distribution curves of photoelectrons. As a test of the experimental apparatus we present photoemission spectra of cesiated silver excited with 4.7 eV photons. Good agreement between the experimental and the calculated distribution curves of photoemitted electrons has been found. Finally, we have briefly discussed the electronic properties of silver in terms of free electron and d-band transitions, together with Auger processes for photon energies near 4 eV.

A new compact spin- and angle-resolving photoelectron spectrometer with a high efficiency.

A portable spin- and angle-resolving photoelectron spectrometer has been constructed, equipped with a newly developed compact retarding-potential Mott-scattering electron spin polarimeter with an efficiency of 1.9 x 10(-4) for a gold target. Based on Monte Carlo calculations for the spin-dependent electron-scattering process and electron ray-tracing calculations, a novel design of the retarding-field electron optics with 0.59 sr collection solid angle for scattered electrons has been accomplished. Utilizing this spectrometer, the spin- and angle-resolved photoelectron spectra have been measured and the spin-dependent electronic structure of Ni(110), Ni(110)-p(2 x 1)O and Ni(110)-c(2 x 2)S along the ${\overline {\Gamma S}}$ line of the Ni(110) surface Brillouin zone have been studied.

Symmetry analysis of the Fermi surface of Bi 2Sr 2CaCu 2O 8 by display analyzer

We have directly observed the Fermi surface of Bi 2Sr 2CaCu 2O 8(Bi(2212)) by a display-type angle-resolved photoelectron spectrometer. The experiment was done at room temperature by using linearly-polarized synchrotron radiation (SR). The photon energy was 32 eV and the incident angle of the photon was perpendicular to the sample surface. Photoelectron angular distribution (PEAD) patterns were measured at various azimuthal angles φ from 0° to 135° in steps of 22.5°, where φ is the angle between the direction of the electric vector of the photon and the sample Cu O bond direction. The observed shape of the Fermi surface is consistent with the band calculation by the FLAPW method [S. Massidda et al., Physica C 152 (1998) 251]. We confirmed the symmetry of the atomic orbital constituting the Fermi surface to bed x 2−y 2 by ‘orbital determination by angular distribution’ (ODAD).

A new compact electron spin polarimeter with a high efficiency

We have developed a new compact retarding-potential Mott spin polarimeter and achieved an efficiency of 1.9×10−4 for gold target operating in 25 keV. A novel design of the retarding field electron optics with 0.59 sr collection solid angle for scattered electrons was adopted based on Monte Carlo calculations for the spin-dependent electron scattering process and electron beam ray-tracing calculations. We have combined the new spin polarimeter with an angle-resolved photoelectron spectrometer and measured the spin- and angle-resolved photoelectron spectra and studied the spin-dependent electronic structure of Ni(110) along the Γ̄S̄ line of its surface Brilluoin zone.

Construction of a Compact Spin- and Angle-Resolved Photoelectron Spectrometer

A compact photoelectron spectrometer has been constructed to analyze energy, momentum and spin of the electronic states in condensed matter. The spectrometer consists of an electron energy analyzer, lens systems and a spin detector. The spin detector is a low-energy diffuse scattering type instrument with a potential of about 100–250 eV. The detector consists of a 90° deflector, a gold target, a four-section anode and lens systems. The detector is about 0.15×0.05×0.05 m3 in size and is rotatable along a single axis in the analysis chamber under ultra-high vacuum conditions. The parameters of the optical elements have been determined through optimization of the photoelectrons from GaAs(100) and with reference to the ray tracing calculation. The performance of the spin detector has been verified by observing the spin-polarized electrons from O/Cs/GaAs(100).

Design of a high-resolution angle-resolving photoelectron spectrometer system

The design and construction details, along with performances, of an angle-resolving electron spectrometer specifically designed for use on the Synchrotron Radiation Research Center in Taiwan are described. The spectrometer is a 160° spherical deflecting-type analyzer with a mean radius of 36.5 mm, including input and output lenses in order to enhance the energy resolution and the count rates. Two real apertures defining an acceptance angle and a probe area are located in the field free region ahead of the input lens, and the entrance and exit apertures of the spherical deflecting sector are set to be virtual. In the design, constant angular resolution, constant energy resolution, and constant transmission are achieved by the spectrometer. The performance of the spectrometer has been tested and is in good agreement with the theoretical calculations.

A new angle-resolving photoelectron spectrometer for photoionisation studies of free atoms and molecules using synchrotron radiation

A newly constructed angle-resolving photoelectron spectrometer and an appropriate computer-based spectrometer control and data-acquisition system, both specifically designed for photoionisation studies of free atoms and molecules using monochromatised synchrotron radiation from the electron storage ring BESSY, are described. Details of an experimental procedure for the determination of high-precision photoelectron angular-distribution parameters β are specified. To illustrate the performance of the described apparatus and procedure, β values for the Kr + (4p) −1 spin—orbit components 2 P 3 2 and 2 P 1 2 , measured using synchrotron radiation in the photon energy range 15–24.8 eV, are presented and compared with available experimental and theoretical literature data. The uncertainties of the reported angular-distribution parameters are considerably smaller than those of earlier data. Hence the angular-distribution parameters of the present study can be very useful for future accurate polarisation determinations of monochromatised synchrotron radiation and for calibration procedures of other angle-resolving photoelectron spectrometers.

A fast multianode detector for solid state ultraviolet photoelectron spectroscopy

A new angle-resolving photoelectron spectrometer has been developed which uses a fast multianode parallel readout. The detector has been designed for high resolution ultraviolet photoelectron spectroscopy from solid surfaces using synchrotron radiation. Examples of initial results obtained with the detector using a rare gas discharge lamp are presented.