We describe fundamental principles and recent advanced applications of photoemission electron microscopy. Photoelectron emission microscope is a powerful analysis tool to visualize photoelectrons emitted from surface with resolving power well below 100 nm. Photoemission Electron Microscopy (PEEM) is mainly utilized to understand local electronic structure, elemental distribution, lattice structure and magnetic domain structure in the combination of synchrotron radiation. We here introduce resent PEEM results applied for nanomaterials such as L10-type FeNi rare metal free magnets and graphene. And its application is now widely spreading for various frontier field such as earth planetary science or ultrafast spin dynamics.
Synchrotron radiation (SR) is a pulsed light source with a temporal width of about 50 picoseconds. Time-resolved soft X-ray photoelectron spectroscopy (PES), which combines SR soft X-ray with ultrashort pulse laser, allows to study the transient variation of electronic structures of materials with a time resolution of 50 picoseconds in a wide range of time scale from picoseconds to milliseconds. In this article, the time-resolved soft X-ray PES system developed at SPring-8 BL07LSU is described to explain the challenges and solutions in the time-resolved PES experiments. Study of carrier dynamics on oxide semiconductor surfaces is presented as one of the applications by time-resolved PES.
We have constructed a near ambient pressure X-ray photoelectron spectroscopy instrument that use with hard X-ray radiation at the BL36XU of SPring-8 and successfully achieved in situ hard X-ray photoelectron spectroscopic measurements of catalytic electrodes of a polymer electrolyte fuel cell under working conditions. The oxidized Pt peaks were observed in the Pt 3d5/2 level of Pt nanoparticles in the cathode, and the peaks clearly depended on the applied voltage between the anode and cathode. This instrument will enable us to observe various fuel cell electrodes during operation in the future, promoting the development of fuel cell electrodes and catalyst materials.
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.
Scanning photoelectron microscopy (SPEM) is one of the most powerful tools for microfabricated electronic device analysis. In order to understand operation characteristics of real devices, “operando analysis”, i.e., measurement during device operation, is needed. In this report, we present our operando SPEM system, called “3D nano-ESCA” using synchrotron radiation soft X-ray. The 3D nano-ESCA enable us to perform nano-scale pin-point analysis and nondestructive depth profiling, thus we can investigate the effect of surfaces, interfaces and defects on transport characteristics. We have carried out the operando SPEM analysis of graphene field effect transistors (FETs) and organic FETs. Charge transfer region at a metal electrode/graphene channel was successfully detected for the first time. Moreover, pin-point photoemission spectroscopy on the channel under biasing at the gate and drain electrodes clarify energy alignment inside the devices.
Time-resolved photoemission spectroscopy (TRPES) implemented by femtosecond pulsed laser sources has become a powerful tool to investigate light-induced dynamics of matter from an electronic structural point of view. We here describe three types of TRPES apparatus developed at ISSP; namely, high-repetition-rate TRPES based on a Yb:fiber laser, high-energy-resolution TRPES based on a Ti:Sapphire laser, and extreme-ultraviolet TRPES based on high harmonics of 20-60 eV. The former two uses 5.9 eV pulses for the probe, and are suited for high precision measurements owing to their high repetition rate and high energy resolution of < 20 meV. The latter is suited for investigating far from equilibrium dynamics, and has the accessibility into core level spectra, full valence band, and entire Brillouin zone.