KREIOS

Hemispherical deflection analyzers are the most widely used energy filters for state-of-the-art electron spectroscopy. Due to the high spherical symmetry, they are also well suited as imaging energy filters for electron microscopy. Here, we review the imaging properties of hemispherical deflection analyzers with emphasis on the application for cathode lens microscopy. In particular, it turns out that aberrations, in general limiting the image resolution, cancel out at the entrance and exit of the analyzer. This finding allows more compact imaging energy filters for momentum microscopy or photoelectron emission microscopy. For instance, high resolution imaging is possible, using only a single hemisphere. Conversely, a double pass hemispherical analyzer can double the energy dispersion, which means it can double the energy resolution at certain transmission, or can multiply the transmission at certain energy resolution.

C. Tusche, Y. J. Chen, C. M. Schneider and J. Kirschner
Ultramicroscopy 206 (2019)

Kagome metals $A{V}_3{\mathrm{Sb}}_5$ ($A=K$, Rb, and Cs) exhibit a characteristic superconducting ground state coexisting with a charge density wave (CDW), whereas the mechanisms of the superconductivity and CDW have yet to be clarified. Here we report a systematic angle-resolved photoemission spectroscopy (ARPES) study of $\mathrm{Cs}(V_{1-x}{\mathrm{Nb}}_x{)}_3{\mathrm{Sb}}_5$ as a function of Nb content $x$, where isovalent Nb substitution causes an enhancement of superconducting transition temperature ($T_c$) and the reduction of CDW temperature ($T_{\mathrm{CDW}}$). We found that the Nb substitution shifts the Sb-derived electron band at the $\Gamma$ point downward and simultaneously moves the V-derived band around the $M$ point upward to lift up the saddle point (SP) away from the Fermi level, leading to the reduction of the CDW-gap magnitude and $T_{\mathrm{CDW}}$. This indicates a primary role of the SP density of states to stabilize the CDW. The present result also suggests that the enhancement of superconductivity by Nb substitution is caused by the cooperation between the expansion of the Sb-derived electron pocket and the recovery of the V-derived density of states at the Fermi level.

Takemi Kato, Yongkai Li, Kosuke Nakayama, Zhiwei Wang, Seigo Souma, Fumihiko Matsui, Miho Kitamura, Koji Horiba, Hiroshi Kumigashira, Takashi Takahashi, Yugui Yao and Takafumi Sato
PHYSICAL REVIEW LETTERS 129, 206402 (2022)

The photoelectron momentum microscope (PMM) in operation at BL6U, an undulator-based soft x-ray beamline at the UVSOR Synchrotron
Facility, offers a new approach forμm-scale momentum-resolved photoelectron spectroscopy (MRPES). A key feature of the PMM is that it
can very effectively reduce radiation-induced damage by directly projecting a single photoelectron constant energy contour in reciprocal
space with a radius of a few Å−1or real space with a radius of a few 100μm onto a two-dimensional detector. This approach was applied to
three-dimensional valence band structureE(k)andE(r)measurements (“stereography”) as functions of photon energy(hν), its polarization
(e), detection position(r), and temperature(T). In this study, we described some examples of possible measurement techniques using a soft
x-ray PMM. We successfully applied this stereography technique toμm-scale MRPES to selectively visualize the single-domain band structure
of twinned face-centered-cubic Ir thin films grown on Al2O3(0001) substrates. The photon energy dependence of the photoelectron intensity
on the Au(111) surface state was measured in detail within the bulk Fermi surface. By changing the temperature of 1T-TaS2, we clarified
the variations in the valence band dispersion associated with chiral charge-density-wave phase transitions. Finally, PMMs for valence band
stereography with various electron analyzers were compared, and the advantages of each were discussed.

Fumihiko Matsui, Kenta Hagiwara, Eiken Nakamura, Takayuki Yano, Hiroyuki Matsuda,
Yasuaki Okano, Satoshi Kera, Eri Hashimoto, Shinji Koh, Keiji Ueno, Takahiro Kobayashi,
Emi Iwamoto, Kazuyuki Sakamoto, Shin-ichiro Tanaka, and Shigemasa Suga
Rev. Sci. Instrum. 94, 083701 (2023)

Chuang, T.-H., Hsu, C.-C., Chiu, W.-S., Jhuang, J.-S., Yeh, I.-C., Chen, R.-S., Gwo, S. & Wei, D.-H.
J. Synchrotron Rad.

The implementation of graphene in semiconducting technology requires precise knowledge about the graphene–semiconductor interface. In our work the structure and electronic properties of the graphene/n-Ge(110) interface are investigated on the local (nm) and macro (from μm to mm) scales via a combination of different microscopic and spectroscopic surface science techniques accompanied by density functional theory calculations. The electronic structure of freestanding graphene remains almost completely intact in this system, with only a moderate n-doping indicating weak interaction between graphene and the Ge substrate. With regard to the optimisation of graphene growth it is found that the substrate temperature is a crucial factor, which determines the graphene layer alignment on the Ge(110) substrate during its growth from the atomic carbon source. Moreover, our results demonstrate that the preparation route for graphene on the doped semiconducting material (n-Ge) leads to the effective segregation of dopants at the interface between graphene and Ge(110). Furthermore, it is shown that these dopant atoms might form regular structures at the graphene/Ge interface and induce the doping of graphene. Our findings help to understand the interface properties of the graphene–semiconductor interfaces and the effect of dopants on the electronic structure of graphene in such systems.

J. Tesch, F. Paschke, M. Fonin, M. Wietstruk, S. Böttcher, R. J. Koch, A. Bostwick, C. Jozwiak, E. Rotenberg, A. Makarova, B. Paulus, E. Voloshina, Y. Dedkov
Nanoscale, 10, pp. 6088-6098