Review
Physics, Condensed Matter
Curran Kalha, Nathalie K. Fernando, Prajna Bhatt, Fredrik O. L. Johansson, Andreas Lindblad, Hakan Rensmo, Leon Zendejas Medina, Rebecka Lindblad, Sebastian Siol, Lars P. H. Jeurgens, Claudia Cancellieri, Kai Rossnagel, Katerina Medjanik, Gerd Schonhense, Marc Simon, Alexander X. Gray, Slavomir Nemsak, Patrick Loemker, Christoph Schlueter, Anna Regoutz
Summary: Hard x-ray photoelectron spectroscopy (HAXPES) is a crucial technique for material characterization, with a growing number of specialized techniques utilizing hard x-rays to provide transformative insights into the nature of materials. This paper offers a historical perspective on HAXPES, from its early developments to state-of-the-art instrumentation, and aims to provide an overview of the technique in 2020 and potential future developments.
JOURNAL OF PHYSICS-CONDENSED MATTER
(2021)
Article
Chemistry, Physical
Yujun Zhang, Jiahui Chen, Keisuke Ikeda, Kohei Yamagami, Yue Wang, Yongseong Choi, Akira Yasui, Jing Ma, Yuanhua Lin, Cewen Nan, Hiroki Wadati
Summary: In this study, the magnetism and electronic structure changes across the AFM-FM transition of Ni-doped FeRh epitaxial thin films were investigated using XMCD and HAXPES techniques. The results showed that the remnant FM phase at low temperature possesses a smaller Rh moment than the normal FM phase, while an increase of Rh 4d density of state at the Fermi level and a possible well-screened Ni 2p state were found in the FM phase. In addition, the FM fluctuation of the inter-site Fe-Fe exchange coupling within the AFM phase was observed.
JOURNAL OF ALLOYS AND COMPOUNDS
(2022)
Article
Chemistry, Multidisciplinary
Akinobu Yamaguchi, Takuo Ohkochi, Masaki Oura, Keisuke Yamada, Tsunemasa Saiki, Satoru Suzuki, Yuichi Utsumi, Aiko Nakao
Summary: The research focuses on the competition between magnetic shape anisotropy and induced uniaxial magnetic anisotropy in the heterojunction between a ferromagnetic layer and a ferroelectric substrate. It reveals the origin of the uniaxial magnetic anisotropy induced from the heterojunction and provides a means for simultaneous control of magnetism, mechanics, and electronics in nano/microsystems consisting of ferromagnetic/ferroelectric materials.
Article
Nanoscience & Nanotechnology
Melanie A. Jenkins, Konner E. K. Holden, Sean W. Smith, Michael T. Brumbach, M. David Henry, Conan Weiland, Joseph C. Woicik, Samantha T. Jaszewski, Jon F. Ihlefeld, John F. Conley
Summary: In this study, energy barriers between various metal electrodes and doped ferroelectric HfO2 were directly measured using internal photoemission (IPE) spectroscopy, and the results were compared with valence band offsets determined by X-ray photoelectron spectroscopy (XPS) and hard X-ray photoelectron spectroscopy (HAXPES). Both XPS and IPE methods showed similar dependence of the HfO2 barrier on metal work function. However, barrier heights determined by XPS and HAXPES were on average about 1.1 eV smaller than those determined by IPE, indicating the presence of negative charge in the HfO2.
ACS APPLIED MATERIALS & INTERFACES
(2021)
Article
Materials Science, Multidisciplinary
Ann Julie U. Holt, Sahar Pakdel, Jonathan Rodriguez-Fernandez, Yu Zhang, Davide Curcio, Zhaozong Sun, Paolo Lacovig, Yong-Xin Yao, Jeppe Lauritsen, Silvano Lizzit, Nicola Lanata, Philip Hofmann, Marco Bianchi, Charlotte E. Sanders
Summary: Through ARPES, direct measurements of the electronic dispersion of single-layer CoO2 were conducted, and the material was determined to be a moderately correlated metal. The study also discussed the effects of substrate and hydroxylation on the electronic structure of CoO2 SL.
Article
Materials Science, Multidisciplinary
G. van der Laan, S. W. Lovesey
Summary: Nonlinear optics, particularly second harmonic generation (SHG), is widely used in modern disciplines for material characterization and bioimaging. A theoretical analysis provides a strong estimate of the energy-integrated SHG response, along with compact spherical multipoles for natural and magnetic circular dichroic signals. Applying symmetry requirements in magnetic neutron scattering and working with electronic multipoles and Racah algebra may have potential utility in various other probes of matter.
Article
Chemistry, Multidisciplinary
Giovanni Chemello, Xenia Knigge, Dmitri Ciornii, Benjamen P. Reed, Andrew J. Pollard, Charles A. Clifford, Tom Howe, Neil Vyas, Vasile-Dan Hodoroaba, Joerg Radnik
Summary: The influence of the morphology of graphene particles on XPS results was studied. It was found that the size of the particles affects the degree of functionalization, and only the combination of XPS and HAXPES allows detection of the functionalization process and provides new insights.
ADVANCED MATERIALS INTERFACES
(2023)
Article
Materials Science, Multidisciplinary
J. G. Tobin, H. Ramanantoanina, C. Daul, P. Roussel, S-W Yu, S. Nowak, R. Alonso-Mori, T. Kroll, D. Nordlund, T-C Weng, D. Sokaras
Summary: Ligand field density functional theory calculations and high-energy-resolution fluorescence detection combined with inverse photoelectron spectroscopy measurements were used to study the 5f electronic structure of the dioxides of thorium, uranium, and plutonium, providing insight into their unoccupied states.
Article
Chemistry, Multidisciplinary
Miranda Martinez, Anil R. R. Chourasia
Summary: The Ti/SnO2 interface was investigated using x-ray photoelectron spectroscopy. Chemical interaction between SnO2 and the titanium overlayer at the interface resulted in the reduction of SnO2 to elemental tin and the oxidation of the titanium overlayer. The interface consisted of elemental Sn, SnO2, elemental titanium, TiO2, and Ti-suboxide. Thermal diffusion of the titanium overlayer was observed in the 200 degrees C samples, leading to complete oxidation of the titanium.
Article
Materials Science, Multidisciplinary
Atsushi Hariki, Keisuke Higashi, Tatsuya Yamaguchi, Jiebin Li, Curran Kalha, Manfred Mascheck, Susanna K. Eriksson, Tomas Wiell, Frank M. F. de Groot, Anna Regoutz
Summary: This paper explores the satellites of the Ti 1s and 2p core level spectra of SrTiO3 and TiO2 using hard x-ray PES. The theoretical analysis emphasizes the importance of higher-order Ti-O charge-transfer processes and provides a robust prescription for using the computationally cheap cluster model in fitting analyses of core level spectra.
Article
Materials Science, Multidisciplinary
Sekhar Chandra Ray
Summary: The electronic and structural properties of MoS2 nanoparticles were studied, and it was found that they exhibit both diamagnetic and ferromagnetic behaviors at around 45 K. The presence of ferromagnetism is significantly enhanced as the temperature decreases, possibly due to factors such as Mo atoms, S vacancies/O vacancies, defective structures, and small nanoparticle sizes. The study suggests the potential technological magnetic applications of MoS2 nanoparticles at low temperatures.
APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING
(2022)
Article
Materials Science, Multidisciplinary
Weon Cheol Lim, Jitendra Pal Singh, Younghak Kim, Jonghan Song, Keun Hwa Chae, Tae-Yeon Seong
Summary: The study shows that thermal annealing significantly affects the properties of zinc oxide thin films, including relaxation of stress, variation in optical band-gap, and occurrence of vacancies and defects. These changes are revealed through X-ray techniques, providing a better understanding of the performance changes in zinc oxide films.
Article
Materials Science, Ceramics
Songhak Yoon, Wenjie Xie, Xingxing Xiao, Stefano Checchia, Mauro Coduri, Peter Schuetzenduebe, Marc Widenmeyer, Stefan G. Ebbinghaus, Benjamin Balke, Anke Weidenkaff, Gisela Schuetz, Kwanghyo Son
Summary: Magnetic properties of perovskite titanates ATiO(3-& delta;) (A = Ca, Sr, Ba) were investigated before and after arc melting. Crystal structure analysis and quantitative chemical element analysis were performed. The magnetic properties were found to be influenced by impurities of 3d elements and the occupation of magnetic ions varied depending on the composition and crystal structure. Furthermore, the formation of oxygen vacancies and reduction of Ti4+ to Ti3+ were also observed during arc melting.
JOURNAL OF THE AMERICAN CERAMIC SOCIETY
(2023)
Article
Chemistry, Physical
Victor da Cruz Pinha Barbosa, Jie Xiong, Phuong Minh Tran, Michael A. McGuire, Jiaqiang Yan, Matthew T. Warren, Rolando Valdes Aguilar, Wenjuan Zhang, Mohit Randeria, Nandini Trivedi, Daniel Haskel, Patrick M. Woodward
Summary: The diversity of magnetic ground states in isoelectronic compounds can be better understood through the study of five double perovskites. Crystallographic distortions play a crucial role in determining the magnetic behaviors of 5d(1) ions, influencing the orbital occupation and ultimately deciding the preferred magnetic ground state.
CHEMISTRY OF MATERIALS
(2022)
Article
Chemistry, Physical
Pankaj Kumar Singh, Keita Shinzato, Hiroyuki Gi, Takayuki Ichikawa, Hiroki Miyaoka
Summary: This study systematically investigates the catalytic properties of group 4-6 element oxides, including TiO2, ZrO2, HfO2, V2O5, Ta2O5, CrO3, MoO3, and WO3, on magnesium hydride (MgH2). The dispersion of each oxide on the MgH2 surface is achieved through ball-milling. The hydrogen desorption properties are analyzed, and the oxides on MgH2 are characterized structurally and spectroscopically. Among the oxides, TiO2, V2O5, ZrO2, and CrO3 exhibit higher catalytic activity, enabling hydrogen desorption at around 200°C. The dispersion of the oxides on Mg is found to be closely related to the catalytic process, except for MoO3. Multi oxide states, particularly the 2+ and 3+ oxidation states of transition metals, contribute to the high catalytic activity.
JOURNAL OF ALLOYS AND COMPOUNDS
(2023)
Article
Nanoscience & Nanotechnology
Judith Gabel, Matthias Pickem, Philipp Scheiderer, Lenart Dudy, Berengar Leikert, Marius Fuchs, Martin Stuebinger, Matthias Schmitt, Julia Kuespert, Giorgio Sangiovanni, Jan M. Tomczak, Karsten Held, Tien-Lin Lee, Ralph Claessen, Michael Sing
Summary: Thin films of transition metal oxides are affected by oxygen adatoms on the surface, leading to the formation of an electronically dead surface layer and altering the band filling and electron correlations. It is important to consider the presence of surface apical oxygen when predicting the behavior of ultrathin films of transition metal oxides.
ADVANCED ELECTRONIC MATERIALS
(2022)
Article
Chemistry, Multidisciplinary
Julian Maklar, Raul Stuehler, Maciej Dendzik, Tommaso Pincelli, Shuo Dong, Samuel Beaulieu, Alexander Neef, Gang Li, Martin Wolf, Ralph Ernstorfer, Ralph Claessen, Laurenz Rettig
Summary: In this study, the electron dynamics of the two-dimensional quantum spin Hall (QSH) candidate bismuthene were investigated using time- and angle-resolved photoemission spectroscopy. Shorter lifetimes of photocarriers in bismuthene compared to conventional semiconductors were observed, which can be attributed to the presence of topological in-gap states. This study marks a critical step toward optical control of QSH functionalities.
Article
Multidisciplinary Sciences
R. Stuehler, A. Kowalewski, F. Reis, D. Jungblut, F. Dominguez, B. Scharf, G. Li, J. Schaefer, E. M. Hankiewicz, R. Claessen
Summary: In this study, the authors demonstrate that topological protection can be lifted by pairwise coupling of 2D TI edges in close proximity. This finding opens up new possibilities for active control of topological protection through inter-edge hybridization.
NATURE COMMUNICATIONS
(2022)
Article
Chemistry, Physical
Jonas Erhardt, Maximilian Bauernfeind, Philipp Eck, Martin Kamp, Judith Gabel, Tien-Lin Lee, Giorgio Sangiovanni, Simon Moser, Ralph Claessen
Summary: Indenene, a large gap quantum spin Hall insulator, is stabilized on SiC substrates and possesses excellent structural and electronic properties. Here, we establish a simple, robust, and scalable fabrication protocol for Indenene, which involves an initial growth stage followed by a short anneal to control the coverage of indium. The specific structural and electronic properties of different coverages produce distinct experimental surface characterization, providing an efficient metric for synthesizing large scale high-quality Indenene on SiC.
JOURNAL OF PHYSICAL CHEMISTRY C
(2022)
Article
Multidisciplinary Sciences
Marcin Syperek, Raul Stuhler, Armando Consiglio, Pawel Holewa, Pawel Wyborski, Lukasz Dusanowski, Felix Reis, Sven Hofling, Ronny Thomale, Werner Hanke, Ralph Claessen, Domenico Di Sante, Christian Schneider
Summary: The optical spectroscopy of ultimately thin materials has greatly benefited our understanding of collective excitations in low-dimensional semiconductors. The authors of this study report the observation of room temperature excitons in a single layer of bismuth atoms epitaxially grown on a SiC substrate, a material with non-trivial global topology. These excitonic and topological physics arise from the same electronic structure.
NATURE COMMUNICATIONS
(2022)
Article
Chemistry, Multidisciplinary
Bing Liu, Tim Wagner, Stefan Enzner, Philipp Eck, Martin Kamp, Giorgio Sangiovanni, Ralph Claessen
Summary: By synthesizing ultrathin Sb films on semi-insulating InSb(111)A substrate, researchers observe a pronounced moire pattern on the Sb films and confirm experimentally that the topological surface state persists and shifts toward lower binding energies with a decrease in Sb thickness, in agreement with theoretical predictions.
Article
Chemistry, Physical
Lenart Dudy, Piotr Chudzinski, Julian Aulbach, Victor Rogalev, Joerg Schaefer, Ralph Claessen
Summary: In this study, we investigated the temperature dependence of the metallic-like bands of Si(553)-Au using angular-resolved photoemission spectroscopy. By overcoming the challenges posed by surface stability and photo-voltage effects, we were able to extract changes in band-filling and Fermi-velocity. Our findings shed light on the nature of the low-temperature phase of the step edge in Si(553)-Au and rule out a structural-related phase transition.
Article
Physics, Multidisciplinary
P. Kagerer, C. I. Fornari, S. Buchberger, T. Tschirner, L. Veyrat, M. Kamp, A. V. Tcakaev, V. Zabolotnyy, S. L. Morelhao, B. Geldiyev, S. Mueller, A. Fedorov, E. Rienks, P. Gargiani, M. Valvidares, L. C. Folkers, A. Isaeva, B. Buechner, V. Hinkov, R. Claessen, H. Bentmann, F. Reinert
Summary: Inducing a magnetically-induced gap in the Dirac point of a three-dimensional topological insulator can result in dissipationless charge and spin currents. In this study, the authors use a ferromagnetic extension technique to create a robust 2D ferromagnetic material on the surface of a 3D topological insulator. The results demonstrate the opening of a sizable magnetic gap in the 2D ferromagnetic phase, while the surface remains gapless in the paramagnetic phase.
PHYSICAL REVIEW RESEARCH
(2023)
Article
Materials Science, Multidisciplinary
Philipp Eck, Carmine Ortix, Armando Consiglio, Jonas Erhardt, Maximilian Bauernfeind, Simon Moser, Ralph Claessen, Domenico Di Sante, Giorgio Sangiovanni
Summary: The recently introduced classification of two-dimensional insulators in terms of topological crystalline in-variants has been extended to quantum spin Hall insulators, and an experimental fingerprint of the obstruction has been measured.
Article
Materials Science, Multidisciplinary
Suhua Jin, Yunyouyou Xia, Wujun Shi, Jiayu Hu, Ralph Claessen, Werner Hanke, Ronny Thomale, Gang Li
Summary: The chiral edge modes in the topological quantum anomalous Hall effect are crucial for future quantum technology and spintronics applications. This study proposes Al2O3 as an ideal substrate for atomic monolayers of Bi and group-III elements, where a large-gap quantum spin Hall effect can be realized. Additional half-passivation with nitrogen suggests a topological phase transition to a large-gap QAH insulator. Effective tight-binding modeling shows that the system is dominated by px, py orbitals with a subdominant pz orbital contribution. The topological phase transition is induced by Zeeman splitting, with no significant role played by off-diagonal spin exchange.
Article
Materials Science, Multidisciplinary
Yunyouyou Xia, Suhua Jin, Jiayu Hu, Ralph Claessen, Werner Hanke, Ronny Thomale, Gang Li
Summary: We extend the px-py large-gap scenario to the band inversion systems and exemplify the mechanism with a family of III-Bi honeycomb monolayers on SiO2. This work enriches the research field of large-gap quantum spin Hall systems.
Article
Materials Science, Multidisciplinary
M. Zapf, M. Schmitt, J. Gabel, P. Scheiderer, M. Stubinger, B. Leikert, G. Sangiovanni, L. Dudy, S. Chernov, S. Babenkov, D. Vasilyev, O. Fedchenko, K. Medjanik, Yu Matveyev, A. Gloskowski, C. Schlueter, T-L Lee, H-J Elmers, G. Schonhense, M. Sing, R. Claessen
Summary: Novel two-dimensional electron systems at the interfaces and surfaces of transition-metal oxides have recently gained attention for their tunable and intriguing properties. In this study, a high-mobility quasi-two-dimensional electron system with strong spin-orbit coupling was induced at the surface of a KTaO3 crystal by pulsed laser deposition of a disordered LaAlO3 film. Through angle-resolved photoelectron spectroscopy, the electronic structure of the buried electron system was mapped out. The results showed a deviation in the band structure from the bulk KTaO3 due to the confinement to the interface, and also confirmed the theoretical expectations of the confined electron system.
Article
Materials Science, Multidisciplinary
Piotr Chudzinski, Julian Aulbach, Joerg Schaefer, Ralph Claessen, Lenart Dudy
Summary: This study investigates the effects of Rashba splitting on two-leg ladders with weakly screened Coulomb interactions, showing a break in the symmetry of scattering channels and leading to new instabilities. Experimental evidence of exotic properties, such as the mixing of magnetism with charge-density wave, is observed, along with differences in signatures of order in single-particle and two-body probes. Findings on the Au-Si(553) platform demonstrate the presence of partial spectral gaps opening and confirm the expected temperature dependence of band backfolding.
Article
Materials Science, Multidisciplinary
Fatima Alarab, Karol Hricovini, Berengar Leikert, Laurent Nicolai, Mauro Fanciulli, Olivier Heckmann, Christine Richter, Lucie Prusakova, Zdenek Jansa, Pavol Sutta, Julien Rault, Patrick Lefevre, Michael Sing, Matthias Muntwiler, Ralph Claessen, Jan Minar
Summary: The electronic properties of SrTiO3 doped with Ni impurities were investigated through a combination of photoelectron spectroscopy and first-principles calculations, confirming the formation of localized 3d-impurity bands in the band gap of SrTiO3.
