Articoli di riviste: "XPS/ARPES"

1

Ostler, Markus, Roland J. Koch, Florian Speck, Felix Fromm, Hendrik Vita, Martin Hundhausen, Karsten Horn e Thomas Seyller. "Decoupling the Graphene Buffer Layer from SiC(0001) via Interface Oxidation". Materials Science Forum 717-720 (maggio 2012): 649–52. http://dx.doi.org/10.4028/www.scientific.net/msf.717-720.649.

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Epitaxial graphene (EG) grown on SiC(0001) resides on the so-called buffer layer. This carbon rich (6√3×6√3)R30° reconstruction is covalently bound to the topmost silicon atoms of the SiC. Decoupling the graphene buffer layer from the SiC interface is a well studied topic since successful intercalation has been shown for hydrogen [1-3]. Recently, intercalation was also shown for oxygen [4, 5]. We present ARPES, XPS and Raman spectroscopy studies to determine the quality of oxygen intercalated buffer layer samples in terms of decoupling and integrity of the transformed graphene layer. The decoupling effect is demonstrated by ARPES measurements showing a graphene-like π band. XPS shows whether the oxidation takes place in the buffer layer or at the interface. Raman spectroscopy is well suited to investigate oxygen induced defects in graphene-like material.

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Chaluvadi, Sandeep, Debashis Mondal, Chiara Bigi, Jun Fujii, Rajdeep Adhikari, Regina Ciancio, Alberta Bonanni et al. "Direct-ARPES and STM Investigation of FeSe Thin Film Growth by Nd:YAG Laser". Coatings 11, n. 3 (26 febbraio 2021): 276. http://dx.doi.org/10.3390/coatings11030276.

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Research on ultrathin quantum materials requires full control of the growth and surface quality of the specimens in order to perform experiments on their atomic structure and electron states leading to ultimate analysis of their intrinsic properties. We report results on epitaxial FeSe thin films grown by pulsed laser deposition (PLD) on CaF2 (001) substrates as obtained by exploiting the advantages of an all-in-situ ultra-high vacuum (UHV) laboratory allowing for direct high-resolution surface analysis by scanning tunnelling microscopy (STM), synchrotron radiation X-ray photoelectron spectroscopy (XPS) and angle-resolved photoemission spectroscopy (ARPES) on fresh surfaces. FeSe PLD growth protocols were fine-tuned by optimizing target-to-substrate distance d and ablation frequency, atomically flat terraces with unit-cell step heights are obtained, overcoming the spiral morphology often observed by others. In-situ ARPES with linearly polarized horizontal and vertical radiation shows hole-like and electron-like pockets at the Γ and M points of the Fermi surface, consistent with previous observations on cleaved single crystal surfaces. The control achieved in growing quantum materials with volatile elements such as Se by in-situ PLD makes it possible to address the fine analysis of the surfaces by in-situ ARPES and XPS. The study opens wide avenues for the PLD based heterostructures as work-bench for the understanding of proximity-driven effects and for the development of prospective devices based on combinations of quantum materials.

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Ozawa, Kenichi, Yoshihiro Aiura, Daisuke Wakabayashi, Hirokazu Tanaka, Takashi Kikuchi, Akio Toyoshima e Kazuhiko Mase. "Beamline commissioning for microscopic measurements with ultraviolet and soft X-ray beam at the upgraded beamline BL-13B of the Photon Factory". Journal of Synchrotron Radiation 29, n. 2 (16 febbraio 2022): 400–408. http://dx.doi.org/10.1107/s160057752200090x.

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Beamline 13 of the Photon Factory has been in operation since 2010 as a vacuum ultraviolet and soft X-ray undulator beamline for X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), and angle-resolved photoelectron spectroscopy (ARPES) experiments. The beamline and the end-station at branch B have been recently upgraded, enabling microscopic XPS, XAS, and ARPES measurements to be performed. In 2015, a planar undulator insertion device was replaced with an APPLE-II (advanced planar polarized light emitter II) undulator. This replacement allows use of linear, circular, and elliptical polarized light between 48 and 2000 eV with photon intensities of 109–1013 photons s−1. For microscopic measurements, a toroidal post-mirror was renewed to have more focused beam with profile sizes of 78 µm (horizontal) × 15 µm (vertical) and 84 µm × 11 µm at photon energies of 100 and 400 eV, respectively. A high-precision sample manipulator composed of an XYZ translator, a rotary feedthrough, and a newly developed goniometer, which is essential for microscopic measurements, has been used to control a sample specimen in six degrees of freedom, i.e. translation in the X, Y, and Z directions and rotation in the polar, azimuthal, and tilt directions. To demonstrate the performance of the focused beams, one- and two-dimensional XPS and XAS scan measurements of a copper grid have been performed. It was indicated from analysis of XPS and XAS intensity maps that the actual spatial resolution can be determined by the beam size.

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Johansson, Leif I., Somsakul Watcharinyanon, Alexei A. Zakharov, Rositza Yakimova e Chariya Virojanadara. "The Registry of Graphene Layers Grown on SiC(000-1)." Materials Science Forum 717-720 (maggio 2012): 613–16. http://dx.doi.org/10.4028/www.scientific.net/msf.717-720.613.

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Graphene samples were grown on the C-face of SiC, at high temperature in a furnace and an Ar ambient, and were investigated using LEEM, XPEEM, LEED, XPS and ARPES. Formation of fairly large grains (crystallographic domains) of graphene exhibiting sharp 1x1 patterns in m-LEED was revealed and that different grains showed different azimuthal orientations. Selective area constant initial energy photoelectron angular distribution patterns recorded showed the same results, ordered grains and no rotational disorder between adjacent layers. A grain size of up to a few mm was obtained on some samples.

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Maier, F., R. Graupner, M. Hollering, L. Hammer, J. Ristein e L. Ley. "The hydrogenated and bare diamond (110) surface: a combined LEED-, XPS-, and ARPES study". Surface Science 443, n. 3 (dicembre 1999): 177–85. http://dx.doi.org/10.1016/s0039-6028(99)01010-9.

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Hollering, M., J. Bernhardt, J. Schardt, A. Ziegler, R. Graupner, B. Mattern, A. P. J. Stampfl, U. Starke, K. Heinz e L. Ley. "Electronic and atomic structure of the6H−SiC(0001¯)surface studied by ARPES, LEED, and XPS". Physical Review B 58, n. 8 (15 agosto 1998): 4992–5000. http://dx.doi.org/10.1103/physrevb.58.4992.

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7

Emtsev, Konstantin V., Thomas Seyller, Florian Speck, Lothar Ley, P. Stojanov, J. D. Riley e R. C. G. Leckey. "Initial Stages of the Graphite-SiC(0001) Interface Formation Studied by Photoelectron Spectroscopy". Materials Science Forum 556-557 (settembre 2007): 525–28. http://dx.doi.org/10.4028/www.scientific.net/msf.556-557.525.

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Graphitization of the 6H-SiC(0001) surface as a function of annealing temperature has been studied by ARPES, high resolution XPS, and LEED. For the initial stage of graphitization – the 6√3 reconstructed surface – we observe σ-bands characteristic of graphitic sp2-bonded carbon. The π-bands are modified by the interaction with the substrate. C1s core level spectra indicate that this layer consists of two inequivalent types of carbon atoms. The next layer of graphite (graphene) formed on top of the 6√3 surface at TA=1250°C-1300°C has an unperturbed electronic structure. Annealing at higher temperatures results in the formation of a multilayer graphite film. It is shown that the atomic arrangement of the interface between graphite and the SiC(0001) surface is practically identical to that of the 6√3 reconstructed layer.

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8

Rybkina, Anna A., Alevtina A. Gogina, Artem V. Tarasov, Ye Xin, Vladimir Yu Voroshnin, Dmitrii A. Pudikov, Ilya I. Klimovskikh et al. "Origin of Giant Rashba Effect in Graphene on Pt/SiC". Symmetry 15, n. 11 (12 novembre 2023): 2052. http://dx.doi.org/10.3390/sym15112052.

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Intercalation of noble metals can produce giant Rashba-type spin–orbit splittings in graphene. The spin–orbit splitting of more than 100 meV has yet to be achieved in graphene on metal or semiconductor substrates. Here, we report the p-type graphene obtained by Pt intercalation of zero-layer graphene on SiC substrate. The spin splitting of ∼200 meV was observed at a wide range of binding energies. Comparing the results of theoretical studies of different models with the experimental ones measured by spin-ARPES, XPS and STM methods, we concluded that inducing giant spin–orbit splitting requires not only a relatively close distance between graphene and Pt layer but also the presence of graphene corrugation caused by a non-flat Pt layer. This makes it possible to find a compromise between strong hybridization and increased spin–orbit interaction. In our case, the Pt submonolayer possesses nanometer-scale lateral ordering under graphene.

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Hung, Nguyen Van. "Contributions to Developments of Photoelectron Spectroscopy and X-ray Absorption Fine Structure Applied to Materials Studies". Communications in Physics 31, n. 2 (15 marzo 2021): 113. http://dx.doi.org/10.15625/0868-3166/15826.

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This work reviews the contributions of author to the developments and applications of Photoelectron Spectroscopy (PES) and X-ray Absorption Fine Structure (XAFS) to materials studies. Focusing on Angle resolved PES (ARPES) the energy distribution is discussed for angle-resolved photoemission from valence bands of single crystals. The important influence of the spectrometer angle of acceptance on the results of X-ray PES (XPS) is investigated in detail. The Plane Density of States (PDOS) is introduced as a new property of the electronic structure. Most meaningful contributions to XAFS consist of the developments of multiple-scattering and anharmonic XAFS theory. Anharmonic correlated Einstein model (ACEM) and anharmonic correlated Debye model (ACDM) have been derived to obtain Debye-Waller factors (DWF) presented in terms of cumulant expansion which describe the thermodynamic properties and anharmonic effects in XAFS of substances contributing to their accurate structural determination. The anharmonic effective potential (AEP) procedure and first shell near neighbor contributions approach have developed to include many-body effects in the one-dimensional model by a simple measure. Based on DWFs a thermodynamic lattice theory has been derived for studying melting curve and eutectic points of binary alloys. Several applications of the derived methods are performed and the good agreement of the calculated results with experiment illustrate the advantages and efficiencies of the achieved developments.

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10

Villarreal, Renan. "(Invited, Digital Presentation) Single-Atom Quantum Magnetism in 2D Materials". ECS Meeting Abstracts MA2022-01, n. 12 (7 luglio 2022): 874. http://dx.doi.org/10.1149/ma2022-0112874mtgabs.

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With the advent of 2D materials, the playground to study spins in dilute and non-dilute phases has expanded. This is appealing for utilizing the additional degrees of freedom of electron systems such as spin and valley and, from the fundamental point of view, to better understand atomic scale magnetic phenomena in low dimensional materials. Dilute magnetism in 2D materials can lead to complex magnetic phenomena (e.g., Kondo effect, RKKY-interactions, quantum relaxation and coherence), with potential for applications in spintronics (e.g., spin FETs) and quantum technologies (e.g., single-atom quantum memories). We are investigating how to selectively incorporate substitutional magnetic atoms (3d transition metals and 4f rare earths) in 2D materials, using ultra low energy ion implantation, and we characterize their structural, electronic, and magnetic properties [1]. Ultra-low energy (ULE) ion implantation allows us to precisely tune the kinetic energy of the ions, providing control over the form of incorporation and concentration while preserving the structural and electronic properties of graphene. Our approach is based on a wide range of characterization techniques (structural and electronic), including scanning tunneling microscopy and spectroscopy (STM/STS), Raman spectroscopy, synchrotron-based X-ray photoelectron spectroscopy (XPS), angle-resolved photoemission spectroscopy (ARPES), X-ray magnetic circular dichroism (XMCD), among others. These experimental studies are complemented by density functional theory (DFT) and molecular dynamics (MD) simulations. The new insights provided by our work establish a framework for the controlled incorporation of magnetic dopants in 2D materials, using ULE ion implantation. [1] P. C. Lin et al., ACS Nano 15(3), 5449-5458 (2021).

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11

Rubano, Andrea, e Domenico Paparo. "Optical Second Harmonic Generation on LaAlO3/SrTiO3 Interfaces: A Review". Materials 16, n. 12 (12 giugno 2023): 4337. http://dx.doi.org/10.3390/ma16124337.

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As we approach the limits of semiconductor technology, the development of new materials and technologies for the new era in electronics is compelling. Among others, perovskite oxide hetero-structures are anticipated to be the best candidates. As in the case of semiconductors, the interface between two given materials can have, and often has, very different properties, compared to the corresponding bulk compounds. Perovskite oxides show spectacular interfacial properties due to the the rearrangement of charges, spins, orbitals and the lattice structure itself, at the interface. Lanthanum aluminate and Strontium titanate hetero-structures (LaAlO3/SrTiO3) can be regarded as a prototype of this wider class of interfaces. Both bulk compounds are plain and (relatively) simple wide-bandgap insulators. Despite this, a conductive two-dimensional electron gas (2DEG) is formed right at the interface when a LaAlO3 thickness of n≥4 unit cells is deposited on a SrTiO3 substrate. The 2DEG is quite thin, being confined in only one or at least very few mono-layers at the interface, on the SrTiO3 side. A very intense and long-lasting study was triggered by this surprising discovery. Many questions regarding the origin and characteristics of the two-dimensional electron gas have been (partially) addressed, others are still open. In particular, this includes the interfacial electronic band structure, the transverse plane spatial homogeneity of the samples and the ultrafast dynamics of the confined carriers. Among a very long list of experimental techniques which have been exploited to study these types of interfaces (ARPES, XPS, AFM, PFM, …and many others), optical Second Harmonic Generation (SHG) was found to be suitable for investigating these types of buried interfaces, thanks to its extreme and selective interface-only sensitivity. The SHG technique has made its contribution to the research in this field in a variety of different and important aspects. In this work we will give a bird’s eye view of the currently available research on this topic and try to sketch out its future perspectives.

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Stania, Roland, Ari Paavo Seitsonen, Hyunjin Jung, David Kunhardt, Alexey A. Popov, Matthias Muntwiler e Thomas Greber. "Correlation of Work Function and Conformation of C₈₀ Endofullerenes on h‐BN/Ni(111)". Advanced Materials Interfaces, 11 gennaio 2024. http://dx.doi.org/10.1002/admi.202300935.

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AbstractChange of conformation or polarization of molecules is an expression of their functionality. If the two correlate, electric fields can change the conformation. In the case of endofullerene single‐molecule magnets the conformation is linked to an electric and a magnetic dipole moment, and therefore magnetoelectric effects are envisoned. The interface system of one monolayer Sc2TbN@C80 on hexagonal boron nitride (h‐BN) on Ni(111) has been studied. The molecular layer is hexagonally close packedbut incommensurate. With photoemission the polarization and the conformation of the molecules are addressed by the work function and angular intensity distributions. Valence band photoemission (ARPES) shows a temperature‐induced energy shift of the C80 molecular orbitals that is parallel to a change in work function of 0.25 eV without charging the molecules. ARPES indicates a modification in molecular conformations between 30 and 300 K. This order–disorder transition involves a polarization change in the interface and is centered at 125 K as observed with high‐resolution X‐ray photoelectron spectroscopy (XPS). The temperature dependence is described with a thermodynamic model that accounts for disordering with an excitation energy of 74 meV into a high entropy ensemble. All experimental results are supported by density functional theory (DFT).

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Cameau, Mathis, Natalia Olszowska, Marcin Rosmus, Mathieu G. Silly, Tristan Cren, Axel Malécot, Pascal David e Marie D'angelo. "Synthesis and characterisation of Cu₂Ge, a new two-dimensional Dirac nodal line semimetal". 2D Materials, 3 maggio 2024. http://dx.doi.org/10.1088/2053-1583/ad471e.

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Abstract Dirac nodal line semimetals are a novel class of topological materials in which the valence and conduction bands touch along lines in the reciprocal space, with linear dispersion. These materials attract a growing attention, but the experimental realizations for two-dimensional systems are sparse. We report here the first experimental realization of a two-dimensional hexagonal monolayerCu2Ge, grown by evaporation of Ge on a Cu(111) substrate. Through a combination of LEED, XPS and ARPES measurements, we show that the surface presents all characteristics expected from calculations for a free-standing Cu2Ge monolayer. More specifically, the preservation of the two concentric nodal lines around the Γ point indicates weak interactions between the Cu2Ge surface and its Cu(111) substrate, making it an ideal system for the study of Dirac nodal line materials.

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Lev, L. L., V. N. Strocov, Y. Y. Lebedinskii, T. Schmitt e A. V. Zenkevich. "Band bending and k -resolved band offsets at the HfO2/n+(p+)Si interfaces explored with synchrotron-radiation ARPES/XPS". Physical Review Materials 6, n. 8 (30 agosto 2022). http://dx.doi.org/10.1103/physrevmaterials.6.084605.

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15

Göhler, Fabian, Philip Schädlich, Niels Rösch, Mike Zeißig e Thomas Seyller. "Transfer doping of epitaxial graphene on SiC(0001) using Cs". 2D Materials, 23 gennaio 2024. http://dx.doi.org/10.1088/2053-1583/ad2192.

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Abstract Control of the charge carrier concentration is essential for applications of graphene. Here, we demonstrate the doping of epitaxial graphene on SiC(0001) via charge transfer from an adsorbed layer of Cs atoms with sub-monolayer coverage. The electronic structure of the graphene is analyzed using X-ray and angle-resolved photoelectron spectroscopy (XPS, ARPES). In H-intercalated, quasi-freestanding monolayer graphene (QFMLG), the Dirac point can be tuned continuously from p-type to strong n-type doping. For strong n-type doping, analysis of the core level binding energies implies a deviation from a rigid band shift. This might be explained by an increased screening of the atomic core potential due to the higher number of charge carriers per C atom in the graphene layer. Furthermore, charge transfer into the SiC substrate leads to a change in band bending at the SiC/QFMLG interface, which saturates into a flat band scenario at higher Cs coverage. An analysis of the Fermi surfaces suggests an increasing electron-phonon-coupling in strongly doped QFMLG. In monolayer graphene (MLG), which is intrinsically n-type doped due to the presence of the buffer layer at the SiC interface, n-type doping can be enhanced by Cs evaporation in a similar fashion. In contrast to QFMLG, core level spectra and Dirac cone position in MLG apparently show a rigid band shift even for very high doping, emphasizing the importance of the substrate.

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Zhu Meng-Long, Yang Jun, Dong Yu-Lan, Zhou Yuan, Shao Yan, Hou Hai-Liang, Chen Zhi-Hui e He Jun. "Atomic and electronic structure of monolayer ferroelectric GeS on Cu(111)". Acta Physica Sinica, 2024, 0. http://dx.doi.org/10.7498/aps.73.20231246.

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Two dimensional ferroelectric materials are interesting for both fundamental properties and potential applications. Especially, Group IV monochalcogenides possess highest thermoelectric performance and intrinsic ferroelectric polarization properties and can sever as a model to explore ferroelectric polarization properties. However, due to the relatively large exfoliation energy, the creation of high-quality and large-size monolayer group IV monochalcogenides is not easy, which seriously hinders the integration of these materials into the fast-developing field of 2D materials and their heterostructures. Herein, monolayer GeS was successfully fabricated on Cu(111) substrate by molecular beam epitaxy method, and the lattice and electronic band structures of monolayer GeS were systematically characterized by high-resolution scanning tunneling microscopy, low-energy electron diffraction, in situ X-ray photoelectron spectroscopy, Raman spectra and angle-resolved photoelectron spectroscopy, and density functional theory calculations. All atomically resolved STM images reveal that the obtained monolayer GeS has an orthogonal lattice structure, which is consisted with theoretical prediction. Meanwhile, the distinct Moiré pattern formed between monolayer GeS and Cu(111) substrate also confirm the orthogonal lattice structure. In order to examine the chemical composition and valence state of as-prepared monolayer GeS, in situ XPS was utilized without air exposure. The measured XPS core levels spectra suggest the valence states of Ge and S elements are identified to be +2 and -2, respectively and the atomic ratio of Ge/S is 1:1.5, which is extremely close to the stoichiometry ratio of 1:1 for GeS. To further corroborate the quality and lattice structure of the monolayer GeS film, ex-situ Raman measurements are also performed for monolayer GeS on HOPG and multilayer graphene substrate. Three well-defined typical characteristic Raman peaks of GeS are observed. Finally, in situ ARPES measurement are conducted to determine the electronic band structure of monolayer GeS on Cu(111). The results demonstrate that the monolayer GeS has a nearly flat band electronic band structure, consistent with our DFT theoretical calculation. The realization and investigation of the monolayer GeS extend the scope of 2D ferroelectric materials and makes it possible to prepare high quality and large size monolayer group IV monochalcogenides, which is beneficial for the application of this main group material to the rapidly developing two-dimensional ferroelectric materials and heterojunction research.

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Articoli di riviste sul tema "XPS/ARPES"

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