Palladium diselenide (PdSe2), a peculiar noble metal dichalcogenide, has emerged as a new two-dimensional material with high predicted carrier mobility and a widely tunable band gap for device ...applications. The inherent in-plane anisotropy endowed by the pentagonal structure further renders PdSe2 promising for novel electronic, photonic, and thermoelectric applications. However, the direct synthesis of few-layer PdSe2 is still challenging and rarely reported. Here, we demonstrate that few-layer, single-crystal PdSe2 flakes can be synthesized at a relatively low growth temperature (300 °C) on sapphire substrates using low-pressure chemical vapor deposition (CVD). The well-defined rectangular domain shape and precisely determined layer number of the CVD-grown PdSe2 enable us to investigate their layer-dependent and in-plane anisotropic properties. The experimentally determined layer-dependent band gap shrinkage combined with first-principle calculations suggest that the interlayer interaction is weaker in few-layer PdSe2 in comparison with that in bulk crystals. Field-effect transistors based on the CVD-grown PdSe2 also show performances comparable to those based on exfoliated samples. The low-temperature synthesis method reported here provides a feasible approach to fabricate high-quality few-layer PdSe2 for device applications.
The Photoelectron‐Related Image and Nano‐Spectroscopy (PRINS) endstation located at the Taiwan Photon Source beamline 27A2 houses a photoelectron momentum microscope capable of performing ...direct‐space imaging, momentum‐space imaging and photoemission spectroscopy with position sensitivity. Here, the performance of this microscope is demonstrated using two in‐house photon sources – an Hg lamp and He(I) radiation – on a standard checkerboard‐patterned specimen and an Au(111) single crystal, respectively. By analyzing the intensity profile of the edge of the Au patterns, the Rashba‐splitting of the Au(111) Shockley surface state at 300 K, and the photoelectron intensity across the Fermi edge at 80 K, the spatial, momentum and energy resolution were estimated to be 50 nm, 0.0172 Å−1 and 26 meV, respectively. Additionally, it is shown that the band structures acquired in either constant energy contour mode or momentum‐resolved photoemission spectroscopy mode were in close agreement.
A microscope hosted at Taiwan Photon Source beamline 27A2 that packs the functions of photoemission electron microscopy and angle‐resolved photoemission spectroscopy into one single instrument is presented.
Synchrotron-based X-ray photoemission electron microscopy (X-PEEM), X-ray photo-electron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS) and ultraviolet visible ...spectroscopy were used to characterize the flotation behaviour of chalcopyrite with xanthate at different processing conditions. The flotation recovery of chalcopyrite decreased from 97% under oxidative conditions (Eh ~385mV SHE, pH4) to 41% at a reductive potential of −100mV SHE (at pH9). X-PEEM images constructed from the metal L3 absorption edges were used to produce near-edge X-ray absorption fine structure (NEXAFS) spectra from regions of interest, allowing the variability in mineral surface chemistry of each mineral particle to be analysed, and the effect of pulp potential (Eh) on the flotation of chalcopyrite to be determined. XPS, ToF-SIMS and NEXAFS analyses of chalcopyrite particles at oxidative conditions show that the surface was mildly oxidised and covered with adsorbed molecular CuEX. The Cu 2p XPS and Cu L2,3 NEXAFS spectra were dominated by CuI species attributed to bulk chalcopyrite and adsorbed CuEX. At a reductive potential of −100mV SHE, an increase in concentration of CuI and FeIII oxides and hydroxides was observed. X-PEEM analysis was able to show the presence of a low percentage of CuII oxides (CuO or Cu(OH)2) with predominantly CuI oxide (Cu2O) which is not evident in Cu 2p XPS spectra.
•X-PEEM, XPS and ToF-SIMS were used to explain the flotation behaviour of chalcopyrite.•XPS analysis showed the presence of only CuI oxides at Eh −100mV SHE.•X-PEEM analysis showed the presence of CuII oxides at Eh −100mV SHE.•Xanthate was desorbed from chalcopyrite surface at Eh −100mV SHE.•Extensive oxidation of Cp particles caused a decrease in recovery at Eh −100mV SHE.
In this study, we performed magneto-optical Kerr effect (MOKE) microscope measurements and X-ray diffraction to examine the hydrogenation effect on the magnetic anisotropy (MA) of Fe40Pd60/Al2O3 thin ...films and its correlation with crystalline structure. The change in magnetic coercivity was observed and attributed to the rotation of MA, which is characterized by the azimuthal angle-dependent MOKE. Hydrogen-enhanced magnetic moment was confirmed by X-ray magnetic circular dichroism. Multi-step etching processes were used to lower the thickness of the FePd alloy coating, and the hydrogenation process triggered the magnetic easy axis to always be parallel to the same direction. The magnetic anisotropy energy (MAE) of FePd film originates from the volume and the interface-contributed MAE. When the MAEs prefer different orientations, the film thickness and the hydrogen absorption will change the dominant term, resulting in the MA rotation. Furthermore, the reversible rotation of magnetism was achieved through hydrogen absorption and desorption without an external magnetic field. These observations are applicable to the development of field-free switched spintronic devices.
•Hydrogenation triggers the rotation of magnetic anisotropy in FePd thin film.•Competition between the volume and interface MAEs in FePd film results in the magnetic rotation.•As confirmed by XMCD, H-absorption enhances the Fe moment and modulates the electron structure.•A field-free 70°-rotation of MA is demonstrated through reversible hydrogenation.
When microscopy meets soft X-ray at TLS and TPS Shiu, Hung-Wei; Chuang, Tzu-Hung; Cheng, Cheng-Maw ...
Journal of electron spectroscopy and related phenomena,
July 2023, 2023-07-00, Volume:
266
Journal Article
Peer reviewed
Microscopy using the soft X-ray as an illumination source can integrate spectroscopy into images. This capability was implemented at Taiwan Light Source (TLS) in the early 2000s through two ...photoelectron-based microscopy stations whose imaging optics is either zone-plate (TLS 09A1) or electron lens (TLS 05B2). The microscopy project was later expanded into multiple stations and beamlines at Taiwan Photon Source (TPS) to take advantage of TPS’s low emittance. In this report, we summarize the activities of soft X-ray microscopy at TLS, followed by the status of microscopy stations under construction at beamline TPS 27A and 39A. The new lineup at TPS is to meet the scientific challenges ahead while carrying the existing activities forward. Both photoemission and transmission X-ray microscopy will be available at TPS.
•This contribution is to pay our respect and celebrate Professor Adam Hitchcock’s contributions to JESRP as an editor for 25 years.•The article describes the past and current status of the soft X-ray spectromicroscopy project at NSRRC.•The spectromicroscopy project was initiated at TLS in the 1990 s and is moving to TPS with expanded capabilities and functionalities.
Organic-molecular magnets based on a metal–organic framework with chemically tuned electronic and magnetic properties have been attracting tremendous attention due to their promising applications in ...molecular magnetic sensors, magnetic particle medicines, molecular spintronics, etc. Here, we investigated the magnetic behavior of a heterojunction comprising a ferromagnetic nickel (Ni) film and an organic semiconductor (OSC) 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ) layer. Through the magneto-optical Kerr effect (MOKE), a photoemission electron microscopy (PEEM), X-ray magnetic circular dichroism (XMCD), and X-ray photoelectron spectroscopy (XPS), we found that the adsorption of F4-TCNQ on Cu(100)/Ni not only reverses the in-plane magnetization direction originally exhibited by the Ni layer but also results in enhanced magnetic ordering. Furthermore, the cyano group (CN) in adsorbed F4-TCNQ was found spin-polarized along with conspicuous charge transfer with Ni. The density functional theory (DFT) calculations suggest that the experimentally found spin polarization originates from hybridization between the CN group’s π orbitals and Ni’s d band. These findings signify that the hybrid states at the organic–ferromagnet interface play a key role in tailoring the magnetic behavior of interfaces. For the case of the F4-TCNQ and Ni heterojunction reported here, interface coupling is an antiferromagnetic one.
Interfacial moments of an antiferromagnet are known for their prominent effects of induced coercivity enhancement and exchange bias in ferromagnetic-antiferromagnetic exchange-coupled systems. Here ...we report that the unpinned moments of an antiferromagnetic face-centered-cubic Mn layer can drive the magnetization of an adjacent Fe film perpendicular owing to a formation of intrinsic perpendicular anisotropy. X-ray magnetic circular dichroism and hysteresis loops show establishment of perpendicular magnetization on Fe/Mn bilayers while temperature was decreased. The fact that the magnitude of perpendicular anisotropy of the Fe layer is enhanced proportionally to the out-of-plane oriented orbital moment of the Mn unpinned layer, rather than that of Fe itself, gives evidence for the Mn unpinned moments to be the origin of the established perpendicular magnetization.
In this study, a Co-thin film was deposited on the van der Waals compound of FePS3 for the investigation of interfacial magnetic coupling, which is crucial to the application in spintronic devices. ...As characterized by atomic force microscopy, the exfoliated FePS3 surface was composed of defects within ±1 monolayer height. The Co thin film covered the FePS3 substrate uniformly with a roughness within ±0.5 nm. The 2 nm-Pd/7 nm-Co/FePS3 exhibited isotropic magnetism in the surface plane and the magnetic coercivity drastically decreased by more than 50% when the temperature was elevated from 85 K to 110–120 K, which is nearly the Néel temperature of FePS3. This observation indicates the interfacial magnetic coupling between Co and FePS3. The Co/FePS3 magnetic coupling is robust even after annealing up to 200 °C. Furthermore, the measurement of X-ray magnetic circular dichroism confirmed the presence of non-compensated Fe moment along the in-plane direction is parallel to the Co magnetization direction. The net Fe-moment is supposed to play an essential role in mediating the magnetic coupling between the in-plane ferromagnetic Co and the perpendicular antiferromagnetic FePS3.
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•The Pd/Co layers covered the FePS3 substrate uniformly with a roughness within ±0.5 nm.•The magnetic coercivity of Co/FePS3 drastically decreased at 110-120 K, indicating the interfacial magnetic coupling.•The Co/FePS3 magnetic coupling is robust even after annealing up to 200 °C.•XMCD confirmed the presence of Fe moment along the inplane direction is parallel to Co.•The net Fe-moment mediated the coupling between the inplane FM-Co and the perpendicular AFM-FePS3.
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•Establishment of exchange bias coupling in annealed Fe/MgO(0 0 1) films.•High thermal stability of exchange bias coupling in annealed Fe/MgO(0 0 1) films.•Promoted exchange bias ...coupling from involving only interface spins to involving the full-volume magnetization of the Fe film.•A formation of FeO-Fe matrix-like structure at Fe-MgO interface is characterized.•Origin of promoted exchange bias coupling in annealed Fe/MgO(0 0 1) is proposed.
MgO-based magnetic heterostructures are crucial building blocks in state-of-the-art spintronic devices. In this study, we performed thermal annealing to control the formation and distribution of FeO across the interface of a Fe-MgO system. The exchange bias phenomenon (i.e., a horizontal shift of magnetic hysteresis loops) was extended from involving only interface spins to involving the full-volume magnetization of the Fe film. The extended and reinforced exchange bias coupling in the annealed Fe/MgO(0 0 1) films can be attributed to the formation of a Fe-FeO matrix-like structure at the Fe/MgO interface under an increasing degree of interface roughness and the reduction or diffusion of oxygen from the interfacial oxides, as indicated by X-ray absorption near edge structures and X-ray reflectivity measurements. Moreover, the thermal stability of exchange bias coupling in the annealed Fe/MgO(0 0 1) films (maximum value at approximately 600 K) was considerably higher than that in conventional thin-film-based Fe/FeO structures (approximately 50 K).
