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Surface-to-volume ratio drives photoelelectron injection from nanoscale gold into electrolyte
摘要： Hot charge carriers from plasmonic nanomaterials currently receive increased attention due to their promising potential in important applications such as solar water splitting. While a number of important contributions were made on plasmonic charge carrier generation and their transfer into the metal’s surrounding in the last decades, the local origin of those carriers is still unclear. With our study employing a nanoscaled bicontinous network of nanoporous gold, we take a comprehensive look at both subtopics in one approach and give unprecedented insights into the physical mechanisms controlling the broadband optical absorption and the generation and injection of hot electrons into an adjacent electrolyte where they enhance electrocatalytic hydrogen evolution. This absorption behavior is very different from the well-known localized surface plasmon resonance effects observed in metallic nanoparticles. For small ligament sizes the plasmon decay in our network is strongly enhanced via surface collisions of electrons. These surface collisions are responsible for the energy transfer to the carriers, thus, the creation of hot electrons from a broad spectrum of photon energies. As we reduce the gold ligament sizes below 30 nm, we demonstrate an occurring transition from absorption that is purely exciting 5d-electrons from deep below the Fermi level to an absorption which significantly excites “free” 6sp-electrons to be emitted. We differentiate these processes via assessing the internal quantum efficiency of the gold network photoelectrode as a function of the feature size providing a size-dependent understanding of the hot electron generation and injection processes in nanoscale plasmonic systems. We demonstrate that the surface effect - compared to the volume effect – becomes dominant and leads to significantly improved efficiencies. The most important fact to recognize is that in the surface photoeffect presented here, absorption and electron transfer are both part of the same quantum mechanical event.
关键词： Hot electron,Photoemission,Water splitting,Hydrogen evolution,Carrier injection,Surface damping,Nanoporous Au
更新于2025-10-22 19:40:53
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Control of plasmon dephasing time using stacked nanogap gold structures for strong near-field enhancement
摘要： The construction of metallic nanostructures with strong near-field enhancement is becoming increasingly significant for the practical use of plasmonic devices, such as plasmonic sensors and light-energy conversion systems. Importantly, the near-field enhancement effect depends on the plasmon dephasing time. Here, we propose a method for controlling plasmon dephasing time by utilizing plasmonic coupling for stronger near-field enhancement. Ordered arrays of stacked nanogap gold (Au) structures composed of a metal/insulator/metal nanostructure were fabricated by electron beam lithography and dry etching processes on a niobium-doped titanium dioxide substrate. The dark plasmon mode was excited by the near-field coupling between the upper and lower Au nanostructures separated by an alumina layer with a thickness of 15 nm. A strong near-field enhancement effect was induced by the localization of the electromagnetic field between the upper and lower Au nanostructures and the longer plasmon dephasing time based on the excitation of the dark plasmon mode. It is noteworthy that the dephasing time of the dark plasmon mode measured by time-resolved photoemission electron microscopy was extended 3-fold compared with that of the plasmon mode of the Au nanoblock, which can be controlled by the structural design of the stacked nanogap Au structures.
关键词： Dark plasmon mode,Plasmon dephasing,Near-field enhancement,Photoemission electron microscopy (PEEM),Surface plasmon resonance
更新于2025-09-23 15:23:52
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studied with angle-resolved photoemission spectroscopy
摘要： We study the band structure of twinned and detwinned BaFe2As2 using angle-resolved photoemission spectroscopy. The combination of measurements in the ordered and normal states along four high-symmetry momentum directions (Γ/Z-X/Y) enables us to identify the complex reconstructed band structure in the ordered state in great detail. We clearly observe the nematic splitting of the dxz and dyz orbitals as well as folding due to magnetic order with a wave vector of (π, π, π). We are able to assign all observed bands. In particular we suggest an assignment of the electron bands different from previous reports. The high-quality spectra allow us to achieve a comprehensive understanding of the band structure of BaFe2As2.
关键词： band structure,BaFe2As2,angle-resolved photoemission spectroscopy,magnetic order,nematic splitting
更新于2025-09-23 15:23:52
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Energy disorder and energy level alignment between host and dopant in organic semiconductors
摘要： Energy level alignment between host and dopant molecules plays a critical role in exciton formation and harvesting in light emission zone of organic light-emitting diodes. Understanding the mechanism for predicting energy level alignment is thus important in materials selection for fabricating high-performance organic light-emitting devices. Here we show that host-dopant energy level alignment strongly depends on film thickness and substrate work function by using X-ray and ultraviolet photoemission spectroscopy. Invariant Gaussian density of states fails to explain the experimental data. We speculate that energy disorder in molecules next to the surface dictates the alignment. Ultraviolet photoemission spectroscopy measurements of several archetypical organic semiconductors confirm our speculation. An empirical interface disorder function is derived and used to construct a functional Gaussian density of states to compute host energy levels. Host-dopant energy level alignment is then computed by applying the universal energy alignment rule and is found in excellent agreement with the experimental data.
关键词： Host-dopant systems,Organic semiconductors,Energy level alignment,Photoemission spectroscopy,Energy disorder
更新于2025-09-23 15:23:52
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Current-induced domain wall oscillations in a nanowire imaged by time-resolved photoemission electron microscopy
摘要： We study reversible domain wall motion in half-ring Ni80Fe20 nanowires on a nanosecond (ns) timescale in a truly current-induced pump-probe experiment using an energy filtered, aberration-corrected photoemission electron microscope. The x-ray magnetic circular dichroism signal is probed at different time delays before, during and after the current pulse in a stroboscopic mode with circularly polarized synchrotron radiation in the energy range of the Fe L3-edge (707 eV). We observe lateral domain wall oscillations with a frequency of ～ 0.4 GHz. Comparing the results to a proposed string model, we find that the domain wall oscillations can be described as string-like asymmetric oscillations.
关键词： Synchrotron radiation,Photoemission electron microscopy,X-ray magnetic circular dichroism,Pump-probe mode
更新于2025-09-23 15:23:52
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Doping modulation of quasi-free-standing monolayer graphene formed on SiC(0001) through Sn1-Ge intercalation
摘要： In order to modulate the transfer doping of quasi-free-standing monolayer graphene (QFMLG) formed on SiC(0001), Ge atoms were intercalated additionally into QFMLG already formed by Sn intercalation between ZL and 6H-SiC(0001). By postannealing the Ge-deposited surface at 600 °C, the Sn1-xGex film with the 4 × √3 structure, composed of a bilayer and adatoms with dangling bonds under QFMLG, has been formed. It turns out that, in this Sn1-xGex film, Ge atoms preferentially occupy the bottom layer bound to the top Si atoms of the substrate, while Sn atoms occupy the top adatom sites. Strong correlation among the electrons localized at these adatom sites induces a semiconducting alloy film. As the postannealing temperature is increased up to 800 °C, the concentration of Ge in the intercalated film of the same 4 × √3 structure is gradually increased and the Dirac point also shifts gradually from ?0.16 eV to +0.20 eV relative to the Fermi level. Such a result confirms that the transfer doping of QFMLG on SiC(0001) has been modulated by varying the alloy composition of the Sn1-xGex interfacial film.
关键词： Scanning tunneling microscopy,Quasi-free-standing graphene,SnGe alloy intercalation,Hubbard band,Doping modulation,Photoemission spectroscopy,SiC(0001)
更新于2025-09-23 15:23:52
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Importance of electron correlations in understanding photoelectron spectroscopy and Weyl character of
摘要： We study the role of electron correlations in the presumed type-II Weyl semimetallic candidate γ-MoTe2 by employing density functional theory (DFT) where the on-site Coulomb repulsion (Hubbard U) for the Mo 4d states is included within the DFT+U scheme. We show that pure DFT calculations fail to describe important features of the light-polarization dependence of the angular resolved photoemission intensity which can be accounted for by including the role of the Hubbard U. At the same time, while pure DFT calculations cannot explain the angular dependence of the Fermi surface as revealed by quantum oscillation experiments (a fact which had raised doubt about the presence of the Weyl physics in γ-MoTe2), inclusion of such on-site Coulomb repulsion can. We find that while the number of Weyl points (WPs) and their position in the Brillouin zone change as a function of U, a pair of such WPs very close to the Fermi level survive the inclusion of these important corrections. Our calculations suggest that the Fermi surface of γ-MoTe2 is in the vicinity of a correlations-induced Lifshitz transition, which can be probed experimentally and its interplay with the Weyl physics might be intriguing.
关键词： electron correlations,Lifshitz transition,angular resolved photoemission,MoTe2,DFT+U,Hubbard U,quantum oscillation,Weyl semimetal,photoelectron spectroscopy
更新于2025-09-23 15:23:52
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Exact Evaluation of K. Jensen's General Thermal-Field-Photoemission Integral
摘要： Jensen has developed a general expression for the current density JGT F emitted from a surface by thermal or field emission, or by a combination of these processes; he has also shown how the same expression may be analytically extended to compute the current density due to photoemission. JGT F is expressed as a single integral, which Jensen evaluates analytically in certain limits and numerically outside those limits. In this paper, we show how the integral may be expressed generally as convergent series that are easily evaluated numerically for all values of the physical parameters. No real or apparent singularities, like those that appear in the function Z defined by Jensen occur in the series obtained here.
关键词： photoemission,field emission,thermal emission,Electron emission
更新于2025-09-23 15:22:29
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Research on the defect types transformation induced by growth temperature of vertical graphene nanosheets
摘要： The in?uence factors on the defect types in vertical graphene nanosheets (VGNs) are widely researched while few systematic research has been reported on the growth temperature, which should play an important role in the transformation of defects types. In this work, VGNs were grown via plasma enhanced chemical vapor deposition (PECVD) method in the atmosphere of CH4, H2 and Ar. Based on SEM, Raman, XPS, NEXAFS and UPS spectrum analysis, we found that the types of defects in VGNs have clearly transformed from vacancy-like to boundary-like, corresponding to the rising growth temperature. Moreover, NEXAFS suggests that features near 7.7 eV are attributed to boundary-like defects, as well as (cid:1)6.7 eV in UPS, providing an intuitive and half-quantitative direction to characterize boundary-like defects in VGNs. Additionally, the sheet resistance (from 1386 to 175 Ohm/Sq) and the wetting angle (from 148(cid:3) to 121(cid:3)) decrease as the temperature rises. It shows that changing the growth temperature, as the easy and effective method, is crucial of modulating the properties of VGNs owning to the transition of defects types from vacancy-like to boundary-like.
关键词： Vertical graphene nanosheets,Near-edge X-ray absorption ?ne structure,Defects type,Ultraviolet photoemission spectroscopy,Modulate properties
更新于2025-09-23 15:22:29
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Growth and physical properties of Ce(O,F)Sb(S,Se)2 single crystals with site-selected chalcogen atoms
摘要： Ce(O,F)Sb(S,Se)2 single crystals were successfully grown using a CsCl/KCl ?ux method. The obtained crystals have a plate-like shape with the typical size of 1–2 mm and well-developed ab-plane, which enables X-ray single crystal structural analysis. The Ce(O,F)Sb(S,Se)2 crystallizes in a monoclinic space group, P21/m, with lattice parameters of a = 4.121(7) ?, b = 4.109(7) ?, c = 13.233(15) ?, β = 97.94(7) °. It is composed of alternate stacking of Ce-(O,F) and Sb-SSe layers, and the Sb-SSe layer includes selective occupation of Se atoms in its in-plane site. The valence state of Ce is estimated to be Ce3+ by X-ray absorption ?ne spectroscopy analysis. The single crystals show an insulating behavior, and a magnetic ordering around 6 K.
关键词： E. Photoemission spectroscopy,B. Flux growth,D. Topological insulator,A. Layered mixed-anion compounds
更新于2025-09-23 15:22:29