Magnetite (Fe3O4) thin films on GaAs have been studied with HArd X-ray PhotoElectron Spectroscopy (HAXPES) and low-energy electron diffraction. Films prepared under different growth conditions are compared with respect to stoichiometry, oxidation, and chemical nature. Employing the considerably enhanced probing depth of HAXPES as compared to conventional x-ray photoelectron spectroscopy (XPS) allows us to investigate the chemical state of the film-substrate interfaces. The degree of oxidation and intermixing at the interface are dependent on the applied growth conditions; in particular, we found that metallic Fe, As2O3, and Ga2O3 exist at the interface. These interface phases might be detrimental for spin injection from magnetite into GaAs.
We report here a general theory describing photoelectron transportation dynamics in GaAs semiconductor photocathodes. Gradient doping is incorporated in the model through the inclusion of directional carrier drift. The time-evolution of electron concentration in the active layer upon the injection of an excitation pulse is solved both numerically and analytically. The predictions of the model are compared with experiments via carrier-induced transient reflectivity change, which is measured for gradient-doped and uniform-doped photocathodes using femtosecond pump-probe reflectometry. Excellent …
We have investigated charge and spin transport in n-type metallic GaAs nanowires (~ 10^17 cm^-3 doping level), grown by hydride vapor phase epitaxy (HVPE) on Si substrates. This was done by exciting the nanowire by tightly-focussed circularly-polarized light and by monitoring the intensity and circular polarization spectrum as a function of distance from the excitation spot. The spin-polarized photoelectrons give rise to a well-defined feature in the nearbandgap spectrum, distinct from the main line due to recombination of the spin-unpolarized electrons of the Fermi sea with the same minority …
Probing La-based nickelates with Ni 1$s$ core-level photoelectron spectroscopy
Tokyo Metropolitan University（东京都立大学）；Waseda University（早稻田大学）；Max Planck Institute for Chemical Physics of Solids（马克斯·普朗克固体化学物理研究所）；Osaka Metropolitan University（大阪公立大学）；National Synchrotron Radiation Research Center（国家同步辐射光研究中心）；Harvard University（哈佛大学）；Cornell University（康奈尔大学）；University of Oklahoma（俄克拉荷马大学）
Emergent behavior at complex oxide interfaces has driven much of the research in the oxide thin film community for the past twenty years. Interfaces have been engineered for potential applications in spintronics, topological quantum computing, and high-speed electronics in cases where the bulk materials would not exhibit the desired properties. Advances in thin film growth have made the synthesis of these interfaces possible, while surface characterization tools such as X-ray photoelectron spectroscopy have been critical to understanding surface and interfacial phenomena in these materials. In…
Owing to their high surface area, their high stability, and their hydrophobicity, periodic mesoporous organosilica (PMO) materials represent promising catalytic support for environmentally friendly chemical processes in water. We investigate here how the calcination of PMO material with benzene linkers (PMOB) allows its functionalization. Conventional and dynamic nuclear polarization (DNP)-enhanced NMR spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy, and X-ray photoelectron spectroscopy prove that calcination at 450 °C results in the oxidation of phenylene bridges int…
Electronic Structure of the Dilute Magnetic Semiconductor $Ga_{1-x}Mn_xP$ from Hard X-ray Photoelectron Spectroscopy and Hard X-ray Angle-Resolved Photoemission
The structure property of non-ideal Si/GaAs heterostructures that were integrated with the ultra-thin oxide (UO) tunneling interfacial layer has been systematically investigated. Si nanomembranes (NMs) were oxidized in different time periods prior to the hetero-integration process to create the non-ideal single-side passivated Si/GaAs heterostructure. The atomic level oxygen distribution and the degree of oxygen content in Si NM and GaAs were carefully investigated using the atom probe tomography (APT) and X-ray photoelectron spectroscopy (XPS) to trace the changes in chemical composition and …
We have successfully demonstrated Si/GaAs p-n heterostructures using Al2O3 ultra-thin oxide interfacial layers. The band diagram and band offsets were investigated using X-ray photoelectron spectroscopy and confirm a small discontinuity in the conduction band (0.03 eV) at the interface. The interface defect density (Dit) values of the heterointerface with different ultra-thin oxide (UO) thicknesses ranged from 0.35 nm to 3.5 nm and were also characterized based on a metal-oxide-semiconductor capacitor (MOSCAP) structure using a capacitance-voltage measurement. The results revealed that a thin …
Lattice matched n-type AlInP(100) charge selective contacts are commonly grown on n-p GaInP(100) top absorbers in high-efficiency III-V multijunction solar or photoelectrochemical cells. The cell performance can be greatly limited by the electron selectivity and valance band offset at this heterointerface. Understanding of the atomic and electronic properties of the GaInP/AlInP heterointerface is crucial for the reduction of photocurrent losses in III-V multijunction devices. In our paper, we investigated chemical composition and electronic properties of n-GaInP/n-AlInP heterostructures by X-r…
X-ray photoelectron diffraction (XPD) has developed into a powerful technique for the structural analysis of solids. Extension of the technique into the hard-X-ray range (hXPD) gives access to true bulk information. Here we give a status report on hXPD experiments using a novel full-field imaging technique: Time-of-flight momentum microscopy (ToF-MM). A special variant of ToF-MM is capable of recording high kinetic energies (up to >7keV) and enlarged k-fields-of-view. We present applications that are specific for high kinetic energies. The strong site specificity of hXPD is exemplified for NbS…
Sub-tesla on-chip nanomagnetic metamaterial platform for angle-resolved photoemission spectroscopy
Yale University（耶鲁大学）；Rice University（莱斯大学）；Boston College（波士顿学院）；Princeton University（普林斯顿大学）；University of Maine（缅因大学）；University of Minnesota（明尼苏达大学）；Georgia Institute of Technology（佐治亚理工学院）；Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory（斯坦福同步辐射光源，SLAC国家加速器实验室）
Observing signatures of light-induced Floquet topological states in materials has been shown to be very challenging. Angle-resolved photoemission spectroscopy (ARPES) is well suited for the investigation of Floquet physics, as it allows to directly probe the dressed electronic states of driven solids. Depending on the system, scattering and decoherence can play an important role, hampering the emergence of Floquet states. Another challenge is to disentangle Floquet side bands from laser-assisted photoemission (LAPE), since both lead to similar signatures in ARPES spectra. Here, we investigate …
In the last decade rare-earth hexaborides have been investigated for their fundamental importance in condensed matter physics, and for their applications in advanced technological fields. Among these compounds, LaB$_6$ has a special place, being a traditional d-band metal without additional f- bands. In this paper we investigate the bulk electronic structure of LaB$_6$ using hard x-ray photoemission spectroscopy, measuring both core-level and angle-resolved valence-band spectra. By comparing La 3d core level spectra to cluster model calculations, we identify well-screened peak residing at a lo…
Probing Electromigration of Oxygen Vacancies in YBa$_2$Cu$_3$O$_{7-δ}$ Devices by Multimodal X-ray Techniques
Universidade Federal de São Carlos（圣卡洛斯联邦大学）；National High Magnetic Field Laboratory, Los Alamos National Laboratory（洛斯阿拉莫斯国家实验室国家高磁场实验室）；Université de Liège（列日大学）；Centro Brasileiro de Pesquisas Físicas（巴西物理研究中心）；Institut de Ciència de Materials de Barcelona, ICMAB-CSIC（巴塞罗那材料科学研究所）；Brazilian Nanotechnology National Laboratory, Brazilian Center for Research in Energy and Materials（巴西纳米技术国家实验室、巴西能源与材料研究中心）
Nano-engineered surface enhanced Raman spectroscopy substrates for probing tissue-material interactions
MIT（麻省理工学院）；University of Wyoming（怀俄明大学）；Brigham and Women's Hospital（布莱根和妇女医院）；Harvard Medical School（哈佛医学院）；Ragon Institute of MGH, MIT and Harvard（MGH、麻省理工学院和哈佛拉贡研究所）；Jameel Clinic for AI & Healthcare, MIT（麻省理工学院贾米尔人工智能与医疗诊所）
