Tantalus,the First Dedicated Synchrotron Radiation Source

Tantalus began as a 240 MeV electron storage ring that served as a testbed for the next-generation accelerator (which eventually would become Fermilab) [1 There are several more extensive papers on the history of Tantalus: David W. Lynch, “The Early Years of Tantalus,” Synch. Rad. News 5, 16 (1992); David W. Lynch, “Tantalus, a 240 MeV Dedicated Source of Synchrotron Radiation, 1968-1986,” J. Synchrotron Rad. 4, 334 (1997); Giorgio Margaritondo, “The Evolution of a Dedicated Synchrotron Light Source,” Physics Today, May (2008), 37.[Taylor &; Francis Online] , [Google Scholar], 2 List of acronyms: AEC–Atomic Energy Commission (evolved into today's Department of Energy); AFOSR–Air Force Office of Scientific Research; NSF–National Science Foundation; FFAG–fixed-field alternating gradient; UHV–ultrahigh vacuum; OSHA–Occupational Safety and Health Administration; EDC–energy distribution curve; CIS–constant initial state; CFS–constant final state; NAS–National Academy of Sciences. [Google Scholar]]. It was to be injected from the 40 MeV FFAG synchrotron that was already operating. Before its completion, funding from the AEC was discontinued. During the time it was in financial limbo, a report from an NAS study group suggested using Tantalus as a source of VUV synchrotron radiation for spectroscopy and possibly other techniques. The AFOSR eventually funded the completion and early use of Tantalus.     

Hard x-ray Zernike microscopy reaches 30 nm resolution

Since its invention in 1930, Zernike phase contrast has been a pillar in optical microscopy and more recently in x-ray microscopy, in particular for low-absorption-contrast biological specimens. We experimentally demonstrate that hard-x-ray Zernike microscopy now reaches a lateral resolution below 30 nm while strongly enhancing the contrast, thus opening many new research opportunities in biomedicine and materials science.     

Present and future role of synchrotron radiation in heterojunction research

We describe the recent contributions made by synchrotron-radiation photoemission spectroscopy in the area of semiconductor-semiconductor interfaces. We discuss in particular the advances made in understanding the band lineups and the consequent band discontinuities. We also analyze the likely developments of this research in the near future, and in particular the crucial question of interface dipoles.     

Photoemission experiments on the valence band of transition metal trichalcogenides

Summary We present a synchrotron radiation photoemission study of the upper-valence-band states of four ZrSe₃-structure compounds: ZrS₃, ZrSe₃, ZrTe₃ and HfSe₃. The sulphide and selenide spectra exhibit a characteristic five-peak structure in agreement with the calculated ZrSe₃ density of states by Myronet al. and by Bullett. The nature of these features is established by an interplay between the rehybridization of paired-anion ligand orbitals and the hybridization of unpaired-anion states with cation states. The spectrum of ZrTe₃ exhibits only three peaks that appear related to three of the sulphide and selenide spectral features. The differences between the sulphide, selenide spectra and the telluride spectra are discussed in terms of the very large distance between pairedanion ligands and neighbour cations in the latter compound.

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Riassunto Si presenta uno studio mediante fotoemissione con luce di sincrotrone degli stati nella banda di valenza superiore di quattro composti con struttura del tipo ZrSe₃: ZrS₃, ZrSe₃, ZrTe₃ e HfSe₃. Gli spettri dei seleniuri e del solfuro presentano una struttura caratteristica a cinque picchi in accordo con le densità degli stati di ZrSe₃ calcolate da Myronet al. e de Bullett. La natura di questi picchi è causata dall’azione combinata della reibridizzazione di orbitali di anioni accoppiati e dell’ibridizzazione di stati di anioni non accoppiati con, stati cationici. Lo spettro di ZrTe₃ presenta solo tre picchi che appaiono collegati a tre dei picchi spettrali, osservati per i seleniuri e per il solfuro. Le differenze fra gli spettri del telloruro e quelli dei seleniuri e del solfuro sono discusse in relazione alla grande distanza fra anioni accoppiati e cationi primi vicini nel telloruro.

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Резюме мы предлагаем результаты исследований фотоэмиссии синхротронного излучения для верхних состояний валентной зоны для четырех соединений со структурой типа ZrSe₃: ZrS₃, ZrSe₃, ZrTe₃ и HfSe₃. Спекты сельфида и селенида обнаруживают структуру с пятью пиками, что согласуется с вычисленной Мироном и др. и Булле плотностью состояний для ZrSe₃. Природа этих особенностей связана с взаимодействием между перегибридизацией орбиталей спаренных анионов и гибридизацией орбиталей не спаренных анионов с катионными состояниями. Спектр ZrTe₃ обнаруживает только три пика, которые, по-видимому, связаны с тремя наблюденными спектральными особенностями сульфида и селенида. Различия между спектрами сульфида и селенида и спектрами теллурида сбсуждаются в терминан очень большого расстояния между спаренными анионами и соседними катионами в теллуриде.

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To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.     

GaSe valence band structure from angle-resolved photoemission spectroscopy

Energy-wavevector dispersion curves for the GaSe valence bands obtained from angle-resolved photoemission spectra are compared with pseudopotential band calculations. It is found that the third density-of-states feature below the top of the valence bands (peak C) is related to the Ga-Se bond rather than the Ga-Ga bond. A peak not appearing in the angle-integrated spectra appears as the most intense feature at normal emission, and helps to identify completely the nature of the valence bands down to 7–8 eV below the Fermi energy.     

Resonant-photoemission identification of the valence states of NiPS3

We monitored the resonant behavior of the Ni d satellite peaks in the valence band photoemission spectra of NiPS₃ at photon energies immediately below and immediately above the Ni3p threshold. The observed resonance gives an unequivocal identification of the satellite peaks and of the corresponding main Ni d features. The study of the electronic structure of this material and of the related compounds FePS₃ and HgPS₃ was extended to unoccupied states by means of partial-yield synchrotron-radiation photoemission spectroscopy.     

Secondary illumination effects in the photoemission spectra of GaAs and CdS

The photoemission spectra of GaAs and CdS are dramatically affected by secondary illumination of the sample. Using synchrotron radiation and a computer lineshape analysis we demonstrate that valence band and core-level spectral features are all rigidly shiftedin energy by a few tenths of an electronvolt under secondary illumination. This provides conclusive evidence that photovoltaic band-bending changes are the only cause of these effects and rules out other possible mechanisms. It is therefore right to use these phenomena for quantitative studies of band bending effects and of ultralow densities of extrinsic or intrinsic surface states.     

One-pot tuning of Au nucleation and growth: from nanoclusters to nanoparticles

We describe a simple and effective method to obtain colloidal surface-functionalized Au nanoparticles. The method is primarily based on irradiation of a gold solution with high-flux X-rays from a synchrotron source in the presence of 11-mercaptoundecanoic acid (MUA). Extensive tests of the products demonstrated high colloidal density as well as excellent stability, shelf life, and biocompatibility. Specific tests with X-ray diffraction, UV-visible spectrometry, visible microscopy, Fourier transform infrared spectroscopy, dark-field visible-light scattering microscopy, and transmission electron microscopy demonstrated that MUA, being an effective surfactant, not only allows tunable size control of the nanoparticles, but also facilitates functionalization. The nanoparticle sizes were 6.45 ± 1.58, 1.83 ± 1.21, 1.52 ± 0.37 and 1.18 ± 0.26 nm with no MUA and with MUA-to-Au ratios of 1:2, 1:1, and 3:1. The MUA additionally enabled functionalization with l-glycine. We thus demonstrated flexibility in controlling the nanoparticle size over a large range with narrow size distribution.