The Xe 5s nondipole photoelectron parameter is obtained experimentally and theoretically from threshold to 200 eV photon energy. Significant nondipole effects are seen even in the threshold region of this valence shell photoionization. In addition, contrary to previous understanding, clear evidence of interchannel coupling among quadrupole photoionization channels is found. DOI: 10.1103/PhysRevLett.91.053002 PACS numbers: 31.25.Eb, 32.80.Fb Until recently, conventional wisdom had assumed nondipole effects in photoionization were negligible at relatively low photon energies, perhaps for energies up to a few keV, but certainly for photon energies below a few hundred eV [1][2][3]. Indeed, despite indications to the contrary [4 -7], the usual practice in the field of photoionization, particularly for experiment, had been to ignore effects beyond the dipole approximation for photon energies as high as several keV. While this may be a reasonable assumption for integrated cross sections, recent work has shown it is certainly wrong for differential cross sections (i.e., photoelectron angular distributions). Experiments have shown the importance of nondipole effects in the 1-3 keV photon-energy region [8,9], in the hundreds-of-eV range [10], and, in one case, at 13 eV [11]. Concurrently, theory has predicted significant nondipole contributions to electron angular distributions for atomic valence shells down to threshold at a few tens of eV photon energy [12 -14].In addition, for dipole photoionization, interchannel coupling, which is simply configuration interaction in the continuum, has been shown to be important for most subshells of most atoms at most energies [15,16]; this work was contrary to the previous conventional wisdom that the independent-particle approximation (IPA) was generally valid away from thresholds. It had been suggested, however, that such interchannel coupling was not important in quadrupole photoionization channels [17], but recent theory has suggested that interchannel coupling can indeed be significant in quadrupole photoionization channels as well [14].To test these two ideas, significant nondipole contributions to the photoionization of a valence shell in the threshold region, and the existence of interchannel coupling effects in quadrupole photoionization channels, we have performed a benchmark experiment on the differential photoionization cross section of Xe 5s from 26 eV (close to threshold) to 200 eV to obtain the nondipole contribution to the photoelectron angular distribution which arises from interference between dipole (E1) and quadrupole (E2) channels. The differential cross section is given by [6,[18][19][20] where is the angle-integrated cross section, is the dipole anisotropy parameter, P 2 cos 3cos 2 ÿ 1=2, and and are nondipole asymmetry parameters. The coordinate axes have the positive x axis along the direction of the photon propagation vector, the z axis along the photon polarization vector, and and are the polar and azimuthal angles of the photoelectron momentum vector. ...

Diamondoids (nanometer-sized diamond-like hydrocarbons) are a novel class of carbon nanomaterials that exhibit negative electron affinity (NEA) and strong electron-phonon scattering. Surface-bound diamondoid monolayers exhibit monochromatic photoemission, a unique property that makes them ideal electron sources for electron-beam lithography and high-resolution electron microscopy. However, these applications are limited by the stability of the chemical bonding of diamondoids on surfaces. Here we demonstrate the stable covalent attachment of diamantane phosphonic dichloride on tungsten/tungsten oxide surfaces. X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared (FTIR) spectroscopy revealed that diamondoid-functionalized tungsten oxide films were stable up to 300-350 °C, a substantial improvement over conventional diamondoid thiolate monolayers on gold, which dissociate at 100-200 °C. Extreme ultraviolet (EUV) light stimulated photoemission from these diamondoid phosphonate monolayers exhibited a characteristic monochromatic NEA peak with 0.2 eV full width at half-maximum (fwhm) at room temperature, showing that the unique monochromatization property of diamondoids remained intact after attachment. Our results demonstrate that phosphonic dichloride functionality is a promising approach for forming stable diamondoid monolayers for elevated temperature and high-current applications such as electron emission and coatings in micro/nano electromechanical systems (MEMS/NEMS).

The production of anionic and cationic fragments of NO has been measured after photoexcitation in the vicinity of the nitrogen 1s threshold. The partial ion yield for the anionic fragment O − , in conjunction with the partial cation yields, can clearly distinguish the shape resonances from doubly excited states. On the N 1s → π * resonances, which are composed of the three intermediate states 2 , 2 − and 2 + in the order of increasing photon energy, the intensity ratios for the NO ++ , O + and O ++ fragments are very different from the total ion yield. An explanation for this behaviour in terms of symmetry is proposed.

Catalytic substrate, which is devoid of expensive noble metals and enzymes for hydrogen peroxide (H2O2), reduction reactions can be obtained via nitrogen doping of graphite. Here, we report a facile fabrication method for obtaining such nitrogen doped graphitized carbon using polyacrylonitrile (PAN) mats and its use in H2O2 sensing. A high degree of graphitization was obtained with a mechanical treatment of the PAN fibers embedded with carbon nanotubes (CNT) prior to the pyrolysis step. The electrochemical testing showed a limit of detection (LOD) 0.609 µM and sensitivity of 2.54 µA cm−2 mM−1. The promising sensing performance of the developed carbon electrodes can be attributed to the presence of high content of pyridinic and graphitic nitrogens in the pyrolytic carbons, as confirmed by X-ray photoelectron spectroscopy. The reported results suggest that, despite their simple fabrication, the hydrogen peroxide sensors developed from pyrolytic carbon nanofibers are comparable with their sophisticated nitrogen-doped graphene counterparts.

We report high efficiency luminescence with a manganese-doped aluminum nitride redemitting phosphor under 254 nm excitation, as well as its excellent lumen maintenance in fluorescent lamp conditions, making it a candidate replacement for the widely deployed europium-doped yttria red phosphor. Solid-state reaction of aluminum nitride powders with manganese metal at 1900 °C, 10 atm N 2 in a reducing environment results in nitrogen deficiency, as revealed diffuse reflectance spectra. When these powders are subsequently annealed in flowing nitrogen at 1650 °C, higher nitrogen content is recovered, resulting in white powders. Silicon was added to samples as an oxygen getter to improve emission efficiency. NEXAFS spectra and DFT calculations indicate that the Mn dopant is divalent. From DFT calculations, the UV absorption band is proposed to be due to an aluminum vacancy coupled with oxygen impurity dopants, and Mn 2+ is assumed to be closely associated with this site. In contrast with some previous reports, we find that the highest quantum efficiency with 254 nm excitation (Q.E. = 0.86±0.14) is obtained in aluminum nitride with a low manganese doping level of 0.06 mol%. The principal Mn 2+ decay of 1.25 ms is assigned to non-interacting Mn sites, while additional components in the microsecond range appear with higher Mn doping, consistent with Mn clustering and resultant exchange coupling. Slower components are present in samples with low Mn doping, as well as strong afterglow, assigned to trapping on shallow traps followed by detrapping and subsequent trapping on Mn.