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1.
Phys Rev Lett ; 109(19): 194801, 2012 Nov 09.
Artículo en Inglés | MEDLINE | ID: mdl-23215388

RESUMEN

Using a vertical undulator, picometer vertical electron beam emittances have been observed at the Australian Synchrotron storage ring. An APPLE-II type undulator was phased to produce a horizontal magnetic field, which creates a synchrotron radiation field that is very sensitive to the vertical electron beam emittance. The measured ratios of undulator spectral peak heights are evaluated by fitting to simulations of the apparatus. With this apparatus immediately available at most existing electron and positron storage rings, we find this to be an appropriate and novel vertical emittance diagnostic.


Asunto(s)
Electrones , Sincrotrones/instrumentación , Diseño de Equipo , Campos Magnéticos
2.
Phys Rev Lett ; 107(17): 175501, 2011 Oct 21.
Artículo en Inglés | MEDLINE | ID: mdl-22107533

RESUMEN

Chiral interfaces and substrates are of increasing importance in the field of enantioselective chemistry. To fully understand the enantiospecific interactions between chiral adsorbate molecules and the chiral substrate, it is vital that the chiral orientation of the substrate is known. In this Letter we demonstrate that full-hemisphere angle-resolved photoemission permits straightforward identification of the orientation of a chiral surface. The technique can be applied to any solid state system for which photoemission measurements are possible.


Asunto(s)
Cobre/química , Espectroscopía de Fotoelectrones/métodos , Modelos Moleculares , Conformación Molecular , Estereoisomerismo , Propiedades de Superficie
3.
Phys Rev Lett ; 107(19): 197601, 2011 Nov 04.
Artículo en Inglés | MEDLINE | ID: mdl-22181644

RESUMEN

We report a study of the electronic properties of the ferromagnetic semiconductor (Ga,Mn)As using magnetic linear dichroism in the angular dependence of Mn 2p photoemission under hard x-ray excitation. Bulk plasmon loss satellites demonstrate that the probed Mn ions are incorporated deep within the GaAs lattice, while the observed large dichroism indicates that the spectra originate from ferromagnetic substitutional Mn. Simulations of the spectra using an Anderson impurity model show that the ferromagnetic Mn 3d electrons of substitutional Mn in (Ga,Mn)As are intermediate between localized and delocalized.

4.
J Phys Condens Matter ; 21(40): 405701, 2009 Oct 07.
Artículo en Inglés | MEDLINE | ID: mdl-21832421

RESUMEN

The Mg K edge photoabsorption spectrum and the B 1s, Mg 1s, Mg 2p and valence band photoemission spectra of polycrystalline magnesium diboride have been measured. The photoabsorption spectra of the diboride and the oxide, which is present as an impurity, were separated by measuring the Auger electron partial yield at electron energies characteristic of each phase. The spectra are consistent with published calculations of the density of unoccupied p symmetry states. Better agreement is obtained with calculations for the ground state of the system than with ones for the excited state. Valence band photoemission spectra were measured at photon energies corresponding to core resonances, but, within the signal to noise level of the spectra, no resonant enhancement was observed. This is consistent with the delocalized nature of the valence band.

5.
Phys Rev Lett ; 94(3): 036106, 2005 Jan 28.
Artículo en Inglés | MEDLINE | ID: mdl-15698289

RESUMEN

Normal incidence x-ray standing wave experiments and density functional theory reveal that 3,4,9,10-perylene-tetracarboxylic-dianhydride chemisorbs on Ag(111) in a nonplanar but vertically distorted configuration. The carboxylic O atoms are 0.18 +/- 0.03 angstroms closer to the surface than the perylene core. The distortion is related to weak, local bonds between carboxylic O atoms and the Ag surface which are coupled--through charge transfer into the former lowest unoccupied molecular orbital--to the primary, extended chemisorption bond via the perylene skeleton.

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