The magnetic circular dichroism ͑MCD͒ of core-level absorption ͑x-ray absorption spectroscopy, XAS͒ spectra in the soft x-ray region has been measured for the ferromagnetic Heusler alloy Co 2 Cr 0.6 Fe 0.4 Al at the Co, Fe, and Cr L II,III edges. The comparison of XAS spectra before and after in situ cleaning of polished surfaces revealed a pronounced selective oxidation of Cr in air. For clean surfaces we observed a MCD for all three elements with Fe showing the largest moment per atom. The MCD can be explained by the density of states of the 3d unoccupied states, predicted by linear muffin-tin orbital atomic sphere approximation. For Fe and Cr the orbital angular momentum component of the magnetic moment is considerably larger than the values reported for metallic alloys, whereas for Co a value close to its bulk value is observed. This observation is discussed in comparison with band structure calculations.

Heusler compounds are promising candidates for future spintronics device applications. The electronic and magnetic properties of Co 2 Cr 0.6 Fe 0.4 Al, an electron-doped derivative of Co 2 CrAl, are investigated using circularly polarized synchrotron radiation and photoemission electron microscopy (PEEM). Element specific imaging reveals needle shaped Cr rich phases in a homogeneous bulk of the Heusler compound. The ferromagnetic domain structure is investigated on an element-resolved basis using x-ray magnetic circular dichroism (XMCD) contrast in PEEM. The structure is characterized by micrometre-size domains with a superimposed fine ripple structure; the lateral resolution in these images is about 100 nm. The domains look identical for Co and Fe giving evidence of a ferromagnetic coupling of these elements. No ferromagnetic contrast is observed at the Cr line. Magnetic spectroscopy exploiting XMCD reveals that the lack of magnetic moment, detected in a SQUID magnetometer, is mainly due to the moment of the Cr atom.

Electron emission from Ag and Au nanoparticle films was studied under excitation with femtosecond-laser pulses with photon energies of 1.55 and 3.1 eV. Films were grown on a glass substrate with particle sizes from the nanometer range to a continuous layer. The transition from a continuous film to a nanoparticle film is accompanied by an increase in photoemission current by more than an order of magnitude. Pump-and-probe experiments with variable delay gave information on the lifetime of the intermediate states. At a fixed pulse power, the emission yield increases as the temporal width of the laser pulses is decreased. Experimental results are interpreted in terms of two different electron emission mechanisms, i.e., multiphoton photoemission and thermionic emission or thermally assisted multiphoton photoemission. The first mechanism prevails for continuous films and larger particles with sizes above several tens of nanometers; the second one prevails for smaller nanoparticles with sizes of a few nanometers.

No abstract

No abstract

No abstract

The importance of high resolution imaging of dopant contrast in semiconductor structures parallels the continuous increase in the degree of their integration and complexity and in the size of substrates. Some scanning electron microscopy modes show moderate contrast between differently doped areas, but its detailed interpretation remains questionable, in particular, as regards the measurement of the dopant concentration. Photoemission spectromicroscopy on silicon substrates with patterns of opposite-type dopants suggests that the p∕n contrast is primarily related to local differences in the absorption of hot electrons along their trajectory toward the surface. This explanation is also expected to be valid in the interpretation of image contrasts formed by secondary electrons or very slow backscattered electrons. Wide-field photoemission electron microscopy has proven itself a fast imaging method providing large p-n contrast and the prospect of high-level resolution.

No abstract