Oxygen on Fe(100): An initial-oxidation study by spin-polarized Auger spectroscopy

Experimental Evidences on Magnetism-Covalent Bonding Interplay in Structural Properties of Solids and during Chemisorption

Valence electrons are one of the main players in solid catalysts and in catalytic reactions, since they are involved in several correlated phenomena like chemical bonding, magnetism, chemisorption, and bond activation. This is particularly true in the case of solid catalysts containing d-transition metals, which exhibit a wide range of magnetic phenomena, from paramagnetism to collective behaviour. Indeed, the electrons of the outer d-shells are, on one hand, involved in the formation of bonds within the structure of a catalyst and on its surface, and, on the other, they are accountable for the magnetic properties of the material. For this reason, the relationship between magnetism and heterogeneous catalysis has been a source of great interest since the mid-20th century. The subject has gained a lot of attention in the last decade, thanks to the orbital engineering of quantum spin-exchange interactions and to the widespread application of external magnetic fields as boosting tools in several catalytic reactions. The topic is discussed here through experimental examples and evidences of the interplay between magnetism and covalent bonding in the structure of solids and during the chemisorption process. Covalent bonding is discussed since it represents one of the strongest contributions to bonds encountered in materials.

Spin Polarized Low Energy Electron Microscopy of Surface Magnetic Structure

Spin polarized low energy electron microscopy (SPLEEM) has been developed for the high resolution imaging of surface magnetic structure. The existing LEEM ha.s been modified by the incorporation of a. GaAs-type spin polarized electron gun. Large image contrast arises due to the spin-dependent exchange scattering, whifle the st.in-orbit contribution vanishes uniquely for the normal incidence/exit geometry used here. Pixel by pixel image subtraction for incident electron beams of opposite polarization yields precisely the spatially resolved Bragg reflection asymmetry observed in spin polarized low energy electron diffraction. The shallow electron penetration depth arising from the strong coulombic interaction is advantageous for separating surface behavior from the normally overwhelning bulk. Therefore, the use of transversally polarizedI electron beams allows the determination of in-plane surface magnetization directions. Fnrthermore, the parallel illumination and detection of SPLEEM makes it possible to image quickly with a. resolution better than 500 Å in the present configuration. A useful and direct. comparison between surface magnetic, structural, and topological features is made possible by the augmentation of the unique imaging capabilities of conventional LEEM with the magnetic sensitivity of SPLEEM. In this manner, the magnetic domain structure of a Co (0001) surface and in-situ grown Co filmns on Mo(110) have been determined.

Spin-polarized electron induced asymmetric reactions in chiral molecules

Understanding the origin of chirality in nature has been an active area of research since the time of Pasteur. In this chapter we examine one possible route by which this asymmetry could have arisen, namely chiral-specific chemistry induced by spin-polarized electrons. The various sources of spin-polarized electrons (parity violation, photoemission, and secondary processes) are discussed. Experiments aimed at exploring these interactions are reviewed starting with those based on the Vester-Ulbricht hypothesis through recent studies of spin polarized secondary electrons from a magnetic substrate. We will conclude with a discussion of possible new avenues of research that could impact this area.