Scanning magneto-optical lens for surface analysis

Abstract

We demonstrate the essential principles for performing a novel form of metastable-atom microscopy, namely focusing and scanning of a He 23S beam. A magneto-optical lens, in conjunction with time-varying magnetic field components, has been used to scan a beam of He 23S atoms across a sample surface in a manner analogous to other scanning probe techniques. The instrument developed is the first to apply methods in the laser manipulation of atoms specifically to the study of surfaces. With the lens in its current arrangement, a beam of He 23S atoms with an intensity of ∼6 × 1012 atoms s−1 cm−2 may be directed anywhere within a sample area of ∼64 mm2 at a focal distance of 1.4 m and with a focal spot full-width at half-maximum of <2 mm. Such control over the intensity and position of the He 23S beam greatly benefits the surface analysis technique of metastable de-excitation spectroscopy, as demonstrated with example spectra from a clean Si(1 1 1) 7 × 7 surface.

Surface Spin Polarization of Fe Nanoclusters

“…3 (a) at ~14 eV is due to both electrons involved in the AN transition originating from the Fermi level, E F . The shoulder just below E F (corresponding to binding energies of a few eV) is due to emission from surface states of the Si(111) 7x7 reconstruction [4] and also Fe 3d electrons [7]. The shoulder at ~10.5 eV arises from emission of Si atomic 3p states found at the surface and in the bulk, and at low kinetic energies emission is dominated by true secondary electrons.…”

“…Nanoclusters were produced using a gas aggregation source coupled to a UHV surface analysis facility that includes a He 2 3 S beamline for metastable de-excitation spectroscopy (MDS) [4]. As is typical for these sources, the size distribution of the clusters follows a lognormal distribution with a most probable particle width of around 11 nm.…”