Pål Palmgren

A spin- and angle-resolving photoelectron spectrometer

A new type of hemispherical electron energy analyzer that permits angle and spin resolved photoelectron spectroscopy has been developed. The analyzer permits standard angle resolved spectra to be recorded with a two-dimensional detector in parallel with spin detection using a mini-Mott polarimeter. General design considerations as well as technical solutions are discussed and test results from the Au(111) surface state are presented.

Ordered phthalocyanine superstructures on Ag(110)

Organic-metal interfaces, in particular, self-assembling systems, are interesting in the field of molecular electronics. In this study, we have investigated the formation of the Ag(110)-iron phthalocyanine (FePc) interface in a coverage range of less than 1 and up to 2 ML using synchrotron based photoelectron spectroscopy and low energy electron diffraction. As-deposited FePc forms a densely packed first layer exhibiting a 3 x 2c(6 x 2) symmetry. Upon thermal treatment the order at the interface is modified depending on the initial FePc coverage, resulting in less densely packed but still ordered superstructures. The first monolayer is relatively strongly bound to the substrate, leading to the formation of an interface state just below the Fermi level. The highest occupied molecular orbital of FePc in the second layer is found at 1 eV higher binding energy compared to the interface state.

Self-ordering of metal-free phthalocyanine on InAs(100) and InSb(100)

The adsorption and surface ordering of metal-free phthalocyanine (H2PC) on InAs(100)(4 x 2)/c(8 x 2) and InSb(100) c(8 x 2) is investigated using scanning tunnelling microscopy (STM) and synchrot ...

Potassium-intercalated H2Pc films: Alkali-induced electronic and geometrical modifications

X-ray spectroscopy studies of potassium intercalated metal-free phthalocyanine multilayers adsorbed on Al(110) have been undertaken. Photoelectron spectroscopy measurements show the presence of several charge states of the molecules upon K intercalation, due to a charge transfer from the alkali. In addition, the comparison of valence band photoemission spectra with the density functional theory calculations of the density of states of the H(2)Pc(-) anion indicates a filling of the formerly lowest unoccupied molecular orbital by charge transfer from the alkali. This is further confirmed by x-ray absorption spectroscopy (XAS) studies, which show a decreased density of unoccupied states. XAS measurements in different experimental geometries reveal that the molecules in the pristine film are standing upright on the surface or are only slightly tilted away from the surface normal but upon K intercalation, the molecular orientation is changed in that the tilt angle of the molecules increases.

Surface Chemistry of Mercury on Zinc and Copper

Thermal desorption Auger electron spectroscopy (TDAES) was used to investigate mercury adsorption on the surfaces of zinc (Zn) and copper (Cu) in the temperature interval of 85 to 298 K. The effects of chlorine and oxygen modifications on the surfaces have also been investigated within the same temperature interval. On single crystalline Zn(0001), no mercury was adsorbed under any temperature or deposition conditions. On polycrystalline Zn at 85 K, a monolayer (ML) of mercury adsorbed, whereas no measurable quantity was observed at room temperature (RT). Predeposited chlorine was removed by exposure to mercury, most probably through formation of volatile HgCl2. Chlorine enhanced the adsorption of mercury on polycrystalline Cu at 87 K, whereas preoxidation reduced the coverage. Low temperatures (LTs) were conducive to mercury adsorption as compared to 298 K for the Cu systems studied. The physisorption of mercury on chlorine and oxygen layers at LTs is discussed, as well as the factors affecting the mechanism of adsorption at RTs. The desorption energies and surface enthalpies have been calculated for each system with mercury adsorption.