title: Metal-passivated PbS nanoparticles: fabrication and characterization.
abstract: Organic-shell-free PbS nanoparticles have been produced in the size range relevant for quantum-dot solar cells (QDSCs) by a vapor aggregation method involving magnetron reactive sputtering. This method creates a beam of free 5-10 nm particles in a vacuum. The dimensions of the particles were estimated after their deposition on a substrate by imaging them using ex situ SEM and HRTEM electron microscopy. The particle structure and chemical composition could be deduced "on the fly", prior to deposition, using X-ray photoelectron spectroscopy (XPS) with tunable synchrotron radiation. Our XPS results suggest that under certain conditions it is possible to fabricate particles with a semiconductor core and 1 to 2 monolayer shells of metallic lead. For this case the absolute energy of the highest occupied molecular orbital (HOMO) in PbS has been determined to be (5.0 ± 0.5) eV below the vacuum level. For such particles deposited on a substrate HRTEM has confirmed the XPS-based conclusions on the crystalline PbS structure of the semiconductor core. Absorption spectroscopy on the deposited film has given a value of ∼1 eV for the lowest exciton. Together with the valence XPS results this has allowed us to reconstruct the energy level scheme of the particles. The results obtained are discussed in the context of the properties of PbS QDSCs.
authors.affiliation: MAX-lab, Lund University, P.O. Box SE-118, 22100 Lund, Sweden. maxim.tchaplyguine@maxlab.lu.se.
authors.forename: M
authors.identifier: http://orcid.org/0000-0001-7359-9200
authors.initials: M
authors.lastname: Tchaplyguine
authors.affiliation: MAX-lab, Lund University, P.O. Box SE-118, 22100 Lund, Sweden. maxim.tchaplyguine@maxlab.lu.se.
authors.forename: M-H
authors.initials: MH
authors.lastname: Mikkelä
authors.affiliation: Synchrotron Radiation Research Division, Department of Physics, Lund University, Box 118, SE-22100 Lund, Sweden.
authors.forename: E
authors.initials: E
authors.lastname: Mårsell
authors.affiliation: MAX-lab, Lund University, P.O. Box SE-118, 22100 Lund, Sweden. maxim.tchaplyguine@maxlab.lu.se.
authors.forename: C
authors.initials: C
authors.lastname: Polley
authors.affiliation: Synchrotron Radiation Research Division, Department of Physics, Lund University, Box 118, SE-22100 Lund, Sweden.
authors.forename: A
authors.initials: A
authors.lastname: Mikkelsen
authors.affiliation: Physical Chemistry, Department of Chemistry, Lund University, Box 124, SE-22100 Lund, Sweden.
authors.forename: W
authors.initials: W
authors.lastname: Zhang
authors.affiliation: Physical Chemistry, Department of Chemistry, Lund University, Box 124, SE-22100 Lund, Sweden.
authors.forename: A
authors.initials: A
authors.lastname: Yartsev
authors.affiliation: nCHREM, Center for analysis and synthesis, Lund University, Box 124, SE-22100 Lund, Sweden.
authors.forename: C J D
authors.initials: CJ
authors.lastname: Hetherington
authors.affiliation: nCHREM, Center for analysis and synthesis, Lund University, Box 124, SE-22100 Lund, Sweden.
authors.forename: L R
authors.initials: LR
authors.lastname: Wallenberg
authors.affiliation: Department of Physics and Astronomy, Uppsala University, Box 516, SE-75120 Uppsala, Sweden.
authors.forename: O
authors.initials: O
authors.lastname: Björneholm