Core and Valence Band Photoemission Study of Highly Strained Ultrathin NiO Films on Pd(100)

Abstract

We discuss the results of an extensive investigation on NiO ultrathin films grown on Pd(100), carried out by means of high-resolution X-ray photoelectron spectroscopy (core levels) and ultraviolet photoelectron spectroscopy (valence band levels). The peculiarity of the investigated system is the rather high lattice mismatch between NiO and the Pd substrate (7.3%). Detailed information on the electronic structure of NiO ultrathin films is obtained as a function of thickness, with a particular emphasis put on the fully wetting single c(4 × 2)-Ni 3 O 4 defective monolayer, up to the bulklike relaxed films, through the intermediate three-dimensional strained islands resulting from a Stranski-Krastanov growth behavior.

Silver nanostructures on a c(4×2)-NiOx/Pd(100) monolayer

“…The XPS region containing the Pd 3p 3/2 and O 1s peaks is rather uninformative, due to the large overlap between the two peaks. Anyway, no significant change in the band envelope as a function of the Ag coverage is observed and the peak positions are those already reported for the substrate (Pd 3p 3/2 component at 531.9 eV, O 1s component at 529.3 eV in NiO x /Pd(1 0 0)) [38]. Fig.…”

“…1a reports the XPS Ni 2p. For a detailed interpretation of the Ni 2p photoemission spectrum of the c(4 · 2) phase we refer the reader to a previous publication [38]. Here it is sufficient to note that as soon as Ag is deposited, a shoulder appears at the higher BE side of the main peak, and the peak maximum progressively shifts towards higher BE while increasing the Ag dose (at 2.5 MLE DE BE = 0.8 eV).…”

“…The most relevant trend is the progressive formation of two distinct peaks in the region between 3 eV and 7 eV which are clearly due to the progressive formation of the Ag 4d band. Just below E F (region between 0 and 3 eV), the changes are less distinct, but one can see that the features peculiar of the c(4 · 2)-NiO x /Pd(1 0 0) system [38] become broader and less intense because of the attenuating effect of the Ag overlayer and of the overlap with its 5sp band.…”

“…In the monolayer (ML) coverage range a new defective NiO x c(4 · 2) structure (x = 1.33) has been thoroughly investigated by both static and dynamic low energy electron diffraction (LEED) [36], STM [37], and photoemission spectroscopy (both valence and core levels) [38]. In the following we present a morphological and chemical characterization of the Ag/ NiO x /Pd(1 0 0) system, prepared by Ag UHV evaporation on the c(4 · 2) NiO x /Pd(1 0 0) ML film, for different Ag coverages.…”

CO optical sensing properties of nanocrystalline ZnO–Au films: Effect of doping with transition metal ions

“…More useful in this respect is to analyze the satellite fingerprint of the photoemission lines, which, in the case of 2p transition metals is very distinctive of the oxidation state [23]. Thus by comparing the positions and relative intensities of the main photoemission peak and satellites [24][25][26][27][28] it can be concluded that all the doping ions are present predominantly as divalent cations. However the low signal to noise ratio prevents excluding the possibility of the presence of small contributions from minority oxidation states.…”