Band alignment at Ag/ZnO(0001) interfaces: A combined soft and hard x-ray photoemission study

Abstract

Band alignment at the interface between evaporated silver films and Zn-or O-terminated polar orientations of ZnO is explored by combining soft and hard X-ray photoemissions on native and hydrogenated surfaces. Ultraviolet Photoemission Spectroscopy (UPS) is used to track variations of work function, band bending, ionization energy and Schottky barrier during silver deposition.The absolute values of band bending and the bulk position of the Fermi level are determined on continuous silver films by HArd X-ray PhotoEmission Spectroscopy (HAXPES) through a dedicated modeling of core levels. Hydrogenation leads to the formation of ∼ 0.3 monolayer of donor-like hydroxyl groups on both ZnO-O and ZnO-Zn surfaces and to the release of metallic zinc on ZnO-Zn. However no transition to an accumulation layer is observed. On bare surfaces, silver adsorption is cationic on ZnO(0001)-O (anionic on ZnO(0001)-Zn) at the earliest stages of growth as expected from polarity healing before adsorbing as a neutral species. UPS and HAXPES data appear quite consistent. The two surfaces undergo rather similar band bendings for all types of preparation. The downward band bending of V bb,ZnO−O = −0.4 eV and V bb,ZnO−Zn = −0.6 eV found for the bare surfaces are reinforced for upon hydrogenation (V bb,ZnO−O+H = −1.1 eV, V bb,ZnO−Zn+H = −1.2 eV). At the interface with Ag, a unique value of band bending of -0.75 eV is observed. While exposure to atomic hydrogen modulates strongly the energetic positions of the surface levels, a similar Schottky barrier of 0.5-0.7 eV is found for thick silver films on the two surfaces.

Doping-Dependent Optical Response of a Hybrid Transparent Conductive Oxide/Plasmonic Medium

“…% AZO films, respectively. These values are consistent, in absolute value, to what happens in other metal NPs/ZnO 71 , 72 and similar Au NPs/oxide systems 73 , 74 and can be sustained by the substrate due to the small volume of Au NPs with respect to the film volume. Increasing further the dopant concentration above the optimal doping condition (4 at.…”

Spectral characteristics upon harvesting plasmonic hot electrons at the Ag/ZnO heteromicrostructures

“…Chernysheva et al have shown the shift in Fermi level of ZnO by B0.04 eV on the Ag/ZnO contact. 65 The work functions for Ag (F M = 4.26 eV) and ZnO (F S = 5.2 eV) have been adopted from the reference of Zheng et al 56 where V 0 defines the defect level and E g the band gap of the semiconductor layer. Adsorbates modify the ionization energy and induce a change in band bending for a perfect Schottky contact (where, F SB is the Schottky barrier of the interface), and construct the interface levels, from which the transition can be shown.…”

“…Adsorbates modify the ionization energy and induce a change in band bending for a perfect Schottky contact (where, F SB is the Schottky barrier of the interface), and construct the interface levels, from which the transition can be shown. 65 The change in the ionization energy with the increasing concentration of Ag on ZnO can be expressed as DI = Dw = eNp > (y)/e 0 , where, e is the electronic charge, N the number of dipoles and p > (y) the perpendicular polarisation through the adsorbate layer. Thus, with the increase in the Ag concentration around ZnO, both of the effects lead to the decrease the difference in valence and conduction bands.…”

“…Therefore, with increase in silver concentration around ZnO, there occurs a successive red shift in photoluminescence spectra. 29,61,65 We have attempted to calculate the distribution of electric field corresponding to a single silver nanoparticle in the assemblies through a finite element method. A representative schematic presentation for the calculation and the corresponding electric field distribution pattern are exhibited in Fig.…”

Core level shifts as indicators of Cr chemistry on hydroxylated α-Al2O3(0001): a combined photoemission and first-principles study

“…3 Chemistry and structure of Cr/alumina Occurring in supported clusters 25 , the Cr 2p 3/2 shifts could involve a final state screening of the positive photo-hole [60][61][62][63] ; an estimate is given by E F,m = αe 2 /4πε 0 R, where R is the particle radius, ε 0 the vacuum permittivity and α a parameter around 0.5 61,62 , so that the observed shift of ∼ 1 eV could stem from clusters of around 1.5 nm in size. However, several arguments favour chemistry instead of electrostatics.…”