Interplay among work function, electronic structure and stoichiometry in nanostructured VO_x films

Abstract

The work function is the parameter of greatest interest in many technological applications involving charge exchange mechanisms at the interface. The possibility to produce samples with a controlled work function is then particularly interesting, albeit challenging. We synthetized nanostructured vanadium oxides films by a room temperature Supersonic Cluster Beam Deposition method, obtaining samples with tunable stoichiometry and work function (3.7-7 eV). We present an investigation of the electronic structure of several vanadium oxides films as a function of the oxygen content via in-situ Auger, valence-band photoemission spectroscopy and work function measurements.The experiments probed the partial 3d density of states, highlighting the presence of strong V3d-O2p and V3d-V4s hybridization which influence 3d occupation. We show how controlling the stoichiometry of the sample implies a control over work function, and that the access to nanoscale quantum confinement can be exploited to increase the work function of the sample relative to the bulk analogue. In general, the knowledge of the interplay among work function, electronic structure, and stoichiometry is strategic to match nanostructured oxides to their target applications.

Stoichiometry and disorder influence over electronic structure in nanostructured VOx films

“…Since XANES probes the empty density of states (DOS), t * 2g and e * g signals can be observed at the O K edge only when t 2g and e g electrons are bound with the O 2p electrons. The presence of t * 2g in VO 0.6 samples (the weak component around 530 eV) can be attributed to the hybridization of V-3d and O-2p electrons in agreement with a previous Auger investigation, which predicts a mixed 4 s − 3d valence band for this suboxide (D'Elia et al 2020b). e * g and t * 2g features are observable on the whole VO x set, even though they are broad and not well separated.…”

“…The NS VO x films were deposited using a combination of the Pulsed Micro-plasma Cluster Source (PMCS) and the Supersonic Cluster Beam Deposition (SCBD) method. SCBD is a well-known synthesis method able to produce cluster assembled NS materials (D'Elia et al 2020b;Borghi et al 2018;Barborini et al 2011). This method offers considerable advantages for neutral cluster manipulation based on effusive beams making the seeded supersonic beam approach very powerful for the deposition of NS films.…”

“…The delay between the gas injection and the discharge firing was 0.51-0.64 ms; the discharge operating voltage was 0.9 kV, and the discharge duration was 60 μs; the pulsed-valve aperture was between 196 and 220 μs; and the pulse repetition rate was 3 Hz, and the Ar-O 2 pressure feeding the Parker valve was 60 bar. All the samples have been synthesized using Ar or Ar-O 2 gas mixture as specified elsewhere (D'Elia et al 2020b). The substrate was kept at ∼ 300 K during the deposition, and the deposited films have been studied in situ using XANES spectroscopy.…”

“…Disordered VO x could benefit from reducing their size to the nanoscale (Jagiello et al 2017;Pasqualini et al 2017;Sartale et al 2013) because of confinement effects over the electronic structure, e.g. quantum confinement enhancement of the work function (D'Elia et al 2020b;Zhou and Zachariah 2012), and because of a large effective surface area (Rezvani et al 2016b;Pinto et al 2016;Pinto et al 2018b).…”

Engineering Porous Silicon Nanowires with Tuneable Electronic Properties

“…In recent years, semiconducting nanowires (NWs), especially silicon-based ones, have been extensively characterized and considered for different applications. Their unique chemical and physical properties and their ideal compatibility with the state-of-the-art Si electronics makes them a suitable candidate for applications in nano-electronics, opto-electronics, solar cells and sensors, in particular to exploit quantum confinement phenomena and its effect on the modulation of the electronic configuration [1][2][3][4]. Porous silicon nanowires (PSNs) have recently triggered attention for their intense visible photoluminescence due to a strong quantum confinement within the pores [1,5].…”