Tuning doping and surface functionalization of columnar oxide films for volatile organic compound sensing: experiments and theory

Abstract

AgO/Ag NPs enhance considerably the selectivity of Fe-doped ZnO surfaces towards ethanol detection.

Surface functionalization of ZnO:Ag columnar thin films with AgAu and AgPt bimetallic alloy nanoparticles as an efficient pathway for highly sensitive gas discrimination and early hazard detection in batteries

“…The impregnation with Table 3 Calculated surface energies after relaxation (g r ) for terminations A and B of the pristine ZnO(10 10) surface. 49 The surface free energies (s) are also reported for both terminations of the Ag-doped ZnO(10 10) surface. The work function (F) values are indicated for the pristine 49 All the VOCs adsorb molecularly on the doped as well as on the NP-decorated ZnO (10 10) surfaces, in line with previous reports.…”

“…More details regarding the stacking of the layers, and a description of the surface terminations and the number of layers with the atoms frozen at their bulk positions can be found elsewhere. 49 The substitutional doping of the ZnO(10 10) surface by Ag and its effect on the surface structure, energies, as well as on the electronic and magnetic properties are now examined. One Zn atom is replaced, in order to model the lowest Ag content value of 2.73 wt%, which is allowed by the size of our 48 formula unit (f.u.)…”

“…Despite modelling a dopant concentration almost threefold higher than the 0.95 wt% used for the experiments, previous works have shown excellent agreement between the two approaches. 32,49 The substitutional doping of the symmetrically inequivalent exposed Zn atoms was inspected, corresponding to the following solid-state reaction, Zn 48 O 48 (10 10) + Ag(fcc) ¼ Zn 47 AgO 48 (10 10) + Zn(hcp) (8) where the face-centred cubic (fcc) Ag and hexagonal close packed (hcp) Zn were modelled using the one and two atoms primitive unit cells, respectively.…”

“…These horizontal and vertical atomic shis are only allowed in the doped termination A due to the large interlayer spacing of 1.848 A between the surface and subsurface planes. 49 In contrast, the densest topmost layers of termination B experience negligible displacements, with the exception of the O atoms surrounding the 3-and 4-fold Ag dopants, which move by 0.43 and 0.15 A, respectively.…”

“…The electronic properties of the doped surfaces were further interrogated by measuring the work function (F) in order to gauge their reactivity as reducing agents. 32,49 The work function is the energy needed to remove an electron from the Fermi level (E F ) of the surface into the electrostatic potential of the vacuum Table 3 shows large reductions of over 50% in the work function values of all the doped surfaces with respect to their pristine counterparts. The absolute value for this type of thermodynamic work is between 2.61 and 2.64 eV for the doped 4-fold position in both terminations.…”