The work is dedicated to the complex theoretical and experimental study of structural, electronic, luminescent and gas-sensing properties of nanostructures based on ZnO (nanoclusters, nanotubes, nanopowders).Density functional theory studies of structural and electronic properties of small clusters were performed. For each cluster an optimization of structure was performed and the basic properties of the electronic structure were established. It was determined that with the increasing of the formula unit number energetically more efficient in the small clusters is stabilization from the ring to fulleren-like structures containing tetragonal and hexagonal faces. Among the clusters (ZnO)12 doped with 3d transition metal atoms the most stable are clusters with Zn substitution. HOMO-LUMO band gap of doped clusters decreases due to p-d hybridization of the impurity atom orbitals with the orbitals of the oxygen atoms.
First principles calculations of the adsorption of molecules of different gases (O2, H2O, CO, NO2, NH3, CH3OH, C3H6O and C2H5OH) on the surface of nanoclusters Zn12O12 were performed. It was determined that the molecules of H2O, CO, NO2, NH3, CH3OH, C3H6O and C2H5OH increase the concentration of the main charge carriers (electrons) in sensor systems, whereas molecule O2, reduce their concentration. Adsorption of molecules causes the reduction of the band gap of nanoclusters. The sharpest decrease is observed for O2 molecules, and among donor molecules the greatest impact was observed with CO and NH3 molecules.
DFT studies of the structural and electronic properties of nanoclusters (ZnO)n (n = 34, 60) in different geometric configurations were conducted. It was established that for the (ZnO)34 nanoclusters, the most stable are fullerene-like hollow structures that satisfy the rule of six isolated quadrangles. For the (ZnO)60 nanoclusters, different types of isomers, including hollow structures and sodalite-like structures composed from (ZnO)12 nanoclusters, were investigated. It was determined that the most energetically favorable structure was sodalite-type structure composed of seven (ZnO)12 clusters.First principle investigations of native point defects in (ZnO)n nanoclusters (n = 34, 60) based on DFT+U approach, for different types of isomers, were performed. The values for formation energy, HOMO–LUMO gap, as well as the partial density of states for each cluster were investigated to establish the influence of the defects on the electronic properties of the (ZnO)n nanoclusters. It was determined that the most favorable defects of the clusters structure were Zn and O vacancies.
