Electric field effect on H f x T i y O 2 ( x + y ) clusters for applications in MOSFETs and DSSCs: a DFT study.

CONTEXT: The structural, electronic, non-linear optical (NLO) and spectral properties of Hf  x  Ti  y  O 2 (  x  + y ) clusters with (  x  +  y  ≤ 6 ) have been studied under the influence of an external electric field using density functional theory (DFT). The effect of variation in the Hf:Ti ratio on different properties of clusters is investigated. The motivation to study Hf  x  Ti  y  O 2 (  x  + y ) clusters lies in the fact that HfTiO thin films have wide applications in various optoelectronic and photovoltaic devices. So, it will be interesting to study the effect of electric field on Hf  x  Ti  y  O 2 (  x  + y ) clusters with the variation in the number of Hf, Ti and O atoms. It is observed that out of all the clusters, Hf 4 Ti 1 O 10 and Hf 5 Ti 1 O 12 are the most stable clusters with high values of binding energy and HOMO-LUMO gap. The application of an external electric field on these most stable clusters distorts their geometry and their HOMO-LUMO gap decreases, dipole moment and polarizability increases as the electric field is increased from 0 a.u. to 340 x 10 − 4 a.u. The applied electric field increases the polar character of clusters due to electron cloud deformation and hence, increases the reactivity of the clusters, thus making these clusters suitable for electrocatalytic reactions. The electric field controlled high values of dielectric constant makes these clusters suitable to be used in the oxide layer of metal oxide semiconductor field effect transistors (MOSFETs) with better capacitance. Under the effect of an electric field, the absorption peaks of UV-VIS spectra gets red-shifted. Due to the tuning of absorption spectra from ultraviolet to visible region, Hf  x  Ti  y  O 2 (  x  + y ) clusters can be thought of as a good replacement for TiO 2 in dye-sensitized solar cells (DSSCs).

METHODS: The computational study of Hf  x  Ti  y  O 2 (  x  + y ) clusters has been performed using DFT. For the ground state of Hf  x  Ti  y  O 2 (  x  + y ) clusters, the optimization and frequency calculations have been performed using hybrid B3LYP (Becke three-parameter exchange functional combined with Lee, Yang and Parr correlation functional) functional with LANL2DZ (Los Alamos National Laboratory effective core potentials with Double Zeta atomic set) basis set under hybrid-GGA (generalized gradient approximation). Optimization and frequency calculations have been performed in each case. The excited state calculations have been carried out within time-dependent DFT formalism for a total of 50 excited states. The computational chemistry software package Gaussian 16 along with its graphical interface Gaussview have been employed for the current study of Hf  x  Ti  y  O 2 (  x  + y ) clusters.