We perform ab initio calculations, based on density functional theory, for substitutional and vacancy defects in the monoclinic hafnium oxide (m-HfO2) and α-quartz (SiO2). The neutral oxygen vacancies and substitutional Si and Hf defects in HfO2 and SiO2, respectively, are investigated. Our calculations show that, for a large range of Hf chemical potential, Si substitutional defects are most likely to form in HfO2, leading to the formation of a silicate layer at the HfO2/Si interface. We also find that it is energetically more favorable to form oxygen vacancies in SiO2 than in HfO2, which implies that oxygen-deficient HfO2 grown on top of SiO2 will consume oxygen from the SiO2.

Designing the next generation of solid-state biosensors requires developing detectors which can operate with high precision at the single-molecule level. Nano-scaled architectures created in two-dimensional hybrid materials offer unprecedented advantages in this regard. Here, we propose and explore a novel system comprising a nanopore formed within a hybrid sheet composed of a graphene nanoroad embedded in a sheet of hexagonal boron nitride (h-BN). The sensitive element of this setup is comprised of an electrically conducting carbon chain forming one edge of the nanopore. This design allows detection of DNA nucleotides translocating through the nanopore based on the current modulation signatures induced in the carbon chain. In order to assess whether this approach is feasible to distinguish the four different nucleotides electrically, we have employed density functional theory combined with the non-equilibrium Green's function method. Our findings show that the current localized in the carbon chain running between the nanopore and h-BN is characteristically modulated by the unique dipole moment of each molecule upon insertion into the pore. Through the analysis of a simple model based on the dipole properties of the hydrogen fluoride molecule we are able to explain the obtained findings.

Recent experiments demonstrated a highly controlled synthesis of in-plane graphene/hexagonal boron nitride heterostructures, thereby paving the way for the development of a new category of hybrid 2D nanodevices with different interfaces. Herein, by employing a combination of density functional theory (DFT) and the non-equilibrium Green's function formalism (NEGF), the gas sensor capability of G-hBN, containing two different interfaces is assessed by exposing it to NO, NO₂, NH₃, and CO₂ gas molecules. Our results show that the strongest interaction occurs between NO_x molecules and G-hBN; meanwhile, NO and NO₂ molecules are more reactive in the interface regions than the pristine ones. In addition, the electron transport properties reveal that for a distinct two-port voltage applied, the gas molecule NO (NO₂) can be detected by large changes in the conductance and CO₂(NH₃) has insignificant signal conductance, leading to selectivity for the gas. The proposed device is a great potential candidate to be applied as a NO_x gas selector through a 2D nanodevice interface.

We have performed ab initio molecular dynamics simulations to generate an atomic structure model of amorphous hafnium oxide $\left(a{\text{-HfO}}_2\right)$ via a melt-and-quench scheme. This structure is analyzed via bond-angle and partial pair distribution functions. These results give a Hf-O average nearest-neighbor distance of $2.2\text{Å}$, which should be compared to the bulk value, which ranges from $1.96$ to $2.54\text{Å}$. We have also investigated the neutral O vacancy and a substitutional Si impurity for various sites, as well as the amorphous phase of ${\text{Hf}}_{1-x}{\text{Si}}_x{\text{O}}_2$ for $x=0.25$, 0.375, and 0.5.