arXiv subjects

José E. Padilha

Publications and source records attributed to José E. Padilha.

3 recordsLinked to original sources

arXiv2023

Bridging Borophene and Metal Surfaces: Structural, Electronic, and Electron Transport Properties

Currently, solid interfaces composed of two-dimensional materials (2D) in contact with metal surfaces (m-surf) have been the subject of intense research, where the borophene bilayer (BBL) has been considered a prominent material for the development of electronic devices based on 2D platforms. In this work, we present a theoretical study of the energetic, structural, and electronic properties of the BBL/m-surf interface, with m-surf = Ag, Au, and Al (111) surfaces, and the electronic transport properties of BBL channels connected to the BBL/m-surf top contacts. We find that the bottom-most BBL layer becomes metalized, due to the orbital hybridization with the metal surface states, resulting in BBL/m-surf ohmic contacts, meanwhile, the inner and top-most boron layers kept their semiconducting character. The net charge transfers reveal that BBL has become $n$-type ($p$-type) doped for m-surf = Ag, and Al (= Au). A thorough structural characterization of the BBL/m-surf interface, using a series of simulations of the X-ray photoelectron spectra, shows that the formation of BBL/m-surf interface is characterized by a redshift of the B-$1s$ spectra. Further electronic transport results revealed the emergence of a Schottky barrier between 0.1 and 0.2\,eV between the BBL/m-surf contact and the BBL channels. We believe that our findings are timely, bringing important contributions to the applicability of borophene bilayers for developing 2D electronic devices.

cond-mat.mtrl-sci↗

arXiv2022

Oxidation of 2D electrenes: structural transition and the formation of half-metallic channels protected by oxide layers

Based on first-principles calculations we performed a systematic study of the energetic stability, structural characterization, and electronic properties of the fully oxidized $A_{2}B$, electrenes, with the following combinations, (i) $A$=Ca, Sr, and Ba for $B$=N; (ii) $A$=Sr and Ba for $B$=P; and Y$_{2}$C, and Ba$_{2}$As. We have considered one side oxidation of single layer electrenes $(O/A_{2}B)$, and two side oxidation of bilayer electrenes $(O/(A_{2}B)_{2}/O)$. We show that the hexagonal lattice of the pristine host is no longer the ground state structure in the oxidized systems. Our total energy results reveal an exothermic structural transition from hexagonal to tetragonal (h$\rightarrow$t) geometry, resulting in layered tetragonal structures [$(AOAB)^{t}$, and $(AO(AB)_{2}AO)^{t}$]. Phonon spectra calculations and molecular dynamic simulations show that the $O/A_{2}B$, and $O/(A_{2}B)_{2}/O$ systems, with $A$=Ba, Ca, Sr, and $B$=N, become dynamically and structurally stable upon such a h$\rightarrow$t transition. Further structural characterizations were performed based on simulations of the near edge X-ray absorption spectroscopy at the nitrogen K-edge. Finally, the electronic structure calculations and transport calculations reveal the formation of half-metallic bands spreading out through the $A$N layers, which are shielded by oxide $A$O sheets. These findings indicate that $(AOAB)^{t}$, and $(AO(AB)_{2}AO)^{t}$, (with $B$=N) are quite interesting platforms for application in spintronics; since the half-metallic channels along the $A$N or $(A\text{N})_2$ layers (core) are protected against the environment conditions by the oxidized $A\text{O}$ sheets (cover shells).

cond-mat.mtrl-sci↗

arXiv2020

Structural Transition in Oxidized Ca$_2$N Electrenes: CaO/CaN 2D heterostructures

Based on first-principles calculations we show that the oxidation of ultrathin films of Ca$_2$N electrides, electrenes, drives a hexagonal$\rightarrow$tetragonal structural transition. The ground state configuration of the oxidized monolayer (ML) and bilayer (BL) systems can be viewed as CaO/CaN and CaO/(CaN)$_2$/CaO two dimensional (2D) heterostructures. In both systems, we found nearly free electron (NFE) states lying near the vacuum level, and the spatial projection reveals that they are localized above the oxidized CaO surface. Focusing on the magnetic properties, we find that the nitrogen atoms of the oxidized Ca$_2$N becomes spin-polarized ($\sim$1 $μ_{\rm B}$/N-atom); where (i) the ferromagnetic and the anti-ferromagnetic phases are nearly degenerated in the ML system, CaO/CaN, while (ii) there is an energetic preference for the ferromagnetic phase in CaO/(CaN)$_2$/CaO. We show that such a FM preference can be strengthened upon mechanical compression. Further electronic structure calculations reveal that the FM CaO/Ca$_2$N/CaO presents half-metallicity, where the metallic channels project (predominantly) on the N-$2p_{x,y}$ orbitals. In addition to the total energy results, molecular dynamic and phonon spectra calculations have been done in order to verify its thermal and structural stabilities. Those findings suggest that CaO/Ca$_2$N/CaO is a quite interesting, and structurally stable, 2D FM heterostructure characterized half-metallic bands sandwiched by NFE states lying on the oxidized surfaces.

cond-mat.mtrl-sci↗