arXiv subjects

Juliana M. Morbec

Publications and source records attributed to Juliana M. Morbec.

5 recordsLinked to original sources

arXiv2026

Self-assembly and Electronic Properties of Graphyne and Graphdiyne Molecular Wires on Metallic Surfaces

Molecular self-assembly on solid surfaces has been the subject of extensive research, motivated by both fundamental and technological interests. On the fundamental side, these studies seek to elucidate the mechanisms governing molecular self-assembly and the resulting surface structures. From an applied perspective, they provide a route toward controlling surface reactions and engineering molecular electronic devices. Here, based on first-principles density functional theory calculations, we present a comprehensive study of self-assembled molecular wires (MWs), composed of graphyne (GY(1D)) and graphdiyne (GYD(1D))-like structures, adsorbed on Au(111), Ag(111), and Al(111) surfaces. Our total-energy calculations reveal that non-aligned MW arrays are energetically preferred on all three metal substrates. The GY(1D) and GYD(1D) molecular wires interact with the metal surfaces through van der Waals (vdW) forces, while their molecular orbitals do not contribute to the formation of metallic interface states. Simulated X-ray photoelectron spectroscopy (XPS) spectra reveal that the C 1s spectral features of the molecular wires are largely preserved upon adsorption, while the absolute binding energies undergo a substantial downshift that is nearly independent of the metal substrate, indicating that metallic screening effects dominate the adsorption-induced core-level shifts. Electronic band-structure calculations further show that the semiconducting character of the molecular wires is retained, resulting in vdW metal-semiconductor heterostructures in which the semiconducting component consists of one-dimensional semiconducting channels. These findings demonstrate that self-assembled graphyne- and graphdiyne-based molecular wires on metal surfaces provide a promising platform for the realization of low-dimensional molecular electronic devices.

cond-mat.mtrl-sci↗

arXiv2019

Molybdenum Disulphide Nanoflakes Grown by Chemical Vapour Deposition on Graphite: Nucleation, Orientation, and Charge Transfer

Two-dimensional molybdenum disulphide on graphene grown by chemical vapour deposition is a promising van der Waals system for applications in optoelectronics and catalysis. To extend the fundamental understanding of growth and intrinsic properties of molybdenum disulphide on graphene, molybdenum disulphide on highly oriented pyrolytic graphite is a suitable model system. Here we show, experimentally and by density-functional-theory calculations, that molybdenum disulphide flakes grow in two orientations. One of the orientations is energetically preferred, the other one is rotated by 30 degree. Because of a high energy barrier confirmed by our calculations both orientations are stable at room temperature and their switching can only be forced by external stimuli, i.e. by a scanning tunneling microscope tip. Combined Kelvin probe microscopy and Raman spectroscopy measurements show that the flakes with a typical size of a few hundred nanometers are less doped than the often studied exfoliated molybdenum disulphide single layer.

cond-mat.mtrl-sci↗

arXiv2016

The role of the van der Waals interactions in the adsorption of anthracene and pentacene on the Ag(111) surface

Using first-principles calculations based on density-functional theory (DFT) we investigated the effects of the van der Waals (vdW) interactions on the structural and electronic properties of anthracene and pentacene adsorbed on the Ag(111) surface. We found that the inclusion of vdW corrections strongly affects the binding of both anthracene/Ag(111) and pentacene/Ag(111), yielding adsorption heights and energies more consistent with the experimental results than standard DFT calculations with generalized gradient approximation (GGA). For anthracene/Ag(111) the effect of the vdW interactions is even more dramatic: we found that pure DFT-GGA calculations (without including vdW corrections) result in preference for a tilted configuration, in contrast to experimental observations of flat-lying adsorption; including vdW corrections, on the other hand, alters the binding geometry of anthracene/Ag(111), favoring the flat configuration. The electronic structure obtained using a self-consistent vdW scheme was found to be nearly indistinguishable from the conventional DFT electronic structure once the correct vdW geometry is employed for these physisorbed systems. Moreover, we show that a vdW correction scheme based on a hybrid functional DFT calculation (HSE) results in an improved description of the highest occupied molecular level of the adsorbed molecules.

cond-mat.mtrl-sci↗

arXiv2013

Jahn-Teller distortion induced magnetic phase transition in cubic BaFeO$_{3}$

Using density functional theory (DFT) with local density approximation (LDA) and generalized gradient approximation (GGA) correlation functionals, the electronic and magnetic structures of cubic BaFeO$_{3}$ in the ferromagnetic (FM) and antiferromagnetic (AFM) states are studied. Our LDA/GGA and LDA$+U$/GGA$+U$ results show that cubic BFO has a FM ground state, in agreement with recent experimental works. Two types of Jahn-Teller (JT) distortions, denoted as JT1 and JT2, are considered. We find FM to ferrimagnetic (FIM) and FM to AFM magnetic phase transitionn in the JT1 and JT2 type of distortions, respectively. Larger strains are required for the FM-AFM transition as compared to the FM-FIM. DFT$+U$ calculations also show that the magnetic moments dramatically decrease at large strains due to strong overlapping between the Fe and O atoms. The origins of these transitions is discussed in terms of a competition between double exchange and superexchange interactions. Oxygen and Fe displacements are therefore responsible for the magnetic phase transitions and the reduction of the magnetic moments.

cond-mat.mtrl-sci↗

arXiv2013

Role of vacancies in the magnetic and electronic properties of SiC nanoribbons: an ab initio study

Using ab-initio calculations based on density functional theory, we investigate the effects of vacancies on the electronic and magnetic properties of zigzag SiC nanoribbons (Z-SiCNR). Single (V_C and V_Si) and double (V_SiV_Si and V_SiV_C) vacancies are observed to induce magnetism in Z-SiCNRs. The presence of a single V_Si does not affect the half-metallic behavior of pristine Z-SiCNRs; however, a single V_C leads to a transition from half-metallic to metallic behavior in Z-SiCNRs due to the edge Si p orbitals and the atoms surrounding the vacancy. The interactions of vacancies with foreign impurity atoms (B and N) are also investigated and it is observed that V_SiN_C does not only suppress the oscillatory type magnetism of V_SiV_C, but also retains the half-metallic character of the pristine Z-SiCNRs. The defect formation energies of vacancies can be reduced by substitutional B and N atoms. We believe that ferromagnetism is expected if Z-SiCNR are grown under suitable conditions.

cond-mat.mtrl-sci↗