arXiv subjects

Regina Ciancio

Publications and source records attributed to Regina Ciancio.

7 recordsLinked to original sources

arXiv2026

Interfacial properties of MoS2 thin films grown on functional substrates

Interface chemistry and defect formation in MoS2 thin films grown on single crystal substrates critically determine the electronic structure of MoS2 and thus can strongly modify material functionality relevant for many applications, including electronics, optoelectronics, and energy related catalysis. We investigate MoS2 grown on three technologically relevant substrates, namely SrTiO3(111), c-axis Al2O3(0001) and 6H-SiC(0001). Experimental investigations by temperature dependent resistivity, photoemission spectroscopy and scanning transmission electron microscopy with coupled energy dispersive spectroscopy, with the support of theoretical calculation by Density Functional Theory, allow the identification of the substrate induced specific defects and their correlation with the electronic properties. Ti interdiffusion in SrTiO3/MoS2 generates donor like states near the Fermi level, leading to metallic transport. Al2O3/MoS2 exhibits a high density of sulfur related defects that introduce localized states and yield nearly temperature independent conductivity. SiC/MoS2 exhibits significant interface disorder resulting in a semiconducting temperature dependent resistivity, yet deviating from the ideal bulk like behavior. These results demonstrate how substrate choice governs defect formation and ultimately dominates the electronic behavior of MoS2 thin films, making the control of film substrate interactions essential for the engineering of new functional devices.

cond-mat.mtrl-sci↗

arXiv2023

Visualising emergent phenomena at oxide interfaces

Knowledge of atomic-level details of structure, chemistry, and electronic states is paramount for a comprehensive understanding of emergent properties at oxide interfaces. We utilise a novel methodology based on atomic-scale electron energy loss spectroscopy (EELS) to spatially map the electronic states tied to the formation of a two-dimensional electron gas (2DEG) at the prototypical non-polar/polar $TiO_2$/$LaAlO_3$ interface. Combined with differential phase contrast analysis we directly visualise the microscopic locations of ions and charge and find that 2DEG states and $Ti^{3+}$ defect states exhibit different spatial distributions. Supported by density functional theory (DFT) and inelastic scattering simulations we examine the role of oxygen vacancies in 2DEG formation. Our work presents a general pathway to directly image emergent phenomena at interfaces using this unique combination of arising microscopy techniques with machine learning assisted data analysis procedures.

cond-mat.mtrl-sci↗

arXiv2022

Disentangling structural and electronic properties in V$_{2}$O$_{3}$ thin films: a genuine non-symmetry breaking Mott transition

Phase transitions are key in determining and controlling the quantum properties of correlated materials. Here, by using the powerful combination of precise material synthesis and angle resolved photoelectron spectroscopy, we show evidence for a genuine Mott transition undressed of any symmetry breaking side effects in the thin-films of V$_{2}$O$_{3}$. In particular, and in sharp contrast with the bulk V$_{2}$O$_{3}$ crystals, we unveil the purely electronic dynamics approaching the metal-insulator transition, disentangled from the structural transformation that is prevented by the residual substrate-induced strain. On approaching the transition, the spectral signal evolves surprisingly slowly over a wide temperature range, the Fermi wave-vector does not change, and the critical temperature appears to be much lower than the one reported for the bulk. Our findings are on one side fundamental in demonstrating the universal benchmarks of a genuine non-symmetry breaking Mott transition, extendable to a large array of correlated quantum systems and, on the other, given that the fatal structural breakdown is avoided, they hold promise of exploiting the metal-insulator transition by implementing V$_{2}$O$_{3}$ thin films in devices.

cond-mat.str-el↗

arXiv2021

All-optical spin injection in silicon revealed by element specific time-resolved Kerr effect

Understanding how a spin current flows across metal-semiconductor interfaces at pico- and femtosecond timescales has implications for ultrafast spintronics, data processing and storage applications. However, the possibility to directly access the propagation of spin currents on such time scales has been hampered by the simultaneous lack of both ultrafast element specific magnetic sensitive probes and tailored metal-semiconductor interfaces. Here, by means of free electron laser-based element sensitive Kerr spectroscopy, we report direct experimental evidence of spin currents across a Ni/Si interface in the form of different magnetodynamics at the Ni M2,3 and Si L2,3 absorption edges. This further allows us to calculate the propagation velocity of the spin current in silicon, which is on the order of 0.2 nm/fs.

cond-mat.mtrl-sci↗

arXiv2019

Untwinned YBa$_2$Cu$_3$O$_{7-δ}$ thin films on MgO substrates: a platform to study strain effects on the local orders in cuprates

We have grown untwinned YBa$_2$Cu$_3$O$_{7-δ}$ (YBCO) films on (110) MgO substrates that were pre-annealed at high temperature in oxygen atmosphere. The annealing results in surface reconstruction with shallow facets, which induce the suppression of the YBCO twinning domains, and the preferential alignment of the CuO chains along one of the in-plane directions of the substrate. Because of the large mismatch between the in-plane lattice parameters of film and substrate, the strain induced by the MgO into the YBCO layer is strong and very peculiar. The YBCO film is compressed, with respect to the bulk, and presents a unidirectional buckling of the atomic planes, along the chains' direction, due to a deformation of the copper-oxygen octahedra. The YBCO films, which can be grown with thicknesses down to few unit cells and oxygen doping levels spanning most of the superconducting dome, are patterned into nanowires with dimensions down to 50 nm. The anisotropies due to the untwinning state are preserved in these structures; moreover, additional anisotropies appear, in ultrathin structures where strain effects become more pronounced. Such untwinned and compressively strained films can therefore be used as a platform to study the interplay between strain and the various local orders in the normal state of YBCO.

cond-mat.supr-con↗

arXiv2019

Selective control of localised vs. delocalised carriers in anatase TiO2 through reaction with O2

Two-dimensional (2D) metallic states induced by oxygen vacancies at oxide surfaces and interfaces provide new opportunities for the development of advanced applications, but the ability to control the behavior of these states is still limited. We used Angle Resolved Photoelectron Spectroscopy combined with density functional theory to study the reactivity of states induced by the oxygen vacancies at the (001)-(1x4) surface of anatase TiO2, where both 2D metallic and deeper lying in-gap states (IGs) are observed. Remarkably, the two states exhibit very different evolution when the surface is exposed to molecular O2: while IGs are almost completely quenched, the metallic states are only weakly affected. The energy scale analysis for the vacancy migration and recombination resulting from the DFT calculations confirms indeed that only the IGs originate from and remain localized at the surface, whereas the metallic states originate from subsurface vacancies, whose migration and recombination at the surface is energetically less favorable rendering them therefore insensitive to oxygen dosing.

cond-mat.mtrl-sci↗

arXiv2017

Transport properties of ultrathin YBa$_2$Cu$_3$O$_{7-δ}$ nanowires: a route to single photon detection

We report on the growth and characterization of ultrathin YBa$_2$Cu$_3$O$_{7-δ}$ (YBCO) films on MgO (110) substrates, which exhibit superconducting properties at thicknesses down to 3 nm. YBCO nanowires, with thicknesses down to 10 nm and widths down to 65 nm, have been also successfully fabricated. The nanowires protected by a Au capping layer show superconducting properties close to the as-grown films, and critical current densities, which are only limited by vortex dynamics. The 10 nm thick YBCO nanowires without the Au capping present hysteretic current voltage characteristics, characterized by a voltage switch which drives the nanowires directly from the superconducting to the normal state. Such bistability is associated in NbN nanowires to the presence of localized normal domains within the superconductor. The presence of the voltage switch, in ultrathin nanostructures characterized by high sheet resistance values, though preserving high quality superconducting properties, make our nanowires very attractive devices to engineer single photon detectors.

cond-mat.supr-con↗