Spectroscopic Evidence of a Dimensionality-Induced Metal-to-Insulator Transition in the Ruddlesden-Popper LaNiO Series.

Perovskite-based heterostructures have recently gained remarkable interest, thanks to atomic-scale precision engineering. These systems are very susceptible to small variations of control parameters, such as two-dimensionality, strain, lattice polarizability, and doping. Focusing on the rare-earth nickelate diagram, LaNiO (LNO) catches the eye, being the only nickelate that does not undergo a metal-to-insulator transition (MIT).

Proximity-Induced Superconductivity in Monolayer MoS.

Proximity effects in superconducting normal (SN) material heterostructures with metals and semiconductors have long been observed and theoretically described in terms of Cooper pair wave functions and Andreev reflections. Whereas the semiconducting -layer materials in the proximity experiments to date have been doped and tens of nanometers thick, we present here a proximity tunneling study involving a pristine single-layer transition-metal dichalcogenide film of MoS placed on top of a Pb thin film. Scanning tunneling microscopy and spectroscopy experiments together with parallel theoretical analysis based on electronic structure calculations and Green's function modeling allow us to unveil a two-step process in which MoS first becomes metallic and then is induced into becoming a conventional s-wave Bardeen-Cooper-Schrieffer-type superconductor.

The Effects of Atomic-Scale Strain Relaxation on the Electronic Properties of Monolayer MoS.

The ability to control nanoscale electronic properties by introducing macroscopic strain is of critical importance for the implementation of two-dimensional (2D) materials into flexible electronics and next-generation strain engineering devices. In this work, we correlate the atomic-scale lattice deformation with a systematic macroscopic bending of monolayer molybdenum disulfide films by using scanning tunneling microscopy and spectroscopy implemented with a custom-built sample holder to control the strain. Using this technique, we are able to induce strains of up to 3% before slipping effects take place and relaxation mechanisms prevail.

Quantifying Wavelength-Dependent Plasmonic Hot Carrier Energy Distributions at Metal/Semiconductor Interfaces.

Hot carriers generated from the nonradiative decay of localized surface plasmons are capable of driving charge-transfer reactions at the surfaces of metal nanostructures. Photocatalytic devices utilizing plasmonic hot carriers are often based on metal nanoparticle/semiconductor heterostructures owing to their efficient electron-hole separation ability. The rapid thermalization of hot carriers generated at the metal nanoparticles yields a distribution of carrier energies that determines the capability of the photocatalytic device to drive redox reactions.

Strain-Engineered Oxygen Vacancies in CaMnO Thin Films.

We demonstrate a novel pathway to control and stabilize oxygen vacancies in complex transition-metal oxide thin films. Using atomic layer-by-layer pulsed laser deposition (PLD) from two separate targets, we synthesize high-quality single-crystalline CaMnO films with systematically varying oxygen vacancy defect formation energies as controlled by coherent tensile strain. The systematic increase of the oxygen vacancy content in CaMnO as a function of applied in-plane strain is observed and confirmed experimentally using high-resolution soft X-ray absorption spectroscopy (XAS) in conjunction with bulk-sensitive hard X-ray photoemission spectroscopy (HAXPES).

Inter-Layer Coupling Induced Valence Band Edge Shift in Mono- to Few-Layer MoS.

Recent progress in the synthesis of monolayer MoS, a two-dimensional direct band-gap semiconductor, is paving new pathways toward atomically thin electronics. Despite the large amount of literature, fundamental gaps remain in understanding electronic properties at the nanoscale. Here, we report a study of highly crystalline islands of MoS grown via a refined chemical vapor deposition synthesis technique.

Quantification of internal electric fields and local polarization in ferroelectric superlattices.

Oxide heterostructure superlattices constitute a new family of materials with tunable ferroelectric properties. While theoretical models predict the presence of nanosized ferroelectric domains in these films, they had not been observed as the magnitude of the response functions challenges the limits of experimental detection. Here, a new protocol in a precise variant of piezoforce microscopy is used to image domains in BaTiO(3)/SrTiO(3) superlattices.

Fully band-resolved scattering rate in MgB2 revealed by the nonlinear hall effect and magnetoresistance measurements.

We have measured the normal state temperature dependence of the Hall effect and magnetoresistance in epitaxial MgB2 thin films with variable disorders characterized by the residual resistance ratio RRR ranging from 4.0 to 33.3.