RESUMEN
Phase transitions are key in determining and controlling the quantum properties of correlated materials. Here, by using the combination of material synthesis and photoelectron spectroscopy, we demonstrate a genuine Mott transition undressed of any symmetry breaking side effects in the thin films of V2O3. In particular and in contrast with the bulk V2O3, 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 slowly over a wide temperature range, the Fermi wave-vector does not change, and the critical temperature is lower than the one reported for the bulk. Our findings are fundamental in demonstrating the universal benchmarks of a genuine nonsymmetry breaking Mott transition, extendable to a large array of correlated quantum systems, and hold promise of exploiting the metal-insulator transition by implementing V2O3 thin films in devices.
RESUMEN
InN quantum dots (QDs) are considered to be promising nanostructures for different device applications. For any hexagonal AB-stacking semiconductor system, polarity is an important feature which affects the electronic properties. Therefore, the determination of this characteristic on any wurtzite (semi)polar III-N compound or alloy is essential for defining its applicability. In this paper, the polarity of InN QDs grown on silicon by indium droplet epitaxy plus nitridation and annealing was determined by a modified approach combining exit wave reconstruction with negative-spherical-aberration high-resolution lattice imaging using TEM. Comparing the micrographs of two QDs from the same TEM specimen with the simulated images of InN slab structures generated under the same conditions as of the experiments, it was confirmed that the QDs of the present study are N polar. Given that the settlement of material's polarity has always been a tedious, indirect and controversial issue, the major value of our proposal is to provide a straightforward procedure to determine the polar direction from atomic-resolution focal series images.
RESUMEN
Strain variation within a nanoparticle plays a crucial role in tuning its properties. High Resolution Transmission Electron Microscopy (HRTEM) images of a nanoparticle supported on amorphous carbon film are used to determine the strain variation. Experimental measurements in this present study on a single crystalline silver nanoparticle exhibited an unexpected high strain variation. Generally, the influence of carbon film is not accounted for during interpretation of measured strain variation. However, experimental observations raise the question whether the supporting carbon film alters the measured strain variation. In order to address this, strain variation within a simulated Ag nanoparticle supported on an amorphous carbon is measured with varying film thicknesses. The results show that supporting carbon film thickness introduces an artefact leading to more strain variation than what is present within an unsupported nanoparticle. Moreover, the variation increases with increasing supporting carbon film thickness. This effect is more pronounced in a thinner nanoparticle. Without considering this influence, the interpretation of strain within a nanoparticle may introduce severe errors which in turn will affect the tunability of desirable properties for different applications. Since strain measurement depends on the accuracy of the atomic position, the interpretation of any result using the atomic position from HRTEM images of a nanoparticle should consider the influence of supporting film.
