111 research outputs found
Phonon properties and photo-thermal oxidation of micromechanically exfoliated antimonene nanosheets
Two-dimensional (2D) sheets of antimonene have attracted increasing attention due to their unique physical and chemical properties prompting potential for diverse applications. We present a facile method to prepare high-quality antimonene nanosheets (ANSs) by micromechanical exfoliation on SiO2/Si substrate. The temperature- and laser power-dependent Raman studies of exfoliated ANSs are reported and analyzed. It was found that both the out-of-plane A1g and the in-plane Eg modes red-shift linearly with increase in temperature, pointing towards anharmonic vibrations of the lattice. The thermal response of the ANSs on a SiO2/Si surface is also described using numerical simulation of the heat transfer to study their laser-induced oxidation mechanisms. These results offer a deeper understanding of the phonon properties and oxidation susceptibility of 2D antimonene paving the way for the development of antimonene-based technologies, such as electronic devices or photothermal cancer therapy
Exciton Gas Compression and Metallic Condensation in a Single Semiconductor Quantum Wire
We study the metal-insulator transition in individual self-assembled quantum
wires and report optical evidences of metallic liquid condensation at low
temperatures. Firstly, we observe that the temperature and power dependence of
the single nanowire photoluminescence follow the evolution expected for an
electron-hole liquid in one dimension. Secondly, we find novel spectral
features that suggest that in this situation the expanding liquid condensate
compresses the exciton gas in real space. Finally, we estimate the critical
density and critical temperature of the phase transition diagram at
cm and K, respectively.Comment: 4 pages, 5 figure
Direct growth of 2D and 3D graphene nano-structures over large glass substrates by tuning a sacrificial Cu-template layer
We demonstrate direct growth of two-dimensional (2D) and three-dimensional (3D) graphene structures on glass substrates. By starting from catalytic copper nanoparticles of different densities and using chemical vapour deposition (CVD) techniques, different 2D and 3D morphologies can be obtained, including graphene sponge-like, nano-ball and conformal graphene structures. More important, we show that the initial copper template can be completely removed via sublimation during CVD and, if need be, subsequent metal etching. This allows optical transmissions close to the bare substrate, which, combined with electrical conductivity make the proposed technique very attractive for creating graphene with high surface to volume ratio for a wide variety of applications, including antiglare display screens, solar cells, light-emitting diodes, gas and biological plasmonic sensors.Peer ReviewedPostprint (author's final draft
Electrically Driven Varifocal Silicon Metalens
Optical metasurfaces have shown to be a powerful approach to planar optical elements, enabling an unprecedented control over light phase and amplitude. At that stage, where a wide variety of static functionalities have been accomplished, most efforts are being directed toward achieving reconfigurable optical elements. Here, we present our approach to an electrically controlled varifocal metalens operating in the visible frequency range. It relies on dynamically controlling the refractive index environment of a silicon metalens by means of an electric resistor embedded into a thermo-optical polymer. We demonstrate precise and continuous tuneability of the focal length and achieve focal length variation larger than the Rayleigh length for voltage as small as 12 V. The system time-response is of the order of 100 ms, with the potential to be reduced with further integration. Finally, the imaging capability of our varifocal metalens is successfully validated in an optical microscopy setting. Compared to conventional bulky reconfigurable lenses, the presented technology is a lightweight and compact solution, offering new opportunities for miniaturized smart imaging devices.Peer ReviewedPostprint (author's final draft
Interplay between optical emission and magnetism in the van der Waals magnetic semiconductor CrSBr in the two-dimensional limit
The Van der Waals semiconductor metamagnet CrSBr offers an ideal platform for
studying the interplay between optical and magnetic properties in the
two-dimensional limit. Here, we carried out an exhaustive optical
characterization of this material by means of temperature and magnetic field
dependent photoluminescence (PL) on flakes of different thicknesses down to the
monolayer. We found a characteristic emission peak that is quenched upon
switching the ferromagnetic layers from an antiparallel to a parallel
configuration and exhibits a different temperature dependence from that of the
peaks commonly ascribed to excitons. The contribution of this peak to the PL is
boosted around 30-40 K, coinciding with the hidden order magnetic transition
temperature. Our findings reveal the connection between the optical and
magnetic properties via the ionization of magnetic donor vacancies. This
behavior enables a useful tool for the optical reading of the magnetic states
in atomically thin layers of CrSBr and shows the potential of the design of
two-dimensional heterostructures with magnetic and excitonic properties.Comment: 20 pages, 5 figure
Charge control in laterally coupled double quantum dots
We investigate the electronic and optical properties of InAs double quantum
dots grown on GaAs (001) and laterally aligned along the [110] crystal
direction. The emission spectrum has been investigated as a function of a
lateral electric field applied along the quantum dot pair mutual axis. The
number of confined electrons can be controlled with the external bias leading
to sharp energy shifts which we use to identify the emission from neutral and
charged exciton complexes. Quantum tunnelling of these electrons is proposed to
explain the reversed ordering of the trion emission lines as compared to that
of excitons in our system.Comment: 4 pages, 4 figures submitted to PRB Rapid Com
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