We report bilayer-graphene field effect transistors operating as Terahertz (THz) broadband photodetectors based on plasma-waves excitation. By employing wide-gate geometries or buried gate configurations, we achieve a responsivity ∼1.2 V/W (1.3 mA/W) and a noise equivalent power ∼2 × 10−9 W/√Hz in the 0.29–0.38 THz range, in photovoltage and photocurrent mode. The potential of this technology for scalability to higher frequencies and the development of flexible devices makes our approach competitive for a future generation of THz detection systems.

Lead halide perovskite nanocrystals are an emerging class of materials that have gained wide interest due to their facile color tuning and high photoluminescence quantum yield; however, the lack of techniques to translate the high performance of nanocrystals into solid films restricts the successful exploitation of such materials in optoelectronic applications. Here, we report a heat-up and large scale synthesis of quantum-confined, blue-emitting CsPbBr3 nanoplatelets (NPLs) that self-assemble into stacked lamellar structures. Spin-coated films fabricated from these NPLs show stable blue emission with a photoluminescence quantum yield (PLQY) of 25%. The morphology and the optoelectronic properties of such films can be dramatically modified by UV-light irradiation under ambient conditions at high power, which transforms the self-assembled stacks of NPLs into much larger structures, such as square-shaped disks and nanobelts. The emission from the transformed thin films is in the green with a record PLQY of 65%, and under femtosecond-pulsed excitation they manifest amplified spontaneous emission with a sharp linewidth of 4 nm at full-width-half-maximum. The transformed films show stable photocurrent with responsivity of up to 15 mA/W and response times of some tens of milliseconds, and are robust under treatment with different solvents. We exploit their insolubility in ethanol to fabricate green emitting, all solution-processed light emitting diodes with external quantum efficiency of 1.1% and luminance of 590 Cd/m2.

Two-dimensional colloidal halide perovskite nanocrystals are promising materials for light emitting applications. Recent studies focused on nanoplatelets that are able to self-assemble and transform on solid substrates. Yet, the mechanism behind the process and the atomic arrangement of their assemblies remain unclear. Here, we present in detail the transformation of self-assembled stacks of CsPbBr₃ nanoplatelets in solution over a period of a few months by using ex-situ transmission electron microscopy and surface analysis. We demonstrate that the transformation mechanism can be understood as oriented attachment, proceeding through the following steps: i) desorption of the ligands from the particles surfaces, causing the seamless atomic merging of nanoplatelet stacks into nanobelts; ii) merging of neighboring nanobelts that form more extended nanoplates; and iii) attachment of nanobelts and nanoplates, forming objects with an atomic structure that resembles a mosaic made of broken nanotiles. We reveal that aged nanobelts and nanoplates, which are mainly stabilized by amine/ammonium ions, link through a bilayer of CsBr, with the atomic columns of neighboring perovskite lattices shifted by a half-unit-cell, forming Ruddlesden-Popper planar faults. We also show, via in-situ monitoring of the nanocrystal photoluminescence combined with transmission electron microscopy analysis, that the transformation is temperature-driven and that it can take place within tens of minutes in solution and in spin-coated films. Understanding this process gives crucial information for the design and fabrication of perovskite materials, where control over the type and density of defects is desired, stimulating the development of perovskite nanocrystal structures with tailored electronic properties.

Hexagonal boron nitride (hBN) is widely used as a protective layer for few-atom-thick crystals and heterostructures (HSs), and it hosts quantum emitters working up to room temperature. In both instances, strain is expected to play an important role, either as an unavoidable presence in the HS fabrication or as a tool to tune the quantum emitter electronic properties. Addressing the role of strain and exploiting its tuning potentiality require the development of efficient methods to control it and of reliable tools to quantify it. Here we present a technique based on hydrogen irradiation to induce the formation of wrinkles and bubbles in hBN, resulting in remarkably high strains of ∼2%. By combining infrared (IR) near-field scanning optical microscopy and micro-Raman measurements with numerical calculations, we characterize the response to strain for both IR-active and Raman-active modes, revealing the potential of the vibrational properties of hBN as highly sensitive strain probes.