RESUMO
Nanocrystals are promising building blocks for the development of low-cost infrared optoelectronics. Gating a nanocrystal film in a phototransistor geometry is commonly proposed as a strategy to tune the signal-to-noise ratio by carefully controlling the carrier density within the semiconductor. However, the performance improvement has so far been quite marginal. With metallic electrodes, the gate dependence of the photocurrent follows the gate-induced change of the dark current. Graphene presents key advantages: (i) infrared transparency that allows back-side illumination, (ii) vertical electric field transparency, and (iii) carrier selectivity under gate bias. Here, we investigate a configuration of 2D/0D infrared photodetectors taking advantage of a high capacitance ionic glass gate, large-scale graphene electrodes, and a HgTe nanocrystals layer of high carrier mobility. The introduction of graphene electrodes combined with ionic glass enables one to reconfigure selectively the HgTe nanocrystals and the graphene electrodes between electron-doped (n) and hole-doped (p) states. We unveil that this functionality enables the design a 2D/0D p-n junction that expands throughout the device, with a built-in electric field that assists charge dissociation. We demonstrate that, in this specific configuration, the signal-to-noise ratio for infrared photodetection can be enhanced by 2 orders of magnitude, and that photovoltaic operation can be achieved. The detectivity now reaches 109 Jones, whereas the device only absorbs 8% of the incident light. Additionally, the time response of the device is fast (<10 µs), which strongly contrasts with the slow response commonly observed for 2D/0D mixed-dimensional heterostructures, where larger photoconduction gains come at the cost of slower response.
RESUMO
Fabrication and spintronics properties of 2D-0D heterostructures are reported. Devices based on graphene ("Gr")-aluminium nanoclusters heterostructures show robust and reproducible single-electron transport features, in addition to spin-dependent functionality when using a top magnetic electrode. The magnetic orientation of this single ferromagnetic electrode enables the modulation of the environmental charge experienced by the aluminium nanoclusters. This anisotropic magneto-Coulomb effect, originating from spin-orbit coupling within the ferromagnetic electrode, provides tunable spin valve-like magnetoresistance signatures without the requirement of spin coherent charge tunneling. These results extend the capability of Gr to act both as electrode and as a platform for the growth of 2D-0D mixed-dimensional van der Waals heterostructures, providing magnetic functionalities in the Coulomb blockade regime on scalable spintronic devices. These heterostructures pave the way towards novel device architectures at the crossroads of 2D material physics and spin electronics.
RESUMO
Large assemblies of self-organized aluminum nanoclusters embedded in an oxide layer are formed on graphene templates and used to build tunnel-junction devices. Unexpectedly, single-electron-transport behavior with well-defined Coulomb oscillations is observed for a record junction area of up to 100 µm2 containing millions of metal islands. Such graphene-metal nanocluster hybrid materials offer new prospects for single-electron electronics.
RESUMO
Unique insights into magnetotransport in 20 nm ligand-free La0.67 Sr0.33 MnO3 perovskite nanocrystals of nearly perfect crystalline quality reveal a chemically altered 0.8 nm thick surface layer that triggers exceptionally large magnetoresistance at low temperature, independently of the spin polarization of the ferromagnetic core. This discovery shows how the nanoscale impacts magnetotransport in a material widely spread as electrode in hybrid spintronic devices.
