Optical Switching of Hole Transfer in Double-Perovskite/Graphene Heterostructure.

Synergically combining their respective ultrahigh charge mobility and strong light absorption, graphene (Gr)/semiconductor heterostructures are promising building blocks for efficient optoelectronics, particularly photodetectors. Charge transfer (CT) across the heterostructure interface crucially determines device efficiency and functionality. Here, it is reported that hole-transfer processes dominate the ultrafast CT across strongly coupled double-perovskite Cs2 AgBiBr6 /graphene (DP/Gr) heterostructures following optical excitation. While holes are the primary charges flowing across interfaces, their transfer direction, as well as efficiency, show a remarkable dependence on the excitation wavelength. For excitation with photon energies below the bandgap of DPs, the photoexcited hot holes in Gr can compete with the thermalization process and inject into in-gap defect states in DPs. In contrast, above-bandgap excitation of DP reverses the hole-transfer direction, leading to hole transfer from the valence band of DPs to Gr. Experimental evidence that increasing the excitation photon energy enhances CT efficiency for both below- and above-bandgap photoexcitation regimes is further provided, unveiling the positive role of excess energy in enhancing interfacial CT. The possibility of switching the hole-transfer direction and thus the interfacial photogating field by tuning the excitation wavelength, provides a novel way to control the interfacial charge flow across a DP/Gr heterojunction.

Chemical Defect-Driven Response on Graphene-Based Chemiresistors for Sub-ppm Ammonia Detection.

Gas sensors are essential in several fields and, in general, features such as high sensitivity, quick response, and fast recovery are required, along with low power consumption and low cost. Graphene is considered a promising material for gas sensing applications, its functionalization often being a requisite. In the present study, we developed competitive and promising gas sensors for ammonia detection. Interestingly, we present an easy and efficient method to functionalize graphene by using diazonium chemistry with different functional groups. Moreover, we prove the superior sensing capability of our covalently modified graphene layers. These experimental data have been consistently interpreted by theoretical calculations, which reveal a defect-driven sensor's response to ammonia. These results open the possibility of a comprehensive design and use of these graphene-based sensors in real applications.

Exploring photosensitization as an efficient antifungal method.

Lipid bilayers containing ergosterol show signs of destruction when they are treated with singlet oxygen, due to the conversion of ergosterol into its peroxy derivative. Applying this previous knowledge, an antifungal method was explored using Candida tropicalis as model, and membrane permeation under photosensitization conditions became evident. These data were complemented through AFM images of artificial lipid bilayers, using cholesterol or ergosterol as structural sterols, showing their corresponding morphologies at the nanoscale. Based on these results, an antifungal method was developed, which shows evidence of the extent of membrane permeation during photosensitization. Such photosensitization offers an effective alternative treatment, especially in membranes with a high ergosterol content, suggesting that this procedure constitutes an easy and efficient antifungal method.