RESUMEN
Rhenium diselenide (ReSe2) has attracted great interest due to its unique anisotropic structure and unusual in-plane anisotropic electrical and optical properties. However, efficient fabrication of large-area and high-quality 2D ReSe2 continuous films has become an increasingly important challenge. In this work, centimeter-scale 2D ReSe2 continuous films with the layer number varying from monolayer to 12 layers were successfully grown on a mica substrate using our space-confined CVD system via changing the position of the substrate. The fluorescence quenching effect and surface enhanced Raman scattering (SERS) effect on 2D ReSe2 films with different layer numbers were investigated using rhodamine 6G (R6G) dye molecules as a Raman probe. The large-area ReSe2 films show the layer-number-dependent nature of the SERS effect and a robust suppression effect of fluorescence. Our work explores the practical application of 2D ReSe2 films for molecular detection via the SERS technique.
RESUMEN
A photodetector based on 2D non-layered materials can easily utilize the photogating effect to achieve considerable photogain, but at the cost of response speed. Here, a rationally designed tunneling heterojunction fabricated by vertical stacking of non-layered In2 S3 and Te flakes is studied systematically. The Te/In2 S3 heterojunctions possess type-II band alignment and can transfer to type-I or type-III depending on the electric field applied, allowing for tunable tunneling of the photoinduced carriers. The Te/In2 S3 tunneling heterojunction exhibits a reverse rectification ratio exceeding 104 , an ultralow forward current of 10-12 A, and a current on/off ratio over 105 . A photodetector based on the heterojunctions shows an ultrahigh photoresponsivity of 146 A W-1 in the visible range. Furthermore, the devices exhibit a response time of 5 ms, which is two and four orders of magnitude faster than that of its constituent In2 S3 and Te. The simultaneously improved photocurrent and response speed are attributed to the direct tunneling of the photoinduced carriers, as well as a combined mechanism of photoconductive and photogating effects. In addition, the photodetector exhibits a clear photovoltaic effect, which can work in a self-powered mode.
RESUMEN
Two-dimensional (2D) semiconductors with atomic layers, and a flat and active surface provide an attractive platform for the study of surface-enhanced Raman scattering (SERS). Many 2D layered materials, including graphene and transition metal dichalcogenide (TMD), have been exploited as potential Raman enhancers for SERS-based molecule sensing. Herein, atomically-thin palladium diselenide (PdSe2) used as a SERS substrate for molecule detection was systematically studied. Stable Raman enhancement for molecules such as rhodamine 6G (R6G), crystal violet (CV), and rhodamine B (RhB) on few-layer PdSe2 has been verified. A detection limit as low as 10-9 M and an enhancement factor of 105 for the R6G molecule on monolayer PdSe2 are achieved. With the insertion of a thin Al2O3 layer, the Raman spectra confirm the predominant charge transfer mechanism for the large Raman enhancement. Furthermore, the strong thickness-dependent properties, good in-plane anisotropy and excellent air-stability of Raman enhancement are also explored for 2D PdSe2. Our findings provide not only a promising Raman enhancement platform for sensing applications but also new insights into the chemical mechanism (CM) process of SERS.
RESUMEN
Mixed-organic-cation FAxMA1-xPbI3 films were prepared using a one-step solution deposition method in ambient air. The formamidinium (FA+) fraction 'x' was varied from 0.1 to 1 by changing the amounts of formamidinium iodide (FAI) and methylammonium iodide (MAI) in the precursor solution. Perovskite solar cells (PSCs) with a structure of FTO glass/compact TiO2/mesoporous TiO2/FAxMA1-xPbI3/carbon electrode were designed and fabricated. The effects of the FA+ fraction 'x' on the structure, morphology and optical properties of the FAxMA1-xPbI3 films as well as the photovoltaic performance of PSCs were studied. The results showed that the photovoltaic inactive δ-phase FAPbI3 can be formed in the presence of high contents of FA+ (x = 0.8 and 1.0). The band gap of FAxMA1-xPbI3 decreased from 1.58 eV to 1.49 eV when the FA+ fraction x increased from 0.1 to 1. The PSCs based on FA0.4MA0.6PbI3 exhibited an optimal photovoltaic performance, yielding Voc of 0.8 V, Jsc of 22.84 mA cm-2, FF of 0.48 and PCE of 8.77%.
RESUMEN
Rational design of hybrid carbon host with high electrical conductivity and strong adsorption toward soluble lithium polysulfides is the main challenge for achieving high-performance lithium-sulfur batteries (LSBs). Herein, novel binder-free Ni@N-doped carbon nanospheres (N-CNSs) films as sulfur host are firstly synthesized via a facile combined hydrothermal-atomic layer deposition method. The cross-linked multilayer N-CNSs films can effectively enhance the electrical conductivity of electrode and provide physical blocking "dams" toward the soluble long-chain polysulfides. Moreover, the doped N heteroatoms and superficial NiO layer on Ni layer can work synergistically to suppress the shuttle of lithium polysulfides by effective chemical interaction/adsorption. In virtue of the unique composite architecture and reinforced dual physical and chemical adsorption to the soluble polysulfides, the obtained Ni@N-CNSs/S electrode is demonstrated with enhanced rate performance (816 mAh g-1 at 2 C) and excellent long cycling life (87% after 200 cycles at 0.1 C), much better than N-CNSs/S electrode and other carbon/S counterparts. Our proposed design strategy offers a promising prospect for construction of advanced sulfur cathodes for applications in LSBs and other energy storage systems.
