Suchergebnisse

Van der Waals materials with narrow energy gaps and efficient response over a broadband optical spectral range are key to widen the energy window of nanoscale optoelectronic devices. Here, we characterize FePS3 as an appealing narrow-gap p-type semiconductor with an efficient broadband photo-response, a high refractive index, and a remarkable resilience against air and light exposure. To enable fast prototyping, we provide a straightforward guideline to determine the thickness of few-layered FePS3 nanosheets extracted from the optical transmission characteristics of several flakes. The analysis of the electrical photo-response of FePS3 devices as a function of the excitation energy confirms a narrow gap suitable for near IR detection (1.23 eV) and, more interestingly, reveals a broad spectral responsivity up to the ultraviolet region. The experimental estimate for the gap energy is corroborated by ab-initio calculations. An analysis of photocurrent as a function of gate voltage and incident power reveals a photo-response dominated by photogating effects. Finally, aging studies of FePS3 nanosheets under ambient conditions show a limited reactivity of the outermost layers of flakes in long exposures to air. ; The present work has received funding from the European Union's Horizon 2020 research and innovation program through the European Research Council grants ERC-2017-StG-755655 2D-TOPSENSE, ERC-2018-AdG-788222 MOL-2D, under the Graphene Flagship through projects GrapheneCore2 (grant nr. 785219), and GrapheneCore3 (grant nr. 881603) and through the COST Action CA15128 MOLSPIN. The authors also acknowledge funding from the Spanish Government through the Unit of Excellence "María de Maeztu" MDM-2015-0538, through projects MAT2017-88377-C2-2-R (AEI/FEDER), MAT2017-88377, MAT2017-89528 (AEI/FEDER), and R.F.'s Juan de la Cierva-formación fellowship FJCI-2017-32919. This work has been supported by the Generalitat Valenciana, through grants CIDEGENT/2018/004, CIDEGENT/2018/005, CDEIGENT/2019/022, the Prometeo Program of Excellence, and M.R.'s APOSTD/2020/249 fellowship.

Single-layer semiconducting transition metal dichalcogenides (2H-TMDs) display robust excitonic photoluminescence emission, which can be improved by controlled changes to the environment and the chemical potential of the material. However, a drastic emission quench has been generally observed when TMDs are stacked in van der Waals heterostructures, which often favor the nonradiative recombination of photocarriers. Herein, we achieve an enhancement of the photoluminescence of single-layer MoS2 on top of van der Waals FePS3. The optimal energy band alignment of this heterostructure preserves light emission of MoS2 against nonradiative interlayer recombination processes and favors the charge transfer from MoS2, an n-type semiconductor, to FePS3, a p-type narrow-gap semiconductor. The strong depletion of carriers in the MoS2 layer is evidenced by a dramatic increase in the spectral weight of neutral excitons, which is strongly modulated by the thickness of the FePS3 underneath, leading to the increase of photoluminescence intensity. The present results demonstrate the potential for the rational design of van der Waals heterostructures with advanced optoelectronic properties. ; The authors acknowledge funding from Generalitat Valenciana through grants IDIFEDER/2020/005, IDIFEDER/2018/061, PROMETEO Program and PO FEDER Program, the APOSTD/2020/249 fellowship for M.R., and support from the Plan Gen-T of Excellence for J.J.B. (CDEIGENT/ 2019/022), J.C.-F. (CIDEGENT/2018/005), and M.R.C (CideGenT2018004); from the Spanish MCINN through grants PLASTOP PID2020-119124RB-I00, 2D-HETEROS PID2020-117152RB-100, and Excellence Unit "María de Maeztu" CEX2019-000919-M; and from the European Union (ERC-2021-StG-101042680 2D-SMARTiES and ERC AdG Mol-2D 788222).

Owing to their higher intrinsic electrical conductivity and chemical stability with respect to their oxide counterparts, nanostructured metal sulfides are expected to revive materials for resistive chemical sensor applications. Herein, we explore the gas sensing behavior of WS2 nanowire-nanoflake hybrid materials and demonstrate their excellent sensitivity (0.043 ppm-1) as well as high selectivity towards H2S relative to CO, NH3, H2, and NO (with corresponding sensitivities of 0.002, 0.0074, 0.0002, and 0.0046 ppm-1, respectively). Gas response measurements, complemented with the results of X-ray photoelectron spectroscopy analysis and first-principles calculations based on density functional theory, suggest that the intrinsic electronic properties of pristine WS2 alone are not sufficient to explain the observed high sensitivity towards H2S. A major role in this behavior is also played by O doping in the S sites of the WS2 lattice. The results of the present study open up new avenues for the use of transition metal disulfide nanomaterials as effective alternatives to metal oxides in future applications for industrial process control, security, and health and environmental safety. ; Funding received from Bio4Energy programme, Academy of Finland (projects Suplacat and ClintoxNP (No. 268944)), University of Oulu (More than Moore research community) and University of Oulu Graduate School (Infotech Oulu) is acknowledged. We acknowledge support from the EU (No. ERC-2016-AdG-694097 QSpec-NewMat) and the Basque Government "Grupos Consolidados UPV/EHU" (No. IT578-13). J. J. B. and L. D. X. thank the EU for the Marie Curie Fellowship (Nos. H2020-MSCA-IF-2016-751047 and H2020-MSCA-IF-2015-709382). A. P. P. thanks postdoctoral fellowship from the Spanish "Juan de la Cierva-incorporación" program (No. IJCI-2014-20147). We also would like to acknowledge Sami Saukko (Center of Microscopy and Nanotechnology, University of Oulu) for his assistance with TEM analyses. A. L. S. acknowledges the Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linköping University (Faculty Grant SFO-Mat-LiU No. 2009-00971). ; Peer reviewed