Monolayer transition metal dichalcogenides are considered to be promising candidates for flexible and transparent optoelectronics applications due to their direct bandgap and strong light-matter ...interactions. Although several monolayer-based photodetectors have been demonstrated, single-layered optical memory devices suitable for high-quality image sensing have received little attention. Here we report a concept for monolayer MoS
optoelectronic memory devices using artificially-structured charge trap layers through the functionalization of the monolayer/dielectric interfaces, leading to localized electronic states that serve as a basis for electrically-induced charge trapping and optically-mediated charge release. Our devices exhibit excellent photo-responsive memory characteristics with a large linear dynamic range of ∼4,700 (73.4 dB) coupled with a low OFF-state current (<4 pA), and a long storage lifetime of over 10
s. In addition, the multi-level detection of up to 8 optical states is successfully demonstrated. These results represent a significant step toward the development of future monolayer optoelectronic memory devices.
CuCo2O4 films with different morphologies of either mesoporous nanosheets, cubic, compact‐granular, or agglomerated embossing structures are fabricated via a hydrothermal growth technique using ...various solvents, and their bifunctional activities, electrochemical energy storage and oxygen evolution reaction (OER) for water splitting catalysis in strong alkaline KOH media, are investigated. It is observed that the solvents play an important role in setting the surface morphology and size of the crystallites by controlling nucleation and growth rate. An optimized mesoporous CuCo2O4 nanosheet electrode shows a high specific capacitance of 1658 F g−1 at 1 A g−1 with excellent restoring capability of ≈99% at 2 A g−1 and superior energy density of 132.64 Wh kg−1 at a power density of 0.72 kW kg−1. The CuCo2O4 electrode also exhibits excellent endurance performance with capacity retention of 90% and coulombic efficiency of ≈99% after 5000 charge/discharge cycles. The best OER activity is obtained from the CuCo2O4 nanosheet sample with the lowest overpotential of ≈290 mV at 20 mA cm−2 and a Tafel slope of 117 mV dec−1. The superior bifunctional electrochemical activity of the mesoporous CuCo2O4 nanosheet is a result of electrochemically favorable 2D morphology, which leads to the formation of a very large electrochemically active surface area.
The direct growth of shape‐controlled CuCo2O4 electrodes on a 3D architecture of Ni foam is achieved via a hydrothermal growth technique using various solvents, followed by air annealing treatment. The high bifunctional electrochemical activity of the mesoporous CuCo2O4 nanosheet is a result of the electrochemically favorable 2D morphology, which leads to the formation of a very large electrochemically active surface area.
van der Waals heterostructures composed of two different monolayer crystals have recently attracted attention as a powerful and versatile platform for studying fundamental physics, as well as having ...great potential in future functional devices because of the diversity in the band alignments and the unique interlayer coupling that occurs at the heterojunction interface. However, despite these attractive features, a fundamental understanding of the underlying physics accounting for the effect of interlayer coupling on the interactions between electrons, photons, and phonons in the stacked heterobilayer is still lacking. Here, we demonstrate a detailed analysis of the strain-dependent excitonic behavior of an epitaxially grown MoS2/WS2 vertical heterostructure under uniaxial tensile and compressive strain that enables the interlayer interactions to be modulated along with the electronic band structure. We find that the strain-modulated interlayer coupling directly affects the characteristic combined vibrational and excitonic properties of each monolayer in the heterobilayer. It is further revealed that the relative photoluminescence intensity ratio of WS2 to MoS2 in our heterobilayer increases monotonically with tensile strain and decreases with compressive strain. We attribute the strain-dependent emission behavior of the heterobilayer to the modulation of the band structure for each monolayer, which is dictated by the alterations in the band gap transitions. These findings present an important pathway toward designing heterostructures and flexible devices.
Abstract
Compared with solid scintillators, liquid scintillators have limited capability in dosimetry and radiography due to their relatively low light yields. Here, we report a new generation of ...highly efficient and low-cost liquid scintillators constructed by surface hybridisation of colloidal metal halide perovskite CsPbA
3
(A: Cl, Br, I) nanocrystals (NCs) with organic molecules (2,5-diphenyloxazole). The hybrid liquid scintillators, compared to state-of-the-art CsI and Gd
2
O
2
S, demonstrate markedly highly competitive radioluminescence quantum yields under X-ray irradiation typically employed in diagnosis and treatment. Experimental and theoretical analyses suggest that the enhanced quantum yield is associated with X-ray photon-induced charge transfer from the organic molecules to the NCs. High-resolution X-ray imaging is demonstrated using a hybrid CsPbBr
3
NC-based liquid scintillator. The novel X-ray scintillation mechanism in our hybrid scintillators could be extended to enhance the quantum yield of various types of scintillators, enabling low-dose radiation detection in various fields, including fundamental science and imaging.
Monolayered, semiconducting MoS2 and their transition metal dichalcogenides (TMDCs) families are promising and low-cost materials for hydrogen generation through electrolytes (HER, hydrogen evolution ...reaction) due to their high activities and electrochemical stability during the reaction. However, there is still a lack of understanding in identifying the underlying mechanism responsible for improving the electrocatalytic properties of theses monolayers. In this work, we investigated the significance of controlling carrier densities in a MoS2 monolayer and in turn the corresponding electrocatalytic behaviors in relation to the energy band structure of MoS2. Surface functionalization was employed to achieve p-doping and n-doping in the MoS2 monolayer that led to MoS2 electrochemical devices with different catalytic performances. Specifically, the electron-rich MoS2 surface showed lower overpotential and Tafel slope compared to the MoS2 with surface functional groups that contributed to p-doping. We attributed such enhancement to the increase in the carrier density and the corresponding Fermi level that accelerated HER and charge transfer kinetics. These findings are of high importance in designing electrocatalysts based on two-dimensional TMDCs.
Two-dimensional (2D) heterostructured or alloyed monolayers composed of transition metal dichalcogenides (TMDCs) have recently emerged as promising materials with great potential for atomically thin ...electronic applications. However, fabrication of such artificial TMDC heterostructures with a sharp interface and a large crystal size still remains a challenge because of the difficulty in controlling various growth parameters simultaneously during the growth process. Here, a facile synthetic protocol designed for the production of the lateral TMDC heterostructured and alloyed monolayers is presented. A chemical vapor deposition approach combined with solution-processed precursor deposition makes it possible to accurately control the sequential introduction time and the supersaturation levels of the vaporized precursors and thus reliably and exclusively produces selective and heterogeneous epitaxial growth of TMDC monolayer crystals. In addition, TMDC core/shell heterostructured (MoS2/alloy, alloy/WS2) or alloyed (Mo1–x W x S2) monolayers are also easily obtained with precisely controlled growth parameters, such as sulfur introduction timing and growth temperature. These results represent a significant step toward the development of various 2D materials with interesting properties.
Abstract
Transition metal dichalcogenide (TMD) layered semiconductors possess immense potential in the design of photonic, electronic, optoelectronic, and sensor devices. However, the sub-bandgap ...light absorption of TMD in the range from near-infrared (NIR) to short-wavelength infrared (SWIR) is insufficient for applications beyond the bandgap limit. Herein, we report that the sub-bandgap photoresponse of MoS
2
/Au heterostructures can be robustly modulated by the electrode fabrication method employed. We observed up to 60% sub-bandgap absorption in the MoS
2
/Au heterostructure, which includes the hybridized interface, where the Au layer was applied via sputter deposition. The greatly enhanced absorption of sub-bandgap light is due to the planar cavity formed by MoS
2
and Au; as such, the absorption spectrum can be tuned by altering the thickness of the MoS
2
layer. Photocurrent in the SWIR wavelength range increases due to increased absorption, which means that broad wavelength detection from visible toward SWIR is possible. We also achieved rapid photoresponse (~150 µs) and high responsivity (17 mA W
−1
) at an excitation wavelength of 1550 nm. Our findings demonstrate a facile method for optical property modulation using metal electrode engineering and for realizing SWIR photodetection in wide-bandgap 2D materials.
High-performance cascaded-junction quantum dot solar cells (CJQDSCs) are fabricated from as-prepared highly monodispersed lead sulfide QDs. The cells have a high power conversion of 9.05% and a ...short-circuit current density of 32.51 mA cm–2. A reliable and effective stratagem for fabricating high-quality lead sulfide quantum dots (QD) is explored through a “monomer” concentration-controlled experiment. Robust QDSC performances with different band gaps are demonstrated from the as-proposed synthesis and processing stratagems. Various potential CJQDSCs can be envisioned from the band edge evolution of the QDs as a function of size and ligands reported here.
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