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Sculpting Artificial Edges in Monolayer MoS <sub/>2</sub> for Controlled Formation of Surface-Enhanced Raman Hotspots
摘要： Hotspot engineering has the potential to transform the field of Surface-Enhanced Raman Spectroscopy (SERS) by enabling ultra-sensitive and reproducible detection of analytes. However, the ability to controllably generate SERS hotspots, with desired location and geometry, over large-area substrates, has remained elusive. In this study, we sculpt artificial edges in monolayer Molybdenum Disulfide (MoS2) by low-power focused laser-cutting. We find that when gold nanoparticles (AuNPs) are deposited on MoS2 by drop-casting, the AuNPs tend to accumulate predominantly along the artificial edges. First-principles density functional theory (DFT) calculations indicate strong binding of AuNPs with the artificial edges due to dangling bonds that are ubiquitous on the un-passivated (laser-cut) edges. The dense accumulation of AuNPs along the artificial edges intensifies plasmonic effects in these regions creating hot spots exclusively along the artificial edges. DFT further indicates that adsorption of AuNPs along the artificial edges prompts a transition from semiconducting to metallic behavior, which can further intensify the plasmonic effect along the artificial edges. These effects are observed exclusively for the sculpted (i.e., cut) edges and not observed for the MoS2 surface (away from the cut edges) or along the natural (passivated) edges of the MoS2 sheet. To demonstrate the practical utility of this concept, we use our substrate to detect Rhodamine B (RhB) with large SERS enhancement (~104) at the hotspots for RhB concentrations as low as ~10-10 M. The single-step laser etching process reported here can be used to controllably generate arrays of SERS hotspots. As such, this concept offers several advantages over previously reported SERS substrates that rely on electro-chemical deposition, e-beam lithography, nanoimprinting or photolithography. While we have focused our study on MoS2, this concept could in principle, be extended to a variety of 2D material platforms.
关键词： focused laser irradiation,MoS2,localized hotspots,artificial edges,SERS
更新于2025-09-23 15:19:57
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Delayed Charge Recombination by Opena??Shell Organics: Its Application in Achieving Superb Photodetectors with Broadband (400a??1160 nm) Ultrahigh Sensitivity and Stability
摘要： Monolayer transition-metal dichalcogenides have inspired worldwide efforts in optoelectronic devices but real applications are hindered with their reduced optical absorption due to their atomically ultrathin signature. In this study, by utilizing their biradical nature such as excellent absorption coefficient, broad bandwidth from the ultraviolet to near-infrared region, and small triplet–singlet energy gap, a series of helicene 5,14-diaryldiindeno[2,1-f:1′,2′-j]picene (DDP) derivatives (1ab, 1ac, and 1bb) are integrated with monolayer MoS2 for extraordinary photodetector performance and outstanding stability. Via comprehensive time-resolved studies, the interfacial charge-transfer process from the DDPs to the MoS2 layer is evidenced by the stabilized exciton property of the organics (1ac)/MoS2 heterostructure. Significantly, the 1ac/MoS2 photodetector exhibits an ultrahigh photoresponsivity of 5 × 107 A W?1 and a fast response speed of 45 ms due to the highly efficient photoexcited carrier separation and the matched type-II energy band alignment. The biradical 1ac/MoS2 hybrid photodetector shows no sign of degradation after one-month operation. The results pave a new avenue for biradical based high-performance and super-broadband optoelectronic devices.
关键词： photodetectors,hybrid structures,MoS2,biradical organic molecules,transition metal dichalcogenides
更新于2025-09-23 15:19:57
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Self-powered and flexible perovskite photodiode/solar cell bifunctional devices with MoS2 hole transport layer
摘要： Hybrid organic-inorganic perovskites are highly attractive for the use in optoelectronic devices, but their instabilities should be solved before the practical applications. As one of the solutions, it is important to find a transport layer that can improve the stability and durability of the devices. Here, we first employ MoS2 for a hole transport layer (HTL) in high-performance flexible p-i-n-type perovskite photodiode (PD)/solar cell bifunctional devices (PPSBs) with co-doped graphene transparent conductive electrodes. The current of the PPSB increases by up to 106 times by illumination even at 0 V, meaning “self-powered”. The PPSB exhibits high responsivity and on/off ratio in a broad spectral range of ultraviolet to visible light at a PD mode and good photovoltaic properties at a solar cell mode. The photoresponse shows only 38 % degradation during 30 days, and the photo-stability is almost perfect under continuous light soaking for 100 h. Flexible PPSB exhibits excellent mechanical properties by maintaining ~57 % of its initial photocurrent even after 3000 bending cycles at a curvature radius of 4 mm. These results suggest that MoS2 films can be successfully used as a HTL in perovskites-based rigid/flexible optoelectronic devices.
关键词： photodiode,co-doping,MoS2,graphene,bifunctional,hole transport layer,perovskite,solar cell,self-powered
更新于2025-09-23 15:19:57
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Passively Q-switched Tm:YAlO3 laser based on WS2/MoS2 two-dimensional nanosheets at 2????m
摘要： A comparison of the pulsed laser performances of 2 μm passively Q-switched Tm:YAlO3 (YAP) lasers based on the use of tungsten disul?de (WS2) and molybdenum disul?de (MoS2) two-dimensional (2D) nanosheets as saturable absorbers is reported. The novel nanosheets were prepared by chemical vapor deposition (CVD) technology. The microstructure and optical characteristics of the nanosheets were investigated experimentally. In a continuous-wave (CW) operation, the maximum output power of 2.8 W was obtained at an absorbed pump power of 6.9 W, with a corresponding slope e?ciency of 46.4%. In a passively Q-switched operation at a pump power of 1.45 W, the average output power, pulse width, repetition rate, pulse energy, and peak power for the Tm:YAP/WS2 laser were 0.11 W, 2.65 μs, 34.7 kHz, 2.9 μJ, and 1.23 W, respectively. As for the Tm:YAP/MoS2 laser, the corresponding values were 0.10 W, 2.5 μs, 24.0 kHz, 3.8 μJ, and 1.55 W.
关键词： WS2/MoS2 nanosheets,Passively Q-switched,Chemical vapor deposition,Tm:YAlO3 laser,2 μm
更新于2025-09-23 15:19:57
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MoS <sub/>2</sub> Assisted Self-Assembled Poly (3-hexylthiophene) Thin Films at Air/Liquid Interface for High-Performance Field-Effect Transistors under Ambient Condition
摘要： It is a key challenge to achieve long-range ordering in nanoscale morphology of π-conjugated polymers for efficient charge transport in organic electronic devices. The long-range ordering and aggregation in poly (3-hexylthiophene) (P3HT) has been accomplished by introducing two dimensional (2D) Molybdenum disulfide (MoS2) nanosheets in polymer matrix followed by ultrasonication in chloroform. Thin films of synthesized P3HT/MoS2 nanocomposites having various fractions of MoS2 in the P3HT matrix have been fabricated on the air/liquid interface. The UV visible absorption spectroscopy has been employed to investigate the nature of aggregation and exciton bandwidth in the resultant films deposited at the air/liquid interface. Moreover, grazing incidence X-ray diffraction (GIXD) analysis, and atomic force microscopy (AFM), reveal the long-range ordering and highly crystalline thin films with the edge-on orientation of polymer chains over the substrate. Further, the impact of aggregation, morphology, and orientation on macroscopic charge transport performance is elaborately estimated by fabricating organic field-effect transistors (OFETs). The hole mobility as high as 0.160 ± 0.007 cm2V-1s-1, has been achieved for P3HT/MoS2 (1%) nanocomposite under ambient condition.
关键词： organic field-effect transistors,MoS2,π-conjugated polymers,nanocomposites,P3HT,charge transport
更新于2025-09-23 15:19:57
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Electrodeposited MoS2 counter electrode for flexible dye sensitized solar cell module with ionic liquid assisted photoelectrode
摘要： Dye-sensitized solar cell (DSSC) offers great advantages includes low cost materials, economic fabrication, suitable for low-light conversion, flexibility option, color design possibilities, etc. In the present study, a semi-transparent, molybdenum disulphide (MoS2) flexible counter electrode (CE) is realized through electrodeposition method. Low temperature processed TiO2 solution is used for photoelectrode (PE) preparation. Conductive ionic liquid (BVImI + LiI) is used to modify the surface of photoelectrode for alteration of conduction band level of PE, towards enriched electron injection rate into TiO2. Flexible dye-sensitized solar cell (f-DSSC) fabricated by sandwich the photoelectrode and counter electrodes, and an ionic liquid electrolyte is injected. The surface modified photoelectrode (SM-PE) assisted test cell (0.16 cm2 active area) witnessed an enhanced current density value 12.46 mA/cm2 and power conversion efficiency (PCE) 4.84% is higher than the normal PE based f-DSSC (11.56 mA/cm2 and 4.35%). For comparison, platinum-based f-DSSC with SM-PE is fabricated, is attained 6.08% of PCE. The f-DSSC sub-module with MoS2-CE gave 4.21% of PCE, the results are presented.
关键词： Surface modification of PE,Imidazolium iodide,Flexible DSSC,Semi-transparent flexible DSSC module,MoS2 counter electrode
更新于2025-09-23 15:19:57
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Topochemical Path in High Lithiation of MoS <sub/>2</sub>
摘要： Lithiation of MoS2/RGO (reduced graphite oxide) electrodes repeatedly reached experimental capacities larger than 1000 mA·g–1, corresponding to at least 6 lithium equivalents per gram of MoS2. At our best knowledge, a convincing explanation is still missing in literature. In most cases, phase separation into Li2S and elemental Mo was assumed to occur. However, this can only explain capacities up to 669 mA·g–1, corresponding to an exchange of four Li. Formation of LiMo alloys could resolve the problem but the Li/Mo system does not contain any binary phases. If signs for Li2S formation were found, indeed experimental capacities were below 700 mAh·g–1. Here we present a topochemical mechanism, which sustains multiple charge/discharge cycles at 1000 mAh·g–1, corresponding to an exchange of at least 6 Li per formula unit MoS2. This topochemical reaction route prevents decomposition into binary phases and thus avoids segregation of the components of MoS2. Throughout the whole lithiation/delithiation process, distinct layers of Mo are preserved but extended or shrunk by slight movements and reshuffling of sulfur and lithium atoms. On addition of 6 Li per formula unit to MoS2, all central sulfur atoms are hosted in mutual Mo–S layers such that formal S2– and Mo2– anions appear coordinated by lithium cations. Indeed, similar structures are known in the field of Zintl phases. Our first-principles crystal structure prediction study describes this topological path through conversion reactions during the lithiation/delithiation processes. All optimized phases along the topological path exhibit a distinct Mo layering giving rise to a series of dominant scattering into pseudo 001 reflections perpendicular to these Mo planes. The mechanism we present here explains why such high capacities can be reached reversibly for MoS2/RGO nano composites.
关键词： topological path,Crystal structure prediction,Total energy calculations,MoS2,Li-Mo-S ternary phases,Li-ion battery,Lithium
更新于2025-09-23 15:19:57
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Energy Band Alignment of a Monolayer MoS <sub/>2</sub> with SiO <sub/>2</sub> and Al <sub/>2</sub> O <sub/>3</sub> Insulators from Internal Photoemission
摘要： Internal photoemission of electrons (IPE) from large area one monolayer 2H-MoS2 films synthesized on top of amorphous (a-) SiO2 or Al2O3 is used to determine the energy of the semiconductor valence band (VB) relative to the reference level of the insulator conduction band (CB). This allows us to compare the VB top energy in MoS2 to that of the (100)Si substrate crystal at the interface with the same insulator. Despite the CB in a–Al2O3 is found to be ~1 eV below that in SiO2 as measured relative to the Si VB edge, the authors observe nearly no shift of the spectral threshold in the case of IPE from the MoS2 VB. This observation indicates violation of electroneutrality at the MoS2/a–Al2O3 interface causing an increase in barrier by ~1 eV. This conclusion is supported by the much weaker field dependence of the IPE threshold at the MoS2/a–Al2O3 interface compared to the MoS2/a–SiO2 one, suggesting the presence of negative charges and/or interface dipoles. Therefore, the commonly accepted electron affinity rule (EAR) appears to be not appropriate to describe the band alignment at 2D/insulator interfaces.
关键词： internal photoemission spectroscopy,MoS2,electron affinity,electron barrier,band alignment
更新于2025-09-19 17:15:36
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Metal-ion bridged high conductive RGO-M-MoS2 (M = Fe3+, Co2+, Ni2+, Cu2+ and Zn2+) composite electrocatalysts for photo-assisted hydrogen evolution
摘要： Efficient photo-electrocatalysts for hydrogen evolution reaction (HER) are synthesized using a facile one-step hydrothermal method. With metal-ion bridges, highly dispersed molybdenum disulfide (MoS2) nanolayers are vertically grown on the reduced graphene oxide (RGO) to form RGO-M-MoS2 photocatalysts for HER, where M = Fe3+, Co2+, Ni2+, Cu2+ and Zn2+. The results show that the cross-bridging ions can modulate the MoS2 growth priority and act as efficient charge transfer channels between RGO and MoS2, and combine the advantages of the high conductivity of graphene with the photo-electrochemical activity of MoS2. The metal-ion bridged MoS2-M-RGO heterostructures demonstrate superior catalytic activity toward hydrogen evolution reaction (HER) in acid medium, evidenced by the remarkable higher catalytic current density at low overpotential compared with that of MoS2-RGO without metal-ion bridge. This study provides a novel and facile route for establishing efficient composite photo-electrocatalysts for water splitting to generate hydrogen.
关键词： hydrogen evolution reaction,MoS2 nanosheets,reduced graphene oxide,metal-ion bridge
更新于2025-09-19 17:15:36
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Study on electronic and optical properties of the twisted and strained MoS2/PtS2 heterogeneous interface
摘要： We report electronic and optical properties of the MoS2/PtS2 heterogeneous interfaces subject to various twisting angles based on the first principles simulation. In order to sustain the structural stability and avoid to have a large size cell, the optimized rotation angles of the MoS2/PtS2 heterogeneous interfaces are 19.1°, 30.0° and 40.9°. It is found from the first principle simulation that the absolute passband amplitude of the refractive index, extinction coefficient, reflectivity and absorption coefficient curves under 30.0° rotation angle are 6–12 times higher than 19.1° and 40.9° rotation angles of the MoS2/PtS2 heterogeneous interfaces. Moreover, under the 30.0° twisting angle, the absorption coefficient in the absorption spectrum can reach to or above 105/cm. The absorption spectrum has a red-shift and a broadening effect with the tensile strain, from roughly 700 nm (0% externally strain) to 1050 nm (5% externally strain). The prominent optical properties of MoS2/PtS2 heterogeneous interface under 30° rotation angle still exist after taking into consideration the spin-orbit coupling (SOC) effect. These results suggest that the MoS2/PtS2 heterogeneous interfaces will have great potential applications in tunable optoelectronic devices.
关键词： Twisting angle,Optical performance,Strain engineering,MoS2/PtS2 heterogeneous structure
更新于2025-09-19 17:15:36