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- 2019
- solar cell
- thin film
- sputtering
- Tungsten di sulfide (WS2)
- Optoelectronic Information Materials and Devices
- Universiti Kebangsaan Malaysia
- German Malaysian Institute
- Universiti Tenaga Nasional
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Investigation of ultrashort laser excitation of aluminum and tungsten by reflectivity measurements
摘要： We determine the laser-induced ablation threshold fluence in air of aluminum and tungsten excited by single near-infrared laser pulses with duration ranging from 15 to 100 fs. The ablation threshold fluence is shown to be constant for both metals, extending the corresponding scaling metrics to few-optical-cycle laser pulses. Meanwhile, the reflectivity is measured providing access to the deposited energy in the studied materials on a wide range of pulse durations and incident fluences below and above the ablation threshold. A simulation approach, based on the two-temperature model and the Drude–Lorentz model, is developed to describe the evolution of the transient thermodynamic and optical characteristics of the solids (lattice and electronic temperatures, reflectivity) following laser excitation. The confrontation between experimental results and simulations highlights the importance of considering a detailed description and evolution of the density of states in transition metals like tungsten.
关键词： Tungsten,Reflectivity,Femtosecond,Ablation,Metals,Ultrashort pulses
更新于2025-09-19 17:13:59
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Effects of oxidation state on photovoltaic properties of reactively magnetron sputtered hole-selective WO<sub>x</sub> contacts in silicon heterojunction solar cells
摘要： The stoichiometry value x of WOx, or its oxidation state, is crucial for improving performances of the hole-selective contact heterojunction silicon solar cell. However, it is challenging to tune the films’ oxidation state using the well-known evaporation method. In this study, a simulation was performed to analyze the effect of x on short-circuit current (Jsc) loss, attributed to the hole-selective contact in the device. Compared to the thickness of WOx layer, x has a more important role in minimizing Jsc loss. Based on the simulation, the WOx/c-Si heterojunction solar cells having hole-selective WOx contacts with tuned x to vary its oxidation state were fabricated using reactive magnetron sputtering. The relationships of the open-circuit voltage (Voc) and Jsc with respect to x were similar. The experimentally determined Jsc increased from 34.7 to 36.6 mA/cm2 when x was increased from 2.72 to 2.77; this result is consistent with the simulation. Nevertheless, fill factor (FF) reduced with the increase of x, owing to the reduced conductivity of WOx. Both oxidation state and film conductivity must be as high as possible to simultaneously achieve high Voc, Jsc, and FF. The lowest x yielded a solar cell efficiency of 13.3%.
关键词： Current loss,Tungsten oxide,Hole-selective contact,Heterojunction solar cell
更新于2025-09-19 17:13:59
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Chiral Second-Harmonic Generation from Monolayer WS <sub/>2</sub> /Aluminum Plasmonic Vortex Metalens
摘要： Two-dimensional spiral plasmonic structures have emerged as a versatile approach to generate near-field vortex fields with tunable topological charges. We demonstrate here a far-field approach to observe the chiral second-harmonic generation (SHG) at designated visible wavelengths from a single plasmonic vortex metalens. This metalens comprises an Archimedean spiral slit fabricated on atomically flat aluminum epitaxial film, which allows for precise tuning of plasmonic resonances and subsequent transfer of two-dimensional materials on top of the spiral slit. The nonlinear optical measurements show a giant SHG circular dichroism. Furthermore, we have achieved an enhanced chiral SHG conversion efficiency (about an order of magnitude greater than the bare aluminum lens) from monolayer tungsten disulfide (WS2)/aluminum metalens, which is designed at the C-exciton resonance of WS2. Since the C-exciton is not a valley exciton, the enhanced chiral SHG in this hybrid system originates from the plasmonic vortex field-enhanced SHG under the optical spin-orbit interaction.
关键词： optical spin-orbit interaction,Surface plasmonic vortex metalens,aluminum epitaxial film,chiral nonlinearity,second-harmonic generation,monolayer tungsten disulfide
更新于2025-09-19 17:13:59
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Fabrication of dopamine enveloped WO3?x quantum dots as single-NIR laser activated photonic nanodrug for synergistic photothermal/photodynamic therapy against cancer
摘要： Tungsten oxide is a promising nanodrug in phototherapy via transforming light energy to reactive oxygen species and heat. Nevertheless, the phototherapeutic activity of the tungsten oxide nanomaterials is generally activated under 980 nm laser, which is close to the absorption of normal tissue, resulting in unfavorable heating effect on normal tissues. Therefore, the tungsten oxide nanomaterials which can be excited under 808 nm are highly required to avoid overheating and obtain deep tissue penetration of near-infrared (NIR) laser. Here, we successfully synthesized a novel dopamine enveloped tungsten oxide nanodots (WO3?x/Dpa-Mel NPs) via facile one-step solvothermal route, using dopamine as the template and reductant in triethylene glycol solvent. Under the 808 nm laser irradiation, the as-obtained WO3?x/Dpa-Mel NPs exhibit excellent photodynamic activity and stability. Meanwhile, the WO3?x/Dpa-Mel NPs also possess high photothermal conversion property. Thus, the photothermal therapy (PTT) and photodynamic therapy (PDT) can be triggered simultaneously under single 808 nm laser irradiation. Additionally, the inherited good biocompatibility and dispersity in aqueous solution from dopamine hydrochloride (Dpa-Mel) also make the WO3?x/Dpa-Mel NPs more suitable for in vivo application. The as-obtained WO3?x/Dpa-Mel NPs exhibit an excellent synergistic phototherapy effect on solid tumor ablation in vivo without damaging healthy tissues under single 808 nm NIR light irradiation, indicating WO3?x/Dpa-Mel NPs can serve as a multifunctional therapeutic nanoplatform to realize the synergistic cancer therapy.
关键词： Photothermal therapy,Combined cancer therapy,Tungsten oxide,Photodynamic therapy
更新于2025-09-19 17:13:59
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Growth of Large-Area, Uniform, Few-Layer Tungsten Disulphide by Thermal Decomposition of Ammonium Tetrathiotungstate
摘要： Two-dimensional transition metal dichalcogenides (2D-TMDCs) such as molybdenum disulphide (2D-MoS2) and tungsten disulphide (2D-WS2) are now established as a class of nanomaterials that can be used in numerous applications due to their tuneable physical and chemical properties [1]. However, in terms of electrical characteristics and photoluminescence efficiency, WS2 typically exhibits superior performance compared with the molybdenum analogue [2,3]. Nevertheless, synthesis of continuous, uniform and thickness controllable 2D-WS2 films for (opto)electronic device fabrication is more challenging compared with better established 2D-MoS2 growth protocols. Therefore, the search for alternative precursors and synthesis approaches of 2D-WS2 that can provide mass production with excellent quality at low cost is highly desirable [1]. In this work, we tackle this issue by refining the solvents recipe with n-methylpyrrolidone, n-butylamine and 2-aminoethanol, which significantly improves the continuity, uniformity and thickness controllability for the spin-coated precursor films. This enables the large-area growth of few-layer WS2 films using thermal decomposition via two-step high temperature annealing without sulphurisation. The few-layer WS2 films were characterised by optical and atomic force microscopy to confirm the continuity and two-dimensional nature of the deposited WS2 films. Raman, photoluminescence and x-ray photoelectron spectroscopy indicate growth of highly crystalline films with an optimum composition of WS2. The electrical response of the WS2 films grown by this method was investigated by interrogating a back-gate thin film transistor utilising a WS2 channel as shown in Figure 1.
关键词： ammonium tetrathiotungstate,Tungsten disulphide,few-layer,large-area growth,thermal decomposition
更新于2025-09-16 10:30:52
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[IEEE 2019 6th International Conference on Space Science and Communication (IconSpace) - Johor Bahru, Malaysia (2019.7.28-2019.7.30)] 2019 6th International Conference on Space Science and Communication (IconSpace) - Investigating the Impact of Deposition Power on PVD Growth WS2 for Solar Cell Application
摘要： Physical Vapor Deposition (PVD) was used to grow ultra-thin tungsten di sulfide (WS2) layers on top of soda lime glass substrates. Deposition power of radio frequency magnetron sputtering was varied (50W, 100 W, 150 W,200 W and 250 W) to study its impact on film characteristics for suitable application in solar cell. Structural, morphological and opto-electrical properties of as grown film were analyzed. Optimized monocrystalline ultra-thin WS2 films of enhance crystallite (690 nm thick) were successfully hoarded with RF power of 150 W under 100oC temperature.
关键词： solar cell,thin film,sputtering,Tungsten di sulfide (WS2)
更新于2025-09-16 10:30:52
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High Sensitivity Hybrid PbS CQD-TMDC Photodetectors up to 2 μm
摘要： Recent approaches to develop infrared photodetectors characterized by high sensitivities, broadband spectral coverage, easy integration with silicon electronics, and low cost have been based on hybrid structures of transition metal dichalcogenides (TMDCs) and PbS colloidal quantum dots (CQDs). However, to date, such photodetectors have been reported with high sensitivity up to 1.5 μm. Here we extend the spectral coverage of this technology toward 2 μm, demonstrating for the ?rst time compelling performance with responsivities 1400 A/W at 1.8 μm with 1 V bias and detectivities as high as 1012 Jones at room temperature. To do this, we studied two TMDC materials as a carrier transport layer, tungsten disul?de (WS2), and molybdenum disul?de (MoS2) and demonstrate that WS2-based hybrid photodetectors outperform those of MoS2 due to a more adequate band alignment that favors carrier transfer from the CQDs.
关键词： quantum dots,tungsten sul?de,infrared photodetectors,lead sul?de,molybdenum sul?de,two-dimensional materials
更新于2025-09-16 10:30:52
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Femtosecond Laser-Induced Electron Emission from Nanodiamond-Coated Tungsten Needle Tips
摘要： We present femtosecond laser-induced electron emission from nanodiamond-coated tungsten tips. Based on the shortness of the femtosecond laser pulses, electrons can be photoexcited for wavelengths from the infrared (1932 nm) to the ultraviolet (235 nm) because multiphoton excitation becomes efficient over the entire spectral range. Depending on the laser wavelength, we find different dominant emission channels identified by the number of photons needed to emit electrons. Based on the band alignment between tungsten and nanodiamond, the relevant emission channels can be identified as specific transitions in diamond and its graphitic boundaries. It is the combination of the character of initial and final states (i.e., bulk or surface-near, direct or indirect excitation in the diamond band structure), the number of photons providing the excitation energy, and the peak intensity of the laser pulses that determines the dominant excitation channel for photoemission. A specific feature of the hydrogen-terminated nanodiamond coating is its negative electron affinity that significantly lowers the work function and enables efficient emission from the conduction band minimum into vacuum without an energy barrier. Emission is stable for bunch charges of up to 400 electrons per laser pulse. We infer a normalized emittance of <0.20 nm rad and a normalized peak brightness of >1.2 × 1012 A m?2 sr?1. The properties of these tips are encouraging for their use as laser-triggered electron sources in applications such as ultrafast electron microscopy as well as diffraction and novel photonics-based laser accelerators.
关键词： nanodiamond,ultrafast electron microscopy,tungsten tips,multiphoton excitation,electron emission,negative electron affinity,femtosecond laser
更新于2025-09-16 10:30:52
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Pulsed Laser Deposition of Nanostructured MoS3/np-Mo//WO3?y Hybrid Catalyst for Enhanced (Photo) Electrochemical Hydrogen Evolution
摘要： Pulsed laser ablation of MoS2 and WO3 targets at appropriate pressures of background gas (Ar, air) were used for the preparation of new hybrid nanostructured catalytic ?lms for hydrogen production in an acid solution. The ?lms consisted of a nanostructured WO3?y underlayer that was covered with composite MoS3/np-Mo nanocatalyst. The use of dry air with pressures of 40 and 80 Pa allowed the formation of porous WO3?y ?lms with cauli?ower- and web-like morphology, respectively. The ablation of the MoS2 target in Ar gas at a pressure of 16 Pa resulted in the formation of amorphous MoS3 ?lms and spherical Mo nanoparticles. The hybrid MoS3/np-Mo//WO3?y ?lms deposited on transparent conducting substrates possessed the enhanced (photo)electrocatalytic performance in comparison with that of any pristine one (MoS3/np-Mo or WO3?y ?lms) with the same loading. Modeling by the kinetic Monte Carlo method indicated that the change in morphology of the deposited WO3?y ?lms could be caused by the transition of ballistic deposition to di?usion limited aggregation of structural units (atoms/clusters) under background gas pressure growth. The factors and mechanisms contributing to the enhancement of the electrocatalytic activity of hybrid nanostructured ?lms and facilitating the e?ective photo-activation of hydrogen evolution in these ?lms are considered.
关键词： pulsed laser deposition,tungsten oxides,transition metal chalcogenides,nanocatalysts,hydrogen evolution reaction,background gas
更新于2025-09-16 10:30:52
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Achieving efficient flexible perovskite solar cells with room-temperature processed tungsten oxide electron transport layer
摘要： For flexible perovskite solar cells, achieving high power conversion efficiency by using a room-temperature technology to fabricate a compact electron transport layer is one of the best options. Here, we develop an annealing-free, dopant-free, and amorphous tungsten oxide as electron transport layer by vacuum evaporation for flexible perovskite solar cells. The compact amorphous tungsten oxide electron transport layer with different thicknesses (0–50 nm) was directly deposited on flexible PEN/ITO substrate. A model of the improvement mechanism is proposed to understand how the thickness tailoring simultaneously enhances the crystallization and relaxes the trade-off between interface recombination and charge transfer. By optimizing the amorphous tungsten oxide thickness, the high homogeneous, uniform, and dense electron transport layer with a thickness of 30 nm is found to not only decrease the pinhole of the perovskite layer, but also enhance charge transport with reducing resistance. Furthermore, the mechanical bending stability revealed that, the fabricated perovskite solar cells show stable power conversion efficiency up to more than 1000 bending cycles. The room-temperature processed fabrication enables the amorphous tungsten oxide to become a potential electron transport layer candidate for the large-scale flexible perovskite solar cells, which becomes compatible with practical roll-to-roll solar cells manufacturing.
关键词： Electron transport layer,Amorphous tungsten oxides,Low temperature,Flexible solar cells,Interface recombination
更新于2025-09-16 10:30:52