Plasmon-enhanced reduced graphene oxide photodetector with monometallic of Au and Ag nanoparticles at VIS-NIR region

Development and characterization of self-powered, highly sensitive optoelectronic device based on PVA-rGO nanofibers/n-Si

This study provided a promising way to fabricate low-cost and high-performance Poly (vinyl alcohol)-reduced graphene oxide (PVA-RGO) nanofibers/n-Si heterojunction photodetector. For this purpose, the hybrid heterojunction with a very-high rectification ratio (2.4 × 106) was achieved by successfully coating PVA-RGO nanofibers on n-Si wafer by electrospinning method. When the electro-optical analysis of the fabricated heterojunction photodetector under visible light depending on the light intensity, ultraviolet (UV) and infrared (IR) lights was examined in detail, it was observed that the photodetector exhibited both self-powered behavior and very high photo-response under each light sources. However, the highest optical performance was obtained under UV (365 nm) originated from PVA-RGO layer and IR (850 nm) light from both interfacial states between PVA-RGO nanofibers and Si and from Si layer. Under 365 nm UV light, the maximum performance values of R, D, ON/OFF ratio, normalized photo-dark-current ratio and external quantum efficiency (%) were obtained as 688 mA W-1, 1.15 × 1015Jones, 2.49 × 106, 8.28 × 1010W-1and 234%, respectively.

Microstrain effects of laser-ablated Au nanoparticles in enhancing CZTS-based 1 Sun photodetector devices

Copper zinc tin sulfide (CZTS) thin films were synthesized on soda lime glass using pulsed laser deposition (PLD) at room temperature. Introducing gold nanoparticles (AuNPs) in a sandwich structure led to increased CZTS particle size and a shift in the localized surface plasmon resonance (LSPR) peak of the AuNPs, influenced by different laser energy levels. The absorption measurements revealed intriguing behavior across the visible and near-infrared (NIR) regions, making these films appealing for 1 Sun photodetectors. Furthermore, the presence of AuNPs in the sandwich structure reduced microstrain effects, measuring 1.94 × 10-3 compared to 3.38 × 10-3 in their absence. This reduction directly enhances carrier transport, which is particularly beneficial for accelerating the performance of photodetector devices. This effect of AuNPs also contributed to higher dielectric coefficients, further improving the photodetector performance. Under 1 Sun illumination conditions, this enhancement resulted in a rapid rising time of 95.4 ms, showcasing the potential for faster photodetection.

Ag-Assisted Dry Exfoliation of Large-Scale and Continuous 2D Monolayers

Two-dimensional (2D) semiconductors have generated considerable attention for high-performance electronics and optoelectronics. However, to date, it is still challenging to mechanically exfoliate large-area and continuous monolayers while retaining their intrinsic properties. Here, we report a simple dry exfoliation approach to produce large-scale and continuous 2D monolayers by using a Ag film as the peeling tape. Importantly, the conducting Ag layer could be converted into AgOx nanoparticles at low annealing temperature, directly decoupling the conducting Ag with the underlayer 2D monolayers without involving any solution or etching process. Electrical characterization of the monolayer MoS2 transistor shows a decent carrier mobility of 42 cm2 V-1 s-1 and on-state current of 142 μA/μm. Finally, a plasmonic enhancement photodetector could be simultaneously realized due to the direct formation of Ag nanoparticles arrays on MoS2 monolayers, without complex approaches for nanoparticle synthesis and integration processes, demonstrating photoresponsivity and detectivity of 6.3 × 105 A/W and 2.3 × 1013 Jones, respectively.

Temperature dependence of electrical conductivity and variable hopping range mechanism on graphene oxide films

The rapid development of optoelectronic applications for optical-to-electrical conversion has increased the interest in graphene oxide material. Here, graphene oxide films (GOF) were used as source material in an infrared photodetector configuration and the temperature dependence of the electrical conductivity was studied. GOF were prepared by the double-thermal decomposition (DTD) method at 973 K, with a fixed carbonization temperature, in a pyrolysis system, under a controlled nitrogen atmosphere, over quartz substrates. Graphene oxide films were mechanically supported in a photodetector configuration on Bakelite substrates and electrically contacted with copper wires and high-purity silver paint. Morphological images from the GOF's surface were taken employing a scanning electron microscope and observed a homogeneous surface which favored the electrical contacts deposition. Vibrational characteristics were studied employing Raman spectroscopy and determined the typical graphene oxide bands. GOF were used to discuss the effect of temperature on the film's electrical conductivity. Current-voltage (I-V) curves were taken for several temperatures varying from 20 to 300 K and the electrical resistance values were obtained from 142.86 to 2.14 kΩ. The GOF electrical conductivity and bandgap energy (E_g) were calculated, and it was found that when increasing temperature, the electrical conductivity increased from 30.33 to 2023.97 S/m, similar to a semiconductor material, and E_g shows a nonlinear change from 0.33 to 0.12 eV, with the increasing temperature. Conduction mechanism was described mainly by three-dimensional variable range hopping (3D VRH). Additionally, measurements of voltage and electrical resistance, as a function of wavelength were considered, for a spectral range between 1300 and 3000 nm. It was evidenced that as the wavelength becomes longer, a greater number of free electrons are generated, which contributes to the electrical current. The external quantum efficiency (EQE) was determined for this proposed photodetector prototype, obtaining a value of 40%, similar to those reported for commercial semiconductor photodetectors. This study provides a groundwork for further development of graphene oxide films with high conductivity in large-scale preparation.

Hybrid UV Photodetector Design Incorporating AuPt Alloy Hybrid Nanoparticles, ZnO Quantum Dots, and Graphene Quantum Dots

A hybrid device scheme is an attractive strategy in the construction of advanced UV photodetectors due to the flexibility in selecting the components and correspondingly improved optoelectronic properties by the cooperation of various components, which cannot be achieved by a single component device. In this work, a novel hybrid UV photodetector (PD) is demonstrated by adapting AuPt alloy hybrid nanoparticles (AHNPs), ZnO quantum dots (QDs), and graphene quantum dots (GQDs), namely, GQD/ZnO/AHNP PD. The optimized device achieves high-end figure-of-merit performance with a responsivity of 2299 mA/W, detectivity of 7.04 × 10¹⁰ jones, and external quantum efficiency of 741%. Enhanced photocurrent can be associated with the hot electron generation around the AuPt AHNPs and swift transfer to the conduction band of ZnO QDs. At the same time, the added carrier injection is achieved by a thin layer of GQDs. High density of hotspots and electromagnetic fields are generated by the strong localized surface plasmon resonance (LSPR) by the uniquely designed AuPt AHNPs with the fully alloyed AuPt NPs and adjacent small background Au NPs. The e-field distribution of various NP configurations is systematically investigated with finite-difference time-domain (FDTD) simulations.

Plasmonically enhanced electrochemistry boosted by nonaqueous solvent

Plasmon excitation of metal electrodes is known to enhance important energy related electrochemical transformations in aqueous media. However, the low solubility of nonpolar gases and molecular reagents involved in many energy conversion reactions limits the number of products formed per unit time in aqueous media. In this Communication, we use linear sweep voltammetry to measure how electrochemical H2O reduction in a nonaqueous solvent, acetonitrile, is enhanced by excitation of a plasmonic electrode. Plasmonically excited electrochemically roughened Au electrodes are found to produce photopotentials as large as 175 mV, which can be harnessed to lower the applied electrical bias required to drive the formation of H2. As the solvent polarity increases, by an increase in the concentration of H2O, the measured photopotential rapidly drops off to ∼50 mV. We propose a mechanism by which an increase in the H2O concentration increasingly stabilizes the photocharged plasmonic electrode, lowering the photopotential available to assist in the electrochemical reaction. Our study demonstrates that solvent polarity is an essential experimental parameter to optimize plasmonic enhancement in electrochemistry.

Direct Synthesis of MoS2 Nanosheets in Reduced Graphene Oxide Nanoscroll for Enhanced Photodetection

Due to their unique tubular and spiral structure, graphene and graphene oxide nanoscrolls (GONS) have shown extensive applications in various fields. However, it is still a challenge to improve the optoelectronic application of graphene and GONS because of the zero bandgap of graphene. Herein, ammonium tetrathiomolybdate ((NH₄)₂MoS₄) was firstly wrapped into the ((NH₄)₂MoS₄@GONS) by molecular combing the mixture of (NH₄)₂MoS₄ and GO solution on hydrophobic substrate. After thermal annealing, the (NH₄)₂MoS₄ and GO were converted to MoS₂ nanosheets and reduced GO (RGO) simultaneously, and, thus, the MoS₂@RGONS was obtained. Raman spectroscopy and high-resolution transmission electron microscopy were used to confirm the formation of MoS₂ nanosheets among the RGONS. The amount of MoS₂ wrapped in RGONS increased with the increasing height of GONS, which is confirmed by the atomic force microscopy and Raman spectroscopy. The as-prepared MoS₂@RGONS showed much better photoresponse than the RGONS under visible light. The photocurrent-to-dark current ratios of photodetectors based on MoS₂@RGONS are ~570, 360 and 140 under blue, red and green lasers, respectively, which are 81, 144 and 35 times of the photodetectors based on RGONS. Moreover, the MoS₂@RGONS-based photodetector exhibited good power-dependent photoresponse. Our work indicates that the MoS₂@RGONS is expected to be a promising material in the fields of optoelectronic devices and flexible electronics.

MoS2-based absorbers with whole visible spectrum coverage and high efficiency

To design highly efficient and broadband nanometer-sized absorbers based on the atomically thin transition metal dichalcogenides (TMDCs), we propose utilizing inclined gold gratings on MoS₂ monolayer. In the case of gold gratings with zero inclination, coverage of the absorption spectrum in the entire visible range occurs between the values of 42% to 73%. Considerable increase in the absorbed light occurs by introducing 13 nm inclination to the gold gratings with equal values of the grating's period and width as 60 nm. With the application of this grating, maximum absorption of 88% is reached and the absorption bandwidth covers the entire visible spectrum with only 12% variation of the absorption value relative to this maximum (88%). Footprints of resonant excitation of two different modes in the absorber structure are evident: the named "reflection" mode and localized surface plasmons (LSPs). Inclination of the gratings leads the LSP modes to slide toward the MoS₂ and causes a remarkable increment in the absorption efficiency. An impressive absorption value of 56% in MoS₂ monolayer is gained by the gold grating's inclination of 17 nm. The designed absorber paves a new way in designing TMDC-based absorbers with extended bandwidths and higher efficiencies.