Blue-shifted Photoluminescence Research Articles

Light-induced transformation of all-inorganic mixed-halide perovskite nanoplatelets: ion migration and coalescence

When exposed to light, the colloidal perovskite nanoplatelets (NPLs) in the film can fuse into larger grains, and this phenomenon was thought to be closely related to ion migration. However, the available CsPbBr3 NPLs are not conducive to directly distinguishing this hypothesis. Herein, we prepare mixed-halide perovskite CsPbBr2.7I0.3 NPLs by a ligand-assisted reprecipitation method and investigate the photoluminescence evolution of NPLs under laser irradiation. At a low-irradiation intensity, 4.5-monolayer NPLs exhibit blue-shifted photoluminescence peaks due to the migration of iodide ions. Under higher laser fluence, a new photoluminescence component appears in the long wavelength region after the spectral blue shift, which is attributed to the coalescence of NPLs according to transmission electron microscopy analysis. A similar spectral evolution is also observed in 8-monolayer NPLs, while only the spectral blue shift caused by ion migration is detected in cuboidal CsPbBr2.7I0.3 nanocrystals. The use of strong bonding ligands can inhibit the fusion process of the NPLs, but not to impede ion migration, suggesting that fusion requires ligand detachment rather than ion migration. Similar suppression effects can be achieved in a vacuum atmosphere. Moreover, we demonstrate that mixed-halide NPLs can be used to realize anti-counterfeiting applications with superior photosensitivity.

Electron irradiation effects on the optical properties of Hf- and Zn-doped β-Ga2O3

Optical and electrical properties of Hf- and Zn-doped β-Ga2O3 samples, which are n-type and insulating, respectively, were altered via high-energy electron irradiation at 2.5 or 0.5 MeV. The β-Ga2O3:Hf samples irradiated with 2.5 MeV electrons experienced a color change from blue to yellow and a large drop in conductivity, attributed to the creation of gallium vacancies, which compensate donors. This irradiation resulted in the absence of free carrier absorption and the presence of Cr3+ photoluminescence (PL). PL mapping prior to irradiation revealed optically active ZnO precipitates that formed during the growth of β-Ga2O3:Zn. These precipitates have a 384 nm (3.23 eV) stacking fault emission in the core; in the outer shell of the precipitate, the PL blue-shifts to 377 nm (3.29 eV) and a broad defect band is observed. After 0.5 MeV electron irradiation, the defect band broadened and increased in intensity. The blue PL band (435 nm) of β-Ga2O3 was enhanced for both Hf- and Zn-doped samples irradiated with 0.5 MeV. This enhancement is correlated with an increase in oxygen vacancies.

Unraveling Exciton-Plasmon Coupling and the PIRET Mechanism in Decorated Silicon Nanowires.

Exciton-plasmon coupling is a fascinating physical phenomenon that has been investigated in various metal semiconductor systems. Intentionally chosen silicon nanowires (SiNWs) systems act as a host material for providing exciton as well as silicon oxide as a thin dielectric. A clear blue-shift in photoluminescence (PL) peak and a significant increase in visible range absorption were observed for metal nanoparticle (MNP) decorated SiNWs (D-SiNWs) which signifies the presence of exciton-plasmon coupling. A further investigation reveals that the possibility of the occurrence of the plasmon-induced resonance energy transfer (PIRET) mechanism is higher. The PL intensity enhancement in Au-decorated SiNWs is higher (∼38 times) in comparison to that in Pt due to the presence of a strong and localized electric field of plasmons near the interface of metal and semiconductors. Moreover, splitting in PL for gold-decorated SiNWs might be due to the presence of dipole-quadrupole coupling along with dipole-dipole coupling, which further increases the strength of the PIRET mechanism.

Highly luminescent CsPbX3@MIL-53(Al) nanoarchitectonics with anomalous stability towards flexible emitting films

The poor stability of perovskite nanomaterials exposed in high temperature, moisture, light radiation, and polar solvent conditions severely restrict their commercial application. To address this issue, the growth in situ of CsPbX3 (X = Cl, Br, I) nanocrystals (NCs) is carried out by using the stable aluminum (Al)-based metal-organic frameworks to create CsPbX3@MIL-53(Al) composites. Compared with pristine CsPbX3 NCs prepared using room temperature ligand assisted re-precipitation synthesis, the CsPbX3@MIL-53(Al) composites exhibit narrow photoluminescence (PL) spectra and greatly improved stability. The green emitting CsPbBr3@MIL-53(Al) composite exhibit narrowed PL spectrum (the full width at half-maximum of PL spectra: 20 nm for the composite and 28 nm for CsPbBr3 NCs) and a blue-shifted PL peak wavelength (517.6 nm for the composite and 527.6 nm for the CsPbBr3 NCs). The relationship of microstructure, components, PL, fluorescence lifetime, and stability are discussed systematically. Anomalous stability against heat-treatment, polar solvent and humidity conditions indicated the composites retained their initial PL intensity after storge more than 4 months in ambient conditions and heat-treated to 120ºC for 5 cycles. The emitting color of CsPbBr3@MIL-53(Al) composites are easily adjusted from blue, green to red by controlling the halide components of precursors. The composite was used to create emitting coating and highly bright flexible emitting films which also reveal high stability, suggesting that in situ encapsulation of CsPbX3 NCs in MIL-53(Al) would supply a novel platform for various emitting devices.

(Invited) Formation and Characterization of Fe-Silicide Nanodots for Optoelectronic Application

We have demonstrated the formation of high areal-density β-FeSi2nanodots (NDs) on SiO2 by remote H2-plasma induced self-assembly of Fe-NDs and subsequent SiH4-exposure at 400°C. Under either 976- or 514.5-nm light excitation of NDs after the SiH4-exposure, stable photoluminescence (PL) signals, being characteristic of the semiconducting phase as β-FeSi2, were observed even at room temperature in the energy region over the indirect bandgap of bulk β-FeSi2 (~0.7 eV). The temperature dependence of PL was confirmed to be weak significantly in comparison to that of bulk bandgap, implying light emission from tightly confined NDs. And also, with a decrease in the average dot size by controlling the initial Fe-film thickness, a clear blue shift in PL was observed. The results are associated with quantum size effect in radiative recombination of photoexcited electron-hole pairs.

Revealing the enhanced crystalline quality mechanism of perovskites produced by microwave-assisted synthesis: toward the fabrications in a fully ambient air environment

The conventional stirring method (CSM) in a nitrogen-controlled glovebox has been widely used to synthesize the Cs/MA/FA precursor solution. However, it involves a long preparation time and limits the fabrication conditions in an ambient environment, hindering their potential for high-end applications and environmental stability. Herein, we systematically developed a fast and efficient microwave-assisted synthesis (MAS) method to produce a high-quality and stable triple cation perovskite (Cs0.1(MA0.17FA0.83)0.9Pb(Br0.17I0.83)3) solution and fabricated a device in ambient conditions. The superiority of using the MAS compared to CSM is manifested by comparing the improvements in crystal nucleation, enhanced optical properties, and its excellent stability with time, owing to the homogeneous heating of the precursor solution during the synthesis method. The MAS-prepared perovskite films showed anomalous photoluminescence blue-shift and linewidth broadening with increasing temperature, emphasizing the unique properties of the triple cation perovskite fabricated. These results were later interpreted and fitted to discuss the induced lattice thermal expansion, structural phase transition, and electron–phonon interactions that highlighted the enhanced crystal quality from the MAS-perovskite films. Considering the substantial fabrication parameters and conditions, the structural and optical stability of the MAS-perovskite films were maintained over time during exposure to air and ultraviolet light, even without encapsulation. To further elucidate the crystal quality improvements from using the MAS-perovskite solution, the fabrication of perovskite transistors in a completely ambient environment resulted in a 10-fold increase in electron carrier mobility compared to the CSM-perovskite devices. The developed synthesis method has contributed significant advantages to enhance the structural and environmental stability of perovskites, making a promising approach for larger-scale and more efficient future optoelectronic device applications.

Gram-scale synthesis of highly doped chlorine graphene quantum dots: Synthesis and photoluminescence properties

Band-gap engineering of graphene-based nanomaterials has a huge influence on their optical and structural properties. Our contribution reports the successful gram-scale synthesis of highly chlorinated graphene quantum dots (Cl-GQDs) via a two-step preparation method. X-ray photoelectron spectroscopy (XPS) proved the successful doping of chlorine atoms into the as-prepared graphene oxide quantum dots (O-GQDs). Time-resolved fluorescence revealed a high decrease in the relaxation lifetime from 690 ps for O-GQDs to 5.3–4 ps for Cl-GQDs. Transmission electron microscopy (TEM) confirms that all nanoparticles are on the quantum scale (4–6 nm). The large blueshift in photoluminescence (PL) 150 nm from the original O-GQD (440 → 290 nm) supports the chlorination effect which enables tuning the band gap of O-GQD.

Photophysical Characterization of Ru Nanoclusters on Nanostructured TiO2 by Time-Resolved Photoluminescence Spectroscopy.

Despite the promising performance of Ru nanoparticles or nanoclusters on nanostructured TiO2 in photocatalytic and photothermal reactions, a mechanistic understanding of the photophysics is limited. The aim of this study is to uncover the nature of light-induced processes in Ru/TiO2 and the role of UV versus visible excitation by time-resolved photoluminescence (PL) spectroscopy. The PL at a 267 nm excitation is predominantly due to TiO2, with a minor contribution of the Ru nanoclusters. Relative to TiO2, the PL of Ru/TiO2 following a 267 nm excitation is significantly blue-shifted, and the bathochromic shift with time is smaller. We show by global analysis of the spectrotemporal PL behavior that for both TiO2 and Ru/TiO2 the bathochromic shift with time is likely caused by the diffusion of electrons from the TiO2 bulk toward the surface. During this directional motion, electrons may recombine (non)radiatively with relatively immobile hole polarons, causing the PL spectrum to red-shift with time following excitation. The blue-shifted PL spectra and smaller bathochromic shift with time for Ru/TiO2 relative to TiO2 indicate surface PL quenching, likely due to charge transfer from the TiO2 surface into the Ru nanoclusters. When deposited on SiO2 and excited at 532 nm, Ru shows a strong emission. The PL of Ru when deposited on TiO2 is completely quenched, demonstrating interfacial charge separation following photoexcitation of the Ru nanoclusters with a close to unity quantum yield. The nature of the charge-transfer phenomena is discussed, and the obtained insights indicate that Ru nanoclusters should be deposited on semiconducting supports to enable highly effective photo(thermal)catalysis.

Octahedron distortion-triggered dipole–spin interaction in multiferroic magnetoelectric perovskites

The design of perovskite structures with multiferroic magnetoelectric coupling effects opens up new opportunities in fields such as the creation of next-generation spin-dependent multistate information storage technologies. In this work, we prepared a transition metal-implanted perovskite with multiferroic magnetoelectric coupling, in which both magnetoelectric coupling and a blueshift of photoluminescence were observed. The introduction of transition metal-generated polarized spin interacts with the electronic orbit through spin–orbital coupling to lead to a pronounced octahedron distortion, where the temperature dependence of the dielectric constant undergoes a ferroelectric polarization transition. An external magnetic field could enhance the strength of spin polarization to further affect the magnitude of electric polarization. Moreover, applying an electric field tunes the distortion of the octahedron dependence of electric polarization to feed back to the change in spin polarization. Overall, the spin polarization-induced electric polarization in perovskites provides a unique approach to realizing the room-temperature magnetoelectric coupling of multiferroic materials.

Bottom-up self-assembly of macroporous ZnO nanostructures for photovoltaic applications

The present study utilized a template-assisted electrodeposition route for the bottom-up epitaxial growth of macroporous zinc oxide nanostructures. To this end, the ZnO seed layer was coated on the p-type silicon substrates using a radio frequency magnetron sputtering technique to form a p-n heterojunction. Then, polymer microspheres were implanted on ZnO/Si substrates to act as a template. Subsequently, ZnO nanostructures were electrodeposited through the interstitial spaces between the microspheres. After the deposition, the microspheres were removed by dissolving in chloroform solvent, forming a porous structure. The planar and cross-sectional electron microscopy analyses exhibited a uniform macroporous morphology with an average pore diameter of ∼1 μm. The pores were homogeneously distributed on the surface of the electrodeposited ZnO layer. The advantage of this technique over the top-down approaches, such as electrochemical etching, is that the porosity and size of pores can be easily adjusted by varying the concentration and diameter of microsphere templates. The optical investigations revealed enhancement in photon absorption and photoluminescence (PL) intensity due to multiple light scattering in the pore walls of the deposited ZnO nanostructures. For the templated sample, a PL blue shift was observed due to the reduction in crystallite size of ZnO nanostructures. A heterojunction thin film solar cell was designed by the metallization of ZnO/p-Si samples to study the power conversion capability of macroporous ZnO nanostructures. The photovoltaic performance of the developed devices was evaluated under a solar light simulator. The device based on the templated sample showed increased shunt resistance and reduced series resistance compared to the flat sample. The optoelectrical results indicated an efficiency improvement for the fabricated solar cells based on the macroporous ZnO sample due to its higher exposed area and increased rate of electron-hole generation.

Passivation capping of InAs surface quantum dots by TMA/Al2O3: PL enhancement and blueshift suppression

Passivation capping that enhances the photoluminescence (PL) of molecular beam epitaxy (MBE)-grown InAs surface quantum dots (SQDs) is realized by ex situ low-temperature atomic layer deposition (ALD)-grown Al2O3. As the Al2O3 cap thickness increased from 2 to 30 nm, the PL intensity was enhanced by 2.7-fold and the blue shift was suppressed. This is in strong contrast to wet chemistry passivation and in situ GaAs capping by MBE, both of which resulted in significant PL blueshift, due to etching in the former, and In/Ga intermixing and strain in the latter. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) reveal that the Al2O3 cap layer mimics the shape of the underlying SQDs. The cross-sectional transmission electron microscopy (TEM) further reveals that the SQD size and shape remained unchanged after Al2O3 capping, which is in strong contrast to MBE-capping. The passivation mechanisms and native oxide reduction by trimethylaluminum (TMA), including self-clean-up reaction through ligand exchange, are discussed based on the results by x-ray photoelectron spectroscopy (XPS). A detailed comparison between Al2O3 and ZnO cap layers reveals the significance of the cap properties on the SQD size/shape and PL blueshift. While the size/shape of SQDs is preserved by Al2O3 capping, the apex is slightly removed by ZnO capping, resulting in a stronger PL blueshift compared to Al2O3.

First Experimental Evidence of Anti-Stokes Laser-Induced Fluorescence Emission in Microdroplets and Microfluidic Systems Driven by Low Thermal Conductivity of Fluorocarbon Carrier Oil

With the advent of many optofluidic and droplet microfluidic applications using laser-induced fluorescence (LIF), the need for a better understanding of the heating effect induced by pump laser excitation sources and good monitoring of temperature inside such confined microsystems started to emerge. We developed a broadband highly sensitive optofluidic detection system, which enabled us to show for the first time that Rhodamine-B dye molecules can exhibit standard photoluminescence as well as blue-shifted photoluminescence. We demonstrate that this phenomenon originates from the interaction between the pump laser beam and dye molecules when surrounded by the low thermal conductive fluorocarbon oil, generally used as a carrier medium in droplet microfluidics. We also show that when the temperature is increased, both Stokes and anti-Stokes fluorescence intensities remain practically constant until a temperature transition is reached, above which the fluorescence intensity starts to decrease linearly with a thermal sensitivity of about −0.4%/°C for Stokes emission or −0.2%/°C for anti-Stokes emission. For an excitation power of 3.5 mW, the temperature transition was found to be about 25 °C, whereas for a smaller excitation power (0.5 mW), the transition temperature was found to be about 36 °C.

Second harmonic generation in air-exposed few-layer black phosphorus

Black phosphorus (BP) shows significant saturable absorption and other unique properties in nonlinear optical effects, and it can be used for nonlinear optical elements and other photonic devices. However, the second harmonic generation (SHG) emission is prohibited due to its inversion symmetry. Here we report emerging SHG emission in BP by exposing BP to oxygen so as to break the inversion symmetry. The intensity of SHG signal shows a dependence on thickness and exposure time. It is interesting to find that the thinner BP flakes have faster SHG intensity change rate. Our results demonstrate that the intensity of SHG signal is attributed to oxidation degree. Air exposure also causes a blue shift of photoluminescence (PL) peaks, which is consistent with our calculation results. Our study demonstrates a feasible approach to modulate the SHG emission of BP, which may provide insights to other inversion symmetric crystals like BP. • We report emerging SHG emission in BP by exposing BP to oxygen so as to break the inversion symmetry. • It is founded that the intensity of SHG signal shows a dependence on thickness and exposure time. • It is founded that air exposure causes a blue shift of PL peaks, which is consistent with our calculation results. The results demonstrate that the intensity of SHG signal is attributed to oxidation degree. • To the best of our knowledge, there is no report on the SHG in BP before. This work demonstrates a feasible approach to modulate the SHG emission of BP, which may provide insights to other inversion symmetric crystals like BP.

Enhanced optoelectrical performance of ultraviolet detectors based on self-assembled porous zinc oxide nanostructures

A templated self-assembly technique was utilized in the present study to grow porous zinc oxide nanostructures. The nanostructures were formed by the electrochemical deposition of ZnO through the interstitial spaces between polymer microsphere templates. After the deposition, polymer microspheres were removed by dissolving in chloroform solvent, leaving porous ZnO nanostructures. This technique is benefited from facile controllability of the pore morphology and size by varying the diameter of microspheres. X-ray diffraction analysis showed a dominant peak corresponding to the hexagonal ZnO structure. Moreover, no significant structural strain was observed after the removal of spheres unlike the other synthesis methods of porous materials. The improved photoluminescence (PL) properties revealed an enhancement in the light capturing capability of the systems due to the multiple scattering of light in the pore walls. The porous sample showed a PL blue-shift compared to the flat one, indicating a reduction in crystallite size of ZnO nanostructures. To assess the photonic applications of synthesized porous ZnO substrates, a metal-semiconductor-metal photodetector was developed via the metallization of ZnO nanostructures, and their optoelectrical properties were tested under UV radiation. The results showed an improvement in photosensitivity and quantum efficiency of devices based on porous ZnO substrates which can be assigned to the larger exposed area and elevated rates of electron-hole generation in this sample.

Piezochromic Tetracoordinate Boron Complex: Blue-Shifted and Enhanced Luminescence.

Achieving blueshifted and enhanced emission from purely organic luminophors remains a major challenge. Herein, we report a tetracoordinate boron complex with polymorphism (Y-phase and O-phase)-dependent luminescence. Impressively, the Y-phase crystals exhibited rare piezochromic luminescent properties such as pressure-induced blue-shifted and enhanced emission. The results of theoretical and experimental tests demonstrated that this phenomenon results from the cooperative effect between the restriction of intramolecular motions and alterable charge transfer (CT) behavior during compression. This work provides an ideal model to investigate the optoelectronic properties of boron complexes. Importantly, manipulating the CT behavior through the electrophilicity of boron atoms may become a new principle for the design of piezochromic materials with blueshifted and enhanced emission.

Analytical Model and Experimental Analysis to Estimate the Interdiffusion and Optoelectronic Properties of Coupled InAs Quantum Dots Post Rapid Thermal Processing

The stoichiometric variations in molecular beam epitaxy (MBE)-grown In(Ga)As quantum dots (QDs) after rapid thermal processing (RTP) is estimated from an analytical model assisted by transmission electron microscopy (TEM) images. A systematically grown multilayer (bi-, penta-, hepta-, and deca-layer) InAs Stranski–Krastanov (SK) QDs coupled electronically to submonolayer (SML) QDs are used in this study. The As-grown (ASG) samples are treated with RTP at temperatures of 650 °C, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$700~^{\circ }\text{C}$ </tex-math></inline-formula> , <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$750~^{\circ }\text{C}$ </tex-math></inline-formula> , and 800 °C for 30 s. Our model estimates a significant diffusion of In atoms in the growth direction compared with the in-plane direction altering the QD dimensions and composition. To check its reliability, we incorporated an eight-band k.p model on all the RTP-treated strained In(Ga)As QD heterostructures. Photoluminescence (PL) measurements reveal a strong correlation with the simulation results; furthermore, a strong PL blueshift (56 nm) and narrow linewidth from 67 nm (ASG) to 33 nm ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$800~^{\circ }\text{C}$ </tex-math></inline-formula> ) are seen due to an increase in the uniformity of QDs supporting the atomic force microscopy (AFM) results. AFM images reveal the formation of highly uniform and dense QDs with increased annealing temperature. The activation energy (AE) shows a decreasing trend due to the reduction in carrier confinement with RTP, agreeing with the analytical model. This is probably the first report that presents the effect of RTP on SK-SML coupled QD devices both in terms of theoretical and experimental analyses. This analytical model can thus be extended to any annealing study and for any material with certain known parameters and is helpful for futuristic studies.

GaInAs/GaAs quantum well intermixing based on SiO2–Cu composite film

Quantum well intermixing (QWI) is widely used in bandgap tuning of optoelectronic materials. In this paper, GaInAs/GaAs QWI is studied based on SiO2–Cu composite layers. The effects of annealing parameter and Cu layer thickness on the photoluminescence (PL) characteristics are analyzed. The results show that the PL blue shift gradually increases with the rise of annealing temperature, and the PL intensity exhibits a peak rise at a temperature that is related to the Cu layer thickness. It is also found that the PL blue shift increases when the thickness of the Cu layer becomes large in the composite film. In addition, multi-cycle annealing can be used to improve the PL properties of the samples, while the PL can have a large blue shift. Compared with SiO2 cap layer, SiO2–Cu composite film exhibits a more significant effect on QWI for GaInAs/GaAs quantum well (QW) materials.

High Energy Limit of the Size-Tunable Photoluminescence of Hydrogen-Terminated Porous Silicon Nanostructures in HF

The photoluminescence (PL) of various porous silicon (PSi) layers was studied during chemical dissolution in HF. The relative PL quantum efficiency of some layers was also monitored. Typically, the PL increased, reached a maximum and then dropped down to complete extinction, accompanied with a PL blueshift. During PL fall, both the PL intensity and layer quantum efficiency fell sharply, accompanied by a decrease in full width at half maximum and a slowing blueshift. In the final stage, the PL intensity decreased without any further blueshift, the saturated PL peak wavelength being ∼515 nm (∼2.4 eV) for most layers, identifying a high energy limit for the achievable PL of hydrogen-terminated Si nanostructures. Our results show that sudden catastrophic mechanical failure of nanostructure cannot explain the sharp PL drop and saturation of PL blueshift. Rather, they support the idea of a critical size (∼1.5–2 nm) below which the PL quantum efficiency vanishes. The possible reasons were discussed, privileging the emergence of structural non-radiative defects below a certain size, though the decreasing intrinsic quantum efficiency of Si nanocrystals with decreasing size could also play an important role. Maximum PL intensity was generally obtained for a peak wavelength of ∼565 nm (∼2.2 eV).

Confining halide perovskite crystals CH3NH3PbBr3 in porous aluminum oxide thin film

In this work, the photoluminescence emission properties of CH3NH3PbBr3 perovskite crystals which encapsulated among the porous thin films of aluminum oxide are studied. These porous layers are made by electrochemical anodizing method. First, aluminum thin film has been deposited by magnetron sputtering deposition method and then by changing anodic voltage, different patterns of porous aluminum oxide films are fabricated. Finally, CH3NH3PbBr3 nanocrystals are synthesized on the Al2O3 porous thin film by one step spin coating method. Morphological studies of porousaluminum oxide thin films are investigated by field emission scanning electron microscopy images and Atomic Force Microscope results. In order to study optical response of CH3NH3PbBr3 erovskite pto structural characteristics of porousthin films, photoluminescence spectroscopy has been employed too. By structural characterization, it is found that the number and the average diameter of the nano-pores are increased by anodic voltage raising. Also, the dependence of the emission properties of the encapsulated crystals on the size of the pores has been determined by the photoluminescence spectroscopy. So that, blue-shifted photoluminescence emission has been observed by the pores diameter reduction. Eventually, by comparing the results of structural and optical characterizations with Bruce model, the fabrication of CH3NH3PbBr3 perovskite nanocrystals within the patterned aluminum oxide mold is confirmed.

Enhanced photoluminescence of monolayer MoS2 on stepped gold structure

Different MoS2/Au heterostructures can play an important role in tuning the photoluminescence (PL) and optoelectrical properties of monolayer MoS2. Previous studies of PL of MoS2/Au heterostructures were mainly limited to the PL enhancement by using different Au nanostructures and PL quenching of monolayer MoS2 on flat Au surfaces. Here, we demonstrate the enhanced excitonic PL emissions of monolayer MoS2/Au heterostructures on Si/SiO2 substrates. By transferring the continuous monolayer MoS2 onto a stepped Au structure consisting of 60-nm and 100-nm Au films, the MoS2/Au-60 and MoS2/Au-100 heterostructures exhibit enhanced PL emissions, each with a blue-shifted PL peak in comparison with the MoS2/SiO2. Furthermore, the PL intensity of MoS2/Au-60 is about twice larger than that of MoS2/Au-100. The different enhanced excitonic PL emissions in MoS2/Au heterostructures can be attributed to the different charge transfer effects modified by the stepped Au structure. This work may provide an insight into the excitonic PL and charge transfer effect of MoS2 on Au film and yield novel phenomena in MoS2/Au heterostructures for further study of PL tuning and optoelectrical properties.