22 research outputs found
Electric-field-induced strong enhancement of electroluminescence in multilayer molybdenum disulfide.
The layered transition metal dichalcogenides have attracted considerable interest for their unique electronic and optical properties. While the monolayer MoS2 exhibits a direct bandgap, the multilayer MoS2 is an indirect bandgap semiconductor and generally optically inactive. Here we report electric-field-induced strong electroluminescence in multilayer MoS2. We show that GaN-Al2O3-MoS2 and GaN-Al2O3-MoS2-Al2O3-graphene vertical heterojunctions can be created with excellent rectification behaviour. Electroluminescence studies demonstrate prominent direct bandgap excitonic emission in multilayer MoS2 over the entire vertical junction area. Importantly, the electroluminescence efficiency observed in multilayer MoS2 is comparable to or higher than that in monolayers. This strong electroluminescence can be attributed to electric-field-induced carrier redistribution from the lowest energy points (indirect bandgap) to higher energy points (direct bandgap) in k-space. The electric-field-induced electroluminescence is general for other layered materials including WSe2 and can open up a new pathway towards transition metal dichalcogenide-based optoelectronic devices
Electric field induced strong enhancement of electroluminescence in multi-Layer MoS2
The layered transition metal dichalcogenides (TMDs) have attracted
considerable interest due to their unique electronic and optical properties.
Here we report electric field induced strong electroluminescence in multi-layer
MoS2 and WSe2. We show that GaN-Al2O3-MoS2 and GaN-Al2O3-MoS2-Al2O3-graphene
vertical heterojunctions can be created with excellent rectification behaviour.
Electroluminescence studies demonstrate prominent direct bandgap excitonic
emission in multi-layer MoS2 over the entire vertical junction area.
Importantly, the electroluminescence efficiency observed in multi-layer MoS2 is
comparable to or even higher than that in monolayers, corresponding to a
relative electroluminescence enhancement factor of >1000 in multi-layer MoS2
when compared to its photoluminescence. This striking enhancement of
electroluminescence can be attributed to the high electric field induced
carrier redistribution from low energy points (indirect bandgap) to high energy
points (direct bandgap) of k-space, arising from the unique band structure of
MoS2 with a much higher density of states at high energy points. The electric
field induced electroluminescence is general for other TMDs including WSe2, and
can provide a fundamental platform to probe the carrier injection, population
and recombination in multi-layer TMDs and open up a new pathway toward TMD
based optoelectronic devices.Comment: 8 pages, 5 figure
Electroluminescence and photocurrent generation from atomically sharp WSe2/MoS2 heterojunction p-n diodes
The p-n diodes represent the most fundamental device building block for
diverse optoelectronic functions, but are difficult to achieve in atomically
thin transition metal dichalcogenides (TMDs) due to the inability to
selectively dope them into p- or n-type semiconductors. Here we report the
first demonstration of an atomically thin and atomically sharp heterojunction
p-n diode by vertically stacking p-type monolayer tungsten diselenide (WSe2)
and n-type few-layer molybdenum disulfide (MoS2). Electrical measurement
demonstrates excellent diode characteristics with well-defined current
rectification behaviour and an ideality factor of 1.2. Photocurrent mapping
shows fast photoresponse over the entire overlapping region with a highest
external quantum efficiency up to 12 %. Electroluminescence studies show
prominent band edge excitonic emission and strikingly enhanced hot electron
luminescence. A systematic investigation shows distinct layer-number dependent
emission characteristics and reveals important insight about the origin of
hot-electron luminescence and the nature of electron-orbital interaction in
TMDs. We believe that these atomically thin heterojunction p-n diodes represent
an interesting system for probing the fundamental electro-optical properties in
TMDs, and can open up a new pathway to novel optoelectronic devices such as
atomically thin photodetectors, photovoltaics, as well as
spin-/valley-polarized light emitting diodes and on-chip lasers.Comment: 27 pages, 7 figure
Wafer-scale growth of large arrays of perovskite microplate crystals for functional electronics and optoelectronics
Methylammonium lead iodide perovskite has attracted intensive interest for
its diverse optoelectronic applications. However, most studies to date have
been limited to bulk thin films that are difficult to implement for integrated
device arrays because of their incompatibility with typical lithography
processes. We report the first patterned growth of regular arrays of perovskite
microplate crystals for functional electronics and optoelectronics. We show
that large arrays of lead iodide microplates can be grown from an aqueous
solution through a seeded growth process and can be further intercalated with
methylammonium iodide to produce perovskite crystals. Structural and optical
characterizations demonstrate that the resulting materials display excellent
crystalline quality and optical properties. We further show that perovskite
crystals can be selectively grown on prepatterned electrode arrays to create
independently addressable photodetector arrays and functional field effect
transistors. The ability to grow perovskite microplates and to precisely place
them at specific locations offers a new material platform for the fundamental
investigation of the electronic and optical properties of perovskite materials
and opens a pathway for integrated electronic and optoelectronic systems.Comment: 8 pages, 4 figure
Rapid Screening of Cadmium in Rice and Identification of Geographical Origins by Spectral Method
The accuracy, repeatability and detection limits of the energy-dispersive X-ray fluorescence (XRF) spectrometer used in this study were tested to verify its suitability for rapid screening of cadmium in samples. Concentrations of cadmium in rice grain samples were tested by the XRF spectrometer. The results showed that the apparatus had good precision around the national limit value (0.2 mg/kg). Raman spectroscopy has been analyzed in the discrimination of rice grain samples from different geographical origins within China. Scanning time has been discussed in order to obtain better Raman features of rice samples. A total of 31 rice samples were analyzed. After spectral data pre-treatment, principal component analysis (PCA), K-means clustering (KMC), hierarchical clustering (HC) and support vector machine (SVM) were performed to discriminate origins of rice samples. The results showed that the geographical origins of rice could be classified using Raman spectroscopy combined with multivariate analysis
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Highly efficient gate-tunable photocurrent generation in vertical heterostructures of layered materials.
Layered materials of graphene and MoSâ‚‚, for example, have recently emerged as an exciting material system for future electronics and optoelectronics. Vertical integration of layered materials can enable the design of novel electronic and photonic devices. Here, we report highly efficient photocurrent generation from vertical heterostructures of layered materials. We show that vertically stacked graphene-MoSâ‚‚-graphene and graphene-MoSâ‚‚-metal junctions can be created with a broad junction area for efficient photon harvesting. The weak electrostatic screening effect of graphene allows the integration of single or dual gates under and/or above the vertical heterostructure to tune the band slope and photocurrent generation. We demonstrate that the amplitude and polarity of the photocurrent in the gated vertical heterostructures can be readily modulated by the electric field of an external gate to achieve a maximum external quantum efficiency of 55% and internal quantum efficiency up to 85%. Our study establishes a method to control photocarrier generation, separation and transport processes using an external electric field
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Electric-field-induced strong enhancement of electroluminescence in multilayer molybdenum disulfide.
The layered transition metal dichalcogenides have attracted considerable interest for their unique electronic and optical properties. While the monolayer MoS2 exhibits a direct bandgap, the multilayer MoS2 is an indirect bandgap semiconductor and generally optically inactive. Here we report electric-field-induced strong electroluminescence in multilayer MoS2. We show that GaN-Al2O3-MoS2 and GaN-Al2O3-MoS2-Al2O3-graphene vertical heterojunctions can be created with excellent rectification behaviour. Electroluminescence studies demonstrate prominent direct bandgap excitonic emission in multilayer MoS2 over the entire vertical junction area. Importantly, the electroluminescence efficiency observed in multilayer MoS2 is comparable to or higher than that in monolayers. This strong electroluminescence can be attributed to electric-field-induced carrier redistribution from the lowest energy points (indirect bandgap) to higher energy points (direct bandgap) in k-space. The electric-field-induced electroluminescence is general for other layered materials including WSe2 and can open up a new pathway towards transition metal dichalcogenide-based optoelectronic devices
van der Waals Heterojunction Devices Based on Organohalide Perovskites and Two-Dimensional Materials
Self-Templating Construction of 3D Hierarchical Macro-/Mesoporous Silicon from OD Silica Nanoparticles
Porous silicon has found wide applications in many different fields including catalysis and lithium-ion batteries. Three-dimensional hierarchical macro-/mesoporous silicon is synthesized from zero-dimensional Stober silica particles through a facile and scalable magnesiothermic reduction process. By systematic structure characterization of the macro-/mesoporous silicon, a self-templating mechanism governing the formation of the porous silicon is proposed. Applications as lithium-ion battery anode and photocatalytic hydrogen evolution catalyst are demonstrated. It is found that the macro-/mesoporous silicon shows significantly improved cyclic and rate performance over the commercial nanosized and micrometer-sized silicon particles. After 300 cycles at 0.2 A g(-1), the reversible specific capacity is still retained as much as 959 mAh g(-1) with a high mass loading density of 1.4 mg cm(-2). With the large current density of 2 A g(-1), a reversible capacity of 632 mAh g(-1) is exhibited. The coexistence of both macro- and mesoporous structures is responsible for the enhanced performance. The macro-/mesoporous silicon also shows superior catalytic performance for photocatalytic hydrogen evolution compared to the silicon nanoparticles