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Register a new userRobust B-exciton emission at room temperature in few-layers of MoS2:Ag nanoheterojunctions embedded into a glass matrix
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Abdus Salam Sarkar Dr
Publication date
2020
fields
Physics
and research's language is
English
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Tailoring the photoluminescence (PL) properties in two-dimensional (2D) molybdenum disulfide (MoS2) crystals using external factors is critical for its use in valleytronic, nanophotonic and optoelectronic applications. Although significant effort has been devoted towards enhancing or manipulating the excitonic emission in MoS2 monolayers, the excitonic emission in few-layers MoS2 has been largely unexplored. Here, we put forward a novel nano-heterojunction system, prepared with a non-lithographic process, to enhance and control such emission. It is based on the incorporation of few-layers MoS2 into a plasmonic silver metaphosphate glass (AgPO3) matrix. It is shown that, apart from the enhancement of the emission of both A and B excitons, the B-excitonic emission dominates the PL intensity. In particular, we observe an almost six-fold enhancement of the B exciton emission, compared to control MoS2 samples. This enhanced PL at room temperature is attributed to an enhanced exciton-plasmon coupling and it is supported by ultrafast time-resolved spectroscopy that reveals plasmon-enhanced electron transfer that takes place in Ag nanoparticles-MoS2 nanoheterojunctions. Our results provide a great avenue to tailor the emission properties of few-layers MoS2, which could find application in emerging valleytronic devices working with B excitons.
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Single-layer transition metal dichalcogenides are at the center of an ever increasing research effort both in terms of fundamental physics and applications. Exciton-phonon coupling plays a key role in determining the (opto)electronic properties of these materials. However, the exciton-phonon coupling strength has not been measured at room temperature. Here, we develop two-dimensional micro-spectroscopy to determine exciton-phonon coupling of single-layer MoSe2. We detect beating signals as a function of waiting time T, induced by the coupling between the A exciton and the A1 optical phonon. Analysis of two-dimensional beating maps combined with simulations provides the exciton-phonon coupling. The Huang-Rhys factor of ~1 is larger than in most other inorganic semiconductor nanostructures. Our technique offers a unique tool to measure exciton-phonon coupling also in other heterogeneous semiconducting systems with a spatial resolution ~260 nm, and will provide design-relevant parameters for the development of optoelectronic devices.
Room temperature operation of a spin exclusive or (XOR) gate was demonstrated in lateral spin valve devices with nondegenerate silicon (Si) channels. The spin XOR gate is a fundamental part of the magnetic logic gate (MLG) that enables reconfigurable and nonvolatile NAND or OR operation in one device. The device for the spin XOR gate consists of three iron (Fe)/cobalt (Co)/magnesium oxide (MgO) electrodes, i.e., two input and one output electrodes. Spins are injected into the Si channel from the input electrodes whose spin angular momentum corresponds to the binary input 1 or 0. The spin drift effect is controlled by a lateral electric field in the Si channel to adjust the spin accumulation voltages under two different parallel configurations, corresponding to (1, 1) and (0, 0), so that they exhibit the same value. As a result, the spin accumulation voltage detected by the output electrode exhibits three different voltages, represented by an XOR gate. The one-dimensional spin drift-diffusion model clearly explains the obtained XOR behavior. Charge current detection of the spin XOR gate is also demonstrated. The detected charge current has a maximum of 0.94 nA, the highest value in spin XOR gates reported thus far. Furthermore, gate voltage modulation of the spin XOR gate is also demonstrated, which enables operation of multiple MLG devices.
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We fabricate large-area atomically thin MoS$_2$ layers through the direct transformation of crystalline molybdenum MoS$_2$ (MoO$_3$) by sulfurization at relatively low temperatures. The obtained MoS2 sheets are polycrystalline (~10-20 nm single-crystal domain size) with areas of up to 300x300 um$^2$ with 2-4 layers in thickness and show a marked p-type behaviour. The synthesized films are characterized by a combination of complementary techniques: Raman spectroscopy, X-ray diffraction, transmission electron microscopy and electronic transport measurements.
To augment the magnetoresistance (MR) ratio of n-type non-degenerate Si-based lateral spin valves (Si-LSVs), we modify the doping profile in the Si layer and introduce a larger local strain into the Si channel by changing a capping insulator. The highest MR ratio of 1.4% is achieved in the Si-LSVs through these improvements, with significant roles played by a reduction in the resistance-area product of the ferromagnetic contacts and an enhancement of the momentum relaxation time in the Si channel.
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