Search query: Emerging photoluminescence in monolayer MoS2

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abstract: Novel physical phenomena can emerge in low dimensional nanomaterials. Bulk MoS(2) a prototypical metal dichalcogenide, is an indirect bandgap semiconductor with negligible photoluminescence. When the MoS(2) crystal is thinned to monolayer, however, a strong photoluminescence emerges, indicating an indirect to direct bandgap transition in this d electron system. This observation shows that quantum confinement in layered d electron materials like MoS(2) provides new opportunities for engineering the electronic structure of matter at the nanoscale.
author_names: Andrea Splendiani

Liang Sun

Yuanbo Zhang

Tianshu Li

Jonghwan Kim

Chi Yung Chim

Giulia Galli

Feng Wang
title: Emerging photoluminescence in monolayer MoS2.
venue: Nano letters
year: 2010

abstract: Novel physical phenomena can emerge in low dimensional nanomaterials. Bulk MoS2, a prototypical metal dichalcogenide, is an indirect bandgap semiconductor with negligible photoluminescence. When the MoS2 crystal is thinned to monolayer, however, a strong photoluminescence emerges, indicating an indirect to direct bandgap transition in this d electron system. This observation shows that quantum confinement in layered d electron materials like MoS2 provides new opportunities for engineering the electronic structure of matter at the nanoscale.
author_names: Andrea Splendiani

Liang Sun

Yangting Zhang

Tianshu Li

Jonghwan Kim

Chi Yung Chim

Giulia Galli

Feng Wang
title: Emerging Photoluminescence in Monolayer
year: 2010

abstract: Molybdenum disulfide (MoS2) is back in the spotlight because of the indirect to direct bandgap tunability and valley related physics emerging in the monolayer regime. However, rigorous control of the monolayer thickness is still a huge challenge for commonly utilized physical exfoliation and chemical synthesis methods. Herein, we have successfully grown predominantly monolayer MoS2 on an inert and nearly lattice matching mica substrate by using a low pressure chemical vapor deposition method. The growth is proposed to be mediated by an epitaxial mechanism, and the epitaxial monolayer MoS2 is intrinsically strained on mica due to a small adlayer substrate lattice mismatch ~2.7% Photoluminescence (PL) measurements indicate strong single exciton emission in as grown MoS2 and room temperature PL helicity (circular polarization ~0.35) on transferred samples, providing straightforward proof of the high quality of the prepared monolayer crystals. The homogeneously strained high quality monolayer MoS2 prepared in this study could competitively be exploited for a variety of future applications.
author_names: Qingqing Ji

Yanfeng Zhang

Teng Gao

Yu Zhang

Dongling Ma

Mengxi Liu

Yubin Chen

Xiao-fen Qiao

Pingheng Tan

Min Kan

Ji Feng

Qiang Sun

Zhongfan Liu
title: Epitaxial monolayer MoS2 on mica with novel photoluminescence.
venue: Nano letters
year: 2013

abstract: The transition metal chalcogenides (TMDs) are gaining increased attention from many scientists recently. Monolayer MoS2 is an emerging layered TMD material with many excellent physical and electrical properties. It can be widely used in catalysis, transistors, optoelectronics and integrated circuits. Here, the large sized monolayer MoS2 is grown on the silicon substrate with a 285 nm thick oxide layer by atmospheric pressure chemical vapor deposition (APCVD) of sulfurized molybdenum trioxide. This method is simple and it does not require vacuum treatment. In addition, the effects of growth conditions, such as sulfur source, molybdenum source, growth temperature, and argon flow rate on the quality and area of MoS2 are further studied systematically. These analysis results help to master the morphology and optical properties of monolayer MoS2. The high quality, excellent performance, and large size monolayer MoS2 under the optimal growth condition is characterized by optical microscopy, AFM, XPS, photoluminescence, and Raman spectroscopy. The Raman spectrum and PL mapping show that the grown MoS2 is a uniform triangular monolayer with a side length of 100 mm, which can pave the way for the applications of photodetectors and transistors.
author_names: Tao Han

Hongxia Liu

Shulong Wang

Wei Li

Shupeng Chen

Xiaoli Yang

M Cai
title: Research on the Factors Affecting the Growth of Large Size Monolayer MoS2 by APCVD
venue: Materials
year: 2018

abstract: We have investigated the quantum efficiency of monolayer MoS2 light emitting devices through detailed temperature and power dependent photoluminescence studies and rate equation analysis. The internal quantum efficiency can reach 45 and 8.3% at 83 and 300 K, respectively. However, efficiency droop is clearly measured with increasing carrier injection due to the unusually large Auger recombination coefficient, which is found to be ~10( 24) cm(6)/s at room temperature, nearly 6 orders of magnitude higher than that of conventional bulk semiconductors. The significantly elevated Auger recombination in the emerging two dimensional (2D) semiconductors is primarily an indirect process and is attributed to the abrupt bounding surfaces and the enhanced correlation, mediated by magnified Coulomb interactions, between electrons and holes confined in a 2D structure.
author_names: Omid Salehzadeh

Nhung Hong Tran

Xiaofeng Liu

Ishiang Shih

Zetian Mi
title: Exciton kinetics, quantum efficiency, and efficiency droop of monolayer MoS2 light emitting devices.
venue: Nano letters
year: 2014

abstract: Monolayer MoS2 is an emerging two dimensional semiconductor that has seen wide applications in optoelectronic and light emitting devices. Here we report on the antenna enhanced spontaneous emission of monolayer MoS2, which has weak absorbance and low intrinsic quantum yield. The ultrathin silver platelet antennas we use can both increase the absorption cross section and improve the transmission efficiency via controlling the optical field at nanometer scale. Experimental results indicate the photoluminescence enhancement can reach 4 times, which is also supported by numerical analysis of both excitation and emission processes with respect to the thickness of spacer layer. This ultrathin structure can facilitate the development of on chip emitters and valley based devices, especially in cases of large area sample or flexible substrate.
author_names: Yingyi Yang

Di Wang

Zheng Jie Tan

Xiang Xiong

Mu Wang

Ruwen Peng

Nicholas Xuanlai Fang
title: Ultrathin platelet antennas mediated light matter interaction in monolayer MoS2.
venue: Optics express
year: 2017

abstract: MoS2 are two dimensional (2D) materials that exhibit emerging photoluminescence (PL) at the monolayer level and have potential optoelectronic applications. Monolayers of MoS2 typically achieved by mechanical exfoliation (Me) chemical vapor deposition (CVD) and chemical exfoliation (Ce) via lithium intercalation contain numerous defects that significantly reduce their PL efficiency. Several studies have reported overcoming poor PL in mechanically exfoliated and CVD grown MoS2, but such studies for chemically exfoliated MoS2 (Ce MoS2) have not been reported. Here, we report a solution based method of enhancing the PL of Ce MoS2 by reacting with molecules with suitable functional groups at high temperatures. Reaction with dodecanethiol (DDT) generates PL that is more intense than mechanically exfoliated MoS2 (Me MoS2) with high crystallinity and has a significantly broader range of wavelengths. Based on ultraviolet visible, Fourier transform infrared, X ray photoemission, and PL spectroscopy as well as transmission electron and PL imaging, we propose that the present method modifies PL properties of Ce MoS2 by simultaneously annealing, replacing molybdenum oxygen with molybdenum sulfur bonds, inducing strain, and generating a nanopolycrystalline structure. This work points to such defect engineering using molecules as an effective means to modify the properties of Ce MoS2 and layered transition metal dichalcogenides more generally.
author_names: Steven Gravelsins

Jangyup Son

Arend M van der Zande

Al-Amin Dhirani
title: A Scalable, Solution Based Approach to Tuning the Solubility and Improving the Photoluminescence of Chemically Exfoliated MoS2.
venue: ACS nano
year: 2019

abstract: Monolayer transition metal dichalcogenides (TMDs) have attracted a lot of attention for their applications in optics and optoelectronics. Molybdenum disulfide (MoS2) as one of those important materials, has been widely investigated due to its direct band gap and photoluminescence (PL) in visible range. Owing to the fact that the monolayer MoS2 suffers low light absorption and emission, surface plasmon polaritons (SPPs) are used to enhance both the excitation and emission efficiencies. Here, we demonstrate that the PL of MoS2 sandwiched between 200 nm diameter gold nanoparticle (AuNP) and 150 nm thick gold film is improved by more than 4 times compared with bare MoS2 sample. This study shows that gap plasmons can possess more optical and optoelectronic applications incorporating with many other emerging two dimensional materials.
author_names: Letian Yu

Di Liu

Xiaozhuo Qi

Xiao Xiong

Lan-Tian Feng

Ming Li

Guo-Ping Guo

Guangcan Guo

Xifeng Ren
title: Gap plasmon enhanced photoluminescence of monolayer MoS 2 in hybrid nanostructure
year: 2018

abstract: Alloying/doping in two dimensional (2D) materials is emerging as an increasingly important strategy due to the wide range bandgap tunability and versatility of these materials. Monolayer 2D transition metal dichalcogenide (TMD) alloy has been investigated both theoretically and experimentally in recent years. Here, we synthesized a bilayer MoS2(1 x)Se2x semiconductor alloy via the chemical vapor deposition technique. The as grown triangular MoS2(1 x)Se2x flakes with size of roughly 10 mm were observed by optical microscope and scanning electron microscope (SEM) The 1.4 1.9 nm thickness of the samples, as measured by AFM, means that bilayer MoS2(1 x)Se2x alloys were grown. The characteristic Raman modes related to Mo S and Mo Se vibrations were observed in the Raman spectrum. Two emission peaks were respectively found, corresponding to the A and B excitons in the photoluminescence (PL) spectrum. XPS measurements confirmed the Se doping of the alloy. The first principles calculation results show a contraction of the band gap value with the increase of Se doping in the MoS2 lattice. Compared with monolayer MoS2(1 x)Se2x alloy, the band bending effect is more obvious, and the bilayer MoS2(1 x)Se2x alloy still shows the direct band gap luminescence characteristic, which has certain guiding significance for the growth of two dimensional materials and for device preparation.
author_names: Wenwen Yao

Zhilin Kang

Jiajun Deng

Yan Chen

Qian Song

Xunlei Ding

Fang Lu

Wen-Jie Wang
title: Synthesis of 2D MoS2(1 x)Se2x semiconductor alloy by chemical vapor deposition
year: 2020

abstract: It is important to study the van der Waals interface in emerging vertical heterostructures based on layered two dimensional (2D) materials. Being atomically thin, 2D materials are susceptible to significant strains as well as charge transfer doping across the interfaces. Here we use Raman and photoluminescence (PL) spectroscopy to study the interface between monolayer graphene/MoS2 heterostructures prepared by mechanical exfoliation and layer by layer transfer. By using correlation analysis between the Raman modes of graphene and MoS2 we show that both layers are subjected to compressive strain and charge transfer doping following mechanical exfoliation and thermal annealing. Furthermore, we show that both strain and carrier concentration can be modulated in the heterostructures with additional thermal annealing. Our study highlights the importance of considering both mechanical and electronic coupling when characterizing the interface in van der Waals heterostructures, and demonstrates a method to tune their electromechanical properties.
author_names: Rahul Rao

Ahmad E Islam

Simranjeet Singh

Rajiv Berry

Roland Kenji Kawakami

Benji Maruyama

Jyoti Katoch
title: Spectroscopic evaluation of charge transfer doping and strain in graphene/ MoS2 heterostructures
venue: Physical Review B
year: 2019