Tunable Direct Bandgap Optical Transitions in MoS₂ Nanocrystals for Photonic Devices

Abstract

Highly luminescent MoS 2 nanocrystals (NCs) with controlled size distribution have been achieved using a simple yet inexpensive and impurity free sono-chemical exfoliation method followed by gradient centrifugation. The size of nanocrystals could be varied within the diameter range of ∼4 to 70 nm. Typical MoS 2 nanocrystal has exhibited high crystalline quality with 0.25 nm lattice fringe spacing for (002) planes for 2-H phase of MoS 2 . Raman spectra has revealed that both out-of-plane and in-plane vibrational modes are stiffen due to the edge effect of MoS 2 NCs. The size tunable optical properties of MoS 2 NCs have been investigated by optical absorption and photoluminescence spectroscopy. The coexistence of direct band gap emission from 2D MoS 2 nanosheets and quantum confined nanocrystals has been achieved. A strong and tunable photoluminescence (560−518 nm) emission due to the quantum size effect of tiny NCs below a critical dimension is reported for the first time. The photocurrent measurement of the Au/MoS 2 −NCs/Au junction has been performed at room temperature to investigate the optical responsivity and switching characteristics, demonstrating the potential of MoS 2 nanocrystals for next generation photonic devices.

Nano Ag‐Decorated MoS2 Nanosheets from 1T to 2H Phase Conversion for Photocatalytically Reducing CO2 to Methanol

“…Meanwhile, multilayer crystals of MoS 2 have semiconductor properties with an indirect band gap of %1.3 eV, [5,6] whereas monolayer MoS 2 shows a direct optical band gap of %1.9 eV. [7][8][9] Such a kind of MoS 2 with an adjustable band gap, therefore, has great significance in research and potential applications in photocatalysis, photoelectronic devices, [10][11][12][13] solar cells, and so on. [14][15][16][17][18][19][20][21][22][23][24] To expand the response range of MoS 2 to UV light, the researchers have explored some methods such as semiconductor recombination, surface reduction, ion doping, precious metal deposition, etc.…”

Novel silicon compatible p-WS22D/3D heterojunction devices exhibiting broadband photoresponse and superior detectivity

“…8 However, few studies have been performed to increase the light-matter interaction in graphene by incorporating it within the microcavity or making hybrid plasmonic nanostructures. [9][10][11] On the other hand, two dimensional TMDs have been found to be attractive in various electronic and optoelectronic devices such as field effect transistors (FET), 12 light emitting diodes (LEDs), 13 photodetectors [14][15] etc. due to their layer dependent energy gap modulation and vivid absorption properties.…”

Emerging technologies for high performance infrared detectors

“…Recently this limitation has been addressed by 2D material synthesized with other semiconductor material, nanostructured or different 2D materials. For example, MoS 2 nanocrystal on silicon on insulator structure [155,156], MoS 2 /bp heterojunctions [157], graphene/ MoTe 2 /graphene heterostructures [158], graphene/MoS 2 heterojunctions, and WSe 2 /MoS 2 heterojunction photodetectors [157] show significant improvement in responsivity to the visible and NIR regions. A recent review paper on different dimensional material heterostructures [159] summarizes the works on different dimensional material for increasing the responsibility of the 2D material in the IRPD.…”