Tunable UV-visible absorption of SnS₂layered quantum dots produced by liquid phase exfoliation

Abstract

4H-SnS layered crystals synthesized by a hydrothermal method were used to obtain via liquid phase exfoliation quantum dots (QDs), consisting of a single layer (SLQDs) or multiple layers (MLQDs). Systematic downshift of the peaks in the Raman spectra of crystals with a decrease in size was observed. The bandgap of layered QDs, estimated by UV-visible absorption spectroscopy and the tunneling current measurements using graphene probes, increases from 2.25 eV to 3.50 eV with decreasing size. 2-4 nm SLQDs, which are transparent in the visible region, show selective absorption and photosensitivity at wavelengths in the ultraviolet region of the spectrum while larger MLQDs (5-90 nm) exhibit a broad band absorption in the visible spectral region and the photoresponse under white light. The results show that the layered quantum dots obtained by liquid phase exfoliation exhibit well-controlled and regulated bandgap absorption in a wide tunable wavelength range. These novel layered quantum dots prepared using an inexpensive method of exfoliation and deposition from solution onto various substrates at room temperature can be used to create highly efficient visible-blind ultraviolet photodetectors and multiple bandgap solar cells.

Shear Exfoliation and Photoresponse of 2D‐Layered Gallium Selenide Nanosheets

“…According to Tauc's explanation, the relation between E g and absorption coefficient ( α ) of a direct bandgap semiconductor could be expressed as follows, where C is a constant and hν is the incident photon. [12, Here in our work, the E g value of GaSe was estimated to be around 2.1 eV.…”

Giant‐Enhanced SnS2 Photodetectors with Broadband Response through Oxygen Plasma Treatment

“…2D tin disulfide (SnS 2 ) is a vital metal dichalcogenide semiconductor primarily due to its layered structure, [ 1 ] wide‐bandgap (2.2–2.4 eV), [ 2,3 ] high absorption coefficient ≈10 4 cm −1 , [ 4 ] and as a cheap and sustainable source among others. [ 5,6 ] These novel properties have made it be widely studied in the application of electronic, [ 7–9 ] optoelectronic, [ 10–13 ] and energy storage. [ 4,5,14 ] In comparison with the famous transition metal dichalcogenides (MoS 2 , WS 2 ), [ 15–19 ] SnS 2 ‐based photodetector has been reported to demonstrate photoresponsivity as high as 261 A W −1 , [ 20 ] and 230 cm 2 V −1 s −1 carrier mobility for solution‐gated field‐effect transistors (FETs), [ 21 ] hence making it a promising candidate in electronic and optoelectronic applications.…”

Molybdenum Disulfide Nanosheet/Quantum Dot Dynamic Memristive Structure Driven by Photoinduced Phase Transition

“…Low‐dimensional materials and structures have attracted considerable interest owing to their outstanding physical and chemical properties. 2D crystals form strong in‐plane chemical bonds with weak out‐of‐plane bonding that allows them to easily exfoliate in 2D nanosheets and 0D QDs, 2D MoS 2 crystals can exist in the form of a thermodynamically stable semiconductor hexagonal phase (2H) with bandgaps varying from 1.2 to 1.9 eV, depending on thickness, and in the form of a metastable metallic tetragonal phase (1T) . The 1T‐MoS 2 phase can form when alkali ions or metal nanoparticles (Au) are intercalated between MoS 2 NS .…”

“…The dependence of the bandgap of QDs on the size was obtained in the effective‐mass approximation (Figure d) where ε is the dielectric constant, µ the reduced mass of exciton, and h is Planck's constant. In the calculations, the following values were used: µ = 0.13m 0 , E g = 1.9 eV, and ε = 12.6 .…”