Metal Nanoclusters Modify the Band Gap and Maintain the Ultrathin Nature of Semiconducting Two-Dimensional Materials

Abstract

Modifying the band gap of semiconducting two-dimensional materials (S2DM) such as monolayer molybdenum disulfide (MoS 2 ) is useful in ultrathin optoelectronic applications. Electron doping is an efficient technique to alter the electronic band gap and change exciton binding energy of MoS 2 , thus modifying the optical band gap. Photoexcited silver nanoclusters (AgNCs) can produce a large number of energetic hot electrons with a lifetime in the hundreds of picosecond timescale. These hot electrons can inject into the conduction band of a single-layered MoS 2 , thereby modifying its optoelectrical properties when AgNCs come in contact with the sheet. Additionally, increasing AgNC coverage density on the MoS 2 surface increases the electron doping density. At low AgNC coverage density, the absorption and photoluminescence (PL) spectrum of MoS 2 are red-shifted as a result of band gap renormalization. The magnitude of the red shift increases as the coverage density of AgNCs is increased before blue-shifting remarkably at a high AgNC coverage. The blue shift is attributed to the population of the high-energy dark excitonic states. The optical band gap of monolayer MoS 2 is also tuned by integration with silver nanodisks (AgND). Unlike the high efficiency and controllable modification of band gap of MoS 2 by AgNCs, photoexcited AgNDs exhibit opposing effects on the band gap of MoS 2 . Photoexcited AgNDs produce a strong electromagnetic field, which changes the spinorbital coupling inside the MoS 2 and so the electronic band gap of MoS 2 . The plasmon field decays generating hot electrons which cross the nanoparticle/MoS 2 Schottky barrier and inject into the conduction band of MoS 2 within a hundred femtoseconds. The limitation of hot electrons of AgNDs is ascribed to the delay in the electron injection process leading to the relaxation of hot electrons, which generates heat that induces the transformation of 2H semiconducting MoS 2 into metallic 1T.

Electron Doping of Semiconducting MoS2 Nanosheets by Silver or Gold Nanoclusters

“…The liquid exfoliation technique was used to prepare the monolayered MoS 2 nanosheets . In summary, 0.15 g of MoS 2 powder (Sigma-Aldrich, 2 μm) was dispersed in 150 mL of N -methyl-2-pyrrolidone (NMP, Sigma-Aldrich) and then sonicated with a probe sonicator (Qsonica, Q700 with a 1/2 inch diameter tip) at a 5 s on/off interval for 3 h at a temperature below 15 °C. − The solution was then centrifuged (Beckman Coulter, Allegra 64R) at 2 K rpm for 10 min to remove large nonexfoliated particles.…”

Molybdenum disulfide composite materials with encapsulated copper nanoparticles as hydrogen evolution catalysts

“…To improve the catalytic performance of those materials, some efficient strategies have been employed. One is to enlarge the specic number of active sites by, for example, exposing more edge sites by introducing more surface defects, [11][12][13][14] one is to dope either metallic or chalcogen heteroatoms into the lattice of this basal 2D catalyst to achieve synergistic effect, 15,16 and the other is to reduce the resistance of material for the sake of achievement of a high current density with a lower overpotential in water electrolysis. [17][18][19][20] In the last routine, graphene and nanotube might be the most popular choice for conductivity enhancement.…”

Tuning the Optical Band Gap of Two-Dimensional WS2 Integrated with Gold Nanocubes by Introducing Palladium Nanostructures

“…10,18 Mono-or few-layered 2H-WS 2 exhibits a direct band gap of ∼2.01 eV, 19 which is attributed to the valance−conduction band electron transitions at the K/K′ point of the Brillouin zone. 18,20 Different techniques are used for electron doping from electron-donating systems to S2DMs including conjugated polymers, 21 plasmonic nanoparticles, 22 and metallic nanoclusters. 22 Plasmonic nanoparticles, for example, gold or silver nanoparticles, interact strongly with the electromagnetic radiation of resonant frequency due to the localized surface plasmon resonance (LSPR) phenomena.…”

“…18,20 Different techniques are used for electron doping from electron-donating systems to S2DMs including conjugated polymers, 21 plasmonic nanoparticles, 22 and metallic nanoclusters. 22 Plasmonic nanoparticles, for example, gold or silver nanoparticles, interact strongly with the electromagnetic radiation of resonant frequency due to the localized surface plasmon resonance (LSPR) phenomena. 23−27 Photoexcitation of plasmonic nanoparticles generates a strong electromagnetic plasmon field and LSPR absorption and scattering spectrum.…”

“…The unique optoelectrical properties of S2DMs arise from their ability to generate highly energetic localized excitons when photoexcited. − These excitons have large electron–hole binding energy (the Coulomb interactions between the electrons and holes). − The localized excitons lead to narrowing the line width of the photoluminescence spectrum (PL) of S2DMs. , Electron doping of S2DMs changes the exciton binding energy and optical band gap ( E Opt ) and thus changes the band edges. − E Opt is used to determine the quasiparticle band gap ( E g ) after adding the exciton binding energy . Tuning the density of electron doping and dielectric function on the surface of S2DMs changes the exciton binding energy, thus E Opt . , Mono- or few-layered 2H-WS 2 exhibits a direct band gap of ∼2.01 eV, which is attributed to the valance–conduction band electron transitions at the K/K′ point of the Brillouin zone. , Different techniques are used for electron doping from electron-donating systems to S2DMs including conjugated polymers, plasmonic nanoparticles, and metallic nanoclusters …”