Ultrafast Carrier and Lattice Dynamics in Plasmonic Nanocrystalline Copper Sulfide Films

Abstract

Excited carrier dynamics in plasmonic nanostructures determines many important optical properties such as nonlinear optical response and photocatalytic activity. Here it is shown that mesoscopic plasmonic covellite nanocrystals with low free‐carrier concentration exhibit a much faster carrier relaxation than in traditional plasmonic materials. A nonequilibrium hot‐carrier population thermalizes within first 20 fs after photoexcitation. A decreased thermalization time in nanocrystals compared to a bulk covellite is consistent with the reduced Coulomb screening in ultrathin films. The subsequent relaxation of thermalized, equilibrium electron gas is faster than in traditional plasmonic metals due to the lower carrier concentration and agrees well with that in a bulk covellite showing no evidence of quantum confinement or hot‐hole trapping at the surface states. The excitation of coherent optical phonon modes in a covellite is also demonstrated, revealing coherent lattice dynamics in plasmonic materials, which until now was mainly limited to dielectrics, semiconductors, and semimetals. These findings show advantages of this new mesoscopic plasmonic material for active control of optical processes.

Carrier density tuning in CuS nanoparticles and thin films by Zn doping via ion exchange

“…We also fabricated thin monolayered films of these nanoparticles with optical properties consistent with the reduction of the plasma frequency during doping. The described approach is important for controlling both plasmonic properties and carrier relaxation rate in nanocrystals 32 as both depend on the free-carrier concentration. The demonstrated tuning of the free-carrier concentration and the associated plasmonic properties of CuS nanocrystals is important for the development new plasmonic platforms with controllable optical properties required for numerous applications in both catalysis and nonlinear optics.…”

“…Thin films of these nanoparticles exhibit optical properties consistent with the observed plasma frequency changes. The control over a free-carrier density was also favorable for tuning the relaxation time of hot-carriers in nanocrystals, 32 required for optimisation of this nanomaterial in photochemical and nonlinear optical applications.…”

Electromagnetic Interference Shielding with 2D Copper Sulfide

“…Furthermore, CuS has a lower carrier concentration (∼3 × 10 21 cm −3 ) than noble metals, which renders the Coulomb screening to be relatively reduced. 50 As a result, CuS has much faster electron−phonon scattering rates compared to conventional metals such as Au and Ag. The fast electron− phonon scattering associated with local carrier relaxation contributes to EM energy being more easily transformed into thermal energy or other forms of energy.…”

“…It has been theoretically predicted that surfaces with Cu and S terminations (depicted in Figure b) have the lowest surface energy, and due to the different terminations of the surface and different electronegativities of Cu and S atoms, the cleaved surfaces favor the formation of local surface dipole layers, which are depicted in Figure d. , Due to the small grain sizes of the CuS nanosheet, the polarization loss from surface dipole layers is greatly enhanced and contributes to increased absorption efficiency, which in turn improves the overall shielding performance (see Supplementary Note 2 for further explanations). Furthermore, CuS has a lower carrier concentration (∼3 × 10 21 cm –3 ) than noble metals, which renders the Coulomb screening to be relatively reduced . As a result, CuS has much faster electron–phonon scattering rates compared to conventional metals such as Au and Ag.…”

Interfacing CrOx and CuS for synergistically enhanced water oxidation catalysis

“…On the other hand, CuS has been proved to assist accelerated charge transfer when loaded on the surface of known catalysts such as TiO 2 [25][26][27] and MoS 2 [28]. It possesses a layered crystal structure with weak van der Waals interactions between individual planar Cu 2 S 2 double layers [29,30]. Owing to this particular feature, it can offer a permeable channel for ion adsorption and transport.…”