Effect of Material and Shape of Nanoparticles on Hot Carrier Generation

Abstract

Nonradiative decay of photoexcited plasmons generates energetic nonthermal charge carriers. These hot charge carriers play a major role in plasmonic photocatalysis and photovoltaics. Therefore, establishing the relationship between the hot carrier generation efficiency and the structural and chemical parameters of nanoparticles is crucial for developing highly efficient plasmonic catalysts and photovoltaic materials. In this study, we compare the quantum efficiency of hot carrier generation between gold (AuNPs) and silver nanoparticles (AgNPs), and spherical (AuNSs) and cubic gold nanoparticles (AuNCs). We construct nanoparticle-on-mirror (NPoM) systems where reactant molecules are positioned in the nanogaps between the nanoparticles and gold films. Excitation of the NPoM at 785 nm, followed by the detection of products using surface-enhanced Raman spectroscopy allows us to measure the plasmon-driven reaction yields. Dividing the reaction yield by the calculated absorption cross section at the excitation laser wavelength provides the efficiency of hot carrier generation per absorbed photon. We reveal that AgNPs are more effective at generating hot carriers than AuNPs, which is consistent with the higher electron-surface scattering rate of AgNPs. The hot carrier generation of AuNCs is marginally better than that of AuNSs, which can be attributed to the enhanced electric fields inside the AuNCs in the nanogap region. This study contributes to a rational design of plasmonic catalysts or photovoltaic materials of higher efficiencies.

Photodissociation of H2 on Ag and Au Nanoparticles: Effect of Size and Plasmon versus Interband Transitions on Threshold Intensities for Dissociation

“…The decay rate is maximum ( b = −1.34) with minimum amplitude ( a = 6.4 × 10 12 ) for Ag n H 2 systems with plasmon frequency (ω 0 = 2.7 eV). This conclusion is in agreement with a recent experiment where Ag NPs are found to be more efficient than Au NPs in generating hot electrons . However, for Au n H 2 systems, the high-frequency (ω 0 = 4 eV) driving provides a larger decay rate as compared to the low-frequency driving as there is a significant interband transition amplitude, see Figure b, while the plasmon amplitude is weak.…”

“…This conclusion is in agreement with a recent experiment where Ag NPs are found to be more efficient than Au NPs in generating hot electrons. 25 However, for Au n H 2 systems, the high-frequency (ω 0 = 4 eV) driving provides a larger decay rate as compared to the lowfrequency driving as there is a significant interband transition amplitude, see Figure 2b, while the plasmon amplitude is weak. For Ag n H 2 particles, there are dominant plasmonic transitions for n ≥ 85, and the plasmon resonance shows larger efficiency for dissociation as compared to the interband transition.…”

“…This can circumvent the problems associated with hot-carrier generation and decay, but efficiency is limited by the requirement that the metal atoms be very near the nanoparticle surface, and that the energy of the charge transfer matches the excitation energy. , LSPR-induced dissociation of small important molecules including H 2 dissociation, − H 2 O splitting, , CO 2 reduction, , NH 3 decomposition, and others , has been reported. The efficiency of plasmon-enhanced dissociation is determined by several factors that influence hot-carrier generation and charge transfer dynamics, including the shape and size of the NPs, and pulse properties such as wavelength, pulse duration, and intensity of the photoexcitation. , …”

“…11,12 LSPR-induced dissociation of small important molecules including H 2 dissociation, 13−16 H 2 O splitting, 17,18 CO 2 reduction, 19,20 NH 3 decomposition, 21 and others 22,23 enhanced dissociation is determined by several factors that influence hot-carrier generation and charge transfer dynamics, including the shape and size of the NPs, and pulse properties such as wavelength, pulse duration, and intensity of the photoexcitation. 24,25 The generation of hot carriers and charge transfer into surface molecules has been described using various theoretical models 26,27 and ab initio calculations. 28,29 Real-time (RT) dynamics of NPs provide an explicit time-dependent perspective and a natural choice when a time-dependent electric field interacts with the system to generate hot carriers, in contrast to the more limited picture obtained from linear response frequency domain calculations.…”

Core–satellite–satellite hierarchical nanostructures: assembly, plasmon coupling, and gap-selective surface-enhanced Raman scattering

“…13,30,31 Nanogaps promote the generation of hot charge carriers, thereby enabling a reaction that is unfeasible without the nanoparticles. [32][33][34][35][36] Plasmonic heating further increases the temperature in the nanogaps. 21,24,37 Thus, nanogaps play a crucial role in plasmonics.…”