Metallic Nanoparticle Network for Photocurrent Generation and Photodetection

Abstract

Metallic gold (Au) nanoparticles (NPs) are of great interest in nanoelectronics, optics, and biotechnology. [1] In particular, Au NPs exhibit surface plasmon resonance (SPR) [2] that is a result of the collective oscillation of conduction electrons induced by incident electromagnetic radiation. When the size of a metal particle is smaller than the wavelength of incident light, the extinction function is dominated by absorption rather than scattering.[3] Therefore, Au NPs exhibit enhanced photoabsorption in the UV-vis region. Indeed, the SPR characteristic of metallic NPs has been utilized for various applications including molecular sensing [4] and sub-wavelength photonics.[5]Photocurrent generation and photodetection are usually based on semiconductors such as Si and TiO 2 . [6,7] The semiconductor band-gap limits the conduction of intrinsic carriers, while the photoexcited electrons have sufficient energy for transport in the conduction band (CB), thus generating relatively large photocurrent. In a metal, however, there is large population of intrinsic electrons near the Fermi level. When a bias is applied, the number of intrinsic conduction electrons far exceeds that of photoelectrons, such that the intrinsic current is much larger than the photocurrent, rendering the detection of photocurrent impractical in current-voltage (I-V) measurements. This is why there has been almost no report in the literature on the usage of metallic NPs for photocurrent applications.[8] Most works [9][10][11][12] use the SPR behavior of Au NPs to enhance photoabsorption in semiconductors. For example, Au or Ag NPs are dispersed in a semiconductor TiO 2 matrix [9] or on Si [10][11][12] to improve the photon-electron conversion. It is hoped that the enhanced photoabsorption associated with Au NPs will trap more incident light and promote charge separation in the semiconductor. In such a scheme, the photoelectrons are still excited from the semiconductor, while the Au NPs act as an absorption-enhancing agent of the semiconductor. There is only one work briefly reporting the photoconductivity of Au NPs, but neither the detailed conduction mechanism nor the application of photodetection are discussed. [8] In this paper, we report the observation of photoexcitation and photocurrent generation directly from ligated metallic NPs instead of semiconductors. We show that Au-NP passivation by alkanethiol ligands significantly hinders the intrinsic electron conduction, thus increasing the relative ratio of photocurrent to intrinsic current, leading to the photoelectron-dominated current in the NP network. We also discuss the mechanism for photocurrent generation and conduction in the Au NP system, and demonstrate the applicability of metallic Au NPs for photodetection.We first present the observation of photocurrent generation in the Au-NP film prepared according to an early work.[13] A detailed description on the preparation and characterization of Au NPs is provided in the Supporting Information (see SI-i and ii). The right inset of Figure 1...

A Percolating Membrane with Superior Polarization and Power Retention for Rechargeable Energy Storage

“…So the thickness‐assisted ion conductivity in Figure 2b is an outcome of the enhanced site connectivity of the percolation membrane. In the literature, similar thickness‐dependent electronic conduction has been observed for percolating Au nanoparticle assembles 24, 25. However, the results in Figure 2b represent the first observation of ionic conduction that is also governed by the percolation mechanism.…”

Unprecedented efficient electron transport across Au nanoparticles with up to 25-nm insulating SiO2-shells

“…Thus, it appears that photocurrent enhancement is correlated with the strength of plasmon-induced d → sp interband transitions in AuNPs, which increase in their absorption cross-section at shorter wavelengths 35 . In the blue-visible region, higher energy electrons were excited and participated in the electron transfer, which finally increase the tunneling probability 36 . In addition, complex plasmonic nanoparticle coupling among 2D close-packed nanomembrane may also result in enhanced interaction between nanoparticles and optical radiation, which ultimately leads to the increase of tunneling current with decreasing the wavelength of light 37–39 .…”

Thermodynamic theory of the plasmoelectric effect

“…Recently, there has been significant interest in the relationship between plasmonic and electrical phenomena 1 2 3 4 5 6 7 8 9 10 11 . For example, localized plasmon resonances have been shown to influence the photoconductivity of films of metal nanoparticles coated with self-assembled monolayers 12 13 , and plasmon-induced hot electrons have been shown to generate macroscopic currents in plasmonic energy conversion devices 6 . Furthermore, it has been demonstrated that electrostatic charging influences the plasmon resonance frequency 11 .…”