Single‐Electron Transfer in Nanoparticle Solids

Abstract

Monolayer-protected nanoparticles exhibit unique electronic conductivity properties, which can be tailored by the combined effects of the conductive inorganic cores and the insulating organic shells. In scanning tunneling spectroscopic (STS) studies of isolated particles, [1][2][3] the resulting currentpotential (I-V) profile generally exhibits a Coulomb blockade in the central region, beyond which a Coulomb staircase (single-electron transfer; SET) may be identified. Such unique characteristics are the fundamental basis for the development of single-electron transistors.[4] By contrast, in studies of nanoparticle ensembles that form (sub)micrometer-thick solid films, [5][6][7][8] typically only linear (Ohmic) I-V behavior is observed, especially at a relatively high voltage bias, because of rampant structural defects within these particle solids that facilitate interparticle charge transfer (e.g., percolation effects). Fundamentally, the collective conductivity properties of organized assemblies of particles are found to be determined not only by the particle chemical structure (core size, shape, and surface ligands), but by the specific chemical environments and interparticle interactions as well.[9]Whereas the electrochemical analogue of the Coulombstaircase phenomenon has been observed in studies of particles dissolved in an electrolyte solution, [10] quantized charge transfer in nanoparticle solids has remained elusive. Thus, an immediate question arises-can single-electron transfer be realized with nanoparticle solids? The fact that nanoparticle solid thin films (monolayers or more complicated organized assemblies) can be readily fabricated by using the LangmuirBlodgett (LB) or self-assembly technique means that achieving solid-state single-electron transfer will offer a significant advance towards the development of nanoparticle-based single-electron transistors [4,11] without the necessity of sophisticated instrumentation (e.g., a scanning tunneling microscope). Herein we report a recent breakthrough using monolayers of moderately disperse gold nanoparticles, in which well-defined single-electron transfer is observed for the first time in the solid state. Our primary goal here is to identify key parameters that are important to realize SET in nanoparticle solid films. As the structural intermediate between isolated particles and thick particle films, particle monolayers exhibit unique electronic conductivity properties. For instance, Heath and co-workers [12] observed an insulator-metal transition of a Langmuir monolayer of alkanethiolate-protected silver (AgSR) nanoparticles when the interparticle spacing was sufficiently small. Such a transition was also manifested in electrochemical impedance measurements, [13] and in scanning electrochemical microscopy (SECM) studies. [14,15] However, in these early studies, [12][13][14][15] the particle-conductivity profiles did not exhibit the characteristics of quantized charging of the particle molecular capacitance, most probably because the particles used were t...

Discrete charge transfer in nanoparticle solid films

“…The overall I-V profiles are in fact very similar to those with a dropcast thick film of the same C6Au particles. 35 It should be noted that the above experimental results represent the first observations of single electron transfer across a particle solid thin film (and the results are very reproducible). 35 The overall behavior is analogous to that of STM-based measurements of individual nanoparticles (both are in the twoelectrode mode).…”

“…35 Fig. 3 (panels A and B) shows the solid-state I-V profiles and differential pulse voltammograms (DPVs) of an LB monolayer of C6Au nanoparticles deposited onto an IDA electrode surface at L = 0.72 nm.…”

“…35 Fig . 4 depicts the I-V profiles at varied temperatures of a C6Au particle monolayer deposited at a shorter interparticle separation, L = 0.62 nm, where the I-V responses exhibit only linear (ohmic) characters within the entire temperature range of 160 to 320 K (and the conductance increases with increasing temperature).…”

Photoconductivity of Langmuir−Blodgett Monolayers of Silicon Nanoparticles

“…38 Such a temperaturedependent variation of charge transfer mechanisms has also been observed with ensembles of transition-metal nanoparticles 39,40 as well as semiconductor quantum dots. 38 Furthermore, it should be noted that at room temperature the particle conductivity reaches ca.…”

One-pot organometallic synthesis of well-controlled gold nanoparticles by gas reduction of Au(I) precursor: a spectroscopic NMR study

“…MNPs are now commonly used in many applications such as electronics [1,2], catalysis [3], environmental sciences [4,5], medicine [6,7], and sensors [8][9][10]. Indeed, highly sensitive miniature sensors require advanced technology coupled with fundamental knowledge of biology, material sciences, and chemistry.…”