Tracking the Effects of Ligands on Oxidative Etching of Gold Nanorods in Graphene Liquid Cell Electron Microscopy

Abstract

Surface ligands impact the properties and chemistry of nanocrystals, but observing ligand binding locations and their effect on nanocrystal shape transformations is challenging. Using graphene liquid cell electron microscopy and the controllable, oxidative etching of gold nanocrystals, the effect of different ligands on nanocrystal etching can be tracked with nanometer spatial resolution. The chemical environment of liquids irradiated with high-energy electrons is complex and potentially harsh, yet it is possible to observe clear evidence for differential binding properties of specific ligands to the nanorods’ surface. Exchanging CTAB ligands for PEG-alkanethiol ligands causes the nanorods to etch at a different, constant rate while still maintaining their aspect ratio. Adding cysteine ligands that bind preferentially to nanorod tips induces etching predominantly on the sides of the rods. This etching at the sides leads to Rayleigh instabilities and eventually breaks apart the nanorod into two separate nanoparticles. The shape transformation is controlled by the interplay between atom removal and diffusion of surface atoms and ligands. These in situ observations are confirmed with ex situ colloidal etching reactions of gold nanorods in solution. The ability to monitor the effect of ligands on nanocrystal shape transformations will enable future in situ studies of nanocrystals surfaces and ligand binding positions.

Visualizing Ligand-Mediated Bimetallic Nanocrystal Formation Pathways with in Situ Liquid-Phase Transmission Electron Microscopy Synthesis

“…Ideally, the electron beam exclusively reduces metal precursors and does not drive undesirable side reactions like oxidation of organic capping ligands or nanoparticles. 41,42 In this paper, we uncover in situ LP-TEM electron beam synthesis conditions for alloyed bimetallic nanoparticles that preserve the salient chemistry of ex situ flask synthesis (Figure 1a). We chose AuCu-alloyed nanocrystals as a model system because of their potential application as a highly active CO 2 electroreduction catalyst.…”

The role of organic ligand shell structures in colloidal nanocrystal synthesis

“…The nature of the ligands dictates the inorganic nanocrystal surface structure 11,19,21,22 , and has been designed to promote surfaces that minimize electronic trap states in quantum dots 15,17,23,24 . A variety of head groups are used to terminate colloidal nanocrystal surfaces, such as carboxylates, amines, phosphonates, thiols and halides, and often a mixture of capping groups is used [15][16][17]20,[25][26][27][28][29][30][31][32] . The amount, type and impurities of the ligands used in nanocrystal synthesis have implications for the nanocrystal size, shape, crystal structure and stability, as well as for their optical and electronic properties 33,34 .Head groups play a critical role in the control of colloidal nanocrystal growth, and different nanocrystal shapes can be formed by manipulating head group binding.…”

Applications of in situ electron microscopy in oxygen electrocatalysis

“…However, the presence of liquid and the cell windows often significantly reduce the spatial resolution of the acquired images. Consequently, it is generally not possible to achieve atomic resolution in LC-(S)TEM, except in a few cases where graphene is used as the cell window material and the liquid layer is very thin [40][41][42] . Furthermore, the radiolysis of water caused by the electron beam irradiation produces various [71] , (B) an in situ electrochemical liquid cell placed in the optical path of TEM, and (C) an electrochemical microchip with micro-fabricated counter electrode (CE), working electrode (WE) and reference electrode (RE).…”