Desorption-Mediated Motion of Nanoparticles at the Liquid–Solid Interface

Abstract

Nanoparticles (NPs) confined in thin layers of liquid within liquid cells used for in situ transmission electron microscopy (TEM) move very slowly, in contrast to free particles in bulk liquid. The reason is still poorly understood. Here, we tracked gold NPs moving in water at the liquid−solid interface with in situ TEM at rates of 100 frames per second. The recorded motion exhibited three key features: (1) it was made up of sustained sequences of "sticky" motion where NPs only moved a few nanometers each time; (2) sporadic long "flights" where the NPs traveled tens to hundreds of nanometers between frames; and (3) "flights" are accompanied by intermittent, fast pivoted rotations. Trajectory analysis shows that the displacements follow a truncated Levy distribution, pointing to desorptionmediated motion of NPs at the liquid−solid interface. We further associate pivoted rotations with a transient "weakly adsorbed" state between desorption and adsorption of NPs. The frequency of desorption was also controlled by electron flux and solution chemistry. We propose that the pattern of motion is the result of an inhomogeneous distribution of surface charges on silicon nitride (SiN x ). Such insight into the interactions between NPs and solid surfaces in liquids is useful for understanding dynamics at liquid−solid interfaces and has general implications for microfluidics, nanotribology, sensing, and self-assembly.

Long-Range Self-Assembly via the Mutual Lorentz Force of Plasmon Radiation

“…S1 (b)] that is marked by stacked Au NPs. We expect that the primary role of the substrate is to suppress the Brownian motion [35] [36]. In bulk NP solution, we measure the diffusion coefficient D = 1.6· 10 -12 m 2 /s via dynamic light scattering, and the equivalent force is expected to be orders of magnitude larger than the mutual Lorentz force calculated here.…”

Liquid‐Phase Transmission Electron Microscopy for Studying Colloidal Inorganic Nanoparticles

“…During TEM measurements, the electron beam induces a positive charge onto the Si 3 N 4 window and the induced surface charge affects the motion of the charged nanoparticles . Liu et al demonstrated that the movement of positively charged (cetyltrimethylammonium (CTA)) and negatively charged (citrate) gold nanoparticles is significantly different because of the positively charged window surface .…”

“…Thus, nanoparticles with induced dipoles are adsorbed onto the wall surface. Chee et al discovered that gold nanoparticles exhibit sticky motion, so that the particles only move a few nanometers with rotational motion on the Si 3 N 4 surfaces ( Figure a,b) . When the absorbed nanoparticles were desorbed from the window with thermal vibration, they flew ≈50 nm and stuck again with fast pivoted rotations.…”

Direct Observation of Growth and Self‐assembly of Pt Nanoclusters in Water with the Aid of a Triblock Polymer Using in situ Liquid Cell Transmission Electron Microscopy (TEM)

“…It has been reported that the high energy electron beam can knock away electrons in the insulating SiN x membrane, making it positively charged, whose charge may then be partially transferred to a nano object on the window and let the nano object be electrostatically repelled from the surface. [30,48] It can be expected that the electron irradiation would cause charge build-up in the imaged region ( Figure 4B). [30] These charge effect would be more obvious in the thin liquid region, as the electrical charges shall be harder to get carried away by the thinner fluid layer.…”