A Chemical Nanoreactor Based on a Levitated Nanoparticle in Vacuum

Abstract

A single levitated nanoparticle is used as a nanoreactor for studying surface chemistry at the nanoscale. Optical levitation under controlled pressure, surrounding gas composition, and humidity provides extreme control over the nanoparticle, including dynamics, charge, and surface chemistry. Using a single nanoparticle avoids ensemble averages and allows studying how the presence of silanol groups at its surface affects the adsorption and desorption of water from the background gas with excellent spatial and temporal resolution. Herein, we demonstrate the potential of this versatile platform by studying the Zhuravlev model in silica particles. In contrast to standard methods, our system allowed the observation of an abrupt and irreversible change in scattering cross section, mass, and mechanical eigenfrequency during the dehydroxylation process, indicating changes in density, refractive index, and volume.

Temperature-free mass tracking of a levitated nanoparticle

“…2 does not exceed 1 s, which corresponds to a relative pressure change of about 0.5%. Since the heating of particles by the laser is inversely proportional to the air pressure in a vacuum environment, [12,28] by fitting the pressure-temperature data of the particle before the abrupt change point (shown in Fig. 4(b)), we can obtain that the internal temperature increase of the particle does not exceed 2.5 K at the moment of the abrupt change.…”

“…The loss of water could introduce a decrease in the oscillator's eigenfrequency and calibration coefficient which has been confirmed by the experiment. [12,22,28,30] The sudden loss of the water molecules inside (or on the surface) of the silica nanoparticles cannot be explained by the loss of surface water layers. Because the water molecules are connected through hydrogen bonds which have a large range of bond energies and correspond to a wide range of desorption temperatures.…”

“…[10,11] The characterization of particle properties is an essential part of nanoparticle and microparticle research, including the weighing of their mass. [12][13][14][15][16][17][18][19][20][21][22] The mass of a nanoparticle is related to its density, size, fill rate, composition, and other properties that provide important criteria for the identification of nanoparticles. Conventionally, a nanoparticle's mass is estimated using data on density, particle size analysis, and particle properties measured on a bunch of particle powder.…”

“…[16,28,29] A significant reduction in the mass of silica nanoparticles is observed. [12,22,28,30] However, comprehensive investigations of this mass-changing process are still lacking. Considering that the mass of most materials changes with increasing temperature, simultaneous high-precision measurement of the mass and temperature of nanoparticles is essential for investigating their property transitions.…”

“…Only one of the mass or temperature can be measured, while the other has to be known beforehand. [31,32] Although there are attempts to estimate the particle temperature by using the scattered light intensity and the gas pressure, [12] the accuracy and reliability of the temperature obtained by this method are very poor.…”