Abstract
Capturing the fast rotational motion of single nanoparticles has been hindered owing to the difficulty of acquiring directional information under the optical diffraction limit. Here, we report the linewidth broadening of the electron spin resonance of single nitrogen vacancy (NV) centers that matches the rotational diffusion constant of the host nanodiamonds. When nanodiamonds are gradually detached from the substrates that they were fixed to, their optically detected spin resonance peaks are broadened by 1.8 MHz, which corresponds to the rotational diffusion constant of nanoparticles with a diameter of 11.4 nm from the Einstein–Smoluchowski relation.
Highlights
Rotations of objects characterize one of the fundamental properties of the dynamics and can be measured by various optical techniques
A new approach that could access the rotational motion of single nanoparticles is to exploit the electron spins of nitrogen vacancy (NV) centers in nanodiamonds
The faster timescale of nanoparticle rotation in the order of the rotational diffusion rate (MHz) has been theoretically predicted[23] as the random walk of the spin precession angle is accumulated as the the geometric phase fluctuation of the NV quantum system; the geometric phase fluctuation leads to dephasing of the electron spin coherence and broadens the electron spin resonance line of NV centers in cw-ODMR detection[23,24,25,26]
Summary
Rotations of objects characterize one of the fundamental properties of the dynamics and can be measured by various optical techniques. The faster timescale of nanoparticle rotation in the order of the rotational diffusion rate (MHz) has been theoretically predicted[23] as the random walk of the spin precession angle is accumulated as the the geometric phase fluctuation of the NV quantum system; the geometric phase fluctuation leads to dephasing of the electron spin coherence and broadens the electron spin resonance line of NV centers in cw-ODMR detection (continuous wave optically detected magnetic resonance)[23,24,25,26]. Our findings may provide a way to measure the rotational Brownian motion of single nanoparticles and enable the exploration of nano-scale fluid mechanics
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