Manipulation and printing of single microscopic particles in fluids

Abstract

Microscopic particles in fluids have intensively been regarded as a fundamental material system in fields as diverse as physics, chemistry, biomedicine, and engineering. The advanced utilization necessitates the ability to manipulate and print such small particles at a single-entity level. However, the fundamental and technological challenges associated with Brownian motion or complex environment remain unresolved. Therefore, it is indeed necessary to develop new techniques that can handle single, functional micro/nanoparticles on demand. This thesis introduces novel strategies to (1) manipulate and (2) print single micro/nanoparticles in fluids. First, we developed an X-ray-powered wireless manipulation technique for microparticles in the aqueous environment. In this study, we for the first time discovered that half-metal coated Janus microparticles can be propelled under X-rays by radiolysis of water that is the decomposition of water molecules due to ionizing radiation. Since X-rays hold an excellent penetrating power deep into the medium, our new technique could enable single particle manipulation in the opaque environment such as whole-body systems where other light sources (UV-Vis-NIR) are not easy to access. Our experimental methodology that enables “steer” and “observe” the X-ray-propulsive particles at a single-particle level is to use a real-time transmission X-ray microscope (TXM) with nanoscale resolution. The Monte Carlo simulation of X-rays dosimetry was performed to investigate the effects of X-rays on the Janus particles. Second, we developed a direct single nanoparticle printing method for nanodiamonds with defect centers (e.g., nitrogen-vacancy centers), which are the most promising room-temperature quantum material but incompatible with traditional micro/nanofabrication processes. The key idea is to exploit electrohydrodynamic dispensing of nanodiamond-laden fluid droplets with sub-attoliter (10-18 L) volume directly on the substrate. We experimentally succeed in direct printing of NV-center nanodiamonds at a single quantum level with a spatial precision of 452 nm finer than the diffraction limit of their fluorescence wavelength. The detailed experimental conditions for controlling the printing quantity and precision will be discussed in this thesis. Our method does not need any lithographic or transfer process, therefore, has the potential to offer a simple and effective route to integrate quantum NV-centers into various nanophotonic quantum devices.