Laser ablation is a method for fabricating various kinds of nanoparticles including semiconductor quantum dots, carbon nanotubes, nanowires, and core shell nanoparticles. In this method, nanoparticles are generated by nucleation and growth of laser-vaporized species in a background gas. The extremely rapid quenching of vapor is advantageous in producing high purity nanoparticles in the quantum size range (< 10 nm). In this review, the formation mechanism of nanoparticles by laser ablation is summarized. Recent progress on the control of nanoparticle size and the challenges for functional nanoparticle synthesis by advanced laser ablation technology are then discussed.

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Our group developed a high-performance unipolar charger for sub-10-nm particles using a surface-discharge microplasma by increasing the charging time and minimizing the electrostatic deposition loss of the charged particles. An investigation of the discharge voltages of various discharge voltage waveforms demonstrated that a sinc function of time, t, that is, (sin ωt)/ωt with a bias voltage, achieved a high extrinsic charging efficiency (a high yield of charged particles) by generating a high concentration of ions and suppressing the electrostatic deposition of the charged particles. In trial operation at the optimal discharge voltage and an aerosol flow rate of 2.5 L/min, the charger attained intrinsic and extrinsic charging efficiencies of 79.3 and 61.4% for 10-nm particles and intrinsic and extrinsic charging efficiencies of 48.0 and 34.6% for 5-nm particles, respectively.

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