Bangwoo Han

Parallel patterning of nanoparticles via electrodynamic focusing of charged aerosols

The development of nanodevices that exploit the unique properties of nanoparticles1,2 will require high-speed methods for patterning surfaces with nanoparticles over large areas and with high resolution3,4,5,6. Moreover, the technique will need to work with both conducting and non-conducting surfaces. Here we report an ion-induced parallel-focusing approach that satisfies all requirements. Charged monodisperse aerosol nanoparticles are deposited onto a surface patterned with a photoresist while ions of the same polarity are introduced into the deposition chamber in the presence of an applied electric field. The ions accumulate on the photoresist, modifying the applied field to produce nanoscopic electrostatic lenses that focus the nanoparticles onto the exposed parts of the surface. We have demonstrated that the technique could produce high-resolution patterns at high speed on both conducting (p-type silicon) and non-conducting (silica) surfaces. Moreover, the feature sizes in the nanoparticle patterns were significantly smaller than those in the original photoresist pattern.

Synthesis of non-agglomerated nanoparticles by an electrospray assisted chemical vapor deposition (ES-CVD) method

Abstract Non-agglomerated spherical silicon, titanium and zirconium oxide nanoparticles were prepared using an electrospray assisted chemical vapor deposition (ES-CVD) process. Metal alkoxides in conjunction with an electrospray method were used to introduce charged precursors into a CVD reactor. The ions are produced during evaporation of the charged droplets, and they probably act as seed nuclei (i.e., ion-induced nucleation) and/or, they are attached to the produced particles. The experimental results were compared with those obtained using a conventional evaporation CVD method. The particles generated using the conventional evaporation method were agglomerated to a considerable extent irregardless of the type of particle. Whereas, at the same conditions, high concentrations of non-agglomerated nanoparticles having diameters in the range of 10– 40 nm were obtained using the ES-CVD method. This appears to be due to the charging effects of the generated particles, that is, the electrostatic dispersion of unipolarly charged particles. The size of the non-agglomerated particles in the ES-CVD method was reduced as the results of the decease in the concentration of precursors introduced by electrospray.

Unipolar Charging of Nanosized Aerosol Particles Using Soft X-ray Photoionization

A unipolar charging device based on a soft X-ray (<9.5 keV) photoionization was developed to investigate the charging efficiency of aerosol nanoparticles. Unipolar charging using a 241 Am charger was also evaluated as a comparison with the characteristics obtained by X-ray charging. The production rate and the concentration of ions generated by the X-ray and 241 Am unipolar chargers were estimated from ion current measurements. Theoretical calculations by the unipolar diffusion charging theory were also carried out and the calculated data were compared with the experimental results. For acquiring a high number of standard nanoparticles, the classification of monodisperse nanoparticles from polydisperse aerosol particles using the X-ray unipolar charger and a differential mobility analyzer (DMA) was also evaluated. The ion production rate of the X-ray unipolar charger was at least 5.5 times higher than that of the 241 Am unipolar charger and the ion concentration was about three times higher. Therefore, the X-ray unipolar charger showed a higher capability for charging aerosol particles of 10-40 nm size in diameter than the 241 Am charger. The charging state of particles produced by the X-ray unipolar charger was in good agreement with theoretical calculations. The X-ray unipolar charger developed herein has potential for use in charging a high number concentration of nanoparticles for use in nanotechnology investigations.

Classification of monodisperse aerosol particles using an adjustable soft X-ray charger

Abstract At high concentrations of ambient bipolar ions, charged aerosol particles show a stationary charging state as a function of particle size. When the particle diameter exceeds 0.1 μm, a considerable fraction of multiply charged particles is present, which hinders size classification of particles, when a differential mobility analyzer (DMA) is used. However, at low ion concentrations, particle charging by the ions can be suppressed, and in principle, the production of multiply charged particles can be reduced even when the particle size is larger than 0.1 μm. In this study, a use of a power-adjustable soft X-ray emitter was investigated for the first time as the ionization source of an aerosol charger. The bipolar ion concentration was found to be adjustable between 10 10 and 10 13 ions/m 3 . Through proper control of the bipolar ion concentration in the soft X-ray aerosol charger, multiply charged particles were reduced to less than 5% of the singly charged particles, while the singly charged particles remained at a relatively high concentration with most of the particles in size range of 0.1–1.0 μm. Therefore, highly monodisperse aerosol particles in the 0.1–1.0-μm-diameter range could be generated using this technique with a commercialized differential mobility analyzer.