This thesis work consists of studies on the development of particle diagnostics and the investigation of dynamic properties of dust particles and its control.
First, diagnostic tools to measure dust particle size and density were developed based on laser-induced incandescence (LII) technique and laser extinction method, respectively. It is important to know particle size and density because they help exploring the transport phenomena of dust particles in plasmas as well as they provide in situ monitoring method during plasma-aided processes. The laser-induced incandescence technique measures time-dependent blackbody radiation emitted from dust particles after they are heated by a short, intensive laser pulse. The size of the particles produced in a low pressure argon-diluted $SiH_4$ plasma was obtained from the decay time of the incandescence light emitted from the particles because the decay time depends on particle size. From the measurement, it was shown that the measurable size ranges from 10 nm to 200 nm and the maximum incident laser fluence should be under $400 mJ/cm^2$ to avoid particle evaporation. On the other hand, measurement of particle density was performed using the single-pass laser extinction method, in which particle density is obtained using the relation between particle density and the difference between two laser beam intensities with and without passing a dusty plasma. The measurement limit of the extinction ratio of the experimental setup based on the single-pass system was about 1 % and it is expected to be improved by employing a multi-pass system. The lowest measurable particle density in an argon DC discharge was about $10^4 cm^{-3}$ for 1.5㎛ diameter particles.
The dynamic properties of dust particles was also studied. Characteristics of the particle trapping such as trap position, oscillation frequency, dust cloud width with respect to plasma condition and particle size were studied by comparative analysis between measurements and the 1-D collisional plasma modeling including ion-neutral collisions. The trap position was found to change according to particle size, electron temperature, and plasma density. Dust charge at the trap position was strongly dependent on electron temperature while its dependence on plasma density was negligible.
The parametric nonlinear oscillation of dust particles in a DC glow discharge at 250 mTorr was investigated while focusing on the role of gas pressure and particle size in the particle oscillation. In order to understand the role of particle size, size dependence of the frequency spectra was studied with three different size particles. From the measured result, it was found that occurrence of the subharmonic peak was highly dependent on particle size and the size determines the restoring force profile. The observations were consistent with modeling. For further understanding, discussions on the role of particle size and gas pressure in nonlinear oscillations were made through numerical calculation of oscillation spectra and force profiles. It turned out that gas pressure affects the oscillation spectra by means of frictional damping rather than the overall net force profile, and the force profile is mainly determined by particle size rather than by gas pressure. It is concluded that occurrence of the subharmonic resonance and the force profile are mostly determined by particle size while the superharmonic resonance and hysteresis are determined by gas pressure through damping rate.
As a final topic, study on the controllability of the dust oscillatory behavior was attempted using AC voltage superposition on the DC cathode as a way of controlling particle charge. It was shown that the AC-superposed cathode was found to make the nonlinearity and the parametric resonance of the particle oscillation weak. The hysteresis in the oscillation spectrum did not occur, and subharmonic resonance peak also disappeared as AC-modulation voltage increased. These changes in oscillation characteristics were confirmed by the charge and force profile calculation. As a result, it was concluded that the cathode AC modulation made the dust oscillatory behavior less nonlinear and less parametrically resonant, which suggested the controllability of the dynamic properties of the particles. The dependence of the oscillation spectrum on AC modulation frequency was investigated to demonstrate the separate control of the dust charge. As the modulation frequency decreased from 5~kHz to 1~kHz under the same AC voltage, the subharmonic peak was weakened with the frequency. It indicates that the dust charge profile mainly determines the behavior of the subharmonic peak, and whether the particle oscillation is parametrically-resonant or not. Consequently, it is demonstrated that it is indeed possible to control the dynamics of dust particles, to some extent, by the independent charge control.
