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The dynamics of carbonaceous nanoparticle (NP) evolution in its cyclic growth process in a capacitively coupled RF plasma is studied using multiple diagnostic methods. We designed a simple method using biased substrates for spatiotemporal collection of growing NPs at different positions inside the particle cloud and at different time steps during the growth cycle. In addition, self-bias voltage and laser light scattering are in situ measured to monitor the nanoparticle growth. Subsequently, the collected nanoparticles are characterized by scanning electron microscopy (SEM). Correlations between the self-bias voltage and SEM results are presented. We show that different threshold potentials are needed to overcome the confinement of the NPs for collection. This is explained with the spatial and temporal variation of the plasma potential, the NP size, and the ion drag inside the particle cloud. Moreover, the arrangement of the locally collected NPs on the substrate is found to depend on the bias voltage applied to it. Finally, we demonstrate the possibility to control the self-organization and deposition patterns of the nanoparticles by changing the substrate orientation. [ABSTRACT FROM AUTHOR]

We experimentally demonstrate that the interaction between plasma and nanometer-sized semiconductor quantum dots (QDs) is directly connected to a change in their photoluminescence (PL) spectrum. This is done by taking in situ, high resolution, and temporally resolved spectra of the light emitted by laser-excited QDs on an electrically floating sample exposed to a low pressure argon plasma. Our results show a fast redshift of the PL emission peak indicating the quantum-confined Stark effect due to plasma-generated excess charges on the substrate and near the QD surface, while other plasma-induced (thermal and ion) effects on longer timescales could clearly be distinguished from these charging effects. The presented results and method open up pathways to direct visualization and understanding of fundamental plasma–particle interactions on nanometer length scales. [ABSTRACT FROM AUTHOR]

This paper reports on the further development and improvement of time-resolved laser-induced photodetachment in concert with microwave cavity resonance spectroscopy. The method is applied to measure—with microsecond time resolution—the decaying density of negative oxygen ions (O−, O , and O) and that of free electrons in the afterglow of a pulsed capacitively coupled radiofrequency-driven oxygen plasma. The afterglow behavior of the electrons shows a significant dependence on the gas pressure between 3 Pa and 6 Pa. For a pressure of 3 Pa, at which the plasma is in the so-called γ-mode, the decay of the negative ion density is slower than that of the electron density, eventually leading to the occurrence of a negative-ion-positive-ion plasma. At a slightly elevated pressure of 6 Pa (and higher), the plasma transits into the so-called α-mode, in which a short period of increased electron density is detected just after switching off the plasma. In the α-mode, the negative ion and electron densities decay within similar timescales, leading to the trapping of negative ions. In this pressure range, the decay of the additional electron density released by the photodetachment of negative ions occurs according to two distinct timescales. However, for increasingly elevated pressures above 10 Pa, the photodetachment signal is characterized by decay with an undershoot, which may indicate a temporary local disturbance of the plasma's quasi-neutrality in the volume irradiated by the laser beam. [ABSTRACT FROM AUTHOR]

The growth kinetics of single-walled carbon nanotubes (SWCNTs) in a low-temperature, low-pressure reactive plasma is investigated using a multiscale numerical simulation, including the plasma sheath and surface diffusion modules. The plasma-related effects on the characteristics of SWCNT growth are studied. It is found that in the presence of reactive radicals in addition to energetic ions inside the plasma sheath area, the effective carbon flux, and the growth rate of SWCNT increase. It is shown that the concentration of atomic hydrogen and hydrocarbon radicals in the plasma plays an important role in the SWCNT growth. The effect of the effective carbon flux on the SWCNT growth rate is quantified. The dependence of the growth parameters on the substrate temperature is also investigated. The effects of the plasma sheath parameters on the growth parameters are different in low- and high-substrate temperature regimes. The optimum substrate temperature and applied DC bias are estimated to maximize the growth rate of the single-walled carbon nanotubes [ABSTRACT FROM AUTHOR]