Dust dynamics during the plasma afterglow

The charge and dynamics of dust particles in an afterglow plasma are studied using a 1D model in the diffusion approximation, taking into account the transition from ambipolar to free diffusion. It is analyzed how external conditions (dust particle size, neutral gas pressure and initial electron density) affect the dust motion. The dust particle dynamics has been examined in microgravity conditions and in presence of gravity. Without gravity, the location of dust particles in plasma volume may change essentially during the afterglow if the dust size and pressure are small (≤ 10 nm and ≤ 30 mTorr, respectively). At small pressures, in the very beginning of afterglow, small nanoparticles move to the plasma boundary because the ion drag force dominates over the electric force. At afterglow times when the electron temperature becomes time-independent, the ion drag force decreases faster with time than the electric force due to the ion density decrease, and dust particles may move to the slab center. In presence of gravity, the effect of gravity force on dust particles is important only at large afterglow times (t ≥ 10 ms), when the electric and ion drag forces are small. The dust dynamics depends essentially on the initial plasma density. If the density is large (~ 1012 cm-3), small nanoparticles (≤ 10 nm) may deposit on plasma walls in the beginning of plasma afterglow because of an enhancement of the ion drag force.

STRUCTURE AND ELECTROPHYSICAL PROPERTIES OF PVDF+PbS/CdS NANOCOMPOSITES

In the given paper were investigated structure and electrophysical properties of PVDF+PbS/CdS nanocomposites. Distribution and the size of PbS and CdS nanoparticles in the polymer matrix has been studied by scanning electron microscopy (JEOL JSM-7600 F). The structure of the nanocomposite samples was investigated by the X-ray diffraction spectroscopy. The dependence of dielectric permittivity at frequency and temperature was investigated. It was shown that the dielectric permittivity of PVDF+PbS/CdS nanocomposite samples was increase in small nanoparticles content. Further increase in the concentration of the filler leads to decrease in the dielectric permittivity. The subsequent decrease in dielectric permittivity at higher nanoparticles content can be explained by the increase in defects in the structure of the nanocomposite.

Calibrating SECCM measurements by means of a nanoelectrode ruler. The intrinsic oxygen reduction activity of PtNi catalyst nanoparticles

Scanning electrochemical cell microscopy (SECCM) is increasingly applied to determine the intrinsic catalytic activity of single electrocatalyst particle. This is especially feasible if the catalyst nanoparticles are large enough that they can be found and counted in post-SECCM scanning electron microscopy images. Evidently, this becomes impossible for very small nanoparticles and hence, a catalytic current measured in one landing zone of the SECCM droplet cannot be correlated to the exact number of catalyst particles. We show, that by introducing a ruler method employing a carbon nanoelectrode decorated with a countable number of the same catalyst particles from which the catalytic activity can be determined, the activity determined using SECCM from many spots can be converted in the intrinsic catalytic activity of a certain number of catalyst nanoparticles.

On the Use of Laser Fragmentation for the Synthesis of Ligand-Free Ultra-Small Iron Nanoparticles in Various Liquid Environments

Traditionally, the synthesis of nanomaterials in the ultra-small size regime (1–3 nm diameter) has been linked with the employment of excessive amounts of hazardous chemicals, inevitably leading to significant environmentally detrimental effects. In the current work, we demonstrate the potential of laser fragmentation in liquids (LFL) to produce highly pure and stable iron ultra-small nanoparticles. This is carried out by reducing the size of carbonyl iron microparticles dispersed in various polar solvents (water, ethanol, ethylene glycol, polyethylene glycol 400) and liquid nitrogen. The explored method enables the fabrication of ligand-free iron oxide ultra-small nanoparticles with diameter in the 1–3 nm range, a tight size distribution, and excellent hydrodynamic stability (zeta potential > 50 mV). The generated particles can be found in different forms, including separated ultra-small NPs, ultra-small NPs forming agglomerates, and ultra-small NPs together with zero-valent iron, iron carbide, or iron oxide NPs embedded in matrices, depending on the employed solvent and their dipolar moment. The LFL technique, aside from avoiding chemical waste generation, does not require any additional chemical agent, other than the precursor microparticles immersed in the corresponding solvent. In contrast to their widely exploited chemically synthesized counterparts, the lack of additives and chemical residuals may be of fundamental interest in sectors requiring colloidal stability and the largest possible number of chemically active sites, making the presented pathway a promising alternative for the clean design of new-generation nanomaterials.