Deterministic nanoassembly: Neutral or plasma route?

It is shown that, owing to selective delivery of ionic and neutral building blocks directly from the ionized gas phase and via surface migration, plasma environments offer a better deal of deterministic synthesis of ordered nanoassemblies compared to thermal chemical vapor deposition. The results of hybrid Monte Carlo (gas phase) and adatom self-organization (surface) simulation suggest that higher aspect ratios and better size and pattern uniformity of carbon nanotip microemitters can be achieved via the plasma route.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87817/2/033109_1.pd

Overcoming the Child-Langmuir law via the magnetic mirror effect

The maximum current in a vacuum tube prescribed by the classical Child-Langmuir law can be overcome, when the space-charge effect of the induced potential is mitigated by the mirror effect in a spatially varying magnetic field. The current could exceed the Child-Langmuir value by as much as a few factors. The regime of practical interest is examined

Microscopic ion fluxes in plasma-aided nanofabrication of ordered carbon nanotip structures

Three-dimensional topography of microscopic ion fluxes in the reactive hydrocarbon-based plasma-aided nanofabrication of ordered arrays of vertically aligned single-crystalline carbon nanotip microemitter structures is simulated by using a Monte Carlo technique. The individual ion trajectories are computed by integrating the ion equations of motion in the electrostatic field created by a biased nanostructured substrate. It is shown that the ion flux focusing onto carbon nanotips is more efficient under the conditions of low potential drop UsUs across the near-substrate plasma sheath. Under low-UsUs conditions, the ion current density onto the surface of individual nanotips is higher for higher-aspect-ratio nanotips and can exceed the mean ion current density onto the entire nanopattern in up to approximately five times. This effect becomes less pronounced with increasing the substrate bias, with the mean relative enhancement of the ion current density ξiξi not exceeding ∼ 1.7∼1.7. The value of ξiξi is higher in denser plasmas and behaves differently with the electron temperature TeTe depending on the substrate bias. When the substrate bias is low, ξiξi decreases with TeTe, with the opposite tendency under higher-UsUs conditions. The results are relevant to the plasma-enhanced chemical-vapor deposition of ordered large-area nanopatterns of vertically aligned carbon nanotips, nanofibers, and nanopyramidal microemitter structures for flat-panel display applications.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87355/2/064304_1.pd

Nanopowder management and control of plasma parameters in electronegative SiH4 plasmas

Management of nanosize powder particles via control of plasma parameters in a low-pressure SiH4 discharge for silicon microfabrication technologies is considered. The spatial profiles of electron and positive/negative ion number densities, electron temperature, and charge of the fine particles are obtained using a self-consistent fluid model of the electronegative plasmas in the parallel plate reactor geometry. The model accounts for variable powder size and number density, powder-charge distribution, local plasma nonuniformity, as well as UV photodetachment of electrons from the nanoparticles. The relations between the equilibrium discharge state and powder properties and the input power and neutral gas pressure are studied. Methods for controlling the electron temperature and SiH3- anion (here assumed to be the powder precursor) density, and hence the powder growth process, are proposed. It is shown that by controlling the neutral gas pressure, input power, and powder size and density, plasma density profiles with high levels of uniformity can be achieved. Management of powder charge distribution is also possible through control of the external parameters

Targeting the cancer cell cycle by cold atmospheric plasma

Cold atmospheric plasma (CAP), a technology based on quasi-neutral ionized gas at low temperatures, is currently being evaluated as a new highly selective alternative addition to existing cancer therapies. Here, we present a first attempt to identify the mechanism of CAP action. CAP induced a robust ~2-fold G2/M increase in two different types of cancer cells with different degrees of tumorigenicity. We hypothesize that the increased sensitivity of cancer cells to CAP treatment is caused by differences in the distribution of cancer cells and normal cells within the cell cycle. The expression of γH2A.X (pSer139), an oxidative stress reporter indicating S-phase damage, is enhanced specifically within CAP treated cells in the S phase of the cell cycle. Together with a significant decrease in EdU-incorporation after CAP, these data suggest that tumorigenic cancer cells are more susceptible to CAP treatment

A Numerical Examination of the Performance of Small Magnetic Nozzle Thrusters

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/143040/1/6.2017-4721.pd

Ablative Z-Pinch Pulsed Plasma Thruster

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/77148/1/AIAA-4362-652.pd

Vaporization of heated materials into discharge plasmas

The vaporization of condensed materials in contact with high-current discharge plasmas is considered. A kinetic numerical method named direct simulation Monte Carlo (DSMC) and analytical kinetic approaches based on the bimodal distribution function approximation are employed. The solution of the kinetic layer problem depends upon the velocity at the outer boundary of the kinetic layer which varies from very small, corresponding to the high-density plasma near the evaporated surface, up to the sound speed, corresponding to evaporation into vacuum. The heavy particles density and temperature at the kinetic and hydrodynamic layer interface were obtained by the analytical method while DSMC calculation makes it possible to obtain the evolution of the particle distribution function within the kinetic layer and the layer thickness. © 2001 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69973/2/JAPIAU-89-6-3095-1.pd

Optimization Issues for a Micropulsed Plasma Thruster

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76083/1/AIAA-13954-648.pd

Propellant Charring in Pulsed Plasma Thrusters

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76437/1/AIAA-2471-899.pd