82 research outputs found
The effect of ambipolar electric fields on the electron heating in capacitive RF plasmas
We investigate the electron heating dynamics in electropositive argon and
helium capacitively coupled RF discharges driven at 13.56 MHz by Particle in
Cell simulations and by an analytical model. The model allows to calculate the
electric field outside the electrode sheaths, space and time resolved within
the RF period. Electrons are found to be heated by strong ambipolar electric
fields outside the sheath during the phase of sheath expansion in addition to
classical sheath expansion heating. By tracing individual electrons we also
show that ionization is primarily caused by electrons that collide with the
expanding sheath edge multiple times during one phase of sheath expansion due
to backscattering towards the sheath by collisions. A synergistic combination
of these different heating events during one phase of sheath expansion is
required to accelerate an electron to energies above the threshold for
ionization. The ambipolar electric field outside the sheath is found to be time
modulated due to a time modulation of the electron mean energy caused by the
presence of sheath expansion heating only during one half of the RF period at a
given electrode. This time modulation results in more electron heating than
cooling inside the region of high electric field outside the sheath on time
average. If an electric field reversal is present during sheath collapse, this
time modulation and, thus, the asymmetry between the phases of sheath expansion
and collapse will be enhanced. We propose that the ambipolar electron heating
should be included in models describing electron heating in capacitive RF
plasmas
Customized ion flux-energy distribution functions in capacitively coupled plasmas by voltage waveform tailoring
We propose a method to generate a single peak at a distinct energy in the ion
flux-energy distribution function (IDF) at the electrode surfaces in
capacitively coupled plasmas. The technique is based on the tailoring of the
driving voltage waveform, i.e. adjusting the phases and amplitudes of the
applied harmonics, to optimize the accumulation of ions created by charge
exchange collisions and their subsequent acceleration by the sheath electric
field. The position of the peak (i.e. the ion energy) and the flux of the ions
within the peak of the IDF can be controlled in a wide domain by tuning the
parameters of the applied RF voltage waveform, allowing optimization of various
applications where surface reactions are induced at particular ion energies
Virtual and accessible reality technologies in the trends of modern enterprise competitiveness
In today's dynamic business environment, any business organization strives to maintain its own
competitive advantage in the market. Therefore, each company develops and implements methods that allow
not only to maintain a stable position, but also to develop and increase the scale of activities in a particular area.
Such methods include various innovative solutions, attraction of highly qualified personnel, improvement of
management system, changes in technological processes in production and many other things. Recently, however,
so-called virtual reality technologies (VR-technologies) have become increasingly popular among companies.
They are becoming increasingly important due to the rapid development of information and communication and
digital technologies, which greatly facilitate and diversify the lives of most people and organizations. Virtual reality
technology is slowly entering the workplace and is used in many fields such as medicine, construction and design,
automotive, military, logistics, architecture and design, education, sports, engineering, design, tourism, and more.
The main advantage of such technologies is the possibility of complete immersion into the created reality,
additionally acquired ability to feel and analyze both positive aspects and negative consequences of planned
actions, as well as to simulate options for future events. Therefore, the use of modern VR technologies by more and
more organizations plays an important role in the development of their competitiveness. According to scientists and
practitioners, the benefits of using such technologies are, first, to create added value for consumers through a new
set of skills and knowledge; second, to give the organization a virtual competitive advantage; third, the achievement
by the company of greater flexibility, dynamism and persuasiveness when using virtual reality to demonstrate its
product (for example, to disassemble and assemble its own products in order to explain the internal mechanism or
something else); fourth, reducing the duration of the production process, which uses VR technology; fifth, reducing
costs and increasing profits for the organization by optimizing processes, which will save resources and time, and
others. The aim of this publication is to investigate the main theoretical and practical aspects of virtualization of
organizations, in particular, the impact of VR-technologies on their competitiveness, to analyze foreign experience
in the use of virtual technologies in business and to summarize proposals for competitive advantage based on
virtual reality technologies
Effects of fast atoms and energy-dependent secondary electron emission yields in PIC/MCC simulations of capacitively coupled plasmas
In most PIC/MCC simulations of radio frequency capacitively coupled plasmas
(CCPs) several simplifications are made: (i) fast neutrals are not traced, (ii)
heavy particle induced excitation and ionization are neglected, (iii) secondary
electron emission from boundary surfaces due to neutral particle impact is not
taken into account, and (iv) the secondary electron emission coefficient is
assumed to be constant, i.e. independent of the incident particle energy and
the surface conditions. Here we question the validity of these simplifications
under conditions typical for plasma processing applications. We study the
effects of including fast neutrals and using realistic energy-dependent
secondary electron emission coefficients for ions and fast neutrals in
simulations of CCPs operated in argon at 13.56 MHz and at neutral gas pressures
between 3 Pa and 100 Pa. We find a strong increase of the plasma density and
the ion flux to the electrodes under most conditions, if these processes are
included realistically in the simulation. The sheath widths are found to be
significantly smaller and the simulation is found to diverge at high pressures
for high voltage amplitudes in qualitative agreement with experimental
findings. By switching individual processes on and off in the simulation we
identify their individual effects on the ionization dynamics and plasma
parameters. We conclude that fast neutrals and energy-dependent secondary
electron emission coefficients must be included in simulations of CCPs in order
to yield realistic results
Kinetic simulation of the sheath dynamics in the intermediate radio-frequency regime
The dynamics of temporally modulated plasma boundary sheaths is studied in
the intermediate radio frequency regime where the applied radio frequency and
the ion plasma frequency are comparable. Two kinetic simulation codes are
employed and their results are compared. The first code is a realization of the
well-known scheme, Particle-In-Cell with Monte Carlo collisions (PIC/MCC) and
simulates the entire discharge, a planar radio frequency capacitively coupled
plasma (RF-CCP) with an additional heating source. The second code is based on
the recently published scheme Ensemble-in-Spacetime (EST); it resolves only the
sheath and requires the time resolved voltage across and the ion flux into the
sheath as input. Ion inertia causes a temporal asymmetry (hysteresis) of the
sheath charge-voltage relation; also other ion transit time effects are found.
The two codes are in good agreement, both with respect to the spatial and
temporal dynamics of the sheath and with respect to the ion energy
distributions at the electrodes. It is concluded that the EST scheme may serve
as an efficient post-processor for fluid or global simulations and for
measurements: It can rapidly and accurately calculate ion distribution
functions even when no genuine kinetic information is available
A scanning drift tube apparatus for spatio-temporal mapping of electron swarms
A "scanning" drift tube apparatus, capable of mapping of the spatio-temporal
evolution of electron swarms, developing between two plane electrodes under the
effect of a homogeneous electric field, is presented. The electron swarms are
initiated by photoelectron pulses and the temporal distributions of the
electron flux are recorded while the electrode gap length (at a fixed electric
field strength) is varied. Operation of the system is tested and verified with
argon gas, the measured data are used for the evaluation of the electron bulk
drift velocity. The experimental results for the space-time maps of the
electron swarms - presented here for the first time - also allow clear
observation of deviations from hydrodynamic transport. The swarm maps are also
reproduced by particle simulations
Kinetic Interpretation of Resonance Phenomena in Low Pressure Capacitively Coupled Radio Frequency Plasmas
The kinetic origin of resonance phenomena in capacitively coupled radio
frequency plasmas is discovered based on particle-based numerical simulations.
The analysis of the spatio-temporal distributions of plasma parameters such as
the densities of hot and cold electrons, as well as the conduction and
displacement currents reveals the mechanism of the formation of multiple
electron beams during sheath expansion. The interplay between highly energetic
beam electrons and low energetic bulk electrons is identified as the physical
origin of the excitation of harmonics in the current
- …