456 resultados para Surface waves
Resumo:
Catalytic probes are used for plasma diagnostics in order to quantify the density of neutral atoms. The probe response primarily depends on the probe material and its surface morphology. Here we report on the design, operation and modelling of the response of niobium pentoxide sensors with a flat and nanowire (NW) surfaces. These sensors were used to detect neutral oxygen atoms in the afterglow region of an inductively coupled rf discharge in oxygen. A very different response of the flat-surface and NW probes to the varying densities of oxygen atoms was explained by modelling heat conduction and taking into account the associated temperature gradients. It was found that the nanostructure probe can measure in a broader range than the flat oxide probe due to an increase in the surface to volume ratio, and the presence of nanostructures which act as a thermal barrier against sensor overheating. These results can be used for the development of the new generation of catalytic probes for gas/discharge diagnostics in a range of industrial and environmental applications.
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An innovative approach to precise tailoring of surface density, shapes, and sizes of single-crystalline α-Fe 2O 3 nanowires and nanobelts by controlling interactions of reactive oxygen plasma-generated species with the Fe surface is proposed. This strongly nonequilibrium, rapid, almost incubation-free, high-rate growth directly from the solid-solid interface can also be applied to other oxide materials and is based on deterministic control of the density of oxygen species and the surface conditions, which determine the nanostructure nucleation and growth.
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The influence of electron heating in the high-frequency surface polariton (SP) field on the dispersion properties of the SPs considered is investigated. High frequency SPs propagate at the interface between an n-type semiconductor with finite electron pressure, and a metal. The nonlinear dispersion relation for the SPs is derived and investigated.
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This contribution provides arguments why and in which cases low-temperature plasmas should be used for nanoscale surface and interface engineering and discusses several advantages offered by plasma-based processes and tools compared to neutral gas fabrication routes. Relevant processes involve nanotexturing (etching, sputtering, nanostructuring, pre-patterning, etc.) and composition/structure control at nanoscales (phases, layering, elemental presence, doping, functionalization, etc.) and complex combinations thereof. A case study in p-Si/n-Si solar cell junction exemplifies a successful use of inductively coupled plasma-assisted RF magnetron sputtering for nanoscale fabrication of a bi-layered stack of unconventionally doped highly-crystalline silicon nanofilms with engineered high-quality interfaces.
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A self-consistent theory of ion-acoustic waves in dusty gas discharge plasmas is presented. The plasma is contaminated by fine dust particles with variable charge. The stationary state of the plasma and the dispersion and damping characteristics of the waves are investigated accounting for ionization, recombination, dust charge relaxation, and dissipation due to electron and ion elastic collisions with neutrals and dusts, as well as charging collisions with the dusts.
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The propagation of Langmuir waves in nonisothermal plasmas contaminated by fine dust particles with variable charge is investigated for a self-consistent closed system. Dust charge relaxation, ionization, recombination, and collisional dissipation are taken into account. It is shown that the otherwise unstable coupling of the Langmuir and dust-charge relaxation modes becomes stable and the Langmuir waves are frequency down-shifted.
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A wave propagation in a complex dusty plasma with negative ions was considered. The relevant processes such as ionization, electron attachment, diffusion, positive-negative ion recombination, plasma particle collisions, as well as elastic Coulomb and inelastic dust-charging collisions were taken self-consistently. It was found that the equilibrium of the plasma as well as the propagation of ion waves were modified to various degrees by these effects.
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Multiscale hybrid simulations that bridge the nine-order-of-magnitude spatial gap between the macroscopic plasma nanotools and microscopic surface processes on nanostructured solids are described. Two specific examples of carbon nanotip-like and semiconductor quantum dot nanopatterns are considered. These simulations are instrumental in developing physical principles of nanoscale assembly processes on solid surfaces exposed to low-temperature plasmas.
Resumo:
The non-linear self-interaction of the potential surface polaritons (SP) which is due to the free carriers dispersion law where nonparabolicity is studied. The SP propagate at the interface between n-type semiconductor and a metal. The self interaction of the SP is shown to be different in semiconductors with normal and inverse zone structures. The results of the SP field envelope evolution are given. The obtained nonlinear frequency shift has been compared with shifts which are due to another self-interaction mechanisms. This comparison shows that the nonlinear self-interaction mechanism, which is due to free carriers spectrum nonparabolicity, is especially significant in narrow-gap semiconductor materials.
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The results of a study on the influence of the nonparabolicity of the free carriers dispersion law on the propagation of surface polaritons (SPs) located near the interface between an n-type semiconductor and a metal arc reported. The semiconductor plasma is assumed to be warm and nonisothermal. The nonparabolicity of the electron dispersion law has two effects. The first one is associated with nonlinear self-interaction of the SPs. The nonlinear dispersion equation and the nonlinear Schrodinger equation for the amplitude of the SP envelope are obtained. The nonlinear evolution of the SP is studied on the base of the above mentioned equations. The second effect results in third harmonics generation. Analysis shows that these third harmonics may appear as a pure surface polariton, a pseudosurface polariton, or a superposition of a volume wave and a SP depending on the wave frequency, electron density and lattice dielectric constant.
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The nonlinear self-interaction of the potential surface magnetoplasmons, propagating across the external magnetic field at the n-type semiconductor-metal interface is described in this manuscript. The studied nonlinearity is due to the free carriers dispersion law nonparabolicity and we show that it acts differently in semiconductor materials with normal and inverse band structures. The results of the nonlinear evolution of the surface magnetoplasmons are presented as well.
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A new source of low-frequency (0.46 MHz) inductively coupled plasmas sustained by the internal planar "unidirectional" RF current driven through a specially designed internal antenna configuration has been developed. The experimental results of the investigation of the optical and global argon plasma parameters by the optical and Langmuir probes are presented. It is shown that the spatial profiles of the electron density, the effective electron temperature and plasma potential feature a great deal of the radial and axial uniformity compared with conventional sources of inductively coupled plasmas with external at coil configurations. The measurements also reveal a weak azimuthal dependence of the global plasma parameters at low values of the input RF power, which was earlier predicted theoretically. The azimuthal dependence of the global plasma parameters vanishes at high input RF powers. Moreover, under certain conditions, the plasma becomes unstable due to spontaneous transitions between low-density (electrostatic, E) and high-density (electromagnetic, H) operating modes. Excellent uniformity of high-density plasmas makes the plasma reactor promising for various plasma processing applications and surface engineering.
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A plasma-assisted concurrent Rf sputtering technique for fabrication of biocompatible, functionally graded CaP-based interlayer on Ti-6Al-4V orthopedic alloy is reported. Each layer in the coating is designed to meet a specific functionality. The adherent to the metal layer features elevated content of Ti and supports excellent ceramic-metal interfacial stability. The middle layer features nanocrystalline structure and mimics natural bone apatites. The technique allows one to reproduce Ca/P ratios intrinsic to major natural calcium phosphates. Surface morphology of the outer, a few to few tens of nanometers thick, layer, has been tailored to fit the requirements for the bio-molecule/protein attachment factors. Various material and surface characterization techniques confirm that the optimal surface morphology of the outer layer is achieved for the process conditions yielding nanocrystalline structure of the middle layer. Preliminary cell culturing tests confirm the link between the tailored nano-scale surface morphology, parameters of the middle nanostructured layer, and overall biocompatibility of the coating.
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Negative ions and negatively charged micro- to nano-meter sized dust grains are ubiquitous in astrophysical as well as industrial processing plasmas. The negative ions can appear in electro-negative plasmas as a result of elementary processes such as dissociative or non-dissociative electron attachment to neutrals. They are usually rather small in number, and in general do not affect the overall plasma behavior. On the other hand, since the dust grains are almost always highly negative, even in small numbers they can take up a considerable proportion of the total negative charge in the system. The presence of dusts can affect the characteristics of most collective processes of the plasma since the charge balance in both the steady and dynamic states can be significantly altered. Another situation that often occurs is that the electron number density becomes small because of their absorption by the dust grains or the discharge walls. In this case the negative ions in the plasma can play a very important role. Here, a self-consistent theory of linear waves in complex laboratory plasmas containing dust grains and negative ions is presented. A comprehensive model for such plasmas including source and sink effects associated with the presence of dust grains and negative ions is introduced. The stationary state of the plasma as well as the dispersion and damping characteristics of the waves are investigated. All relevant processes, such as ionization, diffusion, electron attachment, negative-positive ion recombination, dust charge relaxation, and dissipation due to electron and ion elastic collisions with neutrals and dust particles, as well as charging collisions with the dusts, are taken into consideration.
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The process of resonant generation of the second harmonic of the surface wave, propagating along the external magnetic field at the plasma-metal boundary is considered. The periodic process of the energy exchange between the first and the second harmonics of the wave is investigated as well. It is shown that the process under study is periodic one. The analytical expressions are obtained and numerical estimations are presented for characteristic time of nonlinear energy exchange. The self-action effect of main frequency wave is account for harmonics interaction. It is shown that the effect leads to nonlinear phenomena attenuation, which expresses in narrowing possible value interval of harmonics amplitudes during energy exchange process and in increasing the nonlinear interaction time.