Search

Forces on small plane sputter targets that are exposed to an ion beam at different angles of incidence are investigated. The force exerted on the sputter target is determined in two dimensions by means of an interferometric technique that measures the displacement of the target which is mounted at the end of an elastic cantilever. Different target materials made of silver, copper, aluminum, titanium, graphite, and carbon fiber velvet are studied. The experimental results are compared with a simulation based on the popular SRIM code. The forces are found to be caused predominantly by implanted beam particles and sputtered target atoms and insignificantly by re-emitted beam particles. The material dependent forces are discussed in connection with the simulations and in terms of the sputtering yield and surface topography. In case of the carbon fiber velvet, and in good approximation for graphite, the transferred momentum corresponds almost entirely to the momentum of the impinging beam particles. [ABSTRACT FROM AUTHOR]

Treatment of nanoparticles (NPs) in complex environments, such as plasmas, is of interest for the fabrication of advanced nanomaterials with desired properties and also from a physical point of view. Here, the authors investigate the mutual interaction between silver NPs and a radio frequency (RF) plasma at different conditions by combining a cylindrical hollow electrode with a gas aggregation source. The investigation of the NP deposits and the morphology of the casted films shows that the applied RF discharge significantly changes the path of the NPs as well as the NP size distribution in the beam. Starting from a neutral NP beam, it is observed that most of the NPs leave the plasma region with negative charge(s), yet the fraction of positively charged NPs grows with power. Furthermore, the plasma characteristics are slightly influenced by the NP flux since the passing NPs collect the plasma charge carriers. [ABSTRACT FROM AUTHOR]

A radio frequency (RF) hollow discharge configuration is presented, which makes use of a combination of RF plasma generation and the hollow cathode effect. The system was especially designed for the treatment of nanoparticles, plasma polymerization, and nanocomposite fabrication. The process gas streams through the plasma in the inner of the cylindrical electrode system. In the here presented measurements, pure argon and argon with oxygen admixtures are exemplarily used. The discharge is characterized by probe measurements in the effluent, electrical measurements of the discharge parameters, and visual observations of the plasma glow. It is found that the RF fluctuations of the plasma potential are weak. The plasma potential resembles the one of a DC hollow cathode discharge, the RF hollow electrode acts as a cathode due to the self-bias, and a high voltage sheath forms in its inner cylinder. [ABSTRACT FROM AUTHOR]

The force on microparticles in an energetic ion beam is investigated experimentally. Hollow glass microspheres are injected into the vertically upward directed beam and their trajectories are recorded with a charge-coupled device camera. The net force on the particles is determined by means of the measured vertical acceleration. The resulting beam pressures are compared with Faraday cup measurements of the ion current density and calorimetric measurements of the beam power density. Due to the neutral gas background, the beam consists, besides the ions, of energetic neutral atoms produced by charge-exchange collisions. It is found that the measured composition of the drag force by an ion and a neutral atom component agrees with a beam model that takes charge-exchange collisions into account. Special attention is paid to the momentum contribution from sputtered atoms, which is shown to be negligible in this experiment, but should become measurable in case of materials with high sputtering yields. [ABSTRACT FROM AUTHOR]

A calorimetric probe for plasma diagnostics is presented, which allows measurements of the power taken by a test substrate. The substrate can be biased and used as an electric probe in order to obtain information about the composition of the total heating power. A new calibration technique for calorimetric probes, which uses monoenergetic electrons at low pressure, has been developed for an improved accuracy. The use of the probe is exemplified with an experiment where both energetic neutral atoms and ions heat the test substrate. [ABSTRACT FROM AUTHOR]

A novel experiment for the study of forces on microparticles in ion beams is presented. A broad beam ion source provides a vertically upward directed beam wherein 100 μm hollow glass spheres are injected. The particles are illuminated by a diode laser and recorded with a charge-coupled device camera. From the trajectories the acceleration and the net force on the particles are determined. Information on energetic neutral atoms is achieved, which is not accessible by electrostatic methods. [ABSTRACT FROM AUTHOR]

Small dust clouds, which are confined in an anodic plasma, are studied with respect to their structure and their response to modulation of the anode bias. The dust cloud is displaced from the center of the discharge by a process similar to the void mechanism in radio-frequency discharges under microgravity. The top layers of the dust cloud are in a crystalline state and the cloud performs a slow rotation about the magnetic field direction. For modulation frequencies below 15 Hz, a sloshing and stretching motion in the confining potential well is found. Spontaneously excited dust density waves are observed when the dust cloud exceeds a minimum size. The waves are characterized by sickle-shaped wave fronts. No standing waves were found. The wave dispersion shows an influence of the boundedness of the system in terms of a frequency cutoff. [ABSTRACT FROM AUTHOR]

Experiments on dust-acoustic waves (DAW) in a magnetized anodic plasma are presented for the regime of low collisionality. The dust trapping and the self-excited and synchronized DAW dynamics are studied. Based on Langmuir and emissive probe measurements the dust confinement is found to be well described with respect to size, stability, and position of the dust cloud by an effective potential well formed by ion drag and Coulomb forces. Moreover, the measurements indicate the necessity for a kinetic model for the wave dispersion. By means of singular value decomposition the local wavelengths and growth rates of the waves are measured systematically. It is found that the measured mean wave number is well described by kinetic theory, while the theoretical growth rates overestimate the experiments. A novel observation for the DAW is a systematic variation of the wavelength inside the dust cloud. [ABSTRACT FROM AUTHOR]

A new diagnostic method for magnetized dusty plasmas, the excitation of lower hybrid resonance cones, is investigated experimentally. The resonance cone is excited with a small antenna, and the angular distribution of the wave field with respect to the magnetic field shows a resonant enhancement, which shifts according to the free electron density. It is demonstrated that dust reduces the free electron density in agreement with Langmuir probe results. Wave damping by scattering effects is found negligible. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]