A 2-D dust crystal levitated in the sheath of a modified Gaseous Electronics Conference reference cell is manipulated by heating or cooling the lower electrode. The dust charge is obtained by measuring the global characteristics of the levitated crystal obtained from top-view pictures. From the force balance, the electric field in the sheath is reconstructed. From the Bohm criterion, we conclude that the dust crystal is levitated mainly above and just below the classical Bohm point.

A two-dimensional dust crystal levitated in the sheath of a modified Gaseous Electronics Conference (GEC) reference cell is manipulated by heating or cooling the lower electrode. The dust charge is obtained from top-view pictures of the crystal using a previously developed analytical model. By assuming a simple force balance, and measuring the radial confining force, the vertical electric field profile in the sheath is reconstructed. The dust crystal is shown to levitate on the plasma side of the Bohm point. Finally, it is shown that the ion drag plays an important role in the vertical force balance, even for large dust grains.

A self-consistent fluid model developed for simulations of microgravity dusty plasma experiments has for the first time been used to model asymmetric dusty plasma experiments in a modified Gaseous Electronics Conference (GEC) reference cell with gravity. The numerical results are directly compared with experimental data and the experimentally determined dependence of global discharge parameters on the applied driving potential and neutral gas pressure is found to be well matched by the model. The local profiles important for dust particle transport are studied and compared with experimentally determined profiles. The radial forces in the midplane are presented for the different discharge settings. The differences between the results obtained in the modified GEC cell and the results first reported for the original GEC reference cell are pointed out.

Dust is a common component in plasma systems, from silicon chip manufacturing to comet tails. Dust particle clouds in each of these systems can contaminate synthesis techniques or define the properties of protostellar clouds. Experiments have been conducted to describe the crystal structure within the plasma potential well, but more work needs to be done in order to describe the effect of DC bias on the shape of the potential well and the height of the layers within the potential well. By varying the DC bias in the cell, the height was found to vary experimentally as VDC 2 by experimental and numerical methods, but as VDC 1/2 for a theoretical approach. The cause of this discrepancy is yet unknown but may lie in dust charge variance or faulty assumptions. Characterization of the potential well allows for greater control of the conditions created by the applied voltage when manipulating the particles.

In semiconductor manufacturing, contamination due to particulates significantly decreases the yield and quality of device fabrication, therefore increasing the cost of production. Dust particle clouds can be found in almost all plasma processing environments including both plasma etching devices and in plasma deposition processes. Dust particles suspended within such plasmas will acquire an electric charge from collisions with electrons and ions in the plasma. If the ratio of inter-particle potential energy to the average kinetic energy is sufficient, the particles will form either a "liquid" structure with short-range ordering or a crystalline structure with long-range ordering. Many experiments have been conducted over the past decade on such colloidal plasmas to discover the character of the systems formed, but more work is needed to fully understand these structures. The preponderance of previous experiments used monodisperse spheres to form complex plasma systems. However, most plasma processing environments contain more arbitrary distributions of particle size. In order to examine in more detail the effects of a size distribution, experiments were carried out in a GEC rf reference cell modified for use as a dusty plasma system. Using two monodisperse particle sizes, experiments were conducted to determine the manner in which phase transitions and other thermodynamic properties depended upon the overall dust grain size distribution. Plasma crystals were formed from different mixtures of 8.89 and 6.50 μm monodisperse particles in argon plasma. With the use of various optical techniques, the pair correlation function was determined at different pressures and powers and then compared to measurements obtained for monodisperse spheres.

Summary form only given. Complex plasmas, which consist of micron-sized dust grains immersed in a plasma environment, have been shown to exhibit unusual characteristics that have earned them a place in some papers as the "fifth state of matter." Under the proper conditions, a complex plasma system can form an ordered crystalline state known as a Coulomb or dust crystal. The conditions that lead to this system have been the subject of intense investigation for the past 10-12 years both in the lab and by means of computer modeling. The dynamics of the dust crystal, particularly wave propagation modes such as DIW, DAW and DLW's have also been a subject of great interest. This paper reports a theoretical examination (using the BOX/spl I.bar/TREE code) of a two dimensional (2D) plasma crystal formed from a non-monodisperse set of particles with a specific particle size distribution. These results are compared against experiments carried out in a GEC rf reference cell modified for use as a complex plasma system. In both cases, the pair correlation function was determined and then compared to previous studies using monodisperse spheres. The effect of such a dust size distribution on the ordering (liquid and/or crystalline) of a complex plasma was examined as was its impact on phase transitions, the dispersion properties for the recently theorized out of plane or optical (transverse) DLW and other thermodynamic properties.

Dust particles immersed within a plasma environment, such as those in protostellar clouds, planetary rings or cometary environments, will acquire an electric charge. If the ratio of the inter-particle potential energy to the average kinetic energy is high enough the particles will form either a “liquid” structure with short-range ordering or a crystalline structure with long range ordering. Many experiments have been conducted over the past several years on such colloidal plasmas to discover the nature of the crystals formed, but more work is needed to fully understand these complex colloidal systems. Most previous experiments have employed monodisperse spheres to form Coulomb crystals. However, in nature (as well as in most plasma processing environments) the distribution of particle sizes is more randomized and disperse. This paper reports experiments which were carried out in a GEC rf reference cell modified for use as a dusty plasma system, using varying sizes of particles to determine the manner in which the correlation function depends upon the overall dust grain size distribution. (The correlation function determines the overall crystalline structure of the lattice.) Two dimensional plasma crystals were formed of assorted glass spheres with specific size distributions in an argon plasma. Using various optical techniques, the pair correlation function was determined and compared to those calculated numerically.

Summary form only given. In semiconductor manufacturing, contamination due to particulates significantly decreases the yield and quality of device fabrication, therefore increasing the cost of production. Dust particle clouds can be found in almost all plasma processing environments including both plasma etching devices and plasma deposition processes. Many experiments have been conducted over the past decade on such colloidal plasmas in an attempt to discover the character of the systems formed, but additional work is needed in order to fully understand the physics behind these structures. The majority of complex plasma experiments to date have employed monodisperse spheres when forming ordered dusty plasma systems. However, in the majority of plasma processing environments the particle size distributions are obviously more randomized and disperse. This paper reports experiments carried out in a GEC rf reference cell modified for use as a complex plasma system. Non-monodisperse particles were used to determine the manner in which phase transitions and other thermodynamic properties depend upon the overall dust grain size distribution. Two dimensional (2D) plasma crystals were formed in an Argon plasma using assorted glass spheres with specific size distributions. Employing various, standard optical techniques, the pair correlation function was then determined for different pressures and powers and compared to measurements obtained for monodisperse spheres.