Characterization of Metal and Metal Alloy Films as Contact Materials in MEMS Switches

This study presents a basic step toward the selection methodology of electric contact materials for microelectromechanical systems (MEMS) metal contact switches. This involves the interrelationship between two important parameters, resistivity and hardness, since they provide the guidelines and assessment of contact resistance, wear, deformation and adhesion characteristics of MEMS switches. For this purpose, thin film alloys of three noble metals, platinum (Pt), rhodium (Rh) and ruthenium (Ru) with gold (Au), were investigated. The interrelationship between resistivity and hardness was established for three levels of alloying of these metals with gold. Thin films of gold (Au), platinum (Pt), ruthenium (Rh) and rhodium (Ru) were also characterized to obtain their baseline data for comparison. All films were deposited on silicon substrates. When Ru, Rh and Pt are alloyed with Au, their hardness generally decreases but resistivity increases. This decrease or increase was, in general, dependent upon the amount of alloying

Kaluza-Klein Dark Matter and the Positron Excess

The excess of cosmic positrons observed by the HEAT experiment may be the result of Kaluza-Klein dark matter annihilating in the galactic halo. Kaluza-Klein dark matter annihilates dominantly into charged leptons that yield a large number and hard spectrum of positrons per annihilation. Given a Kaluza-Klein dark matter particle with a mass in the range of 300-400 GeV, no exceptional substructure or clumping is needed in the local distribution of dark matter to generate a positron flux that explains the HEAT observations. This is in contrast to supersymmetric dark matter that requires unnaturally large amounts of dark substructure to produce the observed positron excess. Future astrophysical and collider tests are outlined that will confirm or rule out this explanation of the HEAT data.Comment: 5 pages, 3 figures, REVTeX

Looking Good With Flickr Faves: Gaussian Processes for Finding Difference Makers in Personality Impressions

Flickr allows its users to generate galleries of "faves", i.e., pictures that they have tagged as favourite. According to recent studies, the faves are predictive of the personality traits that people attribute to Flickr users. This article investigates the phenomenon and shows that faves allow one to predict whether a Flickr user is perceived to be above median or not with respect to each of the Big-Five Traits (accuracy up to 79\% depending on the trait). The classifier - based on Gaussian Processes with a new kernel designed for this work - allows one to identify the visual characteristics of faves that better account for the prediction outcome

Selecting Metal Alloy Electric Contact Materials for MEMS Switches

This paper presents a method for selecting metal alloys as the electric contact materials for microelectromechanical systems (MEMS) metal contact switches. This procedure consists of reviewing macro-switch lessons learned, utilizing equilibrium binary alloy phase diagrams, obtaining thin film material properties and, based on a suitable model, predicting contact resistance performance. After determining a candidate alloy material, MEMS switches were designed, fabricated and tested to validate the alloy selection methodology. Minimum average contact resistance values of 1.17 and 1.87 Ω were measured for micro-switches with gold (Au) and gold–platinum (Au–(6.3%)Pt) alloy electric contacts, respectively. In addition, \u27hot-switched\u27 life cycle test results of 1.02 × 108 and 2.70 × 108 cycles were collected for micro-switches with Au and Au–(6.3%)Pt contacts, respectively. These results indicate increased wear with a small increase in contact resistance for MEMS switches with metal alloy electric contacts

Reliability Testing of AlGaN/GaN HEMTs Under Multiple Stressors

We performed an experiment on AlGaN/GaN HEMTs with high voltage and high power as stressors. We found that devices tested under high power generally degraded more than those tested under high voltage. In particular, the high-voltage-tested devices did not degrade significantly as suggested by some papers in the literature. The same papers in the literature also suggest that high voltages cause cracks and pits. However, the high-voltage-tested devices in this study do not exhibit cracks or pits in TEM images, while the high-power-tested devices exhibit pits

A new solution suggesting the need for a new equation

When Victoria Hale first came up with the notion of starting the Institute for OneWorld Health (iOWH), some cautioned that the idea of a non-profit pharmaceutical company developing drugs to treat neglected diseases was a proven loser. The more direct among them might also have inquired why a successful scientist, trained in being analytic, consistent and logical, would undertake such an evidently hopeless project. Yet a few years later, iOWH has not only achieved its first drug approval (i.e. Paramomycin for the treatment of leishmaniasis or ‘black fever’, approved for use in India), it has also seen that same drug included in WHO’s Essential Medicines list, and has research results in the New England Journal of Medicine. This turnaround raises a question: Did skeptics fail to grasp Hale’s clever insights, misjudge the depth of her commitment, or underestimate the extent of her potential good fortune? Put more simply, is Hale’s a story of smarts, guts, and luck

The Green Legacy Project: Evaluating Campus Tree Benefits

Trees on our campus sequester and store carbon, mitigate urban heat island effects, ameliorate air pollution, reduce stormwater runoff, improve water quality, provide habitat for native birds and other animals, and enhance aesthetics. Adequate planning and management of this valuable resource first requires a sound understanding of existing conditions. To this end, a collaborative group of faculty, staff, and students at West Chester University initiated the Green Legacy Project. We conducted an inventory and assessment of north campus tree resources and developed a GIS management database. Approximately 1900 trees cover 16% of north campus, half of which are non-native species. The value of the trees is an estimated $3.2 million with annual benefits of$250,000

Indirect Detection of Kaluza-Klein Dark Matter from Latticized Universal Dimensions

We consider Kaluza-Klein dark matter from latticized universal dimensions. We motivate and investigate two different lattice models, where the models differ in the choice of boundary conditions. The models reproduce relevant features of the continuum model for Kaluza-Klein dark matter. For the model with simple boundary conditions, this is the case even for a model with only a few lattice sites. We study the effects of the latticization on the differential flux of positrons from Kaluza-Klein dark matter annihilation in the galactic halo. We find that for different choices of the compactification radius, the differential positron flux rapidly converges to the continuum model results as a function of the number of lattice sites. In addition, we consider the prospects for upcoming space-based experiments such as PAMELA and AMS-02 to probe the latticization effect.Comment: 25 pages, 9 figures, LaTeX. Final version published in JCA

Modeling Micro-Porous Surfaces for Secondary Electron Emission Control to Suppress Multipactor

This work seeks to understand how the topography of a surface can be engineered to control secondary electron emission (SEE) for multipactor suppression. Two unique, semi-empirical models for the secondary electron yield (SEY) of a micro-porous surface are derived and compared. The first model is based on a two-dimensional (2D) pore geometry. The second model is based on a three-dimensional (3D) pore geometry. The SEY of both models is shown to depend on two categories of surface parameters: chemistry and topography. An important parameter in these models is the probability of electron emissions to escape the surface pores. This probability is shown by both models to depend exclusively on the aspect ratio of the pore (the ratio of the pore height to the pore diameter). The increased accuracy of the 3D model (compared to the 2D model) results in lower electron escape probabilities with the greatest reductions occurring for aspect ratios less than two. In order to validate these models, a variety of micro-porous gold surfaces were designed and fabricated using photolithography and electroplating processes. The use of an additive metal-deposition process (instead of the more commonly used subtractive metal-etch process) provided geometrically ideal pores which were necessary to accurately assess the 2D and 3D models. Comparison of the experimentally measured SEY data with model predictions from both the 2D and 3D models illustrates the improved accuracy of the 3D model. For a micro-porous gold surface consisting of pores with aspect ratios of two and a 50% pore density, the 3D model predicts that the maximum total SEY will be one. This provides optimal engineered surface design objectives to pursue for multipactor suppression using gold surfaces