We present a new method based on B-spline snakes (active contours) for measuring high-accuracy contact angles. In this approach, we avoid making physical assumptions by defining the contour of the drop as a versatile B-spline curve. When useful, we extend this curve by mirror symmetry so that we can take advantage of the reflection of the drop onto the substrate to detect the position of the contact points. To keep a wide range of applicability, we refrain from discretizing the contour of the drop, and we choose to optimize an advanced image-energy term to drive the evolution of the curve. This term has directional gradient and region-based components; additionally, another term-an internal energy-is responsible for the snake elasticity and constrains the parameterization of the spline. While preserving precision at the contact points, we limit the computational complexity by constraining a non-uniform repartition of the control points. The elasticity property of the snake links the local nature of the contact angle to the global contour of the drop. A global knowledge of the drop contour allows us to use the reflection of the drop on the substrate to automatically and precisely detect a line of contact points (vertical position and tilt). We apply cubic-spline interpolation over the image of the drop; then, the evolution procedure takes part in this continuous domain to avoid the inaccuracies introduced by pixelization and discretization.We have programmed our method as a Java software and we make it freely available [A.F. Stalder, DropSnake, Biomedical Imaging Group, EPFL, [ON LINE] visited 2005. http://bigwww.epfl.ch/demo/dropanalysis]. Our experiments result in good accuracy thanks to our high-quality image-interpolation model, while they show applicability to a variety of images thanks to our advanced image-energy term.

Superhydrophobicity is obtained on photolithographically structured silicon surfaces consisting of flat-top pillars after a perfluorosilanization treatment. Systematic static contact angle measurements were carried out on these surfaces as a function of pillar parameters that geometrically determine the surface roughness, including pillar height, diameter, top perimeter, overall filling factor, and disposition. In line with thermodynamics models, two regimes of static contact angles are observed varying each parameter independently: the "Cassie" regime, in which the water drop sits suspended on top of the pillars (referred to as composite), corresponding to experimental contact angles greater than 140-150 degrees, and the "Wenzel" regime, in which water completely wets the asperities (referred to as wetted), corresponding to lower experimental contact angles. A transition between the Cassie and Wenzel regimes corresponds to a set of well-defined parameters. By smoothly depositing water drops on the surfaces, this transition is observed for surface parameter values far from the calculated ones for the thermodynamic transition, therefore offering evidence for the existence of metastable composite states. For all studied parameters, the position of the experimental transition correlates well with a rough estimation of the energy barrier to be overcome from a composite metastable state in order to reach the thermodynamically favored Wenzel state. This energy barrier is estimated as the surface energy variation between the Cassie state and the hypothetical composite state with complete filling of the surface asperities by water, keeping the contact angle constant.

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In micro/nanoelectromechanical systems ͑MEMS/NEMS͒, surface-dominated forces, such as stiction/adhesion and friction, play an important role because of the large surface-area-to-volume ratio. In order to control these forces and wear properties, optimal lubricant systems have been extensively investigated. Perfluoroalkyl self-assembled monolayers ͑SAMs͒ are considered to be a strong candidate since the fluorinated carbon backbones are expected to show lower adhesion and friction. In this paper, surface properties of perfluoroalkylsilane SAMs are investigated and compared with those of standard alkylsilane SAMs. The SAMs are deposited on silicon with a native oxide layer and silica substrates by a vapor deposition process. Surface properties, such as surface energy, water contact angle, roughness, adhesive and friction forces, and wear resistance, are evaluated. An atomic force microscope ͑AFM͒ is used for evaluations of the micro/nanotribological properties. The influence of humidity, temperature, and sliding velocity is also examined. In addition, the tribological mechanisms of the SAMs on molecular scale are discussed based on the AFM observations to aid the design and selection of proper lubricants for MEMS/NEMS.

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Abstract-This paper provides a detailed analysis of gainclamped doped-fiber amplifiers and design guidelines in a wavelength division multiplexed (WDM) networking environment. A simple dynamic model of the doped-fiber amplifier allows us to derive explicit expressions for the small-signal response, which help identify and optimize the most critical parameters for best dynamic performance. The most important parameter is the pump power, which should be chosen 1-2 dB's above its required open-loop value, with all channels present, for the required signal gain. In an all-optical networking scenario with input power per channel as high as 03 dBm the required pump power may well exceed 20 dBm. Thus optimization of other parameters such as laser wavelength and loop loss are important. For best dynamic performance either the loop loss should be extremely small, implying a very large laser flux, or the laser gain variation in response to a perturbation should be large. Accordingly, the laser wavelength should be placed either close to the unity-gain region of the clamped gain profile, or at its peak. Finally, the small signal model for a chain of clamped amplifiers is provided, and it is shown that long chains are vulnerable to low-frequency input signal perturbations.Index Terms-Doped-amplifier gain dynamics, erbium-doped fiber amplifier (EDFA), gain-clamping.

This abstract reports a new anti-stiction coating that improves the releasing of surface-micromachined products. The difference with respect to similar work in this field is the type of molecules used for the coating that impinges the formation of aggregates or chains. These aggregates can he responsible for the stmcture malfunctioning and can even bind the released structures to the substrate. The suppression of these aggregates or chains with our coating has been confirmed by roughness measurements on such coatings. Moreover, we have measured an advancing contact angle of 127", which is the best contact angle obtained on similar coating to our knowledge. And finally, this coating has been successfully used to improve, the release related stiction on MEMS test structures and products.