High-performance surface-micromachined inchworm actuator

This work demonstrates a polycrystalline silicon surface-micromachined inchworm actuator that exhibits high-performance characteristics such as large force (/spl plusmn/0.5 millinewtons), large velocity range (0 to /spl plusmn/4.4 mm/sec), large displacement range (/spl plusmn/100 microns), small step size (/spl plusmn/10, /spl plusmn/40 or /spl plusmn/100 nanometers), low power consumption (nanojoules per cycle), continuous bidirectional operation and relatively small area (600 /spl times/ 200/spl mu/m/sup 2/). An in situ load spring calibrated on a logarithmic scale from micronewtons to millinewtons, optical microscopy and Michelson interferometry are used to characterize its performance. The actuator consists of a force-amplifying plate that spans two voltage-controlled clamps, and walking is achieved by appropriately sequencing signals to these three components. In the clamps, normal force is borne by equipotential rubbing counterfaces, enabling friction to be measured against load. Using different monolayer coatings, we show that the static coefficient of friction can be changed from 0.14 to 1.04, and that it is load-independent over a broad range. We further find that the static coefficient of friction does not accurately predict the force generated by the actuator and attribute this to nanometer-scale presliding tangential deflections.     

Tribological Impact of SiC Encapsulation of Released Polycrystalline Silicon Microstructures

A method for coating released polysilicon microstructures with thin, uniform and conformal coatings of SiC derived from the single source precursor, 1,3-disilabutane (DSB) has been developed. This coating method has been successfully applied to micromechanical test devices which allow evaluation of friction and wear properties of the coating. Here, data on the coefficient of static friction of SiC coatings produced from DSB is presented. Also, a comparative wear study for devices which have been oxidized, treated with an anti-adhesion coating, and SiC coated is shown. Wear is examined by scanning electron microscopy (SEM) on devices which have been cycled repetitively under a nominal load. It is found that the application of a few nanometers-thin SiC coating provides exceptional wear resistance as well as significant reduction in friction on the microscale.     

FURTHER STUDIES ON THE OXIDATION OF HOP RESINS

The autoxidation of humulone, isohumulone, colupulone and cohulupone has been studied using chromatography on an ion-exchange resin. Humulone gave a mixture of products which were largely insoluble in light petroleum whereas most of the products obtained by autoxidation of colupulone were soluble in that solvent. Cohulupone was isolated for the first time from the autoxidation of colupulone. The brewing value of a water-soluble fraction of hops was also examined. The degree of resolution obtained from the ion-exchange chromatographic system enabled a detailed examination of the constituents of hop concentrates and extracts to be made.     

ISOMERIZED HOP EXTRACTS IN EXPERIMENTAL BREWING

The later that isomerized hop extracts were added during the brewing process the better was the utilization. Thin layer chromatography of the beers produced from a range of experimental brews using isomerized hop extracts showed that the ratios of the various bitter substances derived from hops differed only slightly. The utilization of isomerized extract is enhanced if residues normally discarded during the manufacture of extracts are added to wort.     

Tribological Challenges in Micromechanical Systems

Despite much progress in surface micromachining technology, adhesion, friction and wear remain key issues, severely limiting the realization and reliability of many microelectromechanical systems (MEMS) devices. In this article, we focus on the use of molecularly thin organic films as release and anti-stiction coatings for MEMS. The various classes of organic films explored for MEMS are reviewed here, followed by a discussion of the current limitations and areas for improvements for this coating technology.     

Dependence of magnetic domain structure on grain orientation in 3.2% silicon-iron with the (110) [0 0 1] texture

A series of ferromagnetic domain structures in individual grains of (110) [001] textured 3.2% silicon-iron has been observed and measured together with the orientation of the grain. It has been shown that the domain dimensions are inversely proportional to the angle of misorientation of the (110) plane from the grain surface. This is in very good agreement with the theory given by ?pa?ek [1, 2]. The lozenge domain structure has also been investigated as a function of grain orientation and the measurements are in excellent agreement with the theory proposed by Goodenough [5].     

Characterization of pheophytin ground states in Rhodobacter sphaeroides R26 photosynthetic reaction centers from multispin pheophytin enrichment and 2-D 13C MAS NMR dipolar correlation spectroscopy

The electronic ground states of pheophytin cofactors potentially involved in symmetry breaking between the A and B branch for electron transport in the bacterial photosynthetic reaction center have been investigated through a characterization of the electron densities at individual atomic positions of pheophytin a from 13C chemical shift data. A new experimental approach involving multispin 13C labeling and 2-D NMR is presented. Bacterial photosynthetic reaction centers of Rhodobacter sphaeroides R26 were reconstituted with uniformly 13C biosynthetically labeled (plant) Pheo a in the two pheophytin binding sites. From the multispin labeled samples 1-D and 2-D solid-state 13C magic angle spinning NMR spectra could be obtained and used to characterize the pheophytin a ground state in the Rb. sphaeroides R26 RCs, i.e., without a necessity for time-consuming selective labeling strategies involving organic synthesis. From the 2-D solid state 13C-13C correlation spectra collected with spinning speeds of 8 and 10 kHz, with mixing times of 1 and 0.8 ms, many 13C resonances of the [U-13C]Pheo a molecules reconstituted in the RCs could be assigned in a single set of experiments. Parts of the pheophytins interacting with the protein, at the level of 13C shifts modified by binding, could be identified. Small reconstitution shifts are detected for the 17(2) side chain of ring IV. In contrast, there is no evidence for electrostatic differences between the two Pheo a, for instance, due to a possibly strong selective electrostatic interaction with Glu L104 on the active branch. The protonation states appear the same, and the NMR suggests a strong overall similarity between the ground states of the two Pheo a, which is of interest in view of the asymmetry of the electron transfer.     

A New Method to Determine Adhesion of Cantilever Beams Using Beam Height Experimental Data

A new method for calculating the apparent work of adhesion of microfabricated cantilever beams is presented and validated. This technique, based on popular beam mechanics, directly utilizes interferometrically produced deflection experimental data. The data are analyzed based on an energy minimization approach along the lines of a previous methodology. However, the new technique differs in that it does not rely on a priori knowledge of the shape of cantilever beams to evaluate work of adhesion. In order to validate the new method, both synthetic and empirical cantilever beam data were examined. The results show that apparent work of adhesion values calculated using this method agree well with values determined using a technique previously developed and widely accepted.