Alan Feinerman

Osteoblast proliferation on hydroxyapatite thin coatings produced by right angle magnetron sputtering

Right angle magnetron sputtering (RAMS) was used to produce hydroxyapatite (HA) film coatings on pure titanium substrates and oriented silicon wafer (Si(0 0 1)) substrates with flat surfaces as well as engineered surfaces having different forms. Analyses using synchrotron XRD, AFM, XPS, FTIR and SEM with EDS showed that as-sputtered thin coatings consist of highly crystalline hydroxyapatite. The HA coatings induced calcium phosphate precipitation when immersed in simulated body fluid, suggesting in vivo bioactive behavior. In vitro experiments, using murine osteoblasts, showed that cells rapidly adhere, spread and proliferate over the thin coating surface, while simultaneously generating strong in-plane stresses, as observed on SEM images. Human osteoblasts were seeded at a density of 2500 cells cm(-2) on silicon and titanium HA coated substrates by RAMS. Uncoated glass was used as a reference substrate for further counting of cells. The highest proliferation of human osteoblasts was achieved on HA RAMS-coated titanium substrates. These experiments demonstrate that RAMS is a promising coating technique for biomedical applications.

X-ray lathe: An X-ray lithographic exposure tool for nonplanar objects

An X-ray lithography lathe has been developed that can pattern cylindrical, ellipsoidal, and other nonplanar objects. This lathe is capable of patterning on a micron scale a wide variety of shapes including shapes impossible to achieve with a conventional lathe. A cylindrical core covered with a suitable resist is rotated while being exposed with a collimated X-ray source through a mask. The mask absorbs X rays up to a particular radius from the center of the core and the resist beyond that radius is removed in a developer. Several cylindrical cores were coated with poly(methylmethacrylate) (PMMA) 5 to 125 /spl mu/m thick and patterned with X-rays down to a 250-/spl mu/m horizontal scale (along the lathe axis). The exposure time for a cylindrical PMMA layer is /spl sim/three-four times longer than a planar layer with the same thickness. The capabilities of this technology, lathe apparatus, dose calculations, and initial exposure results are described.

Area-tunable micromirror based on electrowetting actuation of liquid-metal droplets

The authors report a micromirror device actuated by electrowetting effect. The micromirror surface is formed by a liquid-metal droplet jetted on a substrate and then topped with a parylene/Teflon coated indium tin oxide glass slide. The droplet is deformed by a voltage applied across the parylene/Teflon film. The radius of micromirror is tuned from 13μm (0V) to 88μm (90V), and the normalized area increases from 0.2 to 0.94 accordingly. The switching time ranges from 1ms for a 350μm diameter droplet to 0.2ms for a 50μm one. A 4×1 micromirror array is demonstrated and switched simultaneously.

Printing superparamagnetic colloidal particle arrays on patterned magnetic film

Thin ferromagnetic film patterned into isolated islands is used to direct the assembly of superparamagnetic colloidal particles into two-dimensional (2D) arrays. It is confirmed that only one particle per island is retained when particles are slightly larger than the island, whereas particles that are smaller can form various patterns on the islands. Ferromagnetic islands positioned under a template of microwells are shown to promote highly regular 2D arrays, and external uniform magnetic field can be used to bias the particles to attract or to repel from the exposed end of the ferromagnetic islands.

Sub-centimeter micromachined electron microscope

A new approach for fabricating macroscopic (∼10×10×10 mm3) structures with micrometer accuracy has been developed. This approach combines the precision of semiconductor processing and fiber optic technologies. A (100) silicon wafer is anisotropically etched to create four orthogonal v‐grooves and an aperture on each 10×12 mm die. Precision 308 μm optical fibers are sandwiched between the die to align the v‐grooves. The fiber is then anodically bonded to the die above and below it. This procedure is repeated to create thick structures and a stack of 5 or 6 die will be used to create a miniature scanning electron microscope (MSEM). Two die in the structure will have a segmented electrode to deflect the beam and correct for astigmatism. The entire structure is ultrahigh vacuum compatible. The performance of a SEM improves as its length is reduced and a sub‐cm 2 keV MSEM with a field emission source should have approximately 1 nm resolution. A low‐voltage high‐resolution MSEM would be useful for the examination of biological specimens and semiconductors with a minimum of damage. The first MSEM will be tested with existing 6 μm thermionic sources. In the future a micromachined field emission source will be used. The stacking technology presented in this paper can produce an array of MSEMs 1–30 mm in length with a 1 mm or larger period. A key question being addressed by this research is the optimum size for a low‐voltage MSEM which will be determined by the required spatial resolution, field of view, and working distance.

Piston-motion micromirror based on electrowetting of liquid metals

This paper reports a new actuating method of a micromirror with piston motion by the electrowetting effect. Liquid metals drops (LMD), gallium and mercury, instead of conventional electrolyte solution, are used in the electrowetting experiments to reduce the vapor pressure and to increase the conductivity. An approximate formula of LMD height changes versus actuated voltage is deduced and the electrowetting setup is improved for actuating the mirror. The actuating performance of the LMD as a pivot is investigated. The hysteresis of contact angle is effectively minimized with argon sputtering the surface of the insulating layer, which makes the deformation of the LMD highly repeatable. The frequency response (0.01 Hz-3 kHz) and 6 vibration modes of the mercury drop are observed. The maximum acceleration of the drop during the actuation is 300 g (g=9/spl middot/8 m/s/sup 2/). We fabricated a 1000 /spl mu/m/spl times/1000 /spl mu/m/spl times/20 /spl mu/m, 50 /spl mu/g micromirror and an actuating circuit based on the electrowetting of liquid metal. With the LMD confine spot, a mercury drop of 500 /spl mu/m in diameter is placed between the mirror and the actuating electrodes. A 440-Hz sinusoidal voltage of 75 V actuates the micromirror, with a maximum of 60 /spl mu/m displacement.

Analysis of interactions for magnetic particles assembling on magnetic templates

Dipole approximations are used to model up to three superparamagnetic particle systems as they assemble on magnetic island templates. It is shown that small variations in the ratio of particle-to-island diameter as well as the particle positions above the island can change magnetic forces from attractive to repulsive. This observation could potentially permit a template to be designed to promote single particle coverage of individual magnetic islands.

Assessing Graduate Student Progress in Engineering Ethics

Under a grant from the National Science Foundation, the authors (and others) undertook to integrate ethics into graduate engineering classes at three universities—and to assess success in a way allowing comparison across classes (and institutions). This paper describes the attempt to carry out that assessment. Standard methods of assessment turned out to demand too much class time. Under pressure from instructors, the authors developed an alternative method that is both specific in content to individual classes and allows comparison across classes. Results are statistically significant for ethical sensitivity and knowledge. They show measurable improvement in a single semester.

Fabrication of micro/nano fluidic channels with sacrificial galvanic coupled metals

We report a new sacrificial method for micro/nano fluidic channel fabrication by galvanic corrosion of coupled metals. Different metal combinations and etchants are investigated for achieving a high channel etching rate with very small channel cross-sections. Channels as well as channel arrays, from 50??m to tens of nanometres wide, are fabricated by using coupled Cr/Cu as the sacrificial layer. The channel etching rate is investigated as a function of time and width. The channel etching rate of the coupled metals is approximately 10 times faster than that of the single metal. This method is advantageous because of the high resolution, relatively high throughput, and the simplicity of the process.

Initial images with a partially micromachined scanning electron microscope

The focusing properties of a microfabricated silicon electrostatic electron lens have been tested in a machine tool fabricated assembly. Images of a 200 mesh gold transmission electron microscopy wire grid at a working distance of 4 mm are being obtained in transmission. The electron source is a zirconiated tungsten thermally assisted Schottky field emitter operating at 1800 K. The electron detector is a Faraday cup. The beam is scanned over the sample using parallel plate deflectors. The silicon lens is 1.64 mm long and consists of three silicon die separated by Pyrex optical fibers. Images of the grid at magnifications >10 000 × are being obtained.