Daniel M. Hartmann

Characterization of a polymer microlens fabricated by use of the hydrophobic effect.

We report a means of fabricating hydrophilic domains in a hydrophobic background by lithographically patterning an adhesive hydrophobic layer. Polymer microlenses were fabricated on these substrates by use of a dip-coating technique. Various lens shapes (circular, elliptical, square) were fabricated on a variety of substrates (SiO(2), SiN, GaAs, InP, etc.), ranging in size from 2 to 500 microm in diameter, with fill factors of up to 90%. Plano-convex and double-convex lenses were fabricated, with f-numbers as low as 1.38 and 1.2, respectively. Optimum lens surfaces deviated from spherical by just +/-5 nm . The lenses are stable at room temperature and exhibit minimal degradation after 24 h at 105 degrees C. The transfer of these polymer lenses to an underlying substrate was also demonstrated.

Optimization and theoretical modeling of polymer microlens arrays fabricated with the hydrophobic effect

High-performance polymer microlens arrays were fabricated by means of withdrawing substrates of patterned wettability from a monomer solution. The f-number (f(#)) of formed microlenses was controlled by adjustment of monomer viscosity and surface tension, substrate dipping angle and withdrawal speed, the array fill factor, and the number of dip coats used. An optimum withdrawal speed was identified at which f(#) was minimized and array uniformity was maximized. At this optimum, arrays of f/3.48 microlenses were fabricated with one dip coat with uniformity of better than Deltaf/f +/- 3.8%. Multiple dip coats allowed for production of f/1.38 lens arrays and uniformity of better than Deltaf/f +/-5.9%. Average f(#)s were reproducible to within 3.5%. A model was developed to describe the fluid-transfer process by which monomer solution assembles on the hydrophilic domains. The model agrees well with experimental trends.

Selective DNA attachment of micro- and nanoscale particles to substrates

Materials formed from micro- and nanoscale particles are of interest because they often exhibit novel optical, electrical, magnetic, chemical, or mechanical properties. In this work, a means of constructing particulate materials using DNA strands to selectively attach micro- and nanoparticles to substrates was demonstrated. Unlike previous schemes, the DNA was anchored covalently to the particles and substrates, rather than through protein intermediaries. Highly reproducible selective attachment of 0.11‐0.87 mm-diameter particles was achieved, with selective:nonselective binding ratios >20:1. Calculations showed that at most 350 and 4200 DNA strands were involved in the binding of the small and large particles, respectively. Experiments showed that the DNA was bent at an angle, relative to the surfaces of their solid supports.

Polymer microlens arrays fabricated using the hydrophobic effect

We report a means of fabricating hydrophilic domains in a hydrophobic background by lithographically patterning an adhesive hydrophobic layer. Organic polymer microlenses have been fabricated on these substrates using a dip-coating technique. Various lens shapes (circular, elliptical, square) have been fabricated on a variety of substrates (SiO2, SiN, GaAs, InP, etc), ranging in size from 2 - 500 micrometers in diameter, and having fill factors of up to 90%. Plano-convex and double-convex lenses have been fabricated as fast as f/1.38 and f/1.2, respectively. The performance of arrays of these microlenses was quantitatively analyzed and optimized.

Heterogeneous integration of optoelectronic components

The heterogeneous integration of optoelectronic, electronic, and micro-mechanical components from different origins and substrates makes possible many advanced systems in diverse applications. Besides the monolithic integration approach, which is the basis for the success of todays silicon industry, various hybrid integration technologies have been explored. These include flip-chip bonding, micro-robotic placement, epitaxial lift-off and direct bonding, substrate removal and bonding, and several self-assembly methods. In this paper, we describe the results of our monolithic integration effort involving a 2 by 2 optoelectronic switching circuit and an 8 by 8 active-pixel sensor array on GaAs substrates, and a 16 by 16 spatial light modulator array produced by flip-chip bonding of III-V multi-quantum-well (MQW) modulators and silicon driver circuits. We also present our preliminary experimental results on the self-assembly of small inorganic devices coated with DNA polymers with self- recognition properties.

Superresolution Using a Vertical-Cavity Surface-Emitting Laser (VCSEL) with a High-Order Laguerre-Gaussian Mode.

A vertical-cavity surface-emitting laser (VCSEL) is current-annealed to operate in the high order (0, 4) Laguerre mode, and this source is used in a superresolution setup to achieve a spot size smaller than the classical diffraction limit. Theory predicts a reduction down to 51% of the classical limit in each dimension (i.e. 4× reduction in area), and a reduction down to 65% (i.e. 2.5× reduction in area) is experimentally demonstrated with a signal-to-noise ratio of >10 dB between the main-lobe and the side-lobe intensities.

DNA-assisted microassembly: a hetrogeneous integration technology for optoelectronics

The integration of optoelectronic and electronic components from different origins and substrates makes possible many advanced systems in diverse applications in photonics. To this end, various hybrid integration technologies including flip-chip bonding, epitaxial lift-off and direct bonding, substrate removal and “applique” bonding, microrobotic pick and place, and self-assembly methods have been explored. In this paper, we will briefly describe and evaluate these approaches for their applications in optoelectronics and focus on a new micro-assembly technology that can pick, place, and bond many devices of different origins and dimensions simultaneously in a parallel fashion on very large surfaces. We will present some of our preliminary results demonstrating the feasibility of this DNA-assisted micro-assembly technique.