Samuel R. Conner

Effect of exposure dose on the replication fidelity and profile of very high aspect ratio microchannels in SU-8

We are interested in using SU-8 dense gratings with very high aspect ratio microchannels as the master mold for fabrication of child molds needed for replication. For such applications, the sidewall taper angle and mask replication fidelity of SU-8 are very important. Increasing the exposure time was experimentally observed to decrease the width of the microchannel and the sidewall angle of SU-8 bars. A new diffraction-refraction-reflection model was also developed. The calculated microchannel width and sidewall angle at high exposure dose agreed well with the experimentally observed values indicating that reflection at the silicon substrate was significant. The larger than calculated actual microchannel width for low exposure dose was shown to be due to leaching of unreacted SU-8 in the developer. Dense gratings of high aspect ratio SU-8 bars separated by high aspect ratio (19.1) microchannels were also demonstrated.

MG 1654+1346 - An Einstein Ring image of a quasar radio lobe

VLA radio images of MG 1654+1346, a candidate for an Einstein Ring gravitational lens, reveal two components which are separated by about 7 arcsec. Two optical counterparts, a 19-mag galaxy coincident with the center of the radio ring and a blue 21-mag stellar object located about 3 arcsec northeast of the galaxy, are identified. A model representing the source as a quasar with two extended radio lobes and the lens as an elliptical potential at the position of the galaxy is found to reasonably reproduce the radio observations. 28 refs.

Argon Plasma Modification of SU-8 for Very High Aspect Ratio and Dense Copper Electroforming

This paper presenis a simple but effective method of increasing the wettability of hydrophobic SU-8 grating for use as a copper electrofonning template. Untreated SU-8 is hydrophobic; unpattemed SU-8 has a water contact angle of 73.1 ′ 2.8° and surface energy of 45.5 ′ 0.3 mJ/m 2 . Argon plasma treatment oxidizes and roughens the surface leading to increased surface energy. For treatment times of 60 s or more with plasma power of 200 W, the surface energy, roughness, and degree of oxidation plateaus; the water contact angle decreases to 29.3 ′ 0.2°; and the true surface energy increases to 54.7 ′ 0.3 mJ/m 2 after 180 s Ar-plasma treatment. Copper electrolyte cannot fill the very high aspect ratio and spatially dense microchannels in untreated SU-8 grating (with water contact angle of 124 ′ 4.6°) so that the electroforming circuit remains open. Using a 180 s Ar-plasma treatment, the SU-8 grating becomes hydrophilic (with water contact angle of 7.9 ′ 1.4°); this enables a dense copper grating with alternate microwalls and microchannels of aspect ratios of 15.3 and 9.2, respectively, over the entire 100-mm-diam area to be successfully fabricated from it. This copper mold was used as a mold for UV embossing, demonstrating the feasibility of this technique for the creation of durable molds for mass replication.

The Gravitationally Lensed Radio Source MG 0751+2716

We report the discovery of a new gravitationally lensed radio source. Radio maps of MG0751+2716 show four lensed images, which, at higher resolution, are resolved into long arcs of emission. A group of galaxies is present in optical images, including the principal lensing galaxy, with a much brighter galaxy just a few arcseconds away. We have measured the redshift of this brighter galaxy. No optical counterpart to the background source has been detected. Lens models that can readily reproduce the lensed image positions all require a substantial shear component. However, neither the very elongated lens nor the bright nearby galaxy are correctly positioned to explain the shear. Lens models which associate the mass with the light of galaxies in the group can produce an acceptable fit, but only with an extreme mass-to-light ratio in one of the minor group members.

Reconciling the image brightness ratios in the gravitational lens system 0957+561

The gravitational lens effect is achromatic, yet observations at different wavelengths have yielded different values for the brightness ratio of the two quasar images, A and B, in 0957+561. The radio observations can be separated into VLBI core and VLBI jet regions, which have different brightness ratios. We show that both VLA and VLBI observations show a quasar VLBI core image flux ratio of about 0.75, consistent with optical flux ratios determined from core emission lines and markedly different from the flux ratio of the VLBI jet images

Faint radio sources and gravitational lensing

Measurements of the surface density of radio sources resulting from a deep VLA integration at 5 GHz and the MIT-Green Bank (MG) II 5 GHz survey are summarized. The faint source counts are combined with previous observations and fitted to a power-law function of surface density vs. limiting flux density. The surface density of radio sources brighter than 1 mJy is k = 0.019 + or - 0.004/arcmin. The power-law exponent is best fit by -0.93 + or - 0.14. Between 15 and 100 mJy, the surface density of radio sources varies nearly as predicted by Euclidian models of the universe. Estimates are given for the number of chance alignments of radio sources in the VLA snapshot observations of the MIT-Princeton-Caltech gravitational lens search. The probability of lens candidate configurations occurring by chance alignment is calculated. 28 refs.

Broad- and narrow-band imaging of the giant radio galaxy Cygnus A

Optical broadband and narrowband images of Cygnus A have been compared to VLA radio images of the source. The zero-redshift H-alpha image reveals the distribution of ionized Galactic material toward the radio source. The low emission values noted imply that the large amounts of Faraday rotation observed toward the radio lobes of the galaxy must be of extragalactic origin. It is shown that the radio-core source is located between two optical broadband peaks in the galaxy nucleus, and that the radial-surface brightness profiles follows a de Vaucouleurs r exp 1/4 law out to at least 31 kpc. It is suggested that the double optical nucleus observed is not caused by a kiloparsec-scale dust lane, but by polar radiation from a core source that is obscured by a disk. 36 refs.

The Angular Size Distribution of 4741 Radio Sources in the MIT-VLA Snapshot Archive

The MIT all-sky and VLA snapshot surveys are described, and the scientific results to date are summarized. The largest angular size distribution is given for 4741 MIT-VLA sources, and a Monte-Carlo algorithm is proposed to model the cosmological evolution of jets in radio-loud AGN. Further progress requires compiling redshifts for a complete sub-sample.

Preliminary VLA Snapshots of Southern Radio Sources from the Parkes-MIT-NRAO (PMN) Survey

Selection criteria for 1800 MIT-VLA snapshots of PMN radio sources are described, and 6 new MG & PMN lens candidates are presented.

Resolution of galaxy and third image of gravitational lens 2016+112

The components of 2016+112 are variable. It is probable that all three compact objects are variable, but the absolute flux density scale is difficult to determine. The strong variation of C is contrary to expectations, because VLBI observations show C is extended and must vary more slowly than a compact object. If the C flux density decrease is due to variation of a third image, this image must have very large percentage flux density changes. Any third image, C′, must be very near C, < 0.19 arcseconds away for images with A/C′ flux density ratios < 2 magnitudes. Component C has been resolved, but measuring the contribution of the quasar image to the radio flux density requires further observations. The Narasimha et al. model that is not excluded by these observations suggests that a massive galaxy is located at the radio component C.