We demonstrate that super-resolution imaging of specimens containing sub-diffraction-limited features is feasible by using dielectric microwires fabricated through capillary force lithography followed by photopatterning. As supplementary micron scale cylindrical lenses, we fabricated uniform-sized microwires with and 5 and 10 μm diameters and refractive index ~1.3-1.6. The microwires are placed in contact with the specimen to collect the information of the sub-wavelength features of the specimen and transmit them to the far-field with magnification enabling imaging with two-fold resolution improvement. Potential applications of our imaging technique include biological imaging, microfluidics, and nanophotonics applications.
We study structural symmetries of two-dimensional (2D) photonic crystals with anisotropic unit cells, including square- and
rectangular-lattices with orientationally modulated elliptic motifs, a compound structure consisting of circles with 6-fold rotational symmetry and elliptical lines with 2-fold symmetry, and a rectangular lattice of aligned ovals, which are created through elastic deformation of an elastomeric membrane with circular pores. We then investigate the photonic bandgap (PBG) properties of the corresponding 2D Si posts, and their tolerance to the structural deviation. We find that in the compound structure the overall PBGs are dominated by the sublattice with a higher symmetry, while the total symmetry is determined by the one with a lower symmetry.
In order to create three-dimensional (3D) photonic crystals (PCs) with large photonic bandgap properties (PBG), it is
necessary to control the 3D fabrication with desired symmetry, high index contrast, and high structural stability. To
rational design the 3D photonic structures fabricated by holographic lithography, we have conducted quantitative
analysis to study structural distortion during each processing step and their impact to PBG. Because of the relatively low
dielectric contrast between typical polymers and air, the directly patterned polymer structures are usually used as
templates for backfilling of high-index materials, followed by removal of the polymer template to realize complete
PBGs. Therefore, the fidelity of the final PCs is critically dependent on the thermal and mechanical robustness of the
polymer templates, the deposition methods (e.g. dry chemical vapor deposition vs. wet chemistry), and the template
removal procedure. Here, we address these challenges using different photoresist systems and deposition methods to
create Si and titania 3D PCs.
Diamond-like silicon photonic crystals were fabricated by sequential chemical vapor deposition of silica and silicon on
polymer templates photopatterned by holographic lithography. The optical properties of the 3D crystals after each
processing step were measured and compared to the corresponding bandgap simulation. The core-shell morphology
formed during CVD process is approximated using two level surfaces.
Photonic crystals have now started to make the transition from basic to applied research, with new
materials systems and device results being published on a frequent basis. While a number of
photonic crystals have been made using organic materials, the lack of high index organic materials
has impeded their development. We have investigated several novel high index organic systems for
use in both 2-D and 3-D photonic crystals. 2-D photonic crystal templates were made by a rapid
multibeam interference method in the photoresist SU-8, using 532nm laser radiation. These samples,
typically on glass, were then infiltrated by a number of methods including from solution and melt, as
well through chemical vapor deposition. Solutions of a titanium precursor with a cured refractive
index of 2.1 at 633nm were infiltrated and cured in the SU-8 structure, with the infiltrant deposited by
both by spin coating and casting. The resulting structure was shown to preserve the six-fold
symmetry of the initial photonic crystal and subsequent firing at high temperature effectively
removed the SU-8 template. We have also explored the infiltration of nanoamorphous carbon into
the photonic crystals using chemical vapor deposition. This material, which is essentially a
carbon-silicon ceramic, has exceptional infrared optical properties with a refractive index > 2 for
wavelengths beyond 2 μm. The SU-8 polymer template has been shown to survive the CVD
deposition process and the resulting infiltrated structure also preserves the initial PC symmetry. A
series of metal-like PCs with a full range of properties is enabled by the ability to dope the
nanoamorphous carbon with metals that possess exceptional refractive indices in the infrared regions
of interest. We have also investigated the potential for nonlinear optical devices based upon
azobenzene copolymer infiltrated silicon PCs and demonstrate the excellent properties of this material
with respect to all-optical effects.
The role of block copolymers as additives for improving resist performance in the area of 193 nm lithography is investigated in this study. We have demonstrated that specifically designed block copolymers when tailored to resist matrices to which they are added can profoundly enhance resist imaging performance. This improvement can be attributed to the ability of the block copolymers to modify surface and interfaces and to control photoacid generator distribution within the resist film. Ion beam techniques such as Rutherford Backscattering and Forward Recoil Spectrometry, used to analyze the distribution and segregation behavior of the photoacid generators and block copolymer additives, will also be described.