Yang, Shu
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Publication Fabrication of Photonic Crystals with high refractive index(2007-03-09) Xu, Yongan; Yang, Shu; Moon, Jun Hyuk; Johnson, Alan T; Dan, Yaping; Perry, Joseph W; Adibi, Ali; Hotchkiss, Peter; Marder, Seth• Complete photonic bandgap • High contrast of refractive index (RI) • Polymer material with a low RI • Inorganic material with a higher RI, such as silicon, titania. • Fabrication of diamond-like PCs by MBIL, • Fabrication of high RI inorganic PCs via double templating, • Core-shell morphology of replica • Pinch-off problem • Development of combined level-surface to address pinch-off problem • Electrodeposition of titania 3D structure • Electrophoretic deposition of surface charged nanoparticlesPublication Self-Actuated, Thermo-Responsive Hydrogel Valves for Lab on a Chip(2005-06-23) Wang, Jing; Chen, Zongyuan; Mauk, Michael; Hong, Kuang-sheng; Yang, Shu; Li, Mengyan; Bau, Haim HAn easy to fabricate, thermally-actuated, self-regulated hydrogel valve for flow control in pneumatically driven, microfluidic systems is described. This microvalve takes advantage of the properties of the hydrogel, poly(N-isopropylacrylamide), as well as the aqueous fluid itself to realize flow control. The valve was designed for use in a diagnostic system fabricated with polycarbonate and aimed at the detection of pathogens in oral fluids at the location of the sample collection. The paper describes the construction and characterization of the hydrogel valves and their application for flow control, sample and reagent metering, sample distribution into multiple analysis paths, and the sealing of a polymerase chain reaction (PCR) reactor to suppress bubble formation. The hydrogel-based flow control is electronically addressable, does not require any moving parts, introduces minimal dead volume, is leakage and contaminant free, and is biocompatible.Publication Distortion of 3D SU8 Photonic Structures Fabricated by Four-beam Holographic Lithography with Umbrella Configuration(2007-12-12) Zhu, Xuelian; Yang, Shu; Xu, YonganWe present a quantitative study of the distortion from a three-term diamond-like structure fabricated in SU8 polymer by four-beam holographic lithography. In the study of the refraction effect, theory suggests that the lattice in SU8 should be elongated in the [111] direction but have no distortion in the (111) plane, and each triangular-like hole array in the (111) plane would rotate by ~30º away from that in air. Our experiments agree with the prediction on the periodicity in the (111) plane and the rotation due to refraction effect, however, we find that the film shrinkage during lithographic process has nearly compensated the predicted elongation in the [111] direction. In study of photonic bandgap (PBG) properties of silicon photonic crystals templated by the SU8 structure, we find that the distortion has decreased quality of PBG.Publication Creating Three-Dimensional Polymeric Microstructures by Multi-Beam Interference Lithography(2005-10-01) Moon, Jun Hyuk; Yang, ShuIt is attractive to produce true three-dimensional (3D) microstructures both rapidly and economically over a large area with negligible defects for a wide range of applications. Multi-beam interference lithography is one of the promising techniques that can create periodic microstructures in polymers without extensive lithography and etching steps. This review discusses the formation of interference patterns, their dependence on beam parameters, the lithographic process, and the applications to the formation of photonic crystals. Various photoresist systems, including thick films of negative-tone and positive-tone photoresists, liquid resins, organic-inorganic hybrids, and holographic polymer-dispersed liquid crystals, are also reviewed.Publication Core-shell diamond-like silicon photonic crystals from 3D polymer templates created by holographic lithography(2006-06-26) Moon, Jun Hyuk; Yang, Shu; Dong, Wenting; Perry, Joseph W; Adibi, Ali; Yang, Seung-ManWe have fabricated diamond-like silicon photonic crystals through a sequential silica/silicon chemical vapor deposition (CVD) process from the corresponding polymer templates photopatterned by holographic lithography. Core-shell morphology is revealed due to the partial backfilling of the interstitial pores. To model the shell formation and investigate its effect to the bandgap properties, we developed a two-parameter level-set approach that closely approximated the core-shell morphology, and compare the bandgap simulation with the measured optical properties of the 3D crystals at each processing step. Both experimental and calculation results suggest that a complete filling is necessary to maximize the photonic bandgap in the diamond-like structures.Publication Porous Biomimetic Microlens Arrays as Multifunctional Optical Structures(2005-12-01) Yang, Shu; Aizenberg, JoannaMicrolenses are important optical components that image, detect and couple light. Most synthetic microlenses, however, have fixed position and shape once they are fabricated. Therefore, the attainable range of their tunability and complexity is rather limited. In comparison, biological world provides a multitude of varied, new paradigms for the development of adaptive optical networks. This review discusses a few inspirational examples of biological lenses and their synthetic analogs. We focus on the fabrication and characterization of biomimetic microlens arrays with integrated pores, whose appearance and function are similar to a highly efficient optical element formed by brittlestars. The complex microlens design can be created by three-beam interference lithography. These synthetic microlenses have strong focusing ability, and the structure can be, therefore, used as an adjustable lithographic mask, and a tunable optical device coupled with the microfluidic system. The replacement of rigid microlenses with soft hydrogels provides means for changing the lens geometry and refractive index continuously in response to external stimuli, resulting in intelligent, multifunctional, tunable optics.Publication Spontaneous Formation of One-dimensions Ripples in Transit to Highly Ordered Two-dimensional Herringbone Structures Through Sequential and Unequal Biaxial Mechanical Stretching(2007-06-11) Lin, Pei-Chun; Yang, ShuThe authors report the formation of various submicron wrinkle patterns and their transition from one-dimensional (1D) ripples to two-dimensional (2D) herringbone structures on poly(dimethylsiloxane) films. Using mechanical force they can separately control the amount and timing of strain applied to the substrate on both planar directions (either simultaneously or sequentially), which appears to be critical to maneuver the pattern formation in real time. They demonstrate reversible transitions from flat to 1D ripple, to ripple with bifurcation, to ripple/herringbone mixed features, and to well-controlled formation of a highly ordered zigzag-based 2D herringbone structures.Publication Strain responsive concave and convex microlens arrays(2007-12-20) Chandra, Dinesh; Yang, Shu; Lin, Pei-ChunWe report the fabrication of single-component, strain responsive microlens arrays with real-time tunability. The concave lens array is fabricated by patterning hard oxide layer on a bidirectionally prestretched soft elastomer, polydimethylsiloxane PDMS followed by confined buckling upon release of the prestrain. The convex microlens array is replica molded from the concave lenses in PDMS. Due to difference in lens formation mechanisms, the two types of lenses show different tunable range of focal length in response to the applied strain: large focal length change is observed from the concave microlens array, whereas that from the convex microlens array is much smaller.Publication Fabricating Three-Dimensional Polymeric Photonic Structures by Multi-Beam Interference Lithography(2006-02-17) Moon, Jun Hyuk; Ford, Jamie; Yang, ShuThe fabrication of true three-dimensional (3D) microstructures both rapidly and economically over a large area with negligible defects is attractive for a wide range of applications. In particular, multi-beam interference lithography is one of the promising techniques that can mass-produce polymeric 3D photonic crystals defect-free over a large area. This review discusses the relationship between beam geometry and the symmetry of the interference patterns, the lithographic process, and various types of photoresist systems, including thick films of negative-tone and positive-tone photoresists, organic-inorganic hybrids, hydrogels, and holographic polymer-dispersed liquid crystals.Publication A Tendon-Driven Origami Hopper Triggered by Proprioceptive Contact Detection(2020-04-06) Chen, Wei-Hsi; Misra, Shivangi; Caporale, J. Diego; Yang, Shu; Sung, Cynthia R.; Koditschek, Daniel EWe report on experiments with a laptop-sized (0.23m, 2.53kg), paper origami robot that exhibits highly dynamic and stable two degree-of-freedom (circular boom) hopping at speeds in excess of 1.5 bl/s (body-lengths per second) at a specific resistance O(1) while achieving aerial phase apex states 25% above the stance height over thousands of cycles. Three conventional brushless DC motors load energy into the folded paper springs through pulley-borne cables whose sudden loss of tension upon touchdown triggers the release of spring potential that accelerates the body back through liftoff to flight with a 20W powerstroke, whereupon the toe angle is adjusted to regulate fore-aft speed. We also demonstrate in the vertical hopping mode the transparency of this actuation scheme by using proprioceptive contact detection with only motor encoder sensing. The combination of actuation and sensing shows potential to lower system complexity for tendon-driven robots. For more information: Kod*lab (link to kodlab.seas.upenn.edu)