Core-shell diamond-like silicon photonic crystals from 3D polymer templates created by holographic lithography

Abstract

. Core-shell diamond-like silicon photonic crystals from 3D polymer templates created by holographic lithography. Retrieved from http://repository.upenn.edu/mse_papers/89Core-shell diamond-like silicon photonic crystals from 3D polymer templates created by holographic lithography AbstractWe 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. Comments Abstract:We 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 twoparameter 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. . 27. The calculated bandgap width is smaller than literature value, which may be attributed to the discrepancy in refractive index of silicon used in calculation and calculation resolution.

Triply Periodic Bicontinuous Structures as Templates for Photonic Crystals: A Pinch‐off Problem

“…[12] Using the previously developed two-parameter level surface we found that the pinch-off occurred at filling fraction of 20%, resulting in no complete photonic bandgap between 2nd and 3rd bands. [12] While searching for an appropriate parallel level surface of the diamond-like structure to more accurately study the pinch-off characteristics, we found that a simple combination a diamondlike level surface with a P level surface, in the same way as we did with D structure, did not represent a parallel surface of the diamond-like structure. Thus, we constructed the surface at the pinch-off by the points with the same distance from the template surface.…”

“…To validate the model that approximates the grown layers using a parallel surface and investigate the effect of incomplete filling on the photonic bandgap properties, we chose a three-term diamond-like structure, which has similar symmetry to the fourterm diamond D structure. More importantly, both the polymer template and its inorganic replica of the three-term diamond-like structures can be fabricated rather conveniently [12] , in contrast to the fabrication of P, G, and D structures by holographic patterning. As seen in Fig.…”

“…[2] One possible solution is to use the above bicontinuous structures as templates and backfill with high refractive index materials, [10] followed by removal of the template to obtain inverted replica. [11,12] High index materials, such as titania, [10] selenium, [13] cadmiumselenium, [13] amorphous silicon, [14,15] and germanium, [16,17] have been deposited through dry process, including chemical vapor deposition (CVD) [14][15][16][17] and melting, [13] and wet chemistry through liquid phase sol-gel reaction and precipitation. [18,19] Typically, a conformal shell is formed and grows continuously normal to the initial surface to fill the interstitial voids (Fig.…”

“…S1). [11,12] Previous studies on templating holographically patterned structures, including silica and silicon replicas of a diamond-like structure through sequential CVD process [12] and an inversed titania structure by atomic layer deposition (ALD) [11] , however, suggest that it is challenging to completely fill the triply periodic templates (see Fig. S2).…”

“…Specifically, we constructed the combined level surface using tubular level surfaces, [20] which provided simple and explicit expression of the parallel surfaces from the template, and much improved coating uniformity in comparison to the two-parameter level set approach we developed earlier. [12] By searching for the pinch-off level surfaces for the grown layers, we calculated the achievable volume fraction and the PBGs at the pinch-off. It was shown that D and G templates could not be completely filled through conformal coating approach (e.g.…”