Dr. Nicholas Sharac Profile

Dr. Nicholas Sharac

Postdoc Research Fellow

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Publications (3)

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Proceedings Article | 21 February 2019 Presentation + Paper

3D-printed infrared metamaterials

N. Sharac, G. R. Iyer, J. Tischler

Proceedings Volume 10926, 109261Q (2019) https://doi.org/10.1117/12.2510994

KEYWORDS: Etching, Dielectrics, Silicon carbide, Silicon, Reactive ion etching, Scanning electron microscopy, Electron beam lithography, Photoresist materials, Phonons, Atomic force microscopy, 3D printing

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Dielectric and semiconductor structures at the nanoscale are increasingly being applied in nanophotonic applications such as enhanced sensing, magnetic field enhancements, and metasurfaces. In contrast to their traditional metal plasmon counterparts -- such as Au and Ag -- dielectric materials benefit from low losses and CMOS compatibility. Here we explore of 3D dielectric structures on the nanometer and micron scales via a new patterning method, which employs both 3D, direct laser write (DLW) and reactive ion etching (RIE). Polymer structures, which are controlled down to the submicron scale both laterally and in height are printed using DLW onto various dielectric materials and are sub sequentially, etched using RIE. By tuning the etch ratio of the dielectric and polymer, the 3D printed pattern is transferred into the dielectric. By patterning a range of different 3D geometries onto Si, SiC, and hBN, we show that this method is applicable to a range of dielectric and semiconductor materials and to a range of different microstructures and nanostructures. Further, we show the possibility of selectively removing the polymer mask without damaging the underlying dielectric material, which enables the possibility of additional fabrication methods, such as for etching thin films.

Proceedings Article | 18 May 2015 Paper

Highly nonlinear sub-micron silicon nitride trench waveguide coated with gold nanoparticles

Yuewang Huang, Qiancheng Zhao, Nicholas Sharac, Regina Ragan, Ozdal Boyraz

Proceedings Volume 9503, 95030H (2015) https://doi.org/10.1117/12.2182290

KEYWORDS: Waveguides, Silicon, Nanoparticles, Gold, Refractive index, Semiconducting wafers, Wave propagation, Etching, Metals, Particles

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We demonstrate the fabrication of a highly nonlinear sub-micron silicon nitride trench waveguide coated with gold nanoparticles for plasmonic enhancement. The average enhancement effect is evaluated by measuring the spectral broadening effect caused by self-phase-modulation. The nonlinear refractive index n₂ was measured to be 7.0917×10^-19 m²/W for a waveguide whose W_open is 5 μm. Several waveguides at different locations on one wafer were measured in order to take the randomness of the nanoparticle distribution into consideration. The largest enhancement is measured to be as high as 10 times. Fabrication of this waveguide started with a MEMS grade photomask. By using conventional optical lithography, the wide linewidth was transferred to a <100> wafer. Then the wafer was etched anisotropically by potassium hydroxide (KOH) to engrave trapezoidal trenches with an angle of 54.7º. Side wall roughness was mitigated by KOH etching and thermal oxidation that was used to generate a buffer layer for silicon nitride waveguide. The guiding material silicon nitride was then deposited by low pressure chemical vapor deposition. The waveguide was then patterned with a chemical template, with 20 nm gold particles being chemically attached to the functionalized poly(methyl methacrylate) domains. Since the particles attached only to the PMMA domains, they were confined to localized regions, therefore forcing the nanoparticles into clusters of various numbers and geometries. Experiments reveal that the waveguide has negligible nonlinear absorption loss, and its nonlinear refractive index can be greatly enhanced by gold nano clusters. The silicon nitride trench waveguide has large nonlinear refractive index, rendering itself promising for nonlinear applications.

Proceedings Article | 11 September 2013 Paper

Tunable nano bead arrays on film for controlling propogation of light

Nicholas Sharac, Himanshu Sharma, Michelle Khine, Regina Ragan

Proceedings Volume 8809, 88091O (2013) https://doi.org/10.1117/12.2026143

KEYWORDS: Etching, Picosecond phenomena, Plasmonics, Nanostructures, Gold, Plasma etching, Surface enhanced Raman spectroscopy, Metals, Scanning electron microscopy, Atomic force microscopy

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Periodic arrays of sub-wavelength structures have garnered significant interest for surface enhanced Raman spectroscopy (SERS) and metal enhanced fluorescence (MEF), and for anti-reflective coating properties. For SERS and MEF, coupling metal nanoparticles with nanometer scale spacing can induce strong local electromagnetic field enhancements at the plasmon resonance, significantly increasing the Raman signal or fluorescence of a molecule. Inspired by moth eyes, metal nanoparticle arrays can reduce the reflection of incident light, shown useful for improving the efficiency of solar cells. Here, we present fabrication of robust, tunable, inexpensive and quickly reproducible gold coated, nanopillar arrays for applications in enhancing Raman/fluorescence signals or antireflective surfaces for efficient solar cells. To create homogenous metallic nanostructures with controllable sizes and interparticle spacings, we have integrated conventional nanosphere lithography techniques with thermally responsive polyolefin (PO) films. Spin coating 500 nm PS beads onto PO substrates, followed by oxygen plasma etching, is used to vary the size and periodicity of the resulting PS nanopillar bead array. A 50 nm thick gold film can then be added using chemical vapor deposition (CVD). Nanostructures were characterized with scanning electron microscopy and atomic force microscopy. When heated from room temperature up to 115oC, structures on PO films undergo a reduction in feature size and interparticle spacing by up to 35 % in length and 50% in surface area.

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