Optical Properties of Aqueous Dispersions of Diamond Nanoparticles Ada-Simona Popescu* a , Boyan Penkov c , Young U. Jung a , Roman Akhmechet c , Andrii B. Golovin a,b , and David T. Crouse a,b a Department of Electrical Engineering, The City College of New York, New York, New York 10031 b Center for Metamaterials, 160 Convent Avenue, Steinman Hall, New York, New York 10031 c Phoebus Optoelectronics, New York, New York 10013 ABSTRACT Optical metasurfaces demonstrate outstanding capabilities of optical parameters modifications by changes in the structural architecture at the nano-scale level. We demonstrate results of electrophoretic experiments that modify the structure of a metasurface by using diamond nanoparticles with sizes much smaller than the wavelength of light; the nanoparticles are suspended in an aqueous solution and a uniform electric field is applied. The electric field controls the concentration of nanoparticles inside the sub-wavelength apertures and on the top plane of the metasurface. The higher concentration of diamond nanoparticles increases the refractive index of the suspension as well as increasing scattering and absorption. Results of optical material parameter characterization for a wavelength of 512 nm are provided for different concentrations of the diamond nanoparticles dispersions. Keywords: metasurface, refractive index, extinction coefficient, diamond nanoparticles, electrophoresis. 1. INTRODUCTION Two-dimensional arrays of sub-wavelength apertures made in thin metal layers are used in modern optical applications as metasurfaces that exhibit frequency selective transmission and reflection 1, 2 . The sizes of the sub-wavelength apertures and the permittivity of the dielectric material inside of the apertures determine the wavelength of maximum transmission of the metasurfaces 3 . One can make the metasuface tunable by varying the electric permittivity of the dielectric inside the apertures. The goal of this work was to explore the tunability of frequency selective metasufaces. For this purpose, we chose diamond nanoparticles (DNPs) and investigated how the variations in the local concentration of the DNPs lead to variations of the dielectric permittivity of the suspension. In our work the variation of local concentration of nanoparticles was achieved by means of electrophoresis. The electrophoretic control of the average dielectric permittivity can be used to tune the transmission and reflection properties of the metasurfaces, which is very attractive for the design of highly efficient light harvesting solar cells 4, 5 . DNPs powder is a very attractive material for the design of optical metamaterials and metasurfaces because of their small size and high value of dielectric permittivity 6, 7 . However, the current knowledge about optical properties of DNPs is limited by experiments and computer models that analyze only the absorption and scattering of light 8-11 . Even though extensively investigated for biomedical applications, the extent of knowledge about the optical properties of the DNP is still limited. We explored the deposition of DNPs with an average diameter of 3-4 nm into subwavelength sized apertures of a metasurface made from gold by using electrophoresis in an aqueous suspension. As optical metasurfaces are usually made from thin films of noble metals, it is convenient to use the 2D gold metasurface as an electrode to conduct electrophoresis of DNPs. The images of DNPs deposited into the apertures were obtained by using scanning electron microscopy (SEM). Previously, fabrication of metal metasurface with a dielectric material within the sub-wavelength sized apertures would require non-reversible processes of sputtering, evaporation, or plasma-enhanced chemical vapor deposition. In contrast, the electrophoretic deposition of DNPs can be reversed by switching the direction of the applied field. However, the concentrated DNPs also increase scattering and absorption of light, as demonstrated in this work by analyzing the average refractive index and extinction coefficients for samples with different DNPs concentrations. *apopesc00@citymail.cuny.edu; phone 1 212 650-7280; fax 1 212 650-7058; http://www.centerformetamaterials.org Nanoengineering: Fabrication, Properties, Optics, and Devices X, edited by Eva M. Campo, Elizabeth A. Dobisz, Louay A. Eldada, Proc. of SPIE Vol. 8816, 88161G · © 2013 SPIE CCC code: 0277-786X/13/$18 · doi: 10.1117/12.2024485 Proc. of SPIE Vol. 8816 88161G-1 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 11/17/2013 Terms of Use: http://spiedl.org/terms