title: Efficient Heterostructures for Combined Interference and Plasmon Resonance Raman Amplification.
abstract: The detection, identification, and quantification of different types of molecules and the optical imaging of, for example, cellular processes are important challenges. Here, we present how interference-enhanced Raman scattering (IERS) in adequately designed heterostructures can provide amplification factors relevant for both detection and imaging. Calculations demonstrate that the key factor is maximizing the absolute value of the refractive indices' difference between dielectric and metal layers. Accordingly, Si/Al/Al2O3/graphene heterostructures have been fabricated by optimizing the thickness and roughness and reaching enhancement values up to 700 for 488 nm excitation. The deviation from the calculated enhancement, 1200, is mainly due to reflectivity losses and roughness of the Al layer. The IERS platforms are also demonstrated to improve significantly the quality of white light images of graphene and are foreseen to be adequate to reveal the morphology of 2D and biological materials. A graphene top layer is adequate for most organic molecule deposition and often quenches possible fluorescence, permitting Raman signal detection, which, for a rhodamine 6G (R6G) monolayer, presents a gain of 400. Without graphene, the nonquenched R6G fluorescence is similarly amplified. The wavelength dependence of the involved refractive indices predicts much higher amplification (around 104) for NIR excitation. These interference platforms can therefore be used to gain contrast and intensity in white light, Raman, and fluorescence imaging. We also demonstrate that surface-enhanced Raman scattering and IERS amplifications can be efficiently combined, leading to a gain of >105(at 488 nm) by depositing a Ag nanostructured transparent film on the IERS platform. When the plasmonic structures deposited on the IERS platforms are optimized, single-molecule detection can be actively envisaged.
authors.affiliation: Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Científicas , Cantoblanco, 28049 Madrid, Spain.
authors.forename: Leo
authors.initials: L
authors.lastname: Alvarez-Fraga
authors.affiliation: Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Científicas , Cantoblanco, 28049 Madrid, Spain.
authors.forename: Esteban
authors.initials: E
authors.lastname: Climent-Pascual
authors.affiliation: Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Científicas , Cantoblanco, 28049 Madrid, Spain.
authors.forename: Montserrat
authors.initials: M
authors.lastname: Aguilar-Pujol
authors.affiliation: Departamento de Física, Escuela Politécnica Superior, Universidad Carlos III de Madrid , Avenida Universidad 30, Leganés, 28911 Madrid, Spain.
authors.forename: Rafael
authors.initials: R
authors.lastname: Ramírez-Jiménez
authors.affiliation: Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Científicas , Cantoblanco, 28049 Madrid, Spain.
authors.forename: Félix
authors.identifier: http://orcid.org/0000-0001-7257-9208
authors.initials: F
authors.lastname: Jiménez-Villacorta
authors.affiliation: Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Científicas , Cantoblanco, 28049 Madrid, Spain.
authors.forename: Carlos
authors.initials: C
authors.lastname: Prieto
authors.affiliation: Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Científicas , Cantoblanco, 28049 Madrid, Spain.
authors.forename: Alicia
authors.identifier: http://orcid.org/0000-0003-4359-9001
authors.initials: A
authors.lastname: de Andrés
keywords: IERS; Raman enhancement; SERS; graphene; imaging; interference; nanoparticles; sensing