title: Nanoscale subsurface- and material-specific identification of single nanoparticles.
abstract: We report on high resolution subsurface and material specific differentiation of silica, Au and silica-capped Au nanoparticles using scattering-type scanning near-field optical microscopy (s-SNOM) in the visible (λ=633 nm) and mid-infrared (λ=10.7 μm) frequencies. Strong optical contrast is observed in the visible wavelength, mainly because of the dipolar plasmon resonance of the embedded Au nanoparticles which is absent in the infrared. We show that the use of small tapping amplitude improves the apparent image contrast in nanoparticles by causing increased tip-particle and reduced tip-substrate interactions. Experimental results are in excellent agreement with extended dipole model calculations modified to include the capping layer characterized by its refractive index.
authors: Department of Physics and Astronomy, California State University Long Beach, CA 90840, USA.
authors: Zachary
authors: Z
authors: Nuño
authors: Brandon
authors: B
authors: Hessler
authors: Jerry
authors: J
authors: Ochoa
authors: Young-Seok
authors: YS
authors: Shon
authors: Codi
authors: C
authors: Bonney
authors: Yohannes
authors: Y
authors: Abate
mesh_terms: D004867:Equipment Design; D006046:Gold / Q000737:chemistry; D007259:Infrared Rays; D008422:Materials Testing; D053768:Metal Nanoparticles / Q000737:chemistry*; D008853:Microscopy / Q000379:methods; D018625:Microscopy, Atomic Force / Q000379:methods; D046529:Microscopy, Electron, Transmission / Q000379:methods; D036103:Nanotechnology / Q000379:methods*; D055095:Optics and Photonics; D012031:Refractometry; D012825:Silicon / Q000737:chemistry; D012822:Silicon Dioxide / Q000737:chemistry; D020349:Surface Plasmon Resonance / Q000379:methods; D013499:Surface Properties
chemical_list: D006046:Gold; D012822:Silicon Dioxide; D012825:Silicon