Eugene Donev

Modulated optical transmission of subwavelength hole arrays in metal-VO2 films

We demonstrate the modulation of the transmission of near-infrared light through a periodic array of subwavelength apertures in Ag–VO2 and Au–VO2 double-layer films using the semiconductor-to-metal phase transition in VO2. The transmitted intensity ratio increases by a factor of 8 as the VO2 goes from the semiconductor to the metal phase. We attribute this modulation to the switchable dielectric-permittivity contrast between the air-filled holes in the array and the surrounding VO2 material, a conjecture that is semiquantitatively confirmed by simulation.

Size effects in the structural phase transition of VO2 nanoparticles studied by surface-enhanced Raman scattering

We report the first experimental application of surface-enhanced Raman scattering (SERS) to the study of the structural phase transition of vanadium dioxide (VO2). Using arrays of gold-capped VO2 nanoparticles (Au+VO2 NPs) and a VO2 film covered with Au islands, we obtained the temperature evolution of the SERS intensity with respect to the amount of accessible material across the monoclinic–tetragonal–monoclinic transformation cycle of VO2. The smallest Au+VO2 NPs displayed the largest deviations from the bulk transition temperatures to complete the transformation, resulting in the widest thermal hysteresis, while the Au+VO2 film exhibited the narrowest hysteresis. The observed size dependence agrees qualitatively with the model of defect-induced nucleation of the VO2 transition, although the magnitude of the hysteresis width and its dependence on NP size were less pronounced than those in a previous study of elastic light scattering from bare VO2 NPs. The discrepancies may stem from the creation of extrinsic nucleation sites in the VO2 NPs during their high-temperature processing in the presence of the Au caps; alternatively, the hystereses of the structural and electronic transitions could each have a different dependence on size. Lastly, we correlate the size dependence of the VO2 SERS intensity with the scattering efficiency of the Au nanoparticles, within the framework of a modified Mie-theory calculation.

Linear and nonlinear plasmonic effects modulated by a metalinsulator transition

Localized and propagating plasmonic effects in noble-metal nanostructures are receiving worldwide attention as potential enabling principles for optical and electro-optic devices. A critical need in plasmonic device design is a general technique for active modulation of the plasmon response. In this paper, we describe the use of a reversible, solid-solid phase transition in VO2 to modulate plasmonic response. Case studies are drawn from experiments on nano structured hole and particle arrays in which VO2 acts as a modulator by altering the local dielectric constant.

Fabricating active plasmonic structures by combining laser-, electron- and ion-beam techniques

The burgeoning interest in sub-wavelength metal optics is fueled by applications ranging from cancer therapy and proteomics to opto-electronics and novel photovoltaic materials. The optical properties of nanoscale metallic structures are determined not only by the electromagnetics of localized and propagating surface plasmons, but also by the details of metal nanoparticle size, shape and spatial arrangement, and dielectric environment. This paper presents several ways in which interesting plasmonic structures and applications are made possible by nanoscale materials synthesis and structuring techniques based on pulsed laser and electron-beam deposition, electron-beam lithography and focused ion-beam nanomachining. Examples include (1) using a focused ion beam to create arrays of subwavelength holes in which the extraordinary optical transmission effect can be switched; (2) fabricating gold::VO2 composite nanoparticles to measure the size dependence of the metal-insulator transition in vanadium dioxide using surface-enhanced Raman scattering; and (3) the construction of heterostructures in which excitons can be coupled to surface plasmons.The burgeoning interest in sub-wavelength metal optics is fueled by applications ranging from cancer therapy and proteomics to opto-electronics and novel photovoltaic materials. The optical properties of nanoscale metallic structures are determined not only by the electromagnetics of localized and propagating surface plasmons, but also by the details of metal nanoparticle size, shape and spatial arrangement, and dielectric environment. This paper presents several ways in which interesting plasmonic structures and applications are made possible by nanoscale materials synthesis and structuring techniques based on pulsed laser and electron-beam deposition, electron-beam lithography and focused ion-beam nanomachining. Examples include (1) using a focused ion beam to create arrays of subwavelength holes in which the extraordinary optical transmission effect can be switched; (2) fabricating gold::VO2 composite nanoparticles to measure the size dependence of the metal-insulator transition in vanadium dioxide usi...

Modulating linear and nonlinear nanoplasmonic effects using the metal-insulator transition in vanadium dioxide

Linear and nonlinear nanoplasmonic effects - such as resonant absorption, second-harmonic generation and extraordinary optical transmission- are modulated in metallic nanostructures when the local dielectric environment is altered by the ultrafast metal-insulator transition in vanadium dioxide.

Nanoscale nonlinear optics coupling plasmonics to the metal-insulator transition in vanadium dioxide

Nanostructured vanadium dioxide and oxide-metal composites exhibit unusual nonlinear optical and plasmonic effects, including size- and shape-dependent optical switching and extraordinary optical transmission controlled by either thermal or ultrafast laser-initiated metal-insulator transition in vanadium dioxide.