Browsing by Subject "Localized surface plasmon"

Now showing 1 - 7 of 7

Open Access
97 percent light absorption in an ultrabroadband frequency range utilizing an ultrathin metal layer: randomly oriented, densely packed dielectric nanowires as an excellent light trapping scaffold
(Royal Society of Chemistry, 2017) Ghobadi, A.; Dereshgi, S. A.; Hajian, H.; Birant, G.; Butun, B.; Bek, A.; Özbay, Ekmel
In this paper, we propose a facile and large scale compatible design to obtain perfect ultrabroadband light absorption using metal-dielectric core-shell nanowires. The design consists of atomic layer deposited (ALD) Pt metal uniformly wrapped around hydrothermally grown titanium dioxide (TiO2) nanowires. It is found that the randomly oriented dense TiO2 nanowires can impose excellent light trapping properties where the existence of an ultrathin Pt layer (with a thickness of 10 nm) can absorb the light in an ultrabroadband frequency range with an amount near unity. Throughout this study, we first investigate the formation of resonant modes in the metallic nanowires. Our findings prove that a nanowire structure can support multiple longitudinal localized surface plasmons (LSPs) along its axis together with transverse resonance modes. Our investigations showed that the spectral position of these resonance peaks can be tuned with the length, radius, and orientation of the nanowire. Therefore, TiO2 random nanowires can contain all of these features simultaneously in which the superposition of responses for these different geometries leads to a flat perfect light absorption. The obtained results demonstrate that taking unique advantages of the ALD method, together with excellent light trapping of chemically synthesized nanowires, a perfect, bifacial, wide angle, and large scale compatible absorber can be made where an excellent performance is achieved while using less materials.
Open Access
Ag@SiO2-embedded InGaN/GaN nanorod array white light-emitting diode with perovskite nanocrystal films
(Elsevier, 2021-10-28) Shin, Do-Y.; Kim, T.; Akyüz, Özgün; Demir, Hilmi Volkan; Lee, In-H.
White light-emitting diodes (LEDs) are great candidates for general lighting. Phosphors have commonly been used for the color conversion layers of white LEDs; however, they backscatter more than half of the down-converted light, which is lost within the device, thus degrading the overall performance. In this study, we propose and demonstrate white LEDs with improved efficiency enabled by the intimate integration of Ag@SiO2-supported blue InGaN/GaN nanorod LEDs together with green- and red-emitting perovskite nanocrystal (PNC) films as color conversion layers. The photoluminescence (PL) intensity of the blue LEDs (BLEDs) was significantly enhanced owing to the localized surface plasmon (LSP) effect of Ag@SiO2 nanoparticles. In addition, the perovskite PL intensity was improved by the high-power BLED backlight. The resulting PL intensity of the Ag@SiO2 nanoparticle-embedded nanorod white LED was 62% greater than that of a planar white LED.
Open Access
Correction to: Active tuning from narrowband to broadband absorbers using a sub-wavelength VO2 embedded layer
(Springer, 2021-02-04) Osgouei, Ataollah Kalantari; Hajian, Hodjat; Khalichi, Bahram; Serebryannikov, Andriy E.; Ghobadi, Amir; Özbay, Ekmel
Metamaterial perfect absorbers (MPAs) with dynamic thermal tuning features are able to control the absorption performance of the resonances, providing diverse applications spanning from optical switches and filters to modulators. In this paper, we propose an MPA with diverse functionalities enabled by vanadium dioxide (VO2) embedded in a metal-dielectric plasmonic structure. For the initial design purpose, a silicon (Si) nanograting on a silver (Ag) mirror is proposed to have multiple resonant responses in the near infrared (NIR) region. Then, the insertion of a thin VO2 layer at the right position enables the design to act as an on/off switch and resonance tuner. In the insulator phase of VO2, in which the permittivity data of VO2 is similar to that of Si, a double strong resonant behavior is achieved within the NIR region. By increasing the temperature, the state of VO2 transforms from insulator to metallic so that the absorption bands turn into three distinct resonant peaks with close spectral positions. Upon this transformation, a new resonance emerges and the existing resonance features experience blue/red shifts in the spectral domain. The superposition of these peaks makes the overall absorption bandwidth broad. Although Si has a small thermo-optic coefficient, owing to strong light confinement in the ultrasmall gaps, a substantial tuning can be achieved within the Si nanogratings. Therefore, the proposed hybrid design can provide multi-resonance tunable features to cover a broad range and can be a promising strategy for the design of linearly thermal-tunable and broadband MPAs. Owing to the proposed double tuning feature, the resonance wavelengths exhibits great sensitivity to temperature, covering a broad wavelength range. Overall, the proposed design strategy demonstrates diverse functionalities enabled by the integration of a thin VO2 layer with plasmonic absorbers.
Open Access
Electroluminescence efficiency enhancement in quantum dot light-emitting diodes by embedding a silver nanoisland layer
(Wiley-VCH Verlag, 2015) Yang, X.; Hernandez-Martinez, P. L.; Dang C.; Mutlugün, E.; Zhang, K.; Demir, Hilmi Volkan; Sun X. W.
A colloidal quantum dot light-emitting diode (QLED) is reported with substantially enhanced electroluminescence by embedding a thin layer of Ag nanoislands into hole transport layer. The maximum external quantum efficiency (EQE) of 7.1% achieved in the present work is the highest efficiency value reported for green-emitting QLEDs with a similar structure, which corresponds to 46% enhancement compared with the reference device. The relevant mechanisms enabling the EQE enhancement are associated with the near-field enhancement via an effective coupling between excitons of the quantum dot emitters and localized surface plasmons around Ag nano-islands, which are found to lead to good agreement between the simulation results and the experimental data, providing us with a useful insight important for plasmonic QLEDs. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Open Access
Plasmonic metamaterial based structures for designing of multiband and thermally tunable light absorbers, multiple thermal infrared emitter, and high-contrast asymmetric transmission optical diode
(2021-07) Osgouei, Ataollah Kalantari
Metamaterials with sub-wavelength nanostructures refer to a class of synthetic materials that possess exotic electromagnetic properties which cannot be observed with natural materials. Negative refractive index, asymmetric light transmission, invisible cloaking, and lasing are examples of these attributes. Among these possible applications, the concept of light confinement and harvesting by subwavelength structures have attracted considerable attention due to their widespread applications ranging from thermal emission, optical modulator, sensing, and photodetectors. Here, we propose and design plasmonic metamaterials with subwavelength structures in four different application areas, namely 1) Hybrid indium tin oxide-Au metamaterial absorber in the visible and near-infrared ranges for selective thermal emissions and sensors. 2) Active tuning from narrowband to broadband absorbers using a sub-wavelength VO2 for optical modulator. 3) A spectrally selective nanoantenna emitter compatible with multiple thermal infrared applications. 4) Diode like high-contrast asymmetric transmission of linearly polarized waves. In the first work, we propose a multi-band Metamaterial Perfect absorber (MPA) with two narrowband absorption responses that are centered on the visible and near-infrared (NIR) wavelengths [773 􀀁􀀂 and 900 􀀁􀀂, respectively] and a broadband absorptive characteristic in another window in the NIR region [ranging from 1,530 􀀁􀀂 to 2,700 􀀁􀀂 with a bandwidth of 1,170 􀀁􀀂]. The MPA comprises a periodic array of self-aligned hybrid indium tin oxide (ITO)-Au split-ring-resonators that are separated from an optically thick bottom reflector with a SiO2 layer. Based on numerical calculations, which are accompanied with a semi-analytical examination, we find that the dual narrowband and broadband responses are attributed to the hybridization of the optical responses of gold as a plasmonic material with the ones of ITO. Note that ITO acts as a low-loss dielectric in the visible range and a lossy plasmonic material in the NIR region. Moreover, due to the applied symmetry in the unit cell of the metamaterial, the proposed MPA represents polarization insensitive and omnidirectional absorptive features. The proposed metastructure can find potential applications in selective thermophotovoltaic devices, thermal emitters, and sensors. In the second work, we propose an MPA with diverse functionalities enabled by vanadium dioxide (VO2) embedded in a metal-dielectric plasmonic structure. For the initial design purpose, a Silicon (Si) nanograting on a Silver (Ag) mirror is proposed to have multiple resonant responses in the near infrared (NIR) region. Then, the insertion of a thin VO2 layer at the right position enables the design to act as an on/off switch and resonance tuner. In the insulator phase of VO2, in which the permittivity data of VO2 is similar to that of Si, a double strong resonant behavior is achieved within the NIR region. By increasing the temperature, the state of VO2 transforms from insulator to metallic so that the absorption bands turn into three distinct resonant peaks with close spectral positions. Upon this transformation, a new resonance emerges and the existing resonance features experience blue/red shifts in the spectral domain. The superposition of these peaks makes the overall absorption bandwidth broad. Although Si has a small thermo-optic coefficient, owing to strong light confinement in the ultrasmall gaps, a substantial tuning can be achieved within the Si nanogratings. Therefore, the proposed hybrid design can provide multi-resonance tunable features to cover a broad range and can be a promising strategy for the design of linearly thermal-tunable and broadband MPAs. Owing to the proposed double tuning feature, the resonance wavelengths exhibits great sensitivity to temperature, covering a broad wavelength range. Overall, the proposed design strategy demonstrates diverse functionalities enabled by the integration of a thin VO2 layer with plasmonic absorbers. In the third work, we design a wavelength-selective nanoantenna emitter based on the excitation of gap-surface plasmon modes using a metal–insulator–metal configuration (silicon dioxide (SiO2) sandwiched between silver (Ag) layers) for satisfying multiple infrared applications. The proposed design, which is called design I, realizes triple narrowband perfect absorptions at the resonance wavelengths of 1524 nm, 2279 nm, and 6000 nm, which perfectly match the atmospheric absorption bands while maintaining relatively low emissivity in the atmospheric transparency windows of 3 − 5 􀀃m and 8 − 12 􀀃m. Later, the functionality of design I is extended, which is called design II, to include a broadband absorption at the near-infrared region to minimize the solar irradiation reflection from the nanoantenna emitter. Finally, single- and three-layer graphene are introduced to provide a real-time tuning of the infrared signature of the proposed nanoantenna emitter (design II). It is also demonstrated that the three-layer graphene structure can suppress an undesired absorption resonance wavelength related to the intrinsic vibrational modes (optical phonons) of the SiO2 layer by 53.19% compared to 25.53% for the single-layer one. The spectral analysis of design I is validated using both analytical and numerical approaches where the numerical simulation domain is extended for the analysis of design II. The thermal characteristic analyses of design I and design II (without/with graphene layers) reveal that infrared signatures of the blackbody radiation are significantly reduced for the whole wavelength spectrum at least by 96% and 91% within a wide temperature ranging from room temperature to 500 􀀄, respectively. In the fourth and final work, we present a narrow-band optical diode with a high-contrast forward-to-backward ratio at the near-infrared (NIR) region. The design has a forward transmission of approximately 88%, and a backward one of less than 3%, yielding a contrast ratio of greater than 14.5 dB at a wavelength of 1550 nm. The structure is composed of a one-dimensional diffraction grating on top of a dielectric slab waveguide, both of which are made of silicon nitride (Si3N4), and all together are placed over a silver (Ag) thin film embedded on a dielectric substrate. Utilizing a dielectric-based diffraction grating waveguide on a thin silver layer leads to the simultaneous excitation of two surface plasmon modes known as long- and short-range surface plasmon polaritons (SPPs) at both interfaces of the metallic layer. The plasmon-tunneling effect, which is the result of the coupling of SPPs excited at the upper interface of the metallic layer to the radiation modes, provides a high asymmetric transmission (AT) property. The spectral response of the proposed high-contrast AT device is verified using both rigorous coupled-wave analysis as an analytical approach and finite difference time domain as a numerical one.
Open Access
Sensitivity comparison of localized plasmon resonance structures and prism coupler
(2014) Kaya, Y.; Ayas S.; Topal, A. E.; Guner, H.; Dana, A.
Plasmon resonances are widely used in biomolecular sensing and continue to be an active research field due to the rich variety of surface and measurement configurations, some of which exhibit down to single molecule level sensitivity. The resonance wavelength shift of the plasmonic structure upon binding of molecules, strongly depends, among other parameters, on how well the field of the resonant mode is confined to the binding site. Here it is shown that, by using properly designed metal-insulator-metal type resonators, improved wavelength response can be achieved with localized surface plasmon resonators (LSPRs) compared to that of the commonly used Kretschmann geometry. Using computational tools we investigate theoretically the refractive index response of several LSPR structures to a 2 nm thin film of binding molecules. LSPR resonators are shown to feature improved sensitivity over conventional Kretschmann geometry in the wavelength interrogation scheme for such a thin film. Moreover, some of the LSPR modes are quasi-omnidirectional and such angular independence (up to 30 angle of incidence) allows higher numerical apertures to be used in colorimetric imaging. Results highlight the potential of LSPRs for biomolecular sensing with high sensitivity and high spatial resolution.
Open Access
Strong coupling between localized and propagating plasmon polaritons
(OSA - The Optical Society, 2015) Balci, S.; Karademir, E.; Kocabas, C.
We investigate plasmon-plasmon (PP) coupling in the strongly interacting regimes by using a tunable plasmonic platform consisting of triangular Ag nanoprisms placed nanometers away from Ag thin films. The nanoprisms are colloidally synthesized using a seed-mediated growth method and having size-tunable localized surface plasmon polariton (SPP) resonances immobilized on Si3N4 films. The PP coupling between the localized SPPs of metal nanoprisms and the propagating SPPs of the metal film is controlled by the nanoprism concentration and the plasmon damping in the metal film. Results reveal that Rabi splitting energy determining the strength of the coupling can reach up to several hundreds meV, thus demonstrating the ultrastrong coupling occurring between localized and propagating SPPs. The metal nanoparticle-metal thin film hybrid system over the square-centimeter areas presented here provides a unique configuration to study PP coupling all the way from the weak to ultrastrong coupling regimes in a broad range of wavelengths.