Browsing by Subject "Plasmon"

Now showing 1 - 8 of 8

Open Access
Coupled plasmonic cavities on moire surfaces
(Springer, 2010-08) Balcı, Sinan; Karabıyık, Mustafa; Kocabaş, Aşkın; Kocabaş, Coşkun; Aydınlı, Atilla
Surface plasmon polariton (SPP) waveguides formed by coupled plasmonic cavities on metallic Moire surfaces have been investigated both experimentally and numerically. The Moire surface, fabricated by interference lithography, contains periodic arrays of one-dimensional cavities. The coupling strength between the cavities has been controlled by changing the periodicities of the Moire surface. The ability to control the coupling strength allows us to tune the dispersion and the group velocity of the plasmonic coupled cavity mode. Reflection measurements and numerical simulation of the array of SPP cavities have shown a coupled resonator type plasmonic waveguide band formation within the band gap. Coupling coefficients of cavities and group velocities of SPPs are calculated for a range of cavity sizes from weakly coupled regime to strongly coupled regime.
Open Access
InGaN green light emitting diodes with deposited nanoparticles
(Elsevier BV, 2007) Butun, B.; Cesario J.; Enoch, S.; Quidant, R.; Özbay, Ekmel
We grew an InGaN/GaN-based light-emitting diode (LED) wafer by metal-organic chemical vapor deposition (MOCVD), fabricated devices by optical lithography, and successfully deposited ellipsoidal Ag nano-particles by way of e-beam lithography on top. The diodes exhibited good device performance, in which we expected an enhancement of the radiated intensity by the simulations and emission measurements. The obtained results showed the feasibility of plasmon-assisted LED emission enhancement.
Open Access
Photocurrent generation in low dimensional nanomaterials
(2022-11) Razeghi, Mohammadali
This thesis focuses on crucial issue on the understanding the underlying mechanisms of photoresponse in low-dimensional nanomaterials. As the size goes down to the micro and nano level, fine features and induced inhomogeneities like strain, thickness variation, substrate, and junctions become influential in determining plausible effects that can explain and control the light-matter interactions in an optoelectronic device. To develop a better understanding of the fundamental physical characteristics of nanomaterials and optimize thermal and electrical transport in nanomaterial devices, microscopic investigation at a single crystal level is required. In this thesis, I investigated photocurrent generation in two extreme cases: metallic silver nanowire (Ag NW) and semiconducting multilayer molybdenum disulfide (MoS2) using scanning photocurrent microscopy (SPCM). SPCM provides spatial mapping of photoresponse along with corresponding reflected light intensity with a few hundred nanometer resolution. Two terminal devices of Ag and Ag network devices are made by drop-casting NW and placing indium as metal contacts. The SPCM maps show that the NW- NW junctions and NW-contacts interface locally enhance the plasmonic field and act as hot spots. The increased temperature at hot spots is enough to modulate the resistance and results in a photo-bolometric response under the bias voltage. To further enhance the photo-bolometric effect, we decorated the nanowires with plasmonic Ag nanoparticles. The nanoparticles increase the number of hot spots and strengthen light coupling into plasmons. We also attributed zero bias response to the photothermoelectric effect. The photocurrent is generated by the Seebeck coefficient difference caused by nanogaps and nonuniformities in the geometry along the Ag NW. The second part of this thesis describes photocurrent generation by substrate engineering of a few-layer MoS2. To partially suspend a crystal, a flake of MoS2 is exfoliated and then transferred on a substrate with rectangular or circular holes. We observed photocurrent generation from the junction of the supported and suspended parts. Substrate effects like induced doping play an essential role in determining the properties of two-dimensional materials. Our investigations show that the Seebeck coefficient of the suspended part is changed due to isolation from the substrate. The difference in the Seebeck coefficient of suspended and supported regions forms a thermoelectric junction. We also investigated the impact of carrier type and concentration on photocurrent generation by gating experiments.
Open Access
Photogeneration of hot plasmonic electrons with metal nanocrystals: quantum description and potential applications
(Elsevier Ltd, 2014-02) Govorov, A. O.; Zhang, H.; Demir, Hilmi Volkan; Gun’ko, Y. K.
he paper reviews physical concepts related to the collective dynamics of plasmon excitations in metal nanocrystals with a focus on the photogeneration of energetic carriers. Using quantum linear response theory, we analyze the wave function of a plasmon in nanostructures of different sizes. Energetic carriers are efficiently generated in small nanocrystals due to the non-conservation of momentum of electrons in a confined nanoscale system. On the other hand, large nanocrystals and nanostructures, when driven by light, produce a relatively small number of carriers with large excitation energies. Another important factor is the polarization of the exciting light. Most efficient generation and injection of high-energy carriers can be realized when the optically induced electric current is along the smallest dimension of a nanostructure and also normal to its walls and, for efficient injection, the current should be normal to the collecting barrier. Other important properties and limitations: (1) intra-band transitions are preferable for generation of energetic electrons and dominate the absorption for relatively long wavelengths (approximately >600 nm), (2) inter-band transitions efficiently generate energetic holes and (3) the carrier-generation and absorption spectra can be significantly different. The described physical properties of metal nanocrystals are essential for a variety of potential applications utilizing hot plasmonic electrons including optoelectronic signal processing, photodetection, photocatalysis and solar-energy harvesting. © 2014 Elsevier Ltd.
Open Access
Plasmon-modulated photoluminescence enhancement in hybrid plasmonic nano-antennas
(IOP Publishing, 2020) Rashed, A. R.; Habib, M.; Das, N.; Özbay, Ekmel; Çağlayan, H.
In this work, we performed a systematic study on a hybrid plasmonic system to elucidate a new insight into the mechanisms governing the fluorescent enhancement process. Our lithographically defined plasmonic nanodisks with various diameters act as receiver and transmitter nano-antennas to outcouple efficiently the photoluminescence of the coupled dye molecules. We show that the enhancement of the spontaneous emission rate arises from the superposition of three principal phenomena: (i) metal enhanced fluorescence, (ii) metal enhanced excitation and (iii) plasmon-modulated photoluminescence of the photoexcited nanostructures. Overall, the observed enhanced emission is attributed to the bi-directional near-field coupling of the fluorescent dye molecules to the localized plasmonic field of nano-antennas. We identify the role of exciton–plasmon coupling in the recombination rate of the sp-band electrons with d-band holes, resulting in the generation of particle plasmons. According to our comprehensive experimental analyses, the mismatch between the enhanced emission and the emission spectrum of the uncoupled dye molecules is attributed to the plasmon-modulated photoluminescence of the photoexcited hybrid plasmonic system.
Open Access
Plasmonic metamaterials and nanocomposites with the narrow transparency window effect in broad extinction spectra
(American Chemical Society, 2014) Zhang, H.; Demir, Hilmi Volkan; Govorov, A. O.
We propose and describe plasmonic nanomaterials with unique optical properties. These nanostructured materials strongly attenuate light across a broad wavelength interval ranged from 400 nm to S pm but exhibit a narrow transparency window centered at a given wavelength. The main elements used in our systems are nanorods and nanocrosses of variable sizes. The nanomaterial can be designed as a solution, nanocomposite film or metastructure. The principle of the formation of the transparency window in the broad extinction spectrum is based on the narrow lines of longitudinal plasmons of single nanorods and nanorod complexes. To realize the spectrum with a transmission window, we design a nanocomposite material as a mixture of nanorods of different sizes. Simultaneously, we exclude nanorods of certain lengths from the nanorod ensemble. The width of the plasmonic transparency window is determined by the intrinsic and radiative broadenings of the nanocrystal plasmons. Nanocrystals can be randomly dispersed in a solution or arranged in metastructures. We show that interactions between nanocrystals in a dense ensemble can destroy the window effect and, simultaneously, we design the metastructure geometries with weak destructive interactions. We also describe the effect of narrowing of the transparency window with increasing the concentration of nanocrystals. Two well-established technologies can be used to fabricate such nano- and metamaterials, the colloidal synthesis, and lithography. Nanocomposites proposed here can be used as optical materials and smart coatings for shielding of electromagnetic radiation in a wide spectral interval with a simultaneous possibility of communication using a narrow transparency window.
Open Access
A spectrally selective gap surface-plasmon-based nanoantenna emitter compatible with multiple thermal infrared applications
(Institute of Physics Publishing Ltd., 2021-08-20) Osgouei, Ataollah Kalantari; Ghobadi, Amir; Khalichi, Bahram; Özbay, Ekmel
Wavelength-selective nanoantenna emitters have attracted considerable attention due to their widespread applications ranging from thermal radiation management to thermophotovoltaics. In this paper, 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 1524nm,2279nm, and 6000nm, which perfectly match the atmospheric absorption bands while maintaining relatively low emissivity in the atmospheric transparency windows of 3-5 µm and 8-12 µm. 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 500K, respectively.
Open Access
A systematic study on Au-capped Si nanowhiskers for size-dependent improved biosensing applications
(Springer, 2020) Şeker, İ.; Karatutlu, Ali; Gölcük, K.; Karakız, M.; Ortaç, Bülend
Reducing the distance between the fluorescence molecules and noble metal (resonant) nanostructures is known to advance the process of electromagnetic coupling and energy transfer, which in return yields fluorescence enhancement particularly exploited for improved biomedical applications. In this study, Au-capped Si nanowhiskers (NWs) at various sizes were fabricated using a vapor–liquid–solid (VLS) mechanism for systematically investigating the dependence of the size of the Au-capped Si NWs on the fluorescence enhancement factor with respect to the fluorescence emission from Rhodamine 6G (Rh-6G) fluorophore. Opposite to what is anticipated from the literature, the maximum enhancement was obtained for the sample for which the Au-nanoparticle (NP) capping is well isolated from the fluorophore and the vertical distance between the fluorophore and the plasmonic metal nanoparticle is largest. Numerical simulations using the finite element method (FEM) were shown to support the experimental optical response results. Four-point probe I-V measurements also show that the Schottky ideality factor of Au-capped Si NWs decays exponentially upon the rise in the fluorescence enhancement factor.