Browsing by Author "Ertürk, H."

Now showing 1 - 7 of 7

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Absorption and plasmon resonance of bi-metallic core-shell nanoparticles on a dielectric substrate
(Begell House Inc., 2019-06) Avşar, D.; Ertürk, H.; Mengüç, Mustafa Pınar; Mechanical Engineering; MENGÜÇ, Mustafa Pınar
Numerical investigation of absorption efficiency profiles and localized surface plasmon resonance (LSPR) wavelengths are performed for metallic core-shell nanoparticles (NPs) placed over a BK7 glass substrate. Gold (Au) and silver (Ag) metallic components are used in two different coreshell structures. This numerical study is performed with vectorized version of the discrete dipole approximation with surface interactions (DDA-SI-v). Absorption enhancement and the hybrid modes of plasmon resonances of the core-shell structures are compared by using a metric that defines a size configuration. It is observed that small volume fraction of the core sizes results in shell domination over the plasmon response. Moreover, an additional study is conducted to discern the sensitivity of the refractive index of nanoparticles in different surrounding environments. With a selected core-shell size configuration of Ag-Au pairs, a significant absorption enhancement with a redshift of LSPR wavelength is observed for both Ag core-Au shell and Au core-Ag shell NPs. These findings show the possible targeted uses of metallic core-shell nanoparticles in local heating, bio-sensing, and material detection applications.
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Discrete dipole approximation with surface interaction
(Elsevier, 2023-01-01) Loke, V. L. Y.; Ertürk, H.; Mengüç, Mustafa Pınar; Mechanical Engineering; MENGÜÇ, Mustafa Pınar
In this chapter, we discuss a methodology to determine absorption and scattering cross sections of particles of different size and shape placed on substrates. This approach is based on the principles of discrete dipole approximation (DDA); however, the interaction matrix between the dipoles is modified to include the effect of the semiinfinite surface by including dipole reflections represented by Sommerfeld integrals. Depending on the direction of an incident plane wave, the particle will be illuminated by the combination of the incident wave with the reflected, transmitted, or evanescent wave. In order to explore problems involving nanomanufacturing or sensing, a new DDA-SI algorithm is constructed as an open-source computational toolbox in a MATLAB environment. Later, two other algorithms (DDA-SI-v and zDDA-SI) were developed to increase the speed of calculations. All three algorithms were considered for atomic force microscopy-based manufacturing applications using dielectric and metallic nanoparticles. Examples of different cases are provided at the end of the chapter.
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Effect of the probe location on the absorption by an array of gold nano-particles on a dielectric surface
(Elsevier, 2017) Moghaddam, S. T.; Avşar, D.; Ertürk, H.; Mengüç, Mustafa Pınar; Mechanical Engineering; MENGÜÇ, Mustafa Pınar
Effect of silicon atomic force microscope probe position and particle spacing on the local absorption of an array of gold nanoparticles placed over a dielectric borosilicate glass surface are evaluated. An improved, vectorized version of discrete dipole approximation coupled with surface interactions is employed throughout the study. It is shown that surface evanescent waves interacting with the system of nanoparticles and atomic force microscope probe result in a near-field coupling between them. This coupling can enhance or reduce the local absorption by the nanoparticles depending on the position of atomic force microscope tip in three-dimensional space and direction of propagation of the surface evanescent wave. The position of the atomic force microscope's tip and spacing that maximize the absorption are identified. This concept can be used for selective heating of nanoparticles placed over a surface that enables precision manufacturing at nanometer scales.
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Enhancing local absorption within a gold nano-sphere on a dielectric surface under an AFM probe
(Elsevier, 2016-07) Moghaddama, S. T.; Ertürk, H.; Mengüç, Mustafa Pınar; Mechanical Engineering; MENGÜÇ, Mustafa Pınar
This study considers enhancing localized absorption by a gold nanoparticle (NP) placed over a substrate where an atomic force microscope (AFM) tip is in close proximity of the particle. The gold NP and AFM tip are interacting with a surface evanescent wave, resulting a near-field coupling between the tip and NP and consequently enhances the absorption. This concept can be used for selective heating of NPs placed over a surface that enables precise manufacturing at nanometer scales. Different tip positions are considered to identify the optimal tip location and the corresponding enhancement limits. The effects of these interactions on the absorption profiles of dielectric core/gold shell NPs are also studied. It is observed that using core–shell nanoparticles with a dielectric core leads to further enhancement of the absorption efficiency and a more uniform distribution of absorption over the shell. Discrete dipole approximation coupled with surface interactions (DDA-SI) is employed throughout the study, and it is vectorized to improve its computational efficiency.
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Optimization of spectrally selective Si/SiO2 based filters for thermophotovoltaic devices
(Elsevier, 2017-08) Khosroshahi, F. K.; Ertürk, H.; Mengüç, Mustafa Pınar; Mechanical Engineering; MENGÜÇ, Mustafa Pınar
Design of a spectrally selective filter based on one-dimensional Si/SiO2 layers is considered for improved performance of thermo-photovoltaic devices. Spectrally selective filters transmit only the convertible radiation from the emitter as non-convertible radiation leads to a reduction in cell efficiency due to heating. The presented Si/SiO2 based filter concept reflects the major part of the undesired range back to the emitter to minimize energy required for the process and it is adaptable to different types of cells and emitters with different temperatures since its cut-off wavelength can be tuned. While this study mainly focuses on InGaSb based thermo-photovoltaic cell, Si, GaSb, and Ga0.78In0.22As0.19Sb0.81 based cells are also examined. Transmittance of the structure is predicted by rigorous coupled wave approach. Genetic algorithm, which is a global optimization method, is used to find the best possible filter structure by considering the overall efficiency as an objective function that is maximized. The simulations show that significant enhancement in the overall system and device efficiency is possible by using such filters with TPV devices. The methodology described in this paper allows for an improved filter design procedure for selected applications.
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Plasmon coupling between complex gold nanostructures and a dielectric substrate
(The Optical Society, 2018-10-20) Fathi, Zahra Rostampour; Mengüç, Mustafa Pınar; Ertürk, H.; Mechanical Engineering; MENGÜÇ, Mustafa Pınar; Fathi, Zahra Rostampour
Intercoupling of an incident electric field in metal nanoparticles causes asymmetric distribution of surface charges, which eventuates in shifting of the surface plasmon resonance frequency. This feature can be used in tuning the surface plasmon resonance and controlling the light absorption in a desired wavelength. This work provides a theoretical study of the plasmonic properties of complex gold nanostructures on a dielectric substrate where the nanoparticles have different morphologies. For analysis, we have developed a discrete dipole approximation with surface interactions-z, which is the third version of the MATLAB-based DDA-SI toolbox. In this version, lower-upper decomposition of the interaction matrix is used as a preconditioning of the LSQR iterative solver. This method accelerates the DDA-SI calculations by decreasing the total number of iteration steps and decreases the relative residual to achieve more accurate results. In the analysis, nanostructures are assumed to be gold dimers, trimers, and quadrumers with different sizes and elongations of cubical or spherical geometries on a BK7 substrate. The results show that absorption spectra exhibit both red- and blueshifted plasmon resonances in array, depending on the particle shape and elongation. The cubic structure of gold array provides the highest absorption efficiency, while the spherical structures give wider bandwidth; the combination of these structures could be used to design a system with intended features. We demonstrate that the geometrical symmetry plays an important role in the plasmon resonance of gold arrays, and it is shifted when the symmetry of the array is broken.
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Plasmonic responses of metallic/dielectric core-shell nanoparticles on a dielectric substrate
(IOP Publishing, 2019-06) Avşar, D.; Ertürk, H.; Mengüç, Mustafa Pınar; Mechanical Engineering; MENGÜÇ, Mustafa Pınar
The effect of material selection on the plasmonic response and local absorption are evaluated for core- shell nanoparticles placed over a BK7 glass substrate. Eight different core-shell pairs are studied using the vectorized version of discrete dipole approximation with surface interactions (DDA-SI). Two classes of dielectric core-metallic shell and metallic core-dielectric shell particles are considered. It is shown that core-shell structures with dielectric materials can have absorption enhancement compared to the bare metallic nanoparticles. Moreover, it is observed that core-shell pairs yield multipeak localized surface plasmon resonance (LSPR) response due to their hybrid structure. Absorption enhancement and LSPR tuning ranges are shown with different dielectric materials that can be used in localized heating of designated core-shell NPs placed over a surface for nanomanufacturing purposes. In order to determine the optimum size configurations, a number of core-shell pairs are explored with specified volumetric filling ratio of core materials.