Browsing by Subject "Metal nanoparticles"
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Item Open Access Amphiphilic peptide coated superparamagnetic iron oxide nanoparticles for in vivo MR tumor imaging(Royal Society of Chemistry, 2016) Ozdemir, A.; Ekiz, M. S.; Dilli, A.; Güler, Mustafa O.; Tekinay, A. B.Magnetic resonance imaging (MRI) is a noninvasive imaging technique that provides high spatial resolution and depth with pronounced soft-tissue contrast for in vivo imaging. A broad variety of strategies have been employed to enhance the diagnostic value of MRI and detect tissue abnormalities at an earlier stage. Superparamagnetic iron oxide nanoparticles (SPIONs) are considered to be suitable candidates for effective imaging due to their small size, versatile functionality and better biocompatibility. Here, we demonstrate that coating SPIONs with proline-rich amphiphilic peptide molecules through noncovalent interactions leads to a water-dispersed hybrid system suitable as an MRI contrast agent. Cellular viability and uptake of amphiphilic peptide coated SPIONs (SPION/K-PA) were evaluated with human vascular endothelial cells (HUVEC) and estrogen receptor (ER) positive human breast adenocarcinoma (MCF-7) cells. The efficiency of SPION/K-PA as MRI contrast agents was analyzed in Sprague-Dawley rats with mammary gland tumors. MR imaging showed that SPION/K-PA effectively accumulated in tumor tissues, enhancing their imaging potential. Although nanoparticles were observed in reticuloendothelial system organs (RES) and especially in the liver and kidney immediately after administration, the MR signal intensity in these organs diminished after 1 h and nanoparticles were subsequently cleared from these organs within two weeks. Histological observations also validated the accumulation of nanoparticles in tumor tissue at 4 h and their bioelimination from the organs of both healthy and tumor-bearing rats after two weeks.Item Open Access Atomic layer deposition: an enabling technology for the growth of functional nanoscale semiconductors(Institute of Physics Publishing, 2017) Bıyıklı, Necmi; Haider A.In this paper, we present the progress in the growth of nanoscale semiconductors grown via atomic layer deposition (ALD). After the adoption by semiconductor chip industry, ALD became a widespread tool to grow functional films and conformal ultra-thin coatings for various applications. Based on self-limiting and ligand-exchange-based surface reactions, ALD enabled the low-temperature growth of nanoscale dielectric, metal, and semiconductor materials. Being able to deposit wafer-scale uniform semiconductor films at relatively low-temperatures, with sub-monolayer thickness control and ultimate conformality, makes ALD attractive for semiconductor device applications. Towards this end, precursors and low-temperature growth recipes are developed to deposit crystalline thin films for compound and elemental semiconductors. Conventional thermal ALD as well as plasma-assisted and radical-enhanced techniques have been exploited to achieve device-compatible film quality. Metal-oxides, III-nitrides, sulfides, and selenides are among the most popular semiconductor material families studied via ALD technology. Besides thin films, ALD can grow nanostructured semiconductors as well using either template-assisted growth methods or bottom-up controlled nucleation mechanisms. Among the demonstrated semiconductor nanostructures are nanoparticles, nano/quantum-dots, nanowires, nanotubes, nanofibers, nanopillars, hollow and core-shell versions of the afore-mentioned nanostructures, and 2D materials including transition metal dichalcogenides and graphene. ALD-grown nanoscale semiconductor materials find applications in a vast amount of applications including functional coatings, catalysis and photocatalysis, renewable energy conversion and storage, chemical sensing, opto-electronics, and flexible electronics. In this review, we give an overview of the current state-of-the-art in ALD-based nanoscale semiconductor research including the already demonstrated and future applications.Item Open Access Chiral ceramic nanoparticles and peptide catalysis(American Chemical Society, 2017) Jiang S.; Chekini, M.; Qu, Z.-B.; Wang Y.; Yeltik A.; Liu, Y.; Kotlyar, A.; Zhang, T.; Li, B.; Demir, Hilmi Volkan; Kotov, N. A.The chirality of nanoparticles (NPs) and their assemblies has been investigated predominantly for noble metals and II-VI semiconductors. However, ceramic NPs represent the majority of nanoscale materials in nature. The robustness and other innate properties of ceramics offer technological opportunities in catalysis, biomedical sciences, and optics. Here we report the preparation of chiral ceramic NPs, as represented by tungsten oxide hydrate, WO3-x·H2O, dispersed in ethanol. The chirality of the metal oxide core, with an average size of ca. 1.6 nm, is imparted by proline (Pro) and aspartic acid (Asp) ligands via bio-to-nano chirality transfer. The amino acids are attached to the NP surface through C-O-W linkages formed from dissociated carboxyl groups and through amino groups weakly coordinated to the NP surface. Surprisingly, the dominant circular dichroism bands for NPs coated by Pro and Asp are different despite the similarity in the geometry of the NPs; they are positioned at 400-700 nm and 500-1100 nm for Pro- and Asp-modified NPs, respectively. The differences in the spectral positions of the main chiroptical band for the two types of NPs are associated with the molecular binding of the two amino acids to the NP surface; Asp has one additional C-O-W linkage compared to Pro, resulting in stronger distortion of the inorganic crystal lattice and greater intensity of CD bands associated with the chirality of the inorganic core. The chirality of WO3-x·H2O atomic structure is confirmed by atomistic molecular dynamics simulations. The proximity of the amino acids to the mineral surface is associated with the catalytic abilities of WO3-x·H2O NPs. We found that NPs facilitate formation of peptide bonds, leading to Asp-Asp and Asp-Pro dipeptides. The chiroptical activity, chemical reactivity, and biocompatibility of tungsten oxide create a unique combination of properties relevant to chiral optics, chemical technologies, and biomedicine.Item Open Access Comparative study of thin film n-i-p a-Si: H solar cells to investigate the effect of absorber layer thickness on the plasmonic enhancement using gold nanoparticles(Elsevier Ltd, 2015) Islam, K.; Chowdhury F.I.; Okyay, Ali Kemal; Nayfeh, A.In this paper, the effect of gold nanoparticles on n-i-p a-Si:H solar cells with different intrinsic layer (i-layer) thicknesses has been studied. 100nm and 500nm i-layer based n-i-p a-Si:H solar cells were fabricated and colloidal gold (Au) nanoparticles dispersed in water-based solution were spin-coated on the top surface of the solar cells. The Au nanoparticles are of spherical shape and have 100nm diameter. Electrical and quantum efficiency measurements were carried out and the results show an increase in short-circuit current density (Jsc), efficiency and external quantum efficiency (EQE) with the incorporation of the nanoparticles on both cells. Jsc increases from 5.91mA/cm2 to 6.5mA/cm2 (~10% relative increase) and efficiency increases from 3.38% to 3.97% (~17.5% relative increase) for the 100nm i-layer solar cell after plasmonic enhancement whereas Jsc increases from 9.34mA/cm2 to 10.1mA/cm2 (~7.5% relative increase) and efficiency increases from 4.27% to 4.99% (~16.9% relative increase) for the 500nm i-layer cell. The results show that plasmonic enhancement is more effective in 100nm than 500nm i-layer thickness for a-Si:H solar cells. Moreover, the results are discussed in terms of light absorption and electron hole pair generation. © 2015 Elsevier Ltd.Item Open Access Cyclodextrin-functionalized mesostructured silica nanoparticles for removal of polycyclic aromatic hydrocarbons(Academic Press Inc., 2017) Topuz, F.; Uyar, T.Polycyclic aromatic hydrocarbons (PAHs) are the byproducts of the incomplete combustion of carbon-based fuels, and have high affinity towards DNA strands, ultimately exerting their carcinogenic effects. They are ubiquitous environmental contaminants, and can accumulate on tissues due to their lipophilic nature. In this article, we describe a novel concept for PAH removal from aqueous solutions using cyclodextrin-functionalized mesostructured silica nanoparticles (CDMSNs) and pristine mesostructured silica nanoparticles (MSNs). The adsorption applications of MSNs are greatly restricted due to the absence of surface functional groups on such particles. In this regard, cyclodextrins can serve as ideal functional molecules with their toroidal, cone-type structure, capable of inclusion-complex formation with many hydrophobic molecules, including genotoxic PAHs. The CDMSNs were synthesized by the surfactant-templated, NaOH-catalyzed condensation reactions of tetraethyl orthosilicate (TEOS) in the presence of two different types of cyclodextrin (i.e. hydroxypropyl-β-cyclodextrin (HP-β-CD) and native β-cyclodextrin (β-CD)). The physical incorporation of CD moieties was supported by XPS, FT-IR, NMR, TGA and solid-state 13C NMR. The CDMSNs were treated with aqueous solutions of five different PAHs (e.g. pyrene, anthracene, phenanthrene, fluorene and fluoranthene). The functionalization of MSNs with cyclodextrin moieties significantly boosted the sorption capacity (q) of the MSNs up to ∼2-fold, and the q ranged between 0.3 and 1.65 mg per gram CDMSNs, of which the performance was comparable to that of the activated carbon.Item Open Access Enhanced non-volatile memory characteristics with quattro-layer graphene nanoplatelets vs. 2.85-nm Si nanoparticles with asymmetric Al2O3/HfO2 tunnel oxide(Springer New York LLC, 2015) El-Atab, N.; Turgut, B. B.; Okyay, Ali Kemal; Nayfeh, M.; Nayfeh, A.In this work, we demonstrate a non-volatile metal-oxide semiconductor (MOS) memory with Quattro-layer graphene nanoplatelets as charge storage layer with asymmetric Al2O3/HfO2 tunnel oxide and we compare it to the same memory structure with 2.85-nm Si nanoparticles charge trapping layer. The results show that graphene nanoplatelets with Al2O3/HfO2 tunnel oxide allow for larger memory windows at the same operating voltages, enhanced retention, and endurance characteristics. The measurements are further confirmed by plotting the energy band diagram of the structures, calculating the quantum tunneling probabilities, and analyzing the charge transport mechanism. Also, the required program time of the memory with ultra-thin asymmetric Al2O3/HfO2 tunnel oxide with graphene nanoplatelets storage layer is calculated under Fowler-Nordheim tunneling regime and found to be 4.1 ns making it the fastest fully programmed MOS memory due to the observed pure electrons storage in the graphene nanoplatelets. With Si nanoparticles, however, the program time is larger due to the mixed charge storage. The results confirm that band-engineering of both tunnel oxide and charge trapping layer is required to enhance the current non-volatile memory characteristics.Item Open Access Facile Synthesis of Three-Dimensional Pt-TiO2Nano-networks: A Highly Active Catalyst for the Hydrolytic Dehydrogenation of Ammonia–Borane(Wiley, 2016) Khalily, M. A.; Eren, H.; Akbayrak, S.; Susapto, H. H.; Bıyıklı, Necmi; Özkar, S.; Güler, Mustafa O.Three‐dimensional (3D) porous metal and metal oxide nanostructures have received considerable interest because organization of inorganic materials into 3D nanomaterials holds extraordinary properties such as low density, high porosity, and high surface area. Supramolecular self‐assembled peptide nanostructures were exploited as an organic template for catalytic 3D Pt‐TiO2 nano‐network fabrication. A 3D peptide nanofiber aerogel was conformally coated with TiO2 by atomic layer deposition (ALD) with angstrom‐level thickness precision. The 3D peptide‐TiO2 nano‐network was further decorated with highly monodisperse Pt nanoparticles by using ozone‐assisted ALD. The 3D TiO2 nano‐network decorated with Pt nanoparticles shows superior catalytic activity in hydrolysis of ammonia–borane, generating three equivalents of H2.Item Open Access Influence of phase function on modeled optical response of nanoparticle-labeled epithelial tissues(2011) Cihan, C.; Arifler, D.Metal nanoparticles can be functionalized with biomolecules to selectively localize in precancerous tissues and can act as optical contrast enhancers for reflectance-based diagnosis of epithelial precancer. We carry out Monte Carlo (MC) simulations to analyze photon propagation through nanoparticle-labeled tissues and to reveal the importance of using a proper form of phase function for modeling purposes. We first employ modified phase functions generated with a weighting scheme that accounts for the relative scattering strengths of unlabeled tissue and nanoparticles. To present a comparative analysis, we repeat ourMCsimulations with simplified functions that only approximate the angular scattering properties of labeled tissues. The results obtained for common optical sensor geometries and biologically relevant labeling schemes indicate that the exact form of the phase function used as model input plays an important role in determining the reflectance response and approximating functions often prove inadequate in predicting the extent of contrast enhancement due to labeling. Detected reflectance intensities computed with different phase functions can differ up to ̃60% and such a significant deviation may even alter the perceived contrast profile. These results need to be taken into account when developing photon propagation models to assess the diagnostic potential of nanoparticle-enhanced optical measurements. © 2011 Society of Photo-Optical Instrumentation Engineers (SPIE).Item Open Access Large area compatible broadband superabsorber surfaces in the VIS-NIR spectrum utilizing metal-insulator-metal stack and plasmonic nanoparticles(OSA - The Optical Society, 2016) Dereshgi, S. A.; Okyay, Ali KemalPlasmonically enhanced absorbing structures have been emerging as strong candidates for photovoltaic (PV) devices. We investigate metal-insulator-metal (MIM) structures that are suitable for tuning spectral absorption properties by modifying layer thicknesses. We have utilized gold and silver nanoparticles to form the top metal (M) region, obtained by dewetting process compatible with large area processes. For the middle (I) and bottom (M) layers, different dielectric materials and metals are investigated. Optimum MIM designs are discussed. We experimentally demonstrate less than 10 percent reflection for most of the visible (VIS) and near infrared (NIR) spectrum. In such stacks, computational analysis shows that the bottom metal is responsible for large portion of absorption with a peak of 80 percent at 1000 nm wavelength for chromium case.Item Open Access Mechanochemical activation and patterning of an adhesive surface toward nanoparticle deposition(American Chemical Society, 2015) Baytekin, H. T.; Baytekin, B.; Huda, S.; Yavuz, Z.; Grzybowski, B. A.Mechanical pulling of adhesive tape creates radicals on the tapes surface. These radicals are capable of reducing metal salts to the corresponding metal nanoparticles. In this way, the mechanically activated tape can be decorated with various types of nanoparticles, including Au, Ag, Pd, or Cu. While retaining their mechanical properties and remaining "sticky, " the tapes can exhibit new properties derived from the presence of metal nanoparticles (e.g., bacteriostaticity, increased electrical conductivity). They can also be patterned with nanoparticles only at selective locations of mechanical activation.Item Open Access Memory effect by charging of ultra‐small 2‐nm laser‐synthesized solution processable Si‐nanoparticles embedded in Si–Al2O3–SiO2 structure(Wiley-VCH Verlag, 2015) El-Atab, N.; Rizk, A.; Tekcan, B.; Alkis, S.; Okyay, Ali Kemal; Nayfeh, A.A memory structure containing ultra-small 2-nm laser-synthesized silicon nanoparticles is demonstrated. The Si-nanoparticles are embedded between an atomic layer deposited high-κ dielectric Al2O3 layer and a sputtered SiO2 layer. A memory effect due to charging of the Si nanoparticles is observed using high frequency C-V measurements. The shift of the threshold voltage obtained from the hysteresis measurements is around 3.3V at 10/-10V gate voltage sweeping. The analysis of the energy band diagram of the memory structure and the negative shift of the programmed C-V curve indicate that holes are tunneling from p-type Si via Fowler-Nordheim tunneling and are being trapped in the Si nanoparticles. In addition, the structures show good endurance characteristic (>105program/erase cycles) and long retention time (>10 years), which make them promising for applications in non-volatile memory devices. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.Item Open Access MIMIM photodetectors using plasmonically enhanced MIM absorbers(SPIE, 2017) Dereshgi, S. Abedini; Okyay, Ali KemalWe demonstrate super absorbing metal-insulator-metal (MIM) stacks and MIMIM photosensitive devices operating at visible and near-infrared (VIS-NIR) spectrum, where absorbing (top) MIM and photocollecting (bottom) MIM can be optimized separately. We investigate different bottom metals in absorbing MIM with nanoparticles realized by dewetting of silver thin film on top. While gold and silver have conventionally been considered the most appropriate plasmonic absorbers, we demonstrate different absorbing metals like aluminum and specifically chromium, with its plasma frequency happening at 850 nm, as more efficient layers for absorption. Absorption in chromium hits 82 percent around 1000 nm. We provide convincing evidences by doing reflection experiment and computational simulations for absorbing MIM part. We also suggest for the first time investigating electric loss tangent of metal or coherently, surface plasmon quality factor of absorbing metals which are reliable tools for engineering different metal layers. They reveal that despite the fact that gold and silver are good plasmonic scatterers in VIS-NIR and reliable absorbers in VIS region, they are not proper choices as absorbers for NIR applications. Once the most optimum absorbing design is pointed out, we integrate it on top of another metal-insulator to form an MIMIM photodetector with tunneling photocurrent path. The final optimized sample consisting of silver - hafnium oxide - chromium - aluminum oxide - silver nanoparticles (from bottom to top) has a dark current of 7nA and a photoresponsivity peak of 0.962 mA/W at 1000 nm and a full width at half maximum of 300 nm, while applied bias is 50 mV and device areas are 300 μm x 600 μm. This photoresponse shows 70 times enhancement compared to former reported spin coated rare nanoparticle MIMIMs.Item Open Access Model-based spectral analysis of photon propagation through nanoparticle-labeled epithelial tissues(SPIE, 2011) Cihan, Can; Arifler, D.Metal nanoparticles can function as optical contrast enhancers for reflectance-based diagnosis of epithelial precancer. We carry out Monte Carlo simulations to model photon propagation through normal tissues, unlabeled precancerous tissues, and precancerous tissues labeled with gold nanospheres and we compute the spectral reflectance response of these different tissue states. The results indicate that nanoparticle-induced changes in the spectral reflectance profile of tissues depend not only on the properties of these particles but also on the source-detector geometry used. When the source and detector fibers are oriented side by side and perpendicular to the tissue surface, the reflectance intensity of precancerous tissue is lower compared to that of normal tissue over the entire wavelength range simulated and addition of nanospheres enhances this negative contrast. When the fibers are tilted toward each other, the reflectance intensity of precancerous tissue is higher compared to that of normal tissue and labeling with nanospheres causes a significant enhancement of this positive contrast. The results also suggest that model-based spectral analysis of photon propagation through nanoparticle-labeled tissues provides a useful framework to quantify the extent of achievable contrast enhancement due to external labeling and to assess the diagnostic potential of nanoparticle-enhanced optical measurements. © 2011 SPIE-OSA.Item Open Access Novel size-tunable and straightforward ultra-small nanoparticle synthesis in a varying concentration range of glycerol as a green reducing solvent(American Chemical Society, 2023-08-08) Munir, Iqra; Yeşilöz, GürkanDespite all the possibilities available so far for the synthesis of nanoparticles (NPs), synthesizing ultra-small (<10 nm) monodispersed particles is still demanding. Getting a particular size with a straightforward method is a trial-and-error approach. To explore this prospective, in the current study, we have introduced a protocol which offers a varying concentration range of glycerol to successfully generate the NPs of repeatable and consistent particle size in each synthesis, thus giving an alternative from lengthy tentative preparations and/or testing protocols. Since synthesizing controlled sized nanoparticles in aqueous medium is somewhat difficult as the balance of particle growth and nucleation is challenging to control, herein, we used a polyol method with glycerol both as a solvent medium as well as reducing species for silver nitrate, as an example model ion source, to execute the nanoparticle synthesis. In order to maintain the stability of the synthesized NPs, polyvinylpyrolidone (PVP) was added as a stabilizer. The synthesis, monodispersity, and stability were confirmed using techniques such as UV–vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS), and X-ray powder diffraction (XRD), while morphological analysis and ultra-small size validation were conducted using TEM, SEM, and AFM. Interestingly, in the various concentrations of glycerol solution used (10–100%), we have observed a tunable linear size range to obtain ultra-small nanoparticles (<10 nm) up to 60% glycerol, while further increasing the glycerol component increased the size approximately to ∼160 nm, providing tunable properties in this synthesis procedure. Hence, this study provides a distinct possibility to obtain ultra-small nanoparticles with a tunable size feature for further applications in numerous fields.Item Open Access Raman enhancement on a broadband meta-surface(American Chemical Society, 2012-07-30) Ayas S.; Güner, H.; Türker, B.; Ekiz, O. O.; Dirisaglik, F.; Okyay, Ali Kemal; Dâna, A.Plasmonic metamaterials allow confinement of light to deep subwavelength dimensions, while allowing for the tailoring of dispersion and electromagnetic mode density to enhance specific photonic properties. Optical resonances of plasmonic molecules have been extensively investigated; however, benefits of strong coupling of dimers have been overlooked. Here, we construct a plasmonic meta-surface through coupling of diatomic plasmonic molecules which contain a heavy and light meta-atom. Presence and coupling of two distinct types of localized modes in the plasmonic molecule allow formation and engineering of a rich band structure in a seemingly simple and common geometry, resulting in a broadband and quasi-omni-directional meta-surface. Surface-enhanced Raman scattering benefits from the simultaneous presence of plasmonic resonances at the excitation and scattering frequencies, and by proper design of the band structure to satisfy this condition, highly repeatable and spatially uniform Raman enhancement is demonstrated. On the basis of calculations of the field enhancement distribution within a unit cell, spatial uniformity of the enhancement at the nanoscale is discussed. Raman scattering constitutes an example of nonlinear optical processes, where the wavelength conversion during scattering may be viewed as a photonic transition between the bands of the meta-material.Item Open Access Simultaneous photoinduced electron transfer and photoinduced CuAAC processes for antibacterial thermosets(Elsevier, 2017) Oz, E.; Uyar, T.; Esen, H.; Tasdelen, M. A.A combination of simultaneous photoinduced electron transfer and photoinduced CuAAC processes enables the in-situ preparation of antibacterial thermosets containing silver nanoparticles (AgNPs) in one-pot. Upon photolysis of photoinitator, the generated radicals not only reduce Cu(II) into Cu(I) activator to catalyst the CuAAC click reaction, but also simultaneously generate AgNPs from AgNO3 through electron transfer reaction. Due to their reduction potentials difference, the polymer matrix is formed before the formation of AgNPs, assisting to eliminate the agglomeration of them. The thermoset structures are confirmed by FT-IR and solubility tests, whereas the presence of AgNPs is proven by transmission electron microscopy with energy dispersive X-ray system analyzer. The samples containing 5 and 10% AgNPs exhibited strong inhibition zones, where all kinds of bacteria (gram-positive (Staphylococcus Aureus) and gram-negative (Escherichia Coli)) were killed in the surrounding of the film samples.Item 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.Item Open Access Sweet plasmonics: sucrose macrocrystals of metal nanoparticles(Tsinghua University Press, 2015-03) Erdem, T.; Soran - Erdem, Z.; Hernandez - Martinez, P. L.; Sharma, V. K.; Akçalı, H.; Akçalı, I.; Gaponik N.; Eychmuller, A.; Demir, Hilmi VolkanThe realization of plasmonic structures generally necessitates expensive fabrication techniques, such as electron beam and focused ion beam lithography, allowing for the top-down fabrication of low-dimensional structures. Another approach to make plasmonic structures in a bottom-up fashion is colloidal synthesis, which is convenient for liquid-state applications or very thin solid films where aggregation problems are an important challenge. The architectures prepared using these methods are typically not robust enough for easy handling and convenient integration. Therefore, developing a new plasmonic robust platform having large-scale dimensions without adversely affecting the plasmonic features is in high demand. As a solution, here we present a new plasmonic composite structure consisting of gold nanoparticles (Au NPs) incorporated into sucrose macrocrystals on a large scale, while preserving the plasmonic nature of the Au NPs and providing robustness in handling at the same time. As a proof of concept demonstration, we present the fluorescence enhancement of green CdTe quantum dots (QDs) via plasmonic coupling with these Au NPs in the sucrose crystals. The obtained composite material exhibits centimeter scale dimensions and the resulting quantum efficiency (QE) is enhanced via the interplay between the Au NPs and CdTe QDs by 58% (from 24% to 38%). Moreover, a shortening in the photoluminescence lifetime from 11.0 to 7.40 ns, which corresponds to a field enhancement factor of 2.4, is observed upon the introduction of Au NPs into the QD incorporated macrocrystals. These results suggest that such "sweet" plasmonic crystals are promising for large-scale robust platforms to embed plasmonic nanoparticles.Item Open Access Synthesis and optical properties of Co and Zn-based metal oxide nanoparticle thin films(Polish Academy of Sciences, 2017) Gungor, E.; Gungor, T.; Calıskan, D.; Özbay, EkmelZnO, Co doped ZnO (ZnO:Co) and CoO thin films were deposited on glass substrates by using the spark discharge technique with Zn-Zn, Zn-Co and Co-Co metal electrodes (tips). The structural and optical properties of the films were characterized by X-ray diffraction, scanning electron microscopy measurements and UV-Vis spectrometry. Cubic phase reflection of CoO (200) was observed in the samples containing Co. The size of nanoparticles had varied between 38 nm and 200 nm in ZnO thin films. When Co electrode was used, spherical structure had deteriorated and clusters of particles, with smaller radii, were observed. In addition, when Co-Co electrode pairs were used, various cavities with different sizes were formed. Especially, it was observed that the optical transmittance had generally increased with the decreasing spark (charge) voltage, while increasing with the number of sparks. The Co-containing samples were green in color and it was observed that the loss of transmission appears in a specific region in the Co-doped ZnO thin films due to characteristic d-d transition of Co2+ ions. The thickness of the films had decreased with the increasing number of sparks. In addition, the band gap energy, Eg, evaluated by UV-Vis spectroscopy measurements has been shifted to higher wavelengths (red shift) for the ZnO:Co thin films.Item Open Access Terahertz time-domain study of silver nanoparticles synthesized by laser ablation in organic liquid(IEEE Microwave Theory and Techniques Society, 2016-07) Koral, C.; Ortaç, B.; Altan, H.We report the investigation of laser-synthesized Ag nanoparticles (Ag-NPs) in an organic liquid environment by using terahertz time-domain spectroscopy (THz-TDS) technique. Colloidal Ag-NPs with an average diameter of 10 nm in two-propanol solution through nanosecond pulsed laser ablation were synthesized. THz-TDS measurements were performed on different volumetric concentration of Ag-NPs suspensions placed in 2-mm path length quartz cuvette. Due to the dispersive and highly absorptive nature of the nano liquids, an approach based on extracting the optical properties through the changes in amplitude and phase solely around the main peak of THz waveform is developed. This approach allowed for an accurate estimation of the complex refractive index of the Metallic-NPs suspension for the different prepared volumetric concentrations. In addition, using Maxwell-Garnett theory, the NP concentration is also extracted. This method shows that the time-domain nature of the THz pulse measurement technique is extremely useful in instances where slight variations in highly dispersive samples need to be investigated.