Browsing by Subject "Optical characterization"
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Item Open Access Developing a transducer based on localized surface plasmon resonance (LSPR) of gold nanostructures for nanobiosensor applications(Trans Tech Publications, 2013) Turhan, Adil Burak; Ataman, D.; Çakmakyapan, S.; Mutlu, M.; Özbay, Ekmel; Vlachos, D. S.; Hristoforou, E.In this work, we report the nanofabrication, optical characterization, and electromagnetic modeling of various nanostructure arrays for localized surface plasmon resonance (LSPR) based biosensing studies. Comparison of the experimental results and simulation outputs of various nanostructure arrays was made and a good correspondence was achieved.Item Open Access Photocatalytic hybrid nanocomposites of metal oxide nanoparticles enhanced towards the visible spectral range(Elsevier, 2011-04-13) Perkgoz, N. K.; Toru, R. S.; Unal, E.; Sefunc, M.A.; Tek, S.; Mutlugun, E.; Soganci, I. M.; Celiker, H.; Celiker, G.; Demir, Hilmi VolkanWe propose and demonstrate photocatalytic hybrid nanocomposites that co-integrate TiO(2) and ZnO nanoparticles in the same host resin to substantially enhance their combined photocatalytic activity in the near-UV and visible spectral ranges, where the intrinsic photocatalytic activity of TiO2 nanoparticles or that of ZnO nanoparticles is individually considerably weak For a comparative study, by embedding TiO(2) nanoparticles of ca. 6 nm and ZnO nanoparticles of ca. 40 nm in the sol-gel matrix of acrylic resin, we make thin film coatings of TiO(2)-ZnO nanoparticles (combination of TiO2 and ZnO, each with a mass ratio of 8.5%), as well as the composite films of TiO(2) nanoparticles alone (17.0%), and ZnO nanoparticles alone (17.0%), and a negative control group with no nanoparticles. For all of these thin films coated on polyvinyl chloride (PVC) polyester, we experimentally study photocatalytic activity and systematically measure spectral degradation (recovery obtained by photocatalytic reactions). This spectral characterization exhibits photodegradation levels of the contaminant at different excitation wavelengths (in the range of 310-469 nm) to distinguish different parts of optical spectrum where TiO(2) and ZnO nanopartides are individually and concurrently active. We observe that the photocatalytic activity is significantly improved towards the visible range with the use of TiO(2)-ZnO combination compared to the individual cases. Particularly for the excitation wavelengths of photochemical reactions longer than 400 nm, where the negative control group and ZnO nanoparticles alone yield no observable photodegradation level and TiO2 nanoparticles alone lead to a low photodegradation level of 14%, the synergic combination of TiO(2)-ZnO nanoparticles achieves a photodegradation level as high as 30%. Investigating their scanning electron microscopy (SEM), X-ray diffraction (XRD), and high resolution transmission electron microscopy (HRTEM), we present evidence of the heterostructure, crystallography, and chemical bonding states for the hybrid TiO(2)-ZnO nanocomposite films, in comparison to the films of only TiO(2) nanoparticles, only ZnO nanoparticles, and no nanoparticles.Item Open Access Substrate impact on the low-temperature growth of GaN thin films by plasma-assisted atomic layer deposition(AVS Science and Technology Society, 2016) Kizir, S.; Haider, A.; Bıyıklı, NecmiGallium nitride (GaN) thin films were grown on Si (100), Si (111), and c-plane sapphire substrates at 200 �C via hollow-cathode plasma-assisted atomic layer deposition (HCPA-ALD) using GaEt3 and N2/H2 plasma as group-III and V precursors, respectively. The main aim of the study was to investigate the impact of substrate on the material properties of low-temperature ALD-grown GaN layers. Structural, chemical, and optical characterizations were carried out in order to evaluate and compare film quality of GaN on different substrates. X-ray reflectivity measurements showed film density values of 5.70, 5.74, and 5.54 g/cm3 for GaN grown on Si (100), Si (111), and sapphire, respectively. Grazing incidence x-ray diffraction measurements exhibited hexagonal wurtzite structure in all HCPA-ALD grown GaN samples. However, dominant diffraction peak for GaN films grown on Si and sapphire substrates were detected differently as (002) and (103), respectively. X-ray diffraction gonio scans measured from GaN grown on c-plane sapphire primarily showed (002) orientation. All samples exhibited similar refractive index values (∼2.17 at 632 nm) with 2-3 at. % of oxygen impurity existing within the bulk of the films. The grain size was calculated as ∼9-10 nm for GaN grown on Si (100) and Si (111) samples while it was ∼5 nm for GaN/sapphire sample. Root-mean-square surface roughness values found as 0.68, 0.76, and 1.83 nm for GaN deposited on Si (100), Si (111), and sapphire, respectively. Another significant difference observed between the samples was the film growth per cycle: GaN/sapphire sample showed a considerable higher thickness value when compared with GaN/Si samples, which might be attributed to a possibly more-efficient nitridation and faster nucleation of sapphire surface.Item Open Access Synthesis of nanoparticles by laser ablation in liquid method and optical applications(Bilkent University, 2023-08) Taylan, UmutPulsed laser ablation in liquids (PLAL) method is a fast, green, and straightforward method that can be used to synthesize pure nanoparticles free of ligands, capping agents, and waste products. Several types of nanoparticles such as metals, oxides, alloys, semiconductors, composite and compound nanoparticles with spherical or complex morphologies can be synthesized with PLAL method. In this thesis, AuCu nanoparticles for photovoltaic application, AgCu nanoparticles for tunable optical properties, CuS/Cu1.8S nanoparticles for photothermal and photoacoustic application, and (Y0.83Yb0.16Er0.01)2O3 nanoparticles for upconversion photoluminescence application are synthesized. The synthesized AuCu nanoparticles are used in organic solar cells and enhanced the photocurrent production, proven by the 21.4% increase in the power conversion efficiency. AgCu nanoparticles show composition and laser fragmentation dependent tunable surface plasmon resonance between 420 nm – 580 nm, giving 160 nm tunability. These nanoparticles also show complex morphologies with Janus nanoparticle and core-shell type configurations. Copper sulphide nanoparticles show a broad absorbance in the NIR region with absorbance peak at 1183 nm. Nanoparticles with 1 mg/mL concentration show a 52.2 °C temperature increase in 3 minutes of 3.23 W/cm2 1080 nm CW laser irradiation. Photoacoustic imaging experiments where copper sulphide nanoparticles are utilized show a significant contrast enhancement compared to ultrasonic imaging at 1 cm depth. The upconversion nanoparticles show an intense red emission at 651 nm from 980 nm laser irradiation and lowered green emission compared to the target material which shows nanoparticles produce more heat compared to the target which can be useful for photoluminescence – photothermal applications.Item Open Access White-emitting conjugated polymer nanoparticles with cross-linked shell for mechanical stability and controllable photometric properties in color-conversion LED applications(2011) Park, Eun-Ju; Erdem, T.; Ibrahimova, V.; Nizamoglu, S.; Demir, Hilmi Volkan; Tuncel, D.We report on the synthesis and characterization of water-dispersible, mechanically stable conjugated polymer nanoparticles (CPNs) in shelled architecture with tunable emission and controllable photometric properties via cross-linking. Using a reprecipitation method, whiteemitting polymer nanoparticles are prepared in different sizes by varying the concentration of polymer; the emission kinetics are tuned by controlling the shell formation. For this purpose, polyfluorene derivatives containing azide groups are selected that can be decomposed under UV light to generate very reactive species, which opportunely facilitate the inter- and intra-cross-linking of polymer chains to form shells. Nanoparticles before and after UV treatment are characterized by various techniques. Their size and morphologies are determined by using dynamic light scattering (DLS) measurements and imaging techniques including scanning electron microscopy (SEM) and atomic force microscopy (AFM). For optical characterization, UV vis and steady-state and timeresolved fluorescent spectroscopies are performed. Solid-state behaviors of these CPNs are also investigated by forming films through drop-casting. Moreover, the photometric calculations are also performed for films and dispersions to determine the color quality. A device has been constructed to show proof-of-principle white light generation from these nanoparticles. Additionally, mechanical stability studies are performed and demonstrated that these nanoparticles are indeed mechanically stable by removing the solvent after cross-linking using a freeze-dryer and redispersing in water and THF. Optical and imaging data confirm that the redispersed particles preserve their shapes and sizes after cross-linking.