Browsing by Subject "Thickness"
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Item Open Access Colorimetric and near-absolute polarization-insensitive refractive-index sensing in all-dielectric guided-mode resonance based metasurface(American Chemical Society, 2019) Yıldırım, Deniz Umut; Ghobadi, Amir; Soydan, Mahmut Can; Gökbayrak, Murat; Toprak, Ahmet; Bütün, Bayram; Özbay, EkmelColorimetric detection of target molecules with insensitivity to incident-light polarization has attracted considerable attention in recent years. This resulted from the ability to provide rapid output and reduced assay times as a result of color changes upon altering the environment that are easily distinguishable by the naked eye. In this paper, we propose a highly sensitive refractive-index sensor, utilizing the excitation of guided modes of a novel two-dimensional periodically modulated dielectric grating-waveguide structure. The optimized nanosensor can numerically excite guided-mode resonances with an ultranarrow linewidth (full width at half-maximum) of 0.58 nm. Sensitivity is numerically investigated by considering the deposition of dielectric layers on the structure. For a layer thickness of 30 nm, the maximum sensitivity reached as high as 110 nm/refractive index unit (RIU), resulting in a very high figure of merit of 190. The fabricated devices with 30 nm aluminum oxide and zinc oxide coatings achieved a maximum sensitivity of 235.2 nm/RIU with a linewidth of 19 nm. Colorimetric detection with polarization insensitivity is confirmed practically by a simple optical microscope. Samples with different coatings have been observed to have clearly distinct colors, while the color of each sample is nearly identical upon azimuthal rotation. Excellent agreement is obtained between the numerical and experimental results regarding the spectral position of the resonances and sensitivity. The proposed device is, therefore, highly promising in efficient, highly sensitive, almost lossless, and compact molecular diagnostics in the field of biomedicine with personalized, label-free, early point-of-care diagnosis and field analysis, drug detection, and environmental monitoring.Item Open Access Continuously tunable emission in inverted type ‐ I CdS/CdSe core/crown semiconductor nanoplatelets(Wiley, 2015-07-15) Delikanlı, S.; Güzeltürk, B.; Hernandez - Martinez, P. L.; Erdem, T.; Keleştemur, Y.; Olutas M.; Akgül, M. Z.; Demir, Hilmi VolkanThe synthesis and unique tunable optical properties of core/crown nanoplatelets having an inverted Type-I heterostructure are presented. Here, colloidal 2D CdS/CdSe heteronanoplatelets are grown with thickness of four monolayers using seed-mediated method. In this work, it is shown that the emission peak of the resulting CdS/CdSe heteronanoplatelets can be continuously spectrally tuned between the peak emission wavelengths of the core only CdS nanoplatelets (421 nm) and CdSe nanoplatelets (515 nm) having the same vertical thickness. In these inverted Type-I nanoplatelets, the unique continuous tunable emission is enabled by adjusting the lateral width of the CdSe crown, having a narrower bandgap, around the core CdS nanoplatelet, having a wider bandgap, as a result of the controlled lateral quantum confinement in the crown region additional to the pure vertical confinement. As a proof-of-concept demonstration, a white light generation is shown by using color conversion with these CdS/CdSe heteronanoplatelets having finely tuned thin crowns, resulting in a color rendering index of 80. The robust control of the electronic structure in such inverted Type-I heteronanoplatelets achieved by tailoring the lateral extent of the crown coating around the core template presents a new enabling pathway for bandgap engineering in solution-processed quantum wells.Item Open Access Cornea engineering on polyester carriers(John Wiley & Sons, Inc., 2006) Zorlutuna, P.; Tezcaner, A.; Kiyat, I.; Aydınlı, Atilla; Hasirci, V.In this study, biodegradable polyester based carriers were designed for tissue engineering of the epithelial and the stromal layers of the cornea, and the final construct was tested in vitro. In the construction of the epithelial layer, micropatterned films were prepared from blends of biodegradable and biocompatible polyesters of natural (PHBV) and synthetic (P(L/DL)LA) origin, and these films were seeded with D407 (retinal pigment epithelial) cells. To improve cell adhesion and growth, the films were coated with fibronectin. To serve as the stromal layer of the cornea, highly porous foams of P(L/DL)LA-PHBV blends were seeded with 3T3 fibroblasts. Cell numbers on the polyester carriers were significantly higher than those on the tissue culture polystyrene control. The cells and the carriers were characterized scanning electron micrographs showed that the foam was highly porous and the pores were interconnected. 3T3 Fibroblasts were distributed quite homogeneously at the seeding site, but probably because of the high thickness of the carrier (∼6 mm); they could not sufficiently populate the core (central parts of the foam) during the test duration. The D407 cells formed multilayers on the micropatterned polyester film. Immunohistochemical studies showed that the cells retained their phenotype during culturing; D407 cells formed tight junctions characteristic of epithelial cells, and 3T3 cells deposited collagen type I into the foams. On the basis of these results, we concluded that the micropatterned films and the foams made of P(L/DL)LA-PHBV blends have a serious potential as tissue engineering carriers for the reconstruction of the epithelial and stromal layers of the cornea.Item Open Access Density profile of a Bose-Einstein condensate inside a pancake-shaped trap: Observational consequences of the dimensional cross-over in the scattering properties(Elsevier Science B.V., 2002) Tanatar, Bilal; Minguzzi, A.; Vignolo, P.; Tosi, M. P.It is theoretically well known that two-dimensionality of the scattering events in a Bose-Einstein condensate introduces a logarithmic dependence on density in the coupling constant entering a mean-field theory of the equilibrium density profile, which becomes dominant as the s-wave scattering length gets larger than the condensate thickness. We trace the regions of experimentally accessible system parameters for which the cross-over between different dimensionality behaviors in the scattering properties may become observable through in situ imaging of the condensed cloud with varying trap anisotropy and scattering length.Item Open Access From aluminum foil to two-dimensional nanocrystals using ultrasonic exfoliation(American Chemical Society, 2021-04-15) Lu, W.; Birmingham, B.; Voronine, D. V.; Stolpman, D.; Ambardar, S.; Erdoğan, Deniz Altunöz; Özensoy, Emrah; Zhang, Z.; Solouki, T.Al nanostructures have unique optical properties such as widely tunable surface plasmon resonances from deep UV to NIR that can be used for label-free fluorescence enhancement and surface-enhanced Raman scattering. Various Al nanostructures have been fabricated using sophisticated “top-down” lithographic and “bottom-up” colloidal methods. Here, we developed a simple and efficient method of synthesizing two-dimensional (2D) aluminum (Al) nanocrystals from commercially available Al foil using ultrasonic exfoliation under ambient environment. 2D Al nanocrystals with sizes from a few hundred nanometers to several micrometers and thickness in the tens of nanometers were isolated through centrifugation separation. The exfoliated 2D Al nanocrystals are covered with a passivated Al2O3 nanolayer. The determined exfoliation mechanism is a combination of the preferred cleavage along the (111) surface planes and layer-by-layer Al2O3 exfoliation from the surface of the 2D Al nanocrystals. We demonstrate that the 2D Al nanocrystals can be assembled at water/air interface and transferred to different substrates to form 2D Al nanocrystal films. These 2D Al nanocrystal films exhibit surface plasmon resonance in the visible spectral range and show enhanced Raman signals of adenine using a 532 nm excitation. These 2D Al nanocrystal films could be further developed for new optical and sensing applications.Item Open Access Growth mechanism of 2D Mo2C on Cu via CVD(American Chemical Society, 2023-7-7) Büke, G. C.; Caylan, Ömer Refet; Oğurtanı, Ö. T.This study investigates the growth of Mo2C crystals via chemical vapor deposition (CVD) in the presence of a carbon (H2/CH4 gas)-containing environment. The study employs both theoretical and experimental approaches to investigate the vertical and lateral (in-plane) growth of Mo2C crystals. A physico-mathematical consideration is applied to develop an analytical forward model, which incorporates bulk diffusivities, surface diffusivities, and solubility gradients for Mo2C crystal growth. Coupled nonlinear flow equations have been advanced for the Mo-, Cu-, Mo2C layer framework and effectively predicted the Mo2C crystal growth rate for both vertical and lateral directions. Forming the Mo2C crystal height and diameter was directly correlated with copper layer thickness and time using the forward model and then validated by the experiments together with SEM and AFM studies. Studies showed that the Cu layer thickness plays a crucial role in controlling the height of the Mo2C crystal while it is not that critical in changing the lateral dimension of the crystal. Beyond simply enhancing Mo2C crystal growth and property-processing relationship, this study demonstrated the synthesis of designer Mo2C, which can be tailored to the needs of specific applications. This forward model will enable us to further enhance and exploit the family of analogs of materials previously demonstrated by other methods.Item Open Access Low-pressure deuterium storage on palladium-coated titanium nanofilms: a versatile model system for tritium-based betavoltaic battery applications(American Chemical Society, 2023-08-30) Ghobadi, Türkan Gamze Ulusoy; Koçak, Yusuf; Jalal, Ahsan; Altınkaynak, Yağmur; Çelik, Gülşah; Semiz, Tolga; Çakır, Cihan; Bütün, Bayram; Özbay, Ekmel; Karadaş, Ferdi; Özensoy, EmrahDeuterium (D2(g)) storage of Pd-coated Ti ultra-thin films at relatively low pressures is fine-tuned by systematically controlling the thicknesses of the catalytic Pd overlayer, underlying Ti ultra-thin film domain, D2(g) pressure (PD2), duration of D2(g) exposure, and the thin film temperature. Structural properties of the Ti/Pd nanofilms are investigated via XRD, XPS, AFM, SEM, and TPD to explore new structure-functionality relationships. Ti/Pd thin film systems are deuterated to obtain a D/Ti ratio of up to 1.53 forming crystallographically ordered titanium deuteride (TiDx) phases with strong Tix+–Dy– electronic interactions and high thermal stability, where >90% of the stored D resides in the Ti component, thermally desorbing at >460 °C in the form of D2(g). Electronic interaction between Pd and D is weak, yielding metallic (Pd0) states where D storage occurs mostly on the Pd film surface (i.e., without forming ordered bulk PdDx phases) leading to the thermal desorption of primarily DOH(g) and D2O(g) at <265 °C. D-storage typically increases with increasing Ti film thickness, PD2, T, and t, whereas D-storage is found to be sensitive to the thickness and the surface roughness of the catalytic Pd overlayer. Optimum Pd film thickness is determined to be 10 nm providing sufficient surface coverage for adequate wetting of the underlying Ti film while offering an appropriate number of surface defects (roughness) for D immobilization and a relatively short transport pathlength for efficient D diffusion from Pd to Ti. The currently used D-storage optimization strategy is also extended to a realistic tritium-based betavoltaic battery (BVB) device producing promising β-particle emission yields of 164 mCi/cm2, an open circuit potential (VOC) of 2.04 V, and a short circuit current (ISC) of 7.2 nA.Item Open Access Molecular scale buckling mechanics in individual aligned single-wall carbon nanotubes on elastomeric substrates(American Chemical Society, 2008) Khang, D. -Y.; Xiao, J.; Kocabaş, Coşkun; MacLaren, S.; Banks, T.; Jiang, H.; Huang, Y. Y.; Rogers, J. A.We have studied the scaling of controlled nonlinear buckling processes in materials with dimensions in the molecular range (i.e., ∼1 nm) through experimental and theoretical studies of buckling in individual single-wall carbon nanotubes on substrates of poly(dimethylsiloxane). The results show not only the ability to create and manipulate patterns of buckling at these molecular scales, but also, that analytical continuum mechanics theory can explain, quantitatively, all measurable aspects of this system. Inverse calculation applied to measurements of diameterdependent buckling wavelengths yields accurate values of the Young’s moduli of individual SWNTs. As an example of the value of this system beyond its use in this type of molecular scale metrology, we implement parallel arrays of buckled SWNTs as a class of mechanically stretchable conductor.Item Open Access Ultra-broadband, wide angle absorber utilizing metal insulator multilayers stack with a multi-thickness metal surface texture(Nature Publishing Group, 2017) Ghobadi, A.; Dereshgi, S. A.; Hajian, H.; Bozok, B.; Butun, B.; Özbay, EkmelIn this paper, we propose a facile route to fabricate a metal insulator multilayer stack to obtain ultra-broadband, wide angle behavior from the structure. The absorber, which covers near infrared (NIR) and visible (Vis) ranges, consists of a metal-insulator-metal-insulator (MIMI) multilayer where the middle metal layer has a variant thickness. It is found that this non-uniform thickness of the metal provides us with an absorption that is much broader compared to planar architecture. In the non-uniform case, each thickness is responsible for a specific wavelength range where the overall absorption is the superposition of these resonant responses and consequently a broad, perfect light absorption is attained. We first numerically examine the impact of different geometries on the overall light absorption property of the multilayer design. Afterward, we fabricate the designs and characterize them to experimentally verify our numerical findings. Characterizations show a good agreement with numerical results where the optimum absorption bandwidth for planar design is found to be 620 nm (380 nm-1000 nm) and it is significantly boosted to an amount of 1060 nm (350 nm-1410 nm) for multi-thickness case. © 2017 The Author(s).