Browsing by Author "Dana, A."

Now showing 1 - 20 of 46

Open Access
All-aluminum hierarchical plasmonic surfaces in the infrared
(The Optical Society, 2016) Ayas S.; Bakan, G.; Dana, A.
All-Aluminum metal-insulator-metal resonator structures withmultiple metal-insulator stacks showing resonances in the mid-infrared(MIR) are fabricated. Ultrathin native Al2O3 is used as the insulator layersenabling simple fabrication of the resonator structures. The structures withtwo oxide layers exhibit two distinct resonances in the MIR. Simulation ofthese structures shows confinement of magnetic field to the thicker bottomoxide at the shorter wavelength resonance and to the thinner top oxide at theother resonance. Simulations of higher order hierarchical structures with 3 and 4 oxide layers show multispectral response with precise control of theoxide thicknesses. The studied structures show great potential for IRapplications that require durability and multispectral characteristics.
Open Access
All-chalcogenide glass omnidirectional photonic band gap variable infrared filters
(AIP Publishing, 2009) Kondakci, H. E.; Yaman, M.; Koylu, O.; Dana, A.; Bayındır, Mehmet
We report on the design, fabrication, and characterization of spatially variable infrared photonic band gap filter that consists of thermally evaporated, high refractive indexcontrast, amorphous chalcogenide glass multilayers. Due to graded thickness structure, the filter exhibits a position dependent stop band and a cavity mode ranging from 1.8 to 3.4 μm3.4 μmwavelengths. Reflection measurements on the variable filter agree well with theoretical calculations. These results pave the way to low-loss infrared mirrors, filters, spectral imaging, and miniaturized spectrometers at infrared region.
Open Access
Atomic force microscopy for the investigation of molecular and cellular behavior
(Elsevier, 2016-10) Ozkan A.D.; Topal, A. E.; Dana, A.; Güler, Mustafa O.; Tekinay, A. B.
The present review details the methods used for the measurement of cells and their exudates using atomic force microscopy (AFM) and outlines the general conclusions drawn by the mechanical characterization of biological materials through this method. AFM is a material characterization technique that can be operated in liquid conditions, allowing its use for the investigation of the mechanical properties of biological materials in their native environments. AFM has been used for the mechanical investigation of proteins, nucleic acids, biofilms, secretions, membrane bilayers, tissues and bacterial or eukaryotic cells; however, comparison between studies is difficult due to variances between tip sizes and morphologies, sample fixation and immobilization strategies, conditions of measurement and the mechanical parameters used for the quantification of biomaterial response. Although standard protocols for the AFM investigation of biological materials are limited and minor differences in measurement conditions may create large discrepancies, the method is nonetheless highly effective for comparatively evaluating the mechanical integrity of biomaterials and can be used for the real-time acquisition of elasticity data following the introduction of a chemical or mechanical stimulus. While it is currently of limited diagnostic value, the technique is also useful for basic research in cancer biology and the characterization of disease progression and wound healing processes.
Open Access
Colorimetric detection of ultrathin dielectrics on strong interference coatings
(OSA - The Optical Society, 2018) Ayas S.; Bakan, G.; Ozgur E.; Celebi, K.; Torunoglu, G.; Dana, A.
Metal films covered with ultrathin lossy dielectrics can exhibit strong interference effects manifested as the broad absorption of the incident light resulting in distinct surface colors. Despite their simple bilayer structures, such surfaces have only recently been scrutinized and applied mainly to color printing. Here, we report the use of such surfaces for colorimetric detection of ultrathin dielectrics. Upon deposition of a nanometer-thick dielectric on the surface, the absorption peak red shifts, changing the surface color. The color contrast between the bare and dielectric-coated surfaces can be detected by the naked eye. The optical responses of the surfaces are characterized for nanometer-thick SiO2, Al2O3, and bovine serum albumin molecules. The results suggest that strong interference surfaces can be employed as biosensors.
Open Access
Counting molecules with a mobile phone camera using plasmonic enhancement
(American Chemical Society, 2014) Ayas S.; Cupallari, A.; Ekiz, O. O.; Kaya, Y.; Dana, A.
Plasmonic field enhancement enables the acquisition of Raman spectra at a single molecule level. Here we investigate the detection of surface enhanced Raman signal using the unmodified image sensor of a smart phone, integrated onto a confocal Raman system. The sensitivity of a contemporary smart phone camera is compared to a photomultiplier and a cooled charge-coupled device. The camera displays a remarkably high sensitivity, enabling the observation of the weak unenhanced Raman scattering signal from a silicon surface, as well as from liquids, such as ethanol. Using high performance wide area plasmonic substrates that enhance the Raman signal 106 to 107 times, blink events typically associated with single molecule motion, are observed on the smart phone camera. Raman spectra can also be collected on the smart phone by converting the camera into a low resolution spectrometer with the inclusion of a collimator and a dispersive optical element in front of the camera. In this way, spectral content of the blink events can be observed on the plasmonic substrate, in real time, at 30 frames per second. (Figure Presented) © 2013 American Chemical Society.
Open Access
The design and fabrication of supramolecular semiconductor nanowires formed by benzothienobenzothiophene (BTBT)-conjugated peptides
(Royal Society of Chemistry, 2018) Khalily, M. A.; Usta, H.; Ozdemir, M.; Bakan, G.; Dikecoglu, F. B.; Edwards-Gayle, C.; Hutchinson, J. A.; Hamley, I. W.; Dana, A.; Güler, Mustafa O.
π-Conjugated small molecules based on a [1]benzothieno[3,2-b]benzothiophene (BTBT) unit are of great research interest in the development of solution-processable semiconducting materials owing to their excellent charge-transport characteristics. However, the BTBT π-core has yet to be demonstrated in the form of electro-active one-dimensional (1D) nanowires that are self-assembled in aqueous media for potential use in bioelectronics and tissue engineering. Here we report the design, synthesis, and self-assembly of benzothienobenzothiophene (BTBT)-peptide conjugates, the BTBT-peptide (BTBT-C3-COHN-Ahx-VVAGKK-Am) and the C8-BTBT-peptide (C8-BTBT-C3-COHN-Ahx-VVAGKK-Am), as β-sheet forming amphiphilic molecules, which self-assemble into highly uniform nanofibers in water with diameters of 11-13(±1) nm and micron-size lengths. Spectroscopic characterization studies demonstrate the J-type π-π interactions among the BTBT molecules within the hydrophobic core of the self-assembled nanofibers yielding an electrical conductivity as high as 6.0 × 10-6 S cm-1. The BTBT π-core is demonstrated, for the first time, in the formation of self-assembled peptide 1D nanostructures in aqueous media for potential use in tissue engineering, bioelectronics and (opto)electronics. The conductivity achieved here is one of the highest reported to date in a non-doped state.
Open Access
Excited-state dynamics and nonlinear optical response of Ge nanocystals embedded in silica matrix
(A I P Publishing LLC, 2006-05-01) Razzani, L.; Gnoli, A.; Righini, M.; Dana, A.; Aydınlı, Atilla
We use a dedicated Z-scan setup, arranged to account for cumulative effects, to study the nonlinear optical response of Ge nanocrystals embedded in silica matrix. Samples are prepared with plasma-enchanced chemical-vapor deposition and post-thermal annealing. We measure a third-order nonlinear refraction coefficient of gamma=1x10(-16) m(2)/W. The nonlinear absorption shows an intensity-independent coefficient of beta=4x10(-10) m/W related to fast processes. In addition, we measure a second beta component around 10(-9) m/W with a relaxation time of 300 mu s that rises linearly with the laser intensity. We associate its origin to the absorption of excited carriers from a surface-defect state with a long depopulation time.
Open Access
Exploiting native Al2O3 for multispectral aluminum plasmonics
(American Chemical Society, 2014) Ayas S.; Topal, A. E.; Cupallari, A.; Güner, H.; Bakan, G.; Dana, A.
Aluminum, despite its abundance and low cost, is usually avoided for plasmonic applications due to losses in visible/infrared regimes and its interband absorption at 800 nm. Yet, it is compatible with silicon CMOS processes, making it a promising alternative for integrated plasmonic applications. It is also well known that a thin layer of native Al2O3 is formed on aluminum when exposed to air, which must be taken into account properly while designing plasmonic structures. Here, for the first time we report exploitation of the native Al2O3 layer for fabrication of periodic metal-insulator-metal (MIM) plasmonic structures that exhibit resonances spanning a wide spectral range, from the near-ultraviolet to mid-infrared region of the spectrum. Through fabrication of silver nanoislands on aluminum surfaces and MIM plasmonic surfaces with a thin native Al2O3 layer, hierarchical plasmonic structures are formed and used in surface-enhanced infrared spectroscopy (SEIRA) and surface-enhanced Raman spectrocopy (SERS) for detection of self-assembled monolayers of dodecanethiol. (Chemical Equation Presented). © 2014 American Chemical Society.
Open Access
Extracting the temperature distribution on a phase-change memory cell during crystallization
(American Institute of Physics Inc., 2016-10) Bakan, G.; Gerislioglu, B.; Dirisaglik, F.; Jurado, Z.; Sullivan, L.; Dana, A.; Lam, C.; Gokirmak A.; Silva, H.
Phase-change memory (PCM) devices are enabled by amorphization- and crystallization-induced changes in the devices' electrical resistances. Amorphization is achieved by melting and quenching the active volume using short duration electrical pulses (∼ns). The crystallization (set) pulse duration, however, is much longer and depends on the cell temperature reached during the pulse. Hence, the temperature-dependent crystallization process of the phase-change materials at the device level has to be well characterized to achieve fast PCM operations. A main challenge is determining the cell temperature during crystallization. Here, we report extraction of the temperature distribution on a lateral PCM cell during a set pulse using measured voltage-current characteristics and thermal modelling. The effect of the thermal properties of materials on the extracted cell temperature is also studied, and a better cell design is proposed for more accurate temperature extraction. The demonstrated study provides promising results for characterization of the temperature-dependent crystallization process within a cell.
Open Access
Fabrication of supramolecular n/p-nanowires via coassembly of oppositely charged peptide-chromophore systems in aqueous media
(American Chemical Society, 2017-07) Khalily, M. A.; Bakan, G.; Kucukoz, B.; Topal, A. E.; Karatay, A.; Yaglioglu, H. G.; Dana, A.; Güler, Mustafa O.
Fabrication of supramolecular electroactive materials at the nanoscale with well-defined size, shape, composition, and organization in aqueous medium is a current challenge. Herein we report construction of supramolecular charge-transfer complex one-dimensional (1D) nanowires consisting of highly ordered mixed-stack π-electron donor-acceptor (D-A) domains. We synthesized n-type and p-type β-sheet forming short peptide-chromophore conjugates, which assemble separately into well-ordered nanofibers in aqueous media. These complementary p-type and n-type nanofibers coassemble via hydrogen bonding, charge-transfer complex, and electrostatic interactions to generate highly uniform supramolecular n/p-coassembled 1D nanowires. This molecular design ensures highly ordered arrangement of D-A stacks within n/p-coassembled supramolecular nanowires. The supramolecular n/p-coassembled nanowires were found to be formed by A-D-A unit cells having an association constant (KA) of 5.18 × 105 M-1. In addition, electrical measurements revealed that supramolecular n/p-coassembled nanowires are approximately 2400 and 10 times more conductive than individual n-type and p-type nanofibers, respectively. This facile strategy allows fabrication of well-defined supramolecular electroactive nanomaterials in aqueous media, which can find a variety of applications in optoelectronics, photovoltaics, organic chromophore arrays, and bioelectronics.
Open Access
Force and time-dependent self-assembly, disruption and recovery of supramolecular peptide amphiphile nanofibers
(Institute of Physics Publishing, 2018) Dikecoglu, F. B.; Topal, A. E.; Ozkan A.D.; Tekin, E. D.; Tekinay, A. B.; Güler, Mustafa O.; Dana, A.
Biological feedback mechanisms exert precise control over the initiation and termination of molecular self-assembly in response to environmental stimuli, while minimizing the formation and propagation of defects through self-repair processes. Peptide amphiphile (PA) molecules can self-assemble at physiological conditions to form supramolecular nanostructures that structurally and functionally resemble the nanofibrous proteins of the extracellular matrix, and their ability to reconfigure themselves in response to external stimuli is crucial for the design of intelligent biomaterials systems. Here, we investigated real-time self-assembly, deformation, and recovery of PA nanofibers in aqueous solution by using a force-stabilizing double-pass scanning atomic force microscopy imaging method to disrupt the self-assembled peptide nanofibers in a force-dependent manner. We demonstrate that nanofiber damage occurs at tip-sample interaction forces exceeding 1 nN, and the damaged fibers subsequently recover when the tip pressure is reduced. Nanofiber ends occasionally fail to reconnect following breakage and continue to grow as two individual nanofibers. Energy minimization calculations of nanofibers with increasing cross-sectional ellipticity (corresponding to varying levels of tip-induced fiber deformation) support our observations, with high-ellipticity nanofibers exhibiting lower stability compared to their non-deformed counterparts. Consequently, tip-mediated mechanical forces can provide an effective means of altering nanofiber integrity and visualizing the self-recovery of PA assemblies.
Open Access
Formation of Ge nanocrystals and SiGe in PECVD grown SiNx: Ge thin films
(Elsevier, 2006) Dana, A.; Tokay, S.; Aydınlı, Atilla
Formation of Ge nanocrystals in SiNx matrices has been studied using plasma enhanced chemical vapor deposition in both as deposited samples as well as in post-vacuum annealed samples. Low temperature and short duration anneals in vacuum resulted in Ge nanocrystals whereas prolonged anneals at higher temperatures resulted in Ge nanocrystals accompanied with SiGe formation at the SiNx/Si interface. Raman Scattering Spectroscopy was extensively used to track the formation of various phonon modes during the diffusion of Ge through SiNx and into the Si substrate.
Open Access
Growth of Ge nanoparticles on SiO2 / Si interfaces during annealing of plasma enhanced chemical vapor deposited thin films
(Elsevier B.V., 2007) Foss, S.; Finstad, T. G.; Dana, A.; Aydınlı, Atilla
Multilayer germanosilicate (Ge:SiO2) films have been grown by plasma enhanced chemical vapor deposition. Each Ge:SiO2 layer is separated by a pure SiO2 layer. The samples were heat treated at 900 °C for 15 and 45 min. Transmission electron microscopy investigations show precipitation of particles in the layers of highest Ge concentration. Furthermore there is evidence of diffusion between the layers. This paper focuses mainly on observed growth of Ge particles close to the interface, caused by Ge diffusion from the Ge:SiO2 layer closest to the interface through a pure SiO2 layer and to the interface. The particles grow as spheres in a direction away from the interface. Particles observed after 15 min anneal time are 4 nm in size and are amorphous, while after 45 min anneal time they are 7 nm in size and have a crystalline diamond type Ge structure.
Open Access
High-refractive-index measurement with an elastromeric grating coupler
(Optical Society of America, 2005) Kocabas, A.; Ay, F.; Dana, A.; Kiyat, A.; Aydınlı, Atilla
An elastomeric grating coupler fabricated by the replica molding technique is used to measure the modal indices of a silicon-on-insulator (SOI) planar waveguide structure. Because of the van der Waals interaction between the grating mold and the waveguide, the elastomeric stamp makes conformal contact with the waveguide surface, inducing a periodic index perturbation at the contact region. The phase of the incident light is changed to match the guided modes of the waveguide. The modal and bulk indices are obtained by measuring the coupling angles. This technique serves to measure the high refractive index with a precision better than 10(-3) and allows the elastomeric stamp to be removed without damaging the surface of the waveguide.
Open Access
Interfiber interactions alter the stiffness of gels formed by supramolecular self-assembled nanofibers
(Elsevier, 2011-02-16) Dagdas, Y. S.; Tombuloglu, A.; Tekinay, A. B.; Dana, A.; Güler, Mustafa O.
Molecular self-assembly is a powerful technique for developing novel nanostructures by using noncovalent interactions such as hydrogen bonding, hydrophobic, electrostatic, metal-ligand, p-p and van der Waals interactions. These interactions are highly dynamic and are often delicate due to their relatively weak nature. However, a sufficient number of these weak interactions can yield a stable assembly. In this work, we studied the mechanical properties of self-assembled peptide amphiphile nanostructures in the nanometre and micrometre scale. Hydrogen bonding, hydrophobic and electrostatic interactions promote self-assembly of peptide amphiphile molecules into nanofibers. Bundles of nanofibers form a three-dimensional network resulting in gel formation. The effect of the nanofiber network on the mechanical properties of the gels was analyzed by AFM, rheology and CD. Concentration and temperature dependent measurements of gel stiffness suggest that the mechanical properties of the gels are determined by a number of factors including the interfiber interactions and mechanical properties of individual nanofibers. We point out that the divergence in gel stiffness may arise from the difference in strength of interfiber bonds based on an energetic model of elastic rod networks, along with continuum mechanical models of bundles of rods. This finding differs from the results observed with traditional polymeric materials. Understanding the mechanisms behind the viscoelastic properties of the gels formed by self-assembling molecules can lead to development of new materials with controlled stiffness. Tissue engineering applications can especially benefit from these materials, where the mechanical properties of the extracellular matrix are crucial for cell fate determination. © The Royal Society of Chemistry 2011.
Open Access
Invisible thin-film patterns with strong infrared emission as an optical security feature
(Wiley-VCH Verlag, 2018) Bakan, G.; Ayas S.; Serhatlioglu, M.; Elbuken, Çağlar; Dana, A.
Spectrally selective thermal emission is in high demand for thermophotovoltaics, radiative cooling, and infrared sensing applications. Spectral control of the emissivity is historically achieved by choosing the material with suitable infrared properties. The recent advancements in nanofabrication techniques that lead to enhanced light-matter interactions enable optical properties like infrared emissivity that are not naturally available. In this study, thermal emitters based on nanometer-thick dielectrics on field-enhancement surfaces as optical security features are proposed. Such a function is achieved by generating patterns by ultrathin dielectrics that are transparent in the visible and exhibit strong infrared absorption in the spectral range of thermal cameras. The invisible patterns are then revealed by thermal imaging. The field-enhancement surfaces enhance the emissivity of the patterns, in turn reduce the minimum temperature to detect the thermal emission down to ≈30 °C from >150 °C to exploit ubiquitous heat sources like the human body. The study provides a framework for the use of thermal emitters as optical security features and demonstrates applications on rigid and flexible substrates.
Open Access
Laser synthesized gold nanoparticles for high sensitive strain gauges
(Elsevier, 2013-12-01) Burzhuev, S.; Dana, A.; Ortac, B.
We demonstrate high strain sensitivity property of gold nanoparticle (Au-NP) thin films fabricated on flexible polydimethylsiloxane (PDMS) substrates. This behavior is attributed to quantum tunneling effect that is highly dependent on nanoparticle separation. Au-NPs were synthesized in water by nanosecond laser ablation method. The clean surface providing high tunneling decay constant, size of the Au-NPs and Au-NPs aggregate clusters offer advantages for high sensitivity strain sensor. We prepared Au-NPs films on flexible PDMS substrate by using hands-on drop-cast method. To obtain high gauge factor (g factor), we investigated the nanoparticles concentration on the substrate. Laser-generated Au-NPs films demonstrated g factor of ∼300 for higher than 0.22% strain and ∼80 for the strain lower than 0.22% strain, which is favorably comparable to reported sensitivities for strain sensors based on Au-NPs. Mechanical characterizations for the prolonged working durations suggest long term stability of the strain sensors. We discuss several models describing conductance of films in low and high strain regimes.
Open Access
License distribution protocols from optical media fingerprints
(Springer International Publishing, 2010) Hammouri, G.; Dana, A.; Sunar, B.
According to the Business Software Alliance about 35% of the global software market, worth $141 Billion, is counterfeit. Most of the counterfeit software is distributed in the form of a compact disc (CD) or a digital video disc (DVD) which is easily copied and sold in street corners all around the world but mostly in developing countries. Given the severity of the problem at hand, a comprehensive solution taking into account the manufacturing process, economical implications, ease of enforcement, and the owner’s rights needs to be developed. While this is an enormous undertaking requiring new schemes at all levels of implementation, in this work, we focus only on a small part of the problem, i.e., secure fingerprinting techniques for optical media.
Open Access
Local delivery of doxorubicin through supramolecular peptide amphiphile nanofiber gels
(Royal Society of Chemistry, 2017) Cinar, G.; Ozdemir, A.; Hamsici, S.; Gunay, G.; Dana, A.; Tekinay, A. B.; Güler, Mustafa O.
Peptide amphiphiles (PAs) self-assemble into supramolecular nanofiber gels that provide a suitable environment for encapsulation of both hydrophobic and hydrophilic molecules. The PA gels have significant advantages for controlled delivery applications due to their high capacity to retain water, biocompatibility, and biodegradability. In this study, we demonstrate injectable supramolecular PA nanofiber gels for drug delivery applications. Doxorubicin (Dox), as a widely used chemotherapeutic drug for breast cancer treatment, was encapsulated within the PA gels prepared at different concentrations. Physical and chemical properties of the gels were characterized, and slow release of the Dox molecules through the supramolecular PA nanofiber gels was studied. In addition, the diffusion constants of the drug molecules within the PA nanofiber gels were estimated using fluorescence recovery after the photobleaching (FRAP) method. The PA nanofiber gels did not show any cytotoxicity and the encapsulation strategy enhanced the activity of drug molecules on cellular viability through prolonged release compared to direct administration under in vitro conditions. Moreover, the local in vivo injection of the Dox encapsulated PA nanofiber gels (Dox/PA) to the tumor site demonstrated the lowest tumor growth rate compared to the direct Dox injection and increased the apoptotic cells within the tumor tissue for local drug release through the PA nanofiber gels under in vivo conditions.
Open Access
Memristive behavior in a junctionless flash memory cell
(American Institute of Physics Inc., 2015) Orak, I.; Ürel, M.; Bakan, G.; Dana, A.
We report charge storage based memristive operation of a junctionless thin film flash memory cell when it is operated as a two terminal device by grounding the gate. Unlike memristors based on nanoionics, the presented device mode, which we refer to as the flashristor mode, potentially allows greater control over the memristive properties, allowing rational design. The mode is demonstrated using a depletion type n-channel ZnO transistor grown by atomic layer deposition (ALD), with HfO2 as the tunnel dielectric, AI2O3 as the control dielectric, and non-stoichiometric silicon nitride as the charge storage layer. The device exhibits the pinched hysteresis of a memristor and in the unoptimized device, R off/R on ratios of about 3 are presented with low operating voltages below 5 V. A simplified model predicts Roff/Ron ratios can be improved significantly by adjusting the native threshold voltage of the devices. The repeatability of the resistive switching is excellent and devices exhibit 106 s retention time, which can, in principle, be improved by engineering the gate stack and storage layer properties. The flashristor mode can find use in analog information processing applications, such as neuromorphic computing, where well-behaving and highly repeatable memristive properties are desirable.