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Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/6
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Publication Open Access Bidirectional optical neuromodulation using capacitive charge-transfer(The Optical Society (OSA) Publishing, 2020) Department of Electrical and Electronics Engineering; N/A; Department of Chemical and Biological Engineering; Department of Molecular Biology and Genetics; Melikov, Rustamzhon; Srivastava, Shashi Bhushan; Karatüm, Onuralp; Nizamoğlu, Sedat; Doğru-Yüksel, Itır Bakış; Dikbaş, Uğur Meriç; Kavaklı, İbrahim Halil; PhD Student; Researcher; PhD Student; Faculty Member; Master Student; Faculty Member; Department of Electrical and Electronics Engineering; Department of Chemical and Biological Engineering; Department of Molecular Biology and Genetics; Graduate School of Sciences and Engineering; College of Engineering; College of Sciences; N/A; N/A; N/A; 130295; N/A; N/A; 40319Artificial control of neural activity allows for understanding complex neural networks and improving therapy of neurological disorders. Here, we demonstrate that utilization of photovoltaic biointerfaces combined with light waveform shaping can generate safe capacitive currents for bidirectional modulation of neurons. The differential photoresponse of the biointerface due to double layer capacitance facilitates the direction control of capacitive currents depending on the slope of light intensity. Moreover, the strength of capacitive currents is controlled by changing the rise and fall time slope of light intensity. This approach allows for high-level control of the hyperpolarization and depolarization of membrane potential at single-cell level. Our results pave the way toward advanced bioelectronic functionalities for wireless and safe control of neural activity.Publication Open Access High-Q, directional and self-assembled random laser emission using spatially localized feedback via cracks(American Institute of Physics (AIP) Publishing, 2020) Pirnat, Gregor; Humar, Matjaz; N/A; Department of Electrical and Electronics Engineering; Department of Chemical and Biological Engineering; Doğru-Yüksel, Itır Bakış; Han, Mertcan; Mağden, Emir Salih; Şenses, Erkan; Nizamoğlu, Sedat; Master Student; Faculty Member; Faculty Member; Department of Electrical and Electronics Engineering; Department of Chemical and Biological Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; 276368; 280298; 130295Lasers based on Fabry-Perot or whispering gallery resonators generally require complex fabrication stages and sensitive alignment of cavity configurations. The structural defects on reflective surfaces result in scattering and induce optical losses that can be detrimental to laser performance. On the other hand, random lasers can be simply obtained by forming disordered gain media and scatterers, but they generally show omnidirectional emission with a low Q-factor. Here, we demonstrate directional random lasers with a high Q-factor emission (similar to 1.5 x 10(4)) via self-assembled microstructural cracks that are spontaneously formed upon radial strain-release of colloidal nanoparticles from the wet to dry phase. The rough sidewalls of cracks facilitate light oscillation via diffuse reflection that forms a spatially localized feedback, and they also serve as the laser out-coupler. These self-assembled cracks exhibit random lasing at optical pump powers as low as tens of mu J/mm(2). We demonstrate a wide variety of random lasers from nano- and biomaterials including silica nanoparticles, fluorescent proteins, and biopolymers. These findings pave the way toward self-assembled, configurable, and scalable random lasers for sensing, displays, and communication applications.Publication Open Access Optofluidic waveguides written in hydrophobic silica aerogels with a femtosecond laser(Society of Photo-optical Instrumentation Engineers (SPIE), 2015) Yalızay, B.; Morova, Y.; Jonas, A.; Aktürk, S.; Department of Physics; Department of Chemical and Biological Engineering; Kiraz, Alper; Erkey, Can; Özbakır, Yaprak; Faculty Member; Faculty Member; Department of Physics; Department of Chemical and Biological Engineering; College of Sciences; 22542; 29633; N/AWe present a new method to form liquid-core optofluidic waveguides inside hydrophobic silica aerogels. Due to their unique material properties, aerogels are very attractive for a wide variety of applications; however, it is very challenging to process them with traditional methods such as milling, drilling, or cutting because of their fragile structure. Therefore, there is a need to develop alternative processes for formation of complex structures within the aerogels without damaging the material. In our study, we used focused femtosecond laser pulses for high-precision ablation of hydrophobic silica aerogels. During the ablation, we directed the laser beam with a galvo-mirror system and, subsequently, focused the beam through a scanning lens on the surface of bulk aerogel which was placed on a three-axis translation stage. We succeeded in obtaining high-quality linear microchannels inside aerogel monoliths by synchronizing the motion of the galvo-mirror scanner and the translation stage. Upon ablation, we created multimode liquid-core optical waveguides by filling the empty channels inside low-refractive index aerogel blocks with high-refractive index ethylene glycol. In order to demonstrate light guiding and measure optical attenuation of these waveguides, we coupled light into the waveguides with an optical fiber and measured the intensity of transmitted light as a function of the propagation distance inside the channel. The measured propagation losses of 9.9 dB/cm demonstrate the potential of aerogel-based waveguides for efficient routing of light in optofluidic lightwave circuits.Publication Open Access Photocatalytic transformation in aerogel-based optofluidic microreactors(Society of Photo-optical Instrumentation Engineers (SPIE), 2018) Department of Chemical and Biological Engineering; Department of Electrical and Electronics Engineering; Department of Physics; Özbakır, Yaprak; Jonas, Alexandr; Kiraz, Alper; Erkey, Can; PhD Student; Other; Faculty Member; Faculty Member; Department of Chemical and Biological Engineering; Department of Electrical and Electronics Engineering; Department of Physics; College of Sciences; College of Engineering; N/A; N/A; 22542; 29633Here, we demonstrate a new type of microphotoreactor formed by a liquid-core optofluidic waveguide fabricated inside aerogel monoliths. It consists of microchannels in a monolithic aerogel block with embedded anatase titania photocatalysts. In this reactor system, aerogel confines core liquid within internal channels and, simultaneously, behave as waveguide cladding due to its extremely low refractive index of similar to 1. Light is confined in the channels and is guided by total internal reflection (TIR) from the channel walls. We first fabricated L-shaped channels within silica aerogel monoliths (rho= 0.22 g/cm(3), n=1.06) without photocatalyst for photolysis reactions. Using the light delivered by waveguiding, photolysis reactions of methylene blue (MB) were carried out in these channels. We demonstrated that MB can be efficiently degraded in our optofluidic photoreactor, with the rate of dye photoconversion increasing linearly with increasing power of incident light. For photocatalytic transformation in this reactor system, titania particles were successfully embedded into the mesoporous network of silica aerogels with varying amount of the titania in the structure from 1.7 wt % to 50 % wt. The presence of titania and its desired crystalline structure in aerogel matrix was confirmed by XRF, XRD patterns and SEM images. Band gap of silica-titania composites was estimated from Tauc plot calculated by Kubelka-Munk function from diffuse reflectance spectra of samples as near expected value of approximate to 3.2 eV. Photocatalytic activity and kinetic properties for photocatalytic degradation of phenol in the channels were investigated by a constant flow rate, and longer-term stability of titania was evaluated.