Browsing by Subject "Etching"
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Item Open Access Analysis of electrical characteristics and magnetic field dependences of YBCO step edge and bicrystal grain boundary junctions for rf-SQUID applications(Institute of Physics, 2004) Fardmanesh, M.; Schubert, J.; Akram, R.; Bick, M.; Banzet, M.; Zander, W.; Zhang, Y.; Krause, H-J.The dc characteristics and magnetic field dependences of Y-Ba-Cu-O bicrystal grain boundary junctions (BGBJs) and step edge junctions (SEJs) were investigated for fabrication of rf-SQUIDs. Test junctions with up to 8 μm widths as well as the junctions of the two types of junction-based rf-SQUID were studied. The SEJs typically showed lower Jc and higher ρN as compared to the BGBJs, resulting in close IcRN products. All the BGBJs showed classical field dependent Ic following their junction width, resembling Fraunhofer patterns. The field sensitivity of the BGBJs' Uc led to low yield submicron BGBJ rf-SQUIDs partially impaired by the Earth's magnetic field. Two major behaviours of low and high field dependences of Ic were observed for the SEJs. Only the low field-sensitive SEJs resulted in micron size junction rf-SQUIDs not impaired by the Earth's magnetic field. The low field-sensitive SEJs led to low I/f noise magnetically stable rf-SQUIDs appropriate for applications in unshielded environments at 77 K.Item Open Access A combinatorial buffered oxide etching method for high-power cladding light stripper(Institute of Electrical and Electronics Engineers Inc., 2019) Yapar-Yıldırım, Elif; Karatutlu, Ali; Balk, Ekin Teslime; Midilli, Yakup; Ortaç, BülendHigh-power fiber lasers have been applied in many areas due to their advantages such as high beam quality, compact structure, flexibility and high efficiency. However, the absorption of the pump light is limited and a residual pumped light keeps propagating in the cladding. This residual pumped light affects the beam quality and can damage the whole system. Therefore, an efficient removal of excess high-power cladding light is critical for the safe operation of the high-power fiber lasers and high beam quality [1]. Adding a new structure to the cladding of the fiber leading to interrupt total internal reflection in the clad and scatter away the unwanted pump light is the generalized approach for a cladding light stripper (CLS) device fabrication. Also, it is important to scatter all the unwanted light uniformly along the CLS. Etching the fiber for surface damage and recoating the fiber [2] are two general methods for stripping the cladding light [3-5].Item Open Access Dependence of the substrate structure and the film growth at the junction of YBCO SEJ rf-SQUIDs on the IBE process and effects on the SQUID's characteristics(Elsevier, 2002) Fardmanesh, Mehdi; Schubert, J.; Akram, Rizwan; Banzet, M.; Zander, W.; Zhang, Y.; Schilling, M.; Krause, H-J.Step edge junction (SEJ) rf-SQUIDs were made of 200 nm thick YBCO films on LaAlO3(100) substrates using pulsed laser deposition technique. The steps on the substrates were developed using a combination of stationary and rotating angled argon ion beams with different beam energies and intensities. While sharp clean steps with heights up to 300 nm were obtained on the substrates using the combinatorial ion beam etching (IBE) process, very shallow ramp-type surfaces were found developing on the bottom of the trench, close to the steps. The ramp-type surfaces were found to be a source of hole-type defects in the films grown at the step edges. High quality films could be obtained on the flat regions away from the steps. Higher defect densities in the films close to the SEJs resulted in devices with higher 1/f noise and wider spread of the junction parameters. The 1/f noise of such devices increased with decreasing temperature. High quality films on sharp clean steps with flat substrate surfaces, developed using optimized combinatorial IBE process, resulted in higher yield of low 1/f noise SQUIDs. The Ic of the junctions and hence the working temperature of the SQUID could also be controlled by the junction width and the step height.Item Open Access Dual-color ultraviolet metal-semiconductor-metal AlGaN photodetectors(AIP Publishing LLC, 2006) Gökkavas, M.; Bütün, S.; Yu, H.; Tut, T.; Bütün, B.; Özbay, EkmelBackilluminated ultraviolet metal-semiconductor-metal photodetectors with different spectral responsivity bands were demonstrated on a single Alx Ga1-x N heterostructure. This was accomplished by the incorporation of an epitaxial filter layer and the recess etching of the surface. The 11 nm full width at half maximum (FWHM) responsivity peak of the detector that was fabricated on the as-grown surface was 0.12 AW at 310 nm with 10 V bias, whereas the 22 nm FWHM responsivity peak of the detector fabricated on the recess-etched surface was 0.1 AW at 254 nm with 25 V bias. Both detectors exhibited excellent dark current characteristics with less than 10 fA leakage current. © 2006 American Institute of Physics.Item Open Access Effect of the superconductivity transition on the response of YBCO edge transition bolometers(2003) Bozbey, Ali; Fardmanesh, Mehdi; Askerzade, I. N.; Banzet, M.; Schubert, J.Dependence of the phase and magnitude of the response of Y-Ba-Cu-O edge transition bolometers on the superconducting transition is studied. The responses of both large and small area devices were investigated and several anomalies are observed. The response of small area LaAlO3 devices considerably differed from that expected based on the dR/dT curve. This discrepancy is observed to be strongly dependent on the superconducting transition. Both the phase and magnitude/(dR/dT) of the response of the devices showed abrupt changes for below the Tc-onset when measured versus temperature, while the phase variation also showed strong dependence on the modulation frequency. We present the analysis and propose mechanisms responsible for the modulation frequency dependence of the response characteristics versus temperature, within the superconductivity transition region of the devices.Item Open Access The effects of surface treatment on optical and vibrational properties of stain-etched silicon(Pergamon Press, 1995) Kalem, Ş.; Göbelek, D.; Kurtar, R.; Mısırlı, Z.; Aydınlı, A.; Ellialtioǧlu, R.The effects of surface treatment on optical and vibrational properties of porous silicon. (por-Si) layers grown on p-type Si wafers by electroless etching technique were studied by FTIR spectroscopy and photoluminescence (PL). The results indicate a correlatiora between the PL intensity and the strength of the absorption bands induced by mulltihydride complexes (SiHn, n ≥ 2). However, similar correlation was also established for monohydride species as evidenced from the layers containing no multihydrides. Furthermore, a new band is observed at 710 cm-1 and assigned to multihydrides suggesting a ne it, local bonding environment in these layers. © 1995.Item Open Access High-performance solar-blind AlGaN photodetectors(IEEE, 2004) Özbay, Ekmel; Bıyıklı, Necmi; Kimukin, İbrahim; Tut, Turgut; Kartaloğlu, Tolga; Aytür, OrhanHigh-performance aluminum gallium nitride (AlGaN)-based solar-blind (SB) photodetectors were demonstrated using different device structures. The Al x-Ga1-xN layers structure were grown by metalorganic chemical vapor deposition (MOCVD) on sapphire structures. n+ and p+ ohmic contacts on GaN were formed with non-annealed titanium (Ti)/aluminum (Al) and nickel (Ni)/ gold (Au) alloys. Spectral UV photoresponse measurements confirmed the solar-blind response of the devices.Item Open Access High-speed characterization of solar-blind AlxGa 1-xN p-i-n photodiodes(Institute of Physics, 2004) Bıyıklı, Necmi; Kimukin, I.; Tut, T.; Kartaloglu, T.; Aytur, O.; Özbay, EkmelWe report on the temporal pulse response measurements of solar-blind AlxGa1-xN-based heterojunction p-i-n photodiodes. High-speed characterization of the fabricated photodiodes was carried out at 267 nm. The bandwidth performance was enhanced by an order of magnitude with the removal of the absorbing p+ GaN cap layer. 30 μm diameter devices exhibited pulse responses with ∼70 ps pulse width and a corresponding 3 dB bandwidth of 1.65 GHz.Item Open Access Highly doped silicon micromachined photonic crystals(IEEE, Piscataway, NJ, United States, 2000) Temelkuran, B.; Bayındır, Mehmet; Özbay, Ekmel; Kavanaugh, J. P.; Sigalas, M. M.; Tuttle, G.Summary form only given. Photonic crystals are periodic structures with the property of reflecting the electromagnetic (EM) waves in all directions within a certain frequency range. These structures can be used to control and manipulate the behaviour of EM waves. Although earlier work concentrated on building these crystals with dielectric materials, there are certain advantages of introducing metals to photonic crystals. First, metals offer a high rejection rate when compared to the dielectric crystals. Second, for microwave applications, the dimensions of metallic crystals can be kept much smaller than the minimum dimensions needed for a typical dielectric crystal. In the paper, we propose a method for the fabrication of layer-by-layer metallic photonic crystals. A similar method had been used by Ozbay et al. to fabricate dielectric photonic crystals using silicon wafers. We fabricated a new layer-by-layer photonic crystal using highly doped silicon wafers.Item Open Access Investigation of the effect of thermal cycling on the device performance of YBa2Cu3O7-δ DC-SQUIDs(2007) Avci I.; Algul, B.P.; Bozbey, A.; Akram, R.; Tepe, M.; Abukay, D.We investigated the effect of thermal cycling on the operational performance of YBa2Cu3O7-δ (YBCO) direct current superconducting quantum interference devices (DC-SQUIDs) fabricated onto 24°SrTiO3 (STO) bicrystal substrates. The devices under investigation consist of directly coupled DC-SQUID magnetometer configurations. Thin films having 200nm thicknesses were deposited by dc-magnetron sputtering and device patterns were made by a standard lithography process and chemical etching. The SQUIDs having 4νm-wide grain boundary Josephson junctions (GBJJs) were characterized by means of critical currents, peak-to-peak output voltages and noise levels, depending on the thermal cycles. In order to achieve a protective layer for the junctions against the undesired effects of thermal cycles and ambient atmosphere during the room temperature storage, the devices were coated with a 400nm thick YBCO layer at room temperature. Since the second layer of amorphous YBCO is completely electrically insulating, it does not affect the operation of the junctions and pick-up coils of magnetometers. This two-layered configuration ensures the protection of the junctions from ambient atmosphere as well as from the effect of water molecules interacting with the film structure during each thermal cycle. © IOP Publishing Ltd.Item Open Access Junction characteristics and magnetic field dependencies of low noise step edge junction Rf-SQUIDs for unshielded applications(IEEE, 2003-06) Fardmanesh, Mehdi; Schubert, J.; Akram, Rizwan; Bozbey, Ali; Bick, M.; Banzet, M.; Lomparski, D.; Zander, W.; Zhang, Y.; Krause, H-J.Step edge grain boundary (GB) junctions and rf-SQUIDs have been made using pulsed laser deposited Y-Ba-Cu-O films on crystalline LaAlO3 substrates. The steps were developed using various ion-beam etching processes resulting in sharp and ramp type step structures. Sharp step based GB junctions showed behavior of serial junctions with resistively shunted junction (RSJ)-like I-V characteristics. The ramped type step structures resulted in relatively high critical current, Ic, junctions and noisy SQUIDs. The sharp steps resulted in low noise rf-SQUIDs with a noise level below 140 fT/Hz12/ down to few Hz at 77 K while measured with conventional tank circuits. The Ic of the junctions and hence the operating temperature range of the SQUIDs made using sharp steps was controlled by both the step height and the junction widths. The junction properties of the SQUIDs were also characterized showing RSJ-like characteristics and magnetic field sensitivities correlated to that of the SQUIDs. Two major low and high background magnetic field sensitivities have been observed for our step edge junctions and the SQUIDs made on sharp steps. High quality step edge junctions with low magnetic field sensitivities made on clean sharp steps resulted in low 1/f noise rf-SQUIDs proper for applications in unshielded environment.Item Open Access Laser photochemical nanostructuring of silicon for surface enhanced raman spectroscopy(Wiley-VCH Verlag GmbH & Co. KGaA, 2022-07-18) Akbıyık, A.; Avishan, N.; Demirtaş, Ö.; Demir, Ahmet Kemal; Yüce, E.; Bek, A.In this work, a novel method of fabricating large-area, low-cost surface-enhanced Raman spectroscopy (SERS) substrates is explained which yields nanostructured surface utilizing laser-induced chemical etching of crystalline silicon (Si) in an hydrofluoric acid solution. Nanostructuring of Si surface is followed by deposition of a thin noble metal layer to complete the fabrication procedure. A 50 nm thick silver (Ag) layer is shown to maximize the SERS performance. The SERS effect is attributed to the electromagnetic field enhancement originating from the nanoscale surface roughness of Si that can be controlled by the illumination power, etch duration, and the spot size of the laser beam. The SERS substrates are found to be capable of detecting a Raman analyte dye molecule down to 10−11 m. SERS performance of the Ag deposited substrates are compared to gold (Au) deposited substrates at 660 and 532 nm excitation. Nanostructured Si surface with Ag exhibits stronger SERS than with Au under 532 nm excitation exhibiting an enhancement factor as high as 109. Raman enhancement factor is calculated both by SERS spectra experimentally, and using finite-elements simulation of the electric field enhancement. The applicability of the fabricated substrates is examined by adsorbing different analytes.Item Open Access Microfabricated ultrasonic transducers: towards robust models and immersion devices(IEEE, 1996-11) Ladabaum, I.; Jin, X.; Soh, H. T.; Pierre, F.; Atalar, Abdullah; Khuri-Yakub, B. T.The successful fabrication of ultrasonic immersion transducers is reported. Transducers are observed to operate from 1 MHz to 20 MHz in water, with the frequency range limited by electronics, not the transducers. Transmission results are included which show that a single pair of transducers is able to operate in water at 4, 6, and 8 MHz with a signal to noise ratio of at least 48 dB. The same transducer pair is shown to operate in air at 6 MHz. A model is introduced which highlights the significant parameters of transducer design. The model enables the design of optimized transducers.Item Open Access Multilayer mXene heterostructures and nanohybrids for multifunctional applications: a review(American Chemical Society, 2022-05-17) Tasnim Mahmud, S.; Bain, S; Hasan, Md Mehdi; Rahman, S.T.; Rhaman, M.; Hossain, M.M.; Ordu, MustafaMXenes (transition metal carbides and nitrides) have experienced exponential growth over the last two decades, thanks to their excellent physical, chemical, and mechanical properties. Intriguing properties like high conductivity, wear, and corrosion resistance while maintaining flexibility are the strong motivation behind the exploration of MXenes. Moreover, the large surface area and unique layered structure enhance the functionality of multilayer-MXene heterostructures and hybrids. This paper reviews the synthesis chemistry, structure properties of multilayer MXenes, and their multifunctional applications. MXene synthesis under different conditions, their hybrids and composites, intercalation, and structural geometries are discussed. The electrical, mechanical, optical, and magnetic properties of MXenes are briefly presented. Recent progress and development in MXene-based heterostructures and nanohybrids for supercapacitors, batteries, environmental and water treatment, antibacterial and tissue engineering, and electromagnetic absorption and shielding are systematically discussed. Finally, research challenges and a perspective in this specified area are addressed for potential developments.Item Open Access Physics and applications of photonic crystals(Nanotechnology Research Center NANOTAM, 2004) Özbay, Ekmel; Bulu I.; Aydin, K.; Caglayan H.; Guven, K.In this article, we investigate how the photonic band gaps and the variety of band dispersions of photonic crystals can be utilized for various applications and how they further give rise to completely novel optical phenomena. The enhancement of spontaneous emission through coupled cavity waveguides in a one-dimensional silicon nitride photonic microcrystal is investigated. We then present the highly directive radiation from sources embedded in two-dimensional photonic crystals. The manifestation of novel and intriguing optical properties of photonic crystals are exemplified experimentally by the negative refraction and the focusing of electromagnetic waves through a photonic crystal slab with subwavelength resolution. © 2004 Elsevier B.V. All rights reserved.Item Open Access A simple approach for the fabrication of 3D microelectrodes for impedimetric sensing(Institute of Physics Publishing, 2015) Guler, M. T.; Bilican, I.; Agan, S.; Elbuken, C.In this paper, we present a very simple method to fabricate three-dimensional (3D) microelectrodes integrated with microfluidic devices. We form the electrodes by etching a microwire placed across a microchannel. For precise control of the electrode spacing, we employ a hydrodynamic focusing microfluidic device and control the width of the etching solution stream. The focused widths of the etchant solution and the etching time determine the gap formed between the electrodes. Using the same microfluidic device, we can fabricate integrated 3D electrodes with different electrode gaps. We have demonstrated the functionality of these electrodes using an impedimetric particle counting setup. Using 3D microelectrodes with a diameter of 25 μm, we have detected 6 μm-diameter polystyrene beads in a buffer solution as well as erythrocytes in a PBS solution. We study the effect of electrode spacing on the signal-to-noise ratio of the impedance signal and we demonstrate that the smaller the electrode spacing the higher the signal obtained from a single microparticle. The sample stream is introduced to the system using the same hydrodynamic focusing device, which ensures the alignment of the sample in between the electrodes. Utilising a 3D hydrodynamic focusing approach, we force all the particles to go through the sensing region of the electrodes. This fabrication scheme not only provides a very low-cost and easy method for rapid prototyping, but which can also be used for applications requiring 3D electric field focused through a narrow section of the microchannel.Item Open Access Slicing crystalline silicon wafer by deep subsurface laser processing and selective chemical etching(Institute of Electrical and Electronics Engineers Inc., 2019) Borra, M. Z.; Nasser, H.; Çiftpınar, E. H.; Turnalı, Ahmet; Deminskyi, Petro; Çolakoğlu, T.; Tokel, Onur; İlday, Fatih Ömer; Pavlov, I.; Turan, R.; Bek, A.In this work, we demonstrate use of laser-induced silicon slicing (LASIS) technique to fabricate crystalline silicon (c-Si) slices [1]. In LASIS method, a nanosecond-pulsed fiber laser operating at 1.55 μm wavelength, focused deep in Si subsurface induces structural modifications near the focal point due to multiphoton absorption. The raster scan of the focal position inside of the sample, positioned in cross-sectional plane with respect to laser beam, produces a quasi-2D modified Si region. The modified Si region is then etched by cupper nitrite (Cu(NO 3 ) 2 )-based selective chemical etchant which selectively targets the laser-modified regions. In order to achieve high etch rate, smooth and defect-free surface; different concentrations of etchant components and etch durations were investigated.Item Open Access Terahertz Bandpass Frequency Selective Surfaces on Glass Substrates Using a Wet Micromachining Process(Springer New York LLC, 2017) Ramzan, Mehrab; Khan, Talha Masood; Bolat, Sami; Nebioglu, Mehmet Ali; Altan, Hakan; Okyay, Ali Kemal; Topallı, KağanThis paper presents terahertz (THz) frequency selective surfaces (FSS) implemented on glass substrate using standard microfabrication techniques. These FSS structures are designed for frequencies around 0.8 THz. A fabrication process is proposed where a 100-μm-thick glass substrate is formed through the HF etching of a standard 500-μm-thick low cost glass wafer. Using this fabrication process, three separate robust designs consisting of single-layer FSS are investigated using high-frequency structural simulator (HFSS). Based on the simulation results, the first design consists of a circular ring slot in a square metallic structure on top of a 100-μm-thick Pyrex glass substrate with 70% transmission bandwidth of approximately 0.07 THz, which remains nearly constant till 30° angle of incidence. The second design consists of a tripole structure on top of a 100-μm-thick Pyrex glass substrate with 65% transmission bandwidth of 0.035 THz, which remains nearly constant till 30° angle of incidence. The third structure consists of a triangular ring slot in a square metal on top of a 100-μm-thick Pyrex glass substrate with 70% transmission bandwidth of 0.051 THz, which remains nearly constant up to 20° angle of incidence. These designs show that the reflections from samples can be reduced compared to the conventional sample holders used in THz spectroscopy applications, by using single layer FSS structures manufactured through a relatively simple fabrication process. Practically, these structures are achieved on a fabricated 285-μm-thick glass substrate. Taking into account the losses and discrepancies in the substrate thickness, the measured results are in good agreement with the electromagnetic simulations. © 2017, Springer Science+Business Media New York.