Browsing by Subject "Chalcogenides"

Now showing 1 - 14 of 14

Open Access
Anharmonicity in GaTe layered crystals
(Wiley-VCH Verlag GmbH & Co. KGaA, 2002) Aydınlı, Atilla; Gasanly, N. M.; Uka, A.; Efeoglu, H.
The temperature dependencies (10-300 K) of seven Raman-active mode frequencies in layered semiconductor gallium telluride have been measured in the frequency range from 25 to 300 cm -1. Softening and broadening of the optical phonon lines are observed with increasing temperature. Comparison between the experimental data and theories of the shift of the phonon lines during heating of the crystal showed that the experimental dependencies can be explained by contributions from thermal expansion and lattice anharmonicity. Lattice anharmonicity is determined to be due to three-phonon processes.
Open Access
Chalcogenide microresonators tailored to distinct morphologies by the shaping of glasses on silica tapers
(OSA - The Optical Society, 2017) Aktaş, O.
Production of chalcogenide (As2Se3) microresonators in sphere, loop, and bottle morphologies by the shaping of glasses at appropriate temperatures between cleaved silica tapers is reported. The quality factors exceed QS = 6.2×105, QB = 6.7 × 105, and QL = 1.6 × 104 for the sphere, bottle, and loop microresonators, respectively. All-optical thermally assisted tuning with a rate of 0.61 nm/mW is demonstrated for a bottle microcavity pumped via a silica taper at a wavelength of 670 nm. This technique enables practical and robust in situ production of chalcogenide microresonators thermally spliced to silica fibers in several morphologies with a wide tuning range of size.
Open Access
Defect luminescence in some layered binary chalcogenide semiconductors
(Scientific.Net, 2002) Aydınlı, Atilla; Gasanly, N. M.
A number of semiconductors such as GaS, GaSe, GaSSe show layered structure where intralayer bonding is strong and interlayer bonding quite weak. With bandgaps mostly in the visible and the near infrared and high crystal structure anisotropy, such semiconductors offer interesting possibilities for optoelectronic applications In this review, we will summarize the recent developments on the photoluminescent properties of these materials such as luminescence due to donor-acceptor pair recombination. As these materials are undoped, the observed photoluminescence is attributed mostly to defect states present in these materials.
Open Access
Exploration of hybrid cladding elements in chalcogenide hollow-core fibers for low-loss mid-infrared transmission
(Elsevier GmbH, 2021-10-27) Khan, Asfandyar; Ordu, Mustafa
Optical losses of chalcogenide negative curvature hollow-core fibers with hybrid cladding elements were numerically investigated in this study. Microstructured cladding formed by the combination of tubular and elliptical elements was designed for low-loss operation in the mid-infrared spectrum. A confinement loss value of 0.287 dB/km was calculated for the proposed ellipse-nested tubular negative curvature fiber with optimized design parameters at 10.6 µm. Achieved confinement losses with the proposed design are several orders of magnitude lower than the tubular/elliptical negative curvature fibers in the targeted spectrum. The effect of the material absorption to the total fiber losses was also investigated along with the confinement losses. Suppression on the higher-order modes by the proposed fiber was numerically observed. The negative curvature fibers are promising for the low-loss guidance of CO2 lasers that are widely used for various applications spanning from material processing to surgery.
Open Access
First Principles Study of Barium Chalcogenides
(2008) Gökoǧlu, G.
In this study, ab initio calculation results of the vibrational properties and elastic parameters as well as characteristic Debye temperature and Poisson's ratios of two barium chalcogenides, BaSe and BaS, which crystallize in NaCl-type structure, were presented. Calculations were based on plane wave basis sets together with ultrasoft pseudopotentials in the framework of density functional theory (DFT) with generalized gradient approximation. Phonon dispersion spectra were obtained using the first principles linear response approach of the density functional perturbation theory (DFPT). The detailed total energy calculations were performed in order to obtain elastic constants using distortions on cubic phase. The calculated structural, elastic, and thermal parameters of BaSe and BaS systems agree well with the available experimental data and theoretical calculations.
Open Access
Hollow core photonic bandgap fibers for medical applications
(2009) Vural, Mert
The design, fabrication and characterization of photonic band gap (PBG) based optical polymer fibers is discussed. Unlike conventional total internal reflection (TIR) fibers, used primarily in telecommunications, PBG fibers can be made hollow core and can be used to guide infrared radiation of any wavelength, a property known as wavelength scalability. Since the electromagnetic radiation is transmitted in the hollow core of the fiber, the intrinsic absorption of the fiber core as well as the insertion Fresnel losses at front and end faces are avoided, giving rise to extraordinarily high power densities to be delivered. The fiber production line includes material characterization, and the design of nanoscale quarter wavestacks using common thermoplastic polymers (poly ether sulphone and poly ether imide) and chalcogenide glasses (As2S3, As2Se3, Ge15As25Se15Te45). The fiber preform is fabricated using rolling mechanism of thermally evaporated chalcogenide glasses on large area polymers. Subsequently, the fiber preforms are thermally drawn to obtain nano-structured PBG fibers.Two different fibers are designed and produced, signifying wavelength scalability of the overall process, for the widely used holmium (Ho:YAG) and carbon dioxide (CO2) medical lasers. The transmission characteristics of the fibers proved that they can be used to safely deliver 15Wlaser power, along a 3 meter fiber with external diameter of 1.5 mm and hollow core diameter of 0.5 mm, corresponding to a laser power density of 1kW/cm2 with a loss of -10dB/m. The PBG fibers are expected to be widely used in high precision surgical laser for incision, photoablation and coagulation where infrared radiation is the radiation of choice for its superior laser-tissue interaction properties.
Open Access
Homogeneity range of ternary 11-type chalcogenides Fe1 + yTe1−xSex
(Springer, 2017) Koz, C.; Rößler, S.; Wirth, S.; Schwarz, U.
The 11-type Fe-chalcogenides belong to the family of Fe-based superconductors. In these compounds, the interstitial Fe is known to strongly influence the magnetic and superconducting properties. Here, we present the chemical homogeneity range of ternary compounds Fe1 + yTe1−xSex based on powder x-ray diffraction, energy dispersive x-ray analysis, and magnetization measurements. Our investigations show that the maximum amount of excess Fe in homogeneous Fe1 + yTe1−xSex decreases with increase in Se substitution for Te. Using our synthesis procedure, single-phase Fe1 + yTe1−xSex, with 0.5 ≤ x < 1 could not be formed for any amount of excess Fe. Further, the superconducting volume fraction in the material is found to be strongly suppressed by excess Fe.
Open Access
Liquid-phase synthesis of nanoparticles and nanostructured materials
(Elsevier, 2018) Karatutlu, A.; Barhoum, A.; Sapelkin, A.
Nanoparticles less than 100nm in size have attracted significant interest over the past 20 years due to their unique properties led by quantum size effect. This chapter evaluates the synthesis methods in liquid phase conducted under operation in high/room temperature and at vacuum/atmospheric environment for nanoparticles and nanostructured materials. We draw attention to the fact that various synthesis methods for formation of colloidally stable matrix-free nanoparticles are available. These methods including chemical stain etching, electrodeposition methods, direct-precipitation methods, sol-gel methods, colloidal synthesis methods, hot-injection synthesis methods, hydrothermal and solvothermal methods, microwave-assisted synthesis methods, ultrasonic synthesis methods, and laser ablation in liquid-phase.
Open Access
Low-temperature photoluminescence study of GaS0.5Se0.5 layered crystals
(Elsevier Science, 2001) Aydnl, A.; Gasanly, N. M.; Gökşen, K.
Photoluminescence (PL) spectra of GaS0.5Se0.5 layered single crystals have been studied in the wavelength range of 565-860 nm and in the temperature range of 15-170 K. Two PL bands centered at 585 nm (2.120 eV) and 640 nm (1.938 eV) were observed at T = 15 K. Variations of both bands were studied as a function of excitation laser intensity in the range from 10-3 to 15.9 W cm-2. These bands are attributed to recombination of charge carriers through donor-acceptor pairs located in the band gap. Radiative transitions from shallow donor levels located at 0.029 and 0.040 eV below the bottom of the conduction band to deep acceptor levels located 0.185 and 0.356 eV above the top of the valence band are suggested to be responsible for the observed A- and B-bands in the PL spectra, respectively. A simple energy level diagram explaining the recombination process is proposed.
Open Access
Mid-infrared negative curvature hollow-core fiber with elliptically nested tubular structure
(Elsevier B.V., 2022-12-24) Khan, Asfandyar; Ordu, Mustafa
Arsenic triselenide chalcogenide negative curvature hollow-core fiber with ellipse-nested tubular cladding elements was numerically presented for the low-loss light guidance in the mid-infrared region. Confinement and total losses were calculated for the fiber with a five-tube design as low as 0.34 dB/km and 4.55 dB/km at 10.6μm, respectively. The single-mode light guidance characteristic of the proposed design was investigated, and a strong suppression on the higher-order modes shows that the fiber design favors the light guidance with the fundamental mode. A dispersion control study was carried out to optimize the primary design parameters to shift the zero-dispersion wavelength close to 10.6μm. The bending loss performance of the proposed design was analyzed in the targeted spectrum. The proposed negative curvature hollow-core fiber could be potentially used in low-loss guidance for high-power lasers and could also be utilized for several other applications, such as surgery and drug delivery in the mid-IR spectrum. © 2022 Elsevier B.V.
Open Access
A motion-and sound-activated, 3D-printed chalcogenide-based triboelectric nanogenerator
(Wiley-VCH Verlag, 2015) Kanik, M.; Say, M. G.; Daglar, B.; Yavuz, A. F.; Dolas, M. H.; El-Ashry, M. M.; Bayındır, Mehmet
A multilayered triboelectric nanogenerator (MULTENG) that can be actuated by acoustic waves, vibration of a moving car, and tapping motion is built using a 3D-printing technique. The MULTENG can generate an open-circuit voltage of up to 396 V and a short-circuit current of up to 1.62 mA, and can power 38 LEDs. The layers of the triboelectric generator are made of polyetherimide nanopillars and chalcogenide core-shell nanofibers.
Open Access
Tapered nanoscale chalcogenide fibers directly drawn from bulk glasses as optical couplers for high-index resonators
(OSA - The Optical Society, 2017) Aktaş, O.; Bayındır, Mehmet
We report production of air-clad tapered chalcogenide fibers by directly drawing bulk glasses between cleaved tips of tapered silica fibers. Exploiting these tapered fibers with nanoscale waists as evanescent optical couplers, we demonstrate phase-matched coupling of light into on-chip whispering gallery mode chalcogenide microresonators with coupling efficiencies as high as 95%. To the best of our knowledge, this is the first-time demonstration of critical coupling into high-index microresonators by using high-index tapered fibers. The tapered chalcogenide fibers can also be utilized as optical couplers for microresonators made of various high-index materials, as well as for nonlinear optical applications.
Open Access
Thermally stimulated currents in n-InS single crystals
(Elsevier Science, 2003) Gasanly, N. M.; Aydınlı, Atilla; Yuksek, N. S.
Thermally stimulated current measurements are carried out on as-grown n-InS single crystals in the temperature range of 10-125 K. Experimental evidence is found for four trapping centers present in InS. They are located at 20, 35, 60 and 130meV. The trap parameters have been determined by various methods of analysis, and they agree well with each other.
Open Access
Tunable ring-coupled Mach-Zehnder interferometer based on lithium niobate
(Taylor and Francis, 2014) Solmaz, M. E.
The fabrication and characterization are reported of a Fano resonance-based electro-optically tunable ring resonator-coupled Mach-Zehnder interferometer device based on a chalcogenide-lithium niobate hybrid waveguide system. The experiments reveal inherent asymmetric lineshapes that can be flipped to a near symmetrical resonance by applying a dc voltage of ~10 V across the electrode at the MZI non-resonator arm. Further increase in voltage yields the reverse of initial asymmetry. The optical filter-based transfer-matrix model easily explains the experimental data and indicates ways to further enhance the usability of such architecture. © 2014 Taylor and Francis.