Browsing by Subject "Scanning electron microscopy"

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Open Access
45-GHz bandwidth-efficiency resonant-cavity-enhanced ITO-Schottky photodiodes
(IEEE, 2001) Bıyıklı, Necmi; Kimukin, I.; Aytür, O.; Gökkavas, M.; Ünlü, M. S.; Özbay, Ekmel
High-speed Schottky photodiodes suffer from low efficiency mainly due to the thin absorption layers and the semitransparent Schottky-contact metals. We have designed, fabricated and characterized high-speed and high-efficiency AlGaAs-GaAs-based Schottky photodiodes using transparent indium-tin-oxide Schottky contact material and resonant cavity enhanced detector structure. The measured devices displayed resonance peaks around 820 nm with 75% maximum peak efficiency and an experimental setup limited temporal response of 11 ps pulsewidth. The resulting 45-GHz bandwidth-efficiency product obtained from these devices corresponds to the best performance reported to date for vertically illuminated Schottky photodiodes.
Open Access
Area-selective atomic layer deposition using an inductively coupled plasma polymerized fluorocarbon layer: A case study for metal oxides
(American Chemical Society, 2016) Haider, A.; Deminskyi, P.; Khan, T. M.; Eren, H.; Bıyıklı, Necmi
Area-selective atomic layer deposition (AS-ALD) has attracted immense attention in recent years for self-aligned accurate pattern placement with subnanometer thickness control. Here, we demonstrate a methodology to achieve AS-ALD by using inductively couple plasma (ICP) grown fluorocarbon polymer film as hydrophobic blocking layer for selective deposition. Our approach has been tested for metal-oxide materials including ZnO, Al2O3, and HfO2. Contact angle, X-ray photoelectron spectroscopy (XPS), spectroscopic ellipsometer, and scanning electron microscopy (SEM) measurements were performed to investigate the blocking ability of plasma polymerized fluorocarbon layers against ALD-grown metal-oxide films. A considerable growth inhibition for ZnO has been observed on fluorocarbon coated Si(100) surfaces, while the same polymerized surface caused a relatively slow nucleation for HfO2 films. No growth selectivity was obtained for Al2O3 films, displaying almost the same nucleation behavior on Si and fluorocarbon surfaces. Thin film patterning has been demonstrated using this strategy by growing ZnO on lithographically patterned fluorocarbon/Si samples. High resolution SEM images and XPS line scan confirmed the successful patterning of ZnO up to a film thickness of ∼15 nm. © 2016 American Chemical Society.
Open Access
Bacteria encapsulated electrospun nanofibrous webs for remediation of methylene blue dye in water
(Elsevier, 2017-04) Sarioglu O.F.; Keskin, N. O. S.; Celebioglu A.; Tekinay, T.; Uyar, Tamer
In this study, preparation and application of novel biocomposite materials that were produced by encapsulation of bacterial cells within electrospun nanofibrous webs are described. A commercial strain of Pseudomonas aeruginosa which has methylene blue (MB) dye remediation capability was selected for encapsulation, and polyvinyl alcohol (PVA) and polyethylene oxide (PEO) were selected as the polymer matrices for the electrospinning of bacteria encapsulated nanofibrous webs. Encapsulation of bacterial cells was monitored by scanning electron microscopy (SEM) and fluorescence microscopy, and the viability of encapsulated bacteria was checked by live/dead staining and viable cell counting assay. Both bacteria/PVA and bacteria/PEO webs have shown a great potential for remediation of MB, yet bacteria/PEO web has shown higher removal performances than bacteria/PVA web, which was probably due to the differences in the initial viable bacterial cells for those two samples. The bacteria encapsulated electrospun nanofibrous webs were stored at 4 °C for three months and they were found as potentially storable for keeping encapsulated bacterial cells alive. Overall, the results suggest that electrospun nanofibrous webs are suitable platforms for preservation of living bacterial cells and they can be used directly as a starting inoculum for bioremediation of water systems.
Open Access
Bacteria immobilized electrospun polycaprolactone and polylactic acid fibrous webs for remediation of textile dyes in water
(Elsevier, 2017-10) Sarioglu O.F.; S. Keskin, N. O.; Celebioglu A.; Tekinay, T.; Uyar, Tamer
In this study, preparation and application of novel biocomposite materials for textile dye removal which are produced by immobilization of specific bacteria onto electrospun nanofibrous webs are presented. A textile dye remediating bacterial isolate, Clavibacter michiganensis, was selected for bacterial immobilization, a commercial reactive textile dye, Setazol Blue BRF-X, was selected as the target contaminant, and electrospun polycaprolactone (PCL) and polylactic acid (PLA) nanofibrous polymeric webs were selected for bacterial integration. Bacterial adhesion onto nanofibrous webs was monitored by scanning electron microscopy (SEM) imaging and optical density (OD) measurements were performed for the detached bacteria. After achieving sufficient amounts of immobilized bacteria on electrospun nanofibrous webs, equivalent web samples were utilized for testing the dye removal capabilities. Both bacteria/PCL and bacteria/PLA webs have shown efficient remediation of Setazol Blue BRF-X dye within 48 h at each tested concentration (50, 100 and 200 mg/L), and their removal performances were very similar to the free-bacteria cells. The bacteria immobilized webs were then tested for five times of reuse at an initial dye concentration of 100 mg/L, and found as potentially reusable with higher bacterial immobilization and faster dye removal capacities at the end of the test. Overall, these findings suggest that electrospun nanofibrous webs are available platforms for bacterial integration and the bacteria immobilized webs can be used as starting inocula for use in remediation of textile dyes in wastewater systems.
Open Access
Bacteria-immobilized electrospun fibrous polymeric webs for hexavalent chromium remediation in water
(Springer Berlin Heidelberg, 2016) Sarioglu, O.F.; Celebioglu A.; Tekinay, T.; Uyar, Tamer
The development of hexavalent chromium remediating fibrous biocomposite mats through the immobilization of a hexavalent chromium reducing bacterial strain, Morganella morganiiSTB5, on the surfaces of electrospun polystyrene and polysulfone webs is described. The bacteria-immobilized biocomposite webs have shown removal yields of 93.60 and 93.79 % for 10 mg/L, 99.47 and 90.78 % for 15 mg/L and 70.41 and 68.27 % for 25 mg/L of initial hexavalent chromium within 72 h, respectively, and could be reused for at least five cycles. Storage test results indicate that the biocomposite mats can be stored without losing their bioremoval capacities. Scanning electron microscopy images of the biocomposite webs demonstrate that biofilms of M. morganii STB5 adhere strongly to the fibrous polymeric surfaces and are retained after repeated cycles of use. Overall, the results suggest that reusable bacteria-immobilized fibrous biocomposite webs might be applicable for continuous hexavalent chromium remediation in water systems.
Open Access
Bismuth nano-Hall probes fabricated by focused ion beam milling for direct magnetic imaging by room temperature scanning Hall probe microscopy
(The Institution of Engineering and Technology (IET), 2001) Sandhu, A.; Masuda, H.; Kurosawa, K.; Oral, A.; Bending, S. J.
Bismuth nano-Hall probes fabricated by using focused ion beam (FIB) milling were studied. The nano-Hall probes were used for direct magnetic imaging of domain structures in low coercivity garnets and demagnetized strontium ferrite permanent magnets. The analysis was performed using room temperature scanning Hall probe microscopy and it was found that the Bi nano-probes could overcome limitations due to surface depletion and large series resistances.
Open Access
Changes in the resistance to corrosion of thermally passivated titanium aluminide during exposure to sodium chloride solution
(Kluwer Academic Publishers, 2015) Saebnoori, E.; Shahrabi, T.; Jafarian H.; Ghaffari, M.
In this study the surface of Ti-47Al-2Cr (at. %) was modified by heating and exposure to nitrogen gas flow to form a predominantly oxide layer on the surface. Samples were then immersed in Ringer's solution and 3.5 wt. % sodium chloride solution and electrochemical impedance spectroscopy tests were performed at regular intervals. The results showed that the layer is highly resistant to corrosion. The equivalent circuit proposed for the impedance curves includes a Warburg element, because diffusion is controlling charge transfer through the passive surface layer. The resistance of the layer was not significantly reduced even after 300 h exposure to solutions and scanning electron micrographs showed the surface was not damaged. © 2013 Springer Science+Business Media Dordrecht.
Open Access
CO2 laser polishing of microfluidic channels fabricated by femtosecond laser assisted carving
(Institute of Physics Publishing, 2016-10) Serhatlioglu, M.; Ortaç, B.; Elbuken, C.; Bıyıklı, Necmi; Solmaz, M. E.
In this study, we investigate the effects of CO2 laser polishing on microscopic structures fabricated by femtosecond laser assisted carving (FLAC). FLAC is the peripheral laser irradiation of 2.5D structures suitable for low repetition rate lasers and is first used to define the microwell structures in fused silica followed by chemical etching. Subsequently, the bottom surface of patterned microwells is irradiated with a pulsed CO2 laser. The surfaces were characterized using an atomic force microscope (AFM) and scanning electron microscope (SEM) in terms of roughness and high quality optical imaging before and after the CO2 laser treatment. The AFM measurements show that the surface roughness improves more than threefold after CO2 laser polishing, which promises good channel quality for applications that require optical imaging. In order to demonstrate the ability of this method to produce low surface roughness systems, we have fabricated a microfluidic channel. The channel is filled with polystyrene bead-laden fluid and imaged with transmission mode microscopy. The high quality optical images prove CO2 laser processing as a practical method to reduce the surface roughness of microfluidic channels fabricated by femtosecond laser irradiation. We further compared the traditional and laser-based glass micromachining approaches, which includes FLAC followed by the CO2 polishing technique.
Open Access
A complementary electrochromic device with highly improved performance based on brick-like hydrated tungsten trioxide film
(American Scientific Publishers, 2012) Jiao, Z.; Wang, J.; Ke, L.; Sun, X. W.; Demir, Hilmi Volkan
Uniform and well adhesive nanostructured hydrated tungsten trioxide (3WO 3•H 2O) films were grown on fluorine doped tin oxide (FTO) substrate via a facile and template-free crystal-seed-assisted hydrothermal method by addition of ammonium sulfate ((NH 4) 2SO 4) and hydrogen peroxide (H 2O 2). X-ray diffraction (XRD) studies indicated that the films are of orthorhombic structure. Scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM) analysis showed that the film was composed of brick-like nanostructures with a preferred growing direction along (002). The influence of seed layer, (NH 4) 2SO 4 and H 2O 2 on the products were also studied. The film showed good cyclic stability, comparable switching speed and coloration efficiency (30.1 cm 2 C -1). A complementary electrochromic device based on the film and Prussian blue depicted highly improved color contrast, coloration/bleaching response (1.8 and 3.7 s respectively) and coloration efficiency (164.6 cm 2 C -1).
Open Access
Compositional homogeneity in a medical-grade stainless steel sintered with a Mn-Si additive
(Elsevier, 2012-06-09) Salahinejad, E.; Hadianfard, M.J.; Ghaffari, M.; Mashhadi, S.B.; Okyay, Ali Kemal
In this paper, chemical composition uniformity in amorphous/ nanocrystallization medical-grade stainless steel (ASTM ID: F2581) sintered with a Mn-Si additive was studied via scanning electron microscopy, energy dispersive X-ray spectroscopy, and transmission electron microscopy. The results show that as a result of sintering at 1000 °C, no dissociation of Mn-Si additive particles embedded in the stainless steel matrix occurs. In contrast, sintering at 1050 °C develops a relatively homogeneous microstructure from the chemical composition viewpoint. The aforementioned phenomena are explained by liquation of the Mn-Si eutectic additive, thereby wetting of the main powder particles, penetrating into the particle contacts and pore zones via capillary forces, and providing a path of high diffusivity.
Open Access
Conducting polymer composites of polypyrrole and a poly(arylene ether ketone)
(1998) Selampinar F.; Akbulut, U.; Toppare L.
Electrically conducting composites of polypyrrole and a poly(arylene ether ketone) were synthesized by electroinitiated polymerization of pyrrole on a poly(arylene ether ketone)-coated platinum electrode. The electrolysis medium was water and p-toluene sulfonic acid. The conductivities of the composites were in the range 1-10 S/cm. The composites were characterized by scanning electron microscopy, Fourier transform infrared, and thermal analyses. The composites were found to be composed of bilayers which can be peeled into two free-standing polymer films. The solution side of the polypyrrole layer of the alloy film contains globular structures, whereas the other side is smoother.
Open Access
Conducting polymer composites of polypyrrole and polyindene
(Elsevier, 1996) Bozkurt, A.; Akbulut, U.; Toppare, L.
Polypyrrole-polyindene composites were prepared via electrochemical methods. Two different approaches were utilized. In the first, the electro-initiated polymerization of indene on a platinum electrode was achieved at 2.0 V versus Ag/Ag+ in acetonitrile. Then the polyindene-coated electrode was used for the electrochemical polymerization of pyrrole at 1.0 V versus Ag/Ag+. In the second case, electrochemical coating of platinum electrode with polypyrrole at 1.0 V versus Ag/Ag+ was carried out and indene was polymerized on the conducting polymer at 2.0 V versus Ag/Ag+ in acetonitrile medium. The characterizations of these composites were done by FT-IR, scanning electron microscopy (SEM) and thermal gravimetric analysis (TGA). Electrical conductivities were evaluated by two-probe and four-probe methods.
Open Access
Conducting polymer composites of polythiophene with natural and synthetic rubbers
(Elsevier, 1996) Yigit, S.; Hacaloglu, J.; Akbulut, U.; Toppare, L.
Electrochemical synthesis of conducting polymer composites of polythiophene was achieved. Synthetic and natural rubbers were used as the insulating polymer matrices. FT-IR, differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and mass spectrometry (MS) were utilized to characterize the composite blends. The conductivity measurements were done by using a standard four-probe technique. The above-mentioned methods show that the resultant composites have different properties compared to polythiophene due to interaction of the rubbers with electrochemical polymerization of thiophene, whereas the same argument is not valid for the polypyrrole synthesis via the same procedure.
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.
Open Access
Dispersion of multi-walled carbon nanotubes in an aqueous medium by water-dispersible conjugated polymer nanoparticles
(2010) Baykal, B.; Ibrahimova, V.; Er, G.; Bengü, E.; Tuncel, D.
Vertically aligned multi-walled carbon nanotubes (MWCNTs) synthesized by the alcohol catalytic CVD (ACCVD) technique are dispersed in water with the aid of water-dispersible conjugated polymer nanoparticles (CPNs). The interactions between CPNs and CNTs are studied with spectroscopy (UV-Vis, fluorescence and Raman) and electron microscopy techniques are used to confirm attachment of CPNs to the CNT sidewalls.
Open Access
Drug delivery system based on cyclodextrin-naproxen inclusion complex incorporated in electrospun polycaprolactone nanofibers
(Elsevier, 2014) Canbolat, M. F.; Celebioglu A.; Uyar, Tamer
In this study, we select naproxen (NAP) as a reference drug and electrospun poly (e-caprolactone) (PCL) nanofibers as a fibrous matrix for our drug-delivery system. NAP was complexed with beta-cyclodextrin (βCD) to form inclusion complex (NAP-βCD-IC) and then NAP-βCD-IC was incorporated into PCL nanofibers via electrospinning. The incorporation of NAP without CD-IC into electrospun PCL was also carried out for a comparative study. Our aim is to analyze the release profiles of NAP from PCL/NAP and PCL/NAP-βCD-IC nanofibers and we investigate the effect of CD-IC on the release behavior of NAP from the nanofibrous PCL matrix. The characterization of NAP-βCD-IC and the presence of CD-IC in PCL/NAP-βCD-IC nanofibers were studied by FTIR, XRD, TGA, NMR and SEM. The SEM imaging of the electrospun PCL/NAP and PCL/NAP-βCD-IC nanofibers reveal that the average fiber diameter of these nanofibers is around 300. nm, in addition, the aggregates of CD-IC in PCL/NAP-βCD-IC nanofibers is observed. The release study of NAP in buffer solution elucidate that the PCL/NAP-βCD-IC nanofibers have higher release amount of NAP than the PCL/NAP nanofibers due to the solubility enhancement of NAP by CD-IC.
Open Access
The effect of gadolinium doping on the structural, magnetic and photoluminescence properties of electrospun bismuth ferrite nanofibers
(Elsevier Ltd, 2015) George Philip G.; Senthamizhan, A.; Srinivasan Natarajan, T.; Chandrasekaran G.; Annal Therese H.
Gadolinium (Gd) doped Bismuth ferrite (BFO) nanofibers (Bi1-xGdxFeO3 (x=0.0, 0.05, 0.10, 0.15 and 0.20)) were synthesized via electrospinning. Scanning Electron Microscope (SEM) analysis showed that the diameter of the nanofibers ranged from 150 to 250 nm. X-Ray Diffraction (XRD) analysis revealed a structural phase transition with varying 'x', the compositions with x≤0.10 have crystal structures with space group R3c, while the compositions with x > 0.10 have crystal structures with space group Pnma. Vibrating Sample Magnetometer (VSM) analysis exhibited the weak ferromagnetic nature of the BFO nanofibers. However an increase in the saturated magnetic moment with increase in Gd dopant concentration was observed. The Photoluminescence (PL) spectra of the Bi:1-x :x nanofibers show enhanced Near Band Emission (NBE) intensity at x=0.10 due to the passivation of oxygen vacancies by Gd doping. © 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Open Access
Effect of milling time on the structure, micro-hardness, and thermal behavior of amorphous/nanocrystalline TiNiCu shape memory alloys developed by mechanical alloying
(Elsevier Ltd, 2014) Alijani F.; Amini, R.; Ghaffari, M.; Alizadeh, M.; Okyay, Ali Kemal
In the present paper, the effect of milling process on the chemical composition, structure, microhardness, and thermal behavior of Ti-41Ni-9Cu compounds developed by mechanical alloying was evaluated. The structural characteristic of the alloyed powders was evaluated by X-ray diffraction (XRD). The chemical composition homogeneity and the powder morphology and size were studied by scanning electron microscopy coupled with electron dispersive X-ray spectroscopy. Moreover, the Vickers micro-indentation hardness of the powders milled for different milling times was determined. Finally, the thermal behavior of the as-milled powders was studied by differential scanning calorimetery. According to the results, at the initial stages of milling (typically 0-12. h), the structure consisted of a Ni solid solution and amorphous phase, and by the milling evolution, nanocrystalline martensite (B19') and austenite (B2) phases were initially formed from the initial materials and then from the amorphous phase. It was found that by the milling development, the composition uniformity is increased, the inter-layer thickness is reduced, and the powders microhardness is initially increased, then reduced, and afterward re-increased. It was also realized that the thermal behavior of the alloyed powders and the structure of heat treated samples is considerably affected by the milling time.
Open Access
Effects of rapid thermal annealing on the structural and local atomic properties of ZnO: Ge nanocomposite thin films
(A I P Publishing LLC, 2015) Ceylan, A.; Rumaiz, A. K.; Caliskan, D.; Ozcan, S.; Özbay, Ekmel; Woicik, J. C.
We have investigated the structural and local atomic properties of Ge nanocrystals (Ge-ncs) embedded ZnO (ZnO: Ge) thin films. The films were deposited by sequential sputtering of ZnO and Ge thin film layers on z-cut quartz substrates followed by an ex-situ rapid thermal annealing (RTA) at 600 °C for 30, 60, and 90 s under forming gas atmosphere. Effects of RTA time on the evolution of Ge-ncs were investigated by x-ray diffraction (XRD), scanning electron microscopy (SEM), hard x-ray photoelectron spectroscopy (HAXPES), and extended x-ray absorption fine structure (EXAFS). XRD patterns have clearly shown that fcc diamond phase Ge-ncs of sizes ranging between 18 and 27 nm are formed upon RTA and no Ge-oxide peak has been detected. However, cross-section SEM images have clearly revealed that after RTA process, Ge layers form varying size nanoclusters composed of Ge-ncs regions. EXAFS performed at the Ge K-edge to probe the local atomic structure of the Ge-ncs has revealed that as prepared ZnO:Ge possesses Ge-oxide but subsequent RTA leads to crystalline Ge structure without the oxide layer. In order to study the occupied electronic structure, HAXPES has been utilized. The peak separation between the Zn 2p and Ge 3d shows no significant change due to RTA. This implies little change in the valence band offset due to RTA. © 2015 AIP Publishing LLC.
Open Access
Electrochemically obtained insulating and conducting polymers and composites of acrylonitrile
(1998) Yilmaz, B.Y.; Akbulut, U.; Toppare L.
Electrochemically obtained polyacrylonitrile and a commercial polyacrylonitrile were heat treated to improve their conductivities. The parameters chosen for heat treatment conditions were the temperature, treatment medium (vacuum or air) and, doping agent. The conductivity of all heat treated polymers was measured. The characterization of the heat treated polymers was made by IR analysis. The composite films of polyacrylonitrile with polypyyrole and polythiophene were electrochemically prepared at different compositions. The change in the conductivity of composites was analyzed as a function of the percent composition of the insulating component. IR, DSC, TGA and SEM analyses were used to characterize the polymer composites.