Browsing by Subject "Coatings"

Now showing 1 - 19 of 19

Open Access
Atomic layer deposition: an enabling technology for the growth of functional nanoscale semiconductors
(Institute of Physics Publishing, 2017) Bıyıklı, Necmi; Haider A.
In this paper, we present the progress in the growth of nanoscale semiconductors grown via atomic layer deposition (ALD). After the adoption by semiconductor chip industry, ALD became a widespread tool to grow functional films and conformal ultra-thin coatings for various applications. Based on self-limiting and ligand-exchange-based surface reactions, ALD enabled the low-temperature growth of nanoscale dielectric, metal, and semiconductor materials. Being able to deposit wafer-scale uniform semiconductor films at relatively low-temperatures, with sub-monolayer thickness control and ultimate conformality, makes ALD attractive for semiconductor device applications. Towards this end, precursors and low-temperature growth recipes are developed to deposit crystalline thin films for compound and elemental semiconductors. Conventional thermal ALD as well as plasma-assisted and radical-enhanced techniques have been exploited to achieve device-compatible film quality. Metal-oxides, III-nitrides, sulfides, and selenides are among the most popular semiconductor material families studied via ALD technology. Besides thin films, ALD can grow nanostructured semiconductors as well using either template-assisted growth methods or bottom-up controlled nucleation mechanisms. Among the demonstrated semiconductor nanostructures are nanoparticles, nano/quantum-dots, nanowires, nanotubes, nanofibers, nanopillars, hollow and core-shell versions of the afore-mentioned nanostructures, and 2D materials including transition metal dichalcogenides and graphene. ALD-grown nanoscale semiconductor materials find applications in a vast amount of applications including functional coatings, catalysis and photocatalysis, renewable energy conversion and storage, chemical sensing, opto-electronics, and flexible electronics. In this review, we give an overview of the current state-of-the-art in ALD-based nanoscale semiconductor research including the already demonstrated and future applications.
Open Access
Electron spectroscopic investigation of Sn coatings on glasses
(Springer, 1996) Süzer, Ş.; Voscoboinikov, T.; Hallam, K. R.; Allen, G. C.
Float glasses of different thicknesses and a conducting tin oxide glass have been investigated using Photo and Auger Electron Spectroscopy induced by AlKα X-rays. On the basis of measured chemical XPS shifts in the binding energies the chemical state of Sn (+2 or +4) incorporated on the float glasses could not be assigned. The use of the Auger parameter allows to separate relaxation and chemical contributions. The derived true chemical shifts of Sn on float-glasses are larger than those of SnO and/or SnO2 due to the larger ionic environment of the glass matrix. Ar+ or HF etching reveals that the concentration of Sn decreases exponentially as a function of depth from the surface. © Springer-Verlag 1996.
Open Access
Electrostatic effects on nanofiber formation of self-assembling peptide amphiphiles
(Elsevier, 2011) Toksoz, S.; Mammadov R.; Tekinay, A. B.; Güler, Mustafa O.
Self-assembling peptide amphiphile molecules have been of interest to various tissue engineering studies. These molecules self-assemble into nanofibers which organize into three-dimensional networks to form hydrocolloid systems mimicking the extracellular matrix. The formation of nanofibers is affected by the electrostatic interactions among the peptides. In this work, we studied the effect of charged groups on the peptides on nanofiber formation. The self-assembly process was studied by pH and zeta potential measurements, FT-IR, circular dichroism, rheology, atomic force microscopy, scanning electron microscopy and transmission electron microscopy. The aggregation of the peptides was triggered upon neutralization of the charged residues by pH change or addition of electrolyte or biomacromolecules. Understanding the controlled formation of the hydrocolloid gels composed of peptide amphiphile nanofibers can lead us to develop in situ gel forming bioactive collagen mimetic nanofibers for various tissue engineering studies including bioactive surface coatings. © 2010 Elsevier Inc.
Open Access
Infrared absorption spectroscopy of monolayers with thin film interference coatings
(Optical Society of America, 2017) Ayas, Sencer; Bakan, Gökhan; Ozgur, E.; Celebi, Kemal; Dana, Aykutlu
We report high performance Infrared spectroscopy platforms based on interference coatings on metal using CaF2 dielectric films and Ge2Sb2Te5 (GST) phase-change films. IR vibrational bands of proteins and organic monolayers are also detected.
Open Access
Investigation of metamaterial coated conducting cylinders for achieving transparency and maximizing radar cross section
(IEEE, 2007) Ircı, Erdinç; Ertürk, Vakur B.
Recently, reducing the radar cross sections (RCS) of various structures to achieve transparency and obtaining resonant structures aimed at increasing the electromagnetic intensities, stored or radiated power levels have been investigated. The transparency and resonance (RCS maximization) conditions investigated in are mainly attributed to pairing of "conjugate" materials: materials which have opposite signs of constitutive parameters [e.g., double-positive (DPS) and double- negative (DNG) or epsilon-negative (ENG) and mu-negative (MNG)]. In the present work, we extend the transparency and resonance conditions for cylindrical structures when the core cylinder is particularly perfect electric conductor (PEC). The appropriate constitutive parameters of such metamaterials are investigated for both TE and TM polarizations. For TE polarization it is found out that, the metamaterial coating permittivity has to be in the 0 < epsivc < epsiv0 interval to achieve transparency, and in the -epsiv0 < epsivc < 0 interval to achieve RCS maximization. As in the case of "conjugate" pairing, transparency and resonance are found to be heavily dependent on the ratio of core-coating radii, instead of the total size of the cylindrical structure. However, unlike the "conjugate" pairing cases, replacing epsiv by mu (and vice versa) does not lead to the same conclusions for TM polarization unless the PEC cylinder is replaced by a perfect magnetic conductor (PMC) cylinder. Yet, RCS maximization can also be achieved in the TM polarization case when coating permeability muc < 0, whereas transparency requires large \muc\ for this polarization. Numerical results, which demonstrate the transparency and RCS maximization phenomena, are given in the form of normalized monostatic and bistatic echo widths.
Open Access
Mechanochemical activation of siliconefor large-scale fabrication of anti-biofouling liquid-like surfaces
(American Chemical Society, 2023-11-13) Celik, N.; Sahin, F.; Ruzi, M.; Ceylan, A.; Butt, H. J.; Önses, Mustafa Serdar
Large-scalepreparationof liquid-likecoatingswithperfecttransparencyvia solventlessand room-temperatureprocessesusinglow-costand biocompatiblematerialsis oftremendousinterestfor a broadrangeof applications.Here,wepresenta mechanochemicalactivationstrategyfor solventlessgraftingof poly(dimethylsiloxane)(PDMS)ontoglass,siliconwafers,and ceramics.Activationis achievedvia ball millingPDMSwithoutusingany solventsor additivespriorto application.Ballmillingresultsin chainscissionand generationof free radicals,allowingroom-temperaturegraftingat durations≤1 h. Thedepositionof ball-milledPDMScan be facilitatedby brushingordrop-casting,enablinglarge-scaleapplications.Theresultingsurfacesfacilitatethe slidingof dropletsat angles<20°for liquidswith surfacetensionrangingfrom 22 to 73 mN/m.An importantapplicationfor publichealthis generatinganti-biofoulingcoatingson sanitaryware.For example,PDMS-graftedsurfacespreparedon a regular-sizetoiletbowlexhibita 105-fold decreasein theattachmentof bacteriafrom urine.Thesefindingshighlightthe significantpotentialof mechanochemicalprocessesfor the practicalpreparationof liquid-likesurfaces.
Open Access
Method for visualizing under-coating corrosion utilizing pH indicators before visible damage
(Elsevier B.V., 2018) Uzundal, C. B.; Ulgut, Burak
A new method for under-coating corrosion visualization is developed. The method detects corrosion through local pH gradients which are visualized by pH indicators. pH gradients are induced in a setup similar to the one popularized by Devanathan. On the uncoated back side of the metal, the sample is cathodically polarized, generating hydrogen gas through electrolysis. The hydrogen generated, diffuses through the metal sample and oxidizes on the anodically polarized painted side wherever the coating develops a defect causing a decrease in the local pH. The local pH is then used in imaging the location of defects through the use of a pH indicator, before any visible corrosion damage occurs on the coated metal sample.
Open Access
Nanocomposite glass coatings containing hexagonal boron nitride nanoparticles
(Pergamon Press, 2016) Çamurlu, H. E.; Akarsu, E.; Arslan, O.; Mathur, S.
Glass coatings composed of SiO2-K2O-Li2O, containing non-modified and fluorosilane modified hexagonal boron nitride (hBN) nanoparticles, were prepared on stainless steel plates through sol-gel spin-coating method. Coatings were examined by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, x-ray diffraction (XRD), atomic force microscopy (AFM) and thermo-gravimetric analysis (TGA). 1.3-2.5 μm thick uniform coatings were obtained after curing at 500 Â°C for 1 h. The coatings adhered well to the steel substrates. It was determined by salt spray tests that the coatings enhance corrosion resistance. The aim of hydrophobic fluorosilane modification of hBN nanoparticles was to enrich hBN quantity on the top surface of the coatings. Coatings containing fluorosilane modified hBN nanoparticles presented slightly lower friction coefficient values than the other coatings.
Open Access
One-Step Fabrication of Biocompatible Multifaceted Nanocomposite Gels and Nanolayers
(American Chemical Society, 2017) Topuz, F.; Bartneck, M.; Pan, Y.; Tacke, F.
Nanocomposite gels are a fascinating class of polymeric materials with an integrative assembly of organic molecules and organic/inorganic nanoparticles, offering a unique hybrid network with synergistic properties. The mechanical properties of such networks are similar to those of natural tissues, which make them ideal biomaterial candidates for tissue engineering applications. Existing nanocomposite gel systems, however, lack many desirable gel properties, and their suitability for surface coatings is often limited. To address this issue, this article aims at generating multifunctional nanocomposite gels that are injectable with an appropriate time window, functional with bicyclononynes (BCN), biocompatible and slowly degradable, and possess high mechanical strength. Further, the in situ network-forming property of the proposed system allows the fabrication of ultrathin nanocomposite coatings in the submicrometer range with tunable wettability and roughness. Multifunctional nanocomposite gels were fabricated under cytocompatible conditions (pH 7.4 and T = 37 °C) using laponite clays, isocyanate (NCO)-terminated sP(EO-stat-PO) macromers, and clickable BCN. Several characterization techniques were employed to elucidate the structure-property relationships of the gels. Even though the NCO-sP(EO-stat-PO) macromers could form a hydrogel network in situ on contact with water, the incorporation of laponite led to significant improvement of the mechanical properties. BCN motifs with carbamate links were used for a metal-free click ligation with azide-functional molecules, and the subsequent gradual release of the tethered molecules through the hydrolysis of carbamate bonds was shown. The biocompatibility of the hydrogels was examined through murine macrophages, showing that the material composition strongly affects cell behavior.
Open Access
Protein-releasing conductive anodized alumina membranes for nerve-interface materials
(Elsevier Ltd, 2016) Altuntas, S.; Buyukserin, F.; Haider, A.; Altinok, B.; Bıyıklı, Necmi; Aslim, B.
Nanoporous anodized alumina membranes (AAMs) have numerous biomedical applications spanning from biosensors to controlled drug delivery and implant coatings. Although the use of AAM as an alternative bone implant surface has been successful, its potential as a neural implant coating remains unclear. Here, we introduce conductive and nerve growth factor-releasing AAM substrates that not only provide the native nanoporous morphology for cell adhesion, but also induce neural differentiation. We recently reported the fabrication of such conductive membranes by coating AAMs with a thin C layer. In this study, we investigated the influence of electrical stimulus, surface topography, and chemistry on cell adhesion, neurite extension, and density by using PC 12 pheochromocytoma cells in a custom-made glass microwell setup. The conductive AAMs showed enhanced neurite extension and generation with the electrical stimulus, but cell adhesion on these substrates was poorer compared to the naked AAMs. The latter nanoporous material presents chemical and topographical features for superior neuronal cell adhesion, but, more importantly, when loaded with nerve growth factor, it can provide neurite extension similar to an electrically stimulated CAAM counterpart.
Open Access
Radar cross-section study of cylindrical cavity-backed apertures with outer or inner material coating: the case of E-polarization
(IEEE, 1993) Çolak, D.; Nosich, A. I.; Altintaş, A.
A dual-series-based solution is obtained for the scattering of an E-polarized plane wave from a cavity-backed aperture which is formed by a slitted infinite circular cylinder coated with absorbing material. The material coating can be done on the inner or outer surface of the cylinder. For both cases, numerical results are presented for the radar cross section and comparisons are given for two different realistic absorbing materials. The radar cross-section results are also given for the aspect angle of the screen. Finally, the dependence of radar cross section on the thickness of the absorbing layer is presented. © 1993 IEEE
Open Access
Radar cross-section study of cylindrical cavity-backed apertures with outer or inner material coating: the case of H-polarization
(Institute of Electrical and Electronics Engineers, 1995-05) Çolak, D.; Nosich, A. I.; Altıntaş, A.
A dual-series-based solution is obtained for the scattering of an H-polarized plane wave from a slitted infinite circular cylinder coated with absorbing material from inside or outside. For both cases, numerical results are presented for the radar cross section and comparisons are given for two different realistic absorbing materials. The radar cross-section dependencies are also given for the aspect angle of the scatterer and the thickness of the absorbing layer.
Open Access
RCS study of cylindrical cavity-backed apertures with outer or inner material coating: the case of e-polarization
(IEEE, 1993) Çolak, Dilek; Altıntaş, Ayhan; Nosich, A. I.
Cavity-backed apertures (CBA) are encountered as parts of any airborne or spaceborne radar targets. Most familiar of them are, probably, air inlets and engine tubes, known to contribute a great deal to radar cross section (RCS) of jet aircraft. In the present study, the dual-series-based solution is obtained for the scattering of an E-polarized plane wave from the cavity-backed aperture which is formed by a slitted infinite circular cylinder coated with absorptive material. The material coating can be done on the inner or outer surface of the cylinder. For both cases, numerical results are presented for the RCS and comparisons of the suppression of RCS are given for two different realistic absorptive materials.
Open Access
Robust superhydrophilic patterning of superhydrophobic ormosil surfaces for high-throughput on-chip screening applications
(Royal Society of Chemistry, 2016) Beyazkilic, P.; Tuvshindorj, U.; Yildirim, A.; Elbuken, C.; Bayındır, Mehmet
This article describes a facile method for the preparation of two-dimensionally patterned superhydrophobic hybrid coatings with controlled wettability. Superhydrophobic coatings were deposited from nanostructured organically modified silica (ormosil) colloids that were synthesized via a simple sol-gel method. On the defined areas of the superhydrophobic ormosil coatings, stable wetted micropatterns were produced using Ultraviolet/Ozone (UV/O) treatment which modifies the surface chemistry from hydrophobic to hydrophilic without changing the surface morphology. The degree of wettability can be precisely controlled depending on the UV/O exposure duration; extremely wetted spots with water contact angle (WCA) of nearly 0° can be obtained. Furthermore, we demonstrated high-throughput biomolecular adsorption and mixing using the superhydrophilic patterns. The proposed superhydrophilic-patterned nanostructured ormosil surfaces with their simple preparation, robust and controlled wettability as well as adaptability on flexible substrates, hold great potential for biomedical and chemical on-chip analysis.
Open Access
Robust superhydrophobic fabrics by infusing structured polydimethylsiloxane films
(John Wiley & Sons, Inc., 2021-06-22) Celik, N.; Torun, I.; Ruzi, M.; Mustafa Serdar, Önses
Superhydrophobic coatings have large application potential in self-cleaning textiles. Low durability, high cost of fabrication, and environmental concerns over the usage of chemicals such as fluorocarbons limit the utilization of superhydrophobic coatings. This study reports a convenient and inexpensive approach to fabricate robust and fluorine-free superhydrophobic fabrics based on the transfer of structured polymer films and hydrophobic nanoparticles. In this approach, polydimethylsiloxane (PDMS) is infused between sheets of fabric and paper, followed by curing and removal of the paper. This process results in a fabric infused with PDMS whose structure is a negative replica of the paper surface. Then, hydrophobic nanoparticles are sprayed onto the structured PDMS side of the fabric. The infusion of PDMS and subsequent deposition of the hydrophobic nanoparticles enables strong bonding, as shown by the excellent solvent stability of the superhydrophobic fabric under ultrasonication. The proposed approach is universal in that it can be applied to almost any textiles, which upon coating, exhibited superhydrophobicity with a water contact angle of 172° and a sliding angle of 3°. Furthermore, the superhydrophobic fabric showed robust durability against water spray impact and mechanical bending where it can keep superhydrophobicity for at least 200 cycles of each test.
Open Access
Self-assembled peptide nanofiber templated ALD growth of TiO2 and ZnO semiconductor nanonetworks
(Wiley - V C H Verlag GmbH & Co. KGaA, 2016) Garifullin, R.; Eren, H.; Ulusoy, T. G.; Okyay, Ali Kemal; Bıyıklı, Necmi; Güler, Mustafa O.
Here peptide amphiphile (PA) nanofiber network is exploited as a three‐dimensional soft template to construct anatase TiO2 and wurtzite ZnO nanonetworks. Atomic layer deposition (ALD) technique is used to coat the organic nanonetwork template with TiO2and ZnO. ALD method enables uniform and conformal coatings with precisely controlled TiO2 and ZnO thickness. The resulting semiconducting metal oxide nanonetworks are utilized as anodic materials in dye‐sensitized solar cells. Effect of metal oxide layer thickness on device performance is studied. The devices based on thin TiO2 coatings (<10 nm) demonstrate considerable dependence on material thickness, whereas thicker (>17 nm) ZnO‐based devices do not show an explicit correlation.
Open Access
Ultrathin phase-change coatings on metals for electrothermally tunable colors
(American Institute of Physics Inc., 2016-08) Bakan, G.; Ayas S.; Saidzoda, T.; Celebi, K.; Dana, A.
Metal surfaces coated with ultrathin lossy dielectrics enable color generation through strong interferences in the visible spectrum. Using a phase-change thin film as the coating layer offers tuning the generated color by crystallization or re-amorphization. Here, we study the optical response of surfaces consisting of thin (5-40 nm) phase-changing Ge2Sb2Te5 (GST) films on metal, primarily Al, layers. A color scale ranging from yellow to red to blue that is obtained using different thicknesses of as-deposited amorphous GST layers turns dim gray upon annealing-induced crystallization of the GST. Moreover, when a relatively thick (>100 nm) and lossless dielectric film is introduced between the GST and Al layers, optical cavity modes are observed, offering a rich color gamut at the expense of the angle independent optical response. Finally, a color pixel structure is proposed for ultrahigh resolution (pixel size: 5 × 5 μm2), non-volatile displays, where the metal layer acting like a mirror is used as a heater element. The electrothermal simulations of such a pixel structure suggest that crystallization and re-amorphization of the GST layer using electrical pulses are possible for electrothermal color tuning.
Open Access
Water-soluble non-polymeric electrospun cyclodextrin nanofiber template for the synthesis of metal oxide tubes by atomic layer deposition
(Royal Society of Chemistry, 2014) Celebioglu A.; Vempati S.; Ozgit Akgun, C.; Bıyıklı, Necmi; Uyar, Tamer
We report on the suitability of water-soluble non-polymeric electrospun cyclodextrin (CD) nanofiber templates by using atomic layer deposition (ALD) to yield metal oxide tubes. To demonstrate this, water-soluble electrospun CD nanofibers were chosen as template to produce metal oxide tubes where we have tested two examples of ALD coatings, namely, Al2O3 and ZnO. After the ALD coating on the CD nanofibers, the CD core is simply dissolved in water to yield metal oxide tubes. Morphological investigations suggested that Al2O3 is smoother in contrast to ZnO which shows a grainy structure. Structural characterization evidenced amorphous Al2O3 and highly crystalline ZnO. Given the applicability of Al2O3 and ZnO in various contexts the ionic states of Al, Zn and O are also investigated. After the washing step to remove the CD core, Al2O3 developed some hydroxylation, while ZnO hosts various oxygen related functional groups.
Open Access
ZnO nanostructures on electrospun nanofibers by atomic layer deposition/hydrothermal growth and their photocatalytic activity
(Materials Research Society, 2014) Kayaci, Fatma; Vempati, Sesha; Ozgit-Akgun, Cagla; Biyikli, Necmi; Uyar, Tamer
A hierarchy of nanostructured-ZnO was fabricated on the electrospun nanofibers by atomic layer deposition (ALD) and hydrothermal growth, subsequently. Firstly, we produced poly(acrylonitrile) (PAN) nanofibers via electrospinning, then ALD process provided a highly uniform and conformai coating of polycrystalline ZnO with a precise control on the thickness (50 nm). In the last step, this ZnO coating depicting dominant oxygen vacancies and significant grain boundaries was used as a seed on which single crystalline ZnO nanoneedles (average diameter and length of ∼25 nm and ∼600 nm, respectively) with high optical quality were hydrothermally grown. The detailed morphological and structural studies were performed on the resulting nanofibers, and the photocatalytic activity (PCA) was tested with reference to the degradation of methylene blue. The results of PCA were discussed in conjunction with photoluminescence response. The nanoneedle structures supported the vectorial transport of photo-charge carriers, which is crucial for high catalytic activity. The enhanced PCA, structural stability and reusability of the PAN/ZnO nanoneedles indicated that this hierarchical structure is a potential candidate for waste water treatment.