Browsing by Subject "Surface treatment"

Now showing 1 - 13 of 13

Open Access
Ab initio temperature dependent studies of the homoepitaxial growth on Si(0 0 1) surface
(2001) Dağ, S.; Çıracı, Salim; Kılıç, Ç.; Fong, C. Y.
We performed ab initio zero temperature and finite temperature molecular dynamics calculations to investigate the homoepitaxial growth on the Si(0 0 1) surface. How do the deposited atoms (adatoms) form addimers and how do the addimers reach their favorable positions at the nucleation site of the growth process are presented. Once two epitaxial addimers, one over the dimer row and oriented perpendicular to the surface dimer bonds and the other over the adjacent trough, are aligned at high temperature, the nucleation site of the growth process is formed. The concerted bond exchange between these addimers and the reconstructed surface dimers is found to be the atomistic mechanism that leads to the homoepitaxial growth. © 2001 Elsevier Science B.V.
Open Access
Bio-inspired hierarchically structured polymer fibers for anisotropic non-wetting surfaces
(Royal Society of Chemistry, 2017) Yunusa, M.; Ozturk, F. E.; Yildirim, A.; Tuvshindorj, U.; Kanik, M.; Bayındır, Mehmet
We demonstrate a rice leaf-like hierarchically textured polymer fiber array for anisotropic non-wetting surfaces. To provide superhydrophobicity in addition to the anisotropic behavior, fiber surfaces are spray coated with organically modified silica nanoparticles. The resulting micro/nano hierarchically structured fiber surfaces demonstrate anisotropic non-wetting properties. We designed various fiber architectures for droplet transportation, mixing, and guiding exploiting the scalability of the fiber texture during thermal drawing; optional nanoparticle surface modification; and inherent flexibility of the fibers.
Open Access
Bioactive peptide functionalized aligned cyclodextrin nanofibers for neurite outgrowth
(Royal Society of Chemistry, 2017) Hamsici, S.; Cinar, G.; Celebioglu A.; Uyar, Tamer; Tekinay, A. B.; Güler, Mustafa O.
Guidance of neurite extension and establishment of neural connectivity hold great importance for neural tissue regeneration and neural conduit implants. Although bioactive-epitope functionalized synthetic or natural polymeric materials have been proposed for the induction of neural regeneration, chemical modifications of these materials for neural differentiation still remain a challenge due to the harsh conditions of chemical reactions, along with non-homogeneous surface modifications. In this study, a facile noncovalent functionalization method is proposed by exploiting host-guest interactions between an adamantane-conjugated laminin derived bioactive IKVAV epitope and electrospun cyclodextrin nanofibers (CDNFs) to fabricate implantable scaffolds for peripheral nerve regeneration. While electrospun CDNFs introduce a three-dimensional biocompatible microenvironment to promote cellular viability and adhesion, the bioactive epitopes presented on the surface of electrospun CDNFs guide the cellular differentiation of PC-12 cells. In addition to materials synthesis and smart functionalization, physical alignment of the electrospun nanofibers guides the cells for enhanced differentiation. Cells cultured on aligned and IKVAV functionalized electrospun CDNFs had significantly higher expression of neuron-specific βIII-tubulin and synaptophysin. The neurite extension is also higher on the bioactive aligned scaffolds compared to random and non-functionalized electrospun CDNFs. Both chemical and physical cues were utilized for an effective neuronal differentiation process. © The Royal Society of Chemistry.
Open Access
Characterization of thermally poled germanosilicate thin films
(Optical Society of American (OSA), 2004) Ozean, A.; Digonnet, M.J.F.; Kino G.S.; Ay F.; Aydınlı, Atilla
We report measurements of the nonlinearity profile of thermally poled low-loss germanosilicate films deposited on fused-silica substrates by PECVD, of interest as potential electro-optic devices. The profiles of films grown and poled under various conditions all exhibit a sharp peak ∼0.5 μm beneath the anode surface, followed by a weaker pedestal of approximately constant amplitude down to a depth of 13-16 μm, without the sign reversal typical of poled undoped fused silica. These features suggest that during poling, the films significantly slow down the injection of positive ions into the structure. After local optimization, we demonstrate a record peak nonlinear coefficient of ∼1.6 pm/V, approximately twice as strong as the highest reliable value reported in thermally poled fused silica glass, a significant improvement that was qualitatively expected from the presence of Ge. ©2004 Optical Society of America.
Open Access
Economic design of EWMA control charts based on loss function
(Elsevier, 2009) Serel, D. A.
For monitoring the stability of a process, various control charts based on exponentially weighted moving average (EWMA) statistics have been proposed in the literature. We study the economic design of EWMA-based mean and dispersion charts when a linear, quadratic, or exponential loss function is used for computing the costs arising from poor quality. The chart parameters (sample size, sampling interval, control limits and smoothing constant) minimizing the overall cost of the control scheme are determined via computational methods. Using numerical examples, we compare the performances of the EWMA charts with Shewhart over(X, -) and S charts, and investigate the sensitivity of the chart parameters to changes in process parameters and loss functions. Numerical results imply that rather than sample size or control limits, the users need to adjust the sampling interval in response to changes in the cost of poor quality.
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.
Open Access
Low-amplitude, force gradient imaging of Cu(100) surface using tunnel current feedback
(Institute of Physics Publishing, 2004) Özer, H. Ö.; Norris, A.; Oral, A.; Hoffmann, P. M.; Pethica, J. B.
The large corrugation amplitudes in scanning tunnelling microscope (STM) images of metal surfaces have been commonly attributed to the action of forces between the tip and the sample. We have investigated the Cu(100) surface using a high-resolution non-contact atomic force microscope/scanning tunnelling microscope (nc-AFM/STM) in UHV. Force gradient and STM topography images were acquired simultaneously using constant tunnelling current feedback. Force gradient images showed atomic resolution whereas STM scans exhibited almost no contrast, corresponding to a flat tip trajectory during scans. The corrugation height in force gradient images was found to increase as the set tunnelling current was increased. Force gradient and tunnel current were directly measured as a function of separation, to determine the operating conditions during imaging. The STM operation regime is found to lie between the minimum of the stiffness curve and the start of repulsive force.
Open Access
Nonlinear laser lithography for enhanced tribological properties
(IEEE, 2015-05) Gnilitskyi, I.; Pavlov, Ihor; Rotundo, F.; Orazi, L.; Martini, C.; İlday, Fatih Ömer
This paper investigates a new field for application of femtosecond laser-induced periodic surface structures (LIPSS). We designed an innovative solution to reduce coefficient of friction of mechanical parts by using the nonlinear laser lithography technique (NLL). © 2015 OSA.
Open Access
Nonlinear laser lithography to control surface properties of stainless steel
(Elsevier BV, 2015) Orazi, L.; Gnilitskyi, I.; Pavlov, I.; Serro, A. P.; Ilday, S.; Ilday, F. O.
In the present work a novel method to improve the surface properties of stainless steel is presented and discussed. The method, based on the use of a high repetition rate femtosecond Yb fibre laser, permits generation of highly reproducible, robust, uniform and periodic nanoscale structures over a large surface area. The technique is characterized by high productivity, which, in its most simple form, does not require special environmental conditioning. Surface morphology is scrutinized through SEM and AFM analyses and wettability behaviour is investigated by means of the sessile drop method using distilled-deionized water. It is shown that optimization of process parameters promotes anisotropic wetting behaviour of the material surface.
Open Access
Quality control chart design under jidoka
(John Wiley & Sons, Inc., 2009) Berk, E.; Toy, A. Ö.
We consider design of control charts in the presence of machine stoppages that are exogenously imposed (as under jidoka practices). Each stoppage creates an opportunity for inspection/repair at reduced cost. We first model a single machine facing opportunities arriving according to a Poisson process, develop the expressions for its operating characteristics and construct the optimization problem for economic design of a control chart. We, then, consider the multiple machine setting where individual machine stoppages may create inspection/repair opportunities for other machines. We develop exact expressions for the cases when all machines are either opportunity-takers or not. On the basis of an approximation for the all-taker case, we then propose an approximate model for the mixed case. In a numerical study, we examine the opportunity taking behavior of machines in both single and multiple machine settings and the impact of such practices on the design of an X̄ - Q C chart. Our findings indicate that incorporating inspection/repair opportunities into QC chart design may provide considerable cost savings.
Open Access
Rapid fabrication of microfluidic PDMS devices from reusable PDMS molds using laser ablation
(Institute of Physics Publishing, 2016) Isiksacan, Z.; Guler, M. T.; Aydogdu, B.; Bilican, I.; Elbuken, C.
The conventional fabrication methods for microfluidic devices require cleanroom processes that are costly and time-consuming. We present a novel, facile, and low-cost method for rapid fabrication of polydimethylsiloxane (PDMS) molds and devices. The method consists of three main fabrication steps: female mold (FM), male mold (MM), and chip fabrication. We use a CO2 laser cutter to pattern a thin, spin-coated PDMS layer for FM fabrication. We then obtain reusable PDMS MM from the FM using PDMS/PDMS casting. Finally, a second casting step is used to replicate PDMS devices from the MM. Demolding of one PDMS layer from another is carried out without any potentially hazardous chemical surface treatment. We have successfully demonstrated that this novel method allows fabrication of microfluidic molds and devices with precise dimensions (thickness, width, length) using a single material, PDMS, which is very common across microfluidic laboratories. The whole process, from idea to device testing, can be completed in 1.5 h in a standard laboratory.
Open Access
Superhydrophobic, hybrid, electrospun cellulose acetate nanofibrous mats for oil/water separation by tailored surface modification
(American Chemical Society, 2016) Arslan, O.; Aytac Z.; Uyar, Tamer
Electrospun cellulose acetate nanofibers (CA-NF) have been modified with perfluoro alkoxysilanes (FS/CA-NF) for tailoring their chemical and physical features aiming oil-water separation purposes. Strikingly, hybrid FS/CA-NF showed that perfluoro groups are rigidly positioned on the outer surface of the nanofibers providing superhydrophobic characteristic with a water contact angle of ∼155°. Detailed analysis showed that hydrolysis/condensation reactions led to the modification of the acetylated β(1 → 4) linked d-glucose chains of CA transforming it into a superhydrophobic nanofibrous mat. Analytical data have revealed that CA-NF surfaces can be selectively controlled for fabricating the durable, robust and water resistant hybrid electrospun nanofibrous mat. The -OH groups available on the CA structure allowed the basic sol-gel reactions started by the reactive FS hybrid precursor system which can be monitored by spectroscopic analysis. Since alkoxysilane groups on the perfluoro silane compound are capable of reacting for condensation together with the CA, superhydrophobic nanofibrous mat is obtained via electrospinning. This structural modification led to the facile fabrication of the novel oil/water nanofibrous separator which functions effectively demonstrated by hexane/oil and water separation experiments. Perfluoro groups consequently modified the hydrophilic CA nanofibers into superhydrophobic character and therefore FS/CA-NF could be quite practical for future applications like water/oil separators, as well as self-cleaning or water resistant nanofibrous structures.
Open Access
XPS and water contact angle measurements on aged and corona-treated PP
(John Wiley & Sons, Inc., 1999) Süzer, S.; Argun, A.; Vatansever, O.; Aral, O.
Effects of corona treatment and aging on commercially produced corona discharged polypropylene (PP) films were followed via surface sensitive roughness analysis by atomic force microscopy (AFM), water contact angle (WCA), and X-ray photoelectron spectroscopic (XPS) measurements. Roughness analysis by AFM gave similar results for both untreated and corona-treated samples. The measured water contact angle decreased after corona treatment but increased with aging. XPS findings revealed that corona treatment caused an increase in the O-containing species on the surface of the films, but the measured O/C atomic ratio decreased with aging. The angle dependence of the observed XPS O/C atomic ratio further revealed that surface modifications by the corona treatment were buried into the polymer away from the surface as a function of aging. This is attributed to a surface rearrangement of the macromolecules in agreement with the findings of Garbassi et al. on oxygen-plasma-treated polypropylene.