Room-temperature interface state analysis of Au/Poly(4-vinyl phenol)/p-Si structure

The Poly(4-vinyl phenol) insulator layer was grown by spin coating technique onto p-Si substrate. Diode ideality factor (n), insulator layer thickness (δ), space charge region width (W_D), interface state density (N_ss), series resistance (R_s), acceptor concentration (N_A) of the Au/Poly(4-vinyl phenol)/p-Si structure have been extracted from the current–voltage (I–V), frequency dependent capacitance–voltage (C–V) and conductance–voltage (G–V) measurements. It is pointed out that the interface states lead to deviation of the ideality factor value from 1 and frequency dispersion of the C–V characteristics. N_ss profiles as a function of (E_ss−E_v) obtained using I–V and low frequency C–V measurements are in good agreement. N_ss values varying between 10¹² and 10¹³ eV⁻¹ cm⁻² mean that Poly(4-vinyl phenol) is a candidate for insulator layer forming on Si as powerful as SiN₄, SnO₂, TiO₂.     

Corneal confocal microscopy and dry eye findings in contact lens discomfort patients

Objectives

To evaluate the corneal confocal microscopy and dry eye findings in patients with contact lens discomfort.

Distribution of cooperative interactions in barnase at different time windows by coarse-grained simulations

The backbone dynamics of barnase has been studied by a recently developed off-lattice Monte Carlo (MC)/Metropolis simulation technique, where a low-resolution model (virtual-bond model) is used together with knowledge-based potentials, with the main emphasis on its cooperative motions at different time windows. The conformations generated around the native state are analysed by time-dependent auto- and cross-conformational correlation functions of the virtual bonds. There exists a correlation between the long time auto-correlated behaviour of the bond rotations and the potential stability of the respective regions. The analysis at different time windows reveals that there are cooperative motions between the bond rotations, which are only near neighbours and basically local motions at all time windows. However, as the time window widens, a progressive increase in the number of correlated pairs, which are separated far along the sequence and are not necessarily close in space, is observed. The structural distribution of these motions shows that the cooperative interactions are not bi-directional and that different residues have a different role within the network of interactions. Thus, the conditions yielding global motion coherence can be accounted for by the existence of anisotropic cooperative long-range interactions among the units in cooperation with the short-range interactions.     

Binding of methyl orange or ethyl orange dyes by some dioxolane copolymers: Synthesis of the copolymers and thermodynamics of the dye–copolymer interactions

The extent of binding of methyl orange or ethyl orange by (2‐phenyl‐1,3‐dioxolane‐4‐yl) methyl methacrylate (PDMMA), 2‐hydroxyethyl methacrylate (HEMA), and vinyl‐pyrrolidone (VPy) copolymers has been investigated by the equilibrium dialysis method. The dialysis experiments have been carried out in a Tris (hydroxy methyl) aminomethane buffer (pH = 7) and at the temperatures of 15, 25, and 35°C. The PDMMA‐co‐HEMA and PDMMA‐co‐VPy copolymers have been prepared in the laboratory by using the related monomers in different ratios. The synthesized products were analyzed by Fourier Transform‐infrared spectroscopy (FTIR), proton nuclear magnetic resonance (¹H NMR) spectroscopy, differential thermal analysis (DTA), and differential scanning calorimetry (DSC) techniques. The binding extent of the dyes by the copolymers was determined by ultraviolet (UV) absorbance measurements. The results indicate that the extent of binding is relatively higher for ethyl orange than that for methyl orange under identical conditions. The binding slightly decrease with increasing temperature, and it is accompanied with favorable free energy, and exothermic enthalpy change within the temperature range studied. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3355–3361, 2004     

pH-induced conformational changes of loosely grafted molecular brushes containing poly(acrylic acid) side chains

A series of water-soluble loosely grafted poly(acrylic acid) (PAA) brushes with four different grafting densities were synthesized by the “grafting from” approach using atom transfer radical polymerization (ATRP). Gel permeation chromatography (GPC) and ¹H NMR spectroscopy were used to provide evidence for formation of the well-defined backbones and the resulting brush copolymers. Atomic force microscopy was used to study the conformation of adsorbed brushes as a function of pH. The adsorbed molecules undergo a globule-to-extended conformational transition as the solution is changed from acidic to basic. This transition was monitored on a mica surface by imaging individual molecules with atomic force microscopy (AFM). The conformational behavior was compared with 100%-grafted PAA brushes. Unlike the loose brushes, the 100%-grafted molecules remained fully extended in a broad range of pH values (pH = 2-9) due to steric repulsion between the densely grafted side chains which is strongly enhanced upon adsorption to a substrate.     

Electrical characterization of a-Si:H(n)/c-Si(p) structure

In this study, n-type hydrogenated amorphous silicon (a-Si:H) was fabricated on p-type crystalline silicon (c-Si) substrates to obtain heterojunction diodes. The amorphous films were obtained by the Plasma Enhanced Chemical Vapor Deposition (PECVD) technique. Temperature dependent current-voltage (I-V-T) measurements and investigation of the dc current injection mechanism of a-Si:H(n)/c-Si(p) device structure have been performed. The series resistance (4.6-8.2 Ω) values displayed nearly temperature independent behavior and the ideality factor varied between 2.7 and 1.6 in the temperature range 100-320 K. The forward bias I-V-T characteristics of c-Si/a-Si:H heterojunctions are found to behave like the Schottky junctions where carrier injection is especially influenced by the carrier generation-recombination in the junction interface formed on the amorphous side. The temperature dependent ideality factor behavior shows that tunneling enhanced recombination is valid rather than thermionic emission theory. In the frame of this model, characteristic tunneling energy and characteristic temperature are found to be 9 meV and 1900 K, respectively. It is concluded that fabricate n-type hydrogenated amorphous silicon is a preferable semiconductor material layer with low interface state density because the temperature dependent interface state density calculations give values of the order of 10¹⁴ eV⁻¹ cm⁻².     

Prediction of wheat quality parameters using near-infrared spectroscopy and artificial neural networks

In wheat and flour processing, the quality control needs quick analytical tools for predicting physical, rheological, and chemical properties. In this study, near infrared reflectance (NIR) spectroscopy combined with artificial neural network (ANN) was used to predict the flour quality parameters that are protein content, moisture content, Zeleny sedimentation, water absorption, dough development time, dough stability time, degree of dough softening, tenacity (P), extensibility (L), P/G, strength, and baking test (loaf volume and loaf weight). A total of 79 flour samples of different wheat varieties grown in different regions of Turkey were chemically analyzed, and the results of both NIR spectrum (400–2,498 nm) and chemical analysis were used to train/test the network by applying various ANN architectures. Prediction of protein, P, P/G, moisture content, Zeleny sedimentation, and water absorption in particular gave a very good accuracy with coefficient of determination (R ²) of 0.952, 0.948, 0.933, 0.920, 0.917, and 0.832, respectively. The results indicate that NIR combined with the ANN can successfully be used to predict the quality parameters of wheat flour.     

Effect of Magnesium and Osteoblast Cell Presence on Hydroxyapatite Formation on (Ti,Mg)N Thin Film Coatings

TiN and (Ti,Mg)N thin film coatings were deposited on Ti substrates by an arc-physical vapor deposition technique. The effect of cell presence on hydroxyapatite (HA) formation was investigated using surfaces with four different Mg contents (0, 8.1, 11.31, and 28.49 at.%). Accelerated corrosion above 10 at.% Mg had a negative effect on the performance in terms of both cell proliferation and mineralization. In the absence of cells, Mg-free TiN coatings and low-Mg (8.1 at.%)-doped (Ti,Mg)N surfaces led to an early HA deposition (after 7 days and 14 days, respectively) in cell culture medium (DMEM), but the crystallinity was low. More crystalline HA structures were obtained in the presence of the cells. HA deposits with an ideal Ca/P ratio were obtained at least a week earlier, at day 14, in TiN and low-Mg (8.1 at.%)-doped (Ti,Mg)N compared with that of high-Mg-containing surfaces (>10 at.%). A thicker mineralized matrix was formed on low-Mg (8.1 at.%)-doped (Ti,Mg)N relative to that of the TiN sample. Low-Mg doping (<10 at.%) into TiN coatings resulted in better cell proliferation and thicker mineralized matrix formation, so it could be a promising alternative for hard tissue applications.     

Intensity modulated short circuit current spectroscopy for solar cells

Understanding charge separation and transport is momentously important for the rectification of solar cell performance. To probe photo-generated carrier dynamics, we implemented intensity modulated short circuit current spectroscopy (IMSCCS) on porous Si and Cu(In_x,Ga_1−x)Se₂ solar cells. In this experiment, the solar cells were lightened with sinusoidally modulated monochromatic light. The photocurrent response of the solar cell as a function of modulation frequency is measured as the optoelectronic transfer function of the system. The optoelectronic transfer function introduces the connection between the modulated light intensity and measured AC current of the solar cell. In this study, interaction of free carriers with the density of states of the porous Si and Cu(In_x, Ga_1−x)Se₂ solar cells was studied on the basis of charge transport time by IMSCCS data.