The behavior of the I-V-T characteristics of inhomogeneous (Ni/Au)-Al0.3Ga0.7N/AlN/GaN heterostructures at high temperatures

Cataloged from PDF version of article.We investigated the behavior of the forward bias current-voltage-temperature (I-V-T) characteristics of inhomogeneous (Ni/Au)-Al0.3Ga0.7N/AlN/GaN heterostructures in the temperature range of 295-415 K. The experimental results show that all forward bias semilogarithmic I-V curves for the different temperatures have a nearly common cross point at a certain bias voltage, even with finite series resistance. At this cross point, the sample current is temperature independent. We also found that the values of series resistance (R-s) that were obtained from Cheung's method are strongly dependent on temperature and the values abnormally increased with increasing temperature. Moreover, the ideality factor (n), zero-bias barrier height (Phi(B0)) obtained from I-V curves, and R-s were found to be strongly temperature dependent and while Phi(B0) increases, n decreases with increasing temperature. Such behavior of Phi(B0) and n is attributed to Schottky barrier inhomogeneities by assuming a Gaussian distribution (GD) of the barrier heights (BHs) at the metal/semiconductor interface. We attempted to draw a Phi(B0) versus q/2kT plot in order to obtain evidence of the GD of BHs, and the values of (Phi) over bar (B0)=1.63 eV and sigma(0)=0.217 V for the mean barrier height and standard deviation at a zero bias, respectively, were obtained from this plot. Therefore, a modified ln(I-0/T-2)-q(2)sigma(2)(0)/2(kT)(2) versus q/kT plot gives Phi(B0) and Richardson constant A(*) as 1.64 eV and 34.25 A/cm(2) K-2, respectively, without using the temperature coefficient of the barrier height. The Richardson constant value of 34.25 A/cm(2) K-2 is very close to the theoretical value of 33.74 A/cm(2) K-2 for undoped Al0,3Ga0,7N. Therefore, it has been concluded that the temperature dependence of the forward I-V characteristics of the (Ni/Au)-Al0.3Ga0.7/AlN/GaN heterostructures can be successfully explained based on the thermionic emission mechanism with the GD of BHs. (c) 2007 American Institute of Physics

Optically trapped bacteria pairs reveal discrete motile response to control aggregation upon cell–cell approach

Aggregation of bacteria plays a key role in the formation of many biofilms. The critical first step is cell–cell approach, and yet the ability of bacteria to control the likelihood of aggregation during this primary phase is unknown. Here, we use optical tweezers to measure the force between isolated Bacillus subtilis cells during approach. As we move the bacteria towards each other, cell motility (bacterial swimming) initiates the generation of repulsive forces at bacterial separations of ~3 μm. Moreover, the motile response displays spatial sensitivity with greater cell–cell repulsion evident as inter-bacterial distances decrease. To examine the environmental influence on the inter-bacterial forces, we perform the experiment with bacteria suspended in Tryptic Soy Broth, NaCl solution and deionised water. Our experiments demonstrate that repulsive forces are strongest in systems that inhibit biofilm formation (Tryptic Soy Broth), while attractive forces are weak and rare, even in systems where biofilms develop (NaCl solution). These results reveal that bacteria are able to control the likelihood of aggregation during the approach phase through a discretely modulated motile response. Clearly, the force-generating motility we observe during approach promotes biofilm prevention, rather than biofilm formation

Bacterial Chemotaxis in an Optical Trap

An optical trapping technique is implemented to investigate the chemotactic behavior of a marine bacterial strain Vibrio alginolyticus. The technique takes the advantage that the bacterium has only a single polar flagellum, which can rotate either in the counter-clock-wise or clock-wise direction. The two rotation states of the motor can be readily and instantaneously resolved in the optical trap, allowing the flagellar motor switching rate to be measured under different chemical stimulations. In this paper the focus will be on the bacterial response to an impulsive change of chemoattractant serine. Despite different propulsion apparati and motility patterns, cells of V. alginolyticus apparently use a similar response as Escherichia coli to regulate their chemotactic behavior. Specifically, we found that the switching rate of the bacterial motor exhibits a biphasic behavior, showing a fast initial response followed by a slow relaxation to the steady-state switching rate . The measured can be mimicked by a model that has been recently proposed for chemotaxis in E. coli. The similarity in the response to the brief chemical stimulation in these two different bacteria is striking, suggesting that the biphasic response may be evolutionarily conserved. This study also demonstrated that optical tweezers can be a useful tool for chemotaxis studies and should be applicable to other polarly flagellated bacteria

(Salvia officinalis) oils

Sage is perennial plant included in the Salvia officinalis species, which belongs to the Labiatea family. It is also known as common sage and garden sage. Medical and culinary use of this medicinal herb dates back to ancient times. The most important components of S. officinalis, which is commonly grown in many Mediterranean countries, are phenolic components. Sage has antimicrobial, antioxidant, antiviral, and immunosuppressive effects, so its medical and aromatic usage is important. In addition to this, sage is used traditionally for different purposes, such as the preservation of natural and processed food, as a sweetener, or for food coloring. © 2016 by Elsevier, Inc.. All rights reserved

Allelopathic Effect of Sage and Turkish Oregano Volatile Oils on In Vitro in Sainfoin (Onobrychis viciifolia)

Sainfoin has little atention for plant tissue culture studies. However, genetic engineering applications of gene transfer can be done today. Therefore, first different methods are used in tissue culture (For example, using of different hormones for plant growing) and be given importance. In this study, the effect of different concentration (0-5-10-20-30 ppm) sage (Salvia officinalis L.) and Turkish oregano (Origanum onites L.) have profound effects on morphology of the tissues that grow from the initial sainfoin explant. The study was arranged in factorials with 6 replications and of variance was done using statistical analysis system (SAS) software. The data collected included the rate of seed germination, plant length, root number and root length. The highest seed germination, plant length and root length was obtained on sage volatile oil. Used both volatile oil reduced the germination ratio. Sage increased the plant and root length. Even so, Turkish orego significantly reduced plant length and is root number increased. © 2013 Copyright Har Krishan Bhalla & Sons

Molecular characterization of triticale genotypes (X triticosecale wittmack) based on ISSR-PCR [Tritikale (X Triticosecale Wittmack) genotiplerinin ISSR-PCR yöntemi ile moleküler düzeyde tanimlanmas]

In this study, genetic distance among 4 triticale cultivars cultivated in our country and 4 triticale lines was examined using the inter simple sequence repeat (ISSR-PCR) method and the 14 of used 16 primers gave polymorphic bands. The average polymorphism rate in the genotypes used in the study was determined as 42.27 %; in addition, in total, 97 bands and 41 polymorphic bands were obtained. Research results showed that the average number of bands per polymorphic primer and the number of polymorphic bands was 6.9 and 2.9, respectively and the similarity ratios between the genotypes used in this study were found to be between 44-89 %. According to the unweighted pair group method with arithmetic mean (UPGMA) analysis results, in terms of genetic similarity, Tacettinbey and Tatlicak 97 varieties were the most distant, but SDÜ-43 and Tacettinbey varieties were the closest among the genotypes. On the other hand, In terms of genetic variation, Karma 2000, Tacettinbey variety and SDÜ-43 line placed in the same group. In this study, establishing to be in attendance of a genetic variation evident and accord with the aim among triticale varieties registered in Turkey, it was understood that ISSR-PCR method was quite reliable and a beneficial technic in selecting of the appropriate methods and from this viewpoint in determining of genotypic the similarity / diversity in the breeding of the line to be the candidate variety. © 2017 Namik Kemal University - Agricultural Faculty. All rights reserved

Current conduction mechanism in Al/p-Si Schottky barrier diodes with native insulator layer at low temperatures

The forward bias current-voltage (I-V) characteristics of Al/p-Si (MS) Schottky diodes with native insulator layer were measured in the temperature range of 80-300 K. The obtained zero bias barrier height Phi(B0)(I-V), ideality factor (n) and series resistance (R-s) determined by using thermionic emission (TE) mechanism show strong temperature dependence. There is a linear correlation between the Phi(B0)(I-V) and n because of the inhomogeneties in the barrier heights (BHs). Calculated values from temperature dependent I-V data reveal an unusual behaviour such that the (Phi(B0)) decreases, as the n and Rs values are increasing with decreasing absolute temperature, and these changes are more pronounced especially at low temperatures. Such temperature dependence of BH is contradictory with the reported negative temperature coefficient of the barrier height. In order to explain this behaviour we have reported a modification in the expression reverse saturation current I,, including the it and the tunnelling factor (alpha X-1/2 delta) estimated to be 15.5. Therefore, corrected effective barrier height Phi(bef.)(I-V) versus temperature has a negative temperature coefficients (alpha = -2.66 x 10(-4) eV/K) and it is in good agreement with negative temperature coefficients (alpha = -4.73 x 10(-4) eV/K) of Si band gap. In addition, the temperature dependent energy distribution of interface states density N-ss profiles was obtained from the forward bias I-V measurements by taking into account the bias dependence of the Phi(e) and n. The forward bias I-V characteristics confirm that the distribution of N-ss, R-s and interfacial insulator layer are important parameters that the current conduction mechanism of NIS Schottky diodes

Origin of forward bias capacitance peak and intersection behavior of C and G/w of Ag/p-InP Schottky barrier diodes

Frequency-dependent electrical characteristics of Ag/p-InP diodes have been determined using impedance spectroscopy at room temperature. Series resistance (R,) and interface state(s) (N-ss) values were extracted from capacitance (C) and conductance (G/w) data using the Nicollian and Goetzberger and Hill-Coleman methods, respectively. C and G/w data were also corrected in the whole measured bias voltage range to obtain real diode capacitance C-c and conductance G(c) values in order to see the effects of R-s. Both the C-V and R-s-V plots showed anomalous peak in depletion region especially at low frequencies due to the existence of N-ss. C-V and G/w-V plots crossed at a certain bias voltage and this point shifted toward negative bias voltages with increasing frequency and then disappeared at 3 MHz. Also, decrease in C values corresponds to an increase in G/w values in the same bias voltages

On the profile of frequency dependent interface states and series resistance in Au/p-InP SBDs prepared with photolithography technique

The frequency dependent of the forward and reverse bias capacitance-voltage (C-V) and conductance-voltage (G/w-V) characteristics of Au/p-InP SBDs have been investigated in the frequency range of 20 kHz-10 MHz and voltage range of -5 - 5 V at room temperature. The effects of surface states (N (ss)) and series resistance (R (s)) on C-V and G/w-V characteristics have been investigated in detail. The frequency dependent N (ss) and R (s) profiles were obtained for various applied bias voltages. The experimental results show that the main electrical parameters of Au/p-InP SBD such as barrier height (I broken vertical bar(B)), the density of acceptor concentration (N (A)), N (ss) and R (s) were found strongly frequency and voltage dependent. The values of C and G/w decrease with increasing frequency due to a continuous distribution of N (ss) localized at the metal/semiconductor (M/S) interface. The effect of R (s) on C and G is found considerably high especially at high frequencies. Therefore, the high frequencies of the values of C and G were corrected for the effect of R (s) in the whole measured bias range to obtain the real diode capacitance C (c) and conductance G (c) using the Nicollian and Goetzberger technique. The distribution profile of R (s)-V gives a peak depending on the frequency especially at low frequencies and disappears with increasing frequencies due to the existence of N (ss) at the M/S interface