168 research outputs found
Bacterial chemotaxis in an optical trap
No full textAn 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 S(t)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 S(t) of the bacterial motor exhibits a biphasic behavior, showing a fast initial response followed by a slow relaxation to the steady-state switching rate S0. The measured S(t)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. © 2011 Altindal et al
Synthesis, characterization, and electrical, electrochemical and gas sensing properties of a novel ball-type four t-butylcalix[4]arene bridged binuclear zinc(II) phthalocyanine
No full text1,3 dimethoxy-4-t-butylcalix[4]arene has been used to synthesize a novel ball-type dimeric zinc(II) phthalocyanine, [Zn2Pc2(tbca)4] that exhibits mixed-valence behaviour and non-Arrhenius type dependence of conductivity
Highly soluble tetrasubstituted lanthanide bis-phthalocyanines; synthesis, characterization, electrical properties and aggregation studies
No full textWe report the synthesis, characterization and electrical properties of lanthanide metal based bis-phthalocyanines, {M[Pc-(beta-HHT)(4)](2)} (HHT: 1-hydroxyhexane-3-ylthio){M = Lu3+(2), Eu3+(3), and Yb3+(4)}. The interaction of bis-phthalocyanines with Ag+ and Pd2+ metal ions were investigated by UV-vis spectroscopy and atomic force microscopy. Thin films of bis-phthalocyanine molecules were prepared by spin-coating method. The surface morphology of thin films were performed with Atomic Force Microscopy as further investigate. The electrical transport properties of ITO/Pc/Al devices were investigated. At low voltages all the films showed an ohmic conduction, whereas at higher voltage levels the conduction is dominated by space charged limited conduction with exponential distribution of trapping levels. Measurements of current density as a function of inverse temperature at constant applied voltage yielded a hole mobility values, mu(p) = 2.12 x 10(-7), 6.72 x 10(-7) and 1.58 x 10(-6) m(2).sn(-1).V-1 for lanthanium phthalocyanines. From the analysis of frequency, omega, dependence of electrical conductivity, sigma(ac). it was found that the sigma(ac) obeys the power law given by sigma(ac) = A omega(s), in which the frequency exponent "s" decreases with temperature
Double-decker sensor phthalocyanines functionalized with 1-hydroxyhexane-3-ylthio moieties; synthesis, characterization, electrical properties and H- or J- type aggregation studies
No full textIn this study, we report the synthesis, characterization, aggregation and electrical properties of softmetal ionophore functional double-decker sensor-phthalocyanines, {([4,5,4',5'4 '',5 '',4 '',5'"]-octakis-(1hydroxyhexane-3-ylthio) phthalocyaninato lanthanium (HI)}) [M(Pc)21, fM = Lu3 (2), Yb3 (3) and La3+ (4)}. The new compounds have been characterized by elemental analysis, MS-TOF, UV-Vis, FT-IR, 1H NMR, and ESR spectral data. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) as complementary techniques were used for investigate the morphology of the 2, 3 and 4 complex. Functionalized phthalocyanines with 1-hydroxyhexane-3-ylthio moieties have been lead to selective metal ion sensor, such as Ag+ and Pd2+1. The temperature dependence of the dc and ac conduction properties of 2, 3 and 4 thin films have been investigated in the frequency range of 40 Hz-10(5) Hz and temperature range between 297 and 500 K. For complex 2 it was found that thermally activated band conduction is the dominant conduction mechanism at high temperatures whereas in the low temperature region the dependence of the dc conductivity on temperature followed Mott's variable range hopping (VRH) model. The ac conductivity showed strong dependence on both temperature and frequency. The temperature dependence of frequency exponent suggested a dominant hopping conduction process. (C) 2015 Elsevier BY. All rights reserved
Effects of the Metal Electrode on Dielectric Constant of MgO Nanoparticles
No full textIn this study, effects of the metal electrode on dielectric properties of MgO nanoparticles were investigated MgCl(2)center dot 6H(2)O were dissolved in ethanol and aged for a long time under stirring. The particles were obtained by precipitation method Crystal structure of particles was investigated using X-ray diffraction In order to determine the electrical properties of the MgO nanoparticles, metal electrodes were deposited onto both sides of the MgO pellets using thermal evaporation method in high vacuum (<10(-6) mbar) Dc and ac electrical properties of two MgO pellets with different metal electrodes (Au and Ag) were determined under vacuum ambient as a function of temperature (293-523 K) ac electrical measurements were earned out between the frequencies 40 Hz-10(5) Hz. Activation energy values of the MgO pellets with different metal electrodes were calculated using the relation sigma(dc) = sigma(o)e(-En/kT) and from slope of the dc conductivity (sigma(dc)) - inverse of temperature (I/T) curve. Dielectric constant was calculated as a function of both frequency and temperature. MgO pellet with Au electrode showed a small decrease with increasing frequency in the measured frequency rang
Synthesis, characterization, conduction and gas sensing properties of novel multinuclear metallo phthalocyanines (Zn, Co) with alkylthio substituents
No full textCompound 1 has been prepared by the reaction of 4-nitrophthalonitrile and 2-nitro-2-methyl-1,3-propanediol by the common method of nucleophilic substitution of an activated nitro group in an aromatic ring. Interesting binuclear metallophthatocyanines (M = Zn and Co), compounds 2 and 3, respectively, of a new type have been synthesized from compound 1, 4,.5-bis(hexylthio)phthalonitrile, and the corresponding metal salts [Zn(OAC)(2) and CoCl2] by the method of statistically mixed condensation. Compound 2 was converted to the tetranuclear zinc (II) phthalocyanine 4 by the reaction with NaOH solution and activated zinc powder in a mixture of MeOH and THF as the solvent. Impedance spectroscopy (IS) and d.c conductivity (sigma(d.c)) measurements were performed on spin coated films of these compounds as a function of temperature (290-400 K) and frequency (40-10(5) Hz.) The sensing properties for volatile organic compounds (VOCs) were also investigated. Although the d.c conductivity shows typical Arrehenius behaviour for compound 2, a discontinous point was observed in the slope of ln sigma(d.c) versus 1/T plot for compound 4. Unlike the films of 2 and 4, the d.c behaviour of compound 3 obeys the variable range hopping (VRH) model. At room temperature, a curved line was observed from the complex plane plots of impedance for all compounds. These curved lines transformed into a full semicircle with increasing temperature. The a.c conductivity of the films is represented by the form omega(s). The dependency of the frequency exponent s on temperature suggests a correlated barrier hopping. A sensor using compound 4 as the sensing layer had the highest sensitivity for all volatile organic compounds investigated and showed complete reversibility even at room temperature. The results indicated that the film of compound 4 has potential as a sensitive coating for the monitoring of VOC vapours. (c) 2005 Elsevier Ltd. All rights reserved
Forward And Reverse Bias Current-Voltage (I-V) Characteristics Of Au/Ca3Co4Ga0,001Ox/n-Si Structures In Temperature Range Of 80-340 K
No full textAu/Ca3Co4Ga0,001Ox/n-Si yapılarda, akım-iletim mekanizmaları 80-340 K sıcaklık aralığında incelendi. LnI-V grafikleri, düşük (0,075-0,250 V) ve orta (0,27-0,70 V) voltajlarda iki lineer bölge sergiledi. Engel yüksekliği (Bo) ve idealite faktörü (n) değerleri bu bölgelerin kesim noktası ve eğimlerinden elde edildi. Bo değeri artan sıcaklıkla artarken n değeri azalmaktadır. Gaussian dağılıma (GD) delil teşkil etmek amacıyla Bo ve (n-1-1) - q/2kT ile Bo - n grafikleri çizildi ve hepsinde farklı eğimli iki lineer bölge gözlendi. Bu bölgeler düşük sıcaklık (LTR): (80-160 K) ve yüksek sıcaklık (HTR): (200-340 K) aralıklarıdır. Ortalama engel yüksekliği ( B  ) ve standart sapma (s) değerleri ΦBo-q/2kT grafiğinden küçük voltajlarda LTR için 0,382 eV, 0,060 V ve HTR için ise 0,850 eV, 0,135 V elde edildi. Orta voltajlarda ise bunlar LTR için 0,364 eV, 0,059 V HTR için 0,806 eV, 0,132 V elde edildi. Bu değerler kullanılarak modifiye Richardson ((Ln(Io/T2)- (q2s2/2k2T2)-q/kT) grafiğinin eğimi ve kesme noktasından ̅Bo ve Richardson sabiti (A*) değerleri sırasıyla düşük voltajlarda; LTR için 131,81 Acm-2K-2, 0,381 eV ve HTR için 129,35 Acm-2K-2, 0, 854 eV elde edilirken orta voltajlarda LTR için 148,01 Acm-2K-2, 0,377 eV ve HTR için 143,77 A.cm-2K-2, 0,812 eV elde edildi. Bu sonuçlar, akım iletim mekanizmasının Termiyonik emisyon (TE) bazlı çift GD ile açıklanabileceğini göstermektedir. Ters beslemde çizilen Ln (Ir/Er)-E0,5 grafikleri de farklı lineer bölge sergiledi ve kesme noktası B(T) ve eğimleri m(T) değerlerinin q/kT'ye karşı grafikleri çizildi. Ca3Co4Ga0,001Ox tabakasının dielektrik sabiti () ve engel yüksekliği (t) sırasıyla bu grafiklerin eğimlerinden sırasıyla 3,1 ve 37,1 meV olarak elde edildi. Bu sonuçlar, Ir-Vr karakteristiklerinin elektrik alana bağımlılığı ile tanımlanabildiğini göstermektedir. Bu nedenle, Au/Ca3Co4Ga0,001Ox/n-Si yapılarda baskın iletim mekanizması Frenkel-Poole eMSyonu (FPE) veya Schottky eMSyonu (SE) ile açıklanabilir. Bu t değeri oldukça düşüktür ve 3,1 olarak bulunan dielektrik sabiti ise SiO2'nin geleneksel dielektrik değerine (3,8) yaklaşmaktadır. Elde edilen sonuçlar, (Ca3Co4Ga0,001Ox) ara yüzey tabakasının esnek, üretimi kolay ve düşük maliyet açısından geleneksel SiO2 yalıtkan tabakanın yerine kullanılabileceğini göstermektedirCurrent transport mechanisms (CTMs) of Au/Ca3Co4Ga0,001Ox/n-Si/Au structures were investigated in the temperature range of 80-340K. LnI-V plots show two distinct linear regions corresponding to low (0,075-0,250 V) and moderate (0,27-0,70 V) biases. The barrier height (BH) Bo and ideality factor (n) values were obtained from the intercept and slope of these plots. While Bo increases with increasing temperature, n decreases. Bo and (n-1-1) vs q/2kT and Bo vs n plots were drawn to get an evidence of Gaussian distribution (GD) of the BHs. These plots, show also two linear regions corresponding to low (80-160K) and high (200-340K) temperatures which are called as LTR and HTR. Mean value ( ̅Bo) and standard deviation (s) were extracted from the intercept and slope of ΦBo vs q/2kT plots for two linear regions as 0,382 eV, 0,060 V for LTR and 0,850 eV, 0,135 V for HTR at low biases and 0,364 eV, 0,059 V for LTR and 0,806 eV, 0,132 V for HTR at moderate biases. ̅Bo and Richardson constant (A*) values were also obtained from the intercept and slope of the modified Richardson (Ln(Io/T2)-(q2s2/2k2T2) vs q/kT) plots as 131,81 Acm-2K-2, 0,381 eV for LTR and 129,35 Acm-2K-2, 0,854 eV for HTR at low biases and 148,01 Acm-2K-2, 0,377 eV for LTR and 143,77 A.cm-2K-2, 0,812 eV for HTR at high biases. CTM can be successfully explain in terms of thermionic emission (TE) with the double GD of BHs. Reverse bias Ln (Ir/Er) vs E0,5 plots show also straight lines with different slopes. Both the intercepts B(T) and slopes m(T) values versus q/kT plots were drawn. These results show that the IR-VR characteristics can be well described by the electric field dependence so the dominant conduction mechanisms are either Frenkel-Poole (FP) emission or Schottky emision (SE). The i and t values were found as 3,1 and 37,1 meV. t is considerably low and the value of i (3,1) is closed to conventional of SiO2 layer (3,8). These results confirmed that (Ca3Co4Ga0,001Ox) layer can be used instead of a conventional of SiO2 layer in the terms of flexibility, easy production and low cost
Metal ion sensing functional mono and double-decker lanthanide phthalocyanines: Synthesis, characterization and electrical properties
No full textWe report, in this study, the preparation, physical characterization metal ion sensing properties of peripherally functionalized ionophore ligand, 4,5-bis(6-hydroxyhexylthio)-1,2-dicyanobenzene (1) and its mono 2,3,7,8,12,13,17,18-octakis(6-hydroxyhexylthio)phthalocyaninatometal (II) {M=Zn(II) (2), Cu(II) (3)} and double-decker lanthanide bis-phthalocyanines, {([4,5,4',5' 4 '',5 '',4'''5''']-tetrakis-(6-hydroxyhexylthio)phthalocyanitlatolanthanium(III)}){M[Pc(S-C(6)H(13)OH)(4)](2)} {M=Eu(III) (4), Yb(III) (5), and Lu(III) (6)}. All benzenes on phthalocyanines are functionalized with hydroxyhexylsulfanyl moieties for potential use as soft metal ion binding, such as Ag(+) and Pd(2+). The temperature dependence of the do and ac conduction properties of 4, 5 and 6 thin films have been investigated in the frequency range of 40-10(5) Hz and temperature range 290-436 K. The do results showed an activated conductivity dependence on temperature for all films. Obtained data reveal that ac conductivity obeys the relation sigma(ac)(omega)=A omega(s) and exponent is found to decrease by increasing temperature. The data obtained results were compared with the prediction of the Quantum Mechanical Tunelling (QMT) and Correlated Barrier Hopping (CBH) models. The analysis showed that the CBH model is the dominant conduction mechanism for the electron transport in the films. The new synthesized compounds have been characterized by elemental analysis, FTIR, (1)H and (13)C NMR, MS, UV-vis and EPR spectral data. (C) 2009 Elsevier B.V. All rights reserved
Synthesis, characterization, and electrical, electrochemical and gas sensing properties of a novel ball-type four t-butylcalix[4]arene bridged binuclear zinc(II) phthalocyanine
No full text1,3 dimethoxy-4-t-butylcalix[4]arene has been used to synthesize a novel ball-type dimeric zinc(II) phthalocyanine, [Zn2Pc2(tbca)4] that exhibits mixed-valence behaviour and non-Arrhenius type dependence of conductivity
THE PREPARATION OF Au/Bi4Ti3O12/SiO2/n-Si STRUCTURES, INVESTIGATION OF THE ELECTRICAL AND DIELECTRIC PROPERTIES BASED ON FREQUENCY AND TEMPERATURE
No full textMetal-ferroelektrik-yalıtkan-yarıiletken (MFIS) yapının, frekans ve sıcaklıga
baglı kapasitans-voltaj (C-V) ve iletkenlik-voltaj (G/w-V) karakteristikleri, seri
direnç (Rs) ve yüzey durum (Nss) etkileri dikkate alınarak, sırasıyla 1 kHz-5
MHz frekans ve 80-400 K sıcaklık aralıgında incelendi. Nss ve Rs degerlerinin
önemli ölçüde frekans ve sıcaklıga baglı oldugu tespit edildi. Rs ve Nss'e baglı
olarak Au/Bi4Ti3O12/SiO2/n-Si yapının C-V-f ve G/w-V-f karakteristikleri,
özellikle düsük frekanslarda, genis bir frekans dagılımı göstermektedir, C-V-T
ve G/w-V-T grafikleri dogru beslemde Rs ve Nss'e baglı olarak anormal pikler
vermektedir. Bu piklerin pozisyonu yıgılma bölgesinden tüketim bölgesine
yönelmekte, kapasitans ve iletkenligin maksimum degerleri artan sıcaklıkla
artmaktadır. Ölçülen kapasitans (Cm) ve iletkenlik (Gm/w) degerleri MFIS
yapının gerçek kapasitans ve iletkenligini bulmak için, seri direnç etkisinden
dolayı düzeltilmistir. Her frekans için, Rs-V egrileri tersinim ve tüketim
bölgeleri arasında anormal pikler göstermekte ve pik pozisyonları artan
frekansla dogru beslem bölgesine kaymaktadır. C-2-V egrisinin, genis bir voltaj
bölgesinde dogrusal olması, arayüzey durumlar ve tersinim tabaka yüklerinin,
tüketim bölgesinde ac sinyali takip edemedigini göstermektedir. Nss artan
frekansla eksponansiyel olarak azalmaktadır. C-V ve G/w-V karakteristikleri
yarıiletkenle, yüzey durumlarının dengede olmasına baglı olarak beklenen davranısı göstermektedir. MFIS yapı için dielektrik sabiti (G'), dielektrik kayıp
(G'') ve dielektrik kayıp açı (tanI) arastırılmıs ve C-V ve G/w-V ölçümlerinden
hesaplanmıstır. Dielektrik parametreler oldukça yüksek sıcaklıkta ve düsük
frekanslarda, frekans ve sıcaklıga hassasiyet göstermektedir. G' ve G'' artan
frekansla azalırken, artan sıcaklıkla artmaktadır. Arayüzey kutuplanması
düsük frekanslarda daha kolay gerçeklesebilmekte ve yarıiletken/yalıtkan
arayüzeyinde arayüzey durum yogunlugu sayısı, MFIS yapının dielektrik özelliklerinin iyilestirilmesine katkı saglamaktadır.
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The frequency and temperature dependent capacitance-voltage (C-V) and
conductance-voltage (G/w-V) characteristics of the metal-ferroelectricinsulator-
semiconductor (MFIS) structure were investigated by considering
series resistance (Rs) and surface state (Nss) effects in the frequency and
temperature ranges of 1 kHz-5 MHz and 80-400 K, respectively. The values of
Nss and Rs were determined to be strongly dependent on the frequency and
temperature. The C-V-f and G/w-V-f characteristics of Au/Bi4Ti3O12/SiO2/n-Si
structure show fairly large frequency dispersion especially at low frequencies,
the C-V-T and G/w-V-T plots exhibit anomalous peaks at forward bias due to
Rs and Nss. These peak positions shift from accumulation to inversion region
and the maximum values of the capacitance and conductance increase with
increasing temperature. The measured capacitance (Cm) and conductance
(Gm/w) values were corrected for the effect of series resistance to obtain the real
capacitance and conductance of MFIS structure. The Rs-V plots exhibit
anomalous peaks between inversion and depletion regions at each frequency
and peak positions shift towards positive bias with increasing frequency. The C-
2-V plot gives a straight line in wide voltage region, indicating that interface
states and inversion layer charges cannot follow the ac signal in the depletion
region. The Nss decreases exponentially with increasing frequency. The C-V and G/w-V characteristics show the expected behavior due to Nss in equilibrium with
the semiconductor. Dielectric constant (G'), dielectric loss (G'') and, dielectric loss
tangent (tanI) were studied for MFIS structure and calculated from C-V and
G/w-V measurements. The dielectric parameters were quite sensitive to
temperature and frequency at relatively high temperatures and at low
frequencies. The G' and G'' were decreasing with increasing frequency while
increasing with increasing temperature. The interfacial polarization can be
more easily occurred at low frequencies, and the number of interface states
density between semiconductor/insulator interfaces, consequently, contributes to the improvement of dielectric properties of MFIS structure
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