Comparable structural and optical properties of 4H-pyrano [3, 2-c] quinoline derivatives thin films

The structural and optical properties of 2-Amino-6-ethyl-5-oxo-4-(3-phenoxyphenyl) - 5, 6- dihydro - 4H-pyrano [3,2-c] quinoline-3- carbonitrile (Ph-HPQ) and 2-Amino-4-(2-chlorophenyl)-6-ethyl-5-oxo-5,6-dihydro-4H-pyrano [3,2-c] quinoline-3-carbonitrile (Ch-HPQ) thin films are studied. The compounds are polycrystalline in as- synthesised powder form; they became nanocrystallites dispersed in amorphous matrix upon thermal deposition to form thin films. FTIR spectral measurements showed no change in chemical bonds of the compounds after being deposited to form thin films. The optical properties have been determined based on spectrophotometer measurements of transmittance and reflectance at nearly normal incidence of light in the spectral range of 200–2500 nm. The absorption parameters, molar extinction coefficient, oscillator strength and electric dipole strength, are reported. The type of electron transition is determined from analysis of absorption coefficient spectra near the onset and optical absorption edges. The onset and optical energy gaps for Ph-HPQ and Ch-HPQ thin films are determined. The single oscillator model is applied to calculate the dispersion parameters of the investigated thin films. In addition, oscillator and dispersion energies, the high-frequency dielectric constant, lattice dielectric constant and ratio of free charge carriers concentrations to their effective masses are evaluated for the compounds under investigation.     

Magnetic interactions and electronic structure of $$\hbox {Pt}_{2}\hbox {Mn}_{1-x}\hbox {Y}_{x} \hbox {Ga (Y = Cr and Fe)}$$ system: An ab-initio calculation

Structural, optical, electrical conductivity and dielectric relaxation properties of bulk 4-amino-3-mercapto-6-(2-(2-thienyl)vinyl)-1,2,4-triazin-5(4H)-one donor (AMT) are studied. The structure of AMT in its powder form was analysed by X-ray diffraction (XRD), infrared spectroscopy (FT-IR) and atomic force microscopy (AFM). AC measurements (impedance, capacitance and phase angle) are done over the temperature range 303–373 K and in the frequency range from 42 Hz to 5 MHz. Analytical approaches for the experimental results of the σ _AC(ω, T) and the temperature behaviour of the frequency exponent show that the correlated barrier hopping (CBH) model is a good model to explain the AC electrical conductivity of bulk AMT organic semiconductor material. Application of the dielectric modulus formulism gives a simple method for evaluating the activation energy of the dielectric relaxation. The activation energy from the DC conductivity and the relaxation time are quite similar suggesting a hopping mechanism for AMT. The optical band gap of AMT is investigated using spectrophotometric measurement of transmittance at normal incidence of light in the wavelength range 300–1100 nm.     

Alternating current characterization of nano-Pt(Ⅱ)octaethylporphyrin(PtOEP) thin film as a new organic semiconductor

Alternating current(AC) conductivity and dielectric properties of thermally evaporated Au/Pt OEP/Au thin films are investigated each as a function of temperature(303 K–473 K) and frequency(50 Hz–5 MHz).The frequency dependence of AC conductivity follows the Jonscher universal dynamic law.The AC-activation energies are determined at different frequencies.It is found that the correlated barrier hopping(CBH) model is the dominant conduction mechanism.The variation of the frequency exponent s with temperature is analyzed in terms of the CBH model.Coulombic barrier height Wm,hopping distance Rω,and the density of localized states N(EF) are valued at different frequencies.Dielectric constant ε_1(ω,T) and dielectric loss ε_2(ω,T) are discussed in terms of the dielectric polarization process.The dielectric modulus shows the non-Debye relaxation in the material.The extracted relaxation time by using the imaginary part of modulus(M')is found to follow the Arrhenius law.     

Hopping type of conduction in (Na0.5Bi0.5)ZrO3 ceramic

Polycrystalline sample with (Na_0.5Bi_0.5)ZrO₃ (NBZ) stoichiometry was prepared using a high-temperature solid-state reaction technique. X-ray diffraction (XRD) analyses indicate the formation of a single-phase perovskite-type orthorhombic structure. AC impedance plot is used as tool to analyse the electrical behaviour of the sample as a function of temperature at different frequency. The AC impedance studies revealed the presence of grain boundary effect and evidence of a negative temperature coefficient of resistance (NTCR) character. Pseudo Cole-Cole and complex electric modulus analyses indicated non-Debye-type dielectric relaxation. The AC conductivity obeys the universal power law. The pair approximation type correlated barrier hopping (CBH) model explains the universal behaviour of the s exponent. The apparent activation energy to the conduction process and minimum hopping distance are discussed.     

Electrical properties and dielectric relaxation of thermally evaporated zinc phthalocyanine thin films

The electrical transport properties and dielectric relaxation of Au/zinc phthalocyanine, ZnPC/Au devices have been investigated. The DC thermal activation energy at temperature region 400-500 K is 0.78 eV. The dominant conduction mechanisms in the device are ohmic conduction below 1 V and space charge limited conduction dominated by exponential trap distribution in potentials >1 V. Some parameters, such as concentration of thermally generated holes in valence band, the trap concentration per unit energy range at the valence band edge, the total concentration of traps and the temperature parameter characterizing the exponential trap distribution and their relation with temperatures have been determined. The AC electrical conductivity, σ_ac, as a function of temperature and frequency has been investigated. It showed a frequency and temperature dependence of AC conductivity for films in the temperature range 300-400 K. The films conductivity in the temperature range 400-435 K increased with increasing temperature and it shows no response for frequency change. The dominant conduction mechanism is the correlated barrier hopping. The temperature and frequency dependence of real and imaginary dielectric constants and loss tangent were investigated.     

Structural and electrical performance of epitaxial InP based heterojunctions prepared by liquid phase epitaxy

Thin films of InP was grown on single crystalline substrates of Si to form InP/Si heterojunctions by liquid phase epitaxy (LPE) and its morphology and crystalline characteristics were achieved. The essential electrical properties and its main parameters were extracted using the current density-voltage. The analysis was done to obtain the rectification characteristics which has its maximum value at a certain voltage of 0.7 V. Moreover, the heterojunction obeys ohmic behavior followed by quadratic space charge limited conduction at lower and higher voltage regions, respectively. The conductivity under AC bias as well as the dielectric behaviors of the heterojunction was explored in the frequency range 100 kHz–5 MHz and in the temperature range 298–623 K. The AC conductivity is interpreted by the correlated barrier hopping model via single polaron with activation energy dependent on the applied frequency. The response of the dielectric constants confirms its remarkable dependence on both frequency and temperature.     

Structure and dielectric behavior of TlSbS2

A comparison of structure and dielectric properties of TlSbS₂ thin films, deposited in different thicknesses (400–4100 Å) by thermal evaporation of TlSbS₂ crystals that were grown by the Stockbarger–Bridgman technique and the bulk material properties of TlSbS₂ are presented. Dielectric constant ε ₁ and dielectric loss ε ₂ have been calculated by measuring capacitance and dielectric loss factor in the frequency range 20 Hz–10 KHz and in the temperature range 273–433 K. It is observed that at 1 kHz frequency and 293 K temperature the dielectric constant of TlSbS₂ thin films is ε ₁=1.8–6 and the dielectric loss of TlSbS₂ thin films is ε ₂=0.5–3 depending on film thickness. In the given intervals, both of dielectric constant and dielectric loss decrease with frequency, but increase with temperature. The maximum barrier height W _m is calculated from the dielectric measurements. The values of W _m for TlSbS₂ films and bulk are obtained as 0.56 eV and 0.62 eV at room temperature, respectively. The obtained values agree with those proposed by the theory of hopping over the potential barrier. The temperature variation of ac conductivity can be reasonably interpreted in terms of the correlated barrier hopping model since it obeys the ω ^s law with a temperature dependent s (s<1) and going down as the temperature is increased. The temperature coefficient of capacitance (TCC) and permittivity (TCP) are evaluated for both thin films and bulk material of TlSbS₂.     

AC conductivity and dielectric properties of bulk tungsten trioxide (WO3)

AC conductivity and dielectric properties of tungsten trioxide (WO₃) in a pellet form were studied in the frequency range from 42 Hz to 5 MHz with a variation of temperature in the range from 303 K to 463 K. AC conductivity, σ_ac(ω) was found to be a function of ω^s where ω is the angular frequency and s is the frequency exponent. The values of s were found to be less than unity and decrease with increasing temperature, which supports the correlated barrier hopping mechanism (CBH) as the dominant mechanism for the conduction in WO₃. The dielectric constant (ε′) and dielectric loss (ε″) were measured. The Cole–Cole diagram determined complex impedance for different temperatures.     

Ac electrical conductivity and dielectric relaxation behavior of amorphous Selinum36 Antimony31Cubber33 thin films

ABSTRACT

The alternating-current (Ac) conductivity measurements and dielectric behaviors were observed in the range of temperature (from 303 to 393?K) and in the frequency range from 10² to10⁶?Hz for amorphous films of Selinum₃₆ Antimony₃₁ Cubber₃₃ chalcogenide glass. The ac conductivity has temperature dependency and the frequency dependency. The reduction of the exponent S values with raising temperature was introduced with the correlated barrier hopping model. The maximum height of the barrier W_M for Sellinum₃₆ Antimony₃₁Cubber₃₃ films is reliable with carrier hopping over a potential barrier. The number of localized states per unit volume at the Fermi level enhances with the elevation of ambient temperature of the film sample. Both dielectric constant ε₁ and loss ε₂ increase with the rise of temperature rising and decrease with frequency. The computation of the dielectric modulus M^/ and M^// revealed that the interfacial is the most suitable polarization type.     

Oxygen-vacancy-related dielectric relaxation and conduction mechanisms in Bi5TiNbWO15 ceramics

This paper reports that the intergrowth ceramics Bi5TiNbWO15 （BW-BTN） have been prepared with the conventional solid-state reaction method. The dielectric and conductivity properties of samples were studied by using the dielectric relaxation and AC impedance spectroscopy in detail. Two distinct relaxation mechanisms were detected both in the plots of dielectric loss （tanδ） and the imaginary part （Z″） versus frequency in the frequency range of 10 Hz-13 MHz. We attribute the higher frequency relaxation process to the hopping process of the oxygen vacancies inside the grains, while the other seems to be associated with the space charges bound at the grain boundary layers. The AC impedance spectroscopy indicates that the conductivities at 625 K for bulk and grain boundary are about 1.12 × 10^-2 S/m and 1.43 × 10^-3 S/m respectively. The accumulation of the space charges in the grain boundary layers induces a space charge potential of 0.52 eV.     

Effect of the film thickness on the impedance behavior of sol–gel Ba0.6Sr0.4TiO3 thin films

Perovskite Ba_0.6Sr_0.4TiO₃ sol–gel thin films with different thicknesses are fabricated as MFM configuration to study the effect of the film thickness on the dielectric relaxation phenomenon and the ionic transport mechanism. The frequency dependent impedance, electric modulus, permittivity and AC conductivity have been investigated in this context. Z? plane for all the tested samples shows two regions, corresponding to the bulk mechanism and the distribution of the grain boundaries–electrodes process. Electric modulus versus frequency plots reveal non-Debye relaxation peaks. The observed decrease in both the impedance and permittivity with the increase in film thickness is attributed to the grain size effect. The frequency dependent conductivity plots show three regions of conduction processes, i.e. low-frequency region due to DC conduction, mid-frequency region due to translational hopping motion and high-frequency region due to localized hopping and/or reorientational motion.     

Dielectric property of CaCu3Ti4O12 thin film grown on Nb-doped SrTiO3(100) single crystal

Thin film of CaCu₃Ti₄O₁₂ (CCTO) has been deposited on Nb-doped SrTiO₃(100) single crystal using pulsed laser deposition. The dielectric constant and AC conductivity of CCTO film in the metal–insulator–metal capacitor configuration over a wide temperature (80 to 500 K) and frequency (100 Hz to 1 MHz) range have been measured. The small dielectric dispersion with frequency observed in the lower temperature region (<300 K) indicates the presence of small defects in the deposited CCTO thin film. The frequency-dependent AC conductivity at lower temperature indicates the hopping conduction. The dielectric dispersion data has been analyzed in the light of both conductivity relaxation and Debye type relaxation with a distribution of relaxation times. Origin of dielectric dispersion is attributed to the distribution of barrier heights such that some charge carriers are confined between long-range potential wells associated with defects and give rise to dipolar polarization, while those carriers which do not encounter long-range potential well give rise to DC conductivity.     

钇掺杂钨酸铅晶体中的极化子和导纳谱

在室温至160 ℃范围内测量了掺钇钨酸铅(PWO∶Y)晶体的直流电导率,证明此时的载流子为极化子.观察到极化子由能带导电到跳跃导电转变引起的电导率极小.在此温区的交流导纳分析给出的交流电导率比直流电导率大三个数量级,说明此时的交流电导率主要是复介电常数的贡献.当样品的电导率和介电常数均随频率而变化时,从交流测量只能得到样品的总的导纳谱，而不能将其中的电导谱和介电谱分开. 关键词： 钨酸铅 电导谱 介电谱 导纳谱 极化子     

Electronic transport mechanisms in tetraphenyleprophyrin thin films

Thermally-evaporated thin films of tetraphenylporphyrin, TPP, with thickness range from (175 to 735) nm had been prepared. Annealing temperatures ranging from (273–473) K do not influence the amorphous structure of these films. The influence of environmental conditions: film thickness, temperature and frequency on the electrical properties of TPP thin films had been reported. It was found that dc conductivity increases with increasing temperature and film thickness. The extrinsic conduction mechanism is operating in temperature range of (293–380) K with activation energy of 0.13 eV. The intrinsic one is in temperatures >380 K via phonon assisted hopping of small polaron with activation energy of 0.855 eV. The ac electrical conductivity and dielectric relaxation in the temperature range (293–473) K and in frequency range (0.1–100) kHz had been also studied. It had been shown that theoretical curves generated from correlated barrier hopping (CBH) model gives the best fitting with experimental results. Analysis of these results proved that conduction occurs at low temperatures (300–370) K by phonon assisted hopping between localized states and it is performed by single polaron hopping process at higher temperatures. The temperature and frequency dependence of both the real and imaginary parts of dielectric constant had been reported.     

Experimental and computational studies of naphthyridine derivatives as corrosion inhibitor for N80 steel in 15% hydrochloric acid

The inhibition effect of three naphthyridine derivatives namely 2-amino-4-(4-methoxyphenyl)-1,8-naphthyridine-3-carbonitrile (ANC-1), 2-amino-4-(4-methylphenyl)-1,8-naphthyridine-3-carbonitrile (ANC-2) and 2-amino-4-(3-nitrophenyl)-1,8-naphthyridine-3-carbonitrile (ANC-3) as corrosion inhibitors for N80 steel in 15% HCl by using gravimetric, electrochemical techniques (EIS and potentiodynamic polarization), SEM, EDX and quantum chemical calculation. The order of inhibition efficiency is ANC-1>ANC-2>ANC-3. Potentiodynamic polarization reveals that these inhibitors are mixed type with predominant cathodic control. Studied inhibitors obey the Langmuir adsorption isotherm. The quantum calculation is in good agreement with experimental results.     

A mild and efficient method for the synthesis of a new class of furo[3,2-c]chromenes in aqueous media

An efficient synthesis of 2-hydroxy-3-[2-oxo-2-phenylethylidene]-2-phenyl-2, 3-dihydro-4 H-furo[3, 2-c]chromene-4(2H)-one is described. This involves the reaction between dibenzoylacetylene and 4-hydroxycoumarine in the presence of NaH (10 mol %) in nearly quantitative yield. Treatment of this heterocyclic system with trimethyl chlorosilane in CHCl₃ leads quantitatively to 4-oxo-3-[2-oxo-2-phenylethylidene]-2-phenyl-3H, 4H-furo[3,2-c]chromene-1-ium chloride. Direct addition of nucleophiles, such as alcohols, amines or trialkyl phosphites to this salt in water as the solvent produces functionalized 2-phenyl-4H-furo[3,2-c] chromen derivatives in excellent yields.     

Electrical and dielectric characterization of Au/ZnO/n-Si device depending frequency and voltage

Au/Zn O/n-type Si device is obtained using atomic layer deposition(ALD) for Zn O layer, and some main electrical parameters are investigated, such as surface/interface state(Nss), barrier height(Φb), series resistance(Rs), donor concentration(Nd), and dielectric characterization depending on frequency or voltage. These parameters are acquired by use of impedance spectroscopy measurements at frequencies ranging from 10 k Hz to 1 MHz and the direct current(DC) bias voltages in a range from-2 V to +2 V at room temperature are used. The main electrical parameters and dielectric parameters,such as dielectric constant(ε"), dielectric loss(ε"), loss tangent(tan δ), the real and imaginary parts of electric modulus(M and M), and alternating current(AC) electrical conductivity(σ) are affected by changing voltage and frequency. The characterizations show that some main electrical parameters usually decrease with increasing frequency because charge carriers at surface states have not enough time to fallow an external AC signal at high frequencies, and all dielectric parameters strongly depend on the voltage and frequency especially in the depletion and accumulation regions. Consequently, it can be concluded that interfacial polarization and interface charges can easily follow AC signal at low frequencies.     

Electrical properties and conduction mechanism in the sodium nickel diphosphate

The Na_3.6Ni_2.2(P₂O₇)₂ compound was obtained by the conventional solid-state reaction. The sample was characterized by X-ray powder diffraction and vibrational and impedance spectroscopy. The AC electrical conductivity and the dielectric relaxation properties of this compound have been investigated by means of impedance spectroscopy measurements over a wide range of frequencies and temperatures, 209 kHz–1 MHz and 564–729 K, respectively. Dielectric data were analyzed using complex electrical modulus M* at various temperatures. The peak positions ω _m of M″ spectra shift toward higher frequencies with increase in temperature. The AC conductivity data fulfill the power law. Application of the correlated barrier hopping model revealed that the ionic conduction takes place by single-polaron and bipolaron hopping processes.     

Electrical transport properties of consolidated ZnSe quantum dots at and above room temperature

Here we report a comprehensive study on the prevailing conduction mechanism and dielectric relaxation behavior of consolidated Zinc Selenide quantum dots in the frequency range of 1 kHz ≤ f ≤ 1.5 MHz and in the temperature range of 298K ≤ T ≤ 573 K. The ac conductivity increases either with increase in temperature or with increase in frequency, which is explained by the Jonscher Power law. At higher temperatures, correlated barrier hopping is found to be the prevalent charge transport mechanism with a maximum barrier height of 0.88 eV. The dielectric constant of the sample is found to exhibit weak temperature dependence. DC conductivity study reveals the semiconducting nature of the sample and it is discussed in the light of polaron hopping conduction. From the impedance spectroscopic study, role of the grains and grain boundaries in the overall electrical transport properties have been elucidated by considering an electrical equivalent circuit (composed of resistances and constant phase elements). Electric modulus study reveals non-Debye responses of the sample in the experimental range.