The effects of preparation temperature on the main electrical parameters of Al/TiO<Subscript>2</Subscript>/p-Si (MIS) structures by using sol–gel method

In this study, the forward bias current–voltage (I–V) and capacitance–voltage (C–V) characteristics of the Al/TiO₂/p-Si (MIS) structures derived using the sol–gel method have been investigated and compared at various preparation temperatures. Experimental results show that the preparation temperatures strongly affect the electrical characteristics, such as ideality factor (n), zero-bias barrier height (), series resistance (R _s ) and interface states (N _ss ). The MIS structures show non-ideal behavior of I–V characteristics with an n varying between 2.17 and 4.61. We have found that the and R _s increase as the n decrease with increasing preparation temperature. The energy distribution profile of N _ss of the Al/TiO₂/p-Si (MIS) structures was obtained from the forward bias I–V characteristics by taking into account both the bias dependence of the effective barrier height () and R _s for various preparation temperatures. The values of N _ss increase from the midgap towards the top of valance band for various preparation temperatures.     

Synthesis, characterization and some properties of novel bis(pentafluorophenyl)methoxyl substituted metal free and metallophthalocyanines

The preparation of some new tetrakis[bis(pentafluorophenyl)methoxyl] substituted metal free and metallophthalocyanine (MPcs) complexes were achieved by the tetramerization of 4-[bis(pentafluorophenyl)methoxy]phthalonitrile with Li metal in pentan-1-ol or metal [Co(II) or Zn(II)] acetates in DMAE, respectively. The structures of the target compounds were confirmed by elemental analysis, IR, UV–vis, ¹H NMR, ¹⁹F NMR and mass spectroscopic methods. MPcs are soluble only in strong and medium polar solvents while the metal free one is soluble in weakly, medium and strong polar solvents. The temperature and frequency dependence of the electrical conductivities were studied on spin coated films of the compounds using dc and impedance spectroscopy techniques in the frequency range from 40 to 10⁵ Hz and within the temperature range from 290 to 440 K. The temperature dependence of the exponent s and conductivity, σ_ac, were completely in agreement with the prediction of the hopping model. The redox properties of the complexes were determined by cyclic voltammetry. The nature of the redox processes was also confirmed using spectroelectrochemical measurements.     

Synthesis,characterization, and electrochemical and electrical properties of novel mononuclear and binuclear ball-type Zn(II) and Co(II) phthalocyanines substituted with 1a,8b-dihydronaphtho[b]naphthofuro-[3,2-d]furan-7,10-diyl

New mononuclear phthalocyanines [Zn(II) 4 and Co(II) 6] and ball-type bisphthalocyanines [Zn(II) 5 and Co(II) 7] have been synthesized from the corresponding compound 3, which can be obtained from the reaction of 4-nitrophthalonitrile 1 with 1a,8b-dihydronaphtho[b]naphthofuro[3,2-d]furan-7,10-diol 2. The novel compounds have been characterized by elemental analysis, UV/Vis, IR, ¹H NMR and MASS spectroscopy. The electrochemical measurements show the formation of various mixed-valence oxidized and reduced species, due to intramolecular interactions between the two phthalocyanine units in the ball-type binuclear metallophthalocyanines. Detailed studies of the effect of temperature on the electronic properties of the films were investigated by dc conductivity and impedance spectroscopy techniques at temperatures between 290 K and 460 K. Thermally activated conductivity dependence on temperature was observed from the dc measurements. The ac results give a power law behavior in which the frequency exponent decreases with temperature. It was observed that the impedance spectra consist of a curved line at low temperature. These curved lines transform into a full semicircle with increasing temperature.     

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.     

Synthesis,characterization, and electrochemical,spectroelectrochemical and electrical measurements of novel ball-type four 1,1′-methylenedinaphthalen-2-ol bridged metal-free,zinc(II) and cobalt(II), and metal-free clamshell phthalocyanines

The new ball-type bisphthalocyanines [metal-free 6, Zn(II) 7 and Co(II) 8] were synthesized from the corresponding 4,4′-[1,1′-methylenebis(naphthalene-2,1-diyl)]bis(oxy)di-phthalonitrile 4, which can be obtained from the reaction of 4-nitrophthalonitrile (2) with 1,1′-methylenedinaphthalen-2-ol 3. A novel clamshell type bisphthalocyanine 5 was synthesized from compound 4 and 4,5-bis(hexylthio)phthalonitrile 1. The novel compounds have been characterized by elemental analysis, UV/Vis, IR, ¹H NMR and MALDI-TOF Mass spectroscopies. The electrochemical and spectroelectrochemical measurements showed the formation of various mixed-valence oxidation and reduction species, due to the strong intramolecular interactions between the two phthalocyanine rings, especially in the ball-type phthalocyanines. The conduction properties of the compounds have been examined by d.c. and impedance spectroscopy measurements as function of temperature and frequency. D.c. conductivity, measured between 290 and 480 K, is thermally activated with the activation energy ranging between 0.62 and 0.84 eV. The a.c. results gave a power law behaviour, σ_a.c. = A(T)ω^s, in which the frequency exponent s decreases with temperature for 6, 7 and 8. The bulk resistance of the samples was derived from complex impedance spectra. It was found that the bulk resistance shows a typical negative temperature coefficient of resistance, decreasing with a rise in temperature, like that of a semiconductor.     

The effect of gamma irradiation on electrical and dielectric properties of organic-based Schottky barrier diodes (SBDs) at room temperature

The effect of ⁶⁰Co (γ-ray) irradiation on the electrical and dielectric properties of Au/Polyvinyl Alcohol (Ni,Zn-doped)/n-Si Schottky barrier diodes (SBDs) has been investigated by using capacitance-voltage (C-V) and conductance-voltage (G/ω-V) measurements at room temperature and 1 MHz. The real capacitance and conductance values were obtained by eliminating series resistance (R_s) effect in the measured capacitance (C_m) and conductance (G_m) values through correction. The experimental values of the dielectric constant (ε′), dielectric loss (ε″), loss tangent (tanδ), ac electrical conductivity (σ_ac) and the real (M′) and imaginary (M″) parts of the electrical modulus were found to be strong functions of radiation and applied bias voltage, especially in the depletion and accumulation regions. In addition, the density distribution of interface states (N_ss) profile was obtained using the high-low frequency capacitance (C_HF-C_LF) method for before and after irradiation. The N_ss-V plots give two distinct peaks for both cases, namely before radiation and after radiation, and those peaks correspond to two different localized interface states regions at M/S interface. The changes in the dielectric properties in the depletion and accumulation regions stem especially from the restructuring and reordering of the charges at interface states and surface polarization whereas those in the accumulation region are caused by series resistance effect.     

Synthesis, interface (Au/M2Pc2/p-Si), electrochemical and electrocatalytic properties of novel ball-type phthalocyanines

The phthalodinitrile derivative (3) was prepared by the reaction of 4,4'-(octahydro-4,7-methano-5H-inden-5-ylidene)bisphenol (1) and 4-nitrophthalonitrile (2) with dry DMF as the solvent in the presence of the base K(2)CO(3) by the method of nucleophilic substitution of an activated nitro group in an aromatic ring. The template reaction of 3 with the corresponding metal salts gave the novel bi-nuclear ball-type metallophthalocyanines, MPcs {M = Co (4), Cu (5), Zn (6)}. Newly synthesized compounds were characterized by elemental analysis, UV-vis, FT-IR (ATR), MALDI-TOF mass and (1)H-NMR spectroscopy techniques. The electronic spectra exhibit an intense π→π* transition of characteristic Q and B bands of the Pc core. The dielectric properties and interface between the spin coated films of 4-6 and a p-type silicon substrate have been studied by fabricating metal-insulator-semiconductor capacitors. The results indicated that the frequency dependence of the dielectric permittivity, ε'(ω), exhibits non-Debye type relaxation for all the temperatures investigated. The ac conductivity results indicated that the conduction mechanism can be explained by a hopping model at low temperatures (<430 K) and a free band conduction mechanism at high temperatures (≥430 K). The density of interface state calculations on these novel compounds showed that the combination of Au/4/p-Si is a promising structure with a high dielectric constant and a low interface trap density suitable for metal-oxide-semiconductor devices. The electrochemical properties of the Pc complexes were examined by cyclic voltammetry, differential voltammetry and controlled potential coulometry on platinum in non-aqueous media. The complexes showed ring-based and/or metal-based mixed-valence behaviours as a result of the remarkable interaction between the two Pc rings and/or metal centres. The mixed-valence splitting values for the complexes suggested that the mixed valence species are considerably stable. The Vulcan XC-72(VC)/Nafion(Nf)/4 modified glassy carbon electrode showed much a higher catalytic performance towards oxygen reduction than those of VC/Nf/5 and VC/Nf/6 modified ones.     

Synthesis and electrical properties of novel supramolecular octa-phthalocyaninato-dicobalt(II)-hexazinc(II) and dicobalt(II)-dimeric-phthalocyanine with six ferrocenylimin pendant groups

In this study supramolecular octakis phthalocyaninato-diCo(II)hexakis-Zn(II) has been synthesized in two steps. Starting with tetracyanodibenzo(1,4,7,10-tetrathia-(12-crown)) (1) and 4-nitro-1,2-dicyanobenzene (2), nitro-substituted dimeric phthalocyanine (3) was synthesized. Compound 3 reacted with unsymmetric Zn(II) phthalocyanine (4) to furnish a supramolecular assemble of a Co(II) dimer with six Zn(II) phthalocyanines through azo bridges (5). Co(II) dimeric phthalocyanine with six ferrocenyl groups (7) was obtained by the condensation of 6 with ferrocenylaldehyde. Compounds 3, 5, 6 and 7 were characterized by elemental analysis, ICP-MS, IR, UV–Vis and ¹H NMR spectroscopy. The electronic properties of a thin film of the compounds were investigated by impedance spectroscopy and d.c. conductivity measurements as a function of temperature. The a.c. conductivity is found to vary with frequency, ω, as ω^s with index s  1, suggesting a hopping conduction mechanism for 3 and 6. Whereas a frequency independent conductivity was observed for 5. It was found that reducing the nitro group to amines and azo coupling by the asymmetric nitro groups increases the electrical conductivity. The higher conductivity of 5 can be attributed to the increase in the mobility of charge carriers due to overlap of the π electron systems along the stacking direction of the molecules.