Dielectric and ac conduction properties of zinc phthalocyanine (ZnPc) thin films
ABSTRACT The dielectric responses of zinc phthalocyanine (ZnPc) thin films, deposited using the vacuum evaporation technique, were studied as functions of frequency and temperature. The conductivity of the deposited films decreases with increase in temperature. The dielectric studies clearly indicated that the Debye type of polarization exists in these films. The relaxation phenomena have been confirmed from the Cole-Cole plot. The relaxation times have been evaluated from the plot and were found to be (τa) 0.0137 and 0.0106 s at 303 and 403 K , respectively. The prevailing conduction mechanism in ZnPc films, under an ac field, was found to be electronic hopping. The activation energy was evaluated from the Arrhenius plot and was found to be 1.28 eV . Based on the structure, and with the help of quantum mechanics calculations, the electronic structure and behavior that upheld our experimental results were identified.
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ABSTRACT: The adsorption geometry and electronic properties of a zinc-phthalocyanine molecule on a Cu(111) substrate are studied by density functional theory. In agreement with experiment, we find remarkable distortions of the molecule, mainly as the central Zn atom tends towards the substrate to minimize the Zn-Cu distance. As a consequence, the Zn-N chemical bonding and energy levels of the molecule are significantly modified. However, charge transfer induces metallic states on the molecule and therefore is more important for the ZnPc/Cu(111) system than the structural distortions.Scientific Reports 04/2013; 3:1705. · 5.08 Impact Factor
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ABSTRACT: The dielectric function of some phthalocyanine compounds (ZnPc, H2Pc, CuPc, and FePc) were investigated by analyzing the measured capacitance and loss tangent data. The real part of the dielectric constant, ε1, varies strongly with frequency and temperature. The frequency dependence was expressed as: ε1 = Aωn, where the index, n, assumes negative values (n < 0). In addition, the imaginary part of the dielectric constant, ε2, is also frequency and temperature dependent. Data analysis confirmed that ε2 = Bωm with values of m less than zero. At low frequencies and all temperatures, a strong dependence is observed, while at higher frequencies, a moderate dependence is obvious especially for the Au-electrode sample. Qualitatively, the type of electrode material had little effect on the behavior of the dielectric constant but did affect its value.Analysis of the AC conductivity dependence on frequency at different temperatures indicated that the correlated barrier hopping (CBH) model is the most suitable mechanism for the AC conduction behavior. Maximum barrier height, W, has been estimated for ZnPc with different electrode materials (Au and Al), and had values between 0.10 and 0.9 eV For both electrode types, the maximum barrier height has strong frequency dependence at high frequency and low temperatures.The relaxation time, τ, for ZnPc and FePc films increases with decreasing frequency. The activation energy was derived from the slopes of τ versus 1/T curves. At low temperatures, an activation energy value of about 0.01 eV and 0.04 eV was estimated for ZnPc and FePc, respectively. The low values of activation energy suggest that the hopping of charge carriers between localized states is the dominant mechanism.Journal of Semiconductors 01/2012; 33(8).
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ABSTRACT: Nanostructured bismuth sulfide thin films were prepared onto glass substrates with particle size of 21nm by thermal evaporation using readily prepared bismuth sulfide nanocrystallite powder. The X-ray diffraction pattern revealed that bismuth sulfide thin films exhibit orthorhombic structure. The existence of quantum confinement effect was confirmed from the observed band gap energy of 1.86eV. AC and DC electrical conductivity of Al/BiSnc/Al structures was investigated in the frequency range 0.5–100kHz at different temperatures (303–463K) under vacuum. The AC conductivity (σac) is found to be proportional to angular frequency (ωs). The obtained experimental result of the AC conductivity showed that the correlated barrier hopping model is the appropriate mechanism for the electron transport in the nanostructured bismuth sulfide thin films. DC conduction mechanism in these films was studied and possible conduction mechanism in the bismuth sulfide thin films was discussed.Applied Surface Science 01/2011; 257(16):7245-7253. · 2.54 Impact Factor