Plasma discharge power dependent AC conductivity of plasma poly(ethylene oxide) thin films

Plasma polymerized poly(ethylene oxide) thin film samples with thickness of 500 nm were deposited using plasma assisted physical vapour deposition at radio-frequency plasma discharge powers of 0, 2, 5 and 30 W, respectively. For comparison, a conventional poly(ethylene oxide) precursor was also investigated. In order to investigate the effect of the plasma discharge power on the cross-linking density of the plasma poly(ethylene oxide) and poly(ethylene oxide) precursors, structural characterization using differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy was performed. Structural analysis showed that the density of cross-linking increased upon increasing the plasma discharge power. This increase was observed as an increase in the dynamic glass transition temperature during the DSC measurements. In addition to these characterizations, the dielectric response of the thin film plasma poly(ethylene oxide) samples and poly(ethylene oxide) precursors were measured. The dielectric spectroscopy results showed that changes in the cross-linking density changed the alternative current (AC) conductivity. The measured glass transition temperatures obtained using DSC are in accordance with the glass transition temperatures obtained from the temperature-dependent AC conductivity results. It was observed that the temperature-dependent AC conductivity exhibits Arrhenius behaviour. The activation energies obtained for the plasma polymer samples showed an increase from 0.38 eV to 0.5 eV upon increasing the plasma discharge power. The plasma discharge power dependent activation energy results also indicate the fragmentation of long polymer chains into more smaller oligomers and radicals occurred upon increasing the plasma power

Thickness dependence of the dielectric properties of thermally evaporated Sb2Te3 thin films

Sb2Te3 thin films of different thickness (23 - 350 nm) were prepared by thermal evaporation technique. The thickness dependence of the ac conductivity and dielectric properties of the Sb2Te3 films have been investigated in the frequency range 10 Hz- 100 kHz and within the temperature range 293-373K. Both the dielectric constant epsilon(1) and dielectric loss factor epsilon(2) were found to depend on frequency, temperature and film thickness. The frequency and temperature dependence of ac conductivity (sigma(ac)(omega)) has also been determined. The ac conductivity of our samples satisfies the well known ac power law; i.e., sigma(ac)(omega) alpha omega(s) where s<1 and independent of the film thickness. The temperature dependence of ac conductivity and parameter s is reasonably well interpreted by the correlated barrier hopping (CBH) model. The activation energies were evaluated for various thicknesses. The temperature coefficient of the capacitance (TCC) and permitivity (TCP) were determined as a function of the film thickness. The microstructure of the samples were analyzed using X-ray diffraction (XRD). This results are discussed on the base of the differences in their morphologies and thicknesses. The tendency for amorphization of the crystalline phases becomes evident as the film thickness increases

AC CONDUCTIVITY AND DIELECTRIC PROPERTIES OF Al2O3 THIN FILMS

Al2O3 thin films of different thicknesses were prepared onto clean glass substrates using ohmic aluminum electrodes. Their dielectric properties and ac conductivity have been investigated in the frequency range 0.1-100KHz and within the temperature range 100-400K. Oxide-layer thicknesses of the films range between 50-1550 angstrom. The dielectric constant epsilon(1). was found to decrease with increasing frequency and increase with temperature in the given intervals. Only ac losses have been investigated due to the smallness of dc losses. The ac conductivity satisfies the power law omega(s). Here the s parameter is in the vicinity of 0.8 and it decreases with increasing temperature. This behaviour of s can comply with CBH model. The activation energy values calculated from ac conductivity and dielectric loss factor measurements are in good agreement with each other. The obtained values agree with the model of hopping of charge carriers by thermal activation between two sites having a coulombic potential well. Film thickness dependence of Temperature Coefficient of Capacitance (TCC) and Temperature Coefficient of Permittivity (TCP) of the Al2O3 thin films were also determined

Structure and dielectric behavior of TlSbS2

A comparison of structure and dielectric properties of TlSbS2 thin films, deposited in different thicknesses (400-4100 ) 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 epsilon (1) and dielectric loss epsilon (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 epsilon (1)=1.8-6 and the dielectric loss of TlSbS2 thin films is epsilon (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 omega (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

Dielectric properties and ac conductivity of TlSbTe2 thin films

We report on dielectric properties and ac conductivity of the TlSbTe2 thin films grown by thermal evaporation on glass substrates at temperature range 293-373 K and measured over frequency range between 10 Hz and 100 kHz. The thicknesses of the films were between 200 angstrom and 4000 angstrom. It was found that dielectric constant (epsilon(1))of the TlSbTe2 films changes between 39 and 740 and dielectric loss (epsilon(2)) between 51-12,000 at 1 kHz and 293 K. The dielectric constant and dielectric loss were found to decrease with increasing frequency and to increase with increasing temperature. The dielectric constant exhibits bulk characteristics as the thickness exceeds 2000 angstrom. The ac conductivity follows sigma(omega)alpha omega(s) relation at frequencies higher than 1 kHz, and the dominant conduction mechanism is found to obey the Correlated Barrier Hopping (CBH) mechanism. At frequencies lower than 1 kHz, the electrical conduction is found to be in accordance with dc conduction mechanism. Analyzing the ac conductivity results, we show that as temperature increases, density of states near fermi level also increses from 1019 to 1021 cm(-3). Using frequency dependence of the dielectric constant, the maximum barrier height (W-m), its temperature and thickness dependences are determined. The values for these parameters seem to agree with the theory of classical hopping of charge carriers over a potential barrier. XRD analysis reveal that crystal structure of bulk TlSbTe2 is rhombohedral, whereas TlSbTe2 thin film is found to be amorphous structure. Morever, the temperature coefficients of capacitance (TCC) and permittivity (TCP) were investigated for thin films of TlSbTe2. (C) 2015 Elsevier Ltd. All rights reserved

Dielectric properties of TlInSe2 ternary compound

The dielectric properties of TlInSe2 grown by direct fusion of their constituent elements were studied in the frequency range of 30 KHz-20 MHz, temperature range of 173-373 K. The dielectric constant and dielectric loss of TlInSe2 were calculated by measuring capacitance (C) and dielectric loss factor (tan d). Both of them were found to decrease with increasing frequency and increase with increasing temperature. This behavior can be explained with two polarization mechanisms in the investigated frequency and temperature range. The relaxation times of these polarization mechanisms were obtained from Cole-Cole fits. At lower frequencies the relaxation time is 10(-6) while it was 10(-8) at the higher frequencies. The maximum barrier height (Wm) was estimated from the dielectric loss measurements. The value of W-m was obtained as 0.1 eV. It was found to increase with increasing temperature