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We investigate the frequency and temperature dependence of the dielectric conductivity and dielectric constant of Al[sub 2]O[sub 3] thin films having ionic structure and compare the results with those obtained for Se thin films having homopolar structure in the 0.1-100 kHz frequency range and in the 100-400 K temperature range. Our samples have a metal-insulator-metal configuration. Oxide-layer thickness ranges between 50 and 1550 Å for Al[sub 2]O[sub 3] films and 150 and 8500 Å for Se films. The existence of a minimum in the imaginary part of dielectric constant versus frequency curves for each thickness of Al[sub 2]O[sub 3] films leads us to conclude that two types of polarization mechanisms are dominant in different frequency regions, depending on the structure of Al[sub 2]O[sub 3] samples, but that only one mechanism dominates in Se samples, which do not have such minima in the imaginary part of their dielectric constant versus frequency curves. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Pure GaAs and GaAs1−xBix alloys with different Bi ratios (1 %, 2.5 %, 3.5 %) fitted with silver contacts were measured with a dielectric spectroscopy device. Dielectric characterization was performed at room temperature in the frequency range of 0.1 Hz to 1 MHz. GaAs exhibits three relaxation regions corresponding to space-charge, dipolar and ionic polarizations in sequence with increasing frequency while GaAs1−xBix samples show only a broad dipolar polarization in the same frequency range. This result proves the filling of the lattice with Bi through making a new bonding reducing the influence of ionic polarization. This finding supports the previous results concerning optical properties of GaAs1−xBix, presented in the literature. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract: The dielectric constant and the dielectric loss of tantalum pentoxide (Ta2O5) thin films, produced by sol–gel spin-coated process on Corning glass substrates, have been investigated in the frequency range of 20–105Hz and the temperature range of 183–403K, using ohmic Al electrodes. The frequency and temperature dependence of relaxation time has also been determined. The capacitance and loss factor were found to decrease with increasing frequency and increase with increasing temperature. The activation energy values were evaluated and a good agreement between the activation energy values obtained from capacitance and dielectric loss factor measurements were observed. [Copyright &y& Elsevier]

Se films were prepared by thermal evaporation technique in thickness range 150–8500 A˚. X-ray diffraction measurements showed that Se films are in the amorphous state. The ac conductivity and dielectric properties of the amorphous Se films have been investigated in the frequency range 100–100 KHz and 100–400 K temperature range. The ac conductivity σac(ω) is found to be proportional to ωs where s<1. The temperature dependence of both ac conductivity and the parameter s is reasonably well interpreted by the correlated barrier (CBH) model. The dc conductivity at the room temperature was also studied in the same thickness range. It was concluded that the same mechanism of carrier motion might be dominant in both ac polarization and dc conduction. This carrier transport mechanism might be electronic. [Copyright &y& Elsevier]

Abstract: The dielectric constant and the dielectric loss of TlSbSe2 thin films, obtained via thermal evaporation of TlSbSe2 crystals grown by Stockber-Bridgman technique, have been measured using ohmic Al electrodes in the frequency range 0.2–100KHz and within the temperature interval 293–353K. The capacitance are found to decrease with increasing frequency and increase with increasing temperature. The activation energy values were evaluated too. A good agreement between the activation energy values obtained from capacitance and dielectric loss factor measurements has been observed. [Copyright &y& Elsevier]

A comparison of structure and dielectric properties of TlSbS thin films, deposited in different thicknesses (400-4100 Å) by thermal evaporation of TlSbS crystals that were grown by the Stockbarger-Bridgman technique and the bulk material properties of TlSbS are presented. Dielectric constant ε and dielectric loss ε 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 TlSbS thin films is ε=1.8-6 and the dielectric loss of TlSbS thin films is ε=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 is calculated from the dielectric measurements. The values of W for TlSbS 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 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 TlSbS. [ABSTRACT FROM AUTHOR]

Bulk TlGaS 2 single crystals were produced by the Bridgman method. TlGaS 2 thin film samples were deposited from bulk crystals by the thermal evaporation technique under a high vacuum. TlGaS 2 thin films were deposited in the 100–750 nm thickness range. Dielectric spectroscopy measurements were operated in the frequency range of 1–105 Hz and temperature range of 273–373 K under the voltage of 1 V (rms). TlGaS 2 thin films have amorphous. Bulk TlGaS 2 has a crystalline structure based on X-Ray diffraction patterns. Three polarization mechanisms were detected from the analysis of Cole-Cole plots. At low frequencies, the effect of interfacial polarization was observed. Toward higher frequencies, two dipolar polarization mechanisms were detected. In comparison to the bulk TlGaS 2 single crystal, the dielectric constant of the thin films has 100–1000 times larger values at frequencies lower than 100 Hz. The thickness limit at which bulk physical properties started has been investigated. The transition thickness between bulk/thin film properties was detected at around 700 nm. The low dielectric constant and the good conductivity around 10−8 S/cm at105 Hz can give opportunities to use these thin films in technological applications. • The interfacial polarization is observed at frequencies lower than 100 Hz. • At higher frequencies, polarization mechanisms having dipolar nature are detected. • At frequencies below 100 Hz, the dielectric constant has 100–1000 times greater values for TlGaS 2 thin films. • The dielectric properties of TlGaS 2 thin films change to bulk dielectric properties with thickness-independent dielectric behavior at 800 nm. • TlGaS 2 thin films are suitable for nano-sized switching and thermoelectric applications. [ABSTRACT FROM AUTHOR]

Abstract: TlSbSe2 samples used for electrical measurements were cleaved from larger crystals grown by using the Bridgman–Stockbarger method. Electrical properties of TlSbSe 2 have been carried out as a function of temperature (203–258K) at different dc electric fields. The dc studies revealed the non-ohmic type of conduction (log I versus log V plot). The field lowering coefficient β is evaluated from log I versus E 1/2 plot. It is found that the dominant conduction mechanism in these samples is Poole–Frenkel type. The activation energies are also calculated at different voltages. It is seen that the activation energy decreases with increase of applied voltage. [Copyright &y& Elsevier]