I. Thurzo

Introduction to a kinetics-sensitive double-step voltcoulometry

As an alternative to the numerous state-of-the-art versions of voltammetry, a kinetics-sensitive double-step voltcoulometry is introduced. The transient current flowing in response to a potential step across the electrochemical cell is integrated and simultaneously processed by a deliberately selected time-domain “cascade” filter, while scanning the applied potential. In contrast to the widely used sampling scheme of sampling the transient current just before and in the end of the excitation pulse, three values of the transient charge are sampled in the interval between subsequent excitation pulses. Each measuring period is preceded by a single measurement of the steady-state current with the excitation pulse being switched off. The latter measurement makes it possible to actively compensate the parasitic charge across the feedback capacitor of the integrator, due to the steady-state current, while storing the steady-state current data. The goal of introducing the third sampling event resides in discrimin...

Dielectric properties of ceria and yttria-stabilized zirconia thin films grown on silicon substrates

Abstract The dielectric permittivities of fcc yttria-stabilized zirconia (YSZ) and ceria (CeO 2 ) thin films as-grown on n-doped Si(100) substrates by electron beam evaporation at 200°C in the metal–insulator–semiconductor (MIS) configuration have been investigated. Two independent methods were used for this purpose, the high frequency limiting capacitance C P and feedback charge C – V plots. The values obtained are 16.8 (YSZ) and 2.8 (CeO 2 ) in the case of C P and 18.3 (YSZ) and 3.4 (CeO 2 ) from the C – V measurements. The hysteresis of C – V curves observed for both Al/YSZ and CeO 2 /Si/Au structures can be ascribed to the slow redistribution of negative mobile charges (oxygen ions O 2− ) present inside the YSZ and CeO 2 films.

Dielectric-polarization phenomena in glasses of the system Ge-S

Abstract The experimental study of electrical transport in GeSx glasses (1.3 ⩽ x ⩽ 1.5) was performed by means of a thermo-stimulated depolarization technique (TSD), charging- and discharging-current and dc-conductivity measurements. It is shown that the results obtained point to non-electronic dielectric polarization phenomena. The nature of the mobile ions is briefly discussed.

Characterization of ceria/yttria stabilized zirconia grown on silicon substrate

Abstract Analyses of phase composition and electrical characterization of double-layer CeO 2 /yttria stabilized zirconia (YSZ) and single-layer CeO 2 , YSZ dielectrics deposited onto Si(100) substrate at 473xa0K by electron beam evaporation as well as characterization of the quality of interfaces between the oxide layers and silicon substrates were performed. The structure of all investigated oxide layers was found to be of the fcc fluorite type. A layer of amorphous SiO 2 was formed at the interface between the oxide layers and the Si substrate. The double-layer CeO 2 /YSZ is a mixed ionic–electronic conductor. The electrical conductivity of investigated oxide layers and the average grain size are changed during a post-deposition thermal treatment. The temperature dependence of the activation energy of electrical conductivity is connected with the different impurity states in the oxide layers. With respect to the lowest density of defects assessed from deep-level transient spectroscopy (DLTS) measurements, the CeO 2 /Si interface seems to be an optimum compared to the other oxide layer configurations.

New experimental facts on the Staebler–Wronski effect

Abstract The affect of light soaking on the gap-state distribution of undoped hydrogenated amorphous silicon (a-Si:H) has been investigated using the charge deep level transient spectroscopy (DLTS) technique. Measured spectra directly show the change in all the gap states (Dh, Dz, De) due to the prolonged illumination with low intensity white light. Results are tentatively interpreted evoking the pecularities of hydrogen diffusion in silicon.

Structural and electrical properties of double-layer ceria/yttria stabilized zirconia deposited on silicon substrate

Abstract Analyses of the phase composition and electrical characterization of double-layer CeO 2 /YSZ and single-layer CeO 2 , YSZ dielectrics grown on a Si (100) substrate at 200°C by electron beam evaporation as well as of the quality of interfaces between the oxide layers and silicon substrates were performed. The structure of all investigated oxide layers was found to be of the fcc fluorite type. The electrical conductivity of the investigated oxide layers and the average grain size change due to the post-deposition thermal treatment. The temperature dependence of the activation energy of the electrical conductivity is associated with different impurity phases in the oxide layers. Due to the lowest density of defects assessed from deep-level-transient-spectroscopy (DLTS) measurements, the CeO 2 /Si interface seems to be an optimum compared to the other oxide layer configurations. The dielectric constants e r (YSZ)=18.3 and e r (CeO 2 )=3.4 were estimated from the accumulation capacitances of the C – V curves.

Exemplifying performance of kinetics-sensitive double-step voltcoulometry : redox reactions of protons in unsupported acids

Abstract An alternative electroanalytical technique to the widely used differential pulse voltammetry (DPV) is presented in connection with monitoring proton redox reactions in strong acids (HCl, H2SO4, HNO3) and in l -ascorbic acid (AA) in the absence of any supporting electrolyte. Contrary to the DPV method, the current flowing through the working electrode in response to a double-step change of the applied potential is first integrated and subsequently processed by a three-channel correlator. Expressing the faradaic transient charge as Q(t)∝tβ, the ratio Rβ=[Q(t1)−2Q(5t1)+Q(9t1)/(Ilimt1), where t1 is the delay of the first sampling event with respect to the trailing edge of the potential double step and Ilim is the limiting current of the corresponding steady-state voltammetric wave, it is calculated and then compared to the values found experimentally. The sensitivity to the kinetics represented as dRβ/dβ has an optimum around β=0.5, a value consistent with the Cottrell equation. The experimental data point to a crucial role of CO2 (H2CO3) dissolved in the acid solution, envisaged as the reversed sign of the measured charge. After deaerating the solution by argon the sign became positive, nevertheless the experimental Rβ values were systematically higher than the predicted ones. The reaction of the protons of AA at negative potentials seems to be of the EC type when proceeding from negative to more positive potentials. Moreover, there is a dominant voltammetric wave of AA at positive potentials coming from an irreversible reaction, accompanied by a relatively weak peak of the correlated charge.

Small-signal deep level transient spectroscopy on hydrogenated amorphous silicon based metal/insulator/semiconductor structures

The high-temperature tail of small-signal deep level transient spectroscopy (DLTS) spectra of hydrogenated amorphous silicon (a-Si:H) based metal/insulator/semiconductor structures has been analyzed in terms of oxidation of some negatively charged mobile hydrogen species at the Al/a-Si:H interface, the excitation pulses of an amplitude of 0.1 V being applied repetitively between the top Al and the bottom (gate) electrodes. The concentration of the mobile hydrogen in the a-Si:H layer has been estimated to an amount up to ≈2×1020u2009cm−3, taking the earlier published data on the diffusion coefficient. Having chosen an appropriate polarity of the excitation pulses, one could observe a DLTS peak moving with applied bias on the temperature axis. The latter is pointing to an energy distribution of states at the Al/a-Si:H interface. The interface state density increases with increasing energy depth of the states. At the ultimate experimentally observable energy of E≈0.95u2009eV below the electron mobility edge Ec a cor...

On the mechanism of dielectric relaxation in vanadium phosphate glasses

Abstract The mechanism of dielectric relaxation in xV2O5−(100−x)P2O5 glasses (x=50−70) has been investigated using the stimulated dielectric relaxation currents (SDRC) technique. The dielectric relaxation in metal-glass-metal systems is found to be non-linear with regard to voltage bias. Schottky barrier formation at the metal-glass interface, rather than a conventional Debye-type relaxation, is suggested to account for the observed behavior. The density of states N(EF) as determined from the SDRC is in excellent agreement with the density of paramagnetic states found by the EPR technique.

Comments on dielectric properties of semiconducting iron phosphate glasses

Abstract The thermally stimulated depolarization (TSD) method is used to investigate dielectric behavior in FeOxue5f8P2O5 glasses with artio α = Fe3+/(Fe3+ + Fe2+) ranging from 0.11 to 0.88. Apart from a space charge polarization a Debye-type dielectric relaxation is found in each of the compositions investigated. The permitivity dispersion ϵS - ϵ∞ related to the latter polarization decreases monotonically with increasing α. Such a behavior is incompatible with either of the known theoretical approaches based primarily on two-site hopping models. In view of this finding the dielectric relaxation is assigned to a Maxwell-Wagner effect resulting from microscopical heterogeneities rather than to the hopping of electrons between ferrous and ferric sites.