Frequency dependence alternating currents

The IV measurements on molecules and monolayers have been carried out almost exclusively using direct current (DC) frequency-dependent alternating current (AC) impedance measurements have rarely been performed, even though a rich spectroscopy may reveal itself, if the IV measurements were followed as a function of frequency v. 

Eckhard, K., T. Erichsen, M. Stratmann, and W. Schuhmann, Frequency-dependent alternating-current scanning electrochemical microscopy (4D AC-SECM) for local visualisation of corrosion sites. Chemistry—A European Journal, 14, 2008, 3968. 

Figure 5.7 Dependencies of Cj on the cathodic current density i at E = O.OV and different angular frequencies of alternating current indicated at the respective lines.

A quadrupole operates by placing both a direct current (DC) field and a time-dependent alternating current (AC) of radio frequency on opposite pairs of the fonr rods. By selecting the optimum AC/DC ratio on each pair of rods, ions of a selected mass... 

There is an important practical distinction between electronic and dipole polarisation whereas the former involves only movement of electrons the latter entails movement of part of or even the whole of the molecule. Molecular movements take a finite time and complete orientation as induced by an alternating current may or may not be possible depending on the frequency of the change of direction of the electric field. Thus at zero frequency the dielectric constant will be at a maximum and this will remain approximately constant until the dipole orientation time is of the same order as the reciprocal of the frequency. Dipole movement will now be limited and the dipole polarisation effect and the dielectric constant will be reduced. As the frequency further increases, the dipole polarisation effect will tend to zero and the dielectric constant will tend to be dependent only on the electronic polarisation Figure 6.3). Where there are two dipole species differing in ease of orientation there will be two points of inflection in the dielectric constant-frequency curve. 

Noise is characterized by the time dependence of noise amplitude A. The measured value of A (the instantaneous value of potential or current) depends to some extent on the time resolution of the measuring device (its frequency bandwidth A/). Since noise always is a signal of alternating sign, its intensity is characterized in terms of the mean square of amplitude, A, over the frequency range A/, and is called (somewhat unfortunately) noise power. The Fourier transform of the experimental time dependence of noise intensity leads to the frequency dependence of noise intensity. In the literature these curves became known as PSD (power spectral density) plots. 

Six [Ln(Pc)2] complexes with heavy lanthanide ions (Ln = Tb, Dy, Ho, Er, Tm or Yb) were investigated by the measurements of alternating current (AC) magnetic susceptibility [18]. Out of the six compounds, [TbPc2] and [DyPc2] were found to show temperature and frequency dependence on AC magnetic susceptibility similar to that observed for the transition-metal SMMs, while the rest did not. Their SMM behaviour have been observed either in bulk, in dilute solid solutions... 

What Is Impedance Spectroscopy The words impedance spectroscopy imply the dependence of impedance on a wavelength and therefore on frequency. The frequency here is not that of an incident light beam, but of an alternative current applied to a cell, and then the question is What is impedance ... 

Equation (7.116) indicates that the charge-potential curves for reversible processes are only dependent on the square wave amplitude Sw and are independent of the frequency / = 1 jh and the staircase amplitude AEs. As a consequence, they are superimposable on those obtained at any differential electrochemical technique, such as DSCVC, provided that the differences between the successive potential pulses coincide (AE = 2 sw)- Moreover, when this difference is much less than RT/F (i.e., less than 25 mV at T = 198 K), the responses obtained in Cyclic Voltammetry (CV), Alternating Current Voltammetry, Potentiometric Stripping Analysis (PSA) and also in any Reciprocal Derivative Chronopotentiometry (RDCP) fulfill [5, 74, 75] ... 

Of more importance is the loss factor, tan 8, denoting the fraction of the transmitted alternating current lost by dissipation in the material. Here large differences occur between polymers, as indicated in Figure 8.10. It appears that polymers with the highest specific resistance also show the lowest dielectric losses. It should be remarked, that the values given are very schematical the losses are strongly dependent on frequency and temperature. 

The electrical properties of polyelectrolyte complexes are more closely related to those of biologically produced solids. The extremely high relative dielectric constants at low frequencies and the dispersion properties of salt-containing polyelectrolyte complexes have not been reported for other synthetic polymers. Neutral polyelectrolyte complexes immersed in dilute salt solution undergo marked changes in alternating current capacitance and resistance upon small variations in the electrolyte concentration. In addition, their frequency-dependence is governed by the nature of the microions. As shown in... 

Immittance — In alternating current (AC) measurements, the term immittance denotes the electric -> impedance and/or the electric admittance of any network of passive and active elements such as the resistors, capacitors, inductors, constant phase elements, transistors, etc. In electrochemical impedance spectroscopy, which utilizes equivalent electrical circuits to simulate the frequency dependence of a given elec-trodic process or electrical double-layer charging, the immittance analysis is applied. 

Figure 166 The time dependence of device luminance (a) for a three layer LED (b) operated at a field ca. lMV/cm as driven by the direct current (DC), alternating current (AC) and pulsed current (PC) modes. The frequency of the pulsed excitation was 1kHz for both the AC and DC modes. After Ref. 586. Copyright 2000 Jpn. JAP, with permission.

Because an electrode does not function as electrode in DC or alternating current high-frequency discharge, the electrode system could be kept outside a glass reactor (capacitive external electrodes) or a coil around a glass tube (inductively coupled external electrode) can be used to create plasma. These modes of coupling could be dealt as a factor in the system-dependent aspect of plasma polymerization, i.e., the basic plasma polymerization remains the same. 

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