Low-Frequency Dielectric Relaxation in Structures Based on Macroporous Silicon with Meso-Macroporous Skin-Layer

The spectra of dielectric relaxation of macroporous silicon with a mesoporous skin layer in the frequency range 1–106 Hz during cooling (up to 293–173 K) and heating (293–333 K) are presented. Macroporous silicon (pore diameter ≈ 2.2–2.7 μm) with a meso-macroporous skin layer was obtained by the method of electrochemical anodic dissolution of monocrystalline silicon in a Unno-Imai cell. A mesoporous skin layer with a thickness of about 100–200 nm in the form of cone-shaped nanostructures with pore diameters near 13–25 nm and sizes of skeletal part about 35–40 nm by ion-electron microscopy was observed. The temperature dependence of the relaxation of the most probable relaxation time is characterized by two linear sections with different slope values; the change in the slope character is observed at T ≈ 250 K. The features of the distribution of relaxation times in meso-macroporous silicon at temperatures of 223, 273, and 293 K are revealed. The Havriliak-Negami approach was used for approximation of the relaxation curves ε″ = f(ν). The existence of a symmetric distribution of relaxers for all temperatures was found (Cole-Cole model). A discussion of results is provided, taking into account the structure of the studied object.

Microwave Dielectric Measurements of 4-Nitroacetanilide at Different Temperatures in Carbon Tetrachloride Solution

The dielectric properties of 4-Nitroacetanilide have been discussed at four different temperatures in the dilute solution of carbon tetrachloride at a fixed frequency of 9.27GHz. The values of dielectric constant (εʹ), dielectric loss (εʺ), permittivity at an optical frequency (ε∞) and permittivity at a static frequency (ε0) are measured at different temperatures and mole fractions. The values of these dielectric parameters are used to calculate the values of relaxation time for overall molecular rotation (τ1), relaxation time for intramolecular rotation (τ2), most probable relaxation time (τ0) and dipole moment (μ) at different temperatures. In the present investigation we have found higher values of τ2 which indicate the existence of more than one relaxation process in the solution. The values of energy activation parameters for dielectric relaxation process (∆Fε, ∆Hε and ∆Sε) and viscous flow process (∆Fη, ∆Hη and ∆Sη) are also determined and compared for 4-Nitroacetanilide with carbon tetrachloride at different temperatures. It is observed that we may treat both the process as a rate process.