Determination of the parameters of semiconducting CdF2:In with Schottky barriers from radio-frequency measurements

Physical properties of semiconducting CdF_2 crystals doped with In are determined from measurements of the radio-frequency response of a sample with Schottky barriers at frequencies 10 - 10^6 Hz. The dc conductivity, the activation energy of the amphoteric impurity, and the total concentration of the active In ions in CdF_2 are found through an equivalent-circuit analysis of the frequency dependencies of the sample complex impedance at temperatures from 20 K to 300 K. Kinetic coefficients determining the thermally induced transitions between the deep and the shallow states of the In impurity and the barrier height between these states are obtained from the time-dependent radio-frequency response after illumination of the material. The results on the low-frequency conductivity in CdF_2:In are compared with submillimeter (10^{11} - 10^{12} Hz) measurements and with room-temperature infrared measurements of undoped CdF_2. The low-frequency impedance measurements of semiconductor samples with Schottky barriers are shown to be a good tool for investigation of the physical properties of semiconductors.Comment: 9 pages, 7 figure

Effect of Electric Field on the Swelling Behavior of Cross-linked Copolymers of Poly(ethylene oxide) Bis-macromonomers with Methacrylic Acid

The hydrogels capable to interpolymer complex formation have been synthesized by direct radical copolymerization of methacrylic acid with poly(ethylene oxide) bis-macromonomer bearing methacrylate terminal groups. The swelling behavior of these hydrogels in electric field has been studied. The hydrogels were shown to undergo contraction or additional swelling depending on solution pH. In weakly acidic region (pH 5.1) the contraction of the network was observed. In these conditions the swelling behavior of the hydrogel is affected by the complex formation between unionized carboxylic groups and oxyethylene units within the networks and the gel sample has relatively low swelling degree and network charge. In basic region (pH 9.18) the polycomplex is destroyed and the network has higher charge density and higher swelling degree. Under the action of electric field such hydrogel swells additionally. An increase in ionic strength of  solution decreases the amplitude of hydrogels contraction