Optical and Electrical Properties of Ion Beam Effects in Ge10Se70Bi20 Thin Films

In this study, chalcogenide material Ge 10 Se 70 Bi 20 thin films have been fabricated utilizing the thermal evaporation technique of bulk samples on glass substrates. After that, the original Ge 10 Se 70 Bi 20 thin films irradiated by different types of an ion beam. The compositions of the original film was determined by the Energy Dispersive X-Ray (EDX). X-ray diffraction (XRD) measurements were performed to characterize and examine the induced variations in the structure of Ge 10 Se 70 Bi 20 films after irradiation. From the optical measurements, the absorption edge, bandgap, Urbach energy, Tauc parameter, and extinction coefficient of the unirradiated and irradiated films were determined. In particular, the DC electrical conductivity increased by two orders after the pure film was exposed to an oxygen ion beam. Besides, the activation energy and Mott’s parameters for the original and irradiated Ge 10 Se 70 Bi 20 films were deduced. The reported variations in absorption coefficient, optical bandgap, dc electrical conductivity, and Mott’s parameters propose that the irradiated Ge 10 Se 70 B 20 thin films can be used in important applications, e.g., optical data storage and optoelectronic devices.

DC electrical conductivity retention and acetone/acetaldehyde sensing on polythiophene/molybdenum disulphide composites

In this study, polythiophene (PTh) and a series of polythiophene/molybdenum disulphide (PTh/MoS2) composites were prepared by in-situ chemical oxidative polymerization method using anhydrous ferric chloride (FeCl3) as an oxidant and chloroform (CHCl3) as a solvent. The successful formation of PTh and PTh/MoS2 composites were confirmed by various techniques such as Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmittance electron microscopy (TEM). DC electrical conductivity and acetone/acetaldehyde sensing studies were carried out by a four-in-line probe device. PTh/MoS2 composites exhibited significantly improved DC electrical conductivity and acetone/acetaldehyde sensing properties as compared to PTh. The electrical properties were investigated in terms of initial conductivity (i.e. conductivity at room temperature) as well as retention of conductivity, i.e. stability under isothermal and cyclic ageing conditions. The maximum initial conductivity, along with the highest conductivity retention, was observed for PTh/MoS2-2 (PTh/MoS2 composite comprising 10% MoS2 with respect to the weight of thiophene monomer). The initial DC electrical conductivity of PTh, PTh/MoS2-1, PTh/MoS2-2 and PTh/MoS2-3 was found to be 5.72 × 10−5 Scm−1, 4.03 × 10−4 Scm−1, 1.09 × 10−3 Scm−1 and 8.96 × 10−4 Scm−1, respectively. The sensing performance at room temperature has been studied in terms of % sensing response, response/recovery time. All the PTh/MoS2 composites based sensors performed much better than PTh. The % sensing response of PTh, PTh/MoS2-1, PTh/MoS2-2 and PTh/MoS2-3 based pellet-shaped sensors towards acetone/acetaldehyde were affirmed as 30.6/22.9, 69.9/47.3, 93.7/70.3, 78.1/65.1, respectively. The purposed sensing mechanism involved the adsorption of acetone/acetaldehyde vapours on the surface of the sensors where electronic interaction between lone pair of electrons on oxygen atoms of the carbonyl group and charge carriers of PTh was responsible for the change in conductivity.

Effects of Counter Anions on AC and DC Electrical Conductivity in Poly(Dimethylsiloxane) Crosslinked by Metal-Ligand Coordination

There is an urgent need for the development of elastic dielectric materials for flexible organic field effect transistors (OFETs). In this work, detailed analysis of the AC and DC electrical conductivity of a series of flexible poly(dimethylsiloxane) (PDMS) polymers crosslinked by metal-ligand coordination in comparison to neat PDMS was performed for the first time by means of broadband dielectric spectroscopy. The ligand was 2,2-bipyridine-4,4-dicarboxylic amide, and Ni2+, Mn2+, and Zn2+ were introduced for Cl−, Br−, and I− salts. Introduction of metal salt and creation of coordination bonds resulted in higher permittivity values increasing in an order: neat PDMS < Ni2+ < Mn2+ < Zn2+; accompanied by conductivity values of the materials increasing in an order: neat PDMS < Cl− < I− < Br−. Conductivity relaxation time plot as a function of temperature, showed Vogel-Fulcher–Tammann dependance for the Br− salts and Arrhenius type for the Cl− and I− salts. Performed study revealed that double-edged challenge can be obtained, i.e., dielectric materials with elevated value of dielectric permittivity without deterioration too much the non-conductive nature of the polymer. This opens up new perspectives for the production of flexible dielectrics suitable for gate insulators in OFETs. Among the synthesized organometallic materials, those with chlorides salts are the most promising for such applications.

Gel point determination of gellan biopolymer gel from DC electrical conductivity

Gellan is an anionic bacterial polysaccharide, which in aqueous solution dissociates into a charged gellan polymer molecule containing carboxyl ions and counter ions and forms thermoreversible gel under appropriate conditions. In this study, we investigated the effect of polymer concentration, the concentration of added monovalent metallic ion, and temperature on the DC electrical conductivity of the gellan. Results suggest that the DC conductivity decreases with the increasing polymer concentrations and the added monovalent metallic ions. Such a decrease in DC conductivity can be attributed to the reduction of the mobility of counter ions due to the increase in the crosslinking density of the gellan network. DC conductivity of gellan gels was increased with temperature, which is interpreted as the dissolution of physically cross-linked networks, thus increasing the mobility of counter ions. The behavior of temperature variation of DC electrical conductivity reveals an abrupt change at a specific temperature, which can be considered a way to determine the gel point or sol–gel transition temperature Tc of this thermoreversible biopolymer gel. This result agrees with that of rheological measurements where the viscosity showed a similar trend with temperature and diverges to infinity at the temperature close to Tc.

Critical Behavior of Electrical Conductivity for Reduced Graphene Oxide/Epoxy Resin Composites

In this paper, we analyze the dc and ac electrical conductivities, in the 240 to 400 K temperature range and 102 to 106 Hz frequency range, of a percolating system synthesized by mixing reduced graphene oxide (rGO) particles in insulating epoxy resin matrix, diglycidyl ether of bisphenol A (DGEBA). We found that the dc electrical conductivity of the samples is strongly related to the rGO content, indicating a percolating behavior with percolation threshold ≈ 4 %. The critical behavior of the dc electrical conductivity as a function of the temperature indicates a strong positive temperature coefficient and a negative temperature coefficient of resistivity below and above the transition temperature Tg, respectively. Moreover, the results showed that the dc conductivity obeys the Arrhenius law and the ac electrical conductivity is both frequency and temperature dependent and follows the Jonscher’s power law. Keywords: Composites, Dielectric properties, Fillers, Glass transition, Graphene.