Electrical Conductivity Studies on Individual Conjugated Polymer Nanowires: Two-Probe and Four-Probe Results

<p>Abstract</p> <p>Two- and four-probe electrical measurements on individual conjugated polymer nanowires with different diameters ranging from 20 to 190 nm have been performed to study their conductivity and nanocontact resistance. The two-probe results reveal that all the measured polymer nanowires with different diameters are semiconducting. However, the four-probe results show that the measured polymer nanowires with diameters of 190, 95&#8211;100, 35&#8211;40 and 20&#8211;25 nm are lying in the insulating, critical, metallic and insulting regimes of metal&#8211;insulator transition, respectively. The 35&#8211;40 nm nanowire displays a metal&#8211;insulator transition at around 35 K. In addition, it was found that the nanocontact resistance is in the magnitude of 10⁴&#937; at room temperature, which is comparable to the intrinsic resistance of the nanowires. These results demonstrate that four-probe electrical measurement is necessary to explore the intrinsic electronic transport properties of isolated nanowires, especially in the case of metallic nanowires, because the metallic nature of the measured nanowires may be coved by the nanocontact resistance that cannot be excluded by a two-probe technique.</p

A reduced sintering temperature and improvement in the microwave dielectric properties of Li₂Mg₃TiO₆ through Ge substitution

In this paper, we demonstrate a strategy to reduce the sintering temperature of titanates through an appropriate amount of Ge substitution for Ti. A series of Li₂Mg₃Ti1-xGexO₆ (x = 0.04, 0.06, 0.08, 0.10, 0.12) ceramics, prepared by a solid-state reaction method, are reported. By controlling the content of the Ge substitution, the sintering temperature of Li₂Mg₃TiO₆ was significantly reduced to 1140 °C. When x = 0.10, the Li₂Mg₃Ti1-xGexO₆ ceramics sintered at 1140 °C for 6 h displayed excellent values of εr = 13.7, Q × f = 131,500 GHz and τf = −34.2 ppm/°C. In addition, the temperature stability was successfully adjusted to be close to zero by adding CaTiO₃ to form a composite ceramic. A temperature stable ceramic 0.96Li₂Mg₃Ti0.9Ge0.1O₆-0.04CaTiO₃ with τf = −3.5 ppm/°C, εr = 14.9 and Q × f = 68,900 GHz was obtained when sintered at 1180 °C. The good dielectric performances of the CaTiO₃-modified Li₂Mg₃Ti0.9Ge0.1O₆ ceramics makes them possible candidates for substrates in microwave integrated circuits

Low‐temperature sintering and thermal stability of Li₂GeO₃‐based microwave dielectric ceramics with low permittivity

Abstract A low‐permittivity dielectric ceramic Li₂GeO₃ was prepared by the solid‐state reaction route. Single‐phase Li₂GeO₃ crystallized in an orthorhombic structure. Dense ceramics with high relative density and homogeneous microstructure were obtained as sintered at 1000‐1100°C. The optimum microwave dielectric properties were achieved in the sample sintered at 1080°C with a high relative density ~ 96%, a relative permittivity εr ~ 6.36, a quality factor Q × f ~ 29 000 GHz (at 14.5 GHz), and a temperature coefficient of resonance frequency τf ~ −72 ppm/°C. The sintering temperature of Li₂GeO₃ was successfully lowered via the appropriate addition of B₂O₃. Only 2 wt.% B₂O₃ addition contributed to a 21.2% decrease in sintering temperature to 850°C without deteriorating the dielectric properties. The temperature dependence of the resonance frequency was successfully suppressed by the addition of TiO₂ to form Li₂TiO₃ with a positive τf value. These results demonstrate potential applications of Li₂GeO₃ in low‐temperature cofiring ceramics technology