Elongated oxide nanostructures have gained much attention in the past decade due to their unique mechanical, optical, and electrical properties. Despite the vast amount of theoretical and experimental work on these materials, the mechanism of water-related electrical conduction in these systems has remained unsolved. In this study, the charge transport processes in hydrothermally synthesized trititanate nanowires (TiONW) at varying relative humidity (RH) have been investigated. Parameters characterizing these processes were extracted from dielectric spectroscopy (DRS) and ionic transient current (ITIC) measurements at room temperature. The dc conductivity varies exponentially with increasing RH. It is suggested to stem mainly from the exponentially increasing charge carrier concentration, while carrier mobility seems to have a much weaker influence on the long-range charge transport. The changes in the constituent parameters of dc conductivity are thought to be due to the changes in the amount, surface structure, and thermodynamic state of adsorbed water, which has been confirmed in the case of ionic mobility with moisture sorption and calorimetric (DSC) investigations. However, the microscopic origin of the exponentially increasing carrier concentration with RH still remains an open question.
Broadband dielectric spectroscopy (BDS) measurements have been carried out on a nanostructured hydrophilic model system to gain insight into the atomistic level mechanism of adsorption-induced dielectric changes. Titanate nanowires (TiONWs) were investigated between 10 mHz and 1 MHz under various humidity conditions. The processes contributing to the measured dielectric response were identified, and their dependence on water surface coverage was discussed in detail. Three relaxation processes and an imperfect ionic conduction were found in the investigated frequency window. Exponential relationships were found between the different dielectric quantities and the amount of adsorbed water. The conductivity variation originates from the exponentially increasing charge carrier concentration, while the relaxations in the middle frequency range have a common, interfacial origin. The high-frequency loss process arises from the orientation relaxation of a real dipolar moiety of the system.
In macromolecular crystallography, a great deal of effort has been invested in understanding radiation‐damage progression. While the sensitivity of protein crystals has been well characterized, crystals of DNA and of DNA–protein complexes have not thus far been studied as thoroughly. Here, a systematic investigation of radiation damage to a crystal of a DNA 16‐mer diffracting to 1.8 Å resolution and held at 100 K, up to an absorbed dose of 45 MGy, is reported. The RIDL (Radiation‐Induced Density Loss) automated computational tool was used for electron‐density analysis. Both the global and specific damage to the DNA crystal as a function of dose were monitored, following careful calibration of the X‐ray flux and beam profile. The DNA crystal was found to be fairly radiation insensitive to both global and specific damage, with half of the initial diffraction intensity being lost at an absorbed average diffraction‐weighted dose, D1/2, of 19 MGy, compared with 9 MGy for chicken egg‐white lysozyme crystals under the same beam conditions but at the higher resolution of 1.4 Å. The coefficient of sensitivity of the DNA crystal was 0.014 Å2 MGy−1, which is similar to that observed for proteins. These results imply that the significantly greater radiation hardness of DNA and RNA compared with protein observed in a DNA–protein complex and an RNA–protein complex could be due to scavenging action by the protein, thereby protecting the DNA and RNA in these studies. In terms of specific damage, the regions of DNA that were found to be sensitive were those associated with some of the bound calcium ions sequestered from the crystallization buffer. In contrast, moieties farther from these sites showed only small changes even at higher doses.
Heat-treated CaFe-layered double hydroxide samples were equilibrated under conditions of various relative humidities (11%, 43% and 75%). Measurements by FT-IR and dielectric relaxation spectroscopies revealed that partial to full reconstruction of the layered structure took place. Water types taking part in the reconstruction process were identified via dielectric relaxation measurements either at 298 K or on the flash-cooled (to 155 K) samples. The dynamics of water molecules at the various positions was also studied by this method, allowing the flash-cooled samples to warm up to 298 K.
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