Functional Properties of Donor (Al) and Acceptor (Cu) Codoped High Dielectric Constant ZnO Nanoparticles

In this work, we have synthesized donor-acceptor (Al-Cu) codoped ZnO nanoparticles with a doping concentration of 0%, 0.25%, 0.5%, and 0.75% by coprecipitation method. The synthesized samples were then annealed at 350°C and 600°C. All the samples showed wurtzite structure of ZnO with no secondary phase. The increase in doping concentration led to deterioration of crystalline quality, while improved crystallinity was observed at higher annealing temperature. The morphological study of these samples showed good grain-to-grain contact with less isolated pores. These samples were further characterized by impedance spectroscopy for analyzing dielectric properties. The values of the real part of dielectric constant and tangent loss showed decreasing trend with frequency. The appearance of semicircular arcs in the impedance complex plane plots indicates contribution of grains and grain boundaries and presence of different relaxation processes. 0.5% Al and Cu codoped ZnO showed the best dielectric response with a high value of dielectric constant and low tangent loss.

Dynamic Wetting of Photo-Responsive Arylazopyrazole Monolayers is Controlled by the Molecular Kinetics of the Monolayer

Smart surfaces that can change their wetting behavior on demand are interesting for applications such as self-cleaning surfaces or lab-on-a-chip devices. In order to functionalize aluminum oxide surfaces, we have synthesized arylazopyrazole phosphonic acids (butyl-AAP-C18PA) that represent a new class of photoswitchable molecules for these oxide surfaces. Butyl-AAP-C18PA monolayers were deposited on alpha-Al2O3(0001) and show reversible E/Z photo-switching with UV (Z) and green (E) light that can trigger contact angle changes of up to ~10°. We monitored these changes on the macroscopic level by recording the dynamic contact angle while the monolayer was switched in situ from the E to the Z state. On the molecular level, time-resolved vibrational sum-frequency generation (SFG) spectroscopy provided information on the kinetic changes within the AAP monolayer and the relevant characteristic time scales for E to Z switching and vice versa. In addition, vibrational SFG at different relative humidity indicates that the thermal stability of the Z configuration is largely influenced by the presence of water and that water can stabilize the Z state and, thus, hinder the AAP monolayer to switch into the E state when it is immersed in H2O. Having established the characteristic times for switching on the molecular scale from SFG spectroscopy, we additional measure the dynamic contact angle. Further, we reveal the time scales of the coupled substrate and droplet dynamics which we have extracted individually. For that, we report on a relaxation model, that can be solved analytically and which is verified via comparison with simulations of a Lennard Jones system and a comparison with experimental data. Indeed, our modelling of these coupled relaxation processes allows us to predict the non-trivial variation of the time-dependence of the contact angle when changing the size of the droplet. The observed slowing-down for E to Z switching upon the presence of the droplet is rationalized in terms of specific interactions of water with the exposed AAP moieties.

Процессы передачи энергии в эвлитите Sr-=SUB=-3-=/SUB=-Y(PO-=SUB=-4-=/SUB=-)-=SUB=-3-=/SUB=-, по отдельности и одновременно легированном ионами Tb-=SUP=-3+-=/SUP=- и Tm-=SUP=-3+-=/SUP=-

In this work the optical spectroscopy and the energy transfer processes involving the Tb3+and Tm3+ ions, have been studied in eulytite double phosphate hosts of the type Sr3Y(PO4)3 doped with various amounts of the two Ln ions. It has been found that several energy transfer and cross-relaxation processes are active in this class of materials, upon excitation in the 5D4 level of Tb, and in the 1G4 one of Tm. In particular, a Tb→Tm transfer of excitation has been found to quench strongly the 5D4 level of Tb. This process occurs with a transfer efficiency increasing from 0.08 to 0.62, for a donor concentration of 2 mol%, and an acceptor concentration increasing from 2 to 15 mol%. The emission spectra are strongly affected by the presence of Tb⟷Tm energy transfer, and Tm→Tm cross relaxation processes.

Спектры поглощения пробного сигнала и резонансной флуоресценции для излучателей при их взаимодействии с локальным окружением в прозрачных средах

The current paper demonstrates theoretical analysis of two types of spectral curves for several configurations of system of two-level light emitters, considering the influence of local field and close environment inside a transparent medium. Probe field absorption spectra and resonant fluorescence spectra are calculated under excitation of a strong monochromatic cw laser. The sensitivity of absorption and emission optical spectroscopy method is compared for revealing the effects of the medium on individual emitters and their ensembles. Spectral curves were calculated for model emitters considering local field influence of a transparent dielectric medium and local electron-phonon interactions, which determined the response of the emitters to an external laser field and effective relaxation mechanisms. The calculation formalism is based on a semiclassical approach, while the relaxation processes associated with the phonon contribution are introduced phenomenologically with references to other studies.

A Nonsymmetric Dy2 Single-Molecule Magnet with two Relaxation Processes Triggered by External Magnetic Field: Theoretical and Integrated EPR study of the Role of Magnetic-Site Dilution

The 1:2 reaction between Dy(O2CMe)34H2O and 1-acetyl-2-napthol (LH) in MeOH has provided access to complex [Dy2L6(MeOH)]MeOH (1.MeOH) in good yield. The structures of the isomorphous complexes 1MeOH and its doped...

Spontaneous Magnetic Fluctuations and Collisionless Regulation of Turbulence in the Earth’s Magnetotail

Among the fundamental and most challenging problems of laboratory, space, and astrophysical plasma physics is to understand the relaxation processes of nearly collisionless plasmas toward quasi-stationary states and the resultant states of electromagnetic plasma turbulence. Recently, it has been argued that solar wind plasma β and temperature anisotropy observations may be regulated by kinetic instabilities such as the ion cyclotron, mirror, electron cyclotron, and firehose instabilities; and it has been argued that magnetic fluctuation observations are consistent with the predictions of the fluctuation–dissipation theorem, even far below the kinetic instability thresholds. Here, using in situ magnetic field and plasma measurements by the THEMIS satellite mission, we show that such regulation seems to occur also in the Earth’s magnetotail plasma sheet at the ion and electron scales. Regardless of the clear differences between the solar wind and the magnetotail environments, our results indicate that spontaneous fluctuations and their collisionless regulation are fundamental features of space and astrophysical plasmas, thereby suggesting the processes is universal.

Применение метода диэлектрической спектроскопии для исследования свойств сыворотки крови мышей со злокачественным асцитом

The article presents the results of a study by the method of dielectric spectroscopy of high-frequency relaxation processes in the blood serum of intact mice and mice vaccinated with an oncological disease - Ehrlich's ascites carcinoma. Using the formalism of the electrical module, the relaxation parameters were calculated for the serum samples of the two studied systems.

Analysis of a Relaxation Process Caused by the Load Variation Adapted on the Basis of Second Order Electrical Model

The relaxation process of lithium batteries caused by load variation is considered. It is shown that such processes have strong dependence on internal physical and chemical processes and battery technical conditions. Theoretical expressions of the relaxation process caused by a step-like load variation have been obtained for 1st and 2nd order equivalent electrical circuits. The experimental investigations show that the obtained models fit the real relaxation processes and the behavior of the identified parameters could be explained by specific features of physical and chemical processes within the lithium battery. It should be noted that the obtained results can be generalized for a different type of electrochemical power source. The proposed approach makes it possible to provide means for electrochemical power source characterization and diagnostic, the main advantages of which are good time localization of measurement procedures and inexpensive apparatus implementation.