ABSTRACT
Presents the device for analysis the thermally stimulated electrical conductivity of composites in the wide temperature range. The main advantage of the module in relation to those described earlier is that it allows experiments both in the mode of measuring the current of thermally stimulated depolarization (TSDC) at low temperatures, and in the mode of measuring the thermally stimulated conductivity current (TSCC) up to very high temperatures. Using PMMA/PVDF mixtures as an example, it is shown that the TSDC method can be used to temperature transitions analysis in the many composite materials at low temperatures. It was also shown on the example of the two-component epoxy networks that the described module makes it possible to study the thermal transitions in the composites materials using the TSCC mode to the high temperatures.
ABSTRACT
We studied magnetostatic response of the Bi0.9La0.1FeO3- KBr composites (BLFO-KBr) consisting of nanosized (≈100 nm) ferrite Bi0.9La0.1FeO3 (BLFO) conjugated with fine grinded ionic conducting KBr. When the fraction of KBr is rather small (less than 15 wt%) the magnetic response of the composite is very weak and similar to that observed for the BLFO (pure KBr matrix without Bi1-xLaxFeO3 has no magnetic response as anticipated). However, when the fraction of KBr increases above 15%, the magnetic response of the composite changes substantially and the field dependence of magnetization reveals ferromagnetic-like hysteresis loop with a remanent magnetization about 0.14 emu/g and coercive field about 1.8 Tesla (at room temperature). Nothing similar to the ferromagnetic-like hysteresis loop can be observed in Bi1-zLazFeO3 ceramics with z ≤ 0.15, which magnetization quasi-linearly increases with magnetic field. Different physical mechanisms were considered to explain the unusual experimental results for BLFO-KBr nanocomposites, but only those among them, which are highly sensitive to the interaction of antiferromagnetic Bi0.9La0.1FeO3 with ionic conductor KBr, can be relevant.
ABSTRACT
Graphene-enhanced Raman scattering (GERS) spectra and coherent anti-Stokes Raman scattering (CARS) of thymine molecules adsorbed on a single-layer graphene were studied. The enhancement factor was shown to depend on the molecular groups of thymine. In the GERS spectra of thymine, the main bands are shifted with respect to those for molecules adsorbed on a glass surface, indicating charge transfer for thymine on graphene. The probable mechanism of the GERS enhancement is discussed. CARS spectra are in accord with the GERS results, which indicates similar benefit from the chemical enhancement.
ABSTRACT
Coherent anti-Stokes Raman scattering (CARS) of carbon nanostructures, namely, highly oriented pyrolytic graphite, graphene nanoplatelets, graphene oxide, and multiwall carbon nanotubes as well CARS spectra of thymine (Thy) molecules adsorbed on graphene oxide were studied. The spectra of the samples were compared with spontaneous Raman scattering (RS) spectra. The CARS spectra of Thy adsorbed on graphene oxide are characterized by shifts of the main bands in comparison with RS. The CARS spectra of the initial nanocarbons are definitely different: for all investigated materials, there is a redistribution of D- and G-mode intensities, significant shift of their frequencies (more than 20 cm(-1)), and appearance of new modes about 1,400 and 1,500 cm(-1). The D band in CARS spectra is less changed than the G band; there is an absence of 2D-mode at 2,600 cm(-1) for graphene and appearance of intensive modes of the second order between 2,400 and 3,000 cm(-1). Multiphonon processes in graphene under many photon excitations seem to be responsible for the features of the CARS spectra. We found an enhancement of the CARS signal from thymine adsorbed on graphene oxide with maximum enhancement factor about 10(5). The probable mechanism of CARS enhancement is discussed.
ABSTRACT
Adsorption of guest molecules on host surfaces can lead to dramatic changes in the spectral properties of the guest. One such effect is surface-enhanced infrared absorption (SEIRA), observed when the guest is adsorbed on, for example, thin films, metal surfaces, or nanotubes. p-Nitrobenzoic acid (p-NBA) exhibits a SEIRA effect when adsorbed on Ag and Au. Herein, the IR spectra of p-NBA adsorbed on a homemade rough Au surface, recorded in reflection mode with an angle of incidence of 16.5°, are reported. This SEIRA experiment reveals more bands than found by previous SEIRA studies. The intensities of both symmetric and asymmetric COO(-) and NO(2) stretching, in-plane CH, and C=C ring stretching modes are enhanced. Theoretical models constructed on the basis of density functional theory reveal the binding mode of p-NBA to gold "particles". The p-NBA anion binds to gold much more strongly than the neutral form, and interaction via the carboxylic oxygen atoms is preferred over the nitro group-gold contact. A significant charge transfer during chemisorption is found, which is considered to be crucial in leading to a high SEIRA enhancement factor.
