Adsorption by graphene sponge (GS) manufactured by annealing nickel-carbon powder mixture in inert atmosphere has been studied. By determining the specific surface area (SSA) for the GS sample, it has been found that Brunauer, Emmett, Teller method (BET) of approximation of experimental isotherms gives wrong results in the pressure range of 0.025–0.12 because adsorption in this pressure region is affected by walls of ampoule. Real SSA value has been found by subtracting pore effect method (SPE) or by BET approximation in a low range of relative pressure of 0.0004–0.002.
E. Laizane, D. Gustina, K. Kundzins, I. Muzikante and J. Teteris
Optically Induced Surface Relief Gratings in Polymer Films Doped With Sulphonyl Group Containing Azobenzene
In holography, more attractive have become azobenzene compounds doped in a polymer matrix (host-guest polymer film) or chemically attached to the polymer. Azobenzene molecules exhibit reversible photoisomerization between trans- and cis-isomers which can form a surface relief grating in the films. The authors investigate the holographic recording and formation of surface relief gratings in a host-guest polymer film with two original azobenzene compounds. Holographic recording with 325 nm laser light was performed in host-guest polymer films with the host being polymethylmetacrylate (PMMA) and the guest - 15 wt% azobenzene molecules (A-45 or A-48). In both cases an increase in the diffraction efficiency at the beginning of the process could be related to the trans-cis-photoisomerization, while the second increase - to the formation of surface relief gratings. The systems with A-45 molecules reach a diffraction efficiency of 0.7%, and with A-48 molecules - of 0.24%. Also, the depth of surface relief gratings is greater in the films with A-45 (35 to 45 nm) than in those with A-48 (4 to 6 nm) molecules.
A. Dravniece, L. Gerca, K. Kundzins, K. Teivena, V. Kampars and M. Rutkis
Single sheet graphene (SG) is an innovative transparent material with high electrical and thermal conduction the use of which in transparent electrodes instead of traditional materials improves the performance of optoelectronic devices. In this study, graphene oxide (GO) has been obtained by a modified Hummer`s method followed by an advanced technique of water removal (lyophilisation). The Langmuir-Blodgett (LB) method was applied to transfer GO from suspension to substrate. To optimize the deposition process, as suspending and spreading solvents the benzene and benzene/methanol mixtures were chosen instead of previously studied water suspensions. The number of GO layers in suspension is reduced by exfoliation in order to obtain a single GO monolayer. For this purpose, sonication and centrifugation of GO sheets are carried out. Finally, the effect of variously treated glass substrate surfaces on the deposition efficiency has been studied. In the work, it is shown that ozonization of glass substrate improves the deposition outcome, while ozonization of indium tin oxide (ITO) glass substrate is necessary to perform such deposition. The obtained GO suspensions and LB thin films have been studied using a scanning electron microscope (SEM)
A cheap, comparatively simple and effective method is proposed for the large quantity production of the sheets of graphenic carbon materials (GCM) by annealing the mixture of nickel powder with a suitable carbon amount at the temperatures close to 1000 ºC. The number of graphene layers in the sheets of GCM may be varied by altering the amount of carbon in the mixture and parameters of annealing and drying of the obtained products. Samples of GCM were prepared in the form of heat-dried GCM paper and in the form of graphene sponge with freeze-drying. The appearance of GCM on the surface of Ni particles was identified using a scanning electron microscope (SEM) at a low accelerating voltage of 5 kV. The thickness and properties of the layers were investigated by electron microscopy and X-ray diffraction. The fabrication processes were carried out at the concentrations of added carbon from 0 to 1 at%. The results obtained are fully consistent with the well-known solid phase reactions of carbon dissolution in Ni at 1000 °C and graphene or graphite precipitation on the surface with cooling down to the room temperatures.