Changes in the mechanical properties of polyimides induced by electron bombardment

The change in the tensile strength and relative elongation of PM polyimide with absorbed dose has been investigated. It is shown that after irradiation with very large doses (5 · 10¹⁰ rad) the mechanical properties are still satisfactory.Scientific Research Institute of Electrophysical Apparatus, Leningrad. Translated from Mekhanika Polimerov, No. 6, pp. 1111–1112, November–December, 1969.     

Multiphoton excitation and dissociation of CH3OH molecules by intense broadband YSGG:Cr:Er laser radiation in the range 2.7 µm

We have observed efficient multiphoton excitation of CH₃OH molecules by broadband pulsed YSGG:Cr:Er-laser radiation (λ=2.7 µm,τ _p =60 ns, and Δν_las～1.5 cm^?1) at fluences of 0.3-600 J/cm² under collisional and collisionless conditions. Multiphoton dissociation of CH₃OH has been realized. We discuss the role of intermode interaction, the intensity of the laser radiation, and the laser bandwidth in the excitation process.     

S-shaped current–voltage characteristics of polymer composite films containing graphene and graphene oxide particles

The resistive switching effects in composite films containing polyfunctional polymers, such as derivatives of carbazole (PVK), fluorene (PFD), and polyvinyl chloride (PVC), and also graphene particles (Gr) and graphene oxide (GO), the concentration of which in the polymer matrices varied in the range from 1 to 3 wt % corresponding to the percolation threshold in such systems, have been studied. The analysis of the elemental composition of the investigated composites by means of X-ray photoelectron spectroscopy have shown that the oxidation degree of Gr in GO is about 9 to 10%. It has been established that a sharp conductivity jump characterized by S-shaped current-voltage curves and the presence of their hysteresis occurs upon applying a voltage pulse to the Au/PVK (PFD; PVC): Gr (GO)/ITO/PET structures, where ITO is indium tin oxide, and PET is poly(ethylene terephthalate), with the switching time, t, in the range from 1 to 30 μs. The observed effects are attributed to the influence of redox reactions taking place on the Gr and GO particles enclosed in the polymer matrix, and the additional influence of thermomechanical properties of the polymer constituent of the matrix.

     

The simplest model of adsorption of molecules with different orientations in adlayer on the stepped surface

In this article we have constructed and studied using the Monte Carlo and transfer-matrix techniques the simple lattice gas models of self-assembled monolayer, which consists of molecules with different orientations in the adlayer on the stepped surfaces. It was shown that in the case of adsorption of complex molecules the surface heterogeneity of stepped type leads to a great variety of ordered structures comparatively with homogeneous one. The constructed models fairly well reproduce the main features of real SAMs consisting of molecules with different orientations with respect to interface and the model ordered phases are also analogues to the structures of real SAMs.     

Devil’s staircase behavior of a dimer adsorption model

We have constructed the simple two-dimensional adsorption model with short range non-competing interactions which demonstrates devil’s staircase of phase transitions. The main factor which leads to the appearance of infinite amount of ordered structures in our model is two competing forms of adsorption. The ground state properties of the model have been analyzed.     

The simulation of the adsorption of unsaturated cyclic hydrocarbons on the (001)-2 × 1 reconstructed silicon surface by the Monte Carlo and transfer-matrix methods

A model of the adsorption of cyclic unsaturated molecules on the Si(001)-2 × 1 reconstructed surface was developed for the example of 1,4-cyclohexadiene, which can be differently adsorbed on surface adsorption centers. Calculations were performed for a grand canonical ensemble by the Monte Carlo and transfer matrix methods. The structure of the ordered phases formed and the conditions of their appearance were studied in detail. It was shown that the suggested model reproduced all the qualitative special features of the system studied and similar systems.     

Current-voltage characteristics of thin Ge2Sb2Te5 films taken using a measuring circuit with a current source

The measuring circuit with a voltage generator, which is traditionally used for studying electric properties of glasslike semiconductors, is compared with an alternative version using a current generator. The results obtained in the latter case reflect the interrelation between the memory formation effect and changes in the electrical parameters more comprehensively. A new electric parameter, viz. hold voltage U _hold, which has not been described earlier, is introduced. The relation between U _hold and the memory formation process during the phase transition is established. The effect of emergence of oscillations in the current-limiting regime in the conduction channel in the film is detected.     

Adsorption of triangular-shaped molecules with directional nearest-neighbor interactions on a triangular lattice

Using Monte Carlo and transfer-matrix methods the lattice gas model of adsorption of triangular-shaped molecules on a triangular lattice is studied. The constructed model takes into account the directionality of pairwise nearest-neighbor interactions between the adsorbed molecules. It is shown that a predominant character of "tip-to-tip" attractive interactions w ₁ always leads to the formation of the honeycomb structure in the adsorption monolayer with local density ρ = 0.66(6). While, the values of "side-to-side" w ₂ and "tip-to-side" w ₃ interactions define the structure of close-packed phase. Depending on the values of the interactions the close-packed phase may have: (a) completely disordered structure; (b) frustrated honeycomb structure which is formed by Langmuir like adsorption onto 2D pores of the honeycomb structure; (c) ordered close-packed structure consisted of the molecules which all have the same orientation relative to each other and relative to the surface.