AbstractProton conductivity in graphene oxide and Nafion films depending on humidity and voltages across electrodes is studied in the model of a field-effect transistor. The electrical characteristics of the films are similar to one another, but the mobility of positive charges in Nafion and the current gain are higher by 2–3 orders of magnitude compared with graphene oxide. The negative ion current in graphene-oxide films at positive bias voltage is significant compared with the proton current (up to ~10%), while it is almost lacking in Nafion films (<1%).

В модели полевого транзистора исследована протонная проводимость в пленках оксида графена (ОГ) и Нафиона в зависимости от влажности и напряжений на электродах. Установлено, что электрические характеристики этих пленок подобны, но подвижность положительных зарядов в Нафионе и усиление тока на ~2 порядка выше, чем в ОГ. В пленках ОГ отрицательно-ионный ток при положительном напряжении смещения составляет заметную величину (до ~10%) от протонного, в то время, как в пленках Нафиона он практически отсутствует (

Proton conductivity in graphene oxide and Nafion films depending on humidity and voltages across electrodes is studied in the model of a field-effect transistor. The electrical characteristics of the films are similar to one another, but the mobility of positive charges in Nafion and the current gain are higher by 2–3 orders of magnitude compared with graphene oxide. The negative ion current in graphene-oxide films at positive bias voltage is significant compared with the proton current (up to ~10%), while it is almost lacking in Nafion films (<1%).

The dark process (posteffect) of increasing the electrical conductivity and spectral absorption in the graphene oxide (GO) film after its preliminary UV irradiation has been studied. The posteffect is due to the conformational relaxation of the structure (flattening) of GO nanosheets after the UV-induced dissociation of oxygen-containing groups. At room temperature, the relaxation time is τ ≈ 300 h and the activation energy in the range of 20–70°C is E a ≈ 0.6 eV.

GO films exhibited dual proton and electron conduction. Proton conduction showed the exponential dependence on relative humidity with the activation energy E a = 0.9 ± 0.05 eV. For the electron conductivity (220–273 K) induced by thermolysis and chemical means E a = 1.15 ± 0.05 eV. With increasing humidity, the electron conduction went down, which was associated with recombination phenomena. The GO films can be regarded as a first example of the mixed electron–proton conduction when sample conductivity can be regulated by external influence (humidity). Field effect is detected and studied in the transistor on the basis of the GO in different types of conduction.

The O/C atomic ratios in films of oxidized and partially reduced graphene oxide are determined via the Rutherford backscattering of H+ ions. In addition, the conductivity σ is measured. It is established that the reduction noticeably decreases the О/С ratio and increases σ by a few orders of magnitude. We demonstrate for the first time the efficiency of Rutherford backscattering in studying graphene-type objects.

Proton (wet atmosphere) and electron (reduced graphene oxide) conductivities can be observed in graphene oxide films. The field effect in a graphene oxide transistor for different conductivity types has been discovered and investigated.

Under the action of ionizing radiation on a PVDF film, fluorine and hydrogen atoms bound to its linear carbon chain with single chemical bonds detach. Free atoms and HF molecules diffuse toward the film surface and escape from it. As a result of irradiation of the sample surface, a fluorine concentration depth profile arises. The fluorine distribution in the PVDF films subjected to long-term X-ray exposure was studied using X-ray photoelectron spectroscopy and Rutherford backscattering spectroscopy. Both methods yield close values of the fluorine concentration at a depth of ∼10 nm.

Electron mobility in a thin silicon layer of a metal-insulator-semiconductor-insulator-metal system is studied as a function of longitudinal and transverse electric fields (in wide ranges of their values), temperature in the range 1.7 to 400 K, and changes in γ-ray irradiation conditions. It is shown that, in the temperature range 400 to ∼100 K, electron mobility increases in accordance with the mechanism of electron scattering at an acoustic phonon, while, with a subsequent decrease in temperature to the temperature of liquid helium, mobility drops because the Coulomb scattering of electrons at charged surface centers starts to dominate. It is demonstrated that as a result of γ-ray irradiation, electron mobility decreases and the degree of this decrease strongly depends on the electrical mode of the sensor during irradiation.

The method of high-frequency capacitance-voltage characteristics was used to study the effect of low-field injection of charge carriers on the electrical properties of metal-SiO2-Si structures with n- and p-type substrates. It is shown that in all cases of injection (irrespective of the polarity of the voltage at the gate), an effective positive charge is generated in the oxide; after completion of the injection, this charge relaxes with characteristic times that depend on the bias voltage applied to the gate and the type of the metal-oxide-semiconductor structure. In the structures with p-Si substrates, in the case of a positive voltage applied to the gate, a capacitance minimum appeared in the inversion portion of the capacitance-voltage characteristics in the course of injection; this effect became more pronounced as the gate voltage was increased. After the injection, the capacitance gradually approached the initial value (before injection).

The design features and main characteristics of the new type of magnetic field converters, i.e., the controllable Field Effect Hall Sensor based on the "silicon-on-insulator" (SOI) structure, are considered. The FEHS design features and the use of SOI structures as the design and technological basis of its production imply the uniqueness of electrical and reliability characteristics.

New circuitry possibilities of magnetic measurements using the controllable field effect Hall sensor (FEHS) as a primary magnetic field converter are considered. The FHP combines the properties of the conventional Hall probe and field-effect transistor with a two-gate control system such as metal--insulator--silicon- insulator-metal. Two field control systems allow control of FEHS parameters, as well as the use of new circuitry to control the dynamic range of magnetosensitivity, operating current stability, and measurement stability improvement under conditions of variable external influences (temperature, radiation background).

The density and porosity of synthetic opals with spheres 315 and 1000 nm in diameter were measured in relation to the annealing temperature. At annealing temperatures of up to 500°C, the seeming density and porosity remain almost unchanged. Then, at temperatures of up to 950°C, the density increases gradually and, accordingly, the porosity decreases due to the collapse of nanopores caused by the sphere substructure. As the annealing temperature increases further, the opal density increases sharply up to 2.22 g/cm3 (which corresponds to the density of amorphous silica) and the open microporosity due to the voids between spheres disappears. Differential thermal and thermogravimetric analyses showed that SiO2 powders with particles with average size of 315 and 1000 nm can have, respectively, two-and three-level systems of micro-and nanopores.

Some adsorption, structural, and annihilation characteristics of synthetic opals are measured. An analysis of these characteristics makes it possible to conclude that the total porosity in opals comprises macropores, which are in essence the voids between structure-forming spheres, and nanopores connected to the substructure of the spheres. The systems of macropores and nanopores are separated by narrow channels that collapse upon the thermal treatment of opals. The sizes of primary a-SiO2 particles and nanopores, which correspond to the voids between these particles, are estimated.

Macroporous silicon is studied by IR absorption spectroscopy, x-ray diffraction, and the electron–positron annihilation method in comparison with single-crystal Si (substrate), polycrystalline Si (powder), anda-SiO2 (silica glass). According to IR absorption data, as-prepared macroporous silicon contains a significant amount of oxidized material. Annihilation spectra of macroporous silicon attest to the presence of a system of nanopores, in which positronium atoms are likely to localize. Diffraction patterns reveal considerable amounts of silicon particles oriented at random. Both the polycrystalline phase and nanopores reside on the surface of macropores.