Twisted multilayer graphene films were synthesized using chemical vapor deposition. The films were treated in oxygen plasma and reduced with hydrazine in the vapor phase to replace inserted oxygen groups with nitrogen ones. Some of the films were treated by hydrazine without preliminary oxidation. The processes of graphene oxidation, reduction and nitridation were characterized using scanning electron microscopy and Raman spectroscopy. Changes in the chemical composition after nitriding of synthesized or oxidized graphene were determined using x-ray photoelectron spectroscopy (XPS). Electrical transport properties of the multilayer graphene films were measured using the Hall and magnetoresistive effect. It was found that pre-oxidation of the film before nitridization makes it possible to increase the amount of graphitized nitrogen, which is a strong donor impurity, by 1.5 times. This leads to a decrease in the concentration of positively charged carriers by more than two times and an increase in the film resistance by more than three times.

An interdigital transducer structure was fabricated from multilayer graphene on the surface of the YZ-cut of a LiNbO3 ferroelectric crystal. The multilayer graphene was prepared by CVD method and transferred onto the surface of the LiNbO3 substrate. The properties of the multilayer graphene film were studied by Raman spectroscopy. A multilayer graphene (MLG) interdigital transducer (IDT) structure for surface acoustic wave (SAW) excitation with a wavelength of Λ=60 μm was fabricated on the surface of the LiNbO3 crystal using electron beam lithography (EBL) and plasma chemical etching. The amplitude–frequency response of the SAW delay time line was measured. The process of SAW excitation by graphene IDT was visualized by scanning electron microscopy. It was demonstrated that the increase in the SAW velocity using graphene was related to the minimization of the IDT mass.

The electron-beam-induced current (EBIC) method is utilized in this work to visualize conductive channels formed in graphene oxide as a result of resistive switching. Using metal–insulator–semiconductor (MIS) structures, an increase in the electron beam induced current by a few orders of magnitude as compared with the EBIC signal in metal–insulator–metal (MIM) structures is achieved. The mechanism of the EBIC image formation related to the conductive channels is explained by the separation and collection of the e-beam generated excess carriers by rectifying barrier nanocontacts formed at the graphene oxide/Si interface during resistive switching. It is shown that the collection efficiency of the formed nanocontacts decreases with the beam energy, in agreement with the theoretical predictions for the Schottky-like nanocontacts. An important advantage of the EBIC method is demonstrated in its ability to monitor the generation and elimination of high density conductive channels even when the current–voltage measurements cannot detect and separate these processes. EBIC study of the dynamics of the conductive channel formation can help better understand the underlying physical mechanisms of their generation.

Уважаемые коллеги!Благодарим Вас за проявленный интерес к Четвертой российской конференции «Графен: молекула и 2D кристалл» и желание принять участие в её работе.Конференция проходит в научно-образовательном центре города Новосибирска -Академгородке.Мероприятие посвящено актуальным направлениям исследований и разработок в области углеродных и низкоразмерных материалов.Проведение конференции поможет координации усилий ученых в решении современных проблем материаловедения и привлечению молодых исследователей для решения актуальных научных задач.Оргкомитет выражает особую благодарность НГУ, Центру компетенций НТИ «Моделирование и разработка новых функциональных материалов с заданными свойствами», компаниям «Диаэм», «НТ-МДТ Спектрум Инструментс» и корпорации "Графеновая Долина" за финансовую поддержку и журналам Аналитика, Наноиндустрия и РЭНСИТ за информационную поддержку.Искренне надеемся, что пребывание в Новосибирском Академгородке и в стенах Новосибирского государственного университета оставит множество положительных эмоций и

Results from studying the effect of an applied electric voltage on the Raman spectrum of graphene deposited on a lithium niobate crystal substrate with a ferroelectric domain structure are presented. The use of the principal component method for data processing in combination with correlation analysis made it possible to reveal the contribution to the change in the spectra associated with the linear deformation of the substrate due to the inverse piezoelectric effect. An effect of the graphene coating peeling was found. Furthermore, bending deformations of the graphene coating associated with the presence of a relief on the substrate were found. An analysis of the change in the spectra of graphene under the application of an electric voltage made it possible to determine the height of this relief.

The process of acoustically stimulated charge transport in the graphene film on the surface of the YZ−cut of a LiNbO3 crystal was investigated. It was found that the dependence of the current in the graphene film on the frequency of the surface acoustic wave (SAW) excitation repeats the amplitude-frequency response of the SAW delay time line. It is shown that increasing the SAW amplitude leads to an increase in the current in the graphene film, and the current in the graphene film depends linearly on the amplitude of the high-frequency input signal supplied to the interdigital transducer (IDT, in dB). It is demonstrated that at a positive bias potential on the graphene film, the SAW propagation allows to change the direction of the current in the graphene film by changing the amplitude of the SAW. It is also shown that in the frequency range of the amplitude-frequency response of the SAW delay time line, the current in the graphene film can vary from positive to negative values depending on the frequency. The capability to control the SAW excitation frequency or the SAW amplitude makes it possible to control the value and direction of the current in the graphene film. The SAW propagation lets to collect and transport the photo-stimulated charges in the graphene film on the crystal surface.

Band structure engineering by changing the parameters of Moire = superlattices enables creation of materials with outstanding properties for twistronics, straintronics and quantum nanoelectronics applications. Herein, twisted multilayer graphene (tMLG) with various combinations of twist angles (0) and numerous Moire = superlattices was synthesized. The strong dependence of the transport properties of tMLG on the structural characteristics was demonstrated using synchrotron-based core-level spectroscopy methods combined with micro-Raman spectroscopy. It has been shown that tMLG with a large content of the twisted phase with the twist angles between the adjacent graphene layers of 0 = 26-30 degrees over the entire tMLG thickness is characterized by a perfect structure of the single layer graphene (SLG) and extraordinary transport characteristics. At low temperatures, the asymmetry of charge carriers and atypical temperature dependence of average carrier mobility m were observed. In such tMLG, m was higher than 105 cm2V-1s-1. Decrease in the content of the twisted phase with 0 = 26-30 degrees, as well as increase in the contents of other twist angles and AB-stacked phase (0 = 0 degrees), leads to a significant decrease in m. Hence, tMLGs are a better choice for the nanoelectronics industry because, having outstanding transport properties, they are, contrary to SLG, insensitive to the specific features of process procedures.

Among the different graphene derivatives, graphene oxide is the most intensively studied material as it exhibits reliable and repeatable resistive switching. The operative mechanisms that are responsible for resistive switching are being intensively investigated, and three models explaining the change in the resistive states have been developed. These models are grounded in the metallic-like filamentary conduction, contact resistance modification and the oxidation of/reduction in the graphene oxide bulk. In this work, using Al/GO/n-Si structures, we demonstrate that all three of these operative mechanisms can simultaneously participate in the resistive switching of graphene oxide. Multiple point-like conduction channels in the graphene oxide films were detected by the electron beam-induced current (EBIC) technique. At the same time, large areas with increased conductivity were also revealed by EBIC. An analysis of these areas by Raman spectroscopy indicates the change in the graphene oxide bulk’s resistive properties. The EBIC data along with the measurements of the capacitance–voltage characteristics provided strong evidence of the involvement of an aluminum/graphene oxide interface in the switching processes. In addition, by using Al/GO/n-Si structures, we were able to identify unique local properties of the formed conductive channels, namely the change of the charge state of a conductive channel due to the creation of negatively charged traps and/or an increase in the GO work function.

Because of their unique atomic structure, 2D materials are able to create an up-to-date paradigm in fundamental science and technology on the way to engineering the band structure and electronic properties of materials on the nanoscale. One of the simplest methods along this path is the superposition of several 2D nanomaterials while simultaneously specifying the twist angle between adjacent layers (θ), which leads to the emergence of Moiré superlattices. The key challenge in 2D nanoelectronics is to obtain a nanomaterial with numerous Moiré superlattices in addition to a high carrier mobility in a stable and easy-to-fabricate material. Here, we demonstrate the possibility of synthesizing twisted multilayer graphene (tMLG) with a number of monolayers NL = 40-250 and predefined narrow ranges of θ = 3-8°, θ = 11-15°, and θ = 26-30°. A 2D nature of the electron transport is observed in the tMLG, and its carrier mobilities are close to those of twisted bilayer graphene (tBLG) (with θ = 30°) between h-BN layers. We demonstrate an undoubtful presence of numerous Moiré superlattices simultaneously throughout the entire tMLG thickness, while the periods of these superlattices are rather close to each other. This offers a challenge of producing a next generation of devices for nanoelectronics, twistronics, and neuromorphic computing for large data applications.

The transport properties, magnetoresistance, and photoresponse are investigated in turbostratic multilayer graphene films grown by chemical vapor deposition.

The photoresponse in multilayer graphene on a lithium niobate crystal (LiNbO3) was studied under the conditions of an electric potential applied to graphene and transmission of a surface acoustic wave (SAW). It is shown that the acoustoelectric current in graphene when irradiated with light either increases or decreases depending on the polarity of the potential applied to graphene. SAW causes the appearance of a periodic charge lattice in graphene, which enhances the interaction with incident light, which leads to an increase in the photoresponse.

In this Letter, we studied the photoresponse in multilayer graphene on a lithium niobate (LiNbO3) crystal under the conditions of an electric potential applied to graphene and transmission of a surface acoustic wave. The acoustoelectric current in graphene when irradiated with light is shown to either increase or decrease depending on the polarity of the potential applied to graphene. A surface acoustic wave causes the appearance of a periodic charge lattice in graphene that enhances the interaction with incident light, which leads to an increase in the photoresponse.

This paper concerns various technological specificity design and manufacturing of radiofrequency graphene-based nanoelectromechanical (GNEMS) switches on a semi-insulating substrate (e.g., GaN or GaAs). GNEMS switches are considered as a prospective solution to improve and miniaturize microwave devices and analog integrated circuits, and to raise their operating frequency limit. In the current research, GNEMS switch technology aspects are considered taking into account modern simulation, design, and fabrication features. Key results of this research include a description of the proposed GNEMS switch structure on GaN and GaAs substrates, the fabrication and test process. A difference between the properties of synthesized and embedded graphene is noted. The microwave performance was evaluated using full-wave numerical simulation in ANSYS HFSS, and the obtained scattering parameters are displayed. All these steps are required to employ GNEMS switches in prospective integrated circuits.

Protective Ni-based coatings for stainless steel current collectors of the planar solid oxide fuel cells (SOFCs) were developed and tested during 21,000 h in contact with lanthanum-strontium manganite cathode material. The compositional and microstructural alterations due to interdiffusion between Ni coating, La0.8Sr0.2MnO3 electrode and commercial Crofer 22 APU steel after long-term testing under the SOFC cathodic conditions, were studied. The results of micro-Raman spectroscopy and electron microscopy analyses showed a dominant role of Mn and Fe diffusion into the protective coating, leading to the formation of NiFe2O4 and MnFe2O4. Although Mn deficiency in the manganite cathode may decrease electrical conductivity, its impact on the overall contact resistance is insignificant. The Ni-based coatings were found to decrease area-specific interfacial resistivity down to 3-4 mOhm x cm(2) for, at least, 21,000 h (>2.5 years) at 1123 K, atmospheric oxygen pressure and current density of 0.5 A/cm(2). (C) 2019 Elsevier B.V. All rights reserved.

Graphene films were grown by the low-pressure chemical vapor deposition with a single injection of acetylene on an iron film catalyst deposited on oxidized silicon substrate. After treatment of the graphene on the iron film with aqueous solution of iron nitrate the structures consisting of quasi-suspended graphene on reaction products of the iron film with iron nitrate were obtained. The electron transport and magnetotransport properties of the films were investigated. The films have a low resistance of 80 Ohm sq−1 and a high sheet carrier density (8 × 1013 cm−2 at room temperature). At temperatures less than 200 K, the dependence of the Hall resistance on the magnetic field is like the abnormal Hall effect. Large positive linear magnetoresistance at a room temperature (60–100%) was observed in the films in a field of 0.6 T, which is attractive for creating magnetoresistive sensors. It was found that the critical magnetic field at which the MR becomes linear is very small (116–650 Oe) and linearly dependent on a temperature. The MR is proportional to the average mobility 〈µ〉. At low temperatures, the magnetoresistance increases with increasing temperature. At higher temperatures the MR decreases with increasing temperature.

Graphene films were grown on an iron film catalyst deposited on oxidized silicon substrate, using the low-pressure chemical vapor deposition. Subsequently the iron film was dissolved with an aqueous solution of iron nitrate. The structures consisting of quasi-suspended graphene on reaction products of an iron film with iron nitrate were obtained. Magnetoresistance properties of the structures were investigated at a room temperature, and the positive magnetoresistance was observed. The maximum magnetoresistance value was 100% in the magnetic field of 0.5T. The dependence of magnetoresistance on the magnetic field was quasi-linear in the range of 0.07–0.5T.

This work presents the experimental investigation of the synthesis of graphene carbon nanocomposites (CNC-G) by carbonization of porous silicon (PS) using CVD method at low temperature of T = 350-500 degrees C. The low-temperature synthesis of CNC-G is explained by a low melting temperature of porous silicon nanocrystallites (ncPS) formed during electrochemical etching.

Hybrid structures composed of graphene films and (0001) graphene ribbons perpendicular to the surface of a graphene-like film have been produced through the catalytic decomposition of a carbon-containing gas on an Al-coated SiO2/Si substrate having Ni catalyst islands on its surface. A hybrid structure has been grown by a one-step chemical vapor deposition process, by admitting acetylene into a chamber for a short time. The hybrid structures thus produced have been used to fabricate Hall sensors with a sensitivity of 3000 Ω/T. The synthesized hybrid structures are potential candidates for use in nanoelectronic devices, energy storage systems, etc. The technique proposed for the growth of such films is compatible with technologies that are employed in the electronics industry.