Resonant Raman scattering on graphene: SERS and gap-mode TERS.

Nanoscale deformations and corrugations occur in graphene-like two-dimensional materials during their incorporation into hybrid structures and real devices, such as sensors based on surface-enhanced Raman scattering (SERS-based sensors). The structural features mentioned above are known to affect the electronic properties of graphene, thus highly sensitive and high-resolution techniques are required to reveal and characterize arising local defects, mechanical deformations, and phase transformations. In this study, we demonstrate that gap-mode tip-enhanced Raman Scattering (gm-TERS), which offers the benefits of structural and chemical analytical methods, allows variations in the structure and mechanical state of a two-dimensional material to be probed with nanoscale spatial resolution. In this work, we demonstrate locally enhanced gm-TERS on a monolayer graphene film placed on a plasmonic substrate with specific diameter gold nanodisks. SERS measurements are employed to determine the optimal disk diameter and excitation wavelength for further realization of gm-TERS. A significant local plasmonic enhancement of the main vibrational modes in graphene by a factor of 100 and a high spatial resolution of 10 nm are achieved in the gm-TERS experiment, making gm-TERS chemical mapping possible. By analyzing the gm-TERS spectra of the graphene film in the local area of a nanodisk, the local tensile mechanical strain in graphene was detected, resulting in a split of the G mode into two components, G+ and G-. Using the frequency split in the positions of G+ and G- modes in the TERS spectra, the stress was estimated to be up to 1.5%. The results demonstrate that gap-mode TERS mapping allows rapid and precise characterization of local structural defects in two-dimensional materials on the nanoscale.

[The results of the study of the focus of initial caries of human tooth enamel in vitro using atomic force microscopy]. / Rezul'taty issledovaniya ochaga nachal'nogo kariesa emali zuba cheloveka in vitro s pomoshch'yu atomno-silovoi mikroskopii.

OBJECTIVE: Identify structural disorders of the surface of the enamel of a human tooth during the development of the carious process in the «white spot¼ stage using atomic force microscopy (AFM). MATERIAL AND METODS: The studies were carried out on 10 molar samples in areas with initial caries in the white spot stage. 6 areas of initial caries were scanned using the atomic force microscope Cetus Light (Nano Scan Technology, Russia) in semi-contact mode. Criteria were proposed for comparing the results of AFM scanning of tooth enamel surface samples and, based on them, the nature of the main structural disorders of the enamel surface in the affected area was determined. RESULTS: For all the samples studied, the healthy enamel surface was smoother compared to the enamel in the area of the clinically visible «white spot¼ and in the immediate vicinity of it. The heterogeneity of the enamel surface in the center of the white spot¼ for all the samples studied was at least 60% higher than at the edge of the process. It was revealed that the heterogeneity of the surface outside the clinically visible white spot at a distance of less than 1 mm from its perimeter is at least 30% higher than that of healthy tissue of the same tooth. It is shown that the heterogeneity of the enamel surface in the center of the caries area in the white spot stage is at least 4 times greater than the heterogeneity of the surface of the healthy enamel of the same tooth, which indicates its demineralization. CONCLUSION: The established features of the spread of the initial carious process can be used in clinical practice for the diagnosis and dynamic observation of the processes of enamel demineralization.

[Assessment of the role of nutritional and genetic determinants in the formation of the risk of diseases associated with folate cycle disorders in the population of the Omsk region].

A number of essential nutrients are involved in the folate cycle, and its effectiveness depends on the sufficient intake of them. In addition, polymorphic variants of the methylenetetrahydrofolate reductase (MTHFR), methionine synthase reductase (MTRR) and methionine synthase (MTR) genes affect a wide range of biochemical reactions of the folate cycle and should also be considered as a risk factor for the development of a number of diseases. The purpose of this research was to study the prevalence of these risk factors. Material and methods. The prevalence of polymorphisms of the folate cycle genes: C677T polymorphism of the MTHFR gene and A66G polymorphism of the MTRR gene in a random stratified (by sex and age) sample of the adult population of the Omsk region [n=139, 51 men, 88 women, aged 18 to 75 years, median age 37 (26; 48) years] was studied. The identification of polymorphisms was carried out by the method of allele-specific polymerase chain reaction with an electrophoretic detection scheme. Using the food intake frequency questionnaire, the dietary intake of nutrients involved in the folate cycle was determined: B vitamins (B6, B2, B9, B12), methionine, choline, in a representative stratified sample of residents of the Omsk region [n=421, 177 men, 244 women, aged 18 to 83 years, median age 37 (23; 57) years]. Results. MTHFR genotypes (A222V С677T C>T) were distributed as follows: CC-type - 51.3%, CT - 41.0%, TT - 7.7%; MTRR genotypes (I22M A>G): AA type - 57.9%, AG - 30.3%, GG - 11.8%. The analysis of actual nutrition showed consumption below the recommended dietary intake of folates in 88.2% persons, vitamin B2 and choline - in 40.5%, vitamin B6 - in 29.2%, methionine - in 22.0%. Vitamin B12 intake was within the recommended range. Conclusion. The totality of the data presented indicates the combined influence and wide distribution of factors that determine the low efficiency of the folate cycle, and, as a result, a high risk of developing a characteristic pathology for the adult population of the region, which determines the need and priorities for prevention measures, including healthy nutrition.

[Total nasal defect reconstruction with nasal prosthesis. Two case reports]. / Zameshchenie total'nogo defekta nosa s pomoshch'yu ekzoproteza. Dva klinicheskikh sluchaya.

Total nasal defects after injures or surgical interventions can negatively affect patient's quality of life. Maxillofacial prosthesis is a contemporarily and reliable solution. This method gives us opportunity to restore missing tissues and helps patients to overcome social and psychological difficulties. In this article we demonstrated advantages and disadvantages of the method in two clinical cases. The application of magnetic and adhesive retention in different cases is described. Also, we outlined clinical and technological steps of maxillofacial prosthesis manufacture. Modified procedure of impression obtaining is offered.

[Tatiana Strelyukhina is an outstanding dentist, scientist, researcher (on the occasion of the 100th anniversary)]. / Tat'yana Fedorovna Strelyukhina ­ vydayushchiisya stomatolog, uchenyi, issledovatel' (k 100-letiyu so dnya rozhdeniya).

The purpose of the work is to present materials on the history of Russian dentistry in connection with the 100th anniversary of an outstanding scientist, clinician, one of the patriarchs of Russian dentistry, a veteran of the great Patriotic war, associate Professor Tatyana Strelyukhina who was at the origins of the specialty and was among the first to create domestic dental materials science.

Electrochemically exfoliated thin Bi2Se3 films and van der Waals heterostructures Bi2Se3/graphene.

Thin Bi2Se3 flakes with few nanometer thicknesses and sized up to 350 µm were created by using electrochemical splitting from high-quality Bi2Se3 bulk monocrystals. The dependence of film resistance on the Bi2Se3 flake thickness demonstrates that, at room temperature, the bulk conductivity becomes negligible in comparison with the surface conductivity for films with thicknesses lower than 80 nm. Unexpectedly, all these films demonstrated p-type conductivity. The doping effect with sulfur or sulfur-related radicals during electrochemical exfoliation is suggested for the p-type conductivity of the exfoliated Bi2Se3 films. The formation of 2-8 nm films was predominantly found. Van der Waals (vdW) heterostructures of Bi2Se3/Graphene/SiO2/Si were created and their properties were compared with that of Bi2Se3 on the SiO2/Si substrate. The increase of the conductivity and carrier mobility in Bi2Se3 flakes of 3-5 times was found for vdW heterostructures with graphene. Thin Bi2Se3 films are potentially interesting for applications for spintronics, nano- and optoelectronics.

[Gastric damage in systemic sarcoidosis]. / Porazhenie zheludka pri sistemnom sarkoidoze.

Sarcoidosis is a multisystem disease of unknown etiology, characterized by specific granulomas without caseous necrosis in the affected organs and tissues. Along with respiratory organs, the gastrointestinal tract may be affected by sarcoidosis. Due to the rarity of gastric involvement of sarcoidosis, substantial difficulties arise in verifying the diagnosis, making a differential diagnosis, and examining gastric biopsy specimens. The paper describes in detail pathological changes in the gastric wall tissue specimen in sarcoidosis and comparatively analyzes the findings with the data available in the literature.

Nanostructuring few-layer graphene films with swift heavy ions for electronic application: tuning of electronic and transport properties.

The morphology and electronic properties of single and few-layer graphene films nanostructured by the impact of heavy high-energy ions have been studied. It is found that ion irradiation leads to the formation of nano-sized pores, or antidots, with sizes ranging from 20 to 60 nm, in the upper one or two layers. The sizes of the pores proved to be roughly independent of the energy of the ions, whereas the areal density of the pores increased with the ion dose. With increasing ion energy (>70 MeV), a profound reduction in the concentration of structural defects (by a factor of 2-5), relatively high mobility values of charge carriers (700-1200 cm2 V-1 s-1) and a transport band gap of about 50 meV were observed in the nanostructured films. The experimental data were rationalized through atomistic simulations of ion impact onto few-layer graphene structures with a thickness matching the experimental samples. We showed that even a single Xe atom with energy in the experimental range produces a considerable amount of damage in the graphene lattice, whereas high dose ion irradiation allows one to propose a high probability of consecutive impacts of several ions onto an area already amorphized by the previous ions, which increases the average radius of the pore to match the experimental results. We also found that the formation of "welded" sheets due to interlayer covalent bonds at the edges and, hence, defect-free antidot arrays is likely at high ion energies (above 70 MeV).

Two-layer and composite films based on oxidized and fluorinated graphene.

This study is devoted to the production and investigation of dielectric films, based on oxidized and fluorinated graphene suspensions. The properties of the graphene oxide films may be greatly improved by adding fluorographene. FG films have transmission in the visible and near infrared ranges equal to 96-98%. Two-layer films of fluorinated graphene on graphene oxide and composite films (composite suspension of fluorinated and oxidized graphene) exhibit good insulating properties. Their leakage currents are lower than that in the graphene oxide or fluorinated graphene by 3-5 orders of magnitude. A significant increase in thermal stability and relatively low charge in the film and at the interface with silicon (3 × 1010-1.4 × 1011 cm-2) are also found for these films. An application of thin fluorographene films (a few nanometers) decorates and eliminates structural defects in the graphene oxide films, resulting in conductivity blocking in graphene oxide. The built-in charge density in the composite film of 10-20% fluorographene in the graphene oxide is much less than in the two-layer film (<1 × 1010 cm-2). The created two-layer and composite films may be practically applied in 2D printed and flexible electronics as insulating films (gate dielectric and interlayer insulator), as well as materials showing the resistive effect.

[Ultrastructural changes of human dental hard tissues during orthodontic treatment with fixed appliances]. / Issledovanie ul'trastrukturnogo sostoianiia tverdykh tkanei zuba pri éksperimental'nom modelirovanii ortodonticheskogo lecheniia nes''emnoi apparaturoi.

The aim of the study was to evaluate ultrastructural changes of dental enamel after fixation of orthodontic appliances, initial influence of orthodontic forces and removal of braces. Five intact permanent tooth extracted for orthodontic reasons were included in the experimental study. Scanning probe microscopy was conducted in 4 random enamel points in each tooth (20 points overall) in semi-contact mode with standard 10 nm probes. The study showed ultrastructural enamel changes such as nanofractures up to 1 mm along the braces locks. The changes correlated with surface morphological features and teeth anatomy and may play an important role in dental decay and non-carious lesions occurring in the course of orthodontic treatment.

Graphene-based humidity sensors: the origin of alternating resistance change.

The response of a graphene-based humidity sensor is considered as a function of film structures. Analysis of the resistance changes due to water molecule adsorption on the graphene or multi-layer graphene (MLG) surface is performed for films with different structures and resistivities from hundreds of ohms/sq to hundreds of kilo-ohms/sq. The results revealed possible increase, decrease and non-monotonous behavior of resistance with changes in film structure. Adsorption of water molecules at grain boundary defects is assumed to lead to an increase in film resistivity due to the donor property of water and the p-type conductivity of graphene. Another type of conductive center with a higher capture cross-section is realized in the case of water molecule adsorption at edge defects in MLG films (the formation of conductive chains with ionic conductivity). If these chains form a continuous network the film resistivity decreases. The result of the competition between the opposite effects of the conductivity compensation and formation of the water-based conductive chains depends on the film structure and determines the response of humidity sensors. Sensor sensitivity is found to increase when only one type of defect determines water adsorption (edge defects or grain boundary defects).

Fluorinated graphene suspension for inkjet printed technologies.

The possibility to control the size of the flakes of graphene suspension in the course of their fluorination in an aqueous hydrofluoric acid solution was demonstrated. The effect of the suspension composition, the fluorination time, temperature and thermal stress on the fragmentation process was investigated. The corrugation of suspension flakes, which occurs at fluorination due to a difference in the constants of graphene and fluorographene lattices, leads to the appearance of nonuniform mechanical stresses. The fact that the flake size after fragmentation is determined by the size of corrugation allows the assumption that the driving force of fragmentation is this mechanical stress. This assumption is confirmed by the break of the corrugated layers from flakes under thermal stress. Moreover, fluorination treatment at elevated temperatures (∼70 °C) significantly accelerates the fragmentation process. Suspensions of fluorinated graphene with nanometer size flakes are of interest for the development of 2D ink-jet printing technologies and production of thermally and chemically stable dielectric films for nanoelectronics. The printed fluorinated graphene films on silicon and flexible substrates have been demonstrated and the charges in metal-insulator-semiconductor structures have been estimated as the ultra low values of (0.5-2) × 10(10) cm(-2).

[Primary and secondary hypophysitis: A clinicomorphological study]. / Pervichnyi i vtorichnyi gipofizit. Kliniko-morfologicheskoe issledovanie.

The paper describes 6 cases of the rare disease - primary and secondary hypophysitis detected by a morphological examination of the material of endoscopic transsphenoidal resection of pituitary neoplasms. It also provides clinical and morphological comparisons and analyzes the data available in the literature.

Differential recruitment of brain networks during visuospatial and color processing: Evidence from ERP microstates.

Recent functional magnetic resonance imaging (fMRI) studies consistently revealed contributions of fronto-parietal and related networks to the execution of a visuospatial judgment task, the so-called "Clock Task". However, due to the low temporal resolution of fMRI, the exact cortical dynamics and timing of processing during task performance could not be resolved until now. In order to clarify the detailed cortical activity and temporal dynamics, 14 healthy subjects performed an established version of the "Clock Task", which comprises a visuospatial task (angle discrimination) and a control task (color discrimination) with the same stimulus material, in an electroencephalography (EEG) experiment. Based on the time-resolved analysis of network activations (microstate analysis), differences in timing between the angle compared to the color discrimination task were found after sensory processing in a time window starting around 200 ms. Significant differences between the two tasks were observed in an analysis window from 192 ms to 776 ms. We divided this window in two parts: an early phase - from 192 ms to ∼440 ms, and a late phase - from ∼440 ms to 776 ms. For both tasks, the order of network activations and the types of networks were the same, but, in each phase, activations for the two conditions were dominated by differing network states with divergent temporal dynamics. Our results provide an important basis for the assessment of deviations in processing dynamics during visuospatial tasks in clinical populations.

Fluorinated graphene dielectric films obtained from functionalized graphene suspension: preparation and properties.

In the present study, we have examined the interaction between a suspension of graphene in dimethylformamide and an aqueous solution of hydrofluoric acid, which was found to result in partial fluorination of suspension flakes. A considerable decrease in the thickness and lateral size of the graphene flakes (up to 1-5 monolayers in thickness and 100-300 nm in diameter) with increasing duration of fluorination treatment is found to be accompanied by a simultaneous transition of the flakes from the conducting to the insulating state. Smooth and uniform insulating films with a roughness of ∼2 nm and thicknesses down to 20 nm were deposited from the suspension on silicon. The electrical and structural properties of the films suggest their use as insulating elements in thin-film nano- and microelectronic device structures. In particular, it was found that the films prepared from the fluorinated suspension display rather high breakdown voltages (field strength of (1-3) × 10(6) V cm(-1)), ultralow densities of charges in the film and at the interface with the silicon substrate in metal-insulator-semiconductor structures (∼(1-5) × 10(10) cm(-2)). Such excellent characteristics of the dielectric film can be compared only to well-developed SiO2 layers. The films from the fluorinated suspension are cheap, practically feasible and easy to produce.

[Evaluation of dental hard tissues by means of atomic force microscopy].

The paper presents modified method of teeth slice preparation for evaluating enamel and dentin morphological structure by means of atomic force microscopy (AFM). The method allows measuring directly and describing hydroxyappatite crystals on nanolevel. Structural properties of dental hard tissues were determined and comparative characteristic of form and density of enamel prisms particles with similar morphological inorganic elements of dentin were specified.

[Peculiarities of the morphological structure of the inorganic component of human dental enamel and dentin at nano-level].

Using the polished sections of 20 permanent human molars and premolars, the regimes of probe atomic force microscopy were assessed that permit the definition of the size, shape, spatial configuration of the structure-forming hydroxyapatite crystals of enamel and dentin inorganic component. It was found that the major part of enamel crystals had the size of 40-60 nm and were more flattened. Dentin crystal average size was equal to 60-80 nm. Microspaces between them had the shape of rotational ellipsoid sized 120 nm by 60 nm.

Extremely high response of electrostatically exfoliated few layer graphene to ammonia adsorption.

Extremely high gas sensing properties of p-type few layer graphene flakes exfoliated from highly oriented pyrolytic graphite have been demonstrated. The current response to ammonia adsorption is strongly dependent on film thickness and is higher than that for graphene by 1-8 orders of magnitude. A maximal response was found for sample thickness ∼ 2 nm. The effect is attributed to the formation of multiple p-n-p junctions at the grain boundaries in the polycrystalline graphene flakes exposed to ammonia-containing ambient.

Production of podophyllotoxin in Linum linearifolium in vitro cultures.

For the first time, callus and suspension cultures of Linum linearifolium were initiated. Podophyllotoxin (PTOX), a strong antitumor precursor, was isolated from the calli and suspension, as a main lignan besides smaller amount of 6-methoxypodophyllotoxin (6MPTOX). L. linearifolium is now the third Linum species of section Syllinum, with PTOX as the main lignan. The amounts of lignans, especially PTOX, found in L. linearifolium cell cultures are quite high within the studied Linum species until now. The antiproliferative effects of extracts were tested in a panel of human tumor cell lines, using the MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide]-dye reduction assay. The lignan mixtures caused concentration-dependent inhibition of malignant cell proliferation and showed moderate cytotoxic activity. The results clearly demonstrate that the lignan mixture of L. linearifolium exerts inhibitory effects against malignant cells.