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Here, we have thoroughly studied the effect of chemistry of graphene derivatives on the composition of N-species after N-doping with the help of core-level spectroscopy techniques. The modulation of the N-species by tailoring the functionalization and atomic structure of graphene derivatives prior to chemical N-doping is experimentally demonstrated for the first time. The large extent of non-terminated or phenol-functionalized graphene edges is found to facilitate the formation of pyridinic nitrogen with its relative content exceeding 72%. In turn, the predominant decoration by the pyrazolic moieties is shown for the perforated and carboxyl-derived graphene layers. The thermal annealing at moderate temperatures of ca.345 °C is shown to equally readjust the composition of N-species in graphene derivatives regardless of their chemistry, nanostructure, and the initial distribution of the N-species. Further examination of N K-edge X-ray absorption spectra (XAS) pointed out that the oxidation of the graphene layer governs the manifestation of the π∗ resonances and configuration of the σ∗ resonance. As a result, a set of facile methods to synthesize graphene derivatives with the desired type of the embedded nitrogen species for the optoelectronic and catalytic applications are proposed and crucial features of their identification using core-level spectroscopy techniques are emphasized.

Here, the synthesis of holey carbonylated (C-ny) graphene derivative and its application for gas sensing is demonstrated. The carbonylation of graphene oxide leads to the 3-fold increase in the concentration of carbonyl groups’ up to 9 at.% with a substantial elimination of other oxygen functionalities. Such a chemical modification is accompanied by the perforation of the graphene layer with the appearance of matrices of nanoscale holes, leading to corrugation of the layer and its sectioning into localized domains of the π-conjugated network. Combined with the predominant presence of carbonyls, granting the specificity in gas molecules adsorption, these features result in the enhanced gas sensing properties of C-ny graphene at room temperature with a selective response to NH3. Opposite chemiresistive response towards ammonia when compared to other analytes, such as ethanol, acetone, CO2, is demonstrated for the C-ny graphene layer both in humid and dry air background. Moreover, a selective discrimination of all of the studied analytes is further approached by employing a vector signal generated by C-ny multielectrode chip. Comparing the experimental results with the calculations performed in framework of density functional theory, we clarify the effect of partial charge transfer caused by water and ammonia adsorption on the chemiresistive response.

The structural and some other characteristics of quasi-freestanding single-layer graphene obtained by annealing of the buffer layer in the flow of hydrogen are studied in comparison with those of conventional epitaxial graphene. The high structural quality and good lateral uniformity of the thus-obtained graphene film are checked and confirmed by the use of such techniques as Raman spectroscopy, atomic force, and Kelvin probe force microscopies. The confirmation of its single-layer and freestanding character is obtained via the analysis of respective data of X-ray photoelectron spectroscopy.

The one-step method for graphene oxide (GO) simultaneous reduction and carboxylation via ultraviolet irradiation in the inert atmosphere has been reported. X-ray photoelectron spectroscopy (XPS) an...

Engineering of the 2D materials' electronic structure is at the forefront of nanomaterials research nowadays, giving an advance in the development of next-generation photonic devices, e-sensing technologies, and smart materials. Herein, employing core-level spectroscopy methods combined with density functional theory (DFT) modeling, the modification of the graphenes' valence band (VB) upon its derivatization by carboxyls and ketones is revealed. The appearance of a set of localized states in the VB of graphene related to molecular orbitals of the introduced functionalities is signified both experimentally and theoretically. Applying the DFT calculations of the density of states projected on the functional groups, their contributions to the VB structure are decomposed. An empirical approach, allowing one to analyze and predict the impact of a certain functional group on the graphenes' electronic structure in terms of examination of the model molecules, mimicking the introduced functionality, is proposed and validated. The interpretation of the arising states origin is made and their designation, pointing out their symmetry type, is proposed. Taken together, these results guide the band structure engineering of graphene derivatives and give a hint on the mechanisms underlying the alteration of the VB structure of 2D materials upon their derivatization.

Scientific reports 10(1), 6902 (2020). doi:10.1038/s41598-020-63935-3, In this paper we present a facile method for the synthesis of aminated graphene derivative through simultaneous reduction and amination of graphene oxide via two-step liquid phase treatment with hydrobromic acid and ammonia solution in mild conditions. The amination degree of the obtained aminated reduced graphene oxide is of about 4 at.%, whereas C/O ratio is up to 8.8 as determined by means of X-ray photoelectron spectroscopy. The chemical reactivity of the introduced amine groups is further verified by successful test covalent bonding of the obtained aminated graphene with 3-Chlorobenzoyl chloride. The morphological features and electronic properties, namely conductivity, valence band structure and work function are studied as well, illustrating the influence of amine groups on graphene structure and physical properties. Particularly, the increase of the electrical conductivity, reduction of the work function value and tendency to form wrinkled and corrugated graphene layers are observed in the aminated graphene derivative compared to the pristine reduced graphene oxide. As obtained aminated graphene could be used for photovoltaic, biosensing and catalysis application as well as a starting material for further chemical modifications., Published by Macmillan Publishers Limited, part of Springer Nature, [London]

Surface electronic properties of the native-oxide-covered and sulfide-passivated InN grown on the Si(111) substrate were studied by photoemission spectroscopy induced by synchrotron radiation, as well as by photoluminescence and atomic-force microscopy. It was found that the treatment of the native-oxide-covered InN surface with the solution of ammonium sulfide in 2-propanol results in the increase of the surface band bending by 0.7–0.8 eV. Sulfide passivation causes increase in the photoluminescence intensity of InN, as well as the appearance of the photovoltage induced by illumination with red light, which is the evidence of the reduction of the surface recombination velocity due to sulfide passivation. These improved electronic properties remain stable for at least 20 months of the exposure in air.

It was revealed that sp3-sp2 rehybridization of carbon atoms on the facets of nanocrystalline paricles of detonation diamond under thermal treatment results in weakening the hardness of its primary agglomerates. That discloses a secret of the unusual high strength of industrial diamond agglomerates and allows obtaining hydrosol of individual diamond nanoparticles ranging of 4–5 nm. Details of sp3-sp2 rehybridization have been studied by number of complementary methods including TEM, AFM, XPS, Raman scattering, X-ray diffraction and dynamic light scattering. A model for complete explanation of the processes during the annealing and obtaining stable hydrosols of 4–5 nm DND particles with different ζ-potentials is suggested. The model reveals the new ways for obtaining nanodiamond sols in other solvents.

We present a study of the process of reduction of thin graphene oxide (GO) films consisting of flakes with lateral size of up to 100 μm through soft ultraviolet irradiation in the argon atmosphere. It was found out that the reduction process leads to a significant decrease in the overall content of the basal-plane functional groups, namely, epoxides and hydroxyls, but with simultaneous increase in the total number of the edge-located carboxyl groups. Obtained transmission electron microscopy images showed that this effect is related to formation of nanoscale holes in the course of reduction. Based on the data obtained, we have proposed a mechanism of the observed GO structural modification in terms of photoinduced chemical reactions between the carbon network and functional groups. These reactions result in progressive growth of the initially existing and newly formed vacancies with formation of the nanoholes with size of up to 100 nm. Thus, reduced graphene oxide films with the restored conjugated networ...

In this work we present a facile method for the synthesis of the carboxylated graphene derivate. The resulting material contains up to 10.9 at.% of carboxyl groups and with negligible content of other oxygen-containing groups. Moreover, formation of large round-shaped nanoscale holes is observed due to the applied synthesis process. The synthesized graphene derivative is of high interest for the sensing applications due to combination of its conductive nature and chemical reactivity provided by the attached carboxyl groups.

A complex study of electrosurface properties has been performed for single-crystalline detonation nanodiamond particles with sizes of 4–5 nm obtained by air annealing of their agglomerates. FTIR spectroscopy and X-ray photoelectron spectroscopy data indicate that the investigated properties result from the presence of two types of ionogenic functional groups on the particle surface, i.e., acidic carboxyl and amphoteric hydroxyl groups. Acid-base potentiometric titration, laser Doppler electrophoresis, and conductometry have been employed to measure the Γ H + (pH) and Γ OH - (pH) adsorption isotherms of potential-determining ions, as well as the pH dependences (in a pH range of 3.5–10.5) of the surface charge density, electrophoretic mobility, and specific surface conductivity of detonation nanodiamond particles in aqueous 0.0001–0.01 M KCl solutions.

In this paper, we for the first time demonstrate efficient nitrogen doping of graphene oxide (GO) with nitrogen concentration of up to 5 at.% via modified Hummers' method. Using X-ray photoelectron spectroscopy (XPS), X-ray absorbance spectroscopy (XAS) and Fourier transform infrared spectroscopy (FTIR) techniques, we have found out graphitic nitrogen to be the dominant type of the implemented nitrogen species. At the same time, the subsequent GO thermal reduction to graphene appears to result in a transformation of the graphitic nitrogen into pyridines and pyrroles. The mechanisms of the observed GO nitrogen doping and conversion of the nitrogen species are proposed, providing an opportunity to control the type and concentration of the implemented nitrogen within the approach. A two-time increase of the graphenes' conductivity is observed due to the performed nitrogen doping. Further comprehensive electrical studies combined with the transmission electron microscopy (TEM) and density functional theory (DFT) modeling have allowed us to estimate the conductivity mechanism and the impact of the implemented nitrogen. As a net result, a simple method to synthesize N-doped graphene with the desired type of the nitrogen species is developed, which leads to new perspective applications for graphene, i.e. supercapacitors, catalysis, and sensors.

This paper reports a facile and green method for conversion of graphene oxide (GO) into graphene by low-temperature heating (80 °C) in the presence of a glass wafer. Compared to conventional GO chemical reduction methods, the presented approach is easy-scalable, operationally simple, and based on the use of a non-toxic recyclable deoxygenation agent. The efficiency of the proposed method is further expanded by the fact that it can be applied for reducing both GO suspensions and large-scale thin films formed on various substrates prior to the reduction process. The quality of the obtained reduced graphene oxide (rGO) strongly depends on the type of the used glass wafer, and, particularly, magnesium silicate glass can provide rGO with the C/O ratio of 7.4 and conductivity of up to 33000 S*cm−1. Based on the data obtained, we have suggested a mechanism of the observed reduction process in terms of the hydrolysis of the glass wafer with subsequent interaction of the leached alkali and alkali earth cations and silicate anions with graphene oxide, resulting in elimination of the oxygen-containing groups from the latter one. The proposed approach can be efficiently used for low-cost bulk-quantity production of graphene and graphene-based materials for a wide field of applications.

Monodisperse carbon nanodots (MCNDs) having an identical composition, structure, shape and size possess identical chemical and physical properties, making them highly promising for various technical and medical applications. Herein, we report a facile and effective route to obtain monodisperse carbon nanodots 3.5 ± 0.9 nm in size by thermal decomposition of organosilane within the pores of monodisperse mesoporous silica particles with subsequent removal of the silica template. Structural studies demonstrated that the MCNDs we synthesized consist of ∼7–10 defective graphene layers that are misoriented with respect to each other and contain various oxygen-containing functional groups. It was demonstrated that, owing to their identical size and chemical composition, the MCNDs are formed via coagulation primary aggregates ∼10–30 nm in size, which are, in turn, combined into secondary porous spherical aggregates ∼100–200 nm in diameter. The processes of coagulation of MCNDs and peptization of their hierarchical aggregates are fully reversible and can be controlled by varying the MCND concentration or the pH value of the hydrosols. Submicrometer spherical aggregates of MCNDs are not disintegrated as the hydrosol is dried. The thus obtained porous spherical aggregates of MCNDs are promising for drug delivery as a self-disassembling container for medicinal preparations.

Graphite oxide (GO) nanofilms on the SiO 2 /Si surface have been studied by photoelectron spectroscopy (XPS) with synchrotron radiation and by Auger electron spectroscopy (AES). Auger electron energies were determined for the basic functional GO groups: hydroxyl (C OH) and epoxide (C O C). The data obtained enabled developing a technique for the GO chemical and elemental composition determination. The technique allows controlling the hydrogen content in GO despite the impossibility of Auger emission from hydrogen.

An aerosol method for deposition of nanometer-thick layers of detonation diamonds has been developed. Application of a suspension of deagglomerated diamond particles onto substrates from an aerosol provides deposition of small-size drops, with the ultrasonic spraying of the suspension precluding formation of secondary agglomerates of nanodiamond particles in the course of sample drying. The layers are promising for high-precision studies of the structure and chemical composition of the surface of isolated nanodiamond particles.

An advanced oxidation process has been implemented for detonation nanodiamond surface chemical modification. The treatment intended for chemical oxidation of detonation nanodiamond surface through reactions with ozone in aqueous media. A number of detonation nanodiamond samples were processed: purified industrial grade and single particle hydrosols of air oxidized and hydrogen annealed detonation nanodiamonds. Comparative analysis of surface chemical composition provided by XPS and FTIR data.

We have studied the UV reduction process of thin graphene oxide films, deposited on silicon substrate from ethanol suspension. Chemical structure of obtained material was analyzed by XPS method. TEM images showed holes formation during reduction process, that are connected into network. Films with observed structure have great variety of possible future applications, such as gas-sensors and different organic/nonorganic nanocompisites.

Effective cross-sections σD(E) of fullerite C60 modification by electrons in the energy range E = 0.25–3000 eV were obtained using electron energy loss spectroscopy. Comparison of σD(E) with cross-section σF(E), describing fragmentation of individual fullerenes C60 in the gas state and known from literature, revealed several orders of magnitude difference between the absolute values of these cross-sections and the inverse behavior of their energy dependencies. This fact evidences that the mechanism of electron-induced destruction of fullerite C60 drastically differs from the one implied by the model of successive fragmentation of separate fullerenes and that condensed fullerenes C60 are radically more stable than it was considered earlier.

Transformation of the chemical composition and electron structure of graphite oxide (GO) nanolayers as a result of their annealing in hydrogen has been studied by X-ray photoelectron spectroscopy using synchrotron radiation. It is established that both the chemical composition and bandgap width of GO can be controlled by varying the temperature and duration of heat treatment. By this means, the properties of GO nanolayers can be smoothly changed from dielectric to semiconductor.

An extremely high rate of destruction of fluorinated fullerite С60F18 by accelerated electrons was revealed. This rate was three orders of magnitude higher than that of the ordinary fullerite C60. High rate of the modification was assumed to be caused by the efficient mechanism of fragmentation of С60F18 molecule compared to the mechanism of polymerization of fullerite C60. The conclusion has been made that films of fluorinated fullerites are perspective as an electron-beam resist for dry nanolithography.

The structure of C1s and F1s core electron levels in C60F18 and C60F36 fluorinated fullerenes has been studied by X-ray photoelectron spectroscopy using synchrotron radiation. It is established that C1s levels of carbon atoms not bound to fluorine in these compounds are shifted down by 1.0 and 1.6 eV relative to the C1s level in the usual C60 fullerene, so that the binding energies of the core electron levels in C60F18 and C60F36 amount to Eb (C1s, C-C) = 285.7 and 286.3 eV, respectively. These values are characteristic and can be used for the identification of both homogeneous fluorinated fullerenes and combined materials comprising a mixture of various fluorinated fullerenes with each other and with different carbon-containing based materials.

Photoemission spectra of solid fluorinated fullerenes C60Fx (x = 18, 36) were measured in comparison with parent C60 using synchrotron radiation (hν = 120 eV) providing the spectra in the density of states mode. Creation of the ion-like bonding of fluorine and disappearance of the π-states were observed to be a result of fluorination. Disappearance of the upper lying π-states was revealed to be a reason of the band gap widening upon fluorination.

Comparative study of near edge X‐ray absorption fine structure spectra (NEXAFS) of fluorinated fullerenes C60Fx (x = 0, 18, 36) has been implemented. Local density of unoccupied states was obtained and an accurate boundary between π* and (π+σ)* states was determined. The experimental evidence was found that unoccupied π*‐ states of C60Fx are delocalized ones and form cluster shells that sequentially disappear in fluorination starting from the highest state. As a result, the density of the lowest π* ‐ state (LUMO) was revealed to remain being constant in fluorination despite the π ‐electron subsystem exhaustion.

A new calculation technique providing correct conversion of experimental data obtained by reflection‐electron‐energy loss spectroscopy (REELS) into respective dielectric functions has been developed. The technique was successfully applied to processing a series of REELS spectra taken from C60 film in the course of its irradiation with the flux of 1.5 keV electrons. As a result, a number of complex dielectric functions e = e1+ie2 corresponding to the different stages of fullerite C60 electron induced modification was obtained for the first time. These data provide an exhaustive characterization of electronic and optical properties of arbitrary modified C60, thereby give a serious impetus to the search for the new technological applications of this material.

We have observed the energy structure in the density of occupied states of graphene grown on n-type 6H-SiC (0001). The structure revealed with photoelectron spectroscopy is described by creation of the quantum well states whose number and the energy position (E1 = 0.3 eV, E2 = 1.2 eV, E3 = 2.6 eV ) coincide with the calculated ones for deep (V = 2.9 eV) and narrow (d = 2.15 A) quantum well formed by potential relief of the valence bands in the structure graphene/n-SiC. We believe that the quantum well states should be formed also in graphene on dielectric and in suspended graphene., Comment: 7 pages, 4 figures

The electronic structure of the solid polycrystalline fluorinated fullerene C60F18 has been investigated by reflection electron‐energy‐loss spectroscopy for the first time. The elementary excitation spectrum of the solid C60F18 was compared with the respective spectrum of the solid C60, and an explanation of their significant similarity in the range of π→π∗ transitions was suggested.

Simulating of fullerite C60 polymerization under the electron beam irradiation was performed within the framework of proposed model. The number of arising covalent bonds was assumed to be proportional to the number of excited and ionized C60 molecules. The polarization, exchange, and muffin‐tin size were taken into account in simulating elastic scattering events; inelastic ones were modeled within the frame of dielectric formalism for scattering on valence electrons and as a binary collisions for ionization of deep atom levels. It was found out that small variations in the momentum‐ and frequency‐dependent loss function may considerably affect both the evolution of low energy secondary electrons and the character of the electron induced structure transformation.

It has been shown that low size dispersion systems of carbon nanoclusters can be fabricated by ion irradiation of fullerite C60 film through a special mask. As the mask, lavsan track membrane with more or less equal pinholes of diameter of about 60 nm was used. STM study showed that fabricated clusters have a form of the cone‐like island with average diameter of about 60 nm and height of about 5 nm.

A model has been suggested, and the simulation of the fullerite C60 polymerization by electrons within the energy range 0.15 ÷ 1.5 keV has been carried out. The number of created intermolecular bonds was assumed to be proportional (with a coefficient k) to the number of excited molecules. Polarization, exchange, and muffin-tin size were taken into account for elastic scattering. Ionization of deep atom levels was treated as a binary collision, and the inelastic scattering by valence electrons was described in the framework of the dielectric formalism. The comparison of results of the simulation with experimental data gave the coefficient of proportionality k∼(2 ÷ 5) · 10−3.

The photoelectron spectra of a C60 fullerene condensate are investigated. Under conditions where the photoionization (HOMO-ɛ 1) and Auger (KVV*) transitions are at resonance, the intensity of molecular lines in the photoelectron spectra increases by a factor of several tens. It is found that even insignificant destruction of the molecular structure of fullurenes under synchrotron radiation leads to quenching of the observed resonance. The quenching of the resonance manifests itself in a decrease in the intensity of the molecular lines in the photoemission spectra. The revealed effect can be used to determine the degree of radiation-induced modification of fullerenes.

The fullerite C60 modification induced by electron irradiation was studied using electron energy loss spectroscopy (EELS). We show that prolonged electron irradiation causes gradual transformation of electron and atomic structures of fullerite C60 films towards respective structures of amorphous carbon. Moreover, strongly modified parts of fullerite C60 films become thermally unevaporable. A possible mechanism of these effects is suggested. Finally, we propose a new original nanolithography technique based on two key ideas: the use of fullerite films as negative electron-beam resist and development of lithographic images by appropriate thermal treatment of these films.

Electron irradiation produces changes in the spectra of elementary excitations of C60 fullerite, which are manifested by decrease in the π-plasmon energy, bandgap width, and energies of the HOMO-LUMO and other molecular transitions, smoothening of the corresponding spectral features, and significant growth in the quasicontinuous low-energy background intensity, the latter being indicative of an increase in the conductivity. The observed “red shifts” are related to collectivization of a part of the π electrons, the formation of chemical bonds between adjacent molecules (polymerization), and the corresponding increase in the proportion of sp 3-hybridized electrons. Characteristic electron energy loss (EEL) spectra of an intact fullerite sample non-perturbed by the polymerization process were measured. The EEL spectra of fullerite exhibit a multipole structure due to the (σ + π)-plasmon and reveal an exciton feature which is highly sensitive with respect to electron irradiation and can be used to characterize the initial fullerite structure and to indicate the polymerization onset.

Photoemission spectra of valence electrons of solid C60F18 were measured in X-ray photon energy range being close to the excitation of fluorine F 1s core electron into the first unoccupied state. Enhancement of photoemission cross sections was revealed due to Auger decay of fluorine vacancy in which electron of neighboring carbon atom takes part.

The concentration and chemical state of copper in the subsurface region of Cu/SiO2 composite films obtained by simultaneous magnetron sputtering from two sources (Cu and SiO2) are determined by x-ray photoelectron spectroscopy (XPS). It is established that copper in the as-grown film is primarily in the form of unoxidized atoms dispersed in a SiO2 matrix. Annealing of the film results in practically no oxidation, but about 70% of the copper atoms condense into metallic clusters with sizes below 10 A in the subsurface region and about 50 A in the bulk of the film. The changes in the binding energy of core electrons, and especially in the energies of Auger electrons, are so large in this situation that photoelectron and Auger spectroscopy are efficient methods for monitoring the chemical state of this composite material.

Auger spectra of thin fullerite (C60) films have been measured under the conditions precluding their electrostatic charging and destruction. The Auger line of these subjects, Ef=268.3±0.2 eV, turned out to lie considerably lower in energy than that of the ion-beam amorphized graphite (EAG=272.3±0.2 eV) and of pyrographite (EPG=271.8±0.5 eV). Fullerite was found to convert to a graphitic form under irradiation by low-intensity electron beams used customarily in AES, reflection EELS, and inverse photoemission spectroscopy. It has been established that such beams produce noticeable changes in the fullerite structure already in a few minutes of irradiation.

A parameter representing the intensity ratio of the two features in the characteristic electron energy loss spectrum that are most sensitive to electron irradiation is proposed for use in characterizing the extent of electron-stimulated modification of fullerite. By normalizing this parameter, we succeeded in obtaining a universal scale for the extent of modification that can be unambiguously related to the π-electron density. The dose dependence of this parameter is shown to be described by one exponential, thus permitting one to conclude that both the polymerization and amorphization of the fullerite are dominated by one mechanism, namely, the formation of intermolecular chemical bonds, which is stimulated by valence-electron excitation. The rate of the electron-stimulated modification, or the dose susceptibility of the material, is defined through the derivative of this parameter. The dependence of this rate on the incident electron energy is obtained. It is shown that structural changes are mainly due to a swarm of numerous secondary and decelerated electrons rather than to the primary electron.

This paper presents an experimental and theoretical study of the electronic structure of the fluorinated fullerene C(60)F(36). UV photoemission spectroscopy (UPS) and near-edge x-ray absorption fine structure (NEXAFS) spectroscopy have been used for probing the density of electronic states in the valence and conduction bands of the compound. An assignment of spectral features was carried out using the results of ab initio B3LYP ground-state calculations of the electronic structure of C(60)F(36). The sample of C(60)F(36) is a mixture of three isomers. The calculations of the density of occupied states of these isomers revealed only a small effect of the pi-system organization on the UPS profile. It was demonstrated that the CK-edge NEXAFS spectrum of the fluorinated fullerene can be successfully modeled using the (Z+1) approach properly treating the core hole impact on the spectral profile.

A new way of controlled fabrication of "metal/insulator/superconductor" (MIS) structures with nano- and subnanometer thickness of layers and interfaces is suggested. The way is based on the effect of ion-induced self-organizing restructuring of the near surface region of high temperature superconductors (HTSC). The chemical bond breaking of metal atoms with oxygen stimulated by the bombarding ions is the first stage of the effect. Then the metal atoms diffuse to the surface and form a metallic segregate in the form of a film or a cluster ensemble depending on the ion energy and irradiation dose. The irradiated region loses its superconductivity and is transformed into insulator. The thickness of the dielectric layer is determined by the penetration depth of ions which can be regulated by variation of their energy. The processes pointed out and the properties of the created structures have been studied using electron spectroscopy. As compared to the known structures, the discovered ones are characterized by qualitatively thinner layers and interfaces.