K. I. Maslakov

X-ray photoelectron spectroscopy reference data for identification of the C3N4 phase in carbon-nitrogen films

The β-C3N4 phase should have a tetrahedral (sp3-bonded) structure resulting in C1s and N1s XPS peaks with only one feature at a position defined by the electronegativity of four CN bonds. In this work we determined the binding energy of the C1s and N1s XPS peaks in melamine (C3N6H6). In this compound the carbon atoms have four bonds with nitrogen atoms (double and two single); the nitrogen atoms have two chemical states: CNC and CNH2. Since the total number of chemical bonds in this compound is the same as in the hypothetical β-C3N4 compound, this compound is more suitable as a C1s XPS reference for the β-C3N4 phase. The binding energy of the C1s and N1s XPS peaks in melamine was determined to be equal to 287.9 and 399.1 eV, respectively. The binding energies were determined relative to the C1s XPS peak for carbon contamination (adventitious carbon).

A superhard diamond-like carbon film

A superhard hydrogen-free amorphous diamond-like carbon (DLC ) film was deposited by pulsed arc discharge using a carbon source accelerator in a vacuum of 2◊10’4 Pa. The growth rate was about 15 nm/min and the optimum ion-plasma energy was about 70 eV. The impact of doping elements (Cu, Zr, Ti, Al, F(Cl ), N ) on the characteristics of DLC films deposited on metal and silicon substrates was studied aiming at the choice of the optimum coating for low friction couples. The microhardness of thick (µ20 mm) DLC films was studied by Knoop and Vickers indentations, medium thick DLC films (1‐3 mm) were investigated using a ‘Fischerscope’, and Young’s module of thin films (20‐70 nm) was studied by laser induced surface acoustic waves. The bonds in DLC films were investigated by electron energy loss spectroscopy (EELS ), X-ray excited Auger electron spectroscopy ( XAES ), and X-ray photoelectron spectroscopy ( XPS). The adhesion of DLC films was defined by the scratch test and Rockwell indentation. The coeYcient of friction of the Patinor DLC film was measured by a rubbing cylinders test and by a pin-on-disk test in laboratory air at about 20% humidity and room temperature. The microhardness of the Patinor DLC film was up to 100 GPa and the density of the film was 3.43‐3.65 g/cm3. The specific wear rate of the Patinor DLC film is comparable to that of other carbon films.

The special features of the Hall effect in GaMnSb layers deposited from a laser plasma

Epitaxial GaMnSb films with Mn contents up to about 10 at. % were obtained by deposition from a laser plasma in vacuum. The growth temperature Ts during deposition was varied from 440 to 200°C, which changed the concentration of holes from 3 × 1019 to 5 × 1020 cm−3, respectively. Structure studies showed that, apart from Mn ions substituting Ga, the GaMnSb layers contained ferromagnetic clusters with Mn and shallow acceptor defects of the GaSb type controlled by the Ts value. Unlike single-phase GaMnSb systems studied earlier with negative anomalous Hall effect values and Curie temperatures not exceeding 30 K, the films obtained in this work exhibited a positive anomalous Hall effect, whose hysteresis character manifested itself up to room temperature and was the more substantial the higher the concentration of holes. The unusual behavior of this effect was interpreted in terms of the interaction of charge carriers with ferromagnetic clusters, which was to a substantial extent determined by the presence of Schottky barriers at the boundary between the clusters and the semiconducting matrix; this interaction increased as the concentration of holes grew. The absence of this effect in semiconducting compounds based on III–V Group elements with MnSb or MnAs ferromagnetic clusters was discussed in the literature; we showed that this absence was most likely related to the low hole concentrations in these objects.

Multilayer structures induced by plasma and laser beam treatments on a-Si:H and a-SiC:H thin films

Si/SiH/CN x and Si/SiC/CN x film structures have been obtained in a two step procedure: a-Si:H and a-SiC:H thin films have been deposited by PECVD from CH 4 /SiH 4 precursors; CN x films have been prepared by exposing the previous obtained samples to a RF plasma beam discharge generated in nitrogen with graphite electrodes. Several samples were submitted to KrF laser irradiation and treated at various incident laser fluences. The samples have been investigated by in depth X-ray Photoelectron Spectroscopy (XPS), Fourier Transform Infrared Spectroscopy (FTIR) and X-Ray Diffraction (XRD). Chemical and structural modifications are induced by the treatments. The promotion of Si-C bonds and the build-up of an intermediate SiCN layer at the a-Si:H/CN x and a-SiC:H/CN x interfaces are proven.

Chemical state of carbon atoms on the surface of nanodiamond particles

Auger electron spectroscopy study of the chemical state of carbon atoms on the surface of nanodiamond particles is performed. Auger spectra of nanodiamond particles indicate that carbon atoms in nanodiamond are in the same state as those in graphite, i.e., in the σs1σp2π1 state, but the π band is displaced 1 eV in energy below the Fermi level. The surface of nanodiamond particles is inert with respect to the ambient medium.

Carboxylated and decarboxylated nanotubes studied by X-ray photoelectron spectroscopy

Carbon nanotubes (CNTs) of the conic and cylindrical structure were studied by X-ray photoelectron spectroscopy in the initial state and after carboxylation and decarboxylation reactions. The O=C—O and C—O groups were revealed on the surface of the chemically modified samples. It was found that both the carboxylated and decarboxylated cylindrical CNTs contain a smaller amount of oxygen than the corresponding conic CNTs apparently due to differences in their structures.

XPS Study of Ion Irradiated and Unirradiated UO2 Thin Films

XPS determination of the oxygen coefficient kO = 2 + x and ionic (U(4+), U(5+), and U(6+)) composition of oxides UO2+x formed on the surfaces of differently oriented (hkl) planes of thin UO2 films on LSAT (Al10La3O51Sr14Ta7) and YSZ (yttria-stabilized zirconia) substrates was performed. The U 4f and O 1s core-electron peak intensities as well as the U 5f relative intensity before and after the (129)Xe(23+) and (238)U(31+) irradiations were employed. It was found that the presence of uranium dioxide film in air results in formation of oxide UO2+x on the surface with mean oxygen coefficients kO in the range 2.07-2.11 on LSAT and 2.17-2.23 on YSZ substrates. These oxygen coefficients depend on the substrate and weakly on the crystallographic orientation. On the basis of the spectral parameters it was established that uranium dioxide films AP2,3 on the LSAT substrates have the smallest kO values, and from the XRD and EBSD results it follows that these samples have a regular monocrystalline structure. The XRD and EBSD results indicate that samples AP5-7 on the YSZ substrates have monocrystalline structure; however, they have the highest kO values. The observed difference in the kO values was probably caused by the different nature of the substrates: the YSZ substrates provide 6.4% compressive strain, whereas (001) LSAT substrates result only in 0.03% tensile strain in the UO2 films. (129)Xe(23+) irradiation (92 MeV, 4.8 × 10(15) ions/cm(2)) of uranium dioxide films on the LSAT substrates was shown to destroy both long-range ordering and uranium close environment, which results in an increase of uranium oxidation state and regrouping of oxygen ions in uranium close environment. (238)U(31+) (110 MeV, 5 × 10(10), 5 × 10(11), 5 × 10(12) ions/cm(2)) irradiations of uranium dioxide films on the YSZ substrates were shown to form the lattice damage only with partial destruction of the long-range ordering.

Hydrodechlorination of chlorobenzene in the presence of Ni/Al2O3 prepared by laser electrodispersion and from a colloidal dispersion

The low-percentage Ni/Al2O3 catalysts with active metal contents of 0.0002–0.1 wt % were prepared using the laser electrodispersion (LED) method and by means of supporting from a colloidal dispersion (CD). Their composition and physicochemical properties were determined by atomic absorption spectrometry, transmission electron microscopy (TEM), and XPS. With the use of TEM, it was found that average size of nickel particles in the LED catalysts was smaller than that in the CD catalysts. According to XPS data, the supporting of a metal onto a substrate by the LED method makes it possible to obtain samples containing Ni metal with a low active metal content (0.03 wt %). They exhibited a high initial activity in the hydrodechlorination reaction of chlorobenzene in a vapor phase, which was performed in a flow system at temperatures of 100–350°C. The CD catalysts were active in this reaction only at temperatures of 300–350°C. Reductive treatment led to the deactivation of LED catalysts and increased the activity and stability of samples prepared by supporting from a CD. The possible reasons for the observed changes are considered.

Interaction of F atoms with SiOCH ultra low-k films. Part II: etching

The etch mechanism of porous SiOCH-based low-k films by F atoms is studied. Five types of ultra-low-k (ULK) SiOCH films with k-values from 1.8 to 2.5 are exposed to F atoms in the far downstream of an SF6 inductively coupled plasma discharge. The evolution of etching with an F dose was studied using various techniques of surface and material analysis such as FTIR, XPS, EDS and SE. It is revealed that the etch mechanism is connected with surface fluorination and formation of –CHxFy species on the surface due to H abstraction by F atoms from –CH3 groups. It is shown that the etching includes two phases. The first one is observed at the low F doses and is connected with chemical modification and etching of walls in the topmost pores, which finishes when the walls are fully etched. At the same time, the additional etching in the underlying pores due to F penetration forms the etch depth profile, after that the second etching phase starts. This phase is characterized by the higher etch rate due to the propagation of the etch depth profile further into the film. The preliminary treatment of pore walls inside porous channels effectively accelerates etching many times compared to non-porous material. The acceleration depends on the modification depth, which in turn is a function of pore structure and interconnectivity as well as the F atom reaction mechanism. The combined random walk (Monte-Carlo) & kinetics model developed to describe F penetration inside SiOCH films together with reactions of F atoms leading to –CHxFy depletion and opening SiOx bonds for F access allowed relating the increased etch rates with increasing the total number of F atom collisions inside interconnected pores. The etch mechanism of SiOCH films is found in many respects to be similar to the SiO2 etch mechanism on the elementary level, but as whole it is ruled by the SiOCH structure: porosity degree, pore size, pore interconnectivity as well as structural features of SiOx bonds.

Interaction of neptunyl with goethite (α-FeOOH), maghemite (γ-Fe2O3), and hematite (α-Fe2O3) in water as probed by X-ray photoelectron spectroscopy

The sorption behavior is studied and the physicochemical neptunium species existing on the surface of goethite (α-FeOOH), maghemite (γ-Fe2O3), and hematite (α-Fe2O3) are determined. Solvent extraction and X-ray photoelectron spectroscopy (XPS) are used to determine the neptunium surface species. The ion and elemental composition of the surface of the minerals and surface neptunyl NpO2+ complexes is determined using these data. Compounds containing neptunium(IV) or neptunium(VI) ions do not appear; rather, neptunyl (Np(V)O2+ group is complexed with surface hydroxide groups of α-FeOOH, γ-Fe2O3, and α-Fe2O3. Presumably, the oxygen atoms of iron oxides and water and/or carbonate (CO32-) or nitrate (NO3-) group lie in the equatorial plane of the neptunyl (NpO2+) group.