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Using the methods of scanning electron microscopy (Scanning Electron Microscope – SEM) and X-ray photoelectron spectroscopy (XPS), changes in the atomic structure and chemical state of multi-walled carbon nanotubes (MWCNTs) due to the action of ion beams of argon and helium with different irradiation parameters were investigated. Based on the experimental XPS and XANES (X-ray absorption near edge structure) data, as well as theoretical data, changes in the density of electronic states near the Fermi level in MWCNTs after ion-beam action were analyzed. It is shown that the use of beams of argon and helium ions can be used for directional functionalization of MWCNTs and applications in the chemical and petrochemical industries.

The specific features of changes in the electronic structure of multi-walled carbon nanotubes (MWCNTs) due to the interaction with an amorphous tin oxide in the SnO x /MWCNT composite formed by magnetron sputtering have been investigated using X-ray spectroscopy. It has been shown that the formation of chemical bonds responsible for significant changes in the local and electronic structures of the outer layers of MWCNTs occurs at the boundaries of the “amorphous oxide/MWCNT” contacts. The vacuum annealing of the composite leads to the disturbance of the chemical interaction at interfaces of the composite and to a partial recovery of the local structure of the outer layers of MWCNTs. A decrease in the amount of oxygen in the tin oxide under vacuum annealing conditions causes an increase in the number of unpaired Sn 5s electrons, which, in turn, enhances the charge transfer through the interfaces in the composite and leads to a splitting of the π*-subsystem of the outer layers of MWCNTs.

The present work represents the approach to develop the novel functional material for gas micro- and nanosensors. The isolated porous silicon arrays have been synthesized using the electrostatic mask method in the electro-chemical chamber. The hybrid material ‘carbon nanotubes-porous silicon’ has been synthesized on the isolated porous silicon arrays with the CVD process. The nanocomposite structure has been synthesized by tin sputtering on the hybrid material ‘carbon nanotubes-porous silicon’. The morphology and electro-physical properties of the nanocomposite structures have been investigated. The test gas sensor based on the nanocomposite structures showed high sensitivity to NO 2 molecule absorption at room temperature.

The gas sensitivity properties of individual composite nanostructures based on multi-walled carbon nanotubes (MWCNT), functionalized by argon ions and coated with tin and titanium oxides, were investigated by the methods of scanning probe microscopy. The Fermi level shift and the change in longitudinal conductance of nanostructure upon absorption of ammonia and nitrogen dioxide are determined. It is shown that the change in conductance of the composite nanostructures correlates with the Fermi level shift under gases exposure as a result of charge carrier concentration changing in the metal oxide surface layers upon adsorption of gas molecules.

The review is devoted to the current state of researches in the field of nanostructures and materials science - nanocomposite materials based on multiwalled carbon nanotubes (MWCNT). Methods of formation, methods of functionalization, physical properties of the nanocomposites based on layers, ensembles and individual MWNTs and nanostructured metal oxides (SnOx and TiOx) have been considered in detail. Prospective applications of the new nanocomposite materials as sensitive media in new generation gas sensors and chemical current sources have been considered.

A change in the local atomic structure and the chemical state of the surface of multi-walled carbon nanotubes (MWCNTs) due to the action of ion beams of various intensities was studied by a complex of scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy. The analysis of structural defects, quantity and composition of functional groups formed on the surface of MWCNTs as a result of ion-beam action is analyzed. It is shown that the use of ion beams of various intensities can be used for the directed functionalization of MWCNTs in the development of composite structural materials.

With the use of X-ray photoelectron spectroscopy (XPS) there have been investigated the changes of the chemical state of nitrogen atoms in the structure of nitrogen-doped multiwalled carbon nanotubes (CNx-MWCNTs) resulting from the impact of pulsed ion beam at various parameters of the beam (energy density, number of pulses). It has been established that irradiation with the pulsed ion beam leads to a reduction of the total amount of nitrogen in CNx nanotubes. It has been shown that a single pulse irradiation of ion beam at the energy densities of 0.5, 1, 1.5 J/cm2 leads to restructuring of the nitrogen from pyridinic and pyrrolic configuration to graphitic state. Complete removal of nitrogen (pyridinic, pyrrolic, graphitic) embedded in the structure of the walls of CNx nanotubes occurs at ten pulses and 1.5 J/cm2.

The impact of a nanosecond high-energy ion beam on the structure and morphology of multilayer carbon nanotubes and their ensembles is studied using transmission electron microscopy and scanning electron microscopy. It is shown that ion-beam irradiation leads to a decrease in the outer diameters of carbon nanotubes, which is related to the destruction of their outer layers. In addition, the secondary growth of carbon nanotubes with smaller diameters and the growth of bulblike formations, inside which structures with interplanar distances that are close to those of nanodiamond are fixed, are observed.

The nanocomposite structures N-MWCNT/TiOx based on nitrogen-doped multi-walled carbon nanotubes (N-MWCNT) have been synthesized using magnetron sputtering. The morphology, structure, composition and also the electro-physical properties of the nanocomposite structures have been investigated. The changes of the Fermi level position and the electrical conductivity of N-MWCNT and N-MWCNT/TiOx structures at the adsorption of the oxidizing and reducing gas molecules have been studied. The obtained nanocomposite structures demonstrate the wide perspectives as the sensing media for gas micro- and nanosensors.

The features of the image contrast of nitrogen-doped multiwall carbon nanotubes (CNTs) in electrostatic force microscopy (EFM) are studied. It is established that the magnitude and shape profile of the EFM signal depend on the CNT conductivity and diameter. It is shown that an increase in the conductivity of CNT leads to increasing magnitude and variation of the shape profile of the EFM signal.

On the basis of spectra obtained through the X-ray Auger-electron spectroscopy (XAES) of carbon (C KVV) and X-ray photoelectron spectroscopy (XPS) of the carbon valence band using the equipment of the Russian–German beam line of the synchrotron radiation facility BESSY II and a Kratos Axis Ultra DLD analytical system, the influence of pulsed ion radiation on the ratio of sp2/sp3-hybridized orbitals of carbon atoms in layers of oriented multi-walled carbon nanotubes (MWCNTs) is investigated. It is shown that when the MWCNTs are subjected to ten pulses, a substantial increase in the proportion of carbon atoms in the sp3 hybridization state occurs compared with MWCNTs subjected to a single pulse. This increase is associated with the formation of thin (

The transformation of the structural phase state and the electronic structure of the SnO2 − x /MWCNT composite has been studied using X-ray spectroscopy and high-resolution transmission electron microscopy. It has been shown that the character of the interaction of the metal-oxide component of the composite with the array of carbon nanotubes depends on the structural state of tin oxide in globules of the metal-oxide component. In the initial composite with a large content of amorphous tin oxide, covalent functionalization of the MWCNT surface occurs. High-vacuum annealing results in the formation of a nanocrystalline structure in globules of the metal-oxide component and is accompanied by changes in the character of its interaction with carbon tubes.

The changes in the electronic structure and phase composition of porous silicon under action of pulsed ionic beams have been studied by X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge spectroscopy (XANES) using synchrotron radiation. The Si 2p and O 1s core photoemission spectra for different photoelectron collection angles, valence band photoemission spectra, and X-ray absorption near-edge fine structure spectrain the region of Si L2,3 edges of the initial and irradiated samples have been analyzed. It has been found that, as a result of the irradiation, a thin oxide film consisting predominantly of higher oxide SiO2 is formed on the porous silicon surface, which increases the energy gap of the silicon oxide. Such film exhibits passivation properties preventing the degradation of the composition and properties of porous silicon in contact with the environment.

The effect of pulsed ion irradiation and vacuum annealing on the ratio of sp2- and sp3-hybridized orbitals of carbon atoms in the layers of oriented multi-walled carbon nanotubes has been studied by analyzing the photoemission spectra of the C1s core level and the valence band of carbon, which were obtained using the equipment of the BESSY II Russian-German beamline of synchrotron radiation and a Riber analytical system. It has been shown that the ion irradiation leads to a significant decrease in the fraction of atoms with the sp3 hybridization of electrons. On the contrary, the annealing reduces the fraction of the sp3-component in the spectra of carbon. Typical features of the valence band of multi-walled carbon nanotubes in the annealed and irradiated states have been established.

The interaction mechanisms between NO2 molecules and the surface of por-Si/SnO x nanocomposites obtained by magnetron deposition and chemical vapor deposition (CVD) are studied by infrared absorption spectroscopy and electron paramagnetic resonance methods. The observed increase in the free carrier concentration in the por-Si/SnO x nanocomposite layers is explained by a change in the charge state of P b centers due to the formation of neutral “surface defect-adsorbed NO2 molecule” complexes with free carrier generation in the crystallite bulk. In the nanocomposite layers grown by the CVD method, the increase in the free hole concentration during NO2 adsorption is much less pronounced in comparison with the composite grown by magnetron deposition, which is caused by the competing interaction channel of NO2 molecules with electrically neutral P b centers.

The origin of the low-frequency band (250–300 cm−1) in the Raman spectra of multi-walled carbon nanotubes (MWCNTs) produced by the CVD method has been studied. The studies performed by Raman spectroscopy, transmission electron microscopy, Auger spectroscopy, and X-ray photoelectron spectroscopy after chemical and thermal treatments allow the assumption that this band belongs to radial vibrations of carbon atoms in internal walls of MWCNTs.

The results of the X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and scanning electron microscopy (SEM) investigations of tin-oxide nanolayers on samples of por-Si/SnOx composites with varying matrix porosity, formed using a powerful ion beam of nanosecond duration, are presented. It is shown that rapid melting and crystallization of the surface leads to the formation of Si nanoparticles with a maximal size of 200 nm. It is established that tin is included in the structure of the nanocomposite in an oxidized state with a small inclusion of metallic β tin. With increasing porosity, the phase composition of the tin nanolayers becomes closer to the state corresponding to the highest tin oxide (SnO2). It is also shown that, upon an increase in the porosity, the intensity of the tin 4d subvalent line increases, which is, apparently, associated with an enhanced degree of hybridization of tin and oxygen atoms. The changes in the elemental composition of the composite and the depth of tin penetration are estimated from the results of ion etching.

Nanocomposite layers based on multiwalled carbon nanotubes (MWCNTs) and non-stoichiometric tin oxide (SnO x ) have been grown by magnetron deposition and CVD methods. In the case of the CVD method, the study of the structure and phase composition of obtained nanocomposite layers has shown that a tin oxide “superlattice” is formed in the MWCNT layer volume, fixed by SnO x islands on the MWCNT surface. During magnetron deposition, the MWCNT surface is uniformly coated with tin oxide islands, which causes a change in properties of individual nanotubes. Electrical measurements have revealed the sensitivity of nanocomposite layers to (NO2)− molecule adsorption, which is qualitatively explained by a change in the conductivity of the semiconductor fraction of p-type MWCNTs.

The electrical characteristics and chemical reactant sensitivity of layers of heterogeneous nanocomposites based on porous silicon and nonstoichiometric tin oxide por-Si/SnO x , fabricated by the magnetron sputtering of tin with subsequent oxidation, are studied. It is shown that, in the nanocomposite layers, a system of distributed heterojunctions (Si/SnO x nanocrystals) forms, which determine the electrical characteristics of such structures. The sensitivity of test sensor structures based on por-Si/SnO x nanocomposites to NO2 is determined. A mechanism for the effect of the adsorption of NO2 molecules on the current-voltage characteristics of the por-Si(p)/SnO x (n) heterojunctions is suggested.

Layers of por-Si/SnO x nanocomposite formed by high-power ion beam irradiation with nanosecond duration have been studied. The results of structural and elemental analyses of these layers are presented. The high sensitivity of this nanocomposite to low NO2 concentrations at room temperature has been revealed.

The layer-by-layer distribution of components in a porous silicon-tin oxide nanocomposite produced by the following three methods is studied by spectroscopic ellipsometry: chemical vapor deposition, atomic layer deposition, and magnetron sputtering. It is shown that, in the nanocomposites fabricated by these methods, SnOx penetrates to a depth more than 400 nm and is nonuniformly distributed over the porous layer thickness. The nanocomposite prepared by magnetron sputtering followed by heat treatment has the maximum penetration depth and the maximum uniformity of layer-by-layer SnOx distribution.

Two-phase nanocomposite layers based on porous silicon and nonstoichiometric tin oxide were fabricated by various methods. The structure, as well as elemental and phase composition, of the obtained nanocomposites were studied using transmission and scanning electron microscopy, Raman spectroscopy, Auger electron spectroscopy, and X-ray photoelectron spectroscopy. The results obtained confirm the formation of nanocomposite layers with a thickness as large as 2 μm thick and SnO x stoichiometry coefficients x = 1.0–2.0. Significant tin diffusion into the porous silicon matrix with D eff ≈ 10−14 cm2 s−1 was observed upon annealing at 770 K. Test sensor structures based on por-Si/SnO x nanocomposite layers grown by magnetron deposition showed fairly high stability of properties and sensitivity to NO2.

The morphological, structural, and electrophysical properties of the layers of nitrogen-containing carbon nanotubes synthesized by pyrolysis of acetonitrile on a silicon oxide-silicon substrate with a Ni layer catalyst, Fe volumetric catalyst obtained by the thermal decomposition of ferrocene ((C5H5)2Fe), and their combination were studied. It was found that the type of catalyst affects the morphology, thickness, homogeneity, structure, and defect content of the obtained films and individual nanotubes. The electrophysical characteristics of the carbon nanotubes are similar and have an activation dependence on temperature.

The effect of ethanol vapor adsorption on the properties of porous silicon-based structures was studied by Raman scattering, infrared spectroscopy, and I–V characteristics. A decrease in the resistance of porous silicon layers and a simultaneous increase in the intensity of the band of infrared absorption caused by the presence of (OH)−…x(OH)− (x = 1, 2, …) groups upon exposure to ethanol vapor and vice versa in the case of degassing were detected. The observed effect is attributed to a change in the depletion region in por-Si skeleton elements due to the electrostatic interaction of (OH)− groups with positively charged surface defects. The effect of hydrogen-bonded Si-OH…OH-C2H5 centers on the increase in the silicon conductivity is discussed.

The method of atomic-force microscopy is used to study the morphology of the surface of porous silicon layers formed on the p-Si substrate and obtained by anodic etching in an electrolyte with addition of free halogens (bromine, iodine) and potassium halogenides (KCl, KI). It is established that the presence of halogens in the electrolyte is conducive to formation of large pores with the diameter as large as 150 nm. The mechanism of an increase in the pore sizes with involvement of halogens is related to an increase in the concentration of free holes due to formation of donor-acceptor pairs in the case of adsorption of halogens on the silicon surface.

The joint conversion of methanol and the lower alkanes C3-C4 on HZSM-5 with SiO2/Al2O3 = 50 was studied. The method of parabolic approximation for finding the response surface maximum was used to determine the optimum technological parameters of the process (temperature and volume rate of methanol supply) that ensured maximum selectivity with respect to alkenes.

Joint conversion of methanol and lower alkanes on modified zeolites of the ZSM-5 type was studied.

Simultaneous conversion of methanol and lower alkanes C3-C4 on high-silica zeolites of ZSM-5 type of various compositions (SiO2/Al2O3 30, 50, 90) was studied. The catalytic activity of zeolite catalysts and their physicochemical properties (acidity, sorption capacity, and pore structure) were evaluated.

The photoluminescence properties of type II GaAs/AlAs superlattices grown on the (311) surface are determined by their polarity. Previous HRTEM investigations demonstrated a corrugation (with height of 1 nm and period of 3.2 nm) of both GaAs/AlAs and AlAs/GaAs interfaces in samples grown on the (311)A surface. In the present study, a lateral periodicity of 3.2 nm is also revealed in HRTEM images of a superlattice grown on the (311)B surface and in their Fourier transforms. However, this periodicity is poorly pronounced, which is due to fuzzy corrugation and the presence of a long-wavelength (>10 nm) disorder. Photoluminescence spectra of the GaAs/AlAs superlattice on the (311)A surface are strongly polarized relative to the direction of interface corrugation, in contrast to the (311)B superlattice, in which the corrugation is weakly pronounced. It was found that the strong mixing between the Θ and X minima of the conduction band, occurring only in sublattices with strongly corrugated interfaces, allows generation of bright red luminescence at 650 nm up to room temperature. The distinctions revealed between the superlattices grown on the (311)A and (311)B surfaces confirm that it is precisely the interface corrugation, and not crystallographic orientation, that governs the optical properties of (311) superlattices.

Interaction of radiation defects with phosphorus atoms in silicon crystals subjected to electron irradiation and thermal treatments was studied under conditions of various degrees of supersaturation with respect to the equilibrium concentration of impurities and point defects. It is shown that, in the course of silicon irradiation, the electron-dose dependences of the phosphorus concentration at the lattice sites (Ps) level off (tend toward a constant value). This constant value is governed by the irradiation temperature. The stages of recovery of the concentration Ps as a result of heat treatments correlate with temperature intervals of dissociation of the vacancy complexes. The results indicate that there are two processes. One process involves the interaction of dopant atoms with silicon self-interstitials and the emergence of interstitial complexes; i.e., this process corresponds to the radiation-stimulated decomposition of a supersaturated solution of an impurity as a result of point-defect generation and ionization. The other process consists in the recombination of interstitial impurities with vacancies at sufficiently high temperatures or in the annihilation of vacancies released during heat treatments with interstitial atoms incorporated into composite defect complexes with the involvement of phosphorus atoms.

Using Raman scattering, it was ascertained that silicon nanocrystals with sizes exceeding 2 nm are formed in amorphous silicon films exposed to nanosecond ultraviolet laser radiation with energy densities ranging from 75 to 150 mJ/cm2; it is shown that these nanocrystals have sizes no smaller than 2 nm and have preferred (100) orientation along the normal to the film surface. In a system of mutually oriented Si nanocrystals, anisotropic behavior of the Raman scattering intensity was experimentally detected in various polarization configurations, which made it possible to determine the volume fraction of oriented nanocrystals. The orientational effect is presumably caused by both the macroscopic fields of elastic stresses in the film and the local fields of elastic stresses around the nanocrystals.

Using two techniques of scanning probe microscopy, the electrical properties (work function, Fermi level position, free carriers' concentration, electrical resistance, conductivity, and carriers' mobility) of individual multiwalled carbon nanotubes were evaluated.

The hemoglobin adsorption in porous silicon is studied by the method of spectroscopic ellipsometry. The layer-by-layer component distribution in the porous silicon-hemoglobin system shows that hemoglobin molecules penetrate through the porous layer with a slight gradient of the protein volume fraction.

Phonon spectra of GaAs/AlAs superlattices (SLs) grown on (311)A, B and (001) surfaces were studied using Raman spectroscopy. The thickness of GaAs layers were varied from 1 to 10 monolayers (MLs); the thickness of AlAs barriers were 8 ML in the (311) direction. Different polarization geometries of Raman scattering were applied to study LO and TO modes. The splitting of TOx (atoms displace in the direction [01] perpendicular to the facets on the (311)A surface) and TOy (atoms displace in the [33] direction parallel to the facets) modes was observed for (311)A SLs. In the case of (311)B SLs no splitting was observed. The phonon anisotropy of (311)A SLs may be indirect evidence of anisotropic structure of quantum objects formed on the (311)A GaAs surface. In the Raman spectra of the SL containing GaAs submonolayers (SML) grown on a (2×4) reconstructed (100) surface, Raman peaks corresponding to additional lateral confinement of LO phonons were observed. The calculations of Raman spectra were carried out using the Born-von-Karman model (taking into account Coulomb interaction in the rigid-ion model) and the Wolkenstein bond polarizability model. According to the calculations, the interface structure strongly influences the Raman spectra of GaAs/AlAs heterostructures containing GaAs SML.

Studying GaAs/AlAs superlattices containing a quantum-well-wire array revealed photoluminescence polarization anisotropy for samples with GaAs layers less than 21 A thick. It was found that polarization for a thickness of more than 40 A was mainly due to valence band anisotropy, whereas polarization for a thickness of less than 21 A was equally attributable to both valence band anisotropy and anisotropy associated with interface corrugation. For a GaAs layer thickness of less than 21 A, a blueshift of the Γ electron-Γ heavy hole transition was observed. In this transition, the position of the peak of photoluminescence from the GaAs/AlAs (311)A superlattices containing a quantum-well-wire array is shifted toward higher energies compared to the (311)B and (100) superlattices containing no quantum-well wire with the same GaAs layer thickness. The conclusion was made that a blueshift is observed in GaAs/AlAs superlattices with GaAs layers less than 21 A thick and a red-shift is observed when the thickness is larger than 43 A.

The phonon-plasmon interaction in tunneling GaAs n /AlAs m superlattices (m=5and 6≥n≥0.6 monolayers) was studied by Raman scattering spectroscopy. The interaction of optical phonons localized in GaAs and AlAs layers with quasi-three-dimensional plasmons strengthens as the thickness of GaAs quantum wells decreases and the electronic states in the superlattices become delocalized due to tunneling. It is assumed that the plasmons also interact with the TO-like phonon modes localized in quantum islands or in thin ruffled layers.

GaAsn/AlAsm superlattices grown on the GaAs (311)A and (311)B surfaces by molecular-beam epitaxy were studied by Raman light scattering. The form of the Raman scattering tensor allowed the TO y and TO x modes to be separately observed using various scattering geometries (the y and x axes correspond to atomic displacements along and across facets formed on the (311)A surface, respectively). The TO1y and TO1x modes exhibited splitting in superlattices grown on a faceted GaAs(311)A surface. The degree of splitting increased for superlattices with an average GaAs layer thickness of 6 monoatomic layers and less. No splitting was observed for superlattices grown under the same conditions on the (311)B surface, which indicates that the splitting effect is probably due to the formation of GaAs quantum wires on the faceted (311)A surface.

Near-edge IR luminescence with peak emission at E = 1.084 eV has been studied in n- and p-type silicon samples with different contents of interstitial oxygen under excitation with a Nd: YAG laser diode. Thermal treatments of the samples demonstrated that the luminescence nearly completely disappears upon thermal treatments at T = 1050°C and is partly restored in two stages in subsequent thermal treatments in the temperature range 550–800°C. The temperature intervals of luminescence quenching and restoration (500–600 and 700–800°C) correlate with the temperature ranges of dissolution for shallow oxygen precipitates (1000°C) and the generation of oxygen-containing thermal defects, the so-called thermal donors of types I and II. The data obtained suggest that the electronic states related to thermal donors are traps for nonequilibrium carriers and the emptying of these traps contributes to the near-edge emission.

The use of Raman scattering in different polarization geometries makes it possible to observe the splitting of transverse optical (TO) phonon modes confined in GaAs/AlAs superlattices grown on faceted GaAs (311)A surfaces. The frequencies of TO modes with atomic displacements in the direction along the facets were observed to be higher than in the transverse one. Increased splitting, up to 3.5 cm − 1, was observed for (311)A superlattices when the average thickness of the GaAs layers was 6 monolayers or less. The splitting was absent in superlattices grown on (311)B surfaces under the same conditions. The effect of splitting is reputed to be caused by corrugation of GaAs/AlAs (311)A interfaces and formation of lateral superlattices or arrays of quantum wires, depending on the GaAs layer thickness.

The Raman spectra and current-voltage characteristics of porous silicon layers are studied before and after exposure to NO2. It is shown that spherical nanocrystallites with the diameter of approximately 6–8 nm are present in the samples’ structure. The effect of NO2 brings about a decrease in the resistance of porous Si by two-three orders of magnitude. An increase in the conductance of the structures at gas concentrations as high as 2000 ppm and a drastic decrease in this conductance if the concentration exceeds the above value are observed. This effect is explained in the context of the model that implies the formation of additional defects of the type of dangling silicon bonds at the Si/SiO2 interface as a result of oxidation of the porous silicon surface. These defects are traps for holes and reduce the increase in the hole concentration.

Anisotropy of Raman scattering is observed in the system of silicon nanocrystals inside amorphous films. The observed anisotropy is established to be the result of planar correlated orientation of nanocrystals which have (1 1 0) orientation in the normal direction. Preferred orientation is proposed to be due to the deformation contribution in the process of nanocrystals formation under nanosecond laser impact.

The efficiency of the introduction of donor centers in oxygen-containing Si by heat treatments at 450°C after preliminary hydrogenation in hydrogen plasma and irradiation with 60Co γ-ray photons was studied. It is shown that the highest rate of the donor-center introduction is observed in the samples that contain atomic hydrogen. Irradiation with 60Co γ-ray photons of Si with a layer preliminarily hydrogenated in hydrogen plasma leads to the release of atomic hydrogen from bound states. This makes the rate of the introduction of donor centers higher in subsequent heat treatments at 450°C.