Search

The results of a study of the unoccupied electronic states of ultrathin films of bis-carboxyphenyl-phthalide (DCA-DPP) and bis-methylphenyl-phthalide (DM-DPP) up to 8 nm thick are presented. The studies are carried out by total current spectroscopy (TCS) in the energy range from 5 to 20 eV above EF during thermal vacuum deposition of these organic films on the surface of highly ordered pyrolytic graphite (HOPG). The values of Evac relative to EF, i.e., the work function of electrons of the DM-DPP films at a film thickness of 5–8 nm are found to be 4.3 ± 0.1 eV. The values of the work function of electrons of the DCA‑DPP films are found to be 3.7 ± 0.1 eV. The structure of the maxima of unoccupied electronic states of DCA-DPP and DM-DPP films in the studied energy range is established. A comparison of the obtained properties of DCA-DPP and DM-DPP films with the properties of films of molecules of unsubstituted diphenylphthalide (DPP) is presented. Thus, the –CH3 substitution of the DPP molecule has almost no effect on the height of the potential barrier between the film and the HOPG surface, while –COOH substitution of the DPP molecule leads to an increase in the height of the potential barrier between the film and the HOPG substrate surface by 0.5–0.6 eV. Substitution of DPP molecules with –COOH functional groups and, thus, the formation of DCA-DPP molecules lead to a shift of two maxima of the fine structure of the total current spectra located at energies in the range from 5 to 8 eV above EF by about 1 eV towards the lower electron energies.

The Mn-substituted NBT ceramics were prepared by the conventional ceramic fabrication technique. X-ray diffraction (XRD) studies indicated the formation of perovskite phase with rhombohedral symmet...

Unoccupied electronic states in the energy range from 5 to 20 eV above the Fermi level have been studied in ultrathin films of dimethyl-substituted thiophene–phenylene cooligomers CH3-phenylene–thiophene–thiophene–phenylene–CH3 (CH3–PTTP–CH3) on polycrystalline gold surfaces of two types: the ex situ Au layer thermally deposited in a special chamber and the in situ Au surface prepared inside an analytical chamber. The film structure is studied by the X-ray diffraction (XRD) method. The formation of a superposition of the amorphous phase and the crystalline phase with period 3.8 nm is discussed. The energy positions of the maxima of the unoccupied electronic states and the character of formation of the boundary potential barrier have been studied by the total current spectroscopy (TCS). The structures of the FSTCS maxima of the 5–7-nm-thick CH3–PTTP–CH3 films are not different when using various types of Au substrates and the ZnO semiconductor surface prepared by atomic layer deposition (ALD). As a CH3–PTTP–CH3 layer is deposited on the ex situ Au and in situ Au surfaces, the electron work function increases insignificantly (by ~0.1 eV) as the coating thickness increases to 5–7 nm. At such thicknesses of the CH3–PTTP–CH3 films, the electron work function is 4.7 ± 0.1 eV in the case of the ex situ Au substrate and 4.9 ± 0.1 eV in the case of the in situ Au substrate. A possible influence of the processes of physicochemical interaction at the boundary between the film and the substrate on the formation of the boundary potential barrier in the structures under study is discussed.

A comparative study has been performed for the structures of the maxima of the density of unoccupied electronic states (DOUS) in ultrathin films of the naphthalene-1,4,5,8-tetracarboxyl acid dianhydride (NTCDA) and naphthalene-1,8-dicarboxyl acid anhydride (NDCA) and two types of films based on phthalides: 3,3-diphenylphthalide (DPP) and 3,3-diphenylphthalide-4',4'-dicarboxyl acid (DPP–DCA). The structures of unoccupied electronic states of the 8–10-nm-thick films have been measured by total current spectroscopy (TCS) in the energy range from 5 to 20 eV above the Fermi level. The experimental results are analyzed by constructing the model total current spectra and the DOUS dependences using the results of calculation of the orbital energy of the molecules under study by the density functional theory (DFT) at the B3LYP/6-31G(d) level. The difference in the DOUS spectra of the NTCDA and NDCA films is the shift of the main DOUS maxima of the NTCDA film to lower energies approximately by 1 eV at energies lower than 12.5 eV; at higher energies, the DOUS maxima are shifted by 1.5–2 eV. The energy positions of the maxima of the total current spectra of the DPP–DCA and DPP films are changed only slightly as various substrates are used: highly ordered pyrolitic graphite (HOPG) and a CdS deposited layer-by-layer. The relative intensities of the maxima are different as various substrates are used. The characteristic shifts of the maxima of the total current spectra of the DPP–DCA films are approximately 1 eV at energies lower 12.5 eV above the Fermi level and 1.5–2 eV at higher energies, as compared to the positions of the corresponding maxima of the DPP films.

The formation of unoccupied electronic states and the boundary potential barrier during thermal deposition of tetracyanoquinodimethane (TCNQ) films to 7 nm in thickness on a (SiO2)n-Si surface has been studied. The electronic characteristics of the surface under study are measured by the total current spectroscopy (TCS) using a testing electron beam with energies from 5 to 20 eV above the Fermi level. The formation of a boundary potential barrier in the (SiO2)n-Si/TCNQ structure is accompanied by an increase in the work function of the surface from 4.2 ± 0.1 to 4.7 ± 0.1 eV. Using the results of the TCS experiments, the DOUS dependences of the TCNQ films have been built. To analyze the experimental DOUS dependences, the orbital energies of the TCNQ molecules are calculated by the density functional theory (DFT) at the B3LYP/6-31G(d) level with subsequent correction and the inclusion of the polarization energy of the condensed medium. In the energy range indicated above, DOUS of the TCNQ films has four main maxima. The DOUS maximum at energy 7.0 eV above EF is predominantly formed by π* orbitals. Three DOUS maxima in the energy range from 8.0 to 20 eV above EF are formed by approximately the same amount of the π* and σ* orbitals.

The results of diagnostics of the atomic composition of a diphenylphthalide (DPP) film thermally precipitated in vacuum by the of X-ray photoelectric spectroscopy (XPS) method are presented. The results of examination of the unoccupied electronic states of the ultrathin DPP films with the thickness up to 10 nm on the surface of the highly oriented pyrolytic graphite (HOPG) by the total current spectroscopy (TCS) method in the energy range from 5 to 20 eV above EF are presented. In this range, the main maxima in the total current spectra are identified. The analysis of the TCS results with consideration of the theoretical calculation results has shown that the low-energy maxima observed at the energies from 6 to 7.5 eV are induced predominately by π* electron orbitals of DPP films. The values of the energy Evac in relation to EF, i.e., of the electron work function in the DPP films at the film thickness of 5–10 nm, are found experimentally at a level of 4.3 ± 0.1 eV. The negative charge transfer from an organic film to the substrate corresponds to the formation of the HOPG/DPP boundary potential barrier during the thermal deposition of the DPP film.

Organosilicon compounds are surprising in the diversity of their applications as a result of the enormous diversity in their structure. Of particular interest are the self-assembling possibilities of silsesquioxane molecules leading to the formation of thin films with thicknesses not exceeding tens of nanometers. To date, only cases of self-organization of molecules with a strongly asymmetrical shape have been known. This study is aimed at obtaining confirmation of self-organization of silsesquioxane molecules in which the π-stacking interaction between arranged spherically symmetrical aromatic rings leads to the formation of a new smectic phase not observed for bulk material. For this purpose, the morphology of growth and the structure of thin octasilsesquioxane layers substituted either with vinyl or phenyl groups was compared. Due to the use of molecular beam technique for thin-film deposition under ultra-high vacuum conditions, any undesirable external influences as well as those associated with the solvent were avoided. The main measurement techniques were the X-Ray Reflectometry and Atomic Force Microscopy, which provided the final proof of the key role of aromatic rings in the self-assembly of these spherically symmetrical molecules.

The structure of polycrystalline materials may differ significantly from that determined from monocrystalline studies. The combination of measurement and calculation techniques is one of the most effective ways to determine structural differences. The use of x-ray powder diffraction (XRD) supported by Monte Carlo calculations as well as complementing these studies with Fourier-transform infrared spectroscopy (FTIR) supported by ab initio calculations helped to determine the structure of octavinyloctasilsequioxane as a powder specimen. The results show a rhombohedral distortion of the cubic-shaped molecule along the ternary axis of the unit cell. Monte Carlo calculations support the model wherein vinyl groups at the Si atom sites along the C 3 axis could be located at one of the three equivalent positions, with the possibility of rapid reorientation. XRD measurements, as a function of temperature, show structural transition from a hexagonal (rhombohedral) to a low symmetry (probably triclinic) orientation, but through an intermediate monoclinic space group.

The atomic composition and the electronic properties of ultrathin films of the four-conjugated rings thiophene/phenylene co-oligomers end-terminated by the −CH 3 and by the -CF 3 radicals vacuum deposited onto the oxidized silicon surface were studied using the X-ray photoelectron spectroscopy (XPS) and total current spectroscopy (TCS) techniques. The relative concentrations of the C, S and F atoms measured from the film deposits were evaluated and were found to correspond to the chemical formulae of the CH 3 -phenylene-thiophene-thiophene-phenylene−CH 3 (CH 3 -PTTP−CH 3 ) and CF 3 -phenylene-thiophene-thiophene-phenylene-CF 3 (CF 3 -PTTP-CF 3 ) molecules studied. The TCS measurements during the increase of the organic layer thickness up to 6 nm on a (SiO 2 )n-Si substrate were used to determine the conduction band peak structure related to the density of the unoccupied electronic states (DOUS) in the range from 5 eV to 22 eV above E F . DOUS of the films investigated was also obtained theoretically by means of ab initio calculations. According to the calculations, the energy position of the lowest unoccupied molecular orbital (LUMO) peak was found at 4.4 eV in the case of the CH 3 -PTTP−CH 3 film and at 3.9 eV in the case of the CF 3 -PTTP-CF 3 film. The effect of fluorine substitution on the DOUS was determined as approximately 2 eV peak shift towards low electron energies in the case of the CF 3 -PTTP-CF 3 film compared to the case of the CH 3 -PTTP−CH 3 film in the electron energy range from 10 eV to 22 eV above E F and as a more complex peak restructuring in the energy range from 5 eV to 10 eV above E F . The DOUS peaks of the two films studied were assigned to molecular orbitals with π* character in the 5–9.5 eV energy range and molecular orbitals with σ* character in the 9.5–22 eV energy range above E F .

The results of a study of the unoccupied electronic states of ultrathin films of phenolphthalein molecules on a ZnO surface formed by atomic layer deposition technique are presented. The atomic composition of the ZnO layer was determined by X-ray photoelectron spectroscopy (XPS) and its crystallinity was characterized using X-ray diffraction. The predominance of the content of O atoms by 5-10%, compared with the content of Zn atoms, was found. The electronic characteristics of the ZnO/phenolphthalein structure were studied using total current spectroscopy (TCS) in the energy range from 5 eV to 20 eV above EF during thermal vacuum deposition of phenolphthalein films up to 8 nm thick. Phenolphthalein molecules contain two hydroxyl functional groups. The TCS results on the phenolphthalein films are compared with the TCS results obtained from films of molecules that represent the backbone of phenolphthalein molecules without hydroxyl groups. The TCS fine structure maxima of phenolphthalein films located in the energy range from 5 eV to 8 eV above EF can be associated with the boundaries of the p* bands of electronic states. The work function of the ZnO surface formed by the ALD method were 4.2±0.1 eV. The deposition of a phenolphthalein film led to a decrease in the work function of the surface by 0.1 eV.

The results of studying the electronic states of the conduction band and interface potential barrier during the formation of ultrathin films of thiophene-phenylene co-oligomer CH3-phenylene-thiophene-thiophene-phenylene-CH3 (CH3-PTTP-CH3) on the surface of ZnO and films of biphenyl tetracarboxylic dianhydride (BPDA) on the ZnO surface are presented. A 100 nm thick ZnO layer was prepared by atomic layer deposition (ALD). Organic CH3-PTTP-CH3 films and BPDA films up to 8 nm thick were formed by thermal vacuum deposition. During film deposition, the electronic characteristics of the surface were studied using total current spectroscopy (TCS) in the energy range from 5 eV to 20 eV above EF. In this energy range, the structure of the maxima of the unoccupied electronic states of CH3-PTTP-CH3 and BPDA films was determined. As a result of the CH3-PTTP-CH3 film deposition, a decrease in the work function to 4.0 eV was found, compared with the value of the work function of 4.2 eV measured from the ALD ZnO substrate. This corresponds to the transfer of a negative charge from the СH3-PTTP-CH3 film to the substrate. The charge transfer at the interface between the BPDA film and the ALD ZnO substrate occurs in the opposite direction, since a 4.7 eV increase of the work function was registered during the formation of this interface. The СH3-PTTP-СH3 and BPDA films studied and the layer-by-layer grown ZnO film represent a continuous coating on sufficiently large surface areas of the order of 10 micrometers x 10 micrometers. The roughness of the ZnO surface does not exceed 4 nm, and the surface roughness of CH3-PTTP-CH3 and BPDA films was 10–15 nm.

The unoccupied electron states and the boundary potential barrier during deposition of ultrathin films of dimethyl-substituted thiophene–phenylene coolygomers of the type of CH3–phenylene–thiophene–thiophene–phenylene–CH3 (CH3–PTTP–CH3) on an oxidized silicon surface have been studied. The electronic characteristics have been measured in the energy range from 5 to 20 eV above the Fermi level using total current spectroscopy (TCS). The structure of the CH3–PTTP–CH3 film surfaces has been studied by atomic force microscopy (AFM), and the atomic compositions of the films have been studied by X-ray photoelectron spectroscopy (XPS). The changes in the maximum intensities measured by the TCS method obtained from the deposited CH3–PTTP–CH3 film and from the substrate during increasing in the organic coating thickness to 6 nm is discussed. The formation of the boundary potential barrier in the n-Si/SiO2/CH3–PTTP–CH3 is accompanied by the decrease in the surface work function from 4.2 ± 0.1 to 4.0 ± 0.1 eV as the organic coating thickness increases to 3 nm. The ratio of atomic concentrations C: S in the CH3–PTTP–CH3 films well corresponds to the chemical formula of CH3–PTTP–CH3 molecules. The roughness of the CH3–PTTP–CH3 coating surface was not higher than 10 nm on the ~10 × 10 μm areas as the total CH3–PTTP–CH3-layer thickness was about 100 nm.

Two types of lead-free Na 0.5 Bi 0.5 TiO 3 ceramics were manufactured by using a high-temperature solid-state reaction technique. X-ray diffraction analysis showed the formation of a single perovskite phase with the rhombohedral symmetry at room temperature. The structural, vibrational, dielectric and ferroelectric properties of these ceramics in unpoled and poled states were investigated. It was shown that a prior E-field poling process significantly influences the properties of these ceramics. This includes changes in the character of e(T)- and tanδ(T) plots, P(E) hysteresis loops, as well as shifts of T d and T R-T . These effects are mainly attributed to the improvement of polarization/domain ordering and transformation of tetragonal regions into rhombohedral phase by applied electric field. This is accompanied by a change of rhombohedral lattice distortion and a change of unit cell constants. The electric field supported and extended the ferroelectric phase existence towards higher temperatures.

Scanning electron microscopy (SEM) and Atomic force microscopy (AFM) have been used to investigate ex-situ the surface topography of SiC layers deposited on Si(100) by Microwave Chemical Vapour Deposition (MWCVD) -S1,S2 layers and Electron Cyclotron Resonance Chemical Vapor Deposition (ECRCVD) – layers S3,S4, using silane, methane, and hydrogen. The effects of sample temperature and gas flow on the nanostructure and microstructure have been investigated. The nanostructure was described by three-dimensional surface roughness analysis based on digital image processing, which gives a tool to quantify different aspects of surface features. A total of 13 different numerical parameters used to describe the surface topography were used. The scanning electron image (SEM) of the microstructure of layers S1, S2, and S4 was similar, however, layer S3 was completely different; appearing like grains. Nonetheless, it can be seen that no grain boundary structure is present in the AFM images.

The self-assembly abilities of Dodecaphenyl Polyhedral Oligomeric Silsesquioxane thin films on Si(1 0 0) surfaces were studied. Due to their thermal properties – relatively low sublimation temperature and preservation of molecular structure – cage type silsesquioxanes are ideal material for the preparation of a thin films by Physical Vapor Deposition. The Ultra-High Vacuum environment and the deposition precision of the PVD method enable the study of early stages of thin film growth and its molecular organization. X-ray Reflectivity and Atomic Force Microscopy measurements allow to pursuit size-effects in the structure of thin films with thickness ranges from less than a single molecular layer up to several tens of layers. Thermal treatment of the thin films triggered phase change: from a poorly ordered polycrystalline film into a well-ordered multilayer structure. Self-assembly of the layers is the effect of the π−stacking of phenyl rings, which force molecules to arrange in a superlattice, forming stacks of alternating organic-inorganic layers.

Na0.5Bi0.5TiO3 ceramics were prepared by a conventional solid-state reaction method and by a hot-pressing route. The influence of sintering conditions on structural, thermal, dielectric and ferroelectric properties of these ceramics was investigated. All obtained samples exhibited a single perovskite phase. It was shown that the sintering conditions significantly influence the properties under investigation. This includes changes in the value of the electric permittivity ϵ and dielectric loss tanδ, a shift of Tm and Td and change of the ferroelectric properties. These effects are mainly related to volatility of the Na and Bi components during the sintering process along with formation of their compensating charge defects, which leads to local structure change.

A new low-lead content 0.975BaTiO3-0.025PbZn1/3Nb2/3O3 (0.975BT-0.025PZN) ceramic with a high relative density and good mechanical quality was fabricated by the SPS method. X-ray diffraction measur...

A glassy carbon electrode modified with reduced graphene oxide (GCE/rGO) is proposed as a novel electrochemical platform for detecting 4-nitrophenol (4-NP). The examined rGOs were synthesized using a straightforward reduction route under hydrothermal conditions (120, 150 and 180 °C). The rGOs were characterized by X-ray photoelectron spectroscopy, Fourier transformed infrared spectroscopy, X-ray diffraction, field-emission scanning electron microscopy and atomic force microscopy. A higher reduction degree was achieved after thermal treatment at 180 °C, as demonstrated by the significant decrease in the oxygen content of the starting GO (from 35.4 to 16.7 at.%) and by the marked restoration of the Csp 2 domains (from 16.1 to 62.4 at.%). The electrochemical activity of GCE/rGOs towards 4-NP was investigated using cyclic voltammetry experiments in a 0.1 M acetate buffer solution (ABS). rGO-180 was selected as the active electrode material of the electrochemical sensor for detecting 4-NP because of the highest measured cathodic reduction current. The results demonstrated an enhancement of the corresponding cathodic currents measured after modification of the GCE and slight changes over the pH range of 4.0–5.0. These results are beneficial for real sample analysis. The sensor worked linearly in the range of 50 to 800 μM and had a detection limit of 42 μM. Interferences of other pollution compounds, such as hydroquinone, catechol and bisphenol A, did not affect the sensing towards 4-NP. The electrode demonstrated good recoveries in real samples and excellent long-term stability (98.98% of the original signal value after 14 days).

Microspheres used in our work were acquired from one of Kazakhstan coal-fueled power plant. The size of the microspheres varied between 45 and 400 μm, the median particle size (D50) was 158 μm. Microscopic analysis revealed that the material consisted mainly of cenospheres. The results of elemental and oxide analysis showed that microspheres were composed of aluminosilicates. Identified crystalline phases were mullite (approx. 12 %) and trace amount of quartz (silica). Microscopic observations of the cross-sectional surface of both unmodified PUR foam and foams modified with microspheres showed a well formed, cellular structure of all materials. The observed cells are polyhedron in shape, most of them are closed, microspheres were uniformly distributed within polymer matrix and placed between cells. The apparent densities calculations of the samples showed that when microspheres were added to the polymer matrix, apparent density of the resulting composite materials increased. The results of elemental analysis pointed out the highest content of all three elements in unmodified PUR foam sample. The addition of the microspheres to the system resulted in decrease of the concentration of all three elements.

The work presents a detailed study on the diamond-like structures doped with Si atoms and biopolymers-based coatings (chitosan, alginate) enriched with Ag nanoparticles (Ag NPs) deposited on the Ti-6Al-7Nb substrate. Multilayers were obtained by Plasma Enhanced Radio Frequency Chemical Vapour Deposition (PE RF CVD) technique and subsequent deposition of biopolymers by immersion method. The impact of Si atoms and Ag NPs on chemical structure, microstructure, topography, cytotoxicity as well as the hardness and Young modulus of the resulting layers was precisely investigated. The most advantageous conditions of plasma functionalization in RF reactor were the mixture of O2-Ar-NH3 in volume ratio of 10/1/9 in the first stage of functionalization (pre-activation). In the case of Si-DLC coatings (up to ca. 19 at.%) the lower silane flow (4 cm3/min) resulted in significant decrease of surface roughness (up to ca. Ra = 0.71 nm) of modified surfaces and increase of hardness reaching ca. 900 nm depth into surface (up to ca. 16 GPa). The most attractive among biopolymer-based coating on Ti-6Al-7Nb in terms of biological activity was chitosan with Ag NPs (diameter of ca. 25 nm) with additional alginate layer. AFM analysis revealed a uniform distribution of Ag NPs in the chitosan matrix. This contributed to advantageous physicochemical and biological properties assuring proper cell adhesion and proliferation. Noteworthy, the resulting surface functionalization of Ti-6Al-7Nb alloy did not cause significant cytotoxicity in vitro, giving a strong hope for perspective applications in implantology.

The results of a study of unoccupied electronic states and the formation of a boundary potential barrier during thermal vacuum deposition of ultrathin films of 4-quaterphenyl oligophenylene on the surface of CdS and on the surface of oxidized silicon are presented. Using X-ray photoelectron spectroscopy (XPS) it was determined, that the atomic concentrations of Cd and S were equal in the surface layer of a 75-nm-thick CdS film formed by atomic layer deposition (ALD). The electronic properties of 4-quaterphenyl films up to 8 nm thick were studied during their deposition on the surface of the CdS layer and on the surface of oxidized silicon using total current spectroscopy (TCS) in the energy range from 5 eV to 20 eV above EF. The energetic position of the main maxima of the fine structure of the total current spectra (FSTCS) of 4-quaterphenyl films was determined. The location of the maxima was reproducible when two selected substrate materials were used. A minor decrease in the work function, from 4.2 eV to 4.1 eV, was registered during the thermal deposition of 4-quaterphenyl onto the CdS surface. During the deposition of a 4-quaterphenyl film on the oxidized silicon surface, an increase in the work function from 4.2 eV to 4.5 eV was found. Possible mechanisms of the physicochemical interaction between the 4-quaterphenyl film and the surface of the investigated substrates, which lead to a difference in the observed values of the work function of the films on these substrates, are discussed.

The results of a study of the unoccupied electronic states of ultrathin films of bis-carboxyphenyl-phthalide (DCA-DPP) and bis-methylphenyl-phthalide (DM-DPP) up to 8 nm thick are presented. The studies were carried out by total current spectroscopy (TCS) technique in the energy range from 5 eV to 20 eV above EF during thermal vacuum deposition of these organic films on the surface of highly oriented pyrolytic graphite (HOPG). The energy Evac relative to EF, that is, the electronic work function of the DM-DPP films, at a film thickness of 5–8 nm was 4.3 ± 0.1 eV. The electronic work function of the DCA-DPP films was 3.7 ± 0.1 eV. The structure of the maxima of the unoccupied electronic states of DCA-DPP films and DM-DPP films in the studied energy range is determined. The properties determined of DCA-DPP and DM-DPP films are compared with the properties of films of unsubstituted diphenylphthalide (DPP). According to our analysis, –CH3 substitution of the DPP molecule practically did not affect the height of the potential barrier between the film and the HOPG surface, and –COOH substitution of the DPP molecule led to an increase in the height of the potential barrier between the film and the HOPG substrate surface by 0.5–0.6 eV. Substitution of DPP molecules with –COOH functional groups which represents formation of DCA-DPP molecules led to a shift of two peaks of the experimental total current spectra located at energies in the range from 5 eV to 8 eV above EF, by about 1 eV towards lower electron energies.

Lead free (Na0.5Bi0.5)1-xSrxTiO3 (x = 0, 0.01 and 0.02) ceramics were produced by a conventional solid-state sintering method. X-ray diffraction analysis shows that the obtained samples possess the perovskite structure with rhombohedral symmetry. The microstructure study shows a dense structure, in agreement with the relative density (above 97%). Dielectric analysis revealed the diffuse character of the electric permittivity anomalies and their shift to a lower temperature range after Sr doping of NBT. The Raman spectra are similar for all samples in agreement with the X-ray diffraction data. The possible origin of the observed effects was discussed.

The results on comparing the peak structure of the density of unoccupied electronic states (DOUS) of ultrathin films of naphthalene anhydride-1,4,5,8-teracabonic acid (NTCDA) and naphthalene-1,8-dicarboxylic acid anhydride (NDCA) and of two types of phthalide-based films: 3,3-bis (phenyl) phthalide (DPP) and 3,3-bis (phenyl) phthalide-4 ′, 4′-dicarboxylic acid (DPP-DCA) are presented. The measurements of the structure of the unoccupied electronic states in the energy range from 5 eV to 20 eV above the Fermi level of the films studied having thickness of 8–10 nm were conducted using the total current spectroscopy (TCS) technique. Analysis of the experimental results was conducted using the model total current spectra and DOUS dependences generated using the calculated orbital energies of the studied molecules by means of the density functional theory (DFT) method at the B3LYP/6-31G(d) level. The difference in the DOUS spectra of NTCDA and NDCA films is characterized by the shift of the main DOUS maxima of the NTCDA film to lower energies by about 1 eV at energies less than 12.5 eV, and at higher energies the DOUS maxima are shifted by 1.5-2 eV. The energy positions of the maxima of the total current spectra of the DPP-DCA and DPP films practically do not change when using various substrates: highly ordered pyrolytic graphite (HOPG) and layer-by-layer deposited CdS. The relative intensities of the maxima differ when using different substrates. The characteristic shift of the maxima of the total current spectra of DPP-DCA films is about 1 eV at energies less than 12.5 eV above the Fermi level and 1.5-2 eV and at higher energies, compared with the position of the corresponding maxima of the DPP films.

The results of the study of the formation of unoccupied electronic states and of the interface potential barrier during thermal deposition of tetracyanoquinodimethane (TCNQ) films, up to 7 nm thick, on the (SiO2)n-Si surface are presented. The electronic properties of the surface under study were determined using the total current spectroscopy (TCS) technique and as testing electron beam with energies in the range from 5 eV to 20 eV above the Fermi level. The formation of a potential barrier in the (SiO2)n-Si / TCNQ structure was accompanied by an increase in the surface work function from 4.2 ± 0.1 eV to 4.7 ± 0.1 eV. Based on the results of TCS experiments, the DOUS function of the studied TCNQ film is constructed. To analyze the experimental DOUS, the orbital energies of the studied TCNQ molecules were calculated using the density functional theory (DFT) method at the B3LYP/6-31G(d) level, which was followed by the correction procedure and by the allowance for the condensed phase polarization energy. DOUS of the TCNQ films has four main maxima in the energy range studied. The DOUS maximum at an energy of 7.0 eV above EF is mainly formed by pi* orbitals. Three DOUS maxima located in the energy range from 8.0 eV to 20 eV above EF are formed by approximately the same number of pi* and sigma* type orbitals.

The behavior of the electric permittivity and polarization of Na0.5K0.5(Nb0.96Sb0.04)O3+0.5mol%MnO2 ceramics as a function of uniaxial pressure (0 – 600 bar) applied perpendicularly to the ac electric field were investigated. The application of a uniaxial pressure causes a reduction of the peak intensity of the electric permittivity (ɛ) and change of the phase transition from first order to second one. The temperature dependence of electric permittivity ɛ shows that the Curie temperature increases with increasing pressure and presents a broadening and flattening of the maximum of ɛ(T). The obtained results suggested an appearance of the dielectric relaxation near the phase transition temperature which strongly coupled with strain induced by the pressure. The effect of uniaxial pressure have an effect on the dynamics of the perovskite lattice.

AbstractThe results of diagnostics of the atomic composition of a diphenylphthalide (DPP) film thermally precipitated in vacuum by the of X-ray photoelectric spectroscopy (XPS) method are presented. The results of examination of the unoccupied electronic states of the ultrathin DPP films with the thickness up to 10 nm on the surface of the highly oriented pyrolytic graphite (HOPG) by the total current spectroscopy (TCS) method in the energy range from 5 to 20 eV above E _F are presented. In this range, the main maxima in the total current spectra are identified. The analysis of the TCS results with consideration of the theoretical calculation results has shown that the low-energy maxima observed at the energies from 6 to 7.5 eV are induced predominately by π* electron orbitals of DPP films. The values of the energy E _vac in relation to E _F, i.e., of the electron work function in the DPP films at the film thickness of 5–10 nm, are found experimentally at a level of 4.3 ± 0.1 eV. The negative charge transfer from an organic film to the substrate corresponds to the formation of the HOPG/DPP boundary potential barrier during the thermal deposition of the DPP film.

There has been an increasing amount of interest in silsesquioxanes recently. The most important group of polyhedral oligomeric silsesqioxanes (POSS) is octasilsesquioxanes. The attention is particularly focused on octahydridooctasilsesquioxanes, also known as T8H. The aim of the presented work is a detailed study of the structure of T8H = H8Si8O12. Powder X-ray diffraction and infrared spectroscopy FTIR are the main measurement techniques on which the detailed structural studies are based. The results undoubtedly point to the conclusion that T8H molecule symmetry is lower (C3i) than expected (Th) and matches site symmetry in the trigonal crystal structure.

Cluster–support interaction in a Au–Fe3O4(0 0 1) system was studied using scanning tunneling microscopy, X-ray photoemission spectroscopy and Mossbauer spectroscopy, in situ, under ultra high vacuum conditions. Deposition of 0.02–5 monolayers of Au resulted in the growth of two- and three-dimensional gold nano-cluster. The positive shift of the Au 4f7/2 electron binding energy for the smallest clusters was correlated with modification of the electronic structure in the surface magnetite layer, as found from Mossbauer analysis, leading to conclusion that a positive charging of small Au clusters can be responsible for their outstanding catalytic activity.

The results of X-ray diffraction (XRD), scanning electron microscopy (SEM) and dielectric measurements performed for samples of the polycrystalline solid solutions of (Ba1-xSrx)TiO3, are presented. An increase of diffuseness of ferroelectric phase transition and a decrease of the temperature Tm (the temperature of the maximum value of the real part of the electric permittivity; ϵ′) with increase of Sr concentration is observed. Values of the phase angle (approximate to −90°) measured in broad range of temperatures suggest the occurrence of polar regions (clusters) in the temperature range of paraelectric (PE)-ferroelectric (FE) phase transition.

AbstractThe unoccupied electron states and the boundary potential barrier during deposition of ultrathin films of dimethyl-substituted thiophene–phenylene coolygomers of the type of CH_3–phenylene–thiophene–thiophene–phenylene–CH_3 (CH_3–PTTP–CH_3) on an oxidized silicon surface have been studied. The electronic characteristics have been measured in the energy range from 5 to 20 eV above the Fermi level using total current spectroscopy (TCS). The structure of the CH_3–PTTP–CH_3 film surfaces has been studied by atomic force microscopy (AFM), and the atomic compositions of the films have been studied by X-ray photoelectron spectroscopy (XPS). The changes in the maximum intensities measured by the TCS method obtained from the deposited CH_3–PTTP–CH_3 film and from the substrate during increasing in the organic coating thickness to 6 nm is discussed. The formation of the boundary potential barrier in the n -Si/SiO_2/CH_3–PTTP–CH_3 is accompanied by the decrease in the surface work function from 4.2 ± 0.1 to 4.0 ± 0.1 eV as the organic coating thickness increases to 3 nm. The ratio of atomic concentrations C: S in the CH_3–PTTP–CH_3 films well corresponds to the chemical formula of CH_3–PTTP–CH_3 molecules. The roughness of the CH_3–PTTP–CH_3 coating surface was not higher than 10 nm on the ~10 × 10 μm areas as the total CH_3–PTTP–CH_3-layer thickness was about 100 nm.

Thermal decomposition of new silsesquioxane materials [(Me 3 Si) 3 CSiMe 2 CH 2 CH 2 SiO 3/2 ] n (PT Si SS), substituted with sterically hindered carbosilane groups, was studied in an inert atmosphere (N 2 ) and air. It was found that a specific degradation of carbosilane moieties occurs at high temperatures. A ceramic residue was obtained > 900 K both in nitrogen (Si x O y C z ) and air (Si x O y ). Thermal rearrangements in the structure of polyhedral and ladder-like PT Si SS were studied, and related to those observed for a polymethylsilsesquioxane resin (PMSS) of regular ladder-like architecture. Thermally induced transformations were evaluated by TGA(DTA)-MS, FTIR, NMR, XRD and SEM.

The interaction between a semi-large aromatic hydrocarbon compound (perylene) and the TiO 2 (1 1 0)-(1 × 1) surface under ultra high vacuum conditions has been probed by X-ray photoemission spectroscopy (XPS), ultraviolet photoemission spectroscopy (UPS) and near-edge X-ray absorption fine structure (NEXAFS) methods. UPS measurements of the adsorbate system have been compared with an experimental UPS spectrum of perylene in the gas phase and a calculated spectrum obtained by means of density functional theory (DFT) methods. NEXAFS results of perylene molecules adsorbed on TiO 2 (1 1 0)-(1 × 1) were compared with data from an α-phase perylene single crystal. A novel analysis of the valence data has been employed to show that no strong chemical interaction takes place between perylene and the TiO 2 (1 1 0)-(1 × 1) surface. Furthermore, angle-dependent NEXAFS measurements and the growth curve results suggest that the perylene molecules are oriented flat down onto the TiO 2 substrate due to weak van der Waals interactions.

Alkoxy derivatives of linear oligomethylsiloxanes were applied as substrates for preparation of novel type, ladder-like polymeric silsesquioxane–siloxane materials. A systematic study of the effect of diverging the structure of a polysiloxane chain (distribution of alkoxysilyl groups along the polymer chain) on the properties of silsesquioxane materials obtained by condensation of ethoxy groups, has been undertaken. A series of polysiloxane materials cross-linked with –SiOSi– bonds, forming ladder-like linkages between main siloxane chains was prepared. There were used siloxanes of a regular structure with formula [M(D 2 D OR ) 10 D 2 M] and [M(D 2 D OR 2 ) 10 D 2 M] ] as well as siloxane oligomers of random distribution of MeSi-OR (D OR ) units along the main siloxane chain [MD (1− x ) D OR x M ( x = 0.3, 0.5, 1.0)]. Alkoxy-functionalized oligosiloxane precursors were cross-linked under hydrolytic condensation conditions catalyzed by HCl/NH 4 OH system or nucleophilic catalysts (TBAF and TBAH). The relationship between the structure of siloxane chain (the amount of Si-OR units and their distribution along the polymer backbone) and the properties of obtained preceramic materials was studied with FTIR (as a main method) and NMR, XRD, DTA. The surface area and pores distributions of the studied samples were measured using nitrogen adsorption methods (BET).

The crystalline form of (CH3)8Si8O12 (T8) was obtained by a novel, high yield synthetic route from cyclosiloxanes. The structure of the compound has been widely studied by vibrational spectroscopy (infrared and Raman spectroscopy), X-ray diffraction and scanning electron microscopy. Applying ab initio calculations with comparison to the vibrational spectra we were able to determine T8 molecule structure. Results of the comparison were treated as initial parameters for full-pattern fit of the X-ray diffraction results. Ideal symmetry, Oh (m 3m) of the T8 molecule and rhombohedral crystal structure of the compound was determined and visualized by graphical model. Microscopic crystallinity was observed by means of SEM. 2008 Elsevier B.V. All rights reserved.

Magnetization and electrical resistivity measurements have been performed on a stoichiometric single crystalline magnetite Fe 3 O 4 thin film (thickness of ca. 500 nm) MBE deposited on MgO (1 0 0) substrate. The aim of these studies was to check the influence of preparation method and sample form (bulk vs. thin film) on magnetic anisotropy properties in magnetite. The film magnetization along 〈0 0 1〉 versus applied magnetic field has been determined both in the direction parallel and perpendicular to the film surface, and at temperatures above and below the Verwey transition. We have found, in agreement with published results, that the in-plane field of 10 kOe was not sufficient to saturate the sample. This can be understood if some additional factor, on top of the bulk magnetocrystalline anisotropy, is taken into account.

Oxyfluoride glasses from the Na2O–Al2O3–SiO2–LaF3 system were obtained as a potencial materials for optoelectronics. The effect of SiO2 content on the tendency to the nanocrystallization of LaF3 as well as the ceramization of the glassy matrix has been studied. Thermal stability of the glass and crystalline phases formed upon heat treatment were determined by DTA/DSC and XRD methods, respectively. The efect of the glass composition on the crystallizing phases was studied by MIR, FIR and Raman scattering methods. AFM method was used to confirm the structural analysis.

Epitaxial Fe3O4(001)/MgO(001) films obtained by reactive molecular beam epitaxy were studied using a combination of in situ scanning tunneling microscopy (STM) and monolayer 57Fe probe Conversion E...

Epitaxial Fe(001) films of a high crystalline and surface quality, as checked in situ with Auger electron spectroscopy, low energy electron diffraction and STM, were grown on MgO(001). Such films show an exceptional corrosion resistance remaining metallic for years at the ambient atmosphere, except of a 5 10 nm surface layer, as found using the conversion electron Mossbauer spectroscopy (GEMS). For more systematic corrosion studies, 50 nm iron films were prepared of the 57 Fe isotope. As-prepared Fe films, exposed to the atmosphere did not show clear morphological and compositional changes, which could be associated with the oxide formation, as checked with contact AFM in air and with CEMS. After exposure of the film to HNO 3 or HCl vapors corrosion was observed with AFM. It resulted in two different types of surface modifications. The first one was seen as a homogenous granular layer with the height amplitude of about 15 nm. Corrosion-induced changes of the second type have a localized character resulting in micrometer sized porous protrusions. The corrosion products were identified as γ-FeOOH. Controlled oxidation of a surface iron layer to epitaxial Fe 3 O 4 passivated the film.

The access to X-rays of third generation synchrotron radiation sources enables studies of dynamics in metallic systems in grazing incidence geometry. Combining grazing incidence reflection of X-rays with nuclear resonant scattering of synchrotron radiation allows depth-selective investigations of hyperfine parameters and diffusion phenomena of iron and iron compounds. The unique feature of this method is its sensitivity to near-surface motions of atoms and not exclusively to the atoms on the surface. The depth sensitivity can be varied between about two and more than 10 nm. A 300 nm thick 57 Fe sample grown by molecular beam epitaxy on a cleaved MgO(0 0 1) substrate was investigated. The diffusion coefficient of iron in the near-surface layer (thickness about 2 nm) is almost two orders of magnitude larger than in bulk bcc iron at the same temperature.

Ultrathin Fe(001) films, of 1-3 atomic layers, were grown on the Au(001)-hex surface by molecular beam epitaxy. The film growth was controlled in situ by LEED and STM. At the initial stages of the iron growth, a monolayer of Au automatically diffuses onto the growing Fe film, preventing it from breaking up into islands. Conversion electron Mossbauer spectroscopy (CEMS) reveals considerable Au-Fe intermixing at the interface, which leads to formation of a two-dimensional alloy. The intermixing is also responsible for certain deterioration of the atomic order and the layer sequence in the artificial FeAu alloy obtained by alternative deposition of Fe(001) and Au(001) monolayers. CEMS data for single Fe films and Fe-Au monoatomic superlattices are compared and discussed basing on the FLAPW calculations using WIEN97 code.

Molecular beam epitaxy grown (001) oriented Cr/Fe/Cr and Cr/Fe/Cr/Fe/Cr sandwiches were characterized using the conversion electron Mossbauer spectroscopy (CEMS), which proved that the FeCr interface extended up to about 2.5 atomic layers. Analysis of the CEMS results was based on a simple alloy-model of the Fe/Cr interface, resulting in concentration profiles of Fe and Cr atoms. The derived interface model was then used to study the effect of thermal annealing on the film properties. The CEMS studies were correlated with the measurements of the indirect exchange coupling followed by the magneto-optic Kerr effect. Whereas CEMS revealed a measurable effect of annealing on the interface atomic structure for the annealing temperature T A = 200°C, the coupling character began to change at considerably higher temperature (about 400 °C).

The (1 0 0) surface of the magnetite thin film has been investigated by low-energy ion scattering in the small-angle geometry and in the temperature range of 85–300 K. Thin film of Fe3O4 was grown on MgO (1 0 0) substrate by the molecular beam epitaxy (MBE) and characterized by low-energy electron diffraction, conversion electron Mossbauer spectroscopy and scanning tunneling microscopy. The scattered ion spectra have shown two maxima, in which the intensity of the maximum at low-energy side increases enormously with increasing bombarding energy values. The temperature dependence of scattering ion yield, R+(T), for 5.0, 5.5 and 6.0 keV Ne+ bombardments exhibit two minima, around 110 K and around 125 K, related to the metal-insulator phase transition of this material. The high-temperature minimum was found to disappear at 6.5 keV Ne+ bombardment, indicating the ion velocity dependence of the character of the R+(T) curve, which has been observed previously for the MBE (1 1 1) magnetite thin film. This phenomenon has been explained in the framework of the resonant and Auger neutralization.

Epitaxial Fe3O4(0 0 1) thin films were grown on MgO(0 0 1) using molecular beam of 57Fe at the oxygen partial pressure of about 1×10−6 mbar. LEED patterns indicated perfect growth with a p(1×1) reconstructed surface (as labeled with respect to the bulk unit cell of magnetite) . In situ UHV conversion electron Mossbauer spectroscopy (CEMS) was applied to investigate the film stoichiometry and composition. CEMS spectra taken for films in the 10 nm range revealed a magnesium rich magnetite MgxFe3−xO4 phase formed at the MgO/Fe3O4 interface. Ex situ Mossbauer measurements proved that the magnetite surface oxidizes when exposed to the atmosphere for a couple of weeks. The oxidized phase was identified as a few nanometers thick surface layer of γ-Fe2O3 formed on Fe3O4. By virtue of the γ-Fe2O3 CEMS pattern, the oxidation can be easily misinterpreted as a surface non-stoichiometry for films studied only ex situ. The oxidation process is reversible and annealing at 600 K in UHV restores the magnetite surface structure. At elevated annealing temperature Fe also diffuses into MgO forming a wustite phase.

Low-energy muon spin rotation (LE-μ+SR) measurements were performed on 3.4 and 9.1 nm epitaxial Cr(0 0 1) films buried by non-magnetic boundary layers to study the collapse of the spin-density wave (SDW) of bulk Cr, which is expected when decreasing the thickness of the film below the modulation period of the SDW ( ≈6 nm ). Magnetic phases of Cr are identified by the fast relaxation of the muon spin polarization. While a reduced Neel temperature of 285 K with respect to the bulk value is found for the 9.1 nm Cr layer, the 3.4 nm film remains in a magnetic phase over the investigated temperature range of 20–320 K.

The (1 1 1) surface of the magnetite thin film has been investigated by low-energy ion scattering (LEIS) in the small-angle geometry and in the temperature range 85–300 K. The thin film has been grown by molecular beam epitaxy (MBE) and characterized by low-energy electron diffraction (LEED), scanning tunneling microscopy (STM) and conversion electron Mossbauer spectroscopy (CEMS). The temperature dependence of the scattered ion yield, R + ( T ), obtained by LEIS technique has shown anomaly around 120 K attributed to the insulator–metallic phase transition of this material. The character of the R + ( T ) curve has been found to depend on the velocity of incoming ions. The resonant and Auger neutralization, which depends on the density of state and on the degree of electron localization, can be responsible for the behavior of the R + ( T ) curve, especially in the phase transition region.

Thin magnetite films grown on cleaved MgO (100) substrates were studied by in-situ conversion electron Mossbauer spectroscopy (CEMS) in the temperature range of 80 K–300 K. The film growth was monitored by low energy electron diffraction revealing a perfect epitaxy in the whole thickness range from 430 nm down to 3 nm. CEMS measurements proved an ideal magnetite stoichiometry of the 430 nm thick film reflected both in the hyperfine pattern and in the Verwey transition. The thinner films showed strong deviation from the bulk properties, which was attributed to the modification of composition at the MgO/Fe3O4 interface, at which a magnesium rich phase is supposed based on CEM spectra. This phase, which was not observed previously, could be detected thanks to highly sensitive low-temperature measurements.

The authors discuss the results of structural investigations (XRD, MIR, Raman) of Polish cherts from different geological formations. The X-ray diffraction analyses explicitly confirmed the presence of moganite, which was identified on the basis of satellite XRD peaks positioned/occurring close to the quartz reflections and the additional reflections with the dhkl values 4.456 and 3.101 Ǻ, and established its amounts as varying between about 1 and above 17 wt%. The mid-infrared and Raman spectroscopy also proved the presence of moganite, indicated by the 695 and 560–555 cm−1 bands, respectively. These analytical finds allow to identify moganite in samples containing various SiO2 polymorphs.