International Journal of Modern Physics B

Numerical and symmetry based analysis of the electron-phonon coupling in graphene have been performed. Symmetry alone predicts the Kohn anomalies, their positions in the Brillouin zone and all quantum numbers of the Kohn modes and the vectors of the Kohn displacements. Dispersion of kink phonons is calculated and found to be similar to the classical phonon spectrum. Interestingly, most of the Γ (including all the acoustic phonons as well) and K modes are shown to be uncoupled to electrons.

Quasi one-dimensional systems, including bio-polymers, nanotubes, nanowires, etc., are in focus of material science and technology for more than two decades. Using recently found quasi one-dimensional conformation classes, which are elementary building blocks of all quasi one-dimensional crystals, we make symmetry based study of their diffraction patterns. In particular, we single out the features distinguishing between the classes, thus enabling to characterize each of them. It turns out that this analysis suffices to find out chiral indices of carbon nanotubes.

Pure titania (TiO₂) nanopowders and TiO₂ doped with 10 mol % of vanadium ions (V³⁺) are synthesized by sol-gel method. The dependence of structural characteristics of nanopowders on synthesis conditions is investigated by X-ray diffraction and Raman spectroscopy. Very intensive modes observed in Raman spectra of all nanopowders are assigned to anatase phase of TiO₂. Additional Raman modes of extremely low intensity which can be related to the presence of small amount of brookite amorphous phase are observed in pure TiO₂ nanopowders. In V-doped nanopowders anatase was the only TiO₂ phase detected. The variations in duration and heating rate of calcination influence slightly the Raman spectra of pure TiO₂, but have a great impact on Raman modes of anatase, as well as the additional Raman modes related to the presence of vanadium oxides in V-doped samples.

Pure and antimony doped barium titanate powders were prepared by polymeric precursors method through Pechini process, which was carried out as a three-stage process from organometallic complex. Obtained powder was pressed into pellets and sintering was performed at 1300 °C for 8 h with heating rate of 10 °C min-1. The formation of phase and crystal structure of pure and Sb-doped barium titanate was approved by XRD analysis, Raman and IR spectroscopy. The influence of Sb doping on microstructure of barium titanate ceramics was investigated by scanning electron microscopy. Therefore, the relation between grain size, structure and properties of the obtained ceramics was analyzed. Influence of Sb doping on barium titanate properties was discussed.

Amorphous polymer-derived Si-C-N ceramics can be doped with different elements (Al, B etc.) through various pre-ceramic polymer routes. Thus, controlling of the high temperature oxidation resistance can be achieved on an atomic level. An important factor for silica layer growth is oxygen diffusion in protective thermally grown layers. In order to get insight of the oxygen diffusion mechanism, analysis should include both, bulk and short-circuit diffusion. XRD measurements of oxidized Si-C-N and SiC revealed the possibility that oxide layers were fully crystallized and are composed of nano-sized cristobalite-like grains. Secondary ion mass spectrometry depth profile analysis after ¹⁸O₂-¹⁶O₂ isotope exchange experiments on oxidized SiC indicated that short-circuit diffusion is probably grain boundary diffusion of molecular oxygen.

Photoconductive and photorefractive characteristics of fullerene- and nanotubes-doped organic thin films based on conjugated organics, such as polyimide, polyaniline, pyridine, etc. have been studied. In addition, the liquid crystal mesophase with nanoobjects has been investigated. The increase of the charge carrier mobility of nanosensitized organics has been established. The nonlinear refraction and cubic nonlinearity have been investigated at wavelength of 532 nm via four-wave mixing technique using Raman-Nath diffraction regime. The thin holographic grating has been written at the spatial frequencies placed in the range of 90-150 mm^-1. The energy density has been chosen in the range of 0.1-0.9 J×cm^-2. The correlation between photoconductive and nonlinear optical parameters has been revealed. The nanostructured materials can be proposed for different area of nano- and microelectronic applications.

Due to their extensive present, important and versatile potential applications, metal hydrides (MH) are among the most investigated solid-state systems. Theoretical, numerical and experimental studies have provided a considerable knowledge about their structure and properties, but in spite of that, the basic electronic principles of various interactions present in MH have not yet been completely resolved. Even in the simplest MH, i.e. alkali hydrides (Alk-H), some trends in physical properties, and especially their deviations, are not well understood. Similar doubts exist for the alkaline-earth hydride (AlkE-H) series, and are even more pronounced for complex systems, like transition metal-doped AlkE-H, alanates and borohydrides. This work is an attempt of explaining some trends in the physical properties of Alk-H and AlkE-H, employing the Bader analysis of the charge distribution topology evaluated by first-principle all-electron calculations. These results are related to some variables commonly used in the explanation of experimental and calculated results, and are also accompanied by simple tight-binding estimations. Such an approach provides a valuable insight in the characteristics of M-H and H-H interactions in these hydrides, and their possible changes along with external parameters, like temperature, pressure, defect or impurity introduction. The knowledge of these basic interactions and processes taking place in simple MH are essential for the design and optimisation of complex MH-systems interesting for practical hydrogen storage applications.

Pt₄Sn_4.4Sb_7.6 (a = 9.3304(2) Å, space group ) is an unfilled skutterudite member of the solid solution Sn_xPt₄Sn_ySb_12-x. In contrast to Sn_xNi₄Sn_ySb_12-y and Sn_xPt₄Sn_ySb_12-x no Sn could be found in the 2a sites of the Sn/Sb framework. Physical properties have been data for Ni₄Sn₃Sb₉ and Ni₄Sn_3.5Sb_8.5. Resistivity measurements for Pt₄Sn_4.4Sb_7.6 reveal a temperature dependent crossover from metallic to semiconducting behaviour connected with a corresponding change from negative to positive thermopower at 30 K. Vicker's hardness, thermal expansion and elastic moduli compare well with values of other Sb- investigated in the temperature range from 4.2 K to 800 K and have been compared with based skutterudites.

Transmission electron microscopy is used to study the structure and phase composition of binary zirconium alloys with Group I-VIII metals produced from metal powders via severe plastic torsional deformation under pressure. The metal contents in the initial mixture, the type of reacting metals, and the degree of deformation are found to affect substantially the structure and phase composition of the alloys synthesized. It is found that the tendency of binary zirconium-based alloys to form an amorphous state depends on the position of an alloying metal in the periodic table. An amorphous state is formed in alloys with Group II (Zn), III (Al), VIII (Co, Ni), and I (Cu) metals; it is not formed in alloys with Group IV (Ti), V (V, Nb), and VI (Mo) metals of the periodic table. Compositions that are close to equiatomic alloys are more favorable for the formation of an amorphous state or the smallest nanograins. In the course of mechanical alloying, high-pressure phases and intermetallic compounds are found to form.

The phase composition and structure of a mixture of aluminum and quartz powders taken in a ratio of 1:1 have been studied after loading by spherical converging shock waves. A number of concentric layers (zones) have been observed in the sample after shock-wave loading. The presence of several zones in the sample reflects the specific features of the processes occurring in different pressure ranges. It has been established that pressures below ~45 GPa cause only additional compacting of the material and deformation of aluminum and quartz. In this case, the quartz grain size substantially decreases up to the transition into the X-ray amorphous state. The attainment of a pressure of ~45 GPa initiates the solid-state reaction of SiO₂ decomposition, which leads to the precipitation of pure silicon and the evolution of oxygen. The beginning of the silicon precipitation and the chemical reaction of Al₂O₃ formation are separated over the pressure scale. The critical pressure, which is necessary for the solid-state chemical reaction of the Al₂O₃ formation, is about 50 GPa.

Three various α-alumina nanopowders have been characterized and their behavior in dry uniaxial pressing followed by pressureless sintering in air investigated. Nearly full dense ceramic material has been obtained at no more than 1300°C and its grain size evaluated by scanning electron microscopy and X-ray line profile analysis as being about 200 nm. The most suitable powder for low temperature sintering was reported to be that consisting of aggregates strong enough to enable their dense packing during the die filling and early period of pressure rise but capable of being destroyed further at final stage of compaction. Several dense samples with grain size on the level of 100 nm and less have been shown to be available at 1150-1200°C if a proper molding technique would be developed.

The new Raster Spring Imaging Mode is developed to study soft and bad – fixed objects in AFM. The normal and lateral force between tip and sample is minimized. We discuss the principle of operation, main features and its prospect for specific applications. Experimental results revealed advantages with regard to other techniques like contact or semicontact mode. The silicon structure measurements with Raster Spring Imaging Mode allow to obtain information of elastic and adhesion properties without losing sight of good topography image.

In this letter we report on successful preparation and characterization of anisotropic gold nanocrystals bio-synthesized by reduction of aqueous chloroaurate ions in pelargonium plant extract. The nanocrystals have been characterized by means of Transmission Electron Microscopy (TEM), UV-VIS absorption spectroscopy and tapping mode atomic force microscopy (TM-AFM). Using these investigation techniques, the successful formation of anisotropic single nanocrystals with the preferential growth direction along the gold (111) plane has been confirmed. The high detail phase images could give us an explanation concerning the growth mechanism of the nanocrystals.

We present a detailed magnetic study of the polycrystalline transition metal oxides Ln_0.7A_0.3TMO₃, Ln = La, Pr; A = Ca, Sr and TM = Mn, Co at low temperatures including electrical resistance, magnetization and ac susceptibility measurements. The effect of the A-site and B-site substitutions on the properties of these compounds is discussed. The results of this analysis indicate that the electrical and magnetic behavior of these compounds have some reminiscences of the manganites having similar formula, but the spin disorder and the grain boundary effects control the properties of these materials.

Indium vanadates for severe applications as photocatalysts, anodes for Li rechargeable batteries or electrochromic devices were prepared via conventional and non-conventional preparation methods. The conventional high temperature solid state reaction was performed at 800°C for 25 hours and the non-conventional microwave-assisted synthesis was performed at 220°C for different reaction times under hydrothermal conditions. The as-prepared powders were characterized in terms of phase composition by X-Ray diffraction analysis (XRD) and infrared spectroscopy (IR) and of powder morphology by scanning electron microscopy (SEM) and BET method. Nanosized indium vanadate powders were successfully synthesized by non-conventional microwave-assisted hydrothermal method. The dense ceramic bodies suitable for electrical conductivity measurements with 96% t.d. were obtained by sintering of powders prepared by high-temperature solid state reaction at 1100°C for 4 h with admission of oleic acid as a binder additive.

The increased use of imaging techniques in diagnostic studies, such as MRI, has contributed to the development of the wide range of new materials which could be successfully used as image improving agents. However, there is a lack of such substances in the area of gastrointestinal tract MRI. Many of the traditionally popular relaxation altering agents show poor results and disadvantages provoking black bowel, side effects of diarrhea and the presence of artifacts arising from clumping. Paramagnetic species seem to be potentially suitable agents for these studies, but contrast opacification has been reported and less than 60% of the gastrointestinal tract magnetic resonance scans showed improved delineation of abdominal pathologies. The new solution has been proposed as zeolites or smectite clays (hectorite and montmorillonite) enclosing of paramagnetic metal ions obtained by ion-exchange methods. However, such materials have problems of leakage of paramagnetic ions causing the appearance of the various side-effects. In this study we show that Co⁺² and Dy⁺³ paramagnetic-pillared bentonites could be successfully used as MRI digestive tract non-leaching contrast agents, altering the longitudinal and transverse relaxation times of fluids in contact with the clay minerals.

With an aim of obtaining aluminum P/M materials strengthened by dispersion of transition metal compounds and solid solution of Mg, Al-2mass%Co and Al-5mass%Co alloys with varied Mg additions of 0, 1 and 5 mass% were prepared by rapid solidification techniques. Rapidly solidified flakes were produced by argon gas atomization and subsequent splat quenching on a water-cooled copper roll. The flakes were consolidated to the P/M (Powder metallurgy process is named as P/M) materials by hot extrusion after vacuum degassing. Cast ingots of these alloys were also hot-extruded under the same conditions to the I/M (Ingot metallurgy process is named as I/M) reference materials. Uniform dispersion of fine intermetallic compounds (Co₂Al₉) was observed in all the as-extruded P/M materials. Added Mg was present as the solute in the P/M and I/M materials alloy even after annealing at 773K. The P/M materials containing Mg exhibited higher hardness and strength than those without Mg at room temperature. Tensile strength increased with increasing amount of Mg in the I/M materials at elevated temperatures. However, strength of the P/M materials decreased with addition of Mg at 573K and 673K. According to the steady state creep rate and creep rapture time, the creep resistance of the P/M materials containing Mg was clearly inferior to that of Mg-free alloys. Thus the positive effects of Mg additions on mechanical properties of the P/M materials of Al-Co-Mg alloys disappeared at high temperature.

The paper is focused on the wear mechanism of orbital forged and equal-channel angular extruded Cu OFHC (oxygen-free high thermal conductivity) material. The wear behaviour of the Cu OFHC material is investigated through pin-on-disc tests. Two different processing conditions have been used, equal-channel angular processing (ECAP) and orbital (radial) forging. The wear investigations in this orbital formed material are unique; additionally wear properties show interesting wear characteristics. Particular attention has also been paid to the friction coefficient and to the role of the wear rate.

This work reports the preparation of SiO₂ and TiO₂/poly (vinyl butyral) nanocomposites with enhanced dynamic mechanical properties. Silica and titania nanoparticles were introduced in the matrix as the neat powder and as colloidal sol using the melt mixing process. Composites reinforced with colloidal sol silica and titania showed higher mechanical properties than the ones reinforced with as-received particles. When sol TiO₂ particles are used, the highest increase of storage modulus of about 54% is obtained for 5 wt% loading, while for sol SiO₂, the storage modulus increases with the addition of nanosilica with the largest increase of about 99% for 7 wt% loading. In addition, nanocomposites were introduced within Kevlar/PVB composites. The addition of 5 wt% silica and titania colloidal sol lead to the remarkable increase of the storage modulus for about 98 and 65%, respectively. Largest contribution of nanoreinforcements in lowering the glass transition temperature is observed for 7 wt% loading of TiO₂ and SiO₂ colloidal sol.

The system of living cells closed in a polymer bead as a matrix is considered in formalism of lattice model extended with compactivity concept developed for complex systems in statistical mechanics of jammed state of matter. Possibility of extension of Edwards concept of compactivity developed for hard irregular grains with friction to living cell systems, is considered if function of cell interactions and properties. Existence of critical points in the course of cell colony grow related to their self assembling and response to polymer hydrogel micro-environment resistance, is analyzed in function of cell volume fraction growth. Based on the theory and experiments it is related to characteristic values of compactivity in analogy to phase transition temperatures. Interpretation of data from literature on cancer cell cluster growth suppression under pressure of microenvironment on the base of model proposed is offered.

In this paper we present applied physics research results of gas-permeable contact lenses (CL) that are manufactured from fluorosilicone acrylate based material (Boston™ type). During contact lenses production the conformation states of polymers belonging to near surface layers of CL surface are changed. Since CL quality crucially depends on surface roughness and optical properties, the properties of surface molecules conformation state and their orientation come into perspective as important factors acting on the molecular level. Therefore, we investigated CL surface by phase contrast atomic force microscopy (PC-AFM), magnetic force microscopy (MFM), and optomagnetic fingerprint (OMF) technique and found out that surface quality and magnetic properties of contact lenses have influence on physical properties of light transmission and that these changes can be detected on the nanolevel of magnetism, as well as optomagnetism. These results carry important biophysically based implications for CL industry, biomedical application industry and applied optical science.