Generalized Transvectants-Rankin–Cohen Brackets

We introduce o(p+1q+1)-invariant bilinear differential operators on the space of tensor densities on Rⁿ generalizing the well-known bilinear sl₂-invariant differential operators in the one-dimensional case, called Transvectants or Rankin–Cohen brackets. We also consider already known linear o(p+1q+1)-invariant differential operators given by powers of the Laplacian.     

Reaction-Induced Transformations in Pt–Sn/SiO2 Catalysts: In Situ 119Sn Mössbauer Study

Reaction-induced separation of tin-rich surface layers and tin-depleted inner region was observed in metallic particles of Pt–Sn/SiO₂ catalysts in two reactions: (i) dechlorination of 1,2-dichloroethane at 473 K (modeling catalytic removal of chlorine from hazardous chlorocarbons) and (ii) oxidation of carbon monoxide at room temperature. In the former, a Pt:Sn catalyst (1:2 atomic ratio, 1 wt% metal content), prepared via co-impregnation, showed high selectivity (>80%) toward ethylene (at the expense of ethane), but only after a prolonged (ca. 24 h) period. In situ Mössbauer studies revealed stabilization of a homogeneous Pt–Sn alloy and SnCl₂ after activation in hydrogen; whereas tin-depleted and tin-rich components were separated after a 24-h period. Hence, inhibition of the hydrogenation activity of Pt, by surface tin enrichment and Cl deposition favors high ethylene selectivity. For the oxidation of CO at room temperature, a catalyst with a Pt:Sn atomic ratio of 3:2 (3 wt% Pt) was prepared by an organometallic (CSR) method using ¹¹⁹Sn(CH₃)₄. Platinum-rich PtSn(1) and tin-rich PtSn(2) components were separated in the Mössbauer spectra of catalyst activated at 570 K. The PtSn(2) component is primarily involved in surface reactions. Both in CO oxidation and the subsequent re-activation in hydrogen at room temperature a reversible PtSn(2) Sn⁴⁺ interconversion occurred. d ln(A ₇₇/A ₃₀₀)/dT data indicate the surface location of the involved components.     

Microstructure and Chemical States of Hydroxyapatite/silk Fibroin Nanocomposites Synthesized via A Wet-mechanochemical Route

Hydroxyapaptite (HAp)/silk fibroin (SF) nanocomposites were prepared via a wet-mechanochemical route at room temperature. The results reveal that the inorganic phase in the composites is carbonate-substituted HAp containing 2.9–3.1 wt% of carbonate ions. The primary HAp crystals are rod-like in shape with a typical size of 20–30nm in length and 8–10nm in width, and lattice parameters a = 9.423, c = 6.888. The self-assembled HAp crystals along their c-axes aggregate into bundles, which are connected with SF fibrils. Consequently, a three-dimensional porous network is formed in the composite, which is beneficial to inducing new bone formation in practical implantation.     

Luminescent CdS Nanoparticles Embedded in Polyethylene Glycol (PEG 300) Matrix Thin Film

A simple method for synthesis of well dispersed cadmium sulphide (CdS) nanoparticles embedded in a polyethylene glycol matrix (PEG 300) in thin film form is presented. The molar ratio of PEG and CdS was varied within the range 70:30 to as high as 50:50. Films with controllable sizes (r 3 –8nm) of nanocrystals could be obtained by adjusting post-deposition annealing temperature (T) and time (t). The obtained films showed systematic variation in optical properties with decreasing crystal size due to quantum confinement. Transmission electron micrographs (TEM) indicated well resolved nanoparticles for films annealed at lower temperature (T = 373K) and time (t < 45 min). Photoluminescence (PL) studies indicated blue shift with decreasing particle size. The films did not degrade with aging in a humid atmosphere (relative humidity 40%) for several weeks.     

Mode-locking of neodymium lasers by glasses doped with PbS nanocrystals

Nonlinear optical absorption properties of silicate glasses doped by the PbS nanocrystals were investigated by means of the picosecond pump-probe absorption spectroscopy and absorption bleaching technique. The glass samples were used as saturable absorbers for passive mode-locking of Nd:YAG and Nd:glass lasers. Application of the PbS doped glass together with the active mode-locking and laser cavity quality control enabled the stable of generation of 28 ps and 5 ps duration pulses in Nd:YAG and Nd:glass lasers respectively. PACS 42.60.Fc; 42.70.Hj; 78.47.+p     

Electroless deposition of Ag on Pd-activated TiN/p-Si(100) substrate

Nano-thick Ag films were electrolessly deposited on TiN/p-Si(100) substrates. The substrates were prepared by sputtering TiN on p-Si(100) wafers. An activation process of the substrates was performed by immersing the substrates in a solution of 0.0019 moLL^-1PdCl₂+0.45 moLL^-1HF+8.7 moLL^-1aceticacid+0.036 moLL^-1 HCl so as to obtain the Pd seed layer. The general composition of the electroless Ag bath was 0.0032 moLL^-1AgNO₃+2.24 moLL^-1NH₃+0.56 moLL^-1aceticacid+0.1 moLL^-1 NH₂NH₂ at pH 10.2. The morphologies of the Pd seed layer and the Ag films were characterized by atomic force microscopy (AFM). The effect of the Pd activation on electroless Ag deposition was tested by open circuit potential with time technology (OCP-t). For comparison, the morphology of the films deposited by electrochemical deposition on the substrates was also studied by AFM. PACS 82.45.Mp; 81.15.Pq; 81.10.Dn     

Influence of Hydrothermal Temperature on Structures and Photovoltaic Properties of SnO2 Nanoparticles

Two SnO₂ nanoparticles were synthesized by hydrothermal method at 170°C and 180°C, respectively. Transmission electron microscope observations reveal that the diameters of both the nanoparticles are around 6nm. At the same time, surface photovoltage spectroscopy measurements show that the nanoparticle synthesized at 180°C has more surface electronic states at 0.3eV below the conduction band than the one synthesized at 170°C. This means that the temperatures chosen in hydrothermal synthesis have significant influence on the surface electronic characteristics of resultant SnO² nanoparticles but the effect on their sizes is not obvious. However, after being calcined at 500°C for 2h, the diameter of the nanoparticle synthesized at 180°C increased to 23nm and that of the nanoparticle synthesized at 170°C increased to 32nm as calculated from X-ray diffraction pattern.     

Synthesis and Properties of Layered Organic–inorganic Hybrid Material: Zn-Al Layered Double Hydroxide–dioctyl Sulfosuccinate Nanocomposite

A layered organic–inorganic hybrid nanocomposite was prepared by using a surfactant, dioctyl sulphosuccinate (DSS) as a guest in Zn-Al layered double hydroxide (LDH) inorganic host by a self-assembly technique. The Zn-Al ratio of the mother liquor was kept constant at 4 at the beginning of the synthesis. Powder X-ray diffractogram shows that the basal spacing of the Zn-Al LDH with sulphate as the intergallery anion (ZASUL) expanded from 11.0 to 26.3Å to accommodate the DSS surfactant anion for the formation of the Zn-Al LDH–DSS layered organic–inorganic hybrid nanocomposite (ZADON). It was also found that the BET surface area reduced by about 90%, from 22.5 to 2.2m²/g, for ZASUL and ZADON, respectively if 0.1M DSS was used for the synthesis of the latter.     

Size and Interface Control of Novel Nanocrystalline Materials Using Pulsed Laser Deposition

We have developed a novel method based upon pulsed laser deposition to produce nanocrystalline materials with an accurate grain size and interface control. Using this method, the grain size in the case of Cu thin films was controlled by introducing a few monolayers of insoluble elements having high surface energy such as W, which increases interfacial energy and provides more nucleation sites. The grain size is determined by the thickness of Cu layer and the substrate temperature at which it transforms into islands (nanocrystalline grains) of fairly uniform size which we desgnate as self-assembling approach. Using this approach, the grain size was reduced from 160nm (Cu or Si (100) substrate) to 70–80nm for a simple W layer (Cu/W/Si (100)) to 4nm for a multilayer (Cu/W/Cu/W/Si (100)) thin film. The hardness of these films was evaluated using a nanoindentation technique, a significant increase in hardness from 2.0GPa for coarse-grained 180nm to 12.5GPa for 7nm films was observed. However, there is decrease in hardness below 7nm for copper nanocrystals. The increase in hardness with the decrease in grain size can be rationalized by Hall–Petch model. However, the decrease in slope and eventually the decrease in hardness below a certain grain size can be explained by a new model based upon grain-boundary deformation (sliding). We also used a similar materials processing approach to produce quantum dots in semiconductor heterostructures consisting of Ge and ZnO dots or nanocrystals in AlN or Al₂O₃ matrix. The latter composites exhibit novel optoelectronic properties with quantum confinement of phonons, electrons, holes and excitons. Similarly, we incorporated metal nanocrystals in ceramics to produce improved mechanical and optical properties.     

Noncommutative Ricci Curvature and Dirac Operator on C q [SL2] at Roots of Unity

We find a unique torsion free Riemannian spin connection for the natural Killing metric on the quantum group C _q [ SL₂], using a recent frame bundle formulation. We find that its covariant Ricci curvature is essentially proportional to the metric (i.e. an Einstein space). We compute the Dirac operator and find for q an odd rth root of unity that its eigenvalues are given by q-integers [m] _q for m=0,1...,r–1 offset by the constant background curvature. We fully solve the Dirac equation for r=3.     

A sensitive non-destructive method for measuring the Nd doping concentration in Nd : YAG with high spatial resolution

This paper reports on an experimental method for measuring in Nd:YAG the Nd doping concentration (C) with high sensitivity (0.01 at.%Nd) and high spatial resolution (50 m). The method is based on the measurement of the fluorescence lifetime _f of the upper Nd laser level. Additional parameters required to determine C are the intrinsic fluorescence lifetime ₀ and the quenching parameter Q. The measured values of _f, ₀ (256.47±0.14 s) and Q (4.45±0.40×10²⁰ cm^-3) allow us to calculate the Nd concentration C with an absolute accuracy of 0.1 at.%Nd. By using this method C is measured at the outer surfaces of standard laser rods and at the faces of boule slices (with diameters of up to 50 mm). The obtained results demonstrate a detection sensitivity of 0.01 at.%Nd. PACS 42.70.Hj; 81.70.Fy     

The Formation of Porous Membranes by Filtration of Aerosol Nanoparticles

Flame-generated aerosol particles of Al₂O₃ were deposited by gas filtration on two types of porous and ceramic tubes of -Al₂O₃ with mean pore diameters of 450 and 2700nm, respectively. The particles were aggregates with average mobility diameters in the range of 30–100nm and primary particle diameters of 4–8nm. The particles are characterized by differential mobility analysis, transmission electron microscopy, and by their specific surface area. The deposited membranes are characterized by gas permeability measurements, scanning electron microscopy, and by their pore size distribution from nitrogen capillary condensation. The particles form a distinct, homogeneous membrane layer with a porosity of 90% on top of the substrate surface and only penetrate slightly into the substrate structure. The mean pore sizes of the deposited membranes determined by nitrogen condensation agree approximately with those determined by gas permeation and the specific surface area. The mean pore diameter varies in the range of 30–70nm. The gas permeability of the deposited membranes is related to the specific surface area but influenced by the high porosity. The mean pore size and the permeability of the membranes are almost independent of the substrate structure.The development of a membrane with uniform properties is preceded by a short initial period in which the deposited particles, with an equivalent membrane thickness of roughly 2m, have a significantly lower permeability than the ultimately developed uniform membrane layer. This effect is particularly significant for the aerosol particles with the lowest mean size, probably due to particles deposited in the pore mouths of the substrate.The particles and the deposited membranes are X-ray amorphous but retain their specific surface area on heating to even high temperatures. When the membranes are heated to 1473K for 10h, X-ray diffraction shows a mixture of - and -alumina, accompanied by a partial disintegration of the membrane and a considerable loss of surface area.     

The Q-switched Nd : YAG and Yb : YAG microchip lasers optimization and comparative analysis

The microchip lasers based on the neodymium or the ytterbium doped yttrium-aluminium garnet crystal and Q-sw itched by the Cr⁴⁺:YAG film are considered. The optimal (maximizing of energy) values of the pumping beam radius, the absorber parameters (the thickness and tetravalent chromium ion concentration), and the output mirror reflectivity are determined. The possibility of higher values of energy in the Yb:YAG laser pulse, in comparison with a more traditional Nd:YAG laser, is also substantiated. PACS 42.60.Gd     

Infrared lattice bands of some pearls

From analysis of anisotropical lattice bands properties of 50 reflection spectra both of the CO stretching and bending bands measured from some pearl (Ca⁺⁺CO ₃ ^–– or Ca⁺⁺HCO ₃ ^–– layer) we discussed following subjects.i) Quantized properties present both in reflectivity and in energy. ii) classifications of the Optical Activity. iii) Polar distributions of the CO₃ oscillators in Ca⁺⁺CO ₃ ^–– surface mono-layer. iv) Force constants of these oscillators. v) Step variation of the dipolemoment and their influences to the degree of Optical Activity. vi) Two types of hysteresis loops of the values of Y_N (M_2Jbend ()/M_1Jstret. ()) derived from the oscillators which are at innert-state, at weak active-state and at active-state.     

Bethe-Salpeter Meson Masses Beyond Ladder Approximation

The effect of quark-gluon vertex dressing on the ground-state masses of the u/d-quark pseudoscalar, vector and axialvector mesons is considered with the Dyson-Schwinger equations. This extends the ladder-rainbow Bethe-Salpeter kernel to two-loops. To render the calculations feasible for this exploratory study, we employ a simple infrared dominant model for the gluon exchange that implements the vertex dressing. The resulting model, involving two distinct representations of the effective gluon exchange kernel, preserves both the axial-vector Ward-Takahashi identity and charge conjugation symmetry. Numerical results confirm that the pseudoscalar meson retains its Goldstone boson character. The vector meson mass, already at a very acceptable value at ladder level, receives only 30MeV of attraction from this vertex dressing. For the axial-vector states, which are about 300MeV too low in ladder approximation, the results are mixed: The 1^+– state receives 290MeV of repulsion, but the 1⁺⁺ state is lowered further by 30MeV. The exotic channels 0^–– and 1^–+ are found to have no states below 1.5GeV in this model.     

Nanometer Calibration Particles: What is Available and What is Needed?

Information on available polystyrene calibration spheres is presented regarding the particle diameter, uncertainty in the size, and the width of the size distribution for particles in a size range between 20 and 100nm. The use of differential mobility analysis for measuring the single primary calibration standard in this size range, 100nm NIST Standard Reference Material®1963, is described along with the key factors in the uncertainty assessment. The issues of differences between international standards and traceability to the NIST Standard are presented. The lack of suitable polystyrene spheres in the 20–40nm size range will be discussed in terms of measurement uncertainty and width of the size distributions. Results on characterizing a new class of molecular particles known as dendrimers will be described and the possibilities of using these as size calibration standards for the size range from 3 to 15nm will be discussed.     

Low-resistivity indium tantalum oxide films by magnetron sputtering

Low-resistivity Ta-doped In₂O₃ (InTaO) films from ceramic targets of In₂O₃ doped with 2, 5, and 10 wt% Ta₂O₅ were deposited on Corning glass # 1737 substrates by magnetron sputtering. The electrical and optical properties of these films were studied. The carrier type of InTaO films was found to be n-type. The resistivity, carrier density, and Hall mobility of InTaO films were in the range of 0.28–200.2×10^-4 cm, 0.2–7.4×10²⁰ cm^-3, and 3–31 cm²V^-1s^-1, respectively. A minimum resistivity of 2.8×10^-4 cm with a mobility of 31 cm²V^-1s^-1 and a high transparency of 85% in the visible were achieved for the InTaO thin films doped with 5 wt% Ta₂O₅. PACS 81.15.Cd; 81.40.Rs; 73.90.+f     

Tailoring of the functional properties of sol–gel films on Pt/TiO2/SiO2/(100)Si substrates: (Pb,La)TiO3/(Pb,Ca)TiO3 multilayer heterostructures

Preferentially oriented sol–gel (Pb,Ca)TiO₃/(Pb,La)TiO₃/(Pb,Ca)TiO₃ and (Pb,La)TiO₃/(Pb,Ca)TiO₃/(Pb,La)TiO₃ multilayer heterostructure thin films deposited on silicon-based substrates have been studied and compared with identically prepared (Pb,La)TiO₃ (PTL) and (Pb,Ca)TiO₃ (PTC) films. The existence in their texture of two components that contribute to the net polarization in the direction normal to the plane of the film, 001 and 111, results in significant ferroelectric and pyroelectric properties. P_r=26 Ccm^-2 and =28.5×10^-9 Ccm^-2K^-1, and P_r=17 Ccm^-2 and =22.8×10^-9 Ccm^-2K^-1, have been achieved, respectively, in the PTL/PTC/PTL and PTC/PTL/PTC heterostructures. The surface roughness of these films provides a high specific surface that can be interesting for infrared detectivity. An increase of the dielectric permittivity in the whole temperature interval up to the transition temperature has been observed for both heterostructures with respect to the PTL and PTC films. This effect is due to a release of stress in the heterostructures that is revealed by the increase of the tetragonal distortion, c/a, of these films. PACS 68.55.Jk; 77.80.-e; 77.84.Dy     

Rapid prototyping of micropower sources by laser direct-write

A laser forward-transfer and micromachining process has been developed to fabricate and optimize mesoscale electrochemical power sources, such as primary Zn–Ag₂O and secondary Li-ion microbatteries. The laser direct-write technique allows for adding, removing and processing the various material systems required for the fabrication of micropower sources on many types of substrates under ambient conditions. In this work, we demonstrate planar zinc–silver oxide alkaline cell configurations with 1.5–1.55 V open-circuit potentials. The 10 mm² samples show a flat discharge behavior under constant-current loads and capacities of 100 Ahcm^-2. Stacked Li-ion cells with 3.80-V open-circuit potentials have also been fabricated and continue to operate after 50 charge/discharge cycles. The 9 mm² samples exhibit capacities of 110 Ahcm^-2. PACS 81.16.Mk; 82.47.Aa; 82.47.Cb     

Tunable single-frequency ultraviolet generation from a continuous-wave Ti : sapphire laser with an intracavity PPLN frequency doubler

We report a single-longitudinal-mode continuous-wave Ti:sapphire ring laser that is intracavity frequency doubled in periodically poled lithium niobate (PPLN). Using a multi-grating PPLN crystal, the second harmonic is tunable from 386 to 403 nm – close to the PPLN ultraviolet absorption edge – with a maximum generated power of 114 mW. The wavelength dependence of the critical operating temperature required to eliminate photorefractive effects in the PPLN crystal is determined. PACS 42.65.Ky; 42.70.Mp; 42.72.Bj