An efficient technique for determining the small-signal equivalent-circuit model of a Metal collector-up Heterojunction Bipolar Transistor (C-up MHBT) is presented. The technique employs analytically derived expressions for direct calculation of HBT T-Model equivalent circuit element values in terms of the measured S-parameters. This approach avoids errors due to uncertainty in fitting to large, over determined equivalent circuits and does not require the use of test structures and extra measurement steps to evaluate parasitics. Physically realistic results are demonstrated under various biasing conditions for the n-p-n InP/InGaAs HBT with metallic collector up structure. The agreement between the measured and model-produced data is excellent over the large frequency range and for several polarizations conditions for devices.

In2S3 thin films containing different quantities of sodium have been synthesized by co-evaporation of sodium and In2S3 powder from separate sources using vacuum thermal evaporation method. Films were deposited on ordinary glass at 240 °C. The process of incorporation of sodium was studied as function of at.% Na. Films have been characterised by means of X-ray diffraction, SEM, EDAX and spectrophotometry. X-ray diffraction analysis confirmed the initial amorphous nature of deposited layers and revealed the formation of In2S3 as function of annealing layers containing sodium in nitrogen at 300 °C for 2 h. Energy Dispersive X-ray Analysis (EDAX) revealed the composition of the films as a function of the sodium incorporation. Surface Electron Microscopy showed that these films were granular and homogenous. The films have an n-type electrical conductivity and their optical direct band gap can be managed between 2.20 and 2.45 eV by controlling their sodium content. The variation of parameters for as-deposited and annealed films has been studied within $x\le 4$ at.% solid solution composition. Thin layers with homogeneous surfaces, direct band gap energy $(E_g)$ of about 2.45 eV for 4 at.% Na and 0.9 μm-thick have been achieved.

Pd/SnO2 composite films were obtained by wet chemical route using SnCl2:2H2O as tin containing precursor and PdCl2 as palladium containing precursor. The bilayer structures were subjected to rapid thermal annealing for the incorporation of Pd in SnO2 matrix. Pd/Sn was varied between 6 to 20% for optimizing the Pd concentration for improved sensitivity. Liquid Petroleum Gas (LPG) sensing properties were also investigated. The films thus obtained were subjected optical, microstructural, FTIR and Raman studies both before and after LPG exposure.

A 3D modelling is used to obtain the expression of excess minority carrier density in base region of a polycrystalline silicon solar cell. The concept of the junction recombination velocity Sf is used to quantify how excess carrier flow through the junction in actual operating conditions. The plot of the photocurrent density allowed study the influence of the grain boundary recombination velocity and grain size on both, the junction recombination velocity and on the back surface recombination velocity of an n +-p-p + solar cell. This study pointed out the importance of the losses at the back side of solar cell. It's also show that the junction recombination velocity is more important for small grain size with large values of grain boundary recombination velocity.

Hybrid materials composed of polyhedral oligomeric silsesquioxanes (POSS) and a polyphenylene vinylene (PPV) derivative were fabricated and characterized by optical and surface spectroscopy. The hybrid thin films have similar optical properties as the pristine polymer but contributions of the POSS are evidenced in infrared spectroscopy. Organic light emitting diodes using the hybrid material as an emitter clearly showed an improvement of the electrical characteristics and the efficiency of the devices as compared to those using the pristine polymer. The effects of POSS incorporation to the polymer are discussed via the obtained results.

A novel approach for determination of refractive index dispersion n(λ) and thickness d of thin films of negligible absorption and weak dispersion is proposed. The calculation procedure is based on determination of the phase thickness of the film in the spectral region of measured transmittance data. All points of measured spectra are included in the calculations. Barium titanate and titanium oxide thin films are investigated and their n(λ) and d are calculated. The approach is validated using Swanepoel's method and it is found to be applicable for relatively thinner films when measured transmittance spectra have one minimum and one maximum only.

This paper presents a unified thermal model, which can describe thethermophysical effects with laser pulse width ranges from nanosecondto femtosecond. Take gold target as an example, the numericalsolutions are obtained from the unified model using a finitedifference method. The temperature distribution of the electron andthe lattice along with space and time at a certain laser fluence ispresented. The time-dependence of lattice and electron temperatureon the surface for different laser fluence is also performed. Thesatisfactory agreement between our numerical results andexperimental results of vaporization threshold indicates that theunified thermal model is correct and reasonable.

We report on the effect of thickness on the structural and electrical properties of permalloy thin films Ni81Fe19 (Py). Permalloy films were deposited onto Si(100) substrates at room temperature using a KrF (wavelength of 248 nm, pulse duration of 30 ns) excimer laser at a fluence of 3 J/cm2. The thickness ranges from 25 nm to 250 nm. The micrographs reveal the formation of irregular droplets with dimensions between 4.6 μm and 0.24 μm. We show that all samples presented a strong $ \langle 100 \rangle$ texture. The lattice constant (a) monotonously increases with increasing thickness. Also, we note that for thickness below 127 nm, the lattice constant (a) is lower than the bulk value, however, for thickness more than 127 nm, (a) is higher than $a_{\rm bulk} $ . The grain size increases from 30 nm to 54 nm as the thickness increases from 45 nm to 250 nm. The different contributions to the electrical resistivity are investigated as a function of the Py thickness.

Successful structural reinforcement of polymer matrices by carbon nanotube has been broadly applied where significant improvement of mechanical properties was achieved at a low carbon nanotube loading rate. The notion of the mechanical properties of aligned composites are better than random ones has been proofed and demonstrated whereas the concept is not easy to implement through carbon nanotube polymer composites by the conventional techniques. Here, we introduce a novel practice to actively align and network the multi-wall carbon nanotubes (MWCNTs) in hot melting high density polyester (HDPE) matrix. In this process, MWCNTs were aligned via AC electric field which induced dipolar interactions among the nanotubes in a hot melting matrix and followed by immobilization by cooling curing matrix under continued application of the anisotropic electric field. In situ SEM verified the electrostatic stabilization of the MWCNTs in the dispersion while the orientation and agglomeration are caused by the dielectrophoretic force. Alignment of MWCNTs was controlled as a function of magnitude, frequency, and application time of the applied dielectrophoresis. In the present work, MWCNTs are not only aligned along the field, but also migrate laterally to form thickness. Eventually, the actively aligned MWCNTs would amplify the hardness and wear-resisting property.

Using electron energy loss spectroscopy in a 100 kV VG scanning transmission electron microscope we study nitrogen doped carbon nanotubes grown via electron cyclotron resonance (ECR) microwave plasma techniques. The process is controlled by direct current (dc) biasing the grid separating the ECR source and the substrate. We show that plasma induced sputtering of the ECR source wall (stainless steel) can lead to significant iron and chromium contamination of growth samples. We identify various Fe, Cr, Ni nitride phases, and propose a growth model based on nitridation-induced metal segregation of steel based FeCrN alloys. Trace Cr doping of nanotube catalysts appears a promising route for introducing large nitrogen concentrations into both single and multi-walled nanotubes and may accelerate nanotube growth rates.

Single-walled carbon nanotubes can be used as electron sources in the process of field emission, and have great potential for practical application of the field emission display (FED) panels with large screen size. We fabricated a FED using the single-walled carbon nanotubes (SWNTs) as the cathode by the screen-printing process. Test showed that the SWNTs emitters exhibit excellent macroscopic emission properties. It has low turn-on voltage (2.7 V/μm) and high brightness, with a high current density of good uniformity and stability. It was observed that the field emission qualitatively follows the conventional Fowler–Nordheim (F–N) theory, and aging treatment played an important role in improving the image uniformity and stability. Compared to other complicated processes, the simple fabrication using screen-printing process seems to be advantageous for practical application.

It is difficult for brittle materials to acquire high machined surface quality as they have low fracture strength. But in the case of nanometric cutting technology, nanometer level machined surface is often acquired by means of ductile material remove mode. In order to investigate physical essence of ductile machining process, this paper carries out molecular dynamics (MD) analysis of nanometric cutting single crystal silicon. The result shows that huge hydrostatic pressure induced in the local area which lead to the silicon atom transform from classical diamond structure (α silicon) to metal structure (β silicon). At the same time, the stress concentration is avoided by uniformly distributed pressure in the cutting area. These two important factors together result in the ductile machining of silicon and then acquire super-smooth surface.

Using ethanol as a solvent p-aminoazobenzene (p-AAZB), an organic nonlinear optical crystal having good optical quality was grown by slow evaporation solution technique. Structural and optical properties were studied by applying XRD and UV-Vis spectroscopy. The measurement of the second harmonic generation was performed using the fundamental Nd:YAG 10 ns laser beam with wavelength 1.064 μm. Dependence of the second order susceptibilities for the two principal second order susceptibility tensor components d 14 and d 25 with the simultaneously applied dc- and UV-laser fields were investigated and discussed.

We have developed an alignment tool for optical lattices with arbitrary beam angles, allowing for optical potentials with a range of geometries and topographies. A calibration procedure has been introduced, giving a precision of 10 mrad in the chosen beam angle, and a high degree of flexibility. The tool has been tested in simplified experiments on the confinement and expansion of cold atoms in one-dimensional and two-dimensional optical lattices, and has proved to work well.

A diode-pumped GaAs-passively-Q-switched intracavity-frequency-doubled Nd:YVO4/YVO4 green laser with a MgO-PPLN is presented. The characteristics of the passively Q-switched green laser pulses have been investigated. At the maximum incident pump power of 5.19 W, the minimum green-light pulse width of 26.4 ns has been obtained at a repetition rate of 134 kHz. The rate equations are presented to simulate the process of the green laser, and the numerical solutions of the coupled rate equations accord with the experimental results.

In this paper, we investigate the propagation of electromagnetic wave in 12-fold symmetric quasiperiod structure employing finite difference time domain (FDTD) method. The quasiperiodic photonic crystal (QPC) consists of a dodecahedral lattice of air holes embedded in a dielectric background. Simulation on wave propagation through a wedge-shaped structure shows that negative refraction can occur at the interface between air and the quasicrystal sample. We further design QPC slab for performance of a high-quality flat lens. Simulation results reveal that non-near-field imaging can be achieved through the QPC slab. TM and TE modes are discussed and both the two modes exhibit the focusing effect. Since the air-hole type QPCs are more easily fabricated and integrated than the dielectric-rod type QPCs, our results might be important to the applications.

Thermodynamic and magnetic measurements of ternary compounds RCo9Si4 with R = Pr, Nd, and Sm were analyzed in order to estimate the magnetic entropy, specific heat jump and effective magnetic moments. The samples show a ferromagnetic behaviour at low temperature with T C varying from 10 to 35 K. The saturation magnetisation M s at 2 K with 6 T is found to be about 23.20, 24.94 and 10.70 emu/g for R = Pr, Nd, and Sm, respectively. The total effective magnetic moments μeff of RCo9Si4 for R = Pr , Nd, and Sm as obtained from the Curie constant C are estimated to be 4.94 μB , 5.26 μB , and 3.90 μB , respectively. The magnetic specific heat jump ΔC p at T C is found to be 12, 3.6, and 10.5 J/mol K for RCo9Si4 with R = Pr, Nd, and Sm, respectively. Magnetic entropy S M associated with the magnetic ordering in RCo9Si4 (R = Pr, Nd and Sm) were estimated to vary from 19.15 J/mol K and 14.90 J/mol K.

Formation of different types of nanosized Al-containing oxide precipitates in an Fe-Cr-Al alloy (PM 2000) was studied by electron energy loss spectroscopy (EELS) using a transmission electron microscope (TEM). It was shown that Y3Al5O12 (garnet) and YAlO3 (perovskite) as well as $\gamma $ -Al2O3 and $\alpha $ -Al2O3 precipitates can be distinguished by analysing the O-K energy loss near-edge structure (ELNES). The formation of interface-specific phases on Al2O3/YAlO3, Al2O3/matrix and Y3Al5O12/matrix interfaces was also investigated by specially resolved EELS analysis. Applicability and sensitivity of the EELS method in the study of steel precipitates were discussed. A sharp pre-peak or “pre-shoulder” in the O-K edge was observed and studied by means of spatially resolved EELS of oxide inclusions. The intense pre-peak was found to be caused by radiation damage induced by the electron beam of the Al hydroxide phase inside Al2O3 inclusions. This phase formed due to the incorporation of hydrogen in the matrix during mechanical alloying in the hydrogen atmosphere. The “pre-shoulder” of the main O-K feature measured on the inclusion/matrix interface results from the formation of a thin Ti-O layer.

In this paper, the ceramic compositions ( $1-x$ )Pb1−w−y Law Sry (Zrz Ti $_{1-z})_{(1-w/4)}$ O3-xBaTiO3, where x = 0.15, 0.25, 0.35 and 0.45, fabricated through solid state reaction method were investigated for phase formation, microstructure, density, dielectric and piezoelectric properties. The combination of the two perovskite structured stoichiometric compositions (i.e., isovalent Sr2+ modified PLZT and BaTiO3) indicated that tetragonality enhanced further due to BaTiO3 concentration in PLSZT lattice. The BaTiO3 in PLSZT ceramics were homogeneously distributed within the two perovskite structured solid solutions. The dielectric characterization indicated that $\varepsilon _{RT}$ enhanced while $\tan\delta _{RT}$ and T c decreased with increasing BT additions into PLSZT perovskite. The maximum $\varepsilon _{RT}$ = 2986 and $\varepsilon _{T_c}$ = 21468 were found in 0.55PLSZT-0.45BT ceramic system. The piezoelectric properties were influenced by both BaTiO3 and Sr2+ modified PLZT perovskite. The influence of BT modified PLSZT ceramics showed significant variations that has been discussed. The piezoelectric properties remarkably enhanced with maximum ( $k_{p} = 0.541$ and $d_{33} = 518$ pC/N) values in the 0.55PLSZT-0.45BT composition and thus, could be a promising candidate among this series for possible capacitor, sensor and actuator applications.

Surface caesium content is known to greatly influence the negative ion yield during SIMS analyses. In NanoSIMS, a 16 keV ion probe of Cs+simultaneously performs the surface enrichment and the sample sputtering. To increase the surface caesium content and thus generate higher ion yields, it is suggested herein to significantly reduce the energy of the primary ions by biasing the sample with a positive voltage slightly smaller than the voltage of 8000 V that is used for primary ion acceleration. Then, once the typical bias voltages are restored, SIMS analysis may carried out with increased sensitivity right from the beginning of the sample erosion. The use of such a procedure may improve many types of SIMS investigations such as thin sections of biological samples, semiconductor wafers shallowly doped over very small areas and small meteorite samples.However, during deceleration close to the sample surface, the beam size is markedly enlarged unless the excitation of the objective lens is corrected. In this study, optics simulations are performed using Simion 8 in order to facilitate adjustment of the experimental setups. An objective lens excitation set at E0P = 0 V and E0S = +5930 V focuses a 100 eV caesium beam into an area 9.2 μm in diameter. Even for a final energy as low as 25 eV, 90% and 50% of the beam is confined to areas of 30 μm and 4 μm in diameter respectively (with electrodes E0Pand E0S set at 3150 and 5450 V and using a beam slightly limited in angle). The procedures being suggested will be confirmed by experimental studies soon to be submitted as complementary contribution. As predicted, caesium rich surfaces greatly improve ion yield and consequently localised SIMS analysis as well.