The bulk micromachining on (010), (110) and (111)A GaAs substrates in the 1 H2SO4:1 H2O2:8 H2O system is investigated. Focus is placed on anisotropy of 3D etching shapes with a special emphasis on convex and concave undercuts which are of prime importance in the wet micromachining of mechanical structures. Etched structures exhibit curved contours and more and less rounded sidewalls showing that the anisotropy is of type 2. This anisotropy can be conveniently described by a kinematic and tensorial model. Hence, a database composed of dissolution constants is further determined from experiments. A self-elaborated simulator which works with the proposed database is used to derive theoretical 3D shapes. Simulated shapes agree well with observed shapes of microstructures. The successful simulations open up two important applications for MEMS: CAD of mask patterns and meshing of simulated shapes for FEM simulation tools.

We have investigated the structural, elastic, electronic, optical and thermal properties of an insulator perovskite CsCdF3 using the pseudo-potential plane wave (PP-PW) scheme in the frame of generalized gradient approximation (GGA) and local density approximation (LDA). The computed lattice parameter and bulk modulus agree reasonably with experimental and previous theoretical works. We find that the cubic Pm-3m crystal symmetry persists throughout the pressure range studied. The anisotropy in CsCdF3 crystal is strong, while, by analyzing the ratio between the bulk and shear moduli, we conclude that CsCdF3 is ductile material. The calculations reveal that CsCdF3 is an indirect-gap insulator under ambient conditions, with the gap increasing under pressure. Also, we present the results of the densities of states and charge densities. The static dielectric constant and static refractive index are proportional to the fundamental indirect band gap Γ-R. The thermal effect on the volume, bulk modulus, heat capacities CV and CP and Debye temperature was predicted using the quasi-harmonic Debye model. To the author's knowledge, most of the studied properties are reported for the first time.

Within Silicon Carbide Junction Field Effect Transistor (SiC-JFET) model, body diode is not extensively studied and almost under-researched. Body diode remains a complex device to study particularly during switching transients. In this paper, the JFET body diode is experimentally demonstrated to be a power PiN diode. Finite element method model based on the device geometry and SiC material is used to accurately simulate this diode. Accurate simulations are necessary for analysis and verification purposes. Simulation relies on component models and associated parameters. The paper focuses on a step-by-step extraction procedure for design parameters of the SiC-JFET body diode. A comparative study between experimental data and simulation results is given to validate the device model and associate parameters.

The electronic transport properties of p-type tin selenide (SnSe) grown by direct vapor transport (DVT) technique were investigated via Hall effect in the temperature range 40 <T< 300 K. The temperature dependence of conductivity revealed the existence of impurity energy level in the band gap of the crystal. The temperature dependence of the carrier concentration was analyzed using the single-donor – single-acceptor model. The Hall mobility increases by decreasing temperature up to 120 K and then decreases along with temperature. The observed temperature dependant mobility in the temperature range 120 <T< 300 K and 40 <T< 120 K was found to be limited by homopolar and ionized impurity mode scatterings respectively.

There is a need to characterize the quality of contacts and the noise properties of new materials deposited or grown as thin films. Poor contacts are interface dominated. Perfect contacts have a negligible interface contribution and there is only a resistance and noise contribution from outside the contact region. The presence of current crowding enhances the resistance and noise contribution. Such contacts are called constriction dominated contacts. The conductive film is characterized by its sheet resistance and normalized conductance fluctuations for a unit surface. The resistance and noise is studied between two circular top electrodes of the same diameter on the conductive. To distinguish between perfect and poor contacts and to characterize the thin film in case of good contacts, we need a set of contacts with different diameters. Models for perfect and poor contacts are investigated. The scaling of resistance and noise with contact radius r is for interface dominated poor contacts: Ri$\propto$ 1/r2 and SRi$\propto$ 1/r6. In contrast, perfect contacts with contact diameter (2r) much smaller than the distance between the centers (2b) show: Rc$\propto$ ln(b/r) and SRc$\propto$ 1/r2. From the resistance and noise measurements between constriction dominated perfect contacts, the sheet resistance and normalized noise of the thin film are calculated.

This paper presents the result of thermodynamic studies on (Se80Te20)100-xAgx ( 1< x < 4) glasses under non isothermal conditions using differential scanning calorimetric technique. The crystallization kinetics has also been discussed. Thermodynamic parameters like entropy difference between glassy and the crystalline phase, difference of Gibbs free energy, specific heat, and the enthalpy released during phase transformation have been evaluated. The heat capacity jump and fragility of these alloys are also calculated. The results show that the stability of sample is minimum for (Se80Te20)99Ag1 and maximum for (Se80Te20)97Ag3 among all the samples.

In this work the main effective parameters on the electrical resistivity of copper nitride thin films are investigated. Copper nitride thin films were successfully deposited on glass substrates by reactive dc magnetron sputtering at room temperature but different sputtering time. Working gas was a mixture of argon and nitrogen with equal amounts. The effect of deposition time on the structural, optical and electrical properties of deposited films was investigated. X-ray diffraction measurements show different lattice orientation in the structure of deposited films. By increasing the time of sputtering an orientation change from (100) to (111) can be observed in the films. Film morphology of samples is not changed with the sputtering time. The optical transmittance of deposited films decreases with increasing the deposition time. Results confirm that when the amount of nitrogen in working gas is 50%, we have more (100) planes in the structure of the deposited films, leads to higher resistivity of the films.

We address the interpretation of the splitting between the ground state excitonic transition which indicates the energy of the lowest direct band gap in AlN bulk films and epilayers, and a 36–38 meV higher energy companion. We demonstrate that this splitting is consistent with the initial interpretation in terms of 1s–2s excitonic splitting by using a calculation of the exciton binding energy which includes mass anisotropy and anisotropy of the dielectric constant. Analytical expressions are proposed to compute the evolution of 1s and 2s excitonic energies using an anisotropy parameter. We show that the values of the dielectric constant that are required to fit the data are $\varepsilon _{\bot}$≈ 8.7 and $\varepsilon _{\parallel}$≈ 10, values different from the couple of values $\varepsilon _{\bot}$≈ 7.33 and $\varepsilon _{\parallel}$≈ 8.45 erroneously obtained after a fitting procedure using a spherical description of the long range Coulomb interaction and the classical textbook n-2 spectrum of the excitonic eigenstates. Starting from now, our values are the recommended ones.

Using a plasma spray torch, nanocrystalline γ-alumina powder has been synthesized in a reactor through oxidation of micron-size aluminum metal powder by in-flight thermal plasma processing. The synthesized particles were characterized by X-ray diffraction (XRD) and field emission transmission electron microscopy (FE-TEM). The particle size was in the range of ~7 to ~56 nm and spherical in shape. Furthermore the nonlinear refractive and absorptive indices of the sample under various intensities using Z-scan and moiré deflectometry techniques by a CW He-Ne laser at 632.8 nm wavelength were measured.

Co-doped GeO2 ceramic films were prepared via a liquid phase co-deposition (LPCD) process. The oxide samples were transformed into Ge1-xCox films (x = 0.75, 3.2 and 11.5%) after annealing under hydrogen atmosphere. The crystallinity of Ge1-xCox film decreases with increasing Co content. The Ge1-xCox films are p-type (hole density 1020 ~ 1021 cm-3). The 3.2% film has higher electrical conductivity and hole density compared with the other two samples. The 0.75% film is superparamagnetic at 300 K while the 3.2% and 11.5% films exhibit blocked superparamagnetic behaviors. Hysteresis loops can be observed in the magnetization curves of the 3.2 and 11.5% samples. The observed ferromagnetisms are on only a local (a few nanometers) scale, which most likely arise from different size and chemical distribution in every sample.

The temperature dependence of the electrical conductivity before and after gamma irradiation of hydrogenated amorphous silicon (a-Si:H) films, prepared by the hot wire method, at a dose of 2 kGy of 60Co gamma irradiation are presented and discussed. Fourier transform infrared spectroscopy (FTIR) measurements provide useful information on the characteristics of bond configurations in a-Si:H before and after gamma irradiation. The conductivity increased and the bond configurations changed significantly after gamma irradiation. The results are explained by the filling of shallow donor states and variation of bond type due to migration of hydrogen atoms under the effect of irradiation. The behaviour of the conductivity is consistent with a hopping mechanism. The temperature dependence of the conductivity of a-Si:H exhibits a $T^{-1/4}$ law, instead of the $T^{-1/2}$ law, after gamma irradiation.

Multi-walled carbon nanotube (MWNT) reinforced cement composites (MWFRCs) were prepared with surfactant dispersion, ultrasonic treatment, and subsequently high-speed shear mixing processes. These MWFRCs were characterized in the fracture toughness property with single edge notch bend method. As found, the addition of nanotubes improves the stress-intensity factor (KIC), critical crack mouth opening displacement (δC) and flexural strength (σs) of the cured nanocomposite, significantly. The maximal enhancement arrives up to 56.4%, 119.4%, and 54.8%, compared to the baseline, respectively. These achievements are mainly attributed to the superior pulling-out effect of dispersed and tough MWNT fiber upon the notched cracks. Incorporation of acid-treated MWNT balances the σs, KIC, and δC values. Additional nanophase carbon black mixed into the above MWFRC further increases the corresponding fracture toughness, while additional short carbon fiber shows a negative effect.

Calcium phosphate based biomaterials are widely used in dentistry and as a bone substitutes in orthopedic applications. Calcium pyrophosphate (CPP) – a type of calcium phosphate and a shortest linear polyphosphate can also be used as a bone graft. Successive applications of theses materials depend on the degree of bio-resorption, mechanical strength and bio-compatibility. Zinc improves the bone activity of osteoblast, promotes the bone regeneration and also stimulates enzyme activity. In the present study Zn doped calcium pyrophosphate dihydrate (Zn-CPPD) nanoparticles were synthesized using surfactant mediated approach with varying [Zn]/[Ca] molar ratio as 0% (pure CPPD), 2%, 5% and, 10%. The crystalline nature and the average crystallite size was studied by Powder XRD. Zinc doping was confirmed by EDAX. The TEM study indicated that pure and Zn doped CPPD nanoparticles were in the range from 4 nm to 40 nm. The presence of various bonds was confirmed by FT-IR spectroscopy. The amount of water of hydration and the thermal stability was studied by thermo-gravimetry. Formation of other phases on heating CPPD at $900^{\circ}$C and $1250^{\circ}$C were identified by the powder XRD. Substitution of Zn content significantly affects the crystallinity and thermal stability of nanoparticles. The results are discussed.

A systematic method for the design of potential microstructure configurations of structural left-handed materials (LHMs) based on topology optimisation technique is presented, and a single objective and a multi-objective optimisation model are proposed. The material considered is a periodic array of dielectric substrates attached with metal film pieces, and the microstructure design of left-handed material is formulated through determining the arrangements of those metal pieces. Different from the conventional configurations of LHMs which consist of magnetic resonators and wires, our results showed that novel integrative configurations without wires can be obtained as microstructures of LHMs. Topology optimisation technique is a universal and effective tool for configuration design of LHMs, and many new structural LHMs with the desired electromagnetic characteristics can be obtained by this systematic approach.

The paper discusses the results of a study on the formation of indium oxide nanoclusters in silica samples implanted with high energy indium ions. Trace quantities of indium oxide were found on as-implanted samples. On annealing in vacuum/oxygen atmosphere significant increase in the quantity of indium oxide phase was observed. A mechanism is proposed for the formation of indium oxide and is mainly attributed to the reaction of metallic indium with the oxygen released from the silica matrix by ballistic process. During annealing in oxygen atmosphere the oxygen diffusing into the silica also plays a role in the oxidation of indium NCs.

Fluorine doped ZnO thin films (FZO) are prepared onto glass substrates at 350 °C by the chemical spray pyrolysis technique. X-ray diffraction spectra show a polycrystalline of ZnO (wurtzite structure) where the amount of fluorine doping affects to preferential orientation (002 plane along c-axis) and does not vary the lattice parameters. Therefore, F introduction in lattice is by the substitution of O-2 ions by F-1 ions. Any variation is observed in transmittance and reflectance measurements in 400–2000 nm wavelength range when samples present F dopant; they have transmittance around 80% in the near infrared and visible zones. The FZO films are degenerate and exhibit n-type electrical conductivity. The best resistivity and mobility are 7.6 × 10-3 Ω cm and 3.77 cm2 V-1 s-1 respectively. The calculated values of the mean free path are very small compared to the grain sizes calculated using XRD measurements. Therefore, we suggest that ionized impurity and/or neutral impurity scattering are the dominant scattering mechanisms in these films.

Zinc oxide (ZnO) nanorods, with different aspect ratios, were synthesised at room temperature via an inexpensive physico-chemical route. The source material was a mixture of zinc acetate dihydrate [ Zn (CH3 COO)2 $\cdot$ 2H2O] , cetyl-trimethyl ammonium bromide [ C19H42BrN] , and sodium hydroxide [NaOH]. The length of the nanorods, as a result of restricted directional growth, was controlled by means of varying the molar ratios of the reactants. As revealed by X-ray diffraction measurements, the as-grown ZnO nanorods exhibited wurtzite crystalline phase, with preferred crystallographic orientation along (101) plane. The visual evidence of the formation of ZnO nanorods was confirmed by transmission electron microscopy studies. The photoluminescence spectra of the ZnO systems show two prominent peaks: a sharp peak located at ~375 nm (UV band) and a broad band peaking at ~480 nm (green band). The UV-to-green PL intensity ratio was found to be improved with enhanced aspect ratio. The aspect ratio dependent tunable optical responses would provide better insight to understand the radiative and non-radiative processes in elongated nanosystems.

In this paper we investigate the optical property of the waveguide-grating structures (WGS) with the grating period in the scale of micrometer, which is larger than the wavelength of the incident light. In such structures, the higher-order diffracted beams can also couple into the waveguide, while in the structure that the period of grating is much smaller than the wavelength of incident light, only the ±1 orders of diffraction can excite the propagation modes of the waveguide. Numerical calculations of extinction of the higher-order structure show that except for the extinction peaks, enhanced transmission can also be obtained, which is also observed in experiment. Further simulations indicate that the enhancement can be tuned by changing the structural and the geometric parameters of the WGS device. In addition, the wavelength that extraordinary transmit is decided by the duty cycles of the gratings, so, the enhancement might be attributed to the phenomena of missing order in gratings with large period.

In this study, TiO2 films were grown at room temperature by sol-gel process using titanium (IV)-isopropylat as precursor. XRD, EDS and MEB analyses proved that an eventual annealing treatment caused the TiO2 amorphous phase to shift to a crystalline anatase phase. Optical measurements were carried out via absorbance spectra in 500–2500 nm wavelength domain. From these optical measurements, the temperature-dependent conjoint optical and thermal properties were deduced using the Amlouk-Boubaker opto-thermal expansivity ψAB.

This paper studies numerically the temperature reached by atomic force microscope tips illuminated by femtosecond laser pulses, in which the laser focusing dependence of tip heating is investigated in detail and the laser heating effects on different tips are discussed too. The results show that tip heating can be significantly reduced if the femtosecond laser is focused tightly on the tip apex.