Sequential Evaporation of Bi-Te Thin Films with Controllable Composition and Their Thermoelectric Transport Properties

We report a simplified sequential evaporation route that can deposit compositionally controllable Bi-Te thermoelectric (TE) thin films without the need for a highly controlled facility. Te and Bi granules were used as starting materials, with their ratio being adjusted to obtain Bi-Te films with different compositions and thicknesses. The as-evaporated and annealed films were subjected to structural and morphological analysis, and their transport properties were measured. X-Ray diffraction data revealed multiple phases for most films. Energy-dispersive x-ray spectroscopy showed that the film composition was Te-enriched due to the large vapor pressure difference of Te and Bi. A Bi₂Te₃ single phase was obtained in the annealed films, having nominal composition of BiTe_1.2. The existence of impurity phases, such as Bi₄Te₃ or elemental Te, was found in all the as-evaporated films and in the annealed films with other nominal Te/Bi ratios, which degraded the TE properties of the films by increasing their electrical conductivity and reducing their Seebeck coefficient. A pure Bi₂Te₃ film with nominal Te/Bi ratio of 1.2 exhibited a maximum power factor of 7.9 × 10^?4 W m^?1 K² after annealing at 200°C. This work demonstrated a simple, undemanding, reliable method to deposit Bi-Te-based TE thin films that can be utilized to fabricate low-cost TE microgenerators.     

Charge trapping and interface states in hydrogen annealed HfO2–Si structures

Metal–oxide–semiconductor (MOS) capacitors based on HfO₂ gate stacks with Al and TiN gates are compared to study the effect of the gate electrode material to the properties of insulator–semiconductor interface. The structures under study were shown to contain interface trap densities of around 2 × 10¹¹ cm⁻² eV⁻¹ for Al gate and up to 5.5 × 10¹² cm⁻² eV⁻¹ for TiN gate. The peak in the surface state distribution was found at 0.19 eV above the valence band edge for Al electrode. The respective capture cross-section is 6 × 10⁻¹⁷ cm² at 200 K.The charge injection experiments have revealed the presence of hole traps inside the dielectric layer. The Al-gate structure contains traps with effective capture cross-section of 1 × 10⁻²⁰ cm², and there are two types of traps in the TiN-gate structure with cross-sections of 3.5 × 10⁻¹⁹ and 1 × 10⁻²⁰ cm². Trap concentration in the structure with Al electrode was considerably lower than in the structure with TiN electrode.     

Photosensitivity of ZnO/CdS/Cu(In,Ga)Se<Subscript>2</Subscript>/Mo thin-film solar cells fabricated on various substrates

The results of measuring the first spectra of relative quantum efficiency for photoconversion in thin-film ZnO/CdS/Cu(In,Ga)Se₂/Mo solar cells fabricated on rigid (glass) and flexible (polyimide) substrates are reported. The character of interband transitions has been studied and the values of the band gap for direct and indirect transitions in thin Cu(In,Ga)Se₂ films are determined. It is found that a shift of the maximal photosensitivity for the obtained solar cells to shorter wavelengths is observed as rigid substrates are replaced by flexible ones. It is concluded that thin-film Cu(In,Ga)Se₂ structures can be used as broad-band photoconverters of solar radiation.     

Soft Mechanical Sensors Through Reverse Actuation in Polypyrrole

The phenomenon of voltage generated from a soft sensor using polypyrrole in response to mechanical deformation is described and investigated. The sensor consists of two polypyrrole layers in contact with an electrolyte and operates in bending mode in air. The magnitude and sign of the induced voltage was found to depend on the type of dopant counter‐ions and the nature of the surrounding electrolyte. The mechanical sensor response is shown to be a “reverse actuation”, generating millivolt signals for millimeter sized deflections or ～ 1000 C m^–3 charge for 1 % strain in the polypyrrole layer. A model based on ‘Deformation Induced Ion Flux' has been proposed whereby the strain induced volume change in the polymer produces a shift in the Donnan equilibrium between mobile dopant ions inside the polymer and in the external electrolyte. A simple thermodynamic model provides reasonable estimates of the size of the voltage and charge produced.     

Encapsulation of Nanoparticles Using Nitrilotriacetic Acid End‐Functionalized Polystyrenes and Their Application for the Separation of Proteins

The use of nitrilotriacetic acid end‐functionalized polystyrenes (NTA‐PS) as a multifunctional nanocarrier for the aqueous dispersion of CdSe, γ‐Fe₂O₃ and gold nanoparticles (NPs) is described. When the amphiphilic end‐ functionalized polystyrenes and NPs are dissolved together in tetrahydrofuran, the addition of water causes the spontaneous formation of micellar aggregates, resulting in the successful encapsulation and aqueous dispersion of NPs. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), photoluminescence (PL) spectroscopy, and vibrating sample magnetometer (VSM) are used to characterize the structure and properties of the NPs‐containing micellar aggregates (nanocarrier). After complexation of Ni²⁺ with NTA on the surface of the nanocarrier containing γ‐Fe₂O₃, specific binding between Ni‐NTA complex and histidine‐tagged (His‐tagged) proteins enables selective separation of His‐tagged proteins using a magnet.     

Validation of coupled codes using VVER plant measurements

A data set of five transients at different VVER type nuclear power plants was collected in order to validate neutron kinetics/thermal hydraulics codes. Two of these transients ‘drop of control rod at nominal power at Bohunice-3’ of VVER-440 type and ‘coast-down of 1 from 3 working MCPs at Kozloduy-6’ of VVER-1000 type, were then utilised for code validation. Eight institutes contributed to the validation with 10 calculations using 5 different combinations of coupled codes. The thermal hydraulic codes were ATHLET, SMABRE and RELAP5 and the neutron kinetic codes DYN3D, HEXTRAN, KIKO3D and BIPR8. The general behaviour of both the transients was quite well calculated with all the codes. Even an elementary modelling of coolant mixing in reactor pressure vessel under asymmetric transients improved correspondence to the measurements. Some differences between the calculations seem to indicate that fuel modelling and treatment of VVER-440 control rods need further consideration. The simultaneous validation interacted with the data collection effort and thus improved its quality. The complexity of data collection systems and sometimes conflicting data, however, called for compromises and interpretation guides that also taught the analysts balanced plant modelling.     

Structure and kinetic studies of U(VI)-benzamidoxime complex in non-aqueous solutions by H- and C-NMR

The structural and kinetic studies of U(VI) complex with benzamidoxime(Hba) as ligand in CD₃COCD₃ have been studied by means of ¹H and ¹³C NMR. The Hba molecule was found to coordinate to UO₂²⁺ in the form of anionic benzamidoximate (ba), and the number of ba coordinated to UO₂²⁺ was determined to be 3 by analyzing the chemical shift of ¹³C NMR signal for Hba in the presence of UO₂²⁺. The exchange rate constants(k_ex) of ba in [UO₂(ba)₃] were determined by the NMR line-broadening method. The kinetic parameters were obtained as follows: k_ex(25°C) = 3.1 × 10³s⁻¹, ΔH^≠ = 35.8 ± 3.5 KJ mol⁻¹, and ΔS^≠ = −65 ± 13.7 J K⁻¹ mol⁻¹. The UV-visible absorption spectra of solutions containing UO₂²⁺ and Hba were also measured. The molar extinction coefficient of the complex was found to be extremely large compared with those of UO₂(L)₅²⁺ (L = unidentate oxygen donor ligands) complexes. This is due to the strong electron withdrawing of UO₂²⁺ from Hba and suggests that an interaction between UO₂²⁺ and Hba is very strong. Such a high affinity of monomeric amidoxime to UO₂²⁺ reasonably explains the high adsorptibility of amidoxime resin to U(VI) species, and is considered to result in the high recovery of U(VI) species from sea water using amidoxime resin.     

The influence of the charged back side on the transmission of highly charged ions through PC nanocapillaries

We have measured the fraction of the ions transmitted through nanocapillaries with their initial charge state for 200 keV Xe⁷⁺ ions impact on a polycarbonate (PC) foil with a thickness of 30 μm and a diameter of 150 nm. An Au film was evaporated on both the front and back side. It is found that more than 97% of the transmitted ions remain in their initial charge state. Then, the transmitted ion fraction and the characteristic tilt angle of 40 keV Xe⁷⁺ ions through this foil and another one with the same thickness and diameter, but evaporated by Au only on the front side, were measured. By comparing the results of these two foils, the influence of the ions deposited in the capillary exit region on the transmitted ion fraction and the characteristic tilt angle is studied. In comparison with the foil evaporated by Au on both sides, the maximum transmitted ion fraction of the foil evaporated by Au on the front side only is nearly 4 times smaller. Also, the characteristic tilt angle is slightly decreased. These results are discussed within the models for the guiding effect.     

Advanced applications in microphotonics using proton beam writing

Proton beam writing (PBW) is a powerful tool for prototyping microphotonic structures in a wide variety of materials including polymers, insulators, semiconductors and metals. Prototyping is achieved either through direct fabrication with the proton beam, or by the fabrication of a master that can be used for replication. In recent times we have explored the use of PBW for various advanced optical applications including fabrication of subwavelength metallic structures and metamaterials, direct write of silicon waveguides for mid IR applications and integrated waveguides for lab-on-a-chip devices. This paper will review the recent progress made in these areas with particular emphasis on the main advantages of using the PBW technique for these novel applications.     

Melting attack of solid plates by a high temperature liquid jet — effect of crust formation

When a molten UO₂ jet impinges on a steel structure in a reactor vessel during a severe accident, the erosion rate of the steel by the molten UO₂ jet is expected to be limited considerably by a UO₂ crust layer forming on a molten steel substrate at the jet/steel plate interface. A series of simulation experiments was performed to study the melting behavior of solid plates by high temperature liquid jets and the effects of crust forming at jet/structure interface. In the first series of experiments, salt (NaCl) was selected as the jet material and tin (Sn) as the solid structure. The experiments were conducted with varying the jet diameter (10 30 mm) and jet temperature (900 1100°C). The jets were accelerated to a range of 3 5 m/s at the nozzle outlet by gravitational force and impinged perpendicularly to the solid plate underneath. Furthermore, to check the effects of the thermo-physical properties on the erosion behaviors, preliminary experiments were performed by using a molten Al₂O₃ jet ( 2200°C) impinging on stainless steel plate at room temperature. The erosion rates obtained in the present experiments were far less than the values predicted by an analytical solution that neglects the existence of a crust layer and its thermal effects. With the inclusion of the crust behavior in the model, the experimental results were predicted fairly well. From the present experiments, a Nusselt number of the turbulent heat transfer, which takes into account simultaneous melting and freezing in the impingement region of a molten jet, is correlated by a Reynolds number and a Prandtl number as follows: Nu_m = 0.0033 Re---Pr.In conclusion, the existence of a crust layer plays an important role in the erosion process of a solid plate by the molten fuel jet with high melting point as in a reactor situation.