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Notes: High throughput, low-temperature deposition, sharp interfaces, and selective deposition with direct ion-, electron-, and photon-beam-controlled techniques are some of the key driving forces for the development of superconducting thin films by metalorganic chemical vapor deposition (MOCVD) technique. In this paper we report on the electrical and structural properties of Y-Ba-Cu-O (YBCO) films deposited by MOCVD on yttrium-stabilized zirconia (YSZ) and BaF2/YSZ substrates using a single-step in situ processing method which requires no further annealing. YBCO films deposited on BaF2/YSZ substrates have zero resistance at 80 K. The films were characterized by energy dispersive x-ray analysis, x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The films on BaF2/YSZ substrates exhibited textured growth having both the c and a axis perpendicular to the substrate. The use of BaF2 as a buffer layer suggests three-dimensional integration of high-temperature superconducting thin film for hybrid superconductor/semiconductor devices as well as superconductor switches and other related devices.

Notes: Abstract Cosmic ray particles passing through dense lower atmosphere of Venus decay giving rise to various charged and neutral particles. The flux and degradation of dominant cascade particles namely neutrinos and pions are computed and ionization contributions at lower altitudes are estimated. Using the height profile of pion flux, the muon flux is computed and used to estimate ionization at lower altitudes. It is shown that cosmic ray produced ionization descends to much lower altitudes intercepting the thickness of Venus cloud deck. The dynamical features of Venus cloud deck are used to allow the likely charging and charge separation processes resulting into cloud-to-cloud lightning discharges.

Notes: Abstract The electrical conductivity, thermoelectric power and dielectric constant of Eu2Ti2O7 single crystal have been studied in the temperature range 300–1000 K. Eu2Ti2O7 is found to be a n-type semiconductor with energy band gap of 2.5 eV. The compound exhibits an extrinsic nature upto 700 K and intrinsic nature above 700 K. Thermoelectric power decreases with temperature in the region 300–700 K whereas it increases with temperature in the region 700–1000 K. Dielectric constant increases with temperature in the entire temperature range studied with a discontinuity atT ∼ 700 K.

Notes: We report here enhancement of nucleation and adhesion of diamond films on nondiamond substrates such as copper, stainless steel, and silicon substrates. The enhancement of nucleation is accomplished by pulsed laser irradiation which converts some of the amorphous carbon on the surface into the diamond phase or forms a reaction product that facilitates nucleation of diamond phase. The laser can also be used to evaporate carbon preferentially, leaving behind diamond particles unaffected. By pulsed laser irradiation it is possible to melt the substrate and embed the diamond particles into it, thus improving the adhesion of the diamond film.

Notes: Rapid isothermal processing (RIP) based on incoherent sources of light is emerging as a reduced thermal budget (product of processing time and temperature) processing technique. As compared to stand alone annealing unit, the in situ RIP unit is very attractive for the next generation of devices. A number of unwanted physical phenomena can be suppressed or completely eliminated in the in situ RIP case leading to improved quality of materials when compared to their ex situ rapid isothermal annealed and furnace annealed counterparts. We have used in situ rapid isothermal processor for the in situ rapid isothermal chemical cleaning of InP and GaAs substrates and in situ metallization of InP and GaAs Schottky diodes. As compared to ex situ annealing, the negligible oxygen content at the surface and interface of in situ RIP samples result in better current-voltage characteristics, lower and compressive stress values, as well as smooth and continuous morphologies of the ohmic contact. In this paper, we have highlighted the role of in situ RIP in the metallization of InP and GaAs devices.

Notes: We have theoretically and experimentally analyzed the laser-induced evaporation process for deposition of superconducting thin films from bulk targets. The spatial thickness variations have been found to be significantly different from a conventional thermal deposition process. Unlike a cos θ thickness variation expected from a thermal evaporation process, the laser evaporation process is characterized by a forward-directed deposit with a sharp variation in its thickness as a function of distance from the center of the deposit. We have studied in detail the interactions of nanosecond excimer laser pulses with bulk YBa2Cu3O7 targets leading to evaporation, plasma formation, and subsequent deposition of thin films. A theoretical model for simulating the pulsed laser evaporation (PLE) process has been developed. This model considers an anisotropic three-dimensional expansion of the laser-generated plasma, initially at high temperature and pressure. The forward-directed nature of laser deposition has been found to result from anisotropic expansion velocities of the plasma edges arising due to the density gradients in the gaseous plasma.The physical process of the laser ablation technique for deposition of thin films can be classified into three separate interaction regimes: (i) interaction of the laser beam with the bulk target, (ii) plasma formation and initial isothermal expansion, and (iii) adiabatic expansion leading to deposition of thin films. The first two regimes occur during the time interval of the laser pulse, while the last regime initiates after the laser pulse terminates. Under PLE conditions, the evaporation of the target is assumed to be thermal in nature, while the plasma expansion dynamics is nonthermal as a result of interaction of the laser beam with the evaporated material. The expansion velocities of the plasma edges are related to the initial dimensions and temperature of the plasma, and the atomic weight of the respective species present in it. Preliminary calculations have been carried out on spatial thickness variations as a function of various parameters in PLE deposited thin films. The effects of the various beam and substrate parameters including energy density and substrate-target distance affecting the nature of deposition of superconducting thin films have been theoretically examined. Experimental results have been obtained from thin films deposited on silicon substrates by XeCl pulsed excimer laser (λ=308 nm, τ=45×10−9 s) irradiation. The spatial thickness and compositional variations in thin films have been determined using Rutherford backscattering technique and the results compared with the theoretical calculations.

Notes: Silicon dioxide films grown by photochemical vapor deposition at different deposition rates are investigated by ellipsometry and Fourier transform infrared measurements. Disagreement in the variation of refractive index with chamber pressure between thin and thick films is interpreted in terms of a deposition rate dependent buildup of internal stress in the film. Direct measurements of curvature show the presence of compressive stress in thick SiO2 films grown at chamber pressures (approximately-greater-than)600 mTorr. Infrared transmission measurements also indicate a change in the structural characteristics of films (probably induced by stress), with increasing deposition rate. Molecular model calculations show a decrease in the Si—O—Si bond angle as the growth pressure increases. Ion implantation seems to release the stress in these films as evidenced by the shift observed in the stretching mode frequency. The relative concentrations of H2O, SiOH, and SiH groups in these films and the effect of annealing on the strength of these modes are also discussed. Reflection infrared measurements at 60° incidence reveal a disorder induced longitudinal-transverse optic pair at around 1200 cm−1.

Notes: Metalorganic chemical vapor deposition (MOCVD) has the potential of emerging as a viable technique to fabricate ribbons, tapes, coated wires, and the deposition of films of high-temperature superconductors, and related materials. As a reduced thermal budget processing technique, rapid isothermal processing (RIP) based on incoherent radiation as the source of energy can be usefully coupled to conventional MOCVD. In this paper we report on the deposition and characterization of high quality superconducting thin films of Y-Ba-Cu-O (YBCO) on yttrium stabilized zirconia substrates by RIP assisted MOCVD. Using O2 gas as the source of oxygen, YBCO films deposited initially at 600 °C for 1 min and at 745 °C for 25 min followed by deposition at 780 °C for 45 s are primarily c-axis oriented and zero resistance is observed at 89–90 K. The zero magnetic field current density at 53 and 77 K are 1.2×106 and 3×105 A/cm2, respectively. By using a mixture of N2O and O2 as the oxygen source substrate temperature was further reduced in the deposition of YBCO films. The films deposited initially at 600 °C for 1 min and than at 720 °C for 30 min are c-axis oriented and with zero resistance being observed at 91 K. The zero magnetic field current densities at 53 and 77 K are 3.4×106 and 1.2×106 A/cm2, respectively. To the best of our knowledge this is the highest value of critical current density, Jc for films deposited by MOCVD at a substrate temperature as low as 720 °C. It is envisioned that high energy photons from the incoherent light source and the use of a mixture of N2O and O2 as the oxygen source, assist chemical reactions and lower overall thermal budget for processing of these films.

Notes: Annealing experiments were carried out on phosphosilicate glass (PSG) films deposited on (100) silicon substrates by using a low-pressure chemical vapor deposition technique. Rapid isothermal processing and conventional furnace heating were used to study the electrical, structural, and mechanical characteristics of these films and the results of the two processes compared. A refractive index of 1.457 was obtained in the rapid isothermal annealing cycle of 800 °C/15S, but was 1.419 for the furnace annealing cycle (i.e., 800 °C/65S). Spreading resistance analysis has shown that the junction depth remains unchanged for an 800 °C/15S rapid isothermal annealing cycle. Stress measurements show that rapid isothermal annealing leads to less strain compared to furnance annealing. The x-ray photoelectron spectroscopy analysis shows that as compared to furnance annealing, rapid isothermal annealing provides a chemically homogenous interface. High-frequency capacitance voltage (C-V) measurements show that furnance-annealed samples are leaky and a higher concentration of oxygen-related defects are present in the PSG/Si interface. On the other hand, because of a relatively clean interface, a well behaved C-V characteristic is observed in the rapid isothermal annealed samples. In summary, as compared to furnace annealing, rapid isothermal annealing resulted in superior structural, mechanical, and electrical properties of PSG films on Si substrates. A plausible explanation of such behavior may be attributed to the difference in the radiation spectra of the two sources of energy.

Notes: The theoretical analysis of thermal effects induced by nanosecond laser irradiation on bulk YBa2Cu3O7 superconductor targets provides insight into the nature of the target's ablation/evaporation characteristics during pulsed laser deposition of superconducting thin films. We have simulated the thermal history of YBa2Cu3O7 targets under intense nanosecond laser irradiation by numerically solving the one dimensional heat flow equation and taking into account the phase changes occurring at the near surface of the target. The numerical method is based on a higher-order finite difference scheme with a smaller truncation error and is not restricted by any stability criterion, thereby allowing faster convergence to the exact solution. Temperature-dependent optical and thermal properties of the irradiated material as well as the temporal variation in the laser intensity can be taken into account by this method. During planar surface evaporation of the target material, the subsurface temperatures were calculated to be higher than the surface temperatures as a result of combination of two unique effects. While the evaporating surface of the target is constantly being cooled due to the latent heat of vaporization, subsurface superheating occurs due to the finite absorption depth of the laser beam. The effects of various laser and target parameters, including pulse energy density, pulse duration, absorption coefficient, thermal conductivity, and latent heat on the transient thermal characteristics of the irradiated target, have been investigated in detail. Subsurface superheating was found to increase with decreasing absorption coefficient and thermal conductivity of the target, and with increasing energy density. The superheating may lead to subsurface nucleation and growth of the gaseous phase which expands rapidly leading to microexplosions and "volume expulsion'' of material from the target.