Annealing effects on zirconium nitride films

ZrN films were deposited by dc reactive magnetron sputtering on silicon substrates under optimized nitrogen partial pressure of 6×10⁻⁵ mbar. Structural, electrical and optical properties were systematically investigated. Films deposited at room temperature exhibited Schottky structure without any silicide interfacial layer. These films have electrical resistivity of 4.23×10⁻³ Ω cm, which were crystalline in nature, with cubic (1 1 1) orientation. Refractive index and extinction coefficient were found to be 1.95 and 0.43, respectively at a wavelength of 350 nm.

Samples were annealed for 1 h in air at two temperatures, 350 and 550 °C. Scanning electron microscopy (SEM) and energy dispersive analysis of X-rays (EDAX) showed alloy penetration pits. Extent of penetration was greater in the films, which were annealed at higher temperature (550 °C). Variation in refractive index was observed in the range of 1.95–1.80 at 350 nm, for the annealed films, with increase in grain size from 7.25 to 11.10 nm. Poly-crystalline nature has been observed with (1 1 1) and (2 0 1) orientations. Resistivity is found to increase from 4.23×10⁻³ to 6.21×10⁻³ Ω cm.     

Influence of oxygen pressure of ZnO/glass substrate produced by pulsed filtered cathodic vacuum arc deposition

The effects of oxygen pressure on the structural and optical properties of high quality transparent conductive ZnO thin films were studied in detail. ZnO thin films were prepared by pulsed filtered cathodic vacuum arc deposition system under various oxygen pressures on glass substrate at room temperature. With increasing oxygen pressure, the structure and optical properties of films change. The structural and optical properties of the ZnO thin films were investigated using X-ray diffraction, transmittance spectrometry, refractive index, oscillator parameters, energy band gap and Urbach tail. The films show c-axis oriented (0 0 2) hexagonal wurtize crystal structure. It has been found that the grain size of ZnO thin films increases from 16.9 to 22.6 nm with the increase of oxygen pressure from 3.8×10⁻⁴ to 6.9×10⁻⁴ Torr and the crystallinity is enhanced. Average transmittance is about 90% in the visible region of the ZnO thin films. From optical transmittance spectra of ZnO films, the absorption edge shifts towards the taller wavelength with an increase in oxygen pressure. The energy band gap decreases from 3.31 to 3.20 eV with an increase in oxygen pressure. The packing density investigation shows in ZnO films high packing densities (above 0.78) can be obtained.     

Hydrogen-induced missing-row reconstructions of Pd(110) studied by scanning tunneling microscopy

The effect of hydrogen adsorption on the Pd(110) surface structure at room temperature has been studied by scanning tunneling microscopy. Depending on the partial pressure of hydrogen two different reconstructions of Pd(110) have been observed: a (1 × 3) phase at hydrogen pressures in the 10⁻⁹ mbar range and an additional (1 × 2) phase at p_H2 ≥ 5 × 10⁻⁸ mbar. Both reconstructions are found to be of the missing-row type. The evolution of the surface reconstructions has been followed in situ.     

Sr-doped LaInO3 and its possible application in a single layer SOFC

The effects of dopants on the electrical conductivity of the perovskite-type oxide LaInO₃ have been investigated. Replacement of La by Sr is the most effective way to enhance the conductivity of LaInO₃, whereas Ca substitution for In is rather difficult due to the large difference in the ion radii. The optimum composition is La_0.9Sr_0.1InO_3−δ whose maximum conductivity is 7.6×10⁻³ S cm⁻¹ at 900°C. The electrical conductivity of La_0.9Sr_0.1InO_3−δ has been measured over a wide range of oxygen partial pressure from pO₂=1 to 10⁻²⁵ atm. P-type and n-type behavior at high and low oxygen partial pressure have been observed, respectively, while at intermediate oxygen partial pressures, the electrical conductivity changes only slightly with the oxygen partial pressure. The concept of a single layer solid oxide fuel cell based on a La_0.9Sr_0.1InO_3−δ ceramic pellet has been tested. A maximum power density of 3 mW cm⁻² at 800°C was achieved when dilute H₂ and air were used as fuel and oxidizing agent, respectively.     

High temperature transport processes in lithium niobate

The electrical conductivity of single crystal lithium niobate (LiNbO₃) was determined as a function of temperature for various oxygen partial pressures. The electrical conductivity is proportional to P_o2^−1/4 which can be explained by a defect equilibrium involving singly ionized oxygen vacancies and electrons.

Measurements of electrical transport numbers at 1000°K show the electrical conductivity of LiNbO₃ to be ionic at one atmosphere of oxygen and electronic at low oxygen partial pressures.

Thermoelectric measurements indicate that LiNbO₃ at low oxygen partial pressures is n-type and that the concentration of electrons at 1000°K and in an atmosphere of 50% C0/50% CO₂a is 4 × 10¹⁷cm³ with a mobility of 1.7 cm²V sec.

The diffusion of oxygen in LiNbO₃ was determined as a function of temperature at an oxygen partial pressure of 70 Torr. by measuring O¹⁸/O¹⁶ isotope exchange with the gas phase as a function of time. The diffusion data may be represented by D = 3.03 × 10⁻⁶ exp (−29.4 kcal mole⁻¹/RT)cm²sec. Consideration of the Nernst-Einstein relation for oxygen and the variation in conductivity with Li₂O activity indicate that the ionic conduction is caused by transport of lithium ions.     

Co dissociation and recombination reactions on Ni(100)

The kinetics of atomic carbon and oxygen buildup on a Ni(100) surface exposed to carbon monoxide at high temperatures have been investigated by Auger electron spectroscopy. The experimental data, taken at different sample temperatures (453 , T 573 K) and at different CO partial pressures (3 ×10⁻⁷ , P_co , 3 ×10⁻¹ mbar) allowed the identification of the CO dissociation mechanism. By fitting the experimental data with a set of rate equations describing CO dissociation, CO reduction of surface oxygen, and C and O recombination, we have been able to determine the pre-exponential factors and the activation energies of these processes.     

Transparent conductive oxide thin films of CdTe-doped indium oxide prepared by pulsed-laser deposition

Transparent conducting oxide thin film CdTe-doped indium oxide (In₂O₃) has been grown by pulsed-laser deposition from a target of CdTe powder embedded in metallic indium. The electro-optical and structural properties were investigated as a function of oxygen partial pressure (PO₂) and substrate temperature (T_s). A film deposited at T_s=420 °C and PO₂=4 Pa shows the minimum resistivity 7.5×10⁻⁴ Ω cm, its optical transmission is 83% and the carrier concentration was 8.9×10²⁰ cm³. The optical band gap and the average roughness of that sample were 3.6 eV and 6.45 Å, respectively. X-ray diffraction studies indicated that the films were polycrystalline. This material is a good candidate for being used as transparent conductor in the CdTe–CdS solar cell.     

Picosecond nonlinear optical response of Ba0.5Sr0.5TiO3 thin films fabricated by pulsed laser deposition

Well-crystallized Ba_0.5Sr_0.5TiO₃ thin films with good surface morphology were prepared on MgO(1 0 0) substrates by pulsed laser deposition technique at a deposition temperature of 800 °C under the oxygen pressure of 2 × 10⁻³ Pa. X-ray diffraction and atomic force microscopy were used to characterize the films. The full width at half maximum of the (0 0 2) Ba_0.5Sr_0.5TiO₃ rocking curve and the root-mean-square surface roughness within the 5 μm × 5 μm area were 0.542° and 0.555 nm, respectively. The nonlinear optical properties of the films were determined by a single beam Z-scan method at a wavelength of 532 nm with laser duration of 55 ps. The results show that Ba_0.5Sr_0.5TiO₃ thin films exhibit a fast third-order nonlinear optical response with the nonlinear refractive index and nonlinear absorption coefficient being n₂ = 5.04 × 10⁻⁶ cm²/kW and β = 3.59 × 10⁻⁶ (m/W), respectively.     

Effect of boron ion implantation on the structural, optical and electrical properties of ZnSe thin films

Zinc Selenide (ZnSe) thin films were deposited onto well cleaned glass substrates using vacuum evaporation technique under a vacuum of 3×10⁻⁵ mbar. The prepared ZnSe samples were implanted with mass analyzed 75 keV B⁺ ions at different doses ranging from 10¹² to 10¹⁶ ions cm⁻². The composition, thickness, microstructures, surface roughness and optical band gap of the as-deposited and boron-implanted films were studied by Rutherford backscattering (RBS), grazing incidence X-ray diffraction, Atomic force microscopy, Raman scattering and transmittance measurements. The RBS analysis indicates that the composition of the as-deposited and boron-implanted films is nearly stoichiometric. The thickness of the as-deposited film is calculated as 230 nm. The structure of the as-deposited and boron-implanted thin films is cubic. It is found that the surface roughness increases on increasing the dose of boron ions. In the optical studies, the optical band gap value decreases with an increase of boron concentration. In the electrical studies, the prepared device gave a very good response in the blue wavelength region.     

LEED studies of the adsorption of CO2 on thin epitaxial NaCl(100) films

The adsorption of CO₂ on the NaCl(100) surface was studied with a high-resolution LEED-system. Measurements without charging up at low electron energies and without damage by the e-beam could be performed by using ultrathin epitaxial films on a conducting Ge(100) substrate. The adsorption behavior was recorded as a function of time and pressure at constant substrate temperatures of 78 and 83 K and CO₂ partial pressures from 4 × 10⁻⁸−2 × 10⁻³ Pa. The adsorption system shows a first-order two-dimensional phase transition to a (2 × 1) superstructure including glide planes (herringbone-like structure) at p = 7.2 × 10⁻⁸Pa (T = 78 K). The condensation of the CO₂ solid is starting at p = 1.5 × 10⁻⁴ Pa (T = 78 K). The LEED-pattern shows in this c(2 × 2) superstructure, which corresponds to the pyrite-like structure of the CO₂ solid. Both observed superstructures are commensurable with the NaCl(100) surface. Observation of island growth shows that the domains of the (2 × 1) superstructures have already at coverage of 5% of a monolayer an average lateral size of at least 200 A.     

A new measurement of the weak magnetism term in the betaspectra of B and N

The betaspectra of ¹²B and ¹²N have been measured with a NaI crystal as spectrometer. Assuming a shape correction factor 1 + aW + bW² and b₋ = 1.106 × 10⁻⁴ MeV⁻², b₊ = −1.397 × 10⁻⁴ MeV⁻², the spectra yield a₋ = (+0.91 ± 0.11) × 10⁻² MeV⁻¹ and a₊ = (−0.07 ± 0.09) × 10⁻² MeV⁻. the a₋ − a₊ = (+0.98 ± 0.09) × 10⁻² MeV⁻¹ is in agreement with the weak magnetism prediction.     

Chemically deposited copper oxide thin films: structural, optical and electrical characteristics

Thin films of copper oxide with thickness ranging from 0.05–0.45 μm were deposited on microscope glass slides by successively dipping them for 20 s each in a solution of 1 M NaOH and then in a solution of copper complex. Temperature of the NaOH solution was varied from 50–90°C, while that of the copper solution was maintained at room temperature. X-ray diffraction patterns showed that the films, as prepared, are of cuprite structure with composition Cu₂O. Annealing the films in air at 350°C converts these films to CuO. This conversion is accompanied by a shift in the optical band gap from 2.1 eV (direct) to 1.75 eV (direct). The films show p-type conductivity, 5×10⁻⁴ Ω⁻¹ cm⁻¹ for a film of thickness 0.15 μm. Electrical conductivity of this film increases by a factor of 3 when illuminated with 1 kW m⁻² tungsten halogen radiation. Annealing in a nitrogen atmosphere at temperatures up to 400°C does not change the composition of the films. However, the conductivity in the dark as well as the photoconductivity of the film increases by an order of magnitude. The electrical conductivity of the CuO thin films produced by air annealing at 400°C, is high, 7×10⁻³ Ω⁻¹ cm⁻¹. These films are also photoconductive.     

Electron-stimulated nitridation of Si(100) in pure ammonia

We present the results of an AES study of the Si(100) electron-stimulated nitridation at RT by ammonia gas. The influence of the gas pressure and electron beam density on the nitridation rate have been determined within the ranges 10⁻⁶–10⁻⁹ Torr and 5 × 10⁻³–5 × 10⁻² A/cm², respectively. The silicon nitride growth rate has been found to be proportional to the electron flux and is enhanced with increased ammonia pressure in the range 10⁻⁹–10⁻⁷ Torr. Beyond 10⁻⁷ Torr the Si nitride growth rate is constant and independent of ammonia pressure. A phenomenological model of electron-stimulated nitridation process is suggested, which is in good agreement with the experimental data. The rate of electron-stimulated nitridation has been deduced.     

Applications of a silicon photodiode detector for radon progeny measurements

An application of our developed silicon photodiode detector for radon progeny measurements is presented in this paper. It was determined the deposition velocity for free (3.6 ± 0.7) × 10⁻³ m s⁻¹ and attached (1.0 ± 0.5) × 10⁻⁵ m s⁻¹ fraction of short living radon progeny.     

Study of cluster decay of Cm using SSNTD

Cluster decay of ²⁴²Cm with emission of ³⁴Si-particles was measured using track-recording phosphate glass detectors. The corresponding partial half-life is (1.4±0.3)×10²³ s. The branching ratio relative to decay is 1.0×10⁻¹⁶ and relative to spontaneous fission 1.6×10⁻⁹.     

Corrosion monitoring of stainless steel 304L in lithium bromide aqueous solution using transmittance optical detection technique

We report a method based on the power ratio of transmittance for monitoring the corrosion rate in stainless steel 304L immersed in an aqueous solution of lithium bromide at 50 wt%, at 70 °C. The optical transmittance measured in the solution contaminated with corrosion oxides at different times of exposure is related to the physical degradation of the stainless steel samples. Lasers at 532 and 632 nm were utilized for monitoring the accumulation of corrosion oxides dissolved in the lithium bromide solution of the metallic samples for 480 h. The change in the optical power of transmittance was 13 μW/480 h measured at 532 nm and 3.6 μW/480 h at 632 nm. The variation of the power ratio for 532 nm was from 0.01 to 0.24, and for 632 nm, from 0.01×10⁻³ to 15.61×10⁻³; this is proportional to an accumulated corrosion rate of [0.0142×10⁻³–0.552×10⁻³ g/cm²] for an exposure time of 432 h.     

Oxygen nonstoichiometry in high-Tc superconductor HoBa2Cu3O6+x and application of coulometric tritration

Nonstoichiometry in the perovskite-type compound, HoBa₂Cu₃O_6+x, was determined as a function of oxygen partial pressure (5 × 10⁻¹ 1 × 10⁵ Pa) in the temperature range of 8631173 K by coulometric titration using a stabilized zirconia electrolyte. Electromotive force of the cell, EMF, was measured as a function of oxygen content at constant temperature, and as a function of temperature at constant oxygen content. The perovskite-type compound was found to have a tendency to decompose into Ho₂O₃, BaO, CuO and some double-oxides at low oxygen partial pressures. Defect equilibria are discussed on the basis of the dependence of nonstoichiometry on oxygen partial pressure. Variation of the relative partial molar entropy with composition is explained in terms of a well-known defect model. A new technique which was developed for measuring the electrical conductivity of a non-stoichiometric oxide, in situ, at constant oxygen content as a function of temperature in the coulometric titration cell, is presented.     

Simultaneous doping with La and Y for Ba- and Ce-sites in BaCeO3 and the ionic conduction

Powder X-ray diffraction (XRD) analysis showed that the single phase perovskite-type structure of Ba_1−xLa_xCe_0.90−xY_0.10+xO₃₋ (0 x 0.40, =0.05) could be maintained in a wide region of doping level by simultaneous partial substitution of La³⁺ for Ba²⁺-site and Y³⁺ for Ce⁴⁺-site in BaCeO₃. The conduction properties of these oxides were investigated using various electrochemical methods in the same concentration of oxygen vacancy (=0.05). At high oxygen partial pressure, these oxides exhibited a mixed oxide ionic and p-type electronic conduction while at low oxygen partial pressure their conduction was almost protonic. Among these oxides, BaCe_0.90Y_0.10O₃₋ exhibited the highest conductivities with a value of 1.24×10⁻¹ S/cm in dry oxygen, and 5.65×10⁻² S/cm in wet hydrogen at 1000°C. Both of the proton and oxide ion conductivities under oxygen and under hydrogen atmospheres decreased monotonically with the increasing substitution for Ba²⁺- and Ce⁴⁺-sites. The decreases in ion conductivities appear to relate to the decreased free volume (V_f) of crystal lattice as well as the increased distortion of lattice from ideal cubic perovskite structure.     

Absolute desorption yields of metastable atoms from the surface of solid rare gases induced by exciton creation

Absolute yields of the metastable excited atoms desorbed from the surfaces of solid Ne and Ar by the creation of surface and bulk excitons have been measured using monochromated synchrotron radiation as a selective excitation source. We have obtained the absolute yields of (2.3 ± 0.7) × 10⁻³, (1.4 ± 0.4) × 10⁻³, and (7.8 ± 2.3) × 10⁻⁴ atoms/photon at the excitation of S1, B1 and S′ exciton for Ne, respectively, and 1 × 10⁻⁵ atoms/photon at S1 excitation for Ar. The probability for metastable atom desorption is found to be about 2 to 10% at the excitation of S1 exciton on the surface of solid Ne.     

Domain wall pinning in polycrystalline perovskite La0.7Sr0.3MnO3

Reversible and irreversible domain wall (DW) motions have been investigated in La_0.7Sr_0.3MnO₃ ceramic samples using frequency-response complex permeability with various amplitudes of AC field. We also examine the effects of temperature in the range from 293 to 368 K and transverse DC magnetic field with a maximum of 4.40×10⁵ A/m on the real part of permeability (μ′). Two relaxations corresponding to reversible wall motions and domain rotations occur in low and high frequency regions, respectively. The irreversible DW displacements can be activated as the amplitude larger than the pinning field of 3 A/m, leading to an increase in μ′. The μ′ obeys a Rayleigh law at the temperature below 343 K or under DC field of less than 4.22×10⁴ A/m. The Rayleigh constant η increases from 5.45×10⁻² to 1.54×10⁻¹ (A/m)⁻¹ as the temperature rises from 293 to 343 K, and η decreases from 5.58×10⁻² to 3.67×10⁻² (A/m)⁻¹ with increasing DC field from 1.99×10³ to 4.22×10⁴ A/m.