Hyperfine interactions in 111Cd-doped lutetium sesquioxide

We report here first Perturbed Angular Correlation (PAC) results of the electric field gradient (EFG) characterisation at ¹¹¹Cd impurities located at both non-equivalent cation sites of the bixbyite structure of Lutetium sesquioxide, between room temperature (RT) and 1273 K. The comparison with results coming from a systematic ¹¹¹Cd PAC study in bixbyites and with point-charge model (PCM) predictions shows the presence of a trapped defect at RT in the neighbourhood of the asymmetric cation site, which is completely removed at T > 623 K. The anomalous EFG temperature dependence in Lu₂O₃ can be described in the frame of a “two-state” model with fluctuating interactions, which enables the experimental determination of the acceptor energy level introduced by the Cd impurity in the band-gap of the semiconductor and the estimation of the oxygen vacancy density in the sample. This revised version was published online in August 2006 with corrections to the Cover Date.     

Work function of indium sesquioxide thin film

This paper reports surface electrical properties of thin film of indium sesquioxide, In₂O₃, during oxidation and reduction at elevated temperatures (298 K and 873 K). The studies involved monitoring of surface potential during oxidation and reduction experiments using work function measurements. The obtained experimental data are considered in terms of the effect of temperature on reactivity between oxygen and In₂O₃, involving chemisorption and oxygen incorporation. The reactivity in the range 298 – 773 K is limited to chemisorption resulting in the formation of surface dipoles exhibiting positive surface charge. Oxidation at 873 K results in slow oxygen incorporation.     

Reducible and non-reducible defect clusters in tin-doped indium oxide

Density functional theory calculations are used to estimate the energy of interstitial oxygen (O_i) released from tin-doped indium oxide (ITO). The currently accepted explanation of defect clusters’ irreducibility is based on different arrangements of doping atoms around O_i. In the present contribution we demonstrate that this concept has only a limited domain of applicability and explains the relative stability of different defect clusters with the same and fixed Sn:O_i ratio. To describe practically the important case of ITO treatment under strong reduction conditions another limiting case of varying Sn:O_i ratio is considered. It is found that in this particular case local coordination of doping atoms around O_i plays only a minor role. The relative stability of the oxidized defect clusters has caused a noticeable change in the electronic part of the defect formation energy, i.e. the chemical potential of the conduction electrons determines the equilibrium concentration of the interstitial oxygen atoms.     

Electrical properties and defect model of tin-doped indium oxide layers

Tin-doped In₂O₃ layers were prepared by the spray technique with doping concentrationsc _Sn between 1 and 20 at. % and annealed at 500 °C in gas atmospheres of varying oxygen partial pressures. The room-temperature electrical properties were measured. Maximum carrier concentrationsN=1.5×10²¹cm^–3 and minimum resistivities =1.3×10^–4 cm are obtained if the layers are doped withc _Sn9 at. % and annealed in an atmosphere of oxygen partial pressurep _O2 10^–20 bar. At fixed doping concentration, the carrier mobility increases with decreasing oxygen pressure. The maximum obtainable mobility can be described in terms of electron scattering by ionized impurities. From an analysis of the carrier concentration and additional precision measurements of the lattice constants and film thicknesses, a defect model for In₂O₃:Sn is developed. This comprises two kinds of interstitial oxygen, one of which is loosely bound to tin, the other forming a strongly bound Sn₂O₄ complex. At low doping concentrationc _Sn4 at. % the carrier concentration is governed by the loosely bound tin-oxygen defects which decompose if the oxygen partial pressure is low. The carrier concentration follows from a relationN=K ₁ ·p _O2 ^–1/8 ·(3 ×10¹⁰ × c_Sn –N)^1/4 with an equilibrium constantK ₁=1.4×10¹⁵ cm^–9/4bar^1/8, determined from our measurements.     

Synthesis and characterization of undoped and tin-doped ZnO nanostructures

In this paper, undoped and tin-doped ZnO nanostructures were grown onto non-conductive substrates by a simple solution method. Structural, morphological, optical and electrical properties of the structures were investigated with respect to tin concentration. From XRD studies, all the ZnO nanostructures were found as hexagonal wurtzite type structures growing preponderantly oriented with c-axis normal to the substrate. An increase in tin content resulted in a decrease in grain size, whereas the dislocation density increases. SEM observations indicated that all the structures were textured throughout the substrates without any cracks or pores. The influence of incorporation of tin on surface morphology of the samples was clearly seen. Average diameter of the nanostructures decreased with increasing tin content. Absorption spectra of the structures revealed that the band gap of the films increases with increasing tin concentration. It is found that the tin-doped samples have higher average transmittance than the undoped one. The 1?% tin-doped sample exhibited ??80?% average transparency, which was the best transparency among the doped samples. Electrical measurements showed that resistivity of the structures increased with increasing dopant concentration. This increasing was attributed due to a decrease in carrier concentration caused by carrier traps at the grain boundaries.     

An investigation into the effects of oxygen plasma discharge on tin-doped indium oxide thin films

The surfaces of tin-doped indium oxide (ITO) thin films for polymer light-emitting electrochemical cells (LECs) were modified by oxygen plasma discharge. The properties of the ITO surfaces were evaluated by means of the measurements of X-ray photoelectron spectroscopy (XPS), contact angle, surface free energy and polarity. The influence of surface properties of the ITO thin films on the performance of polymer LECs was investigated in terms of the turn-on voltage, injection current and luminance. When oxygen plasma discharge was employed to modify the ITO surfaces, the surface properties of ITO are optimized due to the improvement of surface stoichiometry and the enhancement of wettability. And the improved surface properties benefited from the oxygen plasma discharge is observed to decay with the time after the plasma discharge. The difference in chemical composition, surface free energy and polarity between the non-treated and treated ITO surfaces appears to become smaller with the increase of the time after plasma discharge. In addition, the electrical and optical performance of the devices is found to become worse with the increasing time after plasma discharge on ITO substrates. The results demonstrate that the device performance strongly depends on the ITO surface properties and the ITO/organic interface characteristics.     

Hyperfine fields and impurity configurations for indium and palladium in nickel

Hyperfine field distributions and electric field gradients due to impurity configurations in dilute NiPd alloys were measured by time differential perturbed angular correlation techniques, using the nuclear probe¹¹¹Cd(¹¹¹In). The onset of various near neighbour impurity configurations could be followed with increasing Pd impurity concentration from 0.2 to 2.5 at %. An enhancement of their populations due to a strong indium-palladium attraction in nickel was observed. These observations were complemented by measurements at¹⁰⁰Rh (¹⁰⁰Pd) probe nuclei in a Ni_98.5In_1.5 alloy.     

Hyperfine characterization of \beta-zirconium tetrafluoride

The evolution of the hyperfine quadrupole interaction in \beta-ZrF₄ at Zr sites, is measured between 273 and 740 K via the Perturbed Angular Correlations technique. Two different quadrupole interactions, in a ratio 1:2 of relative fractions, are determined. It is observed that the compound remains stable all over the thermal range. Moisture exposure at room temperature seems not to affect the hyperfine interaction suggesting that \beta-ZrF₄ is less sensitive to air water than other varieties of zirconium fluoride. This revised version was published online in July 2006 with corrections to the Cover Date.     

Optimum packing density and crystal structure of tin-doped indium oxide thin films for high-temperature annealing processes

The influence of high-temperature annealing on the electrical properties and microstructure of tin-doped indium oxide (ITO) thin films was investigated as a function of oxygen gas flow ratio to argon gas during the sputtering deposition. The ITO thin films were annealed at 500 °C in air after the deposition. It was found that the ITO thin films, which were deposited in relatively low oxygen gas flow ratio, exhibited high Hall mobility and low-resistivity after the annealing. Furthermore, the X-ray reflectivity and diffraction measurement revealed that the ITO thin film with low-resistivity after annealing exhibited high packing density, smooth surface and low crystallization degree. It can be considered that the carrier electron scattering was suppressed with increasing in the packing density of the ITO thin film; as a result, the Hall mobility and resistivity were improved.     

Detection of impurity segregation in zone-confined, polycrystalline tin-doped indium oxide thin films by STM and AFM

This paper discusses the possibility of using STM and AFM to image the dopant material in a segregated state. Samples of tin-doped indium oxide were prepared using a zone-confining process. The resultant material has dopant species segregated over certain grain boundaries at desired positions while the others remain dopant free. Samples were then imaged using STM, AFM and STEM. Enhanced contrast from the dopant rich grain boundaries and a larger grain size are observed at the surface making an interface with the substrate as compared to the free surface of the sample, while secondary electron STEM images show these grains to be smaller in size and the boundaries to be almost physically flat. This is interpreted to be a consequence of the zone-confining effect.     

A spectroscopic ellipsometry study on the variation of the optical constants of tin-doped indium oxide thin films during crystallization

In this paper, the variation of the optical constants of tin-doped indium oxide thin films during thermal treatment was explored using spectroscopic ellipsometry based on appropriate analysis models combining a Drude absorption edge and Lorentz oscillators. It was found that the refractive indices and the extinction coefficients show different behaviors depending on depth, thermal treatment time and temperature. The optical constants varied more abruptly in the lower part of the films, which confirms the model that crystallization starts from the film-substrate interface. Hall measurement showed that the significant increase in the extinction coefficients in the near infrared range is due to the increased number of free electrons.     

Growth and characterization of indium oxide films

In₂O₃ films have been deposited using chemical spray pyrolysis technique at different substrate temperatures that varied in the range, 250–450 °C. The structural and morphological properties of the as-deposited films were studied using X-ray diffractometer and scanning electron microscope as well as atomic force microscope, respectively. The films formed at a temperature of 400 °C showed body-centered cubic structure with a strong (2 2 2) orientation. The structural parameters such as the crystallite size, lattice strain and texture coefficient of the films were also calculated. The films deposited at a temperature of 400 °C showed an optical transmittance of >85% in the visible region. The change of resistivity, mobility, carrier concentration and activation energies with the deposition temperature was studied. The highest figure of merit for the layers grown at 400 °C was 1.09 × 10⁻³ Ω⁻¹.     

Effect of tin-doped indium oxide film as capping layer on the agglomeration of copper film and the appearance of copper silicide

In this work, the effect of tin-doped indium oxide (ITO) film as capping layer on the agglomeration of copper film and the appearance of copper silicide was studied. Both samples of Cu 100 nm/ITO 10 nm/Si and ITO 20 nm/Cu 100 nm/ITO 10 nm/Si were prepared by sputtering deposition. After annealing in a rapid thermal annealing (RTA) furnace at various temperatures for 5 min in vacuum, the samples were characterized by four probe measurement for sheet resistance, X-ray diffraction (XRD) analysis for phase identification, scanning electron microscopy (SEM) for surface morphology and transmission electron microscopy (TEM) for microstructure.The results show that the sample with ITO capping layer is a good diffusion barrier between copper and silicon at least up to 750 °C, which is 100 °C higher than that of the sample without ITO capping layer. The failure temperature of the sample with ITO capping layer is about 800 °C, which is 100 °C higher than that of the sample without ITO capping layer. The ITO capping layer on Cu/ITO/Si can obstacle the agglomeration of copper film and the appearance of Cu₃Si phase.     

Study of the effect of the oxygen partial pressure on the properties of rf reactive magnetron sputtered tin-doped indium oxide films

The influence of the oxygen partial pressure on the properties of indium tin oxide films deposited by rf reactive magnetron sputtering has been studied. The oxygen partial pressure was varied from 3.2 × 10⁻⁴ to 1.0 × 10⁻³ mbar. It has been found that the 4 × 10⁻⁴ mbar of oxygen partial pressure is a critical point. When the oxygen partial pressure is lower than 4 × 10⁻⁴ mbar, the deposition rate of the films is high; the films have low transmittance and electrical resistivity; the X-ray diffraction shows that the films have a random orientation and the images of the scanning electron microscopy show that the films surface are smooth without structure. When the pressure is higher than 4 × 10⁻⁴ mbar, the deposition rate is low and does not change as the oxygen partial pressure is further increased; the transmittance and the electrical resistivity are both high; the films show the preferred orientation along the (440) direction; the films surface show a clear structure and as the pressure is increased further, the films become porous. Considering both the factor of transmittance and resistivity, the optimum oxygen partial pressure will be 3.6 × 10⁻⁴ mbar. The films prepared at this pressure have 80% transmittance and 9 × 10⁻⁴ Ω cm resistivity.     

Microstructure control of low-resistivity tin-doped indium oxide films grown by photoreaction of nanoparticles using a KrF excimer laser at room temperature

A tin-doped indium oxide (ITO) film on a SiO₂ substrate was prepared by photo-irradiation of spin-coated nanoparticles using a Xe excimer lamp and a KrF excimer laser. The effects of the excimer lamp and the excimer laser on the resistivity, mobility, and carrier concentration of the film were investigated. To better understand how to control the microstructure of the film, we investigated the effect of thickness on the resistivity of a film prepared by the two-step process, and found that the resistivity was higher in a thicker film. Using two-step irradiation plus one-step KrF irradiation in N₂ at room temperature, we produced an ITO film with lowest resistivity of any in this study. The electrical resistivity of this film was 5.94×10⁻⁴ Ω cm. On the other hand, when using a simple thermal process, the resistivity of a film sintered at 500°C in N₂ was 4.10×10⁻³ Ω cm. The differences in resistivity are discussed on the basis of the microstructure of the films using atomic force microscopy and Hall measurements.     

Hyperfine interaction characterization of iron minerals in Brazilian monazite sands

The Mössbauer spectra both at 300 K and 84 K of the naturally occuring monazite sands from the beaches of Marataizes (40°49′ 11.4″ LW and 21°02′ 26.7″ LS) indicate a paramagnetic phase of nearly 21% absorption and three other phases, including magnetic phases, of nearly 4% absorption each. Chemical analysis, X-ray diffraction and X-ray fluorescence alongwith Mössbauer spectra confirm these to be ilmenite, hematite, magnetite and orthopyroxene (chain silicate) minerals. Presence of a number of other non-iron minerals was also detected.     

A novel investigation of tin-doped ferrihydrite nanoparticles

Tin-doped ferrihydrite was synthesized and characterized with powder X-ray diffraction and ⁵⁷Fe and ¹¹⁹Sn Mössbauer spectroscopy to obtain diagnostic and structural information. Samples were prepared with doping concentrations (molar percentages) of 0, 10, 25, 40, 50, 60, 75, and 90% tin. As Sn concentration increases, the 110 reflection plane of ferrihydrite shifts to higher d-values, while the 300 plane d-values increase, reach a maximum and then sharply drop. The δ (isomer shift) and Δ (quadrupole splitting) values for ⁵⁷Fe Mössbauer spectra increase, while the Γ (line width) values stay constant. In ¹¹⁹Sn Mössbauer spectra, δ values decrease with increasing tin substitution while Δ and Γ values increase. After 50% Sn has been substituted, the ferrihydrite becomes oversaturated with surface tin and a secondary tin structure is proposed to develop.     

Synthesis and characterization of indium oxide-hematite magnetic ceramic solid solution

Indium oxide-doped hematite xIn₂O_3*(1-x)??-Fe₂O₃ (molar concentration x = 0.1?C0.7) solid solutions were synthesized using mechanochemical activation by ball milling. XRD patterns yield the dependence of lattice parameters and grain size as function of milling time. After 12 h of milling, the completion of In^3?+? substitution of Fe^3?+? in hematite lattice occurs for x = 0.1. For x = 0.3, 0.5 and 0.7, the substitutions between In^3?+? and Fe^3?+? into hematite and respectively, In₂O₃ lattices occur simultaneously. The lattice parameters of ??-Fe₂O₃ (a and c) and In₂O₃ (a) vary with milling time. For x = 0.1, Mössbauer spectra were fitted with one, two, or three sextets versus milling time, corresponding to gradual substitution of In^3?+? for Fe^3?+? in hematite lattice. For x = 0.3, Mössbauer spectra after milling were fitted with three sextets and two quadrupole-split doublets, representing In^3?+? substitution of Fe^3?+? in hematite lattice and Fe^3?+? substitution of In^3?+? in two different sites of In₂O₃ lattice. For x = 0.5 and 0.7, Mössbauer spectra fitting required two sextets and one quadrupole-split doublet, representing coexistence of In^3?+? substitution of Fe^3?+? in hematite lattice and Fe^3?+? substitution of In^3?+? in indium oxide lattice. The recoilless fraction studied versus milling time for each molar concentration exhibited low values, consistent with the occurrence of nanoparticles in the system. SEM/EDS measurements revealed that the mechanochemical activation by ball milling produced xIn₂O_3*(1-x)??-Fe₂O₃ solid solution system with a wide range of particle size distribution, from nanometer to micrometer, but with a uniform distribution of Fe, In, and O elements.     

Hyperfine spectrum of NaF

The molecular beam electric resonance technique has been used to conduct a high precision examination of the hyperfine spectrum of ²³Na¹⁹F. Coupling constants for the nuclear electric quadrupole interactions, the spin-rotation interactions, the tensor and scalar spin-spin interactions, and their dependence on vibrational and rotational state have been determined.