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Fluorine-doped tin oxide (FTO) thin films were prepared by a radio frequency magnetron sputtering technique. The defects and charge carrier transport behavior in FTO thin films were evaluated during the transition process from amorphous to nanocrystalline structures. The stable lattice structure in FTO thin films was obtained as the annealing temperature reached 400 ° C. Positron annihilation results indicated that defect evolution in the FTO thin films was shown in two stages, formation and reduction of vacancies/vacancy clusters. The carrier mobility of the FTO thin films annealed at 600 ° C was enhanced twice the amount than that of the unannealed samples. The correlation between the results obtained from positron annihilation and the Hall effect revealed the importance of defect scattering in deciding the charge carrier mobility. A defect scattering mechanism was proposed to interpret the noticeable increment of carrier mobility in FTO thin films after thermal treatment. [ABSTRACT FROM AUTHOR]

Fluorine doped tin oxide (FTO) thin films were deposited on glass substrates by e-beam evaporation. Much higher carrier concentration, broader optical band gap, and average transmittance over 80% were obtained with SnF2 doped SnO2 thin films. Positron annihilation results showed that there are two kinds of vacancy clusters with different sizes existing in the annealed FTO thin films, and the concentration of the larger vacancy clusters of VSnO in the thin films increases with increasing SnF2 contents. Meanwhile, photoluminescence spectra results indicated that the better electrical and optical properties of the FTO thin films are attributed to FO substitutions and oxygen vacancies with higher concentration, which are supported by positron annihilation Doppler broadening results and confirmed by X-ray photoelectron spectroscopy. The results showed that widening of the optical band gap of the FTO thin films strongly depends on the carrier concentration, which is interpreted for the Burstein-Moss effect and is associated with the formation of FO and oxygen vacancies with increasing SnF2 content. [ABSTRACT FROM AUTHOR]

Polyamide thin film composite reverse osmosis membranes on porous polysulfone support were prepared using m-phenylenediamine, trimesoyl chloride and dimethyl sulfoxide (DMSO) with various contents as precursors via an interfacial polymerization. The membrane with heterogeneous multilayer structure was depth-profiled by positron annihilation lifetime spectroscopy based on a pulsed slow positron beam and the thickness of the polyamide active layer can be estimated through fitting the results of depth dependence of o-Ps intensity. The free volume characteristics in the polyamide selective layer of the membranes were evaluated and were correlated with the permeation properties. With increasing DMSO content, mean free volume size (VFV) was enlarged, which was responsible for the enhanced water and sodium chloride permeation. However, the salt rejection was significantly decreased with a slight increase in the VFV around a critical value of 88.0 Å3, which was the average size of hydrated sodium and chloride ions. It was well interpreted for that the broadened free volume distribution enables an amount of larger free volumes to be involved in the salt permeation, although little change in VFV was found. [ABSTRACT FROM AUTHOR]

A correction is presented to the article "Vacancy defects and optoelectrical properties for fluorine tin oxide thin films with various SnF2 contents" which appeared in the previous issue of the periodical.

Highlights: [•] Porous silica films were studied by positron annihilation lifetime spectroscopy. [•] Almost no o-Ps annihilates in the entrance channels of cages in the porous films. [•] After trimethylsilylation, an appreciable fraction of Ps is trapped in the entrance. [•] It is possible to estimate the pore entrance size from the trapped o-Ps lifetime. [ABSTRACT FROM AUTHOR]

A pulsed slow-positron beam using 22Na as the positron source has been constructed for characterizing thin polymer films, coating polymer materials and their interfaces. The construction is very simple and the time resolution achieved is about 500 ps, which is sufficient for measuring long-lived positron lifetime components in thin polymer films. The positron lifetime in a 45 nm thick epoxy resin thin film held on a single-crystal silicon substrate has been measured using this pulsed slow-positron beam. Formation of o-positronium (ortho-Ps) is not observed when the incident positron energy is more than about 1 keV. The surface effect of the glass-transition temperature of a 0.3 mm thick polystyrene (PS) film has been also studied. It has been found that the glass-transition temperature of the sub-surface region of PS is lower than that of the PS bulk. [Copyright &y& Elsevier]

A pulsed slow-positron beam has been constructed for applications to polymer films. A new setup of the moderator system and a new design for the bunching signal waveform are introduced. The results show that such a kind of moderator appears to be good one, and that a new waveform for the bunching is very practical. The current pulsed slow-positron beam can be used to characterize polymer films or porous thin films. [Copyright &y& Elsevier]

Lifetimes of ortho-positronium in mesoporous silica films were measured before and after surface trimethylsilylation of –OH groups. Variations of positronium lifetimes in the mesopores upon the surface modification indicate that the interaction between positronium and the pore surface is weakened in the pores, whose surface is covered with –CH3 groups, in comparison with those covered with –OH groups. This is consistent with the authors’ previous observation that positronium slowing down is less efficient in the pores covered with –CH3 groups. The present work demonstrates that in the porosimetric application of positron annihilation lifetime spectroscopy, the interaction between positronium and the pore surface has to be properly taken into consideration. [ABSTRACT FROM AUTHOR]

Defects in undoped and antimony (Sb)-doped tin oxide thin films fabricated via a sol-gel method have been investigated using a slow positron beam by which an annihilation lineshape parameter is used to evaluate defects in the films. With increasing calcination temperature, the resistivity for undoped films increased because of removal of oxygen vacancies in them; however, the resistivity gradually declined for Sb-doped films upon annealing at higher temperatures, mainly due to weakened carrier scattering with fewer residual defects. The results show that defects as well as dopants play an important role in determining the resistivity of tin oxide films. [ABSTRACT FROM AUTHOR]

Indium Tin Oxide (ITO) thin films have been extensively studied for their excellent photoelectric performance. Nevertheless, the diffusion mechanism of doped-tin in ITO thin film is not sufficiently illuminated to date. Herein, the diffusion behaviors of Sn dopant in ITO films fabricated by RF-sputtering were investigated. As-deposited ITO thin films were treated by supercritical CO 2 (SCCO 2) fluid with aqua ammonia, then they were annealed at different temperatures. X-ray diffraction patterns (XRD) showed that the crystallization of ITO films occurred upon annealing above 300 °C, which resulted in the higher mobility of electron carriers. Relatively lower electron carrier concentrations were found for the ITO films after SCCO 2 treatment and successive annealing at temperatures of 500 and 600 °C. X-ray photoelectron spectroscopy (XPS) analysis revealed that the content of tin element near the surface of ITO thin films can be reduced by SCCO 2 fluid treatment. Subsequently, the annealing process results in the diffusion of the tin element to the sub-surface region of the films at different levels depending on the annealing temperature. The present work provides direct evidence for bleaching of tin dopant in the sub-surface region of ITO films by SCCO 2 treatments and diffusion of tin from deeper regions to the sub-surface region of the ITO films upon annealing. [ABSTRACT FROM AUTHOR]

Elemental doping is the main means to regulate the phase transition of vanadium oxide (VO 2); however, the effects of low valence elemental (<4+) doping on the phase transition of VO 2 are still controversial. In the present work, Ni-doped VO 2 films were prepared on quartz glass by direct current reactive magnetron sputtering and subsequent annealing. With the increase of the Ni doping content, the phase transition temperature of heating (T H) of the VO 2 films decreased from 73.4 °C to 52.4 °C. The temperature required for the occurrence of phase transition (T b) was lower than T MIT. Different from the undoped VO 2 film, the Ni-doped VO 2 films had a T b of around 30 °C. XRD and Raman results revealed that some rutile VO 2 microcrystals appeared in the vanadium oxide films because of the lattice distortion by incorporated Ni. Hence, rutile VO 2 micro-crystallinities significantly facilitated the phase transition of monoclinic VO 2 to rutile one. [ABSTRACT FROM AUTHOR]

Various transparent GaN-doped SnO 2 thin films were deposited on glass substrates by e-beam evaporation using GaN:SnO 2 targets of different GaN weight ratios. It is interesting to find that carrier polarity of the thin films was converted from n-type to p-type with increasing GaN ratio higher than 15 wt.%. The n–p transition in GaN-doped SnO 2 thin films was explained for the formation of Ga Sn and N O with increasing GaN doping level in the films, which was identified by Hall measurement and XPS analysis. A transparent thin film p–n junction was successfully fabricated by depositing p-type GaN:SnO 2 thin film on SnO 2 thin film, and a low leakage current (6.2 × 10 −5 A at −4 V) and a low turn-on voltage of 1.69 V were obtained for the p–n junction. [ABSTRACT FROM AUTHOR]

Crystallization of polycarbonate (PC) films as a function of annealing time has been investigated by various methods. A distinct diffraction peak at 17.56°, a sharp decrease of film thickness, an increase of refractive index and branch-type structures on the surface are found merely for the film after crystallization. Interestingly, positron annihilation parameters demonstrate fractional free-volumes in PC films vary significantly not only before crystallization but also at the early stage of annealing, which are not found by other methods. The results show that free-volumes in PC film must be increased remarkably before crystallization, which enables the occurrence of molecule rearrangement. [ABSTRACT FROM AUTHOR]

Temperature dependent conductivities, surface morphologies, defects and antimony valence state of antimony doped tin oxide (ATO) films were investigated. Much higher conductivity is found for the film calcined at 600 °C than 400 °C due to enhancement of Sb 5+ ratio and removal of grain boundaries, vacancies and interstitial dopants; the conductivity increases slightly for the film calcined at 800 °C because of further elimination of vacancy clusters and grain boundaries. A strong temperature dependent conductivity is merely observed in the film calcined at 400 °C Positron annihilation parameter W is well correlated with the conductivity for ATO films. [ABSTRACT FROM AUTHOR]