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Sb-doped SnO2 (ATO) thin films were synthesized via the sol–gel dip-coating method on glass substrates. The XPS and XRD spectra showed that Sb atoms were successfully incorporated into the SnO2 lattice and mostly existed in the form of Sb5+ (~ 90%) in 1 at.% ATO thin films annealed in air and further annealed in vacuum. The transmittance spectra revealed that the average transmittance was more than 75% at the wavelength range of 325–700 nm. The average sheet resistancewas 14.05 kΩ/□ in 1 at.% ATO thin films annealing in air and much less than undoped SnO2. The electric property was better when ATO thin films were further annealing vacuum compared to annealing in air. The average sheet resistance and resistivity of 1 at.% ATO thin films were 2.42 kΩ/□ and 0.035 Ω cm, respectively. The PL showed that electrons transition from a shallow level of VO to the minimum level of conduction band (CBM) increased with increasing of Sb3+ ions. The maximum level of valence band (VBM) and CBM level positions were mainly affected by Sb3+ and Sb5+ energy levels after air annealing, respectively. The behavior of surface carrier transport was investigated after further vacuum annealing. The CBM–VBM level position mainly was affected by VO energy level after further vacuum annealing. It was further proved by the Hall carrier concentration and the electrochemical impedance spectroscopy (EIS). [ABSTRACT FROM AUTHOR]

Transparent and conducting ZnGaO thin films with different nominal Ga content ( x = 0-4%) on flexible polyimide (PI) substrates were successfully synthesized by conventional sol-gel spin coating method. All the films retained a hexagonal wurtzite structure of ZnO and showed preferential c-axis orientation after air and vacuum annealing and good adhesion to flexible PI substrates. Generally, the particles in the films were small and the connectivity between the particles was good, irrespective of doping concentration and treatment ambient. The average transmittances reached 70% for all the films above a cut-off wavelength of ∼500 nm originated from PI substrates. The average sheet resistances decreased suddenly after Ga doping, while increased slightly from x = 3-4%. According to Hall measurement, the broad minimum resistivity of 1-3% Ga doping concentration might be due to the competition of dopant atoms at lattice sites and the segregated ones at the grain boundaries, which could be demonstrated by decreased Hall mobility and increased carrier concentration with increasing Ga doping content. [ABSTRACT FROM AUTHOR]

1% Al-doped ZnO transparent and conducting thin films on flexible polyimide (PI) substrates were successfully synthesized by the conventional sol–gel spin coating method. All the films with different number of layers (9, 10 and 11) retained a hexagonal wurtzite structure of ZnO and showed preferential c -axis orientation. Good adhesion was evidenced by dense microstructure and homogeneously distributed grains of the films on flexible PI substrates. The average transmittances reached 70% for all the films above a cut-off wavelength of ∼500 nm originated from PI substrates. Comparing to the resistance of films annealed in air, the electrical conductivity could be enhanced by further vacuum ( P ∼10 −2 Pa) post-annealing, and lowest resistivity of 2.52×10 −1 Ωcm was obtained in the film with 10 layers. [ABSTRACT FROM AUTHOR]

Abstract: 2at.% Ga-doped Mg x Zn1−x O (x =0–8%) films have been prepared by sol–gel dip-coating method, and the effects of three different post annealing ambient: (a) vacuum annealing under air pressure of ∼10−2 Pa; (b) annealing in nitrogen atmosphere, and (c) annealing in argon-hydrogen (96%argon+4%hydrogen) atmosphere on the electrical and optical properties of the films are investigated. When treated by these three different post-annealing ambient, both the resisitivity and band gap of the films increase with Mg doping contents increasing from 0 to 8at.%. The vacuum annealed films show much lower resistivity than those treated in nitrogen or argon–hydrogen atmosphere, and the transmittance of the vacuum annealed films (∼70%) is also lower than those annealed by the other two methods (∼90%) in visible region. It shows that different post annealing ambient and ion doping could modify the optoelectronic properties of ZnO films. [Copyright &y& Elsevier]

Abstract: The undoped and Ce-doped SnO2 thin films synthesized by a simple sol–gel-dip-coating method on glass substrates were investigated by means of X-ray diffractometer, visible spectrophotometer and photoluminescence (PL) spectroscopy. The samples were polycrystalline thin films with rutile structure of undoped SnO2. A violet PL peak was observed in undoped SnO2 at room temperatures, while a blue PL peak appeared only after introducing Ce3+ ions into the SnO2 host. The effects of Ce doping concentration and heat-treatment temperature on PL of the films were further studied, and the luminescence mechanism was also discussed. [Copyright &y& Elsevier]

Abstract: Nb-doped TiO2 (TNO) thin films were prepared by sol–gel dip-coating method with Nb content in a wide range of 0–20at.%. The prepared films were preheated at 400°C and then undertaken by two different post-annealing processes: (a) three times vacuum annealing and (b) multi-round annealing. The designed multi-round annealing was shown to be an effective way to improve the conductive properties of the films, compared to the traditional vacuum annealing process. The minimum resistivity reached approximately 0.5Ωcm with Nb doping concentration around 12at.%, and the carrier density increased with Nb-doping concentration until the critical point of 12at.%, which might be the optimal doping content for our TNO films prepared by sol–gel method. [Copyright &y& Elsevier]

Abstract Fe-doped ZnO thin films were successfully prepared via the sol-gel spin coating method. Both X-ray diffraction and X-ray photoelectron spectroscopy analysis displayed that Fe atoms were successfully incorporated into the ZnO thin films and existed in the form of Fe2+ mostly in 1 at.% Fe-doped ZnO films, and mainly existed in the form of Fe3+ in higher concentration of the films. Scanning electron microscopy images demonstrated the decrease in crystallite size with increasing Fe concentration. The room temperature photoluminescence revealed that electrons transition from a shallow level of Zn i to top level of valance band increased, while near band edge (NBE) emission reduced with increasing Fe content, which indicated that Fe doping introduce some impurity levels and/or influence on the existing levels and hence affect the type of transition. Furthermore, the behavior of surface carrier transport and interfacial charge transfer are investigated by the photocatalytic activities and electrochemical impedance spectroscopy for undoped and Fe-doped ZnO films and nanorods, to detect the effects of Fe dopant in the form of Fe2+ and Fe3+ ions on photocatalytic performance. Highlights • Fe-doped ZnO thin films and nanorods were prepared by wet solution method. • Fe2+ and Fe3+ ions were both present in Fe-doped ZnO films. • Fe doping could introduce impurity levels and/or affect the type of transition. • ZnO nanorods could effectively enhance the photocatalytic performance. • Fe2+ played a major role in photocatalytic degradation process. [ABSTRACT FROM AUTHOR]

The effects of Yb concentration and annealing temperature on the dielectric constant change of Yb-doped HfO2 thin film were investigated. The results show that the dielectric constant of Yb-doped HfO2 increased when doping with Yb after annealing. Compared with the undoped HfO2, the dielectric constant enhancement may result from the crystallographic change from monoclinic phase to the cubic phase. The Yb-doped HfO2 exhibited a lower leakage current than that of undoped HfO2 thin film. The electrical characteristics of Yb-doped HfO2 thin film illustrated that it is a promising gate dielectric layer for future high dielectric constant (high-k) gate dielectric applications. [ABSTRACT FROM AUTHOR]

Abstract: We developed a scanning microwave microscope (SμM) designed for high-throughput electric-property screening as well as for rapid construction of electronic phase diagrams at low temperatures. As a sensor probe, we used a high-Q λ/4 coaxial cavity resonator to which a thin needle with ball-tip end was attached. The sensor module was mounted on the low-temperature XYZ stage, which allowed us to map out the change of resonance frequency and quality factor due to the local tip-sample interaction at low temperatures. From the measurements of combinatorial thin films, such as Ti1−x Co x O2−δ and Nd0.9Ca0.1Ba2Cu3O7−δ (NCBCO), it was demonstrated that this SμM system has enough performance for the high-throughput characterization of sample conductance under variable temperature conditions. [Copyright &y& Elsevier]

Abstract Monoclinic Ga 2 O 3 (β-Ga 2 O 3) has been considered as a promising candidate for solar-blind photodetector owing to its extremely wide bandgap. However, preparing homogeneous large-area thin films of β-Ga 2 O 3 in a practical way still remains as an upfront challenge. Here we report the growth of β-Ga 2 O 3 thin films on the Sapphire substrate via a low-cost sol-gel spin-coating method followed by a post-annealing process. The structures, surface morphologies and optical properties of the films were characterized using various techniques, including X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM) and ultraviolet–visible (UV–Vis) spectrophotometry. Our results showed that phase-pure β-Ga 2 O 3 polycrystalline films could be formed by sol-gel technique when post-annealed at temperatures 700 °C and higher. All the films showed high transmittance of 90% in UV–Vis light with wavelength above 300 nm and the optical bandgap energy increased monotonously with the annealing temperature. The current-voltage (I–V) tests and time-resolved photoresponse measurements showed that the film annealed at 700 °C has the excellent photoresponse characteristic with a high I photo / I dark ratio (18.34) along with the shortest response time (0.10 s) and decay time (0.10 s), indicating that the sol-gel synthesized β-Ga 2 O 3 films can have great potential for fabricating fast-response solar-blind ultraviolet photodetectors. Graphical abstract Image 1 Highlights • β-Ga 2 O 3 thin films were successfully synthesized by sol-gel method above 700 °C. • The optical bandgap energy increased monotonically with annealing temperature. • The film annealed at 700 °C showed the best deep UV photoresponse performance. [ABSTRACT FROM AUTHOR]

The chemical structures and the optical properties of the Ce-doped HfO x N y thin films were prepared by radio frequency (RF) magnetron sputtering and investigated by using X-ray photoelectron spectroscopy (XPS), ultraviolet–visible (UV–vis) absorption spectrophotometer and photoluminescence (PL) spectroscopy. The results showed that the band gap gradually decreased as the nitrogen incorporation content increased from 1.1% to 8.8%. The PL bands located at 380 nm and 465 nm of the sample as-deposited corresponded to the transition from the oxygen vacancy level to valance band and the 5d-4f transition of the trivalent cerium, respectively. The further study revealed that both two PL bands exhibited red shift phenomenon in the NH 3 -annealed sample, which is due to the decrease of the band gap. [ABSTRACT FROM AUTHOR]

Abstract: The undoped and Ce-doped HfO2 thin films synthesized by magnetron sputtering on silicon substrates were characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL). XRD measurements of these films showed that the crystalline structure depends on the doping concentration. The samples underwent a crystallographic change from monoclinic to cubic phase with increasing doping concentration. A violet PL band associated with oxygen vacancies was observed in undoped HfO2 at room temperature. While a blue PL band appeared after introducing cerium ion into the HfO2 host, which is ascribed to the well-known 5d–4f emission band of the cerium ion. [Copyright &y& Elsevier]

Abstract: Strong phase competitions between the ferromagnetic metal and the charge-ordered-insulator have been induced in a wide temperature range of 10–256K for the shear-strained La0.67Ca0.33MnO3/NdGaO3(001) films. Based on various magnetotransport measurements, the mobility of phase boundaries was inferred to change dramatically with temperature. In the high temperature range where the phase boundaries are movable, strong relaxation in resistivity was observed, while at the frozen temperatures lower than 40K it is weakened. The resistivities tend to relax in accordance with the phase transitions driven by the temperature or magnetic field in the phase separation (PS) background. Moreover, to our surprise, while the melting fields of the insulating phase varied with film thicknesses, for a given film however, they stay unchanged when started with different phase fractions produced by the field or thermal cycling. The results show a crucial role of the inherent strain state in determining PS and phase competitions in these epitaxial thin films. [ABSTRACT FROM AUTHOR]

Transparent and conducting Hf x Zn 1- x O thin films with nominal Hf doping concentration (x = 0–7%) were successfully synthesized on flexible polyimide (PI) substrates by the sol-gel spin coating method. All films showed hexagonal wurtzite structure of ZnO with preferred orientation of c -axis after air and vacuum annealing. The minimum resistivity reached to as low as 6.3 × 10-2 Ω cm after annealed in vacuum atmosphere with 3% Hf content. The carrier concentration increased from 1018 cm-3 to 1019 cm-3, while Hall mobility decreased from 23 cm2v-1s-1 to 3 cm2v-1s-1 with increasing Hf concentration. According to the SEM and XPS analysis, for x = 0–3%, grain boundary scattering was the major factor of mobility, while for x = 5–7%, besides the grain boundary scattering, ionized impurity and natural scattering also play a crucial role in the variation of mobility. The minimum resistivity was due to the competition of increasing carrier concentration and decreasing mobility. [ABSTRACT FROM AUTHOR]

Herein, we are reporting the fabrication of high-performance solar blind photodetectors using β-Ga 2 O 3 thin films of varying thicknesses grown on single crystal (0001) Sapphire substrate by pulsed laser deposition (PLD) technique. Thickness of the β-Ga 2 O 3 films was varied by varying the number of ablating laser shots from 1000 to 15,000 (1 k to 15 k). The effect of thickness on the structure, surface morphology and optical properties of the films was investigated using several state-of-the-art techniques such as X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM) and ultraviolet–visible (UV–Vis) spectroscopy. All the films were found to be made of phase-pure β-Ga 2 O 3 with high crystal quality. The orientation of the films was found to gradually change from (−201) to (−201)/(400) as the number of laser shots increased from 1 k to 15 k. The bandgap of the films made with 1 k laser shots was found to be 5.26 eV which decreased monotonously with increase in number of laser shots and became 4.79 eV for the films made with 15 k laser shots. The detailed time-resolved photoresponse measurements showed that the films made with 2 k shots exhibit the best photoresponse characteristic among all the films with a high I photo / I dark ratio of ∼6.7 × 104 and short rise (0.38 μs) and decay times (142 μs). Our results indicate that the PLD-grown β-Ga 2 O 3 thin films, with optimized thickness, can play a major role in next-generation solar-blind ultraviolet photodetector technology. • Optical bandgap of β-Ga2O3 thin films decreases with increase in films' thickness. • Film thickness is directly related to optical and electrical properties. • High photoresponse is seen with Iphoto/Idark ratio ∼6.7×104 and fast response (0.38 μs) and decay speed (142 μs) in 2k films. [ABSTRACT FROM AUTHOR]