A novel oxynitride semiconductor, ZnSnON, is demonstrated. The design of this material follows the reported anion control strategy (N additives) to diminish the bandgap and the electron effective mass of ZnO on the one hand, and a cation control strategy (Sn additives) to circumvent the chemical stability problems of ZnON on the other. Comparative studies are conducted on the performance and stability of ZnSnON and ZnON films and their thin-film transistors (TFTs). It is shown that ZnSnON possesses superior transport properties and enhanced operation stability simultaneously. Such amelioration is owing to multiple factors, including the amorphous/nanocrystalline mixed phase and the bonding strength increase caused by the Sn-related oxide/oxynitride dominant in the back channel region. In addition, the Sn additives in ZnON do not alter the direct bandgap character, maintaining around 1.6 eV. The ZnSnON-TFT is photosensitive in the whole visible light region with a photoresponsivity higher than 6 × 103 A W−1. Considering the high-mobility, improved operation stability, and visible light sensing capability, this semiconductor can be used in a broad array of applications such as in active-matrix imaging arrays, interactive displays, flat X-ray detectors, etc.

Currently, the limitations of conventional methods for fabricating metamaterials composed of well-aligned nanoscale inclusions either lack the necessary freedom to tune the structural geometry or are difficult for large-area synthesis. In this Communication, the authors propose a fabrication route to create well-ordered silver nano forest/ceramic composite single-layer or multi-layer vertically stacked structures, as a distinctive approach to make large-area nanoscale metamaterials. To take advantage of direct growth, the authors fabricate single-layer nanocomposite films with a well-defined sub-5 nm interwire gap and an average nanowire diameter of ≈3 nm. Further, artificially constructed multilayer metamaterial films are easily fabricated by vertical integration of different single-layer metamaterial films. Based upon the thermodynamics as well as thin film growth dynamics theory, the growth mechanism is presented to elucidate the formation of such structure. Intriguing steady and transient optical properties in these assemblies are demonstrated, owing to their nanoscale structural anisotropy. The studies suggest that the self-organized nanocomposites provide an extensible material platform to manipulate optical response in the region of sub-5 nm scale.

•A novel cermet WTi-Al2O3 is designed for constructing solar absorbing coatings.•The resultant coating exhibits an excellent thermal tolerance at 600 °C.•The coating has a low infrared emissivity of ~10.3% @500 °C after 600 °C annealing.•A mechanism is proposed based on the self-passivation of WTi alloy nanoparticles.Cermet-based solar selective absorbing coatings are widely used, however, the long-term thermal instability and pretty high infrared emissivity at high temperatures (>550 °C) are still challenging issues to be addressed, which essentially lies in suppressing the growing up and agglomeration behaviors of metal nanoparticles (NPs) and maintaining the interface integrity in the multi-layer stacked structure. Herein, we develop and explore WTi-Al2O3 cermet-based absorbing coatings, demonstrating a solar absorptance of ~93% and a very low thermal emissivity of 10.3% @500 °C even after annealing at 600 °C for 840 h in vacuum. It is revealed that the surface segregation of solute Ti atoms from the parent alloyed NPs and their partial oxidation to form protective layer restrain outward diffusion of W element, agglomeration of NPs, and interface structure degradation, in favor of enhancing the thermal tolerance of the coatings. These results suggest that the WTi-Al2O3 based absorbing coating is a good candidate for high-temperature solar thermal conversion.A novel solar selective absorbing coating demonstrates a very low thermal emissivity of ~10.3% @500 °C even after annealing at 600 °C for 840 h with a high solar absorptance of ~93%. In particularly, the thermal stability of the coating is enhanced by innovatively using the segregation of solute and oxide passivation, which is greatly different from the traditional method.Download high-res image (413KB)Download full-size image

The effect of post-annealing on the structural and electrochromic properties of the Mo-doped V2O5 thin films was investigated in this paper. With varying the annealing temperature, the interlayer distance is increased from 1.16 (as-deposited) to 1.38 nm (annealing at 250 °C), and the enlarged interlayer spacing would facilitate ion movement in between the interlayers inside the electrochromic matrix. Therefore, both the optical modulation and color efficiency of the Mo-doped V2O5 thin films are enhanced after appropriate post-annealing treatment. Our results demonstrate that Mo-doped V2O5 material is one of the promising candidates to be used in multi-color electrochromic devices.

In this study, (001) and (101)-orientated polycrystalline SnO films were respectively fabricated. The preferred orientation conversion was observed by modifying the stoichiometry of the SnO films. It was revealed that the O-rich and Sn-rich SnO films favor (001) and (101) grain orientations, respectively. Moreover, based on the Raman selection rule and our experimental results, the 110 cm−1 Raman peak is assigned to the low-frequency Eg mode of SnO. The Raman intensity ratio between the 110 cm−1 and 210 cm−1 peak of SnO increases with the relative texture coefficient of the (101) grain orientation but decreases with that of the (001) one, demonstrating that the Raman characteristic information could be used as fingerprint recognition to mutually predict the crystallographic texture of SnO films.

We developed a facile and environmentally friendly solution-processed method for aluminum oxide (AlOx) dielectrics. The formation and properties of AlOx thin films under various annealing temperatures were intensively investigated by thermogravimetric analysis–differential scanning calorimetry (TGA-DSC), X-ray diffraction (XRD), spectroscopic ellipsometry, atomic force microscopy (AFM), attenuated total reflectance–Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), impedance spectroscopy, and leakage current measurements. The sol–gel-derived AlOx thin film undergoes the decomposition of organic residuals and nitrate groups, as well as conversion of aluminum hydroxides to form aluminum oxide, as the annealing temperature increases. Finally, the AlOx film is used as gate dielectric for a variety of low-temperature solution-processed oxide TFTs. Above all, the In2O3 and InZnO TFTs exhibited high average mobilities of 57.2 cm2 V–1 s–1 and 10.1 cm2 V–1 s–1, as well as an on/off current ratio of ∼105 and low operating voltages of 4 V at a maximum processing temperature of 300 °C. Therefore, the solution-processable AlOx could be a promising candidate dielectric for low-cost, low-temperature, and high-performance oxide electronics.Keywords: aluminum oxide; environmentally friendly; high-performance; low-temperature; oxide thin-film transistors; solution process

For ultrathin semiconductor channels, the surface and interface nature are vital and often dominate the bulk properties to govern the field-effect behaviors. High-performance thin-film transistors (TFTs) rely on the well-defined interface between the channel and gate dielectric, featuring negligible charge trap states and high-speed carrier transport with minimum carrier scattering characters. The passivation process on the back-channel surface of the bottom-gate TFTs is indispensable for suppressing the surface states and blocking the interactions between the semiconductor channel and the surrounding atmosphere. We report a dielectric layer for passivation of the back-channel surface of 20 nm thick tin monoxide (SnO) TFTs to achieve ambipolar operation and complementary metal oxide semiconductor (CMOS) like logic devices. This chemical passivation reduces the subgap states of the ultrathin channel, which offers an opportunity to facilitate the Fermi level shifting upward upon changing the polarity of the gate voltage. With the advent of n-type inversion along with the pristine p-type conduction, it is now possible to realize ambipolar operation using only one channel layer. The CMOS-like logic inverters based on ambipolar SnO TFTs were also demonstrated. Large inverter voltage gains (>100) in combination with wide noise margins are achieved due to high and balanced electron and hole mobilities. The passivation also improves the long-term stability of the devices. The ability to simultaneously achieve field-effect inversion, electrical stability, and logic function in those devices can open up possibilities for the conventional back-channel surface passivation in the CMOS-like electronics.Keywords: ambipolar thin-film transistors; back-channel; CMOS-like inverters; passivation; SnO

In this article, we demonstrate that the Al-alloyed Ag nanoparticle-embedded alumina nanocermet films lead to excellent thermal stability, even at 500 °C for 130 h under an ambient nitrogen atmosphere. The outward diffusion of Al atoms from the AgAl bimetallic alloy nanoparticles and their easy oxidation create an armor layer to suppress the mobility of Ag atoms. Then, the AlAg particles or/and agglomerates with a uniform spherical shape favor higher dispersion concentration within the host matrix, which is beneficial both for high absorptance in the visible range and for the solid localized surface plasmon absorption features in the AgAl–Al2O3 nanocermet films. Based on the AgAl–Al2O3 absorbing layer with sound optical and microstructural stability, we successfully constructed a high-temperature-endurable solar selective absorber. The multilayer stacked absorber demonstrates a high solar absorptance of ∼94.2% and a low thermal emittance of ∼15% (@ 673 K) after annealing at 450 °C for 70 h in an ambient nitrogen atmosphere.Keywords: bimetallic alloy; diffusion; nanocermet thin films; silver nanoparticles; solar selective absorbing coating; thermal stability

High dielectric constant (high-k) Al2O3 thin films were prepared on ITO glasses by reactive RF-magnetron sputtering at room temperature. The effect of substrate bias on the subband structural, morphological, electrode/Al2O3 interfacial and electrical properties of the Al2O3 films is systematically investigated. An optical method based on spectroscopic ellipsometry measurement and modeling is adopted to probe the subband electronic structure, which facilitates us to vividly understand the band-tail and deep-level (4.8–5.0 eV above the valence band maximum) trap states. Well-selected substrate biases can suppress both the trap states due to promoted migration of sputtered particles, which optimizes the leakage current density, breakdown strength, and quadratic voltage coefficient of capacitance. Moreover, high porosity in the unbiased Al2O3 film is considered to induce the absorption of atmospheric moisture and the consequent occurrence of electrolysis reactions at electrode/Al2O3 interface, as a result ruining the electrical properties.Keywords: Al2O3 thin films; breakdown mechanism; leakage current; magnetron sputtering; oxygen vacancy; subband electronic structure;

•Cu/CrNxOy/SiO2 coatings were prepared for flat plate solar thermal collector.•The coating exhibited an absorptivity of 0.947 and an emissivity of 0.05 at 80 °C.•The coatings on Cu substrates were thermally stable at 278 °C in air for 300 h.•The structural, chemical, and optical evolution of the coatings were investigated.•The Achilles' heel for the coatings to sustain high thermal stability was revealed.A solar selective absorber coating of CrNxOy/SiO2 was prepared on Cu (Si) substrate using DC reactive magnetron sputtering technique. The coating exhibits a high absorptivity (α) of 0.947 and a low emissivity (ε) of 0.05 at 80 °C. The spectral selectivity (α/ε) of the coating on Cu substrate is stable (0.930/0.073) even after heat-treatment at 278 °C in air for 300 h, but decreased (0.904/0.135) at 278 °C for 600 h. The determinants to govern the thermal stability were investigated by micro-Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) measurements, which reveal that the element diffusion whether throughout all the stacked layers or near the interface region, the chemical interactions adjacent to the interface, and the interface width broadening are the Achilles' heel for the solar thermal coatings to sustain high thermal stability.

In this paper, SnOx films were produced by reactive radio frequency magnetron sputtering under various oxygen partial pressure (PO) in conjunction with a thermal annealing at 200 °C afterwards. The obtained SnOx films were systematically studied by means of various techniques, including X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, spectroscopic ellipsometry, and Hall-effect measurement. The structural, chemical, and electrical evolution of the SnOx films was found to experience three stages: polycrystalline SnO phase dominated section with p-type conduction at PO ≤ 9.9%; amorphous SnO2 phase dominated area at PO ≥ 12.3%, exhibiting n-type characteristics; and conductivity dilemma area in between the above mentioned sections, featuring the coexistence of SnO and SnO2 phases with compatible and opposite contribution to the conductivity. The polycrystalline to amorphous film structure transition was ascribed to the enhanced crystallization temperature due to the perturbed structural disorder by incorporating Sn4+ into the SnO matrix. The inversion from p-type to n-type conduction with PO variation is believed to result from the competition between the donor and acceptor generation process, i.e., the n-type behavior would be present if the donor effect is overwhelming, and vice versa. In addition, with increasing PO, the refractive index decreased from 3.0 to 1.8 and the band gaps increased from 1.5 to 3.5 eV, respectively.Keywords: ellipsometry; Hall effect; Raman; reactive magnetron sputtering; SnO; SnO2; XPS; XRD;

Sol–gel derived tungsten oxide (WO3) films have been deposited by spin coating route using acetylated peroxotungstic acid (APTA) or a mixture of APTA and polyethylene glycol (PEG) dissolved in ethanol as the precursor solution, followed by thermal treatment in air. The influence of PEG additive and annealing temperature on the structural and electrochromic (EC) behavior of the films have been investigated. For films annealed at 300 °C, a porous nanocrystalline/amorphous microstructure was obtained in the WO3-PEG film, while monoclinic microstructure was formed in the pure WO3 film. Moreover, for the WO3-PEG films, the film microstructure was found to depend on the annealing temperature. Electrochemical studies indicate that the WO3-PEG film annealed at 300 °C (WP-300) exhibits superior EC properties, which produces faster switching speed (tc = 19 s, tb = 3 s),better reversibility (K = 0.97) as well as higher optical modulation (ΔT = 32% at 550 nm) and coloration efficiency (η = 22 cm2/C at 550 nm). Our results suggest that PEG addition in combination with an appropriate annealing treatment can benefit the EC properties, arising from the ease of ion diffusion within the EC material, as evident from the nanocrystallines embedded into the amorphous matrix with a porous character.

A simple, cost-effective, two-step method was proposed for preparing single-phase SnO polycrystalline thin films on quartz. X-ray diffraction (XRD) analysis demonstrated that the annealed films were consisted of polycrystalline α-SnO phase without preferred orientation, and chemical composition analysis of the single phase in nature was analyzed using X-ray photoelectron spectroscopy (XPS). Transmittance spectra in UV−vis−IR range indicated that the average transmittance of both the as-deposited and the annealed SnO thin films was up to 70%. The optical band gap decreased from 3.20 to 2.77 eV after the annealing process, which was attributed to the crystalline size related quantum size effect. Photoluminescence (PL) spectrum of the annealed film showed only a weak peak at 585 nm, and no intrinsic optical transition emission was observed. Moreover, the p-type conductivity of SnO film was confirmed through Hall effect measurement, with Hall mobility of 1.4 cm2 V−1 s−1 and hole concentration of 2.8 × 1016 cm−3.Keywords: optical band gap; p-type conductivity; quantum size effect; thin film transistor;; tin oxide

In this letter, it is proposed that the usage of Al2O3 capping layer can tremendously improve the phase stability of SnO thin films, which allows the accurate determination of the optical constants of the SnO films without the perturbation arising from impurity phases. For the SnO films, the refraction index and extinction coefficient are significantly influenced by the crystallinity. The nondirect optical bandgap of the amorphous SnO films is determined to be 2.27 eV, whereas two nondirect optical transitions are observed in the polycrystalline SnO films and the corresponding gap energies are estimated to be 0.50 and 2.45 eV, respectively.Keywords: disproportionation; oxygen chemical potential; polarizability; spectroscopic ellipsometry; tin monoxide

We report on the fabrication of bottom-gate thin-film transistors (TFTs) using indium-oxide (In2O3) thin films as active channel layers. The films were deposited on thermally grown silicon dioxide (SiO2)/n-type silicon (Si) at room temperature (RT) by radio-frequency (RF) magnetron sputtering. The effect of deposition pressure on the performance of In2O3-TFTs was investigated in detail. A significant improvement of the device performance was observed for In2O3-TFTs with the decrease of the working pressure, which is attributed to enhanced densification, better surface morphology of the In2O3 channel layers prepared at lower deposition pressure. The fabricated TFT with optimal device performance exhibited a field-effect mobility (μFE) of 31.6 cm2 V−1 s−1, a drain current on/off ratio of ∼107, a low off drain current of about 10−10 A and a threshold voltage of 7.8 V. Good device performance and low processing temperature make the In2O3-TFTs suitable for the potential applications in the transparent electronics.

•Cu/CrNxOy/SiO2 coatings were prepared for flat plate solar thermal collector.•The coating exhibited an absorptivity of 0.947 and an emissivity of 0.05 at 80 °C.•The coatings on Cu substrates were thermally stable at 278 °C in air for 300 h.•The structural, chemical, and optical evolution of the coatings were investigated.•The Achilles' heel for the coatings to sustain high thermal stability was revealed.A solar selective absorber coating of CrNxOy/SiO2 was prepared on Cu (Si) substrate using DC reactive magnetron sputtering technique. The coating exhibits a high absorptivity (α) of 0.947 and a low emissivity (ε) of 0.05 at 80 °C. The spectral selectivity (α/ε) of the coating on Cu substrate is stable (0.930/0.073) even after heat-treatment at 278 °C in air for 300 h, but decreased (0.904/0.135) at 278 °C for 600 h. The determinants to govern the thermal stability were investigated by micro-Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) measurements, which reveal that the element diffusion whether throughout all the stacked layers or near the interface region, the chemical interactions adjacent to the interface, and the interface width broadening are the Achilles' heel for the solar thermal coatings to sustain high thermal stability.

Oriented ZnO nanorod arrays and ZnO thin films were simultaneously grown on magnetron sputtered ZnO seed layers through a hydrothermal approach without any metal catalyst. The c-oriented ZnO nanorod arrays were grown on the unannealed ultrathin ZnO seed layer, while the ZnO thin films with (1 0 0) preferred orientation were grown on the annealed ultrathin ZnO seed layer. Thermodynamically preferred (0 0 2) oriented grain growth will be suppressed by the morphology changes of the ultrathin seed layer while the (1 0 0) orientation will preferentially develop instead. Photoluminescence spectroscopy results show that the UV emission peak shifts slightly to shorter wavelength with increasing the annealing temperature of the ultrathin ZnO seed layer.

A novel oxynitride semiconductor, ZnSnON, is demonstrated. The design of this material follows the reported anion control strategy (N additives) to diminish the bandgap and the electron effective mass of ZnO on the one hand, and a cation control strategy (Sn additives) to circumvent the chemical stability problems of ZnON on the other. Comparative studies are conducted on the performance and stability of ZnSnON and ZnON films and their thin-film transistors (TFTs). It is shown that ZnSnON possesses superior transport properties and enhanced operation stability simultaneously. Such amelioration is owing to multiple factors, including the amorphous/nanocrystalline mixed phase and the bonding strength increase caused by the Sn-related oxide/oxynitride dominant in the back channel region. In addition, the Sn additives in ZnON do not alter the direct bandgap character, maintaining around 1.6 eV. The ZnSnON-TFT is photosensitive in the whole visible light region with a photoresponsivity higher than 6 × 103 A W−1. Considering the high-mobility, improved operation stability, and visible light sensing capability, this semiconductor can be used in a broad array of applications such as in active-matrix imaging arrays, interactive displays, flat X-ray detectors, etc.

In this study, (001) and (101)-orientated polycrystalline SnO films were respectively fabricated. The preferred orientation conversion was observed by modifying the stoichiometry of the SnO films. It was revealed that the O-rich and Sn-rich SnO films favor (001) and (101) grain orientations, respectively. Moreover, based on the Raman selection rule and our experimental results, the 110 cm−1 Raman peak is assigned to the low-frequency Eg mode of SnO. The Raman intensity ratio between the 110 cm−1 and 210 cm−1 peak of SnO increases with the relative texture coefficient of the (101) grain orientation but decreases with that of the (001) one, demonstrating that the Raman characteristic information could be used as fingerprint recognition to mutually predict the crystallographic texture of SnO films.