Enhanced Carbon Dioxide Photoconversion Efficiency by 1D Structured Platinized TiO2 Films

A facile development of highly efficient Pt-TiO(2) nanostructured films via versatile gas-phase deposition methods is described. The films have a unique one-dimensional (1D) structure of TiO(2) single crystals coated with ultrafine Pt nanoparticles (NPs, 0.5-2 nm) and exhibit extremely high CO(2) photoreduction efficiency with selective formation of methane (the maximum CH(4) yield of 1361 μmol/g-cat/h). The fast electron-transfer rate in TiO(2) single crystals and the efficient electron-hole separation by the Pt NPs were the main reasons attributable for the enhancement, where the size of the Pt NPs and the unique 1D structure of TiO(2) single crystals played an important role.

We synthesized epitaxial titanium oxide thin films on MgO (100) using a combination of a metalorganic pulsed molecular beam and an oxygen-radical beam. At temperatures below 350°C, titanium oxide (TiO2) thin films were exclusively deposited only when an oxygen-radical beam was irradiated along with Ti(i-OC3H7)4. Above this temperature, TiO2 thin films were deposited both in the presence and absence of the oxygen-radical beam; however, the oxygen-radical beam enhanced the deposition rate as well as the crystallinity of the titanium oxide thin films.

Lead zirconate titanate (PbZrxTi1-xO3, PZT) thin films were deposited on Pt/TiOx/SiO2/Si substrate by RF-magnetron sputtering with a Pb1.2Zr0.3Ti0.7O3 target at room temperature. The Zr K-edge of PZT thin films of different crystallinities were studied by extended x-ray absorption fine structure (EXAFS) spectrum. Scans were made in fluorescence mode to monitor the structural differences between the amorphous thin films and the crystalline thin films. It was found that the local structure of the amorphous thin films was quite different from that of the crystalline thin films from the analyses of the EXAFS spectra. In the amorphous PZT thin films only one oxygen coordination shell can be found. By contrast, in the crystalline PZT thin films, the EXAFS spectrum was fitted with three shells and Zr-Pb bond was found. The oxygen coordination numbers of the amorphous and crystalline PZT thin films were same. The Zr-O bond distance of the amorphous samples were bigger than the crystalline samples. Thus, the influences of the phase transformation on the ferroelectric properties of PZT thin films were interpreted from the angle of the local chemical structures.

Infrared phonon modes and local structure of amorphous and crystalline LaLuO3 thin films

Porous crystalline covalent organic frameworks (COFs) suffer from the difficulty of forming crystalline thin films, which hinders their application in membrane devices. Here, a strategy is developed for forming highly crystalline 2D COFs thin films via unique in situ thermal evaporation followed by solvent vapor annealing. Two different COFs are selected containing 1,3,5-triformylphloroglucinol (Tp), ionic triaminoguanidine hydrochloride (TGCl), and neutral 2,2'-bipyridine-5,5'-diamine (Bpy) monomers because of their common use in energy storage devices. The results show that the condensation rate between the monomers of Tp and ionic TGCl is faster than that of Tp and Bpy during the solvent vapor annealing, which leads to a homogeneous ionic TpTGCl crystalline thin film whereas the neutral TpBpy thin film consists of crystalline islands. AFM nanoindentation revealed a low stiffness of the ionic TpTGCl thin film compared to the neutral TpBpy thin film. Using polycrystalline TpTGCl and TpBpy thin films, Zn-air batteries (ZABs) are produced by covering Zn plates with the ionic TpTGCl (TpTGCl/Zn) and neutral TpBpy (TpBpy/Zn) thin films as anodes. As produced, TpTGCl/Zn-based ZAB exhibits a long cycle life of 91 h due to the high hydroxide ion conductivity and the Zn dendrites suppression.

Tantalum oxide (Ta2O5) thin films were fabricated on Pt-coated Si, n+-Si, and poly-Si substrates by metalorganic solution deposition technique. The effects of postdeposition annealing on the structural, electrical, and optical properties were analyzed. The Ta2O5 films were amorphous up to 600 °C. A well-crystallized orthorhombic phase with strong a-axis orientation was obtained at an annealing temperature of 650 °C. The refractive index was found to increase with annealing temperature and a value of 2.08 (at 630 nm) was obtained for films annealed at 750 °C. The electrical measurements were conducted on metal–insulator–metal (MIM) and metal–insulator–semiconductor capacitors. The dielectric constant of amorphous Ta2O5 thin films was in the range 29.2–29.5 up to 600 °C, while crystalline thin films, annealed in the temperature range 650–750 °C, exhibited enhanced dielectric constant in the range 45.6–51.7. The high dielectric constant in crystalline thin films was attributed to orientation dependence of the dielectric permittivity. The dielectric loss factor did not show any appreciable dependence on the annealing temperature and was in the range 0.006–0.009. The frequency dispersion of the dielectric properties was also analyzed. The films exhibited high resistivities of the order of 1012–1015 Ω cm at an applied electric field of 1 MV/cm in the annealing temperature range of 500–750 °C. The measurement of current–voltage (I–V) characteristics in MIM capacitors indicated the conduction process to be bulk limited. The I–V characteristics were ohmic at low fields, and Poole–Frenkel effect dominated at high fields. The temperature coefficient of capacitance was in the range 52–114 ppm/°C for films annealed in the temperature range 500–750 °C. The bias stability of capacitance, measured at an applied electric field of 1 MV/cm, was better than 1.41% for Ta2O5 films annealed up to 750 °C. For a 0.15-μm-thick film, a unit area capacitance of 3.0 fF/μm2 and a charge storage density of 22.3 fC/μm2 were obtained at an applied electric field of 0.5 MV/cm.

Low temperature magnetron sputtering deposition of hydrogenated microcrystalline silicon thin films without amorphous incubation layers on glass

Nowadays, the conversion efficiency of Cu(In･Ga)Se2 (CIGS)-based solar cell already reached over 20%. CdS thin films prepared by chemical bath deposition (CBD) method are used for CIGS-based thin film solar cells as the buffer layer. Over the past several years, a considerable number of studies have been conducted on ZnS buffer layer prepared by CBD in order to improve in conversion efficiency of CIGS-based solar cells. In addition, application to CIGS-based solar cell of ZnS buffer layer is expected as an eco-friendly solar cell by cadmium-free. However, it was found that ZnS thin films prepared by CBD included ZnO or Zn(OH)2 as different phase [1]. Nakata et. al reported that the conversion efficiency of CIGS-based solar cell using ZnS buffer layer (CBD-ZnS/CIGS) reached over 18% [2]. The problem which we have to consider next is improvement in crystallinity of ZnS thin films prepared by CBD. In this work, we prepared ZnS thin films on quarts (Si02) and SnO2/glass substrates by CBD with the self-catalysis growth process in order to improve crystallinity and quality of CBD-ZnS thin films. The solution to use for CBD were prepared by mixture of 0.2M ZnI2 or ZnSO4, 0.6M (NH2)2CS and 8.0M NH3 aq. In the first, we prepared the particles of ZnS on Si02 or SnO2/glass substrates by CBD at 80℃ for 20 min as initial nucleus (1st step ). After that, the particles of ZnS on Si02 or SnO2/glass substrates grew up to be ZnS thin films by CBD method at 80℃ for 40 min again (2nd step). We found that the surface of ZnS thin films by CBD with the self-catalyst growth process was flat and smooth. Consequently, we concluded that the CBD technique with self-catalyst growth process in order to prepare the particles of ZnS as initial nucleus layer was useful for improvement of crystallinity of ZnS thin films on SnO2/glass. [1] J.Vidal et,al., Thin Solid Films 419 (2002) 118. [2] T.Nakata et.al., Jpn. J. Appl. Phys. 41(2B), L165-L167 (2002)

Photocatalytic degradation of an azo dye X6G in water: A comparative study using nanostructured indium tin oxide and titanium oxide thin films

Photo-assisted crystallization of zirconia thin films and their electrical evaluation

Four solution-processable, linear conjugated polymers of intrinsic porosity are synthesised and tested for gas phase carbon dioxide photoreduction. The polymers’ photoreduction efficiency is investigated as a function of their porosity, optical properties, energy levels and photoluminescence. All polymers successfully form carbon monoxide as the main product, without the addition of metal co-catalysts. The best performing single component polymer yields a rate of 66 μmol h−1 m−2, which we attribute to the polymer exhibiting macroporosity and the longest exciton lifetimes. The addition of copper iodide, as a source of a copper co-catalyst in the polymers shows an increase in rate, with the best performing polymer achieving a rate of 175 μmol h−1 m−2. The polymers are active for over 100 h under operating conditions. This work shows the potential of processable polymers of intrinsic porosity for use in the gas phase photoreduction of carbon dioxide towards solar fuels.

The fabrication process and resistive switching properties of flexible single crystalline LiNbO3 (LN) thin films are reported in this paper. Single crystalline LN thin films are transferred onto polyimide (PI) substrate by crystal‐ion‐slicing (CIS) technique using benzocyclobutene (BCB) as bonding layer. Low energy Ar+ irradiation is carried out to introduce a layer with high concentration oxygen vacancies. Uniform and stable resistive switching behaviors are observed in different memristor cells on the same thin film, which can be attributed to the single crystalline properties of the fabricated LN thin films. The on/off ratio is almost the same even when the LN thin film is bended either to different radii or thousand times. Thus, based on CIS technique and Ar+ irradiation, the fabrication method of flexible single crystalline thin films for flexible memristor is established. These results indicate that single crystalline LN thin film on PI substrate is a promising candidate structure for flexible memristor devices. A novel conduction model combined filamentary mechanism and Schottky emission mechanism is proposed to explain the resistive switching behavior.

Metal-based nanoparticles with antimicrobial activity are gaining a lot of attention in recent years due to the increased antibiotics resistance. The development and the pathogenesis of oral diseases are usually associated with the formation of bacteria biofilms on the surfaces; therefore, it is crucial to investigate the materials and their properties that would reduce bacterial attachment and biofilm formation. This work provides a systematic investigation of the physical-chemical properties and the antibacterial activity of TiO2 thin films decorated by Ag and Au nanoparticles (NP) against Veillonella parvula and Neisseria sicca species associated with oral diseases. TiO2 thin films were formed using reactive magnetron sputtering by obtaining as-deposited amorphous and crystalline TiO2 thin films after annealing. Au and Ag NP were formed using a two-step process: magnetron sputtering of thin metal films and solid-state dewetting. The surface properties and crystallographic nature of TiO2/NP structures were investigated by SEM, XPS, XRD, and optical microscopy. It was found that the higher thickness of Au and Ag thin films results in the formation of the enlarged NPs and increased distance between them, influencing the antibacterial activity of the formed structures. TiO2 surface with AgNP exhibited higher antibacterial efficiency than Au nanostructured titania surfaces and effectively reduced the concentration of the bacteria. The process of the observation and identification of the presence of bacteria using the deep learning technique was realized.

Influence of substrates and e-beam evaporation parameters on the microstructure of nanocrystalline and epitaxially grown Ti thin films

Nanopillar crystalline indium tin oxide (ITO) thin films were deposited on soda-lime glass substrates by radio frequency (RF) magnetron sputtering under the power levels of 100 W, 150 W, 200 W and 250 W. The preparation process of thin films is divided into two steps, firstly, sputtering a very thin and granular crystalline film at the bottom, and then sputtering a nanopillar crystalline film above the bottom film. The structure, morphology, optical and electrical properties of the nanopillar crystalline ITO thin films were investigated. From X-ray diffraction (XRD) analysis, the nanopillar crystalline thin films shows (400) preferred orientation. Due to the effect of the bottom granular grains, the crystallinity of the nanopillar crystals on the upper layer was greatly improved. The nanopillar crystalline ITO thin films exhibited excellent electrical properties, enhanced visible light transmittance and a highly infrared reflectivity in the mid-infrared region. It is noted that the thin film deposited at 200 W showed the best combination of optical and electrical performance, with resistivity of 1.44 × 10−4 Ω cm, average transmittance of 88.49% (with a film thickness of 1031 nm) and IR reflectivity reaching 89.18%.