Top TiO2 Layer Research Articles

Full-Color and Anti-Counterfeit Printings with All-Dielectric Chiral Metasurfaces

Structural color is anticipated to replace pigmented or chemical color due to its superior saturation, resolution, environmental friendliness, and longevity. We achieve a full-color gamut of structural colors and anti-counterfeit functions by an all-dielectric chiral metasurface consisting of half-gammadion-shaped resonators embedded in PMMA and a top TiO2 layer on quartz coated with an ITO layer. The prominent resonance peaks of this embedded chiral metasurface under the cross-polarization condition, which are provided by the polarization conversion features of the chiral structure, lead to extremely saturated structural colors. The color phase mainly depends on the structure’s period, opening up a full-color range well beyond sRGB. Especially, we demonstrate a star with hidden information of the letter “A” and the Chinese word “李龙杰” by taking advantage of the difference in the color phase change under different polarization conditions to decode the information, thus realizing the anti-counterfeiting function. Our proposed embedded chiral metasurface provides dual-function structural colors and is highly promising for micro-display, nanoprinting, anti-counterfeiting, data storage, and information encryption.

Investigation of a Multi-Layer Absorber Exhibiting the Broadband and High Absorptivity in Red Light and Near-Infrared Region.

In this study, an absorber with the characteristics of high absorptivity and ultra-wideband (UWB), which was ranged from the visible light range and near-infrared band, was designed and numerically analyzed using COMSOL Multiphysics® simulation software (version 6.0). The designed absorber was constructed by using two-layer square cubes stacked on the four-layer continuous plane films. The two-layer square cubes were titanium dioxide (TiO2) and titanium (Ti) (from top to bottom) and the four-layer continuous plane films were Poly(N-isopropylacrylamide) (PNIPAAm), Ti, silica (SiO2), and Ti. The analysis results showed that the first reason to cause the high absorptivity in UWB is the anti-reflection effect of top TiO2 layer. The second reason is that the three different resonances, including localized surface plasmon resonance, the propagating surface plasmon resonance, and the Fabry-Perot (FP) cavity resonance, are coexisted in the absorption peaks of the designed absorber and at least two of them can be excited at the same time. The third reason is that two FP resonant cavities were formed in the PNIPAAm and SiO2 dielectric layers. Because of the combination of the anti-reflection effect and the three different resonances, the designed absorber presented the properties of UWB and high absorptivity.

Surface and interface properties of TiO2/CuO thin film bilayers deposited by rf reactive magnetron sputtering

Thin film bilayers of TiO2/CuO with intentionally varied thickness of the top layer of TiO2(25–150 nm) were grown by means of sequential rf magnetron reactive sputtering from Cu and Ti metallic targets in a flow rate-controlled Ar + O2 gas mixture. XRD diffraction in GID configuration, SEM top and cross-sectional images, EDS combined with SEM, XRR profiles, UV–VIS-NIR spectrophotometry and synchrotron soft radiation XAS in TEY mode were used to characterize crystal structure, morphology, the mode of growth, chemical composition, density and roughness as well as the optical and electronic properties of the synthesized thin film bilayers. CuO bottom layer turned out to crystallize in a monoclinic structure while TiO2 top layer remained amorphous. Film roughness of CuO decreased from about 12 nm with the increasing thickness of TiO2 thin film to about 1–2 nm. X-ray absorption spectroscopy demonstrated a presence of Cu+ and Cu2+ in TiO2 top layer of TiO2/CuO heterostructure. The photoelectrochemical measurements revealed that thin film bilayers of TiO2/CuO behaved as photocathodes in the process of water splitting. The photocurrent density was found to be an increasing function of the top TiO2 layer thickness.

Effect of Configuration on the Photocatalytic Activity of AgNPs-TiO2 System

This paper studies the effect of the configuration of silver nanoparticles (AgNPs)-TiO2 on the visible-light-driven photocatalytic activity (PA). Three configurations were fabricated by vacuum thermal deposition: configuration I, AgNPs deposited on the surface of TiO2 thin films; configuration II, AgNPs deposited on a glass and covered by TiO2 thin films; and configuration III, AgNPs deposited on the surface of TiO2 thin films and covered by TiO2. The PAs of the three configurations were studied and compared. Our study indicates that configuration II is the most cost-efficient one, while configuration III could obtain the highest visible light-induced PA. The maximum of PA could be achieved when the top layer of TiO2 is less than 2 nm. The mechanisms were discussed from three aspects, the influence of TiO2 thickness on the localized surface plasma resonance (LSPR) of AgNPs, the separation, and the transportation of hot carriers. By this study, the most effective way to make use of the PA of TiO2-AgNPs was scientifically searched out.

Plasmon resonance effect caused by gold nanoparticles formed on titanium oxide films

Gold nanoparticles were distributed by spray pyrolysis technique on bare glass substrates and on glass covered by titanium dioxide thin films grown by atomic layer deposition, and were embedded in titanium dioxide layers. Plasmonic absorption was detected in the visible spectral range. The particles deposited on glass and on 80nm thick titanium dioxide film resulted in appearance of an absorption band peaking at 550nm. The plasmonic absorption maxima shifted towards longer wavelengths after embedding the particles into a top TiO2 layer. Atomic layer deposition of TiO2 films assisted in fixing and separating the metal particles on the surface, without destructive influence on the plasmonic behaviour.

Band Edge Engineering in BiVO4/TiO2 Heterostructure: Enhanced Photoelectrochemical Performance through Improved Charge Transfer

The efficient separation of photogenerated electron–hole pairs and stability against corrosion are critical preconditions for a photoelectrode to achieve a high photoelectrochemical performance. In this work it is shown how both criteria can be met by employing a heterostructure of bismuth vanadate (BiVO4) and titanium dioxide (TiO2) as the photocatalyst. Using electronic structure calculations, an alteration of the band alignment is predicted at the heterojunction from type I to type II by hydrogen treatment of the top TiO2 layer. Guided by this idea, we have fabricated heterostructures of BiVO4 and TiO2 and studied the effect of hydrogen treatment. The achieved band engineering results in a significant improvement in photocurrent density, up to 4.44 mA cm–2 at 1.23 V vs RHE, and a low onset potential, −0.14 V vs RHE, under visible light illumination. The enhanced photoelectrochemical performance originates in facilitated hole transport to the electrode surface and enhanced photoabsorption in the TiO2 la...

TiO2(R)/VO2(M)/TiO2(A) multilayer film as smart window: Combination of energy-saving, antifogging and self-cleaning functions

A novel Multifunctional TiO2(R)/VO2(M)/TiO2(A) multilayer film is designed and deposited by medium frequency reactive magnetron sputtering. An exciting fact that the antifogging, self-cleaning and energy-saving effects are integrated into the multilayer film could offer significant potential for wider applications of smart window. Thereinto, the bottom TiO2 layer with rutile phase plays an important role in the formation of monoclinic phase of VO2 layer and serves as an antireflection layer. Then, the VO2 layer with dominant monoclinic phase performs an automatic solar/heat control for saving energy. Finally, the top TiO2 layer containing a mixed phase of anatase and rutile displays the remarkable photocatalytic and photoinduced properties. According to optical tests, the multilayer film shows satisfactory optical properties with an excellent solar regulation efficiency (ΔTsol=10.2%) and an applicable luminous transmittance (Tlum-L=30.1%) in a low-temperature state. In addition, the multilayer film implements a photoinduced super-hydrophilicity (~ 2.1°) through UV-irradiation, resulting in an antifogging effect. A high level of photocatalytic activity is detected on the surface of the multilayer film through degradation of stearic acid and rhodamine B.

Enhanced normal-direction excitation and emission of dual-emitting quantum dots on a cascaded photonic crystal surface.

Large normal-direction excitation and emission of dual-emitting quantum dots (QDs) are essential for practical application of QD sensors based on the ratiometric fluorescence response. We have numerically demonstrated an all-dielectric four-layer cascaded photonic crystal (CPC) structure (alternating TiO2 and SiO2/SU8 layers with two dimensional nanoscale patterns in each layer) which is capable of providing normal-direction high Q-factor leaky modes at excitation wavelengths of QDs and two low Q-factor leaky modes coinciding with the two emission peaks of a dual-emitting QD. Normal-direction excitation and far-field emission of the dual-emitting QDs are enhanced significantly when QDs are distributed on/in the top TiO2 layer of the CPC structure, especially in the spatial distribution areas of the resonant leaky modes. QDs can be positioned differently depending on the applications. Positioning QDs on the top TiO2 layer will improve the signal-to-noise ratios of QD biomedical/chemical/temperature sensors, while embedding QDs in the top TiO2 layer will increase the light extraction from the QD light emitting device, making our CPC a versatile optical coupling structure. Our CPC-QD structure is experimentally feasible and robust against the parameter perturbation in real fabrication.

Layered co-sensitization for enhancement of conversion efficiency of natural dye sensitized solar cells

This paper describes a double layered co-sensitization in dye sensitized solar cells (DSSCs) by using natural pigments from Ixora flower (Ixora sp. (Rubiaceae)) and the outer dark purple skin of ‘Kembayau’ (Canarium odontophyllum) fruit. UV–vis absorption data revealed that both dyes were anthocyanins. Co-sensitization was done by first adsorbing the dye from C. odontophyllum into TiO2 electrode by dipping, and then by removing adsorbed dye of the top layer of TiO2 using a de-sorption solution before the Ixora sp. dye was allowed to adsorb. Power conversion efficiency of the co-sensitized solar cell was 1.55%. The conversion efficiencies of DSSCs sensitized with Ixora sp. , C. odontophyllum and the mixture of both dyes (1:1) were 0.96%, 0.59% and 1.13% respectively. The superior conversion efficiency achieved by layered co-sensitization is attributed to the high adsorption capacities of Ixora sp. and C. odontophyllum, and the homogeneous monolayer adsorption of Ixora sp. as revealed by Freundlich and Langmuir adsorption isotherms.

TiO2 Coating for SnO2:F Films Produced by Filtered Cathodic Arc Evaporation for Improved Resistance to H+ Radical Exposure

Titanium dioxide thin films were deposited by filtered cathodic arc evaporation (FCAE) from a Ti target in an oxygen atmosphere onto (a) fluorine-doped tin oxide substrates SnO2:F (FTO) and (b) glass microscope slides. The growth rate calculated from film thickness profilometry measurements was found to be approximately 0.8 nm/s. The films were highly transparent to visible light. x-Ray photoemission spectroscopy analysis of the Ti 2p electron binding- energy shift confirmed the presence of a TiO2 stoichiometric compound. The results for the root-mean-square (RMS) surface roughness of the films deposited onto FTO substrates evaluated by atomic force microscopy suggested nanostructured film surfaces. When exposed to hydrogen plasma, TiO2 films revealed insignificant changes in the optical spectra. The initial sheet resistance of the SnO2:F layer was 14 Ω/sq. The deposition of the top TiO2 layer (45 nm thick) over the FTO electrode resulted in an increase of the sheet resistance of 2 Ω/sq. In addition, the sheet resistance of the double-layer FTO/TiO2 transparent conductive oxide (TCO) electrode increased by 1 Ω/sq as a result of H+ plasma exposure. Regardless of the TiO2 film’s low conductivity, a thin protective layer could be coated onto FTO films (presumably 15 nm thick) due to their high transparency, offering high resistance to aggressive H+ plasma conditions. In this paper we show that ∼50-nm-thick TiO2 coating on FTO films provides sufficient protection against deterioration of transparency and conductivity due to hydrogen radical exposure.

Photocatalysis of Ag-Loaded TiO2 Nanotube Arrays Formed by Atomic Layer Deposition

Anodic aluminum oxide (AAO) film was used as a template to fabricate TiO2 nanotubes. TiO2 was deposited into the AAO pores by atomic layer deposition (ALD) at 100 °C. After the top layer of TiO2 and the AAO template were removed, an ordered array of TiO2 nanotubes remained on the substrate. The tube thickness increased with the cycle number of ALD. The UV–vis absorption spectra of the samples exhibited a red shift as the thickness increased or after annealing. The photocatalytic activity increased with the increase in the wall thickness of TiO2 nanotubes. With deposition of Ag nanoparticles on the tubes, the nanoparticles could act as an electron trapper to slow the electron–hole recombination rate, and thus enhance the efficiency of photodecomposition of methyl orange.

Charge transfer and re-distribution in the TiO2-SrTiO3 hetero-structure

This work examined the charge density distribution in the TiO2-SrTiO3 hetero-structure using thermoelectric data reported in the literature. The first part of our work was to identify the equation necessary to extract charge densities. Our findings suggested that the observed thermoelectric power was best described by an equation applicable to a metal. Together with a distributed model that accounted for the layered structure, we computed the charge densities in the different layers. As observed, the charge density in the SrTiO3 substrate was high (> 1024 m−3) nonetheless in agreement with the value extracted from the depth profile measurement. Proportionally, the interface charge density was also very high (~ 1028 m−3). Using these values, we computed the "effective" charge spread from the sheet conductance data, which was of the order of hundreds of microns. We had found no evidence that such charge spread could have originated from the interface and tended to believe that they were linked to oxygen vacancies embedded in the substrate. This was confirmed by a reduced charge spread when the top TiO2 layer had been removed. In general, we showed that the thermoelectric power and the power factor were dominated by the properties of the substrate.

Synergistic effect of TiO2 and iron oxide supported on fluorocarbon films: Part 2: Long-term stability and influence of reaction parameters on photoactivated degradation of pollutants

The degradation of hydroquinone (HQ) and nalidixic acid (NA) mediated by TiO2 and iron oxide immobilized on functionalized polyvinyl fluoride films (PVFf–TiO2–Fe oxide) in the presence of H2O2 under simulated solar light has been examined. The results show that the contribution of homogeneous photo-Fenton oxidation to the initial mineralization process was low. The degradation rates were not dependant of initial pH. Heterogeneous photocatalytic activity of PVFf–TiO2–Fe oxide was enhanced by increasing temperature, NaCl addition and by long-term utilization.The PVFf–TiO2–Fe oxide surface was characterized by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) at different states of utilization. Correlations between the catalyst surface composition and degradation kinetics are discussed. Long-term stability evaluated by repetitive pollutant degradations was outstanding. The presence of TiO2 seems to (i) limit contact between polymer film and highly reactive radicals in the solution and (ii) act as a charge trap. Moreover, during the photocatalysis mediated by PVFf–TiO2–Fe oxide, some leaching of supported iron increased the amount of the top TiO2 layer exposed to the light increasing the synergistic effects between the two oxides leading to enhanced pollutant degradation.

PHOTO-CATALYTIC TRANSPARENT HEAT MIRROR FILM TiO2/TiN/TiO2

Transparenet heat mirror thin films, having high transmittance in the visible region and high reflectance in the infrared region. TiO/TiN/TiO2 films prepared D.C reactive magnetron sputtering method on glass substrates, play role as transparent heat mirror. Besides, the top TiO2 layer has both photo-catalytic and anti-reflective properties. However, st ong thickness dependence of top layer on catalytic properties is a problem need to solve. The experiment shows optimum thickness in order to have good catalytic properties is above 350 nm. This report, we found relationship among thicknesses of films through calculating and experiment. Films prepared, have both catalytic and transparent heat mirror properties with the bottom Tio, layer thickness of 40-300 nm, the middle TiN layer thickness of 16-22 nm and the top TiO2 layer of above 350 nm.

TiO2/TiN/TiO2 heat mirrors by laser ablation of single TiN target

Titanium oxide (TiO2) and titanium nitride (TiN) multilayered films grown by pulsed laser deposition (PLD) technique have been tested as a heat mirror, which have a high transmittance in the visible region and a high reflectance in the infrared. Three layer TiO2/TiN/TiO2 heat mirrors were grown on Corning glass substrates ablating single TiN target. Switching of TiO2-to-TiN layers composition was achieved by changing gas atmosphere (oxygen-to-nitrogen). Grown TiO2/TiN/TiO2 heat mirrors are highly transparent in visible (above 60% at 525nm), opaque in infrared (10% at 2600nm) and in the range from 400 nm to 2600 nm they possess almost the same properties as films prepared using two targets: TiO2 and TiN. XPS confirms similarity of chemical composition of multilayered TiO2/TiN films prepared by single TiN and two TiO2 and TiN targets techniques. Furthermore, multifunctional self cleaning properties of TiO2/TiN heat mirrors are expected through the precise control of the composition of the top TiO2 layer operating as a photocatalyst.

Effects of titanium nitride coatings on surface and corrosion characteristics of Ni-Ti alloy.

The structure of a titanium nitride film coated by arc ion plating on a Ni-50Ti shape memory alloy was characterized by X-ray photoelectron spectroscopy (XPS). The corrosion behavior of the titanium nitride-coated Ni-50Ti alloy was examined in 0.9% NaCl solution by potentiodynamic polarization measurements and a polarization resistance method. XPS spectra showed that the titanium nitride film consisted of three layers, a top layer of TiO2, a middle layer of TiNx (x > 1), and an inner layer of TiN. The passive current density for the titanium nitride-coated alloy was approximately two orders of magnitude lower than that of the polished alloy in the potential range from the free corrosion potential to +500 mV (vs. Ag/AgCl). Pitting corrosion associated with breakdown of the coated film occurred above this potential. The polarization resistance data also indicated that the corrosion rate of the titanium nitride-coated alloy at the free corrosion potential (+50-+100 mV) was more than one order of magnitude lower than that for the polished alloy.