Dioxide Films Research Articles

Ultra-sensitive humidity sensing based on Coherent perfect absorber-lasing system

Abstract As a singularity in non-Hermitian physics, coherent perfect absorber-lasing (CPAL) point theoretically has an infinite quality factor and can detect small perturbations, so it has potential applications in ultra-sensitive sensors. However, in the radio frequency field, due to deviations in actual components, the system will deviate from the CPAL point and the performance will degrade significantly (the output coefficient amplitude is only 30 dB). At the same time, actual sensing research is also very lacking. Based on these, we demonstrate a CPAL-based sensor system that increases its output coefficient amplitude to 60dB. When using the lasing state as the sensing mode, it has a capacitance detection accuracy of 10 fF. Then a high-frequency capacitive humidity sensor based on polyaniline/graphene oxide/titanium dioxide film is designed. The heterojunction formed between these materials increases the number of active sites for adsorbing water molecules. With the ultra-high capacitance detection accuracy of the CPAL sensor system, it is finally able to distinguish a 1% relative humidity change at 20%RH (corresponding to a 20 fF capacitance change, or a 1.63 dB output coefficient change), showing potential sensing application prospects.

Investigation of the Atomic Layer Deposition of the Titanium Dioxide (TiO2) Film as pH Sensor Using a Switched Capacitor Amplifier

The electrical and chemical properties of the titanium dioxide (TiO2) coated spirals grown by the atomic layer deposition (ALD) technique in two different temperatures of 150 °C and 300 °C are studied. The thickness of the TiO2 layers studied are 20, 40, and 80 nm. A switched capacitor amplifier is used to investigate the pH response and the capacitance of the samples. It is found that the performance of the TiO2 samples depends on either the thickness or the deposition temperature due to the differences in the physical properties of the oxide layer such as surface roughness and film density. The high temperature samples are more crystalline, whereas the low temperature samples are more amorphous. Since there is a low pass filter effect in the electrolyte–sample interface, the TiO2 coated samples show the better response to the pH change for the high temperature samples as the sensor surface area for binding the hydrogen ions is larger and the charge transfer resistance is smaller. Furthermore, more roughness on the surface can be obtained by increasing the thickness, which reduces the charge transfer resistance. In this study, the 80 nm sample deposited at 300 °C gives the best pH response of 40 mV/pH.

Hierarchical-Morphology Metal/Polymer Heterostructure for Scalable Multimodal Thermal Management.

The cooling and heating energy consumption of buildings poses a serious threat to the energy supply and increases greenhouse gas emissions, thus adversely impacting global warming and the long-term climate change trends. Here, inspired by the structure of the louver, this work demonstrates a multimodal device that integrates radiative cooling, natural lighting, and solar heating to deal with the grand challenge of building energy consumption. The blades integrate a selective radiative cooling material with a solar heating material. The selective radiative cooling material (solar reflectance ∼97%, selective emittance ∼0.82 in the 8-13 μm waveband) combines a solar reflective melt-blown polypropylene film and a solar transparent mid-infrared emitter polyethylene/silicon dioxide film. In addition, the heating material (solar absorptance ∼91%, thermal emittance ∼0.04) is zinc (Zn) film deposited with copper (Cu) nanoparticles, based on the Cu-Zn galvanic-displacement reaction. Hence, by rotating the blades, the conversion of radiative cooling, solar heating, and natural lighting functions can be realized. In the daytime, the multimodal device displays a subambient temperature of 4 °C, a superambient temperature of 2 °C, and a superambient temperature of 5 °C for the cooling mode, transmitting mode, and solar heating mode, respectively. On the basis of the energy-savings simulation, integrating these modes and dynamic converting these modes in the corresponding climate could save ∼746 GJ in the contiguous United States for one year (38% of the baseline energy consumption), which is equivalent to ∼147 tons of carbon dioxide emission reduction. Because of its excellent multimodal thermal management performance, this multimodal device will push forward the transformative change of building thermal management toward decarbonization and sustainability and being more green.

Structural and optical properties of TiO2:NiO nanoparticles thin films prepare by chemical spray pyrolysis

The properties of structural and optical of pure and doped nano titanium dioxide (TiO2) films, prepared using chemical spray pyrolysis (CPS) technique, with different nanosize nickel oxide (NiO) concentrations in the range (3-9)wt% have been studied. X-Ray diffraction (XRD) technique where using to analysis the structure properties of the prepared thin films. The results revealed that the structure properties of TiO2 have polycrystalline structure with anatase phase. The parameters, energy gap, extinction coefficient, refractive index, real and imaginary parts were studied using absorbance and transmittance measurements from a computerized ultraviolet visible spectrophotometer (Shimadzu UV-1601 PC) in the wavelengths range (300-800)nm. Optical properties of TiO2 affected by the adding of NiO impurity where the transmittance increased as NiO concentration increased but with more adding the transmittance returned to decrease again. It was found the extinction coefficient, refractive index, real and imaginary parts values decreased with increasing doping percentage up to 7% and then increases occur one more again at 9%. Energy gap values increased after doping with NiO where the values lies in the range was 3.31 to 3.51 eV .

Optical Forces on an Oscillating Dipole Near VO2 Phase Transition

We investigate optical forces on oscillating dipoles close to a phase change vanadium dioxide (VO2) film, which exhibits a metal-insulator transition around 340 K and low thermal hysteresis. This configuration emulates the interaction between an illuminated nanosphere and an interface and we employ a classical description to capture its important aspects. We consider both electric and magnetic dipoles for two different configurations, namely with the dipole moments parallel and perpendicular to the VO2 film. By using Bruggeman theory to describe the effective optical response of the material, we show that the thermal hysteresis present in the VO2 transition clearly shows up in the behavior of optical forces. In the near-field regime, the force on both dipoles can change from attractive to repulsive just by heating (or cooling) the film for a selected frequency range. We also verified that the optical forces are comparable to the Casimir-Polder force in a similar system, revealing the possibility of modulating or even changing the sign of the resultant force on an illuminated nano-object due to the presence of a thermochromic material. We hope that this work contributes to set the grounds for alternative approaches to control light-matter interactions using phase-change materials.

Application of Nano-coating and Chitosan Combination Films on Cantaloupe Preservation.

Fresh-cut cantaloupe faces several quality challenges as an increase of decay rate, browning, respiration and other changes which can reduce the shelf life. Nano-coating combination films as chitosan-nano-silicon dioxide and chitosan-nano-titanium dioxide can extend the shelf life of cantaloupe pieces. Cantaloupes were classified into four sets, Control (C), Chitosan (CTSN), Chitosan-Nano-Silicon Dioxides (CTSN/NSD) and Chitosan-Nano-titanium Dioxide (CTSN/NTD). Coated cantaloupe pieces had the best browning activity of polyphenol oxidase (PPO) (0.26 U/min/g) and the lowest water activity (Aw) (0.89) by chitosan-nano-silicon dioxide films. Chitosan-nano-titanium dioxide films could maintain weight loss (0.93%) and color pigments for L* value. It worked effectively against lipid peroxidation (MDA) (0.15 nmol g-1), Peroxidase Activity (POD) (3.92 U/min/g) and microbial contaminations (6.44 log CFU g-1). Both nano-coating films improved some chemical parameters as Titratable Acidity (TA), Soluble Solid Content (SSC) and pH. Nano-coatings films techniques were recommended for cantaloupes preservation methods.

A Highly Efficient Visible Absorber Coating on a Curved Substrate

In this study, we propose and fabricate a perfect absorber on a planar substrate using alternate silicon dioxide and ultrathin metallic lossy chromium (Cr) films. Furthermore, we transfer the absorber to a curved substrate via an optimization design of symmetric structures. The absorber exhibits a highly efficient absorption and large incident-angular tolerance characteristics in the whole visible region. We investigate each layer contribution to the absorption theoretically, and find that ultrathin (~5 nm) lossy Cr films play a dominant absorptive role. Using the effective interface method, we calculate the phase difference on the lossy Cr front surface. It is close to the destructive interference condition, from which we clarify why the proposed structures can produce a highly efficient absorption.

The Preparation and Characterization of SiO2 Films by Spray Coating Technique for Radiative Cooling Glass Application

Abstract Radiative cooling glass is a new type of energy saving glass products that can prevent incoming heat flux and UV light through the window and transport heat from inside to outside the building by transforming into transparency windows wavelength (TWW). TWW is the wavelength from 8 to 13 microns that is called mid-infrared region (MIR) This MIR region does not interact with the atmosphere and can penetrate to space directly. Therefore, the radiative cooling glass is not only able to save energy in buildings, but it also reduces urban heat island effect. Silicon dioxide (SiO2) film is one component in radiative cooling glass that is employed as an absorption layer to absorb the MIR wavelength and transfer to other layers. This study investigates surface morphology and optical properties of SiO2 film on glass substrate at various coating conditions. A mixture solution of tetraethyl orthosilicate (TEOS), DI water and ethanol were sprayed through the nozzle with different concentration and volume at ambient atmosphere. Optical microscope results show the higher concentration of TEOS gives the rougher surface of SiO2 film due to formation and accumulation of SiO2 particles. However, UV-Vis spectroscopy results show that concentration of TEOS and thickness of the SiO2 film do not influence on percent transmittance of the SiO2 films

Photocatalytic property of polyester fabrics coated with Ag/TiO2 composite films by magnetron sputtering

The Silver/Titanium dioxide film (Ag/TiO2) composite films prepared by two different magnetron sputtering methods were deposited on textile substrates using the characteristics of nano-Ti films oxidized easily in the air. The microstructures and the photocatalytic property of Ag/TiO2 composite films deposited on textile substrates were analyzed, and compared with that of TiO2/Ag composite films also deposited on textile substrates. The experimental results indicated that the Ag film and the TiO2 film were uniformly distributed in layers on the surface of the fabrics. The surface microstructures of Ag/TiO2 composite films deposited on the surface of fabrics was even and dense and was smoother than that of TiO2/Ag composite films. The photocatalytic activity of fabrics coated with TiO2 film prepared by DC magnetron sputtering method was much lower than that of TiO2 films prepared by DC and RF reactive sputtering method because of the structure of TiO2 films formed by oxidation in the air. Due to the effect of the Ag film, the photocatalytic activity of Ag/TiO2 composite films and TiO2/Ag composite films deposited on the fabrics were all improved, and the photocatalytic activity of Ag/TiO2 composite films was the highest, and that of TiO2 films was the smallest.

Hybrid single-layer/bulk tungsten diselenide transistors by lithographic encoding of material thickness in chemical vapor deposition

Schottky-like barriers are an important limitation of the performance of single-layer transition metal dichalcogenide (TMD) transistors; because of the small number of charge carriers in a 2D semiconductor, the screening of metal contacts is inefficient leading to large depletion zones and enhanced reduction of performance compared to conventional bulk Schottky Barriers. Here we demonstrate that lithographic pre-patterning of a growth substrate prior to chemical vapor deposition of a TMD film can shape the TMD material into nanoscale hybrid 2D/3D structures whose bulk-like (3D) portion can be used for metal contacts and efficient charge injection into the single-layer (2D) areas which serve as transistor channels with excellent mobilities and on-off ratios. We observe mobilities of nearly 100 cm2 V−1 s−1 with an on/off ratio >105 for bottom-gated devices (through 300 nm of oxide) at realistic operation temperatures near 100 °C using comparatively long channels (>5 microns) and absent other contact optimization. Our process involves lithographic patterning of a hafnium (IV) dioxide film onto the SiO2/Si substrate prior to TMD growth. Bulk-like 3D WSe2 is observed to grow at the location of the hafnia, while 2D single-layer material is grown in regions of bare SiO2. Systematic evaluation of transport data allows us to extract Schottky barrier heights and other fundamental properties of our hybrid devices.

Study on the chemical bond structure and chemical stability of N doped into TiO 2 film by N ion beam implantation

Titanium dioxide (TiO2) film was deposited by DC pulse magnetron sputtering technique. The surface of TiO2 film was implanted by N ion beam at room temperature and N doped TiO2 (N-TiO2) film was obtained. X-ray diffractometer result showed that with the increase of sputtering power, the crystal structure of TiO2 film changed from amorphous to anatase polycrystalline structure. Transmission electron microscopy result revealed that nanoscale clusters existed in amorphous TiO2 film. The bandgap of TiO2 film was about 3.28 ± 0.05 eV. X-ray photoelectron spectroscopy results revealed that N ion was doped into TiO2 film as Ti–N and Ti–NO bonds. With increasing TiO2 film crystallinity, N atom-percent and ratio of Ti–N to Ti–NO decreased and increased, respectively. TiO2 film deposited with 900 W in sputtering power, N atom-percent decreased to 6.6 at.% and ratio of Ti–N to Ti–NO increased to 0.81:1. The bandgap of N-TiO2 film was about 3.02 ± 0.07 eV. N atom-percent and ratio of Ti–N to Ti–NO kept at 2.73 ± 0.26 at.% and (0.87 ± 0.03):1 for all annealed N-TiO2 films. The bandgap of annealed N-TiO2 film was about 3.16 ± 0.03 eV. So, the crystallinity of TiO2 film was one of most important parameters, which influenced the chemical bond structure and chemical stability of N in TiO2 films.

Heteroepitaxial growth and characterization of monocrystal anatase TiO2 films on epi-GaN (0001)/sapphire substrates

Monocrystal anatase titanium dioxide (a-TiO2) films have been deposited on epi-GaN (0001)/sapphire substrates by the metalorganic chemical vapor deposition (MOCVD) method with the substrate temperature varied from 550 to 700 °C. The structural analyses showed that the film deposited at 650 °C was pure a-TiO2 monocrystal with the best crystalline quality. The epitaxial relationship between the film and GaN epilayer was determined as a-TiO2 (001)‖GaN (0001) with a-TiO2 [110]‖GaN 〈 $$ \bar{1}100 $$ 〉. The elemental composition and proportion were studied by the X-ray photoelectron spectroscopy (XPS) method, which proved the deposited film approximated stoichiometric TiO2. The films showed excellent transparency of ~90 % in the visible range with an optical band gap of 3.33 eV obtained for the 650 °C-deposited sample.

Liquid Phase Deposited TiO<sub>2</sub> Films on Stainless Steel Mesh for Corrosion Resistance Application

Liquid phase deposition (LPD) method was used to prepare corrosion protective titanium dioxide (TiO2) film coatings on the stainless steel mesh which is composed of steel wires at a relatively low temperature (80°C). The as-prepared TiO2 coated samples were characterized using X-ray diffractometry (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectra (EDX). It was observed that the TiO2 film coatings could conformally coat the stainless steel wires which play a significant role in the corrosion resistance. The corrosion resistance of the samples was evaluated using Tafel polarization curves in a three-electrode electrochemical examination system. The TiO2 deposited samples all showed a certain improvement of corrosion resistance. Compared with the sample prepared in the acid condition (PH=3.7), the low alkaline (PH=9.5) sample could provide better corrosion protection which could increase the corrosion potential (Ecorr) from-0.53 V to-0.17 V.

Transparent light-guided plates based on TiO2/Rhodamine6G composite thin films

Abstract Transparent light-guided plates for solar cell application from nano-titanium dioxide (TiO2), rhodamine 6G (R6G) and poly methyl methacrylate (PMMA) composite films were prepared by spin coating technique on glass substrates. Effects of the annealing temperatures and times on the formation of the TiO2 crystalline film that acted as an initial model for the light-scattered layer in solar concentrators were investigated. Physical and morphological properties of the TiO2 film were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and atomic force microscope (AFM). After the annealing process, TiO2 films obviously formed in the anatase phase with the enlarged crystallite size and the high rough surface by the increase of the annealing temperature and the treating time. Meanwhile, the optical properties of the TiO2 thin films were analyzed via a UV–Vis spectrophotometer. The transparency of the film was significantly affected by the annealing temperature and the aging time. Moreover, the light scattering performance of the TiO2 layer cooperated with Rhodamine6G in the PMMA matrix as the preliminary model of light-guide plate was investigated by fluorescence spectra. Strong light emission from the light-guide plate could be significantly enhanced by the existence of the TiO2 crystalline layer acting as the scattering film. Optimized performance of the planar light-guide plate incorporated with Rhodamine6G dye and the light-scattered TiO2 layer was obtained from the film annealed at 500 °C for 5 h.

Formation of Insulating Oxide Films with Hydrolysis Reactions of Alkoxide Precursors in Supercritical Fluid CO2: Chemistry, Morphology, Characterization and Film Thickness

ABSTRACTInsulating silicon dioxide (SiO2) films can be produced by hydrolysis of metal alkoxide tetraethylorthosilicate (TEOS) in the presence of an acid catalyst in supercritical fluid CO2 (sc-CO2). In this study, SiO2 films are formed on different substrates using TEOS as a source of silicon, and acetic acid (HAc) as a catalyst. Water required for the hydrolysis reaction is from in situ generation of esterification and condensation reactions involving HAc and the alcohol produced. The acid catalyzed deposition reaction actually starts at room temperature but produces decent films in sc-CO2 at moderately high temperatures (e.g. 50 °C). Supercritical fluid CO2 is known to have near zero surface tension and provides an ideal medium for fabrication of SiO2 films. Formation of SiO2 films via hydrolysis reaction in sc-CO2 is more rapid compared to the traditional hydrolysis reaction at room temperature. In general, metal alkoxide hydrolysis reactions carried out in a closed sc-CO2 system is not affected by moisture in air compared with traditional open-air hydrolysis systems. Using sc-CO2 as a reaction medium can eliminate undesirable organic solvents utilized in traditional alkoxide hydrolysis reactions.X-ray diffraction (XRD) and electron diffraction (ED) measurements demonstrated that the SiO2 films produced are amorphous. Energy dispersive spectroscopy (EDS), attenuated total reflectance-Fourier transform infrared (ATR-FTIR) and X-ray photoelectron (XPS) spectroscopy show elemental compositions of the films formed on the substrate surfaces to be SiO2. Film thickness formation by controlling the amount of the catalyst is discussed.

Nanoscale doping of compound semiconductors by solid phase dopant diffusion

Achieving damage-free, uniform, abrupt, ultra-shallow junctions while simultaneously controlling the doping concentration on the nanoscale is an ongoing challenge to the scaling down of electronic device dimensions. Here, we demonstrate a simple method of effectively doping ΙΙΙ-V compound semiconductors, specifically InGaAs, by a solid phase doping source. This method is based on the in-diffusion of oxygen and/or silicon from a deposited non-stoichiometric silicon dioxide (SiOx) film on InGaAs, which then acts as donors upon activation by annealing. The dopant profile and concentration can be controlled by the deposited film thickness and thermal annealing parameters, giving active carrier concentration of 1.4 × 1018 cm−3. Our results also indicate that conventional silicon based processes must be carefully reviewed for compound semiconductor device fabrication to prevent unintended doping.

ナノロッド状粒子を用いた二酸化チタン膜の作製と色素増感型太陽電池への応用

ナノロッド状粒子を用いた二酸化チタン膜の作製と色素増感型太陽電池への応用

Sequential Processes to Produce N-TiO2Films Through Rf Plasmas

Using as target a CpTi disk in an atmosphere of argon/oxygen and by rf plasma. First titanium dioxide (TiO 2 ) films were obtained on silicon substrates, and subsequently, these films were doped with nitrogen (N-TiO 2 ). In both processes, along four hours at 390°C of temperature. X-Ray diffraction and Raman spectroscopy confirmed the presence of the nanostructured anatase phase. X-ray photoelectron spectroscopy analyzes indicate that the nitrogen atoms were incorporated into the TiO 2 film with ~33.9 at%. The films reach a thickness of 1.25 μm and 40 nm the average uniformity determined by using an atomic force microscope. Finally, UV-Vis diffuse reflectance spectroscopy outcome evaluated ones an energy band gap reduction from 3.17 eV to 2.95 eV corresponding to TiO 2 films and N-TiO 2 films respectively.

Photolithographic Process for Creating Micro-Grating on Silicon Substrate for Biosensor Application

In this work, we use photolithography in order to fabricate micro-grating structures on silicon. The first step of device was coated by 3.5 μm thick silicon dioxide (SiO2) film on top side, whereas the bottom side was coated with 4.5 μm. Next, we deposited silicon nitride (Si3N4) film of 2 μm by plasma-enhanced chemical vapor deposition, and used photolithography to prepare the gratings. We compared micro-grating period sizes of 1 μm, 0.8 μm and 0.5 μm, and found the 0.5 μm gave the best sensitivity. These devices can be applied with detection in biosensing in the future.

Expeditious detection of ammonia using sputtered TiO2 films

Sputtering power variation plays a vital role in controlling the properties of titanium dioxide (TiO2) films, which in turn have influence on ammonia (NH3) sensing properties. In the present work, TiO2 films were deposited on glass substrates using reactive dc magnetron sputtering at different sputtering powers (100, 150 and 200 W). X-ray diffraction patterns revealed the formation of single phase (anatase) at lower power and mixed phase (anatase and rutile) at higher power. NH3 sensing response was found to be high for the anatase TiO2 film deposited at 150 W. The response values were found to be 1.9–772 for 10–100 ppm of NH3 at room temperature with fast response time (12 s) and recovery time (63 s). The obtained results highlighted the better sensing performance of anatase-TiO2 films towards NH3, due to oxygen vacancies and greater catalytic activity than the mixed phase films. The NH3 adsorption on the TiO2 films followed Elovich equation and the response kinetics were of first order.