Fabrication of SiO<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> double layer thin films with self-cleaning and photocatalytic properties

Transparent antireflective SiO₂/TiO₂ double layer thin films were prepared using a sol–gel method and deposited on glass substrate by spin coating technique. Thin films were characterized using XRD, FE-SEM, AFM, UV–Vis spectroscopy and water contact angle measurements. XRD analysis reveals that the existence of pure anatase phase TiO₂ crystallites in the thin films. FE-SEM analysis confirms the homogeneous dispersion of TiO₂ on SiO₂ layer. Water contact angle on the thin films was measured by a contact angle analyzer under UV light irradiation. The photocatalytic performance of the TiO₂ and SiO₂/TiO₂ thin films was studied by the degradation of methylene blue under UV irradiation. The effect of an intermediate SiO₂ layer on the photocatalytic performance of TiO₂ thin films was examined. SiO₂/TiO₂ double layer thin films showed enhanced photocatalytic activity towards methylene blue dye.     

Supercapacitive performance of chemically synthesized polypyrrole thin films: effect of monomer to oxidant ratio

Polypyrrole (PPY) thin films with different PPY monomer to ammonium peroxidisulphate (APS) oxidant molar ratios have been synthesized using simple and inexpensive chemical oxidative polymerization method. An interrelation between the monomer to oxidant molar ratio, morphology and supercapacitive performance of PPY thin films is studied. Initial polymerization conditions strongly affect the morphology and electrical properties of PPY thin films. Thermo-gravimetric and differential scanning calorimetric curves show the thermal stability of PPY up to 483 K. The supercapacitive performance of PPY films is studied using cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy techniques. In the present work, PPY films deposited with 0.1:0.2 monomer to oxidant molar ratio (pyrrole:APS) show maximum specific capacitance of 754 F g^?1 in 1 M H₂SO₄ electrolyte at the scan rate 5 mV s^?1 in potential window of ?0.4 to +0.6 V/SCE.     

Nano-tribological characteristics of TiO<Subscript>2</Subscript> films on 3-mercaptopropyl trimethoxysilane sulfonated self-assembled monolayer

Silane coupling reagent (3-mercaptopropyl trimethoxysilane (MPTS)) was used to prepare twodimensional self-assembled monolayer (SAM) on silicon substrate. The terminal -SH group was in situ oxidized to −SO₃H group to endow the film with good chemisorption ability. Then TiO₂ thin films were deposited on the oxidized MPTS-SAM to form composite thin films, making use of the chemisorption ability of the −SO₃H group. Atomic force microscope (AFM) and contact angle measurements were used to characterize TiO₂ films. Adhesive force and friction force of TiO₂ thin films and silicon substrate were measured under various applied normal loads and scanning speed of AFM tip. Results showed that the friction force increased with applied normal loads and scanning speed of AFM tip. In order to study the effect of capillary force, tests were performed in various relative humidities. Results showed that the adhesive force of silicon substrate increases with relative humidities and the adhesive force of TiO₂ thin films only increases slightly with relative humidity. Research showed that surfaces with more hydrophobic property revealed the lower adhesive and friction forces.     

Visible light photocatalytic degradation of paraoxon and parathion pesticides on carbon-doped TiO<Subscript>2</Subscript> nanorod thin films

In the present work the nanostructured carbon-doped TiO₂ thin films with nanorod morphology were deposited on glass substrate by a combination of ultrasonic and chemical vapor deposition methods, and for the first time were applied for the photocatalytic degradation of paraoxon and parathion organophosphorus pesticides under visible light irradiation. X-ray Diffraction, X-ray photoelectron spectroscopy, diffuse reflectance spectroscopy, and scanning electron microscopy techniques were used for characterization of the prepared thin films. Obtained results show that presence of carbon element and also special nanorod morphology of the thin films remarkably improve the optical properties of TiO₂ in visible light region and results in the good visible light photocatalytic activity of the thin films for degradation of the pesticides. The photonic efficiencies of the prepared thin films were also examined based on the international ISO-10678:2010 standard protocol for photocatalytic degradation of methylene blue under UV light irradiation. The results show a maximum photonic efficiency of 0.0312% for the carbon-doped TiO₂ thin film with 570 nm thickness, which compared to a reference standard TiO₂ films indicates a 30% improvement in photonic efficiency.     

Characterization and photocatalytic activity of boron-doped TiO<Subscript>2</Subscript> thin films prepared by liquid phase deposition technique

Boron doped TiO₂ thin films have been successfully deposited on glass substrate and silicon wafer at 30°C from an aqueous solution of ammonium hexa-fluoro titanate and boron trifluoride by liquid phase deposition technique. The boric acid was used as an F ⁻ scavenger. The resultant films were characterized by XRD, EDAX, UV and microstructures by SEM. The result shows the deposited film to be amorphous which becomes crystalline between 400 and 500°C. The EDAX and XRD data confirm the existence of boron atom in TiO₂ matrix and a small peak corresponding to rutile phase was also found. Boron doped TiO₂ thin films can be used as photocatalyst for the photodegradation of chlorobenzene which is a great environmental hazard. It was found that chlorobenzene undergoes degradation efficiently in presence of boron doped TiO₂ thin films by exposing its aqueous solution to visible light. The photocatalytic activity increases with increase in the concentration of boron.     

A facile synthesis of α-Ni(OH)2-CNT composite films for supercapacitor application

The α-Ni(OH)₂-CNT composite films have been successfully synthesized by a simple chemical method and their supercapacitive properties were investigated by variation of CNT. The structural, compositional, morphological, wettability and electrochemical properties of the composite films were studied by using various characterization techniques. X-ray diffraction analysis revealed that the synthesized composite films are polycrystalline in nature. FT-Raman spectroscopy result showed the characteristic Raman band of CNT and α-Ni(OH)₂ which confirmed the formation of α-Ni(OH)₂-CNT composite. SEM micrographs showed porous microstructure of the synthesized films and hydrophilic nature of the films was confirmed from wettability studies. Furthermore, the effect of the variation of CNT on the electrochemical properties of the synthesized composite films was discussed. The electrochemical performance of the composite films was studied by using cyclic voltammetry (CV) and Galvanostatic charge–discharge (GCD) techniques. The α-Ni(OH)₂-CNT composite showed highest specific capacitance of 544 F g^?1 with high retention capability of 85% after 1500th cycle and excellent cycling stability.     

Effects of Ni doping on photocatalytic activity of TiO<Subscript>2</Subscript> thin films prepared by liquid phase deposition technique

The TiO₂ thin films doped by Ni uniformly and non-uniformly were prepared on glass substrate from an aqueous solution of ammonium hexa-fluoro titanate and NiF₂ by liquid phase deposition technique. The addition of boric acid as an F ⁻ scavenger will shift the equilibrium to one side and thereby deposition of the film is progressed. The rate of the reaction and the nature of deposition depend on growing time and temperature. The resultant films were characterized by XRD, EDAX, UV and SEM. The result shows that the deposited films have amorphous background, which becomes crystalline at 500°C. The EDAX data confirms the existence of Ni atoms in TiO₂ matrix. XRD analysis reveals the peaks corresponding to Ni but no peak of crystalline NiO was found. The transmittance spectra of Ni uniformly and non-uniformly doped TiO₂ thin films show ‘blue shift and red shift’, respectively. Ni-doped TiO₂ thin films can be used as photocatalyst for the photodegradation of methyl orange dye. It was found that, organic dye undergoes degradation efficiently in presence of non-uniformly Ni-doped TiO₂ thin films when compared to uniformly doped films and pure TiO₂ films under visible light. The photocatalytic activity increases with increase in the concentration of Ni in case of nonuniformly doped thin films but decreases with the concentration when uniformly doped thin films were used.     

Optical and electrical properties of E-Beam deposited TiO<Subscript>2</Subscript>/Si thin films

In this paper, optical and electrical properties of E-Beam deposited TiO₂/Si thin films have been studied and investigated extensively. The films were deposited on p-type (100) silicon wafer by using electron beam evaporation technique. The thickness of the thin films was measured by a spectroscopic reflectometer, which is about 216 nm. The fabricated titanium oxide (TiO₂) thin films were annealed at 800 °C for 1 h under N₂ ambient. X-ray diffraction measurements were performed to study the structure and phase identification of the fabricated TiO₂ thin films. For the optical properties, reflection, transmittance, refractive index and absorption coefficient were obtained and analyzed. The photocurrent and dark current of the fabricated films were measured by I–V measurements. The measurement of the current–voltage (I–V) characteristics possesses good ohmic contact. The electrical characterizations of the films were performed in the range of the low frequencies (50 and 100 kHz) and high frequencies (750 kHz and 1 MHz) by the capacitance–voltage and conductance–voltage measurements at room temperature. The capacitance of the fabricated TiO₂ MOS capacitor at both high and low frequencies increases with the decrease in frequencies. The obtained conductance curves (peaks) increase with the decreasing in the frequencies. This can be due to the interface state density, series resistance and interfacial dielectric of the fabricated MOS capacitors. The variation in the characteristics of the fabricated film shows that TiO₂ is a promising candidate to be used in the optoelectronic and future UV detector applications as a switch, such as an optical amplifier, emitter, and UV light detectors.     

Mn<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles embedded in 3D reduced graphene oxide network as anode for high-performance lithium ion batteries

Mn₃O₄ nanoparticles were in-situ synthesized in the 3D framework of reduced graphene oxide (RGO) by a facile one-step hydrothermal method. In the reduced graphene-Mn₃O₄ (RGM) composite, the RGO network not only serves as a mechanical support to construct a self-supported and binder-free electrode, but also offers 3D continuous conductive network for effective electron transfer. The Mn₃O₄ nanoparticles anchored uniformly across the RGO framework, which provided high capacity and prevented the restacking of the RGO thin sheets. Based on the unique composite structures, strong synergistic effect was achieved between Mn₃O₄ and RGO, resulting in superior specific capacity, enhanced rate capability, stable cycling performance and nearly 100% Coulombic efficiency in the RGM2 composites. With an optimal Mn₃O₄ composition of 44% by weight (similarly hereinafter), the composite exhibits high specific capacities of 696–795 mAh g¹ based on the overall weight of the electrode in 60 cycles at 200 mA g^?1, with a large coulombic efficiency of around 98%. Even at a high current density of 10,000 mA g^?1, the composite can still deliver a capacity of 383 mAh g^?1, demonstrating its excellent rate performance. The outstanding performances of the composites are attributed to the synergistic effect of both components and the hierarchical structure of the composite.     

Conducting polymer and reduced graphene oxide Langmuir–Blodgett films: a hybrid nanostructure for high performance electrode applications

In this work, we prepared a reduced graphene oxide (RGO)/poly(3,4-ethylenedioxythiophene) (PEDOT) hybrid composite with well defined nanostructure. The graphene oxide (GO) was first deposited on substrate through the Langmuir–Blodgett (LB) deposition, which provided a tunable and ordered GO arrangement on substrate. Then the GO LB films were reduced to RGO by following thermal treatment, and a ultrathin conducting polymer (CP) PEDOT was directly coated on RGO through a vapor phase polymerization process. The RGO/PEDOT nanocomposite exhibits excellent electrical conductivity about 377.2 S/cm. Electrochemical activity investigation revealed that this nanocomposite exhibits 213 F/g high specific capacitance at a 0.5 A/g current density and shows better capacitance retention rate than pure PEDOT. The detailed study also confirmed that the arrangement of RGO shows distinct influence on the electrical and electrochemical properties of obtained nanocomposite. Large area RGO/PEDOT nanocomposite with high conductivity and electrochemical activity can be deposited on different substrates. Such high conductivity and electrochemical activity RGO/CP nanocomposite shows promising application future in organic and flexible electrode materials for sustainable energy storage.     

Enhancement of photoelectrochemical performance of CdSe sensitized seeded TiO<Subscript>2</Subscript> films

In this work, we highlight the effect of TiO₂ seed layer (SL) on the photoelectrochemical performances of CdSe/TiO₂ photoanodes (PAs). TiO₂ thin films were prepared by spin coating starting from a sol gel solution containing TiO₂ nanopowder, then sensitized with electrodeposited CdSe nanoparticles. Structural, optical and photoelectrochemical properties of the CdSe/TiO₂ PAs with and without the SL were investigated. Charge accumulation processes and charge transfer characteristics were identified by electrochemical impedance spectroscopy. The introduction of the compact TiO₂ SL was found to significantly increase the electron transport. The photocurrent density produced by the CdSe/TiO₂/SL PA reached 0.95 mA/cm², about two times higher than that performed by the CdSe/TiO₂ PAs. This enhancement might be attributed to a substantial decrease of the leakage current induced by a better crystallization of TiO₂ thin films as well as a higher sensitizing effect of the CdSe nanoparticles.     

One step room temperature photodeposition of Cu/TiO2 composite films and its conversion to CuO/TiO2

Cu/TiO₂ composite films were prepared at low temperature on glass substrates by a photodeposition method. Films were deposited by irradiating the substrate while in contact with an aqueous TiO₂ suspension containing copper(II) nitrate and ethanol. Cu/TiO₂ composite films of 500 nm in thickness were deposited at room temperature after a short irradiation time (15 min) with a 125 W mercury vapour lamp. According to scanning electron microscopy observations, the obtained films were homogeneous and porous. Energy dispersive X-ray spectroscopy analysis revealed a 3:1 Cu:Ti atomic ratio. Grazing angle X-ray diffraction analysis showed that the films contained Cu and TiO₂ as major components and Cu₂O as a minor component. Heat treatment at 400 °C in air for a period of 3 h transformed the initial material into a CuO/TiO₂ composite, improved the adhesion to the substrate and favoured a more regular distribution of copper oxide according to backscattering micrographs.     

A facile way to fabricate graphene sheets on TiO2 nanotube arrays for dye-sensitized solar cell applications

Large-area graphene sheets on TiO₂ nanotube arrays (RGO/TNAs) were fabricated using a simple electrochemical method. The RGO content loaded on the arrays was controlled by changing the electrochemical reaction time. The microstructures and properties of RGO/TNAs were characterized and measured using field emission scanning electron microscopy, X-ray diffraction pattern, X-ray photoelectron spectroscopy, FT-IR spectra, and ultraviolet–visible (UV–Vis) spectroscopy. The results indicated that an appropriate reaction time clearly enhances photoelectrochemical properties, while excessive RGO loading significantly lowers their performance. Remarkably, in sharp contrast to the dye-sensitized solar cells prepared by TNAs as photoanode, the RGO/TNAs showed a significantly enhanced power conversion efficiency of 4.46 %. The improvement of light harvesting is due to the excellent property of RGO and the special structure of the composite.     

Photoinduced properties of nanocrystalline TiO<Subscript>2</Subscript> sol-gel derived thin films

In this paper, nanostructure TiO₂ thin films were deposited on glass substrates by sol-gel dip coating technique. X-ray diffraction and Fourier transform infrared spectroscopy were used to determine film behaviour. The super-hydrophilicity was assessed by contact angle measurement. Photocatalytic properties of these films were evaluated by degradation of methylene blue under UV irradiation. The XRD pattern of TiO₂ powder samples confirmed the presence of polycrystalline anatase phase with a crystal size of 17 nm. The results indicated that UV light irradiation had significant effect on super-hydrophilic and photocatalytic properties of TiO₂ thin films.     

LiFePO<Subscript>4</Subscript>/TiO<Subscript>2</Subscript>/Pt composite film used as effective and robust counter electrode for dye sensitized solar cells

A series of composite films based on LiFePO₄/TiO₂/Pt were synthesized and used as counter electrodes for dye sensitized solar cells (DSSCs). The composites are characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and Brunauer–Emmett–Teller (BET). These analysis results demonstrate that the crystal structure of LiFePO₄ in composite is not changed, and the prepared LiFePO₄/TiO₂/Pt composite films hold a rough surface and porous structure which provide more catalytic activity sites for I₃ ^? reduction and more space for I^?/I₃ ^? diffusion. The DSSC based on LiFePO₄/TiO₂/Pt composite CEs shows a high power conversion efficiency of 6.23% at a low Pt dosage of 2%, comparable to the conventional magnetron sputtering Pt CE (6.31%). The electrochemical analysis reveals that the presented composite CEs have good electrocatalytic activity and low charge transfer resistance. Furthermore, the DSSCs based on LiFePO₄/TiO₂/Pt composite CE exhibit high stability under the continuous tests condition and electrolyte soaking. The results suggest that this LiFePO₄-based composite film could be a perspective electrode for practical application of DSSCs and it maybe provide a potential for further research about photo-charging lithium-ion batteries.     

Electrical behavior of Y-doped Ba<Subscript>0.6</Subscript>Sr<Subscript>0.4</Subscript>TiO<Subscript>3</Subscript> thin films

Ba_0.6Sr_0.4TiO₃ (BST) and 1.5 at% Y-doped Ba_0.6Sr_0.4TiO₃ (Y-BST) thin films have been deposited on single-crystal (100) oriented LaAlO₃ substrates using pulsed-laser deposition technique (PLD), respectively. X-ray diffraction (XRD) scanning revealed that the two kinds of films could be epitaxially grown in pure single-oriented perovskite phases, but Y-BST thin films showed an enhanced crystallization effect. The dielectric properties of the pure and Y-BST thin films were measured at 10 kHz and 300 K with a parallel-plate capacitor configuration. The results revealed that the addition of Y as an acceptor doping is very effective to increase dielectric tunability, and to reduce leakage current of BST thin films. The figure-of-merit (FOM) factor value increases from 17.32 for BST to 25.84 for Y-BST under an applied electric field of 300 kV/cm. The leakage current density of the BST thin films at a negative bias field of 300 kV/cm decreases from 2.45 × 10⁻⁴ A/cm² to 1.55 × 10⁻⁶ A/cm² by Y doping. The obtained results indicated that the Y-doped BST thin film is a promising candidate material for tunable microwave devices.     

Study on chemical vapor deposited copper films on cyano and carboxylic self-assembled monolayer diffusion barriers

Thin copper films were produced by chemical vapor deposition using the precursor Cu^IIbis-hexafluoroacetylacetonate on the SiO₂/Si substrate modified with cyano and carboxylic self-assembled monolayers (SAMs) as diffusion barriers. The characterizations of the deposited copper films were measured by various thin film analysis techniques, i.e., scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy and X-ray diffraction. The comparison between copper deposited on SiO₂ and on the SAM-modified SiO₂ substrates indicates that the copper films tend to be deposited onto the SAM-modified substrate, which is further proved by the calculation results of the interaction energies of copper and the SAMs with density functional theory method.     

Pb/S/1,2-ethanedithiol composite thin films for efficient solid-state quantum-dot sensitized TiO<Subscript>2</Subscript> nanorod array solar cells

The Pb/S/1,2-ethanedithiol composite thin films were successfully deposited on TiO₂ nanorod arrays by spin-coating step-by-step 5 mmol dm^?3 Pb(NO₃)₂, Na₂S and 1% 1,2-ethanedithiol solution and their chemical compositions can be easily adjusted by changing the concentration of Na₂S solution from 5 to 3.5 mmol dm^?3 and 2 mmol dm^?3. The average crystal sizes of Pb/S/1,2-ethanedithiol quantum-dots decreased from 7.9 to 7.1 nm and 6.5 nm with the decrease of the concentration of Na₂S solution and the chemical bonding of Pb²⁺ and S in EDT was chelation of the penta-heterocycle in Pb/S/1,2-ethanedithiol composite thin films. All solid-state Pb/S/1,2-ethanedithiol composite thin film sensitized TiO₂ nanorod array solar cells using 5, 3.5, 2 mmol dm^?3 Na₂S solution exhibited the photoelectric conversion efficiency of 2.68, 3.41 and 4.51% under the illumination of simulated AM 1.5 sunlight (100 mA cm^?2).     

Ionic liquid-assisted one-step hydrothermal synthesis of TiO2-reduced graphene oxide composites

We have demonstrated a facile and efficient strategy for the fabrication of soluble reduced graphene oxide sheets (RGO) and the preparation of titanium oxide (TiO₂) nanoparticle-RGO composites using a modified one-step hydrothermal method. It was found that graphene oxide could be easily reduced under solvothermal conditions with ascorbic acid as reductant, with concomitant growth of TiO₂ particles on the RGO surface. The TiO₂-RGO composite has been thoroughly characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and thermogravimetric analysis. Microscopy techniques (scanning electron microscopy, atomic force microscopy, and transmission electron microscopy) have been employed to probe the morphological characteristics as well as to investigate the exfoliation of RGO sheets. The TiO₂-RGO composite exhibited excellent photocatalysis of hydrogen evolution.      

A facile preparation of graphene/reduced graphene oxide/Ni(OH)2 two dimension nanocomposites for high performance supercapacitors

A Ni(OH)₂ composite with good electrochemical performances was prepared by a facile method. Ni(OH)₂ was homogeneously grown on the hydrophilic graphene/graphene oxide (G/GO) nanosheets, which can be prepared in large scale in my lab. Then G/GO/Ni(OH)₂ was reduced by L-Ascorbic acid to obtain G/RGO/Ni(OH)₂. Caused by the synergy effects among the components, the G/RGO/Ni(OH)₂ electrode showed good electrochemical properties. The G/RGO/Ni(OH)₂ electrode possessed a specific capacitance as high as 1510 F g⁻¹ at 2 A g⁻¹ and even 890 F g⁻¹ at 40 A g⁻¹. An asymmetric supercapacitor device consisting of G/RGO/Ni(OH)₂ and reduced graphene oxide (RGO) was installed and displayed a high energy density of 44.9 W h kg⁻¹ at the power energy density of 400.1 W kg⁻¹. It was verified that the G/GO nanosheets are ideal supporting material in supercapacitor.