Liquid Phase Deposition Method Research Articles

Effects of post-deposition heat treatment on the microstructure and properties of Al-doped ZnO thin films prepared by aqueous phase deposition

In this study, transparent conducting aluminum-doped ZnO thin films (AZO) were deposited on glass substrates by a water-based liquid phase deposition method. The results show that by employing a two-step post-deposition heat treatment, the preferential orientation of ZnO (002) appeared as soon as the polycrystalline films were formed. Under a reducing atmosphere, the crystallinity of the films was effectively improved. Furthermore, the reducing atmosphere was also beneficial for the removal of the residual stress of the prepared films and the c-axis lattice constant was less stretched as compared to those under an inert atmosphere at identical Tp. Both the atomic force micrograph and scanning electron micrograph clearly exhibited that the heat treatment induced considerable grain growth. The X-ray photoelectron spectrum revealed that the heat treatment atmosphere had little impact on the bonding state of zinc and that the reducing atmosphere was favorable for the non-stoichiometric alumina, which in turn, resulted in more oxygen vacancies and led to improvement in electrical conductivity. The ratio of chemisorbed oxygen declined substantially when applying the reducing atmosphere. Accordingly, hydrogen was helpful for the reduction of chemisorbed oxygen onto AZO films. Generally, the electrical resistivity declined linearly with Tp. A minimum resistivity of 9.90×10−3Ω·cm was obtained with a doping concentration of Al/Zn=2.25at.% at Tp=700°C. The largest mean free path of the carriers was 1.2Å, which was much smaller than the observed grain sizes of the AZO films. Accordingly, the grain boundary scattering was not the detrimental scattering mechanism. In contrast, the scattering within the grains was responsible for the low mobility. An increase in optical transparency with the heat treatment temperature was observed due to the compact and smooth topography with larger grains, among which, less porous structures were formed at elevated temperature.

Attenuated total reflection GeO2 hollow waveguide for 9.6–11.7 μm infrared light transmission

We report the preparation and characterization of an attenuated total reflection (ATR) GeO2 hollow waveguide. An internally GeO2-coated silica glass tube (bore size 1.0–1.2 mm, length 1.2 m) was prepared using a homogeneous liquid phase deposition method. Kramers-Kronig analysis reveals that the GeO2 cladding material qualifies as a reflective layer (nr < 1) for the ATR hollow waveguide structure. ATR-transmission of 9.6–11.7 μm light through HE11 mode is confirmed by loss spectrum analysis of the sample. The straight and bending (30°) transmission losses for delivery of a ∼40 W CO2 laser beam (10.6 μm) are 0.56 dB/m and 1.64 dB/m, respectively.

Optical-fiber/TiO2-nanowire-arrays hybrid structures with tubular counterelectrode for dye-sensitized solar cell

We have developed an innovative structure for enhancing the performance of the fiber based 3D DSSC by integrating optical-fiber/TiO2-nanowire-arrays hybrid structures with cylindrical counterelectrodes. The TiO2 nanowire arrays are grown on the optical fiber using liquid phase deposition method and platinum is coated on the inwall of stainless steel capillary tubes using electroless deposition. The 3D DSSC is made by sheathering the tube on the fiber structure. In comparison to planar illumination geometry, the efficiency for the 3D structure has been enhanced by a factor of 3.6. An absolute efficiency of 6% has been demonstrated at an optimal length of TiO2 NWs (12μm). This study demonstrates a new methodology for building flexible and high-efficient fiber based 3D solar cells that can be expanded to concentrating solar cells.

Branched TiO2 Nanorods Covered with TiO2 Nanosheets for Harvesting Solar Energies in Dye-Sensitized Solar Cells

A hierarchical structure of branched TiO2 nanorods covered with TiO2 nanosheets was designed and constructed for harvesting solar energies in dye-sensitized solar cells. Vertical aligned TiO2 nanorod arrays were synthesized on fluorine-doped SnO2 (FTO) by using the electrochemically deposited ZnO nanorod arrays as a template and liquid phase deposition (LPD) method. The resultant TiO2 nanorod was used as a seed and the rutile TiO2 nanorods were firstly synthesized on the surface of anatase TiO2 nanorod by using hydrothermal method. In photocurrent-voltage measurements, 3.56% efficiency was achieved for 1.5um thick nanosheets coated TiO2 nanobranch (NB), which is about 239% higher than the original TiO2 nanorod arrays.

Characteristics of Liquid-Phase-Deposited SrTiO3 Films on GaN and AlGaN/GaN Wafer

Through a simple, low-temperature liquid-phase deposition (LPD) method, SrTiO3 thin films were deposited on GaN as the gate dielectric for metal oxide semiconductor high electron mobility transistor application. X-ray photoelectron spectroscopy was employed to characterize the films. Electrical characteristics of the SrTiO3 films on GaN showed that the lowest leakage current was 4.2x10-9 A/cm2 at -1 MV/cm after annealing at 400°C. AlGaN/GaN MOSHEMTs with LPD-SrTiO3 of 20 nm-thick as the gate dielectric were also fabricated. The suppressed gate leakage current improves both subthreshold slope and on/off current ratio. Wider gate voltage swing and flatter transconductance of the MOSHEMT demonstrate better device linearity.

Near Room-Temperature Liquid-Phase Deposition of Barium-Doped TiO2 on n-GaN and its Application to AlGaN/GaN MOSHEMTs

Barium-doped TiO2 films deposited on GaN layers at low temperature through a simple liquid-phase deposition method is investigated. The use as a gate dielectric in AlGaN/GaN metal-oxide-semiconductor high-electron mobility transistors (MOSHEMTs) is also demonstrated. The electrical characteristics of the metal-oxide-semiconductor (MOS) structure on n-doped GaN show that the leakage current density is about 5.09 × 10-9 A/cm2 at 1 MV/cm, and the breakdown field is more than 13 MV/cm. The maximum drain current density of the AlGaN/GaN MOSHEMTs is higher than that of HEMTs, in which a wider gate voltage swing, a lower sub-threshold swing (112mV/dec), and a higher ION/IOFF ratio (4.5×105) are obtained.

Seed-Mediated Liquid Phase Deposition Method for TiO<sub>2</sub> Nanostructure Growth on ITO Substrate: Effect of Surfactant

This paper reports the study on the effect of the surfactants, cetyltrimethylammonium bromide (CTAB) and hexamethylenetetramine (HMT) on the growth of TiO2 nanostructures on ITO surface. TiO2 nanostructures were prepared using a seed-mediated liquid phase deposition (LPD) method. LPD is an electrolysis deposition of metal oxide via hydrolysis of metal-fluoro complex in the presence of boric acid at ambient temperature. In typical case, this method allows the formation of metal oxide film on the substrate surface. Since the properties strongly depend on shape at this length scale, the morphology control growth of TiO2 nanostructures is highly demanded in order to produce desired properties in application. In this work we demonstrate the growth of wire like structure of TiO2 (instead of film) on ITO surface via a seed-mediated liquid phase deposition in the present of surfactant. In typical result, TiO2 with diameter ca. 40 nm at the bottom of nanowire to ca. 10 nm at the nanowire tip can be successfully grown on the surface. The effect of surfactant and their concentration on the growth characteristics of TiO2 nanostructure will be discussed.

The Optical Properties of Ammonia Treated TiO<sub>2</sub> Nanostructure Prepared by Liquid Phase Deposition Method

. TiO2 was known for its potential in solar cell and photocatalyst application. However the usage of anatase TiO2 in solar cell application has its own disadvantage as TiO2 spectrum was limited to ultraviolet (UV) light limiting its application. It was found that the broader optical absorption of TiO2 can be obtained by nitrogen doping. This paper report the optical properties study of ammonia treated TiO2 nanostructures with various percentage concentration of ammonia. The TiO2 nanostructures was prepared by liquid phase deposition (LPD) method using on ITO substrate and annealed at 450 °C for 1h. The TiO2 nanostructures were characterized with rod-like morphology with length and diameter of ca. 100 nm and ca. 100 nm respectively that vertically oriented on the surface. The optical properties of the samples exhibit strong band near the UV region. The optical properties drastically changed if the samples treated with ammonia, of which exhibit the present of broader absorption band in the visible region. The TiO2 treated ammonia should be find used in photoelectrochemical (PEC) solar cell application.

Synthesis and photoluminescence properties of the ZnO@SnO2 core–shell nanorod arrays

The ZnO@SnO2 core–shell nanorod arrays have been synthesized. As the cores, ZnO nanorod arrays were first prepared by aqueous chemical growth method. Then using a simple liquid-phase deposition method, SnO2 was deposited on the ZnO nanorod arrays. Scanning electron microscopy, transmission electron microscopy, and X-ray diffraction were used to characterize the morphologies and structures of the products. Photoluminescence properties were also investigated. It was found that the ZnO@SnO2 core–shell nanorod arrays showed enhanced UV and green emissions when compared with the bare ZnO nanorod arrays.

Low-Temperature Synthesis and Gas Sensing Properties of Anatase TiO<sub>2</sub> Thin Films

Crystalline anatase TiO2thin films were obtained on glass substrates at 60°C, 75°C and 90°C, respectively, by liquid phase deposition (LPD) method without subsequent heat treatment. X-ray diffraction (XRD), atomic force microscopy (AFM) and UV-Vis spectrophotometer were used to characterize the as-synthesized TiO2thin films. The H2sensing properties of the TiO2thin films based sensors were investigated. The results show that the gas sensors signal Ra/Rg (Ra: resistance in air, Rg: resistance in a sample gas) decreases with the increasing deposition temperature. The TiO2thin films obtained at deposition temperature of 60°C exhibited the maximum H2gas response at 350°C, and the magnitude of the sensor signal and the response time for 500ppm H2was 1.25 and 17s, respectively.

Fabrication of 3D interconnected porousTiO2 nanotubes templatedby poly(vinyl chloride-g-4-vinyl pyridine) for dye-sensitized solar cells

Porous TiO2 nanotube arrays with three-dimensional (3D) interconnectivity wereprepared using a sol–gel process assisted by poly(vinyl chloride-graft-4-vinylpyridine), PVC-g-P4VP graft copolymer and a ZnO nanorod template. A7 µm long ZnO nanorod array was grown from the fluorine-doped tinoxide (FTO) glass via a liquid phase deposition method. TheTiO2 sol–gel solutiontemplated by the PVC-g-P4VP graft copolymer produced a random 3D interconnection betweenthe adjacent ZnO nanorods during spin coating. Upon etching of ZnO,TiO2 nanotubes consisting of 10–15 nm nanoparticles were generated, as confirmed by wide-anglex-ray scattering (WAXS), energy-filtering transmission electron microscopy (EF-TEM) andfield-emission scanning electron microscopy (FE-SEM). The ordered and interconnectednanotube architecture showed an enhanced light scattering effect and increased penetrationof polymer electrolytes in dye-sensitized solar cells (DSSC). The energy conversionefficiency reached 1.82% for liquid electrolyte, and 1.46% for low molecular weight(Mw) and 0.74%for high Mw polymer electrolytes.

The Preparation of a Novel Composite Film Based on Polyoxometalate for Visible Light Photocatalysis

The composite film, FeW11O399-(FeW11)/TiO2/ SiO2, was prepared by liquid phase deposition method (LPD) at low processing temperature for the first time. Formation of the stable composite film is due to strong chemical reaction of ≡Ti-OH from TiO2/SiO2 with the surface oxygen atoms at vacant sites of FeW11. The structural properties of the film were characterized using FT-IR、UV-vis spectra, Elemental Analysis. The experimental results confirmed the retention of the primary Keggin structure and the saturation of the surface of the lacunary FeW11; Formation of Ti–O–Si bond implies that the TiO2 crystallites highly dispersed on the silica surface via oxygen as a bridge. The catalytic activity was tested by the photo-degradation of aqueous azo dye congo red (CR) (0-20 mmol•L-1). The resulting film exhibited efficient visible-light photocatalytic activity to decompose aqueous azo dye CR，which is mainly attributed to long time existence of Fenton-assisted FeW11/TiO2/SiO2 excitation state. According to the experimental results, a synergistic effect mechanism of the photodegradation process is proposed.

Gas-Sensitive Behavior Based on Charge Transfer Processes of a Novel Polyoxometalate (POM)/TiO<sub>2</sub>/SiO<sub>2</sub> Composite Film

The POM/TiO2/SiO2 Supermolecule composite based on POM films were synthesized via an easy liquid phase deposition method (LPD) at low processing temperature for the first time and employed for studying the charge transfer processes between the film and ambient atmospheres. Here the POM is the Keggin type lacunary FeW11O399- (FeW11) polyanion. Gaseous adsorption properties of the films to noxious gases such as NH3 show that the composite is much better than that of the TiO2/SiO2 films, which may be attributed to the enhancement of the gaseous adsorption ability on the film surface as well as the modified charge transfer process between the adsorbed gases and the films due to the inducing of POM into TiO2/SiO2 matrix. In addition, more importantly, compared with the TiO2/SiO2 films, the POM/TiO2/SiO2 films showed relative faster response and recovery time at optimal working temperature of 440 K, indicating that the films have great potential to be designed as gas sensor used at low temperature.

<i>In Situ</i> Template Synthesis Titania Nanotube Array Films on Aluminum Plate

Titanium dioxide nanotube array films on aluminum plate were prepared via liquid phase deposition (LPD) method. The samples were characterized by field-emission scanning electron microscopy (FE-SEM) with energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR). The results show that the nanotube array films’ morphology depends on the anodic aluminum oxide (AAO) structure and deposition time. The titanium dioxide nanotube’s outside diameter is about 250 nm, the wall thickness is approximately 40 nm. The as-prepared TiO2array films are amorphous and anatase appeared after calcining at 400°C for 2 hrs. FT-IR spectrum indicates that there are lots of hydroxyl groups on the surface of AAO. When AAO was immersed into 0.1 M (NH4)2TiF6solution at room temperature, AAO was dissolved in the solution and the holes became wide. The hydrolysis reaction was shifted to the right-hand side, TiO2particles locked in-situ on the inner surface of the anodic alumina pore induced by hydroxyl group, thus nanotube array film was obtained.

Application of liquid phase deposition method for preparation of Co/ZrO x/SiO 2 catalyst with enhanced Fischer–Tropsch synthesis activity: Importance of Co–Zr interaction

Liquid phase deposition (LPD) method using (NH 4) 2ZrO(CO 3) 2 was applied to modifying chemical nature of SiO 2 surface with ZrO x species. ZrO x -modified SiO 2 was then impregnated with Co nitrate solution for preparation of Co/ZrO x /SiO 2 catalysts with 5 and 20 mass% Co loadings. Modification of SiO 2 surface with ZrO x using the LPD method enhanced FTS activity of the Co/ZrO x /SiO 2 catalysts under the reaction conditions of 503 K and 1.1 MPa. The LPD method was superior to other method reported previously such as impregnation and sol–gel methods in terms of surface modification of SiO 2 with ZrO x . H 2-TPR, XRD and hydrogen chemisorption measurements revealed that modification of SiO 2 surface with ZrO x using the LPD method enhanced dispersion of Co 0 without loss of high reducibility of Co. However, degree of Co 0 dispersion was less than that expected from enhancement of activity for the catalysts induced by ZrO x modification, indicating that turnover frequency (TOF) increased in the presence of ZrO x . This effect was particularly important for the catalyst with the low Co loading. Furthermore, in situ DRIFT measurement provided evidence for the formation of specific interaction of Co species with Si–OH and Zr–OH species in the Co/ZrO x /SiO 2 catalysts. It was suggested that the formation of such specific interaction was responsible for not only enhancement of Co 0 dispersion but also increase in TOF of the ZrO x modified catalysts.

Textured zinc oxide prepared by liquid phase deposition (LPD) method and its application in improvement of extraction efficiency for 650 nm resonant-cavity light-emitting diode (RCLED)

In this article, we report on the textured zinc oxide (ZnO) prepared by liquid-phase deposition (LPD) method and apply it as a window layer of 650 nm resonant-cavity light-emitting diode to enhance the extraction efficiency. The treatment solution for LPD ZnO (LPD-ZnO) growth consists of ZnO powder saturated with hydrochloric acid (HCl) and hydrogen peroxide (H 2O 2). Temperature-controlled water bath system was used to maintain a constant temperature of 40 °C in LPD system. The experimental results indicate that the deposition rate was determined by the concentration of H 2O 2 and growth temperature, and the average roughness of LPD-ZnO is dominated by the concentrations of HCl. In order to perform the practicability of LPD-ZnO, the textured LPD-ZnO is used as a window layer of 650 nm AlGaInP/GaInP resonant-cavity light-emitting diode (RCLED) to enhance the light output power. In addition, the calculated results indicate that the optimum roughness for enhancing the light output power of RCLED is in the range of 80–100 nm, which are close to the experimental results. As compared to the conventional RCLED, the RCLED with textured LPD-ZnO, which has the optimum average roughness of 82 nm, performs a high light output power, a high external quantum efficiency, a narrow linewidth of electroluminescence spectrum and the same far-field angle.

Antibacterial Property of Chinese fir/TiO<sub>2</sub> Composite

Small samples of Chinese fir/TiO2 Composite were prepared using sol-gel method and microwave assisted liquid phase deposition (MWLPD) method for the first time. Results of antibacterial test show that during a one year test the samples exhibited prominent, broad-spectrum and long-lasting antibacterial performance, but were also influenced by light exposure and temperature.

Fabrication and photocatalytic activity of TiO2/SiO2 composite nanotubes

TiO2/SiO2 composite nanotube photocatalysts supported on Al substrates were prepared by the anodic aluminum oxide (AAO) liquid-phase deposition method for degradation of 100 mg/L methyl blue (MB). AAO templates were prepared in H3PO4 acidic electrolytes through the two-step anodic oxidation method. The photocatalysts were characterized by field-emission scanning electron microscopy, thermal analysis (TG-DTA), and Fourier-transform infrared, x-ray photoelectron, and UV–Vis diffuse spectroscopies. The results showed that the presence of SiO2 in TiO2 inhibited the crystal phase transformation temperature effectively, with a greater wall thickness of 80–100 nm. It was found that Ti–O–Si bonds were formed on the surface and the surface hydroxyl concentration was increased, resulting in enhanced photocatalytic activity, being about 20% higher than for pure TiO2 films. The calculated band structure for TiO2/SiO2 was investigated using first-principle calculations. The TiO2/SiO2 composite exhibited a wider conduction band which would effectively prohibit recombination of photogenerated electrons and holes.

A novel two-step method to synthesize lotus-leaf-structured TiO 2 nanocrystals with good photocatalytic activity

Lotus-leaf-structured TiO 2 nanocrystals were prepared by a novel simple two-step method. TiO 2 nanocrystals obtained by two-step method exhibited better photocatalytic activity than the as-prepared TiO 2 nanocrystal obtained by one-step liquid phase deposition method. Even compared with commercial TiO 2 photocatalyst with the smaller average size (~ 7 nm), lotus-leaf-structured TiO 2 nanocrystals exhibited better photocatalytic activity. The possible reason for the good photocatalytic activity was also investigated.

Highly ordered transition metal ferrite nanotube arrays synthesized by template-assisted liquid phase deposition

Highly ordered spinel ferrite MxFe3−xO4 (M = Ni, Co, Zn) nanotube arrays were synthesized in anodic aluminium oxide (AAO) templates with a pore size of 200 nm by combining a liquid phase deposition (LPD) method with a template-assisted route. The morphology of the transition metal ferrite nanotubes was characterized by electron microscopy (FE-SEM; TEM, SAED and HRTEM) and atomic force microscopy (AFM), whereas their chemical composition was determined by inductive coupling plasma (ICP). The phase purity was studied by X-ray diffraction (XRD) and the magnetic properties of the nanotubes were measured by SQUID measurements. Unlike the deposition of thin film structures, nanotube arrays form within the pores of the AAO templates in a much shorter time due to the attractive interactions between the positively charged AAO and the negatively charged metal complex species formed in the treatment solution. The as-deposited nanotubes are amorphous in nature and can be converted into polycrystalline metal ferrites via a post-synthesis heat treatment which induce the dehydroxylation, crystallization and formation of the spinel structure. The resulting nanotubes are uniform with smooth surfaces and open ends and their wall thickness can be varied from 4 to 26 nm by increasing the deposition time from 1 to 4 h. Significant differences in the magnetic properties of the ferrite nanotubes have been observed and these differences seem to result from the chemical composition, the wall thickness and the annealing temperature of the spinel ferrite nanotubes.