Liquid Phase Deposition Process Research Articles

Photocatalytic activity of anatase thin films coated cotton fibers prepared via a microwave assisted liquid phase deposition process

Nanocrystalline titanium dioxide thin films in the anatase phase was successfully coated on cotton fibers via a simple microwave (MW) assisted liquid phase deposition (MW-LPD) process with hexafluorotitanate ammonium (NH 4) 2TiF 6 as precursor. Compared with the conventional LPD processes, the MW-LPD technique could provide quickly high yield and crystallinity in a diluted precursor solution at a low temperature. Microwave irradiation penetrated and simultaneously heated the bulk of the material and led to higher heating efficiency with faster processing. The X-ray diffraction (XRD) and selected-area electron diffraction (SAED) studies on these powders indicated that the powders obtained with MW irradiation have much higher crystallinity with a single phase anatase. Scanning electron microscopy (SEM) images showed the information of continuous layers of titania on cotton fibers. UV–vis analyses revealed the coated titania produced an excellent UV protection of the coated fiber. The fibers with anatase coatings showed high photocatalytic property and better repetition on the photodegradation of methylene blue (MB).

Microwave dielectric properties of porous Mg 2SiO 4 filling with TiO 2 prepared by a liquid phase deposition process

Forsterite (Mg 2SiO 4) possesses a high quality factor ( Q· f) of 270,000 GHz and a low dielectric constant ɛ r of 6.8. However, it shows a relatively large negative temperature coefficient of resonant frequency τ f of −73 ppm/°C. For microwave telecommunication, a τ f of nearly 0 ppm/°C is desirable to keep the frequency stability. In order to improve τ f, we have tried to produce pure Mg 2SiO 4–TiO 2 composite ceramics with no secondary phases using a liquid phase deposition (LPD) method. Porous Mg 2SiO 4 ceramics was prepared by sintering Mg 2SiO 4 with polymethyl methacrylate (PMMA) particles, and then TiO 2 was filled in the pores of Mg 2SiO 4 by the LPD method. The porosity and microstructure of porous Mg 2SiO 4 was controlled by amount and particle sizes of PMMA and formation process. τ f of Mg 2SiO 4 filled with TiO 2 by LPD method was improved to −46 ppm/°C.

Growth Behavior of TiO2 Particles via the Liquid Phase Deposition Process

TiO2 particles were obtained from aqueous solutions by the liquid phase deposition (LPD) method. The crystalline anatase TiO2 particles could be prepared below 100°C directly from aqueous solutions. The growth behavior of TiO2 particles via the LPD process was investigated by dynamic light scattering (DLS) measurement and transmission electron microscopy (TEM). From DLS measurement, the particle growth process shows a sigmoidal curve and can be divided into three stages, i.e., the initial stage, the acceleration stage, and the completion stage. TEM measurements revealed that the primary particles with a diameter of ca. 50 nm were deposited at the initial stage. At the acceleration stage, these primary particles were assembled to form raspberry-like particles with a diameter of ca. 300 nm. Finally, the particles were precipitated by further aggregation with the micro-meter size at the completion stage.

Liquid phase deposition silicon dioxide for surface passivation in SiGe metal-semiconductor-metal photodetectors

A low temperature (50 °C) thin oxide passivation layer has been employed to substantially suppress the dark current of SiGe planar metal-semiconductor-metal photodetectors (MSM-PDs). The low temperature oxide layer was prepared by using liquid phase deposition (LPD) process and deposited in regions between the interdigitated electrodes of MSM-PDs. A four time improvement in the dark current of the passivated SiGe device was achieved. The introduction of LPD-oxide passivation layer is believed to suppress surface states situated on SiGe surface and therefore reduce surface leakage. Additionally, such a thin oxide (15 nm) passivation layer did not affect the optical performance of passivated MSM-PDs.

Preparation of anatase nanocrystallines from low concentration precursor solution via a microwave assisted liquid phase deposition (MW-LPD) process

Nanocrystalline titanium dioxide in the anatase phase was successfully prepared via a facile microwave assisted liquid phase deposition (MW-LPD) process with hexafluorotitanate ammonium (NH 4) 2TiF 6 as precursor. Compared with the conventional LPD processes, the MW-LPD technique could provide quickly high yield and crystallinity in a diluted precursor solution at low temperature because the high-frequency microwaves penetrated into the bulk of the material and the volumetric interaction of the electromagnetic fields with the material results in dielectric (volumetric) heating. This led to higher heating efficiency with faster processing. The X-ray diffraction (XRD) and selected-area electron diffraction (SAED) studies on these powders indicated that the powders obtained with MV irradiation have much higher crystallinity with a single phase anatase. Their photocatalytic activities were also investigated by the photodegradation of methylene blue (MB) as a model molecule.

Facile Microwave Assisted Liquid Phase Deposition Process to TiO2 Nanocrystallines

AbstractAnatase nanoparticles were successfully prepared via a facile microwave assisted liquid phase deposition (MW‐LPD) process with hexafluorotitanate ammonium (NH4)2TiF6 as precursor. Compared with the conventional LPD processes, the MW‐LPD technique could provide high yield quickly and crystallinity in a diluted precursor solution at a low temperature. The products were characterized by XRD and TEM. Their photocatalytic activities were also investigated by the photodegradation of methylene blue (MB) as a model molecule.

Nitride-Based UV Metal–Insulator–Semiconductor Photodetector with Liquid-Phase-Deposition Oxide

A low-temperature (30–40°C), low-cost and reliable method of liquid phase deposition (LPD) has been employed to grow SiO2 layers on GaN. The LPD process uses a supersaturated acid aqueous solution of hydrofluosilicic (H2SiF6) as a source liquid and an aqueous solution of boric acid (H3BO3) as a deposition rate controller. In this study, the LPD SiO2 was prepared at 40°C with concentrations of H2SiF6 and H3BO3 at 0.2 and 0.01 M, respectively. The minimum interface-trap density, Dit, of a metal–insulator–semiconductor (MIS) capacitor with a structure of Al/20 nm LPD-SiO2/n-GaN was estimated to be 8.4×1011 cm-2 V-1. Furthermore, a MIS photodetector with a 10-nm-thick LPD-SiO2 layer has been fabricated successfully. The dark current density was as low as 4.41×10-6 A/cm2 for an applied field of 4 MV/cm. A maximum responsivity of 0.112 A/W was observed for incident ultraviolet light of 366 nm with an intensity of 4.15 mW/cm2. Defect-assisted tunneling was invoked to explain these results.

P-42: Development of CNT Cathodes for Field-Emission FPDs by Liquid-Phase Fabrication

Fabrication of CNT pattern by liquid-phase based deposition technique has been studied in Xintek for several years. By using this technique, we successfully fabricated sealed CNT field emission display prototypes with diode structures. The CNT panel size has been scaled up from 4 inch to 8 inch. Patterned CNT cathode was made by incorporating photolithography techniques into the liquid-phase deposition process. CNT pattern size of 50 um was achieved on our standard (unpolished) display substrates. A simple substrate polishing process could reduce the CNT pattern size down to 20 um. It indicates that high-resolution displays are possible by improving the surface smoothness of the substrates. The patterned CNT cathodes demonstrated good field emission characteristics including low turn-on field and high emission current density. However, the emission uniformity remains to be a major concern. The global emission uniformity of the CNT panels can be improved through more engineering efforts. We believe that the emission uniformity in pixel can be enhanced by optimization of the liquid-phase deposition process and CNTs concentration, distribution as well as morphology in the cathodes. Liquid-phase deposition technique can also deposit CNTs into preformed triode structures with the aid of photolithography techniques.

Different effects of alkyl sulfate and alkylbenzene sulfonate surfactants on the synthesis and properties of CuPc/TiO 2 composite films by the liquid-phase deposition (LPD) method

The insoluble copper phthalocyanine (CuPc)/TiO 2 composite thin film has been successfully prepared in an aqueous solution by liquid-phase deposition (LPD) method, applying two surfactants as the solubilizing agents. The two surfactants are sodium dodecyl benzylsulfonate (SDBS) and sodium lauryl sulfate (SDS), selected as the representative of their groups. The deposited films were characterized by UV–vis, SEM, FT-IR, XRD and ICP–AES. Comparing the two composite thin films, it revealed a series of interesting facts. The films showed excellent adherence to the substrate with particle diameter ranging from 20–50 nm in, and 90 and 280 nm in thickness. It is identified that CuPc is coexisting of dimers and monomers form, mainly in dimeric form for both the composite thin films by UV–vis spectroscopy, illustrating that the CuPc is not further aggregated by LPD process. The dependences of deposited amount of Ti and Cu with the reaction time suggested the growing of the films can be easily controlled, the SDBS seems to be hindrance to the growing of the films. After heat treatment at 250 °C for 2 h, the SDS–CuPc/TiO 2 thin film becomes crystallized, but no obvious XRD peak is observed in the SDBS–CuPc/TiO 2 composite thin film.

Synthesis of mesoscopic hollow spheres and inner surface functionalized hollow spheres of titanium dioxide by the liquid phase deposition method

Polystyrene (PS) core–TiO2 shell composite particles and TiO2 hollow spheres were fabricated using the liquid phase deposition (LPD) method. Composite particles were prepared using PS particles as templates. Calcination of the composite particles resulted in TiO2 hollow spheres. Uniform TiO2 hollow spheres were obtained when the reaction time of the LPD process was between 4 and 8 h. Furthermore, we fabricated TiO2 hollow spheres whose inner surfaces were functionalized by Pt particles after platinized PS particles were used as templates. The Pt particles were immobilized on the inner surfaces of the hollow spheres.

Fabrication technique for filling-factor tunable titanium dioxide colloidal crystal replicas

Filling-factor tunable titanium dioxide replicas of colloidal crystals were fabricated by using a liquid phase deposition (LPD) technique. Ammonium hexafluorotitanate [(NH4)2TiF6] was used as a precursor, which was converted slowly to titanium dioxide by hydrolysis with boric acid. After the oxide was formed in voids of latex colloidal crystals, the latex was removed by calcination. By applying the LPD process to the replica again, the filling factor of the replica could be increased in a controllable fashion. With 203 nm template spheres, the peak shift in the ∼490 nm stop band depended linearly on the deposition time for the first 20 min, at a rate of 4.4 nm/min. Thus the position of the Bragg reflection peak could be adjusted precisely by controlling the filling factor of the replica structure.

Quality optimization of liquid phase deposition SiO 2 films on gallium arsenide

For liquid phase deposition (LPD) at room temperature (∼40°C) of silicon dioxide (SiO 2) on gallium arsenide (GaAs) substrate, this study correlates growth solution concentrations with resultant film quality. This LPD process pretreats the GaAs substrate with ammonia solution kept at pH=11–12, thereby generating OH radicals on the GaAs surface which enhance SiO 2 deposition. It is found that growth conditions such as low hydrofluosilic acid concentration, proper boric acid concentration, and low growth rate play important roles in optimizing deposited film quality. When LPD-SiO 2/GaAs grown at optimum conditions is used to fabricate a metal-oxide-semiconductor field effect transistor, the transconductance, g m, is about 68, the drain current, I DS, is 10 mA for gate oxide thickness=20 nm and W/ L=40/2. LPD-SiO 2/GaAs grown at the proposed conditions equals or exceeds the quality of competing techniques, with a process that proceeds rapidly at room temperature and pressure, with inexpensive equipment.

Photocatalytic activity of titanium oxide prepared by liquid phase deposition (LPD)

Titanium oxide powder and thin films were prepared from an (NH4)2TiF6 aqueous solution upon addition of boric acid in a process denoted as liquid phase deposition (LPD). In this process, titanium oxide powder and films were formed by the chemical equilibrium reaction between titanium fluoro-complex ions and metal oxide in the aqueous solution. The prepared powder and deposited films showed some features which differed from titanium oxide prepared from titanium alkoxide. The prepared powder and the deposited films included anatase (TiO2) and showed photocatalytic activity without prior calcination. The decomposition rate of CH3CHO reached a maximum when the powder or films were calcined at 300 °C. The LPD process enabled a uniform layer of TiO2 film to form homogeneously on the entire surface of glass wool. The prepared TiO2 contained fluorine and nitrogen. The amount of these impurities was reduced upon calcination.

On Liquid‐Phase Deposition of Silicon Dioxide by Boric Acid Addition

The current status of liquid‐phase deposition (LPD) of by adding boric acid to a hydrofluosilicic acid is reviewed and compared with some new results from the authors' laboratory. Large discrepancies exist in the literature concerning the effects of various processing parameters on deposition rate. We have shown that much confusion arises from the misconception of using on additive to “saturate” and usng water to “dilute” the growth solution. In this paper the role of as a reagent and the detrimental effect of an additive as seeds for depleting the nutrient in the growth solution if added after the addition are emphasized. Despite the variations between different investigators, the following characteristics of the LPD process are in general agreement: (i) the deposition process is surface controlled, (ii) the deposition rate depends approximately linearly on temperature, (iii) the deposition rate is constant (independent of time) over a wide range of experimental conditions, and (iv) the deposition rate increases with increasing boric acid concentration.

Titanium (IV) Oxide Thin Films Prepared from Aqueous Solution

Abstract Titanium oxide thin film could be prepared from (NH4)2TiF6 aqueous solution with addition of boric acid by Liquid Phase Deposition (LPD) process. The aspect and chemical composition of the deposited films were different according to the concentration range of (NH4)2TiF6 and H3BO3 in the treatment solution. The deposition rate of transparent TiO2 film increased with increasing concentration of added H3BO3.

Reliable fluorinated thin gate oxides prepared by liquid phase deposition following rapid thermal process

A reliable fluorinated thin gate oxide prepared by liquid phase deposition (LPD) following rapid thermal oxidation (RTO) in O/sub 2/ or nitridation (RTN) in N/sub 2/O ambient was reported. Fluorine (F) atoms incorporated into the oxides during LPD process are found to be helpful to the improvement of oxide quality. It is observed that these fluorinated gate oxides show good properties in radiation hardness, charge to breakdown (Q/sub bd/), and oxide breakdown field (E/sub ox/) endurances. Interestingly, the Q/sub bd/'s for the fluorinated gate oxides are 10 times larger than those for the gate oxides prepared by RTO in O/sub 2/ or RTN in N/sub 2/O directly. Some of the E/sub ox/'s are even higher than 17 MV/cm for the samples investigated in this work.

Preparation of fluorinated gate oxides by liquid phase deposition following rapid thermal oxidation

The fluorinated gate oxides grown by the method of liquid phase deposition (LPD) following rapid thermal oxidation (RTO) were studied in this work. Samples with and without aluminum are both investigated in the LPD process. It was found that the amount of F atoms decreases as the LPD oxide was treated subsequently by RTO treatment. For a given time of RTO, the longer the LPD time, the larger the amount of F contained in the gate oxides. But for a given time of LPD, the longer the RTO time, the smaller the amount of F contained in the gate oxides. It was found that the radiation induced oxide charge number density shift ΔNot and the midgap interface trap density shift ΔDitm, and the oxide breakdown field Eox exhibit turnaround dependencies on the LPD growth time. In other words, they are dependent on the amount of F atoms incorporated into the gate oxide. Interestingly, it was found that for the gate oxides grown by the LPD process containing Al have better quality than the LPD without containing Al from the viewpoint of radiation hardness and electric breakdown field.

Formation of silicon dioxide films in acidic solutions

SiO 2 thin films can be formed by immersing a substrate into hexafluorosilisic acid (H 2SiF 6) solution after boric acid is added. This process is called LPD (liquid phase deposition). We found that chemically more stable SiO 2 thin films can be obtained in H 2SiF 6 solution by dissolving aluminum. Films deposited at room temperature by this method were observed to be silicon dioxide by use of IR, XPS and ellipsometry. Several properties of these films and the mechanism of this new LPD process are discussed.

ChemInform Abstract: A New Process for Silica Coating.

AbstractThe developed liquid phase deposition (LPD) process allows the coating of a glass substrate with a uniform and dense silica film by simple immersion of the substrate into H2SiF6 solution supersaturated with silica gel.