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Cold crystallization of SnO2 was realized in aqueous solutions, where crystal growth was controlled to form SnO2 (101) nanosheet assembled films for devices such as chemical sensors. The nanosheets grew directly on a fluorine-doped tin oxide substrate without a seed layer or a buffer layer. The nanosheets had a thickness of 5–10 nm and an in-plane size of 100–1600 nm. Moreover, the large flat surface of the (101) facet was metastable. The thickness of the SnO2 (101) nanosheet assembled film was approximately 800 nm, and the film had a gradient structure that contained many connected nanosheets. TEM results revealed that the predominate branch angles between any two connected nanosheets were 90° and 46.48°, corresponding to type I and type II connections, respectively. These connections were consistent with the calculations based on crystallography. Crystallographic analysis clarified the characteristic crystal growth of the SnO2 (101) nanosheet assembled film in the aqueous solution. Furthermore, we demonstrate that the metastable (101) facet can be exploited to control the rate of crystal growth by adjusting the etching condition.

Nanostructured TiO2 coatings were successfully formed on polyethylene terephthalate (PET) films and fluorine-doped tin oxide (FTO) films in aqueous solutions. They contained an assembly of nanoneedles that grow perpendicular to the films. The surface area of the coatings on PET films reached around 284 times that of a bare PET film. Micro-, nano-, or subnanosized surface roughness and inside pores contributed to the high nitrogen adsorption. The coatings on FTO films showed an acetaldehyde removal rate of 2.80 μmol/h; this value is similar to those of commercial products certified by the Photocatalysis Industry Association of Japan. The rate increased greatly to 10.16 μmol/h upon annealing in air at 500 °C for 4 h; this value exceeded those of commercial products. Further, the coatings showed a NOx removal rate of 1.04 μmol/h; this value is similar to those of commercial products. The rate decreased to 0.42 μmol/h upon annealing. NOx removal was affected by the photocatalyst’s surface area rather than its crystallinity.

Self-assembly of nanocrystals yields wide diversified high-order structures and promises new opportunity for various technological applications. Herein, we developed a facile dip-coating process to fabricate desired patterns of silica nanoparticles with neat edge and high regularity. A micro-pattern of self-assembled monolayer of octadecyltriethoxysilane (OTE) was used as a solution mold for nanoparticle deposition. As a result, self-assembled patterning of nanoparticles could be obtained over wafer-scale areas by using this kind of easy way. Moreover, uniformed mono-layer silica assembly with micro-scale area could be deposited on silicon substrate by tuning the withdrawal speed and concentration of nanoparticle solution. A pre-treatment of vacuum ultraviolet (VUV) irradiation benefits for the orderly arrangement of silica assembly with few cracks. After dip-coating process, super-hydrophilic surface of silica films (

Herein, we study the effect of off-stoichiometry on the properties of a phase change material (PCM)—LiVO2—which is a new type of PCM based on the phase change of electron. The PCM properties such as latent heat, transition temperature, and hysteresis of transition temperature varied linearly with respect to the distance of vanadium ions, which was systematically controlled through off-stoichiometry in the composition of LixVO2+δ (0.85

In this work, Vertically oriented WO 3 nanoflakes array films was synthesized via the template free facile electrodeposition method at room temperature. WO 3 nanoflakes arrays was adopted as an effective cathode electrode material in the electrochemical devices structure. The WO 3 material exhibits superior electrochromic performance shows a larger optical modulation (68.89% at 550 nm), faster response time (t b = 1.93 s, t c = 2.87 s), a higher coloration efficiency of about 154.93 cm 2 C −1 and with excellent cyclic stability over 2000 cycles without any degradation. Futhermore, WO 3 nanoflakes array film was used for the detection of H 2 S gas that showed excellent response. A considerable increase in porosity and high surface roughness could be conducive for such an excellent and superior electrochromic characteristic as well as gas sensing performances. These results indicates that fabricated WO 3 nanoflakes array film by a simple strategy holds a great promise for potential multifunctional applications such as smart windows, gas sensors and optical sensors.

A bridge type structure of the SnO2 nanosheet thin film was formed on the Pt interdigitated-electrodes printed SiO2 substrate via a simple synthesis process. The SnO2 nanosheet has ca. 150 nm of flat plane and extremely thin thickness. In addition, the thin film between Pt interdigitated-electrodes was floated from the substrate. It was found that the sensor signal response considerably increased by using the SnO2 nanosheet thin film with bridge type structure as compared to the SnO2 nanosheet with normal structure, especially for extremely low concentration of nonanal gas which is biomarker of lung cancer. The higher sensing response was attributed to introduction of space under thin film which acts as reaction rooms and provide the plenty of time to stay for the reaction.

This paper reports a facile low temperature hydrothermal process to grow highly porous ZnO nanosheets, self-assembled in rosette-like morphology, over the transparent indium tin oxide (ITO) glass substrate for dye-sensitized solar cell application. The prepared porous nanosheets were examined in detail using several techniques to understand the morphological, structural, compositional, optical and photovoltaic properties. The detailed morphological investigations reveal that the prepared nanosheets are made by the accumulation of small ZnO nanoparticles with typical diameters of 28 ± 3 nm. A systematic growth process to prepare such ZnO nanosheets is also discussed in terms of chemical reactions involved. The prepared nanosheets possess the stoichiometric elemental ratios of Zn and oxygen and exhibiting good crystallinity and wurtzite hexagonal phase along with good optical properties. Furthermore, the prepared ZnO nanosheets on ITO substrates were directly utilized as a photo-anode to fabricate an efficient dye-sensitized solar cell (DSSC), which demonstrated a reasonable light-to-electricity conversion efficiency of ∼3.4% with high short circuit current (JSC) of 9.45 mA cm−2, open circuit voltage (VOC) of 0.654 and fill factor of 0.55. The obtained JSC and the performance of the fabricated DSSC are attributed to the high surface to volume ratio of porous ZnO nanosheets, which delivers the high light harvesting efficiency.

A notably high-capacity antibody adsorbent was prepared using dispersed gold nanoparticles immobilised on a mesoporous silica sheet. The mesoporous silica sheet (MPS sheet) was prepared via a dual-templating method using tetraethoxysilane and 3-aminopropyltriethoxysilane as the silica framework materials. Gold nanoparticles were loaded onto the amino-functionalised surface of the MPS sheet via deposition–precipitation using HAuCl4 as the Au colloid precursor and then crystallised via calcination. The properties of the gold nanoparticle–silica composite and the dispersion of the nanoparticles were characterised using transmission electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction analysis. The surface characteristics of gold nanoparticle composite materials calcined at different temperatures were also evaluated using Fourier transform-infrared spectroscopy, X-ray photoelectron spectroscopy and thermogravimetry data. The silica–gold nanoparticle composite sheet crystallised at 550 °C (sheet-Au-550) was mesoporous in character (pore diameter = 3.8 nm) with a BET surface area of 258.0 m2 g−1. With respect to antibody adsorption, the sheet materials had a relatively higher capacity than the typical cylindrical mesoporous silica, and sheet-Au-550 exhibited a strong performance (maximum adsorption quantity QMax = 0.26 mg IgG per mg carrier). In addition, the IgG adsorption equilibrium for sheet-Au-550 fits the Langmuir isotherm model better than the Freundlich plot model. These results will be very useful for the design of adsorption materials for biomolecules, such as antibodies.

Dense tin oxide films were successfully fabricated in an aqueous solution. The pH of the solutions was controlled to pH 1.3 by addition of HCl. Precise control of solution condition and crystal growth allowed us to obtain dense tin oxide films. Concave–convex surface of fluorine-doped tin oxide (FTO) substrates was entirely-covered with the continuous films. The films were about 65 nm in thickness and had nano-structured surfaces. Morphology of the films was strikingly different from our previous reported nano-sheet assembled structures. The films were not removed from the substrates by strong water flow or air blow to show strong adhesion strength. The aqueous solution process can be applied to surface coating of various materials such as nano/micro-structured surfaces, particles, fibers, polymers, metals or biomaterials.

Transparent ZnO nanowhiskers were synthesized at ambient temperature (5–30 °C) assisted with pH buffer of polyethylenimine from an aqueous solution of sodium hydroxide and zinc acetate. X-ray diffraction, field emission scanning electron microscopy and transmission electron microscopy revealed their crystalline phase, morphology and formation mechanism. The ZnO nuclei were formed at the initial stage in a wide low temperature range by in-situ forced hydrolysis of anhydrous zinc acetate template layer. Subsequently ZnO nanowhiskers were formed on the F-doped SnO 2 -coated glass substrate by heterogeneous nucleation and growth. Lower temperature was found to favor the hydrolysis, whereas higher temperature was found to promote the growth of ZnO. Such synthesized ZnO possessed good crystalline structure. The length, diameter, and density (number of whiskers per unit area) of ZnO nanowhiskers are controllable by simply varying the deposition time and/or solution temperature.

In this study, a SnO2 nanosheet was successfully synthesized under moderate conditions without using any additive. The crystal growth direction and the mainly exposed crystal face of the SnO2 nanosheet were investigated. The relationship between the exposed crystal face and the gas sensing properties was also investigated. It was confirmed that the SnO2 nanosheet has a plain size of ˜100 nm and a mainly exposed (101) plane. The SnO2 nanosheet exhibited selectively higher sensor signal response for H2 than CH4 gas, while the SnO2 nanoparticle with a mainly exposed the most stable (110) plane, which was prepared for comparison purposes, exhibited a selectively lower sensor signal response for H2 than CH4 gas. The 90% response and recovery times for the SnO2 nanosheet were faster than those for the SnO2 nanoparticle for both H2 and CH4 gases. Different chemical states were observed on the SnO2 surfaces. Therefore, it was considered that the reaction with the target gas on the SnO2 nanoparticle was dominantly induced by oxygen adsorbed on the SnO2 surface. However, the reaction was dominantly induced by oxygen bound to Sn on the SnO2 nanosheet, due to the ease of conversion of the Sn valency state according to adsorption and desorption of oxygen on the (101) surface as compared to the (110) surface.

Microporous and mesoporous ZnO nanosheets were successfully synthesized by a low-temperature chemical bath deposition and subsequently thermal decomposition at 250 °C without any templates. Nanosheet-shaped zinc hydroxide nitrate (Zn 3 (OH) 4 (NO 3 ) 2 ) was formed as the precursors at 90 °C for 6 days by chemical bath deposition in a close system. Microporous and mesoporous ZnO nanosheets were obtained from the removing of OH and NO 3 groups from zinc hydroxide nitrate (Zn 3 (OH) 4 (NO 3 ) 2 ) nanosheet-shaped precursors. The pore sizes were distributed in the region of ∼1.3–25 nm with a center at ∼2.4 nm. Such porous and nanosheets structure gave a highest specific surface area of 283.8 m 2 /g.

SnO 2 films were fabricated on fluorine-doped tin oxide (FTO) substrates in aqueous solutions. The films of about 800 nm in thickness grew in the solutions containing SnF 2 of 25 mM at 90 °C for 24 h. They consisted of nanosheets of about 5–10 nm in thickness and about 100–1600 nm in plane size. The films had gradient structure of nanosheets. Smaller nanosheets formed dense structures in a bottom area, while larger nanosheets formed porous structures in a surface area of the films. The SnO 2 films showed higher transparency than bare FTO substrates in a visible light region of 470 to 850 nm. Decrease of reflectance increased transparency. The SnO 2 films had superhydrophilic surfaces of static contact angle below 1°. Nanosheet-assembled structures contributed high hydrophilicity. The surfaces were further modified with light irradiation. High speed camera observation showed that spread speed of water was improved with the irradiation. Removal of surface adsorbed organic molecules and increase in the number of hydroxyl groups brought superhydrophilicity and high spread speed.

SnO2 nanosheet–assembled graded continuous films were successfully fabricated in aqueous solutions containing SnF2 of 250 mM at 90°C. Thickness reached 1200 nm after immersion for 24 h. The nanosheets were 100–500 nm in in-plane sheet size and 5–20 nm in thickness. The graded structures were caused by gradual change in supersaturation degree of the solutions. The films had a-axis orientation, antireflective effect, band gap of 3.63 eV, and superhydrophilic surfaces. In contrast, the films immersed for 20 m showed band gap of 4.04 eV and contact angle of 58°.

Anticorrosive molybdate films composed mainly of Mg(OH)2, MoO2, MoO3, and MgF2 were formed on magnesium alloy AZ31 by chemical conversion. The film had relatively compact surfaces and a thickness of approximately 800 nm. The XPS studies revealed that the film contained Mg, Al, Mo, O, P, S, and F elements. The corrosion resistant performances of the films were investigated by electrochemical measurements. The potentiodynamic polarization curves showed that anodic current densities and corrosion potential of the Mo coated AZ31 were lower and more positive than those of bare AZ31. The EIS measurement and appropriate equivalent circuit models revealed that the corrosion resistance was improved.

In this paper, CeO2 and cobalt-doped CeO2 nanorods synthesized by surfactant free co-precipitation method. The microstructures of the synthesized products were characterized by XRD, FESEM and TEM. The structural properties of the grown nanorods have been investigated using electron diffraction and X-ray diffraction. High resolution transmission electron microscopy studies show the polycrystalline nature of the Co-doped cerium oxide nanorods with a length of about 300 nm and a diameter of about 10 nm were produced. The X-ray Photoelectron spectrum confirms the presence of cobalt in cerium oxide nanorods. From BET, the specific surface area of the CeO2 (Co-doped) nanostructures (131 m2 g−1) is found to be significantly higher than that of pure CeO2 (52 m2 g−1). The Co-doped cerium nanorods exhibit an excellent photocatalytic performance in rapidly degrading azodyes acid orange 7 (AO7) in aqueous solution under UV illumination.

Nanocrystal assembled SnO{sub 2} particles were synthesized in aqueous solutions. The particles showed high BET surface area of 276 m{sup 2}/g. It was much higher than that of our previous studies. BJH analyses indicated that the particles had pores of about 2-5 nm. The particles included two kinds of morphologies. The first particles were about 300-1000 nm in diameter, which were assemblies of acicular crystals of 5-10 nm in width and 100-200 nm in length. They contributed high BET surface area. The second particles were about 10,000-3000 nm in diameter, which were assemblies of ellipse crystals of 100-200 in width and 200-400 nm in length. The ellipse crystals consisted of sheet crystals. They connected with a certain angle and arranged their long direction parallel. - Graphical abstract: Acicular crystal assembled SnO{sub 2} particles and ellipse crystal assembled SnO{sub 2} particles were synthesized in the aqueous solutions. They showed high BET surface area of 276 m{sup 2}/g. Highlights: Black-Right-Pointing-Pointer Unique SnO{sub 2} nanocrystals were synthesized in an aqueous solution. Black-Right-Pointing-Pointer They were acicular crystals and ellipse crystals. Black-Right-Pointing-Pointer They had high BET surface area of 276 m{sup 2}/g.

Characteristic tin oxide films were formed on transparent conductive substrates in aqueous solutions. Surface of the films consisted of ellipse-shaped particles. Particle size in longer or shorter direction was about 300–400 or 200 nm, respectively. In contrast, middle and bottom area of the films were dense structures. Thickness was about 1150 nm. The film was single phase SnO2 with a-axis orientation. The films had chemical ratio of O/Sn = 1.20–1.37 and F/Sn = 0.088–0.124, suggesting fluorine doping. Facile synthesis of tin oxide particulate films had advantages in ordinary temperature synthesis, water solvent process, and low-environmental load.

CeO2 thin films with hexagonal-shaped pores were successfully prepared by a facile electrodeposition at room temperature combined with an etching process. By using electrodeposited ZnO nanorods as a soft template, the morphology, and microstructure of the CeO2 could be controlled. TEM observation indicated that as-prepared CeO2 film is composed of nanocrystals with average size of several nanometers, while XPS analysis showed the coexistence of Ce3+ and Ce4+ in the film. The photoluminescence properties of CeO2 films were measured, which showed much higher sensitivity compared to bare substrate.

Unique structures of TiO2 films were prepared on F-doped SnO2 transparent conductive films in aqueous solutions. They were then covered with dye-labeled proteins. Firstly, influence of film thickness on photoluminescence intensity (PL) and photocurrent (PC) was investigated. PL and PC were improved with the decrease of film thickness. Especially, PC was drastically improved to more than 30 times with the decrease of film thickness. Secondly, a novel technique of solution aging method was applied to form TiO2 structures. PC was successfully improved with this technique. They were candidate materials for bio-semiconductor hybrid devices such as protein sensors.

Pervaporation of ethanol from ethanol/water mixture solution using surface-modified mesoporous silica membranes has been carried out. The mesoporous silica layers were prepared on commercially available porous alumina tubes by dip-coating in a series of silica sols. Subsequently, organosilane compounds with different alkyl chain lengths [CnH2n+1(CH3)2SiCl; n = 1, 3, 8, 12, and 18] were covalently reacted to the surface of these mesoporous layers with high coverage. Surface-modified mesoporous silica membranes showed ethanol permselectivity and the total flux increased with increasing ethanol concentration in feed composition and feed temperature. Ethanol separation factors in the range from 7.90 to 8.24 and total flux of 2.76–2.89 kg·m−2·h−1 were obtained by pervaporation at 323 K and at 5 wt % ethanol feed composition using surface modified membranes. In the presence of 1 wt % acetic acid in a ternary model fermentation (5 wt % ethanol–94 wt % water–1 wt % acetic acid), separation factor and total flux were decreased, and this tendency was minimized by increasing pH above pKa⊖ (pKa⊖ = 4.74 at 298 K) and changing HOAc to OAc− ions in the feed solution.

Morphological change from ZnO films to ZnO prisms is achieved by an electrochemical deposition method on a graphite substrate at the low temperature of 70 °C. The ZnO prisms, which are prism-shaped ZnO rods with a wide diameter, have hexagonal well-defined crystallographic facets. The ZnO prism is 1.4 μm in diameter and 1.3 μm in length. Transmission electron microscopy and electron diffraction patterns indicate that the ZnO prisms have a single-crystalline wurtzite structure with c-axis orientation. Additionally, cathodoluminescence shows that the annealed ZnO prisms in nitrogen gas emit a significant level of near-band-edge ultraviolet light.

Tin oxide nanocrystals with high surface area were first synthesized in aqueous solutions at 50°C. The Brunauer–Emmett–Teller (BET) surface area successfully reached 194 m2/g. It was much higher than that of SnO2 (BET 47.2 m2/g), SnO2 (BET 25.9 m2/g), SnO2 (BET 23 m2/g), and In2O3–SnO2 (BET 3–6 m2/g). N2 adsorption characteristics revealed that they had pores of 1–3 nm, which contributed to the high surface area. Transmission electron microscopy, electron diffraction, and X-ray diffraction indicated the morphology, crystal structure, and chemical composition of nanocrystals. Novel process allowed us to avoid sintering and deformation of the crystals, and hence realized a high surface area and unique morphology.

Two kinds of different ZnO nanostructures, nanotubes, and nanoflowers were synthesized using an aqueous solution approach. It was demonstrated that the addition of Al3+ and ZnO sol causes the different growth behavior of ZnO nanostructures, and leads to the formation of a nanotube array as well as self-assembled nanoflowers, respectively. The effects of reaction parameters on the morphology of ZnO nanostructures were investigated. The present route reports the possibility for morphology control and assembly of ZnO nanostructures on arbitrary substrates at a low temperature on a large scale.

Zn(OH)2/ZnO nanosheet-ZnO nanoarray hybrid structured films were fabricated on F-doped SnO2-coated glass by a dissolution–recrystallization route without any additives. The as-deposited c-axis-oriented ZnO nanowhisker films were soaked in hot distilled water for various periods of time. X-ray diffraction, field-emission scanning electron microscopy, and transmission electron microscopy clarified that the dissolution of ZnO induced Zn(OH)2 to grow on the surface of the ZnO nanowhiskers film by heterogeneous nucleation and growth. The morphology of the Zn(OH)2 nanosheets was found to be controllable by the dissolution–recrystallization of as-deposited ZnO nanowhiskers in hot distilled water. ZnO with an almost identical morphology could also be produced by a dehydration reaction. Given the highly porous nature and the strong adsorption properties of the as-fabricated hybrid structured films, it is expected that they will have a variety of potential applications including dye-sensitized gas sensors and solar cells, and photocatalysis systems.

Porous, transparent and controllable ZnO nanoparticulate films were fabricated by self-hydrolysis of zinc salts in its crystalline water without any additions at 65 °C by an evaporating acetone solvent. The crystallite size of ZnO nanoparticles was about 30 nm, and the thickness of the nanoparticle film was controllable by simply changing the coating times. ZnO nanoparticulate films in thickness of 500 nm showed a high transmittance (>90%) in the visible range and widen bandgap (3.35 eV). The c-axis oriented ZnO nanoarray film was fabricated by a subsequent heterogeneous nucleation and growth in an aqueous solution. As-grown ZnO hybrid films showed a good transmittance (>85%) in the visible range.

Anatase TiO 2 film was deposited on SnO 2 : F substrate in aqueous solution. The film had an assembly of acicular TiO 2 nanocrystals on the surface. The crystals grew along the c -axis, i.e. perpendicular to the substrate. Dye adsorption increased with film thickness. Intensity of photoluminescence originating from the dye adsorbed on the nanostructured film after annealing was 3 times higher than that of thicker particulate film constructed of TiO 2 nanoparticles (P25). Additionally, dye adsorption property of the film without annealing was two times higher than the film with annealing. Consequently, the as-deposited film had high dye adsorption property which is about 6 times higher that that of thicker particulate film constructed of TiO 2 nanoparticles (P25). Assemblies of acicular crystals on the surface increased the surface area and amount of dye adsorption. The film may be useful for biomolecule sensors and dye-sensitized solar cells.

Porous, highly oriented ZnO nanowhisker films were prepared on substrate in a zinc nitrate–hexamethylenetetramine–polyethylenimine aqueous solution at low temperature via a simple two-step method. The effects of temperature and solution concentration on the morphology and transmittance of ZnO nanowhisker films were investigated in situ with the aid of pH changes. During the growth process, the pH value increased slowly with prolonged reaction time at 75 °C and 88 °C after reaching the lowest value. However, a constant pH was maintained for a long time at 65 °C. Porous and transparent ZnO nanowhisker films were produced at temperatures over 80 °C in the 0.025–0.05 M of solution. Concentrated solution resulted in ZnO nanowhisker films with a dense middle layer between the FTO and whiskers, and with bad transmittances in the visible range even at over 80 °C.

A1. Crystal structure A1. X-ray diffraction A2. Growth from solutions B1. Oxides B1. Zinc compounds B2. Semiconducting II-VI materials abstract High-quality zinc oxide (ZnO) films were successfully grown on ZnO-buffered a-plane sapphire (Al2O3 (11 2 ¯ 0)) substrates by controlling temperature for lateral growth using chemical bath deposition (CBD) at a low temperature of 601C. X-ray diffraction analysis and transmission electron microscopy micrographs showed that the ZnO films had a single-crystalline wurtzite structure with c-axis orientation. Rocking curves (o-scans) of the (0 0 0 2) reflections showed a narrow peak with full width at half maximum value of 0.501 for the ZnO film. A reciprocal space map indicated that the lattice parameters of the ZnO film (a ¼ 0.3250 nm and c ¼ 0.5207 nm) were very close to those of the wurtzite- type ZnO. The ZnO film on the ZnO-buffered Al2O3 (11 2 ¯ 0) substrate exhibited n-type conduction, with a carrier concentration of 1.9 � 10 19 cm � 3 and high carrier mobility of 22.6 cm 2 V � 1 s � 1 .

The unique structure of ZnO films obtained from aqueous solution method was investigated. Scanning electron microscopy (SEM) and X-ray powder diffraction (XRD) analyses indicate that unique morphology and structure of the region where precipitation on the substrate may occur in parallel with other regions. This is accompanied by a decrease of the electrical resistivity in the absorbed region. A possible mechanism for the resistivity transformation was discussed.

In 2 O 3 –SnO 2 nanocomposites with controllable morphologies were prepared via a co-precipitation method. The experimental results indicated that variation of In/Sn ratios facilitated the modification of In 2 O 3 –SnO 2 morphology from nanoparticles to nano-toasts and nanorods that possess ultrahigh response and selectivity to ethanol. The results demonstrate the possibility to synthesize one-dimensional and two-dimensional oxide nanocomposites under mild conditions, showing that a soft chemistry route is a promising route for rationally and structurally designing nanomaterials.

Blanket-like assembled ZnO nanowhiskers were fabricated using a freestanding ZnO nanoparticle layer by an aqueous solution deposition. X-ray diffraction and field emission scanning electron microscopy clarified the crystalline phase, orientation, morphology, and microstructure. Thermal treatment of the zinc acetate dihydrate layer resulted in the formation and delamination of the ZnO nanoparticle layer on the glass substrate. The growth habits of ZnO crystals resulted in the growth of ZnO nanowhiskers preferentially orientated along the direction of the c-axis on the whole surface of the freestanding ZnO nanoparticle layer by heterogeneorous nucleation and growth. The hierarchical-structured blanket-like ZnO nanowhisker assemblies can be utilized for dye-sensitive solar cells and gas sensors because of their high surface-to-volume ratio.

The influence of the choice of temperature, pH value, counter-ion, deposition time, and seed layer on the morphology as well as electrical properties of ZnO films grown from chemical bath deposition (CBD) are discussed. Consequently, oriented ZnO films with various microstructures can be synthesized by controlling the solution pH value and counter-ions. Besides, the point at which the seed layer is pre-heated at higher temperature is crucial and can lead to a significant difference in the width of crystals and electrical properties of ZnO films. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A halogen- and acid-free aqueous solution was developed to crystallize anatase TiO2 nano-particles. Spinal or zigzag chains of TiO6 octahedrons were formed from [TiO(C2O4)2]2- ions. They were then gradually transformed into rutile TiO2 in the solutions. Rearrangement of octahedrons realized aqueous phase transition from anatase to rutile.

ZnO nanoarray film was successfully fabricated at low temperature by the in situ forced hydrolysis of an anhydrous zinc acetate layer in an aqueous solution. The forced hydrolysis of anhydrous zinc acetate was investigated over a wide range of low temperatures (40–90 °C) and concentrations (0.01–0.2 M). The in situ forced hydrolysis of the anhydrous zinc acetate precursor layer was most important for the subsequent growth of ZnO nanoarrays by conventional heterogeneous nucleation and growth in a heated aqueous solution. Otherwise, no ZnO nanoarray films were formed. The morphology and crystal structure of the as-deposited ZnO nanoarrays were characterized by field emission scanning electron microscope (FE-SEM) and X-ray diffraction (XRD). Since the forced hydrolysis of anhydrous zinc acetate occurred at over 50 °C, relatively higher temperatures and high concentrations benefitted the faster growth of ZnO nanocrystals.

Unique morphologies of ZnO crystals were grown firstly at the air–liquid interface. The formation of bamboo leaf- and morning glory-like morphologies depended on the exposed crystal face. ZnO nanosheets were formed by selective dissolution, random diffusion, and recrystallization with a preferential orientation at the edge of pre-existing ZnO nanowhiskers, due to the local deviation of the pH value, which are derived from the volatile and highly soluble ammonia molecules at different fine regions. The high-resolution TEM and selected area electron diffraction clarified the formation mechanism.

Tin oxide particles were synthesized in aqueous solutions. They consisted of nanosheets of tin oxide crystals. The sheets were about 50–100 nm in size and 5–10 nm thickness. X-ray diffraction analysis revealed that the particles were crystals of SnO 2 and SnO. The particles had Brunauer–Emmett–Teller (BET) surface area of 85 m 2 /g estimated with N 2 adsorption characteristics. Barrett–Joyner–Halenda (BJH) analysis indicated that mesopores of 3.9 nm in size contributed to the increase surface area.