Nanostructured Titania Films Research Articles

Nanoscale roughness and morphology affect the IsoElectric Point of titania surfaces.

We report on the systematic investigation of the role of surface nanoscale roughness and morphology on the charging behaviour of nanostructured titania (TiO2) surfaces in aqueous solutions. IsoElectric Points (IEPs) of surfaces have been characterized by direct measurement of the electrostatic double layer interactions between titania surfaces and the micrometer-sized spherical silica probe of an atomic force microscope in NaCl aqueous electrolyte. The use of a colloidal probe provides well-defined interaction geometry and allows effectively probing the overall effect of nanoscale morphology. By using supersonic cluster beam deposition to fabricate nanostructured titania films, we achieved a quantitative control over the surface morphological parameters. We performed a systematical exploration of the electrical double layer properties in different interaction regimes characterized by different ratios of characteristic nanometric lengths of the system: the surface rms roughness Rq, the correlation length ξ and the Debye length λD. We observed a remarkable reduction by several pH units of IEP on rough nanostructured surfaces, with respect to flat crystalline rutile TiO2. In order to explain the observed behavior of IEP, we consider the roughness-induced self-overlap of the electrical double layers as a potential source of deviation from the trend expected for flat surfaces.

Characterization of Nanostructured Titania Thin Film and its Application in Gas Sensor

In this paper, Nanostructured Titania (NST) was fabricated by aging titanium film in hydrogen peroxide solution. NST was analyzed and characterized using scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), nano-indentation method and the BET method. Results showed that NST was porous TiO2 with pore diameter of 90-133 nm, hardness of 1.35Gpa, and specific surface area of 37.26 m2/g. Gas sensors using NST film as sensitive material were presented in this paper too. Electrodes were deposited upon NST patterns to create electrical connections. Gas sensors with a simple package were successfully fabricated.

Highly Controlled Dip-Coating Deposition of fct FePt Nanoparticles from Layered Salt Precursor into Nanostructured Thin Films: An Easy Way To Tune Magnetic and Optical Properties

Nanostructured titania films containing hard magnetic FePt nanoparticles were obtained through impregnation and postannealing of salt layered precursor [Fe(H2O)6][PtCl6] nanocrystals. The impregnation was performed by a highly controlled dip-coating process into ethanol based solutions of the salt precursor. The bimetallic salt nanocrystals were formed upon evaporation of the solvent into the cavities of TiO2 template films. The salt was transformed into the hard magnetic fct phase by annealing in reductive atmosphere at 400 °C a particularly low conversion temperature compared with those reported for other synthesis approaches. Two different titania templates were considered. In the first case, the impregnation of 3D mesoporous films was investigated in order to determine the influence of the deposition parameters on the amount of FePt nanoparticles embedded and the final optical and magnetic properties of the layers. In the second case, this approach was further extended to 2D heterogeneous nanoperforated films. The nanoparticles were selectively deposited into the perforations thanks to a prior functionalization of the titania template by the formation of hydrophobic/hydrophilic distinct domains. Interestingly, the coalescence between the magnetic particles was found to be limited due to the low conversion temperature. This procedure of positioning particles onto a 2D nanostructured support constitutes an easy and versatile bottom-up approach toward magnetic arrays with potential application in magnetic data storage devices.

Fabrication and characterization of nanostructured titania films with integrated function from inorganic–organic hybrid materials

Nanostructured titania films are of growing interest due to their application in future photovoltaic technologies. Therefore, a lot of effort has been put into the controlled fabrication and tailoring of titania nanostructures. The controlled sol-gel synthesis of titania, in particular in combination with block copolymer templates, is very promising because of its high control on the nanostructure, easy application and cheap processing possibilities. This tutorial review gives a short overview of the structural control of titania films gained by using templated sol-gel chemistry and shows how this approach is extended by the addition of further functionality to the films. Different expansions of the sol-gel templating are possible by the fabrication of gradient samples, by the addition of a homopolymer, by the combination with micro-fluidics and also by the application of novel precursors for low-temperature processing. Moreover, hierarchically structured titania films can be fabricated via the subsequent application of several sol-gel steps or via the inclusion of colloidal templates in a one-step process. Integrated function in the block copolymer used in the sol-gel synthesis allows for the fabrication of an integrated blocking layer or an integrated hole-conductor. Both approaches grant a one-step fabrication of two components of a working solar cell, which make them very promising towards a cheap solar cell production route. Looking to the complete solar cell, the top contact is also of great importance as it influences the function of the whole solar cell. Thus, the mechanisms acting in the top contact formation are also reviewed. For all these aspects, characterization techniques that allow for a structural investigation of nanostructures inside the active layers are important. Therefore, the characterization techniques that are used in real space as well as in reciprocal space are explained shortly as well.

Physicochemical state of the nanotopographic surface of commercially pure titanium following anodization-hydrothermal treatment reveals significantly improved hydrophilicity and surface energy profiles

A method of coating commercially pure titanium (cpTi) implants with a highly crystalline, thin hydroxyapatite (HA) layer using discharge anodic oxidation followed by hydrothermal treatment (Spark discharged Anodic oxidation treatment ; SA-treated cpTi) has been reported for use in clinical dentistry. We hypothesized that a thin HA layer with high crystallinity and nanostructured anodic titanium oxide film on such SA-treated cpTi implant surfaces might be a crucial function of their surface-specific potential energy. To test this, we analyzed anodic oxide (AO) cpTi and SA-treated cpTi disks by SEM and AFM. Contact angles and surface free energy of each disk surface was measured using FAMAS software. High-magnification SEM and AFM revealed the nanotopographic structure of the anodic titanium oxide film on SA-treated cpTi; however, this was not observed on the AO cpTi surface. The contact angle and surface free energy measurements were also significantly different between AO cpTi and SA-treated cpTi surfaces (Tukey's, P < 0.05). These data indicated that the change of physicochemical properties of an anodic titanium oxide film with HA crystals on an SA-treated cpTi surface may play a key role in the phenomenon of osteoconduction during the process of osseointegration.

Large scale vertical implantation of crystalline titania nanotube arrays

We present simple method to fabricate large scale TiO 2 nanotube arrays of a few tens micrometers length perpendicularly implanted on transparent electroconducting glass substrate. The thickness and morphology of the titania nanotube arrays layer can be easily tuned, enabling designing the optimal architecture of the nanostructured titania film for diverse applications including dye-sensitized solar cell.

Porous and worm-like titanium dioxide nanostructures from PS- b-PEO block copolymer micellar solutions

Mixed micellar systems containing polystyrene- block-poly(ethylene oxide) (PS- b-PEO) diblock copolymers and TiO 2 nanoparticles in a solvent/non-solvent pair were prepared and used as scaffolds in order to obtain nanostructured titania films. The inorganic content was varied in a wide range of compositions, focusing on micellar systems with PS cores and PEO/TiO 2 coronas. The spherical-to-cylindrical micelle transition was achieved by adding a small amount of homopolymer of the same nature of the core-forming block. Thin PS- b-PEO/TiO 2 hybrid films with different morphologies were prepared by spin coating micellar solutions and were transformed into the corresponding titania films by thermal treatments. The degradation of the polymer template and the simultaneous crystallization of titanium dioxide were carried out without collapsing of the nanostructures. As a final result porous and worm-like nanostructured titania films were obtained.

Nanostructured titania films sensitized by quantum dot chalcogenides

The optical and structural properties of cadmium and lead sulfide nanocrystals deposited on mesoporous TiO2 substrates via the successive ionic layer adsorption and reaction method were comparatively investigated by reflectance, transmittance, micro-Raman and photoluminescence measurements. Enhanced interfacial electron transfer is evidenced upon direct growth of both CdS and PbS on TiO2 through the marked quenching of their excitonic emission. The optical absorbance of CdS/TiO2 can be tuned over a narrow spectral range. On the other side PbS/TiO2 exhibits a remarkable band gap tunability extending from the visible to the near infrared range, due to the distinct quantum size effects of PbS quantum dots. However, PbS/TiO2 suffers from severe degradation upon air exposure. Degradation effects are much less pronounced for CdS/TiO2 that is appreciably more stable, though it degrades readily upon visible light illumination.

Modification of Parylene film-coated glass with TiO 2 nanoparticles and its photocatalytic properties

A titania film was deposited on Parylene-coated glass by a one-step, ultrasound-assisted procedure. The TiO 2 nanoparticles formed during the sonochemical hydrolysis of Ti(i-OPr) 4 were thrown to the surface and strongly attached to the Parylene substrate. By using different solvents (water, ethanol or their mixture) and reagent concentrations, the thickness, uniformity and crystallinity of the deposited layer were regulated. PVP was used to stabilize the highly homogeneous distribution of TiO 2 nanocrystals on the Parylene surface. The morphology and structure of the coated films were characterized by physical and chemical methods such as: X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), Rutherford backscattering spectrometry (RBS), and optical spectroscopy. The photocatalytic activity of the titania-modified Parylene film in the photo discoloration of methylene blue was demonstrated. The experimental results revealed a correlation between the uniformity of the nanostructured anatase titania film and its photocatalytic properties.

A simple lift-off-based patterning method for micro- and nanostructuring of functional substrates for cell culture

The ability to produce cell patterning through precise surface engineering has stimulated the development of cellular bioassays that offer new insights on the mechanisms of cell adhesion, proliferation, differentiation and molecular signaling pathways. Here we describe a simple micropatterning technique combining supersonic cluster beam deposition of nanostructured titania films on bovine serum albumin functionalized substrates. A standard lift-off process enables us to generate complementary micropatterns of hydrophobic bovine serum albumin (cell-repellent) and hydrophilic nanostructured TiOx (cell-adhesive). We demonstrate the selective PC12 cell adhesion and growth on biocompatible nanostructured TiOx. We also observed that these functional micropatterned substrates promote a considerable enhancement of cell attachment and proliferation.

Cluster-Assembled Nanostructured Titanium Oxide Films with Tailored Wettability

We report on the production of cluster-assembled nanostructured titanium oxide (ns-TiOx) surfaces with tailored wettability properties. The contact angle of the ns-TiOx surfaces changes in a controllable and reproducible way by changing the morphology through the roughness and/or with annealing the films in air at different temperatures. With increasing the annealing temperature, reversible switching from hydrophobic to hydrophilic behavior can be obtained, due to the removal of organic contaminants and to the increase of surface hydroxyl groups, while control of surface morphology allows fine-tuning of the contact angle within a given wetting regime. Thanks to the possibility of regulating and controlling the surface wettability, ns-TiOx thin films are very promising substrates for protein microarray applications where a reproducible control on protein spot dimension is required.

Preparation of Nano-Structured Titanium Oxide Film by Wet Corrosion Process as an Electrode Material for Biosensor

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Characterization of cluster-assembled nanostructured titanium oxide coatings as substrates for protein arrays

Protein microarray technologies are rapidly expanding to fulfill current needs of proteome discovery for disease management. Nanostructured materials have been shown to present interesting features when used in biological settings: nanostructured titanium oxide film (ns-TiOx), synthesized by supersonic cluster beam deposition (SCBD), has recently emerged as a biocompatible substrate in different biological assays. The ns-TiOx surface is characterized by a morphology at the nanoscale that can be tuned to modulate specific biomolecule–material interactions. Here we present a systematic characterization of ns-TiOx coatings as protein binding surfaces, comparing their performances with those of most common commercial substrates in protein and antibody microarray assays. Through a robust statistical evaluation of repeatability in terms of coefficient of variation (CV) analysis, we demonstrate that ns-TiOx can be used as reliable substrate for biochips in analytical protein microarray application.

Preparation of nano-structured titanium oxide film for biosensor substrate by wet corrosion process

In other to establish a synthesis process of nano-structured titanium oxide film for making highly effective biosensor substrate, the preparation of nanotubular on titanium oxide has been carried out through a corrosion reaction in an alkaline solution. The electron microscopic observations revealed that the surface of the titanium was transformed to potassium titanate gel through the treatment with alkaline solution. The titanium could for different nano-structures with corresponded to the concentration of alkaline (potassium hydroxide: KOH) solution. When the concentration of KOH less than 10 M, a porous structured titanium oxide was obtained. On the other hand, when the concentration of KOH in the solution became higher than 10 M, we could obtain nanotubular structured titanium oxide. These nano-structured titanium oxide films may be applied for highly effective biosensor by immobilization of biomolecules on the surface.

Nanostructuration of titania films prepared by self‐assembly to affect cell adhesion

Nanostructured and dense titania films prepared by evaporation-induced self-assembly (EISA) are shown to possess tunable topographical nanoscale features on the order 2-12 nm. Thermal treatment (calcination) induces a transition from amorphous titania to crystalline anatase that modifies the chemical and structural properties of the surfaces via the migration of matter. For nanostructured films, the nanoporous network changes from organized ellipsoidal pores, approximately 4 nm x 2 nm, to a grid-like structure with pores on the order of 12 nm, whereas dense films show a slight roughening of the surface. Cells seeded on templated films show measurable, statistically significant differences in morphology compared with cells seeded on dense films. Moreover, although crystallization of templated films results in surfaces that promote less well-spread cells with higher circularities, the opposite trend is observed for dense films. As such, these results represent a new method to tailor interfaces for biomaterial applications, using EISA to control material patterning on the nanoscale. This self-assembly based approach allows the patterning on size scales that are inaccessible by most traditional techniques while offering the added potential to package and control the release of bioactive molecules.

Photoinduced hydrophilic and photocatalytic response of hydrothermally grown TiO 2 nanostructured thin films

It is demonstrated that nanostructured titanium (IV) oxide (TiO 2) films can be deposited on glass substrates at 95 °C using hydrothermal growth, their properties being greatly affected by the substrate materials. Anatase TiO 2 films grown on ITO for deposition period of 50 h were observed to exhibit a very efficient, reversible light-induced transition to super-hydrophilicity, reaching a nearly zero contact angle. Enhanced photocatalytic activity (65%) was found for the rutile TiO 2 samples grown on microscope glass, possibly due to their higher roughness with respect to anatase grown on ITO. The effect of the substrate material used is discussed in terms of the TiO 2 phase and morphology control, for the best photoinduced hydrophilic and photocatalytic performance of the samples.

Synthesis and Characterization of Nanostructured Titania Films for Dye-Sensitized Solar Cells

The nature and morphology of titanium dioxide films play a significant role in determining the overall efficiency of dye-sensitized solar cell (DSSCs). In this work, the preparation of nanostructured titania particles by sol-gel method (SG-TiO2) and its characterization were investigated for the application of DSSCs. The samples were characterized by XRD, XPS, FE-SEM, BET and FT-IR analysis. The energy conversion efficiency of SG-TiO2 was approximately 8.3 % under illumination with AM 1.5 (100 mW/cm 2 ) simulated sunlight. DSSCs made of SG-TiO2 nanocrystalline films as photoanodes achieved better energy conversion efficiency compared to those prepared using commercially available Degussa P25.

Optical constants of sol-gel derived TiO2 films characterized by spectroscopic ellipsometry

Nanostructured titanium oxide films were deposited on silicon substrate via sol-gel dip coating method with tetrabutyl titanate as precursor. With reflective spectroscopic ellipsometry, the ellipsometric parameters Ψ and Δ of TiO2 films were measured. Then, with the Cauchy model, the ellipsometric data were fitted, and both the thickness and the optical constants at 380—800 nm wavelength of the films were obtained. A comparison was made between the reflectance of the films derived with the spectrophotometer and the simulated results. Meanwhile, the thickness of the films was calculated by interference method. Moreover, with the atomic force microscopy the surface microstructures of the films annealed at different temperatures were observed, and the relationship between the surface microstructures and optical constants of films was further discussed. The results showed that Cauchy model works well in describing the dispersion relationship of the TiO2 films, and the variation rules of optical constants （the refractive index, the extinction coefficient） with wavelength were obtained. The optical constants of the films were related with the microstructure. Those simulated reflectance spectrum accorded well with the measured result. And with a deviation of only 25%, the calculated value of the thickness was in accordance with which was obtained by spectroscopic ellipsometry.

Electrochemical fabrication of anatase TiO 2 nanostructure as an anode material for aqueous lithium-ion batteries

Nanostructured titanium oxide films are fabricated directly by an anodic electrodeposition strategy at an aqueous TiCl 3 solution. Surface morphology shows that the deposited films are consisted of fine particles having 15–25 nm in diameter. Annealing temperature influences both the crystal structure and the electrochemical performance of the deposited titanium oxide. When the annealing temperature exceeds 300 °C, the poorly crystalline titanium oxide converts into anatase phase. Cyclic voltammograms (CVs) show that the anatase titanium oxide films exhibit reversible insertion/de-insertion of lithium ion in an aqueous LiOH electrolyte. The formation of lithiated titanium oxide is confirmed from an X-ray photoelectron spectroscopy. An optimal annealing temperature is found to be about 400 °C in terms of the CV peak current density. In addition, the diffusion coefficient of lithium ion in cathodic process (1.6 × 10 −15 cm 2 s −1) is higher than that of anodic process (9.4 × 10 −16 cm 2 s −1), probably due to the formation of higher O–Li bond strength during the lithium insertion.

Optical properties of cluster-based titanium and titanium oxide films

The optical properties of nanostructured titanium and titanium oxide films grown on transparent substrates have been investigated. Titanium films were produced either by cluster deposition or by atom deposition, and subsequently the films were oxidised by controlled exposure to oxygen. Optical extinction spectra in the ultraviolet and visible were recorded during film growth and oxidation. Before oxidation the extinction showed the characteristics of metallic titanium, with the spectrum of the cluster-based film indicating a structure of small spherical particles. After oxidation a band gap opened up and the films became transparent in the visible, and peaks appeared in the spectrum of the sample grown by atom deposition.