Investigation on surface properties of TiO2 films modified by DC glow discharge plasma

In the present work, TiO₂ films deposited on polyethylene terephthalate substrates by dip coating technique were subsequently treated by DC glow discharge plasma as a function of discharge potential. Hydrophilicity of these TiO₂ film surfaces was analyzed by contact angle measurements. Atomic force microscopy (AFM) revealed changes in surface morphology of the plasma treated TiO₂ films. Modifications in structural and chemical composition of the TiO₂ films were detected by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The blood compatibility of TiO₂ films was studied by in vitro investigation which includes thrombus formation and whole blood clotting time analysis (WBCT). It was found that the plasma treatment results in blood compatibility enhancement attributed to the structural, chemical and morphological properties of the modified film surfaces.     

Surface functionalization, morphology and thermal properties of polyamide6/O-MMT composite nanofibers by Fe2O3 sputter coating

In the present work, the pure polyamide6 (PA6) nanofiber and PA6/organically modified montmorillonite (O-MMT) composite nanofiber were firstly prepared by a facile compounding process with electrospinning, and then coated by nanosize Fe₂O₃ using magnetron sputter technique. The effects of Fe₂O₃ sputter coating on structures, surface morphology and thermal stability were characterized by scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDX), atomic force microscope (AFM) and thermogravimetric analyses (TGA), respectively. The SEM images showed that the diameters of composite nanofiber were decreased with the loadings of O-MMT and the nanosize Fe₂O₃ is well coated on the surface of the homogeneous and cylindrical nanofibers. The XPS spectra reflected the chemical features of the deposited nanostructures. The EDX confirmed the presence of the O-MMT and Fe₂O₃ in the fibers. The AFM observation revealed that there was a remarkable difference in the surface morphology of composite nanofiber before and after sputter coating. The TGA analysis indicated the barrier effects of silicate clay layers and catalysis effects of Fe₂O₃ improved thermal stability properties of the composite nanofiber.     

Biomimetic Ca-P coating on pre-calcified Ti plates by electrodeposition method

A new electrodeposition method was presented for Ca-P coating on pre-calcified titanium (PTi) plates at room temperature. The biomimetic coating morphology was investigated by scanning electron microscopy (SEM). X-ray photoelectron spectroscopy (XPS) results indicated that the functional TiO_x layer with groups of -Ca and -OH was formed on PTi surface after pre-calcified chemical treatment. The TiO_x layer showed a lower water contact angle and lower surface energy than those of pure titanium surfaces, and the PTi surface natures are benefited by coupling biomimetic Ca-P layer with bioactivity in the electrodeposition process. Moreover, the crystallization of Ca-P precipitate and the bond strength of coating to PTi substrates were improved significantly by post-treatments. Our results suggest this new coating process and its subsequent application to biomedical implant devices.     

Femtosecond pulsed laser deposition of nanostructured TiO2 films

Nanostructured deposits of TiO₂ were grown on Si (1 0 0) substrates by laser ablating a TiO₂ sintered target in vacuum or in oxygen using a Ti:sapphire laser delivering 80 fs pulses. The effect of the laser irradiation wavelength on the obtained nanostructures, was investigated using 800, 400 and 266 nm at different substrate temperatures and pressures of oxygen. The composition of the deposits was characterized using X-ray photoelectron spectroscopy (XPS) and the surface morphology was studied by environmental scanning electron microscopy (ESEM) and atomic force microscopy (AFM). Deposits are absent of microscopic droplets in all conditions explored. The best deposits, constituted by nanoparticles of an average diameter of 30 nm with a narrow size distribution, were obtained at the shorter laser wavelength of 266 nm under vacuum at substrate room temperature.     

Pulsed laser deposition of TiO<Subscript>2</Subscript>: diagnostic of the plume and characterization of nanostructured deposits

Promising applications of TiO₂ nanostructures include the development of optical devices, sensors, photocatalysts and self-cleaning coatings. In view of their importance, research on the synthesis of nanosized TiO₂ is a particularly active field. In this work we report on the investigation of the effect of laser irradiation wavelength (Q-switched Nd:YAG laser at 532, 355 and 266 nm), the temperature of the substrate and the atmosphere of deposition (vacuum, Ar and O₂) that are suitable for obtaining nanostructured deposits from TiO₂ sintered targets. The ablation plume emission is characterized with spectral and temporal resolution by optical emission spectroscopy (OES), while the surface morphology and chemical states of the material deposited on a Si (100) substrate are examined by environmental scanning electron microscopy (ESEM) and atomic force microscopy (AFM) and by X-ray photoelectron spectroscopy (XPS), respectively. Deposits with nanostructured morphology with grain size down to 40 nm and keeping the stoichiometry of the targets were obtained at high temperature, while the highest concentration of particulates was observed at the longest laser wavelength of 532 nm on a substrate heated up to 650°C. In situ characterization of the ablation plume, carried out by OES, indicated the presence of emissions assigned to Ti I, Ti II and O I.     

Surface modification of titanium by nano-TiO2/HA bioceramic coating

A nano-TiO₂/hydroxyapatite composite bioceramic coating was developed and applied to the surfaces of pure titanium discs by the sol-gel method. A TiO₂ anatase bioceramic coating was utilized in the inner layer, which could adhere tightly to the titanium substrate. A porous hydroxyapatite (HA) bioceramic coating was utilized in the outer layer, which has higher solubility and better short-term bioactivity. Conventional HA coatings and commercially pure titanium were used as controls. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed to characterize the crystallization, surface morphology, and thickness of the coatings. The bioactivities of the coatings were evaluated by in vitro osteoblast cultures. Results showed that the nano-TiO₂/HA composite bioceramic coating exhibited good crystallization and homogeneous, nano-scale surface morphology. In addition, the nano-TiO₂/HA coating adhered tightly to the substrate, and the in vitro osteoblast cultures exhibited satisfactory bioactivity.     

Surface morphology of cellulose films prepared by spin coating on silicon oxide substrates pretreated with cationic polyelectrolyte

Flat cellulose films were prepared and morphologically modified by spin coating a cellulose/N-methylmorpholine-N-oxide/H₂O solution onto silicon oxide substrates pre-coated with a cationic polyelectrolyte. Spin-coated cellulose films were allowed to stably form on the silicon oxide substrates by pretreatment with either polydiallyldimethylammonium chloride (PDADMAC) or polyvinylamine (PVAm). The film surfaces obtained were analyzed by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). AFM topographical images of the cellulose film surfaces showed a different morphology depending on the underlying polymer, where PVAm pretreatment brought about an anisotropic surface topology. These results suggest that the specific attraction acting at the cellulose/polymer interface influences both the film formation and surface morphology of the cellulose layer. Differences in the solvent used to precipitate cellulose caused variations in the surface roughness by affecting the cellulose separation behavior. The morphological features of spin-coated cellulose film surfaces could be altered to some extent by these film preparation techniques.     

Titania surface modification and photovoltaic characteristics with tungsten oxide

WO₃-coated TiO₂ film was prepared by depositing TiO₂ suspension containing small amounts of ammonium tungstate solution. The morphology and structure of the samples were characterized with high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and photoluminescence (PL) emission spectrum. The results showed that WO₃ formed a coating layer on surface of TiO₂ and significantly reduced the surface traps of TiO₂ nanoparticles. Transient photovoltage and electrochemical impedance measurements (EIS) were employed to study the charge separation/recombination process. The results revealed that the charge recombination was greatly retarded and the electron lifetime was increased due to the coating layer of WO₃. These observations showed good correlation with current-voltage analyses of dye-sensitized solar cell fabricated from these films, with WO₃ overlayer resulting in an increase in open-circuit voltage of up to 37 mV and 11% improvement in overall device efficiency.     

Surface characterization of TiO2 thin films obtained by high-energy reactive magnetron sputtering

This paper presents the results of surface characterization of TiO₂ thin films deposited on different substrates by the use of high-energy reactive magnetron sputtering. Structural investigations carried out by X-ray diffraction (XRD) and atomic force microscopy (AFM) have shown a strong influence of both the substrate type, and its placement in the deposition chamber (relative to the sputtering target), on the structural properties of the films. In all cases, there is evidence for pseudoepitaxial growth. XRD examination showed existence of TiO₂-rutile phase with preferred (1 1 0) orientation and AFM measurements revealed nanocrystalline structure directly after deposition. X-ray photoelectron spectroscopy analysis showed that the TiO₂ films have stoichiometric composition.     

Ultra-fast laser ablation and deposition of TiO2

In this work we report on the properties of the ablation plume and the characteristics of the films produced by ultra-fast pulsed laser deposition (PLD) of TiO₂ in vacuum. Ablation was induced by using pulses with a duration of ≈300 fs at 527 nm. We discuss both the composition and the expansion dynamics of the TiO₂ plasma plume, measured by exploiting time- and space-resolved emission spectroscopy and gated imaging. The properties of the TiO₂ nanoparticles and nanoparticle-assembled films were characterized using different techniques, i.e. environmental scanning electron microscopy (ESEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). It is suggested that most of the material decomposes in the form of nanoparticles.     

Surface modification of PMMA/O-MMT composite microfibers by TiO2 coating

In the present work, poly(methyl methacrylate) (PMMA)/organically modified montmorillonite (O-MMT) composite microfibers were firstly prepared by emulsion polymerization combined with electrospinning, and then coated by nanosize titanium dioxide (TiO₂) using RF magnetron sputter technique. The modified surfaces of PMMA/O-MMT composite microfibers were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), UV-vis spectroscopy and drop shape analyzer. Finally, the photocatalytic properties of TiO₂ coated PMMA/O-MMT composite microfiber membranes were evaluated by degradation of methylene blue(MB) under UV illumination. The experimental results revealed that anatase-TiO₂ and rutile-TiO₂ nanoparticles were well spread and physically deposited on the surface of PMMA/O-MMT microfibers, and the wettability of the PMMA/O-MMT composite microfibers was improved after surface modification by sputter coating. Furthermore, the PMMA/O-MMT microfibers membrane coated with TiO₂ performed well in photocatalytic degradation of MB.     

XPS surface analysis of monocrystalline silicon solar cells for manufacturing control

X-ray photoelectron spectroscopy (XPS) has been applied to surfaces of silicon wafers in the different stages of the assembly line for large-scale monocrystalline silicon solar cell manufacturing (ISOFOTON, Malaga, Spain). XPS results have shown that a considerable amount of carbon is present on the pyramidal-textured monocrystalline silicon surface. This amount decreases slightly but is still present after the process of phosphor diffusion (p-n junction), as well as after subsequent calcination in humid air for SiO₂ film formation (passivation). This amount of carbon may be buried during the process of CVD coating an anti-reflection TiO₂ film. After calcination of the film in order to obtain the TiO₂ rutile phase, an even higher amount of carbon is detected on the TiO₂ anti-reflection coating surface. This indicates that not all organics from the tetra-isopropile ortho-titanate (TPT) precursor were released from the film. Furthermore, in this case phosphor is found in excess on the SiO₂ wafer surface (dead layer) and also on the rutile TiO₂ surface, indicating that an extra phosphor diffusion from the bulk silicon through the TiO₂ film has taken place during calcination. These results demonstrate how thermal treatments applied in the solar cell manufacturing assembly line can influence and may change the intended compositional distribution. These treatments may also introduce defects that act as recombination centres for charge carriers in the solar cell device. Received: 13 September 2000 / Accepted: 10 January 2001 / Published online: 3 May 2001     

Surface modification of silica-coated zirconia by chemical treatments

Zirconia surface modification by various chemical treatments after silica coating by sandblasting was investigated in this study. The surface of silica-coated dental zirconia was hydroxylated by treatment with different acids at room temperature for 4 h, rinsed with deionized water and air-dried. The modified surfaces were characterized by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Shifts in binding energies for Zr 3d_5/2 and Si 2p peaks were observed after treatment with acids, thereby showing a change in the chemical states of zirconium and silicon on the surface layer of silica-coated zirconia. The XPS analysis revealed that the silica-coated zirconia (SiO₂-ZrO₂) surfaces had changed to hydrous silica-coated zirconia (SiO₂-ZrO₂·nH₂O). One-way ANOVA analysis revealed there was significant difference in both surface roughness parameters of silica-coated zirconia after chemical treatments and the surface topography varied depending on the acid treatment.     

Evolution mechanism of alumina coating layer on rutile TiO2 powders and the pigmentary properties

The evolution of alumina coating layers on rutile TiO₂ particle surfaces was investigated starting from aluminum sulfate by a chemical liquid deposition method. The morphology of the alumina coating layers was determined by transmission electron microscopy. The chemical structure and the evolution mechanism of the alumina coating layers on TiO₂ surfaces were investigated by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and powder X-ray diffraction techniques. The dispersibility of the alumina-coated TiO₂ powders was determined by dynamic laser scattering (DLS) mode. The alumina coating layers existed in boehmite phase, AlOOH, and anchored at the surfaces of TiO₂ via Ti-O-Al bond. The formation of alumina coating layers on TiO₂ surfaces depended on the pH value of the deposition solution and the alumina loading. After coated by alumina layer, the dispersibility, whiteness, brightness, and light scattering index of the resultant samples were promoted.     

Formation of gold nanoparticles in heat-treated reactive co-sputtered Au-SiO2 thin films

In this work, formation of gold nanoparticles in radio frequency (RF) reactive magnetron co-sputtered Au-SiO₂ thin films post annealed at different temperatures in Ar + H₂ atmosphere has been investigated. Optical, surface topography, chemical state and crystalline properties of the prepared films were analyzed by using UV-visible spectrophotometry, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and X-ray diffractometry (XRD) techniques, respectively. Optical absorption spectrum of the Au-SiO₂ thin films annealed at 800 °C showed one surface plasmon resonance (SPR) absorption peak located at 520 nm relating to gold nanoparticles. According to XPS analysis, it was found that the gold nanoparticles had a tendency to accumulate on surface of the heat-treated films in the metallic state. AFM images showed that the nanoparticles were uniformly distributed on the film surface with grain size of about 30 nm. Using XRD analysis average crystalline size of the Au particles was estimated to about 20 nm.     

Electrostatic assembly of Cu2O nanoparticles on DNA templates

In this paper, a method for highly ordered assembly of cuprous oxide (Cu₂O) nanoparticles (NPs) by DNA templates was reported. Cetyltrimethylammonium bromide (CTAB)-capped Cu₂O NPs were adsorbed onto well-aligned λ-DNA chains to form necklace-like one-dimensional (1D) nanostructures. UV-vis, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) were used to characterize the nanostructure. The Cu₂O nanostructures fabricated with the method are both highly ordered and quite straight.     

Characterization of a bioactive nanotextured surface created by controlled chemical oxidation of titanium

Events at bone-implant interfaces are influenced by implant surface properties. Our previous work has revealed that osteogenic activity is enhanced by a nanotextured Ti surface, obtained by controlled chemical oxidation using a H₂SO₄/H₂O₂ mixture. To better understand the origin of this biological effect, we have carried out a characterization of the modified surface at the nanoscale. In particular, the morphology, structure, and chemical composition of the Ti surface were examined thoroughly. X-ray photoelectron spectroscopy (XPS), combined with grazing-angle Fourier-transform infrared (FTIR) spectroscopy, revealed that the oxidized Ti surface consists of almost pure TiO₂ with Ti:O ratio ranging between 1:2.02 and 1:2.08. Raman spectroscopy and X-ray diffraction (XRD) indicated that the chemically treated Ti surface is mainly composed of amorphous titania. Scanning electron microscopy (SEM) clearly showed that the treated Ti substrate becomes highly porous and has a surface consisting of nano-sized pits, which have average diameters and fractal dimensions ranging between 20-22 nm and 1.11-1.17, respectively. Atomic force microscopy (AFM) revealed a three-fold increase in surface roughness. The thickness of the oxide layer on the treated Ti surface is estimated to be ∼32-40 nm. Together, these observations provide a detailed characterization of chemically oxidized Ti surfaces at the nanoscale and offer new prospects for understanding and controlling the relationship between the properties of materials and their interactions with cells. Our work brings us closer to the creation of “intelligent” implant surfaces, capable of selectively influencing cell behavior.     

Physicochemical and photocatalytic activities of self-assembling TiO2 nanoparticles on nanocarbons surface

TiO₂ nanoparticles were self-assembled on three different dimensional nanocarbon (SWCNT, C₆₀ and graphene) surfaces by a uniform thermal reaction. The effective anchoring of TiO₂ nanoparticles on the nanocarbon surfaces was characterized by FT-IR, XRD, XPS, TEM, Raman spectroscopy, PL and UV-Vis. By investigating the effect of different carbon nanostructures on TiO₂ photocatalyst system, we found that the enhancing photocatalytic activities of nanocarbon/TiO₂ (NT) nanocomposites have still related to great adsorbability and effective charge transfer by nanocarbon introduced, however, no more insights can be provided for peculiar properties on different nanostructures, although graphene by itself has an excellent structure and morphology.     

Field-emission enhancement of molybdenum oxide nanowires with nanoprotrusions

The field-emission properties of molybdenum oxide nanowires grown on a silicon substrate and its emission performance in various vacuum gaps are reported in this article. A new kind of molybdenum oxides named nanowires with nanoscale protrusions on their surfaces were grown by thermal vapor deposition with a length of ~1 μm and an average diameter of ~50 nm. The morphology, structure, composition and chemical states of the prepared nanostructures were characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). According to XRD, XPS, and TEM analyses, the synthesized samples were composed of MoO₂ nanowires formed over a thin layer of crystalline Mo₄O₁₁. TEM observation revealed that these nanowires have some nanoscale protrusion on their surface. These nanoprotrusions resulted in enhancement of field-emission properties of nanowires comprising nanoprotrusions. The turn-on emission field and the enhancement factor of this type of nanostructures were measured 0.2 V/μm and 42991 at the vacuum gap of 300 μm, respectively. These excellent emission properties are attributed to the special structure of the nanowires that have potential for utilizing in vacuum nanoelectronic and microelectronic applications.     

Synthesis and application of the solar cell of poly(3-hexylthiophene)/Fe N/titanium dioxide nanocomposite material

A series of nanocomposites of poly(3-hexylthiophene) with Fe N-doped TiO₂ (P3HT/Fe N/TiO₂) were synthesized by the chemical method in situ. The structure of the prepared composites was characterized using X-ray diffraction patterns (XRD), infrared spectroscopy (IR), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). Optical and electrochemical properties were determined using UV-vis spectroscopy, fluorescence spectroscopy, and cyclic voltammetry. These tests indicated that P3HT/Fe N/TiO₂ is a new p-n semiconductor. Two solar cells based on P3HT/Fe N/TiO₂ were manufactured and studied.