Controlled Deposition of Silver Nanoparticles in Mesoporous Single‐ or Multilayer Thin Films: From Tuned Pore Filling to Selective Spatial Location of Nanometric Objects

Silver nanoparticle assemblies are embedded within mesoporous oxide thin films by an in situ mild reduction leading to nanoparticle–mesoporous oxide thin‐film composites (NP@MOTF). A quantitative method based on X‐ray reflectivity is developed and validated with energy dispersive spectroscopy in order to assess pore filling. The use of dilute formaldehyde solutions leads to control over the formation of silver nanoparticles within mesoporous titania films. Inclusion of silver nanoparticles in mesoporous silica requires more drastic conditions. This difference in reactivity can be exploited to selectively synthesize nanoparticles in a predetermined layer of a multilayered mesoporous stack leading to complex 1D‐ordered multilayers with precise spatial location of nanometric objects. The metal oxide nanocomposites synthesized have potential applications in catalysis, optical devices, surface‐enhanced Raman scattering, and metal enhancement fluorescence.     

Deformation of Mesoporous Titania Nanostructures in Contact with D2O Vapor

For many applications, mesoporous titania nanostructures are exposed to water or need to be backfilled via infiltration with an aqueous solution, which can cause deformations of the nanostructure by capillary forces. In this work, the degree of deformation caused by water infiltration in two types of mesoporous, nanostructured titania films exposed to water vapor is compared. The different types of nanostructured titania films are prepared via a polymer template assisted sol–gel synthesis in conjunction with a polymer‐template removal at high‐temperatures under ambient conditions versus nitrogen atmosphere. Information about surface and inner morphology is extracted by scanning electron microscopy and grazing incidence small‐angle neutron scattering (GISANS) measurements, respectively. Furthermore, complementary information on thin film composition and porosity are probed via X‐ray reflectivity. The backfilling induced deformation of near surface structures and structures inside the mesoporous titania films is determined by GISANS before and after D₂O infiltration. The respective atmosphere used for template removal influences the details of the titania nanostructure and strongly impacts the degree of water induced deformation. Drying of the films shows reversibility of the deformation.     

Gold-titania nanocomposite films with a periodic 3D nanostructure

In this study, we synthesized gold-titania nanocomposite thin films by using mesoporous titania thin films formed on indium tin oxide substrates as templates. The pore structure of our mesoporous titania thin films can be described as a periodic 3D pore network by interconnecting 7 nm sized cages. Electrochemical deposition of gold into the pores led to gold-titania nanocomposite films. Both gold and titania form continuous 3D network structures with internal periodicity. Because of the low conductivity of indium tin oxide substrate, the deposited gold formed isotropic islands. The absorption spectrum of the resultant gold-titania nanocomposite thin films showed two peaks, one at 640 nm and the other over a broad range of wavelengths longer than 1500 nm. These peaks grow with the increase of the deposition time but do not change the positions. The optical properties were explained in terms of the unique nanostructure of our gold-titania nanocomposite film.     

Ordered mesoporous silicon through magnesium reduction of polymer templated silica thin films

This paper describes the process of making ordered mesoporous silicon (Si) thin films. The process begins with mesoporous silica (SiO 2) thin films that are produced via evaporation induced self-assembly (EISA) using sol-gel silica precursors with a diblock copolymer template. This results in a film with a cubic lattice of 15 nm diameter pores and 10 nm thick walls. The silicon is produced through reduction of the silica thin films in a magnesium (Mg) vapor at 675 degrees C. Magnesium reduction preserves the ordered pore-solid architecture but replaces the dense silica walls with 10-17 nm silicon crystallites. The resulting porous silicon films are characterized by a combination of low and high angle X-ray diffraction, combined with direct SEM imaging. The result is a straightforward route to the production of ordered nanoporous silicon.     

蒸发诱导自组装仿生合成高有序度三维六方介孔氧化硅薄膜

借鉴自然界生物矿化的形成机理,利用蒸发诱导自组装(EISA)的方法,以十六烷基三甲基溴化铵(CTAB)为结构导向剂,正硅酸乙酯(TEOS)为硅源,通过浸渍提拉在普通玻璃片上制备出高有序度、三维六方结构的介孔氧化硅薄膜,通过XRD、TEM、低温N2吸附/脱附等方法对薄膜进行了表征,并初步讨论了形成三维六方结构的机理.     

Transparent high refractive index nanocomposite thin films

This work reports the preparation of acetic acid-modified TiO₂ nanoparticles by sol–gel synthesis method. The nanoparticles can be incorporated directly into the polymer matrix to form transparent high refractive index nanocomposite thin films. The result shows that increasing the titania content in the hybrid nanocomposite thin films can significantly increase the refractive index. Hybrid nanocomposite thin film with refractive index value of 2.38 had been prepared. All prepared films also exhibit excellent optical transparency in the visible region.     

Confined palladium colloids in mesoporous frameworks for carbon nanotube growth

Palladium colloidal nanoparticles with an average size of approximately 2.4 nm have been incorporated into mesoporous inorganic thin films following a multistep approach. This involves the deposition of mesoporous titania thin films with a thickness of 200 nm by spin-coating on titanium plates with a superhydrophilic titania outer layer and activation by calcination in a vacuum furnace at 573 K. Nanoparticles have been confined within the porous titania network by dip-coating noble metal suspensions onto these mesoporous thin films. Finally, the resulting nanoconfined systems were used as substrates for the growth of oriented carbon nanotubes (CNTs) using plasma-enhanced chemical vapour deposition at 923 K in order to enhance their surface area. These CNTs were tested in the hydrogenation of phenylacetylene by hydrogen in a batch reactor. The initial reaction rate observed on a CNT/TiO₂ structured catalyst was considerably higher than that on 1 wt% Pd/TiO₂ thin films.     

Highly-ordered mesoporous titania thin films prepared via surfactant assembly on conductive indium-tin-oxide/glass substrate and its optical properties

Highly ordered mesoporous titanium dioxide (titania, TiO₂) thin films on indium-tin-oxide (ITO) coated glass were prepared via a Pluronic (P123) block copolymer template and a hydrophilic TiO₂ buffer layer. The contraction of the 3D hexagonal array of P123 micelles upon calcination merges the titania domains on the TiO₂ buffer layer to form mesoporous films with a mesochannel diameter of approximately 10 nm and a pore-to-pore distance of 10 nm. The mesoporous titania films on TiO₂-buffered ITO/glass featured an inverse mesospace with a hexagonally-ordered structure, whereas the films formed without a TiO₂ buffer layer had a disordered microstructure with submicron cracks because of non-uniform water condensation on the hydrophobic ITO/glass surface. The density of the mesoporous film was 83% that of a bulk TiO₂ film. The optical band gap of the mesoporous titania thin film was approximately 3.4 eV, larger than that for nonporous anatase TiO₂ (~ 3.2 eV), suggesting that the nanoscopic grain size leads to an increase in the band gap due to weak quantum confinement effects. The ability to form highly-ordered mesoporous titania films on electrically conductive and transparent substrates offers the potential for facile fabrication of high surface area semiconductive films with small diffusion lengths for optoelectronics applications.     

High thermal stability PS-<Emphasis Type="Italic">b</Emphasis>-PEO templated mesoporous titania film

For many advanced applications, high thermal stability above 400 °C remains as a challenge for the ordered mesoporous titania films. In this work, we attempt to increase the thermal stability of mesoporous structure in titania film crystallization via PS-b-PEO block copolymer templating route. This paper reports the highly crystallized mesoporous titania film on silicon substrate thermally stable at 600 °C. The photocatalytic activity of the titania mesoporous film was also shown to be twice of that templated by F127 for degradation of methylene blue (MB). The present results also indicate that at low crystallinity, photocatalytic activity is controlled primarily by crystal perfection rather that surface area.     

Combining mixed titania morphologies into a complex assembly thin film by iterative block-copolymer-based sol–gel templating

Sol–gel templating combined with iterative spin-coating steps are used to custom-tailor hierarchically structured titania thin films. Using poly(styrene-block-ethylene oxide) P(S-b-PEO) as the structure directing agent, a foam-like structure is combined with nanogranules. Both structural elements are merged into a complex assembly in thin film geometry. The resulting morphology is pictured by SEM and probed with GISAXS. The installed mesoporous titania sandwich structure exhibits holes with a size of 45 nm which makes it promising for applications in photovoltaics or photocatalysis. An optical characterization completes the structural investigation.     

Effects of post-deposition chemical treatment on the formation of mesoporous titania films

Mesoporous titania films have been synthesized by a modified sol–gel method in conjunction with amphiphilic triblock copolymers. The effects of ammonia vapor treatment on the formation of mesoporous structures were investigated. Mesoporous titania films with hexagonal structures were obtained by ammonia vapor treatment. Without ammonia vapor treatment, it was found that the mesoporous structures collapse due to crystallization. The framework of mesoporous titania was found to be amorphous. Mesoporous titania films prepared by ammonia vapor treatment showed thermal stability up to 500 °C. Mesoporous samples showed better photo-catalytic activity than anatase titania films under UV-light irradiation.     

微波等离子体刻蚀处理对金刚石薄膜涂层刀具附着力和切削性能的影响

用HFCVD法在硬质合金（YG6）刀具衬底上沉积金刚石薄膜,用氢微波等离子体刻蚀的方法对衬底进行表面预处理,研究了该预处理技术对WC硬质合金衬底表面成分的影响,进一步探讨了所沉积金刚石薄膜的表面形貌和附着力,并通过难加工材料实际切削试验。研究了所制备的金刚石薄膜涂层刀具的切削性能。试验结果表明,Ar-H2微波等离子体刻蚀脱碳处理是提高金刚石薄膜附着力和改善涂层刀具切削性能的有效预处理方法。     

Etch damage characteristics of TiO2 thin films by capacitively coupled RF Ar plasmas

Etch damage of TiO₂ thin films with the anatase phase by capacitively coupled RF Ar plasmas has been investigated. The plasma etching causes a mixed phase of anatase and rutile or the rutile phase. The effect of Ar plasma etching damage on degenerating TiO₂ thin films is dependent on gas pressure and etching time. The physical etching effect at a low gas pressure (1.3 Pa) contributes to the degradation: the atomic O concentration at the thin film surface is strongly increased. At a high gas pressure (13-27 Pa) and long etching time (60 min), there are a variety of surface defects or pits, which seem to be similar to those for GaN resulting from synergy effect between particle and UV radiation from the plasmas. For the hydrophilicity, the thin film etched at the high gas pressure and a short etching time (5 min) seems to have no etch damage: its contact angle property is almost similar to that for the as-grown thin film, and is independent of the black light irradiation. This result would probably result from formation of donor-like surface defects such as oxygen vacancy.     

Effect of porosity on the Seebeck coefficient of mesoporous TiO2 thin films

Mesoporous TiO₂ films were prepared by using titanium tetraisopropoxide as the titania precursor and triblock copolymer as the structure directing agent. The synthesized mesoporous TiO₂ film was confirmed to have the ordered pore structure with rutile phase by small angle and wide angle X-ray diffraction analyses. The mesoporous TiO₂ film has the porosity range from 21.6 to 35.6%, and its Seebeck coefficient was changed according to its porosity, up to −88.6 μV/K. From the obtained Seebeck coefficient, the ordered mesoporous TiO₂ film was found to be a good candidate of thermal sensing layer of thin film thermal sensor.     

Synthesis and tuning of ordering and crystallinity of mesoporous titanium dioxide film

Synthesis of well-organized and highly crystalline mesoporous titania (TiO₂) film is demonstrated using triblock copolymer (Pluronic P123) as a structure directing template, through the evaporation induced self-assembly (EISA) process. The issue of thermal and structural stability of a mesoporous TiO₂ film was addressed via optimization of annealing temperature and time. An anatase phase, high crystallinity TiO₂ film with ordered pores was obtained at 430 °C after annealing for 15 min. The synthesized film was crack free with TiO₂ nanoparticle size of 10–15 nm, quasi-hexagonal pore diameter in the range of 8–10 nm and film thickness of ~ 150 nm.     

Imaging reflectometry in situ

An innovative method of in situ real-time optical monitoring of thin film deposition and etching is presented. In this technique, intensity maps of a thin film corresponding to a series of wavelengths selected by a monochromator (300-800 nm) are recorded by a CCD camera. From the maps the reflectance spectra at individual points of the sample surface can be extracted. By fitting the reflectance spectra to the theoretical ones, the maps of a thin film morphology (including optical parameters) and their temporal development during technological processes can be obtained. The method was tested by in situ observation of the growth of silicon nitride and silicon oxide thin films prepared by ion beam sputtering and by the monitoring of etching of thermally grown SiO(2) thin films.     

Critical effect of aging condition on mesostructural ordering in mesoporous titania thin film

Here we demonstrate facile synthesis method for formation of highly ordered mesoporous cubic Im-3 m titania thin film. The mesostructural ordering is strongly dependent on the aging condition after the spin-coating. The aging condition under low temperature and low humidity is found as an optimum condition for achieving highly ordered mesostructure in titania thin films. The effects of other important synthetic parameters, such as pH of the precursor solutions and aging periods, on the mesostructural ordering are carefully examined. After the calcination, continuous mesoporous films with partially crystallized frameworks are formed without any cracks. The mesostructure of the calcined films is formed by thermal shrinkage of the original Im-3 m mesostructure. The mesostructural change in the films calcined at various temperatures are studied by using the grazing-incidence small-angle X-ray scattering (GI-SAXS). The GI-SAXS patterns show the strong shrinkage along the perpendicular direction to the substrate by increasing the calcination temperature.     

Synthesis and optical absorption property of ordered macroporous titania film doped with Ag nanoparticles

Ordered macroporous anatase titania films doped with Ag nanoparticles (NPs) were synthesized by infiltrating titania sol into the interstitial voids of polystyrene colloidal sphere templates, removing the templates, immersing the films in a silver nitrate solution, and subsequently reducing in hydrogen atmosphere. Ag NPs were distributed uniformly within the macropores of the anatase titania film. Both the macroporous titania films doped with Ag NPs and those without doping have a blue-shift compared with that of the sol–gel derived titania film. Except for the plasma resonance absorption of Ag NPs, the macroporous titania film doped with Ag NPs also has a red-shift compared with the undoped sample. The macroporous titania film doped with Ag NPs have potential applications in the fields of optics, gas sensors, and catalysis.     

Fabrication of mesoporous titania aerogel film via supercritical drying

Using a supercritical drying method, fluorine-doped tin oxide (FTO) glass was coated with a mesoporous titania aerogel film prepared from titania sols with viscosity between 10 and 60 cP that had been spin coated, immersed in IPA solution, and aged at least 3 weeks. Mesoporous titania aerogel film has an anatase structure, and an average porosity of 76%. It is hydrophilic, and its mechanical strength is improved by heat treatment at over 400 °C for 2 h. After heat treatment, the film retains its anatase structure and has a porosity of 68%. Dye-sensitized solar cells were fabricated using these mesoporous titania aerogel films. The thickness of the film was about 1 μm and the highest photo conversion efficiency, obtained when the film was heat treated at 450 °C for 2 h, was 3.71%.     

Effects of sol aging on mesoporous silica thin films organization

Cetyltrimethylammonium bromide (CTAB) templated mesoporous silica thin films were deposited on glass slides by evaporation-induced self-assembly (EISA) process using a dip-coating method. The effects of sol aging on the mesophase structure of the thin films organization were investigated. Identification of the structures was accomplished by coupling X-ray diffraction (XRD) and transmission electron microscope (TEM) investigations, and corresponding sol was characterized by ²⁹Si solution state nuclear magnetic resonance (²⁹Si NMR) and UV-Vis spectrophotometer for studying the mesophase structure evolution. Results indicate that sol aging has great effects on the mesophase structure of the films organization, which includes degree of order and phase transformation of mesoporous silica thin films. To obtain a better understanding of the effects of sol aging on the mesophase structure, the theories of apparent mass fractal dimension and charge density matching were introduced to explain the self-assembly process.