Densification of sol-gel silica thin films induced by hard X-rays generated by synchrotron radiation

First-principle study of neutron irradiation induced performance degradation of amorphous porous silica

Neutron irradiation induced degradation of porous silica film is studied by Molecular Dynamics and Density-Functional theory-based methods. The degradation of microscopic structure, thermal property, and optical property of porous silica film are systematically investigated. Low-energy recoil is used to simulate the neutron irradiation effect. The pair and bond angle distributions, and coordination number distributions reveal that, under neutron irradiation, the microscopic structure of porous silica film is obviously modified, and the coordination defects are induced. We find that the higher recoil energy, the more coordination defects are formed in the film. The increased defects lead to a decrease in thermal conductivity. In addition, neutron irradiation induces additional optical absorption peaks in UV region and increasement in refractive index, resulting in a noticeable reduction in light transmittance. The detailed calculation of density of states reveals that these optical absorption peaks originate from the irradiation induced defect states in band gap. Our work shows that low-energy neutron irradiation can induce obvious defect density and degrade thermal and optical properties of porous silica film, which are responsible for subsequent laser-induced damage.

X-Ray Lithography for Nanofabrication: Is There a Future?

X-ray lithography has been first proposed almost 50 years ago, and the related LIGA process around 25 years ago. It is therefore a good time to make an analysis of the technique, with its pros and cons. In this perspective article, we describe X-ray lithography’s latest advancements. First, we report the improvement in the fabrication of the high aspect ratio and high-resolution micro/nanostructures. Then, we present the radiation-assisted synthesis and processing of novel materials for the next generation of functional devices. We finally draw our conclusion on the future prospects of the technique.

Comparison between the UV and X-ray Photosensitivities of Hybrid TiO2-SiO2 Thin Layers

The photo-induced effects on sol–gel-based organo TiO₂-SiO₂ thin layers deposited by the dip-coating technique have been investigated using two very different light sources: A light-emitting diode (LED) emitting in the UV (at 365 nm, 3.4 eV) and an X-ray tube producing 40 keV mean-energy photons. The impact of adding a photo-initiator (2,2-dimethoxy-2-phenylacetophenone-DMPA) on the sol–gel photosensitivity is characterized namely in terms of the photo-induced refractive index measured through M-line spectroscopy. Results show that both silica-titania sol–gel films with or without the photo-initiator are photosensitive to both photon sources. The induced refractive index values reveal several features where slightly higher refractive indexes are obtained for the sol–gel containing the photo-initiator. UV and X-ray-induced polymerization degrees are discussed using Fourier-transform infrared (FTIR) spectroscopy where the densification of hybrid TiO₂-SiO₂ layers is related to the consumption of the CH=C groups and to the decomposition of Si-OH and Si-O-CH₃ bonds. X-rays are more efficient at densifying the TiO₂-SiO₂ inorganic and organic network with respect to the UV photons. Hard X-ray photolithography, where no cracks or damages are observed after intense exposition, can be a promising technique to design submicronic-structure patterns on TiO₂-SiO₂ thin layers for the building of optical sensors.

Hard X-rays for processing hybrid organic-inorganic thick films

Hard X-rays, deriving from a synchrotron light source, have been used as an effective tool for processing hybrid organic-inorganic films and thick coatings up to several micrometres. These coatings could be directly modified, in terms of composition and properties, by controlled exposure to X-rays. The physico-chemical properties of the coatings, such as hardness, refractive index and fluorescence, can be properly tuned using the interaction of hard X-rays with the sol-gel hybrid films. The changes in the microstructure have been correlated especially with the modification of the optical and the mechanical properties. A relationship between the degradation rate of the organic groups and the rise of fluorescence from the hybrid material has been observed; nanoindentation analysis of the coatings as a function of the X-ray doses has shown a not linear dependence between thickness and film hardness.

X-ray irradiation induced reduction and nanoclustering of lead in borosilicate glass

Under the influence of X-rays an unexpected formation of pure Pb nanoparticles was observed in PbS-doped borosilicate glass.

Simultaneous microfabrication and tuning of the permselective properties in microporous polymers using X-ray lithography

Microchannels are fabricated using a photosensitive polymer to which microporosity is tuned with different X-ray doses. Using hard X-ray irradiation, the micropattern is positioned with various geometries in a multi-level, three-dimensional structure, while controlling the pore size and transport properties of small molecules. This highly reliable fabrication process has potential for use in microfluidic devices with enhanced transport properties through microchannels.

Combining top-down and bottom-up routes for fabrication of mesoporous titania films containing ceria nanoparticles for free radical scavenging

Nanocomposite thin films formed by mesoporous titania layers loaded with ceria nanoparticles have been obtained by combining bottom-up self-assembly synthesis of a titania matrix with top-down hard X-ray lithography of nanocrystalline cerium oxide. At first the titania mesopores have been impregnated with the ceria precursor solution and then exposed to hard X-rays, which triggered the formation of crystalline cerium oxides within the pores inducing the in situ growth of nanoparticles with average size of 4 nm. It has been observed that the type of coordinating agent in the solution plays a primary role in the formation of nanoparticles. Different patterns have been also produced through deep X-ray lithography by spatially controlling the nanoparticle growth on the micrometer scale. The radical scavenging role of the nanocomposite films has been tested using as a benchmark the UV photodegradation of rhodamine 6G. After impregnation with a rhodamine 6G solution, samples with and without ceria have shown a remarkably different response upon exposure to UV light. The dye photodegradation on the surface of nanocomposite films appears strongly slowed down because of the antioxidation effect of ceria nanoparticles.

Hybrid materials with an increased resistance to hard X-rays using fullerenes as radical sponges

The protection of organic and hybrid organic-inorganic materials from X-ray damage is a fundamental technological issue for broadening the range of applications of these materials. In the present article it is shown that doping hybrid films with fullerenes C(60) gives a significant reduction of damage upon exposure to hard X-rays generated by a synchrotron source. At low X-ray dose the fullerene molecules act as `radical scavengers', considerably reducing the degradation of organic species triggered by radical formation. At higher doses the gradual hydroxylation of the fullerenes converts C(60) into fullerol and a bleaching of the radical sinking properties is observed.

Nanocomposite mesoporous ordered films for lab-on-chip intrinsic surface enhanced Raman scattering detection

Mesoporous nanocomposite materials have been fabricated through integration of evaporation-induced self-assembly and deep X-ray lithography. Micropatterned films made using a mesoporous ordered silica matrix which contains silver nanoparticles have been obtained. The exposure of the mesoporous films to high energy X-rays, which are generated by a synchrotron source, produces several effects: the removal of the surfactant, the densification of the silica backbone and the formation of silver nanoparticles. This integrated process produces a nanocomposite material which has a 2D-hexagonal organized porosity and silver nanoparticles with a sharp size distribution around 5 nm. The patterned nanostructured films have been tested as a lab-on-chip device for intrinsic surface enhanced Raman scattering detection using a solution containing rhodamine 6G in ethanol and measuring Raman response as a function of laser power.