Lingyan Chen

ZrO2 thin films and ZrO2/SiO2 optical reflection filters deposited by sol–gel method

Abstract ZrO2 thin films were deposited by a wet chemical sol–gel method from forced hydrolysis of aqueous ZrOCl2 solution. Transmission electron microscopic observations confirmed the existence of little nanosized monoclinic ZrO2 particles in clear stable ethanolic ZrO2 colloidal suspensions. Twenty layers of ZrO2/SiO2 high reflectance filters using a quarterwave stack were fabricated by sol–gel spin-coating on K9 glass substrate. This filter exhibits a wide reflectance band near 1064 nm and a high transmittance region.

Sol–gel derived ZrO2–SiO2 highly reflective coatings

Abstract In this paper, colloid-based highly reflective coatings consisting of alternating layers of quarterwave thick high- and low-refractive index components were deposited on glass substrates by a sol–gel spin-coating method. SiO 2 was used as the low-refractive index component, and ZrO 2 as the high-refractive index material. The colloidal suspension of ZrO 2 , prepared by hydrothermal hydrolysis of ZrOCl 2 , contained monoclinic nanocrystalline ZrO 2 , with an average particle size of 15 nm. A minimum transmittance of 1% near 1064 nm was obtained from a 20-layer SiO 2 –ZrO 2 /PVP multilayer film. The ZrO 2 particles were deposited in an ethanolic suspension containing polyvinylpyroldione (PVP) as a binder. The maximum transmittance in the visible range was about 85%. A 1-on-1 laser-induced damage threshold of 16 J/cm 2 for the 20-layer SiO 2 –ZrO 2 /PVP film was observed using a Q-switched Nd:YAG high power laser at a wavelength of 1.06 μm and with a pulse width of 2.5 ns.

The investigation of the adsorption character of carbon aerogels

The influence of pyrolysis temperature and density on the microstructure of carbon aerogels is studied by nitrogen adsorption analysis. Resorcinol-formaldehyde (RF) aerogel and carbon aerogels all give type II isotherms and hysteresis loops of type A. Carbon aerogel pyrolized at 600°C has the largest specific surface area (SSA). The trend of pore size distribution of RF aerogel and its pyrolized derivatives is same. Carbon aerogels with low and high density have different pore size distribution, while carbon aerogel with low density has greater SSA.

Physical Properties of Silica Aerogels Prepared with Polyethoxydisiloxanes

Silica aerogels were made by sol-gel techniques using industrial silicon derivatives (polyethoxydisiloxanes, E-40), followed by supercritical drying with ethanol. The morphology and microstructure of the silica aerogels were investigated by using specific surface area, SBET, SEM, TEM and the pore size distribution techniques. The thermal conductivity was also measured as a function of air pressure. The results show that the diameter of the silica particles is about 13 nm and the pore size of the silica aerogels is 20–80 nm. The specific surface area of the silica aerogel is about 470 m2/g and the thermal conductivity of the silica aerogel prepared with E-40 is 0.014 w m−1 K−1 at room temperature and 1 atm.

Silylation of polydiethoxysiloxane derived silica aerogels

Abstract Silica aerogels were prepared with polydiethoxysiloxane (PDEOS) followed by silylation of the alcogels and supercritical drying from ethanol. Trimethylchlorosilane (TMCS) and dimethyldimethoxysilane (DMMOS) were used as the silylation agents. Transmission electron microscopy (TEM) and nitrogen sorption techniques were used to characterize the modified and unmodified silica aerogels. The existence of the methyl groups on the internal surface of aerogels was observed using an infrared and a 29 Si magic angle spinning nuclear magnetic resonance (MAS–NMR) spectrometer. The results indicate that the condensation degree of PDEOS derived silica aerogels is higher than that of TMOS and TEOS derived aerogels. The silylation process removes Si–OH surface groups by promoting silica polycondensation, resulting in a decrease of pore size and an increase of both particle size and specific surface area of the aerogels.

Surface Modification of Silica Aerogels Dried with 2-Methyl-1-Propanol in the Sub-Critical Pressure

Silica aerogels were made by sol-gel techniques using industrial silicon derivatives (polyethoxydisiloxanes, E-40), followed by drying under sub-critical pressure with iso-butanol. The shrinkage (linear), specific surface area, SBET, SEM, TEM and the pore size distribution of the silica aerogels were investigated. The results show that the shrinkage (linear) is below 5%, diameter of the silica particles is about 6 nm and the pore size of the silica aerogels is 10 nm. The specific surface area of the silica aerogel is 559.2 m2/g. IR and NMR techniques were used to determine the organic groups on the silica matrix, GC/MS was also introduced to analyse the composition of the recycled iso-butanol. The surface modification and the reactions of iso-butanol to the silica aerogel are also discussed.

Surface perturbation target for the Rayleigh–Taylor instability in inertial-confinement fusion experiments

A preparation process of a surface perturbation target was introduced in this article. Through laser interference and a nickel-electroplate process, sinusoidal surface perturbation on the photoresist and nickel plate mold with sinusoidal surface perturbation were obtained. We transferred sinusoidal perturbation on brominated polystyrene foils by a spin-coating process. By removing the brominated polystyrene foils from the nickel-plate mold, the brominated polystyrene sinusoidal surface perturbation target was obtained. The transfer precision of the sinusoidal perturbation was measured by scanning electron microscopy. The measurements showed that the surface perturbation was transferred precisely. The surface roughness on the surface perturbation target was about 15.0 nm, analyzed by an α-step apparatus.

SiO2GeO2 binary aerogels with ultralow density

Abstract Interest in the ultralow density X-ray laser target has led to the development of methods for preparing low density materials containing special elements such as Ge and Ta. A new method is used to synthesize ultralow density SiO2GeO2 binary aerogels, the density achieved can be as low as 5 kg/m3 and the weight percent of germanium can be higher than 40. TEM micrographs show that these SiO2GeO2 binary aerogels have a network structure with an average chain diameter of about 8 nm. SEM micrographs show their mesopores to be of the size 102 nm, while their pores of the size 1–102 nm are measured by the N2 adsorption method.

Preparation of zirconia thin films via sol-gel process from inorganic precursor

ZrO2 thin films were prepared by sol-gel technology from suitable zirconia aqueous colloidal suspensions containing nano-crystalline ZrO2 at room temperature synthesized by hydrothermal process from inorganic precursor (ZrOCl2 (DOT) 8 H2O). By adding a soluble organic binder PVP to the suspension prior to application, it substantially increased the coating refractive index and the abrasion- resistance as well as the laser damage threshold. The features of the coatings and the colloidal suspensions were investigated. Multilayer highly reflective dielectric coatings were also elaborated by laying down quarterwave- thick alternating coatings of the binder-aided zirconia and silica, which was prepared with the sol-gel process from TEOS. Laser damage thresholds of 20 and 18 J/cm2 (1064 nm, 1 ns) were achieved for single ZrO2-PVP coating and ZrO2-PVP/SiO2 multilayers respectively.

Preparation of TiO2 nanoparticle thin film with sol-gel process

TiO2 nanoparticle thin films are fabricated via sol-gel process followed by dip and spin coating technique, using Ti(OC4H9)4 as raw material. A complexing agent is used in order to form a stable sol. Experiments show that the colloidal particles in the sols are relatively large under basic catalyst conditions, while under acidic conditions, the colloidal particles are only about several nanometers. The properties and structures of the films are studied. The films are normally homogenous and crack-free. TEM shows that the films are composed of nanoparticles with a certain porosity. Under the thermal treatment of 80 degrees Celsius, the porosity and thickness of the film decrease while the refractive index increases from the original 1.70 to the final 1.89. When the temperature of the thermal treatment goes up, the size of the nanoparticles increases and crystallization occurs.