Fabrication of Dimensional and Structural Controlled Open Pore, Mesoporous Silica Topographies on a Substrate.

Open pore mesoporous silica (MPS) thin films and channels were prepared on a substrate surface. The pore dimension, thickness and ordering of the MPS thin films were controlled by using different concentrations of the precursor and molecular weight of the pluronics. Spectroscopic and microscopic techniques were utilized to determine the alignment and ordering of the pores. Further, MPS channels on a substrate surface were fabricated using commercial available lithographic etch masks followed by an inductively coupled plasma (ICP) etch. Attempts were made to shrink the channel dimension by using a block copolymer (BCP) hard mask methodology. In this regard, polystyrene-b-poly(ethylene oxide) (PS-b-PEO) block copolymer (BCP) thin film forming perpendicularly oriented PEO cylinders in a PS matrix after microphase separation through solvent annealing was used as a structural template. An insitu hard mask methodology was applied which selectively incorporate the metal ions into the PEO microdomains followed by UV/Ozone treatment to generate the iron oxide hard mask nanopatterns. The aspect ratio of the MPS nanochannels can be varied by altering etching time without altering their shape. The MPS nanochannels exhibited good coverage across the entire substrate and allowed direct access to the pore structures.

Synthesis and stability of IR-820 and FITC doped silica nanoparticles.

Fluorescent silica nanoparticles (NPs) have potential in biomedical applications as diagnostics and traceable drug delivery agents. In this study, we have synthesized fluorescent dye grafted silica NPs in two step process. First, a stable method to synthesize various sizes of silica NPs ranging from 20 to 52, 95, 210 and 410nm have been successfully demonstrated. Secondly, as-synthesized silica NPs are readily grafted with some fluorescent dyes like IR-820 and fluorescein isothiocyanate (FITC) dyes by simple impregnation method. IR-820 and FITC dyes are 'activated' by (3-mercaptopropyl)trimethoxysilane (MPTMS) and (3-aminopropyl)triethoxysilane (APTS) respectively prior to the grafting on silica NPs. UV-vis spectroscopy is used to test the stability of dye grafted silica NPs. The fluorescent dye grafted silica NPs are quite stable in aqueous solution. Also, a new type of dual dye-doped hybrid silica nanoparticles has been developed. The combination of microscopic and spectroscopic techniques shows that the synthesis parameters have significant effects on the particle shape and size and is tuneable from a few nanometers to a few hundred nanometers. The ability to create size controlled nanoparticles with associated (optical) functionality may have significant importance in bio-medical imaging.

A positron annihilation spectroscopic investigation of europium-doped cerium oxide nanoparticles.

Doping in ceria (CeO2) nanoparticles with europium (Eu) of varying concentrations (0, 0.1, 0.5, …, 50 atom%) is studied using complementary experimental techniques and novel observations were made during the investigation. The immediate observable effect was a distinct reduction in particle sizes with increasing Eu concentration attributed to the relaxation of strain introduced due to the replacement of Ce(4+) ions by Eu(3+) ions of larger radius. However, this general trend was reversed in the doping concentration range of 0.1-1 atom% due to the reduction of Ce(4+) to Ce(3+) and the formation of anion vacancies. Quantum confinement effects became evident with the increase of band gap energy when the particle sizes reduced below 7-8 nm. Positron annihilation studies indicated the presence of vacancy type defects in the form of vacancy clusters within the nanoparticles. Some positron annihilation was also seen on the surface of crystallites as a result of diffusion of thermalized positrons before annihilation. Coincidence Doppler broadening measurements indicated the annihilation of positrons with electrons of different species of atoms and the characteristic S-W plot showed a kink-like feature at the particle sizes where quantum confinement effects began.