Xiaoxia Zhong

Optical properties of pulsed laser deposited rutile titanium dioxide films on quartz substrates determined by Raman scattering and transmittance spectra

Optical response of rutile TiO2 films grown under different laser energy by pulsed laser deposition has been investigated by Raman scattering and spectral transmittance. Dielectric functions in the photon energy range of 1.24–6.5 eV have been extracted by fitting the experimental data with the Adachi’s model [S. Adachi, Phys. Rev. B 35, 7454 (1987)]. The refractive index dispersion in the transparent region is mainly ascribed to the higher A1-A2 electronic transitions for the rutile TiO2 films. Owing to slightly different crystalline structures and film densities, the optical band gap linearly increases with increasing packing density. The phenomena were confirmed by different theoretical evaluation methods.

Low temperature deposition of nanocrystalline TiO2 films: enhancement of nanocrystal formation by energetic particle bombardment

This paper reports the important role of energetic particle bombardment in achieving low temperature deposition of nanocrystalline TiO2 films by reactive DC magnetron sputtering of Ti targets in a mixture of argon and oxygen. In this work, we studied the effect of particle bombardment in the film deposition process by control of external processing parameters, including total pressure Pt and negative substrate bias Vb. The result shows that the variation of energetic particle bombardment has a significant impact on substrate temperature, crystal structure, surface morphology and refractive index n of deposited TiO2 films and we believe the process of non-equilibrium atomic scale heating caused by energetic particle bombardment is the main reason for the nanocrystal formation at low temperature (below 75 °C).

Nanopore processing in dielectric materials and dielectric template-assisted nanoarray synthesis : Using pulsed bias to enhance process throughput and precision

An effective technique to improve the precision and throughput of energetic ion condensation through dielectric nanoporous templates and reduce nanopore clogging by using finely tuned pulsed bias is proposed. Multiscale numerical simulations of ion deposition show the possibility of controlling the dynamic charge balance on the upper template’s surface to minimize ion deposition on nanopore sidewalls and to deposit ions selectively on the substrate surface in contact with the pore opening. In this way, the shapes of nanodots in template-assisted nanoarray fabrication can be effectively controlled. The results are applicable to various processes involving porous dielectric nanomaterials and dense nanoarrays.

A comparative study of the influence of three pure titanium plates with different micro- and nanotopographic surfaces on preosteoblast behaviors

There is a great demand for dental implants with the ability to accelerate periimplant bone regeneration. Modification of surface micro- and nanotopographies has been revealed to affect bone cell metabolism. In this study, we utilized dielectric barrier discharge (DBD) technology to modify commercially pure titanium (Ti-tr) surfaces and then investigated the cytocompability of DBD-modified Ti surface when compared with machined (Ti-m) and polished (Ti-p) Ti surfaces. These three kinds of Ti plates exhibited different surface energies and topographies at the micro- and nanoscale levels. The DBD-treated pure Ti surface significantly enhances cell adhesion, spread, and proliferation of MC3T3-E1 preosteoblast cells compared with the Ti-p and Ti-m surfaces, suggesting that Ti-tr has better cytocompatibility compared with the other two surfaces. Preosteoblast cells on Ti-m surface exhibited higher alkaline phosphatase activity than cells on Ti-tr and Ti-p surfaces 14 days after seeding. No significant difference in alkaline phosphatase activity was observed between cells grown on Ti-tr and Ti-p surfaces. Our study demonstrated that DBD modification significantly enhanced cell adhesion, spread, and proliferation of preosteoblasts with no negative effects on cell differentiation. Microtopography and nanotopography of the surfaces of different materials and chemical/energetic properties have a synergistic effect on cell attachment, proliferation, and differentiation.

Nanosphere monolayer-templated, ion-assisted nanofeature etching in dielectric materials: a numerical simulation of nanoscale ion flux topography

The results of numerical simulations of nanometer precision distributions of microscopic ion fluxes in ion-assisted etching of nanoscale features on the surfaces of dielectric materials using a self-assembled monolayer of spherical nanoparticles as a mask are presented. It is shown that the ion fluxes to the substrate and nanosphere surfaces can be effectively controlled by the plasma parameters and the external bias applied to the substrate. By proper adjustment of these parameters, the ion flux can be focused onto the areas uncovered by the nanospheres. Under certain conditions, the ion flux distributions feature sophisticated hexagonal patterns, which may lead to very different nanofeature etching profiles. The results presented are generic and suggest viable ways to overcome some of the limitations of the existing plasma-assisted nanolithography.

Ion current distribution during deposition of dielectric material using an insulating porous alumina template

We have presented a numerical simulation of the deposition of dielectric material using an insulating porous template. A Maxwellian distribution has been used to calculate the original ion velocity when the ion leaves the plasma and enters the sheath. The microscopic electrical field over the template is considered to affect the ion motion. It is found that the electron temperature and nanopore structure can change the ion deposition rate effectively. However, the deposition rate decreases only slightly with the rise in plasma density and does not rely on the substrate bias obviously for the reason that the effect of electrical field near the template is limited. The result of our paper indicates that the templated i-PVD of dielectric nanodots is quite different from the templated i-PVD of metallic nanodots, and new ways should be tried for the plasma to fabricate dielectric nanodots using a porous template to make the effect from the electrical field and the substrate bias stronger.

Hydroxyapatite Films Deposited on TiN and TiO2 Buffer Layers by Radio-Frequency Magnetron Sputtering: Comparative Study

A comparative study was presented to demonstrate the clear influence of the different buffer layer (TiN and TiO2) on the HA film. In this study, magnetron sputtering was applied for different film deposition. Nano-indentation was used to examine the mechanical properties of the HA film on both TiN and TiO2 buffer layers. It is found that HA film on TiN buffer layer is harder and the HA film on TiO2 buffers is more rigid. Further more, the simulated body fluid (SBF) soaking test was selected to investigate the properties of the HA/TiN and HA/TiO2 films in the physiological media. The obvious delamination was observed on the surface of HA film on TiN buffer layer, while the surface morphology of HA film on TiO2 buffer layer remained nearly unchanged. The result indicated that TiO2 buffer layer shows a better interfacial bonding to the HA film.