Sihai Cao

A novel BiOCl film with flowerlike hierarchical structures and its optical properties.

A novel BiOCl film with flowerlike hierarchical structures has been fabricated for the first time by dipping Bi film in a mixed solution of H(2)O(2) and HCl. This method presents the advantages of a simple technique, template-free, uniform and controllable morphology, as well as easy mass production. Each flowerlike hierarchical structure is composed of several dozen ultra-thin single-crystal nanopetals which grow along the 110 directions in the tetragonal structure. The layered growth of nanopetals is related to the more marked anion polarization along the c axis and layered stacking of various atoms (Cl-Bi-O-Bi-Cl). The growth mechanism of the BiOCl hierarchical structure is preferred to be a nucleation-dissolution-recrystallization process. A Raman shift originating from laser-induced compressive stress is observed. Photoluminescence (PL) spectra of the BiOCl film show principal green emission, indicating potential applications in optoelectronic devices.

Topotactic transformations of superstructures: from thin films to two-dimensional networks to nested two-dimensional networks.

Design and synthesis of super-nanostructures is one of the key and prominent topics in nanotechnology. Here we propose a novel methodology for synthesizing complex hierarchical superstructures using sacrificial templates composed of ordered two-dimensional (2D) nanostructures through lattice-directed topotactic transformations. The fabricated superstructures are nested 2D orthogonal Bi(2)S(3) networks composed of nanorods. Further investigation indicates that the lattice matching between the product and sacrificial template is the dominant mechanism for the formation of the superstructures, which agrees well with the simulation results based on an anisotropic nucleation and growth analysis. Our approach may provide a promising way toward a lattice-directed nonlithographic nanofabrication technique for making functional porous nanoarchitectures and electronic devices.

Grayscale photomask fabricated by laser direct writing in metallic nano-films

The grayscale photomask plays a key role in grayscale lithography for creating 3D microstructures like micro-optical elements and MEMS structures, but how to fabricate grayscale masks in a cost-effective way is still a big challenge. Here we present novel low cost grayscale masks created in a two-step method by laser direct writing on Sn nano-films, which demonstrate continuous-tone gray levels depended on writing powers. The mechanism of the gray levels is due to the coexistence of the metal and the oxides formed in a laser-induced thermal process. The photomasks reveal good technical properties in fabricating 3D microstructures for practical applications.

Laser direct writing of nanoreliefs in Sn nanofilms.

High-resolution (approximately 200 nm) nanoreliefs, which possess a controllable height change (Deltah, up to film thickness) and transmittance or reflectance, have been successfully fabricated in 12-nm-thick Sn films by using 532 nm pulsed laser direct writing. Different from current micro/nanofabrication techniques, the height change of the nanoreliefs is generated by a laser-induced-thickening process. The majority of the height change comes from a balling and coarsening effect rather than oxidation of grains. Because both optical density and Deltah of the nanoreliefs are almost linear to laser power, the optical images can highly resemble the topographic images. This technique is useful for fabricating complicated nanorelief structures and fine images.

Study on readout durability of super-RENS disk

Characteristics essential for the readout durability of a superresolution near-field structure (super-RENS) disk are studied experimentally by using a home-built optical measuring setup and atomic force microscope, based on a simplified PtOx super-RENS disk. The experimental results show that for a super-RENS disk with constant structure and materials, readout signals including transmittance and reflectance vary with changes in bubble shape and size, indicating that the readout durability of the disk has a strong dependence on bubble stability, which is closely related to the thickness of the cover layer, the recording power and readout power, and the mechanical properties of the dielectric layer. Based on our experimental results, the main direction for improving readout durability is also proposed.

Transparency conversion mechanism and laser induced fast response of bimetallic Bi/In thin film

Transparency conversion mechanism and laser induced fast response velocity of bimetallic Bi/In thin film is studied. Heat-treatment and laser exposure with different pulse width induced transparency is investigated by using ultraviolet-visible (UV-VIS) spectrometer, X-ray diffraction (XRD), Auger Electron Scan (AES), microscope and field emission scanning electron microscopy (FESEM). Research results show that oxidation is regarded as the reason for heat treated and long-pulsed laser exposure induced transparency conversion. Laser ablation is demonstrated to be the main reason for short-pulsed (~7ns) laser induced transparency conversion. For Bi/In thin film covered with a protection layer of (ZnS)0.85(SiO2)0.15 thin film, it exhibit fast response as fast as less than 100ns. The conclusions contribute to understanding and development of materials for thermal resist, photomask, optical storage medium and transparent conductive oxide with better performance.

Ordered Metal Film Pattern with Submicron Period

The wavelength of a metallic wrinkle has been decreased to 500 nm using a polymer/metal bilayer system. The good agreement of experimental results with an existing theory indicates that a continuous mechanical model is still appropriate for polymer/metal bilayer wrinkling even when a metal film is ultrathin at 5 nm thickness. The order of the submicron structure can be effectively controlled by prefabricating structures on polymer underlays. A large-area, cost-effective method of fabricating the submicron structure is provided and shows potential in nanostructure fabrication.

Function of bubble pit in super-RENS storage

In this paper, functions of bubble pit that is formed in a recording process of a super-resolution near-field structure (super-RENS) disk are discussed. The result shows that the recorded bubble pit has a greatly influence on both writing and reading for super-RENS disk. The relationship between the bubble pit and readout signal is also investigated.