Showing papers by "Xiang Zhang published in 2002"

Near-field two-photon nanolithography using an apertureless optical probe

Abstract: Near-field two-photon optical lithography is demonstrated by using ∼120 fs laser pulses at 790 nm in an apertureless near-field optical microscope, which produces lithographic features with ∼70 nm resolution. The technique takes advantage of the field enhancement at the extremity of a metallic probe to induce nanoscale two-photon absorption and polymerization in a commercial photoresist, SU-8. Even without optimization of the resist or laser pulses, the spatial resolution of this technique is as high as λ/10, nearly a factor of 2 better than techniques based on far field two-photon lithography.

The influences of the material properties on ceramic micro-stereolithography

Abstract: Ceramic micro-stereolithography (μSL) was recently introduced in the fabrication of complex 3D ceramic microstructures. Light scattering is found as an important factor in the μSL of ceramics. In this work, the Monte Carlo ray tracing method is employed to investigate the influences of the important materials properties on the scattering during the ceramic μSL. It is found that the scattering is the strongest when the size of the ceramic powders approaches to the laser wavelength (0.364 μm). It was also found that the higher the refractive index contrast between the particle and the resin, the stronger the light scattering. High laser intensity is required to fabricate absorbing ceramic materials to compensate for the laser energy absorbed by the ceramic particle. The μSL of three typical ceramic powders: silica, alumina, and lead zirconate titanate (PZT) are examined by the numerical model. The numerical model has been demonstrated as an efficient tool to optimize the μSL process. Finally, the ceramic micro green structures have been successfully fabricated.

Prediction of stiffness and stresses in z-fibre reinforced composite laminates

Abstract: The mechanical properties of z-pinned composite laminates were examined numerically. Finite element calculations have been performed to understand how the through-thickness reinforcement modifies the engineering elastic constants and local stress distributions. Solutions were found for four basic laminate stacking sequences, all having two percent volume fraction of z-fibres. For the stiffness analysis, a micro-mechanical finite element model was employed that was based on the actual geometric configuration of a z-pinned composite unit cell. The numerical results agreed very well with some published solutions. It showed that by adding 2% volume fraction of z-fibres, the through-thickness Young's modulus was increased by 22–35%. The reductions in the in-plane moduli were contained within 7–10%. The stress analysis showed that interlaminar stress distributions near a laminate free edge were significantly affected when z-fibres were placed within a characteristic distance of one z-fibre diameter from the free edge. Local z-fibres carried significant amount of interlaminar normal and shear stresses.

Experimental and numerical investigations on microstereolithography of ceramics

Abstract: Microstereolithography (μSL) uses laser light to solidify UV-curable resin mixed with concentrated ceramic powders. During the μSL process, the light scattering from the particle suspension is found to significantly influence the fabrication resolution in both lateral and depth dimensions which are critical for the complex three-dimensional (3D) microfabrication. In this work, we performed Monte Carlo simulations and experimental studies to understand the detailed microscale optical scattering, chemical reaction (polymerization), and their influence on critical fabrication parameters. As a result, it was found that due to the scattering, the fabricated line is wider in width and smaller in depth compared with polymeric fabrication at the same condition. The doping technique that we used substantially reduced the light scattering, which in turn enhanced the fabrication precision and control. In addition, the experimental values of curing depth and radius agreed reasonably well with the theoretical modeling...

Effect of Specific Water Quality Parameters on Copper Corrosion

Abstract: The objective of this study is to clearly understand the effect of specific water quality parameters like pH, dissolved oxygen (DO), conductivity, and buffering capacity (attributable to d...

Imaging properties of a metamaterial superlens

Abstract: The subwavelength imaging quality of a metamaterial superlens is studied numerically in the wavevector domain. Examples of image compression and magnification are given and resolution limits are discussed. A minimal resolution of /spl lambda//6 is obtained using a 36 nm silver film at 364 nm wavelength. The simulation also demonstrates the power flux is no longer a good measure to determine the focal plane of a superlens due the elevated field strength at the exit side of the metamaterial slab.

Adhesion force of polymeric three-dimensional microstructures fabricated by microstereolithography

Abstract: The adhesion between microstructures represents a great challenge in reliability of polymeric three-dimensional structures fabricated by microstereolithography (μSL). During the evaporative releasing, the capillary force of the solvent causes the deformation and adhesion of the fabricated beams. We present a method to determine the adhesion force of polymeric microstructures fabricated by μSL. The test structures with parallel beams were fabricated and released from the liquid resin via evaporation. By measuring the relationship between the adhesion length and the geometry of the beams, the adhesion force between two 1,6-hexanediol diacrylate (HDDA) polymeric parallel beams is determined as γ=72±5 mN/m. This simple method and the determined adhesion force provide a key in designing reliable polymeric microelectromechanical systems in preventing the stiction problem.

Fabrication and characterization of THz plasmonic filter

Abstract: Terahertz imaging systems have applications for explosives detection, aircraft guidance and landing in zero-visibility weather condition, as well as terrestrial and astronomical remote sensing. These critical applications need a variety of optical elements in the THz frequency, which has yet to be explored. In this paper, we demonstrate a high pass THz filter which utilizes the lowered plasma frequency of thin metal wire structures. The microstereolithography technique is applied to fabricate the 2D lattice of thin metal cylinders. The reflection property of the filter is characterized by FTIR, and the plasma frequency is determined at 0.7 THz, which agrees with the approximate theory.