Papers by Author: Ming Zhou

Abstract: Regular arrays of micro-pillars and nano-grooves structures on the silicon wafer are fabricated by using soft lithography, and the three dimension morphology of textured surface is observed by using scanning electron microscopy (SEM) and atomic force microscope (AFM). The static water contact angles are measured by using contact angle meter to characterize the wettabilities of these surfaces. To investigate how the presence of topography and the variations of wettability affect the haemocompatibility of textured surface contacted with blood, different patterned surfaces are designed and fabricated, and blood platelet adhesion test is carried out on these surfaces. The adhesion and coagulation of platelets are inspected by scanning electron microscopy (SEM). Experimental data presented in this paper indicate that different surface roughness and wettability are the important factors for blood platelet adhesion. The amount of adsorbed blood platelet is low on textured surfaces, compared with that on the flat surface. Especially, there is no coagulation and activation on the surface with nanometer grooves. That is to say, the superhydrophobic surface is apt to decrease blood platelet adhesion. The study suggests that surface with suitable wettabililty and textured structures exhibits superior blood compatibility.

Abstract: A numerical method based on Finite Difference Time Domain (FDTD) scheme for computing the photonic band-structure of three dimensional photonic crystals is introduced in this paper. Also, the accuracy and stability, numerical dispersion, boundary Conditions as well as excitation attaching to the scheme are detailed analyzed. For checking the method, the simulating results of photonic band structure on two type lattices are presented.

Abstract: Experiment setup of femtosecond laser pump probe was established, the time resolution of time-delay setting reached 67fs. By use of femtosecond laser with width of 30fs and wavelength is 796nm the dependence of transient change of reflectivity on delayed time in GaAs was measured by pump-probe method. By calculating the change of complex index of refraction (%n), free-carrier effect, lattice-temperature and carrier recombination contributions to relaxation curve was analyzed. When the carrier density N is 1.44×1018/cm3, free-carrier contribution to refraction index %nFC is -7.33×10-4, lattice-temperature %nLT is 0.85×10-4. Based on recombination rate equation, recombination lifetime of 980ps was deduced.

Abstract: The photo-polymerization induced by Two-Photon Absorption (TPA) is tightly confined in the focus because the efficiency of TPA is proportional to the square of intensity. Three-dimensional (3D) micro-fabrication can be achieved by controlling the movement of the focus. Based on this theory, a system for 3D-micro-fabrication with femtosecond laser is proposed. The system consists of a laser system, a microscope system, a real-time detection system and a 3D-movement system, etc. The precision of micro-machining reaches a level down to 700nm linewidth. The line width was inversely proportional to the fabrication speed, but proportional to laser power and NA. The experiment results were simulated, beam waist of 0.413μm and TPA cross section of 2×10-54cm4s was obtained. While we tried to optimize parameters, we also did some research about its applications. With TPA photo-polymerization by means of our experimental system, 3D photonic crystal of wood-pile structure twelve layers and photonic crystal fiber are manufactured. These results proved that the micro-fabrication system of TPA can not only obtain the resolution down to sub-micron level, but also realize real 3D micro-fabrication.

Abstract: Submicron-sized top layer was synthesized on an austenitic stainless steel sample by adopting laser shock processing (LSP). The substructures were characterized and examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), moreover, the mechanism of ultra-refinement laser-induced was analyzed. It showed that a refined top surface with average subgrains size of 0.5(m was synthesized by the model of single laser loading, black paint as absorption coating and the peak pressure induced by LSP approximating twice of the dynamic yield strength of target. It indicated that thermoplastic destabilization had happened in heavily localized regions imposed by LSP. Streak-like subgrains were oriented perpendicular to shock wave (Gaussian profile) vector. In order to accommodate plastic strain, streak-like subgrains experienced necking, breaking up and dynamic rotational recrystallization, as a result, the submicron grains were formed on the surface of sample.

Abstract: In this paper, the technique of high energy and short pulse duration laser impact is adopted. The substructural transformation characteristics and mechanisms of the austenitic stainless steel, subjected to strain-rate of 106s-1 order and stress of 2.70GPa, are investigated. SEM observations, there exists regular arrangement of chapped and equiaxed subgrain regions within the original grains. The size of the subgrain ranges from 0.1 to 0.5um; Meanwhile, the compacted deformation twin bundles with about 1um width each twin have been examined in the regions treated. It indicates that the equiaxed subgrains, close to nanometer scale, had evolved in the surface of austenitic stainless steel, and they belong to dynamic rotational recrystallization; Although, twinning deformation is not a frequent phenomenon in terms of austenitic stainless steel at room temperature, it will play a significant role when austenitic stainless steels are submitted to high strain rate and stress. Additionally, X-ray diffraction reveals that the crystal lattice constant is up 1.12% compared to the normal one and no deformation-induced α-martensite and amorphous phase are spotted within the processed regions.