A Comparison in Laser Precision Drilling of Stainless Steel 304 with Nanosecond and Picosecond Laser Pulses

Precision drilling with picosecond laser has been advocated to significantly improve the quality of micro-holes with reduced recast layer thickness and almost no heat affected zone.However,a detailed comparison between nanosecond and picosecond laser drilling techniques has rarely been reported in previous research.In the present study,a series of micro-holes are manufactured on stainless steel 304 using a nanosecond and a picosecond laser drilling system,respectively.The quality of the micro-holes,e.g.,recast layer,micro-crack,circularity,and conicity,etc,is evaluated by employing an optical microscope,an optical interferometer,and a scanning electron microscope.Additionally,the micro-structure of the samples between the edges of the micro-holes and the parent material is compared following etching treatment.The researching results show that a great amount of spattering material accumulated at the entrance ends of the nanosecond laser drilled micro-holes.The formation of a recast layer with a thickness of;5μm is detected on the side walls,associated with initiation of micro-cracks.Tapering phenomenon is also observed and the circularity of the micro-holes is rather poor.With regard to the micro-holes drilled by picosecond laser,the entrance ends,the exit ends,and the side walls are quite smooth without accumulation of spattering material,formation of recast layer and micro-cracks.The circularity of the micro-holes is fairly good without observation of tapering phenomenon.Furthermore,there is no obvious difference as for the micro-structure between the edges of the micro-holes and the parent material.This study proposes a picosecond laser helical drilling technique which can be used for effective manufacturing of high quality micro-holes.

Nanoscale guiding for cold atoms based on surface plasmons along the tips of metallic wedges

We propose a novel scheme to guide neutral cold atoms in a nanoscale region based on surface plasmons （SPs） of one pair and two pairs of tips of metallic wedges with locally enhanced light intensity and sub-optical wavelength resolution. We analyze the near-field intensity distribution of the tip of the metallic wedge by the FDTD method, and study the total intensity as well as the total potential of optical potentials and van der Waals potentials for 87 Rb atoms in the light field of one pair and two pairs of tips of metallic wedges. It shows that the total potentials of one pair and two pairs of tips of metallic wedges can generate a gravito-optical trap and a dark closed trap for nanoscale guiding of neutral cold atoms. Guided atoms can be cooled with efficient intensity-gradient Sisyphus cooling by blue-detuned light field. This provides an important step towards the generation of hybrid systems consisting of isolated atoms and solid devices.

Preparation and Spectral Analysis of Gold Nanoparticles Using Magnetron Sputtering and Thermal Annealing

Gold（Au） nanoparticles were prepared on Au-fi lm-coated K9 glass and silicon substrates by direct current（DC） magnetron sputtering and thermal annealing treatment. The effects of substrate material, annealing temperature, and time on morphologies of Au nanoparticles were investigated, and the formation mechanism of Au nanoparticles was discussed. The experimental results indicate that silicon substrate is more suitable for the formation of Au nanoparticles. On a silicon substrate, Au nanoparticles formed with good spherical shapes at temperature over 700 ℃. It was also found by spectral analysis that the fi eld enhancement factor of the island-shaped Au particles was smaller than that of the granular Au particles; the better the spherical shape as well as the smaller the size and spacing of Au particles, the higher the light absorption rate; the absorption peak had a red shift with increasing particle size and spacing.

Rapid Fabrication of Three-Dimensional Woodpile Photonic Crystals by Means of Two-Photon Photopolymerization

Two-photon photopolymerization （TPP） of femtosecond laser is a promising method to fabricate three-dimensional woodpile photonic crystals （PCs）. We build micro-fabricatlon system based on the principle of TPP. Three- dimensional woodpile PCs consisting of in-plane rod distances ranging from 1000nm to 2000nm are fabricated by focusing femtosecond laser in photosensitive liquid resin ORMOCER. The properties of the PCs are also discussed, and fundamental photonic band gaps in middle-infrared range are measured, whose in-plane rod distances are 1500nm and 2000 nm. Three-dimenslonal woodpile PC devices with desired defects, such as cross-waveguide and micro-laser structures, are introduced easily by TPP. We fabricate the three-dimensional woodpile PCs in the liquid resin at the fast scanning speed of 120μm/s.

Synthesis of Aligned Carbon Nanotubes by Thermal Chemical Vapor Deposition

Single crystal silicon was found to be very beneficial to the growth of aligned carbon nanotubes by chemical vapor deposition with C2H2 as carbon source. A thin film of Ni served as catalyst was deposited on the Si substrate by the K575X Peltier Cooled High Resolution Sputter Coater before growth. The growth properties of carbon nanotubes were studied as a function of the Ni catalyst layer thickness. The diameter, growth rate and areal density of the carbon nanotubes were controlled by the initial thickness of the catalyst layer. Steric hindrance between nanotubes forces them to grow in well-aligned manner at an initial stage of growth. Transmission electron microscope analysis revealed that nanotubes grew by a tip growth mechanism.

On the measurement of slip length for liquid flow over super-hydrophobic surface

To design a surface with large slip or larger drag reduction is a pop issue in the fields of liquid transporting and body swimming. In this context, it is a crucial problem to measure the slip length for these surfaces. Here we propose a novel method by using rheometer for this objective. This method is implemented by designing the distribution of the super-hydrophobic area on the sample. Using this method, a slip length of 40 μm for 70 wt% glycerin flow over a super-hydrophobic surface with stripe structure (the period, width and height of ridges are 150 μm, 40 μm and 65 μm, respectively) is measured. The result shows that the slip length measured using this method is in good agreement with former results measured by other methods. This method is fit for measuring the slip length of super-hydrophobic surface whose structure ranges from microto nanoscale.

Preparation and Photoelectric Properties of Patterned Ag Nanoparticles on FTO/Glass Substrate by Laser Etching and Driving Layer Strategy

An effective method based on laser etching and driving layer strategy was proposed to prepare patterned Ag nanoparticles(Ag NPs)on fluorine-doped tin oxide(FTO)/glass substrate and thus to enhance the photoelectric properties.This method successively included depositing an aluminum-doped zinc oxide(AZO)driving layer,laser etching,depositing an Ag layer,furnace annealing and laser removal.Different AZO and Ag layer thicknesses were adopted,and the surface morphology,crystal structure and photoelectric properties were investigated.An Ag NPs/FTO/glass sample without an AZO driving layer was prepared for comparison.It was found that furnace annealing of the Ag layer combined with the AZO driving layer,rather than that without the AZO driving layer,was more conducive to generating patterned Ag NPs.Using a 20-nmthick AZO layer and a 150-nm-thick Ag layer led to the formation of uniformly distributed Ag NPs being aligned along the laser-etched grooves to form a pattern.The as-obtained sample had the best comprehensive photoelectric property with an average transmittance of 79.95%,a sheet resistance of 7.11Ω/sq and the highest figure of merit of 1.50×10^(-2)Ω^(-1),confirming the feasibility of the proposed method and providing enlightenment for related researches of transparent conductive oxide-based films.

Effect of Annealing on the Morphology,Structure and Photoelectric Properties of AZO/Pt/FTO Trilayer Films

Aluminum-doped zinc oxide/platinum/fluorine-doped tin oxide（AZO/Pt/FTO） trilayer films were prepared by sputtering 5-nm-thick Pt layers and 150-nm-thick AZO layers in sequence on commercial FTO glass.The effects of onestep annealing and layer-by-layer annealing on the morphology,structure and photoelectric properties of the AZO/Pt/FTO trilayer films were comparatively analyzed.It is found that the both annealing approaches increased the grain size and improved the crystallinity of the films,leading to enhancement in transmittance and conductivity.However,layer-by-layer annealing led to the formation of quasi-continuous or continuous AZO layers,different from the sparsely distributed AZO particles brought about by one-step annealing,resulting in excellent optical and electrical properties.Specifically,after layer-by-layer annealing at 400 ℃ for both Pt and AZO layers,the AZO/Pt/FTO trilayer film showed an increase in average transmittance from 71.3% to 85.3% and a decrease in sheet resistance from 7.5 to 5.6 Ω/□,leading to the highest figure of merit of 3.64 × 10^（-2） Ω^（-1）.

3D DNA origami designed with caDNAno

For about three decades, DNA-based nanotechnology has been undergoing development as an assembly method for nanostructured materials. The DNA origami method pioneered by Rothemund paved the way for the formation of 3D structures using DNA self assembly. The origami approach uses a long scaffold strand as the input for the self assembly of a few hundred staple strands into desired shapes. Herein, we present a 3D origami "roller" (75 nm in length) designed using caDNAno software. This has the potential to be used as a template to assemble nanoparticles into different pre-defined shapes. The "roller" was characterized with agarose gel electrophoresis, atomic force microscopy (AFM) and transmission electron microscopy (TEM).