Kedian Wang

Formation of porous structure with subspot size under the irradiation of picosecond laser pulses

A study was presented in this paper on porous structure with microsize holes significantly smaller than laser spot on the stainless steel 304 target surface induced by a picosecond Nd:van regenerative amplified laser, operating at 1064 nm. The target surface variations were studied in air ambience. The estimated surface damage threshold was 0.15 J/cm2. The target specific surface changes and phenomena observed supported a complementary study on the formation and growth of the subspot size pit holes on metal surface with dependence of laser pulse number of 50-1000 and fluences of 0.8 and 1.6 J/cm2. Two kinds of porous structures were presented: periodic holes are formed from Coulomb Explosion during locally spatial modulated ablation, and random holes are formed from the burst of bubbles in overheated liquid during phase explosion. It can be concluded that it is effective to fabricate a large metal surface area of porous structure by laser scanning regime. Generally, it is also difficult for ultrashort laser to fabricate the microporous structures compared with traditional methods. These porous structures potentially have a number of important applications in nanotechnology, industry, nuclear complex, and so forth.

Ablation experiment and threshold calculation of titanium alloy irradiated by ultra-fast pulse laser

The interaction between an ultra-fast pulse laser and a materials surface has become a research hotspot in recent years. Micromachining of titanium alloy with an ultra-fast pulse laser is a very important research direction, and it has very important theoretical significance and application value in investigating the ablation threshold of titanium alloy irradiated by ultra-fast pulse lasers. Irradiated by a picosecond pulse laser with wavelengths of 1064 nm and 532 nm, the surface morphology and feature sizes, including ablation crater width (i.e. diameter), ablation depth, ablation area, ablation volume, single pulse ablation rate, and so forth, of the titanium alloy were studied, and their ablation distributions were obtained. The experimental results show that titanium alloy irradiated by a picosecond pulse infrared laser with a 1064 nm wavelength has better ablation morphology than that of the green picosecond pulse laser with a 532 nm wavelength. The feature sizes are approximately linearly dependen...

Research status and application prospects of manufacturing technology for micro–nano surface structures with low reflectivity

The light trapping surface of micro–nanostructure can significantly improve the performance of optical transmission and can greatly reduce the broadband domain of material surface reflectivity, which means the material surface absorptivity on wide-spectrum signal is enhanced. Several commonly used methods for manufacturing micro–nano surface of light trapping structure with low reflectivity are introduced first, including chemical etching, mechanical grooving, reactive ion etching, common long-pulse laser grooving, and ultra-fast pulse laser processing. This is followed by a comparison of the advantages and disadvantages of these methods. Among these methods, ultra-fast pulse laser processing is an ideal manufacturing technology for fabrication of light trapping structures. The research status of the micro–nano manufacturing technology of structured surfaces for light trapping with low reflectivity is reviewed, and emphasis is given to their application prospects. The research directions and trends of the micro–nano manufacturing technology of structured surfaces for light trapping with low reflectivity are summarized, and broad application prospects and research value in many fields, such as solar cells, solar water heater, building wave-absorbing materials, information acquisition of mechanized equipments, high-radiation heat exchange equipment, solar heating equipment, and solar air conditioner, are pointed out.

Nanospot welding of carbon nanotubes using near-field enhancement effect of AFM probe irradiated by optical fiber probe laser

The miniaturization of electronic devices into the nanometer scale is indispensable for next-generation semiconductor technology, and carbon nanotubes are considered to be the promising candidates for the future interconnection wires. To study carbon nanotube interconnection during nanowelding, we propose a new nanospot welding method with the near-field enhancement effect of the metallic AFM probe tip irradiated by an optical fiber probe laser. Based on theoretically analyzing the near-field enhancement effect, we set up the experimental system for nanospot welding with good interconnection results of silver nanoparticles and carbon nanotubes, not only proving that the interconnection operation of CNTs can be effectively achieved through the melting process of nanoparticles by the thermal AFM probe tip irradiated by an optical fiber probe laser, but also providing a promising technical approach for nanospot welding.

Evolution of nano-ripples on stainless steel irradiated by picosecond laser pulses

The characteristics of laser-induced periodic surface structures are investigated after laser irradiation with a pulse duration (10 ps) under a certain laser fluence (0.27 J/cm2) and pulse number (N = 50–2000). In the experiments, at the lowest number of pulses, ultrafine ripples are observed with sub-200-nm spatial periods and an orientation parallel to laser polarization direction. With the increasing pulse number, a chain of events that has been observed consists of ultrafine ripples followed by a transformation towards regular ripples with an orientation perpendicular to laser polarization direction and holes finally breaking regular ripples. Although the generation of ultrafine and regular ripples upon laser irradiation is a universal phenomenon, the origin behind the transition is discussed here to help understand the exact physical mechanism and their occurrence with their dependence on the irradiation parameters.

Atomistic simulations on the axial nanowelding configuration and contact behavior between Ag nanowire and single-walled carbon nanotubes

As for the interesting new building blocks, the Ag nanowires (AgNWs) and single-walled carbon nanotubes (SWNTs) as the interesting new building blocks are viewed as the promising candidates for the next-generation interconnects due to their most remarkable electrical, thermal, optical, mechanical, and other properties. The axial nanowelding of head-to-head style and side-to-side style is relatively simulated with the molecular dynamics method. As for the head-to-head structural style, SWNTs will move toward the AgNWs and contact with the head of AgNWs. And, the part of the Ag nanowire may be subsequently encapsulated in SWNT with the core-filling Ag atom chain as the final atomic contact configuration during nanowelding, which is related to the nanowelding temperature. When the SWNTs and AgNWs are arranged by the side-to-side contact style, the SWNTs will move along the SWNT surface and may eventually catch up with the AgNW being neck and neck. Aiming at the final axial atomic configurations and the contact behavior during nanowelding process, the related dominant mechanism is revealed in this paper.

New optical near-field nanolithography with optical fiber probe laser irradiating atomic force microscopy probe tip

ABSTRACT A new optical near-field nanolithography scheme with optical fiber probe laser irradiating atomic force microscopy (AFM) probe tip is proposed. Through optical theoretical analysis, if the metallic AFM probe tip is in the evanescent field of optical fiber probe tip, the secondary near-field enhancement effect can appear underneath the metallic AFM probe tip. Based on the independently developed AFM system and optical system, the nanolithography platform is built and nanocraters structures can be successfully created, which demonstrates that the new scheme is an effective and promising nanolithography approach for the future nanoelectronics, nanobiotechnology, nanowelding, etc.

Comparison of femtosecond laser-induced front- and rear-side ablation of films

Femtosecond laser rear-side ablation, in which the laser beam first passes through the substrate, then irradiates on the film at the substrate–film interface, can be used to fabricate films on a transparent substrate. In this method, the material removal mechanism is different from that in front-side ablation, and the ablation occurs in an enclosed space. The different material removal process in rear-side laser ablation will bring about some unique ablation results. In this paper, the material removal mechanisms and ablation results of Cr film in rear-side ablation are investigated by comparing with those in front-side ablation. It is found that rear-side ablation can achieve smaller feature size than front-side ablation, especially when the laser fluence is small. However, owing to its different material breaking and ejecting process, the rear-side ablation tends to have worse bottom morphology and irregular edge morphology. In addition, the microstructures in the two ablations have opposite cross-sectional shapes and the ripple period in rear-side ablation is larger than that in front-side ablation.

Laser-induced graphene: preparation, functionalization and applications

Abstract Recently graphene-based materials (GBMs) have gained tremendous attention for their enormous potentials for various functional devices due to their excellent physical and chemical properties. However, the cost effective synthesis and patterning of carbon nanomaterials are a challenge, which significantly restricts its applications. Therefore, straightforward preparation and processing of GBMs in a scalable approach is still a important goal. In recent years, laser direct writing (LDW) technique provides a powerful processing method for the broad application of laser-induced graphene (LIG) which does not rely on either high temperature or toxic chemicals. This article aims to update the latest results in this rapidly evolving field and to provide critical insights to inspire more exciting developments of LIG and its functionalization. Based on the interaction mechanisms and physical effects, we comparatively review the methods of preparation and functionalization of LIG, including inducing, structuring, doping and hybriding. In this progress report, the applications of LIG and its GBMs patterned by LDW technique were discussed in the fields of optoelectronic devices, energy storage devices, biosensors and biomimetic devices.

Near-field optical characteristics of Ag nanoparticle within the near-field scope of a metallic AFM tip irradiated by SNOM laser

ABSTRACT Based on the near-field optical theory, the near-field characteristics of Ag nanoparticle within the near-field scope of a metallic AFM tip irradiated by optical fiber probe laser are carried out with finite element method. As the laser transmits in optical fiber probe, the light of the various modes is gradually turned off, remaining the HE11 mode laser. Meanwhile, the evanescent field can be produced at the confined aperture, which will also stimulate the near-field enhancement phenomenon of metallic AFM tip and Ag nanoparticle with those extrema appearing in the apex of AFM tip, the upper and lower parts of Ag nanoparticle, and the upper and lower sharp boundary positions at the end of the tapered fiber probe. The related mechanism is revealed and near-field optical characteristics are also analyzed.