The fluidic molecular trajectory and the Nano-droplet production ability

This paper studies the liquid Nano-droplet production ability using molecular dynamics simulation methodology. The research parameter is performed at the temperature of 310 Kelvin (K), the pressing force of 10.0 × 10−10 Newton (N) and the ejective hole diameters of 25 and 40 Angstrom (Å). The research result shows that liquid Nano-droplets finally were not produced for the ejective diameter of 25 Å. The Nano-jets were not only non-destruction from nozzle’s surface to produce the droplets but also movement downward to come back the nozzle’s surface. The molecular trajectory is very zigzag and curved both inside and outside the ejective container. In the contrary, when increasing the ejective diameter to 40 Å, the liquid Nano-droplet was produced in the same the ejective time and compressible force magnitude. The molecular trajectory is quite straight after ejecting out the outside of the container. Meanwhile, for the nozzle diameter size of 40 Å, the Nano-droplet was not only production but also movement up to leave away the nozzle’s surface under same above conditions. That proves that the ejective diameter has the influences to the moveable direction and Nano-droplets formation ability in the whole ejective process

Focusing and delivery of laser radiation for nano- and microfabrication

The recent advances in nanotechnology and nanofabrication motivate the drive to achieve a tighter focusing of light; this requires a high numerical aperture (NA) optical system. The need for high optical resolution has led scientists to discover the use of optical microlens for improving the performance of high numerical aperture (NA) optical systems. By focusing the laser beam through a microlens, the width of the beam can be reduced according to the needs of the application. In this work, the laser beam was focused by a microspherical lens (NA=0.7) into 150 nm or by tapered fibre into 4 μm diameter spots. The measurements indicate the strong influence of tightly focused beams. This thesis comprises of three parts; the first results chapter investigates the choice of material by considering the material properties and feasibility of fabrication (chapter 2). It has been shown in previous studies that the glass transition temperature of the polymer is an important factor in determining the laser ablation rate. High glass transition temperatures make it a good material candidate for optical waveguides. Polycarbonate (PC), polymethylmethacrylate (PMMA), negative photoresist SU-8, and chitosan have been characterised to choose suitable material as a substrate for soft nanolithography (chapter 3). The choice of material due to the glass transition temperature of the material (from literature), material optical properties are investigated experimentally at the range of wavelength from 190 nm to 1000 nm. Laser ablation experiments on PC, PMMA, SU- 8 and chitosan using a 193 nm ArF laser over a fluence range of 10 mJcm−2 –1000 mJcm−2. The ablation threshold at 193nm was found to be 24, 110, 40, and 95 mJ.cm-2 for PC, PMMA, SU-8, and chitosan respectively. The photoresist SU-8 and chitosan were chosen as both materials are biocompatible, and have a high glass transition temperature. Optical properties measured for these materials found that both materials have much higher absorption coefficients (αSU-8 ~ 4.2×105m-1 and αchitosan ~3.3×105m-1) compared with PC and PMMA (αPC =1×105m-1 and αPMMA=2×105m-1 )at 193 nm.The second part of this thesis reports experimental and computational results of an irradiated laser microsphere supported on biocompatible materials; SU-8 photoresist and chitosan (chapter 3). An ArF excimer laser (193 nm wavelength) was used with 11.5 ns pulse width to modify the underlying substrate, producing a single concave dimple. Atomic force microscopy and scanning electron microscope measurements have been used to quantify the shape and size of laser inscribed dimple. The dimple has a diameter of 150 ± 10 nm FWHM and a depth of 190 ± 10nm on SU-8 compared to 180 ± 10 nm FWHM and a depth of 350 ± 10nm on chitosan due to the optical properties of the materials. Finite-difference time-domain (FDTD) simulations were carried out to simulate the propagation of 193 nm laser radiation, focussed by a 1 µm diameter silica sphere. Finite Element Method (FEM) simulations were carried out to calculate laser- induced temperature rise of the both SU-8 and Chitosan layer beneath the microsphere. The SiO2 microsphere acts as a small ball lens tightly focussing the laser radiation. Delivery of the focussed laser radiation locally heats the substrate beneath the microsphere. As a consequence, mass transport takes place, forming a nano dimple.The third part of this thesis presents the use of a CO2 laser (10.6 μm wavelength) for producing microlenses at the end of silica optical fibre (chapter 4). By focused CO2 laser beam, silica optical fiber is irradiated and heated to the softening points (1800 K) of the silica material. Surface tension and the parameters of the fabrication system shape the melted material into a spherical micro-lens or tapered fiber that remains joined to the optical fiber. Different core diameters (125, 400, 600, 1000, and 1500 μm) of multimode fibres have been used for this fabrication. The roughness of the microlens was reduced to less than 20 ± 1 nm roughness by polishing the surface with a CO2 laser at low power (1- 2 W). Throughout this work, different microlenses (ball/parabolic) and tapered fibres were fabricated at the end of silica optical fibre. The minimum spot diameter at FWHM was close to 160 μm and 110 μm for microball and parabolic lenses, respectively. While the tapers had the minimum waist diameters down to 4 μm and maximum taper length of ~ 3.5 mm using silica multi-mode fibre. Finally, the knife-edge technique and He-Ne laser beam (632.8 nm wavelength) were coupled into a fibre to investigate the properties of the microlenses which produced a minimum spot size of 5 ±1 μm at FWHM in the focal region of the tapered fibre lenses of 125, 400 and 600 μm core diameter of the fibre.As a result, Chitosan and SU-8 have been used as substrate materials for recording tightly focussed focal regions, 193nm ArF laser has been used to realise extremely small, 150nm diameter, Photonic Nano Jets (PNJ’s). FDTD optical simulations accurately predict the spatial properties of microsphere PNJ’s emitting at 193. CO2 laser (10.6 μm) radiation has been used to form tapers and spherical lenses on the distal end of optical fibres. Finally, tight focusing using microspheres and lensed optical fibres could be integrated on lab-on- chip platforms for applications such as optical trapping and cell membrane modifications. An important application related to the results of this study is that focusing laser light produces a force that can be used to remove or trap selected cells or large tissue areas from living cell culture down to a resolution of individual single cells and subcellular components similar to organelles or chromosomes, respectively.The nanostructures fabricated in this chapter can be refined to achieve specific dimensions in; diameter, depth, shape, and periodicity so they can be used as antireflective surfaces for solar-cell applications [1].or could be used in drug delivery [2]. While laser microbeams are frequently used for measurement or imaging of biological parameters as well as using the optical tweezer system for trapping or moving of cells, the future medical applications will be focused on micromanipulation or microdissection methods for delivering molecules or nano drugs into a cell [3]. Delivering such nano- drugs into cancer cells requires overcoming the cell membrane by focusing the laser. This phenomenon is named photoporation which is based on the generation of localized transient pores in the cell membrane using the photonic nano jet [4]

Optically Induced Nanostructures

Nanostructuring of materials is a task at the heart of many modern disciplines in mechanical engineering, as well as optics, electronics, and the life sciences. This book includes an introduction to the relevant nonlinear optical processes associated with very short laser pulses for the generation of structures far below the classical optical diffraction limit of about 200 nanometers as well as coverage of state-of-the-art technical and biomedical applications. These applications include silicon and glass wafer processing, production of nanowires, laser transfection and cell reprogramming, optical cleaning, surface treatments of implants, nanowires, 3D nanoprinting, STED lithography, friction modification, and integrated optics. The book highlights also the use of modern femtosecond laser microscopes and nanoscopes as novel nanoprocessing tools

Laser-induced forward transfer (LIFT) of water soluble polyvinyl alcohol (PVA) polymers for use as support material for 3D-printed structures

The additive microfabrication method of laser-induced forward transfer (LIFT) permits the creation of functional microstructures with feature sizes down to below a micrometre [1]. Compared to other additive manufacturing techniques, LIFT can be used to deposit a broad range of materials in a contactless fashion. LIFT features the possibility of building out of plane features, but is currently limited to 2D or 2½D structures [2–4]. That is because printing of 3D structures requires sophisticated printing strategies, such as mechanical support structures and post-processing, as the material to be printed is in the liquid phase. Therefore, we propose the use of water-soluble materials as a support (and sacrificial) material, which can be easily removed after printing, by submerging the printed structure in water, without exposing the sample to more aggressive solvents or sintering treatments. Here, we present studies on LIFT printing of polyvinyl alcohol (PVA) polymer thin films via a picosecond pulsed laser source. Glass carriers are coated with a solution of PVA (donor) and brought into proximity to a receiver substrate (glass, silicon) once dried. Focussing of a laser pulse with a beam radius of 2 µm at the interface of carrier and donor leads to the ejection of a small volume of PVA that is being deposited on a receiver substrate. The effect of laser pulse fluence , donor film thickness and receiver material on the morphology (shape and size) of the deposits are studied. Adhesion of the deposits on the receiver is verified via deposition on various receiver materials and via a tape test. The solubility of PVA after laser irradiation is confirmed via dissolution in de-ionised water. In our study, the feasibility of the concept of printing PVA with the help of LIFT is demonstrated. The transfer process maintains the ability of water solubility of the deposits allowing the use as support material in LIFT printing of complex 3D structures. Future studies will investigate the compatibility (i.e. adhesion) of PVA with relevant donor materials, such as metals and functional polymers. References: [1] A. Piqué and P. Serra (2018) Laser Printing of Functional Materials. Weinheim, Germany: Wiley-VCH Verlag GmbH & Co. KGaA. [2] R. C. Y. Auyeung, H. Kim, A. J. Birnbaum, M. Zalalutdinov, S. A. Mathews, and A. Piqué (2009) Laser decal transfer of freestanding microcantilevers and microbridges, Appl. Phys. A, vol. 97, no. 3, pp. 513–519. [3] C. W. Visser, R. Pohl, C. Sun, G.-W. Römer, B. Huis in ‘t Veld, and D. Lohse (2015) Toward 3D Printing of Pure Metals by Laser-Induced Forward Transfer, Adv. Mater., vol. 27, no. 27, pp. 4087–4092. [4] J. Luo et al. (2017) Printing Functional 3D Microdevices by Laser-Induced Forward Transfer, Small, vol. 13, no. 9, p. 1602553

Femtosecond Laser Joining of Silver Submicron/Nanoparticles

The development of future devices is towards to the miniaturization and performance improvement. This requires the large scale integration of nanodevices. Nanojoining is an essential step for the industrial scale production of nanodevices which possess extensive applications in nanoelectronics, nanophotonics and biomedicines. Many techniques have been developed to produce nanojoining, and among them femtosecond (fs) laser nanojoining is a promising one due to its limited thermal damage to the fabricated nanomaterials. However the fs laser nanojoining technique is still not probably characterized. In this thesis, the research of fs laser nanojoining of silver (Ag) nanomaterials with or without polyvinylpyrrolidone (PVP) coating is conducted in different environments (aqueous solution, air, vacuum), targeting to different application areas. It is reported that the joining behavior of PVP coated Ag nanoparticles (NPs) can be manipulated by controlling the distribution of localized surface plasmon induced electric field enhancement (or hotspots) and/or the decomposition of PVP coatings into amorphous carbon or some ionized products. This facilitates the fabrication of joined-NPs structures with tunable plasmonic properties by tuning the geometries of the structures, for possible application as SERS (surface enhanced Raman spectroscopy) detector. For Ag particles without PVP coating and exposed to vacuum (10-6 Torr), their joining behavior under fs laser radiation is also controlled by the hotspots; and high integrity interconnection of Ag particles can be obtained benefiting from the localized ablation of the particles in the hotspots. The joining efficiency can be improved by introducing reactive oxygen gas which produces external heating to the irradiated particles through O Ag reaction on the surface of Ag particles in the hotspots. Overall, the hotspots-dependent fs laser nanojoining technique which is developed in this research provides an alternative way for precise fabrication of nanodevices based on the interconnection of nanoscale functional components

Laser-based manufacturing routes for functionalizing surfaces

Robust functional surfaces are of a growing industrial interest for a range of optical, easy-to clean, anti-icing and non-fouling applications. At the same time, nature is a great source of inspiration for micro/nano-scale surface structures with tailored functional properties. There are a number of competing technologies for producing such structures but ultrashort laser processing is emerging as one of the most promising for fabricating bio-inspired surfaces. However, the technology has limitations and its capabilities have to be augmented to achieve the required high throughput in manufacturing products that incorporate functional surface topographies. Therefore, this research investigates a promising process chain that combines synergistically the capabilities of laser texturing with complementary surface engineering and replication technologies. Several large-area laser texturing techniques are investigated, namely Direct Laser Writing (DLW), Laser-Induced Periodic Surface Structures (LIPSS) and microlenses-induced Photonic Jet (PJ) texturing. The research advances the knowledge in laser-based surface functionalization and also in factors affecting the functional response and durability of laser structured surfaces

Laser Filamentation Interaction With Materials For Spectroscopic Applications

Laser filamentation is a non-diffracting propagation regime consisting of an intense core that is surrounded by an energy reservoir. For laser ablation based spectroscopy techniques such as Laser Induced Breakdown Spectroscopy (LIBS), laser filamentation enables the remote delivery of high power density laser radiation at long distances. This work shows a quasiconstant filament-induced mass ablation along a 35 m propagation distance. The mass ablated is sufficient for the application of laser filamentation as a sampling tool for plasma based spectroscopy techniques. Within the scope of this study, single-shot ablation was compared with multi-shot ablation. The dependence of ablated mass on the number of pulses was observed to have a quasi-linear dependence on the number of pulses, advantageous for applications such as spectroscopy. Sample metrology showed that both physical and optical material properties have significant effects on the filament-induced ablation behavior. A relatively slow filament-induced plasma expansion was observed, as compared with a focused beam. This suggests that less energy was transferred to the plasma during filamentinduced ablation. The effects of the filament core and the energy reservoir on the filamentinduced ablation and plasma formation were investigated. Goniometric measurements of the filament-induced plasma, along with radiometric calculations, provided the number of emitted photons from a specific atomic transition and sample material. This work advances the understanding of the effects of single filaments on the ablation of solid materials and the understanding of filament-induced plasma dynamics. It has lays the foundation for further quantitative studies of multiple filamentation. The implications of this iv work extend beyond spectroscopy and include any application of filamentation that involves the interaction with a solid materia