Ps Laser Ablation Research Articles

Manufacturing routes for replicating micro and nano surface structures with bio-mimetic applications

In order to broaden the application domain of microsystems-based products, a number of processing chains that are complementary to those used for batch-manufacturing of micro electro mechanical systems (MEMS) have been recently proposed by the research community. Such alternative process chains combine micro and nano structuring technologies for master making with replication techniques for high throughput such as injection moulding (IM). In this research, two new process chains were investigated for replicating structured surfaces that are inspired by nature. In particular, a study was conducted to replicate structures incorporating functional features found on the eye of a household fly and on a shark skin. Such features were initially designed by applying a bio-mimetic modelling approach to generate the 3D models necessary to achieve the targeted surface functionality and thus to investigate the feasibility of “embedding” them in existing and new emerging products. The proposed two process chains employ micro-second (ms) and pico-second (ps) laser ablation and focused ion beam (FIB) milling to perform micro and nano structuring, respectively. The feasibility of applying them for producing masters for replicating bio-inspired surface structures was investigated by performing micro injection moulding trials. The results showed that such micro and nano structured surfaces can be replicated successfully, and the two process chains can be considered as promising manufacturing routes for serial production of parts incorporating bio-inspired surface structures.

Impact of surface topography and laser pulse duration for laser ablation of solar cell front side passivating SiNx layers

Local contact openings in SiNx layers that passivate the front side of solar cells offer an attractive alternative to the current standard “fire-through” screen printing process for front grid fabrication. Additionally, this technology can be used for enabling a selective emitter. In the present paper, we investigate laser ablation of SiNx layers on planar and textured silicon surfaces for various laser wavelengths and pulse durations in the nanosecond (ns) to femtosecond (fs) range. We characterize the dark J-V characteristics of diodes with laser contact openings in the SiNx layer passivating the emitter. Our results show that on alkaline textured surfaces the ablation by a ns laser produces less damage than by an ultrashort pulse laser. The dark currents of alkaline textured diodes treated with picosecond (ps) or fs lasers are one order of magnitude higher than those of ns laser treated diodes. High ideality factors furthermore indicate crystal damage in the ∼500 nm deep space charge region of the diodes. Scanning electron microscope and transmission electron microscope images of textured samples, confirm the presence of extensive and deep crystal damage after ps laser ablation, which are not observed in laser treated samples with planar surfaces. Correspondingly, for planar surfaces we find for both, ns and for ps laser ablated regions, emitter saturation current densities J0e,abl of ∼2 pA/cm2. The recombination in textured samples in contrast differs vastly for ns and ps laser ablation. The ns laser results in an only slightly increased value of 3.7 pA/cm2 while the ps laser treated sample was not evaluable due to severe crystal damage leading to effective lifetimes of <5 μs.

Micromachining of Metals, Alloys, and Ceramics by Picosecond Laser Ablation

Microhole drilling and microstructure machining with a picosecond (ps) Nd:YVO4 laser (pulse duration of 10 ps) in metals, alloys, and ceramics are reported. Blind and through microholes are drilled by percussion drilling as well as trepanning drilling, where the diameters of the holes are in the range of 20–1000 μm. Microfeatures are also machined and the flexibility of ps laser machining is demonstrated. The quality of drilled holes, e.g., recast layer, microcrack, and conicity, and that of the microstructures, are investigated by an optical microscope, a surface profilometer, or a scanning electron microscope. Ps laser ablation rate is studied by experiments and a simplified laser ablation model.

Dendrimer-Capped Nanoparticles Prepared by Picosecond Laser Ablation in Liquid Environment

Fifth generation ethylendiamine-core poly(amidoamine) (PAMAM G5) is presented as an efficient capping agent for the preparation of metal and semiconductor nanoparticles by ps laser ablation in water. In particular, we describe results obtained with the fundamental, second and third harmonic of a ps Nd:YAG laser and the influence of laser wavelength and pulse energy on gold particle production and subsequent photofragmentation. In this framework, the role of the dendrimer and, in particular, its interactions with gold clusters and cations are accounted.

Modeling of multi-burst mode pico-second laser ablation for improved material removal rate

This paper deals with the unique phenomena occurring during the multi-burst mode picosecond (ps) laser ablation of metals through modeling and experimental studies. The two-temperature model (TTM) is used and expanded to calculate the ablation depth in the multi-burst mode. A nonlinear increment of ablation volume is found during the multi-burst laser ablation. The deactivation of ablated material and the application of temperature-dependent electron-phonon coupling are demonstrated to be important to provide reliable results. The simulation results based on this expanded laser ablation model are experimentally validated. A significant increase of ablation rate is found in the multi-burst mode, compared with the single-pulse mode under the same total fluence. This numerical model provides a physical perspective into the energy transport process during multi-burst laser ablation and can be used to study the pulse-to-pulse separation time effect on the ablation rate.

Production and photofragmentation of Au nanoparticles by 355 nm picosecond radiation

Fifth generation ethylendiamine-core poly(amidoamine) (PAMAM G5)-capped-gold-nanoparticles were prepared by ps laser ablation in water, by using the third harmonic of a ps Nd:YAG laser. Post-irradiation with the same wavelength causes efficient photofragmentation of the nanoparticles. We performed a comparison with analogous tests carried out with 532 nm ps pulses. We found that, while 532-nm-fragmentation is a 2-photon photoelectric process, 355-nm-fragmentation is linear.

In Situ Production of Polymer‐Capped Silver Nanoparticles for Optical Biosensing

AbstractSummary: We report on the preparation and spectroscopic characterization of a novel nanocomposite consisting of silver nanoparticles and a fluorescent polymer obtained by in situ ps laser ablation of a silver target. While the polymer is able to detect the fungus Paecilomyces variotii by fluorescence quenching, the composite with silver nanoparticles permits an interaction with both cell walls of spores and mycelia without any appreciable reduction of the overall fluorescence quantum yield.

Production of Nanoparticles with High Repetition Rate Picosecond Laser

The fabrication of silver and gold nanoparticle colloids using the picosecond (10 ps) laser ablation in liquids was studied. The maximum productivity of 8.6 µg/s nanoparticles was achieved with the 10 ps-laser pulses at high pulse energy (110 µJ) and the repetition rate of 50 kHz. A special stirred flow chamber was constructed in order to improve reproducibility and generation speed of nanopar- ticles in flowing liquid during the ps-laser ablation.

Photodegradation of PAMAM G5-stabilized aqueous suspensions of gold nanoparticles

Gold nanoparticles are produced in the form of colloidal suspensions in water by ps laser ablation of a metallic target. The fifth generation of ethylenediamine-core poly(amidoamine) (PAMAM G5) is used as a capping agent. Thanks to the ability of PAMAM to encapsulate and stabilize gold cations within its inner cavities, it is possible to evidence, by simple UV–visible spectroscopy, a photo-fragmentation process induced by the 532 nm radiation, which is resonant with the absorption plasmon band of gold nanoparticles. This effect, that can be also exploited to control the size and shape of gold nanoparticles obtained with different procedures, arises from electron photo-ejection and subsequent charging and disintegration of existing gold nanoparticles into smaller size products.

Time-resolved electron shadowgraphy for 300 ps laser ablation of a copper film

Time-resolved electron shadowgraphy measurement was performed in infrared 300 ps laser ablation of a copper film in order to investigate expanding plasma into vacuum with space-charge separation. The probe-electron pulse was generated by intense femtosecond laser irradiation on a tungsten bulk target. Time-resolved electron shadowgraphs showed evolving “bright” and “shadow” plumes with expanding speeds of 970 and 110 km/s, when the laser intensity was 980 G W/cm2. These are attributed to be space-charge separation field and ion plume, respectively.

Laser ablation and photo-dissociation of solid-nitrogen film by UV ps-laser irradiation

Nitrogen solid film deposited on a copper plate at 10 K was irradiated with a picosecond UV laser at 263 nm in vacuum. Photo-dissociation of nitrogen molecule in the solid film was confirmed by the optical emissions, which were ascribed to atomic nitrogen, during the laser irradiation at the fluence of 5 J cm −2 pulse −1. This photolysis was discussed by the comparison with laser-induced breakdown of nitrogen gas. At the fluence over ca. 10 J cm −2 pulse −1, the ablation of the frozen nitrogen film was observed. Employing the ablation plume including a reactive species such as nitrogen atoms, the surface reaction of a graphite (highly oriented pyrolytic graphite (HOPG)) plate and silicon wafer was studied. XPS analysis indicated that nitrides were formed on the surfaces by the treatment. The ps-laser ablation of nitrogen solid film provides a novel technique for surface modification of materials.

Photothermal conversion dynamics in femtosecond and picosecond discrete laser etching of Cu-phthalocyanine amorphous film analysed by ultrafast UV–VIS absorption spectroscopy

Novel etching of Cu-phthalocyanine (CuPc) amorphous film which is characteristic of ultrashort laser irradiation was successfully confirmed by tuning Ti:Sapphire laser (780 nm) to 150 fs, 250 ps, or 100 ns, and the primary processes were investigated by fs pump-fs probe and ps pump-fs probe spectroscopic measurements. In the fs and ps laser ablation, we have found discrete laser etching in that the etch depth becomes constant and is independent of laser fluence above the ablation threshold, although gradual (normal) etching, in which the etch depth increase continuously with the fluence above ablation threshold, was observed in the ns laser ablation. The transient absorption spectral measurements reveal the nonlinear photothermal conversion processes, corresponding to exciton–exciton annihilation and cyclic multiphotonic absorption. Their time evolutions during and after the excitation pulse duration were considered and elucidated to depend strongly on the excitation pulse width. On the basis of these results, we discuss an ablation mechanism for the ps and fs ablation that the temperature elevation bringing about transient high pressure is responsible for discrete etching.

Short pulse UV laser ablation of solid and liquid gallium

UV laser ablation of gallium from the solid (300 K) and liquid (330K) phase is reported. The ablation is performed by using a 248nm excimer laser with pulse durations of 15 ns and 0.5 ps. The ablated neutrals are ionised by resonant multiphoton ionization with a time-delayed laser (605 nm, 15 ns) and are detected by time-of-flight mass spectroscopy. The ablation threshold fluences, the ablation rates, and the velocity distributions of Ga atoms from the solid and liquid phase for irradiation with 0.5 ps and 15 ns pulses are determined. The threshold fluence for 0.5 ps laser ablation is found to be 7 times lower than that for 15 ns laser ablation and is identical for the solid and liquid samples of gallium. For ns pulses, the threshold fluence is 1.5 times higher for the solid compared to the liquid phase. This difference between the sub-picosecond and nanosecond laser ablation behaviour can be explained by the longer and deeper heat diffusion during the longer laser pulses. The time-of-flight measurements show the thermal behaviour of the removed Ga atoms in both 0.5 ps and 15 ns laser ablation and are fitted to Maxwell-Boltzmann distributions giving translational temperatures of several thousand Kelvin. An increase in the temperature as a function of the ablation laser fluence is observed.

Enhancements in laser ablation inductively coupled plasma-atomic emission spectrometry based on laser properties and ambient environment

Analytical performance of laser ablation inductively coupled plasma-atomic emission spectrometry (ICP-AES) depends critically on the interaction between the laser light and the sample. The analyte emission line intensity in ICP-AES depends on the quantity of mass ablated. The effect of laser parameters (wavelength, pulse duration, and power density) was investigated for increasing the quantity of ablated mass. For fixed laser beam energy, the ablated mass can change 2 to 3 orders of magnitude by changing the laser beam spot size on the sample. The ablated mass quantity also depends on laser pulse duration and wavelength; and on ambient gas in the sample chamber. The shorter the pulse duration and wavelength, the higher the quantity of ablated mass. By using He in the chamber, the amount of mass increases by a factor of 2 for 30 ns excimer laser ablation and by an order of magnitude for ps-laser ablation.