Preparation of silver nanoparticles by laser ablation in polyvinylpyrrolidone solutions

This paper reviews applications of laser-based techniques to the fabrication of microfluidic devices for biochips and addresses some of the challenges associated with the manufacture of these devices. Special emphasis is placed on the use of lasers for the rapid prototyping and production of biochips in particular for applications in which silicon is not the preferred material base. Part I of this review addresses applications and devices using UV lasers for laser ablation and surface treatment of microchannels, in particular in polymers.

Laser processing for bio-microfluidics applications (part II)

Landolt-Bornstein, Zahlenwerte Und Funktionen Aus Physik, Chemie, Astronomie, Geophysik Und Technik

Glass is an excellent material for use as a microfluidic chip substrate because it has great chemical and thermal stability. This work describes a flexible platform for the rapid prototyping of microfluidic chips fabricated from glass. A debris-free laser direct-writing technology that requires no photomask generation is developed. A 266 nm laser with a high repetition rate is employed in laser-induced backside wet etching (LIBWE) for glass machining. A microfluidic pattern is designed using computer drawing software and then automatically translated into computer numerical control motion so that the microtrench is directly fabricated on the glass chip. The overall machining speed can be increased by increasing the repetition rate to ~6 kHz. Without a clean room facility or the highly corrosive acid, HF, the overall development time is within hours. Trenches with complex structures that are hard to fabricate by photolithography were easily produced by laser direct-writing. An integrated microreactor/concentrator is demonstrated. The crack-free and debris-free surface was characterized by SEM and a surface profiler. Various effective etching chemicals for the LIBWE process were investigated to understand the etching mechanism. The minimal laser power used for glass etching was approximately 20 mW for a 6 µm wide microtrench. Several new compounds have been demonstrated to be effective in ablation. The etch threshold is minimum and does not decrease further as the unit length absorbance increases above 8000 in acetone solution.

https://iopscience.iop.org/article/10.1088/0960-1317/15/6/005/pdf

Crack-free direct-writing on glass using a low-power UV laser in the manufacture of a microfluidic chip

Nanosecond-resolved shadowgraphs and optical emission spectra were observed for the laser ablation of a silver plate in water to investigate the formation process of nanoparticles. Optical emissions, a shockwave, and a cavitation bubble were generated sequentially from the target surface after laser irradiation. In the optical emission spectra, continuous bands were observed, which were probably attributable to bremsstrahlung and/or electron–ion recombination. These findings suggest that materials emitted by laser ablation were confined by the surrounding water causing high pressure, which etches the target surface. Results show that nanoparticles are formed in the cavitation bubbles rather than in the bulk water from materials that were emitted via both direct laser ablation and secondary etching. In addition, a second shockwave was observed upon the collapse of the cavitation bubble, indicating that another secondary etching process might accompany nanoparticle formation.

https://iopscience.iop.org/article/10.1143/JJAP.46.1533/pdf

Nanosecond Time-Resolved Observations of Laser Ablation of Silver in Water

Laser-induced backside wet etching (LIBWE) of silica glass plates was performed by the excitation of a pure toluene solution with an ns-pulsed KrF excimer laser at 248 nm. Well-defined grid micro-pattern was fabricated without debris and micro-crack around the etched area. The etch rate, which increased linearly with laser fluence, was 30% higher than that in the case of acetone solution of pyrene dye at a concentration of 0.4 mol dm −3 . To understand the etching mechanism, the formation and propagation of shock wave and bubble were monitored by time-resolved optical microscopy at the interface between the silica glass and the toluene solution during etching process. Transient high pressure as well as high temperature generated by UV laser irradiation plays a key role in the etching process.

Surface micro-fabrication of silica glass by excimer laser irradiation of organic solvent

Laser-induced backside wet etching of fused-silica plates using an aqueous solution of naphthalene-1,3,6-trisulfonic acid trisodium salt (Np(SO3Na)3) is reported. A KrF excimer laser was employed as a light source. The etch rate varied greatly with the concentration of the solution and the laser fluence. For lower concentration solutions, the etch rate increased linearly with laser fluence. For highly concentrated solutions, however, the etch rate increased abruptly at higher fluence. Well-defined line-and-space and grid micropatterns were fabricated using a low etch rate. The etched surface was as flat as the surface of the virgin plates and the etched pattern was free of debris and microcracks. The formation and propagation of shockwaves and bubbles in the solution during the etch process were monitored. High pressure, as well as the high temperature generated by the photothermal process, plays a key role in the etching process.

Laser-induced high-quality etching of fused silica using a novel aqueous medium

Transient processes of laser ablation of a highly laser-absorbing liquid, toluene, were investigated by directly measuring (by using a fast-response pressure gauge) the transient pressure caused by toluene ablation under KrF laser irradiation . The results were compared with time-resolved images . The peak pressure P due to a shock wave decreased slowly with increasing distance d for d=100–1000 μm:P∝d-0.33. By extrapolating P to d=8.9 μm, the optical penetration depth of toluene at λ=248 nm, the estimated initial pressure due to toluene ablation was 65 MPa at 1.0 J cm-2 pulse-1. The estimated initial pressure increased linearly with the fluence. These results help clarify the mechanism of laser-induced backside wet etching.

Transient pressure induced by laser ablation of toluene, a highly laser-absorbing liquid

Microstructures with well-defined 1 μm-scale grating and grid patterns were fabricated on the surfaces of silica glass using a laser-induced backside wet etching (LIBWE) method by nanosecond-pulsed KrF excimer laser irradiation through a mask projection system. In the former case, gratings as narrow as 0.75 μm-sized were successfully etched on the glass surface via fine adjustments to the projection system. To investigate the etching mechanisms, formation and propagation of the shockwave and micro-bubbles after laser irradiation, at the interface of the silica glass and the toluene solution, were monitored using time-resolved shadowgraph microscopy, from the front- and side-view directions.

Micron- and submicron-sized surface patterning of silica glass by LIBWE method

Sapphire plates were etched with the approach of laser-induced backside wet etching (LIBWE) using neat toluene or saturated pyrene/acetone solutions as the etching medium. Using this approach, flexible patterns on the scale of 4-µm can be fabricated on the surface of the plates. The etching process was observed in situ by a CCD camera, which revealed the deposition of black particles and the formation thereafter of a laser-absorbing film in the etched area. By Raman spectroscopic analysis, the film was characterized to be amorphous carbon resulting from the decomposition of toluene or pyrene upon laser irradiation, which is an essential factor contributing to the etching process.

https://iopscience.iop.org/article/10.1143/JJAP.42.L176/pdf

Ximing Ding

Papers

Surface micro-fabrication of silica glass by excimer laser irradiation of organic solvent

Laser-induced high-quality etching of fused silica using a novel aqueous medium

Transient pressure induced by laser ablation of toluene, a highly laser-absorbing liquid

Micron- and submicron-sized surface patterning of silica glass by LIBWE method

Laser-Induced Backside Wet Etching of Sapphire