[en] Resistless microfabrication of Cu thin films on n-type GaAs by projection patterned laser doping using a KrF excimer laser and a SiH₄ gas is described. Copper thin films with a linewidth as narrow as 2.35μm are deposited selectively on the doped region by electroplating in a CuSO₄ aqueous solution. The resistivity of the deposited Cu films is evaluated to be 2.45 x 10^-6 Ω cm, which is compared to that of bulk Cu. Using this technique, nonalloyed ohmic contacts can be formed with a specific contact resistance of 2.32 x 10^-5Ω cm², which is one-thirtieth of that of the conventional alloyed contacts. The mechanism of Cu film deposition by electroplating is discussed

No abstract available

[en] We developed a novel technique fabricating 3D hollow microstructures embedded in photosensitive glass. The fabrication procedure consists of the following three steps: (1) femtosecond laser direct writing, (2) thermal treatment, and (3) wet etching in a diluted HF solution. The developed technique can fabricate various microcomponents such as microfluidics, microvalve, micromirror, microsplitter, freestanding fibre, and microfluidic laser. In this paper, integration of these microcomponents in a single glass chip by a single procedure is demonstrated for 'all-in-one' lab-on-a-chip device manufacture

[en] Full text: Dynamic observation and analysis of the motion of microorganisms is of importance to understand the functions of specific regions in biosamples such as a flagellum for biologists. For this purpose, e. g., studying the rapid motion of the flagellum, a slide glass with a cover glass or a pertri dish is generally used under an optical microscopy equipped with a high-speed camera and a high numerical-aperture objective lens. However, due to the limitation of visually imaging volumes and long observation time, it is very difficult to efficiently capture the flagellum’s moving images and thereby analyze the movement dynamics. We previously reported the use of glass microchip with three-dimensional (3D) microfluidic structures fabricated by femtosecond (fs) laser for scaling down the observation site as well as preventing the evaporation of water in the medium, which successfully performed the dynamic observation of 3D motion of Euglena gracilis (one kind of single-celled, motile microorganisms) with extraordinarily reduced observation time. Considering random swimming behavior of Euglena cells in the previous work, 3D flexible control of the swimming direction of cells in a nondestructive manner will enable us to perform more functional observation for preciously quantitative analysis of flagellar movement. In this paper, we propose the use of monolithically integrated electrofluidic devices in glass based on hybrid fs laser microfabrication for flexible electro-orientation and high-performance observation of 3D motion of Euglena cells. In this process, 3D glass microfluidic structures with the smooth inner surface are first prepared by fs laser direct-write modification followed by annealing, successive chemical etching and additional annealing processes. Then, using the same laser, the water-assisted laser ablation on the internal walls of fabricated glass microfluidic structures is performed in a space-selective manner. Finally, the electroless metal plating performs the selective deposition of conductive metal structures on the ablated regions to realize electrofluidics. Compared with conventional fabrication methods, electrodes with designable geometries can be flexibly prepared at any positions in microchannels by this technique. To test the electro-orientation performance, Euglena cells were introduced into electrofluidic devices. The cells were randomly swimming in the channels when no electric field was applied. Once the proper electric field was applied between the electrodes, the movement of cells dramatically changed to be bidirectionally oriented along the direction of electric field. Particularly, swimming of cells can be oriented along z-direction using outlined square electrodes formed at the top and bottom of the channel, which makes it much easier to observe the flagellar motion from the front side. In contrast, four electrodes confronting each other at a right angle formed on the bottom of the channel successfully demonstrate controllable electro-orientation of cell movement in the x-y plane by changing the direction of electric field generated in the microscale space. The fabricated electrofluidic devices allow us to perform tracking observation of specific cells manipulated with the electric field with high efficiency as well as to quantitatively analyze the effects of electrical forces on manipulation. (author)

[en] A new method for embedding transparent and conductive two- and three-dimensional microstructures in glass is presented. We show that the internal surface of hollow structures fabricated by femtosecond-laser direct writing inside the photosensitive glass can be coated by indium tin oxide (Sn-doped In₂O₃, ITO) using a sol-gel process. The idea of combining two transparent materials with different electrical properties, i.e., insulating and conductive, is very promising and hence it opens new prospects in manufacturing cutting edge microdevices, such as lab-on-a-chips (LOCs) and microelectromechanical systems (MEMS). (orig.)

[en] Femtosecond (fs) laser pulse ablation (pulse duration of 150 fs, wavelength of 775 nm, repetition rate of 1 kHz) of single-crystalline TeO₂ surfaces was performed in air using the direct focusing technique. The lateral and vertical dimensions of laser ablated craters as well as the laser damage thresholds were evaluated for different pulse numbers applied to the same spot. The joint observation using optical microscopy, atomic force microscopy and scanning electron microscopy revealed the surface morphology of the ablated craters and also showed that the ablation threshold depends significantly on the number of laser pulses applied to the same spot due to incubation effects. The incubation effects change the absorption processes involved in fs-laser ablation of the transparent material from multiphoton absorption to a single-photon absorption. These results are discussed on the basis of recent models of the interaction of fs-laser pulses with dielectrics.

[en] Lab-on-a-chip strategies using miniaturized devices enable cells to be cultured in a tridimensional (3D) space that offers a real model mimicking in vivo environment. One may provide architectural configurations relevant for specific tissues to maintain them at adequate temperature, oxygen levels, and pH during the necessary time intervals for observation. Herein, we propose a miniaturized lab-on-chip glass device suitable for simultaneous dosimetry measurements and evaluation of the biological effects of ionizing radiation on cancer cells. For the 3D fabrication of biologically relevant microenvironment, high repetition rate picosecond laser-assisted etching is applied to create microfluidic networks between sealed cell culture chambers in photo-sensitive glasses (PG). To evaluate the radiation dose, we employed collimated X-ray beams to generate free electrons in the PG samples by photoreduction of Ag ions to Ag atoms. A subsequent thermal treatment applied to the PG induced clustering of precipitated Ag atoms to color the exposed area to brown, which allows us to directly evaluate a threshold of the applied X-ray radiation dose applied directly on chip. Based on our glass biochip, we tested the response of human melanoma cancer cells exposed to various X-ray doses. This lab-on-chip platform is a valuable tool to analyze and validate the cellular response to new irradiation strategies as alternatives to conventional radiotherapy methods.

[en] Double-pulse irradiation using a near-IR femtosecond laser (λ = 775 nm) was used to study the mechanism of the laser-induced plasma-assisted ablation (LIPAA) process. The dependence of the ablation depth on the delay time between the first and the second pulse for various target-to-substrate distances was investigated. The first pulse generates the laser-induced plasma from the metal target, but does not induce ablation of the glass substrate. The second pulse induces the high-efficiency ablation of the substrate, delayed by several nanoseconds (ns). A possible mechanism of the conventional LIPAA process using a ns pulsed laser is discussed based on the obtained results