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The laser manipulation of metal spheres in glass has been reported in the present work. Formation of a stainless steel-silver core–shell sphere in the glass has been demonstrated by passing a stainless steel sphere through silver-doped borosilicate glass. Silver-doped glass was obtained using a field-enhanced ion-exchange technique. The sodium ions in the neighborhood of the surface were exchanged with silver ions. A stainless steel sphere was passed through the silver-doped area, silver in the glass got concentrated in the sphere, and a core–shell stainless steel-silver sphere was formed. In the trajectory of the metal sphere migration, the amount of silver decreased, and silver particles were observed. The amounts of silver in the core–shell sphere and that eliminated from the glass, along the trajectory of the migrated metal sphere, were compared. This technique of laser-induced migration in silver-doped glass enables the formation of core–shell-structured metal spheres with the elimination of the silver contained in the glass along the migration trajectory of the sphere. [ABSTRACT FROM AUTHOR]

Several studies have focused on the electrical connections between the front and rear surfaces of stacked substrates in order to improve device performance. The fabrication and mounting process of the substrates involves three steps: (1) through-hole drilling, (2) formation of a conductive path inside the hole, and (3) physical bonding and electrical wiring connection of the substrates. In this paper, we demonstrate a technique for performing the process above simultaneously by laser percussion drilling. A borosilicate glass sample was used as the substrate, while copper was used as the wiring material. The substrate was drilled to a diameter of ~30 μm by laser radiation, while the copper was evaporated and deposited in a ~12-μm-thick layer on the inner surface of a glass-copper hole. Hence, a conductive path was formed inside the glass hole, facilitating bonding and conduction between the glass substrate and the copper sheet. The conductivity and bonding strength per 100 points between the glass surface and the copper sheet were ~5 Ω and ~1 N respectively. Furthermore, gaps were observed between the glass substrate and the copper sheet by energy dispersive X-ray analysis using a scanning electron microscope. However, the glass substrate and the copper sheet were bonded by the formation of a redeposited layer on the inner surface of the hole and in the gap between the glass and copper surfaces. • Drilling, making holes conductive, and material bonding are performed simultaneously. • Conductivity of the formed conductive hole is evaluated. • Factors for foreign material bonding by laser percussion drilling are discussed. [ABSTRACT FROM AUTHOR]

Pulsed-laser-induced glass fiber generation has been reported. We demonstrate a novel glass fiber generation technique by continuous-wave laser illumination and reveal the generation mechanism. In this technique, borosilicate glass, metal foil, and a heat insulator are stacked and clamped by a jig as the sample. Glass fibers are ejected from the side surface of the borosilicate glass by laser illumination of the sample from the borosilicate glass side. SEM observation shows that nanoparticles are attached on the glass fibers. High-speed imaging reveals that small bubbles are formed at the side surface of the borosilicate glass and the bursting of the bubble ejects the fibers. The temperature at the fiber ejection point is estimated to be ~1220 K. The mechanism of the fiber ejection includes the following steps: the metal thin foil heated by the laser increases the temperature of the surrounding glass by heat conduction. Since the absorption coefficient of the glass is increased by increasing the temperature, the glass starts to absorb the laser irradiation. The heated glass softens and bubbles form. When the bubble bursts, molten glass and gas inside the bubble scatter into the air to generate the glass fibers. [ABSTRACT FROM AUTHOR]

In this paper, we describe curved hole drilling via the reflection of a laser beam off the sidewall of the drilled hole. A slightly offset laser beam forms a tilted surface at the bottom of the hole, controlling the angle of curvature. An ultraviolet laser beam operating at a wavelength of 266 nm was used. To visualize the hole formation process, borosilicate glass was used as the laser workpiece. This method was able to drill a curved hole with an average angle of ∼3° with curvature beginning at a depth of 400–600 μm. A curved hole with a diameter of <50 μm was achieved. A branched hole was also demonstrated by using the reflection of the tilted sidewall. The curved hole formation process was recorded with a high speed camera. Once the ablated sidewall reached a certain depth, drilling ceased as the laser energy fell below the ablation threshold. Ultimately, judicious selection of an appropriate laser fluence and sidewall angle allow the formation of curved holes. [ABSTRACT FROM AUTHOR]

• Laser absorption by glass and plasma formation enabled copper implantation. • Melted copper diffused into glass and precipitated as nanoparticles. • The sphere could not be implanted when the plasma propagation speed was > 50 mm/s. Implanting metals in glass can serve many different purposes, ranging from enhancing the electro-optical properties to modifying the mechanical properties of the substrate. One approach involves the use of continuous laser illumination to implant metal spheres by transferring particles from a metal foil in direct contact with one side of the glass substrate. The process, which occurs in a very short period time (in tens of milliseconds), is unidentified: due to the bright thermal emissions, it cannot be directly observed. In this study, the continuous laser heating conditions required for implanting copper spheres in borosilicate glass were investigated via spectroscopy and numerical calculations to estimate the temperature of the copper foil. Emission spectroscopy revealed that the temperature during implantation reached 5100 K, which largely exceeded the temperature threshold for laser absorption (∼2000 K). Under such conditions, the plasma forms and enables the migration of copper particles into the glass host. The plasma propagation speed increased with increasing laser power density. The copper sphere was implanted when the plasma propagation speed was 20–50 mm/s. The copper sphere could not be implanted, and fiber fuse occurred when the plasma propagation speed was higher than 50 mm/s. [ABSTRACT FROM AUTHOR]

Applying voltage to alkali-containing glass, doped with silver ions by the solid-state ion-exchange method, yields silver precipitates inside the glass. We attempted in-situ observation of the precipitation phenomena to elucidate the silver precipitation mechanisms, where the direction of the voltage application was rotated 90 deg. to increase the precipitation area compared to that of our previous method. The results show that the shape of the precipitate changed from clumpy to dendritic as the applied voltage increased. The shape of the precipitate, predicted by the dielectric breakdown model, implied that the higher the precipitation probability (i.e., the higher the frequency of a silver ion to encounter with the precipitate), the more branches the precipitate formed. In addition, the un-doped, silver-doped, and silver-precipitated areas inside the glass were modeled as electrical resistances to predict the growth behavior of the precipitated areas. • Silver precipitates were formed by voltage application to silver ion-doped glass. • Silver precipitation phenomena in silver ion-doped glass was observed in-situ. • Precipitate shape changes from clumpy to dendritic as the applied voltage increases. • Precipitate shape is determined by the ionic mobility of silver in glass. • Time variation of precipitation area is well represented by equivalent circuit model. [ABSTRACT FROM AUTHOR]

Solid-state ion exchange with an applied voltage enables metal doping into alkali-silicate glass surfaces. The effect is especially prominent when silver is a dopant material, with additional voltage application producing silver nanowire networks in a glass substrate. We aimed to improve the wet etching efficiency of a glass substrate using internal networks as penetration paths of etchants. Silver precipitated glass when immersed in hydrofluoric acid (HF), allowing etchant infiltration via cracks around the nanowires. As a result, the silver-precipitated area was selectively dissolved, due to which blind/through-holes were formed with similar shapes. The etch rate (etched depth per unit time) of the silver-precipitated area was 1.9 μm/min, and was 3.3 times higher than that of the as-received glass (0.58 μm/min) in 20 wt% HF at 297 K. • Silver nanowire network was formed by additional voltage application to silver doped glass. • When silver-precipitated glass was immersed in HF, etchant infiltrated via cracks around the nanowires. • Silver-precipitated area was selectively dissolved resulting in blind/through-holes formation. • Etch rate of silver-precipitated area was 3.3 times higher than that of as-received glass. [ABSTRACT FROM AUTHOR]