Two-step hybrid process of movable part inside glass substrate using ultrafast laser

We demonstrate a two-step hybrid process for fabricating movable parts inside glass substrate using the selective laser-induced etching (SLE) process that is consisted of laser-direct writing and wet chemical etching. To obtain an influence by the optical characteristics of a glass substrate when fabricating a 3D microstructure using the SLE, we analyzed the relationship of their dimensions between the designed and the fabricated devices. Two 3D microfluidic devices are designed and fabricated on glass substrates as the demonstrations of the hybrid process: a 3D microfluidic valve device with a movable plug and a 3D microfluidic mixer with a rotatable impeller and multilayer microchannels. The valving plug and the impeller of each device are successfully moved and rotated. The smallest structure is a pillar of the impeller device, and its size is 29 μm (diameter) × 277 μm (height). We expect this study to be extended to potential applications in 3D glass microfabrication and microfluidic systems.

Friction-induced selective etching on silicon by TMAH solution

Friction-induced selective etching provides a new thought direction in the field of nanotechnology with high resolution, low cost, flexibility and site control. In this work, it was found that the scratched area on a silicon surface can play a role as a mask against etching in tetramethyl ammonium hydroxide (TMAH) solution, resulting in the formation of protrusive hillocks. Friction-induced selective etching was found to depend on the temperature and etching time. The hillock height initially increased with the temperature or etching time, and then the hillock disappeared due to the mask etching off. In contrast, the applied normal load for scratching on silicon had little effect on the hillock height produced by selective etching in TMAH solution. Further analysis showed that crystal distortions or crystal amorphization could act as a mask against selective etching on silicon. Through control tip traces for scratching, different patterns can be produced on the silicon surface by friction-induced selective etching in TMAH solution. These results can enrich the fundamental aspects of scanning probe microscope (SPM)-based nanolithography, and provide an alternative method to produce nanostructures for various applications.

Friction-induced selective etching by TMAH solution was proposed for patterning a silicon surface with site control, high flexibility and low cost.

Mechanistic Insight into Etching Chemistry and HF-Assisted Etching of MgO-Al₂O₃-SiO₂ Glass-Ceramic

The present study focuses on the etching conditions and mechanism of MgO-Al₂O₃-SiO₂ glass-ceramic (MAS) in hydrofluoric acid (HF). The results show that the amorphous phase has 218 times higher etching rate than pure cordierite crystal at room temperature. In addition, the activation energies of cordierite and amorphous phases in the HF solution are 52.5 and 30.6 kJ/mol, respectively. The time (t_ad) taken for complete dissolution of the amorphous phase depends on the HF concentration (C_HF). Based on the etching experiments, a new model is established and refined to assess the t_ad evolution. In addition, a highly crystalline cordierite phase, with the high specific surface area (59.4 m²·g⁻¹) and mesoporous structure, has been obtained by HF etching. This paper presents novel insights into the etching chemistry and opens up avenues for further research in the area of cordierite-based catalytic ceramics.

Temperature-Dependent Nanofabrication on Silicon by Friction-Induced Selective Etching

Friction-induced selective etching provides a convenient and practical way for fabricating protrusive nanostructures. A further understanding of this method is very important for establishing a controllable nanofabrication process. In this study, the effect of etching temperature on the formation of protrusive hillocks and surface properties of the etched silicon surface was investigated. It is found that the height of the hillock produced by selective etching increases with the etching temperature before the collapse of the hillock. The temperature-dependent selective etching rate can be fitted well by the Arrhenius equation. The etching at higher temperature can cause rougher silicon surface with a little lower elastic modulus and hardness. The contact angle of the etched silicon surface decreases with the etching temperature. It is also noted that no obvious contamination can be detected on silicon surface after etching at different temperatures. As a result, the optimized condition for the selective etching was addressed. The present study provides a new insight into the control and application of friction-induced selective nanofabrication.