Chun-Yi Chen

Fully Depleted Ti–Nb–Ta–Zr–O Nanotubes: Interfacial Charge Dynamics and Solar Hydrogen Production

Poor kinetics of hole transportation at the electrode/electrolyte interface is regarded as a primary cause for the mediocre performance of n-type TiO2 photoelectrodes. By adopting nanotubes as the electrode backbone, light absorption and carrier collection can be spatially decoupled, allowing n-type TiO2, with its short hole diffusion length, to maximize the use of the available photoexcited charge carriers during operation in photoelectrochemical (PEC) water splitting. Here, we presented a delicate electrochemical anodization process for the preparation of quaternary Ti-Nb-Ta-Zr-O mixed-oxide (denoted as TNTZO) nanotube arrays and demonstrated their utility in PEC water splitting. The charge-transfer dynamics for the electrodes was investigated using time-resolved photoluminescence, electrochemical impedance spectroscopy, and the decay of open-circuit voltage analysis. Data reveal that the superior photoactivity of TNTZO over pristine TiO2 originated from the introduction of Nd, Ta, and Zr elements, which enhanced the amount of accessible charge carriers, modified the electronic structure, and improved the hole injection kinetics for expediting water splitting. By modulating the water content of the electrolyte employed in the anodization process, the wall thickness of the grown TNTZO nanotubes can be reduced to a size smaller than that of the depletion layer thickness, realizing a fully depleted state for charge carriers to further advance the PEC performance. Hydrogen evolution tests demonstrate the practical efficacy of TNTZO for realizing solar hydrogen production. Furthermore, with the composition complexity and fully depleted band structure, the present TNTZO nanotube arrays may offer a feasible and universal platform for the loading of other semiconductors to construct a sophisticated heterostructure photoelectrode paradigm, in which the photoexcited charge carriers can be entirely utilized for efficient solar-to-fuel conversion.

A study on young's modulus of electroplated gold cantilevers for MEMS devices

This paper presents evaluation of the effective Youngs modulus of electroplated gold micro-cantilevers. Youngs modulus is one of the fundamental parameters to design MEMS (microelectromechanical systems) components. Gold electroplated MEMS structures can be used to develop highly-sensitive MEMS sensors, such as accelerometers. With a resonant frequency method, we evaluate gold-electroplated Ti/Au cantilevers by varying both the length and the width. The experimental results showed that the Youngs modulus was dependent on the width, and it was found that the Youngs modulus increased with an increase in the width, which would be useful to design MEMS devices.

Long-term vibration characteristics of MEMS inertial sensors by multi-layer metal technology

This paper presents the long-term vibration characteristics of MEMS inertial sensors developed by multi-layer metal technology based on gold electroplating. We evaluate the change of resonant frequencies of the MEMS inertial sensors and tip displacements of multi-layer metal cantilevers during long-term vibration tests. The vibration tests employ a cyclic input acceleration with the amplitude of 1G. The experimental results show that the inertial sensors have a mechanical tolerance to the vibration up to 107 cycles. Moreover, the cantilever tests suggest that the structure stability of multi-layer metal devices could be higher when the structure thickness becomes thicker. In conclusion, we confirmed that the Ti/Au multi-layer metal structures can be promising components for MEMS inertial sensors.

Study on Ti/Au Two-Layered Cantilevers with Different Aspect Ratio for MEMS Devices

We report the structure stability of Ti/Au two-layered micro-cantilevers with the various ratios of length and width for the first time. The cantilevers were fabricated by gold electroplating, a key technology for post-CMOS process for CMOS-MEMS devices. Ti is conventionally used for adhesion layers of gold electroplating, while the mechanical properties of Ti/Au structures have not been investigated. To evaluate the structure stability, the lengths of Ti/Au cantilevers were varied from 100 μm to 1000 μm. The experimental results showed that the cantilever of less than 500 μm in length and 5 μm in width made the structure more stable. Moreover, the cantilever of 1000 μm-length and 15-μm width showed high flatness. These results reveal the potential of Ti/Au layers to be applied to MEMS structures.

Mechanical Properties of Electrodeposited Gold for MEMS Device

Mechanical properties of electrodeposited gold materials for MEMS device were evaluated by a micro-compression test. The gold electroplating method is considered as a key technology for post-CMOS fabrication process. The micro-compression specimens were 15×15×30 μm3 micro-pillars fabricated by focused ion beam. The gold micro-pillars showed a high compressive strength of 600 MPa. The high strength was suggested to be mainly caused by size of the gold grains, which was found to be about 14.7 nm.