Ying-Kan Yang

Rice-straw-like structure of silicon nanowire arrays for a hydrogen gas sensor

A rice-straw-like silicon nanowire (SiNW) array was developed for hydrogen gas sensing applications. The straight-aligned SiNW array sensor was first fabricated by the metal-assisted electroless etching (MAEE) technique. Rice-straw-like SiNW arrays were formed using a repeated MAEE technique. Hydrogen sensing characteristics were measured for gas concentrations from 20 to 1000 ppm at room temperature. The rice-straw-like SiNW-array-based hydrogen gas sensor performed with low noise and a high response (232.5%) for 1000 ppm hydrogen gas. It was found that the rice-straw-like SiNW-array hydrogen gas sensor had a much better response (approximately 2.5 times) than the straight-aligned SiNW-array sensor. The rice-straw-like SiNW-array structure effectively increased the surface area and the concentration of silicon oxide, which provided additional binding sites for gas molecules. Thus, the rice-straw-like SiNW-array-based hydrogen gas sensor possessed good sensing properties and has the potential for mass production of sensing devices.

Efficiency improvement of silicon nanostructure-based solar cells

Solar cells based on a high-efficiency silicon nanostructure (SNS) were developed using a two-step metal-assisted electroless etching (MAEE) technique, phosphorus silicate glass (PSG) doping and screen printing. This process was used to produce solar cells with a silver nitrate (AgNO3) etching solution in different concentrations. Compared to cells produced using the single MAEE technique, SNS-based solar cells produced with the two-step MAEE technique showed an increase in silicon surface coverage of ~181.1% and a decrease in reflectivity of ~144.3%. The performance of the SNS-based solar cells was found to be optimized (~11.86%) in an SNS with a length of ~300 nm, an aspect ratio of ~5, surface coverage of ~84.9% and a reflectivity of ~6.1%. The ~16.8% increase in power conversion efficiency (PCE) for the SNS-based solar cell indicates good potential for mass production.

Core-shell structure of a silicon nanorod/carbon nanotube field emission cathode

A novel core-shell structure of silicon nanorods/carbon nanotubes (SiNRs/CNTs) is developed for use in field emission cathodes. The CNTs were synthesized on SiNRs, using the Ag-assisted electroless etching technique to form the SiNRs/CNT core-shell structure. This resulting SiNRs/CNT field emission cathode demonstrated improved field emission properties including a lower turn-on electric field Eon (1.3 V/µm, 1 µA/cm2), a lower threshold electric field Eth (1.8 V/µm, 1mA/cm2), and a higher enhancement factor β (2347). These superior properties indicate that this core-shell structure of SiNRs/CNTs has good potential in field emission cathode applications.

Gas ionization sensors with CNT/Ni field cathodes

A simple and low cost method to fabricate gas ionization sensors with CNT/Ni field cathodes on corning glasses using composite plating technique was first developed. The field emission characteristics of the initial CNT/Ni field cathode showed a low turn-on electric field E<inf>on</inf> of about 1.2 V/µm with an emission current density of 1 µA/cm².It was found that the breakdown voltage (V<inf>b</inf>) of the H<inf>2</inf> gas was decreased as the pressure increased from 0.5 to 100 Torr. However; on the contrary, the V<inf>b</inf> of the O<inf>2</inf> gas was increased as the pressure increased. It was observed from the Raman spectra that I<inf>D</inf>/I<inf>G</inf> increased for both of the H<inf>2</inf> and O<inf>2</inf> gases. The full width half maximum (FWHM) around 1580 cm⁻¹ was also increased for both of the H<inf>2</inf> and O<inf>2</inf> gases. Moreover, a shoulder of 1620 cm⁻¹ appeared after the H<inf>2</inf> and O<inf>2</inf> gases sensing measurements. This phenomenon, indicating the degradation of the graphitization, was more obvious for the O<inf>2</inf> gas sensing. The fabrication of the ionization sensors with CNT/Ni field cathode was relatively simple and inexpensive and could be mass-produced.