Yu-Chuan Shih

Wafer Scale Phase-Engineered 1T-and 2H-MoSe2/Mo Core-Shell 3D-Hierarchical Nanostructures toward Efficient Electrocatalytic Hydrogen Evolution Reaction

The necessity for new sources for greener and cleaner energy production to replace the existing ones has been increasingly growing in recent years. Of those new sources, the hydrogen evolution reaction has a large potential. In this work, for the first time, MoSe2 /Mo core-shell 3D-hierarchical nanostructures are created, which are derived from the Mo 3D-hierarchical nanostructures through a low-temperature plasma-assisted selenization process with controlled shapes grown by a glancing angle deposition system.

Roles of oxygen and nitrogen in control of nonlinear resistive behaviors via filamentary and homogeneous switching in an oxynitride thin film memristor

A TiOxNy thin film, which contains controllable concentrations of oxygen and nitrogen by a single-step reactive sputtering process using a non-symmetric Pt electrode as top electrode and TiN as bottom electrode, exhibiting non-linear I–V behavior, was proposed and demonstrated. A switching model of the non-linear I–V switching was built based on diffusion of oxygen vacancies in the TiOxNy film with different ratios of O and N after the SET process. Effects on the switching relationship between TiOxNy and electrodes were investigated to optimize the best conditions for the non-linear behavior. The origin of the nonlinear property was investigated in detail by changing the compositions of oxygen and nitrogen in the TiOxNy thin film. We believe that these findings would open up opportunities to exploit resistive switching mechanisms and simple memristor stacking in next generation crossbar array applications.

Tunable defect engineering in TiON thin films by multi-step sputtering processes: from a Schottky diode to resistive switching memory

The role of defect engineering is essential in resistive switching memory. In this study, multi-step sputtering processes to fabricate TiON for a resistive random access memory (ReRAM) device were demonstrated and detailed mechanisms were systematically investigated. The multi-step sputtered TiON film shows asymmetric defect distribution, exhibiting rectifying characteristics as a Schottky diode and resistive switching behavior as memory, depending on the applied bias. Rectifying properties, including a rectifying ratio of 102 at ±1.5 V, a forward current of ∼2 mA at 1.5 V, a turn-on voltage of 1.5 V and an ideality factor of 4.5, were measured. In addition, compared to a TiON ReRAM device prepared via a single-step sputtering process, TiON film with a gradient distribution of defects exhibits stable switching behavior with a better uniform SET voltage (VSET) and a coefficient of variation (σ/μ) which improves from 0.49 to 0.17. The conduction mechanisms of two kinds of device were investigated via a trap-controlled space charge limit conduction (SCLC) process. The mechanisms of how the distribution of asymmetric defects affects the resistive switching behavior were discussed in detail. The results disclose the possibility of the modulation of defect engineering toward Schottky diode applications, leading to the improvement of ReRAM performance for one-diode one-resistor (1D1R) applications in the future.

Phase-Engineered PtSe2-Layered Films by a Plasma-Assisted Selenization Process toward All PtSe2-Based Field Effect Transistor to Highly Sensitive, Flexible, and Wide-Spectrum Photoresponse Photodetectors

The formation of PtSe2 -layered films is reported in a large area by the direct plasma-assisted selenization of Pt films at a low temperature, where temperatures, as low as 100 °C at the applied plasma power of 400 W can be achieved. As the thickness of the Pt film exceeds 5 nm, the PtSe2 -layered film (five monolayers) exhibits a metallic behavior. A clear p-type semiconducting behavior of the PtSe2 -layered film (≈trilayers) is observed with the average field effective mobility of 0.7 cm2 V-1 s-1 from back-gated transistor measurements as the thickness of the Pt film reaches below 2.5 nm. A full PtSe2 field effect transistor is demonstrated where the thinner PtSe2 , exhibiting a semiconducting behavior, is used as the channel material, and the thicker PtSe2 , exhibiting a metallic behavior, is used as an electrode, yielding an ohmic contact. Furthermore, photodetectors using a few PtSe2 -layered films as an adsorption layer synthesized at the low temperature on a flexible substrate exhibit a wide range of absorption and photoresponse with the highest photocurrent of 9 µA under the laser wavelength of 408 nm. In addition, the device can maintain a high photoresponse under a large bending stress and 1000 bending cycles.

Pressure Welding of Silver Nanowires Networks at Room Temperature as Transparent Electrodes for Efficient Organic Light‐Emitting Diodes

In this work, polymethylmethacrylate (PMMA) as a superior mediate for the pressure welding of silver nanowires (Ag NWs) networks as transparent electrodes without any thermal treatment is demonstrated. After a pressing of 200 kg cm-2 , not only the sheet resistance but also the surface roughness of the PMMA-mediated Ag NWs networks decreases from 2.6 kΩ sq-1 to 34.3 Ω sq-1 and from 76.1 to 12.6 nm, respectively. On the other hand, high transparency of an average transmittance in the visible wavelengths of 93.5% together with a low haze value of 2.58% can be achieved. In terms of optoelectronic applications, the promising potential of the PMMA-mediated pressure-welded Ag NWs networks used as a transparent electrode in a green organic light-emitting diode (OLED) device is also demonstrated. In comparison with the OLED based on commercial tin-doped indium oxide electrode, the increments of power efficiency and external quantum efficiency (EQE) from 80.1 to 85.9 lm w-1 and 19.2% to 19.9% are demonstrated. In addition, the PMMA-mediated pressure welding succeeds in transferring Ag NWs networks to flexible polyethylene naphthalate and polyimide substrates with the sheet resistance of 42 and 91 Ω sq-1 after 10 000 times of bending, respectively.

A superior dye adsorbent towards the hydrogen evolution reaction combining active sites and phase-engineering of (1T/2H) MoS2/α-MoO3 hybrid heterostructured nanoflowers

Here, we demonstrate the successful synthesis of (1T/2H) MoS2/α-MoO3 heterostructured nanoflowers at a low temperature of 200 °C by a one-step hydrothermal method. By tuning the reaction time under the influence of thiourea and hydrazine hydrate, we established a complete phase-engineered MoS2 with 1T and 2H phases on the surface of α-MoO3. Active sites associated with the phase-engineered (1T/2H) MoS2/α-MoO3 hybrid nanoflowers enable them to exhibit dual roles as a superior dye adsorbent and an electrocatalyst towards the hydrogen evolution reaction. The 2H-rich (1T/2H) MoS2/α-MoO3 hybrid heterostructured nanoflowers prepared at 16 h achieved a high surface area of 37.97 m2 g−1, and 97% of the RhB dye with an initial concentration of 47.9 mg L−1 was removed within 10 min through the adsorption process, which is the highest known removal efficiency reported in the literature. As a hydrogen evolution reaction (HER) electrocatalyst in acidic solution, the 1T-rich (1T/2H) MoS2/α-MoO3 hybrid heterostructured nanoflowers prepared at 12 h exhibited a highly efficient catalytic activity by achieving a low overpotential of 232 mV at a current density of 10 mA cm−2, which is comparable to those of previously reported HER catalysts based on MoS2. Moreover, this sample reached a low Tafel slope of 81 mV dec−1 and was stable when operated for more than 1000 cycles.