Tzu-Ho Wu

Porosity-engineered carbons for supercapacitive energy storage using conjugated microporous polymer precursors

Conjugated microporous polymers (CMPs) are considered an important material, combining aspects of both microporosity and extended π-conjugation. However, pristine CMP electrodes suffer from poor electrical conductivity which limits the material in electrochemical applications. In this work, direct carbonisation of conjugated microporous polymers (CMPs) yields porosity-engineered carbons, important for the flow of ions through the electrode. These conductive carbonised CMPs show specific capacitance as high as 260 F g−1, excellent rate capability and no loss in performance after 10 000 charge/discharge cycles. This study provides a procedure to enhance the performance of CMP-based materials, opening up a new source of electroactive materials.

Charge storage mechanism of activated manganese oxide composites for pseudocapacitors

Manganese oxides can undergo an electrochemical activation step that leads to greater capacitances, of which the structural change and mechanism remains poorly understood. Herein we present a wide-ranging study on a manganese oxide synthesised by annealing manganese(II) acetate precursor to 300 °C, which includes in operando monitoring of the structural evolution during the activation process via in situ Raman microscopy. Based on powder X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron and ex situ Raman microscopy, the as prepared manganese oxide was characterised as hausmannite-Mn3O4 with a minor portion of MnO2. The activation process of converting as-prepared hausmannite-Mn3O4 into amorphous MnO2 (with localised birnessite structure) by electrochemical cycling in 0.5 M Na2SO4 was examined. After activation, the activated MnOx exhibited capacitive performance of 174 F g−1 at a mass loading of 0.71 mg cm−2. The charge storage mechanism is proposed as the redox reaction between Mn(III) and Mn(IV) at outer surface active sites, since the disordered birnessite-MnO2 does not provide an ordered layer structure for cations and/or protons to intercalate.

Effects of Surface Treatments on Interfacial Self-Cleaning in Atomic Layer Deposition of Al2O3 on InSb

The atomic layer deposition (ALD) of Al 2 O 3 using trimethylaluminum (TMA) as a metal precursor on an InSb substrate with or without surface pretreatments was investigated. It was found that both in situ TMA/Ar purging (half-ALD cycle) and ex situ CP4A (HNO 3 HF:CH 3 COOH:H 2 O = 2:1:1:10) chemical etching can remove the native oxides on InSb before ALD of Al 2 O 3, and lead to a native-oxides-free Al 2 O 3 /InSb structure. Characteristics of current density-voltage and capacitance-voltage were also investigated to evaluate the insulative and interface quality in a Pt/Al 2 O 3 /Insb metal-oxide-semiconductor structure.

Interfacial Cleaning Effects in Passivating InSb with Al2O3 by Atomic Layer Deposition

Al 2 O 3 was deposited on InSb by atomic layer deposition using trimethyl-aluminum as the metal precursor. Most of the native oxides on InSb substrate were in situ cleaned away from the interface of Al 2 O 3 /Insb, except for a small amount of In 2 O 3 residual, after the deposition-of Al 2 O 3 . Moreover, a slight contamination of In 2 O 3 , In(OH) 3 , and nearly negligible Sb 2 O X was observed on the surface of AI 2 O 3 . The Al 2 O 3 films show a good insulating property (∼10 -9 to 10 -8 A/cm 2 within ± 4 V), and a transition from accumulation to depletion was displayed from the capacitance-voltage relation measured at 77 K.

Thermal Stability Improvement via Cyclic D2O Radical Anneal Interposed in Atomic Layer Deposition Process

Cyclic D 2 O radical anneal was interposed in atomic layer deposition (ALD) of HfO 2 gate dielectrics on Si. A significant improvement on the thermal stability of the gate dielectrics against postdeposition anneal (PDA) can be achieved from the incorporation of this special anneal technique into the ALD process. A low equivalent oxide thickness of the HfO 2 gate dielectrics was retained even after 900°C PDA.

Na0.35MnO2 as an ionic conductor with randomly distributed nano-sized layers

Here we show that through a straightforward synthesis it is possible to create a bulk material, Na0.35MnO2, with isolated sheets. Due to such an arrangement of the oxide layers, this ionic conductor was found to be genuinely pseudocapacitive, with charge storage not limited by diffusion of ions between stacked layers, resulting in capacitance values of 190 F g−1 under exceptionally high current rates of up to 200 A g−1.