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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 685 records · Page 38
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Atomic layer deposition TiO 2 -Al 2 O 3 stack: An improved gate dielectric on Ga-polar GaN metal oxide semiconductor capacitors

This research focuses on the benefits and properties of TiO 2 -Al 2 O 3 nano-stack thin films deposited on Ga 2 O 3 /GaN by plasma-assisted atomic layer deposition (PA-ALD) for gate dielectric development. This combination of materials achieved a high dielectric constant, a low leakage current, and a low interface trap density. Correlations were sought between the films’ structure, composition, and electrical properties. The gate dielectrics were approximately 15 nm thick and contained 5.1 nm TiO 2 , 7.1 nm Al 2 O 3 and 2 nm Ga 2 O 3 as determined by spectroscopic ellipsometry. The interface carbon concentration, as measured by x-ray photoelectron spectroscopy (XPS) depth profile, was negligible for GaN pretreated by thermal oxidation in O 2 for 30 minutes at 850°C. The RMS roughness slightly increased after thermal oxidation and remained the same after ALD of the nano-stack, as determined by atomic force microscopy. The dielectric constant of TiO 2 -Al 2 O 3 on Ga2O3/GaN was increased to 12.5 compared to that of pure Al 2 O 3 (8~9) on GaN. In addition, the nano-stack's capacitance-voltage (C-V) hysteresis was small, with a total trap density of 8.74 × 10 11 cm -2 . The gate leakage current density (J=2.81× 10 -8 A/cm 2 ) was low at +1 V gate bias. These results demonstrate the promising potential of plasma ALD deposited TiO 2 /Al 2 O 3 for serving as the gate oxide on Ga 2 O 3 /GaN based MOS devices.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Porous Carbon/CeO2 Nanoparticles Hybrid Material for High-Capacity Super-Capacitors

The increasing demand for energy storage devices has propelled research for developing efficient supercapacitors (SC) with long cycle life and ultrahigh energy density. Carbon-based materials are commonly used as electrode materials for SC. Herein, we report a new approach to improve the SC performance utilizing a Porous Carbon/Cerium Oxide nanoparticle (PC-CON) hybrid as electrode material synthesized via a low temperature hydrothermal method. Through this approach, charges can be stored not only via electrochemical double layer capacitance (EDLC) from PC but also through pseudo-capacitive effect from CeO2 nanoparticles (NPs). The electrode-electrolyte interaction due to the electrochemical properties of the electrolyte provides a enhanced voltage window for the SC. Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), X-ray Photoelectron Spectroscopy (XPS), and X-Ray Diffraction (XRD) measurements were used for the characterization of this PC/CeO2 hybrid material system. The testing results have shown that a maximum of 500% higher specific capacitance could be obtained using PC/CeO2 instead of using PC only.

Kim, Hoejin↗