Archives: Low Dimensional and Nanomaterials

Vertically-aligned graphene nanowalls grown via plasma-enhanced chemical vapor deposition as a binder-free cathode in Li–O2 batteries

Vertically-aligned graphene nanowalls grown via plasma-enhanced chemical vapor deposition as a binder-free cathode in Li–O2 batteries Chih-Pin Han, Vediyappan Veeramani, Chen-Chih Hsu, Anirudha Jena, Ho Chang, Nai-Chang Yeh, Shu-Fen Hu, and Ru-Shi Liu
https://doi.org/10.1088/1361-6528/aae362

In the present report, vertically-aligned graphene nanowalls are grown on Ni foam (VA-G/NF) using plasma-enhanced chemical vapor deposition method at room temperature. Optimization of the growth conditions provides graphene sheets with controlled defect sites. The unique architecture of the vertically-aligned graphene sheets allows sufficient space for the ionic movement within the sheets and hence enhancing the catalytic activity. Further modification with ruthenium nanoparticles (Ru NPs) drop-casted on VA-G/NF improves the charge overpotential for lithium–oxygen (Li–O2) battery cycles. Such reduction we believe is due to the easier passage of ions between the perpendicularly standing graphene sheets thereby providing ionic channels.

Atomic-Scale Structural and Chemical Characterization of Hexagonal Boron Nitride Layers Synthesized at the Wafer-Scale with Monolayer Thickness Control

Hexagonal boron nitride (h-BN) is a promising two-dimensional insulator with a large band gap and low density of charged impurities that is isostructural and isoelectronic with graphene. Here we report the chemical and atomic-scale structure of CVD-grown wafer-scale (~25 cm2) h-BN sheets ranging in thickness from 1-20 monolayers. Atomic-scale images of h-BN on Au and graphene/Au substrates obtained by scanning tunneling microscopy (STM) reveal high h-BN crystalline quality in monolayer samples. Further characterization of 1-20 monolayer samples indicates uniform thickness for wafer-scale areas; this thickness control is a result of precise control of the precursor flow rate, deposition temperature and pressure. Raman and infrared spectroscopy indicate the presence of B-N bonds and reveal a linear dependence of thickness with growth time. X-ray photoelectron spectroscopy (XPS) shows the film stoichiometry, and the B/N atom ratio in our films is 1 ± 0.6% across the range of thicknesses. Electrical current transport in metal/insulator/metal (Au/h-BN/Au) heterostructures indicates that our CVD-grown h-BN films can act as excellent tunnel barriers with a high hard-breakdown field strength. Our results suggest that large-area h-BN films are structurally, chemically and electronically uniform over the wafer scale, opening the door to pervasive application as a dielectric in layered nanoelectronic and nanophotonic heterostructures.

http://pubs.acs.org/doi/abs/10.1021/acs.chemmater.7b00183

Professor Yeh interviewed by Voice of SCIENCE!

Professor Nai-Chang Yeh, Co-Director of the Kavli Nanoscience Institute (KNI), was recently interviewed by Silver Rose Entertainment and Voice of Science for their series: BADASS WOMEN in SCIENCE for her research efforts on graphene. SRE Studios and Voice of Science are creating a video series to celebrate women working and succeeding in Science Technology Engineering and Math (STEM) fields. The interview was filmed in several of Professor Yeh’s labs with primary emphasis on our room temperature graphene growth process and also on our current research and technological applications of graphene. The interview and video was produced by Micah Haughey and can be found at the following youtube link:
https://www.youtube.com/watch?v=DRlzGJznTiI

Horizons series “Abundant World”

Professor Nai-Chang Yeh, Co-Director of the Kavli Nanoscience Institute (KNI), was featured in a recent episode of the Horizons series “Abundant World” by the BBC World News for her research on graphene. The episode was filmed in one of Professor Yeh’s labs and also at the KNI, with primary emphasis on our room temperature graphene growth process (described by Staff Scientist Dr. David Boyd) and also on our current research and technological applications of graphene (described by Professor Yeh). The “Abundant World” episode was broadcasted on May 13, 14, 15 and 17 of 2016 worldwide by the BBC World News, which can also be found at the following BBC link:

http://www.bbc.com/specialfeatures/horizonsbusiness/seriessix/abundant-world/?vid=p03vmfg1