Category Archives: News

Single-step growth of graphene and graphene-based nanostructures by plasmaenhanced chemical vapor deposition

Our latest review article by Professor Nai-Chang Yeh, Chen-Chih Hsu, Jacob Bagley and
Wei-Shiuan Tseng
The realization of many promising technological applications of graphene and graphene-based
nanostructures depends on the availability of reliable, scalable, high-yield and low-cost synthesis
methods. Plasma enhanced chemical vapor deposition (PECVD) has been a versatile technique
for synthesizing many carbon-based materials, because PECVD provides a rich chemical
environment, including a mixture of radicals, molecules and ions from hydrocarbon precursors,
which enables graphene growth on a variety of material surfaces at lower temperatures and faster
growth than typical thermal chemical vapor deposition. Here we review recent advances in the
PECVD techniques for synthesis of various graphene and graphene-based nanostructures.
Pdf Publication Link
https://iopscience.iop.org/article/10.1088/1361-6528/aafdbf

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.

High-yield single-step catalytic growth of graphene nano-strips by plasma enhanced chemical vapor deposition

“High-yield single-step catalytic growth of graphene nano-strips by plasma enhanced chemical vapor deposition”, Chen-Chih Hsu, Jacob D. Bagley, Marcus L. Teague, Wei-Shiuan Tseng, Kathleen L, Yang, Yiran Zhang, Yiliang Li, Yilun Li, James M. Tour, and N.-C. Yeh, Carbon 129, 527 –536 (2018).

https://www.sciencedirect.com/science/article/pii/S0008622317312915

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

Mn-doping induced ferromagnetism and enhanced superconductivity in Bi4−xMnxO4S3 (0.075 ≤ x ≤ 0.15) [Zhenjie Feng et al., Phys. Rev. B 94, 064522 (2016)]

The physical mechanism for high-temperature superconductivity remains one of the most challenging issues in modern condensed matter physics. Interestingly, one of the commonalities among high-temperature superconducting cuprates and iron-based compounds is their layered structures. Even among conventional superconductors, the highest superconducting transition temperature (Tc) has been found in layered magnesium diboride MgB2. Recently, superconductivity with Tc = 4.5 K was discovered in a new superconductor Bi4O4S3. This compound has a layered structure composed of two superconducting BiS2 layers and spacer layers of Bi4O4(SO4)1x, where x indicates the deficiency of (SO4)2 ions at the interlayer sites. Since the discovery of Bi4O4S3, several other BiS2-based superconductors LnO1xF xBiS2 (Ln = La, Ce, Pr, Nd) with the highest Tc ~ 10.6 K have been reported. Both experimental and theoretical studies to date have indicated that the BiS2 layers play the role of the superconducting planes in these sulfide superconductors, similar to the CuO2 planes in the cuprate superconductors and the Fe2An2 (An = P, As, Se, Te) layers in the iron-based superconductors. A major challenge facing this new class of layered superconductors is to optimize Tc by exploring different spacer layers. Additionally, the effects of doping by either nonmagnetic or magnetic elements are important issues for investigation.

In collaboration with Professor Zhenjie Feng’s group at the Shanghai University in China, we demonstrate in this latest publication that Mn-doping in the layered sulfides Bi4O4S3 leads to stable Bi4xMnxO4S3 compounds that exhibit both long-range ferromagnetism and enhanced superconductivity for 0.075  x  0.15, with a record Tc ~ 15 K amongst all BiS2-based superconductors. Based on our experimental investigations of Bi4xMnxO4S3 and comparative studies of related compounds Bi4xCoxO4S3 and Bi4xNixO4S3, we suggest that that the coexistence of superconductivity and ferromagnetism may be attributed to Mn-doping in the spacer Bi2O2 layers away from the superconducting BiS2 layers, whereas the enhancement of Tc may be due to excess electron transfer to BiS2 from the Mn4+/Mn3+-substitutions in Bi2O2. These findings therefore shed new light on feasible pathways to enhance the Tc values of BiS2-based superconductors.
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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