Congratulations Steve for publishing on ACS Appl. Mater. Interfaces
Abstract: A wide variety of transition metals, including copper and gold, have been successfully used as substrates for graphene growth. On the other hand, it has been challenging to grow graphene on silver, so realistic applications by combining graphene and silver for improved electrode stability and enhanced surface plasmon resonance in organic light-emitting diodes and biosensing have not been realized to date. Here, we demonstrate the surface passivation of silver through the single-step rapid growth of nanocrystalline multilayer graphene on silver via low-temperature plasma-enhanced chemical vapor deposition (PECVD). The effect of the growth time on the graphene quality and the underlying silver characteristics is investigated by Raman spectroscopy, X-ray diffraction, atomic force microscopy, X-ray photoelectron spectroscopy (XPS), and cross-sectional annular dark-field scanning transmission electron microscopy (ADF-STEM). These results reveal nanocrystalline graphene structures with turbostratic layer stacking. Based on the XPS and ADF-STEM results, a PECVD growth mechanism of graphene on silver is proposed. The multilayer graphene also provides excellent long-term protection of the underlying silver surface from oxidation after 5 months of air exposure. This development thus paves the way toward realizing technological applications based on graphene-protected silver surfaces and electrodes as well as hybrid graphene-silver plasmonics.
Click link for details: https://pubs.acs.org/doi/10.1021/acsami.2c21809?fbclid=IwAR3bqN9uEOZX3wAgZ51rTWbhaOapi7Cbf3muFC3eHn-t3xqr0oihl2ARrko
Steve’s research on graphene has been featured on Caltech’s news website.
Check out the link below for more information: https://www.caltech.edu/about/news/graphene-boosts-flexible-and-wearable-electronics
Congratulate Steve for publishing on ACS Appl. Nano Mater. !
Gold is normally considered inert to chemical reaction. Nevertheless, as a common electrode material, it would suffer from corrosion when exposed to certain solutions such as sweat and body fluids. Here, we report low-temperature plasma-enhanced chemical vapor deposition (PECVD) of graphene on gold and demonstrate its feasibility for anticorrosion application. The effects of hydrogen-to-methane ratio and the underlying gold substrate on the graphene growth are investigated, and the growth mechanism of PECVD graphene on gold is proposed. When immersed in an oxygenated saline solution, the PECVD-grown graphene-covered gold surface is found to remain intact after an acceleration soaking test at 90 °C for 24 h, which is in contrast to the degradation of bare gold surface subject to the same test. Our findings suggest that consumer/medical wearables and implantable devices with exposed gold can benefit from the protection of a direct, low-temperature PECVD-grown graphene layer for anticorrosion, thereby prolonging the efficacy and reliability of gold electrode-based biosensors.
Check out a new paper just published on Science Advances: https://www.science.org/doi/10.1126/sciadv.abm0100
Controlling the density of exciton and trion quasiparticles in monolayer two-dimensional (2D) materials at room temperature by nondestructive techniques is highly desired for the development of future optoelectronic devices. Here, the effects of different orbital angular momentum (OAM) lights on monolayer tungsten disulfide at both room temperature and low temperatures are investigated, which reveal simultaneously enhanced exciton intensity and suppressed trion intensity in the photoluminescence spectra with increasing topological charge of the OAM light. In addition, the trion-to-exciton conversion efficiency is found to increase rapidly with the OAM light at low laser power and decrease with increasing power. Moreover, the trion binding energy and the concentration of unbound electrons are estimated, which shed light on how these quantities depend on OAM. A phenomenological model is proposed to account for the experimental data. These findings pave a way toward manipulating the exciton emission in 2D materials with OAM light for optoelectronic applications.
Congratulate Wei-Hsiang for publishing a new paper on Advanced Materials!
Abstract: Monolayer transition metal dichalcogenides (TMDs) have intrinsic valley degrees of freedom, making them appealing for exploiting valleytronic applications in information storage and processing. WS2 monolayer possesses two inequivalent valleys in the Brillouin zone, each valley coupling selectively with a circular polarization of light. The degree of valley polarization (DVP) under the excitation of circularly polarized light (CPL) is a parameter that determines the purity of valley polarized photoluminescence (PL) of monolayer WS2. Here, we report efficient tailoring of valley-polarized PL from monolayer WS2 at room temperature (RT) through surface plasmon-exciton interactions with plasmonic Archimedes spiral (PAS) nanostructures. The DVP of WS2 at RT can be enhanced from < 5% to 40% and 50% by using 2 turns (2T) and 4 turns (4T) of PAS, respectively. Further enhancement and control of excitonic valley polarization is demonstrated by electrostatically doping monolayer WS2. For CPL on WS2-2TPAS heterostructures, the 40% valley polarization is enhanced to 70% by modulating the carrier doping via a backgate, which may be attributed to the screening of momentum-dependent long-range electron-hole exchange interactions. The manifestation of electrical tunibility in the valley-polarized emission from WS2-PAS heterostructures presents a new strategy towards harnessing valley excitons for application in ultrathin valleytronic devices.
Congratulate Steve for publishing a new paper on ACS Applied Materials and Interfaces!
Flexible hybrid electronics and fan-out redistribution layers rely on electroplating Cu on polymers. In this work, direct low-temperature plasma-enhanced chemical vapor deposition (PECVD) of graphene on electroplated Cu over polyimide substrates is demonstrated, and the deposition of graphene is found to passivate and strengthen the electroplated Cu circuit. The effect of the H 2 /CH 4 ratio on the PECVD graphene growth is also investigated, which is shown to affect not only the quality of graphene but also
the durability of Cu. 100,000 cycles of folding with a bending radius of 2.5 mm and the corresponding resistance tests are carried out, revealing that Cu circuits covered by graphene grown with a higher H 2 /CH 4 ratio can sustain many more bending cycles. Additionally, graphene coverage is shown to suppress the formation of copper oxides in ambient environment for at least 8 weeks
after the PECVD process.
Congratulations Dr. Deepan Kishore Kumar on your new journey!! We wish you the best in all your future endeavors. We would like to celebrate his success in graduating Caltech in the upcoming days.
Congratulations Dr. Wei-Hsiang Lin on your new journey! We wish you the best in all your future endeavors. We would like to celebrate his success in graduating Caltech in the upcoming days.