Tag Archives: Low-dimensional Materials

Electrically Tunable and Dramatically Enhanced Valley-Polarized Emission of Monolayer WS2 at Room Temperature with Plasmonic Archimedes Spiral Nanostructures

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.


Polymer-Compatible Low-Temperature Plasma-Enhanced Chemical Vapor Deposition of Graphene on Electroplated Cu for Flexible Hybrid Electronics

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.