Imaging the breaking of electrostatic dams in graphene for ballistic and viscous fluids

Observation of different Li intercalation states and local doping in epitaxial mono- and bilayer graphene on SiC(0001)

Li intercalation is commonly used to enhance the carrier density in epitaxial graphene and mitigate coupling to the substrate. So far, the understanding of the intercalation process, particularly how Li penetrates different layers above the substrate, and its impact on electron transport remains incomplete. Here, we report different phases of Li intercalation and their kinetic processes in epitaxial mono- and bilayer graphene grown on SiC. The distinct doping effects of each intercalation phase are characterized using scanning tunneling spectroscopy. Furthermore, changes in the local conduction regimes are directly mapped by scanning tunneling potentiometry and attributed to different charge transfer states of the intercalated Li. The stable intercalation marked by the formation of Li-Si bonds leads to a significant 56% reduction in sheet resistance of the resulting quasi-free bilayer graphene, as compared to the pristine monolayer graphene.

Feedback enhanced Dyakonov-Shur instability in graphene field-effect transistors

Graphene devices are known to have the potential to operate THz signals. In particular, graphene field-effect transistors (gFETs) have been proposed as devices to host plasmonic instabilities in the THz realm; for instance, Dyakonov-Shur (DS) instability which relies upon dc excitation. In this work, starting from a hydrodynamical description of the charge carriers, we extend the transmission line description of gFETs to a scheme with a positive feedback loop, also considering the effects of delay, which leads to the transcendental Laplace-transform transfer function, with complex frequencys, with terms of the forme-assechk(s)/s, for a givena∈R0+arising from the delay time and withk∈N. Applying the conditions for the excitation of DS instability, we report an enhanced voltage gain in the linear regime that is corroborated by our simulations of the nonlinear hydrodynamic model for the charge carriers. This translates to both greater saturation amplitude-often up to 50% increase-and faster growth rate of the self-oscillations. Thus, we bring forth a prospective concept for the realization of a THz oscillator suitable for future plasmonic circuitry.

Enhanced Electrostatic Safety and Thermal Compatibility of Special Powders Based on Surface Modification

Electrostatic accumulation is associated with almost all powder-conveying processes which could bring about electrostatic discharges. In most cases of industrial accidents, electrostatic discharge is proven to be the primary source of ignition and explosion. Herein, a surface modification process of polyaniline (PANI) is proposed to construct highly exothermic special powders, namely, HMX@PANI energetic composites, with low charge accumulation for improving powder electrostatic safety. Pure HMX are encapsulated within the PANI-conductive polymer layer through simple hydrogen bonding. Simulation results demonstrate that the forming process of HMX/aniline structure is a spontaneously thermodynamical process. The resultant inclusion complex exhibits excellent thermal stability, remarkable compatibility and intensive heat release. Importantly, PANI possesses superior electrostatic mobility characteristics because of the π-conjugated ligand, which can significantly reduce the accumulated charges on the surface of energetic powders. Moreover, the modified explosive has a narrower energy gap, which will improve the electron transition by reducing the energy barrier. The electrostatic accumulation test demonstrates that HMX@PANI composites possess a trace electrostatic accumulation of 34 nC/kg, which is two orders of magnitude lower than that of pure HMX (-6600 nC/kg) and might indicate a higher electrostatic safety. In conclusion, this surface modification process shows great promise for potential applications and could be extensively used in the establishment of high electrostatic safety for special powders.