RESUMEN
Electrostatic gating lies in the heart of field effect transistor (FET) devices and modern integrated circuits. To achieve efficient gate tunability, the gate electrode has to be placed very close to the conduction channel, typically a few nanometers. Remote control of a FET device through a gate electrode located far away is highly desirable, because it not only reduces the complexity of device fabrication, but also enables the design of novel devices with new functionalities. Here, a non-local electrostatic gating effect in graphene devices using scanning near-field optical microscopy (SNOM)-a technique that can probe local charge density in graphene-is reported. Remarkably, the charge density of the graphene region tens of micrometers away from a local gate can be efficiently tuned. The observed non-local gating effect is initially driven by an in-plane electric field induced by the quantum capacitance of graphene, and further largely enhanced by adsorbed polarized water molecules. This study reveals a non-local phenomenon of Dirac electrons, provides a deep understanding of in-plane screening from Dirac electrons, and paves the way for designing novel electronic devices with remote gate control.
RESUMEN
Polaritons in two-dimensional (2D) materials have shown their unique capabilities to concentrate light into deep subwavelength scales. Precise control of the excitation and propagation of 2D polaritons has remained a central challenge for future on-chip nanophotonic devices and circuits. To solve this issue, we exploit Cherenkov radiation, a classic physical phenomenon that occurs when a charged particle moves at a velocity greater than the phase velocity of light in that medium, in low-dimensional material heterostructures. Here, we report an experimental observation of Cherenkov phonon polariton wakes emitted by superluminal one-dimensional plasmon polaritons in a silver nanowire and hexagonal boron nitride heterostructure using near-field infrared nanoscopy. The observed Cherenkov radiation direction and radiation rate exhibit large tunability through varying the excitation frequency. Such tunable Cherenkov phonon polaritons provide opportunities for novel deep subwavelength-scale manipulation of light and nanoscale control of energy flow in low-dimensional material heterostructures.
RESUMEN
Much of the richness and variety of physics today are based on coupling phenomena where multiple interacting systems hybridize into new ones with completely distinct attributes. Recent development in building van der Waals (vdWs) heterostructures from different 2D materials provides exciting possibilities in realizing novel coupling phenomena in a designable manner. Here, with a graphene/hBN/graphene heterostructure, we report near-field infrared nano-imaging of plasmon-plasmon coupling in two vertically separated graphene layers. Emergent symmetric and anti-symmetric coupling modes are directly observed simultaneously. Coupling and decoupling processes are systematically investigated with experiment, simulation and theory. The reported interlayer plasmon-plasmon coupling could serve as an extra degree of freedom to control light propagation at the deep sub-wavelength scale with low loss and provide exciting opportunities for optical chip integration.
RESUMEN
MicroRNAs (miRNAs) delivered by gastric cancer (GC)-secreted extracellular vesicles (GC-EVs) are associated with the immune escape in GC. Microarray analysis based on the GEO: GSE112369 dataset identified the presence of poorly expressed CXXC finger protein 4 (CXXC4) in GC, which was validated in clinical samples of GC patients. Moreover, prediction based on TargetScan analysis demonstrated the putative miR-675-3p binding site in the 3' UTR region of CXXC4. Thereby, our study aims to determine the role of GC-EV-encapsulated miR-675-3p in GC. First, CXXC4 was found to be negatively correlated with programmed cell death 1 ligand 1 (PD-L1). The effects of mitogen-activated protein kinase (MAPK) signaling on GC were evaluated using activator of the MAPK pathway. The overexpression of CXXC4 led to a downregulated MAPK signaling pathway, thus decreasing PD-L1 expression to augment the proliferation and activation of T cells co-cultured with GC HGC-27 cells. GC-EV-encapsulated miR-675-3p negatively regulated the expression of its target gene CXXC4. GC-EV-encapsulated miR-675-3p increased PD-L1 expression to stimulate the immune escape in vitro and EV-encapsulated miR-675-3p accelerated cisplatin resistance in vivo. Collectively, the aforementioned findings present a mechanism in which EV-mediated miR-675-3p upregulates PD-L1 expression, promoting immune escape in GC.