A Kinetic Pathway toward High-Density Ordered N Doping of Epitaxial Graphene on Cu(111) Using C₅NCl₅ Precursors

Pristine graphene possesses high electrical mobility, but its low charge carrier density severely limits its technological significance. Past efforts to increase graphene’s carrier density via chemical doping have shown limited successes, accompanied by substantial reductions in the mobility caused by disordered dopants. Here, based on first-principles calculations, we propose to grow graphene on Cu(111) via self-assembly of C₅NCl₅ molecular precursors to achieve high-density (1/6) and highly ordered nitrogen doping. Such a process relies on the elegant concerted roles played by the London dispersion, chemical, and screened Coulomb repulsive forces in enhancing molecular adsorption, facilitating easy dechlorination, and dictating the overall orientation of the C₅N radicals, respectively. Further growth from the orientationally correlated graphene islands is accompanied by significantly minimized density of grain boundaries as the grains coalesce to form larger N-doped graphene sheets, which are further shown to possess superb electronic properties for future device applications. Initial kinetic processes involved in N-doped graphene growth using C₅NH₅ precursors are also investigated and contrasted with that of C₅NCl₅

Symmetry-Dependent Plasmonic Properties of Three-Dimensional Hybrid Metallic Nanostructure Arrays

We demonstrate the successful fabrication of various well-ordered 3D gold nanostructure arrays using nanosphere lithography method, and further reveal the strong dependence of the optical responses on their in-plane symmetry. For the concentrically stacked ring-cap array, its optical absorption behavior is similar to that of a ring array with the same dimension because they have the same in-plane symmetry. However, for the nonconcentrically stacked hole-cap array, the broken in-plane symmetry results in the appearance of crescent-shaped nanogaps at the interfaces and thus leads to a novel strong plasmon resonance mode. The finite-difference time-domain simulation shows that charge mainly assembles to the sharp edges of the nanogaps at the resonant wavelength and remarkable electric field enhancement is achieved around the sharp edges. Furthermore, the strongest resonance modes of the ring-cap array and hole-cap array show large red shift as the nanostructure size increases. The presented 3D nanostructure arrays may offer a spectrum of applications in sensing

Graphene Thickness Control via Gas-Phase Dynamics in Chemical Vapor Deposition

Graphene has attracted intense research interest due to its exotic properties and potential applications. Chemical vapor deposition (CVD) on Cu foils has shown great promises for macroscopic growth of high-quality graphene. By delicate design and control of the CVD conditions, here we demonstrate that a nonequilibrium steady state can be achieved in the gas phase along the CVD tube, that is, the active species from methane cracking increase in quantity, which results in a thickness increase continually for graphene grown independently at different positions downstream. In contrast, uniform monolayer graphene is achieved everywhere if Cu foils are distributed simultaneously with equal distance in the tube, which is attributed to the tremendous density shrink of the active species in the gas phase due to the sink effect of the Cu substrates. Our results suggest that the gas-phase reactions and dynamics are critical for the CVD growth of graphene and further demonstrate that the graphene thickness from the CVD growth can be fine-tuned by controlling the gas-phase dynamics. A similar strategy is expected to be feasible to control the growth of other nanostructures from gas phases as well

Quantum Percolation and Magnetic Nanodroplet States in Electronically Phase-Separated Manganite Nanowires

One-dimensional (1D) confinement has been revealed to effectively tune the properties of materials in homogeneous states. The 1D physics can be further enriched by electronic inhomogeneity, which unfortunately remains largely unknown. Here we demonstrate the ultrahigh sensitivity to magnetic fluctuations and the tunability of phase stability in the electronic transport properties of self-assembled electronically phase-separated manganite nanowires with extreme aspect ratio. The onset of magnetic nanodroplet state, a precursor to the ferromagnetic metallic state, is unambiguously revealed, which is attributed to the small lateral size of the nanowires that is comparable to the droplet size. Moreover, the quasi-1D anisotropy stabilizes thin insulating domains to form intrinsic tunneling junctions in the low temperature range, which is robust even under magnetic field up to 14 T and thus essentially modifies the classic 1D percolation picture to stabilize a novel quantum percolation state. A new phase diagram is therefore established for the manganite system under quasi-1D confinement for the first time. Our findings offer new insight into understanding and manipulating the colorful properties of the electronically phase-separated systems via dimensionality engineering

Quantum Control of Graphene Plasmon Excitation and Propagation at Heaviside Potential Steps

Quantum mechanical effects of single particles can affect the collective plasmon behaviors substantially. In this work, the quantum control of plasmon excitation and propagation in graphene is demonstrated by adopting the variable quantum transmission of carriers at Heaviside potential steps as a tuning knob. First, the plasmon reflection is revealed to be tunable within a broad range by varying the ratio γ between the carrier energy and potential height, which originates from the quantum mechanical effect of carrier propagation at potential steps. Moreover, the plasmon excitation by free-space photos can be regulated from fully suppressed to fully launched in graphene potential wells also through adjusting γ, which defines the degrees of the carrier confinement in the potential wells. These discovered quantum plasmon effects offer a unified quantum-mechanical solution toward ultimate control of both plasmon launching and propagating, which are indispensable processes in building plasmon circuitry

Optical Manipulation of Rashba Spin–Orbit Coupling at SrTiO₃‑Based Oxide Interfaces

Spin–orbit coupling (SOC) plays a crucial role for spintronics applications. Here we present the first demonstration that the Rashba SOC at the SrTiO₃-based interfaces is highly tunable by photoinduced charge doping, that is, optical gating. Such optical manipulation is nonvolatile after the removal of the illumination in contrast to conventional electrostatic gating and also erasable via a warming–cooling cycle. Moreover, the SOC evolutions tuned by illuminations with different wavelengths at various gate voltages coincide with each other in different doping regions and collectively form an upward-downward trend curve: In response to the increase of conductivity, the SOC strength first increases and then decreases, which can be attributed to the orbital hybridization of Ti 3<i>d</i> subbands. More strikingly, the optical manipulation is effective enough to tune the interferences of Bloch wave functions from constructive to destructive and therefore to realize a transition from weak localization to weak antilocalization. The present findings pave a way toward the exploration of photoinduced nontrivial quantum states and the design of optically controlled spintronic devices

Interlayer Transition and Infrared Photodetection in Atomically Thin Type-II MoTe₂/MoS₂ van der Waals Heterostructures

We demonstrate the type-II staggered band alignment in MoTe₂/MoS₂ van der Waals (vdW) heterostructures and an interlayer optical transition at ∼1.55 μm. The photoinduced charge separation between the MoTe₂/MoS₂ vdW heterostructure is verified by Kelvin probe force microscopy (KPFM) under illumination, density function theory (DFT) simulations and photoluminescence (PL) spectroscopy. Photoelectrical measurements of MoTe₂/MoS₂ vdW heterostructures show a distinct photocurrent response in the infrared regime (1550 nm). The creation of type-II vdW heterostructures with strong interlayer coupling could improve our fundamental understanding of the essential physics behind vdW heterostructures and help the design of next-generation infrared optoelectronics