On-Nanowire Spatial Band Gap Design for White Light Emission

We demonstrated a substrate-moving vapor–liquid–solid (VLS) route for growing composition gradient ZnCdSSe alloy nanowires. Relying on temperature-selected composition deposition along their lengths, single tricolor ZnCdSSe alloy nanowires with engineerable band gap covering the entire visible range were obtained. The photometric property of these tricolor nanowires, which was determined by blue-, green-, and red-color emission intensities, can be in turn controlled by their corresponding emission lengths. More particularly, under carefully selected growth conditions, on-nanowire white light emission has been achieved. Band-gap-engineered semiconductor alloy nanowires demonstrated here may find applications in broad band light absorption and emission devices

Nonlinear Boost of Optical Angular Momentum Selectivity by Hybrid Nanolaser Circuits

Selective control of light is essential for optical science and technology, with numerous applications. However, optical selectivity in the angular momentum of light has been quite limited, remaining constant by increasing the incident light power on previous passive optical devices. Here, we demonstrate a nonlinear boost of optical selectivity in both the spin and orbital angular momentum of light through near-field selective excitation of single-mode nanolasers. Our designed hybrid nanolaser circuits consist of plasmonic metasurfaces and individually placed perovskite nanowires, enabling subwavelength focusing of angular-momentum-distinctive plasmonic fields and further selective excitation of nanolasers in nanowires. The optically selected nanolaser with a nonlinear increase of light emission greatly enhances the baseline optical selectivity offered by the metasurface from about 0.4 up to near unity. Our demonstrated hybrid nanophotonic platform may find important applications in all-optical logic gates and nanowire networks, ultrafast optical switches, nanophotonic detectors, and on-chip optical and quantum information processing

Nonlinear Boost of Optical Angular Momentum Selectivity by Hybrid Nanolaser Circuits

Selective control of light is essential for optical science and technology, with numerous applications. However, optical selectivity in the angular momentum of light has been quite limited, remaining constant by increasing the incident light power on previous passive optical devices. Here, we demonstrate a nonlinear boost of optical selectivity in both the spin and orbital angular momentum of light through near-field selective excitation of single-mode nanolasers. Our designed hybrid nanolaser circuits consist of plasmonic metasurfaces and individually placed perovskite nanowires, enabling subwavelength focusing of angular-momentum-distinctive plasmonic fields and further selective excitation of nanolasers in nanowires. The optically selected nanolaser with a nonlinear increase of light emission greatly enhances the baseline optical selectivity offered by the metasurface from about 0.4 up to near unity. Our demonstrated hybrid nanophotonic platform may find important applications in all-optical logic gates and nanowire networks, ultrafast optical switches, nanophotonic detectors, and on-chip optical and quantum information processing

Nonlinear Boost of Optical Angular Momentum Selectivity by Hybrid Nanolaser Circuits

Selective control of light is essential for optical science and technology, with numerous applications. However, optical selectivity in the angular momentum of light has been quite limited, remaining constant by increasing the incident light power on previous passive optical devices. Here, we demonstrate a nonlinear boost of optical selectivity in both the spin and orbital angular momentum of light through near-field selective excitation of single-mode nanolasers. Our designed hybrid nanolaser circuits consist of plasmonic metasurfaces and individually placed perovskite nanowires, enabling subwavelength focusing of angular-momentum-distinctive plasmonic fields and further selective excitation of nanolasers in nanowires. The optically selected nanolaser with a nonlinear increase of light emission greatly enhances the baseline optical selectivity offered by the metasurface from about 0.4 up to near unity. Our demonstrated hybrid nanophotonic platform may find important applications in all-optical logic gates and nanowire networks, ultrafast optical switches, nanophotonic detectors, and on-chip optical and quantum information processing

Two-Dimensional MoS₂‑Graphene-Based Multilayer van der Waals Heterostructures: Enhanced Charge Transfer and Optical Absorption, and Electric-Field Tunable Dirac Point and Band Gap

Multilayer van der Waals (vdW) heterostructures assembled by diverse atomically thin layers have demonstrated a wide range of fascinating phenomena and novel applications. Understanding the interlayer coupling and its correlation effect is paramount for designing novel vdW heterostructures with desirable physical properties. Using a detailed theoretical study of two-dimensional (2D) MoS₂-graphene (GR)-based heterostructures based on state-of-the-art hybrid density functional theory, we reveal that for 2D few-layer heterostructures, vdW forces between neighboring layers depend on the number of layers. Compared to that in the bilayer, the interlayer coupling in trilayer vdW heterostructures can significantly be enhanced by stacking the third layer, directly supported by short interlayer separations and more interfacial charge transfer. The trilayer shows strong light absorption over a wide range (<700 nm), making it great potential for solar energy harvesting and conversion. Moreover, the Dirac point of GR and band gaps of each layer and trilayer can be readily tuned by the external electric field, verifying multilayer vdW heterostructures with unique optoelectronic properties found by experiments. These results suggest that tuning the vdW interaction, as a new design parameter, would be an effective strategy for devising particular 2D multilayer vdW heterostructures to meet demands in various applications

Room-Temperature Dual-Wavelength Lasing from Single-Nanoribbon Lateral Heterostructures

Nanoscale dual-wavelength lasers are attractive for their potential applications in highly integrated photonic devices. Here we report the growth of nanoribbon lateral heterostructures made of a CdS_<i>x</i>Se_1–<i>x</i> central region with epitaxial CdS lateral sides using a multistep thermal evaporation route with a moving source. Under laser excitation, the emission of these ribbons indicates sandwich-like structures along the width direction, with characteristic red emission in the center and green emission at both edges. More importantly, dual-wavelength lasing with tunable wavelengths is demonstrated at room temperature based on these single-nanoribbon heterostructures for the first time. These achievements represent a significant advance in designing nanoscale dual-wavelength lasers and have the potential to open up new and exciting opportunities for diverse applications in integrated photonics, optoelectronics, and sensing

Tip-Enhanced Raman Spectroscopy of Monolayer MoS₂ on Au(111)

Employing gap-mode plasmons in a scanning tunneling microscope junction, we studied tip-enhanced Raman spectroscopy (TERS) of MoS2 on Au(111). We observed a mode denoted as “m”, positioned to the right of A1′ by a difference of approximately 6 cm–1. In the MoS2 region that is not in direct contact with the Au(111) substrate, the m peak still exists, indicating that the m mode originates from MoS2. The m mode could originate from non-Γ-point phonon modes in the ZO branch or LA(K) + TA(K). Additionally, our investigation reveals that the TERS intensity reaches its maximum by continuing to approach MoS2 after the tip contacts MoS2. The tip displacement required to reach the maximum TERS intensity depends on the tip conditions. Our results provide guidance for obtaining the optimal TERS intensity for MoS2 and have potential application to other two-dimensional transition metal dichalcogenides

Room-Temperature Valley Polarization in Band Gap Engineered WS_2<i>x</i>Se_{2(1–<i>x</i>)} Monolayers: Implications for Spintronics and Valleytronics

The generation and manipulation of valley-spin polarization are essential for two-dimensional (2D) layered transition-metal dichalcogenides for spin-/valleytronic applications. Here, high crystal quality WS2xSe2(1–x) monolayers with sulfur composition tuning from 0 to 1 were prepared through a controlled chemical vapor deposition method. The crystal structure retains perfect C3-rotation symmetry, with the circular polarization degree of second harmonic generation achieving near unit. Both steady-state and time-resolved circular polarization-resolved photoluminescence (PL) characterizations demonstrate that the valley polarization degree of WS2xSe2(1–x) monolayers can be monotonically improved with gradually increasing sulfur concentration. A phenomenological model and the corresponding rate equations were established to describe the valley polarization dynamics of the bandgap engineered monolayer WS2xSe2(1–x), and a real band-edge intervalley scattering lifetime can be determined by fitting the circularly polarized PL decay curves using this model. The physical origin of the phenomenon of increasing degree of valley polarization with the decreasing of the hot electron energy has been revealed due to the continuous tuning of the initially injected polarization with varying the composition ratio. Our work gives insights into the underlying valley depolarization mechanism in 2D alloyed monolayers and provides a potential pathway for controllable synthesis of high-quality atomically thin alloys with tunable valley physics, which contribute to spintronic and valleytronic applications