3 research outputs found
Infrared Nanoimaging Reveals the Surface Metallic Plasmons in Topological Insulator
Surface plasmons
make a high degree of localization of electromagnetic
fields achievable at the vicinity of metal surfaces. Topological insulators
(TIs) are a family of materials which are insulating in the bulk but
have metallic surfaces caused by the strong spin–orbit coupling.
Surface plasmons supported by the surface state on topological insulators
have attracted incredible interests from ultraviolet to mid-infrared
frequencies. In this work, we experimentally investigate the near-field
properties of Bi<sub>2</sub>Te<sub>3</sub> nanosheets using scattering-type
scanning near-field optical microscopy (s-SNOM). The s-SNOM tip enables
to detect significantly enhanced intensity in its near field at precisely
controlled positions with regards to Bi<sub>2</sub>Te<sub>3</sub> structure.
With the help of highly position-selective excitation and high-pixel
real-space mapping, we discover near-field patterns of bright outside
fringes which are associated with its surface-metallic, plasmonic
behavior at mid-infrared frequency. Thereby, we experimentally demonstrate
that the scattered signal responses and near-field amplitudes of outside
fringes can be tailored via mechanical (sheet thickness of Bi<sub>2</sub>Te<sub>3</sub>), electric (electrostatic gating), and optical
(incident wavelength) fashions. The discovery of outside fringes in
TI nanosheets may enable the development of strongly enhanced light–matter
interactions for quantum optical devices, mid-infrared (MIR) and terahertz
detectors or sensors
Highly Efficient and Air-Stable Infrared Photodetector Based on 2D Layered Graphene–Black Phosphorus Heterostructure
The
presence of a direct band gap and high carrier mobility in few-layer
black phosphorus (BP) offers opportunities for using this material
for infrared (IR) light detection. However, the poor air stability
of BP and its large contact resistance with metals pose significant
challenges to the fabrication of highly efficient IR photodetectors
with long lifetimes. In this work, we demonstrate a graphene–BP
heterostructure photodetector with ultrahigh responsivity and long-term
stability at IR wavelengths. In our device architecture, the top layer
of graphene functions not only as an encapsulation layer but also
as a highly efficient transport layer. Under illumination, photoexcited
electron–hole pairs generated in BP are separated and injected
into graphene, significantly reducing the Schottky barrier between
BP and the metal electrodes and leading to efficient photocurrent
extraction. The graphene–BP heterostructure phototransistor
exhibits a long-term photoresponse at near-infrared wavelength (1550
nm) with an ultrahigh photoresponsivity (up to 3.3 × 10<sup>3</sup> A W<sup>–1</sup>), a photoconductive gain (up to 1.13 ×
10<sup>9</sup>), and a rise time of about 4 ms. Considering the thickness-dependent
band gap in BP, this material represents a powerful photodetection
platform that is able to sustain high performance in the IR wavelength
regime with potential applications in remote sensing, biological imaging,
and environmental monitoring
Ultrathin 2D Transition Metal Carbides for Ultrafast Pulsed Fiber Lasers
Two-dimensional
(2D) materials, such as graphene, transition metal
dichalcogenides, and black phosphorus, have attracted intense interest
for applications in ultrafast pulsed laser generation, owing to their
strong light–matter interactions and large optical nonlinearities.
However, due to the mismatch of the bandgap, many of these 2D materials
are not suitable for applications at near-infrared (NIR) waveband.
Here, we report nonlinear optical properties of 2D α-Mo<sub>2</sub>C crystals and the usage of 2D α-Mo<sub>2</sub>C as
a new broadband saturable absorber for pulsed laser generation. It
was found that 2D α-Mo<sub>2</sub>C crystals have excellent
saturable absorption properties in terms of largely tunable modulation
depth and very low saturation intensity. In addition, ultrafast carrier
dynamic results of 2D α-Mo<sub>2</sub>C reveal an ultrashort
intraband carrier recovery time of 0.48 ps at 1.55 ÎĽm. By incorporating
2D α-Mo<sub>2</sub>C saturable absorber into either an Er-doped
or Yb-doped fiber laser, we are able to generate ultrashort pulses
with very stable operation at central wavelengths of 1602.6 and 1061.8
nm, respectively. Our experimental results demonstrate that 2D α-Mo<sub>2</sub>C can be a promising broadband nonlinear optical media for
ultrafast optical applications