(42h) Redox-Directed Self-Assembly of 2D Semiconductor Nanoantenna Heterostructures with Enhanced Optoelectronic Damping and Nonlinear Activity

Redox-directed self-assembly of 2D semiconductor
nanoantenna heterostructures with enhanced damping and nonlinear activity

D. Keith Roper^a,b*_, Greg T. Forcherio^c, Jeremy R. Dunklin^d,
Mourad Benamara^e, Luigi Bonacina^f

^a
Microelectronics
and Photonics Graduate Program, University of Arkansas, Fayetteville, AR
72701        

^b Department of Chemical
Engineering, University of Arkansas, Fayetteville, AR 72701

^cArmy Research Laboratory, Adelphi, MD 20783

^dNational Renewable Energy
Laboratory, Golden, CO 80401

^eInstitute for Nanoscience and
Engineering, University of Arkansas, Fayetteville, AR 72701

^f GAP-Biophotonics, Université de Genève, Genève, CH
1211

      Two-dimensional (2D) semiconductor heterostructures offer compelling
new functionalities, e.g., gate tunability of p-n junction, valleytronics and
anti-ambipolarity as well as unique optical, electronic and transport
properties attributable to distinct atom-scale heterointerfaces. These features
could enable atomically-thin flexible integrated circuits, field effect
transistors and closed-loop resonators. However, directed self-assembly of 2D
semiconductor nanoantenna heterostructures is limited by lack of computational descriptions of fundamental optoelectronic
properties integrated with novel self-assembly processes and microscopic and
spectroscopic analysis to confirm enhanced functionality.

    
This work examined a new redox approach
to direct self-assembly of nanoantenna (NA) at active heterointerfaces of
monolayer (1L) transition metal dichalcogenides (TMD) to modulate electron
transfer and nonlinear activity. Discrete
dipole approximation (DDA) was used to analyze local electromagnetic near
fields and transmission ultraviolet-visible (TUV-vis) extinction spectra (Fig
3) of NA and 1LTMD to identify optimal heterostructure architecture. The electrochemistry
of solution-based metal electroless plating was adapted to self-assemble heterostructures
of 1LTMD and NA by reducing metal salt directly onto exposed edges of solution
exfoliated TMD (Fig 2). Nanometer- and femtosecond-resolved electron energy
loss spectroscopy (EELS) was used to simulate and measure low-energy NA plasmon
modes, damping and electric near fields at the heterointerfaces (Fig 3).

    
DDA (Fig 1) of local electromagnetic fields and field extinction spectra of
1LTMD-NA heterostructures predicted higher optoelectronic activity and
tunability for NA assembled at 1LTMD edges.  Transmission electron microscopy
(TEM; Fig 2) and x-ray photoelectron spectroscopy (XPS) confirmed atomic
structure and chemical bonding, respectively, of NA reduced directly onto 1LTMD
flake edges for the first time.  EELS (Fig 3) showed enhanced plasmon damping resulted
from metal-chalcogenide covalent bonds at the 1LTMD-NA heterointerface.  Comparing
plasmon damping with computed inelastic population decay due to radiative and
intraband mechanisms indicated local electron injection through a Landau
mechanism. Quantum efficiency of injection was up to eleven percent. Mid-bandgap
edge states increased likelihood of nonlinear activity in exfoliated 1LTMD. A tunable femtosecond laser system for Hyper Rayleigh
Scattering (HRS) was used to measure second order nonlinear coefficient of
1LTMD and NA-1LTMD heterostructure. Nonlinear
susceptibilities for 1LTMD exceeding those of conventional materials by >10²
pm/V with concomitant increases in second harmonic generation (SHG) intensity
and two-photon absorption probability were characterized [3]. 

    
Overall, DDA, TEM, XPS, EELS and HRS were coordinated to guide and characterize
a novel method for redox-directed self-assembly of 1LTMD-NA heterostructures.
Results confirmed features of the new heterostructure architectures including
enhanced optoelectronic activity.  Coordinated use of these tools offers a new
integrated approach to tune damping, electric near-field and intrinsic
nonlinear activity at nanoscale heterointerfaces.

 [1] J.R.
Dunklin, D.K. Roper et al., in preparation. [2] G. T. Forcherio, J.R.
Dunklin, D.K. Roper et al., in submission.  [3] G. T. Forcherio, D.K. Roper et
al., in preparation.