Precision Modification of Monolayer Transition Metal Dichalcogenides via Environmental E-Beam Patterning

Abstract

Layered Transition Metal Dichalcogenides (TMDs) are an important class of materials that exhibit a wide variety of optoelectronic properties. The ability to spatially tailor their expansive property-space (e.g., conduction behavior, optical emission, surface interactions) is of special interest for applications including, but not limited to, sensing, bioelectronics, and spintronics/valleytronics. Current methods of property modulation focus on the modification of the basal surfaces and edge sites of the TMDs by the introduction of defects, functionalization with organic or inorganic moieties, alloying, heterostructure formation, and phase engineering. A majority of these methods lack the resolution for the development of next-generation nanoscale devices or are limited in the types of functionalities useful for efficient TMD property modification. In this study, we utilize electron-beam patterning on monolayer TMDs (MoSe2, WSe2 and MoS2) in the presence of a pressure-controlled atmosphere of water vapor within an environmental scanning electron microscope (ESEM). A series of parametric studies show local optical and electronic property modification depending on acceleration voltage, beam current, pressure, and electron dose. The ultimate pattern resolution achieved is 67 ± 9 nm. Raman and photoluminescence spectroscopies coupled with Kelvin Probe Force Microscopy reveal electron dose-dependent p-doping in the patterned regions, which we attribute to functionalization from the products of water vapor radiolysis (oxygen and hydroxyl groups). The modulation of the work function through patterning matches well with Density Functional Theory modeling. Finally, post-functionalization of the patterned areas with an organic fluorophore demonstrates a robust method to achieve nanoscale functionalization with high fidelity.

Valley-Selective Polarization in Twisted Bilayer Graphene Controlled by a Counter-Rotating Bicircular Laser Field

“…nm (k, t) via Equation ( 5), followed by multiplying the off-diagonal element ρ (H) nm (k, t) by exp(− ∆t T 2 ), and finally transformed back to ρ (W) nm (k, t) via Equation (6). The above procedure is repeated until the end of the dynamics evolution.…”

“…Furthermore, recent research has established that electrons in two-dimensional hexagonal materials possess an additional degree of freedom, known as the valley pseudospin, which corresponds to extreme points on the electron band dispersion curve. Such electrons are commonly found in materials such as graphene [4], layered transition metal dichalcogenides [5,6], and Weyl semimetal systems [7][8][9]. For instance, the energy band structure of graphene features two unequal yet degenerate Dirac points on the Fermi surface of the first Brillouin zone (BZ), referred to as the K 1 and K 2 valleys.…”

In situ doping effect in monolayer MoS2 via laser irradiation

“…Bound quasiparticles (excitons and trions) are generally susceptible to factors like intrinsic dopants [31][32][33][34], molecules on the surface of monolayer MoS 2 [34][35][36][37][38], and carrier trapping at the interface between monolayer MoS 2 and the substrate [39]. The high sensitivity to the surrounding environment has led to the discovery of novel properties [31,[40][41][42]. Previous studies have demonstrated the enhancement or quenching of the PL intensity through defect engineering, adsorption of foreign molecules, thermal annealing, and structural disorder [32,43].…”