Proposal for dark exciton based chemical sensors

Abstract

The rapidly increasing use of sensors throughout different research disciplines and the demand for more efficient devices with less power consumption depends critically on the emergence of new sensor materials and novel sensor concepts. Atomically thin transition metal dichalcogenides have a huge potential for sensor development within a wide range of applications. Their optimal surface-to-volume ratio combined with strong light–matter interaction results in a high sensitivity to changes in their surroundings. Here, we present a highly efficient sensing mechanism to detect molecules based on dark excitons in these materials. We show that the presence of molecules with a dipole moment transforms dark states into bright excitons, resulting in an additional pronounced peak in easy accessible optical spectra. This effect exhibits a huge potential for sensor applications, since it offers an unambiguous optical fingerprint for the detection of molecules—in contrast to common sensing schemes relying on small peak shifts and intensity changes.

Dark excitations in monolayer transition metal dichalcogenides

“…Recent theoretical studies have addressed dark excitons [20,22] using first-principles calculations, however, theory for dark and bright trions has so far exclusively been based on models [23][24][25]. We note that Feierabend et al [26] proposed further dark excitons with nonzero momenta. Here, we focus on excitation around ±K.…”

Impact of strain on the optical fingerprint of monolayer transition-metal dichalcogenides

“…Now, we include excitonic effects and investigate how they change in presence of bi-and uniaxial strain. Excitons are integrated by solving the Wannier equation, providing access to eigenvalues and eigenfunctions for all available excitonic states [2,[20][21][22][23]. Furthermore, we derive the TMD Bloch equation for the microscopic polarization p…”

Optical Response From Functionalized Atomically Thin Nanomaterials

“…Here, we have applied a separation ansatz decoupling the relative from the center-ofmass motion with the corresponding center-of-mass momentum Q and relative momentum q with Q = k 2 − k 1 and q = [18,59,60] and the electron (hole) occupations f e(h) q .In the next step, we solve the hybrid Bloch equations for the excitonic microscopic polarization p μ Q with the index μ = (K , ) denoting the K K and K exciton: [23] …”

“…The dark K exciton is only driven in the presence of molecules, which couple to the TMD excitons via the induced dipole field. The corresponding exciton-molecule coupling element reads in excitonic basis [23] …”

“…As a result, the optical response can be exploited for engineering novel chemical sensors molecular switches, and nanoscale photodetectors. [5,9,16,[23][24][25] Promising candidates for the functionalization of nanomaterials are photoactive molecules. The most prominent representative of this class of molecules are spiropyrans, which can be reversibly switched between the open planar merocyanine (MC) and the closed orthogonal spiropyran (SP) conformation.…”