ABSTRACT
The optoelectronic signatures of free-standing few-atomic-layer black phosphorus nanoflakes are analyzed by in situ transmission electron microscopy (TEM). As compared to other 2D materials, the band gap of black phosphorus (BP) is related directly to multiple thicknesses and can be tuned by nanoflake thickness and strain. The photocurrent measurements with the TEM show a stable response to infrared light illumination and change of nanoflakes band gap with deformation while pressing them between two electrodes assembled in the microscope. The photocurrent spectra of an 8- and a 6-layer BP nanoflake samples are comparatively measured. Density functional theory (DFT) calculations are performed to identify the band structure changes of BP during deformations. The results should help to find the best pathways for BP smart band gap engineering via tuning the number of material atomic layers and programmed deformations to promote future optoelectronic applications.
ABSTRACT
Free-standing few-layered MoSe2 nanosheet stacks optoelectronic signatures are analyzed by using light compatible in situ transmission electron microscopy (TEM) utilizing an optical TEM holder allowing for the simultaneous mechanical deformation, electrical probing and light illumination of a sample. Two types of deformation, namely, (i) bending of nanosheets perpendicular to their basal atomic planes and (ii) edge deformation parallel to the basal atomic planes, lead to two distinctly different optomechanical performances of the nanosheet stacks. The former deformation induces a stable but rather marginal increase in photocurrent, whereas the latter mode is prone to unstable nonsystematic photocurrent value changes and a red-shifted photocurrent spectrum. The experimental results are verified by ab initio calculations using density functional theory (DFT).
