Fig. 1: Inelastic electron tunneling spectroscopy probing electron–phonon scatterings in SC-TMD films.
a Schematic viewgraphs of lattice vibration modes that are either weakly (upper) or strongly (lower) coupled to electrons in 2H-SC-TMD layers. b, c Schematic illustrations of electron–phonon scatterings initiated at either the K (b) or Q (c) valley in the momentum space of a 2D hexagonal lattice. d Schematic of the energy-band alignment and quantum tunneling events in a vertical graphite–SC-TMD–graphite planar tunnel junction. Injected electrons within an energy window of eVb either elastically tunnel (red arrows) through the barriers or interact with SC-TMD phonons without (blue arrows) or with (green arrows) a momentum transfer before exiting to a drain electrode. e, f Simplified viewgraphs of the evolutions of differential conductance (G = dI/dVb, e) and a second derivative of tunnel current (dG/dVb = d2I/dVb2, f) as a function of sample-bias voltage (Vb). Experimental signatures of the single- and two-phonon electron–phonon couplings are represented as a dI/dVb increase (e) and a dG/dVb peak or dip (f) at individual phonon energies ħω1 and ħω2 and combined phonon-mode energy ħω3 = ħω1 + ħω2. g–i Inelastic electron tunnel spectra from a mono- (solid blue lines) and bilayer (dotted red line) WSe2 planar tunnel junction at T = 5.7 K. Tunnel electron characteristics are represented in I – Vb (g), dI/dVb – Vb (h), and dG/dVb – Vb (i) curves, respectively. (inset, g) Schematic of our graphite–SC-TMD–graphite vertical planar junction and two-probe electric measurement setup.
