Fig. 1: Optical fiber-integrated graphene ultrafast hot-electron emitter.

a Mechanism of hot-electron emission from graphene after pulsed laser excitation. The carrier distribution evolves from discrete energy levels to quasi-equilibrium thermalization, which is driven by strong electron–electron scattering. The thermalized hot electrons with energies above the graphene work function escape into the vacuum for electron emission. b Illustration of the optical fiber-integrated graphene ultrafast hot-electron source. Graphene is capped onto the end face of an optical fiber and grounded via a pre-deposited gold pattern. Under pulsed laser excitation coupled into the optical fiber, graphene exhibits ultrafast photoluminescence (PL) and photoemission. c Excitation power-dependent ultrafast PL spectra (circles) of optical fiber-integrated graphene. The spectra can be fitted with Planck’s law of blackbody radiation (solid lines). d Derived electron temperature (T_e) as a function of excitation power. Error bars are from fitting standard error. e Collected photoemission current as a function of bias voltage (V_b) under different excitation powers. The current sublinearly increases with V_b. f Excitation power-dependent photoemission current at V_b = 10 V. The current nonlinearly increases with increasing excitation power, with a fitting slope of ~4.8. The error bars are from the standard deviation across about 100 points. g Collected photoemission current as a function of hot-electron temperature. h Richardson‒Dushman plot of the data in (g). The linear fitting yields a work function of 4.1 eV, which is very close to that of suspended graphene. All the acquired data are obtained under 1560 nm pulsed laser excitation with a single-mode optical fiber.