Analytical study of thermally assisted photoelectron emission from real iron surfaces: dependence on temperature and wavelength

Abstract

In our previous papers, two types of dependence of photoelectron emission from real iron surfaces on the temperature and on the wavelength of the irradiating light at normal atmospheric pressure have been reported (Momose et al. in Appl Phys A 117:1525, 2014; 118:637, 2015). The first article reported experimental curves of the intensity versus temperatures in the 298–626 K range under light irradiation with wavelengths of 200, 210, 220, and 230 nm, called as thermally assisted photoelectron emission (TAPE) (Momose et al. 2014), whereas the second article reported experimental curves of the TAPE intensity versus wavelength for irradiating light in the 300–170 nm range at 298, 381, 425, 476, 527, 576, or 626 K (Momose et al. 2015). In the present paper, these two results were simultaneously discussed based on the Fowler–DuBridge (FD) theory, where the intensity of photoelectron emission is described by the two parameters of the work function, ϕ, and a probability factor, αA. It was concluded from the dependence on wavelength (Momose et al. 2015) of the TAPE intensity that the ϕ value and the αA value were represented by a saturation function and a linear function, respectively, with respect to temperature. However, the FD theory using the temperature dependence of ϕ and αA could not yield that of the TAPE intensity (Momose et al. 2014). To resolve the discrepancy between the two kinds of the TAPE measurements, a curve-fitting method is constructed based on the following three assumptions: two types of the photoelectrons are present, namely hot electrons and thermalized electrons; the former are involved in a thermal desorption process of adsorbates and the latter need a thermal activation energy to escape to vacuum; and thermally stimulated exoelectrons are included in the TAPE phenomenon. The results of applying the method to the TAPE glow curves (Momose et al. 2014) concluded that the release of hot electrons into vacuum was suppressed by the adsorbed H2O on the real iron surface and the desorption energy of the adsorbed H2O was 0.43 eV for 200 nm and 0.48 eV for 210 nm light irradiation. It was further confirmed that the activation energy which the thermalized electrons need to escape to vacuum was 0.20 and 0.13 eV for 200 and 210 nm, respectively. The relationship between this activation energy and the wavelength of the irradiated light is consistent with the results of Momose et al. (2014).