Figure 6
Energy diagrams of the solid phase (sample)/gas phase/analyzer system, when the sample and analyzer are grounded (a) and when the sample is biased positively with respect to the analyzer (Vbias = + 30 V). d (~1 mm) is the distance between the sample and the analyzer nozzle. VL and FL designate the vacuum and Fermi level respectively. Φs and Φa are the sample and analyzer work functions, respectively. 1s(gas) is the core-level of a gas phase molecule, of ionization energy IPVL (with respect to VL). KEFL is the kinetic energy of the 1s(gas) photoelectron measured with respect to the analyzer FL. qVcpd is the contact potential between the sample and the analyzer (equal to Φs-Φa, a few eV), and qVbias the applied electrostatic potential energy (−30 eV). While the gas phase spectrum is measured in a potential gradient qVcpd/d of a few eV per mm when the sample is grounded, it is measured in a potential gradient of (qVbias− qVcpd)/d (~qVbias/d), i.e. ~30 eV per mm when the sample is biased. This leads to the spreading of the gas phase 1s core level (1s(gas)) KEFL in the beam-probed region (yellow-shaded) of width ~0.1 mm.
