192 CHEMICAL SENSORS: TECHNOLOGIES. VOLUME 4: SOLID-STATE DEVICES (eV) -0,3 -0,6 2 -0,3 -0,6 0,0 0,5 1,0 1,5 H 2 (%) 2,0 0 3 6 Zeit (h) 9 0 Figure 4.5. Work function change of a rhodium-doped (1400 ppm) platinum layer upon exposure to various hydrogen concentrations. Measurements by a vibrating Kelvin probe at room temperature. of dissociative adsorption. Therefore, the work function change is a function of the target gas con- centration c, i.e., determining means knowing c. To detect a certain gas species, a compatible sensitive layer is needed. A detailed example is pre- sented in Figure 4.5: If a rhodium-doped (1400 ppm) platinum film is exposed to various hydrogen concentrations in synthetic air, the work function of the surface is strongly decreased (left). With re- spect to Eq. (4.3), (right) shows nonlinear behavior with increasing hydrogen concentration. When H 2 (%) (eV) 0,0 Pure Platinum T = 25 °C 0,0