Experimental

Experimental data were acquired at the electron storage ring BESSY (Berlin), where device cooled down to -120^o C was illuminated with monochromatized synchrotron X-rays. The data were taken at the KMC (Krystal MonoChromator) beamline in a wide range of energies from 1487 eV to 5898  eV with the emphasis on the understanding of the device behavior around silicon absorption K edge (1836 eV). That explains the choice of the energy data points for this measurement having higher density around silicon K edge: 1487, 1700, 1740, 1800, 1825, 1832, 1835, 1836.5, 1838, 1840, 1842, 1845, 1847, 1855, 1870, 1900, 2015, 2309, 2622, 3313, 3691, 4090, 4510, 4952, 5414, and 5898  eV. A typical exposure time at each energy was 4000 seconds, with 5 times that amount for the 2015 eV measurement.

Device was clocked by the ACIS electronics with serial register clock frequency of 100 kHz, total system noise at this frequency being about 2 electrons rms. Very low system noise was the crucial factor that allowed us to observe the low energy features discussed below.