Basically, EELS (Electron Energy Loss Spectroscopy) is converted to light using a transmission phosphor, then
converted to electrons using a photomultiplier for serial acquisitions or using a
position-sensitive-detector for parallel acquisition, either a self-scanned
photodiode array (PDA) or a charge-coupled device (CCD) [1 - 2].
In operating process of diode-array detectors, immediately prior to spectrum recording,
all array elements are charged to the same potential (typically 5 V). During
electron exposure, each diode is discharged by an amount which is proportional to
the time-integrated electron flux at the corresponding energy loss. At the end of this
integration period, the diodes are interrogated and the spectrum read out serially as a
chain of pulses, the height (counts) of each pulse representing electron intensity. The signal
is fed into a multichannel analyzer via multichannel scaling (MCS) circuitry.
The diode capacitors lose charge not only through irradiation but also as a result
of their thermal leakage current, which is slightly different for each element of the
array. In order to obtain values which are proportional to spectral intensity,
a leakage or bias spectrum must be subtracted. This bias spectrum is recorded
while electrons are excluded from the array (e.g., TEM screen lowered to block the electron beam) and will
remain the same provided the integration time and array temperature do not vary.
To minimize the noise content of recorded data and allow longer integration times
(without total discharge by thermal leakage), the photodiode array is cooled to −20 °C
by a thermoelectric device.
 O. L. Krivanek, C. C. Ahn & R. B. Keeney, Ultramicroscopy 22, 103 (1987).
 D. McMullan et al., Further development of a parallel EELS CCD detector for
a VG HB501 STEM in EUREM 92 Paris (1992).