Electron microscopy - part 4

SEM Operation

Detectors

SEM Detectors:

Everhart-Thornley detector

• The Everhart-Thornley Detector is SE and BSE detector used in SEMs.

• The detector consists primarily of a scintillator inside a Faraday cage.

Everhart-Thornley detector:

(SNR= signal to noise ratio)

diagram of detector "‘opened up’

• the positive charge (+200) attracts the negative electrons

• samples are put at an angle (\)

Albert Einstein - photoelectric effect

(noble prize)

Semiconductors

G = 1 over the resistance

silicon is an intrinsic semiconductor.

by definition it is an insulator. The small energy gap, with heat, allows electrons to jump the gap!

• diamond is pure carbon, is kind of a semi conductor, but the band gap is too big.

• silicon and germanium, have small energy gaps therefore with a bit of heat are both intrinsic semiconductors.

.

p-ositive

n-egative

GA should be 4p2 that’s why there is a small space!

As- extra electron

instead of being an acceptor it is now a donor as it is so full!

Quadrant Backscatter Detector (QBSD)

have a possibility of 81 different reactions.

Quadrant Backscatter Detector (QBSD)

backscatter detection signal:

metal is bright white

SE1 signal:

backscatter - shows more impurities

Secondary

X-Ray Silicon Drift Detector (SDD)

inside of detector