Scanning Electron Microscopy and X-Ray Microanalysis

211 16

Electrons

holes

X-rays

Au electrode, ~20 nm

Window:

Si 3 N 4 or

polymer supported

on etched Si grid

Active silicon (intrinsic), 0.5 mm SDD

3 mm Si(Li)

• V

Rear Au electrode, ~20 nm

Si 'dead' layer

Al reflective coating,

20 – 50 nm

Basic EDS detection principle

Active area

5 – 100 mm^2

Rear electrode:

SDD: patterned

Si(Li): uniform

Photo-

electron

Hole-electrons

(3.8eV / Pair)

L

K

Dead layer

auger electron

Si K-L 3

hγ-Eκ

SDD backsurface

Central anode,

80 mm diameter

Resistor bridge

Ring electrodes

500 mm

SDDs have a complex

back surface electrode

structure. Applied

potential creates

internal radial

collection channel

Active area 5 – 100 mm^2

X-rays

Photo-

electron

Hole-electrons

(3.8eV / Pair)

L

K

Dead layer

Auger electron

Au contact

Be window

SiKα Si K-L 3

hγ-Eκ

hγ

a

b

. Fig. 16.1 a Basic principle of photon measurement with a semiconductor-based energy dispersive X-ray spectrometer. b Schematic of silicon
drift detector (SDD) design, showing the complex patterned back surface electrode with a small central anode

16 .1 · The Energy Dispersive Spectrometry (EDS) Process