FEI Quanta FEG 250, Руководство пользователя

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Operating Procedures: Obtaining an Image
5-6
SPOT SIZE
The electron beam diameter (usually represented as the Spot size) is
considered to be close to ideal when its edges just touch the
neighbouring spot. If it is too large, overlaps occur and the image
appears out of focus. If it is too small, electronic noise appears in the
image.
There are factory preset Spot numbers selectable from the Column
module / Spot number list box and from the toolbar list box. The last
user spot size value used is also kept in the Spot number list.
Deciding which spot size is suitable for a particular magnification can
be determined when you achieve good focus and astigmatism
correction.
Note:
When changing the spot size, adjustment of the Detector module /
Contrast and / or Brightness may be necessary to optimize the image.
An alternate approach is to use the Auto Contrast Brightness (F9)
function.
The Beam Current
could be controlled by changing the spot size and by selecting the
final lens aperture (see Chapter 2). A hint on a proper setting gives
the following table.
TABLE 5-2 SPOT SIZES AND RECOMMENDATION OF THEIR USE
Spot size Best Use
1, 2 Very high resolution (mag >50 000×)
3, 4, 5 Standard imaging, SE, BSED, LFD, GSED
5, 6 BSED, CL, X-ray analysis, EBSP
TABLE 5-3 OPTIMAL FINAL LENS APERTURE SIZES [µm]
(COLUMN A) AND APPROXIMATE SPOT SIZES
(COLUMN B) AS A FUNCTION OF HIGH VOLTAGE
AND BEAM CURRENT
HV [kV] Beam Current I [nA]
0.01 0.1 1.0 2.0 5.0 10
A B A B A B A B A B A B
0.5 15 3.0 20 4.5 20 6.0 30 6.0 30 6.5 40 7.0
1.0 20 2.0 20 4.0 30 5.0 30 5.5 40 5.5 50 6.0
2.0 20 2.0 20 3.5 30 4.5 40 4.5 50 5.0 50 5.5
5.0 30 1.0 30 2.0 40 3.5 50 4.0 50 4.5 50 5.0
10.0 30 30 2.0 40 3.0 50 3.5 50 4.0 50 4.5
20.0 30 40 1.5 40 3.0 50 3.0 50 4.0 50 4.0
30.0 30 40 1.0 40 3.0 50 3.0 50 4.0 50 4.0