Sharp EL-6490 Manuel d'utilisateur télécharger pdf (Page 14)

A small amount of air is introduced into the specimen chamber.

These air molecules, oxygen and nitrogen, are ionized with the inci-

dent electrons. These ions neutralize electrons on the surface of

the specimen and eliminate charge up effect so that a non conduc-

tive specimen can be observed.

The pressure in the specimen chamber can be varied from 1 Pa to

270 Pa without changing the size of the orifice. JSM-6490LA/JSM-

6490LV has 2 vacuum systems, one high vacuum system and one

low vacuum system dedicated to the low vacuum specimen cham-

ber. The gun chamber and the lenses are always kept in the high

vacuum. The life of a filament is not affected with the use of the low

vacuum SEM mode. The objective lens apertures are placed in the

high vacuum and kept clean for a long period of time.

The conventional secondary electron detector, Everhart and Thornley

detector, does not function in the low vacuum environment. A

backscattered electron detector is widely used instead. JEOL has

developed the high sensitivity semi-conductor backscattered electron

detector, which produces the composition, the topography, and the

shadowed contrast. This unique detector is patented to JEOL.

JEOL has developed a secondary electron detector, which works in

the low vacuum environment. Secondary electron images are suit-

able for observation of surface morphology.

Evacuation system of

Low Vacuum SEM

Low vacuum region

From Non Conductive Specimens to Wet Specimens

The Low Vacuum SEM

The low vacuum SEM, JSM-6490LA/JSM-6490LV, has the low vacu-

um SEM mode in addition to the conventional high vacuum SEM

mode. The low vacuum SEM lets you observe a non-conductive spec-

imen as is and then analyze with EDS. The low vacuum SEM easily

handles a specimen with much outgassing. Wet specimens can be

observed quickly with the freeze dry method in the LV SEM.

Principle of Low Vacuum SEM

Charging Generation of ions

No charging Neutralization of charge



High vacuum region

10m

m

0.5

m

0.1

m

1mm

100

m

10m

Principle of Charge Neutralization

Backscattered Electron Detector

Vacuum System for the LV SEM

Secondary Electron Detector for the

Low Vacuum SEM Mode

VV1

VV5

VV7

VV3

VV2

R. P1

R. P2

D. P

VV6

Electron gun

Objective lens

aperture

Backscattered

electron

detector

Orifice

(Needle valve)

controller

Pirani

gauge

Motor

drive

Foreline trap

Scattered electron

Ion

Electron on a specimen

Backscattered electron image in the low vacuum SEM mode

Specimen : Iron rust

Secondary electron image in the low vacuum SEM mode

1 2 ... 9 10 11 12 13 14 15 16 17 18 19 20

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Sharp EL-6490 Manuel d'utilisateur Page 14

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