GB2095857A - Thinning of specimens for examination under the electron microscope - Google Patents
Thinning of specimens for examination under the electron microscope Download PDFInfo
- Publication number
- GB2095857A GB2095857A GB8207950A GB8207950A GB2095857A GB 2095857 A GB2095857 A GB 2095857A GB 8207950 A GB8207950 A GB 8207950A GB 8207950 A GB8207950 A GB 8207950A GB 2095857 A GB2095857 A GB 2095857A
- Authority
- GB
- United Kingdom
- Prior art keywords
- specimen
- source
- neutral
- penetration
- examination
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
- 238000000034 method Methods 0.000 claims abstract description 33
- 230000007935 neutral effect Effects 0.000 claims abstract description 32
- 239000002245 particle Substances 0.000 claims abstract description 13
- 230000035515 penetration Effects 0.000 claims abstract description 10
- 230000003628 erosive effect Effects 0.000 claims abstract description 8
- 238000001493 electron microscopy Methods 0.000 claims abstract description 6
- 230000001678 irradiating effect Effects 0.000 claims description 2
- 238000000386 microscopy Methods 0.000 claims 1
- 230000004907 flux Effects 0.000 abstract description 3
- 238000004544 sputter deposition Methods 0.000 abstract description 3
- 239000000463 material Substances 0.000 description 14
- 150000002500 ions Chemical class 0.000 description 12
- 238000010884 ion-beam technique Methods 0.000 description 6
- 238000005530 etching Methods 0.000 description 5
- 239000000126 substance Substances 0.000 description 4
- 230000008569 process Effects 0.000 description 3
- 230000009471 action Effects 0.000 description 2
- 150000001768 cations Chemical class 0.000 description 2
- 239000000919 ceramic Substances 0.000 description 2
- 238000003486 chemical etching Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000002360 preparation method Methods 0.000 description 2
- 239000004065 semiconductor Substances 0.000 description 2
- 238000004627 transmission electron microscopy Methods 0.000 description 2
- 238000002441 X-ray diffraction Methods 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 150000001450 anions Chemical class 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 239000000470 constituent Substances 0.000 description 1
- 230000007812 deficiency Effects 0.000 description 1
- 238000011010 flushing procedure Methods 0.000 description 1
- 239000011521 glass Substances 0.000 description 1
- 239000008187 granular material Substances 0.000 description 1
- 230000002401 inhibitory effect Effects 0.000 description 1
- 229910010272 inorganic material Inorganic materials 0.000 description 1
- 239000011147 inorganic material Substances 0.000 description 1
- 238000003780 insertion Methods 0.000 description 1
- 230000037431 insertion Effects 0.000 description 1
- 238000010849 ion bombardment Methods 0.000 description 1
- CPLXHLVBOLITMK-UHFFFAOYSA-N magnesium oxide Inorganic materials [Mg]=O CPLXHLVBOLITMK-UHFFFAOYSA-N 0.000 description 1
- 239000000395 magnesium oxide Substances 0.000 description 1
- AXZKOIWUVFPNLO-UHFFFAOYSA-N magnesium;oxygen(2-) Chemical compound [O-2].[Mg+2] AXZKOIWUVFPNLO-UHFFFAOYSA-N 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 238000001000 micrograph Methods 0.000 description 1
- 230000005012 migration Effects 0.000 description 1
- 238000013508 migration Methods 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- -1 oxygen ions Chemical class 0.000 description 1
- 238000005498 polishing Methods 0.000 description 1
- 239000007779 soft material Substances 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N1/00—Sampling; Preparing specimens for investigation
- G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
- G01N1/32—Polishing; Etching
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
- H01J37/30—Electron-beam or ion-beam tubes for localised treatment of objects
- H01J37/305—Electron-beam or ion-beam tubes for localised treatment of objects for casting, melting, evaporating, or etching
- H01J37/3053—Electron-beam or ion-beam tubes for localised treatment of objects for casting, melting, evaporating, or etching for evaporating or etching
Landscapes
- Chemical & Material Sciences (AREA)
- Physics & Mathematics (AREA)
- Analytical Chemistry (AREA)
- Life Sciences & Earth Sciences (AREA)
- Plasma & Fusion (AREA)
- Health & Medical Sciences (AREA)
- Engineering & Computer Science (AREA)
- Biochemistry (AREA)
- General Health & Medical Sciences (AREA)
- General Physics & Mathematics (AREA)
- Immunology (AREA)
- Pathology (AREA)
- Sampling And Sample Adjustment (AREA)
- Analysing Materials By The Use Of Radiation (AREA)
Abstract
Heretofore specimens have been thinned to penetration for examination by electron microscopy techniques, by ion erosion techniques. A more rapid technique is disclosed employing a beam or beams comprised solely of neutral particles. In tests carried out using this technique the sputtering rate from a sample specimen has been shown to be several percentages greater using a neutral source than from an ion source with the same flux density.
Description
SPECIFICATIONS
Thinning specimens for examination under the electron microscope
The present invention relates to specimen thinning techniques for the preparation of materials for examination under the electron microscope.
The high resolution attainable with transmission electron microscopy makes this an outstanding technique for examining the microstructure of materials. The direct examination of materials by transmission electron microscopy requires that the specimen to be examined is transparent to electrons.
Consequentiy the thickness of the specimens must be restricted to 100 to 200nm.
It has therefore been necessary to develop methods for preparing thin specimens of materials that have widely varying mechanical and chemical properties. Soft materials such as biological specimens, may be prepared by microtoming, although difficulty is sometimes encountered when hard particles are present.
For some metals, semiconductors, and other inorganic materials, chemical etching and electrolytic techniques are suitable. In one widely used method the material to be thinned is placed in a jet etching tank and the etching process observed through a lens with a light source behind the specimen.
The etching action of the jet is maintained until perforation of the specimen occurs. Since the etching action is stronger at the centre of the jet than its periphery, perforation starts at the centre and spreads towards the periphery. Thus the etching process is immediately arrested when perforation occurs by flushing the specimen with an inhibiting wash, leaving adjacent areas around the perforation which are usually sufficiently thin to allow micrographs to be taken during examination under the electron microscope.
For materials for which suitable chemical etchants do not exist, such as some glasses, ceramics, and geological specimens, various mechanical preparation techniques have been tried. The specimens may be crushed and fine slivers selected, or thin sections may be produced by very careful mechanical polishing. These operations require considerable skill and can generally not be applied to brittle granular materials with voids.
A large variety of materials which do not lend themselves to chemical treatment may be thinned by ion erosion.
In typical known thinning equipment ion beams of about 2mm diameter from two sources impinge centrally on either side of a specimen. A hole or perforation is allowed to form in the specimen by the ion beam, which acts in a similar way to the chemical jet during chemical etching, when the ion beam is immediately turned off to leave adjacentthin areas around the perforation transparent to electrons.
Ion erosion has proved an increasingly valuable tool to electron microscopists especially those engaged in examining classes of material such as ceramics, impurity-doped semiconductors and alloys.
Difficulty however arises when dealing with ionic and covalent materials since bombardment with the charged particles of the ion beam may deleteriously affect the structure of the material.
It is an object of the invention to provide a method of thinning specimens by particle bombardment of the specimen, which method obviates the deficiencies of known ion erosion techniques when dealing with ionic and covalent materials.
According to the invention there is provided a method of preparing specimens suitable for examination by electron microscopy techniques comprising providing a source for producing a beam of energetic uncharged or neutral particles, and irradiating a specimen by the beam thereby to erode the specimen to penetration and produce an area surrounding the penetration of suitable thickness for transmission of electrons.
The method of thinning specimens as afforded by the present invention with a neutral beam is particularly advantageous when dealing with ionic and covalent materials since the absence of surface charge reduces migration of any mobile charge constituent of the material being thinned.
Thinning of the specimen using a neutral beam source may be carried out by using two neutral beams on either side of the specimen and thinning to penetration. A more rapid technique may be employed by using one source with the specimen position close to the beam aperture of the source where the intensity and hence the eroding power of the neutral particle beam is the greater.
Any source which is capable of producing a beam of charged particles which can then be neutralised before impinging on the specimen would be suitable, such sources being well known to those skilled in the art.
For example, ions may be passed through a resonance charge exchange tube and the resulting neutral beam allowed to impinge on the specimen. A preferred technique is to use a saddle field source with a neutral output which eliminates the cumbersome charge exchange tube.
Other features and advantages of the present invention will become apparent from the description that follows.
An embodiment of the invention will be described by way of example with reference to the sole accompanying drawing which shows a perspective view of the principal parts of a thinning unit for emitting a beam of neutral particles.
As mentioned earlier the technique for thinning specimens for use in electron microscopy by ion erosion is known, and the saddle field ion source is suitable for providing the neutral beam required to perform the present invention.
A thinning unitforthinning specimens with a neutral beam is shown in Figure 1. It comprises two fine beam neutral saddle field sources 1 and 2 which produce neutral beams 3 and 4 of about 121 mm.
diameter from the cathode apertures 5.
The neutral beams are directed to pass through the centre of a rotatable specimen platform 6 the centre P of which is located on the axis of the pivot of an arm 7 which supports the two sources 1 and 2.
The arm 7 is driven by a servo motor 8 through a
rotary shaft 9. The rotatable arm 7 may be set at an angle relative to the plane of the specimen platform 6 from 0 (glancing incidence) through 90" (normal) to 180 and may be rocked at any amplitude between these limits.
During a thinning process material is controllably removed from either side of the specimen by exposure to the neutral beams from the two diammetrically opposed sources 1 and 2.
The specimen is illuminated and may be observed during processing through a binocular microscope (not shown) mounted above the unit.
Although thinning of the specimen using the unit as described with a neutral beam may be carried out by using two neutral beam sources on either side of the specimen with the specimen held normally at 2 cm. from the aperture of the source, a more rapid technique may be employed by using only one source with the specimen positioned as close as possible to the beam aperture (commensurate with the possibility of insertion and removal of the specimen between the source and the specimen platform 6) where the intensity and hence the eroding power of the neutral particle beam, is the greater.
In practice the preferred beam power of the source is within the range 4 to 8 kV at a plasma current of up to WmA.
Thinning insulating specimens using a beam comprised solely of neutral particles is more rapid than with an ion beam or a beam comprised of a mixture of ions and neutrals of the same energy and flux density.
To compare the effects of ion and neutral bombardment on stoichiometry, thin specimens of magnesium oxide were bombarded from one side of a specimen separately with ions and neutrals. With 6 kV applied to a saddle field source, X-ray analysis showed that cation concentration at the unthinned surface under ion bombardment increased by 80%, while under neutral bombardment the increase was 20%. In addition the sputtering rate of the oxide was 15% greater from a neutral source than from an ion source with the same flux density.
To explain this effect it is proposed that the positively charged ions in an ion beam exert electrostatic forces on ions in the sample. The attractive force on the anions will produce an increase in the preferential sputtering of the oxygen ions with an associated creation of a positively charged surface region. The electrostatic repulsive forces from both the beam and the surface will therefore produce a driving force for cations away from the thinned surface.
With a neutral beam these driving forces will be reduced. Some positive surface charge may still remain however because of secondary electron emission.
Claims (11)
1. A method of preparing specimens suitable for
examination by electron microscopy techniques
comprising providing a source for producing a beam
of energetic uncharged or neutral particles, and
irradiating a specimen by the beam thereby to erode
the specimen to penetration and produce an area
surrounding the penetration of suitable thickness for transimssion electrons.
2. A method as claimed in Claim 1 wherein the specimen is held as close as possible to the aperture of the source where the intensity and hence eroding power of the neutral beam is the greater thereby to rapidly thin the specimen to penetration.
3. A method as claimed in Claim 1 wherin a pair of said neutral beam sources are employed to act on either side of the specimen respectively to thin the specimen to penetration.
4. A method as claimed in Claim 1 wherein the source is a saddle field source.
5. A method as claimed in Claim 1 wherein the source comprises an ion source and a resonance charge exchange tube.
6. Apparatus for preparing specimens suitable for examination by electron microscopy techniques comprising a platform for supporting a specimen, and a source for producing a beam of neutral particles arranged with respect to the specimen such that in use, the beam produced by the source is directed onto the specimen to thereby thin the specimen to penetration.
7. Apparatus as claimed in Claim 6 wherein a said source is positioned on either side of the specimen so that the beams thereof are directable onto the specimen to thin one part thereof to penetration.
8. Apparatus as claimed in Claim 6 wherein the source is a saddle field ion source modified to produce a beam of neutral particles.
9. Apparatus as claimed in Claim 6 wherein the source is an ion source and a resonance charge exchange tube acting therewith to produce the neutral beam.
10. A method of preparing specimens suitable for examination by electron microscopy techniques substantially as hereinbefore described with referpence to and as illustrated in the accompanying drawing.
11. Apparatus for preparing specimens suitable for examination by electron . microscopy techniques substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8207950A GB2095857B (en) | 1981-03-31 | 1982-03-18 | Thinning of specimens for examination under the electron microscope |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8110073 | 1981-03-31 | ||
| GB8207950A GB2095857B (en) | 1981-03-31 | 1982-03-18 | Thinning of specimens for examination under the electron microscope |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB2095857A true GB2095857A (en) | 1982-10-06 |
| GB2095857B GB2095857B (en) | 1984-08-08 |
Family
ID=26278959
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8207950A Expired GB2095857B (en) | 1981-03-31 | 1982-03-18 | Thinning of specimens for examination under the electron microscope |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2095857B (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0651243A1 (en) * | 1993-10-28 | 1995-05-03 | Koninklijke Philips Electronics N.V. | Method of making specimens for an electron microscope |
-
1982
- 1982-03-18 GB GB8207950A patent/GB2095857B/en not_active Expired
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0651243A1 (en) * | 1993-10-28 | 1995-05-03 | Koninklijke Philips Electronics N.V. | Method of making specimens for an electron microscope |
| BE1007675A3 (en) * | 1993-10-28 | 1995-09-12 | Philips Electronics Nv | Process for the production of preparations intended for an electron microscope. |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2095857B (en) | 1984-08-08 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |