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Scanning probe microscopy (tunneling, atomic force, confocal and acoustic) in particle track detectors
Radi__.~Jon Measuremenl$, Vol. 25, Nos 1-4, pp. 745-748, 1995
Elsevier Science Ltd Printed in Great Britain 1350-4487/95 $9.50 + .00
Pergamon
1350-4487(95)00240-$ SCANNING PROBE MICROSCOPY (TUNNELING, ATOMIC FORCE, CONFOCAL AND ACOUSTIC) IN PARTICLE TRACK DETECTORS
J. B. VUKOVI~* and R. ANTANASIJEVICt *Institute of Biophysics, Faculty of Medicine, University of Belgrade, Belgrade, Yugoslavia; and
tlnstitute of Physics, University of Belgrade, Belgrade, Yugoslavia
ABSTRACT The review of modern Scanning probe microscopy (SPM) observation of SSNTD is presented. Papers on Scanning tunneling microscopy (STM) and Scanning force microscopy (SFM) in Particle track detectors (PTD) have already appeared by other reaserchers (Marburg 1990, Beijing 1992). Atomic and submolecular resolution could be achieved. Geometrical structure of the etched tracks has a role in contrast and this is connection of STM and SFM with conventional optical microscopy analysis of tracks on and in solids. In Electronic optical microscopy (EOM) nowadays we have a new promising SPM which produces images formed with the laser light from a limited zone in focal plane. This is Confocal scanning optical microscopy (CSOM), which allows the user to indenpendently image different layers. The track image in detector (as the sum of slices) can be processed to provide all 3-D information. Also, there is a possibility to introduce Scanning acoustic microscopy (SAM) as a new SPM in analysis of etched tracks on and in solids (glass and crystals). Acoustic images are effective in microfractographic studies (finest cracks) and there is a real possibility to detect etched tracks as the surface and subsurface discontinuities.
KEYWORDS Scanning probe microscopy, STM, SFM, CSOM, SAM, Nuclear track detectors.
INTRODUCTION The impressive development of STM(Binning el all., 1982) and also the first derivate from that microscope (especially in biomedicine), i.e. atomic force microscopy (AFM)(Binning, 1986) or Scanning force microscopy, give the chance for successful application in the field of Particle track in solids(PTS). The crystals, glasses and polymers are very suitable for analysis by these microscopes but also probable for metallic compound (as detectors!) where high resolution(HR) is needed. STM and SFM improve the present HR in transmission and scanning electron microscopy (TEM, SEM). Instead of HR in TEM for SFM, P. B. Price (Price, 1993) uses the term "superresolution'. The additional advantage of these microscopes are following track formation (latent track) and track development. The later-beginning and the whole process is for working possibility in connection with SFM in aqueous solutions. In Optical microscopy (OM) or better to say Electronic optical microscopy (EOM) we have also a big scientific leap. This is Confocal scanning optical microscopy (CSOM) or Confocal scanning laser microscopy (CSLM). Confocal means that the objective lens are used twice: to illuminate the sample and to image it. The sample or beam must be scanned to build up image pixel by pixel(Kino, 1989). This image eliminates scattered, reflected or fluorescent light from out of focus planes. CSOM was stimulated by the development in SAM (Lemon and Quate, 1979) where the visualization of sound is a basic principle of SAM. Mechanical property of the sample (sound speed, specific weight, viscosity,...) determined acoustic contrast-mostly in reflection. Microstructures are detected with a high frequency ultrasound (US). US can perform subsurface 25:l/,-xx
745
746
J.B. VUKOVI(~ and R. ANTANASIJEVI(~
imaging and it is possible to use optically opaque materials. The different images can be taken by focussing down in to sample and acoustic slices can be also obtained. Deepest image is not badly affected by the structure from high levels. Now, we don't know about application of SAM in PTS.
STM AND SFM PRINCIPLES AND APPLICATION
STM is based on the quantum mechanical effect of tunneling, in which a particle encounters a barrier. Tiny electrical current (IT) between sharp conducting probe (cantilever/tip) and conducting sample surface flows at very narrow gap (d). Small potential (~IV) is applied (Fig. 1), IT increases exponentially as the distance d decreases. It means that small changes in d (>1pro) can be detected. The surface topography is reflected in the value of IT. The usual mode of operation is to keep IT constant by moving probe towards or away from surface during scanning. A suitable probe is either at distance but also in contact (d--0) with sample, in all three spatial dimensions (X,Y,Z) by the use of piezoelectric actuators.
LASER x \
x ~
CA.NTILE-VER/TIP
.%
DIODE
\",'~.
(detection
"
SURFACE
Fig.1. and 2. STM and SPM outlined shematically. The basic principle of SFM is shown in Fig. 2 where surface is sensed by the force that exerts on the probe tip (cantilever). This force changes from attractive to repulsive as the tip approaches the surface and its magnitude is measured. The optical lever has been applied to measure the displacement of the probe. Reflected laser beam is detected by two segment photodiode. SFM is suitable for nonconducting samples, it means for all our detectors. The application of STM in heavy ion irradiated material started by Wilson et al., 1988). STM imaging of isolated holes in policapbonate after irradiation with 14MeV/u Pb ions and etching gives 50nm pore (Kemmer, 1990). Nowadays the use of SFM is promising ( no need of conducting layer). Among the first picture and observation of radiation damage in policarbonate detector by heavy ions were done by Pengji et al., 1990. The most interesting application of SFM is study of very low velocity ion tracks in mica by Price, 1993. The alpha recoil etch pit showing individual steps that are measured exactly 2nm highly.
CONFOCAL SCANNING OM. PRINCIPLE AND APPLICATION
The first idea for CSOM was done by Minsky, (1957,1961). Petran et al., 1968 invented different types of CSOM. The image could be directly observed with naked eye. For scanning they use Nipkow disc ( point illumination and point detection). In Fig.3 we can see light paths in focus image (a) and out of focus image (b). Main characteristic is that defocused image does not reach photodetector and this image disappears.
SCANNING PROBE MICROSCOPY
ilumination
in
focus
\ /
eyepiece
ivem"~-m (i J object
A
object
out of
ilumination ~ i
focus
~/
eyepiece
oblectmve ~ ~
scanned
747
L_
rector
/ . .-'I'- I
obieet scanned
photodeteetor
Fig. 3. CSOM principle (a) in focus (b) defocused The first application of CSOM in mineral studies and PTS were done by Petford and Miller, (1992). In confocal imaging both illumination and detection are confined to the same spot of the sample. The resolution is also better (order 0.lyre) and the image intensity drops of as the image is defocused. This property makes it possible to image and reconstruct 3-D profiles of structures. Also, edges are sharper and contrast better than using conventional OM. The technique use laser beam as probe in translucent solids. Fission tracks in apatite and muscovite mica (after etching) were studied by CSOM (Petford and Miller, 1993; Petford, 1993). Very interesting characteristics of fission tracks are: white tracks 12.3 ym in length tapering towards end and lies ca 6 #m beneath apatite grain. The stacked image is made up of 12 optical slices at 0.5 #m intervals (Fig. 4). In mica for low angle fission tracks we see interference fringes (Fig. 5). EOM gives electronic images which are very good for image analysis and data manipulation.
Fig. 4. CSOM image of fission track(Petford, 1993 )
Fig. 5. CSOM images of fission tracks in mica (optical sliees)(Petford, 1993)
SCANNING ACOUSTIC MICROSCOPY PRINCIPLE
SAM has very simple physical principle, where spherical interface between saphire rod and coupling fluid (water) acts as a lens for pulsed US waves. After US waves strike the sample and reflection back in to transducer we obtain useful signal for visualization (Fig. 6). The frequency range of US is from 10Mttz to 2GHz. The lens scanned the sample surface and subsurface structures as well to obtain acoustic slices or acoustic thomography (Gremande, 1991). In general, the SAM is useful for visualization of crystal anisotropy and surface cracks. They give strong contrast. The scattering and anisotropy of Reyleigh waves give detection of very fine cracks(Briggs, 1990). This statement gives the chance to use SAM in PTS for etched tracks detection.
748
]. B. VUKOVI(~ and R. ANTANASDEVI(~
IELE£TR O r ~
~
ULTRASONICTRANSDUCER
J, ~
/WATER
~
FOCUSED ULTRASONICBEAM
~
S A M P t . F
Fig. 6. SAM outlined shematically CONCLUSION
SPM is now in trends on investigations of PTS. The number of new SPM is also in different application in life and material science: magnetic and electrostatic force microscope (MFM,EFM), Scanning ion-conductance microscope (SICM), Scanning thermal microscope (SThM), world tiniest thermometer, Lateral force microscope (LFM). The most interesting is Scanning near-field OM (SNOM). This instrument is similar to the STM. The probe is light (laser) and based on fiberoptic illumination which overcomes the diffraction limits (about A/20). Also, photon tunneling is principle of SPTM. We will see the influence of these new SPM in many fields of research and in PTS.
REFERENCES Binning G., Rohrer H., (1982) Surfaces studies by STM, Phys. Rev. Left., 49, 57-61. Binning G., et al. (1986) Atomic Force Microscope, Phys. Rev. Left., 56, 930-933, 1986. Briggs G.A.D. et a1.,(1990) How fine a surface crack can you see with SAM, J. Micros. 159, 15-32. Gremaud G. et a1.,(1991) SAM a Phisicist tool,Europhys. News, 22(9), 1991,167-170. Kemmer H. Graftom (1990), GSI Sci. Report, 249 Kino G. and Corle T.R., (1989) CSOM, Phys. Today, 4P, No9, 55-62. Lemon R. and Quate C.F., (1973) Proc. IEEE Ultrasonic Symp. NY, 18. Minsky M.,(1957, 1961) Microscopy aparatus, US Patent Office Patent No 3013467 Pengji Z. et al., (1990) GSI Sei. Report, 248 Petford N. and Miller J.A., (1992) 3-D imaging of fission fragment track using CSLM., Am. MineralogisL 77, 259-533. Petford N. and Miller J.A., (1993), The Study of fission track and other crystaline defect using CSLM., J. of Microsc. 170, 201-212. Petford N., (1993) Mineral study using CSLM., Microscopy and analysis, (19-21). Petran M. et a1.,(1968) J. Optical Soe. America 58(5), 661-664. Price P.B., (1993) Nuc. Track Radiat. Meas. Vol.22 No 1-4. Wilson I.I-I. et al., (1990) Appl. Phys. Left., ~1, 2039.
Elsevier Science Ltd Printed in Great Britain 1350-4487/95 $9.50 + .00
Pergamon
1350-4487(95)00240-$ SCANNING PROBE MICROSCOPY (TUNNELING, ATOMIC FORCE, CONFOCAL AND ACOUSTIC) IN PARTICLE TRACK DETECTORS
J. B. VUKOVI~* and R. ANTANASIJEVICt *Institute of Biophysics, Faculty of Medicine, University of Belgrade, Belgrade, Yugoslavia; and
tlnstitute of Physics, University of Belgrade, Belgrade, Yugoslavia
ABSTRACT The review of modern Scanning probe microscopy (SPM) observation of SSNTD is presented. Papers on Scanning tunneling microscopy (STM) and Scanning force microscopy (SFM) in Particle track detectors (PTD) have already appeared by other reaserchers (Marburg 1990, Beijing 1992). Atomic and submolecular resolution could be achieved. Geometrical structure of the etched tracks has a role in contrast and this is connection of STM and SFM with conventional optical microscopy analysis of tracks on and in solids. In Electronic optical microscopy (EOM) nowadays we have a new promising SPM which produces images formed with the laser light from a limited zone in focal plane. This is Confocal scanning optical microscopy (CSOM), which allows the user to indenpendently image different layers. The track image in detector (as the sum of slices) can be processed to provide all 3-D information. Also, there is a possibility to introduce Scanning acoustic microscopy (SAM) as a new SPM in analysis of etched tracks on and in solids (glass and crystals). Acoustic images are effective in microfractographic studies (finest cracks) and there is a real possibility to detect etched tracks as the surface and subsurface discontinuities.
KEYWORDS Scanning probe microscopy, STM, SFM, CSOM, SAM, Nuclear track detectors.
INTRODUCTION The impressive development of STM(Binning el all., 1982) and also the first derivate from that microscope (especially in biomedicine), i.e. atomic force microscopy (AFM)(Binning, 1986) or Scanning force microscopy, give the chance for successful application in the field of Particle track in solids(PTS). The crystals, glasses and polymers are very suitable for analysis by these microscopes but also probable for metallic compound (as detectors!) where high resolution(HR) is needed. STM and SFM improve the present HR in transmission and scanning electron microscopy (TEM, SEM). Instead of HR in TEM for SFM, P. B. Price (Price, 1993) uses the term "superresolution'. The additional advantage of these microscopes are following track formation (latent track) and track development. The later-beginning and the whole process is for working possibility in connection with SFM in aqueous solutions. In Optical microscopy (OM) or better to say Electronic optical microscopy (EOM) we have also a big scientific leap. This is Confocal scanning optical microscopy (CSOM) or Confocal scanning laser microscopy (CSLM). Confocal means that the objective lens are used twice: to illuminate the sample and to image it. The sample or beam must be scanned to build up image pixel by pixel(Kino, 1989). This image eliminates scattered, reflected or fluorescent light from out of focus planes. CSOM was stimulated by the development in SAM (Lemon and Quate, 1979) where the visualization of sound is a basic principle of SAM. Mechanical property of the sample (sound speed, specific weight, viscosity,...) determined acoustic contrast-mostly in reflection. Microstructures are detected with a high frequency ultrasound (US). US can perform subsurface 25:l/,-xx
745
746
J.B. VUKOVI(~ and R. ANTANASIJEVI(~
imaging and it is possible to use optically opaque materials. The different images can be taken by focussing down in to sample and acoustic slices can be also obtained. Deepest image is not badly affected by the structure from high levels. Now, we don't know about application of SAM in PTS.
STM AND SFM PRINCIPLES AND APPLICATION
STM is based on the quantum mechanical effect of tunneling, in which a particle encounters a barrier. Tiny electrical current (IT) between sharp conducting probe (cantilever/tip) and conducting sample surface flows at very narrow gap (d). Small potential (~IV) is applied (Fig. 1), IT increases exponentially as the distance d decreases. It means that small changes in d (>1pro) can be detected. The surface topography is reflected in the value of IT. The usual mode of operation is to keep IT constant by moving probe towards or away from surface during scanning. A suitable probe is either at distance but also in contact (d--0) with sample, in all three spatial dimensions (X,Y,Z) by the use of piezoelectric actuators.
LASER x \
x ~
CA.NTILE-VER/TIP
.%
DIODE
\",'~.
(detection
"
SURFACE
Fig.1. and 2. STM and SPM outlined shematically. The basic principle of SFM is shown in Fig. 2 where surface is sensed by the force that exerts on the probe tip (cantilever). This force changes from attractive to repulsive as the tip approaches the surface and its magnitude is measured. The optical lever has been applied to measure the displacement of the probe. Reflected laser beam is detected by two segment photodiode. SFM is suitable for nonconducting samples, it means for all our detectors. The application of STM in heavy ion irradiated material started by Wilson et al., 1988). STM imaging of isolated holes in policapbonate after irradiation with 14MeV/u Pb ions and etching gives 50nm pore (Kemmer, 1990). Nowadays the use of SFM is promising ( no need of conducting layer). Among the first picture and observation of radiation damage in policarbonate detector by heavy ions were done by Pengji et al., 1990. The most interesting application of SFM is study of very low velocity ion tracks in mica by Price, 1993. The alpha recoil etch pit showing individual steps that are measured exactly 2nm highly.
CONFOCAL SCANNING OM. PRINCIPLE AND APPLICATION
The first idea for CSOM was done by Minsky, (1957,1961). Petran et al., 1968 invented different types of CSOM. The image could be directly observed with naked eye. For scanning they use Nipkow disc ( point illumination and point detection). In Fig.3 we can see light paths in focus image (a) and out of focus image (b). Main characteristic is that defocused image does not reach photodetector and this image disappears.
SCANNING PROBE MICROSCOPY
ilumination
in
focus
\ /
eyepiece
ivem"~-m (i J object
A
object
out of
ilumination ~ i
focus
~/
eyepiece
oblectmve ~ ~
scanned
747
L_
rector
/ . .-'I'- I
obieet scanned
photodeteetor
Fig. 3. CSOM principle (a) in focus (b) defocused The first application of CSOM in mineral studies and PTS were done by Petford and Miller, (1992). In confocal imaging both illumination and detection are confined to the same spot of the sample. The resolution is also better (order 0.lyre) and the image intensity drops of as the image is defocused. This property makes it possible to image and reconstruct 3-D profiles of structures. Also, edges are sharper and contrast better than using conventional OM. The technique use laser beam as probe in translucent solids. Fission tracks in apatite and muscovite mica (after etching) were studied by CSOM (Petford and Miller, 1993; Petford, 1993). Very interesting characteristics of fission tracks are: white tracks 12.3 ym in length tapering towards end and lies ca 6 #m beneath apatite grain. The stacked image is made up of 12 optical slices at 0.5 #m intervals (Fig. 4). In mica for low angle fission tracks we see interference fringes (Fig. 5). EOM gives electronic images which are very good for image analysis and data manipulation.
Fig. 4. CSOM image of fission track(Petford, 1993 )
Fig. 5. CSOM images of fission tracks in mica (optical sliees)(Petford, 1993)
SCANNING ACOUSTIC MICROSCOPY PRINCIPLE
SAM has very simple physical principle, where spherical interface between saphire rod and coupling fluid (water) acts as a lens for pulsed US waves. After US waves strike the sample and reflection back in to transducer we obtain useful signal for visualization (Fig. 6). The frequency range of US is from 10Mttz to 2GHz. The lens scanned the sample surface and subsurface structures as well to obtain acoustic slices or acoustic thomography (Gremande, 1991). In general, the SAM is useful for visualization of crystal anisotropy and surface cracks. They give strong contrast. The scattering and anisotropy of Reyleigh waves give detection of very fine cracks(Briggs, 1990). This statement gives the chance to use SAM in PTS for etched tracks detection.
748
]. B. VUKOVI(~ and R. ANTANASDEVI(~
IELE£TR O r ~
~
ULTRASONICTRANSDUCER
J, ~
/WATER
~
FOCUSED ULTRASONICBEAM
~
S A M P t . F
Fig. 6. SAM outlined shematically CONCLUSION
SPM is now in trends on investigations of PTS. The number of new SPM is also in different application in life and material science: magnetic and electrostatic force microscope (MFM,EFM), Scanning ion-conductance microscope (SICM), Scanning thermal microscope (SThM), world tiniest thermometer, Lateral force microscope (LFM). The most interesting is Scanning near-field OM (SNOM). This instrument is similar to the STM. The probe is light (laser) and based on fiberoptic illumination which overcomes the diffraction limits (about A/20). Also, photon tunneling is principle of SPTM. We will see the influence of these new SPM in many fields of research and in PTS.
REFERENCES Binning G., Rohrer H., (1982) Surfaces studies by STM, Phys. Rev. Left., 49, 57-61. Binning G., et al. (1986) Atomic Force Microscope, Phys. Rev. Left., 56, 930-933, 1986. Briggs G.A.D. et a1.,(1990) How fine a surface crack can you see with SAM, J. Micros. 159, 15-32. Gremaud G. et a1.,(1991) SAM a Phisicist tool,Europhys. News, 22(9), 1991,167-170. Kemmer H. Graftom (1990), GSI Sci. Report, 249 Kino G. and Corle T.R., (1989) CSOM, Phys. Today, 4P, No9, 55-62. Lemon R. and Quate C.F., (1973) Proc. IEEE Ultrasonic Symp. NY, 18. Minsky M.,(1957, 1961) Microscopy aparatus, US Patent Office Patent No 3013467 Pengji Z. et al., (1990) GSI Sei. Report, 248 Petford N. and Miller J.A., (1992) 3-D imaging of fission fragment track using CSLM., Am. MineralogisL 77, 259-533. Petford N. and Miller J.A., (1993), The Study of fission track and other crystaline defect using CSLM., J. of Microsc. 170, 201-212. Petford N., (1993) Mineral study using CSLM., Microscopy and analysis, (19-21). Petran M. et a1.,(1968) J. Optical Soe. America 58(5), 661-664. Price P.B., (1993) Nuc. Track Radiat. Meas. Vol.22 No 1-4. Wilson I.I-I. et al., (1990) Appl. Phys. Left., ~1, 2039.