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Polarised emission of the K-band by graphite single crystals
LETTERS
TO THE
is
EDITOR
defects inside of crystallites by atoms from the disordered phase which leads to a quick disappearance of localized spin centers. These defects probably appear when a layer is deposited onto a strongly overcooled substrate[5], and a small amount of activation energy suffices to anneal them out. The change in structure is seen clearly on the electron microscopic photographs of the carbon film evaporated under argon pressure 8 X lo-‘Tr: (a) before heattreatment, (b) after heattreatment to 500°C (Fig. 2). In heattreated layer there may be seen strongly marked canals which separate the individual carbon areas. This is, maybe, evidence for the contraction of the material at the cost of a diminution of the disordered phase. The constant value of the contribution of carriers in the total ESR signal, in this situation, is probably connected with the constant size of crvstallites in the HTT interval considered. How-
ever, a classical interpretation of them as free current carriers, considering the results concerning the energy of activation and the electric conduction might be questionable.
Polarised Emission of the K-band by Graphite Single Crystals
tion varies with the wavelength, as may be seen in Fig. 1, where a selection of the OHM results are arranged in a series to show the change in emission between the ‘a’ and ‘c’ axes. These results confirm that Ergun and Weisweiler [3] were correct in rejecting the analysis of Sagawa[4], although premature in assuming that the K-emission could not be further resolved. Data from the literature on the K-emission of graphite and carbon[2-191 has been arranged in an analogous manner in Fig. 2. Although exact comparisons cannot be drawn between the OHM results and the literature data, the same family of curves can be recognised in each. The literature is understandably sparse in certain parts of the range, but there is close similarity in both sets of data relating to randomly-oriented polycrystalline material. It may be concluded, therefore, that the results from the OHM crystal are unlikely to be vitiated by large changes in sensitivity over the range of the carbon K-band, such as the ‘enhanced reflectivity’ effect demonstrated by Liefeld et al. [20] in the diffraction of oxygen K-radiation by the potassium acid phthalate crystal. Debye-Scherrer powder photographs of the material examined indicated that (i) the pyrolytic graphite was entirely hexagonal, (ii) the particular sample of natural graphite contained an estimated 30 per cent of rhombohedral graphite, and (iii) the vitreous carbon displayed no sharp lines at all. The
(Received 14 August 1972) The author has recently investigated the K-bands emitted by some allotropes and compounds of carbon, using a crystal of octadecyl hydrogen maleate (OHM) as the wavelength-resolving element, in an electron probe microanalyser [l]. The lattice spacing of the OHM analysing crystal is such (2d = 63.35 A) that the Bragg and Brewster angles coincide for carbon K-radiation; thus only radiation with its electric vector perpendicular to the Rowland circle plane is detected at this wavelength. The OHM crystal therefore behaves as a polarising analyser for carbon K-radiation. Samples of natural graphite containing large single crystals, pyrolytic graphite, vitreous carbon and carbon fibre were examined in the instrument described, above, at various orientations relative to the Rowland circle plane, and the prediction of Co&on and Taylor [2] that the r and u bands emitted by a graphite single crystal would show polarisation, has been confirmed. The m-band is emitted parallel to the ‘a’ axis with its electric vector parallel to the ‘c’ axis, and is almost totally polarised. The u-band is partially polarised, the major emission being parallel to the ‘c’ axis with the electric vector parallel to the ‘a’ axis, and the degree of polarisa-
Institute oj Physics Nicholas Copernicus Torun, Poland
S. ORZESZKO Unitlersity
REFERENCES 1. Mrozowski S., Carbon 3,305 (1965); 4,227 (1966); 6, 841 (1968); Arnold G. and Mrozowski S., ibid 6,243 (1968). 2. Antonowicz K., Orzeszko S., Rozp&ch Szczurek T., Carbon 5,261 (196’7). 3. Orzeszko S., to be published.
F. and
4. Presland A. E. B. and White J. R., Carbon 7, 77 (1969). 5. Boiko B. T., Palatnik L. S. and Derevyanchenko A. S., DAN SSSR 2, 179 (1968).
LETTERS
74
TO THE EDITOR
Angle between
I
Material
and the ‘a’ axis of the
mounting
specimen at the
CUIW No.
Rowland circle plane
prepared
Material Pyrolyticgraphite,
surface
method (see Fig. 3)
00
I
mount
0”
I
mO”nt
II=-
I
mount
0”
1 mO”“t
sample ‘A’ 2
Natural graphite (Kropfmiihl)
3
Natural graphite (Kropfmuhl)
4
Pyrolytrc graphite, sample ‘B’
5
Natural graphite
20”
I mount
30
I mount
20”
559 mount
(Kropfmiihl) 6
Natural graphite (Kropfmtihl)
‘i
Natural graphite (Kropfmiihl)
8
Axes 1 to mount surface
Carbon fibres (21 Carbolon)
9
Natural graphite
30--
55” mount
40”
1 mount
(Kropfmbhl) 10
Natural graphite (Kropfmhhl)
11
Paracrystalline
carbon,
Orientation
non-critical
carbon,
Orientation
non-critical
sample ‘A’ 12
Paracrystalline sample ‘B’
13
Natural graphite
50
55” mo”nt
60”
55” mount
70”
55” mount
90’
1 mo”“t
90”
i mount
(Kropfmiihl) 14
Natural graphite (Kropfmiihl)
15
Natural graphite (Kropfmhhl)
16
Pyrolytic graphite, sample ‘B’ Pyrolytic graphite,
265
260
275
270
265
eV
/
sample ‘A’ Carbon tihres
Axes 1 to Rowland circle plane
(21 Carholon)
Fig. 1. K-emission profiles of graphite obtained using the octadecyl hydrogen maleate crystal (see Table top right).
specimen samples were mounted in a conducting metallographic medium, and carefully abraded and polished, so that the orientation of the embedded material relative to the finished surface was accurately known. Ideally, the graphite would have been mounted in a miniature goniometer stage, adjustable under vacuum, to cover the required range of angular relations between the crystal and the X-ray spectrometer. Since the specimen stage of the micro-analyser could only be used to rotate the mounted crystals on an axis coincident with that of the light microscope (see Fig. 3 for a ray diagram of the instrument) it was necessary to mount the graphitic specimens in several orientations relative to the reference plane of the specimen stage in order to achieve the required range. The family of curves representing
Natural graphite
80”
I mount
(Kropfmtihl) Natural graphite
90”
parallel mount
(Kropfmiihl)
the K-emissions of graphite at different orientations reported in Fig. 1, are identified by three parameters; firstly, with the emitting material, secondly, with the angle between the Rowland circle plane and the edge of the graphite basal plant at the mount surface, measured using the protractor graticule in the microscope ocular, and finally, with the particular mounting orientation. The mounting orientations used were determined in the following way. It will be seen by reference to Fig. 3, that if the radiation emitted perpendicular to the basal planes of the graphite crystal is to be directed up the axis of the X-ray spectrometer then the crystal must be mounted so that its basal planes make an angle of 55” with the surface of the mount, and is designated ‘55”mount in the code used to identify the curves in Fig. 1.
LETTERS
TO THE
EDITOR
Similarly, if the spectrometer is to receive radiation when the basal planes of the graphite crystal are parallel to the Rowland circle plane of the Xray spectrometer then the crystal must be mounted with its basal plane perpendicular to the surface of the mount: this is designated ‘I mount’. Samples of flake graphite and carbon fibres were also mounted by direct adhesion of the basal planes (or fibre bundles) parallel to the surface of the mount. This method of mounting (designated ‘parallel niount’) was not eSSent?dl geometrically to com-
H W.B
Light mIcroscope electron beam \
Skinner
1
Mount
55” InO”“+ (b)
H.WE.
Skinner
H.W.B.
Skinner
Fig. 3(a). Instrumental arrangement for determination of the K-emission of graphite. (b) Diagrammatic sections of mounted graphite single crystals. plete the range of observed orientations, but it allowed the examination of flakes of both natural and pyolytic graphite in which the crystal deformation caused by the grinding and pol&hing process was absent, and gave the curve (No. 1, Fig. 1) in which the r-band intensity was perceptibly the lowest. The curves given in Fig. 1 are a selection chosen from many very similar curves, to show the ____
and W L Boun H Brolh.
R Glocker
Fig. 2. K-emission profiles of’ gral)hite taken from the literature. These curccs have been arranged by alignment of the v and v peaks, in order (I- 16) of increasing intensity of the r peak. The original authors’ estimate (when known) is shown bv a mark at 45 x on the cllrve. (see I’able below):
76
LETTERS
TO I-HE EDITOR which, set along the wavelength axis (one for the n-band, five for the o-band) summate to give very closely observed X-ray intensities emitted in the ‘a’ and ‘c’ directions. These parameters are appended m Table 1. The curves so derived for the emission perpendicular to the basal plane are shown in Fig. 4(c). It is hoped that the publication of this data will lead to the derivation of a clearer picture of the orbital structure of graphite, which has in the past been the subject of much interest [21-381. It may also be appropriate to point out that the experimental method here described, is ideally adapted to the rapid measurement of anisotropy in bulk specimens of graphite. Acknowledgement-The author is indebted to Dr. I. F. Ferguson of RFL, Springfields, Preston, for providing the samples of natural graphite, and carrying out the Debye-Scherrer measurements described above. A. A. McFARLANE National Centre of Tribology, Risley Engineering and Materials Laboratory, U.K.A.E.A. R&y Warring-ton,Lanes, England
Fig. 4(a). Taken from Ref. [2]. (b) Polarisation of the graphite K-emission derived from observations made with the OHM crystal (2~ = 63.3 A). (c) Graphite K-emission perpendicular to the basal planes, (virtually all a-band) expressed as a series of Gaussian distributions.
mode of variation between the limits exemplified by curves 1 and 20. They also demonstrate that widely differing modifications of graphite fit into this family of curves. In no case has a polycrystalline result been given that could not have been duplicated by the appropriate orientation of a single crystal. Making use of the fact that the OHM crystal is a polarising analyser for the carbon K-emission, it is possible to divide the graphite K-band into three parts; firstly, the radiation emitted parallel to the basal planes with its electric vector perpendicular to the basal planes; secondly, the radiation emitted. perpendicular to the basal planes with its electric vector parallel to the basal planes; and finally, an intermediate band undistinguishable by polarisation. These three bands (Fig. 4b) are shown under Co&on and Taylor’s predicted emission (Fig. 4a). It has also been observed that it is possible to derive from the OHM experimental data the parameters of six gaussian distributions
REFERENCES 1. McFarlane A. A., 6th Nat. ConjI Sot. Electron Probe Microanalysts Am., Pittsburgh (1971). 2. Coulson C. A. and Taylor R., Proc. Phys. Sot. A65,815 (1952). 3. Ergun S. and Weisweiler W., Carbon 8, 101 (1970). 4. Sagawa T.,J. Phys. Soc.Japun, 21,49 (1966). 5. Prins J. A., 2. Phys. 69,618 (1931). 6. Renninger M., 2. Phys. 78,510 (1932). 7. Broili H., Glocker R. and Kiessig H., 2. Phys. 92,27 (1935). 8. Siegbahn M. and Magnusson T., Z. Phys. 96, l(l935). 9. Hautot A., Ann Phys. 2nd Ser. 4, July-Aug. (1935). 10. Skinner H. W. B., Rep. Prog. Phys. 5,257 (1938). 11. Skinner H. W. B., Phil. Trans. A239,95 (1940). 12. Chalklin F. C., Proc. Roy. Sot. (London) A194, 42 (1948). 13. Henke B. L., White R. and Lundberg B., J. A@. Phys. 48,98 (1956). 14. Lukirskii A. P., Izu. Nauk SSSR. Phys. Ser. NO. 8,25, (1961). 15. Ong P. S., Pittsburgh ConJ Anal. Chem. A@l. Spect. (1964). 16. Fischer D. W. and Baun W. L., J. Chem. Phys. 43,2075 (1965). 17. Manzione A. V. and Fornwalt D. E., Dev. Appb. Spect. V (1966).
LETTERS
TO THE
18. Holliday J. E.,J. Appl. Phys. S&4720 (1967). 19. Henke B. L. and Lent R. E., Advances in X-ray Analysis Vol. 12, Denver (1968). 20. Weisweiler W., Proc. 5th Int. Conjl X-ray 0ptic.s and Microanalysis, Tubingen (1969). 21. Liefeld R. J., Hanzely S., Kirby T. B. and Mott D., Advances in X-ray Analysis, vol. 13, p. 373, Denver (1969). 22. Wallace P. R., Phys. Rev. 71, (1947). C. A., Nature, London 159,265(1947). 23. Co&on 24. Barrio1 J., et al., J. Chim. Phys. 4’1,432 (1950). 25. Brennan R. O., J. Chem. Phys. 20, 1,40 (1952). W. E. and Co&on C. A., Proc. 26. Duncanson Phys. Sot. A65,815 (1952). 27. Lomer W. M., Proc. Roy. Sot. A227,330 (1955). D. F., Proc. Roy. Sot. A227,349 (1955). 28. Johnston
29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39.
77
EDITOR
Johnston D. F., Proc. Roy. Sot. A227,359 (1955). Johnston D. F., Proc. Roy. Sot. A237,48 (1956). Yamazaki M., J. Chem. Phys. 26,930 (1957). McClure J. W., Phys. Rev. 108,612(1957). Slonczewski J. C. and Weiss P. R., Phys. Rev. 109,3,272 (1958). Nozieres P., Phys. Rev. 109,5, 1510 (1958). Peacock T. E. and McWeeny R., Pror. Phys. Sot. LXXIV, 384 (1959). Dutta A. K., Proc. Phys. Sot. LXXIV, 604 (1959). McClure J. W., Proc. 4th Carbon Conf., p. 177, Pergamon Press, Oxford (1960). Some D. E., Proc. 4th Carbon Conf., p. 183, Pergamon Press, Oxford (1960). Felsteiner J., Fox R. and Kahane S., Phys. Lett. 33A, 442 (1970).
APPENDIX Table
I. Parameters
of six gaussian distributions the experimental results
Mean photon energy (eV)
Width of Gaussian (a)
Cl
281.4 279.2
cs
276,s
1.1 1.0 1.1 16 1.6 1.6
Identifying Symbol rr
‘T:3
m.I or,
274.7 270.7 266.5
Maximum relative intensity 1000 825 800 530 200 70
which may be summated approximately Axis of maximum emission a
Minimum relative intensity
to describe
Axis of minimum emission
50
c.
C
600
il
c
600 350 140 10
C C
c
il
a a a
TO THE
is
EDITOR
defects inside of crystallites by atoms from the disordered phase which leads to a quick disappearance of localized spin centers. These defects probably appear when a layer is deposited onto a strongly overcooled substrate[5], and a small amount of activation energy suffices to anneal them out. The change in structure is seen clearly on the electron microscopic photographs of the carbon film evaporated under argon pressure 8 X lo-‘Tr: (a) before heattreatment, (b) after heattreatment to 500°C (Fig. 2). In heattreated layer there may be seen strongly marked canals which separate the individual carbon areas. This is, maybe, evidence for the contraction of the material at the cost of a diminution of the disordered phase. The constant value of the contribution of carriers in the total ESR signal, in this situation, is probably connected with the constant size of crvstallites in the HTT interval considered. How-
ever, a classical interpretation of them as free current carriers, considering the results concerning the energy of activation and the electric conduction might be questionable.
Polarised Emission of the K-band by Graphite Single Crystals
tion varies with the wavelength, as may be seen in Fig. 1, where a selection of the OHM results are arranged in a series to show the change in emission between the ‘a’ and ‘c’ axes. These results confirm that Ergun and Weisweiler [3] were correct in rejecting the analysis of Sagawa[4], although premature in assuming that the K-emission could not be further resolved. Data from the literature on the K-emission of graphite and carbon[2-191 has been arranged in an analogous manner in Fig. 2. Although exact comparisons cannot be drawn between the OHM results and the literature data, the same family of curves can be recognised in each. The literature is understandably sparse in certain parts of the range, but there is close similarity in both sets of data relating to randomly-oriented polycrystalline material. It may be concluded, therefore, that the results from the OHM crystal are unlikely to be vitiated by large changes in sensitivity over the range of the carbon K-band, such as the ‘enhanced reflectivity’ effect demonstrated by Liefeld et al. [20] in the diffraction of oxygen K-radiation by the potassium acid phthalate crystal. Debye-Scherrer powder photographs of the material examined indicated that (i) the pyrolytic graphite was entirely hexagonal, (ii) the particular sample of natural graphite contained an estimated 30 per cent of rhombohedral graphite, and (iii) the vitreous carbon displayed no sharp lines at all. The
(Received 14 August 1972) The author has recently investigated the K-bands emitted by some allotropes and compounds of carbon, using a crystal of octadecyl hydrogen maleate (OHM) as the wavelength-resolving element, in an electron probe microanalyser [l]. The lattice spacing of the OHM analysing crystal is such (2d = 63.35 A) that the Bragg and Brewster angles coincide for carbon K-radiation; thus only radiation with its electric vector perpendicular to the Rowland circle plane is detected at this wavelength. The OHM crystal therefore behaves as a polarising analyser for carbon K-radiation. Samples of natural graphite containing large single crystals, pyrolytic graphite, vitreous carbon and carbon fibre were examined in the instrument described, above, at various orientations relative to the Rowland circle plane, and the prediction of Co&on and Taylor [2] that the r and u bands emitted by a graphite single crystal would show polarisation, has been confirmed. The m-band is emitted parallel to the ‘a’ axis with its electric vector parallel to the ‘c’ axis, and is almost totally polarised. The u-band is partially polarised, the major emission being parallel to the ‘c’ axis with the electric vector parallel to the ‘a’ axis, and the degree of polarisa-
Institute oj Physics Nicholas Copernicus Torun, Poland
S. ORZESZKO Unitlersity
REFERENCES 1. Mrozowski S., Carbon 3,305 (1965); 4,227 (1966); 6, 841 (1968); Arnold G. and Mrozowski S., ibid 6,243 (1968). 2. Antonowicz K., Orzeszko S., Rozp&ch Szczurek T., Carbon 5,261 (196’7). 3. Orzeszko S., to be published.
F. and
4. Presland A. E. B. and White J. R., Carbon 7, 77 (1969). 5. Boiko B. T., Palatnik L. S. and Derevyanchenko A. S., DAN SSSR 2, 179 (1968).
LETTERS
74
TO THE EDITOR
Angle between
I
Material
and the ‘a’ axis of the
mounting
specimen at the
CUIW No.
Rowland circle plane
prepared
Material Pyrolyticgraphite,
surface
method (see Fig. 3)
00
I
mount
0”
I
mO”nt
II=-
I
mount
0”
1 mO”“t
sample ‘A’ 2
Natural graphite (Kropfmiihl)
3
Natural graphite (Kropfmuhl)
4
Pyrolytrc graphite, sample ‘B’
5
Natural graphite
20”
I mount
30
I mount
20”
559 mount
(Kropfmiihl) 6
Natural graphite (Kropfmtihl)
‘i
Natural graphite (Kropfmiihl)
8
Axes 1 to mount surface
Carbon fibres (21 Carbolon)
9
Natural graphite
30--
55” mount
40”
1 mount
(Kropfmbhl) 10
Natural graphite (Kropfmhhl)
11
Paracrystalline
carbon,
Orientation
non-critical
carbon,
Orientation
non-critical
sample ‘A’ 12
Paracrystalline sample ‘B’
13
Natural graphite
50
55” mo”nt
60”
55” mount
70”
55” mount
90’
1 mo”“t
90”
i mount
(Kropfmiihl) 14
Natural graphite (Kropfmiihl)
15
Natural graphite (Kropfmhhl)
16
Pyrolytic graphite, sample ‘B’ Pyrolytic graphite,
265
260
275
270
265
eV
/
sample ‘A’ Carbon tihres
Axes 1 to Rowland circle plane
(21 Carholon)
Fig. 1. K-emission profiles of graphite obtained using the octadecyl hydrogen maleate crystal (see Table top right).
specimen samples were mounted in a conducting metallographic medium, and carefully abraded and polished, so that the orientation of the embedded material relative to the finished surface was accurately known. Ideally, the graphite would have been mounted in a miniature goniometer stage, adjustable under vacuum, to cover the required range of angular relations between the crystal and the X-ray spectrometer. Since the specimen stage of the micro-analyser could only be used to rotate the mounted crystals on an axis coincident with that of the light microscope (see Fig. 3 for a ray diagram of the instrument) it was necessary to mount the graphitic specimens in several orientations relative to the reference plane of the specimen stage in order to achieve the required range. The family of curves representing
Natural graphite
80”
I mount
(Kropfmtihl) Natural graphite
90”
parallel mount
(Kropfmiihl)
the K-emissions of graphite at different orientations reported in Fig. 1, are identified by three parameters; firstly, with the emitting material, secondly, with the angle between the Rowland circle plane and the edge of the graphite basal plant at the mount surface, measured using the protractor graticule in the microscope ocular, and finally, with the particular mounting orientation. The mounting orientations used were determined in the following way. It will be seen by reference to Fig. 3, that if the radiation emitted perpendicular to the basal planes of the graphite crystal is to be directed up the axis of the X-ray spectrometer then the crystal must be mounted so that its basal planes make an angle of 55” with the surface of the mount, and is designated ‘55”mount in the code used to identify the curves in Fig. 1.
LETTERS
TO THE
EDITOR
Similarly, if the spectrometer is to receive radiation when the basal planes of the graphite crystal are parallel to the Rowland circle plane of the Xray spectrometer then the crystal must be mounted with its basal plane perpendicular to the surface of the mount: this is designated ‘I mount’. Samples of flake graphite and carbon fibres were also mounted by direct adhesion of the basal planes (or fibre bundles) parallel to the surface of the mount. This method of mounting (designated ‘parallel niount’) was not eSSent?dl geometrically to com-
H W.B
Light mIcroscope electron beam \
Skinner
1
Mount
55” InO”“+ (b)
H.WE.
Skinner
H.W.B.
Skinner
Fig. 3(a). Instrumental arrangement for determination of the K-emission of graphite. (b) Diagrammatic sections of mounted graphite single crystals. plete the range of observed orientations, but it allowed the examination of flakes of both natural and pyolytic graphite in which the crystal deformation caused by the grinding and pol&hing process was absent, and gave the curve (No. 1, Fig. 1) in which the r-band intensity was perceptibly the lowest. The curves given in Fig. 1 are a selection chosen from many very similar curves, to show the ____
and W L Boun H Brolh.
R Glocker
Fig. 2. K-emission profiles of’ gral)hite taken from the literature. These curccs have been arranged by alignment of the v and v peaks, in order (I- 16) of increasing intensity of the r peak. The original authors’ estimate (when known) is shown bv a mark at 45 x on the cllrve. (see I’able below):
76
LETTERS
TO I-HE EDITOR which, set along the wavelength axis (one for the n-band, five for the o-band) summate to give very closely observed X-ray intensities emitted in the ‘a’ and ‘c’ directions. These parameters are appended m Table 1. The curves so derived for the emission perpendicular to the basal plane are shown in Fig. 4(c). It is hoped that the publication of this data will lead to the derivation of a clearer picture of the orbital structure of graphite, which has in the past been the subject of much interest [21-381. It may also be appropriate to point out that the experimental method here described, is ideally adapted to the rapid measurement of anisotropy in bulk specimens of graphite. Acknowledgement-The author is indebted to Dr. I. F. Ferguson of RFL, Springfields, Preston, for providing the samples of natural graphite, and carrying out the Debye-Scherrer measurements described above. A. A. McFARLANE National Centre of Tribology, Risley Engineering and Materials Laboratory, U.K.A.E.A. R&y Warring-ton,Lanes, England
Fig. 4(a). Taken from Ref. [2]. (b) Polarisation of the graphite K-emission derived from observations made with the OHM crystal (2~ = 63.3 A). (c) Graphite K-emission perpendicular to the basal planes, (virtually all a-band) expressed as a series of Gaussian distributions.
mode of variation between the limits exemplified by curves 1 and 20. They also demonstrate that widely differing modifications of graphite fit into this family of curves. In no case has a polycrystalline result been given that could not have been duplicated by the appropriate orientation of a single crystal. Making use of the fact that the OHM crystal is a polarising analyser for the carbon K-emission, it is possible to divide the graphite K-band into three parts; firstly, the radiation emitted parallel to the basal planes with its electric vector perpendicular to the basal planes; secondly, the radiation emitted. perpendicular to the basal planes with its electric vector parallel to the basal planes; and finally, an intermediate band undistinguishable by polarisation. These three bands (Fig. 4b) are shown under Co&on and Taylor’s predicted emission (Fig. 4a). It has also been observed that it is possible to derive from the OHM experimental data the parameters of six gaussian distributions
REFERENCES 1. McFarlane A. A., 6th Nat. ConjI Sot. Electron Probe Microanalysts Am., Pittsburgh (1971). 2. Coulson C. A. and Taylor R., Proc. Phys. Sot. A65,815 (1952). 3. Ergun S. and Weisweiler W., Carbon 8, 101 (1970). 4. Sagawa T.,J. Phys. Soc.Japun, 21,49 (1966). 5. Prins J. A., 2. Phys. 69,618 (1931). 6. Renninger M., 2. Phys. 78,510 (1932). 7. Broili H., Glocker R. and Kiessig H., 2. Phys. 92,27 (1935). 8. Siegbahn M. and Magnusson T., Z. Phys. 96, l(l935). 9. Hautot A., Ann Phys. 2nd Ser. 4, July-Aug. (1935). 10. Skinner H. W. B., Rep. Prog. Phys. 5,257 (1938). 11. Skinner H. W. B., Phil. Trans. A239,95 (1940). 12. Chalklin F. C., Proc. Roy. Sot. (London) A194, 42 (1948). 13. Henke B. L., White R. and Lundberg B., J. A@. Phys. 48,98 (1956). 14. Lukirskii A. P., Izu. Nauk SSSR. Phys. Ser. NO. 8,25, (1961). 15. Ong P. S., Pittsburgh ConJ Anal. Chem. A@l. Spect. (1964). 16. Fischer D. W. and Baun W. L., J. Chem. Phys. 43,2075 (1965). 17. Manzione A. V. and Fornwalt D. E., Dev. Appb. Spect. V (1966).
LETTERS
TO THE
18. Holliday J. E.,J. Appl. Phys. S&4720 (1967). 19. Henke B. L. and Lent R. E., Advances in X-ray Analysis Vol. 12, Denver (1968). 20. Weisweiler W., Proc. 5th Int. Conjl X-ray 0ptic.s and Microanalysis, Tubingen (1969). 21. Liefeld R. J., Hanzely S., Kirby T. B. and Mott D., Advances in X-ray Analysis, vol. 13, p. 373, Denver (1969). 22. Wallace P. R., Phys. Rev. 71, (1947). C. A., Nature, London 159,265(1947). 23. Co&on 24. Barrio1 J., et al., J. Chim. Phys. 4’1,432 (1950). 25. Brennan R. O., J. Chem. Phys. 20, 1,40 (1952). W. E. and Co&on C. A., Proc. 26. Duncanson Phys. Sot. A65,815 (1952). 27. Lomer W. M., Proc. Roy. Sot. A227,330 (1955). D. F., Proc. Roy. Sot. A227,349 (1955). 28. Johnston
29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39.
77
EDITOR
Johnston D. F., Proc. Roy. Sot. A227,359 (1955). Johnston D. F., Proc. Roy. Sot. A237,48 (1956). Yamazaki M., J. Chem. Phys. 26,930 (1957). McClure J. W., Phys. Rev. 108,612(1957). Slonczewski J. C. and Weiss P. R., Phys. Rev. 109,3,272 (1958). Nozieres P., Phys. Rev. 109,5, 1510 (1958). Peacock T. E. and McWeeny R., Pror. Phys. Sot. LXXIV, 384 (1959). Dutta A. K., Proc. Phys. Sot. LXXIV, 604 (1959). McClure J. W., Proc. 4th Carbon Conf., p. 177, Pergamon Press, Oxford (1960). Some D. E., Proc. 4th Carbon Conf., p. 183, Pergamon Press, Oxford (1960). Felsteiner J., Fox R. and Kahane S., Phys. Lett. 33A, 442 (1970).
APPENDIX Table
I. Parameters
of six gaussian distributions the experimental results
Mean photon energy (eV)
Width of Gaussian (a)
Cl
281.4 279.2
cs
276,s
1.1 1.0 1.1 16 1.6 1.6
Identifying Symbol rr
‘T:3
m.I or,
274.7 270.7 266.5
Maximum relative intensity 1000 825 800 530 200 70
which may be summated approximately Axis of maximum emission a
Minimum relative intensity
to describe
Axis of minimum emission
50
c.
C
600
il
c
600 350 140 10
C C
c
il
a a a