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Reply to comments of H.E. Bishop and J.C. Rivière on “Angular dependences in electron-excited auger emission”
SURFACE
REPLY
SCIENCE 17 (1969) 448-449 0 North-Holland
TO COMMENTS “ANGULAR
OF H. E. BISHOP
DEPENDENCES AUGER
Publishing Co., Amsterdam
AND J. C. RIVIERE
ON
IN ELECTRON-EXCITED EMISSION”
Received 11 June 1969
Bishop and Riviere state that it is necessary to consider the path length through the element dx in order to find the dependence of Auger emission on excitation angle, fi (ref. 1). Their correction would be reasonable if the primary electrons lost a small fraction of their total energy in each ionizing event; but under the conditions of the experiment (primary energy 3 keV and Auger energies ranging over several hundred eV) this is not the case. As Palmberg has noteds), the primary electrons are quite thoroughly scattered in direction as they proceed into the material. It is thus reasonable to assume a sort of diffusion model in which processes occurring inside the material are independent of the initial direction of the electron beam, except for the variation of incident beam density. The correction proposed by Bishop and Rivibre regarding /?-dependence leads to a serious discrepancy between predicted and observed results. The observed dependence thus may be interpreted as verifying Palmberg’s conclusion regarding scattering of the primaries. The comment, regarding my assumption of an exponential decrease in ionization with depth, is well taken. It turns out, however, that whether one assumes this decrease, a constant excitation (approximated by the exponential decrease with large I,) or a constant excitation to a finite range and zero thereafter, the value of the result changes very little so long as IA is much less than the primary electron range. Since the results are quite insensitive to these details, it would be wise to choose the model with the greatest physical appeal, particularly if it leads to mathematical simplicity. The author is grateful cation and to N. Punsky
to Drs. Bishop and Riviere for this useful clarififor stimulating discussions on this matter. L. A. HARRIS
General Electric Research Schenectady,
and Development
New York 12301,
U.S.A. 448
Center,
L. A. HARRIS
References 1) H. E. Bishop and J. C. Rivibre, Surface Sci. 17 (1969) 446. 2) P. W. Palmberg, Appl. Phys. Letters 13 (1968) 183.
449
REPLY
SCIENCE 17 (1969) 448-449 0 North-Holland
TO COMMENTS “ANGULAR
OF H. E. BISHOP
DEPENDENCES AUGER
Publishing Co., Amsterdam
AND J. C. RIVIERE
ON
IN ELECTRON-EXCITED EMISSION”
Received 11 June 1969
Bishop and Riviere state that it is necessary to consider the path length through the element dx in order to find the dependence of Auger emission on excitation angle, fi (ref. 1). Their correction would be reasonable if the primary electrons lost a small fraction of their total energy in each ionizing event; but under the conditions of the experiment (primary energy 3 keV and Auger energies ranging over several hundred eV) this is not the case. As Palmberg has noteds), the primary electrons are quite thoroughly scattered in direction as they proceed into the material. It is thus reasonable to assume a sort of diffusion model in which processes occurring inside the material are independent of the initial direction of the electron beam, except for the variation of incident beam density. The correction proposed by Bishop and Rivibre regarding /?-dependence leads to a serious discrepancy between predicted and observed results. The observed dependence thus may be interpreted as verifying Palmberg’s conclusion regarding scattering of the primaries. The comment, regarding my assumption of an exponential decrease in ionization with depth, is well taken. It turns out, however, that whether one assumes this decrease, a constant excitation (approximated by the exponential decrease with large I,) or a constant excitation to a finite range and zero thereafter, the value of the result changes very little so long as IA is much less than the primary electron range. Since the results are quite insensitive to these details, it would be wise to choose the model with the greatest physical appeal, particularly if it leads to mathematical simplicity. The author is grateful cation and to N. Punsky
to Drs. Bishop and Riviere for this useful clarififor stimulating discussions on this matter. L. A. HARRIS
General Electric Research Schenectady,
and Development
New York 12301,
U.S.A. 448
Center,
L. A. HARRIS
References 1) H. E. Bishop and J. C. Rivibre, Surface Sci. 17 (1969) 446. 2) P. W. Palmberg, Appl. Phys. Letters 13 (1968) 183.
449