EMISSION OF ELECTRONS AND IONS FROM Ar+-ION BOMBARDED SOLID
SURFACES
Katsutoshi Furukawa and Shin-ichi Ohno
Chemistry Division, Japan Atomic Energy Res.
Inst., Tokai-mura, Ibaraki 319-11

Introduction
Electron and ion emission from solid surfaces under bombardment by energetic ions are well known phenomena.
Various models
has been presented to explain qualitative features of the total
yield of emitted electrons or ions. 1 ' 2 )The energy necessary toeject electrons from the solid can be provided from two distinct
sources: the potential energy released upon neutralization and the
kinetic energy of the projectile ion.
But we do not know how toseparate them from each other and whether electrons come from· thecollisions of the projectile with the target atoms or from thecollisions of recoiling atoms inthe solid.
Furthermore, we know
how a sputtering event proceeds but do not know by what mechanism
a fraction of sputterred atoms become ionized.
~lefeel that progress could be made from simultaneous measure-ment of relative ion and electron yield and from measurement ofenergy spectrum of emitted electrons.
Experimentals
Ar+-ion beam was produced by a 100 kV accelerator with aDuoplasmatron, mass-analysed with a double focusing magnet,
and was introduced through a 2-mm limiting aperture onto thespecimen placed in the atmospheric pressure of 10- 7 Torr.
Electrons emitted at 45° angle to the beam were accelerated/deccelerated (by sweeping) to 20 eV energy and analysed by asemispherical-electrostatic analyser with a resolution of E/~E100.
Secondary ions emitted also at 45° were analysed in apole mass spectrometer(ULVAC MSQ-300).

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Results
The targets we used were Al, Si, Ti, Cu, Mo, W, and Pt.
The projectile were 10, 30, and 70-keV Ar+ with current intensity
varying from 10 -9 to 10 -6 A/0.03cm 2 •The total electron yields were found to be in the order:
Al, Pt> Mo> Si, w> Ti >> Cu

B

The ion yields were in the order:
SiAl, Tf> w> Cu> Mo>> Pt>

The observed energy spectrum ofemitted electrons consists of several"lines".
In Fig. 1 is shown thespectrum obtained. using Al as a target
and the components are marked as A, B,Aand C.
Each component behaved differently when the energy or current
intensity of the bombarding Ar+-beam0102030
Electronenergy(eV)
was varied. The heights of the lineFig.l.
Spectrumofl?w energy
A and B increase as the energy orelectrons emitted from Al bombarded. 2current of the ion increases. The
by 5xl0-BA/0.03cm beam of 30 keV
position of line B is around 2.5 toAr+-ion.
3 eV when the bombarding ion energy
is low, but the peak shifts to 3.5~4 eV when the bombarding energy
is 70 keV.
"line C" behaves differently. At bombarding eftergyof 10 keV, the line grows at first rapidly with increasing ion
current (toward ~sao cps at 5xl0- 8A/0.03cm 2 ) and then diminisheswith increase in the ion current. At bombarding energy of 30 and
70 keV, "line C" is weak and increases monotonically with ion
current intensity.
Thus, it is likely that there are several mechanisms operating for the ejection of electrons.In the case of Si and Ti as atarget broad Auger lines due to the target were observed in 20
to 70 eV region.
Moreover, Ar-LMM Auger lines were observed at
120 -- 180 eV when Mo was bombarded.
1) R. A. Baragiola, et al.:Surface Science 90, 240 (1979).
2) P. Williams:ibid., 90, 588 (1979).

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