Retention of Ions Implanted at Non-Normal Incidence
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RETENTION OF IONS IMPLANTED AT NON-NORMAL INCIDENCE K.S. GRABOWSKI*, N.E.W. HARTLEY**, C. R. GOSSETT*, and I. MANNING* *Naval Research Laboratory, Washington, D.C. 20375, **Georgetown University, Washington, D.C. 20007 (Present address: AERE Harwell, UK) ABSTRACT
Future applications of ion implantation require a knowledge of how the retention of implanted ions varies with angle of ion incidence. In this work the retention of 150-keV Ar,Ti,Cr,and Ta ions in AISI-M50 and 52100 bearing steels was measured for incidence angles up to 600 off normal. Fluences between 3x10 15 and 3x1O1 7 /cm 2 were used, typically on 3/8" diameter cylindrical samples. Retention was measured for Ar, Ti, and Cr by ion induced x-ray emission and for Ta by backscattering of He ions. Range and sputtering parameters needed for model calculations were experimentally determined from Ta-implanted thin Fe film samples. Generally, at the low-fluence limit a near-cos 4 dependence obtained while at the high-fluence limit a (cos @)8/3 dependence applied where e is the angle between the sample normal and the beam direction. INTRODUCTION
It is clear that in practical applications it will be necessary to ion implant some metal workpieces at non-normal angles of incidence. Not surprisingly, there is concern that large angles of incidence may limit the benefits obtainable by line-of-site ion implantation. Singer and Jeffries [1] have provided recent evidence that the angle of incidence can be an important factor in determining the friction and wear properties of Ti-implanted steel, substantiating some of these concerns. Since the benefits of ion implantation are typically related to the concentration of the ions at the surface, and the durability of this improvement is likely related to the depth of the distribution, it is appropriate to consider the integrated quantity of implanted ions remaining in the target (the retained dose). This work addresses how the retained dose of Ar, Ti, Cr, and Ta ions implanted into steel depends on the incidence angle of the ion beam. EXPERIMENTAL PROCEDURE
The angle of beam incidence was controlled by implanting a scanned ion beam into symmetrically curved surfaces and into flat samples inclined to the beam. In the majority of this work, Ar, Ti, and Ta ions were implanted into stationary 3/8" diameter cylinders of AISI-M50 and 52100 martensitic bearing steels. M50 has a composition of Fe-4Cr-4Mo-1V-O.8C (in weight percent) and 52100 has a composition of Fe-1.5Cr-I.OC. Both steels were in a hardened and polished condition. A Ta slit 3/16" wide limited the 150-keV ion beams to a specific band across each cylinder. The slit was translated along the cylinder's axis to obtain separate bands for fluences between 3 x 101b and 3 x lol7/cm2 (all fluences specified are for normal incidence). Typically, the chamber pressure 2was 3 x 10-6 torr and the beam current density was between 1 and 15 vA/cm during these implantations. Mat.
Res. Soc. Symp. Proc. Vol.
27 (1984) @Elsevier Science Publishing Co.,
Inc.
616
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