Depth profile of 18O at the titanium surfaces using the nuclear reaction 18O(p, α)15N

Vacuum/volume 39/numbers Printed in Great Britain

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0042-207X/89$3.00+.00 Pergamon Press plc

123 to 12411989

Depth profile of ‘*O at the titanium the nuclear reaction ‘*O( p, a)15N Lu Xiting

and Xie Yuan,

Department

of Technical

Physics, Peking

surfaces

University,

Beijing,

using

PRC

and Liu Jiarui

and Zheng

Zongshuang,

Institute

of Physics, Chinese Academy

of Sciences,

Beijing,

PRC

The 180(p, M)“N nuclear reaction was used to measure the depth profile of la0 within the near-surface region of titanium. The measurements were performed using a 2 x 1.7 MV tandem accelerator. To reduce the depth resolution value Ax, the target was tilted. A good depth resolution Ax N 30 nm within the surface (< 200 nm) of titanium was obtained. The Fourier-transformation method was used in the data processing.

1. Introduction Measurements of “0 have been described in the references’. It is very important to measure depth profiles of ‘“0 in materials. In order to study the oxidation of metals the isotope “0 usually is used as a tracer element. This paper describes the use of the nuclear reaction “O(p, E) “N to measure the depth profile of “0 within the surface (d 200 nm) of titanium by the energy-analysis method. The principle of the energy-analysis method has been described elsewhere2,‘. The Fourier-transformation method“ was used in the data processing.

40

xl. x-x\

30 E c

z

X-X

-x-x_x-x-xc

i

20

t

1

IO 200

2. Experiment and results The experimental set-up for nuclear reaction analysis is shown in Figure I. The depth profile of “0 was performed using the 2 x 1.7MV tandem accelerator at the Institute of Physics, Chinese Academy of Sciences, Beijing, PRC. The incident proton-energy was fixed at 730 keV. The nuclear reaction cross section near that energy is fairly smooth. The target was tilted to reduce the depthresolution value Ax. The incident and outgoing angles to the surface normal of the sample (target) 0, and 0, were 35’ and 65”, respectively. The a-particles were detected by a surface barrier detector which was fixed at an angle Q relative to the ion beam

I

I

I

I

150

100

50

0

x

(nm)

Figure 2. The depth resolution for “O(p, c()“N direction of 150”. The energy resolution of the detecting system was 22 keV for 5.486 MeV (““Am) particles. The beam current was controlled to around 10 nA to avoid the pulse pile-up from the scattering proton. The pulses from the detector were amplified and analysed with a ND-680 computerized MCA system.

600

-

x

Experimental

0

Depth

spectrum

profile

500-

400

-

Chamber

N

3co-

L-______--___A x (nm)

Figure 1. The chamber for nuclear reaction analysis.

Figure 3. The depth profile. 123

Lu Xiting et al: Depth profile of “‘0

Figure 2 shows the depth resolution AX with depth x using our experimental conditions. A Ax of 30 nm was obtained. The Fourier-transformation method was used in the data processing. In Figure 3 the depth profile of “0 in the titanium film is shown. We can see that the difference between the experimental spectrum and the depth profile is not obvious because the depth resolution is good enough. Ion beam techniques are increasingly popular and nuclear reaction analysis in particular is a non-destructive and simple analysis technique for the depth profiling of “0.

124

Acknowledgements We would like to acknowledge the help of Zhu Peiran and Chen Yipin in running the accelerator for these measurements.

References

’ G Amsel et ul, Nucl Instrum Merh, 149, 713 (1978). ‘G Amsel et rrl, Nucl Instrum Met/z, 92, 481 (1971). ’ A Turos <‘Ial, Nucl Insrrum Meth, Ill, 605 (1973). ‘E Sjmtoft P/ al, Nucl1mtrum Meth, 163, 519 (1979)