The diffusion of Ti through Pt thin films was studied, at 200 to 600C, by using 5 different Pt/Ti bilayers which ranged in thickness from 3.5 to 80nm (figure 22, table 27). The accumulation of Ti at the Pt surface layer was measured by means of X-ray photo-electron spectroscopy, in order to deduce the grain boundary diffusion coefficient. The diffusivity values were calculated by using 2 different analytical methods which assumed the operation of type-C kinetics. In the case of Pt layers which were thicker than 20nm, the activation energy for Ti diffusion was found to be equal to 1.22eV. In the case of Pt layers which were thinner than 20nm, there was a thickness dependence of the diffusion kinetics. This resulted in activation energies which were as low as 0.21eV. The X-ray photo-electron spectroscopic results revealed no evidence of Pt-Ti alloy formation in the layers. This suppression of alloy formation was attributed to the presence of O at the Pt/Ti interface during layer deposition.

Determination of Diffusion in Polycrystalline Platinum Thin Films. M.DiBattista, J.W.Schwank: Journal of Applied Physics, 1999, 86[9], 4902-7

 

Figure 22

Grain Boundary Diffusivity of Ti in Pt Films

 

Table 27

Arrhenius Parameters for the Grain Boundary Diffusivity of Ti in Pt Films

 

Thickness (nm)

Technique

Do (cm2/s)

E (kJ/mol)

80

Holloway-McGuire

7.6 x 10-6

121

80

Hwang-Balluffi

2.2 x 10-6

122

50

Holloway-McGuire

4.7 x 10-6

114

50

Hwang-Balluffi

3.5 x 10-8

105

20

Holloway-McGuire

1.4 x 10-8

99.5

20

Hwang-Balluffi

2.5 x 10-9

94.3

6.5

Holloway-McGuire

2.1 x 10-11

57.7

6.5

Hwang-Balluffi

1.2 x 10-11

61.8

3.5

Holloway-McGuire

8.4 x 10-15

19.8

3.5

Hwang-Balluffi

3.7 x 10-15

21.5