Research was carried out into fluctuations in the ion thermo-emission currents (of the 5 alkali metals) from W surfaces. The activation energy for Cs surface diffusion was deduced to be equal 0.29eV. This so-called noise was generated as a result of adsorbate density fluctuations. The latter caused random changes in the work function, which itself influenced the intensity of the emitted ion current. The methods which were used made it possible to determine the ion desorption energy and the surface diffusion energy for the alkali metals. It was suggested that the activation energy for surface diffusion was related to the ionic radius of the alkali metal by:

E (eV) = 0.88 - 0.33R(วบ)

L.Gladyszewski: Surface Science, 1990, 231[1-2], 120-4

 

Table 325

Diffusion of D and H on the (001) Plane of W

at Temperatures of between 78 and 200K

 

System

Coverage

Regime

Do (cm2/s)

E (kcal/mol)

1H[010]

0.06

fast

6.8 x 10-10

1.5

1H[010]

0.06

slow

1.0 x 10-10

1.6

1H[010]

0.3

fast

5.2 x 10-10

2.2

1H[010]

0.3

slow

1.4 x 10-10

2.4

1H[010]

0.6

fast

4.0 x 10-10

2.0

1H[010]

0.6

slow

1.7 x 10-10

2.1

1H[010]

0.9

fast

2.4 x 10-9

2.6

1H[010]

0.9

slow

8.3 x 10-10

2.7

1H[100]

0.06

fast

5.8 x 10-10

1.9

1H[100]

0.06

slow

1.9 x 10-10

2.0

1H[100]

0.3

fast

3.2 x 10-11

1.3

1H[100]

0.3

slow

1.7 x 10-11

1.5

1H[100]

0.6

fast

1.7 x 10-10

1.7

1H[100]

0.6

slow

5.3 x 10-11

1.7

1H[100]

0.9

fast

2.0 x 10-9

2.4

1H[100]

0.9

slow

8.2 x 10-10

2.4

2H[010]

0.06

fast

8.4 x 10-11

1.2

2H[010]

0.06

slow

3.4 x 10-11

1.3

2H[010]

0.3

fast

8.2 x 10-10

2.4

2H[010]

0.3

slow

3.6 x 10-10

2.5

continued

 

Table 325 (continued)

Diffusion of D and H on the (001) Plane of W

at Temperatures of between 78 and 200K

 

System

Coverage

Regime

Do (cm2/s)

E (kcal/mol)

2H[010]

0.6

fast

6.1 x 10-11

1.6

2H[010]

0.6

slow

2.1 x 10-11

1.7

2H[010]

0.9

fast

5.2 x 10-11

1.5

2H[010]

0.9

slow

1.2 x 10-11

1.4

2H[100]

0.06

fast

3.0 x 10-9

2.4

2H[100]

0.06

slow

3.4 x 10-10

2.3

2H[100]

0.3

fast

4.4 x 10-10

2.2

2H[100]

0.3

slow

3.9 x 10-11

1.9

2H[100]

0.6

fast

2.1 x 10-10

1.9

2H[100]

0.6

slow

3.4 x 10-11

1.8

2H[100]

0.9

fast

8.1 x 10-10

2.4

2H[100]

0.9

slow

1.2 x 10-10

2.3