ARGON-TITANIUM HOLLOW CATHODE AFTERGLOW

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ARGON-TITANIUM HOLLOW CATHODE AFTERGLOW

D. Ohebsian, N. Sadeghi, C. Trassy, J. Mermet

To cite this version:

D. Ohebsian, N. Sadeghi, C. Trassy, J. Mermet. ARGON-TITANIUM HOLLOW CATH- ODE AFTERGLOW. Journal de Physique Colloques, 1979, 40 (C7), pp.C7-99-C7-100.

�10.1051/jphyscol:1979749�. �jpa-00219455�

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JOURNAL DE PHYSIQUE CoZZoque C7, suppZ6ment n07, Tome 40, JuiZZet 1979, page C7- 99

ARGON-TITANIUM HOLLOW CATHODE AFTERGLOW

D. 0hebsianN, N. 5adeghii, C. Trassy and J.M. Merrnet i x

* ~ a b o r a t o i r e de Spectrorngtrie Physique, Universitg S c i e n t i f i q u e e t Me'dicaZe de GrenobZe, BP. 53, 38041 GrenobZe cedex, France.

*'~aboratoire de Physico-Chirnie IndustrieZZe I.N.S.A. 69621 ViZZeurbanne Cedex, France.

The mechanisms of t h e energy t r a n s f e r between zetas- measured by the o p t i c a l absorption technique (4).

t a b l e and ionic species of t h e rare gases and metal- For both emission i n t e n s i t y and absorption meas-- l i c atoms a r e responsible f o r the l a s e r action i n ments, t h e photon counting and the data a c c m l a - rare gas-metal vapor discharge. Knowledge of t h e t i o n techniques (5) were used.

mechanisms of t h e production and l o s s of t h e metal- l i c species i n a rare gas plasma i s therefore veSy inportant. The pulsed afterglow technique has a l - ready been used t o study the excited metallic ion production i n He-Cd, He-Zn ( 1 ) and He-Pb ( 2 ) discharge. In these e x p e r h n t s , the discharge c e l l containing metal p e l l e t s i s placed inside an oven t o produce t h e metal vapor a t desired pressure. But this technique cannot be used f o r the m t a l s having a high boiling point. For example a density of 10 ¹¹ atoms i s obtained a t 210°C f o r Zinc but a t 1300°C f o r Titanium.

A s-le way t o produce these metal vapors i s t h e hollow cathode discharge (3). The p r a c t i c a l advan- tage of t h i s process i s t h a t t h e metal vapor i s ge- netared by t h e cathode sputtering a t room tempera-

Fig. (2) shows t h e evolution of the population of

t h e 3 f i n e structure levels

ah2,

₃and

i3~4

^{( a t}

0, 170 and 387 cm1 respectively) of t h e Titanium w u n d s t a t e atoms i n a 0.31 t o r r Argon afterglow.

In t h i s figure we can observe : i ) Titanium atom density Lbtained i s about 10'' atoms em3. i i ) d- ing t h e d i s c h a r g t h e p o p ~ l a t i o n ~ of the three a3FJ levels a r e i n equilibrium by c o l l i s i o n s with t h e energetic electrons of the discharge but a t l a t e afterglow they are i n equilibrium by collisions with t h e Argon atoms a t room temperature. i i i ) dur-

t

ture.

In t h i s c o m i c a t i o n we report t h e first r e s u l t s obtained i n t h e afterglow of a Titanium hollow cathode i n Argon.

Fig. (1) shows the e x p e r h n t a l s e t up. The Titani- um cylindrical cathode (din = 9 mn, 2 = 25 m) i s located inside a quartz c e l l . The Argon buffer gas pressure i s varies from 0.2 t o 5 t o r r and t h e gas flow i s about 1 m sec-'. The discharge current and duration are about 20 mA and 100 vsec respectively.

The d e n s i t i e s of t h e Titanium atoms and ions i n t h e i r ground s t a t e s and Argon metastable atoms was

Fig. 2 : T i m variation of t h e ~ i ( a ~ F ~ ) density i n FLg. 1 : Experimental arrangement a 0.31 t o r r Argon arterglow

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979749

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i n g the f i r s t 100 usec of t h e afterglow there i s a t r a n s f e r of populatiol from t h e a 3 ~ 4 t o t h e a 3 F3 and a3p2 and from a 3 F t o a3F2. i v ) i n l a t e a f t e r

3

glow t h e population of the a3pJ levels decays accord- ing t o an exponential law with a decay t h e p r o p o r t i o n a l t o the Argon atom density, Fig. (3). From t h i s last observation we can conclude t h a t t h e prin- c i p a l mechanism of t h e l o s s of t h e metal vapor den- s i t y i n t h e afterglow i s t h e diffusion of t h e Tita- nium atoms across t h e buffer gas and t h e i r deposi- t i o n on t h e cathode w a l l . The decay t b ( r ) of t h e T i ( a FJ) atoms i n Argon afterglow 3 i s r =

,

where

Do

N is the Argon atom density, A i s the diffusion lengh and Do i s the diffusion coefficient. From t h e slope of Fig. ( 3 ) we can deduce : Do = 3.1 1018 atoms cm-' sec -1

.

We have a l s o observed the population of t h e some ex- c i t e d l e v e l s of Ar, &+, T i and Ti+ i n t h e afterglow.

Fig. ( 4 ) shows t h e time variation of the population of the Ar* (5p 15/21 3), Ar+* (4p 4 ~ 7 / 2 )

,

Ti* (y 3~;)

+*

⁴

and T i ( z G ; , ~ ) levels. The lifetirne of a l l these

n

l e v e l s being d f t h e order of

lo-'

sec, t h e observed time variation is t h a t of the mechanisms responsible f o r t h e population of these levels i n afterglow. For t h e ~ i *

,

^Ar*and Ar+* populations, we f i n d t h e well known behaviour of t h e electron-ion recombination populated levels, t h e involved ions

I

2 3 4

5

6

16 -3 Density

of

A r atoms (10 c m )

Fig. 3 : Variation of t h e decay t i m of t h e T i ( a F ~ ) 3 atoms versus t h e Argon atom density

Fig. 4 : T i m variation of t h e population of Ar

* , + +*

Ar+*, T i

,

T i and T i i n a 0.6 t o r r Argon afterglow.

being Ti+, A r + and Ar++ respectively. On t h e other hand, the behaviour of t h e i n t e n s i t y decay of t h e whole T i I1 t r a n s i t i o n s i s e n t i r e l y d i f f e r e n t and seems t o show t h a t t h e (Ti+)* l e v e l s are populated by an energy t r a n s f e r process. The s i m i l a r i t y i n population of a l l t h e (Ti+)* l e v e l s seems point out that t h e excitation mechanism i s a charge trans- f e r process A r +

+

T i + Ar

+

(Ti+)*

+

AE r a t h e r than t h e Penning ionization by Argon E t a s t a b l e atoms.

The time decay of t h e ground s t a t e ~ i + ions, obtained by o p t i c a l absorption m a s m m n t s i s a l s o shown i n Fig. (4 )

.

FaFEmCES :

(1) G.J. COLLINS, J. Appl. PhyS., 44 '(1973) 4633 (2) L.A. CROSS and M.C. GOKAY, J. Appl. F'hys., 49

(1978) 2639

(3) F.J. de H O G e t a l , J. Appl. Phys., 48 (1977) 3701

(4) J. SABBAGH and N. SADEGHI, J.Q.S.R.T., 17 (1977) 297

(5) N. SADEGHI and J. SABBAGH, Phys. Rev. A, 16 (1977) 2336.