FIELD EVAPORATION CHARGE STATE OF BORON
IONS : A TEMPERATURE EFFECT STUDY
A. Menand, C. Martin, J. Sarrau
To cite this version:
A. Menand, C. Martin, J. Sarrau. FIELD EVAPORATION CHARGE STATE OF BORON
IONS : A TEMPERATURE EFFECT STUDY. Journal de Physique Colloques, 1984, 45 (C9),
pp.C9-95-C9-98. <10.1051/jphyscol:1984917>. <jpa-00224395>
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Submitted on 1 Jan 1984
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JOURNAL DE PHYSIQUE
Colloque C9, supplgment au n012, Tome 45, dgcembre 1984
page C9-95
F I E L D E V A P O R A T I O N CHARGE S T A T E O F BORON I O N S :
A TEMPERATURE E F F E C T STUDY
A. Menand, C. Martin and J.M. Sarrau
L a b o r a t o i r e d e Microscopic 1 o n i q u 2 , F a c u Z t d d e s S c i e n c e s d e Rouen,
BP 6 7 , 7 6 1 3 0 M o n t - S a i n t - A i g n a n , F r a n c e
Resume
- - Une e t u d e d e l a c h a r g e d e s i o n s B o r e d v a p o r 6 s p a r e f f e t d e c h a m p ,
m e t e n e v i d e n c e u n e d i f f g r e n c e p o u r l e s Q t a t s d e c h a r g e d e s i o n s B 1 0 et B 1 l .
C e t t e d i f f e r e n c e d d p e n d d e l a t e m p e r a t u r e d e l ' e c h a n t i l l o n . Une e x p l i c a t i o n
d e cet e f f e t d f i a u d 6 p a r t d e s i o n s B b a s s e t e m p e r a t u r e p a r e f f e t t u n n e l
i o n i q u e e s t donnee.
A b s t r a c t - We h a v e o b s e r v e d the m a s s t o c h a r g e r a t i o o f f i e l d e v a p o r a t e d
Boron i o n s . A d i f f e r e n c e b e t w e e n t h e c h a r g e s t a t e o f B I 0 and Bll i o n s i s
o b s e r v e d . T h i s d i f f e r e n c e i s t e m p e r a t u r e d e p e n d e n t . An e x p l a n a t i o n i s g i v e n
i n t e r m s o f i o n i c t u n n e l i n g d e s o r p t i o n o f Boron i o n s a t l o w t e m p e r a t u r e .
1,
an i s o t o p i c variation in f i e l d evaporation
A s i t h a s b e e n p r e v i o u s l y r e p o r t e d 11
c h a r g e s t a t e o f b o r o n ions h a s b e e n o b s e r v e d . T h e p r o p o r t i o n o f B I D i o n s f i e l d
e v a p o r a t i n g a s d o u b l y c h a r g e d i o n s i s f o u n d t o be l e s s t h a n t h e c o r r e s p o n d i n g f i g u re f o r Bll i o n s . T h i s e f f e c t i s p r e d i c t e d b y t h e p o s t - i o n i s a t i o n m o d e l o f Haydock
and Kingham 121.
BI~
i o n s b e i n g less m a s s i v e t h a n
BI~
i o n s t r a v e l f a s t e r and s o
s p e n d l e s s t i m e i n the " p o s t - i o n i s a t i o n z o n e " i n w h i c h t h e t r a n s i t i o n f r o m B* t o
B ~ ' i s e x p e c t e d t o o c c u r . T h e maximum o f d i f f e r e n c e b e t w e e n t h e p r o b a b i l i t i e s o f
In p r a c t i c e t h e o b s e r p o s t - i o n i s a t i o n c a l c u l a t e d f o r B o r o n i o n s i s AP = 1.6 % 11
v e d d i f f e r e n c e AP
i s much m o r e p r o n o u n c e d t h a n e x p e c t e d w i t h AP
= 4.6 %
1.
ex*,
ex^
f o r e x p e r i m e n t a t 78 K.
I
I t h a s been a s s u m e d b y Menand and Kingham [ 1 t h a t t h i s d i s c r e p a n c y c o u l d b e e x p l a i nerZ i n t e r m s o f e v a p o r a t i o n o f b o r o n i o n s b y i o n i c t u n n e l i n g a t l o w t e m p e r a t u r e .
T h e p u r p o s e o f t h i s p a p e r i s t o t e s t t h i s a s s u m p t i o n b y v a r y i n g the s a m p l e t e m p e rature.
T h e e x p e r i m e n t s w e r e made w i t h
were prepared from t a p e s o f 5 0
electropolishing in a solution
a ToF a t o m p r o b e 13 w i t h a 3 0
a r e a . T i m i n g was b y m e a n s o f a
t i m e o f 5 n s , low temperatures
1
s a m p l e s o f Fe Ni Mo B m e t a l l i c g l a s s , t h e s p e c i m e n s
pm t h i c k n e s s and a b o u t 0 . 2 mm w i d t h , b y a n o d i c
o f lv" % p e r c h l o r i c a c i d i n 2 - B u t o x y e t h a n o l . We u s e d
cm f l i g h t l e n g t h w h i c h a l l o w s a l a r g e a n a l y s i s
t h r e e c h a n n e l 4 0 0 MHz d i g i t a l c o u n t e r w i t h a d e a d
was o b t a i n e d b y m e a n s o f a c r y o g e n e r a t o r .
RESULTS AND DISCUSSION
1
- T.........................................
emperature dependence o f i s o t o p i c e f f e c t
T a b l e 1 g i v e s the r e s u l t s o b t a i n e d a t t e m p e r a t u r e v a l u e s r a n g i n g from 170 K
t o 300 K : 2 0 3 0 4 b o r o n i o n s w e r e d e t e c t e d o f w h i c h 19.88 % w e r e B10 i n good a g r e e -
'UA
CNRS 808
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1984917
JOURNAL DE PHYSIQUE
C9-96
m e n t w i t h t h e i s o t o p i c r e l a t i v e a b u n d a n c e . T h e a v e r a g e p r o p o r t i o n o f B1
i n the
d o u b l y c h a r g e d p e a k i s 19.46 % whereas t h e p r o p o r t i o n o f B10 in t h e s i n g l y c h a r g e d
p e a k i s 20.41 %.
T h e a v e r a g e d i f f e r e n c e AP
i o n i s a t i o n o f B10 and B l l i s 1.5 %.
Experiment
I
2+
Blo
Total
1
2224
Table 1
-
exp
between t h e p r o b a b i l i t i e s o f post-
B::
1
Number o f BZ+
9204
B+
l o t B:;
and B ; ~ i o n s o b s e r v e d i n s e v e n e x p e r i m e n t s o f
Fe N i Mo B , a t t e m p e r a t u r e r a n g i n g f r o m 1 7 0 K t o 3 0 0 K . E a c h e x p e r i m e n t g i v e s a n
2+
2+
2+
e s t i m a t e o f t h e r e l a t i v e a b u n d a n c e O ~ , B and
! ~ B l l ( i . e ( B I O / Z B l o ) and
2+
( B /ZB I ) and o f t h e d i f f e r e n c e i n t h e s e q u a n t i t i e s , Q
I
11
11
exp
T h e r e s u l t s o n t h e a b u n d a n c e o f s i n g l y and d o u b l y c h a r g e d i o n s o f t h e t w o i s o t o p e s
o f b o r o n a t t e m p e r a t u r e b e t w e e n 20 K and 3 0 0 K a r e s u m m a r i s e d i n t a b l e 2 , t h e y
show a s i g n i f i c a n t t e m p e r a t u r e e f f e c t .
Temperature
2+
B1o
B+
B2+
11
B
11
2+
B 10 /ZB10 %
2+
BI1/XBll %
20 K
78 K
170-240 K
300 K
414
102
993
1231
627
108
985
827
1921
448
4034
5170
2028
404
3635
3429
39.8
48.6
50.2
59.8
48.6
52.6
52.6
60.1
Table 2
-
2+
Number o f B l o t
10
+
AP
e*p
+
+
+
+
%
8.8
4
2.4
0.3
+
2+
B l O , B l l and B : ~ i o n s o b s e r v e d i n t h e e x p e r i m e n t s o n
Fe N i M B f o r d i f f e r e n t t e m p e r a t u r e s l y i n g f r o m 20 K t o 3 0 0 K
i s s m a l l 0.3-2.4 % w h i c h
exp
i s c o n s i s t e n t w i t h t h e p r e d i c t e d v a l u e o f 1 . 6 %, b u t a t l o w e r t e m p e r a t u r e AP
exD
i s l a r g e r , u p t o 8 . 8 % a t 20 K. These r e s u l t s s u p p o r t o u r a s s u m p t i o n of i o n i c
t u n n e l i n g a t l o w t e m p e r a t u r e . T h e o c c u r e n c e o f i o n i c t u n n e l i n g means t h a t t h e
l i g h t e r B10 i o n s w i l l b e m o r e e a s i l y f i e l d e v a p o r a t e d t h a n B1
S O t h e y may be
I n the t e m p e r a t u r e r a n g e 170-300 K t h e d i f f e r e n c e AP
.*
evaporated a t f i e l d s t r e n g t h s l i g h t l y lower than Bll.
T h a t i s , if B l l i o n s a r e o n l y
e v a p o r a t e d a t the maximum o f t h e e l e c t r i c f i e l d p u l s e , B10 i o n s may b e e v a p o r a t e d
when the f i e l d i s j u s t less t h a n i t s m a x i m a l v a l u e . As p o s t - i o n i s a t i o n p r o b a b i l i t i e s
are s t r o n g l y dependent o n f i e l d s t r e n g t h 1
o n l y a 0.5 % d i f f e r e n c e i n e v a p o r a t i o n f i e l d s t r e n g t h i s r e q u i r e d t o g i v e .A 3 % d i f f e r e n c e i n p o s t - i o n i s a t i o n p r o b a -
I I,
bilities.
2 - Constant f i e l d s t e n g t h s t u d y
............................
W e h a v e p r e p a r e d a s p e c i m e n w i t h a v e r y narrow t a p e r a n g l e w h i c h m e a n t t h a t t h e
d e s o r p t i o n f i e l d r e m a i n e d c o n s t a n t ( w i t h t h e t i p v o l t a g e h e l d c o n s t a n t ) d u r i n g the
d e s o r p t i o n o f many a t o m s . T h e s t e a d i n e s s o f t h e t i p r a d i u s was v e r i f i e d b y the meas u r e m e n t o f B I V b e f o r e and a f t e r e a c h e x p e r i m e n t . W i t h t h i s s p e c i m e n we h a v e p e r formed e x p e r i m e n t s w i t h i n c r e a s i n g t e m p e r a t u r e ( b y s w i t c h i n g o f f the c r y o g e n i c
r e f r i g e r a t o r ) . So during t h e course o f t h e experiment, and,as t h e evaporated i o n s
w e r e d e t e c t e d , the t i p t e m p e r a t u r e was s l o w l y i n c r e a s i n g . F i g u r e 1 g i v e s t h e cumu-
a t i v e number o f B ~ i+o n s v e r s u s t h e t o t a l number o f Boron d e t e c t e d i o n s , the c o r r e s ponding temperatures a r e a l s o i n d i c a t e d .
F i g . 1 - C u m u l a t i v e number o f B
observed
2+
ions o b s e r v e d a g a i n s t t h e t o t a l number o f B i o n s
T h e s h a r p s l o p e c h a n g e w i t h i n 140 K i s the r e s u l t o f an i n t e r e s t i n g a r t e f a c t . For
t e m p e r a t u r e s u n d e r 140 K the e v a p o r a t i o n r a t e was i n c r e a s i n g v e r y s l o w l y and t h e
to 4.
but near
a v e r a g e number o f d e t e c t e d i o n s p e r p u l s e n l y g n g f r o m 5.
140 K the e v a p o r a t i o n r a t e i n c r e a s e d s u d d e n l y n > 3 , t h r e e Boron ions os m o r e w e r e
produced f o r e a c h p u l s e b u t o b v i o u s l y o n l y 3 ions c o u l d b e s t o r e d i n t h e t h r e e
c h a n n e l s d i g i t a l c o u n t e r . In t h i s s a t u r a t e d r e g i m e d o u b l y c h a r g e d i o n s a p p e a r more
a b u n d a n t b e c a u s e t h e y r e a c h the d e t e c t o r f i r s t .
T h i s s u d d e n i n c r e a s e i n t h e e v a p o r a t i o n r a t e i s i n t e r p r e t e d a s a c h a n g e i n the
e v a p o r a t i o n p r o c e s s from a n e s s e n t i a l l y t u n n e l i n g d e s o r p t i o n o f b o r o n i o n s , t o a n
e s s e n t i a l l y t h e r m a l l y a c t i v a t e d e v a p o r a t i o n . T h e t r a n s i t i o n t e m p e r a t u r e T w i l l be
140
5 K.
+
i s p a r t i c u l a r l y i n t e r e s t i n g t o n o t i c e the s t e a d i n e s s o f the c h a r g e r a t i o
2+
/CB a t l o w and a t h i g h t e m p e r a t u r e ( e x c e p t e d i n the s a t u r a t e d z o n e 140-165 K I .
T h i s i s a n e v i d e n c e f o r the p o s t - i o n i s a t i o n model o f Kingham, t h e c h a r g e s t a t e
It
B
o f b o r o n i o n s i s a f u n c t j o n o f f i e l d and n o t o f t e m p e r a t u r e
Acknowledgements
T h e a u t h o r s w i s h t o t h a n k D r D. R. Kingham f o r f r u i t f u l d i s c u s s i o n s and v a l u a b l e
comments.
JOURNAL DE PHYSIQUE
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