PULSED LASER TREATMENT OF Eu AND La IMPLANTED NICKEL : SURFACE ALLOYING, TRAPPING AND DAMAGE

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PULSED LASER TREATMENT OF Eu AND La

IMPLANTED NICKEL : SURFACE ALLOYING,

TRAPPING AND DAMAGE

G. Battaglin, A. Carnera, J. Chaumont, G. Della Mea, L.F. Donà Dalle Rose,

A. Jain, Vainatey Kulkarni, P. Mazzoldi, A. Miotello, D. Sood

To cite this version:

G. Battaglin, A. Carnera, J. Chaumont, G. Della Mea, L.F. Donà Dalle Rose, et al.. PULSED

LASER TREATMENT OF Eu AND La IMPLANTED NICKEL : SURFACE ALLOYING,

TRAP-PING AND DAMAGE. Journal de Physique Colloques, 1983, 44 (C5), pp.C5-481-C5-488.

�10.1051/jphyscol:1983570�. �jpa-00223155�

Colloque C5, suppl6rnent au nO1O, Tome 44, octobre 1983 _{page C5-481}

PULSED LASER TREATMENT OF E u AND La IMPLANTED N I C K E L

:

SURFACE ALLOYING, TRAPPING AND DAMAGE

G . Battaglin*

,

A. Carnera*, J . Chaumont*:, G . D e l l a Mea*,

L.F. Don2 d a l l e Rose*, A.K. J a i n f " * , V.N. K u l k a r n i * , P . ~ a z z o l d i * , A. ~ i o t e l l o ' and D.K. ~ o o d + +

' I s t i t u t o d i F i s i c a d e Z l r U n i v e r s i t d , 35200 Padova, I t a l y

" L a b o r a t o i r e RenQ Bernas, U n i v e r s i t 6 P a r i s X I , 91406 Orsay Cedex, France ***Nuclear P h y s i c s D i v i s i o n , Bhabha Atomic Research Centre, Bombay 400085, I n d i a

+ I s t i t u t o per %a Ricerca S c i e n t i f i c a e Teeno Zog.tea, 38050 Povo ( P e n t o ) , r t a z y

+'RMIT, Me Zbowne 3000, A u s t r a z i a

~ZsumG

- L ' i r r a d i a t i o n p a r l a s e r d 1 6 c h a n t i l l o n s d e

N i monocri- s t a l l i n s implant& a v e c i o n s de La ou d'Eu p r o d u i t une s o l u t i o n s o l i d e q u i n ' e s t p a s de s u b s t i t u t i o n , un changement du dorn- mage de l a m a t r i c e e t un p i c s u p e r f i c i e l du d i s s o u s . Nous p r g

s e n t o n s une i n t e r p r s t a t i o n de c e s r 6 s u l t a t s e t une a n a l y s e d e s p r o f i l e s de solut6 dans l e contexte de l a d i f f u s i o n d a n s une phase l i q u i d e .

A b s t r a c t

- L a s e r i r r a d i a t i n g o f N i s i n g l e c r y s t a l s i m p l a n t e d

w i t h La o r Eu i o n s produces a non s u b s t i t u t i o n a l s o l i d s o l u - t i o n , a v a r y i n g m a t r i x damage and s o l u t e s u r f a c e peaking. E x p l a n a t i o n of t h e s e r e s u l t s and a n a l y s i s of s o l u t e p r o f i l e s

i n t h e c o n t e x t of a l i q u i d p h a s e d i f f u s i o n model a r e c r e s e n t e d .

I

-

I N T R O D U C T I O N

Survey of ~ u l s e d l a s e r t r e a t m e n t (PLT) s t u d i e s of m e t a l s /I/ shows t h a t t h e t e c h n i q u e h a s been e x t e n s i v e l y used t o produce m e t a s t a b l e

so

l i d s o l u t i o n s (14SS) a t c o n c e n t r a t i o n w e l l above e q u i l i b r i u m l i m i t s . According t o t h e r e c e n t l y proposed g e n e r a l c r i t e r i a /2/ t h e r e q u i r e - ments f o r t h e f o r m a t i o n of MSS by PLT a r e , m i s c i b i l i t y f o r t h e compo- n e n t s i n l i q u i d phase and good l i q u i d phase e p i t a x y (LPE) w i t h h i g h c o o l i n g r a t e s .

The p r e v i o u s PLT s t u d i e s on N i i m p l a n t e d w i t h Pd, Sn / 3 / , T a , Au /3,4/ and H E / 5 / have a l l l e d t o s o l i d s o l u t i o n s i n agreement w i t h t h e above c r i t e r i a . The Eu i m p l a n t e d N i h a s shown a non s u b s t i t u t i o n a l s o l i d so- l u t i o n a f t e r PLT / 6 / , where a s u b s t i t u t i o n a l s o l i d s o l u t i o n would be e x p e c t e d / 2 / . T h i s r e s u l t was e x p l a i n e d i n t e r m s of enhanced d e f e c t t r a p p i n g and d e f e c t - i m n u r i t y i n t e r a c t i o n d u r i n g LPE, c a u s e d ;y t h e l a r g e s i z e d i f f e r e n c e between Eu(1 - 9 9 r a d i u s ) and N i ( 1 - 2 4 A r a d i u s ) atoms. I n o r d e r t o f u r t h e r c o n f i r m t h e i n f l u e n c e of d e f e c t t r a p p i n g on f i n a l phase f o r m a t i o n w e have done PLT o f a n o t h e r s i m i l a r system i . e . La i m p l a n t e d N i .

C5-482 JOURNAL DE PHYSIQUE

0

The r a d i u s of La atoms (1.87 A ) i s l a r g e r t h a n N i and f u r t h e r t h e Ni-La phase diagram /7/ shows a n e g l i g i b l e s o l i d s o l u b i l i t y i n N i b u t complg t e m i s c i b i l i t y i n l i q u i d phase. A non s u b s t i t u t i o n a l s o l i d s o l u t i o n a f t e r PLT i s o b s e r v e d i n t h i s c a s e t o o . I n a d d i t i o n we o b s e r v e a l a r g e l a s e r induced damage i n N i c o n f i r m i n g t h e enhanced d e f e c t t r a p p i n g and d e f e c t - i m p u r i t y i n t e r a c t i o n . Another observed s i m i l a r i t y c o n c e r n s t h e p e a k i n g o f La a t s u r f a c e i n agreement w i t h t h o s e r e p o r t e d f o r p u l s e d l a s e r t r e a t e d samples o f Eu and Hf i m p l a n t e d N i . I n t h i s p a p e r we p r e - s e n t t h e s e r e s u l t s a l o n g w i t h a comparison w i t h t h o s e o f N i ( E u ) . I1

-

EXPERIMENTAL E l e c t r o p o l i s h e d N i s i n g l e c r y s t a l s ( < l o o > o r i e n t a t i o n ) h a v i n g damage f r e e s u r f a c e and m i r r o r l i k e f i n i s h have been implanted w i t h 300 keV

+

Eu o r 250 kev ~ a + + i o n s t o a dose o f 1 x 1 0 ~ 6 atoms/cm2. P u l s e d ruby l a s e r (20 o r 16 n s FWHII) a t e n e r g y d e n s i t i e s up t o 5.2 ~ / c m ~ , was em- ployed f o r c a r r y i n g o u t i r r a d i a t i o n s i n a i r on t o s e v e r a l d i f f e r e n t r e g i o n s o f t h e i m p l a n t e d samples. I n one c a s e i r r a d i a t i o n was perform ed i n vacuum c o n d i t i o n s t o r r ) . From t h e s p a t i a l l y homogenised l a r g e s p o t of 1 5

mm

s i z e a r e g i o n o f 2.5 mm d i a m a t e r was c a r e f u l l y

se

l e c t e d f o r i r r a d i a t i o n which e n s u r e d an u n i f o r m i t y of + l o % o v e r t h e s e l e c t e d a r e a . Samples were a n a l y z e d by R u t h e r f o r d B a c k s c a t t e r i n g (RBS) and c h a n n e l i n g u s i n g a 1.8 MeV 4 ~ e + beam. The b a c k s c a t t e r e d p a r t i c l e s were d e t e c t e d a t 160° u s i n g a s u r f a c e b a r r i e r d e t e c t o r and t h e u s u a l e l e c t r o n i c s w i t h a n o v e r z l l r e s o l u t i o n o f 18 keV FWHM c o r r e s p o n d i n g t o d e p t h r e s o l u t i o n o f 180 A i n N i .

111

- RESULTS

AND DISCUSSION

F i g . 1 shows t h e random and < l o o r c h a n n e l i n g s p e c t r a f o r Eu/La i m p l a n t ed N i b e f o r e and a f t e r l a s e r t r e a t m e n t a t t h e i n d i c a t e d e n e r g y d e n s i - t i e s . The c h a n n e l i n g spectrum of Eu i m p l a n t e d N i shows t h e s u r f a c e da- mage peak, t h e c h a r a c t e r i s t i c ' k n e e ' a t a d e p t h XD=245 nm and minimum y i e l d

xmin

of 1 0 . 5 % , w h i l e t h a t of La i m p l a n t e d N i shows XD a t 148 nm and

xmin=

33%. The v a r i a t i o n i n t h e

x m i n

a f t e r l a s e r t r e a t m e n t a t t h e employed l a s e r e n e r g y d e n s i t i e s i s p l o t t e d i n F i g . 2 f o r b o t h Ni(Eu) and N i ( L a ) systems.

An a b r u p t two f o l d i n c r e a s e i n

xmin

a t . 8 ~ / c m ~ i s s e e n f o r N i (Eu) ( t h e c o r r e s p o n d i n g d e c h a n n e l i n g spectrum n o t shown i n F i g . 1 , i s found i n Ref. / 6 / ) . Such an i n c r e a s i n g h a s been c o r r e l a t e d / 6 / w i t h t h e t h r e s h o l d f o r m e l t i n g o f Eu i m p l a n t e d N i . A t h i g h e r e n e r g y d e n s i t i e s t h e Xmin r e d u c e s and becomes lower t h a n i t s a s i m p l a n t e d v a l u e w h i l e t h e ' k n e e ' moves outwards always t o t h e same d e p t h of 40 nm ( c o i n c i d i n g w i t h t h e measured p r o j e c t e d r a n g e , Rp f o r i m p l a n t e d E u ) . On t h e o t h e r hand t h e regrowth b e h a v i o u r of Ni(La) i s v e r y d i f f e r e n t under PLT. The

33% X m i n o f t h e i m p l a n t e d sample i n c r e a s e s t o 4 1 % w i t h h i g h e r and wider s u r f a c e damage peak a t 1 . 5 J/cm2. The

xmin

and t h e damage peak w i d t h f u r t h e r i n c r e a s e w i t h i n c r e a s i n g e n e r g y d e n s i t y . A s a t u r a t i o n e f f e c t i n t h e minimum y i e l d ( F i g . 2 ) i s s e e n above 3 J/cm2 where t h e a l i g n e d s p e c t r a become a l m o s t f l a t i n d i c a t i n g f o r m a t i o n of p o l y c r y s t a l l i n e l a y e r /8/ o r a deep and uniform damaged zone i n N i . A s f o r t h e s u r f a c e

Pig. 1

- Random and

<loo>

c h a n n e l i n g s p e c t r a o f Eu/La implanted N i be- f o r e and a f t e r l a s e r t r e a t m e n t . The s p e c t r a f o r E u and La a r e magni- f i e d by a f a c t o r o f t e n

.

The random and c h a n n e l i n g y i e l d s f o r b o t h E u and La o v e r l a g i n a l l c a s e s . 10

----

_{----_}

21 J/cm2

---_

Zp=20nsec \ I ,- 20 J/cmZ ---,- Zp

-

16 nsec

---__

_.

\ 10

=

----_

_Zp 2.9 _{= 2 0}

~ / c m Z

_nsec

--- ---_

\ 1 3.0 ~/crn'

---

Zp= 16 nsec

-_

_---

_{-_}

_-.

I 5 I 1.2

M

1.6 , 1.2 1.4 1.6 3.6 J/cm2 10R----_--- 5, = 20 nsec

--

',

I

-

\

3.5 J/cmZ '=---

_{---__}

2,

-

16 nsec

--.

'I

-

I

C5-484 JOURNAL DE PHYSIQUE

Fig.

2

-

Dependance of minimum yield,

x

,

on laser pulse energy for Eu (0) and La implanted ( r )

nickel.

PULSE ENERGY

[~/crn*)

alloy, the as implanted Eu and La form a nonsubstitutional solution in Ni, as it may be seen by the overlap of their backscattering yields in channeling and random directions. This is in agreement with the modif2 ed Hume-rothery rules /9/ which predict nonsubstitutionality for the implanted atoms having a radius 40% greater than the host one. On the other hand, for the reason mentioned in the beginning, PLT is expected to produce substitutional solid solution of Ni(Eu) and Ni(La). On the contrary, both systems form nonsubstitutional solid solution at the em

ployed energy densities (Fig. 1). However, the broadening of the as i_m planted Eu/La profiles after laser treatment confirm liquid phase dif- fusion of Eu/La in Ni. Another feature observed in the solute profiles of Fig. 1 is the appearance of a well defined and sharp surface peak at energy densities around 2 ~ / c m ~ and above. Similar solute surface peaking has been reported for Ni implanted with Hf after laser treat- ment in air.

The observed nonsubstitutionality of Eu/La after laser treatment and the Ni regrowth behaviour can be explained on the basis of defect trap ping during LPE. Channeling and TEM studies /3,6,10/ of laser treated pure Ni single crystals have shown the presence of quenched in de- fects.

From these reported results it becomes clear that the nature and amount of such defects depend on sample orientation laser energy density, pul se duration and other irradiation parameters. In other words we may say that defect trapping depends on the thermal transients i.e. on tern perature gradients, melt depths cooling rates, resolidification velocl ties etc. in the pure Ni samples. For an implanted Ni sample, in addi- tion, the defect trapping will depend on the type and concentration of implanted impurity atoms and on the defect-impurity interaction. It has been shown by positron annihilation studies in Ni /11/ containing dizferent im?urities, that the impurity-defect interaction, more pre- cisely the vacancy impurity binding energy, increases with the size of the impurity atom. Thus an impurity size dependance for defect trap- ping under PLI is expected. On this basis it can be thought that the relatively large sizes of La and Eu in comparison with Ni atoms enhan- ce the defect trapping at the liquid solid interface and the simulta- neously occurring solute trapping to such an extent that substitution

d e f e c t s w i t h i m p u r i t y i s s e e n by t h e clamped ' k n e e ' a t Rp f o r N i ( E u ) ( F i g . I , a l s o s e e / 6 / ) and by t h e enhanced damage f o r N i (La)

.

However, i f w e remind t h a t t h e La and Eu atoms have comparable s i z e t h e question t h e n a r i s e s a b o u t why, a t i n c r e a s i n g p u l s e e n e r g y d e n s i t i e s Ni(La)shows an enhanced damage i n o p p o s i t i o n t o Ni(Eu) b e h a v i o u r . A t f i r s t i t m i g h t a p p e a r t h a t t h i s d i s c r e p a n c y i s c o r r e l a t e d w i t h t h e i n i t i a l d i f f e r e n c e i n t h e damage f o r t h e two systems. However t h i s c a n n o t be t h e c a s e , s i n c e h e a t f l o w c a l c u l a t i o n s f o r N i (performed a s f6r &/I 2 / ) g i v e m e l t d e p t h e x t e n d i n g beyond t h e r e s p e c t i v e damage d e p t h s (XD). T h i s o c c u r s a t e n e r g y d e n s i t i e s 21.4 ~ / c m 2 f o r b o t h p u l s e d u r a t i o n s and o b v i o u s l y damage memory c a n n o t be r e t a i n e d i n t h e l i q u i d phase. P r o b a b l y , t h e de- f e c t i n c o r p o r a t i o n d u r i n g LPE depends, a p a r t from t h e s i z e d i f f e r e n c e between i m p u r i t y and h o s t atoms, on some o t h e r f a c t o r s ( e . g . a t o m i c c o n f i g u r a t i o n o f i m p u r i t y d u r i n g t r a p p i n g ) . I n t h i s r e g a r d it may be h e l p f u l t o mention h e r e t h a t t h e regrowth b e h a v i o u r under PLI ofNi(La) i s i n f l u e n c e d by t h e p r e s e n c e of i m p l a n t e d oxygen ( 1 x 1 0 ~ ~ atom /cm) t o t h e e x t e n t t h a t a s l i g h t improvement i n t h e N i c r y s t a l l i n i t y i s s e e n . The p o s s i b l e mechanisms which c a n g i v e r i s e t o a s o l u t e s u r f a c e peak a f t e r PLT a r e : i ) s e g r e g a t i o n towards s u r f a c e d u r i n g r e s o l i d i f i c a t i o n , ii) i n c o r p o r a t i o n i n a s u r f a c e o x i d e l a y e r produced d u r i n g PLT i n a i r . A d e t a i l e d d i s c u s s i o n /13,14/ of s e g r e g a t i o n e f f e c t s on t h e b a s i s of m e l t f r o n t v e l o c i t i e s s u g g e s t s t h a t t h e s e e f f e c t s a r e i n c o n c e i v a b l e i n case of PLT o f m e t a l s . To e x p e r i m e n t a l l y d e c i d e a b o u t the s o l u t e i n c o r - p o r a t i o n i n a s u r f a c e o x i d e l a y e r we have performed l a s e r i r r a d i a t i o n o f Ni(La) i n a i r and under vacuum ( l o - * t o r r ) c o n d i t i o n s . The r e s u l t s a r e shown i n F i g . 3 . The s u r f a c e peak which i s s e e n under i r r a d i a t i o n i n a i r i s a l m o s t a b s e n t under vacuum. I f t h e peak were due t o s e g r e g a t i o n it o u g h t t o a p p e a r i n b o t h c a s e s . I t s a b s e n c e under vacuum condi- t i o n s c o n f i r m t h e o x i d a t i o n mechanism. A s t o p r o b a b l e s u r f a c e o x i d a - t i o n we f i r s t o b s e r v e t h a t t h e h e a t of f o r m a t i o n o f La203 /15/ (and presumably f o r Eu o x i d e f o r which no d a t a i s a v a i l a b l e ) i s n e g a t i v e and o u t s t a n d i n g l y l a r g e i n a b s o l u t e v a l u e . T h i s means t h a t La (and Eu) o x i d a t i o n i s an e n e r g e t i c a l l y h i g h l y f a v o u r e d p r o c e s s b o t h i n i t s e l f

F i g . 3

- Depth c o n c e n t r a t i o n pro-

f i l e s of La i n N i o b t a i n e d a f t e r l a s e r i r r a d i a t i o n ( T ~ = 16 n s e c ) a t 4.6 ~ / c m ~ i n a i r ( 0 ) and i n vacuum ( 0 ) . The dashed l i n e shows

C5-486 JOURNAL DE PHYSIQUE

and as compared with Ni oxide formation. As a consequence,a strong suy face oxidation may be expected for La and Eu as soon as they get at the Ni surface. An additional indication about oxygen role comes from a comparison between the two La profiles as obtained after PLT of La implanted Ni and La plus 0 implanted Ni. It is observed that in the presence of implanted oxygen La is as a whole less mobile in the li- quid matrix. This supports our view that oxygen acts as a trapping factor for La.

The experimental profile may be reproduced by integrating the impurity diffusion equation which keeps into account La/Eu capture at the li- quid Ni surface due to oxidation processes. These calculations have been performed for the energy densities of 1.4, 2.1 and 2.9 ~ / c m ~ for Ni (Eu) and 1.5, 2 and 2.5 ~ / c m ~ for Ni (La)

.

Similar calculations at higher energy densities are meaningless since the profiles are almost flat and the surface topography appears to be coarse when seen under scanning electron microscope. These features are now accepted as a s& qnature of convective type effects in the molten metals /14,16/. The melt transients for the above mentioned energy densities are determin ed by heat flow calculations / 1 2 / . The reflectivity value of R = . 5 6

was used for the samples /6/. For each energy density the impurity diffusion equation is integrated by a finite difference method and for a time equal to the molten phase duration. Surface capture is introdu- ced by assuming that at each time step a small fraction f of the La concentration in the first layer of the finite difference method is subtracted to the subsequent diffusion process. Thus the calculated La/Eu profile depends on the heat transient details and on two free pg rameters: the liquid diffusion coefficient D and the effective capture parameter f. The calculated profile is finally convoluted using the ex perimental detector resolution and then compared with the experimental profile. Fig. 4 shows the calculated convoluted Eu/La profiles toge- ther with experimental ones.Throuqh the fit procedure values for the effective capture parameter f (which we assume to be the same in all cases for one system) and the diffusion coefficient D are determined. The D values are indicated in the figure and are consistent with the usual liquid phase diffusion coefficients /13,17/. For Eu the D value is found to be lower by a factor of three than that for La. As for the capture parameter f we find its value to be the same for both Ni(Eu) and Ni(La) and equal to . 5 % . In view of the overall smaller surface peak of Eu when compared to the La case the fact that f is the same for both may appear surprising, but this may be due to the slower Eu diffusion coefficient. As it may be noted, the La fit for 2.5 ~/cm' does not reproduce the surface peak completely. In this case, however, Ni evaporation may become important as shown by heat flow calculations. By inclusing a small Ni evaporation in the calculations the improved fitting shown by dashed line in Fig. 4a is obtained. An alternative explanation for the discrepancy may lie in an increased La surface capture at higher temperatures.

(a)

Fig. 4

-

Depth profiles of a) Eu and b) La at the indicated energy dee sities. Full curves show the best fit to observed depth profiles, ob- tained from liquid phase diffusion calculations using indicated diffu- sion coefficients and a surface capture parameter f=0.5% (see maintext). In b) the additional dashed curve for 2.5 ~ / c m ~ refers to a calculation which includes also a small Ni evaporation.

IV

-

CONCLUSIONS

A substitutional solid solution of Eu/La in Ni could not be obtainedby PLT of Eu/La implanted Ni single crystals: this fact is understood on the basis of enhanced defect trapping during the resolidification pro- cess. Completely different Ni regrowth behaviours are observed under PLT of the La and Eu implanted samples. The Eu/La surface peak is at- tributed to a mechanism of solute oxidation and trapping at surface. The liquid phase diffusion calculations including such a trapping mechg nism can satisfactorily explain the solute profiles.

ACKNOWLEDGEMENTS

We thank Mr. A. Rampazzo of the Sezione I.N.F.N. of Padova, for the drawings.

One of us (V.N.K.) will like to thank the International Centre for Theoretical Physics (Trieste) for financial support in the form of a fellowship.

This work has been financially supported by the Piano Finalizzato Me- tallurgia of C.N.R.

JOURNAL DE PHYSIQUE

REFERENCES

/ I / SOOD D . K . , R a d . E f f .

63

( 1 9 8 2 ) 1 4 1 . / 2 / SOOD D . K . , R a d . E f f . L e t t .

67

( 1 9 8 1 ) 1 3 .

/ 3 / BUENE L . , JACOBSON D . C . , NAKAHARA S . , POATE J . M . , DRAPER C.W. and HIRVONEN J . K . , i n " L a s e r a n d E l e c t r o n - B e a m S o l i d I n t e r a c t i o n s and M a t e r i a l s P r o c e s s i n g " , e d i t . b y J . F . G i b b o n s , L . D . H e s s and T.W. S i g m o n , p . 5 8 3 , N o r t h H o l l a n d , N e w Y o r k ( 1 9 8 1 )

.

/ 4 / BUENE L . , POATE J.M., JACOBSON D . C . , DRAPER C.W. a n d HIRVONEN J.K., A p p l . P h y s . L e t t .

32

( 1 9 8 0 ) 3 8 5 .

/ 5 / BUENE L . , KAUFMANN E . N . , KcDONALD M . L . , KOTHAUS K . , VIANDEN R . , F R E I T A G K . and DRAPER C.W., i n " N u c l e a r and E l e c t r o n R e s o n a n c e S p e c t r o s c o p i e s A p p l i e d t o M a t e r i a l s S c i e n c e " , e d i t . b y E . N . K a u f - m a n n and G.K. S h e n o y , p . 3 9 1 , E l s e v i e r N o r t h H o l l a n d , N e w Y o r k ( 1 9 8 1 ) . / 6 / BATTAGLIN G., CARNERA A . , DELLA llEA G . , MAZZOLDI P . , J A I N A . K . ,

KULKARNI V.N. and SOOD D . K . , i n " M e t a s t a b l e M a t e r i a l s F o r m a t i o n b y I o n I m p l a n t a t i o n " , e d i t . b y S . T . P i c r a u x and W . J . C h o y k e , p.

3 3 3 , N o r t h H o l l a n d , N e w Y o r k ( 1 9 8 2 ) .

/ 7 / HANSEN M., " C o n s t i t u t i o n o f B i n a r y ~ l l o y s " , p . 8 8 7 , M c G r a w - H i l l , N e w Y o r k ( 1 9 5 8 ) .

/ 8 / CHU W.K., MAYER J . W . and NICOLET M.A., " B a c k s c a t t e r i n g S p e c t r o m e - t r y " , p. 2 5 1 , A c a d e m i c , N e w Y o r k ( 1 9 7 8 )

.

/ 9 / SOOD D . K . , P h y s . L e t t .

A68

( 1 9 7 8 ) 4 6 9 .

/lo/

NARAYAN J . i n " L a s e r and E l e c t r o n - B e a m I n t e r a c t i o n s w i t h S o l i d s " , e d i t . b y B . R . A p p l e t o n and G.K. C e l l e r , P . 3 8 3 , N o r t h H o l l a n d , New Y o r k ( 1 9 8 2 ) .

/ 1 1 / DLUBEK G . , BREMER 0 . and MEYEN DORF N . , S o l i d S t a t e C o m m u n .

11

( 1 9 7 8 ) 1 2 1 9 .

/ 1 2 / DONA' DALLE ROSE L . F . and MIOTELLO A . , R a d . E f f .

53

( 1 9 8 0 ) 1 9 . / 1 3 / MAZZOLDI P . , DONA' DALLE ROSE L . F . a n d SOOD D . K . , R a d . E f f .

63

( 1 9 8 2 ) 1 0 5 .

/ 1 4 / DONA' DALLE ROSE L . F . , t h i s c o n f e r e n c e .

/ 1 5 / SMITHELLS C . J . , " M e t a l s R e f e r e n c e B o o k " , p . 2 0 6 , B u t t e r w o r t h s , L o n d o n ( 1 9 7 5 )

.

/ 1 6 / J A I N A . K . , KULKARNI V . N . and SOOD D . K . , N u c l . I n s t r u m . M e t h o d s

191

( 1 9 8 1 ) 1 5 1 .