METALLIC GLASS FIELD EMISSION SPECTRA

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METALLIC GLASS FIELD EMISSION SPECTRA

Z. Stepien

To cite this version:

Z. Stepien. METALLIC GLASS FIELD EMISSION SPECTRA. Journal de Physique Colloques, 1989,

50 (C8), pp.C8-109-C8-111. �10.1051/jphyscol:1989819�. �jpa-00229917�

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COLLOQUE DE PHYSIQUE

Colloque C8, suppl6ment au n o 11, Tome 50, novembre 1989

METALLIC GLASS FIELD EMISSION SPECTRA

Z.M. STQPIEN

Physics Institute, Pedagogical University, Zawadzkiego 13/15, PL-42 200 Czestochowa, Poland

A b s t r a c t

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Total energy d i s t r i b u t i o n s <TED> of e l e c t r o n s e m i t t e d a t room and LNz temperatures from a Fe7sSfpBi3 m e t a 1 l . i ~ g l a s s specimen a r e reported. S p e c t r a have been t a k e n i n UHV c o n d i t i o n s from a vacuum cleaned t i p . The r e s u l t s a r e d i s c u s s e d i n terms of t h e hypothesis t h a t t h e t i p s u r f a c e is Fe e n r i c h e d with r e s p e c t t o t h e bulk.

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INTRODUCTION

The s t r u c t u r e and p r o p e r t i e s of m e t a l l i c g l a s s e s have been of wide i n t e r e s t f o r a few years. A l o t of work concerning t h e p r o p e r t i e s of t h e s e m a t e r i a l s technique and

empl0yi

n g d i f f e r e n t experimental h a s been done C 1 - 3 3 ; a l s o some f i e l d i o n and f i e l d e l e c t r o n microscopy s t u d i e s have been r e p o r t e d C 4 - 8 3 .

An advantage of f i e l d emission spectroscopy is t h a t i t is extremely s u r f a c e s e n s i t i v e and may be used a s a t o o l i n s u r f a c e or near s u r f a c e l a y e r e l e c t r o n i c p r o p e r t i e s i n v e s t i g a t i o n s . The possi bi 1 i t y of monitoring a s i g n a l from t h e s u r f a c e only appears p a r t i c u l a r l y i n t e r e s t i n g i n t h e m e t a l l i c g l a s s e m i t t e r s case.where a s u r f a c e l a y e r is expected t o be d i f f e r e n t from t h e bulk m a t e r i a l not only with r e s p e c t t o i t s s t r u c t u r e b u t a l s o i n its composition.

Here, f i e l d emission p a t t e r n s and t o t a l energy d i s t r i b u t i o n c u r v e s from Fe7eSi *Bi3 t i p a r e d e s c r i b e d .

M e t a l l i c g l a s s f o r t h i s experiment,

Fe7eSiPBi9, was chosen a s an element of t h e

isostoichiometric

Me7eSi9Bi3 group, with Me=Fe.Co.Ni. Comparison of t h e emission s p e c t r a of g l a s s e s with those of d i f f e r e n t t r a n s i t i o n metals may h e l p t o , d e c i d e which peaks on RCc;

>

curve a r e connected with Me.

F i e l d emission measurements have been used t o g e t some d a t a about t h e s u r f a c e of t h e g l a s s and t o v e r i f y t h e hypothesis t h a t t h e Fe amount on t h e s u r f a c e is s i g n i f i c a n t l y g r e a t e r t h a n may be expected from t h e Fe: S i : B s t o i c h i o m e t r i c r e l a t i o n .

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EXPERIMENTAL

The t i p s were prepared by electrochemical p o l i s h i n g of t h e amorphous, 0.03 mrn t h i c k . Fe7eSipBia ribbons. P o l i s h i n g process was performed i n 1 0 % HC1 water s o l u t i o n . E m i t t e r s were clamped i n t h e tantalum t u b e s which were s p o t welded t o t u n g s t e n wire loops. E l e c t r i c a l c o n t a c t was improved with a small amount of s i l v e r p a i n t . The loops were mounted on a t y p i c a l "cold

f i n g e r " , and a l l t h i s was p u t

i n t o

t h e s t a i n l e s s - s t e e l vacuum chamber.

Manipulation was p o s s i b l e due t o bellows conection. The chamber was ion-pumped and t h e working p r e s s u r e was l e s s t h e n 2 x l 0 - ' ~ h ~ a . To c l e a n t h e t i p s u r f a c e . b e f o r e each c y c l e of measurements, vacuum f i e l d evaporation was done. D e t a i l s of t h e c l e a n i n g procedure were given elsewhere C 9 3 .

E l e c t r o n s were recorded using a Young t y p e f i e l d emission r e t a r d i n g p o t e n t i a1 a n a l yser

.

The anal y s e r used i n t h i s experiment was a s l i g h t

modification of t h e Plummer and Young one C 1 0 3 . I t s r e s o l u t i o n , e s t i m a t e d by t h e convolution t h e o r y E l l I , was c a . 50 meV. A l l t h e measurements were k a r r i e d out a t room temperature and r e p e a t e d a t LN, temperature.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1989819

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^RESULTS DISCUSSION

Fe78SiPBL3 f i e l d emission p a t t e r n s look l i k e , approximate1 y, b r i g h t c i r c l e s . with t h e emission c o n c e n t r a t e d i n a cone with a s o l i d a n g l e of 0.06 s r . This p i c t u r e a g r e e s with t h e o b s e r v a t i o n of Heinrich and h i s c o w o r k e r s C41. Any changes, i n t h e p a t t e r n s due t o f i e l d evaporation were observed v i s u a l 1 y; both a t room and LN temperature.

From t h e recorded d a t a Fowler -Nordheim c h a r a c t e r i s t i c s and TED, enhancement f a c t o r c u r v e s have been made. The enhancement f a c t o r . RCc>. has been c a l c u l a t e d as t h e d i f f e r e n c e between t h e n a t u r a l l o g a r i t h m s of t h e experimental and f i t t e d f r e e e l e c t r o n curves:

RCc> = I n J Cc>

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I n JfrreCs> ; P X P

c is t h e e l e c t r o n energy measured r e l a t i v e t o t h e Fermi l e v e l .

Fig. 1.

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Enhancement f a c t o r Cexpressed as t h e n a t u r a l logarithm> f o r t h e f i e l d emission from Fe Si B metal 1 i c g l a s s ; T=78 K.

78 P L 3

Typical enhancement f a c t o r f o r 7 8 K, i s shown i n f i g u r e 1. The shape of t h e c u r v e from f i g . 1. seems t o support t h e assumption about a n almost pure Fe s u r f a c e layer.

I f t h i s assumption is accepted, t h e s i m i l a r i t y of t h e TED s p e c t r a f o r t h e g l a s s and t h o s e f o r t h e d i s o r d e r e d Fe a d s o r p t i o n l a y e r should be observed.

I n a d d i t i o n , i t makes i t p o s s i b l e t o e s t i m a t e t h e i r o n atom-substrate

s e p a r a t i o n C121. If t h e f i r s t peak on R C s > curve C~=0.4eV> i s assumed t o be t h e s h i f t e d and broadened i r o n atom ground s t a t e

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f o r i s o l a t e d i r o n atom t h e ground s t a t e , 5 ~ 3 d 6 4 s 2 > , i s 7.87 eV below t h e vacuum l e v e l

-

^{t h i s}

d i s t a n c e is 1.20

A.

This value is i n q u i t e good agreement with t h e v a l u e obtained by Jones and Roberts f o r t h e c a s e of t h r e e amorphous Fe l a y e r s on t u n g s t e n C 1 3 3 . What i s i n t e r e s t i n g , t h e s e a u t h o r s a l s o c o r r e l a t e t h e f i r s t p e a k , l o c a t e d a t t h e ca. 0 . 4 eV, with t h e i r o n atom ground s t a t e . The value, of t h e c a l c u l a t e d d i s t a n c e , 1 . 2 0

x,

^{m a y}s u g g e s t t h a t t h i s is t h e m e t a l l i c bond.

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What i s r e a l y d i f f i c u l t is t h e i n t e r p r e t a t i o n of t h e r e m a i n i n g peaks.There seems t o be a c o r r e l a t i o n between t h e s h a p e of s p e c t r u m and t h e bulk m e t a l l i c g l a s s band s t r u c t u r e . E s t a b l i s h i n g t h i s c o r r e l a t i o n however, i s v e r y d i f f i c u l t as t h e r e is o n l y a l i t t l e d a t a on m e t a l l i c g l a s s band s t r u c t u r e . The o t h e r f a c t o r s which may c o m p l i c a t e t h e p i c t u r e are e l e c t r o n

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e l e c t r o n and e l e c t r o n

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phonon i n t e r a c t i o n s ; t o f i n d t h e r e l a t i v e importance of t h e s e f e a t u r e s f u r t h e r i n v e s t i g a t i o n s are needed.

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ACKNOWLEDGEMENT

The

author

acknowledges w i t h t h a n k s Dr. P. B r q g i e l f o r c r i t i c a l r e a d i n g of t h e m a n u s c r i p t and h e l p f u l comments.

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