MÃ¶ssbauer Spectroscopy and Its Chemical Applications

4 The Use of Conversion Electron Mössbauer Spectroscopy to Study Ion-Implanted Alloys and Archaeological Materials

Downloaded by UNIV LAVAL on October 23, 2015 | http://pubs.acs.org Publication Date: July 1, 1981 | doi: 10.1021/ba-1981-0194.ch004

G. L O N G W O R T H

and R. A T K I N S O N

Nuclear Physics Division, Atomic Energy Research Establishment, Harwell, Oxfordshire, U K

Analysis of

Mössbauer

electron spectra for copper 16

implanted with 1-5 x 10

57

-2

Fe ions cm

foils

suggests that the

iron atoms end up on substitutional sites, with a fraction being associated with nearby lattice defects. S i m i l ar spectra for iron foils implanted with up to 8 Χ -2

cm

contain a component attributable to

17

10

carbon ions

Fe C . 5

2

O n aging

the foils, the carbon atoms migrate appreciably above 4 0 0 ° C . Finally,

Mössbauer

electron and x-ray backscattering are

used to characterize the iron compounds in the glazes on examples

of Attic Black, Samian, and Indian Northern

Black Polished Wares.

n p h e t e c h n i q u e s of c o n v e r s i o n e l e c t r o n Môssbauer spectroscopy ( C E M S ) a n d c o n v e r s i o n x - r a y Môssbauer spectroscopy

( C X M S ) have

been

u s e d i n c r e a s i n g l y i n r e c e n t years, m a i n l y i n t h e s t u d y of o x i d a t i o n p r o d ucts at i r o n o r steel surfaces (1,2).

T h i s c h a p t e r illustrates t h e u s e o f

s u c h t e c h n i q u e s b o t h i n t h e s t u d y of surface alloys p r o d u c e d b y i o n i m p l a n t a t i o n a n d as a t o o l i n a r c h a e o l o g y t o c h a r a c t e r i z e t h e i r o n c o m p o u n d s present i n c e r t a i n types of g l a z e o n p a i n t e d c e r a m i c objects.

Experimental C E M S or C X M S allows the near-surface layers of a sample to be charac terized to a depth of either several tenths of a micron or about t e n microns, respectively. E a c h type of radiation m a y be detected i n a gas-filled propor tional counter. I n the former case, the energy resolution is poor and scattered 0065-2393/81/0194-0101$05.00/0 © 1981 American Chemical Society In Mössbauer Spectroscopy and Its Chemical Applications; Stevens, J., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1981.

102

MOSSBAUER SPECTROSCOPY A N D ITS C H E M I C A L APPLICATIONS

electrons are detected w i t h energies from the K conversion electron energy 7 k e V i n iron) to essentially zero. Thus i n the case of F e the L A u g e r electrons at approximately 5 k e V are detected also. Figure 1 shows a simple backscatter counter viewed from the back through w h i c h either h e l i u m / 5 % methane (electrons) or a r g o n / 1 0 % methane (xrays) is allowed to flow b y means of pipes ( C ) . T h e anode wire ( A ) is 25-/Am stainless steel and is sufficiently long so that end effects are small. T h e gamma-ray beam passes into the counter through the front window, made of Perspex, and is incident on the sample w h i c h is mounted behind a hole i n an aluminum backplate using sealing compound. Electrons backscattered into a solid angle of approximately 2-rr are detected. T h e counter thickness (2 cm) ensures a low efficiency for incident 14-keV gamma radiation while having a relatively h i g h efficiency for scattered electrons. T o set a lower energy threshold i n the pulse height spectrum so as to avoid unnecessary electronic noise, the spectrum measured w i t h the source on resonance w i t h a fluorescer foil for about 30 s is compared w i t h that taken w i t h the source moving so as to destroy resonance. T h e difference between the spectra indicates the energy dependence of the resonant electrons. A conven ient fluorescer foil is Rh F e 10 at. w h i c h is mounted on a movable arm B inside the counter so that it may be removed from the gamma-ray beam once the energy threshold has been set. T h e counter has a good energy resolution for iron K x-rays, and also has been used to measure conversion electrons from either S n or Eu. Since scattered electrons are detected over a range of energies, the amount of depth information i n the spectrum is small. E v e n if electrons are detected over a narrow range of energies using a magnetic or electric spectrometer, the depth information is not directly available since a l l electrons detected at a given energy do not originate at the same scatterer depth. However, spectra measured at several electron energies may be used to produce depth-selective spectra (3,4), although the technique requires the use of scatterers highly enriched i n F e . Nevertheless, when proportional counters are used for samples consisting of natural iron, it is possible to derive a limited amount of depth information. T h e probability that an electron emitted at a certain depth w i l l escape a n d be detected has been determined approximately b y measuring the areas of the


5 7

1 1 9

1 5 1

5 7

A

Figure 1. Simple backscattering counter for conversion electrons or x~ rays. (A) anode; (B) fluorescer foil; (C) gas inlet and outlet pipes

In Mössbauer Spectroscopy and Its Chemical Applications; Stevens, J., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1981.


4.

Ion-Implanted

LONGWORTH A N D ATKINSON

0

[

1

1

0

0-1

0-2

1

1

OA

0-3

103

Alloys

1

0-5

1

1

0-6

X (jjm)

Figure 2.

Relative area T(x) in CEM spectrum attributable to iron atoms within a distance x of scatterer surface as a function of x

C E M spectra for natural iron foils on w h i c h layers of F e , varying from 0.02 to 0.3 /mi, h a d been evaporated. T h e layer thicknesses were determined b y weight. F r o m the variation of area w i t h layer thickness, a graph may be derived (Figure 2) for the relative area i n the C E M spectrum P(x) that is produced b y electrons w i t h i n a distance x from the surface. This suggests that about 5 0 % of the spectrum results from iron atoms w i t h i n the first 0.1/xm below the surface. 5 7

Ion Implantation Ion

implantation provides

a means

of

introducing a

controlled

a m o u n t of a g i v e n a t o m i c species i n t o a target m a t e r i a l . T o d o t h i s , t h e atoms are first i o n i z e d a n d a c c e l e r a t e d to 5 0 - 2 0 0 k e V i n v a c u u m b e f o r e e n t e r i n g t h e target.

T h e ions lose e n e r g y b o t h b y e l e c t r o n i c e x c i t a t i o n

a n d b y elastic collisions w i t h the target atoms, a n d c o m e to rest w i t h a n approximately Gaussian distribution about a mean range

(Figure

3).

T h e w i d t h of t h e d i s t r i b u t i o n is c a u s e d b y t h e statistical n a t u r e of t h e c o l l i s i o n process.

I n polycrystalline materials the range a n d standard

d e v i a t i o n of t h e i m p l a n t e d ions m a y be c a l c u l a t e d a p p r o x i m a t e l y u s i n g t h e t h e o r y of L i n d h a r d , Scharff, a n d S c h i o t t ( L S S ) ( 5 , 6 ) . systems d i s c u s s e d here, 8 5 - k e V

5 7

F o r the two

F e ions o n c o p p e r a n d 4 0 - k e V c a r b o n

ions o n i r o n , t h e a p p r o x i m a t e m e a n ranges a r e 230 A a n d 500 A , w i t h s t a n d a r d d e v i a t i o n s of 90 A a n d 250 A , r e s p e c t i v e l y . I n t h i s w a y l a r g e a m o u n t s of i m p u r i t y atoms m a y b e i n t r o d u c e d i r r e s p e c t i v e of

the u s u a l e q u i l i b r i u m s o l i d s o l u b i l i t i e s . H o w e v e r ,

an

u p p e r l i m i t f o r t h e i m p u r i t y c o n c e n t r a t i o n is set b y s p u t t e r i n g effects



104


Figure 3.

Schematic of ion-implantation

process

w h e r e the i n c o m i n g ions k n o c k off atoms f r o m the target surface.

This

leads to a m a x i m u m r e t a i n e d dose, a n d to a d i s t u r b a n c e of t h e i m p l a n t a t i o n p r o f i l e at h i g h e r doses. T h e effect of i n c r e a s i n g dose is to flatten t h e d i s t r i b u t i o n a n d m o v e i t closer to the target surface.

T h e d e g r e e of

s p u t t e r i n g is u s u a l l y expressed as a s p u t t e r i n g r a t i o , w h i c h is t h e r a t i o of target atoms r e m o v e d p e r i n c i d e n t i o n . W h e n the i n c i d e n t ions u n d e r g o elastic collisions w i t h the host atoms, the l a t t e r are ejected f r o m t h e i r l a t t i c e sites i f t h e t r a n s f e r r e d e n e r g y exceeds a b o u t 25 e V , c r e a t i n g v a c a n c i e s a n d interstitials ( 7 ) .

The recoil

e n e r g y of t h e d i s p l a c e d atoms is often e n o u g h to p r o d u c e

secondary

d i s p l a c e m e n t s , a n d a cascade o f a t o m i c d i s p l a c e m e n t s is f o r m e d .

Towards

the e n d of its p a t h , the i o n creates a l a r g e n u m b e r of a t o m i c d i s p l a c e m e n t s w i t h i n a v e r y s m a l l r e g i o n a n d i n a short a m o u n t of t i m e ( ~

10~

13

s).

H e r e t h e p r o b a b i l i t y of a n i o n o c c u p y i n g a s u b s t i t u t i o n a l site is h i g h . I m p l a n t a t i o n is a l w a y s a c c o m p a n i e d b y r a d i a t i o n d a m a g e , w h i c h m a y l e a d to m i g r a t i o n of the i m p u r i t y atoms at t e m p e r a t u r e s b e l o w w h i c h t h e r m a l d i f f u s i o n is o p e r a t i v e . alloy w i l l depend

T h u s , the final m e t a l l u r g i c a l state of a n

o n t h e extent o f

this radiation-enhanced diffusion

w h i c h is g o v e r n e d b y the n u m b e r of excess v a c a n c i e s a n d i n t e r s t i t i a l atoms c r e a t e d d u r i n g t h e i m p l a n t a t i o n . F o r h i g h i n c i d e n t dose rates i t is also p o s s i b l e f o r the target t e m p e r a t u r e to b e c o m e sufficiently h i g h f o r t h e r m a l d i f f u s i o n to o c c u r .


4.

Ion-Implanted


105

Alloys

A l t h o u g h the s o l u b i l i t y l i m i t s f o r a g i v e n a l l o y m a y b e e x c e e d e d i n i m p l a n t a t i o n , i t m u s t b e e m p h a s i z e d t h a t the s o l i d solutions f o r m e d are m e t a s t a b l e . T h e i r d e c o m p o s i t i o n either b y solute p r e c i p i t a t i o n or b y the f o r m a t i o n of i n t e r m e t a l l i c c o m p o u n d s w i l l o c c u r o n t h e r m a l a n n e a l i n g . S u i t a b l e alloys m a y be p r e p a r e d e i t h e r b y i m p l a n t i n g F e i n t o a n y 5 7

m a t e r i a l or b y i m p l a n t i n g essentially a n y i o n i n t o i r o n . H e r e w e g i v e one e x a m p l e of e a c h t y p e of a l l o y . T h e spectra of the first t y p e are easier to i n t e r p r e t since i n the second

case, p a r t of the scattered

spectrum

comes f r o m i r o n atoms outside the i m p l a n t a t i o n profile.


Studies of Iron-Implanted Copper Alloys I n p r e v i o u s w o r k (8,9,10)

w e h a v e d e m o n s t r a t e d h o w the n o r m a l

s o l u b i l i t i e s of i r o n i n c o p p e r or silver m a y be exceeded.

C E M spectra

w e r e a n a l y z e d to d e t e r m i n e the l o c a l a t o m i c s u r r o u n d i n g s of the i r o n atoms, a n d the d e c o m p o s i t i o n of the phases present w a s s t u d i e d after the samples w e r e a g e d . H e r e w e present s i m i l a r measurements o n c o p p e r foils (12.5 i m p l a n t e d w i t h h i g h doses ( 2 , 3 , 4 , a n d 5 X

10

1 6

ions c m " ) 2

of

o r d e r to s t u d y f u r t h e r a n a n o m a l o u s feature of the s p e c t r u m

5 7

/xm) Fe in

observed

p r e v i o u s l y . T h e changes i n the C E M s p e c t r u m o c c u r r i n g as a f u n c t i o n of i n c r e a s i n g

5 7

F e dose are i l l u s t r a t e d i n F i g u r e 4, w h e r e t h e s p e c t r u m

for a dose of 1 X

10

1 6

ions c m "

is t a k e n f r o m p r e v i o u s w o r k ( 8 ) .

2

The

C E M s p e c t r a w e r e fitted u s i n g a least-squares m i n i m i z a t i o n p r o g r a m w i t h the f o l l o w i n g V o i g t profiles, r e s u l t i n g f r o m a G a u s s i a n d i s t r i b u t i o n of L o r e n t z i a n lines, e a c h h a v i n g the n a t u r a l l i n e w i d t h : 1.

a singlet ( s h i f t S ~ 0.2 m m s " ) r e s u l t i n g f r o m i r o n atoms w i t h a l l 12 c o p p e r nearest n e i g h b o r s — i s o l a t e d i r o n atoms;

2.

a d o u b l e t ( s p l i t t i n g Q ~ 0.6 m m s " ) r e s u l t i n g f r o m i r o n atoms w i t h one or m o r e i r o n nearest n e i g h b o r s ;

3.

a singlet (S ~ —0.09 m m s " ) r e s u l t i n g f r o m i r o n atoms w i t h a l l 12 i r o n nearest n e i g h b o r s ;

4.

a singlet ( S ~ 0.4 m m s " ) not o b s e r v e d i n t h e spectra f o r c o n v e n t i o n a l alloys p r o d u c e d b y m e l t i n g .

1

1

1

1

T h e values for the h y p e r f i n e p a r a m e t e r s d e r i v e d f r o m the fits are s h o w n i n T a b l e I. T h e r e l a t i v e a m p l i t u d e s of L i n e s 1, 2, a n d 3 are g o v e r n e d b y the a r r a n g e m e n t of i r o n atoms o n s u b s t i t u t i o n a l sites. T h e a p p r o x i m a t e i r o n c o n c e n t r a t i o n w a s c a l c u l a t e d , i n c l u d i n g the effects of s p u t t e r i n g , a n d i t w a s s h o w n (8)

t h a t t h e r e are m o r e i r o n - i r o n p a i r s a n d h e n c e

fewer

i s o l a t e d i r o n atoms t h a n e x p e c t e d for a r a n d o m a r r a n g e m e n t . T h u s , the r a d i a t i o n - e n h a n c e d diffusion has p r o m o t e d short-range o r d e r i n g of

the

i r o n atoms. E v e n t u a l l y some i r o n atoms w i l l b e s u r r o u n d e d b y a l l 12 i r o n nearest n e i g h b o r s g i v i n g rise to S i n g l e t 3, s i m i l a r to t h e singlet o b s e r v e d


106

MOSSBAUER


T

1

SPECTROSCOPY A N D ITS C H E M I C A L

1

1

1

1

i

1

APPLICATIONS

r

(mm.s ] 1

VELOCITY

Figure 4. CEM spectra for iron-implanted copper alloys for doses of (A) 1 X 1W«; (B) 3 X IV*; and (C) 5 X 10 Fe ions cm' . The full curves are derived from fits to the data and signify the total fit and component fits described. The zero of the velocity scale refers to the shift of a-iron. 16

Table I.

2

1 2 3 4 5

X X X X X

10 10 10 10 10

1 6 1 6 1 6 1 6 1 6

2

Hyperfine Parameters Derived from Singlet

Dose (ions cm' )

57

(1)

Doublet

S ( mms' )

Area (%)

S (mms' )

0.22 0.23 0.23 0.23 0.22

37 37 31 27 19

0.24 0.20 0.20 0.19 0.19

1

Least-Squares Copper—Iron

1

(2)

Q ( mms' )

Area (%)

0.58 0.66 0.66 0.67 0.66

53 26 28 27 34

1

* S is the shift with respect to a-iron and Q is the quadrupole splitting.


4.

Ion-Implanted

L O N G W O R T H A N D ATKINSON

107

Alloys

f o r fee y - i r o n . T h e r e m a i n i n g i r o n atoms h a v i n g b o t h i r o n a n d c o p p e r n e i g h b o r s w i l l see a finite q u a d r u p o l e i n t e r a c t i o n a t t r i b u t a b l e t o t h e d i s t o r t i o n o f t h e i r e l e c t r o n i c s c r e e n i n g charges

g i v i n g rise t o t h e

(11)

D o u b l e t 2. T h e a p p e a r a n c e o f S i n g l e t 4 a t a b o u t 0.4 m m s " i s u n e x p e c t e d . 1

I n the spectrum for a previous sample ( 5 X 1 0

1 6

ions c m " ) , Singlets 1 2

a n d 4 w e r e fitted t o a b r o a d singlet ( S ~ 0.3 m m s ' ) , a n d i t w a s o b s e r v e d 1

t h a t the w i d t h decreased a n d its shift r e v e r t e d t o t h a t f o r S i n g l e t 1 after the s a m p l e w a s a g e d f o r 2 h at 2 4 5 ° C ( 8 , 9 ) . I t w a s suggested t h a t this singlet w a s a t t r i b u t a b l e to i r o n atoms s i t u a t e d n e a r v a c a n c y clusters t h a t p r o d u c e a decreased S e l e c t r o n d e n s i t y . T h e v a c a n c y clusters d i s p e r s e d at a r e l a t i v e l y l o w t e m p e r a t u r e . I n a p r e v i o u s section i t w a s m e n t i o n e d Downloaded by UNIV LAVAL on October 23, 2015 | http://pubs.acs.org Publication Date: July 1, 1981 | doi: 10.1021/ba-1981-0194.ch004

t h a t i m p l a n t e d atoms create v a c a n c i e s as t h e y c o m e t o rest i n t h e l a t t i c e . H o w e v e r , as t h e d a m a g e is i n a metastable state d u r i n g i m p l a n t a t i o n , s u b s e q u e n t i m p l a n t e d atoms m a y b r e a k u p e x i s t i n g clusters o f v a c a n c i e s a n d t r a p these v a c a n c i e s . T h e present w o r k suggests t h a t t h e a n o m a l o u s l i n e is present f o r doses a b o v e a b o u t 2 X 1 0

1 6

ions c m " , w i t h the r e l a t i v e 2

a m o u n t i n c r e a s i n g w i t h dose. A l t h o u g h the cause is s t i l l n o t e n t i r e l y clear, i t is b e i n g i n v e s t i g a t e d f u r t h e r b y c a r e f u l a g i n g of t h e present samples and

b y electron microscopy.

I t i s i n t e r e s t i n g t o note t h a t t h e "defect-

a s s o c i a t e d " l i n e is n o t present i n t h e spectra f o r c a r b o n - i m p l a n t e d i r o n alloys (see next s e c t i o n ) , a l t h o u g h t h e c a r b o n doses w e r e a n o r d e r of m a g n i t u d e h i g h e r . T h i s illustrates t h e difference b e t w e e n t h e d a m a g e c a u s e d b y l i g h t a n d h e a v y ions.

Studies of Carbon-Implanted Iron Toils I o n i m p l a n t a t i o n p r o v i d e s a means of i m p r o v i n g t h e d u r a b i l i t y o f m e t a l surfaces (12).

A s a n e x a m p l e , the w e a r resistance of steel surfaces

m a y b e i n c r e a s e d b y t w o orders of m a g n i t u d e b y i m p l a n t i n g w i t h l i g h t ions s u c h as n i t r o g e n , c a r b o n , o r b o r o n (13).

F o r these measurements a

Fits to Mossbauer Electron Scattering Spectra of Implanted Alloys 0

Singlet S

(3)

Singlet

1

-0.11 -0.09 -0.09 -0.08 -0.08

s

Area

(mms' )

(

10 20 23 26 24

Area

mms' ) 1

0.42 0.41 0.41 0.37

(4)

(%) 17 19 21 22


108


l o a d e d p i n w e a r s against t h e r o t a t i n g i o n - i m p l a n t e d d i s c , a n d the w e a r rate of the c o u p l e is assessed m a i n l y f r o m t h e loss of m a t e r i a l f r o m t h e p i n a n d f r o m a n analysis of t h e t o t a l w e a r d e b r i s . C E M spectra f o r i r o n foils i m p l a n t e d w i t h n i t r o g e n ions w e r e u s e d (14) w e r e f o r m e d a b o v e a dose of a b o u t 1 X

10

1 7

to s h o w t h a t n i t r i d e s

ions c m " , w h i c h is c o m 2

p a r a b l e to the dose at w h i c h the m a x i m u m increase i n w e a r resistance of steel surfaces h a d b e e n o b s e r v e d (13).

T h e p r i n c i p l e of n i t r i d i n g surfaces

is not n e w a n d has b e e n u s e d p r e v i o u s l y t o h a r d e n surfaces b y i n t r o d u c i n g strong interatomic bonds.

F o r i m p l a n t e d steel, a l t h o u g h t h e o r i g i n a l

p e n e t r a t i o n d e p t h of n i t r o g e n ions is s h a l l o w , t h e i n c r e a s e d w e a r resist a n c e is l o n g l a s t i n g a n d is m a i n t a i n e d e v e n w h e n the w e a r t r a c k is s e v e r a l Downloaded by UNIV LAVAL on October 23, 2015 | http://pubs.acs.org Publication Date: July 1, 1981 | doi: 10.1021/ba-1981-0194.ch004

times the i m p l a n t a t i o n d e p t h i r o n foils s h o w e d

(14)

(12).

A n n e a l i n g the

nitrogen-implanted

changes i n the C E M spectra a b o v e a b o u t 2 7 5 ° C

associated w i t h d i f f u s i o n of the n i t r o g e n atoms w i t h i n t h e i m p l a n t e d l a y e r . A t h i g h e r temperatures ( ~

5 0 0 ° C ) the n i t r o g e n atoms h a d diffused

o u t of the i m p l a n t e d l a y e r i n t o the b u l k of the i r o n f o i l . l o w t e m p e r a t u r e of 2 7 5 ° C c o u l d w e l l b e r e a c h e d

T h e relatively

i n the

near-surface

layers d u r i n g w e a r , a l l o w i n g the n i t r o g e n ions to m i g r a t e to dislocations. This w i l l impede

the m o v e m e n t

of t h e dislocations

a n d g i v e rise to

h a r d e n i n g . A s w e a r p r o c e e d s b o t h the dislocations a n d n i t r o g e n are d r i v e n d e e p e r , thus c o n t i n u o u s l y r e c r e a t i n g a h a r d surface

atoms

(12).

C E M spectra h a v e b e e n m e a s u r e d also for i r o n foils i m p l a n t e d w i t h 4 0 - k e V c a r b o n ions ( F i g u r e 5 ) . 10 (H

1 6

and 1 X ~

10

195 k O e )

ions c m "

T h e spectra for i n c i d e n t doses of 5

X

2

contain components from iron and F e C

(Table II).

F o r the h i g h e r doses as w e l l as t h e i r o n

1 7

3

c o m p o n e n t there is a n i n c r e a s i n g c o n t r i b u t i o n f r o m F e C 5

180, a n d 120 k O e ) .

~

(H

2

220,

A l s o s h o w n i n T a b l e I I a r e the r e t a i n e d doses, p e a k

c a r b o n concentrations, a n d profile p e a k positions as a f u n c t i o n of i n c i d e n t dose, a s s u m i n g a s p u t t e r i n g r a t i o of 0.95

(15,16).

I n t h e absence of

s p u t t e r i n g the m e a n range is 500 A a n d o- is 250 A . T h e effect of s p u t t e r i n g o n the i m p l a n t a t i o n profile is m a r k e d a b o v e a b o u t 2 X 1 0

1 7

ions c m " . 2

F o r this dose the e x p e c t e d p e a k c o n c e n t r a t i o n , ~ 27 at. % , is sufficient to a l l o w the f o r m a t i o n of F e C . 5

2

U s i n g F i g u r e 2 a n d t h e p a r a m e t e r s for

the e x p e c t e d i m p l a n t a t i o n profile w e c a n c a l c u l a t e the e x p e c t e d r e l a t i v e area a t t r i b u t a b l e to c a r b i d e i n the C E M s p e c t r u m .

If w e

approximate

t h e G a u s s i a n profile b y a r e c t a n g u l a r d i s t r i b u t i o n c e n t e r e d at 400 A a n d of w i d t h 500 A

(2a),

t h e n t h e e x p e c t e d c o n t r i b u t i o n f r o m i r o n atoms

w i t h i n this d i s t r i b u t i o n is a b o u t 2 8 % of the t o t a l C E M s p e c t r u m . T h i s is i n g o o d agreement w i t h t h e o b s e r v e d v a l u e of 3 0 % ( T a b l e I I ) .

However,

for greater i n c i d e n t doses, since the p e a k c a r b o n c o n c e n t r a t i o n is m u c h h i g h e r t h a n the c a r b o n c o n c e n t r a t i o n i n F e C , i t is c l e a r that some e x p a n 5

2

s i o n of the i m p l a n t a t i o n profiles m u s t h a v e t a k e n p l a c e . T h e effect of t h e r m a l a n n e a l i n g o n one s a m p l e ( 4 X 1 0

1 7

ions

cm" ) 2

is s h o w n i n F i g u r e 6. N o c h a n g e w a s o b s e r v e d b e l o w a b o u t 4 0 0 ° C w h e n



4.


lon-lmplanted

109

Alloys

1

VELOCITY ( m m s . )

Figure 5. CEM spectra for iron foils in the received condition (ASR) or implanted with 5 X 10 , and 1, 2, 4, 6, and 8 X J O carbon ions cm' 1 7

16

2

Table II. Variation of Retained Dose, Implantation Profile Parameters, and Relative A r e a Attributable to Carbide i n C E M Spectrum, w i t h Implanted Dose for 40-keV Carbon i n Iron, Using a Sputtering Ratio of 0.95 Incident Dose (ions cm' ) 2

5 1 2 4 6 8

X x X X X X

10 io 10 10 10 10

1 6

1 7 1 7 1 7 17 1 7

Retained Dose (ions cm' ) 2

4.90 9.60 1.88 3.40 4.20 4.40

X X X X X X

10 10 10 10 10 10

16 1 6

1 7 1 7 1 7 1 7

Peak Position (A) 500 450 400 300 150 50

Carbon Concentration (at. %) 8.7 15.9 27 40 47 49

Carbide Area (%) ~ 5 9 30 59 61 67


110

mossbauer


T

spectroscopy

i

i

i

and

i

VELOCITY

its

i

chemical

applications

r

(mm.s'1)

Figure 6. CEM spectra for a carbon-implanted iron foil for a dose of 4 X 10 carbon ions cm' as a function of annealing for 1 h at various temperatures 17

2

the c a r b i d e c o n t r i b u t i o n b e g a n to decrease, b e c o m i n g z e r o at a b o u t 6 0 0 ° C . T h i s suggests t h a t a b o v e 4 0 0 ° C t h e r m a l d i f f u s i o n of c a r b o n atoms is sufficient to a l l o w t h e m to m i g r a t e a w a y f r o m t h e i m p l a n t e d l a y e r . S u c h a r e l a t i v e l o w t e m p e r a t u r e m i g h t suggest t h a t t h e c a r b i d e is p r e s e n t i n t h e f o r m of

small precipitates surrounded by

a uniform layer.

a - i r o n r a t h e r t h a n as

I t s h o u l d b e p o s s i b l e to c h e c k

this u s i n g

electron

microscopy. C a r b i d e s p r o d u c e d b y i o n i m p l a n t a t i o n are m o r e stable t h a n n i t r i d e s , a n d therefore m a y s h o w m o r e p r o m i s e f o r i m p r o v e m e n t s i n w e a r resist ance. S u c h w e a r measurements f o r p u r e - i r o n foils i m p l a n t e d w i t h e i t h e r n i t r o g e n o r c a r b o n c u r r e n t l y are i n progress i n c o n j u n c t i o n w i t h M o s s b a u e r measurements. I n this w a y i t s h o u l d b e p o s s i b l e to c h e c k w h e t h e r i n fact the n i t r o g e n / c a r b o n atoms are d r i v e n d e e p e r i n as w e a r proceeds.


4.

Ion-Implanted


111

Alloys

Studies of Glazes on Painted Ceramic Objects T h e r e h a v e b e e n several p u b l i c a t i o n s i n w h i c h M o s s b a u e r a b s o r p t i o n spectra h a v e b e e n u s e d to s t u d y the b o d y f a b r i c of potsherds e x a m p l e , Refs. 17,18,19).

(see,

for

H e r e w e are c o n c e r n e d w i t h i n v e s t i g a t i n g t h e

f e a s i b i l i t y of u s i n g M o s s b a u e r s c a t t e r i n g to e x a m i n e surface glazes. T h e d e c o r a t i o n o n A t t i c p o t t e r y f r e q u e n t l y w a s b a s e d o n the use of b l a c k or r e d colors.

T h e s e colors are associated w i t h v a r i o u s forms

of

i r o n o x i d e d e r i v e d f r o m the i r o n i n t h e o r i g i n a l clay. T h e surface glazes t y p i c a l l y are several tens of m i c r o n s t h i c k a n d thus are a m e n a b l e n o n d e s t r u c t i v e e x a m i n a t i o n b y M o s s b a u e r scattering.

Ideally we

to

may


i d e n t i f y t h e p a r t i c u l a r o x i d e to g a i n i n f o r m a t i o n a b o u t the m e t h o d

of

m a n u f a c t u r e . T h e G r e e k or A t t i c B l a c k W a r e d a t i n g f r o m a r o u n d 500 B C consists of a s h i n y b l a c k gloss o n a r e d b o d y f a b r i c (20).

A t a b o u t the

same t i m e o n the I n d i a n s u b c o n t i n e n t , the P a i n t e d G r e y W a r e of I n d i a h a d r e a c h e d its highest d e v e l o p m e n t i n the N o r t h e r n B l a c k P o l i s h e d W a r e (21).

H e r e the b l a c k gloss is s o m e w h a t d u l l e r a n d is b a s e d o n a grey b o d y

f a b r i c . I n e a c h case the colors w e r e p r o d u c e d essentially u s i n g the same c l a y as i n the b o d y f a b r i c , b y c o n t r o l of t h e a t m o s p h e r e d u r i n g the

firing,

a n d i t is i n t e r e s t i n g to i d e n t i f y a n d c o m p a r e the i r o n - c o n t a i n i n g c o m p o u n d i n e a c h case.

A s a n e x a m p l e of r e d - p a i n t e d p o t t e r y w e s t u d i e d

some samples of r e d S a m i a n W a r e d a t i n g f r o m several centuries later. T h e thickness a n d degree of s i n t e r i n g or v i t r i f i c a t i o n of the surface glazes were investigated using scanning electron microscopy

( S E M ) b y M . S.

T i t e of t h e B r i t i s h M u s e u m R e s e a r c h L a b o r a t o r y . P r e l i m i n a r y results of this c o m b i n e d s t u d y h a v e b e e n p u b l i s h e d p r e v i o u s l y A t t i c Black Ware.

(22).

S E M measurements i n d i c a t e extensive v i t r i f i c a

t i o n of t h e gloss a n d b o d y f a b r i c , t h e gloss b e i n g 2 0 - 3 0 /xm t h i c k . I n one s a m p l e , G A 2 A , t h e gloss w a s f o u n d to consist of t w o layers of r o u g h l y e q u a l t h i c k n e s s , w i t h the outer l a y e r s h o w i n g m o r e v i t r i f i c a t i o n . C X M spectra ( F i g u r e 7) contain magnetic components

(H

~

465 k O e ) that m a y be i d e n t i f i e d w i t h a n i m p u r e f o r m of m a g n e t i t e . is a n a d d i t i o n a l c o m p o n e n t

(H

~

The

489 a n d There

503 k O e ) i n t h e s p e c t r u m for G A 2 A

that is s i m i l a r i n field v a l u e to t h a t i n t h e a b s o r p t i o n spectra ( F i g u r e 8 ) f o r the b o d y f a b r i c (H (hematite).

~

505 k O e ) ; this is a t t r i b u t a b l e to f e r r i c o x i d e

T h e appearance

of t w o different oxides i n t h e gloss

for

G A 2 A is p r o b a b l y associated w i t h the d u a l - l a y e r e d n a t u r e . I t m u s t b e r e m e m b e r e d also t h a t f o r this a p p r o x i m a t e gloss thickness, a b o u t 6 0 %

of

t h e s p e c t r u m c o m e s f r o m the gloss m a t e r i a l , w i t h the r e m a i n d e r c o m i n g f r o m the b o d y f a b r i c . Samian Ware.

B o t h C X M a n d absorption spectra ( F i g u r e s 7 a n d 8)

g i v e a c l e a r i n d i c a t i o n of h e m a t i t e as e x p e c t e d

(H

~

505 k O e ) ,

a g a i n the gloss appears t o b e f u l l y v i t r i f i e d .


and

112


[12% fo

A^\JV^y

Vvft^' Vrfwy/

V**/^

Wv^i

GA 2 A

;15% :

GA1C

0

:10% BM1 =0 0-6%

:


:

:

^ / • V

Vv^-.-Z \*^'j~r

^V*~7\*/ ' V ^ V / ' V ^ y ^ y . ^

BRH1

0 15% IND2

:

0

-0-6%

IND£ -16'

15

10

-15 VELOCITY

(mm.s

1

)

Figure 7. CXM spectra for surface gloss on samples of Greek Attic Black Ware (GA2A, GA1C), Samian Ware (BM1, BRH1), and Indian Northern Black Polished Ware (IND2, IND4)

VELOCITY

(mm.s

- 1

)

Figure 8. Mossbauer spectra for body fabric of Greek Attic Black (GA2A, GA1A), Samian Ware (BM1 BRH1), and Indian Northern Polished Ware (IND2, IND4) 9


Ware Black

4.


Ion-Implanted

113

Alloys

S E M measurements o n t w o sam

Northern Black Polished Ware.

ples i n d i c a t e a gloss thickness o f o n l y 1 0 - 1 5 / m i , w i t h n e i t h e r gloss n o r b o d y f a b r i c b e i n g v i t r i f i e d . B e c a u s e of this r e s t r i c t e d t h i c k n e s s , i t i s n o t s u r p r i s i n g that the C X M a n d a b s o r p t i o n spectra o n f o u r samples are v e r y s i m i l a r ( F i g u r e s 7 a n d 8 ) . T h e y consist o f t w o d o u b l e t s , o n e c o m p r i s i n g a b o u t 6 0 % of t h e t o t a l a r e a a t t r i b u t a b l e t o ferrous ions ( s h i f t S ~ 1.07 mms" , splitting Q ~ 1

2.35 m m s " ) a n d t h e other, t h e r e m a i n i n g 4 0 % , 1

a t t r i b u t a b l e to f e r r i c ions ( S ~ 0.48 m m s " , Q ~ 1.07 m m s " ) . 1

1

F o r the

m e a s u r e d gloss thickness t h e i r o n atoms i n t h e gloss w i l l c o n t r i b u t e o n l y a b o u t 2 0 % of t h e C X M s p e c t r u m .

I n t h e C E M spectra f o r t h e same

samples there is p r e d o m i n a n t l y a d o u b l e t a t t r i b u t a b l e t o f e r r i c ions ( S ~ 0.41 m m s , Q ~ Downloaded by UNIV LAVAL on October 23, 2015 | http://pubs.acs.org Publication Date: July 1, 1981 | doi: 10.1021/ba-1981-0194.ch004

- 1

0.93 m m s " ) . 1

T h i s c o m p r i s e s t h e entire s p e c t r u m f o r

the t w o samples I N D 1 a n d I N D 5, 7 0 % o f t h e s p e c t r u m f o r I N D 4 ( F i g u r e 9 ) , the r e m a i n d e r b e i n g a d o u b l e t a t t r i b u t a b l e to ferrous ions, a n d 5 0 % o f the s p e c t r u m for I N D 2, the r e m a i n d e r b e i n g a m a g n e t i c s p e c t r u m w i t h H ~ 487 k O e ( F i g u r e 9 ) . T h u s , o n l y i n t h e s p e c t r u m f o r t h e gloss o n o n e s a m p l e is there e v i d e n c e f o r a c o m p o n e n t t h a t r e a s o n a b l y m a y b e associated w i t h a n i m p u r e f o r m o f m a g n e t i t e . I t is possible t h a t f o r t h e r e m a i n i n g samples, a n y m a g n e t i t e is i n s u c h a finely d i v i d e d f o r m t h a t i t is s u p e r p a r a m a g n e t i c at r o o m t e m p e r a t u r e . A l t e r n a t i v e l y , t h e l a y e r s t u d i e d b y C E M S

( ~ 10

3

A ) m a y n o t b e c h a r a c t e r i s t i c o f t h e m a i n thickness o f t h e gloss ( ~ 1 0 1

i

i

i

i

i

-06%

.'. .

-0

JV I

:

•' ' •

IND 2

1

-06%

-15

-10

-5 i

0

5 i VELOCITY

Figure 9.

-

INDZ, ' 15 i

10 i (mm s

1

)

CEM spectra for surface gloss on samples of Indian Black Polished Ware (IND2, IND4)

Northern


114


ju,m) b e c a u s e o f t h e effects o f w e a t h e r i n g .

I f this w e r e t h e case, t h e n

n e i t h e r t y p e of s c a t t e r i n g s p e c t r u m w o u l d b e representative o f t h e gloss as a w h o l e . T h e differences i n v i t r i f i c a t i o n b e t w e e n t h e three types of p o t t e r y indicate a lower 800°C)

firing

temperature for Northern B l a c k Polished W a r e

a n d a somewhat

higher temperature for A t t i c B l a c k a n d

S a m i a n W a r e s ( 8 5 0 - 1 0 5 0 ° C ) . W h e n samples of I N D 1 a n d I N D 2 w e r e h e a t e d i n a i r a t 9 0 0 ° C , b o t h gloss a n d b o d y f a b r i c b e c a m e r e d i n c o l o r , indicating

oxidation.

T h e Mossbauer

absorption

spectra

showed

no

c o m p o n e n t a t t r i b u t a b l e to ferrous ions, a n d i n o n e case, I N D 2 s h o w e d a component

a t t r i b u t a b l e t o h e m a t i t e (H ~ 514 k O e , 4 0 % o f t h e t o t a l


a r e a ) . T h e s e results are i n contrast t o those o b t a i n e d o n r e f i r i n g samples of A t t i c B l a c k W a r e i n a i r , w h e n t h e c o l o r o f t h e gloss d i d n o t c h a n g e . T h i s is i n agreement w i t h t h e suggested l o w e r o r i g i n a l firing t e m p e r a t u r e for

N o r t h e r n B l a c k P o l i s h e d W a r e , w h i c h leaves

t h e gloss

partially

v i t r i f i e d a n d thus a b l e to b e r e o x i d i z e d . It is difficult t o i d e n t i f y t h e c o m p o u n d s

r e s p o n s i b l e f o r t h e ferrous

a n d f e r r i c d o u b l e t s i n t h e spectra f o r N o r t h e r n B l a c k P o l i s h e d b o d y f a b r i c o n t h e basis o f t h e i r h y p e r f i n e p a r a m e t e r s because o f t h e r e l a t i v e l a c k of sensitivity o f these p a r a m e t e r s to s t r u c t u r a l changes i n silicate structures. Part of the ferric doublet i n the spectrum for Sample I N D 2, however, appears to result f r o m

finely

d i v i d e d i r o n o x i d e , since a t 4.2 K t h e

s p e c t r u m contains a b o u t 1 5 % o f a m a g n e t i c c o m p o n e n t ( f l ^ 480 k O e ) . A l t h o u g h the amount of information t o be gained from

Mossbauer

s c a t t e r i n g spectra is l i m i t e d b y t h e i r r e l a t i v e l y p o o r q u a l i t y , p a r t i c u l a r l y the C E M spectra, t h e difference b e t w e e n t h e structures o f t h e b l a c k gloss o n A t t i c a n d N o r t h e r n B l a c k P o l i s h e d W a r e is q u i t e a p p a r e n t .

Future

w o r k w i l l d e p e n d u p o n i m p r o v i n g t h e q u a l i t y o f these spectra b y r e d u c i n g the b a c k g r o u n d s c a t t e r i n g i n t h e detector. compounds

Identification of the i r o n

w o u l d b e f a c i l i t a t e d b y m e a s u r i n g t h e s c a t t e r i n g spectra a t

77 K . T h i s w o u l d also a l l o w a m e a s u r e m e n t o f t h e s u p e r p a r a m a g n e t i c f r a c t i o n , f r o m w h i c h a n i d e a o f p a r t i c l e size m a y b e g a i n e d .

Acknowledgments T h e authors w o u l d l i k e to t h a n k T . E . C r a n s h a w a n d R . E . J . W a t k i n s for several f r u i t f u l discussions. T h e c o l l a b o r a t i o n of N . E . W . H a r t l e y i n the w o r k o n c a r b o n - i r o n alloys a n d M . S. T i t e i n t h e w o r k o n p a i n t e d c e r a m i c s is g r a t e f u l l y a c k n o w l e d g e d .

Literature Cited 1. Sette C . A.; Keune, W . Corros. Sci. 1975, 15, 4 4 1 . 2. Graham, M . J.; Mitchell, D . F . ; Channing, D . A . Oxid. Met. 1978, 1 2 , 2 4 7 .



4.


Ion-Implanted

Alloys

115

3. Bäverstam, U . ; Ekdahl, T.; Bohm, C.; Liljequist, D . ; Ringström, B. Nucl. Instr. Meth. 1974, 118, 313. 4. Bodlund-Ringström, B.; Bäverstam, U . ; Bohm, C . J. Vac. Sci. Technol. 1979, 16, 1013. 5. Lindhard, J.; Scharff, M . ; Schiott, H . E . Mater. Fys. Medd. Dan. Vid. Selsk. 1963, 33(14). 6. Matthews, M . D . U K A E A Report, 1973, AERE-R7805. 7. Nelson, R. S. Proc. Roy. Soc. 1969, A311, 53. 8. Longworth, G.; Jain, R. J. Phys. F. 1978, 8, 351. 9. Jain, R.; Longworth, G . J. Phys. F 1978, 8, 363. 10. Longworth, G.; Jain, R. J. Phys. F 1978, 8, 993. 11. Window, B. J. Phys. Chem. Solids 1971, 32, 1059. 12. Dearnaley, G.; Hartley, N . E. W . Thin Solid Film 1978, 54, 215. 13. Hartley, N . E. W . Wear 1975, 34, 427. 14. Longworth, G.; Hartley, N . E . W . Thin Solid Films 1978, 48, 95. 15. Watkins, R. E. J., private communication, 1979. 16. Bert, R.; Charlesworth, J. P. U K A E A Report, 1973, AERE-R7052. 17. Kostikas, A.; Simopoulos, A.; Gangas, N . H . J. Phys. (Paris) 1974, 35, C6-537. 18. Bouchez, R.; Coey, J. M . D . ; Coussement, R.; Schmidt, K. P.; van Rossum, M . ; Aprahamian, J.; Deshayes, J. J. Phys. (Paris) 1974, 35, C6-541. 19. Riederer, J.; Wagner, U . ; Wagner, F . E . Radiochem. Radioanal. Lett. 1979, 40(5), 319. 20. Bimson, M . Antiquaries J. 1956, 36, 200. 21. Hegde, K. T . M . Antiquity, 1975, XLIX, 187. 22. Longworth, G.; Tite, M . S. J. Phys. (Paris) 1979, 40, C2-460. R E C E I V E D June 27,

1980.


MÃ¶ssbauer Spectroscopy and Its Chemical Applications

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