Electron Transfer in Biology and the Solid State - American Chemical

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Organometallic Chemical Vapor Deposition Strategies and Progress in the Preparation of Thin Films of Superconductors Having High Critical Temperatures L a u r e n M. Tonge, D a r r i n S. Richeson, Tobin J. M a r k s , Jing Zhao, Jiming Zhang, Bruce W. Wessels, H e n r y O . M a r c y , and C a r l R . K a n n e w u r f Materials Research Center, Northwestern University, Evanston, IL 60208-3113

Highly oriented films of the high-critical-temperature ductors YBa Cu O , 2

3

7-δ

Bi (Sr,Ca) Cu O , 2

3

2

(T )

supercon

c

and TlBa Ca Cu O

x

2

2

3

be prepared by organometallic chemical vapor deposition by

using

volatile

molecular

β-diketonate

metallic (triphenylbismuth,

(OMCVD)

(acetylacetonate,

valoylmethanate, heptafluorodimethyloctanedionate)

and

cyclopentadienylthallium)

After annealing, zero-resistance

can

x

dipi

organo

precursors.

temperatures for these three films

are 86, 75, and 102 K, respectively. Keys to high-quality

OMCVD

-derived films include the use of fluorocarbon-containing

precursors,

the use of low deposition pressures, the use of water as a reactant gas, and the use of rapid thermal annealing

T H E

techniques.

R E C E N T D I S C O V E R Y O F S E V E R A L C L A S S E S of s u p e r c o n d u c t i n g m i x e d -

m e t a l oxides w i t h c r i t i c a l t e m p e r a t u r e (T ) values greater than 77 Κ has c

s t i m u l a t e d intense w o r l d w i d e scientific interest ( 1 - 3 ) . O n e area of great activity has b e e n t h e d e v e l o p m e n t o f processes to p r o d u c e h i g h - q u a l i t y t h i n films o f these materials (4-6), because i t is l i k e l y that h i g h - T s u p e r c o n d u c c

tors w i l l first have technological i m p a c t i n this f o r m . Efforts to date h a v e p r i m a r i l y c e n t e r e d o n p h y s i c a l vapor d e p o s i t i o n ( P V D ) t e c h n i q u e s s u c h as s p u t t e r i n g , e v a p o r a t i o n , m o l e c u l a r b e a m epitaxy, a n d laser a b l a t i o n (4-6). 0065-2393/90/0226-0351$06.00/0 © 1990 American Chemical Society

In Electron Transfer in Biology and the Solid State; Johnson, M., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1989.

352

E L E C T R O N T R A N S F E R IN BIOLOGY A N D T H E SOLID STATE

A n attractive alternative c h e m i c a l vapor deposition ( C V D ) approach is o r ganometallic c h e m i c a l vapor deposition ( O M C V D ) (7, 8).

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S u c h a process produces films b y u s i n g volatile m e t a l - o r g a n i c m o l e c u l a r precursors and suitably designed gas-phase r e a c t i o n - d e p o s i t i o n c h e m i s t r y . I n p r i n c i p l e , O M C V D offers t h e advantages over P V D o f r e l a t i v e l y s i m p l e apparatus, a m e n a b i l i t y to large-scale d e p o s i t i o n , a b i l i t y to coat v a r i o u s l y shaped objects, adaptability to a w i d e range o f materials, t h e p o s s i b i l i t y o f d e p o s i t i o n at l o w temperatures, a n d t h e possibility o f c r e a t i n g metastable structures. I n d e e d , O M C V D is t h e t e c h n i q u e o f choice for t h e large-scale fabrication o f films o f I I I - V a n d I I - V I semiconductors (7), a n d i t has b e e n u s e d to p r o d u c e films o f a v a r i e t y o f m e t a l oxides (8-12). W i t h regard to p r o d u c i n g h i g h - T s u p e r c o n d u c t i n g t h i n films b y O M C V D , c r u c i a l questions c o n c e r n w h e t h e r suitable precursors a n d d e p osition c h e m i s t r y c a n b e d e v e l o p e d . T h i s chapter reviews recent efforts at N o r t h w e s t e r n U n i v e r s i t y to d e v e l o p O M C V D processes for h i g h - T s u p e r c o n d u c t i n g films a n d describes some o f the properties o f the r e s u l t i n g films. F i l m s o f the Y B a g C u a O ^ , ( B i O ) S r C a „ _ C u 0 , a n d ( T l O ) B a C a _ C u O classes o f superconductors can b e p r e p a r e d o n a variety o f substrates. T h e s e films have excellent phase p u r i t y , h i g h degrees o f preferential o r i e n t a t i o n , a n d good e l e c t r i c a l p r o p e r t i e s . c

c

2

2

1

n

3E

I I I

2

l l

1

l l

I

Strategies for Precursor Design and Deposition Methodology A r e q u i s i t e p r o p e r t y for a l l O M C V D precursors m u s t b e suitable v o l a t i l i t y . A n attractive strategy to achieve this volatility is to m i n i m i z e lattice cohesive energies b y encapsulating t h e m e t a l i o n i n a sterically saturating n o n p o l a r l i g a n d e n v i r o n m e n t (13,14). L i g a n d fluorination is k n o w n to f u r t h e r p r o m o t e volatility (13, 14). F o r large divalent a n d t r i v a l e n t ions (especially C a , S r , B a , a n d Y ) , such r e q u i r e m e n t s c a n b e satisfied o n l y w i t h b u l k y , m u l t i d e n t a t e ligands (15). O t h e r i m p o r t a n t considerations i n p r e c u r s o r s e l e c t i o n i n c l u d e ease o f synthesis, p u r i f i c a t i o n , a n d h a n d l i n g . A l l factors b e i n g e q u a l , air-stable precursors are most desirable because t h e y are m o r e c o n v e n i e n t l y m a n i p u l a t e d a n d r e q u i r e less s p e c i a l i z e d apparatus. F i n a l l y , O M C V D precursors must display appropriate gas-phase reactivity for t h e formation o f films (i.e., a p r e c u r s o r that is c h e m i c a l l y i n e r t w i l l b e useless). 2 +

2 +

2 +

3 +

F o r o u r i n i t i a l h i g h - T O M C V D experiments (16-21), β-diketonate c o m plexes w e r e chosen for C u , Y, C a , S r , a n d B a sources (structure 1). Cu(acac) (acac is acetylacetonate), Y ( d p m ) , C a ( d p m ) , a n d S r ( d p m ) ( d p m is d i p i v a l oylmethanate) are sufficiently volatile to transport the respective metals. I n o u r hands, h o w e v e r , B a ( d p m ) (16, 17) has insufficient volatility. A t t e m p t s to transport it result i n i r r e p r o d u c i b l e vapor pressure characteristics, t h e r m a l d e c o m p o s i t i o n , a n d l o w deposition y i e l d s . I n contrast to B a ( d p m ) , w e f i n d that Ba(fod) (fod is heptafluorodimethyloctanedionate) (16) is m o r e v o l a t i l e , exhibits steady vapor pressure, a n d transports B a at l o w e r temperatures a n d c

2

3

2

2

2

2

2


18.

353

Organometallic Chemical Vapor Deposition

TONGE ET AL.

,0 M

Ri

— C

/

;CH


0 —C

Ri = R

2

= CH

Ri = R

2

= C(CH )

3

3

Ri = C(CH ) ; R 3

3

3

= CF CF CF

2

2

2

M(acac)

n

M(dpm)

n

M(fod)

3

n

1 w i t h far less d e c o m p o s i t i o n . It also serves as a beneficial source of

fluoride

(vide infra). F o r B i a n d T l sources, the organometallic c o m p o u n d s t r i p h e n y l b i s m u t h (structure 2) a n d c y c l o p e n t a d i e n y l t h a l l i u m (structure 3) offer h i g h volatility, air stability, a n d reactivity w i t h respect to d e p o s i t i o n c h e m i s t r y (vide infra). A l l precursors u s e d i n this w o r k w e r e

rigorously

purified by

m u l t i p l e s u b l i m a t i o n or recrystallization.

3

2

W i t h r e g a r d to d e s i g n i n g O M C V D c h e m i s t r y , the goal has b e e n to e m p l o y reagents that cleanly strip ligands from the p r e c u r s o r m o l e c u l e s u n d e r as m i l d conditions as possible, to afford less-volatile p r o d u c t s . I n p r i n c i p l e , s i m p l e oxidation (eq 1) offers one s u c h approach. ML

n

+ 0

2

— M O

+ L oxidation p r o d u c t s

x

(1)

w h e r e M is m e t a l a n d L is l i g a n d . H o w e v e r , it appears to r e q u i r e v e r y h i g h d e p o s i t i o n temperatures for h i g h - T s u p e r c o n d u c t o r O M C V D (19) a n d p r o duces significant y i e l d s of B a F w h e n a p p l i e d to Ba(fod) transport (eq 2) (15, 22). c

2

Ba(fod)

2

+ 0

2

— B a F

2

2

+ other products


(2)

354

E L E C T R O N T R A N S F E R IN B I O L O G Y A N D T H E S O L I D S T A T E

Protonolysis of the precursor m e t a l - l i g a n d b o n d s w i t h w a t e r vapor (eqs 3 a n d 4) appears to b e a cleaner, m i l d e r approach, a n d the h y d r o x i d e p r o d u c t s are e x p e c t e d to u l t i m a t e l y condense a n d y i e l d nonvolatile oxides. L M - O R + H 0 -^-> L M - O H + R O H n

2

L M-R' + H 0 Downloaded by UNIV OF CALIFORNIA SAN FRANCISCO on February 17, 2015 | http://pubs.acs.org Publication Date: May 5, 1989 | doi: 10.1021/ba-1990-0226.ch018

n

(3)

n

L M-OH + R'H

2

(4)

n

F u r t h e r m o r e , w e B n d that w a t e r vapor c a n b e e m p l o y e d to c o n t r o l t h e a m o u n t o f B a F p r o d u c e d i n Ba(fod) O M C V D (eq 5) (16, 22). 2

2

BaF

+ H 0

2

BaO + 2 H F

2

(5)

I n practice, w e find that oxygen saturated w i t h water vapor a n d w a t e r v a p o r alone are excellent reactant gases for the d e p o s i t i o n process. O M C V D was c a r r i e d out at l o w pressure ( 2 6 6 - 6 6 6 P a [ 2 - 5 ton*]) i n a c o l d - w a l l h o r i z o n t a l quartz reactor w i t h separate, p a r a l l e l , h e a t e d q u a r t z i n l e t tubes for i n t r o d u c i n g the precursors i n a n argon stream. L o w - p r e s s u r e operation is p a r t i c u l a r l y useful i n m a x i m i z i n g d e p o s i t i o n y i e l d s at l o w p r e cursor temperatures. Substrates w e r e located o n a c a r b o n susceptor that was h e a t e d w i t h an I R l a m p . Reactant gases w e r e i n t r o d u c e d i m m e d i a t e l y u p stream from the susceptor. Substrates e m p l o y e d i n c l u d e [100] single-crystal M g O , [100] single-crystal S r T i 0 , a n d 9.5 m o l % y t t r i a - s t a b i l i z e d z i r c o n i a (YSZ) w i t h r a n d o m orientation. F o l l o w i n g d e p o s i t i o n , films w e r e a n n e a l e d u n d e r oxygen i n a m a n n e r appropriate to each m a t e r i a l (vide infra). 3

M i c r o s t r u c t u r a l characterization of O M C V D - d e r i v e d films was c a r r i e d out b y X - r a y diffraction ( C u K J , scanning e l e c t r o n m i c r o s c o p y ( S E M ) , scan n i n g A u g e r spectroscopy, a n d energy-dispersive X - r a y analysis ( E D X ) . C h a r g e - t r a n s p o r t characterization e m p l o y e d four-probe t e c h n i q u e s a n d the automated i n s t r u m e n t a t i o n d e s c r i b e d p r e v i o u s l y (23, 24).

OMCVD ofYBa Cu 0 _s Films 2

3

7

D e p o s i t i o n of Y B a C u 0 _ films can b e c a r r i e d out b y u s i n g the p r e c u r sor combinations C u ( a c a c ) 4- Y ( d p m ) + Ba(fod) (16) o r C u ( a c a c ) + Y ( d p m ) + B a ( d p m ) (17), w i t h the f o r m e r precursors p r e f e r r e d (vide supra). I n s u c h e x p e r i m e n t s , source temperatures w e r e 150, 100, a n d 170 °C for the C u , Y, a n d B a precursors, respectively. T h e system pressure was 666 P a (5 torr), the substrate t e m p e r a t u r e was 700 °C, a n d water vapor was e m p l o y e d as the reactant gas. T h e i n i t i a l l y d e p o s i t e d films are largely a m o r phous (as shown b y X - r a y diffraction, F i g u r e 1A) a n d i n s u l a t i n g . A s can also b e seen i n F i g u r e 1 A , the as-deposited films contain traces of B a F . T h e amounts of B a F can be increased b y i n c r e a s i n g the 0 / H 0 ratios i n the reactant gas d u r i n g deposition (16, 22). 2

3

7

8

2

3

3

2

2

2

2

2

2

2


18.

355


TONGE E T AL.

ι ι ι ι ι I ι ι ι ι ι ι ι ι ι I ι ι ι ι ι ι ι ι ι I ι ι ι ι ι ι » ι ι I

m o o

B

CO

o o

m •t-4

00


o o

S-i (d

u CM

*4

^ CO

S

CM O

κ,

CO

MgO

2

^-s

O

ω 2

A

BaF (lll) 2

Y 0 (222) 2

8

I I I I I I » ι ι ι I ι ι ι ι ι ι ι ι ι I ι ι ι ι ι ι ι ι ι I I » ι ι ι ι ι ι ι I

20.0

30.0

40.0 2 θ (Degrees)

50.0

60.0

Figure 1. X-ray diffraction patterns of (A) an as-deposited, OMCVD-derived Y-Ba-Cu-O film on [100] MgO and (B) Y-Ba-Cu-0 film on [100] MgO after annealing.

A n n e a l i n g o f the film i n F i g u r e 1 A u n d e r flowing oxygen for 10 h at 600 °C, 1.5 h at 900 ° C , a n d 10 m i n at 960 °C p r o d u c e s c r y s t a l l i n e , 0 . 5 - 2 . 0 - μ η ι t h i c k films o f t h e Y B a C u 0 _ superconductor ( F i g u r e I B ) . T h e e n h a n c e d relative intensities of the (00Î) reflections versus those i n a r a n d o m l y o r i e n t e d p o w d e r indicate significant preferential orientation o f the crystallite c axes p e r p e n d i c u l a r to the plane o f the substrate. H e n c e , the charge-transporting C u O sheets are o r i e n t e d p a r a l l e l to the plane of the substrate. M e a s u r e m e n t of the c axis l e n g t h indicates an oxygen stoichiometry o f a p p r o x i m a t e l y Y B a C u 0 . T h e r e is no diffraetometric e v i d e n c e for c o n t a m i n a t i n g C u O , B a C u 0 , or B a Y 0 phases (18). P r e l i m i n a r y studies (22) indicate that i n creasing the q u a n t i t y o f B a F increases t h e degree o f p r e f e r e n t i a l c axis 2

2

3

2

3

7

8

6 6

3

4

9

2


356

E L E C T R O N T R A N S F E R IN B I O L O G Y A N D T H E S O L I D STATE

orientation p e r p e n d i c u l a r to the substrate p l a n e . A s i m i l a r effect has b e e n n o t e d i n films d e p o s i t e d b y pyrolysis of m e t a l carboxylate coatings (25). F i g u r e 2 shows v a r i a b l e - t e m p e r a t u r e four-probe r e s i s t i v i t y data for an a n n e a l e d film of the type s h o w n i n F i g u r e I B . T h e m e t a l l i k e b e h a v i o r (dp/ d T > 0) at h i g h e r temperatures is characteristic of r e l a t i v e l y h i g h - q u a l i t y Y B a C u 0 _ 5 films (4-6), as is the onset of the s u p e r c o n d u c t i n g state at ~ 9 0 2

3

7


K . I n this p a r t i c u l a r s p e c i m e n , ρ =

0 occurs at 66.2 Κ (16). A s c a n n i n g

e l e c t r o n m i c r o g r a p h of a t y p i c a l a n n e a l e d Y B a C u 0 _ s film of the t y p e s h o w n 2

3

7

i n F i g u r e I B reveals l - 5 - μ η ι grains e v e n l y d i s t r i b u t e d o v e r the film ( F i g u r e 3). I n an effort to i m p r o v e film charge-transport characteristics a n d to m i n imize

film-substrate

reactions (26), r a p i d t h e r m a l a n n e a l i n g t e c h n i q u e s have

b e e n a p p l i e d (22). A n n e a l i n g as-deposited films i n flowing oxygen for 1.5 h at 870 °C a n d for several seconds at 980 °C c o n s i d e r a b l y enhances g r a i n size a n d grain overlap (evident i n S E M photographs), as w e l l as i n c r e a s i n g the ρ = 0 t e m p e r a t u r e s . T h e resistivity data s h o w n i n F i g u r e 4 indicate ρ = 0 temperatures for the Y B a C u 0 _ films subjected to r a p i d t h e r m a l a n n e a l i n g 2

on S r T i 0

3

3

7

8

a n d Y S Z o f 78 a n d 87 K , r e s p e c t i v e l y . T h e latter t e m p e r a t u r e is

100

150

TEMPERATURE

200 (K)

Figure 2. Variable-temperature four-probe resistivity data for an annealed OMCVD-derived YBa Cu 0 ^film on [100] MgO. 2

3

7



18.

T O N G E E T AL.

357


Figure 3. Scanning electron micrograph of an annealed OMCVD-derived YBa Cu 0 ^film on [100] MgO. 2

3

7

w i t h i n a f e w degrees o f t h e highest values y e t r e p o r t e d for Y B a C u 0 _ 2

3

7

8

films p r e p a r e d b y P V D techniques (4-6).

OMCVD of (BiO) Sr Ca ^Cu O 2

2

n

n

x

Films

I n contrast to t h e Y B a C u 0 _ system, t h e B i - S r - C a - C u - O s u p e r c o n d u c tors e x h i b i t a c o m p l e x crystal c h e m i s t r y w i t h T values as h i g h as 110 Κ (27-30). N e e d l e s s to say, O M C V D , i n u s i n g four sources, presents a great challenge. D e p o s i t i o n of B i - S r - C a - C u - O films was c a r r i e d o u t at 266 P a (2 torr) b y u s i n g t h e precursors B i ( C H ) , C a ( d p m ) , S r ( d p m ) , a n d Cu(acac) w i t h source temperatures of 1 4 5 - 2 3 0 °C a n d a substrate t e m p e r ature o f 550 ° C (31-34). T h e reactant gas was water-vapor-saturated oxygen. 2

3

7

8

c

6

5

3

2

2


2


358

E L E C T R O N TRANSFER IN BIOLOGY A N D T H E SOLID STATE

A l t h o u g h water vapor alone gives acceptable d e p o s i t i o n y i e l d s o f C a , S r , a n d C u oxides, oxygen is necessary to achieve efficient, simultaneous d e p osition o f B i . P r e s u m a b l y t h e h y d r o l y t i c stability o f the B i - p h e n y l b o n d is too great to a l l o w efficient p r o t o n o l y t i c cleavage. F i g u r e 5 A shows that the as-deposited B i - S r - C a - C u - O films are c r y s talline. H o w e v e r , t h e lattice parameters o f c = 24.4 Â a n d a = b = 5.4 Â indicate a p r e v i o u s l y o b s e r v e d (35,36) s e m i c o n d u c t i n g phase. S E M indicates an i r r e g u l a r , p r o b a b l y heterogeneous, film m i c r o s t r u c t u r e ( F i g u r e 6 A ) for the as-deposited films. A n n e a l i n g o f the as-deposited films i n f l o w i n g oxygen for 0.5 h at 600 °C a n d 0.5 h at 865 °C y i e l d s 3 - 6 ^ m - t h i c k films that (by X-ray diffraction, F i g u r e 5B) consist largely of the T = 85 Κ B i ( S r , C a ) C u O phase (27-30, 37, 38). T h e e n h a n c e d intensities o f t h e (001) reflections indicate significant p r e f e r e n t i a l o r i e n t a t i o n o f the crystallite c axes p e r p e n d i c u l a r to t h e surface o f the substrate. T h u s , as i n t h e case o f the Y B a C u 0 _ films, the charge-carrying C u O planes are f o r m e d p a r a l l e l to t h e substrate plane. T h e diffraction data also indicate traces o f the c = 37 A , T = 110 Κ B i ( S r , C a ) C u O phase (27-30, 37, 38), as w e l l as o f the c

2

3

2

c

2

3

7

x

8

2

4

3

x



18.

TONGE ET AL.

—I

359


: I I I I I I I I I I I I > I I » 1 I I I I I I I I I I I I I 1 ι ι ι ι ι ι ι I ι ι ι ι ι

20.0

30.0

40.0

50.0

60.0

2 θ (degrees) Figure 5. Α. X-ray diffraction pattern of an unannealed Bi-Sr-Ca-Cu-O film on [100] MgO. The tentative indexing assumes a tetragonal cell with e = 24.4 Â and a = b = 5.4 λ. Β. X-ray diffraction pattern of an annealed Bi-Sr-Ca-Cu-O film on [100] MgO. The reflections assigned to the T = 110 Κ (x) and semiconducting (o) phases are so indicated. C

aforementioned c = 24.4 Â s e m i c o n d u c t i n g phase. S E M data for a t y p i c a l annealed film r e v e a l a rough surface w i t h g r a i n sizes o f 5 - 1 5 μιη ( F i g u r e 6 B ) . Results o n Y S Z substrates are s i m i l a r . F i g u r e 7 shows charge-transport data for a t y p i c a l annealed O M C V D d e r i v e d B i - S r - C a - C u - O film o n [100] M g O . A s is t y p i c a l o f r e l a t i v e l y h i g h q u a l i t y films, transport is m e t a l l i c ( d p / d T > 0) at h i g h e r temperatures. T h e onset o f superconductivity begins at —110 K , w i t h ρ = 0 at 75 K . P V D d e r i v e d B i - S r - C a - C u - O films have b e e n r e p o r t e d to e x h i b i t ρ = 0 t e m peratures as h i g h as 100 Κ (39), although most reports are i n t h e 7 0 - 8 0 Κ range.

OMCVD of(TlO) Ba Ca ^Cu O m

2

n

n

x

Films

T h e ( T l O ^ B a a C a ^ C u A system (m = 1, 2; η = 1, 2, 3) exhibits t h e greatest m u l t i p l i c i t y o f h i g h - T s u p e r c o n d u c t i n g phases (27-30), i m p r e s s i v e e n v i r o n m e n t a l s t a b i l i t y (40-45), a paucity o f i n t e r g r a n u l a r " w e a k l i n k s " that appears to l i m i t t h e c r i t i c a l c u r r e n t densities o f other h i g h - T materials (44-46), a n d r e p o r t e d T values as h i g h as 122 Κ (26-29). N e v e r t h e l e s s , t h e volatility o f T l 0 a n d T l 0 complicates t h e annealing o f P V D - d e r i v e d c

c

c

2

2

3


E L E C T R O N T R A N S F E R IN BIOLOGY A N D T H E SOLID

STATE


360

Figure 6. A. Scanning electron micrograph of the unanneahd Bi-SrCa-Cu-O film in Figure 5A. B. Scanning electron micrograph of the annealed Bi-Sr-Ca-Cu-O film in Figure 5B. In Electron Transfer in Biology and the Solid State; Johnson, M., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1989.


Figure 7. Variable-temperature four-probe electrical resistivity data for an OMCVD-derived, annealed Bi-Sr-Ca-Cu-O film deposited on [100] MgO.


362


T l - B a - C a - C u - O films, a n d O M C V D w i t h four sources is e x p e c t e d to b e difficult. W e find that excellent h i g h - T T l - B a - C a - C u - 0 films can b e p r e p a r e d b y two c o m p l e m e n t a r y , O M C V D - b a s e d approaches (47). I n one ap p r o a c h , a B a - C a - C u - O film is p r e p a r e d b y O M C V D a n d T l is t h e n i n t r o d u c e d b y vapor diffusion o f the oxides. I n the second a p p r o a c h , T l is i n t r o d u c e d into the B a - C a - C u - O film v i a a n O M C V D process that uses volatile c y c l o p e n t a d i e n y l t h a l l i u m . Downloaded by UNIV OF CALIFORNIA SAN FRANCISCO on February 17, 2015 | http://pubs.acs.org Publication Date: May 5, 1989 | doi: 10.1021/ba-1990-0226.ch018

c

O M C V D of B a - C a - C u - O films was c a r r i e d out u s i n g Ba(fod) , C a ( d p m ) , a n d C u ( a c a c ) as precursors at 666 P a (5 torr) o f pressure i n the reactor d e s c r i b e d . T h e source temperatures w e r e 1 6 0 - 2 1 0 ° C , the substrate t e m p e r a t u r e was 600 ° C , a n d water vapor was e m p l o y e d as the reactant gas. T h e as-deposited films w e r e annealed for 3 h at 800 °C i n flowing oxygen saturated w i t h w a t e r vapor. T h e role o f the water is to r e m o v e excess fluoride from the films (vide supra). 2

2

2

T o i n t r o d u c e T l i n t o the B a - C a - C u - O films b y v a p o r diffusion, the films w e r e h e a t e d u n d e r air for 3 m i n at 870 °C (followed b y s l o w cooling) i n a closed a l u m i n a c r u c i b l e c o n t a i n i n g a p e l l e t o f b u l k T l B a C a C u O . T h i s material serves as a source o f T l 0 a n d T l 0 (40-45). X - r a y diffraction measurements ( F i g u r e 8A) r e v e a l that the films are c o m p o s e d p r i m a r i l y o f the T l B a C a C u 0 , T = 110 Κ phase (40-46). T h e e n h a n c e d (00/) reflection i n t e n s i t i e s i n d i c a t e , as f o r t h e a f o r e m e n t i o n e d Y - B a - C u - O a n d 2

2

2

2

3

2

2

3

x

3

c

CO

A

o o

o

o o

^ o §

s

Λ.

JL_^_J

Β

w

O O

O

I s —I

il -

g s

o

Ο

Ή

^

w

o

.,,11

W J l ....

o

3

JL

I I I I I I I I I I I I I I I I I I I I I I I I I I I „ I I I ιΛι ι ι ι ι ι ι ι

20.0

30.0

40.0

50.0

I—

60.0

2 θ (degrees) Figure 8. X-ray diffraction patterns of (A) a Tl-Ba-Ca-Cu-0 film on YSZ prepared by OMCVD of a Ba-Ca-Cu-O film followed by vapor diffusion of thallium and (Β) a Tl-Ba-Ca-Cu-0 film on YSZ prepared by OMCVD.


18.


TONGE ET AL.

363


B i - S r - C a - C u - O films, h i g h p r e f e r e n t i a l o r i e n t a t i o n of the crystallite c axes p e r p e n d i c u l a r to the substrate p l a n e . S E M data ( F i g u r e 9A) r e v e a l a h i g h l y i r r e g u l a r surface w i t h l - 5 - μ η ι grains. C h a r g e - t r a n s p o r t data ( F i g u r e 10A) for these films r e v e a l m e t a l l i k e character at h i g h e r temperatures a n d a t r a n sition to the s u p e r c o n d u c t i n g state b e g i n n i n g at —120 K . T h e ρ = 0 t e m perature is 102 K . W i t h one recent exception (46), this t e m p e r a t u r e is, to o u r k n o w l e d g e , comparable to the best a c h i e v e d w i t h P V D - d e r i v e d films (40-45). T l i n t r o d u c t i o n i n t o the B a - C a - C u - O films b y O M C V D was c a r r i e d out b y u s i n g T l ( C H ) i n an atmospheric-pressure reactor. T h e source t e m p e r a t u r e was 5 0 - 8 0 ° C , the substrate t e m p e r a t u r e was 300 ° C , the c a r r i e r gas was argon, a n d the reactant gas was water-saturated oxygen. T h e asd e p o s i t e d films are amorphous b y X - r a y diffraction a n d are s e m i c o n d u c t i n g . A n n e a l i n g of these films can b e c a r r i e d out b y r a p i d h e a t i n g (—1 m i n at 800 °C) u n d e r air i n a closed c r u c i b l e or, m o r e satisfactorily, i n the presence of b u l k T l B a C a C u O . to a v o i d t h a l l i u m loss. T h e X - r a y diffraction patterns of these films ( F i g u r e 8B) are s i m i l a r to those d e s c r i b e d . T h i s s i m i l a r i t y indicates the p r e d o m i n a n c e of the T l B a ^ a ^ u ^ T = 110 Κ phase, w i t h the possible presence of traces of other phases. A g a i n , p r e f e r e n t i a l o r i e n tation of the crystallite C u O planes p a r a l l e l to the substrate surface is e v i dent. T h e charge-transport characteristics of the O M C V D - d e r i v e d T l - B a - C a - C u - O films ( F i g u r e 10B) are m e t a l l i k e at h i g h e r t e m p e r a t u r e s , w i t h a s u p e r c o n d u c t i n g onset at —120 Κ a n d ρ = 0 at 100 K . E l e c t r o n micrographs ( F i g u r e 9B) r e v e a l a smoother, m o r e regular surface than i n the case o f films p r e p a r e d b y O M C V D + T 1 0 - T 1 0 vapor diffusion. 5

2

2

3

5

a

c

2

2

3

Conclusions T h e i n i t i a l results of this research effort show that O M C V D is a v i a b l e approach to the synthesis of h i g h - T s u p e r c o n d u c t i n g films. I n d e e d , h i g h l y o r i e n t e d films of the Y B a C u 0 _ , B i ( S r , C a ) C u O , a n d T l B a ^ a a C u ^ superconductors have b e e n p r e p a r e d w i t h zero-resistance t e m p e r a t u r e s of 86, 75, a n d 102 K , respectively. T h e f o l l o w i n g points are p a r t i c u l a r l y n o t e worthy: c

2

3

7

8

2

3

2

x

• the use of Ba(fod) as a volatile B a p r e c u r s o r a n d source of orienting B a F ;

film-

2

2

• the use of low-pressure deposition p r o c e d u r e s ; • the use of water as a p r o t o n o l y t i c reactant gas a n d B a F

2

mod

erator; • the

observation

of

amorphous

Y-Ba-Cu-O

and

Tl-Ba-

C a - C u - O films p r i o r to a n n e a l i n g ;




364

Figure 9. Scanning electron micrograph of (A) the Tl-Ba-Ca-Cu-O film shown in Figure 8A and (B) the Tl-Ba-Ca-Cu-O film shown in Figure 8B.


TONGE ET AL.


365


18.

Ο

50

100

150

TEMPERATURE

200

250

300

(Κ)

Figure 10. Four-probe variable-temperature electrical resistivity data for (A) the Tl-Ba-Ca-Cu-0 film shown in Figure 9A and (B) the Tl-Ba-Ca-Cu-0 film shown in Figure 9B.


366

E L E C T R O N TRANSFER IN BIOLOGY A N D T H E SOLID STATE

• t h e use o f B i ( C H ) a n d T l ( C H ) as volatile B i a n d T l sources, 6

5

3

5

5

respectively; • t h e use o f r a p i d t h e r m a l a n n e a l i n g techniques to i m p r o v e

film

grain structure a n d e l e c t r i c a l p r o p e r t i e s ; a n d • t h e use o f c o m b i n e d O M C V D a n d vapor diffusion techniques


for film d e p o s i t i o n . T h e s e results indicate that m a n y factors i n t h e O M C V D process i n f l u e n c e high-T

c

superconductor

film

stoichiometry

and microstructure

(hence,

charge-transport characteristics) i n a w a y that is not y e t w e l l u n d e r s t o o d . I m p o r t a n t issues to b e addressed c o n c e r n t h e d e v e l o p m e n t o f m o r e v o l a t i l e a n d reactive precursors, u n d e r s t a n d i n g t h e d e p o s i t i o n c h e m i s t r y , u n d e r standing the role i n film g r o w t h o f substrate a n d a d d e d reagents (e.g., B a F ) , 2

understanding the annealing-crystallization chemistry, and understanding film m i c r o s t r u c t u r e - c h a r g e - t r a n s p o r t (especially c r i t i c a l c u r r e n t density) r e lationships. F u r t h e r research w i l l focus u p o n these issues a n d o n d e v e l o p i n g O M C V D routes to o t h e r n o v e l electronic materials.

Acknowledgments T h i s research was s u p p o r t e d b y t h e N a t i o n a l Science F o u n d a t i o n t h r o u g h the N o r t h w e s t e r n M a t e r i a l s Research C e n t e r (Grants D M R 8 5 2 0 2 8 0 a n d D M R 8 8 2 1 5 7 1 ) a n d i n part b y t h e Office o f N a v a l R e s e a r c h a n d A r g o n n e National Laboratory.

References 1. The Chemistry of High-Temperature Superconductors; Nelson, D. L . ; Whittingham, S. M . ; George, T . F., Eds.; ACS Symposium Series 351; American Chemical Society: Washington, D C , 1987. 2. The Chemistry of High-Temperature Superconductors II; Nelson, D. L.; George, T . F., Eds.; ACS Symposium Series 377; American Chemical Society: Washington, D C , 1988. 3. Maple, M . B., E d . MRS Bull. 1989, XIV, No. 1, 20-71, and references therein. 4. Thin Film Processing and Characterization of High-Temperature Superconductors; Harper, J. M . E.; Colton, R. J.; Feldman, L. C., Eds.; American Vacuum Society Series No. 3; American Institute of Physics Conference Proceedings No. 165; American Institute of Physics: New York, 1988. 5. High-Temperature Superconductors II; Capone, D. W., II; Butler, W. H . ; Batlogg, B.; Chu, C. W., Eds.; Extended Abstracts; Materials Research Society: Pittsburgh, PA, 1988. 6. Laibowitz, R. B. In ref. 3; Maple, M . B., E d . ; pp 58-62, and references therein. 7. Dapkus, P. D. Ann. Rev. Mater. Sci. 1982, 12, 243-269. 8. Prakash, H . Prog. Cryst. Growth Charact. 1983, 6, 371-391. 9. Ryabova, L. A. Curr. Topics Mater. Sci. 1981, 7, 587-642. 10. Curtis, B. J.; Brunner, H . R. Mater. Res. Bull. 1975, 10, 515-520.



18.

TONGE ET AL.


367

11. Itoh, H . ; Takeda, T.; Naka, S. J. Mater. Sci. 1986, 21, 3677-3680. 12. Souletie, P.; Bethke, S.; Wessels, B. W.; Pan, H . J. Cryst. Growth, (Proc. Third Int. Conf. II-VI Compounds) 1988, 86, 248-251. 13. Cuellar, Ε. Α.; Miller, S. S.; Marks, T. J . ; Weitz, E . J. Am. Chem. Soc. 1983, 105, 4580-4589. 14. Cuellar, Ε. Α.; Marks, T. J. Inorg. Chem. 1981, 20, 2129-2137. 15. Sievers, R. E.; Sadlowski, J. E . Science 1978, 201, 217-223, and references therein. 16. Zhao, J . ; Dahmen, K . - H . ; Marcy, H . O.; Tonge, L . M . ; Marks, T. J . ; Wessels, B. W.; Kannewurf, C. R. Appl. Phys. Lett. 1988, 53, 1750-1752. 17. Zhao, J.; Dahmen, K.-H.; Marcy, H . O.; Tonge, L . M . ; Wessels, B. W.; Marks, T. J.; Kannewurf, C. R. Solid State Commun. 1989, 69, 187-189. 18. Berry, A. D.; Gaskill, D. K.; Holm, R. T.; Cukauskas, E . J.; Kaplan, R.; Henry, R. L. Appl. Phys. Lett. 1988, 52, 1743-1745. 19. Yamane, H . ; Masumoto, H . ; Hirai, T.; Iwasaki, H . ; Watanabe, K.; Kobayashi, N.; Muto, Y.; Kurosawa, H . Appl. Phys. Lett. 1988, 53, 1548-1550. 20. Panson, A. J . ; Charles, R. G . ; Schmidt, D. N . ; Szedon, J. R.; Machiko, G. J . ; Braginski, A. I. Appl. Phys. Lett. 1988, 53, 1756-1758. 21. Zhang, K.; Kwak, B. S.; Boyd, E . P.; Wright, A. C.; Erbil, A. Appl. Phys. Lett. 1989, 54, 380-382. 22. Zhao, J.; Marcy, H . O.; Tonge, L. M . ; Wessels, B. W.; Marks, T. J.; Kannewurf, C. R. Physica C, 1989, 159, 710-714. 23. Lyding, J. W.; Marcy, H . O.; Marks, T. J . ; Kannewurf, C. R. IEEE Trans. Instrum. Meas. 1988, 37, 76-80. 24. Kanatzidis, M . G . ; Marks, T. J . ; Marcy, H . O.; McCarthy, W. J . ; Kannewurf, C. R. Solid State Commun. 1988, 65, 1333-1337. 25. Gupta, A.; Jagannathan, R.; Cooper, Ε. I.; Geiss, Ε. Α.; Landman, J. I.; Hussey, B. W. Appl. Phys. Lett. 1988, 52, 2077-2079. 26. Cheung, C. T.; Ruckenstein, E . J. Mater. Res. 1989, 4, 1-15, and references therein. 27. Sleight, A. W.; Subramanian, M . A.; Torardi, C. C., ref. 3, pp 45-48, and references therein. 28. Schuller, I. K.; Jorgensen, J. D. In ref. 3; Maple, M . B., E d . ; pp 27-30, and references therein. 29. Maeda, H . ; Tanaka, Y.; Fukutomi, M . ; Asano, T. Jpn. J. Appl. Phys. 1988, 27, L209-L210. 30. Tarascon, J. M . ; LePage, Y.; Barboux, P.; Bagley, B. G . ; Greene, L. H . ; McKinnon, W. R.; Hull, G. W.; Giroud, M . ; Hwang, D. M . Phys. Rev. Β 1988, 37, 9382-9389. 31. Zhang, J.; Zhao, J . ; Marcy, H . O.; Tonge, L. M . ; Wessels, B. W.; Marks, T. J . ; and Kannewurf, C. R. Appl. Phys. Lett. 1989, 54, 1166-1168. 32. Yamane, H . ; Kurosawa, H . ; Hirai, T.; Iwasaki, H . ; Kobayashi, N . ; Muto, Y. Jpn. J. Appl. Phys. 1988, 27, L1495-L1497. 33. Gaskill, D. K.; Berry, A. D.; Cukauskas, E . J . ; Fatemi, M . ; Fox, W. B.; Holm, R. T.; Kaplan, R., presented at the Materials Research Society Fall Meeting, Boston, MA, Nov. 28-Dec. 2, 1988; Abstract F9.8. 34. Kimura, T.; Ihara, M . ; Yamawaki, H . ; Ikeda, K.; Ozeki, M . , presented at the Materials Research Society Fall Meeting, Boston, MA, Nov. 28-Dec. 2, 1988; Abstract F9.7. 35. Mikalsen, D. J . ; Roy, R. Α.; Yee, D. S.; Shivashanker, S. Α.; Cuomo, J. J. J. Mater. Res. 1988, 3, 613-618. 36. Rice, C. E.; Levi, A. F. J.; Fleming, R. M . ; Marsh, P.; Baldwin, K. W.; Anzlowar, M . ; White, A. E.; Short, K. T.; Nakahara, S.; Stormer, H . L . Appl. Phys. Lett. 1988, 52, 1828-1830.



368

E L E C T R O N T R A N S F E R IN B I O L O G Y A N D T H E S O L I D STATE

37. Hazen, R. M . ; Prewitt, C. T.; Angel, R. J.; Ross, N. L . ; Finger, L. W.; Hadi diacos, C. G . ; Veblen, D. R.; Heaney, P. J . ; Hor, P. H . ; Meng, R. L . ; Sun, Y. Y.; Wang, Y. Q.; Xue, Y. Y.; Huang, Z. J . ; Gao, L . ; Bechtold, J . ; Chu, C. W. Phys. Rev. Lett. 1988, 60, 1174-1177. 38. Marshall, A. F.; O h , B.; Spielman, S.; Lee, M . ; Eom, C. B.; Barton, R. W.; Hammond, R. H . ; Kapitulnik, Α.; Beasley, M . R.; Geballe, T. H . Appl. Phys. Lett. 1988, 53, 426-428. 39. Fukutomi, M . ; Machida, J . ; Tanaka, Y.; Asano, T.; Yamamoto, T.; Maeda, H . Jpn. J. Appl. Phys. 1988, 27, L1484-L1486. 40. Ichikawa, Y.; Adachi, H . ; Setsune, K.; Hatta, S.; Hirochi, K.; Wasa, K. Appl. Phys. Lett. 1988, 53, 919-921. 41. Nakao, M . ; Yuasa, R.; Nemoto, M . ; Kuwahara, H . ; Mukaida, H . ; Mizukami, A. Jpn. J. Appl. Phys. 1988, 27, L849-L851. 42. Lee, W. Y.; Lee, V. Y.; Salem, J . ; Huang, T. C.; Savoy, R.; Bullock, D. C.; Parkin, S. S. P. Appl. Phys. Lett. 1988, 53, 329-831. 43. Shih, I.; Qiu, C. X. Appl. Phys. Lett. 1988, 53, 523-525. 44. Ginley, D. S.; Kwak, J. F.; Hellmer, R. P.; Baughman, R. J.; Venturini, E . L . ; Morosin, B. Appl. Phys. Lett. 1988, 53, 406-408. 45. Ginley, D. S.; Kwak, J. F.; Hellmer, R. P.; Baughman, R. J.; Venturini, E . L . ; Mitchell, Μ. Α.; Morosin, B. Physica C 1988, 156, 592-598. 46. Hong, M . ; Liou, S. H . ; Bacon, D. D . ; Grader, G. S.; Kwo, J . ; Kortan, A. R.; Davidson, B. A. Appl. Phys. Lett. 1988, 53, 2102-2104. 47. Richeson, D. S.; Tonge, L. M . ; Zhao, J . ; Zhang, J . ; Marcy, H . O.; Marks, T. J.; Wessels, B. W.; Kannewurf, C. R. Appl. Phys. Lett. 1989, 54, 2154-2156. RECEIVED

for review May 1, 1989.

ACCEPTED

revised manuscript August 2, 1989.


Electron Transfer in Biology and the Solid State - American Chemical

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