Solid State Chemistry: A Contemporary Overview - American

4 Design of a Time-of-Flight Single-Crystal

Downloaded by UNIV OF SOUTHERN CALIFORNIA on June 18, 2016 | http://pubs.acs.org Publication Date: June 1, 1980 | doi: 10.1021/ba-1970-0186.ch004

Diffractometer for the Argonne Prototype Pulsed-Neutron Source S. W .

PETERSON,

A . H. R E I S , J R . , A. J .

SCHULTZ,

and P . DAY

Chemistry Division, Argonne National Laboratory, Argonne, IL 60439

The prototype tron intense

pulsed-neutron neutron

and its expected

successors,

(IPNS

I) and IPNS

supply

neutrons

n · cm-

10

16

time-of-flight

neutron

National

will

(TOF)

community

diffractometer

and utilizing

of the high instantaneous

a broad

designed flux.

facilities

detector

The 20 X 20-cm active

thermal

2-mm

of

the

mode with

oped. provided

first-stage multiwire,

Borkowski-Kopp

area of the detector

double-cathode

spatial

resolution

simultaneous

number

neutron advantage

of a

grid, which

resolution;

the

third

to 106 bytes.

measurement stationary a complete

Data

sphere

of

of fixed crystal and counter Angular

movements

by means

collection

and detector.

of

parameter,

will

with

Laue

a

and

for

minimum

is being

devel-

detector

diffractometer;

translation.

involve

in the

A strategy

positions

crystal

of a four-circle

sion also is made for a detector

data

provide

initial microof x, y, and

of 102-103 reflections

crystal

has a 100

can

data

TOF, is resolvable into 1000 channels. The processor data memory will limit the product

collecting

on

3

100 multiwire

time

A

based

is based on the use of a He-filled, area

be

basis.

to take full

The design

14

will

on a proposal

single-crystal

technique

position-sensitive

P'),

system I 10 -

(0.7-5 Å) is being

about

synchro(ZING

Laboratory

spectrum

X

pulsed

II, at Argonne

the Laue

type.

intense

prime

at 30 or 60 Hz and peak flux levels of

to the scientific

instrument

zero-gradient

prototype

· sec-1. These user-oriented

2

available

source,

generator

Crystal

are provi-

orienta-

0-8412-0472-1/80/33-186-075$05.00/1 ©

1980

A m e r i c a n C h e m i c a l Society

Holt et al.; Solid State Chemistry: A Contemporary Overview Advances in Chemistry; American Chemical Society: Washington, DC, 1980.

76

SOLID S T A T E C H E M I S T R Y :

tion procedures instruments expected IPNS

similar

are to

be

A CONTEMPORARY

to those used in current

being

devised.

greater

than

Data 10

4

four-circle

collection

reflections

OVERVIEW

rates

are

day

at

per

II.

T R or the e x p l o r a t i o n of n e w areas of s o l i d state c h e m i s t r y , i n s t r u m e n t a t i o n m u s t d e v e l o p at the same p a c e a n d l e v e l of s o p h i s t i c a t i o n as Downloaded by UNIV OF SOUTHERN CALIFORNIA on June 18, 2016 | http://pubs.acs.org Publication Date: June 1, 1980 | doi: 10.1021/ba-1970-0186.ch004

t h e e v o l v i n g r e s e a r c h areas. C o n d e n s e d - m a t t e r n e u t r o n d i f f r a c t i o n e x p e r i ments h a v e p r o v e d to be essential to the u n d e r s t a n d i n g of t h e structure of m a t e r i a l s . O n l y three h i g h - f l u x ( a b o u t 1 0

15

n • cm"

2

• sec" ) reactors 1

exist w o r l d w i d e at w h i c h state-of-the-art n e u t r o n - s c a t t e r i n g studies c a n be a c c o m p l i s h e d .

A l t h o u g h t w o of t h e m are i n the U n i t e d States, t h e i r

a v a i l a b i l i t y to the g e n e r a l r e s e a r c h c o m m u n i t y has b e e n q u i t e r e s t r i c t e d I n the f u t u r e , m o r e intense n e u t r o n fluxes ( 1 0 greater)

are n e e d e d to s t u d y m o r e c o m p l e x

w h i c h are i n c r e a s i n g l y b e c o m i n g and biological communities.

1 6

n • cm

- 2

• sec"

condensed-matter

1

or

systems,

concerns of t h e s o l i d state, c h e m i c a l ,

I n a d d i t i o n , h i g h - f l u x sources w o u l d a l l o w

the use of s m a l l e r s a m p l e sizes, t h e r e b y g r e a t l y e x t e n d i n g the r a n g e of materials that c a n b e i n v e s t i g a t e d .

S u c h fluxes are b e y o n d the c u r r e n t

d e s i g n c a p a b i l i t i e s of steady state fission reactors.

However, new high-

flux p u l s e d - n e u t r o n sources w i t h p e a k fluxes that m a y a p p r o a c h 1 0 already under development.

are

1 6

O n e of these is a p u l s e d reactor; t h e others

m a k e use of h i g h - e n e r g y p u l s e d b e a m s f r o m p a r t i c l e accelerators F o r example, high-energy

protons

from

a synchrotron

(2).

source c a n

be

i n j e c t e d i n t o a h e a v y m e t a l target, d i s l o d g i n g l a r g e n u m b e r s of h i g h e n e r g y neutrons, w h i c h , w h e n m o d e r a t e d , epithermal, E >

yield pulsed thermal

Table I.

Name Tohoku Linac Harwell Linac I I ' O R L E A ° (with multiplier) WNR° KENS N I M R O D * (modified) IPNS V IBR-2* 0

6

(and

0.15 e V ) n e u t r o n b e a m s w h o s e p e a k flux c a n be m u c h

Pulsed-Neutron

Location Tohoku, Japan Harwell, U K Oak Ridge, U S Los Alamos, U S Tsukuba, Japan Rutherford, U K Argonne, U S Dubna, USSR

° Existing.


4.

PETERSON E T A L .

Time-oj-Flight

Single-Crystal

h i g h e r t h a n t h a t a v a i l a b l e i n steady state reactors.

77

Diffractometer

A p a r t i a l l i s t i n g of

p r o p o s e d a n d e x i s t i n g p u l s e d sources is s h o w n i n T a b l e I. T h e A r g o n n e N a t i o n a l L a b o r a t o r y I P N S p r o g r a m as d e v e l o p e d

over

the past six years is s h o w n i n T a b l e I I . T h e second, or Z I N G P ' , stage is c u r r e n t l y i n o p e r a t i o n ; h o w e v e r , c o n s t r u c t i o n of I P N S p h a s e I w i l l start in October,

1978, a n d o p e r a t i o n is s c h e d u l e d to b e g i n i n A p r i l ,

1981.

D e v e l o p m e n t of n e u t r o n - s c a t t e r i n g a n d d i f f r a c t i o n i n s t r u m e n t a t i o n t h a t takes a d v a n t a g e of T O F measurements i n h e r e n t i n p u l s e d - b e a m o p e r a t i o n


is a n i n t e g r a l p a r t of the A r g o n n e p r o g r a m .

S i x i n s t r u m e n t s — f o u r of

w h i c h are a l r e a d y , or shortly to be, i n o p e r a t i o n — a r e p l a n n e d f o r the Z I N G P ' p h a s e a n d are l i s t e d i n T a b l e I I I . T h e s m a l l - a n g l e a n d s i n g l e c r y s t a l diffractometers

are c u r r e n t l y i n d e s i g n a n d e a r l y

construction

stages. The

Argonne

pulsed-neutron

facilities are p l a n n e d

and will

be

o p e r a t e d to encourage extensive use b y the entire scientific c o m m u n i t y . W i t h i n this c o n c e p t , the p r o t o t y p e T O F s i n g l e - c r y s t a l n e u t r o n d i f f r a c t i o n system d e s c r i b e d b e l o w is b e i n g d e v e l o p e d .

TOF

Neutron

Techniques

T h e r m a l neutrons m a k e v e r y suitable p r o b e s for c o n d e n s e d

matter

because of t h e i r f a v o r a b l e w a v e l e n g t h , energy, a n d v e l o c i t y p r o p e r t i e s . Thermal

neutron

wavelengths

(1.8 A n o m i n a l )

are

m a g n i t u d e to i n t e r a t o m i c distances a n d to c o m m o n l y

comparable

in

available X - r a y

w a v e l e n g t h s . T h i s fact l e d to the d e v e l o p m e n t of m o n o c h r o m a t i c n e u t r o n t e c h n i q u e s for s t r u c t u r a l research e v e n t h o u g h neutrons l a c k the intense characteristic radiation c o m m o n

to x-rays.

I n the case of c r y s t a l l i n e

p o w d e r samples the c o n v e n t i o n a l t e c h n i q u e uses a fixed w a v e l e n g t h a n d the i n t e n s i t y , I , of the diffracted b e a m is m e a s u r e d as a f u n c t i o n of the

Source Projects

Worldwide Peak

Frequency (Hz)

Method (e", k, n) (e", \, n) (e~, A, n) a n d Spallation Spallation Spallation Spallation Fission

fission

110 150 800 120 15 53 30 5

Thermal Flux (n • cm' • sec ) 2

1

10 1.5 X 1 0 1.5 X 1 0 10 10 4 X 10 10 10 1 2

13 M

1 4 w

15

1 6

'Design and construction stage,


1 5

78


Table II.

Proton Accelerator

Facility ZINGP ZING P' I P N S , Phase I I P N S I I , phase I I

A CONTEMPORARY

OVERVIEW

Argonne National Laboratory

Frequency (Hz)

Z G S ° booster I Z G S booster I I Z G S booster I I HIS

Protons/Pulse

10 30 30 60

6

2.5 I 5 5

X X X X

10 10 10 10

10 1 2 1 2 13


° Zero-gradient synchrotron. s c a t t e r i n g a n g l e 20.

W h e n e v e r the B r a g g e q u a t i o n A =

s i n © is

2d

satisfied, a m a x i m u m is o b s e r v e d i n I versus 20 (A is t h e n e u t r o n w a v e l e n g t h , d is the l a t t i c e s p a c i n g , a n d ® is the B r a g g s c a t t e r i n g a n g l e ) . I n the m o r e r e c e n t l y d e v e l o p e d T O F m e t h o d for n e u t r o n s , t h e roles of A a n d 0 are reversed, a n d neutrons of v a r i a b l e w a v e l e n g t h are u s e d to measure the d i f f r a c t e d b e a m intensities at a fixed angle 20. T h i s m e t h o d is v e r y p o w e r f u l f o r p o w d e r d i f f r a c t i o n , i n p a r t b e c a u s e of its

(3,4,5)

u t i l i z a t i o n of the b r o a d e n e r g y d i s t r i b u t i o n associated w i t h t h e r m a l i z e d neutrons. TOF

techniques have been

a n d the m e t h o d s

(6)

X - r a y L a u e technique.

developed

e x t e n d e d to s i n g l e - c r y s t a l d i f f r a c t i o n , are q u i t e s i m i l a r to the w e l l - k n o w n

I n t h e X - r a y case p o l y c h r o m a t i c r a d i a t i o n is

d i f f r a c t e d f r o m a s t a t i o n a r y s i n g l e c r y s t a l , a n d t h e d i f f r a c t i o n p a t t e r n is recorded on a photographic

film.

F i g u r e 1 shows X - r a y L a u e p a t t e r n s

of m o n o c l i n i c d e c a m e t h y l f e r r o c e n e - t e t r a c y a n o q u i n o d i m e t h a n e

(TCNQ),

a c h a r g e t r a n s f e r c o m p o u n d w i t h i n t e r e s t i n g s o l i d state p r o p e r t i e s .

These

patterns are o b t a i n e d w i t h a s t a t i o n a r y c r y s t a l , u s i n g w h i t e r a d i a t i o n p r o d u c e d f r o m a n M o X - r a y t u b e , a n d t h e y i n d i c a t e the p a t t e r n a n d d e n s i t y of spots that are c h a r a c t e r i s t i c of the m e t h o d .

T h e f a t a l f l a w i n this

o t h e r w i s e u s e f u l m e t h o d is t h a t a l l t h e orders ( n =

1 - » Z) of a B r a g g

p l a n e , w h e r e n is a n i n t e g e r a n d I is one of t h e M i l l e r I n d i c e s hkl, diffract w a v e l e n g t h s A i / n ( A i is the first o r d e r ) at p r e c i s e l y the same angle. Table III.

Z I N G P'

Instruments

A.

Powder Diffractometers 1. H i g h R e s o l u t i o n ; A Q / Q ^ 0 . 3 % 2. H i g h I n t e n s i t y , A Q / Q « 1 %

B.

S i n g l e - C r y s t a l D i f f r a c t o m e t e r , u n i t cells less t h a n 25 A

C.

Small-Angle Diffractometer

D.

° Q

I n e l a s t i c Spectrometers 1. C r y s t a l A n a l y z e r , E < 30 m e V , A J E 2 - 1 0 m e V 2. C h o p p e r Spectrometer, E < 1 e V , &E/E » 0.05 = 4TT sin e/2.


The

PETERSON E T A L .

4.

Time-of-Flight

Single-Crystal

79

Diffractometer

Pulsed-Neutron Source Program Proton Energy (MeV) and Target

Neutrons/ Proton

200 P b 500 500 U 800 U

2 8 20 30

2 3 8

2 3 8

Peak Thermal Neutron Flux (n • cm' • sec' )

2 5 12 12

2

Operation

1

5 X 10 10 7.5 X 1 0 10

J a n u a r y 1974 O c t o b e r 1977 A p r i l , 1981

11

1 4

14

16

High-intensity synchrotron.

6


No. of Neutron Beams

m e a s u r e d i n t e n s i t y is a s u m over a l l the orders. T h i s p r o p e r t y effectively has b l o c k e d t h e d e v e l o p m e n t analysis.

of the X - r a y L a u e m e t h o d f o r s t r u c t u r e

I n the n e u t r o n case the o v e r l a p p i n g orders are separated i n

t i m e , a n d T O F measurements

easily p e r m i t r e s o l u t i o n of

the

orders

a l l o w i n g i n d i v i d u a l hkl values to b e o b t a i n e d r e a d i l y . F i g u r e 2 shows a d i a g r a m of the A r g o n n e s i n g l e - c r y s t a l i n s t r u m e n t ( u n d e r d e s i g n e d to operate i n the L a u e m o d e . k n o w n f o u r - c i r c l e geometry

T h e design (7)

construction) uses t h e w e l l -

for o r i e n t i n g the c r y s t a l a n d r o t a t i n g the

detector i n a h o r i z o n t a l p l a n e a n d also p r o v i d e s a detector t r a n s l a t i o n a l o n g the 20 a r m . T h e k e y to r a p i d d a t a c o l l e c t i o n is the p o s i t i o n - s e n s i t i v e area detector, w h i c h , w h e n o p e r a t e d i n a T O F m o d e , p r o v i d e s a t h r e e d i m e n s i o n a l g r i d w i t h t w o space a n d one t i m e coordinates. detector 10 -10 2

3

A

large

of this t y p e w i l l easily p e r m i t simultaneous m e a s u r e m e n t

of

d i f f r a c t i o n peaks.

Description

of the TOF

Pulsed-Neutron

Source, Chopper, and Beam Line.

Single-Crystal

Diffractometer

T h e b a s i c l a y o u t of t h e n e u t r o n

source, Z I N G P ' , is s h o w n i n F i g u r e 2. H " p a r t i c l e s are i n j e c t e d f r o m a 5 0 - M e V l i n e a r accelerator i n t o a 5 0 0 - M e V s y n c h r o t r o n . T h e H " p a r t i c l e s are s t r i p p e d of t h e i r electrons to f o r m H \ A k i c k e r m a g n e t directs t h e protons

onto a t u n g s t e n target w h e r e

e a c h p r o t o n reacts to

produce

a b o u t 8 neutrons. A p o l y e t h y l e n e m o d e r a t o r , a B e reflector, a n d a l a r g e s h i e l d c o m p l e t e the assembly. T h e Z I N G P ' p r o t o t y p e source is e x p e c t e d to operate at a 3 0 - H z r e p e t i t i o n rate, y i e l d 1 X

10

12

protons per pulse,

a n d g i v e a p e a k t h e r m a l n e u t r o n flux of a p p r o x i m a t e l y 1 0

1 4

n • cm"

2

•

sec" . T h e r e s u l t i n g t h e r m a l n e u t r o n s p e c t r u m is s h o w n i n F i g f i r e 3. 1

T h e s i n g l e - c r y s t a l i n s t r u m e n t w i l l b e p l a c e d 8.5 m f r o m the m o d e r a t o r o n a b e a m l i n e t h a t tapers f r o m a 10 X 1 0 - c m b e a m size at the m o d e r a t o r to 0.5 X 0.5 c m at the s a m p l e . T h e flight p a t h a n d b e a m d i v e r g e n c e are chosen so as to g i v e the best p o s s i b l e trade-off b e t w e e n t i m e r e s o l u t i o n and intensity requirements.


SOLID S T A T E

CHEMISTRY:

A CONTEMPORARY

OVERVIEW


80

Figure 1. Laue diffraction photographs of a monoclinic crystal of decamethylferrocene-TCNQ mounted along the b-axis; the X-ray beam is oriented parallel to the c-axis and a-axis, respectively.




h-»

00

-i

s.

Ο

5.

Ci

G

î

Ο

I

S" (to

ι

ι

i"

r

>

W H

Ο

ta

W H W

82


A CONTEMPORARY

OVERVIEW

3001


CO

1

Figure 3.

2 Wavelength

3 (Angstrom)

4

The thermal neutron source spectrum of ZING

P

S i n c e neutrons p r o d u c e d i n the target a n d p a r t i a l l y t h e r m a l i z e d i n the h y d r o g e n o u s

m o d e r a t o r a p p e a r i n bursts at 1/30-sec i n t e r v a l s , t h e i r

t i m e of a r r i v a l at t h e detector, after s c a t t e r i n g b y t h e s a m p l e , c a n t i m e d r e a d i l y . T h e t i m e t is g i v e n b y t =

be

l/v, w h e r e I is t h e flight p a t h

l e n g t h a n d v is the n e u t r o n v e l o c i t y . T h e n e u t r o n w a v e l e n g t h A is g i v e n b y t h e D e B r o g l i e expression A =

h/mx>, w h e r e h is P l a n c k ' s constant a n d

m is the n e u t r o n mass.

T h u s t h e w a v e l e n g t h is p r o p o r t i o n a l to

a n d is easily o b t a i n e d .

E v e r y n e u t r o n a r r i v i n g at a

TOF

position-sensitive

detector w i t h T O F m e a s u r e m e n t c a p a b i l i t y c a n b e c h a r a c t e r i z e d w i t h x a n d y p o s i t i o n coordinates a n d a t o r A c o o r d i n a t e .

T h e p r e c i s i o n of these

coordinates is l i m i t e d b y the t i m e r e s o l u t i o n , g i v e n l a r g e l y b y t h e n e u t r o n p u l s e w i d t h ( a b o u t 15 /xsec for 1-A n e u t r o n s ) , w h i c h is p r o p o r t i o n a l to w a v e l e n g t h , a n d the flight p a t h l e n g t h a n d b y t h e s p a t i a l r e s o l u t i o n of t h e d e t e c t o r a n d the d a t a storage system. W i t h a flight p a t h of 9 m detector = >

0.5 m )

(source-to-sample

=

8.5 m ,

sample-to-

a n d a 3 0 - c y c l e r e p e t i t i o n rate, neutrons for w h i c h A

14.7 A w i l l b e o v e r t a k e n b y the m u c h faster neutrons of t h e s u c c e e d i n g

pulse.

T h i s f r a m e o v e r l a p c o n d i t i o n , i f present, w o u l d r e s u l t i n assign-


4.

PETERSON E T A L .

Time-oj-Flight

Single-Crystal

83

Diffractometer

merit of i n c o r r e c t w a v e l e n g t h s a n d m u s t b e e l i m i n a t e d . T h e a d d i t i o n of a c h o p p e r

to the system a l l o w s selection of

a limited

wavelength

b a n d , e l i m i n a t i n g b o t h v e r y short a n d v e r y l o n g w a v e l e n g t h n e u t r o n s , w h i c h m a y be u n d e s i r a b l e .

Specifications of s u c h a c h o p p e r are g i v e n

in Table IV. Detector

System

A s w e h a v e seen a b o v e , a stationary c r y s t a l c a n p r o d u c e

several


h u n d r e d s i m u l t a n e o u s L a u e reflections w h e n i r r a d i a t e d b y a p o l y c h r o m a t i c b e a m . W h e n a p u l s e d p o l y c h r o m a t i c b e a m is u s e d , these reflections are separated i n t i m e , a n d a n a p p r o p r i a t e p o s i t i o n - s e n s i t i v e a r e a detector c a n d e t e r m i n e the p o s i t i o n coordinates a n d w a v e l e n g t h associated

with

e a c h reflection, as w e l l as the i n t e n s i t y . T h e detector a d o p t e d for the c u r r e n t i n s t r u m e n t is a H e - f i l l e d , m u l t i w i r e p r o p o r t i o n a l c o u n t e r of the 3

B o r k o w s k i - K o p p type

(8).

The anode-cathode

a s s e m b l y is s h o w n i n

F i g u r e 4, a n d a s i m p l i f i e d d i a g r a m is g i v e n i n F i g u r e 5. T h e detector is filled

to 5 a t m pressure w i t h 3 a t m of

3

H e a n d 2 a t m of X e gas.

n e u t r o n r e a c t i o n w i t h i n the detector is n + J

MeV.

3

H e -»

3

H -|- *P +

The 0.77

T h e X e gas is a d d e d to shorten the p a t h lengths of the r e a c t i o n

p r o d u c t s , a p r o t o n a n d a t r i t o n . T h e energetic t r i t o n a n d p r o t o n generate, b y c o l l i s i o n , electrons that flow t o w a r d the a n o d e a n d p o s i t i v e ions t h a t flow

t o w a r d the cathodes.

T h e p o s i t i v e ions m o v e v e r y s l o w l y , h e n c e

Table IV. Design of Chopper for Single-Crystal D i f f r a c t o m e t e r / Z I N G P ' : Horizontal Axis Specifications: S o u r c e - t o - c h o p p e r e n t r a n c e : 4-0 m S o u r c e - t o - c h o p p e r e x i t : 4.5 m C h o p p e r l e n g t h : 0.5 m C h o p p e r r a d i u s : 0.2 m C h o p p e r v e l o c i t y : 7200 r p m (120 H z ) W a v e l e n g t h range ( f u l l i n t e n s i t y ) : 0.7—5.0 A W a v e l e n g t h r a n g e (opening a n d c l o s i n g ) : 0.5-5.2 A B e a m size a t e n t r a n c e : 5 c m i n d i a m e t e r 4.0 m : F r o n t C h o p p e r F a c e 0.7 A ; v — 5.6505 X 10 m • sec" ; * — 0.7079 X 1 0 ' sec; 30.58° = o p e n i n g angle 5.0 A ; v = 0.7910 X 10 m • s e c ; t = 5.0568 X 10" sec; 218.46° = c l o s i n g angle 3

3

1

3

1

3

4.5 m : B a c k C h o p p e r F a c e 0.7 A ; v = 5.6505 X 1 0 m • sec" ; t = 0.7963 X 1 0 ' sec; 34.40° == o p e n i n g angle 5.0 A ; v = 0.7910 X 1 0 m • sec" ; t = 5.6890 X 10" sec; 245.77° = c l o s i n g angle 3

1

3

3

1

3



84


Figure

4.

A CONTEMPORARY

Anode-cathode assembly for a multiwire, positiorirsensitive proportional counter

OVERVIEW

two-dimensional,

the p u l s e d e t e c t e d at the cathodes is p r i m a r i l y a n i n d u c e d c h a r g e effect d u e to t h e e l e c t r o n a v a l a n c h e n e a r the anode.

T h e difference i n the rise

times of the c u r r e n t p u l s e g e n e r a t e d i n the t w o c a t h o d e

circuits a n d

m e a s u r e d at the t w o ends of e a c h c i r c u i t is u s e d to d e t e r m i n e t h e x a n d y coordinates of the l o c a t i o n of the event.

T h e t w o c a t h o d e grids a r e

orthogonal and strung continuously from

single w i r e s i n t h e p a t t e r n

s h o w n i n F i g u r e 5.

T h e r e s u l t i n g g r i d s h a v e 2 - m m separations i n b o t h

x a n d y (100 t u r n s p e r 2 0 - c m c o u n t e r d i m e n s i o n ) , a n d t h e

expected

s p a t i a l r e s o l u t i o n is a p p r o x i m a t e l y e q u a l to the w i r e s p a c i n g . D a t a Storage and Microprocessor Requirements.

T h e rate of d a t a

collection that becomes possible b y matching high-flux pulsed

sources

w i t h efficient m u l t i d e t e c t o r s is r a t h e r l a r g e , a n d this creates a f o r m i d a b l e d a t a - h a n d l i n g a n d storage p r o b l e m .

T h e m a g n i t u d e of t h e p r o b l e m is

a p p a r e n t w h e n one considers t h a t a single m u l t i d e t e c t o r c a n a c c e p t d a t a at a b o u t 50,000 events p e r s e c o n d a n d e a c h event m u s t b e c o d e d to a n address w i t h a r e s o l u t i o n of 100 X

100 channels f o r s p a t i a l i n f o r m a t i o n

a n d 1000 channels f o r t i m e , g i v i n g a t o t a l of 1 0 p o t e n t i a l storage locations. 7

T h e e l e c t r o n i c d e t e c t i o n system t h a t is b e i n g d e s i g n e d f o r this p u r p o s e a c t u a l l y p r o v i d e s f o r 256 X

256 channels of p o s i t i o n i n f o r m a t i o n a n d a

4 0 9 6 - c h a n n e l t i m e base, w h i c h is a n e v e n l a r g e r m a t r i x . T h e d a t a a c q u i s i t i o n t a s k is s o l v e d b y u s i n g a l o c a l m i c r o p r o c e s s o r a n d a remote Sigma 5 computer.

L o c a t e d next to t h e i n s t r u m e n t is a




00

-4

8

a

î

t

Ô

i

(to"

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ι

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I

ï

Ρ

ES

Ο 25

w »

Η

w

86

SOLED S T A T E C H E M I S T R Y :

"I

10

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•


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• I

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OVERVIEW

T

t

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5•

A CONTEMPORARY

• I

•

I •

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f

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I I t *

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I t I I

i

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I

-re Figure 6. Simulated Laue patterns of a two-dimensional proportional counter. The histogram is for the same crystal orientation as that for the X-ray Laue pattern of Figure 1(a). The units of the ordinate and abscissa are in centimeters. Each asterisk represents a set of h k l values with no order separation in time.

m i c r o p r o c e s s o r w i t h 512 6 4 - b i t w o r d s of w r i t a b l e c o n t r o l store ( a n e w c o n t r o l p r o g r a m c a n b e l o a d e d i n a f e w s e c o n d s ) a n d 1 0 bytes ( 8 b i t s ) 6

of d a t a m e m o r y . T h e m i c r o p r o c e s s o r w i l l p o s i t i o n t h e c r y s t a l a n d detector, r e a d t h e x, y, a n d t i m e a n a l o g to d i g i t a l c o n v e r t e r s ( A D C ' s ) , buffer t h e events i n d a t a m e m o r y , a n d t r a n s m i t [at 10 k i l o b a u d s ( k B d ) ] the a d dresses of o v e r f l o w e d b u f f e r l o c a t i o n s t o a S i g m a 5 c o m p u t e r ( 1 m i d i s t a n t ) . T h e S i g m a w i l l b u i l d t h r e e - d i m e n s i o n a l h i s t o g r a m s a n d store t h e m o n d i s k m e m o r y f o r d i s p l a y a n d m a n i p u l a t i o n b y t h e user at t h e e x p e r i m e n t a l site. T h e S i g m a 5 p r o v i d e s sufficient storage a n d c o m p u t a t i o n a l c a p a c i t y ( i t s u p p o r t s 26 o t h e r u n r e l a t e d e x p e r i m e n t s ) t o s u p p o r t u s e r


4.

PETERSON E T A L .

Time-of-Flight

Single-Crystal

87

Diffractometer

a n d / o r a u t o m a t i c c o n t r o l of t h e e x p e r i m e n t , i n t e r a c t i v e s p e c t r a l s i m u l a t i o n , m a n i p u l a t i o n a n d analysis of the c o l l e c t e d h i s t o g r a m s , a n d p a r t i a l s t r u c t u r e d e t e r m i n a t i o n . S i n c e a d e q u a t e b u f f e r i n g ( 2 5 6 : 1 ) f o r the i n i t i a l d a t a rates w i l l r e q u i r e 8-bit buffers, t h e p r e s e n t m i c r o p r o c e s s o r

data

m e m o r y ( e x p a n d a b l e to 2 X 1 0 b y t e s ) w i l l l i m i t the p r o d u c t of the x, y, 6

a n d t i m e resolutions to 1 0 bytes ( 6 4 X 64 X 256 b e i n g a t y p i c a l c h o i c e ) . 6

A s i m u l a t i o n p r o g r a m has b e e n d e v e l o p e d to generate s a m p l e h i s t o grams of n e u t r o n L a u e patterns.

I n F i g u r e 6 is s h o w n a s i m u l a t e d


h i s t o g r a m of n e u t r o n L a u e d a t a f o r d e c a m e t h y l f e r r o c e n e - T C N Q , w h i c h may be

compared

w i t h the X - r a y L a u e p a t t e r n , F i g u r e 1 ( a ) .

p a t t e r n gives a n i m p r e s s i o n of the n u m b e r of s i m u l t a n e o u s

This

reflections

that c a n b e r e c o r d e d b y a system w i t h sufficient r e s o l u t i o n . User-Oriented

Software

A software p a c k a g e for the T O F s i n g l e - c r y s t a l i n s t r u m e n t is b e i n g d e v e l o p e d w i t h the needs of t h e o c c a s i o n a l o u t s i d e user i n m i n d ; t h a t is, the software w i l l p r o m p t t h e user w h e n i n p u t s are r e q u i r e d . T h e g o a l of t h e software d e v e l o p m e n t is to p r o v i d e a system for a u t o m a t i c c r y s t a l o r i e n t a t i o n a n d d e t e r m i n a t i o n of u n i t c e l l a n d c r y s t a l s y m m e t r y , a u t o m a t i c c o l l e c t i o n of a u n i q u e d a t a set, a n d r e d u c t i o n of the d a t a to a f o r m s u i t a b l e f o r s t r u c t u r e analysis. S i n c e t h e L a u e t e c h n i q u e is essentially novel, new or substantially modified

versions of

older

diffractometer

p r o g r a m s are b e i n g p r e p a r e d for a l l the necessary software. T h e system is b e i n g d e s i g n e d so t h a t a c r y s t a l c a n b e m o u n t e d o n the t w o - c i r c l e H u b e r g o n i o m e t e r

(Figure 2)

i n a general orientation.

T h e orientation matrix, unit cell parameters, and L a u e symmetry then c a n b e d e t e r m i n e d f r o m the L a u e h i s t o g r a m g e n e r a t e d w i t h the c r y s t a l set i n its i n i t i a l o r i e n t a t i o n . T h e flow d i a g r a m of F i g u r e 7 illustrates the process. N strong reflections are selected f r o m the i n i t i a l h i s t o g r a m a n d s t o r e d i n a reflection

file.

The program L B L I N D ,

(BL)

( 9 ) , an auto

m a t i c i n d e x i n g p r o g r a m , operates o n these to d e t e r m i n e i n i t i a l c e l l c o n stants, s y m m e t r y , i n i t i a l o r i e n t a t i o n m a t r i x , a n d reflection i n d i c e s ; L S , a least-squares refinement p r o g r a m , refines t h e u n i t c e l l a n d m a t r i x b y least-squares p r o c e d u r e s ; T H R E , a c r y s t a l o r i e n t a t i o n p r o g r a m u s i n g d a t a f o r t h r e e reflections, generates a n o r i e n t a t i o n m a t r i x a n d u n i t c e l l a n d m a y b e u s e d i n p l a c e of L B L I N D

w h e n three i n d e x e d reflections

are

k n o w n . H R E S , a p r o g r a m f o r d e t e r m i n i n g L a u e spot c o o r d i n a t e s , a l l o w s h i g h - r e s o l u t i o n d e t e r m i n a t i o n b y a process i n v o l v i n g a l l o c a t i o n of

the

buffer m e m o r y to a l i m i t e d r e g i o n of the detector; a n d N E W H , a reflec t i o n i n d e x i n g p r o g r a m , a l l o w s t h e i n d e x i n g of a set of reflections

by

p l a c i n g a n o r i e n t a t i o n m a t r i x i n core. I n t h e d a t a c o l l e c t i o n p o r t i o n the e x p e r i m e n t a l p a r a m e t e r s ,

along

w i t h t h e r e c i p r o c a l l a t t i c e l i m i t s , are f e d i n t o G E N , a r e f l e c t i o n i n d e x i n g


88

SOLID S T A T E

run

A CONTEMPORARY

OVERVIEW

1


^

CHEMISTRY:

Figure 7. The crystal alignment and unit cell determination software flow diagram: (#), reflection number; x = coordinate of peak position on detector in horizontal direction; y = coordinate of peak position on detector in vertical direction; WL = wavelength; width = peak width at half height; TAU = (sin 6)/\; I = IT - BKG; IPK = peak height; IT = total intensity; BKG = background under peak; SIG == standard deviation of I; HSTNUM = histogram number designation. The various programs that may be run are shown in circles.


4.

PETERSON E T AL. Table V . 20 (degrees)

Time-of-Flight

Single-Crystal

N u m b e r of Simultaneous d

min

30 90 180

(A)

A

3.3 1.2 0.83

Reflections

(A)

max

89

Diffractometer

N°' *

16.8 6.1 4.2

20 1100 4400

N = number of reflections = (8 A t / 3 Rdet ) (sin 0) 7 i t c e i i [ ( 1 / X ) — (lXmax )] with Funitceii = (25 A ) ; J?det = crystal-to-detector distance = 30 cm; ^4 = detector area = (20 X 20) c m ; \ * — X i = 6 A , where X is the neutron wavelength; X in = 1 A , 26 = the mean scattering angle in the horizontal plane. Data rate for I P N S I I is about 50,000 reflections per degree; or, alternatively, X-ray-sized samples of about 02-mm edge would give 250 reflections per degree. a

4

2

d e

3

un

mln

3

3

2

det

ma

m

n

m


6

p r o g r a m , w h i c h generates a n h,k,l file f o r d a t a c o l l e c t i o n . PNSET

The program

is u s e d to d e t e r m i n e t h e n u m b e r of c r y s t a l o r i e n t a t i o n s

and

d e t e c t o r angles r e q u i r e d to c o l l e c t a c o m p l e t e d a t a set. T h i s m a p p i n g of r e c i p r o c a l space w i l l b e a c c o m p l i s h e d i n a n o r d e r l y w a y , b u t

adjacent

h i s t o g r a m s w i l l i n e v i t a b l y o v e r l a p , thus p r o v i d i n g , i n c i d e n t a l l y , a d e q u a t e s c a l i n g b e t w e e n reflections. T h e d a t a are c o l l e c t e d i n a s t a t i o n a r y c r y s t a l m o d e , a n d , d e p e n d i n g o n the detector a n d c r y s t a l p o s i t i o n s , t h e n u m b e r of reflections N c o l l e c t e d at e a c h s e t t i n g m a y v a r y g r e a t l y . T a b l e V i n d i c a t e s t h e n u m b e r of s i m u l t a n e o u s reflections t h a t m a y b e c o l l e c t e d at a c e r t a i n 0 a n d a w a v e l e n g t h r a n g e f r o m 1 A to 7 A . A s 0 is i n c r e a s e d , s m a l l e r d spacings are d e t e c t a b l e a n d N increases.

T h e program C D provides

for

s e t t i n g the c h i , p h i , o m e g a , a n d 20 angles t o p r e d e t e r m i n e d v a l u e s a n d f o r c o l l e c t i n g a set of r e f l e c t i o n intensities t h a t c o n s t i t u t e t h e

desired

histogram.

can

During

data collection

the

developing

histogram

be

viewed on a Textronix video display unit. I n the d a t a r e d u c t i o n p h a s e e a c h h i s t o g r a m , w h i c h has b e e n s t o r e d on a S i g m a 5 computer—transferred from the microprocessor to a S i g m a 5 d i s k at e a c h o v e r f l o w

Table V I .

of a n address l o c a t i o n — w i l l b e i n t e g r a t e d to

Advantages and Disadvantages of a T O F PulsedN e u t r o n Single-Crystal Instrument

Advantages: 1. N o s c a n n i n g r e q u i r e d — A i n t e g r a t i o n 2. S p e c t r u m r i c h i n A < 1 A ( s m a l l d ^ ' s m e a s u r a b l e ) 3. A f a c t o r f a v o r s large A ' S 4. S i m u l t a n e o u s m e a s u r e m e n t of m a n y (10^-10 ) hkl's 5. E a c h hkl e a s i l y m e a s u r e d a t s e v e r a l A ' S a l l o w i n g c o r r e c t i o n f o r extinction and multiple diffraction 6. S m a l l e r s a m p l e size w i t h i n c r e a s e d flux 4

3

Disadvantages: 1. Source s p e c t r u m m u s t be a c c u r a t e l y k n o w n 2. E x t i n c t i o n a n d a b s o r p t i o n h a v e a w a v e l e n g t h dependence 3. D e t e c t o r u n i f o r m i t y a n d s t a b i l i t y are c r i t i c a l


90


d e t e r m i n e p e a k intensities a n d b a c k g r o u n d s .

A CONTEMPORARY

OVERVIEW

Corrections then w i l l

be

a p p l i e d for source s p e c t r u m , w a v e l e n g t h v a r i a t i o n of s c a t t e r i n g efficiency, and absorption and extinction.

F i n a l l y , reflections w i l l be sorted a n d

a v e r a g e d , w i t h v a r i o u s s t a t i s t i c a l e r r o r estimates

a p p l i e d to t h e

final

d a t a set. Summary


A

T O F p u l s e d n e u t r o n s i n g l e - c r y s t a l d i f f r a c t i o n system is

developed Laboratory.

being

for the Z I N G P ' a n d I P N S f a c i l i t i e s at A r g o n n e N a t i o n a l T h e advantages a n d distances of this i n s t r u m e n t are s u m

m a r i z e d i n T a b l e V I . W e f e e l t h a t the disadvantages c a n be d e a l t w i t h e x p e r i m e n t a l l y , a n d the advantages

of the system o u t w e i g h those of

c o m p a r a b l e n o n - T O F types of i n s t r u m e n t s . T h e i n s t r u m e n t is i n t e n d e d for use b y a n a t i o n a l user c o m m u n i t y a n d is b e i n g d e s i g n e d a c c o r d i n g l y . Acknowledgments I n a p r o g r a m of this m a g n i t u d e , there are m a n y p e o p l e i n v o l v e d . W e a c k n o w l e d g e the h e l p f r o m these v a r i o u s groups a n d e s p e c i a l l y the following people: J . M . Carpenter and R. K . Crawford, I P N S program; M . K . K o p p , Oak Ridge National Laboratory; F . J . L y n c h and R. Brenner, E l e c t r o n i c s D i v i s i o n , d e t e c t o r d e s i g n a n d f a b r i c a t i o n ; R . K l e b , S o l i d State S c i e n c e D i v i s i o n , b e a m l i n e d e s i g n ; R . A . J a c o b s o n ( I o w a State U n i v e r sity), J . M . Kolenko, C. B . Morgan, R. W . Broach, C. W i l l i , and P. Rogan, C h e m i s t r y D i v i s i o n , software d e s i g n ; J . M . W i l l i a m s , C h e m i s t r y D i v i s i o n , user g r o u p d e v e l o p m e n t ; processor d e s i g n

F . R. Lenkszus, Electronics Division, micro

and development.

W o r k was

performed

under

the

auspices of the D i v i s i o n of B a s i c E n e r g y Sciences of t h e U . S . D e p a r t m e n t of E n e r g y . Glossary of Symbols Adet = d e t e c t o r area CHM = d = EL = h =

Chemistry Division lattice spacing Electronics Division P l a n c k ' s constant

I = intensity I P N S = intense p u l s e d n e u t r o n system I= m = n =

flight p a t h l e n g t h n e u t r o n mass neutron


4.

PETERSON E T A L .

Time-oj-Flight

Single-Crystal

Diffractometer

91

N = n u m b e r of reflections Q «=

4TT

sin ® / A

Rdet =

crystal-to-detector distance

SCD =

single c r y s t a l d i f f r a c t o m e t e r

SSS = S o l i d State S c i e n c e D i v i s i o n t = time

(sec)

T O F = t i m e of v =


ZGS =

flight

neutron velocity zero-gradient synchrotron

Z I N G P ' = z e r o - g r a d i e n t s y n c h r o t r o n intense n e u t r o n generator prototype prime A = neutron wavelength ® =

B r a g g s c a t t e r i n g angle

E = neutron energy 0 = TCNQ = h,k,l =

B r a g g angle tetracyanoquinodimethane M i l l e r indices

A D C = a n a l o g to d i g i t a l c o n v e r t e r Literature

Cited

1. " N e u t r o n Research on Condensed Matter: A Study of the Facilities and Sci entific Opportunities i n the U n i t e d States"; National Research C o u n c i l , National Academy of Science: Washington, D.C., 1977. 2. Carpenter, J. M. Nucl. Instr. and Meth. 1977, 145, 91. 3. Buras, B . ; Leciejewic, T . Nukleonika 1963, 8, 75. 4. Buras, B . ; Leciejewicz, T . Phys. Stat. Sol. 1964, 4, 349. 5. Buras, B . Reactor Centrum Nederland Report, 234, 1975, p. 307. 6. Buras, B . ; M i k k e , K . ; L e b e c h , B . ; Leciejewicz, J. Phys. Stat. Sol. 1965, 11, 567. 7. Meister, H.; Carpenter, J. M.; Peterson, S. W . I P N S Argonne Report N o . 4, December 15, 1978. 8. Borkowski, C . J.; K o p p , M. K . Rev. Sci. Instrum. 1975, 46, 951. 9. Jacobson, R. Department of Chemistry, Iowa State University. RECEIVED

September 13,

1978.


Solid State Chemistry: A Contemporary Overview - American

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