C.-Y. Wei and D. N. Seidman ~istribution of self-interstitials aruund depleted zones in W

we measured and the parent standard distribution is unknown a t start of extcnslve thermally activated rnigrat~on of po111t rlcfrcts.

4 2. EXPERIMENTAL DETAILS

2.1. Specimen chemistry and preparation

2.2. The irradiation procedure ' a specimen had been field-evaporated to a tip radius of 200 to it was cooled to 10 K and. brought to an atomically smooth low-

C.-Y. Wei and D. N. Seidman ~i ,~t r ibul ion of self-inleralitials around depleted zonea in W 1423

Pig. 1

The flux of ions a t the specimen was - 10'' cm-2 s L . .4 seconds was irradiated with a magnetically analysed 18 keV Aui ion be total dose of 5 x l oL3 ions the flux of ions a t thls specime - 2 x l o L 2 cm-' s-'. In both cases the time required to form an ads monolayer was always greater than the irradiation period. .If irradiation each speciment was re-imaged, employing helium as ing gas. a t - Torr. Each specimen was dissected atom employing the pulse-field cvaporation technique (Seidman 19 1978, Seidman el al. 1975 a , b).

For details regarding temperature control and measuremen

lack circles represent atoms and the open circles represent vacancies. st ring is indicated by the solid line and only atomic sites that were

ned within the solid line were counted. I n fig. 1 there are two cies, as indicated by the numbers 4 and 5, and the total number of

camera equipped with a 1000 ft film chamber. The 35 rnm c' analysed with a Vanguard motion analyser which was inte Houston Omnigraphic 200 z-y recorder; see our carlier pub1 further details (Scanlan, Styris, Seidman and Ast 1969, Reavan etal Wilson and Seidman 19'73, Seidman 1976, Wei and Seidman 1978).

5 3. CONTROL EXPERIMENTS

Control expriments were performed on unirradialed tungste mens to detect possible artifact vacancies and SIAs. The term

C:Y. Wei a n d D. N. Seidrnan ~istribution of self-interalitiala around depleted zones i n W 1425

Fig. 2

s tudies: hence, the ar t i fact S I A concentrat ion for t h e plalres near t pole is < 1.4 x 1 V 6 a t . f r . I n conclusion, t h e resul ts pwsented paper were ,101 affected hy t h e presence of a r t i f ac t STAs or vacancies.

$ 4 . RESULTS

4.1. The 30 lie T ' Cr + ion irradiation, partial 121 stereographic projection illuatratinp the location of depleted wnea (DZSa to DZ5e) in the tungsten specimen which wss i r r d k t e d , a t 10 K, with 30 keV Cr+ ions. The ion beam was parallel to the [741] direc- tion. (b) A schematic cross-sectional view of the irradiated F IM specimen showing the relative positions of the DZs.

C.-Y. Wei and D. N. Seidman Distribution of self-Inle~ste'tiala amund depleted zones In W 1429

Figure 4 shows a second example of the contrast pattern of a This SI.4 contrast pattern extends through six (521) planes+ and of 581 frames of cine film were involved in this analysis; only 12 f film are shown in fig. 4. Layer numbers 4, 5, 6 and 7 (we frames 2 358 and 403) contain six vacancies. An extra bright-spot contrast

A computer-generated isometric drawing of the 30 keV CrT i speclrnen is shown in fig. 5. The fire open ellipses represent the

distances; thus, the distances presented represented a lower --denoted by R,i.-to the actual propagation distances. Figure 6 is a

Fig. 6

3 0 - 30 keV Cr+ on W IRRADIATION TEMPERATURE = IOK TOTAL NUMBER OF SIAr -97

A computer-generated isometric drawing showing the relative pos~t~ons of and DZ5a to DZ5e in a tungsten F IM specimen whlch \+a6 ~rradla 30 key Cr.+ Ions at, 10 K . The open ellipses indicate DZsand thesol circles indicate the 81.4s.

0 1 0 0 200 300 400 500 600

('.-Y. Wei a n d D. N. Seidman Distribution of self-interstitials around depleted zones in W 1431

4.2. The 18 keV Au' irradiation Fig. 8

a specimen which had been irradiated with 18 kr1- i\ui i 16

d e k c k d a total of 33 SIAs; all the depleted zones produvrd were 18 keV nu+ on w 1 within 5 30 A of the irradiated surface. The value of' 18 keV and the h

0 ~ ~ ~ 3 0 0 s O O 5 0 0 6 0 0

R,,. (8,

9 5. Drscussro~

5.1. The n u d e r of SIAs detected

A computer-penerated isometric drawing showing the relative positions (solid black circles) in an FIM specimen which was irl-a(?lated '"It:

iolls a t 10 K; the ion beam was parallel to the [ i l l ] dlrect' locations of the DZs are indicated schematically by the ollen

bvious physical reasons for the above d isc repany a re as

?,In this drawing the positions of the DZs are simp. Zd are the initial and final radii of the tip and o is the shank angle detalled vacancy structure of the DZs see Wei el al. (1980) in the region of the tip.

C:Y. Wei a n d D. S. Seidman Distribution of self-inkerslilials around depleted zones in W 1433

the total t ip volume (Vt,,) in our searrh for RIAs. sitrce Fig. 9 h ~ g h - ~ n d e x planes were found to be satisfactory for tlrteciin contrast patterns (Reavan et al. 1971, Seidman anrl 1,ir 1972 COMWSITE DISTRIBUTION man 1973, Wei 1978). 18 W A"' on W

2 0 Lev W+ an W 3 0 keV ~ r + on W

TOTAL NUMBER OF SlAr =I54

Reasons ( 1 ) and (2) are sufficient t o explain the fact t h a t t he t'racti SIAs detccted was - 0.1 of the total number of vacancies yr(~duced. there seems t o be no compelling need to invoke reason number ( 3 ) point is discussed further in 5 5 .2 .

5 .2 . The distribution of ranges of the replacenlenl collision .vuqfcence

The main problem with these range distributions is that U-e know the relationship between them and the parent starli1al.d d idr

PSon assumed a repulsive Born-Mayer potential ( V W - ~ ( ~ ) ) of the

Vw-w(r) = A exp ( - b r ) . (1)

C:Y. Wei and D N. Scidman Dzslrtbutton of self-znlerstztzab around depleted wnes zn W 1435

(in a { I 101-type plane) and

ErLoo = 2A exp (-ia,,b).

directions, respectively; these value8 were calculated employilr (1963) expressions for the total number of collisions in a chain. of zero point and thermal mot,ion of the lattice atoms has been decrease the maximum range of FCSs (see, for example. Srlson. T

ACKNOWLEDGMENTS

technical facilities of the Materials Science Center a t Cornell University.

APPENDIX

Procedure for the determination of the poeit iaa of the SIAs and depleted zones in an F I M specinten

our san~pling procedure as discussed earlier in this section.

l ~ l = l m 1 = g + r l - r o , d

(A 3) ( D F I = r l - r o , (A 4)

L B F D = t J o . (A 5)

Renee the quantity A% is plven by

where the quantity q is given by

(A 7) The quantlty 80 , the angle between the normal vector [h4k414] of the

k414) plane and the w axis, is given by

n the triangle BCO we have

I ~ I =To,

L CBO = %o + A%,

vector [hz k2 12] as the zl axls The vector [h2 k2 12] 1s determined fr the cross-product

Ch2 k2 121 = Ch3 ks 131 x Chi k~ 111.

The u, u and w axes and the orlgln 0 therefore const~tute a recta%* coord~nate system The coord~nates of point C are glven by (u, 8) U,

this rectangular coordinate system The spher~cal coordinates (P . 0, $1' polnt C are shown 111 fie. 10

plane Is a t D In generai, the vector Bd is tllted away from tne" axls by an angle A% The angle A% was determmed by analyslng thef angle BDF, polnt F 1s defined by the expression 1 31 = ro The l e j

rnd P 1 ZI = J[s2 + ro2 - 2870 cos (0, + AO)] (A 12)

L COB = cos-I [..l :&- be angle 0 1s glven by

1

1978) and is available upon request.

REFERENCES

F;RGIFSOY. C., VINEYARD. G. H . , and ENGLERT, A, , 1964, Ph!is. f l ~ f ' 133, ERCIXSOY, C , I'INEYIRD, G . H . , and SHIMCZI, 1965, Phys. Ku? 139, A I L GIBSON. .I. B.. GOLAND, A. X., MILGRAM, M . , and VINEYARD. G

Her . , 120, 1229. oE I,At??AY, J , 1956, SolidSlate Physics, VOI. 2, edited by F. itra rand D.T

can Elsevier), pp. 114-127. X E L S O ~ . R. S., 1963. Phil. Mag., 8, 693; 1968, The Observalion UJ illornic

mn Crystalline Solids (Amsterdam. North~Holland), pp 188-141.

i