MORPHOLOGY OF FINE CRYSTALLITES FORMED BY GAS-EVAPORATION TECHNIQUE. FACE CENTRED METALS (Al, Co, Ni, Cu, Pd, In, Ag, Au AND Pb), SILICON AND GERMANIUM

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MORPHOLOGY OF FINE CRYSTALLITES FORMED

BY GAS-EVAPORATION TECHNIQUE. FACE

CENTRED METALS (Al, Co, Ni, Cu, Pd, In, Ag, Au

AND Pb), SILICON AND GERMANIUM

T. Hayashi, Y. Saito, S. Yatsuya, K. Mihama, R. Uyeda

To cite this version:

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JOURNAL DE PHYSIQUE Colloque C2, supplkment au no 7, Tome 38, Juillet 1977, page C2-191

MORPHOLOGY

OF FINE CRYSTALLITES FORMED

BY GAS-EVAPORATION TECHNIQUE.

FACE CENTRED METALS (Al,

Co,

Ni,

Cu, Pd, In,

Ag,

Au

AND Pb),

SILICON AND GERMANIUM

T. HAYASHI (*),

Y.

SAITO, S. YATSUYA, K. MIHAMA and R. UYEDA (**)

Department of Applied Physics, Faculty of Engineering, Nagoya University, Nagoya, Japan

RbumC.

-

Co, Ni, Cu, Pd, Ag et Au pr6sentent des facibs nettement d6finis.

1) Octakdres.

2) Formes dCriv6es de 1) avec un nombre pair ou impair de plans communs.

3) Bipyramides triangulaires.

4) Plaques triangulaires. 5 ) DBcakdres ou icosabdres.

Al, In et Pb prksentent des facibs moins nets : 1) et 2) seulement.

Le facibs de Ge est icosit6traCdrique et celui de Si est un polytdre limit6 par vingt quatre plans 31 1.

Abstract.

-

Co, Ni, Cu, Pd, Ag and Au showed clean-cut habits :

1) Octahedra.

2) Shapes derived from 1) with odd or even number of twin planes.

3) Triangular bipyramids.

4) Triangular plates.

5) Decahedra or icosahedra.

While Al, In and Pb, less clean-cut habits ; only 1) and 2).

The habit of Ge is icositetrahedra and that of Si, the polyhedra bounded by eight 111 and twenty four 31 1 planes.

1. Introduction.

-

A gashevaporation is an experimental technique similar to the vacuum evaporation. However, it is carried out in an atmosphere of rarefied inactive gas. The evaporated metal vapour is cooled in the gas and form a smoke as seen in figure 1. A typical smoke consists of three zones :

1) dark inner zones, 2) bright intermediate zone and 3) dark outer zone. We collect smoke particles in each zone and study them by electron micros- copy. It has been made clear that they are metal crystallites and show clean-cut habits in many cases [I]. I n the present experiment, nine face centered metaIs (I), silicon and germanium were

investigated. This paper describes the outline of the results, leaving details of experimental techniques and discussion elsewhere.

2. Face centered metals.

-

All the habits observed for these metals are categorized as shown in table I. Six metals, Co, Ni, Cu, Pd, Ag and Au (the first group) showed clean-cut habits under cats. 1- 6, while three metals, Al, In and Pb (the second

(*) Present address : Musashino Electric Communication FIG. 1 . - Metal smoke formed in a work chamber. Laboratow, N.T.T., Midori-cho, Musashino-shi, Tokvo.

(**) present address : ~epartment of Physics, ~ e i j d Univer-

sitv. - . Temvaku, Naszova.

-

.

- -

group), less clean-cut habits under only cats. 1 and

(I) F.c.c. except for indium, which is face centered tetragonal. 2. Figure 2 reproduces a general view of smoke

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C2-192 T. HAYASHI, Y. SAITO, S. YATSUYA, K. MIKAMA AND R. UYEDA

Crystal habits of f.c.c. metals

Category Shape Twins Ref.

-

1 Truncated octahedra none 1, 4 R = 0 - 4 0

2a Truncated octahedra even number none

R = 4 0

2b Polyhedra (Fig. 4) odd number none

R = 40

3 Truncated triangular bipyramids one 1, 4

R = 0 - 1 0 0

4 Truncated triangular plates several 1, 2 1

R = 0 - - x 1 0 0 3

under this category are found in the inner zone as well as in the intermediate zone. However, those with R -- 40 %, the largest of truncation degree, are found only in the inner part of the intermediate zone. It should be added that only this category gives single crystals and all the others in table I, twinned ones.

2 . 2 CAT. 2 POLYHEDRA DERIVED BY ADDING TWIN PLANES TO TRUNCATED OCTAHEDRA.

-

Figure 4 illustrates polyhedra under this category

5a Pentagonal decahedra 1, 3 twinned

5b Icosahedra particles

6 Complicated polyhedra several none

FIG. 2.

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General view of metal smoke particles. Inscribed figures indicate the category nembers in table I. particles in which many of the categories can be recognized. Each of them is described more in detail in the following paragraphs.

2 . 1 CAT. 1 OCTAHEDRA TRUNCATED BY (100).

-

Figure 3 reproduces electron micrographs show- ing various degrees (2) of truncation. Crystallites

(a) (b) (c)

FIG. 3.

-

Electron micrographs, [001] projection, of truncated octahedra (Cat. 1). (a) Pd, R = 15 % ; (b) Pd, R = 30 % and

(c) CU, R = 40 %.

(2) Degree of truncation is conventionally defined as follows :

it is zero for non-truncated shape and R % when the truncating planes cross each edge at R % of its whole length.

FIG. 4. - Polyhedra of cat. 2b. (a) R = 0 % and (b) R = 40 %.

with one twin plane. The number of twin planes is found to be one to several. Provided that they are close to each other, the external shape is approximately truncated octahedra for even numbers (Cat. 2a) and polyhedra as shown in figure 4 for odd numbers (Cat. 2b). Figure 5 reproduces electron micrographs of particles under cats. 2a and b as well as cat. 1. In figures 5b and c the even or odd number of twin planes is distinguished from the contrast of thickness fringes. These particles are almost always with R = 40 % and found in the inner part of the intermediate zone. Figure 6 reproduces an electron micrograph and diffraction pattern of an aluminium particle. This particle has one twin plane (Cat. lb) as is clear from the illustrating diagrams. 2 . 3 CAT. 3 TRUNCATED TRIANGULAR BIPYRA- MIDS.

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Figure 7 shows a- s t a ~ d a r d shape under this category. Actually, various degrees of trunca- - -

tion are found as reproduced in figure 8. The degree for each of a pair of pyramids is almost independent to each other and its value varies from almost zero to 100 %.

2 . 4 CAT. 4 TRUNCATED TRIANGULAR PLATES. - The degree of truncation R = 0 % corresponds to

1

regular triangle and that of R = - x 10096, to 3

regular hexagon. Figure 9 reproduces electron micrographs and diffraction patterns. The degrees around R = 25 % are most frequently observed. From the analysis of diffraction patterns, it is proved that a crystallite under this category has several twin planes parallel to the plate.

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MORPHOLOGY OF FINE CRYSTALLITES FORMED BY GAS-EVAPORATION C2-193

(a) (b) (c)

FIG. 5. - Copper particles of cat. 1 (a) : cat. 2a (b) and cat. 2b (c).

Twin plans

F I ~ , . 0. - I'winned particle of aluminium (Cat. 2b).

FIG. 7. - Standard shape of truncated triangular bipyramid (Cat. 3).

(a) (b) (c) (d)

FIG. 8.

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Electron micrographs of truncated triangular bipyra- rnids (Cat. 3). (a) Cu, R , = R2 = 60 % ; (b) CU, R I = R2 = 0 ;

(c) Ni, R I = 0, Rz = 50 % and (d) Cu, R , = 0, R2 = 100 %.

(a) (b) (c)

FIG. 9. - Electron micrographs of truncated triangular plates.

I

(a)Co,R = O ; ( b ) C o , R = 2 5 % a n d ( c ) P d , R = - X 1 0 0 % . ₃

multiply twinned particles studied in detail by Ogawa and Ino [5].

2 . 6 CAT. 6 IRREGULAR POLYHEDRA WITH NON- PARALLEL TWINS. - This category includes all the irregular particles which cannot be exactly defined. A reason for the difference between the first group and the second group is found in the vapour pressure as seen in table 11, viz. the values for the

Melting point and vapour pressure at it

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C2- 194 T. HAYASHI, Y. SAITO, S. YATSUYA, K. MIHAMA AND R. W E D A

FIG. 10. - Electron micrographs and diffraction pat

FIG. 11. - Electron micrographs and diffraction patterns of germanium particles with an illustration of external shape. first group are larger than lopS torr while those for

the second ones, less than torr. Since the evaporation is carried out at the vapour pressure of around 10-I torr, the temperature for the second group is much higher than the melting point. For this reason the condensation takes place at temperatures much higher than the melting point for the second group, while it can take place near the melting point for the first group. Even for the first group, we infer, for various reasons, that it takes place at high temperatures in the inner part of the intermediate zone. Particles under cat. 1 with R .= 40 % have grown at high temperatures under an approximately thermal equillibrium state. There- fore, they are possibly Wulff polyhedra. Those under cat. 2 have also grown under similar condi- tions. However, twin planes have been introduced at the time of coalescence after the particles were a little cooled. Particles under cats. 3-6 have grown at lower temperatures in kinetic ways through some

imperfections. For this reason, they have sharp corners. No such particles are produced for the second group metals, even when the atmosphere gas is extremely clean.

3. Silicon and Germanium.

-

Figure 10 reproduces electron micrographs of the typical silicon particles. They are bounded by eight ( 1 11

)

and twenty four (31 1

)

planes. On the other hand, the typical germanium particles are bounded only by twenty four (31 1 ) planes. Since both silicon and germanium belong to diamond structure, it is strange that the afferent crystal habits take place. It is also strange that (3 11) prevails over the others because it is not the index for the lowest surface energy. However, the macroscopic features of smokes of these elements are different to each other and the typical habits are not expected to be the equilibrium forms, particularly for germanium. More detailed studies are necessary to make clear these problems.

References

[I] UYEDA, R., J . Cryst. Growth 24/25 (1974) 69. [4] UEDA, K., OYOBUTSURI, (in Japanese) 44 (1975) 611. [2] KIMOTO, K. and NISHIDA, I., Japan J. Appl. Phys. 6 (1967)

1047. [5] OGAWA, Sh. and INO, Sh., Advances in Epitaxy and

[3] KIMOTO, K. and NISHIDA, I., J . Phys. Soc. J a p a n 22 (1967) Endotaxy (VEB Deutscher Verlag fiir Grundstoff