The formation mechanism of single and poly-crystalline Au films, which had been obtained on iron substrate from electroless plating bath containing sodium hypophosphite as a reducing agent, was examined by direct observation and diffraction method of electron microscope.
The following results were obtained:
1) Au micro-particles of less than 100Å in size were observed in the early stage and no coherency was found between the micro-particles and iron substrate.
2) When the Au micro-particles were coalesced and grew up to the size of about 130Å, coherency began to be found between Au-particles and iron substrate. However, there still remained a little misalignment of particles.
3) The misalignment was gradually reduced with the growth of particles and it reached the minimum when the iron surface was completely covered with Au plate crystals, which turned into single-crystalline.
4) The plate crystals again turned to poly-crystalline with the further lapse of plating time owing to the growth of particles having random crystal orientation in defects of the single crystals.
5) The coherencies between the Au plate crystals and iron surface immediately after the surface was covered by the crystals were as follows:
(001) Fe||(001) Au [110] Fe||[010] Au} (1) (110) Fe||(110) Au [001] Fe||[110] Au} (2)
6) In the early stage, Au micro-particles were coalesced with no change of shapes: that is, they did not develop to network structure, different from those obtained by galvanic substitution.
7) The maximum density of Au micro-particles in the deposits obtained by electroless plating was about 2.2×10
12cm
-2.
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