The morphology and crystal growth of copper electrodeposits on copper (110) substrates have been studied by means of optical and electron microscopy and continuous in situ observation. Deposition from an acid sulfate solution resulted in the formation of three kinds of deposit, i.e. 〈100〉 ridges (ridge A), tableland-like deposits (tableland) and 〈110〉 ridges (ridge B), depending on the current density (c.d.) applied. Continuous observation showed that ridges A and B grew by bunching of the initially tiny ridges aligned along respective directions, while tableland developed from tiny 〈100〉 ridges. Abrupt changes in c.d. during deposition caused reversible changes in morphology among the three kinds of deposit, indicating that such morphology is independent of the history or surface topography of the electrodes. However, the c.d. regions for respective deposits shifted remarkably to the higher side with increase in solution temperature, while the addition of hydrochloric acid or triethylamine effected an opposite shift of the c.d. regions. The same kinds of deposit were also obtained from cyanide or perchlorate solution. Based on these results, the formation of the three kinds of deposit on Cu(110) is discussed in relation to deposition mechanism. It is proposed that the anisotropic surface diffusion of adions (or adatoms) along 〈110〉 facilitates the formation of ridge A at low d.c., while in the high c.d. region the stability of the facets becomes a dominant factor determining the ridge B morphology with low index planes. Tableland at medium c.d. is considered to be in a situation intermediate between these two limiting cases.
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