The etching behavior of the inverse {111} planes of undoped, semiconducting, n-type, InSb single crystals was explored. Depending upon the etchant, including anodic dissolution, various etch patterns were obtained on the inverse planes. In general the etch pits on the In{lll} plane were round, and the face was shiny, whereas the face of the inverse plane was dark and rough. The rates of dissolution in the electrolytes used were very low, especially in absence of oxidizers. The components dissolve as In 3 + and Sb 3+. At current densities above 40 or 60 mA cm -2 (on Sb{-1]]} or In{ill}), growth of a black, collodial film of Sb405C12 containing very fine metallic Sb particles occurs on both planes. The Sb particles result from the partial disintegration of InSb. Upon heating the film in vacuum, recrystallization occurs and the Sb aggregates to form larger particles. An explanation is offered for the different behaviors of the inverse {111} planes.
The rest (or corrosion) and dissolution potentials of
normalInSb
single crystals in
normalHCl
were determined. There is no potential difference (within error limits) between the inverse {111} faces in pure
normalHCl
. A difference of up to 44 mV and more develops as soon as the
normalInSb
electrode is anodically dissolved.The potential becomes less noble in the sequence In {111}, {100}, {110},
normalSbfalse{true1¯true1¯true1¯false}
. The Tafel relationship is observed over three decades of current density. With additions of
FeCl3
,
FeCl2
,
K3normalFefalse(CNfalse) 6
,
K4normalFefalse(CNfalse) 6
,
H2C4H4O6
to 2N
normalHCl
, the anodic potentials of both inverse {111} faces are shifted to more active values; the ɛ́Η of In{111} is always nobler than that of
normalSbfalse{true1¯true1¯true1¯false}
. There are indications that the various potentials observed are a function of current density within the pores of a protective layer,
Sb4O5Cl2
. The apparent activation energy, ca. 20 kcal/mole, of the anodic dissolution reaction is nearly the same on all crystallographic planes of
normalInSb
. The rate of anodic dissolution of
normalSbfalse{111false}
in pure
2NnormalHCl
is 3–7 times larger than that of the inverse face at the same potential.
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