vectorized plotmath expressions via substitute()

hi all - i've seen versions of this question before, but none seem to get
directly at my solving my (probably very simple) issue:

i simply want to annotate the tick marks on an axis with (superscripted)
10^x notation, and tried this:

axis(1, at = axTicks(1), as.expression(substitute(10^foo, list(foo =
axTicks(1))))

thinking the as.expression/substitute would create the appropriate
expression vector from the expansion of the foo vector.
i'm continually stuck in the error process, however, with axis() where R
complains that i've only provided a single label.
i must be missing a function that explicitly "unfolds"(?) the result of the
substitute() call, without actually evaluating the contents of that call?

sorry in advance if this is clear in the docs somewhere, though i just
can't seem to locate it :-/