format integer numbers with leading 0

Dear R-er,

I would like format integer number as characters with leading 0 for a 
fixed width, for example:

1 shoud be "01"
2 shoud be "02"
20 should be "20"

Now I use:

x <- c(1, 2, 20)

gsub(" ", "0", format(x, width=2))

But I suspect more elegant way could be done directly with format 
options, but I don't find.

Thanks a lot

Marc