Change width of bars in barchart (R)

I am wondering how to change the width of the bars in the barchart() function.

Here is the code:

rater1 <- c(0.75, 0.66, 0.73,   0.63)
barplot(rater1, ylim=c(0:1),axes = TRUE, names.arg = c("A", "B", "C", "D"), axisnames=TRUE, col="grey70")

Is it also possible to place value labels above the bars?

Thanks.