By default, if you use the plot function on a generated principal component object, you can also retrieve the scree plot. For more details on screeplot, please refer to the following document:

> help(screeplot)  

You can also use nfactors to perform parallel analysis and non-graphical solutions to the Cattell scree test:

> install.packages("nFactors")
> library(nFactors)
> ev = eigen(cor(swiss))
> ap = parallel(subject=nrow(swiss),var=ncol(swiss),rep=100,cent=.05)
> nS = nScree(x=ev$values, aparallel=ap$eigen$qevpea)
> plotnScree(nS)