Check whether network has any isolated cliques

I am looking for a way to check whether a network has any isolated collection of nodes. I mean whether there are any disconnected parts in the network. Is there a general method for this?

Here's an example graph:

library(igraph)
a<-erdos.renyi.game(100,0.1)

I could not find any built in functions for igraph that would do this.

Like this?

library(igraph)
set.seed(1)
a<-erdos.renyi.game(20,0.1)
plot(a)
V(a)[degree(a) == 0]