[R] Question about unicode characters in tcltk

[R Help]

hello list,

Can someone help me figure out why the following code doesn't work?
I'm trying to but both Greek letters and subscripts into a tcltk menu.
 The code creates all the mu's, and the 1 and 2 subscripts, but it
won't create the 0.  Is there a certain set of characters that R won't
recognize the unicode for?  Or am I input the \u2080 incorrectly?

library(tcltk)
m <-tktoplevel()
frame1 <- tkframe(m)
frame2 <- tkframe(m)
frame3 <- tkframe(m)
entry1 <- tkentry(frame1,width=5,bg='white')
entry2 <- tkentry(frame2,width=5,bg='white')
entry3 <- tkentry(frame3,width=5,bg='white')

tkpack(tklabel(frame1,text='\u03bc\u2080'),side='left')
tkpack(tklabel(frame2,text='\u03bc\u2081'),side='left')
tkpack(tklabel(frame3,text='\u03bc\u2082'),side='left')

tkpack(frame1,entry1,side='top')
tkpack(frame2,entry2,side='top')
tkpack(frame3,entry3,side='top')

thanks
-- Sam