sanitize lattice axis labels for tikz device - r

Question

I'm trying to knit a lattice contourplot into a PDF document using knitr and the tikz device but am getting an Error in getMetricsFromLaTeX(TeXMetrics) on compile. Here's the minimal reproducible example:
\documentclass{article}
\begin{document}
<<contourplot,dev='tikz',echo=FALSE>>=
library(lattice)
library(RCurl)
x <- getURL("https://dl.dropboxusercontent.com/u/3966900/likelihoods.csv")
likelihoods <- read.csv(text=x)
cutoffs <- c(- Inf,-2700,-1497,-1486.6,-1486.3,-1486.286,-1486.28513,-1486.285082,-1486.28508033,-1486.285080237, Inf)
contourplot(ll ~ var1*var2,
data = likelihoods,
scales = list(y = list(log = 10)),
at=cutoffs,
label.style='align',
labels=as.character(cutoffs),
xlab='$\\\\\\sigma$')
#
\end{document}
The whole thing works if I remove the scales line (I assume it's the ^ in the axis labels that trips tikz up?) but looks like shit.
It also works if I add sanitize=TRUE to the chunk options and remove two backslashes from the xlab string. In this case, however, the axis label also gets sanitized and I don't get a LaTeX-typeset axis label.
How do I get all of this to work?

Answer 1

To sanitize the axis labels, modify the scales argument in the following way:
# e-notation (like ggplot2)
scales = list(y = list(log=10, at=10**seq(5, 15, 5))))
or
scales = list(y = list(log=10, at=10**seq(5, 15, 5),
label=sprintf("$10^{%d}$", seq(5, 15, 5))))

Answer 2

As Andy Clifton suggests in comments, doing this with ggplot seems to be a hell of a lot easier than getting it to work with lattice:
\documentclass{article}
\begin{document}
<<contourplot,dev='tikz',echo=FALSE,warning=FALSE>>=
library(ggplot2)
library(scales)
library(RCurl)
x <- getURL("https://dl.dropboxusercontent.com/u/3966900/likelihoods.csv")
likelihoods <- read.csv(text=x)
cutoffs <- c(-Inf,-2700,-1497,-1486.6,-1486.3,-1486.286,-1486.28513,-1486.285082,-1486.28508033,-1486.285080237,Inf)
v <- ggplot(likelihoods, aes(var1, var2, z = ll))
v <- v + stat_contour(breaks=cutoffs)
v <- v + scale_y_continuous(trans=log10_trans(),
breaks=c(1e-5,1e0,1e5,1e10,1e15,1e20),
expand = c(0, 0))
v <- v + scale_x_continuous(limits = c(-3, 5),
expand = c(0, 0))
v <- v + theme_bw()
v <- v + ylab('$\\sigma$')
v
#
\end{document}