Exporting graphics with Unicode in R using png() or Cairo(), on Windows

I am able to display Unicode characters on a plot within my R session, but when I try to export the figure using e.g. png(), CairoPNG(), cairo_pdf(), etc., some (although not all) of these fail to appear. For example, the following simple plot shows the correct characters for me in the R window:

plot( 1:9,
   c(280, 540, 750, 1434, 1078, 728, 662, 606, 785),
   pch=-as.hexmode(c("4E00", "4E8C", "4E09", "56DB", "4E94", "516D", "4E03", "516B", "4E5D")),
   xlab="Digit",
   ylab="pixels"

)

However, when I use png() first to try to save this image to disk, the characters are replaced with boxes. The previous discussions on this I managed to find (e.g. here and here) suggested using cairo_pdf. But I get basically the same result with cairo_pdf(), CairoPNG(), cairo_ps(), etc. Changing the locale, as suggested here, also still got the same result.

Some session info:

R version 3.2.2 (2015-08-14)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows 8 x64 (build 9200)

locale:
[1] LC_COLLATE=English_United States.1252  LC_CTYPE=English_United States.1252   
[3] LC_MONETARY=English_United States.1252 LC_NUMERIC=C                          
[5] LC_TIME=English_United States.1252    


attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] yarrr_0.1    lme4_1.1-8   Matrix_1.2-2 boot_1.3-17  Cairo_1.5-9 

loaded via a namespace (and not attached):
[1] minqa_1.2.4     MASS_7.3-43     tools_3.2.2     Rcpp_0.12.4     splines_3.2.2  
[6] nlme_3.1-121    grid_3.2.2      nloptr_1.0.4    lattice_0.20-33

Any suggestions would be greatly appreciated!

EDIT: Fixed a mistake in the code I had posted, sorry about that; you should hopefully be able to replicate the plot now.