library(ggvis)

title <- "CH\u2084 (\u03BC mol)"

mtcars %>%
  ggvis(~wt, ~mpg) %>%
  layer_points() %>% 
  add_axis('x', orient = 'top', title = title) 

如果您将来需要更多特殊字符，请查找它们在这里并寻找C/C++/Java源代码".

In case you need more special characters in the future, look them up here and look for "C/C++/Java source code".