question on writeRaster error

Hello,

I'm trying to save a raster on workspace as GeoTIFF file into a folder
named ST in Desktop

writeRaster(x = ST ,  file = paste(n,"_Rescaled_band",sep=" "),
format="GTiff",  overwrite = T)

and got the following error message :

Error in .local(x, filename, ...) :
  Attempting to write a file to a path that does not exist:
  ST

Thanks for your help.
Regards.