We have made 23 nm period gratings (11.5 nm 1:1 lines and spaces) on diamond substrates using hydrogen silsesquioxane (HSQ) as a resist for electron beam lithography. Reactive ion etching (O2 plasma) is used to transfer high resolution patterns to the diamond substrate with HSQ serving as a mask. We believe this to be the shortest period grating defined by electron beam lithography.
Lister, K. A., Casey, B. G., Dobson, P. S., Thoms, S., Macintyre, D. S., Wilkinson, C. D. W., & Weaver, J. M. R. (2004). Pattern transfer of a 23 nm-period grating and sub-15 nm dots into CVD diamond. Microelectronic engineering, 73, 319-322.