We present the results of a Hubble Space Telescope Wide Field Camera 3 imaging survey of 11 of the lowest mass brown dwarfs in the Pleiades known ( 25 - 40 Â \mbox { M } _ { \mbox { \tiny Jup } } ) .
These objects represent the predecessors to T dwarfs in the field .
Using a semi-empirical binary PSF-fitting technique , we are able to probe to 0 \farcs 03 ( 0.75 pixel ) , better than 2x the WFC3/UVIS diffraction limit .
We did not find any companions to our targets .
From extensive testing of our PSF-fitting method on simulated binaries , we compute detection limits which rule out companions to our targets with mass ratios of q \gtrsim 0.7 and separations a \gtrsim 4 AU .
Thus , our survey is the first to attain the high angular resolution needed to resolve brown dwarf binaries in the Pleiades at separations that are most common in the field population .
We constrain the binary frequency over this range of separation and mass ratio of 25 - 40 Â \mbox { M } _ { \mbox { \tiny Jup } } Â Pleiades brown dwarfs to be < 11 \% for 1 \sigma ( < 26 \% at 2 \sigma ) .
This binary frequency is consistent with both younger and older brown dwarfs in this mass range .