Sonic diamond nano-pore rocket?

I'd like to bounce a propulsion idea off the experts of this group:

Visualize a very small, v-shaped notch in a thin layer of diamond -
maybe 100nm wide and 1000nm deep (just to grab some numbers out of the
air, but thinking that a micron thick layer of diamond could possibly
be manufactured). High energy sound waves arrive simultaneously from
both sides, compressing the notch shut very briefly.

(It might not be necessary to compress the diamond - e.g. one might
vibrate two half-diamonds along the direction of the depth of the
notch, pivoting at the point of the notch. But for now assume we're
actually compressing the diamond longitudinally - i.e. across the
notch.)

The speed of sound in diamond is 12000m/s, and if we assume the
closing rate is twice that (closing from both directions
simultaneously), the 100nm gap would close in about 4pico-second.

A small amount of liquid hydrogen injected at the base of the notch -
say a wedge 200nm deep, 20nm wide at the base and 1cm long - should be
accelerated out of the notch - call it 900nm - within that 4ps. That
would require a minimum exit velocity for the hydrogen of 225000m/s.
(This is assuming instantaneus acceleration followed by constant
velocity - an under-estimate somewhat balancing the loss of closure
velocity as energy is transferred to the hydrogen.

I believe that easily beats modern ion engines for exhaust velocity?