  We have conducted a deep, very long baseline interferometry (VLBI)
observation at 1.4 GHz of an area of sky located within the NOAO Bootes field,
using the NRAO VLBA and 100-m Green Bank Telescope. Applying wide-field VLBI
techniques, a total of 61 sources, selected from a WSRT image, were surveyed
simultaneously with a range of different sensitivities and resolutions. The
inner 0-2', of the field reached an unprecedented 1-sigma rms noise level ~ 9
uJy/beam and yielded 2 detections. A further 7 sources were detected in the
rest of the field. All of the sources have a brightness temperature in excess
of 10^5 K; suggesting they are AGN. Optical identifications are available for 8
of the 9 VLBI detections - only VLBI J142906.6095 remains unidentified (I >
25.6m). Two sources are not detected in K-band (K > 18.5m) suggesting that some
significant fraction of these compact radio sources may be located at z > 1.
The VLBI detection rate for sub-mJy radio sources is 8^{+4}_{-5} %. The VLBI
detection rate for mJy sources is higher, 29^{+11}_{-12}%. This trend is
expected if the radio emission associated with fainter sub-mJy and microJy
sources increasingly arises from extended regions of star formation. The 9 VLBI
detections pin-point the precise location of AGN or candidate AGN, and their
VLBI positions can help to anchor the NOAO Bootes field to the ICRF. The
simultaneous detection of several sub-mJy and mJy radio sources, in a single
observation, suggest that their combined response may be used to self-calibrate
wide-field VLBI data. Future VLBI observations of faint sub-mJy and microJy
radio sources can take full advantage of this "full-beam" calibration
technique.
