A scanning tunneling microscope (STM), operated in vacuum in the field emission mode, has been used to observe the latent image written with a focussed 50 kVe‐beam in a polydiacetylene negative resist. The ability to study the latent image in the undeveloped resist allows the resolution degradation caused by the exposure process to be separated from that occurring during the resist development step. The minimum linewidth observed in the resist is close to 80 nm in both the developed and undeveloped resist. This linewidth is significantly greater than that expected on the basis of the 50 kVe‐beam probe size, electron scattering, and secondary electrons. The results indicate that the resolution degradation occurs during the exposure process rather than during post‐exposure processing. This implies that swelling during development is not the critical problem it is with other negative resists. The quality and accuracy of the STM observations is discussed together with descriptions of related surface modifications createdinsituwith the STM.