In case you have internet, search in google for screw dislocations and HRTEM and look for images. There are many images displayed...Why it shouldn't be visible?   

Thanks Dr. Gert. I thought that they would be invisible because the displacements in screw are parallel to beam direction, they would not be visible in a HRTEM.  But apparently this is only so, if they are imaged end-on.

Hi Gowtham,

I have never seen a screw dislocation in HRTEM mode. But if you consider that the srew dislocation is invisible only in case if the Burgers vector is parallel to the diffracting lattice plane (g.b=0 condition) then you can expect the screw dislocation on image. The g.b=0 condition means that the screw dislocation is invisible only if it is imaged by means of reflection g for which g.b=0. For HRTEM imaging you need many g refelction so my assumption is that the visibility of screw dislovation is possible also in HRTEM. However my next assumption is the strong extinctions in dislocation vicinity will restrain the visibility of dislocation in HRTEM. So I vote for High-resolution STEM imaging where the diffraction type contrast is minimalized. 

Thanks Vladimir,

As a followup, shouldn't the dislocation line be made parallel to the beam for ease of HRTEM? Atleast that is how I understand it.