Partly ballistic propagation of carriers and phonons in single crystals of
the metals Ag and W and the semimetal Bi is studied in real space. The carr
iers are excited by heating a small surface area of the sample by illuminat
ion or electron beam irradiation. Alternatively they are injected through p
oint contacts. They spread out from this point-like source setting up a cha
racteristic anisotropic current pattern representing some kind of fingerpri
nt of the material's band structure. If the sample thickness is comparable
to the mean free path of the carriers, they produce a potential pattern on
the opposite sample surface. We present images of these patterns revealing
the phenomenon of electron focusing, i.e. caustics produced by a diverging
density of trajectories in specific directions. The influence of magnetic f
ields is studied. We give some basic theoretical analysis of the data in te
rms of fully ballistic transport. An outlook into possible future developme
nts and applications of the technique and the completion of the theoretical
model is given. (C) 2000 Elsevier Science B.V. All rights reserved.