  We have carried out a survey of 60 Herbig Ae/Be stars in the 3 micron
wavelength region in search for the rare spectral features at 3.43 and 3.53
micron. These features have been attributed to the presence of large, hot,
hydrogen-terminated nanodiamonds. Only two Herbig Ae/Be stars, HD 97048 and
Elias 3-1 are known to display both these features. We have obtained
medium-resolution spectra (R ~2500) with the ESO near-IR instrument ISAAC in
the 3.15-3.65 micron range. In our sample, no new examples of sources with
prominent nanodiamond features in their 3 micron spectra were discovered
(detection rate less than 4%). We report tentative 3.53 micron detections in
V921 Sco (=CD-42.11721), HD 163296 and T CrA. The sources which display the
nanodiamond features are not exceptional in the group of Herbig stars with
respect to disk properties, stellar characteristics, or disk and stellar
activity. Moreover, the nanodiamond sources are very different from each other
in terms of these parameters. We do not find evidence for a recent supernova in
the vicinity of any of the nanodiamond sources. We have analyzed the PAH 3.3
micron feature and the Pfund delta hydrogen emission line, two other spectral
features which occur in the 3 micron wavelength range. We reinforce the
conclusion of previous authors that flared-disk systems display significantly
more PAH emission than self-shadowed-disk sources. The Pf delta line detection
rate is higher in self-shadowed-disk sources than in the flared-disk systems.
We discuss the possible origin and paucity of the (nano)diamond features in
Herbig stars. Different creation mechanisms have been proposed in the
literature, amongst others in-situ and supernova-induced formation. Our data
set is inconclusive in proving or disproving either formation mechanism.
