  Using angle-resolved photoemission spectroscopy we have studied the
low-energy electronic structure and the Fermi surface topology of
Fe$_{1+y}$Te$_{1-x}$Se$_x$ superconductors. Similar to the known iron pnictides
we observe hole pockets at the center and electron pockets at the corner of the
Brillouin zone (BZ). However, on a finer level, the electronic structure around
the $\Gamma$- and $Z$-points in $k$-space is substantially different from other
iron pnictides, in that we observe two hole pockets at the $\Gamma$-point, and
more interestingly only one hole pocket is seen at the $Z$-point, whereas in
$1111$-, $111$-, and $122$-type compounds, three hole pockets could be readily
found at the zone center. Another major difference noted in the
Fe$_{1+y}$Te$_{1-x}$Se$_x$ superconductors is that the top of innermost
hole-like band moves away from the Fermi level to higher binding energy on
going from $\Gamma$ to $Z$, quite opposite to the iron pnictides. The
polarization dependence of the observed features was used to aid the
attribution of the orbital character of the observed bands. Photon energy
dependent measurements suggest a weak $k_z$ dispersion for the outer hole
pocket and a moderate $k_z$ dispersion for the inner hole pocket. By evaluating
the momentum and energy dependent spectral widths, the single-particle
self-energy was extracted and interestingly this shows a pronounced non-Fermi
liquid behaviour for these compounds. The experimental observations are
discussed in context of electronic band structure calculations and models for
the self-energy such as the spin-fermion model and the marginal-Fermi liquid.
