  We present results from the first large-scale survey of neutron(n)-capture
element abundances in planetary nebulae (PNe). This survey was motivated by the
fact that a PN may be enriched in n-capture elements if its progenitor star
experienced s-process nucleosynthesis during the asymptotic giant branch (AGB)
phase. [Kr III] 2.199 and/or [Se IV] 2.287 $\mu$m were detected in 81 PNe out
of 120 PNe, for a detection rate of nearly 70%. We derive Se and Kr abundances
or upper limits using ionization correction factors derived from
photoionization models. A significant range is found in the Se and Kr
abundances, from near solar (no enrichment), to enriched by a factor of ten.
Our survey has increased the number of PNe with known n-capture element
abundances by an order of magnitude, enabling us to explore correlations
between s-process enrichments and other nebular and central star properties. In
particular, the Se and Kr enrichments display a positive correlation with
nebular C/O ratios, as theoretically expected. Peimbert Type I PNe and bipolar
PNe, whose progenitors are believed to be intermediate-mass stars (>3-4 M_sun),
exhibit little or no s-process enrichment. Interestingly, PNe with H-deficient
[WC] central stars do not exhibit systematically larger s-process enrichments
than other PNe, despite the fact that their central stars are enriched in C and
probably n-capture elements. Finally, the few PNe in our sample with known or
probable binary central star systems exhibit little s-process enrichment, which
may be explained if binary interactions truncated their AGB phases. We also
briefly discuss a new observational program to detect optical emission lines of
n-capture elements, and new atomic data calculations that will greatly improve
the accuracy of n-capture element abundance determinations in PNe.
