  Surface-enhanced Raman spectroscopy (SERS) demands reliable, high enhancement
substrates in order to be used in different fields of application. Here, we
introduce freestanding porous gold membranes (PAuM) as easy to produce,
scalable, mechanically stable, and effective SERS substrates. We fabricate
large-scale sub-30 thick PAuM, that form freestanding membranes with varying
morphologies depending on the nominal gold thickness. These PAuM are
mechanically stable for pressures up to $>3$ bar, and exhibit surface-enhanced
Raman scattering with local enhancement factors of $10^4$ to $10^5$, which we
demonstrate by wavelength-dependent and spatially resolved Raman measurements
using graphene as a local Raman probe. Numerical simulations reveal that the
enhancement arises from individual, nanoscale pores in the membrane acting as
optical slot antennas. Our PAuM are mechanically stable, provide robust SERS
enhancement for excitation power densities up to $10^6$W$\,$cm$^{-2}$, and may
find use as a building block in flow-through sensor applications based on SERS.
