NOVELTY - A polymer film (1) is bombed by high-energy focused heavy ion beam (2) and chemical etching is carried out to remove the portions of film in the zones degraded by ion bombing to obtain pores passing through the film. Heavy-ion bombing is carried out after interposing between the source of heavy ions and polymer film, in proximity to the film, an amplitude mask (3) having an arrangement of nanopores (3a) and thickness sufficient to prevent the passage of heavy ions not directed through nanopores, to obtain a polymer film with a distribution of nanopores.    USE - Production of nanoporous polymeric membrane. Uses include but are not limited to lithium-battery separators, polymer fuel cells, filtering systems, membranes for microfluidic systems, elements for enabling manufacture of other nanostructured components (nanowire sensors, nanostructured electrodes for solar cells and planar optoelectronic devices), nanostructure particles, materials made of nanocomposites, and artificial metamaterials.    ADVANTAGE - The method enables production of nanoporous polymeric membranes having an ordered arrangement (e.g. honeycomb arrangement) of high-aspect-ratio nanopores. A sufficiently thick anodic porous alumina membrane is interposed between the polymer film and source of ions, in such a manner that only the ions selected by the pores of alumina reach the polymer film. Thus this allows, by suitably extending the time of exposure to the ionic beam with respect to the case where alumina mask is not used, degrading the polymer film solely at the alumina pores. The chemical etching process produces a nanoporous polymeric structure with symmetry equivalent to that of porous alumina.    DETAILED DESCRIPTION - A polymer film is bombed by high-energy focused heavy ion beam and a chemical etching is subsequently carried out to remove the portions of film in the zones degraded by the ion bombing in such a manner to obtain pores passing through the film. Heavy-ion bombing is carried out after interposing between the source of heavy ions and the polymer film, in proximity to the film, an amplitude mask having an arrangement of nanopores and thickness sufficient to prevent the passage of the heavy ions which are not directed through the nanopores of the amplitude mask, in such a manner to obtain a polymer film with a distribution of nanopores. The amplitude mask has an ordered honeycomb arrangement of nanopores, so that a corresponding ordered honeycomb distribution of nanopores is obtained in the polymer film. The nanopores obtained in the polymer film have un aspect ratio of greater than 10. The amplitude mask is obtained by positioning over the polymer film a layer of material opaque to ions and depositing a layer of aluminum over the opaque layer, transforming the aluminum layer into anodic porous alumina by anodization, eliminating the barrier layer at the bottom of the pores of the anodic porous alumina through chemical etching, in such a manner to define channels passing through the layer of anodic porous alumina, chemically etching the layer opaque to ions through the pores of the anodic porous alumina in such a manner to obtain in the opaque layer an ordered arrangement of nanopores corresponding to the arrangement of the pores of the anodic porous alumina and thus using the opaque layer with the abovementioned nanopores as an amplitude mask.    DESCRIPTION OF DRAWING(S) - The drawing shows a sectional view explaining the bombing step.    Polymer film (1)    Heavy ion beams (2)    Amplitude mask (3)    Nanopores (3a)