NOVELTY - An iron-microparticle-holding structure (1) comprises iron microparticles (11) having a diameter of 5-20 nm existing individually and containing silicon in portion, held on a substrate (3) in a state buried in surface layer.    USE - Iron-microparticle-holding structure is useful as catalyst for manufacturing carbon nanotubes (all claimed) useful as electron-generation material of field emission display of big screens, and for catalyst electrode layers of fuel cells.    ADVANTAGE - The iron-microparticle-holding structure has excellent oxidation resistance. The size (nm) of iron microparticles is maintained stably. The structure enables easy manufacture of carbon nanotubes excellent in linearity, with excellent reproducibility. A stable state of the surface is maintained for a long period of time.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) carbon nanotube produced on the iron microparticles by carrying out contact reaction of carbon-containing gas with respect to iron microparticles in the structure;    (2) catalyst consisting of the iron microparticles in the structure;    (3) manufacture of carbon nanotubes, which involves using the iron microparticles in the structure as catalyst; and    (4) manufacture of iron-microparticle-holding structure, which involves subjecting precursor (I) containing aluminum layer (9) containing oxygen (7), buffer layer (11) containing silicon, and iron layer formed sequentially on a substrate, or precursor (II) containing aluminum layer containing oxygen, and buffer layer containing alloy layer of silicon and iron formed sequentially on a substrate, to thermal annealing to form iron microparticles.    DESCRIPTION OF DRAWING(S) - The drawing shows a cross-sectional view of the iron-microparticle-holding structure. (Drawing includes non-English language text)    Iron-microparticle-holding structure (1)    Substrate (3)    Aluminum layer (9)    Aluminum (9a)    Buffer layer (11)    Iron microparticles (13)