Thin films of the lanthanoide diphthalocyanines LnPc2 (Ln: Ho, Er) are deposited onto NaCl (001) surfaces by thermal evaporation under high vacuum conditions and analysed by HRTEM. Based on the obtained images a model is describing growth and structure of these films. The thin films consist of columnar crystallites with lateral dimensions of 10 to 100 nm mainly of the tetragonal phase with a two‐molecular base made of the two isomeric forms of the LnPc2 molecule. According to this model each (001) plane of the crystallites is made of exclusively one of the two mirror‐symmetric LnPc2 isomers. The type of isomer is alternating from plane to plane. Depending on the lowest plane the growth of the crystallites is preferably continued laterally in two mirror‐symmetric direction sets, because of the interactions with the substrate. Staggering angles of 36.9° and 53.1°, respectively, between the crystallites occur, as is well known from literature. Small pieces of orthorhombic structure and increased concentrations of lattice defects arise in the regions between the tetragonal crystallites and at the grain boundaries.

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