Crystalline polygermyne—a new compound consisting of H‐terminated germanium double layers (see Figure) stacked to form a three‐dimensional crystal—is reported to have been produced by the topochemical transformation of epitaxial thin CaGe2 films at –30 °C. Polygermyne is found to exhibit strong near‐infrared photoluminescence with an intensity comparable to that of siloxene, its silicon homologue.
Heteroepitaxial AlN films grown on (100)- and (111)-oriented diamond (Cα) substrates by plasma-induced molecular beam epitaxy have been investigated by x-ray diffraction (XRD) and atomic force microscopy (AFM). High quality epitaxial growth of almost strain-free wurtzite AlN is observed for both orientations. For the AlN/Cα(111) heterostructures, the epitaxial orientation relationship (0001)[101̄0] AlN∥(111)[011̄] Cα is obtained. However, a significant fraction of up to 20% of the epitaxial layer is oriented differently with (101̄1) AlN∥(111) Cα. In case of AlN on Cα(100), a double-domain structure with either (0001)[101̄0] AlNI∥(100)[011] Cα or (0001)[1̄21̄0] AlNII∥(100)[011] Cα is found. The linewidths of the XRD ω and 2θ/ω scans of the symmetric AlN 002 reflection have been determined as 1.4 and 0.17° for AlN/Cα(100), 0.55° and 0.11° for AlN/Cα(111), as well as 0.51 and 0.05° for an AlN/sapphire (0001) reference sample grown under similar conditions. Thus, the crystal quality of AlN on Cα(111) is close to that of AlN on sapphire. The corresponding AlN rms roughness values found by AFM are 1.9 nm on Cα(100), 1.7 nm on Cα(111), and 3.2 nm on sapphire (0001), respectively.
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