Structure of the clean Gd₅Ge₄(010) surface

Abstract

We have characterized the (010) surface of Gd5Ge4 using scanning tunneling microscopy (STM) and x-ray photoelectron spectroscopy. Data from different samples have the following features in common: (1) the surface composition equals the bulk composition to within 5 at.%, both after ion etching and after annealing at temperatures of 400-1200 K; and (2) the surface exhibits terraces of two types. The height of the steps between similar terraces corresponds well to the separation between equivalent layers along the h010i direction in the bulk structure. Density functional theory (DFT) shows that the surface energy of the (0001) plane of hexagonal close-packed Gd is lower than that of the (111) plane of diamond-type Ge, suggesting that surfaces of Gd5Ge4 (for comparable density) should be rich in Gd. Indeed, DFT shows that among the bulk terminations of Gd5Ge4, a pure Ge termination is not favored. Each of the three remaining terminations (two pure Gd and one mixed, Gd-Ge) has its minimum surface energy in a different range of the possible Gd chemical potentials, indicating that different terminations may be stable under different conditions. DFT shows that the heights of the steps between dissimilar terraces, measured in STM, are consistent with the two pure Gd terminations. Abstract.We have characterized the (010) surface of Gd5Ge4 using scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy. Data from different samples have the following features in common: (1) Surface composition equals bulk composition to within 5 atomic %, both after ion etching and after annealing at temperatures of 400 K to 1200 K; and (2) The surface exhibits two types of terraces.Step heights between similar terraces correspond well to the separation between equivalent layers along the <010> direction in the bulk structure. Density functional theory (DFT) shows that the surface energy of the (0001) plane of hcp Gd is lower than that of the (111) plane of diamond-type Ge, suggesting that surfaces of Gd5Ge4 (for comparable density) should be Gd-rich. Indeed, among the bulk terminations of Gd5Ge4, DFT shows that a pure Ge termination is not favored. The three remaining terminations (two pure Gd and one mixed DFT shows that step heights between dissimilar terraces, measured in STM, are consistent with the two pure Gd terminations.

The (111) Surface of NaAu2: Structure, Composition, and Stability

“…Some STM and XPS, plus all of the temperature-programmed desorption (TPD) and X-ray diffraction (XRD) work was done at The Ames Laboratory. Details relevant to the EMPA work 14 and to the Ames work 15 are available elsewhere.…”