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Published September 28, 2015 | Published
Journal Article Open

Vibrational dynamics and band structure of methyl-terminated Ge(111)

Abstract

A combined synthesis, experiment, and theory approach, using elastic and inelastic helium atom scattering along with ab initio density functional perturbation theory, has been used to investigate the vibrational dynamics and band structure of a recently synthesized organic-functionalized semiconductor interface. Specifically, the thermal properties and lattice dynamics of the underlying Ge(111) semiconductor crystal in the presence of a commensurate (1 × 1) methyl adlayer were defined for atomically flat methylated Ge(111) surfaces. The mean-square atomic displacements were evaluated by analysis of the thermal attenuation of the elastic He diffraction intensities using the Debye-Waller model, revealing an interface with hybrid characteristics. The methyl adlayer vibrational modes are coupled with the Ge(111) substrate, resulting in significantly softer in-plane motion relative to rigid motion in the surface normal. Inelastic helium time-of-flight measurements revealed the excitations of the Rayleigh wave across the surface Brillouin zone, and such measurements were in agreement with the dispersion curves that were produced using density functional perturbation theory. The dispersion relations for H-Ge(111) indicated that a deviation in energy and lineshape for the Rayleigh wave was present along the nearest-neighbor direction. The effects of mass loading, as determined by calculations for CD_3-Ge(111), as well as by force constants, were less significant than the hybridization between the Rayleigh wave and methyl adlayer librations. The presence of mutually similar hybridization effects for CH_3-Ge(111) and CH_3-Si(111) surfaces extends the understanding of the relationship between the vibrational dynamics and the band structure of various semiconductor surfaces that have been functionalized with organic overlayers.

Additional Information

© 2015 AIP Publishing LLC. Received 17 July 2015; accepted 31 August 2015; published online 25 September 2015. S.J.S. acknowledges support from the Air Force Office of Scientific Research Grant Nos. FA9550-10-1-0219 and FA9550-15-1-0428, and the Material Research Science and Engineering Center at the University of Chicago, Grant No. NSF-DMR-14-20709. N.S.L. acknowledges support from the National Science Foundation (Grant No. CHE-1214152), and research was in part carried out at the Molecular Materials Research Center of the Beckman Institute of the California Institute of Technology.

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August 20, 2023
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