Vibrational dynamics of hydrogen on Ge surfaces

Han, Xu; Balgar, Thorsten; Hasselbrink, Eckart

doi:10.1063/1.3102438

Cited by 16 publications

(16 citation statements)

References 28 publications

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“…Wei and Chou 45 created an 8 × 8 supercell and used the HellmannFeynman theorem to calculate the transverse force constants for surface atoms of bare Ge(111) (−1.937 dyn/cm) and Si(111) (−2.193 dyn/cm), which strengthens this hypothesis of softening. Additionally, Han et al 46 noted that the largest phonon energy in Ge (38 meV) is only about 60% of that in Si (64 meV), which matches well with the relative Rayleigh wave zone-edge energies of these two methyl-terminated interfaces.…”

Section: B Phonon Band Structuresupporting

confidence: 53%

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

Hund

Nihill

Campi

et al. 2015

The Journal of Chemical Physics

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Articles you may be interested inThe interaction of organic adsorbate vibrations with substrate lattice waves in methyl-Si (111) 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. C 2015 AIP Publishing LLC.[http://dx

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Section: B Phonon Band Structuresupporting

confidence: 53%

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

Hund

Nihill

Campi

et al. 2015

The Journal of Chemical Physics

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“…A subtle red-shift, but no dramatic change in integrated peak intensity, of the ν(Ge−H) mode is observed between T sub = 260 and 305°C. Therefore, we can conclude that processes such as adsorbate− phonon coupling 25,26 do not significantly impact oscillator strength over the narrow range of growth temperatures studied here. A saturation dose at T sub = 330°C was not attainable; however, the lack of peak broadening indicates the decrease in intensity is due to coverage.…”

Section: ■ Resultsmentioning

confidence: 80%

Direct Observation of Transient Surface Species during Ge Nanowire Growth and Their Influence on Growth Stability

et al. 2015

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Surface adsorbates are well-established choreographers of material synthesis, but the presence and impact of these short-lived species on semiconductor nanowire growth are largely unknown. Here, we use infrared spectroscopy to directly observe surface adsorbates, hydrogen atoms and methyl groups, chemisorbed to the nanowire sidewall and show they are essential for the stable growth of Ge nanowires via the vapor-liquid-solid mechanism. We quantitatively determine the surface coverage of hydrogen atoms during nanowire growth by comparing ν(Ge-H) absorption bands from operando measurements (i.e., during growth) to those after saturating the nanowire sidewall with hydrogen atoms. This method provides sub-monolayer chemical information at relevant reaction conditions while accounting for the heterogeneity of sidewall surface sites and their evolution during elongation. Our findings demonstrate that changes to surface bonding are critical to understand Ge nanowire synthesis and provide new guidelines for rationally selecting catalysts, forming heterostructures, and controlling dopant profiles.

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“…Applying this theory to the vibrational relaxation of pure light hydrogen adsorbed on Ge͑100͒, we are able to reproduce the measured vibrational lifetime of 1.56 ns at T S = 400 K and also find good agreement with the observed temperature dependence. 9 Moreover, both the calculations and the measurements show the same trend for isotope mixtures-a marked decrease in the vibrational lifetime of H in the presence of D adatoms. Our theoretical analysis shows that changes in the intermediate states involved in the relaxation are responsible for the surprisingly strong influence of the coadsorbate.…”

Section: Introductionmentioning

confidence: 54%

“…9. The cleaned Ge͑100͒ sample is exposed to a flux from a heated capillary doser ͑2200 K͒ with a 50:50 ratio of H 2 and D 2 in the feed.…”

Section: Experimental and Theoretical Methodsmentioning

confidence: 99%

“…Recently, a novel type of isotope effect has been reported, namely, that the vibrational lifetime of H on the Ge͑100͒ surface is reduced by up to a factor of 6 in the presence of D. 9 This surprising finding motivated us to carry out further experimental as well as theoretical research into the mechanism of vibrational energy relaxation of hydrogen on Ge͑100͒. Here, we present a theory based on firstprinciples data that systematically accounts for the vibrational lifetime of pure H, pure D, and isotope-mixed adsorbates.…”

Section: Introductionmentioning

confidence: 99%

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Isotope effects in the vibrational lifetime of hydrogen on germanium(100): Theory and experiment

Sakong

Kratzer

Han

et al. 2009

The Journal of Chemical Physics

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Combining first-principles calculations and sum frequency generation spectroscopy, we elucidate the microscopic details in the relaxation of the stretching vibration of hydrogen adsorbed on Ge(100). The dominant decay channels involve energy transfer from the stretching to the hydrogen bending modes, with the remaining energy difference being transferred to or from substrate phonons. The coupling between stretching and bending modes is treated from first principles using the calculated multidimensional adiabatic potential energy surface, while the coupling to phonons is treated in perturbation theory. For a surface solely saturated with light hydrogen, we calculate a vibrational lifetime of 1.56 ns at 400 K, in good agreement with experiment, and find a similar temperature dependence of the lifetime in both experiment and theory. The calculations show that the stretching energy dissipates to a vibrational state involving four bending quanta of hydrogen, concurrently absorbing a thermally excited surface phonon related to the Ge dimer rocking mode. For a Ge surface saturated with a mixture of H and D, our experiments find that the relaxation rate of the H stretching vibration is markedly increased when compared to a surface saturated with H only. Experimentally, a single decay is observed although H and D atoms will statistically pair on the surface dimers. The vibrational lifetime of the Ge-H stretching mode is up to six times shorter in the presence of adsorbed D atoms. The calculated relaxation rates are consistent with the experimentally observed trend. The theoretical analysis shows that the breaking of symmetry within the Ge surface dimer due to coadsorption of D opens up further relaxation channels that involve absorption or emission of a substrate phonon at various energies. Moreover, the calculations predict an even shorter vibrational lifetime of the Ge-D stretch mode due to efficient coupling to the Ge dimer rocking mode.

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Vibrational dynamics of hydrogen on Ge surfaces

Cited by 16 publications

References 28 publications

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

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

Direct Observation of Transient Surface Species during Ge Nanowire Growth and Their Influence on Growth Stability

Isotope effects in the vibrational lifetime of hydrogen on germanium(100): Theory and experiment

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