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The 15th International Conference on

Vibrations at Surfaces

June 22-26, 2015 ▪ Donostia-San Sebastián, Spain

Donostia Igeldotik

Program

OverviewMondayTuesdayWednesdayThursdayFriday

Thursday June 25

09:00-10:40 Th1: Adsorbate and interface dynamics
10:40-11:20 Coffee break
11:20-13:00 Th2: STM-IETS and beyond
13:00-15:30 Lunch break (on your own)
15:30-16:40 Th3: Molecular films and 2D materials
16:40-17:20 Coffee break
17:20-19:00 Th4: Tip-enhanced vibrational spectroscopies
20:30-23:00 Conference dinner at Cofradía Vasca de Gastronomía, Old Town

Th1: Adsorbate and interface dynamics

Chair: P. Jelínek, Prague, Czech Republic

09:00-09:30 N. Lorente, San Sebastián, Spain
Imaging molecular motions with scanning tunnelling microscopy
09:30-10:00 J. C. Polanyi, Toronto, Canada
The role of vibration in surface-migration
10:00-10:20 T. Kumagai, Berlin, Germany
Local impact on intramolecular H-atom transfer studied by STM and nc-AFM
10:20-10:40 K. Ishioka, Tsukuba, Japan
Plasmon-phonon dynamics at GaP/Si(001) interfaces

Contributed talk

Plasmon-phonon dynamics at GaP/Si(001) interfaces

K. Ishioka1, K. Brixius2, A. Beyer2, W. Stolz2, K. Volz2, U. Höfer2, and H. Petek3

1Nano-characterization Unit, National Institute for Materials Science, Tsukuba, Japan

2Department of Physics and Materials Science Center, Philipps-Universität Marburg, Germany

3Department of Physics and Astronomy, University of Pittsburgh, USA

Charge carriers in impurity-doped semiconductors can behave collectively as a plasma oscillation. In polar semiconductors the plasma couples with the lattice polarization of the longitudinal optical (LO) phonons, resulting in LO phonon-plasmon coupled (LOPC) modes. The LOPC modes in III-V semiconductors can also be observed as coherent oscillations in the time domain. Monitoring the coherent LOPC mode by means of pump-probe reflectivity measurements can give a good measure of the chemically doped and photoexcited carriers, since the frequency and the dephasing rate depends crucially on the carrier type and density. Here we evaluate the charged carriers at the buried interface of GaP/Si(001) by means of coherent phonon spectroscopy. Lattice-matched GaP layers free from dislocations, staking faults or twins can be grown on exact Si(001) substrate by metal organic vapour phase epitaxy (MOVPE) [1]. Anti phase domains (APDs) are still unavoidable, however, and their boundaries consisting of the "wrong" bonds are expected to affect the interfacial electronic states crucially. Figure 1 compares the FT spectra of the anisotropic reflectivity changes of GaP/Si(001) samples with and without anti-phase domains (APDs). The GaP/Si sample without APDs (II) features oscillations due to the optical phonon of Si substrate at 15.6 THz and the LO phonon of GaP at 12 THz. The GaP/Si sample with APDs (I), by contrast, exhibits a prominent broad peak appears, whose frequency downshifts with increasing pump density. Similar mode was observed also for n-type GaAs(001) and assigned as the coherent LO phonon coupled with photoexcited multicomponent plasma [2]. The efficient generation of coherent LOPC mode for the interface sample with APDs indicates the presence of the surface built-in electric field, like for n-doped GaAs, in spite that the GaP film is nominally undoped. Our observation suggests that the boundaries of APDs act as donors.

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Figure 1: FT spectra of anisotropic reflectivity changes of GaP/Si(001) samples with APDs (I) and without APDs (II) pumped at different pump densities.

[1] A. Beyer et al., J. Appl. Phys. 111, 083534 (2012)

[2] A. K. Basak et al., Phys. Rev. B 91, 125201 (2015)