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We report on the electronic properties of n-doped (n ∼ 1018 cm-3) ZnSe/GaAs(001) heterostructures grown by molecular beam epitaxy with pre-deposition of different amounts of Zn or Se in the fractional monolayer range at ZnSe epilayer growth start. Special attention is spent on the depletion layers on both sides of the interface and to the conduction band potential barrier. The depletion layers are studied by Raman spectroscopy and electrochemical capacitance-voltage profiling, while the potential barrier height is derived from temperature-dependent transport across the hetero-interface. We observe a carrier-depleted interface region with an overall thickness of about 50 to 65 nm. For a Zn-rich growth start the thickness contribution on the GaAs-side slightly prevails, but for Se-pre-deposition, the ZnSe-side contribution clearly dominates, and for the highest Se pre-deposition the total depletion width is slightly reduced. The potential barrier is 550 meV for the Zn-rich hetero-interface. With Se pre-deposition it decreases down to about 70 meV, which implies an increase of the conductivity across the hetero-interface by as much as five orders of magnitude. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

The low-temperature electronic properties of rare-earth intermetallics are substantially influenced by the symmetry and magnitude of the crystal electric field. The direct spectroscopic analysis of crystal-field splitting can be challenging, especially in low-dimensional systems, because it requires both high spectral resolution and pronounced sensitivity. We demonstrate the eligibility of electronic Raman spectroscopy for this purpose by the direct determination of the 4ƒ level splitting in ultrathin ordered CePt5 films down to ≈ 1.5 nm thickness on Pt(111). Crystal-field excitations of Ce 4ƒ electrons give rise to Raman peaks at energy losses up to ≈ 25 meV. Three distinct peaks occur which we attribute to inequivalent Ce sites, located (i) at the interface to the substrate, (ii) next to the Pt-terminated film surface, and (iii) in the CePt5 layers in between. The well-resolved Raman signatures allow us to identify a reduced crystal-field splitting at the interface and an enhancement at the surface, highlighting its strong dependence on the local atomic environment. [ABSTRACT FROM AUTHOR]

The vibrational properties of the Au-induced (√3x √3)R 30° reconstruction of the Si(111) surface are investigated by polarized surface Raman spectroscopy and density-functional theory. The Raman measurements are performed in situ at room temperature as well as 20 K, and they reveal the presence of vibrational eigenmodes in the spectral range from 20 to 450 cm-1. In particular, two peaks of E symmetry at 75 and 183 cm-1 dominate the spectra. No substantial difference between room- and low-temperature spectra is observed, suggesting that the system does not undergo a phase transition down to 20 K. First-principles calculations are performed based on the structural models discussed in the literature. The thermodynamically stable conjugate honeycomb-chained-trimer model (CHCT) [Surf. Sci. 275, L691 (1992)] leads to phonon eigenvalues compatible with the experimental observations in the investigated spectral range. On the basis of the phonon eigenfrequencies, symmetries, and Raman intensities, we assign the measured spectral features to the calculated phonon modes. The good agreement between measured and calculated modes provides a strong argument in favor of the CHCT model. [ABSTRACT FROM AUTHOR]

Ordered submonolayers of adsorbate atoms on semiconductor surfaces constitute a playground for electronic correlation effects, which are tightly connected to the local atomic arrangement and the corresponding vibration eigenmodes. We report on a study of the vibration eigenmodes of Au-covered Si(111) surfaces with (5 × 2) reconstruction using polarized Raman spectroscopy and first-principles calculations. Upon Au coverage, the vibration eigenmodes of the clean reconstructed Si(111)- (7 × 7) surface are quenched and replaced by new eigenmodes, determined by the Au- (5 × 2) reconstruction. Several polarization-dependent surface eigenmodes emerge in the spectral range from 25 to 120 cm-1, with the strongest ones at 29, 51, and 106 cm-1. In our first-principles calculations we have determined the vibration frequencies, the corresponding elongation patterns, and the Raman intensities for two different structure models currently discussed in the literature. The best agreement with the experimental results is achieved for a model with 0.7 monolayer coverage and seven Au atoms per unit cell, proposed by S. G. Kwon and M. H. Kang [Phys. Rev. Lett. 113, 086101 (2014)]. [ABSTRACT FROM AUTHOR]