Electronic structure of buried Si layers in GaAs(001) as studied by soft-x-ray emission

Nilsson, P. O.; Kanski, J.; Thordson, J.V.; Andersson, T.; Nordgren, Joseph; Guo, Jinghua; Magnuson, Martin

doi:10.1103/physrevb.52.r8643

Cited by 36 publications

(18 citation statements)

References 11 publications

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“…This effect is significantly larger and completely opposite from that in Si L 2,3 spectra of pure single crystal Si(111). 9,31 The enhanced Si 3d (electron-like) intensity along the c axis of Ti 3 SiC 2 should reduce and compensate for the dominating hole-like Ti 3d bands that give negative contributions to the Seebeck coefficient along the c axis. In particular, it should be noted that this strong intensity of the Si 3d character weighting in the partial DOS observed experimentally along the c axis at room temperature is not at all reproduced in ground state DFT theory at zero Kelvin but is instead opposite in the energy range 1-3 eV below E F .…”

Section: B C K X-ray Absorption and Emissionmentioning

confidence: 99%

Electronic-structure origin of the anisotropic thermopower of nanolaminated Ti3SiC2determined by polarized x-ray spectroscopy and Seebeck measurements

et al. 2012

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Nanolaminated materials exhibit characteristic magnetic, mechanical, and thermoelectric properties, with large contemporary scientific and technological interest. Here we report on the anisotropic Seebeck coefficient in nanolaminated Ti 3 SiC 2 single-crystal thin films and trace the origin to anisotropies in element-specific electronic states. In bulk polycrystalline form, Ti 3 SiC 2 has a virtually zero Seebeck coefficient over a wide temperature range. In contrast, we find that the in-plane (basal ab) Seebeck coefficient of Ti 3 SiC 2 , measured on single-crystal films, has a substantial and positive value of 4-6 μV/K. Employing a combination of polarized angle-dependent x-ray spectroscopy and density functional theory we directly show electronic structure anisotropy in inherently nanolaminated Ti 3 SiC 2 single-crystal thin films as a model system. The density of Ti 3d and C 2p states at the Fermi level in the basal ab plane is about 40% higher than along the c axis. The Seebeck coefficient is related to electron and hole-like bands close to the Fermi level, but in contrast to ground state density functional theory modeling, the electronic structure is also influenced by phonons that need to be taken into account. Positive contribution to the Seebeck coefficient of the element-specific electronic occupations in the basal plane is compensated by 73% enhanced Si 3d electronic states across the laminate plane that give rise to a negative Seebeck coefficient in that direction. Strong phonon vibration modes with three to four times higher frequency along the c axis than along the basal ab plane also influence the electronic population and the measured spectra by the asymmetric average displacements of the Si atoms. These results constitute experimental evidence explaining why the average Seebeck coefficient of Ti 3 SiC 2 in polycrystals is negligible over a wide temperature range. This allows the origin of anisotropy in physical properties of nanolaminated materials to be traced to anisotropies in element-specific electronic states.

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Section: B C K X-ray Absorption and Emissionmentioning

confidence: 99%

Electronic-structure origin of the anisotropic thermopower of nanolaminated Ti3SiC2determined by polarized x-ray spectroscopy and Seebeck measurements

et al. 2012

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“…In a study of Si(100) buried in GaAs, it has been demonstrated that it is in fact possible to extract detailed information about DOS [83]. By irradiating the sample with a bright source, it is possible to detect characteristic fluorescence from buried layers.…”

Section: Buried Atomical Layers and Interfacesmentioning

confidence: 99%

Soft X‐Ray Absorption and Emission Spectroscopy in the Studies of Nanomaterials

Guo¹

2010

X‐Rays in Nanoscience

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“…As in the case of Al, the Si L 2,3 spectrum is dominated by 3s final states and the Si 3p states are dipole forbidden. The spectral profile of Si in Ti 3 SiC 2 also largely differs from spectra of pure Si, which has a pronounced double structure [13]. The spectral shape of Si in Ti 3 SiC 2 is similar to the metal silicides [14].…”

Section: Resultsmentioning

confidence: 80%

“…The measured spectral profiles of Al, Si and Ge are compared to spectra of the pure elements from Refs. [11,13,15] (dashed lines). The Ge spectrum (bottom) was smoothed with a binomial average of the raw data.…”

Section: Resultsmentioning

confidence: 99%

Max-Phases Investigated by Soft X-Ray Emission Spectroscopy

Magnuson

Mechanical Properties and Performance of Engineering Ceramics II: Ceramic Engineering and Science Proceedings, Volume 27, Issue

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The electronic structures of the MAX-phases Ti 3 AlC 2 , Ti 3 SiC 2 and Ti 3 GeC 2 were investigated by soft X-ray emission spectroscopy. These nanolaminated carbide compounds represent a class of layered materials with a combination of properties from both metals and ceramics. The bulksensitive soft X-ray emission technique is shown to be particularly useful for detecting detailed electronic structure information about internal monolayers and interfaces. A weak covalent TiAl bond is manifested by a pronounced shoulder in the Ti L-emission of Ti 3 AlC 2 . When Al is replaced by Si or Ge, the shoulder disappears. Furthermore, the spectral shapes of Al, Si and Ge in the MAX-phases are strongly modified in comparison to the corresponding pure elements. By varying the constituting elements, a change of the electron population is achieved causing a change of covalent bonding between the laminated layers, which enables control of the macroscopic properties of the material. INTRODUCTIONIn the last few years, the interest in ternary carbides and nitrides, so-called M n+1 AX n -phases has grown significantly both from a scientific and a technological point of view [1]. Generally, there are three different kinds of crystal structures of these materials, often denoted 211, 312 and 413, corresponding to n=1, 2 and 3. The letter M denotes an early transition metal, A is an element in the groups IIIA and IVA and X is either carbon or nitrogen. The MAX-phases exhibit a unique combination of metallic and ceramic properties, including high strength and stiffness at high temperature, resistance to oxidation and thermal shock, and display high electrical and thermal conductivity [1]. The unique macroscopic properties of the MAX-phases are related to the underlying nanolaminated crystal structure, the electronic structure and the chemical bonding of the individual atomic layers. For the 312-crystal structure, there are three different carbides, Ti 3 AlC 2 , Ti 3 SiC 2 and Ti 3 GeC 2 . Sintered bulk MAX-compounds are useful in many technological high-temperature applications such as heating elements in ovens. In other applications where e.g., low-friction properties are useful, high-quality thin film coatings of MAX-phases are utilized.

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Electronic structure of buried Si layers in GaAs(001) as studied by soft-x-ray emission

Cited by 36 publications

References 11 publications

Electronic-structure origin of the anisotropic thermopower of nanolaminated Ti3SiC2determined by polarized x-ray spectroscopy and Seebeck measurements

Electronic-structure origin of the anisotropic thermopower of nanolaminated Ti3SiC2determined by polarized x-ray spectroscopy and Seebeck measurements

Soft X‐Ray Absorption and Emission Spectroscopy in the Studies of Nanomaterials

Max-Phases Investigated by Soft X-Ray Emission Spectroscopy

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