Band dispersion of an interface state: Ca<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">F</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>/Si(111)

Ab, McLean; Himpsel, F. J.

doi:10.1103/physrevb.39.1457

Cited by 35 publications

(11 citation statements)

References 18 publications

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“…When the orbitals hybridize to form a bonding combination, their energy is apparently reduced by -1 eV, as indicated by the position of the interface valence band in photoemission spectra. 11 One then anticipates that the corresponding antibonding states will be positioned roughly 1 eV above the Fermi level, producing a semiconducting interface with an energy separation on the order of 2 eV between the valence and conduction bands. Our experimental results yield an interface band gap of 2.4 eV.…”

Section: Exhibit the Same Resonant Features Thus Demonstrating That mentioning

confidence: 99%

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Electronic transitions at theCaF2/Si(111) interface probed by resonant three-wave mixing spectroscopy

et al. 1989

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Resonant optical second-harmonic and sum-frequency generation are applied to probe electronic transitions at the Ca-terminated epitaxial CaF2/Si(l 11) interface. A band gap of 2.4 eV is established for the interface states, a value twice as large as that in bulk Si, but only j of the band gap in CaF2. The experimental three-wave-mixing spectra can be modeled by a two-dimensional band gap and a narrow resonance 150 meV below the band edge, the latter being tentatively assigned to a transition to a bound two-dimensional exciton.PACS 42.65.Ma, Understanding the nature of solid/solid interfaces is an area of great fundamental and practical importance. The characteristics of interfaces strongly influence the behavior of electronic devices with small dimensions and are critical in determining the morphology of thin-film growth, particularly in the case of epitaxial structures. Fully developed buried interfaces present difficulties for analysis: The unique features of the interface are present only in a few atomic layers of material, but the interfacial region will generally be covered by an overlayer of many times this thickness. Consequently, many of the sensitive and highly developed techniques appropriate for surfaces may not be suitable for this interesting class of problems. In this Letter, we present the first application of three-wave-mixing spectroscopy to the problem of solid/solid interfaces. The method is purely optical and can, because of its large probing depth, be used to investigate buried interfaces. It relies on the second-order nonlinear optical processes of second-harmonic and sum-frequency generation. These effects are forbidden (within the electric-dipole approximation) in centrosymmetric media and, hence, exhibit a high degree of sensitivity to interfaces, where the inversion symmetry must be broken. l The technique has been previously employed in studies of the electronic 2,3 and vibrational 4,5 spectra of molecular monolayers. Here we report for three-wave-mixing spectroscopy of the epitaxial interface of CaF2/Si(l 11). This material system 6 " 12 has recently attracted considerable attention as a prototype of a well-controlled semiconductor/insulator interface, as well as for its potential technological importance. The resonant second-harmonic and sum-frequency spectra presented in this work permit a value for the previously unknown interface band gap to be established directly. The observed energy difference of 2.4 eV between the filled and empty interface states stands in marked contrast to the band gaps of the bulk Si (1.1 eV) and CaF2 (12.1 eV), indicating the distinctive nature of the interfacial region.The three-wave-mixing spectra for the CaF2/Si(lll) interface were obtained by exposing the sample to laser radiation from a tunable source. The intensity of the reflected light at the second-harmonic (SH) frequency was measured as a function of wavelength. Sumfrequency (SF) data were collected for mixing of the tunable source with the light from a laser operating at a fixed frequency. Tuna...

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Section: Exhibit the Same Resonant Features Thus Demonstrating That mentioning

confidence: 99%

“…From the measured interface valence-band dispersion and estimated conduction-band dispersion in Ref. 11, we obtain p~~0.6mo for the reduced mass, where mo represents the mass of a free electron. The observed excitonic binding energy 19 of 150 meV is then reproduced by Eq.…”

Section: For a Direct Band Gap In Two Dimensions Juosihco)mentioning

confidence: 99%

Electronic transitions at theCaF2/Si(111) interface probed by resonant three-wave mixing spectroscopy

et al. 1989

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“…Valence-band photoemission, however, does not show the interface to be metallic. 25 One possible explanation is that the interface bands are only pulled below the Fermi level in the presence of the core holes. Another is that we have an additional satellite at about 1 eV that cannot be resolved with our instrument ͑for example, due to crystalfield splitting, as discussed later͒, although this cannot account for the large inelastic tail extending ϳ25 eV ͓see Fig.…”

Section: Fig 3 Ca 2p X-ray Photoelectron Diffraction Modulations ͑A͒mentioning

confidence: 99%

Altered photoemission satellites atCaF2- andSrF2-on-Si(111) int

1996

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Bulk and interface photoemission satellite excitations, measured with x-ray photoelectron spectroscopy and x-ray photoelectron diffraction, are compared for thick, thin, and monolayer films of CaF 2 and SrF 2 on Si͑111͒. Intrinsic satellites are observed for excitation of atoms in the first monolayer, both uncovered and at the buried interface, that differ from those associated with bulk atoms. For F 1s excitation, the bulk and interface satellites differ only in width and amplitude; for the cation core excitations ͑Ca 2p, Sr 3p, and Sr 3d͒, the observed excitation energies and intensities differ both from the equivalent bulk satellites and among the various core hole states. The results yield new information on the nature of the interface bonding, as well as on the origin of both bulk and interface satellites. Several models are considered, including differential screening, dielectric losses, crystal-field and multiplet effects, and interface excitation. The most likely explanation for the new cation satellites at the CaF 2 /Si͑111͒ ͓SrF 2 /Si͑111͔͒ interface is localized excitation of the interface bond, where the interface band gap is controlled by the collapse of the Ca 3d ͑Sr 4d͒ level in the presence of the Ca ͑Sr͒ core hole.

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“…They associate the strong peak at about 2.4 eV to the vertical gap (HOMO-LUMO) transition at the Γ point Fig (6.3) [81,83]. It is originated by the bonding and anti-bonding matching of the Ca + (4s) and the hybridized Si(sp3) orbitals at the interface [78].…”

Section: The 1989 Experimentsmentioning

confidence: 99%

“…• C. The silicon presented a clean (7×7) surface reconstruction [81,82]. 6 After the first layers growth, MBE deposition can continue at lower temperature, diminishing the lattice mismatch.…”

Section: The Si(111)/caf 2 Structure 621 Experimental Samplementioning

confidence: 99%

Second-Harmonic Generation

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Band dispersion of an interface state: CaF2/Si(111)

Cited by 35 publications

References 18 publications

Electronic transitions at theCaF2/Si(111) interface probed by resonant three-wave mixing spectroscopy

Electronic transitions at theCaF2/Si(111) interface probed by resonant three-wave mixing spectroscopy

Altered photoemission satellites atCaF2- andSrF2-on-Si(111) int

Second-Harmonic Generation

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