Chapter 3 Multiple Choice Questions

. At the surface of a free-electron metal having a valence electron density of 65 nm^-3, the expected wavelength of Friedel oscillations perpendicular to the surface will be approximately…

0.20 nm

0.25 nm

0.30 nm

0.35 nm

0.40 nm

. Within a free-electron model, the surface dipole is…

Inversely proportional to the Fermi wavenumber

Independent of the Fermi wavenumber

Inversely proportional to the square of the Fermi wavenumber

Proportional to the Fermi wavenumber

Proportional to the square of the Fermi wavenumber

. The work functions of Cu{111} and Cu{110} are 4.94 eV and 4.48 eV respectively. By how much must their surface dipole densities differ?

Surface dipole density 1.22 D.nm^-2 higher for Cu{111} than for Cu{110}

Surface dipole density 0.61 D.nm^-2 higher for Cu{111} than for Cu{110}

Surface dipole densities are identical for both Cu{111} and Cu{110}

Surface dipole density 0.61 D.nm^-2 lower for Cu{111} than for Cu{110}

Surface dipole density 1.22 D.nm^-2 lower for Cu{111} than for Cu{110}

. Two parallel metal plates face each other across a vacuum gap that is small relative to their lateral extent. The plates are linked by a conducting wire of comparatively negligible thickness, and the two facing surfaces have differing work functions. Ignoring edge effects and the regions within a few nanometres of the plates themselves, which of these statements ought to be true?

The electric field strength is zero throughout the vacuum gap

The electric field strength is greatest at the centre of the vacuum gap

The electric field strength is constant throughout the vacuum gap

The electric field strength is least at the centre of the vacuum gap

The electric field strength varies linearly across the vacuum gap

. Isometric projection of the 1BZ of a bulk crystal onto a surface-parallel plane results in a shape having an area that is necessarily…

Equal to that of the surface 1BZ

Equal to or larger than that of the surface 1BZ

Equal to or smaller than that of the surface 1BZ

Twice that of the surface 1BZ

Half that of the surface 1BZ

. Reconstruction of a crystalline surface results in a surface 1BZ that is necessarily…

Half the size of the ideal surface's 1BZ

Twice the size of the ideal surface's 1BZ

Identical to or larger than the ideal surface's 1BZ

Identical to that of the ideal surface's 1BZ

Identical to or smaller than the ideal surface's 1BZ

. On the Au{111} surface, photoemission experiments indicate the maximum binding energy and effective mass for the Shockley state to be 380 meV and 0.211m_e respectively (m_e being the mass of a free electron). At what wavenumber does the corresponding band cross the Fermi level?

1.30 nm^-1

1.35 nm^-1

1.40 nm^-1

1.45 nm^-1

1.50 nm^-1

. Upon saturation adsorption of Xe on Cu{111} at 40 K, the Shockley surface state of the metal is found to shift rigidly upward in energy, its zone-centre binding energy decreasing from 0.42 eV to 0.32 eV. By approximately what percentage of its clean-surface value must the Fermi wavenumber of this state have decreased?

10.0%

12.5%

15.0%

17.5%

20.0%

. After saturation adsorption of Sb onto a Si{001} surface and subsequent annealing, the connectivity of atoms looks much the same as for the clean surface, except that the top-layer atoms forming the dimers are now Sb rather than Si. Which of these statements is most likely to be true?

The Sb dimers are tilted a little more than the Si dimers were

The Sb dimers are tilted much more than the Si dimers were

The Sb dimers are hardly tilted at all

The Sb dimers are tilted about the same as the Si dimers were

The Sb dimers are tilted a little less than the Si dimers were

. In the extended Blyholder model, individual covalent interactions between a given adsorbate orbital and a specific surface orbital are…

As often attractive as repulsive

Always attractive, never repulsive

Usually attractive, but sometimes repulsive

Always repulsive, never attractive

Usually repulsive, but sometimes attractive

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