Angular Resolved Photoemission Spectroscopy Research Articles

A Photoemission Study of the Epitaxial Growth of Si on Gap(110)

ABSTRACTWe have used angular resolved ultraviolet photoemission spectroscopy to study the epitaxial growth of Si on GaP(110). Surface state emission obscures the top of the valence band (TVB). The Fermi level for the clean GaP(110) surface is 1.20±0.05eV above the TVB. 1ML (monolayer) of Si pins the Fermi level position at 1.40±0.05eV above the TVB. Further deposition of Si leads to a valence band discontinuity ΔEv=1.07 ±0.10eV.

Angular-resolved UV photoemission studies of ordered Sb overlayers on GaAs(110) and GaP(110)

If Sb is deposited in monolayer coverage at room temperature on cleaved GaAs(110) and GaP(110) surfaces, well-ordered overlayers with a p(1 × 1) LEED pattern are formed. The surface electronic band structure of these overlayer systems is studied by angular-resolved UV photoemission spectroscopy (ARUPS). Along the ΓX, ΓX′ and ΓM(GaP) symmetry lines of the p(1 × 1) surface Brillouin zone surface bands are resolved in the upper part of the bulk valence band. On GaAs furthermore parts of surface state bands are detected near X and X′ at energies between 3 and 4 eV below the Fermi level. A comparison with available theoretical band structure calculations yields satisfactory agreement.

Angular-resolved UV photoemission studies of ordered Sb overlayers on GaAs(110) and GaP(110)

If Sb is deposited in monolayer coverage at room temperature on cleaved GaAs(110) and GaP(110) surfaces, well-ordered overlayers with a p(1 × 1) LEED pattern are formed. The surface electronic band structure of these overlayer systems is studied by angular-resolved UV photoemission spectroscopy (ARUPS). Along the Γ X , Γ X′ and Γ M (GaP) symmetry lines of the p(1 × 1) surface Brillouin zone surface bands are resolved in the upper part of the bulk valence band. On GaAs furthermore parts of surface state bands are detected near X and X′ at energies between 3 and 4 eV below the Fermi level. A comparison with available theoretical band structure calculations yields satisfactory agreement.

Surface electronic bands of GaAs(1 1 0)-Sb: An angular resolved photoemission study

Sb deposited in monolayer coverage at 300 K on cleaved GaAs(1 1 0) surfaces forms a well ordered overlayer with a p(1 × 1) LEED pattern. The two dimensional (2 D) surface electronic band structure of this overlayer system is studied by angular resolved UV photoemission spectroscopy (ARUPS) along the Γ X and Γ X symmetry lines of the pp(1 × 1) surface Brillouin zone. Four surface state bands in the energy range down to 5 eV below the upper valence band edge are resolved. A comparison with available theoretical band structure calculations yields satisfactory agreement.

Sodium-induced modifications in the electronic structure of the W(100) surface

Adsorption of sodium on the W(100) surface is studied at room temperature by angular resolved ultraviolet photoemission spectroscopy (ARUPS) and LEED. A reconstruction of the W(100) surface induced by sodium adsorption is observed at least at low coverage. The high-lying tungsten surface states situated at 0.4 eV below the Fermi level at normal emission ( Gamma ) suffer a continuous shift towards higher binding energies when sodium coverage increases. With a monolayer of sodium, the shift attains 2 instead of 1 eV for caesium. The low-lying surface state located at 4.2 eV below the Fermi level at Gamma shifts towards higher binding energies in contrast with caesium adsorption. These effects reveal a stronger sodium atom-substrate interaction than that which occurs in caesium. The description of the Cs/W(100) system may be extended to Na/W(100): the d(z2)-like surface states of W(100) hybridise with the sodium 3s valence states to form a polarised covalent bond.

Microscopic electronic structure and growth mode of Sn/InSb(111) interfaces

The electronic properties and growth mode of Sn/InSb(111) interfaces have been investigated by angular resolved photoemission spectroscopy (ARUPS), high energy electron diffraction (RHEED), and work function measurements. For Sn coverages of ∼1 ML the Fermi level is pinned at the bottom of the conduction band. The interfacial growth is heteroepitaxial and extends to a thickness of ∼5 ML of Sn. This is followed by the formation of diamond structured α-Sn up to ∼40 ML. Beyond this thickness three dimensional island growth starts and the films are a mixture of semiconducting α-Sn and metallic β-Sn. Above ∼120 ML Sn, the surface region consists of pure β-Sn while due to a strong substrate stabilization effect the interface region still consists of the α-Sn phase.

The growth mode of Cu overlayers on Pd(100)

The growth mode of Cu deposits on clean Pd(100) has been studied by means of LEED. AES and angular resolved ultraviolet photoemission spectroscopy. Auger signal versus deposition time curves showed that the growth follows a layer-by-layer mode for two monolayers after which it involves formation of islands as in the Stranski-Krastanov model. Despite the large lattice mismatch between Cu and Pd (7.7%) the substrate p(1×1) LEED pattern persisted with clear distinct spots at least up to the equivalent coverage of 4 ML indicating that Cu starts to grow epitaxially with the Pd lattice constant (pseudomorphic growth). Photoemission results show that the spectrum of the Cu/Pd(100) system does not converge to that of bulk Cu(100) until about 65 ML equivalent coverage. The spectrum below that coverage is composed of separate contributions from the thick regions and from the pseudomorphic basic slab.

The growth mode of Cu overlayers on Pd(100)

The growth mode of Cu deposits on clean Pd(100) has been studied by means of LEED. AES and angular resolved ultraviolet photoemission spectroscopy. Auger signal versus deposition time curves showed that the growth follows a layer-by-layer mode for two monolayers after which it involves formation of islands as in the Stranski-Krastanov model. Despite the large lattice mismatch between Cu and Pd (7.7%) the substrate p(1×1) LEED pattern persisted with clear distinct spots at least up to the equivalent coverage of 4 ML indicating that Cu starts to grow epitaxially with the Pd lattice constant (pseudomorphic growth). Photoemission results show that the spectrum of the Cu/Pd(100) system does not converge to that of bulk Cu(100) until about 65 ML equivalent coverage. The spectrum below that coverage is composed of separate contributions from the thick regions and from the pseudomorphic basic slab.

A simple and compact system for combined angular resolved inverse photoemission and photoemission in the vacuum ultraviolet

A new easily operable bandpass photon detector (h(cross) omega =9.8 eV, Delta E=0.6 eV) and a low voltage electron gun (1-100 eV, Delta E=0.22 eV) serve as a simple and compact apparatus for angular resolved inverse photoemission spectroscopy. This system is combined with a cylindrical mirror analyser for angular resolved photoemission allowing an in situ measurement of the dispersion of unoccupied and occupied electron states in a single ultra-high vacuum chamber.

Wavevector-resolved electron-energy-loss spectroscopy on the dangling-bond states of Ge(111)-(2 × 1)

Electronic surface state transitions at loss energies up to about 1.5 eV are studied by high resolution electron energy loss spectroscopy on Ge(111)-(2 × 1) surfaces prepared by cleavage in UHV. By variation of the primary energy and the detection angle the dependence of the transition energy hω on the wavevector transfer q ∥ is measured. The obtained “dispersion” hω( q ∥) is compared with results from angular resolved photoemission spectroscopy and with band structure calculations for the dangling bond bands.

Adsorption of type III and V elements on GaAs (110)

Angular-resolved photoemission and low energy electron loss spectroscopy (LELS) measurements are reported on GaAs(110) surfaces with adsorbed In, N, P, and As. It is shown that the photoemission from the ’’As dangling bond’’ surface state vanished after In adsorption, whereas the surface photoemission is unaffected by deposition of N, P, or As. This result is confirmed by tight-binding-type surface band structure calculations for models with a relaxed GaAs surface on which adsorbed In is assumed to be bound to the surface As atoms and N, P, or As to the Ga. However, some other observations like the surface Fermi level position and the behavior of the Ga 3d exciton peak in the LELS spectrum cannot be understood from this model.

New interpretation of the angular-resolved photoemission measurements from cleaved silicon

A new interpretation of a recently observed surface state using angular-resolved photoemission spectroscopy near the top of the valence band on the cleaved (111) face of Si has been provided. We are able to explain satisfactorily the observed anisotropy, dispersion and splitting of this peak by examining the electronic structure of a (2 × 1) reconstructed surface.

Measurement of the Angle of Dangling-Bond Photoemission from Cleaved Silicon

The surface state near the top of the valence bands on the cleaved (111) face of Si has been investigated by using angular-resolved photoemission spectroscopy at the photon energy 10.2 eV. Anisotropy, dispersion, and splitting are observed. The results are consistent with an appreciable admixture of ${S}_{2}$ character in this surface-state band.