Comparative angle-resolved photoemission study of Ag nanometer films grown on fcc Fe(111) and bcc Fe(110)

A comparative study of the electronic structures of Ag nanometer films on pseudomorphic metastable fcc Fe(111) and bulklike bcc Fe(110) substrates has been carried out to investigate their quantized electronic structures. From low-energy electron diffraction and angle-resolved photoemission spectra, it has been confirmed that Ag nanofilms on both substrates grow in fcc [111] direction under optimized growth conditions. The photoemission spectra of both Ag nanofilms exhibit spectral features due to quantum-well (QW) states derived from the Ag $sp$ valence electron. The nanofilm-thickness dependences of the binding energy of QW states are reproduced with calculated results based on a phase accumulation model. From the angle-resolved photoemission measurements, the effective mass of QW states along the direction parallel to the nanofilm surface were directly determined. From these results, we discuss the quantized electronic structures in Ag nanofilms grown on both bcc Fe and fcc Fe substrates.

Figure 1

(a) Angle-resolved photoemission spectra at normal emission geometry for Ag nanofilms with various thicknesses, grown on fcc Fe(111) substrate, excited by the He I $(h\nu =21.2\mathrm{eV})$ resonance line at $40\mathrm{K}$. Thickness of Ag nanofilms are indicated for each spectrum. (b) Nanofilm-thickness dependence of the binding energies of quantum-well (QW) states for Ag nanofilms grown on fcc Fe(111) substrate. Solid circles represent experimental data. Solid lines are the calculated results of QW states with $n=1–3$ by the phase accumulation (PA) model.

Figure 2

(a) Angle-resolved photoemission spectra for the $2.0\mathrm{nm}$-thick Ag nanofilm grown on fcc Fe(111) substrate. The polar emission angles with respect to the surface normal are indicated on each spectrum. (b) In-plane dispersion of the QW state in the Ag nanofilm with a thickness $2.0\mathrm{nm}$. The solid line represents the result for the least-squares fit to experimental data.

Figure 3

The nanofilm-thickness dependence of in-plane effective mass of QW states obtained from least-squares fits to experimental data.

Figure 4

(a) Angle-resolved photoemission spectra at normal emission geometry for Ag nanofilms with various thicknesses, grown on bcc Fe(110) substrate, excited by the He I $h\nu =21.2\mathrm{eV}$ resonance line at $40\mathrm{K}$. Thickness of Ag nanofilms are indicated for each spectrum. (b) Nanofilm-thickness dependence of the binding energies of QW states for Ag nanofilms grown on bcc Fe(110) substrate. Solid circles represent experimental data. Solid lines are the calculated results of QW states with $n=1–5$ by the PA model.

Figure 5

(a) Angle-resolved photoemission spectra for the $4.0\mathrm{nm}$-thick Ag nanofilm grown on bcc Fe(110) substrates. The polar emission angles with respect to the surface normal are indicated on each spectrum. (b) In-plane dispersion of the QW states in the Ag nanofilm with a thickness $4.0\mathrm{nm}$. The solid lines represent the results for the least-squares fits to experimental data.

Figure 6

In-plane effective mass of QW state as a function of the binding energy at $\overline{\Gamma }$ point. The solid line represents calculated results for bulk Ag (Ref. 31).