Controlling the Thermal Stability of Thin Films by Interfacial Engineering

The quantized electronic structure in Pb films on Si(111) varies substantially as the film thickness increases. The changes in electronic energy cause the thermal stability of the films to oscillate with an approximate bilayer period. The phase of the oscillations can be controlled by interfacial engineering. Comparison of Pb films prepared on Si(111) terminated by In, Au, and Pb as interfactants reveals a phase reversal. For $\mathrm{Pb}/\mathrm{In}/\mathrm{Si}(111)$, films made of odd numbers of atomic layers (5, 7, and 9) are more stable than the even ones. This trend is reversed for the other two cases.

Figure 1

Measured quantum well state energy levels for Pb films grown on the In-, Au-, and Pb-terminated Si(111) surfaces as a function of film thickness $N$. States are grouped by quantum number $n$ using boxes for each thickness.

Figure 2

(a) Photoemission spectra for a Pb film of coverage $N=8\mathrm{ML}$ grown on In-terminated Si(111) at various annealing temperatures as indicated. At higher temperatures, the film breaks up to form multiple thicknesses including $N=9$. (b) Peak intensity as a function of annealing temperature for the $N=8$ peak. The straight line segments are linear regressions to the data and their intersection point indicates the temperature at which the film breaks up.

Figure 3

Annealing temperature as a function of thickness at which Pb films grown on In-, Au-, and Pb-terminated Si(111) become unstable. Also shown are fits to the results. The dashed curves indicate the envelope functions of the fits.