Quantum-well and modified image-potential states in thin Pb(111) films: an estimate for the local work function

Area of Science:

• Surface Science
• Condensed Matter Physics
• Quantum Mechanics

Background:

• Quantum-confined electronic states, including quantum-well states (QWS) and image-potential states (IPS), are crucial for understanding electron behavior in low-dimensional materials.
• Lead (Pb) films on silicon substrates exhibit unique electronic properties due to quantum confinement effects.

Purpose of the Study:

• To investigate quantum-confined electronic states (QWS and IPS) in thin Pb(111) films grown on Si(111) 7 × 7.
• To determine the local work function of Pb(111) films.
• To explore the influence of scanning tunneling microscopy (STM) tip characteristics on electronic state measurements.

Main Methods:

• Low-temperature scanning tunneling microscopy (STM) and spectroscopy (STS) were employed.
• Constant current mode was used to acquire spectroscopic data.
• Analysis involved plotting emission resonance positions versus n^(2/3) to extrapolate work function.

Main Results:

• The local work function of the Pb(111) film was estimated as W ≃ 3.8 ± 0.1 eV.
• Modifications to the STM tip shape altered the number of emission peaks related to quantized IPS.
• The bluntness of the STM tip affected the prominence of resonance peaks in differential conductance spectra.

Conclusions:

• The local work function estimation is robust against changes in STM tip shape.
• STM tip geometry influences the observation of resonant tunneling via quantized IPS.
• Understanding these electronic states is vital for nanoscale electronic device applications.