Low-temperature scanning tunneling microscopy and spectroscopy measurements of ultrathin Pb films

Abstract

We have investigated the electronic properties of ultrathin Pb films by low temperature scanning tunneling microscopy and spectroscopy. Our results show that 30 nm thick Pb(111) films grown on atomically flat highly oriented pyrolytic graphite (HOPG) and on amorphous SiO2 are both in the strong-coupling limit with transition temperature and energy gap close to the bulk value. Conductance maps and spectroscopy in the vortex state reveal a bound state at the center of the vortices, which suggest that the films are in the clean limit. Measurements of 3 nm Pb films grown on HOPG show a clear crossover to the weak-coupling regime and dirty limit.

Observation of Hidden Parts of Dislocation Loops in Thin Pb Films by Means of Scanning Tunneling Spectroscopy

“…The quantum-size oscillations of the tunneling conductance can be easily detected in Pb(111) films up to 50 monolayers at liquid nitrogen temperatures 51 and up to 100 monolayers at sub-Kelvin temperatures. 52 It is obvious that the energy of electron localized in a one-dimensional infinite potential well is equal to…”

Tunneling interferometry and measurement of the thickness of ultrathin metallic Pb(111) films

“…In this work we discuss the diagnostics of the quality of deposited metallic layers and the presence of foreign inclusions on the example of ultrathin Pb films. Such films appear to be convenient objects for studying quantumsize effects in normal and superconducting metal films [3][4][5][6][7][8][9], peculiarities of the growth of metal nanoislands [9][10][11], vortex states in superconducting nanostructures [12,13], and electronic properties of superconductornormal metal hybrid structures [14]. The main methods for studying electronic states in Pb films are lowtemperature scanning tunneling microscopy (STM) and spectroscopy [3][4][5][6][7][8][9][10][11][12][13][14], transport measurements [15,16], and photoemission studies [16][17][18][19][20][21].…”

“…Peaks of the differential tunneling conductivity were detected for some values of the potential U n of ultrathin Pb film and island samples by tunneling spectroscopy methods [3,[5][6][7][8][9]13]. A correlation between the spectrum of the U n values and the local thickness of the Pb layer was found and interpreted in terms of the resonant tunneling of electrons through quantum-confined levels in a quasi-two-dimensional electron gas.…”

“…Local tunneling spectroscopy [3,[5][6][7][8][9]13] performed for a limited number of points cannot reliably determine the boundaries of regions with a constant thickness of the Pb layer. As far as we know, the application of scanning bias-modulation spectroscopy, which involves simultaneous acquisition of a topographic image and a map of the density of states for a given energy, for ultrathin Pb films has not yet been discussed.…”

Tuning the Proximity Effect through Interface Engineering in a Pb/Graphene/Pt Trilayer System

“…Superconductivity in mesoscopic systems with spatial dimensions smaller than the superconducting coherence length is a subject of great scientific and technological importance and has attracted intense interest for decades. As prototype models, Pb films/islands have been epitaxially grown on various substrates with thickness in atomic precision, and their superconductivity has been studied in situ by low-temperature scanning tunneling microscopy and spectroscopy (LT-STM/STS) in recent years. − Superconducting order remains in atomically thin Pb films grown on Si(111). ,, In contrast, on bulk normal metal substrates, the superconductivity is suppressed due to the superconducting proximity effect, , thus the Pb film cannot show superconductivity until its thickness reaches the coherence length ξ (∼80 nm). The different fate of superconductivity in these systems lies in the different substrate band structure (with or without band gap) in the vicinity of the Fermi level ( E F ).…”