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

Abstract

Local electronic properties of quasi-two-dimensional Pb(111) islands with screw dislocations of different types on their surfaces were experimentally studied by means of lowtemperature scanning tunneling microscopy and spectroscopy in the regime of constant current. A comparison of the topography map, the maps of tunneling current variation, and the differential tunneling conductance acquired simultaneously allows one to visualize the hidden parts of the dislocation loops under the sample surface. We demonstrate that two closely positioned screw dislocations with the opposite Burgers vectors can either (i) connect to each other by the sub-surface dislocation loop or (ii) generate independent hidden edge dislocation lines, which run toward the perimeter of the Pb island. In addition, we found a screw dislocation, which does not produce outcoming sub-surface dislocation loops. Screw dislocations and the hidden dislocation lines are the source of the non-quantized variation of the local thickness of the Pb terraces, affecting the local electronic properties.

Field-Emission Resonances in Thin Metallic Films: Nonexponential Decrease of the Tunneling Current as a Function of the Sample-to-Tip Distance

“…(a) Aligned topography image z ( x , y ) of the surface of the Pb(111) island (image size is 58 × 58 nm 2 , U = 0.5 V, I = 200 pA). The dashed line indicates the position of the hidden monatomic step in the Si(111)­7×7 substrate (the method of visualizing of the hidden defects in Pb films was described in refs − ). The local thickness D of the island in the lower left corner (at the point marked with a boxed ×) is about 10.9 nm with respect to the Si(111)­7×7 surface [i.e., N = D / d ML ≃ 38, d ML = 0.286 nm is the thickness of a Pb monolayer for the Pb(111) surface].…”

“…U = φ s – φ t > 0 is the bias voltage, and n is the FER index equal to the number of electronic half-waves above the sample surface. Adapted from ref . Copyright 2021 American Chemical Society.…”

Study of the Cu(111) Surface by Scanning Tunneling Microscopy: The Morphology Evolution, Reconstructions, Superstructures and Line Defects

“…When the annealing temperature reaches 720 °C (Process Ⅵ), it can be seen that straight edges are still observable on some steps and the other steps present sawtooth-like edges, with the step terraces becoming very smooth, as shown in Figure 2 e. The average step height decreases to 0.66 nm (≈3d), as illustrated by the height profile [drawn along the blue arrow in Figure 2 e] in Figure 2 f. Interestingly, the step terraces show numerous screw dislocations in this process, as indicated by the black arrows in Figure 2 e. This phenomenon has also previously been observed on other cleaned metal surfaces such as Au(111) surface, Ag(111) surface, etc. [ 28 , 29 , 30 ].…”

Oscillatory Bias Dependence of the Visible Height of Monatomic Pb(111) Steps: Consequence of the Quantum-Size Effect for Thin Metallic Films

“…Quantization of the transverse wave vector k ⊥, n and the energy E n for the electronic quantum-well states apparently results in the modification of the energy spectrum. In particular, coherent resonant tunneling through quasi-stationary quantum-well states (see schematic energy diagram in Figure from ref ) leads to the appearance of almost equidistantly positioned peaks on the dependence of the differential tunneling conductance d I /d U on the bias voltage U both for filled and empty electronic states in experiments involving scanning tunneling microscopy and spectroscopy (STM/STS). − …”

“…Two-dimensional Pb(111) islands seem to be convenient objects for studying quantum-size effects in metallic films in normal and superconducting states by means of STM/STS − and by transport and Hall measurements; − for the investigation of electronic properties in superconducting nanostructures , and superconducting two-dimensional materials, hybrid structures superconductor-ferromagnet, − superconductor-normal metal, , and superconductor-topological insulator; and for the investigation of electronic states by means of photoemission electron spectroscopy. , The particular sensitivity of the interference patterns to the variations of the film thickness and the crystalline structure of the interfaces makes it possible to visualize monatomic steps at the upper/lower interfaces, − ,, atomic lattice of the substrate covered by metal, , various inclusions, terraces with nonquantized height variations, and subsurface dislocation loops …”