Layer-by-layer growth of sodium chloride overlayers on an Fe(001)-p(1 × 1)O surface

Abstract

Ultra-thin NaCl films epitaxially grown on an Fe(001)-p(1 × 1)O surface have been investigated in ultra-high vacuum by non-contact atomic force microscopy and low energy electron diffraction. It has been found that at temperatures below 145 °C NaCl initially grows as monoatomic thick islands on substrate terraces, while at temperatures above 175 °C biatomic thick islands are also formed at substrate step edges. Both types of islands have the same Fe(001)-O[100] [parallel] NaCl(001)[110] orientation, leading to a (4 × 4) superstructure, where the NaCl unit cell is oriented at 45° with respect to the substrate. Interestingly, no c(2 × 2) superstructure with the NaCl unit cell oriented at 0° has been observed. The oxygen on the iron surface promotes layer-by-layer growth, resulting in atomically flat films with 40-60 nm wide terraces at coverages ranging from 0.75 to 12 ML. Such NaCl films are of much higher quality than MgO films grown on Fe(001) and Fe(001)-p(1 × 1)O surfaces and represent a unique epitaxial system of an alkali halide on a pure metallic substrate. The reduced number of defects and the layer-by-layer mode of growth make this system very attractive for applications where an atomically defined tunnel barrier is required to control the properties of a device.

Controlling the Electronic and Structural Coupling of C60 Nano Films on Fe(001) through Oxygen Adsorption at the Interface

“…Considering that the electrons emitted from O KLL and Fe LMM transitions are characterized by a similar inelastic mean free path (λ KLL = 10 Å vs λ LMM = 11.9 Å), AES data demonstrate that the oxygen layer remains buried between the Fe topmost layer and the C 60 film. This phenomenology is quite different with respect to that typically observed upon deposition of transition metals on the Fe(001)- p (1 × 1)­O, where oxygen floats on top of the growing film. − Recently, the occurrence of oxygen buried at the interface has been observed in the case of NaCl films deposited on the Fe(001)- p (1 × 1)O substrate . In the low kinetic energy region (see Figure b), the Fe MVV transition is characterized by a metallic peak at about 46 eV and by a shoulder at lower kinetic energy, related to the presence of Fe–O bonds. − The shoulder is present also after C 60 deposition, confirming that the Fe–O bonds are preserved.…”

“…49−54 Recently, the occurrence of oxygen buried at the interface has been observed in the case of NaCl films deposited on the Fe(001)p(1 × 1)O substrate. 55 In the low kinetic energy region (see Figure 4b), the Fe MVV transition is characterized by a metallic peak at about 46 eV and by a shoulder at lower kinetic energy, related to the presence of Fe−O bonds. 56−60 The shoulder is present also after C 60 O is detected at 2.4 ± 0.05 eV below the Fermi level (E F ), while the LUMO and LUMO+1 orbitals are placed at 0.9 ± 0.05 and 2.2 ± 0.05 eV above E F , respectively.…”

Mesoscopic organization of cobalt thin films on clean and oxygen-saturated Fe(001) surfaces

“…(2) Improving heteroepitaxial interfaces, reducing their roughness [29,30] and enhancing their chemical stability [30,31].…”

Room-Temperature Single-Electron Charging Detected by Electrostatic Force Microscopy

“…The epitaxial NaCl film has a (001) orientation and a (4 × 4) symmetry with charge-neutral step edges oriented along the ⟨110⟩ directions of the Fe(001) substrate. It grows in a near perfect layer-by-layer mode, allowing for precise control of the tunnel barrier thickness . Although the underlying step edges of Fe slightly disturb the nearby growth of NaCl, on flat substrate areas the film is characterized by an almost complete sixth ML, and a far from complete seventh ML.…”

“…We utilize an ultra-thin epitaxial NaCl film as the tunnel barrier, grown under ultra-high vacuum (UHV) on the Fe(001)-p(1 × 1)O surface of the Fe back electrode. Our group has recently developed a method to grow such films layer by layer with a small number of defects . Metal nanoparticles, formed by thermally evaporating Au onto the NaCl surface, are used as electron confining nanostructures.…”