scholarly journals Reconstruction of a 2D layer of KBr on Ir(111) and electromechanical alteration by graphene

2021 ◽  
Vol 12 ◽  
pp. 432-439
Author(s):  
Zhao Liu ◽  
Antoine Hinaut ◽  
Stefan Peeters ◽  
Sebastian Scherb ◽  
Ernst Meyer ◽  
...  
Keyword(s):  
Density Functional ◽  
Kelvin Probe ◽  
Functional Theory ◽  
Double Line ◽  
Force Microscopy ◽  
Atomic Force ◽  
Local Charge ◽  
Charge Displacement ◽  
Work Functions ◽  
The Difference

A novel reconstruction of a two-dimensional layer of KBr on an Ir(111) surface is observed by high-resolution noncontact atomic force microscopy and verified by density functional theory (DFT). The observed KBr structure is oriented along the main directions of the Ir(111) surface, but forms a characteristic double-line pattern. Comprehensive calculations by DFT, taking into account the observed periodicities, resulted in a new low-energy reconstruction. However, it is fully relaxed into a common cubic structure when a monolayer of graphene is located between substrate and KBr. By using Kelvin probe force microscopy, the work functions of the reconstructed and the cubic configuration of KBr were measured and indicate, in accordance with the DFT calculations, a difference of nearly 900 meV. The difference is due to the strong interaction and local charge displacement of the K+/Br− ions and the Ir(111) surface, which are reduced by the decoupling effect of graphene, thus yielding different electrical and mechanical properties of the top KBr layer.

Subatomic Resolution in Noncontact Atomic Force Microscopy: Electron Cloud Interactions or Harmonics Processing Artifacts?

2012 ◽  
Author(s):  
C. Alan Wright ◽  
Santiago D. Solares
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Electron Cloud ◽  
Computational Method ◽  
Functional Theory ◽  
Force Microscopy ◽  
Atomic Force ◽  
Imaging Artifacts ◽  
The Individual ◽  
Tungsten Tip

In 2004 Hembacher et al. [Science 305, 380–383 (2004)] reported higher harmonics AFM images of a graphite surface acquired using a tungsten tip which revealed subatomic features. These features were interpreted as the signature of electron bonding lobes at the tip apex atom. We recently applied a computational method based on density functional theory to simulate the images of Hembacher et al. and found that features of subatomic size can indeed be observed under ideal conditions. However, a number of important questions remain open, the most significant of which concerns signal processing. Here we continue our bottom-up analysis by exploring the effects of harmonics processing on the images obtained. Our simulations suggest that there are no imaging artifacts inherent to the filtering process used but that harmonics averaging is not an appropriate method for enhancing subatomic contrast due to variations in the harmonics ratios across the surface. Instead, a promising approach may be the individual mapping of the first two harmonics, which are expected to dominate the contrast under the conditions studied by Hembacher et al.

scholarly journals Nitrous oxide as an effective AFM tip functionalization: a comparative study

2019 ◽  
Vol 10 ◽  
pp. 315-321 ◽  
Author(s):  
Taras Chutora ◽  
Bruno de la Torre ◽  
Pingo Mutombo ◽  
Jack Hellerstedt ◽  
Jaromír Kopeček ◽  
...  
Keyword(s):  
High Resolution ◽  
Density Functional ◽  
High Resolution Imaging ◽  
Functional Theory ◽  
Force Microscopy ◽  
Atomic Force ◽  
Resolution Imaging ◽  
Particle Adsorption ◽  
Metal Tip ◽  
Functionalized Tips

We investigate the possibility of functionalizing Au tips by N2O molecules deposited on a Au(111) surface and their further use for imaging with submolecular resolution. First, we characterize the adsorption of the N2O species on Au(111) by means of atomic force microscopy with CO-functionalized tips and density functional theory (DFT) simulations. Subsequently we devise a method of attaching a single N2O to a metal tip apex and benchmark its high-resolution imaging and spectroscopic capabilities using FePc molecules. Our results demonstrate the feasibility of high-resolution imaging. However, we find an inherent asymmetry of the N2O probe-particle adsorption on the tip apex, in contrast to a CO tip reference. These findings are consistent with DFT calculations of the N2O- and CO tip apexes.

scholarly journals Structurally Driven Environmental Degradation of Friction in MoS2 Films

2021 ◽  
Vol 69 (3) ◽  
Author(s):  
John F. Curry ◽  
Taisuke Ohta ◽  
Frank W. DelRio ◽  
Philip Mantos ◽  
Morgan R. Jones ◽  
...  
Keyword(s):  
Work Function ◽  
Density Functional ◽  
Surface Film ◽  
Kelvin Probe ◽  
Photoelectron Emission ◽  
Friction Behavior ◽  
Functional Theory ◽  
Contact Conditions ◽  
Force Microscopy ◽  
Dynamics Simulations

AbstractWe report an investigation of the friction mechanisms of MoS2 thin films under changing environments and contact conditions using a variety of computational and experimental techniques. Molecular dynamics simulations were used to study the effects of water and molecular oxygen on friction and bonding of MoS2 lamellae during initial sliding. Characterization via photoelectron emission microscopy (PEEM) and Kelvin probe force microscopy (KPFM) were used to determine work function changes in shear modified material within the top few nanometers of MoS2 wear scars. The work function was shown to change with contact conditions and environment, and shown by density functional theory (DFT) calculations and literature reports to be correlated with lamellae size and thickness of the basally oriented surface layer. Results from nanoscale simulations and macroscale experiments suggest that the evolution of the friction behavior of MoS2 is linked primarily to the formation or inhibition of a basally oriented, molecularly thin surface film with long-range order.

Theoretical investigation on the interaction between RhIII octaethylporphyrin and a graphite basal surface: a comparison study of DFT, DFT-D, and AFM

2018 ◽  
Vol 20 (30) ◽  
pp. 20235-20246 ◽  
Author(s):  
Kohei Tada ◽  
Yasushi Maeda ◽  
Hiroyuki Ozaki ◽  
Shingo Tanaka ◽  
Shin-ichi Yamazaki
Keyword(s):  
Density Functional Theory ◽  
Atomic Force Microscopy ◽  
Electronic Structure ◽  
Theoretical Investigation ◽  
Density Functional ◽  
Comparison Study ◽  
Basal Surface ◽  
Functional Theory ◽  
Force Microscopy ◽  
Atomic Force

Using density functional theory based calculations and atomic-force-microscopy observations, we investigated the interaction between [RhIII(OEP)(Cl)] (OEP = octaethylporphyrin) and a graphite basal surface, and the electronic structure of [RhIII(OEP)(Cl)]/graphite.

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