scholarly journals Approaching the forbidden fruit of reaction dynamics: Aiming reagent at selected impact parameters

2018 ◽  
Vol 4 (10) ◽  
pp. eaau2821 ◽  
Author(s):  
Kelvin Anggara ◽  
Lydie Leung ◽  
Matthew J. Timm ◽  
Zhixin Hu ◽  
John C. Polanyi
Keyword(s):  
Impact Parameter ◽  
Reaction Dynamics ◽  
Bimolecular Reaction ◽  
Important Variable ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Stationary Target ◽  
Impact Parameters ◽  
Miss Distance ◽  
The Impact

Collision geometry is central to reaction dynamics. An important variable in collision geometry is the miss-distance between molecules, known as the “impact parameter.” This is averaged in gas-phase molecular beam studies. By aligning molecules on a surface prior to electron-induced dissociation, we select impact parameters in subsequent inelastic collisions. Surface-collimated “projectile” molecules, difluorocarbene (CF2), were aimed at stationary “target” molecules characterized by scanning tunneling microscopy (STM), with the observed scattering interpreted by computational molecular dynamics. Selection of impact parameters showed that head-on collisions favored bimolecular reaction, whereas glancing collisions led only to momentum transfer. These collimated projectiles could be aimed at the wide variety of adsorbed targets identifiable by STM, with the selected impact parameter assisting in the identification of the collision geometry required for reaction.

Electron-induced molecular dissociation at a surface leads to reactive collisions at selected impact parameters

2019 ◽  
Vol 214 ◽  
pp. 89-103 ◽  
Author(s):  
Kelvin Anggara ◽  
Lydie Leung ◽  
Matthew J. Timm ◽  
Zhixin Hu ◽  
John C. Polanyi
Keyword(s):  
Impact Parameter ◽  
Reaction Dynamics ◽  
Molecular Dissociation ◽  
Reactive Collisions ◽  
Impact Parameters ◽  
The Impact ◽  
Collimated Beam

A collimated beam of ‘projectiles’ strikes a chemisorbed ‘target’ thereby selecting the impact parameter, achieving an elusive goal of reaction dynamics.

scholarly journals Templated quasicrystalline ordering of single elements and molecules

2014 ◽  
Vol 70 (a1) ◽  
pp. C81-C81
Author(s):  
H. R. Sharma ◽  
J. A. Smerdon ◽  
K. Nozawa ◽  
K. M. Young ◽  
T. P. Yadav ◽  
...  
Keyword(s):  
Substrate Surface ◽  
Chemical Properties ◽  
Scanning Tunneling ◽  
Three Dimension ◽  
Tunneling Microscopy ◽  
Quantum Size ◽  
Adsorption Energies ◽  
Molecular Layers ◽  
Physical And Chemical ◽  
The Impact

We have used quasicrystals as templates for the exploration of new epitaxial phenomena. Several interesting results have been observed in the growth on surfaces of the common Al-based quasicrystals [1]. These include pseudomorphic monolayers, quasiperiodically modulated multilayer structures, and fivefold-twinned islands with magic heights influenced by quantum size effects [1]. Here we present our recent works on the growth of various elements and molecules on a new substrate, icosahedral (i) Ag-In-Yb quasicrystal, which have resulted in various epitaxial phenomena not observed previously. The growth of Pb on the five-fold surface of i-Ag-In-Yb yields a film which possesses quasicrystalline ordering in three-dimension [2]. Using scanning tunneling microscopy (STM) and DFT calculations of adsorption energies, we find that lead atoms occupy the positions of atoms in the rhombic triacontahedral (RTH) cluster, the building block of the substrate, and thus grow in layers with different heights and adsorption energies. The adlayer–adlayer interaction is crucial for stabilizing the epitaxial quasicrystalline structure. We will also present the first example of quasicrystalline molecular layers. Pentacene adsorbs at tenfold-symmetric sites of Yb atoms around surface-bisected RTH clusters, yielding quasicrystalline order [3]. Similarly, C-60 growth on the five-fold surface of i-Al-Cu-Fe at elevated temperature produces quasicrystalline layer, where the growth is mediated by Fe atoms on the substrate surface [3]. The finding of quasicrystalline thin films of single elements and molecules opens an avenue for further investigation of the impact of the aperiodic atomic order over periodic order on the physical and chemical properties of materials.

Nb-H Thin Films: On Phase Transformation Kinetics

2017 ◽  
Vol 371 ◽  
pp. 160-165
Author(s):  
Vladimir Burlaka ◽  
Kai Nörthemann ◽  
Astrid Pundt
Keyword(s):  
Thin Films ◽  
Phase Transformation ◽  
Scanning Tunneling ◽  
State Change ◽  
Transformation Kinetics ◽  
Tunneling Microscopy ◽  
Fast Phase ◽  
Phase Transformation Kinetics ◽  
Local Lattice ◽  
The Impact

It was recently shown that phases forming in thin films undergo a coherency state change depending on the film thickness. For Nb-H thin films, the coherency state was reported to change at about 38 nm. In this study the impact of the coherency state on the phase transformation kinetics is investigated for Nb films of two different film thicknesses (25 nm and 80 nm), below and above the state change thickness. The phase transformation in thin metal-hydrogen films can be studied by surface topography analyses via scanning tunneling microscopy (STM) because of the strong local lattice expansion of the hydride precipitates. STM on Nb-H reveals fast phase transformation kinetics for the 25 nm Nb-film, and much slower kinetics for the 80 nm film. This is suggested to be related to the change in the coherency between the Nb-matrix and the hydride precipitates.

scholarly journals Transfer of chiral information from a chiral solvent to a two-dimensional network

2017 ◽  
Vol 204 ◽  
pp. 215-231 ◽  
Author(s):  
Iris Destoop ◽  
Andrea Minoia ◽  
Oleksandr Ivasenko ◽  
Aya Noguchi ◽  
Kazukuni Tahara ◽  
...  
Keyword(s):  
Self Assembled Monolayers ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Chiral Induction ◽  
Dimensional Network ◽  
Assembled Monolayers ◽  
Self Assembled ◽  
The Impact ◽  
Atomically Flat ◽  
Origin Of Homochirality

Chiral induction in self-assembled monolayers has garnered considerable attention in the recent past, not only due to its importance in chiral resolution and enantioselective heterogeneous catalysis but also because of its relevance to the origin of homochirality in life. Here, we demonstrate the emergence of homochirality in a supramolecular low-density network formed by achiral molecules at the interface of a chiral solvent and an atomically-flat achiral substrate. We focus on the impact of structure and functionality of the adsorbate and the chiral solvent on the chiral induction efficiency in self-assembled physisorbed monolayers, as revealed by scanning tunneling microscopy. Different induction mechanisms are proposed and evaluated, with the assistance of advanced molecular modeling simulations.

A STUDY OF THE DIFFUSION OF Pb ON THE Au(111) SURFACE BY STM AND EAM-MD SIMULATIONS

1999 ◽  
Vol 06 (05) ◽  
pp. 793-800 ◽  
Author(s):  
M. C. ROBINSON ◽  
A. J. SLAVIN ◽  
K. DE'BELL
Keyword(s):  
Film Growth ◽  
Md Simulations ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Qualitative Comparison ◽  
Embedded Atom ◽  
Surface Reconstructions ◽  
Diffusion Phenomena ◽  
The Impact ◽  
Herringbone Structure

Surface reconstructions often result in novel growth morphologies, and are therefore of potential technological interest. The Au(111) surface will reconstruct into the [Formula: see text] "herringbone" structure. Low coverages (up to 0.3 monolayers) have been studied with scanning tunneling microscopy (STM) at room temperature, to determine the impact of the reconstruction on diffusion and thin film growth. The same system has been studied using embedded-atom model molecular dynamics (EAM-MD). These simulations, in addition to providing morphological information, permit qualitative comparison of diffusion phenomena. Experimental results indicate that initial sites for Pb adsorption are located at the herringbone kinks. For higher coverages, Pb prefers hcp and fcc stacking regions, avoiding the herringbone ridges. The reconstruction is removed for some coverage between 0.05 and 0.2 monolayers. STM and EAM results will be compared.

scholarly journals Charge transport in a single molecule transistor probed by scanning tunneling microscopy

Nanoscale ◽  
2018 ◽  
Vol 10 (3) ◽  
pp. 1487-1493 ◽  
Author(s):  
Samuel Bouvron ◽  
Romain Maurand ◽  
Alexander Graf ◽  
Philipp Erler ◽  
Luca Gragnaniello ◽  
...  
Keyword(s):  
Scanning Tunneling Microscopy ◽  
Charge Transport ◽  
Single Molecule ◽  
Gate Voltage ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
The Impact ◽  
Single Molecule Transistor

Using scanning tunneling microscopy and spectroscopy, we investigate the impact of the gate voltage on the electronic levels of CoPc molecules deposited on top of a graphene/SiO2/Si device.

Probing Surface Roughness and Porosity through Adsorption of Wetting Layers

1994 ◽  
Vol 366 ◽  
Author(s):  
J. Krim ◽  
V. Panella
Keyword(s):  
Surface Tension ◽  
Adsorption Isotherms ◽  
Capillary Condensation ◽  
Scanning Tunneling ◽  
Fractal Nature ◽  
Tunneling Microscopy ◽  
Gold Surfaces ◽  
X Ray ◽  
Adsorption Data ◽  
The Impact

ABSTRACTWe have employed a quartz microbalance technique to record adsorption isotherms on silver and gold surfaces whose roughness has also been characterized by x-ray reflectivity or scanning tunneling microscopy. We observe strikingly different behavior for two different liquid adsorbates (oxygen and nitrogen), and attribute this to a difference in their surface tension. Our results demonstrate the impact that capillary condensation phenomena can have on the interpretation of adsorption data, particularly with regards to the fractal nature of the substrate. Valuable information on surface morphology can nonetheless be obtained from adsorption isotherms, if combined with alternate experimental techniques.

scholarly journals Abnormal conductivity in low-angle twisted bilayer graphene

2020 ◽  
Vol 6 (47) ◽  
pp. eabc5555
Author(s):  
Shuai Zhang ◽  
Aisheng Song ◽  
Lingxiu Chen ◽  
Chengxin Jiang ◽  
Chen Chen ◽  
...  
Keyword(s):  
Density Functional ◽  
Twist Angle ◽  
Van Der Waals ◽  
Density Functional Theory Calculations ◽  
Bilayer Graphene ◽  
Abnormal Behavior ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Van Der Waals Materials ◽  
The Impact

Controlling the interlayer twist angle offers a powerful means for tuning the electronic properties of two-dimensional (2D) van der Waals materials. Typically, the electrical conductivity would increase monotonically with decreasing twist angle owing to the enhanced coupling between adjacent layers. Here, we report a nonmonotonic angle-dependent vertical conductivity across the interface of bilayer graphene with low twist angles. More specifically, the vertical conductivity enhances gradually with decreasing twist angle up to a crossover angle at θc ≈ 5°, and then it drops notably upon further decrease in the twist angle. Revealed by density functional theory calculations and scanning tunneling microscopy, the abnormal behavior is attributed to the unusual reduction in average carrier density originating from local atomic reconstruction. The impact of atomic reconstruction on vertical conductivity is unique for low-angle twisted 2D van der Waals materials and provides a strategy for designing and optimizing their electronic performance.

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