The role of halogens in on-surface Ullmann polymerization

Ullmann coupling is the most common approach to form surface-confined one- and two-dimensional conjugated structures from haloaryl derivatives. The dimensions of the formed nanostructures can be controlled by the number and location of halogens within the molecular precursors. Our study illustrates that the type of halogen plays an essential role in the design, orientation, and extent of the surface-confined organometallic and polymeric nanostructures. We performed a comparative analysis of five 1,4-dihalobenzene molecules containing chlorine, bromine, and iodine on Cu(110) using scanning tunneling microscopy, fast-X-ray photoelectron and near edge X-ray absorption fine structure spectroscopies. Our experimental data identify different molecular structures, reaction temperatures and kinetics depending on the halogen type. Climbing image nudged elastic band simulations further clarify these observations by providing distinct diffusion paths for each halogen species. We show that in addition to the structure of the building blocks, the halogen type has a direct influence on the morphology of surface-confined polymeric structures based on Ullmann coupling.

Download Full-text

Polymorphic self-assembly of pyrazine-based tectons at the solution–solid interface

Beilstein Journal of Nanotechnology ◽

10.3762/bjnano.10.50 ◽

2019 ◽

Vol 10 ◽

pp. 494-499

Author(s):

Achintya Jana ◽

Puneet Mishra ◽

Neeladri Das

Keyword(s):

Hydrogen Bonding ◽

Self Assembly ◽

Building Blocks ◽

Molecular Structures ◽

Scanning Tunneling ◽

Tunneling Microscopy ◽

Equal Distribution ◽

Solid Interface ◽

Supramolecular Architectures ◽

Microscopy Investigation

Exploring the surface self-assembly of small molecules that act as building blocks (tectons) for complex supramolecular structures is crucial for realizing surface-supported functional molecular devices. Here, we report on the synthesis and surface self-assembly of a new pyrazine-derived molecule with pyridine pendants. Ambient scanning tunneling microscopy investigation at the solution–solid interface reveals polymorphic self-assembly of these molecules on a HOPG substrate. Two different molecular packing structures with equal distribution are observed. Detailed analysis of the STM images emphasizes the crucial role of weak intermolecular hydrogen bonding, and molecule–substrate interactions in the formation of the observed polymorphs. Such weak hydrogen bonding interactions are highly desirable for the formation of modular supramolecular architectures since they can provide sufficiently robust molecular structures and also facilitate error correction.

Download Full-text

ON THE ROLE OF Nd/Ba DISORDER ON THE SUPERCONDUCTING PROPERTIES OF Re1(NdxBa2-x)Cu3O7-δ (Re=Nd, Y) THIN FILMS

International Journal of Modern Physics B ◽

10.1142/s0217979200002831 ◽

2000 ◽

Vol 14 (25n27) ◽

pp. 2737-2742

Author(s):

M. SALLUZZO ◽

A. ANDREONE ◽

A. CASSINESE ◽

M. IAVARONE ◽

M. G. MAGLIONE ◽

...

Keyword(s):

Thin Films ◽

Wave Model ◽

Scanning Tunneling ◽

Epitaxial Thin Films ◽

Superconducting Properties ◽

Tunneling Microscopy ◽

Microstrip Resonator ◽

X Ray ◽

Effect Of Impurities

The role of disorder on the superconducting properties of Re 1( Nd x Ba 2-x ) Cu 3 O 7-δ (Re=Nd, Y) epitaxial thin films has been studied. The films are deposited by Ar+O 2 magnetron and diode dc sputtering from targets characterised by different x (0, 0.08 and 0.12). In situ X-ray Photoemission Spectroscopy (XPS), Scanning Tunneling Microscopy (STM), and non-conventinal X-ray diffraction measurements have been used to determine the exact composition and the structural properties of each sample. The temperature dependence of the ab-plane penetratin depth of highly c-axis epitaxial samples, characterised by different Nd/Ba ratios, has been determined by an inverted microstrip resonator technique. Results on the Nd 1+x Ba 2-x Cu 3 O 7-δ system show that only stoichiometric films exhibit a linear penetration depth at low temperature while Nd-rich films show a T 2 law. Preliminary measurements on the Y 1( Nd x Ba 2-x ) Cu 3 O 7-δ system confirm these results. The data are analysed in the framework of the d-wave model taking into account the effect of impurities on the superconducting properties.

Download Full-text

Scanning tunneling microscopy (STM) of DNA and RNA

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100152148 ◽

1989 ◽

Vol 47 ◽

pp. 34-35

Author(s):

Patricia G. Arscott ◽

Gil Lee ◽

Victor A. Bloomfield ◽

D. Fennell Evans

Keyword(s):

Molecular Structures ◽

Inorganic Materials ◽

Resolving Power ◽

Scanning Tunneling ◽

Tunneling Microscopy ◽

Form And Function ◽

Dna And Rna ◽

Calf Thymus ◽

And Function ◽

The Relationship

STM is one of the most promising techniques available for visualizing the fine details of biomolecular structure. It has been used to map the surface topography of inorganic materials in atomic dimensions, and thus has the resolving power not only to determine the conformation of small molecules but to distinguish site-specific features within a molecule. That level of detail is of critical importance in understanding the relationship between form and function in biological systems. The size, shape, and accessibility of molecular structures can be determined much more accurately by STM than by electron microscopy since no staining, shadowing or labeling with heavy metals is required, and there is no exposure to damaging radiation by electrons. Crystallography and most other physical techniques do not give information about individual molecules.We have obtained striking images of DNA and RNA, using calf thymus DNA and two synthetic polynucleotides, poly(dG-me5dC)·poly(dG-me5dC) and poly(rA)·poly(rU).

Download Full-text

A study on α-RuCl3 crystal structure by scanning tunneling microscopy

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100152124 ◽

1989 ◽

Vol 47 ◽

pp. 30-31

Author(s):

H.-J. Cantow ◽

H. Hillebrecht ◽

S. Magonov ◽

H. W. Rotter ◽

G. Thiele

Keyword(s):

Crystal Structure ◽

Density Distribution ◽

Scanning Tunneling Microscopy ◽

Electron Density ◽

Structure Determination ◽

Electron Density Distribution ◽

Scanning Tunneling ◽

Monoclinic Space Group ◽

Tunneling Microscopy ◽

X Ray

From X-ray analysis, the conclusions are drawn from averaged molecular informations. Thus, limitations are caused when analyzing systems whose symmetry is reduced due to interatomic interactions. In contrast, scanning tunneling microscopy (STM) directly images atomic scale surface electron density distribution, with a resolution up to fractions of Angstrom units. The crucial point is the correlation between the electron density distribution and the localization of individual atoms, which is reasonable in many cases. Thus, the use of STM images for crystal structure determination may be permitted. We tried to apply RuCl3 - a layered material with semiconductive properties - for such STM studies. From the X-ray analysis it has been assumed that α-form of this compound crystallizes in the monoclinic space group C2/m (AICI3 type). The chlorine atoms form an almost undistorted cubic closed package while Ru occupies 2/3 of the octahedral holes in every second layer building up a plane hexagon net (graphite net). Idealizing the arrangement of the chlorines a hexagonal symmetry would be expected. X-ray structure determination of isotypic compounds e.g. IrBr3 leads only to averaged positions of the metal atoms as there exist extended stacking faults of the metal layers.

Download Full-text