Maryam Ebrahimi

Lakehead University Thunder Bay Campus · Department of Chemistry

While surface‐confined Ullmann‐type coupling has been widely investigated for its potential to produce π‐conjugated polymers with unique properties, the pathway of this reaction in the presence of adsorbed oxygen has yet to be explored. Here, the effect of oxygen adsorption between different steps of the polymerization reaction is studied, revealin...

The formation of ordered molecular structures on surfaces is determined by the balance between molecule-molecule and molecule-substrate interactions. Whether the aggregation process is guided by non-covalent forces or on-surface reactions, a deeper understanding of these interactions is pivotal to formulating a priori predictions of the final struc...

Ullmann coupling of halogenated aromatics is widely used in on-surface synthesis of two-dimensional (2D) polymers and graphene nanoribbons. It stands out among other reactions for regioselective connecting aromatic monomers into 1D and 2D π-conjugated polymers, whose final structure and properties are determined by the initial building blocks. Than...

Ullmann coupling or, more generally, dehalogenative aryl-aryl coupling, is one of the most widely exploited chemical reactions to obtain one- and two-dimensional polymers on metal surfaces. It is generally described as a two-step reaction: (i) dehalogenation, resulting in the formation of a stable intermediate phase and subsequent (ii) C-C coupling...

Investigating two-dimensional (2D) self-assembled structures of biological monomers governed by intermolecular interactions is a prerequisite to understand the self-assembly of more complex biomolecular systems. 5,6-dihydroxyindole carboxylic acid (DHICA) is one of the building blocks of eumelanin - an irregular heteropolymer and the most common fo...

The integration of molecules with irregular shape into a long-range, dense and periodic lattice represents a unique challenge for the fabrication of engineered molecular scale architectures. The tiling of pentagonal molecules on a 2D plane can be used as a proof-of-principle investigation to overcome this problem since basic geometry dictates that...

The ability of catecholamines to undergo oxidative self-polymerization enables an attractive preparation route of coatings for biotechnology and biomedicine applications. However, efforts toward developing a complete understanding of the mechanism that underpin polymerization have been hindered by the multiple catechol crosslinking reaction pathway...

Understanding how molecules interact to form large scale hierarchical structures on surfaces holds promise for building designer nanoscale constructs with defined chemical and physical properties. Here, we describe early advances in this field and highlight upcoming opportunities and challenges. Both direct intermolecular interactions and those tha...

Achieving precise control of molecular self-assembly to form designed 3-dimensional (3D) structures is a major goal in nanoscale science and technology. Using scanning tunnelling microscopy (STM) and density functional theory (DFT) calculations, we show that a 2D covalent organic framework (COF-1) can template solution-processed C60 guest molecules...

This study shows that surface-supported two-dimensional (2D) porous covalent organic frameworks (COFs) can selectively bind different molecules at specific sites via different types of interactions. Scanning tunneling microscopy (STM) images collected at the liquid/solid interface reveal the adsorption of 1,2,4-trichlorobeznene (TCB) in the hexagon...

.Ullmann coupling is the most common approach to form surface-confined one- and two-dimensional conjugated structures from haloaryl derivatives. The dimension 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 i...

Chemists have long aspired to synthesize two-dimensional polymers that are fully conjugated [mdash] an attribute that imparts potentially useful properties. Just such a material has been prepared using a solid-state polymerization reaction.

Surface-confined polymerization via Ullmann coupling is a promising route to create one- and two-dimensional covalent π-conjugated structures, including the bottom-up growth of graphene nanoribbons. Understanding the mechanism of the Ullmann reaction is needed to provide a platform for rationally controlling the formation of these materials. We use...

The dissociative attachment of hydrogen halides, HCl, HBr and HI, on Si(100) were studied by Scanning Tunneling Microscopy, and modeled by Molecular Dynamics computations based on density functional theory. The relative yields of on-dimer (OD), inter-dimer (ID), and inter-row (IR) products, reported here for the first time, were unaltered by temper...

The catalytic hydrogenation of olefins promoted by transition metals, represented here by the conversion of ethylene with platinum, was studied under a unique regime representing pressures in the mTorr range and single-collision conditions. Isotope labeling was used to follow the concurrent H-D exchange steps that occur during this conversion. Mult...

Combining a photochromic molecule with a semiconducting polymer yields an organic non-volatile, multilevel memory with a current output that can be switched and controlled by light.

The mechanism of the hydrogenation of olefins catalyzed by metal surfaces was probed by using isotope labeling in conjunction with a high-flux effusive molecular beam setup capable of sustaining steady-state conversion under well-controlled ultrahigh vacuum (UHV). The unique conditions afforded by this instrument, namely, a single collision regime...

We show that the surface-supported two-dimensional covalent organic framework (COF) known as COF-1 can act as a host architecture for C60 fullerene molecules, predictably trapping the molecules under a range of conditions. The fullerenes occupy the COF-1 lattice at the solution/solid interface, and in dried films of the COF-1/fullerene network that...

The kinetics of the hydrogenation of ethylene on platinum surfaces was studied by using high-flux effusive molecular beams and reflection–absorption infrared spectroscopy (RAIRS). It was determined that steady-state ethylene conversion with probabilities close to unity could be achieved by using beams with ethylene fluxes equivalent to pressures in...

The hydrogenation of ethylene on Pt(111) single-crystal surfaces was studied by combining measurements of the kinetics of reaction using mass spectrometry detection with the simultaneous characterization of the species present on the surface using reflection–absorption infrared spectroscopy. The kinetics measured by us matches past reports on the s...

Chemical reactivity as a function of chain-length was investigated for three 1-bromoalkanes on silicon. The physisorption and subsequent thermal dissociative attachment of bromoethane (EtBr), 1-bromopropane (PrBr), and 1-bromobutane (BuBr) on Si(100)-c(4X2) were examined by scanning tunneling microscopy in ultrahigh vacuum from 50 to 180 K, and int...

Adsorbates on metals, but not previously on semiconductors, have been observed to display long-range repulsive interactions. On metals, due to efficient dissipation, the repulsions are weak, typically on the order of 5 meV at 10 Å. On the 7×7 reconstruction of the Si(111) surface, charge transport through the surface has been demonstrated by others...

In gaseous or surface reactions, “early” barriers along the reaction coordinate are commonly surmounted by reagent translation, and “late” barriers are surmounted by vibration. Here, we link barrier location to the separation of the reaction products (2H or H + Cl) following dissociative attachment of H2 and HCl at silicon. Two markedly different a...

The room-temperature adsorption and thermal evolution of allylamine on Si(100)2×1 have been investigated by using temperature-dependent X-ray photoelectron spectroscopy (XPS) and thermal desorption spectrometry (TDS). The presence of a broad N 1s feature at 398.9eV, attributed to a N―Si bond, indicates N―H dissociative adsorption. On the other hand...

Vibrational electron energy loss spectroscopy (EELS) has been used to characterize the adsorption of acetic acid on Si(111)7 x 7 at room temperature and as a function of annealing temperature. At room temperature, acetic acid is found to undergo O-H dissociative adsorption to form predominantly unidentate adstructure. The equilibrium geometry and t...

The dissociative adsorption of acrylic acid on Si(100)2×1 at room temperature has been investigated by X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD), as well as density-functional theory (DFT) calculations. Three C 1s features can be attributed to the carboxyl C of bidentate acrylate (at 286.8 eV) and unidentate...

We report first results about the ability of low density amorphous ice nanolayers to behave as a "matrix" and trap monomeric neutral glycine molecules at 125 K, a temperature much greater than the commonly used liquid He temperature region. FTIR-RAS spectra of those monomeric neutral glycine molecules adsorbed on low dense amorphous ice were obtain...

Competition between the CC functional group with the OH group in allyl alcohol and with the CO group in allyl aldehyde in the adsorption and thermal chemistry on Si(1 0 0)2×1 has been studied by X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption (TPD), as well as density-functional theory (DFT) calculations. The similariti...

The structure of beryllium acetylacetonate, Be(acac)(2), was fully optimized at the B3LYP (using the 6-31G*, 6-311G*, and 6-311++G(3df,2p) basis sets), Hartree-Fock, and the Möller-Plesset (using the 6-31G* basis set) levels. The frequency and intensity of the vibrational bands of Be(acac)(2) and its 1,3,5-(13)C; 2,4-(13)C; 3-(2)H; 3-(2)H-2,4-(18)O...

The growth of glycine film by thermal evaporation on Si(111)7 x 7 at room temperature has been studied by X-ray photoemission. In contrast to common carboxylic acids, glycine is found to adsorb on Si(111)7 x 7 dissociatively through cleavage of a N-H bond instead of O-H bond. The intricate evolution of the observed N 1s features at 399.1, 401.4, an...

The dissociative adsorption of acetic acid on Si(100)2×1 at room temperature has been investigated by X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption (TPD), as well as density-functional theory (DFT) calculations. The three C 1s features obtained by XPS measurement can be attributed to the carboxyl C of bidentate acetat...

The adsorption of CCl4 on Si(111)7×7 at room temperature has been characterized by electronic and vibrational electron energy loss spectroscopy (EELS). CCl4 was found to adsorb dissociatively on Si(111)7×7 with the formation of SiCl bond and adsorbed CClx species. At high exposures, CCl4 appears to more readily undergo a greater degree of dechlorin...

Infrared reflection-absorption spectroscopy is used to investigate H2O ice deposited onto non-crystalline (dimers [1]) and polycrystalline (infinite chains [1]) acetic acid films. The condensed water film grown at ˜135 K on these different substrates can be characterized as amorphous dense ice. The H2O molecules are shown to interact mainly with th...