A study of planar anchor groups for graphene-based single-molecule electronics (original) (raw)
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Study of Planar Anchor Groups for Graphene-based Single-Molecule Electronics.
To identify families of stable planar anchor groups for use in single molecule electronics, we report detailed results for the binding energies of two families of anthracene and pyrene derivatives adsorbed onto graphene. We nd that all the selected derivatives functionalized with either electron donating or electron accepting substituents bind more strongly to graphene than the parent non-functionalized anthracene or pyrene. The binding energy is sensitive to the detailed atomic alignment of substituent groups over the graphene substrate leading to larger than expected binding energies for -OH and -CN derivatives. Furthermore, the ordering of the binding energies within the anthracene and pyrene series does not simply follow the electron anities of the substituents. Energy barriers to rotation or displacement on the graphene surface are much lower than binding energies for adsorption and therefore at room temperature, although the molecules are bound to the graphene, they are almost free to move along the graphene surface. Binding energies can be increased by incorporating electrically-inert side chains and are sensitive to the conformation of such chains.
Robust Molecular Anchoring to Graphene Electrodes
Nano Letters
Recent advances in the engineering of picoscale gaps between electroburnt graphene electrodes provide new opportunities for studying electron transport through electrostatically gated single molecules. But first we need to understand and develop strategies for anchoring single molecules to such electrodes. Here, for the first time we present a systematic theoretical study of transport properties using four different modes of anchoring zinc-porphyrin monomer, dimer, and trimer molecular wires to graphene electrodes. These involve either amine anchor groups, covalent CC bonds to the edges of the graphene, or coupling via π−π stacking of planar polyaromatic hydrocarbons formed from pyrene or tetrabenzofluorene (TBF). π−π stacked pyrene anchors are particularly stable, which may be advantageous for forming robust single-molecule transistors. Despite their planar, multiatom coupling to the electrodes, pyrene anchors can exhibit both destructive interference and different degrees of constructive interference, depending on their connectivity to the porphyrin wire, which makes them attractive also for thermoelectricity. TBF anchors are more weakly coupled to both the graphene and the porphyrin wires and induce negative differential conductance at finite source-drain voltages. Furthermore, although direct CC covalent bonding to the edges of graphene electrodes yields the highest electrical conductance, electron transport is significantly affected by the shape and size of the graphene electrodes because the local density of states at the carbon atoms connecting the electrode edges to the molecule is sensitive to the electrode surface shape. This sensitivity suggests that direct CC bonding may be the most desirable for sensing applications. The ordering of the low-bias electrical conductances with different anchors is as follows: direct CC coupling > π−π stacking with the pyrene anchors > direct coupling via amine anchors > π−π stacking with TBF anchors. Despite this dependency of conductances on the mode of anchoring, the decay of conductance with the length of the zinc-porphyrin wires is relatively insensitive with the associated attenuation factor β lying between 0.9 and 0.11 Å −1 .
Impact of edge shape on the functionalities of graphene-based single-molecule electronics devices
Physical Review B, 2012
We present an ab-initio analysis of the impact of edge shape and graphene-molecule anchor coupling on the electronic and transport functionalities of graphene-based molecular electronics devices. We analyze how Fano-like resonances, spin filtering and negative differential resistance effects may or may not arise by modifying suitably the edge shapes and the terminating groups of simple organic molecules. We show that the spin filtering effect is a consequence of the magnetic behavior of zigzag-terminated edges, which is enhanced by furnishing these with a wedge shape. The negative differential resistance effect is originated by the presence of two degenerate electronic states localized at each of the atoms coupling the molecule to graphene which are strongly affected by a bias voltage. The effect could thus be tailored by a suitable choice of the molecule and contact atoms if edge shape could be controlled with atomic precision.
2017
Graphene-based two-dimensional materials have attracted an increasing attention these last years. Among them, the system formed by molecular adsorption on, aim of modifying the conductivity of graphene and make it semiconducting, is of particular interest. We use here hierarchical first-principles simulations to investigate the energetic and electronic properties of an electron-donor, melamine, and an acceptor, NaphtaleneTetraCarboxylic DiImide (NTCDI), and the assembly of their complexes on graphene surface. In particular, the van der Waals-corrected density functional theory (DFT) method is used to compute the interaction and adsorption energies during assembly. The effect of dispersion interactions on both geometries and energies is investigated. Depending on the surface coverage and the molecular organization, there is a significant local deformation of the graphene surface. Self-assembly is driven by the competition between hydrogen bonds in the building blocks and their adsorp...
Anchor Groups for Graphene-Porphyrin Single-Molecule Transistors
Advanced Functional Materials
The effectiveness of five different anchor groups for non-covalent interfacing to graphene electrodes are compared. A family of six molecules is tested in single-molecule junctions: five consist of the same porphyrin core with different anchor groups, and the sixth is a reference molecule without anchor groups. The junction formation probability (JFP) has a strong dependence on the anchor group. Larger anchors give higher binding energies to the graphene surface, correlating with higher JFPs. The best anchor groups tested are 1,3,8-tridodecyloxypyrene and 2,5,8,11,14-pentadodecylhexa-peri-hexabenzocoronene, with JFPs of 36% and 38%, respectively. Many junctions are tested at 77 K for each molecule by measuring source-drain current as a function of bias and gate voltage. For each compound, there is wide variation in the strength of the electronic coupling to the electrodes and in the location of Coulomb peaks. In most cases, this device-to-device variability makes it impossible to observe trends between the anchor and the charge-transport characteristics. Tetrabenzofluorene anchors, which are not π-conjugated with the
On the interaction of polycyclic aromatic compounds with graphene
2012
The adsorption and diffusion of benzene, hexafluorinated benzene, perylene, perylene-3,4,9,10-tetracarboxylic-3,4,9,10-diimide (PTCDI) and perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) on graphene has been studied by density functional means on a generalized gradient approximation level, including a semi-empirical correction to account for dispersive forces. It is shown that for all considered molecules the adsorption strength is mainly due to the latter, with the electronic interaction being relatively small and repulsive.
Journal of Computational Methods in Sciences and Engineering, 2017
The geometry, electronic properties and energy of the complexes formed between an extended graphene and polycyclic aromatic hydrocarbons,PAHs, were investigated at the Density Functional Theory (DFT) level. We have studied the interaction of benzo[a]pyrene, chrysene, benzo[a]anthracene and benzo[b]fluoranthene with graphene models of dimensions of 15 Å × 15 Å and 20 Å × 20 Å. These calculations were performed within the generalized gradient approximation GGA using the HCTH functional and the numerical DNP basis set. According to the results, the HCTH/DNP methodology can qualitatively describe attractive interactions occurring between the weakly-polar systems, verifying the formation of molecular complexes stabilized by Keesom or Debye forces. The interaction dipole moments and polarizabilities indicate that the interaction of permanent dipoles and induced dipoles are responsible for the complex formation in weakly polar PAHs. These results are useful to understand the processes of adsorption of PAHs by graphene.
Flexible Self-Assembled Molecular Templates on Graphene
The Journal of Physical Chemistry C, 2016
We report on molecular self-assembly employing a host−guest architecture to pattern the growth of molecules on graphene model surface. Under suitable conditions, the 1,3,5-benzenetribenzoic acid (BTB) selfassembles into an extended honeycomb mesh on graphene on Ir(111), with the molecules in the network being stabilized by linear hydrogen bonds between the carboxylic groups. The nanopores of the mesh are used to host and govern the assembly of cobalt phthalocyanine (CoPC) guest molecules. We characterize the assembled structures structurally and electronically using low-temperature scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. At a coverage higher than one CoPc per pore, the flexible hydrogen bonds of the host network undergo stretching to accommodate two CoPCs in a single pore. When the pores are uniformly doubly occupied, the guest molecules arrange into a herringbone pattern. This minimizes the energy cost associated with the stretching and twisting of the hydrogen bonds between the BTB molecules. The phenomenon observed here can be used to tailor molecular assemblies on graphene to controllably modify its properties. In addition, it allows the formation of guest monomers and dimers stabilized mechanically on the surface of graphene, an archetypical weakly interacting substrate.