Hybrid-molecular electronics

From this comparison it can be concluded that on the device level there are fundamental limits for the miniaturization of hybrid-molecular electronics, which are not only governed by the size of the molecule but also depend on the size that an electromechanical or capacitative grid has to have in order to influence its energy levels. These architectural issues regarding the interfacing of a molecular device to the outside world or the assembly of many devices into larger circuits will have to be addressed to a larger extent in the near future. 

Unsaturated organic molecules, such as ethylene, can be chemisorbed on transition metal surfaces in two ways, namely in -coordination or di-o coordination. As shown in Fig. 2.24, the n type of bonding of ethylene involves donation of electron density from the doubly occupied n orbital (which is o-symmetric with respect to the normal to the surface) to the metal ds-hybrid orbitals. Electron density is also backdonated from the px and dM metal orbitals into the lowest unoccupied molecular orbital (LUMO) of the ethylene molecule, which is the empty asymmetric 71 orbital. The corresponding overall interaction is relatively weak, thus the sp2 hybridization of the carbon atoms involved in the ethylene double bond is retained. 

Joachim C, Gimzewski JK, Aviram A (2000) Electronics using hybrid-molecular and mono-molecular devices. Nature 408(6812) 541-548... 

Moons E, Bruening M, Shanzer A, Beier J, Cahen D (1996) Electron transfer in hybrid molecular solid-state devices. Synth Met 76 245-248... 

We then investigated the formation of hybrid molecular assemblies in combinations of anionic peptide lipid 9 with cage-type hosts 7 and 8 after a previous method [44], Lamella-type aggregates are observed for a mixture of host 7 and lipid 9 at a 1 20 molar ratio in the dispersion state by negative staining electron microscopy. Phase transition parameters (temperature at peak maximum, T enthalpy change, AH entropy change, dS half-width of an endothermic peak, and hydrodynamic diameters (d,y) for the bilayer... 

The other electron-pair geometries that are listed in Table 9-2 are also related to specific hybrid molecular orbitals, but they are more complicated because they involve midp. In every case, the ami/ orbitals are of the same priflfap l( BMlSqis%mfeehySflffMftrofif feg... 

For a simple MO picture of molecular electronic structure, the same procedures can be followed to classify the symmetries spanned by bond and lone-pair orbitals. For instance, we can envisage the electronic structure of BF3 as involving sp2 hybridization of the atoms. We would then have B and three F Is core orbitals, two sp2 and one jr symmetry lone pair on each F atom, and three sp2 bond orbitals for the three BF bonds. Our analysis above shows that the four core orbitals comprise 2 a and a doubly degenerate e orbital the in-plane lone-pairs transform as a, a 2, and 2 e orbitals the out-of-plane lone pairs transform as a"2 and e" and the three BF bonds as a and e. ... 

A further simple application of the present table , is to the computation of overlap integrals in. which one or both atoms are replaced by groups of atoms. S s of this sort frequently occur when one is working with iron-localized MO s (molecular orbitals) in LCAO approximation. The non-localized MO structure of H20 furnishes a convenient example. Neglecting, p hybridization, the electron conjuration rosy be written ... 

Towards fabrication of SWNT-based molecular electronic devices, two methods have been used to assemble the 03-SWNTs on functionalized SAMs of OPEs, as shown in Figure 5.10. The first, termed chemical assembly , is based on a condensation reaction between the carboxylic acid functionalities of O3-SWNTs and the amine functionalities of SAMs to form amides. The results show that O3 -SWNTs coat the amino-terminated SAM with a high degree of surface coverage. The second method is based on physical adsorption via layer-by-layer (LBL) deposition with bridging of metal cations, i.e., Fe3+ on carboxylate terminated SAMs or Cu2+ on thiol-terminated SAMs. The oxidatively shortened 03 -SWNTs are shown to be perpendicular to the surface with random adsorption of longer tubes. The patterned nanotube assemblies may be useful in hybridized electronic devices, where device functions can be modified by the orientation and stacking of SWNTs, and the properties of the SAM. 

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