Updated Note!: Any serious inquiry about Molecular Electronics Devices and its non-linear I-V Characteristics, should refer to these recent sources, among others:

-Tour, James M; He, Tao (2008), "Electronics: The fourth element", Nature 453: 42–43
-Strukov, Dmitri B; Snider, Gregory S; Stewart, Duncan R; Williams, Stanley R (2008), "The missing memristor found", Nature 453: 80–83

More information about my Surface Chemistry projects and previous projects

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Intro

My research in grad school focused on Molecular Electronics (ME). Nowadays ME has become one of the most important interdisciplinary topics in the field of Nanotechnology. ME capitalizes on cooperative interactions between an organic thin film and uniform, condensed matter. At the nanoscale level, the organic film and the bulk contact find a high affinity to interact chemically and electronically, by means of a coherent high order, reached by the formation of a self-assembled monolayer (SAM).

From an electronic point of view, the result from these organic-bulkphase systems is a non-linear profile with applications as a nano-transistors. These devices operate as logic and memory components at different temperatures, showing switching behavior that can be scaled and used to perform electronic operations as molecular electronic device for sensing, logic and programming, showing a high reproducibility, defect tolerance and robustness. These features hold the foundations for new electronic devices that may assist the integrated circuit industry, which currently faces critical physical and economic challenges as circuitry density, heat dissipation and fabrication costs. It is clear that information technology could be positively affected by ME.

The Chemistry

As an organic chemist, one of my projects was the design, synthesis and testing of new, fully-conjugated organic molecules as candidates for ME. I was directly responsible to synthesize new small aromatic molecules with functional groups of our interest, in order to be use as backbones for larger linear oligomers.

Capitalizing on organometallic chemistry for carbon-carbon bond formation, I carried metal-catalized couplings as the main organic reaction.

Synthetic Design

The synthesis of new oligomers for electronic applications as a SAM, is driven by main two aspects: The geometry and conformation of the oligomer and its electronic nature and ability to go under reduction-oxidation (redox) processes. For the first aspect, I pursued molecular diversity in order to investigate the relation between molecular conformation, SAM formation and electrical outputs under electronic miscroscopy. This has been done experimentally with the assistance of Prof. Paul Weiss group by using imaging techniques on scanning tunneling microscopy (STM).

For the second aspect, we introduced different functional groups on the molecular core that affect its ability to act as a redox device. Theoretical calculations support the hypothesis that electron-withdrawing and electronegative groups such as nitro and atoms such as fluoro, impart a higher chemical and thermal stability to the molecule, promoting a higher electronic charge and conduction that is needed for the molecule to act as a memory and switching device, as well as improving the electron flow by lowering the energy of the molecular frontier orbitals, so they become closer to the Fermi level of the bulk contact.

Analysis

The final aspect is the use and analysis of functional groups that create the required molecular junction with the bulk phase. Our goal is to provide the molecule with an efficient, stable bulk contact-molecule linker that can assure a strong chemical and electronic interaction between the two systems and at the same time reducing resistance, polarization, atomic migration, among other undesired effects that are known to be present at the chemical interface. These aspects are analyzed with different surface techniques, Infrared (IR) and X-ray photoelectron spectroscopy (XPS) Kelvin probe spectroscopy, atomic force microscopy (AFM), STM, cyclic voltrammetry (CV) and ellipsometry.

Below there is a brief description of different oligomers that i have synthesized and studied as potential molecular electonics components.

Improved Synthesis of Molecular Electronics Candidates pre-print (pdf, 500KB).

We covered the synthesis and CV testing of new oligomers, following improved synthetic pathways. The oligomers are nitro substituted, pyridine- chromium- and isatogen-based, including also a novel U-shaped oligomer. All of them contain either thiol-based moieties or isonitrile groups to enable formation of of SAMs on metal subsrates.

Terphenyl Oligomers pre-print(pdf, 510KB).

Terphenyl molecules, as their name states, are based on three adyacent aromatic rings on their core, being longer and showing a lower conformational freedom than typical oligo(phenylene-ethynylene) (OPE). These structural differences are thought to result in new behaviors of the molecule as a SAM and as a part of an molecular electronic testbed. By these means it could give insights about the relation between the electronic response and the conformation of the molecule.

U-shaped Oligomers pre-print 1st paper (pdf, 490KB). pre-print 2nd paper (pdf, 753KB) pre-print 3rd paper (pdf, 293KB).

We have also made efforts in the construction of oligomers dubbed as 'U-Shapped' (US) molecular wires. Again we pursued a better understanding of the corelation between the conformation and extended conjugation of the oligomer and its properties as a SAM. In this work we also analyzed the SAM made of several new U-shaped oligomers, by STM, XPS, CV and ellipsometry.

Pentafluoro OPEs pre-print 1st paper(pdf, 380KB) pre-print 2nd paper(pdf, 459KB).

We presented for the first time a new series of OPEs that require no deprotecion of the alligator clip for SAM formation. Also these fluorinated oligomers showed higher thermal stability, lower energy and smaller molecular orbital gaps that could be translated in a better conductivity, thermal and electronic stability as a part of a electronic device.

OPEs for Selective Attachment pre-print (pdf, 276KB).

Another new serie of OPEs that have two different alligator clips so one of them attaches first to a desire metallic body, and by a in situ deprotection the 2nd alligator clip reaches a different metallic target, becoming a useful linker that have already found applicability to new molecular nanochip.

More information about my Surface chemistry research and my buckyballs research

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