Modifying the axial ligand of diruthenium compounds to be purposed for silicon surface chemistry

Steven P Cummings, Purdue University

Abstract

Due to problems arising from the continuous scaling of silicon based devices, covalent modification of flat silicon surfaces is a key step in integrating CMOS technology and molecular electronics that may lead to novel hybrid microelectronic devices. There is interest in functionalizing a silicon surface with inorganic species due to desirable redox characteristics and the potential for high ground state spins. In order to form devices that are tailor made for certain tasks, it is imperative to understand the charge transfer mechanism between the Si surface and the redox center, in addition to the influence that unpaired electrons will have on the surface current of silicon. In this work, diruthenium paddlewheel compounds have been synthesized and characterized specifically to address these issues. To gain an understanding of the spin effect on the surface current of Si, two series of diruthenium compounds were synthesized. The bis-alkynyl species, Ru2(LL) 4(L)2, have a ground state spin with no unpaired electrons, while the mono-alkynyl species Ru2(LL)4(L)2, have three unpaired electrons. Of the ligands in this work, 3 and 4 amino-phenylacetylene played a very important role. The terminal amino group can be oxidized to a diazonium salt or be allowed to undergo a "Schiff base condensation." The diazonium functional group is desired as it will allow a facile method for deposition of the diruthenium species onto a silicon surface. In order to help interrogate the electron transfer mechanisms, the amino group can also be modified by an on-complex condensation reaction with an aldehyde or acetyl moiety allowing for an increased distance between the Si surface and the diruthenium core. Showing the versatility of using the diruthenium core, a series of dissymmetrical axial compounds, Ru2(LL)4(Lm )(Ln), were synthesized. These compounds display the desirable attributes of: i) high physical and good thermal stability; ii) easily accessible redox states; iii) facile tuning of the electronic structure through equatorial and axial ligand modification. The dissymmetrical compounds were modified to have dissimilar functional groups at the end of each axial ligand, namely thiol and alkyne, making these species "ditopic". Using these two particular functional groups will allow for their use in metal-molecule-semiconductor (MMS) junctions, which are an important step in forming working hybrid devices.

Degree

Ph.D.

Advisors

Tong, Purdue University.

Subject Area

Chemistry|Inorganic chemistry

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