Heterogeneous SAM of ruthenium-alkyl class, redox-active and spin-active molecules functionalized on semiconductor surfaces: A prototype for future device structures

The functionalization of semiconductor surfaces with self assembled monolayers (SAMs) of organic molecules has been driven by the promise of increased device functionality and performance, and has formed the basis of several classes of device structures. Until recently, work has concentrated on inert or non-redox and non-spin active organic molecules which facilitated limited device functionality. In this study we propose the use of a spin-active and redox active molecule in a SAM configuration as the initial prototype for the realization of future devices with increased functionality and performance. The proposed test structure is a heterogeneous SAM (Mixed Adlayer) of a ruthenium-based organic complex, which is the redox-active and spin-active molecule, and a simple inert aromatic thiol, which helps in passivating the GaAs substrate. Homogeneous SAMs of an alkanethiol, aromatic thiol and ruthenium-based complex have been used as comparisons. Surface analysis on the various SAMs have indicated surface coverage values indicative of partial to full monolayer coverage on the GaAs surface which are sufficient for electronic-based purposes. The SAMs have also been investigated as functional layers in metal-molecule-semiconductor (MMS) and metal-graphene-molecule-semiconductor (MGMS) structures where various electronic parameters including barrier heights have been extracted from current-voltage (IV), variable temperature current-voltage (IVT) and capacitance-voltage (CV) analysis. The resulting data, which indicated molecular Schottky barrier modulation, validated the use of the non-destructive top metal contact deposition techniques used: a low energy, indirect path thermal evaporation technique in MMS devices and multi-layered graphene on top of the SAMs with normal e-beam deposition in the MGMS devices. In addition a novel method of graphene patterning has been developed. Possible future applications of both the Mixed Adlayer structure and graphene patterning process have also been mentioned