Dynamics of Reactive Metal Adsorption on Organic Thin Films

Abstract

We have studied the interaction of vapor-deposited Mg and Ca on −CH3, −COOH, −OH, −OCH3, and −CO2CH3 terminated self-assembled monolayers (SAMs) on polycrystalline Au{111} using time-of-flight secondary ion mass spectrometry and density functional theory calculations. Magnesium has a very low initial sticking probability on all of the SAMs studied. It inserts into the C−O bonds of oxygen-containing terminal groups and penetrates through methyl-terminated SAMs. In contrast, vapor-deposited calcium vigorously reacts with all of the SAMs studied to form inorganic products. Ca has a high sticking probability on all of the SAMs studied except for methyl-terminated SAMs. The reaction of these metals with SAMs can be explained by a single, general scheme. In the first stages of deposition at low coverages, metal atoms are only adsorbed if they can form a weak complex at the SAM/vacuum interface; otherwise, they are scattered from the surface. The adsorbed metal atoms then either react with the terminal group or penetrate through the monolayer. For metals that do not form weak complexes, only impinging atoms with sufficient energy to react with the terminal group or the methylene chain will adsorb. For all metals, adsorbed atoms provide nucleation sites for the formation of metallic islands and/or overlayers. These findings contribute to a systematic understanding of the interactions of metals with organic surfaces.

Building Robust and Reliable Molecular Constructs: Patterning, Metallic Contacts, and Layer-by-Layer Assembly

“…48 We have recently demonstrated that the conductivity of a Au/ODT/GaAs device is strongly dependent on its structure, 54 which in turn is related to the metal deposition conditions used. We vapor-deposited 150 Å of Au on an ODT SAM adsorbed on GaAs under three different deposition conditions, (a) direct deposition on a 300 K sample; (b) direct deposition on a 77 K sample; and (c) using a gentle deposition technique, Ar backfilling, on a 300 K sample.…”

Issues and Challenges in Vapor-Deposited Top Metal Contacts for Molecule-Based Electronic Devices

“…For the alkaline earth metals this effect can be useful for generating low work function cathode metal electrodes in organic light emission diodes (OLEDs) and organic electro luminescence display (OELDs). Alkaline earth metals, however, are not only active in injecting electrons into conjugated molecules but also are chemically reactive and can form reaction products with many organic groups [56,57]. In general, the alkali metals are not used for commercial applications but are useful to study for their simple behavior as one electron injection atoms.…”

“…In the case of Mg and Ca depositions on n-alkanethiolate SAMs it was observed that while Mg does not react it does undergo continuous penetration thorough the SAM. In contrast, Ca does react to some extent resulting in calcium carbide species formation [56,57]. In the case of K on an n-alkanethiolate SAM the results are more complicated.…”

“…K deposition on -COOCH 3 [57]. Continuing deposition of Mg forms a top metal layer [62,63], although further analysis of filament generation still has to be performed in order to show reliability of this deposition for M 3 junction fabrication.…”

Towards Molecular Electronics: Solution-Based Methods for Selective Deposition of Metals and Semiconductors

“…Many outcomes have been observed, from metal atom penetration through the organic layer to destruction of the monolayer via carbide formation to formation of strongly bound complexes and stable contact formation [17]. Although the interaction of vapor-deposited metals with SAMs is governed by a single reaction pathway, it is not easy to predict the outcome of a particular interaction [17]. Technologies besides PVD to deposit metals and other materials in Si-based microelectronics include CVD [18], atomic layer deposition (ALD) [19] and electrodeposition [20].…”