Bond Insertion, Complexation, and Penetration Pathways of Vapor-Deposited Aluminum Atoms with HO- and CH₃O-Terminated Organic Monolayers

Abstract

The interaction of vapor-deposited Al atoms with self-assembled monolayers (SAMs) of HS-(CH(2))(16)-X (X = -OH and -OCH(3)) chemisorbed at polycrystalline Au[111] surfaces was studied using time-of-flight secondary-ion mass spectrometry, X-ray photoelectron spectroscopy, and infrared reflectance spectroscopy. Whereas quantum chemical theory calculations show that Al insertion into the C-C, C-H, C-O, and O-H bonds is favorable energetically, it is observed that deposited Al inserts only with the OH SAM to form an -O-Al-H product. This reaction appears to cease prior to complete -OH consumption, and is followed by formation of a few overlayers of a nonmetallic type of phase and finally deposition of a metallic film. In contrast, for the OCH(3) SAM, the deposited Al atoms partition along two parallel paths: nucleation and growth of an overlayer metal film, and penetration through the OCH(3) SAM to the monolayer/Au interface region. By considering a previous observation that a CH(3) terminal group favors penetration as the dominant initial process, and using theory calculations of Al-molecule interaction energies, we suggest that the competition between the penetration and overlayer film nucleation channels is regulated by small differences in the Al-SAM terminal group interaction energies. These results demonstrate the highly subtle effects of surface structure and composition on the nucleation and growth of metal films on organic surfaces and point to a new perspective on organometallic and metal-solvent interactions.

Mechanism of Rectification in Tunneling Junctions Based on Molecules with Asymmetric Potential Drops

“…39,40,44 iii) Most studies have generated top-electrodes by depositing gold or titanium (using electron-beam evaporation or sputtering) onto monolayers of reactive organic molecules. 16,44 It is unlikely that the molecules are not destroyed, or that the monolayer is not penetrated by the highly energetic incoming metal atoms or clusters of atoms. 16 iv) Asymmetric placement of the donor-acceptor moiety inside the junctions may cause rectification that is not inherent to the donor-acceptor design.…”

“…16,44 It is unlikely that the molecules are not destroyed, or that the monolayer is not penetrated by the highly energetic incoming metal atoms or clusters of atoms. 16 iv) Asymmetric placement of the donor-acceptor moiety inside the junctions may cause rectification that is not inherent to the donor-acceptor design. Many studies involve monolayers formed by the Langmuir-Blodgett technique that requires amphiphilic molecules, in which one side of the polar D-σ-A moiety is functionalized with long alkyl tails.…”

Electrical behavior of memory devices based on fluorene-containing organic thin films

“…In the case of self-assembled monolayers, it was observed that Al atoms exhibit a wide range of chemical and physical interactions. 26,27 For example, reactive surfaces, such as -COOH and -OH, can interact with the aluminum to form a series of organometallic complexes in the first few monolayers. In contrast, when the terminal group of the alkyl chain of the self-assembled monolayer contains an unreactive group, such as -CH 3 , penetration of the metal atoms through the monolayer occurs to the Au/ S interface where it forms an adsorbed layer.…”

Molecular Nanoelectronics

“…Several studies [58][59][60][61][62][63] have analyzed (by X-ray photoelectron spectroscopy, infra-red spectroscopy,…) the interaction (bond insertion, complexation…) between the metal atoms and the molecules. When the metal atoms are strongly reactive with the end-groups of the molecules (e.g.…”

“…Al with COOH or OH groups, Ti with COOCH 3 , OH or CN groups….) [58][59][60][61][62][63], a chemical reaction occurs forming a molecular overlayer on top of the monolayer. This overlayer made of organometallic complexes or metal oxides may perturb the electronic coupling between the metal and the molecule, leading, for instance, to partial or total Fermi-level pinning at the interface [64].…”