Chemical Effects of Methyl and Methyl Ester Groups on the Nucleation and Growth of Vapor-Deposited Aluminum Films

Abstract

The interaction of vapor-deposited Al atoms with self-assembled monolayers (SAMs) of HS(CH2)15CH3 and HS(CH2)15CO2CH3 chemisorbed at Au{111} surfaces was studied using X-ray photoelectron spectroscopy, infrared spectroscopy, time-of-flight secondary ion mass spectrometry, and spectroscopic ellipsometry. For the CH3-terminated SAM, no reaction with C−H or C−C bonds was observed. For total Al doses up to ∼12 atoms/nm2, penetration to the Au−S interface occurs with no disruption of the average chain conformation and tilt, indicating formation of a highly uniform ∼1:1 Al adlayer on the Au. Subsequently, penetration ceases and a metallic overlayer begins to form at the SAM−vacuum interface. These results are explained in terms of an initial dynamic hopping of the −S headgroups on the Au lattice, which opens transient diffusion channels to the Au−S interface, and the closing of these channels upon completion of the adlayer. In contrast, Al atom interactions with the CO2CH3-terminated SAM are restricted to the vacuum interface, where in the initial stages discrete organometallic products form via reaction with the CO2CH3 group. First, a 1:1 complex forms with a reduced CO bond and an intact CH3 moiety. Further exposure leads to the additional reaction of about four Al atoms per ester, after which a metallic overlayer nucleates in the form of clusters. After the growth progresses to ∼30 Å, the clusters coalesce into a uniform metallic film. These results illustrate the extraordinary degree of control that organic substrates can exert during the course of metal film formation.

Static SIMS studies of fatty alcohols, amines and esters on gold and aluminium–magnesium alloy surfaces

“…Recent studies have focused on the interaction between the ester functional group and sputter-deposited metal atoms, such as aluminium and chromium. 27,28 Both of these studies provided evidence for the formation of complexes between metal atoms and the ester functional group. In both cases, it has been suggested that the ester molecule remains intact with the attachment of metal atoms to the carbonyl group.…”

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

“…In the case of penetration of nascent metal atoms through dynamic, transient defects, insertion into SÀAu bonds can occur, and if the new S-metal-Au bonding is stronger than S-Au bonds this can result in diminishing of the lateral fluctuations, thereby stopping formation of the temporal vacancy channels, thus limiting the extent of penetration. On the other hand, this freezing process of the lateral positional fluctuation may also lead to new static defects because of the continuing disordering of the SAM molecule positions driven by the incommensurate non-uniform insertion of deposited metal into the SAM-substrate interface [20,21]. In order to avoid introducing chemical reaction products into the junction via reactions of the deposited metal with the SAM and to avoid oxidation or corrosion of the top contact, inert or low reactive metal species, such as Au, Ag, Cu, and Pd, have been used [22][23][24][25][26][27][28].…”

“…Since Al is an important metal for device applications its deposition on SAMs has been extensively studied [20,21,23,32,33,41,50,[65][66][67][68][69]. The critical problem for Al, however, is its facility in penetration along with filament growth.…”

Adhesion, lubrication and wear on the atomic scale

“…At present, the mechanism of ester decomposition on aluminum is unknown. 41,42 Recent spectroscopic work by Hooper et al 43 on an idealized system revealed that vapor-deposited aluminum atoms will react with the CO 2 CH 3 group in a self-assembled monolayer (SAM) of HS CH 2 15 CO 2 CH 3 but will not react with the CH 3 groups in a SAM of HS CH 2 15 CH 3 . Underhill and Timsit 44 investigated the decomposition of short-chain alcohols and carboxylic acids on a clear aluminum surface across a range of temperatures.…”