Photochemical CVD of Ru on functionalized self-assembled monolayers from organometallic precursors

Abstract

Chemical vapor deposition (CVD) is an attractive technique for the metallization of organic thin films because it is selective and the thickness of the deposited film can easily be controlled. However, thermal CVD processes often require high temperatures which are generally incompatible with organic films. In this paper, we perform proof-of-concept studies of photochemical CVD to metallize organic thin films. In this method, a precursor undergoes photolytic decomposition to generate thermally labile intermediates prior to adsorption on the sample. Three readily available Ru precursors, CpRu(CO)Me, (η-allyl)Ru(CO)Br, and (COT)Ru(CO), were employed to investigate the role of precursor quantum yield, ligand chemistry, and the Ru oxidation state on the deposition. To investigate the role of the substrate chemistry on deposition, carboxylic acid-, hydroxyl-, and methyl-terminated self-assembled monolayers were used. The data indicate that moderate quantum yields for ligand loss (φ ≥ 0.4) are required for ruthenium deposition, and the deposition is wavelength dependent. Second, anionic polyhapto ligands such as cyclopentadienyl and allyl are more difficult to remove than carbonyls, halides, and alkyls. Third, in contrast to the atomic layer deposition, acid-base reactions between the precursor and the substrate are more effective for deposition than nucleophilic reactions. Finally, the data suggest that selective deposition can be achieved on organic thin films by judicious choice of precursor and functional groups present on the substrate. These studies thus provide guidelines for the rational design of new precursors specifically for selective photochemical CVD on organic substrates.

Photochemistry of (η3-allyl)Ru(CO)3X Precursors for Photoassisted Chemical Vapor Deposition

“…These reactions were carried out on the roof of the chemistry building (Sisler Hall) at ambient temperatures (25−40 °C). 33 1 H, 13 C, and 31 P NMR spectra were obtained on either a 300 MHz Mercury, 300 MHz Gemini, or 500 MHz Varian Inova instrument. Peaks were referenced to the residual protons of the deuterated solvents.…”

“…9−11 However, due to the need for high substrate temperatures (≥200 °C) to achieve reasonable film growth rates, this technique remains challenging to use with thermally sensitive organic substrates, such as self-assembled monolayers (SAMs). 12,13 Photochemical CVD is a variant of the technique that could be used to metallize organic films by utilizing photoinduced reactions to initiate the decomposition of organometallic precursors. 14 We have recently investigated the application of (η 3allyl)Ru(CO) 3 Br (1a), CpRu(CO) 2 Me, and (COT)Ru(CO) 3 as suitable precursors for photoassisted chemical vapor deposition (PACVD) of ruthenium on functionalized alkanethiolate self-assembled monolayers (SAMs).…”

“…14 We have recently investigated the application of (η 3allyl)Ru(CO) 3 Br (1a), CpRu(CO) 2 Me, and (COT)Ru(CO) 3 as suitable precursors for photoassisted chemical vapor deposition (PACVD) of ruthenium on functionalized alkanethiolate self-assembled monolayers (SAMs). 13 Encouraging deposition results led us to investigate the other halide complexes (η 3 -allyl)Ru(CO) 3 X (Figure 1; 1b, X = Cl; 1c, X = I) for PACVD. Preliminary results suggest that the halogen atom may alter the amount of ruthenium deposited on the functionalized SAMs, which makes a comparison of the photochemistry of 1a−c of interest.…”

“…28−30 While studies of the photochemistry of bromide complex 1a have been reported, 16 the photochemistry of the chloride and iodide complexes 1b,c has not been previously studied. Because the quantum yields for carbonyl loss are expected to affect our PACVD experiments with 1a−c, 13 we have investigated the photochemistry of 1b,c. We now report the quantum yields for CO loss from 1a−c and discuss the halide effect on the photochemical decomposition of (η 3 -allyl)Ru-(CO) 3 X, where X = Cl, Br, I.…”

Photochemistry of 1,5-Cyclooctadiene Platinum Complexes for Photoassisted Chemical Vapor Deposition

“…In developing model systems to study photoassisted CVD of metals, Ru complexes provided an excellent starting point due to the rich photochemistry that had already been reported for Ru compounds and the number of volatile Ru complexes that had been used for thermal CVD. In previous work, we investigated Ru compounds such as (η 3 -allyl)­Ru­(CO) 3 Br, CpRu­(CO) 2 Me, and (COT)­Ru­(CO) 3 as precursors for PACVD on functionalized alkanethiolate self-assembled monolayers (SAMs) . A high quantum yield for ligand loss was postulated to be necessary to generate a sufficient concentration of coordinatively unsaturated species that could react with the functional groups on the SAM surfaces.…”