Room Temperature Atomic Layer-like Deposition of ZnO on Functionalized Self-Assembled Monolayers

Abstract

The room temperature atomic layer-like deposition (ALLD) of ZnO using diethylzinc (DEZ) and water precursors has been investigated on −COOH, −OH, and −CH 3 terminated self-assembled monolayers. The detailed reaction pathways of ZnO ALLD on −COOH and −OH terminated SAMs are different. As expected on −OH terminated SAMs, the DEZ reacts with the hydroxyl group. However, on −COOH terminated SAMs DEZ reacts with both the carbonyl and hydroxyl bonds present and can lead to the formation of a ketone rather than ZnO deposition. The growth rates on these SAMs are different; after the first ALLD cycle the measured growth rates are 3.0 ± 0.1 and 3.4 ± 0.2 Å/cycle on −COOH and −OH terminated SAMs, respectively. XPS analyses show that the initial composition of the deposited layer on −COOH terminated SAMs is similar to Zn(OH) 2 . After five ALLD cycles the −COOH terminated SAM is completely covered, and XPS analyses indicate that the deposited film is composed of ZnO. In contrast on −OH terminated SAMs, the deposited film is ZnO for all ALLD cycles studied. Eight ALLD cycles are required to cover −OH terminated SAMs, suggesting that ZnO first forms islands on the surface. Little or no deposition is observed on −CH 3 terminated SAMs because the methyl group does not react with DEZ. These data indicate that surface functional groups can be employed to control the properties of ZnO films grown by ALD.

Room temperature atomic layerlike deposition of ZnS on organic thin films: Role of substrate functional groups and precursors

“…[41][42][43] Initially, ZnCl 2 was the Zn precursor of choice but thin film electroluminescent displays formed using this precursor suffered from performance issues, which were attributed to residual chloride ions in the ZnS film. 27 On -COOH terminated SAMs, the growth rate per cycle is lower than on -OH terminated SAMs. Diethyl zinc has a number of advantages over other Zn precursors in ALD on organic substrates.…”

“…27 This indicates that the growth rate difference is caused by the adsorption and reaction of DEZ with -OH and -COOH terminal groups. The average measured growth rate on -COOH terminated SAMs, 3.8 6 0.4 Å /cycle, is approximately 10% lower than on -OH terminated SAMs, 4.2 6 0.4 Å /cycle.…”

“…Self-assembled monolayers are ideal model organic surfaces for these types of study because they possess a uniform density of terminal groups and have a well-defined structure. Stable films can be deposited if reactive terminal groups are used such as amines, 23,24 hydroxyls, 27 and carboxylic acids. 21,22 To date, most studies of ALD on SAMs have employed elevated temperatures (>100 C), [23][24][25][26] which can lead to roughening of the deposited layer and/or degradation of the organic layer.…”

“…19 We also note that SAM constructs have many applications from energy harvesting 20 to organic/ molecular electronics. [25][26][27] For example, Chabal and coworkers 25,26 and Shi and Walker 27 have employed -COOH terminated SAMs to deposit nonpenetrating alumina, 25 copper, 26 and zinc oxide 27 films. The precursors may also penetrate through the organic layer and nucleate films on the underlying substrate, e.g., methyl-terminated SAMs.…”

“…21,22 To date, most studies of ALD on SAMs have employed elevated temperatures (>100 C), [23][24][25][26] which can lead to roughening of the deposited layer and/or degradation of the organic layer. In these studies, the metal precursor-containing precursor, trimethyl aluminum (TMA), 25 copper di-sec-butylacetamidinate, 26 or diethyl zinc (DEZ), 27 reacted with the -COOH terminal groups, forming a layer which blocked diffusion of the precursors to the SAM/substrate interface. Stable films can be deposited if reactive terminal groups are used such as amines, 23,24 hydroxyls, 27 and carboxylic acids.…”