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

The room temperature atomic layer-like deposition (ALLD) of ZnO using diethylzinc (DEZ) and water precursors has been investigated on -COOH, -OH, and -CH3 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 angstrom/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 -CH3 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.