Invited Paper TF-MoA6
Nonaqueous Sol-Gel Chemistry in Atomic Layer Deposition

Monday, October 18, 2010, 3:40 pm, Room Pecos

Nonaqueous sol-gel routes are elegant approaches for the synthesis of high quality metal oxide nanomaterials such as pure inorganic nanocrystals [1], ordered hybrid organic-inorganic materials [2] or thin films by atomic layer deposition (ALD) [3]. In this communication, after a short introduction to nonaqueous sol-gel chemistry we will focus on the ALD using nonaqueous sol-gel. In particular, the similarities and differences of the chemical processes taking place in solution and in ALD will be discussed through two examples of recent approaches of metal oxide film deposition

Our approach makes use of metal alkoxides and carboxylic acids as metal and oxygen source, respectively [4]. In the first step, it is expected that the reaction of surface alkoxide species with carboxylic acids leads to surface carboxylate species (eq. 1). In the second step an aprotic condensation reaction between surface carboxylate species and metal alkoxides leads to metal-oxide bonds formation (eq. 2).

≡M-OR’ + RCOOH → ≡M-OOCR + R’OH (1)

≡M-OOCR + M-OR’ → ≡M-O-M≡ + RCOOR’ (2)

This process enables the growth of metal oxides at temperatures as low as 50 °C on various supports.

A comparison of this nonaqueous sol-gel route to ALD approaches using ozone as oxygen source will be made. Although, from a first look it seems that the chemistry responsible for metal oxide formation is very different, this is certainly not the case. As a matter of fact it was recently reported that during the ALD of metal oxides, the exposure to ozone leads to formate, carbonate and hydroxyl groups on the surface [5-7]. According to Goldstein et al., a large amount of formate surface species were formed by the reaction of trimethylaluminium (TMA) and O₃ [5]. Therefore, the formation of surface carboxylic species upon reaction with ozone leads to similar surface states as in the case of reaction with carboxylic acids [4]. These findings will be used to discuss the chemical reactions responsible for the deposition of PbTiO_x using lead bis(3-N,N-dimethylamino-2-methyl-2-propoxide), titanium(IV) isopropoxide and a combination of water and ozone as oxygen sources as recently reported by Hyun Ju Lee et al. [8]

References:

[1] Pinna, N. & Niederberger, M. Angew. Chem. Int. Ed., 2008, 47, 5292

[2] Pinna, N. J. Mater. Chem., 2007, 17, 2769

[3] Clavel, G. et al. J. Mater. Chem, 2009, 19, 454

[4] Rauwel, E. et al. Angew. Chem., Int. Ed., 2008, 47, 3592

[5] Goldstein, D. N. et al. J. Phys. Chem. C, 2008, 112, 19530

[6] Rai, V. R.; Agarwal, J. Phys. Chem. C, 2008, 112, 9552

[7] Kwon, J. et al. Chem. Mater., 2008, 20, 3248

[8] Lee, H. J. et al. ECS Transactions, 2009, 19, 829