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Fang Z.,University of Liverpool | Aspinall H.C.,University of Liverpool | Odedra R.,SAFC Hitech | Potter R.J.,University of Liverpool
Journal of Crystal Growth

TaN x thin films were grown at temperatures ranging from 200 to 375 °C using atomic layer deposition (ALD). Pentakis(dimethylamino)tantalum (PDMAT) was used as a tantalum source with either ammonia or monomethylhydrazine (MMH) as a nitrogen co-reactant. Self-limiting behaviour was observed for both ammonia and MMH processes, with growth rates of 0.6 and 0.4 Å/cycle, respectively at 300 °C. Films deposited using ammonia were found to have a mono-nitride stoichiometry with resistivities as low as 70 m cm. In contrast, films deposited using MMH were found to be nitrogen rich Ta 3N 5 with high resistivities. A Quartz Crystal Microbalance (QCM) was used to measure mass gain and loss during the cyclic ALD processes and the data was used in combination with medium energy ion scattering (MEIS) to elucidate the PDMAT absorption mechanisms. © 2011 Elsevier B.V. All rights reserved. Source

Knisley T.J.,Wayne State University | Ariyasena T.C.,Wayne State University | Sajavaara T.,University of Jyvaskyla | Saly M.J.,SAFC Hitech | Winter C.H.,Wayne State University
Chemistry of Materials

A new low temperature copper atomic layer deposition (ALD) process that employs a three precursor sequence entailing Cu-(OCHMeCH2NMe 2), formic acid, and hydrazine, was described. The growth of copper metal films by ALD was carried out using, formic acid, and anhydrous hydrazine as precursors on Si(100) substrates with the native oxide. The results demonstrate that the film growth at 120°C proceeds by a self-limiting ALD growth mechanism and no copper metal film growth was observed at ≯200°C with processes employing formic acid or hydrazine. The SEM images of a film deposited under the same conditions show no cracks or pinholes and a very uniform surface. Metals such as ruthenium that can catalyze the low temperature elimination of carbon dioxide from formates may not require a reducing precursor. Source

Hollingsworth N.,University of Bath | Johnson A.L.,University of Bath | Kingsley A.,SAFC Hitech | Kociok-Kohn G.,University of Bath | Molloy K.C.,University of Bath

Reaction of ZnMe2 with 1,3-bis(dimethylamino)propan-2-ol (Hbdmap) in 2:1 ratio forms both [MeZn(bdmap)·ZnMe2] 2 (2) and [MeZn(bdmap)]3·ZnMe2 (3) depending on the concentration of the reaction. In the former, ZnMe2 is coordinated to a free N-donor of the bdmap ligand and rather more loosely to the oxygen of the alkoxide. In 3, the ZnMe2 is coordinated to two free N-donors of the bdmap ligand. 2 reacts with O2 at low temperatures with controlled insertion into one of the Zn-C bonds of the coordinated ZnMe2 group to form the peroxide [MeZn(bdmap)] 2MeZnOOMe (4). 4 decomposes slowly, and the hydroxide [MeZn(bdmap)]2MeZnOH (5) was isolated; in addition to 5, two other decomposition products have been unambiguously identified, namely, (MeZn) 5(bdmap)3O (6) and (MeZn)4(bdmap) 4ZnO (7). The formation of these species can be linked to reactions of the hydroxide (5), or its associated radical [MeZn(bdmap)] 2MeZn(O•)], with species such as ZnMe2 or MeZn(bdmap), present is solution as a result of operating Schlenk equilibria. The structure of [MeZn(bdmap)]4 (1) is also reported. © 2010 American Chemical Society. Source

Wu F.,Washington University in St. Louis | Tian L.,Washington University in St. Louis | Kanjolia R.,SAFC Hitech | Singamaneni S.,Washington University in St. Louis | Banerjee P.,Washington University in St. Louis
ACS Applied Materials and Interfaces

We demonstrate conductivity switching from a metal to semiconductor using plasmonic excitation and charge injection in Au-nanorod (AuNRs)-ZnO nanocomposite films. ZnO films 12.6, 20.3, and 35.6 nm were deposited over AuNRs using atomic layer deposition. In dark conditions, the films transitioned from metallic to semiconducting behavior between 150 and 200 K. However, under sub-bandgap, white light illumination, all films behaved as semiconductors from 80 to 320 K. Photoresponse (light/dark conductivity) was strongly dependent on the thickness of ZnO, which was 94.4 for AuNR-12.6 nm ZnO and negligible for AuNR-35.6 nm ZnO. Conductivity switching and thickness dependence of photoresponse were attributed to plasmonically excited electrons injected from AuNRs into ZnO. Activation energies for conduction were extracted for these processes. © 2013 American Chemical Society. Source

Bernal Ramos K.,University of Texas at Dallas | Saly M.J.,SAFC Hitech | Chabal Y.J.,University of Texas at Dallas
Coordination Chemistry Reviews

Deposition of thin films with desired compositions, conformality and bonding to substrates is a key component in nanotechnology research. The growth of metal films by atomic layer deposition (ALD) has become an important field of study due to its wide range of applications. However, metal deposition by ALD has not been a straightforward process for most metals. Precursor design and their reactivity with surfaces, as well as their reactions with different co-reactants, are important factors in the deposition of metals. The growth of noble metals and copper by ALD are the best-established, mainly due to their favorable reduction potentials. However, due to the lack of efficient precursors and co-reactants, the deposition of other metals has been a real challenge and just few reports have been documented. This review discusses the strategies used to achieve successful metal ALD by considering in depth the current challenges associated with the development of these processes, the crucial role that ligands play in the development of new precursors, and how molecular properties can be tuned by intelligent ligand manipulation. In addition, the deposition of some metals and their reaction mechanisms are discussed in some detail. © 2013 Elsevier B.V. Source

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