The need for the conformal deposition of TiO 2 thin films in device fabrication has motivated a search for thermally robust titania precursors with noncorrosive byproducts. Alkylamido-cyclopentadienyl precursors are attractive because they are readily oxidized, yet stable, and afford environmentally mild byproducts. We have explored the deposition of TiO 2 films on OH-terminated SiO 2 surfaces by in situ Fourier transform infrared spectroscopy using a novel titanium precursor [(EtCp)-Ti(NMe 2 ) 3 (1), Et = CH 2 CH 3 ] with either ozone or water. This precursor initially reacts with surface hydroxyl groups at ≥150 °C through the loss of its NMe 2 groups. However, once the precursor is chemisorbed, its subsequent reactivities toward ozone and water are very different. There is a clear reaction with ozone, characterized by the formation of monodentate formate and/or chelate bidentate carbonate surface species; in contrast, there is no detectable reaction with water. For the ozone-based ALD process, the surface formate/carbonate species react with the NMe 2 groups during the subsequent pulse of 1, forming TiOTi bonds. Ligand exchange is observed within the 250−300 °C ALD window. X-ray photoelectron spectroscopy confirms the deposition of stoichiometric TiO 2 films with no detectable impurities. For the water-based process, ligand exchange is not observed. Once 1 is adsorbed, there is no spectroscopic evidence for further reaction. However, there is still TiO 2 deposition under typical ALD conditions. Co-adsorption experiments with controlled vapor pressures of water and 1 indicate that deposition arises solely from 1/water gas-phase reactions. This striking lack of reactivity between chemisorbed 1 and water is attributed to the electronic and steric effects of the EtCp group and facilitates the observation of gas-phase reactions.

Thermal atomic layer etching (ALE) is an emerging technique that involves the sequential removal of monolayers of a film by alternating self-limiting reactions, some of which generate volatile products. Although traditional ALE processes rely on the use of plasma, several thermal ALE processes have recently been developed using hydrogen fluoride (HF) with precursors such as trimethylaluminum (TMA) or tin acetylacetonate. While HF is currently the most effective reagent for ALE, its potential hazards and corrosive nature have motivated searches for alternative chemicals. Herein, we investigate the feasibility of using fluoroform (CHF 3 ) with TMA for the thermal ALE of SiO 2 and Al 2 O 3 surfaces and compare it to the established TMA/HF process. A fundamental mechanistic understanding is derived by combining in situ Fourier transform infrared spectroscopy, ex situ X-ray photoemission spectroscopy, ex situ low-energy ion scattering, and ex situ spectroscopic ellipsometry. Specifically, we determine the role of TMA, the dependence of the etch rate on precursor gas pressure, and the formation of a residual fluoride layer. Although CHF 3 reacts with TMA-treated oxide surfaces, etching is hindered by the concurrent deposition of a fluorinecontaining layer, which makes it unfavorable for etching. Moreover, since fluorine contamination can be deleterious to device performance and its presence in thin films is an inherent problem for established ALE processes using HF, we present a novel method to remove the residual fluorine accumulated during the ALE process by exposure to water vapor. XPS analysis herein reveals that an Al 2 O 3 film etched using TMA/HF at 325 °C contains 25.4 at. % fluorine in the surface region. In situ exposure of this film to water vapor at 325 °C results in ∼90% removal of the fluorine. This simple approach for fluorine removal can easily be applied to ALE-treated films to mitigate contamination and retain surface stoichiometry.

Managing deposition of multilayered nanocrystal quantum dot (NQD) thin films is crucial for future photonic devices to maximize solar energy extraction efficiency. Solution-based NQD deposition methods require additional protection to achieve a discrete layered structure and to prevent optical degradation during processing. An attractive method to passivate and protect NQD films is overcoating with metal oxides, usually grown using atomic layer deposition (ALD). However, a significant quenching of NQD photoluminescence (PL) is typically observed after encapsulation, hindering performance and applicability. Here, we demonstrate a modified gas-phase deposition technique that fully passivates NQD assemblies and, in contrast to standard ALD, maintains PL properties. Combined in situ FTIR and ex situ XPS measurements reveal that upon Al2O3 deposition by ALD, the metal precursor trimethylaluminum (TMA) interacts with oleic acid-capped CdSe–CdS–ZnS core–shell-shell NQDs by reorganizing the ligands and replacing Zn atoms with Al. This modification leads to PL quenching, particularly severe at elevated temperatures (∼100 °C). In contrast, simultaneous exposures of both precursors (TMA and water) lead to metal oxide deposition from gas-phase reactions taking place in the immediate vicinity of the NQD surface, without affecting the chemical nature of the NQDs. Contrary to ALD, this technique retains and even improves NQDs’ photoluminescence, observed as increased PL intensities and longer lifetimes.

Aminosilanes are attractive precursors for atomic layer deposition of silicon oxides and nitrides because they are halide-free and more reactive than chlorosilanes. However, the deposition of silicon nitride on oxide substrates still requires relatively high temperatures. We show here that for a process involving disec-butylaminosilane and hydrazine, the insertion of Al from trimethyl aluminum allows the deposition of silicon nitride films at relatively low temperatures (250 °C). Firstprinciples calculations reveal that the presence of Al increases the binding of molecular hydrazine, thereby effectively enhancing the reactivity of hydrazine with the silicon precursor during the atomic layer deposition process, which leads to nitrogen incorporation into silicon. However, the range of this enhancement is limited to ∼1 nm, requiring additional trimethylaluminum exposures to continue the Si 3 N 4 deposition.

The electrochemical properties of oxygen-deficient tungsten oxide (W 18 O 49 ) nanowires were investigated. The nanowires were prepared via a simple thermal evaporation method. The as-deposited nanowires were 60-90 nm in diameter and several micrometers long as measured by fieldemission scanning electron microscopy. The crystal structure was indexed to the monoclinic W 18 O 49 phase. The electrochemical properties of the nanowires and WO 3 bulk particles were examined by cyclic voltammetry between 2 and 4 V vs Li/Li þ . We found that the nanowires cycle better than the bulk particles. #