Gradient area-selective deposition for seamless gap-filling in 3D nanostructures through surface chemical reactivity control

The integration of bottom-up fabrication techniques and top-down methods can overcome current limits in nanofabrication. For such integration, we propose a gradient area-selective deposition using atomic layer deposition to overcome the inherent limitation of 3D nanofabrication and demonstrate the applicability of the proposed method toward large-scale production of materials. Cp(CH₃)₅Ti(OMe)₃ is used as a molecular surface inhibitor to prevent the growth of TiO₂ film in the next atomic layer deposition process. Cp(CH₃)₅Ti(OMe)₃ adsorption was controlled gradually in a 3D nanoscale hole to achieve gradient TiO₂ growth. This resulted in the formation of perfectly seamless TiO₂ films with a high-aspect-ratio hole structure. The experimental results were consistent with theoretical calculations based on density functional theory, Monte Carlo simulation, and the Johnson-Mehl-Avrami-Kolmogorov model. Since the gradient area-selective deposition TiO₂ film formation is based on the fundamentals of molecular chemical and physical behaviours, this approach can be applied to other material systems in atomic layer deposition.

Fabrication of GdxFeyOz films using an atomic layer deposition-type approach

The growth of complex oxide thin films with atomic precision offers bright prospects to study improved properties and novel functionalities.

Classification of processes for the atomic layer deposition of metals based on mechanistic information from density functional theory calculations

Reaction cycles for the atomic layer deposition (ALD) of metals are presented, based on the incomplete data that exist about their chemical mechanisms, particularly from density functional theory (DFT) calculations. ALD requires self-limiting adsorption of each precursor, which results from exhaustion of adsorbates from previous ALD pulses and possibly from inactivation of the substrate through adsorption itself. Where the latter reaction does not take place, an "abbreviated cycle" still gives self-limiting ALD, but at a much reduced rate of deposition. Here, for example, ALD growth rates are estimated for abbreviated cycles in H₂-based ALD of metals. A wide variety of other processes for the ALD of metals are also outlined and then classified according to which a reagent supplies electrons for reduction of the metal. Detailed results on computing the mechanism of copper ALD by transmetallation are summarized and shown to be consistent with experimental growth rates. Potential routes to the ALD of other transition metals by using complexes of non-innocent diazadienyl ligands as metal sources are also evaluated using DFT.

Modeling Mechanism and Growth Reactions for New Nanofabrication Processes by Atomic Layer Deposition

Recent progress in the simulation of the chemistry of atomic layer deposition (ALD) is presented for technologically important materials such as alumina, silica, and copper metal. Self-limiting chemisorption of precursors onto substrates is studied using density functional theory so as to determine reaction pathways and aid process development. The main challenges for the future of ALD modeling are outlined.

Theoretical study on the initial reaction mechanisms of ansa-metallocene zirconium precursor on hydroxylated Si(1 0 0) surface

The initial reaction mechanisms for depositing ZrO2 thin films using ansa-metallocene zirconium (Cp2CMe2)ZrMe2 precursor were studied by density functional theory (DFT) calculations. The (Cp2CMe2)ZrMe2 precursor could be absorbed on the hydroxylated Si(1 0 0) surface via physisorption. Possible reaction pathways of (Cp2CMe2)ZrMe2 were proposed. For each reaction, the activation energies and reaction energies were compared, and stationary points along the reaction pathways were shown. In addition, the influence of dispersion effects on the reactions was evaluated by non-local dispersion corrected DFT calculations.

Ethanol promoted titanocene Lewis acid catalyzed synthesis of quinazoline derivatives

An efficient strategy to activate air-stable Lewis acid precursor Cp₂TiCl₂ with alcoholic solvent for the rapid synthesis of quinazoline derivatives.

Solvent strategy for unleashing the Lewis acidity of titanocene dichloride for rapid Mannich reactions

The remarkable activation effect of alcohol solvent on kinetically inert titanocene dichloride was found to promote rapid three-component Mannich reactions.

Precursor directed synthesis--"molecular" mechanisms in the Soft Chemistry approaches and their use for template-free synthesis of metal, metal oxide and metal chalcogenide nanoparticles and nanostructures

This review provides an insight into the common reaction mechanisms in Soft Chemistry processes involved in nucleation, growth and aggregation of metal, metal oxide and chalcogenide nanoparticles starting from metal-organic precursors such as metal alkoxides, beta-diketonates, carboxylates and their chalcogene analogues and demonstrates how mastering the precursor chemistry permits us to control the chemical and phase composition, crystallinity, morphology, porosity and surface characteristics of produced nanomaterials.