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Project

Chemisorption reaction mechanisms for ruthenium atomic layer deposition (ALD): an atomistic insight.

In this thesis, we have explored and applied different computational techniques, i.e. density functional theory (DFT), multiconfigurational perturbation, coupled cluster, and density matrix renormalization group (DMRG) methods in order to solve different chemical problems of transition metal (TM) complexes.

In gas phase, we have established a general procedure using high-quality ab initio methods to efficiently study binding energies of metallocene-based complexes. First, the heterolytic dissociation enthalpy in gas phase of a series of first-row metallocenes M(C5H5)2 (MCp2) (M = V, Mn, Fe, and Ni), was studied by (restricted) multiconfigurational perturbation theory and DFT. The results were compared directly to the experimental values, taking into account all necessary contributions to the relative energy. Using ab initio methods, i.e. multiconfigurational perturbation theory (CASPT2, RASPT2, NEVPT2) and restricted coupled cluster theory (CCSD(T)) we extended the work to study the bond dissociation energy in gas phase of a series of metallocenium ions MCp2+ (with M = Ti, V, Cr, Mn, Fe, Co, and Ni). From a comparison between the results obtained from these different methods, and a detailed analysis of their treatment of electron correlation effects, a set of MCp+-Cp binding energies were proposed with an accuracy of 5 kcal/mol. The computed results are in good agreement with the experimental data measured by threshold photoelectron photoion coincidence (TPEPICO) spectroscopy. Applying the general procedure used for the first-row transition metals, we reported a comparative study of the heterolytic and hemolytic dissociation enthalpy in gas phase of two ruthenium complexes served as precursors for Ru ALD, employing both DFT and CASPT2. While both methods predict distinctly different absolute dissociation enthalpies, they agree on the more pronounced stability of the Cp- ligand in RuCpPy (Py=pyrollyl) than in RuCp2.

We also combined high-quality ab initio calculations (CASPT2, RASPT2, and CCSD(T)) in gas phase with DFT results in protein to provide reliable spin state energetics of the [NiFe] hydrogenase. We studied the geometry and singlet-triplet energy difference of two mono-nuclear Ni2+ models related to the active site in the [NiFe] hydrogenase. The singlet state is only ~5.7 kcal/mol more stable than the triplet state, predicted by combining TPSS/MM calculations with accurate CCSD(T) calculations in gas phase.

We finally explored one of the most promising novel methods to treat strongly correlated systems, known as density matrix renormalization group (DMRG-(PT2)). This method was used to study the relative energies between different states of iron-porphyrin models FeL2, Fe(P), and manganese-oxo porphyrin MnO(P)+. We showed that DMRG-PT2 can be a good alternative for CASPT2 with small- and medium-sized active spaces. A more extensive work of DMRG-PT2 will be done in order to better understand its potential and accuracy to study spin state energetics of TM complexes.

On solid surfaces, we have provided atomistic insights into the deposition of ruthenium complexes involved in atomic layer deposition (ALD) by studying the reaction mechanisms using DFT. We studied the reaction mechanism of the two Ru precursors RuCp2 and RuCpPy on different solid surfaces, in order to explain their different behavior in the ALD experiments. We first investigated the adsorption of RuCp2 and RuCpPy on a TiN surface, in combination with experiments based on Rutherford backscattering spectroscopy (RBS). The calculations demonstrated that the RuCpPy precursor chemisorbs on the TiN(100) surface while the RuCp2 precursor only physisorbs. By investigating the reaction mechanisms on bare ruthenium surfaces, i.e., (001), (101), and (100), and H-terminated surfaces, a full picture of Ru ALD was then provided. The calculated results showed that on the Ru surfaces, both RuCp2 and RuCpPy can undergo dehydrogenation and ligand dissociation reactions. Furthermore, RuCpPy is more reactive than RuCp2.

Date:1 Oct 2012 →  30 Sep 2016
Keywords:ALD, Ruthenium, DFT, Mechanism
Disciplines:Biochemistry and metabolism, Medical biochemistry and metabolism, Physical chemistry, Theoretical and computational chemistry, Other chemical sciences, Manufacturing engineering, Safety engineering
Project type:PhD project