First-Principles Study of Amorphous Al2O3 ALD Coating in Li-S Battery Electrode Design

Plasma-enhanced atomic layer deposition (ALD) of metal oxides is a rapidly gaining interest especially in the electronics industry because of its numerous advantages over the thermal process. However, the underlying reaction mechanism is not sufficiently understood, particularly regarding saturation of the reaction and densification of the film. In this work, we employ first principles density functional theory (DFT) to determine the predominant reaction pathways, surface intermediates and by-products formed when constituents of O2-plasma or O3 adsorb onto a methylated surface typical of TMA-based alumina ALD. The main outcomes are that a wide variety of barrierless and highly exothermic reactions can take place. This leads to the spontaneous production of various by-products with low desorption energies and also of surface intermediates from the incomplete combustion of –CH3 ligands. Surface hydroxyl groups are the most frequently observed intermediate and are formed as a consequence of the conservation of atoms and charge when methyl ligands are initially oxidized (rather than from subsequent re-adsorption of molecular water). Anionic intermediates such as formates are also commonly observed at the surface in the simulations. Formaldehyde, CH2O, is the most frequently observed gaseous by-product. Desorption of this by-product leads to saturation of the redox reaction at the level of two singlet oxygen atoms per CH3 group, where the oxidation state of C is zero, rather than further reaction with oxygen to higher oxidation states. We conclude that the self-limiting chemistry that defines ALD comes about in this case through the desorption by-products with partially-oxidised carbon. The simulations also show that densification occurs when ligands are removed or oxidised to intermediates, indicating that there may be an inverse relationship between Al/O coordination numbers in the final film and the concentration of chemically-bound ligands or intermediate fragments covering the surface during each ALD pulse. Therefore reactions that generate a bare surface Al will produce denser films in metal oxide ALD.

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Interaction of Hf Precursor with H2O-terminated Si(001): First Principles Study

MRS Proceedings ◽

10.1557/proc-1155-c01-05 ◽

2009 ◽

Vol 1155 ◽

Author(s):

Dae-Hyun Kim ◽

Dae-Hee Kim ◽

Hwa-Il Seo ◽

Yeong-Cheol Kim

Keyword(s):

Experimental Study ◽

First Principles ◽

Density Functional ◽

Room Temperature ◽

Atomic Layer ◽

Functional Theory ◽

The Third ◽

Layer Deposition ◽

Initial Stage ◽

Dissociation Temperature

AbstractWe investigated the reaction of HfCl4 molecules with a H2O terminated Si (001)-2×1 surface using density functional theory to understand the initial stage of atomic layer deposition (ALD) of HfO2. Half monolayer of H2O molecules were adsorbed on the buckled-down Si atoms of the Si dimers of the Si (001)-2×1 surface below the dissociation temperature of H2O and were dissociated into H and OH at room temperature. This process could make uniform and well-aligned −H and −OH’s on the Si (001) substrate. The reaction of a HfCl4 molecule was more favorable with -OH than -H. The reaction of the HfCl4 molecule with the -OH generated a HCl molecule, and the remaining HfCl3 was attached to the O atom. The first reaction of the HfCl4 molecule with −OH produced 0.21 eV energy benefit. The reaction of the second HfCl4 molecule with the most adjacent −OH of the first one produced 0.28 eV energy benefit. The third and fourth molecules showed same tendency with the first and second ones. The energy differences of the fifth and sixth HfCl4 reactions were -0.01 eV, 0.06 eV, respectively. Therefore, we found that the saturation Hf coverage was approximately 5/8 of the available −OH's, which was 2.08 × 1014 Hf/cm2. The result was well-matched with the experimental study of other group.

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Adsorption and Reaction Behaviors of Hf Precursor with Two Hydroxyls on Si(100): First Principles Study

MRS Proceedings ◽

10.1557/proc-1155-c09-14 ◽

2009 ◽

Vol 1155 ◽

Cited By ~ 1

Author(s):

Dae-Hyun Kim ◽

Dae-Hee Kim ◽

Seo Hwa-Il ◽

Ki-Young Kim ◽

Yeong-Cheol Kim

Keyword(s):

First Principles ◽

Density Functional ◽

Room Temperature ◽

Atomic Layer ◽

Energy Difference ◽

The Other ◽

Reaction Pathways ◽

Si Substrate ◽

Functional Theory ◽

Layer Deposition

AbstractDensity functional theory was used to investigate the adsorption and reaction of HfCl4 with two hydroxyls on Si (001)-2×1 surface in atomic layer deposition (ALD) process. When H2O molecules are adsorbed on Si (001) surface at room temperature, they are dissociated with hydrogens and hydroxyls. There are two dissociation pathways; inter-dimer dissociation and intra-dimer dissociation. The activation energies of these pathways can be converted to the reaction probabilities. It was approximately 2:1. We prepared a reasonable Si substrate which consisted of six inter-dimer dissociated H2O molecules and two intra-dimer dissociated H2O molecules. The HfCl4 must react with two hydroxyls to be a bulk-like structure. There were five reaction pathways where HfCl4 could react with two hydroxyls; inter-dimer, intra-dimer, cross-dimer, inter-row, and cross-row. Inter-row, inter-dimer and intra-dimer were relatively stable among the five reaction pathways based on the energy difference. The electron densities between O and Hf in these three reactions were higher than the others and they had shorter Hf-O and O-O bond lengths than the other two reaction pathways.

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First Principles Mechanistic Study of Self-Limiting Oxidative Adsorption of Remote Oxygen Plasma During the Atomic Layer Deposition of Alumina

10.26434/chemrxiv.6377372.v1 ◽

2018 ◽

Author(s):

Glen N. Fomengia ◽

Michael Nolan ◽

Simon D. Elliott

Keyword(s):

Atomic Layer Deposition ◽

First Principles ◽

Density Functional ◽

Atomic Layer ◽

Molecular Water ◽

Mechanistic Study ◽

Hydroxyl Groups ◽

Layer Deposition ◽

Surface Intermediates ◽

By Products

Plasma-enhanced atomic layer deposition (ALD) of metal oxides is a rapidly gaining interest especially in the electronics industry because of its numerous advantages over the thermal process. However, the underlying reaction mechanism is not sufficiently understood, particularly regarding saturation of the reaction and densification of the film. In this work, we employ first principles density functional theory (DFT) to determine the predominant reaction pathways, surface intermediates and by-products formed when constituents of O2-plasma or O3 adsorb onto a methylated surface typical of TMA-based alumina ALD. The main outcomes are that a wide variety of barrierless and highly exothermic reactions can take place. This leads to the spontaneous production of various by-products with low desorption energies and also of surface intermediates from the incomplete combustion of –CH3 ligands. Surface hydroxyl groups are the most frequently observed intermediate and are formed as a consequence of the conservation of atoms and charge when methyl ligands are initially oxidized (rather than from subsequent re-adsorption of molecular water). Anionic intermediates such as formates are also commonly observed at the surface in the simulations. Formaldehyde, CH2O, is the most frequently observed gaseous by-product. Desorption of this by-product leads to saturation of the redox reaction at the level of two singlet oxygen atoms per CH3 group, where the oxidation state of C is zero, rather than further reaction with oxygen to higher oxidation states. We conclude that the self-limiting chemistry that defines ALD comes about in this case through the desorption by-products with partially-oxidised carbon. The simulations also show that densification occurs when ligands are removed or oxidised to intermediates, indicating that there may be an inverse relationship between Al/O coordination numbers in the final film and the concentration of chemically-bound ligands or intermediate fragments covering the surface during each ALD pulse. Therefore reactions that generate a bare surface Al will produce denser films in metal oxide ALD.

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First-Principles Studies of Nucleation of Atomic-Layered Molybdenum Disulfide by Atomic Layer Deposition

10.18122/td.1821.boisestate ◽

2021 ◽

Author(s):

Matthew Lawson

Keyword(s):

Atomic Layer Deposition ◽

Molybdenum Disulfide ◽

First Principles ◽

Density Functional ◽

Atomic Layer ◽

Atomic Scale ◽

Half Cycle ◽

Scale Thickness ◽

Layer Deposition ◽

Nucleation Mechanisms

This dissertation implements first-principles calculations to understand the nucleation mechanisms for atomic layer deposition (ALD) of molybdenum disulfide (MoS2) using MoF6 and H2S precursors. ALD is a self-limiting process that can deposit a range of materials at the nanoscale, while maintaining chemical stoichiometry, atomic scale thickness control, and can conform to high-aspect ratio substrate designs. ALD is extremely sensitive to surface chemistry and morphology; therefore, it is critical to understand how these factors control deposition. Density functional theory (DFT) was used to understand what factors can control the nucleation for ALD of MoS2 using MoF6 and H2S. Surface hydroxyls on oxide substrates help facilitate the formation of ionic MFx (M = metal, x = 1, 2, 3) species, which thermodynamically drive the first-half cycle of ALD. DFT calculations were supported by experimental measurements to validate computational predictions. DFT and experiment both confirmed that there are different types of nucleation mechanisms during ALD of MoS2. The types of mechanisms depend on which precursor is introduced, and highlights the complexities during nucleation of MoS2 during ALD.

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First-Principles Calculations on the Geometry and Electronic Structure of Rutile TiO2 (110) Surface

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.79-82.1201 ◽

2009 ◽

Vol 79-82 ◽

pp. 1201-1204

Author(s):

Hong Bin Su ◽

Ping Yang ◽

Jin Biao Wang ◽

Nan Huang

Keyword(s):

Oxygen Vacancy ◽

Conduction Band ◽

First Principles ◽

Density Functional ◽

Surface States ◽

Atomic Layer ◽

Left Behind ◽

Lower Conduction Band ◽

Super Cell ◽

Excess Electrons

In this paper, both geometrical and electronic properties of rutile TiO2 (110) surfaces have been investigated using First-Principles Density-Functional calculations with CASTEP code, the model of stoichiometric surface is a (2x1) super-cell which has 12 atomic-layer slabs with the bottom 6 held fixed, the bridging-oxygen vacancy surface has been constructed by removing a neutral bridging oxygen atom from this surface. For the stoichiometric surface, the atom relaxations are: Ti6f (+0.2865Å), Ti5f (-0.1039Å), O3f (+0.2433Å) and Ob (+0.0075Å), we find no reconstruction and no surface states in the band gap, the density of states (DOS) is similar to the bulk except the lower conduction band intensity, in accord with recent experiments. Whereas, as a result of bridging-oxygen vacancy, the atom relaxations exchanged and reconstruction occur. The 2 excess electrons left behind removal of one bridge O atom are localized on the Ti-t2g conduction band orbitals, convert some of the Ti4+ ions into Ti3+ ions and result a compensatory shift in the Fermi level. The band gaps we calculated for stoichiometric surface is similar to the bulk, but its increase can be found for Ob vacancy surface.

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First principles study of the atomic layer deposition of alumina by TMA–H2O-process

Physical Chemistry Chemical Physics ◽

10.1039/c5cp01912e ◽

2015 ◽

Vol 17 (26) ◽

pp. 17322-17334 ◽

Cited By ~ 47

Author(s):

Timo Weckman ◽

Kari Laasonen

Keyword(s):

Atomic Layer Deposition ◽

First Principles ◽

Reaction Mechanisms ◽

Density Functional ◽

Atomic Layer ◽

Functional Study ◽

Density Functional Study ◽

First Principles Study ◽

Layer Deposition

A comprehensive density functional study on the reaction mechanisms during the atomic layer deposition of alumina via trimethylaluminium–waterprocess.

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A Rare Low Spin Co(IV) Bis-Silyldiamide with High Thermal Stability: Exploring the Origin of an Unusual S = 1/2 Configuration

10.26434/chemrxiv.11691825.v2 ◽

2020 ◽

Author(s):

David Zanders ◽

Goran Bačić ◽

Dominique Leckie ◽

Oluwadamilola Odegbesan ◽

Jeremy M. Rawson ◽

...

Keyword(s):

Thermal Stability ◽

Density Functional ◽

Atomic Layer ◽

Epr Spectrum ◽

Functional Theory ◽

Cluster Calculations ◽

Layer Deposition ◽

Starting Point ◽

Higher Spin ◽

Surface Saturation

Attempted preparation of a chelated Co(II) β-silylamide re-sulted in the unprecedented disproportionation to Co(0) and a spirocyclic cobalt(IV) bis(β-silyldiamide): [Co[(NtBu)2SiMe2]2] (1). Compound 1 exhibits a room temperature magnetic moment of 1.8 B.M and a solid state axial EPR spectrum diagnostic of a rare S = 1/2 configuration. Semicanonical coupled-cluster calculations (DLPNO-CCSD(T)) revealed the doublet state was clearly preferred (–27 kcal/mol) over higher spin configurations for which density functional theory (DFT) showed no energetic preference. Unlike other Co(IV) complexes, 1 had remarkable thermal stability, and was demonstrated to form a stable self-limiting monolayer in initial atomic layer deposition (ALD) surface saturation tests. The ease of synthesis and high-stability make 1 an attractive starting point to begin investigating otherwise inaccessible Co(IV) intermediates and synthesizing new materials.

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First-Principles Evaluation of the Potential of Borophene as a Monolayer Transparent Conductor

10.26434/chemrxiv.5439880 ◽

2017 ◽

Author(s):

Lyudmyla Adamska ◽

Sridhar Sadasivam ◽

Jonathan J. Foley ◽

Pierre Darancet ◽

Sahar Sharifzadeh

Keyword(s):

First Principles ◽

Density Functional ◽

State Of The Art ◽

Transparent Electrode ◽

Visible Range ◽

Two Dimensional ◽

Transparent Conductor ◽

Many Body ◽

Functional Theory ◽

Many Body Perturbation Theory

Two-dimensional boron is promising as a tunable monolayer metal for nano-optoelectronics. We study the optoelectronic properties of two likely allotropes of two-dimensional boron using first-principles density functional theory and many-body perturbation theory. We find that both systems are anisotropic metals, with strong energy- and thickness-dependent optical transparency and a weak (<1%) absorbance in the visible range. Additionally, using state-of-the-art methods for the description of the electron-phonon and electron-electron interactions, we show that the electrical conductivity is limited by electron-phonon interactions. Our results indicate that both structures are suitable as a transparent electrode.

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