| 1. |
- D'acunto, Giulio, et al.
(författare)
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Bimolecular Reaction Mechanism in the Amido Complex-Based Atomic Layer Deposition of HfO2
- 2023
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 35:2, s. 529-538
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Tidskriftsartikel (refereegranskat)abstract
- The surface chemistry of the initial growth during the first or first few precursor cycles in atomic layer deposition is decisive for how the growth proceeds later on and thus for the quality of the thin films grown. Yet, although general schemes of the surface chemistry of atomic layer deposition have been developed for many processes and precursors, in many cases, knowledge of this surface chemistry remains far from complete. For the particular case of HfO2 atomic layer deposition on a SiO2 surface from an alkylamido-hafnium precursor and water, we address this lack by carrying out an operando atomic layer deposition experiment during the first cycle of atomic layer deposition. Ambient-pressure X-ray photoelectron spectroscopy and density functional theory together show that the decomposition of the metal precursor on the stoichiometric SiO2 surface in the first half-cycle of atomic layer deposition proceeds via a bimolecular reaction mechanism. The reaction leads to the formation of Hf-bonded methyl methylene imine and free dimethylamine. In addition, ligand exchange takes place involving the surface hydroxyls adsorbed at defect sites of the SiO2 surface.
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| 2. |
- D’Acunto, Giulio, et al.
(författare)
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Oxygen relocation during HfO2 ALD on InAs
- 2022
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Ingår i: Faraday Discussions. - : Royal Society of Chemistry (RSC). - 1359-6640 .- 1364-5498. ; 236, s. 71-85
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Tidskriftsartikel (refereegranskat)abstract
- Atomic layer deposition (ALD) is one of the backbones for today’s electronic device fabrication. A critical property of ALD is the layer-by-layer growth, which gives rise to the atomic-scale accuracy. However, the growth rate - or growth per cycle - can differ significantly depending on the type of system, molecules used, and several other experimental parameters. Typically, ALD growth rates are constant in subsequent ALD cycles, making ALD an outstanding deposition technique. However, contrary to this steady-state - when the ALD process can be entirely decoupled from the substrate on which the material is grown - the deposition’s early stage does not appear to follow the same kinetics, chemistry, and growth rate. Instead, it is to a large extent determined by the surface composition of the substrate. Here, we present evidence of oxygen relocation from the substrate-based oxide, either the thermal or native oxide of InAs, to the overlayer of HfO2 in the initial ALD phase. This phenomenon enables control of the thickness of the initial ALD layer by controlling the surface conditions of the substrate prior to ALD. On the other hand, we observe a complete removal of the native oxide from InAs already during the first ALD half-cycle, even if the thickness of the oxide layer exceeds one monolayer, together with a self-limiting thickness of the ALD layer of a maximum of one monolayer of HfO2. These observations not only highlight several limitations of the widely used ligand exchange model, but they also give promise for a better control of the industrially important self-cleaning effect of III-V semiconductors, which is crucial for future generation high-speed MOS.
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| 3. |
- D'Acunto, Giulio, et al.
(författare)
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Role of Temperature, Pressure, and Surface Oxygen Migration in the Initial Atomic Layer Deposition of HfO2on Anatase TiO2(101)
- 2022
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 126:29, s. 12210-12221
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Tidskriftsartikel (refereegranskat)abstract
- The atomic layer deposition of HfO2on a TiO2(101) surface from tetrakis(dimethylamido)hafnium and water is investigated using a combination of in situ vacuum X-ray photoelectron spectroscopy (XPS) and time-resolved ambient pressure XPS. Precursor pressures and surface temperature are tuned as to map the space state of the deposition. In the initial stages of ALD, a reaction mechanism based on dissociative adsorption dominates over a classic ligand exchange mechanism, typically evoked when metal-amido complexes and water are used as the precursors for metal oxide ALD. Surface species, including a dimethyl ammonium ion and an imine, are identified. It is found that they can be formed only if the active role of the TiO2(101) surface is taken into consideration. The temperature of the surface enhances the formation of these species based on an insertion reaction of a hydrogen atom, which then assists the formation of more than the expected monolayer of HfO2. A HfO2overlayer is produced already during the first half-cycle, enabled by a reduction of the TiO2support. Dosing water at high pressure allows hydroxyl formation, which marks the transition toward a well-described ligand exchange reaction type. From the experiments performed, we find that the ALD of HfO2at room temperature, performed at high pressure, is mainly based on dissociation and that no side reaction occurs. These insights into the ALD reaction mechanism highlight how in situ studies can help understand how deposition parameters affect the growth of HfO2and how the ALD model for transition metal oxide formation from amido complexes and water can be extended.
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| 4. |
- D'Acunto, Giulio, et al.
(författare)
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Time evolution of surface species during the ALD of high-k oxide on InAs
- 2023
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Ingår i: Surfaces and Interfaces. - 2468-0230. ; 39:102927
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Tidskriftsartikel (refereegranskat)abstract
- Understanding the reaction mechanisms involved during the early stage of atomic layer deposition (ALD) of HfO2 on InAs is a key requirement for improving interfaces in III-V semiconductor-based devices. InAs is an excellent candidate to outperform silicon regarding speed and power consumption, and combined with HfO2, it gives promise for a new generation of ultra-fast MOSFETs. However, an improved interface quality and in-depth understanding of the involved surface species are needed. Here, we use in situ and operando ambient pressure XPS to follow in real-time the reaction mechanisms which control the ALD chemistry. Besides the removal of all unwanted oxide from the III-V, the same oxygen atoms are found to form HfOx already from the first half-cycle. In contrast to the standard ALD model, no hydroxyl groups are needed on the InAs surface. Furthermore, we observe an insertion reaction forming unexpected surface species. The second ALD half-cycle allows the immediate removal of all organic species leaving behind a uniform HfO2 layer partially terminated by hydroxyl groups. We find that prolonged exposure times upon both half-cycles guarantee a sharp InAs/HfO2 interface. Such an improved interface is an important step towards fast and sustainable III-V semiconductor-based electronics.
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| 5. |
- Johansson, Niclas, et al.
(författare)
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Sonogashira cross-coupling over Au(1 1 1): from UHV to ambient pressure
- 2017
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Ingår i: Journal of Physics: Condensed Matter. - 1361-648X. ; 29:44
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Tidskriftsartikel (refereegranskat)abstract
- We have studied the reaction of phenylacetylene (PA) with chloro-, bromo-, and iodobenzene on the Au(1 1 1) surface as a model system for the gold-catalysed Sonogashira cross-coupling. Both ultrahigh vacuum-based and ambient pressure x-ray photoelectron spectroscopy show that iodo- and chlorobenzene (IB and CB) undergo the cross-coupling reaction towards diphenylacetylene. Bromobenzene (BB), in contrast, does not react in the UHV experiments. Further, at ambient pressure signs are found for poisoning of the Au(1 1 1) surface by a carbon species formed in the reaction. The understanding obtained in the reaction experiments are based on a thorough investigation of the adsorption of PA, IB, CB, and BB on the Au(1 1 1) surface by soft x-ray absorption spectroscopy and temperature-dependent x-ray photoelectron spectroscopy. In particular, the experiments provide the orientation of the intact adsorbates with respect to the surfaces at liquid nitrogen temperature. Dissociation in the temperature regime between −80 and −15 °C is observed for iodo- and chlorobenzene, but not for BB, in agreement with that only IB and CB, but not BB, react with PA to form diphenylacetylene. The difference is tentatively attributed to a difference in surface orientation of the different halobenzenes.
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| 6. |
- Jones, Rosemary, et al.
(författare)
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AP-XPS Study of Ethanol Adsorption on Rutile TiO2(110)
- 2022
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 126:39, s. 16894-16902
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Tidskriftsartikel (refereegranskat)abstract
- The photoactivity of rutile TiO2(110) renders its surfaces of particular interest for the study of surface reactions. In particular, rutile TiO2(110) surfaces are active for hydrogen production, both via the water splitting process and via ethanol degradation under ultraviolet illumination. The selective photocatalytic dehydrogenation of rutile TiO2(110) is not fully understood yet, and an important question in this context is how ethanol adsorbs onto the rutile TiO2(110) surface under ambient conditions. Here, we present the first in situ experimental study on the absorption of ethanol on rutile TiO2(110) at room temperature and near-ambient conditions. The surface sensitivity of synchrotron-based ambient pressure X-ray photoelectron spectroscopy allows for an in-depth analysis of the surface species (molecular ethanol and ethoxies) and their coverage as well as an estimation of the energy difference between the two species. Through modeling of the O 1s core level and comparison to experimental results we show that both molecular and dissociative adsorption of ethanol occurs. The difference in adsorption energy range calculated from modeling of the O 1s core level was 0.018-0.033 eV, with dissociative adsorption the most energetically favorable. The difference in adsorption energy is almost an order of magnitude lower than previous estimations from theoretical calculations. In addition, we show that at room temperature a multilayer is formed with increasing pressure of ethanol.
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| 7. |
- Jones, Rosemary, et al.
(författare)
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Operando study of HfO2 atomic layer deposition on partially hydroxylated Si(111)
- 2024
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Ingår i: Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films. - 0734-2101. ; 42:2
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Tidskriftsartikel (refereegranskat)abstract
- The introduction of atomic layer deposition (ALD), to the microelectronics industry has introduced a large number of new possible materials able to be deposited in layers with atomic thickness control. One such material is the high-κ oxide HfO2; thermally stable and ultrathin HfO2 films deposited by ALD are a significant contender to replace SiO2 as the gate oxide in capacitor applications. We present a mechanistic study of the first deposition cycle of HfO2 on the Si(111) surface using tetrakis(dimethylamido) hafnium (TDMAHf) and water as precursors using operando ambient pressure x-ray photoelectron spectroscopy. Here, we show that the hydroxylation of the clean Si(111) surface by residual water vapor, resulting in a 0.3 monolayer coverage of hydroxyls, leads to instantaneous full surface coverage of TDMAHf. The change in the atomic ratio of Hf to C/N found during the first deposition half-cycle, however, does not match the assumed immediate ligand loss through reaction with surface hydroxyls. One would expect an immediate loss of ligands, indicated by a Hf:N ratio of approximately 1:3 as TDMAHf deposits onto the surface; however, a Hf:N ratio of 1:3.6 is observed. The partial hydroxylation on the Si(111) surface leads to binding through the TDMAHf ligand N atoms resulting in both N and CH3 being found remaining on the surface post water half-cycle. Although there is evidence of ligand exchange reactions occurring at Si-OH sites, it also seems that N binding can occur on bare Si, highlighting the complexity of the substrate/precursor reaction even when hydroxyls are present. Moreover, the initial low coverage of Si-OH/Si-H appears to severely limit the amount of Hf deposited, which we hypothesize is due to the specific geometry of the initial arrangement of Si-OH/Si-H on the rest- and adatoms.
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| 8. |
- Majeed, Maitham H., et al.
(författare)
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A PdII Carbene Complex with Anthracene Side-Arms for π-Stacking on Reduced Graphene Oxide (rGO) : Activity towards Undirected C–H Oxygenation of Arenes
- 2018
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Ingår i: European Journal of Inorganic Chemistry. - : Wiley. - 1434-1948 .- 1099-0682. ; 2018:43, s. 4742-4746
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Tidskriftsartikel (refereegranskat)abstract
- An N-heterocyclic carbene palladium(II) complex containing two anthracene side arms was immobilized on the surface of reduced graphene oxide (rGO) by π-stacking. The activity of the homogeneous analogue and the supported complex in undirected C–H acetoxylation reaction of arenes was studied. The results show that the catalytic efficiency in acetoxylation of benzene is improved in the immobilized materials compared to the homogeneous analogue. According to XPS analysis, the immobilized catalyst maintains the original oxidation state of PdII after the catalytic reaction.
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| 9. |
- Majeed, Maitham H, et al.
(författare)
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Directed C-H Halogenation Reactions Catalysed by PdII Supported on Polymers under Batch and Continuous Flow Conditions
- 2019
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Ingår i: Chemistry: A European Journal. - : Wiley. - 1521-3765 .- 0947-6539. ; 25:59, s. 13591-13597
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Tidskriftsartikel (refereegranskat)abstract
- A new generation of N-heterocyclic carbene palladium(II) complexes containing vinyl groups in different positions in the backbone of the N-heterocycle have been developed. The fully characterised monomers were copolymerised with divinylbenzene to fabricate robust polymer supported NHC-PdII complexes and these polymers were applied as heterogeneous catalysts in directed C-H halogenation of arenes with a pyridine-type directing group. The catalysts demonstrated medium-high catalytic activity with up to 90 % conversion and 100 % selectivity in chlorination. They are heterogeneous and recyclable (at least six times) with no significant leaching of palladium in batch mode catalysis. The best catalyst was also applied under continuous flow conditions where it disclosed an exceptional activity (90 % conversion) and 100 % selectivity for the mono-halogenated product for at least six days, with no leaching of palladium, no loss of activity and an ability to maintain the original oxidation state of PdII .
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| 10. |
- Majeed, Maitham H., et al.
(författare)
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Polymer-Supported Palladium(II) Carbene Complexes : Catalytic Activity, Recyclability, and Selectivity in C-H Acetoxylation of Arenes
- 2017
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539. ; 23:35, s. 8457-8465
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Tidskriftsartikel (refereegranskat)abstract
- Heterogeneous catalysts for selective oxidation of C-H bonds were synthesized by co-polymerization of new N-heterocyclic carbene-palladium(II) (NHC-PdII) monomers with divinylbenzene. The polymer-supported NHC-PdII-catalysed undirected C-H acetoxylation of simple and methylated arenes as well as polyarenes, with similar or superior efficiency compared to their homogeneous analogues. In particular, the regioselectivity has been improved in the acetoxylation of biphenyl and naphthalene compared to the best homogeneous catalysts. The new polymer-supported catalysts maintain the original oxidation state of PdII after repeated catalytic reactions, and exhibit no significant leaching of palladium. In addition, the new catalysts have been successfully recovered and reused without loss of activity over several cycles of reactions.
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