In-situ optical view onto copper oxidation – role of reactive interfaces and self-heating

Maack, Björn; Nilius, Niklas

doi:10.1016/j.corsci.2019.108112

Cited by 18 publications

(25 citation statements)

References 44 publications

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“…Although the statistical basis of our study is small, a corresponding plot seems to support this relation. Our reasoning is supported by the activation energy for Cu oxidation, as derived from the temperature‐dependent reaction rates discussed in our earlier work . The deduced barrier height of 35 kJ mol −1 is in good agreement with grain boundary diffusion yet much lower than for bulk diffusion.…”

Section: Resultssupporting

confidence: 83%

“…The deduced barrier height of 35 kJ mol −1 is in good agreement with grain boundary diffusion yet much lower than for bulk diffusion. A particular role of grain boundaries was also suggested from transmission electron microscopy data that successfully visualized the preferred copper oxidation along boundary defects . Finally, we have tested a possible interplay between measured oxidation rates and surface roughness of the five different Cu samples; however, could not reveal a convincing relationship (Figure c).…”

Section: Resultsmentioning

confidence: 94%

“…The spectra were fitted with a user‐programmed software to appropriate three‐layer models of the sample, composed of a homogenous Cu 2 O top, a Cu bottom, and a Cu 2 O–Cu mixed layer in between (Figure ) . The interfacial layer accounts for an inhomogeneous metal‐oxide reaction front and mimics an oxidation process that proceeds along grain boundaries of the material . The boundaries were modeled with the Bruggeman mean‐field approach, either as percolated Cu 2 O chains in copper or Cu percolations in Cu 2 O at the beginning and end of the reaction, respectively.…”

Section: Resultsmentioning

confidence: 99%

“…To analyze the oxidation kinetics in more detail, each spectrum of an experimental run has been fitted to the Cu 2 O/Cu 2 O–Cu/Cu three‐layer model shown in Figure f. It should be noted once more that the mixed layer in the center of the slab has been introduced to describe oxidation along the grain boundaries of the film, as discussed in our earlier work . To visualize the level of agreement between experiment and simulation, two arbitrarily selected spectra from each series in Figure a–c are shown together with their best fits in Figure a–c.…”

Section: Resultsmentioning

confidence: 99%

“…However, no deterioration of the experimental results was expected in this case, as copper is chemically inert at room temperature and only roughness and granularity of the films but not the true atomic configuration was in the focus of the measurements. Further details of the setup can be found in the literature …”

Section: Methodsmentioning

confidence: 99%

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Impact of Granularity on the Oxidation Kinetics of Copper

Maack

Nilius

2020

Physica Status Solidi (b)

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Polycrystalline copper films with mean grain sizes varying by three orders of magnitude are prepared to correlate morphology and oxidation kinetics of metals. The films are oxidized to cuprous oxide at well‐defined pressure and temperature conditions, monitoring the progress of the reaction by in situ optical transmission spectroscopy. The oxidation kinetics is retrieved by fitting the optical data to a three‐layer Cu2O/Cu2O–Cu/Cu model with the central layer accounting for the inhomogeneity of the oxidation front due to grain boundaries. The analysis reveals the highest oxidation rates for Cu films with finest granularity, demonstrating the decisive role of grain boundaries for Cu mass transport during oxidation. Moreover, reaction rates are found to differ by one order of magnitude for oxidation along the grain boundaries and into the crystalline Cu grains. In fact, slow oxidation into the Cu crystallites is responsible for an incomplete metal‐oxide conversion in the case of coarse‐granular films. The experiments demonstrate the direct interplay between morphology and oxidation kinetics for metals.

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Section: Resultssupporting

confidence: 83%

Section: Resultsmentioning

confidence: 94%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Impact of Granularity on the Oxidation Kinetics of Copper

Maack

Nilius

2020

Physica Status Solidi (b)

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Fitting A Square Peg into A Round Hole: Shape Control in Phase Transfer of Cubic Gold Nanoparticles

et al. 2021

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Although nanomaterials are widely involved in technological applications, common synthetic recipes for such colloids are restricted to special, optimized conditions, particularly for anisotropic shapes. Ligand exchange is frequently necessary for further functionalization. While such protocols are well established for spherical particles, it is more demanding to keep the corpus for thermodynamically less stable shapes. We highlight the temperature as one key for the formation of anisotropic gold nanoparticles, but also for ligand exchange protocols under shape retention or deliberate reshaping at the example of gold nanocubes. In the first part, the synthesis of CTAB capped gold nanocubes in aqueous solution is examined highlighting the narrow temperature window in which selective adsorption site blocking by bromide ions leads to the formation of gold nanocubes. While too low temperatures yield multiple particle shapes due to a low surface mobility, temperatures above the appropriate window result in more thermodynamically favored shapes. Furthermore, two protocols are presented for the exchange of the ammonium ligand CTAB by oleylamine as an organic amine including water removal from a slurrish water‐amine paste through the gas phase. In turn, precise temperature control allows to either maintain the cubic shape or induce a reshaping process towards other, thermodynamically preferred shapes such as for example truncated octahedra.

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Morphological and Kinetic Insights into Cu₂O–CuO Oxidation

Maack

Nilius

2019

Physica Status Solidi (b)

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The conversion of Cu2O to CuO thin films is probed in situ with UV–vis transmission spectroscopy at various thermodynamic conditions. The obtained spectral series are simulated with different CuO/Cu2O growth models, using the transfer‐matrix method and Bruggeman's mean‐field approach to account for Cu residuals in the oxide matrix. The analysis reveals that Cu2O oxidation proceeds via a flat and homogeneous reaction front, in contrast to polycrystalline copper that preferentially oxidizes along the grain boundaries. The conclusion is supported by the measured activation energy for Cu2O oxidation, which is compatible with Cu diffusion via the bulk oxide and not via line defects. The kinetics of CuO growth is found to follow logarithmic and exponential rate laws at low and high temperature, respectively. While the logarithmic regime is governed by CuO nucleation within the Cu2O phase, the exponential dependence results from self‐heating of the sample in the exothermic reaction. In both cases, traces of unreacted copper are detected in the oxide matrix, giving rise to a characteristic tail in the transmission response.

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In-situ optical view onto copper oxidation – role of reactive interfaces and self-heating

Cited by 18 publications

References 44 publications

Impact of Granularity on the Oxidation Kinetics of Copper

Impact of Granularity on the Oxidation Kinetics of Copper

Fitting A Square Peg into A Round Hole: Shape Control in Phase Transfer of Cubic Gold Nanoparticles

Morphological and Kinetic Insights into Cu₂O–CuO Oxidation

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In-situ optical view onto copper oxidation – role of reactive interfaces and self-heating

Cited by 18 publications

References 44 publications

Impact of Granularity on the Oxidation Kinetics of Copper

Impact of Granularity on the Oxidation Kinetics of Copper

Fitting A Square Peg into A Round Hole: Shape Control in Phase Transfer of Cubic Gold Nanoparticles

Morphological and Kinetic Insights into Cu2O–CuO Oxidation

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Morphological and Kinetic Insights into Cu₂O–CuO Oxidation