Exoelectron emission from magnesium surfaces

Klar, F.; Bansmann, Joachim; Glaefeke, H.; Fitting, H.‐J.; Meiwes‐Broer, Karl‐Heinz

doi:10.1016/s0039-6028(99)00965-6

Cited by 9 publications

(5 citation statements)

References 23 publications

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“…Fortunately, the oxidation of metal surfaces includes reaction steps, e.g., the dissociation, which may occur non-adiabatically on a very short time scale. As a consequence, the reaction excites electron-hole (e-h) pairs in the metal leading to external and internal exoelectron emission [29][30][31][32]. The chemicurrent method allows the detection of chemically induced hot charge carriers [33][34][35].…”

Section: Introductionmentioning

confidence: 99%

Quantum size effects in chemicurrent measurements during low-temperature oxidation of Mg(0001) epilayers

Hagemann

Nienhaus

2014

New J. Phys.

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The reactivity of Mg epilayers on Si(111)-7 × 7 towards molecular oxygen is investigated as a function of the metal film thickness in the range between 7 and 45 monolayers. Quantum well and surface states are characterized with ultraviolet photoelectron spectroscopy demonstrating the epitaxial and single-crystalline structure of the Mg films. The oxidation rate is monitored during the reaction by measuring chemicurrents at 110 K in the Mg/p-Si(111) Schottky diodes due to the non-adiabatic character of at least one step in the reaction chain. For film thicknesses around 9 and 13 monolayers the chemicurrent transients demonstrate that the reaction rate is strongly enhanced by a factor of more than two. With Mg 2p core level spectroscopy, a similar enhancement can be found for the total oxygen uptake for long exposures indicating that the chemicurrent increase measures solely a quantum size effect on the reactivity and no device-related effects. The enhanced reactivity can be explained by the increased first charge transfer into the affinity level of the approaching molecule when a quantum well state appears at the Fermi level and increases the density of electronic states. A linear relationship between the photoelectron intensity at the Fermi level and the maximum chemicurrent is clearly observed. On the other hand, the surface work function and the Schottky barrier height exhibit almost no correlation with the enhanced reactivity.

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Section: Introductionmentioning

confidence: 99%

Quantum size effects in chemicurrent measurements during low-temperature oxidation of Mg(0001) epilayers

Hagemann

Nienhaus

2014

New J. Phys.

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“…DOI The interaction of oxygen molecules with uncovered reactive metal surfaces deposits energies of typically a few electron volts per reaction on the surface [1,2]. The chemical energy that is dissipated nonadiabatically becomes evident by exoelectron emission (EEE) into vacuum and surface chemiluminescence (SCL) [3][4][5][6][7][8][9]. The oxidation of clean Mg surfaces is an example for EEE and SCL [4,[7][8][9].…”

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confidence: 99%

“…The chemical energy that is dissipated nonadiabatically becomes evident by exoelectron emission (EEE) into vacuum and surface chemiluminescence (SCL) [3][4][5][6][7][8][9]. The oxidation of clean Mg surfaces is an example for EEE and SCL [4,[7][8][9]. Upon oxygen exposure, the chemisorptive emission of electrons from Mg is delayed.…”

mentioning

confidence: 99%

“…Thus, the chemicurrents are not influenced by any potential barrier change as in the case of EEE. Figure 1(b) shows three chemicurrent transients recorded at Mg=p-Si111 Schottky diodes with metal VOLUME 93, NUMBER 16 P H Y S I C A L R E V I E W L E T T E R S [8,9] although the Schottky barrier height remains constant. The chemicurrent maximum is found at the O 2 exposure time of 360 s. This finding indicates that the earlier observed EEE traces may not be exclusively explained by work function variations.…”

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confidence: 99%

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Continuous Monitoring of Mg Oxidation by Internal Exoemission

Glass

Nienhaus

2004

Phys. Rev. Lett.

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Thin-film Mg/Si(111) Schottky diodes are exposed to oxygen to detect chemicurrents in the devices. The detected charge is created by nonadiabatic energy dissipation and due to either internal exoemission currents or surface chemiluminescence induced photocurrents. Both contributions can be distinguished by changing the metal film thickness of the device. Auger electron spectroscopy to study the oxygen uptake demonstrates that the chemicurrent transients represent truly the time dependent reaction rate at the surface. Model calculations indicate that the current monitors Mg oxide island nucleation and growth.

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“…The EEE method is based on the non-stationary electron emission that takes place at energy levels lower than the work function. The emission from solids can originate from various external excitations such as mechanical deformation, chemisorption, X-ray irradiation, electron bombardment and phase transitions [ 37 ], which cannot be explained within the framework of the classical photoelectric effect, thermionic emission, secondary electron emission or other well-known processes [ 38 ]. EEE is basically a surface phenomenon, typically provided at the mm scale.…”

Section: Introductionmentioning

confidence: 99%

Effect of Heat Treatment on Microstructure and Selective Corrosion of LPBF-AlSi10Mg by Means of SKPFM and Exo-Electron Emission

et al. 2021

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The paper deals with the evolution of the microstructure of AlSi10Mg alloy obtained by laser powder bed fusion (LPBF), as a function of the post-processing heat treatment temperature. This was approached by complementary methods including FE-scanning electron microscopy, scanning Kelvin probe force microscopy and exo-electron emission techniques. The fast cooling rate of the LPBF process as compared to traditional casting produces a very fine microstructure with high mechanical properties and corrosion resistance. However, the LPBF-AlSi10Mg alloy can be susceptible to selective corrosion at the edge of the melt pools generated by the laser scan tracks. Post-process thermal treatments of the Al alloy induce a marked modification of the silicon network at melt pool edges, in particular at high temperature such as 400 °C. It was found that this is associated to a more homogeneous distribution of Volta potential. Analysis of exo-electron emission confirms the silicon diffusion during thermal treatment. The modification of the silicon network structure of the LPBF-AlSi10Mg during thermal treatment reduces the susceptibility to selective corrosion.

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Exoelectron emission from magnesium surfaces

Cited by 9 publications

References 23 publications

Quantum size effects in chemicurrent measurements during low-temperature oxidation of Mg(0001) epilayers

Quantum size effects in chemicurrent measurements during low-temperature oxidation of Mg(0001) epilayers

Continuous Monitoring of Mg Oxidation by Internal Exoemission

Effect of Heat Treatment on Microstructure and Selective Corrosion of LPBF-AlSi10Mg by Means of SKPFM and Exo-Electron Emission

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