Selective H atom sensors using ultrathin Ag/Si Schottky diodes

Nienhaus, Hermann; Bergh, H. S.; Gergen, B.; Majumdar, Arun; Weinberg, W. H.; McFarland, Eric W.

doi:10.1063/1.123256

Cited by 92 publications

(105 citation statements)

References 15 publications

(8 reference statements)

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“…Experiments developed during the last few years have measured, for example, chemicurrents and creation of hot electrons during the chemisorption of atoms and molecules on metal films and surfaces, [1][2][3][4][5] highly efficient multi-quantum vibrational relaxation of highly vibrationally excited NO molecules scattered from metal surfaces, 6,7 and even electron emission upon scattering of highly vibrationally excited NO from a low work function metal surface. 8 Nevertheless, the fundamental question to be answered now is: how much does the presence of electronic excitations influence the interactions between molecules and metal surfaces?…”

Section: Introductionmentioning

confidence: 99%

Vibrational deexcitation and rotational excitation of H2 and D2 scattered from Cu(111): Adiabatic versus non-adiabatic dynamics

Muzas

Juaristi

Alducin

et al. 2012

The Journal of Chemical Physics

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We have studied survival and rotational excitation probabilities of H 2 (v i = 1, J i = 1) and D 2 (v i = 1, J i = 2) upon scattering from Cu(111) using six-dimensional (6D) adiabatic (quantum and quasi-classical) and non-adiabatic (quasi-classical) dynamics. Non-adiabatic dynamics, based on a friction model, has been used to analyze the role of electron-hole pair excitations. Comparison between adiabatic and non-adiabatic calculations reveals a smaller influence of non-adiabatic effects on the energy dependence of the vibrational deexcitation mechanism than previously suggested by low-dimensional dynamics calculations. Specifically, we show that 6D adiabatic dynamics can account for the increase of vibrational deexcitation as a function of the incidence energy, as well as for the isotope effect observed experimentally in the energy dependence for H 2 (D 2 )/Cu(100). Furthermore, a detailed analysis, based on classical trajectories, reveals that in trajectories leading to vibrational deexcitation, the minimum classical turning point is close to the top site, reflecting the multidimensionally of this mechanism. On this site, the reaction path curvature favors vibrational inelastic scattering. Finally, we show that the probability for a molecule to get close to the top site is higher for H 2 than for D 2 , which explains the isotope effect found experimentally.

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Section: Introductionmentioning

confidence: 99%

Vibrational deexcitation and rotational excitation of H2 and D2 scattered from Cu(111): Adiabatic versus non-adiabatic dynamics

Muzas

Juaristi

Alducin

et al. 2012

The Journal of Chemical Physics

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“…It varied typically between 7% and 25%, where the variations were associated with plasma fluctuations. We also measured an average kinetic energy of the atomic hydrogen of between 300 and 350 K [12]. The total rate of atomic and molecular hydrogen impinging on the diode was approximately constant, 10 13 particles͞s.…”

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confidence: 99%

“…A special light blocking fixture was inserted into the plasma tube to prevent any photon transmission. Design and function of the device are described in detail elsewhere [12]. The content of atomic hydrogen, c H , i.e., the number of atoms relative to the total number of particles in the beam was measured with an in-line mass spectrometer.…”

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confidence: 99%

Electron-Hole Pair Creation at Ag and Cu Surfaces by Adsorption of Atomic Hydrogen and Deuterium

et al. 1999

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Hot electrons and holes created at Ag and Cu surfaces by adsorption of thermal hydrogen and deuterium atoms have been measured directly with ultrathin metal film Schottky diode detectors on Si(111). When the metal surface is exposed to these atoms, charge carriers are excited at the surface, travel ballistically toward the interface, and have been detected as a chemicurrent in the diode. The current decreases with increasing exposure and eventually reaches a constant value at the steady-state coverage. This is the first direct evidence of nonadiabatic energy dissipation during adsorption at transition metal surfaces. [S0031-9007(98) PACS numbers: 82.20. Rp, 34.50.Dy, 79.20.Rf, 82.65.My The pathways of energy dissipation in exothermic reactions at metal surfaces are of fundamental interest but still poorly understood. Bond formation energies of up to several eV are transferred into the substrate. Since bulk phonon energies are typically 2 orders of magnitude smaller, nonadiabatic excitations of electron-hole (e-h) pairs may be a significant alternative to multiple phonon creation [1][2][3][4]. With surface reactions at thermal collision energies, there are a few examples of energy transfer into the electronic system accompanied by light emission (chemiluminescence) [5] and exoelectron ejection [6]. These effects are observed only with the exothermic adsorption of electronegative molecules on reactive metal surfaces. In addition, exoelectron emission requires that the metal has a low work function. Heretofore, there has been no direct experimental evidence for adsorptioninduced e-h pair excitations at transition metal surfaces. Although the maximum energy of any hot charge carriers is smaller than the metal work function, precluding exoelectron emission, the energy may be sufficiently large to enable the charge carriers to be collected by crossing a smaller potential barrier.We demonstrate in the present study that the direct detection of chemisorption-induced e-h pairs is feasible using the Schottky barrier of a transition metal-semiconductor diode detector. We chose the adsorption of atomic hydrogen on Ag and Cu film surfaces as model systems. These metals exhibit high reactivity to atomic hydrogen but negligible dissociative adsorption of H 2 [7]. The formation energy of the H-metal bond is large, about 2.5 eV in both cases [7]. To detect the hot charge carriers, we designed a sensor consisting of a large-area metal-semiconductor contact with an ultrathin metal film. The proposed mechanism of current production in the sensor is illustrated in Fig. 1(a) for the case of hot electrons. The transition metal film is evaporated on n-type Si forming a diode with a Schottky barrier, F. Figure 1(a) shows the Fermi level, E F , the conduction band minimum (CBM) and the valence band maximum (VBM). If the exothermic chemisorption of H atoms creates e-h pairs, hot electrons may travel ballistically through the film and cross the barrier. They can be detected as a current which we hereafter call a chemicurrent. Similarly...

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“…Recently, Nienhaus and coworkers reported the observation of a chemicurrent when a Ag/Si-Schottky diode was exposed to a flux of hydrogen atoms suggesting that a portion of the chemisorption energy is dissipated to electronic degrees of freedom of the substrate [7]. This experiment has stimulated novel theoretical studies [8][9][10][11][12].…”

Section: Introductionmentioning

confidence: 95%

Electronic Excitations in the Course of the Reaction of H with Coinage and Noble Metal Surfaces: A Comparison

Schindler

Diesing

Hasselbrink

2013

Zeitschrift für Physikalische Chemie

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The creation of electronic excitations during the reaction of atomic hydrogen on and with coinage and noble metals has been studied using metal-insulator-metal heterostructures. A characteristic current trace is observed when the outer metal surface of the structure is exposed to a 20 s pulse of H atoms. Comparison to the chemical kinetics allows to disentangle the contributions from the different chemical processes to this current. In the case of the coinage metals studied the observation is interpreted to suggest that predominantly electrons excited in connection with the hydrogen recombination reaction are the source of the current. For Pt such phenomenon is not observed. This difference allows insights into the role of the transition state for the non-adiabaticity in this simple chemical reaction.

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Selective H atom sensors using ultrathin Ag/Si Schottky diodes

Abstract: Published by the AIP PublishingArticles you may be interested in Improved performance of Pd/WO3/SiC Schottky-diode hydrogen gas sensor by using fluorine plasma treatment Appl. Phys. Lett. 107, 073506 (2015)

Cited by 92 publications

References 15 publications

Vibrational deexcitation and rotational excitation of H2 and D2 scattered from Cu(111): Adiabatic versus non-adiabatic dynamics

Vibrational deexcitation and rotational excitation of H2 and D2 scattered from Cu(111): Adiabatic versus non-adiabatic dynamics

Electron-Hole Pair Creation at Ag and Cu Surfaces by Adsorption of Atomic Hydrogen and Deuterium

Electronic Excitations in the Course of the Reaction of H with Coinage and Noble Metal Surfaces: A Comparison

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