STM-induced desorption of hydrogen from Co nanoislands

Sicot, Muriel; Kurnosikov, O Oleg; Adam, Oao Omer; Swagten, Hjm Henk; Koopmans, B.

doi:10.1103/physrevb.77.035417

Cited by 24 publications

(21 citation statements)

References 61 publications

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“…19,20 A current-induced desorption of hydrogen from the Co island surface as reported previously 21 can likewise be excluded as an origin for the observed shift. A field effect would be reversible as observed for noble metal surface states.…”

supporting

confidence: 65%

Local heating at a ferromagnet-metal interface

Néel

Berndt

2009

Applied Physics Letters

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supporting

confidence: 65%

Local heating at a ferromagnet-metal interface

Néel

Berndt

2009

Applied Physics Letters

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“…We demonstrate herein that since those experiments 24,25 were performed at a very low temperature (10 K), higher-density H phases that require activation were not observed. We thoroughly examine the adsorption phases of H on model Co nanoparticles grown on Cu(111) at both 78 and 5 K and use DFT to elucidate the energetics and structure of the various observed H phases.…”

Section: ■ Introductionmentioning

confidence: 80%

Dissociative Hydrogen Adsorption on Close-Packed Cobalt Nanoparticle Surfaces

Lewis

Murphy

et al. 2012

J. Phys. Chem. C

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The dissociative adsorption of hydrogen on cobalt is central to a number of catalytic reactions, yet to date there are relatively few studies examining this important process. Here we utilize Co nanoparticles grown on Cu(111), instead of the traditional planar Co single crystals, to study a more catalytically relevant form of Co. We present scanning tunneling microscopy images of different phases of H on the close-packed Co nanoparticle surfaces with a range of densities. Our data reveal a so-far unreported high coverage phase of H with a (1 × 1) structure and elucidate the importance of spillover from step edges in H adsorption. We also illustrate that, in contrast to the low density phases, the H-(1 × 1) structure can only be formed at an intermediate temperature, indicating that compression to this higher-density phase is activated. Density functional theory calculations yield energies for each of the H overlayer structures, as well as their preferred geometries. This work is the first to report on higher coverage (>0.75 ML) phases of H on Co, which are undoubtedly important in catalytic systems at elevated pressure. Finally, through the use of epitaxial Co nanoparticle growth on Cu(111), we illustrate the importance of step edges in H 2 activation and the formation of dense H phases.

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“…Therefore, the presence of contaminants, in particular of hydrogen, adsorbed on the substrate or the islands can be safely ruled out. Moreover, hydrogen adsorbed on Co islands has recently been shown to desorb by using tunneling currents exceeding 20 nA [22]. In the contact experiments reported here, currents of the order of 10 µA are passed through the islands.…”

mentioning

confidence: 93%

Quantized Conductance of a Single Magnetic Atom

Néel

Berndt

2009

Phys. Rev. Lett.

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A single Co atom adsorbed on Cu(111) or on ferromagnetic Co islands is contacted with nonmagnetic W or ferromagnetic Ni tips in a scanning tunneling microscope. When the Co atom bridges two non-magnetic electrodes conductances of 2 e 2 /h are found. With two ferromagnetic electrodes a conductance of e 2 /h is observed which may indicate fully spin-polarized transport.PACS numbers: 68.37. Ef,72.25.Ba,73.23.Ad,73.63.Rt The conductance of nanometer-sized contacts may be decomposed into contributions of transport eigenchannels according to G = G 0 n i=1 τ i , where G 0 = 2e 2 /h is the quantum of conductance (-e: electron charge, h: Planck's constant), and τ i is the transmission probability of the ith channel [1,2]. The factor 2 in the quantum of conductance is due to spin degeneracy. In contacts involving magnetic electrodes the spin degeneracy of transport channels may be lifted. Each spin-polarized channel then may contribute up to G 0 /2 to the total conductance.A quantized conductance of G 0 /2 is expected when a fully spin-polarized current is transmitted with a probability of 1 through a spin-polarized transport channel. These conditions appear difficult to fulfill. Nevertheless, experimental observations of conductance quantization in units of G 0 /2 have repeatedly been reported [3,4,5,6,7,8]. These conductances were observed with [4,6] or without [3,5,7,8] external magnetic fields, for ferromagnetic [3,4,5,6,7] and non-magnetic electrodes [7,8]. On the other hand, the absence of noninteger conductance quantization has also been inferred from experimental results [9,10]. Untiedt et al. showed that contaminants like H 2 or CO modify the conductance and could, in the case of CO adsorption on Pt electrodes, give rise to a conductance of G 0 /2 [10]. A considerable variety of model calculations [11,12,13,14,15] have been performed and support the notion that conductance quantization in units of G 0 /2 is not expected from the investigated ferromagnetic contacts. It should be noted, however, that the modeling performed so far did not include geometrical relaxations of the contacts although the importance of the detailed atomic arrangement has been emphasized [11,15,16,17].The contradictory conclusions reached from the various experiments may be related to a lack of characterisation of the atomic details of the junction. This problem may be reduced by using a cryogenic scanning tunneling microscope to probe the conductance of clean singleatom contacts in ultra-high vacuum. Here we apply this approach to investigate prototypical junctions. A single magnetic atom on a spin-polarized island or a nonmagnetic substrate is contacted with non-magnetic and ferromagnetic tips. We find that the conductance of a single Co atom is G 0 when two non-magnetic electrodes are used. With ferromagnetic electrodes the conductance is G 0 /2. Conductances of ≈ 0.9 G 0 are observed for a combination of a non-magnetic and a ferromagnetic electrode. In contrast to previous experiments, the contact geometry and chemistry are character...

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STM-induced desorption of hydrogen from Co nanoislands

Cited by 24 publications

References 61 publications

Local heating at a ferromagnet-metal interface

Local heating at a ferromagnet-metal interface

Dissociative Hydrogen Adsorption on Close-Packed Cobalt Nanoparticle Surfaces

Quantized Conductance of a Single Magnetic Atom

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