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K Kern

Publications and source records attributed to K Kern.

At least 37 records · Page 2Linked to original sources
PubMed2003

Giant magnetic anisotropy of single cobalt atoms and nanoparticles.

The isotropic magnetic moment of a free atom is shown to develop giant magnetic anisotropy energy due to symmetry reduction at an atomically ordered surface. Single cobalt atoms deposited onto platinum (111) are found to have a magnetic anisotropy energy of 9 millielectron volts per atom arising from the combination of unquenched orbital moments (1.1 Bohr magnetons) and strong spin-orbit coupling induced by the platinum substrate. By assembling cobalt nanoparticles containing up to 40 atoms, the magnetic anisotropy energy is further shown to be dependent on single-atom coordination changes. These results confirm theoretical predictions and are of fundamental value to understanding how magnetic anisotropy develops in finite-sized magnetic particles.

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PubMed2002

Imaging of electron potential landscapes on Au(111).

The Hohenberg-Kohn theorem states that the ground state electron density completely determines the external potential acting on an electron system. Inspired by this fundamental theorem, we developed a novel approach to map directly the electron potential in surface systems: linear response theory applied to the total electron density as measured with scanning tunneling microscopy determines the external potential. Potential imaging is demonstrated for the s-p derived surface state on Au(111), where the "herringbone" reconstruction induces a periodic potential modulation, the details of which are revealed by our technique.

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PubMed2002

Ferromagnetism in one-dimensional monatomic metal chains.

Two-dimensional systems, such as ultrathin epitaxial films and superlattices, display magnetic properties distinct from bulk materials. A challenging aim of current research in magnetism is to explore structures of still lower dimensionality. As the dimensionality of a physical system is reduced, magnetic ordering tends to decrease as fluctuations become relatively more important. Spin lattice models predict that an infinite one-dimensional linear chain with short-range magnetic interactions spontaneously breaks up into segments with different orientation of the magnetization, thereby prohibiting long-range ferromagnetic order at a finite temperature. These models, however, do not take into account kinetic barriers to reaching equilibrium or interactions with the substrates that support the one-dimensional nanostructures. Here we demonstrate the existence of both short- and long-range ferromagnetic order for one-dimensional monatomic chains of Co constructed on a Pt substrate. We find evidence that the monatomic chains consist of thermally fluctuating segments of ferromagnetically coupled atoms which, below a threshold temperature, evolve into a ferromagnetic long-range-ordered state owing to the presence of anisotropy barriers. The Co chains are characterized by large localized orbital moments and correspondingly large magnetic anisotropy energies compared to two-dimensional films and bulk Co.

Journal Article↗
PubMed2001

Mesoscopic correlation of supramolecular chirality in one-dimensional hydrogen-bonded assemblies.

The ordering of 4-[trans-2-(pyrid-4-yl-vinyl)] benzoic acid, a two-dimensional chiral species, was studied by scanning tunneling microscopy at noble metal surfaces. Homochiral molecules self-assemble in supramolecular chiral hydrogen-bonded twin chains, which order in nanogratings where the supramolecular chirality is strictly correlated over the entire microm domains without intimate molecular contact. Model simulations indicate that the underlying mesoscopic chiral resolution is associated with twin chains acting as chiroselective templates for transient molecular attachment, which process mediates the gratings' evolution.

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PubMed2001

Oxygen dissociation at Pt steps.

Using scanning tunneling microscopy, thermal energy atom scattering, and density functional theory we have characterized O (2) dissociation on Pt(111) stepped surfaces at the atomic scale. The most reactive site is at the top of the Pt steps. In both the molecular precursor state (MPS) and the transition state (TS), the O (2) has its axis aligned parallel to the step edge. Controlled step decoration with Ag monatomic chains was used to locally tune the reactivity of Pt step sites. The enhanced reactivity at the Pt step sites is not caused by a decrease of the local dissociation barriers from the MPS but is related to a stabilization of both the MPS and TS.

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PubMed2000

Dynamics of surface migration in the weak corrugation regime

We report a systematic study for metal-on-metal surface migration in the weak corrugation regime, i.e., with migration barriers falling below approximately 100 meV. The migration characteristics are elucidated by variable-temperature scanning tunneling microscopy observations in the 50-200 K temperature range, which are analyzed by means of nucleation theory. The results demonstrate that, upon entering the weak corrugation regime, the dynamics of the systems are characterized by increasingly reduced effective preexponential factors, while Arrhenius behavior prevails.

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PubMed2000

Methemoglobinemia after topical anesthesia with lidocaine and benzocaine for a difficult intubation.

Methemoglobinemia is an uncommon cause of cyanosis; however, rapid diagnosis is critical to avoid potentially fatal consequences. Several local anesthetics can precipitate methemoglobinemia in susceptible patients. This case report of acute methemoglobinemia occurred during fiberoptic intubation in an awake patient without a past medical history of adverse reactions to local anesthetics.

Adult↗
PubMed1996

Controlled Deposition of Size-Selected Silver Nanoclusters

Variable-temperature scanning tunneling microscopy was used to study the effect of kinetic cluster energy and rare-gas buffer layers on the deposition process of size-selected silver nanoclusters on a platinum(111) surface. Clusters with impact energies of </=1 electron volt per atom could be landed nondestructively on the bare substrate, whereas at higher kinetic energies fragmentation and substrate damage were observed. Clusters with elevated impact energy could be soft-landed via an argon buffer layer on the platinum substrate, which efficiently dissipated the kinetic energy. Nondestructive cluster deposition represents a promising method to produce monodispersed nanostructures at surfaces.

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