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Marz M, Issac A, Fritsch V, Kimouche A, Hoffmann-Vogel R. Real-Space Imaging of Several Molecular Layers of C 60in the Rotational Glass Phase. J Phys Condens Matter 2023. [PMID: 37369226 DOI: 10.1088/1361-648x/ace22b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/29/2023]
Abstract
C60is a model system to study molecule-surface interactions and phase transitions due to its high symmetry and strong covalent π bonding within the molecule versus weak van-der-Waals coupling between neighboring molecules. In the solid, at room temperature, the molecule rotates and behaves as a sphere. However, the pentagonal and hexagonal atomic arrangement imposes deviations from the spherical symmetry that become important at low temperatures. The orientation of the C60can be viewed to represent classic spins. For geometrical reasons the preferred orientation of neighboring C60cannot be satisfied for all of the neighboring molecules, making C60a model for disordered spin systems with frustration. We study several molecular
layers of C<sub>60</sub islands on highly oriented pyrolytic graphite (HOPG) using scanning tunneling microscopy at liquid nitrogen temperatures. By imaging several layers we obtain a limited access to the three-dimensional rotational structure of the molecules in
an island. We find one rotationally disordered layer between two partially rotationally ordered layers with hexagonal patterns. This exotic pattern shows an example of the local distribution of order and disorder in geometrically frustrated systems. Scanning
Tunneling Spectroscopy data confirms the weak interactions of neighboring molecules.
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Affiliation(s)
- Michael Marz
- Karlsruher Institut für Technologie, Wolfgang-Gaede-Str. 1, Karlsruhe, 76128, GERMANY
| | - Andrew Issac
- Physikalisches Institut, Karlsruher Institut für Technologie, Wolfgang-Gaede-Str. 1, Karlsruhe, 76128, GERMANY
| | - Veronika Fritsch
- Experimental Physics VI, University of Augsburg, Center for Electronic Correlations and Magnetism, Augsburg, Bayern, 86159, GERMANY
| | - Amina Kimouche
- Department of Physics and Astronomy, University of Potsdam, Karl-Liebknecht Straße 24-25, Potsdam, 14469, GERMANY
| | - Regina Hoffmann-Vogel
- Department of Physics and Astronomy, University of Potsdam, Karl-Liebknecht Straße 24-25, Potsdam, 14469, GERMANY
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Hauser J, Rothhardt D, Pfender-Siedle R, Hoffmann-Vogel R. Shell effects and free-electrons in electromigrated oxidized Cu-nanocontacts. Nanotechnology 2023; 34:175703. [PMID: 36701800 DOI: 10.1088/1361-6528/acb654] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/09/2022] [Accepted: 01/26/2023] [Indexed: 06/17/2023]
Abstract
Electromigration in interconnects continues to be an important field of study in integrated circuits as the interconnects are planned to shrink in size at comparable pace as the semiconductor functional elements. Through shrinking the interconnects approach the regime where quantum size effects become important. The observation of quantum size and shell effects is usually restricted either to low-temperatures or vacuum conditions or to chemically inert materials such as Au. Here, we show that in electromigrated Cu nanocontacts such effects can be observed at room temperature and room pressure even in the presence of oxidation. Our data provide evidence that the nanocontacts are nearly spherical objects with a triangular-cylindrical symmetry of their electronic wave functions with a stronger free-electron-like character compared to previous results. We do not observe a detrimental effect of oxygen. The presence of shell effects has implications for the technological use of Cu nanocontacts as interconnects in integrated circuits and could lead to the use of electronic wave functions of shells in such interconnects.
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Affiliation(s)
- Julia Hauser
- Physikalisches Institut, Karlsruhe Institute of Technology, D-76128 Karlsruhe, Germany
| | - Daniel Rothhardt
- Department of Physics and Astronomy, University of Potsdam, D-14476 Potsdam-Golm, Germany
| | - Robert Pfender-Siedle
- Physikalisches Institut, Karlsruhe Institute of Technology, D-76128 Karlsruhe, Germany
| | - Regina Hoffmann-Vogel
- Department of Physics and Astronomy, University of Potsdam, D-14476 Potsdam-Golm, Germany
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3
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Schneider S, Bytyqi K, Kohaut S, Bügel P, Weinschenk B, Marz M, Kimouche A, Fink K, Hoffmann-Vogel R. Molecular Self-Assembly of DBBA on Au(111) at Room Temperature. Phys Chem Chem Phys 2022; 24:28371-28380. [DOI: 10.1039/d2cp02268k] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
We have investigated the self-assembly of the graphene nanoribbon molecular precursor 10,10'-dibromo-9,9'-bianthryl (DBBA) on Au(111) with frequency modulation scanning force microscopy (FM-SFM) at room temperature combined with ab initio calculations....
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4
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Wagner P, Foster A, Yi I, Abe M, Sugimoto Y, Hoffmann-Vogel R. Role of tip apices in scanning force spectroscopy on alkali halides at room temperature-chemical nature of the tip apex and atomic-scale deformations. Nanotechnology 2021; 32:035706. [PMID: 33052141 DOI: 10.1088/1361-6528/abbea8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
We have revealed processes of the tip apex distortion in the measurements of non-contact scanning force microscopy. High-spatial-resolution two-dimensional force mapping on KCl(100) surfaces for a large number of tips, seven tips, enabled us to see the complex behavior of the tip apex distortion. The tips are from Si without additional coating, but are altered by the tip-sample interaction and show the behavior of different atomic species. On the KCl(001) surfaces, the tip apex, consisting of K and Cl atoms or of Si, distorted several times while changing the distance even in a weak attractive region. There are variations in rigidity of the tip apex, but all tips distorted in the small attractive region. This complex behavior was categorized in patterns by our analyses. We compare the experimental force-distance data to atomistic simulations using rigid KCl-terminated tips and KCl-terminated tips with an additional KCl-pair designed to perform atomic jumps. We also compare the experimental force-distance data to first principles simulations using Si tips. We mainly find K-terminated tips and Si-terminated tips. We find that Si tips show only one force minimum whereas KCl-terminated tips show two force minima in line with the stronger rigidity of Si compared to KCl. At room temperature, the tip apex atoms can perform atomic jumps that change the atomic configuration of the tip apex.
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Affiliation(s)
- Philipp Wagner
- Physikalisches Institut, Karlsruher Institut für Technologie, D-76128 Karlsruhe, Germany
| | - Adam Foster
- Department of Applied Physics, Aalto University School of Science, PO Box 11100, FI-00076 Aalto, Finland
- WPI Nano Life Science Institute (WPI-NanoLSI), Kanazawa University, Kakuma-machi, Kanazawa 920-1192, Japan
- Graduate School Materials Science in Mainz, Staudinger Weg 9, D-55128, Germany
| | - Insook Yi
- Graduate School of Engineering, Osaka University, Japan
| | - Masayuki Abe
- Graduate School of Engineering, Osaka University, Japan
| | | | - Regina Hoffmann-Vogel
- Department of Physics, University of Konstanz, Universitätsstrasse 10, D-78464 Konstanz, Germany
- Institute of Physics and Astronomy, University of Potsdam, Karl-Liebknecht Strasse 24-25, D-14476 Potsdam-Golm, Germany
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5
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Schneider S, Hoffmann-Vogel R. Electrostatic forces above graphene nanoribbons and edges interpreted as partly hydrogen-free. Nanoscale 2020; 12:17895-17901. [PMID: 32844849 DOI: 10.1039/d0nr03348k] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Graphene nanoribbons' electronic transport properties strongly depend on the type of edge, armchair, zigzag or other, and on edge functionalization that can be used for band-gap engineering. For only partly hydrogenated edges interesting magnetic properties are predicted. Electric charge accumulates at edges and corners. Scanning force microscopy has so far shown the centre of graphene nanoribbons with atomic resolution using a quartz crystal tuning fork sensor of high stiffness. Weak long-range electrostatic forces related to the charge accumulation on the edges of graphene nanoribbons could not be imaged so far. Here, we show the electrostatic forces at the corners and edges of graphene nanoribbons are amenable to measurement. We use soft cantilevers and a bimodal imaging technique to combine enhanced sensitivity to weak long-range electrostatic forces with the high resolution of the second-frequency shift. Additionally, in our work the edges of the nanoribbons are mainly hydrogen-free, opening to the route to investigations of partly hydrogenated magnetic nanoribbons.
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Affiliation(s)
- Sebastian Schneider
- Physikalisches Institut, Karlsruhe Institute of Technology, Karlsruhe, Germany
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Späth T, Popp M, Hoffmann-Vogel R. Film Thickness of Pb Islands on the Si(111) Surface. Phys Rev Lett 2020; 124:016101. [PMID: 31976694 DOI: 10.1103/physrevlett.124.016101] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/13/2018] [Revised: 08/27/2019] [Indexed: 06/10/2023]
Abstract
We analyze topographic scanning force microscopy images together with Kelvin probe images obtained on Pb islands and on the wetting layer on Si(111) for variable annealing times. Within the wetting layer we observe negatively charged Si-rich areas. We show evidence that these Si-rich areas result from islands that have disappeared by coarsening. We argue that the islands are located on Si-rich areas inside the wetting layer such that the Pb/Si interface of the islands is in line with the top of the wetting layer rather than with its interface to the substrate. We propose that the Pb island heights are one atomic layer smaller than previously believed. For the quantum size effect bilayer oscillations of the work function observed in this system, we conclude that for film thicknesses below 9 atomic layers large values of the work function correspond to even numbers of monolayers instead of odd ones. The atomically precise island height is important to understand ultrafast "explosive" island growth in this system.
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Affiliation(s)
- Th Späth
- Physikalisches Institut, Karlsruhe Institute of Technology (KIT), 76131 Karlsruhe, Germany
| | - M Popp
- Physikalisches Institut, Karlsruhe Institute of Technology (KIT), 76131 Karlsruhe, Germany
| | - R Hoffmann-Vogel
- Department of Physics, University of Konstanz, Universitätsstrasse 10, 78464 Konstanz, Germany
- Institut für Physik und Astronomie, Universität Potsdam, Karl-Liebknecht-Strasse 24-25, 14476 Potsdam, Germany
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7
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Seydel E, Hoffmann-Vogel R, Marz M. Epitaxial growth of C 60 on highly oriented pyrolytic graphite surfaces studied at low temperatures. Nanotechnology 2019; 30:025703. [PMID: 30382026 DOI: 10.1088/1361-6528/aae7ed] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Graphite surfaces interact weakly with molecules compared to other conducting surfaces, bringing the molecule-molecule interaction to the foreground. C60 on highly oriented pyrolytic graphite is a model system for studying the molecular self-assembly on surfaces. Our scanning tunneling microscopy measurements at liquid nitrogen temperatures confirm the previously observed island growth mode. Our results indicate that there is an epitaxial relationship of the molecular islands and the substrate with three possible orientations of the islands. For one of these orientations, we determine this epitaxial relationship by analyzing in detail an image taken across a C60 island step edge. In this image we have obtained high-resolution on both the molecular island and the substrate. The result of this analysis is confirmed by two-dimensional Fourier analysis.
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Affiliation(s)
- E Seydel
- Physikalisches Institut, Karlsruhe Institute for Technology (KIT), D-76131 Karlsruhe, Germany
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8
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Abstract
Insulating substrates allow for in-plane contacted molecular electronics devices where the molecule is in contact with the insulator. For the development of such devices it is important to understand the interaction of molecules with insulating surfaces. As substrates, ionic crystals such as KBr, KCl, NaCl and CaF2 are discussed. The surface energies of these substrates are small and as a consequence intrinsic properties of the molecules, such as molecule-molecule interaction, become more important relative to interactions with the substrates. As prototypical molecules, three variants of graphene-related molecules are used, pentacene, [Formula: see text] and PTCDA. Pentacene is a good candidate for molecular electronics applications due to its high charge carrier mobility. It shows mainly an upright standing growth mode and the morphology of the islands is strongly influenced by dewetting. A new second flat-lying phase of the molecule has been observed. Studying the local work function using the Kelvin method reveals details such as line defects in the center of islands. The local work function differences between the upright-standing and flat-lying phase can only be explained by charge transfer that is unusual on ionic crystalline surfaces. [Formula: see text] nucleation and growth is explained by loosely bound molecules at kink sites as nucleation sites. The stability of [Formula: see text] islands as a function of magic numbers is investigated. Peculiar island shapes are obtained from unusual dewetting processes already at work during growth, where molecules 'climb' to the second molecular layer. PTCDA is a prototypical semiconducting molecule with strong quadrupole moment. It grows in the form of elongated islands where the top and the facets can be molecularly resolved. In this way the precise molecular arrangement in the islands is revealed.
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Affiliation(s)
- R Hoffmann-Vogel
- Physikalisches Institut, Karlsruhe Institute of Technology (KIT), D-76131 Karlsruhe, Germany. Institut für Angewandte Physik, Karlsruhe Institute of Technology (KIT), D-76131 Karlsruhe, Germany
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9
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Späth T, Popp M, Pérez León C, Marz M, Hoffmann-Vogel R. Near-equilibrium measurement of quantum size effects using Kelvin probe force microscopy. Nanoscale 2017; 9:7868-7874. [PMID: 28555693 DOI: 10.1039/c7nr01874f] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
In nano-structures such as thin films electron confinement results in the quantization of energy levels in the direction perpendicular to the film. The discretization of the energy levels leads to the oscillatory dependence of many properties on the film thickness due to quantum size effects. Pb on Si(111) is a specially interesting system because a particular relationship between the Pb atomic layer thickness and its Fermi wavelength leads to a periodicity of the oscillation of two atomic layers. Here, we demonstrate how the combination of scanning force microscopy (SFM) and Kelvin probe force microscopy (KPFM) provides a reliable method to monitor the quantum oscillations in the work function of Pb ultra-thin film nano-structures on Si(111). Unlike other techniques, with SFM/KPFM we directly address single Pb islands, determine their height while suppressing the influence of electrostatic forces, and, in addition, simultaneously evaluate their local work function by measurements close to equilibrium, without current-dependent and non-equilibrium effects. Our results evidence even-odd oscillations in the work function as a function of the film thickness that decay linearly with the film thickness, proving that this method provides direct and precise information on the quantum states.
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Affiliation(s)
- Thomas Späth
- Physikalisches Institut, Karlsruhe Institute of Technology (KIT), Wolfgang-Gaede-Str. 1, 76128 Karlsruhe, Germany.
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10
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Arnold D, Marz M, Schneider S, Hoffmann-Vogel R. Structure and local charging of electromigrated Au nanocontacts. Nanotechnology 2017; 28:055206. [PMID: 28032610 DOI: 10.1088/1361-6528/28/5/055206] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
We study the structure and the electronic properties of Au nanocontacts created by controlled electromigration of thin film devices, a method frequently used to contact molecules. In contrast to electromigration testing, a current is applied in a cyclic fashion and during each cycle the resistance increase of the metal upon heating is used to avoid thermal runaway. In this way, nanometer sized-gaps are obtained. The thin film devices with an optimized structure at the origin of the electromigration process are made by shadow evaporation without contamination by organic materials. Defining rounded edges and a thinner area in the center of the device allow to pre-determine the location where the electromigration takes place. Scanning force microscopy images of the pristine Au film and electromigrated contact show its grainy structure. Through electromigration, a 1.5 μm-wide slit is formed, with extensions only on the anode side that had previously not been observed in narrower structures. It is discussed whether this could be explained by asymmetric heating of both electrodes. New grains are formed in the slit and on the extensions on both, the anode and the cathode side. The smaller structures inside the slit lead to an electrode distance below 150 nm. Kelvin probe force microscopy images show a local work function difference with fluctuations of 70 mV on the metal before electromigration. Between the electrodes, disconnected through electromigration, a work function difference of 3.2 V is observed due to charging. Some of the grains newly formed by electromigration are electrically disconnected from the electrodes.
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Affiliation(s)
- D Arnold
- Physikalisches Institut, Karlsruhe Institute of Technology (KIT), D-76131 Karlsruhe, Germany
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11
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Pérez León C, Drees H, Wippermann SM, Marz M, Hoffmann-Vogel R. Atomic-Scale Imaging of the Surface Dipole Distribution of Stepped Surfaces. J Phys Chem Lett 2016; 7:426-30. [PMID: 26758503 DOI: 10.1021/acs.jpclett.5b02650] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
Stepped well-ordered semiconductor surfaces are important as nanotemplates for the fabrication of 1D nanostructures. Therefore, a detailed understanding of the underlying stepped substrates is crucial for advances in this field. Although measurements of step edges are challenging for scanning force microscopy (SFM), here we present simultaneous atomically resolved SFM and Kelvin probe force microscopy (KPFM) images of a silicon vicinal surface. We find that the local contact potential difference is large at the bottom of the steps and at the restatoms on the terraces, whereas it drops at the upper part of the steps and at the adatoms on the terraces. For the interpretation of the data we performed density functional theory (DFT) calculations of the surface dipole distribution. The DFT images accurately reproduce the experiments even without including the tip in the calculations. This underlines that the high-resolution KPFM images are closely related to intrinsic properties of the surface and not only to tip-surface interactions.
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Affiliation(s)
- Carmen Pérez León
- Physikalisches Institut, Karlsruhe Institute of Technology (KIT) , Wolfgang-Gaede-Str. 1, D-76131 Karlsruhe, Germany
| | - Holger Drees
- Physikalisches Institut, Karlsruhe Institute of Technology (KIT) , Wolfgang-Gaede-Str. 1, D-76131 Karlsruhe, Germany
| | | | - Michael Marz
- Physikalisches Institut, Karlsruhe Institute of Technology (KIT) , Wolfgang-Gaede-Str. 1, D-76131 Karlsruhe, Germany
| | - Regina Hoffmann-Vogel
- Physikalisches Institut, Karlsruhe Institute of Technology (KIT) , Wolfgang-Gaede-Str. 1, D-76131 Karlsruhe, Germany
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12
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Hoffmann-Vogel R. Atomistic features in the electrochemical potential drop across a graphene grain boundary. Nanotechnology 2014; 25:480501. [PMID: 25397732 DOI: 10.1088/0957-4484/25/48/480501] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
A recent publication presents a new computational approach to the local electrochemical potential in the vicinity of a graphene grain boundary subject to an in-plane electric current [1]. The local electrochemical potential can be measured using scanning tunneling potentiometry, a method related to scanning tunneling microscopy. The paper predicts that atomistic features should be measurable. These features reflect the local electrochemical potential drop caused by the opaque grain boundary which is non-transparent to ballistic electrons. The paper has implications not only for scanning tunneling potentiometry, but also for Kelvin probe-force microscopy which can also measure the local electrochemical potential. In addition it could help to understand electronic transport across metallic nanocontacts.
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Affiliation(s)
- R Hoffmann-Vogel
- Physikalisches Institut, Karlsruhe Institute of Technology, D-76128 Karlsruhe, Germany
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13
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Reeve RM, Loescher A, Mawass MA, Hoffmann-Vogel R, Kläui M. Domain wall pinning in ultra-narrow electromigrated break junctions. J Phys Condens Matter 2014; 26:474207. [PMID: 25351328 DOI: 10.1088/0953-8984/26/47/474207] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The study of magnetic domain walls in constrained geometries is an important topic, yet when dealing with extreme nanoscale magnetic systems artefacts can often dominate the measurements and obscure the effects of intrinsic magnetic origin. In this work we study the evolution of domain wall depinning in electromigrated ferromagnetic junctions which are both initially fabricated and subsequently tailored in-situ in clean ultra-high vacuum conditions. Carefully designed Ni(80)Fe(20) (Permalloy) notched half-ring structures are fabricated and investigated as a function of constriction width by tailoring the size of the contact using controlled in-situ electromigration. It is found that the domain wall pinning strength is increased on reducing the contact size in line with a reduction of the wall energy in narrower constrictions. Furthermore, the angular dependency and symmetry of the depinning field is measured to determine the full pinning potential for a domain wall in a system with a narrow constriction.
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Affiliation(s)
- Robert M Reeve
- Institut für Physik, Johannes Gutenberg-Universität Mainz, 55099 Mainz, Germany
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14
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Neff JL, Milde P, León CP, Kundrat MD, Eng LM, Jacob CR, Hoffmann-Vogel R. Epitaxial growth of pentacene on alkali halide surfaces studied by Kelvin probe force microscopy. ACS Nano 2014; 8:3294-3301. [PMID: 24601525 DOI: 10.1021/nn404257v] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
In the field of molecular electronics, thin films of molecules adsorbed on insulating surfaces are used as the functional building blocks of electronic devices. Control of the structural and electronic properties of the thin films is required for reliably operating devices. Here, noncontact atomic force and Kelvin probe force microscopies have been used to investigate the growth and electrostatic landscape of pentacene on KBr(001) and KCl(001) surfaces. We have found that, together with molecular islands of upright standing pentacene, a new phase of tilted molecules appears near step edges on KBr. Local contact potential differences (LCPD) have been studied with both Kelvin experiments and density functional theory calculations. Our images reveal that differently oriented molecules display different LCPD and that their value is independent of the number of molecular layers. These results point to the formation of an interface dipole, which may be explained by a partial charge transfer from the pentacene to the surface. Moreover, the monitoring of the evolution of the pentacene islands shows that they are strongly affected by dewetting: Multilayers build up at the expense of monolayers, and in the Kelvin images, previously unknown line defects appear, which reveal the epitaxial growth of pentacene crystals.
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Affiliation(s)
- Julia L Neff
- Physikalisches Institut and DFG-Center for Functional Nanostructures, Karlsruhe Institute of Technology , Wolfgang-Gaede-Straße 1, 76131 Karlsruhe, Germany
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15
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von Bieren A, Patra AK, Krzyk S, Rhensius J, Reeve RM, Heyderman LJ, Hoffmann-Vogel R, Kläui M. Domain-wall induced large magnetoresistance effects at zero applied field in ballistic nanocontacts. Phys Rev Lett 2013; 110:067203. [PMID: 23432298 DOI: 10.1103/physrevlett.110.067203] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/12/2012] [Indexed: 06/01/2023]
Abstract
We determine magnetoresistance effects in stable and clean Permalloy nanocontacts of variable cross section, fabricated by UHV deposition and in situ electromigration. To ascertain the magnetoresistance (MR) effects originating from a magnetic domain wall, we measure the resistance values with and without such a wall at zero applied field. In the ballistic transport regime, the MR ratio reaches up to 50% and exhibits a previously unobserved sign change. Our results can be reproduced by recent atomistic calculations for different atomic configurations of the nanocontact, highlighting the importance of the detailed atomic arrangement for the MR effect.
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Affiliation(s)
- Arndt von Bieren
- Laboratory for Nanomagnetism and Spin Dynamics, École Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland
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16
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Neff JL, Götzen J, Li E, Marz M, Hoffmann-Vogel R. Molecular-resolution imaging of pentacene on KCl(001). Beilstein J Nanotechnol 2012; 3:186-91. [PMID: 22428110 PMCID: PMC3304322 DOI: 10.3762/bjnano.3.20] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/22/2011] [Accepted: 02/03/2012] [Indexed: 05/22/2023]
Abstract
The growth of pentacene on KCl(001) at submonolayer coverage was studied by dynamic scanning force microscopy. At coverages below one monolayer pentacene was found to arrange in islands with an upright configuration. The molecular arrangement was resolved in high-resolution images. In these images two different types of patterns were observed, which switch repeatedly. In addition, defects were found, such as a molecular vacancy and domain boundaries.
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Affiliation(s)
- Julia L Neff
- Physikalisches Institut and DFG-Center for Functional Nanostructures, Karlsruhe Institute of Technology, Wolfgang-Gaede-Str. 1, 76128 Karlsruhe, Germany
| | - Jan Götzen
- Physikalisches Institut and DFG-Center for Functional Nanostructures, Karlsruhe Institute of Technology, Wolfgang-Gaede-Str. 1, 76128 Karlsruhe, Germany
- Mechanical Engineering and Materials Science, Yale University, CT 06511, USA
| | - Enhui Li
- Physikalisches Institut and DFG-Center for Functional Nanostructures, Karlsruhe Institute of Technology, Wolfgang-Gaede-Str. 1, 76128 Karlsruhe, Germany
| | - Michael Marz
- Physikalisches Institut and DFG-Center for Functional Nanostructures, Karlsruhe Institute of Technology, Wolfgang-Gaede-Str. 1, 76128 Karlsruhe, Germany
- National Institute for Materials Science (NIMS), 1-2-1 Sengen, Tsukuba, Ibaraki, Japan
| | - Regina Hoffmann-Vogel
- Physikalisches Institut and DFG-Center for Functional Nanostructures, Karlsruhe Institute of Technology, Wolfgang-Gaede-Str. 1, 76128 Karlsruhe, Germany
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