Browsing by Author "Foster, Adam S."

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  • Ab initio Kinetic Monte Carlo simulations of dissolution at the NaCl-water interface
    (2014) Chen, Jian-Cheng; Reischl, Bernhard; Spijker, Peter; Holmberg, Nico; Laasonen, Kari; Foster, Adam S.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
  • Ab initio study of Cu diffusion in alpha-cristobalite
    (2012) Zelený, M.; Hegedüs, J.; Foster, Adam S.; Drabold, D.A.; Elliott, S.R.; Nieminen, Risto M.
     School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We have studied the geometries, formation energies, migration barriers and diffusion of a copper interstitial with different charge states with and without an external electric field in the α-cristobalite crystalline form of SiO2 using ab initio computer simulation. The most stable state almost throughout the band gap is charge q = + 1. The height of the migration barrier depends slightly on the charge state and varies between 0.11 and 0.18 eV. However, the charge has a strong influence on the shape of the barrier, as metastable states exist in the middle of the diffusion path for Cu with q = + 1. The heights and shapes of barriers also depend on the density of SiO2, because volume expansion has a similar effect to increase the positive charge on Cu. Furthermore, diffusion coefficients have been deduced from our calculations according to transition-state theory and these calculations confirm the experimental result that oxidation of Cu is a necessary condition for diffusion. Our molecular dynamics simulations show a similar ion diffusion, and dependence on charge state. These simulations also confirm the fact that diffusion of ions can be directly simulated using ab initio molecular dynamics.
  • Adsorption and migration of carbon adatoms on carbon nanotubes: Density-functional ab initio and tight-binding studies
    (2004) Krasheninnikov, A. V.; Nordlund, K.; Lehtinen, P. O.; Foster, Adam S.; Ayuela, A.; Nieminen, Risto M.
     School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We employ density-functional plane-wave ab initio and tight-binding methods to study the adsorption and migration of carbon adatoms on single-walled carbon nanotubes. We show that the adatom adsorption and migration energies strongly depend on the nanotube diameter and chirality, which makes the model of the carbon adatom on a flat graphene sheet inappropriate. Calculated migration energies for the adatoms agree well with the activation energies obtained from experiments on annealing of irradiation damage in single-walled nanotubes and attributed to single carbon interstitials.
  • Adsorption and migration of single metal atoms on the calcite (10.4) surface
    (2017-02-15) Pinto, H.; Haapasilta, V.; Lokhandwala, M.; Öberg, S.; Foster, Adam S.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Transition metal atoms are one of the key ingredients in the formation of functional 2D metal organic coordination networks. Additionally, the co-deposition of metal atoms can play an important role in anchoring the molecular structures to the surface at room temperature. To gain control of such processes requires the understanding of adsorption and diffusion properties of the different transition metals on the target surface. Here, we used density functional theory to investigate the adsorption of 3d (Ti, Cr, Fe, Ni, Cu), 4d (Zr, Nb, Mo, Pd, Ag) and 5d (Hf, W, Ir, Pt, Au) transition metal adatoms on the insulating calcite (10.4) surface. We identified the most stable adsorption sites and calculated binding energies and corresponding ground state structures. We find that the preferential adsorption sites are the Ca-Ca bridge sites. Apart from the Cr, Mo, Cu, Ag and Au all the studied metals bind strongly to the calcite surface. The calculated migration barriers for the representative Ag and Fe atoms indicates that the metal adatoms are mobile on the calcite surface at room temperature. Bader analysis suggests that there is no significant charge transfer between the metal adatoms and the calcite surface.
  • Adsorption of acetic and trifluoroacetic acid on the TiO2(110) surface
    (2004) Foster, Adam S.; Nieminen, Risto M.
     School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We use the first-principles static and dynamic simulations to study the adsorption of acetic (CH3COOH) and trifluoroacetic (CF3COOH)acid on the TiO2(110)surface. The most favorable adsorption for both molecules is a dissociative process, which results in the two oxygens of the carboxylate ion bonding to in-plane titanium atoms in the surface. The remaining proton then bonds to a bridging oxygen site, forming a hydroxyl group. We further show that, by comparing the calculated dipoles of the molecules on the surface, it is possible to understand the difference in contrast over the acetate and trifluoroacetate molecules in the atomically resolved noncontact atomic force microscopy images.
  • AFM tip characterization by Kelvin probe force microscopy
    (2010) Barth, C.; Hynninen, T.; Bieletzki, M.; Henry, C. R.; Foster, Adam S.; Esch, F.; Heiz, U.
     School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Reliable determination of the surface potential with spatial resolution is key for understanding complex interfaces that range from nanostructured surfaces to molecular systems to biological membranes. In this context, Kelvin probe force microscopy (KPFM) has become the atomic force microscope (AFM) method of choice for mapping the local electrostatic surface potential as it changes laterally due to variations in the surface work function or surface charge distribution. For reliable KPFM measurements, the influence of the tip on the measured electrostatic surface potential has to be understood. We show here that the mean Kelvin voltage can be used for a straightforward characterization of the electrostatic signature of neutral, charged and polar tips, the starting point for quantitative measurements and for tip-charge control for AFM manipulation experiments. This is proven on thin MgO(001) islands supported on Ag(001) and is supported by theoretical modeling, which shows that single ions or dipoles at the tip apex dominate the mean Kelvin voltage.
  • Atom manipulation on an insulating surface at room temperature
    (2014) Kawai, Shigeki; Foster, Adam S.; Federici Canova, Filippo; Onodera, Hiroshi; Kitamura, Shin-ichi; Meyer, Ernst
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Atomic manipulation enables us to fabricate a unique structure at the atomic scale. So far, many atomic manipulations have been reported on conductive surfaces, mainly at low temperature with scanning tunnelling microscopy, but atomic manipulation on an insulator at room temperature is still a long-standing challenge. Here we present a systematic atomic manipulation on an insulating surface by advanced atomic force microscopy, enabling construction of complex patterns such as a ‘Swiss cross’ of substitutional bromine ions in the sodium chloride surface.
  • Atomic structure and water arrangement on K-feldspar microcline (001)
    (2024-02-21) Dickbreder, Tobias; Sabath, Franziska; Reischl, Bernhard; Nilsson, Rasmus V.E.; Foster, Adam S.; Bechstein, Ralf; Kühnle, Angelika
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The properties of clouds, such as their reflectivity or their likelihood to precipitate, depend on whether the cloud droplets are liquid or frozen. Thus, understanding the ice nucleation mechanisms is essential for the development of reliable climate models. Most ice nucleation in the atmosphere is heterogeneous, i.e., caused by ice nucleating particles such as mineral dusts or organic aerosols. In this regard, K-feldspar minerals have attracted great interest recently as they have been identified as one of the most important ice nucleating particles under mixed-phase cloud conditions. The mechanism by which feldspar minerals facilitate ice nucleation remains, however, elusive. Here, we present atomic force microscopy (AFM) experiments on microcline (001) performed in an ultrahigh vacuum and at the solid-water interface together with density functional theory (DFT) and molecular dynamics (MD) calculations. Our ultrahigh vacuum data reveal features consistent with a hydroxyl-terminated surface. This finding suggests that water in the residual gas readily reacts with the surface. Indeed, the corresponding DFT calculations confirm a dissociative water adsorption. Three-dimensional AFM measurements performed at the mineral-water interface unravel a layered hydration structure with two features per surface unit cell. A comparison with MD calculations suggests that the structure observed in AFM corresponds to the second hydration layer rather than the first water layer. In agreement with previous computation results, no ice-like structure is seen, questioning an explanation of the ice nucleation ability by lattice match. Our results provide an atomic-scale benchmark for the clean and water-covered microcline (001) plane, which is mandatory for understanding the ice nucleation mechanism on feldspar minerals.
  • Atomic Structure of a Spinel-Like Transition Al2O3(100) Surface
    (2014) Jensen, Thomas N.; Meinander, Kristoffer; Helveg, Stig; Foster, Adam S.; Kulju, Sampo; Musso, Tiziana; Lauritsen, Jeppe V.
     School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We study a crystalline epitaxial alumina thin film with the characteristics of a spinel-type transition Al2O3(100)surface by using atom-resolved noncontact atomic force microscopy and density functional theory. It is shown that the films are terminated by an Al-O layer rich in Al vacancies, exhibiting a strong preference for surface hydroxyl group formation in two configurations. The transition alumina films are crystalline and perfectly stable in ambient atmospheres, a quality which is expected to open the door to new fundamental studies of the surfaces of transition aluminas.
  • Atomic-resolution three-dimensional hydration structures on a heterogeneously charged surface
    (2017-12-01) Umeda, Kenichi; Zivanovic, Lidija; Kobayashi, Kei; Ritala, Juha; Kominami, Hiroaki; Spijker, Peter; Foster, Adam S.; Yamada, Hirofumi
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Local hydration structures at the solid-liquid interface around boundary edges on heterostructures are key to an atomic-level understanding of various physical, chemical and biological processes. Recently, we succeeded in visualising atomic-scale three-dimensional hydration structures by using ultra-low noise frequency-modulation atomic force microscopy. However, the time-consuming three-dimensional-map measurements on uneven heterogeneous surfaces have not been achieved due to experimental difficulties, to the best of our knowledge. Here, we report the local hydration structures formed on a heterogeneously charged phyllosilicate surface using a recently established fast and nondestructive acquisition protocol. We discover intermediate regions formed at step edges of the charged surface. By combining with molecular dynamics simulations, we reveal that the distinct structural hydrations are hard to observe in these regions, unlike the charged surface regions, possibly due to the depletion of ions at the edges. Our methodology and findings could be crucial for the exploration of further functionalities.
  • Atomic-scale dissipation processes in dynamic force spectroscopy
    (2011) Kawai, Shigeki; Canova, Filippo Federici; Glatzel, Thilo; Foster, Adam S.; Meyer, Ernst
     School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    A systematic distance-dependent measurement of the quasistatic tip-sample interactions reveals a hidden stochastic dissipative interaction of the atomic-scale contact in dynamic force microscopy. By comparison of experiment with detailed molecular dynamics simulations, we demonstrate that the infrequently observed hysteresis loops are attributed to the formation of atomic chains during tip retraction. These lead to a large magnitude of energy dissipation in a single cycle and dominate the average measured dissipation, while also leading to differences in the forces measured in static and dynamic force microscopy. This paper provides quantitative force measurements and insights into atomic-scale dissipation processes.
  • Atomic-scale study of the adsorption of calcium fluoride on Si(100) at low-coverage regime
    (2011) Chiaravalloti, Franco; Dujardin, Gérald; Riedel, Damien; Pinto, Henry P.; Foster, Adam S.
     School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We investigate, experimentally and theoretically, the initial stage of the formation of Ca/Si and Si/F structures that occurs during the adsorption of CaF2 molecules onto a bare Si(100) surface heated to 1000 K in a low-coverage regime (0.3 monolayer). A low-temperature (5 K) scanning tunneling microscope (STM) is used to observe the topographies and the electronic properties of the exposed silicon surfaces. Our atomic-scale study reveals that several chemical reactions arise during CaF2 deposition, such as dissociation of the CaF2 molecules and etching of the surface silicon dimers. The experimental and calculated STM topographies are compared using the density functional theory, and this comparison enables us to identify two types of reacted structures on the Si(100) surface. The first type of observed complex surface structure consists of large islands formed with a semiperiodic sequence of 3 × 2 unit cells. The second one is made of isolated Ca adatoms adsorbed at specific sites on the Si(100)-2 × 1 surface.
  • Atomically controlled substitutional boron-doping of graphene nanoribbons
    (2015) Kawai, Shigeki; Saito, Shohei; Osumi, Shinichiro; Yamaguchi, Shigehiro; Foster, Adam S.; Spijker, Peter; Meyer, Ernst
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Boron is a unique element in terms of electron deficiency and Lewis acidity. Incorporation of boron atoms into an aromatic carbon framework offers a wide variety of functionality. However, the intrinsic instability of organoboron compounds against moisture and oxygen has delayed the development. Here, we present boron-doped graphene nanoribbons (B-GNRs) of widths of N=7, 14 and 21 by on-surface chemical reactions with an employed organoboron precursor. The location of the boron dopant is well defined in the centre of the B-GNR, corresponding to 4.8 atom%, as programmed. The chemical reactivity of B-GNRs is probed by the adsorption of nitric oxide (NO), which is most effectively trapped by the boron sites, demonstrating the Lewis acid character. Structural properties and the chemical nature of the NO-reacted B-GNR are determined by a combination of scanning tunnelling microscopy, high-resolution atomic force microscopy with a CO tip, and density functional and classical computations.
  • Author Correction: Atomic-resolution three-dimensional hydration structures on a heterogeneously charged surface (Nature Communications DOI: 10.1038/s41467-017-01896-4)
    (2018-12-01) Umeda, Kenichi; Zivanovic, Lidija; Kobayashi, Kei; Ritala, Juha; Kominami, Hiroaki; Spijker, Peter; Foster, Adam S.; Yamada, Hirofumi
     Other contribution
    The original version of the Supplementary Information associated with this Article contained an error in Supplementary Figure 9e,f in which the y-axes were incorrectly labelled from '-40' to '40', rather than the correct '-400' to '400'. The HTML has been updated to include a corrected version of the Supplementary Information. Nature Communications, 2041-1723, Volume 9, Issue 1
  • Automated Tip Functionalization via Machine Learning in Scanning Probe Microscopy
    (2022-04) Alldritt, Benjamin; Urtev, Fedor; Oinonen, Niko; Aapro, Markus; Kannala, Juho; Liljeroth, Peter; Foster, Adam S.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Auto-CO-AFM is an open-source software package for scanning probe microscopes that enables the automatic functionalization of scanning probe tips with carbon monoxide molecules. This enables machine operators to specify the quality of the tip needed utilizing a pre-trained library with off-the-shelf software. From a single image, the software package can determine which molecules on a surface are carbon monoxide, perform the necessary tip functionalization procedures, interface with microscope software to control the tip position, and determine the centeredness of the tip after a successful functionalization. This is of particular interest for atomic force microscopy imaging of molecules on surfaces, where the tip functionalization is a necessary and time consuming step needed for sub-molecular resolution imaging. This package is freely available under the MIT License.
  • B and N ion implantation into carbon nanotubes: Insight from atomistic simulations
    (2005) Kotakoski, J.; Krasheninnikov, A. V.; Ma, Yuchen; Foster, Adam S.; Nordlund, K.; Nieminen, Risto M.
     School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    By employing atomistic computer simulations with empirical potential and density functional force models, we study B/N ion implantation onto carbon nanotubes. We simulate irradiation of single-walled nanotubes with B and N ions and show that up to 40% of the impinging ions can occupy directly the sp2 positions in the nanotube atomic network. We further estimate the optimum ion energies for direct substitution. Ab initio simulations are used to get more insight into the structure of the typical atomic configurations which appear under the impacts of the ions. As annealing should further increase the number of sp2 impurities due to dopant atom migration and annihilation with vacancies, we also study migration of impurity atoms over the tube surface. Our results indicate that irradiation-mediated doping of nanotubes is a promising way to control the nanotube electronic and even mechanical properties due to impurity-stimulated crosslinking of nanotubes.
  • Boundary lubrication with a liquid crystal monolayer
    (2014) Chen, W.; Kulju, S.; Foster, Adam S.; Alava, M. J.; Laurson, L.
     School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We study boundary lubrication characteristics of a liquid crystal (LC) monolayer sheared between two crystalline surfaces by nonequilibrium molecular dynamics simulations, using a simplified rigid bead-necklace model of the LC molecules. We consider LC monolayers confined by surfaces with three different atomic structures, subject to different shearing velocities, thus approximating a wide variety of materials and driving conditions. The time dependence of the friction force is studied and correlated with that of the orientational order exhibited by the LC molecules, arising from the competition between the effect of the structure of the confining surfaces and that of the imposed sliding direction. We show that the observed stick-slip events for low shear rates involve order-disorder transitions, and that the LC monolayer no longer has enough time to reorder at high shear rates, resulting in a smooth sliding regime. An irregular stick-slip phase between the regular stick-slip and smooth sliding is observed for intermediate shear rates regardless of the surface structure.
  • Characterization of a Hexagonal Phosphorus Adlayer on Platinum (111)
    (2015) Heikkinen, Olli; Pinto, Hugo; Sinha, Godhuli; Hämäläinen, Sampsa K.; Sainio, Jani; Öberg, Sven; Briddon, Patric R.; Foster, Adam S.; Lahtinen, Jouko
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
  • Chemical Identification of Ions in Doped NaCl by Scanning Force Microscopy
    (2009) Foster, Adam S.; Barth, Clemens; Henry, Claude R.
     School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    A quantitative comparison between experiment and theory is presented, which shows that all ions of the Suzuki structure on (001) surfaces of Mg2+ or Cd2+ doped NaCl crystals can be identified despite the tip-surface distance, differences in impurity chemistry, and surface termination. The identification can be used to calibrate the potential of the tip's last atom, and it is proposed to use these surfaces for better characterization of deposited nano-objects.
  • Comment on 'Paired Gap States in a Semiconducting Carbon Nanotube: Deep and Shallow Levels'
    (2007) Krasheninnikov, A. V.; Foster, Adam S.; Nieminen, Risto M.
     School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    A Comment on the Letter by Sungjun Lee et al., [Phys. Rev. Lett. 95, 166402 (2005)]. The authors of the Letter offer a Reply.