Atom-by-atom extraction using scanning tunneling microscope tip-cluster interaction

We investigate atomistic details of a single atom extraction process realized by using scanning tunneling microscope (STM) tip-cluster interaction on a Ag(111) surface at 6 K. Single atoms are extracted from a silver cluster one atom at a time using small tunneling biases less than 35 mV and a threshold tunneling resistance of 47 kOhm. A combination of total energy calculations and molecular dynamics simulations shows a lowering of the atom extraction barrier upon approaching the tip to the cluster. Thus, a mere tuning of the proximity between the tip and the cluster governs the extraction process and is sufficient to extract an atom. The atomically precise control and reproducibility of the process are demonstrated by repeatedly extracting single atoms from a silver cluster on an atom-by-atom basis

Manipulating Kondo Temperature via Single Molecule Switching

Two conformations of isolated single TBrPP-Co molecules on a Cu(111) surface are switched by applying +2.2 V voltage pulses from a scanning tunneling microscope tip at 4.6 K. The TBrPP-Co has a spin-active cobalt atom caged at its center and the interaction between the spin of this cobalt atom and free electrons from the Cu(111) substrate can cause a Kondo resonance. Tunneling spectroscopy data reveal that switching from the saddle to a planar molecular conformation enhances spin-electron coupling, which increases the associated Kondo temperature from 130 K to 170 K. This result demonstrates that the Kondo temperature can be manipulated just by changing molecular conformation without altering chemical composition of the molecule.Comment: To appear in Nano Lett (2006

Understanding atom movement during lateral manipulation with the STM tip using a simple simulation method

Kühnle A, Meyer G, Hla SW, Rieder K-H. Understanding atom movement during lateral manipulation with the STM tip using a simple simulation method. Surface Science. 2002;499(1):15-23.We report on a fast simulation method to investigate the movement of an atom induced by the tip during lateral manipulation with a scanning tunneling microscope. The simulation is based on a model assuming the atom moving in the combined potential of tip and surface. The pathway of the tip is subdivided in small steps, and the atomic position for each step is calculated by an iterative algorithm searching for the closest energetic minimum. The method is demonstrated for manipulation on the (111) surface of an fcc metal. Our model calculations predict which energetic minima of the surface are attained by the atom during manipulation. The details of the modelled manipulation curves allow a precise description of the atomic pathway in dependence on manipulation direction and positioning of the tip relative to the atom. Furthermore, the simulation predicts a transition from the so-called pulling to sliding manipulation mode upon reducing tip-surface distance, well in agreement with general experimental observations. To test our algorithm we present experimental results for the manipulation of iodine on Cu(I 11) along the [211] direction and compare them to simulated manipulation curves. The comparison allows for a complete understanding of all details in atomic movements during manipulation along a complicated path. (C) 2001 Published by Elsevier Science B.V

Controlled lateral manipulation of single diiodobenzene molecules on the Cu(111) surface with the tip of a scanning tunnelling microscope

Hla SW, Kühnle A, Bartels L, Meyer G, Rieder KH. Controlled lateral manipulation of single diiodobenzene molecules on the Cu(111) surface with the tip of a scanning tunnelling microscope. Surface Science. 2000;454:1079-1084.We report on the controlled lateral manipulations of adsorbed single diiodobenzene molecules on the Cu(111) surface with a scanning tunnelling microscope (STM) tip at 20 K. The molecular motions in this experiment are mainly induced by the attractive interaction between the tip and the molecule. Even though the leading manipulation mode is 'pulling', a continuous 'sliding' mode can also be induced if we use higher tip-molecule interaction forces. During the manipulation process, the molecules can follow the tip with hops of single or double copper-atomic-site distances and in some cases 'hop-scotch' type movements can also be observed. (C) 2000 Elsevier Science B.V. All rights reserved

Legal coercion, respect & reason-responsive agency

Legal coercion seems morally problematic because it is susceptible to the Hegelian objection that it fails to respect individuals in a way that is ‘due to them as men’. But in what sense does legal coercion fail to do so? And what are the grounds for this requirement to respect? This paper is an attempt to answer these questions. It argues that (a) legal coercion fails to respect individuals as reason-responsive agents; and (b) individuals ought to be respected as such in virtue of the fact that they are human beings. Thus it is in this sense that legal coercion fails to treat individuals with the kind of respect ‘due to them as men’.The Leverhulme Trust (ECF-2012-032); AHRC (AH/H015655/1

Direct Visualization of 3-Dimensional Force and Energy Map of a Single Molecular Switch

Mechanical properties of molecules adsorbed on materials surfaces are increasingly vital for the applications of molecular thin films. Here, we conduct a fundamental research to induce conformational change mechanically on a single molecule and quantify the driving force needed for such molecular shape switch via a low temperature (~ 5K) Scanning Tunneling Microscope (STM) and Qplus Atomic Force Microscope (Q+AFM). Our measurement maps a three-dimensional landscape for mechanical potential and force at single molecule level with high spatial resolution in all three dimensions of a few angstrom (10-10 m). Molecule TBrPP-Co (a cobalt porphyrin) deposited on an atomically clean gold substrate typically has two of its pentagon rings tilted upward and the other two downward. An atomically sharp tip of the STM/Q+AFM, which vibrates with a high frequency (~ 30kHz), is employed to scan the molecule at different heights with 0.1Å increment and meanwhile record tip-molecule interaction strength in the form of tip frequency change. When tip approaches to the threshold distance to the molecule, mechanical force become large enough and cause pentagon rings flip their direction. Due to the sensitive nature of tip-molecule interaction, the rings flipping can be directly visualized by STM, as rings tilting upward exhibit two bright protrusions in contrast to rings downward in image. By processing frequency change, we obtain a three-dimensional mechanical potential and force map for a single molecule with the resolution of angstrom level in all three dimensions. Our preliminary results indicate that an energy barrier of ~400meV needs to be overcome for rings flipping of TBrPP-Co.https://digitalcommons.odu.edu/gradposters2021_sciences/1015/thumbnail.jp

STM observations of a one-dimensional electronic edge state at steps on Cu(111)

Bartels L, Hla SW, Kühnle A, Meyer G, Rieder K-H, Manson JR. STM observations of a one-dimensional electronic edge state at steps on Cu(111). Physical Review B. 2003;67(20):205416.Scanning tunneling microscopy measurements across isolated straight step edges on a Cu(111) surface were carried out for biases between 100 mV and 5 V. In addition to the well known surface state oscillations, and at lower sample bias than the onset of the two-dimensional surface image state, a sharply defined linear protrusion, was observed at the top of the step faces. This linear feature is interpreted as a one-dimensional image state at the step, with its energy modified by a dipolar potential whose appearance is attributed to Smoluchowski smoothing of the electron density at the step edge

Selective nanomanipulation using optical forces

We present a detailed theoretical study of the recent proposal for selective nanomanipulation of nanometric particles above a substrate using near-field optical forces [Chaumet {\it et al.} Phys. Rev. Lett. {\bf 88}, 123601 (2002)]. Evanescent light scattering at the apex of an apertureless near-field probe is used to create an optical trap. The position of the trap is controlled on a nanometric scale via the probe and small objects can be selectively trapped and manipulated. We discuss the influence of the geometry of the particles and the probe on the efficiency of the trap. We also consider the influence of multiple scattering among the particles on the substrate and its effect on the robustness of the trap.Comment: 12 pages, 17 figure

Does ought imply can?

Most philosophers believe that a person can have an obligation only insofar as she is able to fulfil it, a principle generally referred to as “Ought Implies Can”. Arguably, this principle reflects something basic about the ordinary concept of obligation. However, in a paper published recently in this journal, Wesley Buckwalter and John Turri presented evidence for the conclusion that ordinary people in fact reject that principle. With a series of studies, they claimed to have demonstrated that, in people’s judgements, obligations persist irrespective of whether those who hold them have the ability to fulfil them. We argue in this paper that due to some problems in their design, Buckwalter & Turri’s conclusions may not be warranted. We present the results of a series of studies demonstrating the problems with their design and showing that, with an improved design, people judge that obligation depends on ability after all

Sphingosine 1-phosphate modulates antigen capture by murine langerhans cells via the S1P2 receptor subtype

Dendritic cells (DCs) play a pivotal role in the development of cutaneous contact hypersensitivity (CHS) and atopic dermatitis as they capture and process antigen and present it to T lymphocytes in the lymphoid organs. Recently, it has been indicated that a topical application of the sphingolipid sphingosine 1-phosphate (S1P) prevents the inflammatory response in CHS, but the molecular mechanism is not fully elucidated. Here we indicate that treatment of mice with S1P is connected with an impaired antigen uptake by Langerhans cells (LCs), the initial step of CHS. Most of the known actions of S1P are mediated by a family of five specific G protein-coupled receptors. Our results indicate that S1P inhibits macropinocytosis of the murine LC line XS52 via S1P2 receptor stimulation followed by a reduced phosphatidylinositol 3-kinase (PI3K) activity. As down-regulation of S1P2 not only diminished S1P-mediated action but also enhanced the basal activity of LCs on antigen capture, an autocrine action of S1P has been assumed. Actually, S1P is continuously produced by LCs and secreted via the ATP binding cassette transporter ABCC1 to the extracellular environment. Consequently, inhibition of ABCC1, which decreased extracellular S1P levels, markedly increased the antigen uptake by LCs. Moreover, stimulation of sphingosine kinase activity, the crucial enzyme for S1P formation, is connected not only with enhanced S1P levels but also with diminished antigen capture. These results indicate that S1P is essential in LC homeostasis and influences skin immunity. This is of importance as previous reports suggested an alteration of S1P levels in atopic skin lesions