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Search Results: 1 - 10 of 400 matches for " Thilo Glatzel "
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Oriented growth of porphyrin-based molecular wires on ionic crystals analysed by nc-AFM
Thilo Glatzel,Lars Zimmerli,Shigeki Kawai,Ernst Meyer
Beilstein Journal of Nanotechnology , 2011, DOI: 10.3762/bjnano.2.4
Abstract: The growth of molecular assemblies at room temperature on insulating surfaces is one of the main goals in the field of molecular electronics. Recently, the directed growth of porphyrin-based molecular wires on KBr(001) was presented. The molecule–surface interaction associated with a strong dipole moment of the molecules was sufficient to bind them to the surface; while a stabilization of the molecular assemblies was reached due to the intermolecular interaction by π–π binding. Here, we show that the atomic structure of the substrate can control the direction of the wires and consequently, complex molecular assemblies can be formed. The electronic decoupling of the molecules by one or two monolayers of KBr from the Cu(111) substrate is found to be insufficient to enable comparable growth conditions to bulk ionic materials.
The role of the cantilever in Kelvin probe force microscopy measurements
George Elias,Thilo Glatzel,Ernst Meyer,Alex Schwarzman
Beilstein Journal of Nanotechnology , 2011, DOI: 10.3762/bjnano.2.29
Abstract: The role of the cantilever in quantitative Kelvin probe force microscopy (KPFM) is rigorously analyzed. We use the boundary element method to calculate the point spread function of the measuring probe: Tip and cantilever. The calculations show that the cantilever has a very strong effect on the absolute value of the measured contact potential difference even under ultra-high vacuum conditions, and we demonstrate a good agreement between our model and KPFM measurements in ultra-high vacuum of NaCl monolayers grown on Cu(111). The effect of the oscillating cantilever shape on the KPFM resolution and sensitivity has been calculated and found to be relatively small.
Advanced atomic force microscopy techniques
Thilo Glatzel,Hendrik H?lscher,Thomas Schimmel,Mehmet Z. Baykara
Beilstein Journal of Nanotechnology , 2012, DOI: 10.3762/bjnano.3.99
Abstract:
Analytical Approach to the Local Contact Potential Difference on (001) Ionic Surfaces: Implications for Kelvin Probe Force Microscopy
Franck Bocquet,Laurent Nony,Christian Loppacher,Thilo Glatzel
Physics , 2008, DOI: 10.1103/PhysRevB.78.035410
Abstract: An analytical model of the electrostatic force between the tip of a non-contact Atomic Force Microscope (nc-AFM) and the (001) surface of an ionic crystal is reported. The model is able to account for the atomic contrast of the local contact potential difference (CPD) observed while nc-AFM-based Kelvin Probe Force Microscopy (KPFM) experiments. With the goal in mind to put in evidence this short-range electrostatic force, the Madelung potential arising at the surface of the ionic crystal is primarily derived. The expression of the force which is deduced can be split into two major contributions: the first stands for the coupling between the microscopic structure of the tip apex and the capacitor formed between the tip, the ionic crystal and the counter-electrode; the second term depicts the influence of the Madelung surface potential on the mesoscopic part of the tip, independently from its microscopic structure. These short-range electrostatic forces are in the range of ten pico-Newtons. When explicitly considering the crystal polarization, an analytical expression of the bias voltage to be applied on the tip to compensate for the local CPD, i.e. to cancel the short-range electrostatic force, is derived. The compensated CPD has the lateral periodicity of the Madelung surface potential. However, the strong dependence on the tip geometry, the applied modulation voltage as well as the tip-sample distance, which can even lead to an overestimation of the real surface potential, makes quantitative KPFM measurements of the local CPD extremely difficult.
A Multi-scale Approach for Simulations of Kelvin Probe Force Microscopy with Atomic Resolution
Ali Sadeghi,Alexis Baratoff,S. Alireza Ghasemi,Stefan Goedecker,Thilo Glatzel,Shigeki Kawai,Ernst Meyer
Physics , 2012, DOI: 10.1103/PhysRevB.86.075407
Abstract: The distance dependence and atomic-scale contrast observed in nominal contact potential difference (CPD) signals recorded by KPFM on surfaces of insulating and semiconducting samples, have stimulated theoretical attempts to explain such effects. We attack this problem in two steps. First, the electrostatics of the macroscopic tip-cantilever-sample system is treated by a finite-difference method on an adjustable nonuniform mesh. Then the resulting electric field under the tip apex is inserted into a series of atomistic wavelet-based density functional theory (DFT) calculations. Results are shown for a realistic neutral but reactive silicon nano-scale tip interacting with a NaCl(001) sample. Bias-dependent forces and resulting atomic displacements are computed to within an unprecedented accuracy. Theoretical expressions for amplitude modulation (AM) and frequency modulation (FM) KPFM signals and for the corresponding local contact potential differences (LCPD) are obtained by combining the macroscopic and atomistic contributions to the electrostatic force component generated at the voltage modulation frequency, and evaluated for several tip oscillation amplitudes A up to 10 nm. Being essentially constant over a few Volts, the slope of atomistic force versus bias is the basic quantity which determines variations of the atomic-scale LCPD contrast. Already above A = 0.1 nm, the LCPD contrasts in both modes exhibit almost the same spatial dependence as the slope. In the AM mode, this contrast is approximately proportional to $A^{-1/2}$, but remains much weaker than the contrast in the FM mode, which drops somewhat faster as A is increased. These trends are a consequence of the macroscopic contributions to the KPFM signal, which are stronger in the AM-mode and especially important if the sample is an insulator even at sub-nanometer separations where atomic-scale contrast appears.
Probing Atomic Structure and Majorana Wavefunctions in Mono-Atomic Fe-chains on Superconducting Pb-Surface
Remy Pawlak,Marcin Kisiel,Jelena Klinovaja,Tobias Meier,Shigeki Kawai,Thilo Glatzel,Daniel Loss,Ernst Meyer
Physics , 2015,
Abstract: Motivated by the striking promise of quantum computation, Majorana bound states (MBSs) in solid-state systems have attracted wide attention in recent years. In particular, the wavefunction localization of MBSs is a key feature and crucial for their future implementation as qubits. Here, we investigate the spatial and electronic characteristics of topological superconducting chains of iron atoms on the surface of Pb(110) by combining scanning tunneling microscopy (STM) and atomic force microscopy (AFM). We demonstrate that the Fe chains are mono-atomic, structured in a linear fashion, and exhibit zero-bias conductance peaks at their ends which we interprete as signature for a Majorana bound state. Spatially resolved conductance maps of the atomic chains reveal that the MBSs are well localized at the chain ends (below 25 nm), with two localization lengths as predicted by theory. Our observation lends strong support to use MBSs in Fe chains as qubits for quantum computing devices.
Sympathetic Prions
Markus Glatzel
The Scientific World Journal , 2001, DOI: 10.1100/tsw.2001.258
Abstract:
Measuring Soil Fertility under Hagenia abyssinica (Bruce) J. F. Gmel by the Biotest Method
Biruktayet Assefa,Gerhard Glatzel
International Journal of Agronomy , 2010, DOI: 10.1155/2010/845087
Abstract: The experiment was conducted at the Forestry Research Center, Ethiopia in 2008. Soil was sampled under the canopy of Hagenia abyssinica and from farmland area adjacent to the forest to measure fertility of soils by using the biotest with linseed (Linum usitatissimum L.), barley (Hordeum vulgare L.), and wheat (Triticum aestivum L.) as indicators. The experimental design was a completely randomized design comprising of 20 seedlings per study site. Seeds were seeded into polythene plastic bags. Seedling emergence, germination, and survival rate were recorded. Plant height and root collar diameter were measured. Final weight of fresh biomass was measured, and each component was oven-dried at 70°C. Dry weight was recorded at constant weight. Significant differences ( ) were observed between soil treatments. Plants grown on Hagenia-influenced soils attained better performance, suggesting the beneficial role of Hagenia abyssinica in enhancing soil fertility status which in turn results in higher productivity. 1. Introduction In Ethiopia, land degradation in the form of soil erosion and declining soil fertility is a serious constraint to agricultural productivity as well as economic development [1–3]. Land cover change triggered by agricultural land expansion and heavy livestock pressure are the proximate causes for degradation [4–6]. Some of the noticeable problems of soil fertility loss in the highlands include using dung and crop residues as household fuels and animal feeds, declining fallow periods, soil and organic matter burning (guie), and low use of chemical fertilizers [7]. Though the farming system in most part is mixed crop-livestock, nutrient flows between the two are predominantly one sided, with feeding of crop residues to livestock but little or no dung being returned to the soil [7]. Fertility replenishment can only be sustained if the nutrients removed are returned to the soil through addition. Trees on crop land have potential to improve soil fertility due to their organic inputs with nutrient recycling through mineralization [8–12]. Because soils in many parts of Ethiopia have low fertility, farmers are trying to apply inorganic fertilizers to replenish plant nutrients in their crop land. However, with the rising costs of farm inputs, this is becoming less of an option for the majority who do not have enough cash to purchase fertilizers. Therefore, it is critical to look for an option by examining trees that can improve top soil fertility through addition of litter. Hagenia abyssinica (Bruce) J. F. Gmel is an indigenous broad-leaved
Hard x-ray emission spectroscopy: a powerful tool for the characterization of magnetic semiconductors
Mauro Rovezzi,Pieter Glatzel
Physics , 2013, DOI: 10.1088/0268-1242/29/2/023002
Abstract: This review aims to introduce the x-ray emission spectroscopy (XES) and resonant inelastic x-ray scattering (RIXS) techniques to the materials scientist working with magnetic semiconductors (e.g. semiconductors doped with 3d transition metals) for applications in the field of spin-electronics. We focus our attention on the hard part of the x-ray spectrum (above 3 keV) in order to demonstrate a powerful element- and orbital-selective characterization tool in the study of bulk electronic structure. XES and RIXS are photon-in/photon-out second order optical processes described by the Kramers-Heisenberg formula. Nowadays, the availability of third generation synchrotron radiation sources permits applying such techniques also to dilute materials, opening the way for a detailed atomic characterization of impurity-driven materials. We present the K{\beta} XES as a tool to study the occupied valence states (directly, via valence-to-core transitions) and to probe the local spin angular momentum (indirectly, via intra-atomic exchange interaction). The spin sensitivity is employed, in turn, to study the spin-polarized unoccupied states. Finally, the combination of RIXS with magnetic circular dichroism (RIXS-MCD) extends the possibilities of standard magnetic characterization tools.
The Sensorium: A Multimodal Neurofeedback Environment
Thilo Hinterberger
Advances in Human-Computer Interaction , 2011, DOI: 10.1155/2011/724204
Abstract: The Sensorium is a neurofeedback environment that allows people to experience signals from their nonperceptible body processes visually and auditorily. Various (neuro-)physiological rhythms and frequencies are projected simultaneously as soundscapes and “lightscapes” into the environment. A wireless physiological amplifier device sends signals such as EEG and ECG to a computer for real-time processing using the modified brain-computer interface software “Thought Translation Device” (TTD). The TTD performs signal filtering, parametric orchestral sonification, and light control. In a pilot study, 20 participants have been exposed to their ongoing brain and heart signals while sitting inside the Sensorium, a small room equipped with a speaker and lighting system. Almost all of them reported an increase in contentment, relaxation, happiness, and inner harmony. They also reported a widening in their body consciousness. In future, therapeutic paradigms will be developed and the treatment effects on people with psychosomatic diseases will be evaluated. 1. Introduction Neurofeedback (NFB) is a method for training of self-regulation of physiological, especially neurophysiological body signals. It became popular in the 1970s already when the first devices for relaxation training were offered. The self-regulation training was mediated by visual or acoustical real-time display of, for example, the muscular tension measured in the electromyogram (EMG) or the amplitude of the alpha rhythm activity of the electroencephalogram (EEG). The measurement implies electrode sensors to be attached to the brain or other body parts picking up the signals ranged from V up to mV with frequencies between 0 and about 100?Hz. The EEG feedback era first started to become popular after Kamiya published his studies on operant conditioning of the EEG alpha rhythm. He found the alpha amplitude to be connected to the state of relaxation [1]. Since then, many biofeedback devices appeared on the market and often, these devices have been applied in nonscientific settings. Unfortunately, the hypothesis of a clear connection between EEG alpha power and relaxation could not maintain its position after further scientific explorations. The scientific investigations of brain physiological self regulation conducted by Sterman et al. in 1974 described the application of EEG NFB for the therapy of patients with epilepsy [2]. Birbaumer and his group demonstrated the human ability for self regulation of the slow cortical potentials (SCPs); that is, EEG potential shifts below 1?Hz [3, 4]. They also
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