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Scanning gate imaging of quantum point contacts and the origin of the 0.7 anomaly

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Nano Research 2015年第3期8卷 948-956页

作者： Andrea lagallo Nicola Paradiso stefano Roddaro Christian Reichl Werner Wegscheider Giorgio Biasiol Lucia Sorba Fabio Beltram stefan heun National Enterprise for Nanoscience and Nanotechnology (NEST) Istituto Nanoscienze-CNR and Scuola Normale Superiore Piazza San Silvestro 12 56127 Pisa Italy Istituto Offcina dei Materiali CNR Laboratorio TASC 34149 Trieste Italy Solid State Physics Laboratory ETH Zurich Schafmattstrasse 16 8093 Zurich Switzerland

The origin of the anomalous transport feature appearing at a conductance G 0.7× （2e2/h） in quasi-lD ballistic devices-the so-called 0.7 anomaly-represents a long standing puzzle. Several mechanisms have been proposed to explain it, but a general consensus has not been achieved. Proposed explanations have been based on quantum interference, the Kondo effect, Wigner crystallization, and other phenomena. A key open issue is whether the point defects that can occur in these low-dimensional devices are the physical cause behind this conductance anomaly. Here we adopt a scanning gate microscopy technique to map individual impurity positions in several quasi-lD constrictions and correlate these with conductance characteristics. Our data demonstrate that the 0.7 anomaly can be observed irrespective of the presence of localized defects, and we conclude that the 0.7 anomaly is a fundamental property of low-dimensional systems.

关键词： two-dimensional electrongas (2-DEG) scanning gate microscopy 0.7 anomaly

Atomic and electronic structure of Si dangling bonds in quasi-free-standing monolayer graphene

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Nano Research 2018年第2期11卷 864-873页

作者： Yuya Murata Tommaso Cavallucci Valentina Tozzini Niko Pavliček Leo Gross Gerhard Meyer Makoto Takamura Hiroki Hibino Fabio Beltram stefan heun NEST Istituto Nanoscienze-CNR and Scuola Normale Superiore Pisa Italy IBM Research-Zurich Rüschlikon Switzerland NTT Basic Research Laboratories Atsugi Kanagawa Japan

Si dangling bonds at the interface of quasi-free-standing monolayer graphene （QFMLG） are known to act as scattering centers that can severely affect carrier mobility Herein, we investigate the atomic and electronic structure of Si dangling bonds in QFMLG using low-temperature scanning tunneling microscopy/ spectroscopy （STM/STS）, atomic force microscopy （AFM）, and density functional theory （DFT） calculations. Two types of defects with different contrast were observed on a flat graphene terrace by STM and AFM; in particular, their STM contrast varied with the bias voltage. Moreover, these defects showed characteristic STS peaks at different energies, 1.1 and 1.4 eV. The comparison of the experimental data with the DFT calculations indicates that the defects with STS peak energies of 1.1 and 1.4 eV consist of clusters of three and four Si dangling bonds, respectively. The relevance of the present results for the optimization of graphene synthesis is discussed.

关键词： quasi-free-standingmonolayer graphene hydrogen intercalation carrier mobility scanning tunnelingmicroscopy scanning tunnelingspectroscop^atomic force microscop3~density functional theory

Dynamical evolution of Ge quantum dots on Si(111):From island formation to high temperature decay

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Aggregate 2022年第4期3卷 114-120页

作者： Navathej Preetha Genesh Fabrizio De Marchi stefan heun stefano Fontana Rachid Belkhou Rahul Purandare Nunzio Motta Anna Sgarlata Massimo Fanfoni Jennifer MacLeod Oliver MacLean Federico Rosei CentreÉnergie Matériaux et TélécommunicationsInstitut National de la Recherche ScientifiqueQuébecCanada NEST Istituto Nanoscienze-CNR and Scuola Normale SuperiorePisaItaly Sincrotrone Trieste SCpA BasovizzaItaly LURE UniversitéParis-SudOrsay CedexFrance School of Chemistry and Physics and Centre for Materials Science Queensland University of TechnologyBrisbaneAustralia Dipartimento di Fisica Universitàdi Roma“Tor Vergata”RomeItaly Key Laboratory of Functional Materials Physics and Chemistry of the Ministry of Education Jilin Normal UniversityChangchunP.R.China

Heteroepitaxial growth is a process of profound fundamental importance as well as an avenue to realize nanostructures such as Ge/Si quantum dots(QDs),with appealing properties for applications in opto-and ***,controlling the Ge/Si QD size,shape,and composition remains a major obstacle to their practical ***,Ge nanostructures on Si(111)were investigated in situ and in real-time by low energy electron microscopy(LEEM),enabling the observation of the transition from wetting layer formation to 3D island growth and *** island size,shape,and distribution depend strongly on the growth *** the deposition temperature increases,the islands become larger and sparser,consistent with Brownian nucleation and capture *** 550◦C,two distinct Ge/Si nanostructures are formed with bright and dark appearances that correspond to flat,atoll-like and tall,faceted islands,*** annealing,the faceted islands increase in size at the expense of the flat ones,indicating that the faceted islands are thermodynamically more *** contrast,triangular islands with uniform morphology are obtained from deposition at 600◦C,suggesting that the growth more closely follows the ideal *** annealing,the islands formed at 600◦C initially show no change in morphology and size and then rupture simultaneously,signaling a homogeneous chemical potential of the *** observations reveal the role of dynamics and energetics in the evolution of Ge/Si QDs,which can serve as a step towards the precise control over the Ge nanostructure size,shape,composition,and distribution on Si(111).

关键词： epitaxial growth GeSi heterostructures low energy electron microscopy

Modulation of the Nogo signaling pathway to overcome amyloid-β-mediated neurite inhibition in human pluripotent stem cell-derived neurites

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Neural Regeneration Research 2025年第9期20卷 2645-2654页

作者： Kirsty Goncalves stefan Przyborski Department of Biosciences Durham UniversityDurhamUK Reprocell Europe Ltd. GlasgowUK

Neuronal cell death and the loss of connectivity are two of the primary pathological mechanisms underlying Alzheimer's *** accumulation of amyloid-βpeptides,a key hallmark of Alzheimer's disease,is believed to induce neuritic abnormalities,including reduced growth,extension,and abnormal growth cone morphology,all of which contribute to decreased ***,the precise cellular and molecular mechanisms governing this response remain *** this study,we used an innovative approach to demonstrate the effect of amyloid-βon neurite dynamics in both two-dimensional and three-dimensional cultu re systems,in order to provide more physiologically relevant culture *** utilized various methodologies,including the addition of exogenous amyloid-βpeptides to the culture medium,growth substrate coating,and the utilization of human-induced pluripotent stem cell technology,to investigate the effect of endogenous amyloid-βsecretion on neurite outgrowth,thus paving the way for potential future applications in personalized ***,we also explore the involvement of the Nogo signaling cascade in amyloid-β-induced neurite *** demonstrate that inhibition of downstream ROCK and RhoA components of the Nogo signaling pathway,achieved through modulation with Y-27632(a ROCK inhibitor)and Ibuprofen(a Rho A inhibitor),respectively,can restore and even enhance neuronal connectivity in the presence of amyloid-β.In summary,this study not only presents a novel culture approach that offers insights into the biological process of neurite growth and inhibition,but also proposes a specific mechanism for reduced neural connectivity in the presence of amyloid-βpeptides,along with potential intervention points to restore neurite ***,we aim to establish a culture system that has the potential to serve as an assay for measuring preclinical,predictive outcomes of drugs and their ability to promote neurite outgrowth,both generally and in a patie

关键词： Alzheimer's disease induced pluripotent stem cell neurite outgrowth neuron Nogo Rho A ROCK stem cell three-dimensional culture

Generalized Sampling in Shift Invariant Spaces with Frames

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Acta Mathematica Sinica,English Series 2012年第9期28卷 1823-1844页

作者： stefan ERICSSON Department of Engineering Sciences and Mathematics Lule University of Technology

Generalized sampling in a shift invariant subspace V of L2（R） is considered. A function f in V is processed with different filters Lm and then one tries to reconstruct f from the samples L^mf（j＇k）. We develop a theory of how to do this in the case when V possesses a shift invariant frame. Special attention is paid to the question： How to obtain dual frames with compact support？

关键词： Generalized sampling frames Riesz basis reproducing kernel shift invariant spaces

Constitutive relations for the shear band evolution in granular matter under large strain

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Particuology 2008年第6期6卷 501-505页

作者： stefan Luding Multi Scale Mechanics TS CTW UTwente P.O. Box 217 7500 AE Enschede Netherlands

A so-called ＂split-bottom ring shear cell＂ leads to wide shear bands under slow, quasi-static deformation. Unlike normal cylindrical Couette shear cells or rheometers, the bottom plate is split such that the outer part of it can move with the outer wall, while the other part （inner disk） is immobile. From discrete element simulations （DEM）, several continuum fields like the density, velocity, deformation gradient and stress are computed and evaluated with the goal to formulate objective constitutive relations for the powder flow behavior. From a single simulation, by applying time- and （local） space-averaging, a non-linear yield surface is obtained with peculiar stress dependence. The anisotropy is always smaller than the macroscopic friction coefficient. However, the lower bound of anisotropy increases with the strain rate, approaching the maximum according to a stretched exponential with a specific rate that is consistent with a shear path of about one particle diameter.

关键词： Ring shear cell Shear bands DEM simulation Micro-macro transition Objective constitutive relations Yield stress fluid

Experimental investigation on slip conditions during thread rolling with flat dies

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Friction 2024年第1期12卷 136-143页

作者： stefan VOLZ Peter GROCHE Institute for Production Engineering and Forming Machines Technical University DarmstadtOtto-Berndt Straße 2Darmstadt 64287Germany

The process design of flat die rolling operations can be a tedious and costly process due to the challenges posed by small process *** this work,an effort is made to closely investigate and understand the process limits caused by excessive slippage of the *** measurements are carried out to capture the characteristics of excessive slippage and the influence of the stroke rate and the tribological system on this process *** differences in slippage were observed,depending on the tribological *** systems with polymer based lubricants showed excessive slippage at low stroke rates,systems using oil or no lubricant endured higher stroke rates before process limits were *** optical measurements revealed three major forms of slippage:successful rolling without slippage,failure due to excessive slippage at process start,and failure due to excessive slippage at around one workpiece rotation.

关键词： rolling incremental forming thread rolling slippage profile rolling

Influence of sample preparation on nanoindentation results of twinninginduced plasticity steel

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International Journal of Minerals,Metallurgy and Materials 2021年第5期28卷 877-887页

作者： Jiali Zhang stefan Zaefferer Institute for Materials Applications in Mechanical Engineering RWTH Aachen UniversityAachen 52062Germany Max-Planck-Institut für Eisenforschung Düsseldorf 40237Germany

Nanoindentation is an attractive characterization technique,as it not only measures the local properties of a material but also facilitates understanding of deformation mechanisms at submicron ***,because of the complex stress-strain field and the small scale of the deformation under the nanoindenter,the results can be easily influenced by artifacts induced during sample *** this work,a systematic study was conducted to better understand the influence of sample preparation methods on the nanoindentation results of ductile *** experiments were conducted on a steel(Fe-22Mn-0.65C,wt%)with twinning-induced plasticity(TWIP),which was selected for its large grain size and sensitivity to different surface preparation *** grouping the results obtained from each nanoindent,chemical polishing was found to be the best sample preparation method with respect to the resulting mechanical properties of the *** contrast,the presence of a deformation layer left by mechanical polishing and surface damage induced by focused ion beam(FIB)scanning were confirmed by the dislocation-nucleation-induced pop-in events of nanoindentation.

关键词： TWIP steels nanoindentation mechanical polishing chemical polishing pop-in

Hopf algebras and Dyson-Schwinger equations

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Frontiers of physics 2016年第3期11卷 161-177页

作者： stefan Weinzierl PRISMA Cluster of Excellence Institut fiir Physik Johannes Gutenberg- Universitiit Mainz D - 55099 Mainz Germany

In this paper I discuss Hopf algebras and Dyson-Schwinger equations. This paper starts with an introduction to Hopf algebras, followed by a review of the contribution and application of Hopf algebras to particle physi... 详细信息

关键词： Feynman integrals Hopf algebras Dyson-Schwinger equations