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A methodology development for the study of near surface stress gradients

Marques, M. J.; Dias, A. M.; Gergaud, P.; Lebrun, J. L.
Fonte: Universidade de Coimbra Publicador: Universidade de Coimbra
Tipo: Artigo de Revista Científica Formato: aplication/PDF
ENG
Relevância na Pesquisa
55.93%
A modification of the geometry used in the sin2 [psi] technique of X-ray diffraction is described. A modified equation for residual stress determination, including geometric adapted Fij, is presented. This method allows near surface stress gradients determination and is called pseudo-grazing incidence method. The limits of the new technique were first tested on different powder materials with X-ray radiation produced by conventional tubes and by a synchrotron radiation source. The technique was finally applied for the determination of a residual stress profile in a polished molybdenum surface before and after the deposition of a PVD chromium film.; http://www.sciencedirect.com/science/article/B6TXD-40GHPVT-C/1/82a45e55041866281a13e3fc1bf8cc4c

Evaluation of stress-strain behavior of surface treated steels by X-ray diffraction

Coelho, Luís Manuel de Jesus; Batista, A. C.; Nobre, J. P.; Marques, M. J.
Fonte: Instituto Politécnico de Leiria Publicador: Instituto Politécnico de Leiria
Tipo: Artigo de Revista Científica
Publicado em //2011 ENG
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45.9%
X-ray diffraction assisted four-point bending method (XRDABM) enables to analyze the evolution of surface stress with the strain during bending of specimens. This experimental methodology was used to characterize the stressstrain behavior of two plasma nitriding steels, DIN 40 Cr Mn Mo 7 and DIN 32 Cr Mo V 13, with gradients of mechanical properties across the surface layers, allowing the characterization of the in-depth evolution of the local yield strength in the nitrided layer. The results show a significantly increase of the yield strength of the nitride layers and a good agreement between the in-depth evolution of the yield strength and the XRD peak breadth for the two nitrided steels.

A sensitive measure of surface stress in the resting neutrophil.

Needham, D.; Hochmuth, R. M.
Fonte: The Biophysical Society Publicador: The Biophysical Society
Tipo: Artigo de Revista Científica
Publicado em /06/1992 EN
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45.9%
The simplest parameterized model of the "passive" or "resting receptive" neutrophil views the cell as being composed of an outer cortex surrounding an essentially liquid-like highly viscous cytoplasm. This cortex has been measured to maintain a small persistent tension of approximately 0.035 dyn/cm (Evans and Yeung. 1989. Biophys. J. 56:151-160) and is responsible for recovering the spherical shape of the cell after large deformation. The origin of the cortical tension is at present unknown, but speculations are that it may be an active process related to the sensitivity of a given cell to external stimulation and the "passive-active" transition. In order to characterize further this feature of the neutrophil we have used a new micropipet manipulation method to give a sensitive measure of the surface stress as a function of the surface area dilation of the highly ruffled cellular membrane. In the experiment, a single cell is driven down a tapered pipet in a series equilibrium deformation positions. Each equilibrium position represents a balance between the stress in the membrane and the pressure drop across the cell. For most cells that seemed to be "passive," as judged by their spherical appearance and lack of pseudopod activity, area dilations of approximately 30% were accompanied by only a small increase in the membrane tension...

Approaches to Increasing Surface Stress for Improving Signal-to-Noise Ratio of Microcantilever Sensors

Ji, Hai-Feng; Armon, Benjamin D.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 01/03/2010 EN
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46.07%
Microcantilever sensor technology has been steadily growing for the last fifteen years. While we have gained a great amount of knowledge in microcantilever bending due to surface stress changes, which is a unique property of microcantilever sensors, we are still in the early stages of understanding the fundamental surface chemistries of surface-stress-based microcantilever sensors. In general, increasing surface stress, which is caused by interactions on the microcantilever surfaces, would improve the S/N ratio, and subsequently the sensitivity and reliability of microcantilever sensors. In this review, we will summarize: A) the conditions under which a large surface stress can readily be attained, and B) the strategies to increase surface stress in case a large surface stress can not readily be reached. We will also discuss our perspectives on microcantilever sensors based on surface stress changes.

Cantilever measurements of surface stress, surface reconstruction, film stress and magnetoelastic stress of monolayers

Sander, Dirk; Tian, Zhen; Kirschner, Jürgen
Fonte: Molecular Diversity Preservation International (MDPI) Publicador: Molecular Diversity Preservation International (MDPI)
Tipo: Artigo de Revista Científica
Publicado em 29/07/2008 EN
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46.07%
We review the application of cantilever-based stress measurements in surface science and magnetism. The application of thin (thickness appr. 0.1 mm) single crystalline substrates as cantilevers has been used successfully to measure adsorbate-induced surface stress changes, lattice misfit induced film stress, and magneto-elastic stress of ferromagnetic monolayers. Surface stress changes as small as 0.01 N/m can be readily measured, and this translates into a sensitivity for adsorbate-coverage well below 0.01 of one layer. Stress as large as several GPa, beyond the elasticity limits of high strength materials, is measured, and it is ascribed to the lattice misfit between film and substrate. Our results point at the intimate relation between surface stress and surface reconstruction, stress-induced structural changes in epitaxially strained films, and strain-induced modifications of the magneto-elastic coupling in ferromagnetic monolayers.

First-Principles Surface Stress Calculations and Multiscale Deformation Analysis of a Self-Assembled Monolayer Adsorbed on a Micro-Cantilever

Shih, Yu-Ching; Chen, Chuin-Shan; Wu, Kuang-Chong
Fonte: MDPI Publicador: MDPI
Tipo: Artigo de Revista Científica
Publicado em 23/04/2014 EN
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45.96%
Micro-cantilever sensors are widely used to detect biomolecules, chemical gases, and ionic species. However, the theoretical descriptions and predictive modeling of these devices are not well developed, and lag behind advances in fabrication and applications. In this paper, we present a novel multiscale simulation framework for nanomechanical sensors. This framework, combining density functional theory (DFT) calculations and finite element method (FEM) analysis, is capable of analyzing molecular adsorption-induced deformation and stress fields in the sensors from the molecular scale to the device scale. Adsorption of alkanethiolate self-assembled monolayer (SAM) on the Au(111) surface of the micro-cantilever sensor is studied in detail to demonstrate the applicability of this framework. DFT calculations are employed to investigate the molecular adsorption-induced surface stress upon the gold surface. The 3D shell elements with initial stresses obtained from the DFT calculations serve as SAM domains in the adsorption layer, while FEM is employed to analyze the deformation and stress of the sensor devices. We find that the micro-cantilever tip deflection has a linear relationship with the coverage of the SAM domains. With full coverage...

The effect of surface stress on interfacial solitary wave propagation

Hammerton, P. W.; Bassom, Andrew P.
Fonte: Oxford University Press Publicador: Oxford University Press
Tipo: Artigo de Revista Científica Formato: text/html
EN
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46.05%
The propagation of long wavelength disturbances on the surface of a fluid layer of finite depth is considered. Attention is focused on the effect of stress applied at the surface. Constant surface tension leads to a normal stress at the surface, but the presence of a surfactant or the application of an electric field can give rise to tangential stresses. In the large Reynolds number limit, the evolution equation for the surface elevation contains contributions from both boundary layers in the flow; one is adjacent to the free surface while the other lies at the base of the fluid layer.Aweakly non-linear analysis is performed leading to an evolution equation similar to the classic Korteweg-de Vries equation, but modified by additional terms due to the viscosity and to the tangential and normal stress at the surface. It is demonstrated that careful treatment of the boundary layer at the free surface is necessary when the tangential stress at the surface is non-zero. Particular cases of flows with tangential surface stress due the presence of a surfactant or due to an electric field are discussed, and a pseudo-spectral scheme is used in order to obtain some typical numerical results.

Einfluß der absoluten Oberflächenspannung auf die Form dünner Einkristalle: Eine Analyse am Beispiel Si(111); Influence of absolute surface stress on the deformation of thin single crystal sheets: an analysis for Si(111)

Kaiser, Stefan
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Dissertação
DE_DE
Relevância na Pesquisa
66.04%
Obwohl die absolute Oberflächenspannung eine für viele Anwendungen relevante, fundamentale Eigenschaft von Festkörperoberflächen ist, existiert bisher kein Verfahren, mit dem diese makroskopische Größe mit akzeptabler Genauigkeit gemessen werden kann. Änderungen der Oberflächenspannung lassen sich mit der sogenannten Biegebalkenmethode ermitteln, Absolutwerte dagegen nicht. Nach einem von Müller und Kern 1994 aufgestellten Modell hat die absolute Oberflächenspannung einen nicht vernachlässigbaren Einfluß auf die durch die Schwerkraft verursachte Deformation von sehr dünnen, waagerecht aufgehängten Einkristallen. Eine Messung des Effektes ist allerdings technisch anspruchsvoll und wurde in der vorliegenden Arbeit erstmals realisiert. Durch den Einsatz von Phasenschiebungs-Interferometrie ist es gelungen, die Biegelinie eines 25,4 mm langen und ca. 50 Mikrometer dicken Si(111)-Streifen zu bestimmen. Dabei zeigte sich jedoch, daß die Deformation von der absoluten Oberflächenspannung unabhängig ist. Dieses Verhalten konnte durch eine ausführliche theoretische Analyse erklärt werden, wobei das Modell von Müller und Kern widerlegt wurde. Tatsächlich tritt die vorhergesagte Abhängigkeit nur unter speziellen Randbedingungen auf. Aus einem überarbeiteten Modell konnte eine neue Probengeometrie abgeleitet werden...

Surface stress in offshore flow and quasi-frictional decoupling

Mahrt, L.; Vickers, Dean; Sun, Jielun; Crawford, Timothy L.; Crescenti, Gennaro; Frederickson, Paul
Fonte: Escola de Pós-Graduação Naval Publicador: Escola de Pós-Graduação Naval
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
45.95%
Aircraft data collected at approximately 15 m above the sea surface in the coastal zone are analyzed to examine the spatial distribution of surface stress. Advection of stronger turbulence from land dominates the near-surface turbulence for the first few kilometers offshore. With offshore flow of warm air over cold water, strong stratification leads to very small surface stress. Because the stability restricts the momentum transfer to the waves, the aerodynamic surface roughness decreases to very small values, which in turn decreases atmospheric mixing. The redevelopment of the boundary layer farther downstream is examined. Computation of fluxes from observations for stable cases is difficult due to a variety of errors including large random flux errors, possible instrumental loss of small-scale flux, difference between the surface flux and that at the observational level, and inadvertent capture of mesoscale motions in the computed turbulent fluctuations. Although the errors appear to be substantial, the aircraft momentum fluxes compare favorably with those from sonic anemometers on two buoys and a tower at the end of a 570-m pier, even with near collapse of the turbulence.

Towards the nanomechanical actuation and controlled assembly of nanomaterials using charge-transfer reactions in electroactive self-assembled monolayers

Norman, Lana
Fonte: Université de Montréal Publicador: Université de Montréal
Tipo: Thèse ou Mémoire numérique / Electronic Thesis or Dissertation
EN
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46.13%
Les microcantileviers fonctionnalisés offrent une plateforme idéale pour la nano- et micro-mécanique et pour le développement de (bio-) capteurs tres sensible. Le principe d’opération consiste dans des évènements physicochimiques qui se passent du côté fonctionnalisé du microcantilevier induisant une différence de stress de surface entre les deux côtés du cantilevier qui cause une déflexion verticale du levier. Par contre, les facteurs et les phénomènes interfacials qui régissent la nature et l'intensité du stress de surface sont encore méconnus. Pour éclaircir ce phénomène, la première partie de cette thèse porte sur l'étude des réactions de microcantileviers qui sont recouverts d'or et fonctionnalisés par une monocouche auto-assemblée (MAA) électroactive. La formation d'une MAA de ferrocènylundécanethiol (FcC11SH) à la surface d'or d'un microcantilevier est le modèle utilisé pour mieux comprendre le stress de surface induit par l’électrochimie. Les résultats obtenus démontrent qu'une transformation rédox de la MAA de FcC11SH crée un stress de surface qui résulte dans une déflexion verticale du microcantilevier. Dépendamment de la flexibilité du microcantilevier, cette déflexion peut varier de quelques nanomètres à quelques micromètres. L’oxydation de cette MAA de FcC11SH dans un environnement d'ions perchlorate génère un changement de stress de surface compressive. Les résultats indiquent que la déflexion du microcantilevier est due à une tension latérale provenant d'une réorientation et d'une expansion moléculaire lors du transfért de charge et de pairage d’anions. Pour vérifier cette hypothèse...

Capillarity of soft amorphous solids: a microscopic model for surface stress

Weijs, Joost H.; Snoeijer, Jacco H.; Andreotti, Bruno
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 15/10/2013
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46.01%
The elastic deformation of a soft solid induced by capillary forces crucially relies on the excess stress inside the solid-liquid interface. While for a liquid-liquid interface this "surface stress" is strictly identical to the "surface free energy", the thermodynamic Shuttleworth equation implies that this is no longer the case when one of the phases is elastic. Here we develop a microscopic model that incorporates enthalpic interactions and entropic elasticity, based on which we explicitly compute the surface stress and surface free energy. It is found that the compressibility of the interfacial region, through the Poisson ratio near the interface, determines the difference between surface stress and surface energy. We highlight the consequence of this finding by comparing with recent experiments and simulations on partially wetted soft substrates.

Measuring the surface stress polar dependence

Metois, J. J.; Saul, A.; Muller, P.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 15/06/2007
Relevância na Pesquisa
46.02%
While measurements of the polar dependence of the surface free energy are easily available, measurements of the whole polar dependence of the surface stress of a crystal do not exist. In this paper is presented a new procedure that allows, for the first time, the experimental determination of the surface stress polar dependence of a crystal. For this purpose (1) electromigration is used to control the kinetic faceting of surface orientations that belong to the equilibrium shape of the crystal and (2) for each destabilised surface, the period of faceting as well as the crystallographic angles of the appearing facets are measured by AFM. The so-obtained data lead to a set of equations whose mathematical solution, compatible with physical constraints, gives access to the surface stress polar dependence of the whole crystal and thus to a better understanding of surface stress properties.; Comment: 8 pages, 6 Figures

Finite element analysis of surface-stress effects in the Si lattice-parameter measurement

Sasso, Carlo; Quagliotti, Danilo; Massa, Enrico; Mana, Giovanni; Kuetgens, Ulrich
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 19/02/2013
Relevância na Pesquisa
45.96%
A stress exists in solids surfaces, similarly to liquids, also if the underlying bulk material is stress-free. This paper investigates the surface stress effect on the measured value of the Si lattice parameter used to determine the Avogadro constant by counting Si atoms. An elastic-film model has been used to provide a surface load in a finite element analysis of the lattice strain of the x-ray interferometer crystal used to measure the lattice parameter. Eventually, an experiment is proposed to work a lattice parameter measurement out so that there is a visible effect of the surface stress.

Surface stress of Ni adlayers on W(110): the critical role of the surface atomic structure

Stojic, Natasa; Binggeli, Nadia
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 15/03/2012
Relevância na Pesquisa
46.02%
Puzzling trends in surface stress were reported experimentally for Ni/W(110) as a function of Ni coverage. In order to explain this behavior, we have performed a density-functional-theory study of the surface stress and atomic structure of the pseudomorphic and of several different possible 1x7 configurations for this system. For the 1x7 phase, we predict a different, more regular atomic structure than previously proposed based on surface x-ray diffraction. At the same time, we reproduce the unexpected experimental change of surface stress between the pseudomorphic and 1x7 configuration along the crystallographic surface direction which does not undergo density changes. We show that the observed behavior in the surface stress is dominated by the effect of a change in Ni adsorption/coordination sites on the W(110) surface.; Comment: 14 pages, 3 figures Published in J. Phys.: Condens. Matter 24 (2012) 135001

Laplace pressure as a surface stress in fluid vesicles

Guven, Jemal
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 12/02/2006
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46.01%
Consider a surface, enclosing a fixed volume, described by a free-energy depending only on the local geometry; for example, the Canham-Helfrich energy quadratic in the mean curvature describes a fluid membrane. The stress at any point on the surface is determined completely by geometry. In equilibrium, its divergence is proportional to the Laplace pressure, normal to the surface, maintaining the constraint on the volume. It is shown that this source itself can be expressed as the divergence of a position-dependent surface stress. As a consequence, the equilibrium can be described in terms of a conserved `effective' surface stress. Various non-trivial geometrical consequences of this identification are explored. In a cylindrical geometry, the cross-section can be viewed as a closed planar Euler elastic curve. With respect to an appropriate centre the effective stress itself vanishes; this provides a remarkably simple relationship between the curvature and the position along the loop. In two or higher dimensions, it is shown that the only geometry consistent with the vanishing of the effective stress is spherical. It is argued that the appropriate generalization of the loop result will involve `null' stresses.; Comment: 18 pages

Giant magnetoelectric effect induced by intrinsic surface stress in ferroic nanorods

Glinchuk, M. D.; Eliseev, E. A.; Morozovska, A. N.; Blinc, R.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 19/09/2007
Relevância na Pesquisa
45.9%
The general approach for the consideration of the magnetoelectric effects in ferroic nanorods is proposed in the framework of the phenomenological theory. The intrinsic surface stress, magneto- and electrostriction as well as piezoelectric and piezomagnetic effects are included into the free energy. The intrinsic surface stress under the curved nanoparticle surface is shown to play an important role in the shift of ferroelectric and ferromagnetic transition temperatures and built-in magnetic and electric fields appearance, which are inversely proportional to the nanorod radius. We consider the case of quadratic and linear magnetoelectric coupling coefficients. The linear coupling coefficient is radius independent, whereas the quadratic ones include terms inversely proportional to the nanorod radius and thus strongly increase with decrease of the radius. The predicted giant relative dielectric tunability in the vicinity of ferromagnetic and ferroelectric phase transition points induced by quadratic magnetoelectric coupling increases by 2-50 times. The quadratic magnetoelectric coupling dramatically changes the phase diagrams of ferroic nanorods when the radius decreases. In particular the second order phase transition may become a first one...

Homogenization of Rough Surfaces: Effective Surface Stress and Superficial Elasticity

Mohammadi, P.; Liu, L.; Sharma, P.; Kukta, R. V.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 28/12/2011
Relevância na Pesquisa
45.97%
Relating microstructure to properties, electromagnetic, mechanical, thermal and their couplings has been a major focus of mechanics, physics and materials science. The majority of the literature focuses on deriving homogenized constitutive responses for macroscopic composites relating effective properties to various microstructural details. Due to large surface to volume ratio, phenomena at the nanoscale require consideration of surface energy effects and the latter are frequently used to interpret size-effects in material behavior. Elucidation of the effect of surface roughness on the surface stress and elastic behavior is relatively under-studied and quite relevant to the behavior of nanostructures. In this work, we present derivations that relate both periodic and random roughness to the effective surface elastic behavior. We find that the residual surface stress is hardly affected by roughness while the superficial elasticity properties are dramatically altered and, importantly, may also result in a change in its sign - this has ramifications in interpretation of sensing based on frequency measurement changes due to surface elasticity. We show that the square of resonance frequency of a cantilever beam with rough surface decreases as much as three times of its value for flat surface.

Temperature dependence of surface stress across an order-disorder transition: p(1x2)O/W(110)

Stojic, N.; Mentes, T. O.; Binggeli, N.; Nino, M. A.; Locatelli, A.; Bauer, E.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 19/03/2010
Relevância na Pesquisa
45.9%
Strain relaxations of a p(1x2) ordered oxygen layer on W(110) are measured as a function of temperature across the disordering transition using low-energy electron diffraction. The measured strains approach values of 0.027 in the [1-10] and -0.053 in the [001] direction. On the basis of the measured strain relaxations, we give quantitative information on temperature-dependent surface stress using the results of ab initio calculations. From the surface formation energy for different strains, determined by first-principles calculations, we estimate that surface stress changes from -1.1 for the ordered phase to -0.2N/m for the disordered one along [1-10], and from 5.1 to 3.4 N/m along [001]. Moreover, our observation that the strains scale inversely with domain size confirms that the strain relaxation takes place at the domain boundaries.; Comment: 8 pages, 5 figures

The influence of surface stress on dislocation emission from sharp and blunt cracks in f.c.c. metals

Schiotz, J.; Carlsson, A. E.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
45.96%
We use computer simulations to study the behavior of atomically sharp and blunted cracks in various f.c.c. metals. The simulations use effective medium potentials which contain many-body interactions. We find that when using potentials representing platinum and gold a sharp crack is stable with respect to the emission of a dislocation from the crack tip, whereas for all other metals studied the sharp crack is unstable. This result cannot be explained by existing criteria for the intrinsic ductile/brittle behavior of crack tips, but is probably caused by surface stresses. When the crack is no longer atomically sharp dislocation emission becomes easier in all the studied metals. The effect is relatively strong; the critical stress intensity factor for emission to occur is reduced by up to 20%. This behavior appears to be caused by the surface stress near the crack tip. The surface stress is a consequence of the many-body nature of the interatomic interactions. The enhanced dislocation emission can cause an order-of-magnitude increase in the fracture toughness of certain materials, in which a sharp crack would propagate by cleavage. Collisions with already existing dislocations will blunt the crack, if this prevents further propagation of the crack the toughness of the material is dramatically increased.; Comment: LaTeX...

Sensing Cantilever Beam Bending by the Optical Lever Technique and Its Application to Surface Stress

Evans, Drew; Craig, Vincent
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
66.07%
Cantilever beams, both microscopic and macroscopic, are used as sensors in a great variety of applications. An optical lever system is commonly employed to determine the deflection and thereby the profile of the cantilever under load. The sensitivity of the optical lever must be calibrated, and this is usually achieved by application of a known load or deflection to the free end of the cantilever. When the sensing operation involves a different type of load or a combination of types of loadings, the calibration and the deflection values derived from it become invalid. Here we develop a master equation that permits the true deflection of the cantilever to be obtained simply from the measurement of the apparent deflection for uniformly distributed loadings and end-moment loadings. These loadings are relevant to the uniform adsorption or application of material to the cantilever or the application of a surface stress to the cantilever and should assist experimentalists using the optical lever, such as in the atomic force microscope, to measure cantilever deflections in a great variety of sensing applications. We then apply this treatment to the experimental evaluation of surface stress. Three forms of Stoney's equation that relate the apparent deflection to the surface stress...