Method to calculate electric fields at very small tip-sample distances in atomic force microscopy

Copyright 2010 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.A method to calculate electric magnitudes at very small tip-sample distances in atomic force microscopy is presented. We show that the method accurately calculates the electrostatic potential and vertical force for electrostatic force microscopy geometries that cannot be correctly simulated by the standard techniques. This technique can accurately calculate tip-sample distances four orders of magnitude smaller than the tip radius. We also demonstrate that, at this range, traditional techniques underestimate the electrostatic force in almost 30%. Finally, we calculate the jump-to-contact distance for geometries obtained from experiments that combine atomic force microscopy and scanning tunneling microscopy.J. J. Sáenz, P. Varona, E. Serrano, and F. Rodríguez for insightful discussions. This work was supported by Ministerio de Educación y Ciencia Grant Nos. TIN 2007-65989 and Comunidad Autonoma de Madrid S-SEM-0255-200

Influence of the substrate and tip shape on the characterization of thin films by electrostatic force microscopy

Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. G. M. Sacha, "Influence of the Substrate and Tip Shape on the Characterization of Thin Films by Electrostatic Force Microscopy", IEEE Transactions on Nanotechnology, vol.12, no.2, pp.152-156, Marzo 2013.Electrostatic force microscopy has been shown to be a useful tool to determine the dielectric constant of nanoscaled thin films that play a key role in many electrical, optical and biological phenomena. Previous approaches have made use of simple analytical models to analyze the experimental data for these materials. Here we show that the electrostatic force shows a completely different behavior when the shape of the tip and sample are taken into account. We present a complete study of the interaction between the whole tip and the layers below the thin film. We demonstrate that physical magnitudes such as the surface charge density distribution and the size of the materials have a strong influence on the EFM signal. The EFM sensitivity to the substrate below the thin film decreases with the substrate thickness and saturates for thicknesses above two times the length of the tip, when it is close to that of an infinite medium.Author acknowledges interesting discussion from J. J. Sáenz, C. Gómez-Navarro, J. Gómez-Herrero and E. Castellano-Hernández. This work was supported by TIN2010- 19607. Author acknowledges support from the Spanish Ramón y Cajal Program

Finite Conductivity Effects in Electrostatic Force Microscopy on Thin Dielectric Films: A Theoretical Model

A study of the electrostatic force between an Electrostatic Force Microscope tip and a dielectric thin film with finite conductivity is presented. By using the Thomas-Fermi approximation and the method of image charges, we calculate the electrostatic potential and force as a function of the thin film screening length, which is a magnitude related to the amount of free charge in the thin film and is defined as the maximum length that the electric field is able to penetrate in the sample. We show the microscope's signal on dielectric films can change significantly in the presence of a finite conductivity even in the limit of large screening lengths. This is particularly relevant in determining the effective dielectric constant of thin films from Electrostatic Force Microscopy measurements. According to our model, for example, a small conductivity can induce an error of more than two orders of magnitude in the determination of the dielectric constant of a material. Finally, we suggest a method to discriminate between permittivity and conductivity effects by analyzing the dependence of the signal with the tip-sample distance.The authors acknowledge J. J. Saenz, C. Gomez-Navarro, and J. Gomez-Herrero for insightful discussions. This work has been partially funded by the Banco Santander-UAM Research Program. G. M. Sacha acknowledges support from the Spanish Ramon y Cajal Program

Artificial intelligence in nanotechnology

This is the author’s version of a work that was accepted for publication in Nanotechnology. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Nanotechnology 24.45 (2013): 452002During the last decade there has been an increasing use of artificial intelligence tools in nanotechnology research. In this paper we review some of these efforts in the context of interpreting scanning probe microscopy, the study of biological nanosystems, the classification of material properties at the nanoscale, theoretical approaches and simulations in nanoscience, and generally in the design of nanodevices. Current trends and future perspectives in the development of nanocomputing hardware that can boost artificial intelligence based applications are also discussed. Convergence between artificial intelligence and nanotechnology can shape the path for many technological developments in the field of information sciences that will rely on new computer architectures and data representations, hybrid technologies that use biological entities and nanotechnological devices, bioengineering, neuroscience and a large variety of related disciplines

L’architecture à la formation des enseignants: Du tangram aux carreaux Nazari. Firmitas, utilitas et ‘venustas’

El trabajo se ha realizado para valorar la arquitectura como herramienta pedagógica para la adquisición de conceptos geométricos por parte del profesorado de las primeras etapas de la educación. La investigación ha sido incluida dentro del proyecto I+D de referencia EDU2011-29114 y de título Escuelas para la Justicia Social. MÉTODO. La experiencia se ha servido del trabajo previo que han venido desarrollando los autores de este artículo desde el año 2003. Se han resuelto dos encuestas que se han venido usando como pre y postest, para evaluar el nivel de satisfacción y aprovechamiento de los cursos que se han impartido en los Centros Territoriales de Innovación y Formación del profesorado de la Comunidad de Madrid. Del mismo modo se ha secuenciado una serie de sesiones de trabajo con las que atender esta formación específica. RESULTADOS. El hallazgo principal del estudio es la constatación de las posibilidades de la arquitectura como elemento interdisciplinar válido para la adquisición de conocimientos geométricos. DISCUSIÓN. El trabajo se integra junto con otras propuestas innovadoras de didáctica de las Ciencias Experimentales y las Matemáticas de las que solo se reflejan en este artículo las referidas a la geometría. Los comentarios recibidos por parte de los docentes que han sido formados con las mismas son positivos y han sido trasladado a las aulas satisfactoriamente, pero de momento no tenemos registro nominal cuantitativo de sus resultadosThis paper is intended to value Architecture as a pedagogic tool in the acquisition of geometric concepts by teachers at the early stages in Education. This research study has been included in a research project (ref. EDU2011-29114) entitled “Escuelas para la Justicia Social” (“Schools for Social Justice”). METHOD. This experience has been drawn on previous studies which have been conducted by the authors of the present paper since 2003. The designs of two questionnaires have been later used as pre- and post-tests in order to assess the degree of satisfaction and performance achieved throughout a number of courses given in Local Innovation and Teacher Training Centers in the Autonomous Community of Madrid . Similarly, a series of working sessions have been sequenced in order to address this specific training. RESULTS. The main finding of the present study consists in revealing the possibilities offered by Architecture as an interdisciplinary element valid in the acquisition of geometric knowledge. DISCUSSION. The present paper is integrated into other ground-breaking proposals in the field of didactics of Experimental Sciences and Mathematics of which only those pertaining to geometry are under study here. Although the comments received by teachers have been positive and have been successfully implemented in classrooms, at present the authors of this paper still do not have a quantitative nominal register of the resultsLe travail a été effectué pour valoriser l’architecture comme un outil pédagogique pour l’acquisition de concepts géométriques par des enseignants dans les premières étapes d’enseignement. La recherche est encadrée dans le projet R+D de référence EDU2011-29114 dont le titre est: Ecoles pour la Justice Sociale. MÉTHODE. L’expérience est conséquence des travaux pré- cédents qui ont été développés par les auteurs de cet article après 2003. On a fait deux enquêtes qui ont été utilisées comme pré et post-test, pour évaluer le niveau de satisfaction et de réussite dans les cours qui ont été enseignés dans les Centres Territoriaux d’Innovation et de Formation des enseignants à Madrid (*). De la même façon, on a séquencé une série de séances de travail grâce auxquelles on pourrait donner réponse à cette formation spécifique. RÉSULTATS. La principale conclusion de l’étude est la constatation des possibilités de l’architecture comme un élément interdisciplinaire valable pour l’acquisition de connaissances géométriques. DISCUSSION. Le travail est intégré a vec d’autres nouvelles propositions d’enseignement de la Didactique des Sciences Expérimentales et de Mathématiques desquelles on a seulement montré dans cet article celles qui se réfèrent à la géométrie. Les commentaires reçus par les enseignants qui ont été formés sous le même modèle sont favorables et la méthodologie a été implémentée avec succès. Pour le moment les auteurs de l’article n’ont aucune trace nominale quantitative de leurs résultat

Enhanced dielectric constant resolution of thin insulating films by electrostatic force microscopy

This is the author’s version of a work that was accepted for publication in Journal of Physics: Condensed Matter. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Journal of Physics: Condensed Matter 24.15 (2012) 10.1088/0953-8984/24/15/155303Electrostatic Force Microscopy has been shown to be a useful tool to determine the dielectric constant of insulating films of nanometer thicknesses that play a key role in many electrical, optical and biological phenomena. Previous approaches make use of simple analytical formulae to analyse the experimental data for thin insulating films deposited directly on a metallic substrate. Here we show that the sensitivity of the EFM signal to changes in the dielectric constant of the thin film can be enhanced by using dielectric substrates with low dielectric constants. We present detailed numerical calculations of the tip-sample electrostatic interaction in the following set-up: the insulating thin film, a dielectric substrate (or spacing layer) of known low dielectric constant and a metallic electrode. The EFM sensitivity to the dielectric constant increases with the thickness of the spacing layer and saturates for thicknesses above 100-300 nm, when it is close to that of an infinite medium.Authors acknowledge C. Gómez-Navarro, J. Gómez-Herrero, P. Varona and F. Rodríguez for insightful discussions. This work was supported by TIN2010-19607, the Spanish MICINN ( Grant No: FIS2009 − 13430 −C02 − 02 ) and by the Comunidad de Madrid Microseres Program (Grant No: S2009/T IC − 1476). GMS acknowledges support from the Spanish Ramón y Cajal Program

On the use of artificial neural networks in electrostatic force microscopy

The electronic version of this article is the complete one and can be found online at: http://link.springer.com/article/10.1186/1556-276X-7-250Includes the electronic version of the poster presented at the 12th Trends in Nanotechnology International Conference (TNT2011), held in Tenerife (Spain)The use of electrostatic force microscopy (EFM) to characterize and manipulate surfaces at the nanoscale usually faces the problem of dealing with systems where several parameters are not known. Artificial neural networks (ANNs) have demonstrated to be a very useful tool to tackle this type of problems. Here, we show that the use of ANNs allows us to quantitatively estimate magnitudes such as the dielectric constant of thin films. To improve thin film dielectric constant estimations in EFM, we first increase the accuracy of numerical simulations by replacing the standard minimization technique by a method based on ANN learning algorithms. Second, we use the improved numerical results to build a complete training set for a new ANN. The results obtained by the ANN suggest that accurate values for the thin film dielectric constant can only be estimated if the thin film thickness and sample dielectric constant are known.This work was supported by TIN2010-19607 and BFU2009-08473. GMS acknowledges support from the Spanish Ramón y Cajal Program

Introducción a la investigación arqueológica para estudiantes a través de reconstrucciones virtuales

En este artículo se presentan los resultados obtenidos en las actividades de divulgación sobre el funcionamiento de una excavación arqueológica. Las actividades de divulgación se realizaron en centros de educación infantil, primaria y secundaria de la Comunidad de Madrid. El contenido de dichas jornadas se obtuvo durante la cuarta campaña de la misión arqueológica en Luxor de la Universidad de La Laguna, y se dividió en dos partes. La primera fue una reconstrucción virtual de la tumba tebana y la segunda una serie de contenidos audiovisuales relacionados con las actividades realizadas en la excavación. Estos contenidos se presentaron a los estudiantes a través de una aplicación informática muy interactiva a la que tuvieron acceso en las aulas de Informática de sus centros. Los resultados obtenidos indican un altísimo grado de motivación por parte de los estudiantes en el uso de la herramienta, que en ocasiones llega a ser contraproducente en términos de rendimiento en el aprendizaje. Para contrarrestar este efecto negativo, se propone usar técnicas adicionales de motivación que deberán ser usadas de forma simultánea a la presentación de este tipo de aplicaciones.This article presents the results obtained in the dissemination activities on the procedures of an archaeological excavation. The dissemination activities were carried out in early childhood, primary and secondary education centers of the Community of Madrid. The content of these conferences was obtained during the fourth campaign of the archaeological mission of the University of La Laguna in Luxor, and was divided in two parts. First, we developed a virtual reconstruction of the Theban tomb. After this, a series of audiovisual contents related to the activities carried out in the excavation were shown to the students. These audiovisuals were presented to the students through an interactive computer application in the computer rooms of their centers. The results obtained indicate a very high degree of motivation on the part of students in the use of the tool, which sometimes becomes counterproductive in terms of performance in learning. To counteract this negative effect, we propose the use of additional motivational techniques that should be used simultaneously to the presentation of this type of application

Stark effect in a wedge-shaped quantum box

The effect of an external applied electric field on the electronic ground state energy of a quantum box with a geometry defined by a wedge is studied by carrying out a variational calculation. This geometry could be used as an approximation for a tip of a cantilever of an atomic force microscope. We study theoretically the Stark effect as function of the parameters of the wedge: its diameter, angular aperture and thickness; as well as function of the intensity of the external electric field applied along the axis of the wedge in both directions; pushing the carrier towards the wider or the narrower parts. A confining electronic effect, which is sharper as the wedge dimensions are smaller, is clearly observed for the first case. Besides, the sign of the Stark shift changes when the angular aperture is changed from small angles to angles theta>pi. For the opposite field, the electronic confinement for large diameters is very small and it is also observed that the Stark shift is almost independent with respect to the angular aperture.Comment: 23 pages, 9 figures, 1 tabl

Photoinduced Charge Transfer and Trapping on Single Gold Metal Nanoparticles on TiO2

We present a study of the effect of gold nanoparticles (Au NPs) on TiO2 on charge generation and trapping during illumination with photons of energy larger than the substrate band gap. We used a novel characterization technique, photoassisted Kelvin probe force microscopy, to study the process at the single Au NP level. We found that the photoinduced electron transfer from TiO2 to the Au NP increases logarithmically with light intensity due to the combined contribution of electron-hole pair generation in the space charge region in the TiO2-air interface and in the metal-semiconductor junction. Our measurements on single particles provide direct evidence for electron trapping that hinders electron-hole recombination, a key factor in the enhancement of photo(electro)catalytic activity.This work was supported by the Office of Basic Energy Sciences (BES) of the U.S. Department of Energy (DOE) under contract DE-AC02-05CH11231 through the Structure and Dynamics of Materials Interfaces Program (FWP KC31SM) and the Molecular Foundry. M.L. acknowledges funds from Comunidad de Madrid (P2018/EMT-4308), a Fulbright grant PRX16/00564, and the MCIU-AEI-FEDERUE (RTI2018-096937-B-C22 and MAT2014-59772-C2-1-P). J.C. acknowledges financial support from Ministerio de Ciencia e Innovación (MICINN) and the European Union through the project PID2019-104272RB-C52. Also, Y.H. acknowledges financial support from MCIU through MAT2014-59772-C2-2- P and L.M. from EC through ERC-2013-SYG-610256. V.A.P.O. and M.B. acknowledge the financial support from EC through ERC CoG HyMAP 648319, MINECO PID2019- 106315RB-I00 and ENE2017-89170-R, ″Comunidad de Madrid″ and European Structural Funds (FotoArt-CM project S2018/NMT-4367) and Fundación Ramón Areces (Art-Leaf project). M.B. also thanks the Juan de la Cierva Incorporación contract (IJC2019042430-I). X.Z. was supported by the NSF-BSF 359 grant number 1906014. The authors thank Prof. Eran Edri, María Ujué González Sagardoy, and Judit Meseguer- Oliver for fruitful discussions and Asylum customer support for help with modifications of the AFM