Methodology for extraction of space charge density profiles at nanoscale from Kelvin probe force microscopy measurements

International audienceTo understand the physical phenomena occurring at metal/dielectric interfaces, determination of the charge density profile at nanoscale is crucial. To deal with this issue, charges were injected applying a DC voltage on lateral Al-electrodes embedded in a SiN x thin dielectric layer. The surface potential induced by the injected charges was probed by Kelvin probe force microscopy (KPFM). It was found that the KPFM frequency mode is a better adapted method to probe accurately the charge profile. To extract the charge density profile from the surface potential two numerical approaches based on the solution to Poisson's equation for electrostatics were investigated: the second derivative model method, already reported in the literature, and a new 2D method based on the finite element method (FEM). Results highlight that the FEM is more robust to noise or artifacts in the case of a non-flat initial surface potential. Moreover, according to theoretical study the FEM appears to be a good candidate for determining charge density in dielectric films with thicknesses in the range from 10 nm to 10 μm. By applying this method, the charge density profile was determined at nanoscale, highlighting that the charge cloud remains close to the interface

Handling Geometric Features in Nanoscale Characterization of Charge Injection and Transport in thin Dielectric Films

International audienceDue to miniaturization and attractiveness of nanosized and/or nanostructured dielectric layers, characterization at the local scale of charge injection and transport phenomena comes to the fore. To that end the electric modes derived from Atomic Force Microscopy (AFM) are more and more frequently used. In this study, the influence of AFM tip-plane system configuration on the electric field distribution is investigated for homogeneous and heterogeneous (nanostructured) thin dielectric layers. The experimental and computing results reveal that the radial component of the electric field conveys the charge lateral spreading whereas the axial component of the electric field governs the amount of injected charges. The electric field distribution is slightly influenced by the heterogeneity of the material. Moreover, the interpretation of the current measurements requires consideration of the entire electric field distribution and not only the computed field at the contact point

Characterization of the Electrical Behaviour of Thin Dielectric Films at Nanoscale using Methods Derived from Atomic Force Microscopy: Application to Plasma Deposited AgNPs-Based Nanocomposites

International audienceRecent advances in the development of micro-and nano-devices call for applications of thin nanocomposite dielectric films (thickness less than few tens of nanometers) with tuneable electrical properties. For optimization purposes, their behaviour under electrical stress needs to be probed at relevant scale, i.e. nanoscale. To that end electrical modes derived from Atomic Force Microscopy (AFM) appear the best methods due to their nanoscale resolution and non-destructive nature which permits in-situ characterization. The potentialities of electrical modes derived from AFM are presented in this work. The samples under study consist of plasma processed thin dielectric silica layers with embedded silver nanoparticles (AgNPs). Charge injection at local scale, performed by using AFM tip, is investigated by Kelvin Probe Force Microscopy (KPFM). Modulation of the local permittivity induced by the presence of AgNPs is assessed by Electrostatic Force Microscopy (EFM)

Charge injection phenomena at the metal/dielectric interface investigated by Kelvin probe force microscopy

International audienceThe understanding of charge injection mechanism at metal/dielectric interface is crucial in many applications. A direct probe of such phenomenon requires a charge measurement method whose spatial resolution is compatible with the characteristic scale of phenomena occurring after injection, like charge trapping, and with the geometry of samples under investigation. In this paper, charge injection at metal/dielectric interface and their motion in silicon nitride layer under tunable electric field are probed at nanoscale using a technique derived from Atomic Force Microscopy. This was achieved by realizing embedded lateral electrode structures and using surface potential measurement by Kelvin Probe Force Microscopy (KPFM) to provide voltage, field and charge profiles close to the metal/dielectric interface during and after biasing the electrodes. The influence of electric field enhancement at the interface due to the electrode geometry was accounted for. Electron and hole mobility was estimated from surface potential profiles obtained under polarization. Charge dynamic was investigated during depolarization steps

Charges injection investigation at metal/dielectric interfaces by Kelvin Probe Force Microscopy

International audienceCharges injection at metal/dielectric interface and their motion in silicon nitride layer is investigated using samples with embedded lateral electrodes and surface potential measurement by Kelvin Probe Force Microscopy (KPFM). Bipolar charge injection was evidenced using this method. From surface potential profile, charge density distribution is extracted by using Poisson's equation. The evolution of the charge density profile with polarization bias and depolarization time was also investigated

Interface properties in dielectrics: A cross-section analysis by atomic force microscopy

International audienceEven if interfaces are more and more investigated their properties remain partially unknown, especially as regards their electronic properties. This is mainly related to the lack of characterization at relevant scale. In this context, electrical modes derivate from Atomic Force Microscopy appear well adapted. In this paper, a method to probe space charge at nanoscale is proposed. This method is based on surface potential measurement by Kelvin Probe Force Microscopy (KPFM) and post-processing technique based either on numerical derivation or Finite Element Method. Through these methods, densities of interface charges and injected charges were determined at different metal/dielectric interfaces

Space Charge at Nanoscale: Probing Injection and Dynamic Phenomena Under Dark/Light Configurations by Using KPFM and C-AFM

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Adsorption of proteins on solid surfaces containing AgNPs

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Conditionnement d’une surface de SiO2 seule ou additivée de nanoparticules d’argent par des protéines modèles (ASB et Fn) : exploration des forces d’adhésion de Candida albicans

National audienceDepuis plusieurs années, la silice (SiO2) suscite un grand intérêt dans le domaine biomédical. En raison de son utilisation pour la conception d’implants à revêtement antimicrobien ou encore de systèmes de marquage et d’administration de médicaments in vivo, la SiO2 représente un matériau adapté à un usage biomédical. La présence de nanoparticules d’argent (AgNPs) à sa surface ou leur incorporation à quelques nanomètres de la surface conduisent à une modulation des propriétés physico-chimiques et antimicrobiennes de la silice. Toutefois, les propriétés de la SiO2 peuvent être fortement modifiées suite à l’adhésion des protéines sur sa surface : la conformation et l’organisation des protéines adsorbées peuvent ainsi influencer les processus biologiques en lien avec ce matériau, dont l’adhésion microbienne. Dans ce travail, nous avons évalué l’influence des protéines modèles (sérum albumine bovine - SAB ou fibronectine - Fn) adsorbées et déshydratées à la surface de différents substrats de SiO2 ou nanocomposites (couches de silice contenant des AgNPs) sur l’adhésion de Candida albicans IP48.72. Les résultats ont révélé des différences significatives en fonction de la nature de la protéine utilisée. En effet, une augmentation des forces d’adhésion cellulaire a été observée avec la Fn. L’adhésion des levures est alors maintenue même sous l’application des fortes contraintes de cisaillement pariétales. En revanche, la présence de SAB conduit à une diminution d’adhésion cellulaire. Dans ces mêmes conditions, nous avons pu confirmer une amplification de l’adhésion de C. albicans en présence des AgNPs exposées à la surface en raison des forces électrostatiques mises en jeu. Les forces d’adhésion de la levure sont plus faibles lorsque les AgNPs sont enterrées dans la matrice de SiO2. Ceci pourrait être relié à un relargage progressif des Ag+. Quel que soit le procédé d’obtentiondes nanocomposites (AgNPs exposées à la surface ou enterrées), la quasi-totalité des cellules de C. albicans est non viable dès la phase initiale d’adhésion, confirmant l’effet létal de Ag+. La mort cellulaire n’induit pas de diminution de l’adhésion de C. albicans

Multi-dimensional modelling of electrostatic forces between atomic force microscopy tip and dielectric surface

In this paper, simulation results for the electrostatic force between an Atomic Force Microscope (AFM) sensor and the surface of a dielectric are presented for different bias voltages on the tip:. The aim is to analyse force-distance curves as AFM detection mode for electrostatic charges. The sensor is composed of a cantilever supporting a conical tip terminated by a spherical apex; the effect of the cantilever is neglected here. Our model of force curve has been developed using the Finite Volume Method. The scheme is based on the Polynomial Reconstruction Operator – PRO-scheme. First results of the computation of electrostatic force for different tip– sample distances, 0 to 600 nm, and for different DC voltage stress applied to the tip, 6 to 25 V, are shown and compared with experimental data in order to validate our approach.This work was supported by Region Midi-Pyrénées (France), by FEDER Funds through COMPETE Program and by Fundação para a Ciência e a Tecnologia (Portugal), within the Project PEst-C/MAT/UI0013/2011