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G. Gomila - One of the best experts on this subject based on the ideXlab platform.
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internal hydration properties of single bacterial endospores probed by Electrostatic Force microscopy
ACS Nano, 2016Co-Authors: Marc Van Der Hofstadt, Rene Fabregas, Ruben Millansolsona, Antonio Juarez, Laura Fumagalli, G. GomilaAbstract:We show that the internal hydration properties of single Bacillus cereus endospores in air under different relative humidity (RH) conditions can be determined through the measurement of its electric permittivity by means of quantitative Electrostatic Force microscopy (EFM). We show that an increase in the RH from 0% to 80% induces a large increase in the equivalent homogeneous relative electric permittivity of the bacterial endospores, from ∼4 up to ∼17, accompanied only by a small increase in the endospore height, of just a few nanometers. These results correlate the increase of the moisture content of the endospore with the corresponding increase of environmental RH. Three-dimensional finite element numerical calculations, which include the internal structure of the endospores, indicate that the moisture is mainly accumulated in the external layers of the endospore, hence preserving the core of the endospore at low hydration levels. This mechanism is different from what we observe for vegetative bacteri...
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electric polarization properties of single bacteria measured with Electrostatic Force microscopy
ACS Nano, 2014Co-Authors: Daniel Estebanferrer, Antonio Juarez, Laura Fumagalli, Martin A Edwards, G. GomilaAbstract:We quantified the electrical polarization properties of single bacterial cells using Electrostatic Force microscopy. We found that the effective dielectric constant, er,eff, for the four bacterial types investigated (Salmonella typhimurium, Escherchia coli, Lactobacilus sakei, and Listeria innocua) is around 3–5 under dry air conditions. Under ambient humidity, it increases to er,eff ∼ 6–7 for the Gram-negative bacterial types (S. typhimurium and E. coli) and to er,eff ∼15–20 for the Gram-positive ones (L. sakei and L. innocua). We show that the measured effective dielectric constants can be consistently interpreted in terms of the electric polarization properties of the biochemical components of the bacterial cell compartments and of their hydration state. These results demonstrate the potential of electrical studies of single bacterial cells.
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theory of amplitude modulated Electrostatic Force microscopy for dielectric measurements in liquids at mhz frequencies
Nanotechnology, 2013Co-Authors: Georg Gramse, Laura Fumagalli, Martin A Edwards, G. GomilaAbstract:A theoretical analysis of amplitude modulated Electrostatic Force microscopy (AM-EFM) in liquid media at MHz frequencies, based on a simple tip–sample parallel plate model, is presented. The model qualitatively explains the main features of AM-EFM in liquid media and provides a simple explanation of how the measured electric Forces are affected by: the frequency of the applied voltage, the tip–sample distance, the ionic concentration, the relative dielectric constant of the solution, and the relative dielectric constant and thickness of the sample. These results provide a simple framework for the design of AM-EFM measurements for localized dielectric characterization in liquid media.
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nanoscale measurement of the dielectric constant of supported lipid bilayers in aqueous solutions with Electrostatic Force microscopy
Biophysical Journal, 2013Co-Authors: Georg Gramse, Laura Fumagalli, Martin A Edwards, Aurora Dolsperez, G. GomilaAbstract:We present what is, to our knowledge, the first experimental demonstration of dielectric constant measurement and quantification of supported lipid bilayers in electrolyte solutions with nanoscale spatial resolution. The dielectric constant was quantitatively reconstructed with finite element calculations by combining thickness information and local polarization Forces which were measured using an Electrostatic Force microscope adapted to work in a liquid environment. Measurements of submicrometric dipalmitoylphosphatidylcholine lipid bilayer patches gave dielectric constants of er ∼ 3, which are higher than the values typically reported for the hydrophobic part of lipid membranes (er ∼ 2) and suggest a large contribution of the polar headgroup region to the dielectric response of the lipid bilayer. This work opens apparently new possibilities in the study of biomembrane Electrostatics and other bioelectric phenomena.
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quantifying the dielectric constant of thick insulators by Electrostatic Force microscopy effects of the microscopic parts of the probe
Nanotechnology, 2012Co-Authors: Georg Gramse, G. Gomila, Laura FumagalliAbstract:We present a systematic analysis of the effects that the microscopic parts of Electrostatic Force microscopy probes (the cone and cantilever) have on the Electrostatic interaction between the tip apex and thick insulating substrates (thickness > 100 μm). We discuss how these effects can influence the measurement and quantification of the local dielectric constant of the substrates. We propose and experimentally validate a general methodology that takes into account the influence of the cone and the cantilever, thus enabling us to obtain very accurate values of the dielectric constants of thick insulators.
Laura Fumagalli - One of the best experts on this subject based on the ideXlab platform.
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internal hydration properties of single bacterial endospores probed by Electrostatic Force microscopy
ACS Nano, 2016Co-Authors: Marc Van Der Hofstadt, Rene Fabregas, Ruben Millansolsona, Antonio Juarez, Laura Fumagalli, G. GomilaAbstract:We show that the internal hydration properties of single Bacillus cereus endospores in air under different relative humidity (RH) conditions can be determined through the measurement of its electric permittivity by means of quantitative Electrostatic Force microscopy (EFM). We show that an increase in the RH from 0% to 80% induces a large increase in the equivalent homogeneous relative electric permittivity of the bacterial endospores, from ∼4 up to ∼17, accompanied only by a small increase in the endospore height, of just a few nanometers. These results correlate the increase of the moisture content of the endospore with the corresponding increase of environmental RH. Three-dimensional finite element numerical calculations, which include the internal structure of the endospores, indicate that the moisture is mainly accumulated in the external layers of the endospore, hence preserving the core of the endospore at low hydration levels. This mechanism is different from what we observe for vegetative bacteri...
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electric polarization properties of single bacteria measured with Electrostatic Force microscopy
ACS Nano, 2014Co-Authors: Daniel Estebanferrer, Antonio Juarez, Laura Fumagalli, Martin A Edwards, G. GomilaAbstract:We quantified the electrical polarization properties of single bacterial cells using Electrostatic Force microscopy. We found that the effective dielectric constant, er,eff, for the four bacterial types investigated (Salmonella typhimurium, Escherchia coli, Lactobacilus sakei, and Listeria innocua) is around 3–5 under dry air conditions. Under ambient humidity, it increases to er,eff ∼ 6–7 for the Gram-negative bacterial types (S. typhimurium and E. coli) and to er,eff ∼15–20 for the Gram-positive ones (L. sakei and L. innocua). We show that the measured effective dielectric constants can be consistently interpreted in terms of the electric polarization properties of the biochemical components of the bacterial cell compartments and of their hydration state. These results demonstrate the potential of electrical studies of single bacterial cells.
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theory of amplitude modulated Electrostatic Force microscopy for dielectric measurements in liquids at mhz frequencies
Nanotechnology, 2013Co-Authors: Georg Gramse, Laura Fumagalli, Martin A Edwards, G. GomilaAbstract:A theoretical analysis of amplitude modulated Electrostatic Force microscopy (AM-EFM) in liquid media at MHz frequencies, based on a simple tip–sample parallel plate model, is presented. The model qualitatively explains the main features of AM-EFM in liquid media and provides a simple explanation of how the measured electric Forces are affected by: the frequency of the applied voltage, the tip–sample distance, the ionic concentration, the relative dielectric constant of the solution, and the relative dielectric constant and thickness of the sample. These results provide a simple framework for the design of AM-EFM measurements for localized dielectric characterization in liquid media.
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nanoscale measurement of the dielectric constant of supported lipid bilayers in aqueous solutions with Electrostatic Force microscopy
Biophysical Journal, 2013Co-Authors: Georg Gramse, Laura Fumagalli, Martin A Edwards, Aurora Dolsperez, G. GomilaAbstract:We present what is, to our knowledge, the first experimental demonstration of dielectric constant measurement and quantification of supported lipid bilayers in electrolyte solutions with nanoscale spatial resolution. The dielectric constant was quantitatively reconstructed with finite element calculations by combining thickness information and local polarization Forces which were measured using an Electrostatic Force microscope adapted to work in a liquid environment. Measurements of submicrometric dipalmitoylphosphatidylcholine lipid bilayer patches gave dielectric constants of er ∼ 3, which are higher than the values typically reported for the hydrophobic part of lipid membranes (er ∼ 2) and suggest a large contribution of the polar headgroup region to the dielectric response of the lipid bilayer. This work opens apparently new possibilities in the study of biomembrane Electrostatics and other bioelectric phenomena.
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quantifying the dielectric constant of thick insulators by Electrostatic Force microscopy effects of the microscopic parts of the probe
Nanotechnology, 2012Co-Authors: Georg Gramse, G. Gomila, Laura FumagalliAbstract:We present a systematic analysis of the effects that the microscopic parts of Electrostatic Force microscopy probes (the cone and cantilever) have on the Electrostatic interaction between the tip apex and thick insulating substrates (thickness > 100 μm). We discuss how these effects can influence the measurement and quantification of the local dielectric constant of the substrates. We propose and experimentally validate a general methodology that takes into account the influence of the cone and the cantilever, thus enabling us to obtain very accurate values of the dielectric constants of thick insulators.
David S. Ginger - One of the best experts on this subject based on the ideXlab platform.
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fast time resolved Electrostatic Force microscopy achieving sub cycle time resolution
Review of Scientific Instruments, 2016Co-Authors: Durmus U Karatay, Micah S Glaz, Jeffrey S Harrison, Rajiv Giridharagopal, David S. GingerAbstract:The ability to measure microsecond- and nanosecond-scale local dynamics below the diffraction limit with widely available atomic Force microscopy hardware would enable new scientific studies in fields ranging from biology to semiconductor physics. However, commercially available scanning-probe instruments typically offer the ability to measure dynamics only on time scales of milliseconds to seconds. Here, we describe in detail the implementation of fast time-resolved Electrostatic Force microscopy using an oscillating cantilever as a means to measure fast local dynamics following a perturbation to a sample. We show how the phase of the oscillating cantilever relative to the perturbation event is critical to achieving reliable sub-cycle time resolution. We explore how noise affects the achievable time resolution and present empirical guidelines for reducing noise and optimizing experimental parameters. Specifically, we show that reducing the noise on the cantilever by using photothermal excitation instead of piezoacoustic excitation further improves time resolution. We demonstrate the discrimination of signal rise times with time constants as fast as 10 ns, and simultaneous data acquisition and analysis for dramatically improved image acquisition times.
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imaging charge transfer state excitations in polymer fullerene solar cells with time resolved Electrostatic Force microscopy
Journal of Physical Chemistry Letters, 2015Co-Authors: Micah S Glaz, Jeffrey S Harrison, Samuel R. Peurifoy, David C. Coffey, David S. GingerAbstract:We demonstrate nanoscale imaging of charge transfer state photoexcitations in polymer/fullerene bulk heterojunction solar cells using time-resolved Electrostatic Force microscopy (trEFM). We compare local trEFM charging rates and external quantum efficiencies (EQE) for both above-gap and below-gap excitation of the model system poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM). We show that the local trEFM charging rate correlates with device EQE for both above-gap and below-gap photoexcitation, demonstrating that EFM methods have sufficient sensitivity to detect the low EQEs associated with CT state formation, a result that could be useful for probing weak subgap excitations in nanostructured materials such as quantum dot and organometal halide perovskite solar cells. Further, we use trEFM to map spatial variations in EQE arising from subgap CT excitation in organic photovoltaics (OPVs) and find that the local distribution of...
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Time-resolved Electrostatic Force microscopy of polymer solar cells
Nature Materials, 2006Co-Authors: David C. Coffey, David S. GingerAbstract:Blends of conjugated polymers with fullerenes, polymers, or nanocrystals make promising materials for low-cost photovoltaic applications. Different processing conditions affect the efficiencies of these solar cells by creating a variety of nanostructured morphologies, however, the relationship between film structure and device efficiency is not fully understood. We introduce time-resolved Electrostatic Force microscopy (EFM) as a means to measure photoexcited charge in polymer films with a resolution of 100 nm and 100 μs. These EFM measurements correlate well with the external quantum efficiencies measured for a series of polymer photodiodes, providing a direct link between local morphology, local optoelectronic properties and device performance. The data show that the domain centres account for the majority of the photoinduced charge collected in polyfluorene blend devices. These results underscore the importance of controlling not only the length scale of phase separation, but also the composition of the domains when optimizing nanostructured solar cells.
Georg Gramse - One of the best experts on this subject based on the ideXlab platform.
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theory of amplitude modulated Electrostatic Force microscopy for dielectric measurements in liquids at mhz frequencies
Nanotechnology, 2013Co-Authors: Georg Gramse, Laura Fumagalli, Martin A Edwards, G. GomilaAbstract:A theoretical analysis of amplitude modulated Electrostatic Force microscopy (AM-EFM) in liquid media at MHz frequencies, based on a simple tip–sample parallel plate model, is presented. The model qualitatively explains the main features of AM-EFM in liquid media and provides a simple explanation of how the measured electric Forces are affected by: the frequency of the applied voltage, the tip–sample distance, the ionic concentration, the relative dielectric constant of the solution, and the relative dielectric constant and thickness of the sample. These results provide a simple framework for the design of AM-EFM measurements for localized dielectric characterization in liquid media.
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nanoscale measurement of the dielectric constant of supported lipid bilayers in aqueous solutions with Electrostatic Force microscopy
Biophysical Journal, 2013Co-Authors: Georg Gramse, Laura Fumagalli, Martin A Edwards, Aurora Dolsperez, G. GomilaAbstract:We present what is, to our knowledge, the first experimental demonstration of dielectric constant measurement and quantification of supported lipid bilayers in electrolyte solutions with nanoscale spatial resolution. The dielectric constant was quantitatively reconstructed with finite element calculations by combining thickness information and local polarization Forces which were measured using an Electrostatic Force microscope adapted to work in a liquid environment. Measurements of submicrometric dipalmitoylphosphatidylcholine lipid bilayer patches gave dielectric constants of er ∼ 3, which are higher than the values typically reported for the hydrophobic part of lipid membranes (er ∼ 2) and suggest a large contribution of the polar headgroup region to the dielectric response of the lipid bilayer. This work opens apparently new possibilities in the study of biomembrane Electrostatics and other bioelectric phenomena.
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quantifying the dielectric constant of thick insulators by Electrostatic Force microscopy effects of the microscopic parts of the probe
Nanotechnology, 2012Co-Authors: Georg Gramse, G. Gomila, Laura FumagalliAbstract:We present a systematic analysis of the effects that the microscopic parts of Electrostatic Force microscopy probes (the cone and cantilever) have on the Electrostatic interaction between the tip apex and thick insulating substrates (thickness > 100 μm). We discuss how these effects can influence the measurement and quantification of the local dielectric constant of the substrates. We propose and experimentally validate a general methodology that takes into account the influence of the cone and the cantilever, thus enabling us to obtain very accurate values of the dielectric constants of thick insulators.
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quantifying the dielectric constant of thick insulators using Electrostatic Force microscopy
Applied Physics Letters, 2010Co-Authors: Laura Fumagalli, Georg Gramse, Daniel Estebanferrer, Martin A Edwards, G. GomilaAbstract:Quantitative measurement of the low-frequency dielectric constants of thick insulators at the nanoscale is demonstrated utilizing ac Electrostatic Force microscopy combined with finite-element calculations based on a truncated cone with hemispherical apex probe geometry. The method is validated on muscovite mica, borosilicate glass, poly(ethylene naphthalate), and poly(methyl methacrylate). The dielectric constants obtained are essentially given by a nanometric volume located at the dielectric-air interface below the tip, independently of the substrate thickness, provided this is on the hundred micrometer-length scale, or larger.
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quantitative dielectric constant measurement of thin films by dc Electrostatic Force microscopy
Nanotechnology, 2009Co-Authors: Georg Gramse, Laura Fumagalli, Ignacio Casuso, J Toset, G. GomilaAbstract:A simple method to measure the static dielectric constant of thin films with nanometric spatial resolution is presented. The dielectric constant is extracted from DC Electrostatic Force measurements with the use of an accurate analytical model. The method is validated here on thin silicon dioxide films (8 nm thick, dielectric constant approximately 4) and purple membrane monolayers (6 nm thick, dielectric constant approximately 2), providing results in excellent agreement with those recently obtained by nanoscale capacitance microscopy using a current-sensing approach. The main advantage of the Force detection approach resides in its simplicity and direct application on any commercial atomic Force microscope with no need of additional sophisticated electronics, thus being easily available to researchers in materials science, biophysics and semiconductor technology.
J J Saenz - One of the best experts on this subject based on the ideXlab platform.
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contrast inversion in Electrostatic Force microscopy imaging of trapped charges tip sample distance and dielectric constant dependence
Nanotechnology, 2011Co-Authors: Angel Alegria, C Riedel, Richard Arinero, J Colmenero, J J SaenzAbstract:We present a numerical and analytical study of the behavior of both Electrostatic Force and Force gradient created by a charge trapped below the surface of a dielectric on an atomic Force microscope tip as a function of the dielectric constant and tip?sample distance. As expected, the Force decreases monotonously when the dielectric constant increases. However, a maximum in the dielectric constant dependence of the Force gradient is found. This maximum occurs in the typical experimental parameters' range and depends on the tip?sample distance and the sample thickness. The analytical study permits us to understand the physical origin of this phenomenon and is in good agreement with the numerical simulation for small tip?sample distances. We also report a study exemplifying a possible contrast inversion in Electrostatic Force microscopy (EFM) signals while scanning, at different heights, two charges trapped in a sample having heterogeneous dielectric domains. In addition to this particular contrast inversion effect, this study can be considered as a way to gain insight into the mechanisms of EFM image formation as a function of the dielectric constant and tip?sample.
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quantitative theory for the imaging of conducting objects in Electrostatic Force microscopy
Applied Physics Letters, 2006Co-Authors: G M Sacha, J J Saenz, Cristina Gomeznavarro, Julio GomezherreroAbstract:A theoretical method for the imaging of metallic objects in Electrostatic Force microscopy is presented. The technique, based on the generalized image charge method, includes intrinsically the mutual polarization between the tip, the sample, and the metallic objects. Taking also into account the cantilever and macroscopic shape of the tip, the theory gives us a quantitative value for the Electrostatic interaction between the tip and the objects over the surface. Experimental data of frequency shifts in an oscillating tip induced by grounded and isolated nanotubes are analyzed finding an excellent quantitative agreement between experimental data and numerical calculations.
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effective tip radius in Electrostatic Force microscopy
Applied Physics Letters, 2005Co-Authors: G M Sacha, Albert Verdaguer, Javier Martinez, J J Saenz, D F Ogletree, M SalmeronAbstract:A method to determine the effective Electrostatic tip radius of arbitrarily shaped conducting tips in atomic Force microscopy is presented. The method is based on the finding that for conductive samples, the Electrostatic Force can be separated into two contributions: one from a constant background that depends only on the macroscopic shape of the tip (cone or pyramid and cantilever), and another that depends only on the radius of curvature of the tip apex. Based on a simple theoretical expression derived from the generalized image charge method, we show that the tip radius can be directly determined from experimental Force-distance characteristics. For irregular tip shapes, we show that the measured tip radius is the average of two principal curvatures, in agreement with tip shape images obtained by scanning electron microscopy.
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cantilever effects on Electrostatic Force gradient microscopy
Applied Physics Letters, 2004Co-Authors: G M Sacha, J J SaenzAbstract:The effects of the cantilever on Electrostatic Force microscopy are discussed. Numerical calculations of the Electrostatic potential distribution and Force gradient for typical experimental geometries are presented. A simple analytical relation between the calculated Force gradients with and without cantilever is found. The main effect of the cantilever is to reduce the electric field in the tip–sample gap and, as a consequence, the Force gradient can be strongly reduced. This effect can be very important for dielectric films while it can be neglected for metallic samples.