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Santos S.,Masdar Institute of Science and Technology | Barcons V.,Polytechnic University of Catalonia | Verdaguer A.,Center d Investigacio en Nanociencia i Nanotecnologia 2 ICN | Font J.,Polytechnic University of Catalonia | And 3 more authors.
Nanotechnology | Year: 2011

We describe fundamental energy dissipation in dynamic nanoscale processes in terms of the localization of the interactions. In this respect, the areal density of the energy dissipated per cycle and the effective area of interaction in which each process occurs are calculated for four elementary dissipative processes. It is the ratio between these two, which we term M, that provides information about how localized the interactions are. While our results are general, we use concepts from dynamic atomic force microscopy to describe the physical phenomenon. We show that neither the phase lag, nor the magnitude of the energy dissipated alone provide information about how dissipative processes are localized. Instead, M has to be considered. © 2011 IOP Publishing Ltd. Source


Santos S.,Masdar Institute of Science and Technology | Verdaguer A.,Center d Investigacio en Nanociencia i Nanotecnologia 2 ICN | Souier T.,Masdar Institute of Science and Technology | Thomson N.H.,University of Leeds | And 2 more authors.
Nanotechnology | Year: 2011

Measuring the level of hydrophilicity of heterogeneous surfaces and the true height of water layers that form on them in hydrated conditions has a myriad of applications in a wide range of scientific and technological fields. Here, we describe a true non-contact mode of operation of atomic force microscopy in ambient conditions and a method to establish the source of apparent height. A dependency of the measured water height on operational parameters is identified with water perturbations due to uncontrolled modes of imaging where intermittent contact with the water layer, or even the surface, might occur. In this paper we show how to (1)determine when the water is being perturbed and (2)distinguish between four different interaction regimes. Each of the four types of interaction produces measurements ranging from fractions of the true height in one extreme to values which are as large as four times the real height in the other. We show the dependence of apparent height on the interaction regime both theoretically and empirically. The agreement between theory and experiment on a BaF2(111) sample displaying wet and un-wet regions validates our results. © 2011 IOP Publishing Ltd. Source


Font J.,Polytechnic University of Catalonia | Santos S.,Masdar Institute of Science and Technology | Barcons V.,Polytechnic University of Catalonia | Thomson N.H.,University of Leeds | And 3 more authors.
Nanoscale | Year: 2012

In dynamic atomic force microscopy (AFM) the cantilever is vibrated and its dynamics are monitored to probe the sample with nanoscale and atomic resolution. Amplitude and frequency modulation atomic force microscopy (AM-AFM and FM-AFM) have established themselves as the most powerful methods in the field. Nevertheless, it is still debatable whether one or the other technique is preferred in a given medium or experiment. Here, we quantitatively establish and compare the limitations in resolution of both techniques by introducing the concept of spatial horizon (SH) and quantifying it. The SH is the limiting spatial boundary beyond which collective atomic interactions do not affect the detection parameters of a given feedback system. We show that while an FM-AFM feedback can resolve a single atom or atomic defect where an AM feedback might fail, relative contrast is in fact equivalent for both feedback systems. That is, if the AM feedback could detect sufficiently small amplitude shifts and there was no noise, the detection of single atoms or atomic defects would be equivalent in AM-AFM and FM-AFM. © 2012 The Royal Society of Chemistry. Source


Santos S.,Masdar Institute of Science and Technology | Barcons V.,Polytechnic University of Catalonia | Verdaguer A.,Center d Investigacio en Nanociencia i Nanotecnologia 2 ICN | Chiesa M.,Masdar Institute of Science and Technology | Chiesa M.,Massachusetts Institute of Technology
Journal of Applied Physics | Year: 2011

In ambient conditions, nanometric water layers form on hydrophilic surfaces covering them and significantly changing their properties and characteristics. Here we report the excitation of subharmonics in amplitude modulation atomic force microscopy induced by intermittent water contacts. Our simulations show that there are several regimes of operation depending on whether there is perturbation of water layers. Single period orbitals, where subharmonics are never induced, follow only when the tip is either in permanent contact with the water layers or in pure noncontact where the water layers are never perturbed. When the water layers are perturbed subharmonic excitation increases with decreasing oscillation amplitude. We derive an analytical expression which establishes whether water perturbations compromise harmonic motion and show that the predictions are in agreement with numerical simulations. Empirical validation of our interpretation is provided by the observation of a range of values for apparent height of water layers when subharmonic excitation is predicted. © 2011 American Institute of Physics. Source


Cardellach M.,Center d Investigacio en Nanociencia i Nanotecnologia 2 ICN | Verdaguer A.,Center d Investigacio en Nanociencia i Nanotecnologia 2 ICN | Fraxedas J.,Center d Investigacio en Nanociencia i Nanotecnologia 2 ICN
Surface Science | Year: 2011

The interaction of water with freshly cleaved (111) surfaces of isostructural BaF2 and CaF2 single crystals at ambient conditions (room temperature and under controlled humidity) has been studied using scanning force microscopy in different operation modes and optical microscopy. Such surfaces exhibit contrasting behaviors for both materials: while on BaF2(111) two-dimensional water layers are formed after accumulation at step edges, CaF2(111) does not promote the formation of such layers. We attribute such opposed behavior to lattice match (mismatch) between hexagonal water ice and the hexagonal (111) surfaces of BaF 2(CaF2). Optical microscope images reveal that this behavior also determines the way the surfaces become wetted at a macroscopic level. © 2011 Elsevier B.V. All rights reserved. Source

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