Suchergebnisse

Scanning electron microscopy (SEM) is a powerful imaging technique able to obtain astonishing images of the micro- and the nano-world. Unfortunately, the technique has been limited to vacuum conditions for many years. In the last decades, the ability to introduce water vapor into the SEM chamber and still collect the electrons by the detector, combined with the temperature control of the sample, has enabled the study of ice at nanoscale. Astounding images of hexagonal ice crystals suddenly became real. Since these first images were produced, several studies have been focusing their interest on using SEM to study ice nucleation, morphology, thaw, etc. In this paper, we want to review the different investigations devoted to this goal that have been conducted in recent years in the literature and the kind of information, beyond images, that was obtained. We focus our attention on studies trying to clarify the mechanisms of ice nucleation and those devoted to the study of ice dynamics. We also discuss these findings to elucidate the present and future of SEM applied to this field. ; A.V. acknowledges financial support by the Spanish Government under Project No. PID2019-110907GB-I00 and the "Severo Ochoa" Program for Centers of Excellence in R&D (CEX2019-000917-S). ; With funding from the Spanish government through the 'Severo Ochoa Centre of Excellence' accreditation (CEX2019-000917-S). ; Peer reviewed

Among the different aerosol mineral particles that contribute to induce ice nucleation (IN) in the troposphere, feldspars have been identified as the most active. Nevertheless, which surface properties make some feldspars more efficient than others, i.e. able to induce IN at higher temperatures, is still unclear. In addition to that, surface properties of such materials can change as they are exposed to a variety of environmental conditions while traveling through the troposphere. Here, freezing temperature of water droplets deposited on feldspar minerals has been measured as a function of consecutive freeze-thaw cycles. We found an increase of the freezing temperature for the initial cycles followed by approximately constant freezing temperature for consecutive cycles. We call this a "history effect". This effect is more evident for samples aged in standard room conditions and it disappears if the sample is exposed to oxygen plasma. Oxygen plasma generates OH groups at the surface, facilitating IN and cleans the surface from organic contamination, unblocking pores at the surface, believed to be the most active IN sites on feldspars. A similar process is suggested to happen during the history effect, when consecutive freeze-thaw events unblock IN sites. ; The authors thank C. Marcolli for discussion on results and their interpretation. This work has been supported by the Spanish Government under the project PID2019-110907GB-I00 and the ''Severo Ochoa'' Program for Centres of Excellence in R&D (CEX2019-000917-S). E. Pach acknowledges the Spanish Ministry of Science and Technology for the Juan de la Cierva Formation grant. ; With funding from the Spanish government through the 'Severo Ochoa Centre of Excellence' accreditation (CEX2019-000917-S). ; Peer reviewed

The epidemic spread of many viral infections is mediated by the environmental conditions and influenced by the ambient humidity. Single virus particles have been mainly visualized by atomic force microscopy (AFM) in liquid conditions, where the effect of the relative humidity on virus topography and surface cannot be systematically assessed. In this work, we employed multi-frequency AFM, simultaneously with standard topography imaging, to study the nanoscale wetting of individual Tobacco Mosaic virions (TMV) from ambient relative humidity to water condensation (RH > 100%). We recorded amplitude and phase vs. distance curves (APD curves) on top of single virions at various RH and converted them into force vs. distance curves. The high sensitivity of multifrequency AFM to visualize condensed water and sub-micrometer droplets, filling gaps between individual TMV particles at RH > 100%, is demonstrated. Dynamic force spectroscopy allows detecting a thin water layer of thickness ⁓1 nm, adsorbed on the outer surface of single TMV particles at RH < 60%. ; We acknowledge the support of the Diputación Foral de Guipuzcoa under the project Nanoscopía Mojada (PCTi 2015), of the Basque government (PI2013-57, Elkartek ng20), and from grants MAT2013-4006-R, PID2019-104650GB-C22 and Maria de Maeztu "Units of Excellence" program MDM-2016-0618 (all MCIU-MINECO, Spain). TMV solutions were provided by the group of Prof. Christina Wege (Institute for Biomaterials and Biomolecular Systems, University of Stuttgart). A.C. acknowledges Javier Zaldivar (CIC nanoGUNE, Tolosa Hiribidea 76, E-20018 Donostia-San Sebastian) for useful discussions.

Electrochemical phenomena in ferroelectrics are of particular interest for catalysis and sensing applications, with recent studies highlighting the combined role of the ferroelectric polarisation, applied surface voltage and overall switching history. Here, we present a systematic Kelvin probe microscopy study of the effect of relative humidity and polarisation switching history on the surface charge dissipation in ferroelectric Pb(Zr0.2Ti0.8)O3 thin films. We analyse the interaction of surface charges with ferroelectric domains through the framework of physically constrained unsupervised machine learning matrix factorisation, Dictionary Learning, and reveal a complex interplay of voltage-mediated physical processes underlying the observed signal decays. Additional insight into the observed behaviours is given by a Fitzhugh–Nagumo reaction–diffusion model, highlighting the lateral spread and charge passivation process contributors within the Dictionary Learning analysis. ; The authors acknowledge Dr Sergei V. Kalinin of Oak Ridge National Laboratory, for helpful discussions about machine learning and the initial suggestion to explore reaction–diffusion modelling. This work was supported by Division II of the Swiss National Science Foundation under project 200021_178782. A.V. acknowledges support by the Spanish Government under the project PID2019-110907GB-I00 and the "Severo Ochoa" Program for Centres of Excellence in R&D (CEX2019-000917-S). N.D. acknowledges support by the Spanish Government under the project PID2019- 109931GB-I00. N.B.G. acknowledges support by the National Science Foundation under the project DMR-20269676. The authors would like to thank S. Muller for technical support. ; With funding from the Spanish government through the 'Severo Ochoa Centre of Excellence' accreditation (CEX2019-000917-S). ; Peer reviewed

When we speak of nanometric water films on surfaces we are speaking about a truly ubiquitous phenomenon in nature. All surfaces exposed to ambient conditions are covered by a thin film of water that affects or mediates surface chemistry, general physical-chemical processes on surfaces, and even solid–solid interactions. We have investigated this phenomenon for over a decade by exploiting dynamic atomic force microscopy and have (1) described how these layers affect apparent height measurements, (2) analyzed the excitation of subharmonics, (3) investigated its effects on surface functionality over time ("aging"), (4) monitored and quantified the time-dependent wettability of several relevant surfaces such as highly oriented pyrolytic graphite and monolayer systems, and (5) developed high-resolution and highly stable modes of imaging. Here, we discuss these findings to elucidate the present and future of the field. We further provide a brief but general discussion of solvation and hydration layers in vacuum, liquid, and air that center around current controversies and discuss open possibilities in the field. ; S. Santos, T. Olukan and M. Chiesa acknowledge the support from the Arctic Centre for Sustainable Energy (ARC) at UiTthe Arctic University of Norway through Grant No. 310026. A.V. acknowledges financial support by the Spanish Government under Project No. PID2019-110907GB-I00 and the "'Severo Ochoa"' Program for Centres of Excellence in R&D (CEX2019-000917-S). ; Peer reviewed