Cnism Unita Of Padua

Padova, Italy

Cnism Unita Of Padua

Padova, Italy
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Mistura G.,University of Padua | Pozzato A.,CNR Institute of Materials | Pozzato A.,ThunderNIL Srl | Grenci G.,CNR Institute of Materials | And 4 more authors.
Nature Communications | Year: 2013

The exposed surface area of porous materials is usually determined by measuring the mass of adsorbed gas as a function of vapour pressure. Here we report a comprehensive study of adsorption in systems with closed bottom, not interconnected pores exhibiting different degrees of disorder, produced with methods encompassing nanolithography and dry and wet etching. Detailed adsorption studies of these matrices show hysteresis loops, as found always in pores having sizes of tens to hundreds of nanometres. The observed variations in the loop shape are associated with changes in the pore morphology. In regular pores formed by vertical and smooth walls, continuous adsorption is found for the first time in agreement with thermodynamic considerations valid for ideal pores. This suggests that irregularities in the walls and pore openings are the key factors behind the hysteresis phenomenon. Interestingly, pores having rough walls but a pyramidal shape also do not show any hysteresis. © 2013 Macmillan Publishers Limited.


Rascon C.,Charles III University of Madrid | Parry A.O.,Charles III University of Madrid | Parry A.O.,Imperial College London | Nurnberg R.,Imperial College London | And 7 more authors.
Journal of Physics Condensed Matter | Year: 2013

We consider capillary condensation in a deep groove of width L. The transition occurs at a pressure pco (L) described, for large widths, by the Kelvin equation psat - pco (L) = 2σcosθ/L, where θ is the contact angle at the side walls and σ is the surface tension. The order of the transition is determined by the contact angle of the capped end θcap; it is continuous if the liquid completely wets the cap, and first-order otherwise. When the transition is first-order, corner menisci at the bottom of the capillary lead to a pronounced metastability, determined by a complementary Kelvin equation Δp(L) = 2σsinθcap/L. On approaching the wetting temperature of the capillary cap, the corner menisci merge and a single meniscus unbinds from the bottom of the groove. Finite-size scaling shifts, crossover behaviour and critical singularities are determined at mean-field level and beyond. Numerical and experimental results showing the continuous nature of condensation for θcap = 0 and the influence of corner menisci on adsorption isotherms are presented. © 2013 IOP Publishing Ltd.


Pierno M.,University of Padua | Bruschi L.,Cnism Unita Of Padua | Mistura G.,University of Padua | Paolicelli G.,CNR Institute of Neuroscience | And 10 more authors.
Nature Nanotechnology | Year: 2015

The inertial sliding of physisorbed submonolayer islands on crystal surfaces contains unexpected information on the exceptionally smooth sliding state associated with incommensurate superlubricity and on the mechanisms of its disappearance. Here, in a joint quartz crystal microbalance and molecular dynamics simulation case study of Xe on Cu(111), we show how superlubricity emerges in the large size limit of naturally incommensurate Xe islands. As coverage approaches a full monolayer, theory also predicts an abrupt adhesion-driven two-dimensional density compression on the order of several per cent, implying a hysteretic jump from superlubric free islands to a pressurized commensurate immobile monolayer. This scenario is fully supported by the quartz crystal microbalance data, which show remarkably large slip times with increasing submonolayer coverage, signalling superlubricity, followed by a dramatic drop to zero for the dense commensurate monolayer. Careful analysis of this variety of island sliding phenomena will be essential in future applications of friction at crystal/adsorbate interfaces. © 2015 Macmillan Publishers Limited.


PubMed | University of Padua, Cnism Unita Of Padua and CNR Institute of Materials
Type: | Journal: Nature communications | Year: 2013

The exposed surface area of porous materials is usually determined by measuring the mass of adsorbed gas as a function of vapour pressure. Here we report a comprehensive study of adsorption in systems with closed bottom, not interconnected pores exhibiting different degrees of disorder, produced with methods encompassing nanolithography and dry and wet etching. Detailed adsorption studies of these matrices show hysteresis loops, as found always in pores having sizes of tens to hundreds of nanometres. The observed variations in the loop shape are associated with changes in the pore morphology. In regular pores formed by vertical and smooth walls, continuous adsorption is found for the first time in agreement with thermodynamic considerations valid for ideal pores. This suggests that irregularities in the walls and pore openings are the key factors behind the hysteresis phenomenon. Interestingly, pores having rough walls but a pyramidal shape also do not show any hysteresis.


Bruschi L.,Cnism Unita Of Padua | Mistura G.,University of Padua | Park S.-J.,Korea Research Institute of Standards and Science | Lee W.,Korea Research Institute of Standards and Science | Lee W.,Korea University
Adsorption | Year: 2014

We have studied the adsorption of Ar on regular, highly-ordered alumina membranes made by anodization. The straight, non-interconnected pores have nominal diameters of 31 and 83 nm, with a relative dispersion better than 5 % in the pore size. Adsorption isotherms taken on bare membranes with pores of 83 nm present two distinct hysteresis loops. This is found to be a consequence of the fabrication procedure that yields a central circular region formed by open pores surrounded by an outer ring with closed bottom pores of smaller size, about 40 nm. For the membrane with pores of 31 nm, the difference between these pores is much smaller, about 2 nm, and this explains why the isotherms on these membranes show a single hysteresis loop as expected. Detailed real space analysis of the membranes by electron microscopy confirms the adsorption conclusions. © Springer Science+Business Media New York 2014.


Bruschi L.,Cnism Unita Of Padua | Mistura G.,University of Padua
NanoScience and Technology | Year: 2015

The quartz crystal microbalance (QCM) technique is a powerful probe of interfacial phenomena that has been successfully employed to investigate the sliding friction of objects of nanoscopic size subject to lateral speeds as large as a few m/s. After a description of the quartz acoustics, the chapter presents the more common circuits used to drive the QCM and discusses the main problems in the application of such a technique to the study of nanotribolgoy; the quality of the surface electrodes and surface contamination. © 2015 Springer International Publishing Switzerland.


Mistura G.,University of Padua | Bruschi L.,Cnism Unita Of Padua | Lee W.,Korea Research Institute of Standards and Science
Journal of Low Temperature Physics | Year: 2016

Porous anodic aluminum oxide (AAO) is characterized by a regular arrangement of the pores with a narrow pore size distribution over extended areas, uniform pore depth, and solid pore walls without micropores. Thanks to significant improvements in anodization techniques, structural engineering of AAO allows to accurately tailor the pore morphology. These features make porous AAO an excellent substrate to study adsorption phenomena. In this paper, we review recent experiments involving the adsorption in porous AAO. Particular attention will be devoted to adsorption in straight and structured pores with a closed end which shed new light on fundamental issues like the origin of hysteresis in closed end pores and the nature of evaporation from ink-bottle pores. The results will be compared to those obtained in other synthetic materials like porous silicon and silica. © 2016 Springer Science+Business Media New York


Bruschi L.,Cnism Unita Of Padua | Mistura G.,University of Padua | Nguyen P.T.M.,University of Queensland | Do D.D.,University of Queensland | And 4 more authors.
Nanoscale | Year: 2015

We have studied adsorption in regular, self-ordered alumina pores open at both ends or only at one end. The straight, non-connected pores have diameters ranging from 22 to 83 nm, with a relative dispersion below 1% in the pore size. Adsorption isotherms measured in open pores with a torsional microbalance show pronounced hysteresis loops characterized by nearly vertical and parallel adsorption and desorption branches. Blocking one end of the pores with glue has a strong influence on adsorption, as expected from classical macroscopic arguments. However, the experimental measurements show an unexpectedly rich phenomenology dependent on the pore size. For large pores (Dp ≥ 67 nm), the isotherms for closed end pores present much narrower hysteresis loops whose adsorption and desorption boundaries envelop the desorption branches of the isotherms for the corresponding open pores of the same size. The loop for small closed end pores (Dp = 22 nm) is slightly wider than that for open pores while the adsorption branches coincide. For large pores, in contrast, the desorption branches of pores with the same Dp overlap regardless of the pore opening. These observations are in agreement with our grand canonical Monte Carlo (GCMC) simulations for a cylindrical pore model with constrictions, suggesting that the alumina pores could be modeled using a constricted pore model whose adsorption isotherm depends on the ratio of the constriction size to the pore size (Dc/Dp). © The Royal Society of Chemistry 2015.


PubMed | CNR Institute of Neuroscience, University of Padua, Cnism Unita Of Padua, University of Modena and Reggio Emilia and International School for Advanced Studies
Type: Journal Article | Journal: Nature nanotechnology | Year: 2015

The inertial sliding of physisorbed submonolayer islands on crystal surfaces contains unexpected information on the exceptionally smooth sliding state associated with incommensurate superlubricity and on the mechanisms of its disappearance. Here, in a joint quartz crystal microbalance and molecular dynamics simulation case study of Xe on Cu(111), we show how superlubricity emerges in the large size limit of naturally incommensurate Xe islands. As coverage approaches a full monolayer, theory also predicts an abrupt adhesion-driven two-dimensional density compression on the order of several per cent, implying a hysteretic jump from superlubric free islands to a pressurized commensurate immobile monolayer. This scenario is fully supported by the quartz crystal microbalance data, which show remarkably large slip times with increasing submonolayer coverage, signalling superlubricity, followed by a dramatic drop to zero for the dense commensurate monolayer. Careful analysis of this variety of island sliding phenomena will be essential in future applications of friction at crystal/adsorbate interfaces.


PubMed | University of Padua, Cnism Unita Of Padua, University of Queensland and Hankuk University of foreign Studies
Type: Journal Article | Journal: Langmuir : the ACS journal of surfaces and colloids | Year: 2015

We have carried out systematic experiments and numerical simulations of the adsorption on porous anodic aluminum oxide (AAO) duplex layers presenting either an ordered or a disordered interconnecting interface between the large (cavity) and small (constriction) sections of the structured pores. Selective blocking of the pore openings resulted in three different pore topologies: open structured pores, funnel pores, and ink-bottle pores. In the case of the structured pores having an ordered interface, the adsorption isotherms present a rich phenomenology characterized by the presence of two steps in the condensation branch and the opening of one (two) hysteresis loops during evaporation for the ink-bottle (open and funnel) pores. The isotherms can be obtained by summing the isotherms measured on uniform pores having the dimensions of the constrictions or of the cavities. The numerical analysis of the three different pore topologies indicates that the shape of the junction between the two pore sections is only important for the adsorption branch. In particular, a conic junction which resembles that of the AAO pores represents the experimental isotherms for the open and funnel pores better, but the shape of the junction in the ink bottle pores does not matter. The isotherms for the duplex layers with a disordered interface display the same general features found for the ordered duplex layers. In both cases, the adsorption branches coincide and have two steps which are shifted to lower relative pressures compared to those for the ordered duplex. Furthermore, the desorption branches comprise hysteresis loops much wider than those of the ordered duplex layers. Overall, this study highlights the important role played by morphologies where there are interconnections between large and small pores.

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