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Spinodal dewetting is one of the basic processes inducing a spontaneous withdrawal of a liquid from a substrate surface. In the accepted theory, thickness fluctuations generated by thermally activated capillary waves are amplified by the competing actions of surface tension and disjoining pressure. Ubiquitous sub-nanometric substrate roughness also produces thickness fluctuations and may play a role analogous but even more efficient in seeding the process.Analytic calculations valid at the early linear stage of the process and simulations extending the study to its whole non-linear development have been performed to compare features and the relative relevance of the two seeding mechanisms.Calculations and simulations have shown that substrate roughness can replace capillary waves in seeding spinodal dewetting. A typically larger amplitude and a steady nature compared to the transitory one of capillary waves allow us to conclude that, contrary to the common view, substrate roughness is the prevailing seed of the spinodal instability. The consequence of our statement is that spinodal dewetting loses most of its stochastic nature and becomes, in principle, a process that can be tuned by engineering substrate roughness.

Recent studies have suggested that microenvironmental stimuli play a significant role in regulating cellular proliferation and migration, as well as in modulating self-renewal and differentiation processes of mammary cells with stem cell (SCs) properties. Recent advances in micro/nanotechnology and biomaterial synthesis/engineering currently enable the fabrication of innovative tissue culture platforms suitable for maintenance and differentiation of SCs

The lack of engineering systems able to faithfully reproduce complex kidney structures in vitro has made it difficult to efficiently model kidney diseases and development. Using polydimethylsiloxane (PDMS) scaffolds and a kidney-derived cell line we developed a system to rapidly engineer custom-made 3D tubules with typical renal epithelial properties. This system was successfully employed to engineer patient-specific tubules, to model polycystic kidney disease (PKD) and test drug efficacy, and to identify a potential new pharmacological treatment. By optimizing our system we constructed functional ureteric bud (UB)-like tubules from human induced pluripotent stem cells (iPSCs), and identified a combination of growth factors that induces budding morphogenesis like embryonic kidneys do. Finally, we applied this assay to investigate budding defects in UB-like tubules derived from a patient with a PAX2 mutation. Our system enables the modeling of human kidney disease and development, drug testing and discovery, and lays the groundwork for engineering anatomically correct kidney tissues in vitro and developing personalized medicine applications., Highlights • Using PDMS scaffolds and kidney cells we developed a system for rapidly engineering complex and functional kidney tubules • Engineered tubules from patient cells were used to model PKD and test drug efficacy, and identify a potential treatment • Engineered human iPSC-derived UB tubules were used to study normal UB developmental processes and patient specific defects

Excessive use of plastics in daily life and the inappropriate disposal of plastic products are severely affecting wildlife species in both coastal and aquatic environments. Birds are top-predators, exposed to all threats affecting their environments, making them ideal sentinel organisms for monitoring ecosystems change. We set a baseline assessment of the prevalence of marine plastic litter affecting multi-species populations of aquatic birds in southern Portugal. By examining 160 stomach contents from 8 species of aquatic birds, we show that 22.5% were affected by plastic debris. Plastic was found in Ciconia ciconia, Larus fuscus and L. michahellis. Ciconia ciconia ingested the highest amount (number of items and total mass) of plastic debris. Polydimethylsiloxane (PDMS, silicones) was the most abundant polymer and was recorded only in C. ciconia. Plastic ingestion baseline data are of crucial importance to evaluate changes through time and among regions and to define management and conservation strategies.

The integration of constriction structures such as nanopores and nanochannels into fluidic devices discloses powerful biosensing capabilities that can be tuned to a wide range of analytes through conceptually simple size calibrations. The practical implementation of this tuning requires a nontrivial manipulation of matter at nanoscale with further requirements for low complexity and low-cost procedures that may be adapted to industrial production. Here, we review the recent progress on the fabrication techniques of nanopores and nanochannels, together with the efforts to realize their full biosensing potential by understanding and amending the problems still afflicting the measurement performed during operation.

The knowledge of the permeability and diffusivity (the diffusion coefficient) of materials to different gases is essential for a wide range of applications, such as food packaging, gas separation techniques, and vacuum technology. In this paper, we describe a versatile high-vacuum apparatus for permeation measurements, based on a membrane technique, with the aim of increasing the reliability of results and allowing measurements of permeability of different materials whose permeability spanning several orders of magnitude. The apparatus is equipped with a residual gas analyzer for measurements of partial and total pressure, a spinning rotor gauge for accurate determination of pressure, a calibrated leak to determine pumping speed and capacitance diaphragm gauges for accurate pressure measurements greater than 10−2 Pa. The apparatus works in a static or a dynamic mode. Its performance is tested on polydimethylsiloxane with N2 and Viton® with He as tracer gases. The lower measurement limit of the apparatus depends mainly on the degassing of the inner walls of the chamber. With the procedure described in this paper, it is possible measured permeability from 10−5 cm2/s to 10−10 cm2/s.

Recent studies have suggested that microenvironmental stimuli play a significant role in regulating cellular proliferation and migration, as well as in modulating self-renewal and differentiation processes of mammary cells with stem cell (SCs) properties. Recent advances in micro/nanotechnology and biomaterial synthesis/engineering currently enable the fabrication of innovative tissue culture platforms suitable for maintenance and differentiation of SCs in vitro. Here, we report the design and fabrication of an open microfluidic device (OMD) integrating removable poly(e-caprolactone) (PCL) based electrospun scaffolds, and we demonstrate that the OMD allows investigation of the behavior of human cells during in vitro culture in real time. Electrospun scaffolds with modified surface topography and chemistry can influence attachment, proliferation, and differentiation of mammary SCs and epigenetic mechanisms that maintain luminal cell identity as a function of specific morphological or biochemical cues imparted by tailor-made fiber post-treatments. Meanwhile, the OMD architecture allows control of cell seeding and culture conditions to collect more accurate and informative in vitro assays. In perspective, integrated systems could be tailor-made to mimic specific physiological conditions of the local microenvironment and then analyze the response from screening specific drugs for more effective diagnostics, long-term prognostics, and disease intervention in personalized medicine.

Marine litter is widely dispersed throughout coastal environments. Assessing the distribution and accumulation of such contaminants is crucial to understand their environmental impacts. This study presents a baseline for the monitoring of litter and microplastics in intertidal sediments along the Atlantic shores of southern Portugal and Morocco and identifies potential sources of contamination. Although variable, distribution and composition of both litter and microplastics did not follow a latitudinal pattern. Most of the litter had an undifferentiated source. Within the identifiable sources of litter, food packaging, fishing and tobacco were the most abundant, with variable contributions among sites. Over 97% of marine litter retrieved was plastic. Fragments and filaments were the most abundant categories of plastics at sites with the highest and lowest microplastic abundance respectively. Filaments were mainly made of Polypropylene (PP,50%) and Polyethylene terephthalate (PET,29%) while the predominant polymers for fragments were Polyethene (PE, 75%) and PP (25%). Fundacao para a Ciencia e Tecnologia (FCT-MEC, Portugal) [UID/Multi/04326/2019, IF/01413/2014] South African Research Chairs Initiative (SARChI) of the Department of Science and Technology [64801]

This paper describes a procedure to measure the permeability P, diffusivity D, and rate of adsorption k1, thus determining the solubility S and rate of desorption k2 of He, N2, O2, CH4, and CO2 on a polydimethylsiloxane (PDMS) membrane. The described procedure is able to determine experimentally all the physical quantities that characterize the gas transport process through a thin rubber polymer membrane. The experiments were carried out at room temperature and at a transmembrane pressure of 1 atm. The results are in good agreement with the available data in the literature and offer an evaluation of k1 and k2.

We propose ion-induced dewetting of Au thin films as a mechanism to modify and control the morphology of Si nanowires formed through metal-assisted chemical etching. We show that the patterns formed upon irradiation resemble those typical of dewetting phenomena, with a characteristic length in the nanometer range. Irradiated Au films are then used as a template for the fabrication of Si nanowires, and we show that a long-range order exists also in etched substrates, although at much longer length scales in the micrometer range. Investigation of the optical properties reveals that the Si nanowires emit broadband photoluminescence peaked at 700 nm. The proposed synthesis method allows tuning the morphological features of the nanowire bundles at the nanoscale without affecting the optical properties. This approach can be exploited for the engineering of nanowires-based devices where the morphological features become important.

The purpose of this investigation is to fabricate PDMS membranes with reliable surface roughness in order to reduce the surface resistances and to study its impact on the permeation rate. The permeance of CO2 through PDMS membranes with rough surfaces at nanoscale is studied and compared with the one of membranes with flat surfaces. At very low thickness, rough membranes have a permeance greater than that of membranes with flat surfaces. The enhancement occurs in a regime where the gas transport is sorption desorption surface rate limited, and cannot be explained by the increase in surface area due to the corrugation. The analysis, introducing a phenomenological model in analogy with electrical flow, indicates that nano-corrugation reduces the surface resistance. To test the model, the permeance of N2 is also measured in the same experimental conditions and the influence of surface roughness on permeation rate of CO2, He, CH4 and N2 is studied. The comparison among the gases suggests that the Henry’s coefficient depends on the surface roughness and allows discussing the role of roughness on membrane selectivity.

Dewetting of ion-irradiated metal films is a consequence of the local melting occurring during the irradiation. In this study we present the dewetting evolution of Au thin films bombarded with Ga+ ions in a focused ion beam system, pointing out the different surface patterns observed in films having different starting thickness and morphology. In fact, in ion-irradiated films thicker than 2 nm the typical features of dewetted liquids appear, i.e. enlarging dry holes surrounded by metal interconnections. On the other side, a different behavior is observed in thinner discontinuous films, where a dense distribution of circular nanoparticles is formed upon irradiation. We studied the dependence of Au nanoparticles distribution obtained for different ion energies and fluences, determining that a maximum fluence of ∼2 × 1014 Ga/cm2 can be used to achieve a monomodal distribution of nanoparticles with regular shape, before detrimental effects of sputtering occur.

We investigate the role of the substrate morphology in the dewetting of ultrathin chromium films irradiated with 30 keV Ga ions. Silicon surfaces with different roughness were used as substrates for the films. The results of the irradiation experiments and of related simulations indicate that the chromium films can undergo a dewetting-like process through the two standard channels that show up for liquids, namely the spinodal channel, and the dewetting by heterogeneous nucleation. The two processes are competitive, and the prevailing one can be predicted and selected according to the characteristics of the substrate.

Experiments of irradiation with 30 keV Ga ions were conducted on ultrathin chromium films on rippled silicon substrates. The evolution of their surface morphology, as detected by real time scanning electron microscopy, shows an apparent differential sputtering yield for regions of positive and negative curvature which is in contrast with the standard theory for curvature depending sputtering yield. In particular, at the end of the irradiation process, chromium wires are left in the valleys of the substrate. This result was explained in terms of local melting caused by the ion impact and of a process of dewetting under the concurring actions of surface tension and Van der Waals forces while ion sputtering is active. The interpretation of the reported experimental results are fully supported by numeric simulations implementing the same continuum model used to explain ion induced spinodal dewetting. This hierarchical self-organization process breaks the symmetry of previously demonstrated ion induced dewetting, making possible to create new structures by using the same fundamental effects.

Despite the widespread use of triangular nanochannels for the manipulation and analysis of DNA, studies on the confining effects induced by these nanofluidic structures on the molecules are still absent. Here, we perform coarse-grained Monte Carlo simulations to study the conformations of DNA in nanochannels. The influence of the shape of the nanochannel cross section is examined by comparing the elongation of molecules in triangular, rectangular, and square channels. Furthermore, the conformation of λ-DNA under weak confinement is studied both computationally and experimentally. Good agreement between optical measurements and simulations supports the reliability of the numerical model in predicting the molecule conformation, making it a reliable method to obtain information essential in many applications, such as DNA barcoding.

MicroRNAs (miRNAs) modulate gene expression at post-transcriptional level, while their aberrant presence in circulation correlates with the most common human disorders such as cancer, neuro-degenerative and immune-related diseases. Currently, the pre-concentration of such important bio-markers present at low concentrations in biological fluids, which would make their identification and quantification easier, remains a challenging issue for biosensor-based non-invasive analyses. This paper describes a new nanostructure-based polymeric platform for enhancing adsorption capability of microRNAs, such as the cancer-associated miRNA-21. In this purification strategy, a nano-hole pattern was manufactured by Replica Molding (REM) and fabricated on Polydimethylsiloxane (PDMS) large-areas. Interestingly, the microRNAs adsorption is resulted favoured by this proper topography. In planning to concentrate the patient’s miRNAs used as biomarkers, PDMS surfaces with nanostructures were not further coated with any adhesive molecules to prevent forced surface-biomolecule adhesive regions and evaluate the mere influence of the surface topography and the ionic microenvironment. Both the nanopattern and the solution ionic strength promote adsorption of miRNAs by a sensitive and efficient method, which do not need probe immobilization, enzymatic reaction or further treatments. These studies revealed a two-fold higher fluorescent signal after solid-phase purification protocol compared to standard PDMS obtained by spin-coating. While this paper focuses on nanostructure-miRNA adsorption, the general strategy of trapping miRNAs on nano-hole patterns should be broadly applicable for purification of other miRNAs through microfluidic biosensors and should have basic as well as clinical research applications.

Peculiar transport phenomena appear at nanoscale, since surface effects strongly affect the behaviour of fluids. Electrostatic and steric interactions, capillary forces and entropic effects play a key role in the behaviour of fluids and biomolecules. Since these effects strongly depend on the size of the nanofluidic system, a careful characterization of the fluidic environment is necessary. Moreover, the possibility to dynamically modulate the size of nanochannels is very appealing in the field of biomolecule manipulation. Recently, we have developed a lab-on-chip made of poly(dimethylsiloxane) (PDMS). This polymeric device is based on a tuneable nanochannel able to dynamically change its dimension in order to fit the application of interest. In fact, a mechanical compression applied on the top of the elastomeric device squeezes the nanochannel, reducing the channel cross section and allowing a dynamical optimization of the nanostructures. In this paper, this squeezing process is fully characterized both numerically and experimentally. This analysis provides information on the reduction of the nanochannel dimensions induced by compression as a function of the work of adhesion and of the stiffness of the materials composing the device. Moreover, calculations demonstrate the possibility to predict the change of the nanochannel size and shape induced by the compression. The possibility to dynamically tune the channel size opens up new opportunities in biomolecular sensing or sieving and in the study of new hydrodynamics effects.

The paper presents an analysis of the reliability of the method adopted in measuring techniques (particularly in AFM) for determining the fractal properties of rough surfaces. It is established that the parameter α (0 < α < 1) and, correspondingly, the Lipα class cannot be reliably defined using the finite part of the Fourier series and Lorentz theorem. Mandelbrot’s definition and the Lorentz theorem are shown to be insufficient as a theoretical basis for defining fractality experimentally. As a result of the mixing of the two concepts of nonidentity forming the basis of the modern understanding of fractality, there appear inaccuracies. The first concept implies that the fractal function should be perceived as a “broken line”, i.e., a nondifferentiable line. The second obligatory property of the fractal function is the geometrical self-similarity of the function at different scale levels. The examples cited in the paper indicate that these properties do not imply one another as they are different in their essence. A new method is proposed for identification of fractality in experimental research. It is based on checking the geometrical similarity of the additive components of the distribution function of asperity heights. This approach may serve as a basis for developing a new theory of the interactions of fractal rough surfaces.

Raman spectroscopy and mapping, coupled to molecular labelling, is used to analyse and monitor the first stage of carbon nanotube functionalization, i.e. their oxidation, which is usually performed to increase the number of surface carboxylic groups, allowing both a better dispersion in solution and the further attachment of biomolecules. Since the abundance of such surface groups is critical for the final application, it is important to develop a reliable but simple and fast method to investigate their presence on the tube walls. The presented data demonstrate the correlation between the presence and intensity of the Raman peak ascribed to the labelling molecule and the production of COOH groups on the nanotube walls. Between the analysed carbon nanotubes related spectral parameters, the G′ Raman peak position appears to be the most sensitive one to determine the degree of single walled carbon nanotube labelling, which directly depends on the number of COOH groups available for molecular attachment, i.e. on the efficiency of the oxidation treatment.

We present experimental results on simultaneous surface nanostructuring and optical activation of lithium fluoride crystals by 800 eV off-normal Ar + sputtering. Our data demonstrate that the formation of periodic nanostructures is accompanied by the efficient production of stable electronic defects, optically active in the green and red parts of the visible spectra, thus providing the possibility to conceive and fabricate advanced insulating substrates.

We present the first detailed experimental observation and analysis of nanoparticle electrophoresis through a nanochannel obtained with synchronous high-bandwidth electrical and camera recordings. Optically determined particle diffusion coefficients agree with values extracted from fitting electrical transport measurements to distributions from 1D Fokker–Planck diffusion-drift theory. This combined tracking strategy enables optical recognition and electrical characterization of nanoparticles in solution, which can have a broad range of applications in biology and materials science.

We report experimental results on the morphological characterization of WC coatings deposited by High-Velocity-Oxygen-Fuel (HVOF) thermal spraying technique. Optical microscopy has been used to characterize film microstructure from the millimeter down to the micrometer scale; surface roughness and correlation length have been estimated as a function of film thickness. We have observed that analysed specimens display a self-affine morphology with Hurst exponent H = (0.33 ± 0.05), in agreement with the scaling behaviour associated to the Kardar–Parisi–Zhang stochastic growth equation and to discrete ballistic deposition models. Our findings suggest that the introduction of scaling arguments within refined theoretical frameworks, realistically treating local splats interactions, could allow to directly predict the morphological evolution of coatings, partially overcoming the intrinsic complexity of the HVOF thermal spray process.

We report on the experimental evidence of the role of rotational alignment of the gas-phase molecules in the interaction of propylene with Ag(001). Molecular alignment has been controlled by a velocity selection of the impinging molecules, flying in a supersonic seeded molecular beam. The experimental findings indicate that at low surface coverage the sticking probability is independent of molecular alignment, while when coverage exceeds few percent of a monolayer, molecules impinging rotating parallel to the surface (helicopter-like configuration) achieve a higher chance to be trapped than those which impinge rotating perpendicularly (cartwheels). The sudden appearance of a large stereodynamic effect suggests that the adsorption proceeds via a mobile precursor state and is tentatively correlated with a change in the configuration of the added propylene molecules, which adsorb tilted rather than flat at the surface.

Starting from their discovery in 1991, carbon nanotubes have attracted a great attention, thanks to their peculiar mechanical, electrical and elastic properties that could be used to realize new devices in many different fields. For nanotechnology applications it is very important to be able to control not only shape and position but also alignment and orientation of carbon nanotubes, both during the growth and after it. Here we present preliminary results obtained by depositing carbon nanotubes (CNT) solutions on ion sputtered quartz substrates. Atomic force microscopy (AFM) images allow to study both CNTs positioning on the “ripples” generated by Ar+ sputtering on the SiO2 surface and their radial deformation induced by the “rough” surface. Work is now in progress to optimize the sputtering parameters and solution treatment (purification and functionalization) in order to get single CNTs regularly arranged on a patterned surface.

The smoothening process of nanometer-scale ripples grown on the (1 1 0) surface of silver is investigated using thermal energy He atom scattering. Morphological equilibration the corrugated surface is followed in real time in the temperature range between 205 and 230 K. The mean ripple wavelength, Λ , is observed to increase during surface recovery. To take this effect into account the decay time is assumed to scale as Λ 3 . Within this approximation the ripple amplitude is observed to decay linearly with time. The activation energy of the mechanism driving surface relaxation is estimated as (0.46 ± 0.02) eV. The underlying rate limiting process, i.e. adatom detachment from the open 〈0 0 1〉 step edges is evidenced.

We investigated the contact mechanics and friction forces between atomic force microscope (AFM) probes and self-affine fractal carbon films. We studied single-asperity contacts by means of conventional nanometric conical tips whilst custom-designed micrometric flat tips were adopted to form multiple junctions between the probe and the sample. By varying the externally applied load we found that the average frictional force follows a power-law behavior in the single-asperity regime and a linear behavior in the multi-asperity regime. The friction coefficient was the same for carbon specimens having different fractality. We also acquired quasi-static load–displacement curves on micrometric scale, revealing a strong dependence of the average indentation depth on the values of fractal parameters. A comparison of experimental data with contact theories for randomly rough surfaces is provided. © 2003 Elsevier Science B.V. All rights reserved.

We present a novel experimental technique devoted to the investigation of contact mechanics on mesoscopic scale. It consists of an atomic force microscope (AFM) equipped with custom-designed probes with integrated flat micrometric tips. Samples are normally compressed by the flat tips and load–displacement curves are acquired. The latter allow to investigate the mechanical response under a multi-asperity regime not accessible by conventional AFM. Preliminary results are reported for the contact mechanics of nanostructured carbon-based films having a self-affine fractal morphology.

The morphology of the surface of single‐crystalline silicon as a function of the degree of oxidation has been investigated by the method of atomic‐force microscopy. The roughness of the surface at different stages of treatment has been evaluated with the use of topographic images. It has been found that the standard deviation characterizing the distribution of microroughnesses by height, or the roughness, increases with oxidation of the sample. A histogram of the distribution of structural surface elements has been presented. The data obtained can be employed in specifying boundary conditions to gasdynamic problems.

Thin solid films exposed to ion irradiation exhibit a peculiar evolution that can differ substantially from what is observed for bulk samples. The phenomenology of the patterns that self-organize on the substrate is very rich, with morphologies that display several degrees of order upon the modification of initial film characteristics and irradiation parameters. This richness paves the way for the fabrication of novel functional surfaces, but it is also an indication of the complexity of the underlying driving mechanisms. A remarkable simplification for the comprehension of these phenomena can come from the noteworthy similarity of the obtained patterns with those showing up when liquids dewet from their substrates. Here, we analyze the possibility to apply a liquid-like model to explain the morphology evolution of ion bombarded thin films for the whole phenomenology showing up in experiments. In establishing this connection between liquids and ion bombarded thin films, we propose to use also for liquids the insight gained for our system with recent experiments that stress the importance of the substrate topography for the selection of the dewetting mechanism. If confirmed, this result would lead to a reconsideration of the importance of capillary waves in spinodal dewetting, and will help to understand the low reproducibility of the related experimental results.

In the last years, nanopore technology has been increasingly exploited for biomolecule detection and analysis. Recently, the main focus of the research has moved from the study of nucleic acids to the analysis of proteins and DNA-protein complexes. In this paper, chemically functionalized solid-state nanopore has been used to recognize Nuclear Factor-kappa B proteins (NF-κB), that are involved in several disorders and inflammation processes, so that their identification is of crucial importance for prognostic applications. In particular, we show that it is possible to electrically detect the specific interaction between p50, a protein belonging to the NF-κB family, and dsLNA probe molecules covalently attached to the surface of a FIB fabricated SiN pore. The obtained results have been compared with those related to BSA protein, which does not interact with the used probes. Finally, the potential of the device has been further tested by analyzing a whole cell extract. In this case, three principal peaks in the distribution of electrical event duration can be identified, corresponding to different interacting NF-κB complexes, so that the methodology appears to be effective also to study biological samples of considerable complexity. Ultimately, the presented data emphasize the selectivity and versatility of the functionalized nanopore device, demonstrating its applicability in bioanalytics and advanced diagnostics.

The submonolayer homoepitaxial growth on Ag(1 1 0) is studied by using a variable-temperature ultrahigh vacuum scanning tunneling microscope. The evolution of island density is studied as a function of temperature at given flux (≈0.0025 ML s −1 ) and coverage (0.16 ML) to evaluate the energy barriers and the binding energies for the in-channel and cross-channel diffusion. The experimental results are compared with kinetic Monte Carlo simulation.

The electronic and atomic structures of the interfaces formed upon deposition of Gd and Dy onto HOPG(0001) at substrate temperatures of 20 and 300 K have been studied by AES, UPS, XPS, EELS, and LEED. At both temperatures studied, Gd/HOPG interface reproduces atomic structure of HOPG(0001) up to 20 A thicknesses. The analysis performed by AES favors a quasi layer-by-layer growth and diffusion of Gd and Dy into interplane space of graphite even at 20 and 300 K. The structure of Dy/HOPG interface is different from that of the Gd/HOPG system: at thick coverages (45 A) when only Dy features are observed by electron spectroscopy, the LEED pattern typical of clean HOPG(0001) coexists with superstructural rings. Annealing of the interfaces at temperatures up to 1300 K induces, most probably, formation of the ordered carbide-like systems with geometrical structure analogous to that of pristine graphite for Gd-C and superstructure of 3 × 3 type for Dy-C systems.

We show that vibrational energy can be used to tune the chemisorption state of an adsorbed molecule. When dosing C2H4 with a supersonic molecular beam on Ag(0 0 1) we demonstrate by vibrational spectroscopy that, with increasing nozzle temperature, TN, firstly no stable adsorption occurs, then a p-bonded configuration is populated, switching finally to a more strongly, undissociated, di-r-bonded state. Direct dissociation is observed at still higher TN with the formation of dehydrogenated radicals. ” 2000 Elsevier Science B.V. All rights reserved.

The electronic structure and growth mode of C 60 molecules deposited on Ag(001) have been studied as a function of deposition parameters and annealing temperature. The measurements show that C 60 molecules are chemically bound to the Ag(001) surface even when deposited at 150 K, and the bond properties do not change significantly after annealing up to 670 K. In the resulting ordered C 60 overlayer, a mixed contrast of the buckyballs, as seen by scanning tunneling microscopy, is discussed in terms of non-equivalent orientations of the adsorbed molecules.

Surface morphology of a Cu(110) crystal, generated by ion sputtering, has been investigated by scanning tunneling microscopy. Different from recent theoretical predictions and experimental results, normal sputtering produces a well defined ripple structure whose wave vector rotates from $〈001〉$ to $〈1\overline{1}0〉$ by increasing the substrate temperature. Off-normal sputtering at low temperature (180 K) generates ripples whose orientation depends on both ion direction and surface azimuthal orientation. These results are described by a continuum equation which includes both surface curvature dependent erosion terms and diffusion terms accounting for surface anisotropy and Ehrlich-Schwoebel barriers.

We have investigated desorption and dissociation of O2 chemisorbed on Ag(001) induced by collision with hyperthermal Xe and Ar atoms by high resolution electron energy loss spectroscopy and supersonic molecular beam technique. The cross section for both processes increases rapidly both as a function of angle of incidence and of total impact energy of the inert gas atom. While the increase with energy is expected, the increase with the angle is somewhat surprising and is sensibly larger than observed for previously investigated systems. The cross section for desorption decreases moreover with coverage. In the limit of high impact energy and high coverage its value is always larger than the one for dissociation. The branching ratio between the two processes depends thereby on energy and angle of incidence of the inert gas atom. Atomic oxygen is not removed under any impact condition, because of its larger binding energy. In order to explain the experimental results, molecular dynamics simulations have been ...

Understanding energy transfer processes at surfaces is an obliged step for a full description of gas–surface systems and many efforts have been devoted to both theoretical and experimental investigations of the dynamics of gas surface interaction, with particular attention to chemisorption, where chemical bonds are created (between the gas and the metal surface) and broken (the bond between atoms in the molecule, in case of dissociative chemisorption). [1]

Short tubes with diameters of the order of 200 nm were drilled into silicon nitride (Si3N4) membranes of 200 nm thickness by focused ion beam technology and examined as leak elements for vacuum technology applications. These nano-holes exhibit molecular flow in the pressure range from high vacuum up to 10 kPa and can therefore be used as predictable leak elements for any non-condensable gas species. The geometrical dimensions were determined by SEM, STEM and AFM techniques. By Direct Simulation Monte Carlo method the conductances of these short tubes were calculated from the measured dimensions. The calculated conductance agreed with the value measured by comparison with a primary gas flowmeter within their respective uncertainties.

High-resolution microscopy techniques such as electron microscopy, scanning tunnelling microscopy and atomic force microscopy represent well-established, powerful tools for the structural characterization of adsorbed DNA molecules at the nanoscale. Notably, the analysis of DNA contours allows mapping intrinsic curvature and flexibility along the molecular backbone. This is particularly suited to address the impact of the base-pairs sequence on the local conformation of the strands and plays a pivotal role for investigations relating the inherent DNA shape and flexibility to other functional properties. Here, we introduce novel chain descriptors aimed to characterize the local intrinsic curvature and flexibility of adsorbed DNA molecules with unknown orientation. They consist of stochastic functions that couple the curvatures of two nanosized segments, symmetrically placed on the DNA contour. We show that the fine mapping of the ensemble-averaged functions along the molecular backbone generates characteristic patterns of variation that highlight all pairs of tracts with large intrinsic curvature or enhanced flexibility. We demonstrate the practical applicability of the method for DNA chains imaged by atomic force microscopy. Our approach paves the way for the label-free comparative analysis of duplexes, aimed to detect nanoscale conformational changes of physical or biological relevance in large sample numbers.

There is currently a growing interest in control of stretching of DNA inside nanoconfined regions due to the possibility to analyze and manipulate single biomolecules for applications such as DNA mapping and barcoding, which are based on stretching the DNA in a linear fashion. In the present work, we couple Finite Element Methods and Monte Carlo simulations in order to study the conformation of DNA molecules confined in nanofluidic channels with neutral and charged walls. We find that the electrostatic forces become more and more important when lowering the ionic strength of the solution. The influence of the nanochannel cross section geometry is also studied by evaluating the DNA elongation in square, rectangular, and triangular channels. We demonstrate that coupling electrostatically interacting walls with a triangular geometry is an efficient way to stretch DNA molecules at the scale of hundreds of nanometers. The paper reports experimental observations of λ-DNA molecules in poly(dimethylsiloxane) nanochannels filled with solutions of different ionic strength. The results are in good agreement with the theoretical predictions, confirming the crucial role of the electrostatic repulsion of the constraining walls on the molecule stretching.

Aims: Sensitivity, selectivity and tunability are keywords to develop effective and reliable diagnostic and bioanalytical tools. In this context, micro and nanofluidic devices constitute a powerful and versatile answer to the growing and urgent demand for innovative solutions. Nevertheless, a precise control of size and functionality of such structures is necessary for ensuring advanced manipulation and sensing capabilities, up to single molecule level. Methods: We report here on different strategies for the development of micro and nanofluidic platforms for advanced diagnostics based on the exploitation of the elastic properties of deformable materials, and on surface chemical functionalization processes. Results: We demonstrated that applying a macroscopic mechanical compression to elastomeric nanostructures it is possible to increase their confining power and vary the dynamics of DNA translocation process, while the use of the chemical functionalization allows to tune both the size and the functionality of the biosensor. Conclusion: We believe that a smart integration of these two approaches would allow a significant step forward for the fabrication of next-generation lab-on-chip devices for biomedical diagnostic applications.