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International audience; Background Older adults often experience physical, sensory, and cognitive decline. Therefore, they have a high risk of falls, which leads to severe health and psychological consequences and can induce fear of falling. Rehabilitation programs using exergames to prevent falls are being increasingly studied. Medimoov is a movement-based patient-personalized exergame for rehabilitation in older adults. A preliminary study showed that its use may influence functional ability and motivation. Most existing studies that evaluate the use of exergames do not involve an appropriate control group and do not focus on patient-personalized exergames. Objective This study aims to evaluate the effects of Medimoov on risk of falls and fear of falling in older adults compared with standard psychomotor rehabilitation. Methods This is a serial, comparative, randomized controlled group study. Both groups (n=25 in each) will receive psychomotor rehabilitation care. However, the methods of delivery will be different; one group will be exposed to the Medimoov exergame platform, and the other only to traditional means of psychomotor rehabilitation. The selection criteria will be (1) age of 65 years or older, (2) ability to answer a questionnaire, (3) ability to stand in a bipedal position for at least 1 minute, (4) score of 13 or greater on the Short Fall Efficacy Scale, and (5) stable medical condition. An evaluation will be made prior to starting the intervention, after 4 weeks of intervention, and at the end of the intervention (after 8 weeks), and it will focus on (1) risk of falls, (2) fear of falling, and (3) cognitive evaluations. Physical activity outside the session will also be assessed by actimetry. The outcome assessment will be performed according to intention-to-treat analysis. Results The protocol (2019-11-22) has been approved by the Comité de Protection des Personnes Nord-Ouest I–Université de Rouen (2019-A00395-52), which is part of the French national ethical committee. The study received funding in February 2020. As of October 2020 (submission date), and due to the context of the COVID-19 pandemic, a total of 10 participants out of 50 had been enrolled in the study. The projected date for the end of the data collection is December 2021. Data analyses have not been started yet, and publication of the results is expected for Spring 2022. Conclusions The effects of psychomotor rehabilitation using the Medimoov exergame platform on the risk and fear of falls will be evaluated. This pilot study will be the basis for larger trials. Trial Registration ClinicalTrials.gov NCT04134988; https://clinicaltrials.gov/ct2/show/NCT04134988 International Registered Report Identifier (IRRID) DERR1-10.2196/24665

International audience; This PhD project is multidisciplinary, at the intersection of Early Childhood Education, Design, and Human-Computer Interaction. The PhD goal aim at developing new approaches for early childhood education focusing on the role of body in the learning process. We leverage digital tangible and interactive technologies to develop specific scenarios that are evaluated in preschools. Our work proposes novel paradigms and uses of digital technologies currently not found in typical preschool environments.

Traditional science instruction is typically reliant on visual modes of learning, such as textbooks and graphs. Furthermore, since science instruction is often heavily dependent upon visual cues, students with visual impairment often do not have access to the same educational opportunities in most science classes (Jones, Minogue, Oppewal, Cook, & Broadwell, 2006). However, advancements in tactile technology (haptics) are allowing individuals with visual impairments to discover science concepts in revolutionary ways. Haptic feedback devices allow users to experience computer simulations through tactile sensations. Students with visual impairments in science classrooms can now use haptic devices to "feel" objects and processes in science, such as exploring an animal cell's organelles (Jones et al., 2004). Researchers in STEM (science, technology, engineering, and mathematics) education have argued that the widespread use of haptic technology in education could provide a hands-on learning experience that is conducive for learning about difficult science concepts (Young et al., 2011) for students who have typical vision as well as those with visual impairments. Jones, Bokinsky, Tretter, & Negishi (2005) reported equal benefits for students with and without visual impairments in using haptic devices similar to the Falcon to explore unknown shapes. Furthermore, the amount of time it took to complete the investigation of shapes was the same for both groups. Other studies have suggested that haptic devices and computer simulations may "lead to a deeper level of processing" (Jones et al., 2004, p. 55). Unfortunately, haptic devices have not been prominent in science classes because of the cost of the technology and the time needed to train teachers on how to effectively use the technology in the classroom. However, the cost of haptic devices has fallen considerably in recent years (they are now the same price as an inexpensive microscope), and preliminary data suggests that there is potential value in the use of haptic tools to teach abstract science concepts. The study presented here explored the efficacy of a haptic device and a computer simulation to teach students with visual impairments about heat and pressure concepts associated with particle movement. The concept of particle movement is crucial for individuals to understand various interdisciplinary science concepts, such as heat; the formation of viral capsids, proteins, and structures; and processes such as osmosis. The haptic instructional program has been used in a series of studies that allow students to feel particle movement in a closed system (Jones et al., 2013). Students are able to feel how particle movement varies with different temperature and pressure settings without depending on a visual aid for learning. METHODS Instructional program and technology The participants in the present study used the Novint Falcon haptic device from Novint Technologies (see Figure 1). The Novint Falcon is a USB-enabled haptic device that is designed to replace a mouse while a participant is utilizing the computer for simulations or gaming. Participants are able to control the Novint Falcon by holding on to the grip bubble (see Figure 2), which moves in three dimensions: up and down, forwards and backwards, and right to left. While the participant is moving the grip bubble, the Novint Falcon's sensors are able to communicate with the computer, detailing the participant's movement within a computer program. In addition, the grip bubble connected to a computer allows participants to manipulate objects in a computer simulation while providing tactile feedback to the participant. [FIGURE 1 OMITTED] [FIGURE 2 OMITTED] The instructional program ("Pollen Grain") allowed participants to maneuver and control an object (a pollen grain) that was constantly subjected to the random motion of surrounding particles in a closed system (see Figure 3). …

Mechanical properties of biological samples have been imaged with a \textit{Force Feedback Microscope}. Force, force gradient and dissipation are measured simultaneously and quantitatively, merely knowing the AFM cantilever spring constant. Our first results demonstrate that this robust method provides quantitative high resolution force measurements of the interaction The little oscillation imposed to the cantilever and the small value of its stiffness result in a vibrational energy much smaller than the thermal energy, reducing the interaction with the sample to a minimum. We show that the observed mechanical properties of the sample depend on the force applied by the tip and consequently on the sample indentation. Moreover, the frequency of the excitation imposed to the cantilever can be chosen arbitrarily, opening the way to frequency-dependent studies in biomechanics, sort of spectroscopic AFM investigations.

Resume Dans cet article, nous exposons comment une analyse des controverses socioscientifiques soulevees par les nanotechnologies a permis d’eclairer et d’expliciter les choix educatifs sous-tendant l’elaboration d’une sequence pedagogique sur ces developpements qui suscitent des oppositions vives. Nous presentons d’abord un travail d’analyse des controverses mene selon la perspective des etudes sociales sur les sciences. Cette analyse a oriente l’elaboration, suivant l’approche des recherches « design-based », d’une sequence pedagogique qui vise a outiller des eleves de filiere scientifique de l’enseignement secondaire francais pour comprendre les debats sur les nanotechnologies et y participer.

Nanotechnology has been touted as the next ‘industrial revolution’ of our modern age. In order for successful research, development, and social discourses to take place in this field, education research is needed to inform the development of standards, course development, and workforce preparation. In addition, there is a growing need to educate citizens and students about risks, benefits, and social and ethical issues related to nanotechnology. This position paper describes the advancements that have been made in nanoscale science and nanotechnology, and the challenges that exist to educate students and the public about critical nanoscience concepts. This paper reviews the current research on nanotechnology education including curricula, educational programs, informal education, and teacher education. Furthermore, the unique risks, benefits and ethics of these unusual technological applications are described in relation to nanoeducation goals. Finally, we outline needed future research in the areas of na...

This study investigated the efficacy of a real-time, interactive visuohaptic simulation to teach students particulate motion and the concepts of thermal energy, pressure, and random motion. Students were able to experience forces through their own somatosensory system in real time. Participants included 78 middle school students who completed a pre-, post-, and delayed post-assessment of knowledge and a post-assessment of attitudes and investigated particle motion using either the visuohaptic or a control visual simulation. The results showed that there were significant gains in the knowledge of thermal energy, pressure, and random motion for both groups of students from pre- to post-assessment. There were no significant differences in post scores between those students that used visuohaptic technology compared to those in the control group who used only a visual simulation. However, students in the visuohaptic group reported that the investigation was highly interesting and enabled them to better understand particle motion as well as visualize movement. The role of haptic instructional technologies as tools to teach micro- and human-scale phenomena is discussed.

Non-contact interaction between two parallel flat surfaces is a central paradigm in sciences. This situation is the starting point for a wealth of different models: the capacitor description in electrostatics, hydrodynamic flow, thermal exchange, the Casimir force, direct contact study, third body confinement such as liquids or films of soft condensed matter. The control of parallelism is so demanding that no versatile single force machine in this geometry has been proposed so far. Using a combination of nanopositioning based on inertial motors, of microcrystal shaping with a focused-ion beam (FIB) and of accurate in situ and real-time control of surface parallelism with X-ray diffraction, we propose here a “gedanken” surface-force machine that should enable one to measure interactions between movable surfaces separated by gaps in the micrometer and nanometer ranges.

In this article, we measure the viscous damping G″, and the associated stiffness G′, of a liquid flow in sphere-plane geometry over a large frequency range. In this regime, the lubrication approximation is expected to dominate. We first measure the static force applied to the tip. This is made possible thanks to a force feedback method. Adding a sub-nanometer oscillation of the tip, we obtain the dynamic part of the interaction with solely the knowledge of the lever properties in the experimental context using a linear transformation of the amplitude and phase change. Using a Force Feedback Microscope (FFM), we are then able to measure simultaneously the static force, the stiffness, and the dissipative part of the interaction in a broad frequency range using a single AFM probe. Similar measurements have been performed by the Surface Force Apparatus (SFA) with a probe radius hundred times bigger. In this context, the FFM can be called nano-SFA.

International audience; We report the observation of a transition in the dynamical properties of water nano-menicus which dramatically change when probed at different time scales. Using a AFM mode that we name Force Feedback Microscopy, we observe this change in the simultaneous measurements, at different frequencies, of the stiffness G'(N/m), the dissipative coefficient G"(kg/sec) together with the static force. At low frequency we observe a negative stiffness as expected for capillary forces. As the measuring time approaches the microsecond, the dynamic response exhibits a transition toward a very large positive stiffness. When evaporation and condensation gradually lose efficiency, the contact line progressively becomes immobile. This transition is essentially controlled by variations of Laplace pressure. Visco-elastic properties of water nanobridges[1] at very different time scales, have never been investigated despite ubiquitous presence of capillarity. Associated forces are among the most intense at nanoscales with important consequences in soils and granular media. Interest in dynamical properties is immediately raised if one considers interacting surfaces with roughness scales down to nanometer. Even at moderate speeds, such as v=1m/s, characteristic times of surface interaction down to mi-crosecond appear in these conditions. Our measurements approaching these time scales, further strengthen the relevance of the dynamical properties to describe how real surfaces interact and are certainly of crucial importance in numerous AFM experiments [2]. We here report measurements of dynamical properties of a water nanobridge for a continuous range of the surface gap and a frequency bandwidth up to 0.1 MHz. We identify two regimes: one is the thermodynamical equilibrium; the second is out of equilibrium. Evaporation and condensation of water molecules between the liquid and the gas phase ensures that the nano-meniscus curvature is the one at thermo-dynamical equilibrium(2H=-1/r k) where 2H is the water bridge curvature and r k is the Kelvin radius. At time short enough, molecule exchanges between the liquid and the gas phase are no longer efficient and the water nanobridge is led to acquire a constant volume. The liquid bridge relaxation time is the time needed for the bridge to adapt its shape as required by thermodynam-ical equilibrium, when its length h is abruptly changed by δh. This is controlled by molecular transport through diffusion mechanisms in gas phase. This relaxation time τ can be estimated as in SFA context, see Ref.[3]. τ = 2γρr 2 ln(R/ρ)/P sat r k 2 D (1)

We present the novel application of a relatively new technique (nanolithography) to the study of quasicrystalline surface oxidation. The 5-fold surface of an AlPdMn alloy was oxidized using a metallized AFM tip. The electrochemical nature of this process was confirmed by investigating the influence of humidity and polarity of the applied voltage on the quasicrystalline oxide. Oxides of different thickness and adhesive properties were created by altering the applied voltage and the humidity during the lithographic process. The technique can be used in an exhaustive study of properties of the various types of oxides that form on the AlPdMn surface and the preliminary results of one such study are reported.

New types of weak forces measurements with Atomic Force Microscope (AFM) are very challenging for experimental physics and call for new studies on control strategies operating the AFM. It is thus necessary to first develop a precise model of the cantilever with its sharp tip, in interaction with the scanned sample. This paper presents a model of the cantilever, that is based on beam theory and taking into account the influence of the long distance interaction forces.

Mixing molten salts with luminescent conjugated polymers provides the ability to lower the current threshold of organic electroluminescence (EL) devices. However, this process generally results in unwanted premature electrical aging. We used dynamic atomic force microscopy (AFM) in the electric force detection regime to study the phase microseparation occurring in the salt-polymer blend. We found that in the spin-coated layers, the molten salt most often forms discotic, roughly self-organized sub-microdomains. Their size and density strongly depend on the polymer side chains and overall molecular weight, on the molten salt nature, and on their respective concentrations in solution. We show that the diode current is injected into the vicinity of the interface between the salt and polymer domains, since it is proportional to the perimeter of the salt domains per surface unit, as estimated from the AFM images. The electrical aging is attributed to the degradation of the interface between the polymer and salt...

We studied the charge storage and subsequent imaging of silicon quantum dots (SiQD) embedded in a SiO2 film by using atomic-force microscopy (AFM) in tapping and electrostatic force microscopy (EFM) modes. The controllable deposition of both positive and negative localized charges in SiQD is described. The dynamics of the deposited charges is studied and the charge decay time constant is determined from the measurements. A simple analysis is presented to explain the contrast in tapping and EFM images and to quantify the total amount of stored charge.

It was shown recently that the Force Feedback Microscope can avoid the jump-to-contact in Atomic force Microscopy even when the cantilevers used are very soft, thus increasing force resolution. In this letter, we explore theoretical aspects of the associated real time control of the tip position. We take into account lever parameters such as the lever characteristics in its environment, spring constant, mass, dissipation coefficient and the operating conditions such as controller gains, and interaction force. We show how the controller parameters are determined so that the FFM functions at its best and estimate the bandwidth of the system under these conditions.

International audience; The optical transmission and reflection in between two metalized optical fiber tips is studied in the optical near-field and far-field domains. Besides aluminum-coated tips for near-field scanning optical microscopy (NSOM), specifically developed gold-coated fiber tips cut by focused ion beam (FIB) are investigated. Transverse transmission maps of sub-wavelength width clearly evidence optical near-field coupling between the tips for short tip distances and becomes essentially Gaussian-shaped for larger distances in the far-field regime. Moreover concentric reflection fringes observed for NSOM-type tips illustrate the influence of the receiving fiber tip on the emission pattern of the source tip.

The tribological behavior of carbon based thin films is strongly influenced by their chemical composition, polycrystalline structure and surface morphology. We present friction measurements on laser deposited amorphous carbon and carbon nitride (CNchi) thin films using atomic force microscopy. We studied the friction behavior of these films in relation with their structure and surface morphology resulting from the applied deposition parameters. We found high nanoscopic friction for amorphous carbon thin films, medium friction for CN chi and very low friction for graphite. Finally we discuss our findings in terms of the microscopic mechanisms of energy dissipation underlying the observed friction behavior. (C) 2001 Elsevier Science B.V. All rights reserved.

AFM force curve measurements have been performed on layers of entangled multiwall carbon nanotubes, produced by chemical vapor deposition, to measure the nanotubes adhesive and elastic properties. AFM tip radius and nanotube diameter being comparable, these layers are a discrete medium for the force curve measurements. Controlling the tip-layer interaction, we can specifically probe the response of one or several nanotubes. If the tip is strongly pressed against the layer, it interacts with several nanotubes; for a weak interaction, it interacts with only one nano-object. Non-linear behavior in force curves is an evidence for an inelastic response of the nanotubes. Numerical simulations of the layer-AFM tip system mechanical analysis reproduce all the nanotubes adhesion and mechanical experimental features.

X-ray Standing Waves (XSW) in Bragg position are the direct space modulation of the electromagnetic (e.m.) field in a diffracting sample. Specifically in the two beam approximation, a modulation of the e.m. field intensity with a periodicity of 2π/Q// has to be considered in a quasiperiodic structure. As it is fully described within the Dynamical Theory of X-ray Diffraction (DTXD), the XSW can be smoothly displaced with respect to atomic positions in a perfect crystal. This results in a strong modulation of the absorption processes as the crystal position crosses the Bragg condition. In the special case of quasicrystals (QC) the application of this technique, probing the long range order, opens several basic questions. Using a Fibonacci sequence of diffracting planes, we show that the XSW signal highly depends on the qperp component of the Bragg peak. Within this model, we then test the XSW response as phason defects are introduced in the structure. A rapid decrease of the XSW signature is observ...

An X-ray standing waves experiment was performed at the ID32 beam line of the ESRF on an Al–Pd–Mn quasicrystal with the X-ray beam at normal incidence. The X-ray photoemission core levels for each element were recorded to probe the surface. The drain current, i.e. the electron current from ground needed to neutralize the irradiated sample and to compensate the photoemitted electrons was also recorded as a bulk probe that integrates over all atoms of the sample. Within the two-beam approximation applied to quasicrystals, a simple analysis of this effect is proposed. This provides a direct-space illustration of the diffraction process in a quasiperiodic structure.

We have measured the electron energy losses on different Al–Pd–Mn quasicrystal surface states established by low energy electron diffraction, X-ray photoelectron spectroscopy and Auger electron spectroscopy. On the well characterized and ordered Al–Pd–Mn quasicrystalline surfaces, the energy loss signal with an energy of incident electrons at 2 keV shows a strong peak at 16 eV and a satellite at about 33 eV. As the electron primary energy is decreased to 260 eV, an energy loss at 10.5 eV is clearly observed. A short ion bombardment (1 μA at 500 eV during 1 min) erases this loss at 10.5 eV which can be recovered by annealing at 800 K. All these observations are simply attributed to the existence of a bulk plasmon at about 16 eV and a surface plasmon at 10.5 eV. The ratio between these two energies is 1.52. This is quite close to the expected 2 from the classical plasmon model. On the crystalline partially annealed surface, a bulk plasmon is observed at about 16.5 eV. Oxygen-contaminated surface presents a bulk plasmon shifted towards higher energy of about 20 eV.

Fivefold surfaces of Al–Pd–Mn quasicrystal have been prepared under ultra-high vacuum (UHV) by sputtering and annealing above 700 K and characterized by electron diffraction, Auger spectroscopy and X-ray photoemission spectroscopy (LEED, AES, XPS). X-ray reflectivity at grazing incidence reveals that an in situ temperature annealing at 900 K is necessary to irreversibly produce the signature of a flat and bulk terminated surface. Air-AFM investigations of surfaces prepared below or in the vicinity of this transformation temperature show a large scale structure in the micrometer range with high steps and parallel terraces. Terrace morphology is dominated by clusters with a typical size of about 10 nm. Nanometer steps can coexist with this cluster structure. With UHV-STM, terrace roughness based on cluster assembly is found to extend down to the nanometer scale.

Inverse x-ray fluorescence holography was used to explore the local atomic order of a nearly perfect quasicrystal with composition Al70. 4Pd21Mn8.6. We have demonstrated the possibility of direct 3D imaging of the atomic decoration in a quasicrystal. We have obtained the average 3D environment of selected coordination shells around the Mn atoms. These results open the way to obtaining further and more complete information about the various coordination shells in complex materials by measuring multiple energy x-ray holograms at different sites.

A study of the relationship between structure and growth parameters for existing and candidate carbon-based protective coatings has been carried out. In particular, diamond-like carbon (DLC) and carbon nitride thin films were deposited on silicon wafers by pulsed Nd:YAG laser (wavelength 532 nm) ablation of graphite in high vacuum ( p =1.5×10 −7 Pa) and in a nitrogen atmosphere ( p =13 Pa). The composition (N/C ratio), the structural and electronic properties and the surface morphology of the deposited films were investigated as a function of laser fluence (1–12 J/cm 2 ). The highest N/C ratio 0.40 was obtained with a laser fluence of 12 J/cm 2 ; for this nitrogen concentration X-ray photoelectron spectroscopy (XPS) reveals an increase of CN bonds instead of CN bonds with respect to lower concentrations. Electron energy loss spectroscopy (EELS) and XPS show an increase of sp 2 carbon bonded sites in the DLC films deposited with lower laser fluences in agreement with the theory of the so-called sub-implantation model. EELS also reveals a gradient in the chemical nature of the films through the thickness. Atomic force microscopy analysis shows that the root-mean-squared roughness of the DLC samples is about 3 A over the laser fluence range investigated.

Chemical and structural surface evolution of an icosahedral AlPdMn sample was systematically studied after ultrahigh vacuum surface preparations based on ion sputtering followed by annealing. Depending on the annealing temperature we observed different surface phases. For annealing temperatures below 700 K a thin crystalline surface was formed on the quasi-crystal bulk. For annealing temperatures between 700 and 900 K we found a quasi-crystalline surface that can be interpreted as a bulk-terminated one. For high temperature annealing (>950 K) the surface observed at high temperature was different to that obtained after cooling to room temperature. The cooled sample exhibited again a crystalline thick layer. In order to study the eventual influence of the original quasi-periodic structure on the evaporation, we further investigated the high temperature annealing regime from 950 to 1050 K, where we observed the initial stage of a preferential evaporation of manganese atoms. Finally, we obtained direct experimental evidence for a spontaneous deoxidation of the quasi-crystal.

Using a personal computer and a smartphone, iMecaProf is a software that provides a complete teaching environment for practicals associated to a Classical Mechanics course. iMecaProf proposes a visual, real time and interactive representation of data transmitted by a smartphone using the formalism of Classical Mechanics. Using smartphones is more than using a set of sensors. iMecaProf shows students that important concepts of physics they here learn, are necessary to control daily life smartphone operations. This is practical introduction to mechanical microsensors that are nowadays a key technology in advanced trajectory control. First version of iMecaProf can be freely downloaded. It will be tested this academic year in Universit\'e Joseph Fourier (Grenoble, France), Comment: Presented at WCPE 2012 Istanbul

During propagation of brittle cracks in silicon single crystal, steps parallel to the direction of the crack and separated by terraces, are often created. As the crack further propagates, these steps gradually coalesce. This produces the characteristic surface morphology usually identified as a river pattern. An experimental analysis of these river patterns appearing during fractures of silicon single crystals at room temperature is presented. The coalescence of the steps and the coarsening of the terrace widths reveal an effective interaction between the propagating steps. With an interaction between steps supposed to be determined by the size of the terraces, the observed river patterns are numerically reproduced.

4 pages, 3 figures; International audience; Owing to its two dimensional electronic structure, graphene exhibits many unique properties. One of them is a wave vector and temperature dependent plasmon in the infrared range. Theory predicts that due to these plasmons, graphene can be used as a universal material to enhance nanoscale radiative heat exchange for any dielectric substrate. Here we report on radiative heat transfer experiments between SiC and a SiO2 sphere which have non matching phonon polariton frequencies, and thus only weakly exchange heat in near field. We observed that the heat flux contribution of graphene epitaxially grown on SiC dominates at short distances. The influence of plasmons on radiative heat transfer is further supported with measurements for doped silicon. These results highlight graphenes strong potential in photonic nearfield and energy conversion devices.

The force between two particles as a function of distance is one of the most fundamental curves in physics. Here, we describe how the force feedback microscope can routinely measure the tip-surface interaction in the entire range of distances with a sensitivity of 1 pN and in different media. The method allows to measure simultaneously the force, force gradient, and damping from solely the knowledge of the lever spring constant. The jump to contact is avoided and thus it is possible to follow the brutal nucleation of a water bridge between the tip and the surface.

The control of heat flow is a formidable challenge due to lack of good thermal insulators. Promising new oppor-tunities for heat flow control were recently theoretically discovered for radiative heat flow in near field, where large heat flow contrasts may be achieved by tuning electronic excitations on surfaces. Here we show experi-mentally that the phase transition of VO2 entails a change of surface polariton states that significantly affects radiative heat transfer in near field. In all cases the Derjaguin approximation correctly predicted radiative heat transfer in near field, but it underestimated the farfield limit. Our results indicate that heat flow contrasts can be realized in near field that can be larger than those obtained in farfield., 3 figures

It is shown that a graphene layer on top of a dielectric slab can dramatically influence the ability of this dielectric for radiative heat exchange. Effect of graphene is related to thermally excited plasmons. Frequency of these resonances lies in the terahertz region and can be tuned by varying the Fermi level through doping or gating. Heat transfer between two dielectrics covered with graphene can be larger than that between best known materials and even much larger at low temperatures. Moreover, high heat transfer can be significantly modulated by electrical means that opens up new possibilities for very fast manipulations with the heat flux., Comment: 5 pages, 3 figures, submitted to PRL 14.11.2011

We show that functionalized micromechanical bilayer levers can be used as sensitive probes to accurately measure radiative heat flux in vacuum between two materials at the micro scale. By means of calibration to one material these measurements can be made quantitative for radiative heat flux or for either temperature or material emissivity. We discuss issues and opportunities for our method and provide ample technical details regarding its implementation and demonstrate good correspondence with the Stefan Boltzman law. We use this system to probe the phase transition of VO2 and find that radiative heat transfer in farfield between VO2 and glass can be reversibly modulated by a factor of 5., Comment: 14 pages 10 figures

We report on measurements of the Casimir force in a sphere-plane geometry using a cryogenic force microscope to move the force probe in situ over different materials. We show how the electrostatic environment of the interacting surfaces plays an important role in weak force measurements and can overcome the Casimir force at large distance. After minimizing these parasitic forces, we measure the Casimir force between a gold-coated sphere and either a gold-coated or a heavily doped silicon surface in the 100-400 nm distance range. We compare the experimental data with theoretical predictions and discuss the consequence of a systematic error in the scanner calibration on the agreement between experiment and theory. The relative force over the two surfaces compares favorably with theory at short distance, showing that this Casimir force experiment is sensitive to the dielectric properties of the interacting surfaces., accepted for publication in Physical Review B

The low temperature homoepitaxial growth of silicon has been probed in situ by Reflection High Energy Electron Diffraction (RHEED) in a Molecular Beam Epitaxy (MBE) chamber in the temperature range 250 o C-400 o C. The continuous change in the RHEED patterns during the growth of thick films (several hundred angstroms) shows the progressive appearance of a surface roughness during and after the decay of RHEED oscillations. This is a clear evidence for kinetic roughening in the case of silicon epitaxial growth at low temperatures on the Si(111) face. The surface width, σ, measured as the film thickness, h, is increased, can be described by: σ(h, T)∼Ah exp(E f /kT) with E f ∼0.65 eV. This is in marked difference with the kinetic roughening behavior measured during the growth of a metal like iron by means of the same RHEED technique (see Chevrier et al., Europhys. Lett. 8 (1991) 737). Furthermore, an extrapolation of this behavior to epitaxial growths at higher temperatures (T∼600 o C-800 o C) suggests an effective influence of kinetic roughening in the determination of growth temperatures generally used for silicon MBE (i.e. the empirical usual growth temperatures Tepi ∼ 650 o C). During growth at substrate temperatures between 250 o C and 400 o C, the nucleation of misoriented silicon islands takes place following the occurrence of kinetic roughening at the surface. In this range of temperatures, this suggests that the loss of epitaxy occurs on a rough surface through the proliferation of defects and of misoriented crystals

During the course of orthorhombic βFeSi 2 heteroepitaxy on Si substrates under molecular beam epitaxy conditions, several ultra-thin pseudomorphic metastable silicide layers have been observed, e.g. a cubic CsCl phase, a cubic CaF 2 phase and tetragonal αFeSi 2 , recently and surprisingly stabilized at low temperature. We report here on their phase transition towards the stable βFeSi 2 phase via two main kinetic paths, clearly demonstrated for the first time thanks to high-resolution electron microscopy measurements and image simulation. Our results emphasize the relevant influence of the local morphology at the interface in favoring one or another kinetic path, although the common general behavior of the interface development is well reflected in the sequential formation on Si substrate of: epitaxially strained FeSi 2 layer; relaxed FeSi 2 layer mediated by dislocation formation; stable βFeSi 2 .