Implantation and electron emission in cluster-surface collisions

Microscopic processes induced by the controlled deposition of mass selected silver clusters on graphite (HOPG) and Pt(111) are investigated. The implantation of silver clusters into the HOPG surface is analyzed. The first step consists in a systematic study of the implantation depths of AgN+ (N=1,3,7,9,13) clusters into HOPG, as a function of the cluster size and of the incoming energy. This is achieved by controlling the thermal oxidation of the bombarded graphite surface. This process results in etching of the cluster-induced defects to form pits which grow laterally while maintaining the depth of the implanted cluster. The morphology of the surface is characterized by the STM method, which provides information on the microscopic structure of the examined sample. We observe a scaling of the implantation depth with the momentum of the cluster, in agreement with recent results reported in the literature. In particular, a universal behavior is recognized when scaling the momentum with the cluster projected surface. Within this model, we find that the real geometry of the cluster plays a dominant role. It is also explored whether the single cluster behaves as a sum of independent atoms, or if molecular phenomena are present. In particular, we find molecular effects in the stopping power that the cluster experiences in penetrating the substrate. The electron emission induced by cluster-surface collisions is presented as a function of the two different employed substrates (HOPG and Pt(111)), and of size and energy of the incoming AgN+ (N=1,2,3,4,5,7,8,9) clusters. In order to understand the origin of emitted electrons, we investigate the different electron emission and charge transfer processes during the collision. Emission is observed below the classical threshold and results are interpreted within a recent model based on the semi-localization of valence electrons. The substrate itself plays a role in the electron emission processes, and higher emission yields are measured for clusters impact on the Pt(111) target. Molecular effects are also investigated. For both substrates we find a size-dependent sublinear effect at low velocities and a superlinear effect at higher velocities, similar to the case of hydrogen projectiles reported in the literature. We try to find oscillations in the electron emission yield, which would bear information on the charge-exchange processes during the collision as well as on the electronic structure of the cluster and the substrate. Such oscillations - recently suggested in Meiwes-Broer's work - are not clearly identified in our data

Full-hand electrotactile feedback using electronic skin and matrix electrodes for high-bandwidth human–machine interfacing

Tactile feedback is relevant in a broad range of human–machine interaction systems (e.g. teleoperation, virtual reality and prosthetics). The available tactile feedback interfaces comprise few sensing and stimulation units, which limits the amount of information conveyed to the user. The present study describes a novel technology that relies on distributed sensing and stimulation to convey comprehensive tactile feedback to the user of a robotic end effector. The system comprises six flexible sensing arrays (57 sensors) integrated on the fingers and palm of a robotic hand, embedded electronics (64 recording channels), a multichannel stimulator and seven flexible electrodes (64 stimulation pads) placed on the volar side of the subject’s hand. The system was tested in seven subjects asked to recognize contact positions and identify contact sliding on the electronic skin, using distributed anode configuration (DAC) and single dedicated anode configuration. The experiments demonstrated that DAC resulted in substantially better performance. Using DAC, the system successfully translated the contact patterns into electrotactile profiles that the subjects could recognize with satisfactory accuracy (i.e. median{IQR} of 88.6{11}% for static and 93.3{5}% for dynamic patterns). The proposed system is an important step towards the development of a high-density human–machine interfacing between the user and a robotic han

Active haptic perception in robots: a review

In the past few years a new scenario for robot-based applications has emerged. Service and mobile robots have opened new market niches. Also, new frameworks for shop-floor robot applications have been developed. In all these contexts, robots are requested to perform tasks within open-ended conditions, possibly dynamically varying. These new requirements ask also for a change of paradigm in the design of robots: on-line and safe feedback motion control becomes the core of modern robot systems. Future robots will learn autonomously, interact safely and possess qualities like self-maintenance. Attaining these features would have been relatively easy if a complete model of the environment was available, and if the robot actuators could execute motion commands perfectly relative to this model. Unfortunately, a complete world model is not available and robots have to plan and execute the tasks in the presence of environmental uncertainties which makes sensing an important component of new generation robots. For this reason, today\u2019s new generation robots are equipped with more and more sensing components, and consequently they are ready to actively deal with the high complexity of the real world. Complex sensorimotor tasks such as exploration require coordination between the motor system and the sensory feedback. For robot control purposes, sensory feedback should be adequately organized in terms of relevant features and the associated data representation. In this paper, we propose an overall functional picture linking sensing to action in closed-loop sensorimotor control of robots for touch (hands, fingers). Basic qualities of haptic perception in humans inspire the models and categories comprising the proposed classification. The objective is to provide a reasoned, principled perspective on the connections between different taxonomies used in the Robotics and human haptic literature. The specific case of active exploration is chosen to ground interesting use cases. Two reasons motivate this choice. First, in the literature on haptics, exploration has been treated only to a limited extent compared to grasping and manipulation. Second, exploration involves specific robot behaviors that exploit distributed and heterogeneous sensory data

Modeling Electronic Skin Response to Normal Distributed Force

The reference electronic skin is a sensor array based on PVDF (Polyvinylidene fluoride) piezoelectric polymers, coupled to a rigid substrate and covered by an elastomer layer. It is first evaluated how a distributed normal force (Hertzian distribution) is transmitted to an extended PVDF sensor through the elastomer layer. A simplified approach based on Boussinesq’s half-space assumption is used to get a qualitative picture and extensive FEM simulations allow determination of the quantitative response for the actual finite elastomer layer. The ultimate use of the present model is to estimate the electrical sensor output from a measure of a basic mechanical action at the skin surface. However this requires that the PVDF piezoelectric coefficient be known a-priori. This was not the case in the present investigation. However, the numerical model has been used to fit experimental data from a real skin prototype and to estimate the sensor piezoelectric coefficient. It turned out that this value depends on the preload and decreases as a result of PVDF aging and fatigue. This framework contains all the fundamental ingredients of a fully predictive model, suggesting a number of future developments potentially useful for skin design and validation of the fabrication technology

Modeling Electronic Skin Response to Normal Distributed Force

The reference electronic skin is a sensor array based on PVDF (Polyvinylidene fluoride) piezoelectric polymers, coupled to a rigid substrate and covered by an elastomer layer. It is first evaluated how a distributed normal force (Hertzian distribution) is transmitted to an extended PVDF sensor through the elastomer layer. A simplified approach based on Boussinesq’s half-space assumption is used to get a qualitative picture and extensive FEM simulations allow determination of the quantitative response for the actual finite elastomer layer. The ultimate use of the present model is to estimate the electrical sensor output from a measure of a basic mechanical action at the skin surface. However this requires that the PVDF piezoelectric coefficient be known a-priori. This was not the case in the present investigation. However, the numerical model has been used to fit experimental data from a real skin prototype and to estimate the sensor piezoelectric coefficient. It turned out that this value depends on the preload and decreases as a result of PVDF aging and fatigue. This framework contains all the fundamental ingredients of a fully predictive model, suggesting a number of future developments potentially useful for skin design and validation of the fabrication technology

Bending response of PVDF piezoelectric sensors2012 IEEE Sensors

The aim of the present work is to investigate the response to pure bending of a piezoelectric PVDF film as a standing-alone device. A model is proposed and experimental results show that these polymer films enjoy this property, opening very promising scenarios for their integration into flexible tactile sensing system