Littérature scientifique sur le sujet « Nanoposition sensors »

Prototypes of indvidual carbon-nanotube-based nanoposition sensors for detercting approaching, touching, and sliding positions are presented on the bases of the interelectrodedistance-based field emission current change of a nanotube emitterand the resistance change caused by sliding motion of nanotube on an Au substrate. The sensors are constroucted by nanorobotic manipulation and featured by their compact sizes, simple structures, and potential high resolutions. A field-emission-based sensor is characterized by the non-contact configuration and is suitable for approximity sensing or as a position detector for other kinds of sensor. The perfect linearity of the resistance of a nanotube sliding on an Au substrate promises very high resolution for distance measurement. The sensitivity of these sensors has been found to be 7pA per 100nm and 0.24nA/nm respectively in experiments. The transient state from emission to transpot can be used for a touching sensor, and a 52 pA jump has been detected.

Abstract A process flow is described for the low cost, flexible fabrication of metal MEMS with high performance integrated sensing. The process is capable of producing new designs in ≈ 1 week at an average unit cost of <$1k/device even at batch sizes of ≈ 1-10, with expected sensing performance limits of about 135dB over a 10khz sensor bandwidth. This is a ≈20x reduction in cost, ≈25x reduction in time, and potentially >30x increase in sensing dynamic range over comparable state-of-the-art compliant nanopositioners. The Non-Lithographically Based Microfabriction (NLBM) process is uniquely suited to create high performance nanopositioning architectures which are customizable to the positioning requirements of a range of nanoscale applications. These can significantly reduce the cost of nanomanufacturing research and development, as well as accelerate the development of new processes and the testing of fabrication process chains without excess capital investment. A 6-DOF flexural nanopositioner with integrated sensing for all 6-DOF was fabricated using the newly developed process chain. The fabrication process was measured to have ≈30µm alignment. Sensor arm, flexure, and trace widths of 150µm, 150µm and 800µm, respectively, were demonstrated. Process capabilities suggest lower bounds of 25 µm, 50µm and 100µm, respectively. Dynamic range sensing of 52dB was demonstrated for the nanopositioner over a 10kHz sensor bandwidth. Improvements are proposed to approach sensor performance of 132dB over a 10kHz sensor bandwidth.

AbstractA self-mixing interferometer is proposed to measure nanometre-scale optical path length changes in the interferometer’s external cavity. As light source, the developed technique uses a blue emitting GaN laser diode. An external reflector, a silicon mirror, driven by a piezo nanopositioner is used to produce an interference signal which is detected with the monitor photodiode of the laser diode. Changing the optical path length of the external cavity introduces a phase difference to the interference signal. This phase difference is detected using a signal processing algorithm based on Pearson’s correlation coefficient and cubic spline interpolation techniques. The results show that the average deviation between the measured and actual displacements of the silicon mirror is 3.1 nm in the 0–110 nm displacement range. Moreover, the measured displacements follow linearly the actual displacement of the silicon mirror. Finally, the paper considers the effects produced by the temperature and current stability of the laser diode as well as dispersion effects in the external cavity of the interferometer. These reduce the sensor’s measurement accuracy especially in long-term measurements.

Fast, reliable online estimation and model adaptation is the first step towards high-performance model-based nanopositioning control and monitoring systems. This paper considers the identification of parameters and the estimation of states of a nanopositioner with a variable payload based on the novel moving horizon optimized extended Kalman filter (MHEKF). The MHEKF is experimentally tested and verified with measured data from the capacitive displacement sensor. The payload, attached to the nanopositioner's sample platform, suddenly changes during the experiment triggering the transient motion of the vibration signal. The transient is observed through the load dependent parameters of a single-degree-of-freedom vibration model, such as spring, damping, and actuator gain constants. The platform, before and after the payload change, is driven by the excitation signal applied to the piezoelectric actuator. The information regarding displacement and velocity, together with the system parameters and a modeled force disturbance, is estimated through the algorithm involving the iterative sequential quadratic programming (SQP) optimization procedure defined on a moving horizon window. The MHEKF provided superior performance in comparison with the benchmark method, extended Kalman filter (EKF), in terms of faster convergence.

Two important processes are at the base of light-matter interaction: absorption and scattering. The first part of this work focuses on the interaction of light with single absorbers/emitters embedded in thin films. In the second part, diffusion of light through thin films of scattering materials is numerically investigated. Quantum emitters based on organic fluorescent molecules in thin films are investigated in the first part of this thesis. The focus of this work is on the experimental characterization of a specific system consisting of single DBT molecules embedded in a thin crystalline matrix of anthracene. The system under investigation exhibits some unique optical properties that enable its use in many applications, especially as a single-photon source and as a sensitive nanoprobe. In particular, single DBT molecules are very bright and stable within the anthracene matrix. At cryogenic temperatures, dephasing of the molecular dipole due to interactions with the phonons of the matrix vanishes, and as a result the purely electronic transition or 00-ZPL becomes extremely narrow, approaching the limit set by its natural linewidth. Under pulsed excitation, the system can be operated as a source of indistinguishable, lifetime-limited single photons. Furthermore, the spectral shifts of the narrow ZPL can be exploited as a sensitive probing tool for local effects and fields. In this work we perform a complete optical characterization of the DBT in anthracene system. Using a home-built scanning epifluorescence microscope, we study its optical properties at room temperature: fluorescence saturation intensity, dipole orientation and emission pattern, fluorescence and triplet lifetime are investigated. At temperatures down to 3K, we observe a lifetime-limited absorption line. Also, we demonstrate photon antibunching from this system. We then show that single DBT molecules can be effectively used for sensing applications. Indeed, at the nanometre scale, i.e. on a scale of the order of their physical size, the optical properties of a single molecule are affected by the surrounding environment. In particular, we here demonstrate energy transfer between single DBT molecules and a graphene sheet, a process that can be exploited to measure the distance d between a single molecule and the graphene layer. Based on the universality of the energy transfer process and its sole dependence on d, we provide a proof of principle for a nanoscopic ruler. In the second part of this thesis we look at the interaction of light with matter from a different perspective. By means of numerical simulations, we address the problem of light transport in turbid media, with a particular focus on optically thin systems. The problem is usually modelled by the Radiative Transfer Equation and its simple Diffusive Approximation which holds for the case of a single, thick slab of turbid material but fails dramatically for thin systems. Alternatively, the problem of light transport can be modelled as a random walk process and therefore it can be numerically investigated by means of Monte Carlo algorithms. In this work we develop a Monte Carlo software library for light transport in multilayered scattering samples, introducing several advancements over existing Monte Carlo solutions. We use the software to build a lookup table which allows us to solve the so-called inverse problem of light transport in a thin slab, i.e. the determination of the microscopic properties at the base of light propagation (such as the scattering mean free path ls and the scattering anisotropy g) starting from macroscopic ensemble observables. We then study diffusion of light in thin slabs, with a particular attention on transverse transport. Indeed, even if a diffusive behaviour is usually associated with thick, opaque media, as far as in-plane propagation is concerned, transport is unbounded and will eventually become diffusive provided that sufficiently long times are considered. By means of Monte Carlo simulations, we characterise this almost two-dimensional asymptotic diffusive regime that sets in even for optically thin slabs (OT=1). We show that geometric and boundary conditions, such as the refractive index contrast, play an active role in redefining the very asymptotic value of the diffusion coefficient by directly modifying the statistical distributions underlying light transport in a scattering medium.

This paper presents a new silicon-on-insulator-based MEMS nanopositioner that is designed for high-speed on-chip atomic force microscopy (AFM). The device features four electrostatic actuators in a 2-DOF configuration that allows bidirectional actuation of a central stage along two orthogonal axes with displacements greater than ±10μm. The x- and y-axis resonant modes of the stage are located at 1274Hz and 1286Hz, respectively. Integrated electrothermal sensors are used to control the system in closed loop, with a damping controller and an internal model controller being implemented for each axis. The performance of the closed-loop system is demonstrated by performing a 20μm×20μm contact-mode AFM scan via a Lissajous scan trajectory with a 410Hz sinusoidal reference.

Several micro-scale nanopositioning mechanisms, or MEMS nanopositioners, have been developed for application in nanotechnology and optical sensors. In this paper, the design and modeling of these devices is presented along with initial experimental results. The MEMS nanopositioner is comprised of a parallel bi-lever flexure mechanism and a bent-beam thermal actuator. The flexure mechanism is designed to amplify and guide the motion of the actuator with high precision, while the thermal actuator provides the necessary force and displacement. The relationship between the applied voltage and resulting displacement for this mechanism has been calibrated using a scanning electron microscope and a simple image processing technique. A finite difference thermal model along with a FEA representation of the flexure mechanism and actuator is used to estimate the motion range of the device. Results from this method are compared with experimental calibrations, showing that the model provides a sufficient approach to predict the mechanism’s static performance. Finally, an open-loop controller based on calibration data was used to demonstrate the nanopositioning capabilities of these devices. The motion repeatability was found to be less than +/- 7 nm and step sizes well below 50 nm are possible, indicating suitable performance for many nanopositioning applications.