Development and Evaluation of a Tutorial to Improve Students' Understanding of a Lock-in amplifier

A lock-in amplifier is a versatile instrument frequently used in physics research. However, many students struggle with the basic operating principles of a lock-in amplifier which can lead to a variety of difficulties. To improve students' understanding, we have been developing and evaluating a research-based tutorial which makes use of a computer simulation of a lock-in amplifier. The tutorial is based on a field-tested approach in which students realize their difficulties after predicting the outcome of simulated experiments involving a lock-in amplifier and check their predictions using the simulated lock-in amplifier. Then, the tutorial provides guidance and strives to help students develop a coherent understanding of the basics of a lock-in amplifier. The tutorial development involved interviews with physics faculty members and graduate students and iteration of many versions of the tutorial with professors and graduate students. The student difficulties with lock-in amplifiers and the development and assessment of the research-based tutorial to help students develop a functional understanding of this device are discussed.Comment: Currently under review for Phys Rev ST PER. arXiv admin note: text overlap with arXiv:1601.0128

2D open loop trajectory control of a micro-object in a dielectrophoresis-based device.

International audienceIn the last years, industries have shown a global trend to miniaturize the size of the components to micron in order to reduce the dimension of the final product. At this scale, a micro-object behaves differently from the micro-scale and its behavior is affected by additional physical phenomenon such as the dielectrophoresis. Dielectrophoresis (DEP) is used to separate, manipulate and detect micro particles in several domains with high speed and precision, such as in biological cell or Carbon Nano-Tubes (CNTs) manipulations. This paper focuses on developing a 2D direct dynamic model of the microobject behavior on the base of a 3D dielectrophoretic simulator. This 2D dynamic model is used to establish an open loop control law by a numerical inversion. Exploiting this control law, a high speed trajectory tracking and high precision positioning can be achieved. Several simulated and experimental results are shown to evaluate this control strategy and discuss its performance

Regularized characteristic boundary condition for the Lattice Boltzmann methods at high Reynolds number flows

This paper reports the investigations done to adapt the Characteristic Boundary Conditions (CBC) to the Lattice-Boltzmann formalism for high Reynolds number applications. Three CBC formalisms are implemented and tested in an open source LBM code: the baseline one-dimension inviscid (BL-LODI) approach, its extension including the effects of the transverse terms (CBC-2D) and a local streamline approach in which the problem is reformulated in the incident wave framework (LS-LODI). Then all implementations of the CBC methods are tested for a variety of test cases, ranging from canonical problems (such as 2D plane and spherical waves and 2D vortices) to a 2D NACA profile at high Reynolds number (Re = 100,000), representative of aeronautic applications. The LS-LODI approach provides the best results for pure acoustics waves (plane and spherical waves). However, it is not well suited to the outflow of a convected vortex for which the CBC-2D associated with a relaxation on density and transverse waves provides the best results. As regards numerical stability, a regularized adaptation is necessary to increase the Reynolds number. The so-called regularized FD adaptation, a modified regularized approach where the off-equilibrium part of the stress tensor is computed thanks to a finite difference scheme, is the only tested adaptation that can handle the high Reynolds computation

2D robotic control of a planar dielectrophoresis-based system.

International audienceNanosciences have recently proposed a lot of proofs of concept of innovative nanocomponents and especially nanosensors. Going from the current proofs of concept on this scale to reliable industrial systems requires the emergence of a new generation of manufacturing methods able to move, position and sort micro-nano-components. We propose to develop 'No Weight Robots-NWR' that use non-contact transmission of movement (e.g. dielectrophoresis, magnetophoresis) to manipulate micro-nano-objects which could enable simultaneous high throughput and high precision. This paper focuses on developing a 2D robotic control of the trajectory of a microobject manipulated by a dielectrophoresis system. A 2D dynamic model is used to establish an open loop control law by a numerical inversion. Exploiting this control law, a high speed trajectory tracking (10 Hz) and high precision positioning can be achieved. Several simulated and experimental results are shown to evaluate this control strategy and discuss its performance

Multinuclear solid-state NMR investigation of Hexaniobate and Hexatantalate compounds

This work determines the potential of solid-state NMR techniques to probe proton, alkali, and niobium environments in Lindqvist salts. Na7HNb6O19·15H2O (1), K8Nb6O19·16H2O (2), and Na8Ta6O19·24.5H2O (3) have been studied by solid-state static and magic angle spinning (MAS) NMR at high and ultrahigh magnetic field (16.4 and 19.9 T). 1H MAS NMR was found to be a convenient and straightforward tool to discriminate between protonated and nonprotonated clusters AxH8–xM6O19·nH2O (A = alkali ion; M = Nb, Ta). 93Nb MAS NMR studies at different fields and MAS rotation frequencies have been performed on 1. For the first time, the contributions of NbO5Oμ2H sites were clearly distinguished from those assigned to NbO6 sites in the hexaniobate cluster. The strong broadening of the resonances obtained under MAS was interpreted by combining chemical shift anisotropy (CSA) with quadrupolar effects and by using extensive fitting of the line shapes. In order to obtain the highest accuracy for all NMR parameters (CSA and quadrupolar), 93Nb WURST QCPMG spectra in the static mode were recorded at 16.4 T for sample 1. The 93Nb NMR spectra were interpreted in connection with the XRD data available in the literature (i.e., fractional occupancies of the NbO5Oμ2H sites). 1D 23Na MAS and 2D 23Na 3QMAS NMR studies of 1 revealed several distinct sodium sites. The multiplicity of the sites was again compared to structural details previously obtained by single-crystal X-ray diffraction (XRD) studies. The 23Na MAS NMR study of 3 confirmed the presence of a much larger distribution of sodium sites in accordance with the 10 sodium sites predicted by XRD. Finally, the effect of Nb/Ta substitutions in 1 was also probed by multinuclear MAS NMR (1H, 23Na, and 93Nb)

Residual Doping in Homoepitaxial Zinc Oxide Layers Grown by Metal Organic Vapor Phase Epitaxy

International audienceFull maximum entropy mobility spectrum analysis was carried out on the basis of temperature and magneticfield- dependent Hall measurements to assess the transport properties of homoepitaxial metal organic vapor phase epitaxy zinc oxide layers. Two different conductivity channels were clearly identified and the channel with higher mobility and higher carrier concentration is associated with the epitaxial layer. Hydrogen impurity acting as residual donor and as a passivating species for acceptors is proposed to explain the higher carrier concentration and mobility in the epilayer. In contrast to heteroepitaxial layers, no conduction channel is observed from the substrate to epilayer interface

Electronic and physico-chemical properties of nanmetric boron delta-doped diamond structures

Heavily boron doped diamond epilayers with thicknesses ranging from 40 to less than 2 nm and buried between nominally undoped thicker layers have been grown in two different reactors. Two types of [100]-oriented single crystal diamond substrates were used after being characterized by X-ray white beam topography. The chemical composition and thickness of these so-called deltadoped structures have been studied by secondary ion mass spectrometry, transmission electron microscopy, and spectroscopic ellipsometry. Temperature-dependent Hall effect and four probe resistivity measurements have been performed on mesa-patterned Hall bars. The temperature dependence of the hole sheet carrier density and mobility has been investigated over a broad temperature range (6K<T<450 K). Depending on the sample, metallic or non-metallic behavior was observed. A hopping conduction mechanism with an anomalous hopping exponent was detected in the non-metallic samples. All metallic delta-doped layers exhibited the same mobility value, around 3.660.8 cm2/Vs, independently of the layer thickness and the substrate type. Comparison with previously published data and theoretical calculations showed that scattering by ionized impurities explained only partially this low common value. None of the delta-layers showed any sign of confinement-induced mobility enhancement, even for thicknesses lower than 2 nm.14 page

Recent progress of diamond device toward power application

International audienceThe state of the art of the Institut Néel research activity in the field of diamond power devices will be described and discussed. The active layers of the device are based on boron-doped monocristalline (100) diamond (with doping level varying between 1014 to 1021 cm-3) grown on Ib high temperature high pressure (HPHT) diamond substrate. The progresses done on diamond/metal interface, diamond/dielectric interface, or sharp gradient doping, permit recently the fabrication of original structures and devices, which will be detailed here (Schottky diode, boron doped δ-FET and MOS capacitance)