Search

Since 1995, Magnetic Resonance Elastography (MRE) has been constantly developed as a non-invasive diagnostic tool for quantitative mapping of mechanical properties of biological tissues. Indeed, mechanical properties of tissues vary over five orders of magnitude (the shear stiffness is ranging from 102 Pa for fat to 107 Pa for bones). Additionally, these properties depend on the physiological state which explains the granted benefit of MRE for staging liver fibrosis and its potential in numerous medical and biological domains. In comparison to the other modalities used to perform such measurement, Magnetic Resonance (MR) techniques offer the advantages of acquiring 3D high spatial resolution images at high penetration depth. However, performing MRE tissue characterization requires low frequency shear waves propagating in the tissue. Inducing them is the role of a mechanical actuator specifically designed to operate under Magnetic Resonance Imaging (MRI) specific restrictions in terms of electromagnetic compatibility. Facing these restrictions, many different solutions have been proposed while keeping a common structure: a vibration generator, a coupling device transmitting the vibration and a piston responsible for the mechanical coupling of the actuator with the tissue. The following review details the MRI constraints and how they are shaping the existing actuators. An emphasis is put on piezoelectric solutions as they solve the main issues encountered with other actuator technologies. Finally, flexible electroactive materials are reviewed as they could open great perspectives to build new type of mechanical actuators with better adaptability, greater ease-of-use and more compactness of dedicated actuators for MRE of small soft samples and superficial organs such as skin, muscles or breast.

International audience; Over the last four decades, magnetic resonance imaging has become the gold standard imaging technique in many medical diagnoses for brain, cardiac, and liver disease. However, due to low critical mass and great scientific challenges, instrumentation dedicated to preclinical MRI imaging has lagged behind instrumentation for clinical applications. The aim of this paper is to demonstrate that a set of new technologies such as the 3D Molded Interconnect Devices technology preferably named below as 3D Plastronics, 3D Printing, and Microfluidics may be considered to provide a completely new way for designing preclinical MRI setups, i.e., the 3D prototyping and manufacturing of the MR coil, the sample holder, and the peripherals, all together. The fabricated MRI setup can be used both for MRI of small biological samples and for in vivo imaging of a mouse brain. This work is the first step toward the full 3D manufacturing of tailor-mad multifunctional MRI probes.

Omni-directional inductive wireless power transfer to a movable target inside a half-meter cubic emitter box is studied. The innovative point is to use 3D Molded Interconnect Device (3D-MID) coils at the surface of the target with a 3D shape. Transmission of energy at 6.78 MHz is performed experimentally and characterized in terms of power and efficiency. The 3D design of the coils allows maintaining power when the receiver target is translated and rotated inside the emitter box (that is to say allows compensating to a certain extent the misalignment between the emitters and the receivers). A comparison with a simplified model is performed. Lastly, the potential of this technology is discussed.

The aim of this paper is to describe some possibilities allowed by a micro EDM milling machine, which has been entirely developed in our laboratory. Among other features, this machine does not make use of WEDG for fabricating the microtools. Instead of this, a compact low cost electrochemical reactor allows automated etching of tungsten microtools with a diameter ranging from 1 to 30 μm and very high aspect ratio (50-100). Thus, fragile microtools are obtained and regenerated without any intervention by the operator. Micro EDM milling is performed with such microtools thanks to a specially designed electronics based on a parallel architecture with 3 microcontrollers. The electrical signals of the micro discharges are continuously characterized which allow mapping of micro electrical discharges and contacts. It is demonstrated that the spatial distributions of discharges and contacts give valuable information on the micro EDM milling process. During the machining of microchannels in stainless steel, it is reported that the positions of contacts match with a low number of discharges. So, high tool wear and low part removal rate are related to a high number of contacts. Heterogeneous machining along the vertical Z axis and the horizontal XY axis can be also characterized.

International audience; Omnidirectional inductive wireless charging system of a mobile is studied. Instead of using conventional planar coils printed on circuit boards, 3D Molded Interconnect Device (3D-MID) coils are used. The receiver is a single piece that has 3 elliptic inductors pointing in 3 different directions of the space. A half meter cubic box with 4 planar emitting inductors on 4 sides is used to transmit power at 6.78 MHz to the receiver inside the cube, regardless to the position and orientation of the receiver. Measurement results show that the 3D-MD receiver can get a power of 1.4 W at 7.9% efficiency on most of the positions inside the box. When the receiver is at the central position and also in the corners of the box, there is little variation of the transferred power when the receiver turns 360°, which means that it is almost insensitive to angular misalignment. However, when the receiver moves from the center towards the corners, there is a drop or an increase of power, which means that there is a lack of uniformity of the power which transferred near the corners. Ways to improve this point are discussed. However, our conclusion is that 3D-MID technology is an interesting technology for replacing the planar coils used in conventional WPT receivers.

Omnidirectional inductive wireless charging of a $6\times 6\times 6 cm^3$ 3D receiver cube with 6 planar coils inside a $47\times 47\times 47 cm^3$ box with 4 planar emitting coils is studied. The power delivered to the cube in the central position of the box is in the 1 W - 2.4 W range with 6 - 7% transfer efficiency. In this position, the power is insensitive to the pitch angular orientation. When moving the 3D receiver cube toward the corners of the box, there is no sudden drop of transmitted power. However, the delivered power near the corners increases or decreases in an acceptable range depending on the orientations of the magnetic field of the emitters. Perspectives of this work, when replacing the manufacturing of coils based on PCBs technology by 3D Molded Interconnect Device technology, are briefly discussed.

The aim of this paper is to report on the use of Microcontact Printing (μCP) for the manufacturing of 3D Molded Interconnects Devices. Two different approaches are reported. A first one is based on the total metallization of the polymer, μCP of the 3D pattern followed by the wet etching of the non-protected areas of the part (the so-called indirect process). A second approach is based on the combination of radio-frequency (RF) plasma treatment, μCP of a pattern of catalysts on the polymer and metallization by electroless deposition (the so-called direct process). This second process allows metallization of bare polymer parts (free of catalytic species in the bulk) with conductive 3D networks ready for the assembly of SMD devices. Examples of MID devices made with both approaches are reported. Key points like thickness (up to 12-15 μm), conductivity and adhesion of the metallic network are also reviewed. Printing on slope surfaces is demonstrated. Advantages and drawbacks of both processes are discussed.

International audience; The modelization, fabrication and characterization of inductors using Molded Interconnect Device technology for multidirectional inductive proximity sensing is reported. Inductive proximity sensing allows contactless measurement of the position of electrically conductive objects. The principle of measurement relies on the use of an inductor which impedance is modified by the induced eddy currents at the surface of the conductive object. Inductors on LCP polymer are fabricated with MID technology, electroless metallization and electrodeposition of copper. 2D inductors are fabricated and characterized. Key parameter values are analyzed with a simplified model. Then proof of concept for 3D proximity sensing with a MID device is demonstrated.

International audience

International audience; The aim of this paper is to report on micro EDM milling of stainless steel with ultrathin and high aspect ratio microtools and explore possibilities for machining with small discharges using a ballast resistor. Machining of channels is demonstrated with a 9 µm tungsten microtool with 29 nJ/discharge without damaging the tool. Depending on the value of the ballast resistor Rb, the channel width is about 31-36 µm with aspect ratio of 1.4-1.8. The most significant result is that the relative tool wear ratio is below 0.01% when Rb is greater than 100 Ω. It allows machining at 50 V operating voltage with 1 nF working capacitance without using the stray capacitance of the machine.

This paper reports the low cost, high yield chemical vapor deposition synthesis of a potentially novel carbon nanomaterial using nickel nanocluster-catalysed dissociation of acetylene at 700 °C. The resulting ‘carbon nanopearls’ are 150 nm in diameter with ∼85% monodispersity, with a solid structure composed of both amorphous and nanocrystalline (∼2 nm repeat unit) regions. The nanopearls form 3D space-filling ‘strings’ which give rise to a macroscopic foam-like appearance. The nanopearls have been characterized using scanning electron microscopy, high resolution transmission electron microscopy, X-ray microdiffraction, Raman spectroscopy and energy dispersive X-rays. A mechanism for the formation of the nanopearls is proposed based on concentric layers of ∼4×4 nm graphitic flakes. The small radius of curvature of each nanopearl and the corrugation at the atomic scale of the surface resulting from the unclosed graphitic flakes result in excellent field emission properties. It has been demonstrated that a film of conditioned carbon nanopearls exhibits Fowler–Nordheim field emission behavior, with currents of up to 50 μA readily obtainable under continuous emission in moderate vacuum. It is proposed that such emitters would provide significantly higher yield, uniform emission characteristics than non-oriented films of carbon nanotubes due to the reproducibly high density of nanopearl emitter sites.

Carbon nanotubes exhibit extraordinary field emission properties because of their high electrical conductivity, ideal high aspect ratio whisker-like shape for geometrical field enhancement, and remarkable thermal stability. This paper will describe the PECVD growth of vertically aligned arrays of carbon nanotubes which are suitable for use as the electron emitters in a novel type of microwave amplifier capable of producing of order 10 W at 30 GHz.

Plasma enhanced chemical vapour deposition (PECVD) is a controlled technique for the production of vertically aligned multiwall carbon nanotubes for field emission applications. In this paper, we investigate the electrical properties of individual carbon nanotubes which is important for designing field emission devices. PECVD nanotubes exhibit a room temperature resistance of 1–10 kΩ/μm length (resistivity 10 −6 to 10 −5 Ω m) and have a maximum current carrying capability of 0.2–2 mA (current density 10 7 –10 8 A/cm 2 ). The field emission characteristics show that the field enhancement of the structures is strongly related to the geometry (height/radius) of the structures and maximum emission currents of ∼10 μA were obtained. The failure of nanotubes under field emission is also discussed.

The ability to grow carbon nanotubes/nanofibres (CNs) with a high degree of uniformity is desirable in many applications. In this paper, the structural uniformity of CNs produced by plasma enhanced chemical vapour deposition is evaluated for field emission applications. When single isolated CNs were deposited using this technology, the structures exhibited remarkable uniformity in terms of diameter and height (standard deviations were 4.1 and 6.3% respectively of the average diameter and height). The lithographic conditions to achieve a high yield of single CNs are also discussed. Using the height and diameter uniformity statistics, we show that it is indeed possible to accurately predict the average field enhancement factor and the distribution of enhancement factors of the structures, which was confirmed by electrical emission measurements on individual CNs in an array.

The overall aim of this work is to produce arrays of field emitting microguns, based on carbon nanotubes, which can be utilised in the manufacture of large area field emitting displays, parallel e-beam lithography systems and electron sources for high frequency amplifiers. This paper will describe the work carried out to produce patterned arrays of aligned multiwall carbon nanotubes (MWCNTs) using a dc plasma technique and a Ni catalyst. We will discuss how the density of the carbon nanotube/fibres can be varied by reducing the deposition yield through nickel interaction with a diffusion layer or by direct lithographic patterning of the Ni catalyst to precisely define the position of each nanotube/fibre. Details of the field emission behaviour of the different arrays of MWCNTS will also be presented.

Dans un contexte concurrentiel accru, les industries doivent developper de nouvelles solutions pour repondre a des defis majeurs (innovation, design, fonctionnalite, consommation…). La plastronique, qui est au confluent des domaines de la plasturgie et de l’electronique, permet de repondre a ces nouvelles attentes, en proposant des objets intelligents et connectes. Elle offre la possibilite de concevoir des systemes de forme complexe 3D. Dans ce contexte de rupture technologique, l’innovation est a l’interface du genie electrique, de la mecatronique et de la plasturgie. Elle fait egalement appel a des domaines connexes et indispensables tels que la physique et la chimie. La convergence de ces domaines rend indispensable l’acquisition de nouvelles connaissances et competences transverses dans les metiers de demain. Pour repondre a ces besoins, une formation en plastronique est en emergence a l’Universite de Lyon. Les modalites seront decrites dans cet article. Les competences initiales des apprenants seront elargies pour acquerir les bases theoriques et pratiques de la conception de systemes plastroniques. Cette formation s’appuiera sur des projets concrets en lien direct avec les acteurs varies de la filiere (aeronautique, medical, robotique, etc.). Le prototypage y tiendra une place importante, en permettant de confronter les apprenants a des problematiques industrielles concretes.

Experimental measurements have shown that uniform and stable electron emission is obtained from metallic planar surfaces covered with an ultra-thin wide band-gap semiconductor (UTSC) layer, with a threshold of the applied field in the range of 50 V μm −1 and at 300 K. Numerical simulation analysis of a serial two-step mechanism model has been developed. The theoretical results confirm the main experimental characteristics and showed that a band bending of ≈5 eV is obtained for an UTSC layer thickness in the range of 3–7 nm.

Surface modifications of refractory oxide materials covered with a thin layer of metal were produced by bombarding the metal surface with GeV heavy ions or 20–40 MeV cluster C60+ beams. The goal is to realize nanotips at the surface to get new electron emission devices with low applied voltages. The nanotips were produced on free surfaces of refractory oxides (TiO2, Al2O3) by energetic GeV ions or 20–40 MeV C60 cluster beams. They were characterized by atomic force microscopy and transmission electron microscopy. Protrusions of nanometer sizes (1–20 nm) were observed at the surface. The nanotips result from the damage induced by the high level of electronic energy losses leading to the local amorphization of the oxide that surrounded the particle trajectories. To realize an electron emission device a thin layer of metal (Pt) was deposited onto the refractory oxide surface prior to the ion or cluster bombardment. First experiments on electron emission from such bombarded surfaces were performed. Electron emission was observed above a low threshold field with excellent stability even in vacuum to 10−7 torr. The electron energy spectrum was also measured. All these new results showed very specific characteristics.

Nanotips at the surface of refractory materials were produced by bombarding the surfaces with energetic clusters. The goal is to realize new electron emission devices with low applied voltages. The nanotips were produced on single crystal surfaces of TiO 2 rutile by 20–40 MeV C 60 cluster beams and were investigated by atomic force microscopy. Protrusions of nanometer sizes (10–25 nm) were observed at the surface. These nanotips result from the damage induced by the high level of electronic energy losses (up to 80 keV/nm), leading to the local amorphization of the oxide that surrounded the particle trajectories. First experiments on electron emission from such bombarded surfaces covered with a 5 nm platinum film were performed. Electron emission was observed above a low threshold field with excellent stability even in vacuum to 10 −7 Torr. The electron energy spectrum was also measured and has very specific characteristics.

Nanotips are coherent e-beam field emission sources. In a projection microscope the nanotips are point sources which allow the formation of Fresnel projection images with high resolution (

Nanotips are nanoscale protrusions ending in one atom fabricated in vacuum by 2D surface melting and field gradient. They are field emission sources of electrons and ions, producing self-collimated and strongly coherent beams with high brightness. Using the nanotip as the source in a projection microscope results in the Fresnel projection microscope. It allows imaging at energies less than 300 eV of fragile nanoscale structures which are either amplitude or phase nano-objects. Experimental Fresnel images of magnetic nanoparticles show the potential for mapping very weak magnetic stray fields with the Fresnel projection microscope.

We have measured the field electron emission (FE) from a surface covered with two ultrathin layers of semiconductor, 4 nm GaN on 2 nm Al0.5Ga0.5N. The threshold field was 50 V/μm, with stable FE current densities up to 3×10−2 A/cm2. We have also measured the FE dependence with field and temperature and determine then an effective surface tunneling barrier ⩽0.5 eV, coexisting with an effective thermal activation energy of ∼0.85 eV. To interpret these experimental results, we propose a dual-barrier model, related to the nanostructured layers, with a serial two-step mechanism for the electron emission, taking into account the space charge formation in the quantum well structure at the surface.

In their rocksalt structure, rare-earth monosulfides offer a more stable alternative to alkali metals to attain low or negative electron affinity when deposited on various III-V and II-VI semiconductor surfaces. In this article, we first describe the successful deposition of Lanthanum Monosulfide via pulsed laser deposition on Si and MgO substrates and alumina templates. These thin films have been characterized by X-ray diffraction, atomic force microscopy, high resolution transmission electron microscopy, ellipsometry, Raman spectroscopy, ultraviolet photoelectron spectroscopy and Kelvin probe measurements. For both LaS/Si and LaS/MgO thin films, the effective work function of the submicron thick thin films was determined to be about 1 eV from field emission measurements using the Scanning Anode Field Emission Microscopy technique. The physical reasons for these highly desirable low work function properties were explained using a patchwork field emission model of the emitting surface. In this model, nanocrystals of low work function materials having a orientation perpendicular to the surface and outcropping it are surrounded by a matrix of amorphous materials with higher work function. To date, LaS thin films have been used successfully as cold cathode emitters with measured emitted current densities as high as 50 A/cm2. Finally, we describe the successful growth of LaS thin films on InP substrates and, more recently, the production of LaS nanoballs and nanoclusters using Pulsed Laser Ablation.

The characteristics of e-beams held emitted from nanotips, which are atom-sources of electrons, were analysed experimentally for non-magnetic and ferromagnetic nanotips. Their specific characteristics are fully exploited in a versatile low-energy electron projection microscope: the Fresnel projection microscope. Observations of nanometric fibres of carbon and of organic materials were performed with working voltages around 200 V. The images show, in the direct space, details of the objects of less than 1 nm without any magnetic shielding.

Images of nanometric fibres of carbon and of polymers, with observation voltages around 200 V in a Fresnel projection microscope, show details less than one nanometer without any magnetic shielding. No radiation damages are detectable during the observations of the polymers. The images of the nanometric fibres have to be interpreted as Fresnel diffraction patterns from opaque objects.

Field electron emission behavior of individual multiwalled carbon nanotubes (MWNTs), that are elements of a vertically aligned array grown on a Si wafer, were analyzed with a scanning anode field emission microscope. The electron emission of each MWNT followed the conventional Fowler–Nordheim field emission mechanism after their apexes were freed from the erratic adsorption species using a conditioning process at room temperature. The conditioning process led to stable emission currents and reduced their variations ΔI/I to less than 30% between different MWNTs of the array. This opens the possibility for using MWNTs in an array as independent electron sources for massively parallel microguns.

Full text : http://iopscience.iop.org/0960-1317/21/9/095013/pdf/0960-1317_21_9_095013.pdf; International audience; This paper reports on the integration of thick carbon-polydimethylsiloxane (C-PDMS) electrodes in microfluidic systems for electrokinetic operations. The C-PDMS material, obtained by mixing carbon nanopowder and PDMS, preserves PDMS processing properties such as O2 plasma activation and soft-lithography patternability in thick or 3D electrodes. Conductivity in the order of 10 S m−1 was reached for a carbon concentration of 25 wt%. To evaluate the adhesion between PDMS and C-PDMS, we prepared bi-material strips and carried out a manual pull test. The cohesion and robustness of C-PDMS were also evaluated by applying a large range of electric field conditions from dc to ac (300 kHz). No damage to the electrodes or release of carbon was noticed. The use of such a material for electrokinetic manipulation was validated on polystyrene particles and cells. Here, we demonstrate that C-PDMS seems to be a valuable technological solution for electrokinetic in microfluidic and particularly for biological applications such as cell electrofusion, lysis and trapping, which are favored by uniform lateral electric fields across the microchannel section.

A numerical calculation of the patch-field distribution across nano-patchwork surfaces has been developed. Results show that the low work function nanosize zones are intrinsically protected by an electrostatic screen, which is induced by the surrounding area having higher work function. In presence of an applied field, during field emission, a preferential opening of the surface barrier just over the nano-patches induces a field emission array of parallel e-beams whose geometrical distribution is defined by the positions of the nano-patches.

Zinc oxide (ZnO) nanowires were deposited on a plane conductive surface. They were vertically aligned, with 3 µ and 140 nm respectively for the length and the diameter, and with an array density of 10 nanowires/µm². A field emission study by scanning anode field emission microscopy was performed to evaluate the field emission properties. The effective work function is about 1 eV, the threshold of the macroscopic field F app is about 6 V/µm for a current density J FE equal to 0.05 A/m2, which is a rather low field. For J FE greater than 500 A/m2, the nanowires evolved into a bulbous apex by surface diffusion.

International audience; Micro electrical discharge machining in the milling configuration (µEDM milling) allows machining of complex microparts in a flexible way by controlling the erosion process along the 3D path of a thin cylindrical microtool. This technique is attracting growing interest for the processing of mesoscopic and/or high aspect ratio parts. A bottleneck in the development of this technology is the fabrication of thin diameter tools with large aspect ratios. In this paper, we introduce an innovative µEDM milling machine along with a machine entirely developed in our laboratory used to form microtools by electrochemical fabrication. The fabrication process is performed automatically according to a method derived from the technology originally developed for the fabrication of Scanning Tunnelling Microscope (STM) tips. Examples of fabricated tungsten microtools with 4 to 10 µm diameters over a 300 to 800 µm lengths are presented along with preliminary data about the machining of microfluidic channels in stainless steel and titanium.

This work focuses on improving the crystalline property of the LaS thin films by improving the deposition conditions. Many factors can affect the quality of laser deposited films, including vacuum level, laser energy, laser repetition rate, substrate temperature, target to substrate distance, background gas pressure, and substrate bias., 18th International Vacuum Nanoelectronics Conference, 2005

The field emission properties of LaS nanoprotrusions called nanodomes, formed by pulsed laser deposition on porous anodic alumina films, have been analyzed with scanning anode field emission microscopy. The voltage necessary to produce a given field emission current is∼3.5 times less for nanodomes than for thin films. Assuming the same work function for LaS thin films and nanoprotrusions, that is,∼1 eV, a field enhancement factor of∼5.8 is extracted for the nanodome emitters from Fowler-Nordheim plots of the field emission data. This correlates well with the aspect ratio of the tallest nanodomes observed in atomic force micrograph measurements.

Lanthanum monosulfide (LaS) films were grown by pulsed laser deposition on the (100) magnesium oxide (MgO) substrates at an elevated substrate temperature and in a background gas of H2S. The thin films have been characterized by x-ray diffraction (XRD), atomic force microscopy (AFM), and high resolution transmission electron microscopy. The film surface is composed of grainlike features with an average size of approximately 34nm. The root-mean-square variation of the film surface roughness measured over a 2×2μm2 area by AFM was found to be approximately 1.5nm. XRD data indicate that the average size of the nanocrystalline grains in the film is about 26nm, which is about twice the size of the grains found in LaS thin films deposited at room temperature on Si. The field emission (FE) properties of the films have been characterized by scanning anode field emission microscopy and are interpreted in terms of a recently developed patchwork FE model. The FE data indicate that there is roughly a seven times incre...

A new type of nanoscale field emitter array, consisting of carbon nanonecklaces and nanotentacles, has been produced by a novel multi-level self assembly process employing flexible porous alumina films. The field emission characteristics of the carbon nanostructures were measured using a scanning field emission microscope (SAFEM) and they exhibited strong Fowler-Nordheim emission. This new synthetic approach could find potential applications in flexible and inexpensive arrays of nanoscale cold cathode emitters., Nanomaterials Synthesis, Interfacing, and Integrating in Devices, Circuits, and Systems II, September 9-11, 2007, Boston, Massachusetts, United States, Series: Proceedings of SPIE; no. 6768

A systematic study was done in order to relate the current density $J$-applied field $F$ characteristic variation with three emission mechanisms: thermionic, tunneling, and ballistic. All three are now effective during the field emission from cathodes with work function $\ensuremath{\Phi}$ less than $2\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. The current density is computed using the transmission probability for an electron to cross the barrier between the electron sea of the cathode and the vacuum. The corresponding Schr\"odinger equation is solved by means of the self-consistent Lippmann-Schwinger equation, with values of the effective potential corrected with the image potential between the cathode and the anode, and resolved by spatial discretization. This method allows computing the exact current within a zero emitted current approximation. It fills the gap left by the former analytical and numerical resolutions. The $\mathrm{ln}(J∕{F}^{2})$ vs $(1∕F)$ plot shows, from the very beginning of the electron emission, three zones for the current variation. The first zone, corresponding to low applied electric fields, is a nonlinear variation of the current specific to thermionic-field emission; it is followed by a second zone having a linear variation with a slope proportional to ${\ensuremath{\Phi}}^{3∕2}$ characteristic of the conventional Fowler-Nordheim field emission. The third zone, concerning high field values, indicated a current saturation behavior related to a field-induced ballistic emission.

We report a new multi-modal self assembly technique in which a rich structural diversity of distinct moieties emerge when thin films of a wide variety of materials are deposited on nanoporous substrates using different techniques. We also report multi-level self assembly where one set of self assembled nanostructures seeds the self assembly of another set. The multi-modal self assembly has been observed using flexible alumina templates containing hexagonal arrays of cylindrical pores that are 50 nm wide and 500 nm in length and also on nanoporous Si templates. The latter were formed by anodization of thin film alumina templates deposited on platinum coated silicon substrates. The deposition parameters leading to the observation of each of the moieties will be discussed in detail and the field emission (FE) properties, measured by scanning anode field emission microscopy (SAFEM), will be reported., 20th International Vacuum Nanoelectronics Conference, July 8-12, 2007, Chicago, IL, USA

Several nanoscale arrays of metallic, semiconductor, and organic carbon compounds (carbon nanopearls) have been fabricated on nanoporous flexible alumina and silicon templates based on a new self-assembly growth mode. They were obtained using pulsed laser deposition, thermal evaporation, e-beam evaporation, or RF magnetron sputtering. The different moieties that were observed include nanodomes and nanodots (gold, nickel, cobalt, and aluminum nitride), nanonecklaces (carbon nanopearl), and nanopinetrees (gold) self assembled on flexible alumina templates. A nanoneedle array was also self assembled by e-beam evaporation of nickel on silicon substrates that were rendered nanoporous by the use of a porous alumina mask. The physical processes underpinning the new self assembly growth mode have been studied based on extensive characterization of the templates prior to and after deposition of the various metallic, semiconductor, and organic compounds. These include atomic force microscopy (AFM), X-ray diffraction (XRD) analysis, Raman spectroscopy and field emission-scanning electron microscopy (FE-SEM). Some of the arrays have been tested as potential candidates for new cold cathode arrays for vacuum electronic applications using the scanning electron field emission microscopy (SAFEM) technique., 7th IEEE Conference on Nanotechnology, IEEE-NANO 2007, August 2-5, 2007, Hong Kong, Series: Proceedings of the ... IEEE Conference on Nanotechnology; no. 154

In this work, to better understand the field emission behaviour from patchwork cathodes, the FE current is calculated, the transmission probability for an electron to cross the barrier between the electron sea of the patchwork cathode and the vacuum is obtained by solving the Schrodinger equation in its integral Lippmann-Schwinger form by means of a Green's function technique. The main point in this numerical approach is the taking into consideration, for the determination of the surface barrier, of the patch-field which is generated by a difference of order 2 eV across nanometric dimension boundaries between the low patch areas and the high surrounding surface. Quantitative relations of the field emission characteristics will be presented and discussed in function of patch geometries and values. In particular, we will highlight the features of the patchwork cathode that can be obtained from experimental field emission current measurements.

Publisher Summary A planar cathode is a thin-film emitter deposited on a conducting surface. It emits electrons when an electric field is applied by an anode separated from the film front surface by a vacuum gap. This chapter discusses thin film and ultra-thin film planar cathodes with effective low work function. It focuses on basic principles underlying the electron emission to avoid the misinterpretation of experimental results. The chapter describes the two basic mechanisms for extracting electrons from solids to determine the precise limits of the present theoretical approaches—both by analytical and numerical simulations. In the chapter, scanning anode field emission microscopy (SAFEM) is described and experimental results with flat cathodes are presented in a later section with their field emission characteristic analyzed by SAFEM. Spindt field emission arrays (FEAs), which are the heart of field emission displays (FEDs), are basically microfabricated molybdenum tips in gated configuration that use the local field enhancement at the apex of each microtip in front of a gate located at a microscale distance to lower the threshold voltage (100 V), thus enabling field emission.

Three distinct types of nanostructures—nanodomes, nanodots, and nanowires—have been simultaneously self-assembled by pulsed laser deposition of lanthanum monosulfide on anodic alumina films containing hexagonal arrays of pores about 50nm wide and 500nm deep. The nanostructures have been characterized by x-ray diffraction, atomic force microscopy (AFM), and field emission scanning electron microscopy (FE-SEM). Nanodomes preferentially grow on the boundary separating regions (grains) of the alumina template that have near perfect pore ordering, and their density is ∼109∕cm2. The diameter of a nanodome at the base is about 100nm and their aspect ratio (height/diameter at the base) is between 1 and 3. Additionally, nanodots nucleate on top of the alumina walls that separate adjacent pores. They have a diameter of ∼50nm, a density equal to the pore density (1010∕cm2), and an aspect ratio less than 1. Finally, cross sectional FE-SEM images of the templates indicate that LaS nanowires grow inside the pores with ...

Free carbon nanopearl layer cathodes have already proved to be good emitters under poor vacuum conditions. In order to improve the cathode reliability and the cost of fabrication, a new design of nanopearl field emitter has been developed wherein the nanopearls are suspended and protected in a polymer matrix. A polymer embedded carbon nanopearl field emitter of this design has been developed and operated as the ionization source in a commercial time of flight mass spectrometer (TOF-MS) system. Systematic analyses of the effect of acetophenone and 2-nitrotoluene (at pressures of ∼10−5 Torr) on cold cathode behavior inside the TOF-MS have been carried out and results from these studies show that electron emission is not adversely affected.

In this work and with a view to optimizing their FE properties, LaS films of increased crystallinity were obtained by PLD on lattice matched MgO substrates, at elevated substrate temperatures and in a background gas of H2S. The thin films have been characterized by high resolution transmission electron microscopy, atomic force microscopy (AFM), X-ray diffraction, ellipsometry and Raman spectroscopy. The FE properties of the films have been characterized by scanning anode field emission microscopy., 20th International Vacuum Nanoelectronics Conference

Nous presentons dans ce papier un projet de formation innovant relatif au prototypage de circuits et systemes electronique 2D et 3D. Les apprenants seront inities aux technologies de ruptures que sont la plastronique et les circuits imprimes 3D sur support rigide (Molded Interconnect Device ou Dispositifs Interconnectes Moules). Ces dernieres necessitent d’acquerir des competences aussi bien dans le domaine de la plasturgie que dans celui de l’electronique. Alors que la technologie et l’innovation se situent aux interfaces de ces domaines, il est aujourd’hui imperatif de casser les modes de conceptions (usuellement en silo) et de repenser la fiche de route (roadmap). Seule une avancee conjointe permettra d’apporter et d’engranger un savoir-faire innovant pour converger vers des solutions pertinentes et une implementation optimale. Nous souhaitons aller vers la creation d’une plateforme dediee. Cette derniere mutualisera des moyens techniques et humains et affichera une bonne visibilite. Le tissu industriel de la region Rhone-Alpes issue d’une longue histoire est a ce titre, particulierement propice a l’emergence de cette action. Aujourd’hui, un groupe de travail associe des acteurs industriels et academiques avec pour objectif de mettre en place cette formation multi-physiques et multi-domaines alliant electronique, plasturgie, mecatronique…

The microgun is a combination of a nanotip and a microlens which is composed of two planar micron-size bore electrodes and a coplanar four-pole deflector microfabricated on the same Si chip. The focusing and deflection characteristics of the microgun, working as an immersion lens at 100 V, have been studied both experimentally and by numerical simulations. Results show unique electron optics properties due mainly to the coherence of the electron beam emitted from the nanotip and to the noninteraction of the incident electrons with the different microelectrodes. The focus spot can reach nanometric dimensions with minimum aberrations and a deflection amplitude of ∼2.5 mrad/V.

The magnetic leakage fields from the poles of magnetic nanoparticles down to 105–106 spins, isolated or situated at the edges of clusters, are observed with Fresnel projection microscopy by the presence of interference fringes generated by the magnetic phase shifts in the imaging electron beam. The particle shapes and localization of fringes are imaged simultaneously with nanometer spatial resolution at ∼200 V.

Layers of non-directional carbon nanotubes (CNTs) are currently used as field emission (FE) cathodes. The main advantage for such cathodes is the low cost fabrication process using conventional film deposition techniques such as screen-printing or imprint. This advantage is unfortunately counter-balanced by the non-uniformity and low density of the field emission sites, a consequence of its mat-like deposition and the tubular geometry of the CNTs. Recently, by a chemical vapour deposition (CVD) technique, strings of nanoballs of carbon are obtained which are called carbon nanopearls. Due to its string-like structure of nanospheres, the deposited layers of the carbon nanopearls naturally present a higher density of field emission sites. As the nanopearls surface is constituted of graphene, as the carbon nanotubes apex, these field emission sites exhibit the same quality for current stability as observed with the carbon nanotubes. It has been demonstrated that a film of conditioned carbon nanopearls exhibits Fowler-Nordheim field emission behaviour, with currents of up to 50 muA readily obtainable under continuous emission in moderate vacuum. Compared to other graphitic nanostructures, in particular the tubular geometry of CNTs, the nanopearls have the advantage of presenting statistically a high density of apex areas with a small radius of curvature (~75 nm) when deposited on a planar surface. Moreover, these spheres are composed of graphitic flakes that are unclosed at the surface and therefore believed to exhibit many dangling bonds with the potential to enhance the field emission current. These two properties give the nanopearls excellent prospects as a cathode material. To investigate the field emission properties, the nanopearls were directly grown on the end of a metallic wire. The field emission was performed in a conventional field emission microscope environment, with the cathode located a few mm away from a flat screen. Systematic analysis of the field emission properties and behaviour of carbon nanopearls based cathodes were done, in particular the energy distribution measurements under different conditions. A comparative analysis with carbon nanotubes will point out the specific quality related to the nanopearl structure

Thin films of lanthanum monosulfide (LaS) have been successfully deposited on Si and InP substrates by pulsed laser deposition. The values of deposition parameters (chamber pressure, substrate temperature, substrate-to-target separation, laser energy, repetition rate and spot size on the target) leading to a successful growth of cubic rocksalt structure films are identified. For the films grown on Si substrates, the root-mean-square (RMS) variation of surface roughness is found to be 1.74 nm by atomic force microscopy. XRD scans suggest the presence of amorphous regions in the film. This is confirmed by cross-section transmission electron microscopy analysis. For films grown on InP substrates, a thin crystalline film about 500 nm thick followed by an abrupt transition to an amorphous layer about 120 nm thick is observed. The work function of the LaS thin films deposited on Si substrates deduced from Fowler-Nordheim plots at room temperature has a mean value of 0.65 eV, when measured using the scanning field emission microscope technique (SAFEM) at very different locations across the sample. A strong dependence of the field emission current with temperature is also observed. At very large external electric field, the field emission increases dramatically and is no longer of the Fowler-Nordheim type., 18th International Vacuum Nanoelectronics Conference, 2005

Successful growth of lanthanum monosulfide (LaS) nanodot and nanowire arrays has been performed by pulsed laser deposition (PLD) using self-assembled nanoporous alumina templates containing pores about 50 nm wide and 200-300 nm deep. The arrays were characterized by X-ray diffraction, atomic force microscopy (AFM), field emission scanning electron microscopy (FE-SEM) and scanning anode field emission microscopy (SAFEM). The array of LaS nanodots grows selectively at boundaries between different regions of the alumina film with local hexagonal symmetry of pores. The density of these dots is about 109 /cm2. Cross sectional FE-SEM showed that LaS nanowires also grow inside the pores with a density of 1010/cm2 , which is equal to the pore density of the templates. The field emission properties of the LaS nanodots grown on top of the alumina templates were measured using SAFEM. A typical current-voltage characteristic is shown. Using the conventional Fowler-Nordheim relation, the work function of the LaS nanodots has been extracted from the slope of the plot ln(J/F2) vs 1/F, where J is the field emission current density and F is the local applied field. This leads to an outstanding, reproducible effective work function value of ~1 eV for the LaS nanodots. The threshold for an emission current density of 1 mA/cm2 occurs around a 150 V/mum which is considerably lower than the 230 V/mum threshold value reported recently for LaS thin films., 19th International Vacuum Nanoelectronics Conference and 50th International Field Emission Symposium, 2006