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Reducing the emission of secondary electrons from anode materials is critical to improved efficiency and increased performance in high power vacuum electronics for defense systems. The focus of this proposed effort is to leverage advances in materials technology, specifically thin films, to reduce secondary electron generation and outgassing from anode surfaces. By using advanced thin film deposition techniques, hybrid materials can be developed that provide the thermal and electrical conductivity required for operation, while reducing secondary electrons and desorption of gas species from the anode surface. Proposed solutions to these issues need to be robust, yet cost effective and applicable through available manufacturing processes. In this paper, we will introduce an improved mathematical expression for the secondary emission yield as a function of the impact voltage which is an extension of the formula first introduced by Vaughan [1]. Our expression gives a better fit to some of our experimental data of secondary emission yield versus impact voltage for polycrystalline Copper for which the maximum secondary emission yield is only slightly larger than unity.

When (on average) an electron is field emitted from above the Fermi level there is a cooling effect, called Henderson-cooling; when (on average) it is emitted from below the Fermi level then Nottingham-heating occurs. This work compares our earlier used simple estimation to predict this emitted electron energy difference (average energy of emitted electron minus the Fermi level in the cathode) during field emission (FE) from a carbon nanotube [1,2] with a more numerically intensive formula that better captures the effects of Henderson-cooling and Nottingham-heating and the transition between the two regimes [3-5].

Recently, we presented a multiscale model of field emission (FE) from carbon nanotube fibers (CBFs) taking into account Joule heating within the fiber and radiative cooling and the Nottingham effect at the tip of the individual carbon nanotubes in the array located at the fiber tip [1]. The model was used to predicts the fraction of carbon nanotubes (CNTs) being destroyed as a function of the applied external electric field and reproduces many experimental features observed in some recently investigated carbon nanotube fibers such as, order of magnitude of the emission current (mA range), low turn on electric field (fraction of V/μm), deviation from pure Fowler-Nordheim behavior at large applied electric field, hysteresis of the FE characteristics, and a spatial variation of the temperature along the CNF axis with a maximum close to its tip of a few hundred °C. In this work, we report the simulations of the field emission properties from small arrays of carbon nanotube fibers in the presence of shielding effects. The latter are modeled using the line charge model recently developed by Harris et al. [2-5]. The average total emission current and its variance for linear arrays composed of seven carbon nanotube fibers are calculated to show their sensitivity to the morphology of the apex of the individual fibers which are modeled as random arrays of CNTs. In practice, the FE properties of the latter can be strongly dependent of the cutting technique used to form the fiber apexes.

In 2012 TechnipFMC, Cervval and Bureau Veritas initiated a common development program to offer a new tool for the design of offshore structures interacting with ice combining a variety of models and approaches. This numerical tool called Ice-MAS (www.ice-mas.com) is using a multi-agent technology and has the possibility to combine in a common framework multiple phenomena from various natures and heterogeneous scales (i.e. drag, friction, ice-sheet bending failure, local crushing and rubble stack up). It can simulate the ice loadings of a drifting ice-sheet (including ridge or not) on predefined structures such as conical, cylindrical, sloping & vertical wall, artificial islands or more complex geometry by user input file like semi-submersible floaters with pontoon and columns allowing to obtain the detailed results on the different parts of the structure. This paper presents the overall functionalities of Ice-MAS and the different possibilities to model a semi-submersible floater. It will focus on the results obtained for different geometries subject to ice sheet loading through different incidence angles. The issues related to the anchoring of the platform are addressed in a simplified way.

In 2012 TechnipFMC, Cervval and Bureau Veritas initiated a common development program to offer a new tool for the design of offshore structures interacting with ice combining a variety of models and approaches. This numerical tool called Ice-MAS (www.ice-mas.com) is using a multi-agent technology and has the possibility to combine in a common framework multiple phenomena from various natures and heterogeneous scales (i.e. drag, friction, ice-sheet bending failure, local crushing and rubble stack up). The current development phase consists of the determination of the forces generated by an iceberg during an impact on an offshore structure. This paper will provide an overview of the latest Ice-MAS development. It will introduce the main functionalities of the simulation tool and the different options for modelling an offshore structure. It will then focus on the modelling approach used for an iceberg, the calculation of the different hydrodynamic coefficients and their variability according to the separation distance from the structure. The model used to compute the impact load will be detailed, including the local crushing behavior which is simulated by a pressure-area correlation.

Multifunctional smart composites (MSCs) are materials that combine the good electrical and thermal conductivity, high tensile and shear strength, good impact toughness, and high stiffness properties of metals; the light weight and corrosion resistance properties of composites; and the sensing or actuation properties of smart materials. The basic concept for MSCs was first conceived by Daniel Inman and others about 25 years ago. Current laminated carbon and glass fiber polymeric composite materials have high tensile strength and are light in weight, but they still lack good electrical and thermal conductivity, and they are sensitive to delamination. Carbon nanotube yarn and sheets are lightweight, electrically and thermally conductive materials that can be integrated into laminated composite materials to form MSCs. This paper describes the manufacturing of high quality carbon nanotube yarn and sheet used to form MSCs, and integrating the nanotube yarn and sheet into composites at low volume fractions. Various up and coming technical applications of MSCs are discussed including composite toughening for impact and delamination resistance; structural health monitoring; and structural power conduction. The global carbon nanotube overall market size is estimated to grow from $2 Billion in 2015 to $5 Billion by 2020 at a CAGR of 20%. Nanotube yarn and sheet products are predicted to be used in aircraft, wind machines, automobiles, electric machines, textiles, acoustic attenuators, light absorption, electrical wire, sporting equipment, tires, athletic apparel, thermoelectric devices, biomedical devices, lightweight transformers, and electromagnets. In the future, due to the high maximum current density of nanotube conductors, nanotube electromagnetic devices may also become competitive with traditional smart materials in terms of power density.

A multiscale array model has recently been presented to describe field electron emission (FE) from carbon nanotubes (CNTs) on the apex of a carbon nanofiber (CNF) fabricated as a CNT aggregate. The model considered Joule heating, radiative cooling and Henderson/Nottingham cooling/heating, assumed CNT destruction at a specified tip temperature, and predicted the CNT fraction destroyed as a function of macroscopic field, and related current-voltage characteristics. The model reproduces features observed in recent experiments on FE from CNFs, including the emission current order-of-magnitude (mA range), the low turn-on field (fraction of V/μm), deviation at high field from the pure Fowler-Nordheim behavior expected for an undamaged CNT array, loops in current-voltage characteristics, and spatial variation of temperature along the CNF. Here, this array model is used to explore how some details of the CNT arrangement at the fiber apex (especially statistical variations in CNT geometry) might affect overall emission characteristics.

Publisher’s Note: This paper, originally published on 2/22/17, was replaced with a corrected/revised version on 5/16/17. If you downloaded the original PDF but are unable to access the revision, please contact SPIE Digital Library Customer Service for assistance. Metal anodes in high power source (HPS) devices erode during operation due to hydrogen outgassing and plasma formation; both of which are thermally driven phenomena generated by the electron beam impacting the anode’s surface. This limits the lowest achievable pressure in an HPS device, which reduces its efficiency. Laser surface melting the 304 stainless steel anodes by a continuous wave fiber laser showed a reduction in hydrogen outgassing by a factor of ~4 under 50 keV electron bombardment, compared to that from untreated stainless steel. This is attributed to an increase in the grain size (from 40 - 3516 μm2), which effectively reduces the number of characterized grain boundaries that serve as hydrogen trapping sites, making such laser treated metals excellent candidates for use in vacuum electronics.

The observation of a 0.5 conductance plateau in asymmetrically biased quantum point contacts with in-plane side gates has been attributed to the onset of spin-polarized current through these structures. For InAs quantum point contacts with the same width but longer channel length, there is roughly a fourfold increase in the range of common sweep voltage applied to the side gates over which the 0.5 conductance plateau is observed when the QPC aspect ratio (ratio of length over width of the narrow portion of the structure) is increased by a factor 3. Non-equilibrium Green s function simulations indicate that the increase in the size of the 0.5 conductance plateau is due to an increased importance, over a larger range of common sweep voltage, of the effects of electron-electron interactions in QPC devices with larger aspect ratio. The use of asymmetrically biased QPCs with in-plane side gates and large aspect ratio could therefore pave the way to build robust spin injectors and detectors for the successful implementation of spin field effect transistors, 30 pages, 9 figures

With its low work function and high mechanical strength, the LaB

The analytic Wigner function for a single well with infinite walls is extended to the configuration where half of the well is raised and the weighting of the wave functions is in accordance with a thermal Fermi-Dirac distribution. This requires a method for determining the energy eigenstates particularly near the height of the higher half-well. The methods provide a means for constructing analytic and accurate trajectories that can be used to model tunneling times. The fidelity of the trajectory model is assessed with respect to absorption of quanta related to changes within the allowable eigenstates.

The evolution of the 0.5Go (Go = 2e2/h) conductance plateau and the accompanying hysteresis loop in a series of asymmetrically biased InAs based quantum point contacts (QPCs) in the presence of lateral spin-orbit coupling (LSOC) is studied using a number of QPCs with varying lithographic channel width but fixed channel length. It is found that the size of the hysteresis loops is larger for QPCs of smaller aspect ratio (QPC channel width/length) and gradually disappears as their aspect ratio increases. The physical mechanisms responsible for a decrease in size of the hysteresis loops for QPCs with increasing aspect ratio are: (1) multimode transport in QPCs with larger channel width leading to spin-flip scattering events due to both remote impurities in the doping layer of the heterostructure and surface roughness and impurity (dangling bond) scattering on the sidewalls of the narrow portion of the QPC, and (2) an increase in carrier density resulting in a screening of the electron-electron interactions in the QPC channel. Both effects lead to a progressive disappearance of the net spin polarization in the QPC channel and an accompanying reduction in the size of the hysteresis loops as the lithographic width of the QPC channel increases.

The solution to the time-dependent Pauli–Schrodinger equation is written using quaternion algebra, i.e. by expressing the unitary operator describing the time evolution of the Pauli spinor and the Pauli spinor itself as left-chirality quaternions. The quaternion approach is used to express the time evolution of a qubit on the Bloch sphere under the action of the commonly used quantum gates and to implement the two-qubit controlled-NOT (CNOT) gate and the three-qubit Tofolli gate. The quaternion formalism is also applied to describe: (1) a general two-qubit quaternionic gate, (2) the Larmor precession of an electron spin in an uniform magnetic field, and (3) the issue of measurements in quantum mechanics. Finally, the time-dependent Pauli–Schrodinger equation is also solved using right-chirality quaternions.

The Wigner function is assembled from analytic wave functions for a one-dimensional closed system (well with infinite barriers). A sudden change in the boundary potentials allows for the investigation of time-dependent effects in an analytically solvable model. A trajectory model is developed to account for tunneling when the barrier is finite. The behavior of the density (the zeroth moment of the Wigner function) after an abrupt change in potential shows net accumulation and depletion over time for a weighting of energy levels characteristic of the supply function in field emission. However, for a closed system, the methods have application to investigations of tunneling and transmission associated with field and photoemission at short time scales.

Field emission (FE) measurements are reported from carbon nanotube (CNT) fibers and laser-patterned free standing films fabricated by direct online condensation from a floating catalyst chemical vapor deposition reactor. Fiber and film cathodes showed stable emission in the 1–2 mA current (I) range at maximum cathode temperatures less than 1000 °C; film cathodes show localized heating at the triangular tips and higher maximum temperatures than the fibers. Fowler-Nordheim (FN) analysis indicated a change in the morphology of the emitters with increasing external electrical field (Eext). Fiber cathode I-Eext data are interpreted as FN emission from the fiber tip which is eventually limited by space-charge effects. At higher Eext, FN emission from the fiber sidewall occurs. The single fiber cathode stopped emitting abruptly when field induced self-heating effects became significant. For CNT films, self-heating effects can destroy a portion of the film, but FE can still occur from other areas.

Thin films of transition-metal carbides ZrC, HfC, and TiC were deposited by pulsed-laser deposition under vacuum. The surface chemistry of the films was characterized with ultraviolet photoelectron spectroscopy, X-ray photoelectron spectroscopy, and Auger electron spectroscopy in situ. X-ray diffraction was used to characterize the film structure. TiC was shown to be nearly stoichiometric and polycrystalline. The TiC was applied to a vertically aligned carbon nanotube sample and characterized by field emission. Field-emission results showed enhanced current and current density at a film thickness, 5 nm, not previously reported in the literature. Emission from TiC films was also shown to be less affected by adsorbates during field emission. Pulsed-laser deposition of TiC offers a distinct advantage over other techniques in that high-quality films can be obtained under ultrahigh vacuum conditions without the use of a reactive background gas or excessively high annealing temperatures. The application of TiC by pulsed-laser deposition as a cathode coating shows potential for integration into a fabrication process.

Exploitation of the Arctic's resources requires the mastery of the risks caused by extreme ice conditions. The design of offshore structures subjected to extreme ice conditions is a challenge for engineers since there are very few advanced design tools available on the market, especially those able to cope with the large variety of ice interaction and failure mechanisms. Different approaches have been used to model and study ice behavior. Among them are analytical, numerical and empirical approaches with different models being considered. Each model has its own advantages and drawbacks and is only generally dedicated to certain circumstances. In 2012 Technip, Cervval and Bureau Veritas initiated a common development program to offer a new tool for the design of offshore structures interacting with ice (Septseault, 2014, 2015) combining a variety of approaches and models. After three years, the first version of the Ice-MAS software (www.ice-mas.com) is now available. It simulates the ice loadings on a structure and the dynamic behavior of the drifting ice-sheet and floes around. Thanks to multi-agent technology, it is possible to combine in a common framework multiple phenomena from various natures and heterogeneous scales (drag, friction, ice-sheet bending failure, local crushing, rubble stack up) (Le Yaouanq, 2015). This work has been the subject of numerous validations, particularly by comparison with ice basin and in-situ results (Dudal, 2015). The Ice-MAS development program continues in 2016 with the addition of a capability to model the interaction of icebergs with offshore structures. This paper will introduce the co-simulation architecture proposed to simulate the complex interaction between an iceberg and a platform structure. It will focus on the hydrodynamic behavior of the platform and the iceberg including its stability. It will also consider the interaction between both bodies; including the non-linearity of the mooring system (in the case of a floating platform) and the local fracture mechanisms of the iceberg. The objective is to propose a new more accurate design method that will improve the overall ice management system for a project.

Recently, we presented a multiscale model of field electron emission (FE) from carbon nanotube fibers (CNFs), taking into account Joule heating within the fiber, radiative cooling from its surface and Henderson/Nottingham-type cooling and heating effects at the tips of the individual carbon nanotubes (CNTs) located on the fiber apex [1]. The model was used to predict the CNT fraction destroyed as a function of the applied external electric field. The model reproduces many experimental features observed in recent investigations of CNFs, including the emission current order-of-magnitude (mA range), the low turn-on macroscopic field (fraction of V/μm), deviation from pure Fowler-Nordheim behavior at large applied electric field, irreversibility loops in the FE characteristics, and a spatial variation of the temperature along the CNF axis, with a maximum a few hundred oC close to its apex. In this paper, this model is used to investigate how electrostatic screening and details of the CNT array at the fiber apex might affect the overall emission characteristics.

Building on recent efforts [1-4] to characterize carbon nanotube fibers (CNFs) and electron emission [5,6] suitable for compact, high power, high frequency, vacuum electronic devices, this paper describes a proposed exhaustive approach towards optimizing CNF field emission (FE) properties. It outlines how a platform geared towards meaningful comparisons between different CNF-based emitters can be developed. The platform envisages an iterative procedure involving (a) the growth, processing, and functionalization of CNFs, (b) full investigation of the CNF material properties before and after FE diagnosis, and (c) multi-scale modeling of FE properties, including self-heating, shielding effects and beam characteristics in the CNFs and in the emitting carbon nanotubes (CNTs) at the fiber apexes. The modeling would be applicable to a wide variety of CNFs and wire-like sources, and would provide essential feedback to the growth, processing, and functionalization of CNFs, in order to optimize their FE properties (especially long-term stability, low noise, and maximum emission current, current density and brightness.

Floating Liquefied Natural Gas (FLNG) units, which have been under development for decades, are now a reality with Technip delivering the first two major projects in open seas. Both these projects incorporate side-by-side offloading of LNG from the FLNG to the LNGC (LNG Carrier) using loading arm technology. This technology will not be applicable in severe environments. Several tandem LNG offloading systems are proposed by the industry providing greater separation distance between the vessels and higher environmental thresholds. The drawbacks with such systems are the use of a dedicated LNGC fleet with a specific bow loading system or the deployment of long-length floating LNG flexibles (~300 m) to the midship manifold of conventional LNGCs.Recently, Technip has worked with HiLoad LNG to develop a smart LNG offloading system based on already proven and qualified technologies to be operated with conventional LNGCs (without modification). It allows a vessel separation greater than 100 m, high environmental conditions and a minimum length of LNG transfer lines. The system uses the HiLoad LNG DP (dynamically positioned) vessel for the position keeping of the LNGC parallel to the FLNG and Technip's cryogenic flexible pipes for the transfer of LNG and vapor. The system is suitable for either spread- or turret-moored FLNGs.The full-mission bridge at MARIN's Nautical Centre in The Netherlands has been used to simulate normal and emergency operations of the Parallel Loading System by use of a DP System developed by Kongsberg Maritime for this application. Real-time navigation simulations have been conducted with contributions from LNGC and HiLoad captains who have field experience from earlier HiLoad operations in Brazil and the North Sea. These simulations were performed to assess the DP station keeping capabilities and the marine operational procedures under steady and dynamic/changing environmental conditions. Blackout scenarios have also been investigated as part of the simulation work.The simulations have confirmed the ability of the HiLoad DP system to keep the LNGC inside a tight operating ‘green’ envelope during all investigated challenging metocean conditions and that the operation can be safely performed. The HiLoad LNG Parallel Loading System is a smart solution enabling a safe and robust LNG offloading method with use of conventional LNGCs.

A non-equilibrium Green's function formalism is used to study in detail the ballistic conductance of asymmetrically biased side-gated quantum point contacts (QPCs) in the presence of lateral spin-orbit coupling and electron-electron interaction for a wide range of QPC dimensions and gate bias voltage. Various conductance anomalies are predicted below the first quantized conductance plateau (G0=2e2/h) which occur due to spontaneous spin polarization in the narrowest portion of the QPC. The number of observed conductance anomalies increases with increasing aspect ratio (length/width) of the QPC constriction. These anomalies are fingerprints of spin textures in the narrow portion of the QPC., 26 pages, 8 figures

An effective spin concept is introduced to examine the mathematical and physical analogy between phase coherent charge transport in mesoscopic systems and quantum operations on spin based qubits. When coupled with the Bloch sphere concept, this isomorphism allows formulation of transport problems in a language more familiar to researchers in the field of spintronics and quantum computing. We exemplify the synergy between charge tunneling and spin qubit unitary operations by recasting well-known problems of tunneling through a delta scatterer, a resonant tunneling structure, a superlattice structure, and arrays of elastic scatterers, in terms of specific unitary operations (rotations) of a spinor on the Bloch sphere.

Reducing the emission of secondary electrons from materials is critical to improved efficiency and increased performance in high power vacuum electronics. A new mathematical expression for the secondary emission yield (SEY) as a function of the impact voltage up to a maximum of 5 kilovolts is proposed which is an extension of a formula first suggested by Vaughan. The new analytical fit and Vaughan’s fit are compared with SEY experimental data reported by others and measured by our group. The new analytical expression gives good fits to SEY experimental data in all cases, even when the SEY maximum is either slightly larger or below unity, two situations for which Vaughan’s fit is either inadequate or inapplicable.

We have measured the longitudinal (T1) and transverse (T2) spin relaxation times in the organic semiconductor tris(8-hydroxyquinolinolato aluminum)—also known as Alq3—at different temperatures. These measurements shed some light on the spin relaxation mechanisms in the organic. The two most likely mechanisms affecting T1 are hyperfine interactions between carrier and nuclear spins, and the Elliott-Yafet mode. On the other hand, the dominant mechanism affecting T2 of delocalized electrons in Alq3 remains uncertain, but for localized electrons (bound to defect or impurity sites), the dominant mechanism is most likely spin-phonon coupling.

The controlled creation, manipulation and detection of spin-polarized currents by purely electrical means remains a central challenge of spintronics. Efforts to meet this challenge by exploiting the coupling of the electron orbital motion to its spin, in particular Rashba spin-orbit coupling, have so far been unsuccessful. Recently, it has been shown theoretically that the confining potential of a small current-carrying wire with high intrinsic spin-orbit coupling leads to the accumulation of opposite spins at opposite edges of the wire, though not to a spin-polarized current. Here, we present experimental evidence that a quantum point contact -- a short wire -- made from a semiconductor with high intrinsic spin-orbit coupling can generate a completely spin-polarized current when its lateral confinement is made highly asymmetric. By avoiding the use of ferromagnetic contacts or external magnetic fields, such quantum point contacts may make feasible the development of a variety of semiconductor spintronic devices.

In Part I of this article, we introduced the notion of encoding binary bit information in the spin polarization of a single electron confined in a quantum dot and placed in a magnetic field. The spin polarization becomes bistable in a magnetic field and the spin can point either parallel to the field or antiparallel to it. These two polarizations encode the classical binary bits 0 and 1. We showed that since the bits can be switched by simply flipping the electron's spin without physically moving the electron in space and causing a current, the energy dissipated during the bit flip operation could be made very small. In Part II we discuss the notion of using a single electron's spin as a quantum bit (or qubit) that represents information in quantum computers. Just as spin is superior to charge as a vehicle to host classical bit information in classical computers it turns out that spin is superior to charge to host quantum information as well. That is why spin-based quantum information processing is gradually becoming the staple of scalable solid state versions of quantum computers.

We propose a new dual gate spin field effect transistor (SpinFET) consisting of a quasi one-dimensional semiconductor channel sandwiched between two half-metallic contacts. The gate voltage aligns and de-aligns the incident electron energy with Ramsauer resonance levels in the channel, thereby modulating the source-to-drain conductance. The device can be switched from ON to OFF with a few mV change in the gate voltage, resulting in exceedingly low dynamic power dissipation during switching. The conductance ON/OFF ratio stays fairly large ( ∼ 60 ) up to a temperature of 10 K. This conductance ratio is comparable to that achievable with carbon nanotube transistors.

Almost all spintronic transistors (e.g., spin field-effect transistors, spin bipolar transistors, and spin-enhanced MOSFETs) require high efficiency of spin injection from a ferromagnetic contact into a semiconductor channel for proper operation. In this paper, we calculate the efficiency of spin injection from a realistic nonideal ferromagnetic contact into the semiconductor quantum wire channel of a spintronic transistor, taking into account the presence of an axial magnetic field (caused by either the ferromagnetic contact or external agents) and spin orbit interaction. In our calculations, the temperature is assumed to be low enough that phonon scattering is weak and transport is phase-coherent, although not ballistic because of elastic scattering caused by impurities and defects. We consider a single impurity in the channel and show that the conductance depends strongly on the exact location of this impurity because of quantum mechanical interference effects. This is a nuisance since it exacerbates device variability. The ldquosignrdquo of the impurity potential, i.e., whether it is attractive or repulsive, also influences the channel conductance. Surprisingly, at absolute zero temperature, the spin injection efficiency can reach 100% at certain gate biases, even though the ferromagnetic injector is nonideal. However, this efficiency drops rapidly with increasing temperature.

Acid spun carbon nanotube (CNT) fibers were investigated for their field emission properties and performance was determined to be dependent on fiber morphology. The fibers were fabricated by wet-spinning of pre-made CNTs. Fiber morphology was controlled by a fabrication method and processing conditions, as well as purity, size, and type of the CNT starting material. The internal fiber structure consisted of CNT fibrils held together by van der Waals forces. Alignment and packing density of the CNTs affects the fiber’s electrical and thermal conductivity. Fibers with similar diameters and differing morphology were compared, and those composed of the most densely packed and well aligned CNTs were the best field emitters as exhibited by a lower turn-on voltage and a larger field enhancement factor. Fibers with higher electrical and thermal conductivity demonstrated higher maximum current before failure and longer lifetimes. A stable emission current at 3 mA was obtained for 10 h at a field strength of

We propose a spintronic magnetic field sensor, fashioned out of quantum wires, which may be capable of detecting very weak magnetic fields with a sensitivity of ~ 1 femto-Tesla per root Hertz at a temperature of 4.2 K and ~ 80 femto-Tesla per root Hertz at room temperature. Such sensors have applications in magnetometry, quantum computing, solid state nuclear magnetic resonance, magneto-encephalography, mine detection, ground incursion detection and anti-submarine warfare., Will appear in Physica E

We examine the major spin relaxation mechanism (D'yakonov-Perel') in the channel of a spin field-effect transistor (SPINFET) and show analytically that it can be completely eliminated if the channel is a quantum wire and transport is strictly single moded (only the lowest subband is occupied). Single-moded transport also produces the largest "on" to "off" conductance ratio and the largest transconductance of the transistor.

Electro-luminescence is light emission from a solid through which an electric current is passed. Electro-luminescence from organic compounds was discovered in the early '60s, but the subject did not receive much attention until the discovery and development of conductive polymers. Compared to other electro-luminescent technologies (such as inorganic compound semiconductors, porous silicon and liquid crystals), polymer/organic light-emitting diodes (PLEDs/OLEDs) are very attractive. The reasons are their very low operating voltage, high brightness and their tunability to produce the three fundamental colors (red, blue and green). Furthermore, they are lightweight and can be grown on flexible substrates. They are fairly easy and inexpensive to fabricate. Today, PLEDs/OLEDs are suitable for applications such as automotive displays. In the future, they will probably conquer a large portion of the micro display market. Their higher efficiency and lower weight will make them quite competitive with LCD displays, the currently favorite technology. The article concludes that the future of organic light-emitting diodes seems very bright indeed.

We derive an expression for the total spin-splitting energy in an asymmetric quantum dot with ferromagnetic contacts, subjected to a transverse electric field. Such a structure has been shown by one of us to act as a spintronic quantum gate with in-built qubit readers and writers (Phys. Rev. B61, 13813 (2000)). The ferromagnetic contacts result in a magnetic field that causes a Zeeman splitting of the electronic states in the quantum dot. We show that this Zeeman splitting can be finely tuned with a transverse electric field as a result of nonvanishing Rashba spin–orbit coupling in an asymmetric quantum dot. This feature is critical for implementing a quantum gate.

Floating Liquefied Natural Gas (FLNG) units have been under development for decades. They are now becoming a reality, combining the design and installation of LNG units with a traditional " FPSO". Since FLNG facilities handle large flammable gas quantities in a relatively small and congested environment compared to onshore LNG plants, the explosion risk is expected to be higher than some other offshore floating facilities. As a consequence the intensity of the resulting blast loads on the unit can be more severe even if the explosion likelihood is considered low in the design through a frequency analysis. Even if prevention and mitigation measures are implemented to reduce the risk to ALARP (As Low As Reasonably Practicable), Safety Critical Elements (SCE), such as main equipment and structures, shall be designed to withstand the blast event. Since the explosion events are very specific (high intensity and short duration), the common design rules and tools should be updated to take into account this accidental event. In addition, the associated performance criteria for SCEs should be also modified. Finally the entire design shall comply with safety objectives (personnel protection, prevention of escalation). This paper focuses on the philosophy of design against a blast event. It will review the critical functions of the unit that must be maintained during emergency evacuation in order to protect people and, identify the key parameters governing the explosion strength on FLNG. It will show that the derivation of effective explosion loads on structures and equipment based on computational fluid dynamics simulations is not straightforward and requires expertise both in explosion modeling and explosion response. In a second part the paper will show how all the engineering disciplines in Technip individually apply these blast loads into their design through non-linear finite element analyses. Finally, it will highlight the interface between the engineering disciplines and how a consistent demonstration through the design can be achieved in order to fulfill the safety goals, taking engineering further.

We have observed hysteresis between the forward and reverse sweeps of a common mode bias applied to the two in-plane side gates of an asymmetrically biased GaAs quantum point contact. The size of the hysteresis loop increases with the amount of bias asymmetry between the two side gates and depends on the polarity of the bias asymmetry. It is argued that hysteresis may constitute another indirect proof of spontaneous spin polarization in the narrow portion of the quantum point contact., 16 pages, 4 figures. arXiv admin note: text overlap with arXiv:1303.3429

A modified Gummel–Poon model has been developed for the pnp heterojunction bipolar transistor which matches thermionic emission–diffusion of holes across the emitter–base heterojunction with drift–diffusion transport across a graded base. The effects of a high current density on base pushout and the collector junction capacitance have been incorporated to describe the falloff in current gain and high frequency performance. The model's predictions have been compared with reported device measurements and results from a commercial, numerical device simulator for an InP-based device with good agreement found. The model provides an improved description of device performance that will be of use to device designers.

We use an ensemble Monte-Carlo approach to analyze the importance of space-charge effects in the cathode to anode gap region of a recently proposed metal/CdS/LaS cold cathode and its influence on the energy distribution of the electrons collected at the anode. Our analysis is based on a mean-free path approach to include the effects of inelastic scattering in the CdS layer following Fowler–Nordheim injection across the metal/CdS interface. We investigate in detail the regime of current self-quenching and show the importance of the effects of space charge in narrowing the energy of the electron beam collected at the anode. We compare our results to an analytical treatment of the current self-quenching regime based on a hydrodynamic description of electron transport through the gap.

Starting with the 4×4 Luttinger–Kohn Hamiltonian and making use of the axial approximation, we calculate the emitter current as a function of the applied forward emitter-base bias for a typical Pnp AlGaAs/GaAs single heterojunction bipolar transistor (HBT). While including the effects of emitter series resistance and recombination in the quasi-neutral base and emitter-base space-charge region, we then calculate the collector current density versus emitter to base bias and find it to be in excellent agreement with the experimental results for a Al0.4Ga0.6As/GaAs Pnp HBT recently reported in the literature. For that structure, the collector current ideality factor is found to increase from 1.1 at low forward bias VEB to 3.0 at large applied emitter-base forward bias approaching the built-in potential. Experimental values are equal to 1.2 and 2.25 at low and large VEB, respectively.

The effects of Shockley–Read–Hall, Auger, radiative, and intrinsic surface base recombination processes in the emitter-base space-charge region on the current gain of Pnp AlGaAs/GaAs heterojunction bipolar transistors are analyzed. At low forward emitter-base bias, the current gain of a typical Pnp AlGaAs/GaAs heterojunction bipolar transistor is shown to be reduced substantially below its value calculated while neglecting recombination currents in the emitter-base space-charge region. Excellent agreement between theory and experiment is found for the current gain variation versus collector current density for a Pnp device recently reported by Slater et al. [IEEE Electron Device Lett. 15, 91 (1994)].

Starting with Burt’s envelope function theory, we calculate the transmission coefficients of holes across an InP/In1−xGaxAsyP1−y/In0.53Ga0.47As heterointerface while varying the width and gallium and arsenic fractions of the InP lattice-matched quaternary compound (x=0.47y). While comparing our results to the case of an abrupt InP/In0.53Ga0.47As interface, we find that the transmission coefficients of both heavy- and light-holes can be enhanced significantly for a 60-A-wide quaternary layer with an arsenic fraction y=0.4 (x=0.188). This should lead to an enhanced hole injection efficiency of Pnp heterojunction bipolar transistors using the heterointerface analyzed here as an improved design of the emitter-base junction.

For InP-based Pnp heterojunction bipolar transistors (HBTs), a set of epitaxial layers, frequently incorporating quaternaries, is used to make a low resistance electrical contact to the emitter layer. We describe an analytical approach to investigate the nonlinear effects of the multiple heterojunction interfaces on the emitter series resistance and emitter junction current–voltage characteristics of the device. The simulation results show that heterojunction interfaces can contribute a substantial portion (up to 20%) to the total emitter series resistance, especially at high levels of emitter current.

This paper analyzes the effects of optical absorption in the quasi-neutral base region of npn heterojunction bipolar phototransistors (HPT's) on the extent of electron quasi-Fermi level splitting at the emitter-base heterojunction interface. The principle of current balance is used to match the thermionic-field-emission from the emitter with the base electron diffusion current, taking into account the nonuniform optical generation in the base. The increase in minority carrier concentration produced by optical generation in the base leads to a decrease in the quasi-Fermi level splitting at the heterojunction interface which reduces the net electron injection into the base, the emitter injection efficiency and current gain to an extent that depends on the incident optical power and the base-emitter bias.