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We study theoretically electron interference in a Mach-Zehnder-like geometry formed by four zigzag graphene nanoribbons (ZGNRs) arranged in parallel pairs, one on top of the other, such that they form intersection angles of 60º. Depending on the interribbon separation, each intersection can be tuned to act either as an electron beam splitter or as a mirror, enabling tuneable circuitry with interfering pathways. Based on the mean-field Hubbard model and Green's function techniques, we evaluate the electron transport properties of such 8-terminal devices and identify pairs of terminals that are subject to self-interference. We further show that the scattering matrix formalism in the approximation of independent scattering at the four individual junctions provides accurate results as compared with the Green's function description, allowing for a simple interpretation of the interference process between two dominant pathways. This enables us to characterize the device sensitivity to phase shifts from an external magnetic flux according to the Aharonov-Bohm effect as well as from small geometric variations in the two path lengths. The proposed devices could find applications as magnetic field sensors and as detectors of phase shifts induced by local scatterers on the different segments, such as adsorbates, impurities or defects. The setup could also be used to create and study quantum entanglement.

We report on ballistic Hall photovoltammetry as a contactless probe of localized spin excitations. Spins resonating in the near field of a two-dimensional electron system are shown to induce a long range electromotive force that we calculate. We use this coupling mechanism to detect the spin wave eigenmodes of a single ferromagnet of sub-100 nm size. The high sensitivity of this detection technique, $380\text{ }\mathrm{spins}/\sqrt{\mathrm{Hz}}$, and its noninvasiveness present advantages for probing magnetization dynamics and spin transport.

Spherical quartz stones of around 1 cm in diameter have been exposed to anodic arc discharges in a helium atmosphere at 300 Torr. The arc current flowing between the graphite electrodes was set either in continuous DC mode (30–150 A) or in pulsed mode at 2 Hz (220 A peak). The ablation rate in each sample was systematically measured after several seconds of arc plasma treatment. Optical emission spectroscopy (OES) diagnostics and 2D fluid simulations of the arc discharge have shed light on the heat flux transport and the heating mechanisms of the quartz crystals. A linear correlation is found between the absorbed power density and the resulting rate of penetration, which yields a maximal value of 15 cm h−1 for approximately 150 W cm−2. The linear fit on the slope provides a specific energy of 40 kJ cm−3. The incident energy flux onto the sample surface promoted a phase transition from crystalline to glassy silica, as characterized via Raman spectroscopy. This study points out the strong potential of arc plasma technology for geothermal drilling applications.

By means of spin-resolved density functional theory calculations using both atomic orbitals and plane-wave basis codes, we study the electronic and magnetic ground state of single-layer NbSe2. We find that, for all the functionals considered, the most stable solution in this two-dimensional (2D) superconductor is the ferrimagnetic ground state with a magnetic moment of 1.09 μB at the Nb atoms and of 0.05 μB at the Se atoms pointing in the opposite direction. Our calculations show that the ferrimagnetic state precludes the development of charge density wave (CDW) order and their coexistence in the single-layer limit, unless graphene is considered as a substrate. The spin-resolved calculated density of states (DOS), a key fingerprint of the electronic and magnetic structure of a material, unambiguously reproduces the experimental DOS measured by scanning tunneling spectroscopy in single-layer NbSe2. Our work sets magnetism into play in this prototypical correlated 2D material, which is crucial to understand the formation mechanisms of 2D superconductivity and CDW order., We are indebted to Spanish Ministry of Science and Innovation for financial support through Grant FIS2015-64886-C5-5-P and MAT2017-83553-P. MMU acknowledges support by the Spanish MINECO under Grant No. MAT2017-88377-C2-1-R and by the ERC Starting Grant LINKSPM (Grant 758558). EB acknowledges support from the Scientific and Technological Research Council of Turkey (TUBİTAK) under Grant No. 1059B141801387 and DSP from Spanish Ministry of Science and Innovation under Grant PID2019-107338RB-C66.

Low-power memristive devices embedded on graphics or central processing units logic core are a very promising non-von-Neumann approach to improve significantly the speed and power consumption of deep learning accelerators, enhancing their deployment on embedded systems. Among various non-ideal emerging neuromorphic memory devices, synaptic weight hardware implementation using resistive random-access memories (RRAMs) within 1T1R architectures promises high performance on low precision binarized neural networks (BNN). Taking advantage of the RRAM capabilities and allowing to substantially improve the density thanks to the ovonic threshold selector (OTS) selector, this work proposes to replace the standard 1T1R architecture with a denser 1S1R crossbar system, where an HfO2-based resistive oxide memory (OxRAM) is co-integrated with a Ge-Se-Sb-N-based OTS. In this context, an extensive experimental study is performed to optimize the 1S1R stack and programming conditions for extended read window margin and endurance characteristics. Focusing on the standard machine learning MNIST image recognition task, we perform offline training simulations in order to define the constraints on the devices during the training process. A very promising bit error rate of ∼10−3 is demonstrated together with 1S1R 104 error-free programming endurance characteristics, fulfilling the requirements for the application of interest. Based on this simulation and experimental study, BNN figures of merit (system footprint, number of weight updates, accuracy, inference speed, electrical consumption per image classification and tolerance to errors) are optimized by engineering the number of learnable parameters of the system. Altogether, an inherent BNN resilience to 1S1R parasitic bit errors is demonstrated.

Given a compact metric space $X$, we associate to it an inverse sequence of finite $T_0$ topological spaces. The inverse limit of this inverse sequence contains a homeomorphic copy of $X$ that is a strong deformation retract. We provide a method to approximate the homology groups of $X$ and other algebraic invariants. Finally, we study computational aspects and the implementation of this method.

For the layered transition metal dichalcogenide 1T-TaS2, we establish through a unique experimental approach and density functional theory, how ultrafast charge transfer in 1T-TaS2 takes on isotropic three-dimensional character or anisotropic two-dimensional character, depending on the commensurability of the charge density wave phases of 1T-TaS2. The X-ray spectroscopic core-hole-clock method prepares selectively in- and out-of-plane polarized sulfur 3p orbital occupation with respect to the 1T-TaS2 planes and monitors sub-femtosecond wave packet delocalization. Despite being a prototypical two-dimensional material, isotropic three-dimensional charge transfer is found in the commensurate charge density wave phase (CCDW), indicating strong coupling between layers. In contrast, anisotropic two-dimensional charge transfer occurs for the nearly commensurate phase (NCDW). In direct comparison, theory shows that interlayer interaction in the CCDW phase - not layer stacking variations - causes isotropic three-dimensional charge transfer. This is presumably a general mechanism for phase transitions and tailored properties of dichalcogenides with charge density waves., AF acknowledges funding by the Helmholtz Virtual Institute VI 419 and the ERC Advanced Investigator Grant No. 669531 EDAX. NM acknowledges funding by the ERC Advanced Investigator Grant No. 321319 ESUX and support from the Carl Tryggers foundation for Scientifc Research CTS. DS-P and MM acknowledge funding from EU-FP7 project THINFACE (grant No. 607232), Spanish MINECO (grant No. MAT2016-78293-C6-4-R), and Basque Dep.de Educación and UPV/EHU (grant No. IT-756-13).

An experimental study is made of electron tunneling in a resonant-tunneling diode in magnetic fields directed parallel and perpendicular to the planes of the GaAs/Al X Ga 1 − X As heterostructure layers. In particular, phonon replicas on the current–voltage characteristics of the diode are investigated. In the second current derivatives a fine structure of replicas is found. The transformation of the structure of replicas in a perpendicular magnetic field can be qualitatively understood as a manifestation of the transition of polaron states to magnetopolaronic ones.

This is the peer reviewed version of the following article: “Uros, C., Walsh, J., Cernák, M., Labay, C., Canal, J.M., Canal, C. (2019) White paper on the future of plasma science and technology in plastics and textiles. Plasma processes and polymers, 16 1 which has been published in final form at [doi: 10.1002/ppap.201700228]. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving." This white paper considers the future of plasma science and technology related to the manufacturing and modifications of plastics and textiles, summarizing existing efforts and the current state‐of‐art for major topics related to plasma processing techniques. It draws on the frontier of plasma technologies in order to see beyond and identify the grand challenges which we face in the following 5–10 years. To progress and move the frontier forward, the paper highlights the major enabling technologies and topics related to the design of surfaces, coatings and materials with non‐equilibrium plasmas. The aim is to progress the field of plastics and textile production using advanced plasma processing as the key enabling technology which is environmentally friendly, cost efficient, and offers high‐speed processing

We report the energy level alignment evolution of valence and conduction bands of armchair-oriented graphene nanoribbons (aGNR) as their band gap shrinks with increasing width. We use 4,4″-dibromo-para-terphenyl as the molecular precursor on Au(111) to form extended poly-para-phenylene nanowires, which can subsequently be fused sideways to form atomically precise aGNRs of varying widths. We measure the frontier bands by means of scanning tunneling spectroscopy, corroborating that the nanoribbon's band gap is inversely proportional to their width. Interestingly, valence bands are found to show Fermi level pinning as the band gap decreases below a threshold value around 1.7 eV. Such behavior is of critical importance to understand the properties of potential contacts in GNR-based devices. Our measurements further reveal a particularly interesting system for studying Fermi level pinning by modifying an adsorbate's band gap while maintaining an almost unchanged interface chemistry defined by substrate and adsorbate., The project leading to this publication has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No 635919), from the European Union FP7 FET-ICT “Planar Atomic and Molecular Scale devices” (PAMS) project (Contract No. 610446), from the Spanish Ministry of Economy, Industry and Competitiveness (MINECO, Grant No. MAT2016-78293-C6), from the Basque Department of Education (PI-2016-1-0027), and from the University of Padova (Grant CPDA154322, Project AMNES).

Pulsed anodic arc discharge is a novel synthesis method of nanomaterials by means of low-temperature atmospheric plasma. The technique consists in periodically supplying DC power to two vertically aligned electrodes in the form of short unipolar pulses with peak currents of a few hundred Amperes in a helium atmosphere. The pulsed arc plasmas are sustained at frequencies on the order of 1 Hz with around 10% of duty cycle. It constitutes a versatile technique thanks to a series of advantages compared to continuous DC arc processes, in particular, flexibility in the experimental conditions, process stability and repeatability, better utilization of ablating anode material, lower production of macroparticles, and lower thermal loads. Such features are discussed in this article. A brief overview concerning the recent accomplishments of pulsed arc discharge on deposition of carbon nanostructures (graphene and carbon nanotubes) and few-layer flakes of molybdenum disulphide and an outlook on future applications of this method for the discovery of new materials with tailored functional properties are provided.

We extensively characterize the electronic structure of ultranarrow graphene nanoribbons (GNRs) with armchair edges and zigzag termini that have five carbon atoms across their width (5-AGNRs), as synthesized on Au(111). Scanning tunneling spectroscopy measurements on the ribbons, recorded on both the metallic substrate and a decoupling NaCl layer, show well-defined dispersive bands and in-gap states. In combination with theoretical calculations, we show how these in-gap states are topological in nature and localized at the zigzag termini of the nanoribbons. In addition to rationalizing the driving force behind the topological class selection of 5-AGNRs, we also uncover the length-dependent behavior of these end states which transition from singly occupied spin-split states to a closed-shell form as the ribbons become shorter. Finally, we demonstrate the magnetic character of the end states via transport experiments in a model two-terminal device structure in which the ribbons are suspended between the scanning probe and the substrate that both act as leads., We acknowledge funding from the European Union’s Horizon 2020 programme (Grant Agreement Nos. 635919 and 863098 from ERC and FET Open projects, respectively), from the Spanish MINECO (Grant Nos. FIS2017-83780-P and MAT2016-78293-C6), and from the University of the Basque Country (Grant IT1246-19). D.G.O. thanks the Alexander von Humboldt Foundation for supporting his research stay at the MPI, and Klaus Kern for hosting him.

RRAM technology relying on transitional metal oxides (namely OxRAM) is about to reach the industrial stage. Nevertheless the physical-based understanding of the material and process implications at device and circuit levels is still not completely clear, hindering the full industrial exploitation of the OxRAM technology. In this context, this article presents a multi-scale methodology that connects the microscopic material properties to the electrical behavior of OxRAM devices at the circuit level. Microscopic models describing OxRAM operation (i.e., forming, resistive switching) and variability (e.g., cycle-to-cycle, RTN) will be reviewed and used for the development of compact models that will allow investigating the potential of this technology at the circuit level. An overview of some innovative applications involving OxRAM will be finally presented.

This paper presents a way to implement a test structure able to measure accurately a large number of threshold voltage values for Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) matching characterization. A multiplexed system able to select a single transistor among others in a small array is used. This architecture guarantees a similar environment for all transistors in the array, while requiring a small number of pads for measurement. Moreover, the influence of the multiplexer switches can be evaluated: their unwanted contribution to the measurement can therefore be compensated. An experimental study to evaluate the influence of this multiplexer on measurement and the efficiency of the compensation is conducted. Silicon results are presented in order to validate the concept.

Hydrogen molecules can be trapped in the nanocavity formed by the tip of a scanning tunneling microscope and a metal or molecular surface, and produce sharp inelastic non-linearities in the tunneling spectra. Here, we study the interaction effects of hydrogen in a tunneling junction created over Manganese phthalocyanines molecules in two oxidation states. The effect of hydrogen in the tunneling spectra varies strongly depending on the molecular species, but its force spectrum is fairly independent on the molecular state. We find that in mild tunneling conditions hydrogen-induced forces are weakly attractive during a small range of tip sample distance. The van der Waals interaction shows a maximum value of 140 pN, which faintly depends on electrostatic variations along the surface. These results show that AFM can be employed to resolve the complex interaction landscape of a trapped hydrogen molecule and deduce fainter effects such as molecular deformations or dipolar fields., The research was financially supported by the Spanish Ministerio de Economia y Competitividad, MINECO (Grant FIS 2015-62538-ERC, MAT2016-78293-C6, and the Maria de Maeztu Units of Excellence Programme MDM-2016-0618), the Basque Government (Departamento de Industria, grant no. PI-2015-1-42, and Departamento de Educación and UPV/EHU, grant No. IT-756-13), and the European Regional Development Fund (ERDF).

Photovoltage spectroscopy is a beneficial technique to investigate the dynamic properties of the spin excitations of ferromagnetic elements fabricated at the surface of a GaAs/Al 0.33Ga 0.67As heterojunction. This method is of particular interest for probing localized spin wave modes. The high sensitivity of the photovoltage technique arises from the high electron mobility of 2D electrons μ = 1.5 × 10 6 cm 2 • V -1 • S -1 which enables efficient rectification of magnetic moment oscillations through the Hall effect. We report on the discrete structure of spin wave eigenmodes as a function of magnetic field orientation, the shape of Co ferromagnets, and the geometry of nanomagnets. We indicated bonding-Antibonding spin waves when the static magnetic field, is parallel to the short side of the stripe at different microwave frequencies at 4 K. We also observed Damon-Eshbach modes when is parallel to the stripe. Micromagnetic simulations confirm the experimental results. We observe the discrete structure of the photovoltage for individual dots. We also investigate the effect of the magnetocrystalline anisotropy field of Co on ferromagnetic resonance. Our results demonstrate that photovoltage measurements in hybrid semiconductor-ferromagnetic structures provide a sensitive and extended tool for probing the spin waves of small magnets with a size of 80 nm.

Currently, Carbon Fiber Reinforced Non-Metal Composites (CFRC) are commonly applied in structural components of aircrafts. Frequently, these elements need to be drilled for their assembly in the final product. Chips close to powder are formed when this kind of material is machined. Because of this, drilling processes are mostly performed in absence of cutting fluids. High quality requirements are demanded for holes due to the fact than those elements are placed in key components of the aircrafts. The most relevant defects that can be produced in the dry drilling of CFRC are located in the both tool input and tool output. These defects are known as Break-IN (B-IN) and Break-OUT (B-OUT). This paper reports on the results of a comparative study of different methodologies for evaluating those defects. First of them is based on the analysis of the diameter deviation. Second procedure is based on the damaged area. Both parameters have been measured making use of image analysis techniques. Obtained results have revealed that damaged area based method is more sensitive to hole changes.

We report on a sensitive spectroscopic technique for probing the spin excitations of individual submicron magnets. This technique uses a high mobility two dimensional electron gas (2DEG) confined in a GaAs/AlGaAs heterojunction to pick up the oscillating dipolar magnetic field emanating from the individual spin wave modes of micromagnets fabricated at its surface. We review a range of dynamic phenomena that demonstrate the formation of magnetostatic waves in finger gate arrays, dipolar edge spin waves in bar magnets, vortex hysteresis in magnetic dots and the photovoltage dependence on microwave polarization.

Here, the synthesis of Molybdenum Disulphide (MoS2) flakes by means of anodic atmospheric arc discharge is reported for the first time. The vertical electrode configuration consisted of a compound anode (hollow graphite anode filled with MoS2 powder) and a solid graphite cathode placed just above of the compound anode. Arc processes were operated in pulsed mode to preferentially evaporate the powder component from the anode and to minimize Carbon ablation. Pulsed anodic arc discharges were conducted at 2 Hz and 10% duty cycle in 300 Torr of Helium with a peak current of 250-300 A and a peak voltage of 35 V. A probe made of Tungsten wire was placed in the vicinity of the arc column to collect the evaporated material. The measured thickness profile was correlated to the particle flux distribution and it was fitted by a simple model of plasma expansion. During pulse phase, electron density was estimated around 5E22 m-3 or higher, and ion current density was of the order of 10 A/mm2. Morphology, structure and composition of the samples were characterized by Raman spectroscopy, atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The study shows that pulsed arc discharge of the compound anode leads to moderate C deposition combined with MoS2 deposition in the form of fragmented nanocrystals and few atomic monolayers of MoS2. Such synthesis technique is promising to produce new 2D nanomaterials with tailored structure and functionality thanks to the flexibility of pulsed power.

Pulsed arc discharges can improve arc control and tailor the ablation process in the production of 1D and 2D nanostructures from carbon anodes. In this work, low-dimensional carbon nanoparticles have been generated by means of anodic arc discharge in helium atmosphere excited with a square-wave modulated signal (1–5 Hz, 10% duty cycle). The discharges were performed between two graphite electrodes with maximal peak current of 250 A and maximal voltage of 65 V. The erosion rates and conversion efficiency of the ablated anode are compared to reference samples grown in DC steady arc mode. Ablation rates in pulsed arcs are typically of the order of 1 mg s−1. Combination of fast Langmuir probe diagnostics and optical emission spectroscopy provided plasma parameters of the discharges at the arc column. Ranges of 1016–1017 m−3 for electron density and 0.5–2.0 eV for electron temperature are estimated. The obtained samples were characterized with Raman spectroscopy and scanning electron microscopy. The deposit on the cathode after pulsed arc consisted of carbon nanostructures such as graphene nano-platelets and carbon nanotubes. Erosion dynamics of pulsed arc discharge has been described in terms of a global model and compared to steady arc discharge. A correlation is identified among discharge regimes, optical emission patterns and ablation modes. In conclusion, pulsed anodic arc discharge is a very efficient source of carbon nanomaterials. The large control of the discharge characteristics will permit to tailor accurately the production and the properties of carbon nanotubes and graphene. This deposition method is promising for the fabrication of semiconducting nanomaterials with tuneable electrical and optical properties.

Two European GaAs power P-HEMT MMIC processes using representative test structures have been characterized in situ when irradiated by high energy heavy ion radiation beam (420 MeV Xenon source, LET = 46.6 MeV cm2/mg), and under various worst case bias including DC and high drive RF conditions applied. The test methodology conducted has been carefully defined in order to help to early discriminate failure mechanisms induced by biasing stresses from those possibly induced by heavy ion irradiation environment. It is demonstrated that the two P-HEMT processes tested under worst case application biasing conditions (both cumulated DC and RF) are immune to heavy ion radiation stress representative of harsh space environments.

We present a metallographic study of archaeological artefacts of steel, had been found in different archaeological sites, which characteristic microstructures reveal that have been affected by levels of fire. Study was performed using FEG (Field Emission Gun). In the laboratory, they are reproduced structures of steels archaeological.Se presenta un estudio metalográfico de piezas arqueológicas de acero, encontradas en distintos yacimientos arqueológicos, cuyas microestructuras características revelan que se han visto afectadas por niveles de incendio. El estudio se ha realizado mediante FEG (Field Emission Gun). Se han reproducido en el laboratorio las estructuras de los aceros arqueológicos.

We have performed magnetoresistance measurements on a GaAs/AlGaAs two-dimensional electron gas under microwave heating. Both the magneto-oscillations and magnetoresistance minima are used as electron thermometers to determine the electron effective temperature Te. When there is no clear cyclotron gap, it is found that Te determined from these two methods can be substantially different such that we can still distinguish localized electrons from the semiclassical conducting ones. The almost constant Te obtained from the magnetoresistance minima reveals the survived equivalence between different Landau-band tails under insufficient localization.

Continuous phase drift and thermal ordering of the Aharonov-Bohm oscillations in a small ring interferometer have been revealed by numerical calculation of the conductance. It has been found that the sign and rate of change in the oscillation amplitude with increasing temperature depend on the Fermi energy. The calculation results have been compared with the experimental data for the same sample.

27th European Symposium on Reliability of Electron Devices, Failure Physics and Analysis (ESREF), Halle, GERMANY, SEP 19-22, 2016; International audience; Common problems with Oxide-based Resistive Random Access Memory (so-called OxRRAM) are related to high variability in operating conditions and low yield. Although research has taken steps to resolve these issues, variability remains an important characteristic for OxRRAMs. In this paper, a test structure consisting of an OxRRAM matrix where each memory cell can be configured as a ring oscillator is introduced. The oscillation frequency of each memory cell is function of the cell resistance. Thus, the test structure provides within-die accurate information regarding OxRRAM cells variability. The test structure can be used as a powerful tool for process variability monitoring during a new process technology introduction but also for marginal cells detection during process maturity. (C) 2016 Elsevier Ltd. All rights reserved.

Measurements have been made of magneto-transport in GaAs - Ga 1− x Al x As multi-lavers with magnetic fields up to 35 T. At high fields (22 T) a strong, temperature dependent spin splitting of the N = 0 Landau level is observed. This indicates a strong many-body enhancement of the g factor, since the bare spin splitting (0.7 mV) is much less than the broadening parameter Γ (5.3 meV) while the strong temperature dependence below 4.2 K is clear evidence for a temperature dependent enhancement. In the ultra-quantum regime ( ν = 2 πnl 2 0 ≲ 1) the magnetoresistance rises very rapidly in contrast to the predictions of independent electron theories and exhibits a weak thermal activation.

We examine the edge states picture as applied to the electron-hole system, and show that compensated quantum Hall states are fundamentally different to quantum Hall states of single carrier type systems. Measurements of their current driven breakdown are described, and we show that these states have very small breakdown currents. (C) 2001 Elsevier Science B.V. All rights reserved.

The diagonal component of the thermoelectric power in GaInAsInP, GaInAsAlInAs and GaAsGaAlAs heterojunctions and a GaAsGaAlAs superlattice has been studied as a function of magnetic field and temperature. In high magnetic fields, the thermopower shows oscillations proportional to the resistivity oscillations, including features due to spin splittings and the occupation of two electric subbands. The peak values of the thermopower in the GaAsGaAlAs superlattice are almost independent of temperature and close to the theoretical predictions. In contrast, the peak thermopowers measured in the heterojunctions are lower than predicted by factors of between 2 and 50, and decrease with increasing temperature.

In bulk InSe crystals grown by the Bridgman method, electron accumulation layers are formed in the vicinity of stacking faults with charged impurities adsorbed to the defect plane. Shubnikov-de Haas experiments show that the 2D electron gas in InSe observed at low temperatures has a density of 1012 cm-2 and that several dielectric sub-bands are occupied. The g-factor is enhanced by electron-electron interactions. The optical absorption was studied in the frequency range 3-20 meV in perpendicular and tilted magnetic fields up to 8T. The cyclotron resonance at Eres=h(cross) omega c, the intersubband resonance at Eres=E01 and the combined resonance at Eres=E01+h(cross) omega c, are all observed for both parallel and tilted polarisation, where E01 is equal to the sub-band separation as deducted from the Shubnikov-de Haas periodicities. With increasing magnetic fields the exciton-and depolarisation-shifted resonance E01 approaches the true sub-band splitting E01, and is the same time reduced in amplitude. Absorption due to bulk 1s-2p transitions in isolated shallow donors is also observed. The 2p level shows a three-dimensional Zeeman splitting (h(cross) omega c)3D with a weak anomalous mass anisotropy as observed in cyclotron resonance measurements of bulk carriers at temperatures of 30-100K. The effective electronic Rydberg is in agreement with results of exciton spectra.

Transitions between the Landau levels of the lowest electron and hole sub-bands have been observed in the inter-band optical absorption of a modulation doped Ga.47In.53AsAl0.48In.52As superlattice and a Ga0.3In.7AsInP strained layer superlattice, in magnetic fields up to 16T. In the unstrained sample, the energies of transitions up to 250 meV above the GaInAs band gap were found to be well described by a parabolic model for the heavy hole band and the model of Bowers and Yafet for the conduction band. In contrast to previous work on undoped quantum wells, no Coulomb binding effects were observed in this lightly doped sample, and this is attributed to screening of the exciton. In the strained sample, the heavy hole sub-band was found to show highly non-parabolic structure, and this is believed to be due to the effects of biaxial strain on the valence band.

We describe the properties of a strongly interacting two-dimensional (2D) electron gas in high magnetic fields whose properties can be described in terms of the formation of composite fermions at fractional Landau level occupancy. For a Landau level occupancy nu = 1 the excitations correspond to spin waves for high g-factors and magnetic fields, but when the g-factor is reduced close to zero by the use of hydrostatic pressure there is strong evidence for the formation of skyrmions. Studies of composite fermions in the limit of vanishing Zeeman energy also suggest that skyrmionic excitations can occur for composite fermions.

Cyclotron resonance results from GaInAs-InP heterojunctions and superlattices and GaInAs-AlInAs heterojunctions in fields up to 18 T are reported. For low frequencies, the effective mass is compared with the predictions of k · p theory, and the resonance linewidth is fitted to finite range scattering theories. At higher frequencies, the linewidth increases dramatically, while the effective mass deviates from its low-frequency value. These effects are attributed to resonant polaron coupling.

We report results from experimental studies on the current driven breakdown of the quantum Hall effect in an InAs/GaSb-based electron–hole system. We find that the critical currents observed in this system are typically much smaller than those reported for single carrier-type systems. Width dependence measurements show two regimes of behaviour. For sufficiently wide samples, the critical current has a linear dependence on the channel width, while for narrower samples, the critical current has a strong tendency to be vastly reduced. There is a critical width at which this crossover occurs, which is found to depend on the magnetic field, Fermi energy and the ratio between the electron and hole concentrations. We refer to the two regimes as the 'linear regime' and the 'fragile regime'. For samples in the linear regime, critical electric fields or macroscopic critical current densities can be defined. Although the absolute values seem small compared to single carrier-type systems, the values are found to be comparable when scaled by the activation energies. In the fragile regime, the critical current is disproportionately small compared with single carrier-type systems.

Magnetophonon measurements in a GaInAs-AlInAs multi-quantum well show evidence for a remote interaction with AlAs-like phonons in the barriers. The strongest oscillations come from absorption of GaAs-like LO phonons in the wells in contrast to earlier results for high carrier density heterojunctions.

The intensities of the bound to bound transitions of the shallow donors in silicon and CdTe are found to be strongly electric field dependent when observed by photoconductivity techniques at low temperatures. Under these conditions significant differences can be detected between the photoconductive spectrum and the same transitions observed in absorption. The photoconductive peaks are shifted consistently to lower frequency compared with the absorption spectrum and additional peaks appear which are not significant features in absorption. These additional peaks are believed to result from the formation of molecular complexes of donors. The strong electric field dependence of the bound transitions observed in photoconductivity, the shift to lower frequency of the peaks and the enhancement of the additional lines can all be explained qualitatively on the assumption that the mechanism responsible for the generation of the photosignal involves hopping between the excited states of the molecular complexes

Measurements are reported of frequency- and temperature-dependent cyclotron resonance in the ternary alloy GaxIn1-xAs, close to its lattice match with InP. The band-edge effective mass is found to be 0.041 m0 for x=0.47, in agreement with earlier measurements, but it is found that the non-parabolicity of the conduction band is approximately double that expected on the basis of k.p perturbation theory. This is thought to be due to alloy disorder. Magnetophonon resonance was also observed, giving a further measurement of the effective mass, together with the first observation of two-phonon-mode behaviour in this material.

The conduction bands in GaAs and In have been studied very accurately through the cyclotron resonance over a wide range of energies using the photoconductive detection technique. Pronounced band non-parabolicity has been measured in GaAs. Values for the band-edge masses of 0.0660 m0 and 0.07927 m0 respectively have been determined. A five-level k.p model of the band structure in the presence of a magnetic field has been used to describe the data where resonant and non-resonant polaron contributions to electron energies are included in the theory. The non-parabolicity and spin-doublet splitting of the cyclotron resonance are well described by the employed formalism in both materials and the theory also gives a reasonable account of the anisotropy of the band in GaAs. The fit to experimental data allowed the authors to determine the matrix element of momentum Q between the higher conduction and valence bands in both materials.

The quantum Hall effect in InAs/GaSb heterojunctions at very high fields and low temperatures when both the electrons and holes contribute to the quantized Hall conductance was studied. InAs/GaSb were grown by metal organic vapor phase epitaxy and are known to possess a relatively low level of extrinsic doping so that the majority of charge carriers are created by intrinsic charge transfer from the GaSb layers to the InAs layer. The Hall conductance showed a digital sequence oscillating from 0-1-0 conductance quanta and the diagonal resistivity showed oscillatory insulating behavior due to the formation of a total gap in the energy spectrum.

We report measurements of photoluminescence of GaAs/AlGaAs heterojunctions using hydrostatic pressure to reduce the Zeeman energy. A red-shift is observed near nu = 1 which falls with pressure, consistent with theoretical predictions of Skyrmionic exciton recombination energies. When the Zeeman energy is reduced below a critical value the redshift vanishes. (C) 1998 Elsevier Science B.V. All rights reserved.

This paper shows how floating gate (FG) memory cells behavior during retention tests can be predicted relying on static electrical stress tests. Retention tests are usually performed at High or Low Temperature Bake (HTB or LTB respectively) to provide warning of an impending failure of the memory cell capability to store data. Retention tests are very useful to screen out defective cell populations but induce significant test time overhead. To overcome this limitation, a correlation between stress time and retention time is established to anticipate retention test results. Moreover, further investigations are made to provide a physical explanation for the correlation. Indeed, it is shown that the same FG memory tunnel oxide traps are activated during electrical stress tests (high electric field) and retention tests (low electric field).

A new method for preparation of metallographic samples, based on application of phthalocyanine blue diluted with nitrocellulose resin, is presented. A thin layer of the dye was applied onto cast iron or carbon steel samples and alloys prior to observation under optical microscopy. Highly resolved coloured micrographs were obtained for quenching structures or isothermal phase transformation of carbon iron alloys.

This paper presents a numerical analysis of the influence on the fatigue life of hybrid metal/CFRP bolted joints of some deviations in certain assembly parameters. Two types of hybrid joints typically used in aircraft are analyzed, the Ti-6Al-4V/CFRP and the Al-2024-T3/CFRP, riveted with blind bolts. The parameters analyzed are: the thickness of sealant between metal sheet and composite laminate, the angle of countersunk and the adjustment or chamfer at the countersunk-drill zone. The analysis highlights critical areas for fatigue failure and the relative influence of these parameters on the fatigue resistance of the joint.

Magnetotransport of a quasi-three-dimensional (100-nm) HgTe film in quantized magnetic fields has been experimentally investigated. It has been found that the film exhibits pronounced quantization of the Hall resistance accompanied by deep minima of the dissipative resistance. A transition from the three-dimensional behavior of Shubnikov-de Haas oscillations in semiclassical magnetic fields (ωcτq ≤ 1) to a two-dimensional one in the quantum-Hall-effect regime has been discovered. The conduction electron cyclotron effective mass in mercury telluride has been determined from the temperature dependence of the Shubnikov-de Hass oscillations in such magnetic fields.

The objective of this paper is to present a mixed test structure designed to characterize yield losses due to hard defect and back-end process variation (PV) at die and wafer level. A brief overview of the structure, designed using a ST-Microelectronics’ 130 nm technology, is given. This structure is based on a SRAM memory array for detecting hard defects. Moreover each memory cell can be configured in the Ring Oscillator (RO) mode for back-end PV characterization. The structure is tested in both modes (SRAM, RO) using a single test flow. The test data analysis method is presented and applied to experimental results to confirm the ability of the structure to monitor PV and defect density.

Microwave cyclotron resonance of electrons and holes at the metal-to-semimetal transition in HgTe quantum wells with an inversed band structure has been investigated. The resonance has been studied by measuring microwave photoresistance in the frequency range of 35–170 GHz. The effective cyclotron masses of electrons and holes have been determined. A shift of the cyclotron resonance of the two-dimensional electrons at the metal-to-semimetal transition possibly caused by plasma effects in the two-dimensional semimetal has been discovered.

To ensure the reliability of EEPROM devices, it is significant to monitor the evolution of the memory array threshold voltage (V T ) distribution. In this work, impact of endurance and retention tests is evaluated on EEPROMs. Based on the extrinsic V T population evolution, the oxide tunnel trap concentration (Nit) is extracted using a 700 kbits EEPROM test chip. Data retention after Write/Erase (W/E) cycles is one of the most important reliability issues in EEPROM devices. The electric high-field stress induced during W/E cycles is mainly responsible for the degradation of the retention time because it creates intrinsic failures or traps in the EEPROM tunnel oxide. These traps serve as bridges for the trap to trap conduction current (I TAT ) in the tunnel oxide. EEPROM data retention degradation due to this stress-induced leakage current (SILC) impacts directly the EEPROM V T distribution by creating extrinsic populations. To track accurately extrinsic cells' evolution (tail bits), representative of Nit parameter, an innovative experimental plan is proposed.

The interference of magneto-intersubband oscillations and microwave-induced resistance oscillations is studied in high-density triple quantum wells. We give an introduction into magnetotransport in trilayer systems and focus on photoresistance measurements. The power and frequency dependence of the observed magnetoresistance oscillations can be described by the inelastic mechanism of photoresistance, generalized to the three-subband case.

We report on a photovoltage technique that we use to probe spin excitations on submicron scales where surface effects play a dominant role. Localized spin wave modes were detected through the photovoltage induced in a two-dimensional electron gas (2DEG) system formed in a GaAs/ AlGaAs heterojunction. The two-dimensional nature of the detector separates the effects of the in-plane and normal vector components of magnetization. The high sensitivity of the technique arises from the low electron density and high electron mobility of 2DEGs relative to metals. The large magnetoresistance further introduces nonlinearity in the Hall coefficient that magnifies the photovoltage. Localized modes of spin waves confined in the magnetostatic potential of the demagnetizing field are observed. These determine the dynamic properties of the magnetization, which are relevant to high-density information storage.