This survey deals with 1/f noise in homogeneous semiconductor samples. A distinction is made between mobility noise and number noise. It is shown that there always is mobility noise with an /spl alpha/ value with a magnitude in the order of 10/sup -4/. Damaging the crystal has a strong influence on /spl alpha/, /spl alpha/ may increase by orders of magnitude. Some theoretical models are briefly discussed none of them can explain all experimental results. The /spl alpha/ values of several semiconductors are given. These values can be used in calculations of 1/f noise in devices. >

1/f Noise Sources

Phosphate materials are being extensively studied as lithium-ion battery electrodes. In this work, we present a high-throughput ab initio analysis of phosphates as cathode materials. Capacity, voltage, specific energy, energy density, and thermal stability are evaluated computationally on thousands of compounds. The limits in terms of gravimetric and volumetric capacity inherent to the phosphate chemistry are determined. Voltage ranges for all redox couples in phosphates are provided, and the structural factors influencing the voltages are analyzed. We reinvestigate whether phosphate materials are inherently safe and find that, for the same oxidation state, oxygen release happens thermodynamically at lower temperature for phosphates than for oxides. These findings are used to recommend specific chemistries within the phosphate class and to show the intrinsic limits of certain materials of current interest (e.g., LiCoPO4 and LiNiPO4).

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Phosphates as Lithium-Ion Battery Cathodes: An Evaluation Based on High-Throughput ab Initio Calculations

The discovery of new chemistries outperforming current lithium intercalation cathodes is of major technological importance. In this context, polyanionic systems with the potential to exchange multiple electrons per transition metal are particularly interesting because they could combine the safety of polyanion systems with higher specific energy. In this paper, we report on a series of new mixed polyanions compounds of formula AxM(YO3)(XO4) (with A = Na, Li; X = Si, As, P; Y = C, B; M = a redox active metal; and x = 0 to 3) identified by high-throughput ab initio computing. The computed stability of both lithium and sodium-based compounds is analyzed along with the voltage, specific energy and energy density of the lithium-based compounds. This analysis suggests several novel carbonophosphates and carbonosilicates as potential high capacity (>200 mAh/g) and specific energy (>700 Wh/kg) cathode materials for lithium-ion batteries.

Novel mixed polyanions lithium-ion battery cathode materials predicted by high-throughput ab initio computations

The theoretical and experimental results concerning the thermodynamical and low-frequency transport properties of hybrid structures, consisting of spatially separated conventional low-temperature superconductors (S) and ferromagnets (F), are reviewed. Since the superconducting and ferromagnetic parts are assumed to be electrically insulated, no proximity effect is present and thus the interaction between both subsystems is through their respective magnetic stray fields. Depending on the temperature range and the value of the external field Hext, different behavior of such S/F hybrids is anticipated. Rather close to the superconducting phase transition line, when the superconducting state is only weakly developed, the magnetization of the ferromagnet is solely determined by the magnetic history of the system and it is not influenced by the field generated by the supercurrents. In contrast to that, the nonuniform magnetic field pattern, induced by the ferromagnet, strongly affects the nucleation of superconductivity, leading to an exotic dependence of the critical temperature Tc on Hext. Deeper in the superconducting state the effect of the screening currents cannot be neglected anymore. In this region of the phase diagram T–Hext various aspects of the interaction between vortices and magnetic inhomogeneities are discussed. In the last section we briefly summarize the physics of S/F hybrids when the magnetization of the ferromagnet is no longer fixed but can change under the influence of the superconducting currents. As a consequence, the superconductor and ferromagnet become truly coupled and the equilibrium configuration of this 'soft' S/F hybrid requires rearrangements of both superconducting and ferromagnetic characteristics, as compared with 'hard' S/F structures.

https://iopscience.iop.org/article/10.1088/0953-2048/22/5/053001/pdf

Nucleation of superconductivity and vortex matter in superconductor–ferromagnet hybrids

We investigate phase stability and ionic transport mechanisms in two recently discovered superionic conductors, Li3OX (X = Cl, Br), from first principles. These compounds, which have an antiperovskite crystal structure, have potential applications as solid electrolytes in Li-ion batteries. We identify a low-barrier three-atom hop mechanism involving Li interstitial dumbbells. This hop mechanism is facile within the (001) crystallographic planes of the perovskite crystal structure and is evidence for the occurrence of concerted motion, similar to ionic transport in other solid electrolytes. Our first-principles analysis of phase stability predicts that antiperovskite Li3OCl (Li3OBr) is metastable relative to Li2O and LiCl (LiBr) at room temperature. We also find that although the band gap of Li3OCl exceeds 5 eV, the metastable antiperovskite becomes susceptible to decomposition into Li2O2, LiCl and LiClO4 above an applied voltage of 2.5 V, suggesting that these compounds are most suited for low-voltage Li ...

Phase Stability and Transport Mechanisms in Antiperovskite Li3OCl and Li3OBr Superionic Conductors

Inhomogeneous magnetic fields generated by the BaFe12O19 ferromagnetic substrate create a magnetic template for superconducting condensate in the Nb/BaFe12O19 hybrids. Depending on the field and temperature, the magnetic template guides superconductivity to nucleate in different areas: above the magnetic domain walls of the BaFe12O19 forming the domain-wall superconductivity DWS , above the reversed magnetic domains RDS , and above the positive magnetic domains forming bulk superconductivity. The DWS, behaving as a superconducting wire network, survives in a broad field range. The RDS, existing in the form of isolated superconducting islands near the saturation field Hs of BaFe12O19, can be described as a twodimensional two-component random conductor mixture. Being related to the hysteretic domain evolution, superconducting condensate above the reversed domains shows pronounced switching behavior.

Modulation of superconductivity by a magnetic template in Nb/BaFe12O19 hybrids

Certain inventive aspects provide local field imaging with high spatial, time and field resolution by using an array of Hall effect sensors that can be individually read out. The design combines semiconductor Hall sensors and switches that isolate the addressed Hall sensor from the rest of the array. The compact design allows for large and very dense Hall sensor arrays that can be read out in a straightforward way.

Method and apparatus for detecting spatially varying and time-dependent magnetic fields

In this paper the magnetic field detection limits of microscopic Hall sensors are investigated as a function of their lateral size. Hall sensors fabricated from GaAs/AlGaAs heterostructures and silicon are experimentally investigated at different temperatures using Hall effect and noise spectrum measurements. At room temperature a clear size dependence of the detection limit is observed, whereas at low temperatures this dependence is found to disappear. The results are explained using the theory of noise in semiconductors.

Size dependence of microscopic Hall sensor detection limits.

We present direct observation of vortices confined to a superconducting $4\ifmmode\times\else\texttimes\fi{}4\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}{\mathrm{m}}^{2}$ square Pb film at $4.2\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ with a high resolution scanning Hall probe microscope. Integrals of the magnetic field penetrating the square as a function of the applied field show that an applied-field dependence of vorticity $L$ agrees with calculations based on the Ginzburg-Landau (GL) equation for a square sample geometry. From asymmetric field distribution of the confined magnetic flux, the locations of vortices on the square are inferred for vorticities $L=1--5$. The obtained vortex patterns are analogous with the calculations in the framework of the full GL equation for temperatures considerably lower than the superconducting transition temperature ${T}_{c}$.

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Scanning Hall probe microscopy of vortex patterns in a superconducting microsquare

Driven by a clear industrial need for advanced inspection equipment for high-end permanent magnets for drives, sensors, medical applications, consumer electronics and other applications, we present a new magnetic measurement technology, called a ‘magnetic field camera’, a powerful and unique measurement platform for fast and accurate live inspection of both uniaxial and multipole permanent magnets. It is based on high resolution - high speed 2D mapping of the magnetic field distribution, using a patented semiconductor chip with an integrated 2D array of over 16000 microscopic Hall sensors. The measured magnetic field maps are analyzed by powerful data analysis software which uses advanced algorithms to extract unprecedented magnet information from the MagCam measurements. All these quantitative magnet properties can be tested against user-defined quality tolerances for immediate and automated pass/fail or classification analyses, all in real time. The system can be remotely operated using standard industrial communication protocols for integration in production lines. Its applications include inspection of incoming magnets, automated inline magnet quality control and research and development of magnets and magnetic systems and more.

Koen Vervaeke

Papers

Modulation of superconductivity by a magnetic template in Nb/BaFe12O19 hybrids

Method and apparatus for detecting spatially varying and time-dependent magnetic fields

Size dependence of microscopic Hall sensor detection limits.

Scanning Hall probe microscopy of vortex patterns in a superconducting microsquare

Inline magnet inspection using fast high resolution MagCam magnetic field mapping and analysis