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"PHYSICS, APPLIED"
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Wonders beyond numbers : a brief history of all things mathematical
Running in something approaching chronological order, this book shows that every breakthrough in math represents a single step forward, resting on the work of others, and brings to life the importance of numbers, shapes, and patterns in the world around us.
Book
On the strong coupling of polarization and charge trapping in HfO2/Si-based ferroelectric field-effect transistors: overview of device operation and reliability
Ferroelectric field-effect transistors (FeFETs) have become an attractive technology for memory and emerging applications on a silicon electronic platform after the discovery of the ferroelectric phase in silicon-friendly hafnium oxide insulators. In this tutorial, we review one nonideal physical phenomenon that determines the device operation of practical FeFETs based on ferroelectric hafnium oxide (FE-HfO
2
) insulators and silicon channels: polarization-induced electron trapping. The ferroelectric polarization in FE-HfO
2
induces an enormous amount of trapped electron density of an order of 10
14
cm
−2
near the interface between the FE-HfO
2
and interfacial layer, which in turn screens the electric flux from polarization. We examine how electron trapping affects the device operation particularly the polarization switching mechanism, retention characteristics, endurance characteristics, and read-after-write delay. The asymmetric behavior of electron and hole trapping in FeFETs and its impact on the device operation are also discussed. We review several approaches based on different operations, device structure modification, and material engineering to mitigate anomalous electron trapping and improve the device characteristics of FeFETs.
Journal Article
Mixture unified gradient theory: a consistent approach for mechanics of nanobars
The mixture unified gradient theory of elasticity is invoked for the meticulous assessment of peculiar size-dependent behavior of materials with nano-structural features. The size-dependency of the strain gradient theory and the stress gradient theory is consistently integrated with the classical continuum theory within a variational elasticity framework. The boundary-value problem associated with the dynamics of the nano-scale elastic bar is determined and enriched with the proper form of the extra non-standard boundary conditions. The constitutive model of the resultant fields is cast as differential relations in view of the stationarity of the proposed functional. The efficacy of the established generalized continuum theory in the accurate description of the size-effects at the ultra-small scale is put into evidence via electrostatic and elastodynamic analysis of nanobars. The nanoscopic characteristics of the wave dispersion are analytically addressed and appropriately compared with the counterpart experimental measurements. The elastostatic size-dependent behavior of nanobars is rigorously examined by applying an efficacious solution approach. Size-dependent elastostatic response of nanobars with kinematic constraints of interest in nano-mechanics are analytically determined and graphically illustrated. A promising approach to tackling the statics and dynamics of structural bar-type modules of advanced nano-systems is introduced.
Journal Article
Nanoporous adsorbents for hydrogen storage
Hydrogen storage in absorbents as activated carbons has been rarely investigated; however, about 25 years ago, the development of new nanomaterials, initiated by Iijima’s discovery of carbon microtubules, started new hopes. Unfortunately, initial results on high hydrogen uptake in carbon nanotubes at ambient conditions could not be independently reproduced; however, at cryogenic conditions, these novel nanomaterials just behaved as activated carbons with an uptake proportional to the surface area. Shortly after, the development of coordination polymers with permanent porosity opened a new route to nanoporous materials with ultra-high internal surfaces. Mainly metal–organic frameworks (MOFs) have been attracting a great deal of attention in recent years, as very high gravimetric hydrogen capacities can be achieved at 77 K. Cryogenic storage by physisorption of hydrogen molecules will safely operate at low pressures, is fully reversible, and possesses fast kinetics. This mini-review shows the rapid development in this field over the past 25 years. Exemplarily, the main focus is on results obtained in the hydrogen storage laboratory in Stuttgart and their connection to Applied Physics A.
Journal Article
Achievements and perspectives of optical fiber Fabry–Perot cavities
Fabry–Perot interferometers have stimulated numerous scientific and technical applications ranging from high-resolution spectroscopy over metrology, optical filters, to interfaces of light and matter at the quantum limit and more. End facet machining of optical fibers has enabled the miniaturization of optical Fabry–Perot cavities. Integration with fiber wave guide technology allows for small yet open devices with favorable scaling properties including mechanical stability and compact mode geometry. These fiber Fabry–Perot cavities (FFPCs) are stimulating extended applications in many fields including cavity quantum electrodynamics, optomechanics, sensing, nonlinear optics and more. Here we summarize the state of the art of devices based on FFPCs, provide an overview of applications and conclude with expected further research activities.
Journal Article
NbO2-based locally active memristors: from physical mechanisms to performance optimization
Negative differential resistance (NDR) characteristic in NbO
2
-based memristors endows them with the role of selectors, steep-slope transistors, or artificial neurons. However, the underlying microscopic mechanisms involved in electrical operation remain controversial. Meanwhile, the device performance of NbO
2
-based memristors is still unsatisfactory and needs to be further optimized to meet the demands of practical applications. In this article, we review the different types of mechanistic explanations and corresponding physical models for the NDR behavior of NbO
2
devices. The role of material-independent pure electronic conduction mechanism and material-specific insulator–metal transition in triggering the NDR behavior is overviewed. We discuss the pros and cons of NbO
2
-based memristors for selector or neuron applications, respectively. Moreover, starting from the microscopic mechanisms, we emphasize the optimization methods of the NbO
2
device’s critical properties, such as reducing the forming and switching voltages and improving the selectivity and uniformity. Also, the dilemma of co-optimizing the device’s forming voltage and selectivity is discussed. This review illustrates the underlying mechanisms of NDR behavior in NbO
2
-based local active memristors, pointing out the possible direction for device optimization and thus promoting the progress of practical applications.
Journal Article
Mechanisms for point defect-induced functionality in complex perovskite oxides
Perovskite oxides are an extremely versatile class of materials in which functionality can, besides other routes, also be engineered via the deliberate introduction of defects. In this focused review, we will specifically look at mechanistic details of ferroelectric and magnetic functionality introduced, altered, or reinforced by point defects. An ever-growing number of related studies start to provide a basis for the mechanistic understanding of different engineering routes to be exploited in future studies. Nevertheless, this review highlights that the effect of defects is not always easily predicted, given the delicate balance of lattice, charge, spin, and orbital degrees of freedom inherent to the perovskite structure. Systematic studies across various chemistries are thus still very much needed to obtain a more complete basis for defect-engineering ferroelectric and magnetic functionality in perovskite oxides.
Journal Article
Spectroscopic properties of Tb3+ as an ion for visible lasers
In recent years, Tb
3+
-based solid-state lasers with emission in the green and yellow have seen a revival. This was owed to the availability of blue emitting semiconductor-based pump sources and recent findings, which reported more than 60% slope efficiency in the green and about 25% slope efficiency in the yellow. In this paper we review the state of the art of Tb
3+
-based solid-state lasers. We summarize the spectroscopic properties and present new insights, which enable us to provide valuable guidelines and recommendations for the choice of host materials to further improve the performance of Tb
3+
-based solid-state lasers.
Journal Article
A first-principles study on the physical properties of two-dimensional Nb3Cl8, Nb3Br8 and Nb3I8
In a recent advance, Nb
3
Cl
8
two-dimensional crystals with a kagome lattice and electronic topological flat bands have been experimentally fabricated (Sun et al. in Nano Lett 22:4596–4602, 2022). In this work motivated by the aforementioned progress, we conduct first-principles calculations to explore the structural, phonon dispersion relations, single-layer exfoliation energies and mechanical features of the Nb
3
X
8
(
X
= Cl, Br, I) nanosheets. Acquired phonon dispersion relations reveal the dynamical stability of the Nb
3
X
8
(
X
= Cl, Br, I) monolayers. To isolate single-layer crystals from bulk counterparts, we predicted exfoliation energies of 0.24, 0.27 and 0.28 J/m
2
, for the Nb
3
Cl
8
, Nb
3
Br
8
and Nb
3
I
8
monolayers, respectively, which are noticeably lower than that of the graphene. We found that the Nb
3
X
8
monolayers are relatively strong nanosheets with isotropic elasticity and anisotropic tensile strength. It is moreover shown that by increasing the atomic weight of halogen atoms in the Nb
3
X
8
nanosheets, mechanical characteristics decline. Presented results provide a useful vision about the key physical properties of novel 2D systems of Nb
3
X
8
(
X
= Cl, Br, I).
Journal Article
High-power, high-brightness solid-state laser architectures and their characteristics
The development of high-power diode lasers enabled new solid-state laser concepts such as thin-disk, fiber, and Innoslab lasers based on trivalent ytterbium as the laser-active ion, which resulted in a tremendous increase in the efficiency and beam quality of cw lasers compared to previously used lamp-pumped rod or slab lasers and the realization of ultrafast lasers with several 100 W or even kilowatts of average power. In addition to their beneficial thermo-optical properties, these architectures offer characteristic benefits making them especially suitable to obtain dedicated laser properties. This review article comprises milestone developments, characteristic challenges, and benefits, and summarizes the state of the art of high-power solid-state lasers with the focus on ultrafast lasers.
Journal Article