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arXiv2018

The differential build-up factor

The build-factor is a magnitude which allows to correct the photon exponential attenuation model to obtain the real value of a certain dosimetric magnitude, like air exposure. Its main weaknesses are the dependences on the response function of such a magnitude, the geometry, and the source directionality. A formalism to deal with the first is presented in this work, which leads to the definition of the differential build-up factor. Analog Monte Carlo calculations were used to calculate this factor, as well as describing its uncertainty, in the 30 keV to 10 MeV energy range for the most typical materials up to 10 mean-free-paths. Coherent scattering and binding effects were considered in the simulations, which make the results suitable for calculations with the most complete descriptions of the attenuation coefficients. Differences due to geometry, source directionality, and detector response variability were typically found to be up to 30 % in the studied range.

physics.app-ph↗

arXiv2021

A new method in the production of Ac-227, Ra-228, Th-228 and U-232 on Thorium target from different perspective for use in Radioisotope Power Systems and Nuclear Batteries

We recommended a new method from different perspective for the production of Ac-227, Ra-228, Th-228 and U-232 radioisotopes which have an important potential for use in radioisotope power systems (instead of Pu-238) and nuclear batteries, based on long half-life, high power density and low radiation level. In the method, the production of Ac-227, Ra-228, Th-228 and U-232 radioisotopes were performed by particle accelerators on Th-232 targets, instead of uranium, thorium, actinium series etc. in nuclear reactors. For this aim, to produce Ac-227, Ra-228, Th-228 and U-232 radioisotopes, we calculated cross-section and integral yields curves and simulated activities and yields of product for each reaction process under special conditions, such as during irradiation of 24 h in a particle beam current of 1 mA for the energy range of Eprojectile=1000-1 MeV. The obtained data were compared with experimental EXFOR database and theoretical TENDL database in detail. The cross-section, activity and yields results of each nuclear reaction process were analyzed and discussed in terms of the suitable production of Ac-227, Ra-228, Th-228 and U-232 radioisotopes.

nucl-ex↗

arXiv2018

Monitoring of laser metal deposition height by means of coaxial laser triangulation

Laser metal deposition (LMD) is an additive manufacturing technique, whose performances can be influenced by several factors and parameters. Monitoring their evolution allows for a better comprehension and control of the process, hence enhancing the deposition quality. In particular, the deposition height is an important variable that, if it does not match the process growth, can bring to defects and geometrical inaccuracies in the deposited structures. The current work presents a system based on optical triangulation for the height monitoring, implemented on a LMD setup composed of a fiber laser, a deposition head, and an anthropomorphic robot. Its coaxial and non-intrusive configuration allows for flexibility in the deposition strategy and direction. A measurement laser beam is launched through the powder nozzle and hits the melt pool. A coaxial camera acquires the probe spot, whose position is converted to relative height. The device has been demonstrated for monitoring the deposition of a stainless steel cylinder. The measurements allowed to reconstruct a spatial map of the height variation, highlighting a transient in the deposition growth which can be explained in terms of a self-regulating mechanism for the layer thickness.

physics.ins-det↗

arXiv2018

Excimer laser cleaning of black sulphur encrustation from silver surface

The process of localized cleaning of silver sulphide from the silver surface has been investigated in this work. An artificial black encrustation was generated on the silver surface and its laser cleaning was performed using an excimer laser (KrF based) working at a wavelength of 248 nm and pulse width 25 ns. Laser process parameters i.e. laser fluence and number of pulses were used to perform the experiment and after different optical, microstructural, elemental, microhardness and surface topography analysis of the laser ablated zone was performed. The parametric window selected for the excimer laser cleaning were laser fluence (200-400 mJ/cm2), repetition rate 4 Hz and number of pulses (60-300). It was observed that excimer laser is very effective in the cleaning of black encrustation having 6 wt. % of sulphur from the surface without any significant removal of the silver substrate. The fluence value of 260.48 mJ/cm2 was observed as above threshold value for removal of sulphide from the encrusted surface while a fluence of 384.85 mJ/cm2 and 220 pulses showed the maximum removal of sulphur encrustation (0.38 wt. % of sulphur remaining). Formation of the peripheral rim was observed to occur above 280.17 mJ/cm2 of fluence value. The topography of the ablated surface showed a removal of 5-10 um of the sulphide layer from the surface whereas the thickness of the sulphide coating was around 8-10 um. Microhardness value showed a change of microhardness of the silver surface from 75.12 HV0.5 (uncoated parent silver) to 96.07 HV0.5 (centre of the ablated zone).Finally, it was concluded that excimer laser cleaning is a novel method for localized removal of silver sulphide encrustation from silver surface.

physics.chem-ph↗

arXiv2018

Optical inspection of manufactured nanohole arrays to bridge the lab-industry gap

Metallic nanohole arrays have shown their potential as sensing tools. Important research supported by sophisticated laboratory experiments have been recently carried out, that may help to develop practical devices to be implemented in the real life. To get this goal, the gap between industry and technology at the nanoscale level must be overcome. One of the major drawbacks is the quality inspection of the manufactured nanostructured surfaces to ensure a reliable sensing. In this paper we introduce an optical method, based on the Extraordinary Optical Transmission phenomenon, for an inspection of such surfaces at industrial level. Unlike usual techniques like SEM, our method gives at the same time, a quick map of the surface homogeneity together with its local plasmonic performance. Our results show that this method is reproducible and reliable as to give a seal of identification and quality guarantee of the manufactured surface as basic element of a sensing device.

physics.app-ph↗

arXiv2017

The formation of polymer-dopant aggregates as a possible origin of limited doping efficiency at high dopant concentration

The polymer (PBDTTT-c) p-doped with the molecular dopant (Mo(tfd-COCF3)3) exhibits a decline in transport properties at high doping concentrations, which limits the performance attainable through organic semiconductor doping. Scanning Electron Microscopy is used to correlate the evolution of hole conductivity and hopping transport activation energy with the formation of aggregates in the layer. Transmission Electron Microscopy with energy-dispersive X-ray analysis along with liquid-state Nuclear Magnetic Resonance experiments are carried out to determine the composition of the aggregates. This study offers an explanation to the limited efficiency of doping at high dopant concentrations and reinforces the need to increase doping efficiency in order to be able to reduce the dopant concentration and not negatively affect conductivity.

physics.app-ph↗

arXiv2018

Design of nano-scale high static performance phase-change on-off silicon photonic switch

We report design of a high static performance on-off optical switch using nanoscale phase change material Ge2Sb2Te5 embedded into silicon-on-insulator waveguide. This active material can be switched between amorphous and crystalline states using electrical/optical pulses. The fundamental mode propagating through Silicon waveguide drastically alters its properties due to high index change at Si-Ge2Sb2Te5 interfaces and absorption in Ge2Sb2Te5. The optical switch made of Silicon waveguide with Ge2Sb2Te5 of volume 400 nm x 180 nm x 450 nm (length x height x width) embedded in to it, provides high extinction ratio of 43 dB with low insertion loss of 2.76 dB in ON state at communication wavelength of 1550 nm. There is trade-off between insertion loss and extinction ratio. For 10 dB extinction ratio, The insertion loss can be as low as 1.2 dB and corresponding active volume is also pretty low (100 nm x 150 nm x 450 nm (length x height x width)). Further, spectral response investigations reveal that this switch maintains extinction ratio more than 30 dB in wavelength span 1500-1600 nm. The high static performance of optical switch reported here is a direct result of proper dimensional engineering of active volume as well as its incorporation into the silicon-on-insulator waveguide. We also propose figure-of merit for non volatile optical switches that takes into account relevant parameters of static performance.

physics.app-ph↗

arXiv2018

Phononic Casimir corrections for Graphene resonator

By calculating a Casimir energy for the acoustic phonons of Graphene, we find some temperature-dependent corrections for the pretension of a Graphene sheet suspended on a trench. We obtain values of the order of few mN/m for these corrections in fully as well as doubly clamped Graphene on a narrow trench with one nanometer width, at room temperature. These values are considerable compared to the experimental values, and can increase the fundamental resonance frequency of the Graphene. The values of these corrections increase by increasing the temperature, and so they can be utilized for tuning the Graphene pretension.

cond-mat.mes-hall↗

arXiv2019

Interaction of Love waves with coupled cavity modes in a 2D holey phononic crystal

The interaction of Love waves with square array of pillars deposited on a cavity defined in a 2D holey phononic crystal is numerically investigated using Finite Element Method. First, the existence of SH surface modes is demonstrated separately for phononic crystals that consist of square arrayed holes, or rectangular arrayed Ni pillars, respectively in, or on, a SiO2 film deposited on a ST-cut quartz substrate. The coupling between SH modes and torsional mode in pillars induces a transmission dip that occurs at a frequency located in the range of the band-gap of the holey phononic crystal. Second, a cavity is constructed by removing lines of holes in the holey phononic crystal and results in a transmission peak that matches the dip. The optimal geometrical parameters enable us to create a coupling of the cavity mode and the localized pillar mode by introducing lines of pillars into the cavity, which significantly improved the efficiency of the cavity without increasing the crystal size. The obtained results will pave the way to implement advanced designs of high-performance electroacoustic sensors based on coupling modes in phononic crystals.

physics.app-ph↗

arXiv2018

Reconstruction methods for networks: the case of economic and financial systems

When studying social, economic and biological systems, one has often access to only limited information about the structure of the underlying networks. An example of paramount importance is provided by financial systems: information on the interconnections between financial institutions is privacy-protected, dramatically reducing the possibility of correctly estimating crucial systemic properties such as the resilience to the propagation of shocks. The need to compensate for the scarcity of data, while optimally employing the available information, has led to the birth of a research field known as network reconstruction. Since the latter has benefited from the contribution of researchers working in disciplines as different as mathematics, physics and economics, the results achieved so far are still scattered across heterogeneous publications. Most importantly, a systematic comparison of the network reconstruction methods proposed up to now is currently missing. This review aims at providing a unifying framework to present all these studies, mainly focusing on their application to economic and financial networks.

physics.soc-ph↗

arXiv2022

Quantum magnonics: when magnon spintronics meets quantum information science

Spintronics and quantum information science are two promising candidates for innovating information processing technologies. The combination of these two fields enables us to build solid-state platforms for studying quantum phenomena and for realizing multi-functional quantum tasks. For a long time, however, the intersection of these two fields was limited. This situation has changed significantly over the last few years because of the remarkable progress in coding and processing information using magnons. On the other hand, significant advances in understanding the entanglement of quasi-particles and in designing high-quality qubits and photonic cavities for quantum information processing provide physical platforms to integrate magnons with quantum systems. From these endeavours, the highly interdisciplinary field of quantum magnonics emerges, which combines spintronics, quantum optics and quantum information science.Here, we give an overview of the recent developments concerning the quantum states of magnons and their hybridization with mature quantum platforms. First, we review the basic concepts of magnons and quantum entanglement and discuss the generation and manipulation of quantum states of magnons, such as single-magnon states, squeezed states and quantum many-body states including Bose-Einstein condensation and the resulting spin superfluidity. We discuss how magnonic systems can be integrated and entangled with quantum platforms including cavity photons, superconducting qubits, nitrogen-vacancy centers, and phonons for coherent information transfer and collaborative information processing. The implications of these hybrid quantum systems for non-Hermitian physics and parity-time symmetry are highlighted, together with applications in quantum memories and high-precision measurements. Finally, we present an outlook on the opportunities in quantum magnonics.

quant-ph↗

arXiv2018

Precision manufacturing of a lightweight mirror body made by selective laser melting

This article presents a new and individual way to generate opto-mechanical components by Additive Manufacturing, embedded in an established process chain for the fabrication of metal optics. The freedom of design offered by additive techniques gives the opportunity to produce more lightweight parts with improved mechanical stability. The latter is demonstrated by simulations of several models of metal mirrors with a constant outer shape but varying mass reduction factors. The optimized lightweight mirror exhibits $63.5 \%$ of mass reduction and a higher stiffness compared to conventional designs, but it is not manufacturable by cutting techniques. Utilizing Selective Laser Melting instead, a demonstrator of the mentioned topological non-trivial design is manufactured out of AlSi12 alloy powder. It is further shown that -- like in case of a traditional manufactured mirror substrate -- optical quality can be achieved by diamond turning, electroless nickel plating, and polishing techniques, which finally results in $< 150$~nm peak-to-valley shape deviation and a roughness of $< 1$~nm rms in a measurement area of $140 \times 110$ $μ$m${}^2$. Negative implications from the additive manufacturing are shown to be negligible. Further it is shown that surface form is maintained over a two year storage period under ambient conditions.

physics.app-ph↗

arXiv2026

Effects of fuel and soot concentrations on the inception and development of contrails

Fundamental questions related to the roles of fuel type, combustion parameters, and turbulence transport interactions in the inception and growth of contrails have remained intractable in remote sensing and in-flight measurements. Consequently, we developed a novel laboratory-scale facility for studying the inception, growth and persistence of contrails for aircraft-relevant conditions. The set of exhaust conditions, generated using an inverted co-flow soot generator at a set of global equivalence ratio for two fuels - ethylene and propane, is supplied to the contrail tunnel which then mixes with an ambient flow emulating long-haul aircraft cruise conditions (\SI{20.8}{kPa} and \SI{190}{K}). Detailed soot characterization using a scanning mobility particle sizer and transmission electron microscopy is coupled with measurements of instantaneous and averaged scattering intensities from the generated contrails. The experimental results are complemented by numerical simulations of the contrail tunnel using solutions of the Favre-averaged Navier-Stokes (FANS) equation and a two-equation model for handling particulate matter, including soot and ice. Results show the first experimental snapshots of a contrail cross section, highlighting the interaction of turbulent mixing and microphysical growth scales involved in ice nucleation across the shear layers. As expected, the average scattering intensities of contrails increase with soot number concentrations and water vapor content. Comparisons between ethylene and propane exhausts indicate that the scattering propensity of contrails is more sensitive to exhaust water vapor content than to soot concentrations. Finally, depolarization measurements are used to show asphericity in ice crystal habits. Thus, our study present a unique window into contrail formation, theoretical modeling and simulation.

physics.flu-dyn↗

arXiv2019

Laser slicing: a thin film lift-off method for GaN-on-GaN technology

A femtosecond laser focused inside bulk GaN was used to slice a thin GaN film with an epitaxial device structure from a bulk GaN substrate. The demonstrated laser slicing lift-off process did not require any special release layers in the epitaxial structure. GaN film with a thickness of 5 $μ$m and an InGaN LED epitaxial device structure was lifted off a GaN substrate and transferred onto a copper substrate. The electroluminescence of the LED chip after the laser slicing lift-off was demonstrated.

physics.app-ph↗

arXiv2024

A new class of higher-order topological insulators that localize energy at arbitrary multiple sites

$\mathbb{Z}$-classified topological phases lead to larger-than-unity topological states. However, these multiple topological states are only localized at the corners in nonlocal systems. Here, first, we rigorously prove that the multiple topological states of nonlocal Su-Schrieffer-Heeger (SSH) chains can be inherited and realized by local aperiodic chains with only the nearest couplings. Then, we report a new class of higher-order topological insulators constructed with the local aperiodic chains, which can have any integer number of 0D topological states localized at arbitrary positions in the whole domain of the insulators, including within the bulk. The 0D topological states are protected by the local topological marker in each direction, instead of the bulk multipole chiral numbers in the existing work. Our work provides multiple combinations of localized corner-bulk topological states, which enables programmable lasers and sasers by selecting the excitation sites without altering the structure, and thus opens a new avenue to signal enhancement for computing and sensing.

cond-mat.mes-hall↗

arXiv2018

Large enhancement of sensitivity in NiFe/Pt/IrMn-based planar Hall sensors by modifying interface and sensor architecture

The planar Hall sensitivity of obliquely deposited NiFe(10)/Pt(tPt) /IrMn(8)/Pt(3) (nm) trilayer structures has been investigated by introducing interfacial modification and altering sensor geometry. The peak-to-peak PHE voltage and AMR ratio of the sensors exhibit an oscillatory increase as a function of Pt thickness. This behaviour was attributed to the strong electron spin-orbit scattering at the NiFe/Pt interface of the trilayers. The temperature-dependent PHE signal profiles reveal that the Pt-inserted PHE sensors are stable even at 390 K with a high signal-to-noise ratio and an increased sensitivity due to reduction of exchange bias. In order to further increase the sensitivity, we have fabricated PHE sensors for a fixed Pt thickness of 8 Å by using sensor architectures of a cross, tilted-cross, one-ring and five-ring junctions. We have obtained a sensitivity of 3.82 μV/Oe.mA for the cross junction, while it considerably increased to 298.5 μV/Oe.mA for five-ring sensor geometry. The real-time voltage profile of the PHE sensors demonstrate that the sensor states are very stable under various magnetic fields and sensor output voltages turn back to their initial offset values. This provides a great potential for the NiFe/Pt/IrMn-based planar Hall sensors in many sensing applications.

physics.app-ph↗

arXiv2018

Ultrasensitive and fast single wavelength plasmonic hydrogen sensing with anisotropic nanostructured Pd films

Anisotropic nanostructured porous Pd films are fabricated using oblique angle deposition in vacuum on a glass substrate. They display a dichroic response, due to localised surface plasmon resonances (LSPR) within the nanoparticles forming the film, dependent on the incident light polarisation. Ultrasensitive hydrogen sensing is reached by using these films in conjunction with a differential optical technique derived from the reflectance anisotropy spectroscopy. The evolution of the samples optical responses is monitored during the formation of Pd hydride in both the dilute alpha-phase and the dense beta-phase, whilst the samples are exposed to different concentration of H2 in Ar (from 100 percent H2 to a few ppm). The measurements are performed at a single wavelength in the visible range and at 22 deg C. The results show that a quantitative measurement of the hydrogen concentration in a carrier gas can be measured throughout the concentration range. The limit of detection is 10 ppm and the time for detecting the presence of H2 in the carrying gas is below one second at concentration down to 0.25 percent of H2 in Ar. Furthermore, the optical anisotropy of the samples and its evolution with exposure to H2 are correctly reproduced with an effective medium theory.

physics.chem-ph↗

arXiv2018

Electrochemical Sensing of Lead in Drinking Water Using MWCNTs and \b{eta}-Cyclodextrin

Heavy metal pollution is a severe environmental problem affecting many water resources. The non-biodegradable nature of the heavy metals such as lead (Pb) causes severe human health issues, so their cost-effective, sensitive and rapid detection is needed. In this work, we describe a simple, facile and low cost modifications of multiwalled carbon nanotubes (MWCNT) and \b{eta}-cyclodextrin (\b{eta}CD) through non-covalent/physical (Phys) and a covalent Steglich esterification (SE) approaches. The Phys modification approach resulted Pb detection with a limit-of-detection (LoD) of 0.9 ppb, while the SE approach showed an LoD of 2.3 ppb, both of which are well below the WHO Pb concentration guideline of 10 ppb. The MWCNT-\b{eta}CD (Phys) based electrodes show negligible interference with other common heavy metal ions such as Cd2+ and Zn2+. The MWCNT-\b{eta}CD based electrodes were of low-cost owing to their simple synthesis approaches, exhibited good selectivity and reusability. The proposed MWCNT-\b{eta}CD based electrodes is a promising technology in developing a highly affordable and sensitive electrochemical sensing system of Pb in drinking water.

physics.app-ph↗