Debdutta Lahiri - Academia.edu (original) (raw)
Papers by Debdutta Lahiri
We have investigated the short-range-order of Zr69.5Cu12Ni11Al7.5, Zr41.5Ti41.5Ni17 and Zr67Ni33 ... more We have investigated the short-range-order of Zr69.5Cu12Ni11Al7.5, Zr41.5Ti41.5Ni17 and Zr67Ni33 metallic glasses, using X-ray absorption spectroscopy and ab-initio molecular dynamics simulations. The glass-forming-abilities of these alloys degrade as: Zr41.5Ti41.5Ni17 > Zr69.5Cu12Ni11Al7.5 > Zr67Ni33. While superior glass formation ability of the multi-component alloys is understandable from confusion principle, better glass formation ability of Zr41.5Ti41.5Ni17 than Zr69.5Cu12Ni11Al7.5 is paradoxical from confusion viewpoint. We resolve this paradox by quantitatively assessing the relative importance of icosahedral content, configuration diversity, intra-cluster disorder and chemical interaction in these three systems. Our results establish that large difference in these parameters exists 1 Corresponding author. Tel.: + 91 22 2559 2991; fax: + 91 22 2550 5296 Email address: dlahiri@barc.gov.in; debduttalahiri@yahoo.com (D. Lahiri) *Manuscript Click here to view linked Refere...
Journal of Synchrotron Radiation, 2020
The static focusing optics of the existing energy-dispersive XAFS beamline BL-8 have been advanta... more The static focusing optics of the existing energy-dispersive XAFS beamline BL-8 have been advantageously exploited to initiate diamond anvil cell based high-pressure XANES experiments at the Indus-2 synchrotron facility, India. In the framework of the limited photon statistics with the 2.5 GeV bending-magnet source, limited focusing optics and 4 mm-thick diamond windows of the sample cell, a (non-trivial) beamline alignment method for maximizing photon statistics at the sample position has been designed. Key strategies include the selection of a high X-ray energy edge, the truncation of the smallest achievable focal spot size to target size with a slit and optimization of the horizontal slit position for transmission of the desired energy band. A motor-scanning program for precise sample centering has been developed. These details are presented with rationalization for every step. With these strategies, Nb K-edge XANES spectra for Nb2O5 under high pressure (0–16.9 GPa) have been gen...
Materials Research Express, 2018
Practical utilization of room temperature multiferroic BiFeO3 is intrinsically limited by the abs... more Practical utilization of room temperature multiferroic BiFeO3 is intrinsically limited by the absence of ferromagnetism. In this backdrop, development of weak ferromagnetism in 20 nm-sized BiFeO3 nanoparticles is very optimistic. The origin of ferromagnetism is curious and paradoxical from long-range-order perspective since average superexchange angle Fe–O–Fe of the nanoparticle is in antiferromagnetic configuration. In this work, we resolve this paradox by establishing the beneficial role of local disorder with x-ray absorption spectroscopy. We distinguish between the natures of (Bi, Fe)-sublattice disorder and establish their correlation that eventually leads to ferromagnetism. Our results reveal intrinsic large Bi positional disorder, which may be attributed to 6s2 lone pair activity of Bi atom and which leads to greater susceptibility of Bi-sublattice to modification during size reduction. Thus, local (BiO6, FeO6) units are observed to undergo large distortion and rotation respectively. We demonstrate with calculations that FeO6 rotation is geometric consequence of BiO6 distortion. In the case of our BiFeO3 nanoparticles, experimental BiO6 disorder induces FeO6 rotation that drives Fe–O–Fe into ferromagnetic configuration. These local ferromagnetic units give rise to weak magnetism. This structural route to magnetism in BiFeO3 can be generalized to encourage A-site disorder controlled magnetism or any functional octahedral rotation in ABO3 perovsites. The results additionally propagate the effectiveness of particle size-dependence in generating A-site strain rather than chemical doping or external pressure.
![Research paper thumbnail of Understanding temperature and magnetic-field actuated magnetization polarity reversal in the Prussian blue analogue Cu0.73Mn0.77[Fe(CN)6].zH2O, using XMCD](https://attachments.academia-assets.com/111883212/thumbnails/1.jpg)
](Materials Research Express, 2016
We have investigated the microscopic origin of temperature and magnetic-field actuated magnetizat... more We have investigated the microscopic origin of temperature and magnetic-field actuated magnetization reversal in Cu 0. 73 Mn 0.77 [Fe(CN) 6 ].zH 2 O, using XMCD. Our results show a fair deviation from the mean-field-theory in the form of different ordering temperatures of Fe and Mn sublattices. A preferential sign reversal of Mn spin under magnetic field and different spin cant angles for the two sublattices have also been observed. An antiferromagnetic coupling between the Fe and Mn sublattices along with different ordering temperatures (sublattice decoupling) for these sublattices explain the temperature-dependent magnetization reversal. Whereas, Mn spin reversal alone (under external magnetic field) is responsible for the observed field-dependent magnetization reversal. The dissimilar magnetic behavior of Fe and Mn sublattices in this cubic 3d-orbital system has been understood by invoking disparity and competition among inter-sublattice magnetic control parameters, viz. magnetic Zeeman energy, exchange coupling constant and magnetic anisotropy constant. Our results have significant design implications for future magnetic switches, by optimizing the competition among these magnetic control parameters.
Journal of Synchrotron Radiation, 2015
XANES- and EXAFS-based analysis of the Ayurvedic Hg-based nano-drugRasasindurahas been performed ... more XANES- and EXAFS-based analysis of the Ayurvedic Hg-based nano-drugRasasindurahas been performed to seek evidence of its non-toxicity.Rasasindurais determined to be composed of single-phase α-HgS nanoparticles (size ∼24 nm), free of Hg0or organic molecules; its structure is determined to be robust (<3% defects). The non-existence of Hg0implies the absence of Hg-based toxicity and establishes that chemical form, rather than content of heavy metals, is the correct parameter for evaluating the toxicity in these drugs. The stable α-HgS form (strong Hg—S covalent bond and robust particle character) ensures the integrity of the drug during delivery and prevention of its reduction to Hg0within the human body. Further, these comparative studies establish that structural parameters (size dispersion, coordination configuration) are better controlled inRasasindura. This places the Ayurvedic synthesis method on par with contemporary techniques of nanoparticle synthesis.
Journal of Optics, 2015
In this work, we report the first-phase commissioning of High Pressure setup at XAFS beamline (Bl... more In this work, we report the first-phase commissioning of High Pressure setup at XAFS beamline (Bl-08) of Indus-2. This involved installation of vertically focusing bendable elliptical mirror to obtain~50 μm spot size, as required for Diamond Anvil Cell-based High Pressure XAFS experiment. We present details of the mirror alignment procedure, observed deviations from design goals and suggestions for improvement. We provide realistic estimate of the kind of experiments that can be performed in the current setup.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2015
In this work, we report installation of displex cryostat XAFS sample holder at XAFS beamline (BL-... more In this work, we report installation of displex cryostat XAFS sample holder at XAFS beamline (BL-09) of Indus-2 synchrotron facility, India and make critical assessment of feasibility of low-temperature XAFS experiments in terms of data quality and reproducibility, temperature range, calibration and attainable resolution. We adopted the Debye Model-based calibration method by measuring XAFS of standard Au foil with known Debye temperature ðΘ Debye Þ theory Au ¼ 165 K. The data is of good quality and reproducible with international data. By fitting Debye Waller Factor (σ 2 expt ðTÞ), we deduced ðΘ Debye Þ expt Au ¼ 163 K which implies calibration within 2 K. Error bars for σ 2 expt ðTÞ correspond to temperature uncertainty ΔT r 5 K, which defines the temperature resolution for low temperature XAFS experiments. Thus, from both calibration and resolution points-of-view, this work demonstrates the feasibility of low temperature XAFS experiments at BL-09, Indus-2. Feasibility of extending XAFS experiments to lower temperature and unknown samples is discussed.
Journal of Synchrotron Radiation, 2014
Short-range order has been investigated in Zr69.5Cu12Ni11Al7.5and Zr41.5Ti41.5Ni17metallic glasse... more Short-range order has been investigated in Zr69.5Cu12Ni11Al7.5and Zr41.5Ti41.5Ni17metallic glasses using X-ray absorption spectroscopy andab initiomolecular dynamics simulations. While both of these alloys are good glass formers, there is a difference in their glass-forming abilities (Zr41.5Ti41.5Ni17> Zr69.5Cu12Ni11Al7.5). This difference is explained by inciting the relative importance of strong chemical order, icosahedral content, cluster symmetry and configuration diversity.
The Journal of Physical Chemistry B, 2003
Aqueous solutions of Ag-Pt ions and poly(vinyl alcohol) were irradiated with gamma rays at dose r... more Aqueous solutions of Ag-Pt ions and poly(vinyl alcohol) were irradiated with gamma rays at dose rates below 0.5 kGy/h to generate nanoparticles. The nanoparticles were characterized with several experimental techniques. Transmission electron microscopy showed that, surprisingly, the nanoparticles were not spherical but had a high aspect ratio. Wirelike structures were generated with lengths up to 3.5 µm and diameters between 3 and 20 nm. Selected-area diffraction showed that the wires were polycrystalline and that individual grains making up the wires had a face-centered cubic (fcc) structure. The optical absorption of samples, with a Ag/Pt mole ratio higher than 80%, exhibited a Ag surface plasmon absorption band centered around 400 nm. The plasmon band broadened with increasing Pt molar ratio and was replaced by a monotonically decaying background for a Pt molar ratio higher than about 30%. Alloying in the Ag-Pt nanoparticles was investigated with X-ray absorption spectroscopy. The Pt L 3 edge (11.564 keV) was excited to determine the local structure around the Pt atoms. A contraction in the first shell of 0.05 Å was observed, which ruled out the formation of a Ag-Pt homogeneous alloy and suggested the formation of core-shell particles. To understand the mechanism of formation of the nanoparticles, several experimental parameters such as the total radiation dose, type of polymer, metal and polymer concentrations, and type of counterions in solution were varied. The most relevant parameters inducing filament growth were the counterions added to the solution, the mole ratio between the two metals, and the capping polymer. For example, spherical particles resulted if AgNO 3 was used instead of Ag 2 SO 4 , if the Ag/Pt mole ratio was higher than 80% or lower than 20%, and if the degree of hydrolysis of the poly(vinyl alcohol) was higher than 98%.
Physica Scripta, 2005
The quantum physics of light is a most fascinating field. Here I present a very personal viewpoin... more The quantum physics of light is a most fascinating field. Here I present a very personal viewpoint, focusing on my own path to quantum entanglement and then on to applications. I have been fascinated by quantum physics ever since I heard about it for the first time in school. The theory struck me immediately for two reasons: (1) its immense mathematical beauty, and (2) the unparalleled precision to which its predictions have been verified again and again. Particularly fascinating for me were the predictions of quantum mechanics for individual particles, individual quantum systems. Surprisingly, the experimental realization of many of these fundamental phenomena has led to novel ideas for applications. Starting from my early experiments with neutrons, I later became interested in quantum entanglement, initially focusing on multi-particle entanglement like GHZ states. This work opened the experimental possibility to do quantum teleportation and quantum hyper-dense coding. The latter became the first entanglement-based quantum experiment breaking a classical limitation. One of the most fascinating phenomena is entanglement swapping, the teleportation of an entangled state. This phenomenon is fundamentally interesting because it can entangle two pairs of particles which do not share any common past. Surprisingly, it also became an important ingredient in a number of applications, including quantum repeaters which will connect future quantum computers with each other. Another application is entanglement-based quantum cryptography where I present some recent long-distance experiments. Entanglement swapping has also been applied in very recent so-called loophole-free tests of Bell's theorem. Within the physics community such loophole-free experiments are perceived as providing nearly definitive proof that local realism is untenable. While, out of principle, local realism can never be excluded entirely, the 2015 achievements narrow down the remaining possibilities for local realistic explanations of the quantum phenomenon of entanglement in a significant way. These experiments may go down in the history books of science. Future experiments will address particularly the freedom-of-choice loophole using cosmic sources of randomness. Such experiments confirm that unconditionally secure quantum cryptography is possible, since quantum cryptography based on Bell's theorem can provide unconditional security. The fact that the experiments were loophole-free proves that an eavesdropper cannot avoid detection in an experiment that correctly follows the protocol. I finally discuss some recent experiments with single-and entangled-photon states in higher dimensions. Such experiments realized quantum entanglement between two photons, each with quantum numbers beyond 10 000 and also simultaneous entanglement of two photons where each carries more than 100 dimensions. Thus they offer the possibility of quantum communication with more than one bit or qubit per photon. The paper concludes discussing Einstein's contributions and viewpoints of quantum mechanics. Even if some of his positions are not supported by recent experiments, he has to be given credit for the fact that his analysis of fundamental issues gave rise to developments which led to a new information technology. Finally, I reflect on some of the lessons learned by the fact that Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
Materials Research Bulletin, 2007
SnO 2 and 5 at.% V doped SnO 2 samples were prepared by citrate-gel method. From Raman study on v... more SnO 2 and 5 at.% V doped SnO 2 samples were prepared by citrate-gel method. From Raman study on vanadium doped SnO 2 , the existence of phase separated V 2 O 5 clusters has been established. EPR study on the V doped sample clearly revealed the existence of V 4+ ...
Journal of Synchrotron Radiation, 2012
In this work nanoclusters formed in a Pt/Ni/C multi-trilayer by the ion-irradiated method of synt... more In this work nanoclusters formed in a Pt/Ni/C multi-trilayer by the ion-irradiated method of synthesis are characterized. In particular, an attempt to understand the role of interfaces in the synthesis is made. With this objective, ion-irradiation-induced structural changes in a Pt/Ni/C multi-trilayer using X-ray absorption spectroscopy (at the NiK-edge) in conjunction with the X-ray standing-wave technique are investigated. The XANES analysis identifies chemical binding at pristine Ni/C and Ni/Pt interfaces, in contrast with physical adsorption at the Pt/C interface. The chemical nature of the interfaces determines their relative stability with respect to irradiation and controls the extent of metallic diffusion. The most interesting structural change, upon irradiation, is the disruption of the Pt/C interface and subsequent migration of Pt atoms towards pre-diffused Ni atoms within the C layer, leading to the formation of Ni-centered Ni–Pt bimetallic nanoclusters (with Ni:Pt = 60:4...
Journal of Physics: Condensed Matter, 2012
Journal of Physics: Conference Series, 2009
Journal of Physics: Conference Series, 2013
We employ XSW assisted XAFS at Ni K edge to characterize ion-irradiated Pt/Ni/C multilayer, parti... more We employ XSW assisted XAFS at Ni K edge to characterize ion-irradiated Pt/Ni/C multilayer, particularly the nanoclusters formed within C layer, revealed by X-TEM and angleresolved fluorescence studies. Retrieving the structural model from XAFS coordination results involved intriguing steps such as accounting for the intensity variation across the layers, determination of extra pre-diffused Ni into C layer (beyond the reflectivity determined roughness) and decoupling interfacial, layer and cluster coordination. The clusters are determined to be Ni centered Ni-Pt bimetallic nanoclusters (Ni:Pt = 60:40), formed due to irradiation induced diffusion of Pt atoms from the disrupted Pt/C interface towards prediffused Ni atoms present in C layer. They are highly disordered beyond nearest neighbor and resemble glassy structure which could find wide-scale applications in magnetic devices.
Journal of Physics: Conference Series, 2013
Magnetic compensation (zero-moment) has important advantage in spintronics as it does not generat... more Magnetic compensation (zero-moment) has important advantage in spintronics as it does not generate any self stray magnetic field. The physics of magnetic compensation (at a well defined temperature T comp) is well understood in terms of competition and compensation between antiferromagnetically coupled magnetic moments of two rare earth ions. The different thermal evolution of the dissimilar rare earth moments can compensate each other at a particular temperature determined by the concentration of the dopant. We have observed, for the first ever time, "repeated" magnetic compensation in both polycrystalline and single crystals of Nd 0. 8 Tb 0.2 Al 2 (T f1 ~ 86 K and T f2 ~ 34 K). A possible reason could be the nonrandom distribution of magnetic rare earth ions on different crystallographic sites, presenting deviation from mean field like situation. The motivation for XAFS derives from detection of these circumstances. XAFS at Nd, Tb L 3 edges reveals that 25% (Nd,Al) anti-site defect exists in Nd 0. 8 Tb 0.2 Al 2. This implies that Nd atoms occupy two different sites. In contrast, Tb preferentially substitutes only one of the Nd sites. The implication of these results upon magnetic compensation is discussed.
We have investigated the short-range-order of Zr69.5Cu12Ni11Al7.5, Zr41.5Ti41.5Ni17 and Zr67Ni33 ... more We have investigated the short-range-order of Zr69.5Cu12Ni11Al7.5, Zr41.5Ti41.5Ni17 and Zr67Ni33 metallic glasses, using X-ray absorption spectroscopy and ab-initio molecular dynamics simulations. The glass-forming-abilities of these alloys degrade as: Zr41.5Ti41.5Ni17 > Zr69.5Cu12Ni11Al7.5 > Zr67Ni33. While superior glass formation ability of the multi-component alloys is understandable from confusion principle, better glass formation ability of Zr41.5Ti41.5Ni17 than Zr69.5Cu12Ni11Al7.5 is paradoxical from confusion viewpoint. We resolve this paradox by quantitatively assessing the relative importance of icosahedral content, configuration diversity, intra-cluster disorder and chemical interaction in these three systems. Our results establish that large difference in these parameters exists 1 Corresponding author. Tel.: + 91 22 2559 2991; fax: + 91 22 2550 5296 Email address: dlahiri@barc.gov.in; debduttalahiri@yahoo.com (D. Lahiri) *Manuscript Click here to view linked Refere...
Journal of Synchrotron Radiation, 2020
The static focusing optics of the existing energy-dispersive XAFS beamline BL-8 have been advanta... more The static focusing optics of the existing energy-dispersive XAFS beamline BL-8 have been advantageously exploited to initiate diamond anvil cell based high-pressure XANES experiments at the Indus-2 synchrotron facility, India. In the framework of the limited photon statistics with the 2.5 GeV bending-magnet source, limited focusing optics and 4 mm-thick diamond windows of the sample cell, a (non-trivial) beamline alignment method for maximizing photon statistics at the sample position has been designed. Key strategies include the selection of a high X-ray energy edge, the truncation of the smallest achievable focal spot size to target size with a slit and optimization of the horizontal slit position for transmission of the desired energy band. A motor-scanning program for precise sample centering has been developed. These details are presented with rationalization for every step. With these strategies, Nb K-edge XANES spectra for Nb2O5 under high pressure (0–16.9 GPa) have been gen...
Materials Research Express, 2018
Practical utilization of room temperature multiferroic BiFeO3 is intrinsically limited by the abs... more Practical utilization of room temperature multiferroic BiFeO3 is intrinsically limited by the absence of ferromagnetism. In this backdrop, development of weak ferromagnetism in 20 nm-sized BiFeO3 nanoparticles is very optimistic. The origin of ferromagnetism is curious and paradoxical from long-range-order perspective since average superexchange angle Fe–O–Fe of the nanoparticle is in antiferromagnetic configuration. In this work, we resolve this paradox by establishing the beneficial role of local disorder with x-ray absorption spectroscopy. We distinguish between the natures of (Bi, Fe)-sublattice disorder and establish their correlation that eventually leads to ferromagnetism. Our results reveal intrinsic large Bi positional disorder, which may be attributed to 6s2 lone pair activity of Bi atom and which leads to greater susceptibility of Bi-sublattice to modification during size reduction. Thus, local (BiO6, FeO6) units are observed to undergo large distortion and rotation respectively. We demonstrate with calculations that FeO6 rotation is geometric consequence of BiO6 distortion. In the case of our BiFeO3 nanoparticles, experimental BiO6 disorder induces FeO6 rotation that drives Fe–O–Fe into ferromagnetic configuration. These local ferromagnetic units give rise to weak magnetism. This structural route to magnetism in BiFeO3 can be generalized to encourage A-site disorder controlled magnetism or any functional octahedral rotation in ABO3 perovsites. The results additionally propagate the effectiveness of particle size-dependence in generating A-site strain rather than chemical doping or external pressure.
Materials Research Express, 2016
We have investigated the microscopic origin of temperature and magnetic-field actuated magnetizat... more We have investigated the microscopic origin of temperature and magnetic-field actuated magnetization reversal in Cu 0. 73 Mn 0.77 [Fe(CN) 6 ].zH 2 O, using XMCD. Our results show a fair deviation from the mean-field-theory in the form of different ordering temperatures of Fe and Mn sublattices. A preferential sign reversal of Mn spin under magnetic field and different spin cant angles for the two sublattices have also been observed. An antiferromagnetic coupling between the Fe and Mn sublattices along with different ordering temperatures (sublattice decoupling) for these sublattices explain the temperature-dependent magnetization reversal. Whereas, Mn spin reversal alone (under external magnetic field) is responsible for the observed field-dependent magnetization reversal. The dissimilar magnetic behavior of Fe and Mn sublattices in this cubic 3d-orbital system has been understood by invoking disparity and competition among inter-sublattice magnetic control parameters, viz. magnetic Zeeman energy, exchange coupling constant and magnetic anisotropy constant. Our results have significant design implications for future magnetic switches, by optimizing the competition among these magnetic control parameters.
Journal of Synchrotron Radiation, 2015
XANES- and EXAFS-based analysis of the Ayurvedic Hg-based nano-drugRasasindurahas been performed ... more XANES- and EXAFS-based analysis of the Ayurvedic Hg-based nano-drugRasasindurahas been performed to seek evidence of its non-toxicity.Rasasindurais determined to be composed of single-phase α-HgS nanoparticles (size ∼24 nm), free of Hg0or organic molecules; its structure is determined to be robust (<3% defects). The non-existence of Hg0implies the absence of Hg-based toxicity and establishes that chemical form, rather than content of heavy metals, is the correct parameter for evaluating the toxicity in these drugs. The stable α-HgS form (strong Hg—S covalent bond and robust particle character) ensures the integrity of the drug during delivery and prevention of its reduction to Hg0within the human body. Further, these comparative studies establish that structural parameters (size dispersion, coordination configuration) are better controlled inRasasindura. This places the Ayurvedic synthesis method on par with contemporary techniques of nanoparticle synthesis.
Journal of Optics, 2015
In this work, we report the first-phase commissioning of High Pressure setup at XAFS beamline (Bl... more In this work, we report the first-phase commissioning of High Pressure setup at XAFS beamline (Bl-08) of Indus-2. This involved installation of vertically focusing bendable elliptical mirror to obtain~50 μm spot size, as required for Diamond Anvil Cell-based High Pressure XAFS experiment. We present details of the mirror alignment procedure, observed deviations from design goals and suggestions for improvement. We provide realistic estimate of the kind of experiments that can be performed in the current setup.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2015
In this work, we report installation of displex cryostat XAFS sample holder at XAFS beamline (BL-... more In this work, we report installation of displex cryostat XAFS sample holder at XAFS beamline (BL-09) of Indus-2 synchrotron facility, India and make critical assessment of feasibility of low-temperature XAFS experiments in terms of data quality and reproducibility, temperature range, calibration and attainable resolution. We adopted the Debye Model-based calibration method by measuring XAFS of standard Au foil with known Debye temperature ðΘ Debye Þ theory Au ¼ 165 K. The data is of good quality and reproducible with international data. By fitting Debye Waller Factor (σ 2 expt ðTÞ), we deduced ðΘ Debye Þ expt Au ¼ 163 K which implies calibration within 2 K. Error bars for σ 2 expt ðTÞ correspond to temperature uncertainty ΔT r 5 K, which defines the temperature resolution for low temperature XAFS experiments. Thus, from both calibration and resolution points-of-view, this work demonstrates the feasibility of low temperature XAFS experiments at BL-09, Indus-2. Feasibility of extending XAFS experiments to lower temperature and unknown samples is discussed.
Journal of Synchrotron Radiation, 2014
Short-range order has been investigated in Zr69.5Cu12Ni11Al7.5and Zr41.5Ti41.5Ni17metallic glasse... more Short-range order has been investigated in Zr69.5Cu12Ni11Al7.5and Zr41.5Ti41.5Ni17metallic glasses using X-ray absorption spectroscopy andab initiomolecular dynamics simulations. While both of these alloys are good glass formers, there is a difference in their glass-forming abilities (Zr41.5Ti41.5Ni17> Zr69.5Cu12Ni11Al7.5). This difference is explained by inciting the relative importance of strong chemical order, icosahedral content, cluster symmetry and configuration diversity.
The Journal of Physical Chemistry B, 2003
Aqueous solutions of Ag-Pt ions and poly(vinyl alcohol) were irradiated with gamma rays at dose r... more Aqueous solutions of Ag-Pt ions and poly(vinyl alcohol) were irradiated with gamma rays at dose rates below 0.5 kGy/h to generate nanoparticles. The nanoparticles were characterized with several experimental techniques. Transmission electron microscopy showed that, surprisingly, the nanoparticles were not spherical but had a high aspect ratio. Wirelike structures were generated with lengths up to 3.5 µm and diameters between 3 and 20 nm. Selected-area diffraction showed that the wires were polycrystalline and that individual grains making up the wires had a face-centered cubic (fcc) structure. The optical absorption of samples, with a Ag/Pt mole ratio higher than 80%, exhibited a Ag surface plasmon absorption band centered around 400 nm. The plasmon band broadened with increasing Pt molar ratio and was replaced by a monotonically decaying background for a Pt molar ratio higher than about 30%. Alloying in the Ag-Pt nanoparticles was investigated with X-ray absorption spectroscopy. The Pt L 3 edge (11.564 keV) was excited to determine the local structure around the Pt atoms. A contraction in the first shell of 0.05 Å was observed, which ruled out the formation of a Ag-Pt homogeneous alloy and suggested the formation of core-shell particles. To understand the mechanism of formation of the nanoparticles, several experimental parameters such as the total radiation dose, type of polymer, metal and polymer concentrations, and type of counterions in solution were varied. The most relevant parameters inducing filament growth were the counterions added to the solution, the mole ratio between the two metals, and the capping polymer. For example, spherical particles resulted if AgNO 3 was used instead of Ag 2 SO 4 , if the Ag/Pt mole ratio was higher than 80% or lower than 20%, and if the degree of hydrolysis of the poly(vinyl alcohol) was higher than 98%.
Physica Scripta, 2005
The quantum physics of light is a most fascinating field. Here I present a very personal viewpoin... more The quantum physics of light is a most fascinating field. Here I present a very personal viewpoint, focusing on my own path to quantum entanglement and then on to applications. I have been fascinated by quantum physics ever since I heard about it for the first time in school. The theory struck me immediately for two reasons: (1) its immense mathematical beauty, and (2) the unparalleled precision to which its predictions have been verified again and again. Particularly fascinating for me were the predictions of quantum mechanics for individual particles, individual quantum systems. Surprisingly, the experimental realization of many of these fundamental phenomena has led to novel ideas for applications. Starting from my early experiments with neutrons, I later became interested in quantum entanglement, initially focusing on multi-particle entanglement like GHZ states. This work opened the experimental possibility to do quantum teleportation and quantum hyper-dense coding. The latter became the first entanglement-based quantum experiment breaking a classical limitation. One of the most fascinating phenomena is entanglement swapping, the teleportation of an entangled state. This phenomenon is fundamentally interesting because it can entangle two pairs of particles which do not share any common past. Surprisingly, it also became an important ingredient in a number of applications, including quantum repeaters which will connect future quantum computers with each other. Another application is entanglement-based quantum cryptography where I present some recent long-distance experiments. Entanglement swapping has also been applied in very recent so-called loophole-free tests of Bell's theorem. Within the physics community such loophole-free experiments are perceived as providing nearly definitive proof that local realism is untenable. While, out of principle, local realism can never be excluded entirely, the 2015 achievements narrow down the remaining possibilities for local realistic explanations of the quantum phenomenon of entanglement in a significant way. These experiments may go down in the history books of science. Future experiments will address particularly the freedom-of-choice loophole using cosmic sources of randomness. Such experiments confirm that unconditionally secure quantum cryptography is possible, since quantum cryptography based on Bell's theorem can provide unconditional security. The fact that the experiments were loophole-free proves that an eavesdropper cannot avoid detection in an experiment that correctly follows the protocol. I finally discuss some recent experiments with single-and entangled-photon states in higher dimensions. Such experiments realized quantum entanglement between two photons, each with quantum numbers beyond 10 000 and also simultaneous entanglement of two photons where each carries more than 100 dimensions. Thus they offer the possibility of quantum communication with more than one bit or qubit per photon. The paper concludes discussing Einstein's contributions and viewpoints of quantum mechanics. Even if some of his positions are not supported by recent experiments, he has to be given credit for the fact that his analysis of fundamental issues gave rise to developments which led to a new information technology. Finally, I reflect on some of the lessons learned by the fact that Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
Materials Research Bulletin, 2007
SnO 2 and 5 at.% V doped SnO 2 samples were prepared by citrate-gel method. From Raman study on v... more SnO 2 and 5 at.% V doped SnO 2 samples were prepared by citrate-gel method. From Raman study on vanadium doped SnO 2 , the existence of phase separated V 2 O 5 clusters has been established. EPR study on the V doped sample clearly revealed the existence of V 4+ ...
Journal of Synchrotron Radiation, 2012
In this work nanoclusters formed in a Pt/Ni/C multi-trilayer by the ion-irradiated method of synt... more In this work nanoclusters formed in a Pt/Ni/C multi-trilayer by the ion-irradiated method of synthesis are characterized. In particular, an attempt to understand the role of interfaces in the synthesis is made. With this objective, ion-irradiation-induced structural changes in a Pt/Ni/C multi-trilayer using X-ray absorption spectroscopy (at the NiK-edge) in conjunction with the X-ray standing-wave technique are investigated. The XANES analysis identifies chemical binding at pristine Ni/C and Ni/Pt interfaces, in contrast with physical adsorption at the Pt/C interface. The chemical nature of the interfaces determines their relative stability with respect to irradiation and controls the extent of metallic diffusion. The most interesting structural change, upon irradiation, is the disruption of the Pt/C interface and subsequent migration of Pt atoms towards pre-diffused Ni atoms within the C layer, leading to the formation of Ni-centered Ni–Pt bimetallic nanoclusters (with Ni:Pt = 60:4...
Journal of Physics: Condensed Matter, 2012
Journal of Physics: Conference Series, 2009
Journal of Physics: Conference Series, 2013
We employ XSW assisted XAFS at Ni K edge to characterize ion-irradiated Pt/Ni/C multilayer, parti... more We employ XSW assisted XAFS at Ni K edge to characterize ion-irradiated Pt/Ni/C multilayer, particularly the nanoclusters formed within C layer, revealed by X-TEM and angleresolved fluorescence studies. Retrieving the structural model from XAFS coordination results involved intriguing steps such as accounting for the intensity variation across the layers, determination of extra pre-diffused Ni into C layer (beyond the reflectivity determined roughness) and decoupling interfacial, layer and cluster coordination. The clusters are determined to be Ni centered Ni-Pt bimetallic nanoclusters (Ni:Pt = 60:40), formed due to irradiation induced diffusion of Pt atoms from the disrupted Pt/C interface towards prediffused Ni atoms present in C layer. They are highly disordered beyond nearest neighbor and resemble glassy structure which could find wide-scale applications in magnetic devices.
Journal of Physics: Conference Series, 2013
Magnetic compensation (zero-moment) has important advantage in spintronics as it does not generat... more Magnetic compensation (zero-moment) has important advantage in spintronics as it does not generate any self stray magnetic field. The physics of magnetic compensation (at a well defined temperature T comp) is well understood in terms of competition and compensation between antiferromagnetically coupled magnetic moments of two rare earth ions. The different thermal evolution of the dissimilar rare earth moments can compensate each other at a particular temperature determined by the concentration of the dopant. We have observed, for the first ever time, "repeated" magnetic compensation in both polycrystalline and single crystals of Nd 0. 8 Tb 0.2 Al 2 (T f1 ~ 86 K and T f2 ~ 34 K). A possible reason could be the nonrandom distribution of magnetic rare earth ions on different crystallographic sites, presenting deviation from mean field like situation. The motivation for XAFS derives from detection of these circumstances. XAFS at Nd, Tb L 3 edges reveals that 25% (Nd,Al) anti-site defect exists in Nd 0. 8 Tb 0.2 Al 2. This implies that Nd atoms occupy two different sites. In contrast, Tb preferentially substitutes only one of the Nd sites. The implication of these results upon magnetic compensation is discussed.