Publications by authors named "Ivan A Zaluzhnyy"

12 Publications

  • Page 1 of 1

Low-temperature emergent neuromorphic networks with correlated oxide devices.

Proc Natl Acad Sci U S A 2021 Aug;118(35)

Department of Physics, University of California San Diego, La Jolla, CA 92093;

Neuromorphic computing-which aims to mimic the collective and emergent behavior of the brain's neurons, synapses, axons, and dendrites-offers an intriguing, potentially disruptive solution to society's ever-growing computational needs. Although much progress has been made in designing circuit elements that mimic the behavior of neurons and synapses, challenges remain in designing networks of elements that feature a collective response behavior. We present simulations of networks of circuits and devices based on superconducting and Mott-insulating oxides that display a multiplicity of emergent states that depend on the spatial configuration of the network. Our proposed network designs are based on experimentally known ways of tuning the properties of these oxides using light ions. We show how neuronal and synaptic behavior can be achieved with arrays of superconducting Josephson junction loops, all within the same device. We also show how a multiplicity of synaptic states could be achieved by designing arrays of devices based on hydrogenated rare earth nickelates. Together, our results demonstrate a research platform that utilizes the collective macroscopic properties of quantum materials to mimic the emergent behavior found in biological systems.
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http://dx.doi.org/10.1073/pnas.2103934118DOI Listing
August 2021

Extracting contrast in an X-ray speckle visibility spectroscopy experiment under imperfect conditions.

J Synchrotron Radiat 2020 Nov 19;27(Pt 6):1626-1632. Epub 2020 Oct 19.

Department of Physics, University of California, San Diego, La Jolla, CA 92093, USA.

Pump-probe experiments at synchrotrons and free-electron lasers to study ultrafast dynamics in materials far from equilibrium have been well established, but techniques to investigate equilibrium dynamics on the nano- and pico-second timescales remain underdeveloped and experimentally challenging. A promising approach relies on a double-probe X-ray speckle visibility spectroscopy setup at split-and-delay beamlines of X-ray free-electron lasers. However, the logistics in consistently producing two collinear, perfectly overlapping pulses necessary to conduct a faithful experiment is difficult to achieve. In this paper, a method is introduced to extract contrast in the case where an angular misalignment and imperfect overlap exists between the two pulses. Numerical simulations of a dynamical system show that contrast can still be extracted for significant angular misalignments accompanied by partial overlap between the two pulses.
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http://dx.doi.org/10.1107/S1600577520012345DOI Listing
November 2020

Perovskite neural trees.

Nat Commun 2020 05 7;11(1):2245. Epub 2020 May 7.

School of Materials Engineering, Purdue University, West Lafayette, IN, 47907, USA.

Trees are used by animals, humans and machines to classify information and make decisions. Natural tree structures displayed by synapses of the brain involves potentiation and depression capable of branching and is essential for survival and learning. Demonstration of such features in synthetic matter is challenging due to the need to host a complex energy landscape capable of learning, memory and electrical interrogation. We report experimental realization of tree-like conductance states at room temperature in strongly correlated perovskite nickelates by modulating proton distribution under high speed electric pulses. This demonstration represents physical realization of ultrametric trees, a concept from number theory applied to the study of spin glasses in physics that inspired early neural network theory dating almost forty years ago. We apply the tree-like memory features in spiking neural networks to demonstrate high fidelity object recognition, and in future can open new directions for neuromorphic computing and artificial intelligence.
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http://dx.doi.org/10.1038/s41467-020-16105-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7206050PMC
May 2020

Revealing Grain Boundaries and Defect Formation in Nanocrystal Superlattices by Nanodiffraction.

Small 2019 12 14;15(50):e1904954. Epub 2019 Nov 14.

Institute of Physical and Theoretical Chemistry, University of Tübingen, Auf der Morgenstelle 18, 72076, Tübingen, Germany.

X-ray nanodiffraction is applied to study the formation and correlation of domain boundaries in mesocrystalline superlattices of PbS nanocrystals with face-centered cubic structure. Each domain of the superlattice can be described with one of two mesocrystalline polymorphs with different orientational orders. Close to a grain boundary, the lattice constant decreases and the superlattice undergoes an out-of-plane rotation, while the orientation of the nanocrystals with respect to the superlattice remains unchanged. These findings are explained with the release of stress on the expense of specific nanocrystal-substrate interactions. The fact that correlations between adjacent nanocrystals are found to survive the structural changes at most grain boundaries implies that the key to nanocrystal superlattices with macroscopic domain sizes are strengthened interactions with the substrate.
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http://dx.doi.org/10.1002/smll.201904954DOI Listing
December 2019

Publisher Correction: Seeded X-ray free-electron laser generating radiation with laser statistical properties.

Nat Commun 2019 Nov 13;10(1):5217. Epub 2019 Nov 13.

Deutsches Elektronen-Synchrotron DESY, Notkestrasse 85, D-22607, Hamburg, Germany.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.
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http://dx.doi.org/10.1038/s41467-019-13249-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6853951PMC
November 2019

Angular X-Ray Cross-Correlation Analysis (AXCCA): Basic Concepts and Recent Applications to Soft Matter and Nanomaterials.

Materials (Basel) 2019 Oct 23;12(21). Epub 2019 Oct 23.

Deutsches Elektronen-Synchrotron DESY, Notkestrasse 85, D-22607 Hamburg, Germany.

Angular X-ray cross-correlation analysis (AXCCA) is a technique which allows quantitative measurement of the angular anisotropy of X-ray diffraction patterns and provides insights into the orientational order in the system under investigation. This method is based on the evaluation of the angular cross-correlation function of the scattered intensity distribution on a two-dimensional (2D) detector and further averaging over many diffraction patterns for enhancement of the anisotropic signal. Over the last decade, AXCCA was successfully used to study the anisotropy in various soft matter systems, such as solutions of anisotropic particles, liquid crystals, colloidal crystals, superlattices composed by nanoparticles, etc. This review provides an introduction to the technique and gives a survey of the recent experimental work in which AXCCA in combination with micro- or nanofocused X-ray microscopy was used to study the orientational order in various soft matter systems.
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http://dx.doi.org/10.3390/ma12213464DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6862311PMC
October 2019

Ultrafast structural dynamics of photo-reactions observed by time-resolved x-ray cross-correlation analysis.

Struct Dyn 2019 Mar 13;6(2):024301. Epub 2019 Mar 13.

Department of Physics, Technical University of Denmark, DK-2800 Lyngby, Denmark.

We applied angular X-ray Cross-Correlation analysis (XCCA) to scattering images from a femtosecond resolution X-ray free-electron laser pump-probe experiment with solvated PtPOP {[Pt(POH)]} metal complex molecules. The molecules were pumped with linear polarized laser pulses creating an excited state population with a preferred orientational (alignment) direction. Two time scales of 1.9 ± 1.5 ps and 46 ± 10 ps were revealed by angular XCCA associated with structural changes and rotational dephasing of the solvent molecules, respectively. These results illustrate the potential of XCCA to reveal hidden structural information in the analysis of time-resolved x-ray scattering data from molecules in solution.
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http://dx.doi.org/10.1063/1.5086374DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6416776PMC
March 2019

Seeded X-ray free-electron laser generating radiation with laser statistical properties.

Nat Commun 2018 10 29;9(1):4498. Epub 2018 Oct 29.

Deutsches Elektronen-Synchrotron DESY, Notkestrasse 85, D-22607, Hamburg, Germany.

The invention of optical lasers led to a revolution in the field of optics and to the creation of such fields of research as quantum optics. The reason was their unique statistical and coherence properties. The emerging, short-wavelength free-electron lasers (FELs) are sources of very bright coherent extreme-ultraviolet and X-ray radiation with pulse durations on the order of femtoseconds, and are presently considered to be laser sources at these energies. FELs are highly spatially coherent to the first-order but in spite of their name, behave statistically as chaotic sources. Here, we demonstrate experimentally, by combining Hanbury Brown and Twiss interferometry with spectral measurements that the seeded XUV FERMI FEL-2 source does indeed behave statistically as a laser. The results may be useful for quantum optics experiments and for the design and operation of next generation FEL sources.
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http://dx.doi.org/10.1038/s41467-018-06743-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6206026PMC
October 2018

Unravelling the structural rearrangement of polymer colloidal crystals under dry sintering conditions.

Soft Matter 2018 Sep 10;14(33):6849-6856. Epub 2018 Aug 10.

Deutsches Elektronen-Synchrotron DESY, Notkestraße 85, Hamburg D-22607, Germany and National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), Kashirskoye ch. 31, Moscow 115409, Russia.

The structural rearrangement of polystyrene colloidal crystals under dry sintering conditions has been revealed by in situ grazing incidence X-ray scattering. The measured diffraction patterns were analysed using distorted wave Born approximation (DWBA) theory and the structural parameters of the as-grown colloidal crystals of three different particle sizes were determined for the in-plane and out-of-plane directions in a film. By analysing the temperature evolution of the diffraction peak positions, integrated intensities, and widths, the detailed scenario of the structural rearrangement of crystalline domains at the nanoscale has been revealed, including thermal expansion, particle shape transformation and crystal amorphisation. Based on DWBA analysis, we demonstrate that in the process of dry sintering, the shape of colloidal particles in a crystal transforms from a sphere to a polyhedron. Our results deepen the understanding of the thermal annealing of polymer colloidal crystals as an efficient route for the design of new nano-materials.
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http://dx.doi.org/10.1039/c8sm01412dDOI Listing
September 2018

Structural Changes in a Single GaN Nanowire under Applied Voltage Bias.

Nano Lett 2018 09 26;18(9):5446-5452. Epub 2018 Jul 26.

Deutsches Elektronen-Synchrotron DESY , Notkestraße 85 , D-22607 Hamburg , Germany.

GaN nanowires (NWs) are promising building blocks for future optoelectronic devices and nanoelectronics. They exhibit stronger piezoelectric properties than bulk GaN. This phenomena may be crucial for applications of NWs and makes their study highly important. We report on an investigation of the structure evolution of a single GaN NW under an applied voltage bias along polar [0001] crystallographic direction until its mechanical break. The structural changes were investigated using coherent X-ray Bragg diffraction. The three-dimensional (3D) intensity distributions of the NWs without metal contacts, with contacts, and under applied voltage bias in opposite polar directions were analyzed. Coherent X-ray Bragg diffraction revealed the presence of significant bending of the NWs already after metal contacts deposition, which was increased at applied voltage bias. Employing analytical simulations based on elasticity theory and a finite element method (FEM) approach, we developed a 3D model of the NW bending under applied voltage. From this model and our experimental data, we determined the piezoelectric constant of the GaN NW to be about 7.7 pm/V in [0001] crystallographic direction. The ultimate tensile strength of the GaN NW was obtained to be about 1.22 GPa. Our work demonstrates the power of in operando X-ray structural studies of single NWs for their effective design and implementation with desired functional properties.
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http://dx.doi.org/10.1021/acs.nanolett.8b01802DOI Listing
September 2018

Quantifying Angular Correlations between the Atomic Lattice and the Superlattice of Nanocrystals Assembled with Directional Linking.

Nano Lett 2017 06 17;17(6):3511-3517. Epub 2017 May 17.

Eberhard Karls Universität Tübingen , Geschwister-Scholl-Platz, D-72074 Tübingen, Germany.

We show that the combination of X-ray scattering with a nanofocused beam and X-ray cross correlation analysis is an efficient way for the full structural characterization of mesocrystalline nanoparticle assemblies with a single experiment. We analyze several hundred diffraction patterns at individual sample locations, that is, individual grains, to obtain a meaningful statistical distribution of the superlattice and atomic lattice ordering. Simultaneous small- and wide-angle X-ray scattering of the same sample location allows us to determine the structure and orientation of the superlattice as well as the angular correlation of the first two Bragg peaks of the atomic lattices, their orientation with respect to the superlattice, and the average orientational misfit due to local structural disorder. This experiment is particularly advantageous for synthetic mesocrystals made by the simultaneous self-assembly of nanocrystals and surface-functionalization with conductive ligands. While the structural characterization of such materials has been challenging so far, the present method now allows correlating the mesocrystalline structure with optoelectronic properties.
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http://dx.doi.org/10.1021/acs.nanolett.7b00584DOI Listing
June 2017

Local structure of semicrystalline P3HT films probed by nanofocused coherent X-rays.

Phys Chem Chem Phys 2015 Mar;17(11):7404-10

Deutsches Elektronen-Synchrotron DESY, Notkestraße 85, D-22607 Hamburg, Germany.

The hidden structural properties of semicrystalline polymer films are revealed by nanofocused X-ray scattering studies. X-ray cross-correlation analysis (XCCA) is employed to diffraction patterns from blends of poly(3-hexylthiophene) (P3HT) with gold nanoparticles (AuNPs). Spatially resolved maps of orientational distribution of crystalline domains allow us to distinguish sample regions of predominant face-on morphology, with a continuous transition to edge-on morphology. The average size of crystalline domains was determined to be of the order of 10 nm. As compared to pristine P3HT film, the P3HT/AuNPs blend is characterized by substantial ordering of crystalline domains, which can be induced by Au nanoparticles. The inhomogeneous structure of the polymer film is clearly visualized on the spatially resolved nanoscale 2D maps obtained using XCCA. Our results suggest that the observed changes of the polymer matrix within crystalline regions can be attributed to nanoconfinement in the presence of gold nanoparticles.
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http://dx.doi.org/10.1039/c5cp00426hDOI Listing
March 2015
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