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Ultrashort pulsed laser induced complex surface structures generated by tailoring the melt hydrodynamics

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Opto-Electronic Advances 2022年第3期5卷 53-68,I0001页

作者： Fotis Fraggelakis George D.Tsibidis emmanuel stratakis Institute of Electronic Structure and Laser(IESL) Foundation for Research and Technology(FORTH)N.Plastira 100Vassilika VoutonHeraklion 70013Greece Department of Physics University of CreteHeraklion 71003Greece

We present a novel approach for tailoring the laser induced surface topography upon femtosecond(fs)pulsed laser *** method employs spatially controlled double fs laser pulses to actively regulate the hydrodynamic microfluidic motion of the melted layer that gives rise to the structures *** pulse train used,in particular,consists of a previously unexplored spatiotemporal intensity combination including one pulse with Gaussian and another with periodically modulated intensity distribution created by Direct Laser Interference Patterning(DLIP).The interpulse delay is appropriately chosen to reveal the contribution of the microfluidic melt flow,while it is found that the sequence of the Gaussian and DLIP pulses remarkably influences the surface profile *** also demonstrate that both the spatial intensity of the double pulse and the effective number of pulses per irradiation spot can further be modulated to control the formation of complex surface *** underlying physical processes behind the complex patterns’generation were interpreted in terms of a multiscale model combining electron excitation with melt *** believe that this work can constitute a significant step forward towards producing laser induced surface structures on demand by tailoring the melt microfluidic phenomena.

关键词： laser-matter interaction direct laser interference patterning surface functionalization laser micro/nano fabrication

Ultrahigh-resolution nonlinear optical imaging of the armchair orientation in 2D transition metal dichalcogenides

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Light(Science & Applications) 2018年第1期7卷 1072-1080页

作者： Sotiris Psilodimitrakopoulos Leonidas Mouchliadis Ioannis Paradisanos Andreas Lemonis George Kioseoglou emmanuel stratakis Institute of Electronic Structure and Laser Foundation for Research and Technology-HellasHeraklion Crete 71110Greece Department of Physics University of CreteHeraklion Crete 71003Greece Department of Materials Science and Technology University of CreteHeraklion Crete 71003Greece

We used nonlinear laser scanning optical microscopy to study atomically thin transition metal dichalcogenides(TMDs)and revealed,with unprecedented resolution,the orientational distribution of armchair directions and their degree of organization in the two-dimensional(2D)crystal *** particular,we carried out polarization-resolved second-harmonic generation(PSHG)imaging for monolayer WS2 and obtained,with high-precision,the orientation of the main crystallographic axis(armchair orientation)for each individual 120×120 nm^(2) pixel of the 2D crystal *** nanoscale resolution was realized by fitting the experimental PSHG images,obtained with sub-micron precision,to a new generalized theoretical model that accounts for the nonlinear optical properties of *** enabled us to distinguish between different crystallographic domains,locate boundaries and reveal fine *** a consequence,we can calculate the mean orientational average of armchair angle distributions in specific regions of interest and define the corresponding standard deviation as a figure-of-merit for the 2D crystal quality.

关键词： armchair orientation mapping atomically thin transition metal dichalcogenides crystal quality marker graphene-related materials polarization-resolved second-harmonic generation

Omnidirectional iridescence via cylindricallypolarized femtosecond laser processing

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Opto-Electronic Advances 2020年第5期3卷 11-18页

作者： Nikolaos Livakas Evangelos Skoulas emmanuel stratakis Institute of Electronic Structure and Laser Foundation for Research and Technology-HellasHeraklion Crete 71110Greece Department of Materials Science and Technology University of CreteHeraklion Crete 71003Greece Department of Physics University of CreteHeraklion Crete 71003Greece

We report the femtosecond(fs)laser fabrication of biomimetic omnidirectional iridescent metallic surfaces exhibiting efficient diffraction for practically any angle of light *** diffractive behavior is realized by means of multi-directional low-spatial-frequency,laser-induced periodic surface structures(LSFL)formed upon exploiting the cylindrical symmetry of a cylindrical vector(CV)fs *** particularly demonstrate that the multi-directional gratings formed on stainless steel surface by a radially polarized fs beam,could mimic the omnidirectional structural coloration properties found in some natural ***,the fabricated grating structures can spatially disperse the incident light into individual wavelength with high efficiency,exhibiting structural iridescence at all viewing *** calculations using the grating equation reproduced the characteristic variation of the vivid colors observed as a function of incident *** envisage that our results will significantly contribute to the development of new photonic and light sensing devices.

关键词： laser processing structural colors radial polarisation

Highly sensitive ozone and hydrogen sensors based on perovskite microcrystals directly grown on electrodes

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Journal of Materiomics 2022年第2期8卷 446-453页

作者： Aikaterini Argyrou Konstantinos Brintakis Athanasia Kostopoulou Emmanouil Gagaoudakis Ioanna Demeridou Vassilios Binas George Kiriakidis emmanuel stratakis Foundation for Research and Technology Hellas(FORTH) Institute of Electronic Structure&Laser(IESL)P.O.Box 1385Heraklion 70013CreteGreece University of Crete Department of Chemistry71003 HeraklionCreteGreece University of Crete Department of Physics71003 HeraklionCreteGreece Crete Center for Quantum Complexity and Nanotechnology Department of PhysicsUniversity of Crete71003 HeraklionGreece

Highly-sensitive and stable ozone and hydrogen sensing elements were fabricated based on well-crystalline rounded cube-shaped CsPbBr 3 microcrystals,synthesized by a facile solution process per-formed under ambient *** is shown that such elements demonstrate enhanced room tem-perature gas sensing ability compared to the previously reported metal halide and oxide-based *** measurements performed on these sensing components revealed high sensitivity to ultra-low ozone and hydrogen concentrations,namely 4 ppb and 1 ppm respectively,as well as a remarkable repeatability,even after a few months of storage in ambient *** ozone and hydrogen sensors were self-activated,as they did not require the use of UV or heating external stimuli to operate,and exhibited fast detection and short restoration *** such attractive properties along with the simple fabrication process could provide an easy,efficient and low-cost technology for the realization of future gas sensing devices.

关键词： All-inorganic perovskite crystals Solution process Ozone sensing Hydrogen sensing High sensitivity Room-temperature sensor Perovskite sensors

Charge carrier dynamics in different crystal phases of CH_(3)NH_(3)PbI_(3)perovskite

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Opto-Electronic Science 2022年第4期1卷 1-10,22-27页

作者： Efthymis Serpetzoglou Ioannis Konidakis George Kourmoulakis Ioanna Demeridou Konstantinos Chatzimanolis Christos Zervos George Kioseoglou emmanuel Kymakis emmanuel stratakis Institute of Electronic Structure and Laser(IESL) Foundation for Research and Technology-Hellas(FORTH)Herakleio 70013Greece Electrical and Computer Engineering Department Hellenic Mediterranean UniversityHerakleio 71004Greece Department of Materials Science and Technology University of CreteHerakleio 70013Greece Department of Physics University of CreteHerakleio 70013Greece.

Despite that organic-inorganic lead halide perovskites have attracted enormous scientific attention for energy conversion applications over the recent years,the influence of temperature and the type of the employed hole transport layer(HTL)on the charge carrier dynamics and recombination processes in perovskite photovoltaic devices is still largely *** particular,significant knowledge is missing on how these crucial parameters for radiative and non-radiative recombinations,as well as for efficient charge extraction vary among different perovskite crystalline phases that are induced by temperature ***,we perform micro photoluminescence(pPL)and ultrafast time resolved transient absorption spectroscopy(TAS)in Glass/Perovskite and two dierent Glass/ITO/HTL/Perovskite configurations at temperatures below room temperature,in order to probe the charge carrier dynamics of different perovskite crystalline phases,while considering also the effect of the employed HTL ***,CH_(3)NH_(3)Pbb films were deposited on Glass,PEDOT:PSS and PTAA polymers,and the developed Glass/CH_(3)NH_(3)PbI_(3)and Glass/ITO/HTL/CH_(3)NH_(3)PbI_(3)architectures were studied from 85 K up to 215 K in order to explore the charge extraction dynamics of the CH_(3)NH_(3)PbI_(3)orthorhombic and tetragonal crystalline *** is observed an unusual blueshift of the bandgap with temperature and the dual emission at temperature below of 100 K and also,that the charge carrier dynamics,as expressed by hole injection times and free carrier recombination rates,are strongly depended on the actual pervoskite crystal phase,as well as,from the selected hole transport material.

关键词： transient absorption spectroscopy p-photoluminescence variable temperature perovskite crystalline phases hole transport layer charge carrier dynamics

Imaging the crystal orientation of 2D transition metal dichalcogenides using polarization-resolved second-harmonic generation

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Opto-Electronic Advances 2019年第11期2卷 12-19页

作者： George Miltos Maragkakis Sotiris Psilodimitrakopoulos Leonidas Mouchliadis Ioannis Paradisanos Andreas Lemonis George Kioseoglou emmanuel stratakis Institute of Electronic Structure and Laser Foundation for Research and Technology-HellasHeraklion Crete 71110Greece Department of Physics University of CreteHeraklion Crete 71003Greece Department of Materials Science and Technology University of CreteHeraklion Crete 71003Greece

We use laser-scanning nonlinear imaging microscopy in atomically thin transition metal dichalcogenides(TMDs)to reveal information on the crystalline orientation distribution,within the 2D *** particular,we perform polarization-resolved second-harmonic generation(PSHG)imaging in a stationary,raster-scanned chemical vapor deposition(CVD)-grown WS2 flake,in order to obtain with high precision a spatially resolved map of the orientation of its main crystallographic axis(armchair orientation).By fitting the experimental PSHG images of sub-micron resolution into a generalized nonlinear model,we are able to determine the armchair orientation for every pixel of the image of the 2D material,with further improved *** pixel-wise mapping of the armchair orientation of 2D WS2 allows us to distinguish between different domains,reveal fine structure,and estimate the crystal orientation variability,which can be used as a unique crystal quality marker over large *** necessity and superiority of a polarization-resolved analysis over intensity-only measurements is experimentally demonstrated,while the advantages of PSHG over other techniques are analysed and discussed.

关键词： nonlinear imaging of 2D materials crystal orientation mapping crystal quality marker polarization-resolved second-harmonic generation atomically thin transition metal dichalcogenides graphene-related materials

Substrate topography affects PC12 cell differentiation through mechanotransduction mechanisms

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Mechanobiology in Medicine 2024年第1期2卷 86-96页

作者： Lina Papadimitriou Anna Karagiannaki emmanuel stratakis Anthi Ranella Institute of Electronic Structure and Laser Foundation for Research and Technology-Hellas(FORTH)Heraklion71003Greece Department of Physics University of CreteHeraklion71003Greece

Neural stem cells in vivo receive information from biochemical and biophysical cues of their microenvironment that affect their survival,proliferation and differentiation toward specific *** of these conditions in vitro is better achieved in 3D cell *** the cells that grow in scaffold-dependent 3D cultures establish more complex cell-cell and cell-material interactions enabling the study of the various signaling *** biochemical signaling from growth factors and hormones has been extensively studied over the *** recently cumulative evidence demonstrates that cell sensing and response to mechanical stimuli is mediated through mechanotransduction *** individual signaling pathways activated by biochemical or mechanical cues in cells are well-studied,synergistic or antagonistic effects among them need further research to be fully *** understanding of the alteration of the cell behavior due to a microenvironmental cues would be greatly enhanced by the study of key elements that lie in the convergence of biochemical and mechanical *** we analyzed the effect of the substrate topography on the nerve growth factor(NGF)induced differentiation of PC12 *** results showed that the topography interferes with NGF-induced neuronal differentiation and this is reflected in the reduced activation of the integrin-mediated mechanotransduction.

关键词： Neural differentiation Mechanotrunsduction Laser pattern topography Focal adhesion Growth cone

Modelling die filling with charged particles using DEM/CFD

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Particuology 2012年第2期10卷 229-235页

作者： emmanuel Nkem Nwose School of Chemical Engineering University of Birmingham Birmingham B15 2TT UK

The effects of electrostatic charge on powder flow behaviour during die filling in a vacuum and in air were analysed using a coupled discrete element method and computational fluid dynamics （DEM]CFD） code, in which long range electrostatic interactions were implemented. The present 2D simulations revealed that both electrostatic charge and the presence of air can affect the powder flow hehaviour during die filling. It was found that the electrostatic charge inhibited the flow of powders into the die and induced a loose packing structure. At the same filling speed, increasing the electrostatic charge led to a decrease in the fill ratio which quantifies the volumetric occupancy of powder in the die. In addition, increasing the shoe speed caused a further decrease in the fill ratio, which was characterised using the concept of critical filling speed, When the electrostatic charge was low, the air/particle interaction was strong so that a lower critical filling speed was obtained for die filling in air than in a vacuum. With high electrostatic charge, the electrostatic interactions became dominant. Consequently, similar fill ratio and critical filling speed were obtained for die filling in air and in a vacuum.

关键词： DEMCFDElectrostaticsDie fillingPowder flowCohesionCharged particles

Systems Analysis of Vulnerability to Hydrometeorological Threats: An Exploratory Study of Vulnerability Drivers in Northern Zimbabwe

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International Journal of Disaster Risk Science 2019年第2期10卷 204-219页

作者： emmanuel Mavhura Department of Geography Bindura University of Science Education

Disasters result from complex interactions of hazards and vulnerability conditions. Reducing human exposure and sensitivity to threats can reduce disaster impact. Prior knowledge about community vulnerability levels is crucial to minimizing potential losses from future threats. Most vulnerability studies focus on high-impact disasters and their temporal and spatial analyses. Yet highfrequency, low-impact disasters have a cumulative potential to severely disrupt or damage socioeconomic *** is limited knowledge especially in the global south about the creation of vulnerability to hydrometeorological threats. Using a systems approach, this study explores ways in which communities in the northern semiarid tropics of Zimbabwe are vulnerable to hydrometeorological *** predominantly qualitative study used literature review, interviews, transect walks, and focus groups to gather data from selected samples involving smallholder farmers with in-depth knowledge about community vulnerability. The results show that the communities are vulnerable to multiple hydrometeorological threats due to multiple interacting factors including rainfed and floodbased farming, land tenure, topography, climate, and other socioeconomic conditions such as inadequate income sources and high poverty. In order to reduce vulnerability,this study provides five policy options for government and nongovernmental organization interventions, including the need to transform rural economies beyond the traditional rainfed and flood-based farming systems.

关键词： Community vulnerability Flood-based farming Hydrometeorological threats Rainfed agriculture Zimbabwe