Formation Of Self-organized Structures Research Articles

Self-enhanced mobility enables vortex pattern formation in living matter.

Ranging from subcellular organelle biogenesis to embryo development, the formation of self-organized structures is a hallmark of living systems. Whereas the emergence of ordered spatial patterns in biology is often driven by intricate chemical signalling that coordinates cellular behaviour and differentiation1-4, purely physical interactions can drive the formation of regular biological patterns such as crystalline vortex arrays in suspensions of spermatozoa5 and bacteria6. Here we discovered a new route to self-organized pattern formation driven by physical interactions, which creates large-scale regular spatial structures with multiscale ordering. Specifically we found that dense bacterial living matter spontaneously developed a lattice of mesoscale, fast-spinning vortices; these vortices each consisted of around 104-105 motile bacterial cells and were arranged in space at greater than centimetre scale and with apparent hexagonal order, whereas individual cells in the vortices moved in coordinated directions with strong polar and vortical order. Single-cell tracking and numerical simulations suggest that the phenomenon is enabled by self-enhanced mobility in the system-that is, the speed of individual cells increasing with cell-generated collective stresses at a given cell density. Stress-induced mobility enhancement and fluidization is prevalent in dense living matter at various scales of length7-9. Our findings demonstrate that self-enhanced mobility offers a simple physical mechanism for pattern formation in living systems and, more generally, in other active matter systems10 near the boundary of fluid- and solid-like behaviours11-17.

Low-temperature anomalies and nanosized levels formation of self-organized structures in the non-crystalline solids of As(Ge)-S(Se) systems

The relationship between low-temperature anomalies of physical and chemical properties and the formation of self-organized structures in non-crystalline solids of the As(Ge)-S(Se) systems is discussed. Obtained temperature dependences for the specific heat capacity and coefficient of linear expansion in the temperature domain , detailing the linear and nonlinear contributions. The influence of the obtaining conditions of non-crystalline solids on the low-temperature behavior of physico-chemical properties and the change in the ratios of various contributions and temperature intervals is considered. The correlation and common features of the formation of self-organized structures of non-crystalline materials in the region of low temperatures and softening temperatures, manifested in the presence of nanolevels of structuring, are analyzed.

Self-organized vertical multilayer structures in spinodally decomposed TiO2-VO2 films on glass substrates

In this study, we investigated the formation of vertical multilayer structures via phase separation in TiO2-VO2 films on glass substrates. A key point for the formation is to utilize the anisotropy in the spinodal decomposition of the system. Solid-solution films of Ti0.3V0.7O2 were grown on quartz glass substrates using pulsed laser deposition and annealed inside the spinodal region. X-ray diffraction, scanning transmission electron microscopy (STEM) measurements showed that spinodal decomposition occurs along the c-axis, and multilayer structures composed of alternating stacking of Ti- and V-rich phases were formed in the annealed film. In addition, STEM observations revealed that the multilayer structures were aligned vertically on the surface to the glass substrates. In resistivity measurements the annealed film showed a metal-insulator transition with the transition temperature lower than TixV1-xO2 bulk due to the strain effect induced by the coherent interface between Ti- and V-rich phases. The overall results clearly show that vertical multilayer structures were formed via spinodal decomposition along the c-axis direction in the Ti0.3V0.7O2 film on the glass substrates. Our study indicates that anisotropy in the spinodal decomposition is an effective approach for the formation of self-organized vertical multilayer structures in Ti0.3V0.7O2 films on glass substrates, and provides useful guidelines for generating self-organized novel nanostructures on amorphous substrates in oxide films.

Formation of Self-organized Structures in Drying Droplets: a Promising Analytical Tool for Homeopathy Basic Research

The droplet evaporation method (DEM) is based on the evaporation-induced pattern formation in droplets and is applied mainly for diagnosis [1].
 Here, we present a series of experiments performed by our team showing DEMs potential also for homeopathy basic research, in particular, for the investigation of (i) low potencies, (ii) low potency complexes (physical model), and (iii) the action of high potencies (plant-based model).
 
 DEM differentiated significantly between Luffa, Baptisia, Echinacea, and Spongia until 4x [2]. Furthermore, the patterns varied in function of the number of succussion strokes (0, 10, or 100) applied during potentization [3]. The performance of chaotic succussions vs. laminar flow vs. slight mixing during the potentization of Viscum album quercus 3x influenced the DEM patterns; the chaotic succussions reduced, whereas laminar flow enhanced the patterns complexity vs. the unsuccussed control.
 The addition of Mercurius bijodatus 9x to Luffa 4x changed significantly the DEM patterns, even if the material quantity present in the 9x potency lied far beyond that of ultrapure water.
 Leakages obtained by placing healthy or damaged wheat-seeds into Arsenicum album 45x or Zincum metallicum 30c vs. water created significantly different DEM structures [4, 5]. The damaged seeds put into the potency created structures characterized by a higher complexity than those obtained from damaged seeds put into control water. Furthermore, the potency action seemed to correlate positively with the number of succussion strokes applied during potentization, as could be shown by means of DEM patterns and germination rate using the same wheat-seed model [6].
 
 In all our studies, the pattern evaluation was computerized or based on deep-learning algorithms and the robustness of the experimental system was checked by means of systematic control experiments.
 DEM together with other similar methods has also been reviewed by our team for what concerns the application in homeopathy basic research [7].

Examination and modification of Co structures on Ge(001)

High-resolution scanning tunneling microscopy and spectroscopy enlighten the formation and composition of self-organized Co-induced structures on Ge(001). Dimer vacancies due to subsurface Co accumulate and lead to the formation of well-ordered embedded structures which consist of two alternating building blocks. A mismatch in the alternation leads to protrusions at both sides of the structures. The deposition of small amounts of Au changes the internal order of the embedded Co structures and results in longer elongated chains. Supported by Monte Carlo simulations, this modification of chain length is attributed to stress relief due to the insertion of Au-induced dimer vacancies in the Ge(001) surface.

Active Pharmaceutical Ingredient-Ionic Liquids (API-ILs): Nanostructure of the Glassy State Studied by Electron Paramagnetic Resonance Spectroscopy.

Active Pharmaceutical Ingredient-Ionic Liquids (API-ILs) draw increasing interest as a particular class of ILs that possess unusual physicochemical properties along with simultaneous potentials for pharmaceutical applications. Although nanostructuring phenomena were actively investigated in common ILs, their studies in API-ILs are scarce so far. In this work, using the complex methodology of Electron Paramagnetic Resonance (EPR) and dissolved spin probes, we investigate nanostructuring phenomena in a series of API-ILs: [Cnmim][Ibu], [Cnmim][Gly], and [Cnmim][Sal] with n = 2, 4, and 6, respectively. We reveal similar trends for API-ILs and common ILs, as well as peculiarities inherent to the studied API-ILs. Unusual behavior observed for [Cnmim][Ibu] has been assigned to the presence of a non-polar fragment in the [Ibu]− anion, which leads to the formation of more complex nanostructures around the radical compared to common ILs. Understanding general trends in the formation of such self-organized molecular structures is of fundamental interest and importance for applying API-ILs.

(Invited) Second-Layer Growth Kinetics As a Decisive Factor for Non-Equilibrium Thin-Film Morphologies

Understanding and control of cluster growth on solid surfaces is a subject of intensive research to develop materials with new properties. Of particular interest is the self-organized structure formation by deposition of atoms and molecules on surfaces, where the interplay of diffusion, nucleation, aggregation, segregation and superlattice ordering yields a rich variety of growth phenomena [1]. The resulting structures are often frozen-in non-equilibrium structures with properties distinctly different from the equilibrium bulk phases. Here I will discuss the role of second layer nucleation for three-dimensional cluster formation and its influence on cluster morphologies.[1] M. Einax, W. Dieterich, P. Maass, Rev. Mod. Phys. 85, 921 (2013).

Formation of self-organized nano-dimensional structures on InP surfaces using ion irradiation and their wettability: A study based on experimental and theoretical concepts of surface

InP surfaces are bombarded with 50 keV Ar+ ion beam at normal incidence with fluences ranging from∼2 × 1016 to 8 × 1016 ions/cm2. The formation of self-organized nanodots on Indium Phosphide (InP) are captured by Atomic Force Microscope (AFM) and Scanning Electron Microscope (SEM). Uniformity in size of dots is improved for the higher fluences and the surface becomes Indium rich with ion irradiation. Wettability studies show that the surface contact angle (CA) increases with ion irradiation and stabilizes for later fluences. The autocorrelation and height-height correlation function are applied for surface correlation and fractal nature of AFM images. Wetting properties of fractal surfaces are explored. The interface-width is found to increase with the ion fluences. The lateral correlation length is computed using auto-correlation function, while roughness exponent and the fractal dimension were estimated using height-height correlation function. Larger values of interface width indicate the larger self-organized nanodots on the surface. Fractal formations are able to capably disperse or collect mass, energy, and information over large spatial and temporal dimensions. Due to these properties, artificial fractal structures are becoming an essential and fundamental topic of study in applied research.

Evolution of Nanodomains and Formation of Self-Organized Structures during Local Switching in X-Cut LNOI

The features of nanodomain growth during local switching in X-cut lithium niobate on insulator (LNOI) were comprehensively studied using the biased tip of a scanning probe microscope. The obtained results were discussed in terms of the kinetic approach. The revealed differences in domain growth in bulk LN and LNOI were attributed to the higher bulk conductivity of LNOI. The obtained influence of humidity on the shape and growth of isolated domains was attributed to the water meniscus. Analysis of the transition between the “forward growth” and “sideways growth” stages was performed by switching to the stripe electrode. A sand-glass-shaped domain was formed due to growth in the opposite direction after the domain touched the electrode. Stable periodical domain structures down to 300 nm were created and characterized in LNOI. Highly ordered comb-like domains of various alternating lengths, including four- and eight-fold increase periods, were produced by performing biased tip scanning along the Y axis. The obtained knowledge is important for the future development of nanodomain engineering methods in monocrystalline ferroelectric thin films on insulators.

Hydrogen isotope effect on self-organized electron internal transport barrier criticality and role of radial electric field in toroidal plasmas

Self-organized structure formation in magnetically confined plasmas is one of the most attractive subjects in modern experimental physics. Nonequilibrium media are known to often exhibit phenomena that cannot be predicted by superposition of linear theories. One representative example of such phenomena is the hydrogen isotope effect in fusion plasmas, where the larger the mass of the hydrogen isotope fuel is the better the plasma confinement becomes, contrary to what simple scaling models anticipate. In this article, threshold condition of a plasma structure formation is shown to have a strong hydrogen isotope effect. To investigate the underlying mechanism of this isotope effect, the electrostatic potential is directly measured by a heavy ion beam probe. It is elucidated that the core electrostatic potential transition occurs with less input power normalized by plasma density in plasmas with larger isotope mass across the structure formation. This observation is suggestive of the isotope effect in the radial electric field structure formation.

Self-organizing half-wave gratings on the surface of silica glass

The interaction of femtosecond laser pulses with the surface of silica glass has been studied. As a result of interference between the incident radiation and surface plasmon polaritons, the formation of self-organizing subwavelength periodic structures with a period of 250 nm was observed. The minimum pulse energy at which recording occurs without surface ablation has been revealed. Keywords: direct laser recording, femtosecond laser pulses, silica, nanogratings.

Formation of Self-organized Structures of Hybrid Amorphous Materials Based on Polyhedral Silsesquioxanes

The formation of self-organized structures of organic-inorganic hybrid amorphous molecules based on polyhedral silsesquioxanes (POSS) is reported. The hybrid materials were synthesized using POSS as the inorganic core and cyanobiphenyl (CBP) as the organic substituent. The type of structure formed depends on the length of the alkyl spacer used to connect the POSS and CBP groups. The hybrid amorphous material with an alkyl spacer consisting of eleven methylene units resulted in Voronoi-like dot patterns, the size of which are easily controlled by varying the thickness of the initial films.

Self-organized multiscale structures in thermally relativistic electron-positron-ion plasmas

The self-organization of a thermally relativistic magnetized plasma comprising of electrons, positrons and static ions is investigated. The self-organized state is found to be the superposition of three distinct Beltrami fields known as triple Beltrami (TB) state. In general, the eigenvalues associated with the multiscale self-organized vortices may be a pair of complex conjugate and real one. It is shown that all the eigenvalues become real when thermal energy increases or the positron density decreases. The impact of relativistic temperature and positron density on the formation of self-organized structures is investigated. The self-organized field and flow vortices may vary simultaneously on vastly different length scales. The disparate variation of self-organized vortices is important in the context of dynamo theory. The present work is useful to study the formation of multiscale vortices and dynamo mechanisms in multi-species thermally relativistic plasmas.

Heat accumulation during femtosecond laser treatment at high repetition rate – A morphological, chemical and crystallographic characterization of self-organized structures on Ti6Al4V

This study presents a detailed characterization of self-organized nano- and microstructures on Ti6Al4V evoked by different scanning strategies and fluences with a 300 fs laser operating at a laser wavelength of 1030 nm. The resulting surface morphology was visualized via field emission scanning electron microscopy (FEG-SEM) images of the surface and cross-sections. X-ray diffraction (XRD)-analysis was performed to analyse changes in crystal structures. The chemical surface composition of the near-surface layer was determined by X-ray photoelectron spectroscopy (XPS). Results show a significant influence of heat accumulation while processing with high laser repetition rates on the formation, crystallinity and chemical composition of self-organized structures depending on the scanning strategy. The ablation with different laser scanning strategies led to varying dynamics of growth-mechanisms of self-organized structures, formation of intermetallic phases (Ti3Al), sub-oxides and oxides (Ti6O, TiO) as well as ions (Ti3+, Ti4+) in surface layer reliant on applied fluence. Furthermore, investigations revealed a heat-affected zone up to several micrometers in non-ablated material.

Formation of self-organized structures in internal conductor plasma

A possibility of the confinement of two-fluid (electrons and ions) magnetized plasma in a simple cylindrical configuration as well as in a cylindrical geometry with an internal conductor is analyzed. By controlling the characteristics roots of Triple Beltrami state the formation of diamagnetic and paramagnetic structures is investigated for a simple cylindrical geometry. For an internal conductor system, the nature of relaxed structures is only paramagnetic. These paramagnetic structures are independent of the type of the characteristics roots. The results of the present investigation will be helpful to explain the equilibrium structure in the astrophysical objects such as Jupiter magnetosphere which is co-rotated with the planet and in the laboratory.

Multiscale self-organized triple Beltrami states in four-component dusty plasmas

A possibility of four component dusty plasmas to self-oraganzie to Triple Beltrami state (a linear combination of three force-free Beltrami states) has been explored. It is found that the system attains a Triple Beltarmi state when the velocities of electrons and ions become parallel to magnetic field while the two oppositely charged dust grains follow the generalized vorticities. The impact of the densities of species, masses of charged dust grains and Beltrami parameters on the formation of self-organized structures has also been investigated. The present work is useful to study and understand the multi scale magnetic field structures formed in planetary bodies such as ionosphere of Mars, Titan’s lower ionosphere, etc. and in laboratory plasmas.

Structural phase transitions of optical patterns in atomic gases with microwave-controlled Rydberg interactions

Spontaneous symmetry breaking and formation of self-organized structures in nonlinear systems are intriguing and important phenomena in nature. Advancing such research to new nonlinear optical regimes is of much interest for both fundamental physics and practical applications. Here we propose a scheme to realize optical pattern formation in a cold Rydberg atomic gas via electromagnetically induced transparency. We show that, by coupling two Rydberg states with a microwave field (microwave dressing), the nonlocal Kerr nonlinearity of the Rydberg gas can be enhanced significantly and may be tuned actively. Based on such nonlocal Kerr nonlinearity, we demonstrate that a plane-wave state of probe laser field can undergo a modulation instability (MI) and hence spontaneous symmetry breaking, which may result in the emergence of various self-organized optical patterns. Especially, we find that a hexagonal lattice pattern (which is the only optical pattern when the microwave dressing is absent) may develop into several types of square lattice ones when the microwave dressing is applied; moreover, as a outcome of the MI the formation of nonlocal optical solitons is also possible in the system. Different from earlier studies, the optical patterns and nonlocal optical solitons found here can be flexibly manipulated by adjusting the effective probe-field intensity, nonlocality degree of the Kerr nonlinearity, and the strength of the microwave field. Our work opens a route for versatile controls of self-organizations and structural phase transitions of laser light, which may have potential applications in optical information processing and transmission.

Elastic properties of self-organized nanogratings produced by femtosecond laser exposure of fused silica

Under certain exposure conditions, a femtosecond laser beam focused in the bulk of fused silica leads to the formation of self-organized structures consisting of a series of ``nanolayers,'' parallel to one another. Remarkably, this laser-induced nanoscale anisotropy offers the possibility to locally engineer macroscopic properties of a given substrate by selectively exposing it in arbitrarily chosen locations to a laser beam with designed polarization states. Although various physical properties are affected by the laser, this paper specifically discusses in-plane elastic properties of these nanostructures. Using a method based on monitoring resonant properties of vibrating cantilevers combined with a mechanical model of the nanostructures, the Young's moduli of individual nanolayers are calculated and used to define the stiffness matrix of the composite structure. The model shows a good agreement with measured mechanical properties of arbitrarily oriented nanostructures. This work demonstrates the predictability and controllability of laser-induced nanoscale mechanical properties and offers a framework for engineering arbitrary elastic properties through 3D laser writing.

GaN Selective Epitaxy in Sub-Micron Windows with Different Depths Formed by Ion Beam Nanolithography

A significant difference in the growth mechanism of spatially closed structures of gallium nitride during selective growth in submicron windows with and without penetration into the GaN sublayer was demonstrated. The mechanisms of generation and development of dislocations, their role in the formation of self-organizing coaxial structures were modeled.

Observation of a comb-shaped filamentary plasma array under subcritical condition in 303-GHz millimetre-wave air discharge

Gas breakdown in the millimetre-wave frequency band is an interesting phenomenon in nonlinear dynamics such as self-organized structure formation. We observed the transition between two types of filamentary plasma arrays in air discharge driven by a 303-GHz millimetre wave. Plasma is ignited at a parabolic mirror’s focal point in the overcritical condition. One array parallel to the electric field vector appears with a spacing of λ/4 at the focal point. Filaments then separate into plasma lumps ~10 μs after ignition. At 20 μs, a new comb-shaped array grows in the subcritical condition. Filaments are parallel to the incident beam with spacing of 0.96 λ and elongate towards the incident beam. This comb-shaped array appears only in the electric field plane; bulk plasma with a sharp vertex forms in the magnetic field plane. This array is created by a standing wave structure generated by waves diffracted from the plasma surface. Filamentary plasma array formations can influence the energy absorption by the plasma, which is important for engineering applications such as beamed energy propulsion.