Inhomogeneous Growth Research Articles

Beyond 10% efficient CZTSSe thin-film solar cells fabricated by a two-step CdS deposition process

The CZTSSe/CdS interface qualities are vital aspects and factors that would greatly decide the photovoltaic performance of CZTSSe solar cells. High-quality CZTSSe/CdS interfaces could reduce defect density and improve CZTSSe device performance. However, due to the inhomogeneous CZTSSe grain growth in local micro-regions during selenization, void defects would emerge at the CZTSSe/CdS interfaces by traditional CdS deposition method. In order to obtain high-quality CZTSSe/CdS interfaces, a novel method of two-step CdS deposition, with which the two CdS layers were deposited before and after the selenization of CZTS absorbers, was firstly introduced in the work. The first CdS layer with a certain designed thickness was deposited onto the as-deposited CZTS thin films by CBD. Then the thin films were annealed in selenium-containing atmosphere to obtain CZTSSe thin films of large grain sizes. The second CdS layers with different thicknesses were deposited onto the annealed CZTSSe thin films by CBD again. Comparing with that by the traditional one-step CdS deposition method, the efficiencies of CZTSSe solar cells by two-step CdS deposition method show a remarkable increase from 7.25% to 10.19%. An action mechanism for improving device performance by two-step CdS deposition was proposed: The first CdS layer on CZTS precursors could consistently keep a well coverage for the CZTSSe grains on the surfaces during selenization; The second CdS layer could ensure p-n junctions in good condition, which would reduce recombination centers and shunting paths. The results suggest that the two-step CdS deposition process is an effective method to obtain high-quality CZTSSe/CdS interfaces and high-performance solar cell devices.

Cells competition in tumor growth poroelasticity

Growth of biological tissues has been recently treated within the framework of Continuum Mechanics, by adopting heterogeneous poroelastic models where the interaction between soft matrix and interstitial fluid flow is coupled with inelastic effects ad hoc introduced to simulate the macroscopic volumetric growth determined by cells division, cells growth and extracellular matrix changes occurring at the micro-scale level. These continuum models seem to overcome some limitations intrinsically associated to other alternative approaches based on mass balances in multiphase systems, because the crucial role played by residual stresses accompanying growth and nutrients walkway is preserved. Nevertheless, when these strategies are applied to analyze solid tumors, mass growth is usually assigned in a prescribed form that essentially copies the in vitro measured intrinsic growth rates of the cell species. As a consequence, some important cell-cell dynamics governing mass evolution and invasion rates of cancer cells, as well as their coupling with feedback mechanisms associated to in situ stresses, are inevitably lost and thus the spatial distribution and the evolution with time of the growth inside the tumor –which would be results rather than inputs– are forced to enter in the model simply as data. In order to solve this paradox, it is here proposed an enhanced multi-scale poroelastic model undergoing large deformations and embodying inelastic growth, where the net growth terms directly result from the “interspecific” predator-prey (Volterra/Lotka-like) competition occurring at the micro-scale level between healthy and abnormal cell species. In this way, a system of fully-coupled non-linear PDEs is derived to describe how the fight among cell species to grab the available common resources, stress field, pressure gradients, interstitial fluid flows driving nutrients and inhomogeneous growth all simultaneously interact to decide the tumor fate.

Random surface growth and Karlin-McGregor polynomials

We consider consistent dynamics for non-intersecting birth and death chains, originating from dualities of stochastic coalescing flows and one dimensional orthogonal polynomials. As corollaries, we obtain unified and simple probabilistic proofs of certain key intertwining relations between multivariate Markov chains on the levels of some branching graphs. Special cases include the dynamics on the Gelfand-Tsetlin graph considered in the seminal work of Borodin and Olshanski in [10] and the ones on the BC-type graph recently studied by Cuenca in [17]. Moreover, we introduce a general inhomogeneous random growth process with a wall that includes as special cases the ones considered by Borodin and Kuan [8] and Cerenzia [15], that are related to the representation theory of classical groups and also the Jacobi growth process more recently studied by Cerenzia and Kuan [16]. Its most important feature is that, this process retains the determinantal structure of the ones studied previously and for the fully packed initial condition we are able to calculate its correlation kernel explicitly in terms of a contour integral involving orthogonal polynomials. At a certain scaling limit, at a finite distance from the wall, one obtains for a single level discrete determinantal ensembles associated to continuous orthogonal polynomials, that were recently introduced by Borodin and Olshanski in [11], and that depend on the inhomogeneities.

Fluttering of growing leaves as a way to reach flatness: experimental evidence on Persea americana.

Simple leaves show unexpected growth motions: the midrib of the leaves swings periodically in association with buckling events of the leaf blade, giving the impression that the leaves are fluttering. The quantitative kinematic analysis of this motion provides information about the respective growth between the main vein and the lamina. Our three-dimensional reconstruction of an avocado tree leaf shows that the conductor of the motion is the midrib, presenting continuous oscillations and inducing buckling events on the blade. The variations in the folding angle of the leaf show that the lamina is not passive: it responds to the deformation induced by the connection to the midrib to reach a globally flat state. We model this movement as an asymmetric growth of the midrib, which directs an inhomogeneous growth of the lamina, and we suggest how the transition from the folded state to the flat state is mechanically organized.

Revisiting Cu63 NMR evidence for charge order in superconducting La1.885Sr0.115CuO4

The presence of charge and spin stripe order in the La2CuO4-based family of superconductors continues to lead to new insight on the unusual ground state properties of high Tc cuprates. Soon after the discovery of charge stripe order at T(charge)=65K in Nd3+ co-doped LSCO ($T_{c}\simeq6$~K) [Tranquada et al., Nature {\bf 375} (1995) 561], Hunt et al. demonstrated that La$_{1.48}$Nd$_{0.4}$Sr$_{0.12}$CuO$_4$ and superconducting LSCO with x~1/8 (Tc ~ 30K) share nearly identical NMR anomalies near $T_{charge}$ of the former [Phys. Rev. Lett. {\bf 82} (1999) 4300]. Their inevitable conclusion that LSCO also undergoes charge order at a comparable temperature became controversial, because diffraction measurements at the time were unable to detect Bragg peaks associated with charge order. Recent advances in x-ray diffraction techniques finally led to definitive confirmations of the charge order Bragg peaks in LSCO with an onset at as high as T(charge)=80K. Meanwhile, improved instrumental technology has enabled routine NMR measurements that were not feasible two decades ago. Motivated by these new developments, we revisit the charge order transition of a LSCO single crystal based on 63Cu NMR techniques. We demonstrate that 63Cu NMR properties of the nuclear spin $I_{z}$ = -1/2 to +1/2 central transition below T(charge) exhibit unprecedentedly strong dependence on the measurement time scale set by the NMR pulse separation time $\tau$; a new kind of anomalous, very broad wing-like 63Cu NMR signals gradually emerge below T(charge) only for extremely short $\tau \lesssim 4~\mu$s, while the spectral weight of the normal NMR signals is progressively wiped out. The NMR linewidth and relaxation rates depend strongly on $\tau$ below T(charge), and their enhancement in the charge ordered state indicates that charge order turns on strong but inhomogeneous growth of Cu spin-spin correlations.

Inhomogeneity growth in two-component fermionic systems

The dynamics of fermionic many-body systems is investigated in the framework of Boltzmann-Langevin (BL) stochastic one-body approaches. Within the recently introduced BLOB model, we examine the interplay between mean-field effects and two-body correlations, of stochastic nature, for nuclear matter at moderate temperature and in several density conditions, corresponding to stable or mechanically unstable situations. Numerical results are compared to analytic expectations for the fluctuation amplitude of isoscalar and isovector densities, probing the link to the properties of the employed effective interaction, namely symmetry energy (for isovector modes) and incompressibility (for isoscalar modes). For unstable systems, clusterization is observed. The associated features are compared to analytical results for the typical length and time scales characterizing the growth of unstable modes in nuclear matter and for the isotopic variance of the emerging fragments. We show that the BLOB model is generally better suited than simplified approaches previously introduced to solve the BL equation, and it is therefore more advantageous in applications to open systems, like heavy ion collisions.

A computational study of the mechanisms of growth-driven folding patterns on shells, with application to the developing brain

We consider the mechanisms by which folds, or sulci (troughs) and gyri (crests), develop in the brain. This feature, common to many gyrencephalic species including humans, has attracted recent attention from soft matter physicists. It occurs due to inhomogeneous, and predominantly tangential, growth of the cortex, which causes circumferential compression, leading to a bifurcation of the solution path to a folded configuration. The problem can be framed as one of buckling in the regime of linearized elasticity. However, the brain is a very soft solid, which is subject to large strains due to inhomogeneous growth. As a consequence, the morphomechanics of the developing brain demonstrates an extensive post-bifurcation regime. Nonlinear elasticity studies of growth-driven brain folding have established the conditions necessary for the onset of folding, and for its progression to configurations broadly resembling gyrencephalic brains. The reference, unfolded, configurations in these treatments have a high degree of symmetry—typically, ellipsoidal. Depending on the boundary conditions, the folded configurations have symmetric or anti-symmetric patterns. However, these configurations do not approximate the actual morphology of, e.g., human brains, which display unsymmetric folding. More importantly, from a neurodevelopmental standpoint, many of the unsymmetric sulci and gyri are notably robust in their locations. Here, we initiate studies on the physical mechanisms and geometry that control the development of primary sulci and gyri. In this preliminary communication we carry out computations with idealized geometries, boundary conditions and parameters, seeking a pattern resembling one of the first folds to form: the Central Sulcus.

New Insights into Mossy Li Induced Anode Degradation and Its Formation Mechanism in Li–S Batteries

Optimization of cathodes and cell configurations has dramatically improved current Li–S batteries; it is now necessary to rescrutinize failure in Li–S batteries from an anodic perspective. Here, we reveal another possible failure mechanism induced by mossy Li in long-lifespan Li–S batteries and present a factor that might influence the inhomogeneous growth of Li whiskers. The large volume expansion derived from the growth of mossy Li promoted the formation and densification of a crust layer comprising passive sediments, which blocked the charge transfer for the lithium underneath, leading to low lithium utilization and battery failure. Further research showed the growth of mossy Li is related to inhomogeneous stripping, which began at imperfections on the SEI and self-amplified into large irregular pits, from which delicate mossy Li whiskers sprouted preferentially because of the relatively stable environment within. These findings are anticipated to enhance the performance of Li–S batteries and facilitat...

On the influence of inhomogeneous stiffness and growth on mechanical instabilities in the developing brain

The characteristic surface morphology of the mammalian brain is closely correlated with brain function and dysfunction. During development, the initially smooth surface evolves into an elaborately convoluted pattern. Growing evidence suggests that mechanical instabilities emerging from differential growth between a faster growing outer gray matter and a slower growing inner white matter play a major role in brain morphogenesis. Previous studies assume uniform growth and stiffness; yet, recent experiments indicate that the properties of brain tissue are highly inhomogeneous. Here, we hypothesize that regionally varying developmental pathways across the brain result in nonuniform material properties at the onset of cortical folding. We establish a computational model of brain growth to explore the effects of stiffness and growth variations in gray and white matter tissue to mimic cellular processes and evolving tissue microstructure. We present an effective approach to determine critical growth values from geometrical data and systematically study the effect of inhomogeneous material properties on growth-induced primary and secondary instabilities. Our results reveal that critical growth and wavelength strongly depend on the stiffness distribution in the developing brain. Regional variations in cortical growth affect secondary instabilities and evoke highly irregular folding patterns, but characteristic wavelength and critical growth remain relatively stable. The interplay of different influential factors including cortical thickness, brain geometry, stiffness, and growth explains how primary folds are highly preserved across individuals, whereas secondary and tertiary folds vary significantly. Our findings are directly applicable to imaging data of fetal brains and ultimately enable early diagnostics of cortical malformations to improve treatment of neurodevelopmental disorders including epilepsy, autism, spectrum disorders, and schizophrenia.

Rapid Crystallization of All-Inorganic CsPbBr3 Perovskite for High-Brightness Light-Emitting Diodes

Research into perovskite-based light-emitting diodes (PeLEDs) has been rapidly gaining momentum since the initial reports of green-emitting methylammonium lead bromide (CH3NH3PbBr3)-based devices were published. However, issues pertaining to its stability and morphological control still hamper progress toward high performing devices. Solvent engineering, a technique typically employed to modulate film crystallization, offers little opportunity for scale-up due to the tendency for inhomogeneous film growth and low degree of reproducibility. Here, we propose and show a simple gas-facilitated process to deposit a stable, all-inorganic perovskite CsPbBr3 film. The formation of smaller and less percolated grains, which gives rise to enhanced optical properties, highlights the importance of spatial charge confinement in the film. Consequently, the performance of our PeLEDs shows great improvement, with luminance as high as 8218 cd m–2 and turn-on voltage as low as 2.4 V. Concomitantly, the current efficiency and EQE of our device were increased to 0.72 cd A–1 and 0.088%, respectively. High reproducibility in the performance of PeLEDs fabricated using this process opens the path for large-area devices.

Enhancing the strength and ductility in accumulative back extruded WE43 magnesium alloy through achieving bimodal grain size distribution and texture weakening

The microstructure of a rare earth containing magnesium alloy, Mg-4.35Y-3RE-0.36Zr wt%, was engineered through applying accumulative back extrusion (ABE) process. Toward this end, the predetermined ABE cycles were applied at 400°C up to five passes under a punch speed of 5mm/min to study the ultrafine grained microstructure formation and its corresponding texture modification in the experimental material. A variety of bimodal grain size distributions were developed at all deformation conditions. In addition, the dissolution of eutectic phase stimulated the probability of dynamic precipitation of β phase during deformation. The latter caused a pinning effect on the grain boundary and gave rise to an inhomogeneous grain growth thereby intensified a bimodal grain size distribution (bimodality). In addition, the capability of experimental material to shear band formation during straining, even after one ABE pass, induced the level of bimodality. A remarkable grain refinement was achieved inside the shear bands due to the higher magnitude of shearing strain. Furthermore, the shear bands intersections provided suitable conditions for well defined ultrafine grain formation in between primary bands. The formation of noticeable number of these ultrafine grains within the shear bands could decrease the basal intensity thereby inducing a significant texture weakening effect. The obtained results indicated a significant improvement in both the strength (yield and ultimate) and elongation to fracture of the processed material. This was justified considering the effects of grain size, the level of bimodality and the texture weakening.

Revealing the role of strain rate during multi-pass compression in an advanced polycrystalline nickel base superalloy

In the single-pass hot compression of polycrystalline nickel base superalloy, inhomogeneous grain size distribution and grain growth frequently occur. For comparison, a multi-pass compression approach is employed to investigate the effect of strain rate on the flow stress and grain size evolution. By means of imposing different strain rates, the results show that the finest grain size corresponds to the second-pass strain rate of 0.1s−1, while the coarsest grain size arises from a combination of the first-pass strain rate of 0.001s−1 and the second-pass strain rate of 0.01s−1, respectively. A bimodal grain size distribution easily forms under the second-pass strain rate of 0.001s−1. The microscopic analysis discloses the critical roles of dynamic recrystallization (DRX) nucleation rate together with static recrystallization (SRX) in controlling the grain size development. The experimental results provide new insights to optimize the forging process of nickel base superalloy.

Constrained groove pressing and subsequent annealing of Al-Mn-Si alloy: Microstructure evolutions, crystallographic transformations, mechanical properties, electrical conductivity and corrosion resistance

Al-Mn-Si specimens were severe plastic deformed (SPDed) through constrained groove pressing (CGP) by εeff=1.16, 232, and 3.48. CGPed sheets were subsequently annealed at 150, 250 and 350°C to investigate complementary treatment route on macro- and microscale properties of heavily strained alloy. Microstructure evolutions in deformed and post-annealed states along with their associated mechanisms such as recovery, recrystallization and strain induced grain boundary migration (SIGBM) were studied and analyzed. SIGBM as an indication for inhomogeneous grain growth was traced by transformations in grains' aspect ratio. Microanalysis of crystallographic characteristics by means of X-ray diffraction (XRD) patterns revealed that (111) planes were the main crystallographic index in CGPed and annealed alloys since preservation up to 350°C had amplified the (200) and deteriorated the intensity of (311) planes. Dislocation density measurements implied the dynamic recovery occurrence in CGP (εeff=2.32) which had affected mechanical characteristics, electrical conductivity and corrosion resistance of the utilized alloy. Mechanical properties through tension and hardness tests had been examined since the maximum YS, UTS, and hardness of 118MPa and 141MPa, 52Hv obtained for CGPed specimen (εeff=3.48) compared with annealed alloy with the values of 85MPa and 112MPa, and 29Hv, respectively.

Effect of the intermediate sulfide layer on the Cu2ZnSnS4-based solar cells

Cu2ZnSnS4 (CZTS) thin-film solar cells were fabricated using Cu/Sn/Zn and Cu/SnS/Zn precursors. The precursors were prepared using a magnetron-sputtering system with subsequent annealing (sulfurization) in a sulfur atmosphere. Sulfurization was carried out at 580 °C for 1 h in an H2S/N2 environment at atmospheric pressure. The growth behavior of CZTS thin films with different precursors during sulfurization was investigated and their properties were analyzed using X-ray diffraction, scanning electron microscopy with energy-dispersive spectroscopy, and Raman spectroscopy. The CZTS thin film sulfurized using the Cu/Sn/Zn metallic precursor exhibited inhomogeneous growth with detrimental secondary phases, including Cu2S and ZnS, resulting in significant degradation in Voc, Jsc and FF. In contrast, the CZTS thin film formed using a Cu/SnS/Zn precursor showed uniform growth without secondary phases on the surface and 4.1% power conversion efficiency, which was greater than that of the solar cell formed with the metallic precursor.

Biomechanical Analysis of Normal Brain Development during the First Year of Life Using Finite Strain Theory.

The first year of life is the most critical time period for structural and functional development of the human brain. Combining longitudinal MR imaging and finite strain theory, this study aimed to provide new insights into normal brain development through a biomechanical framework. Thirty-three normal infants were longitudinally imaged using MRI from 2 weeks to 1 year of age. Voxel-wise Jacobian determinant was estimated to elucidate volumetric changes while Lagrange strains (both normal and shear strains) were measured to reveal directional growth information every 3 months during the first year of life. Directional normal strain maps revealed that, during the first 6 months, the growth pattern of gray matter is anisotropic and spatially inhomogeneous with higher left-right stretch around the temporal lobe and interhemispheric fissure, anterior-posterior stretch in the frontal and occipital lobes, and superior-inferior stretch in right inferior occipital and right inferior temporal gyri. In contrast, anterior lateral ventricles and insula showed an isotropic stretch pattern. Volumetric and directional growth rates were linearly decreased with age for most of the cortical regions. Our results revealed anisotropic and inhomogeneous brain growth patterns of the human brain during the first year of life using longitudinal MRI and a biomechanical framework.

Perspectives on the mathematics of biological patterning and morphogenesis

A central question in developmental biology is how size and position are determined. The genetic code carries instructions on how to control these properties in order to regulate the pattern and morphology of structures in the developing organism. Transcription and protein translation mechanisms implement these instructions. However, this cannot happen without some manner of sampling of epigenetic information on the current patterns and morphological forms of structures in the organism. Any rigorous description of space- and time-varying patterns and morphological forms reduces to one among various classes of spatio-temporal partial differential equations. Reaction-transport equations represent one such class. Starting from simple Fickian diffusion, the incorporation of reaction, phase segregation and advection terms can represent many of the patterns seen in the animal and plant kingdoms. Morphological form, requiring the development of three-dimensional structure, also can be represented by these equations of mass transport, albeit to a limited degree. The recognition that physical forces play controlling roles in shaping tissues leads to the conclusion that (nonlinear) elasticity governs the development of morphological form. In this setting, inhomogeneous growth drives the elasticity problem. The combination of reaction-transport equations with those of elasto-growth makes accessible a potentially unlimited spectrum of patterning and morphogenetic phenomena in developmental biology. This perspective communication is a survey of the partial differential equations of mathematical physics that have been proposed to govern patterning and morphogenesis in developmental biology. Several numerical examples are included to illustrate these equations and the corresponding physics, with the intention of providing physical insight wherever possible.

Inhomogeneous Degradation Phenomena of NMC Cathode in 18650-Type Lithium-Ion Battery: A Soft X-Ray Absorption Spectroscopic Investigation

IntroductionEstablishment of lifetime prediction methodology for Li-ion batteries (LIBs) is strongly required in order to prolong the lifetime of LIB and to use LIBs in safe. While “square root (SQRT) law” is proposed to predict the lifetime of LIBs [1] based on the formation of an irreversible solid electrolyte interphase (SEI) at anode surface and the electrochemically deactivation of cathode active materials, the SQRT law cannot describe the degradation behavior precisely in while period of LIB operation, especially near the end stage of degradation. In addition, detailed mechanism of degradation also remains unknown. Previously, we reported the detailed structure of SEIs in heavily deteriorated anodes by the Hard X-ray photoemission spectroscopy (HAXPES) and discuss the degradation mechanism focused on inhomogeneous SEI growth [2].In this study, we also investigated the detailed structure of surface in heavily deteriorated cathodes by the soft X-ray absorption spectroscopy (XAS) and then, we discuss the inhomogeneous degradation phenomena of cathode. ExperimentalA commercial 18650-type lithium ion battery cell, which consists of a graphite anode, Li(Ni1-x-y Mn x Co y )O2 cathode, and LiPF6 in a mixture solvent of EC, PC, EMC and DMC as electrolyte, was used in this study. The Cells were charged and discharged with 1C rate (0, 100, 200 and 500cycles) at 25ºC. After the cycle tests, the battery cells were disassembled in an argon glove box, in which the oxygen and water contents were maintained below 1 ppm. The electrodes were washed with highly purified DMC to remove the residual electrolyte components and then, the electrodes were vacuum-dried to evaporate the solvents. All samples were transferred to the analysis chamber by using a transfer vessel.The XAS measurements were carried out at SR Center of Ritsumeikan University on a grating beamline BL-11. We simultaneously obtained the XAS spectra in three different modes, a partial electron yield (PEY) mode, a total electron yield (TEY) mode and a fluorescence yield (FY), whose detection depth correspond to ~ 2 nm, ~ 20 nm and ~ 200 nm, respectively. Results and discussionFigure 1(a) shows the change of discharge capacity retention as a function of SQRT of the number of cycle. Although discharge capacity retention was proportional to SQRT up to 300cycles, sudden reduction was observed around 300cycles. We show the discharge curve of the reassembled coin-type cells operated in a voltage region of 4.2-2.6 V for MNC cathode at a constant current of 0.1 C at 25 °C in Fig. 1(b). In these measurements, we applied the cathode at the inside and outside of the sheet and we observed drastic fade of the cathode capacity at the outside of sheet after 500 cycled.Figure 1 (c), (d) and (e) show Mn L 2,3 –edge, Co L 2,3- edge and Ni L 2,3 –edge XAS spectra of cathode active materials in discharge state (3.6 V) taken by PEY mode, respectively. We can easily find that ratio of lower valence state in each XAS spectra (Mn: ~640 eV, Co: ~779 eV, Ni: ~854 eV) is higher at the outside of cathode sheet after 500 cycled, especially in Mn L 2,3 –edge XAS spectra. On the other hands, we observed the no difference in XAS spectra at the outside and inside of cathode sheet taken by FY mode (shown in Fig. 1(f)). These indicate that the surface of the cathode active materials at the outside of sheet strongly degenerated and the Mn ions were selectively influenced. We also show the Ni L 2,3 –edge XAS spectra in charged state (4.2 V) taken by PEY and FY mode in Fig. 1(g) and Fig. 1(h), respectively. In the NMC cathode, it is well known that only the Ni ions change in valence form Ni2+ to Ni 4+ during the charging process to 4.2V. However, we observed the no change in valence state of Ni ions at the surface and the outside of cathode sheet, indicating the existence of deactivated regions. In addition, the change in valence state of Ni ions at the outside of cathode sheet is smaller than that of the inside at bulky regions.From these results, the sudden reduction of discharge capacity retention was thought to be caused by the deactivation of active materials at the outside of cathode sheet, especially at the surface, in addition to the irreversible loss of Li due to rapid SEI growth at the inside of anode sheet [2]. Acknowledgement The synchrotron experiments were carried out on beamline BL-11 at SR center of Ritsumeikan University and we thank K. Yamanaka for his help in XAS measurements. Figure 1

Striated populations in disordered environments with advection

Growth in static and controlled environments such as a Petri dish can be used to study the spatial population dynamics of microorganisms. However, natural populations such as marine microbes experience fluid advection and often grow up in heterogeneous environments. We investigate a generalized Fisher-Kolmogorov-Petrovsky-Piscounov (FKPP) equation describing single species population subject to a constant flow field and quenched random spatially inhomogeneous growth rates with a fertile overall growth condition. We analytically and numerically demonstrate that the non-equilibrium steady-state population density develops a flow-driven striation pattern. The striations are highly asymmetric with a longitudinal correlation length that diverges linearly with the flow speed and a transverse correlation length that approaches a finite velocity-independent value. Linear response theory is developed to study the statistics of the steady states. Theoretical predictions show excellent agreement with the numerical steady states of the generalized FKPP equation obtained from Lattice Boltzmann simulations. These findings suggest that, although the growth disorder can be spatially uncorrelated, correlated population structures with striations emerge naturally at sufficiently strong advection.

Electrochemomechanics of Electrodes in Li-Ion Batteries: A Review

A Li-ion battery is a system that dynamically couples electrochemistry and mechanics. The electrochemical processes of Li insertion and extraction in the electrodes lead to a wealth of phenomena of mechanics, such as large deformation, plasticity, cavitation, fracture, and fatigue. Likewise, mechanics influences the thermodynamics and kinetics of interfacial reactions, ionic transport, and phase transformation of the electrodes. The emergence of high-capacity batteries particularly enriches the field of electrochemomechanics. This paper reviews recent observations on the intimate coupling between stresses and electrochemical processes, including diffusion-induced stresses, stress-regulated surface charge transfer, interfacial reactions, inhomogeneous growth of lithiated phases, instability of solid-state reaction front (SSRF), as well as lithiation-modulated plasticity and fracture in the electrodes. Most of the coupling effects are at the early stage of study and are to be better understood. We focus on the elaboration of these phenomena using schematic illustration. A deep understanding of the interactions between mechanics and electrochemistry and bridging these interdisciplinary fields can be truly rewarding in the development of resilient high-capacity batteries.

Agitation dependent properties of copper indium diselenide thin films prepared by electrochemical route

CuInSe2 (CIS) thin films have been prepared by potentiostatic electrochemical synthesis route in an aqueous medium. A conventional three-electrode electrochemical geometry was used to study the influence of agitation on electrodeposition of CIS. The co-deposition potentials for Cu-In-Se, −0.4V and −0.6V were optimized by using cyclic voltammetry measurements. The diffusive controlled growth with instantaneous nucleation is observed by Chronoamperometric measurements. X-ray diffraction (XRD) and Raman spectroscopy, UV–Vis spectroscopy, energy dispersive X-ray analysis (EDAX) and scanning electron microscopy (SEM) were employed to study the structural, optical, compositional and morphological properties, respectively. Polycrystalline CIS thin films with tetragonal structure were obtained without agitation, however the secondary phases of CuxSey were attributed with agitation. The Raman results are found to be in good agreement with XRD and EDAX analyses. Without agitation the energy band gap (Eg) was estimated ~1.1eV. The higher values of Eg~1.5 to 1.8eV measured for the samples grown with agitation are proposed due to the inhomogeneous growth of precursors and the change in surface morphology. Uniform, compact and well adherent CIS layers were deposited with and without agitation. The deposition potentials and agitation conditions were found to be greatly affected on the surface morphology. The stoichiometric CIS layer was deposited at −0.6V without agitation.