Non-equilibrium Growth Processes Research Articles

Joule magnetostriction and volume magnetostriction of Iron Gallium thin films

The main aim of this work is to evaluate magnetostriction performances, including Joule magnetostriction and volume magnetostriction, of FeGa thin films synthesized by electrodeposition and ion-beam sputtering. This research demonstrated that the electrodeposited Fe(100-x)Gax (x: 19 ∼ 26) films had a tensile stress, and the ion-beam sputtered Fe81Ga19 film had a compressive stress. In both films, the easy axis of magnetization was in the in-plane direction. Both films exhibited nearly (110)-oriented polycrystalline structures. For the ion-beam sputtered Fe81Ga19 film, the observed volume magnetostriction was 39 ppm, approximately one-third of the Joule magnetostriction of 116 ppm. For electrodeposited Fe81Ga19, the Joule and volume magnetostrictions were 64 ppm and 46 ppm, respectively. An important conclusion of this research was that the FeGa films formed by non-equilibrium growth processes displayed a large volume magnetostriction.

Study of morphological evolution and growth mechanism of CVD grown 2D tin disulfide

Fractal patterns formed during non-equilibrium growth processes and are abundant in nature. However, the mechanism of their formation remains unknown. Several growth factors such as relaxation rate, cooling rate, diffusion anisotropy and growth time were identified for regulating the fractal growth. Nevertheless, most articles focused on regular shaped (such as triangles and hexagons) 2D layered metal dichalcogenides (LMDs), whereas fractals have received less attention. Therefore, understanding the controlled synthesis of LMDs materials with unique edge structures is highly desired for various potential applications. Here, we report large fractal growth of tin disulfide (SnS2) by atmospheric pressure chemical vapor deposition technique. The edge length of the atomically thin SnS2 fractals range from 5 to 100 µm. Our study shows the morphological evolution from fractal to triangular-like structure during the CVD growth process. To understand this phenomenon, we anticipated that the early phase of the growth mostly occurs via kinetic regulated pathway resulting fractal like structure. As the domains go through numerous relaxation phases throughout the edge diffusion process, the morphology gets more compact or regular, indicating increased thermodynamic control over the growth process. We have also provided a physical model for the growth mechanism of CVD grown SnS2.

Kinetic Control of Ultrafast Transient Liquid Assisted Growth of Solution-Derived YBa2 Cu3 O7 -x Superconducting Films.

Transient liquid assisted growth (TLAG) is an ultrafast non-equilibrium growth process mainly governed by kinetic parameters, which are only accessible through fast in situ characterizations. In situ synchrotron X-ray diffraction (XRD) analysis and in situ electrical resistivity measurements are used to derive kinetic diagrams of YBa2 Cu3 O7- x (YBCO) superconducting films prepared via TLAG and to reveal the unique peculiarities of the process. In particular, diagrams for the phase evolution and the YBCO growth rates have been built for the two TLAG routes. It is shown that TLAG transient liquids can be obtained upon the melting of two barium cuprate phases (and not just one), differentiated by their copper oxidation state. This knowledge serves as a guide to determine the processing conditions to reach high performance films at high growth rates. With proper control of these kinetic parameters, films with critical current densities of 2-2.6 MA cm-2 at 77 K and growth rates between 100-2000nm s-1 are reached. These growth rates are 1.5-3 orders of magnitude higher than those of conventional methods.

Understanding the structural diversity of chitins as a versatile biomaterial.

Chitin is one of the most abundant biopolymers, and it has adopted many different structural conformations using a combination of different natural processes like biopolymerization, crystallization and non-equilibrium self-assembly. This leads to a number of striking physical effects like complex light scattering and polarization as well as unique mechanical properties. In doing so, chitin uses a fine balance between the highly ordered chain conformations in the nanofibrils and random disordered structures. In this opinion piece, we discuss the structural hierarchy of chitin, its crystalline states and the natural biosynthesis processes to create such specific structures and diversity. Among the examples we explored, the unified question arises from the generation of completely different bioarchitectures like the Christmas tree-like nanostructures, gyroids or helicoidal geometries using similar dynamic non-equilibrium growth processes. Understanding the in vivo development of such structures from gene expressions, enzymatic activities as well as the chemical matrix employed in different stages of the biosynthesis will allow us to shift the material design paradigms. Certainly, the complexity of the biology requires a collaborative and multi-disciplinary research effort. For the future's advanced technologies, using chitin will ultimately drive many innovations and alternatives using biomimicry in materials science.This article is part of the theme issue ‘Bio-derived and bioinspired sustainable advanced materials for emerging technologies (part 1)'.

Kinetic roughening and nontrivial scaling in the Kardar–Parisi–Zhang growth with long-range temporal correlations

Long-range spatiotemporal correlations may play important roles in non-equilibrium surface growth processes. In order to explore the effects of long-range temporal correlation on dynamic scaling of growing surfaces, we carry out extensive numerical simulations of the (1 + 1)- and (2 + 1)-dimensional Kardar–Parisi–Zhang (KPZ) growth system in the presence of temporally correlated noise, and compare our results with previous theoretical predictions and numerical simulations. We find that surface morphologies are obviously affected with long-range temporal correlations, and as the temporal correlation exponent increases, the KPZ surfaces develop gradually faceted patterns in the saturated growth regimes. Our results show that the temporal correlated KPZ system displays evidently nontrivial dynamic properties when 0 < θ < 0.5, the characteristic roughness exponents satisfy α < α s, and α loc exhibits non-universal scaling within local window sizes, which differs with the existing dynamic scaling hypotheses, both in the (1 + 1)- and (2 + 1)-dimensions.

Preparation of epitaxial yttria-stabilized zirconia with non-quilibrium t' phase and ferroelastic domain by pulsed laser deposition

The non-equilibrium tetragonal t' phase of yttria-stabilizedzirconia (YSZ) plays a key role in improving the toughness of YSZ ceramics owing to its own ferroelastic domain toughening mechanism. Due to the disadvantages of traditional processes for preparing the YSZ t' phase, which requires high heating temperature, difficult to control defects and inability to regulate microstructure, it is not conducive to the preparation of YSZ by these methods. We report the use of substrate clamping and non-equilibrium growth process of PLD to render stable t' epitaxial YSZ films with multiple domain structure on (0001) Al2O3 substrates. Thin film structure and epitaxial relationship with substrate were subsequently analyzed by XRD, RSM, and HRTEM. It was found that the crystal orientation of the YSZ film changes as a function of oxygen pressure during deposition. When oxygenpressure is larger than 100 mtorr, YSZ films with highly oriented ferroelastic domains are obtained. Based on the symmetry relationship, we know that the film has three in-plane domain structures. The epitaxial relationship between the film and the substrate is (002) [110] YSZ // (0001) [112¯0] Al2O3.

Modelling cancer cell budding in-vitro as a self-organised, non-equilibrium growth process

Tissue self-organization into defined and well-controlled three-dimensional structures is essential during development for the generation of organs. A similar, but highly deranged process might also occur during the aberrant growth of cancers, which frequently display a loss of the orderly structures of the tissue of origin, but retain a multicellular organization in the form of spheroids, strands, and buds. The latter structures are often seen when tumors masses switch to an invasive behavior into surrounding tissues. However, the general physical principles governing the self-organized architectures of tumor cell populations remain by and large unclear. In this work, we perform in-vitro experiments to characterize the growth properties of glioblastoma budding emerging from monolayers. We further propose a theoretical model and its finite element implementation to characterize such a topological transition, that is modelled as a self-organised, non-equilibrium phenomenon driven by the trade–off of mechanical forces and physical interactions exerted at cell-cell and cell–substrate adhesions. Notably, the unstable disorder states of uncontrolled cellular proliferation macroscopically emerge as complex spatio–temporal patterns that evolve statistically correlated by a universal law.

Dynamics of surface evolution of rutile TiO2(110) after ion irradiation

ABSTRACTThe dynamics of TiO surfaces evolving under 60 keV Ar ions have been explored here. Dynamic scaling ansatz, height–height correlation (HHC) model and power spectral density (PSD) model have been applied to investigate the growth mechanisms. The surfaces are growing under non-equilibrium growth processes and three separate domains of evolution have been noticed. Early time growth of the surfaces can be characterized by roughness exponent, –0.74, and growth exponent, . Dominance of diffusion is also noticed with Edward Wilkinson (EW) growth scaling. In the next time regime, non-local instabilities get incorporated, due to sputter-induced nanostructuring of the surfaces, resulting in a rapid surface roughening with a high value of β. The surface roughness saturates in late time regime.

Low-Loss and Tunable Localized Mid-Infrared Plasmons in Nanocrystals of Highly Degenerate InN

Plasmonic response of free charges confined in nanostructures of plasmonic materials is a powerful means for manipulating the light-material interaction at the nanoscale and hence has influence on various relevant technologies. In particular, plasmonic materials responsive in the mid-infrared range are technologically important as the mid-infrared is home to the vibrational resonance of molecules and also thermal radiation of hot objects. However, the development of the field is practically challenged with the lack of low-loss materials supporting high quality plasmons in this range of the spectrum. Here, we demonstrate that degenerately doped InN nanocrystals (NCs) support tunable and low-loss plasmon resonance spanning the entire midwave infrared range. Modulating free-carrier concentration is achieved by engineering nitrogen-vacancy defects (InN1- x, 0.017 < x < 0.085) in highly degenerate NCs using a nonequilibrium gas-phase growth process. Despite the significant reduction in the carrier mobility relative to intrinsic InN, the mobility in degenerate InN NCs (>60 cm2/(V s)) remains considerably higher than the carrier mobility reported for other materials NCs such as doped metal oxides, chalcogenides, and noble metals. These findings demonstrate feasibility of controlled tuning of infrared plasmon resonances in a low-loss material of III-V compounds and open a gateway to further studies of these materials nanostructures for infrared plasmonic applications.

Scaling studies of self-affine nanopatterned TiO2 surfaces created via ion implantation

Dynamic Scaling studies have been performed here to investigate the morphological surface evolution of single crystal TiO2(110) surfaces after they are implanted with Cobalt ions. These ion irradiated surfaces develop via non-equilibrium growth processes and display rough interfaces with height fluctuations that demonstrate self-affine behavior. The scaling exponents like Roughness exponent (α), Growth Exponent (β), dynamic exponent (z) and structure factor constant (γ) have been derived here by applying height-height correlation as well as structure factor analysis techniques and show that diffusion plays a pivotal role in the evolution of these self-affine surfaces created after Cobalt ion irradiation.

基于微量热技术研究钼酸钙纳米饼原位生长的热动力学及机理

近年来，对纳米材料的生长过程研究取得了重大的进步，同时也发展了多种方法研究其生长机理。但鲜有方法能够原位的获取纳米材料生长过程的瞬时变化热动力学信息。本文利用高精度、高灵敏度的RD496-III型微量热计获得了CaMoO4纳米饼的生长过程的原位特征热谱信息，结合热动力学方程获取了CaMoO4纳米饼生长的热动力学特征生长参数阐述了其原位生长机理；CaMoO4纳米饼的生长过程经历了反应成核与晶体生长两个阶段，在298.15 K时其反应成核速率和晶体生长速率分别为1.57 × 10−3s−1、3.50 × 10−3s−1，以及深刻的诠释了原位生长过程产生的热变速率与溶液中离子浓度、晶体的成长、溶解、聚集、扩散之间的关系。本文旨在为研究纳米材料原位生长机理提供新的技术方法，进一步为纳米材料非平衡生长过程的热动力学信息的物理化学发展奠定了基础。 In recent years, great progress has been made to investigate the growth process of nanomaterials, and its growth mechanism has also been expanded by various methods. However, there are few methods to acquire the instantaneous thermodynamics information via in situ. In this paper, we use a RD 496-III microcalorimeter with high precision and high sensitivity to obtain the in situ heat flow curves in the growth process of CaMoO4 nanocake. The growth parameters of CaMoO4 nanocake were acquired by thermodynamics equation to investigate the energy and morphology evolution of the CaMoO4 growth mechanism. Results showed that the growth process of CaMoO4 nanocake had gone through two stages, including the phase nucleation and the crystal growth, whose nucleation rate and crystal growth rate were 1.57 × 10−3s−1 and 3.50 × 10−3s−1 respectively at 298.15 K. Moreover, the relationships between the rate of heat change in situ growth process and the ion concentration, crystal growth, dissolution, gathered, and diffusion have been analyzed in-depth. This paper is aimed to provide an effective method to study the in situ crystal growth, and further to build the foundation for thermal dynamic information of non-equilibrium growth process of nanomaterials in physical chemistry development.

Far-from-equilibrium growth of magnetic thin films with Blume-Capel impurities.

We investigate the irreversible growth of (2+1)-dimensional magnetic thin films. The spin variable can adopt three states (s(I)=±1,0), and the system is in contact with a thermal bath of temperature T. The deposition process depends on the change of the configuration energy, which, by analogy to the Blume-Capel Hamiltonian in equilibrium systems, depends on Ising-like couplings between neighboring spins (J) and has a crystal field (D) term that controls the density of nonmagnetic impurities (s(I)=0). Once deposited, particles are not allowed to flip, diffuse, or detach. By means of extensive Monte Carlo simulations, we obtain the phase diagram in the crystal field vs temperature parameter space. We show clear evidence of the existence of a tricritical point located at D(t)/J=1.145(10) and k(B)T(t)/J=0.425(10), which separates a first-order transition curve at lower temperatures from a critical second-order transition curve at higher temperatures, in analogy with the previously studied equilibrium Blume-Capel model. Furthermore, we show that, along the second-order transition curve, the critical behavior of the irreversible growth model can be described by means of the critical exponents of the two-dimensional Ising model under equilibrium conditions. Therefore, our findings provide a link between well-known theoretical equilibrium models and nonequilibrium growth processes that are of great interest for many experimental applications, as well as a paradigmatic topic of study in current statistical physics.

Predictions for p-Type CH3NH3PbI3 Perovskites

Approaches for doping organic–inorganic CH3NH3PbI3 halide perovskite solar cell materials are investigated by density-functional theory calculations of the extrinsic doping properties of CH3NH3PbI3. Our results reveal that p-type CH3NH3PbI3 halide perovskites can be realized by incorporation of some group IA, IB, or VIA elements such as Na, K, Rb, Cu, and O at I-rich growth conditions. We further show that n-type CH3NH3PbI3 halide perovskites are more difficult to realize due to the formation of neutral defects or compensation from intrinsic point defects. Our results suggest that nonequilibrium growth conditions and/or processes may be required to produce n-type CH3NH3PbI3 halide perovskites.

Graphene: Layer‐Stacking Growth and Electrical Transport of Hierarchical Graphene Architectures (Adv. Mater. 20/2014)

A layered stacking growth route for the hierarchical assembly of graphene on a liquid copper catalyst by chemical vapor deposition is described by G. Yu and co-workers on page 3218. These hierarchical graphene architectures, displaying a snow-like morphology, reveal the non-equilibrium growth processes of multi-layer graphene and present electrical anisotropy. This work potentially offers impetus for the application of graphenebased electronics.

Formation and Third-Order Optical Nonlinearities of Fractal Ge Nanocrystals Embedded in Au Matrix

Nonequilibrium growth processes of low-dimensional materials have attracted considerable attention, which controlled micro/nanostructures, properties, and various performances of materials. Semiconductor Ge in contact with some metals, e.g., Au, Pd, and Al, etc., is a class of distinctive materials with noninteger dimensions that differ from integer dimensional materials such as nanoparticles, nanowires, nanorods, nanotubes, nanoribbons, and thin films. Here, Au/Ge bilayer films with interesting fractal Ge nanocrystals were successfully prepared by high-vacuum thermal evaporation techniques. It was found that Ge nanocrystals embedded in Au matrix showed fascinating fractal morphologies with average size of fractal clusters at 550 nm and fractal dimension at 1.756 when the films were annealed at 150 °C for 30 min. Third-order optical nonlinearities of the annealed Au/Ge bilayer films were investigated in detail by Z-scan technique using a femtosecond laser. Experimental results indicated that the nonlinear...

Non-equilibrium Growth Processes of Porous TiO2 Nanocrystal-films during Pulsed Laser Ablation

ABSTRACTWe performed pulsed laser ablation of titanium dioxide (TiO2) target in O2 background gas. Effects of background gas pressure and substrate target distance on the structure of deposited films are clarified. The hierarchical structures are observed when we change scale of observation. The film deposited on the substrate is composed of primary nanocrystal and secondary porous-aggregated-nanostructures. The primary nanocrystal changes from anatase to rutile phase with increasing background gas pressure or substrate target distance. The porosity of secondary aggregated structure increases with increasing background gas pressure or substrate target distance. The similarity between the effects of background gas and substrate target distance indicates that confinement of the plume between target and substrate is important for structural formation. The non-equilibrium aggregation processes of nanocrystals in the plume and on the substrate are essential for the hierarchical structure of the nanocrystal film.

Twisted ZB–CdTe/RS–PbTe (111) heterojunction as a metastable interface structure

The heterostructures of (zinc-blende)–CdTe/(rock-salt)–PbTe are typically found to have their common cubic axes aligned to each other, as in the case of PbTe quantum dots embedded in a CdTe matrix. In this work, we perform both theoretical and experimental studies on the CdTe/PbTe heterostructure in a different geometry: a planar CdTe/PbTe (111) heterostructure. We simulate the epitaxial growth of CdTe (PbTe) on the (111) PbTe (CdTe) substrate, using a density-functional theory. A twisted CdTe/PbTe (111) interface structure has been predicted in the layer-by-layer epitaxial growth on the (111) substrate, in contrast to the non-twisted CdTe/PbTe (111) interface reported in the literature. This predicted structure has been confirmed experimentally in the heterostructure grown by molecular beam epitaxy, using a high-resolution transmission electron microscope. The twisted interface has a lower binding energy than the non-twisted one, indicating that the twisted structure is a metastable phase formed in the non-equilibrium growth process. Additionally, the interface reconstructions of the CdTe/PbTe (111) heterostructure observed by reflection high-energy electron diffraction are explained using the twisted interface model.

Dodecagonal tiling in mesoporous silica

Recent advances in the fabrication of quasicrystals in soft matter systems have increased the length scales for quasicrystals into the mesoscale range (20 to 500 ångströms). Thus far, dendritic liquid crystals, ABC-star polymers, colloids and inorganic nanoparticles have been reported to yield quasicrystals. These quasicrystals offer larger length scales than intermetallic quasicrystals (a few ångströms), thus potentially leading to optical applications through the realization of a complete photonic bandgap induced via multiple scattering of light waves in virtually all directions. However, the materials remain far from structurally ideal, in contrast to their intermetallic counterparts, and fine control over the structure through a self-organization process has yet to be attained. Here we use the well-established self-assembly of surfactant micelles to produce a new class of mesoporous silicas, which exhibit 12-fold (dodecagonal) symmetry in both electron diffraction and morphology. Each particle reveals, in the 12-fold cross-section, an analogue of dodecagonal quasicrystals in the centre surrounded by 12 fans of crystalline domains in the peripheral part. The quasicrystallinity has been verified by selected-area electron diffraction and quantitative phason strain analyses on transmission electron microscope images obtained from the central region. We argue that the structure forms through a non-equilibrium growth process, wherein the competition between different micellar configurations has a central role in tuning the structure. A simple theoretical model successfully reproduces the observed features and thus establishes a link between the formation process and the resulting structure.

Range expansion with mutation and selection: dynamical phase transition in a two-species Eden model

The colonization of unoccupied territory by invading species, known as range expansion, is a spatially heterogeneous non-equilibrium growth process. We introduce a two-species Eden growth model to analyze the interplay between uni-directional (irreversible) mutations and selection at the expanding front. While the evolutionary dynamics leads to coalescence of both wild-type and mutant clusters, the non-homogeneous advance of the colony results in a rough front. We show that roughening and domain dynamics are strongly coupled, resulting in qualitatively altered bulk and front properties. For beneficial mutations the front is quickly taken over by mutants and growth proceeds Eden-like. In contrast, if mutants grow slower than wild-types, there is an antagonism between selection pressure against mutants and growth by the merging of mutant domains with an ensuing absorbing state phase transition to an all-mutant front. We find that surface roughening has a marked effect on the critical properties of the absorbing state phase transition. While reference models, which keep the expanding front flat, exhibit directed percolation critical behavior, the exponents of the two-species Eden model strongly deviate from it. In turn, the mutation-selection process induces an increased surface roughness with exponents distinct from that of the classical Eden model.

First-principles study of defect properties of zinc blende MgTe

We studied the general chemical trends of defect formation in MgTe using first-principles band structure methods. The formation energies and transition energy levels of intrinsic defects and extrinsic impurities and some defect complexes in zinc blende MgTe were calculated systematically using a new hybrid scheme. The limiting factors for $p$- and $n$-type doping in MgTe were investigated. Possible solutions to overcome the doping limitation of MgTe are proposed. The best $p$-type dopant is suggested to be N with nonequilibrium growth process and the best $n$-type dopant is suggested to be I with its doping complex $\mathrm{V}{}_{\mathrm{Mg}}+$ 4I${}_{\mathrm{Te}}$.