Surface Growth Research Articles

Effects of Cp2Mg molar flow rate on structural, optical, and electrical properties of semipolar Mg-doped p-AlGaN epi-layers

The semipolar (11 2‾ 2) plane Mg-doped p-Al0.42Ga0.58N epi-layers were successfully deposited on (10 1‾ 0) m-plane sapphire substrates with metal organic chemical vapor deposition technology. The effects of Cp2Mg molar flow rate on the structural, optical, and electrical properties of p-Al0.42Ga0.58N epitaxial layer were extensively studied. The randomly distributed Mg atoms and/or clusters that partially covered the growth surface were verified to act as an island-like mask to block the propagation of dislocations along the growth direction, resulting in a significant improvement in the crystalline quality of the semipolar Mg-doped p-AlGaN epi-layers. Moreover, two emission peaks with novel behavior were observed in the photoluminescence spectrum and identified to be originated from the transition between the conduction band and the Mg-related shallow acceptor energy level, and the deep Mg-induced compensation donor and the Mg acceptor pair-related transition, respectively. In addition, a hole concentration as high as 1.03 × 1017 cm−3 and a resistivity as low as 12.8 Ω cm were achieved for the semipolar Mg-doped p-Al0.42Ga0.58N epi-layer grown with the optimized Cp2Mg molar flow rate in this study.

Exploring TMA and H2O Flow Rate Effects on Al2O3 Thin Film Deposition by Thermal ALD: Insights from Zero-Dimensional Modeling

This study investigates the impact of vapour-phase precursor flow rates—specifically those of trimethylaluminum (TMA) and deionized water (H2O)—on the deposition of aluminum oxide (Al2O3) thin films through atomic layer deposition (ALD). It explores how these flow rates influence film growth kinetics and surface reactions, which are critical components of the ALD process. The research combines experimental techniques with a zero-dimensional theoretical model, designed specifically to simulate the deposition dynamics. This model integrates factors such as surface reactions and gas partial pressures within the ALD chamber. Experimentally, Al2O3 films were deposited at varied TMA and H2O flow rates, with system conductance guiding these rates across different temperature settings. Film properties were rigorously assessed using optical reflectance methods and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. The experimental findings revealed a pronounced correlation between precursor flow rates and film growth. Specifically, at 150 °C, film thickness reached saturation at a TMA flow rate of 60 sccm, while at 200 °C, thickness peaked and then declined with increasing TMA flow above this rate. Notably, higher temperatures generally resulted in thinner films due to increased desorption rates, whereas higher water flow rates consistently produced thicker films, emphasizing the critical role of water vapour in facilitating surface reactions. This integrative approach not only deepens the understanding of deposition mechanics, particularly highlighting how variations in precursor flow rates distinctly affect the process, but also significantly advances operational parameters for ALD. These insights are invaluable for enhancing the application of ALD technologies across diverse sectors, including microelectronics, photovoltaics, and biomedical coatings, effectively bridging the gap between theoretical predictions and empirical results.

Cu thin film growth on stepped Si substrate: Effects of incident energy and thermal annealing

The existence of defects on the substrate surface is unavoidable and has a significant impact on the determination of surface properties. Among the prevalent types of defects, steps play an important role. In this study, molecular dynamics simulations are employed to explore the growth process of a thin film of Cu on a Si (001) substrate with a step. This research investigates how incident energy and thermal annealing affect the growth mode, surface roughness, film-substrate interface, and dislocation evolution. The results indicate that during the initial stage of the growth, the nucleation phenomenon was observed on terraces. The simulation indicates that the Cu atoms occur in an island growth mode on the stepped substrate. It is found that when the incident energy is increased and thermal annealing is performed, the surface curvature and roughness are reduced. Furthermore, the intermixing thickness at the interface increases due to the variation of the incidence energy. A dislocation analysis revealed that some dislocations disappeared before and after annealing, and a perfect dislocation appeared by increasing the incident energy.

Characterisation of the surface growth of Mucor circinelloides in cheese agar media using predictive mathematical models

The main objective of this work was to characterise the mycelial growth of Mucor circinelloides, one of the fungal contaminants that appear frequently in the artisan cheese production environment. The study uses primary Baranyi and Huang models to compare their parameters and predict M. circinelloides on cheese-based medium (CBA) under diverse environmental conditions (temperature range from 6 to 37 °C and 0 and 1 % NaCl concentration). However, the Baranyi model consistently estimated longer lag phases and higher surface growth rates (sgr) than the Huang model; both models showed adequate best-fit performance (exactly with the mean coefficient of determination R2 = (0.993 ± 0.020 × 10−1). The groups of primary growth parameters were analysed against temperature using the cardinal model (CM) with the following main outputs. The optimal surface growth rates (sgropt) on CBA were 6.8 and 6.5 mm/d calculated with the Baranyi and Huang models, respectively. They were reduced by approximately 46 % on the surface of the agar medium when 1 % NaCl was added. Topt was estimated in a very narrow range of 32.1–32.5 °C from both primary sgr data sets (0 % and 1 % NaCl). Similarly, Tmax values of 37.2 °C and 37.3 °C were estimated for the Baranyi and Huang models, respectively; however, they decreased at 2 °C in CBA with 1 % NaCl (Tmax = 35.1 °C). The application of CM for sgr provided an estimation of the parameter Tmin with negative values that are considered only as a theoretical output. The results provide insight into the modelling and prediction of fungi growth as a function of time and salt concentration, including the times to detect visible mycelial growth of Mucor circinelloides. The mere quantification of this phenomenon can be useful for practice. Adjusting the frequency of the cheese surface washing step with a salt solution at the early stage of ripening properly can prevent the growth of not only fast fungal growers.

Dynamics of the surface growth resulted from sedimentation of spheres in a Hele–Shaw cell containing a low-viscosity fluid

In this paper, we investigate the dynamics of surface growth resulting from sedimentation of spherical granular particles in a fluid environment, using experiments and simulations. In the experimental part, spherical polystyrene particles are poured down from the top of a vertical Hele–Shaw cell and form a 1 + 1-dimensional growing surface. The surface roughness is obtained from the images, and the growth and roughness exponents are measured. In the numerical simulation part, the surface growth process is simulated using the discrete element method, considering the interactions between the grains, and the exponents are calculated. In this method, unlike conventional simulation models, instead of a discrete deposition law, the dynamics of the individual particles throughout the process are obtained, considering different forces acting on the particles. Finally, the simulation results are compared with the experiment, and we see a very good agreement between them. We find different values for the exponents using different methods, indicating that the system is multi-affine and does not obey the scaling laws of affine models.

Modeling the growth of Aspergillus brasiliensis affected by a nonthermal plasma.

The main objective of the study was to develop and validate a model for the growth of Aspergillus brasiliensis on surfaces, specifically on agar culture medium. An additional aim was to determine conditions for complete growth inhibition of this micromycete using two different nonthermal plasma (NTP) sources. The developed model uses two key parameters, namely the growth rate and growth delay, which depend on the cultivation temperature and the amount of inoculum. These parameters well describe the growth of A. brasiliensis and the effect of NTP on it. For complete fungus inactivation, a single 10-minute exposure to a diffuse coplanar surface barrier discharge was sufficient, while a point-to-ring corona discharge required several repeated 10-minute exposures at 24-h intervals. The article presents a model for simulating the surface growth of A. brasiliensis and evaluates the effectiveness of two NTP sources in deactivating fungi on agar media.

Fabrication and characterization of biomineral amphiphilic copolymer hybrid microparticle: Evaluation of storage stability and collagen synthesis property of curcumin

Microencapsulation is an available and effective therapeutic option for entrapping targeted bioactive components. In this study, biomineralization-mediated separation and encapsulation of food-derived bioactive materials in organic materials were conducted, and the storage stability and effectiveness of these materials in the promotion of skin wound healing were assessed. To generate fine-textured and mechanically stable hexagonal particles, the hybrid materials were assembled using CaCO3 mineralized with an amphiphilic copolymer coupled with curcumin (CUR). The synthesized products were characterized using field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, and particle size analysis. The hybrid microparticles contained 1.58 wt% of CUR, and 91% of its initial concentration was retained after storage at four different temperatures. Based on the crystallization mechanism, CUR with an amphiphilic copolymer could be the core component that provides the surface for CaCO3 crystal growth, causing independent formation of the organic–inorganic structures and preventing CUR leaching. Furthermore, the induced hybrid particles were found to promote skin wound healing by stimulating collagen synthesis without inducing cytotoxicity. To the best of our knowledge, this is the first study to demonstrate the potential use of bioactive ingredients with an amphiphilic copolymer combined with biomineralization for formulation purposes and to achieve a skin wound healing effect.

Numerical simulation of soot and NO formation in DME/gasoline laminar co-flow diffusion flames

Dimethyl ether (DME) is regarded as a promising alternative fuel to reduce greenhouse gases and soot emission. However, the application of DME in actual engines is difficult because of its low calorific value and viscosity. DME is commonly utilized as a supplementary component in traditional fuels to enhance their combustion efficiency and emission performance. This study investigated the effect of DME blending on the soot and NO formation in laminar diffusion gasoline flames. The results showed that the peak soot volume fraction (SVF) reduced by 12.3 %, while the peak temperature increased by 19.2 K and the peak concentration of NO increased by 18.2 % when the blending ratio of DME increased from 0 % to 15 %. The primary reason for the reduction in the soot inception rate was the decrease in benzo(ghi)fluoranthene (BGHIF) concentration. The formation of BGHIF was controlled by the C6H5CH3 → A1 → A1-→A1C2H → A2R5 → A2 → A2-→BGHIF pathways. The decrease of initial soot particles led to a reduction in Hydrogen Abstraction Carbon Addition (HACA) surface growth rate. The increase in A4 concentration was due to the increase in the concentration of C4H2 in the reaction A2R5 + C4H2 = A4. Therefore, more benzo[a]pyrene (BAPYR) was formed through A4 + C4H2 = BAPYR, promoted the process of soot condensation. The increase in OH concentration promoted the oxidation of OH, and the decrease in soot inhibited the oxidation of O2. The majority of NO was primarily produced through the NO thermal pathway in the DME/gasoline flame, and N + OH = NO + H was the main reaction to form NO. The increase of O, H and OH radicals caused the increase in NO concentration.

Prediction of morphology of CL-20/TFAZ cocrystal crystals in binary solvents based on modified attachment energy model

Crystal morphology of CL-20/TFAZ cocrystal in vacuum was predicted using the attachment energy (AE) model. Additionally, the modified attachment energy (MAE) model and molecular dynamics (MD) method were utilized to predict the crystal morphology of CL-20/TFAZ cocrystal in four different binary solvents, namely, isopropyl alcohol (IPA)/acetone (AC), IPA/dimethyl sulfoxide (DMSO), IPA/ethyl acetate (EA), and IPA/water (H2O). The radial distribution function (RDF) between the solvent and crystal surface and the mean square displacement (MSD) of the solvent were calculated. The findings showed that the morphology of CL-20/TFAZ cocrystal in vacuum was an irregular polyhedron with eleven important growth surfaces: (001), (1−10), (110), (100), (011), (0−11), (10−1), (020), (0−20), (11−1), and (1−1−1), with the (001) surface having the highest area ratio of 31.693 %. The crystalline morphology in IPA/AC, IPA/DMSO, and IPA/EA solvents was block-shaped, while it was rod-shaped in IPA/H2O. Comparing the RDF values of the four solvents, IPA/H2O exhibited the largest g(r) value and could more easily adsorb onto the crystal surface of CL-20/TFAZ cocrystal. Interestingly, IPA/H2O solvent had the smallest MSD value, suggesting the slowest diffusion rate, while IPA/AC solvent exhibited the fastest diffusion rate. Overall, IPA/EA solvents were more suitable for the formation of CL-20/TFAZ cocrystal.

Effects of Miscut on Step Instabilities in Homo-Epitaxially Grown GaN.

The rough morphology at the growth surface results in the non-uniform distribution of indium composition, intentionally or unintentionally doped impurity, and thus impacts the performance of GaN-based optoelectronic and vertical power electronic devices. We observed the morphologies of unintentionally doped GaN homo-epitaxially grown via MOCVD and identified the relations between rough surfaces and the miscut angle and direction of the substrate. The growth kinetics under the effect of the Ehrlich-Schwoebel barrier were studied, and it was found that asymmetric step motions in samples with a large miscut angle or those grown at high temperature were the causes of step-bunching. Meandering steps were believed to be caused by surface free energy minimization for steps with wide terraces or deviating from the [11¯00] m-direction.

Homogeneous Growth of 3C-SiC Crystal Surface at Solid–Liquid Interface and Its Competitive Relationship

Homogeneous Growth of 3C-SiC Crystal Surface at Solid–Liquid Interface and Its Competitive Relationship

Linkages between urban growth and land surface temperature variations in the Seoul metropolitan area: A spatial first-order difference approach

This study investigates the effects of urban development and expansion on Land Surface Temperature (LST) changes from 2000 to 2018, using the Seoul Metropolitan area (SMA) as a case study area. Along with descriptive analysis, this study uses a spatial first-order difference model to statistically analyze the longitudinal relationship between land use features and LST, including impervious surface (IS), enhanced vegetation index (EVI), anthropogenic factors, and urban spatial and topographical factors as well as urban development types as influential factors on LST variations. Our findings support prior research indicating the cooling effects of vegetation and warming effects of imperviousness. We also found a positive association between detached housing units, manufacturing activities and LST changes and a negative relationship between apartment units, urban parks, service activities and LST changes. More importantly, substantial LST reduction was found in the large-scale high-rise apartment complexes redeveloped from the low-rise, detached housing sites in inner-city infill areas, contrasting with significant LST rise in the suburban new town development. We suggest redevelopment of inner-city low-rise compact areas into high-rise but greener blocks as a LST mitigation strategy, equipped with cooling strategies such as green infrastructure and climate-sensitive design considering local microclimate and natural ventilation.

Dynamic Insights into the Growth Mechanisms of 2D Covalent Organic Frameworks on Graphene Surfaces.

Producing high-quality two-dimensional (2D) covalent organic frameworks (COFs) is crucial for industrial applications. However, this remains significantly challenging with current synthetic techniques. A deep understanding of the intermolecular interactions, reaction temperature, and oligomers is essential to facilitate the growth of highly crystalline COF films. Herein, molecular dynamics simulations were employed to explore the growth of 2D COFs from monomer assemblies on graphene. Our results showed that chain growth reactions dominated the COF surface growth and that van der Waals (vdW) interactions were important in enhancing the crystallinity through monomer preorganization. Moreover, appropriately tuning the reaction temperature improved the COF crystallinity and minimized the effects of amorphous oligomers. Additionally, the strength of the interface between the COF and the graphene substrate indicated that the adhesion force was proportional to the crystallinity of the COF. This work reveals the mechanisms for nucleation and growth of COFs on surfaces and provides theoretical guidance for fabricating high-quality 2D polymer-based crystalline nanomaterials.

Deciphering Clues Regarding Magma Composition Encoded in Quartz‐Hosted Embayments and Melt Inclusions Through Direct Numerical Simulations

AbstractCrystal‐hosted melt embayments and melt inclusions partially record magmatic processes at depth, but it is not always obvious how to interpret this record. One impediment is our incomplete understanding of how embayments and melt inclusions form. In this study, we investigate the formation mechanism of embayments and melt inclusions during quartz growth to quantify the relationship between the compositions of the entrapped and average melt. We study the growth of embayments and inclusions through direct numerical simulations that couple the growth of a crystal surface with the evolution of the concentrations of incompatible components in the surrounding melt. We find that H2O is more enriched in the interior of defects on crystal surface compared to the exterior. The resultant lower disequilibrium in the defect interior causes lower growth rate than in the exterior, elongating the defect into an embayment. If crystal growth stops, the composition in the embayment equilibrates with the average melt within days to months. If crystal growth continues until the embayment neck closes, a melt inclusion forms. The melt entrapped by both embayments and melt inclusions is enriched in incompatible components, such as H2O and CO2. In addition to inclusion size, the enrichment of incompatible components in melt inclusions also depends on component diffusivity and the crystal growth regime. High‐diffusivity components like H2O have similar enrichment levels in all scenarios, while lower‐diffusivity components like CO2 are more enriched in melt inclusions with smaller sizes or formed in continuous crystal growth.

Process development for the production of mesenchymal stromal cell-derived extracellular vesicles in conventional 2D systems

BackgroundIn recent years, the importance of extracellular vesicles (EVs) derived from mesenchymal stromal cells (MSCs) has increased significantly. For their widespread use, a standardized EV manufacturing is needed which often includes conventional, static 2D systems. For these system critical process parameters need to be determined. MethodsWe studied the impact of process parameters on MSC proliferation, MSC-derived particle production including EVs, EV- and MSC-specific marker expression, and particle functionality in a HaCaT cell migration assay. ResultsWe found that cell culture growth surface and media affected MSCs and their secretory behavior. Interestingly, the materials that promoted MSC proliferation did not necessarily result in the most functional MSC-derived particles. In addition, we found that MSCs seeded at 4 × 103 cells cm−2 produced particles with improved functional properties compared to higher seeding densities. MSCs in a highly proliferative state did not produce the most particles, although these particles were significantly more effective in promoting HaCaT cell migration. The same correlation was found when investigating the cultivation temperature. A physiological temperature of 37°C was not optimal for particle yield, although it resulted in the most functional particles. We observed a proliferation-associated particle production and found potential correlations between particle production and glucose consumption, enabling the estimation of final particle yields. ConclusionsOur findings suggest that parameters, which must be defined prior to each individual cultivation and do not require complex and expensive equipment, can significantly increase MSC-derived particle production including EVs. Integrating these parameters into a standardized EV process development paves the way for robust and efficient EV manufacturing for early clinical phases.

A Versatile Deposition Model for Natural and Processed Surfaces

This paper introduces a robust deposition model designed for exploring the growth dynamics of deposits on surfaces under practical conditions. The study addresses the challenge of characterizing the intricate morphology of deposits, exhibiting significant visual variations. A generative approach is deployed to create diverse natural and engineered surface textures, governed by probabilistic principles. The model’s formulation addresses key questions related to deposition initiation, nucleation point behaviour, spatial scaling, deposit growth rates, spread dynamics, and surface mobility. A versatile algorithm, relying on six parameters and employing nested loops and Gaussian sampling, is developed. The algorithm’s efficacy is examined through extensive simulations, involving variations in nucleation scaling densities, aggregate scaling scenarios, spread factors, and diffusion rates. Surface statistics are computed for simulated deposits and analyzed using Fast Fourier Transform (FFT). The resulting database enables quantitative comparisons of surfaces generated with different parameters, where the database-derived parallel coordinates offer guidance for selecting optimal model parameters to achieve desired surface morphologies. The proposed approach is validated against urea-derived deposits, exhibiting statistical consistency and agreement with experimental observations. Overall, the model’s adaptable framework holds promise for understanding and predicting deposit growth on surfaces in diverse practical scenarios.

Nonlinear Growth Dynamics of Neuronal Cells Cultured on Directional Surfaces.

During the development of the nervous system, neuronal cells extend axons and dendrites that form complex neuronal networks, which are essential for transmitting and processing information. Understanding the physical processes that underlie the formation of neuronal networks is essential for gaining a deeper insight into higher-order brain functions such as sensory processing, learning, and memory. In the process of creating networks, axons travel towards other recipient neurons, directed by a combination of internal and external cues that include genetic instructions, biochemical signals, as well as external mechanical and geometrical stimuli. Although there have been significant recent advances, the basic principles governing axonal growth, collective dynamics, and the development of neuronal networks remain poorly understood. In this paper, we present a detailed analysis of nonlinear dynamics for axonal growth on surfaces with periodic geometrical patterns. We show that axonal growth on these surfaces is described by nonlinear Langevin equations with speed-dependent deterministic terms and gaussian stochastic noise. This theoretical model yields a comprehensive description of axonal growth at both intermediate and long time scales (tens of hours after cell plating), and predicts key dynamical parameters, such as speed and angular correlation functions, axonal mean squared lengths, and diffusion (cell motility) coefficients. We use this model to perform simulations of axonal trajectories on the growth surfaces, in turn demonstrating very good agreement between simulated growth and the experimental results. These results provide important insights into the current understanding of the dynamical behavior of neurons, the self-wiring of the nervous system, as well as for designing innovative biomimetic neural network models.

Micromorphology and silicon of the leaf epidermis in the psammophyte Alyssum desertorum are sensitive to soil flooding.

The ultrastructure of the leaf epidermis and the localization and content of silicon in epidermal cells of the psammophyte Alyssum desertorum Stapf (Brassicaceae) were investigated using electron microscopy and laser confocal microscopy. The study aimed to examine the effect of flooding on the epidermal structure of the leaves, study the presence, localization, and content of silicon in the epidermal cells and determine whether changes in soil moisture affect the silicon content in the leaf epidermis. Silicon inclusions were observed in trichomes and typical epidermal cells on both leaf surfaces, with varying content depending on the cell type, leaf surface, and conditions growth. Soil flooding was found to influence the leaf epidermis ultrastructure and the silicon content in the epidermal cells of A. desertorum. Trichomes and pavement cells were identified as the main accumulators of silicon inclusions and wax-like structures. These findings suggest that changes in leaf microstructure and silicon content contribute to the normal functioning of psammophyte plants and can be considered signs of plant phenotypic plasticity and adaptive markers depending on water supply conditions.

Thermo-Structural Characterization of Phase Transitions in Amorphous Griseofulvin: From Sub-Tg Relaxation and Crystal Growth to High-Temperature Decomposition.

The processes of structural relaxation, crystal growth, and thermal decomposition were studied for amorphous griseofulvin (GSF) by means of thermo-analytical, microscopic, spectroscopic, and diffraction techniques. The activation energy of ~395 kJ·mol-1 can be attributed to the structural relaxation motions described in terms of the Tool-Narayanaswamy-Moynihan model. Whereas the bulk amorphous GSF is very stable, the presence of mechanical defects and micro-cracks results in partial crystallization initiated by the transition from the glassy to the under-cooled liquid state (at ~80 °C). A key aspect of this crystal growth mode is the presence of a sufficiently nucleated vicinity of the disrupted amorphous phase; the crystal growth itself is a rate-determining step. The main macroscopic (calorimetrically observed) crystallization process occurs in amorphous GSF at 115-135 °C. In both cases, the common polymorph I is dominantly formed. Whereas the macroscopic crystallization of coarse GSF powder exhibits similar activation energy (~235 kJ·mol-1) as that of microscopically observed growth in bulk material, the activation energy of the fine GSF powder macroscopic crystallization gradually changes (as temperature and/or heating rate increase) from the activation energy of microscopic surface growth (~105 kJ·mol-1) to that observed for the growth in bulk GSF. The macroscopic crystal growth kinetics can be accurately described in terms of the complex mechanism, utilizing two independent autocatalytic Šesták-Berggren processes. Thermal decomposition of GSF proceeds identically in N2 and in air atmospheres with the activation energy of ~105 kJ·mol-1. The coincidence of the GSF melting temperature and the onset of decomposition (both at 200 °C) indicates that evaporation may initiate or compete with the decomposition process.

In-situ surface growth strategy to synthesize MXene@graphdiyne heterostructure for achieving high capacity and desirable stability in lithium-ion batteries

Two-dimensional (2D) heterostructured electrodes, combining graphdiyne (GDY) and MXenes, have exhibited substantial promise in augmenting the mobility of both ionic and electron movement. However, the widespread advancement and industrial utilization have been impeded by intricate manufacturing procedures and insufficient stability. This study introduces a more streamlined, in-situ growth approach for preparing MXene@GDY electrodes, presenting a novel heterostructure. The method simplifies the manufacturing process while enhancing the specific capacity of the electrode and the more stable cycle life of lithium-ion batteries (LIBs). The resulting electrode exhibited an impressive initial specific capacity of 464.4 mA h g−1, maintaining a high capacity of 492.9 mA h g−1 after 100 cycles at 100 mA current density. More importantly, after 1200 cycles, MXene@GDY showed a capacity of 340.7 mA h g−1, significantly outperforming pure MXene, which only reached 122.3 mA h g−1 at a current density of 1.0 A g−1. The proposed in-situ construction of heterojunction on the MXene surface has demonstrated immense potential for designing high-performance electrode materials which are applicable to LIBs.