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9 pages, 3378 KiB

Open AccessArticle

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

by Peng Wu, Jianping Liu, Fangzhi Li, Xiaoyu Ren, Aiqin Tian, Wei Zhou, Fan Zhang, Xuan Li, Bolin Zhou, Masao Ikeda and Hui Yang

Nanomaterials 2024, 14(9), 748; https://doi.org/10.3390/nano14090748 - 25 Apr 2024

Cited by 3 | Viewed by 1438

Abstract

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

[1 \bar{1} 00]

m-direction. Full article

(This article belongs to the Special Issue III-Nitride Semiconductors: Design, Characterization, Applications, and Devices)

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14 pages, 2251 KiB

Open AccessArticle

Impact of Schwoebel Barriers on the Step-Flow Growth of a Multicomponent Crystal

by Alexey Redkov

Crystals 2024, 14(1), 25; https://doi.org/10.3390/cryst14010025 - 26 Dec 2023

Cited by 3 | Viewed by 1805

Abstract

The step-flow and spiral growth of a multicomponent crystal are considered from vapors, taking into account the different possible Schwoebel barriers for each component within the Burton-Cabrera-Frank model. Analytic expressions for the final growth rates of such a multicomponent crystal are determined while considering the kinetic properties of all the individual components and growth conditions. Possible instabilities inherent in the presence of several components are studied, and a stability criterion for the multicomponent case is proposed. It is shown that, in certain cases, nucleation of nanoislands of pure components behind the moving steps can initiate, significantly distorting the growth process. The criterion for the occurrence of such an unstable regime is found. Full article

(This article belongs to the Special Issue Recent Developments of Crystallography in RAS (Russian Academy of Sciences))

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14 pages, 2978 KiB

Open AccessArticle

Temperature Effects in the Initial Stages of Heteroepitaxial Film Growth

by Tung B. T. To and Fábio D. A. Aarão Reis

Surfaces 2022, 5(2), 251-264; https://doi.org/10.3390/surfaces5020018 - 5 Apr 2022

Cited by 4 | Viewed by 2994

Abstract

Kinetic Monte Carlo simulations of a model of thin film heteroepitaxy are performed to investigate the effects of the deposition temperature in the initial growth stages. Broad ranges of the rates of surface processes are used to model materials with several activation energies and several temperature changes, in conditions of larger diffusivity on the substrate in comparison with other film layers. When films with the same coverage are compared, the roughness increases with the deposition temperature in the regimes of island growth, coalescence, and initial formation of the continuous films. Concomitantly, the position of the minimum of the autocorrelation function is displaced to larger sizes. These apparently universal trends are consequences of the formation of wider and taller islands, and are observed with or without Ehrlich-Schwöebel barriers for adatom diffusion at step edges. The roughness increase with temperature qualitatively matches the observations of recent works on the deposition of inorganic and organic materials. In thicker films, simulations with some parameter sets show the decrease of roughness with temperature. In these cases, a re-entrance of roughness may be observed in the initial formation of the continuous films. Full article

(This article belongs to the Collection Featured Articles for Surfaces)

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18 pages, 3912 KiB

Open AccessArticle

Differential Entropy: An Appropriate Analysis to Interpret the Shape Complexity of Self-Similar Organic Islands

by Stefano Chiodini, Pablo Stoliar, Pablo F. Garrido and Cristiano Albonetti

Materials 2021, 14(21), 6529; https://doi.org/10.3390/ma14216529 - 29 Oct 2021

Cited by 3 | Viewed by 2067

Abstract

Differential entropy, along with fractal dimension, is herein employed to describe and interpret the shape complexity of self-similar organic islands. The islands are imaged with in situ Atomic Force Microscopy, following, step-by-step, the evolution of their shape while deposition proceeds. The fractal dimension shows a linear correlation with the film thickness, whereas the differential entropy presents an exponential plateau. Plotting differential entropy versus fractal dimension, a linear correlation can be found. This analysis enables one to discern the 6T growth on different surfaces, i.e., native SiO_x or 6T layer, and suggests a more comprehensive interpretation of the shape evolution. Changes in fractal dimension reflect rougher variations of the island contour, whereas changes in differential entropy correlates with finer contour details. The computation of differential entropy therefore helps to obtain more physical information on the island shape dependence on the substrate, beyond the standard description obtained with the fractal dimension. Full article

(This article belongs to the Section Thin Films and Interfaces)

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10 pages, 2713 KiB

Open AccessArticle

Step Bunches, Nanowires and Other Vicinal “Creatures”—Ehrlich–Schwoebel Effect by Cellular Automata

by Magdalena Załuska-Kotur, Hristina Popova and Vesselin Tonchev

Crystals 2021, 11(9), 1135; https://doi.org/10.3390/cryst11091135 - 18 Sep 2021

Cited by 18 | Viewed by 4035

Abstract

Different patterns can be created on the surface of growing crystals, among which the step bunches and/or step meanders are two of the most studied. The Ehrlich–Schwoebel effect at the surface steps is considered one of the “usual suspects” of such patterning. A direct step barrier is when it is easier to attach a particle to the step from the lower terrace than from the upper terrace. Thus, during the process of crystal growth leads to the formation of meanders, while an inverse barrier leads to step bunching. Based on our vicinal Cellular Automaton model, but this time in (2 + 1)D, we show that the combination of a direct and inverse step barrier and the proper selection of the potential of the well between them leads to the formation of bunched step structures. Following this is the formation of anti-bands. In addition, changing the height of the direct step barrier leads to the growth of nanocolumns, nanowires, and nanopyramids or meanders, in the same system. Full article

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13 pages, 1608 KiB

Open AccessArticle

Atomic-Scale Friction on Monovacancy-Defective Graphene and Single-Layer Molybdenum-Disulfide by Numerical Analysis

by Haosheng Pang, Hongfa Wang, Minglin Li and Chenghui Gao

Nanomaterials 2020, 10(1), 87; https://doi.org/10.3390/nano10010087 - 2 Jan 2020

Cited by 10 | Viewed by 3316

Abstract

Using numerical simulations, we study the atomic-scale frictional behaviors of monovacancy-defective graphene and single-layer molybdenum-disulfide (SLMoS₂) based on the classical Prandtl–Tomlinson (PT) model with a modified interaction potential considering the Schwoebel–Ehrlich barrier. Due to the presence of a monovacancy defect on the surface, the frictional forces were significantly enhanced. The effects of the PT model parameters on the frictional properties of monovacancy-defective graphene and SLMoS₂ were analyzed, and it showed that the spring constant of the pulling spring c_x is the most influential parameter on the stick–slip motion in the vicinity of the vacancy defect. Besides, monovacancy-defective SLMoS₂ is found to be more sensitive to the stick–slip motion at the vacancy defect site than monovacancy-defective graphene, which can be attributed to the complicated three-layer-sandwiched atomic structure of SLMoS₂. The result suggests that the soft tip with a small spring constant can be an ideal candidate for the observation of stick–slip behaviors of the monovacancy-defective surface. This study can fill the gap in atomic-scale friction experiments and molecular dynamics simulations of 2D materials with vacancy-related defects. Full article

(This article belongs to the Section Nanocomposite Materials)

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