Molecular Dynamics Studies of Semiconductor Thin Films and Interfaces

1987 ◽  
Vol 94 ◽  
Author(s):  
Marcia H. Grabow ◽  
George H. Gilmer
Keyword(s):  
Molecular Dynamics ◽  
Energy State ◽  
Layer Growth ◽  
Metastable Equilibrium ◽  
Free Energy Barrier ◽  
Misfit Dislocations ◽  
Layer By Layer ◽  
3 Dimensional ◽  
Smooth Film ◽  
The Stability

ABSTRACTThe structure and stability of thin epitaxial films have been investigated using molecular dynamics computer simulations. One issue of interest is the stability of a smooth film relative to 3-dimensional clusters. The simulation results show that the uniform film is never the lowest energy state for a system with finite misfit. However, the uniform film, produced in a layer-by-layer growth mode, can persist in a metastable state at substantial misfits, e.g. 10% at 1/2 the melting point. This is a result of the large nucleation barrier to the formation of clusters.The second issue is the quality of the interface between the film and the substrate. At equilibrium, the critical thickness for the introduction of misfit dislocations is larger for films on the diamond cubic (100) substrate than on the (111), and differs from predictions based on continuum mechanics. We find that coherent films remain in metastable equilibrium far beyond the critical misfit calculated for full equilibrium, because a large free energy barrier inhibits the introduction of misfit dislocations.

Effects of Stress on Step Energies and Surface Roughness

MRS Bulletin ◽  
1996 ◽  
Vol 21 (4) ◽  
pp. 27-30 ◽  
Author(s):  
Christopher Roland
Keyword(s):  
Thin Films ◽  
Strain Relaxation ◽  
Three Dimensional ◽  
Layer Growth ◽  
Growth Mode ◽  
Misfit Dislocations ◽  
Layer By Layer ◽  
Strained Layers ◽  
The Subject ◽  
Growth Changes

Strain relaxation in lattice-mismatched, heteroepitaxial systems is one of the classic problems in materials physics, which has gained new urgency with the increased applications of strained layers in microelectronic systems. In general both the structure and the integrity of the thin films are strongly influenced by strain. For instance it has long been known that under strain, the growth changes from an initial layer-by-layer growth mode to one with three-dimensional islanding. In the seminal works of van der Merwe, and Matthews and Blakeslee, this change in growth mode is explained in terms of the introduction of strain-relieving misfit dislocations, which appear when the film has reached some critical thickness. Recently it has become clear that this change in growth mode can take place even without the introduction of misfit dislocations. Such dislocation-free coherent islanding, or “roughening,” has been observed experimentally both in Ge/Si and in InGaAs/GaAs systems. Furthermore recent experiments show that in Ge/Si(100) systems, the thin films display a curious asymmetry with respect to the sign of the strain: Films under compression roughen by forming coherent islands while those under tension remain relatively smooth. A possible mechanism behind this strain-induced type of roughening is the subject of this article.

Relationship Between Crystal Defects, Ge Outdiffusion and V/III Ratio in MOVPE Grown (001) GaAs/Ge

1993 ◽  
Vol 319 ◽  
Author(s):  
C. Frigeri ◽  
G. Atrolini ◽  
C. Pelosi ◽  
F. Longo
Keyword(s):  
Stacking Faults ◽  
Layer Growth ◽  
Crystal Defects ◽  
Misfit Dislocations ◽  
Layer By Layer ◽  
Island Growth ◽  
Planar Defects ◽  
Fault Density ◽  
Unintentional Doping ◽  
Enhanced Mobility

AbstractTwo regimes of defect generation have been found in MOVPE GaAs/Ge layers upon changing the V/III ratio between 1.3 and 11.8. For low V/III ratio the layers contained misfit dislocations along with stacking faults that had been generated by dissociation of the misfit dislocations. The stacking fault density increased with decreasing V/III ratio. This might be explained by an enhanced mobility of the dissociated partials due the reduced unintentional doping of the layer caused by reduced Ge outdiffusion from the substrate when V/III is small. The secon regime corresponds to high V/III ratios and is characterized by the absence of misfit dislocations and the presence of a high density of planar defects. This means that breakdown of the 2D layer-by-layer growth occurred and 3D island growth prevailed.

An Investigation of PT/PT (111) Homoepitaxy with Molecular Dynamics Simulation and Static-Energy Calculation.

1993 ◽  
Vol 317 ◽  
Author(s):  
Ruoping wang ◽  
Bryan S. Kalp ◽  
Kristen A. Fichthorn
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulation ◽  
Film Growth ◽  
Effective Medium Theory ◽  
Layer Growth ◽  
Dynamics Simulation ◽  
Energy Calculation ◽  
Layer By Layer ◽  
Static Energy ◽  
Step Edges

ABSTRACTWe present the results of a study of Pt/Pt (111) epitaxial thin-film growth with Molecular-dynamics simulation and static-energy calculation. Interatomic forces are modeled with Corrected-Effective-Medium theory. Atomic details of deposition, such as dissipation of the kinetic energy of an impinging gas atom, adatom motion on and approaching descending step edges, effects of the geometry of a step edge on the interlayer transport of adatoms, etc., have been intensively investigated. We have observed a novel mechanism for adatom incorporation into descending-step edges which involves a concerted motion of the adatom and edge atoms. Our study supports the “island size and shape” model which has been proposed to explain the reentrant layer-by-layer growth mode seen experimentally in Pt/Pt (111) homoepitaxy.

Kinetic pathways leading to layer-by-layer growth from hyperthermal atoms: A multibillion time step molecular dynamics study

2007 ◽  
Vol 76 (11) ◽  
Author(s):  
D. Adamović ◽  
V. Chirita ◽  
E. P. Münger ◽  
L. Hultman ◽  
J. E. Greene
Keyword(s):  
Molecular Dynamics ◽  
Layer Growth ◽  
Layer By Layer ◽  
Time Step

scholarly journals Effects of the Layer Height and Exposure Energy on the Lateral Resolution of Zirconia Parts Printed by Lithography-Based Additive Manufacturing

Materials ◽  
2020 ◽  
Vol 13 (6) ◽  
pp. 1317 ◽  
Author(s):  
Laura Conti ◽  
Daniel Bienenstein ◽  
Mario Borlaf ◽  
Thomas Graule
Keyword(s):  
Additive Manufacturing ◽  
Layer Thickness ◽  
Layer By Layer ◽  
Layer Height ◽  
3 Dimensional ◽  
Stable Part ◽  
The Stability ◽  
Exposure Energy ◽  
The Impact ◽  
Am Processes

Lithography-based ceramics manufacturing (LCM) processes enable the sophisticated 3 dimensional (3D) shaping of ceramics by additive manufacturing (AM). The build-up occurs, like many other AM processes, layer by layer, and is initiated by light. The built-in digital mirror device (DMD) enables the specific exposure of desired pixels for every layer, giving as a consequence a first estimation of the printing resolution in the x and y axes. In this work, a commercial zirconia slurry and the CeraFab 7500, both from Lithoz GmbH (Vienna, Austria), were used to investigate the potential of reaching this resolution. The results showed that the precision of a part is strongly dependent on the applied exposure energy. Higher exposure energies resulted in oversized dimensions of a part, whereas too low energy was not able to guarantee the formation of a stable part. Furthermore, the investigation of the layer thickness showed that the applied exposure energy (mJ/cm2) was acting in a volume, and the impact is visible in x, y, and z dimensions. The lowest applied exposure energy was 83 mJ/cm2 and showed the most accurate results for a layer thickness of 25 μm. With this energy, holes and gaps smaller than 500 μm could be printed; however, the measurements differed significantly from the dimensions defined in the design. Holes and gaps larger than 500 μm showed deviations smaller than 50 μm from the design and could be printed reliably. The thinnest printable gaps were between 100 and 200 μm. Concerning the wall thickness, the experiments were conducted to a height of 1 cm. Taking into account the stability and deformation of the walls as well, the best results after sintering were achieved with thicknesses of 200–300 μm.

Formation of Interfacial Dislocations in Hetero-Epitaxial Layers Grown in Two-Dimensional Mode

1995 ◽  
Vol 399 ◽  
Author(s):  
S. Oktyabrsky ◽  
J. Narayan
Keyword(s):  
Compressive Strain ◽  
Elastic Interaction ◽  
Misfit Strain ◽  
Layer Growth ◽  
Dislocation Network ◽  
Misfit Dislocations ◽  
Layer By Layer ◽  
Two Dimensional ◽  
Transmission Electron ◽  
Interfacial Dislocations

ABSTRACTHigh-resolution transmission electron microscopy has been used to study formation of interfacial defects related to misfit strain accommodation in Ge/Si heterostructures (mismatch 4%) grown in the two-dimensional mode. Special emphasis is placed on the conditions leading to a two-dimensional (layer-by-layer) growth mode. We discuss general features of a dislocation tangle resulted from glide-limited plastic relaxation, typical for highly mismatched (001)-diamond and zinc-blende heterostructures. The evolution of the dislocation network as a function of film thickness and thermal annealing is controlled by growth instabilities and dislocation interactions. The observed correlation in distribution of parallel misfit dislocations including pairing (at <2 nm) of misfit segments from intersecting glide planes and rearrangements in a nonequilibrium dislocation network driven by elastic interaction between 60° dislocation segments in the almost relaxed heterostructures are discussed in detail. Pairing of the 60° glide dislocations results either in their combination to form pure edge 90° dislocations or in the dissociation into partials. We propose and experimentally verify a model for the latter process involving the formation of extrinsic stacking faults in the heterolayers under compressive strain.

scholarly journals SIMULATION OF LAYER BY LAYER GROWTH OF FRACTAL METAL Pt-Rh FILMS

2021 ◽  
pp. 682-692
Author(s):  
Дмитрий Викторович Иванов ◽  
Виталий Александрович Анофриев ◽  
Владимир Александрович Кошелев ◽  
Александр Сергеевич Антонов ◽  
Сергей Александрович Васильев ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Image Analysis ◽  
Fractal Dimension ◽  
Tight Binding ◽  
Computer Experiment ◽  
Layer Growth ◽  
Binding Potential ◽  
Layer By Layer ◽  
Fractal Structures ◽  
Continuous Film

В данной работе методом молекулярной динамики с использованием потенциала сильной связи проведено моделирование процесса молекулярно-лучевой эпитаксии с целью определения закономерностей при формировании фрактальных металлических пленок платины на поверхности родия. Установлена возможность формирования фрактальных структур как в островковых пленках платины на поверхности родия, так и в сплошной пленке. Установлены параметры компьютерного эксперимента, определяющие переход от отдельных островковых пленок к сплошной пленке в указанной системе. С использованием различных программных продуктов Gwyddion и Image Analysis, а также собственной разработки FractalSurface проанализирован диапазон изменения фрактальной размерности при различных условиях молекулярно-динамического эксперимента методом подсчета кубов. Полученные значения фрактальной размерности в целом находятся в приемлемом согласии между собой, однако существует ряд исключений, которые обсуждаются более подробно. Сравнительный анализ получаемых результатов позволяет формулировать рекомендации для методики создания, корректировки и прецизионного контроля при «выращивании» структур с заданной морфологией поверхности. In this work, the molecular dynamics method and the tight-binding potential are used to simulate the process of molecular beam epitaxy in order to determine the regularities in the formation of fractal platinum metal films on the rhodium surface. The possibility of formation of fractal structures both in island platinum films on the rhodium surface and in a continuous film has been established. The parameters of the computer experiment, which determine the transition from individual island films to a continuous film in the indicated system, have been established. Using various software products Gwyddion and Image Analysis, as well as our own software FractalSurface, the range of changes in the fractal dimension has been analyzed under various conditions of a molecular dynamics experiment by the method of cube counting. The obtained values of the fractal dimension are generally in acceptable agreement with each other; however, there is a number of exceptions, which are discussed in more detail. A comparative analysis of the results obtained allows one to formulate recommendations for the methodology for creating, adjusting and precision control when «growing» structures with a given surface morphology.

ZNSE/III–V Heterostructures Grown in a Multichamber MBE System

1987 ◽  
Vol 102 ◽  
Author(s):  
M. C. Tamargo ◽  
J. L. de Miguel ◽  
D. M. Hwang ◽  
B. J. Skromme ◽  
M. H. Meynadier ◽  
...  
Keyword(s):  
Growth Model ◽  
Layer Growth ◽  
Epitaxial Layers ◽  
Layer By Layer ◽  
Bulk Gaas ◽  
Group Iii ◽  
3 Dimensional ◽  
Gaas Substrates

ABSTRACTWe have grown ZnSe epitaxial layers on bulk GaAs substrates and on GaAs epitaxial layers, with both As-rich and Ga-rich surface terminations. We have also grown ZnSe on AlAs epitaxial surfaces with different As to Al ratios. In all cases, abrupt, layer-by-layer growth is observed on the As-rich surfaces, while 3-dimensional nucleation is observed on the group III-rich surfaces. GaAs was also grown on ZnSe layers. In this case, microtwins form at the interface whose density diminishes as the layer is made thicker. A growth model is proposed consistent with these results which requires over-all electronic balance at the interface.

scholarly journals Molecular Simulation Elaborating the Mechanism of 1β-Hydroxy Alantolactone Inhibiting Ubiquitin-Conjugating Enzyme UbcH5s

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Youdong Xu ◽  
Xianli Meng
Keyword(s):  
Molecular Dynamics ◽  
Hydrogen Transfer ◽  
Covalent Bond ◽  
Catalytic Site ◽  
Free Energy Barrier ◽  
Anticancer Activities ◽  
Quantitative Calculation ◽  
Docking Method ◽  
Ubiquitin Conjugating Enzyme ◽  
The Stability

Abstract1β-hydroxy alantolactone, a sesquiterpene lactone, exhibits potent anti-inflammatory and anticancer activities. Recently, it has been found to target UbcH5s by covalently bonding with Cys85 specifically, but the exact molecular basis remains unclear. Here, we analyzed the structural specificity of the catalytic site of UbcH5s by comparing them with other E2 proteins. Molecular dynamics was performed to detect the structural stability of the catalytic site. Docking method was then used to predict conformations of ligand docked at the catalytic site of UbcH5s. The electrostatic surface and charge distribution of ligand and proteins were analyzed by quantitative calculation. Molecular dynamics was used to detect the stability of docking complexes of 1β-hydroxy alantolactone and UbcH5s, the covalently bonded intermediates and the products. The QM/MM methodology was used to calculate the free energy barrier of hydrogen transfer and formation of covalent bond between 15-position carbon of ligand and Cys85. Results revealed that the structure of the catalytic site is stable, and 1β-hydroxy alantolactone can dock at the catalytic site with correct conformation. Molecular dynamics further demonstrates that 1β-hydroxy alantolactone can steadily combine with UbcH5s. Intermediate and product of catalytic reaction are also certified to be stable. Besides, Asp112 and Asn114 function as anchors to fix ligand, ensuring it steadily docked at catalytic site to complete covalent reaction. More importantly, we have found that Cys85 of UbcH5c is more efficient to form a covalent bond with the ligand in comparison with UbcH5a and UbcH5b. Our results successfully explained the mechanism of 1β-hydroxy alantolactone covalently bonding with UbcH5s. Such molecular mechanism may provide a better insight into the molecular development or modification for ubiquitin-related drugs.

The Influence of Strain-Mediated Morphological Changes on the Structural and Optical Properties of MBE-Grown GeSi/Si

1992 ◽  
Vol 281 ◽  
Author(s):  
D. D. Perovic ◽  
J. Whitehurst ◽  
J. P. Noel ◽  
N. L. Rowell ◽  
D. C. Houghton
Keyword(s):  
Elastic Strain ◽  
Morphological Changes ◽  
Broad Band ◽  
Layer Growth ◽  
Atomic Scale ◽  
Misfit Dislocations ◽  
Layer By Layer ◽  
Strained Layer ◽  
Wide Range ◽  
Half Loop

ABSTRACTRecent studies on strained layer heteroepitaxy in high misfit systems (eg. Ge on Si) have clearly indicated the importance of elastic strain on a number of surface-mediated growth effects. In this work we consider the transition from ideal, 2-D layer-by-layer growth to the initial stages of a 3-D growth morphology as a precursor to misfit dislocation injection in GexSi1−x/Si heterostructures with x as low as 0.15. Experimentally, we have studied a wide range of MBE-and CVD-grown single and multilayer GexSi1−x/Si (x<0.5) structures using transmission electron microscopy and photoluminescence spectroscopy. Firstly, we describe a new mechanism for the heterogeneous nucleation of misfit dislocations in strained epitaxial layers, the ‘double half-loop’ source, which originates from atomic-scale (<1.5 nm) interfacial perturbations. Secondly, the atomic-scale dilatational perturbations, which can exist in areal densities up to ∼109 cm−2, have been identified as the origin of intense, broad-band PL from MBE-grown GexSi1−x/Si strained layers. The change in PL behaviour with increasing strained layer thickness has been used to study the effects of elastic strain-induced surface roughening at low misfits.

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