scholarly journals Strain driven phase transition and mechanism for Fe/Ir(111) films

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Chen-Yuan Hsieh ◽  
Pei-Cheng Jiang ◽  
Wei-Hsiang Chen ◽  
Jyh-Shen Tsay
Keyword(s):  
Phase Transition ◽  
Strain Energy ◽  
Critical Thickness ◽  
Face Centered Cubic ◽  
Strain Accumulation ◽  
Strained Layers ◽  
Heterogeneous Interfaces ◽  
Face Centered ◽  
Pseudomorphic Growth ◽  
Limited Distortion

AbstractBy way of introducing heterogeneous interfaces, the stabilization of crystallographic phases is critical to a viable strategy for developing materials with novel characteristics, such as occurrence of new structure phase, anomalous enhancement in magnetic moment, enhancement of efficiency as nanoportals. Because of the different lattice structures at the interface, heterogeneous interfaces serve as a platform for controlling pseudomorphic growth, nanostructure evolution and formation of strained clusters. However, our knowledge related to the strain accumulation phenomenon in ultrathin Fe layers on face-centered cubic (fcc) substrates remains limited. For Fe deposited on Ir(111), here we found the existence of strain accumulation at the interface and demonstrate a strain driven phase transition in which fcc-Fe is transformed to a bcc phase. By substituting the bulk modulus and the shear modulus and the experimental results of lattice parameters in cubic geometry, we obtain the strain energy density for different Fe thicknesses. A limited distortion mechanism is proposed for correlating the increasing interfacial strain energy, the surface energy, and a critical thickness. The calculation shows that the strained layers undergo a phase transition to the bulk structure above the critical thickness. The results are well consistent with experimental measurements. The strain driven phase transition and mechanism presented herein provide a fundamental understanding of strain accumulation at the bcc/fcc interface.

Tetragonal Strain in MBE GexSi1-x Films Grown on (100) Si Observed by Ion Channeling and X-Ray Diffraction

1983 ◽  
Vol 25 ◽  
Author(s):  
A. T. Fiory ◽  
L. C. Feldman ◽  
J. C. Bean ◽  
I. K. Robinson
Keyword(s):  
Molecular Beam ◽  
Critical Thickness ◽  
Ion Beam ◽  
Growth Surface ◽  
X Ray Diffraction ◽  
Strained Layers ◽  
X Ray ◽  
Ion Channeling ◽  
Pseudomorphic Growth ◽  
Beam Damage

ABSTRACTStructure of GexSi1-x alloy films grown on (100) Si by molecular beam epitaxy is analyzed by MeV He+ ion channeling and X-ray diffraction as functions of Ge concentration, film thickness and growth temperature. Critical thicknesses for pseudomorphic growth are determined for x ≤ 0.5, where coherent tetragonally-strained layers are observed. The average strain decreases approximately as the square-root of thickness when the critical thickness is exceeded. At temperatures near the threshold for islanding growth, surface roughness appears as a precursor to degradation of strained-layer epitaxy. No effect on the amount of the tetragonal strain was found in a study of ion-beam damage.

A Numerical Study on the Large Compressive Deformations of Closed-Celled Rubber Foams

2013 ◽  
Vol 444-445 ◽  
pp. 23-26
Author(s):  
Zhi Geng Fan
Keyword(s):  
Strain Energy ◽  
Potential Model ◽  
Numerical Study ◽  
Three Dimensional ◽  
Face Centered Cubic ◽  
Energy Potential ◽  
Compressive Stresses ◽  
Order Of Magnitude ◽  
Face Centered ◽  
In Cells

Three dimensional (3D) cubic models with spherical pores ranged as Face-Centered Cubic (FCC) lattices are constructed to simulate the microstructures of rubber foams with various relative densities. The Mooney-Rivlin strain energy potential model is adopted to characterize the hyperelasticity of the constituent solid from which the foams are made. Large compressive deformations of closed-celled rubber foams are calculated by the iterative algorithm. Numerical results show that with the decreasing of foam relative densities, the effects of air pressures in cells on foam compressive stresses increase. When the ratio of initial Yangs modulus of cell material to the initial air pressure in cells reaches 2 order of magnitude, the influence of air pressures in cells can neglect.

Relaxation of Capped Strained Layers Via the Formation of Microtwins

1990 ◽  
Vol 202 ◽  
Author(s):  
D. M. Hwang ◽  
S. A. Schwarz ◽  
T. S. Ravi ◽  
R. Bhat ◽  
C. Y. Chen
Keyword(s):  
Strain Relaxation ◽  
Stacking Fault ◽  
Face Centered Cubic ◽  
Strained Layers ◽  
Strained Layer ◽  
Fundamental Limitations ◽  
Partial Dislocations ◽  
Relaxation Channel ◽  
Kink Model ◽  
Face Centered

ABSTRACTA new strain relief mechanism in epitaxial layers of lattice mismatched face-centered cubic materials is identified using transmission electron microscopy. For an embedded strained layer near its critical thickness, we find that the primary strain-relaxation channel is through the formation of microtwins. A monolayer microtwin (a stacking fault) spanning the strained layer can form when a pair of partial dislocations of the <112> /6 type with antiparallel Burgers vectors are generated inside the strained layer and glide to the opposite interfaces. A series of partial dislocations can result in a microtwin several monolayers thick. For embedded strained layers of materials with small stacking fault energy, the formation of partial dislocation pairs is an energetically-favored strain relaxation channel, as compared to the formation of perfect dislocation pairs in the conventional double-kink model. Therefore, the mechanism proposed here poses fundamental limitations for strained layer device structures.

Interplay of Strain, Growth Kinetics and Surface Bonding in Growth Modes and Dislocation Generation in Strained Heteroepitaxy

1990 ◽  
Vol 202 ◽  
Author(s):  
C. Snyder ◽  
J. Pamulapati ◽  
B. Orr ◽  
P. K. Bhattacharya ◽  
J. Singh
Keyword(s):  
Growth Kinetics ◽  
Strain Energy ◽  
Critical Thickness ◽  
Dislocation Generation ◽  
3 Dimensional ◽  
Growth Modes ◽  
Atomistic Modelling ◽  
Pseudomorphic Growth

ABSTRACTIn this paper we examine the role of strain and growth kinetics on the growth modes in pseudomorphic growth. Regimes below critical thickness and above critical thickness are examined. Based on atomistic modelling and in-situ RHEED and STM studies we show that a competition between surface chemical energy and strain energy is shown to lead to 3-dimensional blend mode for high strain pseudomorphy. Consequences for dislocation generation are discussed.

scholarly journals A discretization method for predicting the equivalent elastic parameters of the graded lattice structure

2020 ◽  
Vol 12 (12) ◽  
pp. 168781402098437
Author(s):  
Cun Zhao ◽  
Guoxi Li ◽  
Meng Zhang ◽  
Weipeng Luo
Keyword(s):  
Elastic Properties ◽  
Strain Energy ◽  
Lattice Structure ◽  
Cellular Materials ◽  
Face Centered Cubic ◽  
Discretization Method ◽  
Elastic Parameters ◽  
Face Centered ◽  
Equivalent Method ◽  
Graded Lattice

In recent years, cellular materials have been widely studied and applied in aerospace and other fields due to the advantages of lightweight and multi-function. However, it is difficult to predict the equivalent elastic properties of the graded lattice structure and other non-uniform cellular materials because of the complex configuration and non-uniformity. A new discretization method for predicting the equivalent elastic parameters of the graded lattice structure is proposed based on the strain energy equivalent method and the discretization method in this paper. The graded lattice structure is discretized into lattice cells, the equivalent elastic properties are predicted by calculating the global equivalent elastic parameters with the parameters of lattice cells, and the calculation formulas are derived. After that, taking edge cube, face-centered cubic and body-centered cubic lattice as examples, the effectiveness and accuracy of the method are verified by theoretical calculation, numerical analysis, and experiment. The results show that the calculation errors of equivalent elastic parameters are between 4.5%–9.7%, and the errors can be significantly improved by reducing the graded factor. It proves that the proposed discretization method can predict the equivalent elastic parameters of the graded lattice structure effectively, and is suitable for different lattice structures.

A first-principles study of bulk aluminum at high pressure

2015 ◽  
Vol 93 (8) ◽  
pp. 825-829 ◽  
Author(s):  
J.L. Nie ◽  
L. Ao ◽  
F.A. Zhao ◽  
M. Jiang ◽  
X.T. Zu
Keyword(s):  
Phase Transition ◽  
Free Energy ◽  
Gibbs Free Energy ◽  
Density Functional ◽  
Face Centered Cubic ◽  
Grüneisen Parameter ◽  
Gruneisen Parameter ◽  
Transition Pressure ◽  
Phase Transition Pressure ◽  
Face Centered

Using ab initio total energy calculations based on density functional theory and a procedure based on minimization of the Gibbs free energy, we calculate the Gibbs free energy for face-centered cubic and hexagonal close-packed aluminum in the temperature range from 0 to 900 K. It is shown that at zero temperature an fcc → hcp phase transition occurs at 181 GPa, and when the temperature is increased to 900 K the phase transition pressure increases slightly. As the pressure increases, the Grüneisen parameter first decreases significantly, then increase sharply at the phase transition pressure, and finally decrease again with further increasing volume compressibility. It turns out that the temperature and pressure have considerable effects on the Grüneisen parameter in certain ranges.

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