High-resolution RHEED analysis of dynamics of low-temperature superstructure transitions in Ge/Si(001) epitaxial system

2021 ◽  
Vol 33 (11) ◽  
pp. 115603
Author(s):  
Vladimir V Dirko ◽  
Kirill A Lozovoy ◽  
Andrey P Kokhanenko ◽  
Alexander V Voitsekhovskii
Keyword(s):  
Critical Thickness ◽  
Three Dimensional ◽  
Diffraction Method ◽  
High Energy ◽  
Two Dimensional ◽  
A Value ◽  
Wide Range ◽  
Dimensional Growth ◽  
Analysis Of Dynamics ◽  
First Time

Abstract In this paper, we analyze superstructural transitions during epitaxial growth of two-dimensional layers and the formation of quantum dots by the Stranski–Krastanov mechanism in elastically stressed systems by the reflection high-energy electron diffraction method. Detailed dependences of the periodicity parameter N of the 2 × N reconstruction on the effective thickness of the deposited material in a wide range of growth temperatures during epitaxy of germanium on a silicon surface with a crystallographic orientation (001) are obtained. Superstructural transitions and the change in the value of the parameter N at low temperatures of epitaxy in this system have been investigated for the first time. It is shown that the length of dimer rows in such a reconstruction during the growth of pure germanium on silicon can reach a value of no less than N = 11. A relationship is found between the value of the parameter N, determined by elastic strains in the system, and the critical thickness of the transition from two-dimensional to three-dimensional growth. Based on this relationship, a physical mechanism is proposed that explains the nature of the temperature dependence of the critical thickness of the Stranski–Krastanov transition, which has been the subject of constant scientific disputes until now.

Growth Process of Si and GaAs in the Heterostructure GaAs/Si/GaAs(100).

1991 ◽  
Vol 237 ◽  
Author(s):  
M. Lopez ◽  
Y. Takano ◽  
K. Pak ◽  
H. Yonezu
Keyword(s):  
Growth Process ◽  
Three Dimensional ◽  
High Energy ◽  
Two Dimensional ◽  
Spot Intensity ◽  
Interlayer Thickness ◽  
High Energy Electron ◽  
Initial Stage ◽  
Dimensional Growth ◽  
Si Films

ABSTRACTThe growth mode of Si on GaAs(100) substrates and that of GaAs on very thin (1/4 ∼ 3 ML) Si films grown pseudomorphically on GaAs was investigated by observing the behavior of the reflection-high energy electron diffraction (RHEED) specular spot intensity. From the presence of RHEED oscillations during the initial stage of the growth of Si on GaAs we infer a two-dimensional growth with nucleation on the terraces up to a thickness of 3 ML. During the posterior growth of GaAs on the pseudomorphic Si films, a tendency towards three dimensional growth was observed. This tendency increased with the Si interlayer thickness. The causes of the formation of these islands are discussed.

Bending of an Infinite Beam on an Elastic Foundation

1937 ◽  
Vol 4 (1) ◽  
pp. A1-A7 ◽  
Author(s):  
M. A. Biot
Keyword(s):  
Elastic Foundation ◽  
Poisson Ratio ◽  
Elementary Theory ◽  
Three Dimensional ◽  
Bending Moment ◽  
Two Dimensional ◽  
Concentrated Load ◽  
Elastic Continuum ◽  
Infinite Beam ◽  
A Value

Abstract The elementary theory of the bending of a beam on an elastic foundation is based on the assumption that the beam is resting on a continuously distributed set of springs the stiffness of which is defined by a “modulus of the foundation” k. Very seldom, however, does it happen that the foundation is actually constituted this way. Generally, the foundation is an elastic continuum characterized by two elastic constants, a modulus of elasticity E, and a Poisson ratio ν. The problem of the bending of a beam resting on such a foundation has been approached already by various authors. The author attempts to give in this paper a more exact solution of one aspect of this problem, i.e., the case of an infinite beam under a concentrated load. A notable difference exists between the results obtained from the assumptions of a two-dimensional foundation and of a three-dimensional foundation. Bending-moment and deflection curves for the two-dimensional case are shown in Figs. 4 and 5. A value of the modulus k is given for both cases by which the elementary theory can be used and leads to results which are fairly acceptable. These values depend on the stiffness of the beam and on the elasticity of the foundation.

A RHEED Study of MBE Growth of ZnSe on GaAs (111) A-(2 × 2)

2003 ◽  
Vol 10 (04) ◽  
pp. 669-675
Author(s):  
F. S. Gard ◽  
J. D. Riley ◽  
R. Leckey ◽  
B. F. Usher
Keyword(s):  
Growth Rate ◽  
Electron Diffraction ◽  
Substrate Temperature ◽  
Three Dimensional ◽  
High Energy ◽  
Growth Mode ◽  
Two Dimensional ◽  
High Energy Electron ◽  
Mbe Growth ◽  
Atomic Flux

ZnSe epilayers have been grown under various Se/Zn atomic flux ratios in the range of 0.22–2.45 at a substrate temperature of 350°C on Zn pre-exposed GaAs (111) A surfaces. Real time reflection high energy electron diffraction (RHEED) observations have shown a transition from a two-dimensional (2D) to a three-dimensional (3D) growth mode. The transition time depends directly upon the growth rate. A detailed discussion is presented to explore the cause of this change in the growth mode.

scholarly journals The magnetorotational instability prefers three dimensions

2020 ◽  
Vol 476 (2233) ◽  
pp. 20190622
Author(s):  
Jeffrey S. Oishi ◽  
Geoffrey M. Vasil ◽  
Morgan Baxter ◽  
Andrew Swan ◽  
Keaton J. Burns ◽  
...  
Keyword(s):  
Shear Rate ◽  
Angular Velocity ◽  
Laboratory Experiments ◽  
Three Dimensional ◽  
Linear Instability ◽  
Three Dimensions ◽  
Two Dimensional ◽  
Magnetorotational Instability ◽  
Dynamo Action ◽  
Wide Range

The magnetorotational instability (MRI) occurs when a weak magnetic field destabilizes a rotating, electrically conducting fluid with inwardly increasing angular velocity. The MRI is essential to astrophysical disc theory where the shear is typically Keplerian. Internal shear layers in stars may also be MRI-unstable, and they take a wide range of profiles, including near-critical. We show that the fastest growing modes of an ideal magnetofluid are three-dimensional provided the shear rate, S , is near the two-dimensional onset value, S c . For a Keplerian shear, three-dimensional modes are unstable above S  ≈ 0.10 S c , and dominate the two-dimensional modes until S  ≈ 2.05 S c . These three-dimensional modes dominate for shear profiles relevant to stars and at magnetic Prandtl numbers relevant to liquid-metal laboratory experiments. Significant numbers of rapidly growing three-dimensional modes remainy well past 2.05 S c . These finding are significant in three ways. First, weakly nonlinear theory suggests that the MRI saturates by pushing the shear rate to its critical value. This can happen for systems, such as stars and laboratory experiments, that can rearrange their angular velocity profiles. Second, the non-normal character and large transient growth of MRI modes should be important whenever three-dimensionality exists. Finally, three-dimensional growth suggests direct dynamo action driven from the linear instability.

Three-Dimensional Lithography for Rutile TiO2 Single Crystals using Swift Heavy Ions

2003 ◽  
Vol 797 ◽  
Author(s):  
Koichi Awazu ◽  
Makoto Fujimaki ◽  
Yoshimichi Ohki ◽  
Tetsuro Komatsubara
Keyword(s):  
Single Crystal ◽  
Hydrofluoric Acid ◽  
Ion Irradiation ◽  
Three Dimensional ◽  
Heavy Ion ◽  
High Energy ◽  
Stopping Power ◽  
A Value ◽  
Microscopy Measurement ◽  
Electronic Stopping Power

ABSTRACTWe have developed a nano-micro structure fabrication method in rutile TiO2 single crystal by use of swift heavy-ion irradiation. The area where ions heavier than Cl ion accelerated with MeV-order high energy were irradiated was well etched by hydrofluoric acid, by comparison etching was not observed in the pristine TiO2 single crystal. Noticed that the irradiated area could be etched to a depth at which the electronic stopping power of the ion decayed to a value of 6.2keV/nm. We also found that the value of the electronic stopping power was increased, eventually decreased against depth in TiO2 single crystal with, e.g. 84.5MeV Ca ion. Using such a beam, inside of TiO2 single crystal was selectively etched with 20% hydrofluoric acid, while the top surface of TiO2 single crystal subjected to irradiation was not etched. Roughness of the new surface created in the single crystal was within 7nm with the atomic forth microscopy measurement.

Crystallization Time Dependence of Nanohybrid Shish-Kebab Structure in HDPE/PA66 Nanofibers Composites via Solution Crystallization

2011 ◽  
Vol 110-116 ◽  
pp. 3786-3790
Author(s):  
Wen Juan Han ◽  
Guo Qiang Zheng ◽  
Yan Yan Liang ◽  
Chun Tai Liu ◽  
Chang Yu Shen
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Time Dependence ◽  
Isothermal Crystallization ◽  
Three Dimensional ◽  
Crystallization Time ◽  
Two Dimensional ◽  
Solution Crystallization ◽  
Dimensional Growth ◽  
Scanning Electron

In this study, PA66 nanofibers were successfully solution electrospun. The crystalline morphological features of HDPE solution induced by nanofibers were investigated by scanning electron microscopy (SEM). Nanohybrid shish-kebab (NHSK) can be formed in HDPE solution via isothermal crystallization, in which PA66 nanofibers serve as shish and HDPE lamellae act as kebabs surrounding the nanofibers periodically. Additionally, crystallization time has significant effect on the structure of HDPE kebab in NHSK, i.e., as crystallization time increases, the size of the kebab increases and the crystals decorated on PA66 nanofibers exhibit a three-dimensional growth (i.e., aggregate of crystallites) rather than a two-dimensional one (i.e., disc-like lamellae normal to the axis of nanofiber).

Structural modeling and role of HAX-1 as a positive allosteric modulator of human serine protease HtrA2

2019 ◽  
Vol 476 (20) ◽  
pp. 2965-2980
Author(s):  
Lalith K. Chaganti ◽  
Shubhankar Dutta ◽  
Raja Reddy Kuppili ◽  
Mriganka Mandal ◽  
Kakoli Bose
Keyword(s):  
Pdz Domain ◽  
Limited Proteolysis ◽  
Three Dimensional ◽  
Dimensional Structure ◽  
Multifunctional Protein ◽  
Promising Therapeutic Target ◽  
Wide Range ◽  
Structural Details ◽  
Structural Architecture ◽  
First Time

Abstract HAX-1, a multifunctional protein involved in cell proliferation, calcium homeostasis, and regulation of apoptosis, is a promising therapeutic target. It regulates apoptosis through multiple pathways, understanding of which is limited by the obscurity of its structural details and its intricate interaction with its cellular partners. Therefore, using computational modeling, biochemical, functional enzymology and spectroscopic tools, we predicted the structure of HAX-1 as well as delineated its interaction with one of it pro-apoptotic partner, HtrA2. In this study, three-dimensional structure of HAX-1 was predicted by threading and ab initio tools that were validated using limited proteolysis and fluorescence quenching studies. Our pull-down studies distinctly demonstrate that the interaction of HtrA2 with HAX-1 is directly through its protease domain and not via the conventional PDZ domain. Enzymology studies further depicted that HAX-1 acts as an allosteric activator of HtrA2. This ‘allosteric regulation’ offers promising opportunities for the specific control and functional modulation of a wide range of biological processes associated with HtrA2. Hence, this study for the first time dissects the structural architecture of HAX-1 and elucidates its role in PDZ-independent activation of HtrA2.

Mechanics of Die-less Asymmetric Rolling for Fabrication of Compound Curved Plates

2003 ◽  
Vol 125 (4) ◽  
pp. 787-793 ◽  
Author(s):  
Jong-Gye Shin ◽  
Yang-Ryul Choi ◽  
Hyunjune Yim
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Three Dimensional ◽  
Element Model ◽  
Two Dimensional ◽  
Asymmetric Rolling ◽  
Dimensional Finite Element ◽  
Three Dimensional Finite Element ◽  
First Time ◽  
Curvature Control

The mechanics of die-less asymmetric rolling has been investigated in depth, for the first time, using a two-dimensional analytical model and a three-dimensional finite element model. In doing so, the physical understanding of mechanics underlying die-less asymmetric rolling has greatly been enhanced. Moreover, the asymmetry in roller radii was found to be the most effective parameter for curvature control, in the considered ranges of various parameters.

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