scholarly journals Entropic formation of a thermodynamically stable colloidal quasicrystal with negligible phason strain

2021 ◽  
Vol 118 (7) ◽  
pp. e2011799118
Author(s):  
Kwanghwi Je ◽  
Sangmin Lee ◽  
Erin G. Teich ◽  
Michael Engel ◽  
Sharon C. Glotzer
Keyword(s):  
Soft Matter ◽  
Colloidal Particles ◽  
Strain Relaxation ◽  
Recognition Algorithm ◽  
Structural Quality ◽  
Pattern Recognition Algorithm ◽  
Transmission Electron ◽  
Energetic Interactions ◽  
High Degree

Quasicrystals have been discovered in a variety of materials ranging from metals to polymers. Yet, why and how they form is incompletely understood. In situ transmission electron microscopy of alloy quasicrystal formation in metals suggests an error-and-repair mechanism, whereby quasiperiodic crystals grow imperfectly with phason strain present, and only perfect themselves later into a high-quality quasicrystal with negligible phason strain. The growth mechanism has not been investigated for other types of quasicrystals, such as dendrimeric, polymeric, or colloidal quasicrystals. Soft-matter quasicrystals typically result from entropic, rather than energetic, interactions, and are not usually grown (either in laboratories or in silico) into large-volume quasicrystals. Consequently, it is unknown whether soft-matter quasicrystals form with the high degree of structural quality found in metal alloy quasicrystals. Here, we investigate the entropically driven growth of colloidal dodecagonal quasicrystals (DQCs) via computer simulation of systems of hard tetrahedra, which are simple models for anisotropic colloidal particles that form a quasicrystal. Using a pattern recognition algorithm applied to particle trajectories during DQC growth, we analyze phason strain to follow the evolution of quasiperiodic order. As in alloys, we observe high structural quality; DQCs with low phason strain crystallize directly from the melt and only require minimal further reduction of phason strain. We also observe transformation from a denser approximant to the DQC via continuous phason strain relaxation. Our results demonstrate that soft-matter quasicrystals dominated by entropy can be thermodynamically stable and grown with high structural quality––just like their alloy quasicrystal counterparts.

In Situ Electron Microscopy Studies of Surface Dynamical Processes

1998 ◽  
Vol 4 (S2) ◽  
pp. 608-609
Author(s):  
Ruud M. Tromp
Keyword(s):  
Electron Microscopy ◽  
Strain Relaxation ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
Relaxation Phase ◽  
Transmission Electron ◽  
In Situ Electron Microscopy ◽  
Low Energy Electron ◽  
New Machine

To obtain a full and detailed understanding of the spatiotemporal dynamics of surface processes such as epitaxial growth, strain relaxation, phase transformations and phase transitions, chemisorption and etching, in situ real-time observations have proven to be invaluable. The development of two experimental techniques, i.e. Low Energy Electron Microscopy (LEEM) typically operating at electron energies below 10 eV, and Ultra-High-Vacuum Transmission Electron Microscopy (UHV-TEM) at several 100 keV, has made such in situ studies routinely possible. In many cases, the videodata obtained from such experiments are amenable to detailed, quantitative analysis, yielding statistical, kinetic and thermodynamic information that cannot be obtained in any other way.I will discuss recent experimental developments, including the design and construction of a new and improved LEEM instrument. Figure 1 shows a schematic diagram of this new machine. There are several features that distinguishes this design from most other LEEMs. One is the use of a 90 degree deflection magnetic prism array,

Strain relaxation of the In0.53Ga0.47As epi-layer grown on a Si substrate using molecular beam epitaxy

CrystEngComm ◽  
2014 ◽  
Vol 16 (46) ◽  
pp. 10721-10727 ◽  
Author(s):  
Fangliang Gao ◽  
Lei Wen ◽  
Yunfang Guan ◽  
Jingling Li ◽  
Xiaona Zhang ◽  
...  
Keyword(s):  
Molecular Beam Epitaxy ◽  
Low Temperature ◽  
Buffer Layer ◽  
Molecular Beam ◽  
Strain Relaxation ◽  
Si Substrate ◽  
Structural Perfection ◽  
High Degree

The as-grown In0.53Ga0.47As epi-layer grown on Si substrate by using low-temperature In0.4Ga0.6As buffer layer with in-situ annealing is of a high degree of structural perfection.

Qualitative discrimination of yeast fermentation stages based on an olfactory visualization sensor system integrated with a pattern recognition algorithm

2019 ◽  
Vol 11 (26) ◽  
pp. 3294-3300 ◽  
Author(s):  
Weidong Xu ◽  
Hui Jiang ◽  
Tong Liu ◽  
Yinchao He ◽  
Quansheng Chen
Keyword(s):  
Pattern Recognition ◽  
Recognition Algorithm ◽  
Sensor System ◽  
Yeast Fermentation ◽  
Pattern Recognition Algorithm

An olfactory visualization sensor system was developed to verify the feasibility of the in situ monitoring of yeast fermentation stages with a pattern recognition algorithm.

Real Area of Contact in a Soft Transparent Interface by Particle Exclusion Microscopy

2016 ◽  
Vol 138 (4) ◽  
Author(s):  
Kyle D. Schulze ◽  
Alex I. Bennett ◽  
Samantha Marshall ◽  
Kyle G. Rowe ◽  
Alison C. Dunn
Keyword(s):  
Flexible Electronics ◽  
Soft Matter ◽  
Colloidal Particles ◽  
Contact Region ◽  
Real Contact Area ◽  
The Real ◽  
Real Area Of Contact ◽  
Static Indentation ◽  
Real Area

Soft matter mechanics are characterized by high strains and time-dependent elastic properties, which complicate contact mechanics for emerging applications in biomedical surfaces and flexible electronics. In addition, hydrated soft matter precludes using interferometry to observe real areas of contact. In this work, we present a method for measuring the real area of contact in a soft, hydrated, and transparent interface by excluding colloidal particles from the contact region. We confirm the technique by presenting a Hertz-like quasi-static indentation (loading time > 1.4 hrs) by a polyacrylamide probe into a stiff flat surface in a submerged environment. The real contact area and width were calculated from in situ images of the interface processed to reduce image noise and thresholded to define the perimeter of contact. This simple technique of in situ particle exclusion microscopy (PEM) may be widely applicable for determining real areas of contact of soft, transparent interfaces.

Comparison of Growth and Strain Relaxation of Si/Ge Superlattices Under Compressive and Tensile Strain Field

1991 ◽  
Vol 220 ◽  
Author(s):  
Werner Wegscheider ◽  
Karl Eberl ◽  
Gerhard Abstreiter ◽  
Hans Cerva ◽  
Helmut Oppolzer
Keyword(s):  
Growth Parameters ◽  
Strain Relaxation ◽  
Dislocation Nucleation ◽  
Misfit Dislocations ◽  
Partial Dislocations ◽  
Transmission Electron ◽  
Short Period ◽  
Low Energy Electron ◽  
Superlattice Period

ABSTRACTOptimization of growth parameters of short period Si/Ge superlattices (SLs) has been achieved via in situ low-energy electron diffraction (LEED) and Auger electron spectroscopy (AES) measurements during homo- and heteroepitaxy on Si (001) and Ge (001) substrates. Transmission electron microscopy (TEM) reveals that pseudomorphic SimGe12-m (m = 9 and 3 for growth on Si and Ge, respectively) SLs with extended planar layering can be prepared almost defect-free by a modified molecular beam epitaxy (MBE) technique. Whereas the SLs on Ge can be deposited at a constant substrate temperature, high-quality growth on Si demands for temperature variations of more than 100°C within one superlattice period. Strain relaxation of these SLs with increasing number of periods has been directly compared by means of TEM. For the compressively strained structures grown on Si we found misfit dislocations of the type 60° (a/2)<110>. Under opposite strain conditions i.e. for growth on Ge, strain relief occurs only by microtwin formation through successive glide of 90° (a/6)<211> Shockley partial dislocations. This is consistent with a calculation of the activation energy for both cases based on a homogeneous dislocation nucleation model.

scholarly journals Tunable magnetism on the lateral mesoscale by post-processing of Co/Pt heterostructures

2015 ◽  
Vol 6 ◽  
pp. 1082-1090 ◽  
Author(s):  
Oleksandr V Dobrovolskiy ◽  
Maksym Kompaniiets ◽  
Roland Sachser ◽  
Fabrizio Porrati ◽  
Christian Gspan ◽  
...  
Keyword(s):  
Magnetic Properties ◽  
Magnetic Behavior ◽  
Basic Research ◽  
Post Processing ◽  
Transmission Electron ◽  
Spin Dependent Transport ◽  
Complementary Approach ◽  
Dependent Transport ◽  
High Degree

Controlling magnetic properties on the nanometer-scale is essential for basic research in micro-magnetism and spin-dependent transport, as well as for various applications such as magnetic recording, imaging and sensing. This has been accomplished to a very high degree by means of layered heterostructures in the vertical dimension. Here we present a complementary approach that allows for a controlled tuning of the magnetic properties of Co/Pt heterostructures on the lateral mesoscale. By means of in situ post-processing of Pt- and Co-based nano-stripes prepared by focused electron beam induced deposition (FEBID) we are able to locally tune their coercive field and remanent magnetization. Whereas single Co-FEBID nano-stripes show no hysteresis, we find hard-magnetic behavior for post-processed Co/Pt nano-stripes with coercive fields up to 850 Oe. We attribute the observed effects to the locally controlled formation of the CoPt L10 phase, whose presence has been revealed by transmission electron microscopy.

Strain Relaxation of He+ Implanted, Pseudomorphic Si1−xGex Layers on Si(100)

2001 ◽  
Vol 696 ◽  
Author(s):  
B. Holländer ◽  
S. Mantl ◽  
St. Lenk ◽  
H. Trinkaus ◽  
D. Kirch ◽  
...  
Keyword(s):  
Strain Relaxation ◽  
Implantation Dose ◽  
Buffer Layers ◽  
Misfit Dislocations ◽  
Additional Increase ◽  
Dislocation Configuration ◽  
Quantum Well Structures ◽  
Annealing Conditions ◽  
Transmission Electron ◽  
High Degree

AbstractStrain relaxed Si1−xGex buffer layers are of great importance as virtual substrates for Si1−xGex/Si quantum well structures and devices. We apply He+ ion implantation and subsequent annealing on pseudomorphic, MBE-grown Si1−xGex/Si(100) heterostructures with an implantation depth of about 100 nm below the Si1−xGex/Si interface. A narrow defect band is generated inducing the formation of strain relieving misfit dislocations during subsequent thermal annealing. Efficient strain relaxation was demonstrated for Si1−xGex layers with Ge fractions up to 30 at. %. The variation of the implantation dose and the annealing conditions changes the dislocation configuration and the He bubble structure. At a dose of 2×1016 cm−2 a high degree of relaxation is accompanied by a low density of threading dislocations of about 107 cm−2 for a Ge content of 30%. An additional increase of the Ge content can be achieved by annealing in oxygen. The oxidation of Si1−xGex leads to the formation of SiO2 while the Ge atoms are rejected from the oxide leading to a pile-up of Ge below the oxidation front. The heterostructures were analyzed using X-ray diffraction, Rutherford backscattering/channeling spectrometry and transmission electron microscopy.

Real Time Observations of Dislocation-Mediated Plasticity in the Epitaxial AI (011)/Si(100) Thin Film System

2000 ◽  
Vol 619 ◽  
Author(s):  
Eric A. Stach ◽  
U. Dahmen ◽  
W.D. Nix
Keyword(s):  
Strain Relaxation ◽  
Experimental Studies ◽  
Dislocation Motion ◽  
Metal Films ◽  
Silicon Substrates ◽  
Thermally Induced ◽  
Aluminum Films ◽  
Transmission Electron ◽  
Thin Aluminum

ABSTRACTDespite numerous theoretical and experimental studies of strain relaxation in metal films on silicon substrates, the exact mechanisms by which dislocations mediate plasticity in these structures are not well understood. To elucidate these mechanisms, we present results from in-situ transmission electron microscopy annealing of thin aluminum films grown on Si (100). As a model system, we have chosen to focus on aluminum films which contain two (011) epitaxial variants with respect to the silicon substrate. In this paper we discuss our observations of the glide and climb behavior of dislocations in these structures during thermal cycling. These observations give qualitative insight into the mechanisms by which dislocation motion accommodates thermally induced strains in thin metal films.

Structural Characterization of Carbon Materials Prepared at Low Temperature

1995 ◽  
Vol 393 ◽  
Author(s):  
Xiang-Yun Song ◽  
Xi Chu ◽  
Kimio Kinoshita
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Phenol Formaldehyde ◽  
High Capacity ◽  
Lithium Ion ◽  
X Ray Diffraction ◽  
Transmission Electron ◽  
High Degree

ABSTRACTHigh-capacity carbon electrodes for rechageable lithium-ion batteries were prepared by carbonization of thermosetting resins such as phenol-formaldehyde at temperatures between 500°C and 600°C. Their structures were characterized by high resolution transmission electron microscopy, in-situ transmission electron microscopy and x-ray diffraction analysis. These studies suggest that the carbons consist predominantly of disorganized (amorphous) phase. However evidence was found in carbon containing nickel cobalt oxide for the presence of organized graphite-like regions of parallel and curved layer planes. These graphitized structure usually appear as agglomerate particles which are composed of many smaller (100-nm diameter) particles. The high degree of graphitization is attributed to catalytic graphitization that occurs in the presence of the metal oxide.

Effect of the Nitridation of the Sapphire (0001) Substrate on the GaN Growth

1996 ◽  
Vol 449 ◽  
Author(s):  
N. Grandjean ◽  
J. Massies ◽  
P. Vennègues ◽  
M. Laugt ◽  
M. Leroux
Keyword(s):  
Basal Plane ◽  
Early Stage ◽  
High Energy ◽  
Thin Layers ◽  
Structural Quality ◽  
High Energy Electron ◽  
Epitaxial Relationship ◽  
Sapphire Surface ◽  
Transmission Electron

ABSTRACTThe analysis of the sapphire surface nitridation by in situ reflection high-energy electron diffraction evidences the formation of a relaxed AIN layer. Its role on the early stage of the GaN growth is investigated by transmission electron microscopy (TEM). GaN crystallites of high structural quality, with the c axis perpendicular to the sapphire basal plane, are observed when the starting surface is nitridated. On the other hand, the growth of GaN on a bare substrate involves the formation of larger islands with numerous defects. TEM study reveals that the c axis of these latter crystallites is systematically tilted by about 19° with respect to the sapphire basal plane. Actually, this orientation corresponds to a particular epitaxial relationship between GaN and sapphire (0001) substrates. Finally, the optical properties of GaN thin layers are shown to be strongly dependent on the nitridation state of the sapphire surface.

Sign in / Sign up

Export Citation Format

Share Document