Edge effects on band gap energy in bilayer 2H-MoS{sub 2} under uniaxial strain

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dong, Liang; Wang, Jin; Dongare, Avinash M., E-mail: dongare@uconn.edu

2015-06-28

The potential of ultrathin MoS{sub 2} nanostructures for applications in electronic and optoelectronic devices requires a fundamental understanding in their electronic structure as a function of strain. Previous experimental and theoretical studies assume that an identical strain and/or stress state is always maintained in the top and bottom layers of a bilayer MoS{sub 2} film. In this study, a bilayer MoS{sub 2} supercell is constructed differently from the prototypical unit cell in order to investigate the layer-dependent electronic band gap energy in a bilayer MoS{sub 2} film under uniaxial mechanical deformations. The supercell contains an MoS{sub 2} bottom layer andmore » a relatively narrower top layer (nanoribbon with free edges) as a simplified model to simulate the as-grown bilayer MoS{sub 2} flakes with free edges observed experimentally. Our results show that the two layers have different band gap energies under a tensile uniaxial strain, although they remain mutually interacting by van der Waals interactions. The deviation in their band gap energies grows from 0 to 0.42 eV as the uniaxial strain increases from 0% to 6% under both uniaxial strain and stress conditions. The deviation, however, disappears if a compressive uniaxial strain is applied. These results demonstrate that tensile uniaxial strains applied to bilayer MoS{sub 2} films can result in distinct band gap energies in the bilayer structures. Such variations need to be accounted for when analyzing strain effects on electronic properties of bilayer or multilayered 2D materials using experimental methods or in continuum models.« less

Studies of morphological instability and defect formation in heteroepitaxial Si(1-x)Ge(x) thin films via controlled annealing experiments

NASA Astrophysics Data System (ADS)

Ozkan, Cengiz Sinan

Strained layer semiconductor structures provide possibilities for novel electronic devices. When a semiconductor layer is deposited epitaxially onto a single crystal substrate with the same structure but a slightly different lattice parameter, the semiconductor layer grows commensurately with a misfit strain that can be accommodated elastically below a critical thickness. When the critical thickness is exceeded, the elastic strain energy builds up to a point where it becomes energetically favorable to form misfit dislocations. In addition, in the absence of a capping layer, Sisb{1-x}Gesb{x} films exhibit surface roughening via surface diffusion under the effect of a compressive stress which is caused by a lattice mismatch. Surface roughening takes place in the form of ridges aligned along {<}100{>} or {<}110{>} directions depending on the film thickness and the rate of strain relief. Recent work has shown that surface roughening makes a very significant contribution to strain relaxation in heteroepitaxial thin films. At sharp valley regions on the surface, amplified local stresses can cause further defect nucleation and propagation, such as stacking faults and 90sp° dislocations. In addition, capping layers with suitable thickness will surpress surface roughening and keep most of the strain in the film. We study surface roughening and defect formation by conducting controlled annealing experiments on initially flat and defect free films grown by LPCVD in a hydrogen ambient. We study films with both subcritical and supercritical thicknesses. In addition, we compare the relaxation behaviour of capped and uncapped films where surface roughening was inhibited in films with a capping layer. TEM and AFM studies were conducted to study the morphology and microstructure of these films. X-ray diffraction measurements were made to determine the amount of strain relaxation in these films. Further studies of surface roughening on heteroepitaxial films under a positive biaxial stress have shown that, morphological evolution occurs regardless of the sign of stress in the film. Finally, we have studied surface roughening processes in real time by conducting in-situ TEM experiments. We have observed that the kinetics of roughening depend strongly on the annealing ambient.

Interplay between strain, quantum confinement, and ferromagnetism in strained ferromagnetic semiconductor (In,Fe)As thin films

NASA Astrophysics Data System (ADS)

Sasaki, Daisuke; Anh, Le Duc; Nam Hai, Pham; Tanaka, Masaaki

2014-04-01

We systematically investigated the influence of strain on the electronic structure and ferromagnetism of (In,Fe)As thin films. It is found that while the shift of the critical point energies of compressive-strained (In,Fe)As layers grown on (In1-y,Gay)As (y = 0.05, 0.1) buffer layers can be explained by the hydrostatic deformation effect (HDE) alone, those of tensile-strained (In,Fe)As layers grown on (Ga1-z,Alz)Sb (z = 0, 0.5, 1) buffer layers can be explained by the combination of HDE and the quantum confinement effect (QCE). The Curie temperature TC of the (In,Fe)As layers strongly depends on the strain, and shows a maximum for the (In,Fe)As layer grown on a GaSb buffer layer. The strain dependence of TC can be explained by the s-d exchange mechanism taking into account HDE and QCE.

Predictions of High Strain Rate Failure Modes in Layered Aluminum Composites

NASA Astrophysics Data System (ADS)

Khanikar, Prasenjit; Zikry, M. A.

2014-01-01

A dislocation density-based crystalline plasticity formulation, specialized finite-element techniques, and rational crystallographic orientation relations were used to predict and characterize the failure modes associated with the high strain rate behavior of aluminum layered composites. Two alloy layers, a high strength alloy, aluminum 2195, and an aluminum alloy 2139, with high toughness, were modeled with representative microstructures that included precipitates, dispersed particles, and different grain boundary distributions. Different layer arrangements were investigated for high strain rate applications and the optimal arrangement was with the high toughness 2139 layer on the bottom, which provided extensive shear strain localization, and the high strength 2195 layer on the top for high strength resistance The layer thickness of the bottom high toughness layer also affected the bending behavior of the roll-bonded interface and the potential delamination of the layers. Shear strain localization, dynamic cracking, and delamination are the mutually competing failure mechanisms for the layered metallic composite, and control of these failure modes can be used to optimize behavior for high strain rate applications.

Electric field dynamics in nitride structures containing quaternary alloy (Al, In, Ga)N

DOE Office of Scientific and Technical Information (OSTI.GOV)

Borysiuk, J., E-mail: jolanta.borysiuk@ifpan.edu.pl; Faculty of Physics, University of Warsaw, Pasteura 5, 02-093 Warsaw; Sakowski, K.

2016-07-07

Molecular beam epitaxy growth and basic physical properties of quaternary AlInGaN layers, sufficiently thick for construction of electron blocking layers (EBL), embedded in ternary InGaN layers are presented. Transmission electron microscopy (TEM) measurement revealed good crystallographic structure and compositional uniformity of the quaternary layers contained in other nitride layers, which are typical for construction of nitride based devices. The AlInGaN layer was epitaxially compatible to InGaN matrix, strained, and no strain related dislocation creation was observed. The strain penetrated for limited depth, below 3 nm, even for relatively high content of indium (7%). For lower indium content (0.6%), the strain wasmore » below the detection limit by TEM strain analysis. The structures containing quaternary AlInGaN layers were studied by time dependent photoluminescence (PL) at different temperatures and excitation powers. It was shown that PL spectra contain three peaks: high energy donor bound exciton peak from the bulk GaN (DX GaN) and the two peaks (A and B) from InGaN layers. No emission from quaternary AlInGaN layers was observed. An accumulation of electrons on the EBL interface in high-In sample and formation of 2D electron gas (2DEG) was detected. The dynamics of 2DEG was studied by time resolved luminescence revealing strong dependence of emission energy on the 2DEG concentration. Theoretical calculations as well as power-dependence and temperature-dependence analysis showed the importance of electric field inside the structure. At the interface, the field was screened by carriers and could be changed by illumination. From these measurements, the dynamics of electric field was described as the discharge of carriers accumulated on the EBL.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Atwater, Harry A.; Leite, Marina S.; Warmann, Emily C.

A virtual substrate includes a handle support and a strain-relieved single crystalline layer on the handle support. A method of making the virtual substrate includes growing a coherently-strained single crystalline layer on an initial growth substrate, removing the initial growth substrate to relieve the strain on the single crystalline layer, and applying the strain-relieved single crystalline layer on a handle support.

Surface-layer (S-layer) of human and animal Clostridium difficile strains and their behaviour in adherence to epithelial cells and intestinal colonization.

PubMed

Spigaglia, Patrizia; Barketi-Klai, Amira; Collignon, Anne; Mastrantonio, Paola; Barbanti, Fabrizio; Rupnik, Maja; Janezic, Sandra; Kansau, Imad

2013-09-01

Clostridium difficile is a frequent cause of severe, recurrent post-antibiotic diarrhoea and pseudomembranous colitis. The surface layer (S-layer) is the predominant outer surface component of C. difficile which is involved in pathogen-host interactions critical to pathogenesis. In this study, we characterized the S-layer protein A (SlpA) of animal and human strains belonging to different PCR-ribotypes (PR) and compared the in vitro adherence and in vivo colonization properties of strains showing different SlpA variants. Since each SlpA variant has been recently associated with an S-layer cassette, we were able to deduce the cassette for each of our strains. In this study, an identity of 99-100 % was found among the SlpA of isolates belonging to PR 012, 014/020, 045 and 078. One exception was the SlpA of a poultry isolate, PR 014/020, which showed 99 % identity with that of strain 0160, another PR 014/020 which contains an S-layer cassette 6. Interestingly, this cassette has also been found in a PR 018 strain, an emerging virulent type currently predominant in Italy. Five other SlpA variants (v014/020a-e) were identified in strains PR 014/020. In vitro adherence assays and in vivo colonization experiments were performed on five PR 014/020 strains: human 1064 (v014/020e), human 4684/08 (v014/020b), human IT1106 (v078a), poultry P30 (v014/020d) and poultry PB90 (v014/020b) strains. Adhesion assays indicate that C. difficile strains vary in their capacity to adhere to cells in culture and that adhesion seems to be independent of the SlpA variant. Colonization properties were assessed in vivo using a dixenic mouse model of colonization. The kinetics of faecal shedding and caecal colonization were similar when human 4684/08 (v014/020b) strain was compared with human 1064 (v014/020e) and poultry PB90 (v014/020b) strain. In contrast, poultry P30 (v014/020d) strain outcompeted both human 4684/08 (v014/020b) and IT1106 (v078a) strains and its adherence to caeca at day 7 was significantly higher. The peculiar characteristics of C. difficile P30 seem to advantage it in colonizing the intestinal mice niche, increasing its ability to compete and adapt. The results obtained underline the need of an increased attention to the genetic evolution of C. difficile to prevent and limit the consequences of the emergence of increasingly virulent strains.

Strain and stability of ultrathin Ge layers in Si/Ge/Si axial heterojunction nanowires

DOE PAGES

Ross, Frances M.; Stach, Eric A.; Wen, Cheng -Yen; ...

2015-02-05

The abrupt heterointerfaces in the Si/Ge materials system presents useful possibilities for electronic device engineering because the band structure can be affected by strain induced by the lattice mismatch. In planar layers, heterointerfaces with abrupt composition changes are difficult to realize without introducing misfit dislocations. However, in catalytically grown nanowires, abrupt heterointerfaces can be fabricated by appropriate choice of the catalyst. Here we grow nanowires containing Si/Ge and Si/Ge/Si structures respectively with sub-1nm thick Ge "quantum wells" and we measure the interfacial strain fields using geometric phase analysis. Narrow Ge layers show radial strains of several percent, with a correspondingmore » dilation in the axial direction. Si/Ge interfaces show lattice rotation and curvature of the lattice planes. We conclude that high strains can be achieved, compared to what is possible in planar layers. In addition, we study the stability of these heterostructures under heating and electron beam irradiation. The strain and composition gradients are supposed to the cause of the instability for interdiffusion.« less

Ellipsometric study of Si(0.5)Ge(0.5)/Si strained-layer superlattices

NASA Technical Reports Server (NTRS)

Sieg, R. M.; Alterovitz, S. A.; Croke, E. T.; Harrell, M. J.

1993-01-01

An ellipsometric study of two Si(0.5)Ge(0.5)/Si strained-layer super lattices grown by MBE at low temperature (500 C) is presented, and results are compared with x ray diffraction (XRD) estimates. Excellent agreement is obtained between target values, XRD, and ellipsometry when one of two available Si(x)Ge(1-x) databases is used. It is shown that ellipsometry can be used to nondestructively determine the number of superlattice periods, layer thicknesses, Si(x)Ge(1-x) composition, and oxide thickness without resorting to additional sources of information. It was also noted that we do not observe any strain effect on the E(sub 1) critical point.

Use of layer strains in strained-layer superlattices to make devices for operation in new wavelength ranges, E. G. , InAsSb at 8 to 12. mu. m. [InAs/sub 1-x/Sb/sub x/

DOEpatents

Osbourn, G.C.

1983-10-06

An intrinsic semiconductor electro-optical device comprises a p-n junction intrinsically responsive, when cooled, to electromagnetic radiation in the wavelength range of 8 to 12 ..mu..m. This radiation responsive p-n junction comprises a strained-layer superlattice (SLS) of alternating layers of two different III-V semiconductors. The lattice constants of the two semiconductors are mismatched, whereby a total strain is imposed on each pair of alternating semiconductor layers in the SLS structure, the proportion of the total strain which acts on each layer of the pair being proportional to the ratio of the layer thicknesses of each layer in the pair.

Enhancement of indium incorporation to InGaN MQWs on AlN/GaN periodic multilayers

NASA Astrophysics Data System (ADS)

Monavarian, Morteza; Hafiz, Shopan; Das, Saikat; Izyumskaya, Natalia; Özgür, Ümit; Morkoç, Hadis; Avrutin, Vitaliy

2016-02-01

The effect of compressive strain in buffer layer on strain relaxation and indium incorporation in InGaN multi-quantum wells (MQWs) is studied for two sets of samples grown side by side on both relaxed GaN layers and strained 10-pairs of AlN/GaN periodic multilayers. The 14-nm AlN layers were utilized in both multilayers, while GaN thickness was 4.5 and 2.5 nm in the first and the second set, respectively. The obtained results for the InGaN active layers on relaxed GaN and AlN/GaN periodic multilayers indicate enhanced indium incorporation for more relaxed InGaN active layers providing a variety of emission colors from purple to green.

Hydrophobicities of human polymorphonuclear leukocytes and oral Bacteroides and Porphyromonas spp., Wolinella recta, and Eubacterium yurii with special reference to bacterial surface structures.

PubMed

Haapasalo, M; Kerosuo, E; Lounatmaa, K

1990-12-01

The hydrophobicities of human polymorphonuclear leukocytes (PMNLs) and Bacteroides buccae, B. oris, B. oralis, B. veroralis, B. buccalis, B. heparinolyticus, B. intermedius, B. denticola, B. loescheii, B. melaninogenicus, Porphyromonas gingivalis, P. endodontalis, Wolinella recta, and Eubacterium yurii were studied by the hexadecane method. The majority of the strains were equally or less hydrophobic than the PMNLs. Only in the case of E. yurii and the only strain of B. buccalis were all strains more hydrophobic than the PMNLs. However, some strains of B. intermedius, B. oris, B. denticola, and P. gingivalis were also more hydrophobic than the PMNLs. With the exception of B. intermedius and species with a crystalline surface protein layer (S-layer), the strains of all other species with a thick capsule were more hydrophilic than the strains with little or no extracellular polymeric material. All strains of the S-layer species were either quite hydrophilic or hydrophobic depending on the species, totally irrespective of the presence of the capsule. The results suggest that the S-layers of oral anaerobic bacteria may be important determinants of cell surface hydrophobicity.

Mechanical properties of silicon in subsurface damage layer from nano-grinding studied by atomistic simulation

NASA Astrophysics Data System (ADS)

Zhang, Zhiwei; Chen, Pei; Qin, Fei; An, Tong; Yu, Huiping

2018-05-01

Ultra-thin silicon wafer is highly demanded by semi-conductor industry. During wafer thinning process, the grinding technology will inevitably induce damage to the surface and subsurface of silicon wafer. To understand the mechanism of subsurface damage (SSD) layer formation and mechanical properties of SSD layer, atomistic simulation is the effective tool to perform the study, since the SSD layer is in the scale of nanometer and hardly to be separated from underneath undamaged silicon. This paper is devoted to understand the formation of SSD layer, and the difference between mechanical properties of damaged silicon in SSD layer and ideal silicon. With the atomistic model, the nano-grinding process could be performed between a silicon workpiece and diamond tool under different grinding speed. To reach a thinnest SSD layer, nano-grinding speed will be optimized in the range of 50-400 m/s. Mechanical properties of six damaged silicon workpieces with different depths of cut will be studied. The SSD layer from each workpiece will be isolated, and a quasi-static tensile test is simulated to perform on the isolated SSD layer. The obtained stress-strain curve is an illustration of overall mechanical properties of SSD layer. By comparing the stress-strain curves of damaged silicon and ideal silicon, a degradation of Young's modulus, ultimate tensile strength (UTS), and strain at fracture is observed.

Strain relaxation of thick (11–22) semipolar InGaN layer for long wavelength nitride-based device

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Jaehwan; Min, Daehong; Jang, Jongjin

2014-10-28

In this study, the properties of thick stress-relaxed (11–22) semipolar InGaN layers were investigated. Owing to the inclination of growth orientation, misfit dislocations (MDs) occurred at the heterointerface when the strain state of the (11–22) semipolar InGaN layers reached the critical point. We found that unlike InGaN layers based on polar and nonpolar growth orientations, the surface morphologies of the stress-relaxed (11–22) semipolar InGaN layers did not differ from each other and were similar to the morphology of the underlying GaN layer. In addition, misfit strain across the whole InGaN layer was gradually relaxed by MD formation at the heterointerface.more » To minimize the effect of surface roughness and defects in GaN layers on the InGaN layer, we conducted further investigation on a thick (11–22) semipolar InGaN layer grown on an epitaxial lateral overgrown GaN template. We found that the lateral indium composition across the whole stress-relaxed InGaN layer was almost uniform. Therefore, thick stress-relaxed (11–22) semipolar InGaN layers are suitable candidates for use as underlying layers in long-wavelength devices, as they can be used to control strain accumulation in the heterostructure active region without additional influence of surface roughness.« less

Strain Engineering of Epitaxially Transferred, Ultrathin Layers of III-V Semiconductor on Insulator

DTIC Science & Technology

2011-01-01

The structure of the source wafer is shown schematically in Fig. 2a, with both InAs and AlGaSb layers coherently strained to the GaSb 001...is due to the surface plasmon-LO phonon FIG. 2. Color online a The structure of GaSb /AlGaSb/InAs source wafer with an assumed strain state for...insulator layers obtained from an epitaxial transfer process is studied. The as-grown InAs epilayer 10–20 nm thick on the GaSb /AlGaSb source wafer has the

Purification and characterization of Campylobacter rectus surface layer proteins.

PubMed Central

Nitta, H; Holt, S C; Ebersole, J L

1997-01-01

Campylobacter rectus is a putative periodontopathogen which expresses a proteinaceous surface layer (S-layer) external to the outer membrane. S-layers are considered to play a protective role for the microorganism in hostile environments. The S-layer proteins from six different C. rectus strains (five human isolates and a nonhuman primate [NHP] isolate) were isolated, purified, and characterized. The S-layer proteins of these strains varied in molecular mass (ca. 150 to 166 kDa) as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. They all reacted with monospecific rabbit antiserum to the purified S-layer of C. rectus 314, but a quantitative enzyme-linked immunosorbent assay demonstrated a strong antigenic relationship among the five human strains, while the NHP strain, 6250, showed weaker reactivity. Amino acid composition analysis showed that the S-layers of four C. rectus strains contained large proportions of acidic amino acids (13 to 27%) and that >34% of the amino acid residues were hydrophobic. Amino acid sequence analysis of six S-layer proteins revealed that the first 15 amino-terminal amino acids were identical and showed seven residues of identity with the amino-terminal sequence of the Campylobacter fetus S-layer protein SapA1. CNBr peptide profiles of the S-layer proteins from C. rectus 314, ATCC 33238, and 6250 confirmed that the S-layer proteins from the human strains were similar to each other and somewhat different from that of the NHP isolate (strain 6250). However, the S-layer proteins from the two human isolates do show some structural heterogeneity. For example, there was a 17-kDa fragment unique to the C. rectus 314 S-layer. The amino-terminal sequence of this peptide had homology with the C. rectus 51-kDa porin and was composed of nearly 50% hydrophobic residues. Thus, the S-layer protein from C. rectus has structural heterogeneity among different human strains and immunoheterogeneity with the NHP strain. PMID:9009300

Quantitative strain and compositional studies of InxGa1-xAs Epilayer in a GaAs-based pHEMT device structure by TEM techniques.

PubMed

Sridhara Rao, Duggi V; Sankarasubramanian, Ramachandran; Muraleedharan, Kuttanellore; Mehrtens, Thorsten; Rosenauer, Andreas; Banerjee, Dipankar

2014-08-01

In GaAs-based pseudomorphic high-electron mobility transistor device structures, strain and composition of the In x Ga1-x As channel layer are very important as they influence the electronic properties of these devices. In this context, transmission electron microscopy techniques such as (002) dark-field imaging, high-resolution transmission electron microscopy (HRTEM) imaging, scanning transmission electron microscopy-high angle annular dark field (STEM-HAADF) imaging and selected area diffraction, are useful. A quantitative comparative study using these techniques is relevant for assessing the merits and limitations of the respective techniques. In this article, we have investigated strain and composition of the In x Ga1-x As layer with the mentioned techniques and compared the results. The HRTEM images were investigated with strain state analysis. The indium content in this layer was quantified by HAADF imaging and correlated with STEM simulations. The studies showed that the In x Ga1-x As channel layer was pseudomorphically grown leading to tetragonal strain along the [001] growth direction and that the average indium content (x) in the epilayer is ~0.12. We found consistency in the results obtained using various methods of analysis.

Method of transferring strained semiconductor structure

DOEpatents

Nastasi, Michael A [Santa Fe, NM; Shao, Lin [College Station, TX

2009-12-29

The transfer of strained semiconductor layers from one substrate to another substrate involves depositing a multilayer structure on a substrate having surface contaminants. An interface that includes the contaminants is formed in between the deposited layer and the substrate. Hydrogen atoms are introduced into the structure and allowed to diffuse to the interface. Afterward, the deposited multilayer structure is bonded to a second substrate and is separated away at the interface, which results in transferring a multilayer structure from one substrate to the other substrate. The multilayer structure includes at least one strained semiconductor layer and at least one strain-induced seed layer. The strain-induced seed layer can be optionally etched away after the layer transfer.

Effect of elastic strain redistribution on electronic band structures of compressively strained GaInAsP/InP membrane quantum wires

NASA Astrophysics Data System (ADS)

Ferdous, F.; Haque, A.

2007-05-01

The effect of redistribution of elastic strain relaxation on the energy band structures of GaInAsP/InP compressively strained membrane quantum wires fabricated by electron-beam lithography, reactive-ion etching and two-step epitaxial growth is theoretically studied using an 8-band k ṡp method. Anisotropic strain analysis by the finite element method shows that due to etching away the top and the bottom InP clad layers in membrane structures, redistribution of strain occurs. It is found that strain redistribution increases the effective bandgap of membrane quantum wire structures causing a blueshift of the emission frequency. Comparison with effective bandgap calculations neglecting confinement and band mixing demonstrates that neglect of these effects leads to an overestimation of the change in the bandgap. We have also investigated the effect of variation of wire width, barrier strain compensation, number of stacked quantum wire layers, and thickness of the top and the bottom residual InP layers in membrane structures on the change in the effective bandgap of membrane structures.

Influence of metal bonding layer on strain transfer performance of FBG

NASA Astrophysics Data System (ADS)

Liu, Hao; Chen, Weimin; Zhang, Peng; Liu, Li; Shu, Yuejie; Wu, Jun

2013-01-01

Metal bonding layer seriously affects the strain transfer performance of Fiber Bragg Grating (FBG). Based on the mode of FBG strain transfer, the influence of the length, the thickness, Poisson's ratio, elasticity modulus of metal bonding layer on the strain transfer coefficient of FBG is analyzed by numerical simulation. FBG is packaged to steel wire using metal bonding technology of FBG. The tensile tests of different bonding lengths and elasticity modulus are carried out. The result shows the strain transfer coefficient of FBGs are 0.9848,0.962 and their average strain sensitivities are 1.076 pm/μɛ,1.099 pm/μɛ when the metal bonding layer is zinc, whose lengths are 15mm, 20mm, respectively. The strain transfer coefficient of FBG packaged by metal bonding layer raises 8.9 percent compared to epoxy glue package. The preliminary experimental results show that the strain transfer coefficient increases with the length of metal bonding layer, decreases with the thickness of metal bonding layer and the influence of Poisson's ratio can be ignored. The experiment result is general agreement with the analysis and provides guidance for metal package of FBG.

Biomechanical properties of the layered oesophagus and its remodelling in experimental type-1 diabetes.

PubMed

Yang, Jian; Zhao, Jingbo; Liao, Donghua; Gregersen, Hans

2006-01-01

Passive biomechanical properties in term of the stress-strain relationship and the shear modulus were studied in separated muscle layer and mucosa-submucosa layer in the oesophagus of normal and STZ (streptozotocin)-induced diabetic rats. The mucosa-submucosa and muscle layers were separated using microsurgery and studied in vitro using a self-developed test machine. Stepwise elongation and inflation plus continuous twist were applied to the samples. A constitutive equation based on a strain energy function was used for the stress-strain analysis. Five material constants were obtained for both layers. The mucosa-submucosa layer was significantly stiffer than the muscle layer in longitudinal, circumferential and circumferential-longitudinal shear direction. The mechanical constants of the oesophagus show that the oesophageal wall was anisotropic, the stiffness in the longitudinal direction was higher than in the circumferential direction in the intact oesophagus (P < 0.001) and in the muscle layer (P < 0.05). Diabetes-induced pronounced increase in the outer perimeter, inner perimeter and lumen area in both the muscle and mucosa-submucosa layer. The growth of the mucosa-submucosa layer (P < 0.001) was more pronounced than the muscle layer (P < 0.05). Furthermore, the circumferential stiffness of the mucosa-submucosa layer increased 28 days after STZ treatment. In conclusion, the oesophagus is a non-homogeneous anisotropic tube. Thus, the mechanical properties differed between layers as well as in different directions. Morphological and biomechanical remodelling is prominent in the diabetic oesophagus.

INTERLAYER MICROMECHANICS OF THE AORTIC HEART VALVE LEAFLET

PubMed Central

Buchanan, Rachel M.; Sacks, Michael S.

2014-01-01

While the mechanical behaviors of the fibrosa and ventricularis layers of the aortic valve (AV) leaflet are understood, little information exists on their mechanical interactions mediated by the GAG-rich central spongiosa layer. Parametric simulations of the interlayer interactions of the AV leaflets in flexure utilized a tri-layered finite element (FE) model of circumferentially oriented tissue sections to investigate inter-layer sliding hypothesized to occur. Simulation results indicated that the leaflet tissue functions as a tightly bonded structure when the spongiosa effective modulus was at least 25% that of the fibrosa and ventricularis layers. Novel studies that directly measured transmural strain in flexure of AV leaflet tissue specimens validated these findings. Interestingly, a smooth transmural strain distribution indicated that the layers of the leaflet indeed act as a bonded unit, consistent with our previous observations (Stella and Sacks, 2007) of a large number of transverse collagen fibers interconnecting the fibrosa and ventricularis layers. Additionally, when the tri-layered FE model was refined to match the transmural deformations, a layer-specific bimodular material model (resulting in four total moduli) accurately matched the transmural strain and moment-curvature relations simultaneously. Collectively, these results provide evidence, contrary to previous assumptions, that the valve layers function as a bonded structure in the low-strain flexure deformation mode. Most likely, this results directly from the transverse collagen fibers that bind the layers together to disable physical sliding and maintain layer residual stresses. Further, the spongiosa may function as a general dampening layer while the AV leaflets deforms as a homogenous structure despite its heterogeneous architecture. PMID:24292631

Influences of misfit strains on liquid phase heteroepitaxial growth

NASA Astrophysics Data System (ADS)

Lu, Yanli; Peng, Yingying; Yu, Genggeng; Chen, Zheng

2017-10-01

Influences of misfit strains with different signs on liquid phase heteroepitaxial growth are studied by binary phase field crystal model. It is amazing to find that double islands are formed because of lateral and vertical separation. The morphological evolution of epitaxial layer depends on signs of misfit strains. The maximum atomic layer thickness of double islands under negative misfit strain is larger than that of under positive misfit strain at the same evolutional time, and size differences between light and dark islands is much smaller under negative misfit strain than that of under positive misfit strain. In addition, concentration field and density field approximately have similar variational law along x direction under the same misfit strain but show opposite variational trend under misfit strains with different signs. Generally, free energy of epitaxial growth systems keeps similar variational trend under misfit strains with different signs.

A Novel Adjustable Concept for Permeable Gas/Vapor Protective Clothing: Balancing Protection and Thermal Strain.

PubMed

Bogerd, Cornelis Peter; Langenberg, Johannes Pieter; DenHartog, Emiel A

2018-02-13

Armed forces typically have personal protective clothing (PPC) in place to offer protection against chemical, biological, radiological and nuclear (CBRN) agents. The regular soldier is equipped with permeable CBRN-PPC. However, depending on the operational task, these PPCs pose too much thermal strain to the wearer, which results in a higher risk of uncompensable heat stress. This study investigates the possibilities of adjustable CBRN-PPC, consisting of different layers that can be worn separately or in combination with each other. This novel concept aims to achieve optimization between protection and thermal strain during operations. Two CBRN-PPC (protective) layers were obtained from two separate manufacturers: (i) a next-to-skin (NTS) and (ii) a low-burden battle dress uniform (protective BDU). In addition to these layers, a standard (non-CBRN protective) BDU (sBDU) was also made available. The effect of combining clothing layers on the levels of protection were investigated with a Man-In-Simulant Test. Finally, a mechanistic numerical model was employed to give insight into the thermal burden of the evaluated CBRN-PPC concepts. Combining layers results in substantially higher protection that is more than the sum of the individual layers. Reducing the airflow on the protective layer closest to the skin seems to play an important role in this, since combining the NTS with the sBDU also resulted in substantially higher protection. As expected, the thermal strain posed by the different clothing layer combinations decreases as the level of protection decreases. This study has shown that the concept of adjustable protection and thermal strain through multiple layers of CBRN-PPC works. Adjustable CBRN-PPC allows for optimization of the CBRN-PPC in relation to the threat level, thermal environment, and tasks at hand in an operational setting. © The Author(s) 2017. Published by Oxford University Press on behalf of the British Occupational Hygiene Society.

Strain response of thermal barrier coatings captured under extreme engine environments through synchrotron X-ray diffraction

NASA Astrophysics Data System (ADS)

Knipe, Kevin; Manero, Albert; Siddiqui, Sanna F.; Meid, Carla; Wischek, Janine; Okasinski, John; Almer, Jonathan; Karlsson, Anette M.; Bartsch, Marion; Raghavan, Seetha

2014-07-01

The mechanical behaviour of thermal barrier coatings in operation holds the key to understanding durability of jet engine turbine blades. Here we report the results from experiments that monitor strains in the layers of a coating subjected to thermal gradients and mechanical loads representing extreme engine environments. Hollow cylindrical specimens, with electron beam physical vapour deposited coatings, were tested with internal cooling and external heating under various controlled conditions. High-energy synchrotron X-ray measurements captured the in situ strain response through the depth of each layer, revealing the link between these conditions and the evolution of local strains. Results of this study demonstrate that variations in these conditions create corresponding trends in depth-resolved strains with the largest effects displayed at or near the interface with the bond coat. With larger temperature drops across the coating, significant strain gradients are seen, which can contribute to failure modes occurring within the layer adjacent to the interface.

Two distinct Photobacterium populations thrive in ancient Mediterranean sapropels.

PubMed

Süss, Jacqueline; Herrmann, Kerstin; Seidel, Michael; Cypionka, Heribert; Engelen, Bert; Sass, Henrik

2008-04-01

Eastern Mediterranean sediments are characterized by the periodic occurrence of conspicuous, organic matter-rich sapropel layers. Phylogenetic analysis of a large culture collection isolated from these sediments revealed that about one third of the isolates belonged to the genus Photobacterium. In the present study, 22 of these strains were examined with respect to their phylogenetic and metabolic diversity. The strains belonged to two distinct Photobacterium populations (Mediterranean cluster I and II). Strains of cluster I were isolated almost exclusively from organic-rich sapropel layers and were closely affiliated with P. aplysiae (based on their 16S rRNA gene sequences). They possessed almost identical Enterobacterial Repetitive Intergenic Consensus (ERIC) and substrate utilization patterns, even among strains from different sampling sites or from layers differing up to 100,000 years in age. Strains of cluster II originated from sapropels and from the surface and carbon-lean intermediate layers. They were related to Photobacterium frigidiphilum but differed significantly in their fingerprint patterns and substrate spectra, even when these strains were obtained from the same sampling site and layer. Temperature range for growth (4 to 33 degrees C), salinity tolerance (5 to 100 per thousand), pH requirements (5.5-9.3), and the composition of polar membrane lipids were similar for both clusters. All strains grew by fermentation (glucose, organic acids) and all but five by anaerobic respiration (nitrate, dimethyl sulfoxide, anthraquinone disulfonate, or humic acids). These results indicate that the genus Photobacterium forms subsurface populations well adapted to life in the deep biosphere.

Studies of the Initial Stages of Epitaxial Growth of Germanium on Silicon

NASA Astrophysics Data System (ADS)

Krishnamurthy, Mohan

The epitaxial growth of ultra-thin films (< 1nm thick) of Ge on Si(100) has been studied in -situ in an Ultra High Vacuum-Scanning Transmission Electron Microscope. Ge was deposited on clean Si(100) using molecular beam techniques to study two types of growth processes, Molecular Beam Epitaxy (MBE) and Solid Phase MBE. Ge grows in the Stranski-Krastanov growth mode, forming islands after initial layer growth. This islanding transition has been studied with high spatial resolution biassed Secondary Electron Imaging and Auger spectroscopy and imaging. Ex -situ Transmission Electron Microscopy (TEM) and Reflection High Energy Diffraction (RHEED) were also used to characterize the transition. The islanding process and its subsequent evolution was monitored with the help of island size distributions, sensitive to islands above 2nm in size. The studies indicate that Ge forms islands in equilibrium with a 3 monolayer (ML) thick intermediate layer. These islands may initially grow coherently strained (dislocation free) with radii usually below 10nm under the conditions. The strain in these islands reduces the adatom sticking coefficient and strongly influences the microstructural evolution. The intermediate layer may grow metastably under certain conditions to as much as 7 ML before collapsing to its equilibrium form. The influence of three types of adatom sinks--strained islands, dislocated islands and contaminant particles have been studied. The contaminant particles are the strongest sinks, followed by dislocated islands and strained islands. Stepped (vicinal) surfaces (1^circ and 5 ^circ toward {110 }) had no significant influence possibly due to the steps being weak adatom sinks. The coarsening of Ge islands does not follow the Ostwald ripening model at the early stages and is influenced by the supersaturation in the intermediate layer and the strain in the coherent islands. A novel mechanism has been observed, where the larger (dislocated) islands grow at the expense of the unstable intermediate layer while the distribution of smaller (strained) islands is constant. This is possibly due to the lower sticking coefficient at the strained islands.

Effect of Elastic Strain Fluctuation on Atomic Layer Growth of Epitaxial Silicide in Si Nanowires by Point Contact Reactions.

PubMed

Chou, Yi-Chia; Tang, Wei; Chiou, Chien-Jyun; Chen, Kai; Minor, Andrew M; Tu, K N

2015-06-10

Effects of strain impact a range of applications involving mobility change in field-effect-transistors. We report the effect of strain fluctuation on epitaxial growth of NiSi2 in a Si nanowire via point contact and atomic layer reactions, and we discuss the thermodynamic, kinetic, and mechanical implications. The generation and relaxation of strain shown by in situ TEM is periodic and in synchronization with the atomic layer reaction. The Si lattice at the epitaxial interface is under tensile strain, which enables a high solubility of supersaturated interstitial Ni atoms for homogeneous nucleation of an epitaxial atomic layer of the disilicide phase. The tensile strain is reduced locally during the incubation period of nucleation by the dissolution of supersaturated Ni atoms in the Si lattice but the strained-Si state returns once the atomic layer epitaxial growth of NiSi2 occurs by consuming the supersaturated Ni.

Nucleation of ripplocations through atomistic modeling of surface nanoindentation in graphite

NASA Astrophysics Data System (ADS)

Freiberg, D.; Barsoum, M. W.; Tucker, G. J.

2018-05-01

In this work, we study the nucleation and subsequent evolution behavior of ripplocations - a newly proposed strain accommodating defect in layered materials where one, or more, layers buckle orthogonally to the layers - using atomistic modeling of graphite. To that effect, we model the response to cylindrical indenters with radii R of 50, 100, and 250 nm, loaded edge-on into graphite layers and the strain gradient effects beneath the indenter are quantified. We show that the response is initially elastic followed by ripplocation nucleation, and growth of multiple fully reversible ripplocation boundaries below the indenter. In the elastic region, the stress is found to be a function of indentation volume; beyond the elastic regime, the interlayer strain gradient emerges as paramount in the onset of ripplocation nucleation and subsequent in-plane stress relaxation. Furthermore, ripplocation boundaries that nucleate from the alignment of ripplocations on adjacent layers are exceedingly nonlocal and propagate, wavelike, away from the indented surface. This work not only provides a critical understanding of the mechanistic underpinnings of the deformation of layered solids and formation of kink boundaries, but also provides a more complete description of the nucleation mechanics of ripplocations and their strain field dependence.

Piezoresistivity of mechanically drawn single-walled carbon nanotube (SWCNT) thin films-: mechanism and optimizing principle

NASA Astrophysics Data System (ADS)

Obitayo, Waris

The individual carbon nanotube (CNT) based strain sensors have been found to have excellent piezoresistive properties with a reported gauge factor (GF) of up to 3000. This GF on the other hand, has been shown to be structurally dependent on the nanotubes. In contrast, to individual CNT based strain sensors, the ensemble CNT based strain sensors have very low GFs e.g. for a single walled carbon nanotube (SWCNT) thin film strain sensor, GF is ~1. As a result, studies which are mostly numerical/analytical have revealed the dependence of piezoresistivity on key parameters like concentration, orientation, length and diameter, aspect ratio, energy barrier height and Poisson ratio of polymer matrix. The fundamental understanding of the piezoresistive mechanism in an ensemble CNT based strain sensor still remains unclear, largely due to discrepancies in the outcomes of these numerical studies. Besides, there have been little or no experimental confirmation of these studies. The goal of my PhD is to study the mechanism and the optimizing principle of a SWCNT thin film strain sensor and provide experimental validation of the numerical/analytical investigations. The dependence of the piezoresistivity on key parameters like orientation, network density, bundle diameter (effective tunneling area), and length is studied, and how one can effectively optimize the piezoresistive behavior of a SWCNT thin film strain sensors. To reach this goal, my first research accomplishment involves the study of orientation of SWCNTs and its effect on the piezoresistivity of mechanically drawn SWCNT thin film based piezoresistive sensors. Using polarized Raman spectroscopy analysis and coupled electrical-mechanical test, a quantitative relationship between the strain sensitivity and SWCNT alignment order parameter was established. As compared to randomly oriented SWCNT thin films, the one with draw ratio of 3.2 exhibited ~6x increase on the GF. My second accomplishment involves studying the influence of the network density on the piezoresistivity of mechanically drawn SWCNT thin films. Mechanically drawn SWCNT thin films with different layer (or thickness) e.g. 1-layer, 3-layer, 10-layer and 20-layer SWCNT thin films were prepared to understand the variation of SWCNT network density as well as the alignment of SWCNTs on the strain sensitivity. The less entangled SWCNT bundles observed in the sparse network density (1- layer and 3-layer SWCNT thin films) allows for easy alignment and the best gauge factors. As compared to the randomly oriented SWCNT thin films, the one with draw ratio of 3.2 exhibited ~8x increase on the GF for the 1-layer SWCNT thin films while the 20-layer SWCNT thin films exhibited ~3x increase in the GF. My third accomplishment examines the effect of SWCNT bundles with different diameters on the piezoresistive behavior of mechanically drawn SWCNT thin films. SWCNT thin film network of sparse morphology (1-layer) with different bundle sizes were prepared by varying the sonication duration e.g. S0.5hr, S4hr, S10hr and S20hr and using spraying coating. The GF increased by a factor of ~10 when the randomly oriented SWCNT thin film was stretched to a draw ratio of 3.2 for the S0.5hr SWCNT thin films and by a factor of ~2 for the S20hr SWCNT thin films. Three main mechanisms were attributed to this behavior e.g. effect of concentration of exfoliated nanotubes, bundle reduction due to mechanical stretching, and influence of bundle length on the alignment of SWCNTs. Furthermore, information about the average length and length distribution is very essential when investigating the influence of individual nanotube length on the strain sensitivity. With that in mind, we would use our previously developed preparative ultracentrifuge method (PUM), and our newly developed gel electrophoresis and simultaneous Raman and photoluminescence spectroscopy (GEP-SRSPL) to characterize the average length and length distribution of individual SWCNTs respectively.

A novel method for visualising and quantifying through-plane skin layer deformations.

PubMed

Gerhardt, L-C; Schmidt, J; Sanz-Herrera, J A; Baaijens, F P T; Ansari, T; Peters, G W M; Oomens, C W J

2012-10-01

Skin is a multilayer composite and exhibits highly non-linear, viscoelastic, anisotropic material properties. In many consumer product and medical applications (e.g. during shaving, needle insertion, patient re-positioning), large tissue displacements and deformations are involved; consequently large local strains in the skin tissue can occur. Here, we present a novel imaging-based method to study skin deformations and the mechanics of interacting skin layers of full-thickness skin. Shear experiments and real-time video recording were combined with digital image correlation and strain field analysis to visualise and quantify skin layer deformations during dynamic mechanical testing. A global shear strain of 10% was applied to airbrush-patterned porcine skin (thickness: 1.2-1.6mm) using a rotational rheometer. The recordings were analysed with ARAMIS image correlation software, and local skin displacement, strain and stiffness profiles through the skin layers determined. The results of this pilot study revealed inhomogeneous skin deformation, characterised by a gradual transition from a low (2.0-5.0%; epidermis) to high (10-22%; dermis) shear strain regime. Shear moduli ranged from 20 to 130kPa. The herein presented method will be used for more extended studies on viable human skin, and is considered a valuable foundation for further development of constitutive models which can be used in advanced finite element analyses of skin. Copyright © 2012 Elsevier Ltd. All rights reserved.

Study on ion implantation conditions in fabricating compressively strained Si/relaxed Si1-xCx heterostructures using the defect control by ion implantation technique

NASA Astrophysics Data System (ADS)

Arisawa, You; Sawano, Kentarou; Usami, Noritaka

2017-06-01

The influence of ion implantation energies on compressively strained Si/relaxed Si1-xCx heterostructures formed on Ar ion implanted Si substrates was investigated. It was found that relaxation ratio can be enhanced over 100% at relatively low implantation energies, and compressive strain in the topmost Si layer is maximized at 45 keV due to large lattice mismatch. Cross-sectional transmission electron microscope images revealed that defects are localized around the hetero-interface between the Si1-xCx layer and the Ar+-implanted Si substrate when the implantation energy is 45 keV, which decreases the amount of defects in the topmost Si layer and the upper part of the Si1-xCx buffer layer.

Strain engineering in epitaxial Ge1- x Sn x : a path towards low-defect and high Sn-content layers

NASA Astrophysics Data System (ADS)

Margetis, Joe; Yu, Shui-Qing; Bhargava, Nupur; Li, Baohua; Du, Wei; Tolle, John

2017-12-01

The plastic strain relaxation of CVD-grown Ge1-x Sn x layers was investigated in x = 0.09 samples with thicknesses of 152, 180, 257, 570, and 865 nm. X-ray diffraction-reciprocal space mapping was used to determine the strain, composition, and the nature of defects in each layer. Secondary ion mass spectrometry was used to examine the evolution of the compositional profile. These results indicate that growth beyond the critical thickness results in the spontaneous formation of a relaxed and highly defective 9% Sn layer followed by a low defect 12% Sn secondary layer. We find that this growth method can be used to engineer thick, strain-relaxed, and low defect density layers. Furthermore we utilize this strain-dependent Sn incorporation behavior to achieve Sn compositions of 17.5%. Photoluminesence of these layers produces light emission at 3.1 μm.

Transcriptional analysis of liver from chickens with fast (meat bird), moderate (F1 layer x meat bird cross) and low (layer bird) growth potential.

PubMed

Willson, Nicky-Lee; Forder, Rebecca E A; Tearle, Rick; Williams, John L; Hughes, Robert J; Nattrass, Greg S; Hynd, Philip I

2018-05-02

Divergent selection for meat and egg production in poultry has resulted in strains of birds differing widely in traits related to these products. Modern strains of meat birds can reach live weights of 2 kg in 35 d, while layer strains are now capable of producing more than 300 eggs per annum but grow slowly. In this study, RNA-Seq was used to investigate hepatic gene expression between three groups of birds with large differences in growth potential; meat bird, layer strain as well as an F1 layer x meat bird. The objective was to identify differentially expressed (DE) genes between all three strains to elucidate biological factors underpinning variations in growth performance. RNA-Seq analysis was carried out on total RNA extracted from the liver of meat bird (n = 6), F1 layer x meat bird cross (n = 6) and layer strain (n = 6), males. Differential expression of genes were considered significant at P < 0.05, and a false discovery rate of < 0.05, with any fold change considered. In total, 6278 genes were found to be DE with 5832 DE between meat birds and layers (19%), 2935 DE between meat birds and the cross (9.6%) and 493 DE between the cross and layers (1.6%). Comparisons between the three groups identified 155 significant DE genes. Gene ontology (GO) enrichment and Kyoto Encyclopaedia of Genes and Genomes (KEGG) pathway analysis of the 155 DE genes showed the FoxO signalling pathway was most enriched (P = 0.001), including genes related to cell cycle regulation and insulin signalling. Significant GO terms included 'positive regulation of glucose import' and 'cellular response to oxidative stress', which is also consistent with FoxOs regulation of glucose metabolism. There were high correlations between FoxO pathway genes and bodyweight, as well as genes related to glycolysis and bodyweight. This study revealed large transcriptome differences between meat and layer birds. There was significant evidence implicating the FoxO signalling pathway (via cell cycle regulation and altered metabolism) as an active driver of growth variations in chicken. Functional analysis of the FoxO genes is required to understand how they regulate growth and egg production.

A novel method of fabricating laminated silicone stack actuators with pre-strained dielectric layers

NASA Astrophysics Data System (ADS)

Hinitt, Andrew D.; Conn, Andrew T.

2014-03-01

In recent studies, stack based Dielectric Elastomer Actuators (DEAs) have been successfully used in haptic feedback and sensing applications. However, limitations in the fabrication method, and materials used to con- struct stack actuators constrain their force and displacement output per unit volume. This paper focuses on a fabrication process enabling a stacked elastomer actuator to withstand the high tensile forces needed for high power applications, such as mimetics for mammalian muscle contraction (i.e prostheses), whilst requiring low voltage for thickness-mode contractile actuation. Spun elastomer layers are bonded together in a pre-strained state using a conductive adhesive filler, forming a Laminated Inter-Penetrating Network (L-IPN) with repeatable and uniform electrode thickness. The resulting structure utilises the stored strain energy of the dielectric elas- tomer to compress the cured electrode composite material. The method is used to fabricate an L-IPN example, which demonstrated that the bonded L-IPN has high tensile strength normal to the lamination. Additionally, the uniformity and retained dielectric layer pre-strain of the L-IPN are confirmed. The described method is envisaged to be used in a semi-automated assembly of large-scale multi-layer stacks of pre-strained dielectric layers possessing a tensile strength in the range generated by mammalian muscle.

Characterization of strain relaxation behavior in Si1- x Ge x epitaxial layers by dry oxidation

NASA Astrophysics Data System (ADS)

Jang, Hyunchul; Kim, Byongju; Koo, Sangmo; Park, Seran; Ko, Dae-Hong

2017-11-01

We fabricated fully strained Si0.77Ge0.23 epitaxial layers on Si substrates and investigated their strain relaxation behaviors under dry oxidation and the effect of oxidation temperatures and times. After the oxidation process, a Ge-rich layer was formed between the oxide and the remaining Si0.77Ge0.23 layer. Using reciprocal space mapping measurements, we confirmed that the strain of the Si0.77Ge0.23 layers was efficiently relaxed after oxidation, with a maximum relaxation value of 70% after oxidation at 850 °C for 120 min. The surface of Si0.77Ge0.23 layer after strain relaxation by dry oxidation was smoother than a thick Si0.77Ge0.23 layer, which achieved a similar strain relaxation value by increasing the film thickness. Additionally, N2 annealing was performed in order to compare its effect on the relaxation compared to dry oxidation and to identify relaxation mechanisms, other than the thermally driven ones, occurring during dry oxidation.

Using fiber-optic sensor technology to measure strains under the asphalt layer of a flexible pavement structure.

DOT National Transportation Integrated Search

2006-01-01

In this study, a flexible pavement system was instrumented using fiber-optic strain sensors (FOSS). The purpose of this study was to demonstrate the feasibility of a FOSS installation, monitor the long-term strains under repeated traffic loading, and...

A comparative study of live attenuated F strain-derived Mycoplasma gallisepticum vaccines

USDA-ARS?s Scientific Manuscript database

Commercially available attenuated strains of Mycoplasma gallisepticum (MG) are commonly used within the layer industry to control MG-induced mycoplasmosis. Among these are two live MG vaccines derived from the moderately pathogenic MG “chick F” strain. In the present study, the commercially availa...

Myocardial layer-specific analysis in patients with heterozygous familial hypercholesterolemia using speckle tracking echocardiography.

PubMed

Leng, Zhaoting; Li, Rongjuan; Li, Yijia; Wang, Lvya; Wang, Yueli; Yang, Ya

2017-03-01

Familial hypercholesterolemia (FH) is the most common and serious monogenic disorder of lipid metabolism, causing premature coronary heart disease (CHD) due to accelerated atherosclerosis from birth, and the study of left ventricular (LV) function of this disease is seldom. The purpose of this study was to explore the value of layer-specific strain on assessing the early damage of LV function in asymptomatic and left ventricular ejection fraction (LVEF) well-preserved patients with heterozygous FH (HeFH). A total of 49 patients aged 38.7±8.7 diagnosed with heterozygous familial hypercholesterolemia and who had undergone transthoracic echocardiography from 2010 to 2016 were included in this study. A total 32 healthy volunteers aged 35.6±10.3 were included as control group. Longitudinal and circumferential strains of the endocardium, myocardium, and epicardium (LSendo, LSmyo, and LSepi and CSendo, CSmyo, and CSepi) were obtained by a software enabling the analysis of strains in three myocardial layers. In longitudinal strain (LS), the LS of endocardium (LSendo) and the LS of myocardium (LSmyo) are significantly reduced in patients with HeFH (P<.001 in both). In circumferential strain (CS), only the CS of endocardium (CSendo) is significantly reduced (P<.001). The degree of reduction in strain is positively correlated with the TC and LDLC. Layer-specific evaluation of the left ventricle has great value in evaluating early impairment of LV in patients with FH. And this relatively novel technique may made it possible to help us understand the process of LV impairment in patients with FH better, thus preventing further damage. © 2017, Wiley Periodicals, Inc.

Non-linear second harmonic generation (SHG) studies of BaTiO3/SrTiO3 superlattices

NASA Astrophysics Data System (ADS)

Vlahos, Eftihia; Lee, Che-Hui; Wu, Pingping; Wung Bark, Chung; Jang, Ho Won; Folkman, Chad; Hyub Baek, Seung; Park, J. W.; Biegalski, Mike; Tenne, Dmitri; Schlom, Darrell; Chen, Long-Qing; Eom, Chang-Beom; Gopalan, Venkatraman

2010-03-01

Theoretical phase-field simulations predict that certain types of superlattices consisting of alternating (BaTiO3)n/(SrTiO3)n layers have novel vortex domain wall configurations which give rise to exceptionally high polarization tunability combined with negligible polarization hysteresis. Optical second harmonic generation (SHG) was used to probe the phase and transition temperatures of multilayer (BaTiO3)m/(SrTiO3)n superlattices, as a function of epitaxial strain. In addition, in-plane electro-optic measurements were carried out. The experimental results are in excellent agreement both with theoretical predictions, as well as the temperature-strain phase diagram obtained experimentally from UV Raman studies. The ferroelectric, in-plane SHG signal, from the tensile strained SrTiO3 layers reveals an mm2 point group symmetry, whereas the point group symmetry of the compressively strained BaTiO3 layers, was determined to be 4mm.

A two-layered mechanical model of the rat esophagus. Experiment and theory

PubMed Central

Fan, Yanhua; Gregersen, Hans; Kassab, Ghassan S

2004-01-01

Background The function of esophagus is to move food by peristaltic motion which is the result of the interaction of the tissue forces in the esophageal wall and the hydrodynamic forces in the food bolus. The structure of the esophagus is layered. In this paper, the esophagus is treated as a two-layered structure consisting of an inner collagen-rich submucosa layer and an outer muscle layer. We developed a model and experimental setup for determination of elastic moduli in the two layers in circumferential direction and related the measured elastic modulus of the intact esophagus to the elastic modulus computed from the elastic moduli of the two layers. Methods Inflation experiments were done at in vivo length and pressure-diameters relations were recorded for the rat esophagus. Furthermore, the zero-stress state was taken into consideration. Results The radius and the strain increased as function of pressure in the intact as well as in the individual layers of the esophagus. At pressures higher than 1.5 cmH2O the muscle layer had a larger radius and strain than the mucosa-submucosa layer. The strain for the intact esophagus and for the muscle layer was negative at low pressures indicating the presence of residual strains in the tissue. The stress-strain curve for the submucosa-mucosa layer was shifted to the left of the curves for the muscle layer and for the intact esophagus at strains higher than 0.3. The tangent modulus was highest in the submucosa-mucosa layer, indicating that the submucosa-mucosa has the highest stiffness. A good agreement was found between the measured elastic modulus of the intact esophagus and the elastic modulus computed from the elastic moduli of the two separated layers. PMID:15518591

Influence of growth temperature on laser molecular beam epitaxy and properties of GaN layers grown on c-plane sapphire

NASA Astrophysics Data System (ADS)

Dixit, Ripudaman; Tyagi, Prashant; Kushvaha, Sunil Singh; Chockalingam, Sreekumar; Yadav, Brajesh Singh; Sharma, Nita Dilawar; Kumar, M. Senthil

2017-04-01

We have investigated the influence of growth temperature on the in-plane strain, structural, optical and mechanical properties of heteroepitaxially grown GaN layers on sapphire (0001) substrate by laser molecular beam epitaxy (LMBE) technique in the temperature range 500-700 °C. The GaN epitaxial layers are found to have a large in-plane compressive stress of about 1 GPa for low growth temperatures but the strain drastically reduced in the layer grown at 700 °C. The nature of the in-plane strain has been analyzed using high resolution x-ray diffraction, atomic force microscopy (AFM), Raman spectroscopy and photoluminescence (PL) measurements. From AFM, a change in GaN growth mode from grain to island is observed at the high growth temperature above 600 °C. A blue shift of 20-30 meV in near band edge PL emission line has been noticed for the GaN layers containing the large in-plane strain. These observations indicate that the in-plane strain in the GaN layers is dominated by a biaxial strain. Using nanoindentation, it is found that the indentation hardness and Young's modulus of the GaN layers increases with increasing growth temperature. The results disclose the critical role of growth mode in determining the in-plane strain and mechanical properties of the GaN layers grown by LMBE technique.

Effect of strain on the electron effective mobility in biaxially strained silicon inversion layers: An experimental and theoretical analysis via atomic force microscopy measurements and Kubo-Greenwood mobility calculations

NASA Astrophysics Data System (ADS)

Bonno, Olivier; Barraud, Sylvain; Mariolle, Denis; Andrieu, François

2008-03-01

Recently, in order to explain the long-channel electron effective mobility at a high sheet carrier density in strained silicon channel transistors, it has been suggested by [M. V. Fischetti, F. Gamiz, and W. Hansch, J. Appl. Phys. 92, 7230 (2002)] that biaxial tensile strain should smooth the Si/SiO2 interface. To address this topic, the roughness properties of biaxial strained silicon-on-insulator (s-SOI) films are investigated by means of atomic force microscopy. Through in-depth statistical analysis of the digitalized surface profiles, the roughness parameters are extracted for unstrained and strained SOI films, with 0.8% biaxial tensile strain. Especially, it is found that strain significantly reduces the roughness amplitude. Then, mobility calculations in SOI and s-SOI inversion layers are performed in the framework of the Kubo-Greenwood formalism. The model accounts for the main scattering mechanisms that are dominant in the high electron density range, namely phonon and surface roughness. Special attention has been paid to the modeling of the latter by accounting for all the contributions of the potential which arise from the deformed rough interface, and by using a multisubband wavelength-dependent screening model. This model is then applied to study the influence of the surface morphology on the mobility in s-SOI inversion layers. In this context, the mobility gain between s-SOI and unstrained SOI layers is found to agree significantly better with experimental data if the strain-induced decrease of the roughness amplitude is taken into account.

Splitting of the neutral mechanical plane depends on the length of the multi-layer structure of flexible electronics.

PubMed

Li, Shuang; Su, Yewang; Li, Rui

2016-06-01

Multi-layer structures with soft (compliant) interlayers have been widely used in flexible electronics and photonics as an effective design for reducing interactions among the hard (stiff) layers and thus avoiding the premature failure of an entire device. The analytic model for bending of such a structure has not been well established due to its complex mechanical behaviour. Here, we present a rational analytic model, without any parameter fitting, to study the bending of a multi-layer structure on a cylinder, which is often regarded as an important approach to mechanical reliability testing of flexible electronics and photonics. For the first time, our model quantitatively reveals that, as the key for accurate strain control, the splitting of the neutral mechanical plane depends not only on the relative thickness of the middle layer, but also on the length-to-thickness ratio of the multi-layer structure. The model accurately captures the key quantities, including the axial strains in the top and bottom layers, the shear strain in the middle layer and the locations of the neutral mechanical planes of the top and bottom layers. The effects of the length of the multi-layer and the thickness of the middle layer are elaborated. This work is very useful for the design of multi-layer structure-based flexible electronics and photonics.

Splitting of the neutral mechanical plane depends on the length of the multi-layer structure of flexible electronics

PubMed Central

Li, Shuang; Li, Rui

2016-01-01

Multi-layer structures with soft (compliant) interlayers have been widely used in flexible electronics and photonics as an effective design for reducing interactions among the hard (stiff) layers and thus avoiding the premature failure of an entire device. The analytic model for bending of such a structure has not been well established due to its complex mechanical behaviour. Here, we present a rational analytic model, without any parameter fitting, to study the bending of a multi-layer structure on a cylinder, which is often regarded as an important approach to mechanical reliability testing of flexible electronics and photonics. For the first time, our model quantitatively reveals that, as the key for accurate strain control, the splitting of the neutral mechanical plane depends not only on the relative thickness of the middle layer, but also on the length-to-thickness ratio of the multi-layer structure. The model accurately captures the key quantities, including the axial strains in the top and bottom layers, the shear strain in the middle layer and the locations of the neutral mechanical planes of the top and bottom layers. The effects of the length of the multi-layer and the thickness of the middle layer are elaborated. This work is very useful for the design of multi-layer structure-based flexible electronics and photonics. PMID:27436977

Predicting the compressibility behaviour of tire shred samples for landfill applications.

PubMed

Warith, M A; Rao, Sudhakar M

2006-01-01

Tire shreds have been used as an alternative to crushed stones (gravel) as drainage media in landfill leachate collection systems. The highly compressible nature of tire shreds (25-47% axial strain on vertical stress applications of 20-700 kPa) may reduce the thickness of the tire shred drainage layer to less than 300 mm (minimum design requirement) during the life of the municipal solid waste landfill. There hence exists a need to predict axial strains of tire shred samples in response to vertical stress applications so that the initial thickness of the tire shred drainage layer can be corrected for compression. The present study performs one-dimensional compressibility tests on four tire shred samples and compares the results with stress/strain curves from other studies. The stress/strain curves are developed into charts for choosing the correct initial thickness of tire shred layers that maintain the minimum thickness of 300 mm throughout the life of the landfill. The charts are developed for a range of vertical stresses based on the design height of municipal waste cell and bulk unit weight of municipal waste. Experimental results also showed that despite experiencing large axial strains, the average permeability of the tire shred sample consistently remained two to three orders of magnitude higher than the design performance criterion of 0.01cm/s for landfill drainage layers. Laboratory experiments, however, need to verify whether long-term chemical and bio-chemical reactions between landfill leachate and the tire shred layer will deteriorate their mechanical functions (hydraulic conductivity, compressibility, strength) beyond permissible limits for geotechnical applications.

Characterization of crystallographic properties of thin films using X-ray diffraction

NASA Astrophysics Data System (ADS)

Zoo, Yeongseok

2007-12-01

Silver (Ag) has been recognized as one of promising candidates in Ultra-Large Scale Integrated (ULSI) applications in that it has the lowest bulk electrical resistivity of all pure metals and higher electromigration resistance than other interconnect materials. However, low thermal stability on Silicon Dioxide (Si02) at high temperatures (e.g., agglomeration) is considered a drawback for the Ag metallization scheme. Moreover, if a thin film is attached on a substrate, its properties may differ significantly from that of the bulk, since the properties of thin films can be significantly affected by the substrate. In this study, the Coefficient of Thermal Expansion (CTE) and texture evolution of Ag thin films on different substrates were characterized using various analytical techniques. The experimental results showed that the CTE of the Ag thin film was significantly affected by underlying substrate and the surface roughness of substrate. To investigate the alloying effect for Ag meatallization, small amounts of Copper (Cu) were added and characterized using theta-2theta X-ray Diffraction (XRD) scan and pole figure analysis. These XRD techniques are useful for investigating the primary texture of a metal film, (111) in this study, which (111) is the notation of a specific plane in the orthogonal coordinate system. They revealed that the (111) textures of Ag and Ag(Cu) thin films were enhanced with increasing temperature. Comparison of texture profiles between Ag and Ag(Cu) thin films showed that Cu additions enhanced (111) texture in Ag thin films. Accordingly, the texture enhancement in Ag thin films by Cu addition was discussed. Strained Silicon-On-Insulator (SSOI) is being considered as a potential substrate for Complementary Metal-Oxide-Semiconductor (CMOS) technology since the induced strain results in a significant improvement in device performance. High resolution X-ray diffraction (XRD) techniques were used to characterize the perpendicular and parallel strains in SSOI layers. XRD diffraction profiles generated from the crystalline SSOI layer provided a direct measurement of the layer's strain components. In addition, it has demonstrated that the rotational misalignment between the layer and the substrate can be incorporated within the biaxial strain equations for epitaxial layers. Based on these results, the strain behavior of the SSOI layer and the relation between strained Si and SiO2 layers are discussed for annealed samples.

Method of producing strained-layer semiconductor devices via subsurface-patterning

DOEpatents

Dodson, Brian W.

1993-01-01

A method is described for patterning subsurface features in a semiconductor device, wherein the semiconductor device includes an internal strained layer. The method comprises creating a pattern of semiconductor material over the semiconductor device, the semiconductor material having a predetermined thickness which stabilizes areas of the strained semiconductor layer that lie beneath the pattern. Subsequently, a heating step is applied to the semiconductor device to cause a relaxation in areas of the strained layer which do not lie beneath the semiconductor material pattern, whereby dislocations result in the relaxed areas and impair electrical transport therethrough.

Study of low-defect and strain-relaxed GeSn growth via reduced pressure CVD in H2 and N2 carrier gas

NASA Astrophysics Data System (ADS)

Margetis, J.; Mosleh, A.; Al-Kabi, S.; Ghetmiri, S. A.; Du, W.; Dou, W.; Benamara, M.; Li, B.; Mortazavi, M.; Naseem, H. A.; Yu, S.-Q.; Tolle, J.

2017-04-01

High quality, thick (up to 1.1 μm), strain relaxed GeSn alloys were grown on Ge-buffered Si (1 0 0) in an ASM Epsilon® chemical vapor deposition system using SnCl4 and low-cost commercial GeH4 precursors. The significance of surface chemistry in regards to growth rate and Sn-incorporation is discussed by comparing growth kinetics data in H2 and N2 carrier gas. The role of carrier gas is also explored in the suppression of Sn surface segregation and evolution of layer composition and strain profiles via secondary ion mass spectrometry and X-ray diffraction. Transmission electron microscopy revealed the spontaneous compositional splitting and formation of a thin intermediate layer in which dislocations are pinned. This intermediate layer enables the growth of a thick, strain relaxed, and defect-free epitaxial layer on its top. Last, we present photoluminescence results which indicate that both N2 and H2 growth methods produce optoelectronic device quality material.

Linearly polarized photoluminescence of anisotropically strained c-plane GaN layers on stripe-shaped cavity-engineered sapphire substrate

NASA Astrophysics Data System (ADS)

Kim, Jongmyeong; Moon, Daeyoung; Lee, Seungmin; Lee, Donghyun; Yang, Duyoung; Jang, Jeonghwan; Park, Yongjo; Yoon, Euijoon

2018-05-01

Anisotropic in-plane strain and resultant linearly polarized photoluminescence (PL) of c-plane GaN layers were realized by using a stripe-shaped cavity-engineered sapphire substrate (SCES). High resolution X-ray reciprocal space mapping measurements revealed that the GaN layers on the SCES were under significant anisotropic in-plane strain of -0.0140% and -0.1351% along the directions perpendicular and parallel to the stripe pattern, respectively. The anisotropic in-plane strain in the GaN layers was attributed to the anisotropic strain relaxation due to the anisotropic arrangement of cavity-incorporated membranes. Linearly polarized PL behavior such as the observed angle-dependent shift in PL peak position and intensity comparable with the calculated value based on k.p perturbation theory. It was found that the polarized PL behavior was attributed to the modification of valence band structures induced by anisotropic in-plane strain in the GaN layers on the SCES.

Hybrid structure of white layer in high carbon steel - Formation mechanism and its properties.

PubMed

Hossain, Rumana; Pahlevani, Farshid; Witteveen, Evelien; Banerjee, Amborish; Joe, Bill; Prusty, B Gangadhara; Dippenaar, Rian; Sahajwalla, Veena

2017-10-16

This study identifies for the first time, the hybrid structure of the white layer in high carbon steel and describes its formation mechanism and properties. The so-called 'white layer' in steel forms during high strain rate deformation and appears featureless under optical microscopy. While many researchers have investigated the formation of the white layer, there has been no definitive study, nor is there sufficient evidence to fully explain the formation, structure and properties of the layer. In this study, the formation, morphology and mechanical properties of the white layer was determined following impact testing, using a combination of optical and SE- microscopy, HR-EBSD, TKD and TEM as well as nano-indentation hardness measurements and FE modelling. The phase transformation and recrystallization within and near the white layer was also investigated. The microstructure of the steel in the white layer consisted of nano-sized grains of martensite. A very thin layer of austenite with nano sized grains was identified within the white layer by HR-EBSD techniques, the presence of which is attributed to a thermally-induced reverse phase transformation. Overall, the combination of phase transformations, strain hardening and grain refinement led to a hybrid structure and an increase in hardness of the white layer.

Strain mapping in single-layer two-dimensional crystals via Raman activity

NASA Astrophysics Data System (ADS)

Yagmurcukardes, M.; Bacaksiz, C.; Unsal, E.; Akbali, B.; Senger, R. T.; Sahin, H.

2018-03-01

By performing density functional theory-based ab initio calculations, Raman-active phonon modes of single-layer two-dimensional (2D) materials and the effect of in-plane biaxial strain on the peak frequencies and corresponding activities of the Raman-active modes are calculated. Our findings confirm the Raman spectrum of the unstrained 2D crystals and provide expected variations in the Raman-active modes of the crystals under in-plane biaxial strain. The results are summarized as follows: (i) frequencies of the phonon modes soften (harden) under applied tensile (compressive) strains; (ii) the response of the Raman activities to applied strain for the in-plane and out-of-plane vibrational modes have opposite trends, thus, the built-in strains in the materials can be monitored by tracking the relative activities of those modes; (iii) in particular, the A peak in single-layer Si and Ge disappears under a critical tensile strain; (iv) especially in mono- and diatomic single layers, the shift of the peak frequencies is a stronger indication of the strain rather than the change in Raman activities; (v) Raman-active modes of single-layer ReX2 (X =S , Se) are almost irresponsive to the applied strain. Strain-induced modifications in the Raman spectrum of 2D materials in terms of the peak positions and the relative Raman activities of the modes could be a convenient tool for characterization.

Different cross protection scopes of two avian influenza H5N1 vaccines against infection of layer chickens with a heterologous highly pathogenic virus.

PubMed

Poetri, Okti Nadia; Van Boven, Michiel; Koch, Guus; Stegeman, Arjan; Claassen, Ivo; Wayan Wisaksana, I; Bouma, Annemarie

2017-10-01

Avian influenza (AI) virus strains vary in antigenicity, and antigenic differences between circulating field virus and vaccine virus will affect the effectiveness of vaccination of poultry. Antigenic relatedness can be assessed by measuring serological cross-reactivity using haemagglutination inhibition (HI) tests. Our study aims to determine the relation between antigenic relatedness expressed by the Archetti-Horsfall ratio, and reduction of virus transmission of highly pathogenic H5N1 AI strains among vaccinated layers. Two vaccines were examined, derived from H5N1 AI virus strains A/Ck/WJava/Sukabumi/006/2008 and A/Ck/CJava/Karanganyar/051/2009. Transmission experiments were carried out in four vaccine and two control groups, with six sets of 16 specified pathogen free (SPF) layer chickens. Birds were vaccinated at 4weeks of age with one strain and challenge-infected with the homologous or heterologous strain at 8weeks of age. No transmission or virus shedding occurred in groups challenged with the homologous strain. In the group vaccinated with the Karanganyar strain, high cross-HI responses were observed, and no transmission of the Sukabumi strain occurred. However, in the group vaccinated with the Sukabumi strain, cross-HI titres were low, virus shedding was not reduced, and multiple transmissions to contact birds were observed. This study showed large differences in cross-protection of two vaccines based on two different highly pathogenic H5N1 virus strains. This implies that extrapolation of in vitro data to clinical protection and reduction of virus transmission might not be straightforward. Copyright © 2017 Elsevier Ltd. All rights reserved.

Growth of strained Si/relaxed SiGe heterostructures on Si(110) substrates using solid-source molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Arimoto, Keisuke; Nakazawa, Hiroki; Mitsui, Shohei; Utsuyama, Naoto; Yamanaka, Junji; Hara, Kosuke O.; Usami, Noritaka; Nakagawa, Kiyokazu

2017-11-01

A strained Si/relaxed SiGe heterostructure grown on Si(110) substrate is attractive as a platform for high-hole-mobility Si-based electronic devices. To improve the electrical property, a smoother surface is desirable. In this study, we investigated surface morphology and microstructural aspects of strained Si/relaxed SiGe/Si(110) heterostructures grown by solid-source (SS) molecular beam epitaxy (MBE). It was revealed that SSMBE provides a way to grow strained Si/relaxed SiGe heterostructures with smooth surfaces. In addition, it was found that the strain in the SiGe layer of the SSMBE-grown sample is highly anisotropic whereas that of the GSMBE-grown sample is almost biaxially relaxed. Along with the surface morphology, the symmetry in degree of strain relaxation has implications for the electrical property. Results of a calculation shows that anisotropic strain is preferable for device application since it confines holes solely in the strained Si layer where hole mobility is enhanced.

Strain measurement in semiconductor heterostructures by scanning transmission electron microscopy.

PubMed

Müller, Knut; Rosenauer, Andreas; Schowalter, Marco; Zweck, Josef; Fritz, Rafael; Volz, Kerstin

2012-10-01

This article deals with the measurement of strain in semiconductor heterostructures from convergent beam electron diffraction patterns. In particular, three different algorithms in the field of (circular) pattern recognition are presented that are able to detect diffracted disc positions accurately, from which the strain in growth direction is calculated. Although the three approaches are very different as one is based on edge detection, one on rotational averages, and one on cross correlation with masks, it is found that identical strain profiles result for an In x Ga1-x N y As1-y /GaAs heterostructure consisting of five compressively and tensile strained layers. We achieve a precision of strain measurements of 7-9·10-4 and a spatial resolution of 0.5-0.7 nm over the whole width of the layer stack which was 350 nm. Being already very applicable to strain measurements in contemporary nanostructures, we additionally suggest future hardware and software designs optimized for fast and direct acquisition of strain distributions, motivated by the present studies.

Ultrasensitive tunability of the direct bandgap of 2D InSe flakes via strain engineering

NASA Astrophysics Data System (ADS)

Li, Yang; Wang, Tianmeng; Wu, Meng; Cao, Ting; Chen, Yanwen; Sankar, Raman; Ulaganathan, Rajesh K.; Chou, Fangcheng; Wetzel, Christian; Xu, Cheng-Yan; Louie, Steven G.; Shi, Su-Fei

2018-04-01

InSe, a member of the layered materials family, is a superior electronic and optical material which retains a direct bandgap feature from the bulk to atomically thin few-layers and high electronic mobility down to a single layer limit. We, for the first time, exploit strain to drastically modify the bandgap of two-dimensional (2D) InSe nanoflakes. We demonstrated that we could decrease the bandgap of a few-layer InSe flake by 160 meV through applying an in-plane uniaxial tensile strain to 1.06% and increase the bandgap by 79 meV through applying an in-plane uniaxial compressive strain to 0.62%, as evidenced by photoluminescence (PL) spectroscopy. The large reversible bandgap change of ~239 meV arises from a large bandgap change rate (bandgap strain coefficient) of few-layer InSe in response to strain, ~154 meV/% for uniaxial tensile strain and ~140 meV/% for uniaxial compressive strain, representing the most pronounced uniaxial strain-induced bandgap strain coefficient experimentally reported in 2D materials. We developed a theoretical understanding of the strain-induced bandgap change through first-principles DFT and GW calculations. We also confirmed the bandgap change by photoconductivity measurements using excitation light with different photon energies. The highly tunable bandgap of InSe in the infrared regime should enable a wide range of applications, including electro-mechanical, piezoelectric and optoelectronic devices.

Nanoscale self-templating for oxide epitaxy with large symmetry mismatch

DOE PAGES

Gao, Xiang; Lee, Shinbuhm; Nichols, John A.; ...

2016-12-02

Direct observations using scanning transmission electron microscopy unveil an intriguing interfacial bi-layer that enables epitaxial growth of a strain-free, monoclinic, bronze-phase VO 2(B) thin film on a perovskite SrTiO 3 (STO) substrate. For this study, we observe an ultrathin (2–3 unit cells) interlayer best described as highly strained VO 2(B) nanodomains combined with an extra (Ti,V)O 2 layer on the TiO 2 terminated STO (001) surface. By forming a fully coherent interface with the STO substrate and a semi-coherent interface with the strain-free epitaxial VO 2(B) film above, the interfacial bi-layer enables the epitaxial connection of the two materials despitemore » their large symmetry and lattice mismatch.« less

Determination of the strain distribution for the Si3N4 passivated AlGaN/AlN/GaN heterostructure field-effect transistors

NASA Astrophysics Data System (ADS)

Fu, Chen; Lin, Zhaojun; Liu, Yan; Cui, Peng; Lv, Yuanjie; Zhou, Yang; Dai, Gang; Luan, Chongbiao

2017-11-01

A method to determine the strain distribution of the AlGaN barrier layer after the device fabrication and the passivation process has been presented. By fitting the calculated parasitic source access resistance with the measured ones for the AlGaN/AlN/GaN HFETs and using the polarization Coulomb field scattering theory, the strain variation of the AlGaN barrier layer after the passivation process has been quantitatively studied. The results show that the tensile strain in the access regions of the AlGaN barrier layer has been increased by 4.62% for the 250 nm-Si3N4 passivated device, and has been decreased by 2.0% for the 400 nm-Si3N4 passivated device, compared to that of before the passivation, respectively. For the gate region of the two devices, the tensile strain has been decreased by 60.77% and increased by 3.60% after the passivation of different thicknesses, oppositely.

Strain-specific detection of orally administered canine jejunum-dominated Lactobacillus acidophilus LAB20 in dog faeces by real-time PCR targeted to the novel surface layer protein.

PubMed

Tang, Y; Saris, P E J

2013-10-01

Lactobacillus acidophilus LAB20 has potential to be a probiotic strain because it can be present at high numbers in the jejunum of dog. To specifically detect LAB20 from dog faecal samples, a real-time PCR protocol was developed targeting the novel surface (S) layer protein gene of LAB20. The presence of S-layer protein was verified by N-terminal sequencing of the approximately 50-kDa major band from SDS-PAGE gel. The corresponding S-layer gene was amplified by inverse PCR using homology to known S-layers and sequenced. This novel S-layer protein has low sequence similarity to other S-layer proteins in the N-terminal region (32-211 aa, 7-39%). This enabled designing strain-specific PCR primers. The primer set was utilized to study intestinal persistence of LAB20 in dog that was fed with LAB20 fermented milk for 5 days. The results showed that LAB20 can be detected from dog faecal sample after 6 weeks with 10(4·53)  DNA copies g(-1) postadministration. It suggested that LAB20 could be a good candidate to study the mechanism behind its persistence and dominance in dog intestine and maybe utilize it as a probiotic for canine. A real-time PCR method was developed to detect Lactobacillus acidophilus LAB20, a strain that was previously found dominant in canine gastrointestinal (GI) tract. The quantitative detection was based on targeting to variation region of a novel S-layer protein found in LAB20, allowing to specifically enumerate LAB20 from dog faeces. The results showed that the real-time PCR method was sensitive enough to be used in later intervention studies. Interestingly, LAB20 was found to persist in dog GI tract for 6 weeks. Therefore, LAB20 could be a good candidate to study its colonization and potentially utilize as a canine probiotic. © 2013 The Society for Applied Microbiology.

Subcritical crack growth in SiNx thin-film barriers studied by electro-mechanical two-point bending

NASA Astrophysics Data System (ADS)

Guan, Qingling; Laven, Jozua; Bouten, Piet C. P.; de With, Gijsbertus

2013-06-01

Mechanical failure resulting from subcritical crack growth in the SiNx inorganic barrier layer applied on a flexible multilayer structure was studied by an electro-mechanical two-point bending method. A 10 nm conducting tin-doped indium oxide layer was sputtered as an electrical probe to monitor the subcritical crack growth in the 150 nm dielectric SiNx layer carried by a polyethylene naphthalate substrate. In the electro-mechanical two-point bending test, dynamic and static loads were applied to investigate the crack propagation in the barrier layer. As consequence of using two loading modes, the characteristic failure strain and failure time could be determined. The failure probability distribution of strain and lifetime under each loading condition was described by Weibull statistics. In this study, results from the tests in dynamic and static loading modes were linked by a power law description to determine the critical failure over a range of conditions. The fatigue parameter n from the power law reduces greatly from 70 to 31 upon correcting for internal strain. The testing method and analysis tool as described in the paper can be used to understand the limit of thin-film barriers in terms of their mechanical properties.

Stretchable and foldable electronic devices

DOEpatents

Rogers, John A; Huang, Yonggang; Ko, Heung Cho; Stoykovich, Mark; Choi, Won Mook; Song, Jizhou; Ahn, Jong Hyun; Kim, Dae Hyeong

2013-10-08

Disclosed herein are stretchable, foldable and optionally printable, processes for making devices and devices such as semiconductors, electronic circuits and components thereof that are capable of providing good performance when stretched, compressed, flexed or otherwise deformed. Strain isolation layers provide good strain isolation to functional device layers. Multilayer devices are constructed to position a neutral mechanical surface coincident or proximate to a functional layer having a material that is susceptible to strain-induced failure. Neutral mechanical surfaces are positioned by one or more layers having a property that is spatially inhomogeneous, such as by patterning any of the layers of the multilayer device.

Electronic Spectrum of Twisted Graphene Layers under Heterostrain

NASA Astrophysics Data System (ADS)

Huder, Loïc; Artaud, Alexandre; Le Quang, Toai; de Laissardière, Guy Trambly; Jansen, Aloysius G. M.; Lapertot, Gérard; Chapelier, Claude; Renard, Vincent T.

2018-04-01

We demonstrate that stacking layered materials allows a strain engineering where each layer is strained independently, which we call heterostrain. We combine detailed structural and spectroscopic measurements with tight-binding calculations to show that small uniaxial heterostrain suppresses Dirac cones and leads to the emergence of flat bands in twisted graphene layers (TGLs). Moreover, we demonstrate that heterostrain reconstructs, much more severely, the energy spectrum of TGLs than homostrain for which both layers are strained identically, a result which should apply to virtually all van der Waals structures opening exciting possibilities for straintronics with 2D materials.

Stretchable and foldable electronic devices

DOEpatents

Rogers, John A; Huang, Yonggang; Ko, Heung Cho; Stoykovich, Mark; Choi, Won Mook; Song, Jizhou; Ahn, Jong Hyun; Kim, Dae Hyeong

2014-12-09

Disclosed herein are stretchable, foldable and optionally printable, processes for making devices and devices such as semiconductors, electronic circuits and components thereof that are capable of providing good performance when stretched, compressed, flexed or otherwise deformed. Strain isolation layers provide good strain isolation to functional device layers. Multilayer devices are constructed to position a neutral mechanical surface coincident or proximate to a functional layer having a material that is susceptible to strain-induced failure. Neutral mechanical surfaces are positioned by one or more layers having a property that is spatially inhomogeneous, such as by patterning any of the layers of the multilayer device.

Enhanced bending failure strain in biological glass fibers due to internal lamellar architecture.

PubMed

Monn, Michael A; Kesari, Haneesh

2017-12-01

The remarkable mechanical properties of biological structures, like tooth and bone, are often a consequence of their architecture. The tree ring-like layers that comprise the skeletal elements of the marine sponge Euplectella aspergillum are a quintessential example of the intricate architectures prevalent in biological structures. These skeletal elements, known as spicules, are hair-like fibers that consist of a concentric array of silica cylinders separated by thin, organic layers. Thousands of spicules act like roots to anchor the sponge to the sea floor. While spicules have been the subject of several structure-property investigations, those studies have mostly focused on the relationship between the spicule's layered architecture and toughness properties. In contrast, we hypothesize that the spicule's layered architecture enhances its bending failure strain, thereby allowing it to provide a better anchorage to the sea floor. We test our hypothesis by performing three-point bending tests on E. aspergillum spicules, measuring their bending failure strains, and comparing them to those of spicules from a related sponge, Tethya aurantia. The T. aurantia spicules have a similar chemical composition to E. aspergillum spicules but have no architecture. Thus, any difference between the bending failure strains of the two types of spicules can be attributed to the E. aspergillum spicules' layered architecture. We found that the bending failure strains of the E. aspergillum spicules were roughly 2.4 times larger than those of the T. aurantia spicules. Copyright © 2017 Elsevier Ltd. All rights reserved.

Superlattice strain gage

DOEpatents

Noel, B.W.; Smith, D.L.; Sinha, D.N.

1988-06-28

A strain gage comprising a strained-layer superlattice crystal exhibiting piezoelectric properties is described. A substrate upon which such a strained-layer superlattice crystal has been deposited is attached to an element to be monitored for strain. A light source is focused on the superlattice crystal and the light reflected from, passed through, or emitted from the crystal is gathered and compared with previously obtained optical property data to determine the strain in the element. 8 figs.

Electrical and mechanical characterization of nanoscale-layered cellulose-based electro-active paper.

PubMed

Yun, Gyu-Young; Yun, Ki-Ju; Kim, Joo-Hyung; Kim, Jaehwan

2011-01-01

In order to understand the electro-mechanical behavior of piezoelectric electro active paper (EAPap), the converse and direct piezoelectric characterization of cellulose EAPap was studied and compared. A delay between the electrical field and the induced strain of EAPap was observed due to the inner nano-voids or the localized amorphous regions in layer-by-layered structure to capture or hold the electrical charges and remnant ions. The linear relation between electric field and induced strain is also observed. The electro-mechanical performance of EAPap is discussed in detail in this paper.

Electromodulation spectroscopy of direct optical transitions in Ge{sub 1−x}Sn{sub x} layers under hydrostatic pressure and built-in strain

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dybała, F.; Żelazna, K.; Maczko, H.

Unstrained Ge{sub 1−x}Sn{sub x} layers of various Sn concentration (1.5%, 3%, 6% Sn) and Ge{sub 0.97}Sn{sub 0.03} layers with built-in compressive (ε = −0.5%) and tensile (ε = 0.3%) strain are grown by molecular beam epitaxy and studied by electromodulation spectroscopy (i.e., contactless electroreflectance and photoreflectance (PR)). In order to obtain unstrained GeSn layers and layers with different built-in in-plane strains, virtual InGaAs substrates of different compositions are grown prior to the deposition of GeSn layers. For unstrained Ge{sub 1−x}Sn{sub x} layers, the pressure coefficient for the direct band gap transition is determined from PR measurements at various hydrostatic pressures to be 12.2 ± 0.2 meV/kbar, whichmore » is very close to the pressure coefficient for the direct band gap transition in Ge (12.9 meV/kbar). This suggests that the hydrostatic deformation potentials typical of Ge can be applied to describe the pressure-induced changes in the electronic band structure of Ge{sub 1−x}Sn{sub x} alloys with low Sn concentrations. The same conclusion is derived for the uniaxial deformation potential, which describes the splitting between heavy-hole (HH) and light-hole (LH) bands as well as the strain-related shift of the spin-orbit (SO) split-off band. It is observed that the HH, LH, and SO related transitions shift due to compressive and tensile strain according to the Bir-Pikus theory. The dispersions of HH, LH, and SO bands are calculated for compressive and tensile strained Ge{sub 0.97}Sn{sub 0.03} with the 8-band kp Hamiltonian including strain effects, and the mixing of HH and LH bands is discussed. In addition, the dispersion of the electronic band structure is calculated for unstrained Ge{sub 1−x}Sn{sub x} layers (3% and 6% Sn) at high hydrostatic pressure with the 8-band kp Hamiltonian, and the pressure-induced changes in the electronic band structure are discussed.« less

Distribution of elastic strains appearing in gallium arsenide as a result of doping with isovalent impurities of phosphorus and indium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pavlov, D. A.; Bidus, N. V.; Bobrov, A. I., E-mail: bobrov@phys.unn.ru

2015-01-15

The distribution of elastic strains in a system consisting of a quantum-dot layer and a buried GaAs{sub x}P{sub 1−x} layer is studied using geometric phase analysis. A hypothesis is offered concerning the possibility of controlling the process of the formation of InAs quantum dots in a GaAs matrix using a local isovalent phosphorus impurity.

Strain-tolerant ceramic coated seal

DOEpatents

Schienle, James L.; Strangman, Thomas E.

1994-01-01

A metallic regenerator seal is provided having multi-layer coating comprising a NiCrAlY bond layer, a yttria stabilized zirconia (YSZ) intermediate layer, and a ceramic high temperature solid lubricant surface layer comprising zinc oxide, calcium fluoride, and tin oxide. An array of discontinuous grooves is laser machined into the outer surface of the solid lubricant surface layer making the coating strain tolerant.

Depth resolved lattice-charge coupling in epitaxial BiFeO3 thin film

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Hyeon Jun; Lee, Sung Su; Kwak, Jeong Hun

2016-12-01

For epitaxial films, a critical thickness (t c) can create a phenomenological interface between a strained bottom layer and a relaxed top layer. Here, we present an experimental report of how the tc in BiFeO 3 thin films acts as a boundary to determine the crystalline phase, ferroelectricity, and piezoelectricity in 60 nm thick BiFeO 3/SrRuO 3/SrTiO 3 substrate. We found larger Fe cation displacement of the relaxed layer than that of strained layer. In the time-resolved X-ray microdiffraction analyses, the piezoelectric response of the BiFeO 3 film was resolved into a strained layer with an extremely low piezoelectric coefficientmore » of 2.4 pm/V and a relaxed layer with a piezoelectric coefficient of 32 pm/V. The difference in the Fe displacements between the strained and relaxed layers is in good agreement with the differences in the piezoelectric coefficient due to the electromechanical coupling.« less

Depth resolved lattice-charge coupling in epitaxial BiFeO3 thin film

PubMed Central

Lee, Hyeon Jun; Lee, Sung Su; Kwak, Jeong Hun; Kim, Young-Min; Jeong, Hu Young; Borisevich, Albina Y.; Lee, Su Yong; Noh, Do Young; Kwon, Owoong; Kim, Yunseok; Jo, Ji Young

2016-01-01

For epitaxial films, a critical thickness (tc) can create a phenomenological interface between a strained bottom layer and a relaxed top layer. Here, we present an experimental report of how the tc in BiFeO3 thin films acts as a boundary to determine the crystalline phase, ferroelectricity, and piezoelectricity in 60 nm thick BiFeO3/SrRuO3/SrTiO3 substrate. We found larger Fe cation displacement of the relaxed layer than that of strained layer. In the time-resolved X-ray microdiffraction analyses, the piezoelectric response of the BiFeO3 film was resolved into a strained layer with an extremely low piezoelectric coefficient of 2.4 pm/V and a relaxed layer with a piezoelectric coefficient of 32 pm/V. The difference in the Fe displacements between the strained and relaxed layers is in good agreement with the differences in the piezoelectric coefficient due to the electromechanical coupling. PMID:27929103

Strained layer InP/InGaAs quantum well laser

NASA Technical Reports Server (NTRS)

Forouhar, Siamak (Inventor); Larsson, Anders G. (Inventor); Ksendzov, Alexander (Inventor); Lang, Robert J. (Inventor)

1993-01-01

Strained layer single or multiple quantum well lasers include an InP substrate, a pair of lattice-matched InGaAsP quarternary layers epitaxially grown on the substrate surrounding a pair of lattice matched In.sub.0.53 Ga.sub.0.47 As ternary layers surrounding one or more strained active layers of epitaxially grown, lattice-mismatched In.sub.0.75 Ga.sub.0.25 As. The level of strain is selected to control the bandgap energy to produce laser output having a wavelength in the range of 1.6 to 2.5 .mu.m. The multiple quantum well structure uses between each active layer. Diethyl zinc is used for p-type dopant in an InP cladding layer at a concentration level in the range of about 5.times.10.sup.17 /cm.sup.3 to about 2.times.10.sup.18 /cm.sup.3. Hydrogen sulfide is used for n-type dopant in the substrate.

Use of an acidophilic yeast strain to enable the growth of leaching bacteria on solid media.

PubMed

Ngom, Baba; Liang, Yili; Liu, Yi; Yin, Huaqun; Liu, Xueduan

2015-03-01

In this study, a Candida digboiensis strain was isolated from a heap leaching plant in Zambia and used in double-layer agar plate to efficiently isolate and purify leaching bacteria. Unlike Acidiphilium sp., the yeast strain was tetrathionate tolerant and could metabolize a great range of organic compounds including organic acids. These properties allowed the yeast strain to enable and fasten the growth of iron and sulfur oxidizers on double-layer agar plate. The isolates were identified as Acidithiobacillus ferrooxidans FOX1, Leptospirillun ferriphilum BN, and Acidithiobacillus thiooxidans ZMB. These three leaching bacteria were inhibited by organic acids such as acetic and propionic acids; however, their activities were enhanced by Candida digboiensis NB under dissolved organic matter stress.

Determination of atomic vacancies in InAs/GaSb strained-layer superlattices by atomic strain

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Honggyu; Meng, Yifei; Kwon, Ji-Hwan

Determining vacancy in complex crystals or nanostructures represents an outstanding crystallographic problem that has a large impact on technology, especially for semiconductors, where vacancies introduce defect levels and modify the electronic structure. However, vacancy is hard to locate and its structure is difficult to probe experimentally. Reported here are atomic vacancies in the InAs/GaSb strained-layer superlattice (SLS) determined by atomic-resolution strain mapping at picometre precision. It is shown that cation and anion vacancies in the InAs/GaSb SLS give rise to local lattice relaxations, especially the nearest atoms, which can be detected using a statistical method and confirmed by simulation. Themore » ability to map vacancy defect-induced strain and identify its location represents significant progress in the study of vacancy defects in compound semiconductors.« less

Determination of atomic vacancies in InAs/GaSb strained-layer superlattices by atomic strain

DOE PAGES

Kim, Honggyu; Meng, Yifei; Kwon, Ji-Hwan; ...

2018-01-01

Determining vacancy in complex crystals or nanostructures represents an outstanding crystallographic problem that has a large impact on technology, especially for semiconductors, where vacancies introduce defect levels and modify the electronic structure. However, vacancy is hard to locate and its structure is difficult to probe experimentally. Reported here are atomic vacancies in the InAs/GaSb strained-layer superlattice (SLS) determined by atomic-resolution strain mapping at picometre precision. It is shown that cation and anion vacancies in the InAs/GaSb SLS give rise to local lattice relaxations, especially the nearest atoms, which can be detected using a statistical method and confirmed by simulation. Themore » ability to map vacancy defect-induced strain and identify its location represents significant progress in the study of vacancy defects in compound semiconductors.« less

Mesophilic Aeromonas sp. serogroup O:11 resistance to complement-mediated killing.

PubMed Central

Merino, S; Rubires, X; Aguilar, A; Albertí, S; Hernandez-Allés, S; Benedí, V J; Tomas, J M

1996-01-01

The complement activation by and resistance to complement-mediated killing of Aeromonas sp. strains from serogroup O:11 were investigated by using different wild-type strains (with an S-layer characteristic of this serogroup) and their isogenic mutants characterized for their surface components (S-layer and lipopolysaccharide [LPS]). All of the Aeromonas sp. serogroup O:11 wild-type strains are unable to activate complement, which suggested that the S-layer completely covered the LPS molecules. We found that the classical complement pathway is involved in serum killing of susceptible Aeromonas sp. mutant strains of serogroup O11, while the alternative complement pathway seems not to be involved, and that the complement activation seems to be independent of antibody. The smooth mutant strains devoid of the S-layer (S-layer isogenic mutants) or isogenic LPS mutant strains with a complete or rather complete LPS core (also without the S-layer) are able to activate complement but are resistant to complement-mediated killing. The reasons for this resistance are that C3b is rapidly degraded, and therefore the lytic membrane attack complex (C5b-9) is not formed. Isogenic LPS rough mutants with an incomplete LPS core are serum sensitive because they bind more C3b than the resistant strains, the C3b is not completely degraded, and therefore the lytic complex (C5b-9) is formed. PMID:8945581

Subband Structure and Effective Mass in the Inversion Layer of a Strain Si-Based Alloy P-Type MOSFET.

PubMed

Chen, Kuan-Ting; Fan, Jun Wei; Chang, Shu-Tong; Lin, Chung-Yi

2015-03-01

In this paper, the subband structure and effective mass of an Si-based alloy inversion layer in a PMOSFET are studied theoretically. The strain condition considered in our calculations is the intrinsic strain resulting from growth of the silicon-carbon alloy on a (001) Si substrate and mechanical uniaxial stress. The quantum confinement effect resulting from the vertically effective electric field was incorporated into the k · p calculation. The distinct effective mass, such as the quantization effective mass and the density-of-states (DOS) effective mass, as well as the subband structure of the silicon-carbon alloy inversion layer for a PMOSFET under substrate strain and various effective electric field strengths, were all investigated. Ore results show that subband structure of relaxed silicon-carbon alloys with low carbon content are almost the same as silicon. We find that an external stress applied parallel to the channel direction can efficiently reduce the effective mass along the channel direction, thus producing hole mobility enhancement.

Stressor-layer-induced elastic strain sharing in SrTiO 3 complex oxide sheets

DOE PAGES

Tilka, J. A.; Park, J.; Ahn, Y.; ...

2018-02-26

A precisely selected elastic strain can be introduced in submicron-thick single-crystal SrTiO 3 sheets using a silicon nitride stressor layer. A conformal stressor layer deposited using plasma-enhanced chemical vapor deposition produces an elastic strain in the sheet consistent with the magnitude of the nitride residual stress. Synchrotron x-ray nanodiffraction reveals that the strain introduced in the SrTiO 3 sheets is on the order of 10 -4, matching the predictions of an elastic model. Using this approach to elastic strain sharing in complex oxides allows the strain to be selected within a wide and continuous range of values, an effect notmore » achievable in heteroepitaxy on rigid substrates.« less

Stressor-layer-induced elastic strain sharing in SrTiO 3 complex oxide sheets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tilka, J. A.; Park, J.; Ahn, Y.

A precisely selected elastic strain can be introduced in submicron-thick single-crystal SrTiO 3 sheets using a silicon nitride stressor layer. A conformal stressor layer deposited using plasma-enhanced chemical vapor deposition produces an elastic strain in the sheet consistent with the magnitude of the nitride residual stress. Synchrotron x-ray nanodiffraction reveals that the strain introduced in the SrTiO 3 sheets is on the order of 10 -4, matching the predictions of an elastic model. Using this approach to elastic strain sharing in complex oxides allows the strain to be selected within a wide and continuous range of values, an effect notmore » achievable in heteroepitaxy on rigid substrates.« less

Patterns of muscular strain in the embryonic heart wall.

PubMed

Damon, Brooke J; Rémond, Mathieu C; Bigelow, Michael R; Trusk, Thomas C; Xie, Wenjie; Perucchio, Renato; Sedmera, David; Denslow, Stewart; Thompson, Robert P

2009-06-01

The hypothesis that inner layers of contracting muscular tubes undergo greater strain than concentric outer layers was tested by numerical modeling and by confocal microscopy of strain within the wall of the early chick heart. We modeled the looped heart as a thin muscular shell surrounding an inner layer of sponge-like trabeculae by two methods: calculation within a two-dimensional three-variable lumped model and simulated expansion of a three-dimensional, four-layer mesh of finite elements. Analysis of both models, and correlative microscopy of chamber dimensions, sarcomere spacing, and membrane leaks, indicate a gradient of strain decreasing across the wall from highest strain along inner layers. Prediction of wall thickening during expansion was confirmed by ultrasonography of beating hearts. Degree of stretch determined by radial position may thus contribute to observed patterns of regional myocardial conditioning and slowed proliferation, as well as to the morphogenesis of ventricular trabeculae and conduction fascicles. Developmental Dynamics 238:1535-1546, 2009. (c) 2009 Wiley-Liss, Inc.

MBE growth of Topological Isolators based on strained semi-metallic HgCdTe layers

NASA Astrophysics Data System (ADS)

Grendysa, J.; Tomaka, G.; Sliz, P.; Becker, C. R.; Trzyna, M.; Wojnarowska-Nowak, R.; Bobko, E.; Sheregii, E. M.

2017-12-01

Particularities of Molecular Beam Epitaxial (MBE) technology for the growth of Topological Insulators (TI) based on the semi-metal Hg1-xCdx Te are presented. A series of strained layers grown on GaAs substrates with a composition close to the 3D Dirac point were studied. The composition of the layers was verified by means of the position of the E1 maximum in optical reflectivity in the visible region. The surface morphology was determined via atomic force and electron microscopy. Magneto-transport measurements show quantized Hall resistance curves and Shubnikov de Hass oscillations (up to 50 K). It has been demonstrated that a well-developed MBE technology enables one to grow strained Hg1-xCdx Te layers on GaAs/CdTe substrates with a well-defined composition near the 3D Dirac point and consequently allows one to produce a 3D topological Dirac semimetal - 3D analogy of graphene - for future applications.

Formation Energies of Native Point Defects in Strained layer Superlattices (Postprint)

DTIC Science & Technology

2017-06-05

AFRL-RX-WP-JA-2017-0440 FORMATION ENERGIES OF NATIVE POINT DEFECTS IN STRAINED-LAYER SUPERLATTICES (POSTPRINT) Zhi Gang Yu...2017 Interim 11 September 2013 – 31 May 2017 4. TITLE AND SUBTITLE FORMATION ENERGIES OF NATIVE POINT DEFECTS IN STRAINED-LAYER SUPERLATTICES...Hamiltonian, tight-binding Hamiltonian, and Green’s function techniques to obtain energy levels arising from native point defects (NPDs) in InAs-GaSb and

Regional strain variations in the human patellar tendon.

PubMed

Pearson, Stephen J; Ritchings, Tim; Mohamed, Azlan S A

2014-07-01

Characteristics of localized tendon strain in vivo are largely unknown. The present study examines local tendon strain between the deep, middle, and surface structures at the proximal and distal aspects of the patellar tendon during ramped isometric contractions. Male subjects (age 28.0 ± 6.3 yr) were examined for patellar tendon excursion (anterior, midsection, and posterior) during ramped isometric voluntary contractions using real-time B-mode ultrasonography and dynamometry. Regional tendon excursion measurements were compared using an automated pixel tracking method. Strain was determined from the tendon delta length normalized to initial/resting segment length. Strain increased from 10% to 100% of force for all regions. Significantly greater mean strain was seen for the anterior proximal region compared to the posterior and mid layer of the tendon (7.5% ± 1.1% vs 3.7% ± 0.5% vs 5.5% ± 1.0%; P < 0.05). Similarly, the distal posterior region showed greater mean strain compared to the mid and anterior regions (7.9% ± 0.6% vs 5.0% ± 0.6% vs 5.4% ± 0.6%; P < 0.05). Relative changes in strain differences from 50% to 100% of force for the proximal region were greatest for the anterior to midline regions (4.6% ± 0.6% and 5.6% ± 0.6%, respectively) and those for the distal region were also greatest for the anterior to midline regions (4.4% ± 0.2% and 5.3% ± 0.2%, respectively). The largest mean strain for the proximal region was at the anterior layer (7.5% ± 1.1%) and that for the distal tendon region was at the posterior layer (7.9% ± 0.9%). This study shows significant regional differences in strain during ramped isometric contractions for the patellar tendon. Lower proximal strains in the posterior tendon compared to the anterior region may be associated with the suggestion of "stress shielding" as an etiological factor in insertional tendinopathy.

Crack-Free, Soft Wrinkles Enable Switchable Anisotropic Wetting.

PubMed

Rhee, Dongjoon; Lee, Won-Kyu; Odom, Teri W

2017-06-01

Soft skin layers on elastomeric substrates are demonstrated to support mechano-responsive wrinkle patterns that do not exhibit cracking under applied strain. Soft fluoropolymer skin layers on pre-strained poly(dimethylsiloxane) slabs achieved crack-free surface wrinkling at high strain regimes not possible by using conventional stiff skin layers. A side-by-side comparison between the soft and hard skin layers after multiple cycles of stretching and releasing revealed that the soft skin layer enabled dynamic control over wrinkle topography without cracks or delamination. We systematically characterized the evolution of wrinkle wavelength, amplitude, and orientation as a function of tensile strain to resolve the crack-free structural transformation. We demonstrated that wrinkled surfaces can guide water spreading along wrinkle orientation, and hence switchable, anisotropic wetting was realized. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Ellipsometric study of metal-organic chemically vapor deposited III-V semiconductor structures

NASA Technical Reports Server (NTRS)

Alterovitz, Samuel A.; Sekula-Moise, Patricia A.; Sieg, Robert M.; Drotos, Mark N.; Bogner, Nancy A.

1992-01-01

An ellipsometric study of MOCVD-grown layers of AlGaAs and InGaAs in thick films and strained layer complex structures is presented. It is concluded that the ternary composition of thick nonstrained layers can be accurately determined to within experimental errors using numerical algorithms. In the case of complex structures, thickness of all layers and the alloy composition of nonstrained layers can be determined simultaneously, provided that the correlations between parameters is no higher than 0.9.

Effect of lattice mismatch on the magnetic properties of nanometer-thick La0.9Ba0.1MnO3 (LBM) films and LBM/BaTiO3/LBM heterostructures

NASA Astrophysics Data System (ADS)

Mirzadeh Vaghefi, P.; Baghizadeh, A.; Willinger, M.; Lourenço, A. A. C. S.; Amaral, V. S.

2017-12-01

Oxide multiferroic thin films and heterostructures offer a wide range of properties originated from intrinsic coupling between lattice strain and nanoscale magnetic/electronic ordering. La0.9Ba0.1MnO3 (LBM) thin-films and LBM/BaTiO3/LBM (LBMBT) heterostructures were grown on single crystalline [100] silicon and [0001] Al2O3 using RF magnetron sputtering to study the effect of crystallinity and induced lattice mismatch in the film on magnetic properties of deposited films and heterostructures. The thicknesses of the films on Al2O3 and Si are 70 and 145 nm, respectively, and for heterostructures are 40/30/40 nm on both substrates. The microstructure of the films, state of strain and growth orientations was studied by XRD and microscopy techniques. Interplay of microstructure, strain and magnetic properties is further investigated. It is known that the crystal structure of substrates and imposed tensile strain affect the physical properties; i.e. magnetic behavior of the film. The thin layer grown on Al2O3 substrate shows out-of-plane compressive strain, while Si substrate induces tensile strain on the deposited film. The magnetic transition temperatures (Tc) of the LBM film on the Si and Al2O3 substrates are found to be 195 K and 203 K, respectively, slightly higher than the bulk form, 185 K. The LBMBT heterostructure on Si substrate shows drastic decrease in magnetization due to produced defects created by diffusion of Ti ions into magnetic layer. Meanwhile, the Tc in LBMBTs increases in respect to other studied single layers and heterostructure, because of higher tensile strain induced at the interfaces.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Benkert, A.; Schumacher, C.; Brunner, K.

The authors demonstrate in situ high-resolution x-ray diffraction applied during heteroepitaxy on (001)GaAs for instant layer characterization. The current thickness, composition, strain, and relaxation dynamics of pseudomorphic layers are precisely determined from q{sub z} scans at the (113) reflection measured at a molecular beam epitaxy chamber with a conventional x-ray tube in static geometry. A simple fitting routine enables real-time in situ x-ray diffraction analysis of layers as thin as 20 nm. Critical thicknesses for dislocation formation and plastic relaxation of ZnCdSe layers versus Cd content are determined. The strong influence of substrate temperature on heteroepitaxial nucleation process, deposition rate,more » composition, and strain relaxation dynamics of ZnCdSe on GaAs is also studied.« less

Epitaxial growth of highly strained antimonene on Ag(111)

NASA Astrophysics Data System (ADS)

Mao, Ya-Hui; Zhang, Li-Fu; Wang, Hui-Li; Shan, Huan; Zhai, Xiao-Fang; Hu, Zhen-Peng; Zhao, Ai-Di; Wang, Bing

2018-06-01

The synthesis of antimonene, which is a promising group-V 2D material for both fundamental studies and technological applications, remains highly challenging. Thus far, it has been synthesized only by exfoliation or growth on a few substrates. In this study, we show that thin layers of antimonene can be grown on Ag(111) by molecular beam epitaxy. High-resolution scanning tunneling microscopy combined with theoretical calculations revealed that the submonolayer Sb deposited on a Ag(111) surface forms a layer of AgSb2 surface alloy upon annealing. Further deposition of Sb on the AgSb2 surface alloy causes an epitaxial layer of Sb to form, which is identified as antimonene with a buckled honeycomb structure. More interestingly, the lattice constant of the epitaxial antimonene (5 Å) is much larger than that of freestanding antimonene, indicating a high tensile strain of more than 20%. This kind of large strain is expected to make the antimonene a highly promising candidate for roomtemperature quantum spin Hall material.

Strain transfer analysis of optical fiber based sensors embedded in an asphalt pavement structure

NASA Astrophysics Data System (ADS)

Wang, Huaping; Xiang, Ping

2016-07-01

Asphalt pavement is vulnerable to random damage, such as cracking and rutting, which can be proactively identified by distributed optical fiber sensing technology. However, due to the material nature of optical fibers, a bare fiber is apt to be damaged during the construction process of pavements. Thus, a protective layer is needed for this application. Unfortunately, part of the strain of the host material is absorbed by the protective layer when transferring the strain to the sensing fiber. To account for the strain transfer error, in this paper a theoretical analysis of the strain transfer of a three-layered general model has been carried out by introducing Goodman’s hypothesis to describe the interfacial shear stress relationship. The model considers the viscoelastic behavior of the host material and protective layer. The effects of one crack in the host material and the sensing length on strain transfer relationship are been discussed. To validate the effectiveness of the strain transfer analysis, a flexible asphalt-mastic packaged distributed optical fiber sensor was designed and tested in a laboratory environment to monitor the distributed strain and appearance of cracks in an asphalt concrete beam at two different temperatures. The experimental results indicated that the developed strain transfer formula can significantly reduce the strain transfer error, and that the asphalt-mastic packaged optical fiber sensor can successfully monitor the distributed strain and identify local cracks.

Theory of multiple quantum dot formation in strained-layer heteroepitaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Du, Lin; Maroudas, Dimitrios, E-mail: maroudas@ecs.umass.edu

2016-07-11

We develop a theory for the experimentally observed formation of multiple quantum dots (QDs) in strained-layer heteroepitaxy based on surface morphological stability analysis of a coherently strained epitaxial thin film on a crystalline substrate. Using a fully nonlinear model of surface morphological evolution that accounts for a wetting potential contribution to the epitaxial film's free energy as well as surface diffusional anisotropy, we demonstrate the formation of multiple QD patterns in self-consistent dynamical simulations of the evolution of the epitaxial film surface perturbed from its planar state. The simulation predictions are supported by weakly nonlinear analysis of the epitaxial filmmore » surface morphological stability. We find that, in addition to the Stranski-Krastanow instability, long-wavelength perturbations from the planar film surface morphology can trigger a nonlinear instability, resulting in the splitting of a single QD into multiple QDs of smaller sizes, and predict the critical wavelength of the film surface perturbation for the onset of the nonlinear tip-splitting instability. The theory provides a fundamental interpretation for the observations of “QD pairs” or “double QDs” and other multiple QDs reported in experimental studies of epitaxial growth of semiconductor strained layers and sets the stage for precise engineering of tunable-size nanoscale surface features in strained-layer heteroepitaxy by exploiting film surface nonlinear, pattern forming phenomena.« less

Diffusion behavior of Cu/Ta heterogeneous interface under high temperature and high strain: An atomistic investigation

NASA Astrophysics Data System (ADS)

Li, Ganglong; Wu, Houya; Luo, Honglong; Chen, Zhuo; Tay, Andrew A. O.; Zhu, Wenhui

2017-09-01

Three-dimensional (3D) integration technology using Cu interconnections has emerged as a promising solution to improve the performance of silicon microelectronic devices. However, Cu diffuses into SiO2 and requires a barrier layer such as Ta to ensure acceptable reliability. In this paper, the effects of temperature and strain normal to the interface on the inter-diffusion of Cu and Ta at annealing conditions are investigated using a molecular dynamics (MD) technique with embedded atomic method (EAM) potentials. Under thermal annealing conditions without strain, it is found that a Cu-rich diffusion region approximately 2 nm thick is formed at 1000 K after 10 ns of annealing. Ta is capable of diffusing into the interior of Cu but Cu hardly diffuses into the inner lattice of Ta. At the Cu side near the interface an amorphous structure is formed due to the process of diffusion. The diffusion activation energy of Cu and Ta are found to be 0.9769 and 0.586 eV, respectively. However, when a strain is applied, a large number of crystal defects are generated in the sample. As the strain is increased, extrinsic stacking faults (ESFs) and lots of Shockley partial dislocations appear. The density of the dislocations and the diffusion channels increase, promoting the diffusion of Cu atoms into the inner lattice of Ta. The thickness of the diffusion layer increases to 4 times the value when only a temperature load of 700 K is applied. The MD simulations demonstrated that Ta is very effective as a barrier layer under thermal loading only, and its effectiveness is impaired by tensile strain at the Cu/Ta interface. The simulations also clarified the mechanism that caused the impairment. The methodology and approach described in this paper can be followed further to study the effectiveness of barrier layers under various annealing and strain conditions, and to determine the minimum thickness of barrier layers required for a particular application.

Coherency strain engineered decomposition of unstable multilayer alloys for improved thermal stability

NASA Astrophysics Data System (ADS)

Forsén, R.; Ghafoor, N.; Odén, M.

2013-12-01

A concept to improve hardness and thermal stability of unstable multilayer alloys is presented based on control of the coherency strain such that the driving force for decomposition is favorably altered. Cathodic arc evaporated cubic TiCrAlN/Ti1-xCrxN multilayer coatings are used as demonstrators. Upon annealing, the coatings undergo spinodal decomposition into nanometer-sized coherent Ti- and Al-rich cubic domains which is affected by the coherency strain. In addition, the growth of the domains is restricted by the surrounding TiCrN layer compared to a non-layered TiCrAlN coating which together results in an improved thermal stability of the cubic structure. A significant hardness increase is seen during decomposition for the case with high coherency strain while a low coherency strain results in a hardness decrease for high annealing temperatures. The metal diffusion paths during the domain coarsening are affected by strain which in turn is controlled by the Cr-content (x) in the Ti1-xCrxN layers. For x = 0 the diffusion occurs both parallel and perpendicular to the growth direction but for x > =0.9 the diffusion occurs predominantly parallel to the growth direction. Altogether this study shows a structural tool to alter and fine-tune high temperature properties of multicomponent materials.

Analytical and Experimental Characterization of Thick-Section Fiber-Metal Laminates

DTIC Science & Technology

2013-06-01

individual metal layers as loading increases. The off-axis deformation properties of the prepreg layers were modeled by using equivalent constraint models...the degraded stiffness of the prepreg layer is found. At each loading step the stiffness properties of individual layers are calculated. These...predicts stress-strain curves on-axis, additional work is needed to study the local interactions between metal and prepreg layers as damage occurs in each

Highly stretchable strain sensor based on polyurethane substrate using hydrogen bond-assisted laminated structure for monitoring of tiny human motions

NASA Astrophysics Data System (ADS)

Huang, Ying; Zhao, Yunong; Wang, Yang; Guo, Xiaohui; Zhang, Yangyang; Liu, Ping; Liu, Caixia; Zhang, Yugang

2018-03-01

Strain sensors used as flexible and wearable electronic devices have improved prospects in the fields of artificial skin, robotics, human-machine interfaces, and healthcare. This work introduces a highly stretchable fiber-based strain sensor with a laminated structure made up of a graphene nanoplatelet layer and a carbon black/single-walled carbon nanotube synergetic conductive network layer. An ultrathin, flexible, and elastic two-layer polyurethane (PU) yarn substrate was successively deposited by a novel chemical bonding-based layered dip-coating process. These strain sensors demonstrated high stretchability (˜350%), little hysteresis, and long-term durability (over 2400 cycles) due to the favorable tensile properties of the PU substrate. The linearity of the strain sensor could reach an adjusted R-squared of 0.990 at 100% strain, which is better than most of the recently reported strain sensors. Meanwhile, the strain sensor exhibited good sensibility, rapid response, and a lower detection limit. The lower detection limit benefited from the hydrogen bond-assisted laminated structure and continuous conductive path. Finally, a series of experiments were carried out based on the special features of the PU strain sensor to show its capacity of detecting and monitoring tiny human motions.

Speckle-Tracking Layer-Specific Analysis of Myocardial Deformation and Evaluation of Scar Transmurality in Chronic Ischemic Heart Disease.

PubMed

Tarascio, Michela; Leo, Laura Anna; Klersy, Catherine; Murzilli, Romina; Moccetti, Tiziano; Faletra, Francesco Fulvio

2017-07-01

Identification of the extent of scar transmurality in chronic ischemic heart disease is important because it correlates with viability. The aim of this retrospective study was to evaluate whether layer-specific two-dimensional speckle-tracking echocardiography allows distinction of scar presence and transmurality. A total of 70 subjects, 49 with chronic ischemic cardiomyopathy and 21 healthy subjects, underwent two-dimensional speckle-tracking echocardiography and late gadolinium-enhanced cardiac magnetic resonance. Scar extent was determined as the relative amount of hyperenhancement using late gadolinium-enhanced cardiac magnetic resonance in an 18-segment model (0% hyperenhancement = normal; 1%-50% = subendocardial scar; 51%-100% = transmural scar). In the same 18-segment model, peak systolic circumferential strain and longitudinal strain were calculated separately for the endocardial and epicardial layers as well as the full-wall myocardial thickness. All strain parameters showed cutoff values (area under the curve > 0.69) that allowed the discrimination of normal versus scar segments but not of transmural versus subendocardial scars. This was true for all strain parameters analyzed, without differences in efficacy between longitudinal and circumferential strain and subendocardial, subepicardial, and full-wall-thickness strain values. Circumferential and longitudinal strain in normal segments showed transmural and basoapical gradients (greatest values at the subendocardial layer and apex). In segments with scar, transmural gradient was maintained, whereas basoapical gradient was lost because the reduction of strain values in the presence of the scar was greater at the apex. The two-dimensional speckle-tracking echocardiographic values distinguish scar presence but not transmurality; thus, they are not useful predictors of scar segment viability. It remains unclear why there is a greater strain value reduction in the presence of a scar at the apical level. Copyright © 2017 American Society of Echocardiography. Published by Elsevier Inc. All rights reserved.

Critical layer thickness in In/sub 0. 2/Ga/sub 0. 8/As/GaAs single strained quantum well structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fritz, I.J.; Gourley, P.L.; Dawson, L.R.

1987-09-28

We report accurate determination of the critical layer thickness (CLT) for single strained-layer epitaxy in the InGaAs/GaAs system. Our samples were molecular beam epitaxially grown, selectively doped, single quantum well structures comprising a strained In/sub 0.2/Ga/sub 0.8/As layer imbedded in GaAs. We determined the CLT by two sensitive techniques: Hall-effect measurements at 77 K and photoluminescence microscopy. Both techniques indicate a CLT of about 20 nm. This value is close to that determined previously (--15 nm) for comparable strained-layer superlattices, but considerably less than the value of --45 nm suggested by recent x-ray rocking-curve measurements. We show by a simplemore » calculation that photoluminescence microscopy is more than two orders of magnitude more sensitive to dislocations than x-ray diffraction. Our results re-emphasize the necessity of using high-sensitivity techniques for accurate determination of critical layer thicknesses.« less

Graphene-based stretchable and transparent moisture barrier

NASA Astrophysics Data System (ADS)

Won, Sejeong; Van Lam, Do; Lee, Jin Young; Jung, Hyun-June; Hur, Min; Kim, Kwang-Seop; Lee, Hak-Joo; Kim, Jae-Hyun

2018-03-01

We propose an alumina-deposited double-layer graphene (2LG) as a transparent, scalable, and stretchable barrier against moisture; this barrier is indispensable for foldable or stretchable organic displays and electronics. Both the barrier property and stretchability were significantly enhanced through the introduction of 2LG between alumina and a polymeric substrate. 2LG with negligible polymeric residues was coated on the polymeric substrate via a scalable dry transfer method in a roll-to-roll manner; an alumina layer was deposited on the graphene via atomic layer deposition. The effect of the graphene layer on crack generation in the alumina layer was systematically studied under external strain using an in situ micro-tensile tester, and correlations between the deformation-induced defects and water vapor transmission rate were quantitatively analyzed. The enhanced stretchability of alumina-deposited 2LG originated from the interlayer sliding between the graphene layers, which resulted in the crack density of the alumina layer being reduced under external strain.

[ACTIVITY OF ANTIMICROBIAL NANOSTRUCTURED BARRIER LAYERS BASED ON POLYETHYLENETEREPHTHALATE IN RELATION TO CLINICAL STRAINES OF MICROORGANISMS FOR SICK PERSONS OF GASTROENTEROLOGICAL PROFILE].

PubMed

Elinson, V M; Rusanova, E V; Vasilenko, I A; Lyamin, A N; Kostyuchenko, L N

2015-01-01

Homeostasis transgressions of enteral medium including disbiotic ones are often accompanying deseases of digestive tract. Espessially it touches upon sick persons connected with probe nourishing. One of the way for solving this problem is normalization of digestion microflore by means of wares with nanotechnological modifications of walls (probes, stomic tubes) which provide them antimicrobial properties and assist to normalization of digestive microbiotis and enteral homeostasis completely. The aim to study is research of antimicrobial activity of of nanostructured barrier layers based on polyethyleneterephthalate (PET) in relation to clinical straines of microorganisms. For barrier layer creation the approach on the base of methods of ion-plasma technology was used including ion-plasma treatment (nanostructuring) of the surface by ions noble and chemically active gases and following formation nanodimensional carbon films on the surface/ For the study of antimicrobial activity in relation to clinical straines of microorganisms we used the technique which allowed to establish the influence of parting degree of microorganisms suspension and time for samples exposing and microorganisms adsorbed on the surface. In experiment clinical straines obtained from different materials were used: Staphylococcus Hly+ and Calbicans--from pharyngeal mucosa, E. coli--from feces, K.pneumoniae--from urine. Sharing out and species identification of microorganisms were fulfilled according with legasy documents. In results of the study itwas obtained not only the presence of staticticaly confirmed antimicrobial activity of PET samples with nanostructured barrier layers in relation to different stimulators of nosocomical infections but also the influence of different factors connected with formation of nanostructured layers and consequently based with them physicochemical characteristics such as, in particular, surface energy, surface relief parameters, surface charg and others, as well as influence of microorganisms nature onto the interaction of between barrier layers and microorganisms.

Strained-layer epitaxy of germanium-silicon alloys

NASA Astrophysics Data System (ADS)

Bean, J. C.

1985-10-01

Strained-layer epitaxy is presented as a developing technique for combining Si with other materials in order to obtain semiconductors with enhanced electronic properties. The method involves applying layers sufficiently thin so that the atoms deposited match the bonding configurations of the substrate crystal. When deposited on Si, a four-fold bonding pattern is retained, with a lowered interfacial energy and augmented stored strain energy in the epitaxial layer. The main problem which remains is building an epitaxial layer thick enough to yield desired epitaxial properties while avoiding a reversion to an unstrained structure. The application of a Ge layer to Si using MBE is described, along with the formation of heterojunction multi-layer superlattices, which can reduce the dislocation effects in some homojunctions. The technique shows promise for developing materials of use as bipolar transistors, optical detectors and fiber optic transmission devices.

Use of Bacteria To Stabilize Archaeological Iron

PubMed Central

Comensoli, Lucrezia; Maillard, Julien; Albini, Monica; Sandoz, Frederic

2017-01-01

ABSTRACT Iron artifacts are common among the findings of archaeological excavations. The corrosion layer formed on these objects requires stabilization after their recovery, without which the destruction of the item due to physicochemical damage is likely. Current technologies for stabilizing the corrosion layer are lengthy and generate hazardous waste products. Therefore, there is a pressing need for an alternative method for stabilizing the corrosion layer on iron objects. The aim of this study was to evaluate an alternative conservation-restoration method using bacteria. For this, anaerobic iron reduction leading to the formation of stable iron minerals in the presence of chlorine was investigated for two strains of Desulfitobacterium hafniense (strains TCE1 and LBE). Iron reduction was observed for soluble Fe(III) phases as well as for akaganeite, the most troublesome iron compound in the corrosion layer of archaeological iron objects. In terms of biogenic mineral production, differential efficiencies were observed in assays performed on corroded iron coupons. Strain TCE1 produced a homogeneous layer of vivianite covering 80% of the corroded surface, while on the coupons treated with strain LBE, only 10% of the surface was covered by the same mineral. Finally, an attempt to reduce iron on archaeological objects was performed with strain TCE1, which led to the formation of both biogenic vivianite and magnetite on the surface of the artifacts. These results demonstrate the potential of this biological treatment for stabilizing archaeological iron as a promising alternative to traditional conservation-restoration methods. IMPORTANCE Since the Iron Age, iron has been a fundamental material for the building of objects used in everyday life. However, due to its reactivity, iron can be easily corroded, and the physical stability of the object built is at risk. This is particularly true for archaeological objects on which a potentially unstable corrosion layer is formed during the time the object is buried. After excavation, changes in environmental conditions (e.g., higher oxygen concentration or lower humidity) alter the stability of the corrosion layer and can lead to the total destruction of the object. In this study, we demonstrate the feasibility of an innovative treatment based on bacterial iron reduction and biogenic mineral formation to stabilize the corrosion layer and protect these objects. PMID:28283522

The Surface Layer Homology Domain-Containing Proteins of Alkaliphilic Bacillus pseudofirmus OF4 Play an Important Role in Alkaline Adaptation via Peptidoglycan Synthesis.

PubMed

Fujinami, Shun; Ito, Masahiro

2018-01-01

It is well known that the Na + cycle and the cell wall are essential for alkaline adaptation of Na + -dependent alkaliphilic Bacillus species. In Bacillus pseudofirmus OF4, surface layer protein A (SlpA), the most abundant protein in the surface layer (S-layer) of the cell wall, is involved in alkaline adaptation, especially under low Na + concentrations. The presence of a large number of genes that encode S-layer homology (SLH) domain-containing proteins has been suggested from the genome sequence of B. pseudofirmus OF4. However, other than SlpA, the functions of SLH domain-containing proteins are not well known. Therefore, a deletion mutant of the csaB gene, required for the retention of SLH domain-containing proteins on the cell wall, was constructed to investigate its physiological properties. The csaB mutant strain of B. pseudofirmus OF4 had a chained morphology and alkaline sensitivity even under a 230 mM Na + concentration at which there is no growth difference between the parental strain and the slpA mutant strain. Ultra-thin section transmission electron microscopy showed that a csaB mutant strain lacked an S-layer part, and its peptidoglycan (PG) layer was disturbed. The slpA mutant strain also lacked an S-layer part, although its PG layer was not disturbed. These results suggested that the surface layer homology domain-containing proteins of B. pseudofirmus OF4 play an important role in alkaline adaptation via peptidoglycan synthesis.

Loading direction-dependent shear behavior at different temperatures of single-layer chiral graphene sheets

NASA Astrophysics Data System (ADS)

Zhao, Yang; Dong, Shuhong; Yu, Peishi; Zhao, Junhua

2018-06-01

The loading direction-dependent shear behavior of single-layer chiral graphene sheets at different temperatures is studied by molecular dynamics (MD) simulations. Our results show that the shear properties (such as shear stress-strain curves, buckling strains, and failure strains) of chiral graphene sheets strongly depend on the loading direction due to the structural asymmetry. The maximum values of both the critical buckling shear strain and the failure strain under positive shear deformation can be around 1.4 times higher than those under negative shear deformation. For a given chiral graphene sheet, both its failure strain and failure stress decrease with increasing temperature. In particular, the amplitude to wavelength ratio of wrinkles for different chiral graphene sheets under shear deformation using present MD simulations agrees well with that from the existing theory. These findings provide physical insights into the origins of the loading direction-dependent shear behavior of chiral graphene sheets and their potential applications in nanodevices.

Study of Minority Carrier Lifetimes in Very Long Wave Infrared Strained Layer InAs/GaInSb Superlattices (Postprint)

DTIC Science & Technology

2016-09-19

arsenide ; Superlattices ; Absorption ; Engineering ; Long wavelength infrared ; Photodetectors ; Reflectivity ; Sensors 16. SECURITY CLASSIFICATION...So far, the best reported VLWIR D* is 4.5 x 10 10 Jones at 80 K using an InAs/GaSb (noted herein as “binary”) SL Infrared Sensors , Devices, and... temperature on InAs/GaInSb strained layer superlattices for very long wavelength infrared detection”, Appl. Phys. Lett. 101, 171105 (2012). [13] H. J

Surface roughening transition and critical layer thickness in strained-layer heteroepitaxy of EuTe on PbTe (111)

NASA Astrophysics Data System (ADS)

Springholz, G.; Frank, N.; Bauer, G.

1994-05-01

Heteroepitaxial growth of 2% lattice-mismatched EuTe on PbTe (111) by molecular beam epitaxy is investigated in the two-dimensional layer-by-layer growth regime combining in situ reflection high-energy electron diffraction and scanning tunneling microscopy (STM). At the critical layer thickness a distinct surface roughening is observed. The quantitative analysis of STM images yields an increase of the root mean square roughness by a factor of 4 at this roughening transition. Strong evidence is presented that for the used growth conditions this roughening is not caused by strain induced coherent islanding but by misfit dislocations at the onset of strain relaxation.

Magnetic skin layer of NiO(100) probed by polarization-dependent spectromicroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mandal, Suman, E-mail: suman.mandal@sscu.iisc.ernet.in; Menon, Krishnakumar S. R., E-mail: krishna.menon@saha.ac.in; Belkhou, Rachid

2014-06-16

Using polarization-dependent x-ray photoemission electron microscopy, we have investigated the surface effects on antiferromagnetic (AFM) domain formation. Depth-resolved information obtained from our study indicates the presence of strain-induced surface AFM domains on some of the cleaved NiO(100) crystals, which are unusually thinner than bulk AFM domain wall widths (∼150 nm). Existence of such magnetic skin layer is substantiated by exchange-coupled ferromagnetic Fe domains in Fe/NiO(100), thereby evidencing the influence of this surface AFM domains on interfacial magnetic coupling. Our observations demonstrate a depth evolution of AFM structure in presence of induced surface strain, while the surface symmetry-breaking in absence of inducedmore » strain does not modify the bulk AFM domain structure. Realization of such thin surface AFM layer will provide better microscopic understanding of the exchange bias phenomena.« less

Si(111) strained layers on Ge(111): Evidence for c (2 ×4 ) domains

NASA Astrophysics Data System (ADS)

Zhachuk, R.; Coutinho, J.; Dolbak, A.; Cherepanov, V.; Voigtländer, B.

2017-08-01

The tensile-strained Si (111 ) layers grown on top of Ge (111 ) substrates are studied by combining scanning tunneling microscopy, low-energy electron diffraction, and first-principles calculations. It is shown that the layers exhibit c (2 ×4 ) domains, which are separated by domain walls along <1 ¯10 > directions. A model structure for the c (2 ×4 ) domains is proposed, which shows low formation energy and good agreement with the experimental data. The results of our calculations suggest that Ge atoms are likely to replace Si atoms with dangling bonds on the surface (rest-atoms and adatoms), thus significantly lowering the surface energy and inducing the formation of domain walls. The experiments and calculations demonstrate that when surface strain changes from compressive to tensile, the (111) reconstruction converts from dimer-adatom-stacking fault-based to adatom-based structures.

A comparative density functional study on electrical properties of layered penta-graphene

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yu, Zhi Gen, E-mail: yuzg@ihpc.a-star.edu.sg; Zhang, Yong-Wei, E-mail: zhangyw@ihpc.a-star.edu.sg

We present a comparative study of the influence of the number of layers, the biaxial strain in the range of −3% to 3%, and the stacking misalignments on the electronic properties of a new 2D carbon allotrope, penta-graphene (PG), based on hybrid-functional method within the density functional theory (DFT). In comparison with local exchange-correlation approximation in the DFT, the hybrid-functional provides an accurate description on the degree of p{sub z} orbitals localization and bandgap. Importantly, the predicted bandgap of few-layer PG has a weak layer dependence. The bandgap of monolayer PG is 3.27 eV, approximately equal to those of GaN andmore » ZnO; and the bandgap of few-layer PG decreases slowly with the number of layers (N) and converge to 2.57 eV when N ≥ 4. Our calculations using HSE06 functional on few-layer PG reveal that bandgap engineering by stacking misalignment can further tune the bandgap down to 1.37 eV. Importantly, there is no direct-to-indirect bandgap transition in PG by varying strain, layer number, and stacking misalignment. Owing to its tunable, robustly direct, and wide bandgap characteristics, few-layer PG is promising for optoelectronic and photovoltaic applications.« less

Predictions and Experimental Microstructural Characterization of High Strain Rate Failure Modes in Layered Aluminum Composites

NASA Astrophysics Data System (ADS)

Khanikar, Prasenjit

Different aluminum alloys can be combined, as composites, for tailored dynamic applications. Most investigations pertaining to metallic alloy layered composites, however, have been based on quasi-static approaches. The dynamic failure of layered metallic composites, therefore, needs to be characterized in terms of strength, toughness, and fracture response. A dislocation-density based crystalline plasticity formulation, finite-element techniques, rational crystallographic orientation relations and a new fracture methodology were used to predict the failure modes associated with the high strain rate behavior of aluminum layered composites. Two alloy layers, a high strength alloy, aluminum 2195, and an aluminum alloy 2139, with high toughness, were modeled with representative microstructures that included precipitates, dispersed particles, and different grain boundary (GB) distributions. The new fracture methodology, based on an overlap method and phantom nodes, is used with a fracture criteria specialized for fracture on different cleavage planes. One of the objectives of this investigation, therefore, was to determine the optimal arrangements of the 2139 and 2195 aluminum alloys for a metallic layered composite that would combine strength, toughness and fracture resistance for high strain-rate applications. Different layer arrangements were investigated for high strain-rate applications, and the optimal arrangement was with the high toughness 2139 layer on the bottom, which provided extensive shear strain localization, and the high strength 2195 layer on the top for high strength resistance. The layer thickness of the bottom high toughness layer also affected the bending behavior of the roll-boned interface and the potential delamination of the layers. Shear strain localization, dynamic cracking and delamination were the mutually competing failure mechanisms for the layered metallic composite, and control of these failure modes can be optimized for high strain-rate applications. The second major objective of this investigation was the use of recently developed dynamic fracture formulations to model and analyze the crack nucleation and propagation of aluminum layered composites subjected to high strain rate loading conditions and how microstructural effects, such as precipitates, dispersed particles, and GB orientations affect failure evolution. This dynamic fracture approach is used to investigate crack nucleation and crack growth as a function of the different microstructural characteristics of each alloy in layered composites with and without pre-existing cracks. The zigzag nature of the crack paths were mainly due to the microstructural features, such as precipitates and dispersed particles distributions and orientations ahead of the crack front, and it underscored the capabilities of the fracture methodology. The evolution of dislocation density and the formation of localized shear slip contributed to the blunting of the propagating crack. Extensive geometrical and thermal softening due to the localized plastic slip also affected crack path orientations and directions. These softening mechanisms resulted in the switching of cleavage planes, which affected crack path orientations. Interface delamination can also have an important role in the failure and toughening of the layered composites. Different scenarios of delamination were investigated, such as planar crack growth and crack penetration into the layers. The presence of brittle surface oxide platelets in the interface region also significantly influenced the interface delamination process. Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM) and Optical Microscopy (OM) characterization provided further physical insights and validation of the predictive capabilities. The inherent microstructural features of each alloy play a significant role in the dynamic fracture, shear strain localization, and interface delamination of the layered metallic composite. These microstructural features, such as precipitates, dispersed particles, and GB orientations and distributions can be optimized for desired behavior of metallic composites.

Dynamic compressive properties of bovine knee layered tissue

NASA Astrophysics Data System (ADS)

Nishida, Masahiro; Hino, Yuki; Todo, Mitsugu

2015-09-01

In Japan, the most common articular disease is knee osteoarthritis. Among many treatment methodologies, tissue engineering and regenerative medicine have recently received a lot of attention. In this field, cells and scaffolds are important, both ex vivo and in vivo. From the viewpoint of effective treatment, in addition to histological features, the compatibility of mechanical properties is also important. In this study, the dynamic and static compressive properties of bovine articular cartilage-cancellous bone layered tissue were measured using a universal testing machine and a split Hopkinson pressure bar method. The compressive behaviors of bovine articular cartilage-cancellous bone layered tissue were examined. The effects of strain rate on the maximum stress and the slope of stress-strain curves of the bovine articular cartilage-cancellous bone layered tissue were discussed.

Complex strain fields

NASA Astrophysics Data System (ADS)

Bradshaw, P.

Computational techniques for accounting for extra strain rates, abnormal distributions of delta-U/delta-y, fluctuating strain rates, and the effects of body forces in modeling shear flows are discussed. Consideration is given to simple shears where the extra strain rate does not affect turbulence, thin shear layers, moderately thin shear layers, and strongly distorted flows. Attention is given to formulations based on the exact transport equations for Reynolds stress as derived from the time-averaged Navier-Stokes equations. Extra strain rates arise from curvature, lateral divergence, and bulk compression, with Coriolis forces accounting for the first, intensification of the spanwise vorticity for the second, and compression or dilation of the shear layer producing the third. The curvature forces, e.g., buoyancy and Coriolis forces, are responsible for hurricanes and tornadoes.

Study of InGaAs-based modulation doped field effect transistor structures using variable-angle spectroscopic ellipsometry

NASA Technical Reports Server (NTRS)

Alterovitz, S. A.; Sieg, R. M.; Yao, H. D.; Snyder, P. G.; Woollam, J. A.; Pamulapati, J.; Bhattacharya, P. K.; Sekula-Moise, P. A.

1991-01-01

Variable-angle spectroscopic ellipsometry was used to estimate the thicknesses of all layers within the optical penetration depth of InGaAs-based modulation doped field effect transistor structures. Strained and unstrained InGaAs channels were made by molecular beam epitaxy (MBE) on InP substrates and by metal-organic chemical vapor deposition on GaAs substrates. In most cases, ellipsometrically determined thicknesses were within 10% of the growth-calibration results. The MBE-made InGaAs strained layers showed large strain effects, indicating a probable shift in the critical points of their dielectric function toward the InP lattice-matched concentration.

A study of deformation and strain induced in bulk by the oxide layers formation on a Fe-Cr-Al alloy in high-temperature liquid Pb-Bi eutectic

DOE PAGES

Popovic, M. P.; Chen, K.; Shen, H.; ...

2018-03-29

At elevated temperatures, heavy liquid metals and their alloys are known to create a highly corrosive environment that causes irreversible degradation of most iron-based materials. In this paper, it has been found that an appropriate concentration of oxygen in the liquid alloy can significantly reduce this issue by creating a passivating oxide scale that controls diffusion, especially if Al is present in Fe-based materials (by Al-oxide formation). However, the increase of the temperature and of oxygen content in liquid phase leads to the increase of oxygen diffusion into bulk, and to promotion of the internal Al oxidation. This can causemore » a strain in bulk near the oxide layer, due either to mismatch between the thermal expansion coefficients of the oxides and bulk material, or to misfit of the crystal lattices (bulk vs. oxides). This work investigates the strain induced into proximal bulk of a Fe-Cr-Al alloy by oxide layers formation in liquid lead-bismuth eutectic utilizing synchrotron X-ray Laue microdiffraction. Finally, it is found that internal oxidation is the most likely cause for the strain in the metal rather than thermal expansion mismatch as a two-layer problem.« less

A study of deformation and strain induced in bulk by the oxide layers formation on a Fe-Cr-Al alloy in high-temperature liquid Pb-Bi eutectic

DOE Office of Scientific and Technical Information (OSTI.GOV)

Popovic, M. P.; Chen, K.; Shen, H.

At elevated temperatures, heavy liquid metals and their alloys are known to create a highly corrosive environment that causes irreversible degradation of most iron-based materials. In this paper, it has been found that an appropriate concentration of oxygen in the liquid alloy can significantly reduce this issue by creating a passivating oxide scale that controls diffusion, especially if Al is present in Fe-based materials (by Al-oxide formation). However, the increase of the temperature and of oxygen content in liquid phase leads to the increase of oxygen diffusion into bulk, and to promotion of the internal Al oxidation. This can causemore » a strain in bulk near the oxide layer, due either to mismatch between the thermal expansion coefficients of the oxides and bulk material, or to misfit of the crystal lattices (bulk vs. oxides). This work investigates the strain induced into proximal bulk of a Fe-Cr-Al alloy by oxide layers formation in liquid lead-bismuth eutectic utilizing synchrotron X-ray Laue microdiffraction. Finally, it is found that internal oxidation is the most likely cause for the strain in the metal rather than thermal expansion mismatch as a two-layer problem.« less

Transmission electron microscopy study of the formation of epitaxial CoSi2/Si (111) by a room-temperature codeposition technique

NASA Technical Reports Server (NTRS)

D'Anterroches, Cecile; Yakupoglu, H. Nejat; Lin, T. L.; Fathauer, R. W.; Grunthaner, P. J.

1988-01-01

Co and Si have been codeposited on Si (111) substrates near room temperature in a stoichiometric 1:2 ratio in a molecular beam epitaxy system. Annealing of these deposits yields high-quality single-crystal CoSi2 layers. Transmission electron microscopy has been used to examine as-deposited layers and layers annealed at 300, 500, and 600 C. Single-crystal epitaxial grains of CoSi2 embedded in a matrix of amorphous Co/Si are observed in as-deposited samples, while the layer is predominantly single-crystal, inhomogeneously strained CoSi2 at 300 C. At 600 C, a homogeneously strained single-crystal layer with a high density of pinholes is observed. In contrast to other solid phase epitaxy techniques used to grow CoSi2 on Si (111), no intermediate silicide phases are observed prior to the formation of CoSi2.

Layer-by-layer evolution of structure, strain, and activity for the oxygen evolution reaction in graphene-templated Pt monolayers.

PubMed

Abdelhafiz, Ali; Vitale, Adam; Joiner, Corey; Vogel, Eric; Alamgir, Faisal M

2015-03-25

In this study, we explore the dimensional aspect of structure-driven surface properties of metal monolayers grown on a graphene/Au template. Here, surface limited redox replacement (SLRR) is used to provide precise layer-by-layer growth of Pt monolayers on graphene. We find that after a few iterations of SLRR, fully wetted 4-5 monolayer Pt films can be grown on graphene. Incorporating graphene at the Pt-Au interface modifies the growth mechanism, charge transfers, equilibrium interatomic distances, and associated strain of the synthesized Pt monolayers. We find that a single layer of sandwiched graphene is able to induce a 3.5% compressive strain on the Pt adlayer grown on it, and as a result, catalytic activity is increased due to a greater areal density of the Pt layers beyond face-centered-cubic close packing. At the same time, the sandwiched graphene does not obstruct vicinity effects of near-surface electron exchange between the substrate Au and adlayers Pt. X-ray photoelectron spectroscopy (XPS) and extended X-ray absorption fine structure (EXAFS) techniques are used to examine charge mediation across the Pt-graphene-Au junction and the local atomic arrangement as a function of the Pt adlayer dimension. Cyclic voltammetry (CV) and the oxygen reduction reaction (ORR) are used as probes to examine the electrochemically active area of Pt monolayers and catalyst activity, respectively. Results show that the inserted graphene monolayer results in increased activity for the Pt due to a graphene-induced compressive strain, as well as a higher resistance against loss of the catalytically active Pt surface.

Deformation behavior of coherently strained InAs/GaAs(111)A heteroepitaxial systems: Theoretical calculations and experimental measurements

NASA Astrophysics Data System (ADS)

Zepeda-Ruiz, Luis A.; Pelzel, Rodney I.; Nosho, Brett Z.; Weinberg, W. Henry; Maroudas, Dimitrios

2001-09-01

A comprehensive, quantitative analysis is presented of the deformation behavior of coherently strained InAs/GaAs(111)A heteroepitaxial systems. The analysis combines a hierarchical theoretical approach with experimental measurements. Continuum linear elasticity theory is linked with atomic-scale calculations of structural relaxation for detailed theoretical studies of deformation in systems consisting of InAs thin films on thin GaAs(111)A substrates that are mechanically unconstrained at their bases. Molecular-beam epitaxy is used to grow very thin InAs films on both thick and thin GaAs buffer layers on epi-ready GaAs(111)A substrates. The deformation state of these samples is characterized by x-ray diffraction (XRD). The interplanar distances of thin GaAs buffer layers along the [220] and [111] crystallographic directions obtained from the corresponding XRD spectra indicate clearly that thin buffer layers deform parallel to the InAs/GaAs(111)A interfacial plane, thus aiding in the accommodation of the strain induced by lattice mismatch. The experimental measurements are in excellent agreement with the calculated lattice interplanar distances and the corresponding strain fields in the thin mechanically unconstrained substrates considered in the theoretical analysis. Therefore, this work contributes direct evidence in support of our earlier proposal that thin buffer layers in layer-by-layer semiconductor heteroepitaxy exhibit mechanical behavior similar to that of compliant substrates [see, e.g., B. Z. Nosho, L. A. Zepeda-Ruiz, R. I. Pelzel, W. H. Weinberg, and D. Maroudas, Appl. Phys. Lett. 75, 829 (1999)].

Electric Circuit Model Analogy for Equilibrium Lattice Relaxation in Semiconductor Heterostructures

NASA Astrophysics Data System (ADS)

Kujofsa, Tedi; Ayers, John E.

2018-01-01

The design and analysis of semiconductor strained-layer device structures require an understanding of the equilibrium profiles of strain and dislocations associated with mismatched epitaxy. Although it has been shown that the equilibrium configuration for a general semiconductor strained-layer structure may be found numerically by energy minimization using an appropriate partitioning of the structure into sublayers, such an approach is computationally intense and non-intuitive. We have therefore developed a simple electric circuit model approach for the equilibrium analysis of these structures. In it, each sublayer of an epitaxial stack may be represented by an analogous circuit configuration involving an independent current source, a resistor, an independent voltage source, and an ideal diode. A multilayered structure may be built up by the connection of the appropriate number of these building blocks, and the node voltages in the analogous electric circuit correspond to the equilibrium strains in the original epitaxial structure. This enables analysis using widely accessible circuit simulators, and an intuitive understanding of electric circuits can easily be extended to the relaxation of strained-layer structures. Furthermore, the electrical circuit model may be extended to continuously-graded epitaxial layers by considering the limit as the individual sublayer thicknesses are diminished to zero. In this paper, we describe the mathematical foundation of the electrical circuit model, demonstrate its application to several representative structures involving In x Ga1- x As strained layers on GaAs (001) substrates, and develop its extension to continuously-graded layers. This extension allows the development of analytical expressions for the strain, misfit dislocation density, critical layer thickness and widths of misfit dislocation free zones for a continuously-graded layer having an arbitrary compositional profile. It is similar to the transition from circuit theory, using lumped circuit elements, to electromagnetics, using distributed electrical quantities. We show this development using first principles, but, in a more general sense, Maxwell's equations of electromagnetics could be applied.

Control of Ge1-x-ySixSny layer lattice constant for energy band alignment in Ge1-xSnx/Ge1-x-ySixSny heterostructures

NASA Astrophysics Data System (ADS)

Fukuda, Masahiro; Watanabe, Kazuhiro; Sakashita, Mitsuo; Kurosawa, Masashi; Nakatsuka, Osamu; Zaima, Shigeaki

2017-10-01

The energy band alignment of Ge1-xSnx/Ge1-x-ySixSny heterostructures was investigated, and control of the valence band offset at the Ge1-xSnx/Ge1-x-ySixSny heterointerface was achieved by controlling the Si and Sn contents in the Ge1-x-ySixSny layer. The valence band offset in the Ge0.902Sn0.098/Ge0.41Si0.50Sn0.09 heterostructure was evaluated to be as high as 330 meV, and its conduction band offset was estimated to be 150 meV by considering the energy bandgap calculated from the theoretical prediction. In addition, the formation of the strain-relaxed Ge1-x-ySixSny layer was examined and the crystalline structure was characterized. The epitaxial growth of a strain-relaxed Ge0.64Si0.21Sn0.15 layer with the degree of strain relaxation of 55% was examined using a virtual Ge substrate. Moreover, enhancement of the strain relaxation was demonstrated by post-deposition annealing, where a degree of strain relaxation of 70% was achieved after annealing at 400 °C. These results indicate the possibility for enhancing the indirect-direct crossover with a strained and high-Sn-content Ge1-xSnx layer on a strain-relaxed Ge1-x-ySixSny layer, realizing preferable carrier confinement by type-I energy band alignment with high conduction and valence band offsets.

Structural and luminescent Properties of Bulk InAsSb

DTIC Science & Technology

2011-12-21

have used compositionally graded metamorphic buffer layers to accommodate the misfit strain between InAsxSb1-x alloys and GaSb and InSb substrates in...wavelength range. The authors have used compositionally graded metamorphic buffer layers to accommodate the misfit strain between InAsxSb1x alloys...long wave IR range. We used compositionally graded GaInSb, AlGaInSb, and InAsxSb1x metamorphic buffer layers to accommodate the misfit strain between

Indentation and overall compression behavior of multilayered thin-film composites. Effect of undulating layer geometry

DOE PAGES

Jamison, Ryan D.; Shen, Y. -L.

2015-03-19

Two finite element models are used to investigate the behavior of aluminum/silicon carbide thin-film layered composites with imperfect internal geometry when subjected to various loadings. In both models, undulating layers are represented by regular waveforms with various amplitudes, wavelengths, and phase offsets. First, uniaxial compressive loading of the composite is considered. The modulus and stress/strain response of the composite is sensitive to both loading direction and frequency of the undulation. Second, the nanoindentation response of the composite is investigated. The derived hardness and modulus are shown to be sensitive to the presence of undulating layers and the relative size ofmore » the indenter to the undulation. Undulating layers create bands of tensile and compressive stress in the indentation direction that are significantly different from the flat layers. The amount of equivalent plastic strain in the Al layers is increased by the presence of undulating layers. The correlations between the two forms of loading, and the implications to composite property measurement are carefully examined in this study.« less

Activity of lysozyme on Lactobacillus hilgardii strains isolated from Port wine.

PubMed

Dias, Rita; Vilas-Boas, Eduardo; Campos, Francisco M; Hogg, Tim; Couto, José António

2015-08-01

This work evaluated the effect of lysozyme on lactobacilli isolated from Port wine. Bacterial growth experiments were conducted in MRS/TJ medium and inactivation studies were performed in phosphate buffer (KH2PO4), distilled water and wine supplemented with different concentrations of lysozyme. The response of bacteria to lysozyme was found to be highly strain dependent. Some strains of Lactobacillus hilgardii together with Lactobacillus collinoides and Lactobacillus fructivorans were found to be resistant to concentrations of lysozyme as high as 2000 mg/L. It was observed that among the L. hilgardii taxon the resistant strains possess an S-layer coat. Apparently, the strains of L. collinoides and L. fructivorans studied are also S-layer producers as suggested by the total protein profile obtained by SDS-PAGE. Thus, the hypothetical protective role of the S-layer against the action of lysozyme was investigated. From the various treatments used to remove the protein from the surface of the cells, the one employing LiCl (5 M) was the most effective. LiCl pre-treated cells exposed to lysozyme (2000 mg/L) in KH2PO4 buffer maintained its resistance. However, when cells were suspended in distilled water an increased sensitivity to lysozyme was observed. Moreover, it was found that the addition of ethanol (20% v/v) to the suspension medium (distilled water) triggered a strong inactivation effect especially on cells previously treated with LiCl (reduction of >6 CFU log cycles). The results suggest that the S-layer exerts a protective effect against lysozyme and that the cell suspension medium influences the bacteriolysis efficiency. It was also noted that ethanol enhances the inactivation effect of lysozyme. Copyright © 2015 Elsevier Ltd. All rights reserved.

Feeling stretched or compressed? The multiple mechanosensitive responses of wood formation to bending.

PubMed

Roignant, Jeanne; Badel, Éric; Leblanc-Fournier, Nathalie; Brunel-Michac, Nicole; Ruelle, Julien; Moulia, Bruno; Decourteix, Mélanie

2018-05-11

Trees constantly experience wind, perceive resulting mechanical cues, and modify their growth and development accordingly. Previous studies have demonstrated that multiple bending treatments trigger ovalization of the stem and the formation of flexure wood in gymnosperms, but ovalization and flexure wood have rarely been studied in angiosperms, and none of the experiments conducted so far has used multidirectional bending treatments at controlled intensities. Assuming that bending involves tensile and compressive strain, we hypothesized that different local strains may generate specific growth and wood differentiation responses. Basal parts of young poplar stems were subjected to multiple transient controlled unidirectional bending treatments during 8 weeks, which enabled a distinction to be made between the wood formed under tensile or compressive flexural strains. This set-up enabled a local analysis of poplar stem responses to multiple stem bending treatments at growth, anatomical, biochemical and molecular levels. In response to multiple unidirectional bending treatments, poplar stems developed significant cross-sectional ovalization. At the tissue level, some aspects of wood differentiation were similarly modulated in the compressed and stretched zones (vessel frequency and diameter of fibres without a G-layer), whereas other anatomical traits (vessel diameter, G-layer formation, diameter of fibres with a G-layer and microfibril angle) and the expression of fasciclin-encoding genes were differentially modulated in the two zones. This work leads us to propose new terminologies to distinguish the 'flexure wood' produced in response to multiple bidirectional bending treatments from wood produced under transient tensile strain (tensile flexure wood; TFW) or under transient compressive strain (compressive flexure wood; CFW). By highlighting similarities and differences between tension wood and TFW and by demonstrating that plants could have the ability to discriminate positive strains from negative strains, this work provides new insight into the mechanisms of mechanosensitivity in plants.

Thickness dependence of curvature, strain, and response time in ionic electroactive polymer actuators fabricated via layer-by-layer assembly

NASA Astrophysics Data System (ADS)

Montazami, Reza; Liu, Sheng; Liu, Yang; Wang, Dong; Zhang, Qiming; Heflin, James R.

2011-05-01

Ionic electroactive polymer (IEAP) actuators containing porous conductive network composites (CNCs) and ionic liquids can result in high strain and fast response times. Incorporation of spherical gold nanoparticles in the CNC enhances conductivity and porosity, while maintaining relatively small thickness. This leads to improved mechanical strain and bending curvature of the actuators. We have employed the layer-by-layer self-assembly technique to fabricate a CNC with enhanced curvature (0.43 mm-1) and large net intrinsic strain (6.1%). The results demonstrate that curvature and net strain of IEAP actuators due to motion of the anions increase linearly with the thickness of the CNC as a result of the increased volume in which the anions can be stored. In addition, after subtracting the curvature of a bare Nafion actuator without a CNC, it is found that the net intrinsic strain of the CNC layer is independent of thickness for the range of 20-80 nm, indicating that the entire CNC volume contributes equivalently to the actuator motion. Furthermore, the response time of the actuator due to anion motion is independent of CNC thickness, suggesting that traversal through the Nafion membrane is the limiting factor in the anion motion.

Boundary Layer Effect on Behavior of Discrete Models.

PubMed

Eliáš, Jan

2017-02-10

The paper studies systems of rigid bodies with randomly generated geometry interconnected by normal and tangential bonds. The stiffness of these bonds determines the macroscopic elastic modulus while the macroscopic Poisson's ratio of the system is determined solely by the normal/tangential stiffness ratio. Discrete models with no directional bias have the same probability of element orientation for any direction and therefore the same mechanical properties in a statistical sense at any point and direction. However, the layers of elements in the vicinity of the boundary exhibit biased orientation, preferring elements parallel with the boundary. As a consequence, when strain occurs in this direction, the boundary layer becomes stiffer than the interior for the normal/tangential stiffness ratio larger than one, and vice versa. Nonlinear constitutive laws are typically such that the straining of an element in shear results in higher strength and ductility than straining in tension. Since the boundary layer tends, due to the bias in the elemental orientation, to involve more tension than shear at the contacts, it also becomes weaker and less ductile. The paper documents these observations and compares them to the results of theoretical analysis.

Polyurethane nanofiber strain sensors via in situ polymerization of polypyrrole and application to monitoring joint flexion

NASA Astrophysics Data System (ADS)

Kim, Inhwan; Cho, Gilsoo

2018-07-01

Strain sensors made of intrinsically conductive polymers (ICPs) and nanofibers were fabricated and tested for suitability for use in wearable technology. The sensors were fabricated and evaluated based on their surface appearances, and electrical, tensile, and chemical/thermal properties. Polypyrrole (PPy) was in situ polymerized onto polyurethane (PU) nanofiber substrates by exposing pyrrole monomers to ammonium persulfate as oxidant and 2,6-naphthalenedisulfonic acid disodium salt as doping agents in an aqueous bath. The PPy treated PU nanofibers were then coated with polydimethylsiloxane (PDMS). Both pyrrole concentrations and layer numbers were significantly related to change in electrical conductivity. Specimen treated with 0.1 M of PPy and having three layered structure showed the best electrical conductivity. Regarding tensile strength, the in situ polymerization process decreased tensile strength because the oxidant chemically degraded the PU fibers. Adding layers and PDMS treatment generally improved tensile properties while adding layers created fracture parts in the stress–strain curves. The treatment condition of 0.1 M of PPy, two layered, and PDMS treated specimen showed the best tensile properties as a strain sensor. The chemical property evaluation with Fourier transform infrared and x-ray photoelectron spectroscopy tests showed successful PPy polymerization and PDMS treatments. The functional groups and chemical bonds in polyol, urethane linkage, backbone ring structure in PPy, silicon-based functional groups in PDMS, and elemental content changes by treatment at each stage were characterized. The real-time data acquired from the dummy and five human subjects with repetition of motion at three different speeds of 0.16, 0.25 and 0.5 Hz generated similar trends and tendencies. The PU nanofiber sensors based on PPy and PDMS treatments in this study point to the possibility of developing textiles based wearable strain sensors developed using ICPs.

Strain-compensated infrared photodetector and photodetector array

DOEpatents

Kim, Jin K; Hawkins, Samuel D; Klem, John F; Cich, Michael J

2013-05-28

A photodetector is disclosed for the detection of infrared light with a long cutoff wavelength in the range of about 4.5-10 microns. The photodetector, which can be formed on a semiconductor substrate as an nBn device, has a light absorbing region which includes InAsSb light-absorbing layers and tensile-strained layers interspersed between the InAsSb light-absorbing layers. The tensile-strained layers can be formed from GaAs, InAs, InGaAs or a combination of these III-V compound semiconductor materials. A barrier layer in the photodetector can be formed from AlAsSb or AlGaAsSb; and a contact layer in the photodetector can be formed from InAs, GaSb or InAsSb. The photodetector is useful as an individual device, or to form a focal plane array.

Structural evaluation of InAsP/InGaAsP strained-layer superlattices with dislocations as grown by metal-organic molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Nakashima, Kiichi; Sugiura, Hideo

1997-08-01

The relaxation process in InAsP/InGaAsP strained-layer superlattices (SLSs) with interfacial misfit dislocations has been investigated systematically by transmission electron microscopy (TEM) and x-ray analyses. The TEM analysis reveals that dislocations locate a little inside the buffer layer near the interface between the buffer and first well layer in the SLS. The x-ray analysis of (400) azimuthal angle dependence indicates the buffer layer has a large macroscopic tilt. Using a curve fitting analysis of various (hkl) x-ray profiles and reciprocal lattice mapping measurements, residual strain was determined quantitatively, i.e., Δa∥ and Δa⊥, in the SLS and buffer layer. These results reveal that the dislocations mainly cause lattice distortion of the buffer layer rather than relaxation of the SLS layer. The most remarkable result is that the change of a∥ is not equal to that of a⊥ in the buffer layer. This phenomenon strongly suggests that microplastic domains are generated in the buffer layer.

On Compression of a Heavy Compressible Layer of an Elastoplastic or Elastoviscoplastic Medium

NASA Astrophysics Data System (ADS)

Kovtanyuk, L. V.; Panchenko, G. L.

2017-11-01

The problem of deformation of a horizontal plane layer of a compressible material is solved in the framework of the theory of small strains. The upper boundary of the layer is under the action of shear and compressing loads, and the no-slip condition is satisfied on the lower boundary of the layer. The loads increase in absolute value with time, then become constant, and then decrease to zero.Various plasticity conditions are consideredwith regard to the material compressibility, namely, the Coulomb-Mohr plasticity condition, the von Mises-Schleicher plasticity condition, and the same conditions with the viscous properties of the material taken into account. To solve the system of partial differential equations for the components of irreversible strains, a finite-difference scheme is developed for a spatial domain increasing with time. The laws of motion of elastoplastic boundaries are presented, the stresses, strains, rates of strain, and displacements are calculated, and the residual stresses and strains are found.

Strain relaxation in convex-graded InxAl1-xAs (x = 0.05-0.79) metamorphic buffer layers grown by molecular beam epitaxy on GaAs(001)

NASA Astrophysics Data System (ADS)

Solov'ev, V. A.; Chernov, M. Yu; Baidakova, M. V.; Kirilenko, D. A.; Yagovkina, M. A.; Sitnikova, A. A.; Komissarova, T. A.; Kop'ev, P. S.; Ivanov, S. V.

2018-01-01

This paper presents a study of structural properties of InGaAs/InAlAs quantum well (QW) heterostructures with convex-graded InxAl1-xAs (x = 0.05-0.79) metamorphic buffer layers (MBLs) grown by molecular beam epitaxy on GaAs substrates. Mechanisms of elastic strain relaxation in the convex-graded MBLs were studied by the X-ray reciprocal space mapping combined with the data of spatially-resolved selected area electron diffraction implemented in a transmission electron microscope. The strain relaxation degree was approximated for the structures with different values of an In step-back. Strong contribution of the strain relaxation via lattice tilt in addition to the formation of the misfit dislocations has been observed for the convex-graded InAlAs MBL, which results in a reduced threading dislocation density in the QW region as compared to a linear-graded MBL.

Strain, stabilities and electronic properties of hexagonal BN bilayers

NASA Astrophysics Data System (ADS)

Fujimoto, Yoshitaka; Saito, Susumu

Hexagonal boron nitride (h-BN) atomic layers have been regarded as fascinating materials both scientifically and technologically due to the sizable band gap. This sizable band-gap nature of the h-BN atomic layers would provide not only new physical properties but also novel nano- and/or opto-electronics applications. Here, we study the first-principles density-functional study that clarifies the biaxial strain effects on the energetics and the electronic properties of h-BN bilayers. We show that the band gaps of the h-BN bilayers are tunable by applying strains. Furthermore, we show that the biaxial strains can produce a transition from indirect to direct band gaps of the h-BN bilayer. We also discuss that both AA and AB stacking patterns of h-BN bilayer become feasible structures because h-BN bilayers possess two different directions in the stacking patterns. Supported by MEXT Elements Strategy Initiative to Form Core Research Center through Tokodai Institute for Element Strategy, JSPS KAKENHI Grant Numbers JP26390062 and JP25107005.

Template assisted strain tuning and phase stabilization in epitaxial BiFeO3 thin films

NASA Astrophysics Data System (ADS)

Saj Mohan M., M.; Ramadurai, Ranjith

2018-04-01

Strain engineering is a key to develop novel properties in functional materials. We report a strain mediated phase stabilization and epitaxial growth of bismuth ferrite(BiFeO3) thin films on LaAlO3 (LAO) substrates. The strain in the epitaxial layer is controlled by controlling the thickness of bottom electrode where the thickness of the BFO is kept constant. The thickness of La0.7Sr0.3MnO3(LSMO) template layer was optimized to grow completely strained tetragonal, tetragonal/rhombohedral mixed phase and fully relaxed rhombohedral phase of BFO layers. The results were confirmed with coupled-θ-2θ scan, and small area reciprocal space mapping. The piezoelectric d33 (˜ 45-48 pm/V) coefficient of the mixed phase was relatively larger than the strained tetragonal and relaxed rhombohedral phase for a given thickness.

Control of biaxial strain in single-layer molybdenite using local thermal expansion of the substrate

NASA Astrophysics Data System (ADS)

Plechinger, Gerd; Castellanos-Gomez, Andres; Buscema, Michele; van der Zant, Herre S. J.; Steele, Gary A.; Kuc, Agnieszka; Heine, Thomas; Schüller, Christian; Korn, Tobias

2015-03-01

Single-layer MoS2 is a direct-gap semiconductor whose electronic band structure strongly depends on the strain applied to its crystal lattice. While uniaxial strain can be easily applied in a controlled way, e.g., by bending of a flexible substrate with the atomically thin MoS2 layer on top, experimental realization of biaxial strain is more challenging. Here, we exploit the large mismatch between the thermal expansion coefficients of MoS2 and a silicone-based substrate to apply a controllable biaxial tensile strain by heating the substrate with a focused laser. The effect of this biaxial strain is directly observable in optical spectroscopy as a redshift of the MoS2 photoluminescence. We also demonstrate the potential of this method to engineer more complex strain patterns by employing highly absorptive features on the substrate to achieve non-uniform heat profiles. By comparison of the observed redshift to strain-dependent band structure calculations, we estimate the biaxial strain applied by the silicone-based substrate to be up to 0.2%, corresponding to a band gap modulation of 105 meV per percentage of biaxial tensile strain.

HOLEGAGE 1.0 - Strain-Gauge Drilling Analysis Program

NASA Technical Reports Server (NTRS)

Hampton, Roy V.

1992-01-01

Interior stresses inferred from changes in surface strains as hole is drilled. Computes stresses using strain data from each drilled-hole depth layer. Planar stresses computed in three ways: least-squares fit for linear variation with depth, integral method to give incremental stress data for each layer, and/or linear fit to integral data. Written in FORTRAN 77.

Evaluation of indigenous potent mushroom growth promoting bacteria (MGPB) on Agaricus bisporus production.

PubMed

Zarenejad, F; Yakhchali, B; Rasooli, I

2012-01-01

Mushrooms such as Agaricus bisporus, are cultivated for food worldwide. Fruit body initiation in Agaricus bisporus is a phase change from the vegetative to the reproductive stage which depends on the presence of a casing layer with particular physical, chemical and microbiological properties. The phase change is achieved practically by environmental manipulation and the presence of naturally occurring bacteria such as Pseuodomonas putida. In this study, 274 individual bacterial isolates were collected by screening the casing layer of 14 edible mushroom farms. The isolates were analysed with respect to biochemical properties, organic and inorganic phosphate solubilization, production of siderophore and growth in the presence of volatile compound of 1-octen-3-ol. It was found that approximately 97% of the strains were able to grow in the presence of 1-octen-3-ol and 36% were able to solubilize phosphorus. Among the isolates, 23 strains were selected as potent mushroom growth promoting bacteria (MGPB) for inoculation of the casing layer. Field experiments using these strains showed various promoting effects on production of mushroom. Finally, 2 strains (strains Bt4 and Ps7) showing the highest increase in A. bisporus production, were characterized as Pseuodomonas putida by molecular methods and identified as the best suited growth promoting inoculants for application in production farms for increasing the mushroom yield.

Relationships of left ventricular strain and strain rate to wall stress and their afterload dependency.

PubMed

Murai, Daisuke; Yamada, Satoshi; Hayashi, Taichi; Okada, Kazunori; Nishino, Hisao; Nakabachi, Masahiro; Yokoyama, Shinobu; Abe, Ayumu; Ichikawa, Ayako; Ono, Kota; Kaga, Sanae; Iwano, Hiroyuki; Mikami, Taisei; Tsutsui, Hiroyuki

2017-05-01

Whether and how left ventricular (LV) strain and strain rate correlate with wall stress is not known. Furthermore, it is not determined whether strain or strain rate is less dependent on the afterload. In 41 healthy young adults, LV global peak strain and systolic peak strain rate in the longitudinal direction (LS and LSR, respectively) and circumferential direction (CS and CSR, respectively) were measured layer-specifically using speckle tracking echocardiography (STE) before and during a handgrip exercise. Among all the points before and during the exercise, all the STE parameters significantly correlated linearly with wall stress (LS: r = -0.53, p < 0.01, LSR: r = -0.28, p < 0.05, CS in the inner layer: r = -0.72, p < 0.01, CSR in the inner layer: r = -0.47, p < 0.01). Strain more strongly correlated with wall stress than strain rate (r = -0.53 for LS vs. r = -0.28 for LSR, p < 0.05; r = -0.72 for CS vs. r = -0.47 for CSR in the inner layer, p < 0.05), whereas the interobserver variability was similar between strain and strain rate (longitudinal 6.2 vs. 5.2 %, inner circumferential 4.8 vs. 4.7 %, mid-circumferential 7.9 vs. 6.9 %, outer circumferential 10.4 vs. 9.7 %), indicating that the differences in correlation coefficients reflect those in afterload dependency. It was thus concluded that LV strain and strain rate linearly and inversely correlated with wall stress in the longitudinal and circumferential directions, and strain more strongly depended on afterload than did strain rate. Myocardial shortening should be evaluated based on the relationships between these parameters and wall stress.

Strained GaSb/AlAsSb Quantum Wells for p-Channel Field-Effect Transistors

DTIC Science & Technology

2008-01-01

Available online 18 October 2008 PACS: 72.80.Ey 73.61.Ey 81.05.Ea 85.30.Tv Keywords: A3. Molecular beam epitaxy A3. Quantum wells B2. Semiconducting III–V...were grown by molecular beam epitaxy on GaAs substrates. The buffer layer and barrier layers consisted of relaxed AlAsxSb1x. The composition of the...composition in order to control the strain in the GaSb quantum well. The heterostructures studied here are grown by molecular beam epitaxy (MBE) on semi

Functional Genomics of the Aeromonas salmonicida Lipopolysaccharide O-Antigen and A-Layer from Typical and Atypical Strains

PubMed Central

Merino, Susana; de Mendoza, Elena; Canals, Rocío; Tomás, Juan M.

2015-01-01

The A. salmonicida A450 LPS O-antigen, encoded by the wbsalmo gene cluster, is exported through an ABC-2 transporter-dependent pathway. It represents the first example of an O-antigen LPS polysaccharide with three different monosaccharides in their repeating unit assembled by this pathway. Until now, only repeating units with one or two different monosaccharides have been described. Functional genomic analysis of this wbsalmo region is mostly in agreement with the LPS O-antigen structure of acetylated l-rhamnose (Rha), d-glucose (Glc), and 2-amino-2-deoxy-d-mannose (ManN). Between genes of the wbsalmo we found the genes responsible for the biosynthesis and assembly of the S-layer (named A-layer in these strains). Through comparative genomic analysis and in-frame deletions of some of the genes, we concluded that all the A. salmonicida typical and atypical strains, other than A. salmonicida subsp. pectinolytica strains, shared the same wbsalmo and presence of A-layer. A. salmonicida subsp. pectinolytica strains lack wbsalmo and A-layer, two major virulence factors, and this could be the reason they are the only ones not found as fish pathogens. PMID:26082990

Assessment of the growth/etch back technique for the production of Ge strain-relaxed buffers on Si

NASA Astrophysics Data System (ADS)

Hartmann, J. M.; Aubin, J.

2018-04-01

Thick Ge layers grown on Si(0 0 1) are handy for the production of GeOI wafers, as templates for the epitaxy of III-V and GeSn-based heterostructures and so on. Perfecting their crystalline quality would enable to fabricate suspended Ge micro-bridges with extremely high levels of tensile strain (for mid IR lasers). In this study, we have used a low temperature (400 °C)/high temperature (750 °C) approach to deposit with GeH4 various thickness Ge layers in the 0.5 μm - 5 μm range. They were submitted afterwards to short duration thermal cycling under H2 (in between 750 °C and 875-890 °C) to lower the Threading Dislocation Density (TDD). Some of the thickest layers were partly etched at 750 °C with gaseous HCl to recover wafer bows compatible with device processing later on. X-ray Diffraction (XRD) showed that the layers were slightly tensile-strained, with a 104.5-105.5% degree of strain relaxation irrespective of the thickness. The surface was cross-hatched, with a roughness slightly decreasing with the thickness, from 2.0 down to 0.8 nm. The TDD (from Omega scans in XRD) decreased from 8 × 107 cm-2 down to 107 cm-2 as the Ge layer thickness increased from 0.5 up to 5 μm. The lack of improvement when growing 5 μm thick layers then etching a fraction of them with HCl over same thickness layers grown in a single run was at variance with Thin Solid Films 520, 3216 (2012). Low temperature HCl defect decoration confirmed those findings, with (i) a TDD decreasing from slightly more 107 cm-2 down to 5 × 106 cm-2 as the Ge layer thickness increased from 1.3 up to 5 μm and (ii) no TDD hysteresis between growth and growth then HCl etch-back.

Effect of native oxide layers on copper thin-film tensile properties: A reactive molecular dynamics study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Skarlinski, Michael D., E-mail: michael.skarlinski@rochester.edu; Quesnel, David J.; Department of Mechanical Engineering, University of Rochester, Rochester, New York 14627

2015-12-21

Metal-oxide layers are likely to be present on metallic nano-structures due to either environmental exposure during use, or high temperature processing techniques such as annealing. It is well known that nano-structured metals have vastly different mechanical properties from bulk metals; however, difficulties in modeling the transition between metallic and ionic bonding have prevented the computational investigation of the effects of oxide surface layers. Newly developed charge-optimized many body [Liang et al., Mater. Sci. Eng., R 74, 255 (2013)] potentials are used to perform fully reactive molecular dynamics simulations which elucidate the effects that metal-oxide layers have on the mechanical propertiesmore » of a copper thin-film. Simulated tensile tests are performed on thin-films while using different strain-rates, temperatures, and oxide thicknesses to evaluate changes in yield stress, modulus, and failure mechanisms. Findings indicate that copper-thin film mechanical properties are strongly affected by native oxide layers. The formed oxide layers have an amorphous structure with lower Cu-O bond-densities than bulk CuO, and a mixture of Cu{sub 2}O and CuO charge character. It is found that oxidation will cause modifications to the strain response of the elastic modulii, producing a stiffened modulii at low temperatures (<75 K) and low strain values (<5%), and a softened modulii at higher temperatures. While under strain, structural reorganization within the oxide layers facilitates brittle yielding through nucleation of defects across the oxide/metal interface. The oxide-free copper thin-film yielding mechanism is found to be a tensile-axis reorientation and grain creation. The oxide layers change the observed yielding mechanism, allowing for the inner copper thin-film to sustain an FCC-to-BCC transition during yielding. The mechanical properties are fit to a thermodynamic model based on classical nucleation theory. The fit implies that the oxidation of the films reduces the activation volume for yielding.« less

Chemical and morphological characterization of III-V strained layered heterostructures

NASA Astrophysics Data System (ADS)

Gray, Allen Lindsay

This dissertation describes investigations into the chemical and morphological characterization of III-V strained layered heterostructures by high-resolution x-ray diffraction. The purpose of this work is two-fold. The first was to use high-resolution x-ray diffraction coupled with transmission electron microscopy to characterize structurally a quaternary AlGaAsSb/InGaAsSb multiple quantum well heterostructure laser device. A method for uniquely determining the chemical composition of the strain quaternary quantum well, information previously thought to be unattainable using high resolution x-ray diffraction is thoroughly described. The misconception that high-resolution x-ray diffraction can separately find the well and barrier thickness of a multi-quantum well from the pendellosung fringe spacing is corrected, and thus the need for transmission electron microscopy is motivated. Computer simulations show that the key in finding the well composition is the intensity of the -3rd order satellite peaks in the diffraction pattern. The second part of this work addresses the evolution of strain relief in metastable multi-period InGaAs/GaAs multi-layered structures by high-resolution x-ray reciprocal space maps. Results are accompanied by transmission electron and differential contrast microscopy. The evolution of strain relief is tracked from a coherent "pseudomorphic" growth to a dislocated state as a function of period number by examining the x-ray diffuse scatter emanating from the average composition (zeroth-order) of the multi-layer. Relaxation is determined from the relative positions of the substrate with respect to the zeroth-order peak. For the low period number, the diffuse scatter from the multi-layer structure region arises from periodic, coherent crystallites. For the intermediate period number, the displacement fields around the multi-layer structure region transition to random coherent crystallites. At the higher period number, displacement fields of overlapping dislocations from relaxation of the random crystallites cause the initial stages of relaxation of the multi-layer structure. At the highest period number studied, relaxation of the multi-layer structure becomes bi-modal characterized by overlapping dislocations caused by mosaic block relaxation and periodically spaced misfit dislocations formed by 60°-type dislocations. The relaxation of the multi-layer structure has an exponential dependence on the diffuse scatter length-scale, which is shown to be a sensitive measure of the onset of relaxation.

An MBE growth facility for real-time in situ synchrotron x-ray topography studies of strained-layer III-V epitaxial materials

NASA Astrophysics Data System (ADS)

Whitehouse, C. R.; Barnett, S. J.; Soley, D. E. J.; Quarrell, J.; Aldridge, S. J.; Cullis, A. G.; Emeny, M. T.; Johnson, A. D.; Clarke, G. F.; Lamb, W.; Tanner, B. K.; Cottrell, S.; Lunn, B.; Hogg, C.; Hagston, W.

1992-01-01

This paper describes a unique combined UHV MBE growth x-ray topography facility designed to allow the first real-time synchrotron radiation x-ray topography study of strained-layer III-V growth processes. This system will enable unambiguous determination of dislocation nucleation and multiplication processes as a function of controlled variations in growth conditions, and also during post-growth thermal processing. The planned experiments have placed very stringent demands upon the engineering design of the system, and design details regarding the growth chamber; sample manipulator, x-ray optics, and real-time imaging systems are described. Results obtained during a feasibility study are also presented.

An MBE growth facility for real-time in situ synchrotron x-ray topography studies of strained-layer III--V epitaxial materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Whitehouse, C.R.; Barnett, S.J.; Soley, D.E.J.

1992-01-01

This paper describes a unique combined UHV MBE growth x-ray topography facility designed to allow the first real-time synchrotron radiation x-ray topography study of strained-layer III--V growth processes. This system will enable unambiguous determination of dislocation nucleation and multiplication processes as a function of controlled variations in growth conditions, and also during post-growth thermal processing. The planned experiments have placed very stringent demands upon the engineering design of the system, and design details regarding the growth chamber; sample manipulator, x-ray optics, and real-time imaging systems are described. Results obtained during a feasibility study are also presented.

Strain relaxation of thin Si{sub 0.6}Ge{sub 0.4} grown with low-temperature buffers by molecular beam epitaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, M.; Hansson, G. V.; Ni, W.-X.

A double-low-temperature-buffer variable-temperature growth scheme was studied for fabrication of strain-relaxed thin Si{sub 0.6}Ge{sub 0.4} layer on Si(001) by using molecular beam epitaxy (MBE), with particular focuses on the influence of growth temperature of individual low-temperature-buffer layers on the relaxation process and final structural qualities. The low-temperature buffers consisted of a 40 nm Si layer grown at an optimized temperature of {approx}400 deg. C, followed by a 20 nm Si{sub 0.6}Ge{sub 0.4} layer grown at temperatures ranging from 50 to 550 deg. C. A significant relaxation increase together with a surface roughness decrease both by a factor of {approx}2, accompaniedmore » with the cross-hatch/cross-hatch-free surface morphology transition, took place for the sample containing a low-temperature Si{sub 0.6}Ge{sub 0.4} layer that was grown at {approx}200 deg. C. This dramatic change was explained by the association with a certain onset stage of the ordered/disordered growth transition during the low-temperature MBE, where the high density of misfit dislocation segments generated near surface cusps largely facilitated the strain relaxation of the top Si{sub 0.6}Ge{sub 0.4} layer.« less

Protective action of Lactobacillus kefir carrying S-layer protein against Salmonella enterica serovar Enteritidis.

PubMed

Golowczyc, M A; Mobili, P; Garrote, G L; Abraham, A G; De Antoni, G L

2007-09-30

Eight Lactobacillus kefir strains isolated from different kefir grains were tested for their ability to antagonize Salmonella enterica serovar Enteritidis (Salmonella enteritidis) interaction with epithelial cells. L. kefir surface properties such as autoaggregation and coaggregation with Salmonella and adhesion to Caco-2/TC-7 cells were evaluated. L. kefir strains showed significantly different adhesion capacities, six strains were able to autoaggregate and four strains coaggregated with Salmonella. Coincubation of Salmonella with coaggregating L. kefir strains significantly decreased its capacity to adhere to and to invade Caco-2/TC-7 cells. This was not observed with non coaggregating L. kefir strains. Spent culture supernatants of L. kefir contain significant amounts of S-layer proteins. Salmonella pretreated with spent culture supernatants (pH 4.5-4.7) from all tested L. kefir strains showed a significant decrease in association and invasion to Caco-2/TC-7 cells. Artificially acidified MRS containing lactic acid to a final concentration and pH equivalent to lactobacilli spent culture supernatants did not show any protective action. Pretreatment of this pathogen with spent culture supernatants reduced microvilli disorganization produced by Salmonella. In addition, Salmonella pretreated with S-layer proteins extracted from coaggregating and non coaggregating L. kefir strains were unable to invade Caco-2/TC-7 cells. After treatment, L. kefir S-layer protein was detected associated with Salmonella, suggesting a protective role of this protein on association and invasion.

Synchrotron X-ray diffraction investigations on strains in the oxide layer of an irradiated Zircaloy fuel cladding

NASA Astrophysics Data System (ADS)

Chollet, Mélanie; Valance, Stéphane; Abolhassani, Sousan; Stein, Gene; Grolimund, Daniel; Martin, Matthias; Bertsch, Johannes

2017-05-01

For the first time the microstructure of the oxide layer of a Zircaloy-2 cladding after 9 cycles of irradiation in a boiling water reactor has been analyzed with synchrotron micro-X-ray diffraction. Crystallographic strains of the monoclinic and to some extent of the tetragonal ZrO2 are depicted through the thick oxide layer. Thin layers of sub-oxide at the oxide-metal interface as found for autoclave-tested samples and described in the literature, have not been observed in this material maybe resulting from irradiation damage. Shifts of selected diffraction peaks of the monoclinic oxide show that the uniform strain produced during oxidation is orientated in the lattice and displays variations along the oxide layer. Diffraction peaks and their shifts from families of diffracting planes could be translated into a virtual tensor. This virtual tensor exhibits changes through the oxide layer passing by tensile or compressive components.

Computer simulation studies of the growth of strained layers by molecular-beam epitaxy

NASA Astrophysics Data System (ADS)

Faux, D. A.; Gaynor, G.; Carson, C. L.; Hall, C. K.; Bernholc, J.

1990-08-01

Two new types of discrete-space Monte Carlo computer simulation are presented for the modeling of the early stages of strained-layer growth by molecular-beam epitaxy. The simulations are more economical on computer resources than continuous-space Monte Carlo or molecular dynamics. Each model is applied to the study of growth onto a substrate in two dimensions with use of Lennard-Jones interatomic potentials. Up to seven layers are deposited for a variety of lattice mismatches, temperatures, and growth rates. Both simulations give similar results. At small lattice mismatches (<~4%) the growth is in registry with the substrate, while at high mismatches (>~6%) the growth is incommensurate with the substrate. At intermediate mismatches, a transition from registered to incommensurate growth is observed which commences at the top of the crystal and propagates down to the first layer. Faster growth rates are seen to inhibit this transition. The growth mode is van der Merwe (layer-by-layer) at 2% lattice mismatch, but at larger mismatches Volmer-Weber (island) growth is preferred. The Monte Carlo simulations are assessed in the light of these results and the ease at which they can be extended to three dimensions and to more sophisticated potentials is discussed.

Band-edges and band-gap in few-layered transition metal dichalcogenides

NASA Astrophysics Data System (ADS)

Bhunia, Hrishikesh; Pal, Amlan J.

2018-05-01

We have considered liquid-exfoliated transition metal dichalcogenides (WS2, WSe2, MoS2, and MoSe2) and studied their band-edges and band-gap through scanning tunneling spectroscopy (STS) and density of states. A monolayer, bilayer (2L), and trilayer (3L) of each of the layered materials were characterized to derive the energies. Upon an increase in the number of layers, both the band-edges were found to shift towards the Fermi energy. The results from the exfoliated nanosheets have been compared with reported STS studies of MoS2 and WSe2 formed through chemical vapor deposition or molecular beam epitaxy methods; an uncontrolled lattice strain existed in such 2L and 3L nanoflakes due to mismatch in stacking-patterns between the monolayers affecting their energies. In the present work, the layers formed through the liquid-exfoliation process retained their interlayer coupling or stacking-sequence prevalent to the bulk and hence allowed determination of band-energies in these strain-free two-dimensional materials.

Mechanical behaviour near grain boundaries of He-implanted UO2 ceramic polycrystals

NASA Astrophysics Data System (ADS)

Ibrahim, M.; Castelier, É.; Palancher, H.; Bornert, M.; Caré, S.; Micha, J.-S.

2017-01-01

For studying the micromechanical behaviour of UO2 and characterising the intergranular interaction, polycrystals are implanted with helium ions, inducing strains in a thin surface layer. Laue X-ray micro-diffraction is used to measure the strain field in this implanted layer with a spatial resolution of about 1 μm. It allows a 2D mapping of the strain field in a dozen of grains. These measurements show that the induced strain depends mainly on the crystal orientation, and can be evaluated by a semi-analytical mechanical model. A mechanical interaction of the neighbouring grains has also been evidenced near the grain boundaries, which has been well reproduced by a finite element model. This interaction is shown to increase with the implantation energy (i.e. the implantation depth): it can be neglected at low implantation energy (60 keV), but not at higher energy (500 keV).

Highly stretchable and wearable graphene strain sensors with controllable sensitivity for human motion monitoring.

PubMed

Park, Jung Jin; Hyun, Woo Jin; Mun, Sung Cik; Park, Yong Tae; Park, O Ok

2015-03-25

Because of their outstanding electrical and mechanical properties, graphene strain sensors have attracted extensive attention for electronic applications in virtual reality, robotics, medical diagnostics, and healthcare. Although several strain sensors based on graphene have been reported, the stretchability and sensitivity of these sensors remain limited, and also there is a pressing need to develop a practical fabrication process. This paper reports the fabrication and characterization of new types of graphene strain sensors based on stretchable yarns. Highly stretchable, sensitive, and wearable sensors are realized by a layer-by-layer assembly method that is simple, low-cost, scalable, and solution-processable. Because of the yarn structures, these sensors exhibit high stretchability (up to 150%) and versatility, and can detect both large- and small-scale human motions. For this study, wearable electronics are fabricated with implanted sensors that can monitor diverse human motions, including joint movement, phonation, swallowing, and breathing.

Massless Dirac fermions in semimetal HgCdTe

NASA Astrophysics Data System (ADS)

Marchewka, M.; Grendysa, J.; Żak, D.; Tomaka, G.; Śliż, P.; Sheregii, E. M.

2017-01-01

Magneto-transport results obtained for the strained 100 nm thick Hg1-x CdxTe (x=0.135) layer grown by MBE on the CdTe/GaAs substrate are interpreted by the 8×8 kp model with the in-plane tensile strain. The dispersion relation for the investigated structure proves that the Dirac point is located in the gap caused by the strain. It is also shown that the fan of the Landau Levels (LL's) energy calculated for topological protected surface states for the studied HgCdTe alloy corresponds to the fan of the LL's calculated using the graphen-like Hamiltonian which gives excellent agreement with the experimental data for velocity on the Fermi level equal to vf ≈ 0.85×106 m/s. That characterized strained Hg1-x CdxTe layers (0.13 < x < 0.14) are a perfect Topological Insulator with good perspectives of further applications.

Layer-by-Layer Polyelectrolyte Encapsulation of Mycoplasma pneumoniae for Enhanced Raman Detection

PubMed Central

Rivera-Betancourt, Omar E.; Sheppard, Edward S.; Krause, Duncan C.; Dluhy, Richard A.

2014-01-01

Mycoplasma pneumoniae is a major cause of respiratory disease in humans and accounts for as much as 20% of all community-acquired pneumonia. Existing mycoplasma diagnosis is primarily limited by the poor success rate at culturing the bacteria from clinical samples. There is a critical need to develop a new platform for mycoplasma detection that has high sensitivity, specificity, and expediency. Here we report the layer-by-layer (LBL) encapsulation of M. pneumoniae cells with Ag nanoparticles in a matrix of the polyelectrolytes poly(allylamine hydrochloride) (PAH) and poly(styrene sulfonate) (PSS). We evaluated nanoparticle encapsulated mycoplasma cells as a platform for the differentiation of M. pneumoniae strains using surface enhanced Raman scattering (SERS) combined with multivariate statistical analysis. Three separate M. pneumoniae strains (M129, FH and II-3) were studied. Scanning electron microscopy and fluorescence imaging showed that the Ag nanoparticles were incorporated between the oppositely charged polyelectrolyte layers. SERS spectra showed that LBL encapsulation provides excellent spectral reproducibility. Multivariate statistical analysis of the Raman spectra differentiated the three M. pneumoniae strains with 97 – 100% specificity and sensitivity, and low (0.1 – 0.4) root mean square error. These results indicated that nanoparticle and polyelectrolyte encapsulation of M. pneumoniae is a potentially powerful platform for rapid and sensitive SERS-based bacterial identification. PMID:25017005

Growth of Interfacial Intermetallic Compound Layer in Diffusion-Bonded SAC-Cu Solder Joints During Different Types of Thermomechanical Excursion

NASA Astrophysics Data System (ADS)

Kanjilal, Anwesha; Kumar, Praveen

2018-01-01

The effects of mechanical strain on the growth kinetics of interfacial intermetallic compounds (IMCs) sandwiched between Cu substrate and Sn-1.0 wt.%Ag-0.5 wt.%Cu (SAC105) solder have been investigated. Isothermal aging (IA) at 70°C and 125°C, and thermal cycling (TC) as well as thermomechanical cycling (TMC) with shear strain of 12.8% per cycle between -25°C and 125°C were applied to diffusion-bonded solder joints to study the growth behavior of the interfacial IMC layer under various types of thermomechanical excursion (TME). The microstructure of the solder joint tested under each TME was observed at regular intervals. It was observed that the growth rate of the IMC layer was higher in the case of TMC compared with TC or IA. This increased growth rate of the IMC layer in the presence of mechanical strain suggests an additional driving force that enhances the growth kinetics of the IMC. Finite element analysis was performed to gain insight into the effect of TC and TMC on the stress field in the solder joint, especially near the interface between the solder and the substrate. Finally, an analytical model was developed to quantify the effect of strain on the effective diffusivity and express the growth kinetics for all three types of TME using a single expression.

Formation of chocolate-tablet boudins: Results from scaled analogue models

NASA Astrophysics Data System (ADS)

Zulauf, J.; Zulauf, G.; Göttlich, J.; Peinl, M.

2014-11-01

We used power-law viscous plasticine as a rock analogue to simulate chocolate tablet boudinage of rocks undergoing dislocation creep. A competent plasticine layer, oriented perpendicular to the main shortening direction, Z, underwent two phases of plane strain in a weaker plasticine matrix, with the principal stretching axis, X, and the axis of no-change, Y, replacing each other from the first to the second phase. In each phase of plane strain, boudinage was controlled by an initial phase of viscous necking followed by extension fracture along the neck domain. Increase in the magnitude of finite strain (e) and decrease in layer thickness (Hi) result in a decrease in the boudin width (Wa) and an increase in the number of boudins (N). Given the viscosity ratio between layer and matrix (m) is higher than ca. 5, the number of boudins decreases and the boudin width increases with increasing values of m. An unexpected result of the present study is that in each experiment, the number of boudins was significantly higher during the second phase of plane strain. This difference should be related to additional drag of the matrix plasticine on the stiff layer in the neck domains formed during the first phase of boudinage. The aspect ratio of the second generation of boudins (Wd = Wa/Hi) is compatible with aspect ratios of natural boudins and with aspect ratios calculated using analytical solutions.

Integrated studies into characteristics of physical fields using discontinuous geomedium models under external loading

NASA Astrophysics Data System (ADS)

Usoltseva Vostrikov, OM, VI; Tsoy, PA; Semenov, VN

2018-03-01

The article presents the laboratory study of deformation in artificial layered geomaterial samples down to failure with the simultaneous measurement of stresses, strains, micro-strains and signals of microseismic emission. The analysis of the synchronized experimental data made it possible to determine features of change in the microseismicity parameters and micro-strain fields in the samples depending on the deformation stage, and also to reveal the dynamics of evolution of microfailures and the main fracture zone.

Sb-induced strain fluctuations in a strained layer superlattice of InAs/InAsSb

DOE PAGES

Kim, Honggyu; Meng, Yifei; Klem, John F.; ...

2018-04-28

Here, we show that Sb substitution for As in a MBE grown InAs/InAsSb strained layer superlattice (SLS) is accompanied by significant strain fluctuations. The SLS was observed using scanning transmission electron microscopy along the [100] zone axis where the cation and anion atomic columns are separately resolved. Strain analysis based on atomic column positions reveals asymmetrical transitions in the strain profile across the SLS interfaces. The averaged strain profile is quantitatively fitted to the segregation model, which yields a distribution of Sb in agreement with our scanning tunneling microscopy result. The subtraction of the calculated strain reveals an increase inmore » strain fluctuations with the Sb concentration, as well as isolated regions with large strain deviations extending spatially over ~1 nm, which suggest the presence of point defects.« less

Sb-induced strain fluctuations in a strained layer superlattice of InAs/InAsSb

NASA Astrophysics Data System (ADS)

Kim, Honggyu; Meng, Yifei; Klem, John F.; Hawkins, Samuel D.; Kim, Jin K.; Zuo, Jian-Min

2018-04-01

We show that Sb substitution for As in a MBE grown InAs/InAsSb strained layer superlattice (SLS) is accompanied by significant strain fluctuations. The SLS was observed using scanning transmission electron microscopy along the [100] zone axis where the cation and anion atomic columns are separately resolved. Strain analysis based on atomic column positions reveals asymmetrical transitions in the strain profile across the SLS interfaces. The averaged strain profile is quantitatively fitted to the segregation model, which yields a distribution of Sb in agreement with the scanning tunneling microscopy result. The subtraction of the calculated strain reveals an increase in strain fluctuations with the Sb concentration, as well as isolated regions with large strain deviations extending spatially over ˜1 nm, which suggest the presence of point defects.

Sb-induced strain fluctuations in a strained layer superlattice of InAs/InAsSb

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Honggyu; Meng, Yifei; Klem, John F.

Here, we show that Sb substitution for As in a MBE grown InAs/InAsSb strained layer superlattice (SLS) is accompanied by significant strain fluctuations. The SLS was observed using scanning transmission electron microscopy along the [100] zone axis where the cation and anion atomic columns are separately resolved. Strain analysis based on atomic column positions reveals asymmetrical transitions in the strain profile across the SLS interfaces. The averaged strain profile is quantitatively fitted to the segregation model, which yields a distribution of Sb in agreement with our scanning tunneling microscopy result. The subtraction of the calculated strain reveals an increase inmore » strain fluctuations with the Sb concentration, as well as isolated regions with large strain deviations extending spatially over ~1 nm, which suggest the presence of point defects.« less

Structural and Optical Studies of ZnCdSe/ZnSe/ZnMgSSe Separate Confinement Heterostructures with Different Buffer Layers

NASA Astrophysics Data System (ADS)

Tu, Ru-Chin; Su, Yan-Kuin; Huang, Ying-Sheng; Chen, Giin-Sang; Chou, Shu-Tsun

1998-09-01

Detailed structural and optical studies of ZnCdSe/ZnSe/ZnMgSSe separate confinementheterostructures (SCH) grown on ZnSe, ZnSe/ZnSSe strained-layer superlattices (SLS),and GaAs buffer layers at the II VI/GaAs interface have been carried out by employingtransmission electron microscopy, variable temperature photoluminescence (PL), andcontactless electroreflectance (CER) measurements. A significant improvement onthe defect reduction and the optical quality has been observed by using either theZnSe/ZnSSe SLS or GaAs as the buffer layers when compared to that of the sample usingonly ZnSe as the buffer layer. However, the sample grown with the SLS buffer layersreveals a room temperature PL intensity higher than that of the sample grown witha GaAs buffer layer, which may still suffer from the great ionic differences betweenthe II V and III V atoms. Using 15 K CER spectra, we have also studied variousexcitonic transitions originating from strained Zn0.80Cd0.20Se/ZnSe single quantumwell in SCH with different buffer layers. An analysis of the CER spectra has ledto the identification of various excitonic transitions, mnH (L), between the mthconduction band state and the nth heavy (light)-hole band state. An excellentagreement between experiments and theoretical calculations based on the envelopefunction approximation model has been achieved.

Strained layer Fabry-Perot device

DOEpatents

Brennan, Thomas M.; Fritz, Ian J.; Hammons, Burrell E.

1994-01-01

An asymmetric Fabry-Perot reflectance modulator (AFPM) consists of an active region between top and bottom mirrors, the bottom mirror being affixed to a substrate by a buffer layer. The active region comprises a strained-layer region having a bandgap and thickness chosen for resonance at the Fabry-Perot frequency. The mirrors are lattice matched to the active region, and the buffer layer is lattice matched to the mirror at the interface. The device operates at wavelengths of commercially available semiconductor lasers.

EFFECTS OF BROILER REARING ENVIRONMENT ON TRANSMISSION OF F-STRAIN MYCOPLASMA GALLISEPTICUM FROM COMMERCIAL LAYER HENS TO BROILER CHICKENS: ROLE OF ACID-BASE BALANCE

USDA-ARS?s Scientific Manuscript database

Two trials were conducted concurrently to determine and compare, blood pH, blood gases, hematocrit, and hemoglobin in mycoplasma-free, F-strain Mycoplasma gallisepticum (FMG) inoculation layers, and FMG contact-infected broilers. FMG-inoculated layers had the highest partial pressure of O2 and the l...

Raman scattering studies of strain effects in (100) and (311)B GaAs1-xBix epitaxial layers

NASA Astrophysics Data System (ADS)

Steele, J. A.; Lewis, R. A.; Henini, M.; Lemine, O. M.; Alkaoud, A.

2013-11-01

We report room-temperature Raman studies of strained (100) and (311)B GaAs1-xBix epitaxial layers for x ≤ 0.039. The Raman spectra exhibit a two-mode behavior, as well as disorder-activated GaAs-like phonons. The experimental results show that the GaAs-like LO(Γ) mode experiences a strong composition-dependent redshift as a result of alloying. The peak frequency decreases linearly from the value for pure GaAs (˜293 cm-1) with the alloyed Bi fraction x and the introduced in-plane lattice strain ɛ∥, by ΔωLO=Δωalloy-Δωstrain. X-ray diffraction measurements are used to determine x and ɛ∥ allowing Δωalloy to be decoupled and is estimated to be -12(±4) cm-1/x for (100) GaAs1-xBix. ΔωLO is measured to be roughly double for samples grown on (311)B-oriented substrates to that of (100) GaAs. This large difference in redshift is accounted for by examining the Bi induced strain, effects from alloying, and defects formed during high-index (311)B crystal growth.

Investigation of threading dislocation blocking in strained-layer InGaAs/GaAs heterostructures using scanning cathodoluminescence microscopy

NASA Astrophysics Data System (ADS)

Russell, J. J.; Zou, J.; Moon, A. R.; Cockayne, D. J. H.

2000-08-01

Threading dislocation glide relieves strain in strained-layer heterostructures by increasing the total length of interface misfit dislocations. The blocking theory proposed by Freund [J. Appl. Phys. 68, 2073 (1990)] predicts the thickness above which gliding threading dislocations are able to overcome the resistance force produced by existing orthogonal misfit dislocations. A set of wedge-shaped samples of InxGa1-xAs/GaAs (x=0.04) strained-layer heterostructures was grown using molecular-beam epitaxy in order to test the theory of dislocation blocking over a range of thicknesses within one sample. Scanning cathodoluminescence microscopy techniques were used to image the misfit dislocations. The cathodoluminescence results confirm the model proposed by Freund.

Boundary Layer Effect on Behavior of Discrete Models

PubMed Central

Eliáš, Jan

2017-01-01

The paper studies systems of rigid bodies with randomly generated geometry interconnected by normal and tangential bonds. The stiffness of these bonds determines the macroscopic elastic modulus while the macroscopic Poisson’s ratio of the system is determined solely by the normal/tangential stiffness ratio. Discrete models with no directional bias have the same probability of element orientation for any direction and therefore the same mechanical properties in a statistical sense at any point and direction. However, the layers of elements in the vicinity of the boundary exhibit biased orientation, preferring elements parallel with the boundary. As a consequence, when strain occurs in this direction, the boundary layer becomes stiffer than the interior for the normal/tangential stiffness ratio larger than one, and vice versa. Nonlinear constitutive laws are typically such that the straining of an element in shear results in higher strength and ductility than straining in tension. Since the boundary layer tends, due to the bias in the elemental orientation, to involve more tension than shear at the contacts, it also becomes weaker and less ductile. The paper documents these observations and compares them to the results of theoretical analysis. PMID:28772517

Comparative Study of Nondestructive Pavement Testing, MacDill Air Force Base, Florida

DTIC Science & Technology

1987-07-01

a deflection-basin fitting program that prodicts moduli of the pavement layers and subgrade. A layered-elastic program AIRPOD is used in a fatigue...Layered-elastic Limiting stress in PCC; of pavement layers ( AIRPOD ) limiting strain in AC from deflection basin (ELSYM-5) (BASFIT) AFESC Elastic moduli of...need not be made. 121. Pavement evaluation computations were next accomplished using a series of computer programs referred to as ELSYM-5 and AIRPOD

Strain-Engineered Graphene Grown on Hexagonal Boron Nitride by Molecular Beam Epitaxy

PubMed Central

Summerfield, Alex; Davies, Andrew; Cheng, Tin S.; Korolkov, Vladimir V.; Cho, YongJin; Mellor, Christopher J.; Foxon, C. Thomas; Khlobystov, Andrei N.; Watanabe, Kenji; Taniguchi, Takashi; Eaves, Laurence; Novikov, Sergei V.; Beton, Peter H.

2016-01-01

Graphene grown by high temperature molecular beam epitaxy on hexagonal boron nitride (hBN) forms continuous domains with dimensions of order 20 μm, and exhibits moiré patterns with large periodicities, up to ~30 nm, indicating that the layers are highly strained. Topological defects in the moiré patterns are observed and attributed to the relaxation of graphene islands which nucleate at different sites and subsequently coalesce. In addition, cracks are formed leading to strain relaxation, highly anisotropic strain fields, and abrupt boundaries between regions with different moiré periods. These cracks can also be formed by modification of the layers with a local probe resulting in the contraction and physical displacement of graphene layers. The Raman spectra of regions with a large moiré period reveal split and shifted G and 2D peaks confirming the presence of strain. Our work demonstrates a new approach to the growth of epitaxial graphene and a means of generating and modifying strain in graphene. PMID:26928710

Modeling the Effects of Cu Content and Deformation Variables on the High-Temperature Flow Behavior of Dilute Al-Fe-Si Alloys Using an Artificial Neural Network.

PubMed

Shakiba, Mohammad; Parson, Nick; Chen, X-Grant

2016-06-30

The hot deformation behavior of Al-0.12Fe-0.1Si alloys with varied amounts of Cu (0.002-0.31 wt %) was investigated by uniaxial compression tests conducted at different temperatures (400 °C-550 °C) and strain rates (0.01-10 s -1 ). The results demonstrated that flow stress decreased with increasing deformation temperature and decreasing strain rate, while flow stress increased with increasing Cu content for all deformation conditions studied due to the solute drag effect. Based on the experimental data, an artificial neural network (ANN) model was developed to study the relationship between chemical composition, deformation variables and high-temperature flow behavior. A three-layer feed-forward back-propagation artificial neural network with 20 neurons in a hidden layer was established in this study. The input parameters were Cu content, temperature, strain rate and strain, while the flow stress was the output. The performance of the proposed model was evaluated using the K-fold cross-validation method. The results showed excellent generalization capability of the developed model. Sensitivity analysis indicated that the strain rate is the most important parameter, while the Cu content exhibited a modest but significant influence on the flow stress.

Modeling the Effects of Cu Content and Deformation Variables on the High-Temperature Flow Behavior of Dilute Al-Fe-Si Alloys Using an Artificial Neural Network

PubMed Central

Shakiba, Mohammad; Parson, Nick; Chen, X.-Grant

2016-01-01

The hot deformation behavior of Al-0.12Fe-0.1Si alloys with varied amounts of Cu (0.002–0.31 wt %) was investigated by uniaxial compression tests conducted at different temperatures (400 °C–550 °C) and strain rates (0.01–10 s−1). The results demonstrated that flow stress decreased with increasing deformation temperature and decreasing strain rate, while flow stress increased with increasing Cu content for all deformation conditions studied due to the solute drag effect. Based on the experimental data, an artificial neural network (ANN) model was developed to study the relationship between chemical composition, deformation variables and high-temperature flow behavior. A three-layer feed-forward back-propagation artificial neural network with 20 neurons in a hidden layer was established in this study. The input parameters were Cu content, temperature, strain rate and strain, while the flow stress was the output. The performance of the proposed model was evaluated using the K-fold cross-validation method. The results showed excellent generalization capability of the developed model. Sensitivity analysis indicated that the strain rate is the most important parameter, while the Cu content exhibited a modest but significant influence on the flow stress. PMID:28773658

Variation of refractive index in strained In(x)Ga(1-x)As-GaAs heterostructures

NASA Technical Reports Server (NTRS)

Das, U.; Bhattacharya, P. K.

1986-01-01

In(x)Ga(1-x)As-GaAs heterostructures and strained-layer superlattices can be used as optical waveguides. For such applications it is important to know explicitly the refractive index variation with mismatch strain and with alloying in the ternary layer. Starting from the Kramers-Kronig integral dispersion relations, a model has been developed from which the refractive index change in the ternary layer of In(x)Ga(1-x)As-GaAs heterojunctions can be calculated. The results are presented and discussed. The expected changes in a superlattice have been qualitatively predicted.

Influence of TESG layer viscoelasticity on the imaging properties of microlenses

NASA Astrophysics Data System (ADS)

Vasiljević, Darko; Murić, Branka; Pantelić, Dejan; Panić, Bratimir

2012-05-01

Microlenses were produced by the irradiation of a layer of tot'hema and eosin sensitized gelatin (TESG) with laser light (second harmonic Nd:YAG, 532 nm). For this research, eight microlenses were written on a dog-bone-shaped TESG layer. After production, microlenses were uniaxially stretched on a tensile testing machine. Each microlens had different amounts of strain (0, 30, 60, 80, 120, 140, 180 and 240% strain). The influence of TESG layer extensibility on the imaging properties of microlenses was characterized by calculating the root mean square wavefront aberration, the modulation transfer function and the geometrical spot diagram. All microlenses had very good imaging properties and the microlens with 0% strain had diffraction-limited performance.

Strained-layer InGaAs/GaAs/AlGaAs single quantum well lasers with high internal quantum efficiency

NASA Technical Reports Server (NTRS)

Larsson, Anders; Cody, Jeffrey; Lang, Robert J.

1989-01-01

Low threshold current density strained-layer In(0.2)Ga(0.8)As/GaAs/AlGaAs single quantum well lasers, emitting at 980 nm, have been grown by molecular beam epitaxy. Contrary to what has been reported for broad-area lasers with pseudomorphic InGaAs active layers grown by metalorganic chemical vapor deposition, these layers exhibit a high internal quantum efficiency (about 90 percent). The maximum external differential quantum efficiency is 70 percent, limited by an anomalously high internal loss possibly caused by a large lateral spreading of the optical mode. In addition, experimental results supporting the theoretically predicted strain-induced reduction of the valence-band nonparabolicity and density of states are presented.

Mechanical Response Analysis of Long-life Asphalt Pavement Structure of Yunluo High-speed on the Semi-rigid Base

NASA Astrophysics Data System (ADS)

Liu, Feng; Wu, Chuanhai; Xu, Xinquan; Li, Hao; Wang, Zhixiang

2018-01-01

In order to grasp the rule of the strain change of the semi-rigid asphalt pavement structure under the FWD load and provide a reliable theoretical and practical basis for the design of the pavement structure, based on the test section of Guangdong Yunluo expressway, taking FWD as the loading tool, by using the finite element analysis software ANSYS, the internal variation rules of each pavement structural layer were obtained. Based on the results of the theoretical analysis, the measured strain sensor was set up in the corresponding layer of the pavement structure, and the strain test plan was determined. Based on the analysis of the strain data obtained from several structural layers and field monitoring, the rationality of the type pavement structure and the strain test scheme were verified, so as to provide useful help for the design and the maintenance of the pavement structure.

Strain-induced oxygen vacancies in ultrathin epitaxial CaMnO3 films

NASA Astrophysics Data System (ADS)

Chandrasena, Ravini; Yang, Weibing; Lei, Qingyu; Delgado-Jaime, Mario; de Groot, Frank; Arenholz, Elke; Kobayashi, Keisuke; Aschauer, Ulrich; Spaldin, Nicola; Xi, Xiaoxing; Gray, Alexander

Dynamic control of strain-induced ionic defects in transition-metal oxides is considered to be an exciting new avenue towards creating materials with novel electronic, magnetic and structural properties. Here we use atomic layer-by-layer laser molecular beam epitaxy to synthesize high-quality ultrathin single-crystalline CaMnO3 films with systematically varying coherent tensile strain. We then utilize a combination of high-resolution soft x-ray absorption spectroscopy and bulk-sensitive hard x-ray photoemission spectroscopy in conjunction with first-principles theory and core-hole multiplet calculations to establish a direct link between the coherent in-plane strain and the oxygen-vacancy content. We show that the oxygen vacancies are highly mobile, which necessitates an in-situ-grown capping layer in order to preserve the original strain-induced oxygen-vacancy content. Our findings open the door for designing and controlling new ionically active properties in strongly-correlated transition-metal oxides.

Contact Sensor Attachment to Titanium Metal Composites

NASA Technical Reports Server (NTRS)

Vargas-Aburto, Carlos

1997-01-01

A Pd-13wt%Cr solid solution is a promising high-temperature strain gage alloy. In bulk form it has a number of properties that are desirable in a resistance strain gage material, such as a linear electrical-resistance-versus-temperature curve to 1000 C and stable electrical resistance in air at 1000 C. However, unprotected fine wire gages fabricated from this alloy perform well only to 600 C. At higher temperatures severe oxidation degrades their electrical performance. In this work Auger electron spectroscopy has been used to study the oxidation chemistry of the alloy wires and ribbons. Results indicate that the oxidation is caused by a complex mechanism that is not yet fully understood. As expected, during oxidation, a layer of chromium oxide is formed. This layer, however, forms beneath a layer of metallic palladium. The results of this study have increased the understanding of the oxidation mechanism of Pd-13wt%Cr.

Strain and Polarization Studies of InGaN for Optoelectronic, Electronic, and Photovoltaic Applications

DTIC Science & Technology

2009-12-14

10.1 A general QWR within a bimaterial substrate: An eigenstrain γ∗i j is applied to the QWR which is an arbitrarily shaped polygon... eigenstrain [15]. As QWR arrays can be self-organized layer-by- layer and also can be grown in different orientations, a more realistic QWR...is the sum γI j = γeI j + γ ∗ I j (2.3) where γ∗I j is the extended eigenstrain in the QWR, and γeI j the extended strain that appears in the

Flexible Carbon Nanotube Films for High Performance Strain Sensors

PubMed Central

Kanoun, Olfa; Müller, Christian; Benchirouf, Abderahmane; Sanli, Abdulkadir; Dinh, Trong Nghia; Al-Hamry, Ammar; Bu, Lei; Gerlach, Carina; Bouhamed, Ayda

2014-01-01

Compared with traditional conductive fillers, carbon nanotubes (CNTs) have unique advantages, i.e., excellent mechanical properties, high electrical conductivity and thermal stability. Nanocomposites as piezoresistive films provide an interesting approach for the realization of large area strain sensors with high sensitivity and low manufacturing costs. A polymer-based nanocomposite with carbon nanomaterials as conductive filler can be deposited on a flexible substrate of choice and this leads to mechanically flexible layers. Such sensors allow the strain measurement for both integral measurement on a certain surface and local measurement at a certain position depending on the sensor geometry. Strain sensors based on carbon nanostructures can overcome several limitations of conventional strain sensors, e.g., sensitivity, adjustable measurement range and integral measurement on big surfaces. The novel technology allows realizing strain sensors which can be easily integrated even as buried layers in material systems. In this review paper, we discuss the dependence of strain sensitivity on different experimental parameters such as composition of the carbon nanomaterial/polymer layer, type of polymer, fabrication process and processing parameters. The insights about the relationship between film parameters and electromechanical properties can be used to improve the design and fabrication of CNT strain sensors. PMID:24915183

Effect of crystal quality on performance of spin-polarized photocathode

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jin, Xiuguang; Ozdol, Burak; Yamamoto, Masahiro

2014-11-17

GaAs/GaAsP strain-compensated superlattices (SLs) with thickness up to 90-pair were fabricated. Transmission electron microscopy revealed the SLs are of high crystal quality and the introduced strain in SLs layers are fixed in the whole SL layers. With increasing SL pair number, the strain-compensated SLs show a less depolarization than the conventional strained SLs. In spite of the high crystal quality, the strain-compensated SLs also remain slightly depolarized with increasing SL pairs and the decrease in spin-polarization contributes to the spin relaxation time. 24-pair of GaAs/GaAsP strain-compensated SL demonstrates a maximum spin-polarization of 92% with a high quantum efficiency of 1.6%.

Influence of strain and metal thickness on metal-MoS₂ contacts.

PubMed

Saidi, Wissam A

2014-09-07

MoS2 and other transition metal dichalcogenides are considered as potential materials in many applications including future electronics. A prerequisite for these applications is to understand the nature of the MoS2 contact with different metals. We use semi-local density functional theory in conjunction with dispersion corrections to study the heterostructures composed of Pd and Pt monolayers with (111) orientation grown pseudomorphically on MoS2(001). The interface properties are mapped as a function of the number of deposited overlayers, as well as a function of tensile and compressive strains. Although we show that the dependence of the contacts on strain can be fully explained using the d-band model, we find that their evolution with the number of deposited metal layers is markedly different between Pd and Pt, and at variance with the d-band model. Specifically, the Pt/MoS2 heterostructures show an anomalous large stability with the deposition of two metal monolayers for all investigated strains, while Pd/MoS2 exhibits a similar behavior only for compressive strains. It is shown that the results can be rationalized by accounting for second-nearest-neighbor effect that couples MoS2 with the subsurface metal layers. The underpinnings of this behavior are attributed to the larger polarizability and cohesive energy of Pt compared to Pd, that leads to a larger charge-response in the subsurface layers.

Impact of tensile strain on the thermal transport of zigzag hexagonal boron nitride nanoribbon: An equilibrium molecular dynamics study

NASA Astrophysics Data System (ADS)

Navid, Ishtiaque Ahmed; Intisar Khan, Asir; Subrina, Samia

2018-02-01

The thermal conductivity of single layer strained hexagonal boron nitride nanoribbon (h-BNNR) has been computed using the Green—Kubo formulation of Equilibrium Molecular Dynamics (EMD) simulation. We have investigated the impact of strain on thermal transport of h-BNNR by varying the applied tensile strain from 1% upto 5% through uniaxial loading. The thermal conductivity of h-BNNR decreases monotonically with the increase of uniaxial tensile strain keeping the sample size and temperature constant. The thermal conductivity can be reduced upto 86% for an applied uniaxial tensile strain of 5%. The impact of temperature and width variation on the thermal conductivity of h-BNNR has also been studied under different uniaxial tensile strain conditions. With the increase in temperature, the thermal conductivity of strained h-BNNR exhibits a decaying characteristics whereas it shows an opposite pattern with the increasing width. Such study would provide a good insight on the strain tunable thermal transport for the potential device application of boron nitride nanostructures.

Microscopic Electronic and Mechanical Properties of Ultra-Thin Layered Materials

DTIC Science & Technology

2016-07-25

Graphene single layers grown by chemical vapor deposition on single crystal Cu substrates are subject to nonuniform physisorption strains that...the observed highly nonuniform strains. 4. Connecting dopant bond type with electronic structure in N-doped graphene (reference [4]) Robust methods

Theoretical study of strain-dependent optical absorption in a doped self-assembled InAs/InGaAs/GaAs/AlGaAs quantum dot

PubMed Central

Tankasala, Archana; Hsueh, Yuling; Charles, James; Fonseca, Jim; Povolotskyi, Michael; Kim, Jun Oh; Krishna, Sanjay; Allen, Monica S; Allen, Jeffery W; Rahman, Rajib; Klimeck, Gerhard

2018-01-01

A detailed theoretical study of the optical absorption in doped self-assembled quantum dots is presented. A rigorous atomistic strain model as well as a sophisticated 20-band tight-binding model are used to ensure accurate prediction of the single particle states in these devices. We also show that for doped quantum dots, many-particle configuration interaction is also critical to accurately capture the optical transitions of the system. The sophisticated models presented in this work reproduce the experimental results for both undoped and doped quantum dot systems. The effects of alloy mole fraction of the strain controlling layer and quantum dot dimensions are discussed. Increasing the mole fraction of the strain controlling layer leads to a lower energy gap and a larger absorption wavelength. Surprisingly, the absorption wavelength is highly sensitive to the changes in the diameter, but almost insensitive to the changes in dot height. This behavior is explained by a detailed sensitivity analysis of different factors affecting the optical transition energy. PMID:29719758

Three dimensional flow field inside compressor rotor, including blade boundary layers

NASA Technical Reports Server (NTRS)

Galmes, J. M.; Pouagere, M.; Lakshminarayana, B.

1982-01-01

The Reynolds stress equation, pressure strain correlation, and dissipative terms and diffusion are discussed in relation to turbulence modelling using the Reynolds stress model. Algebraic modeling of Reynolds stresses and calculation of the boundary layer over an axial cylinder are examined with regards to the kinetic energy model for turbulence modelling. The numerical analysis of blade and hub wall boundary layers, and an experimental study of rotor blade boundary layer in an axial flow compressor rotor are discussed. The Patankar-Spalding numerical method for two dimensional boundary layers is included.

The S-layer Associated Serine Protease Homolog PrtX Impacts Cell Surface-Mediated Microbe-Host Interactions of Lactobacillus acidophilus NCFM

PubMed Central

Johnson, Brant R.; O’Flaherty, Sarah; Goh, Yong Jun; Carroll, Ian; Barrangou, Rodolphe; Klaenhammer, Todd R.

2017-01-01

Health-promoting aspects attributed to probiotic microorganisms, including adhesion to intestinal epithelia and modulation of the host mucosal immune system, are mediated by proteins found on the bacterial cell surface. Notably, certain probiotic and commensal bacteria contain a surface (S-) layer as the outermost stratum of the cell wall. S-layers are non-covalently bound semi-porous, crystalline arrays of self-assembling, proteinaceous subunits called S-layer proteins (SLPs). Recent evidence has shown that multiple proteins are non-covalently co-localized within the S-layer, designated S-layer associated proteins (SLAPs). In Lactobacillus acidophilus NCFM, SLP and SLAPs have been implicated in both mucosal immunomodulation and adhesion to the host intestinal epithelium. In this study, a S-layer associated serine protease homolog, PrtX (prtX, lba1578), was deleted from the chromosome of L. acidophilus NCFM. Compared to the parent strain, the PrtX-deficient strain (ΔprtX) demonstrated increased autoaggregation, an altered cellular morphology, and pleiotropic increases in adhesion to mucin and fibronectin, in vitro. Furthermore, ΔprtX demonstrated increased in vitro immune stimulation of IL-6, IL-12, and IL-10 compared to wild-type, when exposed to mouse dendritic cells. Finally, in vivo colonization of germ-free mice with ΔprtX led to an increase in epithelial barrier integrity. The absence of PrtX within the exoproteome of a ΔprtX strain caused morphological changes, resulting in a pleiotropic increase of the organisms’ immunomodulatory properties and interactions with some intestinal epithelial cell components. PMID:28713337

Analyzing surface features on icy satellites using a new two-layer analogue model

NASA Astrophysics Data System (ADS)

Morales, K. M.; Leonard, E. J.; Pappalardo, R. T.; Yin, A.

2017-12-01

The appearance of similar surface morphologies across many icy satellites suggests potentially unified formation mechanisms. Constraining the processes that shape the surfaces of these icy worlds is fundamental to understanding their rheology and thermal evolution—factors that have implications for potential habitability. Analogue models have proven useful for investigating and quantifying surface structure formation on Earth, but have only been sparsely applied to icy bodies. In this study, we employ an innovative two-layer analogue model that simulates a warm, ductile ice layer overlain by brittle surface ice on satellites such as Europa and Enceladus. The top, brittle layer is composed of fine-grained sand while the ductile, lower viscosity layer is made of putty. These materials were chosen because they scale up reasonably to the conditions on Europa and Enceladus. Using this analogue model, we investigate the role of the ductile layer in forming contractional structures (e.g. folds) that would compensate for the over-abundance of extensional features observed on icy satellites. We do this by simulating different compressional scenarios in the analogue model and analyzing whether the resulting features resemble those on icy bodies. If the resulting structures are similar, then the model can be used to quantify the deformation by calculating strain. These values can then be scaled up to Europa or Enceladus and used to quantity the observed surface morphologies and the amount of extensional strain accommodated by certain features. This presentation will focus on the resulting surface morphologies and the calculated strain values from several analogue experiments. The methods and findings from this work can then be expanded and used to study other icy bodies, such as Triton, Miranda, Ariel, and Pluto.

Numerical analysis of drilling hole work-hardening effects in hole-drilling residual stress measurement

NASA Astrophysics Data System (ADS)

Li, H.; Liu, Y. H.

2008-11-01

The hole-drilling strain gage method is an effective semi-destructive technique for determining residual stresses in the component. As a mechanical technique, a work-hardening layer will be formed on the surface of the hole after drilling, and affect the strain relaxation. By increasing Young's modulus of the material near the hole, the work-hardening layer is simplified as a heterogeneous annulus. As an example, two finite rectangular plates submitted to different initial stresses are treated, and the relieved strains are measured by finite element simulation. The accuracy of the measurement is estimated by comparing the simulated residual stresses with the given initial ones. The results are shown for various hardness of work-hardening layer. The influence of the relative position of the gages compared with the thickness of the work-hardening layer, and the effect of the ratio of hole diameter to work-hardening layer thickness are analyzed as well.

Optical Properties of Gallium Arsenide and Indium Gallium Arsenide Quantum Wells and Their Applications to Opto-Electronic Devices.

NASA Astrophysics Data System (ADS)

Huang, Daming

1990-01-01

In this thesis we investigate the optical properties of modulation doped GaAs/AlGaAs and strained-layer undoped InGaAs/GaAs multiple quantum well structures (MQWS). The phenomena studied are the effects of carrier, strain, and the electric field on the absorption of excitons. For GaAs/AlGaAs modulation doped MQWS, the quenching of excitons by free carriers has been demonstrated. The comparison of the experimental results with calculations which consider phase space filling, screening, and exchange interaction showed the phase space filling to be the dominant mechanism responsible for the change of oscillator strength and binding energy of excitons associated with partially filled subband. On the other hand, the screening and exchange interaction are equally important to excitons associated with empty subbands. For InGaAs/GaAs strained-layer MQWS, we have demonstrated that the band edges are dramatically modified by strain. We determined the band discontinuities at InGaAs/GaAs interfaces using optical absorption, and showed that in this structure the heavy holes are confined in InGaAs layers while the light holes are in GaAs layers, in contrast to GaAs/AlGaAs MQWS. We also explore applications of GaAs/AlGaAs and InGaAs/GaAs MQWS to opto-electronic devices. The principle of devices investigated is mainly based on the electric field effect on the excitonic absorption in MQWS (the quantum confined Stark effect). Two examples presented in this thesis are the strained-layer InGaAs/GaAs MQWS electroabsorption modulators grown on GaAs substrates and the GaAs/AlGaAs MQWS reflection modulators grown on Si substrates. The large modulation observed in the absorption coefficient by an electric field is expected to facilitate opto-electronic integration.

Phylogeny and S1 Gene Variation of Infectious Bronchitis Virus Detected in Broilers and Layers in Turkey.

PubMed

Yilmaz, Huseyin; Altan, Eda; Cizmecigil, Utku Y; Gurel, Aydin; Ozturk, Gulay Yuzbasioglu; Bamac, Ozge Erdogan; Aydin, Ozge; Britton, Paul; Monne, Isabella; Cetinkaya, Burhan; Morgan, Kenton L; Faburay, Bonto; Richt, Juergen A; Turan, Nuri

2016-09-01

The avian coronavirus infectious bronchitis virus (AvCoV-IBV) is recognized as an important global pathogen because new variants are a continuous threat to the poultry industry worldwide. This study investigates the genetic origin and diversity of AvCoV-IBV by analysis of the S1 sequence derived from 49 broiler flocks and 14 layer flocks in different regions of Turkey. AvCoV-IBV RNA was detected in 41 (83.6%) broiler flocks and nine (64.2%) of the layer flocks by TaqMan real-time RT-PCR. In addition, AvCoV-IBV RNA was detected in the tracheas 27/30 (90%), lungs 31/49 (62.2%), caecal tonsils 7/22 (31.8%), and kidneys 4/49 (8.1%) of broiler flocks examined. Pathologic lesions, hemorrhages, and mononuclear infiltrations were predominantly observed in tracheas and to a lesser extent in the lungs and a few in kidneys. A phylogenetic tree based on partial S1 sequences of the detected AvCoV-IBVs (including isolates) revealed that 1) viruses detected in five broiler flocks were similar to the IBV vaccines Ma5, H120, M41; 2) viruses detected in 24 broiler flocks were similar to those previously reported from Turkey and to Israel variant-2 strains; 3) viruses detected in seven layer flocks were different from those found in any of the broiler flocks but similar to viruses previously reported from Iran, India, and China (similar to Israel variant-1 and 4/91 serotypes); and 4) that the AVCoV-IBV, Israeli variant-2 strain, found to be circulating in Turkey appears to be undergoing molecular evolution. In conclusion, genetically different AvCoV-IBV strains, including vaccine-like strains, based on their partial S1 sequence, are circulating in broiler and layer chicken flocks in Turkey and the Israeli variant-2 strain is undergoing evolution.

Metallic nanoparticle-based strain sensors elaborated by atomic layer deposition

NASA Astrophysics Data System (ADS)

Puyoo, E.; Malhaire, C.; Thomas, D.; Rafaël, R.; R'Mili, M.; Malchère, A.; Roiban, L.; Koneti, S.; Bugnet, M.; Sabac, A.; Le Berre, M.

2017-03-01

Platinum nanoparticle-based strain gauges are elaborated by means of atomic layer deposition on flexible polyimide substrates. Their electro-mechanical response is tested under mechanical bending in both buckling and conformational contact configurations. A maximum gauge factor of 70 is reached at a strain level of 0.5%. Although the exponential dependence of the gauge resistance on strain is attributed to the tunneling effect, it is shown that the majority of the junctions between adjacent Pt nanoparticles are in a short circuit state. Finally, we demonstrate the feasibility of an all-plastic pressure sensor integrating Pt nanoparticle-based strain gauges in a Wheatstone bridge configuration.

Effects of strain and thickness on the electronic and optical behaviors of two-dimensional hexagonal gallium nitride

NASA Astrophysics Data System (ADS)

Behzad, Somayeh

2017-06-01

The full potential linearized augmented plane wave (FP-LAPW) method within the framework of density functional theory has been used to study effects of strain and thickness on the electronic and optical properties of two-dimensional GaN. The band gap of monolayer and bilayer GaN under compressive in-plane strain change from indirect to direct with bond length shortening. Also, the semiconductor to semimetal transition occurs for monolayer and bilayer GaN under in-plane tensile strain with bond length elongation. It is found that the tensile and compressive strains cause the red and blue shifts in the optical spectra, respectively, for both monolayer and bilayer GaN. Applying the perpendicular strain on the bilayer GaN by decreasing the inter layer distance leads to the shift of valence band maximum towards the Γ point in the band structure and shift of peak positions and variation of peak intensities in ε2(ω) spectrum. The results show that the n-layer GaN has an indirect band gap for n < 16. The results suggest that monolayer and multilayer GaN are good candidates for application in optoelectronics and flexible electronics.

Prevention of egg contamination by Salmonella Enteritidis after oral vaccination of laying hens with Salmonella Enteritidis ΔtolC and ΔacrABacrEFmdtABC mutants.

PubMed

Kilroy, Sofie; Raspoet, Ruth; Haesebrouck, Freddy; Ducatelle, Richard; Van Immerseel, Filip

2016-08-12

Vaccination of laying hens has been successfully used to reduce egg contamination by Salmonella Enteritidis, decreasing human salmonellosis cases worldwide. Currently used vaccines for layers are either inactivated vaccines or live attenuated strains produced by mutagenesis. Targeted gene deletion mutants hold promise for future vaccines, because specific bacterial functions can be removed that may improve safety and allow differentiation from field strains. In this study, the efficacy of Salmonella Enteritidis ΔtolC and ΔacrABacrEFmdtABC strains in laying hens as live vaccines was evaluated. The mutants are deficient in either the membrane channel TolC (ΔtolC) or the multi-drug efflux systems acrAB, acrEF and mdtABC (ΔacrABacrEFmdtABC). These strains have a decreased ability for gut and tissue colonization and are unable to survive in egg white, the latter preventing transmission of the vaccine strains to humans. Two groups of 30 laying hens were orally inoculated at day 1, 6 weeks and 16 weeks of age with 10(8) cfu of either vaccine strain, while a third group was left unvaccinated. At 24 weeks of age, the birds were intravenously challenged with 5 × 10(7) cfu Salmonella Enteritidis PT4 S1400/94. The vaccine strains were not shed or detected in the gut, internal organs or eggs, 2 weeks after the third vaccination. The strains significantly protected against gut and internal organ colonization, and completely prevented egg contamination by Salmonella Enteritidis under the conditions of this study. This indicates that Salmonella Enteritidis ΔtolC and ΔacrABacrEFmdtABC strains might be valuable strains for vaccination of layers against Salmonella Enteritidis.

Thermal Strain Analysis of Optic Fiber Sensors

PubMed Central

Her, Shiuh-Chuan; Huang, Chih-Ying

2013-01-01

An optical fiber sensor surface bonded onto a host structure and subjected to a temperature change is analytically studied in this work. The analysis is developed in order to assess the thermal behavior of an optical fiber sensor designed for measuring the strain in the host structure. For a surface bonded optical fiber sensor, the measuring sensitivity is strongly dependent on the bonding characteristics which include the protective coating, adhesive layer and the bonding length. Thermal stresses can be generated due to a mismatch of thermal expansion coefficients between the optical fiber and host structure. The optical fiber thermal strain induced by the host structure is transferred via the adhesive layer and protective coating. In this investigation, an analytical expression of the thermal strain and stress in the optical fiber is presented. The theoretical predictions are validated using the finite element method. Numerical results show that the thermal strain and stress are linearly dependent on the difference in thermal expansion coefficients between the optical fiber and host structure and independent of the thermal expansion coefficients of the adhesive and coating. PMID:23385407

Probing the interaction of noble gases with pristine and nitrogen-doped graphene through Raman spectroscopy

NASA Astrophysics Data System (ADS)

Cunha, Renato; Perea-López, Néstor; Elías, Ana Laura; Fujisawa, Kazunori; Carozo, Victor; Feng, Simin; Lv, Ruitao; dos Santos, Maria Cristina; Terrones, Mauricio; Araujo, Paulo T.

2018-05-01

The interactions of adsorbates with graphene have received increasing attention due to its importance in the development of applications involving graphene-based coatings. Here, we present a study of the adsorption of noble gases on pristine and nitrogen-doped graphene. Single-layer graphene samples were synthesized by chemical vapor deposition (CVD) and transferred to transmission electron microscopy (TEM) grids. Several noble gases were allowed to adsorb on the suspended graphene substrate at very low temperatures. Raman spectra show distinct frequency blue shifts in both the 2D and G bands, which are induced by gas adsorption onto high quality single layer graphene (1LG). These shifts, which we associate with compressive biaxial strain in the graphene layers induced by the noble gases, are negligible for nitrogen-doped graphene. Additionally, a thermal depinning transition, which is related to the desorption of a noble gas layer from the graphene surface at low temperatures (ranging from 20 to 35 K), was also observed at different transition temperatures for different noble gases. These transition temperatures were found to be 25 K for argon and 35 K for xenon. Moreover, we were able to obtain values for the compressive biaxial strain in graphene induced by the adsorbed layer of noble gases, using Raman spectroscopy. Ab initio calculations confirmed the correlation between the noble gas-induced strain and the changes in the Raman features observed.

Poly-L-glutamate/glutamine synthesis in the cell wall of Mycobacterium bovis is regulated in response to nitrogen availability

PubMed Central

2013-01-01

Background The cell wall of pathogenic mycobacteria is known to possess poly-L-glutamine (PLG) layer. PLG synthesis has been directly linked to glutamine synthetase (GS) enzyme. glnA1 gene encodes for GS enzyme in mycobacteria. PLG layer is absent in cell wall of avirulent Mycobacterium smegmatis, although M. smegmatis strain expressing GS enzyme of pathogenic mycobacteria can synthesize PLG layer in the cell wall. The role of GS enzyme has been extensively studied in Mycobacterium tuberculosis, however, little is known about GS enzyme in other mycobacterial species. Mycobacterium bovis, as an intracellular pathogen encounters nitrogen stress inside macrophages, thus it has developed nitrogen assimilatory pathways to survive in adverse conditions. We have investigated the expression and activity of M. bovis GS in response to nitrogen availability and effect on synthesis of PLG layer in the cell wall. M. smegmatis was used as a model to study the behaviour of glnA1 locus of M. bovis. Results We observed that GS expression and activity decreased significantly in high nitrogen grown conditions. In high nitrogen conditions, the amount of PLG in cell wall was drastically reduced (below detectable limits) as compared to low nitrogen condition in M. bovis and in M. smegmatis strain complemented with M. bovis glnA1. Additionally, biofilm formation by M. smegmatis strain complemented with M. bovis glnA1 was increased than the wild type M. smegmatis strain. Conclusions The physiological regulation of GS in M. bovis was found to be similar to that reported in other mycobacteria but this data revealed that PLG synthesis in the cell wall of pathogenic mycobacteria occurs only in nitrogen limiting conditions and on the contrary high nitrogen conditions inhibit PLG synthesis. This indicates that PLG synthesis may be a form of nitrogen assimilatory pathway during ammonium starvation in virulent mycobacteria. Also, we have found that M. smegmatis complemented with M. bovis glnA1 was more efficient in biofilm formation than the wild type strain. This indicates that PLG layer favors biofilm formation. This study demonstrate that the nitrogen availability not only regulates GS expression and activity in M. bovis but also affects cell surface properties by modulating synthesis of PLG. PMID:24112767

Auger electron spectroscopy study of oxidation of a PdCr alloy used for high-temperature sensors

NASA Technical Reports Server (NTRS)

Boyd, Darwin L.; Zeller, Mary V.; Vargas-Aburto, Carlos

1993-01-01

A Pd-13 wt. percent Cr solid solution is a promising high-temperature strain gage alloy. In bulk form it has a number of properties that are desirable in a resistance strain gage material, such as a linear electrical resistance versus temperature curve to 1000 C and stable electrical resistance in air at 1000 C. However, unprotected fine wire gages fabricated from this alloy perform well only to 600 C. At higher temperatures severe oxidation degrades their electrical performance. In this work Auger electron spectroscopy was used to study the oxidation chemistry of the alloy wires and ribbons. Results indicate that the oxidation is caused by a complex mechanism that is not yet fully understood. As expected, during oxidation, a layer of chromium oxide is formed. This layer, however, forms beneath a layer of metallic palladium. The results of this study have increased the understanding of the oxidation mechanism of Pd-13 wt. percent Cr.

Verification of finite element analysis of fixed partial denture with in vitro electronic strain measurement.

PubMed

Wang, Gaoqi; Zhang, Song; Bian, Cuirong; Kong, Hui

2016-01-01

The purpose of the study was to verify the finite element analysis model of three-unite fixed partial denture with in vitro electronic strain analysis and analyze clinical situation with the verified model. First, strain gauges were attached to the critical areas of a three-unit fixed partial denture. Strain values were measured under 300 N load perpendicular to the occlusal plane. Secondly, a three-dimensional finite element model in accordance with the electronic strain analysis experiment was constructed from the scanning data. And the strain values obtained by finite element analysis and in vitro measurements were compared. Finally, the clinical destruction of the fixed partial denture was evaluated with the verified finite element analysis model. There was a mutual agreement and consistency between the finite element analysis results and experimental data. The finite element analysis revealed that failure will occur in the veneer layer on buccal surface of the connector under occlusal force of 570 N. The results indicate that the electronic strain analysis is an appropriate and cost saving method to verify the finite element model. The veneer layer on buccal surface of the connector is the weakest area in the fixed partial denture. Copyright © 2015 Japan Prosthodontic Society. Published by Elsevier Ltd. All rights reserved.

Mechanical loading regulates human MSC differentiation in a multi-layer hydrogel for osteochondral tissue engineering.

PubMed

Steinmetz, Neven J; Aisenbrey, Elizabeth A; Westbrook, Kristofer K; Qi, H Jerry; Bryant, Stephanie J

2015-07-01

A bioinspired multi-layer hydrogel was developed for the encapsulation of human mesenchymal stem cells (hMSCs) as a platform for osteochondral tissue engineering. The spatial presentation of biochemical cues, via incorporation of extracellular matrix analogs, and mechanical cues, via both hydrogel crosslink density and externally applied mechanical loads, were characterized in each layer. A simple sequential photopolymerization method was employed to form stable poly(ethylene glycol)-based hydrogels with a soft cartilage-like layer of chondroitin sulfate and low RGD concentrations, a stiff bone-like layer with high RGD concentrations, and an intermediate interfacial layer. Under a compressive load, the variation in hydrogel stiffness within each layer produced high strains in the soft cartilage-like layer, low strains in the stiff bone-like layer, and moderate strains in the interfacial layer. When hMSC-laden hydrogels were cultured statically in osteochondral differentiation media, the local biochemical and matrix stiffness cues were not sufficient to spatially guide hMSC differentiation after 21 days. However dynamic mechanical stimulation led to differentially high expression of collagens with collagen II in the cartilage-like layer, collagen X in the interfacial layer and collagen I in the bone-like layer and mineral deposits localized to the bone layer. Overall, these findings point to external mechanical stimulation as a potent regulator of hMSC differentiation toward osteochondral cellular phenotypes. Copyright © 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Enhancement of breakdown voltage for fully-vertical GaN-on-Si p-n diode by using strained layer superlattice as drift layer

NASA Astrophysics Data System (ADS)

Mase, Suguru; Hamada, Takeaki; Freedsman, Joseph J.; Egawa, Takashi

2018-06-01

We have demonstrated a vertical GaN-on-Si p-n diode with breakdown voltage (BV) as high as 839 V by using a low Si-doped strained layer superlattice (SLS). The p-n vertical diode fabricated by using the n‑-SLS layer as a part of the drift layer showed a remarkable enhancement in BV, when compared with the conventional n‑-GaN drift layer of similar thickness. The vertical GaN-on-Si p-n diodes with 2.3 μm-thick n‑-GaN drift layer and 3.0 μm-thick n‑-SLS layer exhibited a differential on-resistance of 4.0 Ω · cm2 and a BV of 839 V.

Polymer film strain gauges for measuring large elongations

NASA Astrophysics Data System (ADS)

Kondratov, A. P.; Zueva, A. M.; Varakin, R. S.; Taranec, I. P.; Savenkova, I. A.

2018-02-01

The paper shows the possibility to print polymer strain gages, microstrip lines, coplanar waveguides, and other prints for avionics using printing technology and equipment. The methods of screen and inkjet printing have been complemented by three new operations of preparing print films for application of an electrically conductive ink layer. Such additional operations make it possible to enhance the conductive ink layer adhesion to the film and to manufacture strain gages for measuring large elongations.

Flexible Strain Sensor Based on Layer-by-Layer Self-Assembled Graphene/Polymer Nanocomposite Membrane and Its Sensing Properties

NASA Astrophysics Data System (ADS)

Zhang, Dongzhi; Jiang, Chuanxing; Tong, Jun; Zong, Xiaoqi; Hu, Wei

2018-04-01

Graphene is a potential building block for next generation electronic devices including field-effect transistors, chemical sensors, and radio frequency switches. Investigations of strain application of graphene-based films have emerged in recent years, but the challenges in synthesis and processing achieving control over its fabrication constitute the main obstacles towards device applications. This work presents an alternative approach, layer-by-layer self-assembly, allowing a controllable fabrication of graphene/polymer film strain sensor on flexible substrates of polyimide with interdigital electrodes. Carboxylated graphene and poly (diallyldimethylammonium chloride) (PDDA) were exploited to form hierarchical nanostructure due to electrostatic action. The morphology and structure of the film were inspected by using scanning electron microscopy, x-ray diffraction and Fourier transform infrared spectroscopy. The strain-sensing properties of the graphene/PDDA film sensor were investigated through tuning micrometer caliper exertion and a PC-assisted piezoresistive measurement system. Experimental result shows that the sensor exhibited not only excellent response and reversibility behavior as a function of deflection, but also good repeatability and acceptable linearity. The strain-sensing mechanism of the proposed sensor was attributed to the electrical resistance change resulted from piezoresistive effect.

Highly strain-sensitive magnetostrictive tunnel magnetoresistance junctions

NASA Astrophysics Data System (ADS)

Tavassolizadeh, Ali; Hayes, Patrick; Rott, Karsten; Reiss, Günter; Quandt, Eckhard; Meyners, Dirk

2015-06-01

Tunnel magnetoresistance (TMR) junctions with CoFeB/MgO/CoFeB layers are promising for strain sensing applications due to their high TMR effect and magnetostrictive sense layer (CoFeB). TMR junctions available even in submicron dimensions can serve as strain sensors for microelectromechanical systems devices. Upon stress application, the magnetization configuration of such junctions changes due to the inverse magnetostriction effect resulting in strain-sensitive tunnel resistance. Here, strain sensitivity of round-shaped junctions with diameters of 11.3 μm, 19.2 μm, 30.5 μm, and 41.8 μm were investigated on macroscopic cantilevers using a four-point bending apparatus. This investigation mainly focuses on changes in hard-axis TMR loops caused by the stress-induced anisotropy. A macrospin model is proposed, supported by micromagnetic simulations, which describes the complete rotation of the sense layer magnetization within TMR loops of junctions, exposed to high stress. Below 0.2‰ tensile strain, a representative junction with 30.5 μm diameter exhibits a very large gauge factor of 2150. For such high gauge factor a bias field H = - 3.2 kA / m is applied in an angle equal to 3 π / 2 toward the pinned magnetization of the reference layer. The strain sensitivity strongly depends on the bias field. Applying stress along π / 4 against the induced magnetocrystalline anisotropy, both compressive and tensile strain can be identified by a unique sensor. More importantly, a configuration with a gauge factor of 400 at zero bias field is developed which results in a straightforward and compact measuring setup.

Temperature Evolution During Plane Strain Compression Of Tertiary Oxide Scale On Steel

NASA Astrophysics Data System (ADS)

Suarez, L.; Vanden Eynde, X.; Lamberigts, M.; Houbaert, Y.

2007-04-01

An oxide scale layer always forms at the steel surface during hot rolling. This scale layer separates the work roll from the metal substrate. Understanding the deformation behaviour and mechanical properties of the scale is of great interest because it affects the frictional conditions during hot rolling and the heat-transfer behaviour at the strip-roll interface. A thin wustite scale layer (<20 μm) was created under controlled conditions in an original laboratory device adequately positioned in a compression testing machine to investigate plane strain compression. Oxidation tests were performed on an ULC steel grade. After the oxide growth at 1050°C, plane strain compression (PSC) was performed immediately to simulate the hot rolling process. PSC experiments were performed at a deformation temperature of 1050°C, with reduction ratios from 5 to 70%, and strain rates of 10s-1 under controlled gas atmospheres. Results show that for wustite, ductility is obvious at 1050°C. Even after deformation oxide layers exhibit good adhesion to the substrate and homogeneity over the thickness. The tool/sample temperature difference seems to be the reason for the unexpected ductile behaviour of the scale layer.

Residual strain sensor using Al-packaged optical fiber and Brillouin optical correlation domain analysis.

PubMed

Choi, Bo-Hun; Kwon, Il-Bum

2015-03-09

We propose a distributed residual strain sensor that uses an Al-packaged optical fiber for the first time. The residual strain which causes Brillouin frequency shifts in the optical fiber was measured using Brillouin optical correlation domain analysis with 2 cm spatial resolution. We quantified the Brillouin frequency shifts in the Al-packaged optical fiber by the tensile stress and compared them for a varying number of Al layers in the optical fiber. The Brillouin frequency shift of an optical fiber with one Al layer had a slope of 0.038 MHz/με with respect to tensile stress, which corresponds to 78% of that for an optical fiber without Al layers. After removal of the stress, 87% of the strain remained as residual strain. When different tensile stresses were randomly applied, the strain caused by the highest stress was the only one detected as residual strain. The residual strain was repeatedly measured for a time span of nine months for the purpose of reliability testing, and there was no change in the strain except for a 4% reduction, which is within the error tolerance of the experiment. A composite material plate equipped with our proposed Al-packaged optical fiber sensor was hammered for impact experiment and the residual strain in the plate was successfully detected. We suggest that the Al-packaged optical fiber can be adapted as a distributed strain sensor for smart structures, including aerospace structures.

Spin-valve giant magneto-resistance film with magnetostrictive FeSiB amorphous layer and its application to strain sensors

NASA Astrophysics Data System (ADS)

Hashimoto, Y.; Yamamoto, N.; Kato, T.; Oshima, D.; Iwata, S.

2018-03-01

Giant magneto-resistance (GMR) spin-valve films with an FeSiB/CoFeB free layer were fabricated to detect applied strain in a GMR device. The magnetostriction constant of FeSiB was experimentally determined to have 32 ppm, which was one order of magnitude larger than that of CoFeB. In order to detect the strain sensitively and robustly against magnetic field fluctuation, the magnetic field modulation technique was applied to the GMR device. It was confirmed that the output voltage of the GMR device depends on the strain, and the gauge factor K = 46 was obtained by adjusting the applied DC field intensity and direction. We carried out the simulation based on a macro-spin model assuming uniaxial anisotropy, interlayer coupling between the free and pin layers, strain-induced anisotropy, and Zeeman energy, and succeeded in reproducing the experimental results. The simulation predicts that improving the magnetic properties of GMR films, especially reducing interlayer coupling, will be effective for increasing the output, i.e., the gauge factor, of the GMR strain sensors.

Development of self-powered strain sensor using mechano-luminescent ZnS:Cu and mechano-optoelectronic P3HT

NASA Astrophysics Data System (ADS)

Pulliam, Elias; Hoover, George; Tiparti, Dhruv; Ryu, Donghyeon

2017-04-01

Aerospace structural systems are prone to structural damage during their use by vibration, impact, material degradation, and other factors. Due to the harsh environments in which aerospace structures operate, aerospace structures are susceptible to various types of damage and often their structural integrity is jeopardized unless damage onset is detected in timely manner. Yet, current state-of-the-art sensor technologies are still limited for structural health monitoring (SHM) of aerospace structures due to their high power consumption, need for large form factor design, and manageable integration into aerospace structures. This study proposes a design of multilayered self-powered strain sensor by coupling mechano-luminescent (ML) property of copper-doped zinc sulfide (ZnS:Cu) and mechano-optoelectronic (MO) property of poly(3-hexylthiophene) (P3HT). One functional layer of the self-powered strain sensor is ZnS:Cu-based elastomeric composites that emit light in response to mechanical deformation. Another functional layer is P3HT-based thin films that generate direct current (DC) under light illumination and DC magnitude changes with applied strain. First, ML light emission characteristics of ZnS:Cu-based composites are studied under cyclic tensile strain with two various maximum strain up to 10% and 15% at various loading frequencies from 5 Hz to 20 Hz. Second, piezo-optical properties of P3HT-based thin films are investigated by acquiring light absorption of the thin films at various strains from 0% to 2% tensile strain. Last, micro-mechanical properties of the P3HT-based thin films are characterized using nanoindentation.

Numerical Study of Mechanical Response of Pure Titanium during Shot Peening

NASA Astrophysics Data System (ADS)

Wang, Y. M.; Cheng, J. P.; Yang, H. P.; Zhang, C. H.

2018-05-01

Mechanical response of pure titanium impacted by a steel ball was simulated using finite element method to investigate stress and strain evolution during shot peening. It is indicated that biaxial residual stress was obtained in the surface layer while in the interior triaxial residual stress existed because the S33 was comparable to S11 and S22. With decreasing the depth from the top surface, the stress was higher during impacting, but the stress relief extent became more significant when the ball rebounded. Therefore the maximum residual stress was formed in the subsurface layer with depth of 130 μm. As for the residual strain, it is shown that the maximum residual strain LE33 was obtained at the depth of 60 μm corresponding to the maximum shear stress during impacting.

Altering thermal transport by strained-layer epitaxy

NASA Astrophysics Data System (ADS)

Majdi, Tahereh; Pal, Souvik; Hafreager, Anders; Murad, Sohail; Sahu, Rakesh P.; Puri, Ishwar K.

2018-05-01

Since strain changes the interatomic spacing of matter and alters electron and phonon dispersion, an applied strain can modify the thermal conductivity k of a material. We show how the strain induced by heteroepitaxy is a passive mechanism to change k in a thin film. Molecular dynamics simulations of the deposition and epitaxial growth of ZnTe thin films provide insights into the role of interfacial strain in the conductivity of a deposited film. ZnTe films grow strain-free on lattice-matched ZnTe substrates, but similar thin films grown on a lattice-mismatched CdTe substrate exhibit ˜6% biaxial in-plane tensile strain and ˜7% uniaxial out-of-plane compressive strain. In the T = 700 K-1100 K temperature range, the conductivities of strained ZnTe layers decrease to ˜60% of their unstrained values. The resulting understanding of dk/dT shows that strain engineering can be used to alter the performance of a thermal rectifier and also provides a framework for enhancing thermoelectric devices.

Structure and magnetism of epitaxially strained Pd(001) films on Fe(001): Experiment and theory

NASA Astrophysics Data System (ADS)

Fullerton, Eric E.; Stoeffler, D.; Ounadjela, K.; Heinrich, B.; Celinski, Z.; Bland, J. A. C.

1995-03-01

We present an experimental and theoretical description of the structure and magnetism of epitaxially strained Pd(001) films on Fe(001) and in Fe/Pd/Fe(001) trilayers. The structure is determined by combining reflection high-energy electron diffraction and x-ray diffraction. For Fe/Au(001) bilayers and Fe/Pd/Au(001) trilayers grown by molecular-beam epitaxy on Ag(001), the Fe and Au layers are well represented by their bulk structure, whereas, thin Pd layers have a face-centered tetragonal structure with an in-plane expansion of 4.2% and an out-of-plane contraction of 7.2% (c/a=0.89). Theoretical ab initio studies of the interfacial structure indicate that the structural ground state of the epitaxially strained Pd layer is well described by a fct structure which maintains the bulk Pd atomic volume with small deviations at the interface. For Fe/Pd/Fe trilayers, the interlayer coupling oscillates with a period of 4 monolayers (ML) on a ferromagnetic background that crosses to weak antiferromagnetic coupling for thicknesses >12 ML of Pd. Strong ferromagnetic coupling observed below 5 ML of Pd indicates that 2 ML of Pd at each interface are ferromagnetically ordered. Theoretical studies of Fe3Pdn superlattices (where n is the number of Pd atomic layers) determine the polarization of the Pd layer and the interlayer magnetic coupling to depend strongly on the c/a ratio of the Pd layers. Modeling of a Pd layer with a constant-volume fct structure and one monolayer interfacial roughness find that the first 2 ML of the Pd is polarized in close agreement with the experimental results. Polarized neutron reflectivity results on an Fe(5.6 ML)/Pd(7 ML)/Au(20 ML) sample determine the average moment per Fe atom of 2.66+/-0.05μB. Calculations for the same structure show that this value is consistent with the induced Pd polarization.

Strain effect in epitaxial VO2 thin films grown on sapphire substrates using SnO2 buffer layers

NASA Astrophysics Data System (ADS)

Kim, Heungsoo; Bingham, Nicholas S.; Charipar, Nicholas A.; Piqué, Alberto

2017-10-01

Epitaxial VO2/SnO2 thin film heterostructures were deposited on m-cut sapphire substrates via pulsed laser deposition. By adjusting SnO2 (150 nm) growth conditions, we are able to control the interfacial strain between the VO2 film and SnO2 buffer layer such that the semiconductor-to-metal transition temperature (TC) of VO2 films can be tuned without diminishing the magnitude of the transition. It is shown that in-plane tensile strain and out-of-plane compressive strain of the VO2 film leads to a decrease of Tc. Interestingly, VO2 films on SnO2 buffer layers exhibit a structural phase transition from tetragonal-like VO2 to tetragonal-VO2 during the semiconductor-to-metal transition. These results suggest that the strain generated by SnO2 buffer provides an effective way for tuning the TC of VO2 films.

Indirect assessment of bulk strain soliton velocity in opaque solids

NASA Astrophysics Data System (ADS)

Belashov, A. V.; Beltukov, Y. M.; Petrov, N. V.; Samsonov, A. M.; Semenova, I. V.

2018-03-01

This paper presents a methodology allowing for determination of strain soliton velocity in opaque solid materials. The methodology is based on the analysis of soliton evolution in a layer of a transparent material adhesively bonded to the layer of a material under study. It is shown that the resulting soliton velocity in the complex waveguide equals to the arithmetic mean of soliton velocities in the two component materials. The suggested methodology is best suited for analysis of materials with relatively close elastic parameters and can be applied in research of nonlinear wave processes in opaque composites on the basis of transparent matrices.

Digital model for X-ray diffraction with application to composition and strain determination in strained InAs/GaSb superlattices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meng, Yifei; Kim, Honggyu; Zuo, Jian-Min

2014-07-07

We propose a digital model for high quality superlattices by including fluctuations in the superlattice periods. The composition and strain profiles are assumed to be coherent and persist throughout the superlattice. Using this model, we have significantly improved the fit with experimental X-ray diffraction data recorded from the nominal InAs/GaSb superlattice. The lattice spacing of individual layers inside the superlattice and the extent of interfacial intermixing are refined by including both (002) and (004) and their satellite peaks in the fitting. For the InAs/GaSb strained layer superlattice, results show: (i) the GaSb-on-InAs interface is chemically sharper than the InAs-on-GaSb interface,more » (ii) the GaSb layers experience compressive strain with In incorporation, (iii) there are interfacial strain associated with InSb-like bonds in GaSb and GaAs-like bonds in InAs, (iv) Sb substitutes a significant amount of In inside InAs layer near the InAs-on-GaSb interface. For support, we show that the composition profiles determined by X-ray diffraction are in good agreement with those obtained from atom probe tomography measurement. Comparison with the kinetic growth model shows a good agreement in terms of the composition profiles of anions, while the kinetic model underestimates the intermixing of cations.« less

Validation of Noninvasive In Vivo Compound Ultrasound Strain Imaging Using Histologic Plaque Vulnerability Features.

PubMed

Hansen, Hendrik H G; de Borst, Gert Jan; Bots, Michiel L; Moll, Frans L; Pasterkamp, Gerard; de Korte, Chris L

2016-11-01

Carotid plaque rupture is a major cause of stroke. Key issue for risk stratification is early identification of rupture-prone plaques. A noninvasive technique, compound ultrasound strain imaging, was developed providing high-resolution radial deformation/strain images of atherosclerotic plaques. This study aims at in vivo validation of compound ultrasound strain imaging in patients by relating the measured strains to typical features of vulnerable plaques derived from histology after carotid endarterectomy. Strains were measured in 34 severely stenotic (>70%) carotid arteries at the culprit lesion site within 48 hours before carotid endarterectomy. In all cases, the lumen-wall boundary was identifiable on B-mode ultrasound, and the imaged cross-section did not move out of the imaging plane from systole to diastole. After endarterectomy, the plaques were processed using a validated histology analysis technique. Locally elevated strain values were observed in regions containing predominantly components related to plaque vulnerability, whereas lower values were observed in fibrous, collagen-rich plaques. The median strain of the inner plaque layer (1 mm thickness) was significantly higher (P<0.01) for (fibro)atheromatous (n=20, strain=0.27%) than that for fibrous plaques (n=14, strain=-0.75%). Also, a significantly larger area percentage of the inner layer revealed strains above 0.5% for (fibro)atheromatous (45.30%) compared with fibrous plaques (31.59%). (Fibro)atheromatous plaques were detected with a sensitivity, specificity, positive predictive value, and negative predictive value of 75%, 86%, 88%, and 71%, respectively. Strain did not significantly correlate with fibrous cap thickness, smooth muscle cell, or macrophage concentration. Compound ultrasound strain imaging allows differentiating (fibro)atheromatous from fibrous carotid artery plaques. © 2016 American Heart Association, Inc.

Strained multilayer structures with pseudomorphic GeSiSn layers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Timofeev, V. A., E-mail: Vyacheslav.t@isp.nsc.ru; Nikiforov, A. I.; Tuktamyshev, A. R.

2016-12-15

The temperature and composition dependences of the critical thickness of the 2D–3D transition for a GeSiSn film on Si(100) have been studied. The regularities of the formation of multilayer structures with pseudomorphic GeSiSn layers directly on a Si substrate, without relaxed buffer layers, were investigated for the first time. The possibility of forming multilayer structures based on pseudomorphic GeSiSn layers has been shown and the lattice parameters have been determined using transmission electron microscopy. The grown structures demonstrate photoluminescence for Sn contents from 3.5 to 5% in GeSiSn layers.

The effect of the interaction of cracks in orthotropic layered materials under compressive loading.

PubMed

Winiarski, B; Guz, I A

2008-05-28

The non-classical problem of fracture mechanics of composites compressed along the layers with interfacial cracks is analysed. The statement of the problem is based on the model of piecewise homogeneous medium, the most accurate within the framework of the mechanics of deformable bodies as applied to composites. The condition of plane strain state is examined. The layers are modelled by a transversally isotropic material (a matrix reinforced by continuous parallel fibres). The frictionless Hertzian contact of the crack faces is considered. The complex fracture mechanics problem is solved using the finite-element analysis. The shear mode of stability loss is studied. The results are obtained for the typical dispositions of cracks. It was found that the interacting crack faces, the crack length and the mutual position of cracks influence the critical strain in the composite.

N-Glycosylation Is Important for Proper Haloferax volcanii S-Layer Stability and Function.

PubMed

Tamir, Adi; Eichler, Jerry

2017-03-15

N-Glycosylation, the covalent linkage of glycans to select Asn residues of target proteins, is an almost universal posttranslational modification in archaea. However, whereas roles for N-glycosylation have been defined in eukarya and bacteria, the function of archaeal N-glycosylation remains unclear. Here, the impact of perturbed N-glycosylation on the structure and physiology of the haloarchaeon Haloferax volcanii was considered. Cryo-electron microscopy was used to examine right-side-out membrane vesicles prepared from cells of a parent strain and from strains lacking genes encoding glycosyltransferases involved in assembling the N-linked pentasaccharide decorating the surface layer (S-layer) glycoprotein, the sole component of the S-layer surrounding H. volcanii cells. Whereas a regularly repeating S-layer covered the entire surface of vesicles prepared from parent strain cells, vesicles from the mutant cells were only partially covered. To determine whether such N-glycosylation-related effects on S-layer assembly also affected cell function, the secretion of a reporter protein was addressed in the parent and N-glycosylation mutant strains. Compromised S-layer glycoprotein N-glycosylation resulted in impaired transfer of the reporter past the S-layer and into the growth medium. Finally, an assessment of S-layer glycoprotein susceptibility to added proteases in the mutants revealed that in cells lacking AglD, which is involved in adding the final pentasaccharide sugar, a distinct S-layer glycoprotein conformation was assumed in which the N-terminal region was readily degraded. Perturbed N-glycosylation thus affects S-layer glycoprotein folding. These findings suggest that H. volcanii could adapt to changes in its surroundings by modulating N-glycosylation so as to affect S-layer architecture and function. IMPORTANCE Long held to be a process unique to eukaryotes, it is now accepted that bacteria and archaea also perform N-glycosylation, namely, the covalent attachment of sugars to select asparagine residues of target proteins. Yet, while information on the importance of N-glycosylation in eukaryotes and bacteria is available, the role of this posttranslational modification in archaea remains unclear. Here, insight into the purpose of archaeal N-glycosylation was gained by addressing the surface layer (S-layer) surrounding cells of the halophilic species Haloferax volcanii Relying on mutant strains defective in N-glycosylation, such efforts revealed that compromised N-glycosylation affected S-layer integrity and the transfer of a secreted reporter protein across the S-layer into the growth medium, as well as the conformation of the S-layer glycoprotein, the sole component of the S-layer. Thus, by modifying N-glycosylation, H. volcanii cells can change how they interact with their surroundings. Copyright © 2017 American Society for Microbiology.

Vibration control of beams using stand-off layer damping: finite element modeling and experiments

NASA Astrophysics Data System (ADS)

Chaudry, A.; Baz, A.

2006-03-01

Damping treatments with stand-off layer (SOL) have been widely accepted as an attractive alternative to conventional constrained layer damping (CLD) treatments. Such an acceptance stems from the fact that the SOL, which is simply a slotted spacer layer sandwiched between the viscoelastic layer and the base structure, acts as a strain magnifier that considerably amplifies the shear strain and hence the energy dissipation characteristics of the viscoelastic layer. Accordingly, more effective vibration suppression can be achieved by using SOL as compared to employing CLD. In this paper, a comprehensive finite element model of the stand-off layer constrained damping treatment is developed. The model accounts for the geometrical and physical parameters of the slotted SOL, the viscoelastic, layer the constraining layer, and the base structure. The predictions of the model are validated against the predictions of a distributed transfer function model and a model built using a commercial finite element code (ANSYS). Furthermore, the theoretical predictions are validated experimentally for passive SOL treatments of different configurations. The obtained results indicate a close agreement between theory and experiments. Furthermore, the obtained results demonstrate the effectiveness of the CLD with SOL in enhancing the energy dissipation as compared to the conventional CLD. Extension of the proposed one-dimensional CLD with SOL to more complex structures is a natural extension to the present study.

Implementation of ZnO/ZnMgO strained-layer superlattice for ZnO heteroepitaxial growth on sapphire

NASA Astrophysics Data System (ADS)

Petukhov, Vladimir; Bakin, Andrey; Tsiaoussis, Ioannis; Rothman, Johan; Ivanov, Sergey; Stoemenos, John; Waag, Andreas

2011-05-01

The main challenge in fabrication of ZnO-based devices is the absence of reliable p-type material. This is mostly caused by insufficient crystalline quality of the material and not well-enough-developed native point defect control of ZnO. At present high-quality ZnO wafers are still expensive and ZnO heteroepitaxial layers on sapphire are the most reasonable alternative to homoepitaxial layers. But it is still necessary to improve the crystalline quality of the heteroepitaxial layers. One of the approaches to reduce defect density in heteroepitaxial layers is to introduce a strained-layer superlattice (SL) that could stop dislocation propagation from the substrate-layer interface. In the present paper we have employed fifteen periods of a highly strained SL structure. The structure was grown on a conventional double buffer layer comprising of high-temperature MgO/low-temperature ZnO on sapphire. The influence of the SLs on the properties of the heteroepitaxial ZnO layers is investigated. Electrical measurements of the structure with SL revealed very high values of the carrier mobility up to 210 cm2/Vs at room temperature. Structural characterization of the obtained samples showed that the dislocation density in the following ZnO layer was not reduced. The high mobility signal appears to come from the SL structure or the SL/ZnO interface.

Load Deflection of Dow Corning SE 1700 Face Centered Tetragonal Direct Ink Write Materials: Effect of Thickness and Filament Spacing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Small, Ward; Pearson, Mark A.; Metz, Tom R.

Dow Corning SE 1700 (reinforced polydimethylsiloxane) porous structures were made by direct ink writing (DIW) in a face centered tetragonal (FCT) configuration. The filament diameter was 250 μm. Structures consisting of 4, 8, or 12 layers were fabricated with center-to-center filament spacing (“road width” (RW)) of 475, 500, 525, 550, or 575 μm. Three compressive load-unload cycles to 2000 kPa were performed on four separate areas of each sample; three samples of each thickness and filament spacing were tested. At a given strain during the third loading phase, stress varied inversely with porosity. At 10% strain, the stress was nearlymore » independent of the number of layers (i.e., thickness). At higher strains (20- 40%), the stress was highest for the 4-layer structure; the 8- and 12-layer structures were nearly equivalent suggesting that the load deflection is independent of number of layers above 8 layers. Intra-and inter-sample variability of the load deflection response was higher for thinner and less porous structures.« less

THz-wave generation via difference frequency mixing in strained silicon based waveguide utilizing its second order susceptibility χ((2)).

PubMed

Saito, Kyosuke; Tanabe, Tadao; Oyama, Yutaka

2014-07-14

Terahertz (THz) wave generation via difference frequency mixing (DFM) process in strain silicon membrane waveguides by introducing the straining layer is theoretically investigated. The Si(3)N(4) straining layer induces anisotropic compressive strain in the silicon core and results in the appearance of the bulk second order nonlinear susceptibility χ((2)) by breaking the crystal symmetry. We have proposed waveguide structures for THz wave generation under the DFM process by .using the modal birefringence in the waveguide core. Our simulations show that an output power of up to 0.95 mW can be achieved at 9.09 THz. The strained silicon optical device may open a widow in the field of the silicon-based active THz photonic device applications.

Wave propagation in piezoelectric layered structures of film bulk acoustic resonators.

PubMed

Zhu, Feng; Qian, Zheng-Hua; Wang, Bin

2016-04-01

In this paper, we studied the wave propagation in a piezoelectric layered plate consisting of a piezoelectric thin film on an electroded elastic substrate with or without a driving electrode. Both plane-strain and anti-plane waves were taken into account for the sake of completeness. Numerical results on dispersion relations, cut-off frequencies and vibration distributions of selected modes were given. The effects of mass ratio of driving electrode layer to film layer on the dispersion curve patterns and cut-off frequencies of the plane-strain waves were discussed in detail. Results show that the mass ratio does not change the trend of dispersion curves but larger mass ratio lowers corresponding frequency at a fixed wave number and may extend the frequency range for energy trapping. Those results are of fundamental importance and can be used as a reference to develop effective two-dimensional plate equations for structural analysis and design of film bulk acoustic resonators. Copyright © 2016 Elsevier B.V. All rights reserved.

In vivo measurement of skin surface strain and sub-surface layer deformation induced by natural tissue stretching.

PubMed

Maiti, Raman; Gerhardt, Lutz-Christian; Lee, Zing S; Byers, Robert A; Woods, Daniel; Sanz-Herrera, José A; Franklin, Steve E; Lewis, Roger; Matcher, Stephen J; Carré, Matthew J

2016-09-01

Stratum corneum and epidermal layers change in terms of thickness and roughness with gender, age and anatomical site. Knowledge of the mechanical and tribological properties of skin associated with these structural changes are needed to aid in the design of exoskeletons, prostheses, orthotics, body mounted sensors used for kinematics measurements and in optimum use of wearable on-body devices. In this case study, optical coherence tomography (OCT) and digital image correlation (DIC) were combined to determine skin surface strain and sub-surface deformation behaviour of the volar forearm due to natural tissue stretching. The thickness of the epidermis together with geometry changes of the dermal-epidermal junction boundary were calculated during change in the arm angle, from flexion (90°) to full extension (180°). This posture change caused an increase in skin surface Lagrange strain, typically by 25% which induced considerable morphological changes in the upper skin layers evidenced by reduction of epidermal layer thickness (20%), flattening of the dermal-epidermal junction undulation (45-50% reduction of flatness being expressed as Ra and Rz roughness profile height change) and reduction of skin surface roughness Ra and Rz (40-50%). The newly developed method, DIC combined with OCT imaging, is a powerful, fast and non-invasive methodology to study structural skin changes in real time and the tissue response provoked by mechanical loading or stretching. Copyright © 2016 The Authors. Published by Elsevier Ltd.. All rights reserved.

Formation of a Ge-rich Si1-x Ge x (x > 0.9) fin epitaxial layer condensed by dry oxidation

NASA Astrophysics Data System (ADS)

Jang, Hyunchul; Kim, Byongju; Koo, Sangmo; Ko, Dae-Hong

2017-11-01

We have selectively grown an epitaxial Si0.35Ge0.65 fin layer in a 65 nm oxide trench pattern array and formed a Ge-rich Si1-x Ge x (x > 0.9) fin layer with condensed Ge using dry oxidation. During oxidation of the SiGe fin structure, we found that the compressive strain of the condensed SiGe layer was increased by about 1.3% while Ge was efficiently condensed due to a two-dimensional oxidation reaction. In this paper, we discussed in detail the diffusion during the two-dimensional condensation reaction as well as the asymmetric biaxial strain of the SiGe fin before and after oxidation using a reciprocal space mapping measurement. The application of dry oxidation on selectively grown SiGe fin layer can be an effective method for increasing hole mobility of SiGe fin with increased Ge content and self-induced compressive strain.

Computer-aided study of key factors determining high mechanical properties of nanostructured surface layers in metal-ceramic composites

NASA Astrophysics Data System (ADS)

Konovalenko, Igor S.; Shilko, Evgeny V.; Ovcharenko, Vladimir E.; Psakhie, Sergey G.

2017-12-01

The paper presents the movable cellular automaton method. It is based on numerical models of surface layers of the metal-ceramic composite NiCr-TiC modified under electron beam irradiation in inert gas plasmas. The models take into account different geometric, concentration and mechanical parameters of ceramic and metallic components. The authors study the contributions of key structural factors in mechanical properties of surface layers and determine the ranges of their variations by providing the optimum balance of strength, strain hardening and fracture toughness.

Structural state diagram of concentrated suspensions of jammed soft particles in oscillatory shear flow

NASA Astrophysics Data System (ADS)

Khabaz, Fardin; Cloitre, Michel; Bonnecaze, Roger T.

2018-03-01

In a recent study [Khabaz et al., Phys. Rev. Fluids 2, 093301 (2017), 10.1103/PhysRevFluids.2.093301], we showed that jammed soft particle glasses (SPGs) crystallize and order in steady shear flow. Here we investigate the rheology and microstructures of these suspensions in oscillatory shear flow using particle-dynamics simulations. The microstructures in both types of flows are similar, but their evolutions are very different. In both cases the monodisperse and polydisperse suspensions form crystalline and layered structures, respectively, at high shear rates. The crystals obtained in the oscillatory shear flow show fewer defects compared to those in the steady shear. SPGs remain glassy for maximum oscillatory strains less than about the yield strain of the material. For maximum strains greater than the yield strain, microstructural and rheological transitions occur for SPGs. Polydisperse SPGs rearrange into a layered structure parallel to the flow-vorticity plane for sufficiently high maximum shear rates and maximum strains about 10 times greater than the yield strain. Monodisperse suspensions form a face-centered cubic (FCC) structure when the maximum shear rate is low and hexagonal close-packed (HCP) structure when the maximum shear rate is high. In steady shear, the transition from a glassy state to a layered one for polydisperse suspensions included a significant induction strain before the transformation. In oscillatory shear, the transformation begins to occur immediately and with different microstructural changes. A state diagram for suspensions in large amplitude oscillatory shear flow is found to be in close but not exact agreement with the state diagram for steady shear flow. For more modest amplitudes of around one to five times the yield strain, there is a transition from a glassy structure to FCC and HCP crystals, at low and high frequencies, respectively, for monodisperse suspensions. At moderate frequencies, the transition is from glassy to HCP via an intermediate FCC phase.

Adjustable Membrane Mirrors Incorporating G-Elastomers

NASA Technical Reports Server (NTRS)

Chang, Zensheu; Morgan, Rhonda M.; Xu, Tian-Bing; Su, Ji; Hishinuma, Yoshikazu; Yang, Eui-Hyeok

2008-01-01

Lightweight, flexible, large-aperture mirrors of a type being developed for use in outer space have unimorph structures that enable precise adjustment of their surface figures. A mirror of this type includes a reflective membrane layer bonded with an electrostrictive grafted elastomer (G-elastomer) layer, plus electrodes suitably positioned with respect to these layers. By virtue of the electrostrictive effect, an electric field applied to the G-elastomer membrane induces a strain along the membrane and thus causes a deflection of the mirror surface. Utilizing this effect, the mirror surface figure can be adjusted locally by individually addressing pairs of electrodes. G-elastomers, which were developed at NASA Langley Research Center, were chosen for this development in preference to other electroactive polymers partly because they offer superior electromechanical performance. Whereas other electroactive polymers offer, variously, large strains with low moduli of elasticity or small strains with high moduli of elasticity, G-elastomers offer both large strains (as large as 4 percent) and high moduli of elasticity (about 580 MPa). In addition, G-elastomer layers can be made by standard melt pressing or room-temperature solution casting.

Avalanche atomic switching in strain engineered Sb2Te3-GeTe interfacial phase-change memory cells

NASA Astrophysics Data System (ADS)

Zhou, Xilin; Behera, Jitendra K.; Lv, Shilong; Wu, Liangcai; Song, Zhitang; Simpson, Robert E.

2017-09-01

By confining phase transitions to the nanoscale interface between two different crystals, interfacial phase change memory heterostructures represent the state of the art for energy efficient data storage. We present the effect of strain engineering on the electrical switching performance of the {{Sb}}2{{Te}}3-GeTe superlattice van der Waals devices. Multiple Ge atoms switching through a two-dimensional Te layer reduces the activation barrier for further atoms to switch; an effect that can be enhanced by biaxial strain. The out-of-plane phonon mode of the GeTe crystal remains active in the superlattice heterostructures. The large in-plane biaxial strain imposed by the {{Sb}}2{{Te}}3 layers on the GeTe layers substantially improves the switching speed, reset energy, and cyclability of the superlattice memory devices. Moreover, carefully controlling residual stress in the layers of {{Sb}}2{{Te}}3-GeTe interfacial phase change memories provides a new degree of freedom to design the properties of functional superlattice structures for memory and photonics applications.

Elastic solitons in delaminated bars: splitting leads to fission

NASA Astrophysics Data System (ADS)

Samsonov, A. M.; Dreiden, G. V.; Khusnutdinova, K. R.; Semenova, I. V.

2008-06-01

Recent theoretical and successful experimental studies confirmed existence and demonstrated main properties of bulk strain solitary waves in nonlinearly elastic solid wave guides. Our current research is devoted to nonlinear wave processes in layered elastic wave guides with inhomogeneities modelling delamination. We present first theoretical and experimental results showing the influence of delamination on the parameters of the longitudinal strain solitary wave.

Strain-Modulated Bandgap and Piezo-Resistive Effect in Black Phosphorus Field-Effect Transistors

NASA Astrophysics Data System (ADS)

Zhang, Zuocheng; Li, Likai; Horng, Jason; Wang, Nai Zhou; Yang, Fangyuan; Yu, Yijun; Zhang, Yu; Chen, Guorui; Watanabe, Kenji; Taniguchi, Takashi; Chen, Xian Hui; Wang, Feng; Zhang, Yuanbo

2017-10-01

Energy bandgap largely determines the optical and electronic properties of a semiconductor. Variable bandgap therefore makes versatile functionality possible in a single material. In layered material black phosphorus, the bandgap can be modulated by the number of layers; as a result, few-layer black phosphorus has discrete bandgap values that are relevant for opto-electronic applications in the spectral range from red, in monolayer, to mid-infrared in the bulk limit. Here, we further demonstrate continuous bandgap modulation by mechanical strain applied through flexible substrates. The strain-modulated bandgap significantly alters the charge transport in black phosphorus at room temperature; we for the first time observe a large piezo-resistive effect in black phosphorus field-effect transistors (FETs). The effect opens up opportunities for future development of electro-mechanical transducers based on black phosphorus, and we demonstrate strain gauges constructed from black phosphorus thin crystals.

Strain-Modulated Bandgap and Piezo-Resistive Effect in Black Phosphorus Field-Effect Transistors.

PubMed

Zhang, Zuocheng; Li, Likai; Horng, Jason; Wang, Nai Zhou; Yang, Fangyuan; Yu, Yijun; Zhang, Yu; Chen, Guorui; Watanabe, Kenji; Taniguchi, Takashi; Chen, Xian Hui; Wang, Feng; Zhang, Yuanbo

2017-10-11

Energy bandgap largely determines the optical and electronic properties of a semiconductor. Variable bandgap therefore makes versatile functionality possible in a single material. In layered material black phosphorus, the bandgap can be modulated by the number of layers; as a result, few-layer black phosphorus has discrete bandgap values that are relevant for optoelectronic applications in the spectral range from red, in monolayer, to mid-infrared in the bulk limit. Here, we further demonstrate continuous bandgap modulation by mechanical strain applied through flexible substrates. The strain-modulated bandgap significantly alters the density of thermally activated carriers; we for the first time observe a large piezo-resistive effect in black phosphorus field-effect transistors (FETs) at room temperature. The effect opens up opportunities for future development of electromechanical transducers based on black phosphorus, and we demonstrate an ultrasensitive strain gauge constructed from black phosphorus thin crystals.

Shear flow of dense granular materials near smooth walls. I. Shear localization and constitutive laws in the boundary region.

PubMed

Shojaaee, Zahra; Roux, Jean-Noël; Chevoir, François; Wolf, Dietrich E

2012-07-01

We report on a numerical study of the shear flow of a simple two-dimensional model of a granular material under controlled normal stress between two parallel smooth frictional walls moving with opposite velocities ± V. Discrete simulations, which are carried out with the contact dynamics method in dense assemblies of disks, reveal that, unlike rough walls made of strands of particles, smooth ones can lead to shear strain localization in the boundary layer. Specifically, we observe, for decreasing V, first a fluidlike regime (A), in which the whole granular layer is sheared, with a homogeneous strain rate except near the walls, then (B) a symmetric velocity profile with a solid block in the middle and strain localized near the walls, and finally (C) a state with broken symmetry in which the shear rate is confined to one boundary layer, while the bulk of the material moves together with the opposite wall. Both transitions are independent of system size and occur for specific values of V. Transient times are discussed. We show that the first transition, between regimes A and B, can be deduced from constitutive laws identified for the bulk material and the boundary layer, while the second one could be associated with an instability in the behavior of the boundary layer. The boundary zone constitutive law, however, is observed to depend on the state of the bulk material nearby.

[Screening and optimization of cholesterol conversion strain].

PubMed

Fan, Dan; Xiong, Bingjian; Pang, Cuiping; Zhu, Xiangdong

2014-10-04

Bacterial strain SE-1 capable of transforming cholesterol was isolated from soil and characterized. The transformation products were identified. Fermentation conditions were optimized for conversion. Cholesterol was used as sole carbon source to isolate strain SE-1. Morphology, physiological and biochemical characteristics of strain SE-1 were studied. 16S rRNA gene was sequenced and subjected to phylogenetic analysis. Fermentation supernatants were extracted with chloroform, the transformation products were analyzed by silica gel thin layer chromatography and Sephadex LH20. Their structures were identified by 1H-NMR and 13C-NMR. Fermentation medium including carbon and nitrogen, methods of adding substrates and fermentation conditions for Strain SE-1 were optimized. Strain SE-1 was a Gram-negative bacterium, exhibiting the highest homologs to Burkholderia cepacia based on the physiological analysis. The sequence analysis of 16S rRNA gene of SE-1 strain and comparison with related Burkholderia show that SE-1 strain was very close to B. cepacia (Genbank No. U96927). The similarity was 99%. The result of silica gel thin layer chromatography shows that strain SE-1 transformed cholesterol to two products, 7beta-hydroxycholesterol and the minor product was 7-oxocholesterol. The optimum culture conditions were: molasses 5%, (NH4 )2SO4 0.3%, 4% of inoculation, pH 7.5 and 36 degrees C. Under the optimum culture condition, the conversion rate reached 34.4% when concentration of cholesterol-Tween 80 was 1 g/L. Cholesterol 7beta-hydroxylation conversion rate under optimal conditions was improved by 20.8%. Strain SE-1 isolated from soil is capable of converting cholesterol at lab-scale.

Effect of Prestresses on the Dispersion of Quasi-Lamb Waves in the System Consisting of an Ideal Liquid Layer and a Compressible Elastic Layer

NASA Astrophysics Data System (ADS)

Bagno, A. M.

2017-03-01

The propagation of quasi-Lamb waves in a prestrained compressible elastic layer interacting with a layer of an ideal compressible fluid is studied. The three-dimensional equations of linearized elasticity and the assumption of finite strains for the elastic layer and the three-dimensional linearized Euler equations for the fluid are used. The dispersion curves for the quasi-Lamb modes are plotted over a wide frequency range. The effect of prestresses and the thickness of the elastic and liquid layers on the frequency spectrum of normal quasi-Lamb waves is analyzed. The localization properties of the lower quasi-Lamb modes in the elastic-fluid waveguides are studied. The numerical results are presented in the form of graphs and analyzed

Mobility and Device Applications of Heavily Doped Silicon and Strained SILICON(1-X) Germanium(x) Layers

NASA Astrophysics Data System (ADS)

Carns, Timothy Keith

With the advent of Si molecular beam epitaxy (Si -MBE), a significant amount of research has occurred to seek alternative high conductivity Si-based materials such as rm Si_{1-x}Ge_ {x} and delta-doped Si. These materials have brought improvements in device speeds and current drives with the added advantage of monolithic integration into Si VLSI circuits. The bulk of research in Si-based materials has been devoted to the implementation of strained rm Si_{1-x}Ge_{x} as the base layer of a rm Si_ {1-x}Ge_{x}/Si heterojunction bipolar transistor (HBT). Because of the valence band offset, the rm Si_{1-x}Ge _{x} layer can be heavily doped, leading to lower base sheet resistances and hence, improved speed performances. The Ge content in the base can also be graded to increase the drift field in the base. However, very few hole mobility measurements have been done in these strained layers, leading to limitations in device modeling and in understanding the transport behavior in this important material. In addition to rm Si_{1 -x}Ge_{x}, much potential also exists in using delta-doping in Si for improved conductivities over those of bulk Si. However, as of yet, delta-doped Si has received little attention. Therefore, this dissertation is dedicated to the investigation of both of these Si-based materials (strained rm Si_{1-x}Ge_{x } and delta-doped Si and rm Si_{1-x}Ge_ {x}) for the purpose of obtaining higher conductivities than comparably doped bulk Si. This work is divided into three parts to accomplish this objective. The first part is contained in Chapter 3 and is comprised of a comprehensive characterization of the hole mobility in compressively strained rm Si_{1 -x}Ge_{x}. Few results have been obtained prior to this research which has led to many inaccuracies in device modeling. The second part of this dissertation in Chapters 4 and 5 is devoted to the study of the mobility behavior in both boron and antimony delta-doped Si and rm Si_ {1-x}Ge_{x}. The important discovery of mobility and conductivity enhancement in coupled delta-doped layers is highlighted in Chapter 5. Finally, the third part of this work discusses the implementation of boron delta -doped layers in Si homojunction bipolar transistors and FETs. Chapter 6 includes the fabrication of the first coupled delta-doped base layer Si BJT, the first p-type Si delta-doped layer MESFET, the first coupled delta -doped layer FET, and the first SiGe delta -FET.

Strain-balanced InAs/GaSb type-II superlattice structures and photodiodes grown on InAs substrates by metalorganic chemical vapor deposition

NASA Astrophysics Data System (ADS)

Huang, Yong; Ryou, Jae-Hyun; Dupuis, Russell D.; Zuo, Daniel; Kesler, Benjamin; Chuang, Shun-Lien; Hu, Hefei; Kim, Kyou-Hyun; Ting Lu, Yen; Hsieh, K. C.; Zuo, Jian-Min

2011-07-01

We propose and demonstrate strain-balanced InAs/GaSb type-II superlattices (T2SLs) grown on InAs substrates employing GaAs-like interfacial (IF) layers by metalorganic chemical vapor deposition (MOCVD) for effective strain management, simplified growth scheme, improved materials crystalline quality, and reduced substrate absorption. The in-plane compressive strain from the GaSb layers in the T2SLs on the InAs was completely balanced by the GaAs-like IF layers formed by controlled precursor carry-over and anion exchange effects, avoiding the use of complicated IF layers and precursor switching schemes that were used for the MOCVD growth of T2SLs on GaSb. An infrared (IR) p-i-n photodiode structure with 320-period InAs/GaSb T2SLs on InAs was grown and the fabricated devices show improved performance characteristics with a peak responsivity of ˜1.9 A/W and a detectivity of ˜6.78 × 109 Jones at 8 μm at 78 K. In addition, the InAs buffer layer and substrate show a lower IR absorption coefficient than GaSb substrates in most of the mid- and long-IR spectral range.

Striped, honeycomb, and twisted moiré patterns in surface adsorption systems with highly degenerate commensurate ground states

NASA Astrophysics Data System (ADS)

Elder, K. R.; Achim, C. V.; Granato, E.; Ying, S. C.; Ala-Nissila, T.

2017-11-01

Atomistically thin adsorbate layers on surfaces with a lattice mismatch display complex spatial patterns and ordering due to strain-driven self-organization. In this work, a general formalism to model such ultrathin adsorption layers that properly takes into account the competition between strain and adhesion energy of the layers is presented. The model is based on the amplitude expansion of the two-dimensional phase field crystal (PFC) model, which retains atomistic length scales but allows relaxation of the layers at diffusive time scales. The specific systems considered here include cases where both the film and the adsorption potential can have either honeycomb (H) or triangular (T) symmetry. These systems include the so-called (1 ×1 ) , (√{3 }×√{3 }) R 30∘ , (2 ×2 ) , (√{7 }×√{7 }) R 19 .1∘ , and other higher order states that can contain a multitude of degenerate commensurate ground states. The relevant phase diagrams for many combinations of the H and T systems are mapped out as a function of adhesion strength and misfit strain. The coarsening patterns in some of these systems is also examined. The predictions are in good agreement with existing experimental data for selected strained ultrathin adsorption layers.

Stability of direct band gap under mechanical strains for monolayer MoS2, MoSe2, WS2 and WSe2

NASA Astrophysics Data System (ADS)

Deng, Shuo; Li, Lijie; Li, Min

2018-07-01

Single layer transition-metal dichalcogenides materials (MoS2, MoSe2, WS2 and WSe2) are investigated using the first-principles method with the emphasis on their responses to mechanical strains. All these materials display the direct band gap under a certain range of strains from compressive to tensile (stable range). We have found that this stable range is different for these materials. Through studying on their mechanical properties again using the first-principles approach, it is unveiled that this stable strain range is determined by the Young's modulus. More analysis on strains induced electronic band gap properties have also been conducted.

Strain and Structure Heterogeneity in MoS2 Atomic Layers Grown by Chemical Vapour Deposition

DTIC Science & Technology

2014-11-18

substrate and material. To better explain the experimental results and estimate the strain transferred to MoS2 layer under such tensile tests, a 3D... ACS Nano 7, 7126 7131 (2013). 29. He, K., Poole, C., Mak, K. F. & Shan, J. Experimental demonstration of continuous electronic structure tuning via...transition as it is thinned down from multi layer to monolayer, producing a significant enhancement of photoluminescence (PL) quantum yield as a result of the

Critical thickness and strain relaxation in high-misfit heteroepitaxial systems: PbTe1-xSex on PbSe (001)

NASA Astrophysics Data System (ADS)

Wiesauer, Karin; Springholz, G.

2004-06-01

Strain relaxation and misfit dislocation formation is investigated for the high-misfit PbTe1-xSex/PbSe (001) heteroepitaxial system in which the lattice mismatch varies from 0% to 5.5%. Because a two-dimensional (2D) layer growth prevails for all PbTe1-xSex ternary compositions, the lattice mismatch is relaxed purely by misfit dislocations. In addition, it is found that strain relaxation is not hindered by dislocation kinetics. Therefore, this material combination is an ideal model system for testing the equilibrium Frank van der Merwe and Matthews Blakeslee strain relaxation models. In our experiments, we find significantly lower values of the critical layer thickness as compared to the model predictions. This discrepancy is caused by the inappropriate description of the dislocation self-energies when the layer thickness becomes comparable to the dislocation core radius. To resolve this problem, a modified expression for the dislocation self-energy is proposed. The resulting theoretical critical thicknesses are in excellent agreement with the experimental data. In addition, a remarkable universal scaling behavior is found for the strain relaxation data. This underlines the breakdown of the current strain relaxation models.

Magnetostrictive GMR spin valves with composite FeGa/FeCo free layers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Luping; Institute of Materials Science, School of Materials Science and Engineering, Shanghai University, Shanghai 200072; Zhan, Qingfeng, E-mail: zhanqf@nimte.ac.cn, E-mail: runweili@nimte.ac.cn

2016-03-15

We have fabricated strain-sensitive spin valves on flexible substrates by utilizing the large magnetostrictive FeGa alloy to promote the strain sensitivity and the composite free layer of FeGa/FeCo to avoid the drastic reduction of giant magnetoresistance (GMR) ratio. This kind of spin valve (SV-FeGa/FeCo) displays a MR ratio about 5.9%, which is comparable to that of the conventional spin valve (SV-FeCo) with a single FeCo free layer. Different from the previously reported works on magnetostrictive spin valves, the SV-FeGa/FeCo displays an asymmetric strain dependent GMR behavior. Upon increasing the lateral strain, the MR ratio for the ascending branch decreases moremore » quickly than that for the descending branch, which is ascribed to the formation of a spiraling spin structure around the FeGa/FeCo interface under the combined influences of both magnetic field and mechanical strain. A strain sensitivity of GF = 7.2 was achieved at a magnetic bias field of -30 Oe in flexible SV-FeGa/FeCo, which is significantly larger than that of SV-FeCo.« less

Usefulness of layer-specific strain for identifying complex CAD and predicting the severity of coronary lesions in patients with non-ST-segment elevation acute coronary syndrome: Compared with Syntax score.

PubMed

Zhang, Li; Wu, Wei-Chun; Ma, Hong; Wang, Hao

2016-11-15

Layer-specific strain allows the assessment of the function of every layer of myocardium. To evaluate the changes of non-ST-segment elevation acute coronary syndrome(NSTE-ACS) patients with and without complex coronary artery disease(CAD) by layer-specific strain and determine if myocardial strain can identify complex CAD and assess the severity of coronary lesions as defined by Syntax score (SS). A total of 139 patients undergoing coronary angiography due to suspected NSTE-ACS were prospectively enrolled. Echocardiography was performed 1h before angiography. Global longitudinal strain (GLS), territorial longitudinal strain (TLS), global circumferential strain (GCS) and territorial circumferential strain (TCS) of the three layers of LV wall were assessed by two-dimensional (2D) speckle tracking echocardiography (STE) with layer-specific myocardial deformation quantitative analysis based on the perfusion territories of the three major coronary arteries in an 18-segment model of LV. SS was used for predicting the severity of coronary lesions in patients with complex CAD. 78 had complex CAD, 32 had 1- or 2-vessel disease and 29 had no significant coronary stenosis confirmed by coronary angiography. According to SS value, 78 complex CAD subjects were subdivided into three groups, 24 in group SS 1 (SS≤22), 26 in group SS 2 (SS 23-32) and 28 in group SS 3 (SS≥33). Compared to the other two groups without complex CAD, patients with NSTE-ACS due to complex CAD had worse function in all 3 myocardial layers assessed by GLS, TLS, GCS and TCS. Endocardial GLS and TLS (all, P<0.01) were most affected. The absolute differences between endocardial and epicardial GLS and TLS were lower in magnitude in patients with complex CAD than in those without (all, P<0.001), and the more complex of coronary lesion, the lower magnitude of the parameters(all, P<0.001). Endocardial GLS and TLS were closely correlated with SS value(r=-0.751 and r=-0.753, respectively; P<0.001). By receiver-operating characteristic curve analysis, endocardial GLS and TLS demonstrated the highest area under curve, showing better diagnostic accuracy (endocardial GLS: value<-21.35% had 72% sensitivity, 84% specificity and area under the curve ¼0.846; endocardial TLS: value<-20.15% had 72% sensitivity, 88% specificity and area under the curve ¼0.852) than GCS, TCS, mid-myocardial and epicardial GLS, and TLS(all, P<0.05). Strains, particularly endocardial GLS and TLS measurement by 2DSTE might enable a non-invasive method to identify complex CAD and predict the severity of coronary lesions in patients with NSTE-ACS. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.

Fully integrated carbon nanotube composite thin film strain sensors on flexible substrates for structural health monitoring

NASA Astrophysics Data System (ADS)

Burton, A. R.; Lynch, J. P.; Kurata, M.; Law, K. H.

2017-09-01

Multifunctional thin film materials have opened many opportunities for novel sensing strategies for structural health monitoring. While past work has established methods of optimizing multifunctional materials to exhibit sensing properties, comparatively less work has focused on their integration into fully functional sensing systems capable of being deployed in the field. This study focuses on the advancement of a scalable fabrication process for the integration of multifunctional thin films into a fully integrated sensing system. This is achieved through the development of an optimized fabrication process that can create a broad range of sensing systems using multifunctional materials. A layer-by-layer deposited multifunctional composite consisting of single walled carbon nanotubes (SWNT) in a polyvinyl alcohol and polysodium-4-styrene sulfonate matrix are incorporated with a lithography process to produce a fully integrated sensing system deposited on a flexible substrate. To illustrate the process, a strain sensing platform consisting of a patterned SWNT-composite thin film as a strain-sensitive element within an amplified Wheatstone bridge sensing circuit is presented. Strain sensing is selected because it presents many of the design and processing challenges that are core to patterning multifunctional thin film materials into sensing systems. Strain sensors fabricated on a flexible polyimide substrate are experimentally tested under cyclic loading using standard four-point bending coupons and a partial-scale steel frame assembly under lateral loading. The study reveals the material process is highly repeatable to produce fully integrated strain sensors with linearity and sensitivity exceeding 0.99 and 5 {{V}}/{ε }, respectively. The thin film strain sensors are robust and are capable of high strain measurements beyond 3000 μ {ε }.

A Model of the THUNDER Actuator

NASA Technical Reports Server (NTRS)

Curtis, Alan R. D.

1997-01-01

A THUNDER actuator is a composite of three thin layers, a metal base, a piezoelectric wafer and a metal top cover, bonded together under pressure and at high temperature with the LaRC SI polyimid adhesive. When a voltage is applied between the metal layers across the PZT the actuator will bend and can generate a force. This document develops and describes an analytical model the transduction properties of THUNDER actuators. The model development is divided into three sections. First, a static model is described that relates internal stresses and strains and external displacements to the thermal pre-stress and applied voltage. Second, a dynamic energy based model is described that allows calculation of the resonance frequencies, developed force and electrical input impedance. Finally, a fully coupled electro-mechanical transducer model is described. The model development proceeds by assuming that both the thermal pre-stress and the piezoelectric actuation cause the actuator to deform in a pure bend in a single plane. It is useful to think of this as a two step process, the actuator is held flat, differential stresses induce a bending moment, the actuator is released and it bends. The thermal pre-stress is caused by the different amounts that the constituent layers shrink due to their different coefficients of thermal expansion. The adhesive between layers sets at a high temperature and as the actuator cools, the metal layers shrink more than the PZT. The PZT layer is put into compression while the metal layers are in tension. The piezoelectric actuation has a similar effect. An applied voltage causes the PZT layer to strain, which in turn strains the two metal layers. If the PZT layer expands it will put the metal layers into tension and PZT layer into compression. In both cases, if shear force effects are neglected, the actuator assembly will experience a uniform in-plane strain. As the materials each have a different elastic modulus, different stresses will develop in each layer and these stresses will induce a bending moment. When the actuator is released from its flat configuration, the differential stresses are relieved as the actuator bends.

Whole-Genome Sequence of Aeromonas hydrophila Strain AH-1 (Serotype O11)

PubMed Central

Forn-Cuní, Gabriel; Tomás, Juan M.

2016-01-01

Aeromonas hydrophila is an emerging pathogen of aquatic and terrestrial animals, including humans. Here, we report the whole-genome sequence of the septicemic A. hydrophila AH-1 strain, belonging to the serotype O11, and the first mesophilic Aeromonas with surface layer (S-layer) to be sequenced. PMID:27587829

Applications of 4-state nanomagnetic logic using multiferroic nanomagnets possessing biaxial magnetocrystalline anisotropy and experiments on 2-state multiferroic nanomagnetic logic

NASA Astrophysics Data System (ADS)

D'Souza, Noel Michael

Nanomagnetic logic, incorporating logic bits in the magnetization orientations of single-domain nanomagnets, has garnered attention as an alternative to transistor-based logic due to its non-volatility and unprecedented energy-efficiency. The energy efficiency of this scheme is determined by the method used to flip the magnetization orientations of the nanomagnets in response to one or more inputs and produce the desired output. Unfortunately, the large dissipative losses that occur when nanomagnets are switched with a magnetic field or spin-transfer-torque inhibit the promised energy-efficiency. Another technique offering superior energy efficiency, "straintronics", involves the application of a voltage to a piezoelectric layer to generate a strain which is transferred to an elastically coupled magnetrostrictive layer, causing magnetization rotation. The functionality of this scheme can be enhanced further by introducing magnetocrystalline anisotropy in the magnetostrictive layer, thereby generating four stable magnetization states (instead of the two stable directions produced by shape anisotropy in ellipsoidal nanomagnets). Numerical simulations were performed to implement a low-power universal logic gate (NOR) using such 4-state magnetostrictive/piezoelectric nanomagnets (Ni/PZT) by clocking the piezoelectric layer with a small electrostatic potential (˜0.2 V) to switch the magnetization of the magnetic layer. Unidirectional and reliable logic propagation in this system was also demonstrated theoretically. Besides doubling the logic density (4-state versus 2-state) for logic applications, these four-state nanomagnets can be exploited for higher order applications such as image reconstruction and recognition in the presence of noise, associative memory and neuromorphic computing. Experimental work in strain-based switching has been limited to magnets that are multi-domain or magnets where strain moves domain walls. In this work, we also demonstrate strain-based switching in 2-state single-domain ellipsoidal magnetostrictive nanomagnets of lateral dimensions ˜200 nm fabricated on a piezoelectric substrate (PMN-PT) and studied using Magnetic Force Microscopy (MFM). A nanomagnetic Boolean NOT gate and unidirectional bit information propagation through a finite chain of dipole-coupled nanomagnets are also shown through strain-based "clocking". This is the first experimental demonstration of strain-based switching in nanomagnets and clocking of nanomagnetic logic (Boolean NOT gate), as well as logic propagation in an array of nanomagnets.

Conduction- and Valence-Band Energies in Bulk InAs(1-x)Sb(x) and Type II InAs(1-x) Sb(x)/InAs Strained-Layer Superlattices

DTIC Science & Technology

2013-03-08

tions in the studied SLS structures . The fit of the dependence of the valence- band energy of unstrained InAs1!xSbx on the composition x with a... band . STRUCTURES Bulk InAsSb epilayers on metamorphic buffers and InAsSb/InAs strained-layer superlattices (SLS) were grown on GaSb substrates by solid...meV in InAs and Ev = 0 meV in InSb. For InAsSb with 22.5% Sb grown on GaSb , an unstrained valence- band energy of Ev = !457 meV was obtained. For the

Excitonic fine-structure splitting in telecom-wavelength InAs/GaAs quantum dots: Statistical distribution and height-dependence

DOE Office of Scientific and Technical Information (OSTI.GOV)

Goldmann, Elias, E-mail: goldmann@itp.uni-bremen.de; Barthel, Stefan; Florian, Matthias

The variation of the excitonic fine-structure splitting is studied for semiconductor quantum dots under the influence of a strain-reducing layer, utilized to shift the emission wavelength of the excitonic transition into the telecom-wavelength regime of 1.3–1.5 μm. By means of a sp{sup 3}s{sup *}-tight-binding model and configuration interaction, we calculate wavelength shifts and fine-structure splittings for various quantum dot geometries. We find the splittings remaining small and even decreasing with strain-reducing layer composition for quantum dots with large height. Combined with an observed increased emission efficiency, the applicability for generation of entanglement photons is persistent.

A mechanistic insight into the mechanical role of the stratum corneum during stretching and compression of the skin.

PubMed

Leyva-Mendivil, Maria F; Page, Anton; Bressloff, Neil W; Limbert, Georges

2015-09-01

The study of skin biophysics has largely been driven by consumer goods, biomedical and cosmetic industries which aim to design products that efficiently interact with the skin and/or modify its biophysical properties for health or cosmetic benefits. The skin is a hierarchical biological structure featuring several layers with their own distinct geometry and mechanical properties. Up to now, no computational models of the skin have simultaneously accounted for these geometrical and material characteristics to study their complex biomechanical interactions under particular macroscopic deformation modes. The goal of this study was, therefore, to develop a robust methodology combining histological sections of human skin, image-processing and finite element techniques to address fundamental questions about skin mechanics and, more particularly, about how macroscopic strains are transmitted and modulated through the epidermis and dermis. The work hypothesis was that, as skin deforms under macroscopic loads, the stratum corneum does not experience significant strains but rather folds/unfolds during skin extension/compression. A sample of fresh human mid-back skin was processed for wax histology. Sections were stained and photographed by optical microscopy. The multiple images were stitched together to produce a larger region of interest and segmented to extract the geometry of the stratum corneum, viable epidermis and dermis. From the segmented structures a 2D finite element mesh of the skin composite model was created and geometrically non-linear plane-strain finite element analyses were conducted to study the sensitivity of the model to variations in mechanical properties. The hybrid experimental-computational methodology has offered valuable insights into the simulated mechanics of the skin, and that of the stratum corneum in particular, by providing qualitative and quantitative information on strain magnitude and distribution. Through a complex non-linear interplay, the geometry and mechanical characteristics of the skin layers (and their relative balance), play a critical role in conditioning the skin mechanical response to macroscopic in-plane compression and extension. Topographical features of the skin surface such as furrows were shown to act as an efficient means to deflect, convert and redistribute strain-and so stress-within the stratum corneum, viable epidermis and dermis. Strain reduction and amplification phenomena were also observed and quantified. Despite the small thickness of the stratum corneum, its Young׳s modulus has a significant effect not only on the strain magnitude and directions within the stratum corneum layer but also on those of the underlying layers. This effect is reflected in the deformed shape of the skin surface in simulated compression and extension and is intrinsically linked to the rather complex geometrical characteristics of each skin layer. Moreover, if the Young׳s modulus of the viable epidermis is assumed to be reduced by a factor 12, the area of skin folding is likely to increase under skin compression. These results should be considered in the light of published computational models of the skin which, up to now, have ignored these characteristics. Copyright © 2015 Elsevier Ltd. All rights reserved.

Polar Cation Ordering: A Route to Introducing >10% Bond Strain Into Layered Oxide Films

DOE PAGES

Nelson-Cheeseman, Brittany B.; Zhou, Hua; Balachandran, Prasanna V.; ...

2014-09-05

The 3d transition metal (M) perovskite oxides exhibit a remarkable array of properties, including novel forms of superconductivity, magnetism and multiferroicity. Strain can have a profound effect on many of these properties. This is due to the localized nature of the M 3d orbitals, where even small changes in the M–O bond lengths and M–O–M bond angles produced by strain can be used to tune the 3d– O 2p hybridization, creating large changes in electronic structure. We present a new route to strain the M–O bonds in epitaxial two-dimensional perovskite films by tailoring local electrostatic dipolar interactions within every formulamore » unit via atomic layer-by-layer synthesis. The response of the O anions to the resulting dipole electric fields distorts the M–O bonds by more than 10%, without changing substrate strain or chemical composition. We found that this distortion is largest for the apical oxygen atoms (O ap), and alters the transition metal valence state via self-doping without chemical substitution.« less

3D mechanical stratigraphy of a deformed multi-layer: Linking sedimentary architecture and strain partitioning

NASA Astrophysics Data System (ADS)

Cawood, Adam J.; Bond, Clare E.

2018-01-01

Stratigraphic influence on structural style and strain distribution in deformed sedimentary sequences is well established, in models of 2D mechanical stratigraphy. In this study we attempt to refine existing models of stratigraphic-structure interaction by examining outcrop scale 3D variations in sedimentary architecture and the effects on subsequent deformation. At Monkstone Point, Pembrokeshire, SW Wales, digital mapping and virtual scanline data from a high resolution virtual outcrop have been combined with field observations, sedimentary logs and thin section analysis. Results show that significant variation in strain partitioning is controlled by changes, at a scale of tens of metres, in sedimentary architecture within Upper Carboniferous fluvio-deltaic deposits. Coupled vs uncoupled deformation of the sequence is defined by the composition and lateral continuity of mechanical units and unit interfaces. Where the sedimentary sequence is characterized by gradational changes in composition and grain size, we find that deformation structures are best characterized by patterns of distributed strain. In contrast, distinct compositional changes vertically and in laterally equivalent deposits results in highly partitioned deformation and strain. The mechanical stratigraphy of the study area is inherently 3D in nature, due to lateral and vertical compositional variability. Consideration should be given to 3D variations in mechanical stratigraphy, such as those outlined here, when predicting subsurface deformation in multi-layers.

Comparative study on hydrostatic strain, stress and dislocation density of Al{sub 0.3}Ga{sub 0.7}N/GaN heterostructure before and after a-Si{sub 3}N{sub 4} passivation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dinara, Syed Mukulika, E-mail: smdinara.iit@gmail.com; Jana, Sanjay Kr.; Mukhopadhyay, Partha

2015-08-28

The hydrostatic strain, stress and dislocation densities were comparatively analyzed before and after passivation of amorphous silicon nitride (a-Si{sub 3}N{sub 4}) layer on Al{sub 0.3}Ga{sub 0.7}N/GaN heterostructure by nondestructive high resolution x-ray diffraction (HRXRD) technique. The crystalline quality, in-plane and out-of plane strain were evaluated from triple-axis (TA) (ω-2θ) diffraction profile across the (002) reflection plane and double-axis (DA) (ω-2θ) glancing incidence (GI) diffraction profile across (105) reflection plane. The hydrostatic strain and stress of Al{sub 0.3}Ga{sub 0.7}N barrier layer were increased significantly after passivation and both are tensile in nature. The dislocation density of GaN was also analyzed andmore » no significant change was observed after passivation of the heterostructure. The crystalline quality was not degraded after passivation on the heterostructure confirmed by the full-width-half-maximum (FWHM) analysis.« less

Probing the prodigious strain fringes from Lourdes

NASA Astrophysics Data System (ADS)

Aerden, Domingo G. A. M.; Sayab, Mohammad

2017-12-01

We investigate the kinematics of classic sigmoidal strain fringes from Lourdes (France) and review previous genetic models, strain methods and strain rates for these microstructures. Displacement controlled quartz and calcite fibers within the fringes yield an average strain of 195% with the technique of Ramsay and Huber (1983). This agrees well with strains measured from boudinaged pyrite layers and calcite veins in the same rocks, but conflicts with ca. ∼675% strain in previous analogue models for the studied strain fringes produced by progressive simple shear. We show that the detailed geometry and orientation of fiber patterns are insufficiently explained by simple shear but imply two successive, differently oriented strain fields. Although all strain fringes have the same overall asymmetry, considerable morphological variation resulted from different amounts of rotation of pyrite grains and fringes. Minor rotation led to sharply kinked fibers that record a ca. 70° rotation of the kinematic frame. Larger (up to 145°) rotations, accommodated by antithetic sliding on pyrite-fringe contacts, produced more strongly and smoothly curved fibers. Combined with published Rb-Sr ages for the studied microstructures, our new strain data indicate an average strain rate of 1.41 10-15 s-1 during ca. 37 Myr. continuous growth.

Computational modelling of large deformations in layered-silicate/PET nanocomposites near the glass transition

NASA Astrophysics Data System (ADS)

Figiel, Łukasz; Dunne, Fionn P. E.; Buckley, C. Paul

2010-01-01

Layered-silicate nanoparticles offer a cost-effective reinforcement for thermoplastics. Computational modelling has been employed to study large deformations in layered-silicate/poly(ethylene terephthalate) (PET) nanocomposites near the glass transition, as would be experienced during industrial forming processes such as thermoforming or injection stretch blow moulding. Non-linear numerical modelling was applied, to predict the macroscopic large deformation behaviour, with morphology evolution and deformation occurring at the microscopic level, using the representative volume element (RVE) approach. A physically based elasto-viscoplastic constitutive model, describing the behaviour of the PET matrix within the RVE, was numerically implemented into a finite element solver (ABAQUS) using an UMAT subroutine. The implementation was designed to be robust, for accommodating large rotations and stretches of the matrix local to, and between, the nanoparticles. The nanocomposite morphology was reconstructed at the RVE level using a Monte-Carlo-based algorithm that placed straight, high-aspect ratio particles according to the specified orientation and volume fraction, with the assumption of periodicity. Computational experiments using this methodology enabled prediction of the strain-stiffening behaviour of the nanocomposite, observed experimentally, as functions of strain, strain rate, temperature and particle volume fraction. These results revealed the probable origins of the enhanced strain stiffening observed: (a) evolution of the morphology (through particle re-orientation) and (b) early onset of stress-induced pre-crystallization (and hence lock-up of viscous flow), triggered by the presence of particles. The computational model enabled prediction of the effects of process parameters (strain rate, temperature) on evolution of the morphology, and hence on the end-use properties.

Infrared fingerprints of few-layer black phosphorus.

PubMed

Zhang, Guowei; Huang, Shenyang; Chaves, Andrey; Song, Chaoyu; Özçelik, V Ongun; Low, Tony; Yan, Hugen

2017-01-06

Black phosphorus is an infrared layered material. Its bandgap complements other widely studied two-dimensional materials: zero-gap graphene and visible/near-infrared gap transition metal dichalcogenides. Although highly desirable, a comprehensive infrared characterization is still lacking. Here we report a systematic infrared study of mechanically exfoliated few-layer black phosphorus, with thickness ranging from 2 to 15 layers and photon energy spanning from 0.25 to 1.36 eV. Each few-layer black phosphorus exhibits a thickness-dependent unique infrared spectrum with a series of absorption resonances, which reveals the underlying electronic structure evolution and serves as its infrared fingerprints. Surprisingly, unexpected absorption features, which are associated with the forbidden optical transitions, have been observed. Furthermore, we unambiguously demonstrate that controllable uniaxial strain can be used as a convenient and effective approach to tune the electronic structure of few-layer black phosphorus. Our study paves the way for black phosphorus applications in infrared photonics and optoelectronics.

Hydrogen uptake causes molecular "avalanches" in palladium | Argonne

Science.gov Websites

experimental and calculated strain distributions in the hydrogen-poor phase. The strains are consistent with a trapped hydrogen-rich surface layer. Middle: Comparison between experimental and calculated strain transformation. Comparison between experimental and calculated strain distributions in the hydrogen-poor phase

Mechanical Flexibility of Zinc Oxide Thin-Film Transistors Prepared by Transfer Printing Method

NASA Astrophysics Data System (ADS)

Eun, K. T.; Hwang, W. J.; Sharma, B. K.; Ahn, J. H.; Lee, Y. K.; Choa, S. H.

In the present study, we demonstrate the performance of Zinc oxide thin film transistors (ZnO TFTs) array subjected to the strain under high bending test and the reliability of TFTs was confirmed for the bending fatigue test of 2000 cycles. Initially, ZnO TFTs were fabricated on Si substrate and subsequently transferred on flexible PET substrate using transfer printing process. It was observed that when the bending radius reached ≥ 11 mm then cracks start to initiate first at SiO2 bridges, acting as interconnecting layers among individual TFT. Whatever the strain is applied to the devices, it is almost equivalently adopted by the SiO2 bridges, as they are relatively weak compared to rest of the part. The initial cracking of destructed SiO2 bridge leads to the secondary cracks to the ITO electrodes upon further increment of bending radius. Numerical simulation suggested that the strain of SiO2 layer reached to fracture level of 0.55% which was concentrated at the edge of SiO2 bridge layer. It also suggests that the round shape of SiO2 bridge can be more fruitful to compensate the stress concentration and to prevent failure of device.

The role of SiGe buffer in growth and relaxation of Ge on free-standing Si(001) nano-pillars.

PubMed

Zaumseil, P; Kozlowski, G; Schubert, M A; Yamamoto, Y; Bauer, J; Schülli, T U; Tillack, B; Schroeder, T

2012-09-07

We study the growth and relaxation processes of Ge nano-clusters selectively grown by chemical vapor deposition on free-standing 90 nm wide Si(001) nano-pillars with a thin Si(0.23)Ge(0.77) buffer layer. We found that the dome-shaped SiGe layer with a height of about 28 nm as well as the Ge dot deposited on top of it partially relaxes, mainly by elastic lattice bending. The Si nano-pillar shows a clear compliance behavior-an elastic response of the substrate on the growing film-with the tensile strained top part of the pillar. Additional annealing at 800 °C leads to the generation of misfit dislocation and reduces the compliance effect significantly. This example demonstrates that despite the compressive strain generated due to the surrounding SiO(2) growth mask it is possible to realize an overall tensile strain in the Si nano-pillar and following a compliant substrate effect by using a SiGe buffer layer. We further show that the SiGe buffer is able to improve the structural quality of the Ge nano-dot.

Heat-Assisted Multiferroic Solid-State Memory

PubMed Central

2017-01-01

A heat-assisted multiferroic solid-state memory design is proposed and analysed, based on a PbNbZrSnTiO3 antiferroelectric layer and Ni81Fe19 magnetic free layer. Information is stored as magnetisation direction in the free layer of a magnetic tunnel junction element. The bit writing process is contactless and relies on triggering thermally activated magnetisation switching of the free layer towards a strain-induced anisotropy easy axis. A stress is generated using the antiferroelectric layer by voltage-induced antiferroelectric to ferroelectric phase change, and this is transmitted to the magnetic free layer by strain-mediated coupling. The thermally activated strain-induced magnetisation switching is analysed here using a three-dimensional, temperature-dependent magnetisation dynamics model, based on simultaneous evaluation of the stochastic Landau-Lifshitz-Bloch equation and heat flow equation, together with stochastic thermal fields and magnetoelastic contributions. The magnetisation switching probability is calculated as a function of stress magnitude and maximum heat pulse temperature. An operating region is identified, where magnetisation switching always occurs, with stress values ranging from 80 to 180 MPa, and maximum temperatures normalised to the Curie temperature ranging from 0.65 to 0.99. PMID:28841185

Heat-Assisted Multiferroic Solid-State Memory.

PubMed

Lepadatu, Serban; Vopson, Melvin M

2017-08-25

A heat-assisted multiferroic solid-state memory design is proposed and analysed, based on a PbNbZrSnTiO₃ antiferroelectric layer and Ni 81 Fe 19 magnetic free layer. Information is stored as magnetisation direction in the free layer of a magnetic tunnel junction element. The bit writing process is contactless and relies on triggering thermally activated magnetisation switching of the free layer towards a strain-induced anisotropy easy axis. A stress is generated using the antiferroelectric layer by voltage-induced antiferroelectric to ferroelectric phase change, and this is transmitted to the magnetic free layer by strain-mediated coupling. The thermally activated strain-induced magnetisation switching is analysed here using a three-dimensional, temperature-dependent magnetisation dynamics model, based on simultaneous evaluation of the stochastic Landau-Lifshitz-Bloch equation and heat flow equation, together with stochastic thermal fields and magnetoelastic contributions. The magnetisation switching probability is calculated as a function of stress magnitude and maximum heat pulse temperature. An operating region is identified, where magnetisation switching always occurs, with stress values ranging from 80 to 180 MPa, and maximum temperatures normalised to the Curie temperature ranging from 0.65 to 0.99.

Amplicon Sequencing of the slpH Locus Permits Culture-Independent Strain Typing of Lactobacillus helveticus in Dairy Products

PubMed Central

Moser, Aline; Wüthrich, Daniel; Bruggmann, Rémy; Eugster-Meier, Elisabeth; Meile, Leo; Irmler, Stefan

2017-01-01

The advent of massive parallel sequencing technologies has opened up possibilities for the study of the bacterial diversity of ecosystems without the need for enrichment or single strain isolation. By exploiting 78 genome data-sets from Lactobacillus helveticus strains, we found that the slpH locus that encodes a putative surface layer protein displays sufficient genetic heterogeneity to be a suitable target for strain typing. Based on high-throughput slpH gene sequencing and the detection of single-base DNA sequence variations, we established a culture-independent method to assess the biodiversity of the L. helveticus strains present in fermented dairy food. When we applied the method to study the L. helveticus strain composition in 15 natural whey cultures (NWCs) that were collected at different Gruyère, a protected designation of origin (PDO) production facilities, we detected a total of 10 sequence types (STs). In addition, we monitored the development of a three-strain mix in raclette cheese for 17 weeks. PMID:28775722

Ultralow threading dislocation density in GaN epilayer on near-strain-free GaN compliant buffer layer and its applications in hetero-epitaxial LEDs.

PubMed

Shih, Huan-Yu; Shiojiri, Makoto; Chen, Ching-Hsiang; Yu, Sheng-Fu; Ko, Chung-Ting; Yang, Jer-Ren; Lin, Ray-Ming; Chen, Miin-Jang

2015-09-02

High threading dislocation (TD) density in GaN-based devices is a long unresolved problem because of the large lattice mismatch between GaN and the substrate, which causes a major obstacle for the further improvement of next-generation high-efficiency solid-state lighting and high-power electronics. Here, we report InGaN/GaN LEDs with ultralow TD density and improved efficiency on a sapphire substrate, on which a near strain-free GaN compliant buffer layer was grown by remote plasma atomic layer deposition. This "compliant" buffer layer is capable of relaxing strain due to the absorption of misfit dislocations in a region within ~10 nm from the interface, leading to a high-quality overlying GaN epilayer with an unusual TD density as low as 2.2 × 10(5) cm(-2). In addition, this GaN compliant buffer layer exhibits excellent uniformity up to a 6" wafer, revealing a promising means to realize large-area GaN hetero-epitaxy for efficient LEDs and high-power transistors.

Optoelectronics of supported and suspended 2D semiconductors

NASA Astrophysics Data System (ADS)

Bolotin, Kirill

2014-03-01

Two-dimensional semiconductors, materials such monolayer molybdenum disulfide (MoS2) are characterized by strong spin-orbit and electron-electron interactions. However, both electronic and optoelectronic properties of these materials are dominated by disorder-related scattering. In this talk, we investigate approaches to reduce scattering and explore physical phenomena arising in intrinsic 2D semiconductors. First, we discuss fabrication of pristine suspended monolayer MoS2 and use photocurrent spectroscopy measurements to study excitons in this material. We observe band-edge and van Hove singularity excitons and estimate their binding energies. Furthermore, we study dissociation of these excitons and uncover the mechanism of their contribution to photoresponse of MoS2. Second, we study strain-induced modification of bandstructures of 2D semiconductors. With increasing strain, we find large and controllable band gap reduction of both single- and bi-layer MoS2. We also detect experimental signatures consistent with strain-induced transition from direct to indirect band gap in monolayer MoS2. Finally, we fabricate heterostructures of dissimilar 2D semiconductors and study their photoresponse. For closely spaced 2D semiconductors we detect charge transfer, while for separation larger than 10nm we observe Forster-like energy transfer between excitations in different layers.

Synthesis of Germanium-Tin Alloys by Ion Implantation and Pulsed Laser Melting: Towards a Group IV Direct Band Gap Semiconductor

NASA Astrophysics Data System (ADS)

Tran, Tuan Thien

The germanium-tin (Ge1-xSnx) material system is expected to be a direct bandgap group IV semiconductor at a Sn content of 6.5-11 at.%. Hence there has been much interest in preparing such alloys since they are compatible with silicon and they raise the possibility of integrating photonics functionality into silicon circuitry. However, the maximum solid solubility of Sn in Ge is around 0.5 at.% and non-equilibrium deposition techniques such as molecular beam epitaxy or chemical vapour deposition have been used to achieve the desired high Sn concentrations. In this PhD work, the combination of ion implantation and pulsed laser melting (PLM) is demonstrated to be an alternative promising method to produce a highly Sn concentrated alloy with good crystal quality. In initial studies, it was shown that 100 keV Sn implants followed by PLM produced high quality alloys with up to 6.2 at.%Sn but above these Sn concentrations the crystal quality was poor. The structural properties of the ≤6.2 at.% alloys such as soluble Sn concentration, strain distribution and crystal quality have been characterised by Rutherford backscattering spectrometry (RBS), Raman spectroscopy, X-ray diffraction (XRD) and transmission electron microscopy (TEM). The optical properties and electronic band structure have been studied by spectroscopic ellipsometry. The introduction of substitutional Sn into Ge is shown to either induce a splitting between light and heavy hole subbands or lower the conduction band at the Gamma valley. However, at higher implant doses needed to achieve >6.2 at.% Sn, ion-beam-induced porosity in Ge starts to occur, which drastically reduces the retained amount of the implanted Sn and such microstructure also hinders good crystallisation of the material during PLM. To solve this problem, it was shown that a nanometer thick SiO2 layer deposited on the Ge substrate prior to the implantation can largely eliminate the formation of porosity. This capping SiO2 layer also helps to increase the retained Sn concentration up to 15 at.% after implantation, as well as significantly improving the crystal quality of the Ge-Sn layer after PLM. With the use of the capping layer, a good quality Ge-Sn layer with 9 at.% Sn has been achieved using Sn implants at an energy of 120 keV. However, the thin film alloys produced by 100 keV or 120 keV Sn implantation and PLM are shown to contain compressive strain as a result of the large lattice mismatch between Ge and high Sn content alloys. Such strain compromises the tendency towards a direct bandgap material and hence strain relaxation is highly desirable. A thermal stability study showed that the thin film strained material is metastable up to 400°C, but thereafter Sn comes out of solution and diffuses to the material surface. To investigate a possible pathway to the synthesis of strain-relaxed material, a higher Sn implant energy of 350 keV was used to produce thicker alloy layers. XRD/reciprocal space mapping showed that this thicker alloy material is largely relaxed after PLM, which is beneficial for the direct band gap transition and solves the trade-off between higher Sn concentration and compressive strain. However, RBS indicates a sub-surface band of disorder which suggested a possible mechanism for the strain relaxation. Indeed, TEM examination of such material showed the material relaxed via the generation of non-equilibrium threading defects. Despite such defects, a PL study of this relaxed material found photon emission at a wavelength of 2150 nm for 6-9 at.% Sn alloys. However, the intensity of the emission was variable across different Sn content alloys, presumably as a result of the threading defects. A possible pathway to removing such defects is given that may enable both photodetectors and lasers to be fabricated at wavelengths above 2mum.

Nanometer-Scale Epitaxial Strain Release in Perovskite Heterostructures Using 'SrAlOx' Sliding Buffer Layers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bell, Christopher

2011-08-11

We demonstrate the strain release of LaAlO{sub 3} epitaxial film on SrTiO{sub 3} (001) by inserting ultra-thin 'SrAlO{sub x}' buffer layers. Although SrAlO{sub x} is not a perovskite, nor stable as a single phase in bulk, epitaxy stabilizes the perovskite structure up to a thickness of 2 unit cells (uc). At a critical thickness of 3 uc of SrAlO{sub x}, the interlayer acts as a sliding buffer layer, and abruptly relieves the lattice mismatch between the LaAlO{sub 3} filmand the SrTiO{sub 3} substrate, while maintaining crystallinity. This technique may provide a general approach for strain relaxation of perovskite film farmore » below the thermodynamic critical thickness. A central issue in heteroepitaxial filmgrowth is the inevitable difference in lattice constants between the filmand substrate. Due to this lattice mismatch, thin film are subjected to microstructural strain, which can have a significan effect on the filmproperties. This challenge is especially prominent in the rapidly developing fiel of oxide electronics, where much interest is focused on incorporating the emergent physical properties of oxides in devices. Although strain can be used to great effect to engineer unusual ground states, it is often deleterious for bulk first-orde phase transitions, which are suppressed by the strain and symmetry constraints of the substrate. While there are some reports discussing the control of the lattice mismatch in oxides using thick buffer layers, the materials choice, lattice-tunable range, and control of misfit dislocations are still limited. In this Letter, we report the fabrication of strain-relaxed LaAlO{sub 3} (LAO) thin film on SrTiO{sub 3} (STO) (001) using very thin 'SrAlO{sub x}' (SAO) buffer layers. Whereas for 1 or 2 pseudo-perovskite unit cells (uc) of SAO, the subsequent LAO filmis strained to the substrate, at a critical thickness of 3 uc the SAO interlayer abruptly relieves the lattice mismatch between the LAO and the STO, although maintaining the relative crystalline orientation between the filmand the substrate. For 4 uc or greater, the perovskite epitaxial template is lost and the LAO filmis amorphous. These results suggest that metastable interlayers can be used for strain release on the nanometer scale.« less

A Supercompressible, Elastic, and Bendable Carbon Aerogel with Ultrasensitive Detection Limits for Compression Strain, Pressure, and Bending Angle.

PubMed

Zhuo, Hao; Hu, Yijie; Tong, Xing; Chen, Zehong; Zhong, Linxin; Lai, Haihong; Liu, Linxiang; Jing, Shuangshuang; Liu, Qingzhong; Liu, Chuanfu; Peng, Xinwen; Sun, Runcang

2018-05-01

Ultralight and compressible carbon materials have promising applications in strain and pressure detection. However, it is still difficult to prepare carbon materials with supercompressibility, elasticity, stable strain-electrical signal response, and ultrasensitive detection limits, due to the challenge in structural regulation. Herein, a new strategy to prepare a reduced graphene oxide (rGO)-based lamellar carbon aerogels with unexpected and integrated performances by designing wave-shape rGO layers and enhancing the interaction among the rGO layers is demonstrated. Addition of cellulose nanocrystalline and low-molecular-weight carbon precursors enhances the interaction among rGO layers and thus produces an ultralight, flexible, and superstable structure. The as-prepared carbon aerogel displays a supercompressibility (undergoing an extreme strain of 99%) and elasticity (100% height retention after 10 000 cycles at a strain of 30%), as well as stable strain-current response (at least 10 000 cycles). Particularly, the carbon aerogel is ultrasensitive for detecting tiny change in strain (0.012%) and pressure (0.25 Pa), which are the lowest detection limits for compressible carbon materials reported in the literature. Moreover, the carbon aerogel exhibits excellent bendable performance and can detect an ultralow bending angle of 0.052°. Additionally, the carbon aerogel also demonstrates its promising application as wearable devices. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Strain-Dependent Edge Structures in MoS2 Layers.

PubMed

Tinoco, Miguel; Maduro, Luigi; Masaki, Mukai; Okunishi, Eiji; Conesa-Boj, Sonia

2017-11-08

Edge structures are low-dimensional defects unavoidable in layered materials of the transition metal dichalcogenides (TMD) family. Among the various types of such structures, the armchair (AC) and zigzag (ZZ) edge types are the most common. It has been predicted that the presence of intrinsic strain localized along these edges structures can have direct implications for the customization of their electronic properties. However, pinning down the relation between local structure and electronic properties at these edges is challenging. Here, we quantify the local strain field that arises at the edges of MoS 2 flakes by combining aberration-corrected transmission electron microscopy (TEM) with the geometrical-phase analysis (GPA) method. We also provide further insight on the possible effects of such edge strain on the resulting electronic behavior by means of electron energy loss spectroscopy (EELS) measurements. Our results reveal that the two-dominant edge structures, ZZ and AC, induce the formation of different amounts of localized strain fields. We also show that by varying the free edge curvature from concave to convex, compressive strain turns into tensile strain. These results pave the way toward the customization of edge structures in MoS 2 , which can be used to engineer the properties of layered materials and thus contribute to the optimization of the next generation of atomic-scale electronic devices built upon them.

Long wavelength, high gain InAsSb strained-layer superlattice photoconductive detectors

DOEpatents

Biefeld, Robert M.; Dawson, L. Ralph; Fritz, Ian J.; Kurtz, Steven R.; Zipperian, Thomas E.

1991-01-01

A high gain photoconductive device for 8 to 12 .mu.m wavelength radiation including an active semiconductor region extending from a substrate to an exposed face, the region comprising a strained-layer superlattice of alternating layers of two different InAs.sub.1-x Sb.sub.x compounds having x>0.75. A pair of spaced electrodes are provided on the exposed face, and changes in 8 to 12 .mu.m radiation on the exposed face cause a large photoconductive gain between the spaced electrodes.

Boundary layers at a dynamic interface: Air-sea exchange of heat and mass

NASA Astrophysics Data System (ADS)

Szeri, Andrew J.

2017-04-01

Exchange of mass or heat across a turbulent liquid-gas interface is a problem of critical interest, especially in air-sea transfer of natural and anthropogenic gases involved in the study of climate. The goal in this research area is to determine the gas flux from air to sea or vice versa. For sparingly soluble nonreactive gases, this is controlled by liquid phase turbulent velocity fluctuations that act on the thin species concentration boundary layer on the liquid side of the interface. If the fluctuations in surface-normal velocity w' and gas concentration c' are known, then it is possible to determine the turbulent contribution to the gas flux. However, there is no suitable fundamental direct approach in the general case where neither w' nor c' can be easily measured. A new approach is presented to deduce key aspects about the near-surface turbulent motions from measurements that can be taken by an infrared (IR) camera. An equation is derived with inputs being the surface temperature and heat flux, and a solution method developed for the surface-normal strain experienced over time by boundary layers at the interface. Because the thermal and concentration boundary layers experience the same near-surface fluid motions, the solution for the surface-normal strain determines the gas flux or gas transfer velocity. Examples illustrate the approach in the cases of complete surface renewal, partial surface renewal, and insolation. The prospects for use of the approach in flows characterized by sheared interfaces or rapid boundary layer straining are explored.

In-situ synchrotron micro-diffraction study of surface, interface, grain structure, and strain/stress evolution during Sn whisker/hillock formation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pei, Fei; Jadhav, Nitin; Buchovecky, Eric

2016-03-14

We have performed X-ray synchrotron micro-diffraction measurements to study the processes controlling the formation of hillocks and whiskers in Sn layers on Cu. The studies were done in real-time on Sn layers that were electro-deposited immediately before the X-ray measurements were started. This enabled a region of the sample to be monitored from the as-deposited state until after a hillock feature formed. In addition to measuring the grain orientation and deviatoric strain (via Laue diffraction), the X-ray fluorescence was monitored to quantify the evolution of the Sn surface morphology and the formation of intermetallic compound (IMC) at the Sn-Cu interface.more » The results capture the simultaneous growth of the feature and the corresponding film stress, grain orientation, and IMC formation. The observations are compared with proposed mechanisms for whisker/hillock growth and nucleation.« less

Strain, magnetic anisotropy, and anisotropic magnetoresistance in (Ga,Mn)As on high-index substrates: Application to (113)A -oriented layers

NASA Astrophysics Data System (ADS)

Dreher, L.; Donhauser, D.; Daeubler, J.; Glunk, M.; Rapp, C.; Schoch, W.; Sauer, R.; Limmer, W.

2010-06-01

Based on a detailed theoretical examination of the lattice distortion in high-index epilayers in terms of continuum mechanics, expressions are deduced that allow the calculation and experimental determination of the strain tensor for (hhl) -oriented (Ga,Mn)As layers. Analytical expressions are derived for the strain-dependent free-energy density and for the resistivity tensor for monoclinic and orthorhombic crystal symmetries, phenomenologically describing the magnetic anisotropy and anisotropic magnetoresistance by appropriate anisotropy and resistivity parameters, respectively. Applying the results to (113)A orientation with monoclinic crystal symmetry, the expressions are used to determine the strain tensor and the shear angle of a series of (113)A -oriented (Ga,Mn)As layers by high-resolution x-ray diffraction and to probe the magnetic anisotropy and anisotropic magnetoresistance at 4.2 K by means of angle-dependent magnetotransport. Whereas the transverse-resistivity parameters are nearly unaffected by the magnetic field, the parameters describing the longitudinal resistivity are strongly field dependent.

Strain modulation-enhanced Mg acceptor activation efficiency of Al0.14Ga0.86N/GaN superlattices with AlN interlayer

NASA Astrophysics Data System (ADS)

Wang, Lei; Li, Rui; Li, Ding; Liu, Ningyang; Liu, Lei; Chen, Weihua; Wang, Cunda; Yang, Zhijian; Hu, Xiaodong

2010-02-01

AlN layer was grown as interlayer between undoped GaN and Mg doped Al0.14Ga0.86N/GaN superlattices (SLs) epilayer to modulate the strain distribution between Al0.14Ga0.86N barrier and GaN well layers in SLs sample. Strain relaxation was observed in the SLs sample with AlN interlayer by x-ray diffraction reciprocal space mapping method. The measured hole concentration of SLs sample with AlN interlayer at room temperature was over 1.6×1018 cm-3 but that was only 6.6×1016 cm-3 obtained in SLs sample without AlN interlayer. Variable temperature Hall-effect measurement showed that the acceptor activation energy decreased from 150 to 70 meV after inserting the AlN layer, which indicated that the strain modulation of SLs induced by AlN interlayer was beneficial to the Mg acceptor activation and hole concentration enhancement.

Numerical Characterization of a Composite Bonded Wing-Box

NASA Technical Reports Server (NTRS)

Smeltzer, Stanley S., III; Lovejoy, Andrew E.; Satyanarayana, Arunkumar

2008-01-01

The development of composite wing structures has focused on the use of mechanical fasteners to join heavily-loaded areas, while bonded joints have been used only for select locations. The focus of this paper is the examination of the adhesive layer in a generic bonded wing box that represents a "fastenerless" or unitized structure in order to characterize the general behavior and failure mechanisms. A global/local approach was applied to study the response of the adhesive layer using a global shell model and a local shell/solid model. The wing box was analyzed under load to represent a high-g up-bending condition such that the strains in the composite sandwich face sheets are comparable to an expected design allowable. The global/local analysis indicates that at these wing load levels the strains in the adhesive layer are well within the adhesive's elastic region, such that yielding would not be expected in the adhesive layer. The global/local methodology appears to be a promising approach to evaluate the structural integrity of the adhesively bonded structures.

Spectroscopic ellipsometric characterization of Si/Si(1-x)Ge(x) strained-layer superlattices

NASA Technical Reports Server (NTRS)

Yao, H.; Woollam, J. A.; Wang, P. J.; Tejwani, M. J.; Alterovitz, S. A.

1993-01-01

Spectroscopic ellipsometry (SE) was employed to characterize Si/Si(1-x)Ge(x) strained-layer superlattices. An algorithm was developed, using the available optical constants measured at a number of fixed x values of Ge composition, to compute the dielectric function spectrum of Si(1-x)Ge(x) at an arbitrary x value in the spectral range 17 to 5.6 eV. The ellipsometrically determined superlattice thicknesses and alloy compositional fractions were in excellent agreement with results from high-resolution x ray diffraction studies. The silicon surfaces of the superlattices were subjected to a 9:1 HF cleaning prior to the SE measurements. The HF solution removed silicon oxides on the semiconductor surface, and terminated the Si surface with hydrogen-silicon bonds, which were monitored over a period of several weeks, after the HF cleaning, by SE measurements. An equivalent dielectric layer model was established to describe the hydrogen-terminated Si surface layer. The passivated Si surface remained unchanged for greater than 2 h, and very little surface oxidation took place even over 3 to 4 days.

Defects, strain relaxation, and compositional grading in high indium content InGaN epilayers grown by molecular beam epitaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bazioti, C.; Kehagias, Th.; Pavlidou, E.

2015-10-21

We investigate the structural properties of a series of high alloy content InGaN epilayers grown by plasma-assisted molecular beam epitaxy, employing the deposition temperature as variable under invariant element fluxes. Using transmission electron microscopy methods, distinct strain relaxation modes were observed, depending on the indium content attained through temperature adjustment. At lower indium contents, strain relaxation by V-pit formation dominated, with concurrent formation of an indium-rich interfacial zone. With increasing indium content, this mechanism was gradually substituted by the introduction of a self-formed strained interfacial InGaN layer of lower indium content, as well as multiple intrinsic basal stacking faults andmore » threading dislocations in the rest of the film. We show that this interfacial layer is not chemically abrupt and that major plastic strain relaxation through defect introduction commences upon reaching a critical indium concentration as a result of compositional pulling. Upon further increase of the indium content, this relaxation mode was again gradually succeeded by the increase in the density of misfit dislocations at the InGaN/GaN interface, leading eventually to the suppression of the strained InGaN layer and basal stacking faults.« less

Identifying Deformation and Strain Hardening Behaviors of Nanoscale Metallic Multilayers Through Nano-wear Testing

DOE PAGES

Economy, David Ross; Mara, Nathan A.; Schoeppner, R.; ...

2016-01-13

In complex loading conditions (e.g. sliding contact), mechanical properties, such as strain hardening and initial hardness, will dictate the long-term performance of materials systems. With this in mind, the strain hardening behaviors of Cu/Nb nanoscale metallic multilayer systems were examined by performing nanoindentation tests within nanoscratch wear boxes and undeformed, as-deposited regions. Both the architecture and substrate influence were examined by utilizing three different individual layer thicknesses (2, 20, and 100 nm) and two total film thicknesses (1 and 10 μm). After nano-wear deformation, multilayer systems with thinner layers showed less volume loss as measured by laser scanning microscopy. Additionally,more » the hardness of the deformed regions significantly rose with respect to the as-deposited measurements, which further increased with greater wear loads. Strain hardening exponents for multilayers with thinner layers (2 and 20 nm, n ≈ 0.018 and n ≈ 0.022 respectively) were less than was determined for 100 nm systems (n ≈ 0.041). These results suggest that singledislocation based deformation mechanisms observed for the thinner systems limit the extent of achievable strain hardening. This conclusion indicates that impacts of both architecture strengthening and strain hardening must be considered to accurately predict multilayer performance during sliding contact across varying length scales.« less

Effect of Strain Rate on Joint Strength and Failure Mode of Lead-Free Solder Joints

NASA Astrophysics Data System (ADS)

Lin, Jian; Lei, Yongping; Fu, Hanguang; Guo, Fu

2018-03-01

In surface mount technology, the Sn-3.0Ag-0.5Cu solder joint has a shorter impact lifetime than a traditional lead-tin solder joint. In order to improve the impact property of SnAgCu lead-free solder joints and identify the effect of silver content on tensile strength and impact property, impact experiments were conducted at various strain rates on three selected SnAgCu based solder joints. It was found that joint failure mainly occurred in the solder material with large plastic deformation under low strain rate, while joint failure occurred at the brittle intermetallic compound layer without any plastic deformation at a high strain rate. Joint strength increased with the silver content in SnAgCu alloys in static tensile tests, while the impact property of the solder joint decreased with increasing silver content. When the strain rate was low, plastic deformation occurred with failure and the tensile strength of the Sn-3.0Ag-0.5Cu solder joint was higher than that of Sn-0.3Ag-0.7Cu; when the strain rate was high, joint failure mainly occurred at the brittle interface layer and the Sn-0.3Ag-0.7Cu solder joint had a better impact resistance with a thinner intermetallic compound layer.

Stress and strain evolution of folding rocks

NASA Astrophysics Data System (ADS)

Llorens, Maria-Gema; Griera, Albert; Bons, Paul; Gomez-Rivas, Enrique; Weikusat, Ilka

2015-04-01

One of the main objectives of structural geology is to unravel rock deformation histories. Fold shapes can be used to estimate the orientation and amount of strain associated with folding. However, much more information on rheology and kinematics can potentially be extracted from fold geometries (Llorens et al., 2013a). We can study the development of folds, quantify the relationships between the different parameters that determine their geometries and estimate their mechanical evolution. This approach allows us to better understand and predict not only rock but also ice deformation. One of the main parameters in fold development is the viscosity contrast between the folding layer and the matrix in which it is embedded (m), since it determines the initial fold wavelength and the amplification rate of the developing folds. Moreover, non-linear viscous rheology influences fold geometry too (Llorens et al., 2013b). We present a series of 2-dimensional simulations of folding of viscous single layers in pure and simple shear. We vary different parameters in order to compare and determine their influence on the resulting fold patterns and the associated mechanical response of the material. To perform these simulations we use the software platform ELLE (www.elle.ws) with the non-linear viscous finite element code BASIL. The results show that layers thicken at the beginning of deformation in all simulations, and visible folds start earlier or later depending on the viscosity contrast. When folds start to nucleate the layer maximum shear strain decreases, moving away from the theoretical trend for homogeneous strain (no folding). This allows the accurate determination of the onset of folding. Maximum deviatoric stresses are higher in power-law than in linear-viscosity materials, and it is initially double in pure shear than in simple shear conditions. Therefore, folding a competent layer requires less work in simple than in pure shear. The maximum deviatoric stress difference between pure and simple shear is less pronounced in power-law materials. It also depends on the original orientation of the layer relative to the shear plane, being the shortening rate initially relatively low when the layer makes a low angle with the shear plane. The mechanical behaviour is similar in pure and simple shear when the layer is oriented at a relative high angle (45°). M-G Llorens, PD Bons, A Griera and E Gomez-Rivas (2013a) When do folds unfold during progressive shear?. Geology, 41, 563-566. M-G Llorens, PD Bons, A Griera, E Gomez-Rivas and LA Evans (2013b) Single layer folding in simple shear. Journal of Structural Geology, 50, 209-220.

The role of the heat shock protein Hsp12p in the dynamic response of Saccharomyces cerevisiae to the addition of Congo red.

PubMed

Shamrock, Vanessa J; Duval, Jérôme F L; Lindsey, George G; Gaboriaud, Fabien

2009-05-01

In this study, we investigate the electrohydrodynamic and nanomechanical characteristics of two Saccharomyces cerevisiae yeast strains, a wild-type (WT) strain and a strain overexpressing (OE) Hsp12p, in the presence and absence of hydrophobic Congo red compound. By combining these two advanced biophysical methods, we demonstrate that Hsp12p proteins are mostly located within a thin layer (c. 10 nm thick) positioned at the external side of the cell wall. However, this Hsp12p-enriched layer does not prevent Congo red from entering the cell wall and from interacting with the chitin therein. The entrance of Congo red within the cell wall is reflected in an increase of the turgor pressure for the OE strain and a decrease of that for the WT strain. It is shown that these opposite trends are consistent with significant modulations of the water content within the cell wall from/to the cytoplasm. These are the result of changes in the hydrophobicity/hydrophilicity balance, as governed by the intertwined local concentration variations of Congo red and Hsp12p across the cell wall. In particular, the decrease of the turgor pressure in the case of WT strain upon addition of Congo red is shown to be consistent with an upregulation of Hsp12p in the close vicinity of the plasma membrane.

An MRI-based leg model used to simulate biomechanical phenomena during cuff algometry: a finite element study.

PubMed

Manafi-Khanian, Bahram; Arendt-Nielsen, Lars; Graven-Nielsen, Thomas

2016-03-01

Cuff pressure stimulation is applicable for assessing deep-tissue pain sensitivity by exciting a variety of deep-tissue nociceptors. In this study, the relative transfer of biomechanical stresses and strains from the cuff via the skin to the muscle and the somatic tissue layers around bones were investigated. Cuff pressure was applied on the lower leg at three different stimulation intensities (mild pressure to pain). Three-dimensional finite element models including bones and three different layers of deep tissues were developed based on magnetic resonance images (MRI). The skin indentation maps at mild pressure, pain threshold, and intense painful stimulations were extracted from MRI and applied to the model. The mean stress under the cuff position around tibia was 4.6, 4.9 and around fibula 14.8, 16.4 times greater than mean stress of muscle surface in the same section at pain threshold and intense painful stimulations, respectively. At the same stimulation intensities, the mean strains around tibia were 36.4, 42.3 % and around fibula 32.9, 35.0 %, respectively, of mean strain on the muscle surface. Assuming strain as the ideal stimulus for nociceptors the results suggest that cuff algometry is less capable to challenge the nociceptors of tissues around bones as compared to more superficially located muscles.

Strain relaxation in nm-thick Cu and Cu-alloy films bonded to a rigid substrate

NASA Astrophysics Data System (ADS)

Herrmann, Ashley Ann Elizabeth

In the wide scope of modern technology, nm-thick metallic films are increasingly used as lubrication layers, optical coatings, plating seeds, diffusion barriers, adhesion layers, metal contacts, reaction catalyzers, etc. A prominent example is the use of nm-thick Cu films as electroplating seed layers in the manufacturing of integrated circuits (ICs). These high density circuits are linked by on-chip copper interconnects, which are manufactured by filling Cu into narrow trenches by electroplating. The Cu fill by electroplating requires a thin Cu seed deposited onto high-aspect-ratio trenches. In modern ICs, these trenches are approaching 10 nm or less in width, and the seed layers less than 1 nm in thickness. Since nm-thick Cu seed layers are prone to agglomeration or delamination, achieving uniform, stable and highly-conductive ultra-thin seeds has become a major manufacturing challenge. A fundamental understanding of the strain behavior and thermal stability of nm-thick metal films adhered to a rigid substrate is thus critically needed. In this study, we focus on understanding the deformation modes of nm-thick Cu and Cu-alloy films bonded to a rigid Si substrate and under compressive stress. The strengthening of Cu films through alloying is also studied. In-situ transport measurements are used to monitor the deformation of such films as they are heated from room temperature to 400 °C. Ex-situ AFM is then used to help characterize the mode of strain relaxation. The relaxation modes are known to be sensitive to the wetting and adhesive properties of the film-substrate interface. We use four different liners (Ta, Ru, Mo and Co), interposed between the film and substrate to provide a wide range of interfacial properties to study their effect on the film's thermal stability. Our measurements indicate that when the film/liner interfacial energy is low, grain growth is the dominant relaxation mechanism. As the interface energy increases, grain growth is suppressed, and the strain is relaxed through hillock/island formation instead. The kinetics-limiting parameters for these relaxation modes are identified and used to simulate their kinetics, and a deformation map is then constructed to delineate the conditions under which each mode would prevail. Such a deformation map would prove useful when one seeks to optimize the thermal stability or other mechanical properties in any ultra-thin film system.

Oxygen induced strain field homogenization in AlN nucleation layers and its impact on GaN grown by metal organic vapor phase epitaxy on sapphire: An x-ray diffraction study

NASA Astrophysics Data System (ADS)

Bläsing, J.; Krost, A.; Hertkorn, J.; Scholz, F.; Kirste, L.; Chuvilin, A.; Kaiser, U.

2009-02-01

This paper presents an x-ray study of GaN, which is grown on nominally undoped and oxygen-doped AlN nucleation layers on sapphire substrates by metal organic vapor phase epitaxy. Without additional oxygen doping a trimodal nucleation distribution of AlN is observed leading to inhomogeneous in-plane strain fields, whereas in oxygen-doped layers a homogeneous distribution of nucleation centers is observed. In both types of nucleation layers extremely sharp correlation peaks occur in transverse ω-scans which are attributed to a high density of edge-type dislocations having an in-plane Burgers vector. The correlation peaks are still visible in the (0002) ω-scans of 500 nm GaN which might mislead an observer to conclude incorrectly that there exists an extremely high structural quality. For the undoped nucleation layers depth-sensitive measurements in grazing incidence geometry reveal a strong thickness dependence of the lattice parameter a, whereas no such dependence is observed for doped samples. For oxygen-doped nucleation layers, in cross-sectional transmission electron microscopy images a high density of stacking faults parallel to the substrate surface is found in contrast to undoped nucleation layers where a high density of threading dislocations is visible. GaN of 2.5 μm grown on top of 25 nm AlN nucleation layers with an additional in situ SiN mask show full widths at half maximum of 160″ and 190″ in (0002) and (10-10) high-resolution x-ray diffraction ω-scans, respectively.

Influence of Supplemental Dietary Poultry Fat, Phytase, and 25-Hydroxycholecalciferol on the Performance of Commercial Layers Inoculated Before or at the Onset of Lay with F-Strain Mycoplasma gallisepticum

USDA-ARS?s Scientific Manuscript database

The effects of 2 levels of supplemental dietary poultry fat (PF) and the combination of PF, phytase (PHY) and 25-hydroxycholecalciferol (D3) on the performance of commercial layers inoculated with F-strain Mycoplasma gallisepticum (FMG) were investigated in 2 trials. Sham and FMG inoculations were ...

Growth and characterization of low composition Ge, x in epi-Si1‑x Gex (x  ⩽  10%) active layer for fabrication of hydrogenated bottom solar cell

NASA Astrophysics Data System (ADS)

Ajmal Khan, M.; Sato, R.; Sawano, K.; Sichanugrist, P.; Lukianov, A.; Ishikawa, Y.

2018-05-01

Semiconducting epi-Si1‑x Ge x alloys have promising features as solar cell materials and may be equally important for some other semiconductor device applications. Variation of the germanium compositional, x in epi-Si1‑x Ge x , makes it possible to control the bandgap between 1.12 eV and 0.68 eV for application in bottom solar cells. A low proportion of Ge in SiGe alloy can be used for photovoltaic application in a bottom cell to complete the four-terminal tandem structure with wide bandgap materials. In this research, we aimed to use a low proportion of Ge—about 10%—in strained or relaxed c-Si1‑x Ge x /c-Si heterojunctions (HETs), with or without insertion of a Si buffer layer grown by molecular beam epitaxy, to investigate the influence of the relaxed or strained SiGe active layer on the performance of HET solar cells grown using the plasma enhanced chemical vapor deposition system. Thanks to the c-Si buffer layer at the hetero-interface, the efficiency of these SiGe based HET solar cells was improved from 2.3% to 3.5% (fully strained and with buffer layer). The Jsc was improved, from 8 mA cm‑2 to 15.46 mA cm‑2, which might be supported by strained c-Si buffer layer at the hetero-interface, by improving the crystalline quality.

Quantitative analysis and predictive engineering of self-rolling of nanomembranes under anisotropic mismatch strain

NASA Astrophysics Data System (ADS)

Chen, Cheng; Song, Pengfei; Meng, Fanchao; Li, Xiao; Liu, Xinyu; Song, Jun

2017-12-01

The present work presents a quantitative modeling framework for investigating the self-rolling of nanomembranes under different lattice mismatch strain anisotropy. The effect of transverse mismatch strain on the roll-up direction and curvature has been systematically studied employing both analytical modeling and numerical simulations. The bidirectional nature of the self-rolling of nanomembranes and the critical role of transverse strain in affecting the rolling behaviors have been demonstrated. Two fabrication strategies, i.e., third-layer deposition and corner geometry engineering, have been proposed to predictively manipulate the bidirectional rolling competition of strained nanomembranes, so as to achieve controlled, unidirectional roll-up. In particular for the strategy of corner engineering, microfabrication experiments have been performed to showcase its practical application and effectiveness. Our study offers new mechanistic knowledge towards understanding and predictive engineering of self-rolling of nanomembranes with improved roll-up yield.

High-carrier-density phase in LaTiO3/SrTiO3 superlattices

NASA Astrophysics Data System (ADS)

Park, Se Young; Rabe, Karin; Millis, Andrew

2015-03-01

We investigate superlattices composed of alternating layers of Mott insulating LaTiO3 and band insulating SrTiO3 from first principles, using the density functional theory plus U (DFT+U) method. For values of U above a critical threshold, we find that melting of the Mott-insulating phase can extend from the interface into the LaTiO3 layer, resulting in a sheet carrier density exceeding the density of 0.5 electrons per in-plane unit cell found in previous studies. The critical U for the melting transition is larger than the critical Coulomb correlation required for the insulating LaTiO3, suggesting the existence of a high sheet carrier density phase in LaTiO3/SrTiO3 superlattices. The effects of in-plane strain and varying layer thickness on the melting transition are discussed. For insulating superlattices, we study the strain and thickness dependence of the polarization and its relation to near-interface local atomic distortions. Support: DOE ER 046169, ONR N00014-11-0666.

Reversible loss of Bernal stacking during the deformation of few-layer graphene in nanocomposites.

PubMed

Gong, Lei; Young, Robert J; Kinloch, Ian A; Haigh, Sarah J; Warner, Jamie H; Hinks, Jonathan A; Xu, Ziwei; Li, Li; Ding, Feng; Riaz, Ibtsam; Jalil, Rashid; Novoselov, Kostya S

2013-08-27

The deformation of nanocomposites containing graphene flakes with different numbers of layers has been investigated with the use of Raman spectroscopy. It has been found that there is a shift of the 2D band to lower wavenumber and that the rate of band shift per unit strain tends to decrease as the number of graphene layers increases. It has been demonstrated that band broadening takes place during tensile deformation for mono- and bilayer graphene but that band narrowing occurs when the number of graphene layers is more than two. It is also found that the characteristic asymmetric shape of the 2D Raman band for the graphene with three or more layers changes to a symmetrical shape above about 0.4% strain and that it reverts to an asymmetric shape on unloading. This change in Raman band shape and width has been interpreted as being due to a reversible loss of Bernal stacking in the few-layer graphene during deformation. It has been shown that the elastic strain energy released from the unloading of the inner graphene layers in the few-layer material (~0.2 meV/atom) is similar to the accepted value of the stacking fault energies of graphite and few layer graphene. It is further shown that this loss of Bernal stacking can be accommodated by the formation of arrays of partial dislocations and stacking faults on the basal plane. The effect of the reversible loss of Bernal stacking upon the electronic structure of few-layer graphene and the possibility of using it to modify the electronic structure of few-layer graphene are discussed.

Reversible Loss of Bernal Stacking during the Deformation of Few-Layer Graphene in Nanocomposites

PubMed Central

2013-01-01

The deformation of nanocomposites containing graphene flakes with different numbers of layers has been investigated with the use of Raman spectroscopy. It has been found that there is a shift of the 2D band to lower wavenumber and that the rate of band shift per unit strain tends to decrease as the number of graphene layers increases. It has been demonstrated that band broadening takes place during tensile deformation for mono- and bilayer graphene but that band narrowing occurs when the number of graphene layers is more than two. It is also found that the characteristic asymmetric shape of the 2D Raman band for the graphene with three or more layers changes to a symmetrical shape above about 0.4% strain and that it reverts to an asymmetric shape on unloading. This change in Raman band shape and width has been interpreted as being due to a reversible loss of Bernal stacking in the few-layer graphene during deformation. It has been shown that the elastic strain energy released from the unloading of the inner graphene layers in the few-layer material (∼0.2 meV/atom) is similar to the accepted value of the stacking fault energies of graphite and few layer graphene. It is further shown that this loss of Bernal stacking can be accommodated by the formation of arrays of partial dislocations and stacking faults on the basal plane. The effect of the reversible loss of Bernal stacking upon the electronic structure of few-layer graphene and the possibility of using it to modify the electronic structure of few-layer graphene are discussed. PMID:23899378

Thin-layer chromatographic technique for rapid detection of bacterial phospholipases.

PubMed

Legakis, N J; Papavassiliou, J

1975-11-01

Silica gel thin-layer chromatography was employed to detect lecithinase activity induced from bacterial resting cell preparations induced from bacterial resting cell preparations incubated at 37 C for 4 h in the presence of purified egg yolk lecithin. Bacillus subtilis, Bacillus cereus, Serratia marcescens, and Pseudomonas aeruginosa hydrolyzed lecithin with the formation of free fatty acids as the sole lipid-soluble product. In none of the Escherichia coli and Citrobacter freundii strains tested could lecithinase activity be detected. Four among eight strains of Enterobacter aerogenes and one among 12 strains of Proteus tested produced negligible amounts of free fatty acid.

A Highly Expressed High-Molecular-Weight S-Layer Complex of Pelosinus sp. Strain UFO1 Binds Uranium

PubMed Central

Thorgersen, Michael P.; Lancaster, W. Andrew; Rajeev, Lara; Ge, Xiaoxuan; Vaccaro, Brian J.; Poole, Farris L.; Arkin, Adam P.; Mukhopadhyay, Aindrila

2016-01-01

ABSTRACT Cell suspensions of Pelosinus sp. strain UFO1 were previously shown, using spectroscopic analysis, to sequester uranium as U(IV) complexed with carboxyl and phosphoryl group ligands on proteins. The goal of our present study was to characterize the proteins involved in uranium binding. Virtually all of the uranium in UFO1 cells was associated with a heterodimeric protein, which was termed the uranium-binding complex (UBC). The UBC was composed of two S-layer domain proteins encoded by UFO1_4202 and UFO1_4203. Samples of UBC purified from the membrane fraction contained 3.3 U atoms/heterodimer, but significant amounts of phosphate were not detected. The UBC had an estimated molecular mass by gel filtration chromatography of 15 MDa, and it was proposed to contain 150 heterodimers (UFO1_4203 and UFO1_4202) and about 500 uranium atoms. The UBC was also the dominant extracellular protein, but when purified from the growth medium, it contained only 0.3 U atoms/heterodimer. The two genes encoding the UBC were among the most highly expressed genes within the UFO1 genome, and their expressions were unchanged by the presence or absence of uranium. Therefore, the UBC appears to be constitutively expressed and is the first line of defense against uranium, including by secretion into the extracellular medium. Although S-layer proteins were previously shown to bind U(VI), here we showed that U(IV) binds to S-layer proteins, we identified the proteins involved, and we quantitated the amount of uranium bound. IMPORTANCE Widespread uranium contamination from industrial sources poses hazards to human health and to the environment. Herein, we identified a highly abundant uranium-binding complex (UBC) from Pelosinus sp. strain UFO1. The complex makes up the primary protein component of the S-layer of strain UFO1 and binds 3.3 atoms of U(IV) per heterodimer. While other bacteria have been shown to bind U(VI) on their S-layer, we demonstrate here an example of U(IV) bound by an S-layer complex. The UBC provides a potential tool for the microbiological sequestration of uranium for the cleaning of contaminated environments. PMID:27913415

A Highly Expressed High-Molecular-Weight S-Layer Complex of Pelosinus sp. Strain UFO1 Binds Uranium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thorgersen, Michael P.; Lancaster, W. Andrew; Rajeev, Lara

Cell suspensions of Pelosinus sp. strain UFO1 were previously shown, using spectroscopic analysis, to sequester uranium as U(IV) complexed with carboxyl and phosphoryl group ligands on proteins. The goal of our present study was to characterize the proteins involved in uranium binding. Virtually all of the uranium in UFO1 cells was associated with a heterodimeric protein, which was termed the uranium-binding complex (UBC). The UBC was composed of two S-layer domain proteins encoded by UFO1_4202 and UFO1_4203. Samples of UBC purified from the membrane fraction contained 3.3 U atoms/heterodimer, but significant amounts of phosphate were not detected. The UBC hadmore » an estimated molecular mass by gel filtration chromatography of 15 MDa, and it was proposed to contain 150 heterodimers (UFO1_4203 and UFO1_4202) and about 500 uranium atoms. The UBC was also the dominant extracellular protein, but when purified from the growth medium, it contained only 0.3 U atoms/heterodimer. The two genes encoding the UBC were among the most highly expressed genes within the UFO1 genome, and their expressions were unchanged by the presence or absence of uranium. Therefore, the UBC appears to be constitutively expressed and is the first line of defense against uranium, including by secretion into the extracellular medium. Although S-layer proteins were previously shown to bind U(VI), here we showed that U(IV) binds to S-layer proteins, we identified the proteins involved, and we quantitated the amount of uranium bound. Widespread uranium contamination from industrial sources poses hazards to human health and to the environment. Here in this paper, we identified a highly abundant uranium-binding complex (UBC) from Pelosinus sp. strain UFO1. The complex makes up the primary protein component of the S-layer of strain UFO1 and binds 3.3 atoms of U(IV) per heterodimer. Finally, while other bacteria have been shown to bind U(VI) on their S-layer, we demonstrate here an example of U(IV) bound by an S-layer complex. The UBC provides a potential tool for the microbiological sequestration of uranium for the cleaning of contaminated environments.« less

A Highly Expressed High-Molecular-Weight S-Layer Complex of Pelosinus sp. Strain UFO1 Binds Uranium.

PubMed

Thorgersen, Michael P; Lancaster, W Andrew; Rajeev, Lara; Ge, Xiaoxuan; Vaccaro, Brian J; Poole, Farris L; Arkin, Adam P; Mukhopadhyay, Aindrila; Adams, Michael W W

2017-02-15

Cell suspensions of Pelosinus sp. strain UFO1 were previously shown, using spectroscopic analysis, to sequester uranium as U(IV) complexed with carboxyl and phosphoryl group ligands on proteins. The goal of our present study was to characterize the proteins involved in uranium binding. Virtually all of the uranium in UFO1 cells was associated with a heterodimeric protein, which was termed the uranium-binding complex (UBC). The UBC was composed of two S-layer domain proteins encoded by UFO1_4202 and UFO1_4203. Samples of UBC purified from the membrane fraction contained 3.3 U atoms/heterodimer, but significant amounts of phosphate were not detected. The UBC had an estimated molecular mass by gel filtration chromatography of 15 MDa, and it was proposed to contain 150 heterodimers (UFO1_4203 and UFO1_4202) and about 500 uranium atoms. The UBC was also the dominant extracellular protein, but when purified from the growth medium, it contained only 0.3 U atoms/heterodimer. The two genes encoding the UBC were among the most highly expressed genes within the UFO1 genome, and their expressions were unchanged by the presence or absence of uranium. Therefore, the UBC appears to be constitutively expressed and is the first line of defense against uranium, including by secretion into the extracellular medium. Although S-layer proteins were previously shown to bind U(VI), here we showed that U(IV) binds to S-layer proteins, we identified the proteins involved, and we quantitated the amount of uranium bound. Widespread uranium contamination from industrial sources poses hazards to human health and to the environment. Herein, we identified a highly abundant uranium-binding complex (UBC) from Pelosinus sp. strain UFO1. The complex makes up the primary protein component of the S-layer of strain UFO1 and binds 3.3 atoms of U(IV) per heterodimer. While other bacteria have been shown to bind U(VI) on their S-layer, we demonstrate here an example of U(IV) bound by an S-layer complex. The UBC provides a potential tool for the microbiological sequestration of uranium for the cleaning of contaminated environments. Copyright © 2017 American Society for Microbiology.

XRD measurement of mean thickness, thickness distribution and strain for illite and illite-smectite crystallites by the Bertaut-Warren-Averbach technique

USGS Publications Warehouse

Drits, Victor A.; Eberl, Dennis D.; Środoń, Jan

1998-01-01

A modified version of the Bertaut-Warren-Averbach (BWA) technique (Bertaut 1949, 1950; Warren and Averbach 1950) has been developed to measure coherent scattering domain (CSD) sizes and strains in minerals by analysis of X-ray diffraction (XRD) data. This method is used to measure CSD thickness distributions for calculated and experimental XRD patterns of illites and illite-smectites (I-S). The method almost exactly recovers CSD thickness distributions for calculated illite XRD patterns. Natural I-S samples contain swelling layers that lead to nonperiodic structures in the c* direction and to XRD peaks that are broadened and made asymmetric by mixed layering. Therefore, these peaks cannot be analyzed by the BWA method. These difficulties are overcome by K-saturation and heating prior to X-ray analysis in order to form 10-Å periodic structures. BWA analysis yields the thickness distribution of mixed-layer crystals (coherently diffracting stacks of fundamental illite particles). For most I-S samples, CSD thickness distributions can be approximated by lognormal functions. Mixed-layer crystal mean thickness and expandability then can be used to calculate fundamental illite particle mean thickness. Analyses of the dehydrated, K-saturated samples indicate that basal XRD reflections are broadened by symmetrical strain that may be related to local variations in smectite interlayers caused by dehydration, and that the standard deviation of the strain increases regularly with expandability. The 001 and 002 reflections are affected only slightly by this strain and therefore are suited for CSD thickness analysis. Mean mixed-layer crystal thicknesses for dehydrated I-S measured by the BWA method are very close to those measured by an integral peak width method.

Optical method for the determination of stress in thin films

DOEpatents

Maris, H.J.

1999-01-26

A method and optical system is disclosed for measuring an amount of stress in a film layer disposed over a substrate. The method includes steps of: (A) applying a sequence of optical pump pulses to the film layer, individual ones of said optical pump pulses inducing a propagating strain pulse in the film layer, and for each of the optical pump pulses, applying at least one optical probe pulse, the optical probe pulses being applied with different time delays after the application of the corresponding optical probe pulses; (B) detecting variations in an intensity of a reflection of portions of the optical probe pulses, the variations being due at least in part to the propagation of the strain pulse in the film layer; (C) determining, from the detected intensity variations, a sound velocity in the film layer; and (D) calculating, using the determined sound velocity, the amount of stress in the film layer. In one embodiment of this invention the step of detecting measures a period of an oscillation in the intensity of the reflection of portions of the optical probe pulses, while in another embodiment the step of detecting measures a change in intensity of the reflection of portions of the optical probe pulses and determines a time at which the propagating strain pulse reflects from a boundary of the film layer. 16 figs.

Optical method for the determination of stress in thin films

DOEpatents

Maris, Humphrey J.

1999-01-01

A method and optical system is disclosed for measuring an amount of stress in a film layer disposed over a substrate. The method includes steps of: (A) applying a sequence of optical pump pulses to the film layer, individual ones of said optical pump pulses inducing a propagating strain pulse in the film layer, and for each of the optical pump pulses, applying at least one optical probe pulse, the optical probe pulses being applied with different time delays after the application of the corresponding optical probe pulses; (B) detecting variations in an intensity of a reflection of portions of the optical probe pulses, the variations being due at least in part to the propagation of the strain pulse in the film layer; (C) determining, from the detected intensity variations, a sound velocity in the film layer; and (D) calculating, using the determined sound velocity, the amount of stress in the film layer. In one embodiment of this invention the step of detecting measures a period of an oscillation in the intensity of the reflection of portions of the optical probe pulses, while in another embodiment the step of detecting measures a change in intensity of the reflection of portions of the optical probe pulses and determines a time at which the propagating strain pulse reflects from a boundary of the film layer.

Strain-Engineered Nanomembrane Substrates for Si/SiGe Heterostructures

NASA Astrophysics Data System (ADS)

Sookchoo, Pornsatit

For Group IV materials, including silicon, germanium, and their alloys, although they are most widely used in the electronics industry, the development of photonic devices is hindered by indirect band gaps and large lattice mismatches. Thus, any heterostructures involving Si and Ge (4.17% lattice mismatch) are subject to plastic relaxation by dislocation formation in the heterolayers. These defects make many devices impossible and at minimum degrade the performance of those that are possible. Fabrication using elastic strain engineering in Si/SiGe nanomembranes (NMs) is an approach that is showing promise to overcome this limitation. A key advantage of such NM substrates over conventional bulk substrates is that they are relaxed elastically and therefore free of dislocations that occur in the conventional fabrication of SiGe substrates, which are transferred to the epilayers and roughen film interfaces. In this thesis, I use the strain engineering of NMs or NM stacks to fabricate substrates for the epitaxial growth of many repeating units of Si/SiGe heterostructure, known as a 'superlattice', by the elastic strain sharing of a few periods of the repeating unit of Si/SiGe heterolayers or a Si/SiGe/Si tri-layer structure. In both cases, the process begins with the epitaxial growth of Si/SiGe heterolayers on silicon-on-insulator (SOI), where each layer thickness is designed to stay below its kinetic critical thickness for the formation of dislocations. The heterostructure NMs are then released by etching of the SiO2 sacrificial layer in hydrofluoric acid. The resulting freestanding NMs are elastically relaxed by the sharing of strain between the heterolayers. The NMs can be bonded in-place to their host substrate or transferred to another host substrate for the subsequent growth of many periods of superlattice film. The magnitude of strain sharing in these freestanding NMs is influenced by their layer thicknesses and layer compositions. As illustrated in this dissertation, strain-engineering of such NMs can provide the enabling basis for improved Group IV optoelectronic devices.

Factors influencing epitaxial growth of three-dimensional Ge quantum dot crystals on pit-patterned Si substrate.

PubMed

Ma, Y J; Zhong, Z; Yang, X J; Fan, Y L; Jiang, Z M

2013-01-11

We investigated the molecular beam epitaxy growth of three-dimensional (3D) Ge quantum dot crystals (QDCs) on periodically pit-patterned Si substrates. A series of factors influencing the growth of QDCs were investigated in detail and the optimized growth conditions were found. The growth of the Si buffer layer and the first quantum dot (QD) layer play a key role in the growth of QDCs. The pit facet inclination angle decreased with increasing buffer layer thickness, and its optimized value was found to be around 21°, ensuring that all the QDs in the first layer nucleate within the pits. A large Ge deposition amount in the first QD layer favors strain build-up by QDs, size uniformity of QDs and hence periodicity of the strain distribution; a thin Si spacer layer favors strain correlation along the growth direction; both effects contribute to the vertical ordering of the QDCs. Results obtained by atomic force microscopy and cross-sectional transmission electron microscopy showed that 3D ordering was achieved in the Ge QDCs with the highest ever areal dot density of 1.2 × 10(10) cm(-2), and that the lateral and the vertical interdot spacing were ~10 and ~2.5 nm, respectively.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shah, S.; Ghosh, K.; Jejurikar, S.

Graphical abstract: - Highlights: • Investigation of ground state energy in single and multi-layered InAs/GaAs QD. • Strain reducing layer (InGaAs) prevents the formation of non-radiative. • Strain reducing layer (InGaAs) is responsible for high activation energy. • Significant deviation from the Varshni model, E(T) = E − αT{sup 2}/T + β. - Abstract: Vertically coupled, multilayered InAs/GaAs quantum dots (QDs) covered with thin InGaAs strain-reducing layers (SRLs) are in demand for various technological applications. We investigated low temperature photoluminescence of single and multilayered structures in which the SRL thickness was varied. The SRL layer was responsible for high activationmore » energies. Deviation of experimental data from the Varshni (1967) model, E(T) = E − ∞ T{sup 2}/T + β, suggests that the InAs-layered QDs have properties different from those in bulk material. Anomalous ground-state peak linewidths (FWHM), especially for annealed multilayer structures, were observed. A ground-state peak blue-shift with a broadened linewidth was also observed. Loss of intensity was detected in samples annealed at 800 °C. Presence of SRLs prevents formation of non-radiative centers under high temperature annealing. The results indicate the potential importance of such structures in optoelectronic applications.« less

Effect of double layer thickness on magnetoelectric coupling in multiferroic BaTiO3-Bi0.95Gd0.05FeO3 multilayers

NASA Astrophysics Data System (ADS)

Hohenberger, S.; Lazenka, V.; Temst, K.; Selle, S.; Patzig, C.; Höche, T.; Grundmann, M.; Lorenz, M.

2018-05-01

The effect of double-layer thickness and partial substitution of Bi3+ by Gd3+ is demonstrated for multiferroic BaTiO3–BiFeO3 2–2 heterostructures. Multilayers of 15 double layers of BaTiO3 and Bi0.95Gd0.05FeO3 were deposited onto (0 0 1) oriented SrTiO3 substrates by pulsed laser deposition with various double layer thicknesses. X-ray diffraction and high resolution transmission electron microscopy investigations revealed a systematic strain tuning with layer thickness via coherently strained interfaces. The multilayers show increasingly enhanced magnetoelectric coupling with reduced double layer thickness. The maximum magnetoelectric coupling coefficient was measured to be as high as 50.8 V cm‑1 Oe‑1 in 0 T DC bias magnetic field at room temperature, and 54.9 V cm‑1 Oe‑1 above 3 T for the sample with the thinnest double layer thickness of 22.5 nm. This enhancement is accompanied by progressively increasing perpendicular magnetic anisotropy and compressive out-of-plane strain. To understand the origin of the enhanced magnetoelectric coupling in such multilayers, the temperature and magnetic field dependency of is discussed. The magnetoelectric performance of the Gd3+ substituted samples is found to be slightly enhanced when compared to unsubstituted BaTiO3–BiFeO3 multilayers of comparable double-layer thickness.

Statistical mechanics and scaling of fault populations with increasing strain in the Corinth Rift

NASA Astrophysics Data System (ADS)

Michas, Georgios; Vallianatos, Filippos; Sammonds, Peter

2015-12-01

Scaling properties of fracture/fault systems are studied in order to characterize the mechanical properties of rocks and to provide insight into the mechanisms that govern fault growth. A comprehensive image of the fault network in the Corinth Rift, Greece, obtained through numerous field studies and marine geophysical surveys, allows for the first time such a study over the entire area of the Rift. We compile a detailed fault map of the area and analyze the scaling properties of fault trace-lengths by using a statistical mechanics model, derived in the framework of generalized statistical mechanics and associated maximum entropy principle. By using this framework, a range of asymptotic power-law to exponential-like distributions are derived that can well describe the observed scaling patterns of fault trace-lengths in the Rift. Systematic variations and in particular a transition from asymptotic power-law to exponential-like scaling are observed to be a function of increasing strain in distinct strain regimes in the Rift, providing quantitative evidence for such crustal processes in a single tectonic setting. These results indicate the organization of the fault system as a function of brittle strain in the Earth's crust and suggest there are different mechanisms for fault growth in the distinct parts of the Rift. In addition, other factors such as fault interactions and the thickness of the brittle layer affect how the fault system evolves in time. The results suggest that regional strain, fault interactions and the boundary condition of the brittle layer may control fault growth and the fault network evolution in the Corinth Rift.

Pyramidal dislocation induced strain relaxation in hexagonal structured InGaN/AlGaN/GaN multilayer

NASA Astrophysics Data System (ADS)

Yan, P. F.; Du, K.; Sui, M. L.

2012-10-01

Due to the special dislocation slip systems in hexagonal lattice, dislocation dominated deformations in hexagonal structured multilayers are significantly different from that in cubic structured systems. In this work, we have studied the strain relaxation mechanism in hexagonal structured InGaN/AlGaN/GaN multilayers with transmission electron microscopy. Due to lattice mismatch, the strain relaxation was found initiated with the formation of pyramidal dislocations. Such dislocations locally lie at only one preferential slip direction in the hexagonal lattice. This preferential slip causes a shear stress along the basal planes and consequently leads to dissociation of pyramidal dislocations and operation of the basal plane slip system. The compressive InGaN layers and "weak" AlGaN/InGaN interfaces stimulate the dissociation of pyramidal dislocations at the interfaces. These results enhance the understanding of interactions between dislocations and layer interfaces and shed new lights on deformation mechanism in hexagonal-lattice multilayers.

A phase field crystal model simulation of morphology evolution and misfit dislocation generation in nanoheteroepitaxy

NASA Astrophysics Data System (ADS)

Zhang, J.; Chen, Z.; Cheng, C.; Wang, Y. X.

2017-10-01

A phase field crystal (PFC) model is employed to study morphology evolution of nanoheteroepitaxy and misfit dislocation generation when applied with enhanced supercooling, lattice mismatch and substrate vicinal angle conditions. Misfit strain that rises due to lattice mismatch causes rough surfaces or misfit dislocations, deteriorates film properties, hence, efforts taken to reveal their microscopic mechanism are significant for film quality improvement. Uniform islands, instead of misfit dislocations, are developed in subcritical thickness film, serving as a way of strain relief by surface mechanism. Misfit dislocations generate when strain relief by surface mechanism is deficient in higher supercooling, multilayers of misfit dislocations dominate, but the number of layers reduces gradually when the supercooling is further enhanced. Rough surfaces like islands or cuspate pits are developed which is ascribed to lattice mismatch, multilayers of misfit dislocations generate to further enhance lattice mismatch. Layers of misfit dislocations generate at a thickening position at enhanced substrate vicinal angle, this further enhancing the angle leading to sporadic generation of misfit dislocations.

Model For Bending Actuators That Use Electrostrictive Graft Elastomers

NASA Technical Reports Server (NTRS)

Costen, Robert C.; Su, Ji; Harrison, Joycelyn S.

2001-01-01

Recently, it was reported that an electrostrictive graft elastomer exhibits large electric field-induced strain (4%). Combined with its high mechanical modulus, the elastomer can offer very promising electromechanical properties, in terms of output mechanical energy density, for an electroactive polymeric material. Therefore, it has been considered as one of the candidates that can be used in high performance, low mass actuation devices in many aerospace applications. Various bilayer- based bending actuators have been designed and fabricated. An analytic model based on beam theory in the strength of materials has been derived for the transverse deflection, or curvature, and the longitudinal strain of the bi-layer beam. The curvature and strain are functions of the applied voltage and the thickness, width, and Young s modulus of the active and passive layers. The model can be used to optimize the performance of electrostrictive graft elastomer-based actuators to meet the requirements of various applications. In this presentation, optimization and sensitivity studies are applied to the bending performance of such actuators.

Strain engineering of van der Waals heterostructures.

PubMed

Vermeulen, Paul A; Mulder, Jefta; Momand, Jamo; Kooi, Bart J

2018-01-18

Modifying the strain state of solids allows control over a plethora of functional properties. The weak interlayer bonding in van der Waals (vdWaals) materials such as graphene, hBN, MoS 2 , and Bi 2 Te 3 might seem to exclude strain engineering, since strain would immediately relax at the vdWaals interfaces. Here we present direct observations of the contrary by showing growth of vdWaals heterostructures with persistent in-plane strains up to 5% and we show that strain relaxation follows a not yet reported process distinctly different from strain relaxation in three-dimensionally bonded (3D) materials. For this, 2D bonded Bi 2 Te 3 -Sb 2 Te 3 and 2D/3D bonded Bi 2 Te 3 -GeTe multilayered films are grown using Pulsed Laser Deposition (PLD) and their structure is monitored in situ using Reflective High Energy Electron Diffraction (RHEED) and post situ analysis is performed using Transmission Electron Microscopy (TEM). Strain relaxation is modeled and found to solely depend on the layer being grown and its initial strain. This insight demonstrates that strain engineering of 2D bonded heterostructures obeys different rules than hold for epitaxial 3D materials and opens the door to precise tuning of the strain state of the individual layers to optimize functional performance of vdWaals heterostructures.

Piezoelectric Multilayer-Stacked Hybrid Actuation/Transduction System

NASA Technical Reports Server (NTRS)

Xu, Tian-Bing (Inventor); Jiang, Xiaoning (Inventor); Su, Ji (Inventor)

2014-01-01

A novel full piezoelectric multilayer stacked hybrid actuation/transduction system. The system demonstrates significantly-enhanced electromechanical performance by utilizing the cooperative contributions of the electromechanical responses of multilayer stacked negative and positive strain components. Both experimental and theoretical studies indicate that for this system, the displacement is over three times that of a same-sized conventional flextensional actuator/transducer. The system consists of at least 2 layers which include electromechanically active components. The layers are arranged such that when electric power is applied, one layer contracts in a transverse direction while the second layer expands in a transverse direction which is perpendicular to the transverse direction of the first layer. An alternate embodiment includes a third layer. In this embodiment, the outer two layers contract in parallel transverse directions while the middle layer expands in a transverse direction which is perpendicular to the transverse direction of the outer layers.

MBE grown III-V strain relaxed buffer layers and superlattices characterized by atomic force microscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Howard, A.J.; Fritz, I.J.; Drummond, T.J.

1993-11-01

Using atomic force microscopy (AFM), the authors have investigated the effects of growth temperature and dopant incorporation on the surface morphology of MBE grown graded buffer layers and strained layer superlattices (SLSs) in the InGaAlAs/GaAs and InAsSb/InSb material systems. The AFM results show quantitatively that over the temperature range from 380 to 545 C, graded in{sub x}Al{sub 1{minus}x}As(x = 0.05 {minus} 0.32) buffer layers grown at high temperatures ({approximately}520 C), and graded In{sub x}Ga{sub 1{minus}x}As (x = 0.05 {minus} 0.33) buffer layers and In{sub 0.4}Ga{sub 0.6}As/In{sub 0.26}Al{sub 0.35}Ga{sub 0.39}As SLSs grown at low temperatures ({approximately}400 C) have the lowest RMSmore » roughness. Also, for SLSs InAs{sub 0.21}Sb{sub 0.79}/InSb, undoped layers grown at 470 C were smoother than undoped layers grown at 420 C and Be-doped layers grown at 470 C. These results illustrate the role of surface tension in the growth of strained layer materials near the melting temperature of the InAs{sub x}Sb{sub {minus}x}/InSb superlattice. Nomarski interference and transmission electron microscopies, IR photoluminescence, x-ray diffraction, and photocurrent spectroscopy were also used to evaluate the relative quality of the material but usually, the results were not conclusive.« less

Modal response of a computational vocal fold model with a substrate layer of adipose tissue.

PubMed

Jones, Cameron L; Achuthan, Ajit; Erath, Byron D

2015-02-01

This study demonstrates the effect of a substrate layer of adipose tissue on the modal response of the vocal folds, and hence, on the mechanics of voice production. Modal analysis is performed on the vocal fold structure with a lateral layer of adipose tissue. A finite element model is employed, and the first six mode shapes and modal frequencies are studied. The results show significant changes in modal frequencies and substantial variation in mode shapes depending on the strain rate of the adipose tissue. These findings highlight the importance of considering adipose tissue in computational vocal fold modeling.

Strained layer relaxation effect on current crowding and efficiency improvement of GaN based LED

NASA Astrophysics Data System (ADS)

Aurongzeb, Deeder

2012-02-01

Efficiency droop effect of GaN based LED at high power and high temperature is addressed by several groups based on career delocalization and photon recycling effect(radiative recombination). We extend the previous droop models to optical loss parameters. We correlate stained layer relaxation at high temperature and high current density to carrier delocalization. We propose a third order model and show that Shockley-Hall-Read and Auger recombination effect is not enough to account for the efficiency loss. Several strained layer modification scheme is proposed based on the model.

A chronicle of serologic response in commercial layer chickens to vaccination with commercial F strain Mycoplasma gallisepticum vaccine.

PubMed

Branton, S L; Leigh, S A; Purswell, J L; Evans, J D; Collier, S D; Olanrewaju, H A; Pharr, G T

2010-09-01

Vaccination of multi-age layer operations, wherein one million plus commercial layer chickens are housed, has been spurious until the development of a self-propelled, constant-speed spray vaccinator. Still, even with its use, live Mycoplasma gallisepticum (MG) vaccinations have been questionable in terms of seroconversion. Using the vaccinator as a research tool over the past 5 yr, factors have been elucidated which impact seroconversion to one live MG vaccine in particular, the F strain of MG (FMG). These factors include the type of nozzle used to spray the vaccine, the temperature of the water used to rehydrate and administer the vaccine, and the pH and osmolarity of the fluid used to apply the vaccine. In the present study, one farm was monitored for its seroconversion rates over 4 1/2 yr, during which time the FMG vaccination protocol was amended as factors were identified that enhanced seroconversion rates. The results of this study showed that implementation and inclusion of the optimized factors into the vaccination protocol for FMG enhanced seroconversion rates because they went from an initial 50%-55% positive seroconversion rate to a consistent 100% positive seroconversion rate over the 56-mo study period.

The influence of coating technologies on stress-strain characteristics of the sample at periodic loading

NASA Astrophysics Data System (ADS)

Zakharchenko, K. V.; Zubkov, V. P.; Kapustin, V. I.; Maksimovski, E. A.; Talanin, A. V.

2017-10-01

The article is devoted to the research on influence of coating technologies on stress-strain characteristics of a heterogeneous sample (the substrate-coating system) at periodic stress-controlled loading. The comparison of stress-strain characteristics of samples with three types of surface layer showed that the coatings lead to the change in stress at which inelastic phenomena appear in the material. Apart stress-strain characteristics of samples, microrelief on the samples’ surface and formation of a slipband in the grain structure of the coatings were studied in the experiment. It is stated that cold dynamic spraying, which is performed by centrifugal acceleration of particles in vacuum, makes it possible to obtain a coating with better strength and stress-strain characteristics in comparison with cladding.

Influence of supplemental dietary poultry fat, phytase, and 25-hydroxycholecalciferol on the blood characteristics of commercial layers inoculated before or at the onset of lay with F-strain Mycoplasma gallisepticum

USDA-ARS?s Scientific Manuscript database

The effects of 2 supplemental levels of dietary poultry fat (PF) and the combination of PF, phytase (PHY) and 25-hydroxycholecalciferol [25(OH)D] on the blood characteristics of commercial layers inoculated with F-strain Mycoplasma gallisepticum (FMG) were investigated in 2 trials. Sham and FMG ino...

Influence of supplemental dietary poultry fat, phytase, and 25-hydroxycholecalciferol on the egg characteristics of commercial layers inoculated before or at the onset of lay with F-strain Mycoplasma gallisepticum

USDA-ARS?s Scientific Manuscript database

The effects of 2 supplemental levels of dietary poultry fat (PF) and the combination of PF, phytase (PHY) and 25-hydroxycholecalciferol (D3) on the egg characteristics of commercial layers inoculated with F-strain Mycoplasma gallisepticum (FMG) were investigated in 2 trials. Sham and FMG inoculatio...

The effects of perturbations on the strain distribution in numerical simulations - elasto-viscoplastic modeling of boudinage as a case study

NASA Astrophysics Data System (ADS)

Peters, Max; Karrech, Ali; Poulet, Thomas; Herwegh, Marco; Regenauer-Lieb, Klaus

2014-05-01

During necking of a mechanically stiffer layer embedded in a weaker matrix, relatively large amounts of strain localize in small areas. As this deformation style appears under distinct geological conditions, necking phenomena, e.g. boudinaged veins, are associated with a variety of deformation modes. So far, there exists rather limited knowledge about the origin of instabilities and their role as precursory structures, i.e. strong localization of elastic energy affecting further plastic deformation (e.g. Regenauer-Lieb & Yuen, 1998; 2004; Karrech et al., 2011a). We applied the finite element solver ABAQUS in order to investigate the 2-D strain distribution in layers including different mechanical material properties during plane strain co-axial deformation. First, linear perturbation analyses were performed in order to evaluate the imperfection sensitivity in the elastic and viscous regimes. We perform a classical modal analysis to determine the natural mode shapes and frequencies of our geological structure during arbitrary vibrations. This analysis aims at detecting the eigenmodes of the geological structure, which are sinusoidal vibrations with geometry specific natural modal shapes and frequencies. The eigenvalues represent the nodal points where the onset of (visco)-elasto-plastic localization can initiate in the structure (Rice, 1977). The eigenmodes, eigenvalues and eigenvectors are highly sensitive to the layer-box' aspect ratio and differences in Young's moduli, or effective viscosity, respectively. Boundary effect-free strain propagation occurs for layer-box aspect ratios smaller than 1:10. Second, these preloading structures were used as seeds for imperfections in elasto-viscoplastic numerical modeling of continuous necking of a coarse-grained mineral layer embedded in a finer-grained matrix (pinch-and-swell type of boudinage), following the thermo-mechanical coupling of grain size evolutions by Herwegh et al. (in press). The evolution of symmetric necks seems to coincide with the transition from dislocation to diffusion creep dominated viscous flow with dramatic grain size reduction and grain growth from swell to neck, respectively, at relatively high extensional strains. Strain propagates from initial stress concentrations in the layer (necks) at an angle of 45° into the matrix, in form of conjugate shear band sets. Preliminary results show that pre-calculated eigenmodes (and corresponding imperfection sizes) amplify these concentrations and lead to a significant reduction of computational time for individual simulations. Moreover, the strain imperfections seeded around the pre-calculated distribution severely change the geometry of necking structures and amount of accommodated plastic strain. We reveal that elastic stress concentrations control localized visco-plastic deformation, which is expressed in the plastic strain energy increase in necking structures. These findings underline the importance of the transient (elasticity and strain hardening) deformation regimes as triggers for plastic deformation and the need for thermodynamics-based (total) energy considerations. REFERENCES Herwegh, M., Poulet, T., Karrech, A. and Regenauer-Lieb, K. (in press). From transient to steady state deformation and grain size: A thermodynamic approach using elasto-visco-plastic numerical modeling. Journal of Geophysical Research. Karrech, A., Regenauer-Lieb, K. and Poulet, T. (2011a). A Damaged visco-plasticity model for pressure and temperature sensitive geomaterials. Journal of Engineering Science 49. Regenauer-Lieb, K., Yuen, D., 1998: Rapid conversion of elastic energy into plastic shear heating during incipient necking of the lithosphere. Geophysical Research Letters, 25. Regenauer-Lieb, K., Yuen, D., 2004. Positive feedback of interacting ductile faults from coupling of equation of state, rheology and thermal-mechanics. Physics of the Earth and Planetary Interiors, 142. Rice, J. R. (1977). The localization of plastic deformation. Theoretical and Applied Mechanics. W. T. Koiter. Amsterdam, North-Holland: 207-220.

A benchmark of co-flow and cyclic deposition/etch approaches for the selective epitaxial growth of tensile-strained Si:P

NASA Astrophysics Data System (ADS)

Hartmann, J. M.; Veillerot, M.; Prévitali, B.

2017-10-01

We have compared co-flow and cyclic deposition/etch processes for the selective epitaxial growth of Si:P layers. High growth rates, relatively low resistivities and significant amounts of tensile strain (up to 10 nm min-1, 0.55 mOhm cm and a strain equivalent to 1.06% of substitutional C in Si:C layers) were obtained at 700 °C, 760 Torr with a co-flow approach and a SiH2Cl2 + PH3 + HCl chemistry. This approach was successfully used to thicken the sources and drains regions of n-type fin-shaped Field Effect Transistors. Meanwhile, the (Si2H6 + PH3/HCl + GeH4) CDE process evaluated yielded at 600 °C, 80 Torr even lower resistivities (0.4 mOhm cm, typically), at the cost however of the tensile strain which was lost due to (i) the incorporation of Ge atoms (1.5%, typically) into the lattice during the selective etch steps and (ii) a reduction by a factor of two of the P atomic concentration in CDE layers compared to that in layers grown in a single step (5 × 1020 cm-3 compared to 1021 cm-3).

Ultralow threading dislocation density in GaN epilayer on near-strain-free GaN compliant buffer layer and its applications in hetero-epitaxial LEDs

PubMed Central

Shih, Huan-Yu; Shiojiri, Makoto; Chen, Ching-Hsiang; Yu, Sheng-Fu; Ko, Chung-Ting; Yang, Jer-Ren; Lin, Ray-Ming; Chen, Miin-Jang

2015-01-01

High threading dislocation (TD) density in GaN-based devices is a long unresolved problem because of the large lattice mismatch between GaN and the substrate, which causes a major obstacle for the further improvement of next-generation high-efficiency solid-state lighting and high-power electronics. Here, we report InGaN/GaN LEDs with ultralow TD density and improved efficiency on a sapphire substrate, on which a near strain-free GaN compliant buffer layer was grown by remote plasma atomic layer deposition. This “compliant” buffer layer is capable of relaxing strain due to the absorption of misfit dislocations in a region within ~10 nm from the interface, leading to a high-quality overlying GaN epilayer with an unusual TD density as low as 2.2 × 105 cm−2. In addition, this GaN compliant buffer layer exhibits excellent uniformity up to a 6” wafer, revealing a promising means to realize large-area GaN hetero-epitaxy for efficient LEDs and high-power transistors. PMID:26329829

Geometric consequences of ductile fabric development from brittle shear faults in mafic melt sheets: Evidence from the Sudbury Igneous Complex, Canada

NASA Astrophysics Data System (ADS)

Lenauer, Iris; Riller, Ulrich

2012-02-01

Compared to felsic igneous rocks the genetic relationship between brittle and ductile fabric development and its influence on the geometry of deformed mafic melt sheets has received little attention in structural analyses. We explore these relationships using the Sudbury Igneous Complex (SIC) as an example. The SIC is the relic of a layered impact melt sheet that was transformed into a fold basin, the Sudbury Basin, during Paleoproterozoic deformation at the southern margin of the Archean Superior Province. We studied brittle and ductile strain fabrics on the outcrop and map scales in the southern Sudbury Basin, notably in the Norite and Quartz Gabbro layers of the SIC. Here, deformation is heterogeneous and occurred under variable rheological conditions, evident by the development of brittle shear fractures, brittle-ductile shear zones and pervasive ductile strain. The mineral fabrics formed under low- to middle greenschist-facies metamorphism, whereby brittle deformation caused hydrolytic weakening and ductile fabric development. Principal strain axes inferred from all structural elements are collinear and point to a single deformation regime that led to thinning of SIC layers during progressive deformation. Ductile fabric development profoundly influenced the orientation of SIC material planes, such as lithological contacts and magmatic mineral fabrics. More specifically, these planar structural elements are steep where the SIC underwent large magnitudes of thinning, i.e., in the south limb of the Sudbury Basin. Here, the actual tilt component of material planes is likely smaller than its maximum total rotation (60°) inferred from inclined igneous layering in the Norite. Our field-based study shows that ductile fabric development from brittle faults can have a profound influence on the rotational components of primary material planes in deformed igneous melt sheets.

Assembly and Function of the Bacillus anthracis S-Layer.

PubMed

Missiakas, Dominique; Schneewind, Olaf

2017-09-08

Bacillus anthracis, the anthrax agent, is a member of the Bacillus cereus sensu lato group, which includes invasive pathogens of mammals or insects as well as nonpathogenic environmental strains. The genes for anthrax pathogenesis are located on two large virulence plasmids. Similar virulence plasmids have been acquired by other B. cereus strains and enable the pathogenesis of anthrax-like diseases. Among the virulence factors of B. anthracis is the S-layer-associated protein BslA, which endows bacilli with invasive attributes for mammalian hosts. BslA surface display and function are dependent on the bacterial S-layer, whose constituents assemble by binding to the secondary cell wall polysaccharide (SCWP) via S-layer homology (SLH) domains. B. anthracis and other pathogenic B. cereus isolates harbor genes for the secretion of S-layer proteins, for S-layer assembly, and for synthesis of the SCWP. We review here recent insights into the assembly and function of the S-layer and the SCWP.

Strain Effects in Epitaxial VO2 Thin Films on Columnar Buffer-Layer TiO2/Al2O3 Virtual Substrates.

PubMed

Breckenfeld, Eric; Kim, Heungsoo; Burgess, Katherine; Charipar, Nicholas; Cheng, Shu-Fan; Stroud, Rhonda; Piqué, Alberto

2017-01-18

Epitaxial VO 2 /TiO 2 thin film heterostructures were grown on (100) (m-cut) Al 2 O 3 substrates via pulsed laser deposition. We have demonstrated the ability to reduce the semiconductor-metal transition (SMT) temperature of VO 2 to ∼44 °C while retaining a 4 order of magnitude SMT using the TiO 2 buffer layer. A combination of electrical transport and X-ray diffraction reciprocal space mapping studies help examine the specific strain states of VO 2 /TiO 2 /Al 2 O 3 heterostructures as a function of TiO 2 film growth temperatures. Atomic force microscopy and transmission electron microscopy analyses show that the columnar microstructure present in TiO 2 buffer films is responsible for the partially strained VO 2 film behavior and subsequently favorable transport characteristics with a lower SMT temperature. Such findings are of crucial importance for both the technological implementation of the VO 2 system, where reduction of its SMT temperature is widely sought, as well as the broader complex oxide community, where greater understanding of the evolution of microstructure, strain, and functional properties is a high priority.

Reynolds number scaling of straining motions in turbulence

NASA Astrophysics Data System (ADS)

Elsinga, Gerrit; Ishihara, T.; Goudar, M. V.; da Silva, C. B.; Hunt, J. C. R.

2017-11-01

Strain is an important fluid motion in turbulence as it is associated with the kinetic energy dissipation rate, vorticity stretching, and the dispersion of passive scalars. The present study investigates the scaling of the turbulent straining motions by evaluating the flow in the eigenframe of the local strain-rate tensor. The analysis is based on DNS of homogeneous isotropic turbulence covering a Reynolds number range Reλ = 34.6 - 1131. The resulting flow pattern reveals a shear layer containing tube-like vortices and a dissipation sheet, which both scale on the Kolmogorov length scale, η. The vorticity stretching motions scale on the Taylor length scale, while the flow outside the shear layer scales on the integral length scale. These scaling results are consistent with those in wall-bounded flow, which suggests a quantitative universality between the different flows. The overall coherence length of the vorticity is 120 η in all directions, which is considerably larger than the typical size of individual vortices, and reflects the importance of spatial organization at the small scales. Transitions in flow structure are identified at Reλ 45 and 250. Below these respective Reynolds numbers, the small-scale motions and the vorticity stretching motions appear underdeveloped.

Simulation of Intergranular Ductile Cracking in β Titanium Alloys Based on a Micro-Mechanical Damage Model

PubMed Central

Li, Huan; Li, Jinshan; Tang, Bin; Fan, Jiangkun; Yuan, Huang

2017-01-01

The intergranular crack propagation of the lamellar structure β titanium alloys is investigated by using a modified Gurson-type damage model. The representative microstructure of the lamellar alloy, which consists of the soft α phase layer surrounding the hard grain interiors, is generated based on an advanced Voronoi algorithm. Both the normal fracture due to void growth and the shear fracture associated with void shearing are considered for the grain boundary α layer. The individual phase properties are determined according to the experimental nanoindentation result and the macroscopic stress–strain curve from a uni-axial tensile test. The effects of the strain hardening exponent of the grain interiors and the void shearing mechanism of the grain boundary α layer on fracture toughness and the intergranular crack growth behavior are emphatically studied. The computational predictions indicate that fracture toughness can be increased with increasing the strain hardening ability of the grain interiors and void shearing can be deleterious to fracture toughness. Based on the current simulation technique, qualitative understanding of relationships between the individual phase features and the fracture toughness of the lamellar alloys can be obtained, which provides useful suggestions to the heat treatment process of the β titanium alloys. PMID:29084171

Simulation of Intergranular Ductile Cracking in β Titanium Alloys Based on a Micro-Mechanical Damage Model.

PubMed

Li, Huan; Li, Jinshan; Tang, Bin; Fan, Jiangkun; Yuan, Huang

2017-10-30

The intergranular crack propagation of the lamellar structure β titanium alloys is investigated by using a modified Gurson-type damage model. The representative microstructure of the lamellar alloy, which consists of the soft α phase layer surrounding the hard grain interiors, is generated based on an advanced Voronoi algorithm. Both the normal fracture due to void growth and the shear fracture associated with void shearing are considered for the grain boundary α layer. The individual phase properties are determined according to the experimental nanoindentation result and the macroscopic stress-strain curve from a uni-axial tensile test. The effects of the strain hardening exponent of the grain interiors and the void shearing mechanism of the grain boundary α layer on fracture toughness and the intergranular crack growth behavior are emphatically studied. The computational predictions indicate that fracture toughness can be increased with increasing the strain hardening ability of the grain interiors and void shearing can be deleterious to fracture toughness. Based on the current simulation technique, qualitative understanding of relationships between the individual phase features and the fracture toughness of the lamellar alloys can be obtained, which provides useful suggestions to the heat treatment process of the β titanium alloys.

Topologic connection between 2-D layered structures and 3-D diamond structures for conventional semiconductors

PubMed Central

Wang, Jianwei; Zhang, Yong

2016-01-01

When coming to identify new 2D materials, our intuition would suggest us to look from layered instead of 3D materials. However, since graphite can be hypothetically derived from diamond by stretching it along its [111] axis, many 3D materials can also potentially be explored as new candidates for 2D materials. Using a density functional theory, we perform a systematic study over the common Group IV, III–V, and II–VI semiconductors along different deformation paths to reveal new structures that are topologically connected to but distinctly different from the 3D parent structure. Specifically, we explore two major phase transition paths, originating respectively from wurtzite and NiAs structure, by applying compressive and tensile strain along the symmetry axis, and calculating the total energy changes to search for potential metastable states, as well as phonon spectra to examine the structural stability. Each path is found to further split into two branches under tensile strain–low buckled and high buckled structures, which respectively lead to a low and high buckled monolayer structure. Most promising new layered or planar structures identified include BeO, GaN, and ZnO on the tensile strain side, Ge, Si, and GaP on the compressive strain side. PMID:27090430

Surface Nanocrystallization and Amorphization of Dual-Phase TC11 Titanium Alloys under Laser Induced Ultrahigh Strain-Rate Plastic Deformation

PubMed Central

Luo, Sihai; Zhou, Liucheng; Wang, Xuede; Cao, Xin; Nie, Xiangfan

2018-01-01

As an innovative surface technology for ultrahigh strain-rate plastic deformation, laser shock peening (LSP) was applied to the dual-phase TC11 titanium alloy to fabricate an amorphous and nanocrystalline surface layer at room temperature. X-ray diffraction, transmission electron microscopy, and high-resolution transmission electron microscopy (HRTEM) were used to investigate the microstructural evolution, and the deformation mechanism was discussed. The results showed that a surface nanostructured surface layer was synthesized after LSP treatment with adequate laser parameters. Simultaneously, the behavior of dislocations was also studied for different laser parameters. The rapid slipping, accumulation, annihilation, and rearrangement of dislocations under the laser-induced shock waves contributed greatly to the surface nanocrystallization. In addition, a 10 nm-thick amorphous structure layer was found through HRTEM in the top surface and the formation mechanism was attributed to the local temperature rising to the melting point, followed by its subsequent fast cooling. PMID:29642379

Surface Nanocrystallization and Amorphization of Dual-Phase TC11 Titanium Alloys under Laser Induced Ultrahigh Strain-Rate Plastic Deformation.

PubMed

Luo, Sihai; Zhou, Liucheng; Wang, Xuede; Cao, Xin; Nie, Xiangfan; He, Weifeng

2018-04-06

As an innovative surface technology for ultrahigh strain-rate plastic deformation, laser shock peening (LSP) was applied to the dual-phase TC11 titanium alloy to fabricate an amorphous and nanocrystalline surface layer at room temperature. X-ray diffraction, transmission electron microscopy, and high-resolution transmission electron microscopy (HRTEM) were used to investigate the microstructural evolution, and the deformation mechanism was discussed. The results showed that a surface nanostructured surface layer was synthesized after LSP treatment with adequate laser parameters. Simultaneously, the behavior of dislocations was also studied for different laser parameters. The rapid slipping, accumulation, annihilation, and rearrangement of dislocations under the laser-induced shock waves contributed greatly to the surface nanocrystallization. In addition, a 10 nm-thick amorphous structure layer was found through HRTEM in the top surface and the formation mechanism was attributed to the local temperature rising to the melting point, followed by its subsequent fast cooling.

Carbon nanotubes (CNTs) based strain sensors for a wearable monitoring and biofeedback system for pressure ulcer prevention and rehabilitation.

PubMed

Boissy, Patrick; Genest, Jonathan; Patenaude, Johanne; Poirier, Marie-Sol; Chenel, Vanessa; Béland, Jean-Pierre; Legault, Georges-Auguste; Bernier, Louise; Tapin, Danielle; Beauvais, Jacques

2011-01-01

This paper presents an overview of the functioning principles of CNTs and their electrical and mechanical properties when used as strain sensors and describes a system embodiment for a wearable monitoring and biofeedback platform for use in pressure ulcer prevention and rehabilitation. Two type of CNTs films (multi-layered CNTs film vs purified film) were characterized electrically and mechanically for potential use as source material. The loosely woven CNTs film (multi-layered) showed substantial less sensitivity than the purified CNTs film but had an almost linear response to stress and better mechanical properties. CNTs have the potential to achieve a much higher sensitivity to strain than other piezoresistors based on regular of conductive particles such as commercially available resistive inks and could become an innovative source material for wearable strain sensors. We are currently continuing the characterization of CNTs based strain sensors and exploring their use in a design for 3-axis strain sensors.

The numerical simulation study of the dynamic evolutionary processes in an earthquake cycle on the Longmen Shan Fault

NASA Astrophysics Data System (ADS)

Tao, Wei; Shen, Zheng-Kang; Zhang, Yong

2016-04-01

The Longmen Shan, located in the conjunction of the eastern margin the Tibet plateau and Sichuan basin, is a typical area for studying the deformation pattern of the Tibet plateau. Following the 2008 Mw 7.9 Wenchuan earthquake (WE) rupturing the Longmen Shan Fault (LSF), a great deal of observations and studies on geology, geophysics, and geodesy have been carried out for this region, with results published successively in recent years. Using the 2D viscoelastic finite element model, introducing the rate-state friction law to the fault, this thesis makes modeling of the earthquake recurrence process and the dynamic evolutionary processes in an earthquake cycle of 10 thousand years. By analyzing the displacement, velocity, stresses, strain energy and strain energy increment fields, this work obtains the following conclusions: (1) The maximum coseismic displacement on the fault is on the surface, and the damage on the hanging wall is much more serious than that on the foot wall of the fault. If the detachment layer is absent, the coseismic displacement would be smaller and the relative displacement between the hanging wall and foot wall would also be smaller. (2) In every stage of the earthquake cycle, the velocities (especially the vertical velocities) on the hanging wall of the fault are larger than that on the food wall, and the values and the distribution patterns of the velocity fields are similar. While in the locking stage prior to the earthquake, the velocities in crust and the relative velocities between hanging wall and foot wall decrease. For the model without the detachment layer, the velocities in crust in the post-seismic stage is much larger than those in other stages. (3) The maximum principle stress and the maximum shear stress concentrate around the joint of the fault and detachment layer, therefore the earthquake would nucleate and start here. (4) The strain density distribution patterns in stages of the earthquake cycle are similar. There are two concentration areas in the model, one is located in the mid and upper crust on the hanging wall where the strain energy could be released by permanent deformation like folding, and the other lies in the deep part of the fault where the strain energy could be released by earthquakes. (5) The whole earthquake dynamic process could be clearly reflected by the evolutions of the strain energy increments on the stages of the earthquake cycle. In the inter-seismic period, the strain energy accumulates relatively slowly; prior to the earthquake, the fault is locking and the strain energy accumulates fast, and some of the strain energy is released on the upper crust on the hanging wall of the fault. In coseismic stage, the strain energy is released fast along the fault. In the poseismic stage, the slow accumulation process of strain recovers rapidly as that in the inerseismic period in around one hundred years. The simulation study in this thesis would help better understand the earthquake dynamic process.

Materials properties and dislocation dynamics in InAsP compositionally graded buffers on InP substrates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jandl, Adam, E-mail: jandl@mit.edu; Bulsara, Mayank T.; Fitzgerald, Eugene A.

The properties of InAs{sub x}P{sub 1−x} compositionally graded buffers grown by metal organic chemical vapor deposition are investigated. We report the effects of strain gradient (ε/thickness), growth temperature, and strain initiation sequence (gradual or abrupt strain introduction) on threading dislocation density, surface roughness, epi-layer relaxation, and tilt. We find that gradual introduction of strain causes increased dislocation densities (>10{sup 6}/cm{sup 2}) and tilt of the epi-layer (>0.1°). A method of abrupt strain initiation is proposed which can result in dislocation densities as low as 1.01 × 10{sup 5} cm{sup −2} for films graded from the InP lattice constant to InAs{sub 0.15}P{sub 0.85}.more » A model for a two-energy level dislocation nucleation system is proposed based on our results.« less

Antimicrobial susceptibility pattern of Brachyspira intermedia isolates from European layers.

PubMed

Verlinden, Marc; Boyen, Filip; Pasmans, Frank; Garmyn, An; Haesebrouck, Freddy; Martel, An

2011-09-01

A broth microdilution method was used to determine the antimicrobial susceptibility of 20 Brachyspira intermedia isolates obtained from different layer flocks in Belgium and The Netherlands between 2008 and 2010. The antimicrobial agents used were tylosin, tilmicosin, tiamulin, valnemulin, doxycycline, and lincomycin. The minimal inhibitory concentration (MIC) distribution patterns of tylosin, tilmicosin, lincomycin, and doxycycline were bimodal, demonstrating acquired resistance against doxycycline in three strains, against the macrolides in two strains, and against lincomycin in one strain. The MICs of tiamulin and valnemulin showed a monomodal distribution, but with tailing toward the higher MIC values, possibly suggesting low-level acquired resistance in six isolates. Sequencing revealed a G1058C mutation in the 16S rRNA gene in all doxycycline-resistant strains. The strain resistant to tylosin, tilmicosin, and lincomycin had an A2058T mutation in the 23S rRNA gene.

Tuning of in-plane optical anisotropy by inserting ultra-thin InAs layer at interfaces in (001)-grown GaAs/AlGaAs quantum wells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yu, J. L., E-mail: jlyu@semi.ac.cn; Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing 100083; Key Laboratory of Optoelectronic Materials Chemistry and Physics, Chinese Academy of Sciences, Fuzhou 350002

2015-01-07

The in-plane optical anisotropy (IPOA) in (001)-grown GaAs/AlGaAs quantum wells (QWs) with different well widths varying from 2 nm to 8 nm has been studied by reflectance difference spectroscopy. Ultra-thin InAs layers with thickness ranging from 0.5 monolayer (ML) to 1.5 ML have been inserted at GaAs/AlGaAs interfaces to tune the asymmetry in the QWs. It is demonstrated that the IPOA can be accurately tailored by the thickness of the inserted ultra-thin InAs layer at the interfaces. Strain-induced IPOA has also been extracted by using a stress apparatus. We find that the intensity of the strain-induced IPOA decreases with the thickness ofmore » the inserted InAs layer, while that of the interface-induced IPOA increases with the thickness of the InAs layer. Theoretical calculations based on 6 band k ⋅ p theory have been carried out, and good agreements with experimental results are obtained. Our results demonstrate that, the IPOA of the QWs can be greatly and effectively tuned by inserting an ultra-thin InAs layer with different thicknesses at the interfaces of QWs, which does not significantly influence the transition energies and the transition probability of QWs.« less

Characterization of High Ge Content SiGe Heterostructures and Graded Alloy Layers Using Spectroscopic Ellipsometry

NASA Technical Reports Server (NTRS)

Heyd, A. R.; Alterovitz, S. A.; Croke, E. T.

1995-01-01

Si(x)Ge(1-x)heterostructures on Si substrates have been widely studied due to the maturity of Si technology. However, work on Si(x)Ge)1-x) heterostructures on Ge substrates has not received much attention. A Si(x)Ge(1-x) layer on a Si substrate is under compressive strain while Si(x)Ge(1-x) on Ge is under tensile strain; thus the critical points will behave differently. In order to accurately characterize high Ge content Si(x)Ge(1-x) layers the energy shift algorithm used to calculate alloy compositions, has been modified. These results have been used along with variable angle spectroscopic ellipsometry (VASE) measurements to characterize Si(x)Ge(1-x)/Ge superlattices grown on Ge substrates. The results agree closely with high resolution x-ray diffraction measurements made on the same samples. The modified energy shift algorithm also allows the VASE analysis to be upgraded in order to characterize linearly graded layers. In this work VASE has been used to characterize graded Si(x)Ge(1-x) layers in terms of the total thickness, and the start and end alloy composition. Results are presented for a 1 micrometer Si(x)Ge(1-x) layer linearly graded in the range 0.5 less than or equal to x less than or equal to 1.0.

High strain rate deformation of layered nanocomposites

NASA Astrophysics Data System (ADS)

Lee, Jae-Hwang; Veysset, David; Singer, Jonathan P.; Retsch, Markus; Saini, Gagan; Pezeril, Thomas; Nelson, Keith A.; Thomas, Edwin L.

2012-11-01

Insight into the mechanical behaviour of nanomaterials under the extreme condition of very high deformation rates and to very large strains is needed to provide improved understanding for the development of new protective materials. Applications include protection against bullets for body armour, micrometeorites for satellites, and high-speed particle impact for jet engine turbine blades. Here we use a microscopic ballistic test to report the responses of periodic glassy-rubbery layered block-copolymer nanostructures to impact from hypervelocity micron-sized silica spheres. Entire deformation fields are experimentally visualized at an exceptionally high resolution (below 10 nm) and we discover how the microstructure dissipates the impact energy via layer kinking, layer compression, extreme chain conformational flattening, domain fragmentation and segmental mixing to form a liquid phase. Orientation-dependent experiments show that the dissipation can be enhanced by 30% by proper orientation of the layers.

High strain rate deformation of layered nanocomposites.

PubMed

Lee, Jae-Hwang; Veysset, David; Singer, Jonathan P; Retsch, Markus; Saini, Gagan; Pezeril, Thomas; Nelson, Keith A; Thomas, Edwin L

2012-01-01

Insight into the mechanical behaviour of nanomaterials under the extreme condition of very high deformation rates and to very large strains is needed to provide improved understanding for the development of new protective materials. Applications include protection against bullets for body armour, micrometeorites for satellites, and high-speed particle impact for jet engine turbine blades. Here we use a microscopic ballistic test to report the responses of periodic glassy-rubbery layered block-copolymer nanostructures to impact from hypervelocity micron-sized silica spheres. Entire deformation fields are experimentally visualized at an exceptionally high resolution (below 10 nm) and we discover how the microstructure dissipates the impact energy via layer kinking, layer compression, extreme chain conformational flattening, domain fragmentation and segmental mixing to form a liquid phase. Orientation-dependent experiments show that the dissipation can be enhanced by 30% by proper orientation of the layers.

Mean-velocity profile of smooth channel flow explained by a cospectral budget model with wall-blockage

DOE PAGES

McColl, Kaighin A.; Katul, Gabriel G.; Gentine, Pierre; ...

2016-03-16

A series of recent studies has shown that a model of the turbulent vertical velocity variance spectrum (F vv) combined with a simplified cospectral budget can reproduce many macroscopic flow properties of turbulent wall-bounded flows, including various features of the mean-velocity profile (MVP), i.e., the "law of the wall". While the approach reasonably models the MVP's logarithmic layer, the buffer layer displays insufficient curvature compared to measurements. The assumptions are re-examined here using a direct numerical simulation (DNS) dataset at moderate Reynolds number that includes all the requisite spectral and co-spectral information. Starting with several hypotheses for the cause ofmore » the "missing" curvature in the buffer layer, it is shown that the curvature deficit is mainly due to mismatches between (i) the modelled and DNS-observed pressure-strain terms in the cospectral budget and (ii) the DNS-observed F vv and the idealized form used in previous models. By replacing the current parameterization for the pressure-strain term with an expansive version that directly accounts for wall-blocking effects, the modelled and DNS reported pressure-strain profiles match each other in the buffer and logarithmic layers. Forcing the new model with DNS-reported F vv rather than the idealized form previously used reproduces the missing buffer layer curvature to high fidelity thereby confirming the "spectral link" between F vv and the MVP across the full profile. A broad implication of this work is that much of the macroscopic properties of the flow (such as the MVP) may be derived from the energy distribution in turbulent eddies (i.e., F vv) representing the microstate of the flow, provided the link between them accounts for wall-blocking.« less

Infrared fingerprints of few-layer black phosphorus

PubMed Central

Zhang, Guowei; Huang, Shenyang; Chaves, Andrey; Song, Chaoyu; Özçelik, V. Ongun; Low, Tony; Yan, Hugen

2017-01-01

Black phosphorus is an infrared layered material. Its bandgap complements other widely studied two-dimensional materials: zero-gap graphene and visible/near-infrared gap transition metal dichalcogenides. Although highly desirable, a comprehensive infrared characterization is still lacking. Here we report a systematic infrared study of mechanically exfoliated few-layer black phosphorus, with thickness ranging from 2 to 15 layers and photon energy spanning from 0.25 to 1.36 eV. Each few-layer black phosphorus exhibits a thickness-dependent unique infrared spectrum with a series of absorption resonances, which reveals the underlying electronic structure evolution and serves as its infrared fingerprints. Surprisingly, unexpected absorption features, which are associated with the forbidden optical transitions, have been observed. Furthermore, we unambiguously demonstrate that controllable uniaxial strain can be used as a convenient and effective approach to tune the electronic structure of few-layer black phosphorus. Our study paves the way for black phosphorus applications in infrared photonics and optoelectronics. PMID:28059084

Measurement of strain and tensile force of the supraspinatus tendon under conditions that simulates low angle isometric elevation of the gleno-humeral joint: Influence of adduction torque and joint positioning.

PubMed

Miyamoto, Hiroki; Aoki, Mitsuhiro; Hidaka, Egi; Fujimiya, Mineko; Uchiyama, Eiichi

2017-12-01

Recently, supraspinatus muscle exercise has been reported to treat rotator cuff disease and to recover shoulder function. However, there have been no report on the direct measurement of strain on the supraspinatus tendon during simulated isometric gleno-humeral joint elevation. Ten fresh-frozen shoulder specimens with the rotator cuff complex left intact were used as experimental models. Isometric gleno-humeral joint elevation in a sitting position was reproduced with low angle of step-by-step elevation in the scapular plane and strain was measured on the surface layer of the supraspinatus tendon. In isometric conditions, applied tensile force of the supraspinatus tendon increased significantly with increases in adduction torque on the gleno-humeral joint. Significant increases in the strain on the layer were observed by increase in adduction torque, which were recorded in isometric elevation at -10° and 0°, but little increase in the strain was observed at 10° or greater gleno-humeral elevation. Increased strain on the surface layer of the supraspinatus tendon was observed during isometric gleno-humeral elevation from -10 to 0°. These findings demonstrate a potential risk of inducing overstretching of the supraspinatus tendon during supraspinatus muscle exercise. Copyright © 2017 Elsevier Ltd. All rights reserved.

Finite Element Simulation and X-Ray Microdiffraction Study of Strain Partitioning in a Layered Nanocomposite

DOE PAGES

Barabash, R. I.; Agarwal, V.; Koric, S.; ...

2016-01-01

Tmore » he depth-dependent strain partitioning across the interfaces in the growth direction of the NiAl/Cr(Mo) nanocomposite between the Cr and NiAl lamellae was directly measured experimentally and simulated using a finite element method (FEM). Depth-resolved X-ray microdiffraction demonstrated that in the as-grown state both Cr and NiAl lamellae grow along the 111 direction with the formation of as-grown distinct residual ~0.16% compressive strains for Cr lamellae and ~0.05% tensile strains for NiAl lamellae. hree-dimensional simulations were carried out using an implicit FEM. First simulation was designed to study residual strains in the composite due to cooling resulting in formation of crystals. Strains in the growth direction were computed and compared to those obtained from the microdiffraction experiments. Second simulation was conducted to understand the combined strains resulting from cooling and mechanical indentation of the composite. Numerical results in the growth direction of crystal were compared to experimental results confirming the experimentally observed trends.« less

Guided elastic waves in a pre-stressed compressible interlayer

PubMed

Sotiropoulos

2000-03-01

The propagation of guided elastic waves in a pre-stressed elastic compressible layer embedded in a different compressible material is examined. The waves propagate parallel to the planar layer interfaces as a superposed dynamic stress state on the statically pre-stressed layer and host material. The underlying stress condition in the two materials is characterized by equibiaxial in-plane deformations with common principal axes of strain, one of the axes being perpendicular to the layering. Both materials have arbitrary strain energy functions. The dispersion equation is derived in explicit form. Analysis of the dispersion equation reveals the propagation characteristics and their dependence on frequency, material parameters and stress parameters. Combinations of these parameters are also defined for which guided waves cannot propagate.

SLS complementary logic devices with increase carrier mobility

DOEpatents

Chaffin, R.J.; Osbourn, G.C.; Zipperian, T.E.

1991-07-09

In an electronic device comprising a semiconductor material and having at least one performance characteristic which is limited by the mobility of holes in the semiconductor material, said mobility being limited because of a valence band degeneracy among high-mobility and low-mobility energy levels accessible to said holes at the energy-momentum space maximum, an improvement is provided wherein the semiconductor material is a strained layer superlattice (SLS) whose layer compositions and layer thicknesses are selected so that the strain on the layers predominantly containing said at least one carrier type splits said degeneracy and modifies said energy levels around said energy-momentum space maximum in a manner whereby said limitation on the mobility of said holes is alleviated. 5 figures.

SLS complementary logic devices with increase carrier mobility

DOEpatents

Chaffin, Roger J.; Osbourn, Gordon C.; Zipperian, Thomas E.

1991-01-01

In an electronic device comprising a semiconductor material and having at least one performance characteristic which is limited by the mobility of holes in the semiconductor material, said mobility being limited because of a valence band degeneracy among high-mobility and low-mobility energy levels accessible to said holes at the energy-momentum space maximum, an improvement is provided wherein the semiconductor material is a strained layer superlattice (SLS) whose layer compositions and layer thicknesses are selected so that the strain on the layers predominantly containing said at least one carrier type splits said degeneracy and modifies said energy levels around said energy-momentum space maximum in a manner whereby said limitation on the mobility of said holes is alleviated.

Giant voltage-controlled magnetic anisotropy effect in a crystallographically strained CoFe system

NASA Astrophysics Data System (ADS)

Kato, Yushi; Yoda, Hiroaki; Saito, Yoshiaki; Oikawa, Soichi; Fujii, Keiko; Yoshiki, Masahiko; Koi, Katsuhiko; Sugiyama, Hideyuki; Ishikawa, Mizue; Inokuchi, Tomoaki; Shimomura, Naoharu; Shimizu, Mariko; Shirotori, Satoshi; Altansargai, Buyandalai; Ohsawa, Yuichi; Ikegami, Kazutaka; Tiwari, Ajay; Kurobe, Atsushi

2018-05-01

We experimentally demonstrate a giant voltage-controlled magnetic anisotropy (VCMA) coefficient in a crystallographically strained CoFe layer (∼15 monolayers in thickness) in a MgO/CoFe/Ir system. We observed a strong applied voltage dependence of saturation field and an asymmetric concave behavior with giant VCMA coefficients of ‑758 and 1043 fJ V‑1 m‑1. The result of structural analysis reveals epitaxial growth in MgO/CoFe/Ir layers and the orientation relationship MgO(001)[110] ∥ CoFe(001)[100] ∥ Ir(001)[110]. The CoFe layer has a bcc structure and a tetragonal distortion due to the lattice mismatch; therefore, the CoFe layer has a large perpendicular magnetic anisotropy.

Low-Cost Lattice Matching Zn(Se)Te/Si Composite Substrates for HgCdSe and Type-2 Superlattices

DTIC Science & Technology

2013-09-01

far from optimized. In similar fashion, we studied the impact of Zn/Te flux ratio during ZnTe growth. In this case , three ZnTe(100) layers were...6.1 Å, such as HgCdSe and GaSb-based type-II strained-layer superlattices. In this report, we present our findings on the systematic studies of...versus lattice parameter for several semiconductor material systems. We conducted systematic studies on the MBE growth of ZnTe on Si in both (211) and

Screening and identification of a cutinase-producing Rhodotorula mucilaginosa and properties of the cutinase.

PubMed

Zhang, Xiao-Ning; Ran, Qin-Qin; Zhang, Xuejun

2015-01-01

Eucommia leaf contains large amounts of natural active products. In extracting the substances, the most important is the removal of the cuticle layer on the leaves and the cell wall in the leaves of Eucommia ulmoides. But the removal of the cuticle layer is a technical difficulty now. Cutinase (EC3.1.1.74) is a multifunctional enzyme with a common alpha/beta fold structure belonging to hydroplane that can make a substantial degradation of horny fatty acids. So this study isolated bacteria capable of producing cutinase from the lesion of Eucommia leaves and identified the bacteria. The identification using PCR-RFLP method confirmed that the strain belongs to Rhodotorula mucilaginosa. The fermentation conditions of the strain-producing cutinase were optimized in this study. The finding of cutinase-producing R. mucilaginosa is significant because the yeast is more secure than plant pathogens, being suitable for mass production.

Complexation of Uranium by Cells and S-Layer Sheets of Bacillus sphaericus JG-A12

PubMed Central

Merroun, Mohamed L.; Raff, Johannes; Rossberg, André; Hennig, Christoph; Reich, Tobias; Selenska-Pobell, Sonja

2005-01-01

Bacillus sphaericus JG-A12 is a natural isolate recovered from a uranium mining waste pile near the town of Johanngeorgenstadt in Saxony, Germany. The cells of this strain are enveloped by a highly ordered crystalline proteinaceous surface layer (S-layer) possessing an ability to bind uranium and other heavy metals. Purified and recrystallized S-layer proteins were shown to be phosphorylated by phosphoprotein-specific staining, inductive coupled plasma mass spectrometry analysis, and a colorimetric method. We used extended X-ray absorption fine-structure (EXAFS) spectroscopy to determine the structural parameters of the uranium complexes formed by purified and recrystallized S-layer sheets of B. sphaericus JG-A12. In addition, we investigated the complexation of uranium by the vegetative bacterial cells. The EXAFS analysis demonstrated that in all samples studied, the U(VI) is coordinated to carboxyl groups in a bidentate fashion with an average distance between the U atom and the C atom of 2.88 ± 0.02 Å and to phosphate groups in a monodentate fashion with an average distance between the U atom and the P atom of 3.62 ± 0.02 Å. Transmission electron microscopy showed that the uranium accumulated by the cells of this strain is located in dense deposits at the cell surface. PMID:16151146

Polarization Rotation in Ferroelectric Tricolor PbTiO3/SrTiO3/PbZr0.2Ti0.8O3 Superlattices.

PubMed

Lemée, Nathalie; Infante, Ingrid C; Hubault, Cécile; Boulle, Alexandre; Blanc, Nils; Boudet, Nathalie; Demange, Valérie; Karkut, Michael G

2015-09-16

In ferroelectric thin films, controlling the orientation of the polarization is a key element to controlling their physical properties. We use laboratory and synchrotron X-ray diffraction to investigate ferroelectric bicolor PbTiO3/PbZr0.2Ti0.8O3 and tricolor PbTiO3/SrTiO3/PbZr0.2Ti0.8O3 superlattices and to study the role of the SrTiO3 layers on the domain structure. In the tricolor superlattices, we demonstrate the existence of 180° ferroelectric stripe nanodomains, induced by the depolarization field produced by the SrTiO3 layers. Each ultrathin SrTiO3 layer modifies the electrostatic boundary conditions between the ferroelectric layers compared to the corresponding bicolor structures, leading to the suppression of the a/c polydomain states. Combined with the electrostatic effect, the tensile strain induced by PbZr0.2Ti0.8O3 in the PbTiO3 layers leads to polarization rotation in the system as evidenced by grazing incidence X-ray measurements. This polarization rotation is associated with the monoclinic Mc phase as revealed by the splitting of the (HHL) and (H0L) reciprocal lattice points. This work demonstrates that the tricolor paraelectric/ferroelectric superlattices constitute a tunable system to investigate the concomitant effects of strains and depolarizing fields. Our studies provide a pathway to stabilize a monoclinic symmetry in ferroelectric layers, which is of particular interest for the enhancement of the piezoelectric properties.

Quantitative evaluation of longitudinal strain in layer-specific myocardium during normal pregnancy in China.

PubMed

Cong, Juan; Wang, Zhibin; Jin, Hong; Wang, Wugang; Gong, Kun; Meng, Yuanyuan; Lee, Yong

2016-11-10

The myocardial wall of the left ventricle is a complex, multilayered structure and is not homogenous. The aim of this study was to determine longitudinal strain (LS) in the three myocardial layers in normal pregnant women according to gestation proceedings. The advanced two-dimensional speckle tracking echocardiography (2D STE) was performed on 62 women during each pregnancy trimester and 6 to 9 weeks after delivery, while 30 age-matched, healthy, nonpregnant women served as controls. LS on endocardial, mid-myocardial and epicardial layers at 18 cardiac segments were measured. As gestation proceeded, all of layer-specific LS and global LS progressively decreased, which subsequently recovered postpartum (P < 0.05), and the LS gradient between inner and outer myocardium became greater, which reached its maximum in the late pregnancy. Peak systolic LS was the highest at endocardium and the lowest at epicardium, while the highest at the apical level and the lowest at the base (P < 0.05). In the early pregnancy and postpartum, LS at basal level was homogenous, meanwhile layer-specific LS showed significant differences at mid-ventricular and apical level throughout the progress of normal pregnancy (P < 0.05). Using 2D STE, three-layer assessment of LS can be performed in pregnant women and shall give us new insights into the quantitative analysis of global and regional LV function during pregnancy. Future studies on the detection of pregnancy related heart disease would require these parameters as reference values for each time point of a normal pregnancy.

Ferroelastic switching in a layered-perovskite thin film

PubMed Central

Wang, Chuanshou; Ke, Xiaoxing; Wang, Jianjun; Liang, Renrong; Luo, Zhenlin; Tian, Yu; Yi, Di; Zhang, Qintong; Wang, Jing; Han, Xiu-Feng; Van Tendeloo, Gustaaf; Chen, Long-Qing; Nan, Ce-Wen; Ramesh, Ramamoorthy; Zhang, Jinxing

2016-01-01

A controllable ferroelastic switching in ferroelectric/multiferroic oxides is highly desirable due to the non-volatile strain and possible coupling between lattice and other order parameter in heterostructures. However, a substrate clamping usually inhibits their elastic deformation in thin films without micro/nano-patterned structure so that the integration of the non-volatile strain with thin film devices is challenging. Here, we report that reversible in-plane elastic switching with a non-volatile strain of approximately 0.4% can be achieved in layered-perovskite Bi2WO6 thin films, where the ferroelectric polarization rotates by 90° within four in-plane preferred orientations. Phase-field simulation indicates that the energy barrier of ferroelastic switching in orthorhombic Bi2WO6 film is ten times lower than the one in PbTiO3 films, revealing the origin of the switching with negligible substrate constraint. The reversible control of the in-plane strain in this layered-perovskite thin film demonstrates a new pathway to integrate mechanical deformation with nanoscale electronic and/or magnetoelectronic applications. PMID:26838483

Ferroelastic switching in a layered-perovskite thin film

DOE PAGES

Wang, Chuanshou; Ke, Xiaoxing; Wang, Jianjun; ...

2016-02-03

Here, a controllable ferroelastic switching in ferroelectric/multiferroic oxides is highly desirable due to the non-volatile strain and possible coupling between lattice and other order parameter in heterostructures. However, a substrate clamping usually inhibits their elastic deformation in thin films without micro/nano-patterned structure so that the integration of the non-volatile strain with thin film devices is challenging. Here, we report that reversible in-plane elastic switching with a non-volatile strain of approximately 0.4% can be achieved in layered-perovskite Bi 2WO 6 thin films, where the ferroelectric polarization rotates by 90° within four in-plane preferred orientations. Phase-field simulation indicates that the energy barriermore » of ferroelastic switching in orthorhombic Bi 2WO 6 film is ten times lower than the one in PbTiO 3 films, revealing the origin of the switching with negligible substrate constraint. The reversible control of the in-plane strain in this layered-perovskite thin film demonstrates a new pathway to integrate mechanical deformation with nanoscale electronic and/or magnetoelectronic applications.« less

Direct and indirect band gaps in Ge under biaxial tensile strain investigated by photoluminescence and photoreflectance studies

NASA Astrophysics Data System (ADS)

Saladukha, D.; Clavel, M. B.; Murphy-Armando, F.; Greene-Diniz, G.; Grüning, M.; Hudait, M. K.; Ochalski, T. J.

2018-05-01

Germanium is an indirect semiconductor which attracts particular interest as an electronics and photonics material due to low indirect-to-direct band separation. In this work we bend the bands of Ge by means of biaxial tensile strain in order to achieve a direct band gap. Strain is applied by growth of Ge on a lattice mismatched InGaAs buffer layer with variable In content. Band structure is studied by photoluminescence and photoreflectance, giving the indirect and direct bands of the material. Obtained experimental energy band values are compared with a k .p simulation. Photoreflectance spectra are also simulated and compared with the experiment. The obtained results indicate direct band structure obtained for a Ge sample with 1.94 % strain applied, with preferable Γ valley to heavy hole transition.

3D multicellular model of shock wave-cell interaction.

PubMed

Li, Dongli; Hallack, Andre; Cleveland, Robin O; Jérusalem, Antoine

2018-05-01

Understanding the interaction between shock waves and tissue is critical for ad- vancing the use of shock waves for medical applications, such as cancer therapy. This work aims to study shock wave-cell interaction in a more realistic environment, relevant to in vitro and in vivo studies, by using 3D computational models of healthy and cancerous cells. The results indicate that for a single cell embedded in an extracellular environment, the cellular geometry does not influence significantly the membrane strain but does influence the von Mises stress. On the contrary, the presence of neighbouring cells has a strong effect on the cell response, by increasing fourfold both quantities. The membrane strain response of a cell converges with more than three neighbouring cell layers, indicating that a cluster of four layers of cells is sufficient to model the membrane strain in a large domain of tissue. However, a full 3D tissue model is needed if the stress evaluation is of main interest. A tumour mimicking multicellular spheroid model is also proposed to study mutual interaction between healthy and cancer cells and shows that cancer cells can be specifically targeted in an early stage tumour-mimicking environment. This work presents 3D computational models of shock-wave/cell interaction in a biophysically realistic environment using real cell morphology in tissue-mimicking phantom and multicellular spheroid. Results show that cell morphology does not strongly influence the membrane strain but influences the von Mises stress. While the presence of neighbouring cells significantly increases the cell response, four cell layers are enough to capture the membrane strain change in tissue. However, a full tissue model is necessary if accurate stress analysis is needed. The work also shows that cancer cells can be specifically targetted in early stage tumourmimicking environment. This work is a step towards realistic modelling of shock-wave/cell interactions in tissues and provides insight on the use of 3D models for different scenarios. Copyright © 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Genetic evidence for the involvement of the S-layer protein gene sap and the sporulation genes spo0A, spo0B, and spo0F in Phage AP50c infection of Bacillus anthracis.

PubMed

Plaut, Roger D; Beaber, John W; Zemansky, Jason; Kaur, Ajinder P; George, Matroner; Biswas, Biswajit; Henry, Matthew; Bishop-Lilly, Kimberly A; Mokashi, Vishwesh; Hannah, Ryan M; Pope, Robert K; Read, Timothy D; Stibitz, Scott; Calendar, Richard; Sozhamannan, Shanmuga

2014-03-01

In order to better characterize the Bacillus anthracis typing phage AP50c, we designed a genetic screen to identify its bacterial receptor. Insertions of the transposon mariner or targeted deletions of the structural gene for the S-layer protein Sap and the sporulation genes spo0A, spo0B, and spo0F in B. anthracis Sterne resulted in phage resistance with concomitant defects in phage adsorption and infectivity. Electron microscopy of bacteria incubated with AP50c revealed phage particles associated with the surface of bacilli of the Sterne strain but not with the surfaces of Δsap, Δspo0A, Δspo0B, or Δspo0F mutants. The amount of Sap in the S layer of each of the spo0 mutant strains was substantially reduced compared to that of the parent strain, and incubation of AP50c with purified recombinant Sap led to a substantial reduction in phage activity. Phylogenetic analysis based on whole-genome sequences of B. cereus sensu lato strains revealed several closely related B. cereus and B. thuringiensis strains that carry sap genes with very high similarities to the sap gene of B. anthracis. Complementation of the Δsap mutant in trans with the wild-type B. anthracis sap or the sap gene from either of two different B. cereus strains that are sensitive to AP50c infection restored phage sensitivity, and electron microscopy confirmed attachment of phage particles to the surface of each of the complemented strains. Based on these data, we postulate that Sap is involved in AP50c infectivity, most likely acting as the phage receptor, and that the spo0 genes may regulate synthesis of Sap and/or formation of the S layer.

Genetic Evidence for the Involvement of the S-Layer Protein Gene sap and the Sporulation Genes spo0A, spo0B, and spo0F in Phage AP50c Infection of Bacillus anthracis

PubMed Central

Beaber, John W.; Zemansky, Jason; Kaur, Ajinder P.; George, Matroner; Biswas, Biswajit; Henry, Matthew; Bishop-Lilly, Kimberly A.; Mokashi, Vishwesh; Hannah, Ryan M.; Pope, Robert K.; Read, Timothy D.; Stibitz, Scott; Calendar, Richard; Sozhamannan, Shanmuga

2014-01-01

In order to better characterize the Bacillus anthracis typing phage AP50c, we designed a genetic screen to identify its bacterial receptor. Insertions of the transposon mariner or targeted deletions of the structural gene for the S-layer protein Sap and the sporulation genes spo0A, spo0B, and spo0F in B. anthracis Sterne resulted in phage resistance with concomitant defects in phage adsorption and infectivity. Electron microscopy of bacteria incubated with AP50c revealed phage particles associated with the surface of bacilli of the Sterne strain but not with the surfaces of Δsap, Δspo0A, Δspo0B, or Δspo0F mutants. The amount of Sap in the S layer of each of the spo0 mutant strains was substantially reduced compared to that of the parent strain, and incubation of AP50c with purified recombinant Sap led to a substantial reduction in phage activity. Phylogenetic analysis based on whole-genome sequences of B. cereus sensu lato strains revealed several closely related B. cereus and B. thuringiensis strains that carry sap genes with very high similarities to the sap gene of B. anthracis. Complementation of the Δsap mutant in trans with the wild-type B. anthracis sap or the sap gene from either of two different B. cereus strains that are sensitive to AP50c infection restored phage sensitivity, and electron microscopy confirmed attachment of phage particles to the surface of each of the complemented strains. Based on these data, we postulate that Sap is involved in AP50c infectivity, most likely acting as the phage receptor, and that the spo0 genes may regulate synthesis of Sap and/or formation of the S layer. PMID:24363347

Room temperature direct band gap emission characteristics of surfactant mediated grown compressively strained Ge films

NASA Astrophysics Data System (ADS)

Katiyar, Ajit K.; Grimm, Andreas; Bar, R.; Schmidt, Jan; Wietler, Tobias; Joerg Osten, H.; Ray, Samit K.

2016-10-01

Compressively strained Ge films have been grown on relaxed Si0.45Ge0.55 virtual substrates using molecular beam epitaxy in the presence of Sb as a surfactant. Structural characterization has shown that films grown in the presence of surfactant exhibit very smooth surfaces with a relatively higher strain value in comparison to those grown without any surfactant. The variation of strain with increasing Ge layer thickness was analyzed using Raman spectroscopy. The strain is found to be reduced with increasing film thickness due to the onset of island nucleation following Stranski-Krastanov growth mechanism. No phonon assisted direct band gap photoluminescence from compressively strained Ge films grown on relaxed Si0.45Ge0.55 has been achieved up to room temperature. Excitation power and temperature dependent photoluminescence have been studied in details to investigate the origin of different emission sub-bands.

Experimental studies of compaction and dilatancy during frictional sliding on faults containing gouge

USGS Publications Warehouse

Morrow, C.A.; Byerlee, J.D.

1989-01-01

Transient strength changes are observed in fault gouge materials when the velocity of shearing is varied. A transient stress peak is produced when the strain rate in the gouge is suddenly increased, whereas a transient stress drop results from a sudden change to a slower strain rate. We have studied the mechanism responsible for these observations by performing frictional sliding experiments on sawcut granite samples filled with a layer of several different fault gouge types. Changes in pore volume and strength were monitored as the sliding velocity alternated between fast and slow rates. Pore volume increased at the faster strain rate, indicating a dilation of the gouge layer, whereas volume decreased at the slower rate indicating compaction. These results verify that gouge dilation is a function of strain rate. Pore volume changed until an equilibrium void ratio of the granular material was reached for a particular rate of strain. Using arguments from soil mechanics, we find that the dense gouge was initially overconsolidated relative to the equilibrium level, whereas the loose gouge was initially underconsolidated relative to this level. Therefore, the transient stress behavior must be due to the overconsolidated state of the gouge at the new rate when the velocity is increased and to the underconsolidated state when the velocity is lowered. Time-dependent compaction was also shown to cause a transient stress response similar to the velocity-dependent behavior. This may be important in natural fault gouges as they become consolidated and stronger with time. In addition, the strain hardening of the gouge during shearing was found to be a function of velocity, rendering it difficult to quantify the change in equilibrium shear stress when velocity is varied under certain conditions. ?? 1989.

Piezophototronic Effect in Single-Atomic-Layer MoS2 for Strain-Gated Flexible Optoelectronics.

PubMed

Wu, Wenzhuo; Wang, Lei; Yu, Ruomeng; Liu, Yuanyue; Wei, Su-Huai; Hone, James; Wang, Zhong Lin

2016-10-01

Strain-gated flexible optoelectronics are reported based on monolayer MoS 2 . Utilizing the piezoelectric polarization created at the metal-MoS 2 interface to modulate the separation/transport of photogenerated carriers, the piezophototronic effect is applied to implement atomic-layer-thick phototransistor. Coupling between piezoelectricity and photogenerated carriers may enable the development of novel optoelectronics. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Si Complies with GaN to Overcome Thermal Mismatches for the Heteroepitaxy of Thick GaN on Si.

PubMed

Tanaka, Atsunori; Choi, Woojin; Chen, Renjie; Dayeh, Shadi A

2017-10-01

Heteroepitaxial growth of lattice mismatched materials has advanced through the epitaxy of thin coherently strained layers, the strain sharing in virtual and nanoscale substrates, and the growth of thick films with intermediate strain-relaxed buffer layers. However, the thermal mismatch is not completely resolved in highly mismatched systems such as in GaN-on-Si. Here, geometrical effects and surface faceting to dilate thermal stresses at the surface of selectively grown epitaxial GaN layers on Si are exploited. The growth of thick (19 µm), crack-free, and pure GaN layers on Si with the lowest threading dislocation density of 1.1 × 10 7 cm -2 achieved to date in GaN-on-Si is demonstrated. With these advances, the first vertical GaN metal-insulator-semiconductor field-effect transistors on Si substrates with low leakage currents and high on/off ratios paving the way for a cost-effective high power device paradigm on an Si CMOS platform are demonstrated. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Convergence of separate orbits for enhanced thermoelectric performance of layered ZrS2

NASA Astrophysics Data System (ADS)

Ding, Guangqian; Chen, Jinfeng; Yao, Kailun; Gao, Guoying

2017-07-01

Minimizing the band splitting energy to approach orbital degeneracy has been shown as a route to improved thermoelectric performance. This represents an open opportunity in some promising layered materials where there is a separation of p orbitals at the valence band edge due to the crystal field splitting. In this work, using ab initio calculations and semiclassical Boltzmann transport theory, we try to figure out how orbital degeneracy influences the thermoelectric properties of layered transition-metal dichalcogenide ZrS2. We tune the splitting energy by applying compressive biaxial strain, and find out that near-degeneration at the {{Γ }} point can be achieved for around 3% strain. As expected, the enhanced density-of-states effective mass results in an increased power factor. Interestingly, we also find a marked decline in the lattice thermal conductivity due to the effect of strain on phonon velocities and scattering. The two effects synergetically enhance the figure of merit. Our results highlight the convenience of exploring this optimization route in layered thermoelectric materials with band structures similar to that of ZrS2.

Skin aging as a mechanical phenomenon: The main weak links

PubMed Central

Kruglikov, Ilja L.; Scherer, Philipp E.

2018-01-01

From a mechanical point of view, human skin appears as a layered composite containing the stiff thin cover layer presented by the stratum corneum, below which are the more compliant layers of viable epidermis and dermis and further below the much more compliant adjacent layer of subcutaneous white adipose tissue (sWAT). Upon exposure to a strain, such a multi-layer system demonstrates structural instabilities in its stiffer layers, which in its simplest form is the wrinkling. These instabilities appear hierarchically when the mechanical strain in the skin exceeds some critical values. Their appearance is mainly dependent on the mismatch in mechanical properties between adjacent skin layers or between the skin and sWAT, on the adhesive strength and thickness ratios between the layers, on their bending and tensile stiffness as well as on the value of the stress existing in single layers. Gradual reduction of elastic fibers in aging significantly reduces the skin’s ability to bend, prompting an up to 4-fold reduction of its stability against wrinkling, thereby explaining the role of these fibers in skin aging. While chronological and extrinsic aging differently modify these parameters, they lead to the same end result, reducing the critical strain required for the onset of instabilities. Comparing of mechanical properties of the skin presented as a bi-, tri- or tetra-layer structure demonstrates the particular importance of the papillary dermis in skin aging and provides the arguments to consider the undulations on the dermal-epidermal and dermal-sWAT interfaces as the result of mechanical bifurcation, leading to structural instabilities inside of the skin. According to this model, anti-aging strategies should focus not as much on the reinforcement of the dermis, but rather aim to treat the elastic mismatch between different adjacent layers in the skin and sWAT as well as the adhesion between these layers.

Gender variations in the optical properties of skin in murine animal models

NASA Astrophysics Data System (ADS)

Calabro, Katherine; Curtis, Allison; Galarneau, Jean-Rene; Krucker, Thomas; Bigio, Irving J.

2011-01-01

Gender is identified as a significant source of variation in optical reflectance measurements on mouse skin, with variation in the thickness of the dermal layer being the key explanatory variable. For three different mouse strains, the thickness values of the epidermis, dermis, and hypodermis layers, as measured by histology, are correlated to optical reflectance measurements collected with elastic scattering spectroscopy (ESS). In all three strains, males are found to have up to a 50% increase in dermal thickness, resulting in increases of up to 80% in reflectance values and higher observed scattering coefficients, as compared to females. Collagen in the dermis is identified as the primary source of these differences due to its strong scattering nature; increased dermal thickness leads to a greater photon path length through the collagen, as compared to other layers, resulting in a larger scattering signal. A related increase in the observed absorption coefficient in females is also observed. These results emphasize the importance of considering gender during experimental design in studies that involve photon interaction with mouse skin. The results also elucidate the significant impact that relatively small thickness changes can have on observed optical measurements in layered tissue.

An ultrasonic measurement for in vitro depth-dependent equilibrium strains of articular cartilage in compression

NASA Astrophysics Data System (ADS)

Zheng, Y. P.; Mak, A. F. T.; Lau, K. P.; Qin, L.

2002-09-01

The equilibrium depth-dependent biomechanical properties of articular cartilage were measured using an ultrasound-compression method. Ten cylindrical bovine patella cartilage-bone specimens were tested in compression followed by a period of force-relaxation. A 50 MHz focused ultrasound beam was transmitted into the cartilage specimen through a remaining bone layer and a small hole at the centre of a specimen platform. The ultrasound echoes reflected or scattered within the articular cartilage were collected using the same transducer. The displacements of the tissues at different depths of the articular cartilage were derived from the ultrasound echo signals recorded during the compression and the subsequent force-relaxation. For two steps of 0.1 mm compression, the average strain at the superficial 0.2 mm thick layer (0.35 +/- 0.09) was significantly (p < 0.05) larger than that at the subsequent 0.2 mm thick layer (0.05 +/- 0.07) and that at deeper layers (0.01 +/- 0.02). It was demonstrated that the compressive biomechanical properties of cartilage were highly depth-dependent. The results suggested that the ultrasound-compression method could be a useful tool for the study of the depth-dependent biomechanical properties of articular cartilage.

Effect of Load-Induced Oxygen Absorption in YBa2Cu3O6 + x on Mechanical Properties of the "Polyimide-YBa2Cu3O6 + x " System

NASA Astrophysics Data System (ADS)

Muradov, A. D.; Kyrykbaeva, A. A.

2018-05-01

We have studied the effect of oxygen absorption by disperse powder fillers made of high-temperature superconductor YBa2Cu3O6 + x (YBCO) with concentrations of 0.05, 0.1, and 0.5 mass % on mechanical properties of polyimide composite materials (PCMs) in the form of films. It has been established that an adsorption boundary layer consisting of an aggregate of several transition layers with a varying structure is formed between filler particles and the matrix. A sharp increase in relative elongation (strain) Δɛ c , which is observed for a PCM with YBCO fillers in the form of a jump in the region of loads of 40-47 MPa, is due to the fact that the bonds between the matrix macromolecules and the molecules in the vicinity of the upper boundary layer are ruptured, leading to a strain jump. An increase in the filler concentration increases the rigidity of the bonds between macromolecules in the boundary layers, leads to a shift of Δɛ c to the region of low stresses, and reduces its value.

Effect of Layer-Graded Bond Coats on Edge Stress Concentration and Oxidation Behavior of Thermal Barrier Coatings

NASA Technical Reports Server (NTRS)

Zhu, Dongming; Ghosn, Louis J.; Miller, Robert A.

1998-01-01

Thermal barrier coating (TBC) durability is closely related to design, processing and microstructure of the coating Z, tn systems. Two important issues that must be considered during the design of a thermal barrier coating are thermal expansion and modulus mismatch between the substrate and the ceramic layer, and substrate oxidation. In many cases, both of these issues may be best addressed through the selection of an appropriate bond coat system. In this study, a low thermal expansion and layer-graded bond coat system, that consists of plasma-sprayed FeCoNiCrAl and FeCrAlY coatings, and a high velocity oxyfuel (HVOF) sprayed FeCrAlY coating, is developed to minimize the thermal stresses and provide oxidation resistance. The thermal expansion and oxidation behavior of the coating system are also characterized, and the strain isolation effect of the bond coat system is analyzed using the finite element method (FEM). Experiments and finite element results show that the layer-graded bond coat system possesses lower interfacial stresses. better strain isolation and excellent oxidation resistance. thus significantly improving the coating performance and durability.

Biotransformation of 4-chloro-2-nitrophenol into 5-chloro-2-methylbenzoxazole by a marine Bacillus sp. strain MW-1.

PubMed

Arora, Pankaj Kumar; Jain, Rakesh Kumar

2012-04-01

Decolourization, detoxification and biotransformation of 4-chloro-2-nitrophenol (4C2NP) by Bacillus sp. strain MW-1 were studied. This strain decolorized 4C2NP only in the presence of an additional carbon source. On the basis of thin layer chromatography (TLC), high performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS), 4-chloro-2-aminophenol, 4-chloro-2-acetaminophenol and 5-chloro-2-methylbenzoxazole were identified as metabolites. Resting cells depleted 4C2NP with stoichiometric formation of 5-chloro-2-methyl benzoxazole. This is the first report of the formation of 5-chloro-2-methylbenzoxazole from 4C2NP by any bacterial strain.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Economy, David Ross; Mara, Nathan A.; Schoeppner, R.

In complex loading conditions (e.g. sliding contact), mechanical properties, such as strain hardening and initial hardness, will dictate the long-term performance of materials systems. With this in mind, the strain hardening behaviors of Cu/Nb nanoscale metallic multilayer systems were examined by performing nanoindentation tests within nanoscratch wear boxes and undeformed, as-deposited regions. Both the architecture and substrate influence were examined by utilizing three different individual layer thicknesses (2, 20, and 100 nm) and two total film thicknesses (1 and 10 μm). After nano-wear deformation, multilayer systems with thinner layers showed less volume loss as measured by laser scanning microscopy. Additionally,more » the hardness of the deformed regions significantly rose with respect to the as-deposited measurements, which further increased with greater wear loads. Strain hardening exponents for multilayers with thinner layers (2 and 20 nm, n ≈ 0.018 and n ≈ 0.022 respectively) were less than was determined for 100 nm systems (n ≈ 0.041). These results suggest that singledislocation based deformation mechanisms observed for the thinner systems limit the extent of achievable strain hardening. This conclusion indicates that impacts of both architecture strengthening and strain hardening must be considered to accurately predict multilayer performance during sliding contact across varying length scales.« less

Pseudomorphic GeSiSn, SiSn and Ge layers in strained heterostructures

NASA Astrophysics Data System (ADS)

Timofeev, V. A.; Nikiforov, A. I.; Tuktamyshev, A. R.; Mashanov, V. I.; Loshkarev, I. D.; Bloshkin, A. A.; Gutakovskii, A. K.

2018-04-01

The GeSiSn, SiSn layer growth mechanisms on Si(100) were investigated and the kinetic diagrams of the morphological GeSiSn, SiSn film states in the temperature range of 150 °C-450 °C at the tin content from 0% to 35% were built. The phase diagram of the superstructural change on the surface of Sn grown on Si(100) in the annealing temperature range of 0 °C-850 °C was established. The specular beam oscillations were first obtained during the SiSn film growth from 150 °C to 300 °C at the Sn content up to 35%. The transmission electron microscopy and x-ray diffractometry data confirm the crystal perfection and the pseudomorphic GeSiSn, SiSn film state, and also the presence of smooth heterointerfaces between GeSiSn or SiSn and Si. The photoluminescence for the multilayer periodic GeSiSn/Si structures in the range of 0.6-0.8 eV was detected. The blue shift with the excitation power increase is observed suggesting the presence of a type II heterostructure. The creation of tensile strained Ge films, which are pseudomorphic to the underlying GeSn layer, is confirmed by the results of the formation and analysis of the reciprocal space map in the x-ray diffractometry. The tensile strain in the Ge films reached the value in the range of 0.86%-1.5%. The GeSn buffer layer growth in the Sn content range from 8% to 12% was studied. The band structure of heterosystems based on pseudomorphic GeSiSn, SiSn and Ge layers was calculated and the valence and conduction band subband position dependences on the Sn content were built. Based on the calculation, the Sn content range in the GeSiSn, SiSn, and GeSn layers, which corresponds to the direct bandgap GeSiSn, SiSn, and Ge material, was obtained.

Chromatic Mechanical Response in 2-D Layered Transition Metal Dichalcogenide (TMDs) based Nanocomposites

PubMed Central

Rahneshin, Vahid; Khosravi, Farhad; Ziolkowska, Dominika A.; Jasinski, Jacek B.; Panchapakesan, Balaji

2016-01-01

The ability to convert photons of different wavelengths directly into mechanical motion is of significant interest in many energy conversion and reconfigurable technologies. Here, using few layer 2H-MoS2 nanosheets, layer by layer process of nanocomposite fabrication, and strain engineering, we demonstrate a reversible and chromatic mechanical response in MoS2-nanocomposites between 405 nm to 808 nm with large stress release. The chromatic mechanical response originates from the d orbitals and is related to the strength of the direct exciton resonance A and B of the few layer 2H-MoS2 affecting optical absorption and subsequent mechanical response of the nanocomposite. Applying uniaxial tensile strains to the semiconducting few-layer 2H-MoS2 crystals in the nanocomposite resulted in spatially varying energy levels inside the nanocomposite that enhanced the broadband optical absorption up to 2.3 eV and subsequent mechanical response. The unique photomechanical response in 2H-MoS2 based nanocomposites is a result of the rich d electron physics not available to nanocomposites based on sp bonded graphene and carbon nanotubes, as well as nanocomposite based on metallic nanoparticles. The reversible strain dependent optical absorption suggest applications in broad range of energy conversion technologies that is not achievable using conventional thin film semiconductors. PMID:27713550

Metal-insulator transition in CaVO3 thin films: Interplay between epitaxial strain, dimensional confinement, and surface effects

NASA Astrophysics Data System (ADS)

Beck, Sophie; Sclauzero, Gabriele; Chopra, Uday; Ederer, Claude

2018-02-01

We use density functional theory plus dynamical mean-field theory (DFT+DMFT) to study multiple control parameters for tuning the metal-insulator transition (MIT) in CaVO3 thin films. We focus on separating the effects resulting from substrate-induced epitaxial strain from those related to the reduced thickness of the film. We show that tensile epitaxial strain of around 3%-4% is sufficient to induce a transition to a paramagnetic Mott-insulating phase. This corresponds to the level of strain that could be achieved on a SrTiO3 substrate. Using free-standing slab models, we then demonstrate that reduced film thickness can also cause a MIT in CaVO3, however, only for thicknesses of less than 4 perovskite units. Our calculations indicate that the MIT in such ultrathin films results mainly from a surface-induced crystal-field splitting between the t2 g orbitals, favoring the formation of an orbitally polarized Mott insulator. This surface-induced crystal-field splitting is of the same type as the one resulting from tensile epitaxial strain, and thus the two effects can also cooperate. Furthermore, our calculations confirm an enhancement of correlation effects at the film surface, resulting in a reduced quasiparticle spectral weight in the outermost layer, whereas bulklike properties are recovered within only a few layers away from the surface.

Magnetic anisotropy in (Ga,Mn)As: Influence of epitaxial strain and hole concentration

NASA Astrophysics Data System (ADS)

Glunk, M.; Daeubler, J.; Dreher, L.; Schwaiger, S.; Schoch, W.; Sauer, R.; Limmer, W.; Brandlmaier, A.; Goennenwein, S. T. B.; Bihler, C.; Brandt, M. S.

2009-05-01

We present a systematic study on the influence of epitaxial strain and hole concentration on the magnetic anisotropy in (Ga,Mn)As at 4.2 K. The strain was gradually varied over a wide range from tensile to compressive by growing a series of (Ga,Mn)As layers with 5% Mn on relaxed graded (In,Ga)As/GaAs templates with different In concentration. The hole density, the Curie temperature, and the relaxed lattice constant of the as-grown and annealed (Ga,Mn)As layers turned out to be essentially unaffected by the strain. Angle-dependent magnetotransport measurements performed at different magnetic-field strengths were used to probe the magnetic anisotropy. The measurements reveal a pronounced linear dependence of the uniaxial out-of-plane anisotropy on both strain and hole density. Whereas the uniaxial and cubic in-plane anisotropies are nearly constant, the cubic out-of-plane anisotropy changes sign when the magnetic easy axis flips from in-plane to out-of-plane. The experimental results for the magnetic anisotropy are quantitatively compared with calculations of the free energy based on a mean-field Zener model. Almost perfect agreement between experiment and theory is found for the uniaxial out-of-plane and cubic in-plane anisotropy parameters of the as-grown samples. In addition, magnetostriction constants are derived from the anisotropy data.

Strain Gauges Based on CVD Graphene Layers and Exfoliated Graphene Nanoplatelets with Enhanced Reproducibility and Scalability for Large Quantities

PubMed Central

Yokaribas, Volkan; Schneider, Daniel S.; Friebertshäuser, Philipp; Lemme, Max C.; Fritzen, Claus-Peter

2017-01-01

The two-dimensional material graphene promises a broad variety of sensing activities. Based on its low weight and high versatility, the sensor density can significantly be increased on a structure, which can improve reliability and reduce fluctuation in damage detection strategies such as structural health monitoring (SHM). Moreover; it initializes the basis of structure–sensor fusion towards self-sensing structures. Strain gauges are extensively used sensors in scientific and industrial applications. In this work, sensing in small strain fields (from −0.1% up to 0.1%) with regard to structural dynamics of a mechanical structure is presented with sensitivities comparable to bulk materials by measuring the inherent piezoresistive effect of graphene grown by chemical vapor deposition (CVD) with a very high aspect ratio of approximately 4.86 × 108. It is demonstrated that the increasing number of graphene layers with CVD graphene plays a key role in reproducible strain gauge application since defects of individual layers may become less important in the current path. This may lead to a more stable response and, thus, resulting in a lower scattering.. Further results demonstrate the piezoresistive effect in a network consisting of liquid exfoliated graphene nanoplatelets (GNP), which result in even higher strain sensitivity and reproducibility. A model-assisted approach provides the main parameters to find an optimum of sensitivity and reproducibility of GNP films. The fabricated GNP strain gauges show a minimal deviation in PRE effect with a GF of approximately 5.6 and predict a linear electromechanical behaviour up to 1% strain. Spray deposition is used to develop a low-cost and scalable manufacturing process for GNP strain gauges. In this context, the challenge of reproducible and reliable manufacturing and operating must be overcome. The developed sensors exhibit strain gauges by considering the significant importance of reproducible sensor performances and open the path for graphene strain gauges for potential usages in science and industry. PMID:29258260

Role of the Helicobacter pylori virulence factors vacuolating cytotoxin, CagA, and urease in a mouse model of disease.

PubMed Central

Ghiara, P; Marchetti, M; Blaser, M J; Tummuru, M K; Cover, T L; Segal, E D; Tompkins, L S; Rappuoli, R

1995-01-01

The pathogenic role of Helicobacter pylori virulence factors has been studied with a mouse model of gastric disease. BALB/c mice were treated orally with different amounts of sonic extracts of cytotoxic H. pylori strains (NCTC 11637, 60190, 84-183, and 87A300 [CagA+/Tox+]). The pathological effects on histological sections of gastric mucosae were assessed and were compared with the effects of treatments with extracts from noncytotoxic strains (G21 and G50 [CagA-/Tox-]) and from strains that express either CagA alone (D931 [CagA+/Tox-]) or the cytotoxin alone (G104 [CagA-/Tox+]). The treatment with extracts from cytotoxic strains induced various epithelial lesions (vacuolation, erosions, and ulcerations), recruitment of inflammatory cells in the lamina propria, and a marked reduction of the mucin layer. Extracts of noncytotoxic strains induced mucin depletion but no other significant pathology. Crude extracts of strain D931, expressing CagA alone, caused only mild infiltration of inflammatory cells, whereas extracts of strain G104, expressing cytotoxin alone, induced extensive epithelial damage but little inflammatory reaction. Loss of the mucin layer was not associated with a cytotoxic phenotype, since this loss was observed in mice treated with crude extracts of all strains. The pathogenic roles of CagA, cytotoxin, and urease were further assessed by using extracts of mutant strains of H. pylori defective in the expression of each of these virulence factors. The results obtained suggest that (i) urease activity does not play a significant role in inducing the observed gastric damage, (ii) cytotoxin has an important role in the induction of gastric epithelial cell lesions but not in eliciting inflammation, and (iii) other components present in strains which carry the cagA gene, but distinct from CagA itself, are involved in eliciting the inflammatory response. PMID:7558333

Role of the Helicobacter pylori virulence factors vacuolating cytotoxin, CagA, and urease in a mouse model of disease.

PubMed

Ghiara, P; Marchetti, M; Blaser, M J; Tummuru, M K; Cover, T L; Segal, E D; Tompkins, L S; Rappuoli, R

1995-10-01

The pathogenic role of Helicobacter pylori virulence factors has been studied with a mouse model of gastric disease. BALB/c mice were treated orally with different amounts of sonic extracts of cytotoxic H. pylori strains (NCTC 11637, 60190, 84-183, and 87A300 [CagA+/Tox+]). The pathological effects on histological sections of gastric mucosae were assessed and were compared with the effects of treatments with extracts from noncytotoxic strains (G21 and G50 [CagA-/Tox-]) and from strains that express either CagA alone (D931 [CagA+/Tox-]) or the cytotoxin alone (G104 [CagA-/Tox+]). The treatment with extracts from cytotoxic strains induced various epithelial lesions (vacuolation, erosions, and ulcerations), recruitment of inflammatory cells in the lamina propria, and a marked reduction of the mucin layer. Extracts of noncytotoxic strains induced mucin depletion but no other significant pathology. Crude extracts of strain D931, expressing CagA alone, caused only mild infiltration of inflammatory cells, whereas extracts of strain G104, expressing cytotoxin alone, induced extensive epithelial damage but little inflammatory reaction. Loss of the mucin layer was not associated with a cytotoxic phenotype, since this loss was observed in mice treated with crude extracts of all strains. The pathogenic roles of CagA, cytotoxin, and urease were further assessed by using extracts of mutant strains of H. pylori defective in the expression of each of these virulence factors. The results obtained suggest that (i) urease activity does not play a significant role in inducing the observed gastric damage, (ii) cytotoxin has an important role in the induction of gastric epithelial cell lesions but not in eliciting inflammation, and (iii) other components present in strains which carry the cagA gene, but distinct from CagA itself, are involved in eliciting the inflammatory response.

Delamination Analysis of a Multilayered Two-Dimensional Functionally Graded Cantilever Beam

NASA Astrophysics Data System (ADS)

Rizov, V.

2017-11-01

Delamination fracture behaviour of a multilayered two-dimensional functionally graded cantilever beam is analyzed in terms of the strain energy release rate. The beam is made of an arbitrary number of layers. Perfect adhesion is assumed between layers. Each layer has individual thickness and material properties. Besides, the material is two-dimensional functionally graded in the cross-section of each layer. There is a delamination crack located arbitrary between layers. The beam is loaded by a bending moment applied at the free end of the lower crack arm. The upper crack arm is free of stresses. The solution to strain energy release rate derived is applied to investigate the influence of the crack location and the material gradient on the delamination fracture. The results obtained can be used to optimize the multilayered two-dimensional functionally graded beam structure with respect to the delamination fracture behaviour.

Surface Morphology Transformation Under High-Temperature Annealing of Ge Layers Deposited on Si(100).

PubMed

Shklyaev, A A; Latyshev, A V

2016-12-01

We study the surface morphology and chemical composition of SiGe layers after their formation under high-temperature annealing at 800-1100 °C of 30-150 nm Ge layers deposited on Si(100) at 400-500 °C. It is found that the annealing leads to the appearance of the SiGe layers of two types, i.e., porous and continuous. The continuous layers have a smoothened surface morphology and a high concentration of threading dislocations. The porous and continuous layers can coexist. Their formation conditions and the ratio between their areas on the surface depend on the thickness of deposited Ge layers, as well as on the temperature and the annealing time. The data obtained suggest that the porous SiGe layers are formed due to melting of the strained Ge layers and their solidification in the conditions of SiGe dewetting on Si. The porous and dislocation-rich SiGe layers may have properties interesting for applications.

Analysis of an Interface Crack for a Functionally Graded Strip Sandwiched between Two Homogeneous Layers of Finite Thickness

NASA Technical Reports Server (NTRS)

Shbeeh, N. I.; Binienda, W. K.

1999-01-01

The interface crack problem for a composite layer that consists of a homogeneous substrate, coating and a non-homogeneous interface was formulated for singular integral equations with Cauchy kernels and integrated using the Lobatto-Chebyshev collocation technique. Mixed-mode Stress Intensity Factors and Strain Energy Release Rates were calculated. The Stress Intensity Factors were compared for accuracy with relevant results previously published. The parametric studies were conducted for the various thickness of each layer and for various non-homogeneity ratios. Particular application to the Zirconia thermal barrier on steel substrate is demonstrated.

Controlled drive-in and precipitation of hydrogen during plasma hydrogenation of silicon using a thin compressively strained SiGe layer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Okba, F.; Departement Optique et Mecanique de Precision, Faculte des Sciences de l'Ingenieur, Universite Ferhat Abbas, Setif 19000; Cherkashin, N.

2010-07-19

We have quantitatively studied by transmission electron microscopy the growth kinetics of platelets formed during the continuous hydrogenation of a Si substrate/SiGe/Si heterostructure. We have evidenced and explained the massive transfer of hydrogen from a population of platelets initially generated in the upper Si layer by plasma hydrogenation towards a population of larger platelets located in the SiGe layer. We demonstrate that this type of process can be used not only to precisely localize the micro-cracks, then the fracture line at a given depth but also to 'clean' the top layer from pre-existing defects.

Effect of elastic excitations on the surface structure of hadfield steel under friction

NASA Astrophysics Data System (ADS)

Kolubaev, A. V.; Ivanov, Yu. F.; Sizova, O. V.; Kolubaev, E. A.; Aleshina, E. A.; Gromov, V. E.

2008-02-01

The structure of the Hadfield steel (H13) surface layer forming under dry friction is examined. The deformation of the material under the friction surface is studied at a low slip velocity and a low pressure (much smaller than the yields stress of H13 steel). The phase composition and defect substructure on the friction surface are studied using scanning, optical, and diffraction electron microscopy methods. It is shown that a thin highly deformed nanocrystalline layer arises near the friction surface that transforms into a polycrystalline layer containing deformation twins and dislocations. The nanocrystalline structure and the presence of oxides in the surface layer and friction zone indicate a high temperature and high plastic strains responsible for the formation of the layer. It is suggested that the deformation of the material observed far from the surface is due to elastic wave generation at friction.

Coexistence of antibiotic-producing and antibiotic-sensitive bacteria in biofilms is mediated by resistant bacteria.

PubMed

Narisawa, Naoki; Haruta, Shin; Arai, Hiroyuki; Ishii, Masaharu; Igarashi, Yasuo

2008-06-01

Antibiotic-sensitive bacteria have been found to coexist with antibiotic-producing bacteria in biofilms, but little is known about how the former develop in such an environment. Here we isolated pyocyanin-sensitive bacteria belonging to the genus Brevibacillus from a biofilm derived from soil extract and based on the preestablished biofilm of a pyocyanin producer, Pseudomonas aeruginosa strain P1. In addition, pyocyanin-resistant strains belonging to the genus Raoultella were isolated from the same biofilm. Microbial relationships within biofilms were examined by using three strains, strain P1, Brevibacillus strain S1, and Raoultella strain R1, each of which individually formed a biofilm within 2 days in a flow cell. Strain S1 did not fully develop on the preestablished biofilm of strain P1 during 4 days of cultivation, whereas a mutant of strain P1 which was deficient in pyocyanin production allowed strain S1 to cocolonize within a biofilm. On the other hand, strain R1 developed on the biofilm of strain P1 regardless of pyocyanin production. When mixed 1:1 inocula of strains S1 and R1 were introduced into the strain P1 biofilm, all three species were found in the 4-day biofilm. In the mixed biofilm, strain S1 was surrounded by the layer of strain R1 and seemed to be separated from strain P1 and the outflow solution. However, strain S1 did not survive in a three-species mixed culture under planktonic conditions. These results indicate that the survival of sensitive bacteria in biofilm with a pyocyanin producer is achieved by covering them with a layer of resistant bacteria. We also evaluated the influence of antibiotic production on the producer.

Strained-layer superlattice focal plane array having a planar structure

DOEpatents

Kim, Jin K [Albuquerque, NM; Carroll, Malcolm S [Albuquerque, NM; Gin, Aaron [Albuquerque, NM; Marsh, Phillip F [Lowell, MA; Young, Erik W [Albuquerque, NM; Cich, Michael J [Albuquerque, NM

2010-07-13

An infrared focal plane array (FPA) is disclosed which utilizes a strained-layer superlattice (SLS) formed of alternating layers of InAs and In.sub.xGa.sub.1-xSb with 0.ltoreq.x.ltoreq.0.5 epitaxially grown on a GaSb substrate. The FPA avoids the use of a mesa structure to isolate each photodetector element and instead uses impurity-doped regions formed in or about each photodetector for electrical isolation. This results in a substantially-planar structure in which the SLS is unbroken across the entire width of a 2-D array of the photodetector elements which are capped with an epitaxially-grown passivation layer to reduce or eliminate surface recombination. The FPA has applications for use in the wavelength range of 3-25 .mu.m.

Strained layer superlattice focal plane array having a planar structure

DOEpatents

Kim, Jin K; Carroll, Malcolm S; Gin, Aaron; Marsh, Phillip F; Young, Erik W; Cich, Michael J

2012-10-23

An infrared focal plane array (FPA) is disclosed which utilizes a strained-layer superlattice (SLS) formed of alternating layers of InAs and In.sub.xGa.sub.1-xSb with 0.ltoreq.x.ltoreq.0.5 epitaxially grown on a GaSb substrate. The FPA avoids the use of a mesa structure to isolate each photodetector element and instead uses impurity-doped regions formed in or about each photodetector for electrical isolation. This results in a substantially-planar structure in which the SLS is unbroken across the entire width of a 2-D array of the photodetector elements which are capped with an epitaxially-grown passivation layer to reduce or eliminate surface recombination. The FPA has applications for use in the wavelength range of 3-25 .mu.m.

Strain control of oxygen kinetics in the Ruddlesden-Popper oxide La 1.85Sr 0.15CuO 4

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meyer, Tricia L.; Jacobs, Ryan; Lee, Dongkyu

Oxygen defect control has long been considered an important route to functionalizing complex oxide films. However, the nature of oxygen defects in thin films is often not investigated beyond basic redox chemistry. One of the model examples for oxygen-defect studies is the layered Ruddlesden–Popper phase La 2-xSr x CuO 4-δ (LSCO), in which the superconducting transition temperature is highly sensitive to epitaxial strain. However, previous observations of strain-superconductivity coupling in LSCO thin films were mainly understood in terms of elastic contributions to mechanical buckling, with minimal consideration of kinetic or thermodynamic factors. Here, we report that the oxygen nonstoichiometry commonlymore » reported for strained cuprates is mediated by the strain-modified surface exchange kinetics, rather than reduced thermodynamic oxygen formation energies. Remarkably, tensile-strained LSCO shows nearly an order of magnitude faster oxygen exchange rate than a compressively strained film, providing a strategy for developing high-performance energy materials.« less

Strain control of oxygen kinetics in the Ruddlesden-Popper oxide La 1.85Sr 0.15CuO 4

DOE PAGES

Meyer, Tricia L.; Jacobs, Ryan; Lee, Dongkyu; ...

2018-01-08

Oxygen defect control has long been considered an important route to functionalizing complex oxide films. However, the nature of oxygen defects in thin films is often not investigated beyond basic redox chemistry. One of the model examples for oxygen-defect studies is the layered Ruddlesden–Popper phase La 2-xSr x CuO 4-δ (LSCO), in which the superconducting transition temperature is highly sensitive to epitaxial strain. However, previous observations of strain-superconductivity coupling in LSCO thin films were mainly understood in terms of elastic contributions to mechanical buckling, with minimal consideration of kinetic or thermodynamic factors. Here, we report that the oxygen nonstoichiometry commonlymore » reported for strained cuprates is mediated by the strain-modified surface exchange kinetics, rather than reduced thermodynamic oxygen formation energies. Remarkably, tensile-strained LSCO shows nearly an order of magnitude faster oxygen exchange rate than a compressively strained film, providing a strategy for developing high-performance energy materials.« less

Multicolor Nanostructured High Efficiency Photovoltaic Devices

DTIC Science & Technology

2007-06-30

the surface of strained buffer layer starts to form some nanoholes and nanogrooves. The depth of these nanoholes and nanogrooves is more than 3 nm...This indicates that the nanoholes and nanogrooves are formed not only just in the top GaAs (5 ML) layer, but also deep in the strained GaAsSb buffer...temperature during the InAs growth. As the InAs growth temperature decreases, the density of the nanoholes and nanogrooves is significantly reduced

Barrier Engineered Quantum Dot Infrared Photodetectors

DTIC Science & Technology

2015-06-01

dual-color detectors using InAs/GaSb strained layer superlattices ." In Lester Eastman Conference on High Performance Devices (LEC), 2012, pp. 1-4. IEEE...Gautam, S. S. Krishna, E. P. Smith, S. Johnson, and S. Krishna. "Dual-band pBp detectors based on InAs/GaSb strained layer superlattices ." Infrared ...AFRL-RV-PS- AFRL-RV-PS- TR-2015-0111 TR-2015-0111 BARRIER ENGINEERED QUANTUM DOT INFRARED PHOTODETECTORS Sanjay Krishna Center for High Technology

Dual optical marker Raman characterization of strained GaN-channels on AlN using AlN/GaN/AlN quantum wells and {sup 15}N isotopes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Qi, Meng; Li, Guowang; Protasenko, Vladimir

2015-01-26

This work shows that the combination of ultrathin highly strained GaN quantum wells embedded in an AlN matrix, with controlled isotopic concentrations of Nitrogen enables a dual marker method for Raman spectroscopy. By combining these techniques, we demonstrate the effectiveness in studying strain in the vertical direction. This technique will enable the precise probing of properties of buried active layers in heterostructures, and can be extended in the future to vertical devices such as those used for optical emitters and for power electronics.

Controlling nanoscale acoustic strains in silicon using chirped femtosecond laser pulses

NASA Astrophysics Data System (ADS)

Tzianaki, E.; Bakarezos, M.; Tsibidis, G. D.; Petrakis, S.; Loukakos, P. A.; Kosmidis, C.; Tatarakis, M.; Papadogiannis, N. A.

2016-06-01

The influence of femtosecond laser pulse chirp on laser-generated longitudinal acoustic strains in Si (100) monocrystal substrates is studied. Degenerate femtosecond pump-probe transient reflectivity measurements are performed using a layered structure of thin Ti transducer film on an Si substrate. Experimental results show that acoustic strains, manifested as strong Brillouin oscillations, are more effectively induced when negatively chirped femtosecond laser pulses pump the transducer. These results are theoretically supported by a modified thermo-mechanical model based on the combination of a revised two-temperature model and elasticity theory that takes into account the instantaneous frequency of the chirped femtosecond laser pump pulses.

Integrating Fiber Optic Strain Sensors into Metal Using Ultrasonic Additive Manufacturing

NASA Astrophysics Data System (ADS)

Hehr, Adam; Norfolk, Mark; Wenning, Justin; Sheridan, John; Leser, Paul; Leser, Patrick; Newman, John A.

2018-03-01

Ultrasonic additive manufacturing, a rather new three-dimensional (3D) printing technology, uses ultrasonic energy to produce metallurgical bonds between layers of metal foils near room temperature. This low temperature attribute of the process enables integration of temperature sensitive components, such as fiber optic strain sensors, directly into metal structures. This may be an enabling technology for Digital Twin applications, i.e., virtual model interaction and feedback with live load data. This study evaluates the consolidation quality, interface robustness, and load sensing limits of commercially available fiber optic strain sensors embedded into aluminum alloy 6061. Lastly, an outlook on the technology and its applications is described.

The effect of Au nanoparticles on the strain-dependent electrical properties of CVD graphene

NASA Astrophysics Data System (ADS)

Bai, Jing; Nan, Haiyan; Qi, Han; Bing, Dan; Du, Ruxia

2018-03-01

We conducted an experimental study of the effect of Au nanoparticles (NPs) on the strain-dependent electrical properties in chemical vapor deposition grown graphene. We used 5-nm thick Au NPs as an effective cover (and doping) layer for graphene, and found that Au NPs decrease electrical resistance by two orders of magnitude. In addition, the Au NPs suppress the effect of strain on resistance because the intrinsic topological cracks and grain boundaries in graphene are filled with Au nanoparticles. This method has a big potential to advance industrial production of large-area, high-quality electronic devices and graphene-based transparent electrodes.

Multiscale deformation behavior for multilayered steel by in-situ FE-SEM

NASA Astrophysics Data System (ADS)

Tanaka, Y.; Kishimoto, S.; Yin, F.; Kobayashi, M.; Tomimatsu, T.; Kagawa, K.

2010-03-01

The multi-scale deformation behavior of multi-layered steel during tensile loading was investigated by in-situ FE-SEM observation coupled with multi-scale pattern. The material used was multi-layered steel sheet consisting of martensitic and austenitic stainless steel layers. Prior to in-situ tensile testing, the multi-scale pattern combined with a grid and random dots were fabricated by electron beam lithography on the polished surface in the area of 1 mm2 to facilitate direct observation of multi-scale deformation. Both of the grids with pitches of 10 μm and a random speckle pattern ranging from 200 nm to a few μm sizes were drawn onto the specimen surface at same location. The electron moiré method was applied to measure the strain distribution in the deformed specimens at a millimeter scale and digital images correlation method was applied to measure the in-plane deformation and strain distribution at a micron meter scale acquired before and after at various increments of straining. The results showed that the plastic deformation in the austenitic stainless steel layer was larger than the martensitic steel layer at millimeter scale. However, heterogeneous intrinsic grain-scale plastic deformation was clearly observed and it increased with increasing the plastic deformation.

Strong polarization enhancement in asymmetric three-component ferroelectric superlattices

NASA Astrophysics Data System (ADS)

Lee, Ho Nyung; Christen, Hans M.; Chisholm, Matthew F.; Rouleau, Christopher M.; Lowndes, Douglas H.

2005-01-01

Theoretical predictions-motivated by recent advances in epitaxial engineering-indicate a wealth of complex behaviour arising in superlattices of perovskite-type metal oxides. These include the enhancement of polarization by strain and the possibility of asymmetric properties in three-component superlattices. Here we fabricate superlattices consisting of barium titanate (BaTiO3), strontium titanate (SrTiO3) and calcium titanate (CaTiO3) with atomic-scale control by high-pressure pulsed laser deposition on conducting, atomically flat strontium ruthenate (SrRuO3) layers. The strain in BaTiO3 layers is fully maintained as long as the BaTiO3 thickness does not exceed the combined thicknesses of the CaTiO3 and SrTiO3 layers. By preserving full strain and combining heterointerfacial couplings, we find an overall 50% enhancement of the superlattice global polarization with respect to similarly grown pure BaTiO3, despite the fact that half the layers in the superlattice are nominally non-ferroelectric. We further show that even superlattices containing only single-unit-cell layers of BaTiO3 in a paraelectric matrix remain ferroelectric. Our data reveal that the specific interface structure and local asymmetries play an unexpected role in the polarization enhancement.

Many body calculations of the optoelectronic properties of h-AlN: from 3D to 2D

NASA Astrophysics Data System (ADS)

Kecik, Deniz; Bacaksiz, Cihan; Durgun, Engin; Senger, Tugrul

Outstanding electronic and optical properties of graphene, h-BN, MoS2 etc. motivate the further discovery of novel 2D materials such as AlN, a III-V compound, with remarkable features for potential optoelectronic applications, due to its wide indirect band gap. The layer and strain dependent optoelectronic properties of the recently synthesized monolayer hexagonal AlN (h-AlN) were investigated using density functional and many body perturbation theories, where RPA and BSE were employed on top of the QPG0W0 method. The optical spectra of 1-4 layered h-AlN revealed prominent absorption beyond the visible light regime; absorbance within the UV range increasing with the number of layers. In addition, the applied tensile strain (1 - 7 %) was observed to gradually redshift the absorption spectra. While the many body corrections induced significant blueshift to the optical spectra, evidence of bound excitons were also found for the layered structures. Hence, the optoelectronic properties of layered h-AlN can be tuned by modifying their structure and applying strain, moreover are greatly altered when electron-hole interactions are considered. This work was supported by the Scientific and Technological Research Council of Turkey (TUBITAK, Project No. 113T050).

Piezoelectrically enhanced photocathode

NASA Technical Reports Server (NTRS)

Beach, Robert A. (Inventor); Nikzad, Shouleh (Inventor); Strittmatter, Robert P. (Inventor); Bell, Lloyd Douglas (Inventor)

2009-01-01

A photocathode, for generating electrons in response to incident photons in a photodetector, includes a base layer having a first lattice structure and an active layer having a second lattice structure and epitaxially formed on the base layer, the first and second lattice structures being sufficiently different to create a strain in the active layer with a corresponding piezoelectrically induced polarization field in the active layer, the active layer having a band gap energy corresponding to a desired photon energy.

Biomechanical remodeling of obstructed guinea pig jejunum

PubMed Central

Zhao, Jingbo; Liao, Donghua; Yang, Jian; Gregersen, Hans

2010-01-01

Data on morphological and biomechanical remodeling are needed to understand the mechanisms behind intestinal obstruction. The effect of partial obstruction on mechanical properties with reference to the zero-stress state and on the histomorphological properties of the guinea pig small intestine was determined in this study. Partial obstruction and sham operation were surgically created in mid-jejunum of guinea pigs. The animals survived 2, 4, 7, and 14 days respectively. The age-matched guinea pigs that were not operated served as normal controls. The segment proximal to the obstruction site was used for histological analysis, no-load state and zero-stress state data, and distension test. The segment for distension was immersed in an organ bath and inflated to 10 cmH20. The outer diameter change during the inflation was monitored using a microscope with CCD camera. Circumferential stresses and strains were computed from the diameter, pressure and the zero-stress state data. The opening angle and absolute value of residual strain decreased (P<0.01 and P<0.001) whereas the wall thickness, wall cross-sectional area, and the wall stiffness increased after 7 days obstruction (P<0.05, P<0.01). Histologically, the muscle and submucosa layers, especially the circumferential muscle layer increased in thickness after obstruction. The opening angle and residual strain mainly depended on the thickness of the muscle layer whereas the wall stiffness mainly depended on the thickness of the submucosa layer. In conclusion, the histomorphological and biomechanical properties of small intestine (referenced for the first time to the zero-stress state) remodel proximal to the obstruction site in a time-dependent manner. PMID:20189575

Study of interfacial strain at the α-Al2O3/monolayer MoS2 interface by first principle calculations

NASA Astrophysics Data System (ADS)

Yu, Sheng; Ran, Shunjie; Zhu, Hao; Eshun, Kwesi; Shi, Chen; Jiang, Kai; Gu, Kunming; Seo, Felix Jaetae; Li, Qiliang

2018-01-01

With the advances in two-dimensional (2D) transition metal dichalcogenides (TMDCs) based metal-oxide-semiconductor field-effect transistor (MOSFET), the interface between the semiconductor channel and gate dielectrics has received considerable attention due to its significant impacts on the morphology and charge transport of the devices. In this study, first principle calculations were utilized to investigate the strain effect induced by the interface between crystalline α-Al2O3 (0001)/h-MoS2 monolayer. The results indicate that the 1.3 nm Al2O3 can induce a 0.3% tensile strain on the MoS2 monolayer. The strain monotonically increases with thicker dielectric layers, inducing more significant impact on the properties of MoS2. In addition, the study on temperature effect indicates that the increasing temperature induces monotonic lattice expansion. This study clearly indicates that the dielectric engineering can effectively tune the properties of 2D TMDCs, which is very attractive for nanoelectronics.

Strain-Tuning Atomic Substitution in Two-Dimensional Atomic Crystals.

PubMed

Li, Honglai; Liu, Hongjun; Zhou, Linwei; Wu, Xueping; Pan, Yuhao; Ji, Wei; Zheng, Biyuan; Zhang, Qinglin; Zhuang, Xiujuan; Zhu, Xiaoli; Wang, Xiao; Duan, Xiangfeng; Pan, Anlian

2018-05-22

Atomic substitution offers an important route to achieve compositionally engineered two-dimensional nanostructures and their heterostructures. Despite the recent research progress, the fundamental understanding of the reaction mechanism has still remained unclear. Here, we reveal the atomic substitution mechanism of two-dimensional atomic layered materials. We found that the atomic substitution process depends on the varying lattice constant (strain) in monolayer crystals, dominated by two strain-tuning (self-promoted and self-limited) mechanisms using density functional theory calculations. These mechanisms were experimentally confirmed by the controllable realization of a graded substitution ratio in the monolayers by controlling the substitution temperature and time and further theoretically verified by kinetic Monte Carlo simulations. The strain-tuning atomic substitution processes are of general importance to other two-dimensional layered materials, which offers an interesting route for tailoring electronic and optical properties of these materials.

Size effects on the martensitic phase transformation of NiTi nanograins

NASA Astrophysics Data System (ADS)

Waitz, T.; Antretter, T.; Fischer, F. D.; Simha, N. K.; Karnthaler, H. P.

2007-02-01

The analysis of nanocrystalline NiTi by transmission electron microscopy (TEM) shows that the martensitic transformation proceeds by the formation of atomic-scale twins. Grains of a size less than about 50 nm do not transform to martensite even upon large undercooling. A systematic investigation of these phenomena was carried out elucidating the influence of the grain size on the energy barrier of the transformation. Based on the experiment, nanograins were modeled as spherical inclusions containing (0 0 1) compound twinned martensite. Decomposition of the transformation strains of the inclusions into a shear eigenstrain and a normal eigenstrain facilitates the analytical calculation of shear and normal strain energies in dependence of grain size, twin layer width and elastic properties. Stresses were computed analytically for special cases, otherwise numerically. The shear stresses that alternate from twin layer to twin layer are concentrated at the grain boundaries causing a contribution to the strain energy scaling with the surface area of the inclusion, whereas the strain energy induced by the normal components of the transformation strain and the temperature dependent chemical free energy scale with the volume of the inclusion. In the nanograins these different energy contributions were calculated which allow to predict a critical grain size below which the martensitic transformation becomes unlikely. Finally, the experimental result of the atomic-scale twinning can be explained by analytical calculations that account for the transformation-opposing contributions of the shear strain and the twin boundary energy of the twin-banded morphology of martensitic nanograins.

Reconstruction of loads in the fibrosa and ventricularis of porcine aortic valves.

PubMed

Vesely, I

1996-01-01

The main structural components of aortic valve cusps, the fibrosa and ventricularis, are pre loaded by virtue of their attachment to each other. The fibrosa is under compression and the ventricularis is under tension. Once separated from each other, these internal stresses are relieved, and the fibrosa elongates and the ventricularis shrinks. It then becomes impossible to determine what fraction of the load is carried by the two layers at a given strain, using the standard superposition of tension vs strain curves. To enable the superposition approach, we needed to adjust the tension/ strain curves of the fibrosa and ventricularis, and duplicate the pre load that exists in these layers. We, therefore, iteratively shifted these curves and compared their arithmetic sum to the tension curve for the whole intact cusp, using a sum-of-squares error function. The best fits occurred when the fibrosa and ventricularis were shifted to the right and left by amounts corresponding to a true strain of epsilon = 0.26 and 0.10 for the fibrosa and ventricularis in the radial directions. In the circumferential direction, the best fit was achieved for shifts of epsilon = -0.11 and 0.010 for the fibrosa and ventricularis, respectively. This 26% compressive strain of the radial fibrosa compares well with direct observations. The reconstructed tension curves indicate that the ventricularis carries much of the radial loads, whereas circumferentially the two layers share loads equally up to 25% strain, beyond which the fibrosa takes over.

Integration of graphene sensor with electrochromic device on modulus-gradient polymer for instantaneous strain visualization

NASA Astrophysics Data System (ADS)

Yang, Tingting; Zhong, Yujia; Tao, Dashuai; Li, Xinming; Zang, Xiaobei; Lin, Shuyuan; Jiang, Xin; Li, Zhihong; Zhu, Hongwei

2017-09-01

In nature, some animals change their deceptive coloration for camouflage, temperature preservation or communication. This astonishing function has inspired scientists to replicate the color changing abilities of animals with artificial skin. Recently, some studies have focused on the smart materials and devices with reversible color changing or light-emitting properties for instantaneous strain visualization. However, most of these works only show eye-detectable appearance change when subjected to large mechanical deformation (100%-500% strain), and conspicuous color change at small strain remains rarely explored. In the present study, we developed a user-interactive electronic skin with human-readable optical output by assembling a highly sensitive resistive strain sensor with a stretchable organic electrochromic device (ECD) together. We explored the substrate effect on the electromechanical behavior of graphene and designed a strategy of modulus-gradient structure to employ graphene as both the highly sensitive strain sensing element and the insensitive stretchable electrode of the ECD layer. Subtle strain (0-10%) was enough to evoke an obvious color change, and the RGB value of the color quantified the magnitude of the applied strain. Such high sensitivity to smaller strains (0-10%) with color changing capability will potentially enhance the function of wearable devices, robots and prosthetics in the future.

Bumps and Ridges: Trabeculation Effects in Embryonic Heart Development

NASA Astrophysics Data System (ADS)

Battista, Nicholas; Lane, Andrea; Miller, Laura

2014-11-01

Trabeculae form in developing zebrafish hearts for Re on the order of 0.1; effects of trabeculae in this flow is not well understood. Dynamic processes, such as vortex formation, are important in the generation of shear at the endothelial surface layer and strains at the epithelial layer, which aid in proper morphology and functionality. In this study, CFD is used to quantify the effects of Re and idealized trabeculae height on the resulting flows.

A packaged, low-cost, robust optical fiber strain sensor based on small cladding fiber sandwiched within periodic polymer grating.

PubMed

Chiang, Chia-Chin; Li, Chein-Hsing

2014-06-02

In the present study, a novel packaged long-period fiber grating (PLPFG) strain sensor is first presented. The MEMS process was utilized to fabricate the packaged optical fiber strain sensor. The sensor structure consisted of etched optical fiber sandwiched between two layers of thick photoresist SU-8 3050 and then packaged with poly (dimethylsiloxane) (PDMS) polymer material to construct the PLPFG strain sensor. The PDMS packaging material was used to prevent the glue effect, wherein glue flows into the LPFG structure and reduces coupling strength, in the surface bonding process. Because the fiber grating was packaged with PDMS material, it was effectively protected and made robust. The resonance attenuation dip of PLPFG grows when it is loading. This study explored the size effect of the grating period and fiber diameter of PLPFG via tensile testing. The experimental results found that the best strain sensitivity of the PLPFG strain sensor was -0.0342 dB/με, and that an R2 value of 0.963 was reached.

Temperature-dependent mechanical properties of single-layer molybdenum disulphide: Molecular dynamics nanoindentation simulations

NASA Astrophysics Data System (ADS)

Zhao, Junhua; Jiang, Jin-Wu; Rabczuk, Timon

2013-12-01

The temperature-dependent mechanical properties of single-layer molybdenum disulphide (MoS2) are obtained using molecular dynamics (MD) nanoindentation simulations. The Young's moduli, maximum load stress, and maximum loading strain decrease with increasing temperature from 4.2 K to 500 K. The obtained Young's moduli are in good agreement with those using our MD uniaxial tension simulations and the available experimental results. The tendency of maximum loading strain with different temperature is opposite with that of metal materials due to the short range Stillinger-Weber potentials in MoS2. Furthermore, the indenter tip radius and fitting strain effect on the mechanical properties are also discussed.

Type-II quantum wells with tensile-strained GaAsSb layers for interband cascade lasers with tailored valence band mixing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Motyka, M.; Dyksik, M.; Ryczko, K.

Optical properties of modified type II W-shaped quantum wells have been investigated with the aim to be utilized in interband cascade lasers. The results show that introducing a tensely strained GaAsSb layer, instead of a commonly used compressively strained GaInSb, allows employing the active transition involving valence band states with a significant admixture of the light holes. Theoretical predictions of multiband k·p theory have been experimentally verified by using photoluminescence and polarization dependent photoreflectance measurements. These results open a pathway for practical realization of mid-infrared lasing devices with uncommon polarization properties including, for instance, polarization-independent midinfrared light emitters.

A Case of Loeffler Endocarditis That Showed Endomyocardial Systolic Dysfunction Detected by Layer Specific Strain Analysis.

PubMed

Jin, Xuanyi; Ma, Chunyan; Wang, Yonghuai; Yang, Jun

2017-12-12

Loeffler endocarditis is a rare comprehensive cardiac manifestation caused by eosinophilic cell infiltrations and is present in 50%-60% of patients with hypereosinophilic syndrome (HES). Left ventricle (LV) endocardial systolic dysfunction is a major cause of morbidity and mortality in HES and Loeffler endocarditis. We present a case of Loeffler endocarditis, whose left ventricular (LV) systolic dysfunction and endocardial systolic dysfunction were first neglected by conventional transthoracic echocardiography (TTE), but were later pointed out by layer-specific longitudinal strain analysis. With timely initial therapeutic management, the patient's outcome was remarkable. Thus, we strongly recommend strain analysis as a necessary supplementary test of conventional TTE in all patients with Loeffler endocarditis.

Behavior of fiber reinforced metal laminates at high strain rate

NASA Astrophysics Data System (ADS)

Newaz, Golam; Sasso, Marco; Amodio, Dario; Mancini, Edoardo

2018-05-01

Carbon Fiber Reinforced Aluminum Laminate (CARALL) is a good system for energy absorption through plastic deformation in aluminum and micro-cracking in the composite layers. Moreover, CARALL FMLs also provide excellent impact resistance due to the presence of aluminum layer. The focus of this research is to characterize the CARALL behavior under dynamic conditions. High strain rate tests on sheet laminate samples have been carried out by means of direct Split Hopkinson Tension Bar. The sample geometry and the clamping system were optimized by FEM simulations. The clamping system has been designed and optimized in order reduce impedance disturbance due to the fasteners and to avoid the excessive plastic strain outside the gauge region of the samples.

Synchrotron X-ray measurement techniques for thermal barrier coated cylindrical samples under thermal gradients.

PubMed

Siddiqui, Sanna F; Knipe, Kevin; Manero, Albert; Meid, Carla; Wischek, Janine; Okasinski, John; Almer, Jonathan; Karlsson, Anette M; Bartsch, Marion; Raghavan, Seetha

2013-08-01

Measurement techniques to obtain accurate in situ synchrotron strain measurements of thermal barrier coating systems (TBCs) applied to hollow cylindrical specimens are presented in this work. The Electron Beam Physical Vapor Deposition coated specimens with internal cooling were designed to achieve realistic temperature gradients over the TBC coated material such as that occurring in the turbine blades of aeroengines. Effects of the circular cross section on the x-ray diffraction (XRD) measurements in the various layers, including the thermally grown oxide, are investigated using high-energy synchrotron x-rays. Multiple approaches for beam penetration including collection, tangential, and normal to the layers, along with variations in collection parameters are compared for their ability to attain high-resolution XRD data from the internal layers. This study displays the ability to monitor in situ, the response of the internal layers within the TBC, while implementing a thermal gradient across the thickness of the coated sample. The thermal setup maintained coating surface temperatures in the range of operating conditions, while monitoring the substrate cooling, for a controlled thermal gradient. Through variation in measurement location and beam parameters, sufficient intensities are obtained from the internal layers which can be used for depth resolved strain measurements. Results are used to establish the various techniques for obtaining XRD measurements through multi-layered coating systems and their outcomes will pave the way towards goals in achieving realistic in situ testing of these coatings.

Synchrotron X-ray measurement techniques for thermal barrier coated cylindrical samples under thermal gradients

NASA Astrophysics Data System (ADS)

Siddiqui, Sanna F.; Knipe, Kevin; Manero, Albert; Meid, Carla; Wischek, Janine; Okasinski, John; Almer, Jonathan; Karlsson, Anette M.; Bartsch, Marion; Raghavan, Seetha

2013-08-01

Measurement techniques to obtain accurate in situ synchrotron strain measurements of thermal barrier coating systems (TBCs) applied to hollow cylindrical specimens are presented in this work. The Electron Beam Physical Vapor Deposition coated specimens with internal cooling were designed to achieve realistic temperature gradients over the TBC coated material such as that occurring in the turbine blades of aeroengines. Effects of the circular cross section on the x-ray diffraction (XRD) measurements in the various layers, including the thermally grown oxide, are investigated using high-energy synchrotron x-rays. Multiple approaches for beam penetration including collection, tangential, and normal to the layers, along with variations in collection parameters are compared for their ability to attain high-resolution XRD data from the internal layers. This study displays the ability to monitor in situ, the response of the internal layers within the TBC, while implementing a thermal gradient across the thickness of the coated sample. The thermal setup maintained coating surface temperatures in the range of operating conditions, while monitoring the substrate cooling, for a controlled thermal gradient. Through variation in measurement location and beam parameters, sufficient intensities are obtained from the internal layers which can be used for depth resolved strain measurements. Results are used to establish the various techniques for obtaining XRD measurements through multi-layered coating systems and their outcomes will pave the way towards goals in achieving realistic in situ testing of these coatings.

RBS/Channeling Studies of Swift Heavy Ion Irradiated GaN Layers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sathish, N.; Dhamodaran, S.; Pathak, A. P.

2009-03-10

Epitaxial GaN layers grown by MOCVD on c-plane sapphire substrates were irradiated with 150 MeV Ag ions at a fluence of 5x10{sup 12} ions/cm{sup 2}. Samples used in this study are 2 {mu}m thick GaN layers, with and without a thin AlN cap-layer. Energy dependent RBS/Channeling measurements have been carried out on both irradiated and unirradiated samples for defects characterization. Observed results are compared and correlated with previous HRXRD, AFM and optical studies. The {chi}{sub min} values for unirradiated samples show very high value and the calculated defect densities are of the order of 10{sup 10} cm{sup -2} as expectedmore » in these samples. Effects of irradiation on these samples are different as initial samples had different defect densities. Epitaxial reconstruction of GaN buffer layer has been attributed to the observed changes, which are generally grown to reduce the strain between GaN and Sapphire.« less

Study on the growth mechanism and optical properties of sputtered lead selenide thin films

NASA Astrophysics Data System (ADS)

Sun, Xigui; Gao, Kewei; Pang, Xiaolu; Yang, Huisheng; Volinsky, Alex A.

2015-11-01

Lead selenide thin films with different microstructure were deposited on Si (1 0 0) substrates using magnetron sputtering at 50 °C, 150 °C and 250 °C, respectively. The crystal structure of the sputtered PbSe thin films varies from amorphous crystalline to columnar grain, and then to double-layer (nano-crystalline layer and columnar grain layer) structure as the deposition temperature increases, which is due to the dominating growth mode of the thin films changes from Frank-van der Merwe (or layer-by-layer) growth mode at 50 °C to Volmer-Weber (or 3D island) growth mode at 150 °C, and then to Stranski-Krastanow (or 3D island-on-wetting-layer) growth mode at 250 °C. The growth mechanism of the sputtered PbSe thin films is mainly dominated by the surface and strain energy contributions. Moreover, the strain energy contribution is more prominent when the deposition temperature is less than 180 °C, while, the surface energy contribution is more prominent when the deposition temperature is higher than 180 °C. The absorption spectra of the sputtered PbSe thin films are in 3.1-5 μm range. Besides, the sputtered PbSe thin film prepared at 250 °C has two different optical band gaps due to its unique double-layer structure. According to the theoretical calculation results, the variation of the band gap with the deposition temperature is determined by the shift of the valence band maximum with the lattice constant.

Growth and micro structural studies on Yittria Stabilized Zirconia (YSZ) and Strontium Titanate (STO) buffer layers

NASA Technical Reports Server (NTRS)

Srinivas, S.; Pinto, R.; Pai, S. P.; Dsousa, D. P.; Apte, P. R.; Kumar, D.; Purandare, S. C.; Bhatnagar, A. K.

1995-01-01

Microstructure of Yittria Stabilized Zirconia (YSZ) and Strontium Titanate (STO) of radio frequency magnetron sputtered buffer layers was studied at various sputtering conditions on Si (100), Sapphire and LaAlO3 (100) substrates. The effect of substrate temperatures up to 800 C and sputtering gas pressures in the range of 50 mTorr. of growth conditions was studied. The buffer layers of YSZ and STO showed a strong tendency for columnar growth was observed above 15 mTorr sputtering gas pressure and at high substrate temperatures. Post annealing of these films in oxygen atmosphere reduced the oxygen deficiency and strain generated during growth of the films. Strong c-axis oriented superconducting YBa2Cu3O7-x (YBCO) thin films were obtained on these buffer layers using pulsed laser ablation technique. YBCO films deposited on multilayers of YSZ and STO were shown to have better superconducting properties.

Surfactant-Mediated Growth of Ge/Si(001) Interface Studied by XPD

NASA Astrophysics Data System (ADS)

Gunnella, R.; Castrucci, P.; Pinto, N.; Cucculelli, P.; Davoli, I.; Sébilleau, D.; de Crescenzi, M.

The influence of Sb as a surfactant on the formation of Si/Ge interface is studied by means of XPD (X-ray photoelectron diffraction) and AED (Auger electron diffraction) from Ge and Si core levels. The technique employed is particularly suitable for checking the film tetragonal distortion, the growth morphology and the sharpness of the interface. We found a layer by layer growth mode for 3 ML of Ge on Si(001) and related values of strain of the film close to the value predicted by the elastic theory which enforces the use of such a surfactant to obtain high quality and sharp heterostructures. In addition, studying the influence of 3 ML of the Si cap layer on the 3 ML Ge, we obtain no indication of Ge segregation into the Si cap layer. Finally, evidences of quality degradation after high temperature (T > 600°C) annealing are shown.

Strength and stability analysis of a single-walled black phosphorus tube under axial compression

NASA Astrophysics Data System (ADS)

Cai, Kun; Wan, Jing; Wei, Ning; Qin, Qing H.

2016-07-01

Few-layered black phosphorus materials currently attract much attention due to their special electronic properties. As a consequence, a single-layer black phosphorus (SLBP) nanotube has been theoretically built. The corresponding electronic properties of such a black phosphorus nanotube (BPNT) were also evaluated numerically. However, unlike graphene formed with 2sp2 covalent carbon atoms, SLBP is formed with 3sp3 bonded atoms. It means that the structure from SLBP will possess lower Young’s modulus and mechanical strength than those of carbon nanotubes. In this study, molecular dynamics simulation is performed to investigate the strength and stability of BPNTs affected by the factors of diameter, length, loading speed and temperature. Results are fundamental for investigating the other physical properties of a BPNT acting as a component in a nanodevice. For example, buckling of the BPNT happens earlier than fracture, before which the nanostructure has very small axial strain. For the same BPNT, a higher load speed results in lower critical axial strain and a nanotube with lower axial strain can still be stable at a higher temperature.

Analysis of Composite Panels Subjected to Thermo-Mechanical Loads

NASA Technical Reports Server (NTRS)

Noor, Ahmed K.; Peters, Jeanne M.

1999-01-01

The results of a detailed study of the effect of cutout on the nonlinear response of curved unstiffened panels are presented. The panels are subjected to combined temperature gradient through-the-thickness combined with pressure loading and edge shortening or edge shear. The analysis is based on a first-order, shear deformation, Sanders-Budiansky-type shell theory with the effects of large displacements, moderate rotations, transverse shear deformation, and laminated anisotropic material behavior included. A mixed formulation is used with the fundamental unknowns consisting of the generalized displacements and the stress resultants of the panel. The nonlinear displacements, strain energy, principal strains, transverse shear stresses, transverse shear strain energy density, and their hierarchical sensitivity coefficients are evaluated. The hierarchical sensitivity coefficients measure the sensitivity of the nonlinear response to variations in the panel parameters, as well as in the material properties of the individual layers. Numerical results are presented for cylindrical panels and show the effects of variations in the loading and the size of the cutout on the global and local response quantities as well as their sensitivity to changes in the various panel, layer, and micromechanical parameters.

[Collagenolytic activity in several species of deuteromycetes under various storage conditions].

PubMed

Iakovleva, M B; Khoang, T L; Nikitina, Z K

2006-01-01

The ability of deuteromycetes of the genera Penicillium, Aspergillus, and Botrytis to retain collagenolytic activity was studied after both 2 and 10 years of storage on a Czapek medium under a layer of mineral oil at 4 degrees C, as well as in silica gel granules at 20 and -60 degrees C. The enzymatic activity of several species, including Botrytis terrestris, Penicillium janthinellum, Penicillium chrysogenum, and Penicillium citrinum, was retained under both conditions of storage. Aspergillus repens retained enzymatic activity only if stored under a layer of mineral oil. The viability of conidia and the collagenolytic activity of Botrytis terrestris, P. janthinellum, P. chrysogenum, and Penicillium citrinum, maintained on silica gel for 10 years, depended on the storage temperature. The viability of the test strains improved after storage on a silica gel at -60 degrees C. A strain of Aspergillus repens lost its ability to dissolve collagen at various storage temperatures on the silica gel. The index of lysis for three strains of Penicillium deuteromycetes (Penicillium janthinellum, Penicillium chrysogenum, and Penicillium citrinum) increased after a 10-year storage on silica gel at -60 degrees C.

Microsatellite markers associated with resistance to Marek's disease in commercial layer chickens.

PubMed

McElroy, J P; Dekkers, J C M; Fulton, J E; O'Sullivan, N P; Soller, M; Lipkin, E; Zhang, W; Koehler, K J; Lamont, S J; Cheng, H H

2005-11-01

The objective of the current study was to identify QTL conferring resistance to Marek's disease (MD) in commercial layer chickens. To generate the resource population, 2 partially inbred lines that differed in MD-caused mortality were intermated to produce 5 backcross families. Vaccinated chicks were challenged with very virulent plus (vv+) MD virus strain 648A at 6 d and monitored for MD symptoms. A recent field isolate of the MD virus was used because the lines were resistant to commonly used older laboratory strains. Selective genotyping was employed using 81 microsatellites selected based on prior results with selective DNA pooling. Linear regression and Cox proportional hazard models were used to detect associations between marker genotypes and survival. Significance thresholds were validated by simulation. Seven and 6 markers were significant based on proportion of false positive and false discovery rate thresholds less than 0.2, respectively. Seventeen markers were associated with MD survival considering a comparison-wise error rate of 0.10, which is about twice the number expected by chance, indicating that at least some of the associations represent true effects. Thus, the present study shows that loci affecting MD resistance can be mapped in commercial layer lines. More comprehensive studies are under way to confirm and extend these results.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meisner, L. L., E-mail: llm@ispms.tsc.ru; Meisner, S. N., E-mail: msn@ispms.tsc.ru; National Research Tomsk State University, Tomsk, 634050

This work comprises a study of the influence of the pulse number of low-energy high-current electron beam (LEHCEB) exposure on the value and character of distribution of residual elastic stresses, texturing effects and the relationship between structural-phase states and physical and mechanical properties of the modified surface layers of TiNi alloy. LEHCEB processing of the surface of TiNi samples was carried out using a RITM-SP [3] installation. Energy density of electron beam was constant at E{sub s} = 3.9 ± 0.5 J/cm{sup 2}; pulse duration was 2.8 ± 0.3 μs. The number of pulses in the series was changeable, (n =more » 2–128). It was shown that as the result of multiple LEHCEB processing of TiNi samples, hierarchically organized multilayer structure is formed in the surface layer. The residual stress field of planar type is formed in the modified surface layer as following: in the direction of the normal to the surface the strain component ε{sub ⊥} < 0 (compressing strain), and in a direction parallel to the surface, the strain component ε{sub ||} > 0 (tensile deformation). Texturing effects and the level of residual stresses after LEHCEB processing of TiNi samples with equal energy density of electron beam (∼3.8 J/cm{sup 2}) depend on the number of pulses and increase with the rise of n > 10.« less

Strain-engineered diffusive atomic switching in two-dimensional crystals

PubMed Central

Kalikka, Janne; Zhou, Xilin; Dilcher, Eric; Wall, Simon; Li, Ju; Simpson, Robert E.

2016-01-01

Strain engineering is an emerging route for tuning the bandgap, carrier mobility, chemical reactivity and diffusivity of materials. Here we show how strain can be used to control atomic diffusion in van der Waals heterostructures of two-dimensional (2D) crystals. We use strain to increase the diffusivity of Ge and Te atoms that are confined to 5 Å thick 2D planes within an Sb2Te3–GeTe van der Waals superlattice. The number of quintuple Sb2Te3 2D crystal layers dictates the strain in the GeTe layers and consequently its diffusive atomic disordering. By identifying four critical rules for the superlattice configuration we lay the foundation for a generalizable approach to the design of switchable van der Waals heterostructures. As Sb2Te3–GeTe is a topological insulator, we envision these rules enabling methods to control spin and topological properties of materials in reversible and energy efficient ways. PMID:27329563

Strain dependence of In incorporation in m-oriented GaInN/GaN multi quantum well structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Horenburg, Philipp, E-mail: p.horenburg@tu-braunschweig.de; Buß, Ernst Ronald; Rossow, Uwe

We demonstrate a strong dependence of the indium incorporation efficiency on the strain state in m-oriented GaInN/GaN multi quantum well (MQW) structures. Insertion of a partially relaxed AlInN buffer layer opens up the opportunity to manipulate the strain situation in the MQW grown on top. By lattice-matching this AlInN layer to the c- or a-axis of the underlying GaN, relaxation towards larger a- or smaller c-lattice constants can be induced, respectively. This results in a modified template for the subsequent MQW growth. From X-ray diffraction and photoluminescence measurements, we derive significant effects on the In incorporation efficiency and In concentrationsmore » in the quantum well (QW) up to x = 38% without additional accumulation of strain energy in the QW region. This makes strain manipulation a very promising method for growth of high In-containing MQW structures for efficient, long wavelength light-emitting devices.« less

Sensitivity to disinfection of bacterial indicator organisms for monitoring the Salmonella Enteritidis status of layer farms after cleaning and disinfection.

PubMed

Dewaele, I; Ducatelle, R; Herman, L; Heyndrickx, M; De Reu, K

2011-06-01

The present study evaluated Escherichia coli, Enterococcus faecalis, and Enterococcus hirae as potential indicator organisms for the possible Salmonella Enteritidis (SE) presence in layer farms after cleaning and disinfection by comparing their susceptibility to disinfection. A quantitative suspension disinfection test according to European Standard EN1656 was performed using disinfection products CID20 and Virocid (both from CID Lines, Ieper, Belgium). In a preliminary test, the sensitivity to both disinfection products was compared between ATCC strains of SE, E. coli, En. faecalis, and En. hirae. The sensitivity of SE to disinfection was most comparable to that of E. coli. A second disinfection test compared the elimination of E. coli to SE ATCC strains as well as field strains. Results showed no significant effect regarding the strain (P > 0.05 for CID20 and Virocid), meaning that no difference was detected in sensitivity toward disinfection. When comparing the sensitivity in general at species level for all concentrations of disinfectant used, no significant difference was found between E. coli and SE in sensitivity to Virocid (P > 0.05). In conclusion, because of its similar response to disinfection in a suspension disinfection test, E. coli could be used as an indicator for possible Salmonella presence after cleaning and disinfection.

Mapping Strain Gradients in the FIB-Structured InGaN/GaN Multilayered Films with 3D X-ray Microbeam

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barabash, Rozaliya; Gao, Yanfei; Ice, Gene E

2010-01-01

This research presents a combined experimental-modeling study of lattice rotations and deviatoric strain gradients induced by focused-ion beam (FIB) milling in nitride heterostructures. 3D X-ray polychromatic microdiffraction (PXM) is used to map the local lattice orientation distribution in FIB-structured areas. Results are discussed in connection with microphotoluminescence ({mu}-PL), fluorescent analysis, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) data. It is demonstrated that FIB-milling causes both direct and indirect damage to the InGaN/GaN layers. In films subjected to direct ion beam impact, a narrow amorphidized top layer is formed. Near the milling area, FIB-induced stress relaxation and formation ofmore » complicated 3D strain fields are observed. The resulting lattice orientation changes are found to correlate with a decrease and/or loss of PL intensity, and agree well with finite element simulations of the three-dimensional strain fields near the relaxed trenches. Experimentally, it is found that the lattice surface normal has an in-plane rotation, which only appears in simulations when the GaN-substrate lattice mismatch annihilates the InGaN-substrate mismatch. This behavior further supports the notion that the film/substrate interface is incoherent.« less

Mapping strain gradients in the FIB-structured InGaN/GaN multilayered films with 3D x-ray microbeam.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barabash, R. I.; Gao, Y. F.; Ice, G. E.

2010-11-25

This research presents a combined experimental-modeling study of lattice rotations and deviatoric strain gradients induced by focused-ion beam (FIB) milling in nitride heterostructures. 3D X-ray polychromatic microdiffraction (PXM) is used to map the local lattice orientation distribution in FIB-structured areas. Results are discussed in connection with microphotoluminescence ({mu}-PL), fluorescent analysis, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) data. It is demonstrated that FIB-milling causes both direct and indirect damage to the InGaN/GaN layers. In films subjected to direct ion beam impact, a narrow amorphidized top layer is formed. Near the milling area, FIB-induced stress relaxation and formation ofmore » complicated 3D strain fields are observed. The resulting lattice orientation changes are found to correlate with a decrease and/or loss of PL intensity, and agree well with finite element simulations of the three-dimensional strain fields near the relaxed trenches. Experimentally, it is found that the lattice surface normal has an in-plane rotation, which only appears in simulations when the GaN-substrate lattice mismatch annihilates the InGaN-substrate mismatch. This behavior further supports the notion that the film/substrate interface is incoherent.« less

Experimental study of vorticity-strain rate interaction in turbulent partially-premixed jet flames using tomographic particle image velocimetry

DOE PAGES

Coriton, Bruno; Frank, Jonathan H.

2016-02-16

In turbulent flows, the interaction between vorticity, ω, and strain rate, s, is considered a primary mechanism for the transfer of energy from large to small scales through vortex stretching. The ω-s coupling in turbulent jet flames is investigated using tomographic particle image velocimetry (TPIV). TPIV provides a direct measurement of the three-dimensional velocity field from which ω and s are determined. The effects of combustion and mean shear on the ω-s interaction are investigated in turbulent partially premixed methane/air jet flames with high and low probabilities of localized extinction as well as in a non-reacting isothermal air jet withmore » Reynolds number of approximately 13,000. Results show that combustion causes structures of high vorticity and strain rate to agglomerate in highly correlated, elongated layers that span the height of the probe volume. In the non-reacting jet, these structures have a more varied morphology, greater fragmentation, and are not as well correlated. The enhanced spatiotemporal correlation of vorticity and strain rate in the stable flame results in stronger ω-s interaction characterized by increased enstrophy and strain-rate production rates via vortex stretching and straining, respectively. The probability of preferential local alignment between ω and the eigenvector of the intermediate principal strain rate, s 2, which is intrinsic to the ω-s coupling in turbulent flows, is larger in the flames and increases with the flame stability. The larger mean shear in the flame imposes a preferential orientation of ω and s 2 tangential to the shear layer. The extensive and compressive principal strain rates, s 1 and s 3, respectively, are preferentially oriented at approximately 45° with respect to the jet axis. As a result, the production rates of strain and vorticity tend to be dominated by instances in which ω is parallel to the s 1¯-s 2¯ plane and orthogonal to s 3¯.« less

Optical properties of beryllium-doped GaSb epilayers grown on GaAs substrate

NASA Astrophysics Data System (ADS)

Deng, Zhuo; Chen, Baile; Chen, Xiren; Shao, Jun; Gong, Qian; Liu, Huiyun; Wu, Jiang

2018-05-01

In this work, the effects of p-type beryllium (Be) doping on the optical properties of GaSb epilayers grown on GaAs substrate by Molecular Beam Epitaxy (MBE) have been studied. Temperature- and excitation power-dependent photoluminescence (PL) measurements were performed on both nominally undoped and intentionally Be-doped GaSb layers. Clear PL emissions are observable even at the temperature of 270 K from both layers, indicating the high material quality. In the Be-doped GaSb layer, the transition energies of main PL features exhibit red-shift up to ∼7 meV, and the peak widths characterized by Full-Width-at-Half-Maximum (FWHM) also decrease. In addition, analysis on the PL integrated intensity in the Be-doped sample reveals a gain of emission signal, as well as a larger carrier thermal activation energy. These distinctive PL behaviors identified in the Be-doped GaSb layer suggest that the residual compressive strain is effectively relaxed in the epilayer, due possibly to the reduction of dislocation density in the GaSb layer with the intentional incorporation of Be dopants. Our results confirm the role of Be as a promising dopant in the improvement of crystalline quality in GaSb, which is a crucial factor for growth and fabrication of high quality strain-free GaSb-based devices on foreign substrates.

Measurement of the through thickness compression of a battery separator

NASA Astrophysics Data System (ADS)

Yan, Shutian; Huang, Xiaosong; Xiao, Xinran

2018-04-01

The mechanical integrity of the separator is critical to the reliable operation of a battery. Due to its minimal thickness, compression experiments with a single/a few layers of separator are difficult to perform. In this work, a capacitance based displacement set-up has been developed for the measurement of the through thickness direction (TTD) compression stress-strain behavior of the separator and the investigation of its interaction with the electrode. The experiments were performed for a stack of two layers of Celgard 2400 separator, NMC cathode, and separator/NMC cathode/separator stack in both dry and wet (i.e. submersed in dimethyl carbonate DMC) conditions. The experimental results reveal that the separator compression modulus can be significantly affected by the presence of DMC. The iso-stress based rule of mixtures was used to compute the compressive stress-strain curve for the stack from that of the separator and NMC layer. The computed curve agreed with the experimental curve reasonably well up to about 0.16 strain but deviated significantly to a softer response at higher strains. The results suggest that, in the stack, the TTD compressive deformation of the separator is influenced by the NMC cathode.

Towards the determination of deformation rates - pinch-and-swell structures as a natural and simulated paleo-strain rate gage

NASA Astrophysics Data System (ADS)

Peters, Max; Poulet, Thomas; Karrech, Ali; Regenauer-Lieb, Klaus; Herwegh, Marco

2014-05-01

Layered rocks deformed under viscous deformation conditions frequently show boudinage, a phenomenon that results from differences in effective viscosity between the involved layers. In the case of continuous necking of a mechanically stiffer layer embedded in a weaker matrix, symmetric boudins are interpreted as the result of dominant visco-plastic deformation (Goscombe et al., 2004). However, information on the physical conditions, material properties and deformation processes are yet unknown. Natural samples deformed under low-grade (T<350°C) metamorphic conditions were studied in detail in the Dent de Morcles and Doldenhorn nappes of the Helvetic Alps in order to accurately simulate their deformation styles by numerical models. In these samples, monomineralic calcite (Cc) veins were repeatedly boudinaged on cm- to µm-scale. Remnants of incompletely recrystallized original vein Cc grains in the swells indicate a sequence of deformation twinning, followed by progressive dynamic recrystallization along former twin planes up to complete recrystallization in the pinches (Schmalholz and Maeder, 2012). This sequence suggests dislocation creep to be active as important deformation mechanism. In contrast to the pinch-and-swell structures, the grain size of the Cc in the surrounding matrix is much finer-grained due to pinning by secondary particles, forcing the matrix to deform under viscous granular creep, i.e. by diffusion accommodated grain boundary sliding. The deformation processes observed in the natural samples were incorporated into a numerical model in order to evaluate the rheology of both layer and matrix, using an extension to a user material subroutine (Karrech et al., 2011a) for the finite element solver ABAQUS. We implemented thermo-mechanical coupling allowing elastic, viscous and plastic deformation of Cc (Herwegh et al., in press). We simulate a pure-shear box using finite elements, each representing a grain size distribution, which undergo layer-parallel extension. The box is built up by 3 layers, consisting of a central layer of coarse-grained populations, surrounded by finer-grained populations on bottom and top. The rheology evolves from transient stages (elasticity and strain hardening) to composite viscous flow (GSI & GSS) with increasing shear strain. The small grain sizes in top and bottom layers are strain-invariant and limited in their growth (comparable to Zener pinning) forcing the matrix to deform by exclusively by GSS creep. In contrast, the initially coarse grain sizes of the central layer are allowed to adapt to the physical deformation conditions by either grain growth or grain size reduction following the Paleowattmeter of Austin and Evans (2007) combined with the thermodynamic approach of Regenauer-Lieb and Yuen (2004). Depending on the dissipated energy, grain sizes in these domains vary substantially in space and time. While low strain rates (low stresses) in the swells favor grain growth and GSI dominated deformation, high strain rates in the pinches provoke dramatic grain size reduction with an increasing contribution of GSS as a function of decreasing grain size. The development of symmetric necks observed in nature thus seems to coincide with the transition from dislocation to diffusion creep dominated flow with continuous grain size reduction and growth from swell to neck at relatively high extensional strains. REFERENCES Austin, N. and Evans, B. (2007). Paleowattmeters: A scaling relation for dynamically recrystallized grain size. Geology, 35. Goscombe, B.D., Passchier, C.W. and Hand, M. (2004). Boudinage classification: End-member boudin types and modified boudin structures, Journal of Structural Geology, 26. Herwegh, M., Poulet, T., Karrech, A. and Regenauer-Lieb, K. (in press). From transient to steady state deformation and grain size: A thermodynamic approach using elasto-visco-plastic numerical modeling. Journal of Geophysical Research. Karrech, A., Regenauer-Lieb, K. and Poulet, T. (2011a). A Damaged visco-plasticity model for pressure and temperature sensitive geomaterials. Journal of Engineering Science 49. Regenauer-Lieb, K. and Yuen, D. (2004). Positive feedback of interacting ductile faults from coupling of equation of state, rheology and thermal-mechanics. Physics of the Earth and Planetary Interiors, 142. Schmalholz, S.M. and Maeder, X. (2012). Pinch-and-swell structure and shear zones in viscoplastic layers. Journal of Structural Geology, 34.

Screening high oleaginous Chlorella strains from different climate zones.

PubMed

Xu, Jin; Hu, Hanhua

2013-09-01

In outdoor cultivation, screening strains adapted to a wide temperature range or suitable strains for different environmental temperatures is of great importance. In this study, triacylglycerol (TAG) content of 23 oil-producing Chlorella strains from different climate zones were analyzed by thin layer chromatography. Four selected Chlorella strains (NJ-18, NJ-7, NMX35N and NMX139N) with rather high TAG content had higher total lipid content compared with Chlorella vulgaris SAG 211-11b. In particular, NJ-18 displayed the highest TAG productivity among the four high oil-producing Chlorella strains. Accumulation of TAGs in strain NMX35N changed a little from 30 to 40°C, showing a desirable characteristic of accumulating TAGs at high temperatures. Our results demonstrated that NJ-18 and NMX35N had suitable fatty acid profiles and good adaption to low and high temperatures respectively. Therefore, cultivation of the two Chlorella strains together might be a good option for economic biodiesel production during the whole seasons of the year. Copyright © 2013 Elsevier Ltd. All rights reserved.

Numerical analysis of the effect of surface roughness on mechanical fields in polycrystalline aggregates

NASA Astrophysics Data System (ADS)

Guilhem, Yoann; Basseville, Stéphanie; Curtit, François; Stéphan, Jean-Michel; Cailletaud, Georges

2018-06-01

This paper is dedicated to the study of the influence of surface roughness on local stress and strain fields in polycrystalline aggregates. Finite element computations are performed with a crystal plasticity model on a 316L stainless steel polycrystalline material element with different roughness states on its free surface. The subsequent analysis of the plastic strain localization patterns shows that surface roughness strongly affects the plastic strain localization induced by crystallography. Nevertheless, this effect mainly takes place at the surface and vanishes under the first layer of grains, which implies the existence of a critical perturbed depth. A statistical analysis based on the plastic strain distribution obtained for different roughness levels provides a simple rule to define the size of the affected zone depending on the rough surface parameters.

Methods for determining deformation history for chocolate tablet boudinage with fibrous crystals

NASA Astrophysics Data System (ADS)

Casey, M.; Dietrich, D.; Ramsay, J. G.

1983-02-01

Chocolate tablet boudinage with fibrous crystal growths between the boudinaged plates from two localities were studied. In one, from Leytron, Valais, Switzerland, the deformation history was found to be a succession of plane strain increments with the shortening direction perpendicular to the boudinaged sheet and the extension direction showing a progressive change in orientation within the sheet. The incremental and finite strains were evaluated. The other specimen, from Parys Mountain, Anglesey Great Britain, was found to have a more complex history with diachronous break up of the competent layer and flattening strain increments. It was found that under these circumstances the direct graphical methods of determining finite and incremental strains gave inconsistent results. A numerical model was developed which allowed the simulation of chocolate tablet structure with a complex deformation history. The model was applied to the Anglesey specimen and three possible strain histories for this structure were tried.

Prediction of strain values in reinforcements and concrete of a RC frame using neural networks

NASA Astrophysics Data System (ADS)

Vafaei, Mohammadreza; Alih, Sophia C.; Shad, Hossein; Falah, Ali; Halim, Nur Hajarul Falahi Abdul

2018-03-01

The level of strain in structural elements is an important indicator for the presence of damage and its intensity. Considering this fact, often structural health monitoring systems employ strain gauges to measure strains in critical elements. However, because of their sensitivity to the magnetic fields, inadequate long-term durability especially in harsh environments, difficulties in installation on existing structures, and maintenance cost, installation of strain gauges is not always possible for all structural components. Therefore, a reliable method that can accurately estimate strain values in critical structural elements is necessary for damage identification. In this study, a full-scale test was conducted on a planar RC frame to investigate the capability of neural networks for predicting the strain values. Two neural networks each of which having a single hidden layer was trained to relate the measured rotations and vertical displacements of the frame to the strain values measured at different locations of the frame. Results of trained neural networks indicated that they accurately estimated the strain values both in reinforcements and concrete. In addition, the trained neural networks were capable of predicting strains for the unseen input data set.

Haemagglutination and surface structures in strains of Clostridium spiroforme.

PubMed

Baldassarri, L; Pantosti, A; Caprioli, A; Mastrantonio, P; Donelli, G

1989-07-01

Five strains of Clostridium spiroforme were examined for their surface properties. All strains were able to agglutinate human erythrocytes. Electron microscopy showed a ruthenium red-positive capsule mediating the attachment of bacteria to erythrocytes. Two strains, showing the lowest degree of haemagglutination, exhibited an additional external layer of filamentous structures, possibly interfering with the agglutinating activity. In spite of their agglutinating ability, the C. spiroforme strains did not show surface hydrophobicity, thus suggesting the possible existence of a new type of clostridial adhesin.

Encapsulating Elastically Stretchable Neural Interfaces: Yield, Resolution, and Recording/Stimulation of Neural Activity

PubMed Central

Morrison, Barclay; Goletiani, Cezar; Yu, Zhe; Wagner, Sigurd

2013-01-01

A high resolution elastically stretchable microelectrode array (SMEA) to interface with neural tissue is described. The SMEA consists of an elastomeric substrate, such as poly(dimethylsiloxane) (PDMS), elastically stretchable gold conductors, and an electrically insulating encapsulating layer in which contact holes are opened. We demonstrate the feasibility of producing contact holes with 40 µm × 40 µm openings, show why the adhesion of the encapsulation layer to the underlying silicone substrate is weakened during contact hole fabrication, and provide remedies. These improvements result in greatly increased fabrication yield and reproducibility. An SMEA with 28 microelectrodes was fabricated. The contact holes (100 µm × 100 µm) in the encapsulation layer are only ~10% the size of the previous generation, allowing a larger number of microelectrodes per unit area, thus affording the capability to interface with a smaller neural population per electrode. This new SMEA is used to record spontaneous and evoked activity in organotypic hippocampal tissue slices at 0% strain before stretching, at 5 % and 10 % equibiaxial strain, and again at 0% strain after relaxation. The noise of the recordings increases with increasing strain. The frequency of spontaneous neural activity also increases when the SMEA is stretched. Upon relaxation, the noise returns to pre-stretch levels, while the frequency of neural activity remains elevated. Stimulus-response curves at each strain level are measured. The SMEA shows excellent biocompatibility for at least two weeks. PMID:24093006

Electron Raman scattering in a strained ZnO/MgZnO double quantum well

NASA Astrophysics Data System (ADS)

Mojab-abpardeh, M.; Karimi, M. J.

2018-02-01

In this work, the electron Raman scattering in a strained ZnO / MgZnO double quantum wells is studied. The energy eigenvalues and the wave functions are obtained using the transfer matrix method. The effects of Mg composition, well width and barrier width on the internal electric field in well and barrier layers are investigated. Then, the influences of these parameters on the differential cross-section of electron Raman scattering are studied. Results indicate that the position, magnitude and the number of the peaks depend on the Mg composition, well width and barrier width.

Simulation of hole-mobility in doped relaxed and strained Ge layers

NASA Astrophysics Data System (ADS)

Watling, Jeremy R.; Riddet, Craig; Chan, Morgan Kah H.; Asenov, Asen

2010-11-01

As silicon based metal-oxide-semiconductor field-effect transistors (MOSFETs) are reaching the limits of their performance with scaling, alternative channel materials are being considered to maintain performance in future complementary metal-oxide semiconductor technology generations. Thus there is renewed interest in employing Ge as a channel material in p-MOSFETs, due to the significant improvement in hole mobility as compared to Si. Here we employ full-band Monte Carlo to study hole transport properties in Ge. We present mobility and velocity-field characteristics for different transport directions in p-doped relaxed and strained Ge layers. The simulations are based on a method for over-coming the potentially large dynamic range of scattering rates, which results from the long-range nature of the unscreened Coulombic interaction. Our model for ionized impurity scattering includes the affects of dynamic Lindhard screening, coupled with phase-shift, and multi-ion corrections along with plasmon scattering. We show that all these effects play a role in determining the hole carrier transport in doped Ge layers and cannot be neglected.

Evaluation of implantation-disordering of (InGa)As/GaAs strained-layer superlattices

NASA Astrophysics Data System (ADS)

Myers, D. R.; Barnes, C. E.; Arnold, G. W.; Dawson, L. R.; Biefeld, R. M.; Zipperian, T. E.; Gourley, P. L.; Fritz, I. J.

The optical and transport properties of InO 2GaO 8As/GaAs strained-layer superlattices (SLS's) which were implanted either with 5 x 10 to the 15th power, 250 keV Zn(+) or with 5 x 10 to 14th power/square cm/cm(2), 70 keV Be(+) and annealed under an arsenic overpressure at 600 (0) C were examined. For both cases, electrical activation in the implantation-doped regions equalled that of similar implants and anneals in bulk GaAs, even though the Be implant retained the SLS structure, while the Zn implant intermixed the SLS layers to produce an alloy semiconductor of the average SLS composition. Photoluminescence intensities in the annealed implanted regions were significantly reduced from that of virgin material, apparently due to residual implant damage. Diodes formed from both the Be- and the Zn-implanted SLS' produced electroluminescence internsity comparable to that of grown-junction SLS diodes in the same chemical system, despite the implantation processing and the potential for vertical lattice mismatch in the Zn-disordered SLS device. These results indicate that Zn-disordering can be as useful for strained-layer superlattices as in lattice-matched systems.

Tunable inversion symmetry in heterostructures of layered oxides

NASA Astrophysics Data System (ADS)

Rondinelli, James

Traditional approaches to create and control functional electronic materials have focused on new phases in previously unknown bulk minerals. More recently, interlayer physics has spawned interest in known materials in unexplored atomic scale geometries, especially in complex transition metal oxides (TMO), where heterostructures can be created on demand. In this talk, I show that although epitaxial strain routinely induces (enhances) electric polarizations, biaxial strain can also induce an unanticipated polar-to-nonpolar (P-NP) structural transition in (001) thin films of naturally layered An + 1Bn O3n+1 (n = 1 - ∞) oxides. Density functional theory calculations and a complete phenomenological model for Ca3Ti2O7 are used to show that the origin of the P-NP transition originates from the interplay of trilinear-related lattice mode interactions active in the layered oxides, and those interactions are directly strain tunable. Moreover these layered oxides exhibit a quasi-two dimensional phonon mode-an acoustic branch with quadratic dispersion, enabling unusual membrane effects such as tunable negative thermal expansion. I conclude by emphasizing that broken inversion symmetric structures offer a plentiful playground for realizing new functionalities in thin films, including new multiferroics from polar metals.

A compressibility correction of the pressure strain correlation model in turbulent flow

NASA Astrophysics Data System (ADS)

Klifi, Hechmi; Lili, Taieb

2013-07-01

This paper is devoted to the second-order closure for compressible turbulent flows with special attention paid to modeling the pressure-strain correlation appearing in the Reynolds stress equation. This term appears as the main one responsible for the changes of the turbulence structures that arise from structural compressibility effects. From the analysis and DNS results of Simone et al. and Sarkar, the compressibility effects on the homogeneous turbulence shear flow are parameterized by the gradient Mach number. Several experiment and DNS results suggest that the convective Mach number is appropriate to study the compressibility effects on the mixing layers. The extension of the LRR model recently proposed by Marzougui, Khlifi and Lili for the pressure-strain correlation gives results that are in disagreement with the DNS results of Sarkar for high-speed shear flows. This extension is revised to derive a turbulence model for the pressure-strain correlation in which the compressibility is included in the turbulent Mach number, the gradient Mach number and then the convective Mach number. The behavior of the proposed model is compared to the compressible model of Adumitroiae et al. for the pressure-strain correlation in two turbulent compressible flows: homogeneous shear flow and mixing layers. In compressible homogeneous shear flows, the predicted results are compared with the DNS data of Simone et al. and those of Sarkar. For low compressibility, the two compressible models are similar, but they become substantially different at high compressibilities. The proposed model shows good agreement with all cases of DNS results. Those of Adumitroiae et al. do not reflect any effect of a change in the initial value of the gradient Mach number on the Reynolds stress anisotropy. The models are used to simulate compressible mixing layers. Comparison of our predictions with those of Adumitroiae et al. and with the experimental results of Goebel et al. shows good qualitative agreement.

Effect of spacer layer thickness on structural and optical properties of multi-stack InAs/GaAsSb quantum dots

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Yeongho; Ban, Keun-Yong, E-mail: kban1@asu.edu; Honsberg, Christiana B.

2015-10-26

The structural and optical properties of ten-stack InAs/GaAsSb quantum dots (QDs) with different spacer layer thicknesses (d{sub s} = 2, 5, 10, and 15 nm) are reported. X-ray diffraction analysis reveals that the strain relaxation of the GaAsSb spacers increases linearly from 0% to 67% with larger d{sub s} due to higher elastic stress between the spacer and GaAs matrix. In addition, the dislocation density in the spacers with d{sub s} = 10 nm is lowest as a result of reduced residual strain. The photoluminescence peak energy from the QDs does not change monotonically with increasing d{sub s} due to the competing effects of decreased compressivemore » strain and weak electronic coupling of stacked QD layers. The QD structure with d{sub s} = 10 nm is demonstrated to have improved luminescence properties and higher carrier thermal stability.« less

Anomalous Hall hysteresis in T m3F e5O12/Pt with strain-induced perpendicular magnetic anisotropy

NASA Astrophysics Data System (ADS)

Tang, Chi; Sellappan, Pathikumar; Liu, Yawen; Xu, Yadong; Garay, Javier E.; Shi, Jing

2016-10-01

We demonstrate robust interface strain-induced perpendicular magnetic anisotropy in atomically flat ferrimagnetic insulator T m3F e5O12 (TIG) films grown with pulsed laser deposition on a substituted G d3G a5O12 substrate which maximizes the tensile strain at the interface. In bilayers consisting of Pt and TIG, we observe large squared Hall hysteresis loops over a wide range of thicknesses of Pt at room temperature. When a thin Cu layer is inserted between Pt and TIG, the Hall hysteresis magnitude decays but stays finite as the thickness of Cu increases up to 5 nm. However, if the Cu layer is placed atop Pt instead, the Hall hysteresis magnitude is consistently larger than when the Cu layer with the same thickness is inserted in between for all Cu thicknesses. These results suggest that both the proximity-induced ferromagnetism and spin current contribute to the anomalous Hall effect.

Deterministic strain-induced arrays of quantum emitters in a two-dimensional semiconductor

PubMed Central

Branny, Artur; Kumar, Santosh; Proux, Raphaël; Gerardot, Brian D

2017-01-01

An outstanding challenge in quantum photonics is scalability, which requires positioning of single quantum emitters in a deterministic fashion. Site positioning progress has been made in established platforms including defects in diamond and self-assembled quantum dots, albeit often with compromised coherence and optical quality. The emergence of single quantum emitters in layered transition metal dichalcogenide semiconductors offers new opportunities to construct a scalable quantum architecture. Here, using nanoscale strain engineering, we deterministically achieve a two-dimensional lattice of quantum emitters in an atomically thin semiconductor. We create point-like strain perturbations in mono- and bi-layer WSe2 which locally modify the band-gap, leading to efficient funnelling of excitons towards isolated strain-tuned quantum emitters that exhibit high-purity single photon emission. We achieve near unity emitter creation probability and a mean positioning accuracy of 120±32 nm, which may be improved with further optimization of the nanopillar dimensions. PMID:28530219

Finite strain calculations of continental deformation. I - Method and general results for convergent zones. II - Comparison with the India-Asia collision zone

NASA Technical Reports Server (NTRS)

Houseman, G.; England, P.

1986-01-01

The present investigation has the objective to perform numerical experiments on a rheologically simple continuum model for the continental lithosphere. It is attempted to obtain a better understanding of the dynamics of continental deformation. Calculations are presented of crustal thickness distributions, stress, strain, strain rate fields, latitudinal displacements, and finite rotations, taking into account as basis a model for continental collision which treats the litoshphere as a thin viscous layer subject to indenting boundary conditions. The results of this paper support the conclusions of England and McKenzie (1982) regarding the role of gravity in governing the deformation of a thin viscous layer subject to indenting boundary conditions. The results of the experiments are compared with observations of topography, stress and strain rate fields, and palaeomagnetic latitudinal displacements in Asia.

Improved performance of GaN based light emitting diodes with ex-situ sputtered AlN nucleation layers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Shuo-Wei; Epistar Corporation, Hsinchu 300, Taiwan; Li, Heng

The crystal quality, electrical and optical properties of GaN based light emitting diodes (LEDs) with ex-situ sputtered physical vapor deposition (PVD) aluminum nitride (AlN) nucleation layers were investigated. It was found that the crystal quality in terms of defect density and x-ray diffraction linewidth was greatly improved in comparison to LEDs with in-situ low temperature GaN nucleation layer. The light output power was 3.7% increased and the reverse bias voltage of leakage current was twice on LEDs with ex-situ PVD AlN nucleation layers. However, larger compressive strain was discovered in LEDs with ex-situ PVD AlN nucleation layers. The study showsmore » the potential and constrain in applying ex-situ PVD AlN nucleation layers to fabricate high quality GaN crystals in various optoelectronics.« less

Emplacement history of a thrust sheet based on analysis of pressure solution cleavage and deformed fossils

DOE Office of Scientific and Technical Information (OSTI.GOV)

Protzman, G.M.; Mitra, G.

The emplacement history of a thrust sheet is recorded by the strain accumulated in its hanging wall and footwall. Detailed studies of second order structures and analysis of strain due to pressure solution and plastic deformation allow the authors to determine the deformation history of the Meade thrust in the Idaho - Wyoming thrust belt. Emplacement of the Meade thrust was accompanied by the formation of a series of second order in echelon folds in the footwall. Temporal relations based on detailed structural studies show that these folds, which are confined to the Jurassic Twin Creek Formation, formed progressively inmore » front of the advancing Meade thrust and were successively truncated and overridden by footwall imbricates of the Meade thrust. The Twin Creek Formation in both the hanging wall and footwall of the Meade thrust is penetratively deformed, with a well developed pressure solution cleavage. In addition, plastic strain is recorded by deformed Pentacrinus within fossil hash layers in the Twin Creek. Much of this penetrative deformation took place early in the history of the thrust sheet as layer parallel shortening, and the cleavage and deformed fossils behaved passively during subsequent folding and faulting. The later stages of deformation may be sequentially removed through balancing techniques to track successive steps in the deformation. This strain history, which is typical of an internal thrust sheet, is partly controlled by the lithologies involved, timing between successive thrusts, and the amount of interaction between major faults.« less

Effects of a GaSb buffer layer on an InGaAs overlayer grown on Ge(111) substrates: Strain, twin generation, and surface roughness

NASA Astrophysics Data System (ADS)

Kajikawa, Y.; Nishigaichi, M.; Tenma, S.; Kato, K.; Katsube, S.

2018-04-01

InGaAs layers were grown by molecular-beam epitaxy on nominal and vicinal Ge(111) substrates with inserting GaSb buffer layers. High-resolution X-ray diffraction using symmetric 333 and asymmetric 224 reflections was employed to analyze the crystallographic properties of the grown layers. By using the two reflections, we determined the lattice constants (the unit cell length a and the angle α between axes) of the grown layers with taking into account the rhombohedral distortion of the lattices of the grown layers. This allowed us the independent determination of the strain components (perpendicular and parallel components to the substrate surface, ε⊥ and ε//) and the composition x of the InxGa1-xAs layers by assuming the distortion coefficient D, which is defined as the ratio of ε⊥ against ε//. Furthermore, the twin ratios were determined for the GaSb and the InGaAs layers by comparing asymmetric 224 reflections from the twin domain with that from the normal domain of the layers. As a result, it has been shown that the twin ratio in the InGaAs layer can be decreased to be less than 0.1% by the use of the vicinal substrate together with annealing the GaSb buffer layer during the growth interruption before the InGaAs overgrowth.

Multi-scale finite element analyses for stress and strain evaluations of braid fibril artificial blood vessel and smooth muscle cell.

PubMed

Nakamachi, Eiji; Uchida, Takahiro; Kuramae, Hiroyuki; Morita, Yusuke

2014-08-01

In this study, we developed a multi-scale finite element (FE) analysis code to obtain the stress and strain that occurred in the smooth muscle cell (SMC) at micro-scale, which was seeded in the real fabricated braid fibril artificial blood vessel. This FE code can predict the dynamic response of stress under the blood pressure loading. We try to establish a computer-aided engineering (CAE)-driven scaffold design technique for the blood vessel regeneration. Until now, there occurred the great progresses for the endothelial cell activation and intima layer regeneration in the blood vessel regeneration study. However, there remains the difficulty of the SMC activation and media layer regeneration. Therefore, many researchers are now studying to elucidate the fundamental mechanism of SMC activation and media layer regeneration by using the biomechanical technique. As the numerical tool, we used the dynamic-explicit FE code PAM-CRASH, ESI Ltd. For the material models, the nonlinear viscoelastic constitutive law was adapted for the human blood vessel, SMC and the extra-cellular matrix, and the elastic law for the polyglycolic acid (PGA) fiber. Through macro-FE and micro-FE analyses of fabricated braid fibril tubes by using PGA fiber under the combined conditions of the orientation angle and the pitch of fiber, we searched an appropriate structure for the stress stimulation for SMC functionalization. Objectives of this study are indicated as follows: 1. to analyze the stress and strain of the human blood vessel and SMC, and 2. to calculate stress and strain of the real fabricated braid fibril artificial blood vessel and SMC to search an appropriate PGA fiber structure under combined conditions of PGA fiber numbers, 12 and 24, and the helical orientation angles of fiber, 15, 30, 45, 60, and 75 degrees. Finally, we found a braid fibril tube, which has an angle of 15 degree and 12 PGA fibers, as a most appropriate artificial blood vessel for SMC functionalization. Copyright © 2014 John Wiley & Sons, Ltd.

Strain relaxation in single crystal SrTiO3 grown on Si (001) by molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Choi, Miri; Posadas, Agham; Dargis, Rytis; Shih, Chih-Kang; Demkov, Alexander A.; Triyoso, Dina H.; David Theodore, N.; Dubourdieu, Catherine; Bruley, John; Jordan-Sweet, Jean

2012-03-01

An epitaxial layer of SrTiO3 grown directly on Si may be used as a pseudo-substrate for the integration of perovskite oxides onto silicon. When SrTiO3 is initially grown on Si (001), it is nominally compressively strained. However, by subsequent annealing in oxygen at elevated temperature, an SiOx interlayer can be formed which alters the strain state of SrTiO3. We report a study of strain relaxation in SrTiO3 films grown on Si by molecular beam epitaxy as a function of annealing time and oxygen partial pressure. Using a combination of x-ray diffraction, reflection high energy electron diffraction, and transmission electron microscopy, we describe the process of interfacial oxidation and strain relaxation of SrTiO3 on Si (001). Understanding the process of strain relaxation of SrTiO3 on silicon will be useful for controlling the SrTiO3 lattice constant for lattice matching with functional oxide overlayers.

A study of graphite-epoxy laminate failures due to high transverse shear strains using the multi-span-beam shear test procedure

NASA Technical Reports Server (NTRS)

Jegley, Dawn C.

1989-01-01

The multi-span-beam shear test procedure is used to study failure mechanisms in graphite-epoxy laminates due to high transverse shear strains induced by severe local bending deformations in test specimens. Results of a series of tests on specimens with a variety of stacking sequences, including some with adhesive interleaving, are presented. These results indicate that laminates with stacking sequences with several + or - 45 and 90 deg plies next to each other are more susceptible to failures due to high transverse shear strains than laminates with + or - 45 and 0 deg plies next to each other or with + or - 45 deg plies next to layers of adhesive interleaving. Results of these tests are compared with analytical results based on finite elements.

3D modeling of unconstrained HPT process: role of strain gradient on high deformed microstructure formation

NASA Astrophysics Data System (ADS)

Ben Kaabar, A.; Aoufi, A.; Descartes, S.; Desrayaud, C.

2017-05-01

During tribological contact’s life, different deformation paths lead to the formation of high deformed microstructure, in the near-surface layers of the bodies. The mechanical conditions (high pressure, shear) occurring under contact, are reproduced through unconstrained High Pressure Torsion configuration. A 3D finite element model of this HPT test is developed to study the local deformation history leading to high deformed microstructure with nominal pressure and friction coefficient. For the present numerical study the friction coefficient at the interface sample/anvils is kept constant at 0.3; the material used is high purity iron. The strain distribution in the sample bulk, as well as the main components of the strain gradients according to the spatial coordinates are investigated, with rotation angle of the anvil.

Morphology evolution in strain-compensated multiple quantum well structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ledentsov, N. N., E-mail: nikolay.ledentsov@v-i-systems.com; Shchukin, V. A.; Rouvimov, S.

2014-01-20

Morphology evolution in (In,Ga)As-Ga(As,P) strain-compensated multilayer structures is studied. The effects of nanoscale interface corrugation and phase separation are evident after the third period of the multilayer structure and become more pronounced with each new stack until the sixth period. Then, the interface stabilizes pointing to the formation of strain-balanced equilibrium interface structure. The epitaxial structure remains defect-free up to the maximum number (twenty) of periods studied. In a structure with a high lattice mismatch between the neighboring layers, In{sub 0.40}Ga{sub 0.60}As/GaAs{sub 0.85}P{sub 0.15}, clusters of dislocations are revealed already in the third period. The observed phenomena are critical formore » proper engineering of optoelectronic devices.« less

Nondestructive measurement of esophageal biaxial mechanical properties utilizing sonometry

NASA Astrophysics Data System (ADS)

Aho, Johnathon M.; Qiang, Bo; Wigle, Dennis A.; Tschumperlin, Daniel J.; Urban, Matthew W.

2016-07-01

Malignant esophageal pathology typically requires resection of the esophagus and reconstruction to restore foregut continuity. Reconstruction options are limited and morbid. The esophagus represents a useful target for tissue engineering strategies based on relative simplicity in comparison to other organs. The ideal tissue engineered conduit would have sufficient and ideally matched mechanical tolerances to native esophageal tissue. Current methods for mechanical testing of esophageal tissues both in vivo and ex vivo are typically destructive, alter tissue conformation, ignore anisotropy, or are not able to be performed in fluid media. The aim of this study was to investigate biomechanical properties of swine esophageal tissues through nondestructive testing utilizing sonometry ex vivo. This method allows for biomechanical determination of tissue properties, particularly longitudinal and circumferential moduli and strain energy functions. The relative contribution of mucosal-submucosal layers and muscular layers are compared to composite esophagi. Swine thoracic esophageal tissues (n  =  15) were tested by pressure loading using a continuous pressure pump system to generate stress. Preconditioning of tissue was performed by pressure loading with the pump system and pre-straining the tissue to in vivo length before data was recorded. Sonometry using piezocrystals was utilized to determine longitudinal and circumferential strain on five composite esophagi. Similarly, five mucosa-submucosal and five muscular layers from thoracic esophagi were tested independently. This work on esophageal tissues is consistent with reported uniaxial and biaxial mechanical testing and reported results using strain energy theory and also provides high resolution displacements, preserves native architectural structure and allows assessment of biomechanical properties in fluid media. This method may be of use to characterize mechanical properties of tissue engineered esophageal constructs.

Defect reduction in Si-doped Al{sub 0.45}Ga{sub 0.55}N films by SiN{sub x} interlayer method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Yang; Chen, Shengchang; Kong, Man

2014-01-28

The dislocation density in AlGaN epitaxial layers with Al content as high as 45% grown on sapphire substrates has been effectively reduced by introducing an in-situ deposited SiN{sub x} nanomask layer in this study. By closely monitoring the evolution of numerous material properties, such as surface morphology, dislocation density, photoluminescence, strain states, and electron mobility of the Si-Al{sub 0.45}Ga{sub 0.55}N layers as the functions of SiN{sub x} interlayer growth time, the surface coverage fraction of SiN{sub x} is found to be a crucial factor determining the strain states and dislocation density. The dependence of the strain states and the dislocationmore » density on the surface coverage fraction of SiN{sub x} nanomask supports the very different growth models of Al-rich AlGaN on SiN{sub x} interlayer due to the reduced nucleation selectivity compared with the GaN counterpart. Compared with GaN, which can only nucleate at open pores of SiN{sub x} nanomask, Al-rich AlGaN can simultaneously nucleate at both open pores and SiN{sub x} covered areas. Dislocations will annihilate at the openings due to the 3D growth initiated on the opening area, while 2D growth mode is preserved on SiN{sub x} and the threading dislocations are also preserved. During the following growth process, lateral overgrowth will proceed from the Al{sub 0.45}Ga{sub 0.55}N islands on the openings towards the regions covered by SiN{sub x}, relaxing the compressive strain and bending the dislocations at the same time.« less

Carbon nanotube-embedded advanced aerospace composites for early-stage damage sensing

NASA Astrophysics Data System (ADS)

Nataraj, Latha; Coatney, Michael; Cain, Jason; Hall, Asha

2018-03-01

Fiber reinforced polymer (FRP) composites featuring outstanding fatigue performance, high specific stiffness and strength, and low density have evolved as critical structural materials in aerospace applications. Microscale damage such as fiber breakage, matrix cracking, and delamination could occur in layered composites compromising structural integrity, emphasizing the critical need to monitor structural health. Early damage detection would lead to enhanced reliability, lifetime, and performance while minimizing maintenance time, leading to enormous scientific and technical interest in realizing physically stable, quick responding, and cost effective strain sensing materials, devices, and techniques with high sensitivity over a broad range of the practical strain spectrum. Today's most commonly used strain sensing techniques are metal foil strain gauges and optical fiber sensors. Metal foil gauges offer high stability and cost-effectiveness but can only be surface-mounted and have a low gauge factor. Optical fibers require expensive instrumentation, are mostly insensitive to cracks parallel to the fiber orientation and may lead to crack initiation as the diameter is larger than that of the reinforcement fibers. Carbon nanotubes (CNTs) have attracted much attention due to high aspect ratio and superior electrical, thermal, and mechanical properties. CNTs embedded in layered composites have improved performance. A variety of CNT architectures and configurations have shown improved piezoresistive behavior and stability for sensing applications. However, scaling up and commercialization remain serious challenges. The current study investigates a simple, cost effective and repeatable technique for highly sensitive, stable, linear and repeatable strain sensing for damage detection by integrating CNT laminates into composites.

Interstrain differences of ionotropic glutamate receptor subunits in the hippocampus and induction of hippocampal sclerosis with pilocarpine in mice.

PubMed

Dobó, Endre; Török, Ibolya; Mihály, András; Károly, Norbert; Krisztin-Péva, Beáta

2015-01-01

Rodent strains used in epilepsy research have various neurological characteristics. These differences were suggested to be attributed to the diverse densities of the ionotropic glutamate receptor (iGluR) subunits. However, previous studies failed to find interstrain differences in the hippocampal receptor levels. We supposed that a detailed layer-to-layer analysis of the iGluR subunits in the hippocampus might reveal strain-dependent differences in their base lines and reactions induced by pilocarpine (PILO) between two mouse strains without documented ancestors. Levels of iGluR subunits in Balb/c and NMRI mice were compared using semiquantitative immunohistochemistry. The alterations in the neuronal circuitry were validated by neuropeptide Y (NPY) and neuronal nuclear antigen (NeuN) immunostainings. Immunohistochemistry showed interstrain laminar differences in some subunits of both the control and PILO-treated animals. The seizure-induced irreversible neuronal changes were accompanied by reduced GluA1 and GluA2 levels. Their changes were inversely correlated in the individual NMRI mice by Pearson's method. Increase in NPY immunoreactivity showed positive correlation with GluA1, and negative correlation with GluA2. The NMRI strain was susceptible to PILO-induced hippocampal sclerosis, while the Balb/c animals showed resistance. Basal levels of iGluRs differ in mouse strains, which may account for the interstrain differences in their reactions to the convulsant. Copyright © 2015 Elsevier B.V. All rights reserved.

Impact of textural anisotropy on syn-kinematic partial melting of natural gneisses: an experimental approach.

NASA Astrophysics Data System (ADS)

Ganzhorn, Anne-Céline; Trap, Pierre; Arbaret, Laurent; Champallier, Rémi; Fauconnier, Julien; Labrousse, Loic; Prouteau, Gaëlle

2015-04-01

Partial melting of continental crust is a strong weakening process controlling its rheological behavior and ductile flow of orogens. This strength weakening due to partial melting is commonly constrained experimentally on synthetic starting material with derived rheological law. Such analog starting materials are preferentially used because of their well-constrained composition to test the impact of melt fraction, melt viscosity and melt distribution upon rheology. In nature, incipient melting appears in particular locations where mineral and water contents are favorable, leading to stromatic migmatites with foliation-parallel leucosomes. In addition, leucosomes are commonly located in dilatants structural sites like boudin-necks, in pressure shadows, or in fractures within more competent layers of migmatites. The compositional layering is an important parameter controlling melt flow and rheological behavior of migmatite but has not been tackled experimentally for natural starting material. In this contribution we performed in-situ deformation experiments on natural rock samples in order to test the effect of initial gneissic layering on melt distribution, melt flow and rheological response. In-situ deformation experiments using a Paterson apparatus were performed on two partially melted natural gneissic rocks, named NOP1 & PX28. NOP1, sampled in the Western Gneiss Region (Norway), is biotite-muscovite bearing gneiss with a week foliation and no gneissic layering. PX28, sampled from the Sioule Valley series (French Massif Central), is a paragneiss with a very well pronounced layering with quartz-feldspar-rich and biotite-muscovite-rich layers. Experiments were conducted under pure shear condition at axial strain rate varying from 5*10-6 to 10-3 s-1. The main stress component was maintained perpendicular to the main plane of anisotropy. Confining pressure was 3 kbar and temperature ranges were 750°C and 850-900°C for NOP1 and PX28, respectively. For the 750°C experiments NOP1 was previously hydrated at room pressure and temperature. According to melt fraction, deformation of partially molten gneiss induced different strain patterns. For low melt fraction, at 750°C, deformation within the initially isotropic gneiss NOP1 is localized along large scales shear-zones oriented at about 60° from main stress component σ1. In these zones quartz grains are broken and micas are sheared. Melt is present as thin film (≥20 µm) at muscovite-quartz grain boundaries and intrudes quartz aggregates as injections parallel to σ1. For higher melt fraction, at 850°C, deformation is homogeneously distributed. In the layered gneiss PX28, deformation is partitioned between mica-rich and quartz-rich layers. For low melt fraction, at 850°C, numerous conjugate shear-bands crosscut mica-rich layers. Melt is present around muscovite grains and intrudes quartz grains in the favor of fractures. For high melt fractions, at 900°C, melt assisted creep within mica-rich layers is responsible for boudinage of the quartz-feldspar rich layers. Melt-induced veining assists the transport of melt toward inter-boudin zones. Finite strain pattern and melt distribution after deformation of PX28 attest for appearance of strong pressure gradients leading to efficient melt flow. The subsequent melt redistribution strongly enhance strain partitioning and strength weakening, as shown by differential stress vs. strain graphs. Our experiments have successfully reproduced microstructures commonly observed in migmatitic gneisses like boudinage of less fertile layers. Comparison between non-layered and layered gneisses attest for strong influence of compositional anisotropies inherited from the protolith upon melt distribution and migmatite strength.

Effects of printing-induced interfaces on localized strain within 3D printed hydrogel structures.

PubMed

Christensen, Kyle; Davis, Brian; Jin, Yifei; Huang, Yong

2018-08-01

Additive manufacturing, or 3D printing, is a promising approach for the fabrication of biological structures for regenerative medicine applications using tissue-like materials such as hydrogels. Herein, inkjet printing is implemented as a model droplet-based 3D printing technology for which interfaces have been shown to form between printed lines within printed layers of hydrogel structures. Experimental samples with interfaces in two orientations are fabricated by inkjet printing and control samples with and without interfaces are fabricated by extrusion printing and casting, respectively. The formation of partial and full interfaces is modeled in terms of printing conditions and gelation parameters, and an approach to predicting the ratio of interfacial area to the total contact area between two adjacent lines is presented. Digital image correlation is used to determine strain distributions and identify regions of increased localized deformation for samples under uniaxial tension. Despite the presence of interfaces in inkjet-printed samples, strain distributions are found to be homogeneous regardless of interface orientation, which may be attributed to the multi-layer nature of samples. Conversely, single-layer extrusion-printed samples exhibit localized regions of increased deformation between printed lines, indicating delamination along interfaces. The effective stiffness, failure strength, and failure strain of inkjet-printed samples are found to be dependent on the orientation of interfaces within layers. Specifically, inkjet-printed samples in which tensile forces pull apart interfaces exhibit significantly decreased mechanical properties compared to cast samples. Copyright © 2018 Elsevier B.V. All rights reserved.

Stress generated modifications of epitaxial ferroelectric SrTiO3 films on sapphire

NASA Astrophysics Data System (ADS)

Hollmann, E.; Schubert, J.; Kutzner, R.; Wördenweber, R.

2009-06-01

The effect of lattice-mismatch induced stress upon the crystallographic structure, strain, strain relaxation, and the generation of different types of defects in heteroepitaxially grown SrTiO3 films on CeO2 buffered sapphire is examined. Depending on the thickness of the SrTiO3 layer, characteristic changes in the structural perfection of the layers, their crystallographic orientation with respect to the substrate system, and their strain is observed. For thin films misfit dislocations partially compensate the stress in the SrTiO3 layer, whereas cracks develop in thicker SrTiO3 films. The cracks are orientated along two predominant crystallographic orientations of the sapphire. The structural modifications and the formation of misfit defects and cracks are explained in a model based on lattice misfit induced stress, on the one hand, and energy considerations taking into account the stress release due to crack formation and the energy necessary for the formation of new surfaces at the crack, on the other hand. The impact of lattice misfit is discussed in two steps, i.e., intrinsic and thermal induced misfits during heteroepitaxial film growth at a given temperature and the subsequent cooling of the sample, respectively. The comparison of the theoretical predictions and the experimental observations demonstrate that intrinsic mismatch and thermal mismatch have to be considered in order to explain strain dependent effects in complex heteroepitaxial layer systems such as induced ferroelectricity of SrTiO3 on sapphire.

Optical properties of wide gap semiconductors studied by means of cathodoluminescence

NASA Astrophysics Data System (ADS)

Fischer Ponce, Alec Mirco

III-nitride semiconductors have been found to be a suitable material for the fabrication of light-emitting diodes (LEDs) emitting in the visible and ultraviolet range through the use of indium gallium nitride (InGaN) active layers. Yet, achieving high-efficient and long lasting LEDs in the long wavelength range, especially in the green spectral region, is limited by difficulties of growth of InGaN layers with high indium content. Additionally, device efficiency is strongly dependent on the formation of low-resistive p-type gallium nitride (GaN)-based layers. In this dissertation, the optical properties of wide gap semiconductor are analyzed using cathodoluminescence imaging and spectroscopy, and time-resolved spectroscopic techniques. A transition at 3.2 eV in magnesium (Mg)-doped GaN has been revealed and it has been identified as a Mg-related donor-acceptor pair, which may be responsible for the increase in intensity with increasing magnesium concentration in the commonly observed donor-acceptor pair region. In a separate study, a decrease of the Mg acceptor energy level and the bulk resistivity in Mg-doped InGaN with increasing indium composition is observed, implying that InGaN p-layers should improve the device performance. Next, Mg-doped GaN and InGaN capping layers in LED structures grown under different ambient gases are shown to alter the quantum well (QW) luminescence. QWs grown with InGaN p-layers exhibit an improvement in the luminescence efficiency and a blue-shift due to reduction of the compressive misfit strain in the QWs. However, p-GaN layers grown under hydrogen ambient gas present a blue-shift of the QW emission. Hydrogen diffusion occurring after thermal annealing of the p-GaN layer may explain the reduction of piezoelectric field effects in polar InGaN quantum wells. In another study, InGaN QWs with high indium content grown in non-polar m-plane GaN were found to exhibit stacking faults originating at the first QW, relaxing the misfit strain in the subsequent layers. Finally, the optical and structural properties of highly luminescent zinc oxide (ZnO) tetrapod powders emitting in the visible green spectral range were studied with high spatial resolution. ZnO nanostructures are strong candidates for devices emitting light with very high efficiencies.

Bulk Nonlinear Elastic Strain Waves in a Bilayer Coaxial Cylindrical Rod

NASA Astrophysics Data System (ADS)

Gula, I. A.; Samsonov, A. M.

2017-12-01

The problem of the propagation of long nonlinear elastic strain waves in a bilayer coaxial cylindrical rod with an ideal contact between the layers has been considered. Expressions for transverse displacements through longitudinal displacements have been derived. The former satisfies free boundary conditions and continuity conditions for displacements and stresses at the interlayer interface with the desired accuracy. It has been shown how these expressions generalize the well-known plane-section and Love hypotheses for an isotropic homogeneous rod. An equation for the propagation of a nonlinearly elastic strain longitudinal wave has been derived, and its particular solution in the form of a solitary traveling wave has been studied.

Comparison of different bonding techniques for efficient strain transfer using piezoelectric actuators

NASA Astrophysics Data System (ADS)

Ziss, Dorian; Martín-Sánchez, Javier; Lettner, Thomas; Halilovic, Alma; Trevisi, Giovanna; Trotta, Rinaldo; Rastelli, Armando; Stangl, Julian

2017-04-01

In this paper, strain transfer efficiencies from a single crystalline piezoelectric lead magnesium niobate-lead titanate substrate to a GaAs semiconductor membrane bonded on top are investigated using state-of-the-art x-ray diffraction (XRD) techniques and finite-element-method (FEM) simulations. Two different bonding techniques are studied, namely, gold-thermo-compression and polymer-based SU8 bonding. Our results show a much higher strain-transfer for the "soft" SU8 bonding in comparison to the "hard" bonding via gold-thermo-compression. A comparison between the XRD results and FEM simulations allows us to explain this unexpected result with the presence of complex interface structures between the different layers.

Comparison of different bonding techniques for efficient strain transfer using piezoelectric actuators

PubMed Central

Ziss, Dorian; Martín-Sánchez, Javier; Lettner, Thomas; Halilovic, Alma; Trevisi, Giovanna; Trotta, Rinaldo; Rastelli, Armando; Stangl, Julian

2017-01-01

In this paper, strain transfer efficiencies from a single crystalline piezoelectric lead magnesium niobate-lead titanate substrate to a GaAs semiconductor membrane bonded on top are investigated using state-of-the-art x-ray diffraction (XRD) techniques and finite-element-method (FEM) simulations. Two different bonding techniques are studied, namely, gold-thermo-compression and polymer-based SU8 bonding. Our results show a much higher strain-transfer for the “soft” SU8 bonding in comparison to the “hard” bonding via gold-thermo-compression. A comparison between the XRD results and FEM simulations allows us to explain this unexpected result with the presence of complex interface structures between the different layers. PMID:28522879

Comparison of different bonding techniques for efficient strain transfer using piezoelectric actuators.

PubMed

Ziss, Dorian; Martín-Sánchez, Javier; Lettner, Thomas; Halilovic, Alma; Trevisi, Giovanna; Trotta, Rinaldo; Rastelli, Armando; Stangl, Julian

2017-04-01

In this paper, strain transfer efficiencies from a single crystalline piezoelectric lead magnesium niobate-lead titanate substrate to a GaAs semiconductor membrane bonded on top are investigated using state-of-the-art x-ray diffraction (XRD) techniques and finite-element-method (FEM) simulations. Two different bonding techniques are studied, namely, gold-thermo-compression and polymer-based SU8 bonding. Our results show a much higher strain-transfer for the "soft" SU8 bonding in comparison to the "hard" bonding via gold-thermo-compression. A comparison between the XRD results and FEM simulations allows us to explain this unexpected result with the presence of complex interface structures between the different layers.

Acoustically induced slip in sheared granular layers: Application to dynamic earthquake triggering: TRIGGERED SLIP IN SHEARED GRANULAR GOUGE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ferdowsi, Behrooz; Griffa, Michele; Guyer, Robert A.

A fundamental mystery in earthquake physics is “how can an earthquake be triggered by distant seismic sources?” We use discrete element method simulations of a granular layer, during stick slip, that is subject to transient vibrational excitation to gain further insight into the physics of dynamic earthquake triggering. We also observe delayed triggering of slip in the granular gouge, using Coulomb friction law for grains interaction. We find that at a critical vibrational amplitude (strain) there is an abrupt transition from negligible time-advanced slip (clock advance) to full clock advance; i.e., transient vibration and triggered slip are simultaneous. Moreover, themore » critical strain is of order 10 -6, similar to observations in the laboratory and in Earth. The transition is related to frictional weakening of the granular layer due to a dramatic decrease in coordination number and the weakening of the contact force network. Associated with this frictional weakening is a pronounced decrease in the elastic modulus of the layer. The study has important implications for mechanisms of triggered earthquakes and induced seismic events and points out the underlying processes in response of the fault gouge to dynamic transient stresses.« less

Acoustically induced slip in sheared granular layers: Application to dynamic earthquake triggering: TRIGGERED SLIP IN SHEARED GRANULAR GOUGE

DOE PAGES

Ferdowsi, Behrooz; Griffa, Michele; Guyer, Robert A.; ...

2015-11-19

A fundamental mystery in earthquake physics is “how can an earthquake be triggered by distant seismic sources?” We use discrete element method simulations of a granular layer, during stick slip, that is subject to transient vibrational excitation to gain further insight into the physics of dynamic earthquake triggering. We also observe delayed triggering of slip in the granular gouge, using Coulomb friction law for grains interaction. We find that at a critical vibrational amplitude (strain) there is an abrupt transition from negligible time-advanced slip (clock advance) to full clock advance; i.e., transient vibration and triggered slip are simultaneous. Moreover, themore » critical strain is of order 10 -6, similar to observations in the laboratory and in Earth. The transition is related to frictional weakening of the granular layer due to a dramatic decrease in coordination number and the weakening of the contact force network. Associated with this frictional weakening is a pronounced decrease in the elastic modulus of the layer. The study has important implications for mechanisms of triggered earthquakes and induced seismic events and points out the underlying processes in response of the fault gouge to dynamic transient stresses.« less

Increased Curie Temperature Induced by Orbital Ordering in La0.67Sr0.33MnO3/BaTiO3 Superlattices.

PubMed

Zhang, Fei; Wu, Biao; Zhou, Guowei; Quan, Zhi-Yong; Xu, Xiao-Hong

2018-01-17

Recent theoretical studies indicated that the Curie temperature of perovskite manganite thin films can be increased by more than an order of magnitude by applying appropriate interfacial strain to control orbital ordering. In this work, we demonstrate that the regular intercalation of BaTiO 3 layers between La 0.67 Sr 0.33 MnO 3 layers effectively enhances ferromagnetic order and increases the Curie temperature of La 0.67 Sr 0.33 MnO 3 /BaTiO 3 superlattices. The preferential orbital occupancy of e g (x 2 -y 2 ) in La 0.67 Sr 0.33 MnO 3 layers induced by the tensile strain of BaTiO 3 layers is identified by X-ray linear dichroism measurements. Our results reveal that controlling orbital ordering can effectively improve the Curie temperature of La 0.67 Sr 0.33 MnO 3 films and that in-plane orbital occupancy is beneficial to the double exchange ferromagnetic coupling of thin-film samples. These findings create new opportunities for the design and control of magnetism in artificial structures and pave the way to a variety of novel magnetoelectronic applications that operate far above room temperature.

Quantitative Differentiation of LV Myocardium with and without Layer-Specific Fibrosis Using MRI in Hypertrophic Cardiomyopathy and Layer-Specific Strain TTE Analysis.

PubMed

Funabashi, Nobusada; Takaoka, Hiroyuki; Ozawa, Koya; Kamata, Tomoko; Uehara, Masae; Komuro, Issei; Kobayashi, Yoshio

2018-05-30

To achieve further risk stratification in hypertrophic cardiomyopathy (HCM) patients, we localized and quantified layer-specific LVM fibrosis on MRI in HCM patients using regional layer-specific peak longitudinal strain (PLS) and peak circumferential strain (PCS) in LV myocardium (LVM) on speckle tracking transthoracic echocardiography (TTE). A total of 18 HCM patients (14 males; 58 ± 17 years) underwent 1.5T-MRI and TTE. PLS and PCS in each layer of the LVM (endocardium, epicardium, and whole-layer myocardium) were calculated for 17 AHA-defined lesions. MRI assessment showed that fibrosis was classified as endocardial, epicardial, or whole-layer (= either or both of these). Regional PLS was smaller in fibrotic endocardial lesions than in non-fibrotic endocardial lesions (P = 0.004). To detect LV endocardial lesions with fibrosis, ROC curves of regional PLS revealed an area under the curve (AUC) of 0.609 and a best cut-off point of 13.5%, with sensitivity of 65.3% and specificity of 54.3%. Regional PLS was also smaller in fibrotic epicardial lesions than in non-fibrotic epicardial lesions (P < 0.001). To detect LV epicardial lesions with fibrosis, ROC curves of PLS revealed an AUC of 0.684 and a best cut-off point of 9.5%, with sensitivity of 73.5% and specificity of 55.5%. Using whole-layer myocardium analysis, PLS was smaller in fibrotic lesions than in non-fibrotic lesions (P < 0.001). To detect whole-layer LV lesions with fibrosis, ROC curves of regional PLS revealed an AUC of 0.674 and a best cut-off point of 12.5%, with sensitivity of 79.0% and specificity of 50.7%. There were no significant differences in PCS of LV myocardium (endocardium, epicardium, and whole-layer) between fibrotic and non-fibrotic lesions. Quantitative regional PLS but not PCS in LV endocardium, epicardium, and whole-layer myocardium provides useful non-invasive information for layer-specific localization of fibrosis in HCM patients.

Lactobacillus kefiri shows inter-strain variations in the amino acid sequence of the S-layer proteins.

PubMed

Malamud, Mariano; Carasi, Paula; Bronsoms, Sílvia; Trejo, Sebastián A; Serradell, María de Los Angeles

2017-04-01

The S-layer is a proteinaceous envelope constituted by subunits that self-assemble to form a two-dimensional lattice that covers the surface of different species of Bacteria and Archaea, and it could be involved in cell recognition of microbes among other several distinct functions. In this work, both proteomic and genomic approaches were used to gain knowledge about the sequences of the S-layer protein (SLPs) encoding genes expressed by six aggregative and sixteen non-aggregative strains of potentially probiotic Lactobacillus kefiri. Peptide mass fingerprint (PMF) analysis confirmed the identity of SLPs extracted from L. kefiri, and based on the homology with phylogenetically related species, primers located outside and inside the SLP-genes were employed to amplify genomic DNA. The O-glycosylation site SASSAS was found in all L. kefiri SLPs. Ten strains were selected for sequencing of the complete genes. The total length of the mature proteins varies from 492 to 576 amino acids, and all SLPs have a calculated pI between 9.37 and 9.60. The N-terminal region is relatively conserved and shows a high percentage of positively charged amino acids. Major differences among strains are found in the C-terminal region. Different groups could be distinguished regarding the mature SLPs and the similarities observed in the PMF spectra. Interestingly, SLPs of the aggregative strains are 100% homologous, although these strains were isolated from different kefir grains. This knowledge provides relevant data for better understanding of the mechanisms involved in SLPs functionality and could contribute to the development of products of biotechnological interest from potentially probiotic bacteria.

Dependence of lattice strain relaxation, absorbance, and sheet resistance on thickness in textured ZnO@B transparent conductive oxide for thin-film solar cell applications.

PubMed

Kou, Kuang-Yang; Huang, Yu-En; Chen, Chien-Hsun; Feng, Shih-Wei

2016-01-01

The interplay of surface texture, strain relaxation, absorbance, grain size, and sheet resistance in textured, boron-doped ZnO (ZnO@B), transparent conductive oxide (TCO) materials of different thicknesses used for thin film, solar cell applications is investigated. The residual strain induced by the lattice mismatch and the difference in the thermal expansion coefficient for thicker ZnO@B is relaxed, leading to an increased surface texture, stronger absorbance, larger grain size, and lower sheet resistance. These experimental results reveal the optical and material characteristics of the TCO layer, which could be useful for enhancing the performance of solar cells through an optimized TCO layer.

Distributed parameter modeling to prevent charge cancellation for discrete thickness piezoelectric energy harvester

NASA Astrophysics Data System (ADS)

Krishnasamy, M.; Qian, Feng; Zuo, Lei; Lenka, T. R.

2018-03-01

The charge cancellation due to the change of strain along single continuous piezoelectric layer can remarkably affect the performance of a cantilever based harvester. In this paper, analytical models using distributed parameters are developed with some extent of averting the charge cancellation in cantilever piezoelectric transducer where the piezoelectric layers are segmented at strain nodes of concerned vibration mode. The electrode of piezoelectric segments are parallelly connected with a single external resistive load in the 1st model (Model 1). While each bimorph piezoelectric layers are connected in parallel to a resistor to form an independent circuit in the 2nd model (Model 2). The analytical expressions of the closed-form electromechanical coupling responses in frequency domain under harmonic base excitation are derived based on the Euler-Bernoulli beam assumption for both models. The developed analytical models are validated by COMSOL and experimental results. The results demonstrate that the energy harvesting performance of the developed segmented piezoelectric layer models is better than the traditional model of continuous piezoelectric layer.

Extractable Bacterial Surface Proteins in Probiotic–Host Interaction

PubMed Central

do Carmo, Fillipe L. R.; Rabah, Houem; De Oliveira Carvalho, Rodrigo D.; Gaucher, Floriane; Cordeiro, Barbara F.; da Silva, Sara H.; Le Loir, Yves; Azevedo, Vasco; Jan, Gwénaël

2018-01-01

Some Gram-positive bacteria, including probiotic ones, are covered with an external proteinaceous layer called a surface-layer. Described as a paracrystalline layer and formed by the self-assembly of a surface-layer-protein (Slp), this optional structure is peculiar. The surface layer per se is conserved and encountered in many prokaryotes. However, the sequence of the corresponding Slp protein is highly variable among bacterial species, or even among strains of the same species. Other proteins, including surface layer associated proteins (SLAPs), and other non-covalently surface-bound proteins may also be extracted with this surface structure. They can be involved a various functions. In probiotic Gram-positives, they were shown by different authors and experimental approaches to play a role in key interactions with the host. Depending on the species, and sometime on the strain, they can be involved in stress tolerance, in survival within the host digestive tract, in adhesion to host cells or mucus, or in the modulation of intestinal inflammation. Future trends include the valorization of their properties in the formation of nanoparticles, coating and encapsulation, and in the development of new vaccines. PMID:29670603

High Ms Fe16N2 thin film with Ag under layer on GaAs substrate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Allard Jr, Lawrence Frederick

2016-01-01

(001) textured Fe16N2 thin film with Ag under layer is successfully grown on GaAs substrate using a facing target sputtering (FTS) system. After post annealing, chemically ordered Fe16N2 phase is formed and detected by X-ray diffraction (XRD). High saturation magnetization (Ms) is measured by a vibrating sample magnetometer (VSM). In comparison with Fe16N2 with Ag under layer on MgO substrate and Fe16N2 with Fe under layer on GaAs substrate, the current layer structure shows a higher Ms value, with a magnetically softer feature in contrast to the above cases. In addition, X-ray photoelectron spectroscopy (XPS) is performed to characterize themore » binding energy of N atoms. To verify the role of strain that the FeN layer experiences in the above three structures, Grazing Incidence X-ray Diffraction (GIXRD) is conducted to reveal a large in-plane lattice constant due to the in-plane biaxial tensile strain. INTRODUCTION« less

Bi-layered nanocomposite bandages for controlling microbial infections and overproduction of matrix metalloproteinase activity.

PubMed

Anjana, J; Mohandas, Annapoorna; Seethalakshmy, S; Suresh, Maneesha K; Menon, Riju; Biswas, Raja; Jayakumar, R

2018-04-15

Chronic diabetic wounds is characterised by increased microbial contamination and overproduction of matrix metalloproteases that would degrade the extracellular matrix. A bi-layer bandage was developed, that promotes the inhibition of microbial infections and matrix metalloprotease (MMPs) activity. Bi-layer bandage containing benzalkonium chloride loaded gelatin nanoparticles (BZK GNPs) in chitosan-Hyaluronic acid (HA) as a bottom layer and sodium alendronate containing chitosan as top layer was developed. We hypothesized that the chitosan-gelatin top layer with sodium alendronate could inhibit the MMPs activity, whereas the chitosan-HA bottom layer with BZK GNPs (240±66nm) would enable the elimination of microbes. The porosity, swelling and degradation nature of the prepared Bi-layered bandage was studied. The bottom layer could degrade within 4days whereas the top layer remained upto 7days. The antimicrobial activity of the BZK NPs loaded bandage was determined using normal and clinical strains. Gelatin zymography shows that the proteolytic activity of MMP was inhibited by the bandage. Copyright © 2017 Elsevier B.V. All rights reserved.

Description of chlorophenol-degrading Pseudomonas sp. strains KF1T, KF3, and NKF1 as a new species of the genus Sphingomonas, Sphingomonas subarctica sp. nov.

PubMed

Nohynek, L J; Nurmiaho-Lassila, E L; Suhonen, E L; Busse, H J; Mohammadi, M; Hantula, J; Rainey, F; Salkinoja-Salonen, M S

1996-10-01

Gram-negative polychlorophenol-degrading bacterial strains KF1T (T = type strain), KF3, and NKF1, which were described previously as Pseudomonas saccharophila strains, were studied by chemotaxonomic, genetic, and physiological methods and by electron microscopy and compared with selected xenobiotic compound-degrading bacteria. These strains contained sphingolipids with d-18:0, d-20:1, and d-21:1 as the main dihydrosphingosines, ubiquinone 10 as the main respiratory quinone, and spermidine as the major polyamine, and the DNA G + C content was 66 mol%. The cellular fatty acids included about 60% octadecenoic acid, 9% 2-hydroxymyristic acid, 14% cis-9-hexadecenoic acid, and 10% hexadecanoic acid. These strains exhibited less than 97% 16S ribosomal DNA sequence similarity to all of the other taxa studied. In the DNA-DNA reassociation studies the highest levels of reassociation between these strains and previously described species were less than 40%. Thin sections of cells of strains KF1T, KF3, and NKF1 were examined by electron microscopy, and the results showed that the cells had peculiar concentrically arranged layered membranous blebs that extruded from the outer membrane, especially at the cell division points. On the basis of the results of this study, polychlorophenol-degrading strains KF1T, KF3, and NKF1 are considered members of a new species of the genus Sphingomonas, Sphingomonas subarctica. The polycyclic aromatic hydrocarbon-degrading organism Sphingomonas paucimobilis EPA 505 was closely related to Sphingomonas chlorophenolica as determined by chemotaxonomic, phylogenetic, and physiological criteria. The xenobiotic compound degraders Alcaligenes sp. strain A175 and Pseudomonas sp. strain BN6 were identified as members of species of the genus Sphingomonas.

Mechanisms of flexural flow folding of competent single-layers as evidenced by folded fibrous dolomite veins

NASA Astrophysics Data System (ADS)

Torremans, Koen; Muchez, Philippe; Sintubin, Manuel

2014-12-01

Flexural flow is thought unlikely to occur in naturally deformed, competent isotropic single-layers. In this study we discuss a particular case of folded bedding-parallel fibrous dolomite veins in shale, in which the internal strain pattern and microstructural deformation features provide new insights in the mechanisms enabling flexural flow folding. Strain in the pre-folding veins is accommodated by two main mechanisms: intracrystalline deformation by bending and intergranular deformation with bookshelf rotation of dolomite fibres. The initially orthogonal dolomite fibres allowed a reconstruction of the strain distribution across the folded veins. This analysis shows that the planar mechanical anisotropy created by the fibres causes the veins to approximate flexural flow. During folding, synkinematic veins overgrow the pre-folding fibrous dolomite veins. Microstructures and dolomite growth morphologies reflect growth during progressive fold evolution, with evidence for flexural slip at fold lock-up. Homogeneous flattening, as evidenced by disjunctive axial-planar cleavage, subsequently modified these folds from class 1B to 1C folds. Our study shows that the internal vein fabric has a first-order influence on folding kinematics. Moreover, the fibrous dolomite veins show high viscosity contrasts with the shale matrix, essential in creating transient permeability for subsequent mineralising stages in the later synkinematic veins during progressive folding.

Acute Heat Stress Induces Differential Gene Expressions in the Testes of a Broiler-Type Strain of Taiwan Country Chickens

PubMed Central

Wang, Shih-Han; Cheng, Chuen-Yu; Tang, Pin-Chi; Chen, Chih-Feng; Chen, Hsin-Hsin; Lee, Yen-Pai; Huang, San-Yuan

2015-01-01

The expression of testicular genes following acute heat stress has been reported in layer-type roosters, but few similar studies have been conducted on broilers. This study investigated the effect of acute heat stress on the gene expression in the testes of a broiler-type strain of Taiwan country chickens. Roosters were subjected to acute heat stress (38°C) for 4 h, and then exposed to 25°C, with testes collected 0, 2, and 6 h after the cessation of heat stress, using non-heat-stressed roosters as controls (n = 3 roosters per group). The body temperature and respiratory rate increased significantly (p<0.05) during the heat stress. The numbers of apoptotic cells increased 2 h after the acute heat stress (79 ± 7 vs. 322 ± 192, control vs. heat stress; p<0.05), which was earlier than the time of increase in layer-type roosters. Based on a chicken 44 K oligo microarray, 163 genes were found to be expressed significantly different in the testes of the heat-stressed chickens from those of the controls, including genes involved in the response to stimulus, protein metabolism, signal transduction, cell adhesion, transcription, and apoptosis. The mRNA expressions of upregulated genes, including HSP25, HSP90AA1, HSPA2, and LPAR2, and of downregulated genes, including CDH5, CTNNA3, EHF, CIRBP, SLA, and NTF3, were confirmed through quantitative real-time polymerase chain reaction (qRT-PCR). Moreover, numerous transcripts in the testes exhibited distinct expressions between the heat-stressed broiler-type and layer-type chickens. We concluded that the transcriptional responses of testes to acute heat stress may differ between the broiler-type and layer-type roosters. Whether the differential expression patterns associate with the heat-tolerance in the strains require a further exploration. PMID:25932638

Acute heat stress induces differential gene expressions in the testes of a broiler-type strain of Taiwan country chickens.

PubMed

Wang, Shih-Han; Cheng, Chuen-Yu; Tang, Pin-Chi; Chen, Chih-Feng; Chen, Hsin-Hsin; Lee, Yen-Pai; Huang, San-Yuan

2015-01-01

The expression of testicular genes following acute heat stress has been reported in layer-type roosters, but few similar studies have been conducted on broilers. This study investigated the effect of acute heat stress on the gene expression in the testes of a broiler-type strain of Taiwan country chickens. Roosters were subjected to acute heat stress (38°C) for 4 h, and then exposed to 25°C, with testes collected 0, 2, and 6 h after the cessation of heat stress, using non-heat-stressed roosters as controls (n = 3 roosters per group). The body temperature and respiratory rate increased significantly (p<0.05) during the heat stress. The numbers of apoptotic cells increased 2 h after the acute heat stress (79 ± 7 vs. 322 ± 192, control vs. heat stress; p<0.05), which was earlier than the time of increase in layer-type roosters. Based on a chicken 44 K oligo microarray, 163 genes were found to be expressed significantly different in the testes of the heat-stressed chickens from those of the controls, including genes involved in the response to stimulus, protein metabolism, signal transduction, cell adhesion, transcription, and apoptosis. The mRNA expressions of upregulated genes, including HSP25, HSP90AA1, HSPA2, and LPAR2, and of downregulated genes, including CDH5, CTNNA3, EHF, CIRBP, SLA, and NTF3, were confirmed through quantitative real-time polymerase chain reaction (qRT-PCR). Moreover, numerous transcripts in the testes exhibited distinct expressions between the heat-stressed broiler-type and layer-type chickens. We concluded that the transcriptional responses of testes to acute heat stress may differ between the broiler-type and layer-type roosters. Whether the differential expression patterns associate with the heat-tolerance in the strains require a further exploration.

Design and characterization of thick InxGa1-xAs metamorphic buffer layers grown by hydride vapor phase epitaxy

NASA Astrophysics Data System (ADS)

Schulte, K. L.; Zutter, B. T.; Wood, A. W.; Babcock, S. E.; Kuech, T. F.

2014-03-01

Thick InxGa1-xAs metamorphic buffer layers (MBLs) grown by hydride vapor phase epitaxy (HVPE) were studied. Relationships between MBL properties and growth parameters such as grading rate, cap layer thickness, final xInAs, and deposition temperature (TD) were explored. The MBLs were characterized by measurement of in-plane residual strain (ɛ¦¦), surface etch pit density (EPD), and surface roughness. Capping layer thickness had a strong effect on strain relaxation, with thickly capped samples exhibiting the lowest ɛ¦¦. EPD was higher in samples with thicker caps, reflecting their increased relaxation through dislocation generation. ɛ¦¦ and EPD were weakly affected by the grading rate, making capping layer thickness the primary structural parameter which controls these properties. MBLs graded in discrete steps had similar properties to MBLs with continuous grading. In samples with identical thickness and 10-step grading style, ɛ¦¦ increased almost linearly with final xInAs, while total relaxation stayed relatively constant. Relaxation as a function of xInAs could be described by an equilibrium model in which dislocation nucleation is impeded by the energy of the existing dislocation array. EPD was constant from xInAs = 0 to 0.24 then increased exponentially, which is related to the increased dislocation interaction and blocking seen at higher dislocation densities. RMS roughness increased with xInAs above a certain strain rate (0.15%/µm) samples grown below this level possessed large surface hillocks and high roughness values. The elimination of hillocks at higher values of xInAs is attributed to increased density of surface steps and is related to the out-of-plane component of the burgers vector of the dominant type of 60° dislocation. TD did not affect ɛ¦¦ for samples with a given xInAs. EPD tended to increase with TD, indicating dislocation glide likely is impeded at higher temperatures.

Spacing of bending-induced fractures at saturation: Numerical models and approximate analytical solution

NASA Astrophysics Data System (ADS)

Schöpfer, Martin; Lehner, Florian; Grasemann, Bernhard; Kaserer, Klemens; Hinsch, Ralph

2017-04-01

John G. Ramsay's sketch of structures developed in a layer progressively folded and deformed by tangential longitudinal strain (Figure 7-65 in Folding and Fracturing of Rocks) and the associated strain pattern analysis have been reproduced in many monographs on Structural Geology and are referred to in numerous publications. Although the origin of outer-arc extension fractures is well-understood and documented in many natural examples, geomechanical factors controlling their (finite or saturation) spacing are hitherto unexplored. This study investigates the formation of bending-induced fractures during constant-curvature forced folding using Distinct Element Method (DEM) numerical modelling. The DEM model comprises a central brittle layer embedded within weaker (low modulus) elastic layers; the layer interfaces are frictionless (free slip). Folding of this three-layer system is enforced by a velocity boundary condition at the model base, while a constant overburden pressure is maintained at the model top. The models illustrate several key stages of fracture array development: (i) Prior to the onset of fracture, the neutral surface is located midway between the layer boundaries; (ii) A first set of regularly spaced fractures develops once the tensile stress in the outer-arc equals the tensile strength of the layer. Since the layer boundaries are frictionless, these bending-induced fractures propagate through the entire layer; (iii) After the appearance of the first fracture set, the rate of fracture formation decreases rapidly and so-called infill fractures develop approximately midway between two existing fractures (sequential infilling); (iv) Eventually no new fractures form, irrespective of any further increase in fold curvature (fracture saturation). Analysis of the interfacial normal stress distributions suggests that at saturation the fracture-bound blocks are subjected to a loading condition similar to three-point bending. Using classical beam theory an analytical solution is derived for the critical fracture spacing, i.e. the spacing below which the maximum tensile stress cannot reach the layer strength. The model results are consistent with an approximate analytical solution, and illustrate that the spacing of bending-induced fractures is proportional to layer thickness and a square root function of the ratio of layer tensile strength to confining pressure. Although highly idealised, models and analysis presented in this study offer an explanation for fracture saturation during folding and point towards certain key factors that may control fracture spacing in natural systems.

Characterization of SiGe/Ge heterostructures and graded layers using variable angle spectroscopic ellipsometry

NASA Technical Reports Server (NTRS)

Croke, E. T.; Wang, K. L.; Heyd, A. R.; Alterovitz, S. A.; Lee, C. H.

1996-01-01

Variable angle spectroscopic ellipsometry (VASE) has been used to characterize Si(x)Ge(1-x)/Ge superlattices (SLs) grown on Ge substrates and thick Si(x)Ge(1-x)/Ge heterostructures grown on Si substrates. Our VASE analysis yielded the thicknesses and alloy compositions of all layers within the optical penetration depth of the surface. In addition, strain effects were observed in the VASE results for layers under both compressive and tensile strain. Results for the SL structures were found to be in close agreement with high resolution x-ray diffraction measurements made on the same samples. The VASE analysis has been upgraded to characterize linearly graded Si(x)Ge(1-x) buffer layers. The algorithm has been used to determine the total thickness of the buffer layer along with the start and end alloy composition by breaking the total thickness into many (typically more than 20) equal layers. Our ellipsometric results for 1 (mu)m buffer layers graded in the ranges 0.7 less than or = x less than or = 1.0, and 0.5 less than or = x less than or = 1.0 are presented, and compare favorably with the nominal values.

Haloferax volcanii archaeosortase is required for motility, mating, and C-terminal processing of the S-layer glycoprotein: Haloferax volcanii archeosortase

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abdul Halim, Mohd Farid; Pfeiffer, Friedhelm; Zou, James

2013-05-28

Cell surfaces are decorated by a variety of proteins that facilitate interactions with their environments and support cell stability.These secreted proteins are anchored to the cell by mechanisms that are diverse, and, in archaea, poorly understood. Recently published in silico data suggest that in some species a subset of secreted euryarchaeal proteins, which includes the S-­layer glycoprotein, is processed and covalently linked tot he cell membrane by enzymes referred to as archaeosortases. In silico work led to the proposal that an independent, sortase-like system for proteolysis-coupled carboxy-terminal lipid modification exists in bacteria (exosortase) and archaea (archaeosortase). Here, we provide themore » first in vivo characterization of an archaeosortase in the haloarchaeal model organism Haloferax volcanii. Deletion of the artA gene (HVO_0915) resulted in multiple biological phenotypes: (a) poor growth, especially under low-salt conditions, (b) alterations in cell shape and the S-layer, (c) impaired motility, suppressors of which still exhibit poor growth, and (d) impaired conjugation. We studied one of the ArtA substrates, the S-layer glycoprotein, using detailed proteomic analysis. While the carboxy-terminal region of S-layer glycoproteins, consisting of a threonine-rich O-glycosylated region followed by a hydrophobic transmembrane helix, has been notoriously resistant to any proteomic peptide identification, we were able to identify two overlapping peptides from the transmembrane domain present in the ΔartA strain but not in the wild-type strain. This clearly shows that ArtA is involved in carboxy-terminal posttranslational processing of the S-layer glycoprotein. As it is known from previous studies that a lipid is covalently attached to the carboxy-terminal region of the S-layer glycoprotein, our data strongly support the conclusion that archaeosortase functions analogously to sortase, mediating proteolysis-coupled, covalent cell surface attachment.« less

Strain distribution in thin concrete pavement panels under three-point loading to failure with pre-pulse-pump Brillouin optical time domain analysis (Presentation Video)

NASA Astrophysics Data System (ADS)

Bao, Yi; Cain, John; Chen, Yizheng; Huang, Ying; Chen, Genda; Palek, Leonard

2015-04-01

Thin concrete panels reinforced with alloy polymer macro-synthetic fibers have recently been introduced to rapidly and cost-effectively improve the driving condition of existing roadways by laying down a fabric sheet on the roadways, casting a thin layer of concrete, and then cutting the layer into panels. This study is aimed to understand the strain distribution and potential crack development of concrete panels under three-point loading. To this end, six full-size 6ft×6ft×3in concrete panels were tested to failure in the laboratory. They were instrumented with three types of single-mode optical fiber sensors whose performance and ability to measure the strain distribution and detect cracks were compared. Each optical fiber sensor was spliced and calibrated, and then attached to a fabric sheet using adhesive. A thin layer of mortar (0.25 ~ 0.5 in thick) was cast on the fabric sheet. The three types of distributed sensors were bare SM-28e+ fiber, SM-28e+ fiber with a tight buffer, and concrete crack cable, respectively. The concrete crack cable consisted of one SM-28e+ optical fiber with a tight buffer, one SM-28e+ optical fiber with a loose buffer for temperature compensation, and an outside protective tight sheath. Distributed strains were collected from the three optical fiber sensors with pre-pulse-pump Brillouin optical time domain analysis in room temperature. Among the three sensors, the bare fiber was observed to be most fragile during construction and operation, but most sensitive to strain change or micro-cracks. The concrete crack cable was most rugged, but not as sensitive to micro-cracks and robust in micro-crack measurement as the bare fiber. The ruggedness and sensitivity of the fiber with a tight buffer were in between the bare fiber and the concrete crack cable. The strain distribution resulted from the three optical sensors are in good agreement, and can be applied to successfully locate cracks in the concrete panels. It was observed that the three types of fibers were functional until the concrete panels have experienced inelastic deformation, making the distributed strain sensing technology promising for real applications in pavement engineering.

Evolution of wetting layer in InAs/GaAs quantum dot system

PubMed Central

Ye, XL; Wang, ZG

2006-01-01

For InAs/GaAs quantum dot system, the evolution of the wetting layer (WL) with the InAs deposition thickness has been studied by reflectance difference spectroscopy (RDS). Two transitions related to the heavy- and light-hole in the WL have been distinguished in RD spectra. Taking into account the strain and segregation effects, a model has been presented to deduce the InAs amount in the WL and the segregation coefficient of the indium atoms from the transition energies of heavy- and light-holes. The variation of the InAs amount in the WL and the segregation coefficient are found to rely closely on the growth modes. In addition, the huge dots also exhibits a strong effect on the evolution of the WL. The observed linear dependence of In segregation coefficient upon the InAs amount in the WL demonstrates that the segregation is enhanced by the strain in the WL.

Tensile strain effect in ferroelectric perovskite oxide thin films on spinel magnesium aluminum oxide substrate

NASA Astrophysics Data System (ADS)

Zhou, Xiaolan

Ferroelectrics are used in FeRAM (Ferroelectric random-access memory). Currently (Pb,Zr)TiO3 is the most common ferroelectric material. To get lead-free and high performance ferroelectric material, we investigated perovskite ferroelectric oxides (Ba,Sr)TiO3 and BiFeO3 films with strain. Compressive strain has been investigated intensively, but the effects of tensile strain on the perovskite films have yet to be explored. We have deposited (Ba,Sr)TiO3, BiFeO3 and related films by pulsed laser deposition (PLD) and analyzed the films by X-ray diffractometry (XRD), atomic force microscopy (AFM), etc. To obtain inherently fully strained films, the selection of the appropriate substrates is crucial. MgAl2O4 matches best with good quality and size, yet the spinel structure has an intrinsic incompatibility to that of perovskite. We introduced a rock-salt structure material (Ni 1-xAlxO1+delta) as a buffer layer to mediate the structural mismatch for (Ba,Sr)TiO3 films. With buffer layer Ni1-xAlxO1+delta, we show that the BST films have high quality crystallization and are coherently epitaxial. AFM images show that the films have smoother surfaces when including the buffer layer, indicating an inherent compatibility between BST-NAO and NAO-MAO. In-plane Ferroelectricity measurement shows double hysteresis loops, indicating an antiferroelectric-like behavior: pinned ferroelectric domains with antiparallel alignments of polarization. The Curie temperatures of the coherent fully strained BST films are also measured. It is higher than 900°C, at least 800°C higher than that of bulk. The improved Curie temperature makes the use of BST as FeRAM feasible. We found that the special behaviors of ferroelectricity including hysteresis loop and Curie temperature are due to inherent fully tensile strain. This might be a clue of physics inside ferroelectric stain engineering. An out-of-plane ferroelectricity measurement would provide a full whole story of the tensile strain. However, a well suited electrode material that is both conducting, and full strained on the MgAl2O4 substrate is quite rare. We will supply some answers to this unique problem. XRD results show that Ni1-xAlxO1+delta (x=0.3, 0.4 & 0.5) film, although highly mixed with Al2O3, still takes rock-salt structure and is grown very well on the spinel MgAl 2O4 substrate, with perfect crystallization and a smooth surface. Ni0.7Al0.3O1+ delta and Ni 0.6Al0.4O1+ delta are good buffer layers for perovskite film on spinel MgAl2O4 substrate. Ni 0.5Al0.5O1+ delta could also be a good buffer layer. The structural transition from rock-salt to spinel was found at x=0.67. Tensile strain effects from thermal expansion difference of BiFeO3 films were found. Thermal expansion difference caused strain does not change the ferroelectric property greatly, due to film relaxation. BiFeO3 film with NAO buffer exhibit much larger strain.

Anisotropic spin-density distribution and magnetic anisotropy of strained La1-xSrxMnO3 thin films: angle-dependent x-ray magnetic circular dichroism

NASA Astrophysics Data System (ADS)

Shibata, Goro; Kitamura, Miho; Minohara, Makoto; Yoshimatsu, Kohei; Kadono, Toshiharu; Ishigami, Keisuke; Harano, Takayuki; Takahashi, Yukio; Sakamoto, Shoya; Nonaka, Yosuke; Ikeda, Keisuke; Chi, Zhendong; Furuse, Mitsuho; Fuchino, Shuichiro; Okano, Makoto; Fujihira, Jun-ichi; Uchida, Akira; Watanabe, Kazunori; Fujihira, Hideyuki; Fujihira, Seiichi; Tanaka, Arata; Kumigashira, Hiroshi; Koide, Tsuneharu; Fujimori, Atsushi

2018-01-01

Magnetic anisotropies of ferromagnetic thin films are induced by epitaxial strain from the substrate via strain-induced anisotropy in the orbital magnetic moment and that in the spatial distribution of spin-polarized electrons. However, the preferential orbital occupation in ferromagnetic metallic La1-xSrxMnO3 (LSMO) thin films studied by x-ray linear dichroism (XLD) has always been found out-of-plane for both tensile and compressive epitaxial strain and hence irrespective of the magnetic anisotropy. In order to resolve this mystery, we directly probed the preferential orbital occupation of spin-polarized electrons in LSMO thin films under strain by angle-dependent x-ray magnetic circular dichroism (XMCD). Anisotropy of the spin-density distribution was found to be in-plane for the tensile strain and out-of-plane for the compressive strain, consistent with the observed magnetic anisotropy. The ubiquitous out-of-plane preferential orbital occupation seen by XLD is attributed to the occupation of both spin-up and spin-down out-of-plane orbitals in the surface magnetic dead layer.

Assessment of Fatigue Resistance of Aluminide Layers on MAR 247 Nickel Super Alloy with Full-Field Optical Strain Measurements

NASA Astrophysics Data System (ADS)

Kukla, D.; Brynk, T.; Pakieła, Z.

2017-08-01

This work presents the results of fatigue tests of MAR 247 alloy flat specimens with aluminides layers of 20 or 40 µm thickness obtained in CVD process. Fatigue test was conducted at amplitude equal to half of maximum load and ranging between 300 and 650 MPa (stress asymmetry ratio R = 0, frequency f = 20 Hz). Additionally, 4 of the tests, characterized by the highest amplitude, were accompanied with non-contact strain field measurements by means of electronic speckle pattern interferometry and digital image correlation. Results of these measurements allowed to localize the areas of deformation concentration identified as the damage points of the surface layer or advanced crack presence in core material. Identification and observation of the development of deformation in localization areas allowed to assess fatigue-related phenomena in both layer and substrate materials.

Measurement of strain distribution in bonded joints by fiber Bragg gratings

NASA Astrophysics Data System (ADS)

Guemes, J. Alfredo; Diaz-Carrillo, Sebastian; Menendez, Jose M.

1998-07-01

Due to the small dimensions of the adhesive layer, the high non-uniformity of the strain field and the non linear elastic behavior of the adhesive material, the strain distribution at an adhesive joint can be predicted by FEM, but can not be experimentally obtained with classical approaches; only non standard procedures like Moire interferometry, or special artifacts like KGR extensometers may afford some insights on the behavior of the adhesive. Due to their small size, ensuring low perturbation of the strain field, and their innate ability to measure strain and strain gradient along the sensor, fiber Bragg gratings offer a good opportunity to solve this problem, and it is a good example of situations that may benefit from these new sensors. Fiber Bragg gratings may be placed or at the interface, within the adhesive layer, or embedded at the adherents, if these were made of composite material. Tests may be run at different temperatures, changing the adhesive characteristics from brittle to pseudoplastic without additional difficulties. When loading the joint, the strain field is obtained by analyzing the distorted spectrum of the reflected light pulse; the algorithm for doing it has already been published. A comparison with theoretical results is done, and the validity and utility of these sensors for this and similar applications is demonstrated.

Effects of training to implement new working methods to reduce knee strain in floor layers. A two-year follow-up.

PubMed

Jensen, L K; Friche, C

2008-01-01

Follow-up study after two years to measure the effects of an implementation strategy consisting of information, education and training in the use of new tools and working-methods for the purpose of reducing knee strain and knee complaints in floor layers. Training of floor layers (n = 292) in using new working methods was evaluated by questionnaires during the courses. Two years later, this follow-up included questionnaires for the course participants (n = 216) and a control group of floor layers (not trained on courses) (n = 454). Two years after training, 38% used the new working methods weekly or daily compared to 37% three months after the courses, and 10% before. Among controls, only 16% had used the new working methods weekly or daily. The risk of knee complaints >30 days (OR 2.46, 95% CI 1.03 to 5.83) or locking of the knees (OR 2.89, 95% CI 1.11 to 7.5) was more than double among floor layers who had used the new working-methods for less than one year compared to those who had used them more. The results were adjusted for age, body mass index, and stress. The reduction in more severe knee complaints was greatest if floor layers started to use the new working methods before they developed knee problems. Other musculoskeletal complaints did not increase. This indicates that, within a two-year perspective, the implementation strategy to introduce new working methods in the floor laying trade has been effective; the number of floor layers using the new working-methods has increased, and severe knee problems have reduced.

Residual strain effects on large aspect ratio micro-diaphragms

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hijab, R.S.; Muller, R.S.

1988-09-30

Highly compliant, large aspect ratio diaphragms for use in low-pressure, capacitive-readout sensors, have been investigated. In such structures, unrelaxed strain in the diaphragms can radically alter mechanical behavior. Although strain can be reduced by thermal annealing, it usually reaches a remnant irreducible minimum. The purpose of this paper is to describe techniques that result in low-strain materials and that reduce the effects of residual strain in micro-diaphragms. Square polysilicon grilles and perforated diaphragms made from both single and double polysilicon layers and from single-crystal silicon, with aspect ratios (side/thickness) of up to 1000 and very low compressive strain ({approx}6 {times}more » 10{sup {minus}5}), have been fabricated. Strain reduction is achieved by combining thermal annealing with one of two mechanical design techniques. The first technique makes use of a series of cantilever beams to support the diaphragms. In a second procedure, corrugated surfaces in thinned membranes of single-crystal silicon are formed. The corrugations result from the use of boron doping and anisotropic silicon etching. In both of these techniques to produce low-strain diaphragms, an etched cavity is purposely formed in the substrate crystal below them. Only one-sided processing of wafers is employed, thus aiding reproducibility and providing ease of compatibility with an MOS process. A fast-etching sacrificial-support layer (phosphorus-doped CVD oxide) is used. 4 refs., 10 figs.« less

FAST TRACK COMMUNICATION: Emission wavelength extension of mid-infrared InAsSb/InP nanostructures using InGaAsSb sandwich layers

NASA Astrophysics Data System (ADS)

Lei, W.; Tan, H. H.; Jagadish, C.

2010-08-01

This paper presents a study on the emission wavelength extension of InAsSb nanostructures using InGaAsSb sandwich layers. Due to the reduced lattice mismatch between InAsSb nanostructure layer and buffer/capping layer, the introduction of InGaAsSb sandwich layers leads to larger island size, reduced compressive strain and lower confinement barrier for InAsSb nanostructures, thus resulting in a longer emission wavelength. For InGaAsSb sandwich layers with nominal Sb concentration higher than 10%, type II band alignment is observed for the InAsSb/InGaAsSb heterostructure, which also contributes to the extension of emission wavelength. The InGaAsSb sandwich layers provide an effective approach to extend the emission wavelength of InAsSb nanostructures well beyond 2 µm, which is very useful for device applications in the mid-infrared region.