scholarly journals Analysis of the Basal Plane Dislocation Density and Thermomechanical Stress during 100 mm PVT Growth of 4H-SiC

Materials ◽  
2019 ◽  
Vol 12 (13) ◽  
pp. 2207 ◽  
Author(s):  
Johannes Steiner ◽  
Melissa Roder ◽  
Binh Duong Nguyen ◽  
Stefan Sandfeld ◽  
Andreas Danilewsky ◽  
...  
Keyword(s):  
Basal Plane ◽  
Growth Parameters ◽  
Electronic Devices ◽  
Defect Distribution ◽  
Thermomechanical Stress ◽  
X Ray ◽  
Basal Plane Dislocation ◽  
The Impact ◽  
Koh Etching

Basal plane dislocations (BPDs) in 4H silicon carbide (SiC) crystals grown using the physical vapor transport (PVT) method are diminishing the performance of SiC-based power electronic devices such as pn-junction diodes or MOSFETs. Therefore, understanding the generation and movement of BPDs is crucial to grow SiC suitable for device manufacturing. In this paper, the impact of the cooldown step in PVT-growth on the defect distribution is investigated utilizing two similar SiC seeds and identical growth parameters except for a cooldown duration of 40 h and 70 h, respectively. The two resulting crystals were cut into wafers, which were characterized by birefringence imaging and KOH etching. The initial defect distribution of the seed wafer was characterized by synchrotron white beam X-ray topography (SWXRT) mapping. It was found that the BPD density increases with a prolonged cooldown time. Furthermore, small angle grain boundaries based on threading edge dislocation (TED) arrays, which are normally only inherited by the seed, were also generated in the case of the crystal cooled down in 70 h. The role of temperature gradients inside the crystal during growth and post-growth concerning the generation of shear stress is discussed and supported by numerical calculations.

Starting Point of Step-Bunching Defects on 4H-SiC Si-Face Substrates

2015 ◽  
Vol 821-823 ◽  
pp. 367-370 ◽  
Author(s):  
Kentaro Tamura ◽  
Masayuki Sasaki ◽  
Chiaki Kudou ◽  
Tamotsu Yamashita ◽  
Hideki Sako ◽  
...  
Keyword(s):  
Oxide Layer ◽  
Epitaxial Layer ◽  
Basal Plane ◽  
X Ray ◽  
Step Bunching ◽  
Line Feature ◽  
Starting Point ◽  
Basal Plane Dislocation ◽  
Koh Etching

On 4H-SiC Si-face substrates after H2etching, the defect with “line” feature parallel to a step as “bunched-step line” was observed. Using X-ray topography and KOH etching, we confirmed that the bunched-step line originated from basal plane dislocation (BPD). Use of the substrate with the lowest BPD density will be effective to reduce bunched-step line that would affect oxide layer reliability on an epitaxial layer. However, more detail investigation needs to classify the BPD that would become a starting point of bunched-step line.

Conversion of Basal Plane Dislocations to Threading Edge Dislocations in Growth of Epitaxial Layers on 4H-SiC Substrates with a Vicinal Off-Angle

2014 ◽  
Vol 778-780 ◽  
pp. 99-102 ◽  
Author(s):  
Keiko Masumoto ◽  
Sachiko Ito ◽  
Hideto Goto ◽  
Hirotaka Yamaguchi ◽  
Kentaro Tamura ◽  
...  
Keyword(s):  
Epitaxial Growth ◽  
Edge Dislocation ◽  
Basal Plane ◽  
Conversion Ratio ◽  
Epitaxial Layers ◽  
Etch Pits ◽  
X Ray ◽  
Basal Plane Dislocation ◽  
Edge Dislocations ◽  
Koh Etching

We have investigated a conversion of basal plane dislocation (BPD) to threading edge dislocation (TED) in growth of epitaxial layers (epi-layers) on 4H-SiC vicinal substrates with an off-angle of 0.85° at low C/Si ratio of 0.7 by using deep KOH etching and X-ray topography observations. Deep KOH etching indicated that BPDs in the substrates converted to TEDs in the epi-layers. X-ray topography observations suggested that the conversion occurred during epitaxial growth when the thickness of epi-layers was less than 1.5 μm. We found that the conversion ratio obtained from counting deep KOH etch pits was over 99%.

Factors affecting the amplitude of the τ angle in proteins: a revisitation

2017 ◽  
Vol 73 (7) ◽  
pp. 618-625 ◽  
Author(s):  
Nicole Balasco ◽  
Luciana Esposito ◽  
Luigi Vitagliano
Keyword(s):  
Protein Structures ◽  
Factors Affecting ◽  
X Ray ◽  
Backbone Conformation ◽  
Potential Factors ◽  
The Stability ◽  
Major Factors ◽  
The Impact ◽  
Open Issues

The protein folded state is the result of the fine balance of a variety of different forces. Even minor structural perturbations may have a significant impact on the stability of these macromolecules. Studies carried out in recent decades have led to the convergent view that proteins are endowed with a flexible spine. One of the open issues related to protein local backbone geometry is the identification of the factors that influence the amplitude of the τ (N—Cα—C) angle. Here, statistical analyses performed on an updated ensemble of X-ray protein structures by dissecting the contribution of the major factors that can potentially influence the local backbone geometry of proteins are reported. The data clearly indicate that the local backbone conformation has a prominent impact on the modulation of the τ angle. Therefore, a proper assessment of the impact of the other potential factors can only be appropriately evaluated when small (φ, ψ) regions are considered. Here, it is shown that when the contribution of the backbone conformation is removed by considering small (φ, ψ) areas, an impact of secondary structure, as defined byDSSP, and/or the residue type on τ is still detectable, although to a limited extent. Indeed, distinct τ-value distributions are detected for Pro/Gly and β-branched (Ile/Val) residues. The key role of the local backbone conformation highlighted here supports the use of variable local backbone geometry in protein refinement protocols.

The Impact of EDS In Materials Science Microanalysis

1998 ◽  
Vol 4 (S2) ◽  
pp. 168-169
Author(s):  
D. B. Williams
Keyword(s):  
Materials Science ◽  
X Ray ◽  
Electron Probe Microanalyzer ◽  
Thin Foils ◽  
Analytical Electron ◽  
Analytical Electron Microscope ◽  
Small Collection ◽  
Excellent Energy Resolution ◽  
The Impact

Since its invention in 1968, the EDS has played an essential role in X-ray analysis of materials, at the micrometer level, in the electron probe microanalyzer (EPMA). In the EPMA, the characteristic X-ray intensity from bulk specimens is sufficient that, despite its very small collection angle, the wavelength dispersive spectrometer (WDS) can also be used. Given the excellent energy resolution of the WDS it has often been the spectrometer of choice for bulk quantitative X-ray microanalysis. Therefore, the most important role of the EDS has been in X-ray microanalysis of thin specimens in the analytical electron microscope (AEM) because, in an AEM, the limited confines of the stage mean that EDS is the only viable spectrometer. Since the pioneering work of Cliff and Lorimer in the 1970s, EDS has been the method by which all high spatial resolution X-ray microanalysis of thin foils has been performed.

scholarly journals The impact of dietary supplementation of arginine during gestation in a commercial swine herd: II. Offspring performance

2019 ◽  
Vol 97 (9) ◽  
pp. 3626-3635 ◽  
Author(s):  
Elizabeth A Hines ◽  
Matthew R Romoser ◽  
Zoë E Kiefer ◽  
Aileen F Keating ◽  
Lance H Baumgard ◽  
...  
Keyword(s):  
Production Systems ◽  
Growth Parameters ◽  
Late Gestation ◽  
Swine Herd ◽  
Offspring Performance ◽  
Important Amino Acid ◽  
Carcass Performance ◽  
Dietary Treatments ◽  
The Impact

Abstract Arginine (Arg) is an important amino acid of pig fetal development; however, whether Arg improves postnatal performance is ill-defined. Therefore, the influence of Arg supplementation at different gestational stages on offspring performance was evaluated in a commercial swine herd. Sows (n = 548) were allocated into 4, diet by stage of gestation treatments: Control (n = 143; 0% suppl. Arg), or dietary treatments supplemented with 1% L-Arg (free-base; Ajinomoto Animal Nutrition North America, Inc., Chicago, IL): from 15 to 45 d of gestation (n = 138; Early-Arg); 15 d of gestation to farrowing (n = 139; Full-Arg); and from day 85 of gestation to farrowing (n = 128; Late-Arg). All offspring were individually identified and weighed at birth; at weaning, a subset was selected for evaluation of carcass performance at market. All data were analyzed using birth weight (BiWt) and age as covariates. Wean weights (WW) and prewean (PW) ADG tended to increase (P = 0.06) in progeny from sows supplemented with Arg, as compared to progeny from Control sows. Preplanned contrast comparisons revealed an increased (P = 0.03) BiWt for pigs from sows receiving 1% L-Arg prior to day 45 of gestation (Early-Arg and Full-Arg; 1.38 kg/pig), as compared to pigs from sows not supplemented prior to day 45 of gestation (Control and Late-Arg; 1.34 kg/pig). No difference in BiWt was observed (1.36 kg/pig; P = 0.68) for Arg supplementation after day 85 of gestation (Full-Arg and Late-Arg), as compared to those not receiving Arg supplementation after day 85 (Control and Early-Arg); although WW and PW ADG were greater (P = 0.02), respectively. A 3.6% decrease (P = 0.05) in peak lean accretion ADG occurred when dams received 1% L-Arg prior to day 45 of gestation (Early-Arg and Full-Arg), however, no other significant differences were detected in finishing growth parameters or carcass characteristics (P ≥ 0.1). Pig mortality rates tended (P = 0.07) to decrease in progeny of dams supplemented Arg after day 85 (3.6%) compared to dams not provided additional Arg during late gestation (4.9%). Collectively, these data suggest that Arg provided during late gestation may improve WW and PW ADG, however, finishing performance was not affected. While Arg supplementation provided some moderate production benefits, further investigation is warranted to comprehensively understand the gestational timing and biological role of Arg supplementation during fetal and postnatal development in commercial production systems.

scholarly journals Mechanism of persistence of indigenous bifidobacteria under the impact of acetate in the human colon biotope

2021 ◽  
Vol 98 (3) ◽  
pp. 276-282
Author(s):  
O. V. Bukharin ◽  
S. V. Andryuschenko ◽  
N. B. Perunova ◽  
E. V. Ivanova
Keyword(s):  
Acetic Acid ◽  
Ammonium Acetate ◽  
Growth Parameters ◽  
Bifidobacterium Longum ◽  
Human Colon ◽  
Bifidobacterium Bifidum ◽  
Gram Positive ◽  
Gram Positive Bacteria ◽  
The Impact

Aim. To determine the role of the acetate in the persistence of indigenous bifidobacteria in the colon biotope through the lysozyme resistance in model conditions of the acetylation–deacetylation of peptidoglycan.Materials and methods. The study was performed on 16 strains of the two indigenous bifidobacteria speсies: Bifidobacterium bifidum и Bifidobacterium longum subsp. longum. Bifidobacteria was cultivated in the 0.6% O2 and 9% CO2 atmosphere at the temperature 37ºС in CO2 incubator for 48 hours. The production of the acetate by the bifidobacteria was determined by gas chromatography. The effect of the acetate on the lysozyme resistance of non-indigenous gram-positive bacteria was determined on the Listeria monocytogenes ICIS-280 model strain by the cultivation in LB-Lennox broth with ammonium acetate added in the concentration range matching the concentrations produced by the studied bifidobacteria, in lysozyme serial dilutions at final concentrations 5 μg/ml to 40 μg/ml within 24 hours.Results. It was found that the acetate release of Bifidobacterium longum subsp. longum was on average two times higher that of Bifidobacterium bifidum (27.0 and 14.7 mmol/liter, respectively) and was quite consistent with the concentrations of acetic acid determined in the intestinal contents (up to 50 mmol/liter). Cultivation of bifidobacteria in a medium with lysozyme, ammonium acetate and their combination did not have a significant impact on their growth parameters at the maximum used concentrations of these substances. In the test strain, the addition of ammonium acetate in the range created by bifidobacteria caused a decrease in the minimum inhibitory concentration of lysozyme by more than two times — from 40 μg/ml to less than 20 μg/ml. In the control medium without lysozyme, no inhibition of the growth of the indicator culture was observed up to the maximum concentrations of ammonium acetate.Conclusion. The mechanism of persistence (survival) of indigenous bifidobacteria in the human intestinal biotope has been identified, which is associated with the production of acetic acid at a level that selectively suppresses lysozyme resistance of non-indigenous gram-positive microbiota viareversible deacetylation of peptidoglycan. This allows indigenous bifidobacteria to maintain a stable dominant position in the biotope.

I Love You but I Cyberbully You: The Role of Hostile Sexism

2016 ◽  
Vol 34 (4) ◽  
pp. 812-825 ◽  
Author(s):  
Roberto Martinez-Pecino ◽  
Mercedes Durán
Keyword(s):  
College Students ◽  
Undergraduate Students ◽  
Electronic Devices ◽  
Hostile Sexism ◽  
Regression Analyses ◽  
Dating Relationships ◽  
Cyber Aggression ◽  
Forms Of Violence ◽  
The Impact

Cyberbullying is attracting social, political, and academic interest as the use of electronic devices such as computers and mobile phones by young people has increased dramatically. However, little is known about the factors involved in their perpetration, particularly in the context of college students’ dating relationships. The aim of this study is to examine the involvement of college students in cyberbullying in the context of their dating relationships and to explore the impact of sexism on males’ cyberbullying of their girlfriends. Participants are 219 undergraduate students from a university in the south of Spain. Results showed that 48.4% of participants reported having bullied their partners during the last year via mobile phone and 37.5% via Internet. Males reported a greater extent of cyberbullying of their girlfriends through both means. Regression analyses indicated that males’ levels of hostile sexism are related to males’ cyberbullying of their girlfriends. These findings suggest a modernization in the forms of violence toward women among college students and also expand current literature by revealing the influence of participants’ hostile sexism on this type of cyber aggression against women in dating relationships.

Investigation of Basal Plane Dislocation Reduction/Elimination by Molten KOH-NaOH Eutectic Etching Method

2012 ◽  
Vol 717-720 ◽  
pp. 125-128 ◽  
Author(s):  
Hai Zheng Song ◽  
Tangali S. Sudarshan
Keyword(s):  
Epitaxial Growth ◽  
Basal Plane ◽  
Etch Pits ◽  
Etch Pit ◽  
Etching Method ◽  
Dislocation Reduction ◽  
Short Period ◽  
Basal Plane Dislocation ◽  
Non Destructive ◽  
Koh Etching

An optimized molten KOH-NaOH eutectic etching method is developed to reveal defects in highly n-doped SiC substrates and to pre-treat the substrate prior to epitaxial growth. Different from the conventional KOH etching method, by way of eutectic method, the basal plane dislocation (BPD) conversion in the subsequent epitaxial growth is independent of the etch pit size pre-generated on the substrate. Even with a short period (~3 minutes) of pretreatment which does not generate any visible etch pits or degradation of surface morphology on the substrate, an epilayer with low BPD density -2 is still achieved. This simple and non-destructive method shows high potential to be practically employed as one of the basic pretreatment steps to the substrates in SiC epitaxial growth in order to achieve very low or free BPD density.

VF Degradation of 4H-SiC PiN Diodes Using Low-BPD Wafers

2014 ◽  
Vol 778-780 ◽  
pp. 851-854 ◽  
Author(s):  
Chiharu Ota ◽  
Johji Nishio ◽  
Kazuto Takao ◽  
Takashi Shinohe
Keyword(s):  
Basal Plane ◽  
Stacking Faults ◽  
Optical Observation ◽  
Etch Pits ◽  
Pin Diodes ◽  
Bipolar Devices ◽  
Basal Plane Dislocation ◽  
Pl Mapping ◽  
Koh Etching ◽  
Free Area

In this paper, we found origin of VFdegradation of SiC bipolar devices other than a basal plane dislocation (BPD) in the SiC substrate. A VFdegradation of the 4H-SiC PiN diodes with low-BPD wafers was evaluated and its origins were discussed. Some diodes suffered VFdegradation, even though they were fabricated on BPD-free area. PL mapping, TEM image, and optical observation after KOH etching showed that there were Shockley stacking faults and combined etch-pits arrays, which were presumed to be caused by the device process.

Characterization and Reduction of Defects in 4H-SiC Substrate and Homo-Epitaxial Wafer

2020 ◽  
Vol 1004 ◽  
pp. 387-392 ◽  
Author(s):  
Long Yang ◽  
Li Xia Zhao ◽  
Hui Wang Wu ◽  
Yafei Liu ◽  
Tuerxun Ailihumaer ◽  
...  
Keyword(s):  
Basal Plane ◽  
Chemical Vapor ◽  
Vapor Transport ◽  
Etching Time ◽  
X Ray ◽  
Half Loop ◽  
Dislocation Behavior ◽  
Edge Dislocations ◽  
Defect Morphology ◽  
Koh Etching

4H-SiC substrates and homo-epitaxial layers were obtained using the traditional methods of physical vapor transport and chemical vapor deposition. Defect morphology has been studied using both Synchrotron White Beam X-ray Topography and Monochromatic Beam X-ray Topography. Molten KOH etching method was adopted to further investigate the dislocation behavior mechanisms. Deflected dislocations were observed at the periphery regions in both substrate and epitaxial wafers. 3C polytypes and half loop arrays were observed in the 4H-SiC epitaxial wafer. It is also found that the majority of basal plane dislocations are converted to threading edge dislocations in the epitaxial wafer samples. The proportion of BPD to TED conversion depends on the surface step morphology and growth mode in epitaxial growth which in turn depends on the C/Si ratio. By the optimization of etching time prior to epitaxy and C/Si ratio, high-quality epitaxial wafers with extremely low basal plane dislocations densities (＜0.1 cm-2) was obtained.

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