scholarly journals Influence of Morphological Changes in a Source Material on the Growth Interface of 4H-SiC Single Crystals

Materials ◽  
2019 ◽  
Vol 12 (16) ◽  
pp. 2591 ◽  
Author(s):  
Matthias Arzig ◽  
Johannes Steiner ◽  
Michael Salamon ◽  
Norman Uhlmann ◽  
Peter J. Wellmann
Keyword(s):  
Thermal Conductivity ◽  
Morphological Changes ◽  
Laser Flash ◽  
Source Material ◽  
Ex Situ ◽  
Growth Interface ◽  
Bulk Growth ◽  
Before And After ◽  
Conductivity Models

In this study, the change of mass distribution in a source material is tracked using an in situ computer tomography (CT) setup during the bulk growth of 4H- silicon carbide (SiC) via physical vapor depostion (PVT). The changing properties of the source material due to recrystallization and densification are evaluated. Laser flash measurement showed that the thermal properties of different regions of the source material change significantly before and after the growth run. The Si-depleted area at the bottom of the crucible is thermally insulating, while the residual SiC source showed increased thermal conductivity compared to the initially charged powder. Ex situ CT measurements revealed a needle-like structure with elongated pores causing anisotropic behavior for the heat conductivity. Models to assess the thermal conductivity are applied in order to calculate the changes in the temperature field in the crucible and the changes in growth kinetics are discussed.

Growth Conditions and In Situ Computed Tomography Analysis of Facetted Bulk Growth of SiC Boules

2018 ◽  
Vol 924 ◽  
pp. 245-248
Author(s):  
Matthias Arzig ◽  
Michael Salamon ◽  
Norman Uhlmann ◽  
Bertil A. Johansen ◽  
Peter J. Wellmann
Keyword(s):  
Computed Tomography ◽  
Packing Density ◽  
Thermal Gradient ◽  
Growth Conditions ◽  
Source Material ◽  
Lateral Growth ◽  
Growth Interface ◽  
Bulk Growth ◽  
Tomography Analysis

Two 3inch SiC boules were grown in a PVT setup using source material of different packing density. During the growth, in-situ computed tomography of the growing boules showed differences in the development of the growth interface. A slightly bent growth interface was found for the smaller packing density. For the higher packing density the resulting crystal exhibits the onset of 6 pyramidal facets on its flanks. Besides that, strong anisotropic lateral growth was found on its (000-1) facet. Numerical simulations show an impact of the powder on the thermal gradient in the growth cell and therefore on the supersaturation. It is discussed that a higher supersaturation can account for the anisotropy in the growth rate of the [1-100] and the [11-20] direction.

scholarly journals Application of the MSAP Technique to Evaluate Epigenetic Changes in Plant Conservation

2020 ◽  
Vol 21 (20) ◽  
pp. 7459
Author(s):  
María Elena González-Benito ◽  
Miguel Ángel Ibáñez ◽  
Michela Pirredda ◽  
Sara Mira ◽  
Carmen Martín
Keyword(s):  
Dna Methylation ◽  
In Situ Conservation ◽  
Plant Conservation ◽  
Ex Situ ◽  
Conservation Strategies ◽  
Regenerated Plants ◽  
Before And After ◽  
Methylation Patterns

Epigenetic variation, and particularly DNA methylation, is involved in plasticity and responses to changes in the environment. Conservation biology studies have focused on the measurement of this variation to establish demographic parameters, diversity levels and population structure to design the appropriate conservation strategies. However, in ex situ conservation approaches, the main objective is to guarantee the characteristics of the conserved material (phenotype and epi-genetic). We review the use of the Methylation Sensitive Amplified Polymorphism (MSAP) technique to detect changes in the DNA methylation patterns of plant material conserved by the main ex situ plant conservation methods: seed banks, in vitro slow growth and cryopreservation. Comparison of DNA methylation patterns before and after conservation is a useful tool to check the fidelity of the regenerated plants, and, at the same time, may be related with other genetic variations that might appear during the conservation process (i.e., somaclonal variation). Analyses of MSAP profiles can be useful in the management of ex situ plant conservation but differs in the approach used in the in situ conservation. Likewise, an easy-to-use methodology is necessary for a rapid interpretation of data, in order to be readily implemented by conservation managers.

scholarly journals Optimization of the SiC Powder Source Material for Improved Process Conditions During PVT Growth of SiC Boules

Materials ◽  
2019 ◽  
Vol 12 (19) ◽  
pp. 3272
Author(s):  
Ellefsen ◽  
Arzig ◽  
Steiner ◽  
Wellmann ◽  
Runde
Keyword(s):  
Crystal Growth ◽  
Size Distribution ◽  
Growth Conditions ◽  
Source Material ◽  
Process Time ◽  
Process Conditions ◽  
Powder Size ◽  
Growth Interface ◽  
X Ray

We have studied the influence of different SiC powder size distributions and the sublimation behavior during physical vapor transport growth of SiC in a 75 mm and 100 mm crystal processing configuration. The evolution of the source material as well as of the crystal growth interface was carried out using in situ 3D X-ray computed tomography (75 mm crystals) and in situ 2D X-ray visualization (100 mm crystals). Beside the SiC powder size distribution, the source materials differed in the maximum packaging density and thermal properties. In this latter case of the highest packaging density, the in situ X-ray studies revealed an improved growth interface stability that enabled a much longer crystal growth process. During process time, the sublimation-recrystallization behavior showed a much smoother morphology change and slower materials consumption, as well as a much more stable shape of the growth interface than in the cases of the less dense SiC source. By adapting the size distribution of the SiC source material we achieved to significantly enhance stable growth conditions.

Application of In Situ 3D Computed Tomography during PVT Growth of 4H-SiC for the Study of Source Material Consumption under Varying Growth Conditions

2016 ◽  
Vol 858 ◽  
pp. 49-52 ◽  
Author(s):  
P.J. Wellmann ◽  
Lars Fahlbusch ◽  
Michael Salamon ◽  
Norman Uhlmann
Keyword(s):  
Growth Parameters ◽  
Growth Conditions ◽  
Source Material ◽  
Gas Pressure ◽  
Inert Gas ◽  
Material Surface ◽  
Growth Interface ◽  
Axial Temperature ◽  
The Stability

2D and 3D in-situ X-ray visualization was applied to study the behavior of the SiC source material during PVT growth under various growth conditions. Experiments were carried out in two growth chambers for the growth of 3 inch and 4 inch crystals. Growth parameters were varied in the gas room in terms of axial temperature and inert gas pressure. The study addresses the stability of the SiC source material surface. It is shown that a higher inert gas pressure (e.g. 25 mbar) inhibits an unintentional upward evolution of the SiC feedstock that interferes with the crystal growth interface. The latter is related to a suppression of a pronounced recrystallization inside the SiC source. For a low inert gas pressure (e.g. 10 mbar) it is concluded that the axial temperature gradient inside the source material needs to be decreased to less than ca. 10 K/cm.

Studying the Progress of Sintering in Ferrous Powder Compacts by In-Situ Measuring the Thermal Conductivity

2018 ◽  
Vol 18 (2) ◽  
pp. 80-95
Author(s):  
H. Danninger ◽  
G. Leitner ◽  
Ch. Gierl-Mayer
Keyword(s):  
Thermal Conductivity ◽  
Laser Flash ◽  
Sintering Process ◽  
In Situ Characterization ◽  
Dimensional Changes ◽  
Flow Through ◽  
Powder Compacts ◽  
Good Agreement

Abstract In situ characterization of the sintering process is a difficult task, in particular for systems without pronounced dimensional changes. Dilatometry is not too helpful in those cases, and therefore other properties have to be recorded. In the present study, sintering of ferrous powder compacts was studied in situ by measuring the thermal diffusivity a using a laser flash apparatus. This property is a measure to characterise the heat flow through a material; it depends on the contact area between the particles and thus reveals their change during sintering. It is shown that the change of a during sintering of ferrous compacts is much less pronounced than in the case of cemented carbides which is not surprising when regarding the widely differing porosity changes. The results are however in good agreement with expectations when considering some experimental limitations. The trend for the thermal conductivity λ. which can be calculated from a, the specific heat and the density, is in good agreement with that found for the electrical conductivity, both properties being linked through Wiedemann-Franz’ law.

In-Situ Observation Of Aln Formation During Nitridation Of Sapphire By Ultrahigh Vacuum Transmission Electron Microscopy

1997 ◽  
Vol 482 ◽  
Author(s):  
M. Yeadon ◽  
M. T. Marshall ◽  
F. Hamdani ◽  
S. Pekin ◽  
H. Morkoc ◽  
...  
Keyword(s):  
Ultrahigh Vacuum ◽  
Ex Situ ◽  
In Situ Observation ◽  
Island Growth ◽  
Kinetic Measurements ◽  
Transmission Electron ◽  
Before And After ◽  
Subsequent Exposure ◽  
Diffraction Patterns

AbstractUsing a novel ultrahigh vacuum transmission electron microscope (UHV TEM) with insitu molecular beam epitaxy capability we have studied the nitridation of (0001) sapphire upon exposure to ammonia. Atomically flat sapphire surfaces for the experiments were obtained by high temperature annealing. Subsequent exposure to ammonia flow at 950°C led to the successful synthesis of epitaxial AIN; the films were characterized in-situ using TEM. Complimentary ex-situ atomic force microscopy (AFM) was also performed in order to characterize the surface morphology before and after nitridation.The experiments indicate that AIN grows by a 3D island growth mechanism. Electron diffraction patterns suggest an abrupt AIN/sapphire interface with no evidence of the formation of Al–O–N compounds. The rate limiting step in the nitridation reaction appears to be the diffusion of nitrogen and oxygen species between the free surface of the growing AIN film and the reaction interface. It is inferred from kinetic measurements that diffusion of these species occurs along the boundaries between coalescing AIN islands.

scholarly journals Interface Orientation Distribution during Grain Growth in Bulk SrTiO3 Measured by Means of 3D X-Ray Diffraction Contrast Tomography

2012 ◽  
Vol 1421 ◽  
Author(s):  
Melanie Syha ◽  
Wolfgang Rheinheimer ◽  
Michael Bäurer ◽  
Erik M. Lauridsen ◽  
Wolfgang Ludwig ◽  
...  
Keyword(s):  
Grain Growth ◽  
Morphological Changes ◽  
Orientation Distribution ◽  
Ex Situ ◽  
X Ray Diffraction ◽  
Systematic Analysis ◽  
X Ray ◽  
Diffraction Contrast ◽  
Before And After ◽  
Interface Orientation

ABSTRACT3D x-ray diffraction contrast tomography (DCT) is a non-destructive technique for the determination of grain shape and crystallography in polycrystalline bulk materials. Using this technique, a strontium titanate specimen was repeatedly measured between annealing steps.. A systematic analysis of the growth history of selected grains before and after the ex-situ annealing step allows to extract the topological and morphological changes during grain growth. Furthermore, misorientation as well as interface orientation information of the microstructure reconstructions have been determined. The interface normal distribution clearly shows a preference for (100) oriented interfaces in the selected grains when annealed at 1600°C. This observation can be connected to existent interfacial energy estimations resulting from capillarity vector reconstructions.

Real-Time Measurement of the Evolution of Growth Facets during SiC PVT Bulk Growth Using 3-D X-Ray Computed Tomography

2014 ◽  
Vol 778-780 ◽  
pp. 9-12 ◽  
Author(s):  
Georg Neubauer ◽  
Michael Salamon ◽  
Norman Uhlmann ◽  
Peter J. Wellmann
Keyword(s):  
Computed Tomography ◽  
Real Time ◽  
High Precision ◽  
Growth Interface ◽  
X Ray ◽  
Bulk Growth ◽  
Real Time Measurement ◽  
Growth System ◽  
X Ray Computed

In this paper, we present our new setup and technique for obtaining a real-time 3-D volume shape of the SiC crystal using X-ray computed tomography (CT). Hence, it is possible to determine in-situ the shape of the growth interface with high precision at growth temperatures above 2000 °C in a conventional 3" physical vapor transport (PVT) growth system. We show that the size and shape of a facet can be monitored at different stages during growth and furthermore the crystals face boundary can be determined with high precision throughout the whole growth process.

scholarly journals In-situ and ex-situ measurements of thermal conductivity of supercapacitors

Energy ◽  
2014 ◽  
Vol 78 ◽  
pp. 373-383 ◽  
Author(s):  
H.H. Hauge ◽  
V. Presser ◽  
O. Burheim
Keyword(s):  
Thermal Conductivity ◽  
Ex Situ

scholarly journals Chemical Composition and Microhardness of Human Enamel Treated with Fluoridated Whintening Agents. A Study in Situ

2017 ◽  
Vol 11 (1) ◽  
pp. 34-40
Author(s):  
Thais de Mendonça Petta ◽  
Yasmin do Socorro Batista de Lima Gomes ◽  
Renata Antunes Esteves ◽  
Kelson do Carmo Freitas Faial ◽  
Roberta Souza D`Almeida Couto ◽  
...  
Keyword(s):  
Hydrogen Peroxide ◽  
Morphological Changes ◽  
Dental Enamel ◽  
Hardness Test ◽  
Knoop Hardness ◽  
Control Group ◽  
High Concentration ◽  
Significance Level ◽  
Before And After

Background: Dental whitening has been increasingly sought out to improve dental aesthetics, but may cause chemical and morphological changes in dental enamel surfaces. Objective: Assess in situ the effects of high-concentration hydrogen peroxide with and without fluoride on human dental enamel using the ion chromatography test (IC) and the Knoop hardness test (KHN). Material and Methods: Nineteen enamel specimens were prepared using third human molars. These specimens were fixed on molars of volunteers and were divided into groups: OP38-Opalescence Boost PF38%, PO37-Pola Office 37.5% and CO-Control group. For chemical analysis (n= 3), the dentin layer was removed, keeping only the enamel, which was subjected to acidic digestion by microwave radiation. It was necessary to perform sample dilutions for the elements fluorine (F), calcium (Ca) and phosphorus (P) for quantification using the IC test. The KHN (n= 5) was performed before and after the treatments. Five indentations were made, separated by 100 µm, for each specimen using a load of 25 gf for 5 seconds in the microdurometer. The data were analyzed using ANOVA with a 5% significance level. Results: The OP38 group had the largest concentrations of F, Ca and P ions. The PO37 group showed the lowest concentrations of F and Ca ions. The average KHN was not significantly different between the OP38 and PO37 groups. Conclusion: Enamel whitened with hydrogen peroxide containing fluoride had greater concentrations of F, Ca and P ions. The presence of fluoride in the whitening agent did not influence the enamel microhardness.

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