Non-destructive Detection and Visualization of Extended Defects in 4H-SiC Epilayers

2010 ◽  
Vol 1246 ◽  
Author(s):  
Gan Feng ◽  
Jun Suda ◽  
Tsunenobu Kimoto

AbstractThe extended defects, such as dislocations and in-grown stacking faults (IGSFs), in 4H-SiC epilayers have been detected and visualized by a non-destructive method, the micro photoluminescence (μ-PL) intensity mapping method, at room temperature. The one-to-one correspondence between the extended defects and the μ-PL mapping contrast has been successfully obtained. A threading dislocation corresponds to a dark circle with the reduced intensity in the μ-PL mapping image performed at 390 nm, while a basal plane dislocation dissociates into a single Shockley SF during the measurements. Three kinds of IGSFs have been identified in the samples. Each kind of IGSF shows the distinct PL emission located at 460 nm, 480 nm, and 500 nm, respectively. The shapes and distributions of IGSFs have also been profiled by μ-PL intensity mapping.

2011 ◽  
Vol 679-680 ◽  
pp. 302-305 ◽  
Author(s):  
Gan Feng ◽  
Jun Suda ◽  
Tsunenobu Kimoto

Dislocations in 4H-SiC epilayers were imaged nondestructively by means of micro photoluminescence (-PL) mapping at room temperature. The one-to-one correspondence between the individual dislocations and the -PL mapping contrast has been consistently obtained. By analyzing the reduction of the intensity in the -PL mapping image performed at 390 nm (near band-edge emission), we were able to distinguish threading screw dislocations and threading edge dislocations. Furthermore, the contrast of dislocations in PL-intensity mapping image greatly depends on the carrier lifetimes of the 4H-SiC epilayers. Lifetimes longer than 0.5 s are essential to obtain a discernible contrast for the individual dislocations.


2010 ◽  
Vol 645-648 ◽  
pp. 355-358 ◽  
Author(s):  
Rii Hirano ◽  
Michio Tajima ◽  
Kohei M. Itoh

We investigated the optical properties of stacking faults (SFs) in cubic silicon carbide by photoluminescence (PL) spectroscopy and mapping. The room-temperature PL spectra consisted of a 2.3 eV peak due to nitrogen and two undefined broad peaks at 1.7 eV and 0.95 eV. On the PL intensity mapping for the 2.3 eV peak, SFs appeared as dark lines. SFs which expose carbon atoms (SFC) and silicon atoms (SFSi) on the surface appeared as bright lines and dark lines, respectively, in PL mapping for the 1.7 eV and 0.95 eV peaks. We believe the two undefined peaks are associated with SFC. This technique allows us to detect SFs nondestructively and to distinguish between SFC and SFSi. We further suggest the presence of inhomogeneous stress around SFCs based on the broadening of the 2.3 eV peak.


2013 ◽  
pp. 32-47
Author(s):  
S. V. Osipov

Geobotanical mapping of the territory in riverheads Bureya of 4500 sq.km is carried out and the map of a actual vegetation cover of scale 1 : 200 000 is prepared. The legend of the map is presented in the form of the text with three-level hierarchy of classes. At the heart of structure of a legend of the map such regularities of a vegetation cover, as its latitudinal zonality / altitudinal belts, situation in a relief and dynamic series lie. The largest divisions of the legend reflect, first, change of large classes of mesocombinations of vegetation at the level of belts and, secondly, distinction in a boreal - forestry belt between a vegetation cover of tops and slopes of mountains, on the one hand, and the bottoms of river valleys, with another. Divisions of the legend of the second level reflect, first, vegetation changes in the form of high-rise and barrier changes of subbelts, secondly, distinctions of a vegetation cover in different geomorphological conditions (small and average river valleys, northern slopes, etc.). Divisions of the legend of the second level correspond to dynamic series of units of the third level. Essential addition to it are block diagrams of dynamics of a vegetation cover.


2013 ◽  
Vol 740-742 ◽  
pp. 91-94 ◽  
Author(s):  
Balaji Raghothamachar ◽  
Yu Yang ◽  
Rafael Dalmau ◽  
Baxter Moody ◽  
H. Spalding Craft ◽  
...  

A systematic study on the density and distribution of extended defects in a typical single crystal AlN boule grown by the physical vapor transport (PVT) method has been carried out in order to gain a detailed understanding of the formation of defects such as dislocations and low angle grain boundaries (LAGBs). Boule surface studies reveal that LAGBs are nucleated during initial stages of growth and propagate to the end of growth. Basal plane dislocations (BPDs) are generated during growth due to thermal gradient stresses. Higher BPD densities are found near the LAGBs at the boule edges due to additional stresses from constrained growth. Threading edge dislocations (TEDs) are typically replicated from the seed, and LAGBs composed of arrays of threading dislocation walls are formed to accommodate the c-axis rotation between different groups of threading screw dislocation (TSD) mediated growth centers.


1995 ◽  
Vol 09 (02) ◽  
pp. 103-111
Author(s):  
C. Y. PAN ◽  
H.Q. LIN

By applying a unified real space renormalization group (URG) mapping method, we study the one-dimensional spin-1/2 Ising model with a transverse field (ITF). Unlike the other real space renormalization group methods, the URG method describes the properties of the model at both zero and finite temperatures in a unified way. The results obtained are in good agreement with that obtained by other methods. Application of the URG method to other quantum spin systems is discussed.


2006 ◽  
Vol 527-529 ◽  
pp. 375-378 ◽  
Author(s):  
Toshiyuki Miyanagi ◽  
Hidekazu Tsuchida ◽  
Isaho Kamata ◽  
Tomonori Nakamura ◽  
R. Ishii ◽  
...  

We provide evidence of shrinking of Shockley-type stacking faults (SSFs) in the SiC epitaxial layer by high temperature annealing. Photoluminescence (PL) mapping in combination with high-power laser irradiation makes it possible to investigate the formation of SSFs, which lie between a pair of partial dislocations formed by dissociation of a basal plane dislocation (BPD), without fabrication of pin diodes. Using this technique, we investigated the annealing effect on SSFs. Comparing before and after annealing at 600°C for 10 min, it became obvious that high-temperature annealing results in shrinking of the faulted area of the SSFs. The SSFs form into the same features as those before annealing when high-power laser irradiation is performed again on the same area. This result shows that the faulted area of SSFs shrinks by 600°C annealing but the nuclei of SSFs (BPDs) do not disappear.


2012 ◽  
Vol 504-506 ◽  
pp. 1177-1182 ◽  
Author(s):  
Fritz Klocke ◽  
David Welling ◽  
Jens Dieckmann ◽  
Drazen Veselovac ◽  
Roberto Perez

This paper deals with developments of Wire-EDM technologies for fir tree slot production. The aim of these developments is to substitute certain conventional processes within turbine manufacturing that have been identified as non-optimal like the critical broaching process. Thereby the negative characteristics like inflexible manufacturing processes, high machine tool investment costs and huge energy consumption can be abolished. The objective targets of the conducted research are to meet all safety requirements of the critical components and get an economic manufacturing process. In the first step a special brass wire technology for cutting Ni-based super alloys was developed. Main focus was to meet the requirements of fir tree production concerning aspects of surface integrity and geometry. To measure these aspects on the one hand non-destructive analyses have been performed to guarantee surface roughness and accuracy. On the other hand destructive analyses in terms of cross section polishing for showing thermal influenced rim zones have been prepared. A capable Wire-EDM process is presented.


Author(s):  
Bernd Jürgen Fitzner

Abstract: Stone monuments represent an important part of our world´s cultural heritage. The awareness of increasing stone damage on monuments and the danger of irretrievable loss of cultural heritage have resulted in great efforts worldwide for sustainable monument preservation. A precise damage diagnosis with the comprehensive characterization, interpretation and rating of stone damage represents the basis for effective and economic monument preservation measures. The experienced methodological approach to the assessment of stone damage combines in situ investigation and laboratory studies. The monument mapping method is presented as an established non-destructive procedure for in situ studies on stone damage. It can be applied to all stone types and to all kinds of stone monuments. The use of weathering forms, damage categories and damage indices for the registration, documentation, quantitative evaluation and rating of stone damage is explained. Furthermore, complementary in situ measurements are discussed. A wide range of analytical procedures and weathering simulation tests contribute to modern damage diagnosis on stone monuments.Keywords: damage, stone, monumentsResumo: INVESTIGAÇÃO SOBRE DANOS DO INTEMPERISMO PARA MONUMENTOS EM PEDRA. Os monumentos em pedra representam uma parte importante do patrimônio cultural do mundo. A consciência do aumento dos danos causados ao material pétreo nesses monumentos e o perigo de perda irrecuperável desse património resultaram em grandes esforços a nível mundial para a preservação sustentável desses monumentos. Um diagnóstico preciso de danos com a caracterização, interpretação e avaliação abrangentes desses danos causados às pedras representa a base para a adoção de medidas de conservação eficazes e econômicas. A abordagem metodológica a ser adotada para a avaliação desses danos deve combinar a investigação in situ e estudos laboratoriais. Nessa abordagem o mapeamento de monumentos é apresentado como um procedimento não destrutivo estabelecido para os estudos in situ sobre danos causados às pedras, podendo ser aplicado a todos os tipos de pedra e a todos os tipos de monumentos construídos com a pedra. Nesse trabalho, o uso de formas de intemperismo, categorias de danos e índices de danos para o registro, documentação, avaliação quantitativa e classificação de danos para a pedra é explicado. Além disso, discutem-se medidas complementares a serem adotadas in situ. Uma ampla gama de procedimentos analíticos e testes de simulação de meteorização contribuem para o diagnóstico de danos modernos em monumentos construídos em pedra.Palavras Chave: dano, pedra, monumentos


2020 ◽  
Vol 493 (4) ◽  
pp. 5434-5455 ◽  
Author(s):  
Marta Spinelli ◽  
Anna Zoldan ◽  
Gabriella De Lucia ◽  
Lizhi Xie ◽  
Matteo Viel

ABSTRACT We present a comprehensive analysis of atomic hydrogen (H i) properties using a semi-analytical model of galaxy formation and N-body simulations covering a large cosmological volume at high resolution. We examine the H i mass function and the H i density, characterizing both their redshift evolution and their dependence on hosting halo mass. We analyse the H i content of dark matter haloes in the local Universe and up to redshift z = 5, discussing the contribution of different galaxy properties. We find that different assembly history plays a crucial role in the scatter of this relation. We propose new fitting functions useful for constructing mock H i maps with halo occupation distribution techniques. We investigate the H i clustering properties relevant for future 21 cm intensity mapping (IM) experiments, including the H i bias and the shot-noise level. The H i bias increases with redshift and it is roughly flat on the largest scales probed. The scale dependence is found at progressively larger scales with increasing redshift, apart from a dip feature at z = 0. The shot-noise values are consistent with the ones inferred by independent studies, confirming that shot noise will not be a limiting factor for IM experiments. We detail the contribution from various galaxy properties on the H i power spectrum and their relation to the halo bias. We find that H i poor satellite galaxies play an important role at the scales of the one-halo term. Finally, we present the 21 cm signal in redshift space, a fundamental prediction to be tested against data from future radio telescopes such as Square Kilometre Array.


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