scholarly journals Formation mechanism of threading-dislocation array in AlN layers grown on 6H-SiC (0001) substrates with 3-bilayer-high surface steps

2014 ◽  
Vol 105 (7) ◽  
pp. 071603 ◽  
Author(s):  
Hironori Okumura ◽  
Tsunenobu Kimoto ◽  
Jun Suda
Keyword(s):  
Formation Mechanism ◽  
High Surface ◽  
Threading Dislocation ◽  
Dislocation Array ◽  
Surface Steps

Influence Of Substrate Off-Cut On The Defect Structure In Relaxed Graded Si-Ge/Si Layers

1996 ◽  
Vol 442 ◽  
Author(s):  
Srikanth B. Samavedam ◽  
F. Romanato ◽  
M. S. Goorsky ◽  
E. A. Fitzgerald
Keyword(s):  
Surface Roughness ◽  
Dislocation Structure ◽  
High Speed ◽  
High Surface ◽  
Substantial Improvement ◽  
Threading Dislocation ◽  
Threading Dislocation Density ◽  
Graded Layers ◽  
Spatially Variant ◽  
Edge Dislocations

AbstractRelaxed graded Si-Ge/Si layers can be used in a variety of micro-electronics applications such as templates for III-V/Si integration, in high speed field effect transistor (FET) structures and as detectors in optical communication. Each of these applications requires a different final Ge concentration in the graded Si-Ge layer. With increasing Ge content in the graded layer, some of the materials concerns that need to be addressed are- (i) a high surface roughness, (ii) the formation of dislocation pile-ups, and (iii) an increase in the threading dislocation density. We have shown that there is a substantial improvement in the surface roughness and the dislocation pile-up density of the graded Si-Ge layers by depositing on (001) 6° off-cut substrates. The substrate miscut also facilitates favorable intersections of {111} planes that aid reactions between the 60° dislocations to form edge dislocations with Burgers vectors of the type 1/2<110> and <100> resulting in a novel hexagonal dislocation structure. Such reactions occurred more readily in the Ge-rich regions of the graded layers where the growth temperature was high enough to aid dislocation climb. The edge dislocations with in-plane Burgers vectors lack a tilt component and the decreased rate of tilting in the Ge-rich regions is confirmed by triple crystal X-ray reciprocal space maps. This novel dislocation structure offers opportunities to explore new processes which may eliminate spatially variant strain fields in relaxed epitaxial layers.

scholarly journals Formation Mechanism and Porosity Development in Porous Boron Nitride

2021 ◽  
Author(s):  
Anouk L'Hermitte ◽  
Daniel M. Dawson ◽  
Pilar Ferrer ◽  
Kanak Roy ◽  
Georg Held ◽  
...  
Keyword(s):  
Boron Nitride ◽  
Formation Mechanism ◽  
High Surface ◽  
Scale Up ◽  
High Surface Area ◽  
Inorganic Materials ◽  
Full Potential ◽  
Gaseous Species ◽  
Water Cleaning ◽  
Porosity Development

In the past decade, porous boron nitride (BN) has proven promising as a novel class of inorganic materials in the field of separations and particularly adsorption. Owing to its high surface area and thermal stability, porous BN has been researched for CO2 capture and water cleaning, for instance. However, most research remains at laboratory scale due to a lack of understanding of the formation mechanism of porous BN, which is still largely a ‘black box’ and prevents scale-up. Partial reaction pathways have been unveiled, but they omit critical steps in the formation, including the porosity development, which is key to adsorption. To unlock the potential of porous BN at a larger scale, we have investigated its formation from the perspective of both chemical formation and porosity development. We have characterised reaction intermediates obtained at different temperatures with a range of analytical and spectroscopic tools. Using these analyses, we propose a mechanism that highlights the key stages of BN formation and its porosity, including the intermediates and gaseous species formed in the process. We identified that the formation of non-porous carbon nitride is crucial to form porous BN with release of porogens, such as HCN and CO2. This work paves the way for scaled-up processes to use porous BN to its full potential at industrial level for gas and liquid separations.

Electron Microscopy Investigation of the Role of Surface Steps in the Generation of Dislocations during MOCVD Growth of GaN on 4H-SiC

2006 ◽  
Vol 527-529 ◽  
pp. 1509-1512 ◽  
Author(s):  
N.D. Bassim ◽  
Mark E. Twigg ◽  
Michael A. Mastro ◽  
Philip G. Neudeck ◽  
Charles R. Eddy ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Substrate Surface ◽  
Atomic Scale ◽  
Threading Dislocation ◽  
Threading Dislocations ◽  
Misfit Dislocations ◽  
Nucleation Layer ◽  
Plan View ◽  
Surface Steps

Through the use of specially-prepared on-axis SiC substrates with patterned mesa tops completely free of atomic-scale surface steps, we have previously reported the growth of highquality GaN heteroepitaxial films with greatly reduced threading dislocation densities on the order of 107/cm2. In these films, we reported a defect substructure in which lateral a-type dislocations are present in the nucleation layer but do not bow into threading dislocations during the subsequent GaN growth. This study focuses further on the role of SiC substrate surface steps in the generation of misfit, a-type, and threading dislocations at the heteroepitaxial interface. By using weak-beam imaging (both to eliminate Moiré effects and to observe narrow dislocation images) from plan-view transmission electron microscopy (TEM), we identify dislocations generated on stepped and unstepped mesas and compare their geometries. We observe that misfit dislocations nucleated on an unstepped SiC mesa are confined to one set of a-type Burgers vectors of the form g=1/3 [2110] _ _ , straight and well-ordered so that they are less likely to interact with each other. On the other hand, misfit dislocation structures on a stepped SiC mesa surface are not nearly as well-ordered, having bowed structure with threading dislocations that appear to nucleate at SiC surface steps.

scholarly journals Synthesis of MnO2–CuO–Fe2O3/CNTs catalysts: low-temperature SCR activity and formation mechanism

2019 ◽  
Vol 10 ◽  
pp. 848-855
Author(s):  
Yanbing Zhang ◽  
Lihua Liu ◽  
Yingzan Chen ◽  
Xianglong Cheng ◽  
Chengjian Song ◽  
...  
Keyword(s):  
Low Temperature ◽  
Formation Mechanism ◽  
High Surface ◽  
Surface Oxygen ◽  
Low Dimensional ◽  
Low Temperature Scr

MnO2–CuO–Fe2O3/CNTs catalysts, as a low-dimensional material, were fabricated by a mild redox strategy and used in denitration reactions. A formation mechanism of the catalysts was proposed. NO conversions of 4% MnO2–CuO–Fe2O3/CNTs catalyst of 43.1–87.9% at 80–180 °C were achieved, which was ascribed to the generation of amorphous MnO2, CuO and Fe2O3, and a high surface-oxygen (Os) content.

Double pendeo-epitaxial growth of GaN films with low density of threading dislocation

2001 ◽  
Vol 693 ◽  
Author(s):  
Y. K. Hong ◽  
H. S. Jung ◽  
C-H. Hong ◽  
M.H. Kim ◽  
S-J. Leem
Keyword(s):  
Epitaxial Growth ◽  
Defect Density ◽  
Chemical Vapor ◽  
Band Edge Emission ◽  
Threading Dislocation ◽  
Low Density ◽  
Force Microscopy ◽  
Surface Steps ◽  
Defective Region ◽  
Vertical Growth Rate

AbstractA double pendeo-epitaxy technique for growing uniformly GaN films with low defect density over the entire surface of a substrate has been achieved by metalorganic chemical vapor deposition(MOCVD). The structural properties of the first pendeo-epitaxial layers were optimized with the ratio of the lateral to the vertical growth rate, which is strongly affected by the growth temperature and the TMGa flow rate. The second pendeo-epitaxial growth was performed on the first regrown layers after removing a high defective region originating from underlying GaN seed layer. From the analysis of atomic force microscopy(AFM) images, the termination of surface steps by threading dislocations were not observed at the second regrown GaN layers. This result implies that a very low density of threading dislocation exists on the GaN surface. Cathodoluminescence(CL) results showed a strong band-edge emission from the all regrown regions.

Defects In 4H Silicon Carbide CVD Epilayers

1996 ◽  
Vol 442 ◽  
Author(s):  
L. Zhou ◽  
P. Pirouz ◽  
J. A. Powell
Keyword(s):  
Formation Mechanism ◽  
Chemical Vapor ◽  
Cross Sectional ◽  
Plan View ◽  
Force Microscopy ◽  
Atomic Force ◽  
Surface Steps ◽  
Transmission Electron ◽  
Surface Decoration ◽  
Decoration Technique

AbstractThe characteristic defects of 4H-SiC homoepitaxial thin films grown on bulk substrates using chemical vapor deposition (CVD) are described based on transmission electron microscopy (TEM), atomic force microscopy (AFM) and surface decoration studies. Emphasis is placed on understanding the formation mechanism of surface triangular defects. Cross-sectional TEM observations revealed the existence of two variants of 3C-SiC inclusions in 4H epitaxial films. In the plan-view orientation, g4H = 3304 type reflections were found useful for distinguishing the two variants of 3C-SiC platelets that are present in the 4H epilayer. A decoration technique was employed to reveal the relationship between the 3C platelets and surface features, e.g., surface steps. A formation mechanism for surface triangular defects is proposed, which is partially confirmed by the etch pit patterns obtained on the epilayer surfaces after a molten KOH etch.

Localization of Adenosine Triphosphatase Activity in the Phleom of Nicotiana Tabacum

1972 ◽  
Vol 30 ◽  
pp. 230-231
Author(s):  
James Cronshaw ◽  
Jamison E. Gilder
Keyword(s):  
Plasma Membrane ◽  
Atpase Activity ◽  
Adenosine Triphosphatase ◽  
Higher Plants ◽  
High Surface ◽  
Root Tip ◽  
Animal Cells ◽  
Physiological Processes ◽  
Tip Cells ◽  
Atpase Localization

Adenosine triphosphatase (ATPase) activity has been shown to be associated with numerous physiological processes in both plants and animal cells. Biochemical studies have shown that in higher plants ATPase activity is high in cell wall preparations and is associated with the plasma membrane, nuclei, mitochondria, chloroplasts and lysosomes. However, there have been only a few ATPase localization studies of higher plants at the electron microscope level. Poux (1967) demonstrated ATPase activity associated with most cellular organelles in the protoderm cells of Cucumis roots. Hall (1971) has demonstrated ATPase activity in root tip cells of Zea mays. There was high surface activity largely associated with the plasma membrane and plasmodesmata. ATPase activity was also demonstrated in mitochondria, dictyosomes, endoplasmic reticulum and plastids.

Role of boundaries in the crystallization of amorphous films

1988 ◽  
Vol 46 ◽  
pp. 626-627
Author(s):  
D. A. Smith
Keyword(s):  
Low Temperature ◽  
Amorphous State ◽  
Nucleation And Growth ◽  
Amorphous Films ◽  
Island Nucleation ◽  
Surface Steps ◽  
Transmission Electron ◽  
Component Systems ◽  
Temperature Deposition

The nucleation and growth processes which lead to the formation of a thin film are particularly amenable to investigation by transmission electron microscopy either in situ or subsequent to deposition. In situ studies have enabled the observation of island nucleation and growth, together with addition of atoms to surface steps. This paper is concerned with post-deposition crystallization of amorphous alloys. It will be argued that the processes occurring during low temperature deposition of one component systems are related but the evidence is mainly indirect. Amorphous films result when the deposition conditions such as low temperature or the presence of impurities (intentional or unintentional) preclude the atomic mobility necessary for crystallization. Representative examples of this behavior are CVD silicon grown below about 670°C, metalloids, such as antimony deposited at room temperature, binary alloys or compounds such as Cu-Ag or Cr O2, respectively. Elemental metals are not stable in the amorphous state.

In Situ microscopy of the anodic etching of silicon

1995 ◽  
Vol 53 ◽  
pp. 232-233
Author(s):  
Frances M. Ross ◽  
Peter C. Searson
Keyword(s):  
Composite Structures ◽  
High Surface ◽  
High Surface Area ◽  
Chemical Properties ◽  
Selective Etching ◽  
Silicon On Insulator ◽  
Second Phase ◽  
Porous Layers ◽  
New Class ◽  
Porous Semiconductors

Porous semiconductors represent a relatively new class of materials formed by the selective etching of a single or polycrystalline substrate. Although porous silicon has received considerable attention due to its novel optical properties1, porous layers can be formed in other semiconductors such as GaAs and GaP. These materials are characterised by very high surface area and by electrical, optical and chemical properties that may differ considerably from bulk. The properties depend on the pore morphology, which can be controlled by adjusting the processing conditions and the dopant concentration. A number of novel structures can be fabricated using selective etching. For example, self-supporting membranes can be made by growing pores through a wafer, films with modulated pore structure can be fabricated by varying the applied potential during growth, composite structures can be prepared by depositing a second phase into the pores and silicon-on-insulator structures can be formed by oxidising a buried porous layer. In all these applications the ability to grow nanostructures controllably is critical.

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