Microstructure, growth mechanisms and electro-optical properties of heteroepitaxial GaN layers on sapphire (0001) substrates

We investigate the structure, growth morphology and the related electro-optical properties of gallium nitride (GaN) films deposited on (0001) sapphire substrates by gas source molecular beam epitaxy (GSMBE) and use transmismission electron microscopy, atomic force microscopy and scanning tunneling microscopy, photoluminescence (PL) and cathodoluminescence (CL). We find two types of specimens: one type which shows a strong UV luminescence (band-to-band transition at 358nm/3.46eV) in CL and PL and only faint yellow luminescence (Gaussian shaped CL/PL peaks at around 528nm/2.35eV), specimen ‘B’, and another type, which shows a strong UV and a comparably strong yellow luminescence, specimen ‘Y’. These two types of specimens have a rough layer surface, specimen ‘Y’ even an islanded one with, facetted hexagonal islands with a width of 1-2μm at a height of 50nm. A correlation of spectrally resolved CL images to the observed defect structure shows: (i) the yellow luminescence is homogeneously distributed over the complete specimen for ‘B’ and ‘Y’ specimens. Our investigations strongly suggest the yellow luminescence to be related to screw dislocations with , which are found randomly distributed in ‘B’ and ‘Y’ specimens with a high density of 1.3·109cm−2; (ii) the strong UV luminescence in ‘Y’ specimens is located in the troughs between adjacent surface islands, where dislocations essentially in small angle grain boundaries of edge type, i.e. with or are located; (iii) in the case of the ‘B’ specimens these dislocations are randomly distributed and so is the luminescence.

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Scanning tunneling microscopy and atomic force microscopy: New tools for biology

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100155864 ◽

1989 ◽

Vol 47 ◽

pp. 778-779

Author(s):

CE Bracker ◽

P. K. Hansma

Keyword(s):

Physical Property ◽

Scanning Probe ◽

Scanning Tunneling ◽

Small Scale ◽

Tunneling Microscopy ◽

Force Microscopy ◽

New Family ◽

Small Probe ◽

Atomic Force ◽

Transmission Electron

A new family of scanning probe microscopes has emerged that is opening new horizons for investigating the fine structure of matter. The earliest and best known of these instruments is the scanning tunneling microscope (STM). First published in 1982, the STM earned the 1986 Nobel Prize in Physics for two of its inventors, G. Binnig and H. Rohrer. They shared the prize with E. Ruska for his work that had led to the development of the transmission electron microscope half a century earlier. It seems appropriate that the award embodied this particular blend of the old and the new because it demonstrated to the world a long overdue respect for the enormous contributions electron microscopy has made to the understanding of matter, and at the same time it signalled the dawn of a new age in microscopy. What we are seeing is a revolution in microscopy and a redefinition of the concept of a microscope.Several kinds of scanning probe microscopes now exist, and the number is increasing. What they share in common is a small probe that is scanned over the surface of a specimen and measures a physical property on a very small scale, at or near the surface. Scanning probes can measure temperature, magnetic fields, tunneling currents, voltage, force, and ion currents, among others.

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Exploring Intramolecular Methyl–Methyl Coupling on a Metal Surface for Edge-Extended Graphene Nanoribbons

Organic Materials ◽

10.1055/s-0041-1726295 ◽

2021 ◽

Vol 03 (02) ◽

pp. 128-133

Author(s):

Zijie Qiu ◽

Qiang Sun ◽

Shiyong Wang ◽

Gabriela Borin Barin ◽

Bastian Dumslaff ◽

...

Keyword(s):

Raman Spectroscopy ◽

Atomic Force Microscopy ◽

High Resolution ◽

Graphene Nanoribbons ◽

Scanning Tunneling ◽

Tunneling Microscopy ◽

Force Microscopy ◽

Methyl Methyl ◽

Atomic Force ◽

Edge Extension

Intramolecular methyl–methyl coupling on Au (111) is explored as a new on-surface protocol for edge extension in graphene nanoribbons (GNRs). Characterized by high-resolution scanning tunneling microscopy, noncontact atomic force microscopy, and Raman spectroscopy, the methyl–methyl coupling is proven to indeed proceed at the armchair edges of the GNRs, forming six-membered rings with sp3- or sp2-hybridized carbons.

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SCANNING PROBE MICROSCOPY BASED NANOSCALE PATTERNING AND FABRICATION

COSMOS ◽

10.1142/s0219607707000207 ◽

2007 ◽

Vol 03 (01) ◽

pp. 1-21 ◽

Cited By ~ 2

Author(s):

XIAN NING XIE ◽

HONG JING CHUNG ◽

ANDREW THYE SHEN WEE

Keyword(s):

Integrated Circuits ◽

Scanning Probe Microscopy ◽

Scanning Probe ◽

Scanning Tunneling ◽

Tunneling Microscopy ◽

Force Microscopy ◽

Nanoscale Patterning ◽

Atomic Force ◽

Probe Microscope ◽

Molecular Manipulation

Nanotechnology is vital to the fabrication of integrated circuits, memory devices, display units, biochips and biosensors. Scanning probe microscope (SPM) has emerged to be a unique tool for materials structuring and patterning with atomic and molecular resolution. SPM includes scanning tunneling microscopy (STM) and atomic force microscopy (AFM). In this chapter, we selectively discuss the atomic and molecular manipulation capabilities of STM nanolithography. As for AFM nanolithography, we focus on those nanopatterning techniques involving water and/or air when operated in ambient. The typical methods, mechanisms and applications of selected SPM nanolithographic techniques in nanoscale structuring and fabrication are reviewed.

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Combined atomic force microscopy and scanning tunneling microscopy imaging of cross-sectioned GaN light-emitting diodes

Scanning ◽

10.1002/sca.4950250109 ◽

2006 ◽

Vol 25 (1) ◽

pp. 45-51 ◽

Cited By ~ 1

Author(s):

J. W. Bender ◽

M. E. Salmon ◽

P. E. Russell

Keyword(s):

Atomic Force Microscopy ◽

Scanning Tunneling Microscopy ◽

Light Emitting Diodes ◽

Scanning Tunneling ◽

Tunneling Microscopy ◽

Microscopy Imaging ◽

Light Emitting ◽

Force Microscopy ◽

Atomic Force

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Micromechanisms of Hydrogen-Assisted Cracking in Super Duplex Stainless Steel Investigated by Scanning Probe Microscopy

Volume 6B: Materials and Fabrication ◽

10.1115/pvp2014-28181 ◽

2014 ◽

Cited By ~ 1

Author(s):

Bai An ◽

Takashi Iijima ◽

Chris San Marchi ◽

Brian Somerday

Keyword(s):

Stainless Steel ◽

Duplex Stainless Steel ◽

Scanning Tunneling ◽

Super Duplex Stainless Steel ◽

Tunneling Microscopy ◽

Force Microscopy ◽

Atomic Force ◽

Hydrogen Assisted Cracking ◽

Cracking Mechanisms ◽

Localized Plastic Deformation

Understanding the micromechanisms of hydrogen-assisted fracture in multiphase metals is of great scientific and engineering importance. By using a combination of scanning electron microscopy (SEM), scanning tunneling microscopy (STM), atomic force microscopy (AFM) and magnetic force microscopy (MFM), the micromorphology of fracture surface and microcrack formation in hydrogen-precharged super duplex stainless steel 2507 are characterized from microscale to nanoscale. The results reveal that the fracture surfaces consist of quasi-brittle facets with riverlike patterns at the microscale, which exhibit rough irregular patterns or remarkable quasi-periodic corrugation patterns at the nanoscale that can be correlated with highly localized plastic deformation. The microcracks preferentially initiate and propagate in ferrite phase and are stopped or deflected by the boundaries of the austenite phase. The hydrogen-assisted cracking mechanisms in super duplex stainless steel are discussed according to the experimental results and hydrogen-enhanced localized plasticity theory.

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Asphaltenes: Fundamental Principles to Oilfield Applications

10.2118/206091-ms ◽

2021 ◽

Author(s):

Oliver Mullins ◽

Andrew Pomerantz ◽

Yunlong Zhang

Keyword(s):

Scanning Tunneling ◽

Quasi Equilibrium ◽

Molecular Architecture ◽

Tunneling Microscopy ◽

Force Microscopy ◽

Viscous Oil ◽

Atomic Force ◽

Fluid Process ◽

Onset Pressure ◽

Reservoir Connectivity

Abstract The sophisticated molecular imaging methods, atomic force microscopy (AFM) and scanning tunneling microscopy (STM), have been utilized to image individual asphaltene molecules, both their atoms and bonds, and their electronic structure. The stunning images have confirmed previous results and have all but resolved the long-standing uncertainties regarding asphaltene molecular architecture. Asphaltenes are also known to have a strong propensity to aggregate. The dominante asphaltene molecular structure and hierarchical nanocolloidal structures have been resolved and codified in the Yen-Mullins model. Use of this model in a simple polymer solution theory has given the first equation of state (EoS) for asphaltene gradients in oilfield reservoirs, the Flory-Huggins-Zuo EoS. With this EoS it is now possible to address reservoir connectivity in new ways; equilibrated asphaltenes imply reservoir connectivity. For reservoirs with disequilibrium of contained fluids, there is often a fluid process occurring in geologic time that precludes equilibrium. The collection of processes leading to equilibrium and those that preclude equilibrium constitute a new technical discipline, reservoir fluid geodynamics (RFG). Several reservoirs are reviewed employing RFG evaluation of connectivity via asphaltene thermodynamics. RFG processes in reservoris often include diffusion, RFG models incorporating simple solution to the diffusion equation coupled with quasi-equilibrium with the FHZ EoS are shown to apply for timelines up to 50 million years, the age of charge in a reservoir. When gas (or condensates) diffuse into oil, the asphaltenes are destabilized and can convect to the base of the reservoir. Increasing asphaltene onset pressure as well as viscous oil and tar mats can be consequences. Depending on specifics of the process, either gooey tar or coal-like asphaltene deposits can form. In addition, the asphaltene structures illuminated by AFM are now being used to account for interfacial properties using simple thermodynamics. At long last, asphaltenes are no longer the enigmatic component of crude oil, instead the resolution of asphaltene structures and dynamics has led to new thermodynamic applications in reservoirs, the new discipline RFG, and a new understanding of tar mats.

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