Electron Microscope Study of Strain in InGaN Quantum Wells in GaN Nanowires

2009 ◽  
Vol 1184 ◽  
Author(s):  
Roy Geiss ◽  
Kris Bertness ◽  
Alexana Roshko ◽  
David Read
Keyword(s):  
Electron Microscope ◽  
Quantum Wells ◽  
Cross Sections ◽  
Lattice Spacing ◽  
Gan Nanowires ◽  
Transmission Electron ◽  
Lattice Images ◽  
Electron Microscopes ◽  
Scanning Electron Microscopes ◽  
Ingan Quantum Wells

AbstractStrains in GaN nanowires with InGaN quantum wells (QW) were measured from transmission electron microscope (TEM) images. The nanowires, all from a single growth run, are single crystals of the wurtzite structure that grow along the <0001> direction, and are approximately 1000 nm long and 60 nm to 130 nm wide with hexagonal cross-sections. The In concentration in the QWs ranges from 12 to 15 at %, as determined by energy dispersive spectroscopy in both the transmission and scanning electron microscopes. Fourier transform (FT) analyses of <0002> and <1100> lattice images of the QW region show a 4 to 10 % increase of the c-axis lattice spacing, across the full specimen width, and essentially no change in the a-axis value. The magnitude of the changes in the c-axis lattice spacing far exceeds values that would be expected by using a linear Vegard's law for GaN – InN with the measured In concentration. Therefore the increases are considered to represent tensile strains in the <0001> direction. Visual representations of the location and extent of the strained regions were produced by constructing inverse FT (IFT) images from selected regions in the FT covering the range of c-axis lattice parameters in and near the QW. The present strain values for InGaN QW in nanowires are larger than any found in the literature to date for other forms of InxGa1-xN (QW)/GaN.

The Observation of NBC Precipitates In Steels In The Nanometer Range Using A Field Emission Gun Scanning Electron Microscope

1997 ◽  
Vol 3 (S2) ◽  
pp. 1243-1244 ◽  
Author(s):  
Raynald Gauvin ◽  
Steve Yue
Keyword(s):  
Electron Microscope ◽  
Scanning Electron Microscope ◽  
Field Emission ◽  
Incident Electron Energy ◽  
Beam Diameter ◽  
Probe Diameter ◽  
Transmission Electron ◽  
Electron Microscopes ◽  
Scanning Electron Microscopes ◽  
Scanning Electron

The observation of microstructural features smaller than 300 nm is generally performed using Transmission Electron Microscopy (TEM) because conventional Scanning Electron Microscopes (SEM) do not have the resolution to image such small phases. Since the early 1990’s, a new generation of microscopes is now available on the market. These are the Field Emission Gun Scanning Electron Microscope with a virtual secondary electron detector. The field emission gun gives a higher brightness than those obtained using conventional electron filaments allowing enough electrons to be collected to operate the microscope with incident electron energy, E0, below 5 keV with probe diameter smaller than 5 nm. At 1 keV, the electron range is 60 nm in aluminum and 10 nm in iron (computed using the CASINO program). Since the electron beam diameter is smaller than 5 nm at 1 keV, the resolution of these microscopes becomes closer to that of TEM.

The Morphology of Obliterative Arterial Diseases in Statu Nascendi

1979 ◽  
Author(s):  
M. Marshall ◽  
J. Staubesand ◽  
H. Hese
Keyword(s):  
Risk Factors ◽  
Electron Microscope ◽  
Blood Platelet ◽  
Arterial Disease ◽  
Transmission Electron ◽  
Electron Microscopes ◽  
Scanning Electron Microscopes ◽  
Mini Pigs ◽  
Scanning Electron ◽  
Blood Platelet Aggregation

The arteries of mini pigs which had been exposed to the local or systemic action of recognised ‘risk factors’ for arterial disease were examined with the light microscope, and the transmission and scanning electron microscopes. Initially the scanning instrument revealed adhesions of platelets in different stages of development, but showed an apparently intact endothelium. With the transmission electron microscope, however, degenerative changes in the endothelium could be observed. Increased blood platelet aggregation was also present. After a few weeks we could see a remarkable focal thickening of the intima, together with deposits on the endothelium of platelets, erythrocytes and fibrin (“mixed microparietal thrombosis”). After 6 months fully developed arteriosclerosis of the abdominal aorta had appeared.

scholarly journals Sub-Ångstrom Low-Voltage Performance of a Monochromated, Aberration-Corrected Transmission Electron Microscope

2010 ◽  
Vol 16 (4) ◽  
pp. 386-392 ◽  
Author(s):  
David C. Bell ◽  
Christopher J. Russo ◽  
Gerd Benner
Keyword(s):  
Electron Microscope ◽  
Electron Energy ◽  
Transmission Electron Microscope ◽  
Cross Sections ◽  
Materials Science ◽  
Low Voltage ◽  
Transmission Electron ◽  
Electron Microscopes ◽  
Voltage Performance ◽  
Aberration Corrected

AbstractLowering the electron energy in the transmission electron microscope allows for a significant improvement in contrast of light elements and reduces knock-on damage for most materials. If low-voltage electron microscopes are defined as those with accelerating voltages below 100 kV, the introduction of aberration correctors and monochromators to the electron microscope column enables Ångstrom-level resolution, which was previously reserved for higher voltage instruments. Decreasing electron energy has three important advantages: (1) knock-on damage is lower, which is critically important for sensitive materials such as graphene and carbon nanotubes; (2) cross sections for electron-energy-loss spectroscopy increase, improving signal-to-noise for chemical analysis; (3) elastic scattering cross sections increase, improving contrast in high-resolution, zero-loss images. The results presented indicate that decreasing the acceleration voltage from 200 kV to 80 kV in a monochromated, aberration-corrected microscope enhances the contrast while retaining sub-Ångstrom resolution. These improvements in low-voltage performance are expected to produce many new results and enable a wealth of new experiments in materials science.

Microstructure of InGaN Quantum Wells

1997 ◽  
Vol 482 ◽  
Author(s):  
F. A. Ponce ◽  
D. Cherns ◽  
W. Goetz ◽  
R. S. Kern
Keyword(s):  
Electron Microscopy ◽  
Quantum Wells ◽  
Dark Field ◽  
Growth Surface ◽  
Misfit Dislocations ◽  
Inhomogeneous Distribution ◽  
Adjacent Layer ◽  
Transmission Electron ◽  
Lattice Images ◽  
Ingan Quantum Wells

AbstractThe microstructure of lnxGal-xN quantum wells with intermediate indium concentrations (x = 0.28 and 0.52) has been studied using transmission electron microscopy. High-resolution lattice images and dark-field images taken under high tilt conditions indicate that the quantum wells are inhomogeneous in character. Most of the area of the quantum wells is pseudomorphic with the GaN adjacent layer. However, misfit dislocations are sometimes observed, although with an inhomogeneous distribution. Strained cluster regions are observed in the high-indium concentration quantum wells, with dimensions ranging fi'om 3 to 10 nm in diameter. Evidence is presented suggesting the extent of clustering depends on the exact orientation of the growth surface which is related to the columnar nature of the GaN/sapphire epitaxy.

The Use of a Lanthanum Hexaboride Filament in a Transmission Electron Microscope - The Philips EM-400

1977 ◽  
Vol 35 ◽  
pp. 64-65 ◽  
Author(s):  
V. R. Mumaw ◽  
B. L. Munger
Keyword(s):  
Electron Microscope ◽  
Transmission Electron Microscope ◽  
Lanthanum Hexaboride ◽  
Electron Source ◽  
Transmission Electron ◽  
Electron Microscopes ◽  
Scanning Electron Microscopes ◽  
Scanning Electron

The use of lanthanum hexaboride (LaBg) as an electron source in scanning electron microscopes equipped with an ion pumped emission chamber at less than 10~6 torr, has proven to be very advantageous. It was not until the introduction of the Philips EM-400 that a standard commercially available transmission electron microscope was differentially pumped between the emission chamber and the viewing chamber and capable of achieving a vacuum suitable for utilizing this type of electron source.Only minor modifications were necessary to use the LaBg filament (Kimbal Physics, Wilton, N.H.) in the Philips EM-400 electron microscope. The Wehnelt cap was modified so that the Wehnelt aperture can be removed without disassembly of the cap (Fig. 1). The Wehnelt aperture is 0.7 mm in diameter. A simple spanner wrench is used to remove the Wehnelt aperture. Rough centering of the filament was quite easy using a Zeiss operating stereomicroscope at 25X with the Wehnelt aperture removed.

Semiconductor X-Ray Detection in the Electron Microscope

1969 ◽  
Vol 27 ◽  
pp. 130-131
Author(s):  
R. H. Duff ◽  
S. L. Bender
Keyword(s):  
Electron Microscope ◽  
Solid State ◽  
High Resolution ◽  
Gas Flow ◽  
X Ray ◽  
Solid State Detectors ◽  
Transmission Electron ◽  
Electron Microscopes ◽  
Scanning Electron Microscopes ◽  
Conventional Transmission Electron Microscope

With the introduction of solid state detectors having resolutions of 300 eV or better, the feasibility of an efficient, nongeometry dependent X-ray detector of high resolution became a reality. The use of X-ray detecting systems in conjunction with electron microscopes has been limited to the dispersive type which is highly dependent on geometry or to the gas flow proportional counter which has poor resolution. Recently, high resolution solid state detectors have been used with scanning electron microscopes; however, no use has been made of them in the conventional transmission electron microscope. The usefulness of an elemental analysis together with morphological and crystallographic information is obvious.

7-beam lattice images of (110) oriented Ge

1978 ◽  
Vol 36 (1) ◽  
pp. 290-291
Author(s):  
J.R. Parsons ◽  
C.W. Hoelke
Keyword(s):  
Image Features ◽  
Objective Lens ◽  
Lattice Plane ◽  
Lattice Image ◽  
Crystalline Defects ◽  
Transmission Electron ◽  
Lattice Images ◽  
Electron Microscopes ◽  
Structural Aspects ◽  
Beam Lattice

The direct imaging of a crystal lattice has intrigued electron microscopists for many years. What is of interest, of course, is the way in which defects perturb their atomic regularity. There are problems, however, when one wishes to relate aperiodic image features to structural aspects of crystalline defects. If the defect is inclined to the foil plane and if, as is the case with present 100 kV transmission electron microscopes, the objective lens is not perfect, then terminating fringes and fringe bending seen in the image cannot be related in a simple way to lattice plane geometry in the specimen (1).The purpose of the present work was to devise an experimental test which could be used to confirm, or not, the existence of a one-to-one correspondence between lattice image and specimen structure over the desired range of specimen spacings. Through a study of computed images the following test emerged.

Remote On-Line Control of a High-Voltage in situ Transmission Electron Microscope with A Rational User Interface

1996 ◽  
Vol 54 ◽  
pp. 384-385
Author(s):  
M.A. O’Keefe ◽  
J. Taylor ◽  
D. Owen ◽  
B. Crowley ◽  
K.H. Westmacott ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Electron Microscope ◽  
User Interface ◽  
Transmission Electron Microscope ◽  
High Voltage ◽  
Materials Science ◽  
Transmission Electron ◽  
On Line ◽  
Electron Microscopes

Remote on-line electron microscopy is rapidly becoming more available as improvements continue to be developed in the software and hardware of interfaces and networks. Scanning electron microscopes have been driven remotely across both wide and local area networks. Initial implementations with transmission electron microscopes have targeted unique facilities like an advanced analytical electron microscope, a biological 3-D IVEM and a HVEM capable of in situ materials science applications. As implementations of on-line transmission electron microscopy become more widespread, it is essential that suitable standards be developed and followed. Two such standards have been proposed for a high-level protocol language for on-line access, and we have proposed a rational graphical user interface. The user interface we present here is based on experience gained with a full-function materials science application providing users of the National Center for Electron Microscopy with remote on-line access to a 1.5MeV Kratos EM-1500 in situ high-voltage transmission electron microscope via existing wide area networks. We have developed and implemented, and are continuing to refine, a set of tools, protocols, and interfaces to run the Kratos EM-1500 on-line for collaborative research. Computer tools for capturing and manipulating real-time video signals are integrated into a standardized user interface that may be used for remote access to any transmission electron microscope equipped with a suitable control computer.

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