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Michael A. O'keefe - One of the best experts on this subject based on the ideXlab platform.
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Towards half-Angstrom resolution: From One Angstrom Microscope to TEAM
2020Co-Authors: Michael A. O'keefeAbstract:Author(s): O'Keefe, Michael A. | Abstract: Sub-Angstrom resolution is important for nanotechnology. Metal atoms can be routinely imaged in TEM specimens at resolutions from 2Angstrom to 1.5Angstrom. Better resolutions (~1Angstrom) are required to "see" lighter atoms such as carbon, nitrogen and lithium. Once Cs is corrected, microscope information limit controls resolution. The one-Angstrom microscope project at LBNL has demonstrated the capability of 0.78angsrom resolution at 300keV. The Transmission Electron Achromatic Microscope (TEAM) is proposed to reach resolutions of 0.5Angstrom using hardware correction of Cs, a monochromator (to reduce electron-beam energy spread and improve its information limit beyond that of the One-Angstrom microscope), and chromatic aberration correction to allow a range of electron energies to be focussed together. Methods employed in design and implementation of the successful One-Angstrom microscope project can be used to determine appropriate parameters for the TEAM. Calculations show that a Cc corrector is not required for TEAM to reach 0. 5Angstrom at 300keV or 200keV, provided that energy spreads can be reduced to 0.4eV and 0.2eV respectively. These values allow substantial beam current. At lower voltages, TEAM would require stricter limits on energy spread to reach the targeted 0.5Angstrom resolution. No improvement in HT stability is required to improve the information limit per se since the monochromator determines the energy spread in the beam. However, improved HT will improve the beam current statistics (number of electrons passing through the monochromator) by placing more of the electrons closer to the center of the energy-spread distribution.
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Imaging Lithium Atoms at Sub-Angstrom Resolution
Lawrence Berkeley National Laboratory, 2005Co-Authors: Michael A. O'keefe, Yang Shao-hornAbstract:John Cowley and his group at ASU were pioneers in the use of transmission electron microscopy (TEM) for high-resolution imaging. Three decades ago they achieved images showing the crystal unit cell content at better than 4A resolution. Over the years, this achievement has inspired improvements in resolution that have enabled researchers to pinpoint the positions of heavy atom columns within the cell. More recently, this ability has been extended to light atoms as resolution has improved. Sub-Angstrom resolution has enabled researchers to image the columns of light atoms (carbon, oxygen and nitrogen) that are present in many complex structures. By using sub-Angstrom focal-series reconstruction of the specimen exit surface wave to image columns of cobalt, oxygen, and lithium atoms in a transition metal oxide structure commonly used as positive electrodes in lithium rechargeable batteries, we show that the range of detectable light atoms extends to lithium. HRTEM at sub-Angstrom resolution will provide the essential role of experimental verification for the emergent nanotech revolution. Our results foreshadow those to be expected from next-generation TEMs with CS-corrected lenses and monochromated electron beams.
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Seeing Atoms at Sub-Ångstrom Resolution with Aberration-Corrected TEM
Microscopy and Microanalysis, 2004Co-Authors: Michael A. O'keefeAbstract:Author(s): O'Keefe, Michael A. | Abstract: Hardware and software correction of spherical aberration have each produced sub-Angstrom images, and allowed the imaging of light atoms such as oxygen. The LBNL One-Angstrom Microscope (O Angstrom M) combines a modified CM300FEG/UT TEM with FEI focal-series reconstruction software to achieve sub-Angstrom resolution to 0.78 Angstrom. Modifications include hardware correction of 3-fold astigmatism to 0.68 Angstrom and information limit extension to 0.78 Angstrom. The O Angstrom M can image atoms as light (small) as nitrogen, carbon, and lithium. Focal-series reconstruction (FSR) compensates for imperfect objective lens transfer, and provides improvement over any single image. Reconstructed O Angstrom M images, assembled from 20-member focal series, are "cleaner" than single-shot images, due to lack of second-order contributions. However, second-order components can be removed from single images by subtracting a minimum-contrast image, thus extending the interpretable specimen thickness. In general, TEM images are able to depict atom positions just as well as do FSR images, provided both have the same resolution.
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Reaching sub-Angstrom resolution with a mid-voltage TEM
Lawrence Berkeley National Laboratory, 2004Co-Authors: Michael A. O'keefe, Crispin J.d. Hetherington, E. Chris NelsonAbstract:Phase-contrast imaging in the high-resolution electron micrscope produces images with peaks at atom positions by extracting the spatial distribution of the relative phase from the electron wave. Usually, the electron wave is imaged by direct interference of diffracted beams at optimum focus. Instead, the One-Angstrom Microscope uses focal-series reconstruction software to derive the relative electron phase from a series of images taken over a range of focus, with peaks that correspond to the atom positions at a resolution that extends to the microscope information limit. Tests using a silicon specimen tilted into [112] orientation show that the O Angstrom M has achieved a world-record resolution of 0.78 Angstrom.
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Sub-Angstrom electron microscopy for sub-Angstrom nano-metrology
2004Co-Authors: Michael A. O'keefe, Lawrence F. AllardAbstract:The revolution in nanoscale science and technology requires instrumentation for observation and metrology - we must be able to see and measure what we build. Because nano-devices operate on the level of a few molecules, or even a few atoms, accurate atomic-scale imaging is called for. High-resolution aberration-corrected electron microscopes (both TEM and STEM) can provide valuable measurements at the sub-Angstrom level. Over the next decade, extension of TEM and STEM resolutions to half-Angstrom levels by next-generation aberration-corrected electron microscopes will advance the capabilities of these essential tools for atomic-scale structural characterization. Because improvements in resolution allow for separation of atom columns in many more projection directions, these microscopes will provide much improved three-dimensional characterization of the shape and internal structure of nanodevices and catalyst nanoparticles (perhaps even true 3-D imaging), and hence provide essential feedback in the nano-theory/construction/measurement loop.
B N Holben - One of the best experts on this subject based on the ideXlab platform.
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Angstrom exponent and bimodal aerosol size distributions
Journal of Geophysical Research, 2006Co-Authors: Gregory L Schuster, Oleg Dubovik, B N HolbenAbstract:[1] Power laws have long been used to describe the spectral dependence of aerosol extinction, and the wavelength exponent of the aerosol extinction law is commonly referred to as the Angstrom exponent. The Angstrom exponent is often used as a qualitative indicator of aerosol particle size, with values greater than 2 indicating small particles associated with combustion byproducts, and values less than 1 indicating large particles like sea salt and dust. In this study, we investigate the relationship between the Angstrom exponent and the mode parameters of bimodal aerosol size distributions using Mie theory calculations and Aerosol Robotic Network (AERONET) retrievals. We find that Angstrom exponents based upon seven wavelengths (0.34, 0.38, 0.44, 0.5, 0.67, 0.87, and 1.02 μm) are sensitive to the volume fraction of aerosols with radii less then 0.6 μm but not to the fine mode effective radius. The Angstrom exponent is also known to vary with wavelength, which is commonly referred to as curvature; we show how the spectral curvature can provide additional information about aerosol size distributions for intermediate values of the Angstrom exponent. Curvature also has a significant effect on the conclusions that can be drawn about two-wavelength Angstrom exponents; long wavelengths (0.67, 0.87 μm) are sensitive to fine mode volume fraction of aerosols but not fine mode effective radius, while short wavelengths (0.38, 0.44 μm) are sensitive to the fine mode effective radius but not the fine mode volume fraction.
Gunther G Andersson - One of the best experts on this subject based on the ideXlab platform.
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experimental depth profiles of surfactants ions and solvent at the Angstrom scale studies of cationic and anionic surfactants and their salting out
Journal of Physical Chemistry B, 2020Co-Authors: Xianyuan Zhao, Gilbert M Nathanson, Gunther G AnderssonAbstract:Neutral impact ion scattering spectroscopy (NICISS) is used to measure the depth profiles of ionic surfactants, counterions, and solvent molecules on the Angstrom scale. The chosen surfactants are 0.010 m tetrahexylammonium bromide (THA+/Br–) and 0.0050 m sodium dodecyl sulfate (Na+/DS–) in the absence and presence of 0.30 m NaBr in liquid glycerol. NICISS determines the depth profiles of the elements C, O, Na, S, and Br through the loss in energy of 5 keV He atoms that travel into and out of the liquid, which is then converted into depth. In the absence of NaBr, we find that THA+ and its Br– counterion segregate together because of charge attraction, forming a narrow double layer that is 10 A wide and 150 times more concentrated than in the bulk. With the addition of NaBr, THA+ is “salted out” to the surface, increasing the interfacial Br– concentration by 3-fold and spreading the anions over a ∼30 A depth. Added NaBr similarly increases the interfacial concentration of DS– ions and broadens their positions. Conversely, the dissolved Br– ions are significantly depleted over a depth of 0–40 A from the surface because of charge repulsion from DS– ions within the interfacial region. These different interfacial Br– propensities correlate with previously measured gas–liquid reactivities: gaseous Cl2 readily reacts with Br– ions in the presence of THA+ but drops 70-fold in the presence of DS–, demonstrating that surfactant headgroup charge controls the reactivity of Br– through changes in its depth profile.
Ks Knight - One of the best experts on this subject based on the ideXlab platform.
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The crystal structure of perdeuterated methanol monoammoniate (CD3OD center dot ND3) determined from neutron powder diffraction data at 4.2 and 180 K
Journal of Applied Crystallography, 2009Co-Authors: Ks KnightAbstract:The crystal structure of perdeuterated methanol monoammoniate, CD3OD center dot ND3, has been solved from neutron powder diffraction data collected at 4.2 and 180 K. The crystal structure is orthorhombic, space group Pbca (Z = 8), with unit-cell dimensions a = 11.02320 (7), b = 7.66074 (6), c = 7.59129 (6) Angstrom, V = 641.053 (5) Angstrom(3) [rho(calc) = 1162.782 (9) kg m(-3)] at 4.2 K, and a = 11.21169 (5), b = 7.74663 (4), c = 7.68077 (5) Angstrom, V = 667.097 (4) Angstrom(3) [rho(calc) = 1117.386 (7) kg m(-3)] at 180 K. The crystal structure was determined by ab initio methods from the powder data; atomic coordinates and anisotropic displacement parameters were subsequently refined by the Rietveld method to Rp < 3% at both temperatures. The crystal comprises a sheet-like structure in the bc crystallographic plane, consisting of strongly hydrogen bonded elements; these sheets are stacked along the a axis, and adjacent sheets are linked by what may be comparatively weak C-D center dot center dot center dot O hydrogen bonds. Within the strongly bonded sheet structure, ND3 molecules are tetrahedrally coordinated by the hydroxy moieties of the methanol molecule, accepting one hydrogen bond (O-D center dot center dot center dot N) of length similar to 1.75 Angstrom, and donating three hydrogen bonds (N-D center dot center dot center dot O) of length 2.15-2.25 Angstrom. Two of the methyl deuterons appear to participate in weak interlayer hydrogen bonds (C-D center dot center dot center dot O) of length 2.7-2.8 Angstrom. The hydrogen bonds are ordered at both 4.2 and 180 K. The relative volume change on warming from 4.2 to 180 K, Delta V/V, is +4.06%, which is comparable to, but more nearly isotropic (as determined from the relative change in axial lengths, e. g. Delta a/a) than, that observed in deuterated methanol monohydrate.
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The crystal structure and thermal expansion tensor of MgSO4-11D(2)O(meridianiite) determined by neutron powder diffraction
PHYS CHEM MINER, 2008Co-Authors: Ks KnightAbstract:We have collected high-resolution neutron powder diffraction patterns from MgSO4 center dot 11D(2)O over the temperature range 4.2-250 K. The crystal is triclinic, space-group P (1) over bar (Z = 2) with a = 6.72746(6) Angstrom, b = 6.78141(6) Angstrom, c = 17.31803(13) Angstrom, alpha = 88.2062(6)degrees, beta = 89.4473(8)degrees, gamma = 62.6075(5)degrees, and V = 701.140(6) Angstrom(3) at 4.2 K, and a = 6.75081(3) Angstrom, b = 6.81463(3) Angstrom, c = 17.29241(6) Angstrom, alpha = 88.1183(3)degrees, beta = 89.4808(3)degrees, gamma = 62.6891(3)degrees, and V = 706.450(3) Angstrom(3) at 250 K. Structures were refined to wRp = 3.99 and 2.84% at 4.2 and 250 K, respectively. The temperature dependence of the lattice parameters over the intervening range have been fitted with a modified Einstein oscillator model which was used to obtain the coefficients of the thermal expansion tensor. The volume thermal expansion, alpha(V), is considerably smaller than ice Ih at all temperatures, and smaller even than MgSO4 center dot 7D(2)O (although partial derivative alpha(V)/partial derivative T is very similar for both sulfates); MgSO4 center dot 11D(2)O exhibits negative alpha(V) below 55 K (compared to 70 K in D2O ice Ih and 20 K in MgSO4 center dot 7D(2)O) The relationship between the magnitude and orientation of the principal axes of the expansion tensor and the main structural elements are discussed.
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Crystal structures and thermal expansion of alpha-MgSO4 and beta-MgSO4 from 4.2 to 300 K by neutron powder diffraction
Journal of Applied Crystallography, 2007Co-Authors: Ks KnightAbstract:Detailed neutron powder diffraction measurements have been carried out on two polymorphs of anhydrous magnesium sulfate, alpha-MgSO4 and beta-MgSO4. alpha-MgSO4 is orthorhombic, space group Cmcm (Z = 4); at 4.2 K the unit-cell dimensions are a = 5.16863 (3), b = 7.86781 (5), c = 6.46674 (5) Angstrom, V = 262.975 (2) Angstrom(3) [rho(calc) = 3040.16 (2) kg m(-3)], and at 300 K, a = 5.17471 (3), b = 7.87563 (5), c = 6.49517 (5) Angstrom, V = 264.705 (2) Angstrom(3) [rho(calc) = 3020.29 (2) kg m(-3)]. The axial and volumetric thermal expansion coefficients are positive at all temperatures and exhibit no unusual behaviour. Structures were refined at 4.2 and 300 K to R-P < 3%; less precise structural parameters were determined during warming from 4.2 to 300 K. beta-MgSO4 has a more complex structure, crystallizing in space group Pbnm (Z = 4); the unit-cell dimensions at 4.2 K are a = 4.73431 (8), b = 8.58170 (12), c = 6.67266 (11) Angstrom, V = 271.100 (5) Angstrom(3) [rho(calc) = 2949.04 (5) kg m(-3)], and at 300 K, a = 4.74598 (7), b = 8.58310 (10), c = 6.70933 (10) Angstrom, V = 273.306 (4) Angstrom(3) [rho(calc) = 2925.42 (4) kg m(-3)]. The thermal expansivities of the a and c axes, and the volumetric thermal expansion coefficient, are positive at all temperatures and normally behaved. However, the thermal expansion of the b axis is both very small and negative below similar to 125 K. Structural and thermal motion parameters for beta-MgSO4 as a function of temperature are also reported.
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Neutron powder diffraction studies of sulfuric acid hydrates. I. The structure of sulfuric acid hemitriskaidekahydrate D2SO4 center dot 6 1/2D(2)O
J CHEM PHYS, 2006Co-Authors: Ks KnightAbstract:We report the first neutron diffraction data from D(2)SO(4)(.)6 1/2D(2)O. The crystal is monoclinic, space group Cm, with four formula units per unit cell. At 4.2 K the unit cell dimensions are a = 6.253 26(4) Angstrom, b= 26.813 62(10) Angstrom, c= 5.908 45 (2) Angstrom, and beta = 112.1939 (3)degrees [V= 917.286(6) Angstrom(3) and rho((deuterated)) = 1664.14(2) kg m(-3)]. The deuteron positions refined from the neutron data are in agreement with those established by single crystal x-ray analysis [D. Mootz and A. Merschenz-Quack, Z. Naturforsch. B 42, 1231 (1987)], but not with those found from the ab initio simulation of Hirsch and Ojamae [Acta Crystallogr, Sect. B: Struct. Sci. 60, 179 (2004)]. The crystal consists of SO42-, D3O+ ions, and D2O molecules hydrogen bonded to form a layered structure in which sheets of "icelike" D3O+ and D2O are separated by layers of opposing SO42- tetrahedra. (c) 2006 American Institute of Physics.
Ren Bao Liu - One of the best experts on this subject based on the ideXlab platform.
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Angstrom-Resolution Magnetic Resonance Imaging of Single Molecules via Wave-Function Fingerprints of Nuclear Spins
Physical Review Applied, 2016Co-Authors: Wen Long Ma, Ren Bao LiuAbstract:Single-molecule sensitivity of nuclear magnetic resonance (NMR) and Angstrom resolution of magnetic resonance imaging (MRI) are the highest challenges in magnetic microscopy. Recent development in dynamical-decoupling- (DD) enhanced diamond quantum sensing has enabled single-nucleus NMR and nanoscale NMR. Similar to conventional NMR and MRI, current DD-based quantum sensing utilizes the “frequency fingerprints” of target nuclear spins. The frequency fingerprints by their nature cannot resolve different nuclear spins that have the same noise frequency or differentiate different types of correlations in nuclear-spin clusters, which limit the resolution of single-molecule MRI. Here we show that this limitation can be overcome by using “wave-function fingerprints” of target nuclear spins, which is much more sensitive than the frequency fingerprints to the weak hyperfine interaction between the targets and a sensor under resonant DD control. We demonstrate a scheme of Angstrom-resolution MRI that is capable of counting and individually localizing single nuclear spins of the same frequency and characterizing the correlations in nuclear-spin clusters. A nitrogen-vacancy-center spin sensor near a diamond surface, provided that the coherence time is improved by surface engineering in the near future, may be employed to determine with Angstrom resolution the positions and conformation of single molecules that are isotope labeled. The scheme in this work offers an approach to breaking the resolution limit set by the “frequency gradients” in conventional MRI and to reaching the Angstrom-scale resolution.
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Scheme of Angstrom-resolution magnetic resonance imaging of single molecules via wavefunction fingerprints of nuclear spins
arXiv:1510.04081 [quant-ph], 2015Co-Authors: Wen Long Ma, Ren Bao LiuAbstract:Nuclear magnetic resonance (NMR) with single molecule sensitivity and magnetic resonance imaging (MRI) with Angstrom resolution are the highest challenges in magnetic microscopy. Recent development in dynamical decoupling (DD) enhanced diamond quantum sensing has enabled NMR of single nuclear spins and nanoscale NMR. Similar to conventional NMR and MRI, current DD-based quantum sensing utilizes the frequency fingerprints of target nuclear spins. Such schemes, however, cannot resolve different nuclear spins that have the same noise frequency or differentiate different types of correlations in nuclear spin clusters, which set an important limitation to resolution of single-molecule MRI. Here we show that this limitation can be overcome by using wavefunction fingerprints of target nuclear spins, which is much more sensitive than the frequency fingerprints to weak hyperfine interaction between the targets and a sensor under resonant DD control. We demonstrate a scheme of Angstrom-resolution MRI that is capable of counting and individually localising single nuclear spins of the same frequency and characterizing correlations in nuclear spin clusters. A nitrogen-vacancy centre spin sensor near a diamond surface, provided that the coherence time is improved by surface-engineering in the near future, may be employed to determine, with Angstrom-resolution, the positions and conformation of single molecules that are isotope-labelled. The scheme in this work, using the quantum nature of target nuclear spins, offers an approach to breaking the resolution limit set by frequency gradients in conventional MRI and to reaching the Angstrom-scale resolution.