Ultrathin Platinum Crystal Surface Structures

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100118849 ◽

1985 ◽

Vol 43 ◽

pp. 394-395

Author(s):

R. L. Hines

Keyword(s):

Crystal Surface ◽

Surface Structures ◽

Platinum Surface ◽

Platinum Surfaces ◽

Resolution Level ◽

Experimental Facilities ◽

Carbon Backing ◽

Mesh Grid ◽

Atom Layer

The importance of atom layer terraces or steps on platinum surfaces used for catalysis as discussed by Somorjai justifies an extensive investigation of the structure of platinum surfaces through electron microscopy at the atomic resolution level. Experimental and theoretical difficulties complicate the quantitative determination of platinum surface structures but qualitative observation of surface structures on platinum crystals is now possible with good experimental facilities.Ultrathin platinum crystals with nominal 111 orientation are prepared using the procedure reported by Hines without the application of a carbon backing layer. Platinum films with thicknesses of about ten atom layers are strong enough so that they can be mounted on grids to provide ultrathin platinum crystals for examination of surface structure. Crystals as thin as possible are desired to minimize the theoretical difficulties in analyzing image contrast to determine structure. With the current preparation procedures the crystals frequently cover complete openings on a 400 mesh grid.

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Experimental Determination of the Effective Resolution Limit in Thick Specimens at High Voltages

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100116942 ◽

1975 ◽

Vol 33 ◽

pp. 664-665

Author(s):

Mircea Fotino

Keyword(s):

Experimental Approach ◽

Chromatic Aberration ◽

Resolving Power ◽

Biological Research ◽

Specimen Thickness ◽

Resolution Limit ◽

High Voltage Electron Microscopy ◽

Voltage Electron ◽

Resolution Level

The use of thick specimens (0.5 μm to 5.0 μm or more) is one of the most resourceful applications of high-voltage electron microscopy in biological research. However, the energy loss experienced by the electron beam in the specimen results in chromatic aberration and thus in a deterioration of the effective resolving power. This sets a limit to the maximum usable specimen thickness when investigating structures requiring a certain resolution level.An experimental approach is here described in which the deterioration of the resolving power as a function of specimen thickness is determined. In a manner similar to the Rayleigh criterion in which two image points are considered resolved at the resolution limit when their profiles overlap such that the minimum of one coincides with the maximum of the other, the resolution attainable in thick sections can be measured by the distance from minimum to maximum (or, equivalently, from 10% to 90% maximum) of the broadened profile of a well-defined step-like object placed on the specimen.

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Anisotropy of Nanoindentation – a tool for the determination of nanocrystal orientation ?

MRS Proceedings ◽

10.1557/proc-779-w5.14 ◽

2003 ◽

Vol 779 ◽

Author(s):

David Christopher ◽

Steven Kenny ◽

Roger Smith ◽

Asta Richter ◽

Bodo Wolf ◽

...

Keyword(s):

Crystal Surface ◽

Scanning Force Microscopy ◽

Depth Range ◽

Dislocation Loops ◽

Force Microscopy ◽

Pile Up ◽

Out Of Plane ◽

Scanning Force ◽

Dynamics Simulations

AbstractThe pile up patterns arising in nanoindentation are shown to be indicative of the sample crystal symmetry. To explain and interpret these patterns, complementary molecular dynamics simulations and experiments have been performed to determine the atomistic mechanisms of the nanoindentation process in single crystal Fe{110}. The simulations show that dislocation loops start from the tip and end on the crystal surface propagating outwards along the four in-plane <111> directions. These loops carry material away from the indenter and form bumps on the surface along these directions separated from the piled-up material around the indenter hole. Atoms also move in the two out-of-plane <111> directions causing propagation of subsurface defects and pile-up around the hole. This finding is confirmed by scanning force microscopy mapping of the imprint, the piling-up pattern proving a suitable indicator of the surface crystallography. Experimental force-depth curves over the depth range of a few nanometers do not appear smooth and show distinct pop-ins. On the sub-nanometer scale these pop-ins are also visible in the simulation curves and occur as a result of the initiation of the dislocation loops from the tip.

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A new computational strategy to calculate the surface energy of a dipolar crystal surface

CrystEngComm ◽

10.1039/d1ce00403d ◽

2021 ◽

Author(s):

Marco Bruno ◽

Stefano Ghignone

Keyword(s):

Dipole Moment ◽

Surface Energy ◽

Energy Surface ◽

Crystal Surface ◽

Computational Strategy

Determination of the energy surface, γ_((hkl)) (J/m2), of crystal polar faces is a very difficult task, for the presence of a dipole moment perpendicular to these surfaces that prevents the...

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Applications of Leed to the Determination of Surface Structures on Metals

Electronic Structure and Reactivity of Metal Surfaces ◽

10.1007/978-1-4684-2796-7_10 ◽

1976 ◽

pp. 289-339 ◽

Cited By ~ 2

Author(s):

S. Andersson

Keyword(s):

Surface Structures

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In situ determination of the electrochemically active platinum surface area: key to improvement of solid acid fuel cells

Journal of Materials Chemistry A ◽

10.1039/c7ta10110d ◽

2018 ◽

Vol 6 (6) ◽

pp. 2700-2707 ◽

Cited By ~ 10

Author(s):

Felix P. Lohmann-Richters ◽

Bernd Abel ◽

Áron Varga

Keyword(s):

Fuel Cells ◽

Solid Electrolyte ◽

Surface Area ◽

Solid Acid ◽

Oxide Reduction ◽

Electrolyte System ◽

Platinum Surface ◽

Electrochemically Active

Surface oxide reduction is demonstrated for measuring the active Pt surface area in a solid electrolyte system at 240 °C.

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The Adsorption, Desorption, and Exchange Reactions of Oxygen, Hydrogen, and Water on Platinum Surfaces. II. Hydrogen Adsorption, Exchange, and Equilibration

Canadian Journal of Chemistry ◽

10.1139/v75-041 ◽

1975 ◽

Vol 53 (2) ◽

pp. 298-306 ◽

Cited By ~ 8

Author(s):

Y. K. Peng ◽

P. T. Dawson

Keyword(s):

Hydrogen Adsorption ◽

Surface Composition ◽

Co Adsorption ◽

Exchange Reactions ◽

Platinum Surface ◽

Polycrystalline Platinum ◽

Platinum Surfaces ◽

Exponential Factors ◽

Apparent Activation Energies ◽

Adsorption Desorption

The adsorption, desorption, exchange, and equilibration reactions of hydrogen and deuterium on a platinum filament have been investigated by thermal desorption mass spectrometry. A surface saturated with hydrogen at 120 °K has a coverage 4.2 × 1014 molecules cm−2 and gives desorption spectra with four distinct peaks: β1,(165 °K), β2(220 °K), β3(280 °K), and β4(350 °K). Apparent activation energies and pre-exponential factors were determined for the β2-, β3-, and β4-peaks. For both co-adsorption and sequential adsorption of H2 and D2 the mass 2, 3, and 4 desorption spectra have identical shapes and the gas desorbs at equilibrium throughout. It is concluded that hydrogen adsorbs dissociatively. Exchange and equilibration were studied at 120, 210, and 285 °K by determining the surface composition and isotope distribution after varying fractions of preadsorbed H had been replaced. Following exchange at 120 °K the desorption spectra show a higher D content and a lack of equilibrium in the desorbing gas at low temperature. In most other experiments the mass 2,3, and 4 desorption spectra had identical shapes and the gas desorbed at equilibrium. The results are interpreted by a model which requires that the polycrystalline platinum surface is intrinsically heterogeneous. It appears that different mechanisms are unnecessary to interpret the differences in kinetics observed for exchange and equilibration at low temperatures.

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Limitations of LEED-Structure Determination of Reconstructed Crystal Surfaces

Zeitschrift für Naturforschung A ◽

10.1515/zna-1982-1001 ◽

1982 ◽

Vol 37 (10) ◽

pp. 1103-1118 ◽

Cited By ~ 3

Author(s):

H. Jagodzinski

Keyword(s):

Structure Determination ◽

Crystal Surface ◽

Dimensional Space ◽

Point Group ◽

Two Dimensional ◽

Crystal Surfaces ◽

Difficult Situation ◽

3 Dimensional ◽

Lattice Constants

Although a strictly ordered reconstructed crystal surface may have the two-dimensional symmetry prescribed by the bulk (two-dimensional subsymmetry of the 3-dimensional space group), it belongs more frequently to a subgroup. In the LEED-pattern a lower symmetry of the translation group can easily be detected on account of the superstructure reflections observed. In this case anti-phase domains can hardly be avoided. An even more difficult situation arises if the symmetry of the point group is violated, although the symmetry of the diffraction pattern is not altered at the end of the reconstruction. Twin domains without changes of lattice constants have to be taken into account.Dynamical scattering of anti-phase domains is calculated by applying the "Cluster embedded chain"-method for various distributions of domains. It is shown that the incoherent superposition of scattering amplitudes, normally applied in LEED-calculations may lead to serious errors in structure determination. This effect is even more pronounced for twin domains. As an example we discuss the reconstruction of the (001)-surface of Si and Ge, and show that the wellknown (2 X 1)-structure is an averaged structure only, consisting of anti-phase domains with the (4 x 2)-structure. It may be concluded therefrom that none of the present model structures of this reconstruction agrees with this experimental observation.

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