An analytical solution to the problem of frost growth and densification on flat surfaces

An approach utilizing multiple scales and matched asymptotic expansions is developed for the description of small perturbations at large distances from a thin airfoil oscillating harmonically in a uniform supersonic flow. The problem of determining the unsteady perturbation potential is formulated in general, and an analytical solution is derived for an airfoil with parabolic or flat surfaces. The results describe the flow ahead of the region influenced by the trailing edge. The variation in the pressure jump across an attached leading-edge shock wave is also obtained.

Download Full-text

HREM observation of dislocations near room temperature fractures in silicon

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100106521 ◽

1988 ◽

Vol 46 ◽

pp. 892-893

Author(s):

M. H. Rhee ◽

W. A. Coghlan

Keyword(s):

Cross Section ◽

Room Temperature ◽

Single Crystal Silicon ◽

Dislocation Nucleation ◽

Back Side ◽

Ion Milling ◽

Crystal Silicon ◽

Flat Surfaces ◽

Induced Fractures ◽

Vicker’S Microhardness

Silicon is believed to be an almost perfectly brittle material with cleavage occurring on {111} planes. In such a material at room temperature cleavage is expected to occur prior to any dislocation nucleation. This behavior suggests that cleavage fracture may be used to produce usable flat surfaces. Attempts to show this have failed. Such fractures produced in semiconductor silicon tend to occur on planes of variable orientation resulting in surfaces with a poor surface finish. In order to learn more about the mechanisms involved in fracture of silicon we began a HREM study of hardness indent induced fractures in thin samples of oxidized silicon.Samples of single crystal silicon were oxidized in air for 100 hours at 1000°C. Two pieces of this material were glued together and 500 μm thick cross-section samples were cut from the combined piece. The cross-section samples were indented using a Vicker's microhardness tester to produce cracks. The cracks in the samples were preserved by thinning from the back side using a combination of mechanical grinding and ion milling.

Download Full-text

A TEM study of electron tunneling in biological macromolecules

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100125634 ◽

1987 ◽

Vol 45 ◽

pp. 140-141

Author(s):

J. A. Panitz

Keyword(s):

Stark Effect ◽

Electron Tunneling ◽

Imaging Modality ◽

Tunneling Current ◽

Biological Species ◽

Scanning Tunneling ◽

Biological Macromolecules ◽

Flat Surfaces ◽

Virus Particles ◽

Stm Images

Tunneling is a ubiquitous phenomenon. Alpha particle disintegration, the Stark effect, superconductivity in thin films, field-emission, and field-ionization are examples of electron tunneling phenomena. In the scanning tunneling microscope (STM) electron tunneling is used as an imaging modality. STM images of flat surfaces show structure at the atomic level. However, STM images of large biological species deposited onto flat surfaces are disappointing. For example, unstained virus particles imaged in the STM do not resemble their TEM counterparts.It is not clear how an STM image of a biological species is formed. Most biological species are large compared to the nominal electrode separation of ∼ 1nm that is required for electron tunneling. To form an image of a biological species, the tunneling electrodes must be separated by a distance that would normally be too large for a tunneling current to be observed.

Download Full-text

On the Faceting of Polar Ceramic Surfaces: Microscopy and Holography Studies of MGO(111) Surfaces

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100164295 ◽

1996 ◽

Vol 54 ◽

pp. 366-367

Author(s):

M. Gajdardziska-Josifovska ◽

B. G. Frost ◽

E. Völkl ◽

L. F. Allard

Keyword(s):

Electron Microscopy ◽

High Vacuum ◽

Ultra High Vacuum ◽

Electron Holography ◽

Flat Surfaces ◽

Transmission Electron ◽

Excess Surface ◽

Polar Surfaces ◽

Salt Structure ◽

Crystallographic Planes

Polar surfaces are those crystallographic faces of ionically bonded solids which, when bulk terminated, have excess surface charge and a non-zero dipole moment perpendicular to the surface. In the case of crystals with a rock salt structure, {111} faces are the exemplary polar surfaces. It is commonly believed that such polar surfaces facet into neutral crystallographic planes to minimize their surface energy. This assumption is based on the seminal work of Henrich which has shown faceting of the MgO(111) surface into {100} planes giving rise to three sided pyramids that have been observed by scanning electron microscopy. These surfaces had been prepared by mechanical polishing and phosphoric acid etching, followed by Ar+ sputtering and 1400 K annealing in ultra-high vacuum (UHV). More recent reflection electron microscopy studies of MgO(111) surfaces, annealed in the presence of oxygen at higher temperatures, have revealed relatively flat surfaces stabilized by an oxygen rich reconstruction. In this work we employ a combination of optical microscopy, transmission electron microscopy, and electron holography to further study the issue of surface faceting.

Download Full-text