Incorporation of rare earths into II - VI compounds during MBE growth: optical and structural studies of Sm-doped tellurides

The understanding of ribosome structure has advanced considerably in the last several years. Biochemists have characterized the constituent proteins and rRNA's of ribosomes. Complete sequences have been determined for some ribosomal proteins and specific antibodies have been prepared against all E. coli small subunit proteins. In addition, a number of naturally occuring systems of three dimensional ribosome crystals which are suitable for structural studies have been observed in eukaryotes. Although the crystals are, in general, too small for X-ray diffraction, their size is ideal for electron microscopy.

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Structural Studies on Mitotic Spindle Fibres

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100070345 ◽

1978 ◽

Vol 36 (3) ◽

pp. 615-626

Author(s):

J.R. Mcintosh

Keyword(s):

Chemical Composition ◽

Mitotic Spindle ◽

Structural Studies ◽

Mitotic Apparatus ◽

Chemical Studies ◽

Medical Interest ◽

Spindle Fibres

The mitotic apparatus is a structure of obvious biological and medical interest, but it has proved to be a difficult cellular machine to understand. The chemical composition of the spindle is only slightly elucidated, largely because of the difficulties in preparing useful isolates of the structure. Chemical studies of the mitotic spindle have been reviewed elsewhere (Mcintosh, 1977), and will not be discussed further here. One would think that structural studies on the mitotic apparatus (MA) in situ would be straightforward, but even with this approach there is some disagreement in the results obtained with various methods and by different investigators. In this paper I will review briefly the approaches which have been used in structural studies of the MA, pointing out the strengths and problems of each approach. I will summarize the principal findings of the different methods, and identify what seem to be fruitful avenues for further work.

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Image registration with a computer driven S.T.E.M.

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100107630 ◽

1978 ◽

Vol 36 (1) ◽

pp. 98-99

Author(s):

A.M.H. Schepman ◽

J.A.P. van der Voort ◽

J.E. Mellema

Keyword(s):

Spot Size ◽

Scanning Transmission Electron Microscope ◽

Small Computer ◽

Structural Studies ◽

Area Of Interest ◽

Transmission Electron ◽

Scanning Transmission ◽

Specimen Area ◽

On Line ◽

Minimum Distances

A Scanning Transmission Electron Microscope (STEM) was coupled to a small computer. The system (see Fig. 1) has been built using a Philips EM400, equipped with a scanning attachment and a DEC PDP11/34 computer with 34K memory. The gun (Fig. 2) consists of a continuously renewed tip of radius 0.2 to 0.4 μm of a tungsten wire heated just below its melting point by a focussed laser beam (1). On-line operation procedures were developped aiming at the reduction of the amount of radiation of the specimen area of interest, while selecting the various imaging parameters and upon registration of the information content. Whereas the theoretical limiting spot size is 0.75 nm (2), routine resolution checks showed minimum distances in the order 1.2 to 1.5 nm between corresponding intensity maxima in successive scans. This value is sufficient for structural studies of regular biological material to test the performance of STEM over high resolution CTEM.

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The Fine Structure of Phloem Cells

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100119867 ◽

1985 ◽

Vol 43 ◽

pp. 632-635

Author(s):

James Cronshaw

Keyword(s):

Structural Studies ◽

High Concentration ◽

Long Distance ◽

Phloem Tissue ◽

Sieve Elements ◽

Long Distance Transport ◽

P Protein ◽

Companion Cells ◽

Electron Microscopical ◽

Distance Transport

Long distance transport in plants takes place in phloem tissue which has characteristic cells, the sieve elements. At maturity these cells have sieve areas in their end walls with specialized perforations. They are associated with companion cells, parenchyma cells, and in some species, with transfer cells. The protoplast of the functioning sieve element contains a high concentration of sugar, and consequently a high hydrostatic pressure, which makes it extremely difficult to fix mature sieve elements for electron microscopical observation without the formation of surge artifacts. Despite many structural studies which have attempted to prevent surge artifacts, several features of mature sieve elements, such as the distribution of P-protein and the nature of the contents of the sieve area pores, remain controversial.

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Microstructural investigation of surface roughness in MBE-grown AlAs

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100138646 ◽

1995 ◽

Vol 53 ◽

pp. 454-455

Author(s):

R. Rajesh ◽

R. Droopad ◽

C. H. Kuo ◽

R. W. Carpenter ◽

G. N. Maracas

Keyword(s):

Thin Film ◽

Real Time ◽

Growth Control ◽

Native Oxide ◽

Effusion Cell ◽

Surface Oxide Layer ◽

Microstructural Investigation ◽

Mbe Growth ◽

Film Substrate ◽

And Control

Knowledge of material pseudodielectric functions at MBE growth temperatures is essential for achieving in-situ, real time growth control. This allows us to accurately monitor and control thicknesses of the layers during growth. Undesired effusion cell temperature fluctuations during growth can thus be compensated for in real-time by spectroscopic ellipsometry. The accuracy in determining pseudodielectric functions is increased if one does not require applying a structure model to correct for the presence of an unknown surface layer such as a native oxide. Performing these measurements in an MBE reactor on as-grown material gives us this advantage. Thus, a simple three phase model (vacuum/thin film/substrate) can be used to obtain thin film data without uncertainties arising from a surface oxide layer of unknown composition and temperature dependence.In this study, we obtain the pseudodielectric functions of MBE-grown AlAs from growth temperature (650°C) to room temperature (30°C). The profile of the wavelength-dependent function from the ellipsometry data indicated a rough surface after growth of 0.5 μm of AlAs at a substrate temperature of 600°C, which is typical for MBE-growth of GaAs.

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