Re: Amphipleura pellucida pix & paper

On 20 Mar 2007 03:32:20 -0700, "rene" <renevanwezel@xxxxxxxxxxx>
wrote:

Hi Gary, can you do measurements of the valve thicknesson different
spots?? I do think the perpendicular striae (interstriae really) are
thickened silica ribs, and the area in between the pores is very thin.
It's the latter thickness that I expect to vary between strains/
localities. Why? well, I cannot say for sure but I can think of a
quite a few environmental variables that could have an influence on
this. As far as I know Klaus thinks there might be a correlation with
altitude. Not sure Irish samples will give more information in this
respect.

I'm slated to get diatoms from Rio Santa Cruz (Argentina, I think)
rather than Ireland. Specimens from UK, Ireland, Mallorca all should
be pretty much the same. Altitude is an interesting and un-settled
variable.

The thickness of the side faces are pretty consistent radially from
the longitudinal axis. I got readings between 90nm and 120nm and
wound up calling it 100nm in the pore drawing. These were taken at 30
degrees tilt. Vertical dimensioning requires tilt correction while
horizontal does not. I checked the dimensions both ways and got the
same results. All of the diatom is SiO2 as confirmed by EDS.



Why would not high NA and/or lower Lambda be needed to resolve the
outer pores? The discussion of Raleigh Criteria clearly points out
the difficulty with the smaller dimensions of the outer pores. Since
they are smaller, not as much light would pass through them.

Well, I'm talking now from my intuition, I would think two tiny
pointsources would be easier to image then two large pores with a tiny
bit of wall in between (assuming the distance is the same). On the
other hand, if you could manage to image this in darkfield, the tiny
bits of wall would then become the luminous points.
I suppose the ideal situation would be a similar amount of wall in
between the pores.

I think some physical optics person could address this. I'm not
versed on this subject.


The> question is if the diatom is placed concave side up, then how
does the
transmitted light behave coming through the small pore then up and out
the larger inside pore?

Yes. Good question. This might be of influence at these critical
conditions.
Nevertheless, the wall is not black and white but nearly translucent,
so I cannot really defend that theoretically. Mounting medium also has
an influence in this: if imaging from within, it means looking through
a thicker layer of mountant compared to a valve that lies directly
with the slits against the coverglass. As diatom mountants differ in
refraction index from coverglass/immersion oil, this would introduce
sferical abberation.

Yes, this could be. since I don't do LM of these specimens, your
reasoning seems logical. The other factor might be that the glass and
diatom SiO2 are amorphous. Glass is and SiO2 usually is. Without a
lattice, this may affect contrast. I've checked orientation of
Sapphire to basal and R planes and they can vary quite substantially.
This affects their strength and optical properties.


I have not tried this myself since I think it is
a futile effort and I prefer to get useable results via SEM.

:-) Well, it sure is a great exercise in getting the LM setup exactly
right.

Your SEM pix did not clearly resolve the pores and especially the
angular characteristics of the inside to outside of the pores. All I
found was the pix. What was your total setup? Were these specimens
coated and with what? What WD, KV, etc.?

No, this was an old SEM (Cambridge S100) for biological stuff: insects/
botanical. Mainly used up to 5-10K. I think I used 25KV, gold
sputtered samples (actually: Klaus Kemp material). As I intended this
for measurements, I took images without tilting, so you wouldn't see
more detail of the pores, but from my memory there wasn't much more I
could make visible. It would do better with a field emmission gun but
with all the limitations of this instrument it just wouldn't stand up
against a more modern version. WD was 24mm, couldn't get it much
closer. When I asked the service engineer he said this was the
designed distance where it performed optimally.

Wow...24mm. That is too great to get decent resolution if any at all.
All of my pix except the last two are planar. Figure 7 is looking
right through the inside of the diatom to the outside. It shows the
"rotated" smaller outside pores. It is difficult to get good contrast
for this since I am using the top (good) and bottom (sorta OK) to
define the edges based on coating at the bottom. Since there is only
about 20A of fine Pd, there just isn't a lot of contrast through the
pore. The low KV was optimized for resolution and morphology. I did
some other pix at 5KV and 1KV and got essentially the same results.
The surface on the inside is rough and consists of tiny mounds of
SiO2. In comparison, the outside is much smoother.

René.


gg

Kiss French. Drink California.

gary at gaugler dot com
.

Relevant Pages

  • Re: More on A.pellucida
    ... NoSpam mentioned "plugged pores" which triggered a thought. ... diatom, that is views with the concave side poining up. ... While I have been able to resolve the striae I was unable to re- ... Since I do not have a stage micrometer I determined the distance ...
    (sci.techniques.microscopy)
  • Re: More on A.pellucida
    ... Regarding the pores I have the following to say. ... I reproduce TEM-images from the article "Fine structure of the Diatom ... While I have been able to resolve the striae I was unable to re- ... Since I do not have a stage micrometer I determined the distance ...
    (sci.techniques.microscopy)
  • Re: Amphipleura pellucida pix & paper
    ... I found time to look at the Stoermer paper. ... I would like to refer to the pores, in cross-section, that are shown at the ... is for a living diatom. ... Keg shape would imply symmetry which the pores do not have. ...
    (sci.techniques.microscopy)
  • Re: Amphipleura pellucida pix & paper
    ... slit-like pores on the outside of the valve. ... there still is the question of total wall thickness between pores ... bars perpendicular to the length axis of the diatom, ...
    (sci.techniques.microscopy)
  • Re: Amphipleura pellucida pix & paper
    ... slit-like pores on the outside of the valve. ... easier to resolve then the bigger sized inside of the pores, ... bars perpendicular to the length axis of the diatom, ...
    (sci.techniques.microscopy)