Get your own Free Home PageFrom oldest to most recent - - -Updated on 9 Sep 1997 -
- - Return
to PVSEM Page
ESEM USERS - 18 Feb 1994
RE: ESEM USERS - 18 Feb 1994
Re: SEM, ESEM examination of soils - 27 Mar
1996
Variable pressure vs conventional SEM -
20 May 1996
Variable pressure/Environmental
SEM - 21 Aug 1996
Re: afm tip
characterization - 5 Nov 1996
Re: sem sand
samples - 11 Nov 1996
Variable Pressure SEM -
12 Nov 1996
Re: Variable Pressure SEM - 14
Nov 1996
Short History of ESEM (longish!) -
16 Nov 1996
Re: Short History of ESEM
(longish!) - 18 Nov 1996
Variable pressure
SEM- seek more history info - 18 Nov 1996
SEM
at high chamber pressures. - 19 Nov 1996
Horizontal detector on ESEM - 22 Nov 1996
Re: EM fields - 9 Dec 1996
Re: SEM Filter Samples - 11 Dec 1996
Re: Please Define Townsend's 2nd ionoization coef - 13 Dec
1996
Re: Please Define Townsend's 2nd ionoization coef - 13 Dec 1996
Re: Please Define Townsend's 2nd ionoization coef - 13 Dec 1996
Fri, 18 Feb 1994 13:28:05 EDT Date: Fri,
18 Feb 1994 10:45:24 -0600 (MDT)
Return-path: <JRMICHA@saix367.sandia.gov> (Michael, Joseph)
Subject: ESEM USERS
To: microscopy@anlemc.msd.anl.gov
Here's a question for all of you Electroscan ESEM users. I am trying to
do some hot stage experiments in the Electroscan ESEm at the University
of New Mexico. My problem occured when I tried to image at 5000x at a temperature
of about 500C. The image drifted in a cyclic manner, I presume due to the
furnace controller varying the current to the heater. Has anyone overcome
this problem in the ESEM? My second question is, how high in temperature
can I go with the plastic light pipe for the backscattered electron detector?
Has anyone used a glass light pipe? I appreciate any info that can be supplied.
Joe Michael
Return to the List of Archived Articles
Fri, 18 Feb 1994 14:33:32 EDT Date: Fri,
18 Feb 1994 13:30:24 -0600
From: Stuart McKernan <stuartm@maroon.tc.umn.edu>
Subject: RE: ESEM USERS
To: microscopy@anlemc.msd.anl.gov
Reply-to: Stuart McKernan <stuartm@maroon.tc.umn.edu>
In message <9401187615.AA761597124@CCSMTP.SANDIA.GOV> Michael, Joseph
writes:
>Here's a question for all of you Electroscan ESEM users. I am trying
to do some hot stage experiments in the Electroscan ESEm at the University
of New Mexico. My problem occured when I tried to image at 5000x at a temperature
of
>about 500C. The image drifted in a cyclic manner, I presume due to the
furnace
>controller varying the current to the heater. Has anyone overcome this
problem
>in the ESEM?
I have overcome the problem by not using the controller. By controlling
the poewr manually it obviously takes a lot longer to reach a stable temperature,
but once there the power input is constant and presumably exactly matches
the power lost from the stage. Very stable images can be obtained under
these circumstances.
>My second question is, how high in temperature can I go with the plastic
light pipe for the backscattered electron detector?
Not tried it, but would also like to know.
Stuart McKernan stuartm@maroon.tc.umn.edu
Chemical Engineering and Materials Science OR High Resolution Microscopy
Center University of Minnesota, Minneapolis, MN 55455
Return to the List of Archived Articles
Date: Wed, 27 Mar 1996 10:03:45 +0000
From: m.dickson@unsw.edu.au (melvyn dickson) Subject: Re: SEM, ESEM examination
of soils To: microscopy@Sparc5.Microscopy.Com
Cc: m.dickson@unsw.edu.au
Hello out there,
Local microbiologists want to look at soil samples and the resident microboal
flora. My EM lab has all the usual SEM and TEM methods on tap and are doing
a library search but if anyone out there has personal experience of
A: looking for (or at) microbes in soil (ON soil) with frozen-hydrated specimens
or
B: untreated soil in an environmental SEM.
we would be very interested to learn of your experiences. Thanks in advance,
Mel Dickson.
Return to the List of Archived Articles
Date: Mon, 20 May 1996 10:17:20 -0400
From: Mary Anton <semlab@mail.ims.uconn.edu>
Subject: Variable pressure vs conventional SEM
To: microscopy@Sparc5.Microscopy.Com
Hi to all,
Thank you for the many helpful responses to my LaB6/digital imaging questions.
I am adding a new wrinkle to my SEM purchasing plans (for a Materials Science
service laboratory); namely, the variable pressure SEM--which can be run
in the conventional or variable pressure mode. I anticipate the use of the
variable pressure option to initially be low--less than 20%. My problem
is that I want to run a LaB6 filament in conventional SEM mode and occasionally
use the variable pressure mode ( the latter buys me a capability I don't
presently have). Would I have to change to a W filament for the occasional
variable pressure application? I would appreciate any comments, especially
regarding potential problems with these variable pressure type SEMs. Examples
of uses in the non-biological fields for the variable pressure mode would
also be appreciated.
Regards,
Mary Anton
University of Connecticut
Storrs, CT
USA
Return to the List of Archived Articles
Date: Wed, 21 Aug 1996 08:27:40 +0000
From: Keith Ryan
Subject: Variable pressure/Environmental SEM
To: microscopy@Sparc5.Microscopy.Com
Dear All
As the manager of some ageing EM equipment, ever hopeful of funding
etc., I would appreciate any comments on the usefulness or otherwise of
the type SEM's which offer 'poor' vacuum in the specimen chamber so
that wet/fresh specimens can be examined.
Our problem is that we do marine biology and most specimens come with a
layer of salt water or, if dissected, then a film of body fluid. What
happens to the surface layer - I know from cryo that after sublimation
we are left with a driedsalt layer which can be unhelpful! Sometimes I
have been known to rinse specimens in fresh water - that helps! Any
comments would be welcomed
With best wishes
Keith Ryan
Plymouth Marine Laboratory
Citadel Hill
Plymouth Devon PL1 2PB
England
Tel: ++44 1752 633294
Fax: ++44 1752 633102
e-mail: k.ryan@pml.ac.uk
PML web site: http://www.npm.ac.uk/pml
Return to the List of Archived Articles
Date: Tue, 5 Nov 1996 08:45:37 +0000
To: Paul Demkowicz
Microscopy@Sparc5.Microscopy.Com
From: Larry Stoter
Subject: Re: afm tip characterization
>I have produced some AFM tips (ESP single cantilever silicon) with small,
>non conductive crystals grown on the tip apex (crystal size is approx.
>0.1- 0.5um) and I would like to characterize their morphology with either
>SEM or AFM.
snips ...
>If anyone has been successful in a similar endeavor, your suggestions
>would be most appreciated!
>
>Also, I have read a paper whose authors imaged an AFM tip using AFM but I
>have had little success with this technique. Has anyone succeeded in
>doing this who could offer suggestions?
>
>Sincerely,
>
>*****************************************************************
>Paul Demkowicz
>University of Florida
I haven't tried it but one instrument that would probably do what you want
is the Philips/Electroscan FEG ESEM which is certainly capable of producing
very good high magnification images from non-conducting specimens. I'd
guess most low vacuum/variable pressure FEG SEMs would produce some good
images.
Regards,
Larry Stoter
Return to the List of Archived Articles
Date: Mon, 11 Nov 1996 17:41:16 -0600
From: "Stuart McKernan"
Reply-To: "Stuart McKernan"
To: dlietz@trentu.ca
Cc: microscopy@Sparc5.Microscopy.Com
Subject: Re: sem sand samples
Responding to the message of <01IBQ0R7WCKY007YL9@TrentU.ca>
from dlietz@trentu.ca (deborah Lietz):
> > I have been given sand samples containing cyanobacteria which have been
> >grown on the sand. I am having problems getting the samples to stay on the
> >stubs. The sand crusts are too fragile to push down onto double sided tape
> >and conductive paint is just soaked up by the sand but it really doesn't
> >make it adhere. Does anyone have any suggestions? Any replys would be
> >greatly appreciated.
> >
We have been able to image bacteria on wet sand by just placing the sand into
the Peltier stage and imaging in the Environmental SEM. The samples do not need
any further handling (no coating for example) and the Peltier stage allows us to
examine them in the fully hydrated state.
If you do not have access to an ESEM try Chris Gilpin at the University of
Manchester (email cgilpin@man.ac.uk)
Good luck
Stuart McKernan stuartm@maroon.tc.umn.edu
CIE Microscopy Facility, University of Minnesota Office: (612) 626-7942
100 Union Street S. E., Minneapolis, MN 55455 Lab: (612) 624-6590
Return to the List of Archived Articles
Date: Tue, 12 Nov 1996 12:10:26 -0800
From: "MIchael D. Warfield"
Organization: Hughes Space & Communications
To: Microscopy@Sparc5.Microscopy.Com
Subject: Variable Pressure SEM
X-URL: http://www.msa.microscopy.com/RefEdu.html
I am looking for reference material about application work being done
using the new variable pressure sems. Can you point me to any specific
references of libraries that might have such materials.
Mike Warfield
Return to the List of Archived Articles
Date: Thu, 14 Nov 1996 14:10:12 +0100
From: Joergen Bilde-Soerensen 5802
Subject: Re: Variable Pressure SEM
To: mdwarfield@CCGATE.HAC.COM
Cc: Microscopy@Sparc5.Microscopy.Com
Organization: Risoe National Laboratory, Denmark
Mike Warfield wrote:
>I am looking for reference material about application work being
>done using the new variable pressure sems. Can you point me to any
>specific references of libraries that might have such materials.
Dear Mike,
You can find a bibliography of environmental scanning electron
microscopy in:
G. D. Danilatos, Microscopy Research and Technique, vol. 25 (1993)
page 529-534.
There is also a bibliography in ElectroScan's homepages on the
address:
http://www.electroscan.com/bibliog.html
One major problem in the application of variable pressure SEMs is
that the spatial resolution for X-ray spectrometry deteriorates with
increasing pressure because the primary electrons are scattered on
the gas and therefore ends up far from the electron beam target
point. Concerning ways to overcome this procblem we have recently
published two conference papers:
J. B. Bilde-Sorensen and C. C.Appel, Proc. 48th Annual Meeting of the
Scandinavian Society for Electron Microscopy, Aarhus, 2-5 June 1996.
p. 4-5
J. B. Bilde-Sorensen and C. C. Appel, Proc. 11th European Congress on
Microscopy EUREM'96, Dublin, 26-30 August 1996. Session T6.
Best wishes,
Jorgen.
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
J. B. Bilde-Soerensen
Materials Department
Risoe National Laboratory
DK-4000 Roskilde
Denmark
e-mail: j.bilde@risoe.dk
phone: +45 46 77 58 02 (direct)
phone: +45 46 77 46 77 (switchboard)
fax: +45 46 35 11 73
Return to the List of Archived Articles
Date: Sat, 16 Nov 1996 17:37:00 +1100
To: Microscopy@Sparc5.Microscopy.Com
From: Jim Darley
Subject: Short History of ESEM (longish!)
A Short History of the ESEM.
Recently a couple of correspondents touched on the
development of the ESEM and other variable pressure type SEMs. The history
of the development of these instruments is rather more fascinating than
most movie scripts. I do not have time to write that book, but a few
snippets are appropriate fare for microscopy.com.
In one paragraph: What is the ESEM? Specimens for SEM observation must be
preserved, dried with minimal distortion and metal coated to conduct excess
electrons to ground. The ESEM is a commercial SEM-type instrument which
employs low to no vacuum near the specimen. This is achieved through
differential pumping, vacuum-limiting apertures and very short distances
between the final aperture and the specimen. Scanning is a time-sequential
process. In the gaseous detector, similar to other types, if more electrons
emerge from the specimen at an instant in time, then greater interaction
occurs with gases in proximity and a stronger detector signal is translated
into a brighter spot on the CRT during the scanning process. Essentially, an
ESEM can look at "live", hydrated and uncoated specimens.
Viv Robinson was Gerry Danilatos' supervisor at the University of New South
Wales. Robinson was instrumental in the development of the wide-angle BS
detector which carries his name and which, in my experience, is the best BS
detector.
The early developments of the various inventions which were
crucial to the variable pressure SEM must be very largely, if not entirely,
attributed to Danilatos, who by then was working in Robinson's lab, but with
his own research grant. Later they fell out and Danilatos had a term
appointment at CSIRO's Wool Research Division. For his work he adapted an
ancient JEOL SEM which was changed beyond recognition. The instrument was
owned by the Uni of NSW but Danilatos was allowed to move it to CSIRO.
He is of Greek origin and despite the language problems he
would have had back then, he was able to obtain a PhD in physics. He was a
highly task-oriented worker and not a good mixer; his achievements were
astonishing. Still under 35 years old when his contract at CSIRO terminated,
he had over 100 publications, several patents, was an Editor for at least
one international journal - and he could not get a job anywhere!
There can be little doubt that his job prospects were
adversely affected by one or two science administrators who seemingly had
developed a penchant to actively discourage his employment by others. Why?
We can only speculate, a touch of racism, a bit of professional jealousy,
gutlessness or poor judgement.
Australia has given rise to quite a few outstanding electron microscopists.
Like the proverbial prophet, however, Danilatos is still not recognised here
as the country's most outstanding electron microscopist.
With a young family to worry about and his job at an end, he invested his
scarce funds in a trip, visiting all significant EM manufacturers around the
world to present his invention and to request that they would consider
manufacturing an SEM based on some of his patents.
The answers were variations on the theme: "Interesting, but
too limited in application, no commercial possibilities" and unspoken "but
it was not invented here". Then the break-through: AMR's management too
had turned him down, but some of the engineers were convinced of the
invention's potential. They formed a company, raised venture capital and the
ESEM was in gestation.
Danilatos became an ESEM Research Director. With that lofty
title he worked for some years in Sydney at his Bondi Beach house. The
ESEM's "ancestor" was the centrepiece in his living room. He would start up
the ancient JEOL's pump system before breakfast. Quite a few publications
were produced in that remarkable setting.
I have lost contact with Gerry Danilatos; I last saw him at
the 10th Australian EM Conference, Perth, February 1988. For all I know, he
is still labouring away at Bondi Beach, but I doubt it. There are now six
ESEM instruments in Oz. Philips bought out ESEM in 1996 and other
manufacturers make other, patent-skirting variable pressure SEMs.
No doubt others researchers have made important
contributions to the ESEM's development, but with the variable pressure
systems, several vital detector systems and the initiating of the commercial
development to his credit, Gerry Danilatos has to be regarded as Father and
Godfather of these instruments.
JK Galbraith observed that modern inventions are too complex and must be the
products of a team effort; the lonely genius is an anachronism. This is
generally true and bringing an instrument like the ESEM into production does
require a large team. However, in our times it is a singular event when one
person can make such a large contribution to the development of a very
complex instrument.
Jim Darley
PS I will make this page, perhaps slightly modified, accessible through our
Links page, see URL below.
Probing & Structure
(Microscopy Supplies & Accessories)
PO Box 111, Thuringowa QLD 4817 Australia
Phone +61 77 740 370 Fax: +61 77 892 313
A great microscopy site: http://www.ultra.net.au/~pns/
Return to the List of Archived Articles
Date: Mon, 18 Nov 1996 10:46:27 +1100
To: Microscopy@Sparc5.Microscopy.Com
From: Jim Darley
Subject: Variable pressure SEM- seek more history info
Further to my posting on ESEM history: The intent was to correct the
information given in another posting and to highlight some not well known
aspects of the ESEM's history. Although I believe that that posting is true
in its essential elements, I accept that to be more useful, even a brief
history should be more broadly based. I certainly still do not want to write
"that book" but feel obliged to enlarge a bit on the development of the
variable pressure SEMs.
I ask that any additional, pertinent information is emailed to me.
Especially wanted are hard facts, dates, events and publications (I will
utilize those on the ESEM site and I have many of the old references
available).
Obviously such a history is for microscopists interest and would not change
legal facts or outcomes.
Eventually I will post a fuller (but still brief) history on this
server and post/link that history also with the LINKS of my site.
Perhaps the sciences (particularly EM) do not sufficiently value their
heritage and it is regrettable that names like: Knoll, Ruska, von Ardenne &
Oatley already would be unknown to most electron microscopists - at least
Wehnelt or Everhard & Thornly have a lasting tribute. Now may be a good time
to collect and write up the essential facts which led to the development of
the variable pressure SEM class of electron microscope.
Be assured that I am open-minded and without vested interest in these
instruments - other than that my agency sells a wide range of microscopy
supplies, some of which happen to be suitable for use with the variable
pressure SEMs.
Jim Darley
Probing & Structure
(Microscopy Supplies & Accessories)
PO Box 111, Thuringowa QLD 4817 Australia
Phone +61 77 740 370 Fax: +61 77 892 313
A great microscopy site: http://www.ultra.net.au/~pns/
Return to the List of Archived Articles
Date: 18 Nov 1996 10:04:53 Z
From: "Marcel Paques"
To: "microscopy@Sparc5.Microscopy.Com"
Subject: Re: Short History of ESEM (longish!)
Dear colleagues,
A small contribution to the "short history of ESEM".
The history of "environmental-EM" (actually ETEM) started in the Isleworth
Research Laboratory of Unilever Research in the UK. The first ETEM was designed
by J.A. Swift in 1970. In the following years G.R. Wight developed the first
ESEM at the Unilever Research Lab at Port Sunlight (UK). This work was published
in 1979.
>From 1981 G.D. Danilatos started to publish on the developments of ESEM which
resulted in the introduction of a commercial instrument in 1988.
Regards,
Marcel Paques
Unilever Research Laboratory Vlaardingen
The Netherlands
e-mail: Marcel.Paques@unilever.com
___________________________ Reply Separator_______________________________
Subject: Short History of ESEM (longish!)
Author: p&s@ultra.net.au at INTERNET
Date: 16/11/96 11:40
A Short History of the ESEM.
Recently a couple of correspondents touched on the
development of the ESEM and other variable pressure type SEMs. The history of
the development of these instruments is rather more fascinating than most
movie scripts. I do not have time to write that book, but a few snippets are
appropriate fare for microscopy.com.
In one paragraph: What is the ESEM? Specimens for SEM observation must be
preserved, dried with minimal distortion and metal coated to conduct excess
electrons to ground. The ESEM is a commercial SEM-type instrument which
employs low to no vacuum near the specimen. This is achieved through
differential pumping, vacuum-limiting apertures and very short distances
between the final aperture and the specimen. Scanning is a time-sequential
process. In the gaseous detector, similar to other types, if more electrons
emerge from the specimen at an instant in time, then greater interaction
occurs with gases in proximity and a stronger detector signal is translated
into a brighter spot on the CRT during the scanning process. Essentially, an
ESEM can look at "live", hydrated and uncoated specimens.
Viv Robinson was Gerry Danilatos' supervisor at the University of New South
Wales. Robinson was instrumental in the development of the wide-angle BS
detector which carries his name and which, in my experience, is the best BS
detector.
The early developments of the various inventions which were
crucial to the variable pressure SEM must be very largely, if not entirely,
attributed to Danilatos, who by then was working in Robinson's lab, but with
his own research grant. Later they fell out and Danilatos had a term
appointment at CSIRO's Wool Research Division. For his work he adapted an
ancient JEOL SEM which was changed beyond recognition. The instrument was
owned by the Uni of NSW but Danilatos was allowed to move it to CSIRO.
He is of Greek origin and despite the language problems he
would have had back then, he was able to obtain a PhD in physics. He was a
highly task-oriented worker and not a good mixer; his achievements were
astonishing. Still under 35 years old when his contract at CSIRO terminated,
he had over 100 publications, several patents, was an Editor for at least one
international journal - and he could not get a job anywhere!
There can be little doubt that his job prospects were
adversely affected by one or two science administrators who seemingly had
developed a penchant to actively discourage his employment by others. Why?
We can only speculate, a touch of racism, a bit of professional jealousy,
gutlessness or poor judgement.
Australia has given rise to quite a few outstanding electron microscopists.
Like the proverbial prophet, however, Danilatos is still not recognised here
as the country's most outstanding electron microscopist.
With a young family to worry about and his job at an end, he invested his
scarce funds in a trip, visiting all significant EM manufacturers around the
world to present his invention and to request that they would consider
manufacturing an SEM based on some of his patents.
The answers were variations on the theme: "Interesting, but
too limited in application, no commercial possibilities" and unspoken "but
it was not invented here". Then the break-through: AMR's management too
had turned him down, but some of the engineers were convinced of the
invention's potential. They formed a company, raised venture capital and the
ESEM was in gestation.
Danilatos became an ESEM Research Director. With that lofty
title he worked for some years in Sydney at his Bondi Beach house. The
ESEM's "ancestor" was the centrepiece in his living room. He would start up
the ancient JEOL's pump system before breakfast. Quite a few publications
were produced in that remarkable setting.
I have lost contact with Gerry Danilatos; I last saw him at
the 10th Australian EM Conference, Perth, February 1988. For all I know, he
is still labouring away at Bondi Beach, but I doubt it. There are now six
ESEM instruments in Oz. Philips bought out ESEM in 1996 and other
manufacturers make other, patent-skirting variable pressure SEMs.
No doubt others researchers have made important
contributions to the ESEM's development, but with the variable pressure
systems, several vital detector systems and the initiating of the commercial
development to his credit, Gerry Danilatos has to be regarded as Father and
Godfather of these instruments.
JK Galbraith observed that modern inventions are too complex and must be the
products of a team effort; the lonely genius is an anachronism. This is
generally true and bringing an instrument like the ESEM into production does
require a large team. However, in our times it is a singular event when one
person can make such a large contribution to the development of a very
complex instrument.
Jim Darley
PS I will make this page, perhaps slightly modified, accessible through our
Links page, see URL below.
Probing & Structure
(Microscopy Supplies & Accessories)
PO Box 111, Thuringowa QLD 4817 Australia
Phone +61 77 740 370 Fax: +61 77 892 313
A great microscopy site: http://www.ultra.net.au/~pns/
Return to the List of Archived Articles
Date: Tue, 19 Nov 1996 09:33:27 +1000
To: microscopy@Sparc5.Microscopy.Com
From: etpsemra@geko.net.au (Viv Robinson)
Subject: SEM at high chamber pressures.
Colleagues,
Several claims have been made lately about the development of SEMs
with higher pressure in the specimen chamber, in controlled environment
conditions. These instruments were first published by myself in 1974, see
reference below. (max pressure 5 torr). They were introduced commercially
by ISI/Akashi in conjunction with ETP Semra in 1978. To the best of my
knowledge, these references predate all other references. It is this work
which has resulted in some 2,000 of these types of SEMs being sold, out
selling ESEM by a factor of about 10.
One author has suggested Danilatos is the inventor of this
technology. Below is a copy of an updated review of the development of
SEM at high chamber pressures. You will see from it, my work predates all
of his by several years. I am wondering if he ever read my papers. I
believe this work pre-dates all other successful attempts at specimens in a
SEM specimen chamber at high pressures.
A REVIEW OF THE DEVELOPMENT OF SCANNING ELECTRON
MICROSCOPY AT HIGH CHAMBER PRESSURES
Vivian Robinson,
ETP Semra Pty. Ltd.,
244 Canterbury Road,
Canterbury, NSW, 2193
Australia
Ever since electron microscopes were developed, it has been the
goal of microscopists to observe specimens in their natural state, free
from artefacts which can often be introduced through specimen preparation.
For most biological specimens, that includes the presence of water.
With a pressure of 10exp-4 torr or lower required to operate a scanning
electron microscope (SEM), liquid water, which required a pressure of above
5 torr, was clearly a problem.
Although several attempts had been made to examine hydrated
specimens in a SEM, the first published results of water imaged in a stable
and reproducible manner in the SEM, were presented at the Eighth
International Congress on Electron Microscopy in Canberra in 1974
(Robinson, 1974). This represented an increase in the pressure
capability of almost 5 orders of magnitude, from less than 10exp-4 torr, to
5 torr.
Separation of the 5 torr water vapour in the specimen chamber from
the high vacuum in the electron optics column, was achieved by using a
single differentially pumped aperture. Although attempts at using thin
films for the separation had been made, they failed because they scattered
the electrons too much, even though there was no absorption. (Perhaps that
would not pose a problem with some of the thin window materials now
available.) Calculations based upon Duschman (1949), showed that the
pressure drop across a single 100mm aperture would enable a pressure of
below 10exp-4 torr to be sustained in the gun region of the SEM, whilst a
pressure of up to 10 torr was maintained in the specimen chamber, providing
the pumping speed above the aperture was greater than 10 litre/sec.
Another problem to be overcome was how to form an image? The
conventional Everhart-Thornley (E-T) secondary electron (SE) detector,
required a pressure of less than 10-4 torr to operate. Specimen current
imaging was not considered useful because ionisation of the gas molecules
could interfere with the adsorbed current. It was decided to use a wide
angle scintillator photomultiplier backscattered electron (BSE) detector
(Robinson 1974b; 1975a). These detectors could give images with similar
signal to noise and resolution as could be achieved with an E-T SE
detector.
There was still one further problem to be overcome. How to
reduce the path the electrons travelled through the higher pressure, and
thus limit the beam scattering and associated loss of image detail? This
required two steps; lowering the final aperture to reduce the distance the
electrons had to travel; and lowering the temperature of the chamber to
make sure the water vapour was never at a higher pressure. The
description of the experimental arrangement used in a modified JEOL JSM 2
SEM, was described in greater detail in a few publications. By using a
short, less than 5mm, working distance and a cooled specimen chamber, with
the specimen surrounded by an ice and water reservoir, it was possible to
produce some good images, up to x 2,000, of specimens containing liquid
water (Robinson, 1975b; 1976a; 1976b).
This system enabled hydrated specimens to be examined at
magnifications from x100 to x2000, with the water present in a stable
liquid state. The leak rate of the water from the specimen chamber,
approximately 10exp-3 torr litre/sec., was sufficiently slow that the
specimen would remain hydrated for several hours. The use of a 100 micron
aperture and the inability to alter the position of the cross over point of
the scan coils, meant that the minimum magnification attainable was x100
times.
Whilst using this technique, it was noticed that all specimens
viewed at chamber pressures above approximately 0.1 torr, were free from
charging artefacts (Robinson, 1975c). The first explanation was that it
was due to residual water in the specimen, rendering it slightly
conducting. This was determined to be an inadequate explanation and a new
one, in terms of ionisation of the residual gas molecules, was developed.
Moncrieff et al (1978), calculated the effect of ionisation due to the
incident beam, the BSEs, the charge build up on the specimen, the SEs
accelerated by the charge buildup, the positive ions attracted to the
specimen, the SEs released by the positive ions impinging upon the
surface, and the cumulative effect of these further SEs producing more
ions. They also measured these cumulative effects and showed that the
elimination of charging artefacts was due almost exclusively to the
ionisation mentioned above. Essentially, this established that as long as
the gas could be ionised, which was a property of all gases, and the
specimen could emit SEs and BSEs, which is a property of all solid and
liquid specimens, it was possible to examine a specimen in a SEM, free from
charging artefacts, at any accelerating voltage. Should an image still
display some intensity fluctuation charging artefacts, it was merely
necessary to increase the pressure of the residual gas. This increased
the ionisation effect and charging would be eliminated every time.
One other problem was how much did the gas interfere with the
electron beam? Moncrieff et al (1979) gave a very good dissertation of
the amount of scattering of the electrons by the residual gas molecules.
They calculated the elastic and inelastic scattering from nitrogen
molecules, and compared the results with experimental observation They
showed that following a single event, an electron would be scattered tens
to thousands of microns from the original beam trajectory, and would
contribute only to a background signal, which could be removed by
subtracting away some of the DC signal level. Those electrons which had
not been scattered would continue on to form a beam diameter which had the
same Gaussian FWHM diameter as would have existed without any beam
scattering. In other words, even if 90% of the electrons in the beam were
scattered, the unscattered electrons would still form a beam with the same
diameter as if there were no scattering. 90% beam scattering did not mean
90% reduction of resolution, it resulted only in minor a minor
deterioration in attainable resolution.
By that stage, the results achieved had established parameters for
high pressure SEMs. The next task was to extend the capability to the
limits determinable from the knowledge. The results of Moncrieff et al.
(1979), showed that as the pressure was increased, shorter path lengths
between the final aperture and the specimen were necessary to keep beam
scattering to minimum and thus form an usable image. For a pressure of
50 torr, this distance was less than 0.5mm, and 50 torr became the upper
practical limit of SEM using this type of technology.
Even then, 50 torr posed great problems for a single differentially
pumped aperture. For a pressure of 50 torr to be maintained on one side
of a single aperture, with 10-4 torr on the other side, an aperture
diameter of about 13 micron was required. This placed such a severe
limitation on the minimum size of the specimen which could be examined, as
to be of little practical use. To overcome this, it was necessary to have
an intermediate pressure by using two differentially pumped apertures.
Danilatos and Robinson (1979) constructed a system having this capability
and showed that this was usable. A pressure of 50 torr was equivalent to
saturated water vapour pressure at body temperature, plus a further partial
pressure of over 10 torr, for such gases as oxygen and effectively made it
possible to examine biological specimens in conditions which were close to
those necessary to support cell motility.
By the end of 1979, researchers at The University of New South
Wales, Sydney, Australia, led by myself, had developed the following
capabilities towards imaging specimens under high vapour pressure
conditions:-
a) Established differentially pumped apertures as
adequate for pressure separation in an SEM.
b) Established the parameters for the scattering of the
electron beam by the residual gas molecules.
c) Established an upper practical working pressure limit
of 50 torr, with higher pressures producing too short
a working distance requirement.
d) Shown how the ionisation of the residual gas was
responsible for the elimination of charging
artefacts.
e) Demonstrated the ability to form images of a wide
variety of specimens under a wide variety of
pressures, with and without hydration.
Neal and Mills (1980), built this type of system in a Cambridge
Stereoscan MkII SEM and were able to obtain video images of the adsorption
of water into sponge material, as well as other effects. Again, the
pressure limitation of 5 torr meant that it had to be cooled. They gave
an extended description of environmental SEM operating conditions.
Similar results have also been achieved by others, for example Shah and
Beckett (1979).
Having established the parameter for the capability to examine
specimens at higher vapour pressures, the next step was to establish
reasons for doing it. After all, at this time, most microscopists were
intent to look at their specimens in a cleaner vacuum system and to suggest
that there were advantages to be gained from going to higher pressures was
going against known convention. However, it was the ability to look at
insulating specimens at high, above 10kV, accelerating voltages, without
charging artefacts which proved to be most valuable. This capability
occurred at pressures of approximately 0.1 torr, for most working
distances. The amount of beam scattering was generally less than 10%.
As 0.1 torr was generally greater than the partial pressure of most oils
and waxes at room temperature, this capability enabled these and most other
out gassing specimens to be examined at voltages and currents suitable for
X-ray analysis, without charging artefacts. This whole situation ,
including TEM, STEM and SEM controlled environment operation, was reviewed
in 1984 (Robinson, 1984).
Interest in this capability was generated by ETP Semra Pty Ltd
which, in 1978, manufactured a device which was initially called an
environmental cell modification. This was later changed to Charge Free
Anti-contamination System (CFAS). This device enabled the specimen
chamber to be pumped by a rotary pump to a pressure controllable between
0.05 torr and 2 torr. The aperture remained a few mm inside the final
lens and an image was formed by detecting backscattered electrons. Over
one hundred of these were sold on Akashi/ISI SEMs. By 1980, Akashi
integrated a CFAS into one of their SEMs and called the integrated system
WET SEM. Over the next few years, they sold several hundred of these
systems, mostly in Japan. Despite many years of my talking to the SEM
manufacturers outside Japan, there was very little interest in building
this type of instrument. As Akashi increased its market share by actively
promoting this technique, the other major Japanese SEM manufacturers
followed, JEOL with their LV (Low Vacuum) SEM and Hitachi with their N
(Natural) SEM. Initially their sales were limited to the Japanese market,
which was perceived as being different from other markets. However, with
continued pushing by Mr Ruscica (Electron Detectors Inc) and myself on how
these devices were promoted in Japan and how a similar approach could work
in USA, sales started slowly in USA, but soon increased rapidly. AMRAY
Inc realised the potential of this type of instrument and introduced their
ECO (Environment COntrolled) SEM in 1993. Gresham Camscan introduced
their EnVac SEM. When Leica and Zeiss amalgamated to form LEO, their
first product was their VP (Variable Pressure) SEM. Philips introduced
their CP (Controlled Pressure) SEM in 1996. RJ Lee Instruments Ltd has
released their variable pressure SEM.
By 1996, the major SEM manufacturers had all released a SEM which
had the capability to examine specimens in a controllable pressure
environment in the specimen chamber of their SEM. For some SEM companies,
it was noticed that their sales of tungsten filament SEMs were almost
exclusively due to this type of SEM. These SEMs all used a single
differentialy pumped final aperture inside the final lens as a pressure
limiting aperture and a backscattered electron detector to collect a signal
to form an image. Although exact sales of this type of microscope are not
known, sales by ETP Semra Pty Ltd, of wide angle scintillator type BSE
detectors to be included in SEMs of this capability exceed 1500. Not all
of this type of SEM are fitted with a scintillator type BSE detector, and I
am unaware of the sales of solid state detectors for this purpose. I will
leave it to the imagination of your readers to determine how many of this
type of SEM have been sold, but as a conservative guess, a figure of 2000
SEMs would not be unrealistic.
While this was occurring, Danilatos continued researching higher
pressure capabilities, attempting to image at atmospheric pressure (1981).
However, this pressure placed such a severe limitation on depth of focus
and working distance that there was no further interest in that work. He
also commenced work on a secondary electron (SE) detector capable of
operating at higher specimen chamber pressures (Danilatos, 1983). Images
obtained with this environmental SE detector have displayed approximately
the same resolution capability as those obtained with an efficient BSE
detector, from similar specimens.
Much work has been performed on the development of new types of
electron guns, for example, the LaB6 and thermal and cold field emission,
to obtain greater resolution and through that greater specimen information.
The information gained from the ability to examine specimens in their
natural state, while not as spectacularly demonstrable as the improvements
to gun, is never the less making a quiet revolution to the information
which can be achieved from the specimen. It will not be long, given a
combination of the higher brightness electron gun and improvements to
detector performance, before images from hydrated biological specimens will
show as much detail as is currently achieved from dehydrated and gold
coated specimens imaged with a conventional tungsten filament.
List of References:
Robinson V N E: A wet stage modification to a scanning electron microscope;
Electron Microscopy/1974, Proc. 8th Int. Cong., Ed. J V Sanders and D J
Goodchild, Aust. Acad. Sci., Canberra, Vol. 2 (1974a) pp 50 - 51.
Dushman S: Scientific foundations of vacuum technique; John Wiley and Sons,
New York, Ch. 2 (1949).
Robinson V N E: The construction and uses of an efficient backscattered
electron detector for scanning electron microscopy; J. Phys. E: Sci.
Instrum., Vol. 7, pp 650 - 652 (1974b).
Robinson V N E: Backscattered electron imaging; Scanning Electron
Micrscopy/1975, Symp. Proc., Ed. O Johari, IITRI, Chicago, (1975a) pp 51 -
60.
Robinson V N E: A wet stage modification to a scanning electron microscope;
J. Microscopy, Vol. 103, pp 71 - 77 (1975b).
Robinson V N E: Scanning electron microscope environmental cells; Scanning
Electron Micrscopy/1976, Vol. 1, Symp. Proc., Ed. O Johari, and I Corvin,
IITRI, Chicago (1976a) pp 91 - 100.
Robinson V N E: The examination of hydrated biological specimens in a
scanning electron microscope environmental cell; Electron Microscopy/1976,
Proc. 6th Europ. Cong., Ed. Y Ben-Shaul, Tal International, Jerusalem, Vol
2 (1976b) pp 85 - 90.
Robinson V N E: The elimination of charging artefacts in the scanning
electron microscope; J. Phys. E: Sci. Instrum., Vol. 8, pp 638 - 640
(1975c).
Moncrieff D A, Robinson V N E, Harris L B, Neutralisation of insulating
surfaces in the scanning electron microscope, J. Phys. D: Appl. Phys. Vol.
12, pp 2315 - 2325 (1978).
Moncrieff D A, Barker P R, Robinson V N E: Electron scattering by gas in
the scanning electron microscope; J. Phys. D: Appl. Phys., Vol. 12, pp 481
- 487 (1979).
Danilatos G D, Robinson V N E: Principles of scanning electron microscopy
at high specimen chamber pressures; Scanning Vol. 2, pp 72 - 82 (1979).
Neal R J, Mills A Jr: Dynamic hydration studies in an SEM; Scanning, Vol.
3, pp 292 - 300 (1980).
Shah J S, Beckett A: A preliminary evaluation of moist environment ambient
temperature scanning electron microscopy (MEATSEM); Micron, Vol. 10, pp 13
- 23 (1979).
Danilatos G D: Design and construction of an atmospheric or environmental
SEM (Part 1), Scanning Vol. 4, 9 - 20 (1981).
Danilatos G D: A gaseous detector device for an environmental SEM; Micron
and Microscopica Acta, Vol. 14, pp 41 - 52 (1983)
Robinson V N E: The examination of hydrated specimens in electron
microscopes; in Echlin P, Analysis of organic and biological surfaces, John
Wiley and Sons, New York.
Jim, now that you have read the dates of my work, don't you think
these are somewhat ahead of those published by Danilatos? If you believe
he single handedly invented the environmental microscope, please show me
some dates of work which he has published which pre date my work.
As for some of his other statements. As can be seen from the
above references, the early work on environemntal SEMs and looking at
hydrated and live specimens was almost entirely the work of VNE Robinson
and his crew and was largely finished by the time Danilatos joined my team
on ARGS grant B75/15588. He was employed on ARGS funding obtained by
myself from 3 January, 1978 until 30 June, 1981. My project under that
grant was to increase the pressure to its limits and then apply it to
biological applications. Together we extended the limit to 50 torr. At
that stage Danilatos wished to extend the results to atmospheric pressure,
while I considered that too impractical. As it was The University of New
South Wales policy to let researchers try their project, he was allowed to
explore his project on that grant. You will note that he did not
acknowledge the receipt of any grant in his paper Danilatos GD An
atmospheric scanning electron microscope, Scanning vol 3, 215 (1980).
100 papers and still under the age of 35! Perhaps he could like
to list them all. "... he adapted an ancient JEOL SEM ..." In 1980,
that JEOL JSM 2 was only 12 years old, well within the expcted active life
of a SEM. It had been used by myself to look at liquid water since 1974.
As for "science administrators who developed a penchant ...", they allowed
him to take that SEM into his post University activities, an activity of
which I do not think has been extended to anyone else. It certainly was
not extended to myself when I left The University of New South Wales.
Racism? The University of New South Wales had a long history of employing
people from many different ethnic backgrounds. Professional jealousy?
Gutlessness? Strong words! Poor judgement - well that fits someone we
know.
For your information, there are about 2,000 variable pressure SEM
systems sold through the world since their release by ISI/Akashi in
conjunction with ETP Semra Pty Ltd in 1978. They were first called
Environmental Cell Modifications (ECM), quiclkly followed by Charge Free
Anti-contamination Systems (CFAS) and WET-SEM. They operated at pressures
up to 2 torr, almost 5 orders of magnitude above the previous specimen
chamber limit of 10exp-4 torr. These were commercialy available since
1978, before Danilatos even commenced publication. In 1974 the technology
to build these to 5 torr was published, 5 years before Danilatos' first
paper. Together Danilatos and I extended this pressure to 50 torr, with
him working on a research grant I obtained. True, Danilatos did attempt
atmospheric pressure, but he failed and 50 torr is the practical limit with
todays technology. That is hardly the work of a lonely genius.
So what did Danilatos do to deserve the title of Father and
Godfather of variable pressure SEMs?
1) First to image liquid water in a stable manner in an SEM?
Not before Robinson in 1974.
2) First to image liquid water at room temperature? See
Danilatos and Robinson reference above.
3) First to image at 50 torr specimen chamber pressure? See
Danilatos and Robinson reference above?
4) First to image at atmospheric pressure? First to attempt -
full marks for trying - but the results were not satisfactory
and no one is interested in or extending the work.
5) First to commercialise SEM with high pressure in the specimen
chamber. No! ISI/Akashi/ETP Semra in 1978, to a maximum
pressure of 2 torr.
6) First to determine the effect of beam scatterering. See
Moncreiff, Barker and Robinson (1979) reference cited above.
7) First to calculate the effect of ionisation and SE and BSE
yield on charge elimination. See Moncreiff, Robinson and
Harris (1978) reference cited above.
In 1978, the scientific work was extended to 5 torr and
commercialisation of the product to 2 torr had already occurred. Those
represent a minimum of four and almost five orders of magnitude increase in
available pressure in a SEM specimen chamber. Danilatos worked with me to
extend this to 50 torr, an increase of only one order of magnitude. He
worked with ElectroScan to increase the commercial limit to 20 torr, again
an increase of only one order of magnitude over ISI/Akashi's 2 torr in
1978.
8) Developed a Gaseous SE detector. His first US patent, No
4,823,006, dated April 18, 1989, is in the name of Danilatos
and Lewis! It post dates by almost 2 years a patent
application by JS Shah, the HH Wills Physics Laboratory,
University of Bristol, GB patent No 2,186,737, dated 19
August, 1987, in which reference is made to
"... means for collecting the specimen current generated by
the electron beam from the specimen, and biassing means for
producing a substantial electric field at the surface of the
specimen ..." (Claim 1)
All his own work?
".. other manufacturers make other, patent skirting variable
pressure SEMs." ElectroScan's patent only applies to a gaseous secondary
electron detector, not to differentialy pumped aperture systems or
backscattered electron detectors, which were used in these applications
years before ElectroScan was formed as a company. As mentioned earlier,
over 2,000 of these have been sold world wide by more than six different
companies, compared to about 200 ESEMs from ElectroScan. These 2,000 were
done using a technology which extended the upper SEM chamber pressure by
some five (5) orders of magnitude, using technology developed primarily by
myself. ESEM has sold about 10% of that number and only increased the
commercially available pressure capability by 1 to 1.5 orders of magnitude.
Vivian Robinson
ETP Semra Pty Ltd
Return to the List of Archived Articles
From: GARONEL@cliffy.polaroid.com
Date: Fri, 22 Nov 1996 09:10 -0400 (EDT)
Subject: Horizontal detector on ESEM
To: Microscopy@Sparc5.Microscopy.Com
Hi Everyone!
To save money (sound familiar), we have recently placed a horizontal
EDS detector on an ESEM (Electroscan E-3) from an old 'scope. The
optimum geometry for the ESEM is not horizontal but a detector with a
30 degree snout and use of their long working distance detector. It
would be difficult to tilt the sample 30 degrees because of the very
short working distance with that detector. I am curious if there are
other users out there who are working with horizontal detectors in
their ESEM's. If so, please contact me at GaroneL@Polaroid.com
Thanks in advance,
Lynne
Return to the List of Archived Articles
Date: Mon, 9 Dec 1996 12:58:22 -0600
From: "Mike Bench"
Date: Wed, 11 Dec 1996 12:06:50 +1000 To: Microscopy@Sparc5.Microscopy.Com From: W.Jablonski@csl.utas.edu.au (Wis Jablonski) Subject: Re: SEM Filter Samples > Hello, > > I have an environmental engineer who is interested at looking at > bacterial samples that have been filtered. He wants to look at the > bacteria on the filters themselves. Does anyone know how to process > such samples? Do I let the filters air-dry or should I fix, > dehydrate, and CPD the filters? Any help would be much appreciated. > > Thank you in advance, > > Ginger Baker > EM Lab Manager > Dept. APP > 250 Veterinary Medicine > Oklahoma State University > Stillwater, OK 74078 > (405) 744-6765 > FAX: (405) 744-5275 > Email: lizard@okway.okstate.edu > >Dear Ginger, Use ESEM ( environmental scanning electron microscope) equipped with a cold stage going down to 1-2 degrees C. You will be able to use wet filter with a bacterial deposit on it and to dry carefully water out while in the microscope. For a short time ~ 5 minutes, you should be able to see and identify your bacteria without substantial distortion. Alternatively, fix them with 1% of OsO4 in water while on filters and repeat as above. Use 20 kV and high condenser setting (60-70%) for artefact free observation. Cheers, Wis Jablonski OiC EM/X-ray Microanalysis, CSL, University of Tasmania Return to the List of Archived Articles
From: mfriesel@ix.netcom.com Subject: Re: Please Define Townsend's 2nd ionoization coef Date: Fri, 13 Dec 1996 08:19:49 -0700 Michael Supp wrote: > > I need to know how to define Townsend's 2nd ionoization coefficient. I > have the description in words for the coef., but no eqn as to what it >is > equal to. > > There is a paper in Scanning Vol 18, 467-473 (1996) by P. Meredith, A.M. > Donald and B. Thiel "Electro-Gas Interactions in the Enviromental > Scanning Electron Microscopes Gaseous Detector" that derives various > equations that describe theoretically the interactions of electrons with > gases and materials. However the authors fail to define the above > coefficient. I have chased down several papers/books that again deal > with some of the same eqns but none offer a definition of the coef. > The Townsend coefficient is the number of ionizing collisions by an electron per unit path length in the direction of an applied electric field. It seems like a reasonable form for the coefficient would be T = klds where d is the target density, s is the single target ionization cross section for the interaction, k would represent the density-dependent overlap of target cross-sections, and l the mean actual path length travelled by the electron per unit distance travelled in the direction of the applied field. Return to the List of Archived Articles
From: amiller@nmsu.edu (A. MILLER) Subject: Re: Please Define Townsend's 2nd ionoization coef Date: 13 Dec 1996 15:17:57 GMT Michael Supp (supp@ridgefield.sdr.slb.com) wrote: : I need to know how to define Townsend's 2nd ionoization coefficient. I : have the description in words for the coef., but no eqn as to what it is : equal to. If we are thinking of the same thing ("gamma", the ratio of the average number of secondary electrons emitted froma cathode for each new positive ion formed in gas {Townsend discharge}), then I think that there exists no equation giving the value of gamma in terms of "fundamental quantities". My old book "Theory of Gaseous Conduction and Electronics" by Maxwell and Benedict (McGraw Hill, 1941) represents gamma as a fucntion of (F/p) - where F is field strength ("E") and p is pressure. See their figure 8-12, page 284 if you can find the book in your library. Or look for the BIG gaseous electronics book by L. Loeb. The coefficient is also discussed in Sanborn C. Brown's book ("Introduction to Electrical Disharges in Gases", John Wiley & Sons, 1966), page 119 and following. August Miller Return to the List of Archived Articles
From: Anders Larsson
Return to current posts
Return to PVSEM page
Get your own Free Home PageDanilatos || ESEM Research Laboratory ||Prototype ESEM ||Low Bias GDD ||High Bias GDD ||Color Imaging || TV Imaging || BSE Imaging || ASEM|| Commercial ESEM ||Index
