Scanning electron scope available

[rjlittlefield]

The following information was passed along to me by an individual who is not a member of our forum but wondered if some of you might be interested. The opportunity seemed unusual enough that I agreed to post it for her.

Hi Folks,

I hope that you all will consider this post on-topic. If not,
please accept my apologies.

I have an older Cambridge Instruments Stereoscan 90 electron
microscope that I would like to sell. I acquired the tool as part
of an estate sale and have been told that it works fine. I've seen
some very impressive photos created by the machine.

Being both a geek and a photographer I'd love to keep the thing to
play with. That said I just don't have the time to devote to
learning it nor do I have the room to store it.

Are any of you interested in purchasing this type of tool? Serious
inquiries are welcome to contact me directly and I'll share what
info I have.

Thanks,
Jessica Bussert

Jessica asks to be contacted at jessicadiane65@yahoo.com .

This message has been cross-posted from the Yahoo Microscope group.

--Rik

[lauriek]

Rik,

I definitely can't afford this atm (probably couldn't even afford to have it shipped to the UK) but it's always been a bit of a dream of mine to own one of these beasties, and as I read in another thread that you get to play with one of these at work, a couple of questions come to mind!

Am I right in saying that a SEM allows us to look at smaller objects than we can normally look at with optical systems because after a certain magnification, the wavelength of light is too large to allow us to see any more detail. Is that the (roughly) 1200x - 1500x that I see as the maximum magnification on expensive microscopes?

Assuming this is correct, what sort of scale is this, what I mean is - what's the smallest thing we can look at with optical systems, and what is the equivalent for an SEM - can an SEM look at an atom for instance? I presume it cannot, or you could not see any detail of an atom, or would an atom look like a sphere because that is the shape of it's 'field'? (sorry if I'm using incorrect terms here, my understanding of atoms etc is only sort of high school level!)

Can you look at the structure of a virus with an SEM?

How hard are they to use? I presume you cannot just shove an ant on a slide and stick it in an SEM and 'shoot' it? What sort of preparatory work do you have to do on subjects? (And how on earth would you go about preparing something like a virus, which is too small to see with optical equipment???)

Sorry that's more questions than I intended, please feel free to ignore some if they will take too much typing to answer or if they are downright silly!!!)

[rjlittlefield]

Laurie,

I don't actually get to play with electron scopes at work. The yucca moth was a one-time opportunity that tagged along with a collaboration between the biologist and my lab.

To answer your questions, though...

Am I right in saying that a SEM allows us to look at smaller objects than we can normally look at with optical systems because after a certain magnification, the wavelength of light is too large to allow us to see any more detail. Is that the (roughly) 1200x - 1500x that I see as the maximum magnification on expensive microscopes?

Exactly.

what's the smallest thing we can look at with optical systems, and what is the equivalent for an SEM - can an SEM look at an atom for instance?

For mid-spectrum visible light, the minimum feature size is about 0.2 micron [ref], but that's for a subject that's mounted and viewed with an oil immersion lens. In air, it would be about 0.3 micron. For your 10X NA 0.3 objective, it's about 1 micron. (That's why you need roughly speaking 5 micron pixels to get the most out of that objective without relay optics. 1 micron on the subject is 10 microns on the sensor, and you need at least two pixels per feature.)

Scanning electron microscopes are about 500 times better, with minimum feature size of around 1 nm = 0.001 micron. See the Wikipedia article for discussion.

Atoms are too small for SEM. Viruses and very large molecules can be seen, but I'm not sure how far you'd want to go with "look at the structure of a virus". Typical virus sizes are listed by Wikipedia as being 10-300 nm, so the images would be fairly fuzzy.

How hard are they to use? I presume you cannot just shove an ant on a slide and stick it in an SEM and 'shoot' it? What sort of preparatory work do you have to do on subjects?

Specimen prep varies widely and has gotten a lot easier in recent years. In the early days, it was required to have a completely dry specimen, then coat it with a thin layer of metal. These days, there are "environmental" SEMs that can even work with moist specimens.

In the case of the yucca moth, the specimen was dry but uncoated. No further prep was required. The micrographer suggested that better images could be obtained by coating the specimen with a thin layer of amorphous carbon (a few atoms thick and completely transparent), but the biologist declined that option because the specimen was one-of-a-kind and destined to become the type specimen for that species.

--Rik

[Hairyduck]

problem with them is that they cost a fortune to maintain and if left unused for many years are pretty much useless, you also need some high vac equipment, sputtering gear and some expensive/dangerouus chemistry, which takes it out of the reach of the man on the street

[rjlittlefield]

Yep. There's been rather an extensive thread of discussion about those issues over in the Yahoo Microscope group, in response to Jessica's posting there. Probably no need to rehash them here.

--Rik

[Mike B in OKlahoma]

Older SEMs are also a radiation hazard, though an extremely trivial one! I am the manager of the regulatory group in my state that deals with radiation safety. In the old days SEMs were required to be registered like an X-ray machine, though we don't do that anymore as they have gotten better.

Believe it or not, just today at work I got a call from a company that wants to trash an old one (doesn't work reliably, and spare parts aren't available so don't get excited). They wanted to do it in a way that complies with the regulations. It must be a special day on the calendar for surplus electron microscopes....

[Danny]

I've actually said to Tom for a looooong time that if I ever win the lottery here, we are getting an SEM and its being based in Hawaii for us to share. So who's in

Danny.

[g4lab]

SEMs are among the coolest of instruments you can be privileged to play with in this modern world. Even better if you get paid to do so. And better yet if they have an Energy Dispersive X ray Fluorescence elemental analyzer and mapper attached.

But even when they are new they are very twitchy. Sometimes things go wrong and even the factory service guys can't figure it. out. Service contracts are like $10,000 a year from the manufacturer's and maybe 4,000 or 5,000 from independent service guys most of whom are former manufacturer's service guys. It you don't have and pay for a service contract you better be prepared to do all the work yourself. Mostly not moonshot tech but may be quite labor intensive. Parts are difficult to come by especially for older scopes.

Most scopes consist of two equipment bays the column and the control panel which tend to be about 1000 lbs and 700 lbs respectively. I never worried much about X rays but if the scope is from a couple of decades ago you might want to worry about PCB containing oil in the High Voltage tank. (BTW, Are you comfortable working with very high voltage power supplies??) If there is an Xray spectrometer, then usually a third equipment bay. (and all the warnings about service contracts as well)

None of the people who make, sell, and service these things are the slightest bit interested in hobbyists. They are interested in Universities and Corporations with budgets to make it worth their while. And departments in the latter who actually have such instruments up and running invariably have a technician employed full time whose job is the care and feeding of these wonderful thorobreds.

They also take up alot of floorspace and are usually used in a darkened room. Most are equipped with Polaroid oscilloscope cameras to record the images. Old ones never have computer capture interfaces. These are available but cost thousands of dollars. Everything costs thousands of dollars. Stuff for them DOES appear on ebay though,, regularly, and even for cheep. So do scopes, from guys who saw in the local auction description,, that the company paid $250,000 for the unit fifteen years ago. They are rudely surprised, when they get scrap price at the junkyard for it , when it doesn't sell.

There are many correct comments on the thread Rik pointed to.

I am not trying to dissuade anyone. But one needs to know what one is getting into. If its not fixable you will need a big lift gate truck to take it to the junkyard.
This is not an endeavor, to be taken lightly.

Looking at viral structure is better done in a Transmission Electron Microscope (TEM) which are an even bigger pia. Preparation of of specimens for TEM is the subject of graduate level courses. Fixation embedment , cutting of ultra thin sections (thickness gaged by interference colors) Very labor intensive and requiring high psychomotor skills and hand eye coordination. SEMs cannot image atoms or molecules TEMs have been made to do so by diffraction methods which are very advanced. (More graduate courses. Done by physicists not biologists)

Preparation of specimens usually (except in new ESEMs= environmental SEMs) requires dehydrating and evaporating a conductive coating onto the surface to drain the electrons and prevent charge buildup which prevents imaging. This is done in a vacuum evaporator (large; size of a washer dryer) or a sputterer (desktop; size of a large microwave) both expensive, but do turn up on ebay.

But they actually aren't very hard to drive at all. Alot of what you already know about photography and imaging is applicable. There are a lot of knobs but so what.