Discussion: DIY SEM/FIB
Heath Matlock
been for awhile it seems, but there's a distinct lack of any reference
to building a scanning electron microscope or focused ion beam system
on the cheap. Discuss and link if possible please.
--
Heath Matlock
+1 256 274 4225
J. S. John
>
> There are quite a few plans on building your own STM on the web, have
> been for awhile it seems, but there's a distinct lack of any reference
> to building a scanning electron microscope or focused ion beam system
> on the cheap. Discuss and link if possible please.
>
and found some articles on how to make one. The problem I ran into was
learning about the probes and cantilever system. I think the probe
tips require a lot of precision. So I put the idea aside for now
until winter break.
Bryan Bishop
> On Tue, Oct 20, 2009 at 9:45 PM, Heath Matlock wrote:
>> There are quite a few plans on building your own STM on the web, have
>> been for awhile it seems, but there's a distinct lack of any reference
>> to building a scanning electron microscope or focused ion beam system
>> on the cheap. Discuss and link if possible please.
>
> That's true. I been looking into atomic force microscopy in particular
> and found some articles on how to make one. The problem I ran into was
> learning about the probes and cantilever system. I think the probe
> tips require a lot of precision. So I put the idea aside for now
> until winter break.
You don't need to do atoms immediately with your AFM setup. How about
trying to nail down millimeter and then micrometer textures? This way,
you can visually confirm if the data that you're seeing matches what
you see through your trusty microscope, or in the case of millimeter
scale scans, what you see through your crusty eyes.
J. S. John
> You don't need to do atoms immediately with your AFM setup. How about
> trying to nail down millimeter and then micrometer textures? This way,
> you can visually confirm if the data that you're seeing matches what
> you see through your trusty microscope, or in the case of millimeter
> scale scans, what you see through your crusty eyes.
I never thought of scaling from large to small. That's good. Just an
idea but is it possible to somehow use the needle in a hard drive as a
probe or will the attractive forces in the metal interfere?
Bryan Bishop
> On Tue, Oct 20, 2009 at 10:30 PM, Bryan Bishop wrote:
>> You don't need to do atoms immediately with your AFM setup. How about
>> trying to nail down millimeter and then micrometer textures? This way,
>> you can visually confirm if the data that you're seeing matches what
>> you see through your trusty microscope, or in the case of millimeter
>> scale scans, what you see through your crusty eyes.
>
> I never thought of scaling from large to small. That's good. Just an
> idea but is it possible to somehow use the needle in a hard drive as a
> probe or will the attractive forces in the metal interfere?
IIRC, tungsten probes/tips are to be sharp by aqueous potassium
hydroxide and hydrofluoric acid. Slowly pulling tungsten wire out of
an acid bath should cause (to some extent) the liquid to adhere to the
retracting tip for a little bit, and slowly etching away until the end
of the tip becomes super sharp. I don't recommend dealing with
hydrofluoric acid, however. Anyway, for starters, I've heard that a
sharp razor blade is good enough, if you can get the wire to fracture
to your will.
I'd like to one day find cheap piezo tubes, even though in the mean
time I'm perfectly happy hacking on piezos scavenged from headphones.
"Ask for price" is not cool.
J. S. John
> I'd like to one day find cheap piezo tubes, even though in the mean
> time I'm perfectly happy hacking on piezos scavenged from headphones.
> "Ask for price" is not cool.
>
What are piezo tubes? I saw something on google but no idea what it is.
Thanks
Bryan Bishop
> On Tue, Oct 20, 2009 at 10:45 PM, Bryan Bishop wrote:
>> I'd like to one day find cheap piezo tubes, even though in the mean
>> time I'm perfectly happy hacking on piezos scavenged from headphones.
>> "Ask for price" is not cool.
>
> What are piezo tubes? I saw something on google but no idea what it is.
Standard image:
http://img.alibaba.com/photo/11352477/Tube_piezoelectric_ceramic_using_for_ultrasonic_sonar_hydrophone.jpg
Operating idea:
http://www.azonano.com/images/Article_Images/ImageForArticle_2114(3).jpg
Think of this as doing some awesome raster scanning.
Eugen Leitl
>
> There are quite a few plans on building your own STM on the web, have
> been for awhile it seems, but there's a distinct lack of any reference
> to building a scanning electron microscope or focused ion beam system
> on the cheap. Discuss and link if possible please.
Well, it starts with an (U)HV chamber, or, rather, the absence thereof.
You need at least a pre-vacuum pump, an oil diffusion pump (preferrably,
with a cryotrap), or a turbovac.
I know of a precisely one person who keeps such in the house in working
condition. I think it was much easier when Scientific American actually
published challenging designs amateurs did (1960s/1970s). In case you
have a decent library, I recommend you sample those.
--
Eugen* Leitl <a href="http://leitl.org">leitl</a> http://leitl.org
______________________________________________________________
ICBM: 48.07100, 11.36820 http://www.ativel.com http://postbiota.org
8B29F6BE: 099D 78BA 2FD3 B014 B08A 7779 75B0 2443 8B29 F6BE
Cathal Garvey
Best to avoid HF.
Eugen Leitl
You're exaggerating a smidgen. But, I would also advise against working
with concentrated HF, especially anhydrous HF if you don't know what
you're doing. Especially in a domestic setting.
> Best to avoid HF.
Cathal Garvey
It's a similar case for divers in Ireland (unless things have changed in the last 3ish years): if you get the bends, you're flown to a pressure chamber in Wales/England for treatment. We haven't bothered buying a pressure chamber here yet. :P
Simon Quellen Field
Electro-etching in salt water works fine.
I assume everyone interested in this has already seen
"http://www.geocities.com/spm_stm/Project.html"
"http://www.springerlink.com/content/24341g648g00128u/"
I have some ideas for a scanning near-field optical microscope I have been meaning
to try for a while now, but it is a little too ambitious for my current audience. The idea
is to fix a single molecule of something fluorescent to a microscope cover slip, and
vibrate it horizontally using a speaker or piezo element, On top of that is another
cover slip with the sample fixed to it, face down towards the fluorescent molecule.
A sub-wavelength layer of immersion oil separates the sample from the molecule.
The sample is vibrated vertically, so you have a raster. An avalanche photodiode
or a photomultiplier tube sits above the sample, with a low pass optical filter
keeping out the ultraviolet from an ultraviolet LED below that excites the molecule.
My latest science fiction novel A Twisted Garden is now available in bookstores.
Gene Hacker
lead barium titanate powder and a hydraulic press.
Also on electron microscopes, if we want to image biological samples
we'd have to treat them in order to make them visible to the
microscope. Usually this entails rapid freezing(requires liquid
nitrogen) and exotic chemicals. One would also need a vacuum pump
too... Fortunately there happens to be a contest to do all of this:
http://www.intellectualpornography.com/2009/10/one-oclock-daily---a-prize-for-layman-science.html
Nathan McCorkle
I am in lab with HF about 20 ft from me right now.... in fact I did a
buffered HF etch about 1.5 hours ago, just make sure you A) dont screw
up, B) have personal protective gear (full length apron, thick long
gloves, full face shield) C) have Calgonate on hand, D) have a shower
in lab, E) have an escape safety plan and get to a hospital where they
basically inject you/ put you on a drip of calcium gluconate, and keep
you in homeostasis otherwise.
I wonder why Ireland doesn't have any calcium gluconate? I think
that's the only treatment hospitals really offer.
>
> Best to avoid HF.
>
> >
>
--
Rochester Institute of Technology
College of Science, Biotechnology/Bioinformatics
Meredith L. Patterson
>
> On Wed, Oct 21, 2009 at 6:10 AM, Cathal Garvey <cathal...@gmail.com> wrote:
>>> I don't recommend dealing with hydrofluoric acid, however.
>> Apparently it's a requirement here in Ireland that if one is working with
>> HF, a helicopter must be waiting nearby with the engine spun up and ready.
>> Because you'll need an airlift to England for the nearest HF-burn treatment
>> ward. And let's be realistic, you're dead by the time you get there from
>> blood loss and acute respiratory acidosis.
>
> HAHAHAHHAHAHAHAHA
>
> I am in lab with HF about 20 ft from me right now.... in fact I did a
> buffered HF etch about 1.5 hours ago
Thanks for jogging my memory, Nathan. I knew I'd used HF at some point
in the past, but couldn't remember exactly when -- high school chem
didn't sound quite right (though my chem teacher had a great story
about the none-too-bright brown-noser who wanted to score some points
by cleaning up the stockroom, and "helpfully" decanted a liter of HF
from a cruddy old plastic bottle into a fresh, clean glass one...),
and I'm pretty sure HF wasn't one of the supplies Dad kept in the
garage.
Nope ... it was seventh grade art class, where we used HF-based
etching cream and contact paper to etch designs into glass and
mirrors.
Granted, etching cream isn't especially concentrated, and as a gel
it's quite a bit less splashy than, say, the 12M HCl that I keep under
my sink, but it's still HF, and a local education board was totally
okay with a bunch of rambunctious twelve-year-olds using it.
Point being, the form of a substance is just as important as its
formula. Etching cream isn't going to leap out of the bottle, slit
your throat and rape your pets just because it's got hydrofluoric acid
in it. Concentrated hydrogen peroxide will fuck you up good and proper
if you spill it on you, yet people use it in 30% or 40% concentration
to bleach their hair all the time -- and dab it on wounds as a
disinfectant at much, much lower concentrations.
Perhaps Cathal was talking about high-molarity HF? I'd be surprised if
all of Ireland's etched glass were imported.
Cheers,
--mlp
Jake
first-aid kit with HF treatment cream in it here. From my
understanding it isn't all that dangerous. The only report I really
read about it was someone who used it as a rust remover and had his
hands exposed for an extended period. I think the guy ended up with
paralyzed arms, but he lived.
It really shouldn't be that hard to take standard precautions and have
some treatment cream handy.
-Jake
Eugen Leitl
> It really shouldn't be that hard to take standard precautions and have
> some treatment cream handy.
See, this is the problem I have at times with this group.
"I worked with a diluted HF solution once, and I didn't lose
a finger, so it's safe for small furry mammals everywhere".
No, it isn't. Sending such a message to hobbyists can get people hurt.
Hurt as in working with concentrated HF in holey gloves for hours,
or think concentrated HF and anhydrous HF is the same thing. No,
it isn't.
If you want to look for another things you shouldn't work at home,
go to http://pipeline.corante.com/archives/things_i_wont_work_with/
Again, just because you (think) you can handle something don't
assume everybody else can. GAR.
Meredith L. Patterson
> Hurt as in working with concentrated HF in holey gloves for hours,
> or think concentrated HF and anhydrous HF is the same thing. No,
> it isn't.
Did anyone say it was?
Reading back up the thread, it was Bryan who mentioned using HF to
sharpen the tip of a tungsten wire (by slowly drawing it out of a
bath), but he didn't mention whether the HF was to be dilute,
concentrated or anhydrous. Cathal likewise didn't mention the
concentration of the HF that requires a helicopter. You cautioned
against working with concentrated or anhydrous HF in a non-laboratory
setting, but no one's even fuckin' mentioned what molarity of HF one
uses to sharpen these things. If etching cream would work, then, why,
yes, Eugen, one could take suitable safety measures at home.
Numbers. They matter.
--mlp
Aaron Hicks
HF presents a problem in the prehospital setting from sopping up calcium ions; very painful. Something like 10-20 square inches of dermal exposure can be life-threatening, and all bets are off for head-neck-face exposure. A special compression dressing is used to cut down circulation in the affected areas, in conjunction with calcium gluconate applied topically as well as by IV push if necessary. It can sequester enough calcium ions that the heart can stop pumping.
A glass etchant based on ammonium bifluoride is available at hobby stores; I have no idea if it could replace HF for this application or not, but it's out there.
-AJ
J. S. John
<sfi...@scitoys.com> wrote:
> I assume everyone interested in this has already seen
> "http://www.geocities.com/spm_stm/Project.html"
> "http://www.springerlink.com/content/24341g648g00128u/"
>
it again. Now I bookmark everything
Eugen Leitl
>
> On Wed, Oct 21, 2009 at 10:39 PM, Eugen Leitl <eu...@leitl.org> wrote:
> > Hurt as in working with concentrated HF in holey gloves for hours,
> > or think concentrated HF and anhydrous HF is the same thing. No,
> > it isn't.
>
> Did anyone say it was?
Yes, by using blanket statements in a virtual penile metrology
contest. "You think that's dangerous? Why, I worked with..." etc.
> Reading back up the thread, it was Bryan who mentioned using HF to
> sharpen the tip of a tungsten wire (by slowly drawing it out of a
> bath), but he didn't mention whether the HF was to be dilute,
> concentrated or anhydrous. Cathal likewise didn't mention the
> concentration of the HF that requires a helicopter. You cautioned
> against working with concentrated or anhydrous HF in a non-laboratory
> setting, but no one's even fuckin' mentioned what molarity of HF one
> uses to sharpen these things. If etching cream would work, then, why,
> yes, Eugen, one could take suitable safety measures at home.
>
> Numbers. They matter.
Fucking exactly. Yes, Meredith, thanks for being so fucking in violent
fucking agreement. Can we proceed with the actual discussion now? Thanks so much.
Jake
> Fucking exactly. Yes, Meredith, thanks for being so fucking in violent
> fucking agreement. Can we proceed with the actual discussion now? Thanks so much.
deep breath and think of your happy place.
All sorts of lab chemicals are dangerous if handled improperly or if
the user is ignorant to their effect. HF isn't particularly more
dangerous than most lab chemicals. I don't see why you have to
fearmonger so much over it. If you handle it properly, have HF
treatment cream on hand, and can tell a doctor what you've been
exposed to and what the treatment is then there's no reason to worry
so much. If you take those precautions and are armed with knowledge
about the substance then you're in no more danger from it than from
anything else in the lab.
-Jake
Meredith L. Patterson
> On Wed, Oct 21, 2009 at 10:52:22PM +0200, Meredith L. Patterson wrote:
>> Reading back up the thread, it was Bryan who mentioned using HF to
>> sharpen the tip of a tungsten wire (by slowly drawing it out of a
>> bath), but he didn't mention whether the HF was to be dilute,
>> concentrated or anhydrous. Cathal likewise didn't mention the
>> concentration of the HF that requires a helicopter. You cautioned
>> against working with concentrated or anhydrous HF in a non-laboratory
>> setting, but no one's even fuckin' mentioned what molarity of HF one
>> uses to sharpen these things. If etching cream would work, then, why,
>> yes, Eugen, one could take suitable safety measures at home.
>>
>> Numbers. They matter.
>
> Fucking exactly. Yes, Meredith, thanks for being so fucking in violent
> fucking agreement. Can we proceed with the actual discussion now? Thanks so much.
Oh, I had a point there, and if you missed it then it's likely others
not so clever did as well. Which is simply: when dealing with
hazardous substances or procedures, proper safety measures are
determined in large part by the mass, volume, and concentration of the
reagents and apparatus. 3% H2O2 will remove bloodstains from clothing;
30% H2O2 will remove mucous membranes from your body. A
millimolar-scale exothermic reaction that runs away will leave glass
shards all over your fume hood and the floor in front of it; a
2500-gallon exothermic reaction that runs away will drive a
four-inch-wide metal shaft through concrete
(http://pipeline.corante.com/archives/2009/09/18/175_times_and_then_the_catastrophe.php).
Wear protective gear accordingly.
Cheers,
--mlp
Meredith L. Patterson
> A glass etchant based on ammonium bifluoride is available at hobby stores; I
> have no idea if it could replace HF for this application or not, but it's
> out there.
Good question. HF and NH4HF2 both attack silica, which is why they're
used as etchants; both reactions are a route to silicon tetrafluoride.
A quick google search turned up some papers on using ammonium
bifluoride to fluorinate scheelite (CaWO4), but as that yields
tungsten compounds, it doesn't sound like that will help for this
application. From Bryan's short description, it sounds like the whole
point is to produce a sharp point mechanically through dissolution.
That said, here's a nifty summary of things that dissolve tungsten:
The one that stands out to me is phosphoric acid. Concentrated
phosphoric acid is quite viscous (the pure stuff is solid at room
temperature), and as such, you don't have to worry about vapor
pressure the way you do with concentrated HCl or HF. It's still a
gloves-and-goggles situation, but if you knock it over it's going to
ooze at you rather than splashing.
NaOH in 5% H2O2 looks promising too.
Cheers,
--mlp
Aaron Hicks
That said, here's a nifty summary of things that dissolve tungsten:
http://books.google.be/books?id=foLRISkt9gcC&pg=PA54&lpg=PA54&dq=%22hydrofluoric+acid%22+tungsten&source=bl&ots=-rxKzap_B2&sig=sBfDg8qgvSR99OmUsykIybyTN5M&hl=en&ei=Q4XfSuXHOpCI4QaiuPkL&sa=X&oi=book_result&ct=result&resnum=8&ved=0CCgQ6AEwBw
The one that stands out to me is phosphoric acid. Concentrated
phosphoric acid is quite viscous (the pure stuff is solid at room
temperature), and as such, you don't have to worry about vapor
pressure the way you do with concentrated HCl or HF. It's still a
gloves-and-goggles situation, but if you knock it over it's going to
ooze at you rather than splashing.
NaOH in 5% H2O2 looks promising too.
That nitric acid is ~1/10th as fast as HF, and that hydrochloric is slightly slower than nitric is useful; one could get muriatic from a pool supply store and use that.
-AJ
Simon Quellen Field
printed circuit boards, where a large amateur community exists.
"http://www.google.com/search?q=ferric+chloride+price"
Meredith L. Patterson
> Iron chloride stands out; that used to be the etchant solution one could buy
> at Radio Shack for etching your own copper boards. No idea if it can still
> be purchased locally; haven't needed the stuff for years.
As of 2004 you could still buy it at Radio Shack. It smells like
rotting batteries and will chew up bare skin, so standard ventilation
and corrosive-substance warnings apply, but at least it's easy to come
by.
> That nitric acid is ~1/10th as fast as HF, and that hydrochloric is slightly
> slower than nitric is useful; one could get muriatic from a pool supply
> store and use that.
Actually, judging by that table, I'd go with repeated dipping in 10%
KOH solution with an aquarium bubbler and a magnetic stirrer, in a
really really big beaker.
Cheers,
--mlp
Heath Matlock
1. Design and fabrication of a scanning electron microscope using a
finite element analysis for electron optical system.pdf
2. Electron Gun Using a Field Emission Source.pdf
3. Titanium nitride coated tungsten cold field emission sources.pdf
The first paper wore me out, so I slacked on 2 and 3 which deals with
specifics of fabrication (which is a tad important), so I may have to
follow up later. Also there were a few nice flow control charts that I
took pictures of, may try to upload these later or create my own using
some language. But enough chatter here are the random notes (note, I
repeat myself a few times):
#before designing the sem, beam trajectory analyses in the sem column
were performed for various types of lenses and apertures using the
opera-3d sofware. perhaps elmer, code_aster, and calculix will
suffice.
controller:
fully digital (non-analog)
controlled all components:
created appropriate current in each coil
high voltage source of 2 to 25kV
lenses to focus the electron beam
vacuum system to maintain the high vacuum inside the column and the chamber
scan generator to scan the electron beam along the specimen
amplifier to amplify the detected secondary electrons
analog-to-digital converter to convert the amplified signal into a
digital one
monitored signals from the driver
connected to computer via RS232 serial port
electromagnetics lenses
vacuum line (tmp, valve, gauge)
optical column:
electron gun (tungsten filament): #a pointed whisker of tungsten
will emit electrons when a negative potential is applied. Currents as
high as 1 mA can be obtained from a piece of tungsten only a few
thousand angstroms in diameter.
three electrodes:
cathode:
tungsten wire filament bent in the shape of a hairpin, 0.15mm
diameter #tungsten cathodes are widely used because they are both
reliable and inexpensive
stable operation at 2700k
low working function of 4.5 eV
high mechanical strength
wehnelt cylinder:
induced the electron beam production from the cathode
#bias voltage to keep the current constant.
# the purpose of the wehnelt electrode is to control the electric
field close to the cathode so that electrons are emitted from only a
small area of the cathode and are subsequently focused into a narrow
beam suitable for further de-magnification by a series of electron
lenses to form the final electron probe
#the cross over/gap between the wehnelt cylinder and anode is ~30μm
anode:
used to accelerate the electron beam after it left the cathode
induced by the wehnelt cylinder
alignment coil
condenser lens_1
electron beam sleeve (Φ1 [mm], 5 E.) (made of conductive phosphorous
copper) and aperture
condenser lens_2
scanning deflection coils
objective lens
aperture
stigmator
#the emitted electron beam current, which passed through a 5 mm hole,
was measured at a Faraday cup connected to an electrometer (Keithley
6517) that could measure pi-coampere-level current.
#electron beam was aligned mechanically and electrically in the
electron gun to measure the electron beam current at the Faraday Cup
electrical power system:
high voltage source #looks to be dc with about 5 resistors, bias p/s
and resistor
three parts that helped with the emission of electrons by:
controlling the heating of the filament
induction of the cathode
acceleration of the electron beam
# when scanning the electron beam, the high voltages applied on the
electrodes shoulds be stable without severe voltage ripples that are
less than 10^-3 % of the reference voltage
#voltages applied on the tungsten filament, cathode, and wehnelt
cylinder ranged from -5 to 25 kV, and the anode was electrically
grounded.
#The bias between the cathode and the Wehnelt is often produced by a
simple feedback consisting of a resistor connected in series with the
cathode. As the electron current emitted from the cathode increases,
the cathode becomes more positive with respect to the Wehnelt so that
the emitted current is stabilized
electric stabilizer circut:
monitors the beam current and alters the bias voltage to keep the
current constant
#A magnetic lens is most frequently used for narrowing the beam by
driving a magnetic field-applied electric current on the coil[8]. By
changing the coil current, the focal length can be adjusted, ensuring
a highly focused beam. This magnetic flux causes the electron beam to
deflect, which is explained by Lorenz's law.
two condenser lenses and one objective lens:
used to demagnify the electron the electron beam spot down to a few
nanometers from the large crossover diameter at the wehnelt cylinder
in the electron gun.
gun alignment coil (4-pole electromagneite)
condenser lenses:
first condenser lens coil:
located right after the anode
functioned as a focusing device for the electron beam
second condenser lens coil:
used to demagnify the electron beam again
scanning coil (upper and lower)
objective lens coil:
further focused the electron beam
last aperature:
small hole made of non-magnetic refractory metal
intercepted the electrons that passed through the periphery of the lenses
allowed only electrons in the dominant part of the whole electron
beam to pass through
the size of the last aperature was predominant in determining the
beam size, brightness, diverging angle, and depth of focus. the
smaller the last aperture, the higher the resolution.
#six apertures were used in this sem
objective lens final aperture (Φ0.2 [mm])
Stigmator (8-pole electromagnetic)
SE detection
chamber and 3 axis stage
case surrounding the mini-SEM
#thermal emission experiments were performed in a specially
manufactured vacuum chamber, the vacuum maintained un 10^-5 torr.
#"Since the magnetic field depends on the coil current and number of
turns, the lens parameters, such as beam energy, width of coils, and
inner and outer diameters of the coils, lens geometry, and design,
were determined with special care."
soft and pure iron material used to generate magnetic field
magnetic field sensor (PASCO C1-652CA)
scan generator:
recieved x and y-axis signals from the PC
scanned the electron beam by sending signals to the lens controller
and the deflection amplifier to set a certain magnifacation value
as desired magnification value was obtained, the focused electron
beam scanned the specimen, emitting numerous secondary electrons
sensor:
detected the secondary electrons
located at the pre-amplification stage
#sec.electrons were later amplified by a photo multiplier tube
#signal converted and fed into a usb data acquisition board (ni-6251,
national instruments) installed on the pc. pc processes signal and
emits to monitor
vacuum sensor
valve sensor
#both checked the status of the chamber so that the vacuum value could
also be displayed
main dsp board:
controlled each controller
received the keypad input
displayed the current value
switching mode power supply (SMPS):
supplied power to each controller
power panel:
supplied electric power to:
rotary pump
turbo pump
leak valve
#paper 2
# The field emission properties of reactive magnetron sputtered TiN on
W tips were studied.
cold field emitters (CFEs):
of interest for vacuum microelectronic device applications because they offer:
low energy spreads
low power consumption
high current densities
can be unstable under poor vacuum and high current conditions:
this can be addressed by the use of higher strength, more inert,
and lower work function materials such as:
transition metal carbides
nitrides
comparable to transition metals in:
conductivities:
thermal
electrical
comparable to covalently bonded materials in:
hardness
inertness
high melting points
# for a rapid, prelimnary evaluation, films were deposited onto
conventional, electrochemicall etched W tips
they were characterized using a variety of technniques:
TEM
RBS
# paper3
a piece of 0.125 mm diam tungsten wire 1-3 mm long is spot-welded onto
a preformed 0.2 mm diam tungsten filament which is hairpin shaped. The
assembly is electropolished, and the tip is etched by immersit it in a
one normal sodium hydroxide (NaOH) solution and by applying 12 V dc
between the tip and a remote electrode in the solution.
So where to start?
--
Heath Matlock
+1 256 274 4225
Cathal Garvey
1) I was under the impression that one generally only used HF for its super-powerful high-molar form, as lower concentrations would behave much like weaker acids at higher concentrations. So, what I'm referring to is probably therefore for high-molarity solutions. That said, in Ireland I wouldn't put it past the healthcare/insurance/government axis to issue a blanket statement because...
2) We have one of the dumbest healthcare systems in Europe, it's semi-privatised. They don't want to treat anything they're not confident about, and HF is just probably one of those things. Although I would point out that in the bad HF burns, you'll need more than a drip. You'd probably need defibrillation, first thing in the door, because your heart will have stopped from acidosis! :P Other treatments applied accordingly as needed.
Aaron Hicks
We always used the stuff in 3% solution for cleaning up glassware; HF is one of the few products that can dissolve glass, and in order to touch up oily spots or other problems on borosilicate, other acids won't do that. A good nitric acid bath will, in many instances, get rid of organic debris and sometimes staining, but it won't remove the glass itself- again, unlike HF. Other, nastier solutions exist ("piranha" solution consisting of 30% hydrogen peroxide mixed 50/50 with con sulfuric acid, heated to the boiling point comes to mind), but these cannot be stored in a squirt bottle next to the sink. :)
I don't know about speed with respect to HF injury; the anecdotes I've always heard concerned a lot of pain, with cardiac effects coming late (after several hours).
Moving on...
-AJ
Cathal Garvey
Nathan McCorkle
you need to scan it in the X and Y? A super awesome scanner or syringe
pump? I want to move around gold atoms, one by one.
On Thu, Oct 22, 2009 at 4:11 PM, Cathal Garvey <cathal...@gmail.com> wrote:
> Indeed! Back to the SEM discussion. I am eager to visualise my DNA!
>
> >
>
Nathan McCorkle
> HF is not necessary.
> Electro-etching in salt water works fine.
>
> I assume everyone interested in this has already seen
> "http://www.geocities.com/spm_stm/Project.html"
> "http://www.springerlink.com/content/24341g648g00128u/"
>
> I have some ideas for a scanning near-field optical microscope I have been
> meaning
> to try for a while now, but it is a little too ambitious for my current
> audience. The idea
> is to fix a single molecule of something fluorescent to a microscope cover
> slip, and
> vibrate it horizontally using a speaker or piezo element, On top of that is
> another
> cover slip with the sample fixed to it, face down towards the fluorescent
> molecule.
> A sub-wavelength layer of immersion oil separates the sample from the
> molecule.
>
> The sample is vibrated vertically, so you have a raster. An avalanche
> photodiode
> or a photomultiplier tube sits above the sample, with a low pass optical
> filter
> keeping out the ultraviolet from an ultraviolet LED below that excites the
> molecule.
is doing something similar, except pulsing a laser at the vibrating
piezo, and an optical raman edge filter (these are high pass I
believe). There was a lock-in amplifier somewhere too, I think, but
that might have been for controlling the piezo frequency. I can't
rememeber.
This is one of his papers, it mentions that the laser is a cheap CW
laser pointer type:
http://diyhpl.us/~nmz787/pdf/Apertureless_near-field_far-field_CW_two-photon_microscope_for_biological_and_material_imaging_and_spectroscopic_applications.pdf