Colin, We know that with a dose of 20-30 electrons per A^2, a lot of image processing, and insane amount of luck, one can reconstruct cryoEM images to 3 A resolution or better. A typical protein molecule is say 100 A in diameter, which is ~8000 A^2 in projection. So, in an ideal case one needs only 240,000 electrons to record an image of a protein molecule with a signal extending to 3A resolution.
Jacob, Yes, you are correct. Jom et al. manipulate electron bunches of 1+ Mln electrons, which should be enough to record an image of a protein molecule. Best, Petr On Apr 14, 2011, at 11:13 PM, Colin Nave wrote: > Petr > Yes, I saw the figure. Similar ones appear in the Hastings et. al. paper (the > SLAC one I referenced). They use a much higher energy beam to get the short > pulse length. > > I still believe the issues are > > 1. For diffraction, can you get a low enough electron beam divergence to > resolve larger unit cells? The peaks appear rather broad in the foil > experiments. Luiten et. al. believe they can extend the technique to resolve > cells of a few tens of nm which would be fine. Their ideas for doing this > appear to be quite novel. I don't know if they have demonstrated this though. > 2. Given the above, will there be enough electrons in one of the short pulses > to get enough statistics for a biological molecule or protein nano-crystal? I > have not seen calculations for this for electron beams (as has been done for > the FEL x-ray beams). Actually it should be quite easy to do as the cross > sections are all available. > 3. For imaging (i.e. using an objective lens) is the blurring I mention going > to be a fundamental limitation and what will this limitation be? > > These instruments would be useful for material science applications and fast > chemistry investigations where some of the above issues would not be > relevant. Not sure for imaging biological molecules. We will see. > > Finally saying Phys Rev Let is not a high impact journal would probably upset > my physicist colleagues - that's fine though! > > Regards > Colin > >> -----Original Message----- >> From: CCP4 bulletin board [mailto:CCP4BB@JISCMAIL.AC.UK] On Behalf Of >> Petr Leiman >> Sent: 14 April 2011 21:07 >> To: CCP4BB@JISCMAIL.AC.UK >> Subject: Re: [ccp4bb] Femtosecond Electron Beam >> >> Dear Colin and all interested in the FEL development. >> >> Please look at the figures in the first link I mentioned. Jom Luiten et >> al. are able to record a 1.25 A resolution diffraction pattern of a >> gold foil using a pulse compressed to 50 fs. Ahmed Zewail is a pioneer >> of the technique but as far as I know his instrumentation is nowhere >> near Jom's amazing machine. >> >> Why Jom's paper was not published in one of the high profile journals, >> ahem, magazines, is a mystery to me. >> >> Petr >> >> On Apr 14, 2011, at 9:11 PM, Colin Nave wrote: >> >>> Petr has provided the Eindhoven links. >>> >>> For more details on fast electron imaging (as opposed to diffraction) >> see https://e-reports-ext.llnl.gov/pdf/343044.pdf >>> >>> Apparently stochastic scattering of the electrons at the high current >> densities necessary for short pulsed sources result in blurring in the >> image. The paper says that 10nm spatial and 10ps temporal resolution >> could be achieved with 5MeV electrons and annular dark field imaging. >>> >>> Of course more recent developments at Eindhoven and elsewhere might >> get round some of the limitations. >>> >>> >>> Colin >>> >>>> -----Original Message----- >>>> From: CCP4 bulletin board [mailto:CCP4BB@JISCMAIL.AC.UK] On Behalf >> Of >>>> Petr Leiman >>>> Sent: 14 April 2011 16:23 >>>> To: CCP4BB@JISCMAIL.AC.UK >>>> Subject: Re: [ccp4bb] Femtosecond Electron Beam >>>> >>>> People are looking into how to fit the old retired MeV microscopes >> with >>>> pulsed electron guns (problem is there are very few of those beasts >>>> left). If this works, such a machine will produce equivalent results >> to >>>> FEL but at a fraction of the cost. >>>> >>>> The group at Eindhoven, which Colin had mentioned, has already made >> a >>>> significant progress in achieving both time and spatial coherence. >> They >>>> are able to manipulate electrons in ultrashort electron bunches akin >> to >>>> spins in an NMR machine: >>>> http://prl.aps.org/abstract/PRL/v105/i26/e264801 >>>> http://jap.aip.org/resource/1/japiau/v109/i3/p033302_s1 >>>> And this is due to the fact that electrons can be focused with >> lenses. >>>> Amazing stuff. We will hear more about this for sure. >>>> >>>> Sincerely, >>>> >>>> Petr >>>> >>>> ________________________________________ >>>> From: CCP4 bulletin board [CCP4BB@JISCMAIL.AC.UK] on behalf of Colin >>>> Nave [colin.n...@diamond.ac.uk] >>>> Sent: Thursday, April 14, 2011 16:50 >>>> To: CCP4BB@JISCMAIL.AC.UK >>>> Subject: Re: [ccp4bb] Femtosecond Electron Beam >>>> >>>> Jacob >>>> Very good question. >>>> >>>> People are considering this sort of thing. See for example >>>> http://www-spires.slac.stanford.edu/cgi-wrap/getdoc/slac-pub- >> 12162.pdf >>>> >>>> Due to coulomb explosion one normally needs MeV beams to get the >> short >>>> bunch length. MeV beams also give a more reasonable penetration >> depth >>>> (not relevant for single molecules). I think the problem is that the >>>> divergence is too high to resolve diffraction spots from protein >>>> crystals (or in other words insufficient coherence). Probably fine >> for >>>> many small molecule crystals though. You mentioned single molecules, >>>> presumably protein molecules and I think the same would apply if >> trying >>>> to observe the scattering. >>>> >>>> One could try imaging (i.e. with an electron lens) rather than do >>>> diffraction. I presume this is what you mean by "focussed to solve >> the >>>> phase problem". However, I understand that there are problems with >> this >>>> as well for MeV beams but I can't remember the exact details. Can >> look >>>> it up if you are interested. >>>> >>>> There could of course be technical advances which would make some of >>>> these ideas possible. I think a group at Eindhoven have plans to get >>>> round some of the problems. Again I would have to look up the >> details. >>>> >>>> Regards >>>> Colin >>>> >>>> >>>> >>>> >>>> >>>>> -----Original Message----- >>>>> From: CCP4 bulletin board [mailto:CCP4BB@JISCMAIL.AC.UK] On Behalf >> Of >>>>> Jacob Keller >>>>> Sent: 14 April 2011 14:39 >>>>> To: CCP4BB@JISCMAIL.AC.UK >>>>> Subject: [ccp4bb] Femtosecond Electron Beam >>>>> >>>>> Dear Crystallographers, >>>>> >>>>> is there any reason why we are not considering using super-intense >>>>> femtosecond electron bursts, instead of photons? Since the >> scattering >>>>> of electrons is much more efficient, and because they can be >> focussed >>>>> to solve the phase problem, it seems that it might be worthwhile to >>>>> explore that route of single-molecule structure solution by using >>>>> electrospray techniques similar to the recently-reported results >>>> using >>>>> the FEL. Is there some technical limitation which would hinder this >>>>> possibility? >>>>> >>>>> JPK >>>>> >>>>> -- >>>>> ******************************************* >>>>> Jacob Pearson Keller >>>>> Northwestern University >>>>> Medical Scientist Training Program >>>>> cel: 773.608.9185 >>>>> email: j-kell...@northwestern.edu >>>>> *******************************************
