24 research outputs found
The effect of inhomogenities on single molecule imaging by hard XFEL pulses
We study the local distortion of the atomic structure in small biological
samples illuminated by x-ray free electron laser (XFEL) pulses. We concentrate
on the effect of inhomogenities: heavy atoms in a light matrix and
non-homogeneous spatial distribution of atoms. In biological systems we find
both. Using molecular-dynamics type modeling it is shown that the local
distortions about heavy atoms are larger than the average distortion in the
light matrix. Further it is also shown that the large spatial density
fluctuations also significantly alter the time evolution of atomic
displacements as compared to samples with uniform density. This fact has
serious consequences on single particle imaging. This is discussed and the
possibility of a correction is envisaged.Comment: Movies: http://www.szfki.hu/~jurek/art2009_1/index.htm
Mire jó a röntgenvonalzó? | What is the Use of an X-ray Ruler? Determining Atomic Structure with the Use of X-ray Radiation
A mai technikai civilizációnkban mind több és mind kifinomultabb eszközt
használunk. Az ezeket felĂ©pĂtĹ‘ anyagok tulajdonságait egyre pontosabban
kell ismerni, és képesnek kell lenni arra, hogy ezeket az igényekhez
igazĂtsuk. A tulajdonságokat alapvetĹ‘en az alkotĂł atomok milyensĂ©ge Ă©s
térbeli rendje, vagyis az atomi szerkezet határozza meg. E szerkezet pontos
ismerete elengedhetetlen ahhoz, hogy jĂł Ă©s megbĂzhatĂł gĂ©pkocsikat, elektronikus
eszközöket vagy Ă©ppen orvosságokat állĂtsunk elĹ‘. A kĂ©rdĂ©s fontosságát
talán az is mutatja, hogy az elmúlt száz évben számos módszert
dolgoztak ki az atomi szerkezet meghatározására. Ezek közül a legszélesebb
körben elterjedt a röntgensugárzással való szerkezetmeghatározás. Az
ezzel kapcsolatos kĂsĂ©rleti Ă©s elmĂ©leti munkákĂ©rt kilenc Nobel-dĂjat adtak.
Az előadás keretében bemutatjuk a röntgensugárzással való atomi szerkezetmeghatározás
alapelveit, nehézségeit, és kitérünk a jövőbeli lehetőségekre
is. | Our technical civilization is based on an increasing number
of more and more sophisticated tools. To tailor these to our
needs we have to know their properties with high precision.
Most of the characteristics of the materials are determined by
the type and arrangement of the atomic constituent, i.e. the
atomic structure. The knowledge of this structure allows us
to construct high quality, reliable cars, electronic devices or
medicines. However, to do all these we need methods to
determine the atomic order.
We learn why waves are suitable for measuring distances, and
why x-rays are used for determination of atomic distances.
We also learn how to produce x-rays (traditional x-ray tube
and synchrotron source) and how the atomic structure is
actually determined by x-ray. The power of x-ray structure
determination is illustrated through examples. Theoretical
and practical problems of the structure determination are
outlined. Solutions to these problems are given, including
the experimental possibilities offered by the new type of
future x-ray sources, the x-ray free electron lasers.
Beside the practical importance of structure determination,
the aim of the research in this field is to obtain qualitatively
new information and to understand how nature works
Dynamics in a cluster under the influence of intense femtosecond hard x-ray pulses
In this paper we examine the behavior of small cluster of atoms in a short
(10-50 fs) very intense hard x-ray (10 keV) pulse. We use numerical modeling
based on the non-relativistic classical equation of motion. Quantum processes
are taken into account by the respective cross sections. We show that there is
a Coulomb explosion, which has a different dynamics than one finds in classical
laser driven cluster explosions. We discuss the consequences of our results to
single molecule imaging by the free electron laser pulses.Comment: 14 pages, 13 figure
The effect of tamper layer on the explosion dynamics of atom clusters
The behavior of small samples in very short and intense hard x-ray pulses is
studied by molecular dynamics type calculations. The main emphasis is put on
the effect of various tamper layers about the sample. This is discussed from
the point of view of structural imaging of single particles, including not only
the distortion of the structure but also the background conditions. A detailed
picture is given about the Coulomb explosion, with explanation of the tampering
mechanism. It is shown that a thin water layer is efficient in slowing down the
distortion of the atomic structure, but it gives a significant contribution to
the background
Measurement of synchrotron-radiation-excited Kossel patterns
Kossel line patterns contain information on the crystalline structure, such as the
magnitude and the phase of Bragg reflections. For technical reasons, most of
these patterns are obtained using electron beam excitation, which leads to
surface sensitivity that limits the spatial extent of the structural information. To
obtain the atomic structure in bulk volumes, X-rays should be used as the
excitation radiation. However, there are technical problems, such as the need
for high resolution, low noise, large dynamic range, photon counting, twodimensional
pixel detectors and the small spot size of the exciting beam, which
have prevented the widespread use of Kossel pattern analysis. Here, an
experimental setup is described, which can be used for the measurement of
Kossel patterns in a reasonable time and with high resolution to recover
structural information
Rugalmas röntgenszórás a szerkezetkutatásban = Elastic x-ray scattering in structural research
Kutatásaink az atomi szerkezet röntgensugárzással valĂł vizsgálatát cĂ©lozták. Ezen belĂĽl kutatásunk három fĹ‘ irányban folyt: 1. Megvizsgáltuk, hogy a közeljövĹ‘ben Ă©pĂĽlĹ‘ lineáris gyorsĂtĂłkon alapulĂł szabad elektron lĂ©zer tĂpusĂş röntgenforrásokkal (Free Electron Laser, FEL) lesz-e lehetĹ‘sĂ©g egyedi, kis, nem-periodikus rĂ©szecskĂ©k atomi szintű szerkezet-meghatározására. MegállapĂtottuk, hogy a sikeres szerkezet-meghatározáshoz a tervezetnĂ©l rövidebb impulzushosszal rendelkezĹ‘ forrásokra lesz szĂĽksĂ©g. Megmutattuk, hogy a folytonos szĂłráskĂ©pbĹ‘l a "Fineup input-output" algoritmus egy mĂłdosĂtott változatával rekonstruálhatĂł az eredeti atomi szerkezet. RĂ©szletesen diszkutáltuk, hogy a teljes 3D szĂłráskĂ©p előállĂtásához szĂĽksĂ©ges klasszifikáciĂłs eljárás milyen feltĂ©telek között működik. 2. A holografikus mĂłdszerekkel rokon mĂ©rĂ©si eljárások elmĂ©leti Ă©s gyakorlati megvalĂłsĂtásán dolgoztunk. SzĂ©lesĂtettĂĽk a röntgen fluoreszcens holográfia alkalmazási terĂĽletĂ©t, kĂ©t Ăşj anyag vizsgálatával (ThAs Se Kondo rendszer Ă©s La1-xSrxMnO3 mágneses kolosszális mágneses ellenállást mutatĂł rendszer). Egy Ăşj mĂ©rĂ©si eljárást vezettĂĽnk be, a szögintegrált rugalmas szĂłrást, amely számos elĹ‘nyös tulajdonsággal rendelkezik a hagyományos szerkezet-meghatározĂł mĂ©rĂ©sekkel összehasonlĂtva. 3. Hagyományos röntgendiffrakciĂłs mĂłdszerekkel vizsgáltuk ismeretlen, Ăşj anyagok szerkezetĂ©t. Meghatároztuk, fullerĂ©n Ă©s kubán molekulák alkotta vegyĂĽletek szerkezetĂ©t, Ă©s tanulmányoztuk a hĹ‘mĂ©rsĂ©kletváltozás eredmĂ©nyekĂ©nt lĂ©trejövĹ‘ fázisátalakulásokat. | We worked on atomic level structure determination by x-rays. Our research was centered on three main points: 1. We examined the possibility of structure reconstruction of small, non-periodic single particles using x-ray free electron laser type sources. We have shown that the pulse length has to be significantly shortened (compared to present day planes) for successful reconstruction. Further, we illustrated that a modified version of the Fineup input-output algorithm can be used to reconstruct the original atomic structure. We also discussed in detail the conditions in which the classification process could work. 2. We worked on theoretical and practical sides of holographic and related methods. We applied x-ray fluorescent holography to a Kondo system (ThAsSe) and a colossal magnetic resistivity material (La1-xSrxMnO3), this way widening the application of holography. We introduced a new measuring method (the angular integrated elastic scattering), which has several advantages compared to classical methods. 3. Using traditional x-ray diffraction techniques we investigated the atomic structure of new compounds. We determined the structure of new fullerene-cubane compounds and studied the phase transitions as a function of the temperature
Holografikus módszerek a szerkezetkutatásban = Holographic methods in structural research
Az atomi felbontásĂş röntgen holográfia elmĂ©leti alapjait 1991-ben dolgoztuk ki Ă©s nĂ©hány Ă©vel kĂ©sĹ‘bb vĂ©geztĂĽk el az elsĹ‘ sikeres kĂsĂ©rletet. Jelen pályázat fĹ‘ cĂ©lja az atomi felbontásĂş röntgen holográfia Ă©s egy Ăşj, a holográfiával rokon mĂ©rĂ©si mĂłdszer, a szögátlagolt rugalmas szĂłrás továbbfejlesztĂ©se Ă©s alkalmazása volt. Holográfia mĂ©rĂ©sek segĂtsĂ©gĂ©vel kimutattuk, hogy a La0.7Sr0.3MnO3 kristály fázisátalakulásánál nem lĂ©p fel statikus Jahn-Teller torzulás, ahogy korábban feltĂ©teleztĂ©k. KĂsĂ©rleti adatokbĂłl megmutattuk, hogy a szögátlagolt szĂłrás eredmĂ©nyekĂ©nt kapott kĂ©p ugyanazt az informáciĂłt hordozza, mint a hagyományos egykristály diffrakciĂł során egyenkĂ©nt összegyűjtött intenzitás adatok. MegvalĂłsĂtottunk egy Ăşjfajta elektron holográfia mĂ©rĂ©st egy erre a cĂ©lra átĂ©pĂtett pásztázĂł elektron mikroszkĂłp segĂtsĂ©gĂ©vel. EredmĂ©nyeket Ă©rtĂĽnk el a holografikus Ă©s diffrakciĂłs kiĂ©rtĂ©kelĂ©si mĂłdszerek továbbfejlesztĂ©se terĂ©n. Kidolgoztunk egy eljárást a kis intenzitásĂş szĂłráskĂ©pek osztályozására a röntgen szabadelektron lĂ©zereknĂ©l egyedĂĽlállĂł molekulákon vĂ©gzendĹ‘ szĂłráskĂsĂ©rletekhez. | The theoretical foundations of atomic resolution x-ray holography were developed in 1991, and followed by the first successful experiment a few years later. The aim of the present project was the further development and application of the atomic resolution x-ray holography and a new related method, the angular integrated elastic scattering. Based on holography measurements, we have shown that in spite of earlier predictions, no static Jahn-Teller distortion occurs at the phase transition of the La0.7Sr0.3MnO3 crystal. We have shown from experimental data that the angular integrated elastic scattering pattern contains the same information as the intensity data of the conventional x-ray diffraction experiments. A novel electron holography experiment was realized using a scanning electron microscope modified for this purpose. Further development of holographic and diffraction evaluation methods was achieved. We have also developed a new method for the classification of low-intensity diffraction patterns for the single molecule imaging experiments of the x-ray free electron lasers