IJS KOLOKVIJ, Sreda, 12. 10. 2016; ob 13. uri; prof. dr. Peter A. van Aken

[Tanja Debevec]

Vabimo vas na 4. predavanje iz sklopa "Kolokviji na IJS" v letu 2016/17, ki bo v sredo, 12. oktobra 2016, ob 13. uri v Veliki predavalnici Instituta »Jožef Stefan«  na Jamovi cesti 39 v Ljubljani. Napovednik predavanja najdete tudi na naslovu http://www.ijs.si/ijsw/Koledar_prireditev, posnetke preteklih predavanj pa na http://videolectures.net/kolokviji_ijs. 

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prof. dr. Peter A. van Aken

Max Planck Institute for Solid State Research, Stuttgart, Nemčija

 

Strukturni defekti in lokalna kemija vmesnih struktur kompleksnih oksidnih medfaznih mej

 

Fizikalne in kemijske lastnosti oksidov prehodnih kovin, kot so feroelektričnost, magnetizem, ionska in elektronska prevodnost,  so odvisne predvsem od  njihovih kristalnih struktur, ki so bile v preteklih letih intenzivno raziskovane. Zamenjava kationov v kompleksnih oksidih je učinkovit način za razvoj različnih funkcionalnosti preko dopiranja, spreminjanja elektronskih pasov ali uporabe kemijskega tlaka. Sklopitev med nabojem in spinskimi prostostnimi stopnjami preko stičnih mej ter profili koncentracij nosilcev naboja imajo na primer velik vpliv na pojav superprevodnosti v nizkodimenzionalnih sistemih. Superprevodnost nastopi, ko izolatorsko spojino dopiramo preko kritične koncentracije. Obenem lahko magnetno obnašanje in prevodnost superstruktur kompleksnih oksidnih supercelic prilagajamo z debelino plasti in z izbiro primernega vmesnega sloja.

Na voljo imamo različne metode za rast nadzorovanih supercelic, med katerimi je verjetno najbolj priljubljeno pulzno lasersko nanašanje (ang. pulsed laser deposition, PLD). Vse popularnejša je uporaba epitaksije z molekularnim curkom (ang. molecular beam epitaxy, MBE) zaradi nadzorovane hitrosti depozicije in prilagodljivosti uporabe posameznih virov elementov, s katero lahko teoretično spreminjamo kemijsko sestavo od plasti do plasti. PLD zahteva višje temperature in tlake kot MBE ter višje energije delcev v curku, kar povzroča hrapavost površine. V predavanju bomo predstavili probleme mapiranja lokalnih struktur in površinske kemije faznih mej različnih kompleksnih oksidov s pomočjo vrstičnega presevnega elektronskega mikroskopa (S-TEM) v kombinaciji z energijsko-disperzijsko spektroskopijo rentgenskih žarkov (ang. energy-dispersive x-ray spectroscopy, EDXS) in spektroskopijo merjenja izgub energije elektronov (ang. electron energy-loss spectroscopy, EELS). EELS omogoča lokalno analizo kemijske sestave in vezi kot tudi elektronskih in magnetnih struktur, zato je kombinacija EELS in S-TEM idealna za študij povezav strukturnih lastnosti na atomski ravni.

Predavanje bo v angleščini.

Lepo vabljeni!

 

 

 




We invite you to the 4th Institute colloquium in the academic year 2016/17. The colloquium will be held on Wednesday October 12, 2016 at 1 PM in the main Institute lecture hall, Jamova 39, Ljubljana. To read the abstract click  http://www.ijs.si/ijsw/Koledar_prireditev. Past colloquia are posted on  http://videolectures.net/kolokviji_ijs.

 

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prof. dr. Peter A. van Aken

Max Planck Institute for Solid State Research, Stuttgart, Germany

 

Structural defects and local interfacial chemistry of complex oxide heterointerfaces

 

Transition metal oxide superlattices have been widely investigated during recent years as they are one of the largest material groups where physical and chemical properties such as ferroelectricity, magnetism, ionic and electronic conductivity are closely coupled to structural parameters. Cation sub­sti­tution in complex oxides is an effective way to develop the functionalities through carrier doping, band engineering, or application of chemical pressure. For example, the coupling between charge and spin degrees of freedom across the interfaces and the local charge carrier concentration profiles have profound influences on the occurrence of superconductivity in low dimensional systems. Super­conductivity arises when a parent insulator compound is doped beyond some critical con-centration. Furthermore, the magnetic behaviour and conductivity of complex oxide superlattices can be tuned by controlling the layer thickness and by selecting appropriate intervening layer materials. 

 

Various methods for growing controlled superlattice structures exist, a favourite has been pulsed laser deposition (PLD), but molecular beam epitaxy (MBE) is now also popular because of the controlled deposition rate and the flexibility allowed by the use of individual element sources. In theory, this allows composition control to the level of individual atomic layers. The PLD process requires higher temperatures and pressures than MBE. It also involves significantly higher energies for the impinging particles, which has potential implications for the interface roughness. In this presentation, I will discuss mapping of the local structure and interfacial chemistry of various complex oxide hetero-interfaces through advanced scanning transmission electron microscopy (STEM) in combination with energy-dispersive x-ray (EDX) analysis and electron energy-loss spectroscopy (EELS). EELS allows for local probing of chemical composition and bonding, as well as electronic and magnetic structure, making the combination of STEM and EELS ideal for discovery of structure-property correlations at the atomic scale.

 

Cordially invited!

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