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Computational investigations towards tailor-made Si/Ge semiconductors

Computational investigations towards tailor-made Si/Ge semiconductors. Treffen der Christiane Nüsslein- Volhard Stipendiatinnen am 19.07.2013. Laura-Alice Jantke , Chair of Inorganic Chemistry with Focus on New Materials (Prof. Dr. T. F. Fässler ), TU München. Introduction.

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Computational investigations towards tailor-made Si/Ge semiconductors

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  1. Computational investigations towardstailor-made Si/Ge semiconductors Treffen der Christiane Nüsslein-Volhard Stipendiatinnen am 19.07.2013 Laura-Alice Jantke, ChairofInorganic Chemistry with Focus on New Materials (Prof. Dr. T. F. Fässler), TU München

  2. Introduction chemistry.about.com, 04.07.2013

  3. Carbon Group Introduction chemistry.about.com, 04.07.2013

  4. The Carbon Group CarbonPure Carbonisknown in severalmodifications, ofwhichfourarethemostfamous: Diamond1 Cubicmodificationof C with all C-atoms in tetragonal environment • insulatorwithhighesthardnessof all knownelements • colorless Grapheneand Fullerene2 Graphite1 LayeredstructureofCarbon • Soft material withelectricconductivity in onedirection • greywith metallic luster • layerscaneasilybeshiftedagainsteachother • Promising materials for catalysis, super- and semi-conductors, medical use … • thin, strong, transparent and flexible as a 2D layer 1 Holleman, Wiberg, Lehrbuch der Anorganischen Chemie, 100. Auflage, Walter de Gruyter, Berlin, New York 1985. 2 Geim, A. K.; Novoselov, K. S.; Nature Materials 6 (3),2007, 183–191. Figure: http://www.jameshedberg.com/lettera/2010/07/05/graphene-models/

  5. Introduction The reasonforthese large differencesisthechange in thecrystalstructure! Diamond Eachatomis tetragonal bondedto 4 other C-atoms (109.4°angles) Graphite Atoms have 3 neighborsandconjugatedlonepairs (electroncloudsaroundeverylayer)

  6. Silicon and Germanium both are semiconductors • solar cells • microchips • LEDs Attempts for improving the properties of such materials • band gap tuning • Either with doping/replacing atoms with others • Or with changing the crystal structure = modification • open framework materials with space for moving ions picture: Siemens-Pressebild, solar parc in South France

  7. New Materials Twoapproachestowardsthecreationofnewand promising materials • Modificationsof well-knownstructures, hereα-Silicon (cubicdiamondstructureof Si) • Foremostcomputationalapproach • Polymerizationofknownbuildingblockswithingivenlimitations, herethe Zintl-type ions [E9]4–and [E4]4– (E = Si, Ge, Sn) • Alreadydone, but limitsforpolymerizationandformationofbuildingblockshavetobeunderstood

  8. New Materials Twoapproachestowardsthecreationofnewand promising materials • Modificationsof well-knownstructures, hereα-Silicon (cubicdiamondstructureof Si) • Foremostcomputationalapproach • Polymerizationofknownbuildingblockswithingivenlimitations, herethe Zintl-type ions [E9]4–and [E4]4– (E = Si, Ge, Sn) • Alreadydone, but limitsforpolymerizationandformationofbuildingblockshavetobeunderstood

  9. 1. New Silicon modificationsbased on α-Si • Cut through ab-plane • 2b-Si • Approachingblack resp. whiteatoms • 3b-Si • Stackinglayers • 4b-Si Stegmaier, S.; Kim, S.-J.; Henze, A.; Fässler, T. F., J. Am. Chem. Soc. 2013.

  10. 1. New Silicon modificationsbased on α-Si • Cut through ab-plane • 2b-Si • Approachingblack resp. whiteatoms • 3b-Si • Stackinglayers • 4b-Si

  11. 1. New Silicon modificationsbased on α-Si • Cut through ab-plane • 2b-Si • Approachingblack resp. whiteatoms • 3b-Si • Stackinglayers • 4b-Si

  12. 1. New Silicon modificationsbased on α-Si • Many created structures are already known for Si or other elements, e.g. the NaSnZn or LiSiB system • Different band gaps • Vast variety of structural features suitable for semi-conductors

  13. New Materials Twoapproachestowardsthecreationofnewand promising materials • Modificationsof well-knownstructures, hereα-Silicon (cubicdiamondstructureof Si) • Foremostcomputationalapproach • Polymerizationofknownbuildingblockswithingivenlimitations, herethe Zintl-type ions [E9]4–and [E4]4– (E = Si, Ge, Sn) • Alreadydone, but limitsforpolymerizationandformationofbuildingblockshavetobeunderstood

  14. Understanding [E9]4– A Zintl-cluster withC4vsymmetry • Onemolecularclusterwithsharedelectronshells • Actinglikebeing a fourfoldnegativelychargedion – a „superion“ • The reactivity, electrondistribution, andstructuralflexibilityis different foreachsite • Solidsmadeofaresalt-likeandtheionis soluble

  15. Understanding [E9]4– The frameworkcan also bemadeof Si AND Ge • All isomersof Si8Ge and [Si7Ge2]4–show different total energies open face< cap < cappedsquare • The partial chargeis different foreachsite open face> cap> cappedsquare • theflexibilityofthestructurediffersforeachsite [1] L. Jantke, A. J. Karttunen, T. F. Fässler, submittedtoInorg. Chem.

  16. Understanding [E9]4– Investigationsbased on Rb4Si7.8Ge1.2(NH3)51-2 E1: 40.1(9)% E2: 25.4(9)% E3: 11.2(8)% E4: 20.9(9)% 24.4% E5: - E6: 9.4(9)% E7: - E8: - 2.3% E9: 3,7(9)% 3.7% The experiment indicates different probabilities for finding Ge in each position The computational analysis shows exactly the same! [1] M. Waibel, C. B. Benda, B. Wahl, T. F. Fässler, Chem. Eur. J.2011, 17, 12928. [2] L. Jantke, A. J. Karttunen, T. F. Fässler, submittedtoInorg. Chem.

  17. Understanding [E9]4– Whyisthisimportantforbuildingnewmaterials? Ifcertainpositionsshouldbereplacedwith Ge/Si, oneshouldknowthelimitsfordoing so! Karttunen, A. J.; Faessler, T. F.; Linnolahti, M.; Pakkanen, T. A.,ChemPhysChem2010,11 (9), 1944-1950.

  18. Understanding possiblebuildingblocks Such clusterscan also befilledwithmetals Change ofgap Real doping in molecularscale Hlukhyy, V.; He, H., Jantke, L.-A.; Fässler, T. F.; Chem Eur. J.2012, 18 (38), 12000.

  19. The smaller [E4]4–clusters [E4]4– and all mixturesthereofaspartof a salt • The mixingpropertiesof Si and Ge analyzed in themostaccessiblesaltA4E4 (A = K, Rb, Cs)1 • Experiment andcalculationsshowthatmixingof homoatomic clustersandtheformationofmixedclustersispossible • I couldassignthe Raman spectrumandthepowderdiffractogramto all kindsofclustersandindentifycertainfingerprintsforeachspecies [1] Jantke, L.-A.; Karttunen, A. J.; Fässler, T. F., unpublishedresults.

  20. The smaller [E4]4–clusters Solving[E4]4–is not very trivial1 • The electronic propertiesof[Ge4]4–areanalyzedforunderstandingtheprocessofsolvingthem • Polymerizationof such buildingblocksseemstobe a lotharder… [1] Stegmaier, S.; Waibel, M.; Henze, A.; Jankte, L.-A.; Karttunen, A. J.; Fässler, T. F., J. Am. Chem. Soc.2012, 134 (35), 14450.

  21. Thankyouverymuchforyorattention! Thomas Fässler, AnttiKarttunen Rosalie Jantke&Family Christiane-Nüsslein-VolhardStiftung Laura-Alice Jantke, ChairofInorganic Chemistry with Focus on New Materials (Prof. Dr. T. F. Fässler), TU München

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