X-ray absorption spectroscopy investigation of structurally modified lithium niobate crystals [Elektronische Ressource] / von Tonya Vitova. Universität Bonn, Physikalisches Institut

Tonya Vitova

Sujets

• Physik

Informations

• Publié par: rheinische_friedrich-wilhelms-universitat_bonn
• Publié le: 01 janvier 2009
• Nombre de lectures: 4
• Langue: English
• Poids de l'ouvrage: 7 Mo

Extrait

..
UNIVERSITAT BONN
Physikalisches Institut
X-ray absorption spectroscopy investigation of
structurally modified lithium niobate crystals
von
Tonya Vitova
Thetypeandconcentrationofimpuritycentersindifferentvalencestates
are crucial for tuning the photorefractive properties of doped Lithium
Niobate (LN) crystals. X-ray Absorption Spectroscopy (XAS) is an ap-
propriate tool for studying the local structure of impurity centers. XAS
combined with absorption in UV/VIS/IR and High Resolution X-ray
Emission Spectroscopy (HRXES) provide information about the valence
state of the dopant ions in as-grown, reduced or oxidized doped LN crys-
1+ 2+ 2+ 3+tals. Cu (Cu and Cu ) and Fe (Fe and Fe ) atoms are found in two
different valence states, whereas there are indications for a third Mn va-
2+ 3+lency, in addition to Mn and Mn in manganese-doped LN crystals.
One of the charge compensation mechanisms during reduction of copper-
doped LN crystals is outgassing of oxygen atoms. Cu ions in the reduced
1+crystals have at least two different site symmetries: twofold (Cu ) and
2+sixfold(Cu )coordinatedbyOatoms.FeandMnatomsarecoordinated
bysixOatoms.CuandFeionsarefoundtooccupy onlyLisites,whereas
Mn ions are also incorporated into Li and Nb sites. The refractive index
3 2+change in LNcrystals irradiatedwith He ionsiscaused by structurally
disordered centers, where Nb atoms are displaced from normal crystal-
lographic sites and Li or/and O vacancies are present.
Post address: BONN-IR-2008-03
Nussallee 12 Bonn University
53115 Bonn February 2008
Germany ISSN-0172-8741..
UNIVERSITAT BONN
Physikalisches Institut
X-ray absorption spectroscopy investigation of
structurally modified lithium niobate crystals
von
Tonya Vitova
Dieser Forschungsbericht wurde als Dissertation von der Mathematisch - Naturwissenschaftlichen
Fakulta¨t der Universita¨t Bonn angenommen.
Tag der Promotion: 8.02.2008
Referent: Prof. Dr. J. Hormes
Korreferent: Prof. Dr. K. Maier
Diese Dissertation ist auf dem Hochschulschriftenserver der ULB Bonn unter http://hss.ulb.uni-
bonn.de/diss online elektronisch publiziert.
Erscheinungsjahr: 2009To my parents and my VladyContents
1 Motivation 1
2 Fundamentals of XAS 4
2.1 The X-ray absorption process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.2 The XANES spectrum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2.1 Qualitative interpretation of a XANES spectrum . . . . . . . . . . . . . . . . 7
2.2.2 Quantitative interpretation of a XANES spectrum . . . . . . . . . . . . . . . 8
2.3 The EXAFS spectrum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.3.1 Quantitative interpretation of an EXAFS spectrum . . . . . . . . . . . . . . 12
3 Fundamentals of High Resolution X-ray Emission Spectroscopy (HRXES) 17
3.1 Non-resonant HRXES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
3.2 Resonant HRXES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.2.1 Extended resonant HRXES . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
4 The experiments 25
4.1 ANKA and DORIS III . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
4.2 The INE-Beamline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
4.2.1 The measuring modes and the experimental set-up . . . . . . . . . . . . . . 27
4.2.2 The Double Crystal Monochromator (DCM) . . . . . . . . . . . . . . . . . . 30
4.2.3 The samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
4.3 The W1 beamline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
5 Lithium niobate 35
5.1 Growth, defects and structure of the lithium niobate crystals . . . . . . . . . . . . . 35
5.2 Absorption spectra of lithium niobate from IR to hard X-ray regions . . . . . . . . . 36
iContents
6 Doped lithium niobate 40
6.1 Copper-doped lithium niobate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
6.1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
6.1.2 Preparation of the samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
6.1.3 Experiment, methods and data evaluation . . . . . . . . . . . . . . . . . . . 42
6.1.4 Results and discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
6.1.5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
6.2 Manganese-doped lithium niobate . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
6.2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
6.2.2 Samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
6.2.3 Experimental details . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
6.2.4 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
6.2.5 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
6.2.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
6.3 Iron-doped lithium niobate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
6.3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
6.3.2 Samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
6.3.3 Experimental details . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
6.3.4 Results and discussions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
6.3.5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
6.4 Bond Valence Model (BVM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
3 2+7 Lithium niobate irradiated with He ions 79
7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
7.2 Preparation of the samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
7.3 Experiment, methods and data evaluation . . . . . . . . . . . . . . . . . . . . . . . 81
7.4 Results and discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
7.4.1 XANES analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
7.4.2 EXAFS analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
7.5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
8 Summary and outlook 88
A ThestudiedLNclusterandgraphicalcomparison oftheCu,MnandFeEXAFS
results 91
iiContents
B MoO nanoparticles supported on Mesoporous SBA-15: Characterization of3
startingmaterialsandtheproductsusingX-rayscattering,Physisorption,Trans-
mission Electron microscopy, Raman and XAFS spectroscopy 95
B.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
B.2 Experimental section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
B.2.1 Synthesis of pristine Mesoporous SBA-15 . . . . . . . . . . . . . . . . . . . . 96
B.2.2 Synthesis of MoO /SBA-15 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 963
B.3 Results and discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
B.3.1 Powder X-ray Diffraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
B.3.2 Raman spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
B.3.3 Nitrogen physisorption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
B.3.4 Transmission Electron Microscopy and Scanning Electron Microscopy . . . . 103
B.3.5 XAFS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
B.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
iiiChapter 1
Motivation
The increased requirements for larger memory capacities have boosted the development of new
data storage technologies. However, even nowadays, most data storage is based on surface record-
ing technologies, e.g., compact discs, which restricts the usable memory of a storage with a fixed
size. For example, the capacity of a compact disc is about 1 gigabyte, while a disc produced by
InPhase, a holographic technology company, can store up to 200 gigabytes [73]. Another drawback
is the recording speed, which is determined by the bit by bit saving of information. The idea for
implementing the wide use of holografic data storage originates from 1963, when Pieter van Heer-
den, who was working on holographic technologies at Polaroid’s labs in Cambridge Massachusetts,
proposeda storage method basedon alight-inducedrefractiveindexpattern [186]. Theinformation
is stored in the volume of a storage material allowing terabytes memory capacity on half the size of
afloppydisc.Therecordingspeed isincreased byordersof magnitudesincethebits arereplaced by
pages. For data recording a wave called data (data wave), obtained by illuminating from behind a
data page, andareferencewaveinterfere.When thisinterferingpattern illuminates a lightsensitive
material, organic or inorganic [122], its microstructure changes in the light regions. The data wave
is reconstructed by illuminating the storage with the reference wave. Volume recording of pages
with inf