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Studies on Domain Wall Properties andDynamics in KTiOPO4 and Rb-doped KTiOPO4
KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

KTiOPO4 (KTP) and Rb-doped KTP (RKTP) are two of the most attractive nonlinear opticalmaterials for engineering of periodically poled domain structures, commonly used as frequencyconversiondevices for laser radiation via the quasi-phase matching (QPM) technique. Thesematerials have excellent non-linearity, wide transparency windows and high resistance to opticaldamage. Furthermore their large domain-velocity anisotropy allows the fabrication of highaspect-ratio domain structures, needed for many QPM applications. To create highly efficientdevices, precise control over the structure uniformity and duty-cycle is required. Constantimprovement of the domain engineering techniques has allowed pushing the limits of theachievable domain aspect-ratio. For this development to continue, a deeper understanding of theformation dynamics and stability of the domain gratings is of utmost importance. As the domainsizein nanostructured devices decreases, the density of the domains walls (DWs) increases andtheir properties are ever more important for device performance. Indeed, more knowledge on thedomain wall properties, and the means to engineer them, could enable new applicationsexploiting these properties.This thesis presents studies on domain wall properties and dynamics in KTP and RKTP. Thesub-millisecond dynamics of grating formation in RKTP under an applied electric field has beenstudied in the high-field regime using online second harmonic generation. The effects ofdifferent pulse shapes were compared and single triangular pulses were found to be superior interms of the resulting grating quality.The high-temperature stability of domain gratings was investigated. The domain wall motioninduced by annealing was shown to be highly anisotropic along the a- and b-crystal axes, anddependent on the period of the grating period.The local charge transportation at the domains and domain walls in KTP was characterized usingatomic force microscopy, demonstrating a fourfold increase of conductivity at the walls.Voltage-cycling measurements revealed memristive-like characteristics, attributed to the effectof ionic motion and local charge accumulation. The enhanced conductivity of charged domainwalls was used as an imaging tool, to study domain wall dynamics while inducing motionthrough the application of an external field.Finally, the interplay between ionic motion, spontaneous polarization and polarization reversalwas investigated, showing direct evidence of elastic modulus modification during localpolarization switching.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2017.
Series
TRITA-FYS, ISSN 0280-316X ; 2017:71
National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
URN: urn:nbn:se:kth:diva-217379ISBN: 978-91-7729-598-3 (print)OAI: oai:DiVA.org:kth-217379DiVA: diva2:1156153
Public defence
2017-12-08, FA31, Roslagstullsbacken 21, Stockholm, 10:00 (English)
Supervisors
Funder
Swedish Foundation for Strategic Research Swedish Research Council
Note

QC 20171113

Available from: 2017-11-13 Created: 2017-11-10 Last updated: 2017-11-13Bibliographically approved
List of papers
1. Studies of sub-millisecond domain dynamics in periodically poled Rb-doped KTiOPO4, using online in situ second harmonic generation
Open this publication in new window or tab >>Studies of sub-millisecond domain dynamics in periodically poled Rb-doped KTiOPO4, using online in situ second harmonic generation
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2015 (English)In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 23, no 16, 20332-20339 p.Article in journal (Refereed) Published
Abstract [en]

The temporal evolution of in situ second-harmonic generation was employed to study domain dynamics during periodic poling in Rb-doped KTP. With this method we investigated the influence of various poling parameters, including electric-field pulse shape, pulse magnitude, and number of pulses, on the quality of the QPM structure. It was found that the grating formation can be a sub-millisecond process and the benefits of using symmetric triangular electric-field pulse shape over square pulse shape in the single-pulse poling regime were demonstrated. Multiple-pulse poling with triangular pulses was shown to have a detrimental effect on the QPM structure quality, while multiple square pulses can provide additional flexibility to the structuring process.

Place, publisher, year, edition, pages
[Lindgren, Gustav; Zukauskas, Andrius; Pasiskevicius, Valdas; Laurell, Fredrik; Canalias, Carlota] Royal Inst Technol, Dept Appl Phys, S-10691 Stockholm, Sweden.: , 2015
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-174241 (URN)10.1364/OE.23.020332 (DOI)000361036400012 ()26367888 (PubMedID)2-s2.0-84957568116 (Scopus ID)
Note

QC 20151014

Available from: 2015-10-14 Created: 2015-10-02 Last updated: 2017-11-10Bibliographically approved
2. Thermal stability of ferroelectric domain gratings in Rb-doped KTP
Open this publication in new window or tab >>Thermal stability of ferroelectric domain gratings in Rb-doped KTP
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2015 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 107, no 8, 082906Article in journal (Refereed) Published
Abstract [en]

We study the thermal stability of domain walls in periodically poled Rb-doped KTP crystals. Domain-wall motion is observed after annealing the crystals above 550 degrees C. This motion is highly anisotropic along the a- and b- crystallographic axes. Along the b-axis domain wall motion is in the order of tens of micrometers. In the a-direction, it results in either three orders of magnitude smaller domain wall displacement or in domain merging, depending on the initial domain configuration. We show that the thermal stability of the domain gratings depends on their periodicity, resulting in complete backswitching for sub-micrometer domains annealed at 730 degrees C.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2015
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-173981 (URN)10.1063/1.4929817 (DOI)000360593900056 ()2-s2.0-84940524547 (Scopus ID)
Funder
Swedish Foundation for Strategic Research Swedish Research Council
Note

QC 20151005

Available from: 2015-10-05 Created: 2015-09-24 Last updated: 2017-11-10Bibliographically approved
3. Domain wall conductivity in KTiOPO4 crystals
Open this publication in new window or tab >>Domain wall conductivity in KTiOPO4 crystals
2017 (English)In: APL Materials, ISSN 2166-532X, Vol. 5, no 7, 076108Article in journal (Refereed) Published
Abstract [en]

We study the local ionic conductivity of ferroelectric domain walls and domains in KTiOPO4 single-crystals. We show a fourfold increase in conductivity at the domain walls, compared to that of the domains, attributed to an increased concentration of defects. Our current-voltage measurements reveal memristive-like behavior associated with topographic changes and permanent charge displacement. This behavior is observed for all the voltage sweep-rates at the domain walls, while it only occurs for low frequencies at the domains. We attribute these findings to the redistribution of ions due to the applied bias and their effect on the tip-sample barrier.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2017
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-212946 (URN)10.1063/1.4995651 (DOI)000406640500024 ()2-s2.0-85026263836 (Scopus ID)
Funder
Swedish Foundation for Strategic Research Swedish Research Council
Note

QC 20170825

Available from: 2017-08-25 Created: 2017-08-25 Last updated: 2017-11-10Bibliographically approved
4. Conductive properties of charged domain walls in motion in KTiOPO4
Open this publication in new window or tab >>Conductive properties of charged domain walls in motion in KTiOPO4
(English)In: Article in journal (Refereed) Submitted
National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
urn:nbn:se:kth:diva-217478 (URN)
Note

QC 20171113

Available from: 2017-11-13 Created: 2017-11-13 Last updated: 2017-11-13Bibliographically approved
5. Direct evidence of ionic migration during local ferroelectric switching
Open this publication in new window or tab >>Direct evidence of ionic migration during local ferroelectric switching
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(English)In: Article in journal (Refereed) Epub ahead of print
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-217481 (URN)
Note

QC 20171113

Available from: 2017-11-13 Created: 2017-11-13 Last updated: 2017-11-13Bibliographically approved

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