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Engineering ferroelectric domains and charge transport by proton exchange in lithium niobate
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Ferroelectrics are dielectric materials possessing a switchable spontaneous polarization, which have attracted a growing interest for a broad variety of applications such as ferroelectric lithography, artificial photosynthesis, random and dynamic access memories (FeRAMs and DRAM), but also for the fabrication of devices for nonlinear optics, etc. All the aforementioned applications rely on the control of the ferroelectric domains arrangement, or the charge distribution and transport. In this regard, the main prerequisite is the engineering of the spontaneous polarization, obtained by reversing its orientation or locally inhibiting it. In the latter case, the interface created by the spatial discontinuity of the spontaneous polarization generates local charge accumulation, which can be used to extend the capabilities of ferroelectric materials.

This thesis shows how engineering the spontaneous polarization in lithium niobate (LN) by means of proton exchange (PE), a temperature-activated ion exchange process, can be used to develop novel approaches for ferroelectric domain structuring, as well as fabrication of self-assembled nanostructures and control of ionic/electronic transport in this crystal.

In particular, it is shown how the electrostatic charge at PE:LN junctions lying below the crystal surface can effectively counteract lateral domain broadening, which in standard electric field poling hampers the fabrication of ferroelectric gratings for Quasi-Phase Matching with periods shorter than 10 μm. By using such an approach, ferroelectric gratings with periods as small as ~ 8 μm are fabricated and characterized for efficient nonlinear optical applications. The viability of the approach for the fabrication of denser gratings is also investigated.

 The charge distribution at PE:LN junctions lying on the crystal surface is modelled and used to drive the deposition of self-assembled nanowires by means of silver photoreduction. Such a novel approach for PE lithography is characterized for different experimental conditions. The results highlight a marked influence of the orientation of the spontaneous polarization, the deposition times, as well as the reactants concentrations and the doping of the substrate with MgO.

Based on the fact that proton exchange locally reduces the spontaneous polarization, a quick and non-destructive method for imaging PE regions in lithium niobate with nanoscale resolution is also developed by using Piezoresponse Force Microscopy. Moreover the relative reduction of the piezoelectric d33 coefficient associated to PE is estimated in lithium niobate substrates with and without MgO-doping.

Finally, by using advanced Scanning Probe Microscopy techniques, the features of charge transport in PE regions are further investigated with nanoscale resolution. A strong unipolar response is found and interpreted in light of ionic-electronic motion coupling due to the interplay of interstitial protons in the PE regions, nanoscale electrochemical reactions at the tip-surface interface, and rectifying metal-PE junctions.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. , xviii, 153 p.
Series
TRITA-FYS, ISSN 0280-316X ; 2015:15
Keyword [en]
Lithium niobate, Ferroelectrics
National Category
Nano Technology
Research subject
Materials Science and Engineering; Physics
Identifiers
URN: urn:nbn:se:kth:diva-162269ISBN: 978-91-7595-482-0 OAI: oai:DiVA.org:kth-162269DiVA: diva2:797695
Public defence
2015-04-15, Fd5, Albanova University Center, Roslagstullsbacken 21, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20150325

Available from: 2015-03-25 Created: 2015-03-24 Last updated: 2017-02-22Bibliographically approved
List of papers
1. Electrostatic control of the domain switching dynamics in congruent LiNbO3 via periodic proton-exchange
Open this publication in new window or tab >>Electrostatic control of the domain switching dynamics in congruent LiNbO3 via periodic proton-exchange
2011 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 98, no 12, 122910Article in journal (Refereed) Published
Abstract [en]

We propose a model for the poling-inhibiting action of proton-exchange, associated to nonuniform fields induced in the crystal by the vanishing of ferroelectricity in the beta-phase of HxLi1-xNbO3. Predictions are corroborated by experimental results on the poling of 0.5 mm thick congruent LiNbO3 substrates with periods around 8 mu m, yielding regular bulk domain structures with aspect ratios as high as 250.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2011
Keyword
LITHIUM-NIOBATE, WAVE-GUIDES, POLED LINBO3
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-32642 (URN)10.1063/1.3571559 (DOI)000288808200065 ()2-s2.0-79953868812 (Scopus ID)
Funder
Swedish Research Council
Note

QC 20110418

Available from: 2011-04-18 Created: 2011-04-18 Last updated: 2017-12-11Bibliographically approved
2. Two-dimensional domain engineering in LiNbO3 via a hybrid patterning technique
Open this publication in new window or tab >>Two-dimensional domain engineering in LiNbO3 via a hybrid patterning technique
2011 (English)In: Optical Materials Express, ISSN 2159-3930, E-ISSN 2159-3930, Vol. 1, no 3, 365-371 p.Article in journal (Refereed) Published
Abstract [en]

We propose a novel electric field poling technique for the fabrication of nonlinear photonic crystals in congruent LiNbO3 substrates, based on a hybrid bi-dimensional mask, which combines periodic proton-exchange and electrode patterns. With it we demonstrate rectangular bulk lattices with a periodicity of 8 µm x 6.78 µm in 500 µm-thick substrates.

Keyword
Electric field poling, Electrode pattern, Nonlinear photonic crystals, Patterning techniques, Proton-exchange, Two-dimensional domain
National Category
Nano Technology
Identifiers
urn:nbn:se:kth:diva-38035 (URN)10.1364/OME.1.000365 (DOI)000299047600006 ()2-s2.0-84862220434 (Scopus ID)
Funder
Swedish Research Council, VR 621-2008-3601Swedish Research Council, PIEF-GA-2009-234798 622-2010-526
Note

QC 20110930

Available from: 2011-08-19 Created: 2011-08-19 Last updated: 2017-12-08Bibliographically approved
3. Nanoscale characterization of beta-phase HxLi1-xNbO3 layers by piezoresponse force microscopy
Open this publication in new window or tab >>Nanoscale characterization of beta-phase HxLi1-xNbO3 layers by piezoresponse force microscopy
2014 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 116, no 6, 066815- p.Article in journal (Refereed) Published
Abstract [en]

We investigate a non-destructive approach for the characterization of proton exchanged layers in LiNbO3 with sub-micrometric resolution by means of piezoresponse force microscopy (PFM). Through systematic analyses, we identify a clear correlation between optical measurements on the extraordinary refractive index and PFM measurements on the piezoelectric d(33) coefficient. Furthermore, we quantify the reduction of the latter induced by proton exchange as 83 +/- 2% and 68 +/- 3% of the LiNbO3 value, for undoped and 5mol. % MgO-doped substrates, respectively.

Keyword
Niobium oxide, Optical data processing, Refractive index, Nanoscale characterization, Non destructive, Optical measurement, Piezoresponse force microscopy, Proton exchange, Proton exchanged, Systematic analysis
National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-152585 (URN)10.1063/1.4891352 (DOI)000341179400093 ()2-s2.0-84906303081 (Scopus ID)
Funder
Swedish Research Council, VR 622-2010-526 621-2011-4040
Note

QC 20140929

Available from: 2014-09-29 Created: 2014-09-29 Last updated: 2017-12-05Bibliographically approved
4. Photoreduction of SERS-Active Metallic Nanostructures on Chemically Patterned Ferroelectric Crystals
Open this publication in new window or tab >>Photoreduction of SERS-Active Metallic Nanostructures on Chemically Patterned Ferroelectric Crystals
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2012 (English)In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 6, no 8, 7373-7380 p.Article in journal (Refereed) Published
Abstract [en]

Photodeposition of metallic nanostructures onto ferroelectric surfaces is typically based on patterning local surface reactivity via electric field poling. Here, we demonstrate metal deposition onto substrates which have been chemically patterned via proton exchange (i.e., without polarization reversal). The chemical patterning provides the ability to tailor the electrostatic fields near the surface of lithium niobate crystals, and these engineered fields are used to fabricate metallic nanostructures. The effect of the proton exchange process on the piezoelectric and electrostatic properties of the surface is characterized using voltage-modulated atomic force microscopy techniques, which, combined with modeling of the electric fields at the surface of the crystal, reveal that the deposition occurs preferentially along the boundary between ferroelectric and proton-exchanged regions. The metallic nanostructures have been further functionalized with a target probe molecule, 4-aminothiophenol, from which surface-enhanced Raman scattering (SERS) signal is detected, demonstrating the suitability of chemically patterned ferroelectrics as SERS-active templates.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2012
Keyword
ferroelectrics, lithium niobate, nanofabrixcation, Raman, photochemistry
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-104098 (URN)10.1021/nn3025145 (DOI)000307988900098 ()2-s2.0-84865594484 (Scopus ID)
Funder
Swedish Research Council, 622-2010-526Swedish Research Council, 621-2011-4040EU, European Research Council, PIEF-2009-234798
Note

QC 20150624

Available from: 2012-10-29 Created: 2012-10-29 Last updated: 2017-12-07Bibliographically approved
5. Growth mechanism of photoreduced silver nanostructures on periodically proton exchanged lithium niobate: Time and concentration dependence
Open this publication in new window or tab >>Growth mechanism of photoreduced silver nanostructures on periodically proton exchanged lithium niobate: Time and concentration dependence
Show others...
2013 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 113, no 18, 187212-1-187212-7 p.Article in journal (Refereed) Published
Abstract [en]

Photodeposition of metallic nanostructures onto ferroelectric surfaces, which have been chemically patterned using a proton exchange process, has recently been demonstrated. By varying the molar concentration of the AgNO 3 solution and the illumination time, one can determine the initial nucleation sites, control the rate of nucleation and the height of silver nanostructures formed, and study the mechanisms by which these processes occurs. The nanoparticles are found to deposit preferentially in the boundary between ferroelectric and proton exchanged regions, in an area proton exchanged via lateral diffusion under the masking layer used for chemical patterning, consistent with our previous results. Using a short illumination time (3 min), we are able to determine that the initial nucleation of the silver nanostructure, having a width of 0.17 ± 0.02 μm and a height of 1.61 ± 0.98 nm, occurs near the edge of the reactive ion etched area within this lateral diffusion region. Over longer illumination times (15 min), we find that the silver deposition has spread to a width of 1.29 ± 0.06 μm, extending across the entire lateral diffusion region. We report that at a high molar concentration of AgNO3 (10-2 M), the amount of silver deposition for 5 min UV illumination is greater (2.88 ± 0.58 nm) compared to that at low (10-4 M) concentrations (0.78 ± 0.35 nm), however, this is not the case for longer time periods. With increasing illumination time (15 min), experiments at 10-4 M had greater overall deposition, 6.90 ± 1.52 nm, compared to 4.50 ± 0.76 nm at 10 -2 M. For longer exposure times (30 min) at 10-2 M, the nanostructure height is 4.72 ± 0.59 nm, suggesting a saturation in the nanostructure height. The results are discussed in terms of the electric double layer that forms at the crystal surface. There is an order of magnitude difference between the Debye lengths for 10-2 and 10-4 M solutions, i.e., 3.04 vs. 30.40 nm, which suggests the Debye length plays a role in the availability of Ag ions at the surface.

Keyword
Chemical patterning, Concentration dependence, Electric double layer, Ferroelectric surfaces, Metallic nanostructure, Molar concentration, Proton exchange process, Silver nanostructures, Deposition, Diffusion, Ferroelectricity, Nucleation, Nanostructures
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-134472 (URN)10.1063/1.4801963 (DOI)000319294100118 ()2-s2.0-84878027065 (Scopus ID)
Conference
21st IEEE International Symposium on Applications of Ferroelectrics held jointly with 11th European Conference on the Applications of Polar Dielectrics and 4th Conference on Piezoresponse Force Microscopy and Nanoscale Phenomena in Polar Materials, Univ Aveiro, Aveiro, Portugal, July 09-13, 2012
Note

QC 20131129

Available from: 2013-11-29 Created: 2013-11-25 Last updated: 2017-12-06Bibliographically approved
6. Direct shape control of photoreduced nanostructures on proton exchanged ferroelectric templates
Open this publication in new window or tab >>Direct shape control of photoreduced nanostructures on proton exchanged ferroelectric templates
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2013 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 102, no 4, 042908- p.Article in journal (Refereed) Published
Abstract [en]

Photoreduction on a periodically proton exchanged ferroelectric crystal leads to the formation of periodic metallic nanostructures on the surface. By varying the depth of the proton exchange (PE) from 0.59 to 3.10 mu m in congruent lithium niobate crystals, the width of the lateral diffusion region formed by protons diffusing under the mask layer can be controlled. The resulting deposition occurs in the PE region with the shallowest PE depth and preferentially in the lateral diffusion region for greater PE depths. PE depth-control provides a route for the fabrication of complex metallic nanostructures with controlled dimensions on chemically patterned ferroelectric templates.

Keyword
Wave-Guides, Photochemical Reduction, Linbo3, Surface
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-119475 (URN)10.1063/1.4789412 (DOI)000314723600065 ()2-s2.0-84873595914 (Scopus ID)
Funder
Swedish Research Council, VR 622-2010-526 621-2011-4040
Note

QC 20130315

Available from: 2013-03-15 Created: 2013-03-14 Last updated: 2017-12-06Bibliographically approved
7. Photoreduction of metal nanostructures on periodically proton exchanged MgO-doped lithium niobate crystals
Open this publication in new window or tab >>Photoreduction of metal nanostructures on periodically proton exchanged MgO-doped lithium niobate crystals
Show others...
2013 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 103, no 18, 182904- p.Article in journal (Refereed) Published
Abstract [en]

Local reactivity on periodically proton exchanged lithium niobate (PPE: LN) surfaces is a promising route for the fabrication of regularly spaced nanostructures. Here, using MgO-doped PPE: LN templates, we investigate the influence of the doping on the nanostructure formation as a function of the proton exchange (PE) depth. The deposition is found to occur preferentially along the boundary between MgO-doped LN and the PE region when the PE depth is at least 1.73 mu m, however, for shallower depths, deposition occurs across the entire PE region. The results are found to be consistent with an increased photoconductivity of the MgO-doped LN.

Keyword
Charge-Transport Processes, Wave-Guides, Photorefractive Crystals, Linbo3, Nanoparticles, Reduction, Template, Titanate, Surface, Silver
National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-139226 (URN)10.1063/1.4827541 (DOI)000327816000053 ()2-s2.0-84889639728 (Scopus ID)
Funder
Swedish Research Council, VR 622-2010-526 621-2011-4040
Note

QC 20140110

Available from: 2014-01-10 Created: 2014-01-08 Last updated: 2017-12-06Bibliographically approved

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