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Photoreduction of metal nanostructures on periodically proton exchanged MgO-doped lithium niobate crystals
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
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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.

Place, publisher, year, edition, pages
2013. Vol. 103, no 18, 182904- p.
Keyword [en]
Charge-Transport Processes, Wave-Guides, Photorefractive Crystals, Linbo3, Nanoparticles, Reduction, Template, Titanate, Surface, Silver
National Category
Other Physics Topics
URN: urn:nbn:se:kth:diva-139226DOI: 10.1063/1.4827541ISI: 000327816000053ScopusID: 2-s2.0-84889639728OAI: diva2:685952
Swedish Research Council, VR 622-2010-526 621-2011-4040

QC 20140110

Available from: 2014-01-10 Created: 2014-01-08 Last updated: 2015-03-25Bibliographically approved
In thesis
1. Engineering ferroelectric domains and charge transport by proton exchange in lithium niobate
Open this publication in new window or tab >>Engineering ferroelectric domains and charge transport by proton exchange in lithium niobate
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.
TRITA-FYS, ISSN 0280-316X ; 2015:15
Lithium niobate, Ferroelectrics
National Category
Nano Technology
Research subject
Materials Science and Engineering; Physics
urn:nbn:se:kth:diva-162269 (URN)978-97-7595-482-0 (ISBN)
Public defence
2015-04-15, Fd5, Albanova University Center, Roslagstullsbacken 21, KTH, Stockholm, 10:00 (English)

QC 20150325

Available from: 2015-03-25 Created: 2015-03-24 Last updated: 2015-04-10Bibliographically approved

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