| 1. |
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| 2. |
- Al-Shammari, Rusul M., et al.
(författare)
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Antibacterial properties of lithium niobate crystal substrates
- 2023
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Ingår i: International Journal of Optomechatronics. - : Informa UK Limited. - 1559-9612 .- 1559-9620. ; 17:1
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Tidskriftsartikel (refereegranskat)abstract
- The bactericidal properties of chemically patterned lithium niobate substrates under a super-bandgap UV light source is established. UV irradiation of lithium niobate surfaces inoculated with bacteria leads to antimicrobial activity compared to a glass substrate under similar conditions, as determined by surface enhanced Raman spectroscopy and corroborated with a fluorescence-based live/dead assay. This finding may expand the possible biomedical applications of lithium niobate.
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| 3. |
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| 4. |
- Al-Shammari, Rusul M., et al.
(författare)
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Single-Molecule Nonresonant Wide-Field Surface-Enhanced Raman Scattering from Ferroelectrically Defined Au Nanoparticle Microarrays
- 2018
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Ingår i: ACS Omega. - : AMER CHEMICAL SOC. - 2470-1343. ; 3:3, s. 3165-3172
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Tidskriftsartikel (refereegranskat)abstract
- Single-molecule detection by surface-enhanced Raman scattering (SERS) is a powerful spectroscopic technique that is of interest for the sensor development field. An important aspect of optimizing the materials used in SERS-based sensors is the ability to have a high density of "hot spots" that enhance the SERS sensitivity to the single-molecule level. Photodeposition of gold (Au) nanoparticles through electric-field-directed self-assembly on a periodically proton-exchanged lithium niobate (PPELN) substrate provides conditions to form well-ordered microscale features consisting of closely packed Au nanoparticles. The resulting Au nanoparticle microstructure arrays (microarrays) are plasmon-active and support nonresonant single-molecule SERS at ultralow concentrations (<10(-9)-10(-13) M) with excitation power densities <1 x 10(-3) W cm(-2) using wide-field imaging. The microarrays offer excellent SERS reproducibility, with an intensity variation of <7.5% across the substrate. As most biomarkers and molecules do not support resonance enhancement, this work demonstrates that PPELN is a suitable template for high-sensitivity, nonresonant sensing applications.
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| 5. |
- Al-Shammari, Rusul M., et al.
(författare)
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Tunable Wettability of Ferroelectric Lithium Niobate Surfaces : The Role of Engineered Microstructure and Tailored Metallic Nanostructures
- 2017
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Ingår i: The Journal of Physical Chemistry C. - : AMER CHEMICAL SOC. - 1932-7447 .- 1932-7455. ; 121:12, s. 6643-6649
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Tidskriftsartikel (refereegranskat)abstract
- An important aspect of optimizing micro- and optofluidic devices for lab on -a-chip systems is the ability to engineer materials properties including surface structure and charge to control wettability. Biocompatible ferroelectric lithium niobate (LN), which is well-known for acoustic and nonlinear optical applications, has recently found potential micro- and optofluidic applications. However, the tunable wettability of such substrates has yet to be explored in detail. Here, we show that the contact angle of LN substrates can be reproducibly tailored between similar to 7 degrees and similar to 421 degrees by controlling the surface topography and chemistry at the nano- and micrometer scale via ferroelectric domain and polarization engineering and polarization-directed photoassisted deposition of metallic nanostructures.
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| 6. |
- Balobaid, Laila, et al.
(författare)
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Direct shape control of photoreduced nanostructures on proton exchanged ferroelectric templates
- 2013
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 102:4, s. 042908-
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 7. |
- Balobaid, Laila, et al.
(författare)
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Photoreduction of metal nanostructures on periodically proton exchanged MgO-doped lithium niobate crystals
- 2013
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 103:18, s. 182904-
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 8. |
- Carville, N. Craig, et al.
(författare)
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Biocompatibility of ferroelectric lithium niobate and the influence of polarization charge on osteoblast proliferation and function
- 2015
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Ingår i: Journal of Biomedical Materials Research. Part A. - : John Wiley and Sons. - 1549-3296 .- 1552-4965. ; 103:8, s. 2540-2548
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Tidskriftsartikel (refereegranskat)abstract
- In this work, the influence of substrate surface charge on in vitro osteoblast cell proliferation on ferroelectric lithium niobate (LN) crystal surfaces is investigated. LN has a spontaneous polarization along the z-axis and is thus characterized by positive and negative bound polarization charge at the +z and -z surfaces. Biocompatibility of LN was demonstrated via culturing and fluorescence imaging of MC3T3 osteoblast cells for up to 11 days. The cells showed enhanced proliferation rates and improved osteoblast function through mineral formation on the positively and negatively charged LN surfaces compared to electrostatically neutral x-cut LN and a glass cover slip control. These results highlight the potential of LN as a template for investigating the role of charge on cellular processes.
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| 9. |
- Carville, N. Craig, et al.
(författare)
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Biocompatible Gold Nanoparticle Arrays Photodeposited on Periodically Proton Exchanged Lithium Niobate
- 2016
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Ingår i: ACS Biomaterials Science & Engineering. - : American Chemical Society (ACS). - 2373-9878. ; 2:8, s. 1351-1356
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Tidskriftsartikel (refereegranskat)abstract
- Photodeposition of silver nanoparticles onto chemically patterned lithium niobate having alternating lithium niobate and proton exchanged regions has been previously investigated. Here, the spatially defined photodeposition of gold nanoparticles onto periodically proton exchanged lithium niobate is demonstrated. It is shown that the location where the gold nanoparticles form can be tailored by altering the concentration of HAuCl4. This enables the possibility to sequentially deposit gold and silver in different locations to create bimetallic arrays. The cytocompatibility of photodeposited gold, silver, and bimetallic ferroelectric templates to osteoblast-like cells is also investigated. Gold samples provide significantly greater cell biocompatibility than silver samples. These results highlight a potential route for using photodeposited gold on lithium niobate as a template for applications in cellular biosensing.
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| 10. |
- Carville, N. C., et al.
(författare)
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Growth mechanism of photoreduced silver nanostructures on periodically proton exchanged lithium niobate : Time and concentration dependence
- 2013
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 113:18, s. 187212-1-187212-7
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 11. |
- Carville, N. Craig, et al.
(författare)
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Influence of annealing on the photodeposition of silver on periodically poled lithium niobate
- 2016
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Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 119:5
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Tidskriftsartikel (refereegranskat)abstract
- The preferential deposition of metal nanoparticles onto periodically poled lithium niobate surfaces, whereby photogenerated electrons accumulate in accordance with local electric fields and reduce metal ions from solution, is known to depend on the intensity and wavelength of the illumination and the concentration of the solution used. Here, it is shown that for identical deposition conditions (wavelength, intensity, concentration), post-poling annealing for 10 h at 200 degrees C modifies the surface reactivity through the reorientation of internal defect fields. Whereas silver nanoparticles deposit preferentially on the +z domains on unannealed crystals, the deposition occurs preferentially along 180 degrees domain walls for annealed crystals. In neither case is the deposition selective; limited deposition occurs also on the unannealed -z domain surface and on both annealed domain surfaces. The observed behavior is attributed to a relaxation of the poling-induced defect frustration mediated by Li+ ion mobility during annealing, which affects the accumulation of electrons, thereby changing the surface reactivity. The evolution of the defect field with temperature is corroborated using Raman spectroscopy.
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| 12. |
- Carville, N. Craig, et al.
(författare)
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Photoreduction of SERS-Active Metallic Nanostructures on Chemically Patterned Ferroelectric Crystals
- 2012
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 6:8, s. 7373-7380
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 13. |
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| 14. |
- Damm, S., et al.
(författare)
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Formation of ferroelectrically defined Ag nanoarray patterns
- 2014
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE - International Society for Optical Engineering. - 9781628410747
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Konferensbidrag (refereegranskat)abstract
- In order to produce the most effective Ag nanoarrays for plasmon enhanced fluorescence and Raman scattering made using ferroelectric substrates, the optimum conditions for the creation of arrays must be identified. We study here Ag nanopattern arrays formed using ferroelectric lithography based on periodically proton exchanged (PPE) template methods. We examine different conditions in regard to deposition of Ag nanoparticles and analyze the plasmon enhanced signal from the resulting nanoarray. We apply FLIM (fluorescence lifetime imaging) to assess different Ag nanoarray preparation conditions on fluorescence emission from selected fluorphores. In addition, we apply Raman and luminescence spectroscopy with AFM (atomic force microscopy) to study the plasmon enhancement of luminescence and Raman from the Ag nanoarrays.
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| 15. |
- Damm, Signe, et al.
(författare)
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Plasmon enhanced Raman from Ag nanopatterns made using periodically poled lithium niobate and periodically proton exchanged template methods
- 2012
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 116:50, s. 26543-26550
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Tidskriftsartikel (refereegranskat)abstract
- We study Ag nanopattern arrays formed using ferroelectric lithography based on two separate approaches, i.e., periodically poled lithium niobate (PPLN) and periodically proton exchanged (PPE) template methods. We demonstrate that such nanoarrays are plasmon active. Raman spectroscopy was applied to study molecular probe 4-aminothiophenol (4-ABT) absorbed onto a silver nanostructured array. The observed Raman spectra show peaks arising from b2 modes, which occur for plasmon enhanced Raman from 4-ABT in place of a1 modes, which occur in normal Raman scattering. We demonstrate that the PPLN and PPE substrates possess different plasmonic properties with PPE creating a stronger SERS signal relative to PPLN substrates.
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| 16. |
- Damm, Signe, et al.
(författare)
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Protein assemblies on ferroelectrically patterned microarrays of Ag nanoparticles
- 2017
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Ingår i: Ferroelectrics (Print). - : TAYLOR & FRANCIS LTD. - 0015-0193 .- 1563-5112. ; 515:1, s. 141-148
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Tidskriftsartikel (refereegranskat)abstract
- Nano-bio interfaces play a significant role in assay device design and performance, here we study the use of a combined plasmonic and ferroelectric active substrate design for protein assemblies on a plasmon active array. We demonstrate that biotinylation and protein assemblies can bemade onmetal nanoparticles patterned on ferroelectric substrates. These results inturndemonstratethat ferroelectric substrates combined with active plasmonics is potentially applicable as substrates for biological assays.
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| 17. |
- Damm, S., et al.
(författare)
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SERS from Ag and Au nanoarrays made using photochemical patterning
- 2013
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Ingår i: 2013 Conference on Lasers and Electro-Optics Europe and International Quantum Electronics Conference, CLEO/Europe-IQEC 2013. - : IEEE Computer Society. ; , s. 6801468-
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Konferensbidrag (refereegranskat)abstract
- Metallic nanostructures made from 'coinage' metals such as silver or gold, yield plasmons when light creates a collective oscillation of the conduction electrons on the surface of the metal, creating a greatly enhanced electromagnetic field [1-3]. The specific properties of the plasmonic structures have been found to be greatly dependent on factors such as size, shape, and dielectric environment [1-3]. These properties have been exploited in a variety of plasmonic applications ranging from sensing to enhanced fluorescence [4].
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| 18. |
- Damm, Signe, et al.
(författare)
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Surface enhanced luminescence and Raman scattering from ferroelectrically defined Ag nanopatterned arrays
- 2013
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 103:8, s. 083105-
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Tidskriftsartikel (refereegranskat)abstract
- Ag nanopatterned arrays prepared using periodically proton exchanged templates have been demonstrated to support surface enhanced luminescence. Fluorescence lifetime imaging reveals that luminescence intensity is greatest on Ag and that the lifetime of the molecular probe is reduced, in line with a surface enhanced luminescence mechanism. Studies establish that the substrate simultaneously supports surface enhanced luminescence and Raman scattering. Spatial dependence along the nanopatterned arrays shows <7% variation in Raman scattering signal intensity, offering high reproducibility for practical applications. Fluorophores emitting near the plasmon absorption maxima are enhanced 4-fold.
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| 19. |
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| 20. |
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| 21. |
- Manzo, Michele, et al.
(författare)
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Electrostatic control of the domain switching dynamics in congruent LiNbO3 via periodic proton-exchange
- 2011
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Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 98:12
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 22. |
- Manzo, Michele
(författare)
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Engineering ferroelectric domains and charge transport by proton exchange in lithium niobate
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 23. |
- Manzo, Michele, et al.
(författare)
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Lithium Niobate : The Silicon of Photonics!
- 2013
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Ingår i: Nano-Optics for Enhancing Light-Matter Interactions on a Molecular Scale. - Dordrecht : Springer Netherlands. - 9789400753129 - 9789400753136 ; , s. 421-422
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Bokkapitel (refereegranskat)abstract
- Lithium Niobate and its isomorphs (e.g. LiTaO3) is an artificial ferroelectric crystal belonging to the 3 m crystallografic group [1]. It is characterised by large pyroelectric, piezoelectric, acusto-optic, nonlinear and electro-optic coefficients features and is one of the key materials for the fabrication of integrated optical devices [2]. LiNbO3 is one of the most versatile and widely used material in photonics, with a broad range of applications ranging from acoustic-wave transducers and filters in mobile telephones, to optical modulators and wavelength converters in fibre telecommunication systems, to name just a few. Recent advances in linear and nonlinear microstructuring technologies on the LiNbO3 material platform, involving domain engineering by electric field poling techniques as well as ion-exchange processes and etching techniques, enable the fabrication of both linear and nonlinear photonic crystals as showed in Fig. 42.1.
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| 24. |
- Manzo, Michele, et al.
(författare)
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Nanoscale characterization of beta-phase HxLi1-xNbO3 layers by piezoresponse force microscopy
- 2014
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 116:6, s. 066815-
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 25. |
- Manzo, Michele, 1984-, et al.
(författare)
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Piezoresponse force microscopyon proton exchanged LiNbO3 layers
- 2012
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We use piezoresponse force microscopy for high-resolution investigations on protonexchanged LiNbO3 surfaces. We also quantify the reduction of the d33 nonlinear coefficientinduced by proton exchange in congruent LiNbO3 substrates with and without Mg-doping.
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| 26. |
- Manzo, Michele, et al.
(författare)
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Two-dimensional domain engineering in LiNbO3 via a hybrid patterning technique
- 2011
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Ingår i: Proceedings of Advances in Optical Materials 2011. - Washington, D.C. : Optical Society of America. - 9781557529046
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Konferensbidrag (refereegranskat)abstract
- We propose a novel electric field poling technique employing selective proton exchange and resist patterning to fabricate nonlinear photonic crystals in LiNbO3. We demonstrate 2D tetragonal bulk lattices with 8x6.78µm2 periodicity in 0.5mm substrates.
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| 27. |
- Manzo, Michele, 1984-, et al.
(författare)
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Two-dimensional domain engineering in LiNbO3 via a hybrid patterning technique
- 2011
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Ingår i: Optical Materials Express. - 2159-3930 .- 2159-3930. ; 1:3, s. 365-371
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 28. |
- Neumayer, Sabine, et al.
(författare)
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Interface modulated currents in periodically proton exchanged Mg doped lithium niobate
- 2016
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Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 119:11
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Tidskriftsartikel (refereegranskat)abstract
- Conductivity in Mg doped lithium niobate (Mg:LN) plays a key role in the reduction of photorefraction and is therefore widely exploited in optical devices. However, charge transport through Mg:LN and across interfaces such as electrodes also yields potential electronic applications in devices with switchable conductivity states. Furthermore, the introduction of proton exchanged (PE) phases in Mg:LN enhances ionic conductivity, thus providing tailorability of conduction mechanisms and functionality dependent on sample composition. To facilitate the construction and design of such multifunctional electronic devices based on periodically PE Mg:LN or similar ferroelectric semiconductors, fundamental understanding of charge transport in these materials, as well as the impact of internal and external interfaces, is essential. In order to gain insight into polarization and interface dependent conductivity due to band bending, UV illumination, and chemical reactivity, wedge shaped samples consisting of polar oriented Mg:LN and PE phases were investigated using conductive atomic force microscopy. In Mg:LN, three conductivity states (on/off/transient) were observed under UV illumination, controllable by the polarity of the sample and the externally applied electric field. Measurements of currents originating from electrochemical reactions at the metal electrode–PE phase interfaces demonstrate a memresistive and rectifying capability of the PE phase. Furthermore, internal interfaces such as domain walls and Mg:LN–PE phase boundaries were found to play a major role in the accumulation of charge carriers due to polarization gradients, which can lead to increased currents. The insight gained from these findings yield the potential for multifunctional applications such as switchable UV sensitive micro- and nanoelectronic devices and bistable memristors.
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| 29. |
- Neumayer, Sabine M., et al.
(författare)
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Interface and thickness dependent domain switching and stability in Mg doped lithium niobate
- 2015
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Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 118:22
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Tidskriftsartikel (refereegranskat)abstract
- Controlling ferroelectric switching in Mg doped lithium niobate (Mg: LN) is of fundamental importance for optical device and domain wall electronics applications that require precise domain patterns. Stable ferroelectric switching has been previously observed in undoped LN layers above proton exchanged (PE) phases that exhibit reduced polarization, whereas PE layers have been found to inhibit lateral domain growth. Here, Mg doping, which is known to significantly alter ferroelectric switching properties including coercive field and switching currents, is shown to inhibit domain nucleation and stability in Mg: LN above buried PE phases that allow for precise ferroelectric patterning via domain growth control. Furthermore, piezoresponse force microscopy (PFM) and switching spectroscopy PFM reveal that the voltage at which polarization switches from the "up" to the "down" state increases with increasing thickness in pure Mg: LN, whereas the voltage required for stable back switching to the original "up" state does not exhibit this thickness dependence. This behavior is consistent with the presence of an internal frozen defect field. The inhibition of domain nucleation above PE interfaces, observed in this study, is a phenomenon that occurs in Mg: LN but not in undoped samples and is mainly ascribed to a remaining frozen polarization in the PE phase that opposes polarization reversal. This reduced frozen depolarization field in the PE phase also influences the depolarization field of the Mg: LN layer above due to the presence of uncompensated polarization charge at the PE-Mg: LN boundary. These alterations in internal electric fields within the sample cause long-range lattice distortions in Mg: LN via electromechanical coupling, which were corroborated with complimentary Raman measurements.
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| 30. |
- Neumayer, Sabine M., et al.
(författare)
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Thickness, humidity, and polarization dependent ferroelectric switching and conductivity in Mg doped lithium niobate
- 2015
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Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 118:24
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Tidskriftsartikel (refereegranskat)abstract
- Mg doped lithium niobate (Mg:LN) exhibits several advantages over undoped LN such as resistance to photorefraction, lower coercive fields, and p-type conductivity that is particularly pronounced at domain walls and opens up a range of applications, e.g., in domain wall electronics. Engineering of precise domain patterns necessitates well founded knowledge of switching kinetics, which can differ significantly from that of undoped LN. In this work, the role of humidity and sample composition in polarization reversal has been investigated under application of the same voltage waveform. Control over domain sizes has been achieved by varying the sample thickness and initial polarization as well as atmospheric conditions. In addition, local introduction of proton exchanged phases allows for inhibition of domain nucleation or destabilization, which can be utilized to modify domain patterns. Polarization dependent current flow, attributed to charged domain walls and band bending, demonstrates the rectifying ability of Mg: LN in combination with suitable metal electrodes that allow for further tailoring of conductivity.
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| 31. |
- Zisis, G., et al.
(författare)
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UV laser-induced poling inhibition in proton exchanged LiNbO3 crystals
- 2017
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Ingår i: Applied physics. B, Lasers and optics (Print). - : Springer. - 0946-2171 .- 1432-0649. ; 123:4
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Tidskriftsartikel (refereegranskat)abstract
- The applicability of the UV laser-induced poling inhibition method for ferroelectric domain engineering in proton exchanged lithium niobate planar waveguides is investigated. Our results indicate that intense UV irradiation of proton exchanged lithium niobate samples can, indeed, produce poling inhibited domains in this material under certain irradiation conditions. However, there is strong indication that the temperature gradient that is formed during UV irradiation modifies the local proton concentration leading to changes in the refractive index profile of the original planar waveguide.
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