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Direct Observation of Core-Shell Structures in Individual Lead Titanate Ferroelectric Nanostructures by Tip-Enhanced Refractive Index Mapping
摘要： Ferroelectrics undergo a size-driven phase transition at the nanoscale below which the spontaneous polarization, their defining property, irrevocably ceases. This threshold often referred to as the superparaelectric limit has tremendous technological relevance in an era of progressing integration. Just as the balance of short-range elastic and long-range electrostatic ordering in bulk, the critical size depends on temperature. Room-temperature tip-enhanced Raman spectroscopy (TERS) imaging of individual lead titanate (PbTiO3) nanoislands is reported with a spatial resolution of ≈3 nm. Monitoring the spectral shift of the gold-tip enhanced luminescence, which depends on the local refractive index, images grains composing the nanoislands. The wavelength of the enhanced luminescence shifts between the grains and their boundaries indicating the predicted core–shell structure of ferroelectric and paraelectric phase. The shear force configuration rules out the distance dependence of capacitive plasmonic coupling between tip and substrate as the origin of the observed shift. As the reported temperature-changes in nonresonant TERS do not account for noticeable thermal effects, the underlying, even though weak, tip-enhanced Raman spectrum of the grain core reflects PbTiO3 close to the ferroelectric-to-paraelectric phase transition which is primarily related to the finite size of the grains.
关键词： ferroelectric,tip-enhanced Raman spectroscopy,core–shell structure,local refractive index imaging,lead titanate
更新于2025-09-23 15:21:01
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Lead Doped Ti-Oxo Clusters as Molecular Models of Perovskite-type PbTiO3 and Electron Transport Material in Solar Cells
摘要： In this work, we successfully prepared Pb-doped titanium-oxo clusters with core structures as isolated perovskite PbTiO3 species. In the obtained highly symmetric Pb8Ti7-oxo cluster, the central TiO6 octahedra are orthogonally extended to adjacent ones in corner-sharing way and the doped 8 Pb ions form a cubic arrangement, making it the first molecular model of perovskite PbTiO3. Moreover, they show high solution stability confirmed by MALDI-TOF-MS measurements. Based on solution processability, they can be easily spin-coated into homogeneous films, which were further applied as electron transport materials in perovskite solar cells to give the average PCE of ～15 % and improved device stability. The developed bottom-up cluster assembly method opens an efficient way for the construction of atomically precise models of perovskite metal oxides, and provides potential molecular tools to extend their applications.
关键词： perovskite,solar cells,cluster compounds,lead titanate,titanium-oxo cluster
更新于2025-09-23 15:19:57
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Texture and phase variation of ALD PbTiO <sub/>3</sub> films crystallized by rapid thermal anneal
摘要： PbTiO3 (lead titanate) thin films were deposited by atomic layer deposition (ALD) and crystallized via rapid thermal anneal. The films were grown using lead bis(3-N,N-dimethyl-2-methyl-2-propanoxide) and tetrakis dimethylamino titanium as cation precursors. A combination of H2O and ozone was used as oxidizers. Phase-pure, stoichiometric PbTiO3 was confirmed using x-ray diffraction, Rutherford backscattering spectroscopy, and scanning transmission electron microscopy. Ferroelectric hysteresis loops obtained by patterning circular capacitors with areas of 4.92 × 10?4 cm2 indicate a Pmax = 48 μC/cm2, 2Pr = 60 μC/cm2, Ec1 = ?73 kV/cm, Ec2 = 125 kV/cm, and a leakage current density of 15 μA/cm2 at 138 kV/cm. Capacitance versus voltage measurements were used to obtain a maximum dielectric constant of 290 at 85 kV/cm and loss tangent under 4% tested in the range of ±275 kV/cm. ALD PbTiO3 grown with near-ideal cation ratios crystallized into randomly oriented perovskite grains when grown on a sputtered Pt-coated Si substrate. A variation of rapid thermal anneal temperatures, ramp rates, and nucleation layers was investigated and did not have a significant effect on perovskite grain orientation.
关键词： texture,ferroelectric,lead titanate,rapid thermal anneal,atomic layer deposition
更新于2025-09-19 17:15:36