Investigation of novel ferroelectrics and their electrical and optical applicaitons
Bibliographic record
Abstract
Ferroelectrics are considered essential components in a wide spectrum of electrical and optical applications, including but not limited to ferroelectric random access memory (FeRAM), piezoelectric transducers, and optical waveguides and modulators, owing to their remarkable ferroelectric, piezoelectric, and electro-optic properties. The research presented in this thesis provides a comprehensive investigation, including theoretical principles, fabrication technology, performance optimization, and electrical/optical applications, of two innovative ferroelectric materials, namely, Nd-doped bismuth titanate (BNdT) and bismuth ferrite (BFO). We start by describing the fabrication procedure, and then study the dependence of ferroelectric properties on various fabrication parameters. By varying the post annealing temperature and tuning the elemental constituents, ferroelectrics with optimized performance parameters are demonstrated in our work. Then, we further our study into the optical characterization, and provide a systematic investigation of BNdT optical properties for the first time. Optical parameters including the optical transmittance, refractive index, extinction coefficient, and optical band gap energy, are examined and their correlation with different fabrication variables and microstructure properties is studied both experimentally and theoretically. In the third part of this thesis, by introducing the optimized BNdT ferroelectric thin film as a seeding layer for the BFO, we report the first room temperature (RT) ferroelectric measurement of pure BFO.We further advance our study by investigating the photovoltaic nature of multiferroic BFO, and report enhanced photovoltaic performance of the BFO material in a graphene/polycrystalline BFO/Pt heterojunction structure for the first time. The unique properties of the graphene electrode lead to a short circuit current density of 61 μA/cm2 and an open circuit voltage of 0.52 V in the heterojunction. These values are much higher than the results previously reported in the literature. A theoretical model that takes into consideration the ferroelectric polarization, interface states, and energy band bending effect, is constructed to describe the ferroelectric photovoltaic effect and carrier transport behaviour for the first time. Key photovoltaic parameters, such as conversion efficiency, illumination intensity response, ON/OFF characteristics, minority carrier lifetime, and external quantum efficiency (EQE), are investigated through both theory and measurements. Finally, to improve the existing photovoltaic performance of the graphene/polycrystalline BFO/Pt heterojunction, two independent chemical and physical routines, are processed and compared. It can be seen that the photocurrent density exhibits a significant improvement from 61 μA/cm2 to 8.67 mA/cm2 (~150 fold) after HNO3 treatment, while a considerable enhancement of ~5 fold is seen with QDs filling/sensitizing. An optical application of a photosensitive detector and an electrical application of a tunable switch are also demonstrated as two interesting applications of the BFO photovoltaic effect. Research in the field of novel ferroelectrics continues to thrive, and a number of interesting theoretical and application studies are currently underway. The results achieved in this thesis may provide a useful understanding of the principles and properties of two such ferroelectrics, and can serve as assistance in future research perspectives.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".