Shape-controlled monolayer MoSe2 flakes by chemical vapor deposition towards tuning the photoluminescence emission

In this study, we report on the controllable chemical vapor deposition (CVD) synthesis of monolayer MoSe2 flakes with different shapes such as hexagons, triangles, sawtooth hexagons, dendrites and fractals deposited on SiO2/Si substrates. This broad range of morphologies is due to the change in the vapor composition resulting from the confinement of the MoO3 and Se vapor and to the variation in the growth rate of the variable shaped MoSe2 crystals. It is also revealed that the photoluminescence (PL) response of the MoSe2 flakes is strongly affected by their shape and size. Our findings will open new avenues towards achieving morphology-controlled monolayer MoSe2 flakes for optoelectronic and energy harvesting systems.This work was supported by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding Contracts UIDB/04540/2020, UIDB/00100/2020 and UIDB/04650/2020. The author C. G. acknowledges a scholarship funded by the UIDB/04540/2020 contract. The author K. G. would like to thank the statutory grant (No. 8211104160) of Department of Quantum Technologies of Wroclaw University of Science and Technology

Progress and perspective on different strategies to achieve wake-up-free ferroelectric hafnia and zirconia-based thin films

In the last decade orthorhombic hafnia and zirconia films have attracted tremendous attention arising from the discovery of ferroelectricity at the nanoscale. However, an initial wake-up pre-cycling is usually needed to achieve a ferroelectric behaviour in these films. Recently, different strategies, such as microstructure tailoring, defect, bulk and interface engineering, doping, NH3 plasma treatment and epitaxial growth, have been employed to obtain wake-up free orthorhombic ferroelectric hafnia and zirconia films. In this work we review recent developments in obtaining polar hafnia and zirconia-based thin films without the need of any wake-up cycling. In particular, we discuss the rhombohedral phase of hafnia/ zirconia, which under a constrained environment exhibits wake-up-free ferroelectric behaviour. This phase could have a strong impact on the current investigations of ferroelectric binary oxide materials and pave the way toward exploiting ferroelectric behaviour for next-generation memory and logic gate applications.This work was supported by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding Contract UIDB/04650/2020 and by DST-SERB, Govt. of India through Grant Nr. ECR/2017/00006. R. F. Negrea and L. Pintilie acknowledge funding through project CEPROFER/ PN-III-P4-ID-PCCF-2016-0047 (contract 16/2018, funded by UEFISCDI). J.L.M-D. thanks the Royal Academy of Engineering Chair in Emerging Technologies Grant, CIET1819_24, the EPSRC grant EP/T012218/1- ECCS – EPSRC, and the grant EU-H2020-ERC-ADG # 882929, EROS

Are lead-free relaxor ferroelectric materials the most promising candidates for energy storage capacitors?

Dielectric capacitors offer high-power density and ultrafast discharging times as compared to electrochemical capacitors and batteries, making them potential candidates for pulsed power technologies (PPT). However, low energy density in different dielectric materials such as linear dielectrics (LDs), ferroelectrics (FEs), and anti-ferroelectric (AFEs) owing to their low polarization, large hysteresis loss and low breakdown strength, respectively, limits their real time applications. Thus, achieving a material with high dielectric constant, large dielectric breakdown strength and slim hysteresis is imperative to obtain superior energy performance. In this context, relaxor ferroelectrics (RFEs) emerged as the most promising solution for energy storage capacitors. This review starts with a brief introduction of different energy storage devices and current advances of dielectric capacitors in PPT. The latest developments on lead-free RFEs including bismuth alkali titanate based, barium titanate based, alkaline niobite based perovskites both in ceramics and thin films are comprehensively discussed. Further, we highlight the different strategies used to enhance their energy storage performance to meet the requirements of the energy storage world. We also provide future guidelines in this field and therefore, this article opens a window for the current advancement in the energy storage properties of RFEs in a systematic way.This study has been partially supported by (i) DST-SERB, Govt. of India through Grant ECR/2017/000068 (KCS), (ii) UGC through grant nos. F.4-5(59-FRP)/ 2014(BSR) and (iii) Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding UIDB/FIS/04650/2020 (JPBS). The author A. R. Jayakrishnan acknowledges the Central University of Tamil Nadu, India for his Ph. D fellowship. The authors acknowledge the CERIC-ERIC Consortium for access to experimental facilities and financial support under proposal 20192055

Effect of the thickness on the photocatalytic and the photocurrent properties of ZnO films deposited by spray pyrolysis

In this work, we have investigated the structure, morphology, photoluminescence, photocatalytic and photocurrent properties of ZnO thin films as a function of their film thickness (tZnO) fabricated via ultrasonic spray pyrolysis technique. The X-Ray diffraction patterns exhibited the formation of polycrystalline wurtzite phase of ZnO. Scanning electron microscopy images showed the uniform morphology with nanorod structure. The photosensitivity and photocatalytic efficiency are found to be optimum at tZnO = 1200 nm and are attributed to the improved photogeneration of charge carriers and higher concentration of oxygen vacancies. A direct correlation is established between the photosensitivity and photodegradation process. The incident photon-to-electron conversion efficiency (IPCE) and photocatalytic efficiency for the ZnO film at tZnO = 1200 nm are estimated to be 31.5% and 100% respectively. The obtained result suggests that ZnO thin films are potential candidates for applications in various optoelectronic devices.This study has been partially supported by Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding UIDB/FIS/04650/2020 (JPBS) and DST SERB Project ECR/2017/002537(K.K.). Author KVA acknowledges DST, Govt. of India for the Inspire fellowship (IF170601)

Large ferro–pyro–phototronic effect in 0.5Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 thin films integrated on silicon for photodetection

Coupling together the ferroelectric, pyroelectric, and photovoltaic characteristics within a single material is a novel way to improve the performance of photodetectors. In this work, we take advantage of the triple multifunctionality shown by 0.5Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 (BCZT), as demonstrated in an Al/Si/SiOx/BCZT/ITO thin-film device. The Si/SiOx acts as an n-type layer to form a metal–ferroelectric–insulator–semiconductor heterostructure with the BCZT, and with Al and ITO as electrodes. The photo-response of the device, with excitation from a violet laser (405 nm wavelength), is carefully investigated, and it is shown that the photodetector performance is invariant with the chopper frequency owing to the pyro-phototronic effect, which corresponds to the coupling together of the pyroelectric and photovoltaic responses. However, the photodetector performance was significantly better than that of the devices operating based only on the pyro-phototronic effect by a factor of 4, due to the presence of ferroelectricity in the system. Thus, after a poling voltage of −15 V, for a laser power density of 230 mW/cm2 and at a chopper frequency of 400 Hz, optimized responsivity, detectivity, and sensitivity values of 13.1 mA/W, 1.7 × 1010 Jones, and 26.9, respectively, are achieved. Furthermore, ultrafast rise and fall times of 2.4 and 1.5 µs, respectively, are obtained, which are 35,000 and 36,000 times faster rise and fall responses, respectively, than previous reports of devices with the ferro–pyro–phototronic effect. This is understood based on the much faster ferroelectric switching in ferroelectric thin films owing to the predominant 180° domains in a single direction out of plane.This work was supported by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding Contracts UIDB/04650/2020. This project has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No 958174 (M-ERA-NET3/0003/2021—NanOx4EStor). The authors would also like to thank engineer José Santos for technical support at the Thin Film Laboratory. J. L. M.-D. and R. L. Z. H. are grateful for EPSRC CAM-IES grant EP/P007767/. R. L. Z. H. also acknowledges support from the Royal Academy of Engineering under the Research Fellowships scheme (No.: RF\201718\1701). J. L. M.-D. acknowledges support from the Royal Academy of Engineering Chair in Emerging Technologies scheme (No.: CIET1819_24) and the ERC grant EROS, EU-H2020-ERC-ADG # 882929

Ferroelectricity and negative piezoelectric coefficient in orthorhombic phase pure ZrO2 thin films

A new approach for epitaxial stabilisation of ferroelectric orthorhombic (o-) ZrO2 films with negative piezoelectric coefficient in ∼ 8nm thick films grown by ion-beam sputtering is demonstrated. Films on (011)-Nb:SrTiO3 gave the oriented o-phase, as confirmed by transmission electron microscopy and electron backscatter diffraction mapping, grazing incidence x-ray diffraction and Raman spectroscopy. Scanning probe microscopy techniques and macroscopic polarization-electric field hysteresis loops show ferroelectric behavior, with saturation polarization of ∼14.3 µC/cm2, remnant polarization of ∼9.3 µC/cm2 and coercive field ∼1.2 MV/cm. In contrast to the o-films grown on (011)-Nb:SrTiO3, films grown on (001)-Nb:SrTiO3 showed mixed monoclinic (m-) and o-phases causing an inferior remnant polarization of ∼4.8 µC/cm2, over 50% lower than the one observed for the film grown on (011)-Nb:SrTiO3. Density functional theory (DFT) calculations of the SrTiO3/ZrO2 interfaces support the experimental findings of a stable polar o-phase for growth on (011) Nb:SrTiO3, and they also explain the negative piezoelectric coefficient.This work was supported by: (i) the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding Contract UIDB/04650/2020 and (ii) Project NECL - NORTE-01-0145-FEDER-022096 and Project UID/NAN/50024/2019. This work has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 958174 (M-ERA-NET3/0003/2021 - NanOx4EStor). This work was also developed within the scope of the project CICECO-Aveiro Institute of Materials, UIDB/50011/2020 & UIDP/50011/2020, financed by national funds through the Portuguese Foundation for Science and Technology/MCTES. It is also funded by national funds (OE), through FCT – Fundação para a Ciência e a Tecnologia, I.P., in the scope of the framework contract foreseen in the numbers 4, 5 and 6 of the article 23, of the Decree-Law 57/2016, of August 29, changed by Law 57/2017, of July 19.The calculations were carried out at the OBLIVION Supercomputer (based at the High Performance Computing Center - University of Évora) funded by the ENGAGE SKA Research Infrastructure (reference POCI-01-0145-FEDER-022217 - COMPETE 2020 and the Foundation for Science and Technology, Portugal) and by the BigData@UE project (reference ALT20-03-0246-FEDER-000033 - FEDER and the Alentejo 2020 Regional Operational Program). Oblivion resources were accessed through the advanced computing projects CPCA/A2/5649/2020 and CPCA/A2/4628/2020, funded by FCT I.P. The authors gratefully acknowledge the HPC RIVR consortium (www.hpc-rivr.si) and EuroHPC JU (eurohpc-ju.europa.eu) for funding this research by providing computing resources of the HPC system Vega at the Institute of Information Science (www.izum.si)The calculations were carried out at the OBLIVION Supercomputer (based at the High Performance Computing Center - University of Évora) funded by the ENGAGE SKA Research Infrastructure (reference POCI-01-0145-FEDER-022217 - COMPETE 2020 and the Foundation for Science and Technology, Portugal) and by the BigData@UE project (reference ALT20-03-0246-FEDER-000033 - FEDER and the Alentejo 2020 Regional Operational Program). Oblivion resources were accessed through the advanced computing projects CPCA/A2/5649/2020 and CPCA/A2/4628/2020, funded by FCT I.P. The authors gratefully acknowledge the HPC RIVR consortium (www.hpc-rivr.si) and EuroHPC JU (eurohpc-ju.europa.eu) for funding this research by providing computing resources of the HPC system Vega at the Institute of Information Science (www.izum.si

Energy harvesting technologies for structural health monitoring of airplane components - a review

With the aim of increasing the efficiency of maintenance and fuel usage in airplanes, structural health monitoring (SHM) of critical composite structures is increasingly expected and required. The optimized usage of this concept is subject of intensive work in the framework of the EU COST Action CA18203 "Optimising Design for Inspection" (ODIN). In this context, a thorough review of a broad range of energy harvesting (EH) technologies to be potentially used as power sources for the acoustic emission and guided wave propagation sensors of the considered SHM systems, as well as for the respective data elaboration and wireless communication modules, is provided in this work. EH devices based on the usage of kinetic energy, thermal gradients, solar radiation, airflow, and other viable energy sources, proposed so far in the literature, are thus described with a critical review of the respective specific power levels, of their potential placement on airplanes, as well as the consequently necessary power management architectures. The guidelines provided for the selection of the most appropriate EH and power management technologies create the preconditions to develop a new class of autonomous sensor nodes for the in-process, non-destructive SHM of airplane components.The work of S. Zelenika, P. Gljušcic, E. Kamenar and Ž. Vrcan is partly enabled by using the equipment funded via the EU European Regional Development Fund (ERDF) project no. RC.2.2.06-0001: “Research Infrastructure for Campus-based Laboratories at the University of Rijeka (RISK)” and partly supported by the University of Rijeka, Croatia, project uniri-tehnic-18-32 „Advanced mechatronics devices for smart technological solutions“. Z. Hadas, P. Tofel and O. Ševecek acknowledge the support provided via the Czech Science Foundation project GA19-17457S „Manufacturing and analysis of flexible piezoelectric layers for smart engineering”. J. Hlinka, F. Ksica and O. Rubes gratefully acknowledge the financial support provided by the ESIF, EU Operational Programme Research, Development and Education within the research project Center of Advanced Aerospace Technology (Reg. No.: CZ.02.1.01/0.0/0.0/16_019/0000826) at the Faculty of Mechanical Engineering, Brno University of Technology. V. Pakrashi would like to acknowledge UCD Energy Institute, Marine and Renewable Energy Ireland (MaREI) centre Ireland, Strengthening Infrastructure Risk Assessment in the Atlantic Area (SIRMA) Grant No. EAPA\826/2018, EU INTERREG Atlantic Area and Aquaculture Operations with Reliable Flexible Shielding Technologies for Prevention of Infestation in Offshore and Coastal Areas (FLEXAQUA), MarTera Era-Net cofund PBA/BIO/18/02 projects. The work of J.P.B. Silva is partially supported by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding UIDB/FIS/04650/2020. M. Mrlik gratefully acknowledges the support of the Ministry of Education, Youth and Sports of the Czech Republic-DKRVO (RP/CPS/2020/003

MAMMALS IN PORTUGAL : A data set of terrestrial, volant, and marine mammal occurrences in P ortugal

Mammals are threatened worldwide, with 26% of all species being includedin the IUCN threatened categories. This overall pattern is primarily associatedwith habitat loss or degradation, and human persecution for terrestrial mam-mals, and pollution, open net fishing, climate change, and prey depletion formarine mammals. Mammals play a key role in maintaining ecosystems func-tionality and resilience, and therefore information on their distribution is cru-cial to delineate and support conservation actions. MAMMALS INPORTUGAL is a publicly available data set compiling unpublishedgeoreferenced occurrence records of 92 terrestrial, volant, and marine mam-mals in mainland Portugal and archipelagos of the Azores and Madeira thatincludes 105,026 data entries between 1873 and 2021 (72% of the data occur-ring in 2000 and 2021). The methods used to collect the data were: live obser-vations/captures (43%), sign surveys (35%), camera trapping (16%),bioacoustics surveys (4%) and radiotracking, and inquiries that represent lessthan 1% of the records. The data set includes 13 types of records: (1) burrowsjsoil moundsjtunnel, (2) capture, (3) colony, (4) dead animaljhairjskullsjjaws, (5) genetic confirmation, (6) inquiries, (7) observation of live animal (8),observation in shelters, (9) photo trappingjvideo, (10) predators dietjpelletsjpine cones/nuts, (11) scatjtrackjditch, (12) telemetry and (13) vocalizationjecholocation. The spatial uncertainty of most records ranges between 0 and100 m (76%). Rodentia (n=31,573) has the highest number of records followedby Chiroptera (n=18,857), Carnivora (n=18,594), Lagomorpha (n=17,496),Cetartiodactyla (n=11,568) and Eulipotyphla (n=7008). The data setincludes records of species classified by the IUCN as threatened(e.g.,Oryctolagus cuniculus[n=12,159],Monachus monachus[n=1,512],andLynx pardinus[n=197]). We believe that this data set may stimulate thepublication of other European countries data sets that would certainly contrib-ute to ecology and conservation-related research, and therefore assisting onthe development of more accurate and tailored conservation managementstrategies for each species. There are no copyright restrictions; please cite thisdata paper when the data are used in publications.info:eu-repo/semantics/publishedVersio

Mammals in Portugal: a data set of terrestrial, volant, and marine mammal occurrences in Portugal

Mammals are threatened worldwide, with ~26% of all species being included in the IUCN threatened categories. This overall pattern is primarily associated with habitat loss or degradation, and human persecution for terrestrial mammals, and pollution, open net fishing, climate change, and prey depletion for marine mammals. Mammals play a key role in maintaining ecosystems functionality and resilience, and therefore information on their distribution is crucial to delineate and support conservation actions. MAMMALS IN PORTUGAL is a publicly available data set compiling unpublished georeferenced occurrence records of 92 terrestrial, volant, and marine mammals in mainland Portugal and archipelagos of the Azores and Madeira that includes 105,026 data entries between 1873 and 2021 (72% of the data occurring in 2000 and 2021). The methods used to collect the data were: live observations/captures (43%), sign surveys (35%), camera trapping (16%), bioacoustics surveys (4%) and radiotracking, and inquiries that represent less than 1% of the records. The data set includes 13 types of records: (1) burrows | soil mounds | tunnel, (2) capture, (3) colony, (4) dead animal | hair | skulls | jaws, (5) genetic confirmation, (6) inquiries, (7) observation of live animal (8), observation in shelters, (9) photo trapping | video, (10) predators diet | pellets | pine cones/nuts, (11) scat | track | ditch, (12) telemetry and (13) vocalization | echolocation. The spatial uncertainty of most records ranges between 0 and 100 m (76%). Rodentia (n =31,573) has the highest number of records followed by Chiroptera (n = 18,857), Carnivora (n = 18,594), Lagomorpha (n = 17,496), Cetartiodactyla (n = 11,568) and Eulipotyphla (n = 7008). The data set includes records of species classified by the IUCN as threatened (e.g., Oryctolagus cuniculus [n = 12,159], Monachus monachus [n = 1,512], and Lynx pardinus [n = 197]). We believe that this data set may stimulate the publication of other European countries data sets that would certainly contribute to ecology and conservation-related research, and therefore assisting on the development of more accurate and tailored conservation management strategies for each species. There are no copyright restrictions; please cite this data paper when the data are used in publications

Growth and study of layered ferroelectric thin film materials based on stacked structures of (BST) layers

Tese de doutoramento em Ciências (área de especialização em Física)Barium strontium titanate (BST) has been considered as a potential candidate for various applications due to its unique properties, such as the ferroelectric, dielectric properties in addition to eco friendly nature. Moreover, its properties can be tailored for specific applications by controlling the barium to strontium ratio. Due to their technological importance, in the present thesis, thin films with different ratios Ba/Sr (80/20 and 100/0) were grown by pulsed laser deposition (PLD) and characterized in order to investigate their properties and potential to be integrated in some applications, particularly non-volatile ferroelectric random access memories. Present thesis has been divided into eight chapters. Chapter 1 presents the motivation and the scope of thesis. Chapter 2 discloses literature survey, general and technological importance of BST. Chapter 3 describes the thin films deposition procedure and characterization techniques. Chapter 4 mainly focuses on the effect of various deposition parameters on the physical properties of BST thin films. Firstly, the effect of pulse-repetition frequencies (PRFs) on BST growth and consequently on their functional properties was studied. In spite of the x-ray diffraction suggested a crystalline nature of the deposited films and Rutherford backscattering spectrometry measurements confirms the same stoichiometry in the films and target, scanning transmission electron microscopy and transmission electron microscopy images have revealed that a BST amorphous layer of considerable thickness is formed at the interface between the film and the Pt layer in the films deposited at 10 Hz. The presence of the amorphous layer was interpreted taking into account the PRF used during the deposition. The dielectric and electric properties were explained by a model, where a low-permittivity amorphous layer is connected in series with the crystalline BST layer. Secondly, the influence of oxygen partial pressure on the ferroelectric properties of Ba0.8Sr0.2TiO3 thin films has been highlighted. It is observed that the PO2 during the deposition plays an important role on the tetragonal distortion ratio, surface morphology, dielectric permittivity, ferroelectric polarization, switching response and leakage currents of the films. In-plane strain changes from tensile to compressive with increase in PO2. As a consequence, the films grown at 7.5 Pa show the superior dielectric and ferroelectric properties and also exhibit the good polarization stability. The butterfly features of the capacitance-voltage characteristics and the bell shape curve in polarization current were attributed to the domain reversal process. In chapter 5, the effect of the Pt bottom electrode texture on the tetragonality, orientation and physical properties of BST thin films is presented. A strong relation was found between the electrode texture and the tetragonality and orientation of BST films. As a consequence, the properties like dielectric permittivity, polarization, switching time and leakage currents were found to depend on the selected substrate. Chapter 6 demonstrates the Laser Assisted-Annealing (LAA) effect on crystallization process. By adjusting LAA conditions, like frequency of the laser and number of shots, BST thin films with pure perovskite phase on bare glass and platinized substrates, at room temperature and in an air environment were grown. The LAA technique was also applied to BST/ITO/glass heterostructures, as an attempt to produce BST thin films in cheap substrate to be used in optoelectronic devices. Through an elevation of the substrate temperature during LAA, this technique has been successfully applied allowing the elimination of cracks in the films. Chapter 7 depicts the growth and ferroelectric properties of BaTiO3 thin films fabricated by PLD. It was found that the preferred oriented films can be grown on platinized silicon by adjusting the laser frequency. Moreover, the structural, morphological, ferroelectric, dielectric and electrical properties were found to be strongly dependent on the laser frequency. The BaTiO3 films deposited at 1 Hz on platinized substrates shows high (001) orientation and superior ferroelectric properties similar to the ones found on epitaxial films grown on single-crystalline oxide substrate. This study suggests that the improvement of the ferroelectric properties is closely related to the preferred orientation, low strain and homogenous grain distribution in BaTiO3 the films. Chapter 8 gives the overall conclusions, the correlations and the future work.O titanato de bário e estrôncio (BST) tem sido considerado como um potencial candidato para ser utilizado em diversas aplicações, devido às suas propriedades ferroelétricas e dielétricas únicas e à sua natureza ecológica. Para além disso, as suas propriedades podem ser otimizadas para aplicações específicas, controlando a razão Ba/Sr. Devido à sua importância tecnológica, na presente tese, filmes finos com diferentes razões Ba/Sr (80/20 e 100/0) foram depositados pela técnica de ablação laser (PLD) e caraterizados com o objetivo de investigar as suas propriedades e de avaliar o seu potencial para serem integrados em algumas aplicações, em particular nas memórias ferroelétricas não voláteis de acesso aleatório. A presente tese foi dividida em oito capítulos. O capítulo 1 descreve a motivação da opção por esta temática, bem como o âmbito desta tese. O capítulo 2 apresenta o quadro teórico da tese como resultado de uma pesquisa bibliográfica e demonstra a importância tecnológica do BST. O capítulo 3 descreve o procedimento utilizado na deposição dos filmes bem como as técnicas de caraterização utilizadas. O capítulo 4 centra-se essencialmente no efeito de vários parâmetros de deposição nas propriedades físicas dos filmes finos de BST. Em primeiro lugar, o efeito da frequência de repetição do pulso (PRF) no crescimento dos filmes de Ba0.8Sr0.2TiO3 e, consequentemente, nas suas propriedades funcionais foram estudadas. Apesar da difração de raios-X sugerir uma natureza cristalina dos filmes depositados e a espectrometria por retrodifusão de Rutherford (RBS) confirmar a mesma estequiometria nos filmes e no alvo, as imagens de microscopia eletrónica de varrimento e de microscopia eletrónica de transmissão revelaram que uma camada amorfa de BST de espessura considerável é formada na interface entre o próprio filme e a camada de Pt nos filmes depositados a 10 Hz. A presença da camada amorfa foi interpretada tendo em conta a PRF utilizada durante a deposição. As propriedades dielétricas e elétricas foram explicadas através de um modelo, em que uma camada amorfa, de permitividade menor, se encontra ligada em série com a camada de BST cristalina. Posteriormente, a influência da pressão parcial de oxigénio (PO2) nas propriedades ferroelétricas de filmes finos de Ba0.8Sr0.2TiO3 foi destacada. Observa-se que a PO2 durante a deposição desempenha um papel importante na distorção tetragonal, na morfologia da superfície, na permitividade dielétrica, polarização ferroelétrica, comutação de resposta e correntes de fuga dos filmes. A tensão no plano da amostra passa de tração para compressão com o aumento da PO2. Como consequência, os filmes crescidos a 7.5 Pa evidenciam propriedades dielétricas e ferroelétricas superiores, para além de boa resistência à fadiga. A existência da figura “borboleta” caraterística nas medidas de capacitânciatensão e a curva em forma de sino nas correntes de polarização foram atribuídas ao processo de reversão de domínios. No capítulo 5 é apresentado o efeito da textura do elétrodo inferior (Pt) na tetragonalidade, na orientação e nas propriedades físicas dos filmes finos de BST. Daqui se infere que as propriedades como a permitividade dielétrica, a polarização, o tempo de comutação e as correntes de fuga dependem do substrato selecionado. O capítulo 6 demonstra o efeito do recozimento assistido por laser (LAA) no processo de cristalização. Através do ajuste das condições do LAA, tais como a frequência do laser e o número de pulsos, foi possível fazer crescer filmes finos de BST com a fase pura perovskite sobre vidro e sobre substratos platinados, à temperatura ambiente e à pressão atmosférica. A técnica de LAA foi também aplicada a heteroestruturas de BST/ITO/vidro, como uma tentativa para produzir filmes finos de BST em substratos com baixo custo para serem usados em dispositivos optoelectrónicos. Através de uma elevação da temperatura do substrato durante o LAA, esta técnica foi aplicada com êxito, permitindo que as fissuras nos filmes fossem eliminadas. O capítulo 7 ilustra o crescimento e as propriedades ferroelétricas dos filmes finos de BaTiO3 fabricados por PLD. Verifica-se que filmes preferencialmente orientados podem ser crescidos em substratos platinados através do ajuste da frequência do laser. Assim, as propriedades estruturais, morfológicas, dielétricas, ferroelétricas e elétricas dependem fortemente da frequência do laser. Os filmes depositados de BaTiO3 a 1 Hz em substratos platinados evidenciam uma elevada orientação (001) e excelentes propriedades ferroelétricas semelhantes às encontradas em filmes epitaxiais depositados em substratos monocristalinos. Este estudo sugere que a melhoria das propriedades ferroelétricas está intimamente relacionada com a orientação preferencial, baixa tensão e distribuição homogénea de grãos nos filmes de BaTiO3. No capítulo 8 são apresentadas as conclusões gerais, as correlações possíveis e as recomendações para trabalhos futuros sobre a mesma temática