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                              PCE95/2017

 

Cod proiect: PN-III-P4-ID-PCE-2016-0911

Abstract

The scientific goal of this proposal is to study the cooperative effects of driven structural and compositional constrains induced in BiFeO3/LaFeO3 perovskites oxide thin films on their functional properties, especially the photocatalytic ones such as water splitting and organic pollutant degradations. Inducing defects, e.g. oxygen vacancies, structural strain through different substrates and substrate surface - plane terminations in BiFeO3/LaFeO3 heterostructure will be done in conjunction with their functional properties evaluations.       
The epitaxial BFO/LFO heterostructure will be obtained by Pulsed Laser Deposition method assisted by reflection high-energy electron diffraction system for layer by layer growth monitoring, at different oxygen partial pressure during film growth. The oxygen vacancies, meaning A-site cation deficiency- can be easily introduced by PLD method into the thin film structure in precise locations - at the interface between the film and substrate or at surface of the film, as M. Huijben et al have shown for the SrTiO3/LaAlO3 heterostructure. 
Evaluation of the BFO/LFO heterostructure photocatalytic degradation of organic pollutant and photoelectrochemical water splitting efficiencies will be performed as a function of induced constrains. 

Obiectivul stiintific al proiectului este studiul efectelor constrangerilor structurale și stoechiometrice, induse în filmele subtiri de oxizi perovskitici BiFeO3/LaFeO3 asupra proprietatilor functionale ale acestora, în special asupra celor fotocatalitice, pentru aplicații în fotocataliza apei și degradarea de compusi poluatori organici. Evaluarea proprietatilor functionale va fi corelata cu deformarile structurale induse de folosirea diferitelor tipuri de substrate și planuri terminale ale substratelor și cu defectele induse (ex. vacanțe de oxigen).

Heterostructurile epitaxiale BFO/LFO vor fi depuse prin ablatie laser asistata de RHEED (reflection high-energy electron diffraction) pentru monitorizarea creșterii strat cu strat, la diferite presiuni partiale de oxigen. Vacanțele de oxigen (deficiente de cationi pe site-ul A) pot fi ușor induse prin metoda PLD, în locatii controlate: la interfata film-substrat, sau la suprafața filmului depus, după cum au arătat M. Huijben și colaboratorii pentru heterostructuri SrTiO3/LaAlO3.

Eficienta fotocatalitica a heterostructurilor BFO/LFO pentru degradarea compusilor poluatori organici și pentru cataliza foto-electrochimica a apei va fi evaluata ca funcție de constrangerile induse.

 

About ISCOPE

The main objective is to study the cooperative effects of driven structural and stoichiometric constrains induced in BiFeO3/LaFeO3 perovskites oxide thin films on their functional properties, especially the photocatalytic ones such as water splitting and organic pollutant degradations.  

 

Different types of BFO/LFO heterostructures will be obtained by PLD and PLD assisted RHEED techniques, and the effect of the oxygen vacancies and structural deformation induced by the substrate on the photocatalytic degradation efficiencies of persistent organic pollutants as well as on the photoelectrochemical water splitting efficiencies will be revealed.

Obiectivul principal este studiul efectelor constrangerilor structurale și stoechiometrice, induse în filmele subtiri de oxizi perovskitici BiFeO3/LaFeO3, asupra proprietatilor functionale ale acestora, în special asupra celor fotocatalitice, pentru aplicații în fotocataliza apei și degradarea de compusi poluatori organici.

 

Vor fi depuse diverse tipuri de heterostructuri BFO/LFO, prin tehnici PLD și PLD asistat de RHEED. Va fi studiat efectul vacantelor de oxigen și al deformarilor structurale induse de substrat asupra eficientei de degradare fotocatalitica a compusilor organici poluatori persistenti și asupra eficientei în fotocataliza apei.

 

Stage 1 - Evaluation of the physical and chemical properties of BFO and LFO thin layers grown under various structural deformation conditions, and the effects of the introduction of oxygen vacancies.

Act 1.1 - Deposition of BFO and LFO thin layers by PLD and RHEED-assisted PLD on various mono-crystalline substrates and introduction of oxygen vacancies.

Act 1.2 - Investigation of physical and chemical properties of PLD deposited BFO and LFO layers

Act 1.3 - Management, results analysis, dissemination, editing

Duration of Stage 1: July 12, 2017 – December 31, 2017

Government funding for 2017: RON 291.596

During this stage the main goal was especially related to the experiments preparation by adapting the PLD deposition systems for obtaining BiFeO3 and LaFeO3 thin films and/or heterostructures – Figure 1. Project management specific activities have been conducted, such as specific material acquisition and creating the project’s web page. Furthermore, preliminary experiments were performed for BiFeO3 and LaFeO3 thin film deposition using targets purchased from LTS Ceramics. The main scientific purpose of this stage was to determine the optimal experimental conditions for obtaining BFO and LFO epitaxial thin films with different thicknesses. Also, scientific documentation was performed regarding novelties published in the literature, especially those related to the applicability of BiFeO3 and LaFeO3 epitaxial thin films in water photolysis and degradation of persistent organic pollutants.

                                                                           Figure 1. RHEED assisted PLD system

Stage 2 - Evaluation of the effects of the introduction of oxygen vacancies, and the use of substrates with different structural parameters, on the physical and chemical properties of BFO/LFO heterostructures.

Act 2.1 - Growth of BFO/LFO heterostructures, by PLD and RHEED-assisted PLD in various substrates, with various grades of oxygen defficiency.

Act 2.2 - Characterization of the physical and chemical properties of BFO/LFO heterostructures

Act 2.3 - Management, results analysis, dissemination, editing

During this stage, the main research activities carried out focused on obtaining perovskite thin films of LaFeO3 and BiFeO3 as well as heterostructures of LFO/BFO in various growth geometries and induction of controlled structural deformations by using monocrystalline substrates with different lattice constants of perovskite materials. Moreover, thin films of LFO and LFO / BFO heterostructures were obtained and characterized under special experimental conditions in order to induce oxygen vacancies. The heterostructures and thin layers thus obtained were integrated into photoelectrochemical testing devices to determine the photoelectrochemical efficiency of water molecule dissociation. The first objective of this stage was based on the generation of oxygen vacancies in the structure of LFO thin films, these vacancies aiming to improve the efficiencies for the generation of hydrogen in the case of the photochemical decomposition reaction of the water molecule. Also, these efficiencies can be improved by inducing crystallographic deformations as a result of changing the substrate associated with the deposition of LFO and BFO materials. As substrates, besides those of Pt-Si, STO (SrTiO3), STON (SrTiO3 doped with Nb) which have been used so far, the following substrates have also been used: GSO (GdScO3), LAO (LaAlO3), LSAT ((LaAlO3) 0.3 (Sr2AlTaO6) 0.7), YSZ (ZrO2 stabilized by Y2O3, 8% mol Y2O3).

In this way, different degrees of structural deformation can be induced in the structure of perovskite materials depending on the network constants of the substrates, this being an essential part of this stage. Moreover, the study of the latest developments in the literature, especially those targeting LFO and BFO perovskite materials, was conducted.

Induction of structural deformations in the thin layers of LaFeO3: epitaxial strain, oxygen vacancies.

- structural details for LaFeO3 thin films: the approximate LFO structure with a pseudo-cubic structure has a network constant of 3.93 Å indicating a very good compatibility with the cubic structure of the Nb-STO substrate (3.905 Å) with a mismatch deviation of only 0.64% for the 2 film/substrate lattice parameters. Thus, the LFO film may have two possible crystallographic orientations LFO (110) || STO (001), (α domains) and LFO (001) || STO (001) (β domains) - Figure 2.

              Figure 2.  Crystallographic orientations in LFO films -orthorhombic films grown on STO-cubic substrate

Influence of oxygen content on the physico-chemical properties of LaFeO3 thin films:

Figure 3. AFM morphological analyzes performed on LaFeO3/Nb samples: SrTiO3 obtained at different P oxigen values: a) 0.05 mbar, b) 0.25 mbar, c) 0.3 mbar, d) 0.6 mbar and e) 0.9 mbar.

Figure 4. XRD results: 2q-ω diffractograms for LFO/STON thin films around reflections (002)

Figure 5. The evolution of the photoelectrochemical performances of the LaFeO3 thin films in relation to P oxygen values used in the growth process.

Stage 3 - Evaluation of the photocatalytic properties of BFO/LFO  heterostructures

Act 3.1 - Obtaining by PLD of thin films of BFO/LFO and LFO/BFO heterostructures under optimized experimental conditions

Act 3.2 - Integration of thin films in photo-anode devices for photocatalytic reactions

Act 3.3 - Evaluation of the photocatalytic and photoelectrochemical properties of BFO / LFO and LFO / BFO heterostructures

The main research activities carried out during this stage were based on obtaining thin perovskite films of LaFeO3, as well as LFO/BFO heterostructures under previously optimized experimental conditions. The morphological, optical, structural and photoelectrochemical properties of the LFO/BFO and BFO/LFO heterostructures were investigated. The next step was integrating the thin films into photoelectrochemical testing devices for determining photocatalytic activities in the case of water molecule decomposition reactions.

The first objective of this stage was to obtain thin films of LFO/BFO and BFO/LFO heterostructures using the best experimental conditions for PLD deposition. In order to achieve this, the deposition conditions were optimized for both thin films of LFO, the effect of the varying the partial oxygen pressure on the functional properties being observed, as well as for the thin films of SrRuO3 used as the lower electrode.

The second objective of this stage was to integrate the thin films into photo-anode devices and using them in photocatalytic reactions. For this, the photoelectrochemical measurement system was optimized in terms of laser focusing used for the irradiation of the samples, as well as the composition of the electrolytic solutions used for these measurements. The photoelectrochemical measurement system was connected with a gas-chromatographic system for the direct determination of the gaseous reaction products resulting from the photocatalytic reactions of the water molecule breaking.

An essential part of this stage is the study of the functional properties of LFO/BFO heterostructures depending on the type of material on the surface of the heterostructure, more precisely, the effect generated as a result of the order in which the perovskite materials were deposited on the substrate was investigated, BFO/LFO/STON and LFO/BFO/STON respectively. The purpose was to combine the functional properties of the LFO (chemical stability and high absorption in the visible field) with those of the BFO bismuth ferrite (electrical properties). In addition, the study of the latest news from the literature was conducted and the project website was updated.

 

- Integrating the BFO/LFO and LFO/BFO thin films into test structures to determine the functional properties: obtaining photo-anodes based on BFO/LFO/STON and LFO/ BFO/STON heterostructures for evaluating the breaking efficiency of the water molecule using a photoelectrochemistry system assisted by a gas chromatograph - Figure 6.

Etapa 1 - Evaluarea proprietatilor fizico-chimice ale straturilor subtiri de BFO si LFO obtinute in conditii de deformare structurala diferita si a efectelor inducerii de vacante de oxigen.

Act 1.1 - Depunerea de straturi subtiri de BFO si LFO prin PLD si PLD asistata de RHEED pe substraturi monocristaline diferite si inducerea de vacante de oxigen.

Act 1.2 - Investigarea proprietatilor chimice si fizice ale straturilor de BFO si LFO depuse prin PLD

Act 1.3 - Management, analiza rezultatelor, diseminarea, editare

Durata etapei 1: 12 iulie-31 decembrie 2017

Valoarea alocata proiectului de la bugetul de stat pentru 2017: 291.596 ron

In cadrul acestei etape principalul scop a fost in special legat de pregatirea experimentelor prin adaptarea sistemelor de depunere PLD pentru obtinerea de  filme subtiri  si/sau heterostructuri de BiFeO3 si LaFeO3. Au fost desfasurate activitati specifice managementului de proiect cum ar fi achizitionarea materialelor necesare si realizarea paginii de web a proiectului. Au fost de asemenea efectuate experimente preliminare de depunere de filme subtiri de BiFeO3 si LaFeO3 din tinte achizitionate de la compania LTS Ceramics.

 

Principalul scop stiintific al acestei etape a fost de a determina conditiile experimentale optime pentru obtinerea de straturi subtiri epitaxiale de BFO si LFO si cu grosimi diferite. De asemenea, au fost intreprinse actiuni de documentare, privind ultimele noutati publicate in literatura, in special cele legate de aplicabilitatea filmelor subtiri epitaxiale de BiFeO3 si LaFeO3 in fotoliza apei si degradarea poluantilor organici persistenti. 

Etapa 2 - Evaluarea efectelor inducerii de vacante de oxigen si a folosirii de substrate avand diferiti parametri structurali asupra proprietatilor fizice si chimice ale heterostructurilor de BFO/LFO.

Act 2.1 - Cresterea de heterostructuri de BFO/LFO prin PLD si PLD asistat de RHEED pe diferite substraturi, cu diferite niveluri de vacante de oxigen.

Act 2.2 - Caracterizarea proprietatilor fizice si chimice ale heterostructurilor de BFO/LFO

Act 2.3 - Management, analiza rezultatelor, diseminarea, editare

In cadrul acestei etape principalele activitati de cercetare efectuate s-au axat pe obtinerea de straturi subtiri perovskitice de LaFeO3 si BiFeO3 precum si de heterostructuri LFO/BFO in diverse geometrii de crestere si inducerea de deformari structurale controlate prin utilizarea de substraturi monocristaline cu constante de retea diferite de ale materialelor perovskitice.

De asemenea, au fost obtinute si caracterizate filme subtiri de LFO si heterostructuri LFO/BFO  in conditii experimentale speciale pentru a induce vacante de oxigen. Heterostructurile si straturile subtiri astfel obtinute au fost integrate in dispozitive de testare fotoelectrochimica pentru determinarea eficientei fotoelectrochimice de disociere a moleculei de apa. 

Primul obiectiv al acestei etape a avut la baza generarea de vacante de oxigen in structura filmelor subtiri de LFO, aceste vacante avand scopul de a imbunatati eficientele pentru generarea hidrogenului in cazul reactiei de descompunere fotochimica a moleculei de apa. De asemenea, aceste eficiente pot fi imbunatatite prin inducerea de deformari cristalografice ca urmare a schimbarii substratului aferent depunerii materialelor de LFO si BFO. Ca si substraturi, pe langa cele de Pt-Si, STO (SrTiO3), STON (SrTiO3 dopat cu Nb) ce au fost utilizate si pana in prezent, s-au folosit si substraturile urmatoare: GSO (GdScO3), LAO (LaAlO3), LSAT ((LaAlO3)0.3 (Sr2AlTaO6)0.7), YSZ ( ZrO2 stabilizat de Y2O3 , 8 % mole Y2O3).

In acest mod, se pot induce diferite grade de deformare structurala in structura materialelor perovskitce  in functie de constantele de retea a substraturilor, acest lucru reprezentand o parte esentiala a acestei etape. Pe langa acestea, a fost efectuat studiul ultimelor noutati din literatura, in special a celor care vizeaza materiale perovskitice de tip LFO si BFO.

-  Inducerea de deformari structurale in straturile subtiri de LaFeO3:  epitaxial strain, vacante de oxigen

- detalii structurale pentru straturile subtiri de LaFeO3 :  structura LFO  aproximata cu o structura pseudo-cubica are  o constanta de retea de 3.93 Å ce indica o foarte  buna compatibilitate cu structura cubica a substratului de Nb-STO (3.905 Å) cu o abatere (mismatch)  a celor 2 parametrii de retea film/substrat de numai 0.64 %.  Astfel, flmul de LFO poate o avea doua posibile orientari cristalograficeLFO(110)||STO(001) ,(domenii α) si LFO(001)||STO(001) (domenii ß) – Figura 2. Orientarile cristalografice in filmele de LFO-ortorombic crescut pe substrat de STO-cubic

 

- Influenta continutului de oxigen asupra proprietatilor fizico-chimice ale straturilor subtiri de LaFeO3 :

Figura 3. Analize morfologice AFM efectuate pe probe de LaFeO3/Nb :SrTiO3obtinute la diverse valori Poxigen: a) 0.05 mbar, b) 0.25 mbar, c) 0.3 mbar, d) 0.6 mbar  si e) 0.9 mbar.

 

 

 

 

Figura 4.   Difractogramele 2q-ω pentru straturile subtiri de LFO/STON in jurul reflectiilor (002)

Figura 5. Evolutia performantelor photoelectrochimice  ale straturilor subtiri de LaFeO3 in functie de valorile Poxygen utilizate in procesul de crestere.

Etapa 3 - Evaluarea proprietatilor fotocatalitice de degradare a poluantilor organici si de disociere a moleculei de apa ale heterostructurilor de BFO/LFO

Act 3.1 - Obtinerea prin PLD de straturi subtiri de tip heterostructuri BFO/LFO, cat si LFO/BFO in conditii experimentale optimizate

Act 3.2 - Integrarea straturilor subtiri in dispozitive de tip fotoanod pentru utilizarea in reactii fotocatalitice

Act 3.3 - Evaluarea proprietatilor fotocatalitice si fotoelectrochimice ale heterostructurilor de BFO/LFO si LFO/BFO.

Principalele activitati de cercetare efectuate in cadrul acestei etape au la baza obtinerea de straturi subtiri perovskitice de LaFeO3, precum si de heterostructuri de LFO/BFO in conditii experimentale anterior optimizate. Proprietatile morfologice, optice, structurale si fotoelectrochimice ale heterostructurilor de LFO/BFO si BFO/LFO au fost investigate. Integrarea filmelor subtiri in dispozitive de testare fotoelectrochimica pentru determinarea activitatilor fotocatalitice in cazul reactiilor de descompunere a moleculei de apa a fost urmatorul pas.

 Primul obiectiv al acestei etape a constat in obtinerea de straturi subtiri de   heterostructuri de tip LFO/BFO si BFO/LFO utilizand cele mai bune conditii experimentale de depunere prin PLD. Pentru aceasta, au fost optimizate conditiile de depunere atat pentru straturile subtiri de LFO, efectul variatiei presiunii partiale de oxigen asupra proprietatilor functionale  fiind dezvaluit, cat si pentru stratul subtire de SrRuO3 folosit ca electrod inferior.  

  Cel de-al doilea obiectiv al acestei etape a constat din integrarea straturilor subtiri in dispozitive de tip fotoanod pentru utilizarea in reactii fotocatalitice. Pentru aceasta a fost optimizat sistemul de masurare fotoelectrochimica din punct de vedere al focalizarii laserului folosit pentru iradierea probelor, dar si a compozitiei solutiilor electrolitice utilizate in cazul acestor masuratori. Sistemul de masura fotoelectrochimic  a fost conectat cu un sistem gaz-cromatograf pentru determinarea directa a produsilor de reactie gazosi rezultati in urma reactiilor fotocatalitice de spargere a moleculei de apa.  

O parte esentiala a acestei etape o reprezinta studiul proprietatilor functionale ale heterostructurilor de LFO/BFO in functie de tip de material de la suprafata heterostructurii, mai exact, s-au investigat efectul generat ca urmare a ordinii in care materialele perovskitice au fost depuse pe substrat, BFO/LFO/STON si respectiv LFO/BFO/STON. Scopul a fost imbinarea proprietatilor functionale ale LFO (stabilitate chimica si absorbtie ridicata in domeniul vizibil), cu cele ale  feritei de bismut BFO (proprietati electrice). Pe langa acestea, a fost efectuat studiul ultimelor noutati din literatura si a fost actualizat site-ul proiectului.   

 

- Integrarea straturilor subtiri de BFO/LFO si LFO/BFO in structuri de test pentru determinarea proprietatilor functionale:  obtinerea de fotoanozi bazati pe heterostructuri BFO/LFO/STON si LFO/BFO/STON pentru  evaluarea eficientei de  spargere a molecului de apa utilizand un sistem fotoelectrochimic asistat de un cromatograf de gaze- Figura 6.

Figura 6. Schema experimentala a sistemului fotoelectrochimic PEC asistat de un cromatograf de gaz

 
 

Dissemination of Stage I:

 

- European congress and exhibition on advanced materials and processes - Euromat 2017, September 12-22, 2017 in Thessaloniki, Greece – invited lecture "Bi-BASED NANOSTRUCTURES PRODUCED BY LASER ABLATION AND THEIR FUNCTIONAL PROPERTIES TAILORED BY COMPLEX ENSEMBLES OF NANOSCALE PHASE/NANODOMAIN FLUCTUATIONS", Session Title: Deposition and nanostructuring assisted by ion and laser irradiation

 

- Fall Meeting of The European Materials Research Society, September 18-21, 2017 in Warsaw, Poland – poster "Cation doping and epitaxial strain dependence of functional properties in perovskite thin films obtained by laser techniques", in Advanced oxide materials – growth, characterization and applications

Dissemination of Stage II:

- E-MRS Spring Meeting, in Strasbourg, France: poster: “Enhancing the multifunctionality of thin films through complex engineered nanoscale phases/nanodomains”

- European Materials Research Society SPRING Meeting in Strasbourg, Franta- poster „Enabling multifunctionality of laser processed nanostructures through complex ensembles of chemical pressure and epitaxial strain"

-European Materials Research Society FALL Meeting  in Varsovia, Polonia – oral "Structural, optical and photocatalytic properties of BiFeO3/LaFeO3 epitaxial heterostructures"

 

- 6th Venice International School on Lasers in Materials Science, in Venice, Italy -oral - “Synthesis, characterization and applications of layered    double hydroxides with interlayer organic dyes "

- ISCP-INDLAS 2018 Modern Laser Applications, Alba Iulia, Romania, invited : “Raising the multifunctionality of laser processed perovskite thin films/nanostructures through chemical pressure and epitaxial strain.”

- In press: "Laser Processing of Nanostructures: Enhancing Functional Properties of Lead-Free Perovskite Nanostructures Through Chemical Pressure and Epitaxial Strain." Nicu D. Scarisoreanu, Floriana Craciun, Maria Dinescu, Valentin Ion, Andreea Andrei, Antoniu Moldovan,  Valentin Teodorescu, Cornel Ghica, Ruxandra Birjega, Chapter in "Functional nanostructured interfaces for environmental science and biomedical applications", Elsevier Inc., ISBN: 9780128144015 (2019)

                                                                 Dissemination of Stage III:

- European Materials Research Society FALL Meeting 2019, symposium N: Advanced catalytic materials for (photo) electrochemical energy conversion- poster "Bismuth ferrite thin films as photocatalyst for solar water splitting"; 

- European Materials Research Society FALL Meeting 2019, symposium N: Advanced catalytic materials for (photo)electrochemical energy conversion- oral- "Production of solar hydrogen from water via photoelectrochemical route using heterostructures of bismuth and lanthanum ferrites"

- in press:- "The effects of the oxygen content on the photoelectrochemical properties of LaFeO3 perovskite thin films obtained by pulsed laser deposition", Florin Andrei; Iulian Boerasu; Ruxandra Birjega; Antoniu Moldovan; Maria Dinescu; Valentin Ion; Cristian Mihailescu; Nicu Scarisoreanu; Victor Leca, Applied Physics A

 

Contact us

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Email & Phone:

Address

 

 

Departament of Lasers, NILPRP

409 Strada Atomiștilor
Măgurele, 077125
Romania

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