Armando Cardoso Lourenço

Armando Cardoso Lourenço
University of Aveiro | UA · Division of Physics

PhD, Physics

About

49
Publications
2,134
Reads
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229
Citations
Additional affiliations
November 1995 - January 2015
University of Aveiro
Position
  • Professor (Assistant)
September 1990 - December 1990
Max Planck Institute for Solid State Research
Position
  • Student
Description
  • YBCO thin films using PLD
September 1989 - March 1990
The University of Warwick
Position
  • Erasmus Student
Description
  • Erasmus Student

Publications

Publications (49)
Article
The usage of heterostructures of ferromagnetic and ferroelectric materials, as a means of achieving magnetoelectric multiferroic coupling, is a widely used approach which has been showing promising results. Along this line of thought, the deposition of BaTiO3 and Fe multilayers on LaAlO3, MgO, Al2O3 and SrTiO3 substrates using RF-magnetron sputteri...
Article
Full-text available
We report an effect of giant surface modification of a 5.6 nm thick BaTiO₃ film grown on Si (100) substrate under poling by conductive tip of a scanning probe microscope (SPM). The surface can be locally elevated by about 9 nm under -20 V applied during scanning, resulting in the maximum strain of 160%. The threshold voltage for the surface modific...
Article
Oxide multiferroic thin films and heterostructures offer a wide range of properties originated from intrinsic coupling between lattice strain and nanoscale magnetic/electronic ordering. La0.9Ba0.1MnO3 (LBM) thin-films and LBM/BaTiO3/ LBM (LBMBT) heterostructures were grown on single crystalline [100] silicon and [0001] Al2O3 using RF magnetron sput...
Article
Alnico V thin film samples with the thickness of 100 nm were prepared by radio-frequency sputtering on Si substrates with and without a SiO2 layer. Heat treatment of the as-deposited thin films in above ambient pressure in an Ar atmosphere at a temperature range of 600–900°C, followed by quenching and/or slow cooling, leads to higher coercivity val...
Article
Full-text available
The existence of extended defects (i.e., dislocations) in inorganic semiconductors, such as GaN or ZnO, responsible for broad emission peaks in photoluminescence analysis remains unresolved. The possible assignments of these luminescence bands are still matter of discussion. In this study, two different zinc oxide samples, grown under different oxy...
Article
Full-text available
Ni2MnGa thin films raise great interest due to their properties, which provide them with strong potential for technological applications. Ni2MnGa thin films were prepared by r.f. sputtering deposition on Si substrates at low temperature (400 degrees C). Film thicknesses in the range 10-120 nm were obtained. A study of the structural, magnetic and e...
Article
High quality YBa2Cu3O6+x (YBCO) superconducting thin films were implanted with the radioactive 197m Hg (T1/2 = 24 h) isotope to low fluences of 10^13 atoms/cm^2 and 60 keV energy. The lattice location and stability of the implanted Hg were studied combining the Perturbed Angular Correlation (PAC) and Emission Channeling (EC) techniques. We show tha...
Article
In this work ZnO thin films were deposited on different substrates, glass, silicon (100), and MgO (100) using rf-magnetron sputtering at low temperature in order to promote a large defect density, aiming to study a possible correlation with the observed violet/blue emission band. The peak position, width and low energy band shape asymmetry of the v...
Article
The deposition of a thin magnesium metallic interlayer on an Si substrate prior to the deposition of an oxide thin film using rf-sputtering was investigated. The deposition of high-κ HfO2 thin film was more particularly studied and it was demonstrated that the metallic interlayer acts as an oxygen barrier, preventing the formation of a low-κ layer...
Article
In this paper, we report a preparation of multiferroic heterostructure from thin film of Ni-Mn-Ga (NMG) alloy and lead magnesium niobate-lead titanate (PMN-PT) with effective magnetoelectric (ME) coupling between the film as ferromagnetic material and PMN-PT as piezoelectric material. The heterostructure was prepared by relatively low temperature (...
Article
Full-text available
A thin metallic interlayer was deposited on Si and Si/SiO2 substrate prior to the sputtering of HfO2 films. The metallic interlayer, in fact, acts as an oxygen barrier during the HfO2 deposition, preventing the formation of a low-κ layer at the high-κ/Si interface. After annealing, the metal diffuses in the HfO2 film. When the thickness of the meta...
Article
We report on a study where the properties of films obtained by RF-magnetron sputtering and by Selenization of elemental precursor layers are analysed by Raman scattering, x-ray diffraction and optical measurements. Three routes were followed to prepare CIS films on glass. CIS type-I was prepared by selenization at various temperatures, CIS type-II...
Article
Zinc oxide nanowires have been grown on alumina substrate by thermal evaporation of zinc nanopowder in the presence of oxygen flow. The growth was performed under ambient pressure and without the use of foreign catalyst. Scanning electron microscopy (SEM) observation showed that the as-grown sample consists of bulk ZnO crystal on the substrate surf...
Article
Full-text available
Low temperature (400°C) deposition of ferromagnetic Ni-Mn-Ga thin films is successfully performed via rf magnetron sputtering technique using co-deposition of two targets Ni 50 Mn 50 and Ni 50 Ga 50 on sapphire (0001) and Si (100) substrates. The films are in part amorphous with significant degree of crystallinity. The obtained crystallographic str...
Conference Paper
The effect of a thin metallic interlayer deposited on Si substrate prior the sputtering of HfO2 films was investigated. It was shown that the metallic interlayer acts as an oxygen barrier during the HfO2 deposition. After annealing, the metal diffuses into the HfO2 film and prevents the formation of a low-kappa layer at the high-kappa/Si interface....
Article
A detailed study of the magnetization NI(H, T) of bulk ceramic La2.3Ca1.3MnO3 (T-c = 267 K) in the paramagnetic phase is presented. Near T-c (T - T-c < 30 K) first-order phase transition features are found. At low magnetic fields (H: 0.3-50 Oe), a sequence of step and plateaus in the effective Curie constant C(T) = M(T - T-c)/H is found, accompanie...
Article
A study of transport and magnetic properties of Cd manganites in bulk ceramic and thin films is presented. Although Cd and Ca ions have the same valence and similar cation sizes, their incorporation into vacancy doped La manganites induces different properties. Both series are ferromagnetic with the usual peak in magnetoresistance close to Tc, but...
Article
The effects of La manganite doping by Ca and A-site vacancies are compared in thin films and bulk ceramics. In bulk, rombohedric, orthorhombic or mixed manganite crystallographic phases are found, depending on the Ca content. It is found that up to a certain level, the increase of Tc by Ca and vacancy doping is cumulative. Maximum Tc obtained in bu...
Article
Non-linear resistivity in La0.78Ca0.25MnO3 epitaxial thin films is studied using 2-contact dynamic measurements. Non-linear V-I is obtained below Tc (~220K). Evaporated gold or direct silver-paste contacts give similar results. dV/dI at high voltages (~1V) follows the usual four-point resistance results, but at lower voltages an additional contribu...
Article
Full-text available
Although Cd and Ca ions have the same valence and cation size, their incorporation into vacancy-doped La manganites induce different properties. While the incorporation of Ca leads to high Tc up to 250 K and induces a metallic-like behaviour, the incorporation of Cd severely reduces Tc and promotes insulator-like behaviour. In this work, the Cd hyp...
Article
Full-text available
Recent results on the study of high-TC superconductors using the e−–γperturbed angular correlation technique are presented. The basic features of the experimental equipment and its installation at the ISOLDE facility are briefly described. Results obtained from 197mHg implanted into high quality Y1Ba2Cu3O6+δ epitaxy thin films are presented and dis...
Article
Epitaxial thin films of La0.62±0.05Ca0.33±0.02MnO 3-δ were grown by laser ablation on SrTiO3. On (100) substrates the films grow with the larger c axis perpendicular to the plane. The films deposited on (110) SrTiO3 grow with both the c (long) axis and a (or b, short) axis in the plane of the film. The electrical resistivity (ρ) and the magnetoresi...
Article
Thin films of La0.62±0.05Ca0.33±0.02MnO3−δ were grown by laser ablation on (100) LaAlO3, (100) and (110) SrTiO3 substrates. Detailed structural characterization by X-ray diffraction, texture and RBS-channeling shows that the films grow epitaxially, with either the manganite c-axis perpendicular to or in the plane of the films. Using the same deposi...
Article
The radioactive isotope 197m Hg was implanted at 60 keV with low fuences (10^13 ions/cm^2 ) into YBa2Cu3O6+x (YBCO) superconducting thin films at ISOLDE/CERN. We report on the Hg dynamics and stability inside the YBCO lattice as a function of annealing temperature up to 890 K in vacuum or O2 atmosphere. The perturbed angular correlation (PAC) techn...
Article
Aerosol-assisted MOCVD was used to grow simultaneously thin films of La-Ca-MnO3 system on MgO(1 0 0) and LaAlO3(1 0 0) substrates. The films deposited on LaAlO3 have better structural quality, and higher magnetization. In films with Mn excess Tc can be enhanced, upon oxygen annealing, up to almost the room temperature. The annealing degrades the ma...
Article
Thin films of La0.62+/-0.05Ca0.33+/-0.02MnO3-δ were grown by laser ablation on SrTiO3 with 100 and 110 orientations. We find that the films grow epitaxially, with either the c-axis perpendicular or in the plane of the films. Using the same deposition conditions, films on both substrates have similar characteristics. Anisotropic behaviour of the mag...
Article
Full-text available
Oriented thin films of the La–Ca–MnO3 system with several Mn-excess compositions were prepared by aerosol-assisted metalorganic chemical vapor deposition. Depositions both on MgO (100) and LaAlO3 (100) substrates were performed at temperatures between 700 and 800 °C, with 30 min in situ oxygen annealing at the deposition temperature. The films depo...
Article
The radioactive isotope 197mHg was implanted at 60 keV with low fluences (1013 ions/cm2) into YBa2Cu3O6+x (YBCO) superconducting thin films at ISOLDE/CERN. We report on the Hg dynamics and stability inside the YBCO lattice as a function of annealing temperature up to 890 K in a vacuum or O2 atmosphere. The perturbed angular correlation (PAC) techni...
Article
High quality YBa2Cu3O6+x (YBCO) superconducting thin films were implanted with the radioactive 197mHg (T1/2=24 h) isotope to low fluences of 1013 atoms/cm2 and 60 keV energy. The lattice location and stability of the implanted Hg were studied combining the Perturbed Angular Correlation (PAC) and Emission Channeling (EC) techniques. We show that Hg...
Article
In situ grown superconducting thin films of YBa2Cu3O7- delta (YBCO) and the tunnel junctions of YBa2Cu3O7- delta /PrBa2Cu3O7/YBa2Cu3O7- delta are deposited at Ts approximately=570 degrees C using plasma-assisted laser ablation. The influence of O2 plasma on the superconducting properties of the films is explored in detail. The films show epitaxial...
Conference Paper
New applications of radio isotopes for research in solid state physics are steadily growing due to the large variety of intense radioactive ion beams which are provided by the on-line coupling of high resolution isotope separators to particle accelerators, such as the ISOLDE facility at CERN. There, new experiments are performed by an increasing nu...
Article
Full-text available
The magnetic behavior of bulk La2/3Ca1/3MnO3 (TC = 267 K) at low fields in the paramagnetic phase was studied. Near TC(T−TC<30 K) we find a sequence of steplike features in the effective Curie constant C(T) = M(T−TC)/H at well defined temperatures and intermediate plateaus, accompanied by temperature hysteresis. On approaching TC, the C values at e...
Article
We prepared bulk ceramics and thin films in the La1-xCaxMnO3 system. The ceramics (x=0.25, 0.33) were prepared by standard techniques with a final sintering at 1300°C. The thin films were prepared on MgO (100) substrates by excimer laser ablation, using the bulk material as a target, and by aerosol-assisted MOCVD. In both methods a substrate temper...
Article
An aerosol-assisted metalorganic chemical vapour deposition (MOCVD) reactor with a cold wall is applied in preparing magnetoresistive La1-xCaxMnO3 films. X-Ray diffraction and SEM were used for material characterization. Oriented films are obtained at substrate temperatures above 630°C. The electrical and magnetic properties are comparable to the b...
Conference Paper
High temperature thin films with CuO2 planes oriented perpendicular to the substrate open a possible way to fabricate planar Josephson junctions, because unlike in c-axis oriented films the superconducting coherence length of the films is relatively large perpendicular to the surface. In our experiments we demonstrate that the use of (110) oriented...
Conference Paper
The interface structures of YBa2Cu3O7-d (YBCO) thin films, as prepared by pulsed laser deposition, on substrates of diferent materials have been investigated by transmission electron microscopy (TEM). It is found that the interfaces on SrTiO3 substrate are in general sharper than those on LaAlO3, where extended defects such as misoriented grains an...
Article
As-deposited superconducting films of Y1Ba2Cu3O7−δ with zero resistance at a temperature of ⋍ 80 K have been successfully grown using a Nd:YAG laser. A substrate temperature in the range 450–550°C was found most appropriate. The use of a Nd:YAG laser instead of an excimer laser is likely to improve the cost effectiveness of the laser ablation techn...
Article
The growth of YBa2Cu3O7−δ (YBCO) thin films on SrTiO3 oriented substrates has been studied using the pulsed laser deposition technique in order to develop a method for preparing high-Tc thin films with the c-axis aligned along the [001] direction in the substrate plane. The films obtained by the combination of heteroepitaxial growth at low substrat...
Article
Thin films of YBa2Cu3O7−δ are grown using plasma assisted laser ablation. Nd:YAG as well as excimer laser are used for the deposition. A comparison between various superconducting properties of insitu grown YBCO films by Nd:YAG and excimer laser is presented. Preliminary results of various measurements on heterostructures are discussed.
Article
In situ grown superconducting thin films of YBa 2 Cu 3 O 7- delta (YBCO) and the tunnel junctions of

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