Title: font: times; size: 18 point; style: plain ... · chemical etching to create microcavities in...

Preface

Dear Colleagues, Friends and Students

It is a great pleasure to welcome you to the “1as Jornadas de Engenharia

Física e Física Experimental”, held in Physics and Astronomy Department,

Faculty of Sciences of Porto University (DFA-FCUP) in 19th February of

2016. We hope that the scientific programme we have put together will be

of great interest to all of you.

This workshop has the mission to disseminate the current challenges and

outlook in the areas of Engineering Physics and Experimental Physics,

offering testimonies from Directors of integrated Research Institutes of

DFA-FCUP, including INESC TEC and IFIMUP, and providing scientific

talks from Ph.D. students and flash presentations from Master students

from those centers. Moreover, some examples of successful professionals

in various fields of Engineering Physics will be presented. Finally, during

the coffee break, a poster session engaging postgraduate students will

occur.

The presence of these participants offers unique opportunities for students

to contact with the research and professional world. This will be of utmost

importance especially for the younger ones since it is a unique opportunity

to realize the full extent of the universe of Engineering Physics and

Experimental Physics.

Also for Professors/Researchers and Staff it will be an opportunity to

acquaint with the state-of-the-art of the research developed at DFA-FCUP.

Finally, this is an opportunity for socialization between all members of the

DFA-FCUP.

We wish you a stimulating and pleasant meeting.

On behalf of the Scientific and Organizing Committees,

Y o u r s S i n c e r e l y ,

André Pereira Orlando Frazão

Organização

André Pereira Orlando Frazão

Comissão Científica

Abílio Almeida André Pereira Ariel Guerreiro Carla Rosa Helder Crespo Joaquim Agostinho Moreira João Pedro Araujo João Ventura Manuel Bastos Marques Orlando Frazão Paulo Marques Pedro Jorge Susana Silva

Comissão Organizadora

Ana Pires João Horta Leandro Martins Paula Quitério NEF/DFA – Núcleo de Estudantes de Física / Departamento de Física e Astronomia SPIE UP Student Chapter: André Gomes Catarina Monteiro Nuno Silva Ricardo André

Programa

14h00-14h10 Boas vindas pelo DFA

14h10-14h35 João Pedro Araújo – IFIMUP-IN

14h35-14h45 Ricardo André – Focused ion beam milling of tapered fiber tip probes

14h45-14h55 Ivo Nascimento – Optical current sensor for metering and protection applications

14H55-15h05 Miguel Canhota – Self-diffraction and transient-grating dispersion-scan and their application to the measurement of sub-4-fs pulses

15h05-15h15 João Azevedo – Harvesting Solar Energy: New Frontiers

15h15-15h25 Diogo Costa – Spin Transfer Torque Nano-Oscillators

15h25-16h15 Apresentações Flash

16h15-16h45 Coffee break e Sessão de Posters

16h45-17h10 Paulo Marques – INESC TEC

17h10-17h20 Vídeo com testemunhos de alumni

17h20-17h30 Fecho da sessão

Oral Presentations

Focused Ion Beam Milling of Tapered Fiber Tip Probes

Ricardo André, Manuel B. Marques and Orlando Frazão

INESC TEC and Department of Physics and Astronomy, Faculty of Sciences, University of Porto, Rua do Campo Alegre 687, 4150-179 Porto, Portugal

Abstract:. Focused ion beam technology is combined with dynamic chemical etching to create microcavities in tapered optical fiber tips, resulting in fiber probes for temperature and refractive index sensing. Dynamic chemical etching uses hydrofluoric acid and a syringe pump to etch standard optical fibers into cone structures called tapered fiber tips where the length, shape, and cone angle can be precisely controlled. On these tips, focused ion beam is used to mill several different types of Fabry-Perot microcavities. Two main cavity types are initially compared and then combined to form a third, complex cavity structure. In the first case, a gap is milled on the tapered fiber tip which allows the external medium to penetrate the light guiding region and thus presents sensitivity to external refractive index changes. In the second, two slots that function as mirrors are milled on the tip creating a silica cavity that is only sensitive to temperature changes. Finally, both cavities are combined on a single tapered fiber tip, resulting in a multi-cavity structure capable of discriminating between temperature and refractive index variations. This dual characterization is performed with the aid of a fast Fourier transform method to separate the contributions of each cavity and thus of temperature and refractive index. Ultimately, a tapered optical fiber tip probe with sub-standard dimensions containing a multi-cavity structure is projected, fabricated, characterized and applied as a sensing element for simultaneous temperature and refractive index discrimination. These microprobes can then be applied for biosensing in small organisms and even cells.

References and links

1. C. A. Volkert and A. M. Minor, "Focused Ion Beam Microscopy and Micromachining," MRS Bull. 32, 389–399 (2007).

2. L. H. Haber, R. D. Schaller, J. C. Johnson, and R. J. Saykally, "Shape control of near-field probes using dynamic meniscus etching.," J. Microsc. 214, 27–35 (2004).

3. J. Kou, J. Feng, L. Ye, F. Xu, and Y. Lu, "Miniaturized fiber taper reflective interferometer for high temperature measurement," Opt. Express 18, 14245–14250 (2010).

4. R. M. André, S. Pevec, M. Becker, J. Dellith, M. Rothhardt, M. B. Marques, D. Donlagic, H. Bartelt, and O. Frazão, "Focused ion beam post-processing of optical fiber Fabry-Perot cavities for sensing applications.," Opt. Express 22, 13102–8 (2014).

Optical current sensor for metering and protection applications

I. M. Nascimento1,2, J. M. Baptista1,3, P. A. S. Jorge1,2

1INESC TEC, Rua do Campo Alegre, 687, 4169-007 Porto, Portugal. 2Department of Physics and Astronomy, Faculty of Sciences of University of Porto, Rua do Campo Alegre 687,

4169-007 Porto, Portugal. 3Faculty of Exact Sciences and Engineering of University of Madeira, Funchal, Portugal.

Abstract:. The measurement of electric energy is fundamental to estimate the quantity of energy needed for the electric grid. Traditionally, electric current transformers technology has been used. However in a high voltage environment, these systems can easily get damaged by heat, short-circuits or atmospheric electrical discharges, so it is required to employ protection circuits and insulation which requires constant maintenance. Another problem derives from the fact that these sensors have high dimensions and weight and cannot be suspended on the electric line. Therefore, in order to achieve smarter grids is necessary to improve the sensor technology [1,2]. Fiber optic magnetic field sensors have been studied over the years. Special interest has been shown in the high power industry owing to its intrinsic insulation (silica), immunity to electromagnetic interference, high dynamic range and bandwidth and possibility to employ remote interrogation [3].

A clamp-on optical current sensor prototype for metering and protection applications in high power systems was developed and characterized. The system is based on the Faraday effect in a low birefringence, high Verdet constant, 80 mm long SF57 Schott glass prism. A nylon support was also fabricated to encapsulate and protect the sensor, maintaining the GRIN lens alignment, responsible for injecting and collecting the light. Furthermore, a portable acquisition system nursing two photodetectors, an anolog-digital converter and a computer with a LabVIEW program was projected. The sensor operates at 830 nm and employing a quadrature polarimetric detection scheme, higher stability is achived. Results have showed the sensor could be used as a class 1 device for nominal currents higher than 900 ARMS. Nevertheless, considering the sensor intrinsic precision error, its performance can increase to fit 0.1 class [4].

Detection of transient pulses was also demonstrated by monitoring the switch-on operation of a current source, where several pulses under 10 μs were detected. Overall, the results demonstrate the viability of a single bulk prism optical current sensor to be used both as a metering and a protection device in high power systems applications.


1. H. J. El-Khozondar, M. S. Muller, R. J. El-Khozondar, and A. W. Koch, "Magnetic field inhomogeneity induced on the Magneto-optical current sensors," in Information Photonics (2011), pp. 1–2.

2. F. Rahmatian, "High-Voltage Current and Voltage Sensors for a Smarter Transmission Grid and their Use in Live-Line Testing and Calibration," in Power and Energy Society General Meeting (2010), pp. 10–12.

3. R. M. Silva, H. Martins, I. Nascimento, J. M. Baptista, A. L. Ribeiro, J. L. Santos, P. Jorge, and O. Frazão, "Optical Current Sensors for High Power Systems: A Review," Appl. Sci. 2, 602–628 (2012).

4. I. M. Nascimento, A. C. S. Brígida, J. M. Baptista, J. C. W. A. Costa, M. A. G. Martinez, and P. A. S. Jorge, "Novel optical current sensor for metering and protection in high power applications," Instrum. Sci. Technol. 44, 148–162 (2016).

Harvesting Solar Energy: New Frontiers

João Azevedo1,2, Célia Sousa1, Adélio Mendes2 and João Araújo1

1IFIMUP and IN-Institute of Nanoscience and Nanotechnology, Departamento de Físsica e Astronomia, Universidade do Porto, Rua do Campo Alegre 687, 4169-007 Porto, Portugal

2 LEPABE – Faculdade de Engenharia, Universidade do Porto, Rua Dr Roberto Frias, 4200-465 Porto, Portugal

Abstract:. The possibility of producing chemical fuels from solar energy has become increasingly attractive as sustainable, clean and efficient solution to our ever-growing energy demands. Photoelectrochemical (PEC) water splitting has been much improved since the first reports in the 70s1 and nowadays researchers aim to find inexpensive, efficient and stable materials to perform PEC water splitting. Cuprous oxide, Cu2O, is very interesting since it has a 2 eV bandgap with favorable energy band positions, good conductivity and it can be processed with low-cost methods such as electrodeposition.2 Although efficient it is not stable in contact with the electrolyte, decomposing completely after few minutes.

For real applications, much more is required and new strategies are needed to overcome this limitation. In this work, we focus on improving the Cu2O stability up to ~60 h with only 10 % loss. Electrodeposition and atomic layer deposition (ALD) were used to synthesize the Cu2O and for overlayer deposition, respectively, and are here described.3 A simple low-cost solution was developed to greatly enhance the Cu2O photocathode stability. Steam treatments employed on Cu2O/AZO/TiO2 photocathodes allow for stability improvement using both RuO2 and Pt catalysts.4 Also, an alternative protective layer is explored exhibiting great stability, maintaining 90 % of its initial photocurrent after 57 h of sustained photoelectrochemical water reduction.5 These new results open a much-needed window to make this semiconductor a strong competitor for solar water splitting applications.

Although hydrogen is very promssing as a clean and safe energy storage solution, solar water splitting kinetics can be considered sluggish compared to other fast redox shuttles. Some of the most efficient PEC redox reactions can be found in redox flow batteries (RFB) but no promising solar charging solution has been proposed yet. Here we describe the first unbiased solar redox flow battery for solar energy storage solutions. Two different configurations are discussed.6,7 A CdS and α-Fe2O3 are used as photoelectrodes to charge RFB with competive photocurrents. Surface treatments are discussed to improve performance of these devicees.


1. A. Fujishima, K. Honda, Nature, 238(3), 37-38, 1972.

2. A. Paracchino, V. Laporte, K. Sivula, M. Gratzel, E. Thimsen, Nature Materials, 10(6), 456-461, 2011.

3. S.D. Tilley, M. Schreier, J. Azevedo, M. Stefik, M. Graetzel, Advanced Functional Materials, 24(3), 303-311, 2014.

4. J. Azevedo, L. Steier, P. Dias, M. Stefik, C.T. Sousa, J.P. Araujo, A. Mendes, M. Gratzel, S.D. Tilley, Energy & Environmental Science, 7, 4044-4052, 2014.

5. J. Azevedo, S.D. Tilley, M. Schreier, M. Stefik, C. Sousa, J.P. Araújo, A. Mendes, M. Grätzel, M.T. Mayer, (submitted to Nano Energy).

6. J. Azevedo, T. Seipp, J. Burfeind, C.T. Sousa, A. Bentien, J. Araujo, A. Mendes, (submitted to Nano Energy).

7. J. Azevedo, K. Wedege, A. Khataee, A. Mendes, A. Bentien, M.T. Mayer, (submitted to Angewandte Chemie International Edition).

Self-diffraction and transient-grating dispersion scan and their application to the

measurement of sub-4-fs pulses

Miguel Canhota1, Francisco Silva1, Rosa Weigand2, Helder Crespo1

1Department of Physics and Astronomy, Faculty of Sciences, University of Porto, Rua do Campo Alegre, 4169-007 Porto, Portugal

2Departamento de Óptica, Facultad de Ciencias Físicas, Universidad Complutense de Madrid, 28040 Madrid, Spain

Abstract:. The dispersion-scan (d-scan) is a recent ultrafast pulse measurement technique [1], relying on the manipulation of the total dispersion incurred by the pulse while traveling through a standard pulse compressor setup comprised of double-angle chirped mirrors (DCMs) and a pair of glass wedges, for example fused silica. The amount of glass traversed by the pulse is an independent variable that can be controlled with the insertion of one of the wedges. While the DCMs impart negative dispersion, the variable positive dispersion introduced by the wedges will vary the total dispersion of the pulse to be measured. In the case of the well established second-harmonic d-scan (SHG d-scan), the measurement of the second-harmonic signal after the compressor allows us to draw a two-dimensional trace of the SHG spectrum vs wedge insertion. With this trace and knowing the linear spectrum of the light source it is possible to retrieve the pulse through a mathematical optimization algorithm. We report on two novel variations of the dispersion-scan (d-scan) technique for the measurement of ultrafast laser pulses based on third-order nonlinearities, namely self-diffraction (SD) and transient-grating (TG) d-scan. Sub-4-fs pulses produced in a hollow-core fiber and chirped mirror compressor were successfully measured using these two techniques, and the results were compared to standard second-harmonic generation (SHG) d-scan [2].


1. Miranda, M., Fordell, T., Arnold, C., L’Huillier, A. & Crespo, H. Simultaneous compression and characterization of ultrashort laser pulses using chirped mirrors and glass wedges. Opt. Express 20, 688–97 (2012).

2. Silva, F. et al. Simultaneous compression, characterization and phase stabilization of GW-level 1.4 cycle VIS-NIR femtosecond pulses using a single dispersion-scan setup. Opt. Express 22, 10181–91 (2014).

Ultrafast phenomena in spintronic devices

J. D. Costa1,2, R. Ferreira1, P.P. Freitas1 and J. Ventura2

1International Iberian Nanotechnology Laboratory (INL), Av. Mestre José Veiga s/n, 4715-330 Braga, Portugal 2IN-IFIMUP, Rua do Campo Alegre, 687 4169-007 Porto, Portugal

Abstract:. The term spintronics refers to phenomena in which it is the spin and not the charge of the electron that plays the most significant role in electronic components. In particular, magnetic tunnel junctions (MTJs) are spintronic structures constituted by two ferromagnetic layers separated by a nanometric insulating barrier. These structures depict tunneling magnetoresistance (TMR) which consists in a resistance variation when passing from the parallel to the antiparallel alignment of the ferromagnetic moments.

Current research is focusing in the recent discovered possibility to control the magnetization of magnets at the nano scale using locally polarized electrical currents (spin transfer torque; STT).The nanofabrication of MTJs, in conjugation with high TMR and low resistance × area product (RA), allowed the development of novel devices that explore the STT mechanism. Spin transfer torque nano-oscillators (STNOs) are one of the best positioned to reach industrial commercialization. STNOs use the STT effect to achieve RF emission through persistent magnetic dynamics induced by DC currents. However, some requirements such as a large output power (Pout ~ 1 µW) and narrow linewidths (Γ < 1 MHz) were not achieved so far.

We characterized STNOs from their nanofabrication process to their measured RF emission. In particular we were able to maximize the output power of the STNOs up to 200 nW through precise control of the insulating barrier thickness. Moreover, we will present fundamental studies on the ultrafast electronic dynamics of materials used in spintronics applications. In particular, we showed that the THz transmission can be used to probe the resistance state of materials that depict magnetoresistance [1]. We also unreveled a novel method for the generation of electrical currents in the femtosecond timescale [2].


[1] J. D. Costa, T. J. Huisman, R. V. Mikhaylovskiy, I. Razdolski, J. Ventura, J. M. Teixeira, D. S. Schmool, G. N. Kakazei, S. Cardoso, P. P. Freitas, T. Rasing, and a. V. Kimel, “Terahertz dynamics of spins and charges in CoFe/Al2O3 multilayers,” Phys. Rev. B, vol. 91, no. 10, p. 104407, 2015.

[2] T. J. Huisman, R. V. Mikhaylovskiy, J. D. Costa, F. Freimuth, E. Paz, J. Ventura, P. P. Freitas, S. Blügel, Y. Mokrousov, T. Rasing, and a. V. Kimel, “Femtosecond control of electric currents in metallic ferromagnetic heterostructures,” Nat. Nanotechnol., no. February, pp. 2–6, 2016.

Posters

Mach-Zehnder based on large Knot Fiber Resonator for refractive index sensing

André D. Gomes1 and Orlando Frazão1

1INESC TEC and Department of Physics and Astronomy, Faculty of Sciences, University of Porto, Rua do Campo Alegre 687, 4150-179 Porto, Portugal

Abstract:. Optical fiber sensors used as refractometers have drawn many attentions due to their compact size and high resolution1. Among this sensors, the all-fiber Mach-Zehnder interferometers (MZI)1-2 and the microfiber knot resonators3,4 were the subject of many researches due to their high sensitivity, broad measurement range and compact size4. The MZI technique uses the phase shift of the guided light created by the analyzed media to determine its refractive index. For this purpose, many configurations have been developed and presented. Microfiber resonators applied as sensing elements were also widely studied. To this class of devices belong the microfiber knot resonators (MKR), which are produced tying a knot in an optical microfiber taper to form a ring geometry with micrometer dimensions5. The taper in the knotted zone allows the evanescent field of light to couple between the adjacent sections of the fiber creating resonance without the need for a precise alignment. This kind of sensor can be used for refractive index sensing and for temperature sensing, especially using polymer MKR.

In this work, a Mach-Zehnder based on a large knot fiber resonator (MZ-LKR) with a few millimeters diameter for refractive index sensing of liquids is presented. To produce the knot, a taper with around 60µm diameter fabricated using a CO2 laser was used. A sensitivity of 642±29nm/RIU is obtained for refractive index sensing within a range from 1.3735 to 1.428 and with a resolution of 0.009RIU. In temperature, a sensitivity of -42±9pm/ºC was achieved. There is a low influence of temperature in the refractive index change: 6.5×10-5RIU/ºC. The sensor is reproducible, however, the sensor must be characterized when fabricated because the shape of the knot will be slightly different, inducing a phase shift.

References

1. Z. Tian, S. S. H. Yam, J. Barnes, W. Bock, P. Greig, J. M. Fraser, H. P. Loock and R. D. Oleschuk, “Refractive index sensing with Mach-Zehnder interferometer based on concatenating two single-mode fiber tapers,” IEEE Photonics Technol. Lett. 20(8), 626-628 (2008).

2. T. Schubert, N. Haase and H. Kück, “Refractive-index measurements using an integrated Mach-Zehnder interferometer,” Sensors Actuators A 60(100), 108-112 (1997).

3. X. Li and H. Ding, “A Stable Evanescent Field-Based Microfiber Knot Resonator Refractive Index Sensor,” IEEE Photonics Technol. Lett. 26(16), 1625-1628 (2014).

4. K.-S. Lim, I. Aryanfar, W.-Y. Chong, Y.-K. Cheong, S. W. Harun and H. Ahmad, “Integrated microfibre device for refractive index and temperature sensing,” Sensors (Basel). 12(9), 11782-11789 (2012).

5. L. Xiao and T. A. Birks, “High finesse microfiber knot resonators made from double-ended tapered fibers,” Opt. Lett. 36(7), 1098-1100 (2011).

Temperature-independent multi-parameter measurement based on a tapered Bragg fibre

Tiago J.M. Martins1, Manuel B. Marques1, Philippe Roy2, Raphaël Jamier2, Sébastien Février2, and Orlando Frazão1

1INESC TEC- Instituto de Engenharia de Sistemas e Computadores - Tecnologia e Ciência and Department of Physics and Astronomy, Faculty of Sciences, University of Porto, Rua do Campo Alegre 687, 4169-007 Porto,

Portugal 2 XLIM – Institut de recherche, 123, avenue Albert Thomas – 87060 LIMOGES CEDEX

Abstract:. Temperature-independent strain and angle measurement is

achieved resorting to a taper fabricated on a Bragg fibre using a laser. The characteristic bimodal interference of an untapered Bragg fibre is rendered multimode after taper fabrication and the resulting transmission spectra are analysed as strain, applied angle and temperature change. The intrinsic strain sensitivity exhibited by the Bragg fibre is increased 15 fold after tapering and reaches

. Angle and temperature measurements are also performed

with maximum sensitivities of and , respectively. The difference in wavelength shift promoted by variations in strain, angle and temperature for the two fringes studied is examined and strain and angle sensing with little temperature sensitivity is

achieved, presenting a response of and ,

respectively, for strain values up to and angles up to . Simultaneous angle and strain measurement is demonstrated.

References

1. P. Yeh, A. Yariv, E. Marom, “Theory of Bragg fiber”, J. Opt. Soc. Am., 68(8), 1196-1201 (1978).

2. S. Février, P. Viale, F. Gérôme, P. Leproux, P. Roy, J.-M. Blondy, B. Dussardier, G. Monnom, “Very large effective area singlemode photonic bandgap fibre”, Electron. Lett., 39(2), 140-1242 ( 2003).

3. R. Jamier, N. Ducros, S. Février, M. E., Likhachev, M. Y. Salganskii, “Tight control of the spectral broadening obtained by nonlinear conversion in a photonic bandgap fiber”, Proc. CLEO/IQEC, Paper JWA53 (2009).

4. F. Gérôme, S. Février, A. D. Pryamikov, J.-L. Auguste, R. Jamier, J.-M. Blondy, M. E. Likhachev, M. M. Bubnov, S. L. Semjonov, E. M. Dianov, “Highly dispersive large mode area photonic bandgap fiber”, Opt. Lett., 32(10), 1208-1210 (2007).

5. O. Frazão, L. M. N. Amaral, J. M. Baptista, P. Roy, R. Jamier, S. Février, “Strain and temperature discrimination using modal interferometry in Bragg fibers, IEEE Photon. Tech. Lett., 22(21), 1616-1618 (2010).

6. O. Frazão, M. A. Melo, P. V. S. Marques, J. L. Santos, “Chirped Bragg grating fabricated in fused fibre taper for strain-temperature discrimination”, Meas. Sci. Technol., 16(4), 984-988 (2005).

7. O. Frazão, L. Marques, J. M. Marques, J. M. Baptista, J. L. Santos, “Simple sensing head geometry using fibre Bragg gratings for strain-temperature discrimination”, Opt. Comm., 279(1), 68-71 (2007).

8. S. Rota-Rodrigo, M. López-Amo, J. Kobelke, K. Schustes, J.L. Santos, O. Frazão, “Multimodal interferometer based on a suspended core fiber for simultaneous measurement of physical parameters”, IEEE J. Light. Tech., 33(12), 2468-2473 (2015).

9. W. Du, X. Tao, H.-y., ”Temperature independent strain measurement with a fiber grating tapered cavity sensor”, IEEE Photon. Tech. Lett., 11(5), 596-598 (1999).

10. J. Villatoro, V. P. Minkovich, D. Monzón-Hernández, “Temperature-independent strain sensor made from tapered holey optical fiber”, Opt. Lett, 31(3), 305-307 (2006).

11. J. P. Moura, S. O. Silva, M. Becker, M. Rothardt, H. Bartelt, J. L. Santos, O. Frazão, “Optical inclinometer based on a phase-shifted Bragg grating in a taper configuration”, IEEE Photon. Tech. Lett., 26(4), 405-407 (2014).

Numerical simulations of flexible thermoelectrics

S. F. Teixeira1, P. Resende1, A. M. Pereira1

1 IFIMUP-IN, Department of Physics and Astronomy, Faculty of Sciences of University of Porto, Portugal

Abstract: Energy is one of the main requests of our society nowadays since our modern world depends largely on energy to live. The necessity for the improvement of energy generation boosts the search of alternative energy generation with special attention on its harvesting. Thermoelectrics appear as one of the best candidates since around 60% of the wasted energy is in the form of heat. Thermoelectric generators are small, portable, possess no moving parts and require almost no maintenance. These qualities make them an improved way of generating energy. However, their efficiency is still low for large scale applications. Thus, the study and improvement of their efficiency is of utmost importance. In this poster, thermoelectric generators and devices are explained. Simulations performed using the COMSOL Multiphysics software regarding the efficiency of thermoelectric devices are presented and its results are discussed, emphasising how to optimize and improve devices’ operation. Finally, developed flexible thermoelectric devices and their COMSOL's simulation will be presented and explained. A comparison with their simulation will also be commented.


1. Teixeira, S. F. and Pereira, A.M., “Geometrical optimization of a Thermoelectric Device: numerical simulations”, submitted to Applied Energy

2. COMSOL Multiphysics, “Thermoelectric Leg” http://www.comsol.com/model/thermoelectric-leg-16365 [Online last access 09-February-2016]

3. Song, Youngsup, et al. "Electrodeposition of thermoelectric Bi2Te3 thin films with added surfactant." Current Applie Physics 15.3 (2015): 261-264.

4. Xiao, Feng, et al. "Recent progress in electrodeposition of thermoelectric thin films and nanostructures." Electrochimica Acta 53.28 (2008): 8103-8117.

5. Sander, Melissa S., et al. "Fabrication of High‐Density, High Aspect Ratio, Large‐Area Bismuth Telluride Nanowire Arrays by Electrodeposition into Porous Anodic Alumina Templates." Advanced Materials 14.9 (2002): 665-667.

http://www.comsol.com/model/thermoelectric-leg-16365

Hidrostatic Pressure in CdCr2S4: Effect on local magnetic clusters

G.N.P. Oliveira1,2, A. M. dos Santos3, Z. Gai4, J. P. Araújo2, A.M.L. Lopes2 and A.M.

Pereira2

1CFNUL - Centro de Física Nuclear, Universidade de Lisboa, Av. Prof. Gama Pinto, 2, 1649-003, Lisboa,

Portugal 2IFIMUP and IN-Institute of Nanoscience and Nanotechnology, Departamento de Física e Astronomia da

Faculdade de Ciências da Universidade do Porto, Rua do Campo Alegre, 687, 4169-007 Porto, Portugal 3Quantum Condensed Matter Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6393,

USA 4Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831- 6393,

USA

Abstract:. Modern society has a critical demand for materials with multifunctional physical properties. They have become an integrating part of many applications, especially those that display a strong coupling between magnetic and polar degrees of freedom, the so-called magnetoelectrics. These materials, promise a paradigm-shift on technologies for magnetic data storage, high-frequency magnetic devices, spintronics, and micro-electromechanical systems.1,2

The clear

determination of the complex interplay between electronic, magnetic, and lattice degrees of freedom usually is the solution to explain the mechanisms behind the exhibited physical properties.3

Among the numerous materials with an intimate coupling between all the degrees of freedom are the group of ACr2X4 spinels (A= Zn, Cd,

Hg; X= O, S, Se).4The tight alliance between structural, vibrational,

magnetic, and charge degrees of freedom, makes the variation of lattice by external pressure an appealing route for studying the physical properties of these materials. Measuring the pressure dependence of the magnetic transition temperature may assist in getting new insights about the ordering mechanism and its relationship to the electronic structure (e.g. disordered local moments coupled with frustration mechanisms). In fact, external pressures are known to control bond lengths and bond angles as well as the degree of overlap between electron orbitals in solids. A shift and/or split of the energy levels and changes in exchange interactions strength in response to pressure variations can also occur. External pressures when compared to the chemical pressure, is a cleaner tool to avoid substitutional induced disorder and spurious effects due to different chemical compositions. Several studies reported structural and electronic transitions under pressure for various Cr-based spinels. Nevertheless, studies on the relaxor-like temperature zone are not yet reported.

Our results of dc magnetisation measurements under hydrostatic pressure for the CdCr2S4 spinel compound will be presented. The measurements have been performed on a polycrystalline sample under different applied hydrostatic pressures (up to 14 kbar) in the 30-220 K temperature range (with 3 Oe applied magnetic field). The anomalous behaviour of the magnetic susceptibility indicates that the local-cluster- phase that exists at low applied magnetic fields5

persists with applied

pressures up to 14 kbar and has a dependency on the applied pressure. This effect will be presented and discussed in the framework of the complex competition between the electric, magnetic, and lattice interactions.


1. T. Kimura, T. Goto, H. Shintani, K. Ishizaka, T.-h. Arima, and Y. Tokura, “Magnetic control of ferroelectric polarization” , Nature 426, 55 (2003).

2. T. Goto, T. Kimura, G. Lawes, A. P. Ramirez, and Y. Tokura, “Ferroelectricity and Giant Magnetocapacitance in Perovskite Rare-earth Manganites”, Phys. Rev. Lett. 92, 257201 (2004).

3. 3. J. Hemberger, P. Lunkenheimer, et al, “Relaxor Ferroelectricity and Colossal Magnetocapacitive Coupling in Ferromagnetic CdCr2S4”, Nature 434, 364 (2005).

4. M. Matsuda, K. Ohoyama, et al, “Universal Magnetic Structure of the Half-Magnetization Phase in Cr-Based Spinels”, Phys. Rev. Lett. 104, 47201 (2010).

5. G. N. P. Oliveira, et al, “Dynamic Off-Centering of Cr3+ Ions and Short-Range Magneto-Electric Clusters in CdCr2S4”, Phys. Rev. B 86, 224418 (2012).

On the operating conditions of solid-state magnetic refrigerations

Bernardo Bordalo1, Daniel Silva1, Joel Puga1, Joana Oliveira2, André Pereira1,3, João

Ventura1 and João Araújo1

1IFIMUP and IN-Institute of Nanoscience and Nanotechnology, Departamento de Física e Astronomia, Faculdade de Ciências, Rua do Campo Alegre 687, 4169-007 Porto, Portugal;

2CFP, Department of Physics Engineering, FEUP, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal; 3Blackett Laboratory, Imperial College, London SW7 2AZ, United Kingdom;

Abstract: Based on a previous study [1] a numerical study was made to assess the working conditions for a solid state, thermal switch (TS) based magnetocaloric refrigerator. A magnetocaloric material (MCM) presents a rise in its temperature when exposed to a magnetic field and a decrease in its temperature as the field is removed (the contrary effect is also possible) [2]. A TS is an idealized material whose thermal conductivity changes with an external stimulus, e.g. La0.7Ca0.3MnO3 with a magnetic field [3]. The device and its operating cycle are shown in Fig. 1, where we can see the tandem working of the two TSs. In effect, this alternating conductivity turns the device into a thermal diode, where heat is driven in a single main direction. The MCM considered was pure Gd [4], surrounded by two TSs based on three different materials: Cu, Al2O3 and La0.7Ca0.3MnO3 [3, 5, 6].

Fig. 1 Solid-state magnetic refrigerator architecture and simulation border conditions. A darker colour indicates higher conductivity (k) for the thermal switches. The wavy arrows represent the heat flow direction and their thickness its magnitude. When a magnetic field is applied, heat from the MCM is drained to the fixed temperature border through TS1. After the field is removed the now cold MCM absorbs heat from the CB through TS2. The cycle repeats with a frequency f.


1. D. J. Silva, B. D. Bordalo, A. M. Pereira, J. Ventura, and J. P. Araújo, “Solid state magnetic refrigerator,”

Appl. Energy 93, 570–574 (2012).

2. V. K. Pecharsky and K. a. Gschneidner, “Tunable magnetic regenerator alloys with a giant magnetocaloric

effect for magnetic refrigeration from ∼20 to ∼290 K,” Appl. Phys. Lett. 70, 3299 (1997).

3. I. Mansuri, M. W. Shaikh, E. Khan, and D. Varshney, “Thermal conductivity analysis of lanthanum doped

manganites,” AIP Conf. Proc. 1591, 1124–1126 (2014).

4. T. F. Petersen, N. Pryds, A. Smith, J. Hattel, H. Schmidt, and H. J. Høgaard Knudsen, “Two-dimensional

mathematical model of a reciprocating room-temperature Active Magnetic Regenerator,” Int. J. Refrig. 31

(3), 432–443 (2008).

5. O. A. Shlyakhtin, Y. J. Oh, and Y. D. Tretyakov, “Preparation of dense La0.7Ca0.3MnO3 ceramics from

freeze-dried precursors,” J. Eur. Ceram. Soc. 20 (12), 2047–2054 (2000).

6. W. Zi-hua and X. Huaqing, “Influence of annealing on specific heat of La0.7Ca0.3MnO3,” Phys. B

Condens. Matter 405 (6), 1523–1525 (2010).

Voltage-assisted switching in magnetic tunnel junctions

Leandro Martins1,2, João Ventura1, Ricardo Ferreira2, Paulo Freitas2

1 IFIMUP-IN, DFA, FCUP, Rua do Campo Alegre, 4169-007 Porto, Portugal. 2 INL, Avenida Mestre José Veiga, 4715-330 Braga, Portugal.

Abstract: Spintronics has received a significant interest in the last decades, resulting in the development of magnetic nanostructured devices with important applications in the electronics industry, namely the much desired magnetic random-access memory (MRAM). Without any doubts, the magnetic tunnel junction (MTJ) is one of the most important nanostructured devices fabricated to date. Specifically, the MgO based MTJ has the largest potential, due to its physical properties and excellent performance, proved by the high tunnel magnetoresistance (TMR) values presented at room temperature (up to 600%). However, and although all the progress made to date, there are still critical issues to be solved. In particular, the main concern for memory applications is the high energy necessary to make each MTJ functional. Many methods have been used to solve this problem, namely the fabrication of MTJs with perpendicular magnetic anisotropy (PMA) based on a spin tranfer torque (STT) switching process. Here, for CoFeB/MgO/CoFeB MTJs with PMA, one pretends to study the effect of a bias voltage in decreasing the necessary energy for switching.


1. S. Yuasa et al., “Giant tunnel magnetoresistance in magnetic tunnel junctions with a crystalline MgO(001) barrier”, Journal of Physics D: Applied Physics, vol. 40, no. 21, p. R337, 2007.

2. W. G. Wang et al., “Electric-field-assisted switching in magnetic tunnel junctions”, Nature Materials, vol. 11, no. 1, pp. 64-68, 2012.

Ag-based Resistive Switching Nanostructures

C. Dias1, L. Guerra1, H. Lv2, P. Aguiar3,4, J. P. Araújo1, S. Cardoso2, P. P. Freitas2 and J. Ventura1

1IFIMUP and IN-Institute of Nanoscience and Nanotechnology, and Department of Physics and Astronomy, Faculty of Sciences, University of Porto, Rua do Campo Alegre, 678, 4169-007 Porto, Portugal

2INESC-MN and IN-Institute of Nanoscience and Nanotechnology, Rua Alves Redol, 9, 1000-029 Lisboa, Portugal.

3Instituto de Investigação e Inovação em Saúde, Universidade do Porto, Portugal 4INEB - Instituto de Engenharia Biomédica, Universidade do Porto, Rua do Campo Alegre 823, 4150-180

Porto, Portugal

Abstract: Present computer processing capabilities are becoming a restriction to meet modern technological needs. Therefore, approaches beyond the von Neumann architecture are imperative and the brain's operation and structure are truly attractive models1. Memristors are characterized by a nonlinear relationship between current history and voltage (resistive switching phenomenon)2 and were shown to present properties resembling those of neural synapses. They can thus be used in networks capable of mimicking the learning and adaptation characteristics of human brains3.

We studied the resistive switching in nanostructures with an electrolyte (here Ag2S) and one active electrode, and others with a gradient of Ag in a Si layer. The phenomenon was attributed in both structures to the formation and rupture of metallic filaments due to ionic diffusion inside the active layer4. We also observed activity-dependent modifications when applying successive voltage, thus making a parallel with biological synaptic plasticity.

The study of the impact of non-ideal devices or device faults in the performance of memory networks was performed by numerically evaluating a memristor-based Willshaw associative memory network5,6. Adopting a binary operation, the capacity and robustness to noise of the network were evaluated as a function of defects probability and device parameter variations.

Is summary, Ag-based devices may present continuous conduction changes, a behavior analogous to biological synapses, due to Ag filaments formation and rupture. Furthermore, in a memristor-based artificial neural network, defects and variability do not imply (to some extent) the catastrophic operation failure.


1. Y. Shimeng, Y. Wu, R. Jeyasingh, D. Kuzum, and H.-S. P. Wong, “An electronic synapse device based on metal oxide resistive switching memory for neuromorphic computation,” IEEE Trans. Electron Devices 58(8), 2729-2737 (2011).

2. L. Chua, “Memristor-The missing circuit element,” IEEE Trans. Circuit Theory 18(5), 507-519 (1971).

3. M. Prezioso, F. Merrikh-Bayat, B. D. Hoskins, G. C. Adam, K. K. Likharev, and D. B. Strukov, “Training and operation of an integrated neuromorphic network based on metal-oxide memristors,” Nature 521, 61–64 (2015).

4. K. Terabe, T. Hasegawa, C. Liang, and M. Aono, “Control of local ion transport to create unique functional nanodevices based on ionic conductors,” Sci. Tech. Adv. Mater. 8(6), 536-542 (2007).

5. D. Willshaw, O. P. Buneman, and H. C. Longuet-Higgins, “Non-Holographic Associative Memory,” Nature 222, 960-962 (1969).

6. C. Dias, L. M. Guerra, J. Ventura, and P. Aguiar, “Memristor-based Willshaw network: Capacity and robustness to noise in the presence of defects,” Appl. Phys. Lett. 106(22), 223505 (2015).

Triboelectric Nanogenerators for Textile and Shoes

A. Gomes1 , J. O. Ventura 1 , A. M. Pereira 1

1IFIMUP and IN- – Institute of Nanoscience and Nanotechnology and Dep. Física e Astronomia, Univ. Porto, Rua do Campo Alegre 687, 4169-007 Porto, Portugal.

Abstract:. There is a growing need for autonomous sensors and independent power sources, so the development of new technologies for the harvesting of mechanical energy is on essential research field1. Consequently, in 2012 the first Triboelectric Nanogenerator were invented, developed on the basis of electrostatic and contact electrifcation2. There are also named triboelectrification, that is a processes that generate a charge distribution at the interface of materials that come into contact3. Triboelectric nanogenerators have numerous advantages: extremely high output voltage, good energy conversion efficiency, low cost, high versatility and environmental friendliness. Recently, triboelectric nanogenerators were demonstrated that can harvest energy from human body movements and that can be integrated in clothes and shoe4. This has led to a great development in the application fields of human healthy monitoring and surgery tools. Due to their exibility they can be fabricated in various configurations and consequently have different applications.


1. Wang et al. Nanotechnology-enabled energy harvesting for self-powered micro-/nanosystems. Angewandte Chemie International Edition, 51(47):11700{11721, 2012.

2. Feng-Ru Fan, Zhong-Qun Tian, and Zhong Lin Wang. Flexible triboelectric generator. Nan Energy, 1(2):328{334, 2012.

3. Xiaonan Wen, Yuanjie Su, Ya Yang, Hulin Zhang, and Zhong Lin Wang. Applicability of triboelectric generator over a wide range of temperature. Nano Energy,4:150,-156, 2014.

4. Minjeong Ha, Jonghwa Park, Youngoh Lee, and Hyun-hyub Ko. Triboelectric generators and sensors for self-powered wearable electronics. ACS nano, 9(4):3421-3427, 2015.

Triboelectric nanogenerators: a new dynamic route for energy harvesting

Cátia R. S. Rodrigues1, Carla A. S. Alves1, Filipe Falcão1, Joel Puga1, João O.

Ventura1 and André M. Pereira1

1Institute of Nanoscience and Nanotechnology and Department of Physics and Astronomy, Faculty of Sciences, University of Porto, Rua do Campo Alegre 687, 4169-007 Porto, Portugal.

Abstract: There is a large amount of energy sources in our living environment, such as dissipated heat, mechanical deformation and static charges, which can be harvested and converted into electricity. With this in mind, self-powered nanosystems, the so-called nanogenerators (NGs), have been developed for several different applications in a wide range of areas, such as personal electronics, environmental monitoring and medical science. In particular, triboelectric nanogenerators (TENGs) convert external mechanical energy into electricity by the conjunction of triboelectric and electrostatic effects, which are a universally known phenomena. They have the potential to harvest energy from our own body movements (as in our muscle stretching and contracting), rotating tires, acoustic/ultrasonic waves, ocean waves and tides, mechanical vibration, wind and blood flow [1,2].

Triboelectric materials possess the property of becoming electrically charged upon friction with other triboelectric materials, creating positive or negative charges depending on the materials’ tendency to gain or lose electrons. A TENG is basically composed by two triboelectric materials with different polarity, a spacer between them and two metal electrodes. When these two materials are periodically contacted and separated, the potential difference between the metal electrodes of the two triboelectric surfaces periodically varies, which drives the electrons to flow between the two metal electrodes and generate a continuous output [3]. To optimize the performance of TENGs, one requires more practical designs and careful optimization of the tribo-pair materials, including the modification of its surface morphology.

In our project work, the main objective was to develop a triboelectric nanogenerator able to harvest energy from water motions. So, we demonstrated an innovative type of triboelectric nanogenerator for effectively harvesting water energy, especially for weak-water flows. The rotary TENG was designed to operate in three different triboelectric configurations.

References

1. Z. L. Wang, “Triboelectric Nanogenerators as New Energy Technology for Self-Powered Systems and as Active Mechanical and Chemical Sensors,” ACS Nano, vol. 7, no. 11, pp. 9533–9557, 2013.

2. G. Zhu, B. Peng, J. Chen, Q. Jing, and Z. L. Wang, “Triboelectric nanogenerators as a new energy technology: From fundamentals, devices, to applications,” Nano Energy, vol. 14, pp. 126 – 138, 2015.

3. G. Cheng, Z. H. Lin, Z. L. Du, and Z. L. Wang, “Simultaneously Harvesting Electrostatic and Mechanical Energies from Flowing Water by a Hybridized Triboelectric Nanogenerator,” ACS Nano, vol. 8, no. 2, pp. 1932–1939, 2014.

FemtoEtch – Micromaquinação com laser femtosegundo e aplicação em microfluídica

João Maia1 , Vítor Amorim1 , Daniel Alexandre1 and Paulo Marques1

1Departamento de Física e Astronomia, Faculdade de Ciências da Universidade do Porto, Rua do Campo Alegre, Porto, Portugal

Abstract:. Lab-on-a-chip systems for applications in microfluidics and optofluidics can be produced by lithographic techniques or by laser direct writing. In this report the basis of these techniques is discussed, as well as the advantages and disadvantages of each method, focusing more on the FLICE technique. The FLICE technique consists of femtosecond laser direct writing followed by wet etching with HF. This method enables 3D fabrication of lab-on-chip systems, as well as monolithic integration of optical layers with microfluidic systems. Some results obtained in silica using this technique are presented and compared with those reported in literature.


1. Roberto Osellame; Giulio Cerullo; and Roberta Ramponi. Femtosecond Laser Micromachining. 2012.

2. Yves Bellouard; Ali Said; Mark Dugan; and Philippe Bado. Fabrication of high-aspect ratio, microfluidic channels and tunnels using femtosecond laser pulses and chemical etching. Optics Express, 12(10), May 2004.

3. Stephen PaulChi Ho. Femtosecond Laser Microfabrication of Optofluidic Lab-on-a-Chip with Selective Chemical Etching. PhD thesis, University of Toronto, 2013.

4. Diogo Pereira Lopes. Femtosecond laser direct writing: fabrication and characterization of waveguides and gratings. Master's thesis, Faculdade de Ciências da Universidade do Porto, 2014.

5. Koji Sugioka and Ya Cheng. Femtosecond Laser 3D Micromachining for Microfluidic and Optofluidic Applications. Springer, 2014.

Fluidic-Based Thermal Switch

M. M. Dias1,2, J. B. Puga1,4, B. D. Bordalo1,2, D. J. Silva1,2, J. H. Belo1,2, J. P.

Araújo1,2, J. C. R. E. Oliveira3,4, A. M. Pereira1,2, J. Ventura1,2

1 IFIMUP and IN-Institute of Nanoscience and Nanotechnology 2 Astronomy and Physics Departament, Faculty of Sciences of the University of Porto

3 Centro de Fisica do Porto. 4 Faculty of Engineering of the University of Porto.

Abstract:. Here we present the state of the art related with thermal switches, indicating the different types reported in the literature, their advantages and disadvantages, with a focus on fluidic thermal switches1. Therefore, we also provide a section dedicated to ferrofluids and their thermal characteristics with and without the influence of an applied magnetic field2. The proposed thermal switch prototype is then presented along with initial experimental results. The initial work provides an insight to the temperature changes between the thermal switch’s plates under different operating frequencies as well as its thermal behavior using a FLIR thermal camera.


1. Andrej Kitanovski, Jaka Tusek, Urban Tomc, Uros Plaznik, Marko Ozbolt, and Alojz Poredos. Magnetocaloric Energy Conversion: From Theory to Applications. Springer, 2014.

2. Qiang Li, Yimin Xuan, and Jian Wang. Experimental investigations on transport properties of magnetic fluids. Exp. Therm. Fluid Sci., 30(2):109-116, nov 2005.

Flexible N-type Bi2Te3 based Thermoelectric Generator for small scale energy harvesting

P. M. Resende1 and A. M. Pereira1

1IFIMUP and IN-Institute of Nanoscience and Nanotechnology and Dep. Física e Astronomia, Universidade do Porto, Rua do Campo Alegre 687, 4169-007 Porto, Portugal

Abstract:. Between 2000 and 2010, human activities have released into the atmosphere around 10 Giga-tons of greenhouse gases, with major sources being the energy (47%) and industry sector (30%). Despite the application of measures to decrease emissions, the amount of greenhouse gases still exhibits and increased trend. The world energetic demand will only increase this trend unless new and reliable methods are employed. Themoelectricity appear as a new method for energy harvesting, generating electric power from waste heat, an inevitable consequence of the present systems. Thermoelectric generators (TEG) are composed of thermoelectric materials that harness temperature to create electric power, and these have already been implemented in several areas, such as space-probes and automotive engines, and more recently as a promising method to power wearable biosensors, irradiating the need for batteries or other external power supplies. In this work, a prototype of a flexible TEG based on n-type Bi2Te3 is presented, where the fabrication and output of the device is analyzed and discussed.


1. IPCC, 2014: Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, R.K. Pachauri and L.A. Meyer (eds.)]. IPCC, Geneva, Switzerland, 151 pp.

2. J. Yang and T. Caillat, Thermoelectric Materials for Space and Automotive Power Generation, MRS Bulletin, 31 (2006), 224-229

3. V. Misra et al., Flexible Technologies for Self-Powered Wearable Health and Environmental Sensing, Proceedings of the IEEE, 103(4), April 2015, 665-681

4. C. J. Vineis, A. Shakouri, A. Majumdar and M. G. Kanatzidis, Nanostructured Thermoelectrics: Big Efficiency Gains from Small Features, Advanced Materials, 22 (2010), 3970-3980

Development and optimization of thermoelectric

devices based on Bi2Te3

Inês Cruz1, Joana Fonseca2, Ana Pires1, André Pereira1 1 IFIMUP and IN – Institute os Nanoscience and Nanotechnology and Department of Physics and Astronomy

2 CeNTI – Centre for Nanotechnology and Smart Materials

Abstract:. Escalating demands for energy consumption in last decades and the consequent scarcity of natural resources exploited so far, led us closer to a global energy crisis1,2. Improvements in energy saving, sustainable production and recovery methods are urgent. Thermoelectric phenomena, which involve the conversion between thermal and electrical energy3, can play an important role in the energy paradigma. This work present an overview on state-of-art in thermoelectrics and unveil a lack of reported works on screen printing technique4, which is extremely used on the industry of exible eletronics devices. Also Bi2Te3 is endorsed as a prime thermoelectric material with the best performance values for near-room temperature applications, both for micro and nano scale, with a unique set of characteristics that make it the most suitable material to fabricate devices. This scarcity combined with the micro/nanostructure of Bi2Te3 unveil the screen printing to be a new breakthrough on thermoelectric generators fabrication process, due to the several advantages discussed along this document. Photolithography is another approach that is mentioned to reach a exible thermoelectric generator. It is also presented the future work for the final internship report. Finally, it is presented the strategies to address the main goal of this project, namely to conceive a thermoelectric generator's prototype for energy harvesting through economically viable production techniques.


1. Energy Information Administration (EIA), “International Energy Outlook 2014”, U.S. Energy Information Administration - EIA (2014).

2. British Petroleum. “BP Statistical Review of World Energy”, Technical Report June, British Petroleum (2015).

3. G. J. Snyder and E S Toberer. “Complex thermoelectric materials”, Nature Materials, 7(2), 105-114 (2008).

4. H. B. Lee, H. J. Yang, J. H. We, K. Kim, K. C. Choi and B. J. Cho, “Thin-film thermoelectric module for power generator applications using a screen-printing method”, Journal of Electronic Materials, 40(5), 615-619 (2011).

Fabrication of integrated optical devices in Polymers and Glasses by Femtosecond Laser

Direct Writing

Vítor Amorim1, João Maia1, Daniel Alexandre1, Paulo Marques1

1Departamento de Física e Astronomia da Universidade do Porto, Rua do Campo Alegre 687, 4169-007 Porto, Portugal

Abstract: For light to be manipulated photonic devices were developed to enable, for instance, optical splitting, multi/demultiplexing and optical switching. There are several fabrication techniques available to develop photonic devices, from which femtosecond direct writing is investigated here. This technique has clear advantages over the industry standard planar lightwave circuit (PLC) technology, such as its true 3D capability of writing that enables new geometries, feature that is impossible with other techniques that are based on photolithography, and the high writing resolution inherent to the nonlinear absorption process.

Femtosecond direct writing was discovered by Davis1 and his coworkers in 1996, which reported a permanent refractive index modification, of a transparent material, within the focal volume of a focused laser beam beneath the surface. Using this characteristic and by choosing the correct parameters an increase in the refractive index of the material at the focus can occur, and by translation of the sample a waveguide can be produced. Since then several materials were used to produce waveguides, from glasses to polymers and even crystals. The losses of the waveguides produced have been decreasing, being the minimum propagation losses reported at telecom wavelengths (1550 nm) 0.2 dB/cm for a single scan2 and 0.12 dB/cm for multiple scans3.

One trend that as appeared in the recent years is the lab-on-chip concept. This concept is based on monolithic chips that integrate both optical layers and microfluidic channels, both produced by this technique. Here the microfluidic channels are written with the femtosecond laser and then placed on a bath of HF that will etch the exposed region at higher rates. These monolithic chips can, depending on the purpose, be used for sensing or manipulation of biomolecules and cells4,5.


1. K. Davis, K. Miura, N. Sugimoto and K. Hirao, "Writing waveguides in glass with a femtosecond laser.", Optics letters 21(21) 1729-1731 (1996).

2. S. Eaton, H. Zhang, P. Herman, F. Yoshino, L. Shah, J. Bovatsek and A. Arai, "Heat accumulation effects in femtosecond laser-written waveguides with variable repetition rate.", Optics express 13(12) ,4708-4716 (2005).

3. Y. Nasu, M. Kohtoku and Y. Hibino, "Low-loss waveguides written with a femtosecond laser for flexible interconnection in a planar light-wave circuit", Optics Letters 30(7) ,723 (2005).

4. A. Crespi, Y. Gu, B. Ngamsom, H. Hoekstra, C. Dongre, M. Pollnau, R. Ramponi, H. Vlekkert,P. Watts, G. Cerullo and R. Osellame, "Three-dimensional Mach-Zehnder interferometer in a microfluidic chip for spatially-resolved label-free detection", Lab on a Chip 10(9), 1167-1173 (2010).

5. N. Bellini, K. Vishnubhatla, F. Bragheri, L. Ferrara, P. Minzioni, R. Ramponi, I. Cristiani and R. Osellame, "Femtosecond laser fabricated monolithic chip for optical trapping and stretching of single cells", Optics Express 18(5) 4679-4688 (2010).

Ferroelectric and magnetoelectric mechanisms of low Fe3+ doped TbMnO3

R. Vilarinho1, E. Queirós2, D. J. Passos1, D. A. Mota1, P. B. Tavares2, M. Mihalik jr.3,

M. Zentkova3, M. Mihalik3, A. Almeida1 and J. Agostinho Moreira1

1IFIMUP and IN-Institute of Nanoscience and Nanotechnology, Physics and Astronomy Department of Faculty of Sciences of University of Porto, Porto, Portugal

2Centro de Química, Universidade de Tras-os-Montes e Alto Douro, Vila Real, Portugal 3Institute of Experimental Physics, SAS, Watsonova 47, 040 01 Kosice, Slovakia

Abstract:. TbMnO3 is a well-known multiferroic material. Its phase sequence is reported in the literature, and can be summarized as follows. At TN = 41 K, TbMnO3 undergoes a magnetic phase transition into a incommensurate antiferromagnetic phase, with a longitudinal spin density wave propagating along the a-axis, in a Pbnm symmetry setting. Below Tlock = 27 K, a commensurate cycloidal magnetic order in the bc-plane becomes stable, which allows for the emergence of spontaneous electric polarization along the c-axis, according to the Dzyaloshinskii-Moriya mechanism.1 On further cooling, Tb3+ spins order independently from the Mn3+ sublattice at T1 = 7 K.1

Recently it has been shown that the inclusion of a magnetic non-active Jahn-Teller cation (Co3+, Cr3+, Fe3+) in the octahedral site of TbMnO3, even in small concentrations, is a very effective route to reach a substantial change of its physical properties.2 These studies however have been mainly focused on the effect on the magnetic behavior, and only few on the consequent ferroelectricity and magnetoelectric coupling, which still deserves attention since the interpretation of the experimental results through the role played by the electroncs of the eg-orbitals is controversial.2,3

This work aims at unraveling the effect of Fe3+ substitution, up to x = 0.05, in the magnetic, ferroelectric and magnetoelectric properties of the TbMn1-xFexO3 system, both as a function of temperature and applied magnetic field, up to 9 T. A strong decrease of the polarization with increasing Fe3+ substitution is observed. However, within the stability range, a significant increase of the magnetic sensitivity of the polarization is obtained. Above 4% of Fe-concentration, a non-polar, weak ferromagnetic phase emerges, in good agreement with the predictions of the Dzyalowshinskii-Moriya model.4 These results reveal the crucial effect of Fe3+ substitution, and are discussed in the scope of available theoretical framework, understood as a consequence of the competition between ferromagnetic and antiferromagnetic interactions, very sensitive to both local fields and distortions.3


1. T. Kimura et al. Nature 426, 55-58 (2003)

2. Y. Guo et al. Journal of Applied Physics 116, 063905 (2014)

3. V. Cuartero et al. Physical Review Letter 99, 037209 (2008)

4. R. Vilarinho et al, submitted (2016)

Design of Novel Flexible Supercapacitors for Textile Applications using Nanomaterials

Rui Santos Costa1, Clara Pereira2 and André M. Pereira2

1 IFIMUP and IN – Institute of Nanoscience and Nanotechnology, Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, 4169-007 Porto, Portugal

2 REQUIMTE/LAQV, Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade do Porto, 4169-007 Porto, Portugal

Abstract:. The growth of energy consumption in the world and the scarcity of non-renewable energies have boosted the production of clean energy. However, it is useless to produce renewable energy if there aren’t efficient ways of storing energy. To achieve this goal, it is necessary to develop energy storage devices that are efficient, environmentally-friendly and low-cost. In this context, two large classes of energy storage devices emerged: batteries and supercapacitors (SCs).1 SCs have shown to have excellent properties that differentiate them from batteries and make them more attractive. In particular, their high power density, long life cycles, low toxicity and, more recently, flexibility (flexible SCs).2 SCs consist of two electrodes separated by an electrolyte and can be categorized into three types based on the energy storage mechanism: electrochemical double-layer capacitor (EDLC), pseudocapacitor and hybrid supercapacitor. The materials that constitute the electrodes vary for each type of SC: in EDLCs, the electrodes are made of carbon materials, whereas in pseudocapacitors the electrodes are composed of metals oxides/hydroxides or conductive polymers. In hybrid SCs, the electrodes can be of the abovementioned classes of materials or lithium intercalated compounds.3 Electrolytes can be divided into four groups: aqueous, ionic liquids, solid-state polymers and salts dissolved in organic solvents. In terms of electrolytes, there is no difference between the different types of SCs.4 In EDLCs, energy storage results from the physical charge accumulation at the interface between the electrode and electrolyte. In contrast to EDLCs, in pseudocapacitors the electricity is generated by conversion of electrochemical energy through redox reactions that occur at the electrodes. Hybrids SCs involve both types of energy storage mechanisms.5 The new generation of energy storage devices are flexible and wearable SCs due to their potential applications in flexible electronics, printable electronics, smart textiles, wearable electronics and integrated systems.6


1. Winter, M., Brodd, R., What are batteries, fuel cells, and supercapacitors?, Chem. Rev. 2004, 104, 4245-4269.

2. Yu, A. et al., Electrochemical Supercapacitors for Energy Storage and Delivery: Fundamentals and Applications, CRC Press, Taylor & Francis Group, 1st Edition, Boca Raton, USA, 2013.

3. Wang, G. et al., A review of electrode materials for electrochemical supercapacitors, Chem. Soc. Rev. 2012, 41, 797-828.

4. Beguin, F., Frackowiak, E., Supercapacitors: Materials, Systems and Applications, Wiley, Verlag GmbH & Co. KGaA, 1st Edition, Weinheim, Germany, 2013.

5. Shi, F. et al., Metal oxide/hydroxide-based materials for supercapacitors, RSC Adv. 2014, 4, 41910-41921.

6. Wang, X. et al., Flexible energy-storage devices: Design consideration and recent progress, Adv. Mater. 2014, 26, 4763-4782.

Study of the TiO2 nanotubes growth with the anodization charge curves

Paula Quitério1, Arlete Apolinário1,2, Célia Sousa1, José D. Costa1, João Ventura1

and João P. Araújo1

1IFIMUP-IN, Departamento de Física e Astronomia, Faculdade de Ciências da Universidade do Porto, Portugal

2LEPABE, Departamento de Engenharia Química, Faculdade de Engenharia da Universidade do Porto, Portugal

Abstract:. Titanium dioxide (TiO2) has important and distinct properties thar make it highly attractable for energy harvesting applications, in particular the dye-sensitized solar cells (DSCs).1 Structures such as TiO2 nanotubes (NTs) have been widely investigated for potential improving electron transport and charge separation efficiency in such devices. TiO2 NTs can be easily produced by electrochemical anodization in fluoride based electrolytes. In this process, NTs grow by phenomena of field-assisted oxidation-dissolution (occurring at the NTs bottom) and chemical dissolution mainly at NTs tops. During anodization, the evolution of the current density (j) over time (t) describes the underlying mechanisms of the NTs formation and growth.2,3 Contrarily to the anodic nanoporous Al2O3 case, the anodic TiO2 NTs reveals a non-steady-state anodization, where the oxidation rate is higher comparing with dissolution, leading to a progressive increase of the oxide barrier layer thickness (δb) and limiting the NTs growth with anodization time.4 In this work we performed Ti anodizations with different anodization times. We studied the correlation between charge (Q) curves [obtained by the integration of the traditional j(t) curves] with the length (L) of the obtained TiO2 NTs templates (Figure 1). The anodization curves j and Q are important tools to understand the growth mechanisms inherent to anodization process.

Figure 1. a) Comparison between the TiO2 NTs template thickness average and the Q curve of a 3 days anodization sample as a function of time; b) Cross-section SEM image of a TiO2 NTs template (the inset shows higher magnification).


1. M. Gratzel, “Photoelectrochemical cells,” Nature 414, 338-344 (2001).

2. A. Apolinário, C. T. Sousa, J. Ventura, J. D. Costa, D. C. Leitao, J. M. Moreira, J. B. Sousa, L. Andrade, A. M. Mendes and J. P. Araújo, “The role of the Ti surface roughness on the self-ordering of TiO2 nanotubes: a detailed study of the growth mechanism,” J. Phys. Chem. A 2(24), 9067-9078 (2014).

3. P. Quiterio, A. Apolinario, C. T. Sousa, J. D. Costa, J. Ventura and J. P. Araujo, “The cyclic nature of porosity in anodic TiO2 nanotube arrays,” J. Mater. Chem. A 3(7), 3692-3698 (2015).

4. A. Apolinario, P. Quiterio, C. T. Sousa, J. Ventura, J. B. Sousa, L. Andrade, A. M. Mendes and J. P. Araujo, “Modeling the Growth Kinetics of Anodic TiO2 Nanotubes,” J. Phys. Chem. Lett. 6(5), 845-851 (2015).

Fabrication of biocompatible gold mushroom shaped microelectrodes for the recording of

neuronal signals

M. Cerquido 1, D. Leitao 2 , M. Proença 1, C. Dias 1, S. Cardoso 2, P. P. Freitas 2, P.

Aguiar 3 4 , J. Ventura 1

1) IFIMUP and IN, and Department of Physics and Astronomy, Faculty of Sciences, University of Porto, Rua do Campo Alegre, 678, 4169-007 Porto, Portugal

2) INESC-MN and IN, Rua Alves Redol, 9, 1000-029 Lisboa, Portugal

3) Instituto de Investigação e Inovação em Saúde, Universidade do Porto, Portugal

4) INEB - Instituto de Engenharia Biomédica, Universidade do Porto

Abstract: Human beings search for new knowledge about understanding the human body and improving the treatment of brain diseases. Here review the state-of-art of how the nervous systems operates and describe several electrophysiology techniques that allow measuring and recording the electrical activity of the neurons. Gold mushrooms-shaped microelectrode arrays, is a recent electrophysiology technique that, due to its properties, was here chosen to develop. Here we state its advantages, how to fabricate this type of devices and the first proof-of-concept results.


1. Micha E Spira and Aviad Hai. “Multi-electrode array technologies for neuroscience and cardiology”. In: Nature nanotechnology 8.2 (2013), pp. 83–9

2. David Sterratt et al. Principles of computational modelling in neuroscience. Cambridge University Press, 2011, pp. 1–132

3. Aviad Hai et al. “Spine-shaped gold protrusions improve the adherence and electrical coupling of neurons with the surface of micro-electronic devices”. In: Journal of The Royal Society Interface (2009), pp. 1153–1165.

4. Silviya M Ojovan et al. “A feasibility study of multi-site, intracellular recordings from mammalian neurons by extracellular gold mushroom-shaped microelectrodes”. In: Scientific reports 5 (2015), pp. 14–100

5. Gregory Panaitov et al. “Fabrication of gold micro-spine structures for improvement of cell/device adhesion”. In: Microelectronic engineering 88.8 (2011), pp. 1840–1844.

PVDF based fiber optic sensors

A. V. Rodrigues1,2, O. Frazão1, A. M. Pereira2

1INESC, Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, 687, 4169-007 Porto, Portugal.

2IFIMUP and IN-Institute of Nanoscience and Nanotechnology, Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, 687, 4169-007 Porto, Portugal.

Abstract:. Electroactive polymers are very attractive in numerous applications as sensors, actuators and also biomedical applications and others. The importance of electroactive properties as piezoelectricity and pyroelectricity are presented for different applications. One of the most important polymers, and the first one to show ferroelectric properties, is polyvinyldene fluoride, known just as PVDF, is discussed. PVDF is the focus of many investigations and has a very wide span of applications. Since PVDF has different crystalline structures and the β phase presents the most ferroelectricity, the correct identification of this phase is vital for technological applications. The main characterization techniques of PVDF and some sensing devices using this polymer are presented.


1. M. Imai, et al., “Piezoelectric copolymer jacketed single-mode fibers for electric-field sensor application,” Journal of Applied Physics, 60(6), 1916, 1986.

2. Hari Singh Nalwa, “Ferroelectric Polymers: Chemistry, Physics, and applications,” 1995.

3. P. Martins, A. C. Lopes, and S. Lanceros-Mendez. “Electroactive phases of poly(vinylidene fluoride): Determination, processing and applications,” Progress in Polymer Science, 39(4), 683–706, 2014.

Modeling structure and magnetic properties of magnetic materials to tune the Magnetocaloric

Materials

Rui Costa1, J. H. Belo1, M. Barbosa1, J. P. Araújo1, A. M. Pereira1

1IFIMUP and IN-Institute of Nanoscience and Nanotechnology, Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, 687, 4169-007 Porto, Portugal.

Abstract: In the last few years, magnetocaloric materials have received a lot of attention due to their potential in the cooling industry, as well as, their importance for academic research. Several materials exhibiting giant magnetocaloric effect (GMCE) were discovered, mostly notably, the R5(Si,Ge)4 family which has a wide range of compounds presenting distinct properties among themselves. In particular, the Er5Si4, is an interesting case to study because it shows an apparent (de)coupling between the magnetic and crystal structure since it can only be accomplished a structural-only transition at relatively high magnetic fields. It is also the only element of this family that shows the reversible martensitic-like distortion from orthorhombic to monoclinic on cooling. The aim of the work is to explain this reversible magnetic-field-induced structural transition through first principles with the aid of the program package “WIEN2k”.


1. Gordon J. Miller, “Complex rare-earth tetrelides, RE5(SixGe1-x)4: New materials for magnetic refrigeration and a superb playground for solid state chemistry,” Chemitry Society Reviews 35(9), 799 (2006).

2. V. K. Pecharsky, A. O. Pecharsky, Yu Mozharivskyj, K. A. Gschneidner Jr., and G. J. Miller, “Decoupling of the Magnetic and Structural Transformations in Er5Si4,” Physical Review Letters 91(20), 207205 (2003).

3. C. Magen, C. Ritter, L. Morellon, P. A. Algarabel, M. R. Ibarra, A. O. Tsokol, K. A. Gschneidner Jr., and V. K. Pecharsky, “Magnetic-field-induced structural transformation in Er5Si4,” Physical Review B 74(17), 174413 (2006).

4. A. M. Pereira, J. P. Araújo, M. E. Braga, R. P. Pinto, J. Ventura, F. C. Correia, J. M. Teixeira, J. B. Sousa, C. Magen, P. A. Algarabel, et al, “Transport and magnetic properties of the Er5Si4 compound,” Journal of Alloys and Compounds 423(1), 66 (2006).

5. V. Franco, J. S. Blázquez, B. Ingale, and A. Conde, “The magnetocaloric effect and magnetic refrigeration near room temperature: materials and models,” Materials Research 42(1), 305 (2012).

Development of Novel Thermomagnetic Devices Based on the Spin Seebeck Effect

Joana Silva1, João Ventura1, André Pereira1

1IFIMUP and IN-Institute of Nanoscience and Nanotechnology, and Departamento de Fisica, Faculdade de Ciencias, Universidade do Porto, Rua do Campo Alegre, 687, 4169-007 Porto, Portugal

Abstract: The search for novel energy harvesting devices has led to the discovery of the Spin Seebeck Effect (SSE) in 2008. It consists on the conversion of heat into an electric current and establishes an outstanding new concept for thermoelectric generation.

This effect is based on a material under a temperature gradient that thermally generates a spin current that is further injected into an adjacent metal, which then converts it into a voltage by means of the Inverse Spin Hall Effect. So far, the SSE has been observed in ferromagnetic (and ferrimagnetic) metals, semiconductors and in non-magnetic materials. In the present work, it is presented the physical background and the related effects that originate the Spin Seebeck effect and allow its measurement. The controversy of the origin of the generated voltage in literature is exposed, followed by a detailed analysis on the different configurations and issues regarding this effect.

Moreover the current state-of-art in the field and the new trends are presented with special focus on the design of new energy generators. Finally the future perspectives and the main conclusions are presented followed by a critical analysis about what should be the next steps in the field.


1. K. Uchida, S. Takahashi, K. Harii, J. Ieda, W. Koshibae, K. Ando, S. Maekawa, and E. Saitoh, “Observation of the spin seebeck effect,” Nature, vol. 455, no. 7214, pp. 778–781, 2008.

2. A. Kehlberger, “Origin of the spin seebeck effect - phd thesis,” 2015.

3. C. Jaworski, J. Yang, S. Mack, D. Awschalom, J. Heremans, and R. Myers, “Observation of the spin-seebeck effect in a ferromagnetic semiconductor,” Nature materials, vol. 9, no. 11, pp. 898–903, 2010.

4. K. Uchida, J. Xiao, H. Adachi, J. Ohe, S. Takahashi, J. Ieda, T. Ota, Y. Kajiwara, H. Umezawa, H. Kawai, et al., “Spin seebeck insulator,” Nature materials, vol. 9, no. 11, pp. 894–897, 2010.

5. C. Jaworski, R. Myers, E. Johnston-Halperin, and J. Heremans, “Giant spin seebeck effect in a non-magnetic material,” Nature, vol. 487, no. 7406, pp. 210–213, 2012.

6. C. Jaworski, J. Yang, S. Mack, D. Awschalom, R. Myers, and J. Heremans, “Phonon driven spin distribution due to the spin-seebeck effect,” arXiv preprint arXiv:1102.1024, 2011.

7. S. O. Demokritov and A. N. Slavin, Magnonics: From fundamentals to applications, vol. 125. Springer Science & Business Media, 2012.

8. D. Meier, D. Reinhardt, M. van Straaten, C. Klewe, M. Althammer, M. Schreier, S. T. Goennenwein, A. Gupta, M. Schmid, C. H. Back, et al., “Longitudinal spin seebeck effect contribution in transverse spin seebeck effect experiments in pt/yig and pt/nfo,” Nature communications, vol. 6, 2015.

9. D. Meier, D. Reinhardt, M. Schmid, C. H. Back, J.-M. Schmalhorst, T. Kuschel, and G. Reiss, “Influence of heat flow directions on nernst effects in py/pt bilayers,” Physical Review B, vol. 88, no. 18, p. 184425, 2013.

10. K.-i. Uchida, H. Adachi, T. Ota, H. Nakayama, S. Maekawa, and E. Saitoh, “Observation of longitudinal spin-seebeck effect in magnetic insulators,” Applied Physics Letters, vol. 97, no. 17, p. 172505, 2010.

11. M. Schmid, S. Srichandan, D. Meier, T. Kuschel, J.-M. Schmalhorst, M. Vogel, G. Reiss, C. Strunk, and C. H. Back, “Transverse spin seebeck effect versus anomalous and planar nernst effects in permalloy thin films,” Physical review letters, vol. 111, no. 18, p. 187201, 2013.

12. A. Kehlberger, U. Ritzmann, D. Hinzke, E.-J. Guo, J. Cramer, G. Jakob, M. C. Onbasli, D. H. Kim, C. A. Ross, M. B. Jungfleisch, et al., “Length scale of the spin seebeck effect,” Physical review letters, vol. 115, no. 9, p. 096602, 2015.

Analysis of Signal Saturation in a Fiber Ring Resonator integrating an Intensity Sensor

Regina Magalhães1, Susana O. Silva1, Orlando Frazão1 1INESC, Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Rua do Campo

Alegre, 687, 4169-007 Porto, Portugal.

Abstract:. In this work is presented a wide study of signal saturation in a Fiber Ring Resonator integrating an intensity sensor, in order to establish comparisons with a theoretical added-signal obtained by the sum of several impulses. Implementing a setup with a cavity round trip

of 5.7 s, it is demonstrated that a test pulse width close to the cavity round trip time causes saturation of the signal. It is studied the behavior

of the signal with a 100 nm, a 5 s and a 20 s pulse width.


1. Meyer, R. E., et al. "Passive fiber-optic ring resonator for rotation sensing." Optics letters 8.12 (1983): 644-646.

2. Küng, A., et al. "Optical fiber ring resonator characterization by optical time-domain reflectometry." Optics letters 22.2 (1997): 90-92.

3. Capmany, José, and Miguel A. Muriel. "Double-cavity fiber structures as all optical timing extraction circuits for gigabit networks." Fiber & Integrated Optics 12.3 (1993): 247-255.

4. Küng A., J. Budin, L. Thévenaz and P. A. Robert “Rayleigh fiber optics gyroscope,” IEEE Photonics Technology Letters, 9.7 (1997): 973.

5. Magalhães, R., S. O. Silva, and O. Frazão. "Fiber ring resonator using a cavity ring‐down interrogation technique for curvature sensing." Microwave and Optical Technology Letters 58.2 (2016): 267-270.

6. Passos, D. J., et al. "Fiber cavity ring-down using an optical time-domain reflectometer."Photonic Sensors 4.4 (2014): 295-299.

7. Silva, S., et al. "Fiber-Optic Cavity Ring Down Using an Added-Signal for Curvature Sensing." Photonics Technology Letters, IEEE 27.19 (2015): 2079-2082.

Influence of short time milling in R5(Si,Ge)4, R = Gd and Tb, magnetocaloric materials

A.L. Pires1, J.H. Belo1, J. Turcaud3, G.N.P. Oliveira1,2, J.P. Araújo1, A. Berenov3,

L.F. Cohen3, A.M.L. Lopes1, A.M. Pereira1

1 IFIMUP and IN – Institute of Nanoscience and Nanotechnology 2 CFNUL — Centro de Física Nuclear da Universidade de Lisboa

3 Blackett Laboratory, Imperial College [email protected]

Abstract: Currently, the study of the magnetocaloric effect (MCE) at different dimensions has grown interest due the possibility to tayloring their MCE and understand the confinement phenomena [1]. In this context, the aim of the present work was to investigated the effect of the short ball milling (BM) times (< 2.5 h) on atomic structure, morphology, magnetic and MCE on R5(Si,Ge)4 R = Gd, Tb alloys [2]. For this, buttons of Gd5Si1.3Ge2.7 and Tb5Si2Ge2 were ground using the BM technique with different times, with the purpose of reducing the particle size. For both compositions the main differences are a consequence of the milling effect on the coupling of the structural and magnetic transitions. In the Gd5Si1.3Ge2.7 case, a second-order phase transition emerges at high temperatures as a result of ball milling. Therefore, a decrease in the MCE of 35% after 150 min of milling (Fig. 1) was obtained. Inversely effect is observed in Tb5Si2Ge2 where a 23% increase of the MCE was achieved (Fig. 1), driven by the enhancement of the coupling between magnetic and structural transitions arising from internal strain promoted by the milling process.

Fig. 1: Maximum value of magnetic entropy change as a function of milling times for a) Gd5Si1.3Ge2.7 and b) Tb5Si2Ge2.

References

1. Moya, X. et al. Nature Materials 13 (2014) 439–450

2. Pires, A. P. et al. Materials and Design 85 (2015) 32-38.

Polymer Optical Fiber based Sensors

M. F. S. Ferreiraa,b, M. B. Marquesa,b, O. Frazãoa,b

aINESC TEC and Department of Physics and Astronomy, Faculty of Sciences, University of Porto, Rua do Campo Alegre 687, 4150-179 Porto, Portugal.

bDept. of Physics and Astronomy, Faculty of Sciences, University of Porto, Rua do Campo Alegre 687, 4169-007 Porto, Portugal

Abstract: Polymer Optical Fibers (POF) have always been around for the same time as Standard Optical Fibers. This fibers can be made from polystyrene, polycarbonates and polymethyl methacrylate (PMMA) [1] which makes them resistant to damage. One of the main disadvantages of POF is the high attenuation, but with the improvements over time they have become a very interesting alternative to silica fibers. In order to fabricate sensor devices with POF, different options are being studied. Here we report the fabrication and application of Long Period Gratings (LPG) and Fiber Bragg Gratings (FBG) in POF as sensors and applications for Microstructured Polimer Optical Fibers (MPOF).

References

[1] P. Polishuk, “Plastic optical fibers branch out,” IEEE Commun. Mag., vol. 44, no. 9, pp. 1–21, 2006.

Optical Sensors Based on Fabry-Perot Interferometry

Catarina S. Monteiro1,2, Orlando Frazão1 1INESC TEC, Rua do Campo Alegre, 687, 4169-007 Porto, Portugal; 2Faculdade de Ciências da Universidade

do Porto, Rua do Campo Alegre, 687, 4169-007 Porto, Portugal

Abstract: Sensors based on optical fiber are a great alternative over conventional sensors and are being applied in harsh environments and in minimally invasive applications. Optical fiber dimensions, biocompatibility, capacity of adhesion to biological tissues and immunity to electromagnetic interference make optical fiber sensors a great alternative over conventional sensors in biomedical applications. The development of new pressure sensors based on Fabry-Perot interferometry, resorting to hollow core silica tubes and microstructured optical fiber, is the aim of this work. Strain, temperature and pressure are the main interest physical parameters to study for the development of the new sensors.


1. P. Roriz, O. Frazão, A. B. Lobo-Ribeiro, J. L. Santos, and J. A. Simões, “Review of fiber-optic pressure sensors for biomedical and biomechanical applications,” J. Biomed. Opt. 18(5), 50903 (2013).

2. B. H. Lee, Y. H. Kim, K. S. Park, J. B. Eom, M. J. Kim, B. S. Rho, and H. Y. Choi, “Interferometric fiber optic sensors,” Sensors 12(3), 2467–2486 (2012).

3. X. Wang, J. Xu, Y. Zhu, K. L. Cooper, and A. Wang, “All-fused-silica miniature optical fiber tip pressure sensor,” Opt. Lett 31(7), 885–877 (2006).

Non-destructive guided wave damage detection using FBG sensors

Luís Costa1, Matthieu Gresil2, Orlando Frazão1 1INESC, Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Rua do Campo

Alegre, 687, 4169-007 Porto, Portugal. 2i-Composites lab, School of Materials, University of Manchester, 79 Sackville Street, Manchester M1 3NJ,

United Kingdom

Abstract: This work presented a setup for the non-destructive evaluation of damage and defects on composite materials, through guided Lamb wave propagation and detection using fiber Bragg gratings (FBG). A PZT emitter was used to propagate Lamb waves on a Carbon Fibre Reinforced Polymer (CFRP) plate, measured using PZT and FBG sensors. The FBG and PZT sensitivities to symmetric (S0) and anti-symmetric (A0) wave modes were compared, for both longitudinal and transverse emission. The setup was then used for the detection of a simulated defect at different angles. The FBG sensor was shown to provide comparable results with the more established PZT, presenting orientation-dependent sensitivity, as well as a greater sensitivity to the longitudinally emitted A0 mode.

______________________________________________________________________________________________


1. Tua, P. S., Quek, S. T., & Wang, Q. (2004). Detection of cracks in plates using piezo-actuated Lamb waves. Smart Materials and Structures, 13(4), 643–660.

2. K. Diamanti and C. Soutis, “Structural health monitoring techniques for aircraft composite structures,” Prog. Aerosp. Sci., vol. 46, no. 8, pp. 342–352, 2010.

3. Rao Y.J.; “In Fibre Bragg grating sensors”, Meas. Sci. Technol., vol. 8, no.4, p335, 1997.

______________________________________________________________________________________________

Magnetization Dynamics in the Sub-10-femtosecond Range

C. S. Gonçalves1, A. S. Silva1, D. Navas1, P. Tourón Touceda1, M. Canhota1,

Y. Hinschberger1, M. Miranda2, F. Silva1, H. Crespo1 and D. S. Schmool3

1 Departamento de Física e Astronomia e IFIMUP-IN, Faculdade de Ciências, Universidade do Porto, Rua Campo Alegre 687, 4169-007 Porto, Portugal.

2 Department of Physiscs, Lund University, P.O. Box 118, SE-221 00 Lund, Sweden. 3 Laboratoire PROMES CNRS (UPR 8521), Université de Perpignan Via Domitia, Perpignan, France.

Abstract:. Using our home-built dual-colour ultrafast pump-probe apparatus we have performed ultrafast demagnetization measurements of a GdFeCo thin film induced by sub-10-fs laser pulses. Time-resolved femtosecond pump-probe measurements based on the magneto-optical Kerr effect have provided an invaluable tool for the study of ultrafast magnetic dynamics in many relevant systems [1-4]. Although rapid advances in ultrafast optical methods have allowed the temporal resolution to be gradually improved, the most recent measurements are typically limited to few tens of fs. Therefore, achieving a high temporal resolution (sub-10 femtosecond timescale) in pump-probe time-resolved experiments is very important for studying ultrafast processes in matter. In order to deal with this problem, we have designed and built a non-degenerate ultrafast pump-probe apparatus based on a novel dual-colour scheme achieving the highest temporal resolution for a system of this type [5]. The hollow-core fibre (HCF) compressor behind our design is extremely broadband, from 450 to 1050 nm, with a Fourier-limit of below 3 fs [6]. Via dichroic beam-splitting and careful dispersion compensation, we generate dual-colour pump and probe pulses with sub-10 fs durations. Our system has been fully optically characterized using d-scan techniques. To demonstrate the essential capability of our set-up, we have measured the ultrafast demagnetization and precessional dynamics in a ferrimagnetic GdFeCo thin film [7]. We observe a strong demagnetization of around 30% and field-dependent precessional dynamics for pump beam fluence of around 2.7 mJ/cm2.


1. E. Beaurepaire, J.-C. Merle, A. Daunois and J.-Y. Bigot, “Ultrafast spin dynamics in ferromagnetic nickel” Phys. Rev. Lett. 76, 4250-4253 (1996).

2. G. P. Zhang, W. Hübner, E. Beaurepaire and J.-Y. Bigot, “Laser-induced ultrafast demagnetization: Femtomagnetism, a new frontier?” Topics of Applied Physics: Spin Dynamics in Confined Magnetic Structures I, B. Hillebrands and K. Ounadjela (eds), Springer-Verlag Berlin Heidelberg 2002, 83, pp. 245-289 (2002).

3. A. Kirilyuk, A. V. Kimel and T. Rasing, “Laser-induced magnetization dynamics and reversal in ferrimagnetic alloys” Rep. Prog. Phys. 72, 026501 (2013).

4. J.-Y. Bigot, M. Vomir and E. Beaurepaire, “Coherent ultrafast magnetism induced by femtosecond laser pulses” Nature Physics 5, 515-520 (2009).

5. C.S. Gonçalves, A. S. Silva, D. Navas, M. Miranda, F. Silva, P. Oliveira, H. Crespo and D.S. Schmool, “A Dual-Colour Architecture for Pump-Probe Spectroscopy of Ultrafast Magnetization Dynamics in the Sub-10-femtosecond Range”, accepted for publication, Scientific Reports (2016).

6. F. Silva, M. Miranda, B. Alonso, J. Rauschenberger, V. Pervak and H. Crespo, “Simultaneous compression, characterization and phase stabilization of GW-level 1.4 cycle VIS-NIR femtosecond pulses using a single dispersion-scan setup” Opt. Express, 22, 10181-10191 (2014).

7. C.D. Stanciu, A. V. Kimel, F. Hansteen, A. Tsukamoto, A. Itoh, A. Kirilyuk and Th. Rasing, “Ultrafast

spin dynamics across compensation points in ferrimagnetic GdFeCo: The role of angular momentum

compensation” Phys. Rev. B 73, 220402(R) (2006).

The ESO Very Large Telescope Interferometer GRAVITY instrument: an

overview

Narsireddy Anugu1, Antonio Amorim2, Paulo Garcia1, Paulo Gordo2 and GRAVITY consortium

1Faculty of Engineering, University of Porto, Porto, Portugal; 2Faculty of Sciences, University of Lisbon, Portugal

Abstract: At the centre of the Milky Way galaxy, the Galactic Centre, there exists a super-massive black-hole with over four million solar masses. Near infrared flares are observed at the position of the supermassive black-hole. The GRAVITY instrument was designed to be able to astronometrically monitor the flares to probe how and if they move around the super-massive black hole. This requires an astrometric precision of the order of the angular size of the Schwarzschild radius, for this super-massive black-hole: 10 micro arc-seconds. This precision would allow us to probe origin of these flares, the space-time around the supermassive black hole and testing stellar dynamics in the strong field gravity (Eisenhauer et al. 2011).

GRAVITY (Eisenhauer et al. 2011) is a beam combiner instrument operating in the astronomical K-band (2.2 micrometres). It combines the four 8 m telescopes beams of the Very Large Telescope Interferometer. The GRAVITY subsystems include: a) wavefront sensors; b) acquisition camera and beam stabilization system (Gordo et al. 2014; Pfuhl et al. 2014); c) fringe tracker; d) metrology system and e) a novel fibre-fed integrated optics; d) a spectrograph with a resolution of up to 4.000.

GRAVITY has been built by GRAVITY consortium consisting of several European institutes led by Max Planck Institute for Extraterrestrial Physics, Germany. The team of SIM/CENTRA of Portugal contributed the acquisition camera. It is a very important subsystem and enables beam stabilization.

GRAVITY installed and got its first light in the end of 2015. Until now, GRAVITY has been tested with four 1.8 m telescopes. The first observations of Galactic Center black-hole is planned with the four 8 m telescopes in the mid-2016.


1. Eisenhauer, Frank, Wolfgang Brandner, Christian Straubmeier, Karine Perraut, Stefan Gillessen, Jorge Lima, Thomas Henning, Paulo Garcia, Stefan Kellner, and Gerardo Avila. 2011. “GRAVITY : Observing the Universe in Motion,” no. March: 16–24.

2. Gordo, Paulo, Antonio Amorim, Jorge Abreu, Frank Eisenhauer, Narsireddy Anugu, Paulo Garcia, Oliver Pfuhl, et al. 2014. “Integration and Testing of the GRAVITY Infrared Camera for Multiple Telescope Optical Beam Analysis.” In SPIE Astronomical Telescopes + Instrumentation, edited by Jayadev K. Rajagopal, Michelle J. Creech-Eakman, and Fabien Malbet, 42:91461V. Springer. Doi:10.1117/12.2056572.

3. Pfuhl, O., M. Haug, F. Eisenhauer, S. Kellner, F. Haussmann, G. Perrin, S. Gillessen, et al. 2014. “The Fiber Coupler and Beam Stabilization System of the GRAVITY Interferometer.” In SPIE Astronomical Telescopes + Instrumentation, edited by Jayadev K. Rajagopal, Michelle J. Creech-Eakman, and Fabien Malbet, 914623.

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