Quantum entanglement of photons and Bell theorem test at CEMS

Photonics and Quantum Optics Research Unit of Center of Excellence for Advanced Materials and Sensors at the Ruđer Bošković Institute announces realization and measurement of quantum entanglement of photon pairs. The experimental setup is schematically shown in the figure. A 405 nm wavelength purple laser beam is fed into Sagnac interferometer containing a periodically-poled crystal of potassium titanil-phosphate (PPKTP), schematically shown below on the left. The actual setup is shown on the right. Thanks to the nonlinear optical nature of the crystal and the specifically selected orientation of its lattice axes, some of the purple photons undergo a process of spontaneous parametric downconversion and thus split into a pair of infrared photons that are quantum entangled in polarization. Quantum entanglement of photons was evaluated in two ways.

 

First, we measured correlation of polarization of paired photons. To that end, each photon is sent to one of the polarization-measuring stations, named Alice and Bob. The actual setup is shown below. Alice and Bob are each realized as a polarizer mounted on computer-controlled, motorized mount, followed by an optical-fiber-coupled photon detector, as shown in the photo of the actual setup.

Alice can measure polarization along one of 4 special orientations (horizontal (H), vertical (V), diagonal (D) and anti-diagonal (A)). For each of the Alice’s orientations, Bob rotates his polarization analyzer for a full circle and they evaluate probability of measuring a photon polarization along their respective orientation, as a function of Bob’s analyzer angle. The probability forms a sinusoidal fringe, as shown in the figure below. Visibility greater than 50% for all 4 fringes is not possible if photons in a pair have predetermined polarizations. On the other hand, if photons are entangled, then visibility of all 4 fringes can reach the theoretical maximum of 100%. With our source we have obtained: V= (99,8 +/- 0,6) %, V= (99,7 +/- 0,4) %, V= (98,5 +/- 0,4) %, V= (98,3 +/- 0,4) %, as shown in the figure, which indicates near-maximal entanglement of photons.

We also used the Bell’s theorem and performed measurement of Clauser, Horne, Shimony, Holt (CHSH) parameter S, to test the CHSH form of Bell’s inequality. Classical physics predicts S ≤ 2, while quantum physics allows 2 < S ≤ 2√2  2.828. We have experimentally obtained the value of S = 2,803 +/- 0,007 which is more than 114 standard deviations greater than the maximum value of 2 allowed by classical physics, again indicating the near-maximal entanglement.

These results demonstrate the non-local behaviour of quantum-entangled photon pairs, which is that the measurement of polarization performed on one photon has an immediate impact on the result of measurement of polarization on the other photon.

An Overview of Organized and Planned Conferences

Laboratory for ion beam interactions has long and fruitful experience in organization of international research meetings connected to development and applications of ion beam analysis and ion beam modification techniques as well as related developments of accelerator and detector technology. Since the formation of national center of excellence CEMS, research unit Ion beam physics and technology has organized, or plans organization of many international research meetings.

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Direct photo-capacitive neurostimulation using organic pigments

Localized stimulation of neurons in a safe and effective way is important for both research and therapeutic purposes. The currently available solutions based on micro- and nano-electrodes as well as on ion delivery platforms for neuronal electrical communications led to bioelectronic therapies and opened a new window of research in neuroscience. An important limitation of this approach is the need for wiring the electrode at the site of neurostimulation. The motivation for wireless access to the stimulation site has led to optogenic approaches, necessitating genetically modified  targeted neurons for the expression of light sensitive ion channels. Conventional approaches to addressing the wireless connectivity problem that does not include genetic modification include photoelectric stimulation in which the silicon solar cell of micrometric dimensions is attached to the neuronal excitation electrodes. These solutions are used in clinical applications as artificial retinas that are implanted into blind patients with damaged photoreceptors in the retina.

Electric field distribution arround the electrode for direct photocapacitive stimulation a) and d) made of b) organic pigments of p-type (H2PC) and n-type (PTCDI). c) Energy diagram of the electrode, e) schematic representation of the electrode operation.

A new approach to electrical stimulation of neurons comes from the Organic Electronics Laboratory from the University of Linköping in Sweden. Scientists in the group of prof.dr. Eric Glowacki, in which CEMS member Vedran Đerek participated as a post-doctoral student, presented a new approach to photoelectric stimulation of neurons using thin layers of organic semiconductors – cheap pigments used in cosmetics and the color industry (Advanced Materials, https: //doi.org/10.1002/adma.201707292). These pigments represent a class of new functional materials that are stable under physiological conditions, so they do not need to be protected from water encapsulation influence. The nature of the stimulus is completely capacitive, meaning that active materials – pigments – do not participate in chemical reactions during stimulation, therefore the device is persistent and can not introduce harmful substances into the body. The working principle was demonstrated by associates from prof.dr. Hanein group from Israel on the model of blind chicken retina, where in-vitro neurostimulation of retina neurons was demonstrated.

The Robin Hood Solver software package was used to calculate the three-dimensional distribution of electric potential around the photo-capacitive excitation electrode, which was provided by one of the authors of the package, dr. Predrag Lazić from IRB. The successful advancement of CEMS in the bioelectronic direction with the use of new functional materials can be a motivation for future research in which it would be possible to use the previously developed and explored materials within the framework of CEMS.

Foto: Thor Balkhed, LiU
Illustration source: https://doi.org/10.1002/adma.201707292

Ostvareno generiranje parova polarizacijski spregnutih fotona

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Sa zadovoljstvom objavljujemo da je 9. travnja 2018. istraživači Istraživačke jedinice Fotonika i kvantna optika Znanstvenog centra izvrsnosti za napredne materijale i senzore, na Institutu Ruđer Bošković, dovršili su gradnju eksperimentalnog postava izvora parova spregnutih fotona zasnovanog na procesu spontane parametarske pretvorbe (Engl. spontaneous parametric downconversion (SPDC), kolinearni proces tipa II) fotona valne duljine 405 nm u parove infracrvenih fotona u PPKTP kristalu te optičkom postavu u Sagnac-ovoj konfiguraciji. Izvor stabilno generira koincidentne parove polarizacijski spregnutih fotona.

Iako je kvantno sprezanje fotona poznato, ovaj kontraintuitivni efekt i dalje je predmet intenzivnog istraživanja kako na fundamentalnoj tako i na razini mogućih primjena u kvantnoj komunikaciji, kvantnom računanju i kvantnoj metrologiji. Ostvareni rezultat je ključan za buduća istraživanja ove grupe.

Arbitrarily exhaustive generation of contextual sets

Recently obtained results published in Pavičić, M., Arbitrarily exhaustive hypergraph generation of 4-, 6-, 8-, 16-, and 32-dimensional quantum contextual sets, Physical Review A, 95, 06212–1-25 (2017) will be implemented in a series of experiments in the CEMS Research Unit Photonics and Quantum Optics.

Quantum contextuality is a property of quantum systems not to have predetermined values of their observables, in contrast to classical systems. Take an entangled photon pair. Each of the photons is genuinely unpolarized before we let them through polarizers.  After polarizers, measurements find the photons in definite polarization states. Can we assume that these polarizations were somehow predetermined when the pair was created? The so-called contextual sets of states of photons prove that we cannot. Such sets are not of just of a foundational theoretical interest. Recently, it turned out that the “contextuality is the source of a quantum computer’s power” (Nature; cited in the paper). Therefore, it is important for future applications and implementations to find new classes, instances, and structure of contextual sets as well as to design algorithms and programs for obtaining them. In this paper, arbitrary exhaustive hypergraph-based generation of the most explored contextual sets, Kochen-Specker (KS) ones, is carried out in up to 32 dimensions.

Twelve classes of critical KS sets (the ones that cannot be simplified further) are generated and analyzed, huge number of novel types and instances of them obtained and numerous properties of theirs found. Several thousand times more types and instances of KS sets than previously known are generated. All KS sets in three of the classes and in the upper part of a fourth are novel. The generation was carried out with the help of McKay-Megill-Pavičić (MMP) hypergraph language, algorithms, and programs which generate KS sets (see the feature image for two hypergraphs of 8-dim KS sets; also the figure below) strictly following their definition from the Kochen-Specker theorem, which itself celebrates semicentennial this year. This is in contrast to parity proof based algorithms which prevail in the literature and for which the majority of KS sets and even a whole KS class (as the one shown in the Figure below) are simply invisible.

[SEMINAR] Glass based structures fabricated by rf-sputtering

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Dr. Alessandro Chiasera (Consiglio Nazionale delle Ricerche – Istituto di Fotonica e Nanotechologie) će održati predavanje naslova: “Strukture na bazi stakla proizvedene pomoću Rf-sputteringa”. Predavanje će obuhvaćati opis proizvodnje jednodimenzionalnih fotoničkih kristala pomoću rf-sputteringa te njihovu karakterizaciju u vidu prostorno ovisne luminiscencije navedenih fotoničkih struktura i njihova lasiranja. Predavanje će biti održano u dvorani “Ivan Supek” u prvom krilu IRB-a u utorak 30.5.2017 u 12h 30 min.

 

[SEMINAR] Kemijska pohrana vodika u kondenziranoj materiji

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Pozivamo Vas na predavanje dr.sc. Nikole Biliškova naslova “Kemijska pohrana vodika u kondenziranoj materiji” u srijedu 9.11.2016. u 14 sati u predavaonici I krila IRB-a.

Vodik se kroz zadnjih nekoliko desetljeća razmatra kao efikasan nosilac energije, koji bi unaprijedio efikasnost obnovljivih izvora energije. No, konvencionalnom pohranom vodika u plinskoj i tekućoj fazi osigurava se samo vrlo ograničeni sadržaj energije. Zato se razvija koncept kemisorpcijske pohrane u kondenziranoj materiji kao najefikasniji način pohrane vodika. Poteškoće povezane s razvojem takvih sustava za pohranu vodika učinile su tu problematiku jednom od ključnih suvremenih znanstvenih i tehnoloških izazova pri realizaciji široke upotrebe vodika kao nosača energije u bezugljičnoj „vodikovoj ekonomiji“. Iako je taj problem uglavnom kemijske naravi, pronalazak efikasnih sustava, koji zadovoljavaju sve zacrtane tehnološke potrebe, zahtijeva interdisciplinarni pristup.
Predavač će dati pregled dosadašnjih istraživanja na tom polju, koja se provode u Laboratoriju za kemiju čvrstog stanja i kompleksnih spojeva u kontekstu međunarodnih trendova na tom polju, uz naročit naglasak na najnovije rezultate. Također, bit će izneseni i planovi za budućnost, koji su se dijelom već počeli realizirati.

Priopcenje za javnost povodom opstruiranja financiranja iz EU fondova od strane MZOS-a

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PRIOPĆENJE ZA JAVNOST Zagreb, 7. lipnja 2016.

Otvoreno pismo ministru znanosti, obrazovanja i sporta Predragu Šustaru:

Opstruiranjem financiranja iz EU fondova hrvatskih znanstvenih centara izvrsnosti ugrožava se 50 milijuna eura iz strukturnih fondova i radna mjesta za hrvatske znanstvenike – traži se hitna reakcija ministra Šustara!

Pedeset milijuna eura, upitna radna mjesta za čak tri stotine doktoranada i postdoktoranada, te riskiranje penala od Europske komisije, samo su dio crne statistike koja ozbiljno prijeti Republici Hrvatskoj (RH), a odvija se u sjeni problema s kurikularnom reformom.

Deset znanstvenih centara izvrsnosti proglašenih od strane Ministarstva znanosti obrazovanje i sporta (MZOS) tijekom 2014. i 2015. godine na prijedlog Nacionalnog vijeća za znanost, visoko obrazovanje i tehnološki razvoj, posljednjih su nekoliko mjeseci postalo taocem MZOS-a.

Naime, RH se strateški odredila kroz Operativni program (OP) za financiranje Znanstvenih centara izvrsnosti (2014 – 2020), te se prema Operativnom programu očekuje 50 milijuna eura iz Europskog fonda za regionalni razvoj (ERDF) koji bi bili na raspolaganju proglašenim centrima.

Kako bi centri mogli iskoristiti europska sredstva, MZOS je obvezan raspisati natječaj. Prvi indikativni rok za raspisivanje natječaja bio je 31. ožujka, te je pomaknut na 1. lipnja 2016., a natječaj još nije raspisan.

Unatoč brojnim službenim molbama za poštivanjem obveza koje su voditelji Znanstvenih centara izvrsnosti posljednjih mjeseci dostavili ministru Šustaru i premijeru Oreškoviću s upozorenjem da je RH preuzela obvezu te je dužna raspisati planirani natječaj iz strukturnih fondova u sklopu kojih bi se izvršila evaluacija planiranih troškova u okviru pojedinih centara, s današnjim datumom MZOS još uvijek nije aktivirao natječaj Europskog fonda za regionalni razvoj (ERDF) koji bi omogućio povlačenje čak 50 milijuna eura za Znanstvene centre izvrsnosti. Time se ozbiljno ugrožava realizacija znanstvenih aktivnosti proglašenih ZCI-a i gubitak 50 milijuna eura iz EU te zapošljavanje 300 mladih stručnjaka.

Podsjetimo, MZOS je proglasio Znanstvene centre izvrsnosti iz područja prirodnih, biomedicinskih, biotehničkih i tehničkih znanosti nakon zahtjevnih kriterija javnog natječaja, uključujući opsežne domaće i međunarodne recenzije i intervjue s voditeljima predloženih centara koji su proveli Agencija za znanost i visoko obrazovanje (AZVO) i Nacionalno vijeće za znanost, visoko obrazovanje i tehnološki razvoj. MZOS je potom temeljem članka 29. stavka 2. Zakona o znanstvenoj djelatnosti i visokom obrazovanju (Narodne novine, broj: 123/2003, 105/2004, 174/2004, 2/2007 – Odluka Ustavnog suda Republike Hrvatske, 46/2007, 45/2009,63/2011,94/2013, 139/13 i 101/2014 – Odluka i Rješenje Ustavnog suda Republike Hrvatske) proglasilo znanstvene centre izvrsnosti RH, čiji su članovi izvrsni hrvatski znanstvenici, među nositeljima međunarodne prepoznatljivosti hrvatske znanosti.

Proces prijave, vrednovanja i odabira centara trajao je tri godine, a Vlada RH je nakon provedenog postupka recenzija uskladila program centara s nacionalnim prioritetima i oni su u skladu sa Strategijom pametne specijalizacije (S3). Ovu Strategiju su više od dvije godine izrađivali brojni eksperti iz javnog i privatnog sektora koji se bave istraživanjem i razvojem, te ju je usvojio Hrvatski sabor i Europska komisija za znanost.

Cilj proglašenja centara je bio omogućiti izvrsnim hrvatskim znanstvenicima i institucijama uvjete za vrhunski istraživački rad kroz stabilno i pojačano financiranje te edukaciju mladih znanstvenika i značajan doprinos gospodarstvu RH.

Slijedom navedenog, proizlazi da se nepoštivanjem zadanih obveza od strane MZOS-a te neprovođenjem preuzetih obveza direktno ugrožavaju nacionalni interesi.

Nažalost, jedan od glavnih protivnika ustroja hrvatskih centara izvrsnosti, kao i od strane Europske komisije usvojene pametne specijalizacije (S3) RH, a koja je jedan od glavnih preduvjeta za povlačenje sredstava iz strukturnih fondova, je pomoćnik ministra za znanost dr. sc. Krešimir Zadro.

Poštovani ministre Šustar, otvorenim pismom javnosti obraćamo Vam se ispred svih Znanstvenih centara izvrsnosti (ZCI) iz područja prirodnih, biomedicinskih, biotehničkih i tehničkih znanosti sa zahtjevom da se javno očitujete o razlozima nepoštivanja odluka Vlade RH i neprovođenju usvojenih programa financiranja hrvatskih centara izvrsnosti iz EU fondova te datumu raspisivanja natječaja kako bi se izbjegao crni scenarij.

Vjerujemo da niste spremni potpuno ignorirati izvrsne hrvatske znanstvene skupine i propustiti priliku da se kroz usvojeni program pametne specijalizacije povuku sredstva u iznosu od 50 milijuna eura iz strukturnih fondova.

U situaciji kad se domaća sredstva za znanost i istraživanje sustavno režu, kad se događa egzodus najboljih mladih obrazovanih stručnjaka, znanstvena istraživanja i inovacije preživljavaju velikim dijelom zbog izvrsnosti istraživačkih skupina i velikih napora znanstvenika u povlačenju sredstva iz programa Europske unije, ovakvo opstruiranje rada Znanstvenih centara izvrsnosti da osiguraju europska sredstva za rad i zapošljavanje stručnog kadra je nedopustivo!

S poštovanjem,
voditelji proglašenih Znanstvenih centara izvrsnosti (STEM područja):

Znanstveni centar izvrsnosti za napredne materijale i senzore,
Institut Ruđer Bošković i Institut za fiziku, Zagreb

Dr. sc. Milko Jakšić – Milko.Jaksic@irb.hr
Dr. sc. Mile Ivanda – Mile.Ivanda@irb.hr
Dr. sc. Mario Stipčević – Mario.Stipcevic@irb.hr
Dr. sc. Marko Kralj – mkralj@ifs.hr

Znanstveni centar izvrsnosti za reproduktivnu i regenerativnu medicinu,

Medicinski fakultet, Sveučilište u Zagrebu,
Akademik prof. dr.sc. Slobodan Vukičević – slobodan.vukicevic@mef.hr
Prof. dr. sc. Davor Ježek – davor.jezek@mef.hr

Znanstveni centar izvrsnosti za virusnu imunologiju i cjepiva,
Medicinski fakultet, Sveučilište u Rijeci
Prof. dr. sc. Stipan Jonjić – stipan.jonjic@medri.uniri.hr

Znanstveni centar izvrsnosti za znanost i tehnologiju – STIM, Sveučilište u Splitu
Prof. dr. dr. h.c. Vlasta Bonačić-Koutecky – vbk@cms.hu-berlin.de

Znanstveni centar izvrsnosti za bioraznolikost i molekularno oplemenjivanje bilja, Agronomski fakultet , Sveučilište u Zagrebu
Prof. dr. sc. Zlatko Šatović – zsatovic@agr.hr

Znanstveni centar izvrsnosti za bioprospecting mora
Institut Ruđer Bošković, Zagreb
Dr.sc. Rozelindra Čož-Rakovac – Rozelindra.Coz-Rakovac@irb.hr

Znanstveni centar izvrsnosti za kvantne i kompleksne sustave te reprezentacije Liejevih algebri, Prirodoslovno-matematički fakultet, Sveučilište u Zagrebu

Prof.dr.sc Hrvoje Buljan – hbuljan@phy.hr
Prof. dr. sc. Pavle Pandžić – pandzic@math.hr

Znanstveni centar izvrsnosti za personaliziranu brigu o zdravlju,

Sveučilište Josip Juraj Strossmayer u Osijeku
Prof. dr. sc. Gordan Lauc – glauc@pharma.hr
Prof. dr. sc. Ines Drenjančević – ines.drenjancevic.peric@mefos.hr

Znanstveni centar izvrsnosti za temeljnu, kliničku i translacijsku neuroznanost, Medicinski fakultet, Sveučilište u Zagrebu
Prof. dr. sc. Miloš Judaš – mjudas@hiim.hr

Znanstveni centar izvrsnosti za znanost o podatcima i kooperativne sustave, Fakultet elektrotehnike i računarstva, Sveučilište u Zagrebu

Prof.dr.sc. Sven Lončarić – sven.loncaric@fer.hr
Prof. dr. sc. Ivan Petrović – ivan.petrovic@fer.hr

Priopćenje voditelja proglašenih
            Znanstvenih centara izvrsnosti (STEM područja)             ___________________________________________________________________________________________________

Physics of the Dark Universe Paper “KWISP: An ultra-sensitive force sensor for the Dark Energy sector”

One of the remaining puzzles in physics is the composition of the Universe. Now days we believe that it is made of about 5% ordinary matter, 25% dark matter and 70% of dark energy. Our knowledge about the nature of the dark constituents of the Universe is very feeble. They were introduced to explain some observational data. In particular the dark energy was introduced to explain the observed acceleration in the expansion rate of the Universe. One of the possible mechanisms would be the existence of a light scalar field. To render it compatible with General Relativity in the solar system and “fifth force” searches on Earth they have to be screened. One possibility is a so called “chameleon” mechanism which renders their effective mass dependent on the local matter density. In case they exist they can be produced in the Sun and detected on Earth by a suitable sensor. The detection mechanism relies on the equivalent of the radiation pressure, where solar chameleons impinge on a mobile surface and transfer momentum to it which displaces it from the equilibrium position.

CERN_Courier

Such a sensor has been built and tested in cooperation with the optics laboratory at INFN Trieste where the sensor was situated before transferring it to the final setup at CERN which was noted in the CERN Courier article (see picture). It is based on a thin silicon nitride micro-membrane placed inside a Fabry–Perot optical cavity. By monitoring the cavity characteristic frequencies it is possible to detect the tiny membrane displacements caused by an applied force. Its application to experiments in the Dark Energy sector, such as those for Chameleon-type WISPs, is particularly attractive, as it enables a search for their direct coupling to matter. The sensitivity and the absolute force calibration are given in the article published in the journal Physics of the Dark Universe (impact factor 8.57).

 

Manipulation of macroscopic nano-patterned graphene

Nano-rippled graphene is a structurally modified graphene with a large range of possible applications including sensors, electrodes, optoelectronics, spintronics, and straintronics. In this work, published in the journal Carbon 96 (2016) 243, our colleagues I. Šrut Rakić and M. Kralj from Institute of Physics, together with D. Čapeta (PMF) and M. Plodinec (IRB) have shown that it is possible to synthesize macroscopic graphene sample with well-defined uniaxial periodic modulation on a vicinal metal surface and transfer it to a dielectric support without losing nano-rippled structure.

Transfer schematics

Figure 1. (a) – (d) Schematic representation of the graphene transfer procedure steps. (e) Photograph of the Ir(332) crystal covered with graphene monolayer after the sample has been taken out of UHV. (f) Photograph of an experimental setup for the bubbling transfer. (g) Optical microscopy image (x80 magnification) of the sample during the under-potential treatment. Inset shows the magnified region marked by a black rectangle where the intercalation front indicated by a black arrow can be seen. (h) Photograph of a graphene sheet after the transfer to Si/SiO2.

Structurally modified graphene recently came into focus of graphene research bringing a promise for a wider range of possible graphene applications. The key feature of such systems is a presence of curvature in graphene typically accompanied by strain. Strain has a great effect on graphene electronic structure, conductivity, optical response, and even spin transport which can then be exploited in a rippled system for fabricating targeted optoelectronic, spintronic or generally strain facilitated electronic (straintronic) devices. Moreover, properties of the rippled graphene can be useful for various sensors, electrodes, coatings and even for hydrogen storage. Therefore, it is of great importance to be able to produce a device based on rippled graphene with well-defined uniaxial, 1D, periodic modulation. The key for making such a device is the ability to synthesize and transfer structurally modified graphene to a desirable substrate of interest.

SPM karakterizacija

Figure 2. (a) – (d) AFM topographs at several different locations at the same sample. (e) Fourier transform image of (c) confirming the 1D ordering with a periodicity of 67 nm. (f) AFM line profile corresponding to the green line in (d). Inset shows a simplified ripple cross-section used for strain calculation.

Raman characterization

Figure 3. (a) Raman spectrum of the graphene sample on Si/SiO2 recorded with an unpolarized laser light. (b) A schematic model of the polarized laser light Raman measurement. Black arrows mark laser polarization and blue arrow marks a direction of the graphene ripples. (c) Polar plot showing positions of the 2D peak with polarized light for different laser polarization angle. (d) Raman spectra of two 2D graphene peaks for two different angles of light polarization separated by 90°.

In this paper published in Carbon (IF=6.196) the authors showed that it is possible to grow periodically nano-rippled graphene on a mm scale using a prestructured stepped Ir(332) substrate. The team carried out a transfer of such 1D modulated graphene onto a Si/SiO2 wafer adapting a method called bubbling transfer (Figure 1). The key finding upon the transfer came from AFM (atomic force microscopy) characterization showing that graphene has kept its original periodic 1D rippled structure (Figure 2). Additionally, the presence of uniaxial strain in graphene was confirmed by adapting Raman spectroscopy for polarized measurements where the laser polarization was rotated in a controlled way with respect to macroscopic ripple direction, resolving between strained and unstrained directions in graphene (Figure 3).

This work presents a collaborative interinstitutional effort within the CEMS and brings a relevant achievement for a large scale graphene applications.