Publications

2018

Mueller matrix ellipsometric study of multilayer spin-VCSEL structures with local optical anisotropy
- Fördös T.
- Postava K.
- Jaffrès H.
- Quang To D.
- Pištora J.
- Drouhin H.
Applied Physics Letters, American Institute of Physics, 2018, 112 (22), pp.221106. Spin-laser structures such as spin-polarized vertical-cavity surface-emitting lasers are semiconductor devices in which the radiative recombination processes involving spin-polarized carriers result in an emission of circularly polarized photons. Nevertheless, additional linear in-plane anisotropies in the cavity, e.g., interfacial and surface anisotropies, generally lead to preferential linearly polarized laser emission and to possible coupling between modes. We present Mueller matrix ellipsometric study of non-intentionally doped InGaAs/GaAsP laser structures devoted for optical pumping operations in the spectral range from 0.73 to 6.4 eV in order to disentangle surface and quantum wells contributions to the linear optical birefringence of the structures. The measurement of full 4 × 4 Mueller matrix for multiple angles of incidence and in-plane azimuthal angles in combination with proper parametrization of optical functions has been used for extraction of optical permittivity tensor components along [110] and [110] crystal axis of surface strained layers and quantum wells grown on [001]-substrate. Such spectral dependence of optical tensor elements is crucial for modeling of spin-laser eigenmodes, resonance conditions, and also for understanding of sources of structure anisotropies. (10.1063/1.5009411)
DOI : 10.1063/1.5009411
Laser induced phase transition in epitaxial FeRh layers studied by pump-probe valence band photoemission
- Pressacco Federico
- Uhlíř Vojtěch
- Gatti Matteo
- Nicolaou Alessandro
- Bendounan Azzedine
- Arregi Jon Ander
- Patel Sheena
- Fullerton Eric E.
- Krizmancic Damjan
- Sirotti Fausto
Structural Dynamics, AIP Publishing, 2018, 5 (3), pp.034501. We use time-resolved X-ray photoelectron spectroscopy to probe the electronic and magnetization dynamics in FeRh films after ultrafast laser excitations. We present experimental and theoretical results which investigate the electronic structure of FeRh during the first-order phase transition, identifying a clear signature of the magnetic phase. We find that a spin polarized feature at the Fermi edge is a fingerprint of the magnetic status of the system that is independent of the long-range ferromagnetic alignment of the magnetic domains. We use this feature to follow the phase transition induced by a laser pulse in a pump-probe experiment and find that the magnetic transition occurs in less than 50 ps and reaches its maximum in 100 ps. (10.1063/1.5027809)
DOI : 10.1063/1.5027809
Superconductivity, pseudo-gap, and stripe correlations in high-T c cuprates
- Zhang Zailan
- Denis Sylvain
- Lebert Blair W.
- Bertran Francois
- Le Fèvre Patrick
- Taleb-Ibrahimi Amina
- Castellan John-Paul
- Bolloc'H David Le
- Jacques Vincent L.R.
- Sidis Yvan
- Baptiste Benoit
- Decorse Claudia
- Berthet Patrick
- Perfetti Luca
- d'Astuto Matteo
Physica B: Condensed Matter, Elsevier, 2018, 536, pp.747-751. Under-doped La-214 cuprates show a charge-and spin-modulation known as " stripes " [1]. These stripe modulations are (quasi)-static close to 1/8 hole doping where superconductivity is suppressed. The pseudo-gap phase of other cuprate compounds recently also revealed charge modulation, but interpreted rather as a charge density wave (CDW) [2, 3, 4], that possibly competes with superconductivity. In this context, to better understand the interplay between the stripe phase and the superconductivity, we use angle-resolved photoemission spectroscopy to study the electronic band structure and gap in La-214 cuprates near 1/8 doping (La 2−x−y Nd y Sr x CuO 4 (x = 0.12; y = 0.0 & 0.4)) and compare with the previous results in the same system [5] and La 1.86 Ba 0.14 CuO 4 [6]. Our data shows a loss of spectral intensity towards the end of the Fermi arcs, that is possibly due to a strong renormalisation, as already pointed out elsewhere * matteo.dastuto@neel.cnrs.fr-Institut Néel CNRS-25, av des Martyrs-38042 Grenoble cedex 9; tel: (+33)(0)4 76 88 12 84 [5], with a noisy but still measurable gap. On the nodal direction no gap is observed within our statistics, but a sizeable decrease in intensity with temperature. Moreover, we do not see any shadow band, but our Fermi surface can be well modelled with a single electron band calculation in the tight binding approximation, even very close to the 1/8 doping La 2−x−y Nd y Sr x CuO 4 with and without Nd substitution. (10.1016/j.physb.2017.10.096)
DOI : 10.1016/j.physb.2017.10.096
Linear electro-optic effect in semiconductors: Ab initio description of the electronic contribution
- Prussel Lucie
- Véniard Valérie
Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2018, 97 (20). (10.1103/PhysRevB.97.205201)
DOI : 10.1103/PhysRevB.97.205201
The GW approximation: content, successes and limitations
- Reining Lucia
Wiley Interdisciplinary Reviews: Computational Molecular Science, Wiley, 2018, 8 (3), pp.e1344. (10.1002/wcms.1344)
DOI : 10.1002/wcms.1344
RE2O3 -alkaline earth-aluminosilicate fiber glasses: Melt properties, crystallization, and the network structures
- Charpentier Thibault
- Ollier Nadège
- Li Hong
Journal of Non-Crystalline Solids, Elsevier, 2018, 492, pp.115 - 125. Glasses and/or glass fibers of a new glass system, RE2O3 (RE = Sc,Y, La)-MgO-CaO-Al2O3-SiO2, were studied in detail, covering rare earth (RE) effects on high temperature viscosity, liquidus temperature and crystalline phases, softening and glass transition temperature, and speciation reactions of aluminum (AlOx, x = 4, 5) and silicate network (Qn, n = 4, 3, 2) using 27Al and 29Si MAS NMR and Raman spectroscopic methods. Rare earth oxides (RE2O3) were shown to have a dual functionality, i.e., decreasing melt viscosity like a network modifier depolymerizing glass network, but increasing viscosity at low temperature, i.e., glass softening temperature (Tsoft) and transition temperature (Tg), strengthening the glass network functioning like Al2O3. Liquidus temperature (TLiq) was found to be sensitive to the type of RE2O3 modifications in terms of their ionic field strength (IFS); Sc3+ of the highest IFS increased, but La3+ of the lowest IFS decreased TLiq. Effect of Y3+ (intermediate IFS) on TLiq resembles Sc3+ only at higher concentration. The overall results suggest that RE ions of different IFS have different “true” solubility limits in the host glass matrix, above which RE2Si2O7 crystallizes. All of the glasses with and without RE2O3 contained predominately four-fold coordinated aluminum, AlO4; yet replacement of CaO by RE2O3 increased AlO5 according to 27Al MQMAS NMR spectroscopic measurements. Raman spectroscopic results suggested that depolymerization of the silicate network. (10.1016/j.jnoncrysol.2018.04.028)
DOI : 10.1016/j.jnoncrysol.2018.04.028
Growth of vertically aligned carbon nanotubes on aluminum foils
- Reynaud Cécile
- Nassoy F.
- Pinault M.
- Descarpentries J.
- Coulon P-E
- Mayne-L'Hermite M.
, 2018. Forests of vertically aligned carbon nanotubes (VACNTs) are attractive nanomaterials because of their unique structural, electrical and thermal properties. However, many applications require their growth on metallic substrates. Catalytic chemical vapor deposition (CCVD) is the best method to grow them but the catalytic particles can diffuse rapidly into the metal subsurface and thus become inactive. In this communication, I will address this issue through the recent results obtained in our laboratory. I will show how it is possible to grow VACNT on carbon fibers, stainless steel and aluminum surfaces by a single-step process, namely the aerosol assisted CCVD, where the catalyst and carbon precursors are injected simultaneously. In the case of aluminum, due to its low melting temperature, the synthesis of VACNT requires a significant reduction in the growth temperature as compared to conventional substrates. Our results show that, with our single-step process, it is possible to obtain clean, long and dense VACNTs, with a growth rate at the best state of the art level for such a low temperature. A particular attention has been paid to the study of the CNT/Al interface. The results suggest the crucial role of the interface for an efficient and reproducible VACNT growth. Finally, I will show that the aerosol-assisted CCVD process can be scaled-up to enable the fabrication of innovative ultracapacitors based on VACNTs grown on aluminum foils.
X-ray characterization of textured tungsten coatings.
- Baldinozzi Gianguido
- Pontikis Vassilis
- Maroutian Thomas
- Lecoeur Philippe
, 2018.
Nonlocal and Nonadiabatic Effects in the Charge-Density Response of Solids: A Time-Dependent Density-Functional Approach
- Panholzer Martin
- Gatti Matteo
- Reining Lucia
Physical Review Letters, American Physical Society, 2018, 120 (16). (10.1103/PhysRevLett.120.166402)
DOI : 10.1103/PhysRevLett.120.166402
EPR reversible signature of self-trapped holes in fictive temperature-treated silica glass
- Lancry Matthieu
- Ollier Nadège
- Babu B.
- Herrero Christian
- Poumellec Bertrand
Journal of Applied Physics, American Institute of Physics, 2018, 123 (11), pp.113101. (10.1063/1.5023310)
DOI : 10.1063/1.5023310
A logical loophole in the derivation of the Bell inequalities
- Coddens Gerrit
, 2018. The Bell inequalities are based on a tacit assumption of a COMMON probability distribution that precludes their application to the experiments of Aspect et al.
Nonlocal Coulomb correlations in pure and electron-doped Sr2IrO4: Spectral functions, Fermi surface, and pseudo-gap-like spectral weight distributions from oriented cluster dynamical mean-field theory
- Martins Cyril
- Lenz Benjamin
- Perfetti Luca
- Brouet Véronique
- Bertrand François
- Biermann Silke
Physical Review Materials, American Physical Society, 2018, 2 (3), pp.032001(R). We address the role of nonlocal Coulomb correlations and short-range magnetic fluctuations in the high-temperature phase of Sr2IrO4 within state-of-the-art spectroscopic and first-principles theoretical methods. Introducing an “oriented-cluster dynamical mean-field scheme”, we compute momentum-resolved spectral functions, which we find to be in excellent agreement with angle-resolved photoemission spectra. We show that while short-range antiferromagnetic fluctuations are crucial to accounting for the electronic properties of Sr2IrO4 even in the high-temperature paramagnetic phase, long-range magnetic order is not a necessary ingredient of the insulating state. Upon doping, an exotic metallic state is generated, exhibiting cuprate-like pseudo-gap spectral properties, for which we propose a surprisingly simple theoretical mechanism. (10.1103/PhysRevMaterials.2.032001)
DOI : 10.1103/PhysRevMaterials.2.032001
Dynamical correlation effects in a weakly correlated material: Inelastic x-ray scattering and photoemission spectra of beryllium
- Seidu Azimatu
- Marini Andrea
- Gatti Matteo
Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2018, 97 (12). (10.1103/PhysRevB.97.125144)
DOI : 10.1103/PhysRevB.97.125144
Many-body perturbation theory and non-perturbative approaches: screened interaction as the key ingredient
- Tarantino Walter
- Mendoza Bernardo S.
- Romaniello Pina
- Berger Arjan
- Reining Lucia
Journal of Physics: Condensed Matter, IOP Publishing [1989-....], 2018, 30 (13), pp.135602. (10.1088/1361-648X/aaaeab)
DOI : 10.1088/1361-648X/aaaeab
Rendering SU(3) intuitive: Symmetries of Lorentz tensors
- Coddens Gerrit
, 2018. Under a Lorentz transformation of the electromagnetic field (E, cB) the quantity E$^2$ − c$^2$B$^2$ remains preserved. A Lorentz transformation does not preserve the energy density ε$_0$ (E$^2$ + c$^2$B$^2$) of the field. One can thus ask which are the transformations that preserve the quantity E$^2$ + c$^2$B$^2$. We show that the symmetry group of such transformations is isomorphic to SU(3). We can thus use these transformations of the electromagnetic field as a model to visualize what happens in SU(3) by analogy, just like we can use the rotation group SU(2) as a model to visualize what happens in the isospin group SU(2) by analogy.
Effect of Defect Production on Photoluminescence Properties in He ion Implanted Methylammonium Lead Tri-Iodide Perovskite Layers
- Aversa Pierfrancesco
- Lee Heejae
- Kim Minjin
- Plantevin Olivier
- Cavani Olivier
- Ollier Nadège
- Geffroy Bernard
- Corbel Catherine
, 2018.
Hydrodynamic Heat Transport Regime in Bismuth: A Theoretical Viewpoint
- Markov Maxime
- Sjakste Jelena
- Barbarino Giuliana
- Fugallo Giorgia
- Paulatto Lorenzo
- Lazzeri Michele
- Mauri Francesco
- Vast Nathalie
Physical Review Letters, American Physical Society, 2018, 120 (7). Bismuth is one of the rare materials in which second sound has been experimentally observed. Our exact calculations of thermal transport with the Boltzmann equation predict the occurrence of this Poiseuille phonon flow between ≈1.5 and ≈3.5 K, in a sample size of 3.86 and 9.06 mm, consistent with the experimental observations. Hydrodynamic heat flow characteristics are given for any temperature: heat wave propagation length, drift velocity, and Knudsen number. We discuss a gedanken experiment allowing us to assess the presence of a hydrodynamic regime in any bulk material. (10.1103/PhysRevLett.120.075901)
DOI : 10.1103/PhysRevLett.120.075901
Colour centre recovery in yttria-stabilised zirconia: photo-induced versus thermal processes
- Costantini Jean-Marc
- Touati Nadia
- Binet Laurent
- Lelong Gerald
- Guillaumet Maxime
- Beuneu François
Philosophical Magazine, Taylor & Francis, 2018, 98 (14), pp.1241-1255. The photo-annealing of colour centres in yttria-stabilized zirconia (YSZ) was studied by electron paramagnetic resonance spectroscopy upon UV-ray or laser light illumination, and compared to thermal annealing. Stable hole centres (HCs) were produced in as-grown YSZ single crystals by UV-ray irradiation at room temperature. The numbers of HCs decays to non-zero asymptotic values when UV light is set off. The HCs produced by 200-MeV Au ion irradiation are partially bleached by UV light, whereas the F$^+$-type centres (involving oxygen vacancies) were left unchanged. In contrast, a significant photo-annealing of the latter point defects was achieved in 1.4-MeV electron-irradiated YSZ by 553-nm laser light irradiation, inside the absorption band of F$^+$-type centres centred at a wavelength $\sim$550 nm. Thermal annealing of F$^+$-type centres was also followed by UV-visible absorption spectroscopy. Almost complete photo-bleaching by laser irradiation was achieved like for thermal bleaching at $\sim$500K. Kinetic rate models of colour-centre evolution are proposed for the photo-induced processes and correlated to the thermally-activated ones. (10.1080/14786435.2018.1432907)
DOI : 10.1080/14786435.2018.1432907
Energy relaxation mechanism of hot-electron ensembles in GaAs: Theoretical and experimental study of its temperature dependence
- Sjakste Jelena
- Vast Nathalie
- Barbarino Giuliana
- Calandra Matteo
- Mauri Francesco
- Kanasaki Junichi
- Tanimura Hiroshi
- Tanimura Katsumi
Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2018, 97 (6), pp.64302 - 64302. We have recently demonstrated that the fast momentum relaxation due to electron-phonon scattering of hot electrons excited into the conduction band of GaAs leads to the formation of hot-electron ensembles spread over the Brillouin zone. In the present work, we study the energy relaxation of hot-electron ensembles in GaAs, by means of ab initio calculations and time-, energy-, and momentum-resolved spectroscopy. We theoretically show that when the temperature decreases, the energy relaxation time ascribed to electron-phonon interaction becomes faster than at ambient temperature and prove that this is indeed the case in the experimental results. (10.1103/PhysRevB.97.064302)
DOI : 10.1103/PhysRevB.97.064302
Lattice constant in nonstoichiometric uranium dioxide from first principles
- Bruneval Fabien
- Freyss Michel
- Crocombette Jean-Paul
Physical Review Materials, American Physical Society, 2018, 2, pp.023801. Nonstoichiometric uranium dioxide experiences a shrinkage of its lattice constant with increasing oxygen content, in both the hypostoichiometric and the hyperstoichiometric regimes. Based on first-principles calculations within the density functional theory (DFT)+$U$ approximation, we have developed a point defect model that accounts for the volume of relaxation of the most significant intrinsic defects of UO$_2$. Our point defect model takes special care of the treatment of the charged defects in the equilibration of the model and in the determination of reliable defect volumes of formation. In the hypostoichiometric regime, the oxygen vacancies are dominant and explain the lattice constant variation with their surprisingly positive volume of relaxation. In the hyperstoichiometric regime, the uranium vacancies are predicted to be the dominating defect,in contradiction with experimental observations. However, disregarding uranium vacancies allows us to recover a good match for the lattice-constant variation as a function of stoichiometry. This can be considered a clue that the uranium vacancies are indeed absent in UO$_{2+x}$ , possibly due to the very slow diffusion of uranium. (10.1103/PhysRevMaterials.2.023801)
DOI : 10.1103/PhysRevMaterials.2.023801
Observation of large multiple scattering effects in ultrafast electron diffraction on monocrystalline silicon
- González Vallejo Isabel
- Gallé Geoffrey
- Arnaud Brice
- Scott Shelley
- Lagally Max
- Boschetto Davide
- Coulon Pierre-Eugène
- Rizza Giancarlo
- Houdellier Florent
- Le Bolloc'H David
- Faure Jérôme
Physical Review B, American Physical Society, 2018, 97 (5), pp.54302. We report on ultrafast electron diffraction on high quality single crystal silicon. The ultrafast dynamics of the Bragg peaks exhibits a giant photoinduced response which can only be explained in the framework of dynamical diffraction theory, taking into account multiple scattering of the probing electrons in the sample. In particular, we show that lattice heating following photoexcitation can cause an unexpected increase of the Bragg peak intensities, in contradiction with the well-known Debye-Waller effect. We anticipate that multiple scattering should be systematically considered in ultrafast electron diffraction on high quality crystals as it dominates the Bragg peak dynamics. In addition, taking into account multiple scattering effects opens the way to quantitative studies of nonequilibrium dynamics of defects in quasiperfect crystals. (10.1103/PhysRevB.97.054302)
DOI : 10.1103/PhysRevB.97.054302
Amyloid Fibril Analysis using Single Nanopore
- Giamblanco N.
- Coglitore D.
- Ma T.
- Coulon Pierre-Eugène
- Balanzat E.
- Bechelany Mikhael
- Janot J.M.
- Balme Sebastien
Biophysical Journal, Biophysical Society, 2018, 114 (3), pp.181a. Solid-state nanopores are versatile tools for single molecule sensing. Because their sizes can be tuned from few nm until hundreds nanometers, they are particularly promise to characterize the biomacromolecule assembly. We were interested by the detection of amyloid fibril obtained from model proteins. To reach this goal three main problems have to be tackle. First, the protein unfolding usually promotes the adsorption at solid/liquid interfaces especially by non-electrostatic interactions inducing the nanopore fouling. Second, the protein amyloid fibrils are more rigid than polymer chain. Thus their translocations require an important energy overcome to barrier of entrance and the one to escape. This is amplified by the adsorption. Finally, the characterization of the fibrillation kinetic imposes to work with very stable nanopores. We have produced different nanopores to evaluate their potentiality for amyloid fibril detection. Then, these nanopores were functionalized with PEG chain, in order to prevent the unspecific adsorption and improve their lifetime. We have studied the translocation of small protein aggregate as well as large fibrils through these nanopores. The SiN nanopore coated with PEG is limited to the detection of small protein aggregate. However, it allows the relative current blockade is related to the morphology of the aggregate. The conical nanopore on PET performed by track-etched technique is the most suitable to follow the growing of amyloid fibril due to a longer lifetime and an optimum geometry which allow to decrease the energy barrier of entrance. (10.1016/j.bpj.2017.11.1010)
DOI : 10.1016/j.bpj.2017.11.1010
Systèmes auxiliaires pour les observables : approximation du connecteur dynamique locale pour les spectres d'addition et d'émission d'électrons
- Vanzini Marco
, 2018. Cette thèse propose une méthode théorique innovante pour l'étude des spectres d'excitation à un électron, mesurée par spectroscopie de photoémission directe et inverse.La plupart des calculs actuels au niveau de l’état de l’art reposent sur des fonctions de Green à plusieurs corps et des self-énergies complexes et non locales, évaluées spécifiquement pour chaque matériau. Même lorsque les spectres calculés sont en très bon accord avec les expériences, le coût de calcul est très important. La raison est que la méthode elle-même n'est pas efficace, car elle fournit beaucoup d'informations superflues qui ne sont pas nécessaires pour l'interprétation des données expérimentales.Dans cette thèse, nous proposons deux raccourcis par rapport à la méthode standard. Le premier est l'introduction d'un système auxiliaire qui cible, en principe, le spectre d'excitation du système réel. L'exemple type est la théorie de la fonctionnelle de la densité, pour lequel le système auxiliaire est le système de Kohn-Sham : elle reproduit exactement la densité du système réel par l'intermédiaire d'un potentiel réel et statique, le potentiel de Kohn-Sham. La théorie de la fonctionnelle de la densité est, cependant, une théorie de l'état fondamental, qui ne fournit que rarement des propriétés d'état excités : un exemple est le fameux problème de la sous-estimation de la bande interdite. Le potentiel que nous proposons (le potentiel spectral), local et dépendant de la fréquence, mais réelle, peut être considéré comme une généralisation dynamique du potentiel de Kohn-Sham qui donne en principe le spectre exact.Le deuxième raccourci est l'idée de calculer ce potentiel une fois pour toute dans un système modèle, le gaz d'électrons homogène, et de le tabuler. Pour étudier des matériaux réels, nous concevons un connecteur qui prescrit l'utilisation des résultats du gaz pour calculer les spectres électroniques.La première partie de la thèse traite de l'idée de systèmes auxiliaires, montrant le cadre général dans lequel ils peuvent être introduits et les équations qu'ils doivent satisfaire. Nous utilisons des modèles de Hubbard solubles exactement pour mieux comprendre le rôle du potentiel spectral ; en particulier, il est démontré que le potentiel peut être défini uniquement chaque fois que le spectre est non nul, et donne toujours les spectres attendus, même lorsque la partie imaginaire ou les contributions non locales de la self-énergie jouent un rôle de premier plan.Dans la deuxième partie de la thèse, nous nous concentrons sur les calculs pour les systèmes réels. Nous évaluons d'abord le potentiel spectral dans le gaz d'électrons homogène, puis l'importons dans le système auxiliaire pour évaluer le spectre d'excitation. Toute l’interdependence non triviale entre l'interaction électronique et l'inhomogénéité du système réel entre dans la forme du connecteur. Trouver une expression pour cela est le véritable défi de la procédure. Nous proposons une approximation raisonnable basée sur les propriétés locales du système, que nous appelons approximation du connecteur dynamique local.Nous mettons en œuvre cette procédure pour quatre prototypes de matériaux différents : le sodium, un métal presque homogène ; l'aluminium, encore un métal mais moins homogène ; le silicium, un semi-conducteur ; l'argon, un isolant inhomogène. Les spectres que nous obtenons avec cette approche concordent de manière impressionnante avec ceux qui sont évalués via la self-énergie, très coûteuse en temps de calcul, démontrant ainsi le potentiel de cette théorie.
High-pressure phases of VO 2 from the combination of Raman scattering and ab initio structural search
- Balédent Victor
- Cerqueira Tiago
- Sarmiento-Perez Rafael
- Shukla Abhay
- Bellin Christophe
- Marsi Marino
- Itié Jean-Paul
- Gatti Matteo
- Marques Miguel
- Botti Silvana
- Rueff Jean-Pascal
Physical Review B, American Physical Society, 2018, 97 (2), pp.024107. Despite more than 50 years of investigation, the understanding of the metal-insulator transition in $VO_2$ remains incomplete and requires additional experimental and theoretical works. Using Raman scattering under pressure, we first confirm the known transition around 11 GPa affecting the V orbital occupancy in the absence of structural changes. Moreover, we disclose a transition around 19 GPa involving the V orbitals together with a structural distortion, revealed by the splitting of a phonon branch associated with the V chains. The high-pressure metallic $X$ phase is found to be of low symmetry and becomes the lowest-enthalpy structure at high pressure by ab initio structural prediction calculations. In contrast to a well-established picture of the metal-insulator transition (i.e., the Peierls transition), the high-pressure metallic phase here is of lower symmetry than the ambient pressure insulating phase. (10.1103/PhysRevB.97.024107)
DOI : 10.1103/PhysRevB.97.024107
Combined EPR and photoluminescence study of electron and proton irradiated 3C-SiC
- Al Atem Abdul Salam
- Bratus Victor
- Canut Bruno
- Lefèvre Jérémie
- Guillot G
- Bluet Jean-Marie
, 2018. In past few years, point defects in silicon carbide (SiC) have been identified as promising for applications in quantum technologies [1]. A variety of point defects in hexagonal SiC [2], including VSi and VSiVC have been optically isolated and used as single defect-based spin qubits with long coherence time [3-5]. All of this, proves that these point defects allow the SiC to be a very favorable candidate for quantum applications especially, solid state quantum bits (Qubits) and single photon source (SPS). Most of these studies were carried out on the hexagonal polytypes 4H-SiC and 6H-SiC, although the 3C-SiC polytype presents the unique advantage of integration possibility on standard Si wafer. This is due to the amount of defects (dislocation mainly) in the 3C-SiC heteroepitaxy on Si which are detrimental for long coherence time considering Qubit application. Consequently, the goal of the present study is the investigation of point defects formation after implantation by proton H + (300 keV) and irradiation by electron e-(0.8 and 2 MeV) in 3C-SiC (respectively 3C-SiC and 3C-SiC<e>) for SPS application purpose. Toward this end, we have combined two characterization techniques, the photoluminescence (PL) and the electron paramagnetic resonance (EPR). PL (12K) and EPR (70-300K) measurements will be presented in order to analyze precisely the signatures of point defects generated after these two types of irradiations. The effects of the thermal annealing (500-1000°C) were also investigated. PL spectra both for 3C-SiC and 3C-SiC<e> are presented in figure 1 for the annealing temperatures giving the highest PL signal (1000°C for 3C-SiC and 750°C for 3C-SiC<e>). We notice first that the whole PL signal is higher for 3C-SiC. In this case the spectrum is dominated by the DI defect line (possibly related to antisite pair [6]) and the E line (attributed to Si vacancy [7, 8]) while in electron irradiated sample the  line (attributed to CSiVC in a 3C-SiC nanocrystal [8]) dominates as previously reported [9]. A strong zero phonon line at 1.6 eV also appears for 3C-SiC with its phonon replica. This line was previously observed also for neutron and proton irradiated 3C-SiC and at present is of unknown origin [10, 11]. In the infrared range, the proton implantation is also more efficient to produce the VcVsi PL line with an optimum luminescence for 750°C annealing. All together, these results show that, even if the energy transferred to the host atoms during electron irradiation is quite above the displacement thresholds for both C and Si, defects involving Si vacancy are more pronounced in 3C-SiC samples. EPR spectra for 3C-SiC for isochronal annealing (30 min.) at different temperatures are presented in figure 2. The spin-three-half negatively-charged Si vacancy (the T1 center) is a dominant defect in 3C-SiC epitaxial layers corresponding to the E line in the PL spectra. Similar to neutron irradiated 3C-SiC crystals the as-implanted not annealed 3C-SiC samples demonstrate an isotropic spectrum with the g-value of 2.0029 and a superhyperfine doublet with a splitting typical to the T1 center (10.4028/www.scientific.net/MSF.963.301)
DOI : 10.4028/www.scientific.net/MSF.963.301

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