Joao Guilherme Martins Correia

CERN | CERN

Local distortions in perovskite-like orthochromites are of extreme importance for the properties they exhibit. Here, we present the results of structural and DC magnetisation measurements combined with local probe studies in polycrystalline ErCrO3. The electric field gradient (EFG) parameters’ evolution with temperature shows two clear signals of l...

Finding suitable p-type dopants, as well as reliable doping and characterization methods for the emerging wide bandgap semiconductor β - Ga2O3 could strongly influence and contribute to the development of the next generation of power electronics. In this work, we combine easily accessible ion implantation, diffusion and nuclear transmutation method...

The interest in Be as an impurity in GaN stems from the challenge to understand why GaN can be doped p type with Mg, while this does not work for Be. While theory has actually predicted an acceptor level for Be that is shallower than Mg, it was also argued that Be is not a suitable acceptor because its amphoteric nature, i.e., its tendency to occup...

Profound understanding of the local electronic and defect structure in semiconductors always plays a vital role in the further developing of applications of such materials. In the present work an investigation of the electronic structure in hydrogenated TiO2 (rutile) thin films is conducted by virtue of Time-Differential γ-γ Perturbed Angular Corre...

The β decay of the neutron-rich In134 and In135 was investigated experimentally in order to provide new insights into the nuclear structure of the tin isotopes with magic proton number Z=50 above the N=82 shell. The β-delayed γ-ray spectroscopy measurement was performed at the ISOLDE facility at CERN, where indium isotopes were selectively laser-io...

We examined the interaction between adatoms and graphene for Ag, Cd, In and Hg by density functional theory. We establish a relation between the binding energy and the electric-field gradient tensor (EFG) for each atom, which indicates that hyperfine interactions can be used to probe the binding and stability of adatoms on graphene. The EFG is also...

Recent developments in position sensitive detectors pave a way towards the efficient realization of Rutherford Backscattering Spectrometry/Channeling experiments in blocking geometry. Here we report on the use of a Timepix position sensitive detector (PSD) for this kind of studies. The blocking geometry in combination with a PSD brings the advantag...

Accurate nuclear quadrupole moment values are essential as benchmarks for nuclear structure models and for the interpretation of experimentally determined nuclear quadrupole interactions in terms of electronic and molecular structure. Here, we present a novel route to such data by combining perturbed γ-γ angular correlation measurements on free sma...

The interest in understanding the interaction between graphene and atoms that are adsorbed on its surface (adatoms) spans a wide range of research fields and applications, for example, to controllably change the properties of graphene in electronic devices or to detect those changes in graphene-based sensors. We present a density functional theory...

The lattice location of ion implanted radioactive ²⁴Na (t1/2 = 14.96 h) in GaN and AlN was determined using the emission channeling technique at the ISOLDE/CERN facility. In the room temperature as-implanted state in both GaN and AlN, the majority of the sodium atoms are found on interstitial sites near the octahedral position, with a minority on c...

The lattice location of ion implanted radioactive ²⁴Na (t1/2 = 14.96 h) in GaN and AlN was determined using the emission channeling technique at the ISOLDE/CERN facility. In the room temperature as-implanted state in both GaN and AlN, the majority of the sodium atoms are found on interstitial sites near the octahedral position, with a minority on c...

We demonstrate formation of the ideal split-vacancy configuration of the Sn-vacancy center upon implantation into natural diamond. Using β− emission channeling following low fluence Sn121 implantation (2×1012 atoms/cm2, 60 keV) at the ISOLDE facility at CERN, we directly identified and quantified the atomic configurations of the Sn-related centers....

Background Human leukocyte antigen (HLA) B*51 allele is the most important genetic factor in susceptibility to Behçet’s disease (BD), an immune-mediated systemic disorder of unknown etiology, characterized by recurrent episodes of inflammatory manifestations. In fact there is a considerable clinical overlap of BD with autoinflammatory syndromes. As...

Rare-earth orthochromites with distorted perovskite structure (e.g. RCrO3, R = Sm, Gd) have been under strong debate with respect to the origin of their ferroelectric order. Of particular interest is the question of whether such orthochromites are, in fact, magnetically driven improper ferroelectrics, as many rare-earth manganites or orthoferrites....

The acquisition of two-dimensional (2D) channeling patterns is gaining increased popularity within the ion beam community. However, with the exception of emission channeling experiments for the lattice location of radioactive impurities, quantitative analysis of such patterns is rarely found. We present a general description of the statistical data...

In (Ga,Mn)As, a model dilute magnetic semiconductor, the electric and magnetic properties are strongly influenced by the lattice sites occupied by the Mn atoms. In particular, the highest Curie temperatures are achieved upon thermal annealing in a narrow temperature window around 200∘C, by promoting the diffusion of interstitial Mn towards the surf...

Finding suitable p-type dopants, as well as reliable doping and characterization methods for the emerging wide bandgap semiconductor $\beta$-$Ga_2O_3$ could strongly influence and contribute to the development of the next generation of power electronic. In this work, we combine easily accessible ion implantation, diffusion and nuclear transmutation...

Finding suitable p-type dopants, as well as reliable doping and characterization methods for the emerging wide bandgap semiconductor β-Ga2O3 could strongly influence and contribute to the development of the next generation of power electronics. In this work, we combine easily accessible ion implantation, diffusion and nuclear transmutation methods...

A new approach to observe the radiative decay of the Th229 nuclear isomer, and to determine its energy and radiative lifetime, is presented. Situated at a uniquely low excitation energy, this nuclear state might be a key ingredient for the development of a nuclear clock or a nuclear laser and, the search for time variations of fundamental constants...

We report on the lattice location of low-fluence ion implanted ¹²⁴In in single-crystalline 3C-SiC by means of the emission channeling technique using radioactive isotopes produced at the ISOLDE/CERN facility. In the sample implanted at room temperature to a fluence of 4 × 1012 cm⁻², 60(9)% of the In atoms were found slightly displaced (0.12–0.20 Å)...

A new approach to observe the radiative decay of the $^{229}$Th nuclear isomer, and to determine its energy and radiative lifetime, is presented. Situated at a uniquely low excitation energy, this nuclear state might be a key ingredient for the development of a nuclear clock, a nuclear laser and the search for time variations of the fundamental con...

Strain is a critical parameter affecting the growth and the performance of many semiconductor systems but, at the same time, the accurate determination of strain profiles in heterostructures can be challenging, especially at the nanoscale. Ion channelling/blocking is a powerful technique for the detection of the strain state of thin films, normally...

Using radioactive isotopes produced at the CERN-ISOLDE facility, the lattice location of the implanted transition metal (TM) ions ⁵⁶Mn, ⁵⁹Fe and ⁶⁵Ni in n-type single-crystalline hexagonal 6H-SiC was studied by means of the emission channeling technique. TM probes on carbon coordinated tetrahedral interstitial sites (T C) and on substitutional sili...

γ−Fe and related alloys are model systems of the coupling between structure and magnetism in solids. Since different electronic states (with different volumes and magnetic ordering states) are closely spaced in energy, small perturbations can alter which one is the actual ground state. Here, we demonstrate that the ferromagnetic state of γ−Fe nanop...

Solid State research at ISOLDE has been running since the mid-1970s and accounts for about 10-15% of the overall physics programme. ISOLDE is the world flagship for the on-line production of exotic radioactive isotopes, with high yields, high elemental selectivity and isotopic purity. Consequently, it hosts a panoply of state-of-the-art nuclear tec...

We have investigated the lattice location of implanted transition metal (TM) ⁵⁶Mn, ⁵⁹Fe and ⁶⁵Ni ions in undoped single-crystalline cubic 3C-SiC by means of the emission channeling technique using radioactive isotopes produced at the CERN-ISOLDE facility. We find that in the room temperature as-implanted state, most Mn, Fe and Ni atoms occupy carbo...

Time differential perturbed angular correlation (TDPAC) of γ-rays spectroscopy has been applied in chemistry and biochemistry for decades. Herein we aim to present a comprehensive review of chemical and biochemical applications of TDPAC spectroscopy conducted at ISOLDE over the past ~15 years, including elucidation of metal site structure and dynam...

We present a study of TiO2 single crystals from the point of view of the dopant atom that simultaneously behaves as the probing element. We used gamma-gamma time dependent perturbed angular correlations working with selected tracer elements (¹¹¹In/ ¹¹¹Cd, 111mCd/ ¹¹¹Cd) together to investigate the different behavior of Cd and In dopants, particular...

The angular distribution of β ⁻ particles emitted by the radioactive isotope ²⁴Na was monitored following implantation into ZnO single crystals at fluences above 5 × 10¹² cm⁻² at CERN's ISOLDE facility. We identified sodium on two distinct sites: on substitutional Zn sites and on interstitial sites that are close to the so-called octahedral site. T...

Time Differential Perturbed Angular Correlation of γ-rays (TDPAC) experiments were performed for the first time in the decay of 68m Cu produced at the ISOLDE facility at CERN. Due to the short half-life of the source isotope, the measurements were carried out online. The intermediate state offers the unique opportunity to study the electromagnetic...

In 2010 we presented an update of the nuclear quadrupole moments (Q) for the Cd and Zn isotopes, based essentially on straightforward density functional (DF) calculations (H. Haas and J.G. Correia, Hyperfine Interact 198, 133–137 (2010)). It has been apparent for some years that the standard DF procedure obviously fails, however, to reproduce the k...

Mn-doped Si has attracted significant interest in the context of dilute magnetic semiconductors. We investigated the lattice location of implanted Mn in silicon of different doping types (n, \(n^+\) and \(p^+\)) in the highly dilute regime. Three different lattice sites were identified by means of emission channeling experiments: ideal substitution...

The VITO (Versatile Ion-polarized Techniques Online) project is a new experimental setup at the ISOLDE facility at CERN. VITO is a dedicated beam line for producing laser-induced spin-polarized beams of both, atoms and ions, and it has been commissioned in response to the continuously growing demand for the use of spin-polarized beams. The new VITO...

Although the formation of transition metal-boron pairs is currently well established in silicon processing, the geometry of these complexes is still not completely understood. We investigated the lattice location of the transition metals manganese, iron, cobalt and nickel in n- and -type silicon by means of electron emission channeling. For mangane...

Diffuse alveolar hemorrhage (DAH) is a rare but potentially catastrophic manifestation with a high mortality. Among rheumatologic diseases, it occurs most frequently in patients with systemic lupus erythematosus (SLE) and systemic vasculitis. Despite new diagnostic tools and therapies, it remains a diagnostic and therapeutic challenge. The aim of t...

Background Inflammation is a well-known key component in type 2 diabetes, obesity and cardiovascular disease. It is then expected that patients with chronic inflammatory diseases such as Rheumatoid Arthritis (RA) are at increased riskof metabolic syndrome and its components. Objectives To define the prevalence of metabolic comorbidities (obesity, d...

We determined the lattice location of Mn in ferromagnetic (Ga,Mn)As using the electron emission channeling technique. We show that interstitial Mn occupies the tetrahedral site with As nearest neighbors (TAs) both before and after thermal annealing at 200 °C, whereas the occupancy of the tetrahedral site with Ga nearest neighbors (TGa) is negligibl...

30 keV 111mCd and 50 keV 199mHg beams from ISOLDE were used to implant on preformed targets of C60 with a thickness of 1 mg cm−2. Endofullerene compounds, viz. 111mCd@C60 and 199mHg@C60 formed during implantation were separated by filtration through micropore filter paper followed by solvent extraction. Dried samples of the endofullerene compounds...

The magnetic and electric properties of impurities in semiconductors are strongly dependent on the lattice sites which they occupy. While the majority site can often be predicted based on chemical similarities with the host elements and is usually simple to confirm experimentally, minority sites are far more complicated to predict, detect and ident...

We model the ferroelectric and paraelectric phases in the YMnO3 and YMn2O5, compounds with discussion of the hyperfine parameters at the atomic nuclei: electric field gradient and magnetic hyperfine field, using first-principles density functional theory FP-L/APW+lo method (WIEN2K code). The differences of the changes in hyperfine properties and th...

We report perturbed angular correlation measurements with (111m)Cd/(111)Cd and (111)In/(111)Cd probes, at the ISOLDE-CERN facility, in the manganite compounds BaMnO3, with the 6H and 15R polymorphs, and SrMnO3, with the 4H polymorph. The electric field gradient (EFG) is measured, and found approximately constant in a large temperature range for all...

Ga2O3 bulk single crystals have been implanted with 300 keV Europium ions to fluences ranging from 1×1013 to 4×1015 at/cm2. The damage build-up and Eu-incorporation was assessed by Rutherford Backscattering Spectrometry in the channeling mode (RBS/C). RBS/C results suggest that implantation causes a mixture of defect clusters and extended defects s...

The LaMnO 3.08 manganite system was studied as a function of temperature ranging from 10 up to 292 K using the perturbed angular correlation local probe technique at ISOLDE-CERN facility. The electrical field gradient (EFG) measurements performed across the different temperatures revealed a single EFG distribution, corresponding to a unique probe l...

We report on the lattice location and thermal stability of Fe in n +- and p +-type silicon. By means of emission channeling we have observed Fe on ideal substitutional sites, sites located in between bond-centered (BC) and substitutional sites, and sites displaced from tetrahedral towards anti-bonding sites. Here, we focus our analysis on the ident...

We have studied the lattice location of implanted nickel in silicon, for different doping types (n, n+, and p+). By means of on-line emission channeling, 65Ni was identified on three different sites of the diamond lattice: ideal substitutional sites, displaced bond-center towards substitutional sites (near-BC), and displaced tetrahedral interstitia...

The lattice site location of radioactive 27Mg implanted in AlN was determined by means of emission channeling. The majority of the 27Mg was found to substitute for Al, yet significant fractions (up to 33%) were also identified close to the octahedral interstitial site. The activation energy for interstitial Mg diffusion is estimated to be between 1...

We present emission channeling experiments on the lattice location of Er in CZ Si single crystals with a well-defined O concentration of 6.5–6.6×1017 cm−3 and 60 keV-implanted Tm+Er doses ranging from 4.3×1012 to 3.6×1013 cm−2. The experimental results are compared with the predictions of a simulator which models the formation of ErnOm clusters on...

We report on the lattice location of Mn in wurtzite GaN using β− emission channeling. In addition to the majority substituting for Ga, we locate up to 20% of the Mn atoms in N sites. We propose that the incorporation of Mn in N sites is enabled under sufficiently high concentrations of N vacancies, and stabilized by a highly charged state of the Mn...

We report on β− emission channeling experiments on the lattice location and thermal stability of Mn impurities (<0.05%) in both semi-insulating and heavily n-type doped GaAs. In addition to the majority of the Mn impurities substituting for Ga, up to 30% occupy tetrahedral interstitial sites with As nearest neighbors. Whereas the interstitial fract...

In this work we report on the lattice site location of rare earths in single-crystalline ZnO by means of the emission channeling (EC) technique. Following low dose (3x10E13at/cm2) 60 keV ion implantation of the precursor isotope 169Yb, a position-sensitive electron detector was used to monitor the angular distribution of the conversion electrons em...

YBa2Cu3O6+x (YBCO) superconducting thin films implanted with low doses of radioactive 197mHg and 199mHg isotopes were studied with a combination of nuclear and non-nuclear characterization techniques. We show that after implantation Hg lies on an unique site in the YBCO lattice and the critical temperature increases slightly with the increase of th...

High quality YBa2Cu3O6+x (YBCO) superconducting thin films were implanted with the radioactive 197m Hg (T1/2 = 24 h) isotope to low fluences of 10^13 atoms/cm^2 and 60 keV energy. The lattice location and stability of the implanted Hg were studied combining the Perturbed Angular Correlation (PAC) and Emission Channeling (EC) techniques. We show tha...

Electric field gradients (EFG) on mercury sites of the Hg1201 high-TC superconductors were measured with the perturbed angular correlation (PAC) technique. In Hg1201 samples where PAC detects higher oxygen content the EFGs have decreased to lower values indicating an elongation of the Hg-apical oxygen dumbbell. On the same samples the asymmetry par...

We report on the lattice location of implanted 59Fe in n+- and p+-type Si by means of emission channeling. We found clear evidence that the preferred lattice location of Fe changes with the doping of the material. While in n+-type Si Fe prefers displaced bond-centered (BC) sites for annealing temperatures up to 600ºC, changing to ideal substitution...

As the intrinsic origin of the high-temperature ferromagnetism often observed in wide-gap dilute magnetic semiconductors becomes increasingly debated, there is a growing need for comprehensive studies on the single-phase region of the phase diagram of these materials. Here we report on the magnetic and structural properties of Fe-doped ZnO prepared...

The evolution of the local Jahn-Teller distortion across the LaMnO3+Δ phase diagram was obtained using the perturbed angular correlation local probe technique. We found that upon doping, the local distortion decreases continuously with increasing doping and that no fully Jahn-Teller distorted Mn(3+)O6 octahedra are observed within the orthorhombic...

We report on the lattice location of implanted Ni in ZnO using the β- emission channeling technique. In addition to the majority substituting for the cation (Zn), a significant fraction of the Ni atoms occupy anion (O) sites. Since Ni is chemically more similar to Zn than it is to O, the observed O substitution is rather puzzling. We discuss these...

Highly ordered La(2/3)Ca(1/3)MnO(3) nanotube arrays were successfully synthesized by a simple and rapid process, combining nanoporous alumina template-assisted synthesis with microwave irradiation. The method offers a quick hands-on route to produce manganite bulk sample and nanotube arrays at relative low-temperatures. We obtain thin wall nanotube...

30 keV 111mCd and 50 keV 199mHg beams from ISOLDE were used to implant on preformed target of C60 with the thickness of 1 mg/cm2. Endofullerene compounds, viz.,111mCd@C60 and 199mHg@C60 formed during implantation were separated by filtration through micropore filter paper followed by solvent extraction. Dried samples of the endofullerene compounds...

The concept and functionality of an apparatus dedicated to emission channeling experiments using short-lived isotopes on-line at ISOLDE∕CERN is described. The setup is assembled in two functional blocks - (a) base stand including beam collimation, implantation and measurement chamber, cryogenic extension, and vacuum control system and (b) Panmure g...

Combined high precision RBS/channeling, NRA/channeling and perturbed angular correlation studies were used to characterize near-stoichiometric and congruent LiNbO3 crystals. In congruent LiNbO3 two non-equivalent Li sites are distinguished whereas in near-stoichiometric LiNbO3 only one of them exists. A comparison of the experimental results with M...

The versatility of perturbed angular correlations (PAC) in the study of nanostructures and thin films is demonstrated, namely for the specific cases of ZnO/CdxZn1−xO thin films and Ga2O3 powder pellets and nanowires, examples of transparent conductive oxides. PAC measurements as a function of annealing temperature were performed after implantation...

Applications of nanomaterials rely on their tunable properties with large-scale integration feasibility. Advantages can be envisaged by merging nanostructures with thin film technologies, where ion implantation can be used as an integrated part of the processes. Still, ion implantation carries along with its benefits undesired intrinsic defects. Tw...

The LaMnO 3.08 manganite system was studied as a function of temperature ranging from 10 up to 292 K using the perturbed angular correlation local probe technique at ISOLDE-CERN facility. The electrical field gradient (EFG) measurements performed across the different temperatures revealed a single EFG distribution, corresponding to a unique probe l...