Ionut Balasa - Academia.edu (original) (raw)

Papers by Ionut Balasa

Materials for quantum technology, Nov 14, 2022

The negatively charged nitrogen-vacancy centre (so-called NV-centre) in diamond is one of the mos... more The negatively charged nitrogen-vacancy centre (so-called NV-centre) in diamond is one of the most promising systems for applications in quantum technologies because of the possibility to optically manipulate and read out the spin state of this defect, even at room temperature. Nevertheless, obtaining high NV densities (>500 ppb) close to the surface (5–20 nm) while maintaining good spin properties remain challenging. In this work we rely on a versatile ion implantation system allowing both implanting nitrogen using N2 + and creating vacancies with He+ ion bombardment at variable energies and fluence to create shallow NV ensembles. By optimizing the ion irradiation conditions as well as the surface preparation prior to treatment we successfully increase the amount of created colour centres while demonstrating narrow magnetic resonance linewidths.

To Illi and my family Life does not conclude. And life knows nothing of names. This tree, tremulo... more To Illi and my family Life does not conclude. And life knows nothing of names. This tree, tremulous pulse of new leaves. I am this tree. Tree, cloud; tomorrow book or wind: the book I read, the wind I drink. All outside, wandering.

Materials for Quantum Technology

The aim of this work is the study, the design and the nanofabrication of innovative plasmonic nan... more The aim of this work is the study, the design and the nanofabrication of innovative plasmonic nanostructured materials to develop label-free optical biosensors. Noble metalbased nanostructures have gained interest in the last years due to their extraordinary optical properties, which allow to develop optical biosensors able to detect very low concentrations of specific biomolecules, called analyte, down to the picomolar range. Such biosensors rely on the Surface Plasmon Resonance (SPR) excitation which occurs under specific conditions that depend both on the morphology of the nanostructure and on the adjacent dielectric medium. Therefore, the binding of the biomolecules to metal surfaces is revealed as a change in the SPR condition. Four kinds of nanostructures are investigated in this work: ordered and disordered nanohole array (o-NHA, d-NHA), nanoprism array (NPA) and nanodisk array (NDA). The o-NHA and d-NHA consist of a thin metallic film (50 - 100 nm) patterned with, respective...

Materials

In recent years the quest for novel materials possessing peculiar abilities of manipulating light... more In recent years the quest for novel materials possessing peculiar abilities of manipulating light at the nanoscale has been significantly boosted due to the strict demands of advanced nanophotonics and quantum technologies. In this framework radiative decay engineering of quantum emitters is of paramount importance for developing efficient single-photon sources or nanolasers. Hyperbolic metamaterials stand out among the best cutting-edge candidates for photoluminescence control owing to their potentially unlimited photonic density of states and their ability to sustain high-k modes that allow us to strongly enhance the radiative decay rate of quantum light emitters. The aim of the present paper is to show how Au/Al2O3 hyperbolic multilayers can be used to selectively control the photoluminescence of coupled Eu3+ emitters. We point out an enhancement of the Eu3+ transitions when they are in the hyperbolic regime of the metamaterials and a significant alteration of the ED and MD branc...

Physical Review Applied

Metamaterials with properly engineered linear and nonlinear optical response are of great interes... more Metamaterials with properly engineered linear and nonlinear optical response are of great interest for many advanced applications in nanophotonics and quantum optics. In the present work, we perform a detailed spectral investigation of the third-order nonlinear optical properties (nonlinear refractive index and nonlinear absorption coefficient) of-near-zero Au/Al 2 O 3 multilayer metamaterials in a broad range of the visible spectrum across their-near-zero (ENZ) wavelength, at different incidence angles with TEand TM-polarized light. Multilayers with different gold filling fractions (16 and 33%) are produced by magnetron sputtering to tune the spectral position of the-near-zero wavelength. The results demonstrate that a continuous modulation of the linear and nonlinear optical parameters of these metamaterials can be obtained as a function of the angle of incidence, with a peak of the nonlinear optical coefficients close to the ENZ wavelength. A model is proposed to describe the nonlinear optical response of the metamaterials, and an optimal agreement between experimental and simulated results is obtained in all the configurations explored. This model represents a useful tool to design multilayer metamaterials with tailored nonlinear optical properties, to be used in different experimental configurations.

OSA Nonlinear Optics 2021, 2021

We demonstrate the angle, polarization and intensity tunability of the optical Kerr effect in gol... more We demonstrate the angle, polarization and intensity tunability of the optical Kerr effect in gold/alumina metamaterials investigated by the z-scan technique. We propose a model to predict their effective nonlinear refractive index and absorption coefficient.

The linear and nonlinear optical properties of nanostructured materials have been the object of n... more The linear and nonlinear optical properties of nanostructured materials have been the object of numerous studies due to the possibility of tailoring these properties by manipulation of their material structure; composition, particle size, and shape are some of the parameters considered for tuning the nonlinear response. The localized surface plasmon resonances encountered for metallic inclusions in dielectric media have been thoroughly investigated. Most systems consist of randomly placed nanoparticles contained in another medium. Due to the randomness of the system, the response of such a system can be seen as an incoherent addition of the individual response of each nanoparticle. By contrast, an ordered array of nanoelements in principle would allow a response that is the coherent addition of the individual element responses, and hence large effective nonlinear parameters can be expected that will also exhibit the symmetry properties of the structure. In this work, we will present...

Physical Review Applied, 2020

We study, both experimentally and theoretically, the modification of Er 3+ photoluminescence prop... more We study, both experimentally and theoretically, the modification of Er 3+ photoluminescence properties in Si dielectric nanoslots. The ultrathin nanoslot (down to 5-nm thickness), filled with Er in SiO 2 , boosts the electric and magnetic local density of states via coherent near-field interaction. We report an experimental 20-fold enhancement of the radiative decay rate with negligible losses. Moreover, via modifying the geometry of the all-dielectric nanoslot, the outcoupling of the emitted radiation to the far field can be strongly improved, without affecting the strong decay-rate enhancement given by the nanoslot structure. Indeed, for a periodic square array of slotted nanopillars an almost one-order-of-magnitude-higher Er 3+ PL intensity is measured with respect to the unpatterned structures. This has a direct impact on the design of more efficient CMOS-compatible light sources operating at telecom wavelengths.

Applied Surface Science, 2021

Abstract The sensing mechanism of plasmonic nanohole arrays is investigated and a novel model is ... more Abstract The sensing mechanism of plasmonic nanohole arrays is investigated and a novel model is proposed to interpret their optical response over a wide dynamic range of concentrations ( 10 - 13 - 10 - 5 M), based on a double-Langmuir model. This model describes the signal response of the analyte binding as the sum of two independent contributions which are related to two different surface regions of the biosensor, namely the top gold surface of the nanohole array and the lateral gold area inside the nanoholes. Numerical simulations highlight the different near-field behaviour of these two regions and their very different refractive index sensitivities, which both support the double-Langmuir model. This is corroborated by experimental biosensing measurements with gold nanohole arrays with hexagonal symmetry, synthesized by nanosphere lithography. Their sensing performances are optimized by numerical simulations by changing their geometrical parameters (i.e., lattice constant, nanohole diameter and height) in order to achieve a maximum sensitivity. For the biosensing experiments, the biotin-streptavidin complex is used as a benchmark test for the optimized nanohole array and a robust calibration is provided by the double-Langmuir model obtaining a limit of detection of 0.3 ng/mL, which corresponds to an absolute analyte quantity of 0.02 fmol.

Nanoscale Advances, 2020

Non-interacting, disordered plasmonic nanodisk arrays have competitive performances for local and... more Non-interacting, disordered plasmonic nanodisk arrays have competitive performances for local and bulk sensing and a large stability basin around the maximum sensitivities.

Surface and Coatings Technology, 2020

Abstract The stability upon air-annealing of uncapped Au-Co thin films is investigated. The analy... more Abstract The stability upon air-annealing of uncapped Au-Co thin films is investigated. The analysis focuses on the modifications of the crystalline fraction of the films produced by physical vapor deposition. The film with the highest Au concentration exhibits the strongest diffraction signal, corresponding to a Au-rich fcc AuxCo1−x solid solution alloy, with nanocrystals which have a rod-like shape. Air annealing induces a progressive de-alloying which is complete at 500 °C, as shown by X-ray Absorption Spectroscopy and X-ray diffraction. The film, that is directly exposed to the oxidizing atmosphere, undergoes a de-wetting process, likely triggered by Au. X-ray nanoimaging mapping enlightens the presence of interpenetrating sub-μm Au and Co3O4 domains. This peculiar annealed nanostructured system can have interesting applications in the field of catalysis.

Applied Surface Science, 2019

We evaluate the performance of an adhesion buffer layer between ordered metal nanoparticle arrays... more We evaluate the performance of an adhesion buffer layer between ordered metal nanoparticle arrays and dielectric substrates on the particles' morphological manipulation by pulsed laser irradiation. The experiments are performed irradiating with only one nanosecond pulse at 355 nm, triangular nanoprism arrays fabricated by nanosphere lithography (polystyrene spheres with 1030 nm in diameter), followed by film deposition by magnetron sputtering. The reshaping of the nanoprisms into spheres as result of laser-induced melting is investigated for three different materials: prisms made of Cr, Au and Au with a buffer layer made of Cr (Au/Cr). These elements are chosen because their interfacial interaction with the substrates (soda-lime glass and fused silica) is quite different. Our results show that single pulse irradiation at fluences above the metal melting threshold allows the formation of disorder spheres for the case of Au, but ordered spheres for the cases of Cr and Cr/Au. Therefore, the function of the buffer layer is to improve the adhesion between the prisms and the substrate, thus allowing their reshaping by laser-induced melting but preserving their position. The strong interaction between Cr and the substrate is also exploited for the nanostructuration of the substrate by the formation of ordered holes with submicrometer dimensions. These findings reboot laser postprocessing of ordered structures fabricated by nanosphere lithography exploit to explore new capacities of nanostructuration.

Materials Science in Semiconductor Processing, 2019

The capability to develop novel nanomaterials with properly tailored optical properties is of gre... more The capability to develop novel nanomaterials with properly tailored optical properties is of great interest for many nanophotonic applications. In the present work, 2D-ordered plasmonic nanoarrays with different morphologies, as nanoprism, nanoparticle, nanohole and semi-nanoshell arrays, are realized by nanosphere lithography, combining metal depositions, reactive ion etching and thermal treatments. By controlling the processing parameters, the plasmonic properties of the nanoarrays can be tailored, engineering the optical functionalities of the plasmonic nanosystems. Some selected examples are presented to show the potentialities of the synthesized nanoarrays in different fields: to realize ultra-fast and tunable nonlinear optical materials, to enhance the quantum efficiency of nearby rare-earth emitters and to develop high-sensitivity, label-free biosensors. The versatility of the fabrication technique gives the possibility to design different configurations and many other applications can be envisaged for these plasmonic nanoarrays in advanced nanophotonic devices.

physica status solidi (a), 2017

Plasmonic nanostructures have been the object of strong scientific interest in the last decade fo... more Plasmonic nanostructures have been the object of strong scientific interest in the last decade for their linear and nonlinear optical properties. The present work is focused on the capability to control and enhance the Er 3þ emission efficiency in silica by near-field coupling with plasmonic and pre-plasmonic nanostructures. The results shows that more than one order of magnitude Er 3þ PL enhancement can be obtained with ultra-small pre-plasmonic Ag clusters synthesized by ion implantation and thermal annealing. Moreover, resonantly coupled extended plasmonic nanostructures in the form of gold nanohole arrays can efficiently interact with the Er ions, leading to a 20-fold increase of their radiative emission at 1.54 μm.