Controlling the helicity of light by electrical magnetization switching

Controlling the intensity of emitted light and charge current is the basis of transferring and processing information1. By contrast, robust information storage and magnetic random-access memories are implemented using the spin of the carrier and the associated magnetization in ferromagnets2. The missing link between the respective disciplines of photonics, electronics and spintronics is to modulate the circular polarization of the emitted light, rather than its intensity, by electrically controlled magnetization. Here we demonstrate that this missing link is established at room temperature and zero applied magnetic field in light-emitting diodes2-7, through the transfer of angular momentum between photons, electrons and ferromagnets. With spin-orbit torque8-11, a charge current generates also a spin current to electrically switch the magnetization. This switching determines the spin orientation of injected carriers into semiconductors, in which the transfer of angular momentum from the electron spin to photon controls the circular polarization of the emitted light2. The spin-photon conversion with the nonvolatile control of magnetization opens paths to seamlessly integrate information transfer, processing and storage. Our results provide substantial advances towards electrically controlled ultrafast modulation of circular polarization and spin injection with magnetization dynamics for the next-generation information and communication technology12, including space-light data transfer. The same operating principle in scaled-down structures or using two-dimensional materials will enable transformative opportunities for quantum information processing with spin-controlled single-photon sources, as well as for implementing spin-dependent time-resolved spectroscopies.

Hyperdoped Si nanocrystals embedded in silica for infrared plasmonics

We present the experimental realization of plasmonic hyperdoped Si nanocrystals embedded in silica via a combination of sequential low energy ion implantation and rapid thermal annealing. We show that phosphorus dopants are incorporated into the nanocrystal cores at concentrations up to six times higher than P solid solubility in bulk Si by combining 3D mapping with atom probe tomography and analytical transmission electron microscopy. We shed light on the origin of nanocrystal growth at high P doses, which we attribute to Si recoiling atoms generated in the matrix by P implantation, which likely increase Si diffusivity and feed the Si nanocrystals. We show that dopant activation enables partial nanocrystal surface passivation that can be completed by forming gas annealing. Such surface passivation is a critical step in the formation of plasmon resonance, especially for small nanocrystals. We find that the activation rate in these small doped Si nanocrystals is the same as in bulk Si under the same doping conditions.

Highly Luminescent and Photostable Core/Shell/Shell ZnSeS/Cu:ZnS/ZnS Quantum Dots Prepared via a Mild Aqueous Route

An aqueous-phase synthesis of 3-mercaptopropionic acid (3-MPA)-capped core/shell/shell ZnSeS/Cu:ZnS/ZnS QDs was developed. The influence of the Cu-dopant location on the photoluminescence (PL) emission intensity was investigated, and the results show that the introduction of the Cu dopant in the first ZnS shell leads to QDs exhibiting the highest PL quantum yield (25%). The influence of the Cu-loading in the dots on the PL emission was also studied, and a shift from blue-green to green was observed with the increase of the Cu doping from 1.25 to 7.5%. ZnSeS/Cu:ZnS/ZnS QDs exhibit an average diameter of 2.1 ± 0.3 nm and are stable for weeks in aqueous solution. Moreover, the dots were found to be photostable under the continuous illumination of an Hg-Xe lamp and in the presence of oxygen, indicating their high potential for applications such as sensing or bio-imaging.

Mn-Doped Quinary Ag-In-Ga-Zn-S Quantum Dots for Dual-Modal Imaging

Doping of transition metals within a semiconductor quantum dot (QD) has a high impact on the optical and magnetic properties of the QD. In this study, we report the synthesis of Mn²⁺-doped Ag-In-Ga-Zn-S (Mn:AIGZS) QDs via thermolysis of a dithiocarbamate complex of Ag⁺, In³⁺, Ga³⁺, and Zn²⁺ and of Mn(stearate)₂ in oleylamine. The influence of the Mn²⁺ loading on the photoluminescence (PL) and magnetic properties of the dots are investigated. Mn:AIGZS QDs exhibit a diameter of ca. 2 nm, a high PL quantum yield (up to 41.3% for a 2.5% doping in Mn²⁺), and robust photo- and colloidal stabilities. The optical properties of Mn:AIGZS QDs are preserved upon transfer into water using the glutathione tetramethylammonium ligand. At the same time, Mn:AIGZS QDs exhibit high relaxivity (r ₁ = 0.15 mM^-1 s^-1 and r ₂ = 0.57 mM^-1 s^-1 at 298 K and 2.34 T), which shows their potential applicability for bimodal PL/magnetic resonance imaging (MRI) probes.

Influence of phosphorus on the growth and the photoluminescence properties of Si-NCs formed in P-doped SiO/SiO2 multilayers

This work reports on the influence of phosphorous atoms on the phase separation process and optical properties of silicon nanocrystals (Si-NCs) embedded in phosphorus doped SiO/SiO₂ multilayers. Doped SiO/SiO₂ multilayers with different P contents have been prepared by co-evaporation and subsequently annealed at different temperatures up to 1100 °C. The sample structure and the localization of P atoms were both studied at the nanoscale by scanning transmission electron microscopy and atom probe tomography. It is found that P incorporation modifies the mechanism of Si-NC growth by promoting the phase separation during the post-growth-annealing step, leading to nanocrystal formation at lower annealing temperatures as compared to undoped Si-NCs. Hence, the maximum of Si-NC related photoluminescence (PL) intensity is achieved for annealing temperatures lower than 900 °C. It is also demonstrated that the Si-NCs mean size increases in the presence of P, which is accompanied by a redshift of the Si-NC related emission. The influence of the phosphorus content on the PL properties is studied using both room temperature and low temperature measurements. It is shown that for a P content lower than about 0.1 at%, P atoms contribute to significantly improve the PL intensity. This effect is attributed to the P-induced-reduction of the number of non-radiative defects at the interface between Si-NCs and SiO₂ matrix, which is discussed in comparison with hydrogen passivation of Si-NCs. In contrast, for increasing P contents, the PL intensity strongly decreases, which is explained by the growth of Si-NCs reaching sizes that are too large to ensure quantum confinement and to the localization of P atoms inside Si-NCs.

Large Perpendicular Magnetic Anisotropy in Ta/CoFeB/MgO on Full-Coverage Monolayer MoS2 and First-Principles Study of Its Electronic Structure

A perpendicularly magnetized spin injector with a high Curie temperature is a prerequisite for developing spin optoelectronic devices on two-dimensional (2D) materials working at room temperature (RT) with zero applied magnetic field. Here, we report the growth of Ta/CoFeB/MgO structures with large perpendicular magnetic anisotropy (PMA) on full-coverage monolayer (ML) molybdenum disulfide (MoS₂). A large perpendicular interface anisotropy energy of 0.975 mJ/m² has been obtained at the CoFeB/MgO interface, comparable to that observed in magnetic tunnel junction systems. It is found that the insertion of MgO between the ferromagnetic (FM) metal and the 2D material can effectively prevent the diffusion of the FM atoms into the 2D material. Moreover, the MoS₂ ML favors a MgO(001) texture and plays a critical role in establishing the large PMA. First-principles calculations on a similar Fe/MgO/MoS₂ structure reveal that the MgO thickness can modify the MoS₂ band structure, from a direct band gap with 3ML-MgO to an indirect band gap with 7 ML-MgO. The proximity effect induced by Fe results in splitting of 10 meV in the valence band at the Γ point for the 3ML-MgO structure, while it is negligible for the 7 ML-MgO structure. These results pave the way to develop RT spin optoelectronic devices based on 2D transition-metal dichalcogenide materials.

Dielectric function of vanadium oxide thin films by thermal annealing

The dielectric function of ${{\rm{VO}}_x}$ and ${{\rm{V}}_2}{{\rm{O}}_5}$ thin films is determined with the use of a spectroscopic Mueller matrix ellipsometer from 1.5 to 5.0 eV. The complex dielectric function of the films is calculated using the measured Mueller matrices filtered with the Cloude decomposition. ${{\rm{VO}}_x}$ shows high absorption in the UV region, a Tauc-Lorentz gap around 2.4 eV, and non-vanishing absorption in the visible. ${{\rm{V}}_2}{{\rm{O}}_5}$ shows a high absorption band centered at 2.87 eV, an indirect optical band gap at 1.95 eV, and a direct optical band gap at 2.33 eV. The ellipsometric characterization is supported by Raman, x-ray photoelectron, and photoluminescence spectroscopy.

One-Step Synthesis of Diamine-Functionalized Graphene Quantum Dots from Graphene Oxide and Their Chelating and Antioxidant Activities

2,2'-(Ethylenedioxy)bis(ethylamine)-functionalized graphene quantum dots (GQDs) were prepared under mild conditions from graphene oxide (GO) via oxidative fragmentation. The as-prepared GQDs have an average diameter of ca. 4 nm, possess good colloidal stability, and emit strong green-yellow light with a photoluminescence (PL) quantum yield of 22% upon excitation at 375 nm. We also demonstrated that the GQDs exhibit high photostability and the PL intensity is poorly affected while tuning the pH from 1 to 8. Finally, GQDs can be used to chelate Fe(II) and Cu(II) cations, scavenge radicals, and reduce Fe(III) into Fe(II). These chelating and reducing properties that associate to the low cytotoxicity of GQDs show that these nanoparticles are of high interest as antioxidants for health applications.

Evidence of a strong perpendicular magnetic anisotropy in Au/Co/MgO/GaN heterostructures

We report a strong perpendicular magnetic anisotropy (PMA) in Au/Co/MgO/GaN heterostructures from both experiments and first-principles calculations. The Au/Co/MgO heterostructures have been grown by molecular beam epitaxy (MBE) on GaN/sapphire substrates. By carefully optimizing the growth conditions, we obtained a fully epitaxial structure with a crystalline orientation relationship Au(111)[1̄10]//Co(0001)[112̄0]//MgO(111)[101̄]//GaN(0002)[112̄0]. More interestingly, we demonstrate that a 4.6 nm thick Co film grown on MgO/GaN still exhibits a large perpendicular magnetic anisotropy. First-principles calculations performed on the Co (4ML)/MgO(111) structure showed that the MgO(111) surface can strongly enhance the magnetic anisotropy energy by 40% compared to a reference 4ML thick Co hcp film. Our layer-resolved and orbital-hybridization resolved anisotropy analyses helped to clarify that the origin of the PMA enhancement is due to the interfacial hybridization of O 2p and Co 3d orbitals at the Co/MgO interface. The perpendicularly magnetized Au/Co/MgO/GaN heterostructures are promising for efficient spin injection and detection in GaN based opto-electronics without any external magnetic field.

Photon management properties of Yb-doped SnO2 nanoparticles synthesized by the sol-gel technique

SnO2 is a transparent large band gap semiconductor, particularly interesting for optoelectronic and photovoltaic devices, mainly because its conduction can be easily tuned by doping or by modulating the amount of oxygen vacancies. Besides, rare earth doping was successfully exploited for up conversion properties. Here we report on the functionalization of SnO2 nanoparticles with optically active Yb3+ ions using the sol-gel method, which allows UV to NIR spectral (down) conversion. As starting solutions we used stable non-alkoxide metal-organic compounds, which is rather uncommon. Transmission electron microscopy analysis demonstrated the formation of small well-crystallized nanoparticles while X-ray photoelectron spectroscopy measurements have revealed that the Yb is well inserted in the host matrix and has a 3+ valence state. All nanoparticles present large absorption in the UV-visible range (250 to 550 nm) and a band gap that decreases down to 2.72 eV upon doping. The UV energy converted into NIR on the basis of efficient energy transfer from SnO2 to the Yb3+ ions ranges between 250 and 400 nm. Reference undoped SnO2 nanoparticles with a mean size of 20 nm allow converting UV light into broad visible emission centered at 650 nm. The incorporation of up to 3.5 at% of Yb3+ ions into the SnO2 host matrix results in a spectacular decrease of the nanoparticle size down to 6.6 nm. This allowed also the shift of the photoluminescence to NIR in the 970-1050 nm range. The energy level structure of Yb3+ in SnO2 was successfully determined from the deconvolution of the Yb emission. This emission is significantly enhanced by increasing the doping level. All optical measurements suggest that these nanoparticles can be efficiently used as down-shifting converters.

Highly fluorescent, color tunable and magnetic quaternary Ag–In–Mn–Zn–S quantum dots

We report a simple and effective synthesis of Mn : AIZS quantum dots exhibiting color-tunable photoluminescence emission and magnetic properties.

Single step electrodeposition process using ionic liquid to grow highly luminescent silicon/rare earth (Er, Tb) thin films with tunable composition

A one-step method for the electrodeposition of silicon-erbium (Si/Er) and silicon-terbium (Si/Tb) thin films using room temperature ionic liquid (RTIL) has been successfully developed. By playing with the electrochemical parameters, the concentration of incorporated rare earth (RE) ions (Er3+ and Tb3+) in the thin films can be tuned. The obtained thin films have been characterized by electron microscopy and composition analysis techniques. The structural quality of the obtained thin films is characterized by a uniform distribution of Si atoms and RE ions throughout the thickness. The study of the optical properties, carried out by photoluminescence (PL) spectroscopy, demonstrates the efficient optical activity of the films with typical Er and Tb luminescence at room temperature depending on the RE content. The deposition method described is a promising strategy for incorporating RE ions in semiconducting thin films to achieve materials for opto-electronic applications.

Insight into photon conversion of Nd3+ doped low temperature grown p and n type tin oxide thin films

p and n type SnO_x thin films are successfully functionalized with optically active Nd³⁺ ions for efficient UV photon conversion.

The structural and optical properties of SiO2/Si rich SiNx multilayers containing Si-ncs

This work reports on the structural and optical properties of multilayers composed of silicon dioxide (SiO2) and silicon rich silicon nitride (SRN) films. These nanometer scale layers have been alternately deposited by electron cyclotron resonance plasma enhanced chemical vapor deposition (ECR-PECVD) on quartz and silicon (Si) substrates. The samples have then been annealed at high temperature in order to obtain a crystallization of the Si atoms present in excess in the SRN films. The formation of crystalline Si has been witnessed by high resolution transmission electron microscopy (HREM) and micro-Raman measurements. Estimation of the Si-nanocrystal (Si-nc) sizes was possible by correlating the Raman's confinement model, the photoluminescence measurements and HREM imaging. The results clearly show that the band-gap of the Si-ncs formed can be controlled by this multilayer approach.

Influence of the implantation profiles of Si(+) on the dielectric function and optical transitions in silicon nanocrystals

We report optical characterization of silicon nanocrystals embedded in silica thin films by spectroscopic ellipsometry (SE). Silicon nanocrystals (nc-Si) are produced by single energy ion implantation and multienergy Si(+) ion implantation into 250 nm of thermal oxide (SiO(2)) layers on silicon substrate. After thermal annealing, the obtained nc-Si have a Gaussian and uniform profiles for single and multienergy implantation, respectively. SE measurements are performed at room temperature at spectral range from 0.6 to 6.5 eV using the photoelastic modulated spectroscopic ellipsometer. Physical models based on the Maxwell-Garnet approximation combined with Forouhi-Bloomer dispersion formulas and wavelength by wavelength inversion are developed to extract the optical parameters of the layers. The complex dielectric function epsilon(E)=epsilon(r)(E)-iepsilon(i)(E) of nc-Si is determined and analyzed. The obtained epsilon(E) spectra of both uniform and Gaussian profiles are given and compared with those of bulk Si. The nc-Si exhibit a significant reduction of the dielectric function in comparison with bulk Si. We have determined the optical transitions E(1) and E(2) corresponding to Van Hove singularities in the joint density of states. A reduction of the amplitude of E(1) peak with a very weak shift of its energy position is observed. The transition E(2) is characterized by a rather broad peak; the amplitude of this peak is more important than that of E(1). The extended Forouhi-Bloomer model to semiconductor is also used to determine the dielectric functions of nc-Si and optical transitions. In epsilon(i)(E) spectra of nc-Si we have observed that not only the optical transition E(1) peak reduced but it tends to disappear and to form with E(2) only a single broad peak centered at around 4.3 eV. The influence of the distribution profile on the sample's structural and optical characteristics is also investigated. Defects caused by implantation are identified by analyzing the dielectric function behavior. For more reliability, photoluminescence analysis are used to obtain direct optical responses of nc-Si.

Personality and object relations in patients with affective disorders: idiographic research by means of the repertory grid technique

BACKGROUND

This paper presents an idiographic approach to evaluate the self concept and the self-object-relationship of patients suffering from affective disorders.

METHODS

Significant dimensions of the personality and the object relations of 127 depressive patients and 34 orthopaedic patients were investigated with the repertory grid-technique. The self concept and the object relations were compared by means of nomothetically used idiographic results after recovery from manifest depression.

RESULTS

'Low self esteem' was frequently found in patients with a long lasting course of illness and the ICD-10-diagnoses of 'bipolar affective disorder' and 'dysthymia'. The object relations of the depressive sample were characterised by the dimension 'symbiotic near'; 'ambivalent' and 'indifferent' partnership relationships were found much more frequently in the controls.

CONCLUSIONS

The idiographic results help to differentiate the spectrum of affective disorders. They underline the importance of the interpersonal dimension of depression and may be used as a basis of a therapeutic appraisal.

LIMITATIONS

The repertory grid-technique may not be used as a diagnostic instrument. However, the combination of idiographic results with further clinical informations enables the multidimensional assessment of the self concept and psychosocial coping mechanisms.

[Interaction between an antifungal heptaene, amphotericin B and cholesterol in vitro, as detected by circular dichroism and absorption. Influence of temperature]

The polyene antibiotic "Amphotericin B" can interact with sterols, cholesterol or ergosterol in aqueous and hydroalcoholic media and a correlative striking spectral change appears between 300 and 420 nm in the CD and absorption spectra. Using these spectroscopic methods we have determined that the influence of temperature between 4 and 80 degrees C is very important. The higher the temperature the most rapid is the modification of the spectra. Thus, the "Amphotericin B"-sterol complex is more easily formed when heating. We have not found any reversibility at 80 degrees C.