Magnetic Anisotropy of Co2+ as Signature of Intrinsic Ferromagnetism in ZnO:Co

We report on the magnetic properties of thoroughly characterized Zn1-xCoxO epitaxial thin films, with low Co concentration, x=0.003-0.005. Magnetic and EPR measurements, combined with crystal field theory, reveal that isolated Co2+ ions in ZnO possess a strong single ion anisotropy which leads to an "easy plane" ferromagnetic state when the ferromagnetic Co-Co interaction is considered. We suggest that the peculiarities of the magnetization process of this state can be viewed as a signature of intrinsic ferromagnetism in ZnO:Co materials.Comment: 4 pages, 4 figure

Built-in electric-field effects in wurtzite AlGaN/GaN quantum wells

AlGaN/GaN quantum well (QW) structures are grown on c-plane sapphire substrates by molecular beam epitaxy. Control at the monolayer scale of the well thickness is achieved and sharp QW interfaces are demonstrated by the low photoluminescence linewidth. The QW transition energy as a function of the well width evidences a quantum-confined Stark effect due to the presence of a strong built-in electric field. Its origin is discussed in terms of piezoelectricity and spontaneous polarization. Its magnitude versus the Al mole fraction is determined. The role of the sample structure geometry on the electric field is exemplified by changing the thickness of the AlGaN barriers in multiple-QW structures. Straightforward electrostatic arguments well account for the overall trends of the electric-field variations. (C) 1999 American Institute of Physics. [S0021- 8979(99)07719-1]

Molecular beam epitaxy of high quality InGaN alloys using ammonia: Optical and structural properties

The growth of InGaN layers was carried out by molecular beam epitaxy (MBE). The nitrogen precursor was ammonia. The optical and structural properties of the InGaN layers have been investigated by transmission electron microscopy (TEM), x-ray diffraction (XRD) and photoluminescence (PL). For optimized growth conditions, the PL spectrum of InGaN (x=0.1) alloy is narrow (FWHM less than or equal to 50 meV) and the Stokes shift measured by PL excitation is weak (<50 meV), i.e. near band edge transitions are observed. Under these conditions, flat surfaces can be obtained, and InGaN/GaN quantum wells (QWs) with sharp interfaces can be grown. On the other hand, when growth conditions depart from a narrow optimum window, the structural quality of the samples strongly degrade, whereas the luminescence spectra are dominated by deep levels, exhibiting a strong Stokes shift. MBE grown light emitting diodes (LEDs) using InGaN/GaN QWs have been fabricated. Their electroluminescence (EL) peaks at 440 nm at 300K

Magnetic Anisotropy of Co2+ as Signature of Intrinsic Ferromagnetism in ZnO:Co

4 pages, 4 figuresWe report on the magnetic properties of thoroughly characterized Zn1-xCoxO epitaxial thin films, with low Co concentration, x=0.003-0.005. Magnetic and EPR measurements, combined with crystal field theory, reveal that isolated Co2+ ions in ZnO possess a strong single ion anisotropy which leads to an "easy plane" ferromagnetic state when the ferromagnetic Co-Co interaction is considered. We suggest that the peculiarities of the magnetization process of this state can be viewed as a signature of intrinsic ferromagnetism in ZnO:Co materials

Health Research on Immunization after 2016: the need for a plural methodological approach

In French : https://hal.archives-ouvertes.fr/hal-03675482International audienceThe current “generalized digitization” of society is influencing the health environment, healthcare organizations as well as actors. In this context, human and social sciences deconstruct, nuance and sometimes even challenge certain preconceived ideas and/or dominant discourses.In this book, researchers of four nationalities and three different disciplines have agreed to open the “black box” of their work. They display their scientific practices from the perspective of epistemology, ethics and methodology. They present and analyze their values and postulates but, also, what may have influenced the project, the definition of the object and objectives, as well as their approaches. In a contextual way, the first part presents some changes in environments and info-communicational practices related to digital health. The second part opens space to reflect on ethics and deontology. Finally, postulating that scientific fact is not an essence but the result of a process, the last part discusses the methods implemented, which may be different from those initially envisaged.This book is dedicated to the researchers and postgraduate students in the human and social sciences as well as the health practitioners likely to collaborate with them