Publications

Rolled-up nanostructures formed from lattice mismatched III-V heterojunction films by taking advantage of a strain-induced self-rolling mechanism represent a useful type of building blocks for nanotechnology, with possible applications in high-speed microelectronic and optoelectronic devices. This work investigated the effect of illumination on the hydrofluoric acid etching of AlAs sacrificial layers with systematically varied thicknesses in order to release and roll up MBE grown InGaAs/GaAs bilayers. Based on this "etch suppression effect" (ESE), we propose an illumination-assisted technique that offers an advantage over other methods of rolling up nano-objects on a substrate from inherently strained films because it allows control over the positioning of rolled-up micro- and nanotubes independently from lithographic methods. For thicknesses of AlAs below 10 nm, we found two etching regimes for the area under illumination: one at low illumination intensities, in which the etching and releasing proceeds as expected and one at higher intensities in which the etching and any releasing are completely suppressed. The "etch suppression" area is well defined by the illumination spot, which can be used to realize well-controlled heterogeneously etched regions on the same sample.

The low frequency collective movements of proteins associated with biologically relevant conformational transitions are situated in the terahertz (THz) spectral region. THz spectroscopy experiments have revealed that each molecular species has a unique absorption pattern in THz domain. We used time-domain THz spectroscopy (TDS) to study the conformation and flexibility of bovine serum albumin (BSA), a protein whose 3D structure is unknown. We performed THz spectroscopy experiments on lyophilized BSA. Theoretical spectra were obtained by normal modes analysis performed on BSA structures generated by homology modeling and molecular dynamics simulations. The agreement between experimental and theoretical data allowed us to validate the model of BSA and also to gain insight into BSA vibrations in THz domain.

Barium neodymium titanate (BNT) material was prepared and characterized. The very high dielectric constant, high Qxf product and controllable temperature coefficient recommend the BNT material for microwave applications. Slot coupled antennas with BNT resonators are investigated. The resonator shape effect on the antenna bandwidth is discussed.

A strong focus on Superparamagnetic Iron Oxide Nanoparticles (SPIOs) has been appreciated recently especially for their use in Magnetic Resonance Imaging (MRI). However, some questions are being raised over these particles due to their long-term toxicity related to the production of toxic free iron during their biodegradation. Here we show by Electron Microscopy how SPIOs (P904) (Guerbet, Paris) are degraded after they are taken up by macrophages, so that iron from the SPIO core is progressively incorporated into the iron-storing protein ferritin (a nontoxic form of iron).

In this paper we present a resonant antenna based on a composite right/left handed metamaterial structure. The antenna is designed to operate at the zero-order resonance. The antenna was fabricated and used in measuring the coverage of a UMTS cell.

3-[2-(dimethylamino) ethyl]-6-nitroquinazolin-4(3H)-one, labeled BG1188, is a new synthesized compound, out of a series of quinazoline derivatives developed to fight the multidrug resistance of antibiotics acquired by bacteria. A characterization of the BG1188 powder was made using FTIR spectra in order to evidence the functional groups in the medicine's molecule. The ultraviolet-visible (UV-Vis) absorption spectra were used to study the stability of the BG1188 solutions in two solvents and at different temperatures. BG1188 concentration in ultrapure water was varied between 2x10(-3)M (stock solution) and 10(-6)M. The concentration recommended by higher activity on bacteria was 10(-3)M. For the same reason, this was the utilized concentration of BG1188 in dimethyl sulfoxide (DMSO). Time stability was characterized by comparing the time evolution of the UV-Vis absorption spectra of the BG1188 solutions in ultrapure deionized water or in DMSO. The spectra were recorded daily for about 4 months after the preparation for the BG1188 solutions in ultrapure water. Generally, samples are stable within the experimental errors at concentrations higher than 10(-5)M, but the stability time interval may vary from 119 days at 10(-4)M to 34 days at 10-5M. Time evolution of the absorption spectra at 10-3M in ultrapure water shows reproducibility within the measuring errors (+/- 1.045%) for time intervals up to 1032 hours (more than 40 days) after preparation. On the other hand, BG1188 solutions in DMSO may be considered unstable because the absorption spectra modify in terms of peak shapes and intensities, indicating that the samples exhibit modifications immediately after preparation. Regardless the solvent used, some aggregation phenomena took place and wire-like aggregates were observed in all the solutions with the naked eye. These aggregates were analyzed, tentatively, using optical microscopy and FTIR.

Sucrose is a natural osmolyte accumulated in the cells of organisms as they adapt to environmental stress. In vitro sucrose increases protein stability and forces partially unfolded structures to refold. Thin films of sucrose (C12H22O11) were deposited on thin cut glass substrates by the thermal evaporation technique (P similar to 10(-5) torr). Characteristics of thin films were put into evidence by Fourier Transform Infrared Spectroscopy (FTIR), X-ray Photoelectron Spectroscopy (XPS), scanning electron microscopy (SEM), and differential thermal analysis and thermal gravimetric analysis (TG/DTA). The experimental results confirm a uniform deposition of an adherent layer. In this paper we present a part of the characteristics of sucrose thin films deposited on glass in medium vacuum conditions, as a part of a culture medium for osteoblast cells. Osteoblast cells were used to determine proliferation, viability, and cytotoxicity interactions with sucrose powder and sucrose thin films. The osteoblast cells have been provided from the American Type Culture Collection (ATCC) Centre. The outcome of this study demonstrated the effectiveness of sucrose thin films as a possible nontoxic agent for biomedical applications.

Multilayer spin valve structures of type AF/F/Cu/F and AF/F/MgO/F (AF=antiferromagnetic layer and F=ferromagnetic layer) have been prepared by sputtering in radiofrequence. The samples were investigated at room temperature by magneto-optic Kerr effect and conversion electron Mossbauer spectroscopy, before and after thermal hydrogenation. Additional magnetic peculiarities were observed at low temperatures via SQUID magnetometry. The effect of the thermal hydrogenation on the magnetic properties of the systems was discussed with respect to the changes in the local spin configuration, observed by Mssbauer spectroscopy.

One of the clues in detection in modern physics is the development of detector materials able to produce simultaneously two or more different processes, as well as the measurement of the physical quantities associated to these processes in order to discriminate and to identify different particles. In the same time, the absorption of radiation in matter is not a continuous process and due to the interaction mechanism it is localized. As a result, for short time, transient processes are produced, some of them used in detection, other producing disorder that affects the properties of the detector material. In the present paper the thermal spike model is extended and used for semiconductors and liquefied noble gases used as target media for detectors. Both classes of materials are very promising for the detection of heavy particles in nuclear and astroparticle physics.

The long time degradation produced by particles and ions in crystalline materials used for devices to work in space, or for detectors in HEP and astroparticles, is characterised by the non-ionising energy loss, which is calculated in the frame of an analytical model. The transient phenomena as short time degradation are characterised by the time and space dependencies of the lattice and electron temperatures near the projectile trajectory. These processes are considered in the frame of a thermal spike model, which takes into account both ionization and nuclear energy loss processes.