Biomedical subjects

R Prazeres

Publications and source records attributed to R Prazeres.

8 recordsLinked to original sources

PubMed2005

Local infrared microspectroscopy with subwavelength spatial resolution with an atomic force microscope tip used as a photothermal sensor.

We describe a new method of infrared microspectroscopy. It is intended for performing chemical mapping of various objects with subwavelength lateral resolution by using the infrared vibrational signature characterizing different molecular species. We use the photothermal expansion effect, detected by an atomic force microscope tip, probing the local transient deformation induced by an infrared pulsed laser tuned at a sample absorbing wavelength. We show that this new tool opens the way for measuring and identifying spectroscopic contrasts not accessible by far-field or near-field optical methods and with a subwavelength lateral resolution.

Escherichia coli↗

PubMed2002

Long polaron lifetime in InAs/GaAs self-assembled quantum dots.

We have investigated the polaron dynamics in n-doped InAs/GaAs self-assembled quantum dots by pump-probe midinfrared spectroscopy. A long T1 polaron decay time is measured at both low temperature and room temperature, with values around 70 and 37 ps, respectively. The decay time decreases for energies closer to the optical phonon energy. The relaxation is explained by the strong coupling for the electron-phonon interaction and by the finite lifetime of the optical phonons. We show that, even for a large detuning of 19 meV from the LO photon energy in GaAs, the carrier relaxation remains phonon assisted.

Journal Article↗

PubMed1998

Spectroscopic Techniques using Synchrotron Radiation and Free-Electron and Conventional Lasers.

Considerable progress in the investigation of the electronic and vibrational properties of atoms, molecules, materials, surfaces and interfaces has been achieved by combining different photon sources of complementary characteristics. In this paper some experimental results obtained recently at LURE by using two synchronized sources, such as the IR free-electron laser (FEL) CLIO, the VUV storage ring FEL, synchrotron radiation and table lasers, are presented. Using CLIO synchronized with a YAG laser allows the investigation of the vibrational properties of adsorbed species by the non-linear optical technique of visible-IR sum (difference) frequency generation, as shown for the adsorption of hydrogen on platinum in the electrochemical environment. The second result reported here relates to the study of the intersubband stimulated emission in GaAs/GaAlAs quantum wells by pump-probe experiments using the two-colour configuration of CLIO. The combination of a mode-locked Ar(+) laser and synchrotron radiation has been used for investigations in a pump-probe arrangement of the ionization of Xe atoms via the resonant state Xe* 5p(5)5d [3/2](1). The final example is a time-resolved core-level spectroscopy study of photoexcited Si(111) 2 x 1 surfaces by using a combination of the naturally synchronized UV storage ring laser and synchrotron radiation.

Journal Article↗

PubMed1996