Optically triggered surface channel MESFETs were fabricated on commercial polycrystalline diamond to be tested as
fast UV activated switches. Devices with an opaque-gate and asymmetric structure were designed in order to improve
charges photogeneration within gate-drain region. The sensitivity to UV light was demonstrated by using both modulated
over gap radiation and laser pulses at 193 nm, well over the diamond band gap. Linearity with the power light was
demonstrated as well as the parabolic dependence of the photogenerated current on the gate-source voltage when the
transistor is in saturation. The transient response to 193 nm laser pulses in the nanosecond regime shows as the
photogeneration process and charges collection to the drain contact are completed in a time scale of few nanoseconds.
Polycrystalline diamond detector prototypes suitable for x-ray spectroscopy were realized and tested. Thick diamond specimens, mechanically polished to reduce the surface roughness, were selected for prototypes development. Noble metal contacts were deposited on both faces, whereas multistrip structures were defined by photolithography on the growth face only with the aim of reducing the coupling capacitances and to allow characterization tests either in
planar or sandwich configuration. Leakage currents as low as 20 pA at 500 V were measured on a 270μm thick device. The x-ray sensitivity was tested monitoring the photocurrent as a function of the applied voltage under continuous 8.05 keV Cu Kα irradiation. Studies in pulsed mode were also performed by using a commercial miniature x-ray source. Pulse height distributions were carried out with a system composed of a charge-sensitive preamplifier and a digital pulse processor multi-channel analyzer. Analysis was carried out around Ta Lα and Cu Kα characteristic lines. Realized prototypes were able to resolve such two characteristic lines only 90 eV apart. Energy resolutions better than 3% have been evaluated for one of the prototype at 8.14 keV. Such features address very good energy resolving capabilities and the suitability of polished polycrystalline diamond in x-ray spectroscopy.
The pressure dependence of the phonon spectrum of three La1 - xCaxMnO3 - δ manganites have been studied by means of Far-IR absorption spectroscopy coupled with a Diamond Anvil Cell. The effect of the applied pressure on the charge delocalization have been investigated defining the nature of the metallization process in the low-frequency domain.
SINBAD, the infrared beamline which extracts radiation from the DA(Phi) NE collider of the Laboratori Nazionali di Frascati, will be operating in the fall of 1999. The optical layout of SINBAD, fully designed by ray tracing simulation, includes six mirrors which transfer and focus the radiation to an interferometer placed more than 20 m from the source. The actual brilliance gain at the entrance of the interferometer has been accurately evaluated by simulating the expected aberrations, the mirror roughness, and diffraction effects.
Both the angular and the spectral distribution of the Infrared Synchrotron Radiation emitted by an undulator of Super-ACO have been measured. Structures due to undulator edges, as well as contributions from the edge emission of a bending magnet placed behind the undulator, have been observed. Detailed calculations including all these sources are in excellent agreement with the measurements, provided that both velocity and acceleration terms are considered.
We report on the status of the first Italian Infrared Synchrotron Radiation Beamline SINBAD (Synchrotron INfrared Beamline At DA(Phi) NE), that has been designed to work at wavelengths greater than 10 micrometers . SINBAD is being installed on DA(Phi) NE, the new collider of the Laboratori Nazionali di Frascati designed to work at 0.51 GeV with a beam current of 2 to 5 A. The infrared radiation extracted from a bending magnet under an angle of 50 X 50 mrad will be two orders of magnitude more brilliant than that of a black body at 2000 K at a wavelength of 100 micrometers . The beamline layout, which consists of two planar mirrors, two toroidal mirrors and one aspherical mirror, has been designed by ray tracing simulation. In this layout one ellipsoid focuses the radiation on a wedged CVD diamond-film window, the beam is then re-focused again on the entrance of an interferometer. With a calculated transmittance of the optics between 60% and 80% at 50 micrometers , this beamline will allow experiments which require a very high brilliance in the far infrared.