A. De Sio

Spectral response of large area CVD diamond photoconductors for space applications in the vacuum UV

Abstract This work reports on the development and characterization of large area (1 cm2) vacuum UV CVD diamond photodetectors to address the requirements of space missions where pixel and 2D arrays are used. The quality of the CVD diamond was characterized by photoluminescence and Raman spectroscopy. The performance of these devices in the dark and under illumination was investigated and the results compared to those from small area detectors based on similar material. Planar and transverse electrode configurations were used in order to evaluate the possibility of producing imaging detectors. The spectral analysis of the photocurrent was measured as a function of several functional parameters and experimental conditions.

Bunch by bunch beam monitoring in 3rd and 4th generation lightsources by means of single crystal diamond detectors and quantumwell devices

New generation Synchrotron Radiation (SR) sources and Free Electron Lasers (FEL) require novel concepts of beam diagnostics to keep photon beams under surveillance, asking for simultaneous position and intensity monitoring. To deal with high power load and short time pulses provided by these sources, novel materials and methods are needed for the next generation BPMs. Diamond is a promising material for the production of semitransparent in situ X-ray BPMs withstanding the high dose rates of SR rings and high energy FELs. We report on the development of freestanding, single crystal CVD diamond detectors. Performances in both low and radio frequency SR beam monitoring are presented. For the former, sensitivity deviation was found to be approximately 2%; a 0.05% relative precision in the intensity measurements and a 0.1-μm precision in the position encoding have been estimated. For the latter, single-shot characterizations revealed sub-nanosecond rise-times and spatial precisions below 6 μm, which allowed bunch-by-bunch monitoring in multi-bunch operation. Preliminary measurements at the Fermi FEL have been performed with this detector, extracting quantitative intensity and position information for FEL pulses (~ 100 fs, energy 12 ÷ 60 eV), with a long-term spatial precision of about 85 μm; results on FEL radiation damages are also reported. Due to their direct, low-energy band gap, InGaAs quantum well devices too may be used as fast detectors for photons ranging from visible to X-ray. Results are reported which show the capability of a novel InGaAs/InAlAs device to detect intensity and position of 100-fs-wide laser pulses.

IMRT field profiling by high-quality polycrystalline CVD diamond

A dosimeter made with state of art polycrystalline Chemical Vapour Deposited (pCVD) diamond for applications in clinical radiotherapy has been manufactured, based on a large area (2.5 × 2.5 cm2) film equipped with a matrix of contacts. A dose profile under an Intensity Modulated Radiotherapy (IMRT) beam for prostate cancer has been monitored using a set of in-line pads along a section of the field map. Results compare well with data obtained with a commercial bidimensional silicon dosimeter, confirming that our pCVD diamond device is suitable for mapping the conformed dose in IMRT treatments.

X-Ray Beam Position Monitor Based on a Single Crystal Diamond Performing Bunch by Bunch Detection

Diamond is a promising material for the production of semitransparent in situ photon beam monitors which can withstand the high dose rates occurring in new generation synchrotron radiation storage rings and in free electron lasers. We report on the development of a 500 mu m thick freestanding, single crystal chemical vapor deposited diamond detector with segmented electrodes. Performances in both low and radio frequency beam monitoring are presented as well. By using charge integration techniques at a frame rate of 6.5 kHz in combination with a needle synchrotron radiation beam and mesh scans, the inhomogeneity of the sensor was found to be of the order of 2%; with a measured electronics noise of 2 pA / root Hz a 0.05% relative precision in the intensity measurements (at 1 mu A) and a 0.1 mu m resolution in the position encoding have been estimated. Moreover, the high electron-hole mobility of diamond compared with other active materials enables very fast charge collection characterized by rise-times below 1 ns; this allowed us to utilize single pulse integration to simultaneously detect the intensity and the position of each synchrotron radiation photon bunch generated by a bending magnet

Bidimensional polycrystalline CVD diamond detector for Intensity Modulated Radiation Therapy pre-treatment verifications

This study aims at investigating the possible employment for pre-treatment verifications in Intensity Modulated Radiation Therapy (IMRT) of a polycrystalline Chemical Vapour Deposited (pCVD) diamond bidimensional detector. The pCVD device, with an area of 2.5 × 2.5 cm2 (12 × 12 pixels), has been used to measure dose maps of a 10 MVRX prostatic IMRT field. Its response was compared both with a commercial bi-dimensional detector made with silicon and with Treatment Planning System (TPS) calculations.Measurement provided promising results on a map of 1.8 × 12.6 cm2. Absorbed doses measured along IMRT profiles by our device are consistent with the ones acquired with the commercial device and an overall good agreement with respect to the TPS was found for the diamond dosimeter.

Single-crystal diamond MIS diode for deep UV detection

Due to its exceptional physical properties, synthetic diamond is an ideal material for the realization of UV and X-ray detectors to be used for the characterization of laser-generated plasmas. Diamond detectors are able to operate at high temperatures and in the presence of high fluxes of ionizing radiation, where traditional silicon-based detectors usually fail. In this paper, we report on Raman and electro-optical characterization of a structure consisting of intrinsic diamond/boron-doped diamond homoepitaxially grown by chemical vapor deposition onto a commercial high pressure high temperature Ib-type diamond substrate using a 1% CH4/H2 gas mixture. A metal–insulator–semiconductor (MIS) diode was obtained by thermally evaporating an aluminum contact on the growth surface of the intrinsic layer. The detection capability of this device operating in transverse configuration was measured in the deep UV spectral range. The device sensitivity has been estimated at different biasing voltages and at two wavelengths having different penetration depths into the material. The device was also tested at zero biasing voltage (photovoltaic mode operation), showing quite a good photoresponse. These results suggest that MIS structures based on high-quality homoepitaxial diamonds may be successfully utilized for photodetection even at zero bias.

Zero bias thermally stimulated currents in synthetic diamond

Zero bias thermally stimulated currents (ZBTSCs) have been observed in single crystal high pressure high temperature (HPHT) and polycrystalline chemical vapor deposited (pCVD) diamond films. The ZBTSC technique is characterized by an increased sensitivity with respect to a standard TSC analysis. Due to the absence of the thermally activated background current, new TSC peaks have been observed in both HPHT and pCVD diamond films, related to shallow activation energies usually obscured by the emission of the dominant impurities. The ZBTSC peaks are explained in terms of defect discharge in the nonequilibrium potential distribution created by a nonuniform traps filling at the metal-diamond junctions. The electric field due to the charged defects has been estimated in a quasizero bias TSC experiment by applying an external bias.

Physical vapor deposition synthesis of amorphous silicate layers and nanostructures as cosmic dust analogs

Cosmic dust grains (CD) are part of the evolution of stars and planetary systems and pervade the interstellar medium. Thus, their spectral signature may be used to deduce the physical features of the observed astronomical objects or to study many physical and chemical processes in the interstellar medium. However, CD samples are available only from sample-and-return space missions. Thus, they are rare and not sufficient to be used to perform laboratory experiments of astrophysical interest, such as to produce reference spectra. In this contribution, we describe a new physical vapor deposition (PVD) technique that allows the production of amorphous samples with controlled chemical and morphological characteristics. In particular, this technique was developed to grow uniform or microstructured layers of Mg-Fe amorphous silicates (olivine or pyroxene) that are materials of wide interest for laboratory experiments. We discuss the first results that were achieved by applying this new synthesis method. The layers were studied by combining infrared spectroscopy, scanning electron microscopy, and X-ray spectroscopy. The X-ray microscopy was used for the first time to characterize the internal structure of the grains in these synthetic samples. Finally, future improvements of the technique and foreseen applications are discussed.

Polycrystalline CVD diamond dosimeters for Intensity Modulated Radiotherapy (IMRT)

Diamond has a potential for Intensity Modulated Radiotherapy (IMRT) applications, being a solid-state nearly tissue equivalent material, with the possibility to be grown in large diameter wafers by Chemical Vapour Deposition (CVD). We present a monolithic polycrystalline CVD diamond dosimeter and first results in an IMRT beam. Our device shows to be able to cope with the complex temporal/spatial structure of the IMRT field.

An innovative photochemical facility at DAΦNE-L

An on-going project for a photochemical facility at the DAFNE-L laboratory at the Frascati National Laboratories of INFN (National Institute of Nuclear Physics) is presented. Such a facility takes advantage from the combined capabilities of two different synchrotron radiation beam-lines. The first operates in the visible-UV and is used as a strong excitation and irradiation light-source in which both intensity and spectral range can be selected to fulfil the experiment requirements. The second is an infrared beamline equipped by FTIR micro-spectroscopy and imaging facility. An optical fiber allows UV irradiation of samples directly into the FTIR interferometer or the microscope. Thus, fast photo-chemical reactions can be analysed in real time, letting unveil inter-phases not normally observable by analysing the reagents and products of the reaction itself. Complex unstable systems can be irradiated and analysed without changing the sample condition (morphology, humidity, irradiation etc.). Preliminary experiments, validating most of the facility capability, will be presented.