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Priming by X-rays or by beta-rays is generally needed in order to qualify CVD diamond for nuclear detection or for dosimetry. The priming effect is usually attributed in filling the hole traps, which are responsible for the charge collection efficiency of the detector. Emptying the filled traps can be easily detected by Thermoluminescence (TL), which is considered to be a measure of the absorbed dose. In this work, we prove that below-gap photocurrent (BGPC) can also be used in the same way and it is dominated by the optical detrapping of holes from the same centers. Time dependence of this beta-rays induced persistent photocurrent (PPC), which in fact, depends only on the total number of photons impinging onto the sample. In fact, at long times or for large number of photons, the photocurrent approaches to the same limit of PC for a null dose. The hole trapping centers distribution seems to extend from 1.25 to 2.5 eV valence band.

IonoLuminescence (IL) and ThermoLuminescence (TL) techniques have been used in order to characterize the defects induced by doping due to different precursors in cubic boron nitride (c-BN) growth. Crystallites of dimensions of the order of 10-40 μm obtained by HPHT (High Pressure and High Temperature) method were used. Protons microbeams of 2 MeV - corresponding to a penetration depth of 26 μm in c-BN - with a spot diameter of few pm, in connection with an ellipsoidal mirror characterized by a large light collection efficiency and a 0.25 m monochromator, allowed to acquire wide area luminescence spectra. We observed that IL spectra for samples characterized by a large Mg content, as obtained by PIXE (Particle Induced X-ray Emission) analysis, displayed three peaks at 1.95 eV, 3.2 eV and 3.9 eV respectively, while in samples with a large Ca content a fourth peak appeared around 1.7 eV. Even if the number of available samples was relatively low, a fair correlation was observed between the total area under the peaks at 1.7 and 1.95 eV and the total Ca content (up to 25 ppm) on one side and between the total area under the peak at 3.9 eV and the total Mg content (up to 100 ppm), even if this peak appeared with a much smaller intensity also in all the other samples. Moreover, TL measurements were carried out from RT up to 400 °C with a standard Harshaw TL reader after the exposure of samples to some Gy doses from a collimated α-particle 241 Am source. Specimens obtained by a Mg-based precursor did not show any thermoluminescence, while samples obtained by a Ca-based precursor showed a large and very reproducible TL spectrum. From the initial rise TL method, coupled to a preheating in order to separate the contributions from different traps, three series of centres were found out at 0.21, 0.35 and 0.6 eV. Samples obtained without a Ca-based precursor probably have a level at 0.45 eV instead of at 0.35 eV and, likely, there is also another level at 0.52 eV in Ca-doped platelets.

We have measured current–voltage characteristic, blue‐violet electroluminescence (EL) and subgap photocurrent spectra of free standing polycrystalline chemical vapor deposited diamond film. The current increases as a power law function of the voltage with an exponent of about 5.5. The EL spectra show a main luminescence band peaked at 3.0 eV, whose intensity increases linearly with the electric current. The photocurrent increases rapidly with the photon energy in the range from 2.0 to 3.5 eV and then tends to saturate. It is found that all these results can be consistently explained in relation to gap states centered at 3.0 eV above the valence band.

Local anodic oxidation (LAO) of hydrogenated CVD diamond surfaces was carefully investigated as a function of the scanning speed, relative humidity and bias voltage. As examples, perfect control of the width of the oxidised lines between 80 and 110 nm was demonstrated for scanning speeds between 20 and 110 nm s-1, at 60% relative humidity, and between 45 and 90 nm by switching the humidity from 40% to 60%. The oxidation process is indicated by the decay of the current during the LAO process, which is concluded in about 10 s. The interpretation of the results, which in the literature oscillates between digging grooves and the creation of oxidised bumps, is still quite difficult, since it depends on the AFM mode ('contact' or 'non-contact') which was used for LAO. A true oxidation process is more likely to occur, as indicated by the present results, and this is in agreement with the presence of oxygen in surface analysis data.

Chemical vapor deposition diamond has been discussed extensively as an alternate sensor material for use very close to the interaction region of the LHC where extreme radiation conditions exist. During the last few years diamond devices have been manufactured and tested with LHC electronics with the goal of creating a detector usable by all LHC experiment. Extensive progress on diamond quality, on the development of diamond trackers and on radiation hardness studies has been made. Transforming the technology to the LHC specific requirements is now underway. In this paper we present the recent progress achieved.

Diamond is a promising sensor material for future collider experiments due to its radiation hardness. Diamond pixel sensors have been bump bonded to an ATLAS pixel readout chip using PbSn solder bumps. Single chip devices have been characterised by lab measurements and in a high-energy pion beam at CERN. Results on charge collection, spatial resolution, efficiency and the charge carrier lifetime are presented.

TRIBICC ( Time Resolved Ion Beam Induced Charge Collection ) represents a further improvement with respect to more traditional IBICC, since it can supply not only the charge collection efficiency ( and consequently data on mobility and trapping time of carriers in drift regions ), but also its time behaviour. At long collection times, it can supply informations about diffusion lenghts and lifetimes of carriers in the diffusion regions, which are always present in undepleted devices such as power devices. These data are of paramount importance as inputs for device simulation codes. A more general and more powerful TRIBICC method is presented in this work by using Gunn’s theorem and a particular formulation of the generation function in order to solve the adjoint of the continuity equation. This method represents a strong improvement with respect to a previous one, in which lateral IBIC was used. An application of this method to a commercial power device is presented and discussed. By using microbeams, life...

The paper gives new results on the radiation tolerance of CVD diamond for irradiation with 300 MeV/c pions and 24 GeV/c protons. The measured charge signal spectrum is compared at several irradiation levels with the spectrum calculated by a model. Irradiation by particles causes damage leading to a decrease of the charge signal. However, both the measurements and the outcome from the model show that for tracker applications this drawback is at least partly counterbalanced by a narrowing of the distribution curve of the charge signal. As a result, the efficiency of a CVD diamond tracker is less affected by irradiation than the mean charge signal.

Data obtained from ion beam induced charge collection measurements on "detector grade" CVD diamond samples have been used in order to "simulate" the collection of charge produced by a minimum ionizing particle. It turns out that both the electric field and the charge collection length are not uniform in the depth of the sample, whereas the profile of the charge collection efficiency is compatible with a linear behaviour of the product (mobility) x (lifetime) of carriers. This is here proposed as a new "linear model", which is fully compatible with the "old" linear model in all the cases where the electric field is uniform. The contribution of electrons to the charge pulse seems to be in this case more important than that of holes. The homogeneity of the CVD diamond detector as a tracker for minimum ionising particles is higher than for low energy protons and it displays a behaviour as a function of the length scale which is in a relatively good agreement with data reported from measurements with diamond strip detectors. (C) 2002 Elsevier Science B.V. All rights reserved.

A lateral micro-ion beam induced charge technique has been used to obtain the charge collection efficiency (CCE) profiles at different biases applied on the growth electrode of chemical vapor deposition (CVD) diamond. A new linear model, only related to characteristic parameters (mobility x lifetime product) of CVD diamond, was reasonably proposed and checked by fitting the CCE profile. The results confirm that: (1) this CVD diamond is similar to a n-p junction film with bulk volume p type on the substrate side at the positive bias applied on the growth side; (2) in the case of negative bias, space charge on both sides may arise from donors/acceptors of the film and electrons/holes injected from the growth/ substrate side, but in the middle no space charge exists due to the electron-hole neutralization. (C) 2002 Elsevier Science B.V. All rights reserved.

Ion beam-induced charge collection (IBICC) method is a very sensitive technique to investigate the electronic features of semiconductor materials and devices. This technique consists in measuring the charge induced at the electrode by the motion of free carriers generated by a spatially scanned focused energetic ion beam. The measurement of the charge collection efficiency as a function of the ion impact position allows the electronic features of semiconductor materials and devices to be mapped. We used the micro-beam facility of the Ruder Boskovic Institute in Zagreb (HR) to perform lateral IBICC measurements of virgin, Au doped and strongly irradiated (frontal irradiation with 6.5 MeV He 2+ ions for a total dose of 2E12 ions/cm 2 ) p + /n/n + silicon diodes in order to evaluate charge collection profiles (CCPs) under different applied bias conditions. Basic transport parameters (minority carrier diffusion length, depletion region width) have been extracted from the experimental profiles by using a mathematical procedure based on the extended Ramo's theorem. The irradiated sample shows CCPs strongly influenced by the radiation damage as evidenced by a drop of charge collection efficiency which occurs at the end of the He 2+ ion penetration range.

Diamond is an ideal material to fabricate dosimeters because it is tissue equivalent, chemically stable, non-toxic, mechanical and radiation hard. Chemical vapour deposition technique (CVD) allows for the fabrication of small diamond detectors, which can be considered for in vivo dose measurements. We have fabricated microdosimeters by depositing thin diamond films (

Using the new ion beam-induced luminescence (IBIL) apparatus in National Legnaro Laboratories, Italy, a series of measurements concerning both wide-area luminescence spectra and monochromatic luminescence maps with a space resolution of a few μm has been carried out on several CVD diamond and c-BN samples. Protons of 2 MeV with a penetration depth of approximately 25 μm have been used in order to investigate the materials in the bulk. These measurements have been correlated with particle-induced X-ray emission (PIXE) and EPR data. The measurements have been performed at increasing proton doses in order to also investigate the radiation hardness of luminescence peaks. The results indicate that ionoluminescence of CVD diamond is dominated by three bands at approximately 2, 2.4 and 2.9 eV, with the intermediate band being very radiation-hard, and the other two radiation-weak. The band at 2 eV is correlated with N content, and is particularly high in samples with poor electronic properties. IBIL in c-BN is also dominated by three bands, one at approximately 2 eV, and the other two at higher energies with respect to CVD diamond. All these three bands seem to be relatively radiation-hard with respect to CVD diamond, and to be related to defects induced by doping.

CVD diamond detectors are of interest for charged particle detection and tracking due to their high radiation tolerance. In this article, we present, for the first time, beam test results from recently manufactured CVD diamond strip detectors and their behavior under low doses of electrons from a β-source and the performance before and after intense (>10 15 /cm 2 ) proton- and pion-irradiations. We find that low dose irradiation increase the signal-to-noise ratio (pumping of the signal) and slightly deteriorate the spatial resolution. Intense irradiation with protons 2.2×10 15 p / cm 2 lowers the signal-to-noise ratio slightly. Intense irradiation with pions 2.9×10 15 π / cm 2 lowers the signal-to-noise ratio more. The spatial resolution of the diamond sensors improves after irradiations.

The paper reviews measurements of the radiation tolerance of CVD diamond for irradiation with 24 GeV/c protons, 300 MeV/c pions and 1 MeV neutrons. For proton and neutron irradiation, the measured charge signal spectrum is compared with the spectrum calculated by a model. Irradiation by particles causes radiation damage leading to a decrease of the charge signal. However, both the measurements and the outcome from the model shows that for tracker applications this drawback is at least partly counterbalanced by a narrowing of the distribution curve of the charge signal. In addition, we observed after proton irradiation at the charge signal spectrum a decrease of the number of small signals. As a result, the efficiency of a CVD diamond tracker is less affected by irradiation than the mean charge signal. (11 refs).

Diamond is a nearly ideal material for detecting ionising radiation. Its outstanding radiation hardness, fast charge collection and low leakage current allow it to be used in high radiation environments. These characteristics make diamond sensors particularly appealing for use in the next generation of pixel detectors. Over the last year, the RD42 collaboration has worked with several groups that have developed pixel readout electronics in order to optimise diamond sensors for bump-bonding. This effort resulted in an operational diamond pixel sensor that was tested in a pion beam. We demonstrate that greater than 98% of the channels were successfully bump-bonded and functioning. The device shows good overall hit efficiency as well as clear spatial hit correlation to tracks measured in a silicon reference telescope. A position resolution of 14.8 μm was observed, consistent with expectations given the detector pitch.

In order to investigate the homogeneity of the transport properties in diamond, IBIC (ion beam induced charge) technique has been widely used, in consideration of the very high electrical resistivity of undoped CVD diamond. However, even if detailed maps of the combined electron-hole drift or collection length have been obtained, some effects occurring during measurements, mainly due to space-charge produced by trapped charge, probably contribute to mask reality. These effects could be responsible for electrical polarisation, by means of which the collection efficiency may decay with time, or even for the dependence of the results on the pulse counting rate. The strong polarisation observed in some samples is an indication of poor electronic properties. Good samples do not polarise at all, but in all cases display collection efficiency maps which depend both on the type of radiation used, on its energy and on total dose delivered to them. In general, but not always, the collection efficiency improves both in average value and in homogeneity through the sample: this could be an indication that the sample is not totally depleted by the applied bias because of space charge. There are also indications that the material quality improves from the substrate side to the growth side, and that drift length for electrons is longer than for holes, at least in some samples. These and other observations and conclusions gathered during years of IBIC measurements will be presented and discussed, in order to illuminate this still relatively unknown material, CVD diamond.

This paper reviews the development of CVD diamond pixel detectors. The preparation of the diamond pixel sensors for bump-bonding to the pixel readout electronics for the LHC and the results from beam tests carried out at CERN are described.

IBIC (Ion Beam Induced Charge) in its “lateral”version is a powerful method for mapping the drift length of carriers in a depletion region of a semiconductor device. This technique has been recently used in order to measure the drift length and to profile the electric field in a p+/nSi junction and in a totally depleted CdTe nuclear detector. Problems in data analysis arise when the device is not totally depleted and diffusion regions are present. These problems are generally solved by a sharp separation between the two regions, which is not the real case, since a smooth transition exists between high and low electric field regions and a back electrode induced field could also be present. In order to overcome these difficulties, a new theoretical approach based on the extended Ramo’s theorem has been developed. This theory allows diffusion length to be accurately evaluated taking into account the effects of the finite integration time of the electronic chain.

We present a systematic study of the growth of polycrystalline diamond thin films on W wires and tips by hot filament assisted chemical vapor deposition for x-ray detection purposes. We carry out correlations between scanning electron microscopy (SEM) observations and micro- Raman spectra, while varying different growth parameters. SEM observations show a uniform covering of the substrate, with growth rates ranging from 0.5 to 1.5 micrometers /h. All (mu) - R spectra show a well defined diamond peak at 1330.8-1333.7 cm-1 together with abroad structure at 1400-1600 cm-1 and a luminescence background extending over the whole scanned range. A close analysis shows that best quality is obtained with the lowest diameter substrates, at the lowest CH4 concentration and at a low pressure. Some depositions have been studied as x-ray detectors and their sensitivity at low energy and 6 MeV beam evaluated, showing a good response with respect to standard ionization chambers.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Diamond radiation sensors produced by chemical vapour deposition are studied for the application as tracking detectors in high luminosity experiments. Sensors with a charge collection distance up to 250 μm have been manufactured. Their radiation hardness has been studied with pions, proton and neutrons up to fluences of 1.9×10 15 π cm −2 , 5×10 15 p cm −2 and 1.35×10 15 n cm −2 , respectively. Diamond micro-strip detectors with 50 μm pitch have been exposed in a high-energy test beam in order to investigate their charge collection properties. The measured spatial resolution using a centre-of-gravity position finding algorithm corresponds to the digital resolution for this strip pitch. First results from a strip tracker with a 2×4 cm 2 surface area are reported as well as the performance of a diamond tracker read out by radiation-hard electronics with 25 ns shaping time. Diamond pixel sensors have been prepared to match the geometries of the recently available read-out chip prototypes for ATLAS and CMS. Beam test results are shown from a diamond detector bump-bonded to an ATLAS prototype read-out. They demonstrate a 98% bump-bonding efficiency and a digital resolution in both dimensions.

A new version of the classical IBIC technique is presented together with a comparison between IBIC and IBIL microscopy with the aim of obtaining maps of radiative recombination centers in technologically advanced materials. In some cases (Si,CCdTe) the method is used to profile the electrical field in the bulk of the sample, in other cases (GaAs, CVD diamond) maps of charge collection length are obtained and compared with morphological and structural features. A model for the interpretation of both IBIC and IBIL maps and spectra is presented and qualitatively discussed. In our opinion, maps of the IBIL IBIC ratio could be used in order to obtain maps of radiative recombination centers.

Proton microbeams of energy from 3 to 5 MeV have been used to investigate the cross section of Si, CdTe and CVD diamond samples by recording the charge pulses delivered at the electrodes by the single protons with a charge-sensitive electronic chain. The investigated depth varies from 50 to 140 μm depending on the proton energy and on the material. In the case of an homogeneous material (Si, CdTe), lifetime and mobility values can be obtained, together with the in-depth electrical field profiles. For polycrystalline materials, the maps of collection efficiency can be correlated with morphological maps putting in evidence a columnar-like structure due to the film growth mechanism. In these cases, it is relatively difficult to separate the effects due to the electric field from the carriers transport properties (mobility, lifetime). Anyway, maps of collection length are quite important in order to detect the electrical inhomogeneities of polycrystalline materials.

CVD (Chemical Vapour Deposited) diamond samples have been characterized by using Am-241 alpha particles in order to look for specific differences of the transport properties between electrons and holes. The effects of “priming” or exposing the samples to large doses of x-rays and to day light and to monochromatic light have been analyzed in some details with respect to charge collection efficiency and to counting efficiency values and their decay as a function of time. It turns out that the effect of priming is slightly larger for holes than for electrons and that only wavelengths in the interval between 350 and 550 nm are effective in changing the collection length. In this interval, hole collection efficiency is decreasing, while for electrons it increases. A possible interpretation of all these effects is presented and discussed, taking also into account luminescence and photoconductivity data.

CVD diamond could be an electroluminescent material. While its photoluminescent and cathodoluminescent properties are relatively well known, the electroluminescent ones have not been intensively investigated. The electroluminescent emission of CVD diamond is reminescent of the so-called “band A”; it is centered at 2.8 eV and extends from 2.6 to 3 eV. The luminescenceintensity increases linearly with the electric current and corresponds to a superquadratic regime of I-V characteristics in the dark and to a quadratic regime under a λ = 442 nm illumination. The I-V characteristics can be related to space charge limited current (SCLC) phenomena. Besides, the temperature behaviour of electroluminescence and of photoexcited current can be put into relation with the presence of a deep state in the bandgap where injected carriers from both electrodes recombine. The electroluminescent emission, even in a wavelength region far away from the photopic response, is clearly and strongly visible at naked eye. The luminescence efficiency is being discussed in order to consider CVD diamond as a material for optoelectronic devices.

Miniature metal-diamond wire detectors have been fabricated by Hot Filament Chemical Vapor Deposition (HFCVD) method and characterized as x-ray dosimeters in the energy range 50 keV–250 keV. Linearity of the response and the sensitivity as a function of energy have been accurately determined in a range routinely used for x-ray radiotherapy. With a Mo wire substrate, a 10 μm thick CVD diamond film can reach sensitivities of the order of 4×10−8 A/Gy/min, more than one order of magnitude larger than for a 6 cm3 standard ionization chamber.

Alpha particles were used for the first time to characterize the transport properties of polycrystalline CVD diamond films. The advantages with respect to other techniques which make use of β particles or light are that it is easier to discriminate between holes and electrons, and localization of deposited energy is more precise because a particles do not suffer from energy loss fluctuations and straggling. The results indicate that, on average, the transport properties of electrons and holes in CVD diamond are roughly the same and that lifetimes are in the range 0.3-1 ns. The broad distribution of collected energies is indicative of strong inhomogeneities in the transport of electrons and holes which are assumed to be related to the presence of crystalline grains of different dimensions. The values quoted in the literature for average carrier collection lengths, and obtained using minimum ionizing particles, are likely to be ascribed to charge transport in grains of dimensions in the range 10–100 μm.

We analyzed the physical properties of hydrogenated amorphous silicon (a-Si:H) samples grown by plasma-enhanced chemical vapor deposition, by means of infrared spectroscopy, mass-density, and optical measurements. We applied the usual infrared spectroscopic techniques to evaluate the amount of incorporated hydrogen and to investigate the influence of the Si-H bonding configurations on the optical and electronic properties of a-Si:H obtained by this widely used deposition process, and with parameters so chosen as to obtain films having state of the art characteristics. We carried out an exhaustive study of the different infrared absorption peaks, generally ascribed to different bonding configurations of H in Si, with a view to distinguishing the different contributions of SiH, ${\mathrm{SiH}}_{2}$ (${\mathrm{SiH}}_{2}$${)}_{\mathit{n}}$ to the spectral response of the material and to relating them to deposition temperature. The correlation of this infrared spectral analysis with mass-density measurements has evidenced that, for hydrogen content below 10 at. %, isolated SiH and ${\mathrm{SiH}}_{2}$ bonds occur, whereas, with higher hydrogen concentrations, the formation of (${\mathrm{SiH}}_{2}$${)}_{\mathit{n}}$ chains gives rise to empty cavities where hydrogen is preferentially incorporated. In addition, optical measurements show that samples deposited at temperatures below 170 \ifmmode^\circ\else\textdegree\fi{}C exhibit energy gaps and defect densities, which are quite different to those expected if only the effects of SiH groups are considered.

Simulations of spectroscopic performances of CdTe detectors by means of a Monte Carlo code have been recently reported. The computer code was demonstrated to be an extremely useful tool in simulating the spectral response of CdTe to gamma rays and in understanding the detailed effects of physical and electronic parameters on the experimental performances. In the present work, the attention is focused on the various aspects of the CdTe response to Co gamma rays, in an energy range which is extremely interesting for practical applications of CdTe spectroscopy. Spectra are presented for different experimental conditions particularly in connection with the rise time distributions and with the spatial distribution of the electric field in the detector. A precise correlation is established between the energy distribution and the pulse rise time distribution: the spectra obtained by a selection of a particular rise time interval are presented and discussed, and the conditions for reaching the best energy resolution are indicated. These conditions depend on the material quality and on the electrical field distribution.

An a-Si:HJCsI(T1) X-ray survey monitor working in photovoltaic modeC. Manfredotti, F. Fizzotti, E. Sacchi, E. Vittone, M. Boero1t and U. Nastasi#) Experimental Physics Department, University ofTorino and INFN-Sez. Torino, via P.Giuria 1,10125 Torino (I)*) Radiotherapy Dept., Ospedale S.Giovanni Battista, via S.Massimo 24, 10100 Torino (I)ABSTRACTA study concerning the use of a 1 cm2 p-i-n a-Si:H strucwre coupled to a 1 cm CsI(T1) scintillator is presented anddiscussed as a survey meter in the range from 20 to 125 keV X-ray peak energy. The p-i-n diode is deposited on comingglass 7059 covered by 1 m TCO (Transparent Conductive Oxide) by a standard PECVD (Plasma Enhanced ChemicalVapor Deposition). A particular mesa etch, coupled with standard photolithography, lowers dark current in the pAregion, allowing therefore the use of the detector in the photovoltaic mode. The detector sensitivity well goes below 1mrad/h, even without any current integration and, moreover, it increases from 20 keY to 125 keV, allowing for aneffective energy identification by using standard film-badge filters. In this work, we descilbe the details of detectorfabrication, the various steps of detector simulation in order to look for detector performances improvements, and the

Photosensitive a-Si:H p-i-n diodes, working in photovoltaic mode, have been coupled to CsI(T1) scintillators for dosimetry applications to X-ray monitoring in the energy range from 50 keV up to 15 MeV. A “mesa” approach for p-i-n diodes has been adopted both in order to better define the geometry and to obtain very low dark current. In order to optimize the geometry, a computer program has been created which simulates light generation in the scintillator, the collection by the detector and the photovoltaic current obtained as a function of exposure rate.Measurements have been carried out in the X-rays energy ranges 50-240 keV, at 6MeV and at 15 MeV. Detectors are linear in response and shows a good sensitivity, with the capability of measuring dose rates as low as 60 mR/h.The agreement between experimental data and simulation outputs can be considered good.

The effect of incorporation of SiH2 on a-Si:H matrix on the optical properties has been investigated on some details. It is shown that SiH2 incorporation is responsible for a further increase of the optical gap, and also for an increase in disorder. For concentrations larger than 15% approximately, microvoids are probably created and SiH2, which is covering their inner surfaces, seems not to affect the optical properties further on. The results indicate also clearly that the effect of autoannealing of the film during its growth cannot be neglected and that a new parameter should be retained, i.e. the total deposition time.

The paper reports results on intrinsic, device-quality amorphous silicon obtained with use of photothermal deflection spectroscopy. The gap-states distribution is obtained by means of a simple and reliable derivative procedure on the absorption-coefficient spectra. A comparison with other models is made. Finally, it is shown that the peak energy of the defects can be different for surface and bulk states, and so a shift of the occupied defect peak is observed if a considerable number of surface states are introduced. This explains the higher values for the dangling-bond correlation energy obtained by means of optical methods and agrees with other experimental evaluations of the distribution of surface states such as those carried out by means of total-yield spectroscopy.

Bulk YBCO samples have been prepared for the first time by using Metal-Organic Deposition (MOD) technique.Solutions of Y, Ba and Cu neodecanoates have been used in order to obtain directly YBCO powders (not exactly, but approximately stoichiometric) after a back-up and a pyrolysis step at 500°C. The powders have been successively pressed and subjected to two annealing steps in order to built up the YBCO structure, to increase grain dimensions and to adjust oxygen stoichiometry. The samples, which are disk-shaped, 1 mm thick and 1 cm wide, display a sharp superconducting transition at 93 K and possess a relatively large critical current.Diffraction patterns indicate a strong degree of orientation of (a,b) planes along the surface. The superconducting gap has been measured by SIS' tunneling with Nb and by investigation on SS' Andreev reflection.

A new PHOTO-CVD apparatus has been built in order to deposit a – Si : H films and other kinds of amorphous thin films by a technique which is both simple and versatile. This apparatus is composed of three chambers connected together: a load-lock chamber, a process chamber and a third chamber for in-situ analysis of deposited films. A peculiarity of the lamp, a dielectric discharge lamp which can work with noble gases like Xe or Kr, is that it can be completely dismounted without breaking the vacuum in order to clean the optical MgF2 window. By this method, the deposition chamber can be kept in very clean conditions. In this apparatus, we started to deposit a – SixC1−x: H of very good quality, taking their thickness into account. These films have been completely characterized by chemical (RBS, ERDA) and optical (PDS) methods. Their quality can be compared with quality of a – Si : H samples of the same thickness obtained by PECVD.

Optical, electronic and structural properties of a-Si:H samples grown by Low Pressure Chemical Vapor Deposition have been investigated by means of IR spectroscopy, Raman scattering and Photothermal Deflection Spectros-copy.Samples grown at different positions along the tube show very different properties that can be related to the amount of H and to the nature of the Si-H bonds.The most important parameters governing the thermally excited growth of a-Si:H are presented and discussed.

Utilisation de la spectroscopie infrarouge, de l'analyse de la detection du recul elastique (ERDA), et de l'evolution de l'hydrogene pour determiner la quantite d'hydrogene dans les films a-Si:H prepares par depot chimique en phase vapeur a basse pression. Utilisation de l'analyse ERDA pour calibrer (etalonner) les resultats obtenus par les spectres vibrationnels IR des LPCVD a-Si:H. La comparaison des deux ensembles de donnees permet d'evaluer les charges dipolaires effectives pour le doublet du mode d'etirement a 2000-2100 cm −1 . Les valeurs obtenues jusqu'ici sont compatibles avec la theorie et sont en bon accord avec les donnees experimentales obtenues sur des echantillons prepares aux moyens de techniques de depot differentes. Caracterisation de la liaison de l'hydrogene, en liaison avec la presence de vides dans le materiau

Breast cancer is a major cause of death among black women. At Cook County Hospital in Chicago, a hospital serving a predominantly black population, only 31% of breast cancers were localized at the time of diagnosis in the years 1980-1983. A survey of patient records in the largest primary care clinic in the hospital revealed that only 2% of eligible patients had received mammograms in 1982. A nurse-run breast cancer detection program was begun in mid-1983. Since that time the proportion of women who have received periodic breast examinations has increased from 26% to 46% (P less than 0.001) and periodic mammograms have increased from 2% to 41% (P less than 0.001). The proportion of women having received breast self-examination teaching increased from 10% to 58% (P less than 0.001). The proportion of localized breast cancer was significantly greater for those women whose cancer was diagnosed through the screening program (44 of 72, 61%) compared to other clinical areas (71 of 213, 33%) in the years 1984 through 1986 (P less than 0.001). There has been a significant increase in the percentage of localized breast cancer at Cook County Hospital comparing 1980-1983 statistics (31%), before the Breast Cancer Detection Program was fully established, with 1984-1986 statistics (40%) (P less than 0.02).

Both the optical and transport properties of a-Si: H have been suitably parametrized as a function of Urbach’s tail logarithmic slope Eo, surface density of states Ns and optical absorption normalization parameter αo, in order to reduce the number of parameters used for p-i-n solar cell S, simulation. The transient photovoltaic effect has been simulated by a Monte Carlo multitrapping computer model in order to investigate the possibility of its use for p-i-n solar cell diagnostics.

SUMMARY The efficacy of cricoid pressure (Sellick’s manoeuvre) was evaluated for use in paediatric anaesthesia. From studies on eight infant cadavers, cricoid pressure was found to be effective in occluding the oesophagus in the presence or absence of a nasogastric tube despite an intra-oesophageal pressure of 100 cm H,O. In anaesthetized paediatric patients, cricoid pressure did not directly occlude any of the oesophageal tubes previously filled with contrast material. A nasogastric tube need not be withdrawn before induction of anaesthesia. It can act as a “blow-off” valve if a rise in intragastric pressure occurs while cricoid pressure will prevent regurgitation of gastric contents into the pharynx.

CVD diamond films show both at optical microscope and at SEM a quasi-columnar structure, not homogeneously distributed in the bulk which is agreed to be responsible for the relatively large charge collection lengths measured in the material. In this work, we present the first data on charge collection efficiency distributions as measured directly in the bulk by a 3 Meν proton microbeam. The results indicate that the material is really non-homogeneous, that only few columns are really connecting both electrodes and that, finally, a real connection exists between the morphological structure and the maps of collection efficiency distribution.

Chemical vapor deposition (CVD) diamond is a radiation-hard sensor material that may be used for charged particle tracking near the interaction region in experiments at high-luminosity colliders. The goal of the work described in this paper is to investigate the use of several detector planes made of CVD diamond strip sensors for charged particle tracking. Toward this end, a tracking telescope composed entirely of CVD diamond planes has been constructed. The telescope was tested in muon beams, and its tracking capability has been investigated.

We present recent results on the use of Chemical Vapor Deposition (CVD) diamond microstrip detectors for charged particle tracking. A series of detectors was fabricated using 1 x 1 cm 2 diamonds. Good signal-to-noise ratios were observed using both slow and fast readout electronics. For slow readout electronics, 2 μs shaping time, the most probable signal-to-noise ratio was 50 to 1. For fast readout electronics, 25 ns peaking time, the most probable signal-to-noise ratio was 7 to 1. Using the first 2 x 4 cm 2 diamond from a production CVD reactor with slow readout electronics, the most probable signal-to-noise ratio was 23 to 1. The spatial resolution achieved for the detectors was consistent with the digital resolution expected from the detector pitch.

The effect of the polycrystalline morphology of CVD diamond on its electronic properties has been investigated by nuclear techniques, essentially by using the sample as a nuclear detector. A particular version of a proton microbeam technique has been used for the first time in order to study the inhomogeneities of carrier transport properties. The data have been correlated with results obtained by other techniques such as SEM, XPS, and EPMA. A good evidence has been gathered for the connection between the grain dimensions and the drift length of carriers in CVD diamond and for the high electric activity of grain boundaries. A model for trapping and recombination at grain boundaries, which could give a crude, but quite general exploration of electronic behavior of CVD diamond, is presented and discussed. Possible consequences presented on the applications of CVD diamond as a nuclear particle detector and as UV light emitting diode are also briefly described. L'effect de la morphologie policristalline du diamant CVD sur ses proprietes electroniques a eteecherche par des techniques nucleaires, essentielment en utilisant L'echantillon comme detecteur nucleaire. Une version particuliere de la technique du microfaiseau des protons a ete utilisee pour la premiere fois pour etudier les inhomogeneites des proprietes de transport de charge. Les informations ont ete mises au correlation avec les resultats obtenus par des autres techniques (SEM, XPS, EPMA). On a reussi a mettre en evidence la liason entre les dimension des grains, la longeur de “drift” des charges dans le diamant CVD et la grande activite electrique du bord de grain. Un modele approxime de recombinaison et “trapping” est presente et discute ainsi que L'exploration du comportement electrique du diamant CVD. On illustre des possibilites d'applications du diamant CVD comme detecteur nucleaire et comme diode emetteur de radiation UV.

CVD diamond nuclear detectors have been investigated with 241Am α particles and with 90Sr β particles in various conditions of bias polarization and irradiation geometry. It is proved that the parameter indicated as collection distance in the literature is an average value defined over a broad distribution which should be related to the grain size distribution inside the detector and, likely, also to fluctuations of the electrical field inside the grains. The sampling techniques used to detect the pulses normally select the largest values of the collection distances, as underscored by results obtained from our measurements with β particles by using these techniques; results have been found to be in good agreement with literature data. The collection length distribution has been found to be compatible with a superposition of two log-normal distributions, which are typical of grain dimension distributions in polycrystalline materials. It can be argued that grain size is a limiting factor for the collection distance and contributes with its fluctuations to the broadening of the pulses height spectrum of a minimum ionizing particle (MIP) in CVD diamond detectors. It can also be argued that sampling techniques suffer from pulse counting losses, which should be partly due to grain boundary effects.

Ion micro-beams are very efficient probes to characterize wide gap semiconductors. Ion beam induced charge (IBIC) technique has been extensively used to investigate the transport properties of diamond samples. Due to its scintillating nature, diamond is also suitable to be characterized by ionoluminescence. Similar to cathodoluminescence, this technique can be employed as a sensitive method to map radiative recombination centres. Thus, a combination of IBIC and IBIL (ion beam induced luminescence) in a nuclear microprobe represents a powerful analytical tool to get complementary information on the electronic properties of diamond. In this work we explore the combined use of IBIL and IBIC as a tool to characterize the electronic and scintillating properties of “detector grade” CVD diamond samples. IBIC maps show typical columnar structures easily referable to the crystal morphology, whereas IBIL maps put in evidence regions where radiative recombination occurs. Furthermore, IBIC and IBIL maps are almost complementary even if care has to be taken in comparison because of the evolving aspect of the IBIC maps as a function of the absorption dose.