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We report findings on the Ion Beam Induced Charge (IBIC) characterization of a 4H-SiC Schottky barrier diode (SBD), in terms of the modification of the Charge Collection Efficiency (CCE) distribution induced by 20 MeV C ions irradiations with fluences ranging from 20 to 200 ions/um2. The lateral IBIC microscopy with 4 MeV protons over the SBD cross section, carried out on the pristine diode evidenced the widening of the depletion layer extension as function of the applied bias and allowed the measurement of the minority carrier diffusion lengths. After the irradiation with C ions, lateral IBIC showed a significant modification of the CCE distribution, with a progressive shrinkage of the depletion layer as the fluence of the damaging C ions increases. A simple electrostatic model ruled out that the shrinkage is due to the implanted charge and ascribed the perturbation of the electrostatic landscape to radiation-induced defects with positive charge state.

The investigation of secondary effects induced by ionizing radiation represents a new and ever-growing research field in radiobiology. This new paradigm cannot be investigated only using standard instrumentation and methodologies, but rather requires novel technologies to achieve significant progress. In this framework, we developed diamond-based sensors that allow simultaneous real-time measurements with a high spatial resolution of the secretory activity of a network of cells cultured on the device, as well as of the dose at which they are exposed during irradiation experiments. The devices were functionally characterized by testing both the above-mentioned detection schemes, namely: amperometric measurements of neurotransmitter release from excitable cells (such as dopamine or adrenaline) and dosimetric evaluation using different ionizing particles (alpha particle and X-ray photons). Finally, the sensors were employed to investigate the effects induced by X-rays on the exocytotic activity of PC12 neuroendocrine cells by monitoring the modulation of the dopamine release in real-time.

We describe benchmark experiments to evaluate the frictional properties of laser patterned low-density polyethylene as a function of sliding velocity, normal force, and humidity. The pattern is a square lattice of square cavities with sub-mm spacing. We find that dynamic friction decreases compared to nonpatterned surfaces, since stress concentrations lead to early detachment, and that stick-slip behavior is also affected. Friction increases with humidity, and the onset of stick-slip events occurs in the high humidity regime. Experimental results are compared with numerical simulations of a simplified 2D spring-block model. A good qualitative agreement can be obtained by introducing a deviation from the linear behavior of the Amontons-Coulomb law with the load due to a saturation in the effective contact area with pressure. This also leads to the improvement of the quantitative results of the spring-block model by reducing the discrepancy with the experimental results, indicating the robustness of the adopted simplified approach, which could be adopted to design patterned surfaces with controlled friction properties.

This paper describes both an experimental methodology based on the Ion Beam Induced Charge (IBIC) technique and the relevant interpretative model, which were adopted to characterize the electronic features of power diodes. IBIC spectra were acquired using different proton energies (from 1.2 to 2.0 MeV), angles of incidence, and applied bias voltages. The modulation of the ion probe range, combined with the modulation of the extensions of the depletion layer, allowed the charge collection efficiency scale to be accurately calibrated, the dead layer beneath the thick (6 micrometer) Al electrode and the minority carrier lifetime to be measured. The analysis was performed by using a simplified model extracted from the basic IBIC theory, which proved to be suitable to interpret the behaviour of the IBIC spectra as a function of all the experimental conditions and to characterize the devices, both for what concerns the electrostatics and the recombination processes., Comment: 24 pagese,10 figures

Diamond based p-i-n light-emitting diodes, developed to electrically drive single-photon sources in the visible spectral region at room temperature, have the potential to play a key role in quantum based technologies. In order to gain more insight into the charge injection mechanism occurring in these diodes, we carried out an experiment aimed to investigate the electrostatics and the charge carrier transport by the Ion Beam Induced Charge (IBIC) technique, using 1 MeV He microbeam raster scanning of p-i-n structures fabricated in a high purity diamond substrate, using lithographic masking and P and B ion implantation doping. Charge Collection Efficiency (CCE) maps obtained at low ion fluence, show that induced charge pulses arise only from the P-implanted region, whereas no IBIC signals arise from the B-implanted region. This result suggests the formation of a slightly p-type doped substrate, forming a n + -p-p + , rather than the expected p-i-n, structure. However, for high fluence scans of small areas covering the intrinsic gap, CCE maps are more uniform and compatible with a p-i-n structure, suggesting the occurrence of a “priming effect”, which saturates acceptor levels resulting in a decrease of the effective doping of the diamond substrate.

Multiferroic thick nanocomposite films of (1 − x )(0.3CoFe 2 O 4 -0.7BiFeO 3 )- x Polyvinylidene difluoride (CFO-BFO/PVDF) with x variations 0.20, 0.30 and 0.40 were synthesized using hot press method. Detailed measurements of structural, dielectric, magnetic and magnetoelectric data have been reported. Structural characterization reveals the presence of all the three distinct phases viz. CFO, BFO and PVDF. The dielectric loss as low as 0.05 has been observed for composite film with 40 mol% of PVDF. The AC conductivity (5.9 × 10 −8 Ω −1 cm −1 ) of composite film ( x = 0.40) is found to be much lower as compared to CFO-BFO ceramic. The electric poling of composite film (with x = 0.30) leads to substantial increase in saturation (2M s ) and remnant magnetization (2M r ). A significant magnetoelectric effect with magnetoelectric voltage coefficient ( α ME ) ∼ 22.128 mV/cm Oe has been observed for composite film with x = 0.40, which is possibly a consequence of implicit mechanical interaction between CFO and BFO through PVDF matrix. Hence these nanocomposite films hold a great potential to be promising candidates for multiferroic devices.

International audience; In sight of the luminosity increase of the High Luminosity-LHC (HL-LHC), most experiments at the CERN Large Hadron Collider (LHC) are planning upgrades for their innermost layers in the next 5–10 years. These upgrades will require more radiation tolerant technologies than exist today. Usage of Chemical Vapor Deposition (CVD) diamond as detector material is one of the potentially interesting technologies for the upgrade. CVD diamond has been used extensively in the beam condition monitors of BaBar, Belle, CDF and all LHC experiments. Measurements of the radiation tolerance of the highest quality polycrystalline CVD material for a range of proton energies, pions and neutrons obtained with this material are presented. In addition, new results on the evolution of various semiconductor parameters as a function of the dose rate are described.

The planned upgrade of the LHC to the High-Luminosity-LHC will push the luminosity limits above the original design values. Since the current detectors will not be able to cope with this environment ATLAS and CMS are doing research to find more radiation tolerant technologies for their innermost tracking layers. Chemical Vapour Deposition (CVD) diamond is an excellent candidate for this purpose. Detectors out of this material are already established in the highest irradiation regimes for the beam condition monitors at LHC. The RD42 collaboration is leading an effort to use CVD diamonds also as sensor material for the future tracking detectors. The signal behaviour of highly irradiated diamonds is presented as well as the recent study of the signal dependence on incident particle flux. There is also a recent development towards 3D detectors and especially 3D detectors with a pixel readout based on diamond sensors.

In this paper, we describe an experiment aimed to measure the physical observables, which can be used for the assessment of the radiation hardness of commercially available silicon photo diodes commonly used as nuclear detectors in particle accelerator laboratories. The experiment adopted the methodology developed during the International Atomic Energy Agency (IAEA) Coordinated Research Project (CRP No. F11016) “Utilization of Ion Accelerators for Studying and Modelling Ion Induced Radiation Defects in Semiconductors and Insulators”. This methodology is based on the selective irradiation of micrometer-sized regions with different fluences of MeV ions using an ion microbeam and on the measurement of the charge collection efficiency (CCE) degradation by Ion Beam Induced Charge (IBIC) microscopy performed in full depletion condition, using different probing ions. The IBIC results are analyzed through a theoretical approach based on the Shockley-Read-Hall model for the free carrier recombination in the presence of ion-induced deep traps. This interpretative model allows the evaluation of the material radiation hardness in terms of recombination parameters for both electrons and holes. The device under study in this experiment was a commercial p-i-n photodiode, which was initially characterized by i) standard electronic characterization techniques to determine its doping and ii) the Angle-Resolved IBIC to evaluate its effective entrance window. Nine regions of (100 × 100) µm2 were irradiated with 11.25 MeV He ions up to a maximum fluence of 3·1012 ions/cm2. The CCE degradation was measured by the IBIC technique using 11.25 MeV He and 1.4 MeV He as probing ions. The model presented here proved to be effective for fitting the experimental data. The fitting parameters correspond to the recombination coefficients, which are the key parameters for the characterization of the effects of radiation damage in semiconductors., This work has been carried out within the IAEA coordinated research project F11016. “Utilization of Ion Accelerators for Studying and Modelling of Radiation Induced Defects in Semiconductors and Insulators”. It has been in part supported by Croatian Science Foundation (Croatia) under the project MIOBICC (No. 8127). EV acknowledges support from the project “Departments of Excellence” (L. 232/2016), funded by the Italian Ministry of Education, University and Research (MIUR) and from the experiment “ASIDI” of the Italian Institute for Nuclear Physics (INFN). The support by Australian government through the NCRIS funding scheme is acknowledged as well.

We report on a novel synthetic pathway for the chemical functionalization of nanodiamonds with porphyrin. To this scope, the NDs, after a thermal treatment essential to organize the crystal surface, were derivatized with reactive moieties useful to conjugate the ND with porphyrin. Untreated and modified nanoparticles were systematically characterized by X-ray photoelectron, Raman, photoluminescence and infrared spectroscopies with the purpose of evaluating the effects due to the crystals manipulation and confirming the efficacy of the proposed approach. An investigation of the effects induced to the samples by laser irradiation (probe for Raman and PL spectroscopies) was performed, highlighting the significant increase of temperature that is associated to the redshift of Raman diamond peak.

The investigation of materials under extreme pressure conditions requires high-performance cells whose design invariably involves trade-offs between the maximum achievable pressure, the allowed sample volume, and the possibility of real-time pressure monitoring. With a newly conceived hybrid piston-clamped anvil cell, we offer a relatively simple and versatile system, suitable for nuclear magnetic resonance experiments up to 4.4 GPa. Finite-element models, taking into account mechanical and thermal conditions, were used to optimize and validate the design prior to the realization of the device. Cell body and gaskets were made of beryllium-copper alloy and the pistons and pusher were made of tungsten carbide, while the anvils consist of zirconium dioxide. The low-temperature pressure cell performance was tested by monitoring in situ the pressure-dependent 63Cu nuclear-quadrupole-resonance signal of Cu2O.

Accelerator-based nuclear techniques are an important tool for the modification and characterization of surfaces in general, down to a depth of around one micrometer. For oxide semiconductors used in solar energy conversion, the surface plays a critical role in facilitating the use of solar photon energy to obtain hydrogen via spontaneous water oxidation. For such a process, the required surface properties are complex and include specific chemical composition, as well as the defect composition, and both of these characteristics may be augmented using accelerator-based nuclear techniques. The targeted modification of surfaces makes use of ion implantation for changing the chemical composition, and ion irradiation for changing the defect structure. The defect formation is a very complex process, and in this work we placed more emphasis on this aspect. We attempted to present the defect formation under the irradiation of ion beams at the two extremes: formation of extensive and large-scale cluster defects; and formation of small-scale point defects. In addition, we review the main characterization techniques based on ion beams, with examples from work carried out on semiconductors and oxide semiconductors.

Proceedings of the 13th Pisa Meeting on Advanced Detectors : Frontier Detectors for Frontier Physics, 24-30 May 2015, La Biodola, Italy.; International audience; In the present study, results towards the development of a 3D diamond sensor are presented. Conductive channels are produced inside the sensor bulk using a femtosecond laser. This electrode geometry allows full charge collection even for low quality diamond sensors. Results from testbeam show that charge is collected by these electrodes. In order to understand the channel growth parameters, with the goal of producing low resistivity channels, the conductive channels produced with a different laser setup are evaluated by Raman spectroscopy.

Boron is the most effective dopant element in diamond and the capability to introduce high densities of boron makes ion implantation a potential key technology to verify superconductivity in diamond. However, its optimization involves many experimental parameters (i.e. ion energy, fluence, current, annealing times and temperature) and the effectiveness of B implantation to induce superconductivity in diamond is still to be demonstrated. So far, a limited number of works in the range of high (i.e.>5 MeV) B ion energies have been carried, despite the promising perspective offered by deep implantation to fabricate sub-superficial superconductive structures in diamond. To this scope, in the present work, we report on the study of the structural effects of high-energy boron ion irradiation on diamond. Monocrystalline diamond sample was irradiated with an 8 MeV 11B microbeam across multiple square areas, characterized by a different combination of fluences and ion currents. After the implantation, the sample was characterized by Raman spectroscopy and Atomic Force Microscopy to assess its structural modifications and the related surface swelling. Significant variations related to the irradiation condition have been determined, The present work was supported by the Grant “Departments of Excellence” (L. 232/2016), funded by the Italian Ministry of Education, University and Research (MIUR), by the Italian Institute for Nuclear Physics (INFN) within the experiments “ASIDI” and “DIACELL” and by CRT Foundation within the MiRaDS project

We investigate the microscopic mechanism responsible for the change of macroscopic electrical properties of the $\mathrm{B}{\mathrm{i}}_{2}\mathrm{S}{\mathrm{r}}_{2}\mathrm{CaC}{\mathrm{u}}_{2}{\mathrm{O}}_{8+\ensuremath{\delta}}$ high-temperature superconductor induced by intense synchrotron hard x-ray beams. The possible effects of secondary electrons on the oxygen content via the knock-on interaction are studied by Monte Carlo simulations. The change in the oxygen content expected from the knock-on model is computed convoluting the fluence of photogenerated electrons in the material with the Seitz-Koehler cross section. This approach has been adopted to analyze several experimental irradiation sessions with increasing x-ray fluences. A close comparison between the expected variations in oxygen content and the experimental results allows determining the irradiation regime in which the knock-on mechanism can satisfactorily explain the observed changes. Finally, we estimate the threshold displacement energy of loosely bound oxygen atoms in this material ${T}_{d}=0.{15}_{\ensuremath{-}0.01}^{+0.025}\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$.

Thanks to its excellent mechanical properties, graphene is particularly suited for the realization of suspended membranes. The present paper deals with one possible application of such membranes that is the realization of suspended lithographic masks for shadow evaporation onto a substrate. This technique, which is largely used for realizing mesoscopic devices, where the quality requirements for the junctions prevent the exposure to ambient air and the occurrence of quantum phenomena requires highly defined structures, can be improved by the use of pure 2-dimensional masks, like graphene ones. Advantages and differences of this material with respect to commonly employed polymers are presented and discussed.

The effect of laser irradiation on chemically vapor deposited (CVD) graphene was studied by analyzing the temporal evolution of Raman spectra acquired under various illumination conditions. The spectra showed that the normalized intensity of the defect-related peak increases with the square root of the exposure time and varies almost linearly with the laser power density. Furthermore, the hardness of graphene to radiation damage depends on its intrinsic structural quality. The results suggest that, contrary to the common belief, micro-Raman spectroscopy cannot be considered a noninvasive tool for the characterization of graphene. The experimental observations are compatible with a model that we derived from the interpretative approach of the Staebler–Wronski effect in hydrogenated amorphous silicon; this approach assumes that the recombination of photoexcited carriers induces the breaking of weak C–C bonds.

We present the analysis of the charge collection efficiency (CCE) degradation of float zone grown n -type silicon detectors irradiated with 1.3, 2.0 and 3.0 MeV protons. The analysis was carried out by irradiating small regions (50 × 50 μm 2 ) with a proton microbeam at fluences ranging from 10 11 to 4·10 12 ions/cm 2 and probing the effect of irradiation by measuring the 4.5 MeV Li ion induced charge in full depletion conditions. The CCE degradation as function of the proton fluence shows an unexpected deviation from the linear behavior predicted by the Shockley–Read–Hall model of carrier recombination. The build-up of excess hydrogen related donors due to proton irradiations is suggested to be the cause of a significant perturbation of the electrostatic properties of the diode, which drastically change the electron trajectories and hence the induced charge mechanism.

Chemical vapor deposition (CVD) on Cu thin films is a promising approach for the large area formation of graphene on dielectric substrates, but a fine control of the deposition parameters is required to avoid dewetting of the Cu catalyst. In this paper we report on the study of the Cu dewetting phenomena by monitoring the intensity of the infra-red emission from the film surface during rapid thermal CVD of graphene. The reduction of Cu film coverage consequent to dewetting is detected as a variation of sample's emissivity. Results indicate three time constants of dewetting, describing three typical stages, hole formation, propagation and ligament breakup. Slowing the first incubation stage by tuning pressure in the chamber allows for an effective surface activation resulting in the deposition of graphene at temperatures lower than those in the case of Cu foils.

11th International Conference on Position Sensitive Detectors (PSD11),3–8 sept. 2017, The Open University, Milton Keynes, UK.; International audience; Beam test results of the radiation tolerance study of chemical vapour deposition (CVD) diamond against different particle species and energies is presented. We also present beam test results on the independence of signal size on incident particle rate in charged particle detectors based on un-irradiated and irradiated poly-crystalline CVD diamond over a range of particle fluxes from 2 kHz/cm2 to 10 MHz/cm2. The pulse height of the sensors was measured with readout electronics with a peaking time of 6 ns. In addition functionality of poly-crystalline CVD diamond 3D devices was demonstrated in beam tests and 3D diamond detectors are shown to be a promising technology for applications in future high luminosity experiments.

In the present work, we report on the monolithic fabrication by means of ion beam lithography of hollow micro-channels within a diamond substrate, to be employed for microfluidic applications. The fabrication strategy takes advantage of ion beam induced damage to convert diamond into graphite, which is characterized by a higher reactivity to oxidative etching with respect to the chemically inert pristine structure. This phase transition occurs in sub-superficial layers thanks to the peculiar damage profile of MeV ions, which mostly damage the target material at their end of range. The structures were obtained by irradiating commercial CVD diamond samples with a micrometric collimated C+ ion beam at three different energies (4 MeV, 3.5 MeV and 3 MeV) at a total fluence of 2 × 1016 cm−2. The chosen multiple-energy implantation strategy allows to obtain a thick box-like highly damaged region ranging from 1.6 μm to 2.1 μm below the sample surface. High-temperature annealing was performed to both promote the graphitization of the ion-induced amorphous layer and to recover the pristine crystalline structure in the cap layer. Finally, the graphite was removed by ozone etching, obtaining monolithic microfluidic structures. These prototypal microfluidic devices were tested injecting aqueous solutions and the evidence of the passage of fluids through the channels was confirmed by confocal fluorescent microscopy.

Chemical vapor deposition (CVD) of graphene onto Cu substrates is a very promising approach for large-scale production. When dealing with Cu thin films instead of foils, there are additional problems related to the stability of the film at high temperatures. We show that the film rupture and agglomeration can be prevented by monitoring in-situ dewetting dynamics of the catalytist. We investigated the possibility to perform CVD of graphene onto Cu films, 200 nm thick, at low-pressure conditions, with ethanol or methane as C precursors. Same recipes applied on Cu foils lead to worse results highlighting the important role played by the substrate thickness to achieve a high catalytic activity. The influence on the deposition quality of parameters such as time, temperature and hydrogen flow is then discussed.

In a multi-electrode device, the motion of free charge carriers generated by ionizing radiation induces currents on all the electrodes surrounding the active region [1] . The amount of charge induced in each sensitive electrode is a function of the device geometry, the transport parameters and the generation profile. Hence this charge sharing effect allows the signal from each sensitive electrode to provide information about the electrical characteristics of the device, as well as information on the location and the profile of each ionization track. The effectiveness of such approach was recently demonstrated in Ion Beam Induced Charge (IBIC) experiments carried out using a 2 MeV He microbeam scanning over a sub-100 μm scale silicon device, where the ion strike location point was evaluated through a comparative analysis of the charge induced in two independent surface electrodes coupled to independent data acquisition systems [2] . In this report, we show that the Monte Carlo method [3] can be efficiently exploited to simulate this IBIC experiment and to model the experimental data, shedding light on the role played by carrier diffusion, electronic noise and ion beam spot size on the induction of charge in the sensitive electrodes. Moreover, the Monte Carlo method shows that information on the ion strike position can be obtained from the charge signals from the sensitive electrodes.

We present a detailed study of simulated and experimentally observed factors which influence the formation of wires in p-type silicon which is irradiated with a high energy, small diameter proton beam, and subsequently electrochemically etched in dilute hydrofluoric acid. A better understanding of the variety of factors influencing wire formation enables a better control of their size, gap between adjacent wires and shape. This addresses a previous limitation in fabricating such structures, such as uncontrollable wire shape and undefined minimum gaps. Furthermore it removes limitations in their application in photonics, such as the difficulty in coupling light between adjacent waveguides, a smearing of the band gap of photonic crystals due to imperfect periodicity, and difficulty in moving the photonic band gap towards near infra-red range. Therefore, the present work allows better control in fabricating components for three dimensional silicon machining and silicon photonics using ion irradiation in conjunction with electrochemical etching.

The acronym IBIC (Ion Beam Induced Charge) was coined in early 1990's to indicate a scanning microscopy technique which uses MeV ion beams as probes to image the basic electronic properties of semiconductor materials and devices. Since then, IBIC has become a widespread analytical technique to characterize materials for electronics or for radiation detection, as testified by more than 200 papers published so far in peer-reviewed journals. Its success stems from the valuable information IBIC can provide on charge transport phenomena occurring in finished devices, not easily obtainable by other analytical techniques. However, IBIC analysis requires a robust theoretical background to correctly interpret experimental data. In order to illustrate the importance of using a rigorous mathematical formalism, we present in this paper a benchmark IBIC experiment aimed to test the validity of the interpretative model based on the Gunn's theorem and to provide an example of the analytical capability of IBIC to characterize semiconductor devices., 22 pages, 7 figures

Deep Ion Beam Lithography (DIBL) has been used for the direct writing of buried graphitic regions in monocrystalline diamond with micrometric resolution. Aiming at the development and the characterization of a fully ion-beam-micromachined solid state ionization chamber, a device with interdigitated electrodes was fabricated by using a 1.8 MeV He+ ion microbeam scanning on a homoepitaxial, grown by chemical vapour deposition (CVD). In order to evaluate the ionizing-radiation-detection performance of the device, charge collection efficiency (CCE) maps were extracted from Ion Beam Induced Charge (IBIC) measurements carried out by probing different arrangements of buried microelectrodes. The analysis of the CCE maps allowed for an exhaustive evaluation of the detector features, in particular the individuation of the different role played by electrons and holes in the formation of the induced charge pulses. Finally, a comparison of the performances of the detector with buried graphitic electrodes with those relevant to conventional metallic surface electrodes evidenced the formation of a dead layer overlying the buried electrodes as a result of the fabrication process., Comment: 17 pages, 6 figures

This paper investigates both theoretically and experimentally the charge collection efficiency (CCE) degradation in silicon diodes induced by energetic ions. Ion Beam Induced Charge (IBIC) measurements carried out on n- and p-type silicon diodes which were previously irradiated with MeV He ions show evidence that the CCE degradation does not only depend on the mass, energy and fluence of the damaging ion, but also depends on the ion probe species and on the polarization state of the device. A general one-dimensional model is derived, which accounts for the ion-induced defect distribution, the ionization profile of the probing ion and the charge induction mechanism. Using the ionizing and non-ionizing energy loss profiles resulting from simulations based on the binary collision approximation and on the electrostatic/transport parameters of the diode under study as input, the model is able to accurately reproduce the experimental CCE degradation curves without introducing any phenomenological additional term or formula. Although limited to low level of damage, the model is quite general, including the displacement damage approach as a special case and can be applied to any semiconductor device. It provides a method to measure the capture coefficients of the radiation induced recombination centres. They can be considered indexes, which can contribute to assessing the relative radiation hardness of semiconductor materials., This work has been carried out within the IAEA Coordinated Research Project No. F11016 “Utilization of Ion Accelerators for Studying and Modelling Ion Induced Radiation Defects in Semiconductors and Insulators” and has been supported in part by Croatian Science Foundation under the project MIOBICC (8127).

The Ion Beam Induced Charge Collection (IBIC) technique was used to map the charge collection efficiency (CCE) of a 4H-SiC photodetector with coplanar interdigitated Schottky barrier electrodes and a common ohmic contact on the back side. IBIC maps were obtained using focused proton beams with energies of 0.9 MeV and 1.5 MeV, at different bias voltages and different sensitive electrode configurations (charge collection at the top Schottky or at the back Ohmic contact). These different experimental conditions have been modeled using a two dimensional finite element code to solve the adjoint carrier continuity equations and the results obtained have been compared with experimental results. The excellent consistency between the simulated and experimental CCE maps allows an exhaustive interpretation of the charge collection mechanisms occurring in pixellated or strip detectors., Comment: 22 pages, 11 figures

In the present work we report about the investigation of the conduction mechanism of sp2 carbon micro-channels buried in single crystal diamond. The structures are fabricated with a novel technique which employs a MeV focused ion-beam to damage diamond in conjunction with variable thickness masks. This process changes significantly the structural proprieties of the target material, because the ion nuclear energy loss induces carbon conversion from sp3 to sp2 state mainly at the end of range of the ions (few micrometers). Furthermore, placing a mask with increasing thickness on the sample it is possible to modulate the channels depth at their endpoints, allowing their electrical connection with the surface. A single-crystal HPHT diamond sample was implanted with 1.8 MeV He+ ions at room temperature, the implantation fluence was set in the range 2.1x10^16 - 6.3x10^17 ions cm^-2, determining the formation of buried micro-channels at 3 um. After deposition of metallic contacts at the channels' endpoints, the electrical characterization was performed measuring the I-V curves at variable temperatures in the 80-690 K range. The Variable Range Hopping model was used to fit the experimental data in the ohmic regime, allowing the estimation of characteristic parameters such as the density of localized states at the Fermi level. A value of 5.5x10^17 states cm-3 eV-1 was obtained, in satisfactory agreement with values previously reported in literature. The power-law dependence between current and voltage is consistent with the space charge limited mechanism at moderate electric fields., Comment: 17 pages, 8 figures

Proceedings of the 37 International Conference on High Energy Physics (ICHEP 2014), 2-9 July 2014, Valencia, Spain. Editors M. Aguilar-Benítez, J. Fuster, S. Martí-García, A. Santamaría.; International audience; Diamond devices have now become ubiquitous in the LHC experiments, finding applications in beam background monitoring and luminosity measuring systems. This sensor material is now maturing to the point that the large pads in existing diamond detectors are being replaced by highly granular tracking devices, in both pixel and strip configurations, for detector systems that will be used in Run II at the LHC and beyond. The RD42 collaboration has continued to seek out additional diamond manufacturers and quantify the limits of the radiation tolerance of this material. The ATLAS experiment has recently installed, and is now commissioning a fully-fledged pixel tracking detector system based on diamond sensors. Finally, RD42 has recently demonstrated the viability of 3D biased diamond sensors that can be operated at very low voltages with full charge collection. These proceedings describe all of these advances.

The transport properties of a 4H-SiC Schottky diode have been investigated by the Ion Beam Induced Charge (IBIC) technique in lateral geometry through the analysis of the charge collection efficiency (CCE) profile at a fixed applied reverse bias voltage. The cross section of the sample orthogonal to the electrodes was irradiated by a rarefied 4 MeV proton microbeam and the charge pulses have been recorded as function of incident proton position with a spatial resolution of 2 um. The CCE profile shows a broad plateau with CCE values close to 100% occurring at the depletion layer, whereas in the neutral region, the exponentially decreasing profile indicates the dominant role played by the diffusion transport mechanism. Mapping of charge pulses was accomplished by a novel computational approach, which consists in mapping the Gunn's weighting potential by solving the electrostatic problem by finite element method and hence evaluating the induced charge at the sensing electrode by a Monte Carlo method. The combination of these two computational methods enabled an exhaustive interpretation of the experimental profiles and allowed an accurate evaluation both of the electrical characteristics of the active region (e.g. electric field profiles) and of basic transport parameters (i. e. diffusion length and minority carrier lifetime)., Comment: 25 pages, 5 figures

We present experimental results and numerical simulations to investigate the modification of structural-mechanical properties of ion-implanted single-crystal diamond. A phenomenological model is used to derive an analytical expression for the variation of mass density and elastic properties as a function of damage density in the crystal. These relations are applied together with SRIM Monte Carlo simulations to set up Finite Element simulations for the determination of internal strains and surface deformation of MeV-ion-implanted diamond samples. The results are validated through comparison with high resolution X-ray diffraction and white-light interferometric profilometry experiments. The former are carried out on 180 keV B implanted diamond samples, to determine the induced structural variation, in terms of lattice spacing and disorder, whilst the latter are performed on 1.8 MeV He implanted diamond samples to measure surface swelling. The effect of thermal processing on the evolution of the structural-mechanical properties of damaged diamond is also evaluated by performing the same profilometric measurements after annealing at 1000 {\deg}C, and modeling the obtained trends with a suitably modified analytical model. The results allow the development of a coherent model describing the effects of MeV-ion-induced damage on the structural-mechanical properties of single-crystal diamond. In particular, we suggest a more reliable method to determine the so-called diamond "graphitization threshold" for the considered implantation type., Comment: 19 pages, 4 figures

In this investigation a technology has been developed to use diamond electrodes in Micro Electrode Arrays (MEAs) on a transparent sapphire substrate, thus combining the outstanding electrochemical properties of boron-doped diamond electrodes (BDD) with the transparency needed for simultaneous fluorescence analysis. Nanodiamond films were grown on double side polished sapphire substrates by hot filament CVD (HFCVD) and Bias Enhanced Nucleation (BEN). A simple four microelectrode array (quadrupole) has been fabricated, fully characterized in optical and electrochemical properties, and tested with adrenal chromaffin cells, identifying amperometric spikes by the four recording diamond electrodes, corresponding to the oxidation current of catecholamine molecules.

The exposure of H-terminated nanocrystalline diamond (NCD) to ultraviolet (UV) light in air and at room temperature modifies the features of the diamond surface, in terms of wettability, electrical conductivity and chemical reactivity. This allows the development of a soft, dry and non invasive method to tailor the surface properties for the development of new chem- or bio-sensors. In this work, we report about the analysis of hydrogen terminated nanocrystalline diamond films grown by hot-filament technique and of their surface modification following UV light exposure. This UV treatment induces an hydrophobic to hydrophilic transformation and an outstanding increase of the electrical resistivity (> 10 5 ). X-ray (XPS) and ultraviolet (UPS) photoelectron spectroscopy provide insight into the role of chemisorbed oxygen on the modification of the valence band and on the transformation of the electron affinity (from negative to positive) at the diamond surface.

Diamond surface hydrogenation is generally carried out with atomic hydrogen obtained by either microwave plasma or heated filaments. Both these techniques present some drawbacks, given by some instabilities and containment difficulties in the former case, and by some surface contamination by the elements of the filaments themselves, which must be very close to the substrate, in the latter. Surface hydrogenation can be easily obtained by molecular hydrogen, at substrate temperatures not much different from those used in the above methods, but only via thermal means and without the aforementioned drawbacks. In this paper we describe a systematic study carried out on hydrogenated surfaces obtained at different temperatures, from 700 to 900 °C, and on different diamond materials (natural and HPHT), by exposing different surfaces such as (100), (111) and (110) to molecular hydrogen. The results indicate that values of surface resistivity are comparable to those obtained using hot filaments, particularly at temperatures around 800 °C, and that the activation energy related to the establishment of surface conductivity is relatively low. Surface resistivity, XPS (X-ray Photoelectron Spectroscopy), AFM and µ-FTIR in reflection-transmission mode data indicate that the efficiency of surface hydrogenation with the consequent low values of surface resistivity is quite similar for the three surface orientations, but also that in the case of (100) orientation this efficiency is lower.

A new ionoluminescence (IL) apparatus has been successfully installed at the external scanning microbeam facility of the 3 MV Tandetron accelerator of the INFN LABEC in Firenze; the apparatus for photon detection has been fully integrated in the existing ion beam analysis (IBA) set-up, for the simultaneous acquisition of IL and PIXE/PIGE/BS spectra and maps. The potential of the new set-up is illustrated in this paper by some results extracted by the analysis of art objects and advanced semiconductor materials. In particular, the adequacy of the new IBA set-up in the field of cultural heritage is pointed out by the coupled PIXE/IL micro-analysis of a lapis lazuli stone; concerning applications in material science, IL spectra from a N doped diamond sample were acquired and compared with CL analyses to evaluate the relevant sensitivities and the effect of ion damage.

The control of the carrier lifetime profile in semiconductor power devices is of fundamental importance to optimize device parameters. With respect to traditional technologies such as diffusion of metallic impurities, light ion irradiation at low doses provides precise spatial localization of defects acting as carrier traps and recombination centres. Hence, the generation of suitable lifetime profiles obtained by controlling ion fluence and energy allows the reduction of turn-off times and switching losses in power electronic devices. In order to characterise the effects of ion irradiation on carrier lifetime profiles, we have used the ion beam induced charge collection (IBIC) technique in lateral geometry to measure charge collection efficiency (CCE) profiles in silicon p+/n/n+ diodes under different applied bias conditions before and after a frontal 6.5 MeV He++ ion implantation at a total fluence of 2 × 10 12 ions/cm 2 . After the irradiation, the profile shows a clear drop of charge collection efficiency which occurs at the end of the ion range. The formalism based on Shockley–Ramo–Gunn’s theorem was applied to interpret the CCE profiles in both virgin and irradiated samples and to assess the free carrier lifetime profile modification following the radiation damage.

We report experimental evidence of a substantial reduction of the sheet resistance of a commercially available (110) oriented natural diamond surface after exposure not to atomic but to molecular hydrogen. In a conventional CVD reactor, we have merely exposed the sample to high purity molecular hydrogen fluxes at 800 °C. After exposure to air, the surface conductivity increased several orders of magnitude as measured by a professional collinear four-point probe head with tungsten carbide tips. After annealing at 900 °C in vacuum (P

When a thin gold layer is deposited onto the native oxide of a silicon wafer and is annealed at temperatures greater than 600 °C, peculiar circular features, few micrometers in diameter, with a regular polygon at the centre of each circle, reminiscent of so called “alien” crop circles, can be observed. A model has been recently proposed in Matthews et al. [1], where the formation of such circular structures is attributed to the interdiffusion of gold and silicon through holes in the native oxide induced by the weakening of the amorphous silica matrix occurring during the annealing process. The rupture of the liquid Au/Si eutectic disc surrounding the pinhole in the oxide causes the debris to be pulled to the edges of the disk, forming Au droplets around it and leaving an empty zone of bare silicon oxide. In this paper, we present a morphological study and a RBS/PIXE analyses of these circular structures, carried out by scanning electron microscopy and by 4 MeV C microbeam, respectively. The results confirm the depletion of gold in the denuded circular zones, and the presence of gold droplets in the centers, which can be attributed to the Au segregation occurring during the cooling stage.

In this work, we present an investigation by Kelvin Probe Microscopy (KPM) of buried graphitic microchannels fabricated in single-crystal diamond by direct MeV ion microbeam writing. Metal deposition of variable-thickness masks was adopted to implant channels with emerging endpoints and high temperature annealing was performed in order to induce the graphitization of the highly-damaged buried region. When an electrical current was flowing through the biased buried channel, the structure was clearly evidenced by KPM maps of the electrical potential of the surface region overlying the channel at increasing distances from the grounded electrode. The KPM profiling shows regions of opposite contrast located at different distances from the endpoints of the channel. This effect is attributed to the different electrical conduction properties of the surface and of the buried graphitic layer. The model adopted to interpret these KPM maps and profiles proved to be suitable for the electronic characterization of buried conductive channels, providing a non-invasive method to measure the local resistivity with a micrometer resolution. The results demonstrate the potential of the technique as a powerful diagnostic tool to monitor the functionality of all-carbon graphite/diamond devices to be fabricated by MeV ion beam lithography., 21 pages, 5 figures

CVD diamond, as other wide energy gap semiconductors or insulators, is known to present polarization effects when used as a nuclear particle detector, which are due to the building up of an internal space-charge electric field and are responsible for “memory” effects if the polarization is not erased. Polarization effects are larger when the thickness of the sample is longer than the drift length of carriers and give rise to a shortening of the electric field region inside the sample. In this work, IBIC (Ion Beam Induced Charge) measurements with 1 and 2 MeV proton beams have been carried out on a relatively thin CVD diamond sample with the conclusion that no memory or hysteresis effects were present even by switching from one polarity to the opposite one in subsequent measurements. However, it resulted that the values of the charge collection efficiency (cce) did depend on counting rate and the lowering at large counting rates was attributed to a local polarization due to trapping. Finally, in some cases cce turned out to be larger than 1, a result which could be either due to local detrapping or to non-blocking contacts.

Charge collection efficiency (CCE) profiles of a semi-insulating (SI) gallium arsenide LEC (Liquid Encapsulated Czochralski) Schottky diode have been investigated by lateral Ion Beam Induced Charge collection (IBIC) technique. A focussed 2.4 MeV proton microbeam was scanned over the cleaved surface of a SI-GaAs diode and the charge collection efficiency was evaluated as a function of the ion beam position at different bias voltages. By fitting the CCE profiles with the equations derived by the Shockley–Ramo–Gunn’s theorem, drift lengths of electrons and holes were obtained. Experimental results are consistent with previous OBIC (Optical Beam Induced Current) and SP (Surface Potential) measurements and confirm the model based on the formation of a Mott barrier due to the enhanced electron capture cross section in high field conditions.

Tracking detectors have become an important ingredient in high-energy physics experiments. In order to survive the harsh detection environment of the large hadron collider (LHC), trackers need to have special properties. They must be radiation hard, provide fast collection of charge, be as thin as possible and remove heat from readout electronics. The unique properties of diamond allow it to fulfill these requirements. In this work we present an investigation of the charge transport and luminescence properties of “detector grade” artificial chemical vapour deposition (CVD) diamond devices developed within the CERN RD42 collaboration, performed by means of X-ray micro-beam induced current collection (XBICC) and X-ray micro-beam induced luminescence (XBIL) techniques. XBICC technique allows quantitative estimates of the transport parameters of the material to be evaluated and mapped with micrometric spatial resolution. In particular, the high resolution and sensitivity of the technique has allowed a quantitative study of the inhomogeneity of the charge transport parameter defined as the product of mobility and lifetime for both electron and holes. XBIL represents a technique complementary to ion beam induced luminescence (IBIL), which has already been used by our group, since X-ray energy loss profile in the material is different from that of MeV ions. X-ray induced luminescence maps have been performed simultaneously with induced photocurrent maps, to correlate charge transport and induced luminescence properties of diamond. Simultaneous XBICC and XBIL maps exhibit features of partial complementarity that have been interpreted on the basis of considerations on radiative and non-radiative recombination processes which compete with charge transport efficiency.

Ion beam induced charge collection (IBIC) is a powerful experimental technique to characterise semiconductor materials and devices. It is based on the measurement of the charge induced in a given electrode by the motion of charge carriers generated by MeV ions. The problem of IBIC pulse formation is usually solved by the Shockley–Ramo theorem in which charge carriers are moving in presence of an electric field and all the electrodes are maintained at constant potentials. This theoretical model was demonstrated according to basic electrostatic principles and was first applied to evaluate the induced currents in vacuum tubes and then in semiconductor devices even in presence of stationary space charge. However, the basic assumption underlying such theorems is the independence of the space charge distribution on the applied bias voltage. Such a hypothesis is clearly not valid in partially depleted semiconductor devices where the extension of the depletion region depends on the conditions of the boundary electrodes. We present in this paper a new theoretical approach based on a general expression for electrostatic induction deduced by J.B. Gunn in 1964, which overcomes any limitation on space charge distribution. The resulting simple new formalism reduces to the Ramo–Shockley theorem as a special case. In order to clarify this theoretical approach, some simple IBIC experiments on semiconductor p–n and Schottky diodes are presented and discussed.

Ion microbeam techniques like ion beam-induced charge collection (IBICC) are very powerful methods in order to investigate and to map the transport properties in different technologically important semiconductors and in particular in materials proposed for nuclear detection. Time-resolved ion beam-induced charge collection (TRIBICC) represents a further improvement with respect to more traditional IBICC, since it can supply not only the charge collection efficiency (and through it data on mobility and trapping time of carriers in drift regions) but also the time behaviours of the charge collection. For long collection times, this means to gather information, also about diffusion lengths and lifetimes of carriers in the diffusion regions, which are always present in undepleted electronic devices, in particular power devices, and which are of paramount importance as inputs for simulation codes. By TRIBICC, in fact, some difficulties could be avoided in analysis of data collected in cases when lifetimes and shaping times of electronic chain are similar, and the sensitivity of the method is worse. In order to suitably analyse TRIBICC data, a theoretical model should be available: in general, Ramo's theorem is used, but its validity in cases when space charge is present is questionable. A more general and powerful 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 in the time-dependent case. An application of this method to a commercial power device is presented and discussed.

We have used a micrometer size X-ray beam generated from a synchrotron light source at the European Synchrotron Radiation Facility (ESRF) in Grenoble and a 2 MeV proton micro-beam at the Italian National Laboratory (LNL) of Legnaro to image the electronic transport properties of a CVD diamond detector developed within the CERN RD42 collaboration. The focused X-rays or protons are scanned over the device surface, and the induced current or charge pulse is measured and plotted on two dimensional maps. Due to the polycrystalline nature of the material, the maps are not homogeneous and both the techniques show structures ascribable to diamond grains. It was found that the uniformity of the maps depends on the lateral scale (binning) and on the analytical depth of the micro-probes.