The development of CVD grown single-crystal Diamond-on-Iridium (DOD sensors for charged-particle detection in hadrons and nuclei physics research is reviewed. A variety of samples grown at the University of Augsburg has been investigated with alpha and beta sources in the laboratory, swift ions from the heavy-ion synchrotron SIS in Darmstadt, and relativistic protons from the COoler-SYnchrotron COSY in Julich. The results obtained by means of I-E(V) studies, transient-current techniques (TCT), alpha-spectroscopy, and heavy-ion time-of-flight (ToF) measurements are compared to those of commercially available \polycrystalline and homoepitaxial single crystal CVD diamond sensors of electronic grade quality. In many aspects, the performance of DOI sensors was found quite similar to that of homoepitaxial counters, and in any case far superior to that of polycrystalline detectors. Under single-carrier drift conditions, the CCE and energy resolution (delta E/E) for holes reached levels CCEh > 95% and delta E/E-h similar to 0.3%, respectively, which correspond to values of the Schubweg w(h,e) well above the detector thickness. In contrast, the CCEe for electrons was typically lower than similar to 40%, leading to appreciable reduction of the detection efficiency in the dual-carrier drift mode (CCE similar to 60%), which characterizes the experiments with swift heavy ions and high-energy particles. We measured transport parameters comparable to those of homoepitaxial devices: mu(h)(0) similar to 3080-1756 and mu(e)(0) similar to 2276-1150 cm(2)/Vs, v(sat)(h) similar to(1.7-1.4) *10(7) and v(sat)(e) similar to(1.5-1.0)* 10(7) cm/s, as well as intrinsic time resolutions sigma(i) similar to 15 ps. It is shown, that substantial improvements have been achieved in recent years, albeit reproducibility and the understanding of the reduced electron collection remain challenging issues. Prime novelty: Comprehensive electrical characterization of intrinsic single-crystal CVD Diamond-OnIridium sensors produced at the University of Augsburg and their classification into the range of commercial electronic grade polycrystalline and homoepitaxial diamond sensors supplied by Element Six.

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/cm(2) to 10 MHz/cm(2). 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.

Direct laser writing of conductive paths in synthetic diamond is of interest for implementation in radiation detection and clinical dosimetry. Unraveling the microscopic processes involved in laser irradiation of diamond below and close to the graphitization threshold under the same conditions as the experimental procedure used to produce three-dimensional devices is necessary to tune the laser parameters to optimal results. To this purpose a transient currents technique has been used to measure laser-induced current signals in monocrystalline diamond detectors in a wide range of laser intensities and at different bias voltages. The current transients vs time and the overall charge collected have been compared with theoretical simulations of the carrier dynamics along the duration and after the conclusion of the 30 fs laser pulse. The generated charge has been derived from the collected charge by evaluation of the lifetime of the carriers. The plasma volume has also been evaluated by measuring the modified region. The theoretical simulation has been implemented in the framework of the empirical pseudopotential method extended to include time-dependent couplings of valence electrons to the radiation field. The simulation, in the low-intensity regime, I similar to 1 TW/cm(2), predicts substantial deviation from the traditional multiphoton ionization, due to nonperturbative effects involving electrons from degenerate valence bands. For strong field with intensity of about 50 TW/cm(2), nonadiabatic effects of electron-hole pair excitation become prominent with high carrier densities eventually causing the optical breakdown of diamond. The comparison of theoretical prediction with experimental data of laser-generated charge vs laser energy density yields a good quantitative agreement over six orders of magnitude. At the highest intensities the change of slope in the trend is explained taking into account the dependence of the optical parameters and the carrier mobility on plasma density.

Continuous Position Sensitive Diamond Detector (CPSDD) development started by using the single crystal (sc) diamond material. The intrinsic high detection efficiency of sc diamond, providing a high Signal to Noise (S/N) ratio, allowed the full testing of CPSDD with alpha-particles. However, due to the size limitations of sc diamond, the development of Large Area CPSDD (LACPSDD) naturally evolved towards the use of polycrystalline (pc) diamond material, produced by chemical vapor deposition (CVD). The charge generated by the particle or radiation impact is collected through diamond like carbon (DLC) layers and associated metallic electrodes deposited on the sides of the pc diamond plate. The incident particle position can be obtained via charge division measurement by using charge sensitive amplifiers (CSA) connected to each electrode. In this paper we report the improvement in LACPSDD design by showing results obtained for two pc diamond detector (pcDD) structures. The first pcDD has a DLC layer with four electrodes at the corners of the front side, whereas the back side is fully metallized. The second pcDD has DLC layers on both sides of the detector plate, each equipped with two parallel electrode strips, along the x and y axis, respectively. Experimental results on the first pcDD showed an ion rate limitation, caused by the increase in the detector time constant (because of the larger detection area), and a low S/N ratio, due to the specific reduced signal associated with low Charge Collection Efficiency (CCE) of pc diamond. Subsequently, by using an optimized electronics and a better pc diamond (higher CCE), the second pcDD shows a higher S/N ratio, as well as a lower time constant. This paper presents simulation results on the time constant and an analytical evaluation of the S/N ratio, which serve to optimize the pc LACPSDDs. We also show experimental test results with alpha-particles, as well as Ni-54 (1.7 AGeV) and C-12 (11.4 AMeV) ion beams.Prime Novelty Statement: This paper presents the first large area continuous position sensitive diamond detectors implemented on polycrystalline CVD diamond material for single ionizing particle detection. (C) 2016 Elsevier B.V. All rights reserved.

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.

Short current pulses of width around 1ns are generated by 50μm thickness single crystal diamond detectors, which makes them very attractive for fast timing nuclear experiments. The shape of the pulse is greatly affected by the applied electric field that influences both the pulse rise time and its width. An exponential behaviour is found for the rise time and pulse width vs electric field. Measurements performed with high bandwidth electronics yield rise time down to 300ps. It is also shown that for pulse duration in the nanosecond range, alternative electronic systems to the bulky and costly digital oscilloscopes, are commercially available.

Diamond detectors are usually produced from the electronic (detector) grade diamond material in a form of thin plate or film. In order to produce diamond detector, the plate has to be equipped with suitable (most often metallic) electrodes. Such metallic electrodes were and still are produced at GSI Target Laboratory by sputtering of one or more thin metal layers on the surface of the diamond. A particular electrode structure in that case is obtained by using stencil masks that are also a limiting factor since the minimal obtainable structure is of about 100 μm. To overcome this limitation the laser lithography system (shown in Fig. 1) was acquired and put into the operation in the GSI Detector Laboratory.

Typical size of the chemical vapor deposition (CVD) homoepitaxially grown diamond material (also known as the single crystal SC) is limited to some 5 x 5 mm due to the availability of growth substrates made from the highpressure high-temperature (HPHT) diamond. Presently, the only material readily available for the production of diamond detectors with larger area (∼10 cm) is polycrystalline (PC) film grown on silicon wafers with electronic characteristics far inferior in comparison to SC material. In order to produce a large-surface high-quality material for diamond detectors different techniques for heteroepitaxial growing of diamond films are being investigated and developed at the University of Augsburg. By using yttriumstabilized zirconium oxide (YSZ) buffer layer to produce iridium terminated substrate on silicon wafers [1] one can grow diamond films (also know as the diamond on iridium DoI) that are far more homogeneous than PC, however, still burdened with defects. In last few years a remarkable improvement in lowering of the level of impurities and defects was achieved so that the presently produced samples while still not comparable to SC material are far superior to any PC material. Most significant structural defect arising in heteroepitaxial growth are dislocations.In a recent study [2] in which the density of threading dislocations was determined by few methods over a large sample thickness, an inverse growth depth behaviour was found. While this at least in principle confirms that films with very low density of dislocations can be grown, presently procedure would not be economically effective therefore different growing techniques e.g. epitaxial lateral overgrowth are being developed. In order to assess the quality i.e. electronic characteristics of new DoI samples a typical measurement of the charge collection efficiency (CCE) is performed by using the transient current technique (TCT). Alpha particles (Am) are used to test the sample with different polarizations and drift fields so that the properties for both types of charge carriers can be evaluated. In Fig. 1 the set of measurements with a recent DoI sample of 190 μm thickness at different drift fields is presented showing the saturation at values above 0.8 V/μm. While the overall triangular shape of wave forms indicate the presence of the charge recombination defects, additional flat-top slope is related to losses due to the charge carrier trapping within the sample. For this sample we have measured an average CCE of about 60% for holes, which is below the level of the best samples ∗This work was supported in part by HadronPhysics3 (grant agreement No 283286 under the EU FP7.) † m.kis@gsi.de Figure 1: Pulse-shapes (waveforms) obtained for the drift of holes across the sample. The CCE is determined by waveform integration. Each waveform is an average from 1000 recorded events.

The evolution of our understanding of these properties of diamond material, which are crucial for the application of diamond detectors under harsh radiation and temperature conditions, is reviewed. The fundamental research performed in the 1920s on the photoconductivity of natural diamonds has led to the very first observations that defined diamond of being capable of "counting particles and photons". From 1920 to 2010, there has been an ever-growing demand for detector instrumentation for nuclear physics experiments, augmented and ameliorated by every new generation of particle accelerators that pushed forward the technology for growth and postprocessing of advanced artificial diamond materials for these purposes. Special attention is given to the quest of the origin of the "famous" radiation hardness of diamond, since this is, among the long list of favorable characteristics, one of the most important properties that make diamond sensors competitive to traditional devices, in particular to gas chambers, silicon diodes, and scintillator counters. The second unique property of the diamond materials is the high mobility of both charge carriers, which, in many applications, counterbalances the drawback of the small detector signal amplitudes-the latter originates from the otherwise favorable wide band gap of diamond. Illustrative examples with some active diamond detector arrangements that operate under extreme conditions in present experiments complete this report.

The development of dislocation density and micro-strain in heteroepitaxial diamond films on iridium was measured over more than two decades of thickness up to d ≈ 1 mm. Simple mathematical scaling laws were derived for the decrease of dislocation density with increasing film thickness and for its correlation with micro-strain. The Raman line width as a measure of micro-strain showed a huge decrease to 1.86 cm−1, close to the value of perfect single crystals. The charge collection properties of particle detectors built from this material yield efficiencies higher than 90% in the hole-drift mode, approaching the performance of homoepitaxial films.

This article reports on the development and the first applications of a new spectrometer which enables the precise and time-resolved measurement of both the energy loss and the charge-state distribution of ion beams with 10 < Z < 30 at energies of 4–8 MeV/u after their interaction with a laser-generated plasma. The spectrometer is based on five 20 × 7 mm2 large and 20 μm thick polycrystalline diamond samples produced via the Chemical Vapour Deposition (CVD) process and was designed with the help of ion-optical simulations. First experiments with the spectrometer were successfully carried out at GSI using 48Ca ions at an energy of 4.8 MeV/u interacting with a carbon plasma generated by the laser irradiation of a thin foil target. Owing to the high rate capability and the short response time of the spectrometer, pulsed ion beams with 103–104 ions per bunch at a bunch frequency of 108 MHz could be detected. The temporal evolution of the five main charge states of the calcium ion beams as well as the corresponding energy loss values could be measured simultaneously. Due to the outstanding properties of diamond as a particle detector, a beam energy resolution \documentclass[12pt]{minimal}\begin{document}$\frac{\Delta E}{E}$\end{document}ΔEE ≈ 0.1% could be reached using the presented experimental method, while a precision of 10% in the energy loss and charge-state distribution data was obtained.

We report on the high statistics two-pion correlation functions from pp collisions at $\sqrt{s}=0.9$ TeV and $\sqrt{s}$=7 TeV, measured by the ALICE experiment at the Large Hadron Collider. The correlation functions as well as the extracted source radii scale with event multiplicity and pair momentum. When analyzed in the same multiplicity and pair transverse momentum range, the correlation is similar at the two collision energies. A three-dimensional femtoscopic analysis shows an increase of the emission zone with increasing event multiplicity as well as decreasing homogeneity lengths with increasing transverse momentum. The latter trend gets more pronounced as multiplicity increases. This suggests the development of space-momentum correlations, at least for collisions producing a high multiplicity of particles. We consider these trends in the context of previous femtoscopic studies in high-energy hadron and heavy-ion collisions, and discuss possible underlying physics mechanisms. Detailed analysis of the correlation reveals an exponential shape in the outward and longitudinal directions, while the sideward remains a Gaussian. This is interpreted as a result of a significant contribution of strongly decaying resonances to the emission region shape. Significant non-femtoscopic correlations are observed, and are argued to be the consequence of "mini-jet"-like structures extending to low $p_{\rm T}$. They are well reproduced by the Monte-Carlo generators and seen also in $\pi^+\pi^-$ correlations.

This paper describes operation principles and the in-beam performance of Start Detector (SD) assemblies consisting of Diamond Detectors (DDs) grown by Chemical Vapour Deposition (CVD) and Front End Electronics (FEE) which have been designed for and used in various nuclear physics experiments at GSI Helmholtz Center for Heavy Ion Research in Darmstadt.In parallel to the FEE design we have performed extensive calculations to model the dependence of the signal-to-noise ratio (S/N) and the time resolution sigma(t) on various quantities such as the collected charge Q(col), the detector capacitance C(D), the temperature T, and finally the noise contribution and bandwidth of the amplifier.In combination with the new FEEs (including an application-specific integrated circuit, ASIC) we have tested both polycrystalline and single-crystal diamonds of various sizes and thicknesses with relativistic ion beams ranging from protons to heaviest ions.For heavy ions all setups deliver time resolutions sigma(t) < 60 ps. In case of protons the small primary detector signals require single-crystals as material and more elaborated designs like segmentation of the detector area and the increase of the amplifier input impedance. The best time resolution obtained for relativistic protons was sigma(t) = 117 ps.

The inclusive transverse momentum ($p_{\rm T}$) distributions of primary charged particles are measured in the pseudo-rapidity range $|\eta|<0.8$ as a function of event centrality in Pb-Pb collisions at $\sqrt{s_{\rm{NN}}}=2.76$ TeV with ALICE at the LHC. The data are presented in the $p_{\rm T}$ range $0.1530$ GeV/$c$. In peripheral collisions (70-80%), the suppression is weaker with $R_{\rm{AA}} \approx 0.7$ almost independently of $p_{\rm T}$. The measured nuclear modification factors are compared to other measurements and model calculations.

We report on the high statistics two-pion correlation functions from pp collisions at root s = 0.9 TeV and root s = 7 TeV, measured by the ALICE experiment at the Large Hadron Collider. The correlation functions as well as the extracted source radii scale with event multiplicity and pair momentum. When analyzed in the same multiplicity and pair transverse momentum range, the correlation is similar at the two collision energies. A three-dimensional femtoscopic analysis shows an increase of the emission zone with increasing event multiplicity as well as decreasing homogeneity lengths with increasing transverse momentum. The latter trend gets more pronounced as multiplicity increases. This suggests the development of space-momentum correlations, at least for collisions producing a high multiplicity of particles. We consider these trends in the context of previous femtoscopic studies in high-energy hadron and heavy-ion collisions and discuss possible underlying physics mechanisms. Detailed analysis of the correlation reveals an exponential shape in the outward and longitudinal directions, while the sideward remains a Gaussian. This is interpreted as a result of a significant contribution of strongly decaying resonances to the emission region shape. Significant nonfemtoscopic correlations are observed, and are argued to be the consequence of "mini-jet"-like structures extending to low p(t). They are well reproduced by the Monte-Carlo generators and seen also in pi(+)pi(-) correlations.

The properties of CVD Diamond (CVDD) detectors such as high mobility of charge carriers, radiation hardness, and low dark conductivity provide a detector material, which is suggested to be applied in high intensity heavy-ion beam environments where classical detector devices cannot be operated [1]. In the future FAIR experiments radiation-hard materials with large area will be required for a variety of detection applications. Heteroepitaxial 'quasi' single crystal CVD diamond grown on wafer-scale Ir/YSZ/Si(001) substrates was investigated as an alternative to small-area homoepitaxial single crystal CVDD (scCVDD). Recent samples D1 and D2 of thicknesses dD1 = 290μm and dD2 = 320μm, respectively, showed interesting results in terms of structural homogeneity, charge collection efficiency, and dark conductivity.

In the last year, we continued with the development of large-area diamond sensors grown at the University of Augsburg by chemical vapour deposition (CVD) on wafer scale Ir/YSZ/Si(001) substrates. Early results of diamondon-iridium (DoI) sensors [1] were indicating significant defect densities within the detector bulk, which led to reduced charge collection efficiencies CCE = QColl/QGen= 40% (with QGen the particle induced charge and QColl the charge measured by the sensor) and broad spectra of energy resolution δE/E ≈ 30%. These values were obtained with traversing Am-α-particles for the favourable case of a sensor of thickness d = 12μm = α-range in diamond. A remarkable improvement of the crystal-quality has been achieved in 2010 by using ultra-pure H2/CH4 gas mixtures and optimized growth techniques [2]. Two DoI samples D1 and D2 of thicknesses dD1 = 293 μm and dD2 = 320 μm, respectively, were investigated. Ti/Pt/Au quadrant electrodes with common mass potential were applied in order to prove the spatial homogeneity of the detector performance. Almost symmetrical IED characteristics with respect to the bias polarity were obtained for each sector, while the dark current at electric fields ED ≥ ± 2 V/μm were of the order of 10 A, well comparable to homoepitaxial single-crystal (SC) diamond sensors.