The fast neutron response of a single-crystal diamond (SCD) detector was studied up to 300 degrees C. The SCD detector was fabricated using a 5 mm x 5 mm x 0.4 mm substrate with premetallization treatments for obtaining oxygen terminated surfaces. The electrical contacts to the detector were provided by Cr/Au metallization. The performance of the fabricated detector was investigated using leakage current versus bias voltage (I-V) measurements and using pulse height spectra measurements with 5.5 MeV alphas and 14 MeV fast neutrons. The leakage current was observed to be about 400-600 pA at a field of 1 V/mu m. From the full-width half-maximum of the alpha peak at 5.5 MeV, an energy resolution of about 2.1 +/- 0.1% was estimated. The fast neutron response measurements were carried out using a 14 MeV deuterium-tritium neutron source. No measurable degradation of the detector performance was observed up to the maximum studied temperature of 300 degrees C. The neutron spectrum obtained at 300 degrees C showed a well-defined peak at 8.5 MeV due to the C-12(n, alpha)Be-9 reaction which was the same as that observed at room temperature. Considering the total integrated counts, the detector sensitivity was observed to be 10(-2) count per neutron. The results presented in this paper demonstrate for the first time the high temperature operation of an SCD detector up to 300 degrees C. These results also suggest that such SCD detectors could be used at higher temperatures for neutron diagnostics in the future fusion plasma facilities such as International Thermonuclear Experimental Reactor.

Prototype single crystal diamond detectors with different types of metallization and post metallization treatment were fabricated for the applications requiring fast neutron measurements in the Indian Test Blanket Module (TBM) at the International Thermonuclear Experimental Reactor (ITER) Experiment. The detectors were characterized by leakage current measurements to ascertain that the leakage currents are low and breakdown voltages are higher than the voltage required for full charge collection. The detector response to charged particles was evaluated using a 238+239 Pu dual energy alpha source. The detectors showed an energy resolution of about 2% at 5.5MeV. In order to study their suitability for the operation at higher temperatures, leakage current variation and alpha response were studied up to 300°C. At 300°C, peaks corresponding to 5.156MeV and 5.499MeV alphas could be separated and there was no significant degradation of energy resolution. Finally, the detector response to fast neutrons was evaluated using a Deuterium-Tritium (D-T) neutron generator. The observed spectrum showed peaks corresponding to various channels of n-C interactions with a clear isolated peak corresponding to ~8.5MeV alphas. The detectors also showed high sensitivity of 3.4×10−2cps/n/(cm2s)–4.5×10−2cps/n/(cm2s) and excellent linearity of response in terms of count rate at different neutron flux in the observed range of 3.2×105n/(cm2s) to 2.0×106n/(cm2s).

Chemical vapor deposition has opened the possibility to grow high purity synthetic diamond at relatively low cost. This has opened up uses of diamond based detectors for wide range of applications. These detectors are most suitable for harsh environments where standard semiconductor detectors cannot work. In this paper, we present the fabrication details and performance study of polycrystalline diamond based radiation detector. Effect of different operating parameters such as bias voltage and shaping time for charge collection on the performance of detector has been studied.

Double sided DC-coupled silicon strip detectors with geometry of 65mm×65mm have been developed in India for nuclear physics experiments. The detectors have 64 P+ strips on the front side and 64 N+ strips on the backside with a pitch of 0.9mm. These detectors were fabricated using a twelve mask layer process involving double sided wafer processing technology. Semiconductor process and device simulations were carried out in order to theoretically estimate the impact of important design and process parameters on the breakdown voltage of detectors. The performance of the first lot of prototype detectors has been studied using static characterization tests and using an alpha source. The characterization results demonstrate that the detectors have low leakage currents and good uniformity over the detector area of about 40cm2. Overview of the detector design, fabrication process, simulation results and initial characterization results of the detectors are presented in this paper.

Diamond detectors have been fabricated using commercially available detector grade polycrystalline CVD substrates for fast neutron measurement in the Indian TBM Experiment at the upcoming ITER facility. Subsequent to fabrication, the detectors were characterized for leakage current and for response to alpha particles from 238+239Pu source. The detectors were observed to have low leakage currents at a field of 1Vµm−1. The stability of the alpha response and improvement in the count rate were achieved by β-irradiation using 90Sr β source. The fast neutron response of the detectors was studied using a D–T fast neutron source in India. The detectors showed linear response in the measured neutron flux of 2.86×105–8.76×106ncm−2s−1. The neutron response of detectors of 100µm and 300µm thicknesses was compared experimentally to study the neutron response dependence on detector thickness. Experimental results show that the detector of 100µm thickness has better performance compared to the detector of thickness of 300µm. The results presented in this paper confirm the suitability of commercially available films from Diamond Materials, GmbH, Germany for detector fabrication for fast neutron monitoring. The details of detector fabrication and results of characterization are presented in this paper.

Diamond detectors using polycrystalline CVD diamond substrates of thickness 300μm and 100μm were fabricated for fast neutron monitoring application.. The characterization of detectors was carried out using various tests such as leakage current, capacitance and alpha particle response. The performance of detectors was evaluated for fast neutrons at different neutron yields. The results presented in this work demonstrate that the diamond detectors will be suitable for monitoring fast neutrons.

The field emission properties of ion irradiated multiwalled carbon nanotubes (MWCNTs) and doublewalled carbon nanotubes (DWCNTs) have been studied. The carbon nanotubes synthesized by a chemical vapor deposition method were irradiated by high energy (90 MeV) Au ions with different ion fluence from 4x1011 to 1x1013 ions/cm2 . After ion irradiation, the field emission properties of MWCNTs and DWCNTs were greatly influenced. The change in the emission characteristics is due to structural defects caused by the high energy ion irradiation. The emission characteristic of MWCNTs was improved and turn-on field decreased from 5.43 to 3.10 V/m by ion irradiation. Noticeable improvement in emission characteristics of MWCNTs was observed at a fluence of 1x 10 13 ions/cm2. The emission characteristics of DWCNTs deteriorated and the turn-on field was increased from 2.44 to 7.76 V/m. This results show the distinctly different behavior of ion irradiated MWCNTs and DWCNTs.

Possible lattice incorporation sites for Ni in diamond have been investigated using ab initio density functional theoretical calculations. The results have been used to compute x-ray absorption near-edge structure spectra which were compared to spectroscopic measurements performed on a diamond single crystal grown at high pressure and high temperature in a nickel solvent. Ni at divacancy sites is proposed to be the most stable and probable configuration in this crystal.

The electrical properties of boron doped diamond layers after deuterium diffusion have been investigated by Hall effect and capacitance voltage measurements. It is found that (i) the deuterated boron doped diamond layers are inhomogeneous after the deuterium diffusion, resulting in conducting and insulating areas; (ii) negative and positive Hall voltages are measured on the same boron doped sample after deuterium diffusion, depending on the contact geometry (negative with van der Pauw and positive with mesa etched Hall bar); and (iii) in the conducting area, the majority of the boron-deuterium complexes are not ionized after the deuterium diffusion. The detailed electrical measurements using mesa-insulating Hall bar structures revealed that the existence of inhomogeneous regions with conducting and insulating areas is the most probable source of wrong n-type conductivity in deuterated boron doped diamond layers of this work. In the light of this result, the possibility of an incorrect assignment of a shallow donor previously reported in deuterated boron doped diamond is discussed. Finally, confirmation is given that the boron deuterium complexes created after the deuterium diffusion are neutral in p-type diamond.

We report on the electronic charge transfer in cobalt doped fullerene thin films by means of near-edge x-ray-absorption fine structure (NEXAFS) spectroscopy measurement. Co-doped fullerene films were prepared by co-deposition technique and subjected to energetic ion irradiation (120MeV Au) for possibly alignment or interconnect of randomly distributed metal particles. Polarization dependent NEXAFS spectra revealed the alignment of Co and C atoms along the irradiated ionic path. The structural changes in Co-doped as-deposited and ion irradiated fullerene films were investigated by means of Raman spectroscopy measurements. Downshift of pentagonal pinch mode Ag(2) in Raman spectroscopy indicated the electronic charge transfer from Co atom to fullerene molecules, which is further confirmed by NEXAFS at C K-edge for Co-doped fullerene films.

In the present work, we report on the magneto-transport properties of graphitic based materials (graphene, few-layer graphene, and bulk graphite) in very high magnetic field. Quantum Hall Effect (QHE) has been studied in graphitic systems in very high pulsed magnetic field (up to B = 57 T ) and at low temperature (≤ 4 K). Graphene sample shows well-defined Hall resistance plateaus at filling factors v = 2,6,10, etc. Few-layer graphene systems display clear signatures of standard and unconventional QHE. Magneto-transport studies on bulk highly oriented pyrolytic graphite show a charge density wave transition at strong enough magnetic field as well as Hall coefficient sign reversal.

This paper presents a review of the properties induced by the presence of hydrogen in monocrystalline boron-doped diamond (BDD) and proposes a comparison with results obtained on polycrystalline materials. Hydrogen diffusion, luminescence and electrical properties show the passivation of boron acceptors in diamond by the formation of (B,H) complexes, in both monocrystalline and polycrystalline forms, but at a different level. This behaviour raises open questions concerning the role of structural defects in the passivation of boron impurities by hydrogenation. Based on the assessment of the high thermal stability of (B,H) complexes, this approach leads to a route to provide patterned diamond conductive structures for micro as well as for nanotechnology applications.

Deep hole traps in boron-doped diamond epitaxial layers are studied by means of several types of deep-level transient spectroscopy and density-functional theory calculations. Standard deep-level transient spectroscopy and high-resolution isothermal transient spectroscopy permit to identify nine deep hole traps. Their capture cross-sections and ionization energies are systematically determined. In parallel, the ionization energies of donor and acceptor levels related to boron- and/or hydrogen-related complexes in diamond are assessed by ab initio calculations in this work and summarized with others from the literature including native defects. Tentative assignments of the measured deep hole traps to the calculated ones are proposed.

Ion beam irradiation of materials can cause defect creation as well as defect annealing depending on the ion beam parameters such as ion fluence and the energy loss of ions in materials. In present review, we report the behaviour of carbon nanotubes under exteme conditions such as laser irradiation and ion irradiation. The reorientation of the crystalline planes in confined single crystal nickel nanorods inside carbon nano tube, induced by heavy ion irradiation, is reported. Axial buckling of nickel nanorods as well as walls of carbon nano tubes in nickel encapsulated carbon nano tubes under swift heavy ion irradiation at high fluence is observed. At high fluence, amorphization of nickel nanorods inside carbon nanotubes is also observed. Axial buckling and amorphization under ion irradiation at high fluence are dependent on the number of walls in carbon nanotubes. High resolution transmission electron microscopy was used to investigate the reorientations, buckling and amorphization of metal filled nanotubes. Synthesis of carbon nanowires by ion irradiation of fullerene and their field emission properties with comparison to that of unirradiated and irradiated carbon nanotubes are reported. An international scenario with future prospects of ion beam studies in carbon nanotube is briefed.

We investigate the quantum Hall regime in a graphene flake with different levels of disorder. Under high magnetic field, an unexpected decrease in the Hall resistance occurs when only the zeroth-energy Landau level is populated. The presence of disorder rules out the expected appearance of the $\ensuremath{\nu}=0$ quantum Hall plateau as in the case of pristine graphene. Instead, we propose an alternative explanation based on the coexistence of two types of carriers, electrons and holes, induced by high magnetic field, in the presence of disorder.

The effects of ion irradiation on electrical and magnetic properties of C60 films are investigated and correlated to changes of structure. Conducting nanowires are formed along the linear path of swift heavy ions. Their continuity and radial dimension are correlated with the energy density deposited by such ions in electronic excitations. Whatever the slowing down process of ions, irradiation at high ion fluences induces the formation of an amorphous C phase exhibiting a ferromagnetic response up to room temperature. An additional paramagnetic signal is recorded from films irradiated with swift ions, which is ascribed to the formation of oriented defects decorated with oxygen.

The effects of intense laser and energetic ion irradiation on Raman vibrational modes of Multiwalled Carbon Nanotubes have been investigated. The intensity ratio of D and G modes decreases with increase in laser power density and remains almost constant with decrease of laser power density. The intensity ratio of D mode to G mode for ion irradiated Multiwalled Carbon Nanotubes decreases at low fluence (4 x 10(11) ions/cm(2)) and increases further with increase in ion fluence. The results show that ion irradiation at low fluence and laser irradiation lead to purification/ordering of the nanotubes. (C) 2008 Elsevier B.V. All rights reserved.

We report the x-ray magnetic circular dichroism (XMCD) studies on Fe doped fullerene thin film and bulk highly oriented pyrolytic graphite. The element-specific hysteresis curves were recorded by measuring the XMCD at the Fe L3 edge as a function of the applied field strength at different temperatures. These investigations suggest that Fe doped fullerene is ferromagnetic at room temperature, while Fe atoms are driven to a nonmagnetic/paramagnetic state with the interaction of graphite matrix.