X-ray induced photocurrent characteristics of CVD diamond detectors with different carbon electrodes

Schirru, F.; Lohstroh, A.; Jayawardena, K. D. G. Imalka; Henley, Simon J.; Sellin, P.J.

doi:10.1088/1748-0221/8/12/c12046

Cited by 6 publications

(6 citation statements)

References 17 publications

(30 reference statements)

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“…In this experiment, the shutter of the X-ray source was alternately opened and closed for periods of 30 s with a fixed dose rate of 7 mGy/s. Similar to inorganic X-ray detectors, our devices showed linear relationships between the photocurrent and dose rate following the Fowler model [ 19 ].…”

Section: Resultsmentioning

confidence: 99%

Enhancement of X-ray detection by single-walled carbon nanotube enriched flexible polymer composite

et al. 2014

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Although organic-based direct conversion X-ray detectors have been developed, their photocurrent generation efficiency has been limited by recombination of excitons due to the intrinsically poor electrical properties of organic materials. In this report, we fabricated a polymer-based flexible X-ray detector and enhanced the X-ray detection sensitivity using a single-walled carbon nanotube (SWNT) enriched polymer composite. When this SWNT enriched polymer composite was used as the active layer of an X-ray detector, it efficiently separated charges at the interface between the SWNTs and polymer, preventing recombination of X-ray-induced excitons. This increased the photocurrent generation efficiency, as measured from current-voltage characteristics. Therefore, X-ray-induced photocurrent and X-ray detection sensitivity were enhanced as the concentration of SWNTs in the composite was increased. However, this benefit was counterbalanced by the slow and unstable time-dependent response at high SWNT concentrations, arising from reduced Schottky barrier heights between the active layer and electrodes. At high SWNT concentration, the dark current also increased due to the reduced Schottky barrier height, leading to decrease the signal-to-noise ratio (SNR) of the device. Experimental results indicated that 0.005 wt.% SWNT in the composite was the optimum composition for practical X-ray detector operation because it showed enhanced performance in both sensitivity and SNR. In mechanical flexibility tests, the device exhibited a stable response up to a bending radius of 0.5 cm, and the device had no noticeable change in diode current after 1,000 bending cycles.PACS code8.67.ScElectronic supplementary materialThe online version of this article (doi:10.1186/1556-276X-9-610) contains supplementary material, which is available to authorized users.

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Section: Resultsmentioning

confidence: 99%

Enhancement of X-ray detection by single-walled carbon nanotube enriched flexible polymer composite

et al. 2014

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“…However, in many cases, it is possible to improve the electrical conduction at the diamond/metal interface by inducing a graphitic layer underneath the diamond substrate surface [77]. Preferred materials for diamond dosimeters electrodes are Al [68,78,79], Cr/Au [65,67,80], Ag [81]. Amorphous carbon blended with nickel (C/Ni) electrodes for polycrystalline and monocrystalline diamonds are also used to produce near-tissue equivalent detectors [51,82].…”

Section: Diamond Contactsmentioning

confidence: 99%

“…demonstrated that diamond-like-carbon multi-layer contacts permit the fabrication of devices with a remarkable sensitivity to very low dose rates using the bias voltage as a key operative parameter for different dose rate ranges. Concerning the importance of contact shape, both circular [68,79,81] and square contacts [85] are widely used without evidence of advantages of one over the other.…”

Section: Diamond Contactsmentioning

confidence: 99%

Diamond Detectors for Radiotherapy X-Ray Small Beam Dosimetry

et al. 2021

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Many new X-Ray treatment machines using small and/or non-standard radiation fields, e.g., Tomotherapy, Cyber-knife, and linear accelerators equipped with high-resolution multi-leaf collimators and on-board imaging system, have been introduced in the radiotherapy clinical routine within the last few years. The introduction of these new treatment modalities has led to the development of high conformal radiotherapy treatment techniques like Intensity Modulated photon Radiation Therapy, Volumetric Modulated Arc Therapy, and stereotactic radiotherapy. When using these treatment techniques, patients are exposed to non-uniform radiation fields, high dose gradients, time and space variation of dose rates, and beam energy spectrum. This makes reaching the required degree of accuracy in clinical dosimetry even more demanding. Continuing to use standard field procedures and detectors in fields smaller than 3 × 3 cm2, will generate a reduced accuracy of clinical dosimetry, running the risk to overshadowing the progress made so far in radiotherapy applications. These dosimetric issues represent a new challenge for medical physicists. To choose the most appropriate detector for small field dosimetry, different features must be considered. Short- and long-term stability, linear response to the absorbed dose and dose rate, no energy and angular dependence, are all needed but not sufficient. The two most sought-after attributes for small field dosimetry are water equivalence and small highly sensitive (high sensitivity) volumes. Both these requirements aim at minimizing perturbations of charged particle fluence approaching the Charged Particle Equilibrium condition as much as possible, while maintaining high spatial resolution by reducing the averaging effect for non-uniform radiation fields. A compromise between different features is necessary because no dosimeter currently fulfills all requirements, but diamond properties seem promising and could lead to a marked improvement. Diamonds have long been used as materials for dosimeters, but natural diamonds were only first used for medical applications in the 80 s. The availability of reproducible synthetic diamonds at a lower cost compared to natural ones made the diffusion of diamonds in dosimetry possible. This paper aims to review the use of synthetic poly and single-crystal diamond dosimeters in radiotherapy, focusing on their performance under MegaVoltage photon beams. Both commercial and prototype diamond dosimeters behaviour are described and analyzed. Moreover, this paper will report the main related results in literature, considering diamond development issues like growth modalities, electrical contacts, packaging, readout electronics, and how do they affect all the dosimetric parameters of interest such as signal linearity, energy dependence, dose-rate dependence, reproducibility, rise and decay times.

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“…A diamond photodiode was characterised under the illumination of soft X-rays (0.25 keV to 7 keV) at room temperature [36]; the electron-hole pair creation energy was reported to be 13.25 eV ± 0.5 eV. The effect of different amorphous carbon electrodes on CVD diamond detectors has been studied [37]; whilst the devices showed low leakage currents (bulk resistivity of at least 2.8 × 10 14 Ω cm at applied electric field strengths of ± 0.3 V μm -1 ), a reported drawback was the instability of the photocurrent generated from illumination of a Mo target X-ray tube, at high applied potential differences [37]. In other work, a single crystal CVD diamond detector was characterised under the illumination of 10.6 keV and 12.5 keV X-rays; a linear response as a function of photon flux was measured [38].…”

Section: Introductionmentioning

confidence: 99%