Photoconduction in a Polydiacetylene Crystal

Reimer, B.; Baessler, H.

doi:10.1002/pssa.2210320211

Cited by 70 publications

(5 citation statements)

References 10 publications

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“…With the addition of an unexposed film, the samples were scanned at the lateral center location of the scanner. Finally, to aid in the demonstration of the LRA correction method, we exposed a 15×15 cm 2 field at the center of several 20.3×25.4 cm 2 EBT-XD films using doses of 10, 20, and 40 Gy and the conditions previously described. These films were scanned at the lateral center location and also at locations where one edge of the film was at the lateral limit of the scan window.…”

Section: A Film and Exposuresmentioning

confidence: 99%

“…Since the EBT3 film exhibits preferential alignment of the LiPCDA particles and chromophores of this type polarize transmitted light, 2 it is believed that the shape of the particles in EBT3 influences the lateral response artifact (LRA) of this film. On a flatbed scanner, the polarized transmitted light is guided to the CCD detector by a series of mirrors and a lens.…”

Section: Introductionmentioning

confidence: 99%

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Technical Note: On GAFChromic EBT‐XD film and the lateral response artifact

Lewis¹,

Chan

2016

Medical Physics

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Purpose: The new radiochromic film, GAFChromic EBT-XD, contains the same active material, lithium-10,12-pentacosadiynoate, as GAFChromic EBT3, but the crystalline form is different. This work investigates the effect of this change on the well-known lateral response artifact when EBT-XD film is digitized on a flatbed scanner. Methods: The dose response of a single production lot of EBT-XD was characterized by scanning an unexposed film plus a set of films exposed to doses between 2.5 and 50 Gy using 6 MV photons. To characterize the lateral response artifact, the authors used the unexposed film plus a subset of samples exposed to doses between 20 and 50 Gy. Digital images of these films were acquired at seven discrete lateral locations perpendicular to the scan direction on three Epson 10000XL scanners. Using measurements at the discrete lateral positions, the scanner responses were determined as a function of the lateral position of the film. From the data for each scanner, a set of coefficients were derived whereby measured response values could be corrected to remove the effects of the lateral response artifact. The EBT-XD data were analyzed as in their previous work and compared to results reported for EBT3 in that paper. Results: For films scanned in the same orientation and having equal responses, the authors found that the lateral response artifact for EBT-XD and EBT3 films was remarkably similar. For both films, the artifact increases with increased net response. However, as EBT-XD is less sensitive than EBT3, a greater exposure dose is required to reach the same net response. On this basis, the lower sensitivity of EBT-XD relative to EBT3 results in less net response change for equal exposure and a reduction in the impact of the lateral response artifact. Conclusions: The shape of the crystalline active component in EBT-XD and EBT3 does not affect the fundamental existence of the lateral response artifact when the films are digitized on flatbed scanners. Owing its lower sensitivity, EBT-XD film requires higher dose to reach the same response as EBT3, resulting in lesser impact of the lateral response artifact. For doses >10 Gy, the slopes of the EBT-XD red and green channel dose response curves are greater than the corresponding ones for EBT3. For these two reasons, the authors prefer EBT-XD for doses exceeding about 10 Gy. C 2016 American Association of Physicists in Medicine. [http://dx

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Section: A Film and Exposuresmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Technical Note: On GAFChromic EBT‐XD film and the lateral response artifact

Lewis¹,

Chan

2016

Medical Physics

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“…This in turn has led to the measurement of a number of physical properties of this polymer (Stevens et al 1978) and several theoretical studies (Parry 1976, Boudreaux 1975, Cojan et al 1977, Wilson 1975, Philpott 1977 as well. Experi mental studies led to the suggestion th a t there occurs a phase transition involv ing two extreme geometries (Iqbal et al 1977) and th a t an exciton model provides a better description of the excited state properties of this polymer than a band picture (Muller et al 1977, Schermann & Wegner 1974, Reimer & Bassler 1975.…”

Section: Conjugated One and Two Dimensional Polymersmentioning

confidence: 99%

Conjugated one and two dimensional polymers

1979

Proc. R. Soc. Lond. A

395

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The band structures of some existing and hypothetical one and two dimensional conjugated polymers are examined in this work. The aim is to explore how the band gap sizes and the occurrence of partially filled bands are related to unit cell constitution and the geometrical disposition of the atoms in the unit cell. Among the polymers explored are poly-acetylene, polydiacetylene, polyphenylene, polyacene, graphite, boron nitride, polynitrile, polycyanonitrile, polypyridinopyridine, paracyanogen, the C 3 N net, (SN) x , (XCNSN) x , and C 2 S 3 N 6 net.

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“…As long recognized, this channel of nuclear spin relaxation is key to inducing helicity-dependent nuclear spin order, and thus forms the foundation of OPNMR. 22 More recently a second mechanism was proposed 23 and verified experimentally 20,21 whereby fluctuating electric field gradients in the vicinity of the intermittently photoelectron-occupied defects lead to nuclear spin relaxation via quadrupolar interactions. Such fluctuations are inherently insensitive to light helicity, such that quadrupolar relaxation always drives the nuclear spin ensemble towards equilibrium at the applied magnetic field and temperature.…”

Section: A Hyperfine Versus Quadrupolar Relaxationmentioning

confidence: 92%

“…As the number of photoelectrons increase, the role of these fluctuations in driving relaxation diminishes and an inverted, hyperfineinduced NMR signal is observed, as expected for illumination with σ + helicity. 10,22 The transformation of the NMR line shape poses, however, an intriguing problem: In our experiments we are able to spectroscopically identify contributions from bulk nuclear spins owing to the long-range strain introduced in the sample during cooling (see Sec. II).…”

Section: A Hyperfine Versus Quadrupolar Relaxationmentioning

confidence: 99%

Near-band-gap photoinduced nuclear spin dynamics in semi-insulating GaAs: Hyperfine- and quadrupolar-driven relaxation

King

Reimer

et al. 2013

Phys. Rev. B

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Understanding and manipulating spin polarization and transport in the vicinity of semiconductor-hosted defects is a problem of present technological and fundamental importance. Here, we use high-field magnetic resonance to monitor the relaxation dynamics of spin-3/2 nuclei in semi-insulating GaAs. Our experiments benefit from the conditions created in the limit of low illumination intensities, where intermittent occupation of the defect site by photoexcited electrons leads to electric field gradient fluctuations and concomitant spin relaxation of the neighboring quadrupolar nuclei. We find indication of a heterogeneous distribution of polarization, governed by different classes of defects activated by either weak or strong laser excitation. Upon application of a train of light pulses of variable repetition rate and on/off ratio, we uncover an intriguing regime of mesoscale nuclear spin diffusion restricted by long-range, nonuniform electric field gradients. Given the slow time scale governing nuclear spin evolution, such optically induced polarization patterns could be exploited as a contrast mechanism to expose dark lattice defects or localized charges with nanoscale resolution.

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Photoconduction in a Polydiacetylene Crystal

Cited by 70 publications

References 10 publications

Technical Note: On GAFChromic EBT‐XD film and the lateral response artifact

Technical Note: On GAFChromic EBT‐XD film and the lateral response artifact

Conjugated one and two dimensional polymers

Near-band-gap photoinduced nuclear spin dynamics in semi-insulating GaAs: Hyperfine- and quadrupolar-driven relaxation

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