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

Han H, Lee S, Seo J, Mahata C, Cho SH, Han AR, Hong KS, Park JH, Soh MJ, Park C, Lee T - Nanoscale Res Lett (2014)

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Nanobio Device Laboratory, School of Electrical and Electronic Engineering, Yonsei University, 50 Yonsei-ro, Seodaemun-Gu, Seoul, 120-749, Republic of Korea, kamacoon@yonsei.ac.kr.

ABSTRACT

Unlabelled: 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 code: 8.67.Sc.

No MeSH data available.


X-ray detection sensitivity and signal-to-noise ratio of the fabricated devices. (a) X-ray detection sensitivity and (b) signal-to-noise ratio of the devices with three different SWNT concentrations as a function of the reverse bias voltage.
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Fig4: X-ray detection sensitivity and signal-to-noise ratio of the fabricated devices. (a) X-ray detection sensitivity and (b) signal-to-noise ratio of the devices with three different SWNT concentrations as a function of the reverse bias voltage.

Mentions: X-ray detection sensitivity is an important factor for the evaluation of the X-ray detector. Figure 4a shows the calculated X-ray detection sensitivity as a function of reverse bias voltage for the devices with three different SWNT concentrations. The sensitivity of the device was obtained by dividing the slope of the photocurrent versus dose rate graph (Figure 3a,b,c) by the active volume of the device (3 mm × 3 mm × 5 μm). All of the devices showed positive correlation between the sensitivity and applied voltage, which was due to the longer carrier drift length of the X-ray-induced charges at high electric field strength [25]. Similar to the photocurrent, it was observed that the sensitivity of the devices increased when SWNTs were included in the active layer. At a reverse bias voltage of 150 V, for instance, the sensitivities of the devices with SWNT concentrations of 0, 0.005, and 0.01 wt.% were 12.5, 16.9, and 38.9 μC/mGy/cm3, respectively. This implies that our SWNT enriched polymer composite efficiently enhances the performance of the polymer-based X-ray detector.


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

Han H, Lee S, Seo J, Mahata C, Cho SH, Han AR, Hong KS, Park JH, Soh MJ, Park C, Lee T - Nanoscale Res Lett (2014)

X-ray detection sensitivity and signal-to-noise ratio of the fabricated devices. (a) X-ray detection sensitivity and (b) signal-to-noise ratio of the devices with three different SWNT concentrations as a function of the reverse bias voltage.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4493992&req=5

Fig4: X-ray detection sensitivity and signal-to-noise ratio of the fabricated devices. (a) X-ray detection sensitivity and (b) signal-to-noise ratio of the devices with three different SWNT concentrations as a function of the reverse bias voltage.
Mentions: X-ray detection sensitivity is an important factor for the evaluation of the X-ray detector. Figure 4a shows the calculated X-ray detection sensitivity as a function of reverse bias voltage for the devices with three different SWNT concentrations. The sensitivity of the device was obtained by dividing the slope of the photocurrent versus dose rate graph (Figure 3a,b,c) by the active volume of the device (3 mm × 3 mm × 5 μm). All of the devices showed positive correlation between the sensitivity and applied voltage, which was due to the longer carrier drift length of the X-ray-induced charges at high electric field strength [25]. Similar to the photocurrent, it was observed that the sensitivity of the devices increased when SWNTs were included in the active layer. At a reverse bias voltage of 150 V, for instance, the sensitivities of the devices with SWNT concentrations of 0, 0.005, and 0.01 wt.% were 12.5, 16.9, and 38.9 μC/mGy/cm3, respectively. This implies that our SWNT enriched polymer composite efficiently enhances the performance of the polymer-based X-ray detector.

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Nanobio Device Laboratory, School of Electrical and Electronic Engineering, Yonsei University, 50 Yonsei-ro, Seodaemun-Gu, Seoul, 120-749, Republic of Korea, kamacoon@yonsei.ac.kr.

ABSTRACT

Unlabelled: 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 code: 8.67.Sc.

No MeSH data available.