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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.


Related in: MedlinePlus

Photocurrents and band diagram of the fabricated devices. Photocurrents of devices with three different SWNT concentrations as a function of applied X-ray dose rate under the reverse bias voltages of (a) 60 V, (b) 90 V, and (c) 120 V. Insets show the devices' time-dependent responses. (d) Band diagram of the flexible X-ray detector. Charges can be easily injected into the active layer through the reduced Schottky barrier between the active layer and electrodes.
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Fig3: Photocurrents and band diagram of the fabricated devices. Photocurrents of devices with three different SWNT concentrations as a function of applied X-ray dose rate under the reverse bias voltages of (a) 60 V, (b) 90 V, and (c) 120 V. Insets show the devices' time-dependent responses. (d) Band diagram of the flexible X-ray detector. Charges can be easily injected into the active layer through the reduced Schottky barrier between the active layer and electrodes.

Mentions: Figure 2b shows the X-ray-induced photocurrent as a function of reverse bias voltage for the devices with three different SWNT concentrations. The reverse bias voltage applied ranged from 0 to 150 V with an X-ray dose rate of 7 mGy/s. The photocurrents were calculated by subtracting the dark current from the X-ray irradiated current. It was clearly observed that the photocurrents of the X-ray detectors were increased for all applied operational voltages when the SWNTs were included in the active layer. Especially, under high electric field, the photocurrents were considerably increased as the SWNT concentration increases. For instance, at a reverse bias voltage of 150 V, the photocurrents of the devices increased from 2.86 to 10.67 nA, which is about 273% larger, by increasing the SWNT concentration from 0 to 0.01 wt.% as listed in Table 1. When the reverse bias voltage increased, the devices also showed different photocurrent increase tendencies depending on the concentration of SWNT. The 0.000 wt.% SWNT and 0.005 wt.% SWNT devices showed a saturating photocurrent tendency, whereas the 0.010 wt.% SWNT device showed a non-saturating photocurrent tendency. These differences according to the SWNT concentration were possibly due to charge injection from the electrodes caused by a reduction in the Schottky barrier height between the active layer and each electrode at a high SWNT concentration (this will be discussed in more detail in the next section; see also Figure 3d).Table 1


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)

Photocurrents and band diagram of the fabricated devices. Photocurrents of devices with three different SWNT concentrations as a function of applied X-ray dose rate under the reverse bias voltages of (a) 60 V, (b) 90 V, and (c) 120 V. Insets show the devices' time-dependent responses. (d) Band diagram of the flexible X-ray detector. Charges can be easily injected into the active layer through the reduced Schottky barrier between the active layer and electrodes.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Fig3: Photocurrents and band diagram of the fabricated devices. Photocurrents of devices with three different SWNT concentrations as a function of applied X-ray dose rate under the reverse bias voltages of (a) 60 V, (b) 90 V, and (c) 120 V. Insets show the devices' time-dependent responses. (d) Band diagram of the flexible X-ray detector. Charges can be easily injected into the active layer through the reduced Schottky barrier between the active layer and electrodes.
Mentions: Figure 2b shows the X-ray-induced photocurrent as a function of reverse bias voltage for the devices with three different SWNT concentrations. The reverse bias voltage applied ranged from 0 to 150 V with an X-ray dose rate of 7 mGy/s. The photocurrents were calculated by subtracting the dark current from the X-ray irradiated current. It was clearly observed that the photocurrents of the X-ray detectors were increased for all applied operational voltages when the SWNTs were included in the active layer. Especially, under high electric field, the photocurrents were considerably increased as the SWNT concentration increases. For instance, at a reverse bias voltage of 150 V, the photocurrents of the devices increased from 2.86 to 10.67 nA, which is about 273% larger, by increasing the SWNT concentration from 0 to 0.01 wt.% as listed in Table 1. When the reverse bias voltage increased, the devices also showed different photocurrent increase tendencies depending on the concentration of SWNT. The 0.000 wt.% SWNT and 0.005 wt.% SWNT devices showed a saturating photocurrent tendency, whereas the 0.010 wt.% SWNT device showed a non-saturating photocurrent tendency. These differences according to the SWNT concentration were possibly due to charge injection from the electrodes caused by a reduction in the Schottky barrier height between the active layer and each electrode at a high SWNT concentration (this will be discussed in more detail in the next section; see also Figure 3d).Table 1

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.


Related in: MedlinePlus