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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

Current-voltage characteristics and photocurrents of the fabricated devices. (a) Dark current-voltage characteristics of flexible X-ray detectors with various SWNT concentrations. Ambipolar characteristics were observed as SWNT concentration was increased. (b) Photocurrents as a function of applied reverse bias voltage for devices with different SWNT concentrations. Photocurrent was enhanced with increasing SWNT concentration up to 10.67 nA at 150 V for the 0.010 wt.% SWNT device.
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Fig2: Current-voltage characteristics and photocurrents of the fabricated devices. (a) Dark current-voltage characteristics of flexible X-ray detectors with various SWNT concentrations. Ambipolar characteristics were observed as SWNT concentration was increased. (b) Photocurrents as a function of applied reverse bias voltage for devices with different SWNT concentrations. Photocurrent was enhanced with increasing SWNT concentration up to 10.67 nA at 150 V for the 0.010 wt.% SWNT device.

Mentions: Figure 2a shows the dark I-V characteristics of the devices with various SWNT concentrations under voltages ranging from -150 to 150 V applied to the Au electrode. In the case of the polymer device without SWNTs (0.000 wt.% SWNT), the I-V curve showed rectifying behavior with low reverse bias current. As the SWNT concentration was increased from 0 to 0.01 wt.%, the resulting I-V curves of the devices still showed similar rectifying behavior. However, after the concentration of SWNTs was increased above 0.015 wt.%, the device showed ambipolar characteristics. At excessively high carbon nanotube concentrations, it is known that electrical properties of devices are determined by the carbon nanotubes than the polymer [18]. Under the domination of SWNTs, it is natural that the electrical property of the device shows ambipolar characteristic because the SWNT we used has metallic property. To verify this, we also fabricated a similar device using the composite of insulating poly(methyl methacrylate) (PMMA) and SWNT as the active layer. As shown in Figure S3 in Additional file 1, the I-V characteristic of the SWNT/PMMA device showed ambipolar characteristics at a high SWNT concentration (0.1 wt.%).Figure 2


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)

Current-voltage characteristics and photocurrents of the fabricated devices. (a) Dark current-voltage characteristics of flexible X-ray detectors with various SWNT concentrations. Ambipolar characteristics were observed as SWNT concentration was increased. (b) Photocurrents as a function of applied reverse bias voltage for devices with different SWNT concentrations. Photocurrent was enhanced with increasing SWNT concentration up to 10.67 nA at 150 V for the 0.010 wt.% SWNT device.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Fig2: Current-voltage characteristics and photocurrents of the fabricated devices. (a) Dark current-voltage characteristics of flexible X-ray detectors with various SWNT concentrations. Ambipolar characteristics were observed as SWNT concentration was increased. (b) Photocurrents as a function of applied reverse bias voltage for devices with different SWNT concentrations. Photocurrent was enhanced with increasing SWNT concentration up to 10.67 nA at 150 V for the 0.010 wt.% SWNT device.
Mentions: Figure 2a shows the dark I-V characteristics of the devices with various SWNT concentrations under voltages ranging from -150 to 150 V applied to the Au electrode. In the case of the polymer device without SWNTs (0.000 wt.% SWNT), the I-V curve showed rectifying behavior with low reverse bias current. As the SWNT concentration was increased from 0 to 0.01 wt.%, the resulting I-V curves of the devices still showed similar rectifying behavior. However, after the concentration of SWNTs was increased above 0.015 wt.%, the device showed ambipolar characteristics. At excessively high carbon nanotube concentrations, it is known that electrical properties of devices are determined by the carbon nanotubes than the polymer [18]. Under the domination of SWNTs, it is natural that the electrical property of the device shows ambipolar characteristic because the SWNT we used has metallic property. To verify this, we also fabricated a similar device using the composite of insulating poly(methyl methacrylate) (PMMA) and SWNT as the active layer. As shown in Figure S3 in Additional file 1, the I-V characteristic of the SWNT/PMMA device showed ambipolar characteristics at a high SWNT concentration (0.1 wt.%).Figure 2

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