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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

Schematic illustrations and SEM image of the fabricated devices. (a) Schematic illustration of the fabricated flexible X-ray detector structure and (b) SEM image of the composite layer (0.1 wt.% SWNT concentration). Schematic illustration of charge separation in (c) a pure p-type polymer device and (d) a SWNT enriched polymer composite device.
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Fig1: Schematic illustrations and SEM image of the fabricated devices. (a) Schematic illustration of the fabricated flexible X-ray detector structure and (b) SEM image of the composite layer (0.1 wt.% SWNT concentration). Schematic illustration of charge separation in (c) a pure p-type polymer device and (d) a SWNT enriched polymer composite device.

Mentions: Figure 1a schematically illustrates the SWNT enriched polymer composite-based flexible X-ray detector. In this report, we used PS-b-PPP, a conjugated block copolymer, as a dispersant, which allows a uniform distribution of SWNTs in both the solution and composite film [14]. The distribution of SWNTs in the composite film was observed by using the SEM image. Figure 1b shows a top-view SEM image of the SWNT enriched polymer composite film at 0.1 wt.% SWNT concentration, and there was no observation of severe agglomeration of SWNTs in the composite. In addition, we also confirmed the distribution of SWNTs in both the solution and composite film through optical images (Figure S1 and S2 in Additional file 1). Without the dispersant, SWNTs in the toluene solution were bundled to each other and sank to the bottom of the vial within a few minutes. However, with the dispersant, SWNTs were well-dispersed in toluene solution and no aggregation was observed even after 1 month of storage at room temperature (Figure S1 in Additional file 1). As shown in Figure S2 in Additional file 1, the composite film without the dispersant showed a large aggregation of SWNTs, whereas the composite film with the dispersant showed a smooth film morphology without any dark spots.Figure 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)

Schematic illustrations and SEM image of the fabricated devices. (a) Schematic illustration of the fabricated flexible X-ray detector structure and (b) SEM image of the composite layer (0.1 wt.% SWNT concentration). Schematic illustration of charge separation in (c) a pure p-type polymer device and (d) a SWNT enriched polymer composite device.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Fig1: Schematic illustrations and SEM image of the fabricated devices. (a) Schematic illustration of the fabricated flexible X-ray detector structure and (b) SEM image of the composite layer (0.1 wt.% SWNT concentration). Schematic illustration of charge separation in (c) a pure p-type polymer device and (d) a SWNT enriched polymer composite device.
Mentions: Figure 1a schematically illustrates the SWNT enriched polymer composite-based flexible X-ray detector. In this report, we used PS-b-PPP, a conjugated block copolymer, as a dispersant, which allows a uniform distribution of SWNTs in both the solution and composite film [14]. The distribution of SWNTs in the composite film was observed by using the SEM image. Figure 1b shows a top-view SEM image of the SWNT enriched polymer composite film at 0.1 wt.% SWNT concentration, and there was no observation of severe agglomeration of SWNTs in the composite. In addition, we also confirmed the distribution of SWNTs in both the solution and composite film through optical images (Figure S1 and S2 in Additional file 1). Without the dispersant, SWNTs in the toluene solution were bundled to each other and sank to the bottom of the vial within a few minutes. However, with the dispersant, SWNTs were well-dispersed in toluene solution and no aggregation was observed even after 1 month of storage at room temperature (Figure S1 in Additional file 1). As shown in Figure S2 in Additional file 1, the composite film without the dispersant showed a large aggregation of SWNTs, whereas the composite film with the dispersant showed a smooth film morphology without any dark spots.Figure 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