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Fabrication and NO2 gas sensing performance of TeO2-core/CuO-shell heterostructure nanorod sensors.

Park S, Kim S, Sun GJ, In Lee W, Kim KK, Lee C - Nanoscale Res Lett (2014)

Bottom Line: TeO2-nanostructured sensors are seldom reported compared to other metal oxide semiconductor materials such as ZnO, In2O3, TiO2, Ga2O3, etc.These responses were stronger than or comparable to those of many other metal oxide nanostructures, suggesting that TeO2 is also a promising sensor material.The responses of the core-shell nanorods were 1.2 to 2.1 times higher than those of pristine TeO2 nanorods over the same NO2 concentration range.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Materials Science and Engineering, Inha University, 253 Yonghyun-dong, Nam-gu, Incheon 402-751, Republic of Korea.

ABSTRACT

Unlabelled: TeO2-nanostructured sensors are seldom reported compared to other metal oxide semiconductor materials such as ZnO, In2O3, TiO2, Ga2O3, etc. TeO2/CuO core-shell nanorods were fabricated by thermal evaporation of Te powder followed by sputter deposition of CuO. Scanning electron microscopy and X-ray diffraction showed that each nanorod consisted of a single crystal TeO2 core and a polycrystalline CuO shell with a thickness of approximately 7 nm. The TeO2/CuO core-shell one-dimensional (1D) nanostructures exhibited a bamboo leaf-like morphology. The core-shell nanorods were 100 to 300 nm in diameter and up to 30 μm in length. The multiple networked TeO2/CuO core-shell nanorod sensor showed responses of 142% to 425% to 0.5- to 10-ppm NO2 at 150°C. These responses were stronger than or comparable to those of many other metal oxide nanostructures, suggesting that TeO2 is also a promising sensor material. The responses of the core-shell nanorods were 1.2 to 2.1 times higher than those of pristine TeO2 nanorods over the same NO2 concentration range. The underlying mechanism for the enhanced NO2 sensing properties of the core-shell nanorod sensor can be explained by the potential barrier-controlled carrier transport mechanism.

Pacs: 61.46. + w; 07.07.Df; 73.22.-f.

No MeSH data available.


Schematic energy diagram showing three different potential barriers. Schematic energy diagram showing three different potential barriers formed in the multiple networked TeO2/CuO core-shell nanorod sensor: (a) one at a TeO2/CuO core-shell interface and another at a polycrystalline CuO shell grain boundary and (b) the third at a nanorod-nanorod contact.
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Figure 5: Schematic energy diagram showing three different potential barriers. Schematic energy diagram showing three different potential barriers formed in the multiple networked TeO2/CuO core-shell nanorod sensor: (a) one at a TeO2/CuO core-shell interface and another at a polycrystalline CuO shell grain boundary and (b) the third at a nanorod-nanorod contact.

Mentions: The underlying mechanism of the enhanced TeO2/CuO core-shell nanorods can be explained using a barrier-controlled carrier transport mechanism [9,10]. Potential barriers form at three places in the multiple networked TeO2/CuO core-shell nanorod sensor: at the core-shell interface, the shell grain boundary [40], and the nanorod-nanorod contact. First, the potential barrier at core-shell interface is due to the high density of interface states in the TeO2-CuO interfacial region. The carriers near the interface are trapped by interface states, so that a depletion layer forms over the TeO2 core region near the interface to the CuO shell region near the interface. In addition to depletion layer formation, a potential barrier is created at the core-shell interface due to the carrier trapping as shown in Figure 5a [41]. The potential barrier is drawn in the negative energy direction, i.e. the downward direction in Figure 5a because the carriers trapped in the interface are mostly holes residing in p-type TeO2 core and the p-type CuO shell in the vicinity of the core-shell interface. The other two potential barriers that should be overcome by carriers on their pathways before they reach the electrode of the sensor are at the CuO-CuO homojunction, where two nanorods contact each other (Figure 5b) and at the grain boundary in the polycrystalline CuO shell layers (Figure 5a). The contributions of these two potential barriers might be smaller than that of the potential barrier at the TeO2-CuO interface because of much smaller numbers of grain boundaries and nanorod-nanorod contacts compared to that of the core-shell interfaces. Each nanorod has a core-shell interface, whereas a CuO shell contains a small number of grain boundaries because it is as thin as approximately 7 nm and the possibility of two nanorods contacting each other in a multiple networked nanorod sensor is generally quite low. Carrier transport is facilitated or restrained because of these energy barriers by adsorption and desorption of gas molecules, resulting in a larger change in resistance, i.e., an enhanced response of the core-shell nanorod sensor to NO2 gas. In other words, the heights of the potential barriers are modulated at the three places, resulting in enhanced response of the sensor to the gas.


Fabrication and NO2 gas sensing performance of TeO2-core/CuO-shell heterostructure nanorod sensors.

Park S, Kim S, Sun GJ, In Lee W, Kim KK, Lee C - Nanoscale Res Lett (2014)

Schematic energy diagram showing three different potential barriers. Schematic energy diagram showing three different potential barriers formed in the multiple networked TeO2/CuO core-shell nanorod sensor: (a) one at a TeO2/CuO core-shell interface and another at a polycrystalline CuO shell grain boundary and (b) the third at a nanorod-nanorod contact.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4256961&req=5

Figure 5: Schematic energy diagram showing three different potential barriers. Schematic energy diagram showing three different potential barriers formed in the multiple networked TeO2/CuO core-shell nanorod sensor: (a) one at a TeO2/CuO core-shell interface and another at a polycrystalline CuO shell grain boundary and (b) the third at a nanorod-nanorod contact.
Mentions: The underlying mechanism of the enhanced TeO2/CuO core-shell nanorods can be explained using a barrier-controlled carrier transport mechanism [9,10]. Potential barriers form at three places in the multiple networked TeO2/CuO core-shell nanorod sensor: at the core-shell interface, the shell grain boundary [40], and the nanorod-nanorod contact. First, the potential barrier at core-shell interface is due to the high density of interface states in the TeO2-CuO interfacial region. The carriers near the interface are trapped by interface states, so that a depletion layer forms over the TeO2 core region near the interface to the CuO shell region near the interface. In addition to depletion layer formation, a potential barrier is created at the core-shell interface due to the carrier trapping as shown in Figure 5a [41]. The potential barrier is drawn in the negative energy direction, i.e. the downward direction in Figure 5a because the carriers trapped in the interface are mostly holes residing in p-type TeO2 core and the p-type CuO shell in the vicinity of the core-shell interface. The other two potential barriers that should be overcome by carriers on their pathways before they reach the electrode of the sensor are at the CuO-CuO homojunction, where two nanorods contact each other (Figure 5b) and at the grain boundary in the polycrystalline CuO shell layers (Figure 5a). The contributions of these two potential barriers might be smaller than that of the potential barrier at the TeO2-CuO interface because of much smaller numbers of grain boundaries and nanorod-nanorod contacts compared to that of the core-shell interfaces. Each nanorod has a core-shell interface, whereas a CuO shell contains a small number of grain boundaries because it is as thin as approximately 7 nm and the possibility of two nanorods contacting each other in a multiple networked nanorod sensor is generally quite low. Carrier transport is facilitated or restrained because of these energy barriers by adsorption and desorption of gas molecules, resulting in a larger change in resistance, i.e., an enhanced response of the core-shell nanorod sensor to NO2 gas. In other words, the heights of the potential barriers are modulated at the three places, resulting in enhanced response of the sensor to the gas.

Bottom Line: TeO2-nanostructured sensors are seldom reported compared to other metal oxide semiconductor materials such as ZnO, In2O3, TiO2, Ga2O3, etc.These responses were stronger than or comparable to those of many other metal oxide nanostructures, suggesting that TeO2 is also a promising sensor material.The responses of the core-shell nanorods were 1.2 to 2.1 times higher than those of pristine TeO2 nanorods over the same NO2 concentration range.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Materials Science and Engineering, Inha University, 253 Yonghyun-dong, Nam-gu, Incheon 402-751, Republic of Korea.

ABSTRACT

Unlabelled: TeO2-nanostructured sensors are seldom reported compared to other metal oxide semiconductor materials such as ZnO, In2O3, TiO2, Ga2O3, etc. TeO2/CuO core-shell nanorods were fabricated by thermal evaporation of Te powder followed by sputter deposition of CuO. Scanning electron microscopy and X-ray diffraction showed that each nanorod consisted of a single crystal TeO2 core and a polycrystalline CuO shell with a thickness of approximately 7 nm. The TeO2/CuO core-shell one-dimensional (1D) nanostructures exhibited a bamboo leaf-like morphology. The core-shell nanorods were 100 to 300 nm in diameter and up to 30 μm in length. The multiple networked TeO2/CuO core-shell nanorod sensor showed responses of 142% to 425% to 0.5- to 10-ppm NO2 at 150°C. These responses were stronger than or comparable to those of many other metal oxide nanostructures, suggesting that TeO2 is also a promising sensor material. The responses of the core-shell nanorods were 1.2 to 2.1 times higher than those of pristine TeO2 nanorods over the same NO2 concentration range. The underlying mechanism for the enhanced NO2 sensing properties of the core-shell nanorod sensor can be explained by the potential barrier-controlled carrier transport mechanism.

Pacs: 61.46. + w; 07.07.Df; 73.22.-f.

No MeSH data available.