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Photocurrent generation in carbon nanotube/cubic-phase HfO 2 nanoparticle hybrid nanocomposites

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ABSTRACT

A hybrid material consisting of nonfunctionalized multiwall carbon nanotubes (MWCNTs) and cubic-phase HfO2 nanoparticles (NPs) with an average diameter of 2.6 nm has been synthesized. Free standing HfO2 NPs present unusual optical properties and a strong photoluminescence emission in the visible region, originating from surface defects. Transmission electron microscopy studies show that these NPs decorate the MWCNTs on topological defect sites. The electronic structure of the C K-edge in the nanocomposites was probed by electron energy loss spectroscopy, highlighting the key role of the MWCNT growth defects in anchoring HfO2 NPs. A combined optical emission and absorption spectroscopy approach illustrated that, in contrast to HfO2 NPs, the metallic MWCNTs do not emit light but instead expose their discrete electronic structure in the absorption spectra. The hybrid material manifests characteristic absorption features with a gradual merger of the MWCNT π-plasmon resonance band with the intrinsic defect band and fundamental edge of HfO2. The photoluminescence of the nanocomposites indicates features attributed to combined effects of charge desaturation of HfO2 surface states and charge transfer to the MWCNTs with an overall reduction of radiative recombination. Finally, photocurrent generation under UV–vis illumination suggests that a HfO2 NP/MWCNT hybrid system can be used as a flexible nanodevice for light harvesting applications.

No MeSH data available.


(a) I–V characteristic of a nanohybrid material in the dark (full line) and under illumination (dots) vs bias voltage. In the inset, a schematic illustration of the measurement set up is given. (b) On/off cycle photoresponse of MWCNT:HfO2 excited with UV–vis light (at 10 mV).
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Figure 5: (a) I–V characteristic of a nanohybrid material in the dark (full line) and under illumination (dots) vs bias voltage. In the inset, a schematic illustration of the measurement set up is given. (b) On/off cycle photoresponse of MWCNT:HfO2 excited with UV–vis light (at 10 mV).

Mentions: For the electrical characterization, the nanocomposite is deposited on a glass slide and contacted using a micromanipulator manual probe station as shown in inset of Fig. 5. The dark current–voltage characteristic is mostly linear, as expected for an ohmic conduction through metallic MWCNTs (Fig. 5). No influence of the concentration of HfO2 NPs decorating the MWCNTs is noticed in the dark I–V curves. UV illumination (365 nm) also has no detectable effect on bare MWCNTs. Although it was reported that MWCNTs generate a photocurrent [62], this effect is generally weak with respect to the dark current in the absence of additional Schottky or p–n junction to enhance the photoresponse [63]. This agrees well with the PL measurements of the nanocomposites (see Fig. 2) showing no additional spectral features apart from emission peaks associated with Hf3+ and O2− states in HfO2 and thus supporting the metallic nature of the MWCNTs. For the MWCNT:HfO2 hybrid material, a clear shift of the I–V curve is observed in Fig. 5 upon UV illumination. In the present experiment, the short-circuit current (ISC) is 0.7 µA and the open-circuit voltage (Voc) is −12 mV. The photoresponse under UV excitation is sizeable with a higher quantity of the agglomerated HfO2:CNT density. The I–V characteristic is still mainly linear, with a relatively weak decrease of the resistivity, which is consistent with the fact that the electrical transport is dominated by the conduction through the metallic MWCNTs [64]. Under zero bias a photocurrent is generated, indicating that the MWCNT:HfO2 nanocomposite acts as a photovoltaic cell. The on/off cycle measurements show a square and well-defined photoresponse after turn-on and turn-off illumination (Fig. 5).


Photocurrent generation in carbon nanotube/cubic-phase HfO 2 nanoparticle hybrid nanocomposites
(a) I–V characteristic of a nanohybrid material in the dark (full line) and under illumination (dots) vs bias voltage. In the inset, a schematic illustration of the measurement set up is given. (b) On/off cycle photoresponse of MWCNT:HfO2 excited with UV–vis light (at 10 mV).
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Related In: Results  -  Collection

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Figure 5: (a) I–V characteristic of a nanohybrid material in the dark (full line) and under illumination (dots) vs bias voltage. In the inset, a schematic illustration of the measurement set up is given. (b) On/off cycle photoresponse of MWCNT:HfO2 excited with UV–vis light (at 10 mV).
Mentions: For the electrical characterization, the nanocomposite is deposited on a glass slide and contacted using a micromanipulator manual probe station as shown in inset of Fig. 5. The dark current–voltage characteristic is mostly linear, as expected for an ohmic conduction through metallic MWCNTs (Fig. 5). No influence of the concentration of HfO2 NPs decorating the MWCNTs is noticed in the dark I–V curves. UV illumination (365 nm) also has no detectable effect on bare MWCNTs. Although it was reported that MWCNTs generate a photocurrent [62], this effect is generally weak with respect to the dark current in the absence of additional Schottky or p–n junction to enhance the photoresponse [63]. This agrees well with the PL measurements of the nanocomposites (see Fig. 2) showing no additional spectral features apart from emission peaks associated with Hf3+ and O2− states in HfO2 and thus supporting the metallic nature of the MWCNTs. For the MWCNT:HfO2 hybrid material, a clear shift of the I–V curve is observed in Fig. 5 upon UV illumination. In the present experiment, the short-circuit current (ISC) is 0.7 µA and the open-circuit voltage (Voc) is −12 mV. The photoresponse under UV excitation is sizeable with a higher quantity of the agglomerated HfO2:CNT density. The I–V characteristic is still mainly linear, with a relatively weak decrease of the resistivity, which is consistent with the fact that the electrical transport is dominated by the conduction through the metallic MWCNTs [64]. Under zero bias a photocurrent is generated, indicating that the MWCNT:HfO2 nanocomposite acts as a photovoltaic cell. The on/off cycle measurements show a square and well-defined photoresponse after turn-on and turn-off illumination (Fig. 5).

View Article: PubMed Central - HTML - PubMed

ABSTRACT

A hybrid material consisting of nonfunctionalized multiwall carbon nanotubes (MWCNTs) and cubic-phase HfO2 nanoparticles (NPs) with an average diameter of 2.6 nm has been synthesized. Free standing HfO2 NPs present unusual optical properties and a strong photoluminescence emission in the visible region, originating from surface defects. Transmission electron microscopy studies show that these NPs decorate the MWCNTs on topological defect sites. The electronic structure of the C K-edge in the nanocomposites was probed by electron energy loss spectroscopy, highlighting the key role of the MWCNT growth defects in anchoring HfO2 NPs. A combined optical emission and absorption spectroscopy approach illustrated that, in contrast to HfO2 NPs, the metallic MWCNTs do not emit light but instead expose their discrete electronic structure in the absorption spectra. The hybrid material manifests characteristic absorption features with a gradual merger of the MWCNT π-plasmon resonance band with the intrinsic defect band and fundamental edge of HfO2. The photoluminescence of the nanocomposites indicates features attributed to combined effects of charge desaturation of HfO2 surface states and charge transfer to the MWCNTs with an overall reduction of radiative recombination. Finally, photocurrent generation under UV–vis illumination suggests that a HfO2 NP/MWCNT hybrid system can be used as a flexible nanodevice for light harvesting applications.

No MeSH data available.