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Oxygen sensitivity of atomically passivated CdS nanocrystal films

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Abstract
CdS nanocrystals (NCs) synthesized by colloidal chemistry methods have been intensively studied for various applications. However, little attention has been paid to the interaction between the oxygen molecules present in air and the NC surface, which has a strong influence on the electrical properties of NC films. Here, we discuss the effect of oxygen adsorption at the NC surface on the photoconductivity of CdS NC films that were treated by propyltrichlorosilane, which is known to replace the native ligands at the NC surface with chloride ions. The photocurrent voltage (Ply) characteristics of NC@Cl films recorded under oxygen atmosphere reveal a significant reduction in the photocurrent, as compared to those recorded under argon or vacuum. We demonstrate that this reduction can be related to adsorbed oxygen ions that effectively passivate the NC surface. This passivation reduces the free electron concentration and thereby reduces the photocurrent. Furthermore, we have investigated the light intensity dependence of the photocurrent dynamics of our devices in argon and in oxygen. These measurements confirm that the adsorption of oxygen is a photo-assisted process. Eventually, the potential of using our devices as oxygen sensors is assessed. A remarkable sensitivity of 35 is obtained at room temperature for 10% (concentration) oxygen flow, which is at least one order of magnitude higher than the results reported in the literature. Our work clarifies the mechanism of the photoconductivity reduction in CdS NC films upon oxygen adsorption and opens up opportunities of exploring such devices for gas sensing applications.
Keywords
CdS nanocrystal films, photoconductivity, oxygen adsorption, surface passivation, oxygen sensing, COLLOIDAL NANOCRYSTALS, LIGAND PASSIVATION, CHEMISORPTION, CRYSTALS, SURFACES, SENSOR, PHOTOCONDUCTIVITY, ADSORPTION, DESORPTION

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MLA
Maserati, Lorenzo et al. “Oxygen Sensitivity of Atomically Passivated CdS Nanocrystal Films.” ACS APPLIED MATERIALS & INTERFACES 6.12 (2014): 9517–9523. Print.
APA
Maserati, L., Moreels, I., Prato, M., Krahne, R., Manna, L., & Zhang, Y. (2014). Oxygen sensitivity of atomically passivated CdS nanocrystal films. ACS APPLIED MATERIALS & INTERFACES, 6(12), 9517–9523.
Chicago author-date
Maserati, Lorenzo, Iwan Moreels, Mirko Prato, Roman Krahne, Liberato Manna, and Yang Zhang. 2014. “Oxygen Sensitivity of Atomically Passivated CdS Nanocrystal Films.” Acs Applied Materials & Interfaces 6 (12): 9517–9523.
Chicago author-date (all authors)
Maserati, Lorenzo, Iwan Moreels, Mirko Prato, Roman Krahne, Liberato Manna, and Yang Zhang. 2014. “Oxygen Sensitivity of Atomically Passivated CdS Nanocrystal Films.” Acs Applied Materials & Interfaces 6 (12): 9517–9523.
Vancouver
1.
Maserati L, Moreels I, Prato M, Krahne R, Manna L, Zhang Y. Oxygen sensitivity of atomically passivated CdS nanocrystal films. ACS APPLIED MATERIALS & INTERFACES. 2014;6(12):9517–23.
IEEE
[1]
L. Maserati, I. Moreels, M. Prato, R. Krahne, L. Manna, and Y. Zhang, “Oxygen sensitivity of atomically passivated CdS nanocrystal films,” ACS APPLIED MATERIALS & INTERFACES, vol. 6, no. 12, pp. 9517–9523, 2014.
@article{8538101,
  abstract     = {CdS nanocrystals (NCs) synthesized by colloidal chemistry methods have been intensively studied for various applications. However, little attention has been paid to the interaction between the oxygen molecules present in air and the NC surface, which has a strong influence on the electrical properties of NC films. Here, we discuss the effect of oxygen adsorption at the NC surface on the photoconductivity of CdS NC films that were treated by propyltrichlorosilane, which is known to replace the native ligands at the NC surface with chloride ions. The photocurrent voltage (Ply) characteristics of NC@Cl films recorded under oxygen atmosphere reveal a significant reduction in the photocurrent, as compared to those recorded under argon or vacuum. We demonstrate that this reduction can be related to adsorbed oxygen ions that effectively passivate the NC surface. This passivation reduces the free electron concentration and thereby reduces the photocurrent. Furthermore, we have investigated the light intensity dependence of the photocurrent dynamics of our devices in argon and in oxygen. These measurements confirm that the adsorption of oxygen is a photo-assisted process. Eventually, the potential of using our devices as oxygen sensors is assessed. A remarkable sensitivity of 35 is obtained at room temperature for 10% (concentration) oxygen flow, which is at least one order of magnitude higher than the results reported in the literature. Our work clarifies the mechanism of the photoconductivity reduction in CdS NC films upon oxygen adsorption and opens up opportunities of exploring such devices for gas sensing applications.},
  author       = {Maserati, Lorenzo and Moreels, Iwan and Prato, Mirko and Krahne, Roman and Manna, Liberato and Zhang, Yang},
  issn         = {1944-8244},
  journal      = {ACS APPLIED MATERIALS & INTERFACES},
  keywords     = {CdS nanocrystal films,photoconductivity,oxygen adsorption,surface passivation,oxygen sensing,COLLOIDAL NANOCRYSTALS,LIGAND PASSIVATION,CHEMISORPTION,CRYSTALS,SURFACES,SENSOR,PHOTOCONDUCTIVITY,ADSORPTION,DESORPTION},
  language     = {eng},
  number       = {12},
  pages        = {9517--9523},
  title        = {Oxygen sensitivity of atomically passivated CdS nanocrystal films},
  url          = {http://dx.doi.org/10.1021/am501906y},
  volume       = {6},
  year         = {2014},
}

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