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Photo-oxidation of Ge Nanocrystals: Kinetic Measurements by In Situ Raman Spectroscopy

Published online by Cambridge University Press:  01 February 2011

I. D. Sharp ,
Q. Xu ,
C. W. Yuan ,
J. W. Beeman ,
J. W. Ager III ,
D. C. Chrzan  and
E. E. Haller
I. D. Sharp
Affiliation:
EEHaller@lbl.gov, Lawrence Berkeley National Laboratory, Materials Sciences Division, 1 Cyclotron Rd. 2 R0200, Berkeley, CA, 94720, United States
Q. Xu
Affiliation:
qing.s.xu@gmail.com, Lawrence Berkeley National Laboratory, Materials Sciences Division, Berkeley, CA, 94720, United States
C. W. Yuan
Affiliation:
world21@berkeley.edu, Lawrence Berkeley National Laboratory, Materials Sciences Division, Berkeley, CA, 94720, United States
J. W. Beeman
Affiliation:
jwbeeman@lbl.gov, Lawrence Berkeley National Laboratory, Materials Sciences Division, Berkeley, CA, 94720, United States
J. W. Ager III
Affiliation:
jwager@lbl.gov, Lawrence Berkeley National Laboratory, Materials Sciences Division, Berkeley, CA, 94720, United States
D. C. Chrzan
Affiliation:
dcchrzan@berkeley.edu, Lawrence Berkeley National Laboratory, Materials Sciences Division, Berkeley, CA, 94720, United States
E. E. Haller
Affiliation:
eehaller@lbl.gov, Lawrence Berkeley National Laboratory, Materials Sciences Division, Berkeley, CA, 94720, United States
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Abstract

Ge nanocrystals are formed in silica by ion beam synthesis and are subsequently exposed by selective HF etching of the silica. Under ambient conditions, the exposed nanocrystals are stable after formation of a protective native oxide shell of no more than a few monolayers. However, under visible laser illumination at room temperature and in the presence of O2, the nanocrystals rapidly oxidize. The oxidation rate was monitored by measuring the Raman spectra of the Ge nanocrystals in-situ. The intensity ratio of the anti-Stokes to the Stokes line indicated that no significant laser-induced heating of illuminated nanocrystals occurs. Therefore, the oxidation reaction rate enhancement is due to a photo-chemical process. The oxidation rate varies nearly linearly with the logarithm of the laser intensity, and at constant laser intensity the rate increases with increasing photon energy. These kinetic measurements, along with the power dependencies, are described quantitatively by an electron active oxidation mechanism involving tunneling of optically excited electrons through the forming oxide skin and subsequent transport of oxygen ions to the Ge nanocrystal surface.

Keywords

oxidationnanostructurephotochemical
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 958: Symposium L – Group IV Semiconductor Nanostructures—2006 , 2006 , 0958-L03-08
Copyright
Copyright © Materials Research Society 2007

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References

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