Evaporation and deposition of alkyl-capped silicon nanocrystals in ultrahigh vacuum

Abstract

Nanocrystals are under active investigation because of their interesting size-dependent properties1,2 and potential applications3,4,5. Silicon nanocrystals have been studied for possible uses in optoelectronics6, and may be relevant to the understanding of natural processes such as lightning strikes7. Gas-phase methods can be used to prepare nanocrystals, and mass spectrometric techniques have been used to analyse Au8,9 and CdSe clusters10. However, it is difficult to study nanocrystals by such methods unless they are synthesized in the gas phase11. In particular, pre-prepared nanocrystals are generally difficult to sublime without decomposition. Here we report the observation that films of alkyl-capped silicon nanocrystals evaporate upon heating in ultrahigh vacuum at 200 °C, and the vapour of intact nanocrystals can be collected on a variety of solid substrates. This effect may be useful for the controlled preparation of new quantum-confined silicon structures and could facilitate their mass spectroscopic study and size-selection12.

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Figure 1: Photoemission spectra of C11-SiNCs on a gold nitride foil.
Figure 2: Aberration-corrected STEM of evaporated C11-SiNCs.
Figure 3: Atomic force microscopy of C11-SiNCs evaporated onto Si(111) surfaces.
Figure 4: Raman and luminescence spectra of C11-SiNCs before and after evaporation.

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Acknowledgements

The Engineering and Physical Sciences Research Council (EPSRC) and the Centre of Excellence for Nanotechnology, Micro and Photonic Systems (CeNAMPs) are acknowledged for funding this work. We also acknowledge the European Commission Access to Research Infrastructure (EC-ARI) programme support for work undertaken at MAXLAB. The advice of D. Robbins is appreciated. J. G. Grossmann (Council for the Central Laboratory of the Research Councils (CCLRC)) Daresbury Laboratory, Daresbury, Warrington, Cheshire, UK) and K. Liddell (School of Chemical Engineering and Advanced Materials, University of Newcastle upon Tyne) are thanked for their help with SAXS and X-ray diffraction measurements, respectively.

Author information

L.S. and Y.C. developed the evaporation apparatus; Y.C. carried out AFM, Raman and photoluminescence measurements. Y.C., L.S., S.K. and L.K. performed photoemission studies, P.R.C., U.B. and M.G. carried out TEM imaging and EEL spectra. L.H.L., N.O'F. and T.A.A. developed the preparation method and FTIR characterization. Y.C. and T.A.A. carried out SAXS measurements. S.N.P. characterized the samples by STM. L.S., Y.C., A.H. and B.R.H. analysed data and wrote the manuscript. All authors discussed the results and commented on the manuscript.

Correspondence to Satheesh Krishnamurthy or Samson N. Patole or Lars H. Lie or Benjamin R. Horrocks.

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The authors declare no competing financial interests.

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Supplementary Information

Supplementary methods, table and figures S1–S16 (PDF 2466 kb)

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Chao, Y., Šiller, L., Krishnamurthy, S. et al. Evaporation and deposition of alkyl-capped silicon nanocrystals in ultrahigh vacuum. Nature Nanotech 2, 486–489 (2007). https://doi.org/10.1038/nnano.2007.224

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