X-ray absorption spectroscopy from H-passivated porous Si and oxidized Si nanocrystals

Conference · Tue Nov 01 04:00:00 EST 1994

OSTI ID:79699

Schuppler, S; Marcus, M A ^[1]; Friedman, S L ^[2]

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1. AT and T Bell Labs., Murray Hill, NJ (United States)
2. Stanford Univ., Palo Alto, CA (United States). Dept. of Applied Physics; and others

Quantum confinement in nanoscale Si structures is widely believed to be responsible for the visible luminescence observed from anodically etched porous silicon (por-Si), but little is known about the actual size or shape of these structures. Extended x-ray absorption fine structure data from a wide variety of por-Si samples show significantly reduced average Si coordination numbers due to the sizable contribution of surface-coordinated H. (The IUSI ratios, as large as 1.2, were independently confirmed by ir-absorption and {alpha}-recoil measurements.) The Si coordinations imply very large surface/volume ratios, enabling the average Si structures to be identified as crystalline particles (not wires) whose dimensions are typically <15 {Angstrom}. Comparison of the size-dependent peak luminescence energies with those of oxidized Si nanocrystals, whose shapes are known, shows remarkable agreement. Furthermore, near-edge x-ray absorption fine structure measurements of the nanocrystals shows the outer oxide and interfacial suboxide layers to be constant over a wide range of nanocrystal sizes. The combination of these results effectively rules out surface species as being responsible for the observed visible luminescence in por-Si, and strongly supports quantum confinement as the dominant mechanism occurring in Si particles which are substantially smaller than previously reported or proposed.

• Research Organization: Lawrence Berkeley Lab., CA (United States)
• Sponsoring Organization: USDOE, Washington, DC (United States); Alexander von Humboldt-Stiftung, Bonn (Germany)
• DOE Contract Number: AC03-76SF00098
• OSTI ID: 79699
• Report Number(s): LBL--36911; CONF-941144--149; ON: DE95012352
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
COORDINATION NUMBER
LUMINESCENCE
PHOTOLUMINESCENCE
POROUS MATERIALS
SILICON