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Influence of surface properties on the electrical conductivity of silicon nanomembranes.

Zhao X, Scott SA, Huang M, Peng W, Kiefer AM, Flack FS, Savage DE, Lagally MG - Nanoscale Res Lett (2011)

Bottom Line: Two surface modifications, vacuum hydrogenation (VH) and hydrofluoric acid (HF) cleaning, of silicon nanomembranes (SiNMs) that nominally have the same effect, the hydrogen termination of the surface, are compared.Re-oxidation rates after these treatments also differ.We pinpoint the likely cause of the differences.PACS: 73.63.-b, 62.23.Kn, 73.40.Ty.

View Article: PubMed Central - HTML - PubMed

Affiliation: University of Wisconsin-Madison, Madison WI 53706, USA. lagally@engr.wisc.edu.

ABSTRACT
Because of the large surface-to-volume ratio, the conductivity of semiconductor nanostructures is very sensitive to surface chemical and structural conditions. Two surface modifications, vacuum hydrogenation (VH) and hydrofluoric acid (HF) cleaning, of silicon nanomembranes (SiNMs) that nominally have the same effect, the hydrogen termination of the surface, are compared. The sheet resistance of the SiNMs, measured by the van der Pauw method, shows that HF etching produces at least an order of magnitude larger drop in sheet resistance than that caused by VH treatment, relative to the very high sheet resistance of samples terminated with native oxide. Re-oxidation rates after these treatments also differ. X-ray photoelectron spectroscopy measurements are consistent with the electrical-conductivity results. We pinpoint the likely cause of the differences.PACS: 73.63.-b, 62.23.Kn, 73.40.Ty.

No MeSH data available.


Related in: MedlinePlus

Si 2p XPS core level peaks for Si and SiO2. As a function of exposure time in air: red solid lines, blue dashed lines, and black dotted line correspond to samples treated by VH, HF, and with native-oxide surface, respectively. Take-off angle is 15°, pass energy is 35.75 eV. The top curve has been shifted by approximately 0.4 eV to facilitate comparison with the other curves. This shift is presumably due to surface charging.
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Figure 4: Si 2p XPS core level peaks for Si and SiO2. As a function of exposure time in air: red solid lines, blue dashed lines, and black dotted line correspond to samples treated by VH, HF, and with native-oxide surface, respectively. Take-off angle is 15°, pass energy is 35.75 eV. The top curve has been shifted by approximately 0.4 eV to facilitate comparison with the other curves. This shift is presumably due to surface charging.

Mentions: There is XPS support for this conclusion. Figure 4 shows the Si 2p core level peak and corresponding chemically shifted peak due to presence of oxide as a function of exposure time in air. It is clear that with a 2-h exposure to air, the Si 2p core level peak in SiO2 of the sample treated by VH is stronger than that of sample treated by HF, indicating that the VH-terminated sample has a higher oxidation rate at the beginning. As the samples continue to oxidize, the magnitudes of the chemically shifted Si 2p core level peaks for each sample type become closer and eventually reach a similar peak height after an 8-h exposure to air. As oxidation continues past 1 day, the peak for the HF-treated sample becomes stronger than that for VH-treated sample and continues to increase over the 18 days of measurements, almost reaching the level of the sample with a native-oxide surface. Comparison of O1s peaks confirms increasing oxidation, relative to the initial stages (Figure 3), but at different rates, as predicted from the sheet resistance data. These observations are in excellent agreement with the results of the electrical measurements shown in Figures 1 and 2. From the inset in Figure 2, it is clear that within 1 day after surface modification, the sheet resistances of both sample types reach a similar value of around 3 × 107 ohms/square.


Influence of surface properties on the electrical conductivity of silicon nanomembranes.

Zhao X, Scott SA, Huang M, Peng W, Kiefer AM, Flack FS, Savage DE, Lagally MG - Nanoscale Res Lett (2011)

Si 2p XPS core level peaks for Si and SiO2. As a function of exposure time in air: red solid lines, blue dashed lines, and black dotted line correspond to samples treated by VH, HF, and with native-oxide surface, respectively. Take-off angle is 15°, pass energy is 35.75 eV. The top curve has been shifted by approximately 0.4 eV to facilitate comparison with the other curves. This shift is presumably due to surface charging.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211497&req=5

Figure 4: Si 2p XPS core level peaks for Si and SiO2. As a function of exposure time in air: red solid lines, blue dashed lines, and black dotted line correspond to samples treated by VH, HF, and with native-oxide surface, respectively. Take-off angle is 15°, pass energy is 35.75 eV. The top curve has been shifted by approximately 0.4 eV to facilitate comparison with the other curves. This shift is presumably due to surface charging.
Mentions: There is XPS support for this conclusion. Figure 4 shows the Si 2p core level peak and corresponding chemically shifted peak due to presence of oxide as a function of exposure time in air. It is clear that with a 2-h exposure to air, the Si 2p core level peak in SiO2 of the sample treated by VH is stronger than that of sample treated by HF, indicating that the VH-terminated sample has a higher oxidation rate at the beginning. As the samples continue to oxidize, the magnitudes of the chemically shifted Si 2p core level peaks for each sample type become closer and eventually reach a similar peak height after an 8-h exposure to air. As oxidation continues past 1 day, the peak for the HF-treated sample becomes stronger than that for VH-treated sample and continues to increase over the 18 days of measurements, almost reaching the level of the sample with a native-oxide surface. Comparison of O1s peaks confirms increasing oxidation, relative to the initial stages (Figure 3), but at different rates, as predicted from the sheet resistance data. These observations are in excellent agreement with the results of the electrical measurements shown in Figures 1 and 2. From the inset in Figure 2, it is clear that within 1 day after surface modification, the sheet resistances of both sample types reach a similar value of around 3 × 107 ohms/square.

Bottom Line: Two surface modifications, vacuum hydrogenation (VH) and hydrofluoric acid (HF) cleaning, of silicon nanomembranes (SiNMs) that nominally have the same effect, the hydrogen termination of the surface, are compared.Re-oxidation rates after these treatments also differ.We pinpoint the likely cause of the differences.PACS: 73.63.-b, 62.23.Kn, 73.40.Ty.

View Article: PubMed Central - HTML - PubMed

Affiliation: University of Wisconsin-Madison, Madison WI 53706, USA. lagally@engr.wisc.edu.

ABSTRACT
Because of the large surface-to-volume ratio, the conductivity of semiconductor nanostructures is very sensitive to surface chemical and structural conditions. Two surface modifications, vacuum hydrogenation (VH) and hydrofluoric acid (HF) cleaning, of silicon nanomembranes (SiNMs) that nominally have the same effect, the hydrogen termination of the surface, are compared. The sheet resistance of the SiNMs, measured by the van der Pauw method, shows that HF etching produces at least an order of magnitude larger drop in sheet resistance than that caused by VH treatment, relative to the very high sheet resistance of samples terminated with native oxide. Re-oxidation rates after these treatments also differ. X-ray photoelectron spectroscopy measurements are consistent with the electrical-conductivity results. We pinpoint the likely cause of the differences.PACS: 73.63.-b, 62.23.Kn, 73.40.Ty.

No MeSH data available.


Related in: MedlinePlus