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Size-dependent visible absorption and fast photoluminescence decay dynamics from freestanding strained silicon nanocrystals.

Dhara S, Giri P - Nanoscale Res Lett (2011)

Bottom Line: Si NCs with sizes in the range of approximately 5-40 nm show size-dependent visible absorption in the range of 575-722 nm, while NCs of average size <10 nm exhibit strong PL emission at 580-585 nm.The Raman scattering studies show non-monotonic shift of the TO phonon modes as a function of size because of competing effect of strain and phonon confinement.Our studies rule out the influence of defects in the PL emission, and we propose that owing to the combined effect of strain and quantum confinement, the strained Si NCs exhibit direct band gap-like behavior.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Physics, Indian Institute of Technology Guwahati, Guwahati-781039, India. pravat_g@yahoo.com.

ABSTRACT
In this article, we report on the visible absorption, photoluminescence (PL), and fast PL decay dynamics from freestanding Si nanocrystals (NCs) that are anisotropically strained. Direct evidence of strain-induced dislocations is shown from high-resolution transmission electron microscopy images. Si NCs with sizes in the range of approximately 5-40 nm show size-dependent visible absorption in the range of 575-722 nm, while NCs of average size <10 nm exhibit strong PL emission at 580-585 nm. The PL decay shows an exponential decay in the nanosecond time scale. The Raman scattering studies show non-monotonic shift of the TO phonon modes as a function of size because of competing effect of strain and phonon confinement. Our studies rule out the influence of defects in the PL emission, and we propose that owing to the combined effect of strain and quantum confinement, the strained Si NCs exhibit direct band gap-like behavior.

No MeSH data available.


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Steady-state PL and PL decay dynamics spectra of the freestanding Si NCs. (a) Room temperature PL spectra of as-prepared Si-30. Two Gaussian peaks are fitted (solid line) to the experimental data (symbol). Inset shows PL spectra for two different excitation wavelengths. (b) PL spectra for as-prepared Si-40. Fitted peaks are shown with solid line. The inset shows the broad PL spectra of different samples after room temperature prolonged oxidation of the Si-NCs. (c, d) The PL decay dynamics (intensity in logarithmic scale) of Si-NCs for Si-30 and Si-40 at emission wavelengths 585 and 580 nm, respectively. The exponential fits are shown with solid line in each case.
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Figure 3: Steady-state PL and PL decay dynamics spectra of the freestanding Si NCs. (a) Room temperature PL spectra of as-prepared Si-30. Two Gaussian peaks are fitted (solid line) to the experimental data (symbol). Inset shows PL spectra for two different excitation wavelengths. (b) PL spectra for as-prepared Si-40. Fitted peaks are shown with solid line. The inset shows the broad PL spectra of different samples after room temperature prolonged oxidation of the Si-NCs. (c, d) The PL decay dynamics (intensity in logarithmic scale) of Si-NCs for Si-30 and Si-40 at emission wavelengths 585 and 580 nm, respectively. The exponential fits are shown with solid line in each case.

Mentions: The Si NCs in Si-30 and Si-40 show strong PL emission in the visible region, which requires fitting of two Gaussian peaks, as shown in Figure 3a,b. The centers of the two peaks are located at 585 and 640 nm for Si-30, and 580 and 613 nm for Si-40, respectively. The emission peaks for the Si-40 is blue shifted, and the peak intensity is also enhanced compared with Si-30. It is noted that no visible PL emission was detected from the as-prepared NCs in Si-5, Si-10, and Si-20, all of which have average NC sizes above 10 nm. However, after prolonged storage in ambient air that causes a thicker oxide layer on the Si NCs, we observe a broad PL emission band at approximately 750 nm from all the samples excited with 488-nm laser, as shown in inset of Figure 3b. As the PL data shown in Figure 3a,b are recorded soon after the milling process, native oxide layer thickness is too small to contribute toward any discernable peak at approximately 750 nm in Figure 3a,b. The approximately 750-nm broad peak is attributed to oxygen-related-defect states in surface oxide layer [13].


Size-dependent visible absorption and fast photoluminescence decay dynamics from freestanding strained silicon nanocrystals.

Dhara S, Giri P - Nanoscale Res Lett (2011)

Steady-state PL and PL decay dynamics spectra of the freestanding Si NCs. (a) Room temperature PL spectra of as-prepared Si-30. Two Gaussian peaks are fitted (solid line) to the experimental data (symbol). Inset shows PL spectra for two different excitation wavelengths. (b) PL spectra for as-prepared Si-40. Fitted peaks are shown with solid line. The inset shows the broad PL spectra of different samples after room temperature prolonged oxidation of the Si-NCs. (c, d) The PL decay dynamics (intensity in logarithmic scale) of Si-NCs for Si-30 and Si-40 at emission wavelengths 585 and 580 nm, respectively. The exponential fits are shown with solid line in each case.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211408&req=5

Figure 3: Steady-state PL and PL decay dynamics spectra of the freestanding Si NCs. (a) Room temperature PL spectra of as-prepared Si-30. Two Gaussian peaks are fitted (solid line) to the experimental data (symbol). Inset shows PL spectra for two different excitation wavelengths. (b) PL spectra for as-prepared Si-40. Fitted peaks are shown with solid line. The inset shows the broad PL spectra of different samples after room temperature prolonged oxidation of the Si-NCs. (c, d) The PL decay dynamics (intensity in logarithmic scale) of Si-NCs for Si-30 and Si-40 at emission wavelengths 585 and 580 nm, respectively. The exponential fits are shown with solid line in each case.
Mentions: The Si NCs in Si-30 and Si-40 show strong PL emission in the visible region, which requires fitting of two Gaussian peaks, as shown in Figure 3a,b. The centers of the two peaks are located at 585 and 640 nm for Si-30, and 580 and 613 nm for Si-40, respectively. The emission peaks for the Si-40 is blue shifted, and the peak intensity is also enhanced compared with Si-30. It is noted that no visible PL emission was detected from the as-prepared NCs in Si-5, Si-10, and Si-20, all of which have average NC sizes above 10 nm. However, after prolonged storage in ambient air that causes a thicker oxide layer on the Si NCs, we observe a broad PL emission band at approximately 750 nm from all the samples excited with 488-nm laser, as shown in inset of Figure 3b. As the PL data shown in Figure 3a,b are recorded soon after the milling process, native oxide layer thickness is too small to contribute toward any discernable peak at approximately 750 nm in Figure 3a,b. The approximately 750-nm broad peak is attributed to oxygen-related-defect states in surface oxide layer [13].

Bottom Line: Si NCs with sizes in the range of approximately 5-40 nm show size-dependent visible absorption in the range of 575-722 nm, while NCs of average size <10 nm exhibit strong PL emission at 580-585 nm.The Raman scattering studies show non-monotonic shift of the TO phonon modes as a function of size because of competing effect of strain and phonon confinement.Our studies rule out the influence of defects in the PL emission, and we propose that owing to the combined effect of strain and quantum confinement, the strained Si NCs exhibit direct band gap-like behavior.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Physics, Indian Institute of Technology Guwahati, Guwahati-781039, India. pravat_g@yahoo.com.

ABSTRACT
In this article, we report on the visible absorption, photoluminescence (PL), and fast PL decay dynamics from freestanding Si nanocrystals (NCs) that are anisotropically strained. Direct evidence of strain-induced dislocations is shown from high-resolution transmission electron microscopy images. Si NCs with sizes in the range of approximately 5-40 nm show size-dependent visible absorption in the range of 575-722 nm, while NCs of average size <10 nm exhibit strong PL emission at 580-585 nm. The PL decay shows an exponential decay in the nanosecond time scale. The Raman scattering studies show non-monotonic shift of the TO phonon modes as a function of size because of competing effect of strain and phonon confinement. Our studies rule out the influence of defects in the PL emission, and we propose that owing to the combined effect of strain and quantum confinement, the strained Si NCs exhibit direct band gap-like behavior.

No MeSH data available.


Related in: MedlinePlus