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Structural origin of light emission in germanium quantum dots.

Little W, Karatutlu A, Bolmatov D, Trachenko K, Sapelkin AV, Cibin G, Taylor R, Mosselmans F, Dent AJ, Mountjoy G - Sci Rep (2014)

Bottom Line: Two sets of nanoparticles were studied, with oxygen and hydrogen terminated surfaces.We found that in oxygen terminated nanoparticles its the oxide-rich regions that are responsible for the light emission.In hydrogen terminated nanoparticles we established that structurally disordered Ge regions contribute to the luminescence.

View Article: PubMed Central - PubMed

Affiliation: Center for Condensed Matter and Materials Physics, School of Physics and Astronomy, Queen Mary, University of London, Mile End Road, London E1 4NS, UK.

ABSTRACT
We used a combination of optically-detected x-ray absorption spectroscopy with molecular dynamics simulations to explore the origins of light emission in small (5 nm to 9 nm) Ge nanoparticles. Two sets of nanoparticles were studied, with oxygen and hydrogen terminated surfaces. We show that optically-detected x-ray absorption spectroscopy shows sufficient sensitivity to reveal the different origins of light emission in these two sets of samples. We found that in oxygen terminated nanoparticles its the oxide-rich regions that are responsible for the light emission. In hydrogen terminated nanoparticles we established that structurally disordered Ge regions contribute to the luminescence. Using a combination of molecular dynamics simulations and optically-detected x-ray absorption spectroscopy we show that these disordered regions correspond to the disordered layer a few Å thick at the surface of the simulated nanoparticle.

No MeSH data available.


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XEOL, the corresponding OD-XAS, and structural data for Ge QDs.(a), XEOL data used to extract structural information. Red rectangle indicates the position of the band used to collect OD-XAS. (b), OD-XAS data used to obtain structural information. Data for oxygen-terminated samples are shifted along x-axis for clarity. (c), Structural data extracted from transmission measurements and presented as the normalized magnitude of the Fourier transform. Reference bulk c-Ge data are also shown and positions of the coordination shells related to the oxide and pure Ge are marked (Ge1, Ge2 and Ge3 corresponds to first, second and third shells in diamond-type Ge). (d), Structural data extracted from OD-EXAFS presented as the normalized magnitude of the Fourier transform (see Methods section) with the coordination shells around Ge marked, and sample surface conditions indicated in parentheses.
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f2: XEOL, the corresponding OD-XAS, and structural data for Ge QDs.(a), XEOL data used to extract structural information. Red rectangle indicates the position of the band used to collect OD-XAS. (b), OD-XAS data used to obtain structural information. Data for oxygen-terminated samples are shifted along x-axis for clarity. (c), Structural data extracted from transmission measurements and presented as the normalized magnitude of the Fourier transform. Reference bulk c-Ge data are also shown and positions of the coordination shells related to the oxide and pure Ge are marked (Ge1, Ge2 and Ge3 corresponds to first, second and third shells in diamond-type Ge). (d), Structural data extracted from OD-EXAFS presented as the normalized magnitude of the Fourier transform (see Methods section) with the coordination shells around Ge marked, and sample surface conditions indicated in parentheses.

Mentions: A comparison of the results of the analysis of the transmission and OD-XAS data collected at the Ge K-edge at T = 100 K for all three types of QDs studied are shown in Fig. 2. XEOL signal used to acquire the OD-XAS data can be seen in Fig. 2, a. The OD-XAS data obtained from XEOL are shown in Fig. 2, b. These data were used to extract the corresponding extended x-ray absorption fine structure (EXAFS) signals from which detailed structural information was obtained (see Supplement). Looking at the positions of the peaks in the magnitude of the Fourier Transform (FT) of EXAFS for oxygen-terminated samples collected in transmission mode (Fig. 2, c) one can see the signal corresponding to Ge-O bond at around 1.7 Å together with the signal at 2.45 Å corresponding to Ge-Ge bond in a diamond-type structure (see Table I in the Supplement for details). The relatively strong Ge-O peak (see Fig. 2, c) indicates significant oxygen content in oxidised samples. In OD-XAS data for oxygen-terminated samples no coordination shell at around 2.45 Å is observed at all while Ge-O signal can still be clearly seen (Fig. 2, d). For the hydrogen-terminated sample we find that only signals corresponding to Ge coordination shells are observed in transmission data and no oxygen related peaks are detected while hydrogen atoms are too weakly scattering to be seen. In the data extracted from OD-XAS of the hydrogen terminated sample once again only Ge-Ge signal is detected. However, this time only a single peak was observed corresponding to the first coordination shell. These results suggest that OD-XAS provides information different from that obtained from the transmission data as it is sampling substructures contributing to the luminescence.


Structural origin of light emission in germanium quantum dots.

Little W, Karatutlu A, Bolmatov D, Trachenko K, Sapelkin AV, Cibin G, Taylor R, Mosselmans F, Dent AJ, Mountjoy G - Sci Rep (2014)

XEOL, the corresponding OD-XAS, and structural data for Ge QDs.(a), XEOL data used to extract structural information. Red rectangle indicates the position of the band used to collect OD-XAS. (b), OD-XAS data used to obtain structural information. Data for oxygen-terminated samples are shifted along x-axis for clarity. (c), Structural data extracted from transmission measurements and presented as the normalized magnitude of the Fourier transform. Reference bulk c-Ge data are also shown and positions of the coordination shells related to the oxide and pure Ge are marked (Ge1, Ge2 and Ge3 corresponds to first, second and third shells in diamond-type Ge). (d), Structural data extracted from OD-EXAFS presented as the normalized magnitude of the Fourier transform (see Methods section) with the coordination shells around Ge marked, and sample surface conditions indicated in parentheses.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4260222&req=5

f2: XEOL, the corresponding OD-XAS, and structural data for Ge QDs.(a), XEOL data used to extract structural information. Red rectangle indicates the position of the band used to collect OD-XAS. (b), OD-XAS data used to obtain structural information. Data for oxygen-terminated samples are shifted along x-axis for clarity. (c), Structural data extracted from transmission measurements and presented as the normalized magnitude of the Fourier transform. Reference bulk c-Ge data are also shown and positions of the coordination shells related to the oxide and pure Ge are marked (Ge1, Ge2 and Ge3 corresponds to first, second and third shells in diamond-type Ge). (d), Structural data extracted from OD-EXAFS presented as the normalized magnitude of the Fourier transform (see Methods section) with the coordination shells around Ge marked, and sample surface conditions indicated in parentheses.
Mentions: A comparison of the results of the analysis of the transmission and OD-XAS data collected at the Ge K-edge at T = 100 K for all three types of QDs studied are shown in Fig. 2. XEOL signal used to acquire the OD-XAS data can be seen in Fig. 2, a. The OD-XAS data obtained from XEOL are shown in Fig. 2, b. These data were used to extract the corresponding extended x-ray absorption fine structure (EXAFS) signals from which detailed structural information was obtained (see Supplement). Looking at the positions of the peaks in the magnitude of the Fourier Transform (FT) of EXAFS for oxygen-terminated samples collected in transmission mode (Fig. 2, c) one can see the signal corresponding to Ge-O bond at around 1.7 Å together with the signal at 2.45 Å corresponding to Ge-Ge bond in a diamond-type structure (see Table I in the Supplement for details). The relatively strong Ge-O peak (see Fig. 2, c) indicates significant oxygen content in oxidised samples. In OD-XAS data for oxygen-terminated samples no coordination shell at around 2.45 Å is observed at all while Ge-O signal can still be clearly seen (Fig. 2, d). For the hydrogen-terminated sample we find that only signals corresponding to Ge coordination shells are observed in transmission data and no oxygen related peaks are detected while hydrogen atoms are too weakly scattering to be seen. In the data extracted from OD-XAS of the hydrogen terminated sample once again only Ge-Ge signal is detected. However, this time only a single peak was observed corresponding to the first coordination shell. These results suggest that OD-XAS provides information different from that obtained from the transmission data as it is sampling substructures contributing to the luminescence.

Bottom Line: Two sets of nanoparticles were studied, with oxygen and hydrogen terminated surfaces.We found that in oxygen terminated nanoparticles its the oxide-rich regions that are responsible for the light emission.In hydrogen terminated nanoparticles we established that structurally disordered Ge regions contribute to the luminescence.

View Article: PubMed Central - PubMed

Affiliation: Center for Condensed Matter and Materials Physics, School of Physics and Astronomy, Queen Mary, University of London, Mile End Road, London E1 4NS, UK.

ABSTRACT
We used a combination of optically-detected x-ray absorption spectroscopy with molecular dynamics simulations to explore the origins of light emission in small (5 nm to 9 nm) Ge nanoparticles. Two sets of nanoparticles were studied, with oxygen and hydrogen terminated surfaces. We show that optically-detected x-ray absorption spectroscopy shows sufficient sensitivity to reveal the different origins of light emission in these two sets of samples. We found that in oxygen terminated nanoparticles its the oxide-rich regions that are responsible for the light emission. In hydrogen terminated nanoparticles we established that structurally disordered Ge regions contribute to the luminescence. Using a combination of molecular dynamics simulations and optically-detected x-ray absorption spectroscopy we show that these disordered regions correspond to the disordered layer a few Å thick at the surface of the simulated nanoparticle.

No MeSH data available.


Related in: MedlinePlus