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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.


Results obtained from molecular dynamics simulations.(a), a 5 nm Ge particle generated by molecular dynamics simulations with the surface showing clear signs of disorder. (b), RDFs extracted as a function of distance d from the surface. Numbers in Å designate a corresponding RDF.
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f3: Results obtained from molecular dynamics simulations.(a), a 5 nm Ge particle generated by molecular dynamics simulations with the surface showing clear signs of disorder. (b), RDFs extracted as a function of distance d from the surface. Numbers in Å designate a corresponding RDF.

Mentions: To understand the effect of reduced dimensionality on the OD-XAS signal and to provide a source of information to constrain structural parameters (e.g. distances and numbers of neighbours), we have performed MD simulations of bulk Ge (to test simulation settings) and of a Ge QD. The system size was approximately 50 Å involving about 6,000 atoms. The bulk configuration with periodic boundary conditions was equilibrated for 50 ps at 100 K. To simulate a finite-size Ge nanoparticle with a free surface the cell size was increased by 20 Å - a distance larger than the potential cut-off. This resulted in atoms in the outmost layers being connected to vacuum, and induced surface relaxation (see Fig. 3, a). To quantify the effect of surface relaxation we have extracted the radial distribution functions (RDF) as a function of distance d from the surface towards the centre of the particle. In Fig. 3, b we plot RDFs for different values of d, and observe a clear bi-modal distribution of distances at the interface between the core and the surface as d increases towards the centre of a nanoparticle. This bi-modal distribution suggests that the interfacial layer is structurally different from the crystalline core. This in turn would suggest a distinctive difference in the electronic and optical properties of the interface as compared to that of the core.


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)

Results obtained from molecular dynamics simulations.(a), a 5 nm Ge particle generated by molecular dynamics simulations with the surface showing clear signs of disorder. (b), RDFs extracted as a function of distance d from the surface. Numbers in Å designate a corresponding RDF.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f3: Results obtained from molecular dynamics simulations.(a), a 5 nm Ge particle generated by molecular dynamics simulations with the surface showing clear signs of disorder. (b), RDFs extracted as a function of distance d from the surface. Numbers in Å designate a corresponding RDF.
Mentions: To understand the effect of reduced dimensionality on the OD-XAS signal and to provide a source of information to constrain structural parameters (e.g. distances and numbers of neighbours), we have performed MD simulations of bulk Ge (to test simulation settings) and of a Ge QD. The system size was approximately 50 Å involving about 6,000 atoms. The bulk configuration with periodic boundary conditions was equilibrated for 50 ps at 100 K. To simulate a finite-size Ge nanoparticle with a free surface the cell size was increased by 20 Å - a distance larger than the potential cut-off. This resulted in atoms in the outmost layers being connected to vacuum, and induced surface relaxation (see Fig. 3, a). To quantify the effect of surface relaxation we have extracted the radial distribution functions (RDF) as a function of distance d from the surface towards the centre of the particle. In Fig. 3, b we plot RDFs for different values of d, and observe a clear bi-modal distribution of distances at the interface between the core and the surface as d increases towards the centre of a nanoparticle. This bi-modal distribution suggests that the interfacial layer is structurally different from the crystalline core. This in turn would suggest a distinctive difference in the electronic and optical properties of the interface as compared to that of the core.

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.