6 research outputs found
Light emission from silicon with tin-containing nanocrystals
Tin-containing nanocrystals, embedded in silicon, have been fabricated by
growing an epitaxial layer of Si_{1-x-y}Sn_{x}C_{y}, where x = 1.6 % and y =
0.04 %, followed by annealing at various temperatures ranging from 650 to 900
degrees C. The nanocrystal density and average diameters are determined by
scanning transmission-electron microscopy to ~ 10^{17} cm^{-3} and ~ 5 nm,
respectively. Photoluminescence spectroscopy demonstrates that the light
emission is very pronounced for samples annealed at 725 degrees C, and
Rutherford back-scattering spectrometry shows that the nanocrystals are
predominantly in the diamond-structured phase at this particular annealing
temperature. The origin of the light emission is discussed.Comment: 5 pages, 3 figures, submitted to AIP Advance
Strongly enhanced upconversion in trivalent erbium ions by tailored gold nanostructures: Toward high-efficient silicon-based photovoltaics
Upconversion of sub-band-gap photons constitutes a promising way for
improving the efficiency of silicon-based solar cells beyond the
Shockley-Queisser limit. 1500 to 980 nm upconversion by trivalent erbium ions
is well-suited for this purpose, but the small absorption cross section hinders
real-world applications. We employ tailored gold nanostructures to vastly
improve the upconversion efficiency in erbium-doped TiO thin films. The
nanostructures are found using topology optimization and parameter optimization
and fabricated by electron beam lithography. In qualitative agreement with a
theoretical model, the samples show substantial electric-field enhancements
inside the upconverting films for excitation at 1500 nm for both s- and
p-polarization under a wide range of incidence angles and excitation
intensities. An unprecedented upconversion enhancement of 913(51) is observed
at an excitation intensity of 1.7 Wcm. We derive a semi-empirical
expression for the photonically enhanced upconversion efficiency, valid for all
excitation intensities. This allows us to determine the upconversion properties
needed to achieve significant improvements in real-world solar-cell devices
through photonic-enhanced upconversion.Comment: 9 pages (main text), 4 figures, 1 supporting information of 15 page
Time-resolved infrared photoluminescence spectroscopy using parametric three-wave mixing with angle-tuned phase matching
Electron energy-loss spectroscopy of single nanocrystals: Mapping of tin allotropes
Using monochromated electron energy-loss spectroscopy (EELS), we are able to map different allotropes in Sn-nanocrystals embedded in Si. It is demonstrated that α-Sn and β-Sn, as well as an interface related plasmon, can be distinguished in embedded Sn-nanostructures. The EELS data is interpreted by standard non-negative matrix factorization followed by a manual Lorentzian decomposition. The decomposition allows for a more physical understanding of the EELS mapping without reducing the level of information. Extending the analysis from a reference system to smaller nanocrystals demonstrates that allotrope determination in nanoscale systems down below 5 nm is possible. Such local information proves the use of monochromated EELS mapping as a powerful technique to study nanoscale systems. This possibility enables investigation of small nanostructures that cannot be investigated through other means, allowing for a better understanding and thus leading to realizations that can result in nanomaterials with improved properties
Deciphering the Alphabet of Disorder—Glu and Asp Act Differently on Local but Not Global Properties
Compared to folded proteins, the sequences of intrinsically disordered proteins (IDPs) are enriched in polar and charged amino acids. Glutamate is one of the most enriched amino acids in IDPs, while the chemically similar amino acid aspartate is less enriched. So far, the underlying functional differences between glutamates and aspartates in IDPs remain poorly understood. In this study, we examine the differential effects of aspartate and glutamates in IDPs by comparing the function and conformational ensemble of glutamate and aspartate variants of the disordered protein Dss1, using a range of assays, including interaction studies, nuclear magnetic resonance spectroscopy, small-angle X-ray scattering and molecular dynamics simulation. First, we analyze the sequences of the rapidly growing database of experimentally verified IDPs (DisProt) and show that glutamate enrichment is not caused by a taxonomy bias in IDPs. From analyses of local and global structural properties as well as cell growth and protein-protein interactions using a model acidic IDP from yeast and three Glu/Asp variants, we find that while the Glu/Asp variants support similar function and global dimensions, the variants differ in their binding affinities and population of local transient structural elements. We speculate that these local structural differences may play roles in functional diversity, where glutamates can support increased helicity, important for folding and binding, while aspartates support extended structures and form helical caps, as well as playing more relevant roles in, e.g., transactivation domains and ion-binding