Ordered GeSi nanorings grown on patterned Si (001) substrates

An easy approach to fabricate ordered pattern using nanosphere lithography and reactive iron etching technology was demonstrated. Long-range ordered GeSi nanorings with 430 nm period were grown on patterned Si (001) substrates by molecular beam epitaxy. The size and shape of rings were closely associated with the size of capped GeSi quantum dots and the Si capping processes. Statistical analysis on the lateral size distribution shows that the high growth temperature and the long-term annealing can improve the uniformity of nanorings

Evolution of thin protecting Si-layer on Mn0.5Si0.5 layer at low temperatures

Evolution of 2-nm-thick protecting Si-layer on amorphous Mn0.5Si0.5 films at elevated temperatures was investigated by using conductive atom force microscopy (CAFM) and other structure and composition characterization methods. At a temperature of 300 degrees C, a dramatic change was observed in surface morphology with many islands forming on the surface. Those islands were SiO2 islands rather than Si ones. Further studies showed that those islands formed via first oxidation of the Si cap layer followed by the agglomeration of this SiO2 layer. Because Si cap layer has widely been used as protecting materials to prevent the surface from oxidizing and contamination, this study provides an insight on the effectiveness of thin protecting Si-layer at low temperatures. (C) 2015 Elsevier B.V. All rights reserved

Plasmon-gating photoluminescence in graphene/GeSi quantum dots hybrid structures

The ability to control light-matter interaction is central to several potential applications in lasing, sensing, and communication. Graphene plasmons provide a way of strongly enhancing the interaction and realizing ultrathin optoelectronic devices. Here, we find that photoluminescence (PL) intensities of the graphene/GeSi quantum dots hybrid structures are saturated and quenched under positive and negative voltages at the excitation of 325 nm, respectively. A mechanism called plasmon-gating effect is proposed to reveal the PL dependence of the hybrid structures on the external electric field. On the contrary, the PL intensities at the excitation of 405 and 795 nm of the hybrid structures are quenched due to the charge transfer by tuning the Fermi level of graphene or the blocking of the excitons recombination by excitons separation effect. The results also provide an evidence for the charge transfer mechanism. The plasmon gating effect on the PL provides a new way to control the optical properties of graphene/QD hybrid structures

Enhancement of Er3+ emission from an Er-Si codoped Al 2O3 film by stacking Si-doped Al2O3 sublayers

A multilayer film (multi-film), consisting of alternate Er-Si-codoped Al2O3 (ESA) and Si-doped Al2O3 (SA) sublayers, is synthesized by co-sputtering from separated Er, Si, and Al 2O3 targets. The dependence of Er3+ related photoluminescence (PL) properties on annealing temperatures over 700-1100°C is studied. The maximum intensity of Er3+ photoluminance (PL), about 10 times higher than that of the monolayer film, is obtained from the multi-film annealed at 950°C. The enhancement of Er3+ PL intensity is attributed to the energy transfer from the silicon nanocrystals (Si-NCs) to the neighboring Er3+ ions. The effective characteristic interaction distance (or the critical ET length) between Er and carriers (Si-NCs) is ∼3 nm. The PL intensity exhibits a nonmonotonic temperature dependence. Meanwhile, the PL integrated intensity at room temperature is about 30% higher than that at 14 K. © 2011 Chinese Physical Society and IOP Publishing Ltd.Peer Reviewe

Investigation on Ge surface diffusion via growing Ge quantum dots on top of Si pillars

We report on a simple and intuitionistic experimental method to quantitatively measure surface diffusion lengths of Ge adatoms on Si(001) substrates and its activation energy Ea, which is achieved by growing Ge quantum dots (QDs) on top surfaces of Si pillars with different radii and taking an advantage of preferential nucleation and growth of Ge QDs at the top surface edge of the pillars. Diffusion length of Ge adatom can directly be measured and determined by the radius of the pillar below which no QDs will nucleate and grow at the central region of the top surface of the Si pillar. With a growth rate v fixed at 0.1 Å/s, by changing the growth temperature, the diffusion lengths at different temperatures would be obtained. Arrhenius plot of diffusion length as a function of growth temperature gives the value of Ea of 1.37 eV. Likewise, with a growth rate v fixed at 0.05 Å/s, the Ea value is obtained to be 1.38 eV. Two Ea values agree well with each other, implying that the method is reliable and self-consistent. Moreover, for a fixed growth temperature, the surface diffusion lengths are found to be directly proportional to 1 / ν . It also agrees well with the theoretical prediction, further demonstrating the reliability of the method