Tunable diameter and spacing of double Ge quantum dots using highly-controllable spacers and selective oxidation of SiGe.

We report the novel tunability of the diameters and spacings of paired Ge double quantum dots (DQDs) using nano-spacer technology in combination with selective oxidation of Si0.85Ge0.15 at high temperature. Pairs of spherical-shaped Ge QDs were formed by the selective oxidation of poly-SiGe spacer islands at each sidewall corner of the nano-patterned Si3N4/poly-Si ridges. The diameters of the Ge spherical QDs are essentially determined by geometrical conditions (height, width, and length) of the nano-patterned spacer islands of poly-SiGe, which are tunable by adjusting the process times of deposition and etch back for poly-SiGe spacer layers in combination with the exposure dose of electron-beam lithography. Most importantly, the separations between the Ge DQDs are controllable by adjusting the widths of the poly-Si/Si3N4 ridges and the thermal oxidation times. Our self-organization and self-alignment approach achieved high symmetry within the Ge DQDs in terms of the individual QD diameters as well as the coupling barriers between the QDs and external electrodes in close proximity.

Ge nanodot-mediated densification and crystallization of low-pressure chemical vapor deposited Si3N4 for advanced complementary metal-oxide-semiconductor photonics and electronics applications.

A new phenomenon of highly localized, nanoscale densification and crystallization of silicon-nitride (Si3N4) layers has been observed. A drastic reduction in the thermal budget (temperature and processing time) for local densification and even nanocrystallization of low-pressure chemical vapor deposited amorphous Si3N4 layers is mediated by the presence of Ge, Si, and O interstitials in close proximity to the Si3N4. The enhancement of localized densification and nanocrystallization observed in Si3N4 layers appears to be catalyzed by proximal Ge quantum dots (QDs) 'migrating' through the Si3N4/Si layers and are influenced by the oxidation time and Ge QD size. Implications of the highly localized, nanoscale densification and crystallization of silicon-nitride (Si3N4) layers for photonic and electronic device applications are discussed.

Influence of magnetoplasmonic γ-Fe2O3/Au core/shell nanoparticles on low-field nuclear magnetic resonance.

Magnetoplasmonic nanoparticles, composed of a plasmonic layer and a magnetic core, have been widely shown as promising contrast agents for magnetic resonance imaging (MRI) applications. However, their application in low-field nuclear magnetic resonance (LFNMR) research remains scarce. Here we synthesised γ-Fe2O3/Au core/shell (γ-Fe2O3@Au) nanoparticles and subsequently used them in a homemade, high-Tc, superconducting quantum interference device (SQUID) LFNMR system. Remarkably, we found that both the proton spin-lattice relaxation time (T1) and proton spin-spin relaxation time (T2) were influenced by the presence of γ-Fe2O3@Au nanoparticles. Unlike the spin-spin relaxation rate (1/T2), the spin-lattice relaxation rate (1/T1) was found to be further enhanced upon exposing the γ-Fe2O3@Au nanoparticles to 532 nm light during NMR measurements. We showed that the photothermal effect of the plasmonic gold layer after absorbing light energy was responsible for the observed change in T1. This result reveals a promising method to actively control the contrast of T1 and T2 in low-field (LF) MRI applications.