Crystallization of Ge-rich GST leads to phase separation, a characteristic which explains their superior properties for electronic memory devices

The formation and evolution of small cluster defects in 500 eV, ${\text{1×10}}^{15}\hspace{0.17em}{\mathrm{cm}}^{\text{−2}}$ boron-implanted silicon is investigated. These clusters are identified by high-resolution transmission electron microscopy (TEM) as small dislocation loops lying on {100} planes with an interstitial character. Weak-beam dark-field TEM analysis shows that, during annealing at 650 °C, they evolve following an Ostwald ripening mechanism. Spike anneals at high temperatures make them dissolve but an immobile boron peak is still detected in the secondary ion mass spectroscopy profiles. Upon oxidation, the average size of the clusters increases, while boron electrical deactivation occurs. These results strongly indicate that the observed clusters contain both boron interstitials and silicon self-interstitials atoms.

We report on electron spin resonance (ESR) spectroscopy of boron-vacancy (${\mathrm{V}}_{\mathrm{B}}^{-}$) centers hosted in isotopically engineered hexagonal boron nitride (hBN) crystals. We first show that isotopic purification of hBN with ${}^{15}\mathrm{N}$ yields a simplified and well-resolved hyperfine structure of ${\mathrm{V}}_{\mathrm{B}}^{-}$ centers, while purification with ${}^{10}\mathrm{B}$ leads to narrower ESR linewidths. These results establish isotopically purified $\mathrm{h}{}^{10}\mathrm{B}{}^{15}\mathrm{N}$ crystals as the optimal host material for future use of ${\mathrm{V}}_{\mathrm{B}}^{-}$ spin defects in quantum technologies. Capitalizing on these findings, we then demonstrate optically induced polarization of ${}^{15}\mathrm{N}$ nuclei in $\mathrm{h}{}^{10}\mathrm{B}{}^{15}\mathrm{N}$, whose mechanism relies on electron-nuclear spin mixing in the ${\mathrm{V}}_{\mathrm{B}}^{-}$ ground state. This work opens up new prospects for future developments of spin-based quantum sensors and simulators on a two-dimensional material platform.

Ion implantation followed by high temperature annealing can be used to synthesize group IV semiconducting nanoparticles in ${\mathrm{SiO}}_{\mathrm{2}}.$ The density and the size distribution of these nanocrystals obviously depend on the implantation and annealing conditions. While their size can be measured by “classical” transmission electron microscopy techniques, their density cannot because no diffraction occurs in the amorphous matrix. In this letter, we use electron energy loss spectroscopy to overcome this problem. We have measured the evolution of the size distribution, the density, and the atomic fraction occupied by the Ge precipitates during annealing. We show that the nanocrystals grow in size and reduce their density, while the overall number of atoms they contain remains constant. This observation proves that the nanoparticles undergo a conservative ripening during annealing.