This study investigates the ion irradiation induced phase transition in gallium oxide (Ga2O3) from the 𝜷 to the 𝜸 phase, the role of defects during the transformation, and the quality of the resulting crystal structure. Using a multi-method analysis approach including X-ray diffraction (XRD), transmission electron microscopy (TEM), Rutherford backscattering spectrometry in channeling mode (RBS/c), Doppler broadening variable energy positron annihilation spectroscopy (DB-VEPAS), and variable energy positron annihilation lifetime spectroscopy (VEPALS) supported by density functional theory (DFT) calculations, defects at all the relevant stages of the phase transition are characterized. A reduction in backscattering yield is observed in RBS/c spectra after the transition to the 𝜸 phase. This goes hand in hand with a significant decrease in the positron trapping center density due to generation of embedded vacancies intrinsic for the 𝜸–Ga2O3 but too shallow in order to trap positrons. A comparison of the observed positron lifetime of 𝜸–Ga2O3 with different theoretical models shows good agreement with the three-site 𝜸 phase approach. A characteristic increase in the effective positron diffusion length and the positron lifetime at the transition point from 𝜷–Ga2O3 to 𝜸–Ga2O3 enables visualization of the phase transition with positrons for the first time.Moreover, a subsequent reduction of these quantities with increasing irradiation fluence is observed, which attributes to further evolution of the 𝜸–Ga2O3 and changes in the gallium vacancy density as well as relative occupation in the crystal lattice.

We report the etching of and electronic transport in nanoribbons of graphene sandwiched between atomically flat hexagonal boron nitride (h-BN). The etching of ribbons of varying width was achieved with a focused beam of 30 keV He⁺ ions. Using in-situ electrical measurements, we established a critical dose of 7000 ions nm⁻² for creating a 10 nm wide insulating barrier between a nanoribbon and the rest of the encapsulated graphene. Subsequently, we measured the transport properties of the ion-beam etched graphene nanoribbons. Conductance measurements at 4 K show an energy gap, that increases with decreasing ribbon width. The narrowest ribbons show a weak dependence of the conductance on the Fermi energy. Furthermore, we observed power-law scaling in the measured current-voltage (I-V) curves, indicating that the conductance in the helium-ion-beam etched encapsulated graphene nanoribbons is governed by Coulomb blockade.