Photoelectron Holographic Atomic Arrangement Imaging of Cleaved Bimetal-intercalated Graphite Superconductor Surface

Effects of Oxygen on Lattice Defects in Single-Crystalline Mg2Si Thermoelectrics

Lattice defect engineering has attracted attention due to its ability to develop thermoelectric materials with low thermal conductivity. For Mg₂Si single crystals (SCs), Si vacancy (V_Si) defects can be introduced and consequently result in the formation of dislocation cores. These lattice defects confer Mg₂Si SCs with a lower thermal conductivity compared to Mg₂Si polycrystals. To reveal a mechanism for the stabilisation of V_Si in the Mg₂Si SCs, we investigated the effects of oxygen (O) on lattice defects by performing electronic structure calculations, secondary ion mass spectrometry, X-ray photoelectron spectroscopy, and photoelectron holography. On the basis of these calculations, we predicted that O stabilised the formation of V_Si when it was located at the Si site or at an interstitial site. All experiments confirmed the presence of O inside the Mg₂Si SCs. However, O was suggested to be located not at the specific site in the crystal lattice of Mg₂Si but at dislocation cores. The interaction between O and the dislocation cores in the Mg₂Si SC is expected to immobilise dislocation cores, leading to the stabilisation of V_Si formation.

Individual Atomic Imaging of Multiple Dopant Sites in As-Doped Si Using Spectro-Photoelectron Holography

The atomic scale characterization of dopant atoms in semiconductor devices to establish correlations with the electrical activation of these atoms is essential to the advancement of contemporary semiconductor process technology. Spectro-photoelectron holography combined with first-principles simulations can determine the local three-dimensional atomic structures of dopant elements, which in turn affect their electronic states. In the work reported herein, this technique was used to examine arsenic (As) atoms doped into a silicon (Si) crystal. As 3d core level photoelectron spectroscopy demonstrated the presence of three types of As atoms at a total concentration of approximately 10²⁰ cm^-3, denoted as BEH, BEM, and BEL. On the basis of Hall effect measurements, the BEH atoms corresponded to electrically active As occupying substitutional sites and exhibiting larger thermal fluctuations than the Si atoms, while the BEM atoms corresponded to electrically inactive As embedded in the As_nV (n = 2-4) type clusters. Finally, the BEL atoms were assigned to electrically inactive As in locally disordered structures.