Surface-Originated Weak Confinement in Tetrahedral Indium Arsenide Quantum Dots.

While the shape-dependent quantum confinement (QC) effect in anisotropic semiconductor nanocrystals has been extensively studied, the QC in facet-specified polyhedral quantum dots (QDs) remains underexplored. Recently, tetrahedral nanocrystals have gained prominence in III-V nanocrystal synthesis. In our study, we successfully synthesized well-faceted tetrahedral InAs QDs with a first excitonic absorption extending up to 1700 nm. We observed an unconventional sizing curve, indicating weaker confinement than for equivalently volumed spherical QDs. The (111) surface states of InAs QDs persist at the conduction band minimum state even after ligand passivation with a significantly reduced band gap, which places tetrahedral QDs at lower energies in the sizing curve. Consequently, films composed of tetrahedral QDs demonstrate an extended photoresponse into the short-wave infrared region, compared to isovolume spherical QD films.

Direct Observation of Atomic Step-Assisted Stabilization of Polar Surfaces.

Polar surfaces are intrinsically unstable and thus highly reactive due to the uncompensated surface charges. The charge compensation is accompanied by various surface reconstructions, establishing novel functionality for their applications. The present in situ atomic-scale electron microscopy study directly shows that the atomic step and step-assisted reconstruction play central roles in the charge compensation of polar oxide surfaces. The flat (LaO)+ -terminated LaAlO3 (001) polar surface, when annealed at high temperature in vacuum, transits to the (015) vicinal surface via the dynamic motion and interaction of atomic steps. While the (015) vicinal surface possesses zero polarization along the surface normal, a thermodynamic ground state is achieved when the in-plane polarization is fully compensated via the reconstruction of step-edge atoms; the step-edge La atoms are displaced from their ordinary atomic sites toward the adjacent Al step-edge sites, resulting in the formation of negatively charged La vacancies at the corresponding step edges. As confirmed by first-principles calculations, the observed step reconstruction of (015) vicinal surface can completely cancel both out-of-plane and in-plane electric fields. This hitherto unknown mechanism reveals the central role of step reconstruction in stabilizing a polar surface, providing valuable insights for understanding the novel charge compensation mechanism accompanied by the step reconstruction.

Anti-phase boundary accelerated exsolution of nanoparticles in non-stoichiometric perovskite thin films.

Exsolution of excess transition metal cations from a non-stoichiometric perovskite oxide has sparked interest as a facile route for the formation of stable nanoparticles on the oxide surface. However, the atomic-scale mechanism of this nanoparticle formation remains largely unknown. The present in situ scanning transmission electron microscopy combined with density functional theory calculation revealed that the anti-phase boundaries (APBs) characterized by the a/2 < 011> type lattice displacement accommodate the excess B-site cation (Ni) through the edge-sharing of BO6 octahedra in a non-stoichiometric ABO3 perovskite oxide (La0.2Sr0.7Ni0.1Ti0.9O3-δ) and provide the fast diffusion pathways for nanoparticle formation by exsolution. Moreover, the APBs further promote the outward diffusion of the excess Ni toward the surface as the segregation energy of Ni is lower at the APB/surface intersection. The formation of nanoparticles occurs through the two-step crystallization mechanism, i.e., the nucleation of an amorphous phase followed by crystallization, and via reactive wetting on the oxide support, which facilitates the formation of a stable triple junction and coherent interface, leading to the distinct socketing of nanoparticles to the oxide support. The atomic-scale mechanism unveiled in this study can provide insights into the design of highly stable nanostructures.

The origin of jerky dislocation motion in high-entropy alloys.

Dislocations in single-phase concentrated random alloys, including high-entropy alloys (HEAs), repeatedly encounter pinning during glide, resulting in jerky dislocation motion. While solute-dislocation interaction is well understood in conventional alloys, the origin of individual pinning points in concentrated random alloys is a matter of debate. In this work, we investigate the origin of dislocation pinning in the CoCrFeMnNi HEA. In-situ transmission electron microscopy studies reveal wavy dislocation lines and a jagged glide motion under external loading, even though no segregation or clustering is found around Shockley partial dislocations. Atomistic simulations reproduce the jerky dislocation motion and link the repeated pinning to local fluctuations in the Peierls friction. We demonstrate that the density of high local Peierls friction is proportional to the critical stress required for dislocation glide and the dislocation mobility.

Error correction for rotationally asymmetric surface deviation testing based on rotational shears.

We present a practical method for absolute testing of rotationally asymmetric surface deviation based on rotation averaging, additional compensation, and azimuthal errors correction. The errors of angular orders kNθ neglected in the traditional multiangle averaging method can be reconstructed and compensated with the help of least-squares fitting of Zernike polynomials by an additional rotation measurement with a suitable selection of rotation angles. The estimation algorithm adopts the least-squares technique to eliminate azimuthal errors caused by rotation inaccuracy. The unknown relative alignment of the measurements also can be estimated through the differences in measurement results at overlapping areas. The method proposed combines the advantages of the single-rotation and multiangle averaging methods and realizes a balance between the efficiency and accuracy of the measurements. Experimental results show that the method proposed can obtain high accuracy even with fewer rotation measurements.