To investigate the hybrid effect of steel-polypropylene fiber on the macroscopic mechanical properties , fracture properties and microstructure of the interfacial transition zones (ITZs) of concrete, 16 composite splitting tensile test and three-point bending test specimens with different volume fractions of steel and polypropylene fibers were tested by using the MTS and SEM. The results showed that the hybrid fibers significantly affected the interfacial fracture properties. The 0.4%PF+ 1.0%SF hybrid fiber composition is recommended, while a 30% decrease in interfacial fracture toughness and fracture energy occurs when the concrete contains 0.4%PF+ 1.5%SF. Fiber type affects the aggregate-mortar interface's ITZ micromorphology and has different influence mechanisms.

Columnar $\left(\mathrm{In,Ga}\right)\mathrm{As}$ quantum dots (QDs) with homogeneous composition and shape in the growth direction are realized by molecular-beam epitaxy on $\mathrm{GaAs}\left(100\right)$ substrates. The columnar $\left(\mathrm{In,Ga}\right)\mathrm{As}$ QDs are formed on $\mathrm{InAs}$ seed QDs by alternating deposition of thin $\mathrm{GaAs}$ intermediate layers and monolayers of $\mathrm{InAs}$ with extended growth interruptions after each layer. The height of the columnar $\left(\mathrm{In,Ga}\right)\mathrm{As}$ QDs is controlled by varying the number of stacked $\mathrm{GaAs}∕\mathrm{InAs}$ layers. The structural and optical properties are studied by cross-sectional scanning tunneling microscopy, atomic force microscopy, and photoluminescence spectroscopy. With increase of the aspect ratio of the columnar QDs, the emission wavelength is redshifted and the linewidth is reduced.