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Oligosilanes bridging microgaps between silicon microcrystallites were investigated as a possible model for the origin of the intense visible photoluminescence of porous silicon by means of the semiempirical molecular‐orbital method. The incomplete structural relaxation of the oligosilane bridge after the photoexcitation was found to be a key factor to give the visible photoluminescence. The calculated structure‐insensitive photoexcitation energy around 3.3 eV and the structure‐sensitive light emission energy around 1.2–2.1 eV are consistent with the experimental evidence. The sufficient transition probabilities between the concerning electronic states support the high efficiency of photoluminescence. Durabiliy of the structure under the photoexcitation was also suggested. The model is valid even if the silicon microcrystallites are partly or thoroughly replaced by silicon oxides particles as is more realistic for the porous silicon exposed to the air.

SiO2/poly-Si/SiO2 double-barrier structures fabricated by radio-frequency magnetron sputtering are shown to exhibit negative differential resistance (NDR) that is attributed to resonant tunneling (RT) at low temperatures. An annealing process conducted after the multilayer deposition is found to effectively yield stable NDR. Five percent of all of the fabricated devices exhibit clear NDR below 50 K. Other devices with the same multilayered structure exhibit staircase-like current–voltage curves caused by the Coulomb blockade (CB) or by interplay between the RT and CB. The requisites of the poly-Si layer microstructures for the realization of stable RT are elucidated.

Single‐crystalline aluminum layer buried in α‐Al2O3 has been synthesized by high‐dose ion implantation of aluminum ions at an elevated temperature. It has been revealed by a high‐resolution transmission electron microscope that the aluminum layer has interfaces which are remarkably smooth and abrupt within a few atomic layers. This observation is comparable to that in mesotaxy of silicides buried in silicon.