Enhancement of the Seebeck coefficient (S ) without reducing the electrical conductivity (sigma) is essential to realize practical thermoelectric materials exhibiting a dimensionless figure of merit (ZT=S2 x sigma x T x kappa-1) exceeding 2, where T is the absolute temperature and kappa is the thermal conductivity. Here, we demonstrate that a high-density two-dimensional electron gas (2DEG) confined within a unit cell layer thickness in SrTiO(3) yields unusually large |S|, approximately five times larger than that of SrTiO(3) bulks, while maintaining a high sigma2DEG. In the best case, we observe |S|=850 microV K-1 and sigma2DEG=1.4 x 10(3) S cm-1. In addition, by using the kappa of bulk single-crystal SrTiO(3) at room temperature, we estimate ZT approximately 2.4 for the 2DEG, corresponding to ZT approximately 0.24 for a complete device having the 2DEG as the active region. The present approach using a 2DEG provides a new route to realize practical thermoelectric materials without the use of toxic heavy elements.

We report two-dimensional Seebeck coefficients (∣S∣2D) of [(SrTiO3)x∕(SrTi0.8Nb0.2O3)y]20 (x=1–60, y=1–20) superlattices, which were grown on the (100) face of insulating LaAlO3 substrates to clarify the origin of the giant ∣S∣2D values of the SrTiO3 superlattices [H. Ohta et al., Nat. Mater. 6, 129 (2007)]. The ∣S∣2D values of the [(SrTiO3)17∕(SrTi0.8Nb0.2O3)y]20 superlattices increased proportionally to y−0.5 and reached 320μVK−1 (y=1), which is approximately five times larger than that of the SrTi0.8Nb0.2O3 bulk (∣S∣3D=61μVK−1). The slope of the log∣S∣2D-logy plots was −0.5, proving that the density of states in the ground state for SrTiO3 increases inversely proportionally to y. The critical barrier thickness for quantum electron confinement was also clarified to be 6.25nm (16 unit cells of SrTiO3).

Herein we report the carrier transport properties of [(SrTiO 3 ) x /(SrTi 0:8 Nb 0:2 O 3 ) 1 ] 20 (x ¼ 0 -50) superlattices at high temperatures (T ¼ 300 -900 K). Significant structural changes were not observed in the superlattices after annealing at 900 K in a vacuum. The Seebeck coefficient of the [(SrTiO 3 ) 20 /(SrTi 0:8 Nb 0:2 O 3 ) 1 ] 20 superlattice, which was 300 VÁK À1 at room temperature, gradually increased with temperature and reached 450 VÁK À1 at 900 K, which is $3 times larger than that of bulk SrTi 0:8 Nb 0:2 O 3 . These observations provide clear evidence that the superlattice is stable and exhibits a giant Seebeck coefficient even at high temperature.

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The formation of micellar solutions with hydrophilic surfactants is generally used to include oily substances into transparent water-based formulae. However, a restriction exists on hydrophilic surfactants due to their sticky feeling arising from long hydrophilic groups. We found a stable transparent dispersion of a lipophilic polyether-modified silicone PEMS in combination with an ionic surfactant by a certain procedure. Various analyses revealed that it is a 10 100 nm sized vesicle micelle complex consisting of bi-molecular membranes. Although there are several reports on the vesicle formation of PEMS, the practical stability has been insufficient because of the high fluidity of the membrane. The present vesicle micelle complex can solubilize silicone oils, which have been considered difficult, resulting in a feature of good spreadability onto surfaces. In addition to that, it shows a non-sticky, highly permeable feeling owing to the formation of a lamellar liquid crystalline phase by a water evaporation on application despite the high glycerol concentration. The present moisturizing lotion fulfilled mutually exclusive events of high skin hydration to prepare for future skincare items a moisturizing lotion with an important function and a highly comfortable texture.