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To enhance thermoelectric performance by utilizing topological properties of topological insulators has attracted increasing attention. Here, we show that as grain size decreases from microns to ∼80 nm in thickness, the electron mobility μ increases steeply from 12–15 cm2 V−1 s−1 to ∼600 cm2 V−1 s−1, owing to the contribution of increased topologically protected conducting surfaces. Simultaneously, its lattice thermal conductivity is lowered by ∼30%–50% due to enhanced phonon scattering from the increased grain boundaries. As a result, thermoelectric figure of merit, ZT, of all the fine-grained samples is improved. Specifically, a maximum value of ZT = ∼0.63 is achieved for Bi2Se3 at T = ∼570 K.

The optical and structural properties of InGaN/GaN multi-quantum wells (MQWs) with different thicknesses of low temperature grown GaN cap layers are investigated. It is found that the MQW emission energy red-shifts and the peak intensity decreases with increasing GaN cap layer thickness, which may be partly caused by increased floating indium atoms accumulated at quantum well (QW) surface. They will result in the increased interface roughness, higher defect density, and even lead to a thermal degradation of QW layers. An extra growth interruption introduced before the growth of GaN cap layer can help with evaporating the floating indium atoms, and therefore is an effective method to improve the optical properties of high indium content InGaN/GaN MQWs.

Summary Afforestation is an important means of controlling desertification and of restoring vegetation on land that has become desert. The procedure leads to changes in the dynamics of organic carbon (C) in the soil as xerophytic shrubs are established, but the dynamics are still poorly understood, partly because of the lack of long‐term observations. Progressive measures to bind sand dunes along the route of the Baotou–Lanzhou railway on the south eastern edge of the Tengger Desert in China, which were begun in 1956, provide the opportunity to study such changes. We sampled the topsoil (0–10 cm) from 10 sites that represent a chronosequence and vary in age from 1 to 57 years since sand‐binding measures and afforestation were begun. These measures evidently trapped increasing amounts of clay and silt, and with them increased the concentrations of both available phosphorus (P) and available potassium (K). By analysing the organic C in the samples we have been able to describe quantitatively the changes in several C fractions over time. We found that total C, its light and heavy fractions, dissolved C and microbial C all increase slowly at first after afforestation, then more rapidly, and then at a decreasing rate. They seem to be examples of logistic growth and could be described by logistic equations. The light fraction increased faster than the total C, as did the microbial C during the first 19 years. The light C fraction was the most sensitive for identifying changes in soil C after afforestation. Over the full 57 years, the contributions of the light and microbial fractions to total C increased, while those of the heavy fraction and dissolved C decreased. Our results suggest that the proportion of C in labile pools increased, but the proportion in stable pools decreased, which would increase the risk of substantial losses of C caused by potential global warming and human‐induced disturbances.

Direct CVD deposition of dense, continuous, and adherent diamond films on conventional Fe-based alloys has long been considered impossible. The current study demonstrates that such a deposition can be realized on Al, Cr-modified Fe-based alloy substrate (FeAl or FeCrAl). To clarify the fundamental mechanism of Al, Cr in promoting diamond growth and enhancing interfacial adhesion, fine structure and chemical analysis around the diamond film-substrate interface have been comprehensively characterized by transmission electron microscopy. An intermediate graphite layer forms on those Al-free substrates such as pure Fe and FeCr, which significantly deteriorates the interfacial adhesion of diamond. In contrast, such a graphite layer is absent on the FeAl and FeCrAl substrates, whereas a very thin Al-rich amorphous oxide sublayer is always identified between the diamond film and substrate interface. These comparative results indicate that the Al-rich interfacial oxide layer acts as an effective barrier to prevent the formation of graphite phase and consequently enhance diamond growth and adhesion. The adhesion of diamond film formed on FeCrAl is especially superior to that formed on FeAl substrate. This can be further attributed to a synergetic effect including the reduced fraction of Al and the decreased substrate thermal-expansion coefficient on FeCrAl in comparison with FeAl, and a mechanical interlocking effect due to the formation of interfacial chromium carbides. Accordingly, a mechanism model is proposed to account for the different interfacial adhesion of diamond grown on the various Fe-based substrates.

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The significant effect of the thickness of Ni film on the performance of the Ohmic contact of Ni/Au to p-GaN is studied. The Ni/Au metal films with thickness of 15/50 nm on p-GaN led to better electrical characteristics, showing a lower specific contact resistivity after annealing in the presence of oxygen. Both the formation of a NiO layer and the evolution of metal structure on the sample surface and at the interface with p-GaN were checked by transmission electron microscopy and energy-dispersive x-ray spectroscopy. The experimental results indicate that a too thin Ni film cannot form enough NiO to decrease the barrier height and get Ohmic contact to p-GaN, while a too thick Ni film will transform into too thick NiO cover on the sample surface and thus will also deteriorate the electrical conductivity of sample.