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The transient heat conduction equation for the 2D electron gas layer in GaN high‐electron‐mobility transistors is developed. The Schottky barrier height and the conduction band offset seen by electrons in the 2D electron gas layer will be reduced due to self‐heating in the 2D electron gas of GaN high‐electron‐mobility transistors via quantum coupling. Such a reduction will lead to a shift in the threshold voltage. To address this issue, an analytical physical model of self‐heating in the 2D electron gas of a GaN high‐electron‐mobility transistor via quantum coupling impacts on its threshold voltage instability is proposed. The proposed model forecasts that the threshold voltage can have an exponentially dependent relation with the reciprocal of the recovery time after the stress voltage is released, as well as dependencies on the square of the drift velocity, the gate voltage, and the surrounding temperature. The experimentally observed threshold voltage shifts of GaN high‐electron‐mobility transistors confirm such dependent relationships predicted by the proposed physical model. This article provides evidence that the combination of self‐heating in the 2D electron gas layer and quantum coupling may be a possible physical origin of the threshold voltage instability in GaN high‐electron‐mobility transistors. [ABSTRACT FROM AUTHOR]

The flora of China is well known for its high diversity and endemism. Identifying centers of endemism and designating conservation priorities are essential goals for biodiversity studies. However, there is no comprehensive study from a rigorous phylogenetic perspective to understand patterns of diversity and endemism and to guide biodiversity conservation in China. We conducted a spatial phylogenetic analysis of the Chinese angiosperm flora at the generic level to identify centers of neo‐ and paleo‐endemism. Our results indicate that: (i) the majority of grid cells in China with significantly high phylogenetic endemism (PE) were located in the mountainous regions; (ii) four of the nine centers of endemism recognized, located in northern and western China, were recognized for the first time; (iii) arid and semiarid regions in Northwest China were commonly linked to significant PE, consistent with other spatial phylogenetic studies worldwide; and (iv) six high‐priority conservation gaps were detected by overlaying the boundaries of China's nature reserves on all significant PE cells. Overall, we conclude that the mountains of southern and northern China contain both paleo‐endemics (ancient relictual lineages) and neo‐endemics (recently diverged lineages). The areas we highlight as conservation priorities are important for broad‐scale planning, especially in the context of evolutionary history preservation. [ABSTRACT FROM AUTHOR]

Metal doping has long been recognized as a general strategy to modify electronic properties of semiconductors. The purpose here is to understand the behavior of oxygen vacancy when existing together with a metal dopant in rutile TiO2 through first‐principles calculation. For the coexistence of an oxygen vacancy and an Ag/Hf dopant, the dopant local effect determines that the formation energy of the oxygen vacancy depends on distances from it to the Ag/Hf dopant. Increased formation energy of an oxygen vacancy adjacent to an Ag dopant is attributed to the fact that the holes produced because of lower valence of Ag than Ti are filled by electrons left by the oxygen vacancy. The same valence of Hf as Ti results in that the electrostatic repulsive force pushes the Hf dopant outward from nearby oxygen vacancy, which lowers the formation energy of the oxygen vacancy. Furthermore, oxygen vacancies coexisting with an Ag/Hf dopant are of interest for investigating the effect of metal doping on the reliability of conductive filaments. The Hf dopant adjacent to the oxygen vacancies greatly enhances the strength of a conductive filament. The built‐in electric fields from localized electrons are considered as the seed action of metal doping in resistive switching devices. [ABSTRACT FROM AUTHOR]

Barrier height of AlGaN/GaN transistor is lowered by the quantum coupling of hot electrons with large transverse energy via electro‐thermal effect. The coupling effectively raises the quantized levels of hot electrons, changes the electron density of the two‐dimensional electron gas, and consequently decreases the source drain current of the transistor. Based on the theory of quantum coupling of hot electrons, the current reduction is successfully modeled. The model is able to explain the effect of gate voltage, device temperature, gate length, gate metals, passivation, field‐plate structure, traps, and electron‐phonon interaction on current reduction. It also predicts a relative decrease of 4.6% in the source drain current caused by the quantum coupling at moderately low electron temperature of 1771 K. [ABSTRACT FROM AUTHOR]

The effect of Cu/O/Ti interstitials on the visible-light absorption in Cu2O/TiO2 heterojunctions has been investigated by ab initio methods. The three interstitials are, respectively, doped at the interface of the Cu2O/TiO2 heterojunctions. The Ti interstitial efficiently improves the visible-light absorption, whereas the O interstitial reduces the visible-light absorption. An independent characteristic of the visible-light absorption is found for doping with the Cu interstitial. These phenomena originate from the different concentrations of delocalized electrons induced by the doping atom. The doping with Ti atoms could induce the aggregation of Cu ions, which release more delocalized electrons and so improve the visible-light absorption in a Cu2O/TiO2 heterojunction. [ABSTRACT FROM AUTHOR]

Ab initio calculations on the interaction of the oxygen vacancy and its impact on the transmission coefficients in oxygen-deficient TiO2 are reported. It is found that the separated oxygen vacancies or divacancies produce partial shallow defect energy levels below the conduction-band edge as weak interactions between these vacancies. On the contrary, for the ordering oxygen divacancies, we observe that the defect energy levels fill in the bandgap. A much higher extent is found for the ordering oxygen divacancies in both columns of the supercell due to the appearance of many reduced Ti3+ ions. As a result, these oxygen divacancies expand the transmission range and improve the transmission coefficients. The microscopic origin of the oxygen-vacancy interaction is helpful to clarify the mechanism of the resistive switching phenomenon. [ABSTRACT FROM AUTHOR]

It remains unclear whether the latitudinal diversity gradients of micro- and macro-organisms are driven by the same macro-environmental variables. We used the newly completed species catalog and distribution information of bryophytes in China to explore their spatial species richness patterns, and to investigate the underlying roles of energy availability, climatic seasonality, and environmental heterogeneity in shaping these patterns. We then compared these patterns to those found for woody plants. We found that, unlike woody plants, mosses and liverworts showed only weakly negative latitudinal trends in species richness. The spatial patterns of liverwort richness and moss richness were overwhelmingly explained by contemporary environmental variables, although explained variation was lower than that for woody plants. Similar to woody plants, energy and climatic seasonality hypotheses dominate as explanatory variables but show high redundancy in shaping the distribution of bryophytes. Water variables, that is, the annual availability, intra-annual variability and spatial heterogeneity in precipitation, played a predominant role in explaining spatial variation of species richness of bryophytes, especially for liverworts, whereas woody plant richness was affected most by temperature variables. We suggest that further research on spatial patterns of bryophytes should incorporate the knowledge on their ecophysiology and evolution. [ABSTRACT FROM AUTHOR]

The Qinghai-Tibetan Plateau (QTP), known as 'the Roof of the World', is one of the most unique and vulnerable biodiversity regions on Earth. However, the spatial patterns and determinants of vascular plant diversity on the QTP are still poorly documented, despite a number of publications focusing on its flora. Using extensively compiled data gathered from local flora and specimen records, we evaluated the relative importance of water, energy, and habitat heterogeneity-related variables in shaping the distribution of vascular plant diversity (species, genus, family, herb, woody plants). We found that higher richness always occurred in the south and east of the QTP, especially along the Himalayas, and that habitat heterogeneity, water, and energy variables are important determinants of vascular plant richness patterns on the QTP. The explanatory power of most single predictors was obviously different across life forms, with woody plant richness generally more sensitive to most environmental factors than herb richness. In addition, the explanatory power of habitat heterogeneity models, combined water and energy models, and environmental models increased as the taxonomic level increased from species to family. The results highlight that correlations between plant richness and environmental variables vary with life form and taxonomic scale, and suggest that the explanatory power of variables will change in different spatial scales due to the proportion of life forms and the asymmetric effects of these drivers on life form richness. [ABSTRACT FROM AUTHOR]

The properties and behavior of a single Au atom supported anatase TiO2(001) surface are calculated using density functional theory (DFT) methods. The structures and energies of adsorbed single Au on an anatase TiO2(001) surface with surface oxygen vacancy, as well as subsurface oxygen vacancy, are systematically determined. Initially, the surface threefold coordinated oxygen vacancy adjacent to a single Au atom, rather than the surface two‐fold coordinated oxygen vacancy and subsurface threefold coordinated oxygen vacancy, results in more stability for anatase TiO2(001) surface with an Au adatom. Afterwards, the CO molecule is more strongly adsorbed on the single Au‐supported TiO2(001) surface with surface threefold coordinated oxygen vacancy when comparing to other structures. This is attributed to the more negatively charged Au single‐atom caused by a surface threefold coordinated oxygen vacancy presents concededly active for CO adsorption. The structures and energies of adsorbed single Au on anatase TiO2(001) surface with various oxygen vacancies are systematically addressed. The surface oxygen vacancy adjacent the adsorbed atomic Au increased the stability of atomic Au and further improved the adsorption of CO molecules. This is attributed to the oxygen vacancy above resulting in the presence of a charge reservoir in atomic Au. [ABSTRACT FROM AUTHOR]