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Soil carbon isotopes (δ13C) provide reliable insights for studying soil carbon turnover at a long-term scale. The Tibetan Plateau (TP), often referred as "the third pole of the earth", is highly sensitive to global climate change, and exhibits an early warning signal of global warming. Although many studies detected soil δ13C variability at site scales, there is still a knowledge gap existing in the spatial pattern of soil δ13C across the TP. In this study, we compiled a database of 198 topsoil δ13C observations from published literatures and used a modified multi-layer perceptron (MLP) neural network algorithm to predict the spatial pattern of topsoil δ13C and β (indicating the decomposition rate of soil organic carbon (SOC), calculated as δ13C divided by logarithmically converted SOC) at 500m resolution. Results showed that MLP model effectively predicted topsoil δ13C with a model efficiency of 0.72 and a root mean square error of 1.16‰. Topsoil δ13C varied significantly across different ecosystem types (p < 0.001) with a mean δ13C of –25.89 ± 1.15‰ (mean ± standard deviation) for forests, –24.91 ± 1.03‰ for shrublands, –22.95 ± 1.44‰ for grasslands, and –18.88 ± 2.37‰ for deserts. Furthermore, there was an increasing trend of predicted δ13C from the southeastern to the northwestern TP, likely linked to vegetation type and climatic conditions. β values were low in the eastern TP and higher in the northern and northwestern TP, indicating faster SOC turnover rate in the east TP compared to the north and northwest. This study represents the first effort to develop a fine resolution product of topsoil δ13C and β across the TP, which could provide an independent, data-driven benchmark for biogeochemical cycling models to study SOC turnover and terrestrial carbon-climate feedback over the TP under climate change. [ABSTRACT FROM AUTHOR]

Heterostructure composed of electron-doped high-Tc superconductor La1.89Ce0.11CuO4 (LCCO), ferroelectric Ba0.5 Sr0.5 TiO3 (BST) and colossal magnetoresistance (CMR) La0.67 Sr0.33 MnO3 (LSMO) thin films were deposited on the (001) SrTiO3 (STO) substrate by pulsed laser deposition method. The current-voltage measurement shows that the LCCO/BST/LSMO structure has strong rectification comparing to the LCCO/LSMO, LCCO/BST and BST/LSMO bilayer structures. The experiment indicates that both the BST and LCCO layers play important roles in the rectifying effect in the oxide heterostructures. We discuss the mechanism of their rectification based on the energy band bending as well as the depletion and the diffusion of the charge carriers at the interfaces. The growth conditions and the multilayer features as well as the properties of individual material in the heterostructures were also investigated. [ABSTRACT FROM AUTHOR]

Leakage current of Pt/(Ba0.7Sr0.3)TiO3 (BST)/YBa2Cu3O7-δ capacitors on a (001) SrTiO3 substrate was studied. By modeling a low-dielectric constant layer, a so-called dead layer, between the Pt/BST interface as a parasitic capacitor in series with the bulk layer capacitor, the leakage current of Pt/BST interface was well analyzed based on the modified Schottky emission equation. Furthermore, a two-step schematic energy band diagram is proposed to explain the carrier transport through the Pt/BST interface. [ABSTRACT FROM AUTHOR]

We investigated the structure and transport properties of GdBa[sub 2]Cu[sub 3]O[sub 7] films on SrTiO[sub 3](001) and NdGaO[sub 3](001). We found that the films can be grown pseudomorphically up to at least 42 nm thickness on SrTiO[sub 3] whereas the critical thickness is less than 14 nm for films on NdGaO[sub 3]. The carrier density of pseudomorphic films on SrTiO[sub 3] is tuned by the pseudomorphic stress field and films on SrTiO[sub 3] show higher T[sup *] and lower T[sub c] compared to films of the same thickness on NdGaO[sub 3]. For a 28 nm thick GdBa[sub 2]Cu[sub 3]O[sub 7] film on SrTiO[sub 3], the hole density per CuO[sub 2] plane is reduced to 0.12, compared to 0.16 for the optimally doped and stress-free RBa[sub 2]Cu[sub 3]O[sub 7]. The measured temperature dependence of J[sub c] can be understood and described by interface stress pinning. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Undoped and Fe-doped liquid encapsulated Czochralski (LEC) InP has been studied by Hall effect, current-voltage (I-V), and infrared absorption (IR) spectroscopy. The results indicate that a native hydrogen vacancy complex donor defect exists in as-grown LEC InP. By studying the IR results, it is found that the concentration of this donor defect in Fe-doped InP is much higher than that in undoped InP. This result is consistent with the observation that a much higher concentration of Fe[sup 2+] than the apparent net donor concentration is needed to achieve the semi-insulating (SI) property in InP. By studying the I-V and IR results of Fe-doped InP wafers sliced from different positions on an ingot, the high concentration of Fe[sup 2+] is found to correlate with the existence of this hydrogen complex. The concentration of this donor defect is high in wafers from the top of an ingot. Correspondingly, a higher concentration of Fe[sup 2+] can be detected in these wafers. These results reveal the influence of the complex defect on the compensation and uniformity of Fe-doped SI InP materials. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Single-phased, single-oriented thin films of Mn-doped ZnAs-based diluted magnetic semiconductor (DMS) Ba1-xKx(Zn1-yMny)2As2 (x = 0.03, 0.08; y = 0.15) have been deposited on Si, SrTiO3, LaAlO3, (La,Sr)(Al,Ta)O3, and MgAl2O4 substrates, respectively. Utilizing a combined synthesis and characterization system excluding the air and further optimizing the deposition parameters, high-quality thin films could be obtained and be measured showing that they can keep inactive-in-air up to more than 90 hours characterized by electrical transport measurements. In comparison with films of x = 0.03 which possess relatively higher resistivity, weaker magnetic performances, and larger energy gap, thin films of x = 0.08 show better electrical and magnetic performances. Strong magnetic anisotropy was found in films of x = 0.08 grown on (La,Sr)(Al,Ta)O3 substrate with their magnetic polarization aligned almost solely on the film growth direction. [ABSTRACT FROM AUTHOR]