Electron scattering times in ZnO based polar heterostructures

The remarkable historic advances experienced in condensed matter physics have been enabled through the continued exploration and proliferation of increasingly richer and cleaner material systems. In this work, we report on the scattering times of charge carriers confined in state-of-the-art MgZnO/ZnO heterostructures displaying electron mobilities in excess of 10⁶ cm²/V s. Through an examination of low field quantum oscillations, we obtain the effective mass of charge carriers, along with the transport and quantum scattering times. These times compare favorably with high mobility AlGaAs/GaAs heterostructures, suggesting the quality of MgZnO/ZnO heterostructures now rivals that of traditional semiconductors

Precise calibration of Mg concentration in Mg_xZn_(1−x)O thin films grown on ZnO substrates

The growth techniques for Mg_xZn_(1−x)O thin films have advanced at a rapid pace in recent years, enabling the application of this material to a wide range of optical and electrical applications. In designing structures and optimizing device performances, it is crucial that the Mg content of the alloy be controllable and precisely determined. In this study, we have established laboratory-based methods to determine the Mg content of Mg_xZn_(1−x)O thin films grown on ZnO substrates, ranging from the solubility limit of x ∼ 0.4 to the dilute limit of x < 0.01. For the absolute determination of Mg content, Rutherford backscattering spectroscopy is used for the high Mg region above x = 0.14, while secondary ion mass spectroscopy is employed to quantify low Mg content. As a lab-based method to determine the Mg content, c-axis length is measured by x-ray diffraction and is well associated with Mg content. The interpolation enables the determination of Mg content to x = 0.023, where the peak from the ZnO substrate overlaps the Mg_xZn_(1−x)O peak in standard laboratory equipment, and thus limits quantitative determination. At dilute Mg contents below x = 0.023, the localized exciton peak energy of the Mg_xZn_(1−x)O films as measured by photoluminescence is found to show a linear Mg content dependence, which is well resolved from the free exciton peak of ZnO substrate down to x = 0.0043. Our results demonstrate that x-ray diffraction and photoluminescence in combination are appropriate methods to determine Mg content in a wide Mg range from x = 0.004 to 0.40 in a laboratory environment

Precise calibration of Mg concentration in Mg_xZn_(1−x)O thin films grown on ZnO substrates

The growth techniques for Mg_xZn_(1−x)O thin films have advanced at a rapid pace in recent years, enabling the application of this material to a wide range of optical and electrical applications. In designing structures and optimizing device performances, it is crucial that the Mg content of the alloy be controllable and precisely determined. In this study, we have established laboratory-based methods to determine the Mg content of Mg_xZn_(1−x)O thin films grown on ZnO substrates, ranging from the solubility limit of x ∼ 0.4 to the dilute limit of x < 0.01. For the absolute determination of Mg content, Rutherford backscattering spectroscopy is used for the high Mg region above x = 0.14, while secondary ion mass spectroscopy is employed to quantify low Mg content. As a lab-based method to determine the Mg content, c-axis length is measured by x-ray diffraction and is well associated with Mg content. The interpolation enables the determination of Mg content to x = 0.023, where the peak from the ZnO substrate overlaps the Mg_xZn_(1−x)O peak in standard laboratory equipment, and thus limits quantitative determination. At dilute Mg contents below x = 0.023, the localized exciton peak energy of the Mg_xZn_(1−x)O films as measured by photoluminescence is found to show a linear Mg content dependence, which is well resolved from the free exciton peak of ZnO substrate down to x = 0.0043. Our results demonstrate that x-ray diffraction and photoluminescence in combination are appropriate methods to determine Mg content in a wide Mg range from x = 0.004 to 0.40 in a laboratory environment

Ballistic transport in periodically modulated MgZnO/ZnO two-dimensional electron systems

We report the fabrication of both antidot lattices and unidirectional stripe patterns upon molecular beam epitaxy grown MgZnO/ZnO heterostructures. The magnetoresistance of these high mobility devices exhibits commensurability oscillations associated with ballistic transport of carriers executing orbital motion within the geometry of the imposed modulation

Ballistic transport in periodically modulated MgZnO/ZnO two-dimensional electron systems

We report the fabrication of both antidot lattices and unidirectional stripe patterns upon molecular beam epitaxy grown MgZnO/ZnO heterostructures. The magnetoresistance of these high mobility devices exhibits commensurability oscillations associated with ballistic transport of carriers executing orbital motion within the geometry of the imposed modulation

Preferential antitumor effect of the Src inhibitor dasatinib associated with a decreased proportion of aldehyde dehydrogenase 1-positive cells in breast cancer cells of the basal B subtype

<p>Abstract</p> <p>Background</p> <p>Recent studies have suggested that the Src inhibitor dasatinib preferentially inhibits the growth of breast cancer cells of the basal-like subtype. To clarify this finding and further investigate combined antitumor effects of dasatinib with cytotoxic agents, a panel of breast cancer cell lines of various subtypes was treated with dasatinib and/or chemotherapeutic agents.</p> <p>Methods</p> <p>Seven human breast cancer cell lines were treated with dasatinib and/or seven chemotherapeutic agents. Effects of the treatments on c-Src activation, cell growth, cell cycle, apoptosis and the proportion of aldehyde dehydrogenase (ALDH) 1-positive cells were examined.</p> <p>Results</p> <p>The 50%-growth inhibitory concentrations (IC₅₀s) of dasatinib were much lower in two basal B cell lines than those in the other cell lines. The IC₅₀s of chemotherapeutic agents were not substantially different among the cell lines. Dasatinib enhanced antitumor activity of etoposide in the basal B cell lines. Dasatinib induced a G1-S blockade with a slight apoptosis, and a combined treatment of dasatinib with etoposide also induced a G1-S blockade in the basal B cell lines. Dasatinib decreased the expression levels of phosphorylated Src in all cell lines. Interestingly, dasatinib significantly decreased the proportion of ALDH1-positive cells in the basal B cell lines but not in the other cell lines.</p> <p>Conclusions</p> <p>The present study indicates that dasatinib preferentially inhibits the growth of breast cancer cells of the basal B subtype associated with a significant loss of putative cancer stem cell population. A combined use of dasatinib with etoposide additively inhibits their growth. Further studies targeting breast cancers of the basal B subtype using dasatinib with cytotoxic agents are warranted.</p

Hypersensitive to Red and Blue 1 and Its Modification by Protein Phosphatase 7 Are Implicated in the Control of Arabidopsis Stomatal Aperture

The stomatal pores are located on the plant leaf epidermis and regulate CO2 uptake for photosynthesis and the loss of water by transpiration. Their stomatal aperture therefore affects photosynthesis, water use efficiency, and agricultural crop yields. Blue light, one of the environmental signals that regulates the plant stomatal aperture, is perceived by the blue/UV-A light-absorbing cryptochromes and phototropins. The signal transduction cascades that link the perception of light to the stomatal opening response are still largely unknown. Here, we report two new players, Hypersensitive to Red and Blue 1 (HRB1) and Protein Phosphatase 7 (PP7), and their genetic and biochemical interactions in the control of stomatal aperture. Mutations in either HRB1 or PP7 lead to the misregulation of the stomatal aperture and reduce water loss under blue light. Both HRB1 and PP7 are expressed in the guard cells in response to a light-to-dark or dark-to-light transition. HRB1 interacts with PP7 through its N-terminal ZZ-type zinc finger motif and requires a functional PP7 for its stomatal opening response. HRB1 is phosphorylated in vivo, and PP7 can dephosphorylate HRB1. HRB1 is mostly dephosphorylated in a protein complex of 193 kDa in the dark, and blue light increases complex size to 285 kDa. In the pp7 mutant, this size shift is impaired, and HRB1 is predominately phosphorylated. We propose that a modification of HRB1 by PP7 under blue light is essential to acquire a proper conformation or to bring in new components for the assembly of a functional HRB1 protein complex. Guard cells control stomatal opening in response to multiple environmental or biotic stimuli. This study may furnish strategies that allow plants to enjoy the advantages of both constitutive and ABA-induced protection under water-limiting conditions