Electronic-structure evolution of SrFeO3-x during topotactic phase transformation

Oxygen-vacancy-induced topotactic phase transformation between the ABO2.5 brownmillerite structure and the ABO3 perovskite structure attracts ever-increasing attention due to the perspective applications in catalysis, clean energy field, and memristors. However, a detailed investigation of the electronic-structure evolution during the topotactic phase transformation for understanding the underlying mechanism is highly desired. In this work, multiple analytical methods were used to explore evolution of the electronic structure of SrFeO3-x thin films during the topotactic phase transformation. The results show that the increase in oxygen content produces a new unoccupied state of O 2p character near the Fermi energy, inducing the insulator-to-metal transition. More importantly, the hole states are more likely constrained to the dx2-y2 orbital than to the d3z2-r2 orbital. Our results reveal an unambiguous evolution of the electronic structure of SrFeO3-x films during topotactic phase transformation, which is crucial not only for fundamental understanding but also for perspective applications such as solid-state oxide fuel cells, catalysts, and memristor devices.

Cleanroom Fan Energy Reduction—Airflow Control Retrofit Based on Continuous, Real-time Particle Sensing

Cleanrooms are utilized in electronics, semiconductor, aerospace, pharmaceutical, automotive, optical, medical device, and food processing facilities where air cleanliness is required to prevent defects in high-tech or high-value products. Compared to general commercial space, cleanrooms typically use 5 to 50 times the energy for the same area. One key reason is the high volume of conditioned and filtered air required to make the room air cleaner, which is measured in room-average particle concentration. The technology in this study uses real-time continuous particle sensors as feedback signals to automatically adjust fan speed. The system can modulate fan speed and provide the correct amount of airflow into the cleanroom to prevent over-supply and save energy. In typical manufacturing cleanrooms, the unoccupied state (evenings and weekends) is approximately two times longer than the occupied state (operational work hours), and particle generation (from personnel, equipment, and process) is much lower during the unoccupied state. Limited components and parts are required to apply the technology in this study into the design of a new cleanroom or to integrate the technology into existing cleanroom fan systems.

The Plug Domain of Yeast Sec61p Is Important for Efficient Protein Translocation, but Is Not Essential for Cell Viability

The Sec61/SecY translocon mediates translocation of proteins across the membrane and integration of membrane proteins into the lipid bilayer. The structure of the translocon revealed a plug domain blocking the pore on the lumenal side. It was proposed to be important for gating the protein conducting channel and for maintaining the permeability barrier in its unoccupied state. Here, we analyzed in yeast the effect of introducing destabilizing point mutations in the plug domain or of its partial or complete deletion. Unexpectedly, even when the entire plug domain was deleted, cells were viable without growth phenotype. They showed an effect on signal sequence orientation of diagnostic signal-anchor proteins, a minor defect in cotranslational and a significant deficiency in posttranslational translocation. Steady-state levels of the mutant protein were reduced, and when coexpressed with wild-type Sec61p, the mutant lacking the plug competed poorly for complex partners. The results suggest that the plug is unlikely to be important for sealing the translocation pore in yeast but that it plays a role in stabilizing Sec61p during translocon formation.

Comparison of Indoor Environment of a Locally Concentrated Cleanroom at Occupied and Unoccupied Status by Numerical Method

The existing standard for cleanrooms is based on an unoccupied state where there are no people or furniture inside the room. However, the distribution of airflow and particles in a cleanroom may differ significantly in an occupied state with the presence of people and furniture. This paper first validates a numerical model for simulating the air distribution in a locally concentrated cleanroom. Then the indoor airflow and the pollutant concentration in a locally concentrated bio-clean operation room (BCOR) are simulated at both occupied and unoccupied states by the validated model. The comparison of results shows the environment is very different between the two cases. Thus, human bodies and furniture should be properly considered when evaluating the environment in the locally concentrated cleanroom.

QUANTUM WELL LUMINESCENCE FROM METALLIC MONOLAYERS

The emission of visible light is observed from the metallic quantum well system Na on Cu(111) when electrons tunnel from the tip of a scanning tunnelling microscope to an unoccupied state of the sample. Spectral analysis of the emission along with tunnelling spectroscopy is used to show that the emission is comprised of two components. A sharp spectral feature is found to be due to an interband transition between quantum well states of the Na layer. The other component is similar to plasmon-mediated emission observed previously from clean metal surfaces. The results suggest that light emission is a unique local probe of the electronic structure of quantum well systems.