Atomic scale properties of interior interfaces of semiconductor heterostructures as determined by quasi-digital highly selective etching and atomic force microscopy

We report on first experiments combining quasi-digital highly selective etching and atomic force microscopy (AFM) to examine the interior interfaces of semiconductor heterostructures. Lattice matched (GaIn)As/InP heterostructures grown by metalorganic vapour-phase epitaxy (MOVPE) are taken as a model system to check the capabilities of this new method. Standard selective etchants for different material systems have been optimized in selectivity and etch rate to achieve a quasi-digital etching behaviour. In this way, the real structure of interior interfaces can be determined by AFM. We find a significant difference between the surface of the heterostructure and the interior interfaces.     

Experimental Study on Optic Fiber Sensing System for Simultaneous Measurement of Curent and Voltage Using One Lo-Bi Fiber

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Possibility of measuring exchange force through force microscopy

This article describes the possibility of measuring exchange force through atomic force microscopy (AFM), based on the results of first-principles calculations for the exchange force between two magnetic Fe(001) films. We observed strong variation of the exchange force relative to the surface site. The magnitude of the force variation was larger than the force sensitivity of conventional AFM. These results suggest that a surface magnetic image with atomic resolution can be achieved by measuring the exchange force.     

How to measure energy dissipation in dynamic mode atomic force microscopy

When studying a mechanical system like an atomic force microscope (AFM) in dynamic mode it is intuitive and instructive to analyse the forces involved in tip–sample interaction. A different but complementary approach is based on analysing the energy that is dissipated when the tip periodically interacts with the sample surface. This method does not require solving the differential equation of motion for the oscillating cantilever, but is based entirely on the analysis of the energy flow in and out of the dynamic system. Therefore the problem of finding a realistic model to describe the tip–sample interaction in terms of non-linear force–distance dependencies and damping effects is omitted. Instead, it is possible to determine the energy dissipated by the tip–sample interaction directly by measuring such quantities as oscillation amplitude, frequency, phase shift and drive amplitude. The method proved to be important when interpreting phase data obtained in tapping mode, but is also applicable to a variety of scanning probe microscopes operating in different dynamic modes. Additional electronics were designed to allow a direct mapping of local energy dissipation while scanning a sample surface. By applying this technique to the cross-section of a polymer blend a material specific contrast was observed.     

Hadron masses and matrix elements from the QCD Schrödinger functional

We explain how masses and matrix elements can be computed in lattice QCD using Schrödinger functional boundary conditions. Numerical results in the quenched approximation demonstrate that good precision can be achieved. For a statistical sample of the same size, our hadron masses have a precision similar to what is achieved with standard methods, but for the computation of matrix elements such as the pseudoscalar decay constant the Schrödinger functional technique turns out to be much more efficient than the known alternatives.     

Performance at 10–50 K of Bi-2212/Ag multilayer tape fabricated by using pre-annealing and intermediate rolling process

High-transport critical current density (J_c-oxide)>500 kA/cm² at 4.2 K, 10 T can be obtained for Bi-2212/Ag tapes fabricated by using pre-annealing and intermediate rolling (PAIR) and melt-solidification process. In this paper, we report high-temperature properties of PAIR-processed Bi-2212/Ag multilayer tape in order to show their potential for practical applications operated at cryocooling temperatures. Magnetic field dependence and angular dependence of critical current (I_c) are investigated at temperatures ranging 10–50 K by using helium gas cooling and liquid neon. Field-temperature curves for I_c=0.2 and 2.0 A are also determined in order to show the approximation of the irreversible field. High-temperature performance of the tape is attractive to consider future applications. For example, the best sample carries I_c=267 A (engineering-J_c=303 A/mm², J_c-oxide=151 kA/cm²) and 92 A (104 A/mm², 52 kA/cm²) at 27.1 K (in liquid neon), in magnetic fields (parallel to the tape surface) of 2 and 10 T, respectively. Engineering-J_c of 100 A/mm² is obtained even in the perpendicular field of 0.5 T at 27.1 K.     

Edge assisted epitaxy of CsPbBr3 nanoplates on Bi2O2Se nanosheets for enhanced photoresponse

Bi$_{2}$O$_{2}$Se has been proved to be a promising candidate for electronic and optoelectronic devices due to their unique physical properties. However, it is still a great challenge to construct the heterostructures with direct epitaxy of hetero semiconductor materials on Bi$_{2}$O$_{2}$Se nanosheets. Here, a two-step chemical vapor deposition (CVD) route was used to directly grow the CsPbBr$_{3}$ nanoplate-Bi$_{2}$O$_{2}$Se nanosheet heterostructures. The CsPbBr$_{3}$ nanoplates were selectively grown on the Bi$_{2}$O$_{2}$Se nanosheet along the edges, where the dangling bonds provide the nucleation sites. The epitaxial relationships between CsPbBr$_{3}$ and Bi$_{2}$O$_{2}$Se were determined as ${[200]}_{\rm Bi_{2}O_{2}Se}||{[110]}_{\rm CsPbBr_{3}}$ and ${[110]}_{\rm Bi_{2}O_{2}Se}||{[200]}_{\rm CsPbBr_{3}}$ by transmission electron microscopy characterization. The photoluminescence (PL) results reveal that the formation of heterostructures results in the remarkable PL quenching due to the type-I band arrangement at CsPbBr$_{3}$/Bi$_{2}$O$_{2}$Se interface, which was confirmed by ultraviolet photoelectron spectroscopy (UPS) and Kelvin probe measurements, and makes the photogenerated carriers transfer from CsPbBr$_{3}$ to Bi$_{2}$O$_{2}$Se. Importantly, the photodetectors based on the heterostructures exhibit a 4-time increase in the responsivity compared to those based on the pristine Bi$_{2}$O$_{2}$Se sheets, and the fast rise and decay time in microsecond. These results indicate that the direct epitaxy of the CsPbBr$_{3}$ plates on the Bi$_{2}$O$_{2}$Se sheet may improve the optoelectronic performance of Bi$_{2}$O$_{2}$Se based devices.     

Efficiently enhanced energy storage performance of Ba2Bi4Ti5O18 film by co-doping Fe3+ and Ta5+ ion with larger radius

We present an efficient strategy, that is the co-substitution of Fe³⁺ and Ta⁵⁺ ions with large radius for Ti⁴⁺ ion, to enhance energy storage performance of Ba₂Bi₄Ti₅O₁₈ film. For the films co-doped with Fe³⁺ and Ta⁵⁺ ions, the maximum polarization under the same external electric field is improved because the radius of Fe³⁺ and Ta⁵⁺ ions is larger than that of Ti⁴⁺ ion. Moreover, due to the composition and chemical disorder, the relaxor properties are also slightly improved, which can not be achieved by the film doped with Fe³⁺ ions only. What is more, for the films doped with Fe³⁺ ion only, the leakage current density increases greatly due to the charge imbalance, resulting in a significant decrease in breakdown strength. It is worth mentioning that the breakdown strength of Fe³⁺ and Ta⁵⁺ ions co-doped film does not decrease due to the charge balance. Another important point is the recoverable energy storage density of the films co-doped with Fe³⁺ and Ta⁵⁺ ions has been greatly improved based on the fact that the maximum external electric field does not decrease and the maximum polarization under the same external electric field increases. On top of that, the hysteresis of the polarization has also been improved. Finally, the co-doped films with Fe³⁺ and Ta⁵⁺ ions have good frequency and temperature stability.     

Observation of the V2O5(001) surface using ambient atomic force microscopy

Constant force images of the V₂O₅(001) surface were recorded in ambient conditions with atomic force microscopy. All images exhibit the 11.5 Å × 3.5 Å. periodicity expected for a bulk terminated surface. However, images reveal differences from the ideal structure. The experimental results are interpreted in terms of preferential adsorption sites for water molecules. Because these sites are thought to influence the catalytic properties of the surface, their characterization is an important step towards understanding how the atomic-scale structure of a surface influences its properties.