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Influence of the width and Al composition of one well in asymmetric Al0.85Ga0.15N/GaN double quantum wells (DQWs) on the absorption coefficients and the wavelengths of the intersubband transitions (ISBTs) has been investigated by solving the Schrödinger and Poisson equations self-consistently. When the well width is chosen to be 1.91 nm, the three-energy-level DQWs are realized. The ISBT between the first odd order and the second even order subbands (the 1odd-2even ISBT) has comparable absorption coefficient with the 1odd-2odd ISBT. Their wavelengths are located at 1.3 and 1.54 μm, respectively. When the well width is 2.77 nm, the four-energy-level DQWs are realized. The 1odd-2even and the 1even-2odd ISBTs have comparable absorption coefficients. Their wavelengths are located at 1.41 and 2.54 μm, respectively. The energy separation between the excited subbands is determined to have the minimum value of 144 meV due to the band anticrossing interaction. The calculated results give possible application to ultrafast two-color optoelectronic devices operating within the optical communication wavelength range. [ABSTRACT FROM AUTHOR]

The influence of the polarization-induced electric field on the wavelength and the absorption coefficient of the intersubband transitions (ISBTs) in AlxGa1-xN/GaN coupled double quantum wells (DQWs) have been investigated by self-consistent calculation. It is found that the wavelength of the ISBT between the first odd order and the second even order subbands (the 1odd-2even ISBT) can be shortened to 1.3 μm owing to the Stark shift induced by the polarization effect. The absorption coefficient of the 1odd-2even ISBT decreases by increasing the polarization field discontinuity. On the other hand, a shorter wavelength and a larger absorption coefficient of the ISBTs are obtained by decreasing the width of the central barrier of AlxGa1-xN/GaN DQWs. The results are beneficial to achieving devices operation within the optical communication wavelength range. [ABSTRACT FROM AUTHOR]

First-principle calculation was carried out to systematically investigate carbon monoxide (CO) adsorption on pristine and cobalt (Co)-doped phosphorenes (Co-bP). Whether or not CO is adsorped, pristine phosphorene is a direct-band-gap semiconductor. However, the bandgap of Co-bP experiences direct-to-indirect transition after CO molecule adsorption, which will affect optical absorption considerably, implying that Co doping can enhance the sensitivity of phosphorene as a CO gas sensor. Moreover, Co doping can improve an adsorption energy of CO to 1.31 eV, as compared with pristine phosphorene (0.12 eV), also indicating that Co-bP is energetically favorable for CO gas sensing. [ABSTRACT FROM AUTHOR]

The article reports on research which has been conducted to test bias of estimating equations in weighted regression with partially missing covariates. Statistics made use of parametric and semiparametric tests as diagnostic tools for the combined package of the primary regression model and the missingness assumptions. It illustrated the result of the test via small scale simulation study.

Utilizing solar energy to split water (photocatalytic water-splitting) is a good solution for global warming. However, it is difficult to find suitable materials for photocatalytic water-splitting. In this paper, through HSE06 and GW-BSE calculations, it is found that vdWHs with Se facing g-GeC (WSSe/g-GeC vdWHs) are an ideal photocatalytic material. The WSSe/g-GeC vdWHs can form a II-type band alignment, and the band gap exceeds the free energy of water splitting. The built-in electric field from Janus WSSe and vdWHs can effectively separate photo-generated electron–hole pairs and improve carrier lifetime. Compared with single-layer WSSe, WSSe/g-GeC vdWHs exhibit smaller exciton binding energy, especially for the WSSe/g-GeC vdWH I stacking (0.32 eV). Furthermore, WSSe/g-GeC vdWHs are of high absorption coefficient in the visible light regions, showing significant advantages of using solar energy. These findings imply that the WSSe/g-GeC vdWHs are promising as candidate material for photocatalytic water-splitting. [ABSTRACT FROM AUTHOR]

The vibration behavior of doubly clamped silicon nanowires with square cross sections is studied by molecular dynamics method. Silicon nanowires have lengths ranging from 4.888 to 12.491nm and cross sections ranging from 1.22nm × 1.22nm to 3.39nm × 3.39 nm. The size dependence of the resonant frequency is studied in detail. The results show that the vibration behavior of Si nanowire is quite different from the macroscopic beam, and the resonant frequency is much higher than the result based on the continuum theory, but close to the theoretical result based on the semicontinuum approach. Surface reconstruction can strongly affect on vibration behavior. These results demonstrate that the classic theory may not be suitable for analysis of performances of nanostructures, and the conclusion of the study has a certain practical significance on related fields. [ABSTRACT FROM AUTHOR]