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Electromechanical property of a p-type single-crystal silicon nanoplate is modelled by a microscopic approach where the hole quantization effect and the spin–orbit coupling effect are taken into account. The visible anisotropic subband structures are calculated by solving self-consistently the stress-dependent 6 × 6 κ p Schrodinger equation with the Poisson equation. The strong mixing among heavy, light, and split-off holes is quantitatively assessed. The influences of the thickness and the temperature on the piezoresistive coefficient are quantitatively investigated by using the hole concentrations and the effective masses from the complex dispersion structure of the valence band with and without stresses. Our results show that the stress determines the extent to which the band is mixed. The hole quantization effect increases as the thickness decreases, and therefore the valence band is strongly reshaped, resulting in the size-dependent piezoresistivity of the silicon nanoplate. The piezoresistive coefficient increases almost 4 times as the thickness reduces from the bulk to 3 nm, exhibiting a promising application in mechanical sensors.

Influence of width of left well in AlxGa1-xN/GaN double quantum wells (DQWs) on absorption coefficients and wavelengths of the intersubband transitions (ISBTs) is investigated by solving the Schrodinger and Poisson equations self-consistently. When the width of left well is 1.79nm, three-energy-level DQWs are realized. The ISBT between the first odd and second odd order subbands (the 1odd-2odd ISBT) has a comparable absorption coefficient with the 1odd-2even ISBT. Their wavelengths are located at 1.3 and 1.55μm, respectively. When the width of left well is 1.48nm, a four-energy-level DQWs is realized. The calculated results have a possible application to ultrafast two-colour optoelectronic devices operating within the optical communication wavelength range.

The influence of the polarization-induced electric field and other parameters on the subband structure in AlxGa1−xN /GaN coupled double quantum wells (DQWs) has been studied by solving the Schrodinger and Poisson equations self-consistently. It is found that the polarization effect leads to an asymmetric potential profile of AlxGa1−xN/GaN DQWs although the two wells have the same width and depth. The polarization effect also leads to a very large Stark shift between the odd and the even order subband levels that can reach 0.54 eV. Due to the polarization-induced Stark shift, the wavelength of the intersubband transition between the first odd order and the second even order subband levels becomes smaller, which is useful for realization of optoelectronic devices operating within the telecommunication window region.

The direct in situ observation of fullerene formation encapsulated within a graphene ridge has been made possible using an aberration corrected transmission electron microscope (AC-TEM). An atom-by-atom mechanism was proposed based on in situ AC-TEM observations. First principle calculations found a continuous energy decrease upon the addition of carbon atoms to the edge of the graphene flakes, which mimics the fullerene growth steps and supports the atom-by-atom mechanism. The ridged graphene structure worked as a container for pinning small graphene flakes and capturing carbon atoms, which increased the growth probability of the fullerene structure within the small encapsulated space.

Dependences of anticrossing gaps between pairs of subbands in AlxGa1−xN/GaN double quantum wells (DQWs) on the width and the Al composition of the central barrier of the DQWs and on the well width of the DQWs have been investigated by solving the Schrodinger and Poisson equations self-consistently. It is found that the anticrossing gaps are not influenced by the polarization-induced electric field in the DQWs. The anticrossing gaps decrease with increasing the width and the Al composition of the central barrier of the DQWs, as well as with the increasing well width of the DQWs. According to the results of the calculation, the anticrossing gaps can reach 150 meV in AlxGa1−xN/GaN DQWs. There is significant coupling between the two wells of the DQWs when the width of the central barrier of the DQWs is narrower than 2 nm.

In this work, we used in situ aberration-corrected transmission electron microscopy (AC-TEM) to observe the coalescence of gold nanoparticles. We observed a critical edge-to-edge distance d(c)(e) ~ 0.5 nm below which the two particles will coalesce rapidly (jump-to-coalescence). A model based on the single-atom-triggered rapid particle contraction was proposed and verified by first-principles calculations, in which evident energy decrease was detected when adding a gold atom between two gold nanoparticles. Our ex situ TEM study of sputtering-deposited gold nanoparticles on different substrates with varied time also supports the jump-to-contact mechanism. This observation afforded physical insight into the fundamental growth mechanism during dynamic particle coalescence processes.

By solving the Schrdinger and Poisson equations self-consistently, the central barrier height, central barrier width, well width, and doping concentration in the barriers of symmetric Al 0.75 Ga 0.25 N/GaN double quantum wells (DQWs) have been studied to investigate their influences on the wavelength and absorption coefficient of intersubband transitions (ISBTs). A smaller wavelength of the ISBT between the first odd and the second even order subbands ( S 1odd - S 2even ISBT) in Al 0.75 Ga 0.25 N/GaN DQWs and a larger absorption coefficient of the S 1odd - S 2even ISBT were obtained with decreased central barrier height, when the central barrier height was larger than 0.62 eV. The wavelength of the S 1odd - S 2even ISBT decreases, and the absorption coefficient of the S 1odd - S 2even ISBT increases, when the width of the central barrier is reduced. On the other hand, decreasing the width of the well will result in smaller wavelength of the S 1odd - S 2even ISBT and larger absorption coefficient of the S 1odd - S 2even ISBT when the width of the well is narrower than 1.9 nm. When doping concentration in the barriers is smaller than 10 18 /cm 3 ， the wavelength of the S 1odd - S 2even ISBT is unchanged, while the absorption coefficient of the S 1odd - S 2even ISBT increases with the doping concentration. These results provide useful guidance for realization of ultrafast two-color optoelectronic devices operating in the optical communication wavelength range.