Potential well

About: Potential well is a research topic. Over the lifetime, 1430 publications have been published within this topic receiving 30812 citations.

The surface termination effect on the quantum confinement and electron affinities of 3C-SiC quantum dots: a first-principles study

Abstract: In light of the established differences between the quantum confinement effect and the electron affinities between hydrogen-passivated C and Si quantum dots, we carried out theoretical investigations on SiC quantum dots, with surfaces uniformly terminated by C–H or Si–H bonds, to explore the role of surface terminations on these two aspects. Surprisingly, it was found that the quantum confinement effect is present (or absent) in the highest occupied (or lowest unoccupied) molecular orbital of the SiC quantum dots regardless of their surface terminations. Thus, the quantum confinement effect related to the energy gap observed experimentally (Phys. Rev. Lett., 2005, 94, 026102) is contributed to by the size-dependence of the highest occupied states; the absence of quantum confinement in the lowest unoccupied states is in contrary to the usual belief based on hydrogen-passivated C quantum dots. However, the cause of the absence of the quantum confinement in C nanodots is not transferable to SiC. We propose a model that provides a clear explanation for all findings on the basis of the nearest-neighbor and next-nearest-neighbor interactions between the valence atomic p-orbital in the frontier occupied/unoccupied states. We also found that the electron affinities of the SiC quantum dots, which closely depend on the surface environments, are negative for the C–H termination and positive for the Si–H termination. The prediction of negative electron affinities in SiC quantum dots by simple C–H termination indicates a promising application for these materials in electron-emitter devices. Our model predicts that GeC quantum dots with hydrogen passivation exhibit similar features to SiC quantum dots and our study confirms the crucial role that the surface environment plays in these nanoscale systems.

Inherent structures in the potential energy landscape of solid 4He

Abstract: We study the potential energy landscape (many‐atom potential energy as a function of atomic positions) of solid hcp 4He in the vicinity of the 0 K crystal structure using an accurate pair potential. At the melting point, the potential energy of the helium lattice is far above the minimum hcp interatomic potential energy. We confirm previous conclusions (based on less accurate potentials) that all of the classical phonon frequencies at the 0 K melting pressure are imaginary, indicating that the melting‐point crystal corresponds to a local maximum in the potential landscape; a pressure of about 1300 bar, however, makes it a local minimum. We find that the atomic arrangements that lie at local minima in the potential landscape (‘‘inherent structures’’) are glassy and porous, and have much lower potential energy than the crystalline form at the same density. We have quantitatively characterized the glassy structures by their radial distribution functions and coordination number distributions; they qualitatively resemble inherent structures for classical monatomic liquids, but exhibit differences of detail. A model variational calculation has been carried out for the melting‐density ground state. It utilizes separate basis functions for each of the inherent structures, predicts a large Lindemann ratio for the crystal, and indicates that the probability distribution is a maximum at the perfect lattice configuration.

Defect-related optical bandgap narrowing and visible photoluminescence of hydrothermal-derived SnO 2 nanoparticles

Abstract: Tin oxide (SnO2) nanoparticles are fabricated by a novel hydrothermal route using H2O2 as oxidizer without adding any corrosive acids or bases. The morphology, composition, and microstructure are characterized by transmission electron microscopy, X-ray diffraction (XRD) and Raman spectra. XRD analysis reveals the formation of single phase rutile type tetragonal structure of all samples which is further supported by Raman studies. The average crystallite size is observed to vary from 2.8 to 4.2 nm as the reacting temperature increases from 120 to 180 °C, suggesting the promotion of crystal growth with increasing temperature. Raman spectroscopy measurement presents the existence of the defect modes, of which the mode at about 565 cm−1 is identified to relate to oxygen vacancies as this mode becomes more prominent in the as-grown sample. Unusual optical band gap narrowing and the excitation wavelength dependent visible luminescence are observed, and both are supposed to be induced by the intrinsic defects. The photoluminescence (PL) spectra of all samples consist of two defect-related subbands, i.e., orange and blue luminescence bands. The two subbands are attributed to optical transitions in oxygen vacancies and some intrinsic surface states, respectively. Spectral analysis suggests that the excitation wavelength dependences of the two subbands are due to a distribution of the band gap of the nanoparticles induced by the internal strain, defect concentration as well as the quantum confinement effect. This work provides a feasible route to modulate the band gap and defect emissions and a good understanding of the PL behavior in the present SnO2 nanoparticles.