H. Q. Yu

Lamellar nanostructures of silicon heterogeneously solidified on graphite sheets

Molecular dynamics simulations are performed to examine the heterogeneous solidification of silicon on foreign graphite sheets (GSs). It clearly indicates that silicon atoms are concentrated to form hierarchical nanostructures composed of equidistant nanolayers. Graphite plate induces strong ordered liquid silicon layers near the surfaces of GSs. This study suggests ordered liquid layers should be the early form of the solid crystal, which determine the subsequent nucleation. The confined nanospace between two GSs favors the solidification and results in the decrease in the distance between layers. GSs make silicon atoms solidify into an hcp crystal rather than fcc structure.

Nonlinear optical response of Au nanorods for broadband pulse modulation in bulk visible lasers

Due to the lack of suitable optical modulators, directly generated Pr3+- and Dy3+-doped bulk visible lasers are limited in the continuous-wave operation; yet, pulsed visible lasers are only sparingly reported recently. It has been theoretically predicated that Au nanorods could modulate the visible light operation, based on the nonlinear optical response of surface plasmon resonance. Here, we demonstrate the saturable absorption properties of Au nanorods in the visible region and experimentally realized the pulsed visible lasers over the spectral range of orange (605 nm), red (639 nm), and deep red (721 nm) with Au nanorods as the optical modulator. We show that Au nanorods have a broad nonlinear optical response and can serve as a type of broadband, low-cost, and eco-friendly candidate for optical switchers in the visible region. Our work also advocates the promise of plasmonic nanostructures for the development of pulsed lasers and other plasmonic devices.

Power-law scaling of dynamical and structural signatures in liquid metallic nano-film

Structural and dynamical features of a liquid metallic nano-film during cooling are investigated by molecular dynamics simulations. Several unique structural transformations from liquid to nano-crystalline or glass are observed. Moreover, the crystalline fraction change and motion propensity are discussed in detail. Results indicate a close relation between the local structural ordering and the dynamic signature. We use a new parameter P(a,τ,ν) as an effective indicator for predicting both local structural order and motion propensity in a metallic nano-film, and find that the fraction of crystalline clusters follows a negative power-law scaling with the cooling rate increasing, which is the inverse of P(a,τ,ν).

Methane Molecules Drive Water Molecules along Diameter-Gradient SWCNTs with Junctions

We report the transport behavior of water molecules along a system of coaxial single-walled carbon nanotubes (SWCNTs) of different diameters with junctions under the driving force of methane molecules. The junctions are potential barriers to the transport of water molecules through SWCNTs. However, methane molecules can overcome these potential barriers and pull the water molecules across the junction region from one compartment to the next. Although a junction is an obstacle to water transport through SWCNTs, the presence of more junctions gives methane molecules a longer lasting driving force that helps them to pull the water molecules out of the SWCNTs.

Elongation behavior and local amorphization of metallic nanowire with glassy shell and crystalline core

Dynamic elongation of the core/shell CuZr metallic nanowire (MNW) has been examined by molecular dynamics (MD) methods. Results indicate that the deformation region in the core/shell MNW represents an evident martensitic phase-transforming feature, which subsequently results in local amorphization. Meanwhile, the finite-size effect on the MNW with different crystalline-amorphous ratio is discussed. In addition, Honeycutt and Anderson (HA) bond-type index during elongation provides reliable evidence to explain why these phenomena take place in the MNW. Our results illustrate that the corresponding martensitic phase transformation and local amorphization are closely related to the finite-size effect and crystalline-amorphous interfaces.

TRAVELING BEHAVIOR OF A WATER CLUSTER RELEASED FROM A CARBON NANOTUBE

Molecular dynamics simulation is used to observe the traveling behavior of a water cluster released from the interior of single-walled carbon nanotube (SWCNT) to a graphite sheet. The simulation results reveal that there is a need for the water cluster overcoming the energy barrier of the binding energy between the water cluster and the SWCNT to escape from the tube. The water cluster undergoes a three-dimensional motion when released from the SWCNT, due to the effect of the thermal velocity. When encountering the graphite sheet in the forward direction, the x axis impact velocity has much effect on the delivery of the water cluster. The fact that the water cluster is bounced back reduces the possibility of being captured by the graphite sheet, resulting in a decrease in the delivery efficiency of the water cluster. The presence of the electric charges can help the graphite sheet to effectively trap the water cluster. These results have implications for the design and fabrication of novel drug delivery devices.

HETEROGENEOUS SOLIDIFICATION OF ALUMINUM ON BORON-NITRIDE NANOTUBE

Molecular dynamics simulations are carried out to examine the heterogeneous solidification of aluminum solution seeded by foreign boron-nitride nanotubes (BNNTs). The final structure indicates noticeably that Al atoms are concentrated to form incredible hierarchical nanostructures composed of coaxial and equidistant cylindrical shells with the BNNTs as the heterogeneous core. The structures of so-formed Al cylinders show strict structural matching and strong structural relevance with BNNTs. Heterogeneous solidification occurred on BNNTs follows a spiral nucleating mechanism. Heredity effect of these hollow cylinders can be clearly observed during the heterogeneous nucleation. The uniform internal potential field around BNNTs is found to be responsible for the formation of the coaxial cylindrical Al shells.