Hanchen Huang

Schwoebel-Ehrlich barrier: from two to three dimensions

The Schwoebel-Ehrlich barrier—the additional barrier for an adatom to diffuse down a surface step—dictates the growth modes of thin films. The conventional concept of this barrier is two dimensional (2D), with the surface step being one monolayer. We propose the concept of a three-dimensional (3D) Schwoebel-Ehrlich barrier, and identify the 2D to 3D transition, taking aluminum as a prototype and using the molecular statics method. Our results show that: (1) substantial differences exist between the 2D and 3D barriers; (2) the transition completes in four monolayers; and (3) there is a major disparity in the 3D barriers between two facets; further, alteration of this disparity using surfactants can lead to the dominance of surface facet against thermodynamics.

Do Twin Boundaries Always Strengthen Metal Nanowires

It has been widely reported that twin boundaries strengthen nanowires regardless of their morphology—that is, the strength of nanowires goes up as twin spacing goes down. This article shows that twin boundaries do not always strengthen nanowires. Using classical molecular dynamics simulations, the authors show that whether twin boundaries strengthen nanowires depends on the necessary stress for dislocation nucleation, which in turn depends on surface morphologies. When nanowires are circular cylindrical, the necessary stress of dislocation nucleation is high and the presence of twin boundaries lowers this stress; twin boundaries soften nanowires. In contrast, when nanowires are square cylindrical, the necessary stress of dislocation nucleation is low, and a higher stress is required for dislocations to penetrate twin boundaries; they strengthen nanowires.

Functionalized aligned silver nanorod arrays for glucose sensing through surface enhanced Raman scattering

Glucose detection through surface enhanced Raman scattering (SERS) has recently attracted a lot of interest due to its potential as a minimally-invasive, in vivo sensing technology. However, the application of SERS to glucose detection is greatly limited because of its small Raman scattering cross-section and low affinity with bare metal surfaces. In this work, an active SERS substrate composed of nearly aligned silver nanorods with uniform distribution was fabricated using high vacuum electron beam physical vapor deposition. A monolayer of 4-mercaptophenylboronic acid (MPBA) was self-assembled on the Ag nanorod surfaces, through the covalent interaction between its thio group and the Ag surface, thus resulting in a functional SERS substrate for glucose detection. The results from X-ray photoelectron spectroscopy and Raman spectroscopy clearly indicate that MPBA was successfully functionalized on the Ag nanorod surfaces. The specific binding of glucose with the boronic acid motif in MPBA significantly affects the SERS signal of MPBA on Ag nanorods, which can be measured and correlated to glucose concentrations. Quantitative detection of glucose in a clinically relevant (0–20 mM) concentration range was successfully demonstrated. The fundamental mechanism behind this approach was also discussed, and both electromagnetic and chemical enhancement mechanisms are attributed to the enhanced SERS signals. These results provide new insights into the development of SERS-based glucose sensors using Ag nanorod arrays.

Enhanced thermal stability of Ag nanorods through capping

Ag nanorods may serve as sensors in the detection of trace amounts of chemical agents, even single molecules, through surface enhanced Raman spectroscopy (SERS). However, thermal coarsening of Ag nanorods near room temperature limits their applications. This letter proposes the use of a thin oxide capping layer to enhance the thermal stability of Ag nanorods beyond 100 °C. Using electron microscopy characterization and SERS tests, the authors show that the proposed method is effective in stabilizing both morphology and sensitivity of Ag nanorods. The results of this work extend the applicability of Ag nanorods as chemical sensors to higher temperatures.

Airtight metallic sealing at room temperature under small mechanical pressure

Metallic seals can be resistant to air leakage, resistant to degradation under heat, and capable of carrying mechanical loads. Various technologies – such as organic solar cells and organic light emitting diodes – need, at least benefit from, such metallic seals. However, these technologies involve polymeric materials and can tolerate neither the high-temperature nor the high-pressure processes of conventional metallic sealing. Recent progress in nanorod growth opens the door to metallic sealing for these technologies. Here, we report a process of metallic sealing using small well-separated Ag nanorods; the process is at room temperature, under a small mechanical pressure of 9.0u2005MPa, and also in ambient. The metallic seals have an air leak rate of 1.1 × 10−3u2005cm3atm/m2/day, and a mechanical shear strength higher than 8.9u2005MPa. This leak rate meets the requirements of organic solar cells and organic light emitting diodes.

Sum Rule Identities and the Duality Relation for the Potts n -Point Boundary Correlation Function

It is shown that certain sum rule identities exist which relate correlation functions for n Potts spins on the boundary of a planar lattice for

Shape and surface chemistry effects on the cytotoxicity and cellular uptake of metallic nanorods and nanospheres.

nensuremath{ge}4

Smallest separation of nanorods from physical vapor deposition

. Explicit expressions of the identities are obtained for

Atom diffusion of small Cu clusters across facet–facet barriers over Cu{1 1 1} surfaces

nphantom{rule{0ex}{0ex}}=phantom{rule{0ex}{0ex}}4

Combined Hydrophobicity and Mechanical Durability through Surface Nanoengineering

. It is also shown that the identities provide the missing link needed for a complete determination of the duality relation for the n-point boundary correlation function. The