Chuin-Shan Chen

First-principles study on variation of lattice parameters of mullite Al4+2xSi2−2xO10−x (x = 0.125, 0.250, 0.375)

Abstract Mullite (Al4+2xSi2-2xO10-x) is known to exhibit a very distinct compositional variation in which the lattice constant in the a direction expands linearly, while that in the b direction slightly contracts with an increase of the x-value. In this study, first-principles density functional theory (DFT) simulations were applied to examine the cause. The atomic structure and charge density were examined. We found that the local charge redistribution due to a newly formed vacancy leads to the onset and recurrence of localized atomic relaxation. The charge redistribution and atomic relaxation causes the clockwise and counterclockwise rotations of the neighboring octahedral units. These rotations contribute to expansion in the a-axis and contraction in the b-axis. The mechanism is supported by the previous experimental measurements of the Al-O2 bond lengths projecting in the (001) plane. We conclude that the rotations of the octahedral units are the fundamental mechanism responsible for compositionally induced variations of mullite. Results derived from simulations also provide evidence for a preferred occurrence of oxygen vacancies parallel to the crystallographic b axis. It thus supports earlier findings of a partial ordering in mullite.

Spatially resolved study of InGaN photoluminescence enhancement by single Ag nanoparticles

Spatially resolved photoluminescence (PL) of an InGaN/GaN multiple quantum well (QW) structure covered by Ag nanoparticles (NPs) is studied using confocal microscopy. Up to fourfold enhancement of PL intensity due to the coupling of the QWs with localized surface plasmons (LSPs) induced on single Ag NPs is demonstrated. The enhancement is accompanied by a redshift of the PL spectral peak position towards the LSP resonance wavelength. The correlation between PL intensity and spectral position indicates that the enhancement is stronger in the sample areas emitting at wavelengths that are a better match with the LSP resonance wavelength. The enhancement of light emission and extraction facilitated by photon coupling with LSP in a single Ag NP is demonstrated.

Multiscale analysis of adsorption-induced surface stress of alkanethiol on microcantilever

A multiscale scheme was developed to evaluate adsorption-induced surface stresses in an alkanethiol-passivated Au(111)-modified microcantilever surface using first-principle density-functional theory calculations. In particular, the effect of alkyl chain length on the generated surface stresses was considered in detail. It was found that the majority of the surface stress originated from re-organization of the first two Au atom layers that lie in close proximity to the adsorption site. The difference in the calculated surface stresses, which were consistent with experimental measurements, was determined to be approximately −0.05Nm −1 per two carbons added to the alkanethiol chain. S Online supplementary data available from stacks.iop.org/JPhysD/46/035301/mmedia (Some figures may appear in colour only in the online journal)

Ab‐initio and Multiscale Study of Surface Stresses from Alkanethiolate Self‐Assembled Monolayers on Gold

The self‐assembled monolayers (SAMs) absorbed on surface attract much attention due to their diverse applications for biosensing, biorecognition and molecular electronics. In this work, we study absorption‐induced surface stresses and microcantilever motion in Alkanethiolate SAMs on Au surface. A multiscale method is developed to link atomistic information with continuum description. The adsorption mechanisms of bio‐molecules for SAMs adsorbed on Au are studied through ab‐initio simulation. Adsorption‐induced stresses for different SAMs are calculated by the multiscale method developed herein. Calculated deflection based on the adsorption‐induced stress agrees with experimental measurements. The results give insight into the atomic forces and positions that play a key role in producing adsorption‐induced surface stresses and resultant mechanical bending of microcantilevers.

Alkanethiol Self-Assembled Monolayers on Microcantilever Biosensor

Microcantilever-based biosensors are rapidly becoming an enabling sensing technology for a variety of label-free biological applications due to their wide applicability, versatility and low cost. It is thus imperative for us to reveal the physical origin of adsorption-induced deformation, and to further analyze its implication of microscopic mechanisms on macroscopic deformation. In the paper, we study adsorption-induced surface stresses and microcantilever motion in alkanethiolate SAMs on Au surface. We develop a multiscale method that can analyze deformation of micro-cantilever beam subjected to bio-adsorption mechanisms calculated by ab-initio simulation and classical molecular dynamics. The adsorption mechanisms of different SAMs adsorbed on Au(111) surface, in the dry and liquid phase, are studied by ab-initio simulation and the adsorption-induced stresses are calculated through the multiscale method. The results give insight into the atomic forces and positions that play a key role in producing adsorption-induced surface stresses and resultant mechanical bending of microcantilevers.© 2010 ASME