Distortion of terahertz signals due to imperfect synchronization with chirped probe pulses.

Terahertz (THz) signals measured by means of the spectral-encoding technique with different temporal discrepancies between probe pulses and THz signals are investigated. It is found that imperfect synchronization between the chirped probe and THz pulses induce a distortion and this distortion affects significantly the retrieved THz spectrum if the temporal discrepancy is large. The distortion becomes more prominent if the probe pulse length is less than the optimal chirped probe pulse duration. A simple approach is proposed to realize the synchronization and minimize the distortion. THz signals from a high-voltage-biased air plasma filament are measured with this approach and distortion similar to the simulation results is observed.

Wide-field single metal nanoparticle spectroscopy for high throughput localized surface plasmon resonance sensing.

Noble metal nanoparticles (mNPs) have a distinct extinction spectrum arising from their ability to support Localized Surface Plasmon Resonance (LSPR). Single-particle biosensing with LSPR is label free and offers a number of advantages, including single molecular sensitivity, multiplex detection, and in vivo quantification of chemical species etc. In this article, we introduce Single-particle LSPR Imaging (SLI), a wide-field spectral imaging method for high throughput LSPR biosensing. The SLI utilizes a transmission grating to generate the diffraction spectra from multiple mNPs, which are captured using a Charge Coupled Device (CCD). With the SLI, we are able to simultaneously image and track the spectral changes of up to 50 mNPs in a single (∼1 s) exposure and yet still retain a reasonable spectral resolution for biosensing. Using the SLI, we could observe spectral shift under different local refractive index environments and demonstrate biosensing using biotin-streptavidin as a model system. To the best of our knowledge, this is the first time a transmission grating based spectral imaging approach has been used for mNPs LSPR sensing. The higher throughput LSPR sensing, offered by SLI, opens up a new possibility of performing label-free, single-molecule experiments in a high-throughput manner.

Delayed onset of photochromism in molybdenum oxide films caused by photoinduced defect formation.

We report the photochromic properties of amorphous MoO3 films deposited by dc sputtering with different O2 flow rates. The kinetics of film coloration under UV light irradiation is determined using optical transmission spectroscopy. Changes in the absorbance and refractive index were derived from the analysis of transmittance spectra. The absorbance spectra exhibited a growing broad peak centered around 830 nm, which was induced by the UV irradiation. In the early stages of irradiation, the absorbance of the films did not change but their refractive indices did change. This induction time was correlated with the O2 partial pressure during the film deposition, which was controlled by the O2 flow rate. The origins of this observation are discussed.

Dynamical observation of bamboo-like carbon nanotube growth.

The growth dynamics of bamboo-like multiwalled carbon nanotubes (BCNTs) via catalytic decomposition of C2H2 on Ni catalyst at 650 degrees C was observed in real time using an in situ ultrahigh vacuum transmission electron microscope. During BCNT growth, the shape of the catalyst particle changes constantly but remains metallic and crystalline. Graphene sheets (bamboo knots) within the nanotube preferentially nucleate on the multistep Ni-graphite edges at the point where the graphene joins the catalyst particle, where it is stabilized by both the graphene walls and the Ni catalyst surface. The growth of a complete inner graphene layer growth prior to contraction of the Ni catalyst particle due to restoring cohesive forces will result in a complete BCNT knot whereas partial growth of the inner wall will lead to an incomplete BCNT knot.

Direct observation of single-walled carbon nanotube growth at the atomistic scale.

The growth dynamics of a single-walled carbon nanotube (SWNT) is observed in real-time using an in situ ultrahigh vacuum transmission electron microscope at 650 degrees C. SWNTs preferentially grow on smaller sized catalyst particles (diameter