The development of ultrafast X-ray free-electron laser (XFEL) sources and third-generation synchrotrons has opened many new horizons for the study of complex molecular structures and their reaction kinetics. An essential element of these types of experiment is the method used for sample delivery. Microfluidics technology provides the ideal platform for performing these types of measurements since it enables control, manipulation and delivery of small volumes of fluid inside microchannels. Several key functions including mixing, particle separation, and injection, can be integrated on a single chip making the technology very attractive for use in Xray characterisation of molecular dynamics. Key challenges however, in using microfluidics to both mix and deliver samples, include chemical inertness and mechanical stability of the devices, particularly at micron length scales. Here we report a repeatable method for fabricating microfluidic mixer-jet devices based on photolithography and SU8 with a glass substrate. In experiments we have shown that these devices can withstand the high gas pressures required to produce stable, long-range, liquid jets. Coupled with their chemical inertness and reproducibility this makes them promising candidates for time-resolved X-ray diffraction measurements of molecular dynamics. Incorporating an integrated serpentine micromixer capable of homogeneous mixing prior to the liquid jet the devices presented here can be applied to the study of the dynamics of chemically driven biomolecular reactions. The focus of the current work is on the experimental characterization of the mixer through analysis of the concentration profiles along the length of the serpentineshaped microchannel.
Nanofabrication of metamaterials based on thin metallic films have resulted in a host of different designs that support Extraordinary Optical Transmission (EOT). In contrast to the more widely studied circular-shaped apertures, cross-shaped apertures have characteristics which can be modified in response to linearly polarized light, opening up new pathways for light manipulation at the nanoscale. Here we present a systematic study of the influence of device geometry and composition on the functional characteristics of polarisation controlled optical plasmonic devices. We also discuss some issues that arise using the focused ion beam (FIB) milling technique to fabricate optical metamaterials. In particular, we show that producing high-quality patterns lead to a significant over-deposition of the substrate material. This effect significantly alters the metal surface chemistry, which poses a considerable obstacle for applications involving molecular and bio sensing. This work lays the foundation for the optimisation of the properties of optical plasmonic devices for a wide-range of applications including colour filtering and bio-sensing.
Plasmonic devices provide a unique sensitivity to changes in the permittivity of the immediate, near-surface environment. In this work we explore the use of dual pitch plasmonic devices combined with microfluidics for polarization enhanced colour sensing of a chemicals’ refractive index. We demonstrate that the use of cross-shaped apertures can produce polarization tunable color based sensing in the optical regime and show that the spectral variations as a function of the incident polarization can be decomposed into contributions from the two orthogonal modes that characterize the dual pitch plasmonic device. Finally we demonstrate that the use of the full colour spectrum in the visible range in combination with polarization control enables sensing ‘by-eye’ of refractive index changes below 1 × 10-3 RIU.
Engineered materials with feature sizes on the order of a few nanometres offer the potential for producing metamaterials with properties which may differ significantly from their bulk counterpart. Here we describe the production of plasmonic colour filters using periodic arrays of nanoscale cross shaped apertures fabricated in optically opaque silver films. Due to its relatively low loss in the visible and near infrared range, silver is a popular choice for plasmonic devices, however it is also unstable in wet or even ambient conditions. Here we show that ultra-thin layers of Diamond-Like Carbon (DLC) can be used to prevent degradation due to oxidative stress, ageing and corrosion. We demonstrate that DLC effectively protects the sub-micron features which make up the plasmonic colour filter under both atmospheric conditions and accelerated aging using iodine gas. Through a systematic study we confirm that the nanometre thick DLC layers have no effect on the device functionality or performance.
The requirements on the spatial and temporal coherence for conventional Coherent Diffractive Imaging
(CDI) have been well-established in the literature based on Shannon sampling of the diffracted intensities. The
spatial coherence length of the illumination must be larger than twice the lateral dimensions of the sample whilst the
temporal coherence length must be larger than the maximum optical path length difference between the two edges of
the sample for the highest order diffraction peaks. However, recent approaches to CDI which have included
knowledge of the spatial and temporal coherence information in the image reconstruction have allowed us to relax
these conventional coherence constraints, extending the applicability of the technique to less coherent sources. In
light of these developments it is useful to revisit the idea of a coherence limit in partially coherent CDI and establish
a ‘universal’ limit on the partial coherence that can be tolerated without any loss of information. In this paper we
present a simple and straightforward description of the limit of spatial and temporal coherence in partially coherent
CDI.
The effect of electron beam dose and low accelerating voltage on diamond-like-carbon (DLC) deposition rate and the resulting current-voltage characteristics in thin metal/DLC/semiconductor junctions was studied. We show that thicker DLC films can be obtained using lower accelerating voltages (2 kV) than when using higher accelerating voltage (20 kV). However, under the conditions used the insulating performance of the thicker films is worse than the thinner films. We attribute this effect to the variation of tunnelling barrier height in DLC deposited using different accelerating voltages. DLC films with a tunnelling barrier height of up to 3.12 eV were obtained using a 20 kV electron-beam, while only 0.73 eV was achieved for 2 kV DLC films.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print format on
SPIE.org.