ABSTRACT
Bolometers are thermal detectors widely applied in the mid-infrared (MIR) wavelength range. In an integrated sensing system on chip, a broadband scalable bolometer absorbing the light over the whole MIR wavelength range could play an important role. In this work, we have developed a waveguide-based bolometer operating in the wavelength range of 3.72-3.88 µm on the amorphous silicon (a-Si) platform. Significant improvements in the bolometer design result in a 20× improved responsivity compared to earlier work on silicon-on-insulator (SOI). The bolometer offers 24.62% change in resistance per milliwatt of input power at 3.8 µm wavelength. The thermal conductance of the bolometer is 3.86×10-5W/K, and an improvement as large as 3 orders magnitude may be possible in the future through redesign of the device geometry.
ABSTRACT
We present interlayer slope waveguides, designed to guide light from one level to another in a multi-layer silicon photonics platform. The waveguide is fabricated from hydrogenated amorphous silicon (a-Si:H) film, deposited using hot-wire chemical vapor deposition (HWCVD) at a temperature of 230°C. The interlayer slope waveguide is comprises of a lower level input waveguide and an upper level output waveguide, connected by a waveguide on a slope, with vertical separation to isolate other crossing waveguides. Measured loss of 0.17 dB/slope was obtained for waveguide dimensions of 600 nm waveguide width (w) and 400 nm core thickness (h) at a wavelength of 1550 nm and for transverse electric (TE) mode polarization.
ABSTRACT
Recently, a comprehensive three dimensional computational model based on rigorous coupled wave analysis (RCWA) has been developed to investigate the properties of surface plasmons resident on metal coated arrays of inverted pyramidal pits used for SERS sensing applications in the form of 'klarite'. This simulation tool allows the identification of a variety of dispersive features including propagating and localized surface plasmons as well as simple diffraction relating to the influence of geometrical features. In this paper, we investigate the influence of non-conformality of the gold coating over the internal surfaces of the inverted pyramidal pits on plasmon dispersion. Modeling reveals very strong changes in plasmon behavior as a function of gold layer conformality. Dependent upon conformality of the gold coating we find that the nano-textured metallic surface can behave either as an efficient broadband mirror-like reflector or as an efficient broadband, wide angle absorber at infrared wavelengths. Creation of a broadband wide angle absorbing surface such as this has important implications for photovoltaic cells. For sensing applications, understanding the effect of metal layer conformality on plasmon dispersion gives clear insight into how to further improve the SERS enhancement factor.
ABSTRACT
Wellens' syndrome is characterized by T-wave changes in electrocardiogram (EKG) during pain-free period in a patient with intermittent angina chest pain. It carries significant diagnostic and prognostic value because this syndrome represents a pre-infarction stage of coronary artery disease involving proximal left anterior descending (LAD) artery, which can subsequently lead to extensive anterior myocardial infarctions (MIs) and even death without coronary angioplasty. Therefore, it is crucial for every physician to recognize EKG features of Wellens' syndrome in order to take appropriate immediate intervention to reduce mortality and morbidity for MI. Here, we report a case of an overweight man with 35 pack-year of smoking history who presented to Easton Hospital with intermittent pressing chest pain of 5/6 times within 10 day-period and was found to have type A Wellens' sign, which was biphasic T-waves in precordial leads V2 and V3 during pain-free period with no cardiac enzymes elevation. He was given therapeutic lovenox and subsequently underwent coronary angioplasty and had 95-99% occlusion in proximal LAD artery. The unique feature of our case was that Wellens' type B EKG changes were seen after reduction of stenosis with LAD artery stent, which was likely explained by the reperfusion of the ischemic myocardium. Therefore, it is important for physicians to recognize EKG features of Wellens' syndrome in order to take appropriate therapy to reducing mortality and morbidity form impending MI.
ABSTRACT
Design and fabrication of three-dimensionally structured, gold membranes containing hexagonally close-packed microcavities with nanopores in the base, are described. Our aim is to create a nanoporous structure with localized enhancement of the fluorescence or Raman scattering at, and in the nanopore when excited with light of approximately 600 nm, with a view to provide sensitive detection of biomolecules. A range of geometries of the nanopore integrated into hexagonally close-packed assemblies of gold micro-cavities was first evaluated theoretically. The optimal size and shape of the nanopore in a single microcavity were then considered to provide the highest localized plasmon enhancement (of fluorescence or Raman scattering) at the very center of the nanopore for a bioanalyte traversing through. The optimized design was established to be a 1200 nm diameter cavity of 600 nm depth with a 50 nm square nanopore with rounded corners in the base. A gold 3D-structured membrane containing these sized microcavities with the integrated nanopore was successfully fabricated and 'proof of concept' Raman scattering experiments are described.
ABSTRACT
Three-dimensionally structured gold membrane films with nanopores of defined, periodic geometries are designed and fabricated to provide the spatially localised enhancement of electric fields by manipulation of the plasmons inside nanopores. Square nanopores of different size and orientation relative to the pyramid are considered for films in aqueous and air environments, which allow for control of the position of electric fields within the structure. Designs suitable for use with 780 nm light were created. Here, periodic pyramidal cavities produced by potassium hydroxide etching to the {111} planes of (100) silicon substrates are used as templates for creating a periodic, pyramidal structured, free-standing thin gold film. Consistent with the findings from the theoretical studies, a nano-sized hole of 50 nm square was milled through the gold film at a specific location in the cavity to provide electric field control which can subsequently used for enhancement of fluorescence or Raman scattering of molecules in the nanopore.
