Hiroshi Mizuta, Zakaria Moktadir, Stuart Boden, Nima Kalhor, Shuojin Hang, Marek Schmidt, Nguyen Tien Cuong, Dam Hieu Chi, Nobuo Otsuka, Manoharan Muruganathan, Yoshishige Tsuchiya, Harold Chong, Harvey Rutt, Darren Bagnall
In this paper we first present a new fabrication process of downscaled graphene nanodevices based on direct milling of
graphene using an atomic-size helium ion beam. We address the issue of contamination caused by the electron-beam
lithography process to pattern the contact metals prior to the ultrafine milling process in the helium ion microscope
(HIM). We then present our recent experimental study of the effects of the helium ion exposure on the carrier transport
properties. By varying the time of helium ion bombardment onto a bilayer graphene nanoribbon transistor, the change in
the transfer characteristics is investigated along with underlying carrier scattering mechanisms. Finally we study the
effects of various single defects introduced into extremely-scaled armchair graphene nanoribbons on the carrier transport
properties using ab initio simulation.
Sentinel Lymph Node Biopsy (SLNB) is an increasingly standard procedure to help oncologists accurately stage cancers.
It is performed as an alternative to full axillary lymph node dissection in breast cancer patients, reducing the risk of longterm
health problems associated with lymph node removal. Intraoperative analysis is currently performed using touchprint
cytology, which can introduce significant delay into the procedure. Spectral imaging is forming a multi-plane image
where reflected intensities from a number of spectral bands are recorded at each pixel in the spatial plane. We investigate
the possibility of using spectral imaging to assess sentinel lymph nodes of breast cancer patients with a view to
eventually developing an optical technique that could significantly reduce the time required to perform this procedure.
We investigate previously reported spectra of normal and metastatic tissue in the visible and near infrared region, using
them as the basis of dummy spectral images. We analyse these images using the spectral angle map (SAM), a tool
routinely used in other fields where spectral imaging is prevalent. We simulate random noise in these images in order to
determine whether the SAM can discriminate between normal and metastatic pixels as the quality of the images
deteriorates. We show that even in cases where noise levels are up to 20% of the maximum signal, the spectral angle
map can distinguish healthy pixels from metastatic. We believe that this makes spectral imaging a good candidate for
further study in the development of an optical SLNB.
A new clinical diagnostic instrument for urea breath test (UBT) based non-invasive detection of Helicobacter
Pylori is presented here. Its compact and low cost design makes it an economical and commercial alternative
for the more expensive Isotope Ratio Mass Spectrometer (IRMS). The instrument is essentially a two channel
non-dispersive IR spectrometer that performs high precision ratio measurements of the two carbon isotopomers
(12CO2 and 13CO2) present in exhaled breath. A balanced absorption system configuration was designed where
the two channel path lengths would roughly be in the ratio of their concentrations. Equilibrium between the
transmitted channel intensities was maintained by using a novel feedback servo mechanism to adjust the length
of the 13C channel cell. Extensive computational simulations were performed to study the effect of various
possible interferents and their results were considered in the design of the instrument so as to achieve the desired
measurement precision of 1%. Specially designed gas cells and a custom made gas filling rig were also developed.
A complete virtual interface for both instrument control and data acquisition was implemented in LABVIEW.
Initial tests were used to validate the theory and a basic working device was demonstrated.
Several designs of infrared absorption based gas detector use a Fabry-Perot Interferometer (FPI) to modulate the incident light. In these systems, generally the FPI's fringes are matched with very well defined rotational absorption lines of a target molecule such as CO2, CO, N2O, CH4, etc. In order to obtain modulation the cavity length of the FPI is scanned over one half of the reference wavelength. In this work, we present a simple analytical method based on the Fourier Transform that describes the performance of these systems. Using this method the optimal reflectivity and optical spacing of the FPI can be determined. Furthermore, the modulated signal generated by the system as a function of the cavity length scan can be calculated by applying the inverse Fourier Transform. Finally, this method describes the underlying reasons why for some filters the background amplitude is severe, and gives guidance on the choice of optimised filters. Our method evaluates the optimal FPI parameters and the modulated signal much faster than the direct numerical computation which is used currently. Simulation results for different molecules in combination with diverse filters shapes are presented, with a comparison to directly computed results.
The parasitic background signal produced by gas detectors using a Fabry-Pérot interferometer (FPI) as a modulator is shown to be very sensitive to the infrared bandpass filter characteristics. This parasitic signal is generally the feature limiting the sensitivity of such devices. We review this problem, and provide a general approach to filter choice that minimizes the background amplitude for this kind of detection system. It is shown that in general filters with very abrupt transitions from the stop to passband are in fact undesirable, and fortuitously the optimum choice of filter leads to easily realized, low-cost designs.
Stable CO2 isotope breath test are established as a valuable tool in diagnostic and investigate medicine. The instrument conventionally used is an Isotope Ratio Mass Spectrometer, however, the expensive and complexity of such an instrument severely restricts the widespread and routine use of isotope tests. To realize their full potential an alternative instrument which is reliable, uncomplicated, insensitive to environmental and component fluctuations and affordable is required.
The SPRITE (Signal Processing in the Element) detector comprises a long thin filament of mercury cadmium telluride. The filament is divided into two sections, the integration and readout regions. Ambipolar drift speed in the filament is matched to the scanning speed in a thermal imager, and the device performs in the element the functions normally achieved with time-delay-and-integrate electronics. We consider the optimum choice of integration section length having regard to the trade-off between high and low spatial frequency performance. The readout section length can also be optimized, in this case the noise performance of the detector preamplifier is an important consideration, because both noise and responsivity of the detector fall at high frequencies.
Germanium and silicon optical transmissive components are widely used in infrared lenses, filter substrates, etc. We demonstrate that severe loss can be induced in some germanium samples by illumination in the visible or near infrared with power densities in the region of watts per square centimeter. The absorption arises from light hole to heavy hole inter valence band transitions. The strength of the absorption induced depends on a number of parameters not normally controlled in optical applications, such as minority carrier lifetime and surface recombination velocity. The effect is very much weaker in silicon.
Laser action in Neodymium doped inorganic aprotic solvents POC13 and Se0C12 has been known formany years, but there has been little work in this field recently. Very little work has been reportedon ions other than Nd3+. The ability to readily change the dopant, vary concentrations, add co-dopantsetc at low cost is attractive, and using modern laser techniques it is possible that these materialsmight again be useful. In particular there are a variety of possible solvents which have not beenexploited to date which offer the possibility of tailoring the non-radiative rates of the various levelsfor the particular transition required.
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