The paper presents the design principles of a degenerate mode resonant mass sensor in which the unloaded sensor takes the form of a cyclically symmetric structure. The simplest structure with these features is a circular diaphragm and its properties are exploited in this paper. Such structures support pairs of independent modes of vibration which share a common natural frequency and these are referred to as degenerate modes. If extra mass is added to the structure over predefined regions, then the degeneracy can be broken and this produces a separation of the previously identical frequencies. This frequency split is the output of the sensor and is proportional to the added mass. Such a sensor is self-compensating, and ambient effects which equally influence both modes, such as temperature and in-plane stress, do not add to the frequency split. A Lagrangian approach is used to derive the relationship between added mass and frequency split.

This paper presents a discussion on the fabrication, characterization and testing of a degenerate mode resonant mass sensor which takes the form of a crystalline silicon MEMS circular diaphragm. The device is fabricated from the device layer of a SOI wafer which is bonded anodically to a Pyrex substrate. The efficacy of the fabrication process is assessed. Characterization of the diaphragm is performed by actuating the diaphragm electrostatically and measuring its response using optical surface profilometry and laser Doppler vibrometry. The temperature stability of the degenerate modes of vibration is investigated and it is shown that the initial frequency split in the resonant frequencies of these modes does not change significantly with temperature. Structures which present a symmetric surface profile after processing show remarkable temperature stability. The performance of the device as a mass sensor has been evaluated by functionalizing specific sectors of the diaphragm to provide bonding sites for a S100ββ protein. Added masses down to a level of 9 pg were detected.

The growth of Al:ZnO nanorods on a silicon substrate using a low-temperature thermal evaporation method is reported. The samples were fabricated within a horizontal quartz tube under controlled supply of O2 gas where Zn and Al powders were previously mixed and heated at 700°C. This allows the reactant vapors to deposit onto the substrate placed vertically above the source materials. Both the undoped and doped samples were characterized using scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), high-resolution transmission electron microscopy (HRTEM) and photoluminescence (PL) measurements. It was observed that randomly oriented nanowires were formed with varying nanostructures as the dopant concentrations were increased from 0.6 at.% to 11.3 at.% with the appearance of ‘pencil-like’ shape at 2.4 at.%, measuring between 260 to 350 nm and 720 nm in diameter and length, respectively. The HRTEM images revealed nanorods fringes of 0.46 nm wide, an equivalent to the lattice constant of ZnO and correspond to the (0001) fringes with regard to the growth direction. The as-prepared Al:ZnO samples exhibited a strong UV emission band located at approximately 389 nm (E g  = 3.19 eV) with multiple other low intensity peaks appeared at wavelengths greater than 400 nm contributed by oxygen vacancies. The results showed the importance of Al doping that played an important role on the morphology and optical properties of ZnO nanostructures. This may led to potential nanodevices in sensor and biological applications.

Thermoluminescent dosimeter (TLD) of carbon–doped aluminium oxide (α–Al2O3:C) produced in the form of single crystals show high sensitivity to ionizing radiation (about 40–60 times higher than TLD–100 (LiF:Mg,Ti)). The present article offers a review of the materials preparation and corresponding thermoluminescence (TL) properties of α–Al2O3:C subjected to various types of ionizing radiations. Different methods of α–Al2O3:C preparation in form of single crystal and thin films are reviewed. The development of methods of preparation is based on the approaches that involve the evaluation of the luminescence light yield in TL process. Most of the methods used were suitable, but each of these methods has their advantages and disadvantages depending on the required form of materials. Considering the results presented by various authors, possible better method of material preparation is proposed. The potential alternative fabrication technique of α–Al2O3:C thin film by using radio–frequency magnetron sputtering is briefly discussed.

This work examined the thermoluminescence dosimetry characteristics of Ag-doped ZnO thin films. The hydrothermal method was employed to synthesize Ag-doped ZnO thin films with variant molarity of Ag (0, 0.5, 1.0, 3.0, and 5.0 mol%). The structure, morphology, and optical characteristics were investigated using X-ray diffraction (XRD), scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX), photoluminescence (PL), and UV–vis spectrophotometers. The thermoluminescence characteristics were examined by exposing the samples to X-ray radiation. It was obtained that the highest TL intensity for Ag-doped ZnO thin films appeared to correspond to 0.5 mol% of Ag, when the films were exposed to X-ray radiation. The results further showed that the glow curve has a single peak at 240–325 °C, with its maximum at 270 °C, which corresponded to the heating rate of 5 °C/s. The results of the annealing procedures showed the best TL response was found at 400 °C and 30 min. The dose–response revealed a good linear up to 4 Gy. The proposed sensitivity was 1.8 times higher than the TLD 100 chips. The thermal fading was recorded at 8% for 1 Gy and 20% for 4 Gy in the first hour. After 45 days of irradiation, the signal loss was recorded at 32% and 40% for the cases of 1 Gy and 4 Gy, respectively. The obtained optical fading results confirmed that all samples’ stored signals were affected by the exposure to sunlight, which decreased up to 70% after 6 h. This new dosimeter exhibits good properties for radiation measurement, given its overgrowth (in terms of the glow curve) within 30 s (similar to the TLD 100 case), simple annealing procedure, and high sensitivity (two times that of the TLD 100).

No abstract

The dosimetric properties of synthetic ZnO/Ag/ZnO multilayer film are investigated. The proposed dosimeter was prepared by radio frequency and direct current RF/DC sputtering and irradiated with X-ray doses up to 4 Gy. The properties of thermoluminescence (TL) such as glow curve, dose-response, homogeneity batches, sensitivity, minimum detectable dose (MMD), precision, kinetic parameters (activation energy E, frequency factor S), and percentage depth dose (PDD) were studied. The thin film appeared to have an excellent linear response, and the sensitivity was almost twice the commercial TLD. The readout of the homogeneity and PDD are the same properties of TLD-100. These desirable qualities demonstrated the versatility of this novel synthetic thin film in applications involving radiation detection.

Measure Projection Analysis (MPA) method based on EEGLAB and Matlab Toolbox is used to analyze the projections of brain signal sources that are responsible for the measured potentials at the scalp electrodes. These projections are based on probabilistic multi subject algorithm abandoning the notion of distinct independent component clusters. It examines voxel by voxel for brain regions having event related independent components process dynamics that exhibit statistically significant consistency across subjects by probability density representation. Neuron source locations are responsible in generating current in different brain regions through the measured potentials. The projections of visual evoked potentials (VEP) sources in different age groups are investigated. The result shows a slight difference in the projections with respect to the age. These findings represent the maturity level and re-grasp the development of brain and visual pathway with age.