Electrical Conductance at Directly Bonded Si/Si Interfaces in Dependence on Oxygen Concentration in Bonding Ambient

Direct semiconductor wafer bonding is a versatile fabrication scheme for high-performance optoelectronic devices. In the present study, the influence of oxygen concentration in the bonding ambient on the electrical conductance at directly bonded Si/Si interfaces is experimentally investigated in relation to interfacial oxidation. The interfacial electrical conductivity is observed higher for lower oxygen concentration at each bonding temperature in the range of 200 °C–400 °C. Ohmic contact characteristics are found attainable in the bonded interfaces by proper choice of bonding conditions. To support the electrical conductance trend, an X-ray photoelectron spectroscopy analysis confirms the extent of interfacial oxidation to be higher for lower oxygen concentration and higher bonding temperature. In addition, solar cell fabrication and operation with a current path through the bonded interface are demonstrated by using the bonding method in a low oxygen concentration ambient. The energy conversion efficiency of the bonded cell is observed comparable to that of an unbonded reference, to thus verify the suitability of the bonding scheme for device applications

Glass Patterning: Technologies and Applications

In this work, we review the progress in recent studies on glass patterning including technologies and applications. Four technologies for glass micromachining including wet etching, sandblasting, reactive ion etching, and glass reflow process are analyzed. Advantages as well as disadvantages of each method are presented and discussed in light of the experiments. Various microsystem applications using the above glass patterning technologies like thermal sensors, hermetically packaged capacitive silicon resonators, optical modulator devices, glass microfluidics, micro-heaters, and vacuum-sealed capacitive micromachined ultrasonic transducer arrays are reported

Nano and Microsensors for Mammalian Cell Studies

This review presents several sensors with dimensions at the nano- and micro-scale used for biological applications. Two types of cantilever beams employed as highly sensitive temperature sensors with biological applications will be presented. One type of cantilever beam is fabricated from composite materials and is operated in the deflection mode. In order to achieve the high sensitivity required for detection of heat generated by a single mammalian cell, the cantilever beam temperature sensor presented in this review was microprocessed with a length at the microscale and a thickness in the nanoscale dimension. The second type of cantilever beam presented in this review was operated in the resonant frequency regime. The working principle of the vibrating cantilever beam temperature sensor is based on shifts in resonant frequency in response to temperature variations generated by mammalian cells. Besides the cantilever beam biosensors, two biosensors based on the electric cell-substrate impedance sensing (ECIS) used to monitor mammalian cells attachment and viability will be presented in this review. These ECIS sensors have dimensions at the microscale, with the gold films used for electrodes having thickness at the nanoscale. These micro/nano biosensors and their mammalian cell applications presented in the review demonstrates the diversity of the biosensor technology and applications

Investigation of the feasibility of a simple method for verifying the motion of a binary multileaf collimator synchronized with the rotation of the gantry for helical tomotherapy

In this paper, we suggest a new method for verifying the motion of a binary multileaf collimator (MLC) in helical tomotherapy. For this we used a combination of a cylindrical scintillator and a general-purpose camcorder. The camcorder records the light from the scintillator following photon irradiation, which we use to track the motion of the binary MLC. The purpose of this study is to demonstrate the feasibility of this method as a binary MLC quality assurance (QA) tool. First, the verification was performed using a simple binary MLC pattern with a constant leaf open time; secondly, verification using the binary MLC pattern used in a clinical setting was also performed. Sinograms of simple binary MLC patterns, in which leaves that were open were detected as "open" from the measured light, define the sensitivity which, in this case, was 1.000. On the other hand, the specificity, which gives the fraction of closed leaves detected as "closed", was 0.919. The leaf open error identified by our method was -1.3 +/- 7.5%. The 68.6% of observed leaves were performed within +/- 3% relative error. The leaf open error was expressed by the relative errors calculated on the sinogram. In the clinical binary MLC pattern, the sensitivity and specificity were 0.994 and 0.997, respectively. The measurement could be performed with -3.4 +/- 8.0% leaf open error. The 77.5% of observed leaves were performed within +/- 3% relative error. With this method, we can easily verify the motion of the binary MLC, and the measurement unit developed was found to be an effective QA tool.ArticleJOURNAL OF APPLIED CLINICAL MEDICAL PHYSICS. 13(1):27-43 (2012)journal articl

Temperature Changes in Brown Adipocytes Detected with a Bimaterial Microcantilever

AbstractMammalian cells must produce heat to maintain body temperature and support other biological activities. Methods to measure a cell’s thermogenic ability by inserting a thermometer into the cell or measuring the rate of oxygen consumption in a closed vessel can disturb its natural state. Here, we developed a noninvasive system for measuring a cell’s heat production with a bimaterial microcantilever. This method is suitable for investigating the heat-generating properties of cells in their native state, because changes in cell temperature can be measured from the bending of the microcantilever, without damaging the cell and restricting its supply of dissolved oxygen. Thus, we were able to measure increases in cell temperature of <1 K in a small number of murine brown adipocytes (n = 4–7 cells) stimulated with norepinephrine, and observed a slow increase in temperature over several hours. This long-term heat production suggests that, in addition to converting fatty acids into heat energy, brown adipocytes may also adjust protein expression to raise their own temperature, to generate more heat. We expect this bimaterial microcantilever system to prove useful for determining a cell’s state by measuring thermal characteristics

Spin fluctuations from Bogoliubov Fermi surfaces in the superconducting state of S-substituted FeSe

The study of the iron-based superconductor, FeSe, has resulted in various topics, such as the interplay among superconductivity, nematicity, and magnetism, Bardeen-Cooper-Schrieffer Bose-Einstein-condensation (BCS-BEC) crossover, and Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superconductivity. Recently, topologically protected nodal Fermi surfaces, referred to as Bogoliubov Fermi surfaces (BFSs), have garnered much attention. A theoretical model for the S-substituted FeSe system demonstrated that BFSs can manifest under the conditions of spin-orbit coupling, multi-band systems, and superconductivity with time-reversal symmetry breaking. Here we report the observation of spin fluctuations originating from BFSs in the superconducting (SC) state via $^{77}$Se-nuclear magnetic resonance measurements to 100 mK. In a heavily S-substituted FeSe, we found an anomalous enhancement of low-energy spin fluctuations deep in the SC state, which cannot be explained by an impurity effect. Such unusual behavior implies the presence of significant spin fluctuations of Bogoliubov quasiparticles, which are associated with possible nesting properties between BFSs

Early detection of cognitive decline in Alzheimer’s disease using eye tracking

BackgroundPatients with Alzheimer’s disease (AD) are known to exhibit visuospatial processing impairment, as reflected in eye movements from the early stages of the disease. We investigated whether the pattern of gaze exploration during visual tasks could be useful for detecting cognitive decline at the earliest stage.MethodsSixteen AD patients (age: 79.1 ± 7.9 years, Mini Mental State Examination [MMSE] score: 17.7 ± 5.3, mean ± standard deviation) and 16 control subjects (age: 79.4 ± 4.6, MMSE score: 26.9 ± 2.4) participated. In the visual memory task, subjects memorized presented line drawings for later recall. In the visual search tasks, they searched for a target Landolt ring of specific orientation (serial search task) or color (pop-out task) embedded among arrays of distractors. Using video-oculography, saccade parameters, patterns of gaze exploration, and pupil size change during task performance were recorded and compared between AD and control subjects.ResultsIn the visual memory task, the number of informative regions of interest (ROIs) fixated was significantly reduced in AD patients compared to control subjects. In the visual search task, AD patients took a significantly longer time and more saccades to detect the target in the serial but not in pop-out search. In both tasks, there was no significant difference in the saccade frequency and amplitude between groups. On-task pupil modulation during the serial search task was decreased in AD. The number of ROIs fixated in the visual memory task and search time and saccade numbers in the serial search task differentiated both groups of subjects with high sensitivity, whereas saccade parameters of pupil size modulation were effective in confirming normal cognition from cognitive decline with high specificity.DiscussionReduced fixation on informative ROIs reflected impaired attentional allocation. Increased search time and saccade numbers in the visual search task indicated inefficient visual processing. Decreased on-task pupil size during visual search suggested decreased pupil modulation with cognitive load in AD patients, reflecting impaired function of the locus coeruleus. When patients perform the combination of these tasks to visualize multiple aspects of visuospatial processing, cognitive decline can be detected at an early stage with high sensitivity and specificity and its progression be evaluated

Duplication and Gene Conversion in the Drosophila melanogaster Genome

Using the genomic sequences of Drosophila melanogaster subgroup, the pattern of gene duplications was investigated with special attention to interlocus gene conversion. Our fine-scale analysis with careful visual inspections enabled accurate identification of a number of duplicated blocks (genomic regions). The orthologous parts of those duplicated blocks were also identified in the D. simulans and D. sechellia genomes, by which we were able to clearly classify the duplicated blocks into post- and pre-speciation blocks. We found 31 post-speciation duplicated genes, from which the rate of gene duplication (from one copy to two copies) is estimated to be 1.0×10−9 per single-copy gene per year. The role of interlocus gene conversion was observed in several respects in our data: (1) synonymous divergence between a duplicated pair is overall very low. Consequently, the gene duplication rate would be seriously overestimated by counting duplicated genes with low divergence; (2) the sizes of young duplicated blocks are generally large. We postulate that the degeneration of gene conversion around the edges could explain the shrinkage of “identifiable” duplicated regions; and (3) elevated paralogous divergence is observed around the edges in many duplicated blocks, supporting our gene conversion–degeneration model. Our analysis demonstrated that gene conversion between duplicated regions is a common and genome-wide phenomenon in the Drosophila genomes, and that its role should be especially significant in the early stages of duplicated genes. Based on a population genetic prediction, we applied a new genome-scan method to test for signatures of selection for neofunctionalization and found a strong signature in a pair of transporter genes