86 research outputs found
Microstructure versus Size: Mechanical Properties of Electroplated Single Crystalline Cu Nanopillars
We report results of uniaxial compression experiments on single-crystalline Cu nanopillars with nonzero initial dislocation densities produced without focused ion beam (FIB). Remarkably, we find the same power-law size-driven strengthening as FIB-fabricated face-centered cubic micropillars. TEM analysis reveals that initial dislocation density in our FIB-less pillars and those produced by FIB are on the order of 10^(14) m^(-2) suggesting that mechanical response of nanoscale crystals is a stronger function of initial microstructure than of size regardless of fabrication method
Faraday cage angled-etching of nanostructures in bulk dielectrics
For many emerging optoelectronic materials, heteroepitaxial growth techniques
do not offer the same high material quality afforded by bulk, single-crystal
growth. However, the need for optical, electrical, or mechanical isolation at
the nanoscale level often necessitates the use of a dissimilar substrate, upon
which the active device layer stands. Faraday cage angled-etching (FCAE)
obviates the need for these planar, thin-film technologies by enabling in-situ
device release and isolation through an angled-etching process. By placing a
Faraday cage around the sample during inductively-coupled plasma reactive ion
etching (ICP-RIE), the etching plasma develops an equipotential at the cage
surface, directing ions normal to its face. In this Article, the effects
Faraday cage angle, mesh size, and sample placement have on etch angle,
uniformity, and mask selectivity are investigated within a silicon etching
platform. Simulation results qualitatively confirm experiments and help to
clarify the physical mechanisms at work. These results will help guide FCAE
process design across a wide range of material platforms
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Free-Standing Nanomechanical and Nanophotonic Structures in Single-Crystal Diamond
Realizing complex three-dimensional structures in a range of material systems is critical to a variety of emerging nanotechnologies. This is particularly true of nanomechanical and nanophotonic systems, both relying on free-standing small-scale components. In the case of nanomechanics, necessary mechanical degrees of freedom require physically isolated structures, such as suspended beams, cantilevers, and membranes. For nanophotonics, elements like waveguides and photonic crystal cavities rely on light confinement provided by total internal reflection or distributed Bragg reflection, both of which require refractive index contrast between the device and surrounding medium (often air). Such suspended nanostructures are typically fabricated in a heterolayer structure, comprising of device (top) and sacrificial (middle) layers supported by a substrate (bottom), using standard surface nanomachining techniques. A selective, isotropic etch is then used to remove the sacrificial layer, resulting in free-standing devices. While high-quality, crystalline, thin film heterolayer structures are readily available for silicon (as silicon-on-insulator (SOI)) or III-V semiconductors (i.e. GaAs/AlGaAs), there remains an extensive list of materials with attractive electro-optic, piezoelectric, quantum optical, and other properties for which high quality single-crystal thin film heterolayer structures are not available. These include complex metal oxides like lithium niobate (LiNbO3), silicon-based compounds such as silicon carbide (SiC), III-V nitrides including gallium nitride (GaN), and inert single-crystals such as diamond.
Diamond is especially attractive for a variety of nanoscale technologies due to its exceptional physical and chemical properties, including high mechanical hardness, stiffness, and thermal conductivity. Optically, it is transparent over a wide wavelength range (from 220 nm to the far infrared), has a high refractive index (n ~ 2.4), and is host to a vast inventory of luminescent defect centers (many with direct optical access to highly coherent electron and nuclear spins). Diamond has many potential applications ranging from radio frequency nanoelectromechanical systems (RF-NEMS), to all-optical signal processing and quantum optics. Despite the commercial availability of wafer-scale nanocrystalline diamond thin films on foreign substrates (namely SiO2), this diamond-on-insulator (DOI) platform typically exhibits inferior material properties due to friction, scattering, and absorption losses at grain boundaries, significant surface roughness, and large interfacial stresses. In the absence of suitable heteroepitaxial diamond growth, substantial research and development efforts have focused on novel processing techniques to yield nanoscale single-crystal diamond mechanical and optical elements.
In this thesis, we demonstrate a scalable ‘angled-etching’ nanofabrication method for realizing nanomechanical systems and nanophotonic networks starting from bulk single-crystal diamond substrates. Angled-etching employs anisotropic oxygen-based plasma etching at an oblique angle to the substrate surface, resulting in suspended optical structures with triangular cross-sections. Using this approach, we first realize single-crystal diamond nanomechanical resonant structures. These nanoscale diamond resonators exhibit high mechanical quality-factors (approaching Q ~ 10^5) with mechanical resonances up to 10 MHz.
Next, we demonstrate engineered nanophotonic structures, specifically racetrack resonators and photonic crystal cavities, in bulk single-crystal diamond. Our devices feature large optical Q-factors, in excess of 10^5, and operate over a wide wavelength range, spanning visible and telecom. These newly developed high-Q diamond optical nanocavities open the door for a wealth of applications, ranging from nonlinear optics and chemical sensing, to quantum information processing and cavity optomechanics. Beyond isolated nanophotonic devices, we also developed free-standing angled-etched diamond waveguides which efficiently route photons between optical nanocavities, realizing true on-chip diamond nanophotonic networks. A high efficiency fiber-optical interface with aforementioned on-chip diamond nanophotonic networks, achieving > 90% power coupling, is also demonstrated.
Lastly, we demonstrate a cavity-optomechanical system in single-crystal diamond, which builds upon previously realized diamond nanobeam photonic crystal cavities fabricated by angled-etching. Specifically, we demonstrate diamond optomechanical crystals (OMCs), where the engineered co-localization of photons and phonons in a quasi-periodic diamond nanostructure leads to coupling of an optical cavity field to a mechanical mode via the radiation pressure of light. In contrast to other material systems, diamond OMCs possess large intracavity photon capacity and sufficient optomechanical coupling rates to exceed a cooperativity of ~ 1 at room temperature and realize large amplitude optomechanical self-oscillations.Engineering and Applied Sciences - Applied Physic
Medication use by middle-aged and older participants of an exercise study: results from the Brain in Motion study
BACKGROUND: Over the past 50 years, there has been an increase in the utilization of prescribed, over-the-counter (OTC) medications, and natural health products. Although it is known that medication use is common among older persons, accurate data on the patterns of use, including the quantity and type of medications consumed in a generally healthy older population from a Canadian perspective are lacking. In this study, we study the pattern of medication use in a sedentary but otherwise healthy older persons use and determined if there was an association between medication use and aerobic fitness level. METHODS: All participants enrolled in the Brain in Motion study provided the name, formulation, dosage and frequency of any medications they were consuming at the time of their baseline assessment. Maximal aerobic capacity (VO(2)max) was determined on each participant. RESULTS: Two hundred seventy one participants (mean age 65.9 ± 6.5 years; range 55–92; 54.6% females) were enrolled. Most were taking one or more (1+) prescribed medication (n = 204, 75.3%), 1+ natural health product (n = 221, 81.5%) and/or 1+ over-the-counter (OTC) drug (n = 174, 64.2%). The most commonly used prescribed medications were HMG-CoA reductase inhibitors (statins) (n = 52, 19.2%). The most common natural health product was vitamin D (n = 201, 74.2%). For OTC drugs, non-steroidal anti-inflammatories (n = 82, 30.3%) were the most common. Females were more likely than males to take 1+ OTC medications, as well as supplements. Those over 65 years of age were more likely to consume prescription drugs than their counterparts (p ≤ 0.05). Subjects taking more than two prescribed or OTC medications were less physically fit as determined by their VO(2)max. The average daily Vitamin D intake was 1896.3 IU per participant. CONCLUSIONS: Medication use was common in otherwise healthy older individuals. Consumption was higher among females and those older than 65 years. Vitamin D intake was over two-fold higher than the recommended 800 IU/day for older persons, but within the tolerable upper intake of 4,000 IU/day. The appropriateness of the high rate of medication use in this generally healthy population deserves further investigation
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