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Thermal imaging diagnostics was used as a surface temperature mapping tool to characterize the energy density distribution of a high-intensity pulsed ion beam. This approach was tested on the TEMP-6 accelerator (200–250 kV, 150 ns). The beam composition included carbon ions (85%) and protons, and the energy density in the focus was 5–12 J/cm2. Targets of stainless steel, titanium, brass, copper, and tungsten were examined. Our observations show that the maximum energy density measured with the thermal imaging diagnostics considerably exceeds the ablation threshold of the targets. An analysis of the overheating mechanisms of each target was carried out, including metastable overheating of the target to above its boiling temperature during rapid heating; formation, migration, and the subsequent annealing of fast radiation-induced defects in the target under ion beam irradiation. This expands the range of energy density measurement for this thermal imaging diagnostics from 2–3 J/cm2 up to 10–12 J/cm2 but introduces error into the results of measurement. For a stainless steel target, this error exceeds 15% at an energy density of more than 4 J/cm2. A method of correcting the results of the thermal imaging diagnostics is developed for a pulsed ion beam under conditions of intense ablation of the target material.
We study the shape and motion of gas bubbles in a liquid flowing through a horizontal or slightly inclined thin annulus. Experimental data show that in the horizontal annulus, bubbles develop a unique ‘tadpole-like’ shape with a semi-circular cap and a highly stretched tail. As the annulus is inclined, the bubble tail tends to vanish, resulting in a significant decrease of bubble length. To model the bubble evolution, the thin annulus is conceptualised as a ‘Hele-Shaw’ cell in a curvilinear space. The three-dimensional flow within the cell is represented by a gap-averaged, two-dimensional model, which achieved a close match to the experimental data. The numerical model is further used to investigate the effects of gap thickness and pipe diameter on the bubble behaviour. The mechanism for the semi-circular cap formation is interpreted based on an analogous irrotational flow field around a circular cylinder, based on which a theoretical solution to the bubble velocity is derived. The bubble motion and cap geometry is mainly controlled by the gravitational component perpendicular to the flow direction. The bubble elongation in the horizontal annulus is caused by the buoyancy that moves the bubble to the top of the annulus. However, as the annulus is inclined, the gravitational component parallel to the flow direction becomes important, causing bubble separation at the tail and reduction in bubble length.
To study the clinical effect of lens cleaning paper patching on traumatic eardrum perforations.
A total of 122 patients were divided into 2 groups, of which 56 patients were treated with lens cleaning paper patching and 66 acted as controls. The closure rate and healing time were compared between the two groups.
The healing rate of small perforations was 96.4 per cent (27 out of 28) in the patching group and 90 per cent (27 out of 30) in the control group. The difference was not statistically significant (p > 0.05). The healing rate of large perforations was 89.3 per cent (25 out of 28) and 80.6 per cent (29 out of 36) in the two groups, respectively. The difference was statistically significant (p < 0.05). The healing time of large perforations was shorter in the patching group than in the control group (p < 0.01).
Patching with lens cleaning paper under an endoscope can accelerate the closure of large traumatic eardrum perforations.
In this paper, we propose a double balanced mixer with a tunable Marchand balun. The circuit is designed in a SiGe BiCMOS process using Schottky diodes. The tunability of the Marchand balun is used to enhance critical parameters for double balanced mixers. The local oscillator-IF isolation can be changed from –51 to –60.5 dB by tuning. Similarly, the IIP2 can be improved from 41.3 to 48.7 dBm at 11 GHz, while the input referred 1-dB compression point is kept constant at 8 dBm. The tuning have no influence on conversion loss, which remains at 8.8 dB at a LO power level of 11 dBm at the center frequency of 11 GHz. The mixer has a 3 dB bandwidth from 8 to 13 GHz, covering the entire X-band. The full mixer has a size of 2050 μm × 1000 μm.
Ag–reduced graphene oxide (Ag/rGO) nanoparticle composites were synthesized through a facile one-step hydrothermal reaction using GO and silver carbonate (Ag2CO3) as raw materials. The homogeneous silver nanospheres with an average size of 50 nm well dispersed on the surface of rGO were obtained without other additives. During the formation process, GO both promotes the dispersion of Ag2CO3 in aqueous solution and acts as the substrate of silver cations, and the hydrolysis of Ag2CO3 provides silver cations and alkaline condition. Moreover, GO further serves as reducing agent to generate elemental silver in the alkaline condition. The as-prepared materials exhibit excellent surface-enhanced Raman scattering activities when used to detect the Raman signals of R6G absorbed on the Ag/rGO substrate.
In this study, CeO2 nanowires–reduced graphene oxide hybrids (CeO2 NWs–RGO) were synthesized by a green hydrothermal method using CeO2 NWs and graphene oxide (GO) as raw materials. During the process of reduction of GO, hydrothermal condition with supercritical water provides thermal and chemical factors to synthesize RGO. The photocatalytic experimental results show that the CeO2 NWs–RGO hybrids exhibit enhanced photocatalytic activity for degradation of Rhodamine B (RhB) under UV-light irradiation. It is found that the degree of photocatalytic activity enhancement strongly depends on the mass ratio of RGO in the hybrids, and the remarkable photocatalytic activity is 20 times that of pristine CeO2 NWs when the loading amount of RGO is 8.0 wt%. The enhancement of photocatalytic activity can be attributed to the excellently elevated absorption ability for the dye through π–π conjugation as well as the effective inhibition of the recombination of photogenerated electrons because of the electronic interaction between CeO2 NWs and RGO sheets.
For the gate last approach of a high K metal gate scheme used in advanced CMOS technology, various materials were tested as wetting layers to allow Aluminum (Al) gap fill at gate widths of10 to 45 nanometers. In this study, Titanium (Ti) and Cobalt (Co) were investigated as a wetting layer for Al gap fill. It was discovered that Al-Ti and Al-Co alloys were formed during high temperature Al deposition. Alloys were characterized using XRD. Alloy’s impacts on line resistivity and subsequent Al Chemical Mechanical Polish (Al CMP) were also investigated. In addition, a model was established to predict the alloy type and alloy mole% with respect to feature size. The predicted Al mole% by this model correlated very well with 1) line resistivity trend and 2) morphologies. The model also predicted that due to Al lower electro-chemical potential than Ti, Co or its alloys, galvanic corrosion could take place depending on the chemical environment in the Al CMP slurry. Different slurry or cleaning chemical may reduce or increase the risk of galvanic corrosion. The knowledge gained with the help of the model provides clear directions on selection criteria for wetting layers, optimization for deposition processes and Al CMP consumable design to meet the challenges.
Indium containing III-Nitride layers are predominantly grown by heteroepitaxy on foreign substrates, most often Al2O3, SiC and Si. We have investigated the epitaxial growth of InxGa1-xN (InGaN) alloys on Ge substrates. First we looked at the influence of buffer layers between the InGaN and Ge substrate. When applying a high temperature (850 °C) GaN buffer, the InGaN showed superior crystal quality. Furthermore the influence of growth parameters on the structural quality and composition of InGaN layers has been looked into. For a fixed gallium and nitrogen supply, the indium beam flux was increased incrementally. For both nitrogen- as well as for metal (Ga + In) rich growth conditions, the In incorporation increases for increasing In flux. However, for metal rich growth conditions, segregation of metallic In is observed. An optimum in crystal quality is obtained for a metal:nitrogen flux ratio close to unity. The XRD FWHM of the GaN (0002) reflection increases significantly after InGaN growth. Apparently the presence of indium deteriorates the GaN buffer during InGaN growth. The mechanism of the effect is not known yet.
In this study, the AC magnetic permeability of polycrystalline Fe81Ga19 alloy (Galfenol), without crystal orientation under both the bias applied fields and frequencies, was investigated by the method of measuring inductance of ring specimens. The results showed that the AC permeability of the alloy can reach more than 160 Gs/Oe under the conditions of low frequencies or quasi-static state. The permeability decreased with the increase of frequency. When the frequency was higher than 6 kHz, the permeability decreased slowly, and gradually stabilized with the increase of frequency. When applying a little of parallel bias magnetic field, the permeability decreases obviously with the increase of frequency. But applying a perpendicular bias magnetic fields, the permeability of the only initial point of the measuring frequency decreases a little compared to the permeability without bias field.
Optical measurements have been performed on heavily carbon doped GaAs layers grown on semi-insulating GaAs substrates by MOMBE (metal-organic molecule beam epitaxy). Photoluminescence excitation (PLE) spectroscopy was used to measure the onsets of optical absorption in these GaAs:C epilayers. It was found that in samples with free carrier concentrations of 6.2×1019, 1.6×1020, and 4.1×1020cm−3, optical absorption begins at 1.40, 1.52, and 1.53 ev, respectively. Combined with the band gap narrowing data from photoluminescence (PL) spectra, we estimated Fermi level locations relative to the top of the valence band. We also measured reflectance in the near infrared region and estimated the effective mass of free holes using a classical two-oscillator model.
Retention of the enhanced properties reported for nanograined metallic systems requires that the nanostructure be insensitive to temperature and deformation. In situ transmission electron microscopy annealing experiments were employed to investigate the structural changes associated with the formation of micron-sized grains in nanograined evaporated gold thin films. This abnormal grain growth occurs randomly throughout the film. Twinning but not dislocation slip occurs in the growing grains until the grain size is in the hundreds of nanometer range. The twins appear to hinder growth and for grain growth to continue the twins must either be annihilated or be able to grow with the grain concurrently.
A unique superelastic NiTi Retractable Bone Probe was designed which can diagnose anatomical structures not previously possible. A number of design considerations which entered into the final device configuration will be discussed. Potential applications for this new probe will be presented.
Using theoretical models, we consider the sound velocities and elastic constants of ceramics containing pores. As an example, we consider alumina. However, the approach applies to all ceramics. As a point of departure, we consider spherical pores. For all the usual elastic constants–Young modulus, shear modulus, bulk modulus, Poisson ratio–we give relationships for both the forward and inverse cases: predicting the porous ceramic properties and estimating the pore-free ceramic properties. Following a suggestion by Hasselman and Fulrath that sintering or hot pressing can produce cylindrical pores, we derive a relationship for the elastic constants of a distribution of randomly oriented long cylinders (c/a + ∞, the prolate-spheroid limit). This model predicts elastic constants lower than for spherical pores, but well above measurement. We obtain agreement with observation by assuming the pores are oblate spheroids. For alumina, the necessary aspect ratio equals oneninth. Besides pore aspect ratio, the model requires only the pore-free alumina elastic constants. It contains no adjustable parameters.
The principles for an electrochemical digital etching method for compound semiconductors are described and initial results reported. The method is designed to allow atomic level control over the etching process, resulting in the removal of a bilayer of the compound for each cycle. An atomic layer of one element is removed at one potential and then an atomic layer of the second element is removed at a second potential to complete one cycle. The results reported here are for the etching of CdTe. For CdTe, Te is stripped by reduction to Te2- while Cd is stripped by oxidation to Cd2+. Underpotentials are chosen so that only the top atomic layer of an element is removed. Potentials sufficient to strip the elemėnt from the bulk of the CdTe substrate are avoided. Application of the method should involve the use of a simple electrochemical cell, with solution convection. The substrate is placed in the cell and a square wave applied, where each cycle results in the dissolution of a bilayer of the compound. The two potentials of the square wave correspond to underpotential stripping potentials for Cd and Te respectively. Directions for the future development of this etching method are discussed.
MOCVD and MBE grown GaN were implanted with Ar, Mg, Si, Be, C, and O, and annealed in a conventional oven under flowing NH3 or N2 gas. Absorption measurements confirmed that implantation damage was annealed out after 90 minutes at a temperature of 1000 °C. Surface damage caused by NH3 annealing was evident in absorption and photoluminescence measurements for annealing temperatures of over 1000 °C. Although most of the implants showed no unique luminescence peaks, systematic changes in the relative intensities of the exciton, donor-acceptor pair, and yellow peaks were noted. The Mg implanted samples showed evidence of the acceptor bound exciton line at 3.44 eV, and a unique peak at 3.3 eV possibly due to a Mg free-to-bound transition.
Photoreflectance spectroscopy (PR) and spectral ellipsometry (SE) have been used to characterize the doping and structure of heterojunction bipolar transistors (HBT). This information provides a more complete description of the epitaxial HBT structure than is possible by relying solely on electrical characterization of specially processed test structures. Additional benefit is derived from the nondestructive nature of both SE and PR. The measurements are fast enough to be implemented on all production-bound HBT material. We describe our recent results comparing capacitance-voltage measurements with PRderived doping levels in the emitter layer of the HBT. We also describe some work comparing SE fit results with Auger electron spectroscopy depth profiles for InGaAs contact layer composition and thickness.
The development of optical technologies requires the fabrication of reliable optical switching and limiting devices. Optical switches modulate the transmission or reflection of incident light, while optical limiters serve to limit transmission to prevent the transmitted light intensity from exceeding a defined level. A major application of optical limiters is to protect delicate sensors.