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For qualitative prediction of chip morphology and quantitative prediction of burr size,
2D and 3D finite element (FE) based turning models have been developed in this paper.
Coupled temperature-displacement machining simulations exploiting the capabilities of
Abaqus® with a particular industrial turning insert and a newly proposed geometrical
version of this insert have been performed. Limitations of 2D models in defining the chip
morphologies and surface topologies have been discussed. The phenomenological findings on
the Poisson burr (Side burr) formation using 3D cutting models have been highlighted.
Bespoke geometry of the turning insert has been found helpful in reducing the Poisson burr
formation, as it reduces the contact pressures at the edges of tool rake face-workpiece
interface. Lower contact pressures serve to decrease the material flow towards workpiece
edges (out of plane deformation). In contrast, higher contact pressures at tool rake
face-workpiece interface lead to more material flow towards workpiece edges resulting in
longer burr. Simulation results of chip morphologies and cutting forces for turning an
aluminum alloy A2024-T351 have been compared with the experimental ones. Finally, it has
been concluded that the newly proposed geometry of the insert not only decreases the burr
but also helpful in lessening the magnitude of tool-workpiece initial impact.
Lithographically prepared gold nanodots and nanowires were placed onto a thermal sensor film to measure heat absorption. These identical wires are also subjected to dark field scattering measurements allowing for a comparison between absorption and scattering at the excitation wavelength. An increasing liner trend is found to exist between nanowires of increasing aspect ratio. The nanostructures also exhibit a decreasing temperature change with increasing wire length with a constant laser flux of 1.3 x 1010 W/m2.
Magneto-optical properties of Ni- and Co-doped amorphous AlN thin films were investigated as a function of post grown annealing temperature using magneto-optical Kerr effect (MOKE) spectroscopy. The x-ray diffraction spectra confirmed that the as-grown material is amorphous and retained its morphology after thermal treatment; however the sample morphology strongly depends on the concentration of incorporated transition metals. We observed with help of transmission electron microscopy and atomic force microscopy that the films surface containing TMs with concentrations larger than ∼10 at.% undergo morphological changes suggesting possible Ni and Co atom clustering. Significant enhancement of the polar Kerr rotation signal was observed for Ni- and Co-doped a-AlN materials annealed above 300 °C in nitrogen. The studied materials have shown strong magnetic isotropy in polar geometry whereas the MOKE measurements in longitudinal geometry did not show an explicit signal for the transition metals doped a-AlN studied.
In this research work, a model has been proposed in view of the recent experimental demonstration using Calcium (Ca) as a contact metal to realize the n-type carbon nanotube field effect transistors (CNTFET). In order to fully optimize this proposed device model, effects of different parameters like the work function, oxide thickness, the oxide capacitance and the source velocity limits were studied. Among all the parameters, the work function of the contact metal plays an important role for controlling the flow of carriers through the carbon nanotube channel and to reduce the threshold voltage. A semi-classical simulation of the proposed n-type CNTFET has been performed. Results show an excellent subthreshold swing value of 62.91 mV/decade, close to the International Technology Roadmap for Semiconductor (ITRS) specifications.
Silicon Carbide (SiC) nanofibers were synthesized from SiC powder dispersed in polyethylene oxide (PEO) solution in Chloroform using the electrospinning technique. The as-spun fibers were then annealed at 1000ËC to 7 hours. The average diameter of the annealed fibers is 500 nm while the length of the annealed fibers is about 50 Âµm. The fibers were characterized using scanning electron microscope (SEM), X-ray diffraction (XRD) and Cathodoluminescence (CL). PL spectra from the annealed SiC fibers show a broad emission in the red-infrared spectral regime. The main peak is centered at 774 nm while the shoulder on the left is at 740 nm
We report on the luminescence of rare earth (RE) (Sm, Er, Tm) ions doped ZnO films grown by the rf-magnetron sputtering technique. Samples were insitu doped with Sm ion or with Sm, Er, and Tm ions simultaneously without any intentional co-dopants and deposited on c-Si or quartz substrates at low temperatures. Selected ZnO:RE samples were thermally annealed in 200ºC-1000ºC temperature range in oxygen or argon gas at ambient pressure. As-grown and annealed samples were amorphous (a-ZnO) as was confirmed by the X-ray analysis. Furthermore, a-ZnO:RE samples were investigated by energy diffraction, photoluminescence and cathodoluminescence. In general, CL spectra of as-grown RE-doped a-ZnO films show characteristic emission lines due to 4f-shell transitions of RE3+ ions. Optical excitation of as-grown a-ZnO doped with RE ions using above the bandgap excitation resulted in strong host emission overlapped with weak RE3+ emission bands. It was observed that a thermal annealing process promotes changes of RE ions' environments resulting in significant 4f-shell transition luminescence intensity quenching.
Deep level transient spectroscopy (DLTS) is the best technique for monitoring and characterizing deep levels introduced intentionally or occurring naturally in semiconductor materials and complete devices. DLTS has the advantage over all the techniques used to-date in that it fulfils almost all the requirements for a complete characterization of a deep centre and their correlation with the device properties. In particular the method can determine the activation energy of a deep level, its capture cross-section and concentration and can distinguish between traps and recombination centers.
In this invited paper we provide an overview of the extensive R & D work that has been carrier out by the authors on the identification of the recombination and compensator centers in Si and III-V compound materials for space solar cells. In addition, we present an overview of key problems that remain in the understanding of the role of the point defects and their correlation with the solar cell parameters.
Surface coating of carbon nanotubes and carbon nanofibers can significantly improve their properties such as electrical, thermal, magnetic, acoustic, vibration, catalytic, optical properties. This paper presents a novel method to coat carbon nanotubes and carbon nanofibers by using as-prepared carbon nanopaper sheets. The carbon nanopaper sheet consisted of randomly oriented single-walled nanotubes and vapor grown carbon nanofibers, which formed into a highly uniform non-woven material. This flexible and lightweight material was coated with nickel by laser pulse deposition. The effects of deposition parameters on the morphology of the nanotubes and nanofibers will be studied using scanning electron microscopy. The electrical conductivities of carbon nanopaper sheets associated with deposition parameters will be characterized using four-point probe method. The deposition parameters will be optimized to achieve a highly conductive carbon nanopaper sheet.
β-Ga2O3 nanostructures including nanowires, nanorods, nano and micro-pillars, nanosheets and nanobelts were successfully fabricated by simple and efficient thermal evaporation and condensation technique under argon flow.. The structures have been investigated by the electron microscope, XRD and EDX techniques and shown that nanostructures are predominatly β-Ga2O3 without other crystallographic phases. Cathodouminescence of as-grown nanostructures was investigated in the 10-300 K temperature range and exhibit luminescence band centered at 485 nm at 300 K due to donor-acceptor pair recombination. A new luminescence band centered at 387 nm developes at temperature below 150 K due to self-trapped exciton recombination.
ZnO nanofibers doped with Ga, In and Er metals have been fabricated by electrospinning technique. The diameter of the fibers was in the range of 0.5-2 μm and the length can be up to several feet. After spinning fabrication step the samples were dried out and annealed at 900 °C in air. Room temperature photoluminescence (PL) spectra measured for undoped and In- and Ga-doped ZnO fiber samples exhibit only a strong near band edge (NBE) emission at ∼380 nm with very weak green band at 525 nm. In contrary, the PL spectrum of Er-doped ZnO fibers shows a very weak NBE and strong green emission band at ∼550 nm at 300 K. The electrospinning mechanism used for the fabrication of nanofibers was found to be productive, simple and easy to implement disregarding of the doping type and concentration.
Electrically conducting fibers of polyaniline doped with Camphorsulfonic acid PAn.HCSA in the Polyethylene Oxide (PEO) matrix were prepared using the non-mechanical electrospinning technique. The morphology of the fibers was studied using the scanning electron microscope (SEM) and Transmission electron microscope (TEM), showing a uniform thickness along the fiber length. The fibers had a diameter ranging from 800nm to 2μm. The electrical conductivity of the non-woven fibrous mat and the cast film was measured using the four-point probe method, for different concentrations of Pan.HCSA in the blend. Some possible factors affecting the electrical conductivity of the fibers/films were discussed.
Ultra-Fine ZnO nanobelts are grown via thermal evaporation and condensation method without the use of any catalyst on the substrates. These nanobelts have an average width of about 5.8 nm. Photoluminescence spectra reveal that there is a blue shift in the near band edge ultra violet emission from 381 nm to 367 nm equal to 124 meV. These ultra-fine nanobelts have been studied for size induced optical and electrical properties.
Novel ZnO nanostructures such as hollow nanospheres, nano-cages, nanoneedles, tetra-pods, nanowires, aligned nanorods and nanotubes are synthesized via thermal evaporation of ZnO and graphite powder mixtures in reduced oxygen atmosphere in the presence of argon and nitrogen flows. The ZnO nanostructures, especially nanospheres, have a unique shape and are hollow inside with walls densely decorated with aligned nanowires. Photoluminescence of synthesized ZnO structures measured at 300 K exhibits a strong near band edge peak at ∼380 nm and deep level green band centered at ∼550 nm. Fabricated ZnO structures can be studied for various applications in optoelectronics and sensors.
We report the results of comparison of radiation-induced defects (1 MeV electrons) in n+-p-p+ Si diodes doped with gallium or boron ranging in concentration from 8 × 1014 to 5 × 1016 cm-3, together with the impact of oxygen on radiation –induced defects. Present results provide evidence for new defects states in addition to those previously reported in gallium- and boron-doped Si. The combined boron and gallium data provide enough information to gain valuable insight into the role of the dopants on radiation-induced defects in Si. The interesting new future of our results is that the gallium appears to strongly suppress the radiation induced defect, especially hole level EV+0.36 eV, which is thought to act as a recombination center. Similarly the dominant electron level at EC-0.18 eV in B-doped Si (which act as a donor) has not been observed in Ga-doped CZ-grown Si.
We report the results of comparison of radiation-induced defects (1 MeV
electrons) in n+-p-p+ Si diodes doped with gallium or
boron ranging in concentration from 8 × 1014 to 5 ×
1016 cm−3, together with the impact of oxygen on
radiation –induced defects. Present results provide evidence for new defects
states in addition to those previously reported in gallium- and boron-doped
Si. The combined boron and gallium data provide enough information to gain
valuable insight into the role of the dopants on radiation-induced defects
in Si. The interesting new future of our results is that the gallium appears
to strongly suppress the radiation induced defect, especially hole level
EV+0.36 eV, which is thought to act as a recombination center.
Similarly the dominant electron level at EC-0.18 eV in B-doped Si
(which act as a donor) has not been observed in Ga-doped CZ-grown Si.
Studies on the electrical conductivity of molecular beam deposited carbon films after annealing of the carbon films have been carried out. Detailed temperature dependence of conductivity on the as-deposited and on annealed samples has been investigated. The results were interpreted in terms of a model which includes a variable range hopping and strongly scattering metallic components. A correlation between annealing behavior of the electrical conductivity and the results of x-ray photoelectron spectroscopy and Raman spectroscopy is presented.
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