Bulletin of the American Physical Society
Annual Meeting of the Four Corners Section of the APS
Volume 59, Number 11
Friday–Saturday, October 17–18, 2014; Orem, Utah
Session B2: Material Science I |
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Chair: Richard Sonnenfeld, New Mexico Institute of Mining and Technology Room: Science Building 246 |
Friday, October 17, 2014 10:15AM - 10:39AM |
B2.00001: Selective epitaxial growth solutions for Si based alloys; Si:C:P, Si:P, Si:C, i-Si Invited Speaker: Doran Weeks Strain enhancing techniques for boosting carrier mobility in PMOS transistors has been in production since the 90 nm process node. SiGe alloys are used to induce compressive strain initially in planar MOSFETs and more recently in finFET device channels thereby increasing the hole mobility. For the NMOS transistor the use of tensile strain to enhance electron mobility has only recently been applied starting at the 20 nm node. This is accomplished by alloying silicon with carbon and/or phosphorus both of which have smaller atomic radii than silicon thus generating the desired strain. SiC:P and to a lesser extent Si:P alloys pose new challenges not encountered with SiGe:B PMOS stressors. Among these challenges are the low solubility limits which require low temperature metastable growth techniques such as chemical vapor deposition (CVD) to be employed. This presentation reviews the history and performance enhancements of PMOS stressors and presents recent accomplishments related to NMOS SiC:P and Si:P stressors processed on finFET structures. [Preview Abstract] |
Friday, October 17, 2014 10:39AM - 10:51AM |
B2.00002: Measurement of Thermal Effects by Thermoelectric Coolers Ji Zhang, Jessica Gifford, Charles Snider, Gejian Zhao, Dongrin Kim, Nathaniel Vargas, Tingyong Chen Recently, electron transport induced by a thermal gradient in magnetic materials has attracted a great deal of attention since it has a potential to create pure spin current for spin caloritronics. However, unlike voltage potential, the exact thermal gradient direction is experimentally difficult to control, which has already caused misinterpretation of the thermal effects. In this work, we demonstrate that thermoelectric coolers based on the Peltier effect can be utilized to controllably measure thermal effects. Temperature gradient from positive to negative polarity can be induced simply by reversing an electric driven current and low noise measurements can be achieved using a square wave driven current. We show that in Bi both the Nernst and the Seebeck effects are present if the temperature gradient is not along the appropriate direction and the potential induced by the two effects can be separated by analysis of the data. With a well-defined temperature gradient, we show that the thermal effect in Py, Py/Pt, Co and Co/Pt films are mostly anomalous Nernst effect, with the same angular symmetry as the anomalous Hall effects measured in these polycrystalline films. [Preview Abstract] |
Friday, October 17, 2014 10:51AM - 11:03AM |
B2.00003: Detection of Percolation in Hermetic Single-Device Human Implants by Ion Beam Analysis (IBA) Nicole Herbots, M.W. Mangus, M. Neric, A.J. Woolson, R.J. Culbertson, B.J. Wilkens, A.W. Causey, A.L. Brimhall, C.F. Watson, S.A. Sinha, A.J. Acharya Percolation of bodily fluids into medical implants limits device lifetimes to less than a week in permanent glucose sensors for diabetics. Rutherford Backscattering Spectrometry (RBS) can detect C, O, Na from these fluids. But the RBS detection limit, \textbf{D}$^{\mathrm{\mathbf{min}}}$, is inadequate for low Z elements in higher Z substrates. With 2 MeV $^{4}$He$^{2+}$, \textbf{D}$^{\mathrm{\mathbf{min}}}$ of C in Si is $\sim$ 5 ML. The 4.265 $\pm$ 0.05 MeV $^{12}$C($\alpha $,$\alpha )^{12}$C Nuclear Resonance Analysis (NRA) reduces \textbf{D}$^{\mathrm{\mathbf{min,\thinspace C\thinspace }}}_{\mathrm{\mathbf{Si}}}$ to $\sim$ 0.05 ML. Next, NRA combined with channeling can lower \textbf{D}$_{\mathrm{\mathbf{min}}}$ by 20-50, with \textbf{D}$^{\mathrm{\mathbf{min,\thinspace C\thinspace }}}_{\mathrm{\mathbf{Si}}}$ \textless 0.002 ML for C. Thirdly, geometry, such as the tilt angle of the \textless 111\textgreater axis with the Si(100) surface almost doubles the sampled depth, reducing \textbf{D}$^{\mathrm{\mathbf{min,\thinspace C\thinspace}}}_{\mathrm{\mathbf{Si}}}$ by 1.7. Low \textbf{D}$^{\mathrm{\mathbf{min,Na}}}$ is needed as mobile Na ions destroys electronic sensors. In this work, \textbf{D}$^{\mathrm{\mathbf{min,Na}}}$ is increased using $^{4}$He$^{2+}$ near 4.68 MeV, by a factor 1.44. C, O and Na from blood and saline are studied. [Preview Abstract] |
Friday, October 17, 2014 11:03AM - 11:15AM |
B2.00004: Cathodolumiescence Studies of the Density of States of Disordered Silicon Dioxide JR Dennison, Amberly Evans Jensen Electron bombardment measurements have shown that disordered SiO$_{\mathrm{2}}$ exhibits cathodoluminescence, with an overall intensity that varies with incident electron beam energy and current density, sample temperature, exposure time, and wavelength. A simple model based on the defect density of states---used to explain electron transport in highly disordered insulating materials---has been extended to predict the relative cathodoluminescent intensity and spectral radiance for disordered SiO$_{\mathrm{2}}$ as a function of these variables. The spectral radiance exhibited four distinct bands, corresponding to four distinct energy distributions of defect states within the band gap; each showed different temperature dependence. These localized defect or ``trap'' states of disordered SiO$_{\mathrm{2}}$ are due to structural or substitutional chemical defects. The cathodoluminescence data were fit with the proposed model using mean shallow trap energy, deep trap energies, saturation dose rate, and energy-dependent penetration depth as fitting parameters. The model was able to explain all the qualitative features of the data and found good agreement with the physical parameters as measured by other methods. [Preview Abstract] |
Friday, October 17, 2014 11:15AM - 11:27AM |
B2.00005: Determination of Spin Polarization Using Fe-Superconductor SmO$_{0.82}$F$_{0.18}$FeAs Jessica Gifford, B.B. Chen, Ji Zhang, Gejian Zhao, Dongrin Kim, D. Wu, Tingyong Chen In a half-metallic spin-polarized current, spin of conduction electrons are aligned in one direction but electrons pair with opposite spin orientations in a singlet superconductor. Thus a half-metallic current cannot enter into a singlet superconductor, which can be utilized to measure spin polarization of magnetic materials via Andreev reflection spectroscopy (ARS). Since transition temperatures of most conventional superconductors are below 10 K, spin polarization is measured only at low temperatures by ARS. The recently discovered Fe-superconductors can have a transition temperatures close to 60 K, much higher than that of the conventional superconductors. In this work, we utilized a (1111) Fe superconductor SmO$_{0.82}$F$_{0.18}$FeAs and Pb to measure the spin polarization of a highly spin-polarized material, La$_{0.67}$Sr$_{0.33}$MnO$_{3}$. The determined spin polarization value using the Fe superconductor is the same as that using Pb, indicating that the Fe superconductor can be utilized to measure spin polarization of magnetic materials. Furthermore, we show that the spin polarization can be measured up to 52 K, the transition temperature of SmO$_{0.82}$F$_{0.18}$FeAs. [Preview Abstract] |
Friday, October 17, 2014 11:27AM - 11:39AM |
B2.00006: Measurement of Anomalous Nernst Effect in Py/Pt and Co/Pt films Salar Simaie, Ji Zhang, Jessica Gifford, Gejian Zhao, Dongrin Kim, Nathaniel Vargas, Tingyong Chen In metallic materials, electrons diffuse differently depending on the temperature distribution. Along the temperature gradient, an e.m.f. is induced, called the Seebeck effect. In an external magnetic field, an e.m.f is induced perpendicular to the thermal gradient, which is called the Nernst effect. In magnetic materials, it is called the anomalous Nernst effect because of the magnetization, similar to the anomalous Hall effect. Recently, thermal effects in magnetic materials have attracted a great deal of attention because of their potential to generate pure spin currents using a thermal gradient, such as the spin Seebeck effect. However, unlike electric potential, the exact thermal gradient direction is experimentally difficult to control, which has already caused misinterpretation of the thermal effects in Py and Py/Pt films. In this work, we measure the anomalous Nernst effect in Co/Pt and Py/Pt films with a well-defined thermal gradient induced by two thermoelectric coolers based on the Peltier effect. Reverse of the thermal gradient results in a reversed e.m.f. The angular dependence shows the same symmetry as the anomalous Hall effect in these polycrystalline films. [Preview Abstract] |
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