Bulletin of the American Physical Society
Annual Meeting of the APS Four Corners Section
Volume 60, Number 11
Friday–Saturday, October 16–17, 2015; Tempe, Arizona
Session K5: Materials IX: Surfaces and Interfaces |
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Chair: Brandon Runnels, University of Colorado, Colorado Springs Room: PSA104 |
Saturday, October 17, 2015 1:12PM - 1:24PM |
K5.00001: Plasma enhanced atomic layer deposition of ultrathin oxides on graphene Christie J. Trimble, Anna M. Zaniewski, Manpuneet Kaur, Trevor Van Engelhoven, Robert J. Nemanich Graphene, a single atomic layer of sp2 bonded carbon atoms, possesses extreme material properties that give rise to a variety of potential electronic applications. Many of these possibilities require the combination of graphene with dielectric materials such as metal oxides. While many dielectric deposition techniques exist, plasma enhanced atomic layer deposition (PEALD) has been shown to produce ultrathin dielectric films with superior densities and interfaces. However, exposure to oxygen plasma can cause graphene to deteriorate, and therefore the degree to which PEALD on graphene can be achieved without significant damage to the graphene layer is not well understood. In this project, we perform PEALD of aluminum oxide on graphene, investigating a range of plasma conditions across a single sample. We characterize both oxide growth and graphene deterioration post deposition using spectroscopic analysis and atomic force microscopy. By our method we achieve ultrathin ($<$1 nm) aluminum oxide films atop graphene. [Preview Abstract] |
Saturday, October 17, 2015 1:24PM - 1:36PM |
K5.00002: Analysis of monolayer MoS2 films grown by CVD: Correlating RBS and SEM results through AES. Emanuel Borcean, Chad Lunceford, Jeff Drucker Auger electron spectroscopy (AES), Rutherford backscattering spectrometry (RBS), and scanning electron microscopy (SEM) were used to quantitatively analyze MoS$_{2}$ films grown using chemical vapor deposition (CVD). A bulk MoS$_{2}$ standard is used to determine the peak height ratios of the Mo$_{MNN}$ and S$_{LMM}$ Auger transitions for stoichiometric MoS$_{2}$. This result is employed to assess the stoichiometry of the CVD-grown films. This analysis is valid since the energies and thus mean free paths of the Mo$_{MNN}$ and S$_{LMM}$ Auger electrons are nearly the same. The Mo$_{MNN}$ Auger peak height is calibrated using RBS so that the Mo coverage can be quantified along the sample to assess its uniformity. By assuming that the islands observed in SEM are stoichiometric MoS$_{2}$, it is also possible to quantify the S Auger signal along the substrate. These results are being analyzed to determine whether they can resolve the discrepancy between the Mo coverage measured using RBS and the fraction of substrate area covered by MoS$_{2}$ islands observed in SEM images. [Preview Abstract] |
Saturday, October 17, 2015 1:36PM - 1:48PM |
K5.00003: Incorporating Si into cubic boron nitride films via plasma enhanced CVD: Can n-type doping be achieved? . Shammas Silicon has been reported as an n-type dopant for cubic boron nitride (c-BN) crystals synthesized via high pressure high temperature synthesis and for films deposited via physical vapor deposition. Recent advances in deposition techniques have allowed for c-BN films to be deposited via plasma enhanced chemical vapor deposition (PECVD) employing fluorine chemistry. Such films have been reported to exhibit a negative electron affinity (NEA) surface. As a consequence of the NEA surface, electrons excited to the conduction band can be emitted into a vacuum without having to overcome an additional energy barrier. The effects of n-type doping and an NEA surface could yield a low work function material, with potential for applications utilizing electron emission. To date, the electronic structure, work function, etc. of Si-doped c-BN films deposited via PECVD has not been reported. Photoelectron spectroscopy is used to probe the surfaces of c-BN films containing Si to determine the Fermi level position and deduce if doping can be realized. This research is supported by the Office of Naval Research through grant # N00014-10-1-0540. [Preview Abstract] |
Saturday, October 17, 2015 1:48PM - 2:00PM |
K5.00004: Measuring Surface Energy and Reactivity of SiO2 Using the Van Oss Theory and Three Liquid Contact Angle Analysis Ashley A. Mascareno, Alex L. Brimhall, Ender W. Davis, Matthew T. Bade, Nithin Kannan, Abijith Krishnan, Dr. Nicole Herbots, Clarizza F. Watson Surface energies $\gamma^T$ can characterize reactivity for Wet NanoBonding$^{\mathrm{TM}}$ of Si(100) and SiO$_2$, a $200^{\circ}$C process where surfaces cross-bond. The Van Oss theory models $\gamma^T$ via 3 interaction energies, $\gamma^{LW}$ for Lifshitz-Van der Waals (LW) interactions, $\gamma^-$ for electron acceptors and $\gamma^+$ for donors, with $\gamma^T=\gamma^{LW}+2\sqrt{\gamma^+\gamma^-}$. To calculate $\gamma^{LW}$, $\gamma^+$, and $\gamma^-$, contact angles for 3 different liquids are measured in a Class 100 hood. For precision, 4-8 droplets are used instead of 1. Three SiO$_2$/Si(100) structures are analyzed: amorphous thermal a-SiO$_2$, HF-etched thermal a-SiO$_2$, and ordered 2 nm-thick c-SiO$_2$ produced by the Herbots-Atluri (H-A) process. In thermal a-SiO$_2$ surfaces, $\gamma^T=45\pm 2\frac{mJ}{m^2}$, while in more defective HF-etched a-SiO$_2$, $\gamma^T=57.5+/-2 \frac{mJ}{m^2}$. Because HF-etching yields a $\gamma^T$ closer to $\gamma^T$ of H$_2$O ($72\pm 0.4 \frac{mJ}{m^2}$), HF-etching makes the surface more hydrophilic. In contrast, in hydrophobic, ordered 2nm-thick H-A c-SiO$_2$, $\gamma^T=37.3\pm 2 \frac{mJ}{m^2}$. In ordered c-SiO$_2$, $\gamma^{LW}=.98\gamma^T$. However, for etched a-SiO$_2$, $\gamma^{LW}=.65\gamma ^T$ and $\gamma^-=.48\gamma^T$. [Preview Abstract] |
Saturday, October 17, 2015 2:00PM - 2:12PM |
K5.00005: Contribution of Lifshitz-Van der Waals Interactions to the Surface Energy $\gamma^T$ of Si(100)-based Surfaces using the Van Oss-Young-Dupre Model Alex L. Brimhall, Ashley A. Mascareno, Ender W. Davis, Matthew T. Bade, Nithin Kannan, Abijith Krishnan, Nicole Herbots, Clarizza F. Watson Surface energy $\gamma^T$ is studied via 3 Liquid Contact Angle Analysis (3LCAA) to optimize Wet NanoBonding$^\mathrm{TM}$, where surfaces hermetically cross-bond by anneal $<200^{\circ}$C. Applications lie in electronic sensors in saline environments. The Van Oss theory models interactions with dipoles (Lifshitz-Van der Waals) $\gamma^{LW}$, electron donors $\gamma^+$, and acceptors $\gamma^-$. Combining the equations of Van Oss and Young-Dupre yield the total $\gamma^T$ and its 3 components. Contact angles for 3 different liquids are measured with the sessile drop method on 4-8 drops per liquid for accuracy, in a Class 100 hood. Si wafers are studied after RCA clean or Herbots-Atluri (H-A) processing. After H-A, 2 sets are treated with Rapid Thermal Anneal or Oxidation (RTA or RTO). $\gamma^T$ is higher for the more defective, hydrophilic RCA cleaned Si ($47.3\pm 0.5 \frac{mJ}{m^2}$), while it is lower for the more ordered, hydrophobic H-A surfaces ($37.3\pm1.5 \frac{mJ}{m^2}$) and RTO ($34.5\pm 0.5 \frac{mJ}{m^2}$). In addition, $\gamma^{LW}$ interactions account for 90 to 98$\%$ of $\gamma^T$ in ordered oxides, unlike in hydrophilic surfaces (76.5$\%$). This indicates that 3LCAA can detect decreases in surface interaction from surface defects, impurities, and dangling bonds. [Preview Abstract] |
Saturday, October 17, 2015 2:12PM - 2:24PM |
K5.00006: Optimizing Wet NanoBonding$^\mathrm{TM}$ using Three Liquid Contact Angle Analysis of Surface Energy and Reactivity Ender W. Davis, Nicole Herbots, Robert J. Culbertson, Alex L. Brimhall, Ashley A. Mascareno, Clarizza F. Watson, Abijith Krishnan, Nithin Kannan, Matthew T. Bade Silicon-based surfaces, such as thermally-grown amorphous a-SiO$_2$ and Si(100), are hermetically bonded using wet NanoBonding$^\mathrm{TM}$. Initial surfaces are modified to favor electron exchange and cross-bonding. a-SiO$_2$ is etched with hydrofluoric acid (HF), while $\beta$-cSiO$_2$ is grown on Si(100). Next, both are NanoBonded under steam pressurization. NanoBonding can bond medical, marine, and air sensors to their electronics, and be used in night vision goggles and solar cells. To optimize cross-bonding, surface energy $\gamma^T$ is studied via 3 liquid contact angle analysis (3LCAA) and the Van Oss theory. This models $\gamma^T$ via 3 components: $\gamma^{LW}$ for dipole interactions, $\gamma^+$ for electron donors, and $\gamma^-$ for acceptors. 3LCAA extracts contact angles from 3 liquids with known surface energies: water, glycerin, and $\alpha$-bromonaphthalene. We use several droplets of each liquid on the surface to improve accuracy. $\gamma^+$ accounts for little to none of the surface energy of all surfaces, but the annealing in Wet NanoBonding significantly increases $\gamma^+$ in $\beta$-cSiO$_2$. Conversely, HF etching significantly increases $\gamma^-$ for a-SiO$_2$. This donor/acceptor imbalance enhances reactivity and NanoBonding between the surfaces. [Preview Abstract] |
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