Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session L41: Ripples, Grain Boundaries, & Interfaces |
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Sponsoring Units: DCMP Chair: Mina Yoon, Oak Ridge National Laboratory Room: Colorado Convention Center 504 |
Tuesday, March 6, 2007 2:30PM - 2:42PM |
L41.00001: Gas cluster ion irradiation in formation of nano-ripple structures on silicon surfaces and its applications to producing III-nitride nanorods O. Lozano, X.M. Wang, Q.Y. Chen, J.R. Liu, P.V. Chinta, P.V. Wadekar, Wei-Kan Chu, H.W. Seo, L.W. Tu, Y.T. Lin, Y.L. Cheng Gas cluster ion beams (GCIB) have been used to fabricate nano-ripple structures on Si substrates. In this work, using (Ar)$_{n}^{+}$ clusters at 30 kV acceleration, where n$\approx $3,000, we have observed nano-ripple formations on the silicon surface after GCIB bombardment. The wavelength, amplitude and the dimensions of the ripples were studied in an effort to characterize the morphology as a function of angle of incidence, crystallographic orientations of the substrate, and the ion dosages. The underlying physics of ripple formation will be discussed and fabrication of nanorods on rippled (111)-Si substrates using III-nitrides, such as GaN, InGaN, and InAlN, will be presented. [Preview Abstract] |
Tuesday, March 6, 2007 2:42PM - 2:54PM |
L41.00002: Studies of Ripple Formation on Si Surfaces During Ar$^{+}$ Ion Bombardment Gozde Ozaydin, Karl F. Ludwig, Hua Zhou, Randall L. Headrick A study of formation of ripples on Si surfaces during bombardment with Ar$^{+}$ ions is reported. Real-time grazing incidence small-angle x-ray scattering (GISAXS) measurements are performed at the National Synchrotron Light Source. Si (100) samples are bombarded by Ar$^{+}$ ions from a PHI sputter gun at off-normal incidence. The formation of ripple structures is monitored in real time. The effects of different ion energies and high temperatures on the formation of these ripples are studied. A separate study on the smoothening of ripples by ion bombardment at normal incidence is also performed. The real time smoothening of these ripples is monitored using GISAXS during ion bombardment of the surface at room temperature and at higher temperatures. The effects of ion energy and substrate temperature on the smoothening of ripples are discussed. [Preview Abstract] |
Tuesday, March 6, 2007 2:54PM - 3:06PM |
L41.00003: Vertical Asymmetry and the Ripple Rotation Transition in the Epitaxial Growth and Erosion on (110) Crystal Surfaces Leonardo Golubovic, Artem Levandovsky We theoretically elucidate the ripple rotation transition on Ag(110) crystal surface experimentally studied by de Mongeot and co-workers, as the transition between the Rectangular Rippled states (checker-board structures of alternating rectangular pyramids and pits). We show that the experimental diffraction patterns can be understood only by invoking the vertical growth asymmetry. Interestingly, we find that the ripple rotation transition occurs over an extended parameter range: The transition point where the qualitative change of the near in-phase patterns occurs turns out to be different from the one where the change of the out-of phase patterns occurs. In the proximity of the former transition point we find the four-lobe near in-phase diffraction pattern with the four peaks along the principal axed of the (110) surface, in accord with the experiments on Ag(110). Moreover, on the two sides of the extended ripple rotation transition, we find two novel interfacial states induced by the vertical asymmetry. [Preview Abstract] |
Tuesday, March 6, 2007 3:06PM - 3:18PM |
L41.00004: Light scattering as a technique to probe grain boundary melting Erik Thomson, John Wettlaufer, Larry Wilen Near phase equilibrium, bulk properties of polycrystalline materials are strongly influenced by an interlinked network of grain interfaces. While numerical simulations and theory have supported the idea of disorder along \textit{grain boundaries}, direct experimental access to the interface between two crystals of any material, in thermodynamic equilibrium, has been limited. The transparency, birefringency, and melting temperature of polycrystalline ice lend it to experimental probing. By scattering the collimated light of a 2.3 mW He-Ne laser off of the boundary of a hexagonal ice bi-crystal, prepared within a controlled ice growth cell, the boundary is directly explored. Reflected light intensity is measured as a function of the thermodynamic variables: temperature and impurity concentration. C-axis orientation can be determined by a systematic analysis of extinction angles for individual crystals held between cross polarizors. Assuming the index of refraction for bulk water, for any melted layer, a change in reflected signal strength of greater than 10{\%}, for a 1.5 nm melt layer, is expected. Results are compared with a recent theoretical study of impurity driven grain boundary melting [1], which found evidence for a wetted liquid layer separating individual grains within polycrystalline ice. [1] Benatov, L. and J.S. Wettlaufer, 2004. Abrupt grain boundary melting in ice. \textit{Phys. Rev. E}, 70, 061606. [Preview Abstract] |
Tuesday, March 6, 2007 3:18PM - 3:30PM |
L41.00005: Adatoms, Grain Boundaries, and Thin Film Growth Stress Edmund Webb III, Stephen Foiles, Chun-Wei Pao, David Srolovitz, Jerrold Floro Atomistic simulations will be presented revealing fundamental stress generation mechanisms during later stages of thin film growth when substrate coverage is complete and the film is thickening. Typically, films exhibit texture with grain boundaries intersecting the surface. In situ growth stress experiments reveal compressive stress generation during this stage; if growth is interrupted, experiments show a relaxation in compressive stress with a characteristic rate. An existing theory proposes that, during deposition, adatoms incorporate into grain boundaries, generating compressive stress. However, debate exists regarding this mechanism and data observed in growth interrupt experiments. Simulations will demonstrate that adatoms are strongly attracted to grain boundaries and readily incorporate into them. Furthermore, adatom incorporation generates compressive stress in accord with experiments. A model is presented establishing a quantitative link between adatom incorporation into grain boundaries and the resultant stress generated. [Preview Abstract] |
Tuesday, March 6, 2007 3:30PM - 3:42PM |
L41.00006: Grain-boundary grooving and agglomeration of alloy thin films: phase-field simulations Mathieu Bouville, Dongzhi Chi, David J. Srolovitz A common failure mode in polycrystalline thin films is grain- boundary grooving through the thickness of the film. This can bring the surface in contact with the substrate, leading to film agglomeration. Although grain-boundary grooving has received a great deal of attention over the past half-century, the extant models are too idealized to be useful to predict agglomeration in most technologically interesting materials, such as multicomponent alloy films. We relax many of the assumptions made in the classical analysis, thereby finding unprecedented richness in the problem. Our approach employs a phase-field model for grain-boundary grooving and agglomeration of polycrystalline alloy thin films. In particular, we study the effects of slow-diffusing species on grooving rate. As the groove grows, the slow species becomes concentrated near the groove tip so that further grooving is limited by the rate at which it diffuses away from the tip. At early times the dominant diffusion path is along the boundary, while at late times it is parallel to the substrate. This change in path strongly affects the time- dependence of grain boundary grooving and increases the time to agglomeration. The present model provides a tool for agglomeration-resistant thin film alloy design. [Preview Abstract] |
Tuesday, March 6, 2007 3:42PM - 3:54PM |
L41.00007: Enhanced growth instability of strained film on curved substrate Yu Zhang, Hangyao Wang, Feng Liu We report linear stability analysis of a strained film on a curved surface. We show that the growth of a strained film is inherently less stable on a curved substrate than on a flat substrate. For small surface undulation, the lowest strain energy stat4e is for the film surface to adopt the same wavelength as the substrate surface in an anti-phase configuration. Our analysis provides some qualitative understanding of directed self-assembly of quantum dots on patterned substrates. [Preview Abstract] |
Tuesday, March 6, 2007 3:54PM - 4:06PM |
L41.00008: Si-Ge Intermixing and the 5x5-(111) Surface Reconstruction Demetra Psiachos, M. J. Stott We present \textit{ab initio} results of the energetics and structure of a Si(111)-5x5 slab with two bilayers of Ge(5x5) adsorbed on it. We explore the aspects of this Si-Ge surface structure with those of an analogous pure Ge(111)-5x5 slab and we note many important differences such as the larger corrugation of the adatom heights in the former compared with the latter. \textit{Ab initio} results are also obtained for the effects of Si-Ge intermixing at the Si-Ge interface. These shed light on this transport mechanism as a way of lowering the strain. [Preview Abstract] |
Tuesday, March 6, 2007 4:06PM - 4:18PM |
L41.00009: Ti as an Interface Stabilizer for Fe/Al and Al/Fe Interfaces W. Priyantha, A. Comouth, A. Kayani, H. Chen, M. Kopczyk, R.J. Smith, D. McCready The use of ultra-thin metal interlayers to stabilize metal-metal interfaces and to limit interdiffusion has drawn much attention over the past few years, driven by a variety of technological applications. Earlier we reported that using a Ti monolayer as an interlayer stopped diffusion at the Fe/Al(001) interface. These findings encouraged us to explore the use of interlayer structures for thin films of technological interest deposited on Si wafers at room temperature using RF sputtering. AlFe and FeAl metal layers, with and without a Ti stabilizing interlayer, were studied using Rutherford backscattering (RBS) and X-ray reflectivity (XRR). Analysis revealed that FeAl and AlFe films without a Ti interlayer on SiO2/Si wafers showed considerable Fe-Al intermixing, especially when the Fe layer was deposited on top of the Al layer. With a Ti interlayer present at the interface both AlFe and FeAl interfaces exhibited less interdiffusion. [Preview Abstract] |
Tuesday, March 6, 2007 4:18PM - 4:30PM |
L41.00010: Impurity Segregation at the Si/SiO$_{2}$ Interface A. G. Marinopoulos, K. van Benthem, S. Rashkeev, S. J. Pennycook, S. T. Pantelides It is a widely known fact that impurities tend to segregate at interfaces between two materials. Here we report first-principles density-functional calculations and Z-contrast scanning transmission electron microscopy and demonstrate that impurities may either segregate or avoid the Si-SiO$_{2}$ interface, depending on their chemical identity and which side of the interface they originate from. Segregation mechanisms can be very different depending on the chemical nature of the impurity. In particular, we show that in the ``alternate dielectric'' Si-SiO$_{2}$-HfO$_{2}$ structure, which is highly promising for cutting-edge Si-based metal-oxide-semiconductor FET, individual Hf atoms, which enter the SiO$_{2}$ interlayer during high-temperature annealing, avoid the interface: both Z-contrast imaging and theory find that individual Hf atoms stay away from the nominal interface by about 2.5 to 3 {\AA}. In contrast, theory finds that Hf as a substitutional impurity in Si can reach the interface and in fact segregates in a single plane at substitutional sites at the nominal interface plane. This behavior is in contradiction to other dopant impurities such as As or P, which segregate at the interface only in the form of substitutional dimers in which the impurities achieve threefold coordination. (AFOSR/DOE in part) [Preview Abstract] |
Tuesday, March 6, 2007 4:30PM - 4:42PM |
L41.00011: Temperature Induced Modifications of SiC Interfaces studied by High Resolution Electron Energy Loss Spectroscopy J.A. Schaefer, M. Eremtchenko, J. Uhlig, A. Neumann, R. Oettking, S.I.-U. Ahmed High resolution electron energy loss spectroscopy (HREELS) is a fascinating tool for studying electronic and vibrational properties in the near surface regime. For SiC, a wide band gap semiconductor suited for several applications, the surface and interface chemical reactivity needs to be thoroughly understood. In addition to atmospheric adsorbates, C- and Si-terminated cub- and hex-SiC, changes in carrier concentration profiles and band bendings can be monitored by comparing HREELS-data with dielectric theory. There, the surface state density related to the reconstruction type and surface composition is important together with the substrate temperature. For oxygen on 6H-SiC (0001), we observed for the first time new vibrational modes linked to distinct Si-O-Si vibrations, namely its asymmetric- and symmetric stretching vibrations and wagging motion. The energy and intensity of the asymmetric stretching frequency is analogous to the initial stage oxidation of Si surfaces. [Preview Abstract] |
Tuesday, March 6, 2007 4:42PM - 4:54PM |
L41.00012: ABSTRACT HAS BEEN MOVED TO X19.00015 |
Tuesday, March 6, 2007 4:54PM - 5:06PM |
L41.00013: Measurement of Young's modulus of thin films using modal characterization. Dragoslav Grbovic, Nickolay Lavrik, Panos Datskos We present a method for experimentally measuring Young's moduli of thin films using micro-electro-mechanical systems (MEMS). Properties of thin films often differ from those in bulk material and, moreover, depend on deposition method. In this work, we describe the results of measurements of Young's modulus of titanium (Ti) thin film deposited by sputtering. We deposit Ti on microcantilever structures with specified dimensions and known material properties and then experimentally measure the frequency shifts for the first several resonant modes. Using the acquired resonant frequencies in finite element analysis, we obtain the Young's modulus of the deposited Ti film. Our results show that Young's modulus of Ti film deposited by sputtering varies with thickness from $\sim $60 GPa for 35 nm film to $\sim $73 GPa for 100 nm film. This approach is fast and independent of material or deposition method. It is especially valuable in determining effective Young's moduli of composite and nanostructured thin film materials with complex relationships between their composition and their properties. [Preview Abstract] |
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