Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session A20: Multilayers, Thin Films, and Interfaces |
Hide Abstracts |
Sponsoring Units: DCMP Chair: Igor Roshchin, UCSD Room: LACC 407 |
Monday, March 21, 2005 8:00AM - 8:12AM |
A20.00001: Preparation and Friction Property of Dendritic Thin Film Qing Zhang, Lynden Archer To investigate the effect of film structure on their friction properties, thin films with dendritic structure were prepared on silicon surfaces by step-growth propagation, and their friction properties were studied by AFM. The molecular structure of grafted layer was adjusted by controlling the generations of grafting reaction and the concentration of functional groups on the surface. X-ray Photoelectron Spectroscopy measurements indicate systematic increased packing density of grafted dendritic layer as the generation of reaction and the functional group concentration increases. These structural variations were found to strongly influence their friction properties. The friction coefficients were found to increase with increasing the packing density of the grafted dendritic layer, and in the dynamic friction measurement (friction as a function of sliding velocity), a plateau was found for grafted layers with high packing densities. Analysis using a thermally activated model suggests that the lower mobility of molecules in densely packed films leads to longer relaxation time and higher friction coefficient compared with molecules in loosely packed layers. [Preview Abstract] |
Monday, March 21, 2005 8:12AM - 8:24AM |
A20.00002: Mechanical Properties of Electrophoretically-Deposited CdSe Nanocrystal Films Shengguo Jia, Mohammad Islam, Yuqi Xia, Ben Smith, Sarbajit Banerjee, Yikang Deng, Joze Bevk, Jeffrey Kysar, Irving Herman Approaches to measuring and then minimizing the strain in electrophoretically deposited CdSe nanocrystal films are investigated. Under some conditions, fractured films are seen for films thicker than a critical thickness of about 0.8 microns for 3.2 nm nanocrystals. Cracking and some delamination are seen by SEM and AFM, and they are attributed to high strain energy in this film. The deposition conditions are varied to minimize this strain, which is thought to be due to the evaporation of residual hexane solvent after electrophoretic deposition - which changes the equilibrium separation of the nanocrystal cores. In situ observation confirms this assumption about the origin of film strain. These CdSe nanocrystal films become mechanically stronger and more resistant to chemical dissolution after being treated by cross-linker molecules such as 1,6-hexanedithiol and 1,7-heptanediamine. [Preview Abstract] |
Monday, March 21, 2005 8:24AM - 8:36AM |
A20.00003: Growth and Characterization of Ultrathin Epitaxial Graphite films on Silicon Carbide Tianbo Li, Asmerom Ogbazghi, Xuebin Li, Zhimin Song, Claire Berger, Walt de Heer, Phillip First Ultrathin graphite films grown on 4H/6H SiC (0001) surface were investigated through Auger electron spectroscopy, LEED and STM. Graphite films, 1-6 graphene layers thick, were grown on both the Si- and C-terminated faces via thermal desorption of silicon. Film thickness was measured by modeling the Si:C Auger intensities. The $6\sqrt 3 \times 6\sqrt 3 _{ }$LEED pattern on SiC (0001) surface after annealing above 1250$^{o}$C can be explained by double-scattering theory with a $6\times 6$surface corrugation grating on both the graphite and the SiC. STM on the graphitized surface shows ``$6\times 6$'' domains typically 50 nm in size. Images indicate that the graphite films are continuous over substrate steps, but differences in the local electronic structure have been found for adjacent domains via STS. Magnetoconductance measurements on Hall bars created from these films demonstrate that the graphene/SiC system could be a promising platform for new integrated ballistic-carrier devices based on nano-patterned epitaxial graphene. [Preview Abstract] |
Monday, March 21, 2005 8:36AM - 8:48AM |
A20.00004: Transition Layers in Co Films on Cu with Oxygen as Interface Surfactant Probed by Soft-X-Ray Resonant Magnetic Scattering (SXRMS) Zhiwei Li, Eric Wiedemann, Don Savage, Max Lagally Understanding the effect of surfactants on the magnetic properties of thin films is critical to understanding such diverse phenomena as spin-dependent transport (e.g., giant magnetoresistance [GMR]) and coupling between magnetic films. Interfacial morphology in ferromagnetic [FM] materials may be characterized as a combination of chemical and magnetic boundaries. Previous work by Kelly [1] and Barnes [2], used the diffusely scattered component of SXRMS to compare the magnetic and chemical roughness of the upper interface of 70 A Co films that were either bare or Fe-capped. The chemical and magnetic upper boundaries within the Co differed in the absence of an adjoining Fe layer, due to a transition layer of spins that do not follow applied magnetic fields. Although the bottom interface contributed very little to the resultant scattering, its relative contribution could not be resolved. By performing specular SXRMS over a wide range of incident angles, we are able to determine a depth profile of the magnetization in 30A thick Co films. The 30 A Co was sputter deposited on a 100{\AA}Cu/Si substrate. The Cu is partly deposited using oxygen as surfactant. We find a difference in the thickness of the magnetic transition layer in films grown with and without oxygen. [1] J.J. Kelly IV, et al. J. Appl. Phys. v.91 pp.9978-9986 (2002). [2] B.M. Barnes, Z. Li et. al J. Appl. Phys. \textbf{95}, 6654 (2004) Funding provided by ONR. Funding for the Synchrotron Radiation Center provided by NSF under Award No. DMR-0084402 [Preview Abstract] |
Monday, March 21, 2005 8:48AM - 9:00AM |
A20.00005: The role that varying nanocrystallinity plays in the thermodynamics of CoO films Daniel Queen, Frances Hellman, Yunjun Tang Understanding the phase stability of nanocrystalline materials is a necessary step in developing a clear picture of mesoscopic physics. These materials are known to show excess specific heat at low temperatures similar to that seen in glassy and amorphous systems. The entropy associated with this excess specific heat can greatly effect the stability of these nanostructured materials. A systematic study of the thermodynamics of these systems over a wide temperature range has yet to be done. Thin films offer a novel way to explore the contributions of particle size and surface areas. We present results of heat capacity measurements on CoO thin films and CoO/MgO multilayers from 2K to 500K. Recent results show an increase in excess specific heat with decreasing particle size. Thanks to DOE for support. [Preview Abstract] |
Monday, March 21, 2005 9:00AM - 9:12AM |
A20.00006: Charge exchange of Si ions with clean and I-covered Al(100) Xiaojian Chen, Zdenek Sroubek, Jory Yarmoff Ion-surface charge exchange is a central process in many surface analysis and processing methods. Charge exchange of alkali, halogen and noble gas ions with surfaces has been investigated in previous ion scattering studies, while the interaction between a semiconductor atom and a metal surface has not been measured despite its importance. Si$^{+}$ ions were incident on an atomically clean Al (100) surface in ultra-high vacuum. The absolute ionization probability of scattered Si and recoiled Al were measured with time-of-flight, and detailed spectra of the ion yield were collected with an electrostatic analyzer. All of the scattered Si was neutralized, as expected for resonant charge transfer (RCT) of Si, which has a large ionization potential. Multi-charged recoiled Al ions were emitted, however. Surprisingly, Si scattered from iodine adatoms is partially ionized and the ionization changes little with respect to the coverage, energy and exit angle. This is in direct contrast to Li scattering from I/Fe*, and cannot be explained by RCT. * J.A. Yarmoff, Y. Yang and Z. Sroubek, Phys. Rev. Lett. \textbf{91}, 086104/1-4 (2003). [Preview Abstract] |
Monday, March 21, 2005 9:12AM - 9:24AM |
A20.00007: Momentum and thickness-dependent evolution of quantum well states in the Cu/Co/Cu(001) system M.A. Van Hove, J.M. An, A. Canning, L.-W. Wang, E. Rotenberg, Y.Z. Wu, Z.Q. Qiu Experimental advances in sample fabrication allow the observation of individual quantum well (QW) states from discrete atomic layer thicknesses. We present comprehensive angle-resolved photoemission measurements of the Fermi surface and underlying band structure of QW states in Cu/Co/Cu(001). Compared to bands from normal emission, we find a complicated evolution of QW states as a function of the thickness of both the copper overlayer and the cobalt barrier layer, as well as of the emission angle. This reveals a very high sensitivity of ``off-normal'' QW states to film thickness. Self-consistent calculations reveal a significant interaction between the QW states in the Cu overlayer and the Co barrier states, which leads to the observed complex behavior in particular ranges of energy and emission angle. [Preview Abstract] |
Monday, March 21, 2005 9:24AM - 9:36AM |
A20.00008: Finite size effects on multilayer relaxations Erik Holmstr\"om, Anders Niklasson, Nicolas Bock, Sven Rudin, John Wills We calculate the out of plane layer relaxations of thin embedded metallic films as a function of film thickness. The relaxations show an oscillating behavior that is consistent with superimposed surface-induced Friedel oscillations of the charge density of the film. Additionally there is an effect on the relaxation from the interaction between the surfaces that is analogous to the change in density of states that is induced by quantum well states. The calculations are performed by means of pseudopotential, first principles calculations in the framework of the Vienna ab initio simulation package (VASP). [Preview Abstract] |
Monday, March 21, 2005 9:36AM - 9:48AM |
A20.00009: Noise in Half-Metallic Ferromagnetic Thin Films Siddhartha Ghosh, Karl Hultquist, Subhrangshu Mallik, Guoxing Miao, Arunava Gupta Half metallic oxides are one of the most potential materials for the spintronics application, such as tunnel magnetoresistance. Among different half-metals CrO$_{2}$ is the only binary oxide that is ferromagnetic metal and shows almost 100{\%} spin polarization at the Fermi level. However, CrO$_{2}$ films have higher low frequency noise, which is an order of magnitude more than the metal film noise. This phenomenon restricts these films for applications such as integrated spin based sensor. We have measured the low frequency flicker (1/f) noise for CrO$_{2}$ film grown on TiO$_{2}$ substrate grown by CVD over different temperature and bias range. Our aim is to understand and relate the low frequency noise to grain boundaries, defects etc. Bias and temperature were varied during measurements. The noise is almost constant over the ``zero-current'' region of the current-voltage characteristics. At an elevated temperature the width of the ``zero-current'' region decreases and as a consequence the current increases for the same bias. Increase in noise level is observed with increase in sample temperature. The same increase in noise level is observed when we increase the sample volume for a particular temperature and bias. As expected the noise level is higher than in metal metal films. In our results we can clearly see the effect of the temperature and the size for the CrO$_{2}$ film. [Preview Abstract] |
Monday, March 21, 2005 9:48AM - 10:00AM |
A20.00010: Heteroepitaxial growth and electronic structure of LaVO$_{3}$ films on SrTiO$_{3}$ Yasushi Hotta, Yasushige Mukunoki, Tomofumi Susaki, Harold Y. Hwang In perovskite transition metal oxides, a relatively small variation in lattice constants allows the study of heteroepitaxial growth for a wide range of materials combinations. Recently, perovskite oxides have been extensively studied to understand their growth dynamics on an atomic scale, and to investigate their physical properties. The growth behavior of films can strongly depend on the terminating layer of the substrate surface. In this study, we investigated the growth dynamics and physical properties of heteroepitaxial LaVO$_{3}$ films grown on SrTiO$_{3}$. In particular, we found optimal growth conditions to obtain two-dimensional growth of atomically flat epitaxial LaVO$_{3}$ films. [Preview Abstract] |
Monday, March 21, 2005 10:00AM - 10:12AM |
A20.00011: Suppressed Magnetization in La$_{0.7}$Ca$_{0.3}$MnO$_3$ / YBa$_2$Cu$_3$O$_{7-\delta}$ superlattices S.G.E. te Velthuis, A. Hoffmann, Z. Sefrioui, J. Santamaria, M.R. Fitzsimmons, S. Park, M. Varela Ferromagnetic/superconducting heterostructures are the subject of intense research, as these two types of long-range order are generally mutually exclusive and give rise to a variety of proximity phenomena. There is interest in studying these effects in superlattices of high T$_{c}$ superconductors and colossal magnetoresistance oxides, where the superconducting and ferromagnetic properties are depend strongly on the charge carrier density and thus charge transfer across the interface may be important. In a series of La$_{0.7}$Ca$_{0.3}$MnO$_3 $/YBa$_2$Cu$_3$O$_{7-\delta}$ superlattices, SQUID magnetometry showed that the LCMO saturation magnetization is significantly reduced. Polarized neutron reflectometry determined that the reduced moment is due to an inhomogenous magnetization profile. Specifically, the magnetization in each LCMO layer is suppressed close to the interfaces with the YBCO, possibly due to charge transfer across the interface. [Preview Abstract] |
Monday, March 21, 2005 10:12AM - 10:24AM |
A20.00012: Microscopic magnetic structure of cuprate/manganite superlattices Jacques Chakhalian, Christian Bernhard, Jorg Strempfer, Bernhard Keimer, Jochen Stahn, Christof Niedermayer, Thomas Gutberlet, John Freeland, George Srajer, Julio Cezar Superconductivity and ferromagnetism are conventionally distinguished by mutually incompatible order parameters. However, the proximity of those materials in the artificially fabricated nanofilms of $\mathrm{YBa_2Cu_3O_7/La_{2/3}Ca_{1/3}MnO_3}$ (HTSC/FM) gives rise to new phenomena that do not exist in the isolated materials. We report on the first microscopic magnetization measurements by means of neutron reflectivity and resonant X-ray absorption. Our experimental results are consistent with the recently predicted "inverse" magnetic proximity effect. The analysis of neutron reflectivity data allows us to identify a likely magnetization profile, namely a sizable magnetic moment within the SC layer coupled antiferromagneticaly to the one in the FM layer. The scenario is supported by an anomalous superconductivity-induced enhancement of the off-specular reflection and by x-ray absorption, which testify to a strong mutual interaction of SC and FM order parameters. [Preview Abstract] |
|
A20.00013: Crystalline $\gamma$-Al$_2$O$_3$ barrier for magnetite-based Magnetic Tunnel Junctions Alexandre M. Bataille, Jean-Baptiste Moussy, Susana Gota, Marie-Jo Guittet, Martine Gautier-Soyer Magnetite Fe$_3$O$_4$ is an interesting material for spintronics because it is expected to exhibit a very high spin polarization at room temperature. In this framework, we have developed an Oxygen Plasma Assisted Molecular Beam Epitaxy setup well suited to the growth of Fe$_3$O$_4$/Al$_2$O$_3$ bilayers. We have successfully grown highly insulating, 1.5 to 2 nm-thick crystalline $\gamma$-Al$_2$O$_3$ layers free of pinholes. The Fe$_3$O$_4$ layer is unaffected by the deposition of the Al$_2$O$_3$ barrier as evidenced by thorough magnetic, chemical and structural characterizations. These breakthroughs pave the way to all-oxide Fe$_3$O$_4$/Al$_2$O$_3$/Fe$_3$O$_4$ fully epitaxial magnetic tunnel junctions. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700