Session W5: Thin Film Growth and Processing

Etch induced losses in high Q-value superconducting resonators

We have investigated how the microwave loss in coplanar wave-guide titanium nitride resonators fabricated on Si wafers is affected by the choice of etch method used to pattern the resonators. Three different etches has been investigated, one fluorine based reactive etch, one chlorine based reactive ion etch, and one argon ion mill. At high microwave probe powers, the two different reactive etches show low internal loss whereas the milled samples show dramatically higher loss. At single photon powers we observe that the fluorine etch resonators exhibit substantially lower loss than the chlorine etched resonators. In the single photon limit we observe loss tangents of $1\cdot 10^{-6}$ for the fluorine etched, $4\cdot 10^{-6}$ to $5.5\cdot 10^{-6}$ for the chlorine etch and $1.4\cdot 10^{-4}$ for the argon ion mill. We compare these results to numerically calculated filling factors and find that the chlorine etch Si surface has a higher loss tangent than the fluorine etched surface. We also find that re-deposition of Silicon onto the titanium nitride surfaces is the probable cause of the high loss observed for argon ion milled resonators.   

Atomic Layer Deposition Films as Diffusion Barriers for Silver Artifacts

Atomic layer deposition (ALD) was investigated as a means to create transparent oxide diffusion barrier coatings to reduce the rate of tarnishing for silver objects in museum collections. Accelerated aging by heating various thicknesses (5 to 100nm) of ALD alumina (Al$_{2}$O$_{3})$ thin films on sterling and fine silver was used to determine the effectiveness of alumina as a barrier to silver oxidation. The effect of aging temperature on the thickness of the tarnish layer (Ag$_{2}$S) created at the interface of the ALD coating and the bulk silver substrate was determined by reflectance spectroscopy and X-Ray Photoelectric Spectroscopy (XPS). Reflectance spectroscopy was an effective rapid screening tool to determine tarnishing rates and the coating's visual impact. X-Ray Photoelectric Spectroscopy (XPS), and Time of Flight Secondary Ion Mass Spectroscopy (ToF-SIMS) analysis showed a phase transformation in the Ag$_{2}$S tarnish layer at 177\r{ }C and saturation in the thickness of the silver sulfide layer, indicating possible self-passivation of the tarnish layer.   

Normal versus anomalous roughening of electrodeposited Prussian Blue layers

Electrochemically deposited Prussian Blue films on gold over silicon substrates are studied by various microscopy methods. Film surface features and roughness scaling suggest faceted anomalous roughening. However, accounting for the time increase of adsorption rate, which reduces surface diffusion lengths as the film grows, a scenario of diffusion-dominated growth (Mullins-Herring class) emerges. A significant effect of the diffusion-to-deposition ratio on the roughness scaling is found, consistently with the close packed surface morphology and formation of a film with single crystalline grains. That effect also explains the striking difference of exponents obtained from the anomalous and normal scaling interpretations.   

Continuum Description of Atomistics for Nanomechanics of Grain Boundary Embrittlement in FCC Metals

A nonlinear field projection method has been developed to study nanometer scale mechanical properties of grain boundaries in nanocrystalline FCC metals [1]. The nonlinear field projection is based on the principle of virtual work, for virtual variations of atomic positions in equilibrium through nonlocal interatomic interactions such as EAM potential interaction, to get field-projected subatomic-resolution traction distributions on various grain boundaries. The analyses show that the field projected traction produces periodic concentrated compression sites on the grain boundary, which act as crack trapping or dislocation nucleation sites. The field projection was also used to assess the nanometer scale failure processes of Cu $\Sigma 5$ and $\Sigma 9$ grain boundaries doped with Pb. It was revealed that the most significant atomic rearrangement is dislocation emission which requires local GB slip, and some Pb locks the local GB slip and in turn, embrittles the GB. Reference: [1] C.-K. Wang, et al., 2011, \textit{MRS Proceedings}, Vol. 1297, DOI: 10.1557/opl.2011.678.   

Coherent Surface X-ray Scattering: Observation of Pt (001) Step-Flow Motion

We recently [1] observed oscillations of speckle intensities from the Pt (001) surface at high temperatures (T $>$ 1620K), persisting for tens of minutes. Using a model of hex-reconstructed terraces we showed that the observed oscillations come from surface dynamics due to sublimation induced step-flow motion. Our results demonstrate the possibility that coherent surface x-ray scattering (CSXS) can be applied to monitor the real-time evolution of surfaces. Hopefully CSXS can be extended further to in-situ ``real-world'' environments. This work and the use of the Advanced Photon Source were supported by the U.S. DOE, Office of Basic Energy Sciences under Contract No. DE-AC02-06CH11357. The work at Safarik University was supported by VEGA 1/0138/10 and VVCE-0058-007.\\[4pt] [1] M.S. Pierce, et al., Appl. Phys. Lett. 99, 121910 (2011).   

Study of Electrode Surface Dynamics Using Coherent Surface X-ray Scattering

We present successful efforts to develop a new surface x-ray scattering technique that allows in-situ measurements of surface dynamics in electrochemical systems. The technique, sensitive to the microstates of the system, can measure the transient dynamics of phase relaxation from one phase to another upon changing electrochemical conditions, as well as the equilibrium dynamics of microstates even if the electrode macroscopic state appears static. We will discuss the underlying physics of surface x-ray speckle correlation spectroscopy and present our recent study of Au (100) surface in vacuum, water, and electrolytes.   

Effect of tensile misfit dislocation on diffusion of Ni adatom on Ni/Cu(111): a Molecular Dynamics study

We apply molecular dynamics and molecular static methods to calculate the effect of tensile misfit dislocation on Ni adatom diffusion for Ni/Cu(111) system and compare the results with those calculated previously for Cu adatom on the Cu/Ni(111) system [1] which has compressive dislocation. Our Ni/Cu(111) substrate model system consists of 5 layers of Ni on top of a 7-layer Cu(111) slab which after energy minimization displays an isolated misfit dislocation buried at the Cu-Ni interface, causing the Ni film to be under tensile stress. In contrast to the isotropic trajectory that emerges on a defect-free surface, in this tensile stressed system we find that presence of the defect under the surface strongly affects the adatom trajectory, introducing anisotropy in atomic diffusion similar to compressive system, but with the difference: tensile misfit dislocation enhances diffusion in the direction perpendicular to the misfit dislocation line and decreases it in the direction parallel to it, whereas compressive dislocation induces the opposite behavior. We present the calculated energy barriers for the adatom and compare them with adatom diffusion on defect -- free and on the surface containing compressive dislocation. \\[4pt] [1] M. Aminpour, O. Trushin, and T. S. Rahman, Physical Review B, 84, 035455 (2011).   

Enhancement of Ag Cluster Mobility on Ag(111) Surface by clustering with Chlorine

Chlorine is observed to accelerate the fragmentation of Ag nanostructures deposited on graphite. To understand the role of chlorine in the stability of Ag nanostructures, we have studied the formation and diffusion of Ag$_{n}$ and Ag$_{n}$Cl$_{m}$ (n= 1 to 4) clusters on Ag(111) surface, using density functional theory (DFT) with generalized gradient approximations (GGA) and the projector-augmented wave method. Our calculation shows that the formation energies and diffusion barriers of Ag$_{n}$ clusters are both lowered by clustering with chlorine when n=1, 3 and 4, indicating the enhancement of mass transport on Ag(111) surface. (AgCl)$_{n}$ clusters (n=1, 3 and 4) are good candidates for surface mass transport units. We have also studied a chloridized Ag$_{55}$ cluster and an Ag$_{55}$-Ag$_{55}$ neck structure. Chlorine is found to loosen the Ag$_{55}$ structure and weaken the binding between the Ag$_{55}$ bulbs in the neck structure.   

Growth and Characterization of Metal Oxides Layers on CVD Graphene

Thin metal oxide layers deposited on graphene can be utilized as dielectric barriers between ferromagnetic metals and graphene to help overcome conductivity mismatch between the metal and graphene. Furthermore, these layers have been shown to increase the spin relaxation time measured utilizing non local detection and spin precession measurements. However, simply depositing metal oxide layers such as aluminum oxide on graphene results in non uniform film lowering the quality of the interface barrier. This presentation will show our work growing uniform aluminum oxide layers on graphene under ultra high vacuum conditions utilizing a Ti seed layer. The surface roughness of the films was measured with atomic force microscopy with and without titanium seed layers. The results show titanium seed layers reduced the surface roughness by a factor of 4 indicating a more uniform film. In addition, X-ray photoelectron spectroscopy results will be presented to confirm the stoichiometry of the films.   

Ab-initio study on stabilized ZnO (0001) polar surface with graphene substrate

First-principles calculations have been performed on interfaces between zinc oxide (0001) surfaces and graphene layer. By modifying the initial interface configurations we have found the energetically stable interface structure. Results indicate that the unstable polar ZnO (0001) surface could be stabilized by the graphene layer. Further analyses show that the structure stabilization could be well understood by the charge transfer between the carbon atoms and oxygen atoms. This suggests that polar ZnO (0001) surfaces can be obtained in experiments by growing them on graphene substrates.