Composition Graded, Epitaxial Oxide Nanostructures: Fabrication and Properties NSF NIRT Grant # Jiechao Jiang 1, Chonglin Chen 2, Amar S. Bhalla 2, Gemunu Gunaratne 3 and Efstathios I. Meletis 1 1 University of Texas at Arlington, Arlington, Texas; 2 University of Texas at San Antonio, San Antonio, Texas; 3 University of Houston, Houston, Texas U H Perovskite oxides are of enormous fundamental interest and technological importance due to their intriguing properties. These properties can be tailored for a wide range of applications in magnetic, magneto-electronic, photonic, and spintronic technology. Graded structures with a high perpendicular anisotropy arising from composition and structure variation, either continuously or discretely (composite, modulated layers): produce coexistence of different cross coupled properties with the expectation to produce new materials; have a “product” property that is not available in the individual component phases providing an additional degree of freedom in the design of nanodevices; yield new fundamental knowledge on self-organization of 1-D, epitaxial, oxide nanostructures with graded composition; open up various new possibilities of designing new multiferroic (having ferroelastic, magnetic, electric properties) nanoscale structures with unusual cross coupled properties. Ferroelectric, compositionally gradient thin films have been shown to tremendously enhance piezoelectric response due to the build-in strain gradient. The coexistence of different properties that can be coupled in nanocomposite thin films has stimulated much scientific and technological interest since the coupling can provide new property tenability. Challenges exist in extending these compositional variations from thin films to nanopillars since the fabrication of compositionally graded and modulated composite nanopillars by self-organization has not yet been attempted. OBJECTIVES BACKGROUND (I) Nano Patterns in Structurally Gradient Epitaxial La 0.5 Ba 0.5 CoO 3 Films Fabricate and investigate the principles of formation of Nano Patterned Structures in Structurally Gradient Epitaxial La 0.5 Ba 0.5 CoO 3 Films Fabricate and study the formation mechanism of Nano-finger Structures in Epitaxial Mn-doped Ba(Zr,Ti)O 3 Thin Films Fabriacte and study the properties of interface engineered ferroelectric BaTiO 3 //SrTiO 3 heterostructures on Si (001) Theoretically identify relationships between characteristics of nanostructures and materials properties The specifications and long term vision have been discussed with the project team members during the kickoff meeting (Oct. 1st, 2007, UTA). These specifications were updated during the 2 nd (05/26/08, UTSA), 3 rd (10/16/2008, UH), 4 th (11/6/09, UTA) and 5 th (5/4/10, UTA) project meeting according to the project feedback mechanism. Fig. 11 (a) Piezo response 2×2  m phase profile of as-deposited 20%BaZrO 3 -80%BaTiO 3 film, locations with black color are in phase with preset phase (b) ±5V DC bias sweep showing typical hysteresis for piezoelectric materials and an approximately 180  phase change that saturated at ~4V DC electric field. (III) Nano Physical Property Measurements of Epitaxial Ba(Zr,Ti)O 3 Thin Films. As a continuation and extension of the project regarding film property, nano physical property measurements have been setup to systematically study the nano dielectric and piezoelectric properties. Figure 11 is the Scanning Piezoelectric Microscopy (SPM) imaging and the hysteresis loop measured from a highly epitaxial Ba(Zr,Ti)O 3 thin films on MgO with SrRuO 3 bottom electrode fabricated by using pulsed laser ablation. The BZT film has very uniform phase (same phase) and the film is somewhat the domain clamped at the interface. The nature and the strain effect from the interface is under investigation and will be reported soon. (V) Theory and Modeling of Self-assembling of Nanostructured Films A technique to control the deposition using a mask placed a finite distance above the substrate is introduced. The mask is required to have symmetries depending on those of the self-assembled array: if the self-assembled array is square, the mask consists of two sets of stripes oriented normal to each other. The width of the stripes and the inter-stripe distance depends on the diffusion coefficient of the deposit atoms on the substrate. Large- scale perfect arrays can be created in (1) an isotropic model of monolayer self-assembly, and (2) an anisotropic model of quantum dot formation. A patent has been applied for this technique. A statistical mechanical model of H-absorption in graphene is introduced. The basic model for energy was derived using previously published results on the energies for absorbing H-atoms on graphene. We showed that these energies were consistent with a Ising-type model, and constructed a continuum model consistent with this discrete case. We computed the phase portrait for this problem, which agrees with several experimental observations. Education and Outreach UTA MSE sponsors ASM International Materials Science Camp every year. This camp is designed for middle and high school students and exposes them to the world of Materials Science and Engineering. Fig Summer ASM International Materials Science Camp on UTA campus demonstrates surface structure of the legs of insects. Fig. 5 Part of this project highlighted on the cover of Chemistry of Materials (bottom right). Fig. 4 (a) T-dependent magnetization of LBCO films at the fields of 0 and 500 Oe and magnetic- filed dependent magnetization at different T (inset). (b) T-dependent electrical resistance in the magnetic fields of 0, 3 and 7 T (inset: magnetic-field-dependent MR behavior at different T). Fig. 2 (a) X-TEM of LBCO/STO; (b) SAED from LBCO/ STO interface; (c) X-HRTEM of LBCO/STO showing 2 layered structure of the film (inset: FT of LBCO-2 layer). Fig. 3(a) plan-view HRTEM image showing nano patterns (inset: SAED); (b) X- (c) plan-view HRTEM of a boundary; (d) illustration of the boundary viewed along (001]LBCO; (e) and (f) illustration of the boundary formed at the (La,Ba)O and CoO 2 layers, respectively. (III) Interface Engineered Ferroelectric BaTiO 3 //SrTiO 3 Heterostructures on Si (001) Fig. 18 (a) Piezo response 2×2  m phase profile of as-deposited 20%BaZrO 3 -80%BaTiO 3 film, locations with black color are in phase with preset phase (b) ±5V DC bias sweep showing typical hysteresis for piezoelectric materials and an approximately 180  phase change that saturated at ~4V DC electric field. (IV) Nano Physical Property Measurements of Epitaxial Ba(Zr,Ti)O 3 Thin Films As a continuation and extension of the project regarding film property, nano physical property measurements have been setup to systematically study the nano dielectric and piezoelectric properties. Figure 11 is the Scanning Piezoelectric Microscopy (SPM) imaging and the hysteresis loop measured from a highly epitaxial Ba(Zr,Ti)O 3 thin films on MgO with SrRuO 3 bottom electrode fabricated by using pulsed laser ablation. The BZT film has very uniform phase (same phase) and the film is somewhat the domain clamped at the interface. The nature and the strain effect from the interface is under investigation and will be reported soon. Ferroelectric BaTiO 3 //SrTiO 3 multilayered thin films with clear interface structures were successfully fabricated on the Si (100). A new piezoelectric phenomenon that the clamped polarization domains can be adjusted by the periodicity numbers were observed, which can be used to design and fabricate the new concept device. Fig. 13 XRD of the BTO/STO multilayered thin films grown on Si (100). Fig. 14 XTEM of the BTO/STO multilayer films show clear multilayered interface structures and nanopillar structures. Fig. 15 The P-V hysteresis loops showing (a) unusual hysteresis loops indicating existence of the clamped polarization domains, (b) circular loop and almost the same spontaneous polarization after reversing the voltage leads, (c) normal hysteresis loops with very small spontaneous and remnant polarization after taking both electrode leads on the top of multilayered thin films verifying the existing of the clamped polarization domains, (d)the difference of using three measurement methods. Fig. 16 P-V hysteresis loops as a function of driven voltages up to 19.5V, indicating that the multilayered film is very hard to breakdown. Fig. 17. P-V hysteresis loops of the films at 9V showing the increase of the spontaneous and clamped polarization intensities with the periodicity numbers (II) Nano-finger Structures in Epitaxial Mn-doped Ba(Zr,Ti)O 3 Thin Films Fig. 11 HRTEM showing epitaxial grain and twin-coupled domain joined on (110) and (111) planes Fig. 10 Illustration of the epilayer joins a twin domain by sharing (110) plane. Fig. 12 Atomic structure of the Mn:BZT (110) twin boundary common plane Fig. 9 Illustration showing reduction of the epitaxial grain size by forming alternating twin boundaries along the (110) and (111). Fig. 12 Atomic structure of the Mn:BZT (110) twin boundary common plane Fig. 6 θ-2θ XRD of a Mn:BZT film on MgO (001) substrate and an AFM image (inset). Fig. 7 (a) XTEM image of Mn:BZT/MgO sample viewed along [100] MgO ; (b) and (c) SAED from the top layer of the film and the interfacial area, respectively; (d) XTEM image of Mn:BZT/MgO viewed along [110]MgO. Fig. 8 (a) Plan-view TEM image of the nanofinger layer at the top surface and SAED (inset); (b) and (c) dark filed image of the (110) and (1-10), respectively; (d) plan-view TEM image of the bottom layer of the Mn:BZT film near the interface.