Hl Xin

Effect of biaxial strain on the electrical and magnetic properties of (001) La0.7Sr0.3MnO3 thin films

We have studied the effect of biaxial strain on thin films of (001) La0.7Sr0.3MnO3. We deposited films by reactive molecular-beam epitaxy on different single crystalline substrates, varying the substrate-induced biaxial strain from −2.3% to +3.2%. Magnetization and electrical transport measurements reveal that the dependence of the Curie temperature on biaxial strain is in very good agreement with the theoretical predictions of Millis et al. [J. Appl. Phys. 83, 1588 (1998)].

Atomic-resolution spectroscopic imaging of oxide interfaces

Perovskite oxides show a rich variety of electronic phases in bulk. The prospect of combining these phases at the atomic scale has fueled the interest in oxide heterostructures. The existence of interfaces can, however, greatly affect the macroscopic properties of these structures, leading on the one hand to exotic new phases stabilized at the interface or on the other hand to the degradation of bulk-like properties. With recent advances in electron microscopy the composition and bonding at such buried interfaces can now be imaged with atomic resolution. The bonding information is obtained from the near-edge fine-structure of core-level electron energy loss spectra. Here, we discuss the near-edge fine-structure focusing on the O-K and transition metal L 2,3 edges which are of particular importance for the family of perovskite oxides. Spectroscopic imaging of a vanadate/titanate heterostructure demonstrates the capability of the technique to characterize atomic-scale interdiffusion at interfaces. Resolution limits in spectroscopic imaging due to inelastic delocalization effects are discussed.

Analytical electron microscopy of black carbon and microaggregated mineral matter in Amazonian dark Earth.

Black carbon (BC) is one of the most stable forms of soil organic matter. Its surface functional groups and structure have been well characterized by a range of analytical methods. However, little is known about the mechanisms of interactions between the BC particles and the surrounding mineral matter. In this paper a range of microscopy techniques, such as transmission electron microscopy and scanning transmission electron microscopy, were used to investigate the possible reactions of BC particles within microaggregates (<2 mm) found in Amazonian dark Earth. Attention is given to the interactions that occur at the interfacial regions between the organic and inorganic phases. Examination of Amazonian dark Earth showed that the carbon‐rich phase detected within the BC particles has a significant calcium concentration and a high density of micropores was found at the BC–mineral interface. These observations provide evidence to support suggested mechanisms of interaction between these phases.

One Million EEL Spectra Acquisition with Aberration-Corrected STEM: 2-D Chemical Investigation of a Statistically Significant Ensemble of Nanocatalysts

Aberration-corrected scanning transmission electron microscopes (STEM) can achieve high probing currents while maintaining an Ångstrom-scale probe for analytical mapping. If aided by another correcting module for improved coupling of the inelastic signal into an electron energy loss spectrometer, the collection efficiency on a thin specimen can be well over 90%. This large usable current allows an electron energy loss spectrum (EELS) with identifiable compositional and bonding information to be recorded in just a few tens of milliseconds and a 64x64-pixel spectroscopic map to be acquired in just a few minutes or less. Using an EELS-optimized system, a 100KeV Nion UltraSTEM, enabled us to collect more than one million EEL spectra providing chemical maps of hundreds of Pt-Co core-shell structured nanocatalysts before and after fuel cell operations. The unprecedented quantity of data allows us to draw statistically significant conclusions about the chemical microstructure and correlations among microscopic degrees of freedom. We show for example, the preferential segregation of a single atomic layer Pt skin on the {111} facets of annealed Pt-Co nanoparticles. However, the complexity of the large and spatially-correlated data sets poses challenges in collection, analysis and presentation. We discuss new and borrowed strategies for elegantly condensing information and providing new opportunities to chemically explore an ensemble of heterogeneous nanomaterials at atomic resolution.

Measurements of Porous Networks in Low-k Dielectric by Three-dimensional Electron Tomography

The size, distribution and connectivity of the pore network in a porous dielectric determine the electrical and mechanical properties of the overall thin film. The dielectric constant ue0c0 of the material is typically determined by electrical measurements of capacitive devices, but only indirect measurement methods have been applied to determine bulk physical pore parameters [1]. It is challenging to determine the microscopic parameters of the network as pore sizes approach atomic dimensions, because assumptions based on bulk properties for continuous media are not valid at these length scales. Therefore, a direct determination of the three-dimensional microscopic porous structure is needed to test the properties of low-ue0c0 dielectrics designed for nanometer-scale integrated circuits.

Removing Elastic Scattering Effects from Chemical Maps Taken under Incoherent Conditions

1. Monash Centre for Electron Microscopy, Monash University, Victoria 3800, Australia 2. CEMES-CNRS, Universite ́ de Toulouse, nMat Group, BP94347, 31055, Toulouse Cedex 4, France 3. Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York 11973, USA 4. Department of Materials Science and Engineering, Cornell University, Ithaca, New York 14853, USA 5. School of Applied and Engineering Physics, Cornell University, Ithaca, New York 14853, USA 6. Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons, Peter Gruenberg Institute, Forschungszentrum Juelich, Juelich 52425, Germany

3-D Tracking and Visualization of Hundreds of Fuel Cell Nanocatalysts During Electrochemical Aging

Extended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.