Wafer-Scale Nanopatterning and Translation into High-Performance Piezoelectric Nanowires

The development of a facile method for fabricating one-dimensional, precisely positioned nanostructures over large areas offers exciting opportunities in fundamental research and innovative applications. Large-scale nanofabrication methods have been restricted in accessibility due to their complexity and cost. Likewise, bottom-up synthesis of nanowires has been limited in methods to assemble these structures at precisely defined locations. Nanomaterials such as PbZr_xTi_(1−x)O_3 (PZT) nanowires (NWs)—which may be useful for nonvolatile memory storage (FeRAM), nanoactuation, and nanoscale power generation—are difficult to synthesize without suffering from polycrystallinity or poor stoichiometric control. Here, we report a novel fabrication method which requires only low-resolution photolithography and electrochemical etching to generate ultrasmooth NWs over wafer scales. These nanostructures are subsequently used as patterning templates to generate PZT nanowires with the highest reported piezoelectric performance (d_(eff) ~ 145 pm/V). The combined large-scale nanopatterning with hierarchical assembly of functional nanomaterials could yield breakthroughs in areas ranging from nanodevice arrays to nanodevice powering

Magnetic and Magnetotransport Properties of La0.7ca0.3mn1-x(zn,cu)xo3

Magnetic and magnetotransport properties of two perovskite manganite samples of La0.7Ca0.3Mn0.9Zn0.1O3 and La0.7Ca0.3Mn0.95Cu0.05O3 prepared by conventional solid-state reaction have been studied in detail. Experimental results revealed that the temperature dependences of magnetization and resistance varied strongly around the phase-transition temperature. Maximum magnetoresistance (MR) values of La0.7Ca0.3Mn0.9Zn0.1O3 and La0.7Ca0.3Mn0.95Cu0.05O3 under an applied field of 400 Oe were about 21.4 % and 11.0 %, respectively. The maximum magnetic-entropy change (ΔSM) was 2.73 J/kg.K for La0.7Ca0.3Mn0.9Zn0.1O3, and 3.34 J/kg.K for La0.7Ca0.3Mn0.95Cu0.05O3 when the applied field was 45 kOe. Both the MR and ΔSM values obtained from two samples were smaller than those of the parent compound La0.7Ca0.3MnO3. This was due to the change in the Mn3+/Mn4+ ratio caused by Zn and Cu dopants, which led to a change in the type of the ferromagneticparamagnetic phase transition

Radioscience simulations in General Relativity and in alternative theories of gravity

In this communication, we focus on the possibility to test GR with radioscience experiments. We present a new software that in a first step simulates the Range/Doppler signals directly from the space time metric (thus in GR and in alternative theories of gravity). In a second step, a least-squares fit of the involved parameters is performed in GR. This software allows one to get the order of magnitude and the signature of the modifications induced by an alternative theory of gravity on radioscience signals. As examples, we present some simulations for the Cassini mission in Post-Einsteinian gravity and with the MOND External Field Effect.Comment: 4 pages; Proceedings of "Les Rencontres de Moriond 2011 - Gravitation session

Unveiling the atomic position of C in Mn5Ge3 Cx thin films

Heavily carbon-doped Mn5Ge3 is a unique compound for spintronics applications as it meets all the requirements for spin injection and detection in group-IV semiconductors. Despite the great improvement of the magnetic properties induced by C incorporation into Mn5Ge3 compounds, very little information is available on its structural properties and the genuine role played by C atoms. In this paper, we have used a combination of advanced techniques to extensively characterize the structural and magnetic properties of Mn5Ge3Cx films grown on Ge(111) by solid phase epitaxy as a function of C concentration. The increase of the Curie temperature induced by C doping up to 435 K is accompanied by a decrease of the out-of-plane c-lattice parameter. The Mn and C chemical environments and positions in the Mn5Ge3 lattice have been thoroughly investigated using x-ray absorption spectroscopy techniques (x-ray absorption near-edge structures and extended x-ray absorption fine structures) and scanning transmission electronic microscopy (STEM) combined to electron energy loss spectroscopy for the chemical analysis. The results have been systematically compared to a variety of structures that were identified as favorable in terms of formation energy by ab initio calculations. For x≤0.5, the C atoms are mainly located in the octahedral voids formed by Mn atoms, which is confirmed by simulations and seen for the first time in real space by STEM. However, the latter reveals an inhomogeneous C incorporation, which is qualitatively correlated to the broad magnetic transition temperature. A higher C concentration leads to the formation of manganese carbide clusters that we identified as Mn23C6. Interestingly, other types of defects, such as interstitial Ge atoms, vacancies of Mn, and their association into line defects have been detected. They take part in the strain relaxation process and are likely to be intimately related to the growth process. This paper provides a complete picture of the structure of Mn5Ge3Cx in thin films grown by solid phase epitaxy, which is essential for optimizing their magnetic properties

Discovering Valuable Items from Massive Data

Suppose there is a large collection of items, each with an associated cost and an inherent utility that is revealed only once we commit to selecting it. Given a budget on the cumulative cost of the selected items, how can we pick a subset of maximal value? This task generalizes several important problems such as multi-arm bandits, active search and the knapsack problem. We present an algorithm, GP-Select, which utilizes prior knowledge about similarity be- tween items, expressed as a kernel function. GP-Select uses Gaussian process prediction to balance exploration (estimating the unknown value of items) and exploitation (selecting items of high value). We extend GP-Select to be able to discover sets that simultaneously have high utility and are diverse. Our preference for diversity can be specified as an arbitrary monotone submodular function that quantifies the diminishing returns obtained when selecting similar items. Furthermore, we exploit the structure of the model updates to achieve an order of magnitude (up to 40X) speedup in our experiments without resorting to approximations. We provide strong guarantees on the performance of GP-Select and apply it to three real-world case studies of industrial relevance: (1) Refreshing a repository of prices in a Global Distribution System for the travel industry, (2) Identifying diverse, binding-affine peptides in a vaccine de- sign task and (3) Maximizing clicks in a web-scale recommender system by recommending items to users

q-Deformation of W(2,2) Lie algebra associated with quantum groups

An explicit realization of the W(2,2) Lie algebra is presented using the famous bosonic and fermionic oscillators in physics, which is then used to construct the q-deformation of this Lie algebra. Furthermore, the quantum group structures on the q-deformation of this Lie algebra are completely determined.Comment: 12 page