Sculpting nanoelectrodes with a transmission electron beam for electrical and geometrical characterization of nanoparticles

A method to produce metal electrodes with a gap of a few nanometers with a highly focused electron beam in a transmission electron microscope (TEM) is described. With this method the electrical and geometrical characterization of the same particle is possible. The I-V characteristics of a gold particle trapped between such electrodes showed the expected single-electron tunneling behavior, with a Coulomb gap corresponding to the geometry of the particle as observed with high-resolution TEM.     

Atomic structure of grain boundaries and surfaces in YBa2Cu3O7−δ and LaBaCaCu3O7−δ

High-resolution electron microscopy (HREM) studies of grain boundaries and fractured surfaces in both the tetragonal and orthorhombic phases of dense (>90%) YBa₂Cu₃O_7?δ and tetragonal LaBaCaCu₃O_7?δ have been conducted. Grain boundaries in polycrystalline YBa₂Cu₃O_7?δ are found to be frequently parallel to a (001) plane of one of the adjacent grains, with a structure similar to that of the (001) surface of fractured YBa₂Cu₃O_7-gd. Matching of experimental and calculated images shows that the outermost surface layer in this compound is a deformed BaO layer. Both grain boundaries and fractured surfaces in LaBaCaCu₃O_7?δ show no such tendency for preferential orientation of the interface plane. Results indicate that the low critical currents observed in sintered materials are caused by textured grain growth in combination with the atomic structure of the grain boundary plane, and the intercalation of off-stoichiometric species near the grain boundary.     

Private and public green spaces: meaningful but different settings

There is an increased demand for more dwelling space in Western countries. In the Netherlands, this is expressed as an overwhelming preference for a single-family dwelling with a garden. In contrast to these consumer preferences, governments pursue a compact-city agenda, which implies high-density and mixed-use cities. This gap between consumer preference and government policy has led many policy makers, planners and developers to design dwelling concepts for urban areas in which the private domestic garden is substituted by public green space. In this paper we investigate whether this substitution makes sense or not by comparing the meanings people attach to both concepts. Our results clearly show that unique combinations of functions and meanings are attached to the domestic garden and public green space. Key aspects of public green space are its contribution to the livability of the dwelling environment and to the experience of nature. A key feature of the domestic garden is that it is considered as an outdoor extension of the dwelling that affords casual leisure. So, public and private green spaces are not just simple substitutes for each other.     

Preparation of TEM samples for hard ceramic powders

It is challenging to prepare a good sample for high-resolution electron microscopy of polycrystalline ceramic powders containing hard particles or particles with a strong preferential cleavage. Here we demonstrate that embedding the particles in a Cu matrix in a pressed pellet allows for straightforward conventional ion milling. The method is applied to powders of Mg10Ir19B16 and Na0.5CoO2 to show its feasibility, whereby transmission electron microscopy (TEM) samples with crystalline areas thinner than 10 nm can be obtained easily.     

Applying an information transmission approach to extract valence electron information from reconstructed exit waves

The knowledge of the valence electron distribution is essential for understanding the properties of materials. However this information is difficult to obtain from HREM images because it is easily obscured by the large scattering contribution of core electrons and by the strong dynamical scattering process. In order to develop a sensitive method to extract the information of valence electrons, we have used an information transmission approach to describe the electron interaction with the object. The scattered electron wave is decomposed in a set of basic functions, which are the eigen functions of the Hamiltonian of the projected electrostatic object potential. Each basic function behaves as a communication channel that transfers the information of the object with its own transmission characteristic. By properly combining the components of the different channels, it is possible to design a scheme to extract the information of valence electron distribution from a series of exit waves. The method is described theoretically and demonstrated by means of computer simulations.     

Periodic capacity management under a lead-time performance constraint

In this paper, we study a production system that operates under a lead-time performance constraint which guarantees the completion of an order before a pre-determined lead-time with a certain probability. The demand arrival times and the service requirements for the orders are random. To reduce the capacity-related operational costs, the production system under study has the option to use flexible capacity. We focus on periodic capacity policies and model the production system as a queuing system that can change its capacity periodically and choose to operate in one of the two levels: a permanent capacity level and a permanent plus contingent capacity level. Contingent capacity is supplied if needed at the start of a period, and is available during that period, at a cost rate that is decreasing in period length in different functional forms. Next, we propose a search algorithm that finds the capacity levels and the switching point that minimizes the capacity-related costs for a given period length. The behaviour of the capacity-related costs changes drastically under different period lengths and cost structures. In our computational study, we observe that the periodic capacity flexibility can reduce the capacity-related operational costs significantly (up to 35%). However, in order to achieve these savings, the period length must be chosen carefully depending on ambition level and capacity-related costs. We also observe that the percentage savings are higher for more ambitious lead-time performance constraints. Moreover, we observe that the use of contingent capacity makes the total system costs more insensitive to the lead-time performance requirements.     

Effect of Growth-Induced Linear Defects on High Frequency Properties of Pulse-Laser Deposited YBa2Cu3O7?δ Films

Growth-induced linear defects are shown to strongly affect the microwave surface resistance, R_s, of highly biaxially oriented high temperature superconductor (HTS) YBa₂Cu₃O_7– (YBCO) films. Measured R_s(77 K) turned out to be 4–5 times higher than in single crystals. The films were deposited by modified pulse-laser technique, J_c(77 K) = (3-6) × 10⁶ A/cm², onto LaAlO₃ substrates. R_s(T) was measured at 134 GHz and 20–100 K. TEM/HREM study of YBCO films deposited at T_s = 750°C–780°C revealed a reduction of edge dislocation density with T_s increase (from 2 · 10¹¹ to 10¹⁰ lines/cm²). YBCO films deposited at T_s = 780°C exhibited the smallest R_s(77 K, 134 GHz) < 120 m and the lowest density of dislocations detected by HREM and X-ray analysis. A nature of the dislocation effect is discussed within a model of local anisotropic elastic deformation in a vicinity of dislocation cores, where T_c variation and an enhancement of normal quasiparticle density are significant.     

The optimisation of solid–liquid extraction of antioxidants from apple pomace by response surface methodology

Response surface methodology using two food grade solvents, acetone and ethanol, was used to optimise antioxidant extraction from industrially generated apple pomace. Efficiency of extraction was optimised by measuring antioxidant activity, phenol content and three individual polyphenol groups. Conditions for optimal antioxidant activity as measured by the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay were 56% ethanol, 80 °C and 31 min. Using these conditions an antioxidant value of 444 mg Trolox/100 g DW was obtained. For acetone extraction the optimal conditions were 65% acetone, 25 °C and 60 min, resulting in an antioxidant value of 436 mg Trolox/100 g DW. Both ethanol and acetone would be suitable to replace methanol for a food grade and more environmental friendly solid–liquid extraction of antioxidants.