SummaryPartially wetting water droplets with sizes smaller than the capillary length acquire a distinct spherical cap shape controlled by the equilibrium contact angle, which is specific for different substrates and conditions. Images of such droplets in an environmental scanning electron microscope (ESEM) show strong topographic contrast. This contrast across the droplets can be analysed within a simple theoretical model, as the droplet sides are inclined smooth surfaces. Very small droplets have ESEM intensity profiles which deviate from this topographic model. Such deviations indicate that other sources of electron signal may be important for such droplets, and also demonstrate the limits of the analytical model. For droplets sufficiently large that they lie within the range of the topographic contrast model, values of contact angles on different substrates can be deduced. These are found to agree with independent direct measurements, as well as the results given in the literature. The possibilities of using this technique to analyse physical properties of different substrates are discussed.
Epitaxial films may be released from growth substrates and transferred to structurally and chemically incompatible substrates, but epitaxial films of transition metal perovskite oxides have not been transferred to electroactive substrates for voltage control of their myriad functional properties. Here we demonstrate good strain transmission at the incoherent interface between a strain-released film of epitaxially grown ferromagnetic La 0.7 Sr 0.3 MnO 3 and an electroactive substrate of ferroelectric 0.68Pb(Mg 1/3 Nb 2/3)O 3-0.32PbTiO 3 in a different crystallographic orientation. Our strain-mediated magnetoelectric coupling compares well with respect to epitaxial heterostructures, where the epitaxy responsible for strong coupling can degrade film magnetization via strain and dislocations. Moreover, the electrical switching of magnetic anisotropy is repeatable and non-volatile. High-resolution magnetic vector maps reveal that micromagnetic behaviour is governed by electrically controlled strain and cracks in the film. Our demonstration should inspire others to control the physical/ chemical properties in strain-released epitaxial oxide films by using electroactive substrates to impart strain via non-epitaxial interfaces.
pling α and the inverse of the total capacitance of the resonator [22]. Recently, single-shot readout of the singlettriplet states in a double QD has been demonstrated with gate-based sensors, using a variety of resonator parameters to achieve a range of readout fidelities (for a given integration time): 73% (2.6 ms) [23], 82.9% (300 µs) [24], 98% (6 µs) [25] to 99% (1 ms; using ancillary 'sensor' QD and reservoir) [26].Amplifiers based on Josephson junctions have greatly improved signal-to-noise ratios (SNRs) in the field of superconducting circuits [27-32] -they typically operate at frequencies of several GHz and near the quantum limit of noise introduced by the amplifier (or indeed below, for a single quadrature using squeezing) [33][34][35][36][37][38]. Adopting such approaches in the measurement of QDs at RF/microwave frequencies is expected to lead to corresponding improvements in SNR. While this can in principle be achieved at operating frequencies of 4-8 GHz that are typical for Josephson-junction based amplifiers, as demonstrated using an InAs double QD, Josephson parametric amplifier (JPA) and coplanar waveguide resonator [39], lower frequency operation ( 1 GHz) becomes necessary [40] for studying lower QD tunneling rates, at which exchange interaction is more easily controlled, and for enabling off-chip resonator fabrication. Suitable amplifiers are available in such a frequency range, for example: a JPA operating at 600 MHz with a noise temperature of T JPA = 105 mK [41] or a SQUID amplifier chain with T SQUID = 52 mK at 538 MHz [42]. Building on such developments, readout of a GaAs based arXiv:1907.09429v2 [cond-mat.mes-hall]
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