Anisotropic magnetoresistances and intrinsic adiabatic transport features are generated on quantum Hall samples based on an ͑Al,Ga͒As/GaAs heterostructure with alloyed Au/Ge/Ni contacts. We succeed to probe the microscopic origin of these transport features with a cryogenic scanning force microscope by measuring the local potential distribution within the two-dimensional electron system ͑2DES͒. These local measurements reveal the presence of an incompressible strip in front of contacts with insulating properties depending on the orientation of the contact/2DES interface line relatively to the crystal axes of the heterostructure. Such an observation gives another microscopic meaning to the term "nonideal contact" used in context with the Landauer-Büttiker formalism applied to the quantum Hall effect.Few cryogenic scanning force microscopy ͑SFM͒ measurements exist on probing the electrostatic potential distribution in two-dimensional electron systems ͑2DES͒ realized in ͑Al,Ga͒As/GaAs heterostructures under quantum Hall conditions. 1,2 Those results measured over the whole 2DES demonstrated the important role of compressible and incompressible strips 3,4 for the current distribution in quantum Hall samples. Despite of these experimental findings, the edgestate picture 5 remains the widely used model to describe the magnetotransport in quantum Hall devices, also in the context of topological insulators. 6 Its success has been partly legitimated by its ability to include contact effects 7 and to explain adiabatic magnetotransport features 8 -such as the disappearance of peaks in the Shubnikov-de Haas ͑SdH͒ oscillations, the extension of quantum Hall plateaus to lower magnetic fields, and the existence of nonlocal resistances. 9 In this Rapid Communication, we manage a comparison between magnetotransport and scanning force microscopy investigations on Hall bar samples showing adiabatic transport features without the use of gates. The SFM measurements present potential distributions from which we conclude that the incompressible strip in front of alloyed contacts possesses different insulating properties depending of the orientation relatively to the crystal axes of the underlying heterostructure. This result shows how to include contacts and interpret adiabatic features in terms of compressible/incompressible strips and what is the microscopic origin of anisotropy in magnetoresistances.The samples used here are based on an ͑Al,Ga͒As/GaAs heterostructure containing the 2DES at the heterojunction interface 60 nm below the surface. The electron density and mobility at 1.3 K are 3.6ϫ 10 15 m −2 and 160 m 2 ͑V s͒ −1 , respectively. Such conditions lead to high electron mobility samples with an electron mean-free path l Ϸ 13 m, which is three times larger than in Ref. 2. Our Hall bars as depicted in Fig. 1 are defined by optical lithography and wet etching. Au/Ge/Ni film is alloyed to achieve low resistive contacts to the 2DES by following our standard recipe. 10 After annealing, the remaining 2DES has a size of about 10 m w...

Scanning tunneling spectroscopies are performed below 100 mK on polycrystalline boron-doped diamond films characterized by transmission electron microscopy and transport measurements. We demonstrate a strong correlation between the local superconductivity strength and the granular structure of the films. The study of the spectral shape, amplitude, and temperature dependence of the superconductivity gap enables us to differentiate intrinsically superconducting grains that follow the BCS model, from grains showing a different behavior involving the superconducting proximity effect. DOI: 10.1103/PhysRevB.82.033306 PACS number͑s͒: 73.22.Ϫf, 73.61.Cw, 74.45.ϩc, 74.81.Bd Over the last few years, superconductivity has been discovered in heavily doped group IV covalent semiconductors, 1 in particular, diamond 2 and silicon. 3 In the case of diamond, low-temperature superconductivity appears at the same doping level than the metallic state created by heavy boron doping. 4 Evidence for a pairing mechanism mediated by phonons in the weak-coupling limit has been provided among others by very low-temperature scanning tunneling spectroscopy of single-crystal epilayers. 5Polycrystalline diamond films can be a new model system for the general issue of the nature of superconductivity in strongly disordered metals. 6 In such systems, disorder sits either at the atomic scale, in which case electronic excitations can become localized so that superconductivity vanishes 7 or at a larger scale, for instance, that of a granular structure, in which case the two competing mechanisms are the Coulomb blockade and the superconducting proximity effect. 8,9 Nevertheless, recent studies of polycrystalline diamond films 10,11 did not provide a clear picture on the coexistence between superconductivity and disorder in these films.In this Brief Report, we report a study of the local superconducting and structural properties of high-quality polycrystalline boron-doped diamond by very low-temperature scanning tunneling microscopy ͑STM͒. The granular structure was consistently characterized by STM and transmission electron microscopy ͑TEM͒. In contrast with epitaxial films, a strong correlation is observed between the granular microstructure and the superconductivity local strength. The spatial evolution and temperature dependence of the local electronic density of states are consistent with the picture of an assembly of grains, which either follow the BCS model or present another superconducting behavior involving the superconducting proximity effect.Boron-doped polycrystalline diamond thin films of different thicknesses were grown as described elsewhere 12,13 by microwave plasma-enhanced chemical-vapor deposition from hydrogen-rich methane-trimethylborane-hydrogen gaseous mixtures on ultrasonically seeded quartz ͑sample A͒ and oxidized silicon ͑sample B͒ substrates. As shown by Figs. 1͑a͒ and 1͑b͒ displaying, respectively, a very lowtemperature STM ͑Refs. 14 and 15͒ topography of sample A and a TEM cross section in bright-field condition of sa...

The deposition of cellulose nanocrystals (CNCs) on a supported lipid bilayer (SLB) was investigated at different length scales. Quartz crystal microbalance with dissipation monitoring (QCM-D) was used to probe the bilayer formation and to show for the first time the CNC deposition onto the SLB. Specifically, classical QCM-D measurements gave estimation of the adsorbed hydrated mass and the corresponding film thickness, whereas complementary experiments using D2O as the solvent allowed the quantitative determination of the hydration of the CNC layer, showing a high hydration value. Scanning force microscopy (SFM) and total internal reflection fluorescence microscopy (TIRF) were used to probe the homogeneity of the deposited layers, revealing the structural details at the particle and film length scales, respectively, thus giving information on the effect of CNC concentration on the surface coverage. The results showed that the adsorption of CNCs on the supported lipid membrane depended on lipid composition, CNC concentration, and pH conditions, and that the binding process was governed by electrostatic interactions. Under suitable conditions, a uniform film was formed, with thickness corresponding to a CNC monolayer, which provides the basis for a relevant 2D model of a primary plant cell wall.