Search

We report on in situ space charge spectroscopy measurements on low-temperature [ABSTRACT FROM AUTHOR]

For measuring nanoscale displacements, air/vacuum tunnelling is the most sensitivemethod. However, the alignment mechanism is difficult to scale down for integrateddevices. Here, we present a tunnelling displacement sensor based on a squeezablemolecular bilayer, which was built from two stacked self-assembled monolayers ofmercaptohexadecanoic acid. The bilayer provides an inherent vertical alignmentbetween the tunnelling electrodes. Squeezing of the bilayer leads to an exponentialchange in the tunnel current. Nanometre displacement sensitivity was achieved. [ABSTRACT FROM AUTHOR]

Determining the scattering potential landscape for two-dimensional superlattices provides key insight into fundamental quantum electron phenomena. Theoretical and semiempirical methods have been extensively used to simulate confinement effects of the two-dimensional electron gas (2DEG) on superlattices with a single scatterer in the form of vicinal surfaces and dislocation networks or isolated structures such as quantum corrals and vacancy islands. However, the complexity of the problem increases when the building blocks (or scatterers) are heterogeneous, as in metal-organic nanoporous networks (MONNs), since additional potentials may come into play. Therefore, the parametrization of the surface potential landscape is often inaccurate, leading to incorrect scattering potentials. Here, we address this issue with a combination of scanning tunneling microscopy/spectroscopy, angle resolved photoemission spectroscopy and Kelvin probe force microscopy measurements together with electron plane-wave expansion simulations on a MONN grown on Cu(111). This experimental-theory approach, enables us to capture the 2DEG response to the intricate scattering potential landscape, and reveals systematic modeling procedures. Starting from a realistic geometry of the system, we determine the repulsive scattering potentials for both molecules and coordinated metal adatoms, the latter contradicting the established simulation framework. Moreover, we reveal local asymmetries and subtle renormalization effects of the 2DEG that relate to the interaction of the MONN and the underlying substrate. [ABSTRACT FROM AUTHOR]

First mirrors are the key element of all optical and laser diagnostics in ITER. Facing the plasma directly, the surface of the first mirrors could be sputtered by energetic particles or deposited with contaminants eroded from the first wall (tungsten and beryllium), which would result in the degradation of the reflectivity. The impurity deposits emphasize the necessity of the first mirror in situ cleaning for ITER. The mock-up first mirror system for ITER edge Thomson scattering diagnostics has been cleaned in EAST for the first time in a tokamak using radio frequency capacitively coupled plasma. The cleaning properties, namely the removal of contaminants and homogeneity of cleaning were investigated with molybdenum mirror insets (25 mm diameter) located at five positions over the mock-up plate (center to edge) on which 10 nm of aluminum oxide, used as beryllium proxy, were deposited. The cleaning efficiency was evaluated using energy dispersive x-ray spectroscopy, reflectivity measurements and x-ray photoelectron spectroscopy. Using argon or neon plasma without magnetic field in the laboratory and with a 1.7 T magnetic field in the EAST tokamak, the aluminum oxide films were homogeneously removed. The full recovery of the mirrors’ reflectivity was attained after cleaning in EAST with the magnetic field, and the cleaning efficiency was about 40 times higher than that without the magnetic field. All these results are promising for the plasma cleaning baseline scenario of ITER. [ABSTRACT FROM AUTHOR]

We studied atomic contact potential variations of Si(111)-7 x 7 by Kelvin probe force microscopy with the amplitude modulation technique at the second resonance of a silicon cantilever. Enhanced sensitivity due to the high mechanical quality factor in ultra-high vacuum enabled local contact potential difference (LCPD) measurements of individual adatoms. The contrast of the measured LCPD map became stronger by reducing the tip-sample distance, and the averaged LCPD value shifted to more negative. The short-range interaction, arising from the covalent bonding interactions, strongly affects the LCPD measurement. Theoretical calculations indicate that the amplitude modulation method has a higher sensitivity than the frequency modulation method in practical cases. The tip-sample distance dependence of LCPD was investigated by numerical calculations. [ABSTRACT FROM AUTHOR]

The motion of rigid nanorods caused by the normal vibrations of a nanotip rastering a flat surface is described within an original collisional model. Provided that the friction between the nanorods and the surface is sufficiently high, the direction of motion and the orientation of the nanorods are determined by two pairs of differential equations. In the limiting case of thin nanowires, the direction of motion is precisely related to the length of the nanowire, the tip radius and the density of the scan lines. At the same time the wire oscillates perpendicularly to this direction in a characteristic wobbling motion. Similar conclusions approximately hold also when the rod thickness is not negligible (compared to its length), as shown by a comparison between numerical solutions of our model and measurements on gold nanorods manipulated on a silicon oxide surface. Our results open the path to understanding and controlling the manipulation of arbitrarily shaped nanoparticles. [ABSTRACT FROM AUTHOR]

Novel phenomena accompanying atomic-scale friction are studied on NaCl(001) by the combination of quasistatic lateral force measurements with dynamic measurements of contact resonance frequencies. For loads up to a few nN the flexural resonance is tracked by a phase-locked-loop by the use of small oscillation amplitude (50 pm). The contact resonance varies during the stick stages, which demonstrates that the dynamic measurement provides additional information about small changes of the stressed contact. Improved sensitivity is also observed across atomic-scale defects which are clearly observed in the contact frequency channel. The low lateral contact stiffness inferred from the observed torsional resonance agrees well with that deduced from the quasistatic measurements and strongly suggests that the contact is atomic-sized. [ABSTRACT FROM AUTHOR]