A rapid, nondestructive, and accurate method for determining the normal spring constants of scanning probe microscopy cantilevers is presented. Spring constants are determined using a commercial combination atomic force microscope and nanoindentation apparatus configured with a W-indenter tip geometrically configured into either a scanning tunneling microscope pointed tip or chisel shape that may be placed onto the cantilever of interest with high accuracy. A load is applied to the cantilever tip and the corresponding displacement is measured. From the force–displacement curve, the spring constant is determined. For cantilevers with spring constants greater than 1 N/m, the derived spring constants are believed to be accurate to within ±10%, with better accuracy for stiffer levers. This method has been used to measure the stiffness of cantilevers from several manufacturers.

The force constants of a variety of atomic force microscope (AFM) levers were measured using a nanoindentation apparatus attached to an AFM. This method is both non-destructive and precise, with uncertainties in the measurement being less than 10%. The levers from ThermoMicroscopes ® , Nanosensors ® , and NT-MDT were characterized. The results indicate that force constants generally fall within the manufacturers' broad specifications, but that variations are large even for nominally identical levers from the same wafer. This variation suggests that variations in the mechanical properties and/or thickness across the lever are large and have a length scale of the order of a few millimeters. It is also evident that the variation in force constants is considerably larger for short levers than for long levers.

We present evidence suggesting that Ihas and Sanders' intermediate mobility exotic negative ions can nucleate quantised vortex rings in superfluid 4He when subjected to strong enough electric fields.Several years ago, Doake and Gribbon discovered [1] that there can exist in He II a fast ion which, unlike the normal negative ion [2], may be accelerated to the Landau critical velocity v L for roton creation without undergoing metamorphosis to a charged vortex ring, even under the saturated vapour pressure. Although Doake and Gribbon were unable to ascertain the physical conditions needed to generate this mysterious entity reproducibly, Ihas and Sanders showed [3,4] soon afterwards that the vital factor apparently lay in the provision of an electrical discharge in the vapour above the surface of the liquid. The latter authors also discovered that the glow discharge source produces not only the normal and fast negative ions, but also (astonishingly) a large number of other types of negative ion with low-field mobilities lying intermediate between those of the fast and normal ions.The existence of this unexpected plethora of exotic negative charge carriers in He II constitutes an intriguing and still unsolved theoretical problem. Although the structure of the normal negative ion is understood in considerable detail [2] the nature(s) of the fast *

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Low-energy electron diffraction (LEED) measurements have detected seven solid phases for monolayer ethylene on graphite. Electron-beam induced effects (which presumably include decomposition and/or polymerization of the adsorbed ethylene) were minimized by exposing the adsorbed layer to the nanoamp beam for <100 s per crystal; data were obtained from four different crystals. We concentrate here on the phase transitions from the molecular-axisorientationally disordered low density (DLD) phase to the newly discovered commensurate molecular-axis-disordered low density (CDLD) phase and on the melting of the CDLD phase. The change in the principle q vector in the DLD-CDLD phase transition is presented for several different coverages. These data indicate an interesting incommensurate–commensurate (IC–C) transition which has not been suspected from previous studies. This transition preempts the melting transition: as a consequence we can rule out the possibility of a continuous melting transition as suggested by earlier heat capacity and neutron scattering experiments. In addition, LEED images of the fluid phase produced by melting of the CDLD phase are presented which show a modulated-ring-type structure.