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Compact metal probes: A solution for atomic force microscopy based tip-enhanced Raman spectroscopy Rev. Sci. Instrum. 83, 123708 (2012) Note: Radiofrequency scanning probe microscopy using vertically oriented cantilevers Rev. Sci. Instrum. 83, 126103 (2012) Switching spectroscopic measurement of surface potentials on ferroelectric surfaces via an open-loop Kelvin probe force microscopy method Appl. Phys. Lett. 101, 242906 (2012) Enhanced quality factors and force sensitivity by attaching magnetic beads to cantilevers for atomic force microscopy in liquid J. Appl. Phys. 112, 114324 (2012) Invited Review Article: High-speed flexure-guided nanopositioning: Mechanical design and control issues Rev. Sci. Instrum. 83, 121101 (2012) Additional information on Rev. Sci. Instrum. The spring constant of an atomic force microscope cantilever is often needed for quantitative measurements. The calibration method of Sader et al. [Rev. Sci. Instrum. 70, 3967 (1999)] for a rectangular cantilever requires measurement of the resonant frequency and quality factor in fluid (typically air), and knowledge of its plan view dimensions. This intrinsically uses the hydrodynamic function for a cantilever of rectangular plan view geometry. Here, we present hydrodynamic functions for a series of irregular and non-rectangular atomic force microscope cantilevers that are commonly used in practice. Cantilever geometries of arrow shape, small aspect ratio rectangular, quasi-rectangular, irregular rectangular, non-ideal trapezoidal cross sections, and V-shape are all studied. This enables the spring constants of all these cantilevers to be accurately and routinely determined through measurement of their resonant frequency and quality factor in fluid (such as air). An approximate formulation of the hydrodynamic function for microcantilevers of arbitrary geometry is also proposed. Implementation of the method and its performance in the presence of uncertainties and non-idealities is discussed, together with conversion factors for the static and dynamic spring constants of these cantilevers. These results are expected to be of particular value to the design and application of micro-and nanomechanical systems in general.

Spectroscopic and dynamical properties of the Ar,,-HCO+ ( n = 1 -13) cluster series have been explored by exciting the chromophore HCO+ in the vicinity of its Y I C-H stretch transition. Spectra were obtained by mass selecting the clusters, exposing them to tunable, pulsed IR light (0.02 cm-' bandwidth), and monitoring the fragment intensity as a function of laser frequency. The V I band of the Ar-HCO+ dimer is rotationally resolved and has a form consistent with a linear proton-bound complex. Analysis in terms of a pseudodiatomic Hamiltonian yields the following parameters: YO = 2815.063 f 0.020 cm-', B" = 0.06646 f 0.000 08 cm-',line widths indicate a lifetime of more than 250 ps for the optically prepared state. The V I vibrational bands of the larger Ar,-HCO+ clusters, while lacking resolved rotational structure, are still reasonably narrow (< 10 cm-I) and decrease in width as the cluster size increases. Excitation of the V I transition in Ar,-HCO' ( n = 2-13) results in the production of a relatively narrow range of daughter ions. Incremental Ar binding energies are extracted from the branching ratio data using a statistical model which takes into account the kinetic energy of the departing Ar atoms. The variation with cluster size of the binding energies, vibrational band shifts, and combination band spacings are argued to be evidence for Ar,?-HCO+ structures where Ar atoms form primary and secondary solvation rings about a linear Ar-HCO+ core with shell completion at n = 12. This view is consistent with simple empirical potential energy calculations.

An ion mobility mass spectrometry apparatus for investigating the photoisomerization and photodissociation of electrosprayed molecular ions in the gas phase is described. The device consists of a drift tube mobility spectrometer, with access for a laser beam that intercepts the drifting ion packet either coaxially or transversely, followed by a quadrupole mass filter. An ion gate halfway along the drift region allows the instrument to be used as a tandem ion mobility spectrometer, enabling mobility selection of ions prior to irradiation, with the photoisomer ions being separated over the second half of the drift tube. The utility of the device is illustrated with photoisomerization and photodissociation action spectra of carbocyanine molecular cations. The mobility resolution of the device for singly charged ions is typically 80 and it has a mass range of 100-440 Da, with the lower limit determined by the drive frequency for the ion funnels, and the upper limit by the quadrupole mass filter.

A combined experimental and theoretical study of the structural properties of the H 2 -HCO ϩ ion-neutral complex has been undertaken. Infrared vibrational predissociation spectra of mass selected H 2 -HCO ϩ complexes in the 2500-4200 cm Ϫ1 range display several vibrational bands, the most intense arising from excitation of the C-H and H 2 stretch vibrations. The latter exhibits resolved rotational structure, being composed of ⌺-⌺ and ⌸-⌸ subbands as expected for a parallel transition of complex with a T-shaped minimum energy geometry. The determined ground state molecular constants are in good agreement with ones obtained by ab initio calculations conducted at the QCISD͑T͒/6 -311G(2d f ,2pd) level. The complex is composed of largely undistorted H 2 and HCO ϩ subunits, has a T-shaped minimum energy geometry with an H 2 •••HCO ϩ intermolecular bondlength of approximately 1.75 Å. Broadening of the higher J lines in the P and R branches of the ⌸-⌸ subband is proposed to be due to asymmetry type doubling, the magnitude of which is consistent with the calculated barrier to H 2 internal rotation. The lower J lines in the ⌺-⌺ and ⌸-⌸ subbands have widths of 0.06 cm Ϫ1 , around three times larger than the laser bandwidth, corresponding to a decay time of Ϸ90 ps for the upper level. The absence of discernible rotational structure in the 2 band suggests that it has predissociation lifetime of less than 1 ps.