A novel scanning probe microscopy technique has allowed dielectrophoretic force imaging with nanoscale spatial resolution. Dielectrophoresis (DEP) traditionally describes the mobility of polarizable particles in inhomogeneous alternating current (ac) electric fields. Integrating DEP with atomic force microscopy allows for noncontact imaging with the image contrast related to the local electric polarizability. By tuning the ac frequency, dielectric spectroscopy can be performed at solid/liquid interfaces with high spatial resolution. In studies of cells, the frequency-dependent dielectrophoretic force is sensitive to biologically relevant electrical properties, including local membrane capacitance and ion mobility. Consequently, dielectrophoretic force microscopy is well suited for in vitro noncontact scanning probe microscopy of biological systems.

A compact tandem mass spectrometer containing two quadrupole mass analyzers (Q), two octapole ion guides (o) and a static quadrupole ion beam-bending lens (q) (QoqoQ configuration) has been built for the study of ion/surface collisions. Positive or negative ions are generated by either electron impact ionization or chemical ionization, selected by mass-to-charge ratio using the first quadrupole mass analyzer, guided by the first octapole ion guide, bent by a static quadrupole lens through 90°, and then focused onto a surface at an angle of 45° with reference to the surface normal. The secondary ions generated from collisions with the target surface are collected at an emergent angle of 45°, guided by the second octapole ion guide, mass-analyzed by the second quadrupole mass analyzer, and finally detected. The collision energy can be varied from 0 to 500 eV. The primary ions can also be made to pass straight through the quadrupole bending lens and then examined by an electron multiplier prior to surface collisions. The surface can be introduced into the ion/surface collision region without venting the main chamber. The capabilities of the QoqoQ instrument are demonstrated by a variety of ion/surface collisional processes in the 10s of eV laboratory translational energy range. These include surface-induced dissociation, charge permutation, surface analysis via chemical sputtering, and selective surface modification via ion/surface reactions.