Structures for lossless ion manipulations
Structures for lossless ion manipulations (SLIM) are a form of ion optics to which various radio frequency and dc electric potentials can be applied and used to enable a broad range of ion manipulations, such as separations based upon ion mobility spectrometry, reactions (unimolecular, ion-molecule, and ion-ion), and storage (i.e. ion trapping). SLIM was developed by Richard D. Smith and coworkers at PNNL and are generally fabricated from arrays of electrodes on evenly spaced planar surfaces. In SLIM, ions move in the space between the two surfaces, in directions controlled using electric fields , and also moved between different of multi-level SLIM, as can be constructed from a stack of PCBs. The lossless nature of SLIM is derived from the use of rf electric fields, and particularly the pseudo potential derived from the inhomogeneous electric fields resulting from rf of appropriate frequency applied to multiple adjacent electrodes, and that serves to prevent ions from closely approaching the electrodes and surface where loss would conventionally be expected. SLIM are generally used in conjunction with mass spectrometry for analytical applications. Construction. The first SLIM were fabricated using printed circuit board technology (PCB), and used to  demonstrate a range of simple ion manipulations in gases at low pressures (a few torr). This SLIM technology has conceptual similarities with integrated electronic circuits, but instead of moving electrons we use electric fields to create pathways, switches, etc. to manipulate ions in the gas phase. SLIM devices can enable complex sequences of ion separations, transfers and trapping to occur in the space between two surfaces positioned (e.g., ~4 mm apart) and each patterned with conductive electrodes. The SLIM devices use the inhomogeneous electric fields created by arrays of closely spaced electrodes to which readily generated peak-to-peak RF  voltages (e.g., Vp-p ~ 100 V; ~ 1 MHz) are applied with opposite polarity on adjacent electrodes to create effective potential fields that prevent ions from approaching the surfaces. The confinement functions over a range of pressures (<0.1 torr to ~50 torr), and over an adjustable mass-to-charge ratio ("m/z") range (e.g., "m/z" 200 to >2000). This effective potential works in conjunction with DC potentials applied to side electrodes to prevent ion losses, and allows creating ion traps and conduits in the gap between the two surfaces for the effectively lossless storage and movement  of ions as a result of any gradient in the applied DC fields. The operating pressure for SLIM devices has initially been reported to be in the 1-10 torr range, and a range well suited for applications of ion mobility separations.