Co-investigator Luis Velasquez-Garcia (Heller)
In recent years, there has been a desire to scale down linear quadrupoles. The key advantages of this miniaturization are the portability it enables and the reduction of pump power needed due to the relaxation on operational pressure. Attempts at making microelectromechanical systems-based linear quadrupoles met with varying degrees of success. Producing these devices involved some combination of precision machining or microfabrication and downstream assembly. For miniature quadrupole mass filters to be mass-produced cheaply and efficiently, manual assembly should be removed from the process.
A purely microfabricated quadrupole mass filter consisting of a planar design and a rectangular electrode geometry has been made. Rectangular rods were utilized since they are most amenably shaped for planar microfabrication. This deviation from the conventional round rod geometry required optimization and analysis. After we minimized unwanted effects through various simulations, we proposed a design, conceived a process flow, and fabricated the Micro-Square Electrode Quadrupole Mass Filter (MuSE-QMF). The process requires the bonding of five silicon wafers and the use of deep reactive ion etching to pattern the features. It is a relatively simple process, furthering the case for mass-production of these devices.
This non-conventional design will introduce non-linear resonances that manifest as peak splitting in the mass spectrum. Reported work involving linear quadrupoles operated in the second stability region shows improved peak shape without these splits. It is believed that operating this device in the second stability region will provide a means to overcome the nonlinear resonances introduced by the square electrode geometry. Successful implementation of this device will lead into arrayed configurations for parallel analysis and aligned quadrupoles operated in tandem for enhanced resolution.