All-photoplastic, soft cantilever cassette probe for scanning force microscopy

Abstract

Multiple single-lever probes for scanning force microscopy arranged in a cassette design and made of a low-stiffness photoplastic material have been developed and successfully tested by imaging DNA molecules. The new concept consists of a column of a one-dimensional array of cantilevers with integrated tips, the first of which is used for imaging and the others are spares in case the first one becomes degraded. When this happens, the lever is mechanically removed from the chip so that the next spare becomes ready for scanning. The probes are fabricated of a photoplastic material, which allows simple batch fabrication and facilitates realization of specific mechanical properties for cantilevers—such as low stiffness—that are very difficult to achieve with classical silicon technology. The batch fabrication process, based on spin coating and subsequent near-ultraviolet exposure and development steps of the photoplastic SU-8, results in well-controlled and uniform mechanical properties of the probes within the same chip, as well as for different chips over a 4 in. wafer. Successful images of soft, condensed-matter samples were taken using these cassette probes, making consecutive readdressing of the same DNA molecule with two different cantilevers possible. Thus, a worn-out cantilever can be replaced by a new fresh one with only small positional adjustments and without any changes in the operating conditions. This ease of operation was provided by the cassette concept and the excellent uniformity of the mechanical cantilever characteristics.