Observation of Analyte-Induced Deflections for Uncoated Microcantilevers using the Focused Ion Beam Procedure

It has been found that structural modifications, involving the creation of submicron scale grooves on uncoated silicon nitride microcantilevers, allow microcantilevers to display analyte-induced deflections which have not been previously observed. The submicron grooves were created through the use of a focused ion beam procedure to mill deep and narrow grooves without the subsequent deposition of a chemically reactive coating. These modifications significantly increase (by approximately 400%) an uncoated microcantilever’s ability detect analytes such as water vapor, ethyl alcohol, acetone vapor, argon, and 1-mononitrotoluene. The intention of the experiment was to achieve greater microcantilever deflections by increasing an uncoated microcantilever’s surface energy and surface area through the least amount of surface modifications. Accordingly, one to three grooves with a depth greater than the thickness of the microcantilevers were achieved by milling the grooves at a maximum angle of 45 degrees. One microcantilever, with a 100 nm wide groove (milled at an angle of 45 degrees relative to the surface normal and to a depth of 1.3 micrometers) deflected by 400 nm in the presence of an argon-ethanol mixture. The same microcantilever also exhibited a deflection magnitude which increased with gas concentration. When comparing the set of milled microcantilevers used in this experiment, deflections were found to increase as the width of the grooves decreased and the depth and number of grooves increased.