AlMo Nanocomposite Characterization, Device Fabrication and Biosensors

• Author / Creator

  van den Hurk, Remko V

• Nanocomposite materials are multiphase materials where at least one of the dimensions of one of the materials is less than 100 nm in size. The primary goal of nanocomposite materials development is to create material properties that are not available in traditional materials. AlMo nanocomposites can be fabricated by co-sputtering Al and Mo. A particular ratio with interesting properties is 68 atomic % Al and 32 atomic % Mo. Due to very low surface roughness and small grain size, it can be used to form ultrathin, ultrasmooth devices. Furthermore, the nanocomposite has good conductivity (in the metallic range). Such membranes have potential applications in micro- and nano-electromechanical systems which require thin, strong and conductive materials. The objectives of this work were to further the characterization of the AlMo nanocomposite material for potential applications, fabricate devices for such potential applications and implement one or more of the devices in a proof of concept of the potential of the AlMo nanocomposite material. A number of properties of the nanocomposite were assessed. The values determined for density, hardness, Young’s Modulus, Poisson’s ratio and resistivity were generally in good agreement with previously published calculations and/or results. Ultrathin very high-aspect ratio AlMo nanomembranes as thin as 10 nm were fabricated, and bulge and burst pressure measurements were performed. The fracture strength of the nanocomposite was found to be 1.89±0.45 GPa, which compares favorably to the measured fracture strength of fabricated silicon nitride membranes which was 3.28±0.28 GPa. Since the tensile strength is comparable to that of silicon nitride, it is reasonable to use the AlMo nanocomposite as a hybrid conductive/structural layer in devices. The effect of temperature annealing and deposition pressure on the intrinsic stress was measured, as was the effect of deposition pressure on resistivity. Both annealing and alteration of the deposition stress were shown to be effective methods for adjusting the intrinsic stress of the AlMo nanocomposite, and thus the resonance frequency of the membranes. This can be valuable for energy harvesting and biosensor applications to increase efficiency or sensitivity, respectively. Following characterization of the AlMo nanocomposite and AlMo nanomembranes, additional device fabrication was performed. Ni proof masses were electrodeposited onto AlMo membranes. Proof masses can be used to adjust the resonance frequency of devices, as was observed when the resonance frequency of these membranes was measured. The second set of devices was freestanding Archimedes spirals. They were fabricated via a lift-off procedure and two-step release methods consisting of a deep reactive ion etch and a XeF2 gas etch. The design of the spirals was similar to that used in an energy harvester for pacemakers, but at a much smaller scale. The third set of devices consisted of two-armed nano-cantilevers with potential applications as sensors. The paddles were fabricated through electron beam lithography, a lift-off process and a XeF2 gas etch release step. Such cantilevers, as they are conductive, could be used for potentiometric measurements of cantilever deflection where molecules bind to the cantilever surface. The third element of the thesis concerns the implementation of the ultrathin AlMo membranes for resonance-based biosensors. A number of processes were used to successfully link detection molecules to the surface of the membranes. Several detection molecules were employed, including two monoclonal antibodies (Abs), and GP10, a bacteriophage tail spike protein. The monoclonal Ab 3D9S was utilized to capture bovine herpesvirus-1, the monoclonal Ab 11B6 was used to capture the hexon protein of hemorrhagic enteritis virus, and bacteriophage GP10 protein was used to capture Mycobacteria smegmatis and Mycobacteria avium (M. Avium). The change in resonance frequency of the membranes upon capture of protein, virus or bacteria was recorded. Calculations of the added mass were performed. Images of the membranes were taken, which showed that the change in resonance frequency and calculated added mass largely matched the quantity of material visible on the membrane surface. These results demonstrated the successful detection of bovine herpesvirus-1 and M. Avium through resonance measurements using the AlMo membranes. Furthermore, the M. Avium results indicate that the change in resonance frequency is related to the total mass that is captured on the surface.

• Subjects / Keywords

  • Device Fabrication
  • Characterization
  • AlMo Nanocomposite
  • Biosensor

• Graduation date

  Spring 2019

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-cw5h-ga78

• License

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