Silicon nitride cantilevers with oxidation-sharpened silicon tips for atomic force microscopy

Edward L. Ginzton Lab., Stanford Univ., CA
Journal of Microelectromechanical Systems (Impact Factor: 2.13). 09/2002; DOI: 10.1109/JMEMS.2002.800924
Source: IEEE Xplore

ABSTRACT High-resolution atomic force microscopy (AFM) of soft or fragile samples requires a cantilever with a low spring constant and a sharp tip. We have developed a novel process for making such cantilevers from silicon nitride with oxidation-sharpened silicon tips. First, we made and sharpened silicon tips on a silicon wafer. Next, we deposited a thin film of silicon nitride over the tips and etched it to define nitride cantilevers and to remove it from the tips so that they protruded through the cantilevers. Finally, we etched from the back side to release the cantilevers by removing the silicon substrate. We characterized the resulting cantilevers by imaging them with a scanning electron microscope, by measuring their thermal noise spectra, and by using them to image a test sample in contact mode. A representative cantilever had a spring constant of ∼0.06 N/m, and the tip had a radius of 9.2 nm and a cone angle of 36° over 3 μm of tip length. These cantilevers are capable of higher resolution imaging than commercially available nitride cantilevers with oxidation-sharpened nitride tips, and they are especially useful for imaging large vertical features.

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We have developed a new hybrid AFM probe combining an SU-8 polymer body with a full tungsten cantilever having a nanometric tip. The fabrication is based on surface micromachining a silicon wafer, where tungsten is sputter deposited in oxidation sharpened moulds to yield sharp tips with radius below 20 nm. The material properties of tungsten were measured, yielding a hardness of 14 GPa, a specific resistivity of 14.8 μohm cm and Young’s modulus of 380 GPa. Analyses of the probes show a mechanical quality factor of 90 in air, and a low contact resistance of 25 ohm on a gold sample is measured. AFM imaging is demonstrated. As a step in the development of a robust electrically conducting AFM probe, the results are very promising.
    Nanotechnology 01/2006; · 3.84 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Microcantilevers fabricated by microelectromechanical system processes were used to study the residual stresses in the film/substrate systems. Aluminum films were deposited on silicon nitride substrates by thermal evaporation at room and elevated temperatures, and residual stresses were characterized from the deflection profiles of the Al/SiNx microcantilevers. The Al/SiNx microcantilever beam made of room-temperature-deposited Al film was found to deflect toward the substrate side, which in turn resulted in compressive residual stress in the film. In contrary, the microcantilever of Al film deposited at 105 °C was found to deflect toward the side of Al film when the thickness ratio of film to substrate was greater than 0.31 and the residual film stresses were tensile. The axes with zero bending strain component and zero stresses, i.e., the bending and the neutral axes in the film/substrate system were also investigated. The results can be applied to the arm of the atomic force microscope to characterize its deflection and stresses.
    Journal of Materials Research. 05/2011; 26(10):1279 - 1284.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Thin and short cantilevers possess both a low force constant and a high resonance frequency, thus are highly desirable for atomic force microscope (AFM) imaging and force measurement. In this work, small silicon (Si) cantilevers integrating with a Si tip were fabricated from silicon-on-oxide (SOI) wafers that were used for reducing the variation of thickness of the cantilevers. Our fabrication process provided SOI chips containing 40 silicon cantilevers integrating with an ultra-sharp Si tip. We showed that the resolution of images obtained with these tips was much higher than those obtained with the commercial tips, while the force constants were much less, that is, more suitable for imaging soft samples. The availability of such SOI chips greatly facilitates large scale modification of the surfaces of the silicon cantilever tips with a monolayer of oligo(ethylene glycol) derivatives that resist the non-specific interactions with proteins, rendering them most suitable for imaging and measurement of biological samples.
    Sensors and Actuators A-physical - SENSOR ACTUATOR A-PHYS. 01/2006; 126(2):369-374.


1 Download