A nano-cantilever TEM-AFM for in-situ measurement
- Contact Researcher: Pascal Martin Dr.
- Hosted LIMMS Japanese Laboratory: Kawakatsu Lab --- thematiques
- Mass detection
- Context :
Micromachined resonating sensors play an important role for sensing a small interaction force between a tip and a surface as much as 5.6x10-18 N, as well as for a mass sensor. A number of applications, such as force microscopy, magnetometry, and charge detection stimulate continuous efforts to improve the performance of oscillators.
For the purpose of improvement in resolution of force gradient and mass detection in atomic microscopy (AFM), we have started the development of a mass sensor, based on a silicon nanometre-scale resonating cantilever, which is expected to achieve a mass sensitivity of around 10−19 g.
It is known that there are two kinds of sensing methods of molecules or atoms as a very sensitive chemical sensor or mass sensor; one is to detect the static bending caused by surface stress due to molecule absorption onto a flexible cantilever on which chemical active layer is coated. This method is believed to be very sensitive, however, quantitative evaluation is difficult because the stress induced by the adsorption is unpredictable. Furthermore, the drifts of the signal caused by the optical sensing system make long-time measurements difficult. The other method is to use resonant frequency changes due to mass loading; it especially seems to be effective when mass loading does not cause surface stress. Many efforts have been done to raise the sensitivity of the resonating mass sensor. Undesired effects that cause the drift of the resonant frequency, like contamination, mechanical instability, and temperature change, should be avoided as much as possible. Reduction of the noise level down to the thermal noise of the cantilever is necessary to bring out the optimal performance of the cantilever.
Miniaturization of the cantilever, which allows an increase in w0 while keeping k and Q to a designated range, is an effective method to improve AFM. We succeeded in fabrication of a single crystal Si cantilever with several microns size and measurement of its mechanical characteristics. We built an UHV-STM-AFM, which can accommodate a cantilever with a resonance frequency up to 100 MHz. A heterodyne Doppler interferometer was selected for the detection of the cantilever motion with high resonance frequency instead of the commonly used optical lever method.
A laser Doppler interferometer optical probe measuring 2mm in diameter was designed to fit between the upper and lower yokes of an UHV transmission electron microscope. TEM visualization of atom and molecule switching and simultaneous mass measurement with a nano-cantilever is in preparation.
- N. Lavrik, Rev. Sci. Instrum., Vol. 75, No. 7, 2004
- H. Kawakatsu, Rev. Sci. Instrum., Vol. 73, No. 3, 2002