Ultra High Frequency Cantilever Measurement Using M150 MEMS Analyzer

By AZoNano.com Staff Writers

Topics Covered

Introduction
The M150 MEMS Analyzer
High Frequency Cantilever
Tuning of AFM Cantilever
Measuring AFM Cantilever Using M150 MEMS Analyzer
Conclusion
About Ardic Instruments

Introduction

The advances in atomic force microscope (AFM) technology have significantly improved the scan speed. The advent of high frequency cantilevers not only helps higher speed AFMs, but also facilitates higher resolution imaging.

The accurate tuning of the AFM to the resonance frequency of the cantilever is critical to the AC Mode (or Semi-Contact Mode). However, used cantilevers or cantilevers containing manufacturing defects can cause inconsistent resonance frequencies. Hence, measuring the resonance frequencies is equally important for both user and the manufacturer.

The M150 MEMS Analyzer

The M150 MEMS Analyzer is utilized in the characterization of mechanical properties of microstructures. The analyzer’s simple point-and-shoot laser optical system enables users to rapidly acquire resonance peaks of a microstructure by means of real-time Fourier transform (FFT) and wide bandwidth frequency scanning.

The ability of non-contact optical measurement makes the M150 MEMS Analyzer a highly efficient tool to measure resonance frequencies without modifying the properties of the sample.

High Frequency Cantilever

High frequency cantilevers are generally used for high-speed scans. They are engineered to have a low spring constant and high resonance frequency to achieve increased scan rate and resolution. Hence, their appearance is thinner and tinier than conventional cantilevers. Resonance frequency (fc) and spring constant (kc) are expressed mathematically as follows:

 

Where d is the cantilever depth; w is the width, L is the length; E is the Young's module; and ρ is the material‘s density. Silicon nitride is generally used as the cantilever material with Young’s module and material density as follows:

From the aforementioned mathematical expressions, having smaller dimensions of the cantilever design is essential to achieve high fc and low kc characteristics of a high frequency cantilever design. Moreover, high frequency tip cantilevers need to have lower noise density to minimize thermal noise as described by the formula of Thermal noise, √((k_B * T) / kc), where k_B is the Boltzmann's constant; and T is the temperature in K.

Tuning of AFM Cantilever

AFMs perform measurement of surface characteristics by detecting forces between the sample surface and cantilever tip. The cantilever needs to have a specific elasticity and work at its resonance frequency range during the analysis.

When a high quality AFM cantilever is operated at the resonance frequency range mentioned by the original manufacturer, the resonance frequency is a single peak in nearly all ideal situations.

Conversely, finding the resonance frequency of a low quality cantilever during its operation is a challenging task because of excess noise.

The M150 MEMS Analyzer can be used in the characterization of the quality of AFM cantilevers by monitoring their FFT peaks, enabling users to confirm cantilever resonance frequencies and manufacturers to corroborate the manufacturing quality of their probes.

Measuring AFM Cantilever Using M150 MEMS Analyzer

Here, the M150 MEMS Analyzer is used to verify whether the resonance frequency of a high frequency cantilever is in the range mentioned by the manufacturer. The sample is a NanoWorld Arrow-UHF-SPL cantilever with depth of 0.7µm, width of 42µm, and length of 35µm.

The Arrow-UHF-SPL is an ultra-high frequency probe with dimensions smaller than conventional cantilevers. It can resonate at a very high frequency. The resonance frequency range of the cantilever mentioned by the manufacturer is 0.7 ~ 2.0MHz.

The Arrow-UHF-SPL probe is loaded into the M150 MEMS Analyzer and is measured for three points across its length. Then, each scan is set to run for 60s per point, at resonant peaks set between 1Hz and 4.2MHz during real- time Fourier transform.

The results of the resonant frequency measurement of the Arrow-UHF-SPL by the M150 MEMS Analyzer are listed in Table 1, showing a resonant frequency value of 1.538MHz, which is within the range provided by the manufacturer. The measurement results for the three spots are delineated in Figures 1, 2, and 3.

Table 1. Results of Arrow UHF-SPL measurement by M150 Analyzer

Location 1st spot 2nd spot 3rd spot
Tune frequency 1538544Hz 1538544Hz 1538544Hz

Figure 1. First Spot

Figure 2. Second Spot

Figure 3. Third Spot

In this analysis, scanning of the spots was performed from left to right across the length of the cantilever and he peak wave was measured from high to low. The detected resonance frequency was the probe’s first vibration mode.

Conclusion

The results demonstrate the ability of the M150 MEMS Analyzer to yield a highly precise measurement of a high frequency probe, which is becoming increasingly crucial in sophisticated AFM applications.

About Ardic Instruments

Ardic Instruments is an analytical equipment manufacturer aiming to serve the global scientific community with the best customer experience possible. Through a transparent, accessible, and community-driven approach, Ardic Instruments fosters a direct channel of communication between the end-user and the manufacturer.

Ardic Instruments produces atomic force microscopes, MEMS analyzers, and label-free molecular diagnostic platforms for both academic and industrial applications.

This information has been sourced, reviewed and adapted from materials provided by Ardic Instruments.

For more information on this source, please visit Ardic Instruments.

Date Added: Nov 27, 2013 | Updated: Nov 27, 2013
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